Scientific Output

Over 10.000 scientific papers have been published by members of the Materials Chain since the foundation of the University Alliance Ruhr in 2010. This tremendous output is proof of the excellent environment the Ruhr Area provides for research in the field of materials science and technology.

Below, you can either scroll through the complete list of our annually published material, search for a specific author or term via the free text search, or use the interactive keyword cloud to get to know our research strengths. You can also review the publication record of every Materials Chain member via his or her personal member’s page.

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  • 2021 • 873 (tBuN)SiMe2NMe2-A new N,N ′-κ 2-monoanionic ligand for atomic layer deposition precursors
    Griffiths, M.B.E. and Zanders, D. and Land, M.A. and Masuda, J.D. and Devi, A. and Barry, S.T.
    Journal of Vacuum Science and Technology A: Vacuum, Surfaces and Films 39 (2021)
    Eight new atomic layer deposition (ALD) precursors were synthesized using a ligand that is new to the field of ALD: (tBuNH)SiMe2NMe2. Complexes containing Mg, V, Mn, Fe, Co, Ni, and Zn were found to be tetrahedral, and Li complexes form more complex structures. These compounds performed exceptionally well by thermogravimetric analysis (TGA). All compounds except for one Li species and the Fe complex left residual masses below 5%, similar or better than the analogous amidinate complexes. In particular, the Co(II) complex is very thermally robust and performs very well during a TGA stress test, surpassing temperatures above 200 °C. These compounds are the first of a family of precursors containing this type of monoanionic N-Si-N ligand and are prime candidates for ALD process development. © 2021 Author(s).
    view abstractdoi: 10.1116/6.0000795
  • 2021 • 872 3D Printed Al2O3for Terahertz Technology
    Ornik, J. and Sakaki, M. and Koch, M. and Balzer, J.C. and Benson, N.
    IEEE Access 9 5986-5993 (2021)
    In this work we demonstrate that 3D printed Al2O3 is a promising material for prototyping and precise fabrication of quasi-optical devices in the terahertz frequency range. The 3D printed Al2O3 exhibits a low absorption coefficient ( α < 2cm-1 at 1 THz) and a high refractive index ( n >3 ). The printing resolution in the sub 50μ m range allows for the implementation of structures in the 0.3-3.0 THz range on the subwavelength scale. Furthermore, the printing process enables the realization of crystalline solids, which allows the use of the Al2O3 birefringence effect. Here, a Δ n 0.05 was achieved and used for the implementation of λ /2-wave plates working at 1 THz. The material properties and wave plates were characterized using a terahertz time-domain spectrometer. © 2013 IEEE.
    view abstractdoi: 10.1109/ACCESS.2020.3047514
  • 2021 • 871 A 32x24 pixel SPAD detector system for LiDAR and quantum imaging
    Haase, J.F. and Grollius, S. and Grosse, S. and Buchner, A. and Ligges, M.
    Proceedings of SPIE - The International Society for Optical Engineering 11693 (2021)
    We have developed a 32x24 pixel sensor array based on single-photon avalanche diodes (SPADs). Beside conventional 2-dimensional imaging, this sensor allows for precise timing of single-photon arrival times which can be exploited in a variety of technical and scientific approaches like 3D image acquisition, quantum imaging and quantum random number generation. Thus, such a sensor is eligible for many fields of application such as autonomous driving, remote and non-lineof-sight sensing, safety, robotics and more recently random number generation for statistical applications or data encryption. The novel sensor contains CMOS integrated backside illuminated SPADs which are connected to an underlying read-out IC by wafer-to-wafer bonding. Their single-photon sensitivity (quantum efficiency QE=60 % @ 580 nm) and high-speed performance (readout frequency o '"= 25 kHz, temporal resolution tTDC = 312.5 ps) make the sensor a promising choice for, e.g. quantum imaging with photon-pairs where a 2-dimensional spatial and temporal resolution are as crucial as a low noise level. SPADs also offer exciting opportunities for random number generation by using the randomness of photon generation paired with time-resolved detection and post-processing. Another potential application of the sensor is light detection and ranging for which we integrated the sensor into a demonstrator system for direct time-of-flight measurements. It is capable of coincidence detection using 4 SPADs in each pixel, which allows for background light suppression in outdoor situations. This combination of single-photon sensitivity, precise photon arrival timing and our recent developments in wafer-to-wafer bonding technology gives access to a new generation of optical sensors for a variety of applications. © 2021 SPIE.
    view abstractdoi: 10.1117/12.2578775
  • 2021 • 870 A bioinspired oxoiron(iv) motif supported on a N2S2macrocyclic ligand
    Deutscher, J. and Gerschel, P. and Warm, K. and Kuhlmann, U. and Mebs, S. and Haumann, M. and Dau, H. and Hildebrandt, P. and Apfel, U.-P. and Ray, K.
    Chemical Communications 57 2947-2950 (2021)
    A mononuclear oxoiron(iv) complex1-transbearing two equatorial sulfur ligations is synthesized and characterized as an active-site model of the elusive sulfur-ligated FeIVO intermediates in non-heme iron oxygenases. The introduction of sulfur ligands weakens the Fe-O bond and enhances the oxidative reactivity of the FeIVO unit with a diminished deuterium kinetic isotope effect, thereby providing a compelling rationale for nature's use of thecis-thiolate ligated oxoiron(iv) motif in key metabolic transformations. © The Royal Society of Chemistry 2021.
    view abstractdoi: 10.1039/d1cc00250c
  • 2021 • 869 A bright and fast source of coherent single photons
    Tomm, N. and Javadi, A. and Antoniadis, N.O. and Najer, D. and Löbl, M.C. and Korsch, A.R. and Schott, R. and Valentin, S.R. and Wieck, A.D. and Ludwig, Ar. and Warburton, R.J.
    Nature Nanotechnology (2021)
    A single-photon source is an enabling technology in device-independent quantum communication1, quantum simulation2,3, and linear optics-based4 and measurement-based quantum computing5. These applications employ many photons and place stringent requirements on the efficiency of single-photon creation. The scaling on efficiency is typically an exponential function of the number of photons. Schemes taking full advantage of quantum superpositions also depend sensitively on the coherence of the photons, that is, their indistinguishability6. Here, we report a single-photon source with a high end-to-end efficiency. We employ gated quantum dots in an open, tunable microcavity7. The gating provides control of the charge and electrical tuning of the emission frequency; the high-quality material ensures low noise; and the tunability of the microcavity compensates for the lack of control in quantum dot position and emission frequency. Transmission through the top mirror is the dominant escape route for photons from the microcavity, and this output is well matched to a single-mode fibre. With this design, we can create a single photon at the output of the final optical fibre on-demand with a probability of up to 57% and with an average two-photon interference visibility of 97.5%. Coherence persists in trains of thousands of photons with single-photon creation at a repetition rate of 1 GHz. © 2021, The Author(s), under exclusive licence to Springer Nature Limited.
    view abstractdoi: 10.1038/s41565-020-00831-x
  • 2021 • 868 A Career in Catalysis: Robert Schlögl
    Bao, X. and Behrens, M. and Ertl, G. and Fu, Q. and Knop-Gericke, A. and Lunkenbein, T. and Muhler, M. and Schmidt, C.M. and Trunschke, A.
    ACS Catalysis 11 6243-6260 (2021)
    "Why?"is the question that initiates science. "Why?"is also the answer that maintains science. This interrogative adverb fuels the scientific career of Robert Schlögl. Robert is a dedicated solid-state chemist who has found his specialization in untangling the working principles of heterogeneous catalysts under realistic conditions. As such he combines the full complexity of real catalysts with tailor-made operando experiments to overcome pressure, material, and complexity gaps. His ability to quickly abstract the meaning of spectroscopic and microscopic data, his talent to ask the right question paired with curiosity, diligence, and creativity have made him a world-leading expert in heterogeneous catalysis and energy science. His scientific passion is focused on untangling chemical dynamics as well as working principles and understanding the important interplay of geometric and electronic structures in functional materials. Thereby his research interests involve ammonia and methanol synthesis, carbon materials in catalysis, hydrogenation, and dehydrogenation, selective oxidation, and the development of operando setups for microscopy and spectroscopy. He also has a strong commitment to society in scientifically accelerating the energy transition ("Energiewende") in Europe, where he focuses on CO2 utilization and hydrogen as an energy carrier. This is manifested in three recent large Germany-wide projects: Carbon2Chem, CatLab, and TransHyDe. ©
    view abstractdoi: 10.1021/acscatal.1c01165
  • 2021 • 867 A combination of anti-pd-l1 treatment and therapeutic vaccination facilitates improved retroviral clearance via reactivation of highly exhausted t cells
    Knuschke, T. and Kollenda, S. and Wenzek, C. and Zelinskyy, G. and Steinbach, P. and Dittmer, U. and Buer, J. and Epple, M. and Westendorf, A.M.
    mBio 12 1-16 (2021)
    PD-1-targeted therapies have shown modest antiviral effects in pre-clinical models of chronic viral infection. Thus, novel therapy protocols are necessary to enhance T cell immunity and viral control to overcome T cell dysfunction and immunosuppression. Here, we demonstrate that nanoparticle-based therapeutic vaccination improved PD-1-targeted therapy during chronic infection with Friend retrovirus (FV). Prevention of inhibitory signals by blocking PD-L1 in combination with therapeutic vaccination with nanoparticles containing the microbial compound CpG and a CD8+ T cell Gag epitope peptide synergistically enhanced functional virus-specific CD8+ T cell responses and improved viral clearance. We characterized the CD8+ T cell populations that were affected by this combination therapy, demonstrating that new effector cells were generated and that exhausted CD8+ T cells were reactivated at the same time. While CD8+ T cells with high PD-1 (PD-1hi) expression turned into a large population of granzyme B-expressing CD8+ T cells after combination therapy, CXCR5-expressing follicular cytotoxic CD8+ T cells also expanded to a high degree. Thus, our study describes averyefficient approach to enhance virus control and may help us to understand the mechanisms of combination immunotherapy reactivating CD8+ Tcellimmu-nity. A better understanding of CD8+ T cell immunity during combination therapy will be important for developing efficient checkpoint therapies against chronic viral infections and cancer. IMPORTANCE Despite significant efforts, vaccines are not yet available for every infectious pathogen, and the search for a protective approach to prevent the estab-lishment of chronic infections, i.e., with HIV, continues. Immune checkpoint therapies targeting inhibitory receptors, such as PD-1, have shown impressive results against solid tumors. However, immune checkpoint therapies have not yet been licensed to treat chronic viral infections, since a blockade of inhibitory receptors alone provides only limited benefit, as demonstrated in preclinical models of chronic viral infection. Thus, there is a high interest in the development of potent combination immunotherapies. Here, we tested whether the combination of a PD-L1 blockade and therapeutic vaccination with functionalized nanoparticles is a potent therapy during chronic Friend retrovirus infection. We demonstrate that the combination therapy induced a synergistic reinvigoration of the exhausted vi-rus-specific CD8+ T cell immunity. Taken together, our results provide further information on how to improve PD-1-targeted therapies during chronic viral infection and cancer. © 2021 Knuschke et al.
    view abstractdoi: 10.1128/mBio.02121-20
  • 2021 • 866 A combined experimental and first-principles based assessment of finite-temperature thermodynamic properties of intermetallic al3sc
    Gupta, A. and Tas, B. and Korbmacher, D. and Dutta, B. and Neitzel, Y. and Grabowski, B. and Hickel, T. and Esin, V. and Divinski, S.V. and Wilde, G. and Neugebauer, J.
    Materials 14 (2021)
    We present a first-principles assessment of the finite-temperature thermodynamic properties of the intermetallic Al3Sc phase including the complete spectrum of excitations and compare the theoretical findings with our dilatometric and calorimetric measurements. While significant electronic contributions to the heat capacity and thermal expansion are observed near the melting temperature, anharmonic contributions, and electron–phonon coupling effects are found to be relatively small. On the one hand, these accurate methods are used to demonstrate shortcomings of empirical predictions of phase stabilities such as the Neumann–Kopp rule. On the other hand, their combination with elasticity theory was found to provide an upper limit for the size of Al3Sc nanoprecipitates needed to maintain coherency with the host matrix. The chemo-mechanical coupling being responsible for the coherency loss of strengthening precipitates is revealed by a combination of state-of-the-art simulations and dedicated experiments. These findings can be exploited to fine-tune the microstructure of Al-Sc-based alloys to approach optimum mechanical properties. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/ma14081837
  • 2021 • 865 A comparative study of micro-mechanical models for fiber pullout behavior of reinforced high performance concrete
    Storm, J. and Pise, M. and Brands, D. and Schröder, J. and Kaliske, M.
    Engineering Fracture Mechanics 243 (2021)
    The pseudo-ductile material behavior of fiber reinforced high performance concrete is mainly characterized by the fiber pullout process. Thereby, complex fiber–concrete interactions, i.e. interface debonding, concrete micro cracks, slippage, adhesion and further unknown processes, are commonly investigated in single-fiber pullout tests. The study in this contribution is based on the experimental results of Gebuhr etal., (2019) and compares three different numerical models applied to the fiber pullout test. An accurate and efficient model for fiber pullout behavior forms the basis for the prediction of the overall behavior by means of composite models or multi-scale approaches in subsequent studies. © 2020 Elsevier Ltd
    view abstractdoi: 10.1016/j.engfracmech.2020.107506
  • 2021 • 864 A Digital Forensic Approach for Optimizing the Investigation of Hit-and-Run Accidents
    Waltereit, M. and Uphoff, M. and Zdankin, P. and Matkovic, V. and Weis, T.
    Lecture Notes of the Institute for Computer Sciences, Social-Informatics and Telecommunications Engineering, LNICST 351 204-223 (2021)
    We present a novel digital forensic approach that facilitates the investigation of hit-and-run accidents. Based on wheel speeds gathered by forensic data loggers, our approach provides a priority ranking of the suspects in order to optimize further investigations. For this, we propose two investigation steps to get key information about a suspect’s trip. First, we analyze the likely traveled routes of a suspect to determine whether the suspect could have been at the accident location. Second, we analyze the driving behavior of the suspect in terms of aggressiveness, since aggressive driving behavior is a major reason for traffic accidents. Our evaluation with real driving experiments shows that our approach is suitable for analyzing likely routes and driving behavior in order to prioritize suspects in an investigation. © 2021, ICST Institute for Computer Sciences, Social Informatics and Telecommunications Engineering.
    view abstractdoi: 10.1007/978-3-030-68734-2_11
  • 2021 • 863 A dithiacyclam-coordinated silver(i) polymer with anti-cancer stem cell activity
    Johnson, A. and Iffland, L. and Singh, K. and Apfel, U.-P. and Suntharalingam, K.
    Dalton Transactions 50 5779-5783 (2021)
    A cancer stem cell (CSC) active, solution stable, silver(i) polymeric complex bearing a dithiacyclam ligand is reported. The complex displays similar potency towards CSCs to salinomycin in monolayer and three-dimensional cultures. Mechanistic studies suggest CSC death results from cytosol entry, an increase in intracellular reactive oxygen species, and caspase-dependent apoptosis. © The Royal Society of Chemistry 2021.
    view abstractdoi: 10.1039/d1dt01155c
  • 2021 • 862 A finite deformation isogeometric finite element approach to fibre-reinforced composites with fibre bending stiffness
    Witt, C. and Kaiser, T. and Menzel, A.
    Journal of Engineering Mathematics 128 (2021)
    It is a common technique in many fields of engineering to reinforce materials with certain types of fibres in order to enhance the mechanical properties of the overall material. Specific simulation methods help to predict the behaviour of these composites in advance. In this regard, a widely established approach is the incorporation of the fibre direction vector as an additional argument of the energy function in order to capture the specific material properties in the fibre direction. While this model represents the transverse isotropy of a material, it cannot capture effects that result from a bending of the fibres and does not include any length scale that might allow the simulation of size effects. In this contribution, an enhanced approach is considered which relies on the introduction of higher-gradient contributions of the deformation map in the stored energy density function and which eventually allows accounting for fibre bending stiffness in simulations. The respective gradient fields are approximated by NURBS basis functions within an isogeometric finite element framework by taking advantage of their characteristic continuity properties. The isogeometric finite element approach that is presented in this contribution for fibre-reinforced composites with fibre bending stiffness accounts for finite deformations. It is shown that the proposed method is in accordance with semi-analytical solutions for a representative boundary value problem. In an additional example it is observed that the initial fibre orientation and the particular bending stiffness of the fibres influence the deformation as well as the stress response of the material. © 2021, The Author(s).
    view abstractdoi: 10.1007/s10665-021-10117-3
  • 2021 • 861 A finite element implementation of the stress gradient theory
    Kaiser, T. and Forest, S. and Menzel, A.
    Meccanica 56 1109-1128 (2021)
    In this contribution, a finite element implementation of the stress gradient theory is proposed. The implementation relies on a reformulation of the governing set of partial differential equations in terms of one primary tensor-valued field variable of third order, the so-called generalised displacement field. Whereas the volumetric part of the generalised displacement field is closely related to the classic displacement field, the deviatoric part can be interpreted in terms of micro-displacements. The associated weak formulation moreover stipulates boundary conditions in terms of the normal projection of the generalised displacement field or of the (complete) stress tensor. A detailed study of representative boundary value problems of stress gradient elasticity shows the applicability of the proposed formulation. In particular, the finite element implementation is validated based on the analytical solutions for a cylindrical bar under tension and torsion derived by means of Bessel functions. In both tension and torsion cases, a smaller is softer size effect is evidenced in striking contrast to the corresponding strain gradient elasticity solutions. © 2021, The Author(s).
    view abstractdoi: 10.1007/s11012-020-01266-3
  • 2021 • 860 A fully automated approach to calculate the melting temperature of elemental crystals
    Zhu, L.-F. and Janssen, J. and Ishibashi, S. and Körmann, F. and Grabowski, B. and Neugebauer, J.
    Computational Materials Science 187 (2021)
    The interface method is a well established approach for predicting melting points of materials using interatomic potentials. However, applying the interface method is tedious and involves significant human intervention. The whole procedure involves several successive tasks: estimate a rough melting point, set up the interface structure, run molecular dynamic calculations and analyze the data. Loop calculations are necessary if the predicted melting point is different from the estimated one by more than a certain convergence criterion, or if full melting/solidification occurs. In this case monitoring the solid–liquid phase transition in the interface structure becomes critical. As different initial random seeds for the molecular dynamic simulations within the interface method induce slightly different melting points, a few ten or hundred interface method calculations with different random seeds are necessary for performing a statistical analysis on these melting points. Considering all these technical details, the work load for manually executing and combining the various involved scripts and programs quickly becomes prohibitive. To simplify and automatize the whole procedure, we have implemented the interface method into pyiron (http://pyiron.org). Our fully automatized procedure allows to efficiently and precisely predict melting points of stable unaries represented by arbitrary potentials with only two user-specified parameters (interatomic potential file and element). For metastable or dynamically unstable unary phases, the crystal structure needs to be provided as an additional parameter. We have applied our automatized approach on fcc Al, Ni, dynamically unstable bcc Ti and hcp Mg and employed a large set of available interatomic potentials. Melting points for classical interatomic potentials of these metals have been obtained with a numerical precision well below 1 K. © 2020 The Authors
    view abstractdoi: 10.1016/j.commatsci.2020.110065
  • 2021 • 859 A general, implicit, finite-strain FE 2 framework for the simulation of dynamic problems on two scales
    Tamsen, E. and Balzani, D.
    Computational Mechanics 67 1375-1394 (2021)
    In this paper we present a fully-coupled, two-scale homogenization method for dynamic loading in the spirit of FE2 methods. The framework considers the balance of linear momentum including inertia at the microscale to capture possible dynamic effects arising from micro heterogeneities. A finite-strain formulation is adapted to account for geometrical nonlinearities enabling the study of e.g. plasticity or fiber pullout, which may be associated with large deformations. A consistent kinematic scale link is established as displacement constraint on the whole representative volume element. The consistent macroscopic material tangent moduli are derived including micro inertia in closed form. These can easily be calculated with a loop over all microscopic finite elements, only applying existing assembly and solving procedures. Thus, making it suitable for standard finite element program architectures. Numerical examples of a layered periodic material are presented and compared to direct numerical simulations to demonstrate the capability of the proposed framework. In addition, a simulation of a split Hopkinson tension test showcases the applicability of the framework to engineering problems. © 2021, The Author(s).
    view abstractdoi: 10.1007/s00466-021-01993-8
  • 2021 • 858 A Highly-Efficient Oxygen Evolution Electrocatalyst Derived from a Metal-Organic Framework and Ketjenblack Carbon Material
    Öztürk, S. and Moon, G.-H. and Spieß, A. and Budiyanto, E. and Roitsch, S. and Tüysüz, H. and Janiak, C.
    ChemPlusChem (2021)
    The composite of the metal-organic framework (MOF) Ni(Fe)-MOF-74 and the highly conductive carbon material ketjenblack (KB) could be easily obtained from the in-situ MOF synthesis in a one-step solvothermal reaction. The composite material features a remarkable electrochemical oxygen evolution reaction (OER) performance where the overpotential at 10 mA/cm2 and the current density at 1.7 VRHE are recorded as 0.274 VRHE and 650 mA/cm2, respectively, in 1 mol/L KOH. In particular, the activation of nickel-iron clusters from the MOF under an applied anodic bias steadily boosts the OER performance. Although Ni(Fe)-MOF-74 goes through some structural modification during the electrochemical measurements, the stabilized and optimized composite material shows excellent OER performance. This simple strategy to design highly-efficient electrocatalysts, utilizing readily available precursors and carbon materials, will leverage the use of diverse metal-organic complexes into electrode fabrication with a high energy conversion efficiency. © 2021 The Authors. ChemPlusChem published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/cplu.202100278
  • 2021 • 857 A High-Pressure High-Temperature Column for the Simulation of Hydrothermal Water Circulation at Laboratory Scale
    Frank, S. and Zuber, P. and Pollak, S. and Heinze, T. and Schreuer, J. and Wohnlich, S.
    Geotechnical Testing Journal 44 (2021)
    Modeling the geothermal energy production cycle of a deep geothermal system at laboratory scale is challenging because of high-temperature and pressure conditions. In this work, a high-pressure high-temperature column to simulate production, heat transfer, and reinjection of a geothermal fluid in a fractured rock system is presented. The column includes two independently heated pressure vessels, a heat exchanger, and sensors for temperatures, pressures, flow rate, electric conductivity, and pH value of the circulating fluid at different locations. The presented column enables the quantitative analysis of coupled hydro-thermo-chemical processes in fractured rock cores close to in situ geothermal conditions. Heat extraction and reinjection of geothermal fluids into fractured reservoirs can be reproduced because of the possibility of heating and cooling of the circulating fluid. Further, it is possible to inject a second fluid phase into the column to investigate additional processes, such as mineral precipitation during reinjection. In this work, we present the experimental setup of the column and first results showing the capability of the system. © 2021 ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959.
    view abstractdoi: 10.1520/GTJ20200020
  • 2021 • 856 A hybrid H1× H(curl) finite element formulation for a relaxed micromorphic continuum model of antiplane shear
    Sky, A. and Neunteufel, M. and Münch, I. and Schöberl, J. and Neff, P.
    Computational Mechanics (2021)
    One approach for the simulation of metamaterials is to extend an associated continuum theory concerning its kinematic equations, and the relaxed micromorphic continuum represents such a model. It incorporates the Curl of the nonsymmetric microdistortion in the free energy function. This suggests the existence of solutions not belonging to H1, such that standard nodal H1-finite elements yield unsatisfactory convergence rates and might be incapable of finding the exact solution. Our approach is to use base functions stemming from both Hilbert spaces H1 and H(curl) , demonstrating the central role of such combinations for this class of problems. For simplicity, a reduced two-dimensional relaxed micromorphic continuum describing antiplane shear is introduced, preserving the main computational traits of the three-dimensional version. This model is then used for the formulation and a multi step investigation of a viable finite element solution, encompassing examinations of existence and uniqueness of both standard and mixed formulations and their respective convergence rates. © 2021, The Author(s).
    view abstractdoi: 10.1007/s00466-021-02002-8
  • 2021 • 855 A hysteresis model for the unfrozen liquid content in freezing porous media
    Saberi, P.S. and Meschke, G.
    Computers and Geotechnics 134 (2021)
    The description of the freezing characteristics of porous media is one of the most conspicuous ingredients in flow and heat transport models that involve freezing and thawing processes. Unfrozen liquid content (ULC) shows strong hysteresis during freezing and thawing cycles in different types of soils and other porous media. We discuss the possible mechanisms of hysteresis in porous media and develop a numerical model for the unfrozen liquid content that is capable of describing the hysteresis phenomenon in freezing and thawing cycles. We present a coupled finite element model as the framework for the numerical simulation of fluid flow and heat transport in partially frozen porous media. The implementation aspects of the ULC model as well as its integration into numerical codes are discussed in detail. We investigate the potential impact of the hysteresis phenomenon on the numerical simulation of transport processes in porous media through benchmark examples and validate the behavior of the model against available laboratory measurement data. © 2021
    view abstractdoi: 10.1016/j.compgeo.2021.104048
  • 2021 • 854 A mathematical model to describe the inner contour of moineau stators
    Oezkaya, E. and Fuss, M. and Biermann, D.
    Journal of Manufacturing Science and Engineering, Transactions of the ASME 143 (2021)
    Bore holes with a large length to diameter ratio of up to l/d = 100 are typically produced using the single-tube deep hole drilling method also named BTA (Boring and Trepanning Association) deep hole drilling method. However, there are various technical applications requiring deep, complex, epitrochoid-similar and helical inner contours, such as stators used in Moineau motors and pumps. According to the current state of the art, epitrochoid-similar contours for small diameters with large drilling depths can only be produced using a special machining process which is referred to a chamber-boring process. In this paper, a developed mathematical model will be presented that describes the epitrochoid-similar contour exactly. This allows the determination of the position-dependent speed and acceleration of the tool, which are necessary for designing the joints and components of the tool system. In addition, this mathematical model can be used for a subsequent Laplace-transformation, so that could be used for a further optimization of the process dynamic in the future. Copyright © 2020 by ASME
    view abstractdoi: 10.1115/1.4048437
  • 2021 • 853 A mechanical analysis of chemically stimulated linear shape memory polymer actuation
    Dumlu, H. and Marquardt, A. and Zirdehi, E.M. and Varnik, F. and Shen, Y. and Neuking, K. and Eggeler, G.
    Materials 14 1-21 (2021)
    In the present work, we study the role of programming strain (50% and 100%), end loads (0, 0.5, 1.0, and 1.5 MPa), and chemical environments (acetone, ethanol, and water) on the exploitable stroke of linear shape memory polymer (SMP) actuators made from ESTANE ETE 75DT3 (SMP-E). Dynamic mechanical thermal analysis (DMTA) shows how the uptake of solvents results in a decrease in the glass temperature of the molecular switch component of SMP-E. A novel in situ technique allows chemically studying triggered shape recovery as a function of time. It is found that the velocity of actuation decreases in the order acetone > ethanol > water, while the exploitable strokes shows the inverse tendency and increases in the order water > ethanol > acetone. The results are interpreted on the basis of the underlying chemical (how solvents affect thermophysical properties) and micromechanical processes (the phenomenological spring dashpot model of Lethersich type rationalizes the behavior). The study provides initial data which can be used for micromechanical modeling of chemically triggered actuation of SMPs. The results are discussed in the light of underlying chemical and mechanical elementary processes, and areas in need of further work are highlighted. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/ma14030481
  • 2021 • 852 A Minimally Invasive Monitoring Concept for Plasma-Assisted Surface Treatments in PET Bottles
    Pohle, D. and Mitschker, F. and Jenderny, J. and Rudolph, M. and Schulz, C. and Awakowicz, P. and Rolfes, I.
    2020 50th European Microwave Conference, EuMC 2020 479-482 (2021)
    This paper presents a novel approach to plasma monitoring in the context of plasma-assisted surface treatments in PET bottles. In industrial state-of-the-art production of PET-based beverage bottles, a so-called Plasmaline antenna is inserted into the bottle which provides both process gases and microwave excitation to generate the plasma state required for coating or sterilization on its inside. The proposed concept based on the planar multipole resonance probe (pMRP) allows for a non-invasive supervision of the plasma from the outside of the bottle wall. Since plasma and probe head are only separated by dielectric materials in between, the sensor's electric field is able to interact with the plasma and the resonance behavior that occurs can be evaluated and tracked. The performance of the concept regarding changes of the plasma electron frequency and the electron collision frequency are investigated within 3D full-wave simulations in CST Microwave Studio. Measurements of an argon plasma are presented as a proof-of-concept, with the plasma being monitored from the plasma-remote side of a PET bottle section. © 2021 EuMA.
    view abstractdoi: 10.23919/EuMC48046.2021.9338200
  • 2021 • 851 A mixed-charge polyelectrolyte complex nanofiltration membrane: Preparation, performance and stability
    Zelner, M. and Jahn, P. and Ulbricht, M. and Freger, V.
    Journal of Membrane Science 636 (2021)
    Ion selectivity of nanofiltration (NF) membranes is a critical factor in NF treatment of scaling-prone multi-ion effluents, such as wastewater. When removal of multivalent ions in such effluents is unnecessary or undesired, adjusting their rejection may mitigate scaling, in which case membranes combining oppositely charged electrolytes enable a tunable selectivity towards such ions. Here we report the fabrication of a new tunable and highly stable polyelectrolyte complex NF membrane prepared by successively coating an ultrafiltration membrane support with negatively charged Nafion and positively charged polyvinylamine (PVAm) layers. While Nafion thickness controls the membrane permeability, the second PVAm coating is critical for eliminating defects in the Nafion layer and readily tunes the membrane net charge and, hence, ion selectivity via PVAm concentration in the coating solution. In this manner, a membrane with good permeability, balanced charge, and, therefore, equal (“symmetric”) rejection of divalent anions and cations is obtained. The membrane performance is unaffected by exposure to 10% salt in water; such remarkable stability for a polyelectrolyte-based membrane makes it potentially attractive for the treatment of wastewater effluents and brackish water sources. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.memsci.2021.119579
  • 2021 • 850 A modified tool design for the drilling of high-performance aerospace materials
    Iovkov, I. and Bücker, M. and Biermann, D.
    CIRP Annals 70 83-86 (2021)
    High-performance Ni- and Ti-based materials are generally difficult to machine. Drilling in particular is highly demanding for the applied tools due to challenging thermal stress. This paper describes a novel modification for twist drills which significantly improves the cooling and lubrication of the main and secondary cutting edges and leads to an enhancement in process productivity. Within the scope of this work, the achievable improvements with regard to wear progress, cutting edge temperature and cutting fluid flow when machining Inconel 718 are analysed. The solution developed could also prove its efficiency in the machining of titanium-based alloy Ti6Al4V. © 2021 The Author(s)
    view abstractdoi: 10.1016/j.cirp.2021.04.024
  • 2021 • 849 A new approach for open-end sequential change point monitoring
    Gösmann, J. and Kley, T. and Dette, H.
    Journal of Time Series Analysis 42 63-84 (2021)
    We propose a new sequential monitoring scheme for changes in the parameters of a multivariate time series. In contrast to procedures proposed in the literature which compare an estimator from the training sample with an estimator calculated from the remaining data, we suggest to divide the sample at each time point after the training sample. Estimators from the sample before and after all separation points are then continuously compared calculating a maximum of norms of their differences. For open-end scenarios our approach yields an asymptotic level (Formula presented.) procedure, which is consistent under the alternative of a change in the parameter. By means of a simulation study it is demonstrated that the new method outperforms the commonly used procedures with respect to power and the feasibility of our approach is illustrated by analyzing two data examples. © 2020 The Authors. Journal of Time Series Analysis published by John Wiley & Sons Ltd.
    view abstractdoi: 10.1111/jtsa.12555
  • 2021 • 848 A new diffuse-interface approximation of the willmore flow
    Rätz, A. and Röger, M.
    ESAIM - Control, Optimisation and Calculus of Variations 27 (2021)
    Standard diffuse approximations of the Willmore flow often lead to intersecting phase boundaries that in many cases do not correspond to the intended sharp interface evolution. Here we introduce a new two-variable diffuse approximation that includes a rather simple but efficient penalization of the deviation from a quasi-one dimensional structure of the phase fields. We justify the approximation property by a Gamma convergence result for the energies and a matched asymptotic expansion for the flow. Ground states of the energy are shown to be one-dimensional, in contrast to the presence of saddle solutions for the usual diffuse approximation. Finally we present numerical simulations that illustrate the approximation property and apply our new approach to problems where the usual approach leads to an undesired behavior. © EDP Sciences, SMAI 2021.
    view abstractdoi: 10.1051/cocv/2021013
  • 2021 • 847 A new perspective on flux and slope limiting in discontinuous Galerkin methods for hyperbolic conservation laws
    Kuzmin, D.
    Computer Methods in Applied Mechanics and Engineering 373 (2021)
    In this work, we discuss and develop multidimensional limiting techniques for discontinuous Galerkin (DG) discretizations of scalar hyperbolic problems. To ensure that each cell average satisfies a local discrete maximum principle (DMP), we impose inequality constraints on the local Lax–Friedrichs fluxes of a piecewise-linear (P1) approximation. Since the piecewise-constant (P0) version corresponds to a property-preserving low-order finite volume method, the validity of DMP conditions can always be enforced using slope and/or flux limiters. We show that the (currently rather uncommon) use of direct flux limiting makes it possible to construct more accurate DMP-satisfying approximations in which a weak form of slope limiting is used to prevent unbounded growth of solution gradients. After presenting two flux limiters that ensure the validity of local DMPs for cell averages, we discuss the design of slope limiters based on different kinds of inequality constraints. In particular, we derive new limiting procedures based on flux constraints and constraints for directional derivatives. The latter approach makes it possible to preserve directional monotonicity in applications to problems that require different treatment of different space directions. At the flux limiting stage, the anisotropy of the problem at hand can be taken into account by using a customized definition of local bounds for the DMP constraints. At the slope limiting stage, we adjust the magnitude of individual directional derivatives using low-order reconstructions from cell averages to define the bounds. In this way, we avoid unnecessary limiting of well-resolved derivatives at smooth peaks and in internal/boundary layers. The properties of selected algorithms are explored in numerical studies for DG-P1 discretizations of two-dimensional test problems. In the context of hp-adaptive DG methods, the new limiting procedures can be used in P1 subcells of macroelements marked as ‘troubled’ by a smoothness indicator. © 2020 Elsevier B.V.
    view abstractdoi: 10.1016/j.cma.2020.113569
  • 2021 • 846 A new water-soluble thermosensitive star-like copolymer as a promising carrier of the chemotherapeutic drug doxorubicin
    Chernykh, M. and Zavalny, D. and Sokolova, V. and Ponomarenko, S. and Prylutska, S. and Kuziv, Y. and Chumachenko, V. and Marynin, A. and Kutsevol, N. and Epple, M. and Ritter, U. and Piosik, J. and Prylutskyy, Y.
    Materials 14 (2021)
    A new water-soluble thermosensitive star-like copolymer, dextran-graft-poly-N-iso-propilacrylamide (D-g-PNIPAM), was created and characterized by various techniques (size-exclusion chromatography, differential scanning calorimetry, Fourier-transform infrared (FTIR) spectroscopy, and dynamic light scattering (DLS) spectroscopy). The viability of cancer cell lines (human transformed cervix epithelial cells, HeLa) as a model for cancer cells was studied using MTT and Live/Dead assays after incubation with a D-g-PNIPAM copolymer as a carrier for the drug doxorubicin (Dox) as well as a D-g-PNIPAM + Dox mixture as a function of the concentration. FTIR spectroscopy clearly indicated the complex formation of Dox with the D-g-PNIPAM copolymer. The size distribution of particles in Hank’s solution was determined by the DLS technique at different temperatures. The in vitro uptake of the studied D-g-PNIPAM + Dox nanoparticles into cancer cells was demonstrated by confocal laser scanning microscopy. It was found that D-g-PNIPAM + Dox nanoparticles in contrast to Dox alone showed higher toxicity toward cancer cells. All of the aforementioned facts indicate a possibility of further preclinical studies of the water-soluble D-g-PNIPAM particles’ behavior in animal tumor models in vivo as promising carriers of anticancer agents. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/ma14133517
  • 2021 • 845 A note on optimal designs for estimating the slope of a polynomial regression
    Dette, H. and Melas, V.B. and Shpilev, P.
    Statistics and Probability Letters 170 (2021)
    In this note we consider the optimal design problem for estimating the slope of a polynomial regression with no intercept at a given point, say z. In contrast to previous work, we investigate the model on the non-symmetric interval. © 2020 Elsevier B.V.
    view abstractdoi: 10.1016/j.spl.2020.108992
  • 2021 • 844 A numerical method to compute global resonant vibrations of ships at forward speed in oblique waves
    Riesner, M. and el Moctar, O.
    Applied Ocean Research 108 (2021)
    Resonant wave-induced vibrations of a ship hull girder, known as “springing”, is an important issue when addressing fatigue aging of the steel structure. To compute resonant wave-induced vibrations, fluid-structure interactions and associated structural and hydrodynamic properties need to be addressed. This paper introduces a time-domain numerical method that predicts higher-order springing taking into account forward speed. Structural dynamics were computed based on a beam element approach that considers vertical and horizontal bending as well as nonuniform torsion. Furthermore, mass and stiffness matrices accounted for strong coupling effects between hull girder bending and torsion. The hydrodynamic solver coupled the fully nonlinear stationary free surface flow with the oscillatory flow and considered geometrical nonlinearities caused by the changing wetted surface due to the incident waves, nonlinear rigid body motions and linear elastic vibrations. Numerical predictions were validated against model tests of a post-Panamax containerships at forward speed. Dry and wet natural frequencies and midship vertical bending, horizontal bending and torsional moments induced by higher order springing vibrations compared favourably to experimental measurements. © 2020
    view abstractdoi: 10.1016/j.apor.2020.102520
  • 2021 • 843 A numerical method to improve the representativeness of real microstructure cut-outs applied in finite element simulations
    Schneider, Y. and Wasserbäch, W. and Schmauder, S. and Zhou, Z. and Zielke, R. and Tillmann, W.
    Crystals 11 (2021)
    To improve the representativeness of a real microstructural cut-out for modeling purposes, a numerical method named as “boundary pixel color alteration (BPCA)” is presented to modify measured 2D microstructure cut-outs. Its physical background is related to the phase growth. For the application, the precondition is that the representativeness of the microstructure is already satisfied to a certain extent. This method resolves the problem that the phase composition of a small cut-out can have a large discrepancy to the real one. The main idea is to change the pixel color among neighboring pixels belonging to different phases. Our process simultaneously maintains most of the characteristics of the original morphology and is applicable for nearly all kinds of multi-phase or polycrystalline metallic alloys, as well. From our axisymmetric finite element (FE) simulations (ABAQUS ) applied with 2D real microstructures, it shows that the volume ratios of microstructural phases, as a function of the structure position to the symmetric axis, converge to phase area ratios in the 2D cut-out, even though the axisymmetric element volume is position dependent. A mathematical proof provides the reason for the aforementioned convergence. As examples to achieve real compositions and to numerically prove the aforementioned convergence, four different materials including multiphase polycrystals are implemented. An improvement of the predicted FE result is presented for the application of a modified microstructure (with a higher representativeness) compared to the original one. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/cryst11040382
  • 2021 • 842 A parabolic free boundary problem arising in a model of cell polarization
    Logioti, A. and Niethammer, B. and Roger, M. and Velazquez, J.J.L.
    SIAM Journal on Mathematical Analysis 53 1214-1238 (2021)
    The amplification of an external signal is a key step in direction sensing of biological cells. We consider a simple model for the response to a time-depending signal, which was previously proposed by the last three authors. The model consists of a bulk-surface reaction-diffusion model. We prove that in a suitable asymptotic limit the system converges to a bulk-surface parabolic obstacle-type problem. For this model and a reduction to a nonlocal surface equation we show an L1contraction property and, in the case of time-constant signals, the stability of stationary states. © 2021 Society for Industrial and Applied Mathematics.
    view abstractdoi: 10.1137/20M1349114
  • 2021 • 841 A positivity-preserving and conservative intersection-distribution-based remapping algorithm for staggered ALE hydrodynamics on arbitrary meshes
    Kenamond, M. and Kuzmin, D. and Shashkov, M.
    Journal of Computational Physics 435 (2021)
    We introduce new intersection-distribution-based remapping tools for indirect staggered arbitrary Lagrangian-Eulerian (ALE) simulations of multi-material shock hydrodynamics on arbitrary meshes. In addition to conserving momentum and total energy, the three-stage remapper proposed in this work preserves non-negativity of the internal energy. At the first stage, we construct slope-limited piecewise-linear reconstructions of all conserved quantities on zones of the source mesh and perform intersection-based remap to obtain bound-preserving zonal quantities on the target mesh. At the second stage, we define bound-preserving nodal quantities of the staggered ALE discretization as convex combinations of corner quantities. The nodal internal energy is corrected in a way which keeps it non-negative, while providing exact conservation of total energy. At the final stage, we distribute the non-negative nodal internal energy to corners, zones and materials using non-negative weights. Proofs of positivity preservation are provided for each stage. This work is a natural extension of our paper [14] in which a similar intersection-distribution-based remapping procedure was employed. The original version used a nodal kinetic energy fix which did not provably ensure positivity preservation for the zonal internal energy after the final distribution stage. The new algorithm cures this potential drawback by using ‘coordinated’ limiters for piecewise-linear reconstructions, remapping the internal energy to nodes and correcting it before redistribution. The effectiveness of the new nodal fix is illustrated by numerical examples. © 2021 Elsevier Inc.
    view abstractdoi: 10.1016/j.jcp.2021.110254
  • 2021 • 840 A safety cap protects hydrogenase from oxygen attack
    Winkler, M. and Duan, J. and Rutz, A. and Felbek, C. and Scholtysek, L. and Lampret, O. and Jaenecke, J. and Apfel, U.-P. and Gilardi, G. and Valetti, F. and Fourmond, V. and Hofmann, E. and Léger, C. and Happe, T.
    Nature Communications 12 (2021)
    [FeFe]-hydrogenases are efficient H2-catalysts, yet upon contact with dioxygen their catalytic cofactor (H-cluster) is irreversibly inactivated. Here, we combine X-ray crystallography, rational protein design, direct electrochemistry, and Fourier-transform infrared spectroscopy to describe a protein morphing mechanism that controls the reversible transition between the catalytic Hox-state and the inactive but oxygen-resistant Hinact-state in [FeFe]-hydrogenase CbA5H of Clostridium beijerinckii. The X-ray structure of air-exposed CbA5H reveals that a conserved cysteine residue in the local environment of the active site (H-cluster) directly coordinates the substrate-binding site, providing a safety cap that prevents O2-binding and consequently, cofactor degradation. This protection mechanism depends on three non-conserved amino acids situated approximately 13 Å away from the H-cluster, demonstrating that the 1st coordination sphere chemistry of the H-cluster can be remote-controlled by distant residues. © 2021, The Author(s).
    view abstractdoi: 10.1038/s41467-020-20861-2
  • 2021 • 839 A Selection of Benchmark Problems in Solid Mechanics and Applied Mathematics
    Schröder, J. and Wick, T. and Reese, S. and Wriggers, P. and Müller, R. and Kollmannsberger, S. and Kästner, M. and Schwarz, A. and Igelbüscher, M. and Viebahn, N. and Bayat, H.R. and Wulfinghoff, S. and Mang, K. and Rank, E. ...
    Archives of Computational Methods in Engineering 28 713-751 (2021)
    In this contribution we provide benchmark problems in the field of computational solid mechanics. In detail, we address classical fields as elasticity, incompressibility, material interfaces, thin structures and plasticity at finite deformations. For this we describe explicit setups of the benchmarks and introduce the numerical schemes. For the computations the various participating groups use different (mixed) Galerkin finite element and isogeometric analysis formulations. Some programming codes are available open-source. The output is measured in terms of carefully designed quantities of interest that allow for a comparison of other models, discretizations, and implementations. Furthermore, computational robustness is shown in terms of mesh refinement studies. This paper presents benchmarks, which were developed within the Priority Programme of the German Research Foundation ‘SPP 1748 Reliable Simulation Techniques in Solid Mechanics—Development of Non-Standard Discretisation Methods, Mechanical and Mathematical Analysis’. © 2020, The Author(s).
    view abstractdoi: 10.1007/s11831-020-09477-3
  • 2021 • 838 A self-matched leaky-wave antenna for ultrahigh-field magnetic resonance imaging with low specific absorption rate
    Solomakha, G. and Svejda, J.T. and van Leeuwen, C. and Rennings, A. and Raaijmakers, A.J. and Glybovski, S. and Erni, D.
    Nature Communications 12 (2021)
    The technology of magnetic resonance imaging is developing towards higher magnetic fields to improve resolution and contrast. However, whole-body imaging at 7 T or even higher flux densities remains challenging due to wave interference, tissue inhomogeneities, and high RF power deposition. Nowadays, proper RF excitation of a human body in prostate and cardiac MRI is only possible to achieve by using phased arrays of antennas attached to the body (so-called surface coils). Due to safety concerns, the design of such coils aims at minimization of the local specific absorption rate (SAR), keeping the highest possible RF signal in the region of interest. Most previously demonstrated approaches were based on resonant structures such as e.g. dipoles, capacitively-loaded loops, TEM-line sections. In this study, we show that there is a better compromise between the transmit signal B1+ and the local SAR using non-resonant surface coils generating a low electric field in the proximity of their conductors. With this aim, we propose and experimentally demonstrate a leaky-wave antenna implemented as a periodically-slotted microstrip transmission line. Due to its non-resonant radiation, it induces only slightly over half the peak local SAR compared to a state-of-the-art dipole antenna but has the same transmit efficiency in prostate imaging at 7 T. Unlike other antennas for MRI, the leaky-wave antenna does not require to be tuned and matched when placed on a body, which makes it easy-to-use in prostate imaging at 7 T MRI. © 2021, The Author(s).
    view abstractdoi: 10.1038/s41467-020-20708-w
  • 2021 • 837 A silicon carbide-based highly transparent passivating contact for crystalline silicon solar cells approaching efficiencies of 24%
    Köhler, M. and Pomaska, M. and Procel, P. and Santbergen, R. and Zamchiy, A. and Macco, B. and Lambertz, A. and Duan, W. and Cao, P. and Klingebiel, B. and Li, S. and Eberst, A. and Luysberg, M. and Qiu, K. and Isabella, O. and F...
    Nature Energy 6 529-537 (2021)
    A highly transparent passivating contact (TPC) as front contact for crystalline silicon (c-Si) solar cells could in principle combine high conductivity, excellent surface passivation and high optical transparency. However, the simultaneous optimization of these features remains challenging. Here, we present a TPC consisting of a silicon-oxide tunnel layer followed by two layers of hydrogenated nanocrystalline silicon carbide (nc-SiC:H(n)) deposited at different temperatures and a sputtered indium tin oxide (ITO) layer (c-Si(n)/SiO2/nc-SiC:H(n)/ITO). While the wide band gap of nc-SiC:H(n) ensures high optical transparency, the double layer design enables good passivation and high conductivity translating into an improved short-circuit current density (40.87 mA cm−2), fill factor (80.9%) and efficiency of 23.99 ± 0.29% (certified). Additionally, this contact avoids the need for additional hydrogenation or high-temperature postdeposition annealing steps. We investigate the passivation mechanism and working principle of the TPC and provide a loss analysis based on numerical simulations outlining pathways towards conversion efficiencies of 26%. © 2021, The Author(s).
    view abstractdoi: 10.1038/s41560-021-00806-9
  • 2021 • 836 A similarity measure for second order properties of non-stationary functional time series with applications to clustering and testing
    van Delft, A. and Dette, H.
    Bernoulli 27 469-501 (2021)
    Due to the surge of data storage techniques, the need for the development of appropriate techniques to identify patterns and to extract knowledge from the resulting enormous data sets, which can be viewed as collections of dependent functional data, is of increasing interest in many scientific areas. We develop a similarity measure for spectral density operators of a collection of functional time series, which is based on the aggregation of Hilbert–Schmidt differences of the individual time-varying spectral density operators. Under fairly general conditions, the asymptotic properties of the corresponding estimator are derived and asymptotic normality is established. The introduced statistic lends itself naturally to quantify (dis)-similarity between functional time series, which we subsequently exploit in order to build a spectral clustering algorithm. Our algorithm is the first of its kind in the analysis of non-stationary (functional) time series and enables to discover particular patterns by grouping together ‘similar’ series into clusters, thereby reducing the complexity of the analysis considerably. The algorithm is simple to implement and computationally feasible. As a further application, we provide a simple test for the hypothesis that the second order properties of two non-stationary functional time series coincide. © 2021 ISI/BS.
    view abstractdoi: 10.3150/20-BEJ1246
  • 2021 • 835 A stochastic Gronwall inequality and applications to moments, strong completeness, strong local Lipschitz continuity, and perturbations
    Hudde, A. and Hutzenthaler, M. and Mazzonetto, S.
    Annales de l'institut Henri Poincare (B) Probability and Statistics 57 603-626 (2021)
    There are numerous applications of the classical (deterministic) Gronwall inequality. Recently, Michael Scheutzow discovered a stochastic Gronwall inequality which provides upper bounds for p-th moments, p ∈ (0, 1), of the supremum of nonnegative scalar continuous processes which satisfy a linear integral inequality. In this article we complement this with upper bounds for p-th moments, p ∈ [2,∞), of the supremum of general Itô processes which satisfy a suitable one-sided affine-linear growth condition. As example applications, we improve known results on strong local Lipschitz continuity in the starting point of solutions of stochastic differential equations (SDEs), on (exponential) moment estimates for SDEs, on strong completeness of SDEs, and on perturbation estimates for SDEs. © 2021 Institute of Mathematical Statistics. All rights reserved.
    view abstractdoi: 10.1214/20-AIHP1064
  • 2021 • 834 A Tandem Solar Biofuel Cell: Harnessing Energy from Light and Biofuels
    Riedel, M. and Höfs, S. and Ruff, A. and Schuhmann, W. and Lisdat, F.
    Angewandte Chemie - International Edition 60 2078-2083 (2021)
    We report on a photobioelectrochemical fuel cell consisting of a glucose-oxidase-modified BiFeO3 photobiocathode and a quantum-dot-sensitized inverse opal TiO2 photobioanode linked to FAD glucose dehydrogenase via a redox polymer. Both photobioelectrodes are driven by enzymatic glucose conversion. Whereas the photobioanode can collect electrons from sugar oxidation at rather low potential, the photobiocathode shows reduction currents at rather high potential. The electrodes can be arranged in a sandwich-like manner due to the semi-transparent nature of BiFeO3, which also guarantees a simultaneous excitation of the photobioanode when illuminated via the cathode side. This tandem cell can generate electricity under illumination and in the presence of glucose and provides an exceptionally high OCV of about 1 V. The developed semi-artificial system has significant implications for the integration of biocatalysts in photoactive entities for bioenergetic purposes, and it opens up a new path toward generation of electricity from sunlight and (bio)fuels. © 2020 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/anie.202012089
  • 2021 • 833 A taxonomy for data ecosystems
    Gelhaar, J. and Groß, T. and Otto, B.
    Proceedings of the Annual Hawaii International Conference on System Sciences 2020-January 6113-6122 (2021)
    In the increasingly interconnected business world, economic value is less and less created by one company alone but rather through the combination and enrichment of data by various actors in so-called data ecosystems. The research field around data ecosystems is, however, still in its infancy. With this study, we want to address this issue and contribute to a deeper understanding of data ecosystems. Therefore, we develop a taxonomy for data ecosystems which is grounded both theoretically through the linkage to the scientific knowledge base and empirically through the analyses of data ecosystem use cases. The resulting taxonomy consists of key dimensions and characteristics of data ecosystems and contributes to a better scientific understanding of this concept. Practitioners can use the taxonomy as an instrument to further understand, design and manage the data ecosystems their organizations are involved in. © 2021 IEEE Computer Society. All rights reserved.
    view abstract
  • 2021 • 832 A Time-Simultaneous Multigrid Method for Parabolic Evolution Equations
    Dünnebacke, J. and Turek, S. and Zajac, P. and Sokolov, A.
    Lecture Notes in Computational Science and Engineering 139 333-342 (2021)
    We present a time-simultaneous multigrid scheme for parabolic equations that is motivated by blocking multiple time steps together. The resulting method is closely related to multigrid waveform relaxation and is robust with respect to the spatial and temporal grid size and the number of simultaneously computed time steps. We give an intuitive understanding of the convergence behavior and briefly discuss how the theory for multigrid waveform relaxation can be applied in some special cases. Finally, some numerical results for linear and also nonlinear test cases are shown. © 2021, Springer Nature Switzerland AG.
    view abstractdoi: 10.1007/978-3-030-55874-1_32
  • 2021 • 831 A unified description of non-radiative voltage losses in organic solar cells
    Chen, X.-K. and Qian, D. and Wang, Y. and Kirchartz, T. and Tress, W. and Yao, H. and Yuan, J. and Hülsbeck, M. and Zhang, M. and Zou, Y. and Sun, Y. and Li, Y. and Hou, J. and Inganäs, O. and Coropceanu, V. and Bredas, J.-L. and Gao, F.
    Nature Energy (2021)
    Recent advances in organic solar cells based on non-fullerene acceptors (NFAs) come with reduced non-radiative voltage losses (ΔVnr). Here we show that, in contrast to the energy-gap-law dependence observed in conventional donor:fullerene blends, the ΔVnr values in state-of-the-art donor:NFA organic solar cells show no correlation with the energies of charge-transfer electronic states at donor:acceptor interfaces. By combining temperature-dependent electroluminescence experiments and dynamic vibronic simulations, we provide a unified description of ΔVnr for both fullerene- and NFA-based devices. We highlight the critical role that the thermal population of local exciton states plays in low-ΔVnr systems. An important finding is that the photoluminescence yield of the pristine materials defines the lower limit of ΔVnr. We also demonstrate that the reduction in ΔVnr (for example, &lt;0.2 V) can be obtained without sacrificing charge generation efficiency. Our work suggests designing donor and acceptor materials with high luminescence efficiency and complementary optical absorption bands extending into the near-infrared region. © 2021, The Author(s), under exclusive licence to Springer Nature Limited.
    view abstractdoi: 10.1038/s41560-021-00843-4
  • 2021 • 830 A vehicle guidance model with a close-to-reality driver model and different levels of vehicle automation
    Ma, X. and Hu, X. and Schweig, S. and Pragalathan, J. and Schramm, D.
    Applied Sciences (Switzerland) 11 1-11 (2021)
    This paper presents a microscopic vehicle guidance model which adapts to different levels of vehicle automation. Independent of the vehicle, the driver model built is different from the common microscopic simulation models that regard the driver and the vehicle as a unit. The term “Vehicle Guidance Model” covers, here, both the human driver as well as a combination of human driver and driver assistance system up to fully autonomously operated vehicles without a (human) driver. Therefore, the vehicle guidance model can be combined with different kinds of vehicle models. As a result, the combination of different types of driver (human/machine) and different types of vehicle (internal combustion engine/electric) can be simulated. Mainly two parts constitute the vehicle guidance model in this paper: The first part is a traditional microscopic car-following model adjusted according to different degrees of automation level. The adjusted model represents the automation level for the present and the near and the more distant future. The second part is a fuzzy control model that describes how humans adjust the pedal position when they want to reach a target speed with their vehicle. An experiment with 34 subjects was carried out with a driving simulator based on the experimental data and the fuzzy control strategy was determined. Finally, when comparing the simulated model data and actual driving data, it is found that the fuzzy model for the human driver can reproduce the behavior of human participants almost accurately. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/app11010380
  • 2021 • 829 A W-Band Transceiver Chip for Future 5G Communications in InP-DHBT Technology
    Hossain, M. and Shivan, T. and Hrobak, M. and Al-Sawaf, T. and Stoppel, D. and Yacoub, H. and Weimann, N. and Heinrich, W. and Krozer, V.
    EuMIC 2020 - 2020 15th European Microwave Integrated Circuits Conference 193-196 (2021)
    This paper presents a W-band transceiver chip using InP-DHBT technology for future 5G application. It consists of a transceiver switch, a medium power amplifier (MPA) and a low noise amplifier (LNA) in 0.8 µm InP-DHBT technology. The switch operates from 75 GHz to 110 GHz and simulation results show more than 20 dB isolation and 1 dB output power (P1dBout) of 15 dBm. The measured MPA exhibits 16 dBm saturated output power (Psat) with 18 % power added efficiency (PAE) at 90 GHz. The measured LNA small signal gain is higher than 30 dB from 75 to 110 GHz and the measured noise figure values are below 9 dB. After integrating individual components (switch, LNA and PA), the entire transceiver chip achieves a measured isolation of more than 15 dB. The entire circuit consumes total 280 mW DC power. The chip area is only 2.5x1.5 mm2, To the knowledge of the authors, this is the first monolithically integrated transceiver covering the W-band for future 5G communication reported so far. © 2021 EuMA.
    view abstract
  • 2021 • 828 Ab initio based models for temperature-dependent magnetochemical interplay in bcc Fe-Mn alloys
    Schneider, A. and Fu, C.-C. and Waseda, O. and Barreteau, C. and Hickel, T.
    Physical Review B 103 (2021)
    Body-centered cubic (bcc) Fe-Mn systems are known to exhibit a complex and atypical magnetic behavior from both experiments and 0 K electronic-structure calculations, which is due to the half-filled 3d band of Mn. We propose effective interaction models for these alloys, which contain both atomic-spin and chemical variables. They were parameterized on a set of key density functional theory (DFT) data, with the inclusion of noncollinear magnetic configurations being indispensable. Two distinct approaches, namely a knowledge-driven and a machine-learning approach have been employed for the fitting. Employing these models in atomic Monte Carlo simulations enables the prediction of magnetic and thermodynamic properties of the Fe-Mn alloys, and their coupling, as functions of temperature. This includes the decrease of Curie temperature with increasing Mn concentration, the temperature evolution of the mixing enthalpy, and its correlation with the alloy magnetization. Also, going beyond the defect-free systems, we determined the binding free energy between a vacancy and a Mn atom, which is a key parameter controlling the atomic transport in Fe-Mn alloys. © 2021 American Physical Society.
    view abstractdoi: 10.1103/PhysRevB.103.024421
  • 2021 • 827 Ab initio study of the structural response to magnetic disorder and van der Waals interactions in FeSe
    Lochner, F. and Eremin, I.M. and Hickel, T. and Neugebauer, J.
    Physical Review B 103 (2021)
    The electronic structure in unconventional superconductors holds a key to understanding the momentum-dependent pairing interactions and the resulting superconducting gap function. In superconducting Fe-based chalcogenides, there have been controversial results regarding the importance of the kz dependence of the electronic dispersion, the gap structure, and the pairing mechanisms. Here, we use density functional theory to investigate the underlying structural properties in combination with a sophisticated real-space treatment of magnetic disorder for the prototype system FeSe. Our calculations demonstrate that interlayer and intralayer interactions need to be considered and that charge-driven van der Waals interactions between Se atoms instead of magnetic coupling effects drive the interlayer binding. The methodological advances and physical insights are important for upcoming investigations of the three-dimensional effects, including nontrivial topology, of FeSe1-xTex and FeSe1-xSx systems. © 2021 American Physical Society.
    view abstractdoi: 10.1103/PhysRevB.103.054506
  • 2021 • 826 Achieving ultra-low friction with diamond/metal systems in extreme environments
    Stoyanov, P. and Merz, R. and Stricker, M. and Kopnarski, M. and Dienwiebel, M.
    Materials 14 (2021)
    In the search for achieving ultra-low friction for applications in extreme environments, we evaluate the interfacial processes of diamond/tungsten sliding contacts using an on-line macro-tribometer and a micro-tribometer in an ultra-high vacuum. The coefficient of friction for the tests with the on-line tribometer remained considerably low for unlubricated sliding of tungsten, which correlated well with the relatively low wear rates and low roughness on the wear track throughout the sliding. Ex situ analysis was performed by means of XPS and SEM-FIB in order to better understand the underlying mechanisms of low friction and low-wear sliding. The analysis did not reveal any evidence of tribofilm or transferfilm formation on the counterface, indicating the absence of significant bonding between the diamond and tungsten surfaces, which correlated well with the low-friction values. The minimal adhesive interaction and material transfer can possibly be explained by the low initial roughness values as well as high cohesive bonding energies of the two materials. The appearance of the wear track as well as the relatively higher roughness perpendicular to the sliding indicated that abrasion was the main wear mechanism. In order to elucidate the low friction of this tribocouple, we performed micro-tribological experiments in ultra-high vacuum conditions. The results show that the friction coefficient was reduced significantly in UHV. In addition, subsequently to baking the chamber, the coefficient of friction approached ultra-low values. Based on the results obtained in this study, the diamond/tungsten tribocouple seems promising for tribological interfaces in spacecraft systems, which can improve the durability of the components. © 2021 by the authors Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/ma14143791
  • 2021 • 825 Acoustic waveform inversion in frequency domain: Application to a tunnel environment
    Riedel, C. and Musayev, K. and Baitsch, M. and Zhu, H. and Hackl, K.
    Underground Space (China) (2021)
    Waveform inversion is an approach used to find an optimal model for the velocity field of a ground structure such that the dynamic response is close enough to the given seismic data. First, a suitable numerical approach is employed to establish a realistic forward computer model. The forward problem is solved in the frequency domain using higher-order finite elements. The velocity field is inverted over a specific number of discrete frequencies, thereby reducing the computational cost of the forward calculation and the nonlinearity of the inverse problem. The results are presented for different frequency sets and with different source and receiver locations for a two-dimensional model. The influence of attenuation effects is also investigated. The results of two blind tests are presented where only the seismic records of an unknown synthetic model with an inhomogeneous material parameter distribution are provided to mimic a more realistic case. Finally, the result of the inversion in a three-dimensional space is illustrated. © 2021 Tongji University
    view abstractdoi: 10.1016/j.undsp.2021.01.001
  • 2021 • 824 Activation of Molecular Hydrogen by Inter- and Intramolecular Al−N Lewis Pairs
    Bodach, A. and Nöthling, N. and Felderhoff, M.
    European Journal of Inorganic Chemistry 2021 1240-1243 (2021)
    The field of frustrated Lewis pair chemistry offers many opportunities to activate molecular hydrogen, but Al−N systems have not been established yet. In this work, we describe several intermolecular classical Al−N Lewis pairs and an intramolecular ortho-ala-aminoarene for the activation of molecular hydrogen. Their ability was investigated using the isotope exchange reaction from HD to H2 and D2. The herein studied intermolecular Lewis pairs were based on alkylalanes and N-methyldiphenylamine, while the intramolecular Lewis pair was (o-TMP−C6H4)AlH2 ((2-(2,2,6,6-tetramethyl-piperidin-1-yl)phenyl)-aluminium dihydride). The activation of molecular hydrogen was carried out in toluene under mild conditions and monitored by 1H and 2H NMR spectroscopy. Furthermore, the Al−N interaction has been probed by 27Al NMR and crystallographic studies. Additionally, the crystal structure of pure AliBu3 was determined. These studies may attribute the pronounced reactivities of these Al−N compounds to elongated Al−N bond lengths. © 2021 The Authors. European Journal of Inorganic Chemistry published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/ejic.202001152
  • 2021 • 823 Adaptation of cluster analysis methods to optimize a biomechanical motion model of humans in a nursing bed
    Demmer, J. and Kitzig, A. and Stockmanns, G. and Naroska, E. and Viga, R. and Grabmaier, A.
    European Signal Processing Conference 2021-January 1323-1327 (2021)
    The paper considers the optimization of a Hidden-Markov Model (HMM) based method for the generation of averaged motion sequences. To create averaged motion sequences, motion sequences of different test persons were originally recorded with a motion capture system (MoCap system) and then averaged using an HMM approach. The resulting averaged data sets, however, partly showed serious motion artifacts and uncoordinated intermediate movements, especially in the extremities. The aim of this work was to combine only movements with similar courses in the extremities by a suitable cluster analysis. For each test person, model body descriptions of 21 body elements are available, each of which is represented in three-dimensional time series. For optimization, the MoCap data are first compared using time warp edit distance (TWED) and clustered using an agglomerative hierarchical procedure. Finally, the data of the resulting clusters are used to generate new averaged motion sequences using the HMM approach. The resulting averaged data can be used, for example, in a simulation in a multilevel biomechanical model. © 2021 European Signal Processing Conference, EUSIPCO. All rights reserved.
    view abstractdoi: 10.23919/Eusipco47968.2020.9287503
  • 2021 • 822 Adaptive sampling point planning for free-form surface inspection under multi-geometric constraints
    Yi, B. and Qiao, F. and Huang, N. and Wang, X. and Wu, S. and Biermann, D.
    Precision Engineering 72 95-101 (2021)
    Free-form surfaces have been widely used in aerospace, automotive and other fields. Due to its complex geometry, free-form surface inspection is generally conducted by touch-trigger or measuring probe-based Coordinate Measurement Machines or On-machine Measurement. Sampling strategy plays a decisive role in improving both measurement accuracy and efficiency, which is determined by sample size and distribution of sample points. However, it is difficult to simultaneously take the surface curvature, sampling density and approximation error into account, considering the complexity of surface geometry. In this paper, triangle mesh simplification is innovatively adopted in sampling planning to achieve multi-geometric constraints. As triangle mesh has outstanding advantages in representing the surface features, strong stability and is easy to modify its structure, free-form surface is converted to a dense triangle mesh. Triangle mesh simplification is implemented by iteratively contracting triangle edges. An improved quadric error metric is established to decide contraction order and optimal target vertices under discrete curvature constraint. Sampling density is controlled by limiting the triangle edge length. Detailed adaptive sampling algorithm under multi-geometric constraints is then developed. Both simulation and experiment are conducted to validate feasibility and robustness of the proposed method. The results are compared with uniform sampling and existing adaptive sampling strategy to show that the proposed method can prominently reduce sampling error when sample size is small. © 2021 Elsevier Inc.
    view abstractdoi: 10.1016/j.precisioneng.2021.04.009
  • 2021 • 821 Adaptive thermodynamic topology optimization
    Vogel, A. and Junker, P.
    Structural and Multidisciplinary Optimization 63 95-119 (2021)
    The benefit of adaptive meshing strategies for a recently introduced thermodynamic topology optimization is presented. Employing an elementwise gradient penalization, stability is obtained and checkerboarding prevented while very fine structures can be resolved sharply using adaptive meshing at material-void interfaces. The usage of coarse elements and thereby smaller design space does not restrict the obtainable structures if a proper adaptive remeshing is considered during the optimization. Qualitatively equal structures and quantitatively the same stiffness as for uniform meshing are obtained with less degrees of freedom, memory requirement and overall optimization runtime. In addition, the adaptivity can be used to zoom into coarse global structures to better resolve details of interesting spots such as truss nodes. © 2020, The Author(s).
    view abstractdoi: 10.1007/s00158-020-02667-4
  • 2021 • 820 Additive manufacturing of PA12 carbon nanotube composites with a novel laser polymer deposition process
    Wencke, Y.L. and Kutlu, Y. and Seefeldt, M. and Esen, C. and Ostendorf, A. and Luinstra, G.A.
    Journal of Applied Polymer Science 138 (2021)
    The facile manufacture of PA12 MWCNT/silica (50/50 by weight) nanocomposite powders through a high energy mixing process is presented, which are useful to generate 3D objects by a novel Laser Polymer Deposition (LPD) process. The mixing as well as the LPD process led to no discernible changes in the material properties (DSC, SEM, LD) of the core-shell nanocomposites, enabling the recycling of unconverted powder. The built parts yield ultimate tensile stresses and Young's modulus at 10%–20% of the bulk material. Partially unmolten particles and voids were identified as the main mechanical failure mechanism in the built parts. The mechanical properties are better with low additive content (Young's modulus: 89.8 ± 5.4 MPa; UTS: 12.9 ± 5.3 MPa with 0.25 wt% additives). Electronic conductivity up to the region of moderate conductivity could be achieved by multiwalled carbon nanotube (MWCNT) network formation (8 × 10−4 S cm−1 at 1.25 wt% of additives). A variant of the processing strategy revealed that a higher mechanical strength can be achieved by a laser induced remelting of the traces following their initial construction. © 2020 The Authors. Journal of Applied Polymer Science published by Wiley Periodicals LLC.
    view abstractdoi: 10.1002/app.50395
  • 2021 • 819 Adhesion area estimation using backscatter image gray level masking of uncoated tungsten carbide tools
    Alammari, Y. and Iovkov, I. and Berger, S. and Saelzer, J. and Biermann, D.
    Wear 476 (2021)
    Machining tribology research reveals that adhesion of the workpiece material to the cutting tool is an important aspect that governs a number of physical parameters within the tool-chip interface. Adhesion is especially a concern during machining difficult-to-cut materials such as nickel-based alloys. Adhesion may cause tool wear that leads to premature tool failure, or it may trigger other wear modes, hindering machinability and reducing product quality. Many researchers are investigating adhesion fundamentals, adhesion quantification being an indispensable tool. The research suggests strategies to reduce adhesion's undesirable effects. However, when many experimental trials are required, time-consuming adhesion quantification may cause a bottleneck. This study proposes an efficient adhesion area quantification method using image processing of discrete gray intensities on backscatter images of uncoated tungsten carbide inserts, revealed by scanning inserts through an electron microscope. The obtained images are analyzed statistically from their gray-level intensity distribution. A recognizable gray-level range, located around a peak in the histogram, corresponds to adhered material and can easily be distinguished from the background tool material. Hence, adhesion pixels are masked and counted in a statistically controlled manner. The total adhesion area is subsequently quantified by summing the total number of adhesion pixel areas. This method is applied to quantify the resulting adhesion for a variation of the cutting speed, based on a number of orthogonal machining trials carried out on nickel-based superalloy NiCr19Fe19Nb5Mo3 (2.4668), using uncoated tungsten carbide inserts. K-means clustering algorithm is applied for image segmentation, and elemental mapping is obtained by energy dispersive x-ray spectroscopy; both are used to evaluate the effectiveness of the proposed method. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.wear.2021.203666
  • 2021 • 818 Adjusting residual stresses by flexible stress superposition in incremental sheet metal forming
    Maaß, F. and Hahn, M. and Tekkaya, A.E.
    Archive of Applied Mechanics 91 3489-3499 (2021)
    Process-induced residual stresses significantly influence the mechanical properties of a formed component. A polymer pad is used as a flexible die in two-point incremental forming to induce compressive residual stresses in the component during the forming process. Experimental and numerical results illustrate the influence of compressive stress superposition on the component properties. It is shown that the active support, using a geometry-independent polyurethane die, causes beneficial compressive residual stresses on the tool side compared to the tensile residual stresses induced by the single-point incremental forming process without such a supporting die. © 2021, The Author(s).
    view abstractdoi: 10.1007/s00419-021-01929-x
  • 2021 • 817 Advanced characterisation techniques: Multi-scale,: In situ, and time-resolved: General discussion
    Brammer, L. and Burrows, A.D. and Chong, S.Y.-L. and Craig, G. and Evans, J. and Farha, O. and Farrusseng, D. and Fischer, M. and Goodwin, A. and Huang, Z. and Johnson, B. and Kaskel, S. and Kitagawa, S. and Lavenn, C. and Lee, A....
    Faraday Discussions 225 152-167 (2021)
    doi: 10.1039/D0FD90032J
  • 2021 • 816 Alumina-Protected, Durable and Photostable Zinc Sulfide Particles from Scalable Atomic Layer Deposition
    Lange, T. and Reichenberger, S. and Rohe, M. and Bartsch, M. and Kampermann, L. and Klein, J. and Strunk, J. and Bacher, G. and Schlögl, R. and Barcikowski, S.
    Advanced Functional Materials 31 (2021)
    Zinc sulfide has unique and easily modifiable photophysical properties and is a promising candidate for photocatalysis and optoelectronic devices. However, ZnS suffers from corrosive decomposition during excitation processes like UV irradiation, which drastically limits its field of potential applications. For the first time, complete photostabilization of individual ZnS particles by a dense, durable, and only 3-nm-thick Al2O3 layer, produced by rotary atomic layer deposition (ALD) is reported. In contrast to bare ZnS, the coated particles do not suffer from photocorrosive degradation even under long-term or high power UV irradiation. The presence of a protection layer covering the entire ZnS surface is additionally confirmed by microscopic and spectroscopic investigations of particle cross-sections. Further, complete inhibition of the reaction between Ag+ ions added as the analyte and the ZnS surface is observed. Durability tests of the as-prepared Al2O3 layer upon prolonged exposure to water reveal a significant decrease in the protection capability of the layer, which is ascribed to the hydrolysis of the amorphous Al2O3. A calcination step at 1000 °C after the ALD treatment, which leads to crystallization of the amorphous Al2O3 layer, successfully suppresses this hydrolysis and produces an insulating, dense, and inert protection layer. © 2021 The Authors. Advanced Functional Materials published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/adfm.202009323
  • 2021 • 815 Amino−Organolithium Compounds and their Aggregation for the Synthesis of Amino−Organoaluminium Compounds
    Bodach, A. and Ortmeyer, J. and Herrmann, B. and Felderhoff, M.
    European Journal of Inorganic Chemistry 2021 2248-2256 (2021)
    Here, we present a thorough structural study of small, easily accessible amino−organolithium compounds with bridging phenyl and naphthyl moieties. Their crystal structures most likely represent their aggregation as tetramers and dimers in both hydrocarbon and ethereal solvents. These amino−organolithium compounds were further used to generate their corresponding aluminium compounds as a model system. Their crystal structures are reported too. All structures are discussed with a focus on the different steric demands and bridging moieties. Additionally, the crystal structures of neophyllithium and decomposition products of some of the compounds mentioned above are reported. This study provides additional data for the future design and synthesis of amine stabilised organolithium and -aluminium compounds. © 2021 The Authors. European Journal of Inorganic Chemistry published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/ejic.202100224
  • 2021 • 814 Ammonia Synthesis and Mechanochemistry
    Felderhoff, M.
    Joule 5 297-299 (2021)
    Ammonia synthesis is one of the world's largest chemical processes and therefore also one of the world's largest CO2 emitters. New developments that operate under milder reaction conditions and environmentally friendly methods for supplying the feedstock for ammonia can significantly reduce these emissions. Mechanochemical processes have been in the focus of chemist for several years. Consequently, mechanochemical processes for the synthesis of ammonia are under development. © 2021 Elsevier Inc. Ammonia synthesis is one of the world's largest chemical processes and therefore also one of the world's largest CO2 emitters. New developments that operate under milder reaction conditions and environmentally friendly methods for supplying the feedstock for ammonia can significantly reduce these emissions. Mechanochemical processes have been in the focus of chemist for several years. Consequently, mechanochemical processes for the synthesis of ammonia are under development. © 2021 Elsevier Inc.
    view abstractdoi: 10.1016/j.joule.2021.01.009
  • 2021 • 813 Amphiphilic poly(arylene ether sulfone) multiblock copolymers with quaternary ammonium groups for novel thin-film composite nanofiltration membranes
    Wieczorek, J. and Ulbricht, M.
    Polymer 217 (2021)
    Amphiphilic poly(arylene ether sulfone) (PAES) multiblock copolymers with quaternary ammonium groups were evaluated as tunable, size-selective barrier material in thin-film composite (TFC) nanofiltration membranes. Using a two-step synthesis, well-defined PAES multiblock copolymers with molecular weight (Mn) of at least 50 kg/mol were obtained. Conversion to anion-exchange polymers was accomplished by block-selective bromination of methyl side groups at adjusted degree of functionalization and subsequent quantitative amination using triethanolamine. A library of copolymers with varied block length ratios and ion-exchange capacities (IEC; up to 2 mmol/g) was obtained. PAES multiblock copolymers with suited hydrophilic/hydrophobic balance to yield films that are stable in water were further evaluated. Film casting of solutions of anion-exchange copolymers on a porous polyacrylonitrile support and solvent evaporation yielded TFC membranes with barrier layer thickness in the range of 1.5–1.9 μm. Nanofiltration performance was measured with glycerine, glucose, sucrose, NaCl, MgCl2 and FeCl3 in water. While for a random copolymer with similar composition and same thickness, no water flux could be measured, the novel TFC membranes had permeances in the range of 1 L m−2 bar−1·h−1, at &gt;99.9% rejection for glucose. Permeance increased and rejection (for glycerine and salt) decreased systematically with increasing IEC; an additional influence of block length ratio was identified. A membrane made from a block copolymer with longer hydrophobic block and moderate IEC of 0.9 mmol/g showed the best “trade-off” between permeability and selectivity. Furthermore, the stability of the novel membranes under oxidative disinfection conditions was demonstrated. © 2021 Elsevier Ltd
    view abstractdoi: 10.1016/j.polymer.2021.123446
  • 2021 • 812 Amphiphilic Zwitterionic Acrylate/Methacrylate Copolymers for Marine Fouling-Release Coatings
    Koschitzki, F. and Wanka, R. and Sobota, L. and Gardner, H. and Hunsucker, K.Z. and Swain, G.W. and Rosenhahn, A.
    Langmuir 37 5591-5600 (2021)
    Methacrylate and acrylate monomers are popular building blocks for antifouling (AF) and fouling-release (FR) coatings to counteract marine biofouling. They are used in various combinations and often combined into amphiphilic materials. This study investigated the FR properties of amphiphilic ethylene glycol dicyclopentenyl ether acrylate (DCPEA) and the corresponding methacrylate (DCPEMA) blended with 5 wt % zwitterionic carboxybetaine acrylate (CBA) and the corresponding methacrylate (CBMA). A series of (co)polymers with different acrylate/methacrylate compositions were synthesized and tested against the attachment of the diatom Navicula perminuta and in short-term dynamic field exposure experiments. The more hydrophobic methacrylate DCPEMA homopolymer outperformed its acrylate counterpart DCPEA. Incorporated zwitterionic functionality of both CBMA and CBA imparted ultralow fouling capability in the amphiphilic polymers toward diatom attachment, whereas in the real ocean environment, only the employment of CBMA reduced marine biofouling. Moreover, it was observed that CBA-containing coatings showed different surface morphologies and roughnesses compared to the CBMA analogues. Particularly, a high impact was found when acrylic CBA was mixed with methacrylic DCPEMA. While the wettability of the coatings was comparable, investigated methacrylates in general exhibited superior fouling resistance compared to the acrylates. © 2021 American Chemical Society. All rights reserved.
    view abstractdoi: 10.1021/acs.langmuir.1c00428
  • 2021 • 811 An Adaptive Finite Element Scheme for the Hellinger-Reissner Elasticity Mixed Eigenvalue Problem
    Bertrand, F. and Boffi, D. and Ma, R.
    Computational Methods in Applied Mathematics 21 501-512 (2021)
    In this paper, we study the approximation of eigenvalues arising from the mixed Hellinger-Reissner elasticity problem by using a simple finite element introduced recently by one of the authors. We prove that the method converges when a residual type error estimator is considered and that the estimator decays optimally with respect to the number of degrees of freedom. A postprocessing technique originally proposed in a different context is discussed and tested numerically. © 2021 Walter de Gruyter GmbH, Berlin/Boston 2021.
    view abstractdoi: 10.1515/cmam-2020-0034
  • 2021 • 810 An Algorithm for Dependency-Preserving Smart Home Updates
    Zdankin, P. and Schaffeld, M. and Waltereit, M. and Carl, O. and Weis, T.
    2021 IEEE International Conference on Pervasive Computing and Communications Workshops and other Affiliated Events, PerCom Workshops 2021 527-532 (2021)
    The update process of devices in a smart home is a complex endeavour. Individual device updates can influence the functionality of others, as devices may depend on other devices. The problems that are caused by breaking updates manifest only after the updates are performed and reverting them is generally impossible. In this paper, we propose an algorithm that is able to consider dependencies in a smart home system and, based on this, finds updates that preserve existing dependencies. These updates are not inspected in isolation but in combination with other updates. However, ideal solutions often depend on user preferences and the implications of one update over another can have far-reaching consequences that require filtration and recommendations. © 2021 IEEE.
    view abstractdoi: 10.1109/PerComWorkshops51409.2021.9431040
  • 2021 • 809 An approach to detect white spots during pre-turning of da718 components
    Pfirrmann, D. and Baumann, J. and Krebs, E. and Biermann, D. and Wiederkehr, P.
    Journal of Manufacturing and Materials Processing 5 (2021)
    The increasing demand for high-performance components is leading to a greater use of advanced alloys such as DA718, which is, e.g., used in engine parts due to its high-temperature strength. The strict quality requirements pose major challenges for the machining of engine components for aircrafts. Quality deviations along the value chain can lead to high costs due to rework and, in the worst case, rejections in order to prevent material failure within a safety-critical environment. These deviations include, e.g., an increased surface roughness, deviations in the shape tolerances as well as increased internal stresses or surface deformations. Material defects are an additional reason to reject the manufactured components. These are usually inspected only at the end of the value chain and—due to measurement limitations—only if they occur close to the surface of the workpiece. Ultrasonic testing is used in order to detect defects near the surface of the raw part. For the evaluation of the finished part, etching and optical inspection of the surface is used. However, defects inside the components cannot be detected in this way. If material defects are located in areas subjected to intense load changes and high temperatures, the components have to be rejected since engine parts require a high level of fatigue strength. Such rejects constitute a significant economic risk, as a large part of the added value has already been completed and a significant amount of machine time has been invested. Thus, an identification of material defects in an earlier stage of the manufacturing process is required. In this paper, fundamental investigations on machining artificially generated material defects in a micro-milling process and the signal analysis during the pre-turning of turbine disks made of nickel-based materials like DA718 will be presented. Based on force measurements, characteristic signals were identified that could indicate material defects during the turning process. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/jmmp5020057
  • 2021 • 808 An energy-relaxation-based framework for the modeling of magnetic shape memory alloys—Simulation of three-dimensional effects under homogeneous loading conditions
    Bartel, T. and Kiefer, B. and Menzel, A.
    International Journal of Solids and Structures 208-209 221-234 (2021)
    It is known from experimental findings that three-dimensional effects can have a strong influence on magnetic shape memory behavior. Such phenomena are, however, often neglected in MSMA constitutive models, as they only become meaningful under complex loading conditions. The extensions of our original modeling framework, cf. Bartel et al. (2020), to include 3D-effects is threefold: (i) vector-valued microstructural variables are now elements in R3, i.e. no longer parameterizable in polar coordinates, (ii) a third tetragonal martensite variant may form/vanish by switching from/back into both other variants, and (iii) a more general and robust algorithmic treatment is necessary. The latter includes the implementation of a staggered Augmented Lagrangian scheme to handle the now much larger and numerically more advanced sets of equality and inequality constraints. In this context, two extended model formulations are presented. The first considers a first-order, two-variant laminate approach (rank-one convexification), in which domain magnetizations, interface orientations etc. are now three-dimensional vectors. The second model is based on a convexification approach, for which the incorporation of the third martensitic variant is quite natural. Numerical examples are investigated to test the generalized modeling framework. Firstly, it is confirmed that both extended models recover the solution of the previously established two-dimensional model for a simple loading case. Secondly, response predictions for more complex loading scenarios (non-proportional bi-axial stresses, orthogonal magnetic field), motivated by experiments, are investigated. It is found that capturing the formation, elimination and mutual interaction of all martensitic variants as well as general three-dimensional magnetization vector orientations is of key importance under these conditions. The extended convexification model and modified algorithmic formulation are shown to reliably handle even such general cases. © 2020 Elsevier Ltd
    view abstractdoi: 10.1016/j.ijsolstr.2020.10.024
  • 2021 • 807 An extended Hamilton principle as unifying theory for coupled problems and dissipative microstructure evolution
    Junker, P. and Balzani, D.
    Continuum Mechanics and Thermodynamics (2021)
    An established strategy for material modeling is provided by energy-based principles such that evolution equations in terms of ordinary differential equations can be derived. However, there exist a variety of material models that also need to take into account non-local effects to capture microstructure evolution. In this case, the evolution of microstructure is described by a partial differential equation. In this contribution, we present how Hamilton’s principle provides a physically sound strategy for the derivation of transient field equations for all state variables. Therefore, we begin with a demonstration how Hamilton’s principle generalizes the principle of stationary action for rigid bodies. Furthermore, we show that the basic idea behind Hamilton’s principle is not restricted to isothermal mechanical processes. In contrast, we propose an extended Hamilton principle which is applicable to coupled problems and dissipative microstructure evolution. As example, we demonstrate how the field equations for all state variables for thermo-mechanically coupled problems, i.e., displacements, temperature, and internal variables, result from the stationarity of the extended Hamilton functional. The relation to other principles, as the principle of virtual work and Onsager’s principle, is given. Finally, exemplary material models demonstrate how to use the extended Hamilton principle for thermo-mechanically coupled elastic, gradient-enhanced, rate-dependent, and rate-independent materials. © 2021, The Author(s).
    view abstractdoi: 10.1007/s00161-021-01017-z
  • 2021 • 806 An extended model of the ISO-2631 standard to objectify the ride comfort in autonomous driving
    Burkhard, G. and Berger, T. and Enders, E. and Schramm, D.
    Work 68 S37-S45 (2021)
    BACKGROUND: With the development of autonomous driving, the occupants' comfort perception and their activities during the drive are becoming increasingly the focus of research. Especially in one of the first applications, a drive on a motorway, vertical dynamics play a major role. OBJECTIVE: To be able to robustly objectify ride comfort, better models need to be developed. Initial studies have shown, that the current ISO-2631 standard creates good results in the objectification and can be regarded as benchmark. METHODS: To increase the accuracy in objectification, an extended model with the occupants' head as additional measuring point is introduced. Instead of the known frequency filters, weighting (k-factors) is used to differentiate possible excitations. For comparing the model with the ISO-2631, a simulator study with 5 excitations and 50 inattentive subjects is carried out. RESULTS: Evaluating the study with the ISO-2631, 3 out of 5 excitations indicate a significant difference between the occupant's impression and the calculated comfort value. In comparison the extended model has no significant difference. CONCLUSION: The results further show, that inattentive occupants move their heads significantly more. By measuring accelerations of the head, the extended model creates equivalent or more accurate comfort values than the ISO-2631. © 2021 - IOS Press. All rights reserved.
    view abstractdoi: 10.3233/WOR-208004
  • 2021 • 805 An user-centred AI-based assistance system to encounter pandemics in clinical environments: A concept overview
    Wiede, C. and Seidel, R. and Wuerich, C. and Haskovic, D. and Hirtz, G. and Grabmaier, A.
    VISIGRAPP 2021 - Proceedings of the 16th International Joint Conference on Computer Vision, Imaging and Computer Graphics Theory and Applications 4 693-700 (2021)
    The current coronavirus pandemic has highlighted the need for enhanced digital technologies to provide high quality care to patients in hospitals while protecting the health and safety of the medical staff. It can also be expected that there will be a second and third wave in the corona pandemic and that preparation for future pandemics must be made. In order to close this emerging gap, we propose a concept aiming at boosting the adoption of AI and robotic related technologies to ensure sustainable, patient-centred care in hospitals. The planned assistance system will provide a continuous and safe monitoring of patients in the whole hospital environment from entrance to the ward, including data security and protection. The benefits consist in a fast detection of possible infected persons, a continuous monitoring of patients, a support by robots to reduce physical contacts during epidemics, and an automatic disinfection by robots. In addition to the technical challenges, medical, social and economic challenges for such an assistance system are discussed. Copyright © 2021 by SCITEPRESS - Science and Technology Publications, Lda. All rights reserved.
    view abstract
  • 2021 • 804 Analysis and Modelling of the Antenna Mode and Structural Mode Scattering of a Dielectric Resonator
    Alhaj Abbas, A. and Khaliel, M. and Abuelhaija, A. and El-Absi, M. and Alam, J. and Solbach, K. and Kaiser, T.
    15th European Conference on Antennas and Propagation, EuCAP 2021 (2021)
    This paper presents an analysis of the backscattering of a dielectric resonator (DR) due to the antenna mode and the structural mode. More specifically, we focus on the structural mode scattering since the discussion of the RCS of DRs in the past has concentrated on analyzing the 'Eigenmodes' only. Therefore, we present evidence for its existence and provide a qualitative and quantitative approximation. It is found that the structural scattering of a DR with high rel. permittivity can be approximated by the scattering of a metal body of the same dimensions as the DR. Furthermore, a mathematical model of the antenna mode scattering is provided using the multipole expansion and with the aid of filter theory. As a result of the superposition of both scattering modes, it is found that the structural mode scattering slightly alters the appearance of the 'Eigenmodes' in frequency position, scattering level, quality factor, and shape. © 2021 EurAAP.
    view abstractdoi: 10.23919/EuCAP51087.2021.9411078
  • 2021 • 803 Analysis of proximity consequences of coil windings in electromagnetic forming
    Goyal, S.P. and Lashkari, M. and Elsayed, A. and Hahn, M. and Tekkaya, A.E.
    Journal of Manufacturing and Materials Processing 5 (2021)
    Multiturn coils are required for manufacturing sheet metal parts with varying depths and special geometrical features using electromagnetic forming (EMF). Due to close coil turns, the physical phenomena of the proximity effect and Lorentz forces between the parallel coil windings are observed. This work attempts to investigate the mechanical consequences of these phenomena using numerical and experimental methods. A numerical model was developed in LS-DYNA. It was validated using experimental post-mortem strain and laser-based velocity measurements after and during the experiments, respectively. It was observed that the proximity effect in the parallel conductors led to current density localization at the closest or furthest ends of the conductor cross-section and high local curvature of the formed sheet. Further analysis of the forces between two coil windings explained the departure from the “inverse-distance” rule observed in the literature. Finally, some measures to prevent or reduce undesired coil deformation are provided. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/jmmp5020045
  • 2021 • 802 Analysis on the mechanical response of composite pressure vessels during internal pressure loading: FE modeling and experimental correlation
    Nebe, M. and Soriano, A. and Braun, C. and Middendorf, P. and Walther, F.
    Composites Part B: Engineering 212 (2021)
    Commercial development of gaseous hydrogen storage in fuel cell electric vehicles is inevitably subjected to reliable and cost-effective design of composite pressure vessels. In this context, certainty in the design process is sought, which is determined by how well the vessel's mechanical response is understood, but more importantly to which accuracy the final collapse can be predicted. As such, a symbiosis of numerical and experimental work appears as a leading path towards robust design methodologies, where both analyses complement and scrutinize each others validity. This research presents the analysis on the mechanical response of composite pressure vessels during internal pressure loading through the correlation of numerical and experimental results on various degrees of complexity. Based on an extensive experimental dataset, a three-dimensional FE model is implemented on a realistic vessel geometry, evaluating its constitutively elastic behavior, and its response under failure and damage progression. Likewise, an established experimental framework is used to derive data by means of contour scans, outer surface strains, airborne acoustic emissions and final burst pressure. The precise recreation of the vessel geometry, together with the detailed analysis approach, permits to show a reasonable agreement between the predicted and the measured structural responses, the sequence of damage onset, and the final collapse occurring in the cylindrical region (<1%). Discrepancies still exist because of the remaining uncertainty concerning the individual layer geometry and the characterization of damage in the helical plies. Altogether, through the alignment of experimental and numerical analyses, this work provides the base for further optimization frameworks, in which an adequate representation of the vessel's meridional thickness profile and material properties stands out as necessary feat to accurately reproduce the mechanical response and final strength in a time- and cost-effective design process. © 2020 Elsevier Ltd
    view abstractdoi: 10.1016/j.compositesb.2020.108550
  • 2021 • 801 Analytical evaluation of signal‐to‐noise ratios for avalanche-and single‐photon avalanche diodes
    Buchner, A. and Hadrath, S. and Burkard, R. and Kolb, F.M. and Ruskowski, J. and Ligges, M. and Grabmaier, A.
    Sensors 21 (2021)
    Performance of systems for optical detection depends on the choice of the right detector for the right application. Designers of optical systems for ranging applications can choose from a variety of highly sensitive photodetectors, of which the two most prominent ones are linear mode avalanche photodiodes (LM‐APDs or APDs) and Geiger‐mode APDs or single‐photon avalanche diodes (SPADs). Both achieve high responsivity and fast optical response, while maintaining low noise characteristics, which is crucial in low‐light applications such as fluorescence lifetime measurements or high intensity measurements, for example, Light Detection and Ranging (LiDAR), in outdoor scenarios. The signal‐to‐noise ratio (SNR) of detectors is used as an analytical, scenario-dependent tool to simplify detector choice for optical system designers depending on technologi-cally achievable photodiode parameters. In this article, analytical methods are used to obtain a uni-versal SNR comparison of APDs and SPADs for the first time. Different signal and ambient light power levels are evaluated. The low noise characteristic of a typical SPAD leads to high SNR in scenarios with overall low signal power, but high background illumination can saturate the detec-tor. LM‐APDs achieve higher SNR in systems with higher signal and noise power but compromise signals with low power because of the noise characteristic of the diode and its readout electronics. Besides pure differentiation of signal levels without time information, ranging performance in LiDAR with time‐dependent signals is discussed for a reference distance of 100 m. This evaluation should support LiDAR system designers in choosing a matching photodiode and allows for further discussion regarding future technological development and multi pixel detector designs in a com-mon framework. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/s21082887
  • 2021 • 800 Analytical solution of the cylindrical torsion problem for the relaxed micromorphic continuum and other generalized continua (including full derivations)
    Rizzi, G. and Hütter, G. and Khan, H. and Ghiba, I.-D. and Madeo, A. and Neff, P.
    Mathematics and Mechanics of Solids (2021)
    We solve the St. Venant torsion problem for an infinite cylindrical rod whose behaviour is described by a family of isotropic generalized continua, including the relaxed micromorphic and classical micromorphic model. The results can be used to determine the material parameters of these models. Special attention is given to the possible nonphysical stiffness singularity for a vanishing rod diameter, because slender specimens are, in general, described as stiffer. © The Author(s) 2021.
    view abstractdoi: 10.1177/10812865211023530
  • 2021 • 799 Analytical solutions of the cylindrical bending problem for the relaxed micromorphic continuum and other generalized continua
    Rizzi, G. and Hütter, G. and Madeo, A. and Neff, P.
    Continuum Mechanics and Thermodynamics 33 1505-1539 (2021)
    We consider the cylindrical bending problem for an infinite plate as modeled with a family of generalized continuum models, including the micromorphic approach. The models allow to describe length scale effects in the sense that thinner specimens are comparatively stiffer. We provide the analytical solution for each case and exhibits the predicted bending stiffness. The relaxed micromorphic continuum shows bounded bending stiffness for arbitrary thin specimens, while classical micromorphic continuum or gradient elasticity as well as Cosserat models (Neff et al. in Acta Mechanica 211(3–4):237–249, 2010) exhibit unphysical unbounded bending stiffness for arbitrary thin specimens. This finding highlights the advantage of using the relaxed micromorphic model, which has a definite limit stiffness for small samples and which aids in identifying the relevant material parameters. © 2021, The Author(s), under exclusive licence to Springer-Verlag GmbH, DE part of Springer Nature.
    view abstractdoi: 10.1007/s00161-021-00984-7
  • 2021 • 798 Analytical solutions of the simple shear problem for micromorphic models and other generalized continua
    Rizzi, G. and Hütter, G. and Madeo, A. and Neff, P.
    Archive of Applied Mechanics (2021)
    To draw conclusions as regards the stability and modelling limits of the investigated continuum, we consider a family of infinitesimal isotropic generalized continuum models (Mindlin–Eringen micromorphic, relaxed micromorphic continuum, Cosserat, micropolar, microstretch, microstrain, microvoid, indeterminate couple stress, second gradient elasticity, etc.) and solve analytically the simple shear problem of an infinite stripe. A qualitative measure characterizing the different generalized continuum moduli is given by the shear stiffness μ∗. This stiffness is in general length-scale dependent. Interesting limit cases are highlighted, which allow to interpret some of the appearing material parameter of the investigated continua. © 2021, The Author(s), under exclusive licence to Springer-Verlag GmbH, DE part of Springer Nature.
    view abstractdoi: 10.1007/s00419-021-01881-w
  • 2021 • 797 Angular dependence of Hall effect and magnetoresistance in SrRuO3- SrIrO3 heterostructures
    Esser, S. and Wu, J. and Esser, S. and Gruhl, R. and Jesche, A. and Roddatis, V. and Moshnyaga, V. and Pentcheva, R. and Gegenwart, P.
    Physical Review B 103 (2021)
    The perovskite SrRuO3 is a prototypical itinerant ferromagnet which allows interface engineering of its electronic and magnetic properties. We report the synthesis and investigation of atomically flat artificial multilayers of SrRuO3 with the spin-orbit semimetal SrIrO3 in combination with band-structure calculations with a Hubbard U term and topological analysis. The latter reveal an electronic reconstruction and emergence of flat Ru-4dxz bands near the interface, ferromagnetic interlayer coupling, and a negative Berry-curvature contribution to the anomalous Hall effect. We analyze the Hall effect and magnetoresistance measurements as a function of the field angle from an out-of-plane towards an in-plane orientation (either parallel or perpendicular to the current direction) by a two-channel model. The magnetic easy direction is tilted by about 20∘ from the sample normal for low magnetic fields, rotating towards the out-of-plane direction by increasing fields. Fully strained epitaxial growth enables a strong anisotropy of magnetoresistance. An additional Hall effect contribution, not accounted for by the two-channel model, is compatible with stable skyrmions only up to a critical angle of roughly 45∘ from the sample normal. Within about 20∘ from the thin film plane an additional peaklike contribution to the Hall effect suggests the formation of a nontrivial spin structure. © 2021 American Physical Society.
    view abstractdoi: 10.1103/PhysRevB.103.214430
  • 2021 • 796 Angular-dependent interatomic potential for large-scale atomistic simulation of iron: Development and comprehensive comparison with existing interatomic models
    Starikov, S. and Smirnova, D. and Pradhan, T. and Lysogorskiy, Y. and Chapman, H. and Mrovec, M. and Drautz, R.
    Physical Review Materials 5 (2021)
    The development of classical interatomic potential for iron is a quite demanding task with a long history background. A new interatomic potential for simulation of iron was created with a focus on description of crystal defects properties. In contrast with previous studies, here the potential development was based on force-matching method that requires only ab initio data as reference values. To verify our model, we studied various features of body-centered-cubic iron including the properties of point defects (vacancy and self-interstitial atom), the Peierls energy barrier for dislocations (screw and mix types), and the formation energies of planar defects (surfaces, grain boundaries, and stacking fault). The verification also implies thorough comparison of a potential with 11 other interatomic potentials reported in literature. This potential correctly reproduces the largest number of iron characteristics which ensures its advantage and wider applicability range compared to the other considered classical potentials. Here application of the model is illustrated by estimation of self-diffusion coefficients and the calculation of fcc lattice properties at high temperature. © 2021 American Physical Society.
    view abstractdoi: 10.1103/PhysRevMaterials.5.063607
  • 2021 • 795 Anisotropic expansion of drifting spin helices in GaAs quantum wells
    Anghel, S. and Poshakinskiy, A.V. and Schiller, K. and Passmann, F. and Ruppert, C. and Tarasenko, S.A. and Yusa, G. and Mano, T. and Noda, T. and Betz, M.
    Physical Review B 103 (2021)
    The drift of electron spin helices in an external in-plane electric field in GaAs quantum wells is studied by means of time-resolved magneto-optical Kerr microscopy. The evolution of the spin distribution measured for different excitation powers reveals that, for short delay times and higher excitation powers, the spin helix drift slows down while its envelope becomes anisotropic. The effect is understood as a local decrease of the electron gas mobility due to electron collisions with nonequilibrium holes within the excitation spot and is reproduced well in the kinetic theory framework. For larger delay times, when the electrons constituting the spin helix and nonequilibrium holes are separated by an electric field, the spin helix drift accelerates and the mobility reaches its unperturbed value again. © 2021 American Physical Society.
    view abstractdoi: 10.1103/PhysRevB.103.035429
  • 2021 • 794 Aperture Synthesis Method to Investigate on the Reflection Properties of Typical Road Surfaces
    Jebramcik, J. and Rolfes, I. and Barowski, J.
    2020 50th European Microwave Conference, EuMC 2020 634-637 (2021)
    In this contribution, a millimeter wave FMCW (frequency modulated continuous wave) radar is utilized to investigate the surface reflection of an asphalt sample at 80 GHz. Since the reflection properties of such a rough surface usually strongly depend on the characteristics of the antenna (i.e. opening angle, spot on sample) that is used in the measurement, a more generalized approach is presented here. Based on the backprojection algorithm, the measurement data, obtained by a relatively undirected antenna, are used to infer the reflection properties for different antenna systems with other radiation patterns. Exemplary measurement results are presented in this paper, proving the suitability of the proposed method. © 2021 EuMA.
    view abstractdoi: 10.23919/EuMC48046.2021.9338033
  • 2021 • 793 A-posteriori LES assessment of subgrid-scale closures for bounded passive scalars
    Engelmann, L. and Klein, M. and Kempf, A.M.
    Computers and Fluids 218 (2021)
    Scale similarity or gradient models represent attractive, functionally simple expressions for large eddy simulation (LES) subgridscale (SGS) models, showing excellent behaviour in a-priori LES studies for small to moderate filter sizes. However, when applied a-posteriori to real LES calculations, they frequently suffer from numerically unstable behavior. A recent regularization approach revealed promising results for both wall-bounded and free turbulent flows. One attractive feature of this modelling strategy is that it can potentially be applied in many different contexts, such as momentum transport in single or two phase flows, different fluids such as non-Newtonian fluids, etc. The aim of the present study is to test the application of this regularisation technique to turbulent transport of bounded passive scalars. The performance of the model together with suitable discretization strategies will be assessed for turbulent plane free jet simulations. LES results will be benchmarked against DNS calculations of the same configuration obtained with the same code. The new model exhibits good results for momentum and scalar transport, outperforming standard eddy-viscosity models particularly with respect to the prediction of second order moments. Further, they provide good stability and are easy to implement. While the influence of the SGS model for scalar transport is not negligible, it is shown that an appropriate momentum SGS-closure is likely to be more important. © 2021
    view abstractdoi: 10.1016/j.compfluid.2021.104840
  • 2021 • 792 Application of artificial neural networks for active roll control based on actor-critic reinforcement learning
    Bahr, M. and Reicherts, S. and Sieberg, P. and Morss, L. and Schramm, D.
    Advances in Intelligent Systems and Computing 1260 AISC 61-82 (2021)
    This work shows the application of artificial neural networks for the control task of the roll angle in passenger cars. The training of the artificial neural network is based on the specific actor-critic reinforcement learning training algorithm. It is implemented and trained utilizing the Python API for TensorFlow and set up in a co-simulation with the vehicle simulation realized in IPG CarMaker via MATLAB/Simulink to enable online learning. Subsequently it is validated in different representative driving maneuvers. For showing the practicability of the resulting neural controller it is also validated for different vehicle classes with respect to their corresponding structure, geometries and components. An analytical approach to adjust the resulting controller to various vehicle bodies dependent on physical correlations is presented. © Springer Nature Switzerland AG 2021.
    view abstractdoi: 10.1007/978-3-030-55867-3_4
  • 2021 • 791 Application of interpolation methods for the determination of position-dependent frequency response functions for the simulation of 5-axis milling processes
    Wilck, I. and Wirtz, A. and Biermann, D. and Wiederkehr, P.
    Production Engineering (2021)
    The occurrence of chatter vibrations in 5-axis milling processes is a common problem and can result in part failure, surface defects and increased wear of the cutting tool and the machine tool. In order to prevent process vibrations, machining processes can be optimized by utilizing geometric physically-based simulation systems. Since the modal parameters of the machine tool are dependent on the position of the linear and rotary axes, the dynamic behavior of milling processes can change along the NC path despite constant engagement conditions. In order to model the pose-dependent modal properties at the tool tip, the frequency response functions (FRFs) were measured at different locations of the workspace of the machine tool for various poses of the rotary axis of the spindle. To take the varying compliance within the workspace of a machine tool into account in a geometric physically-based milling process simulation, different interpolation methods for interpolating FRFs or parameter values of oscillator-based compliance models (OPV) were applied. For validation, the resulting models were analyzed and compared to measured data. In OPV interpolation, the individual oscillation modes were interpolated in their respective characteristics based on the oscillator parameters (eigenfrequencies, modal masses and damping values). In FRF interpolation, however, there was no differentiation between the modes, resulting in a wrong interpolation. It can therefore provide good results when only a small shift of the eigenfrequencies is expected, as in case of the analyzed machine tool, with only small movements of the translatory axes. © 2021, The Author(s).
    view abstractdoi: 10.1007/s11740-021-01072-0
  • 2021 • 790 Application of nanoindentation technique to test surface hardness and residual stress of NiTi alloy after femtosecond laser shock peening
    Wang, H. and Gurevich, E.L. and Ostendorf, A.
    Proceedings of SPIE - The International Society for Optical Engineering 11679 (2021)
    Laser shock peening is a new and important surface treatment technique that can enhance the mechanical properties of metal materials. Normally, the nanosecond laser with pulse-width between 5 ns and 20 ns is used to induce a high-pressure shock wave that can generate plastic deformation in the top layer of metals. The femtosecond laser shock peening in the air has been studied recently, which can induce higher pressure shock wave than that of traditional nanosecond laser shock peening in a very short time. The NiTi alloy is processed by femtosecond laser shock peening, then a nanoindentation device is used to measure its surface hardness and residual stress. The hardness results of NiTi alloy before and after treatment show that the femtosecond laser shock peening can increase the hardness of NiTi alloy, which also shows that the femtosecond laser can be used to perform laser shock peening on NiTi alloy without coating. © 2021 SPIE.
    view abstractdoi: 10.1117/12.2593092
  • 2021 • 789 Application-oriented assessment of the interlayer tensile strength of additively manufactured polymers
    Striemann, P. and Huelsbusch, D. and Niedermeier, M. and Walther, F.
    Additive Manufacturing 46 (2021)
    Extrusion-based additive manufacturing is often characterized with process-property-structure relationships, which lead to superimposed process-related effects. This study aims to separate superimposed effects, which occur due to the change of the process parameter layer height. The mechanical properties, in particular the interlayer tensile strength, are used to characterize the material capability in manufacturing direction z according to ASTM F2971. Different surface textures in the form of idealized, polished specimens and application-oriented, as built specimens complete the experimental design. The investigations highlight a decreasing primary surface profile and a higher material capability with decreasing layer height. The special design of experimental setup enables a retrospective data analysis that separates process-induced effects. Hence, the exact assignment of the proportions of process interactions is disclosed. The study results in a novel approach for characterizing extrusion-based additively manufactured polymer. The basic principle is to replace the common component testing by characterizing idealized material properties and calculating back to application-oriented conditions. The possibility of application-oriented correction factors based on idealized characterized material properties enables the change from component testing to material testing. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.addma.2021.102095
  • 2021 • 788 Applying machine learning to optical coherence tomography images for automated tissue classification in brain metastases
    Möller, J. and Bartsch, A. and Lenz, M. and Tischoff, I. and Krug, R. and Welp, H. and Hofmann, M.R. and Schmieder, K. and Miller, D.
    International Journal of Computer Assisted Radiology and Surgery (2021)
    Purpose: A precise resection of the entire tumor tissue during surgery for brain metastases is essential to reduce local recurrence. Conventional intraoperative imaging techniques all have limitations in detecting tumor remnants. Therefore, there is a need for innovative new imaging methods such as optical coherence tomography (OCT). The purpose of this study is to discriminate brain metastases from healthy brain tissue in an ex vivo setting by applying texture analysis and machine learning algorithms for tissue classification to OCT images. Methods: Tumor and healthy tissue samples were collected during resection of brain metastases. Samples were imaged using OCT. Texture features were extracted from B-scans. Then, a machine learning algorithm using principal component analysis (PCA) and support vector machines (SVM) was applied to the OCT scans for classification. As a gold standard, an experienced pathologist examined the tissue samples histologically and determined the percentage of vital tumor, necrosis and healthy tissue of each sample. A total of 14.336 B-scans from 14 tissue samples were included in the classification analysis. Results: We were able to discriminate vital tumor from healthy brain tissue with an accuracy of 95.75%. By comparing necrotic tissue and healthy tissue, a classification accuracy of 99.10% was obtained. A generalized classification between brain metastases (vital tumor and necrosis) and healthy tissue was achieved with an accuracy of 96.83%. Conclusions: An automated classification of brain metastases and healthy brain tissue is feasible using OCT imaging, extracted texture features and machine learning with PCA and SVM. The established approach can prospectively provide the surgeon with additional information about the tissue, thus optimizing the extent of tumor resection and minimizing the risk of local recurrences. © 2021, The Author(s).
    view abstractdoi: 10.1007/s11548-021-02412-2
  • 2021 • 787 Artificial weathering mechanisms of uncoated structural polyethylene terephthalate fabrics with focus on tensile strength degradation
    Asadi, H. and Uhlemann, J. and Stranghoener, N. and Ulbricht, M.
    Materials 14 1-24 (2021)
    In the past five decades, reinforced coated textile membranes have been used increasingly as building materials, which are environmentally exposed. Thus, their weathering degradation over the service life must be taken into account in design, fabrication, and construction. Regarding such structural membranes, PVC (polyvinylchloride)-coated PET (polyethylene terephthalate) fabric is one of the most common commercially available types. This paper focuses on the backbone of it, i.e., the woven PET fabric. Herein, weathering of uncoated PET, as the load-bearing component of the composite PET-PVC, was studied. This study assessed the uniaxial tensile strength degradation mechanisms of uncoated PET fabric during artificial accelerated weathering tests. For this purpose, exploratory data analysis was carried out to analyze the chemical and physical changes which were traced by Fourier transform infrared spectroscopy and molecular weight measurements. Finally, with the help of degradation mechanisms determined from the aforementioned evaluations, a degradation pathway network model was constructed. With that, the relationship between applied stress, mecha-nistic variables, structural changes, and performance level responses (tensile strength degradation) was assessed. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/ma14030618
  • 2021 • 786 Assessment of a complete and classified platelet proteome from genome-wide transcripts of human platelets and megakaryocytes covering platelet functions
    Huang, J. and Swieringa, F. and Solari, F.A. and Provenzale, I. and Grassi, L. and De Simone, I. and Baaten, C.C.F.M.J. and Cavill, R. and Sickmann, A. and Frontini, M. and Heemskerk, J.W.M.
    Scientific Reports 11 (2021)
    Novel platelet and megakaryocyte transcriptome analysis allows prediction of the full or theoretical proteome of a representative human platelet. Here, we integrated the established platelet proteomes from six cohorts of healthy subjects, encompassing 5.2 k proteins, with two novel genome-wide transcriptomes (57.8 k mRNAs). For 14.8 k protein-coding transcripts, we assigned the proteins to 21 UniProt-based classes, based on their preferential intracellular localization and presumed function. This classified transcriptome-proteome profile of platelets revealed: (i) Absence of 37.2 k genome-wide transcripts. (ii) High quantitative similarity of platelet and megakaryocyte transcriptomes (R = 0.75) for 14.8 k protein-coding genes, but not for 3.8 k RNA genes or 1.9 k pseudogenes (R = 0.43–0.54), suggesting redistribution of mRNAs upon platelet shedding from megakaryocytes. (iii) Copy numbers of 3.5 k proteins that were restricted in size by the corresponding transcript levels (iv) Near complete coverage of identified proteins in the relevant transcriptome (log2fpkm > 0.20) except for plasma-derived secretory proteins, pointing to adhesion and uptake of such proteins. (v) Underrepresentation in the identified proteome of nuclear-related, membrane and signaling proteins, as well proteins with low-level transcripts. We then constructed a prediction model, based on protein function, transcript level and (peri)nuclear localization, and calculated the achievable proteome at ~ 10 k proteins. Model validation identified 1.0 k additional proteins in the predicted classes. Network and database analysis revealed the presence of 2.4 k proteins with a possible role in thrombosis and hemostasis, and 138 proteins linked to platelet-related disorders. This genome-wide platelet transcriptome and (non)identified proteome database thus provides a scaffold for discovering the roles of unknown platelet proteins in health and disease. © 2021, The Author(s).
    view abstractdoi: 10.1038/s41598-021-91661-x
  • 2021 • 785 Assessment of a Dual Kalman Filter-Based Approach for Input/Output Estimation in an Aluminum Plate
    Sattarifar, A. and Nestorović, T.
    Lecture Notes in Civil Engineering 127 584-593 (2021)
    Vulnerability of structures to damage during their service time brings up the necessity of design and implementation of an intelligent procedure to assure the health of the structure. In the sight of this requisite, current work deals with extending the capability of a dual Kalman filter (DKF) state estimation scheme to assist vibration-based health monitoring methods. This is met by estimating the response of the structure for locations at which a sensor cannot be placed. The capability of the DKF method in the estimation of states of a linear system with an unknown input has been presented in various recent works. In this paper, a DKF approach incorporated with a reduced order structural model (in this case an aluminum plate) is utilized to obtain an estimation of applied force and the response of the structure in terms of acceleration, velocity, and displacement. These estimations are based on measured accelerations at a limited number of points on the aluminum plate as well as the state-space model of the dynamic system. Numerical simulations and experimental works are performed to obtain the mentioned datasets. To assess the robustness of the method concerning various conditions, the effect of the frequency, as well as type of the function of the input force on the validity of the method, is presented. Moreover, it is shown to what extent the number of selected modes in model reduction procedure can influence the accuracy of the DKF technique. © 2021, Springer Nature Switzerland AG.
    view abstractdoi: 10.1007/978-3-030-64594-6_57
  • 2021 • 784 Assessment of flow aggressiveness and erosion damage topography for different gap widths in ultrasonic cavitation testing
    Schreiner, F. and Hanke, S. and Skoda, R.
    Wear 484-485 (2021)
    Incubation time and erosion rate of C15 steel (SAE 1016) are measured in a cavitation test-rig utilizing an ultrasonic horn. The gap width (separation distance) between horn tip and stationary sample is varied and effects on material damage are studied. Cavitation erosion shows a local maximum for a gap width of 0.5 mm at the stationary specimen, while it continuously rises on the horn tip with rising gap width. A characteristic erosion pattern develops at horn tip and stationary specimen. By a-posteriori surface erosion topography measurements, radial erosion depth profiles are evaluated. Together with scanning electron microscopy investigations, they provide information on the spatial distribution of the flow aggressiveness and on wear mechanisms. By means of computational fluid dynamics (CFD) results, the local surface erosion topography is associated to harmonic and subharmonic collapse events within the gap. Pressure measurements have been performed by piezoelectric polyvinylidene fluoride (PVDF) sensors, mounted in central as well as eccentric position on the specimen surface. A local mean of the erosion depth profile is evaluated on the surface portion that corresponds to the PVDF sensor locations. By temporally high-resolved pressure data, a cumulative force load is evaluated. For larger gap width, a good correlation of cumulative force load with the inverse incubation time, erosion rate, as well as mean erosion depth is obtained, while for the smallest gap width of 0.3 mm, the correlation deteriorates. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.wear.2021.203989
  • 2021 • 783 Assessment of galvanostatic anodic polarization to accelerate the corrosion of the bioresorbable magnesium alloy we43
    Wegner, N. and Walther, F.
    Applied Sciences (Switzerland) 11 1-15 (2021)
    In the field of surgery, bioresorbable magnesium is considered a promising candidate. Its low corrosion resistance, which is disadvantageous for technical application, is advantageous for surgery since the implant fully degrades in the presence of the water-based body fluids, and after a defined time the regenerating bone takes over its function again. Therefore, knowledge of the corrosion behavior over several months is essential. For this reason, an in vitro short-time testing method is developed to accelerate the corrosion progress by galvanostatic anodic polarization without influencing the macroscopic corrosion morphology. The initial corrosion rate of the magnesium alloy WE43 is calculated by detection of the hydrogen volume produced in an immersion test. In a corresponding experimental setup, a galvanostatic anodic polarization is applied with a three-electrode system. The application range for the polarization is determined based on the corrosion current density from potentiodynamic polarization. To correlate the initial corrosion rate, and accelerated dissolution rate, the corrosion morphologies of both test strategies are characterized by microscopy images, as well as energy dispersive X-ray spectroscopy and Fourier-transform infrared spectroscopy. The results demonstrate that the dissolution rate can be increased in the order of decades with the limitation of a changed corrosion morphology with increasing polarization. With this approach, it is possible to characterize and exclude new unsuitable magnesium alloys in a time-efficient manner before they are used in subsequent preclinical studies. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/app11052128
  • 2021 • 782 Assessment of wave induced higher order resonant vibrations of ships at forward speed
    Riesner, M. and el Moctar, O.
    Journal of Fluids and Structures 103 (2021)
    An efficient nonlinear time domain method computed higher order springing induced vertical bending vibrations of ships in waves. A weakly nonlinear time domain approach obtained the hydrodynamic response of the elastic hull girder, and a linear finite element model based on Timoshenko's beam theory calculated its structural response. Coupling of the fully nonlinear stationary forward speed problem with the weakly nonlinear elastic body seakeeping problem constituted the major progress. We demonstrated that accounting for the nonlinear stationary forward speed problem significantly affected the prediction of springing-induced vibrations. Rigid body motions were computed via a nonlinear equations of motion. Elastic vibrations were computed using the modal superposition technique based on linear elastic motion equations. Radiation forces of the moving and vibrating hull structure (rigid body and elastic) were computed via convolution integrals, and Froude–Krylov and hydrostatic forces were combined and integrated over the instantaneous wetted surface. A waterline integral accounted for nonlinear effects of radiation and diffraction forces due to the changing wetted surface. A two-way coupling algorithm ensured accurate convergence. Comparisons of the numerically calculated midship vertical bending moment of a large container ship with experimental results showed good agreement. Investigations of the subject container ship advancing at forward speeds of 15 and 22kn in regular head waves focused on second, third, and fourth order springing. © 2021 Elsevier Ltd
    view abstractdoi: 10.1016/j.jfluidstructs.2021.103262
  • 2021 • 781 Asymmetric Rydberg blockade of giant excitons in Cuprous Oxide
    Heckötter, J. and Walther, V. and Scheel, S. and Bayer, M. and Pohl, T. and Aßmann, M.
    Nature Communications 12 (2021)
    The ability to generate and control strong long-range interactions via highly excited electronic states has been the foundation for recent breakthroughs in a host of areas, from atomic and molecular physics to quantum optics and technology. Rydberg excitons provide a promising solid-state realization of such highly excited states, for which record-breaking orbital sizes of up to a micrometer have indeed been observed in cuprous oxide semiconductors. Here, we demonstrate the generation and control of strong exciton interactions in this material by optically producing two distinct quantum states of Rydberg excitons. This is made possible by two-color pump-probe experiments that allow for a detailed probing of the interactions. Our experiments reveal the emergence of strong spatial correlations and an inter-state Rydberg blockade that extends over remarkably large distances of several micrometers. The generated many-body states of semiconductor excitons exhibit universal properties that only depend on the shape of the interaction potential and yield clear evidence for its vastly extended-range and power-law character. © 2021, The Author(s).
    view abstractdoi: 10.1038/s41467-021-23852-z
  • 2021 • 780 Atmospheric pressure metal-organic chemical vapor deposition (AP-MOCVD) growth of undoped and aluminium-doped ZnO thin film using hot wall reactor
    Nebatti Ech Chergui, A. and Pflitsch, C. and Atakan, B.
    Surfaces and Interfaces 22 (2021)
    In this contribution, a hot wall reactor via economic atmospheric pressure metal-organic chemical vapor deposition (AP-MOCVD) was adopted for Un-doped and Al-doped Zinc oxide films were deposited on borosilicate glass and silicon substrates. To avoid the use of an expensive vacuum system, all experiments were realized at atmospheric pressure. The chemical reagents used for this experiment are Zinc acetylacetonate (Zn(acac)2) and aluminium acetylacetonates (Al (acac)2) under atmospheric conditions. The obtained films are characterized by X-ray diffraction (XRD),scanning electron microscopy (SEM), energy dispersive X-ray (EDX) and Uv-–vis spectrometer, respectively. As results, it is found that The un-doped ZnO films are polycrystalline. However, a significant enhancement in the intensity of the relevant (100) reflection is observed when Zinc oxide films are doped with Al. It is also observed that the Al-doped Zinc oxide films present higher transparency in the visible region and resistivities of 2.55 ohm cm and 1.44 ohm cm for un-doped and Al doped films respectively © 2020
    view abstractdoi: 10.1016/j.surfin.2020.100883
  • 2021 • 779 Atmospheric-pressure particle mass spectrometer for investigating particle growth in spray flames
    Suleiman, S. and Nanjaiah, M. and Skenderovic, I. and Rosenberger, T. and Kunze, F. and Wlokas, I. and Kruis, F.E. and Wiggers, H. and Schulz, C.
    Journal of Aerosol Science 158 (2021)
    In this work, we introduce a new particle mass spectrometer (AP-PMS) that is able to detect particle-size distributions at ambient pressure using a three-stage pumping design. This device is demonstrated for direct sampling from the particle formation in spray-flame synthesis of iron oxide nanoparticles. Aerosol sampling is performed by a probe with integrated dilution that has been characterized and configured by computational fluid dynamics simulations and the chamber-skimmer system has been investigated by schlieren imaging. The system was validated by detailed characterization of a standardized sooting flame and by iron oxide nanoparticles generated in the SpraySyn burner from iron nitrate dissolved in a mixture of ethanol and 2-ethylhexanoic acid. The PMS results are compared to additional inline measurements with SMPS and ELPI + as well as with TEM measurements of thermophoretically sampled materials from the same location in the spray flame. © 2021 The Authors
    view abstractdoi: 10.1016/j.jaerosci.2021.105827
  • 2021 • 778 Atomic layer deposition of dielectric Y2O3thin films from a homoleptic yttrium formamidinate precursor and water
    Boysen, N. and Zanders, D. and Berning, T. and Beer, S.M.J. and Rogalla, D. and Bock, C. and Devi, A.
    RSC Advances 11 2565-2574 (2021)
    We report the application of tris(N,N′-diisopropyl-formamidinato)yttrium(iii) [Y(DPfAMD)3] as a promising precursor in a water-assisted thermal atomic layer deposition (ALD) process for the fabrication of high quality Y2O3 thin films in a wide temperature range of 150 °C to 325 °C. This precursor exhibits distinct advantages such as improved chemical and thermal stability over the existing Y2O3 ALD precursors including the homoleptic and closely related yttrium tris-amidinate [Y(DPAMD)3] and tris-guanidinate [Y(DPDMG)3], leading to excellent thin film characteristics. Smooth, homogeneous, and polycrystalline (fcc) Y2O3 thin films were deposited at 300 °C with a growth rate of 1.36 Å per cycle. At this temperature, contamination levels of C and N were under the detectable limits of nuclear reaction analysis (NRA), while X-ray photoelectron spectroscopy (XPS) measurements confirmed the high purity and stoichiometry of the thin films. From the electrical characterization of metal-insulator-semiconductor (MIS) devices, a permittivity of 13.9 at 1 MHz could be obtained, while the electric breakdown field is in the range of 4.2 and 6.1 MV cm-1. Furthermore, an interface trap density of 1.25 × 1011 cm-2 and low leakage current density around 10-7 A cm-2 at 2 MV cm-1 are determined, which satisfies the requirements of gate oxides for complementary metal-oxide-semiconductor (CMOS) based applications. © 2021 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/d0ra09876k
  • 2021 • 777 Atomic oxygen generation in atmospheric pressure RF plasma jets driven by tailored voltage waveforms in mixtures of He and O2
    Korolov, I. and Steuer, D. and Bischoff, L. and Hübner, G. and Liu, Y. and Schulz-Von der Gathen, V. and Böke, M. and Mussenbrock, T. and Schulze, J.
    Journal of Physics D: Applied Physics 54 (2021)
    Absolute atomic oxygen densities measured space resolved in the active plasma volume of a COST microplasma reference jet operated in He/O2 and driven by tailored voltage waveforms are presented. The measurements are performed for different shapes of the driving voltage waveform, oxygen admixture concentrations, and peak-to-peak voltages. Peaks- and valleys-waveforms constructed based on different numbers of consecutive harmonics, N, of the fundamental frequency f 0 =13.56 MHz, different relative phases and amplitudes are used. The results show that the density of atomic oxygen can be controlled and optimized by voltage waveform tailoring (VWT). It is significantly enhanced by increasing the number of consecutive driving harmonics at fixed peak-to-peak voltage. The shape of the measured density profiles in the direction perpendicular to the electrodes can be controlled by VWT as well. For N >1 and peaks-/valleys-waveforms, it exhibits a strong spatial asymmetry with a maximum at one of the electrodes due to the spatially asymmetric electron power absorption dynamics. Thus, the atomic oxygen flux can be directed primarily towards one of the electrodes. The generation of atomic oxygen can be further optimized by changing the reactive gas admixture and by tuning the peak-to-peak voltage amplitude. The obtained results are understood based on a detailed analysis of the spatio-temporal dynamics of energetic electrons revealed by phase resolved optical emission spectroscopy. © 2021 Institute of Physics Publishing. All rights reserved.
    view abstractdoi: 10.1088/1361-6463/abd20e
  • 2021 • 776 Atomic-Precision Tailoring of Au–Ag Core–Shell Composite Nanoparticles for Direct Electrochemical-Plasmonic Hydrogen Evolution in Water Splitting
    Mo, J. and Barbosa, E.C.M. and Wu, S. and Li, Y. and Sun, Y. and Xiang, W. and Li, T. and Pu, S. and Robertson, A. and Wu, T.-S. and Soo, Y.-L. and Alves, T.V. and Camargo, P.H.C. and Kuo, W. and Tsang, S.C.E.
    Advanced Functional Materials (2021)
    Traditionally, bandgap materials are a prerequisite to photocatalysis since they can harness a reasonable range of the solar spectrum. However, the high impedance across the bandgap and the low concentration of intrinsic charge carriers have limited their energy conversion. By contrast, metallic nanoparticles possess a sea of free electrons that can effectively promote the transition to the excited state for reactions. Here, an atomic layer of a bimetallic concoction of silver–gold shells is precisely fabricated onto an Au core via a sonochemical dispersion approach to form a core–shell of Au–Ag that exploits the wide availability of excited states of Ag while maintaining an efficient localized surface plasmon resonance (LSPR) of Au. Catalytic results demonstrate that this mix of Ag and Au can convert solar energy to hydrogen at high efficiency with an increase of 112.5% at an optimized potential of −0.5 V when compared to light-off conditions under the electrochemical LSPR. This outperforms the commercial Pt catalysts by 62.1% with a hydrogen production rate of 1870 µmol g−1 h−1 at room temperature. This study opens a new route for tuning the range of light capture of hydrogen evolution reaction catalysts using fabricated core–shell material through the combination of LSPR with electrochemical means. © 2021 Wiley-VCH GmbH
    view abstractdoi: 10.1002/adfm.202102517
  • 2021 • 775 Atomistic investigation of machinability of monocrystalline 3C–SiC in elliptical vibration-assisted diamond cutting
    Zhao, L. and Zhang, J. and Zhang, J. and Hartmaier, A.
    Ceramics International 47 2358-2366 (2021)
    Deformation-induced characteristics of surface layer strongly rely on loading condition-related operating deformation modes. In the current study we reveal the mechanisms governing machined surface formation of hard brittle monocrystalline 3C–SiC in ultrasonic elliptical vibration-assisted diamond cutting by molecular dynamics simulations. Simulation results show different deformation modes including phase transformation, dislocation activity, and crack nucleation and propagation, as well as their correlations with surface integrity in terms of machined surface morphology and subsurface damage. In particular, molecular dynamics simulations of ordinary cutting are also carried out, which demonstrate the effectiveness of applying ultrasonic vibration of cutting tool in decreasing machining force and suppressing crack events, i.e., promoting ductile-mode cutting for achieving high surface integrity. The physical mechanism governing the machining differences between the two machining processes are also revealed. Furthermore, the effect of cutting depth on machined surface integrity under vibration-assisted cutting and ordinary cutting is addressed. © 2020 Elsevier Ltd and Techna Group S.r.l.
    view abstractdoi: 10.1016/j.ceramint.2020.09.078
  • 2021 • 774 Augmented Reality Application for the Mobile Measurement of Strain Distributions
    Mogylenko, O. and Selvaggio, A. and Upadhya, S. and Grodotzki, J. and Tekkaya, A.E.
    Advances in Intelligent Systems and Computing 1231 AISC 235-245 (2021)
    In mechanical engineering studies hands-on laboratories are an integral part of the students’ education. In manufacturing related fields, material characterization labs are often used to enable students to foster their understanding of different materials. To enhance the laboratory experience and to educate about specific aspects of the uniaxial tensile test, an Augmented Reality (AR) application has been developed. With this applications, it is possible to visualize the inhomogeneous strain field that arises during the experiment on the surface of the specimen. The technical components and structure of the implementation are described in this paper. The usability of several algorithms, technical and software implementation is discussed and evaluated. © 2021, Springer Nature Switzerland AG.
    view abstractdoi: 10.1007/978-3-030-52575-0_19
  • 2021 • 773 Augmented semantic segmentation for the digitization of grinding tools based on deep learning
    Wiederkehr, P. and Finkeldey, F. and Merhofe, T.
    CIRP Annals 70 297-300 (2021)
    In order to analyze various process characteristics, grinding simulations can be used, which need accurate models of the tool and the individual grains. For this purpose, grinding tools can be digitized. To identify characteristic grains from a large number of measurements, each individual grain has to be analyzed and separated from the bond manually. Therefore, a deep learning-based methodology was developed to achieve a high segmentation accuracy of the grain boundaries efficiently. Additionally, a data augmentation approach was investigated to limit the data necessary for learning. The model transferability was quantified by analyzing different states of tool wear. © 2021 CIRP
    view abstractdoi: 10.1016/j.cirp.2021.04.051
  • 2021 • 772 Automated assessment of a kinetic database for fcc Co-Cr-Fe-Mn-Ni high entropy alloys
    Abrahams, K. and Zomorodpoosh, S. and Khorasgani, A.R. and Roslyakova, I. and Steinbach, I. and Kundin, J.
    Modelling and Simulation in Materials Science and Engineering 29 (2021)
    The development of accurate kinetic databases by parametrizing the composition and temperature dependence of elemental atomic mobilities, is essential for correct multicomponent calculations and simulations. In this work the automated assessment procedure for the establishment of CALPHAD-type kinetic databases is proposed, including the storage of raw data and assessment results, automatic weighting of data, parameter selection and automated reassessments. This allows the establishment of reproducible up-to-date databases. The proposed software, written in python, is applied to the assessment of a kinetic database for the fcc Co-Cr-Fe-Mn-Ni high entropy alloy using only tracer diffusion data for a sharp separation of thermodynamic and kinetic data. The established database is valid for the whole composition range of the five-component high entropy alloy. © 2021 The Author(s). Published by IOP Publishing Ltd Printed in the UK
    view abstractdoi: 10.1088/1361-651X/abf62b
  • 2021 • 771 Automated image analysis for quantification of materials microstructure evolution
    Ahmed, M. and Horst, O.M. and Obaied, A. and Steinbach, I. and Roslyakova, I.
    Modelling and Simulation in Materials Science and Engineering 29 (2021)
    In this work, an automated image analysis procedure for the quantification of microstructure evolution during creep is proposed for evaluating scanning electron microscopy micrographs of a single crystal Ni-based superalloy before and after creep at 950 °C and 350 MPa. scanning electron microscopy-micrographs of γ/γ′ microstructures are transformed into binary images. Image analysis, which involves pixel by pixel classification and feature extraction, is then combined with a supervised machine learning algorithm to improve the binarization and the quality of the results. The binarization of the gray scale images is not always straight forward, especially when the difference in gray levels between the γ-channels and the γ′-phase is small. To optimize feature extraction, we utilized a series of bilateral filters as well as a machine learning algorithm, known as the gradient boosting method, that was used for training and classifying the micrograph pixels. After testing the two methods, the gradient boosting method was identified as the most effective. Subsequently, a Python routine was written and implemented for the automated quantification of the γ′ area fraction and the γ channel width. Our machine learning method is documented and the results of the automatic procedure are discussed based on results which we previously reported in the literature. © 2021 The Author(s). Published by IOP Publishing Ltd.
    view abstractdoi: 10.1088/1361-651X/abfd1a
  • 2021 • 770 B2 ordering in body-centered-cubic AlNbTiV refractory high-entropy alloys
    Körmann, F. and Kostiuchenko, T. and Shapeev, A. and Neugebauer, J.
    Physical Review Materials 5 (2021)
    The phase stability of a bcc AlNbTiV high-entropy alloy at elevated temperatures is studied using a combination of machine-learning interatomic potentials, first-principles calculations, and Monte Carlo simulations. The simulations reveal a B2 ordering below about 1700 K, mainly caused by a strong site preference of Al and Ti. A much weaker site preference for V and Nb is observed, strongly affecting the alloys total configurational entropy. The underlying mechanisms of the B2 phase stability as opposed to the random solid solution are discussed in terms of a high persisting configurational entropy of the B2 phase due to strong sublattice site disorder. © 2021 authors.
    view abstractdoi: 10.1103/PhysRevMaterials.5.053803
  • 2021 • 769 Band-gap solitons in nonlinear photonic crystal waveguides and their application for functional all-optical logic gating
    Jandieri, V. and Khomeriki, R. and Onoprishvili, T. and Erni, D. and Chotorlishvili, L. and Werner, D.H. and Berakdar, J.
    Photonics 8 (2021)
    This review paper summarizes our previous findings regarding propagation characteristics of band-gap temporal solitons in photonic crystal waveguides with Kerr-type nonlinearity and a realization of functional and easily scalable all-optical NOT, AND and NAND logic gates. The proposed structure consists of a planar air-hole type photonic crystal in crystalline silicon as the nonlinear background material. A main advantage of proposing the gap-soliton as a signal carrier is that, by operating in the true time-domain, the temporal soliton maintains a stable pulse envelope during each logical operation. Hence, multiple concatenated all-optical logic gates can be easily realized paving the way to multiple-input ultrafast full-optical digital signal processing. In the suggested setup, due to the gap-soliton features, there is no need to amplify the output signal after each operation which can be directly used as a new input signal for another logical operation. The efficiency of the proposed logic gates as well as their scalability is validated using our original rigorous theoretical formalism confirmed by full-wave computational electromagnetics. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/photonics8070250
  • 2021 • 768 Basic Machine Learning Approaches for the Acceleration of PDE Simulations and Realization in the FEAT3 Software
    Ruelmann, H. and Geveler, M. and Ribbrock, D. and Zajac, P. and Turek, S.
    Lecture Notes in Computational Science and Engineering 139 449-457 (2021)
    In this paper we present a holistic software approach based on the FEAT3 software for solving multidimensional PDEs with the Finite Element Method that is built for a maximum of performance, scalability, maintainability and extensibility. We introduce basic paradigms how modern computational hardware architectures such as GPUs are exploited in a numerically scalable fashion. We show, how the framework is extended to make even the most recent advances on the hardware market accessible to the framework, exemplified by the ubiquitous trend to customize chips for Machine Learning. We can demonstrate that for a numerically challenging model problem, artificial neural networks can be used while preserving a classical simulation solution pipeline through the incorporation of a neural network preconditioner in the linear solver. © 2021, Springer Nature Switzerland AG.
    view abstractdoi: 10.1007/978-3-030-55874-1_44
  • 2021 • 767 B-Cu-Zn Gas Diffusion Electrodes for CO2 Electroreduction to C2+ Products at High Current Densities
    Song, Y. and Junqueira, J.R.C. and Sikdar, N. and Öhl, D. and Dieckhöfer, S. and Quast, T. and Seisel, S. and Masa, J. and Andronescu, C. and Schuhmann, W.
    Angewandte Chemie - International Edition 60 9135-9141 (2021)
    Electroreduction of CO2 to multi-carbon products has attracted considerable attention as it provides an avenue to high-density renewable energy storage. However, the selectivity and stability under high current densities are rarely reported. Herein, B-doped Cu (B-Cu) and B-Cu-Zn gas diffusion electrodes (GDE) were developed for highly selective and stable CO2 conversion to C2+ products at industrially relevant current densities. The B-Cu GDE exhibited a high Faradaic efficiency of 79 % for C2+ products formation at a current density of −200 mA cm−2 and a potential of −0.45 V vs. RHE. The long-term stability for C2+ formation was substantially improved by incorporating an optimal amount of Zn. Operando Raman spectra confirm the retained Cu+ species under CO2 reduction conditions and the lower overpotential for *OCO formation upon incorporation of Zn, which lead to the excellent conversion of CO2 to C2+ products on B-Cu-Zn GDEs. © 2021 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/anie.202016898
  • 2021 • 766 Beam divergence reduction of vortex waves with a tailored lens and a tailored reflector
    Hassan, M.H. and Sievert, B. and Svejda, J.T. and Ahmed, A.M. and Barowski, J. and Rennings, A. and Rolfes, I. and Sezgin, A. and Erni, D.
    IEEE Access 9 9800-9811 (2021)
    Reducing the strong beam divergence inherent to Orbital Angular Momentum waves (also known as OAM waves or vortex waves), a tailored lens and a tailored reflector are presented in this study. The generation of the OAM waves is accomplished by a Uniform Circular Patch Antenna Array (UCA) operating at 10 GHz. Here, the tailored lens and reflector are set up by two correspondingly designed shape functions rotated around the antenna's center axis in broadside direction (i.e. body of revolution approach). Initially, the tailored lens is introduced to be compared to the UCA in the presence and absence of the conventional lens separately. Upon the usage of the tailored lens, a gain improvement of 5.8 dB has been obtained in the simulation compared to a gain of 4.8 dB in the measurement. On the other hand, the tailored reflector is set under the same procedure to be compared also to the UCA with and without a conventional reflector. Both of the reflectors are simulated under idealized conditions with the aid of an OAM impressed field source used as an emitter for a meaningful comparison. The simulated gain has shown a better performance accomplished by the tailored reflector as the height r0 reaches a level less than 1.5 λ as well as the opening angle θ is less than 38° (given an UCA with an element separation distance d=λ/2). Furthermore, three different ground plane shapes with realistic UCA are applied for the simulation procedure where each of them is perturbing the radiation of the reflector. All of the lenses and the reflectors are manufactured and later measured in an anechoic chamber to undergo a comparison with the simulated results. This article demonstrates that the vortex waves need a tailored lens or a tailored reflector to decrease the beam divergence effectively especially when the radius of the UCA becomes increasingly large. © 2013 IEEE.
    view abstractdoi: 10.1109/ACCESS.2021.3050043
  • 2021 • 765 Bearable Local Stress of High-Strength SFRC
    Plückelmann, S. and Breitenbücher, R. and Smarslik, M. and Mark, P.
    RILEM Bookseries 30 176-188 (2021)
    In the case of partial-area loading, compressive forces are transmitted into concrete members only over a limited area. For plain concretes and conventionally reinforced concretes, numerous investigations have already been carried out analyzing the load-bearing behavior under partial-area loading. Due to the tendency towards higher concrete strengths and the increasingly widespread use of steel fibers in recent years, it becomes also necessary to investigate the performance of high-strength steel fiber reinforced concrete (SFRC) under partial-area loading. This paper describes experimental tests on high-strength steel fiber reinforced concrete under partial-area loading with spatial and plane load distribution. Different area ratios and concretes with different fiber types and contents as well as fiber cocktails were considered. On the basis of the test results, a calculation approach is proposed for the determination of the bearable ultimate local stress. It is shown that by referring to the flexural tensile strength, instead of the compressive strength, as in the case of common calculation approaches, a more precise approximation of the ultimate local stresses for high-strength steel fiber reinforced concrete is possible. © 2021, RILEM.
    view abstractdoi: 10.1007/978-3-030-58482-5_16
  • 2021 • 764 Benchmark for the coupled magneto-mechanical boundary value problem in magneto-active elastomers
    Metsch, P. and Schiedung, R. and Steinbach, I. and Kästner, M.
    Materials 14 (2021)
    Within this contribution, a novel benchmark problem for the coupled magneto-mechanical boundary value problem in magneto-active elastomers is presented. Being derived from an experimental analysis of magnetically induced interactions in these materials, the problem under investigation allows us to validate different modeling strategies by means of a simple setup with only a few influencing factors. Here, results of a sharp-interface Lagrangian finite element framework and a diffuse-interface Eulerian approach based on the application of a spectral solver on a fixed grid are compared for the simplified two-dimensional as well as the general three-dimensional case. After influences of different boundary conditions and the sample size are analyzed, the results of both strategies are examined: For the material models under consideration, a good agreement of them is found, while all discrepancies can be ascribed to well-known effects described in the literature. Thus, the benchmark problem can be seen as a basis for future comparisons with both other modeling strategies and more elaborate material models. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/ma14092380
  • 2021 • 763 Beschreibung der Festigkeit von Fels unter echten triaxialen Bedingungen mit der Grenzbedingung nach Mogi-Coulomb
    Kosmann, B. and Perau, E.
    Geotechnik (2021)
    Describing rock strength under true triaxial conditions with the limit condition of Mogi-Coulomb. It is known that investigations of rock strength under true triaxial conditions can show the influence of the mean principal stress on failure. For numerical calculations of tunnels and boreholes, where the mean and minimum principal stresses are not identical, limit conditions that take into account the influence of the mean principal stress would be advantageous. With the limit condition according to Mogi-Coulomb, unlike with the well-known limit condition according to Mohr-Coulomb, the influence of the mean principal stress can be taken into account. At the same time, however, these two limit conditions are identical for triaxial extension and compression. In order to be able to map limit states even more appropriate, the modified limit condition according to Mogi-Coulomb is presented in this article. In this modified form, the limit conditions according to Drucker-Prager and von Mises are included as a special case. In order to understand the Mogi-Coulomb criterion and to show possible applications, the present article shows its form, the influence of the parameters, the convexity and parameter acquisition of laboratory tests are examined. , Ernst und Sohn. All rights reserved.
    view abstractdoi: 10.1002/gete.202000013
  • 2021 • 762 Beyond Temperature Glide: The Compressor is Key to Realizing Benefits of Zeotropic Mixtures in Heat Pumps
    Roskosch, D. and Venzik, V. and Schilling, J. and Bardow, A. and Atakan, B.
    Energy Technology 9 (2021)
    Zeotropic mixtures are widely discussed as alternative refrigerants for vapor-compression cooling appliances and heat pumps. Mixtures can increase efficiency due to their nonisothermal phase change. In theoretical studies, zeotropic mixtures show significant benefits for efficiency if the temperature glide of the mixture matches the temperature change in the heat transfer fluids. Such large benefits have never been observed in experiments. First, this article clarifies the gap between simulations and experiments. Second, it is shown how zeotropic mixtures could increase efficiency in real plants. The analysis is based on experimental results from a heat pump with three zeotropic mixtures and on theoretical studies that also include a physical compressor model. The compressor performance is shown to depend strongly on composition. Therefore, the compressor efficiency is the key parameter for large benefits of zeotropic mixtures beyond well-matching temperature glides. Based on these findings, a fluid database is screened for fluids with well-matching temperature glides and high compressor efficiencies, utilizing a physical compressor model. As a result of the screening, the zeotropic mixture R152a/R32 is identified. The corresponding simulations show that zeotropic mixtures can achieve large benefits in heat pump efficiency if the pure components have similar and high compressor efficiencies. © 2021 The Authors. Energy Technology published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/ente.202000955
  • 2021 • 761 Biological and Medical Applications of Calcium Phosphate Nanoparticles
    Sokolova, V. and Epple, M.
    Chemistry - A European Journal 27 7471-7488 (2021)
    Calcium phosphate nanoparticles have a high biocompatibility and biodegradability due to their chemical similarity to human hard tissue, for example, bone and teeth. They can be used as efficient carriers for different kinds of biomolecules such as nucleic acids, proteins, peptides, antibodies, or drugs, which alone are not able to enter cells where their biological effect is required. They can be loaded with cargo molecules by incorporating them, unlike solid nanoparticles, and also by surface functionalization. This offers protection, for example, against nucleases, and the possibility for cell targeting. If such nanoparticles are functionalized with fluorescing dyes, they can be applied for imaging in vitro and in vivo. Synthesis, functionalization and cell uptake mechanisms of calcium phosphate nanoparticles are discussed together with applications in transfection, gene silencing, imaging, immunization, and bone substitution. Biodistribution data of calcium phosphate nanoparticles in vivo are reviewed. © 2021 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/chem.202005257
  • 2021 • 760 Biomineralization, dissolution and cellular studies of silicate bioceramics prepared from eggshell and rice husk
    Choudhary, R. and Venkatraman, S.K. and Bulygina, I. and Senatov, F. and Kaloshkin, S. and Anisimova, N. and Kiselevskiy, M. and Knyazeva, M. and Kukui, D. and Walther, F. and Swamiappan, S.
    Materials Science and Engineering C 118 (2021)
    The current investigation aims to replace the synthetic starting materials with biowaste to synthesize and explore three different silicate bioceramics. Pure silica from rice husk was extracted by decomposition of rice husk in muffle furnace followed by alkali treatment and acid precipitation. Raw eggshell and extracted silica were utilized for the preparation of wollastonite, diopside and forsterite by the solid-state method. The TG-DSC analysis shows that the crystallization temperature of wollastonite, diopside and forsterite was found to be 883 °C, 870 °C and 980 °C, respectively. The phase purity of wollastonite was attained at 1100 °C whereas diopside and forsterite were composed of secondary phases even after calcination at 1250 °C and 1300 °C respectively. All three materials behaved differently when exposed to the physiological environment, as wollastonite exhibited remarkable apatite deposition within 3 days whereas a distinct apatite phase was noticed on the surface of diopside after 2 weeks and forsterite shows the formation of apatite phase after five weeks of immersion. The rapid dissolution of Mg2+ ion from forsterite lowered the leaching of silicate ions into the simulated body fluid leading to poor apatite deposition over its surface. Chemical composition was found to plays a key role in the biomineralization ability of these bioceramics. Hemolysis and Lactate Dehydrogenase (LDH) release assays were performed to evaluate the hemocompatibility of silicate ceramics cultured at different concentrations (62.5, 125, and 250 μg/mL) with red blood cells and mononuclear leucocytes (MLs) of mice. The hemolytic activity of all the tested bioceramics was insignificant (less than 1%). The interaction between diopside and mouse multipotent mesenchymal stromal cells (MMSCs) caused a negligible increase in the number of apoptosis-associated Annexin V-binding cells whereas forsterite and wollastonite induced an increase in the number of the apoptotic cells only at the concentration of 250 μg/mL. The LDH assay did not show statistically significant changes in the proliferation of MMSCs after treatment with the bioceramics at the tested concentrations when compared to control (p &gt; 0.05). This finding showed that the death of a part of cells during the first 24 h of incubation did not prevent the proliferation of MMSCs incubated with diopside, forsterite and wollastonite for 72 h. © 2020 Elsevier B.V.
    view abstractdoi: 10.1016/j.msec.2020.111456
  • 2021 • 759 Blockelm - A public blockchain freight exchange protocol
    Wester, M. and Otto, B.
    Proceedings of the Annual Hawaii International Conference on System Sciences 2020-January 5587-5596 (2021)
    Freight exchanges are central to the logistics industry, as they reduce empty runs and meet spot demands. To improve their efficiency in terms of automation and enhance trust between the participants, we propose a decentralized freight exchange implemented using public blockchains. With our solution, we also address shortcomings of public blockchains, such as scalability and privacy. We present two artifacts: a general architecture for an electronic logistics marketplace (ELM) and a concrete implementation as the proof of concept for a freight exchange. The solution is implemented using two off-the-shelf public blockchains and a public distributed file system. Additionally, we investigate the implications for the general ELM model and show that an ELM based on a blockchain can be viewed as infrastructure rather than a market participant. © 2021 IEEE Computer Society. All rights reserved.
    view abstract
  • 2021 • 758 Boiling eggs, radiation damage, and the Arrhenius plot
    Lorke, A.
    Physics Today 74 66-67 (2021)
    doi: 10.1063/PT.3.4757
  • 2021 • 757 Bright Electrically Controllable Quantum-Dot-Molecule Devices Fabricated by In Situ Electron-Beam Lithography
    Schall, J. and Deconinck, M. and Bart, N. and Florian, M. and von Helversen, M. and Dangel, C. and Schmidt, R. and Bremer, L. and Bopp, F. and Hüllen, I. and Gies, C. and Reuter, D. and Wieck, A.D. and Rodt, S. and Finley, J.J. a...
    Advanced Quantum Technologies 4 (2021)
    Self-organized semiconductor quantum dots represent almost ideal two-level systems, which have strong potential to applications in photonic quantum technologies. For instance, they can act as emitters in close-to-ideal quantum light sources. Coupled quantum dot systems with significantly increased functionality are potentially of even stronger interest since they can be used to host ultra-stable singlet-triplet spin qubits for efficient spin-photon interfaces and for deterministic photonic 2D cluster-state generation. An advanced quantum dot molecule (QDM) device is realized and excellent optical properties are demonstrated. The device includes electrically controllable QDMs based on stacked quantum dots in a pin-diode structure. The QDMs are deterministically integrated into a photonic structure with a circular Bragg grating using in situ electron beam lithography. A photon extraction efficiency of up to (24 ± 4)% is measured in good agreement with numerical simulations. The coupling character of the QDMs is clearly demonstrated by bias voltage dependent spectroscopy that also controls the orbital couplings of the QDMs and their charge state in quantitative agreement with theory. The QDM devices show excellent single-photon emission properties with a multi-photon suppression of (Formula presented.). These metrics make the developed QDM devices attractive building blocks for use in future photonic quantum networks using advanced nanophotonic hardware. © 2021 The Authors. Advanced Quantum Technologies published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/qute.202100002
  • 2021 • 756 Bulk electronic structure of lanthanum hexaboride (La B6) by hard x-ray angle-resolved photoelectron spectroscopy
    Rattanachata, A. and Nicolaï, L.C. and Martins, H.P. and Conti, G. and Verstraete, M.J. and Gehlmann, M. and Ueda, S. and Kobayashi, K. and Vishik, I. and Schneider, C.M. and Fadley, C.S. and Gray, A.X. and Minár, J. and Nemšák, S.
    Physical Review Materials 5 (2021)
    In the last decade rare-earth hexaborides have been investigated for their fundamental importance in condensed matter, and for their applications in advanced technological fields. Among these compounds, LaB6 has a special place, being a traditional d-band metal without additional f bands. In order to understand the bulk electronic structure of the more complex rare-earth hexaborides, in this paper we investigate the bulk electronic structure of LaB6 using tender/hard x-ray photoemission spectroscopy, measuring both core-level and angle-resolved valence-band spectra. Furthermore, we compare the La 3d core level spectrum to cluster model calculations in order to understand the bulklike core-hole screening effects. The results show that the La 3d well-screened peak is at a lower binding energy compared to the main poorly screened peak; the relative intensity between these peaks depends on how strong the hybridization is between La and B atoms. We show that the recoil effect, negligible in the soft x-ray regime, becomes prominent at higher kinetic energies for lighter elements, such as boron, but is still negligible for heavy elements, such as lanthanum. In addition, we report the bulklike band structure of LaB6 determined by tender/hard x-ray angle-resolved photoemission spectroscopy (HARPES). We compare HARPES experimental results to the free-electron final-state calculations and to the more precise one-step photoemission theory including matrix element and phonon excitation effects. The agreement between the features present in the experimental ARPES data and the theoretical calculations is very good. In addition, we consider the nature and the magnitude of phonon excitations in order to interpret HARPES experimental data measured at different temperatures and excitation energies. We demonstrate that the one-step theory of photoemission and HARPES experiments provides, at present, the only approach capable of probing, both experimentally and theoretically, true "bulklike"electronic band structure of rare-earth hexaborides and strongly correlated materials. © 2021 American Physical Society.
    view abstractdoi: 10.1103/PhysRevMaterials.5.055002
  • 2021 • 755 Cahn–Hilliard phase field theory coupled to mechanics: Fundamentals, numerical implementation and application to topology optimization
    Bartels, A. and Kurzeja, P. and Mosler, J.
    Computer Methods in Applied Mechanics and Engineering 383 (2021)
    The presented framework couples the Cahn–Hilliard phase field theory to continuum mechanics using a variational principle. All equations follow consistently from stationary of a rate potential and yield a physically sound homogenization. Static and kinematic compatibility at the material interfaces are naturally guaranteed. In order to enforce admissibility of the phase field parameter, nonlinear complementary conditions are considered and embedded into the algorithmic formulation. Eventually, the variationally consistent framework also features topology optimization automatically. In contrast to other approaches that start from the optimization problem, the present formulation starts from a more comprehensive energy potential. This perspective allows to explore the natural physical mechanisms that control the system's compliance (e.g., interface evolution) and that drive maximum structural performance (changing the direction of the evolution equation with respect to the phase field parameter). Furthermore, this perspective efficiently couples the physical constraints (e.g., mass and momentum conservation). Energetically optimized microstructures and an optimized beam structure illustrate the applicability as well as the numerical performance of the elaborated framework. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.cma.2021.113918
  • 2021 • 754 Capsules from synthetic diblock-peptides as potential artificial oxygen carriers
    Feng, H. and Linders, J. and Myszkowska, S. and Mayer, C.
    Journal of Microencapsulation 38 276-284 (2021)
    The design of an encapsulation system consisting of a synthetic peptide which is fully biodegradable into non-toxic constituents. This system should be capable of encapsulating perfluorinated hydrocarbons and should be a promising basis for oxygen carriers to be used as artificial blood replacement. A diblock-peptide is synthesised following a phosgene-free method and characterised by 1H-NMR. Subsequently, this diblock-peptide is self-assembled with perfluorodecalin (PFD) to form PFD-filled capsules as potential artificial oxygen carriers allowing for rapid oxygen uptake and release. The diblock-peptide Bu-PAsp10-PPhe10 is successfully synthesised and used to encapsulate PFD. The capsules have a spherical shape with an average diameter of 360 nm in stable aqueous dispersion. NMR measurements prove their physical capability for reversible uptake and release of oxygen. The resulting capsules are expected to be fully biodegradable and possibly could act as oxygen carriers for artificial blood replacement. © 2021 Informa UK Limited, trading as Taylor & Francis Group.
    view abstractdoi: 10.1080/02652048.2021.1903594
  • 2021 • 753 Carbonaceous Oxygen Evolution Reaction Catalysts: From Defect and Doping-Induced Activity over Hybrid Compounds to Ordered Framework Structures
    Zoller, F. and Häringer, S. and Böhm, D. and Luxa, J. and Sofer, Z. and Fattakhova-Rohlfing, D.
    Small (2021)
    Oxygen evolution reaction (OER) is expected to be of great importance for the future energy conversion and storage in form of hydrogen by water electrolysis. Besides the traditional noble-metal or transition metal oxide-based catalysts, carbonaceous electrocatalysts are of great interest due to their huge structural and compositional variety and unrestricted abundance. This review provides a summary of recent advances in the field of carbon-based OER catalysts ranging from “pure” or unintentionally doped carbon allotropes over heteroatom-doped carbonaceous materials and carbon/transition metal compounds to metal oxide composites where the role of carbon is mainly assigned to be a conductive support. Furthermore, the review discusses the recent developments in the field of ordered carbon framework structures (metal organic framework and covalent organic framework structures) that potentially allow a rational design of heteroatom-doped 3D porous structures with defined composition and spatial arrangement of doping atoms to deepen the understanding on the OER mechanism on carbonaceous structures in the future. Besides introducing the structural and compositional origin of electrochemical activity, the review discusses the mechanism of the catalytic activity of carbonaceous materials, their stability under OER conditions, and potential synergistic effects in combination with metal (or metal oxide) co-catalysts. © 2021 The Authors. Small published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/smll.202007484
  • 2021 • 752 Carrier-phase DNS of detailed NOx formation in early-stage pulverized coal combustion with fuel-bound nitrogen
    Shamooni, A. and Debiagi, P. and Wang, B. and Luu, T.D. and Stein, O.T. and Kronenburg, A. and Bagheri, G. and Stagni, A. and Frassoldati, A. and Faravelli, T. and Kempf, A.M. and Wen, X. and Hasse, C.
    Fuel 291 (2021)
    Carrier-phase direct numerical simulation of detailed NOx formation in pulverized coal flames (PCC) with fuel-bound nitrogen is conducted in a 3D temporally evolving mixing layer setup where Lagrangian particles (Colombian bituminous coal) in an air stream (upper half of the domain) mix with the products of lean volatile/air combustion in the lower stream. The release of fuel-N is represented by ammonia, hydrogen cyanide, and a lumped nitrogenated tar (pyridine). Devolatilization is modeled by fitting a 2-step pyrolysis approach to the detailed heterogeneous PoliMi kinetics. A comprehensive homogeneous mechanism including all standard pathways of NOx and pyridine oxidation is adopted. Results show a partition of NO in two distinct branches of scatter plots of NO mass fraction vs. volatile mixture fraction after flame establishment, corresponding to NO in the lower stream flame region and hot spots near the upper stream. The contribution of NO2, prompt, and thermal mechanisms to total NOx is limited in the early stages of PCC. The main source of NO is fuel-N, with NH being the most important precursor. Pyridine plays an important role for NO production in the upper stream through CN formed from CHCHCN. CN and ammonia oxidation have the highest contribution to NH production. Regarding NO destruction, NO reactions with HCCO, CHi and C through the reburn process constitute the largest share. NO conversion to N2O by NH followed by conversion of N2O to N2 and NO+N→N2+O are the two most important pathways directly reducing NO to N2. © 2020 Elsevier Ltd
    view abstractdoi: 10.1016/j.fuel.2020.119998
  • 2021 • 751 Catalyst-enhanced plasma oxidation of n-butane over α-MnO2 in a temperature-controlled twin surface dielectric barrier discharge reactor
    Peters, N. and Schücke, L. and Ollegott, K. and Oberste-Beulmann, C. and Awakowicz, P. and Muhler, M.
    Plasma Processes and Polymers (2021)
    A twin surface dielectric barrier discharge is used for the catalyst-enhanced plasma oxidation of 300 ppm n-butane in synthetic air. Plasma-only operation results in the conversion of n-butane into CO and CO2. Conversion is improved by increasing the temperature of the feed gas, but selectivity shifts to undesired CO. α-MnO2 is used as a catalyst deposited on the electrodes by spray coating with a distance of 1.5 mm between the uncoated grid lines and the square catalyst patches to prevent the inhibition of plasma ignition. The catalyst strongly influences selectivity, reaching 40% conversion and 73% selectivity to CO2 at a specific energy density of 390 J·L−1 and 140°C, which is far below the onset temperature of thermocatalytic n-butane conversion. © 2021 The Authors. Plasma Processes and Polymers published by Wiley-VCH GmbH.
    view abstractdoi: 10.1002/ppap.202000127
  • 2021 • 750 Catalytic Hydrodesulfurization of Gaseous Fuels with Autogenously Formed Hydrogen
    Optenhostert, T. and Puthenkalam, S. and Stegmann, N. and Steffen, M. and Schmidt, W.
    Chemie-Ingenieur-Technik 93 1028-1032 (2021)
    Hydrogen production from gaseous fuels, such as natural or liquefied petroleum gas, for fuel cell application requires feedstock free of catalyst poisons. As sulfur is one of the main poisons, different methods are employed to remove sulfur species. We propose a process not requiring external hydrogen feed to the feedstock. The hydrogen for the hydrogenation of the sulfur species is obtained directly from the hydrocarbon matrix reacting on a zeolite catalyst. The result is a desulfurization process with considerably simplified process management and a superior process startup. © 2021 The Authors. Chemie Ingenieur Technik published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/cite.202000173
  • 2021 • 749 Catalytic influence of mineral compounds on the reactivity of cellulose-derived char in O2-, CO2-, and H2O-containing atmospheres
    Pflieger, C. and Lotz, K. and Hilse, N. and Berger, C.M. and Schiemann, M. and Debiagi, P. and Hasse, C. and Scherer, V. and Muhler, M.
    Fuel 287 (2021)
    The catalytic effects of mineral compounds on the conversion of a biomass-derived char in air- and oxyfuel-related atmospheres were investigated by thermogravimetric analysis at atmospheric pressure. The applied char originated from the hydrothermal carbonization (HTC) of cellulose followed by pyrolysis at 1073 K and subsequent mixing with 20 wt% of minerals by grinding to achieve tight contact. The reactivities of the mineral-loaded HTC chars were evaluated based on isothermal experiments in O2-, CO2-, and H2O-containing atmospheres as a function of their composition applying a magnetic suspension balance. The reactivity sequence K2CO3 &gt; Na2CO3 ≫ Fe2O3 &gt; CaO &gt; MgO ≥ mineral-free was derived consistently for char oxidation in O2/inert as well as for char gasification in diluted H2O and CO2 mixtures. In addition to this qualitative assessment, the kinetic experiments were first modelled based on a simple global nth-order power-law rate expression. Then, the more complex Carbon Burnout Kinetics (CBK/G) model and the PoliMi model were applied. All three modeling approaches enabled a systematic quantification of the catalytic effects and led to a comparable lowering in the apparent activation energy. In combination with the kinetic parameters determined for the mineral-free char, the lowered apparent activation energies specific for the applied mineral and atmosphere facilitate the implementation of catalytic effects on the conversion of biomass-derived char into combustion models. © 2020 Elsevier Ltd
    view abstractdoi: 10.1016/j.fuel.2020.119584
  • 2021 • 748 Catalytic reactions in ball mills
    Amrute, A.P. and Schüth, F.
    Catalysis 33 307-346 (2021)
    Over the past two decades mechanochemistry has emerged as an important tool in catalysis research. It has not only shown promise for catalyst synthesis, resulting in properties that are often unattainable by conventional methods, but is also a very effective tool for performing catalytic reactions with exceptional selectivities. Besides, in several instances, it allows reactions under much milder conditions compared to thermochemical methods. In this chapter, we attempt to give an overview of these efforts with a focus on catalytic reactions in ball mills. Through the selection of prominent examples from the literature, from early mentions in 300 B.C. to recent times, we try to analyze how mechanical forces lead to chemical reactions and what effect they cause to materials or chemical reactions. We also discuss the state-of-the-art milling devices, and then cover broadly chemical reactions in ball mills. The latter part briefly tackles materials synthesis, but mainly focuses on chemical reactions of solid-solid and gas-solid nature from both organic synthesis and heterogeneous catalysis. The chapter also touches on the aspects of in situ analysis and scale-up with relevant literature. The latter areas are currently in the focus of attention to develop deeper understanding and to eventually find ways to make mechanocatalysis industrially applicable. © The Royal Society of Chemistry 2021.
    view abstractdoi: 10.1039/9781839163128-00307
  • 2021 • 747 Central non-linear model-based predictive vehicle dynamics control
    Sieberg, P.M. and Schramm, D.
    Applied Sciences (Switzerland) 11 (2021)
    Considering automated driving, vehicle dynamics control systems are also a crucial aspect. Vehicle dynamics control systems serve as an important influence factor on safety and ride comfort. By reducing the driver’s responsibility through partially or fully automated driving functions, the occupants’ perception of safety and ride comfort changes. Both aspects are focused even more and have to be enhanced. In general, research on vehicle dynamics control systems is a field that has already been well researched. With regard to the mentioned aspects, however, a central control structure features sufficient potential by exploiting synergies. Furthermore, a predictive mode of operation can contribute to achieve these objectives, since the vehicle can act in a predictive manner instead of merely reacting. Consequently, this contribution presents a central predictive control system by means of a non-linear model-based predictive control algorithm. In this context, roll, self-steering and pitch behavior are considered as control objectives. The active roll stabilization demonstrates an excellent control quality with a root mean squared error of 7.6953 × 10−3 rad averaged over both validation maneuvers. Compared to a vehicle utilizing a conventional control approach combined with a skyhook damping, pitching movements are reduced by 19.75%. Furthermore, an understeering behavior is maintained, which corresponds to the self-steering behavior of the passive vehicle. In general, the central predictive control, thus, increases both ride comfort and safety in a holistic way. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/app11104687
  • 2021 • 746 Challenges in the Application of Manganese Oxide Powders as OER Electrocatalysts: Synthesis, Characterization, Activity and Stability of Nine Different MnxOy Compounds
    Heese-Gärtlein, J. and Rabe, A. and Behrens, M.
    Zeitschrift fur Anorganische und Allgemeine Chemie 647 1363-1372 (2021)
    Manganese oxides are seen as potential electrocatalysts for the alkaline oxygen evolution reaction (OER). To find the most suitable OER catalyst among the large number of known manganese oxide compounds, several comparative studies of selected MnxOy materials in water oxidation catalysis were reported in recent years with, in some cases, conflicting results. In this study, nine different manganese oxide powders differing in structure and/or composition were synthesized, characterized and compared regarding their OER activity and stability using a consistent set of experimental parameters. It turned out that the activity generally depends strongly on the manganese oxide compound. α-MnO2 manganese oxides of the hollandite-type were found to be more active than those with a lower oxidation state or other crystal structures. The most active catalyst cryptomelane, α-(K)MnO2, reached a current density of 10 mA/cm2 at 1.77±0.02 V in LSV measurements. At a potential of 1.8 V, the current density was approximately 15 mA cm−2. In contrast, the samples with the lowest activity exhibited values less than 1 mA cm−2 at the same potential. The stability experiments revealed a fast decrease in activity of all samples within the first minutes of measurement and an almost complete activity loss after 60 min. Conductivity differences are discussed as a likely reason for the observed differences in performance. © 2021 The Authors. Zeitschrift für anorganische und allgemeine Chemie published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/zaac.202000180
  • 2021 • 745 CHAPTER 6: Molecular Tweezers and Clips that Modify Protein Function
    Alavijeh, N.S. and Kirupakaran, A. and Klärner, F.-G. and Schrader, T.
    Monographs in Supramolecular Chemistry 2021-January 161-198 (2021)
    Protein recognition by designed protein ligands is highly challenging, but bears great opportunities. Supramolecular chemists have recently been able to synthesize tailored ligands with remarkable protein recognition properties which are absent in the natural binding partners, and which lead to synergistic effects, positive cooperativity and exquisite selectivity. Thus, the combination of powerful charged interactions with hydrophobic forces has recently led to new prototypes of protein surface binders. This review summarizes the development of molecular tweezers (part 1) and clips (part 2) as unique tools for protein recognition. The parts begin with molecular tweezers for basic amino acid inclusion and the discovery of diphosphate clips for efficient cofactor binding, respectively. Gratifyingly, both host molecules complement each other due to their different molecular shapes. Molecular tweezers will be presented first in their interaction with amino acids and small disordered peptides, where they generally complex each Lys and Arg; then the review will proceed to tweezer complexation with protein surfaces, elucidating the preference for well-accessible basic residues and various examples of protein targeting and interference with protein-protein interactions. Finally, we discuss the advantages of additional recognition elements on the tweezer skeleton, which opens the door to numerous advanced applications in chemical biology and drug discovery. For the clips, we describe in detail the inclusion of two important cationic cofactors, followed by applications on cofactor-mediated enzymatic processes. © The Royal Society of Chemistry 2021.
    view abstractdoi: 10.1039/9781788019798-00161
  • 2021 • 744 Characterisation of an artesian groundwater system in the Valle de Iglesia in the Central Andes of Argentina
    Hinzer, I. and Altherr, M. and Christiansen, R. and Schreuer, J. and Wohnlich, S.
    International Journal of Earth Sciences (2021)
    Despite its location in the “Arid Diagonal” of South America, the Valle de Iglesia contains a number of artesian springs, the most important of which are the Baños Pismanta thermal springs, which release water at ~ 45 °C. Despite the scarcity of water resources in the Valle de Iglesia, there have been few attempts to study these springs in any detail. In this study, &gt; 50 springs are described, each characterised by small volcano-like mud structures up to 15 m tall. Hydrogeological and hydrochemical analyses of the groundwater system in the Valle de Iglesia were performed to improve our understanding of the subsurface water flow and of the connections between the subsurface water and the associated systems of faults and springs. Site measurements were made, and the concentrations of the main ions and trace elements were also determined by laboratory analysis of water samples. The samples obtained from the spring were rich in Na–HCO3–SO4 and Na–SO4–HCO3, but the surface water samples from the Agua Negra River were rich in Ca–SO4–HCO3. The temperature of the springs was in the range 20–45 °C. Both the temperatures and the ionic ratios are compatible with the presence of a deep hydraulic circulation system. The oxidation of sulphide minerals nearby the magmatic rocks and volcanic edifices causes the mobilisation of arsenic, which accumulates in the groundwater due to the low annual rainfall. The concentrations of arsenic in the spring water samples were therefore higher than the current limit set by the World Health Organisation, meaning that the water is not suitable for human consumption. © 2021, The Author(s).
    view abstractdoi: 10.1007/s00531-021-02058-0
  • 2021 • 743 Characterization of a surface plasmon antenna fabricated on a gate-defined lateral quantum dot
    Fukai, R. and Sakai, Y. and Nakagawa, T. and Fujita, T. and Kiyama, H. and Ludwig, Ar. and Wieck, A.D. and Oiwa, A.
    Japanese Journal of Applied Physics 60 (2021)
    Quantum repeater composed of a quantum memory and an interface between photon qubits and memory qubits is indispensable for long-distance quantum communication. Gate-defined lateral quantum dots (QDs) can be a suitable platform for such quantum repeaters because of its aptitude for spin qubit and feasibility of quantum state transfer from photon polarization to electron spin. So far, the reported photoelectron excitation probabilities in such a QD are not high enough to implement practical repeater protocols. To improve the photoexcitation probability, we combine a surface plasmon antenna (SPA) with QDs. We fabricated a SPA designed to enhance the optical transmission to the QDs in a practical illumination setup in a refrigerator and characterized the fabricated antenna by measuring photocurrents at room temperature. © 2021 The Japan Society of Applied Physics
    view abstractdoi: 10.35848/1347-4065/abd533
  • 2021 • 742 Characterization of tracers for two-color laser-induced fluorescence thermometry of liquid-phase temperature in ethanol, 2–ethylhexanoic-acid/ethanol mixtures, 1-butanol, and o-xylene
    Prenting, M.M. and Shilikhin, M. and Dreier, T. and Schulz, C. and Endres, T.
    Applied Optics 60 C98-C113 (2021)
    The fluorescence spectra of dye solutions change their spectral signature with temperature. This effect is frequently used for temperature imaging in liquids and sprays based on two-color laser-induced fluorescence (2cLIF) measurements by simultaneously detecting the fluorescence intensity in two separate wavelength channels resulting in a temperature-sensitive ratio. In this work, we recorded temperature-dependent absorption and fluorescence spectra of solutions of five laser dyes (coumarin 152, coumarin 153, rhodamine B, pyrromethene 597, and DCM) dissolved in ethanol, a 35/65 vol.% mixture of ethanol/2-ethylhexanoic acid, ethanol/hexamethylsiloxane, o-xylene, and 1-butanol to investigate their potential as temperature tracers in evaporating and burning sprays. The dissolved tracers were excited at either 266, 355, and 532 nm (depending on the tracer) for temperatures between 296 and 393 K (depending on the solvent) and for concentrations ranging between 0.1 and 10 mg/l. Absorption and fluorescence spectra of the tracers were investigated for their temperature dependence, the magnitude of signal re-absorption, the impact of different solvents, and varying two-component solvent compositions. Based on the measured fluorescence spectra, the tracers were analyzed for their 2cLIF temperature sensitivity in the respective solvents. Coumarin 152 showed for single-component solvents the overall best spectroscopic properties for our specific measurement situation related to temperature imaging measurements in spray-flame synthesis of nanoparticles as demonstrated previously in ethanol spray flames [Exp. Fluids 61, 77 (2020)]. © 2021 Optical Society of America
    view abstractdoi: 10.1364/AO.419684
  • 2021 • 741 Characterizing soot in TEM images using a convolutional neural network
    Sipkens, T.A. and Frei, M. and Baldelli, A. and Kirchen, P. and Kruis, F.E. and Rogak, S.N.
    Powder Technology 387 313-324 (2021)
    Soot is an important material with impacts that depend on particle morphology. Transmission electron microscopy (TEM) represents one of the most direct routes to qualitatively assess particle characteristics. However, producing quantitative information requires robust image processing tools, which is complicated by the low image contrast and complex aggregated morphologies characteristic of soot. The current work presents a new convolutional neural network explicitly trained to characterize soot, using pre-classified images of particles from a natural gas engine; a laboratory gas flare; and a marine engine. The results are compared against other existing classifiers before considering the effect that the classifiers have on automated primary particle size methods. Estimates of the overall uncertainties between fully automated approaches of aggregate characterization range from 25% in dp,100 to 85% in DTEM. A consistent correlation is observed between projected-area equivalent diameter and primary particle size across all of the techniques. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.powtec.2021.04.026
  • 2021 • 740 Charge Regulation at a Nanoporous Two-Dimensional Interface
    Ghosh, M. and Junker, M.A. and Van Lent, R.T.M. and Madauß, L. and Schleberger, M. and Lebius, H. and Benyagoub, A. and Wood, J.A. and Lammertink, R.G.H.
    ACS Omega 6 2487-2493 (2021)
    In this work, we have studied the pH-dependent surface charge nature of nanoporous graphene. This has been investigated by membrane potential and by streaming current measurements, both with varying pH. We observed a lowering of the membrane potential with decreasing pH for a fixed concentration gradient of potassium chloride (KCl) in the Donnan dominated regime. Interestingly, the potential reverses its sign close to pH 4. The fitted value of effective fixed ion concentration (C¯ R) in the membrane also follows the same trend. The streaming current measurements show a similar trend with sign reversal around pH 4.2. The zeta potential data from the streaming current measurement is further analyzed using a 1-pK model. The model is used to determine a representative pK (acid-base equilibrium constant) of 4.2 for the surface of these perforated graphene membranes. In addition, we have also theoretically investigated the effect of the PET support in our membrane potential measurement using numerical simulations. Our results indicate that the concentration drop inside the PET support can be a major contributor (up to 85%) for a significant deviation of the membrane potential from the ideal Nernst potential. © 2021 The Authors. Published by American Chemical Society.
    view abstractdoi: 10.1021/acsomega.0c03958
  • 2021 • 739 Chemical heterogeneity enhances hydrogen resistance in high-strength steels
    Sun, B. and Lu, W. and Gault, B. and Ding, R. and Makineni, S.K. and Wan, D. and Wu, C.-H. and Chen, H. and Ponge, D. and Raabe, D.
    Nature Materials (2021)
    The antagonism between strength and resistance to hydrogen embrittlement in metallic materials is an intrinsic obstacle to the design of lightweight yet reliable structural components operated in hydrogen-containing environments. Economical and scalable microstructural solutions to this challenge must be found. Here, we introduce a counterintuitive strategy to exploit the typically undesired chemical heterogeneity within the material’s microstructure that enables local enhancement of crack resistance and local hydrogen trapping. We use this approach in a manganese-containing high-strength steel and produce a high dispersion of manganese-rich zones within the microstructure. These solute-rich buffer regions allow for local micro-tuning of the phase stability, arresting hydrogen-induced microcracks and thus interrupting the percolation of hydrogen-assisted damage. This results in a superior hydrogen embrittlement resistance (better by a factor of two) without sacrificing the material’s strength and ductility. The strategy of exploiting chemical heterogeneities, rather than avoiding them, broadens the horizon for microstructure engineering via advanced thermomechanical processing. © 2021, The Author(s).
    view abstractdoi: 10.1038/s41563-021-01050-y
  • 2021 • 738 Chemical Vapor Deposition of Hollow Graphitic Spheres for Improved Electrochemical Durability
    Knossalla, J. and Mielby, J. and Göhl, D. and Wang, F.R. and Jalalpoor, D. and Hopf, A. and Mayrhofer, K.J.J. and Ledendecker, M. and Schüth, F.
    ACS Applied Energy Materials 4 5840-5847 (2021)
    The wet-chemical synthesis of hollow graphitic spheres, a highly defined model catalyst support for electrocatalytic processes, is laborious and not scalable, which hampers potential applications. Here, we present insights into the chemical vapor deposition (CVD) of ferrocene as a simple, scalable method to synthesize hollow graphitic spheres (HGScvd). During the CVD process, iron and carbon are embedded in the pores of a mesoporous silica template. In a subsequent annealing step, iron facilitates the synthesis of highly ordered graphite structures. We found that the applied temperature treatment allows for controlling of the degree of graphitization and the textural properties of HGScvd. Further, we demonstrate that platinum loaded on HGScvd is significantly more stable during electrochemical degradation protocols than catalysts based on commercial high surface area carbons. The established CVD process allows the scalable synthesis of highly defined HGS and therefore removes one obstacle for a broader application. © 2021 The Authors. Published by American Chemical Society.
    view abstractdoi: 10.1021/acsaem.1c00643
  • 2021 • 737 Chemically induced local lattice distortions versus structural phase transformations in compositionally complex alloys
    Ikeda, Y. and Gubaev, K. and Neugebauer, J. and Grabowski, B. and Körmann, F.
    npj Computational Materials 7 (2021)
    Recent experiments show that the chemical composition of body-centered cubic (bcc) refractory high entropy alloys (HEAs) can be tuned to enable transformation-induced plasticity (TRIP), which significantly improves the ductility of these alloys. This calls for an accurate and efficient method to map the structural stability as a function of composition. A key challenge for atomistic simulations is to separate the structural transformation between the bcc and the ω phases from the intrinsic local lattice distortions in such chemically disordered alloys. To solve this issue, we develop a method that utilizes a symmetry analysis to detect differences in the crystal structures. Utilizing this method in combination with ab initio calculations, we demonstrate that local lattice distortions largely affect the phase stability of Ti–Zr–Hf–Ta and Ti–Zr–Nb–Hf–Ta HEAs. If relaxation effects are properly taken into account, the predicted compositions near the bcc–hcp energetic equilibrium are close to the experimental compositions, for which good strength and ductility due to the TRIP effect are observed. © 2021, The Author(s).
    view abstractdoi: 10.1038/s41524-021-00502-y
  • 2021 • 736 Chemomechanical Simulation of Microtubule Dynamics With Explicit Lateral Bond Dynamics
    Schmidt, M. and Kierfeld, J.
    Frontiers in Physics 9 (2021)
    We introduce and parameterize a chemomechanical model of microtubule dynamics on the dimer level, which is based on the allosteric tubulin model and includes attachment, detachment and hydrolysis of tubulin dimers as well as stretching of lateral bonds, bending at longitudinal junctions, and the possibility of lateral bond rupture and formation. The model is computationally efficient such that we reach sufficiently long simulation times to observe repeated catastrophe and rescue events at realistic tubulin concentrations and hydrolysis rates, which allows us to deduce catastrophe and rescue rates. The chemomechanical model also allows us to gain insight into microscopic features of the GTP-tubulin cap structure and microscopic structural features triggering microtubule catastrophes and rescues. Dilution simulations show qualitative agreement with experiments. We also explore the consequences of a possible feedback of mechanical forces onto the hydrolysis process and the GTP-tubulin cap structure. © Copyright © 2021 Schmidt and Kierfeld.
    view abstractdoi: 10.3389/fphy.2021.673875
  • 2021 • 735 Chern insulating phases and thermoelectric properties of EuO/MgO(001) superlattices
    Köksal, O. and Pentcheva, R.
    Physical Review B 103 (2021)
    The topological and thermoelectric properties of (EuO)n/(MgO)m(001) superlattices (SLs) are explored using density functional theory calculations including a Hubbard U term together with Boltzmann transport theory. In (EuO)1/(MgO)3(001) SL at the lattice constant of MgO a sizable band gap of 0.51 eV is opened by spin-orbit coupling (SOC) due to a band inversion between occupied localized Eu 4f and empty 5d conduction states. This inversion between bands of opposite parity is accompanied by a reorientation in the spin texture along the contour of band inversion surrounding the Γ point and leads to a Chern insulator with C = -1, also confirmed by the single edge state. Moreover, this Chern insulating phase shows promising thermoelectric properties, e.g., a Seebeck coefficient between 400 and 800μVK-1. A similar SOC-induced band inversion takes place also in the ferromagnetic semimetallic (EuO)2/(MgO)2(001) SL. Despite the vanishing band gap, it leads to a substantial anomalous Hall conductivity with values up to -1.04 e2/h and somewhat lower Seebeck coefficient. Both cases emphasize the relation between nontrivial topological bands and thermoelectricity also in systems with broken inversion symmetry. © 2021 American Physical Society.
    view abstractdoi: 10.1103/PhysRevB.103.045135
  • 2021 • 734 Chip formation simulation and analysis of the mechanical loads during micro single-lip deep hole drilling of Inconel 718 with varying cooling lubricant pressure
    Oezkaya, E. and Michel, S. and Biermann, D.
    Production Engineering 15 299-309 (2021)
    The micro single-lip deep hole drilling process is subjected to many difficulties. Especially the machining of difficult-to-cut materials like the nickel-based alloy Inconel 718 results in high thermal and mechanical loads. Irregularities in the drilling process, which lead to early tool failures must be avoided. A major challenge for micro single-lip deep hole drilling is to generate favorable chips and guarantee good chip removal. Since the chip flute of single-lip deep hole drilling tools is straight, the only mechanism to transport the chips and remove them from the bore hole is the coolant flow. In this paper the mechanical loads and the resulting chip formation for various cooling lubricant pressures are analyzed using tools with a diameter of d = 2 mm. In the experiments feed force, drilling torque, tool wear, bore hole quality as well as diameter and roundness deviations were evaluated. Individual chips are digitized and prepared as CAD models for the future consideration of the chip removal in flow simulations of the cooling lubricant. Additional FEM computational analyses of the three-dimensional chip formation with a geometric representation of the chip shape were carried out. This way not only provides valuable validated information about the process and the chip formation but also creates a basis for further investigations, which will allow an innovative simulation of the coolant flow and considers the chip formation and the chip shape. © 2021, German Academic Society for Production Engineering (WGP).
    view abstractdoi: 10.1007/s11740-021-01021-x
  • 2021 • 733 Chipless frequency-coded RFID tags integrating high-Q resonators and dielectric rod antennas
    Burmeister, T. and Jimenez-Saez, A. and Sakaki, M. and Schusler, M. and Sanchez-Pastor, J. and Benson, N. and Jakoby, R.
    15th European Conference on Antennas and Propagation, EuCAP 2021 (2021)
    A possible passive infrastructure for mm-wave self localization systems is proposed in this paper. W-band photonic crystal based high-Q resonators coupled to free space by a dielectric rod antenna are employed. Q-factors of approximately 300 and wireless tag readout over 10 cm can be achieved using Rogers RT/duroid® 6010.2LM. The maximum readout range increases to 40 cm when lower-loss additively manufactured Alumina tags are used. Development of a 3 bit prototype tag is successful, demonstrating the possibility to increase the number of resonators per tag using the presented approach. © 2021 EurAAP.
    view abstractdoi: 10.23919/EuCAP51087.2021.9410915
  • 2021 • 732 Closing the Gap for Electronic Short-Circuiting: Photosystem I Mixed Monolayers Enable Improved Anisotropic Electron Flow in Biophotovoltaic Devices
    Wang, P. and Frank, A. and Zhao, F. and Szczesny, J. and Junqueira, J.R.C. and Zacarias, S. and Ruff, A. and Nowaczyk, M.M. and Pereira, I.A.C. and Rögner, M. and Conzuelo, F. and Schuhmann, W.
    Angewandte Chemie - International Edition 60 2000-2006 (2021)
    Well-defined assemblies of photosynthetic protein complexes are required for an optimal performance of semi-artificial energy conversion devices, capable of providing unidirectional electron flow when light-harvesting proteins are interfaced with electrode surfaces. We present mixed photosystem I (PSI) monolayers constituted of native cyanobacterial PSI trimers in combination with isolated PSI monomers from the same organism. The resulting compact arrangement ensures a high density of photoactive protein complexes per unit area, providing the basis to effectively minimize short-circuiting processes that typically limit the performance of PSI-based bioelectrodes. The PSI film is further interfaced with redox polymers for optimal electron transfer, enabling highly efficient light-induced photocurrent generation. Coupling of the photocathode with a [NiFeSe]-hydrogenase confirms the possibility to realize light-induced H2 evolution. © 2020 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/anie.202008958
  • 2021 • 731 Coatability of diamond-like carbon on 316L stainless steel printed by binder jetting
    Tillmann, W. and Lopes Dias, N.F. and Stangier, D. and Schaak, C. and Höges, S.
    Additive Manufacturing 44 (2021)
    Diamond-like carbon (DLC) coatings are efficient in improving surface properties of functional components and parts. For conventionally manufactured materials and products, the DLC coatings are on a high level of development and industrially well established. However, with the advent of additive manufacturing technologies and the unique microstructure of the produced parts, so far the properties of the DLC coatings on these surfaces have not been extensively investigated. Additively manufactured materials possess process-related structural characteristics, such as residual porosity or an anisotropic material behavior, thereby leading to distinguished properties of the substrate/coating system compared to conventionally fabricated substrate materials. Therefore, 316L substrates are produced with an intended residual porosity and different building directions by binder jetting and subsequently coated with DLC in a magnetron sputtering process. Conventionally manufactured 316L substrates were also coated to evaluate the manufacturing effects on the DLC properties. Based on the analysis of DLC coated open pores, a model is developed to describe the growth mechanisms of thin PVD coatings on open pores of different size. The thin DLC coating entirely covers residual porosity when the pore size (opening diameter) is smaller than or equal to the coating thickness of ~3 µm. Independently of the residual porosity or building orientation, the DLC coating provides a high hardness of 24 GPa and reveals a high adhesion strength to all binder jetted 316 L substrates. Compared to conventional manufacturing routes, the combination of additive manufacturing and DLC deposition is a competitive approach to fabricate complex-shaped components and parts with enhanced surface properties. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.addma.2021.102064
  • 2021 • 730 Coating of cochlear implant electrodes with bioactive DNA-loaded calcium phosphate nanoparticles for the local transfection of stimulatory proteins
    Wey, K. and Schirrmann, R. and Diesing, D. and Lang, S. and Brandau, S. and Hansen, S. and Epple, M.
    Biomaterials 276 (2021)
    Calcium phosphate nanoparticles were loaded with nucleic acids to enhance the on-growth of tissue to a cochlear implant electrode. The nanoparticle deposition on a metallic electrode surface is possible by electrophoretic deposition (EPD) or layer-by-layer deposition (LbL). Impedance spectroscopy showed that the coating layer did not interrupt the electrical conductance at physiological frequencies and beyond (1–40,000 Hz). The transfection was demonstrated with the model cell lines HeLa and 3T3 as well as with primary explanted spiral ganglion neurons (rat) with the model protein enhanced green fluorescent protein (EGFP). The expression of the functional protein brain-derived neurotrophic factor (BDNF) was also shown. Thus, a coating of inner-ear cochlear implant electrodes with nanoparticles that carry nucleic acids will enhance the ongrowth of spiral ganglion cell axons for an improved transmission of electrical pulses. © 2021 Elsevier Ltd
    view abstractdoi: 10.1016/j.biomaterials.2021.121009
  • 2021 • 729 Cobalt Metal ALD: Understanding the Mechanism and Role of Zinc Alkyl Precursors as Reductants for Low-Resistivity Co Thin Films
    Zanders, D. and Liu, J. and Obenlüneschloß, J. and Bock, C. and Rogalla, D. and Mai, L. and Nolan, M. and Barry, S.T. and Devi, A.
    Chemistry of Materials (2021)
    In this work, we report a new and promising approach toward the atomic layer deposition (ALD) of metallic Co thin films. Utilizing the simple and known CoCl2(TMEDA) (TMEDA = N,N,N′,N′-tetramethylethylenediamine) precursor in combination with the intramolecularly stabilized Zn aminoalkyl compound Zn(DMP)2 (DMP = dimethylaminopropyl) as an auxiliary reducing agent, a thermal ALD process is developed that enables the deposition of Zn-free Co thin films. ALD studies demonstrate the saturation behavior of both precursors and linearity depending on the applied number of cycles as well as temperature dependency of film growth in a regime of 140-215 °C. While the process optimization is carried out on Si with native oxide, additional growth studies are conducted on Au and Pt substrates. This study is complemented by initial reactivity and suitability tests of several potential Zn alkyl-reducing agents. For the CoCl2(TMEDA)-Zn(DMP)2 combination, these findings allow us to propose a series of elemental reaction steps hypothetically leading to pure Co film formation in the ALD process whose feasibility is probed by a set of density functional theory (DFT) calculations. The DFT results show that for reactions of the precursors in the gas phase and on Co(111) substrate surfaces, a pathway involving C-C coupling and diamine formation through reductive elimination of an intermediate Co(II) alkyl species is preferred. Co thin films with an average thickness of 10-25 nm obtained from the process are subjected to thorough analysis comprising atomic force microscopy, scanning electron microscopy, and Rutherford backscattering spectrometry/nuclear reaction analysis as well as depth profiling X-ray photoemission spectroscopy (XPS). From XPS analysis, it was found that graphitic and carbidic carbon coexist in the Co metal film bulk. Despite carbon concentrations of ∼20 at. % in the Co thin film bulk, resistivity measurements for ∼22 nm thick films grown on a defined SiO2 insulator layer yield highly promising values in a range of 15-20 μω cm without any postgrowth treatment. © 2021 American Chemical Society.
    view abstractdoi: 10.1021/acs.chemmater.1c00877
  • 2021 • 728 Co-Crystal Screening by Vapor Sorption of Organic Solvents
    Veith, H. and Luebbert, C. and Rodríguez-Hornedo, N. and Sadowski, G.
    Crystal Growth and Design (2021)
    The formulation of active pharmaceutical ingredients (APIs) as pharmaceutical co-crystals (CCs) is a promising way to overcome the poor aqueous solubility and therewith poor bioavailability of many APIs. Identifying suitable coformers (CFs) that form CCs with the API is a major challenge during CC development. In this work, we developed a material-sparing and simple approach to identify whether a certain API/CF combination can form CCs. This approach is based on the solvent vapor sorption of API/CF combinations in a dynamic vapor-sorption apparatus. CC formation is detected based on the solvent vapor uptake behavior of an API/CF crystal mixture. This screening approach was applied for carbamazepine (CBZ)/nicotinamide and CBZ/acetylsalicylic acid systems using ethanol and methanol as the volatile solvents. CC formation was observed for both systems with both solvents used. Additionally, the process and success of CC formation by vapor sorption is explained by predicted phase diagrams using the Perturbed-Chain Statistical Associating Fluid Theory. The developed approach is beneficial over co-grinding and other batch crystallization approaches in that it can be performed with only a few milligrams of the API, low solvent consumption, and a solvent sorption versus time behavior for identifying CC formation. © 2021 American Chemical Society.
    view abstractdoi: 10.1021/acs.cgd.1c00355
  • 2021 • 727 Coexistence of Short- And Long-Range Ferromagnetic Proximity Effects in a Fe/(Cd,Mg)Te/CdTe Quantum Well Hybrid Structure
    Kalitukha, I.V. and Ken, O.S. and Korenev, V.L. and Akimov, I.A. and Sapega, V.F. and Yakovlev, D.R. and Dimitriev, G.S. and Langer, L. and Karczewski, G. and Chusnutdinow, S. and Wojtowicz, T. and Bayer, M.
    Nano Letters 21 2370-2375 (2021)
    In a Fe/(Cd,Mg)Te/CdTe quantum well hybrid structure, short-range and long-range ferromagnetic proximity effects are found to coexist. The former is observed for conduction band electrons, while the latter is observed for holes bound to shallow acceptors in the CdTe quantum well. These effects arise from the interaction of charge carriers confined in the quantum well with different ferromagnets, where electrons interact with the Fe film and holes with an interfacial ferromagnet at the Fe/(Cd,Mg)Te interface. The two proximity effects originate from fundamentally different physical mechanisms. The short-range proximity effect for electrons is determined by the overlap of their wave functions with d-electrons of the Fe film. On the contrary, the long-range effect for holes bound to acceptors is not associated with overlapping wave functions and can be mediated by elliptically polarized phonons. The coexistence of the two ferromagnetic proximity effects reveals the presence of a nontrivial spin texture within the same heterostructure. © 2021 American Chemical Society. All rights reserved.
    view abstractdoi: 10.1021/acs.nanolett.0c04218
  • 2021 • 726 Coherent Beam Splitting of Flying Electrons Driven by a Surface Acoustic Wave
    Ito, R. and Takada, S. and Ludwig, Ar. and Wieck, A.D. and Tarucha, S. and Yamamoto, M.
    Physical Review Letters 126 (2021)
    We develop a coherent beam splitter for single electrons driven through two tunnel-coupled quantum wires by surface acoustic waves (SAWs). The output current through each wire oscillates with gate voltages to tune the tunnel coupling and potential difference between the wires. This oscillation is assigned to coherent electron tunneling motion that can be used to encode a flying qubit and is well reproduced by numerical calculations of time evolution of the SAW-driven single electrons. The oscillation visibility is currently limited to about 3%, but robust against decoherence, indicating that the SAW electron can serve as a novel platform for a solid-state flying qubit. © 2021 American Physical Society.
    view abstractdoi: 10.1103/PhysRevLett.126.070501
  • 2021 • 725 Coherent Spin-Photon Interface with Waveguide Induced Cycling Transitions
    Appel, M.H. and Tiranov, A. and Javadi, A. and Löbl, M.C. and Wang, Y. and Scholz, S. and Wieck, A.D. and Ludwig, Ar. and Warburton, R.J. and Lodahl, P.
    Physical Review Letters 126 (2021)
    Solid-state quantum dots are promising candidates for efficient light-matter interfaces connecting internal spin degrees of freedom to the states of emitted photons. However, selection rules prevent the combination of efficient spin control and optical cyclicity in this platform. By utilizing a photonic crystal waveguide we here experimentally demonstrate optical cyclicity up to ≈15 through photonic state engineering while achieving high fidelity spin initialization and coherent optical spin control. These capabilities pave the way towards scalable multiphoton entanglement generation and on-chip spin-photon gates. © 2021 American Physical Society. All rights reserved.
    view abstractdoi: 10.1103/PhysRevLett.126.013602
  • 2021 • 724 Coin minting by additive manufacturing and forming
    Pragana, J.P.M. and Rosenthal, S. and Alexandrino, P. and Araújo, A. and Bragança, I.M.F. and Silva, C.M.A. and Leitão, P.J. and Tekkaya, A.E. and Martins, P.A.F.
    Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture 235 819-828 (2021)
    Additive manufacturing is proposed as a novel alternative to coin blank’s production routes based on rolling, blanking and edge rimming. The presentation draws from laser powder bed fusion of cylinders, slicing into individual coin blanks by electro discharge machining and surface preparation by polishing, to coin minting in a laboratory press-tool system. Special emphasis is given to material deposition and coin minting due to the originality of producing coin blanks with complex intricate contoured holes and to the necessity of subjecting the additive manufactured coin blanks to extreme compressive stresses that are typical of coin minting. Numerical and experimental results confirm the excellent performance of the additive manufactured coin blanks. The new design layouts included in the additive manufactured coin blanks open the way to produce high value-added singular collector coins, which are disruptively different from those available in the market nowadays. © IMechE 2020.
    view abstractdoi: 10.1177/0954405420971128
  • 2021 • 723 Colloidal stability, cytotoxicity, and cellular uptake of HfO2 nanoparticles
    McGinnity, T.L. and Sokolova, V. and Prymak, O. and Nallathamby, P.D. and Epple, M. and Roeder, R.K.
    Journal of Biomedical Materials Research - Part B Applied Biomaterials (2021)
    The colloidal stability, cytotoxicity, and cellular uptake of hafnium oxide (HfO2) nanoparticles (NPs) were investigated in vitro to assess safety and efficacy for use as a deliverable theranostic in nanomedicine. Monoclinic HfO2 NPs, ~60–90 nm in diameter and ellipsoidal in shape, were directly prepared without calcination by a hydrothermal synthesis at 83% yield. The as-prepared, bare HfO2 NPs exhibited colloidal stability in cell culture media for at least 10 days without significant agglomeration or settling. The viability (live/dead assay) of human epithelial cells (HeLa) and monocyte-derived macrophages (THP-1) did not fall below 95% of untreated cells after up to 24 h exposure to HfO2 NPs at concentrations up to 0.80 mg/ml. Similarly, the mitochondrial activity (MTT assay) of HeLa and THP-1 cells did not fall below 80% of untreated cells after up to 24 h exposure to HfO2 NPs at concentrations up to 0.40 mg/ml. Cellular uptake was confirmed and visualized in both HeLa and THP-1 cells by fluorescence microscopy of HfO2 NPs labeled with Cy5 and transmission electron microscopy (TEM) of bare HfO2 NPs. TEM micrographs provided direct observation of macropinocytosis and endosomal compartmentalization within 4 h of exposure. Thus, the HfO2 NPs in this study exhibited colloidal stability, cytocompatibility, and cellular uptake for potential use as a deliverable theranostic in nanomedicine. © 2021 Wiley Periodicals LLC
    view abstractdoi: 10.1002/jbm.b.34800
  • 2021 • 722 Columnar Thermal Barrier Coatings Produced by Different Thermal Spray Processes
    Kumar, N. and Gupta, M. and Mack, D.E. and Mauer, G. and Vaßen, R.
    Journal of Thermal Spray Technology (2021)
    Suspension plasma spraying (SPS) and plasma spray-physical vapor deposition (PS-PVD) are the only thermal spray technologies shown to be capable of producing TBCs with columnar microstructures similar to the electron beam-physical vapor deposition (EB-PVD) process but at higher deposition rates and relatively lower costs. The objective of this study was to achieve fundamental understanding of the effect of different columnar microstructures produced by these two thermal spray processes on their insulation and lifetime performance and propose an optimized columnar microstructure. Characterization of TBCs in terms of microstructure, thermal conductivity, thermal cyclic fatigue lifetime and burner rig lifetime was performed. The results were compared with TBCs produced by the standard thermal spray technique, atmospheric plasma spraying (APS). Bondcoats deposited by the emerging high-velocity air fuel (HVAF) spraying were compared to the standard vacuum plasma-sprayed (VPS) bondcoats to investigate the influence of the bondcoat deposition process as well as topcoat–bondcoat interface topography. The results showed that the dense PS-PVD-processed TBC had the highest lifetime, although at an expense of the highest thermal conductivity. The reason for this behavior was attributed to the dense intracolumnar structure, wide intercolumnar gaps and high column density, thus improving the strain tolerance and fracture toughness. © 2021, The Author(s).
    view abstractdoi: 10.1007/s11666-021-01228-5
  • 2021 • 721 Combinatorial exploration of B2/L21 precipitation strengthened AlCrFeNiTi compositionally complex alloys
    Wolff-Goodrich, S. and Marshal, A. and Pradeep, K.G. and Dehm, G. and Schneider, J.M. and Liebscher, C.H.
    Journal of Alloys and Compounds 853 (2021)
    Using both novel high-throughput screening via combinatorial thin film deposition and conventional bulk alloy synthesis techniques, a large region of the AlCrFeNiTi composition space has been probed for alloys that could serve as low cost alternatives to nickel-base superalloys for medium-to-high temperature structural applications. Phase formation trends in this highly complex alloying system have been determined using characterisation techniques that span multiple length scales—from bulk X-ray diffraction and differential scanning calorimetry to atomically resolved scanning transmission electron microscopy and energy dispersive X-ray spectroscopy. A large region of stability for both disordered A2 and ordered B2/L21 type phases is observed, with several compositions exhibiting fine-scaled precipitation structures of these two phases. For alloys with ≥20 at.% Al, the precipitation structure was further refined to a nano-scale lamellar arrangement of A2 and B2/L21 phases. Formation of C14 Laves phase, especially for compositions with &gt;10 at.% Ti, has consistently been observed. We include a screening of the mechanical properties based on nanoindentation and macroscopic hardness test data correlated with scanning electron microscope (SEM) observations of the hardness indents. The phase formation trends observed by both combinatorial thin film deposition and bulk alloy synthesis are discussed in detail for samples in the as-deposited and as-cast conditions, respectively. © 2020 Elsevier Ltd
    view abstractdoi: 10.1016/j.jallcom.2020.156111
  • 2021 • 720 Combining crystalline and polymeric excipients in API solid dispersions – Opportunity or risk?
    Veith, H. and Wiechert, F. and Luebbert, C. and Sadowski, G.
    European Journal of Pharmaceutics and Biopharmaceutics 158 323-335 (2021)
    Amorphous solid dispersions (ASDs) are often metastable against crystallization of the active pharmaceutical ingredient (API) and thus might undergo unwanted changes during storage. The crystallization tendency of ASDs is influenced by the API crystallization driving force (CDF) and the mobility of the molecules in the ASD. Low molecular weight-excipients are known to stabilize amorphous APIs in so-called co-amorphous formulations. Due to their success in stabilizing co-amorphous APIs, low-molecular weight excipients might also enhance the stability of polymeric ASDs. In this work, we investigated the potential of combined low-molecular weight excipient/polymer formulations with in-silico tools and validated the predictions with long-term stability tests of the most promising excipient/polymer combinations. The considered critical quality attributes for the ASDs were the occurrence of amorphous phase separation, API CDF, and molecular mobility in the ASD. As an example, carbamazepine/polyvinylpyrrolidone ASDs were investigated combined with the excipients fructose, lactose, sucrose, trehalose, saccharin, tryptophan, and urea. Although all excipients had a negative impact on the ASD stability, saccharin still turned out to be the most promising one. Long-term stability studies with ASDs containing either saccharin or tryptophan verified -in agreement to the predictions- that API crystallization occurred faster than in the reference ASDs without additional excipient. This work showed that the addition of crystalline excipients to polymeric ASDs might not only offer opportunities but might also bear risks for the long-term stability of the ASD, even though the crystalline excipient stabilizes the polymer-free API. Consequently, excipients should be evaluated based on the thermodynamic phase behavior of the individual mixture of API/polymer/excipient, rather than based on pure-component properties of the excipient only. In-silico predictions proposed in this work remarkably decrease the number of screening tests for identifying suitable formulation excipients. © 2020 Elsevier B.V.
    view abstractdoi: 10.1016/j.ejpb.2020.11.025
  • 2021 • 719 Combining machine learning and domain decomposition methods for the solution of partial differential equations—A review
    Heinlein, A. and Klawonn, A. and Lanser, M. and Weber, J.
    GAMM Mitteilungen 44 (2021)
    Scientific machine learning (SciML), an area of research where techniques from machine learning and scientific computing are combined, has become of increasing importance and receives growing attention. Here, our focus is on a very specific area within SciML given by the combination of domain decomposition methods (DDMs) with machine learning techniques for the solution of partial differential equations. The aim of the present work is to make an attempt of providing a review of existing and also new approaches within this field as well as to present some known results in a unified framework; no claim of completeness is made. As a concrete example of machine learning enhanced DDMs, an approach is presented which uses neural networks to reduce the computational effort in adaptive DDMs while retaining their robustness. More precisely, deep neural networks are used to predict the geometric location of constraints which are needed to define a robust coarse space. Additionally, two recently published deep domain decomposition approaches are presented in a unified framework. Both approaches use physics-constrained neural networks to replace the discretization and solution of the subdomain problems of a given decomposition of the computational domain. Finally, a brief overview is given of several further approaches which combine machine learning with ideas from DDMs to either increase the performance of already existing algorithms or to create completely new methods. © 2021 The Authors. GAMM - Mitteilungen published by Wiley-VCH GmbH.
    view abstractdoi: 10.1002/gamm.202100001
  • 2021 • 718 Combining Switchable Phase-Change Materials and Phase-Transition Materials for Thermally Regulated Smart Mid-Infrared Modulators
    Lyu, X. and Heßler, A. and Wang, X. and Cao, Y. and Song, L. and Ludwig, Al. and Wuttig, M. and Taubner, T.
    Advanced Optical Materials (2021)
    Phase-change materials (PCMs) and phase-transition materials (PTMs) both show a large contrast in their respective optical properties upon switching, enabling compact optical components with diverse functionalities like sensing, thermal imaging, and data recording. However, their switching properties differ significantly, that is, the switching is non-volatile for PCMs while volatile for PTMs. Here, new-generation smart mid-infrared modulators with switchable transmission, reflection, and absorption are demonstrated conceptually and experimentally, which combine one PCM (Ge3Sb2Te6 or In3SbTe2) with one PTM (VO2) as two active layers. The bottom VO2 layer is employed as a thermally regulated (modulated) dynamic mirror, facilitating the switching of transmission between “on” state (using VO2 in its semiconducting state at temperatures below its phase transition temperature Tc) and “off” state (metallic VO2 at temperatures above Tc). The PCM layer on top of the metallic VO2 layer is used either for continuously adjusting the absorption peak spectrally (by up to 1.8 µm using different phases of Ge3Sb2Te6) or for switching between absorption mode (A = 0.99 with amorphous In3SbTe2) and reflection mode (R = 0.85 with crystalline In3SbTe2). The presented concept of merging static, non-volatile thermal switching (via PCMs) with dynamic, volatile thermal modulation (via PTMs) empowers a new generation of optical devices for smart optical switching, for example in spectrally tunable safety optical switches. © 2021 The Authors. Advanced Optical Materials published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/adom.202100417
  • 2021 • 717 Comment on "giant pyroelectric energy harvesting and a negative electrocaloric effect in multilayered nanostructures" by G. Vats, A. Kumar, N. Ortega, C. R. Bowen and R. S. Katiyar,: Energy Environ. Sci., 2016, 9, 1335
    Chen, X. and Shvartsman, V. and Lupascu, D.C. and Zhang, Q.M.
    Energy and Environmental Science 14 1612-1614 (2021)
    Vats et al. (2016) reported a giant negative electrocaloric effect in multi-ferroic layers. The results were deduced using the polarization from partially switched polarization loops and the Maxwell relation on the electrocaloric effect. First of all, fundamentally, the change of these polarizations with temperature, as presented in their Fig. 5, has no relation with the electrocaloric effect and hence cannot be used to deduce the ECE using the Maxwell relation. Moreover, we are troubled by the data presented in their Fig. 6, which were, as claimed by authors, deduced from the polarization data in their Fig. 5 and the Maxwell relation. We find that the ECE results presented in their Fig. 6 have no direct relation with the polarization-temperature data in their Fig. 5. © 2021 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/d0ee02548h
  • 2021 • 716 Comment on “Resolving spatial and energetic distributions of trap states in metal halide perovskite solar cells”
    Ravishankar, S. and Unold, T. and Kirchartz, T.
    Science 371 (2021)
    doi: 10.1126/science.abd8014
  • 2021 • 715 Comparative study of hydrogen embrittlement resistance between additively and conventionally manufactured 304L austenitic stainless steels
    Lee, D.-H. and Sun, B. and Lee, S. and Ponge, D. and Jägle, E.A. and Raabe, D.
    Materials Science and Engineering A 803 (2021)
    Hydrogen embrittlement in 304L austenitic stainless steel fabricated by laser powder-bed-fusion (LPBF) was investigated and compared to conventionally produced 304L samples with two different processing histories; casting plus annealing (CA) and CA plus thermomechanical treatment (CA-TMT). Interestingly, no significant difference in the amount of deformation-induced α′ martensite between the LPBF and CA-TMT samples was observed, suggesting that the solidification substructure in the LPBF sample enhanced the strength without promoting the harmful hydrogen embrittlement effect. These results are discussed in terms of the chemical inhomogeneity, hydrogen-assisted cracking behavior, and hydrogen diffusion and trapping in the present 304L samples. © 2020
    view abstractdoi: 10.1016/j.msea.2020.140499
  • 2021 • 714 Comparing the Activity of Complex Solid Solution Electrocatalysts Using Inflection Points of Voltammetric Activity Curves as Activity Descriptors
    Löffler, T. and Waag, F. and Gökce, B. and Ludwig, Al. and Barcikowski, S. and Schuhmann, W.
    ACS Catalysis 11 1014-1023 (2021)
    Complex solid solution (CSS) (often denoted as high-entropy alloy) electrocatalysts enable access to unique possibilities for tailoring active sites while overcoming ever-existing limitations in electrocatalysis by unique interactions of various elements in direct neighborhood. The challenge lies in the development of strategies, which allow for systematic design of element combination and composition optimization in the multinary composition space. This challenge is accompanied by a lack of a suitable analysis method of experimental activity measurements, which can cope with the complex surface structure of this catalyst class. In this work, we propose the advantageous use of inflection points of voltammetric activity curves as activity descriptors enabling to correlate the potential of individual surface site groups to the respective peaks in the adsorption energy distribution pattern. This concept allows to methodologically gather information about the importance of each element in a CSS with respect to activity and stability of the relevant active sites and provides the basis for a guideline for systematic composition optimization. Further, the effect of phase stability on specific surface site groups as induced by degradation of the CSS phase or oxidation can be monitored. These concepts are experimentally evaluated using Cr-Mn-Fe-Co-Ni as a model system. Nanoparticles are synthesized with systematically varied compositions by means of scalable laser ablation synthesis using a multinary target. The composition is optimized with respect to the electrocatalytic activity for the oxygen reduction reaction (ORR) by varying its Mn content via laser ablation synthesis in ethanol. Subsequently, the concept is applied using rotating disk electrodes for ORR analysis in alkaline media. © 2021 American Chemical Society. All rights reserved.
    view abstractdoi: 10.1021/acscatal.0c03313
  • 2021 • 713 Comparison between optical coherence tomography imaging and histological sections of peripheral nerves
    Carolus, A.E. and Möller, J. and Hofmann, M.R. and van de Nes, J.A.P. and Welp, H. and Schmieder, K. and Brenke, C.
    Journal of Neurosurgery 134 270-277 (2021)
    OBJECTIVE Optical coherence tomography (OCT) is an imaging technique that uses the light-backscattering properties of different tissue types to generate an image. In an earlier feasibility study the authors showed that it can be applied to visualize human peripheral nerves. As a follow-up, this paper focuses on the interpretation of the images obtained. METHODS Ten different short peripheral nerve specimens were retained following surgery. In a first step they were examined by OCT during, or directly after, surgery. In a second step the nerve specimens were subjected to histological examination. Various steps of image processing were applied to the OCT raw data acquired. The improved OCT images were compared with the sections stained by H & E. The authors assigned the structures in the images to the various nerve components including perineurium, fascicles, and intrafascicular microstructures. RESULTS The results show that OCT is able to resolve the myelinated axons. A weighted averaging filter helps in identifying the borders of structural features and reduces artifacts at the same time. Tissue-remodeling processes due to injury (perineural fibrosis or neuroma) led to more homogeneous light backscattering. Anterograde axonal degeneration due to sharp injury led to a loss of visible axons and to an increase of light-backscattering tissue as well. However, the depth of light penetration is too small to allow generation of a complete picture of the nerve. CONCLUSIONS OCT is the first in vivo imaging technique that is able to resolve a nerve’s structures down to the level of myelinated axons. It can yield information about focal and segmental pathologies. © AANS 2021, except where prohibited by US copyright law
    view abstractdoi: 10.3171/2019.8.JNS191278
  • 2021 • 712 Comparison of damage mechanisms: Acoustic cavitation versus series of single laser-induced bubbles
    Hanke, S. and Kaiser, S.A.
    Wear 476 (2021)
    Cavitation is the formation and collapse of bubbles due to pressure changes in fluids. In the vicinity of a solid surface, shock waves, an impinging water jet, and other effects of collapsing bubbles may cause severe damage. Cavitation erosion is extensively studied using techniques generating clouds of bubbles, e.g. flow channels or ultrasonic oscillations. Single bubbles can be generated in a highly controlled manner by evaporating fluid by a short laser pulse. This technique is typically used to study bubble dynamics and the damage from one single bubble on very soft materials. In the present study, two austenitic steels and a NiAl-bronze are exposed to standard acoustic cavitation and repeated laser-induced single bubbles. The evolution of surface damage and the underlying mechanisms are investigated. Surface changes are not observed before 200 single bubbles. After 50,000 bubbles the three alloys are still within the incubation phase. Comparable damage mechanisms act on the materials under both testing techniques. Since the surface area affected by repeated single bubbles is relatively small (≈500 μm diameter), the weight loss could not be measured and correlations are based on surface roughening and the mechanisms of damage specific for each material. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.wear.2021.203641
  • 2021 • 711 Comparison of Hilbert Transform and Complex Demodulation for Defect Identification in Cutting Discs using Vibration-Based Feature Extraction
    Priebe, S. and Brackmann, L. and Alabd-Allah, A. and Butt, S. and Röttger, A. and Meschke, G. and Mueller, I.
    Lecture Notes in Civil Engineering 127 564-572 (2021)
    This paper presents a novel concept for vibration-based feature extraction to identify damages in cutting discs of Tunnel Boring Machines (TBM). Defect frequencies resulting from repeated interaction of rock and disc defects are analysed. The data set is represented by the normal force acting on the edge of a cutting disc and the rock. Two different methods, the Hilbert transform and the complex demodulation, are used to generate the envelope of the time series, which was used to analyse whether the signal shows a feature representing an existing defect in the frequency domain. For the first proof of concept two numerical models were used - a multi-body system and a peridynamics 3D model simulating time series of normal forces. With both models, the linear motion of the disc on a rock sample with constant velocity was simulated. An experimental setup, mechanically similar to the simulations, was used in two experiments for further comparison. All implemented defects could be detected using vibration data of forces and one of the proposed data analysis techniques. © 2021, Springer Nature Switzerland AG.
    view abstractdoi: 10.1007/978-3-030-64594-6_55
  • 2021 • 710 Comparison of the processability and influence on the microstructure of different starting powder blends for laser powder bed fusion of a fe3.5 si1.5 c alloy
    Strauch, A.L. and Uhlenwinkel, V. and Steinbacher, M. and Großwendt, F. and Röttger, A. and Chehreh, A.B. and Walther, F. and Fechte-Heinen, R.
    Metals 11 (2021)
    This paper examines different blends of starting materials for alloy development in the laser powder bed fusion (LPBF) process. By using blends of individual elemental, ferroalloy and carbide powders instead of a pre-alloyed gas-atomized starting powder, elaborate gas-atomization processes for the production of individual starting powders with varying alloy compositions can be omitted. In this work the model alloy Fe3.5 Si1.5 C is produced by LPBF from different blends of pure elemental, binary and ternary powders. Three powder blends were processed. The base material for all powder blends is a commercial gas-atomized Fe powder. In the first blend this Fe powder is admixed with SiC, in the second with the ternary raw alloy FeSiC and in the third with FeSi and FeC. After characterizing the powder properties and performing LPBF parameter studies for each powder blend, the microstructures and the mechanical properties of the LPBF-manufactured samples were analyzed. Therefore, investigations were carried out by scanning electron microscopy, wave length dispersive x-ray spectroscopy and micro hardness testing. It was shown that the admixed SiC dissolves completely during LPBF. But the obtained microstructure consisting of bainite, martensite, ferrite and retained austenite is inhomogeneous. The use of the lower melting ferroalloys FeSi and FeC as well as the ternary ferroalloy FeSiC leads to an increased chemical homogeneity after LPBF-processing. However, the particle size of the used components plays a decisive role for the dissolution behavior in LPBF. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/met11071107
  • 2021 • 709 Complex-Solid-Solution Electrocatalyst Discovery by Computational Prediction and High-Throughput Experimentation**
    Batchelor, T.A.A. and Löffler, T. and Xiao, B. and Krysiak, O.A. and Strotkötter, V. and Pedersen, J.K. and Clausen, C.M. and Savan, A. and Li, Y. and Schuhmann, W. and Rossmeisl, J. and Ludwig, Al.
    Angewandte Chemie - International Edition (2021)
    Complex solid solutions (“high entropy alloys”), comprising five or more principal elements, promise a paradigm change in electrocatalysis due to the availability of millions of different active sites with unique arrangements of multiple elements directly neighbouring a binding site. Thus, strong electronic and geometric effects are induced, which are known as effective tools to tune activity. With the example of the oxygen reduction reaction, we show that by utilising a data-driven discovery cycle, the multidimensionality challenge raised by this catalyst class can be mastered. Iteratively refined computational models predict activity trends around which continuous composition-spread thin-film libraries are synthesised. High-throughput characterisation datasets are then used as input for refinement of the model. The refined model correctly predicts activity maxima of the exemplary model system Ag-Ir-Pd-Pt-Ru. The method can identify optimal complex-solid-solution materials for electrocatalytic reactions in an unprecedented manner. © 2021 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/anie.202014374
  • 2021 • 708 Computational generation of virtual concrete mesostructures
    Holla, V. and Vu, G. and Timothy, J.J. and Diewald, F. and Gehlen, C. and Meschke, G.
    Materials 14 (2021)
    Concrete is a heterogeneous material with a disordered material morphology that strongly governs the behaviour of the material. In this contribution, we present a computational tool called the Concrete Mesostructure Generator (CMG) for the generation of ultra-realistic virtual concrete morphologies for mesoscale and multiscale computational modelling and the simulation of concrete. Given an aggregate size distribution, realistic generic concrete aggregates are generated by a sequential reduction of a cuboid to generate a polyhedron with multiple faces. Thereafter, concave depressions are introduced in the polyhedron using Gaussian surfaces. The generated aggregates are assembled into the mesostructure using a hierarchic random sequential adsorption algorithm. The virtual mesostructures are first calibrated using laboratory measurements of aggregate distributions. The model is validated by comparing the elastic properties obtained from laboratory testing of concrete specimens with the elastic properties obtained using computational homogenisation of virtual concrete mesostructures. Finally, a 3D-convolutional neural network is trained to directly generate elastic properties from voxel data. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/ma14143782
  • 2021 • 707 Computational study of simultaneous positive and negative streamer propagation in a twin surface dielectric barrier discharge via 2D PIC simulations
    Zhang, Q.-Z. and Nguyen-Smith, R.T. and Beckfeld, F. and Liu, Y. and Mussenbrock, T. and Awakowicz, P. and Schulze, J.
    Plasma Sources Science and Technology 30 (2021)
    The propagation mechanisms of plasma streamers have been observed and investigated in a surface dielectric barrier discharge (SDBD) using 2D particle in cell simulations. The investigations are carried out under a simulated air mixture, 80% N2 and 20% O2, at atmospheric pressure, 100 kPa, under both DC conditions and a pulsed DC waveform that represent AC conditions. The simulated geometry is a simplification of the symmetric and fully exposed SDBD resulting in the simultaneous ignition of both positive and negative streamers on either side of the Al2O3 dielectric barrier. In order to determine the interactivity of the two streamers, the propagation behavior for the positive and negative streamers are investigated both independently and simultaneously under identical constant voltage conditions. An additional focus is implored under a fast sub nanosecond rise time square voltage pulse alternating between positive and negative voltage conditions, thus providing insight into the dynamics of the streamers under alternating polarity switches. It is shown that the simultaneous ignition of both streamers, as well as using the pulsed DC conditions, providing both an enhanced discharge and an increased surface coverage. It is also shown that additional streamer branching may occur in a cross section that is difficult to experimentally observe. The enhanced discharge and surface coverage may be beneficial to many applications such as, but are not limited to: air purification, volatile organic compound removal, and plasma enhanced catalysis. © 2021 IOP Publishing Ltd.
    view abstractdoi: 10.1088/1361-6595/abf598
  • 2021 • 706 Computing low-frequency vibration energy with Hölder singularities as durability predictive criterion of random road excitation
    Chin, C.H. and Abdullah, S. and Singh, S.S.K. and Ariffin, A.K. and Schramm, D.
    Soft Computing (2021)
    This study aims to compute low-frequency energy with Hölder singularities in vibration signals of suspension system to predict the durability of coil spring. High frequencies in vibrations often had minimal contribution towards fatigue damage due to low amplitude range and thus induce errors in energy analysis of vibration signals. Since traditional low-pass method had not only been ineffective in reducing high frequencies, it also resulted in the loss of signal information. This study had therefore proposed characterising low-frequency energy for road excitations using Hölder singularities and power spectral analyses. Singularities and low-frequency energy of road vibration signals would first be identified through Hölder local regularity analysis. This was then followed by fatigue life prediction using the strain-life approaches (i.e. Coffin-Manson, Morrow and Smith–Watson–Topper models). The energy-based fatigue life prediction models had not only shown good fit with R2 values higher than 0.8, but had also demonstrated an accurate prediction of fatigue life with more than 95% of the data being within the acceptance boundary. The Morrow-based model provided the highest accuracy in fatigue life prediction because of its highest R2 value of 0.8625 and 100% data survival in the fatigue life correlation study. This showed that energy-based fatigue life prediction models provide an accurate and effective prediction of the durability performance. This study proposed a more precise energy characterisation method for energy-based durability prediction of suspension coil spring under random loading conditions. © 2021, The Author(s), under exclusive licence to Springer-Verlag GmbH, DE part of Springer Nature.
    view abstractdoi: 10.1007/s00500-021-05640-5
  • 2021 • 705 Concentration polarization enabled reactive coating of nanofiltration membranes with zwitterionic hydrogel
    May, P. and Laghmari, S. and Ulbricht, M.
    Membranes 11 (2021)
    In this study, the bottleneck challenge of membrane fouling is addressed via establishing a scalable concentration polarization (CP) enabled and surface‐selective hydrogel coating using zwitterionic cross‐linkable macromolecules as building blocks. First, a novel methacrylate‐based copolymer with sulfobetain and methacrylate side groups was prepared in a simple three‐step syn-thesis. Polymer gelation initiated by a redox initiator system (ammonium persulfate and tetrameth-ylethylenediamine) for radical cross‐linking was studied in bulk in order to identify minimum (“critical”) concentrations to obtain a hydrogel. In situ reactive coating of a polyamide nanofiltration membrane was achieved via filtration of a mixture of the reactive compounds, utilizing CP to meet critical gelation conditions solely within the boundary layer. Because the feasibility was studied and demonstrated in dead‐end filtration mode, the variable extent of CP was estimated in the frame of the film model, with an iterative calculation using experimental data as input. This allowed to dis-cuss the influence of parameters such as solution composition or filtration rate on the actual polymer concentration and resulting hydrogel formation at the membrane surface. The zwitterionic hydro-gel‐coated membranes exhibited lower surface charge and higher flux during protein filtration, both compared to pristine membranes. Salt rejection was found to remain unchanged. Results further reveal that the hydrogel coating thickness and consequently the reduction in membrane permeance due to the coating can be tuned by variation of filtration time and polymer feed concentration, il-lustrating the novel modification method’s promising potential for scale‐up to real applications. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/membranes11030187
  • 2021 • 704 Configurational Entropy Driven High-Pressure Behaviour of a Flexible Metal–Organic Framework (MOF)
    Vervoorts, P. and Keupp, J. and Schneemann, A. and Hobday, C.L. and Daisenberger, D. and Fischer, R.A. and Schmid, R. and Kieslich, G.
    Angewandte Chemie - International Edition 60 787-793 (2021)
    Flexible metal–organic frameworks (MOFs) show large structural flexibility as a function of temperature or (gas)pressure variation, a fascinating property of high technological and scientific relevance. The targeted design of flexible MOFs demands control over the macroscopic thermodynamics as determined by microscopic chemical interactions and remains an open challenge. Herein we apply high-pressure powder X-ray diffraction and molecular dynamics simulations to gain insight into the microscopic chemical factors that determine the high-pressure macroscopic thermodynamics of two flexible pillared-layer MOFs. For the first time we identify configurational entropy that originates from side-chain modifications of the linker as the key factor determining the thermodynamics in a flexible MOF. The study shows that configurational entropy is an important yet largely overlooked parameter, providing an intriguing perspective of how to chemically access the underlying free energy landscape in MOFs. © 2020 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/anie.202011004
  • 2021 • 703 Confocal laser scanning holographic microscopy of buried structures
    Schnitzler, L. and Neutsch, K. and Schellenberg, F. and Hofmann, M.R. and Gerhardt, N.C.
    Applied Optics 60 A8-A14 (2021)
    In this paper, we present a confocal laser scanning holographic microscope for the investigation of buried structures. The multimodal system combines high diffraction limited resolution and high signal-to-noise-ratio with the ability of phase acquisition. The amplitude and phase imaging capabilities of the system are shown on a test target. For the investigation of buried integrated semiconductor structures, we expand our system with an optical beam induced current modality that provides additional structure-sensitive contrast. We demonstrate the performance of the multimodal system by imaging the buried structures of a microcontroller through the silicon backside of its housing in reflection geometry. © 2020 Optical Society of America
    view abstractdoi: 10.1364/AO.403687
  • 2021 • 702 Considering Non-Surface Scattering in Physical Optics Approximations
    Garten, O. and Statz, C. and Gerling, S. and Jebramcik, J. and Barowski, J. and Plettemeier, D. and Rolfes, I.
    IEEE Transactions on Antennas and Propagation (2021)
    This work addresses the issue of volume scattering effects within the context of the physical optics (PO) approach. This decreases the modeling and computational effort to simulate scattering from complex material compositions. It is shown that there is a natural progression from the classical PO for perfect electric conductors over the PO for dielectric scatterers towards the proposed formulation Four specializations of the general algorithm are presented to emphasize the versatility of this approach. Details regarding the implementation of the proposed examples are described. Results for each of the special cases are shown and compared to commercially available full-wave solvers of CST and FEKO. CCBY
    view abstractdoi: 10.1109/TAP.2021.3060043
  • 2021 • 701 Constant temperature approach for the assessment of injection molding parameter influence on the fatigue behavior of short glass fiber reinforced polyamide 6
    Mrzljak, S. and Delp, A. and Schlink, A. and Zarges, J.-C. and Hülsbusch, D. and Heim, H.-P. and Walther, F.
    Polymers 13 (2021)
    Short glass fiber reinforced plastics (SGFRP) offer superior mechanical properties compared to polymers, while still also enabling almost unlimited geometric variations of components at large-scale production. PA6-GF30 represents one of the most used SGFRP for series components, but the impact of injection molding process parameters on the fatigue properties is still insufficiently investigated. In this study, various injection molding parameter configurations were investigated on PA6-GF30. To take the significant frequency dependency into account, tension–tension fatigue tests were performed using multiple amplitude tests, considering surface temperature-adjusted frequency to limit self-heating. The frequency adjustment leads to shorter testing durations as well as up to 20% higher lifetime under fatigue loading. A higher melt temperature and volume flow rate during injection molding lead to an increase of 16% regarding fatigue life. In situ X-ray microtomography analysis revealed that this result was attributed to a stronger fiber alignment with larger fiber lengths in the flow direction. Using digital volume correlation, differences of up to 100% in local strain values at the same stress level for different injection molding process parameters were identified. The results prove that the injection molding parameters have a high influence on the fatigue properties and thus offer a large optimization potential, e.g., with regard to the component design. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/polym13101569
  • 2021 • 700 Constitutive modeling of cyclic plasticity at elevated temperatures for a nickel-based superalloy
    Shahmardani, M. and Hartmaier, A.
    International Journal of Fatigue 151 (2021)
    During the operation of turbines in jet engines or in power plants, high thermal and intermittent mechanical loads appear, which can lead to high-temperature fatigue failure if thermal and mechanical loads vary at the same time. Since fatigue testing is a time-consuming process, it is important to develop realistic material models with predictive capabilities that are able to extrapolate the limited experimental results for cyclic plasticity within a wide range of temperatures. To accomplish this, an approach based on a representative volume element (RVE), mimicking the typical γ/γ′ microstructure of a Ni-based single crystal superalloy, is adopted for cyclic loading conditions. With the help of this RVE, the temperature- and deformation-dependent internal stresses in the microstructure can be taken into account in a realistic manner, which proves to be essential in understanding the fatigue behavior of this material. The material behavior in the elastic regime is described by temperature-dependent anisotropic elastic constants. The flow rule for plastic deformation is governed by the thermal activation of various slip systems in the γ matrix, the γ′ precipitate and also by cube slip along the γ/γ′ microstructure. This phenomenological crystal plasticity/creep model takes different mechanisms into account, including thermally activated dislocation slip, the internal stresses due to inhomogeneous strains in different regions of γ matrix channels and in γ′ precipitates, the softening effect due to dislocation climb, the formation of 〈112〉 dislocation ribbons for precipitate shearing, and Kear-Wilsdorf locks. This constitutive law is parameterized based on experimental data for the CMSX-4 single-crystal superalloy by applying an inverse analysis to identify the material parameters based on many low cycle fatigue tests in the intermediate temperature and high stress regime. The identified material parameters could predict cyclic plasticity and low cycle fatigue behavior at different temperatures. The model does not only reliably reproduce the experimental results along different crystallographic loading directions, but it also reveals the relative importance of the different deformation mechanisms for the fatigue behavior under various conditions. © 2021 Elsevier Ltd
    view abstractdoi: 10.1016/j.ijfatigue.2021.106353
  • 2021 • 699 Control of electron velocity distributions at the wafer by tailored voltage waveforms in capacitively coupled plasmas to compensate surface charging in high-aspect ratio etch features
    Hartmann, P. and Wang, L. and Nösges, K. and Berger, B. and Wilczek, S. and Brinkmann, R.P. and Mussenbrock, T. and Juhasz, Z. and Donkó, Z. and Derzsi, A. and Lee, E. and Schulze, J.
    Journal of Physics D: Applied Physics 54 (2021)
    Low pressure single- or dual-frequency capacitively coupled radio frequency (RF) plasmas are frequently used for high-aspect ratio (HAR) dielectric etching due to their capability to generate vertical ion bombardment of the wafer at high energies. Electrons typically reach the wafer at low energies and with a wide angular distribution during the local sheath collapse. Thus, in contrast to positive ions, electrons cannot propagate deeply into HAR etch features and the bottom as well as the sidewalls of such trenches can charge up positively, while the mask charges negatively. This causes etch stops and distortion of profile shapes. Here, we investigate low pressure, high voltage capacitively coupled RF argon gas discharges by Particle-In-Cell/Monte Carlo collisions simulations and demonstrate that this problem can be solved by Voltage Waveform Tailoring, i.e. the velocity and angular distribution of electrons impacting on the electrodes can be tuned towards high velocities and small angles to the surface-normal, while keeping the energies of the impacting ions high. The applied voltage waveforms consist of a base frequency of 400 kHz with 10 kV amplitude and a series of higher harmonics. A high frequency component at 40 or 60 MHz is used additionally. Square voltage waveforms with different rise-times are examined as well. We show that high fluxes of electrons towards the wafer at normal velocities of up to 2.2 × 107 m s-1 (corresponding to 1.4 keV energy) can be realized. © 2021 The Author(s). Published by IOP Publishing Ltd.
    view abstractdoi: 10.1088/1361-6463/abf229
  • 2021 • 698 Control of Marine Bacteria and Diatom Biofouling by Constant and Alternating Potentials
    Schwarze, J. and Schuhmann, W. and Rosenhahn, A.
    Langmuir 37 7464-7472 (2021)
    The application of electrochemical potentials to surfaces is an easy and direct way to alter surface charge density, the structure of the electrochemical double layer, and the presence of electrochemically activated species. On such electrified interfaces the formation of biofilms is reduced. Here we investigate how applied potentials alter the colonization of surfaces by the marine bacterium Cobetia marina and the marine diatom Navicula perminuta. Different constant potentials between-0.8 and 0.6 V as well as regular switching between two potentials were investigated, and their influence on the attachment of the two biofilm-forming microorganisms on gold-coated working electrodes was quantified. Reduced bacteria and diatom attachment were found when negative potentials and alternating potentials were applied. The results are discussed on the basis of the electrochemical processes occurring at the working electrode in artificial seawater as revealed by cyclic voltammetry. © 2021 American Chemical Society. All rights reserved.
    view abstractdoi: 10.1021/acs.langmuir.1c00865
  • 2021 • 697 Control of residual oxygen of the process atmosphere during laser-powder bed fusion processing of Ti-6Al-4V
    Pauzon, C. and Dietrich, K. and Forêt, P. and Dubiez-Le Goff, S. and Hryha, E. and Witt, G.
    Additive Manufacturing 38 (2021)
    The effect of the residual oxygen concentration in the process atmosphere during laser-powder bed fusion (L-PBF) of Ti-6Al-4V was investigated, using an external oxygen monitoring system equipped with two types of oxygen sensors typically used in L-PBF hardware: a lambda probe and an electrochemical oxygen sensor. The recordings of the oxygen variations during L-PBF highlighted that the electrochemical sensor is more reliable than the lambda probe, whose signal showed a maximum deviation of about 700 ppm O2 after 7 h, attributed to its sensitivity to hydrogen present in the system. The study revealed that proper monitoring of the oxygen in the laboratory scale L-PBF system used is necessary to limit oxygen and nitrogen pick-ups by the built material. Concentrations as high as 2200 ppm O2 and 500 ppm N2 in the Ti-6Al-4V part built under standard conditions were measured, compared to maximum levels of 1800 ppm O2 and 250 ppm N2 with the external oxygen control. In addition, the findings underline the critical effect of the component design, such as the high aspect ratio columns or the lattice structures, on the heat accumulation in case of Ti-6Al-4V, leading to enhanced oxygen and nitrogen pick-up, as high as 600 ppm O2 and 150 ppm N2 difference between the bottom and top of the cylindrical samples of 70 mm height used in this study. The determination of tensile properties of samples built at different heights put in evidence the detrimental effect of the oxygen increase with build height on the ductility, which decreased from 12% to below 6% between the bottom and top positions. This work highlights that the possible presence of impurities in the L-PBF atmosphere can have harmful impact on the properties of Ti-6Al-4V components, which can be mitigated adjusting the oxygen control system. © 2020 The Authors
    view abstractdoi: 10.1016/j.addma.2020.101765
  • 2021 • 696 Controlled growth of ordered monolayers of N-heterocyclic carbenes on silicon
    Franz, M. and Chandola, S. and Koy, M. and Zielinski, R. and Aldahhak, H. and Das, M. and Freitag, M. and Gerstmann, U. and Liebig, D. and Hoffmann, A.K. and Rosin, M. and Schmidt, W.G. and Hogan, C. and Glorius, F. and Esser, N. ...
    Nature Chemistry (2021)
    N-Heterocyclic carbenes (NHCs) are promising modifiers and anchors for surface functionalization and offer some advantages over thiol-based systems. Because of their strong binding affinity and high electron donation, NHCs can dramatically change the properties of the surfaces to which they are bonded. Highly ordered NHC monolayers have so far been limited to metal surfaces. Silicon, however, remains the element of choice in semiconductor devices and its modification is therefore of utmost importance for electronic industries. Here, a comprehensive study on the adsorption of NHCs on silicon is presented. We find covalently bound NHC molecules in an upright adsorption geometry and demonstrate the formation of highly ordered monolayers exhibiting good thermal stability and strong work function reductions. The structure and ordering of the monolayers is controlled by the substrate geometry and reactivity and in particular by the NHC side groups. These findings pave the way towards a tailor-made organic functionalization of silicon surfaces and, thanks to the high modularity of NHCs, new electronic and optoelectronic applications. [Figure not available: see fulltext.] © 2021, The Author(s), under exclusive licence to Springer Nature Limited.
    view abstractdoi: 10.1038/s41557-021-00721-2
  • 2021 • 695 Controlling Oxygen Reduction Selectivity through Steric Effects: Electrocatalytic Two-Electron and Four-Electron Oxygen Reduction with Cobalt Porphyrin Atropisomers
    Lv, B. and Li, X. and Guo, K. and Ma, J. and Wang, Y. and Lei, H. and Wang, F. and Jin, X. and Zhang, Q. and Zhang, W. and Long, R. and Xiong, Y. and Apfel, U.-P. and Cao, R.
    Angewandte Chemie - International Edition 60 12742-12746 (2021)
    Achieving a selective 2 e− or 4 e− oxygen reduction reaction (ORR) is critical but challenging. Herein, we report controlling ORR selectivity of Co porphyrins by tuning only steric effects. We designed Co porphyrin 1 with meso-phenyls each bearing a bulky ortho-amido group. Due to the resulted steric hinderance, 1 has four atropisomers with similar electronic structures but dissimilar steric effects. Isomers αβαβ and αααα catalyze ORR with n=2.10 and 3.75 (n is the electron number transferred per O2), respectively, but ααββ and αααβ show poor selectivity with n=2.89–3.10. Isomer αβαβ catalyzes 2 e− ORR by preventing a bimolecular O2 activation path, while αααα improves 4 e− ORR selectivity by improving O2 binding at its pocket, a feature confirmed by spectroscopy methods, including O K-edge near-edge X-ray absorption fine structure. This work represents an unparalleled example to improve 2 e− and 4 e− ORR by tuning only steric effects without changing molecular and electronic structures. © 2021 Wiley-VCH GmbH
    view abstractdoi: 10.1002/anie.202102523
  • 2021 • 694 Controlling the emission time of photon echoes by optical freezing of exciton dephasing and rephasing in quantum-dot ensembles
    Reichelt, M. and Rose, H. and Kosarev, A.N. and Poltavtsev, S.V. and Bayer, M. and Akimov, I.A. and Schneider, C. and Kamp, M. and Höfling, S. and Meier, T.
    Proceedings of SPIE - The International Society for Optical Engineering 11684 (2021)
    Following the ultrafast optical excitation of an inhomogeneously broadened ensemble, the macroscopic optical polarization decays rapidly due to dephasing. This destructive interference is, however, reversible in photon echo experiments. Here, we propose a concept in which a control pulse slows down either the dephasing or the rephasing of the exciton ensemble during its presence. We analyze and visualize this optical freezing process by showing and discussing results for different single and multiple sequences of control pulses using a simple model of inhomogeneously broadened two-level systems. This idea has been realized in experiments performed on self-assembled (In,Ga)As quantum dots where it was possible to retard or advance the photon echo emission time by several picoseconds. The measurements are in very good agreement with numerical simulations for a more realistic model which, in particular, takes the spatial shape of the laser pulses into account. © 2021 SPIE.
    view abstractdoi: 10.1117/12.2576887
  • 2021 • 693 Controlling the lithium proton exchange of LLZO to enable reproducible processing and performance optimization
    Rosen, M. and Ye, R. and Mann, M. and Lobe, S. and Finsterbusch, M. and Guillon, O. and Fattakhova-Rohlfing, D.
    Journal of Materials Chemistry A 9 4831-4840 (2021)
    Ceramic solid state-electrolytes attract significant attention due to their intrinsic safety and, in the case of the garnet type Li6.45Al0.05La3Zr1.6Ta0.4O12(LLZO), the possibility to use Li-metal anodes to provide high energy densities on a cell and battery level. However, one of the major obstacles hindering their wide-spread application is the translation and optimization of production processes from laboratory to industrial scale. Even though the plausibility of manufacturing components and cellsviawet processing routes like tape casting and screen printing has been shown, the impact of the sensitivity of LLZO to air and protic solvents due to Li+/H+-exchange is not fully understood yet. An uncontrolled alteration of the powder surface results in poorly reproducible processing characteristics and electrochemical performance of the final battery components and full cells. This knowledge gap is the cause of the large performance variations reported across different research labs worldwide and is unacceptable for up-scaling to industrial level. To close this gap, the influence of the Li+/H+-exchange taking place at various steps in the manufacturing process was systematically investigated in this study. For the first time, this allowed a mechanistic understanding of its impact on the processability itself and on the resulting electrochemical performance of a free-standing LLZO separator. The importance of a close control of the pre-treatment and storage conditions of LLZO, as well as contact time with the solvent could be extracted for each step of the manufacturing process. As a result, we were able to optimize the processing of thin, dense, free standing LLZO separators and significantly improve the total Li-ion conductivity to 3.90 × 10−4S cm−1and the critical current density to over 300 μA cm−2without making structural changes to separator or the starting material. These findings do not only enable a deeper understanding and control over the manufacturing process, but also show potential for further improvement of cell concepts already existing in literature. © The Royal Society of Chemistry 2021.
    view abstractdoi: 10.1039/d0ta11096e
  • 2021 • 692 Controlling the Surface Functionalization of Ultrasmall Gold Nanoparticles by Sequence-Defined Macromolecules
    van der Meer, S.B. and Seiler, T. and Buchmann, C. and Partalidou, G. and Boden, S. and Loza, K. and Heggen, M. and Linders, J. and Prymak, O. and Oliveira, C.L.P. and Hartmann, L. and Epple, M.
    Chemistry - A European Journal 27 1451-1464 (2021)
    Ultrasmall gold nanoparticles (diameter about 2 nm) were surface-functionalized with cysteine-carrying precision macromolecules. These consisted of sequence-defined oligo(amidoamine)s (OAAs) with either two or six cysteine molecules for binding to the gold surface and either with or without a PEG chain (3400 Da). They were characterized by 1H NMR spectroscopy, 1H NMR diffusion-ordered spectroscopy (DOSY), small-angle X-ray scattering (SAXS), and high-resolution transmission electron microscopy. The number of precision macromolecules per nanoparticle was determined after fluorescent labeling by UV spectroscopy and also by quantitative 1H NMR spectroscopy. Each nanoparticle carried between 40 and 100 OAA ligands, depending on the number of cysteine units per OAA. The footprint of each ligand was about 0.074 nm2 per cysteine molecule. OAAs are well suited to stabilize ultrasmall gold nanoparticles by selective surface conjugation and can be used to selectively cover their surface. The presence of the PEG chain considerably increased the hydrodynamic diameter of both dissolved macromolecules and macromolecule-conjugated gold nanoparticles. © 2020 The Authors. Published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/chem.202003804
  • 2021 • 691 Control‐oriented characterization of product properties during hot hole‐flanging of X46Cr13 sheet material in a progressive‐die
    Martschin, J. and Meya, R. and Klöser, D. and Meurer, T. and Tekkaya, A.E.
    Metals 11 1-14 (2021)
    Robust and versatile production is enabled by a closed‐loop control of product properties. This essentially relies on the characterization of the interaction between properties and available degrees of freedom to control the process. In particular, this work examines the setting of collar height, thinning, curvature, and hardness during hot hole‐flanging of X46Cr13 sheet material with simultaneous heat treatment to identify approaches for a closed‐loop property control in hot hole-flanging during multi‐stage hot sheet metal forming. To scrutinize the adjustability of the hardness of X46Cr13 sheet material by heat treatment with rapid heating and short dwell times, quenching tests with austenitizing temperatures from 900 to 1100 °C and dwell times from 1 to 300 s were carried out. A hardness between 317 and 680 HV10 was measured. By analyzing the force-displacement curve and the contact situation between tools and blank during hot hole‐flanging, an understanding for the process was established. To determine the adjustability of geometrical collar properties and the hardness of the collar, collars were formed at punch speeds between 5 and 100 mm/s and at different temperatures. Here, a dependency of the geometry of the collar on temperature and punch speed as well as setting of the hardness was demonstrated. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/met11020349
  • 2021 • 690 Convergence analysis of the scaled boundary finite element method for the Laplace equation
    Bertrand, F. and Boffi, D. and G. de Diego, G.
    Advances in Computational Mathematics 47 (2021)
    The scaled boundary finite element method (SBFEM) is a relatively recent boundary element method that allows the approximation of solutions to partial differential equations (PDEs) without the need of a fundamental solution. A theoretical framework for the convergence analysis of SBFEM is proposed here. This is achieved by defining a space of semi-discrete functions and constructing an interpolation operator onto this space. We prove error estimates for this interpolation operator and show that optimal convergence to the solution can be obtained in SBFEM. These theoretical results are backed by two numerical examples. © 2021, The Author(s).
    view abstractdoi: 10.1007/s10444-021-09852-z
  • 2021 • 689 Co-production of industrial services [Ko-Produktion industrieller Dienstleistungen]
    Austerjost, M. and Kreyenborg, A. and Kiklhorn, D. and Azkan, C. and Graefenstein, J. and Hefft, D. and Henke, M.
    ZWF Zeitschrift fuer Wirtschaftlichen Fabrikbetrieb 116 153-156 (2021)
    The co-production of industrial services offers enormous potential, especially for German medium-sized companies. However, up to now there is a lack of a common language that guarantees efficient and secure work-cooperation of different companies at network level. The SealedServices research project is therefore developing a cooperative value creation network with which Internet-based services can be realized independently by SMEs. © 2021 Walter de Gruyter GmbH, Berlin/Boston, Germany.
    view abstractdoi: 10.1515/zwf-2021-0030
  • 2021 • 688 Correcting Intraday Periodicity Bias in Realized Volatility Measures
    Dette, H. and Golosnoy, V. and Kellermann, J.
    Econometrics and Statistics (2021)
    Diurnal fluctuations in volatility are a well-documented stylized fact of intraday price data. This warrants an investigation how this intraday periodicity (IP) affects both finite sample as well as asymptotic properties of several popular realized estimators of daily integrated volatility which are based on functionals of a finite number of intraday returns. It turns out that most of the estimators considered in this study exhibit a finite-sample bias due to IP, which can however get negligible when the number of intraday returns diverges to infinity. The appropriate correction factors for this bias are derived based on estimates of the IP. The adequacy of the new corrections is evaluated by means of a Monte Carlo simulation study and an empirical example. © 2021 EcoSta Econometrics and Statistics
    view abstractdoi: 10.1016/j.ecosta.2021.03.002
  • 2021 • 687 Correction to: Modeling of cutting forces in trochoidal milling with respect to wear-dependent topographic changes (Production Engineering, (2021), 10.1007/s11740-021-01060-4)
    Bergmann, J.A. and Potthoff, N. and Rickhoff, T. and Wiederkehr, P.
    Production Engineering (2021)
    Due to technical problems, section 2.1 contained a misplaced symbol after publication of the paper. The description of workpiece dimensions has been corrected for the missing symbol. Original article corrected. © 2021, © The Author(s).
    view abstractdoi: 10.1007/s11740-021-01065-z
  • 2021 • 686 Correlating the Synthesis, Structure, and Catalytic Performance of Pt-Re/TiO2for the Aqueous-Phase Hydrogenation of Carboxylic Acid Derivatives
    Haus, M.O. and Meledin, A. and Leiting, S. and Louven, Y. and Roubicek, N.C. and Moos, S. and Weidenthaler, C. and Weirich, T.E. and Palkovits, R.
    ACS Catalysis 11 5119-5134 (2021)
    Pt-Re bimetallic catalysts have many applications, ranging from catalytic reforming to the reduction of carboxylic acid derivatives. However, the exact role of Re in these systems has remained a matter of discussion, partly due to the plethora of suggested synthesis protocols and analysis conditions. This study presents an extensive comparison of such literature protocols and the resulting materials. In detail, characterization by N2 physisorption, X-ray diffraction, temperature-programmed reduction, CO pulse chemisorption, Fourier-transform infrared spectroscopy of adsorbed CO, scanning transmission electron microscopy, energy-dispersive X-ray spectroscopy, and in situ X-ray photoelectron spectroscopy is combined with catalytic testing to yield synthesis-structure-activity correlations. Accordingly, the investigated catalysts share common features, such as Pt0 nanoparticles (1-4 nm) decorated with partially reduced Re species (ReOx-y). The remaining rhenium oxide is spread over the TiO2 support and enhances Pt dispersion in sequential impregnation protocols. While differences in the number of active sites (Pt0/ReOx-y) mostly explain catalytic results, small variations in the extent of Re reduction and site composition cause additional modulations. The optimal bimetallic catalyst outperforms Ru/C (previous benchmark) in the reduction of N-(2-hydroxyethyl)succinimide, an important step in the production of a bio-based polyvinylpyrrolidone polymer. © 2021 American Chemical Society. All rights reserved.
    view abstractdoi: 10.1021/acscatal.0c05612
  • 2021 • 685 Correlation of load drop and crack initiation criteria in fatigue life experiments of metallic materials
    Heckmann, K. and Sievers, J. and Schopf, T. and Lücker, L. and Schmiedt-Kalenborn, A. and Walther, F. and Starke, P. and Acosta, R. and Boller, C.
    Engineering Fracture Mechanics 251 (2021)
    The simulation and assessment of fatigue damage of metallic materials are strongly dependent on the definition of critical damage initiation, i.e. the formation of a crack after a certain number of cycles under fatigue loading. To get this described in an appropriate way classical fatigue analysis needs to be combined with fracture mechanics to obtain a realistic size of an initiating macro crack in a component in the end. Ultimately, this size depends on the procedure of how fatigue life curves are generated from the fatigue tests performed. In this paper strain-controlled fatigue tests and fractographic results have been combined with a computational assessment to better understand the relationship between a traditional load drop criterion characterizing the size of a crack being initiated. It is stated that the location of an initiating crack versus the location of an extensometer applied to the specimen can have an influence on the crack size being initiated and thus the fatigue life for a load drop criterion being fixed. A relationship is proposed to link a crack size dependent on the fatigue test evaluation scheme with the fatigue life, which can be used in engineering assessments. The relevance of practical application cases is discussed. © 2021 Elsevier Ltd
    view abstractdoi: 10.1016/j.engfracmech.2021.107785
  • 2021 • 684 Corrigendum to “A hysteresis model for the unfrozen liquid content in freezing porous media” [Comput. Geotech. 134 (2021) 104048] (Computers and Geotechnics (2021) 134, (S0266352X21000513), (10.1016/j.compgeo.2021.104048))
    Saberi, P.S. and König, C. and Meschke, G.
    Computers and Geotechnics (2021)
    The authors regret that the contributions of Dr. C. König in the supervision of the first author and in making the software ‘Spring’ used partially for the analyses reported in the paper available have not been adequately reflected in the list of authors of the original paper. The model has been developed as part of the Master's thesis of the first author, who was supported by the company ‘delta H Ingenieurgesellschaft’ during his stay at the company, and also has been co-supervised by the CEO, Dr. C. König. Therefore, the corrected list of authors reads as provided in this corrigendum article updated as above. To acknowledge the contribution of ‘delta H Ingenieurgesellschaft’, the Section ‘Acknowledgement’ has been modified by adding following sentences: Financial support to the first author was provided by ‘delta h Ingenieurgesellschaft’. The first and third authors also appreciate the use of the software ‘Spring’ for performing the first benchmark reported in the paper. Finally, the contributions of Dr. C. König to the present paper are accounted for by adding the following line in the ‘CRediT authorship contribution statement’: Christoph König: Supervision, Writing - review & editing, Funding acquisition. The authors would like to apologise for any inconvenience caused. © 2021
    view abstractdoi: 10.1016/j.compgeo.2021.104298
  • 2021 • 683 Co-Sintering Study of Na0.67[Ni0.1Fe0.1Mn0.8]O2 and NaSICON Electrolyte–Paving the way to High Energy Density All-Solid-State Batteries
    Dück, G. and Naqash, S. and Finsterbusch, M. and Breuer, U. and Guillon, O. and Fattakhova-Rohlfing, D.
    Frontiers in Energy Research 9 (2021)
    Sodium is a promising candidate for stationary storage applications, especially when the demand for lithium-ion batteries increases due to electromobility applications. Even though its energy density is lower, Na-ion technology is estimated to lead to a cost reduction of 30% compared to Li-ion technology. To improve safety as well as energy density, Na-based all-solid-state-batteries featuring solid electrolytes such as beta-alumina and sodium superionic conductors and cathode materials such as Na3V2(PO4)3 and NaxCoO2 have been developed over the past years. However, the biggest challenge are mixed cathodes with highly conductive interfaces, especially when co-sintering the materials. For example, a promising sodium superionic conductor type Na3Zr2Si2PO12 electrolyte sinters at 1,250°C, whereas the corresponding Na3V2PO12 cathode decomposes at temperatures higher than 900°C, posing a bottleneck. Thus in this paper, we synthesized Na0.62 [Ni0.10Fe0.10Mn0.80]O2 as cathode material for all-solid-state sodium-ion batteries via a relatively cheap and easy solution-assisted solid state reaction processing route. The thermal investigations of the pure cathode material found no degradation up to 1,260°C, making it a perfect match for Na3.4Zr2Si2.4P0.6O12 electrolyte. In our aim to produce a co-sintered mixed cathode, electron microscopy investigation showed a highly dense microstructure and the elemental mapping performed via energy dispersive X-ray spectroscopy and secondary ion mass spectrometry confirm that Na3.4Zr2Si2.4P0.6O12 and Na0.62 [Ni0.10Fe0.10Mn0.80]O2 do not react during sintering. However, the active cathode material forms a sodium rich and a sodium deficient phase which needs further investigation to understand the origin and its impact on the electrochemical performance. © Copyright © 2021 Dück, Naqash, Finsterbusch, Breuer, Guillon and Fattakhova-Rohlfing.
    view abstractdoi: 10.3389/fenrg.2021.689416
  • 2021 • 682 Cotton as Precursor for the Preparation of Porous Cellulose Adsorbers
    Wittmar, A.S.M. and Baumert, D. and Ulbricht, M.
    Macromolecular Materials and Engineering 306 (2021)
    Natural biopolymer-based porous spherical adsorbers from cellulose have good efficiency for removal of metal ion pollutants from aqueous media. However, high purity celluloses, most commonly used as precursors for preparation of the adsorber spheres, require complex synthesis processes, which consume energy and chemicals, and may thus lead to other types of pollution. In this work, the possibility to prepare cellulose-based porous spherical adsorbers directly from cotton, using an ionic liquid-based platform is analyzed in detail. The dissolution of microcrystalline cellulose (MCC), as reference, and of cotton in ionic liquid-based solvents and the properties of the obtained polymer solutions are investigated in order to evaluate their processability toward porous macrospheres using the drop shaping cum non-solvent induced phase separation process. The properties of the prepared spheres are assessed. The dissolution of cotton is more difficult than the dissolution of MCC and the formed cotton-based solutions are considerably more viscous, which makes their processability possible only after careful adjustment of the cotton solution concentration. The maximum adsorption capacities toward Cu2+ are ≈110 and ≈72 mg/g for the porous cotton-based spheres prepared from 1-ethyl-3-methylimidazolium acetate ([Emim][OAc]):dimethylsulfoxide (DMSO) = 2:1 and 1-butyl-3-methylimidazolium acetate ([Bmim][OAc]):DMSO = 2:1 solutions, respectively. © 2021 The Authors. Macromolecular Materials and Engineering published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/mame.202000778
  • 2021 • 681 Coupling of the phase field approach to the Armstrong-Frederick model for the simulation of ductile damage under cyclic load
    Aygün, S. and Wiegold, T. and Klinge, S.
    International Journal of Plasticity 143 (2021)
    The present contribution proposes a thermodynamically consistent model for the simulation of the ductile damage. The model couples the phase field method of fracture to the Armstrong-Frederick plasticity model with kinematic hardening. The latter is particularly suitable for simulating the material behavior under a cyclic load. The model relies on the minimum principle of the dissipation potential. However, the application of this approach is challenging since potentials of coupled methods are defined in different spaces: The dissipation potential of the phase field model is expressed in terms of rates of internal variables, whereas the Armstrong-Frederick model proposes a formulation depending on thermodynamic forces. For this reason, a unique formulation requires the Legendre transformation of one of the potentials. The present work performs the transformation of the Armstrong-Frederick potential, such that final formulation is only expressed in the space of rates of internal variables. With the assumption for the free energy and the joint dissipation potential at hand, the derivation of evolution equations is straightforward. The application of the model is illustrated by selected numerical examples studying the material response for different load cases and sample geometries. The paper provides a comparison with the experimental results as well. © 2021 Elsevier Ltd
    view abstractdoi: 10.1016/j.ijplas.2021.103021
  • 2021 • 680 Cross-section-phenomena in rotary drums with sectional internals
    Priessen, J. and Kawka, T. and Behrens, M. and Schultz, H.J.
    Powder Technology 381 229-244 (2021)
    The effect of sectional internals on the solid bed cross section in rotary drums is investigated with a novel, fully optical accessible rotary drum apparatus for different internal configurations. The impact on mixing behavior is analyzed for different section numbers and filling degrees as well as material configurations. The mixing kinetics is affected positively by the sections, particularly for lower rotational speeds and filling degrees. The goodness of mixing in segregating particulate systems can be improved by sectional internals. Additionally to mixing effects, the impact of sectional internals on phase interfaces of the cross section is analyzed. A mathematical model description of the solid bed cross section is created and validated with the experimental data. The gas/solid interface is increasing logarithmically compared to the bare drum. The solid/inner wall interface is increasing linearly with the number of sections and the solid/outer wall interface is not affected significantly by sectional internals. © 2020 Elsevier B.V.
    view abstractdoi: 10.1016/j.powtec.2020.11.048
  • 2021 • 679 Crumpled few-layer graphene: Connection between morphology and optical properties
    Musikhin, S. and Talebi-Moghaddam, S. and Corbin, J.C. and Smallwood, G.J. and Schulz, C. and Daun, K.J.
    Carbon 182 677-690 (2021)
    Comprehensive characterization of crumpled graphene materials is required to understand their morphologically dependent properties. This study connects the optical properties of crumpled few-layer graphene (FLG) aerosols and colloidal suspensions with particle morphology. The mass absorption cross-section (MAC) of crumpled FLG was measured in the aerosol phase and it is shown that such aerosols absorb visible light more efficiently than soot aerosols. The UV–Vis spectra of FLG suspensions in ethanol were correlated with the mean nanoparticle layer number and the lateral size. The measured optical properties were also simulated using discrete dipole approximation (DDA) applied to volume-reconstructed particles with refractive indices of graphene and graphite from literature. The measurements were more closely reproduced using the refractive index of graphite pellets rather than flat graphene on a substrate. Moreover, we show that a simpler Rayleigh–Debye–Gans (RDG) model can predict the wavelength dependence of the crumpled FLG absorption cross-section. © 2021
    view abstractdoi: 10.1016/j.carbon.2021.06.052
  • 2021 • 678 Crystallographic Orientation Analysis of Nanocrystalline Tungsten Thin Film Using TEM Precession Electron Diffraction and SEM Transmission Kikuchi Diffraction
    Jeong, J. and Jang, W.-S. and Kim, K.H. and Kostka, A. and Gu, G. and Kim, Y.-M. and Oh, S.H.
    Microscopy and Microanalysis 27 237-249 (2021)
    Two advanced, automated crystal orientation mapping techniques suited for nanocrystalline materials - precession electron diffraction (PED) in transmission electron microscopy (TEM) and on-axis transmission Kikuchi diffraction (TKD) in scanning electron microscopy (SEM) - are evaluated by comparing the orientation maps obtained from the identical location on a 30 nm-thick nanocrystalline tungsten (W) thin film. A side-by-side comparison of the orientation maps directly showed that the large-scale orientation features are almost identical. However, there are differences in the fine details, which arise from the fundamentally different nature of the spot pattern and Kikuchi line pattern in terms of the excitation volume and the angular resolution. While TEM-PED is more reliable to characterize grains oriented along low-index zone axes, the high angular resolution of SEM-TKD allows the detection of small misorientation between grains and thus yields better quantification and statistical analysis of grain orientation. Given that both TEM-PED and SEM-TKD orientation mapping techniques are complementary tools for nanocrystalline materials, one can be favorably selected depending on the requirements of the analysis, as they have competitive performance in terms of angular resolution and texture quantification. Copyright © The Author(s), 2021. Published by Cambridge University Press on behalf of the Microscopy Society of America.
    view abstractdoi: 10.1017/S1431927621000027
  • 2021 • 677 Current Trends in Metal–Organic and Covalent Organic Framework Membrane Materials
    Hosseini Monjezi, B. and Kutonova, K. and Tsotsalas, M. and Henke, S. and Knebel, A.
    Angewandte Chemie - International Edition (2021)
    Metal–organic frameworks (MOFs) and covalent organic frameworks (COFs) have been thoroughly investigated with regards to applications in gas separation membranes in the past years. More recently, new preparation methods for MOFs and COFs as particles and thin-film membranes, as well as for mixed-matrix membranes (MMMs) have been developed. We will highlight novel processes and highly functional materials: Zeolitic imidazolate frameworks (ZIFs) can be transformed into glasses and we will give an insight into their use for membranes. In addition, liquids with permanent porosity offer solution processability for the manufacture of extremely potent MMMs. Also, MOF materials influenced by external stimuli give new directions for the enhancement of performance by in situ techniques. Presently, COFs with their large pores are useful in quantum sieving applications, and by exploiting the stacking behavior also molecular sieving COF membranes are possible. Similarly, porous polymers can be constructed using MOF templates, which then find use in gas separation membranes. © 2020 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/anie.202015790
  • 2021 • 676 Cutting path-dependent machinability of SiCp/Al composite under multi-step ultra-precision diamond cutting
    LU, S. and ZHANG, J. and LI, Z. and ZHANG, J. and WANG, X. and HARTMAIER, A. and XU, J. and YAN, Y. and SUN, T.
    Chinese Journal of Aeronautics 34 241-252 (2021)
    Particle-tool interactions, which govern the synergetic deformation of SiC particle reinforced Al matrix composites under mechanical machining, strongly depend on the geometry of particle position residing on cutting path. In the present work, we investigate the influence of cutting path on the machinability of a SiCp/Al composite in multi-step ultra-precision diamond cutting by combining finite element simulations with experimental observations and characterization. Be consistent with experimentally characterized microstructures, the simulated SiCp/Al composite is considered to be composed of randomly distributed polygonally-shaped SiC particles with a volume fraction of 25vol%. A multi-step cutting strategy with depths of cut ranging from 2 to 10 μm is adopted to achieve an ultimate depth of cut of 10 μm. Intrinsic material parameters and extrinsic cutting conditions utilized in finite element simulations of SiCp/Al cutting are consistent with those used in corresponding experiments. Simulation results reveal different particle-tool interactions and failure modes of SiC particles, as well as their correlations with machining force evolution, residual stress distribution and machined surface topography. A detailed comparison between numerical simulation results and experimental data of multi-step diamond cutting of SiCp/Al composite reveals a substantial impact of the number of cutting steps on particle-tool interactions and machined surface quality. These findings provide guidelines for achieving high surface finish of SiCp/Al composites by ultra-precision diamond cutting. © 2020 Chinese Society of Aeronautics and Astronautics
    view abstractdoi: 10.1016/j.cja.2020.07.039
  • 2021 • 675 Cyclophane with eclipsed pyrene units enables construction of spin interfaces with chemical accuracy
    Metzelaars, M. and Schleicher, S. and Hattori, T. and Borca, B. and Matthes, F. and Sanz, S. and Bürgler, D.E. and Rawson, J. and Schneider, C.M. and Kögerler, P.
    Chemical Science 12 8430-8437 (2021)
    Advanced functionality in molecular electronics and spintronics is orchestrated by exact molecular arrangements at metal surfaces, but the strategies for constructing such arrangements remain limited. Here, we report the synthesis and surface hybridization of a cyclophane that comprises two pyrene groups fastened together by two ferrocene pillars. Crystallographic structure analysis revealed pyrene planes separated by ∼352 pm and stacked in an eclipsed geometry that approximates the rare configuration of AA-stacked bilayer graphene. We deposited this cyclophane onto surfaces of Cu(111) and Co(111) at submonolayer coverage and studied the resulting hybrid entities with scanning tunnelling microscopy (STM). We found distinct characteristics of this cyclophane on each metal surface: on non-magnetic Cu(111), physisorption occurred and the two pyrene groups remained electronically coupled to each other; on ferromagnetic Co(111) nanoislands, chemisorption occurred and the two pyrene groups became electronically decoupled. Spin-polarized STM measurements revealed that the ferrocene groups had spin polarization opposite to that of the surrounding Co metal, while the pyrene stack had no spin polarization. Comparisons to the non-stacked analogue comprising only one pyrene group bolster our interpretation of the cyclophane's STM features. The design strategy presented herein can be extended to realize versatile, three-dimensional platforms in single-molecule electronics and spintronics. © The Royal Society of Chemistry 2021.
    view abstractdoi: 10.1039/d1sc01036k
  • 2021 • 674 Damage mechanisms in cavitation erosion of nitrogen-containing austenitic steels in 3.5% NaCl solution
    Paolantonio, M. and Hanke, S.
    Wear 464-465 (2021)
    Interruptions of the passive layer of stainless steels by cavitation erosion expose the bare metal surface to the environment and can lead to cavitation-erosion-corrosion damage and synergistic effects. However, the probability for pitting corrosion is decreased during cavitation exposure of stainless steels in chloride solutions because mechanical passive film removal shifts corrosion potentials to lower cathodic values. In this study, the impact of 3.5 wt% NaCl in water on mass loss and damage features of two austenitic stainless N-containing steels is investigated to amend the understanding of cavitation erosion of passivating steels. Ultrasonic cavitation tests were carried out on steels 316LVM and CNMo0.95 in distilled water and 3.5% NaCl solution. Exposed surfaces were characterized qualitatively by light- and electron-microscopy and quantitatively by confocal microscopy. Damage mechanisms vary between the two steels but not with NaCl content in the solution. 316LVM also displayed the same mass loss in both solutions. CNMo0.95 possesses twice the strength as 316LVM, resulting in lower intensities of ductile damage mechanisms and slower damage progression. Mass loss of CNMo0.95 was lower in 3.5% NaCl solution compared to distilled water, which was primarily assigned to the effect of the salt content in the water on cavitation bubble formation. © 2020 Elsevier B.V.
    view abstractdoi: 10.1016/j.wear.2020.203526
  • 2021 • 673 Data compilation regarding the effects of grain size and temperature on the strength of the single-phase FCC CrFeNi medium-entropy alloy
    Schneider, M. and Laplanche, G.
    Data in Brief 34 (2021)
    In the present article, we present a data compilation reflecting recrystallized microstructures and the corresponding mechanical properties of an equiatomic, single-phase face-centered cubic (FCC) CrFeNi medium-entropy alloy (MEA). For the analysis, interpretation, and discussion of the data, the reader can refer to the original research article entitled “Effects of temperature on mechanical properties and deformation mechanisms of the equiatomic CrFeNi medium-entropy alloy”, see Ref. (Schneider and Laplanche, Acta Mater. 204, 2020). The data related to recrystallized microstructures comprise raw backscatter electron (BSE) micrographs (tif-files) obtained using a scanning electron microscope (SEM) for six grain sizes in the range [10–160 µm], optical micrographs of the alloy with the largest grain size (d = 327 µm), pdf-reports and tables presenting the corresponding grain-size distributions (d, accounting for grain boundaries only) and crystallite-size distributions (c, which accounts for both grain and annealing twin boundaries), the annealing twin thicknesses (t), the average number of annealing twin boundaries per grain (n), and the average Taylor factor (M) of each recrystallized microstructure. These are benchmark datasets that may serve to develop new algorithms for the automated evaluation of microstructural parameters. Such algorithms would help to speed up the analyses of microstructures and improve their reliability. Furthermore, several groups pointed out that in addition to the mean grain size, other microstructural parameters such as the grain size distribution (Raeisinia et al., Model. Simul. Mater. Sc. 16, 2008) and the average number of twins per grain (Schneider et al., Int. J. Plasticity, 124, 2020) may affect some material properties (e.g. Hall-Petch strengthening). Therefore, an effort was made here to determine and report almost all the microstructural parameters describing recrystallized microstructures of FCC alloys. The mechanical-properties data are provided as excel-sheets in which the raw stress-strain curves can be found. Compression tests for alloys with different grain sizes were performed at room temperature. Additional compression tests and tensile tests for the grain size d = 160 µm were performed at temperatures between 77 K and 873 K. Characteristic mechanical properties, such as yield stresses at 0.2% plastic strain (σ0.2%) and Hall-Petch parameters (σ0 and ky) are given for all temperatures in the tables below. Moreover, the Hall-Petch parameters as well as the mechanical data reported in the present study could be used for data mining and implemented in programs used for alloy design. © 2021 The Author(s)
    view abstractdoi: 10.1016/j.dib.2020.106712
  • 2021 • 672 Decay of quantum sensitivity due to three-body loss in Bose-Einstein condensates
    Rätzel, D. and Schützhold, R.
    Physical Review A 103 (2021)
    In view of the coherent properties of a large number of atoms, Bose-Einstein condensates (BECs) have a high potential for sensing applications. Several proposals have been put forward to use collective excitations such as phonons in BECs for quantum-enhanced sensing in quantum metrology. However, the associated highly nonclassical states tend to be very vulnerable to decoherence. In this article, we investigate the effect of decoherence due to the omnipresent process of three-body loss in BECs. We find strong restrictions for a wide range of parameters, and we discuss possibilities to limit these restrictions. © 2021 American Physical Society.
    view abstractdoi: 10.1103/PhysRevA.103.063321
  • 2021 • 671 Dedicated setup to isolate plasma catalysis mechanisms
    Stewig, C. and Urbanietz, T. and Chauvet, L. and Böke, M. and Von Keudell, A.
    Journal of Physics D: Applied Physics 54 (2021)
    Plasma catalysis, the combination of plasma and catalysis, is used to achieve efficient molecule conversion, supporting the flexibility of operating parameters and feed gases. By combining plasmas with conventional thermal catalysis, the temperature windows may be changed and the process may be made insensitive to catalyst poisoning. However, understanding plasma catalysis mechanisms is extremely difficult, due to the strong coupling between plasma, gas-phase chemistry and surface. A multitude of reaction pathways may be enhanced or reduced by the presence of a plasma that provides excited species as reaction partners. We developed a robust setup to analyse those processes, based on a parallel-plate atmospheric-pressure plasma jet that allows a plug flow design. The plasma chemistry is analysed by Fourier transform infrared absorption spectroscopy and mass spectrometry. The electrodes in contact with the plasma are temperature controlled and can easily be replaced to apply a catalyst on top of them. The basic characteristics of the setup are discussed and three examples for its application are given: (a) the analysis of methane oxidation using the plug flow scheme; (b) the plasma catalytic conversion of CO2, and (c) the plasma catalytic conversion of methane in methane–oxygen mixtures. © 2021 IOP Publishing Ltd.
    view abstractdoi: 10.1088/1361-6463/abd65b
  • 2021 • 670 Deep learning for visualization and novelty detection in large X-ray diffraction datasets
    Banko, L. and Maffettone, P.M. and Naujoks, D. and Olds, D. and Ludwig, Al.
    npj Computational Materials 7 (2021)
    We apply variational autoencoders (VAE) to X-ray diffraction (XRD) data analysis on both simulated and experimental thin-film data. We show that crystal structure representations learned by a VAE reveal latent information, such as the structural similarity of textured diffraction patterns. While other artificial intelligence (AI) agents are effective at classifying XRD data into known phases, a similarly conditioned VAE is uniquely effective at knowing what it doesn’t know: it can rapidly identify data outside the distribution it was trained on, such as novel phases and mixtures. These capabilities demonstrate that a VAE is a valuable AI agent for aiding materials discovery and understanding XRD measurements both ‘on-the-fly’ and during post hoc analysis. © 2021, The Author(s).
    view abstractdoi: 10.1038/s41524-021-00575-9
  • 2021 • 669 Defect phases–thermodynamics and impact on material properties
    Korte-Kerzel, S. and Hickel, T. and Huber, L. and Raabe, D. and Sandlöbes-Haut, S. and Todorova, M. and Neugebauer, J.
    International Materials Reviews (2021)
    Two approaches in materials physics have proven immensely successful in alloy design: First, thermodynamic and kinetic descriptions for tailoring and processing alloys to achieve a desired microstructure. Second, crystal defect manipulation to control strength, formability and corrosion resistance. However, to date, the two concepts remain essentially decoupled. A bridge is needed between these powerful approaches to achieve a single conceptual framework. Considering defects and their thermodynamic state holistically as ‘defect phases’, provides a future materials design strategy by jointly treating the thermodynamic stability of both, the local crystalline structure and the distribution of elements at defects. Here, we suggest that these concepts are naturally linked by defect phase diagrams describing the coexistence and transitions of defect phases. Construction of these defect phase diagrams will require new quantitative descriptors. We believe such a framework will enable a paradigm shift in the description and design of future engineering materials. © 2021 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group.
    view abstractdoi: 10.1080/09506608.2021.1930734
  • 2021 • 668 Defect tolerant device geometries for lead-halide perovskites
    Das, B. and Liu, Z. and Aguilera, I. and Rau, U. and Kirchartz, T.
    Materials Advances 2 3655-3670 (2021)
    The term "defect tolerance"is widely used in the literature to describe materials such as lead-halides perovskites, where solution-processed polycrystalline thin films exhibit long non-radiative lifetimes of microseconds or longer. Studies on defect tolerance of materials mostly look at the properties of the host material and/or the chemical nature of defects that affect their capture coefficients. However, the recombination activity of a defect is not only a function of its capture coefficients but also depends on the electrostatics and the design of the layer stack of a photovoltaic device. Here we study the influence of device geometry on defect tolerance by combining calculations of capture coefficients with device simulations. We derive generic device design principles which can inhibit recombination inside a photovoltaic device for a given set of capture coefficients based on the idea of slowing down the slower of the two processes (electron and hole capture) even further by modifying electron and hole injection into the absorber layer. We use the material parameters and typical p-i-n device geometry representing methylammonium lead halide perovskites solar cells to illustrate the application of our generic design principles to improve specific devices. © 2021 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/d0ma00902d
  • 2021 • 667 Deformation and damage assessments of two dp1000 steels using a micromechanical modelling method
    Habibi, N. and Vajragupta, N. and Münstermann, S.
    Crystals 11 (2021)
    Damage characterization and micromechanical modelling in dual-phase (DP) steels have recently drawn attention, since any changes in the alloying elements or process route strongly influence the microstructural features, deformation behavior of the phases, and damage to the micro-mechanisms, and subsequently the particular mechanical properties of the material. This approach can be used to stablish microstructure–properties relationships. For instance, the effects of local damage from shear cutting on edge crack sensitivity in the following deformation process can be studied. This work evaluated the deformation and damage behaviors of two DP1000 steels using a microstructure-based approach to estimate the edge cracking resistance. Phase fraction, grain size, phase distribution, and texture were analyzed using electron backscatter diffraction and secondary electron detectors of a scanning electron microscope and employed in 3D representative volume elements. The deformation behavior of the ferrite phase was defined using a crystal plasticity model, which was calibrated through nanoindentation tests. Various loading conditions, including uniaxial tension, equi-biaxial tension, plane strain tension, and shearing, along with the maximum shear stress criterion were applied to investigate the damage initiation and describe the edge cracking sensitivity of the studied steels. The results revealed that a homogenous microstructure leads to homogenous stress–strain partitioning, delayed damage initiation, and high edge cracking resistance. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/cryst11070805
  • 2021 • 666 Deformation measurement of a monopile subject to vortex- induced vibration using digital image correlation
    Tödter, S. and el Sheshtawy, H. and Neugebauer, J. and el Moctar, O. and Schellin, T.E.
    Ocean Engineering 221 (2021)
    Monopile towers used for offshore wind turbines are sensitive to Vortex-Induced Vibration (VIV). Here, their structural response to VIV was experimentally investigated with models of a partially and a fully immerged offshore monopile. The partially and fully immersed model cylinders had aspect ratios of 18.75 and 28.13, respectively. They were subject to reduced velocities of up to 9.78 and 5.45, respectively, corresponding to Reynolds numbers of up to 77120 and 63680, respectively. Normalised transverse motion amplitudes of up to 1.19 were measured. “Strouhal-like” numbers down to 0.13 were obtained, and they decreased with increasing flow velocity and corresponding motion amplitude. The 3D Digital Image Correlation (DIC) processing method was used to measure response without influencing model properties and the flow field. To assess the suitability of DIC for VIV investigations, results obtained from the conventional technique using triaxial accelerometers were compared. The influence of different processing methods, pattern designs and their assemblies, the repeatability of the model tests, and the influence of ventilation were investigated also. Additionally, forces and torques were measured directly. Results from these three measurement techniques were compared and discussed. © 2020
    view abstractdoi: 10.1016/j.oceaneng.2020.108548
  • 2021 • 665 Degradation behavior of the MgO/HA surface ceramic nano-composites in the simulated body fluid and its use as a potential bone implant
    Khalili, V. and Frenzel, J. and Eggeler, G.
    Materials Chemistry and Physics 258 (2021)
    In this work, we studied the effects of hot isostatic pressing and surface anodizing on the behavior of an in-situ surface modified magnesium matrix nano-composite with different wt.% of hydroxyapatite by stir-centrifugal casting. The hot isostatic pressing and anodizing were conducted to reduce the defects and to replace the surface of Mg/HA with a ceramic matrix nano-composite layer of MgO/HA, respectively. The composition of the conversion layer of anodizing was evaluated using energy dispersive spectroscopy and X-ray diffraction. The electrochemical tests were conducted in the simulated body fluid. The results show that the dominant deposition is vertical Mg(OH)2 nano-rods on the hot isostatic pressed-anodized surface during immersion in the simulated body fluid. According to the electrochemical results, a homogeneous distribution of 1.8 wt% nano-hydroxyapatite in the magnesium oxide matrix with a well-arranged nanostructure on the surface, after hot isostatic pressing and anodizing, reduces the H2 release and corrosion rate. Also, the mentioned specimen demonstrates the lowest thermodynamic tendency for corrosion (−1.345 V) and the corrosion rate of 3.8388 mm × year−1 with the highest protection efficiency of 42.26% compared to the as-cast pure magnesium. Therefore, it can be considered as a promising material in designing biomedical bone implants. © 2020 Elsevier B.V.
    view abstractdoi: 10.1016/j.matchemphys.2020.123965
  • 2021 • 664 Delivery of toll-like receptor 3 ligand poly(I:C) to the liver by calcium phosphate nanoparticles conjugated with an F4/80 antibody exerts an anti-hepatitis B virus effect in a mouse model
    Du, Y. and Yang, X. and Li, J. and Sokolova, V. and Zou, S. and Han, M. and Yan, H. and Wey, K. and Lu, M. and Dittmer, U. and Yang, D. and Epple, M. and Wu, J.
    Acta Biomaterialia (2021)
    Hepatitis B virus (HBV) is a global health issue, but currently available anti-HBV drugs have limited success. Previously, introduction of the Toll-like receptor (TLR)-3 ligand poly(I:C) to the liver via hydrodynamic injection (HI) was shown to effectively suppress HBV replication in a chronic HBV replication mouse model. However, this method cannot be applied in human beings. To improve the liver targeting of poly(I:C) via intravenous injection, calcium phosphate nanoparticles (CPNs) carrying poly(I:C) with or without antibodies were constructed, and their anti-HBV effects were investigated. We found that significantly more anti-F4/80-conjugated and IgG2α-conjugated nanoparticles were taken up in liver cells both in vivo and in vitro. In addition, these nanoparticles produced pronounced immunostimulatory effects in vitro in primary liver cells. Importantly, treatment with nanoparticles carrying poly(I:C) increased the production of intrahepatic cytokines and chemokines and enhanced T cell responses, significantly reducing HBsAg, HBeAg and HBV DNA levels in the mice. Compared to nonconjugated and isotype-antibody-conjugated nanoparticles, the anti-F4/80-conjugated nanoparticles demonstrated the strongest anti-HBV effects. In summary, nanoparticles carrying poly(I:C) conjugated with an F4/80 antibody promoted liver targeting, and they may represent a suitable alternative to HI for future anti-HBV treatment. Statement of Significance: HBV chronically infects approximately 250 million individuals worldwide but current anti-HBV drugs have limited success. Introduction of toll-like receptor 3 ligand poly(I:C) into liver by hydrodynamic injection has been proven to promote HBV clearance in mouse model. However, this technique is not clinically suitable for human patients. We have constructed calcium phosphate nanoparticles carrying poly(I:C) with specific antibody targeting liver nonparenchymal cells. The uptake into relevant liver cells and the anti-HBV effects were studied. After intravenous injection into mice, the uptake rate of anti-F4/80-conjugated nanoparticels was enhanced in liver, and these nanoparticles exert effective anti-HBV effects in vivo. This may provide important insight into future HBV immunotherapy based on nanoparticle-mediated drug delivery. © 2021 Acta Materialia Inc.
    view abstractdoi: 10.1016/j.actbio.2021.01.045
  • 2021 • 663 Density-based grain boundary phase diagrams: Application to Fe-Mn-Cr, Fe-Mn-Ni, Fe-Mn-Co, Fe-Cr-Ni and Fe-Cr-Co alloy systems
    Wang, L. and Darvishi Kamachali, R.
    Acta Materialia 207 (2021)
    Phase diagrams are the roadmaps for designing bulk phases. Similar to bulk, grain boundaries can possess various phases, but their phase diagrams remain largely unknown. Using a recently introduced density-based model, here we devise a strategy for computing multi-component grain boundary phase diagrams based on available bulk (CALPHAD) thermodynamic data. Fe-Mn-Cr, Fe-Mn-Ni, Fe-Mn-Co, Fe-Cr-Ni and Fe-Cr-Co alloy systems, as important ternary bases for several trending steels and high-entropy alloys, are studied. We found that despite its solute segregation enrichment, a grain boundary can have lower solubility limit than its corresponding bulk, promoting an interfacial chemical decomposition upon solute segregation. This is revealed here for the Fe-Mn-base alloy systems. The origins of this counter-intuitive feature are traced back to two effects, i.e., the magnetic ordering effect and the low cohesive energy of Mn solute element. Different aspects of interfacial phase stability and GB co-segregation in ternary alloys are investigated as well. We show that the concentration gradient energy contributions reduce segregation level but increase grain boundary solubility limit, stabilizing the GB against a chemical decomposition. Density-based grain boundary phase diagrams offer guidelines for systematic investigation of interfacial phase changes with applications to microstructure defects engineering. © 2021 Acta Materialia Inc.
    view abstractdoi: 10.1016/j.actamat.2021.116668
  • 2021 • 662 Dependence of the magnetoelectric coupling on elastic and dielectric properties of two-phase multiferroic composites
    Naveed-Ul-Haq, M. and Shvartsman, V.V. and Samulionis, V. and Ivanov, M. and Banys, J. and Lupascu, D.C.
    Journal of Materials Science 56 14978-14988 (2021)
    We report on temperature-dependent studies of ultrasonic and dielectric properties of (x)0.5(Ba0.7Ca0.3)Ti03–0.5Ba(Ti0.8Zr0.2)O3(BCZT)/(1 − x)NiFe2O4 (BCZT/NFO) composite multiferroics and their relationship to the magnetoelectric (ME) effect in these materials. The most decisive factor in the maximization of the ME effect is the strong elastic softening of the BCZT phase at the phase transition between its ferroelectric phases with orthorhombic and tetragonal symmetry. The proximity of this phase transition to room temperature makes the system promising for practical applications of the ME effect. The magnetostrictive phase does not play any direct role in the determination of the ME temperature dependence because of its weakly temperature-dependent mechanical properties. © 2021, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.
    view abstractdoi: 10.1007/s10853-021-06271-9
  • 2021 • 661 Depth-sensing ductile and brittle deformation in 3C-SiC under Berkovich nanoindentation
    Zhao, L. and Zhang, J. and Pfetzing, J. and Alam, M. and Hartmaier, A.
    Materials and Design 197 (2021)
    The interplay between ductile and brittle deformation modes in hard brittle materials exhibits a strong size effect. In the present work, indentation depth-dependent deformation mechanisms of single-crystal 3C-SiC under Berkovich nanoindentation are elucidated by finite element simulations and corresponding experiments. A novel finite element framework, that combines a crystal plasticity constitutive model for describing dislocation slip-based ductile deformation and a cohesive zone model for capturing crack initiation and propagation-induced brittle fracture, is established. The utilized parameters in the crystal plasticity model of 3C-SiC are calibrated according to the load-displacement curves obtained from corresponding Berkovich nanoindentation experiments. Subsequent finite element simulations and experiments of nanoindentation jointly reveal co-existing microscopic plastic deformation and brittle fracture of 3C-SiC at different indentation depths, which significantly affect the observed macroscopic mechanical response and surface pile-up topography. In particular, the predicted morphology of surface cracks at an indentation depth of 500 nm agrees well with experimental observation, and the correlation of crack initiation and propagation with surface pile-up topography is theoretically analyzed. © 2020 The Authors
    view abstractdoi: 10.1016/j.matdes.2020.109223
  • 2021 • 660 Design and Characterization of a Screw Extrusion Hot-End for Fused Deposition Modeling
    Feuerbach, T. and Thommes, M.
    Molecules (Basel, Switzerland) 26 (2021)
    The filament is the most widespread feedstock material form used for fused deposition modeling printers. Filaments must be manufactured with tight dimensional tolerances, both to be processable in the hot-end and to obtain printed objects of high quality. The ability to successfully feed the filament into the printer is also related to the mechanical properties of the filament, which are often insufficient for pharmaceutically relevant excipients. In the scope of this work, an 8 mm single screw hot-end was designed and characterized, which allows direct printing of materials from their powder form and does not require an intermediate filament. The capability of the hot-end to increase the range of applicable excipients to fused deposition modeling was demonstrated by processing and printing several excipients that are not suitable for fused deposition modeling in their filament forms, such as ethylene vinyl acetate and poly(1-vinylpyrrolidone-co-vinyl acetate). The conveying characteristic of the screw was investigated experimentally with all materials and was in agreement with an established model from literature. The complete design information, such as the screw geometry and the hot-end dimensions, is provided in this work.
    view abstractdoi: 10.3390/molecules26030590
  • 2021 • 659 Design and perspective of amorphous metal nanoparticles from laser synthesis and processing
    Liang, S.-X. and Zhang, L.-C. and Reichenberger, S. and Barcikowski, S.
    Physical Chemistry Chemical Physics 23 11121-11154 (2021)
    Amorphous metal nanoparticles (A-NPs) have aroused great interest in their structural disordering nature and combined downsizing strategies (e.g. nanoscaling), both of which are beneficial for highly strengthened properties compared to their crystalline counterparts. Conventional synthesis strategies easily induce product contamination and/or size limitations, which largely narrow their applications. In recent years, laser ablation in liquid (LAL) and laser fragmentation in liquid (LFL) as "green"and scalable colloid synthesis methodologies have attracted extensive enthusiasm in the production of ultrapure crystalline NPs, while they also show promising potential for the production of A-NPs. Yet, the amorphization in such methods still lacks sufficient rules to follow regarding the formation mechanism and criteria. To that end, this article reviews amorphous metal oxide and carbide NPs from LAL and LFL in terms of NP types, liquid selection, target elements, laser parameters, and possible formation mechanism, all of which play a significant role in the competitive relationship between amorphization and crystallization. Furthermore, we provide the prospect of laser-generated metallic glass nanoparticles (MG-NPs) from MG targets. The current and potential applications of A-NPs are also discussed, categorized by the attractive application fields e.g. in catalysis and magnetism. The present work aims to give possible selection rules and perspective on the design of colloidal A-NPs as well as the synthesis criteria of MG-NPs from laser-based strategies. This journal is © 2021 the Owner Societies.
    view abstractdoi: 10.1039/d1cp00701g
  • 2021 • 658 Design of Cu- and Ag-containing amorphous carbon multilayers with improved tribo-mechanical properties
    Tillmann, W. and Lopes Dias, N.F. and Stangier, D. and Matveev, S. and Arne Thomann, C. and Debus, J.
    Materials Letters 284 (2021)
    The modification of amorphous carbon (a–C) films by adding either Cu or Ag is a common approach to tailor the film properties. These films become less hard, while they demonstrate higher friction and lower wear resistance than a–C. To enhance tribologically relevant features, multilayers of alternating a–C and a–C:Cu or a–C:Ag layers are synthetized by magnetron sputtering. The a–C/a–C:Cu and a–C/a–C:Ag multilayers possess a bilayer period of ~200 nm, a layer ratio of 1, and a bilayer number of 5. These structures are characterized by higher hardness and lower friction and wear against 100Cr6 counterparts as compared to monolayered a–C:Cu and a–C:Ag. © 2020 Elsevier B.V.
    view abstractdoi: 10.1016/j.matlet.2020.128905
  • 2021 • 657 Design of refractory compositionally complex alloys with optimal mechanical properties
    Ferrari, A. and Lysogorskiy, Y. and Drautz, R.
    Physical Review Materials 5 (2021)
    We use an analytical model to propose candidate compositionally complex alloys of the Mo-Nb-Ta-W family with optimal yield stress. We then introduce a computationally tractable method based on first-principles calculations to model phase equilibria in complex alloys at arbitrary concentrations. We utilize this method to predict the phase diagram at the optimized compositions and observe a tendency towards ordering for some of the proposed alloys. By combining yield stress data and thermodynamic equilibria, we suggest two alloy compositions with optimal mechanical properties and a strong solid solution forming ability for further experimental validation. © 2021 American Physical Society.
    view abstractdoi: 10.1103/PhysRevMaterials.5.063606
  • 2021 • 656 Design Strategies for Electrocatalysts from an Electrochemist's Perspective
    Linnemann, J. and Kanokkanchana, K. and Tschulik, K.
    ACS Catalysis 11 5318-5346 (2021)
    The aim to produce highly active, selective, and long-lived electrocatalysts by design drives major research efforts toward gaining fundamental understanding of the relationship between material properties and their catalytic performance. Surface characterization tools enable to assess atomic scale information on the complexity of electrocatalyst materials. Advancing electrochemical methodologies to adequately characterize such systems was less of a research focus point. In this Review, we shed light on the ability to gain fundamental insights into electrocatalysis from a complementary perspective and establish corresponding design strategies. These may rely on adopting the perceptions and models of other subareas of electrochemistry, such as corrosion, battery research, or electrodeposition. Concepts on how to account for and improve mass transport, manage gas bubble release, or exploit magnetic fields are highlighted in this respect. Particular attention is paid to deriving design strategies for nanoelectrocatalysts, which is often impeded, as structural and physical material properties are buried in electrochemical data of whole electrodes or even devices. Thus, a second major approach focuses on overcoming this difference in the considered level of complexity by methods of single-entity electrochemistry. The gained understanding of intrinsic catalyst performance may allow to rationally advance design concepts with increased complexity, such as three-dimensional electrode architectures. Many materials undergo structural changes upon formation of the working catalyst. Accordingly, developing "precatalysts"with low hindrance of the electrochemical transformation to the active catalyst is suggested as a final design strategy. ©
    view abstractdoi: 10.1021/acscatal.0c04118
  • 2021 • 655 Detailed analysis of early-stage NOxformation in turbulent pulverized coal combustion with fuel-bound nitrogen
    Wen, X. and Shamooni, A. and Stein, O.T. and Cai, L. and Kronenburg, A. and Pitsch, H. and Kempf, A.M. and Hasse, C.
    Proceedings of the Combustion Institute 38 4111-4119 (2021)
    A carrier-phase direct numerical simulation (CP-DNS) of pulverized coal combustion in a mixing layer is performed, considering three NOx formation mechanisms (fuel-NOx, thermal-NOx and prompt-NOx). Detailed analyses, including reaction path analysis, chemical timescale analysis, and a priori and budget analyses are conducted to investigate the NOx production mechanisms and the performance of the flamelet model. Considering the high computational cost of CP-DNS, this work focuses on the early phase governed by devolatilization, where char reactions are less important. The reaction path analyses show that the principal thermal-NO reaction contributes to the net consumption of NO in fuel-bound nitrogen pulverized coal flames, which is essentially different from fuel-nitrogen-free flames. The chemical timescale analyses show that the production rates of NOx species are faster than those of major species, which confirms the suitability of the flamelet tables. The a priori analyses show that the gas temperature and major/intermediate species can be predicted well by the flamelet model, while the NOx species show significant discrepancies in certain regions. Finally, the budget analyses explain why the flamelet model performs differently for major/intermediate and NOx species. © 2020 The Combustion Institute.
    view abstractdoi: 10.1016/j.proci.2020.06.317
  • 2021 • 654 Detailed simulations of the DLR auto-igniting pulsed jet experiment
    Inanc, E. and Lipkowicz, J.T. and Kempf, A.M.
    Fuel 284 (2021)
    Numerical simulations of an auto-igniting pulsed jet in a vitiated co-flow experiment by DLR (German Aerospace Center) are conducted by highly-resolved large-eddy simulations using direct chemistry with an augmented reduced mechanism. The experiments consist of two operation modes: continuous injection used for code-verification and pulsed injection utilized for fundamental investigation of auto-ignition dynamics. Initially, reference one-dimensional self-igniting counter-flow flames are investigated. Then, a grid convergence study has been performed. It is shown that even a coarser grid would be sufficient to describe the ignition chemistry since the ignition kernel appears at low velocities and fuel-lean conditions in zones of low scalar dissipation rates. For the statistically steady jet, numerical predictions are in a very good agreement with the experiments, giving confidence in the applied models. For the pulsed jet, all of the predicted ignition delay times and locations are in the range of the experimental observations. Time-resolved statistics reveal that thermochemical properties of the gas in a pulsed jet achieve states that are impossible to reproduce in laminar conditions. For further analysis, hydroxyl and formaldehyde are chosen as a marker for the established flame and for the ignition, respectively. In laminar conditions, these two species are perfectly correlated. However, the unsteady dynamics of the pulsed jet invalidates the correlation between the minor species chemistry prior to ignition. This yields the discrepancy in the auto-ignition delay time and the location of the ignition kernel between different pulses, as the thermochemical state needed for the ignition occurs in a random manner. © 2020 Elsevier Ltd
    view abstractdoi: 10.1016/j.fuel.2020.118947
  • 2021 • 653 Detecting relevant differences in the covariance operators of functional time series: a sup-norm approach
    Dette, H. and Kokot, K.
    Annals of the Institute of Statistical Mathematics (2021)
    In this paper we propose statistical inference tools for the covariance operators of functional time series in the two sample and change point problem. In contrast to most of the literature, the focus of our approach is not testing the null hypothesis of exact equality of the covariance operators. Instead, we propose to formulate the null hypotheses in the form that “the distance between the operators is small”, where we measure deviations by the sup-norm. We provide powerful bootstrap tests for these type of hypotheses, investigate their asymptotic properties and study their finite sample properties by means of a simulation study. © 2021, The Institute of Statistical Mathematics, Tokyo.
    view abstractdoi: 10.1007/s10463-021-00795-2
  • 2021 • 652 Detecting structural breaks in eigensystems of functional time series
    Dette, H. and Kutta, T.
    Electronic Journal of Statistics 15 944-983 (2021)
    Detecting structural changes in functional data is a prominent topic in statistical literature. However not all trends in the data are important in applications, but only those of large enough influence. In this paper we address the problem of identifying relevant changes in the eigenfunctions and eigenvalues of covariance kernels of L2[0, 1]-valued time series. By selfnormalization techniques we derive pivotal, asymptotically consistent tests for relevant changes in these characteristics of the second order structure and investigate their finite sample properties in a simulation study. The applicability of our approach is demonstrated analyzing German annual temperature data. © 2021, Institute of Mathematical Statistics. All rights reserved.
    view abstractdoi: 10.1214/20-EJS1796
  • 2021 • 651 Detection of fatigue induced fracture of prestressing steel by means of monitoring of experiment and structure [Detektieren ermüdungsbedingter spannstahlbrüche mittels rissmonitoring im versuch und am bauwerk]
    Heinrich, J. and Maurer, R. and Leckey, K. and Müller, C.H. and Ickstadt, K.
    Bauingenieur 96 92-101 (2021)
    On a prestressed concrete bridge in the region of the point of zero moment due to permanent load systematic crack formations with crack widths up to 0.5 mm were de-tected. These cracks were a consequence of the restraint mo-ments due to temperature (∆TM), which have not been considered at that time. As a result of the cracks, the tendons were endangered by fatigue. Even with more refined methods, it was not possible to verify sufficient fatigue resistance. In addi-tion, the overall structural condition was in a poor state. There-fore, the road authority decided to build a new bridge as repla-cement as soon as possible. Up to that point the structural safety of the bridge had to be ensured. For this purpose, conti-nuous crack monitoring was carried out for the critical areas. Fatigue tests on prestressed concrete components at TU Dortmund University formed the basis for its evaluation. These tests succeeded in reliably identifying individual wire breaks during the ongoing test and in developing a prognosis method for the remaining service life. The experiences and difficulties of transferring these methods to a real structure are reported. © 2021, VDI Fachmedien GmBbH & Co. All rights reserved.
    view abstractdoi: 10.37544/0005-6650-2021-03-60
  • 2021 • 650 Determination of inherent dissolution performance of drug substances
    Sleziona, D. and Mattusch, A. and Schaldach, G. and Ely, D.R. and Sadowski, G. and Thommes, M.
    Pharmaceutics 13 1-12 (2021)
    The dissolution behavior of novel active pharmaceutical ingredients (API) is a crucial parameter in drug formulation since it frequently affects the drug release. Generally, a distinction is made between surface-reaction-and diffusion-controlled drug release. Therefore, dissolution studies such as the intrinsic dissolution test defined in the pharmacopeia have been performed for many years. In order to overcome the disadvantages of the common intrinsic dissolution test, a new experimental setup was developed within this study. Specifically, a flow channel was designed and tested for measuring the mass transfer from a flat, solid surface dissolving into a fluid flowing over the surface with well-defined flow conditions. A mathematical model was developed that distinguishes between surface-reaction-and diffusion-limited drug release based on experimental data. Three different drugs—benzocaine, theophylline and griseofulvin—were used to investigate the mass flux during dissolution due to surface reaction, diffusion and convection kinetics. This new technique shows potential to be a valuable tool for the identification of formulation strategies. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/pharmaceutics13020146
  • 2021 • 649 Determination of residual dimethyl sulfoxide by high-resolution continuum source graphite furnace molecular absorption spectrometry
    Huang, M.D. and Esser, N. and Hinrichs, K. and Tan, Q. and Rappich, J. and Nickel, N.H. and Dittrich, T.
    Spectrochimica Acta - Part B Atomic Spectroscopy 177 (2021)
    High-resolution continuum source molecular absorption spectrometry (HR-CSMAS) has been extended to the determination of sulfur-containing organic molecule, on the example of dimethyl sulfoxide (DMSO) as a residual solvent in CH3NH3PbI3 perovskite thin films. For this purpose, DMSO molecules were converted into CS molecules by pyrolysis in a graphite furnace at low temperature and the sulfur content was determined by measuring molecular absorption of CS at 258.055 nm. An aqueous solution of DMSO was used for calibration. A characteristic mass of 17 ng was achieved for S after pyrolysis at 160 °C by using Pd as a chemical modifier. Furthermore, the content of DMSO was normalized to that of Pb whereas the content of Pb was determined by reducing the Pb in the perovskite to metallic Pb with Zn powder and measuring absorption of the weak Pb line at 261.418 nm by high-resolution continuum source atomic absorption spectrometry (HR-CSAAS). The Pb content remained constant whereas the S/Pb molar ratio decreased with increasing annealing time. Our results open new opportunities for the characterization of residual DMSO in wide classes of materials. © 2020 Elsevier B.V.
    view abstractdoi: 10.1016/j.sab.2020.106050
  • 2021 • 648 Determining Chemical Reaction Systems in Plasma-Assisted Conversion of Methane Using Genetic Algorithms
    Reiser, D. and von Keudell, A. and Urbanietz, T.
    Plasma Chemistry and Plasma Processing 41 793-813 (2021)
    Even for processes with only a few gas species involved the detailed description of plasma-assisted conversion processes in gas mixtures requires a large amount of processes to be taken into account and a large number of neutral and charged particles must be considered. In addition, setting up the corresponding reaction kinetics model needs the knowledge of the rate coefficients and their temperature dependence for all possible reactions between those species. Reduced reaction networks offer a simplified and pragmatic way to obtain an overall reaction kinetics model, already useful for the analysis of experimental data even if not all details of chemistry can be covered. In this paper we present a derivation of a data driven reduced model for plasma-assisted conversion of methane in an helium environment. By consideration of a small number of elementary reactions, a simple model is set up. Experimental data are analyzed by a genetic algorithm that provides best-fit approximations for the open parameters of the model. In a further step non-relevant parameters of the model are identified and a further model reduction is achieved. The data driven analysis of methane conversion serves as an illustrative example of the proposed method. The parameters and reaction channels found are compared with known results from the literature. The method is described in detail. The main goal of this work is to present the potential of this data driven method for a simplified and pragmatic modeling in the increasingly important field of plasma-assisted catalytic processes. © 2021, The Author(s).
    view abstractdoi: 10.1007/s11090-021-10159-6
  • 2021 • 647 Determining interface fracture toughness in multi layered environmental barrier coatings with laser textured silicon bond coat
    Wolf, M. and Kakisawa, H. and Süß, F. and Mack, D.E. and Vaßen, R.
    Coatings 11 1-14 (2021)
    In the high temperature combustion atmosphere inside of aircraft turbines, the currently used ceramic matrix composites require a protective environmental barrier coating (EBC) to mitigate corrosion of the turbine parts. Besides thermomechanical and thermochemical properties like matching thermal expansion coefficient (CTE) and a high resistance against corrosive media, mechanical properties like a high adhesion strength are also necessary for a long lifetime of the EBC. In the present work, the adhesion between an air plasma sprayed silicon bond coat and a vacuum plasma sprayed ytterbium disilicate topcoat was aimed to be enhanced by a laser surface structuring of the Si bond coat. An increase in interface toughness was assumed, since the introduction of structures would lead to an increased mechanical interlocking at the rougher bond coat interface. The interface toughness was measured by a new testing method, which allows the testing of specific interfaces. The results demonstrate a clear increase of the toughness from an original bond coat/topcoat interface (8.6 J/m2) compared to a laser structured interface (14.7 J/m2). Observations in the crack propagation indicates that the laser structuring may have led to a strengthening of the upper bond coat area by sintering. Furthermore, in addition to cohesive failure components, adhesive components can also be observed, which could have influenced the determined toughness. © 2021 by the authors.
    view abstractdoi: 10.3390/coatings11010055
  • 2021 • 646 Development of Fluorescent Chemosensors for Amino-sugars
    Yadav, R. and Kwamen, C. and Niemeyer, J.
    Israel Journal of Chemistry (2021)
    In this account, we describe the application of a series of multidentate BINOL-based phosphoric acids for the fluorescence-based chemosensing of amino sugars. To this end, we developed a novel synthetic protocol for three isomerically pure phosphoric acid monoesters of the type ArOP(O)(OH)2. These were investigated with respect to their binding towards amino sugars (glucosamine, galactosamine and mannosamine) in comparison to the previously reported diesters of the type (ArO)2P(O)(OH). We could find that the diesters show no significant binding, while the monoesters can be used as hosts for amino sugars. Indeed, one host selectively binds to galactosamine, while a second host binds both glucosamine and mannosamine. This allows the fluorescence-based detection and discrimination of the amino sugars by a novel class of phosphate-based supramolecular hosts. © 2021 The Authors. Israel Journal of Chemistry published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/ijch.202000104
  • 2021 • 645 Dielectric Properties of Nanoconfined Water: A Canonical Thermopotentiostat Approach
    Deißenbeck, F. and Freysoldt, C. and Todorova, M. and Neugebauer, J. and Wippermann, S.
    Physical Review Letters 126 (2021)
    We introduce a novel approach to sample the canonical ensemble at constant temperature and applied electric potential. Our approach can be straightforwardly implemented into any density-functional theory code. Using thermopotentiostat molecular dynamics simulations allows us to compute the dielectric constant of nanoconfined water without any assumptions for the dielectric volume. Compared to the commonly used approach of calculating dielectric properties from polarization fluctuations, our thermopotentiostat technique reduces the required computational time by 2 orders of magnitude. © 2021 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the "https://creativecommons.org/licenses/by/4.0/"Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.
    view abstractdoi: 10.1103/PhysRevLett.126.136803
  • 2021 • 644 Differentiability of semigroups of stochastic differential equations with Hölder-continuous diffusion coefficients
    Hutzenthaler, M. and Pieper, D.
    Alea (Rio de Janeiro) 18 309-324 (2021)
    Differentiability of semigroups is useful for many applications. Here we focus on stochastic differential equations whose diffusion coefficient is the square root of a differentiable function but not differentiable itself. For every m ∈ {0, 1, 2} we establish an upper bound for a Cm-norm of the semigroup of such a diffusion in terms of the Cm-norms of the drift coefficient and of the squared diffusion coefficient. The constants in our upper bound are often bounded in the dimension. Our estimates are thus suitable for analyzing certain high-dimensional and infinitedimensional degenerate stochastic differential equations. © 2021,Alea (Rio de Janeiro) All Rights Reserved
    view abstractdoi: 10.30757/ALEA.V18-14
  • 2021 • 643 Digital holography for spatially resolved analysis of the semiconductor optical response
    Besaga, V.R. and Gerhardt, N.C. and Hofmann, M.R.
    Applied Optics 60 A15-A20 (2021)
    We present spatially resolved measurements of the below-band-gap carrier-induced absorption and concurrent phase change in a semiconductor with the help of transmission digital holography. The application is demonstrated for a bulk GaAs sample, while the holograms are recorded with a conventional CMOS sensor. We show that the phase information enables spatially resolved monitoring of excess carrier distributions. Based on that, we discuss a phase-based approach for separation of carrier and heat related effects in the semiconductor optical response. © 2020 Optical Society of America.
    view abstractdoi: 10.1364/AO.402488
  • 2021 • 642 Dipolar-stabilized first and second-order antiskyrmions in ferrimagnetic multilayers
    Heigl, M. and Koraltan, S. and Vaňatka, M. and Kraft, R. and Abert, C. and Vogler, C. and Semisalova, A. and Che, P. and Ullrich, A. and Schmidt, T. and Hintermayr, J. and Grundler, D. and Farle, M. and Urbánek, M. and Suess, D....
    Nature Communications 12 (2021)
    Skyrmions and antiskyrmions are topologically protected spin structures with opposite vorticities. Particularly in coexisting phases, these two types of magnetic quasi-particles may show fascinating physics and potential for spintronic devices. While skyrmions are observed in a wide range of materials, until now antiskyrmions were exclusive to materials with D2d symmetry. In this work, we show first and second-order antiskyrmions stabilized by magnetic dipole–dipole interaction in Fe/Gd-based multilayers. We modify the magnetic properties of the multilayers by Ir insertion layers. Using Lorentz transmission electron microscopy imaging, we observe coexisting antiskyrmions, Bloch skyrmions, and type-2 bubbles and determine the range of material properties and magnetic fields where the different spin objects form and dissipate. We perform micromagnetic simulations to obtain more insight into the studied system and conclude that the reduction of saturation magnetization and uniaxial magnetic anisotropy leads to the existence of this zoo of different spin objects and that they are primarily stabilized by dipolar interaction. © 2021, The Author(s).
    view abstractdoi: 10.1038/s41467-021-22600-7
  • 2021 • 641 Direct gas phase synthesis of amorphous Si/C nanoparticles as anode material for lithium ion battery
    Orthner, H. and Wiggers, H. and Loewenich, M. and Kilian, S. and Bade, S. and Lyubina, J.
    Journal of Alloys and Compounds 870 (2021)
    High specific capacity of silicon is very attractive for its application as anode material in lithium ion batteries. However, the implementation of silicon is challenging due to its large volume expansion on lithiation leading to pulverization and buildup of a solid-electrolyte interphase. Nanostructuring and design of silicon alloys are a promising strategy to circumvent these challenges. Here we demonstrate an industrially scalable gas phase synthesis method using thermal decomposition of silane and ethylene to produce novel amorphous silicon/carbon-based particles with enhanced electrochemical performance. Fundamental principles and kinetics considerations for the design of high-performance silicon/carbon-based materials are discussed. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.jallcom.2021.159315
  • 2021 • 640 Direct generation of 3D structures by laser polymer deposition
    Thiele, M. and Kutlu, Y. and Dobbelstein, H. and Petermann, M. and Esen, C. and Ostendorf, A.
    Journal of Laser Applications 33 (2021)
    Additive manufacturing with polymers is typically performed using techniques such as stereolithography, selective laser sintering (SLS), or fused deposition modeling. SLS of unmodified powders with CO2 lasers represents the state of the art in powder-based polymer additive manufacturing. In the presented work, thermoplastic polyurethane was successfully processed for the first time with a powder feed technique, which is similar to the well-known laser metal deposition. The powder material was doped with carbon black in order to increase the absorptivity of the powder material for laser radiation in the near-infrared range. Various geometries were produced using a standard laser cladding setup with a modified powder feeding system and an Nd:YAG laser. The powder material and the generated structures were characterized by scanning electron microscopy. Structural properties, e.g., porosity, were controlled by different fabrication strategies and process parameters. Furthermore, hybrid structures consisting of metal and polymer parts were successfully produced in the same experimental setup by using two different powder feeders. © 2021 Author(s).
    view abstractdoi: 10.2351/7.0000166
  • 2021 • 639 Discontinuous drilling of inconel 718
    Wolf, T. and Iovkov, I. and Biermann, D.
    MM Science Journal 2021 4569-4575 (2021)
    Inconel 718 as one of the most common nickel-base alloys is mainly characterized by its high-temperature strength. Thus, in particular drilling is subject to high tool wear due to high thermomechanical loads on the cutting edges. To reduce those effects an alternative process design of discontinuous drilling was developed which contains a periodical interruption of the machining process with the aim of a targeted wetting and cooling of the tool at regular intervals. Thus, a significant reduction of the thermal load on the tool should provide a benefit to the drilling process and extend the tool life. Numerical and experimental investigations were used to analyze the introduced process strategy modification. © 2021, MM publishing Ltd.. All rights reserved.
    view abstractdoi: 10.17973/MMSJ.2021_7_2021061
  • 2021 • 638 Discrimination of ablation, shielding, and interface layer effects on the steady-state formation of persistent bubbles under liquid flow conditions during laser synthesis of colloids
    Kalus, M.-R. and Lanyumba, R. and Barcikowski, S. and Gökce, B.
    Journal of Flow Chemistry (2021)
    Over the past decade, laser ablation in liquids (LAL) was established as an innovative nanoparticle synthesis method obeying the principles of green chemistry. While one of the main advantages of this method is the absence of stabilizers leading to nanoparticles with “clean” ligand-free surfaces, its main disadvantage is the comparably low nanoparticle production efficiency dampening the sustainability of the method and preventing the use of laser-synthesized nanoparticles in applications that require high amounts of material. In this study, the effects of productivity-dampening entities that become particularly relevant for LAL with high repetition rate lasers, i.e., persistent bubbles or colloidal nanoparticles (NPs), on the synthesis of colloidal gold nanoparticles in different solvents are studied. Especially under batch ablation conditions in highly viscous liquids with prolonged ablation times both shielding entities are closely interconnected and need to be disentangled. By performing liquid flow-assisted nanosecond laser ablation of gold in liquids with different viscosity and nanoparticle or bubble diffusivity, it is shown that a steady-state is reached after a few seconds with fixed individual contributions of bubble- and colloid-induced shielding effects. By analyzing dimensionless numbers (i.e., Axial Peclet, Reynolds, and Schmidt) it is demonstrated how these shielding effects strongly depend on the liquid’s transport properties and the flow-induced formation of an interface layer along the target surface. In highly viscous liquids, the transport of NPs and persistent bubbles within this interface layer is strongly diffusion-controlled. This diffusion-limitation not only affects the agglomeration of the NPs but also leads to high local densities of NPs and bubbles near the target surface, shielding up to 80% of the laser power. Hence, the ablation rate does not only depend on the total amount of shielding matter in the flow channel, but also on the location of the persistent bubbles and NPs. By comparing LAL in different liquids, it is demonstrated that 30 times more gas is produced per ablated amount of substance in acetone and ethylene glycol compared to ablation in water. This finding confirms that chemical effects contribute to the liquid’s decomposition and the ablation yield as well. Furthermore, it is shown that the highest ablation efficiencies and monodisperse qualities are achieved in liquids with the lowest viscosities and gas formation rates at the highest volumetric flow rates. © 2021, The Author(s).
    view abstractdoi: 10.1007/s41981-021-00144-7
  • 2021 • 637 Dislocation networks in gamma/gamma’-microstructures formed during selective laser melting of a Ni-base superalloy
    Heep, L. and Schwalbe, C. and Heinze, C. and Dlouhy, A. and Rae, C.M.F. and Eggeler, G.
    Scripta Materialia 190 121-125 (2021)
    A dislocation network which formed during selective laser melting (SLM) of a Ni-base superalloy was analyzed using scanning transmission electron microscopy (STEM). This network traverses an ordered Gamma'-phase domain, in between two adjacent Gamma-solid solution regions. The Gamma’-phase region has formed when two Gamma’-phase particles have started to coalesce, trapping the dislocation network in this ordered region so that it formed two dislocation families with pairs of anti-phase boundary (APB) coupled super partial dislocations. The network features are presented and unusual features (twist character and low APB energies), not previously reported, are discussed. © 2020
    view abstractdoi: 10.1016/j.scriptamat.2020.08.019
  • 2021 • 636 Dispersion relation of nutation surface spin waves in ferromagnets
    Cherkasskii, M. and Farle, M. and Semisalova, A.
    Physical Review B 103 (2021)
    Inertia effects in magnetization dynamics are theoretically shown to result in a different type of spin waves, i.e., nutation surface spin waves, which propagate at terahertz frequencies in in-plane magnetized ferromagnetic thin films. Considering the magnetostatic limit, i.e., neglecting exchange coupling, we calculate dispersion relation and group velocity, which we find to be slower than the velocity of conventional (precession) spin waves. In addition, we find that the nutation surface spin waves are backward spin waves. Furthermore, we show that inertia causes a decrease of the frequency of the precession spin waves, namely magnetostatic surface spin waves and backward volume magnetostatic spin waves. The magnitude of the decrease depends on the magnetic properties of the film and its geometry. © 2021 authors.
    view abstractdoi: 10.1103/PhysRevB.103.174435
  • 2021 • 635 Distant spin entanglement via fast and coherent electron shuttling
    Jadot, B. and Mortemousque, P.-A. and Chanrion, E. and Thiney, V. and Ludwig, Ar. and Wieck, A.D. and Urdampilleta, M. and Bäuerle, C. and Meunier, T.
    Nature Nanotechnology 16 570-575 (2021)
    In the quest for large-scale quantum computing, networked quantum computers offer a natural path towards scalability. While recent experiments have demonstrated nearest neighbour entanglement for electron spin qubits in semiconductors, on-chip long-distance entanglement could bring more versatility to connect quantum core units. Here, we employ the moving trapping potential of a surface acoustic wave to realize the controlled and coherent transfer of a pair of entangled electron spins between two distant quantum dots. The subsequent electron displacement induces coherent spin rotations, which drives spin quantum interferences. We observe high-contrast interference as a signature of the preservation of the entanglement all along the displacement procedure, which includes a separation of the two spins by a distance of 6 μm. This work opens the route towards fast on-chip deterministic interconnection of remote quantum bits in semiconductor quantum circuits. © 2021, The Author(s), under exclusive licence to Springer Nature Limited.
    view abstractdoi: 10.1038/s41565-021-00846-y
  • 2021 • 634 Distinguishing persistent effects in an undoped GaAs/AlGaAs quantum well by top-gate-dependent illumination
    Fujita, T. and Hayashi, R. and Kohda, M. and Ritzmann, J. and Ludwig, Ar. and Nitta, J. and Wieck, A.D. and Oiwa, A.
    Journal of Applied Physics 129 (2021)
    Persistent photoconductivity of GaAs/AlGaAs heterostructures has hampered the measurement of charge- and spin-related quantum effects in gate-defined quantum devices and integrated charge sensors due to Si-dopant-related deep donor levels (DX centers). In this study, this effect is overcome by using an undoped GaAs/AlGaAs heterostructure for photonic purposes. We also measure the electron transport before and after LED illumination at low temperatures. In addition to a regular rapid saturation showing the increased carrier density, a slow accumulation of illumination effects appeared when different top-gate voltages were applied during illumination, which indicated the redistribution of charge at the oxide-GaAs interface. This study provides interesting insights into the development of optically stable devices for efficient semiconductor quantum interfaces. © 2021 Author(s).
    view abstractdoi: 10.1063/5.0047558
  • 2021 • 633 DRIE Si Nanowire Arrays Supported Nano-Carbon Film for Deriving High Specific Energy Supercapacitors On-Chip
    Lu, P. and Chen, X. and Ohlckers, P. and Halvorsen, E. and Hoffmann, M. and Müller, L.
    Journal of Physics: Conference Series 1837 (2021)
    Supercapacitor is a promising solution to storage of pulsed energy generated by MEMS energy harvesting systems, relying on its faster charging/discharging capability than secondary battery. To improve the energy density of on-chip supercapacitor which shows potential for integration with MEMS devices, in this paper we first present a successful electrode design for high specific energy pseudo-supercapacitors on the basis of deep reactive ion etched Si nanowire array supported nano-carbon matrix. Widely used pseudo-capacitive manganese oxide active material is facilely deposited into the conductive nano-carbon matrix by a chemical bath deposition. The derived electrode exhibits a remarkable capacitance increase (around 4.5x enhancement) compared with the nano-carbon matrix benefiting from the contribution of pseudo-capacitive manganese oxide. Assembled sandwich prototype on-chip supercapacitors with a symmetric configuration offer a high specific capacitance of 741.6 mF cm-2 when discharged at 1 mA cm-2, and the energy density can attain as high as 51.5 ?Wh cm-2. The achieved high specific energy makes such on-chip supercapacitors attractive in the field of energy collection when cooperated with micro-or nano-energy generators. © Published under licence by IOP Publishing Ltd.
    view abstractdoi: 10.1088/1742-6596/1837/1/012005
  • 2021 • 632 Durability prediction of coil spring through multibody-dynamics-based strain generation
    Chin, C.H. and Abdullah, S. and Singh, S.S.K. and Schramm, D. and Ariffin, A.K.
    Mechanical Systems and Signal Processing 154 (2021)
    The purpose of this study is to develop an acceleration-strain conversion model that considers torsional strain and spring curvature effects in inducing strain for a suspension coil spring. Measurements of strain–time histories at the coil spring are limited by complex geometry and insufficient workspace. This condition increases the demand for strain signal generation through multibody dynamics (MBD) simulation, reducing the need for real strain measurement of coil spring. Road tests were conducted to obtain the unsprung mass acceleration and strain signals of a coil spring under four road conditions (rural, industrial, highway, and campus road). Quarter-car suspension MBD simulation was modelled to simulate the deflection of a spring excited under unsprung mass acceleration. By using this model, simulated strain data with similar properties as the experimental data were generated for fatigue life prediction. The predicted fatigue life from the generated strain indicated a good correlation with the experimental fatigue life within the boundary and showed very low normalised root-mean-square error (NRMSE) between 4 × 10−6 and 2 × 10−4. Finally, it is suggested that the acceleration-strain conversion model showed an enhanced performance for producing realistic strain signals in accurately predicting the durability of coil spring. This can, therefore, further reduce the need for real strain measurement at the coil spring that can result in an erroneous signal. © 2020
    view abstractdoi: 10.1016/j.ymssp.2020.107580
  • 2021 • 631 Dynamic simulation of high-purity twin-bed N2-PSA plants
    Marcinek, A. and Möller, A. and Guderian, J. and Bathen, D.
    Adsorption (2021)
    At present, nitrogen production from air by pressure swing adsorption (PSA) is simulated almost exclusively at low product purity levels (&lt; 99% N2). However, with increasing global demand for highly purified gases provided by energy-efficient separation processes the requirement for either extensive experimental research in the high-purity range or predictive computer simulations arises. This paper presents a mathematical model of a twin-bed PSA plant equipped with a carbon molecular sieve (Shirasagi MSC CT-350) for the generation of high-purity nitrogen (99.9–99.999% N2). The model is implemented in the process simulator Aspen Adsorption™. The influence of operating conditions as well as the cycle organisation on the process performance is validated, especially the influence of pressure, temperature, half-cycle time, purge flow rate, and cutting time. The precision of the performance prediction by numerical simulations is critically discussed. Based on the new insights efficiency improvement strategies with a focus on reduced energy consumption are introduced and discussed by means of radar charts. © 2021, The Author(s).
    view abstractdoi: 10.1007/s10450-021-00320-0
  • 2021 • 630 Dynamical properties of a driven dissipative dimerized S= 12 chain
    Yarmohammadi, M. and Meyer, C. and Fauseweh, B. and Normand, B. and Uhrig, G.S.
    Physical Review B 103 (2021)
    We consider the dynamical properties of a gapped quantum spin system coupled to the electric field of a laser, which drives the resonant excitation of specific phonon modes that modulate the magnetic interactions. We deduce the quantum master equations governing the time-evolution of both the lattice and spin sectors, by developing a Lindblad formalism with bath operators providing an explicit description of their respective phonon-mediated damping terms. We investigate the nonequilibrium steady states (NESS) of the spin system established by a continuous driving, delineating parameter regimes in driving frequency, damping, and spin-phonon coupling for the establishment of physically meaningful NESS and their related nontrivial properties. Focusing on the regime of generic weak spin-phonon coupling, we characterize the NESS by their frequency and wave-vector content, explore their transient and relaxation behavior, and discuss the energy flow, the system temperature, and the critical role of the type of bath adopted. Our study lays a foundation for the quantitative modeling of experiments currently being designed to control coherent many-body spin states in quantum magnetic materials. © 2021 American Physical Society.
    view abstractdoi: 10.1103/PhysRevB.103.045132
  • 2021 • 629 Dynamics of contact electrification
    Kaponig, M. and Mölleken, A. and Nienhaus, H. and Möller, R.
    Science Advances 7 (2021)
    Although the electrical charging of objects brought into contact has been observed for at least 2000 years, the details of the underlying mechanism are still not yet fully understood. The present paper deals with the very basic process of contact electrification between two metals. We have developed an experimental method to follow the charge of a small sphere bouncing on a grounded planar electrode on a time scale down to 1 s. It reveals that the sphere is discharged in the moment of contact, which lasts about 6 to 8 s. However, at the very moment of disruption of the electrical contact, it regains charge far beyond the expectation according to the contact potential difference. The excess charge rises with increasing contact area. Copyright © 2021 The Authors, some rights reserved.
    view abstractdoi: 10.1126/sciadv.abg7595
  • 2021 • 628 Editorial
    Bambach, M. and Beese, A.M. and Lin, F. and Tekkaya, A.E.
    Journal of Materials Processing Technology 294 (2021)
    doi: 10.1016/j.jmatprotec.2021.117103
  • 2021 • 627 Editorial for ADAC issue 2 of volume 15 (2021)
    Vichi, M. and Cerioli, A. and Kestler, H. and Okada, A. and Weihs, C.
    Advances in Data Analysis and Classification 15 261-265 (2021)
    doi: 10.1007/s11634-021-00443-w
  • 2021 • 626 Effect of composition on polarization hysteresis and energy storage ability of p(Vdf-trfe-cfe) relaxor terpolymers
    Hambal, Y. and Shvartsman, V.V. and Lewin, D. and Huat, C.H. and Chen, X. and Michiels, I. and Zhang, Q. and Lupascu, D.C.
    Polymers 13 (2021)
    The temperature dependence of the dielectric permittivity and polarization hysteresis loops of P(VDF-TrFE-CFE) polymer films with different compositions are studied. Among them, the three compositions, 51.3/48.7/6.2, 59.8/40.2/7.3, and 70/30/8.1, are characterized for the first time. Relaxor behavior is confirmed for all studied samples. Increasing the CFE content results in lowering the freezing temperature and stabilizes the ergodic relaxor state. The observed double hysteresis loops are related to the field-induced transition to a ferroelectric state. The critical field corresponding to this transition varies with the composition and temperature; it becomes larger for temperatures far from the freezing temperature. The energy storage performance is evaluated from the analysis of unipolar polarization hysteresis loops. P(VDF-TrFE-CFE) 59.8/40.2/7.3 shows the largest energy density of about 5 J·cm−3 (at the field of 200 MV·m−1) and a charge–discharge efficiency of 63%, which iscomparable with the best literature data for the neat terpolymers. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/polym13081343
  • 2021 • 625 Effect of cooling rate on the microstructure and mechanical properties of a low-carbon low-alloyed steel
    Wang, H. and Cao, L. and Li, Y. and Schneider, M. and Detemple, E. and Eggeler, G.
    Journal of Materials Science 56 11098-11113 (2021)
    Heavy plate steels with bainitic microstructures are widely used in industry due to their good combination of strength and toughness. However, obtaining optimal mechanical properties is often challenging due to the complex bainitic microstructures and multiple phase constitutions caused by different cooling rates through the plate thickness. Here, both conventional and advanced microstructural characterization techniques which bridge the meso- and atomic-scales were applied to investigate how microstructure/mechanical property-relationships of a low-carbon low-alloyed steel are affected by phase transformations during continuous cooling. Mechanical tests show that the yield strength increases monotonically when cooling rates increase up to 90 K/s. The present study shows that this is associated with a decrease in the volume fraction of polygonal ferrite (PF) and a refinement of the substructure of degenerated upper bainite (DUB). The fine DUB substructures feature C-rich retained austenite/martensite-austenite (RA/M-A) constitutes which decorate the elongated micrograin boundaries in ferrite. A further increase in strength is observed when needle-shaped cementite precipitates form during water quenching within elongated micrograins. Pure martensite islands on the elongated micrograin boundaries lead to a decreased ductility. The implications for thick section plate processing are discussed based on the findings of the present work. © 2021, The Author(s).
    view abstractdoi: 10.1007/s10853-021-05974-3
  • 2021 • 624 Effect of interface dislocations on mass flow during high temperature and low stress creep of single crystal Ni-base superalloys
    He, J. and Cao, L. and Makineni, S.K. and Gault, B. and Eggeler, G.
    Scripta Materialia 191 23-28 (2021)
    In this work, the nanometer-scale mass flow coupled to dislocation processes near the γ/γ′-interface during high temperature and low stress creep of a model Ni-base single crystal superalloy is investigated. In the early creep stages, the dislocation networks in the γ-phase at γ/γ′-interfaces attract γ-stabilizing elements like Cr, Co and in particular Re, resulting in compositional gradients close to the interface. At larger strains, where dislocations frequently cut into the γ′-phase, this local interfacial enrichment in these elements is no longer observed. The cutting dislocations take part of the segregated atoms away, whilst the remaining atoms are released and diffuse back into the γ-channels. © 2020
    view abstractdoi: 10.1016/j.scriptamat.2020.09.016
  • 2021 • 623 Effect of Multilayer Termination on Nonspecific Protein Adsorption and Antifouling Activity of Alginate-Based Layer-by-Layer Coatings
    Gnanasampanthan, T. and Beyer, C.D. and Yu, W. and Karthäuser, J.F. and Wanka, R. and Spöllmann, S. and Becker, H.-W. and Aldred, N. and Clare, A.S. and Rosenhahn, A.
    Langmuir 37 5950-5963 (2021)
    Layer-by-layer (LbL) assembly is a versatile platform for applying coatings and studying the properties of promising compounds for antifouling applications. Here, alginate-based LbL coatings were fabricated by alternating the deposition of alginic acid and chitosan or polyethylenimine to form multilayer coatings. Films were prepared with either odd or even bilayer numbers to investigate if the termination of the LbL coatings affects the physicochemical properties, resistance against the nonspecific adsorption (NSA) of proteins, and antifouling efficacy. The hydrophilic films, which were characterized using spectroscopic ellipsometry, water contact angle goniometry, ATR-FTIR spectroscopy, AFM, XPS, and SPR spectroscopy, revealed high swelling in water and strongly reduced the NSA of proteins compared to the hydrophobic reference. While the choice of the polycation was important for the protein resistance of the LbL coatings, the termination mattered less. The attachment of diatoms and settling of barnacle cypris larvae revealed good antifouling properties that were controlled by the termination and the charge density of the LbL films. ©
    view abstractdoi: 10.1021/acs.langmuir.1c00491
  • 2021 • 622 Effect of process parameters on wavy interfacial morphology during magnetic pulse welding
    Zhang, S. and Lueg-Althoff, J. and Hahn, M. and Tekkaya, A.E. and Kinsey, B.
    Journal of Manufacturing Science and Engineering, Transactions of the ASME 143 (2021)
    Magnetic pulse welding (MPW) is a solid-state welding process that bonds similar and dissimilar metals using a high velocity collision. In this paper, effects of impact velocity, target tube thickness, and mandrel inclusion on the interfacial morphology were investigated through the welding of tubular parts, Al6060T4 (flyer) to Cu-ETP (target), by electromagnetic compression. The hypothesis tested in this research is that a “well-supported target,” i.e., either a thick target or the support of a mandrel, allows for vortices to be created at the interface during MPW provided that the impact velocity is sufficient. The mandrel used in the experiments was polyurethane with a Shore hardness of 92A, which was pre-stressed via a washer and nut. The impact velocity was measured via photon Doppler velocimetry (PDV) and used for the setup of numerical simulations. A 2D axisymmetric numerical model was implemented in LS-DYNA to predict the interfacial morphology. Thermal analyses in the numerical model were used to predict the local melting locations and compared with experimental observations. Both experimental and numerical results showed that the interfacial wavelength increased with an increase in the impact velocity and target thickness. Similarly, a thin target with mandrel support also caused an increase in the wavelength. Vortices were only generated with appropriate impact velocities and well-supported targets, i.e., again either a thick target or the support of a mandrel. Copyright © 2020 by ASME
    view abstractdoi: 10.1115/1.4048516
  • 2021 • 621 Effect of synthesis temperature on the phase formation of NiTiAlFeCr compositionally complex alloy thin films
    Marshal, A. and Singh, P. and Music, D. and Wolff-Goodrich, S. and Evertz, S. and Schökel, A. and Johnson, D.D. and Dehm, G. and Liebscher, C.H. and Schneider, J.M.
    Journal of Alloys and Compounds 854 (2021)
    The synthesis temperature dependent phase formation of Ni10Ti10Al25Fe35Cr20 thin films is compared to a bulk processed sample of identical composition. The as-cast alloy exhibits a dual-phase microstructure which is composed of a disordered BCC phase and AlNiTi-based B2- and/or L21-ordered phase(s). Formation of the BCC phase as well as an ordered AlNi-based B2 phase is observed for a thin film synthesised at 500 °C (ratio of synthesis temperature of thin film to melting temperature of bulk alloy: T/Tm = 0.49), which is attributed to both surface and bulk diffusion mediated growth. Post deposition annealing at 900 °C (T/Tm = 0.75) of a thin film deposited without intentional heating results in the formation of NiAlTi-based B2 and/or L21-phase(s) similar to the bulk sample, which is attributed to bulk diffusion. Depositions conducted at room temperature without intentional substrate heating (T/Tm = 0.20) resulted in the formation of an X-ray amorphous phase, while a substrate temperature increase to 175 °C (T/Tm = 0.28) causes the formation of a BCC phase. Atom probe tomography of the thin films deposited without intentional substrate heating and at 175 °C indicates the formation of ∼5 nm and ∼10 nm FeAl-rich domains, respectively. This can be rationalized based on the activation energy for surface diffusion, as Ti and Ni exhibt 2.5 to 4 times larger activation energy barriers than Al, Fe and Cr. It is evident from the homologous temperature that the phase formation observed at 500 °C (T/Tm = 0.49) is a result of both surface and bulk diffusion. As the temperature is reduced, the formation of FeAl-rich domains can be understood based on the differences in activation energy for surface diffusion and is consistent with kinetically limited thin film growth. © 2020 Elsevier B.V.
    view abstractdoi: 10.1016/j.jallcom.2020.155178
  • 2021 • 620 Effects of Automated Vehicles on Traffic Flow with Different Levels of Automation
    Ma, X. and Hu, X. and Weber, T. and Schramm, D.
    IEEE Access 9 3630-3637 (2021)
    Highly automated vehicles are regarded as the next revolution of the transport system. Automated vehicles include a spectrum from vehicles with driver assistance systems through to highly automated vehicles. These vehicles will only gradually appear in the overall vehicle fleet. Their impact as part of future traffic is of reference value for transport decision-makers. The present paper starts from assumptions for the shares of vehicles with different levels of automation in 2030 and 2050 (representing the near and far-distant future) and compares the effects of these automated vehicles on traffic flow using microscopic traffic simulations. The simulated vehicles include non-assisted vehicles, semi-automated vehicles with driver assistance systems, and fully autonomous vehicles. To obtain a more realistic result, a traffic scenario of the city of Duisburg is used in this thesis. With the support of the city administration, existing data of the origin/target matrix, detector data including induction loops, and cameras were available. Thus, the data of the origin/target matrix are used to generate the real traffic scenario and the detector data to investigate the accuracy of the generated traffic. The result shows that automated vehicles would have a positive impact on traffic, a proportion of automated vehicles can reduce the average travel time. For areas with different traffic conditions, the degree of impact of automated vehicles can be very different. © 2013 IEEE.
    view abstractdoi: 10.1109/ACCESS.2020.3048289
  • 2021 • 619 Effects of temperature on mechanical properties and deformation mechanisms of the equiatomic CrFeNi medium-entropy alloy
    Schneider, M. and Laplanche, G.
    Acta Materialia 204 (2021)
    An equiatomic CrFeNi medium-entropy alloy (MEA) that constitutes a cornerstone of austenitic stainless steels and Fe-based superalloys is investigated. Anneals at various temperatures revealed that CrFeNi forms a stable face-centered cubic (FCC) solid solution above ~1223 K. Based on this result, this alloy was cold-worked and recrystallized between 1273 K and 1473 K to produce different grain sizes. Compression tests were carried out at 293 K to investigate grain boundary strengthening (Hall-Petch slope: 966 MPa µm1/2) and this contribution was then subtracted from the overall strength to reveal the intrinsic uniaxial lattice strength (80 MPa). Additional compression and tensile tests were performed between 77 K and 873 K to study the effect of temperature on mechanical properties and deformation mechanisms. Ductility, yield and ultimate tensile strengths increased with decreasing temperature. To reveal the active deformation mechanisms in CrFeNi with the coarsest grain size (160 µm), tensile tests at 77 K and 293 K were interrupted at different strains followed by transmission electron microscopy analyses. In all cases, the deformation was accommodated by dislocation glide at low strains, while twinning additionally occurred above a critical resolved shear stress of 165 MPa, which was roughly temperature independent. This value compares well with predictions (180 MPa) based on the Kibey's model for twin nucleation. Moreover, the fact that this value is roughly temperature-independent is also consistent with the Kibey's model since the twin nucleation barrier (unstable twin stacking fault energy) of FCC metals and alloys does not vary significantly with temperature. © 2020 Acta Materialia Inc.
    view abstractdoi: 10.1016/j.actamat.2020.11.012
  • 2021 • 618 Efficient electronic passivation scheme for computing low-symmetry compound semiconductor surfaces in density-functional theory slab calculations
    Yoo, S.-H. and Lymperakis, L. and Neugebauer, J.
    Physical Review Materials 5 (2021)
    Removing artificial bands from the back side of surface slabs with pseudohydrogen atoms has become the method of choice to boost the convergence of density-functional theory (DFT) surface calculation with respect to slab thickness. In this paper we apply this approach to semipolar compound semiconductor surfaces, which have recently become attractive for device applications. We show that approaches employing saturation of dangling bonds by pseudohydrogen atoms alone are inadequate to properly passivate the surfaces, remove spurious surface states from the fundamental band gap, and achieve flat band conditions in the slab. We propose and successfully apply to technologically interesting semipolar wurtzite surfaces of III-N, III-V, and II-VI semiconductors a reconstruction-inspired passivation scheme that utilizes native anions to passivate cation dangling bonds and pseudohydrogen atoms to obey the electron counting rule and compensate for polarization-induced surface-bound charges. This scheme is generic and robust and can be straightforwardly implemented in DFT investigations of low-symmetry surfaces as well as in high-throughput and machine learning studies. © 2021 authors.
    view abstractdoi: 10.1103/PhysRevMaterials.5.044605
  • 2021 • 617 Efficient implementation of atom-density representations
    Musil, F. and Veit, M. and Goscinski, A. and Fraux, G. and Willatt, M.J. and Stricker, M. and Junge, T. and Ceriotti, M.
    Journal of Chemical Physics 154 (2021)
    Physically motivated and mathematically robust atom-centered representations of molecular structures are key to the success of modern atomistic machine learning. They lie at the foundation of a wide range of methods to predict the properties of both materials and molecules and to explore and visualize their chemical structures and compositions. Recently, it has become clear that many of the most effective representations share a fundamental formal connection. They can all be expressed as a discretization of n-body correlation functions of the local atom density, suggesting the opportunity of standardizing and, more importantly, optimizing their evaluation. We present an implementation, named librascal, whose modular design lends itself both to developing refinements to the density-based formalism and to rapid prototyping for new developments of rotationally equivariant atomistic representations. As an example, we discuss smooth overlap of atomic position (SOAP) features, perhaps the most widely used member of this family of representations, to show how the expansion of the local density can be optimized for any choice of radial basis sets. We discuss the representation in the context of a kernel ridge regression model, commonly used with SOAP features, and analyze how the computational effort scales for each of the individual steps of the calculation. By applying data reduction techniques in feature space, we show how to reduce the total computational cost by a factor of up to 4 without affecting the model's symmetry properties and without significantly impacting its accuracy. © 2021 Author(s).
    view abstractdoi: 10.1063/5.0044689
  • 2021 • 616 eIF5A hypusination, boosted by dietary spermidine, protects from premature brain aging and mitochondrial dysfunction
    Liang, Y. and Piao, C. and Beuschel, C.B. and Toppe, D. and Kollipara, L. and Bogdanow, B. and Maglione, M. and Lützkendorf, J. and See, J.C.K. and Huang, S. and Conrad, T.O.F. and Kintscher, U. and Madeo, F. and Liu, F. and Sick...
    Cell Reports 35 (2021)
    Mitochondrial function declines during brain aging and is suspected to play a key role in age-induced cognitive decline and neurodegeneration. Supplementing levels of spermidine, a body-endogenous metabolite, has been shown to promote mitochondrial respiration and delay aspects of brain aging. Spermidine serves as the amino-butyl group donor for the synthesis of hypusine (Nε-[4-amino-2-hydroxybutyl]-lysine) at a specific lysine residue of the eukaryotic translation initiation factor 5A (eIF5A). Here, we show that in the Drosophila brain, hypusinated eIF5A levels decline with age but can be boosted by dietary spermidine. Several genetic regimes of attenuating eIF5A hypusination all similarly affect brain mitochondrial respiration resembling age-typical mitochondrial decay and also provoke a premature aging of locomotion and memory formation in adult Drosophilae. eIF5A hypusination, conserved through all eukaryotes as an obviously critical effector of spermidine, might thus be an important diagnostic and therapeutic avenue in aspects of brain aging provoked by mitochondrial decline. © 2021 The Author(s)
    view abstractdoi: 10.1016/j.celrep.2021.108941
  • 2021 • 615 Elaborating Mechanisms behind the Durability of Tough Polylactide Monofilaments under Elevated Temperature and Humidity Conditions
    Schippers, C. and Bahners, T. and Gutmann, J.S. and Tsarkova, L.A.
    ACS Applied Polymer Materials 3 1406-1414 (2021)
    Melt-spun poly(l-lactic acid) (PLA) monofilaments with excellent toughness have been subjected to environmental weathering under varying temperatures in the range of 50-70 °C, that is, below and close to the glass transition temperature Tg, and at 20-95% relative humidity in order to follow the evolution of their mechanical performance. Environmentally triggered structural changes and the hydrolytic degradation of the monofilaments have been evaluated by analysis of their thermal and mechanical properties as well as their long-term relaxation behavior using a self-developed model. Despite structural changes, the fibers demonstrate a long-term preservation of the toughness under environmental conditions of physical aging. The mechanisms behind the observed durability of the PLA material are attributed to the relaxation of the confined amorphous phase presumably as a result of the local chain scission. Conditions when hydrolytic degradation leads to mechanical failure correspond to an absolute humidity of 90 g/m3 independent of the temperature of the aging. Presented results reveal a persistence of the mechanical performance of PLA fibers upon aging under moderate conditions, thus offering possible design strategies toward tough and durable PLA materials for sustainable technologies. ©
    view abstractdoi: 10.1021/acsapm.0c01274
  • 2021 • 614 Electroabsorption in gated GaAs nanophotonic waveguides
    Wang, Y. and Uppu, R. and Zhou, X. and Papon, C. and Scholz, S. and Wieck, A.D. and Ludwig, Ar. and Lodahl, P. and Midolo, L.
    Applied Physics Letters 118 (2021)
    We report on the analysis of electroabsorption in thin GaAs/Al0.3Ga0.7As nanophotonic waveguides with an embedded p-i-n junction. By measuring the transmission through waveguides of different lengths, we derive the propagation loss as a function of electric field, wavelength, and temperature. The results are in good agreement with the Franz-Keldysh model of electroabsorption extending over 200 meV below the GaAs bandgap, i.e., in the wavelength range of 910-970 nm. We find a pronounced residual absorption in forward bias, which we attribute to Fermi-level pinning at the waveguide surface, producing over 20 dB/mm loss at room temperature. These results are essential for understanding the origin of loss in nanophotonic devices operating in the emission range of self-assembled InAs semiconductor quantum dots toward the realization of scalable quantum photonic integrated circuits. © 2021 Author(s).
    view abstractdoi: 10.1063/5.0039373
  • 2021 • 613 Electrocatalysis in confined space
    Andronescu, C. and Masa, J. and Tilley, R.D. and Gooding, J.J. and Schuhmann, W.
    Current Opinion in Electrochemistry 25 (2021)
    The complex interplay of restricted mass transport leading to local accumulation or depletion of educts, intermediates, products, counterions and co-ions influences the reactions at the active sites of electrocatalysts when electrodes are rough, three-dimensionally mesoporous or nanoporous. This influence is important with regard to activity, and even more to selectivity, of electrocatalytic reactions. The underlying principles are discussed based on the growing awareness of these considerations over recent years. © 2020 Elsevier B.V.
    view abstractdoi: 10.1016/j.coelec.2020.100644
  • 2021 • 612 Electrocatalytic oxidation of 2-propanol on PtxIr100-x bifunctional electrocatalysts – A thin-film materials library study
    Kormányos, A. and Savan, A. and Ludwig, Al. and Speck, F.D. and Mayrhofer, K.J.J. and Cherevko, S.
    Journal of Catalysis 396 387-394 (2021)
    Due to the high demand for renewable and infrastructure compatible energy conversion and storage technologies, research on organic fuel cells receives increasing interest again recently. Organic fuels such as alcohols provide an attractive avenue to overcome the drawbacks of hydrogen as an energy carrier. Particularly interesting are secondary alcohols that almost exclusively form ketones as the final oxidation product, as they can be utilized in “zero emission” concepts without CO2 as a by-product. The state-of-the-art electrocatalyst in secondary alcohol oxidation is Pt-Ru, which demonstrates low onset potentials for the oxidation of the most facile secondary alcohol isopropanol. Yet, the achievable current densities are still relatively low and decrease rapidly due to the formed product acetone, which can poison the catalyst surface over time. Therefore, there is an inevitable need for the development of novel electrocatalyst materials circumventing these challenges. In this study, we employ a high-throughput electrochemical approach coupled to on-line inductively-coupled plasma mass spectrometry to map the composition-dependent activity and stability of PtxIr100-x alloy electrocatalysts toward the electro-oxidation of isopropanol. The activity and stability of magnetron sputtered PtxIr100-x material libraries are studied in 0.1 M HClO4 both in the absence and presence of isopropanol. The highest current densities are achieved for the sample containing the least amount of Ir (3.4 at.%), with a continuous decrease with the increasing amount of Ir. The alloys are inactive towards the oxidation of isopropanol when the amount of Ir exceeded 80 at%. The presence of isopropanol also has a notable effect on stability: while dissolution rates do not change in the case of pure Pt and Ir, a significant increase in stability is observed for the PtxIr100-x thin-film samples at all applied upper potential limits. This is explained by the strong adsorption of acetone on the surface of the catalyst that inhibits the formation of surface oxides. © 2021 Elsevier Inc.
    view abstractdoi: 10.1016/j.jcat.2021.02.021
  • 2021 • 611 Electrocatalytic Oxidation of Glycerol Using Solid-State Synthesised Nickel Boride: Impact of Key Electrolysis Parameters on Product Selectivity
    Brix, A.C. and Morales, D.M. and Braun, M. and Jambrec, D. and Junqueira, J.R.C. and Cychy, S. and Seisel, S. and Masa, J. and Muhler, M. and Andronescu, C. and Schuhmann, W.
    ChemElectroChem 8 2336-2342 (2021)
    Water electrolysis is a promising technology for sustainable hydrogen production; however, its commercialisation is limited by sluggish kinetics of the oxygen evolution reaction (OER). A potential alternative to the OER is hence required and is seen in the electrocatalytic glycerol oxidation reaction (GOR) as it offers concomitant value-added product generation from a cheap and abundant feedstock. Here, we show a facile solid-state synthesis method to obtain Ni-boride, a non-noble metal-based catalyst subsequently used in an in-depth study of the GOR product distribution as a function of key electrolysis parameters. Highly crystalline, mixed-phase Ni borides were obtained, and their synthesis was successfully optimised regarding GOR activity. Long-term chronoamperometry was conducted in a circular flow-through cell and samples were analysed by HPLC. It is shown that the formation of lactic acid, one of the most valuable GOR products, can be enhanced by optimising the electrolyte composition and the applied potential. © 2021 The Authors. ChemElectroChem published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/celc.202100739
  • 2021 • 610 Electrochemical CO2 Reduction: Tailoring Catalyst Layers in Gas Diffusion Electrodes
    Junge Puring, K. and Siegmund, D. and Timm, J. and Möllenbruck, F. and Schemme, S. and Marschall, R. and Apfel, U.-P.
    Advanced Sustainable Systems 5 (2021)
    The electrochemical conversion of CO2 into commodity chemicals or fuels is an attractive reaction for sustainable CO2 utilization. In this context, the application of gas diffusion electrodes is promising due to efficient CO2 mass transport. Herein, a scalable and reproducible method is presented for polytetrafluoroethylene (PTFE)-bound copper gas diffusion electrodes (GDEs) via the dry-pressing method and compositional parameters are emphasized to alter such electrodes. The assembly of the catalytic layer plays a critical role in the electrode performance, as elevated bulk hydrophobicity coupled with good surface wettability is observed to offer highest performance in 0.5 m KHCO3. With optimized electrodes, formate, CO, and H2 are obtained at a current density of 25 mA cm−2 as main products in 1 m KOH in faradaic efficiencies (FEs) of 27%, 30%, and 36%. At 200 mA cm−2, an altered product composition with ethylene (33% FE) and ethanol (9% FE) along with H2 (33% FE) is observed. In addition, n-propanol is observed with 7% faradaic efficiency. The results indicate that the composition of the GDE has a severe influence on the electrode performance and setting proper hydrophobicity gradients within the electrode is key toward developing a successful electrochemical CO2 reduction. © 2020 The Authors. Published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/adsu.202000088
  • 2021 • 609 Electron beam powder bed fusion of γ‐titanium aluminide: Effect of processing parameters on part density, surface characteristics and aluminum content
    Moritz, J. and Teschke, M. and Marquardt, A. and Stepien, L. and López, E. and Brückner, F. and Macias Barrientos, M. and Walther, F. and Leyens, C.
    Metals 11 (2021)
    Gamma titanium aluminides are very interesting for their use in high‐performance applications such as aircraft engines due to their low density, high stiffness and favorable hightemperature properties. However, the pronounced brittleness of these intermetallic alloys is a major challenge for their processing through conventional fabrication methods. Additive manufacturing by means of electron beam powder bed fusion (EB‐PBF) significantly improves the processability of titanium aluminides due to the high preheating temperatures and facilitates complex components. The objective of this study was to determine a suitable processing window for EB‐PBF of the TNM‐B1 alloy (Ti‐43.5Al‐4Nb‐1Mo‐0.1B), using an increased aluminum content in the powder raw material to compensate for evaporation losses during the process. Design of experiments was used to evaluate the effect of beam current, scan speed, focus offset, line offset and layer thickness on porosity. Top surface roughness was assessed through laser scanning confocal microscopy. Scanning electron microscopy, electron backscatter diffraction (EBSD) and energydispersive X‐ray spectroscopy (EDX) were used for microstructural investigation and to analyze aluminum loss depending on the volumetric energy density used in EB‐PBF. An optimized process parameter set for achieving part densities of 99.9% and smooth top surfaces was derived. The results regarding microstructures and aluminum evaporation suggest a solidification via the β‐phase. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/met11071093
  • 2021 • 608 Electron capture and emission dynamics of self-assembled quantum dots far from equilibrium with the environment
    Schnorr, L. and Labes, J. and Kürten, L. and Heinzel, T. and Rothfuchs-Engels, C. and Scholz, S. and Ludwig, A. and Wieck, A.D.
    Physical Review B 104 (2021)
    The electron transfer dynamics between self-assembled quantum dots and their environment are measured under nonequilibrium conditions by time-dependent capacitance spectroscopy. The quantum dots are embedded in a wide spacer, which inhibits elastic tunneling to or from the reservoirs. At certain bias voltages, electron capture and emission are both significant. A rate equation model is used to determine the corresponding transfer rates and the average occupation numbers of the dots as a function of the bias voltage. ©2021 American Physical Society
    view abstractdoi: 10.1103/PhysRevB.104.035303
  • 2021 • 607 Electron heating mode transitions in radio-frequency driven micro atmospheric pressure plasma jets in He/O2: A fluid dynamics approach
    Liu, Y. and Korolov, I. and Hemke, T. and Bischoff, L. and Hübner, G. and Schulze, J. and Mussenbrock, T.
    Journal of Physics D: Applied Physics 54 (2021)
    A two-dimensional fluid model is used to investigate the electron heating dynamics and the production of neutral species in a capacitively coupled radio-frequency micro atmospheric pressure helium plasma jet - specifically the COST jet - with a small oxygen admixture. Electron heating mode transitions are found to be induced by varying the driving voltage amplitude and the O2 concentration numerically and experimentally. The helium metastable density, and the charged species densities are highly relevant to the electron heating dynamics. By analyzing the creation and destruction mechanisms of the negative ions, we find that the generation of negative ions strongly depends on the O2 concentration. The increase of the electronegativity with the increasing O2 concentration leads to an enhancement of the bulk drift electric field. The distributions of the different neutral species densities along the direction of the gas flow inside the jet, as well as in the effluent differ a lot due to the relevant chemical reaction rates and the effect of the gas flow. The simulated results show that a fluid model can be an effective tool for qualitative investigations of micro atmospheric pressure plasma jets. © 2021 The Author(s). Published by IOP Publishing Ltd.
    view abstractdoi: 10.1088/1361-6463/abf370
  • 2021 • 606 Electronic interactions between graphene and cobaltite thin film La0.7Sr0.3CoO3 and its magnetic consequences
    Othmen, Z. and Othmen, R. and Daoudi, K. and Boudard, M. and Cavanna, A. and Madouri, A. and Gemeiner, P. and Lupascu, D.C. and Oueslati, M. and Dkhil, B.
    Surfaces and Interfaces 23 (2021)
    We have successfully synthesized and transferred graphene (Gr) monolayers on top of epitaxial mixed valence La0.7Sr0.3CoO3 (LSCO) thin films. Raman spectroscopy reveals that Jahn-Teller (JT) modes associated with the oxygen octahedral distortions usually unobserved for bare LSCO are activated by the deposited graphene. The appearance of these JT modes in the Gr/LSCO heterostructure is attributed to the electronic interactions at the interface between the graphene and the LSCO thin film promoting intermediate spin states of the Co ions. As a result, the magnetic properties of LSCO are affected. Indeed, magnetization measurements show a phase transition at ~135 K which is due to the presence of the graphene while the ferromagnetic transition of bare LSCO films is observed at~200 K. This magnetic phase is confirmed by Raman spectroscopy measurements as a function of temperature revealing a vibrational transition around the same temperature. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.surfin.2020.100919
  • 2021 • 605 Elemental segregation to lattice defects in the CrMnFeCoNi high-entropy alloy during high temperature exposures
    Heczko, M. and Mazánová, V. and Gröger, R. and Záležák, T. and Hooshmand, M.S. and George, E.P. and Mills, M.J. and Dlouhý, A.
    Acta Materialia 208 (2021)
    The influence of small plastic pre-strains on the elevated-temperature stability and microstructure of the equiatomic CrMnFeCoNi FCC solid solution is investigated. Particular attention is given to whether any of the alloy elements segregate to individual dislocations. To that end, CrMnFeCoNi samples were first deformed in tension at room temperature to plastic strains of 0.2 and 2.3%, and subsequently annealed at 973 K for 800 hours. The pre-strains activated planar slip of 1/2&lt;110&gt;-type dislocations on {111}-type glide planes. Interactions of this planar slip with special Σ3 grain boundaries formed a large number of dislocation segments with a &lt;110&gt;-type crystallographic orientation suitable for a credible end-on analysis of dislocation cores in HR-STEM. The cores of the 1/2&lt;110&gt; dislocations pushed up against the investigated grain boundaries were found to be close to the compact configuration. Within the sensitivity of the Super-X EDS mapping, no concentration gradient was detected near dislocations that would indicate enrichment at dislocation cores of any of the elemental constituents of the alloy after the pre-deformation and annealing. However, a Cr-rich tetragonal sigma phase nucleated and grew at grain boundary triple junctions during this anneal, processes that were not accelerated by the enhanced dislocation density present after pre-strain. A clear chromium gradient was observed in the Cr-depleted zones near grain boundaries suggesting that Cr transport occurred by relatively slow diffusion from the bulk to the grain boundaries and then by relatively fast diffusion along the grain boundaries to the precipitates. Accompanying the Cr depletion near grain boundaries is a simultaneous Ni and Mn enrichment, which promotes formation of the L10 NiMn phase that is observed on the grain boundaries after prolonged annealing. © 2021
    view abstractdoi: 10.1016/j.actamat.2021.116719
  • 2021 • 604 Elucidation of mass transfer mechanisms in pellet formation by spheronization
    Evers, M. and Mattusch, A. and Weis, D. and Garcia, E. and Antonyuk, S. and Thommes, M.
    European Journal of Pharmaceutics and Biopharmaceutics 160 92-99 (2021)
    Previously published mechanisms of pellet formation during extrusion-spheronization include a transfer of material between different granules. This research aimed to specify the origin of this transfered mass, enabling further insight into the extrusion-spheronization process. Granules of various diameters were rounded simultaniously in a spheronizer to ascertain if mass transfer between smaller and larger granules is truly in balance, or if mass transfer from smaller to larger granules is preferred. Granules were also marked with a fluorescent tracer to enable quantification of mass transfer. By using differently sized and shaped granules as starting material, different modes of mass transfer were investigated. Samples were taken after various process durations to investigate the kinetics of the tranfer mechanism. It was found that both small and large granules dispense and receive mass during spheronization. In general, small granules increase their size, while large granules maintain their size or show a slight size decrease, resulting in the particularly narrow monomodal size distribution. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.ejpb.2021.01.013
  • 2021 • 603 Energetic characterization of faujasite zeolites using a sensor gas calorimeter
    Mauer, V. and Bläker, C. and Pasel, C. and Bathen, D.
    Catalysts 11 1-19 (2021)
    In addition to the adsorption mechanism, the heat released during exothermic adsorption influences the chemical reactions that follow during heterogeneous catalysis. Both steps depend on the structure and surface chemistry of the catalyst. An example of a typical catalyst is the faujasite zeolite. For faujasite zeolites, the influence of the Si/Al ratio and the number of Na+ and Ca2+ cations on the heat of adsorption was therefore investigated in a systematic study. A comparison between a NaX (Sodium type X faujasite) and a NaY (Sodium type Y faujasite) zeolite reveals that a higher Si/Al ratio and therefore a smaller number of the cations in faujasite zeolites leads to lower loadings and heats. The exchange of Na+ cations for Ca2+ cations also has an influence on the adsorption process. Loadings and heats first decrease slightly at a low degree of exchange and increase significantly with higher calcium contents. If stronger interactions are required for heterogeneous catalysis, then the CaNaX zeolites must have a degree of exchange above 53%. The energetic contributions show that the highest‐quality adsorption sites III and III’ make a contribution to the load‐dependent heat of adsorption, which is about 1.4 times (site III) and about 1.8 times (site III’) larger than that of adsorption site II. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/catal11010098
  • 2021 • 602 Enhancing Engineering Education by Virtual Laboratories: A Comparison Between Two Different Approaches
    Keddi, D. and Frerich, S.
    Advances in Intelligent Systems and Computing 1231 AISC 359-365 (2021)
    The aim of this contribution is to compare two different settings of two virtual laboratories. Both of them are situated in the context of chemical engineering. One of them is used as online preparation for international students, while the other is implemented in lectures and seminars as demonstrating unit of subjects related to porous materials. While the online preparation for international students has already been at use, the demonstration unit is still work in progress. The students benefit from this kind of digital preparation to a high degree. Theoretical knowledge is available on an individual level, and they can choose time and place when to attend the courses. Many students mastered their course, understood the underlying concepts, and also exceeded usual expectations with their final reports. Regarding their comments, the implemented visualizations were highly appreciated, and the students also rated the set-ups as affirmative. However, a reasonable amount of participants complained about the absence of a real person in charge throughout the experiment, as they have experienced it in hands-on laboratories on site. Although it was found that virtual laboratories are an appropriate way to explain scientific topics, it can be observed that the actual implementation is still facing some issues. This contribution gives an overview of experiences made and discusses the potential for future applications of virtual laboratories in engineering education. © 2021, Springer Nature Switzerland AG.
    view abstractdoi: 10.1007/978-3-030-52575-0_30
  • 2021 • 601 Entropic regularization of continuous optimal transport problems
    Clason, C. and Lorenz, D.A. and Mahler, H. and Wirth, B.
    Journal of Mathematical Analysis and Applications 494 (2021)
    We analyze continuous optimal transport problems in the so-called Kantorovich form, where we seek a transport plan between two marginals that are probability measures on compact subsets of Euclidean space. We consider the case of regularization with the negative entropy with respect to the Lebesgue measure, which has attracted attention because it can be solved by the very simple Sinkhorn algorithm. We first analyze the regularized problem in the context of classical Fenchel duality and derive a strong duality result for a predual problem in the space of continuous functions. However, this problem may not admit a minimizer, which prevents obtaining primal-dual optimality conditions. We then show that the primal problem is naturally analyzed in the Orlicz space of functions with finite entropy in the sense that the entropically regularized problem admits a minimizer if and only if the marginals have finite entropy. We then derive a dual problem in the corresponding dual space, for which existence can be shown by purely variational arguments and primal-dual optimality conditions can be derived. For marginals that do not have finite entropy, we finally show Gamma-convergence of the regularized problem with smoothed marginals to the original Kantorovich problem. © 2020 Elsevier Inc.
    view abstractdoi: 10.1016/j.jmaa.2020.124432
  • 2021 • 600 Enzyme-induced mineralization of hydrogels with amorphous calcium carbonate for fast synthesis of ultrastiff, strong and tough organic–inorganic double networks
    Milovanovic, M. and Mihailowitsch, L. and Santhirasegaran, M. and Brandt, V. and Tiller, J.C.
    Journal of Materials Science 56 15299-15312 (2021)
    Abstract: Hydrogels with good mechanical properties have great importance in biological and medical applications. Double-network (DN) hydrogels were found to be very tough materials. If one of the two network phases is an inorganic material, the DN hydrogels also become very stiff without losing their toughness. So far, the only example of such an organic–inorganic DN hydrogel is based on calcium phosphate, which takes about a week to be formed as an amorphous inorganic phase by enzyme-induced mineralization. An alternative organic–inorganic DN hydrogel, based on amorphous CaCO3, which can be formed as inorganic phase within hours, was designed in this study. The precipitation of CaCO3 within a hydrogel was induced by urease and a urea/CaCl2 calcification medium. The amorphous character of the CaCO3 was retained by using the previously reported crystallization inhibiting effects of N-(phosphonomethyl)glycine (PMGly). The connection between organic and inorganic phases via reversible bonds was realized by the introduction of ionic groups. The best results were obtained by copolymerization of acrylamide (AAm) and sodium acrylate (SA), which led to water-swollen organic–inorganic DN hydrogels with a high Young’s modulus (455 ± 80 MPa), remarkable tensile strength (3.4 ± 0.7 MPa) and fracture toughness (1.1 ± 0.2 kJ m−2). Graphical Abstract: The present manuscript describes the method of enzymatic mineralization of hydrogels for the production of ultrastiff and strong composite hydrogels. By forming a double-network structure based on an organic and an inorganic phase, it is possible to improve the mechanical properties of a hydrogel, such as stiffness and strength, by several orders of magnitude. The key to this is the formation of a percolating, amorphous inorganic phase, which is achieved by inhibiting crystallization of precipitated amorphous CaCO3 with N-(phosphonomethyl)glycine and controlling the nanostructure with co polymerized sodium acrylate. This creates ultrastiff, strong and tough organic–inorganic double-network hydrogels. [Figure not available: see fulltext.]. © 2021, The Author(s).
    view abstractdoi: 10.1007/s10853-021-06204-6
  • 2021 • 599 Enzyme-Inspired Iron Porphyrins for Improved Electrocatalytic Oxygen Reduction and Evolution Reactions
    Xie, L. and Zhang, X.-P. and Zhao, B. and Li, P. and Qi, J. and Guo, X. and Wang, B. and Lei, H. and Zhang, W. and Apfel, U.-P. and Cao, R.
    Angewandte Chemie - International Edition 60 7576-7581 (2021)
    Nature uses Fe porphyrin sites for the oxygen reduction reaction (ORR). Synthetic Fe porphyrins have been extensively studied as ORR catalysts, but activity improvement is required. On the other hand, Fe porphyrins have been rarely shown to be efficient for the oxygen evolution reaction (OER). We herein report an enzyme-inspired Fe porphyrin 1 as an efficient catalyst for both ORR and OER. Complex 1, which bears a tethered imidazole for Fe binding, beats imidazole-free analogue 2, with an anodic shift of ORR half-wave potential by 160 mV and a decrease of OER overpotential by 150 mV to get the benchmark current density at 10 mA cm−2. Theoretical studies suggested that hydroxide attack to a formal FeV=O form the O−O bond. The axial imidazole can prevent the formation of trans HO-FeV=O, which is less effective to form O−O bond with hydroxide. As a practical demonstration, we assembled rechargeable Zn-air battery with 1, which shows equal performance to that with Pt/Ir-based materials. © 2021 Wiley-VCH GmbH
    view abstractdoi: 10.1002/anie.202015478
  • 2021 • 598 ePC-SAFT advanced - Part I: Physical meaning of including a concentration-dependent dielectric constant in the born term and in the Debye-Hückel theory
    Bülow, M. and Ascani, M. and Held, C.
    Fluid Phase Equilibria 535 (2021)
    The transition from aqueous electrolyte systems to non-aqueous electrolyte systems is highly demanded in industrial applications and especially challenging for physics-based thermodynamic models. Electrolyte thermodynamics is a complex matter, and still not all physico-chemical effects are accounted for in state-of-the-art equations of state. The dielectric constant of non-aqueous electrolyte systems changes drastically compared to aqueous systems. One main consequence is that ions are very differently solvated in non-aqueous medium compared to aqueous medium. The Born term represents a methodology to account for the influence of solvation energies of ions, which is based on influences of solvent and salt on the dielectric constant. Utilizing the Born term in electrolyte models is extensively debated, and it is often reasonably neglected in predominantly aqueous systems. Yet, it has a significant influence on transferability from aqueous to non-aqueous media i.e., systems with a large difference in polarity or permittivity compared to aqueous systems. In this work, a modified Born term was combined with electrolyte Perturbed-Chain Statistical Associating Fluid Theory (ePC-SAFT) by introducing additionally a salt concentration-dependent dielectric constant, henceforth called altered Born contribution. The new methodology was validated against infinite dilution properties for ion-solvent interactions: Gibbs energy of hydration and Gibbs energy of transfer of alkali halides from water to alcoholic solvents. Further, mean ionic activity coefficients (MIACs) of alkali halides in alcoholic solvents were quantitatively correct predicted with the advanced ePC-SAFT approach. Original ePC-SAFT parameters were applied for all predictions, and no further binary parameters were adjusted. Based on the success of the model predictions, the transferability of pure-ion ePC-SAFT parameters to organic solvents was verified and the incorporation of concentration-dependent dielectric constant into the altered Born contribution and Debye-Hückel theory was proven to be meaningful methods for the transfer of electrolyte thermodynamic models from aqueous to non-aqueous systems. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.fluid.2021.112967
  • 2021 • 597 ePC-SAFT advanced – Part II: Application to Salt Solubility in Ionic and Organic Solvents and the Impact of Ion Pairing
    Bülow, M. and Ascani, M. and Held, C.
    Fluid Phase Equilibria 537 (2021)
    The applications of electrolyte thermodynamic models to non-aqueous systems is of great value to reduce experimental effort and gain inside into molecular interactions. A large-scale application is for example the design of advanced battery electrolytes. For non-aqueous electrolyte systems, the Born term was found to be important, as it accounts for the transfer of ions from water into non-aqueous medium. In part one of this study [Bülow et al., Fluid Phase Equilibria 2021, 112967] the Born term was combined with a concentration-dependent dielectric constant within the ePC-SAFT framework (electrolyte Perturbed-Chain Statistical Associating Fluid Theory). In the present work, the Bjerrum treatment for ion pairing was included in the Debye-Hückel framework within ePC-SAFT. The approach was validated by experimental data for the dissociation of salts in organic solvents derived from conductivity measurements. Further, solubility was modeled of alkali halides in organic solvents and in ionic liquids. Modeling solubility required access to the solubility product KSP, which does not depend on the solvent. The approach within this work was to first determine KSP using experimental solubility data in water and the respective ePC-SAFT predicted activity coefficients prior to predict activity coefficients in non-aqueous medium, finally yielding solubility. The so-determined solubility values were found to be in reasonable agreement with the experimental data without fitting model parameters to any data of the non-aqueous solutions. The solubility product requires the solid form of the precipitating salt to be equal for all solvents; as alkali salts precipitate from aqueous solutions as hydrates, the method cannot be applied. Therefore, a methodology is presented to extrapolate the high-temperature KSP of anhydrates to lower temperature. Using the so-extrapolated KSP allowed predicting solubility of non-solvates in other solvents. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.fluid.2021.112989
  • 2021 • 596 Epitaxy Induced Highly Ordered Sm2Co17-SmCo5Nanoscale Thin-Film Magnets
    Sharma, S. and Zintler, A. and Günzing, D. and Lill, J. and Meira, D.M. and Eilhardt, R. and Singh, H.K. and Xie, R. and Gkouzia, G. and Major, M. and Radulov, I. and Komissinskiy, P. and Zhang, H. and Skokov, K. and Wende, H. an...
    ACS Applied Materials and Interfaces (2021)
    Utilizing the molecular beam epitaxy technique, a nanoscale thin-film magnet of c-axis-oriented Sm2Co17 and SmCo5 phases is stabilized. While typically in the prototype Sm(Co, Fe, Cu, Zr)7.5-8 pinning-type magnets, an ordered nanocomposite is formed by complex thermal treatments, here, a one-step approach to induce controlled phase separation in a binary Sm-Co system is shown. A detailed analysis of the extended X-ray absorption fine structure confirmed the coexistence of Sm2Co17 and SmCo5 phases with 65% Sm2Co17 and 35% SmCo5. The SmCo5 phase is stabilized directly on an Al2O3 substrate up to a thickness of 4 nm followed by a matrix of Sm2Co17 intermixed with SmCo5. This structural transition takes place through coherent atomic layers, as revealed by scanning transmission electron microscopy. Highly crystalline growth of well-aligned Sm2Co17 and SmCo5 phases with coherent interfaces result in strong exchange interaction, leading to enhanced magnetization and magnetic coupling. The arrangement of Sm2Co17 and SmCo5 phases at the nanoscale is reflected in the observed magnetocrystalline anisotropy and coercivity. As next-generation permanent magnets require designing of materials at an atomic level, this work enhances our understanding of self-assembling and functioning of nanophased magnets and contributes to establishing new concepts to engineer the microstructure for beyond state-of-the-art magnets. ©
    view abstractdoi: 10.1021/acsami.1c04780
  • 2021 • 595 Estimating cardiomyofiber strain in vivo by solving a computational model
    Perotti, L.E. and Verzhbinsky, I.A. and Moulin, K. and Cork, T.E. and Loecher, M. and Balzani, D. and Ennis, D.B.
    Medical Image Analysis 68 (2021)
    Since heart contraction results from the electrically activated contraction of millions of cardiomyocytes, a measure of cardiomyocyte shortening mechanistically underlies cardiac contraction. In this work we aim to measure preferential aggregate cardiomyocyte (“myofiber”) strains based on Magnetic Resonance Imaging (MRI) data acquired to measure both voxel-wise displacements through systole and myofiber orientation. In order to reduce the effect of experimental noise on the computed myofiber strains, we recast the strains calculation as the solution of a boundary value problem (BVP). This approach does not require a calibrated material model, and consequently is independent of specific myocardial material properties. The solution to this auxiliary BVP is the displacement field corresponding to assigned values of myofiber strains. The actual myofiber strains are then determined by minimizing the difference between computed and measured displacements. The approach is validated using an analytical phantom, for which the ground-truth solution is known. The method is applied to compute myofiber strains using in vivo displacement and myofiber MRI data acquired in a mid-ventricular left ventricle section in N=8 swine subjects. The proposed method shows a more physiological distribution of myofiber strains compared to standard approaches that directly differentiate the displacement field. © 2020
    view abstractdoi: 10.1016/j.media.2020.101932
  • 2021 • 594 Evaluation of accuracy of traffic flow generation in SUMO
    Ma, X. and Hu, X. and Weber, T. and Schramm, D.
    Applied Sciences (Switzerland) 11 (2021)
    A traffic simulation of the Jianghan Zone in Wuhan, China was carried out. In order to simulate genuine traffic flow without traditional hard-to-implement data collection methods, geographic population distribution data were gathered from the public information and traffic flow was generated by ActivityGen in SUMO (Simulation of Urban Mobility). For the sake of discovering the accuracy of the simulated traffic, real-time road condition and traffic prediction based on previous data on same time of each road in this area was compared. The results show that traffic flow generated from geographic population distribution data has referential meanings and with more detailed model classification, simulated traffic data can be closer to real conditions. This may offer a new way to generate traffic flow for researchers working in traffic simulation area. Further improvement of the accuracy in traffic flow generation by geographic population needs to pay more attention on special places like hospital and train stations. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/app11062584
  • 2021 • 593 Evaluation of antithrombogenic pHPC on CoCr substrates for biomedical applications
    Bannewitz, C. and Lenz-Habijan, T. and Lentz, J. and Peters, M. and Trösken, V. and Siebert, S. and Weber, S. and Theisen, W. and Henkes, H. and Monstadt, H.
    Coatings 11 1-12 (2021)
    Bare metal endovascular implants pose a significant risk of causing thrombogenic complications. Antithrombogenic surface modifications, such as phenox’s “Hydrophilic Polymer Coating” (pHPC), which was originally developed for NiTi implants, decrease the thrombogenicity of metal surfaces. In this study, the transferability of pHPC onto biomedical CoCr-based alloys is examined. Coated surfaces were characterized via contact-angle measurement and atomic force microscopy. The equivalence of the antithrombogenic effect in contact with whole human blood was demonstrated in vitro for CoCr plates compared to NiTi plates on a platform shaker and for braided devices in a Chandler loop. Platelet adhesion was assessed via scanning electron microscopy and fluorescence microscopy. The coating efficiency of pHPC on CoCr plates was confirmed by a reduction of the contact angle from 84.4° ± 5.1° to 36.2° - 5.2°. The surface roughness was not affected by the application of pHPC. Platelet adhesion was significantly reduced on pHPC-coated specimens. The platelet covered area was reduced by 85% for coated CoCr plates compared to uncoated samples. Uncoated braided devices were completely covered by platelets, while on the pHPC-coated samples, very few platelets were visible. In conclusion, the antithrombogenic effect of pHPC coating can be successfully applied on CoCr plates as well as stent-like CoCr braids. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/coatings11010093
  • 2021 • 592 Evaluation of log P, pK a, and log D predictions from the SAMPL7 blind challenge
    Bergazin, T.D. and Tielker, N. and Zhang, Y. and Mao, J. and Gunner, M.R. and Francisco, K. and Ballatore, C. and Kast, S.M. and Mobley, D.L.
    Journal of Computer-Aided Molecular Design (2021)
    The Statistical Assessment of Modeling of Proteins and Ligands (SAMPL) challenges focuses the computational modeling community on areas in need of improvement for rational drug design. The SAMPL7 physical property challenge dealt with prediction of octanol-water partition coefficients and pKa for 22 compounds. The dataset was composed of a series of N-acylsulfonamides and related bioisosteres. 17 research groups participated in the log P challenge, submitting 33 blind submissions total. For the pKa challenge, 7 different groups participated, submitting 9 blind submissions in total. Overall, the accuracy of octanol-water log P predictions in the SAMPL7 challenge was lower than octanol-water log P predictions in SAMPL6, likely due to a more diverse dataset. Compared to the SAMPL6 pKa challenge, accuracy remains unchanged in SAMPL7. Interestingly, here, though macroscopic pKa values were often predicted with reasonable accuracy, there was dramatically more disagreement among participants as to which microscopic transitions produced these values (with methods often disagreeing even as to the sign of the free energy change associated with certain transitions), indicating far more work needs to be done on pKa prediction methods. © 2021, The Author(s).
    view abstractdoi: 10.1007/s10822-021-00397-3
  • 2021 • 591 Event-Chain Monte-Carlo Simulations of Dense Soft Matter Systems
    Kampmann, T.A. and Müller, D. and Weise, L.P. and Vorsmann, C.F. and Kierfeld, J.
    Frontiers in Physics 9 (2021)
    We discuss the rejection-free event-chain Monte-Carlo algorithm and several applications to dense soft matter systems. Event-chain Monte-Carlo is an alternative to standard local Markov-chain Monte-Carlo schemes, which are based on detailed balance, for example the well-known Metropolis-Hastings algorithm. Event-chain Monte-Carlo is a Markov chain Monte-Carlo scheme that uses so-called lifting moves to achieve global balance without rejections (maximal global balance). It has been originally developed for hard sphere systems but is applicable to many soft matter systems and particularly suited for dense soft matter systems with hard core interactions, where it gives significant performance gains compared to a local Monte-Carlo simulation. The algorithm can be generalized to deal with soft interactions and with three-particle interactions, as they naturally arise, for example, in bead-spring models of polymers with bending rigidity. We present results for polymer melts, where the event-chain algorithm can be used for an efficient initialization. We then move on to large systems of semiflexible polymers that form bundles by attractive interactions and can serve as model systems for actin filaments in the cytoskeleton. The event chain algorithm shows that these systems form networks of bundles which coarsen similar to a foam. Finally, we present results on liquid crystal systems, where the event-chain algorithm can equilibrate large systems containing additional colloidal disks very efficiently, which reveals the parallel chaining of disks. © Copyright © 2021 Kampmann, Müller, Weise, Vorsmann and Kierfeld.
    view abstractdoi: 10.3389/fphy.2021.635886
  • 2021 • 590 Examination of the Liquid Volume Inside Metal Tanks Using Noncontact EMATs from Outside
    Rieger, K. and Erni, D. and Rueter, D.
    IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control 68 1314-1327 (2021)
    This article discusses ultrasound echo examination of the liquid volume inside a metal enclosure using noncontact electromagnetic acoustic transducers (EMATs) from outside the tank. Because only longitudinal sound waves exist in liquids, a novel and powerful EMAT design (kA currents in small coils) with a specifically enhanced transduction of longitudinal ultrasound is presented. Different wall materials (aluminum, steel, and stainless steel) and working frequencies are considered. A particular challenge, in addition to the already weak EMAT signals across an air gap, is the highly reflective interface between the metal wall and liquid because the acoustic impedances of the two media differ considerably. With thicker metal walls (here, 3mm), only either low frequencies < 100 kHz or frequencies close to the corresponding thickness resonance of the wall (here, about 1 MHz) are more suitable. The higher frequencies are preferred, as they show advantages due to a directed beam profile, shorter wavelengths in the liquid, and an overall better pulse fidelity. The simultaneous operation of several and closely neighboring EMATs demonstrates the feasibility of more demanding detection tasks, ultimately leading toward a 3-D localization inside the liquid using a noncontact EMAT array with eight independent elements. © 1986-2012 IEEE.
    view abstractdoi: 10.1109/TUFFC.2020.3022946
  • 2021 • 589 Exchange interaction in the yellow exciton series of cuprous oxide
    Rommel, P. and Main, J. and Farenbruch, A. and Yakovlev, D.R. and Bayer, M.
    Physical Review B 103 (2021)
    We experimentally and numerically investigate the exchange interaction of the yellow excitons in cuprous oxide. By varying the material parameters in the numerical calculations, we can interpret experimental findings and understand their origin in the complex band structure and central-cell corrections. In particular, we experimentally observe the reversal of the ortho- and paraexciton for the 2S yellow exciton and explain this phenomenon by an avoided crossing with the green 1S orthoexciton in a detailed numerical analysis. Furthermore, we discuss the exchange splitting as a function of the principal quantum number n and its deviation from the n-3 behavior expected from a hydrogenlike model. We also explain why the observed exchange splitting of the green 1S exciton is more than twice the splitting of the yellow 1S state. © 2021 American Physical Society.
    view abstractdoi: 10.1103/PhysRevB.103.075202
  • 2021 • 588 Existence results for non-homogeneous boundary conditions in the relaxed micromorphic model
    Ghiba, I.-D. and Neff, P. and Owczarek, S.
    Mathematical Methods in the Applied Sciences 44 2040-2049 (2021)
    In this paper, we notice a property of the extension operator from the space of tangential traces of H(curl; Ω) in the context of the linear relaxed micromorphic model, a theory that is recently used to describe the behavior of some metamaterials showing unorthodox behaviors with respect to elastic wave propagation. We show that the new property is important for existence results of strong solution for non-homogeneous boundary condition in both the dynamic and the static case. © 2020 John Wiley & Sons, Ltd.
    view abstractdoi: 10.1002/mma.6913
  • 2021 • 587 Experiences with establishing a simulation scenario of the city of Duisburg with real traffic volume
    Ma, X. and Hu, X. and Weber, T. and Schramm, D.
    Applied Sciences (Switzerland) 11 1-11 (2021)
    This article presents the experience of building a simulation scenario of the whole city of Duisburg using real traffic data. The establishment of the simulation scenario is based on road network and traffic volume. In most cases, it is hard to collect all data sources with high precision. Moreover, it is time-consuming to set up a realistic traffic scenario. Even with available data, conversion, calibration, and validation all take a large effort. With the increase of the respective simulation area, the difficulty and workload rise. In this study, a simulation scenario of the whole city of Duisburg with the road network area of 232 km2 and Origin/Destination (OD) matrix area over 800 km2 was established in the software package SUMO. Four cases with different networks and traffic volumes were built and compared with real traffic data collected from induction loops. The percentage of simulated traffic volume in real traffic volume range can be up to 72.22%. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/app11031193
  • 2021 • 586 Experimental analysis of tilt angle-dependent dynamic properties of a 5-axis milling center
    Wirtz, A. and Wilck, I. and Schmidt, N. and Biermann, D. and Wiederkehr, P.
    Manufacturing Letters 29 47-51 (2021)
    Free-formed surfaces, e.g. of dies, can be finished using 5-axis milling processes. Due to the varying tool-engagement situations and the dynamic behavior of the tool-spindle-machine system, the avoidance of chatter vibrations is challenging for these processes. Since the dynamic behavior depends on the position of the axes, the process stability can be improved by choosing beneficial tilt angles along the NC path. In this paper, a geometric physically-based process simulation was used to investigate the dependence of the calculated stability limit on the tilt angle and the speed-dependent parameters of the force model. © 2021 Society of Manufacturing Engineers (SME)
    view abstractdoi: 10.1016/j.mfglet.2021.04.007
  • 2021 • 585 Experimental and numerical investigation on the impact response of CFRP under 3-point-bending
    Nebe, M. and Schmack, T. and Schaefer, T. and Walther, F.
    Composites Part C: Open Access 4 (2021)
    The strain rate-dependent material characteristic of carbon fiber reinforced plastics (CFRP) is widely known and has been investigated in detail at coupon level. In this study, for the first time the strain rate dependent characteristic of a three-dimensional CFRP structure was investigated. The evolution of the determined strain rate dependency was correlated with the results at coupon level. For this purpose two special 3-point-bending fixtures were developed to obtain the flexural impact response of the investigated T700S DT120 prepreg system at coupon and component (hat profile) level. The rectangular coupon specimens were loaded with quasi-static to intermediate impact velocities from 3.3×10−5 to 10m s−1, while the structural sub components were tested using impact velocities from 3.3×10−5 to 1m s−1. With increasing impact velocities, the experimental tests showed a significant increase in force at first failure and maximum deflection at coupon level. The increases in force were of 52% and 120%, respectively. However, the increase for structural hat profile components was just 12.4% due to a different failure mode. The observed initial failure modes were compressive failure provoked by fiber kinking for the coupon and interlaminar shear failure for the structural component. Regardless of the different failure modes this work proves the necessity of considering the strain rate dependency of a composite material to accurately predict the maximum load capacity of a CFRP structure during a dynamic load event. Additionally, the comparison of the experimental results restults to numerical results revealed weaknesses in the prediction accuracy of the currently used models. © 2020 The Authors
    view abstractdoi: 10.1016/j.jcomc.2020.100079
  • 2021 • 584 Experimental and statistical analysis of the wear of diamond impregnated tools
    Malevich, N. and Müller, C.H. and Dreier, J. and Kansteiner, M. and Biermann, D. and De Pinho Ferreira, M. and Tillmann, W.
    Wear 468-469 (2021)
    Diamond impregnated tools are considered which are used to machine concrete. During their application, the bonding as well as the diamonds need to wear down in a certain way to gain a sharp tool. This required wear is called self-sharpening and means a continuous exposure of new diamonds. Within the development phase of diamond tools, time and cost intensive testing is necessary for the assessment of the tool performance. Hence, an extrapolation based on a minimal amount of testing is desirable to forecast the tool lifetime. A further reduction of the development and testing cost can be achieved by reducing the data needed to forecast the tool performance. Within this paper, the development of a statistical model is shown which was used to forecast the lifetime of the single diamonds on the tool. The statistical analysis is based on single segment tests which were carried out with different segment specification. During the tests, the exposed and broken out diamonds were counted to serve as the necessary input data for the statistical analysis. The counting of the diamonds on the segment was done in two different ways: based on the 2-dimensional microscopic pictures made after every minute of drilling and based on the 3-dimensional surface measurements made after every 5 min of drilling. It turns out that these two approaches of the wear analysis provide similar results. © 2020 Elsevier B.V.
    view abstractdoi: 10.1016/j.wear.2020.203574
  • 2021 • 583 Experimental investigation of centrifugal flow in rotor–stator cavities at high reynolds numbers > 108
    Schröder, T.R. and Schuster, S. and Brillert, D.
    International Journal of Turbomachinery, Propulsion and Power 6 (2021)
    The designers of radial turbomachinery need detailed information on the impact of the side chamber flow on axial thrust and torque. A previous paper investigated centripetal flow through narrow rotor–stator cavities and compared axial thrust, rotor torque and radial pressure distribution to the case without through-flow. Consequently, this paper extends the investigated range to centrifugal through-flow as it may occur in the hub side chamber of radial turbomachinery. The chosen operating conditions are representative of high-pressure centrifugal compressors used in, for example, carbon capture and storage applications as well as hydrogen compression. To date, only the Reynolds number range up to Re = 2 · 107 has been investigated for centrifugal through-flow. This paper extends the range to Reynolds numbers of Re = 2 · 108 and reports results of experimental and numerical investigations. It focuses on the radial pressure distribution in the rotor–stator cavity and shows the influence of the Reynolds number, cavity width and centrifugal mass flow rate. It therefore extends the range of available valid data that can be used to design radial turbomachinery. Additionally, this analysis compares the results to data and models from scientific literature, showing that in the higher Reynolds number range, a new correlation is required. Finally, the analysis of velocity profiles and wall shear delineates the switch from purely radial outflow in the cavity to outflow on the rotor and inflow on the stator at high Reynolds numbers in comparison to the results reported by others for Reynolds numbers up to Re = 2 · 107. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/ijtpp6020013
  • 2021 • 582 Experimental investigations of micro-meso damage evolution for a co/wc-type tool material with application of digital image correlation and machine learning
    Schneider, Y. and Zielke, R. and Xu, C. and Tayyab, M. and Weber, U. and Schmauder, S. and Tillmann, W.
    Materials 14 (2021)
    Commercial Co/WC/diamond composites are hard metals and very useful as a kind of tool material, for which both ductile and quasi-brittle behaviors are possible. This work experimentally investigates their damage evolution dependence on microstructural features. The current study investigates a different type of Co/WC-type tool material which contains 90vol.% Co instead of the usual < 50vol.%. The studied composites showed quasi-brittle behavior. An in-house-designed testing machine realizes the in-situ micro-computed tomography (µCT) under loading. This advanced equipment can record local damage in 3D during the loading. The digital image correlation technique delivers local displacement/strain maps in 2D and 3D based on tomographic images. As shown by nanoindentation tests, matrix regions near diamond particles do not possess higher hardness values than other regions. Since local positions with high stress are often coincident with those with high strain, diamonds, which aim to achieve composites with high hardnesses, contribute to the strength less than the WC phase. Samples that illustrated quasi-brittle behavior possess about 100–130 MPa higher tensile strengths than those with ductile behavior. Voids and their connections (forming mini/small cracks) dominant the detected damages, which means void initiation, growth, and coalescence should be the damage mechanisms. The void appears in the form of debonding. Still, it is uncovered that debonding between Co-diamonds plays a major role in provoking fatal fractures for composites with quasi-brittle behavior. An optimized microstructure should avoid diamond clusters and their local volume concentrations. To improve the time efficiency and the object-identification accuracy in µCT image segmentation, machine learning (ML), U-Net in the convolutional neural network (deep learning), is applied. This method takes only about 40 min to segment more than 700 images, i.e., a great improvement of the time efficiency compared to the manual work and the accuracy maintained. The results mentioned above demonstrate knowledge about the strengthening and damage mechanisms for Co/WC/diamond composites with > 50vol.% Co. The material properties for such tool materials (> 50vol.% Co) is rarely published until now. Efforts made in the ML part contribute to the realization of autonomous processing procedures in big-data-driven science applied in materials science. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/ma14133562
  • 2021 • 581 Experimental investigations on the pressure fluctuations in the sealing gap of Dry gas seals with embedded pressure sensors
    Luo, J. and Brillert, D.
    Journal of Engineering for Gas Turbines and Power 143 (2021)
    Dry gas-lubricated noncontacting mechanical seals (DGSs), most commonly found in centrifugal compressors, prevent the process of gas flow into the atmosphere. Especially when high speed is combined with high pressure, DGS is the preferred choice over other sealing alternatives. Even though the noncontacting seal is proved reliable, the ultrathin gas film can still lead to a host of potential problems due to possible contact. In order to investigate the flow field in the sealing gap and to facilitate the numerical prediction of the seal performance, a dedicated test facility is developed to carry out the measurement of key parameters in the gas film. Gas in the sealing film varies according to the seal inlet pressure, and the thickness of gas film depends on this fluctuated pressure. In this paper, the test facility, measurement methods, and the first results of static pressure measurements in the sealing gap of the DGS obtained in the described test facility are presented. An industry DGS with three-dimensional grooves on the surface of the rotating ring, where experimental investigations take place, is used. The static pressure in the gas film is measured, up to 20 bar and 8100 rpm, by several high-frequency ultraminiature pressure transducers embedded into the stationary ring. The experimental results are discussed and compared with the numerical model programed in MATLAB (Luo, J., Dohmen, H. J., and Benra, F. K., 2018, "Coupled Thermal-Structural-Fluid Numerical Analysis of Gas Lubricated Mechanical Seals,"ASME Paper No. GT2018-75458), the characteristic and magnitude of which have a good agreement with the numerical simulations. It suggests the feasibility of measuring pressure profiles of the standard industry DGS under pressurized dynamic operating conditions without altering the key components of the seal, and thereby affecting the seal performance. Copyright © 2021 by ASME.
    view abstractdoi: 10.1115/1.4049662
  • 2021 • 580 Experimental multi-scale approach to determine the local mechanical properties of foam base material in polyisocyanurate metal panels
    Gahlen, P. and Fröbel, S. and Karbach, A. and Gabriel, D. and Stommel, M.
    Polymer Testing 93 (2021)
    Polyisocyanurate (PIR) foams were examined regarding their local chemical composition using ATR-IR spectroscopy. As a special parameter the PIR: Amide III intensity ratio is to be mentioned, which represents the quantity of the formed PIR groups. Based on the local PIR: Amide III intensity ratio, the mechanical properties (Young's modulus) of the foam base material were analyzed at defined positions by AFM and Nanoindentation. It turned out that the AFM method is only suitable for qualitative analysis, because the values differ strongly from macroscopic measurements. For the measurements using nanoindentation, a new embedding method was developed, which achieves significantly more realistic and reproducible results compared to the embedding method used in the literature and shows a very good agreement with the macroscopic values. In general, it has been shown that a higher PIR: Amide III intensity ratio tends to lead to a higher Young's modulus. Nevertheless, there are other, currently unknown characteristic values which also influence the Young's modulus. © 2020 The Author(s)
    view abstractdoi: 10.1016/j.polymertesting.2020.106965
  • 2021 • 579 Experimental Reconstruction of the Few-Photon Nonlinear Scattering Matrix from a Single Quantum Dot in a Nanophotonic Waveguide
    Le Jeannic, H. and Ramos, T. and Simonsen, S.F. and Pregnolato, T. and Liu, Z. and Schott, R. and Wieck, A.D. and Ludwig, Ar. and Rotenberg, N. and García-Ripoll, J.J. and Lodahl, P.
    Physical Review Letters 126 (2021)
    Coherent photon-emitter interfaces offer a way to mediate efficient nonlinear photon-photon interactions, much needed for quantum information processing. Here we experimentally study the case of a two-level emitter, a quantum dot, coupled to a single optical mode in a nanophotonic waveguide.We carry out few-photon transport experiments and record the statistics of the light to reconstructthe scattering matrix elements of one- and two-photon components. This provides direct insight to the complex nonlinear photon interaction that contains rich many-body physics. © 2021 American Physical Society.
    view abstractdoi: 10.1103/PhysRevLett.126.023603
  • 2021 • 578 Experimental validation of formula for calculation thermal diffusivity in superlattices performed using a combination of two frequency-domain methods: Photothermal infrared radiometry and thermoreflectance
    Pawlak, M. and Kruck, T. and Spitzer, N. and Dziczek, D. and Ludwig, Ar. and Wieck, A.D.
    Applied Sciences (Switzerland) 11 (2021)
    In this paper, we validate two theoretical formula used to characterize thermal transport of superlattices at different temperatures. These formulas are used to measure cross-plane thermal conductivity and thermal boundary resistance, when it is not possible to obtain heat capacity or thermal diffusivity and in-plane thermal conductivity. We find that the most common formula for calculating thermal diffusivity and heat capacity (and density) can be used in a temperature range of −50 °C to 50 °C. This confirms that the heat capacity in the very thin silicon membranes is the same as in bulk silicon, as was preliminary investigated using an elastic continuum model. Based on the obtained thermal parameters, we can fully characterize the sample using a new procedure for characterization of the in-plane and cross-plane thermal transport properties of thin-layer and superlattice semiconductor samples. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/app11136125
  • 2021 • 577 Exploring Metamaterials’ Structures Through the Relaxed Micromorphic Model: Switching an Acoustic Screen Into an Acoustic Absorber
    Rizzi, G. and Collet, M. and Demore, F. and Eidel, B. and Neff, P. and Madeo, A.
    Frontiers in Materials 7 (2021)
    While the design of always new metamaterials with exotic static and dynamic properties is attracting deep attention in the last decades, little effort is made to explore their interactions with other materials. This prevents the conception of (meta-)structures that can enhance metamaterials’ unusual behaviors and that can be employed in real engineering applications. In this paper, we give a first answer to this challenging problem by showing that the relaxed micromorphic model with zero static characteristic length can be usefully applied to describe the refractive properties of simple meta-structures for extended frequency ranges and for any direction of propagation of the incident wave. Thanks to the simplified model’s structure, we are able to efficiently explore different configurations and to show that a given meta-structure can drastically change its overall refractive behavior when varying the elastic properties of specific meta-structural elements. In some cases, changing the stiffness of a homogeneous material which is in contact with a metamaterial’s slab, reverses the structure’s refractive behavior by switching it from an acoustic screen (total reflection) into an acoustic absorber (total transmission). The present paper clearly indicates that, while the study and enhancement of the intrinsic metamaterials’ properties is certainly of great importance, it is even more challenging to enable the conception of meta-structures that can eventually boost the use of metamaterials in real-case applications. © Copyright © 2021 Rizzi, Collet, Demore, Eidel, Neff and Madeo.
    view abstractdoi: 10.3389/fmats.2020.589701
  • 2021 • 576 Extremely Low Vapor-Pressure Data as Access to PC-SAFT Parameter Estimation for Ionic Liquids and Modeling of Precursor Solubility in Ionic Liquids
    Bülow, M. and Greive, M. and Zaitsau, D.H. and Verevkin, S.P. and Held, C.
    ChemistryOpen (2021)
    Precursor solubility is a crucial factor in industrial applications, dominating the outcome of reactions and purification steps. The outcome and success of thermodynamic modelling of this industrially important property with equations of states, such as Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT), vastly depends on the quality of the pure-component parameters. The pure-component parameters for low-volatile compounds such as ionic liquids (ILs) have been commonly estimated using mixture properties, e. g. the osmotic pressure of aqueous solutions. This leads to parameters that depend on the solvent, and transferability to other mixtures often causes poor modeling results. Mixture-independent experimental properties would be a more suitable basis for the parameter estimation offering a way to universal parameter sets. Model parameters for ILs are available in the literature [10.1016/j.fluid.2012.05.029], but they were estimated using pure-IL density data. The present work focuses on a step towards a more universal estimation strategy that includes new experimental vapor-pressure data of the pure IL. ILs exhibit an almost negligible vapor pressure in magnitude of usually 10−5 Pa even at elevated temperatures. In this work, such vapor-pressure data of a series of 1-ethyl-3-methyl-imidazolium-based [C2mim]-ILs with various IL-anions (e. g. tetrafluoroborate [BF4]−, hexafluorophosphate [PF6]−, bis(trifluoromethylsulfonyl)imide [NTf2]−) were experimentally determined and subsequently used for PC-SAFT parameter estimation. The so-determined parameters were used to predict experimental molecular precursor solubility in ILs and infinitely diluted activity coefficients of various solvents in ILs. The parameters were further compared to modeling results using classical parametrization methods (use of liquid-density data only for the molecular PC-SAFT and the ion-based electrolyte PC-SAFT). As a result, the modeled precursor solubilities using the new approach are much more precise than using the classical parametrization methods, and required binary parameters were found to be much smaller (if needed). In sum, including the pure-component vapor-pressure data of ILs opens the door towards parameter estimation that is not biased by mixture data. This procedure might be suitable also for polymers and for all kind of ionic species but needs extension to ion-specific parametrization in the long term. © 2021 The Authors. Published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/open.202000258
  • 2021 • 575 Fabrication of Gd: XFeyOzfilms using an atomic layer deposition-type approach
    Yu, P. and Beer, S.M.J. and Devi, A. and Coll, M.
    CrystEngComm 23 730-740 (2021)
    The growth of complex oxide thin films with atomic precision offers bright prospects to study improved properties and novel functionalities. Here we tackle the fabrication of gadolinium iron oxide thin films by an atomic layer deposition-type approach in which iron and gadolinium tailor-made metalorganic precursors (bis(N-isopropyl ketoiminate)iron(ii), [Fe(ipki)2] and tris(N,N′-diisopropyl-2-dimethylamido-guanidinato)gadolinium(iii), [Gd(DPDMG)3]) are alternately reacted with ozone and deposited on silicon substrates at 250 °C. The structure, chemical composition and magnetic properties of the resulting films are compared with those obtained from a commercially available ferrocene precursor [Fe(Cp)2] and [Gd(DPDMG)3]. All films resulted in cation ratio close to nominal stoichiometry with negligible amount of organic species. The tailor-made metalorganic precursors, designed to provide similar thermal behavior, result in the formation of polycrystalline Gd3Fe5O12 films coexisting with GdFeO3, Gd2O3 and Fe2O3 whereas the combination of [Fe(Cp)2] and [Gd(DPDMG)3] mainly favors the formation of Gd3Fe5O12 films coexisting with traces of Gd2O3. This study demonstrates that this is a viable route to prepare complex GdxFeyOz films and could be used for the design of complex oxide films with improved properties upon rigorous study of the compatibility of metalorganic precursors. © The Royal Society of Chemistry.
    view abstractdoi: 10.1039/d0ce01252a
  • 2021 • 574 Faceting diagram for Ag segregation induced nanofaceting at an asymmetric Cu tilt grain boundary
    Peter, N.J. and Duarte, M.J. and Kirchlechner, C. and Liebscher, C.H. and Dehm, G.
    Acta Materialia 214 (2021)
    In this work, we experimentally establish the isothermal nanofacet evolution at an asymmetric ∑5 tilt grain boundary in the Cu-Ag system using a diffusion couple approach. We investigate the nanofacet formation along the grain boundary in dependence of the Ag solute excess concentration. The initial grain boundary dissociates into asymmetric Ag-lean segments and Ag-rich symmetric (210) segments. Increasing Ag excess leads to an increase in Ag-rich facet segment length, while the length of the asymmetric facets remains constant. From this, we construct a grain boundary nanofaceting diagram deduced from our experiments relating local atomic structure, overall inclination and Ag solute excess. © 2021 The Author(s)
    view abstractdoi: 10.1016/j.actamat.2021.116960
  • 2021 • 573 Failure criterion for PA 12 multi-jet fusion additive manufactured parts
    Osswald, P.V. and Obst, P. and Mazzei Capote, G.A. and Friedrich, M. and Rietzel, D. and Witt, G.
    Additive Manufacturing 37 (2021)
    Offering the possibility of producing complex geometries in a compressed product development cycle, it comes as no surprise that additive manufacturing (AM) techniques have become attractive to multiple industries, including the automotive and aerospace segments. Unfortunately, the ubiquitous stratified build approach used by these technologies is responsible for the pain point that hinders their adoption in production of parts that will be subjected to complex loads: the junction of adjacent layers tends to have subpar mechanical properties when compared to those of the bulk material, and thus, assessing the structural integrity of an AM part becomes difficult. In the advent of the industrialization of series production of AM parts for the automotive industry, the necessity to understand and predict how and why AM parts fail under complex stress states becomes of paramount importance. This paper applies a failure criterion for materials with anisotropic properties with stress interactions, to predict failure of multi-jet fusion (MJF) parts manufactured using polyamide 12 powder. The results are compared to the failure surfaces of Selective Laser Sintering (SLS) components. Special test specimens were designed, produced, and tested to measure failure under tensile, compressive, shear, and combined loading scenarios. The results show that much like SLS, MJF parts have a notable difference in tensile and compressive strengths. Unlike SLS however, MJF parts do not exhibit a strong interaction between stresses when under combined loading. The experimental data shows an excellent fit with the failure criterion, precisely capturing the strength behavior of MJF printed parts under complex loading conditions. Of great interest in this study is that the stress interactions with MJF parts were determined to be negligible when compared to SLS specimens, which emphasizes the fact that when performing stress analyses, each one of these powder-based additive manufacturing techniques must be treated differently. © 2020 Elsevier B.V.
    view abstractdoi: 10.1016/j.addma.2020.101668
  • 2021 • 572 Failure mode map for E-PBF manufactured Ti6Al4V sandwich panels
    Kotzem, D. and Tazerout, D. and Arold, T. and Niendorf, T. and Walther, F.
    Engineering Failure Analysis 121 (2021)
    In the present work the mechanical properties and failure modes of Ti6Al4V sandwich panels made by electron beam powder bed fusion (E-PBF) were investigated. Analytical models were employed to predict the most probable failure mode of the specimen by adjusting the dimensions of the core and the face sheet. Thereby, different failure modes such as core failure, face wrinkling and face yielding were taken into account in the analytical model. Subsequently, a failure mode map was constructed. Sandwich panels for experimental validation were manufactured by E-PBF. The deformation response of the sandwich panels under three-point bending load was characterized until failure. A good agreement between analytical predictions and experimental data was found. © 2020 Elsevier Ltd
    view abstractdoi: 10.1016/j.engfailanal.2020.105159
  • 2021 • 571 Fe/Co and Ni/Co-pentlandite type electrocatalysts for the hydrogen evolution reaction
    Smialkowski, M. and Tetzlaff, D. and Hensgen, L. and Siegmund, D. and Apfel, U.-P.
    Chinese Journal of Catalysis 42 1360-1369 (2021)
    Metal-rich transition metal sulfides recently gained increasing attention as electrocatalysts for the hydrogen evolution reaction (HER), as they are capable to overcome major challenges faced by sulfide-rich metal catalysts such as limited conductivity and the necessity of nanostructuring. Herein, we present the synthesis, characterization and electrocatalytic investigation of ternary metal-rich sulfide composites FexCo9–xS8 as well as NiyCo9–yS8 (x = y = 0–4.5), which possess pentlandite-type structures. In this study, we show a stepwise alteration of the binary cobalt pentlandite Co9S8 and report on the replacement of cobalt with up to 4.5 equivalents of either iron or nickel. These altered pentlandite composites facilitate the proton reduction in acidic media at different temperatures. We furthermore show that the stoichiometric variation has a decisive influence on the electrochemical activation/deactivation behavior of the catalysts under reductive electrocatalytic conditions. Here, Co-deficient composites display an improved HER performance in contrast to Co9S8. Notably, Ni/Co compounds generally tend to show higher catalytic activities towards HER than their respective Fe/Co compounds. © 2021 Dalian Institute of Chemical Physics, the Chinese Academy of Sciences
    view abstractdoi: 10.1016/S1872-2067(20)63682-8
  • 2021 • 570 Feature extraction and neural network-based analysis on time-correlated LiDAR histograms
    Chen, G. and Gembaczka, P. and Wiede, C. and Kokozinski, R.
    PHOTOPTICS 2021 - Proceedings of the 9th International Conference on Photonics, Optics and Laser Technology 17-22 (2021)
    Time correlated single photon counting (TCSPC) is used to obtain the time-of-flight (TOF) information generated by single-photon avalanche diodes. With restricted measurements per histogram and the presence of high background light, it is challenging to obtain the TOF information in the statistical histogram. In order to improve the robustness under these conditions, the concept of machine learning is applied to the statistical histogram. Using the multi-peak extraction method, introduced by us, followed by the neural-network-based multi-peak analysis, the analysis and resources can be focused on a small amount of critical information in the histogram. Multiple possible TOF positions are evaluated and the correlated soft-decisions are assigned. The proposed method has higher robustness in allocating the coarse position (± 5 %) of TOF in harsh conditions than the case using classical digital processing. Thus, it can be applied to improve the system robustness, especially in the case of high background light. Copyright © 2021 by SCITEPRESS – Science and Technology Publications, Lda. All rights reserved.
    view abstract
  • 2021 • 569 Femtosecond pulse generation from external cavity diode laser based on self-mode-locking
    Alloush, M.A. and Brenner, C. and Calò, C. and Hofmann, M.R.
    Optics letters 46 344-347 (2021)
    In this Letter, we report optical pulse generation from a single-section diode gain chip, employed in an external cavity geometry based on the self-mode-locking regime. The gain chip emits light at 1550 nm wavelength range. The external cavity is operated at various repetition rates, ranging from 1 to 2.5 GHz. An optical pulse width of approximately 650 fs is obtained by fitting a Lorentzian distribution. A low RF spectral width of 78.875 kHz is measured corresponding to a low pulse-to-pulse RMS timing jitter of 1.273 ps. This system paves the way towards ultra-compact, cost-effective, and chirp-compensated femtosecond laser pulse sources with adjustable repetition rates.
    view abstractdoi: 10.1364/OL.415336
  • 2021 • 568 Ferrous to Ferric Transition in Fe-Phthalocyanine Driven by NO2 Exposure
    Cojocariu, I. and Carlotto, S. and Sturmeit, H.M. and Zamborlini, G. and Cinchetti, M. and Cossaro, A. and Verdini, A. and Floreano, L. and Jugovac, M. and Puschnig, P. and Piamonteze, C. and Casarin, M. and Feyer, V. and Schneider, C.M.
    Chemistry - A European Journal 27 3526-3535 (2021)
    Due to its unique magnetic properties offered by the open-shell electronic structure of the central metal ion, and for being an effective catalyst in a wide variety of reactions, iron phthalocyanine has drawn significant interest from the scientific community. Nevertheless, upon surface deposition, the magnetic properties of the molecular layer can be significantly affected by the coupling occurring at the interface, and the more reactive the surface, the stronger is the impact on the spin state. Here, we show that on Cu(100), indeed, the strong hybridization between the Fe d-states of FePc and the sp-band of the copper substrate modifies the charge distribution in the molecule, significantly influencing the magnetic properties of the iron ion. The FeII ion is stabilized in the low singlet spin state (S=0), leading to the complete quenching of the molecule magnetic moment. By exploiting the FePc/Cu(100) interface, we demonstrate that NO2 dissociation can be used to gradually change the magnetic properties of the iron ion, by trimming the gas dosage. For lower doses, the FePc film is decoupled from the copper substrate, restoring the gas phase triplet spin state (S=1). A higher dose induces the transition from ferrous to ferric phthalocyanine, in its intermediate spin state, with enhanced magnetic moment due to the interaction with the atomic ligands. Remarkably, in this way, three different spin configurations have been observed within the same metalorganic/metal interface by exposing it to different doses of NO2 at room temperature. © 2020 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/chem.202004932
  • 2021 • 567 FibeR-CNN: Expanding Mask R-CNN to improve image-based fiber analysis
    Frei, M. and Kruis, F.E.
    Powder Technology 377 974-991 (2021)
    Fiber-shaped materials (e.g. carbon nano tubes) are of great relevance, due to their unique properties but also the health risk they can impose. Unfortunately, image-based analysis of fibers still involves manual annotation, which is a time-consuming and costly process. We therefore propose the use of region-based convolutional neural networks (R-CNNs) to automate this task. Mask R-CNN, the most widely used R-CNN for semantic segmentation tasks, is prone to errors when it comes to the analysis of fiber-shaped objects. Hence, a new architecture – FibeR-CNN – is introduced and validated. FibeR-CNN combines two established R-CNN architectures (Mask and Keypoint R-CNN) and adds additional network heads for the prediction of fiber widths and lengths. As a result, FibeR-CNN is able to surpass the mean average precision of Mask R-CNN by 33% (11 percentage points) on a novel test data set of fiber images. © 2020 Elsevier B.V.
    view abstractdoi: 10.1016/j.powtec.2020.08.034
  • 2021 • 566 Finite-size correction for slab supercell calculations of materials with spontaneous polarization
    Yoo, S.-H. and Todorova, M. and Wickramaratne, D. and Weston, L. and Walle, C.G.V. and Neugebauer, J.
    npj Computational Materials 7 (2021)
    The repeated slab approach has become a de facto standard to accurately describe surface properties of materials by density functional theory calculations with periodic boundary conditions. For materials exhibiting spontaneous polarization, we show that the conventional scheme of passivation with pseudo hydrogen is unable to realize a charge-neutral surface. The presence of a net surface charge induces via Gauss’s law a macroscopic electric field through the slab and results in poor size convergence with respect to the thickness of the slab. We propose a modified passivation method that accounts for the effect of spontaneous polarization, describes the correct bulk limits and boosts convergence with respect to slab thickness. The robustness, reliability, and superior convergence of energetics and electronic structure achieved by the proposed method are demonstrated using the example of polar ZnO surfaces. © 2021, The Author(s).
    view abstractdoi: 10.1038/s41524-021-00529-1
  • 2021 • 565 Finite-temperature interplay of structural stability, chemical complexity, and elastic properties of bcc multicomponent alloys from ab initio trained machine-learning potentials
    Gubaev, K. and Ikeda, Y. and Tasnádi, F. and Neugebauer, J. and Shapeev, A.V. and Grabowski, B. and Körmann, F.
    Physical Review Materials 5 (2021)
    An active learning approach to train machine-learning interatomic potentials (moment tensor potentials) for multicomponent alloys to ab initio data is presented. Employing this approach, the disordered body-centered cubic (bcc) TiZrHfTax system with varying Ta concentration is investigated via molecular dynamics simulations. Our results show a strong interplay between elastic properties and the structural ω phase stability, strongly affecting the mechanical properties. Based on these insights we systematically screen composition space for regimes where elastic constants show little or no temperature dependence (elinvar effect). © 2021 American Physical Society.
    view abstractdoi: 10.1103/PhysRevMaterials.5.073801
  • 2021 • 564 Firm efficiency and stock returns during the COVID-19 crisis
    Neukirchen, D. and Engelhardt, N. and Krause, M. and Posch, P.N.
    Finance Research Letters (2021)
    We investigate the relationship between firm efficiency and stock returns during the COVID-19 pandemic. We find that highly efficient firms experienced at least 9.44 percentage points higher cumulative returns during the market collapse. A long-short portfolio consisting of efficient and inefficient firms would have also yielded a significantly positive weekly return of 3.53% on average. Overall, our results show that firm efficiency has significant explanatory power for stock returns during the crisis period. © 2021 Elsevier Inc.
    view abstractdoi: 10.1016/j.frl.2021.102037
  • 2021 • 563 First-principles computational exploration of ferromagnetism in monolayer GaS via substitutional doping
    Khan, R. and Rahman, A.U. and Zhang, Q. and Kratzer, P. and Ramay, S.M.
    Journal of Physics Condensed Matter 33 (2021)
    Using first-principles calculations, functionalization of the monolayer-GaS crystal structure through N or Cr-doping at all possible lattice sites has been investigated. Our results show that pristine monolayer-GaS is an indirect-bandgap, non-magnetic semiconductor. The bandgap can be tuned and a magnetic moment (MM) can be induced by the introduction of N or Cr atomic anion/cation doping in monolayer GaS. For instance, the intrinsic character of monolayer GaS can be changed by substitution of N for the S-site to p-type, while substitution of Cr at the S-site or Ga-site induces half-metallicity at sufficiently high concentrations. The defect states are located in the electronic bandgap region of the GaS monolayer. These findings help to extend the application of monolayer-GaS structures in nano-electronics and spintronics. Since the S-sites at the surface are more easily accessible to doping in experiment, we chose the S-site for further investigations. Finally, we perform calculations with ferromagnetic (FM) and antiferromagnetic (AFM) alignment of the MMs at the dopants. For pairs of impurities of the same species at low concentrations we find Cr atoms to prefer the FM state, while N atoms prefer the AFM state, both for impurities on opposite surfaces of the GaS monolayer and for impurities sharing a common Ga neighbor sitting at the same surface. Extending our study to higher concentrations of Cr atoms, we find that clusters of four Cr atoms prefer AFM coupling, whereas the FM coupling is retained for Cr atoms at larger distance arranged on a honeycomb lattice. For the latter arrangement, we estimate the FM Curie temperature T C to be 241 K. We conclude that the Cr-doped monolayer-GaS crystal structure offers enhanced electronic and magnetic properties and is an appealing candidate for spintronic devices operating close to room temperature. © 2021 IOP Publishing Ltd.
    view abstractdoi: 10.1088/1361-648X/ac04ce
  • 2021 • 562 Flexibilization of Biorefineries: Tuning Lignin Hydrogenation by Hydrogen Partial Pressure
    Cao, Z. and Xu, Y. and Lyu, P. and Dierks, M. and Morales-García, Á. and Schrader, W. and Nachtigall, P. and Schüth, F.
    ChemSusChem 14 373-378 (2021)
    The present study describes an interesting and practical catalytic system that allows flexible conversion of lignin into aromatic or aliphatic hydrocarbons, depending on the hydrogen partial pressure. A combination of experiment and theory shows that the product distribution between aromatics and aliphatics can be simply tuned by controlling the availability of hydrogen on the catalyst surface. Noticeably, these pathways lead to almost complete oxygen removal from lignin biomass, yielding high-quality hydrocarbons. Thus, hydrogen–lignin co-refining by using this catalytic system provides high flexibility in hydrogen storage/consumption towards meeting different regional and temporal demands. © 2020 The Authors. ChemSusChem published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/cssc.202002248
  • 2021 • 561 Force reduction by electrical assistance in incremental sheet-bulk metal forming of gears
    Wernicke, S. and Hahn, M. and Detzel, A. and Tillmann, W. and Stangier, D. and Lopes Dias, N.F. and Tekkaya, A.E.
    Journal of Materials Processing Technology 296 (2021)
    Producing load-adapted and functionally integrated components by flexible and resource efficient processes has gained importance within industries like the automotive sector in recent years. A promising new class of processes that enables a local adaption of the sheet thickness is Sheet-Bulk Metal Forming (SBMF). While the incremental procedure (iSBMF) only requires a moderate forming force, forming of high strength steels leads to a tool load resulting in a significantly reduced tool life. One approach to reduce tool loads is the utilization of the so called electroplastic effect (EPE). This study for the first time identifies the potential of the EPE on a temporary reduction of the forming force during the iSBMF of gears targeting an improvement of the tool life. The steel grades DC04 and HSM700 HD are characterized considering the EPE under uniaxial tension. Based on the characterization, the current density and temperature increase are modelled numerically and analytically for the incremental gear forming process. Moreover, the impact of EPE on strain hardening, grain texture and forming force is determined. By a local insulation of the forming tool based on a PVD coating and the application of an electrical current, a temporary force reduction of up to 55 % is observed whereas the strain hardening effect remains almost unaffected. © 2021
    view abstractdoi: 10.1016/j.jmatprotec.2021.117194
  • 2021 • 560 Formation of Co-Au Core-shell nanoparticles with thin gold shells and soft magnetic ϵ?cobalt cores ruled by thermodynamics and kinetics
    Johny, J. and Kamp, M. and Prymak, O. and Tymoczko, A. and Wiedwald, U. and Rehbock, C. and Schürmann, U. and Popescu, R. and Gerthsen, D. and Kienle, L. and Shaji, S. and Barcikowski, S.
    Journal of Physical Chemistry C 125 9534-9549 (2021)
    Bimetallic core-shell nanoparticles (CSNPs), where a ferromagnetic core (e.g., Co) is surrounded by a noblemetal thin plasmonic shell (e.g., Au), are highly interesting for applications in biomedicine and catalysis. Chemical synthesis of such structures, however, requires multistep procedures and often suffers from impaired oxidation resistance of the core. Here, we utilized a one-step environmentally friendly laser ablation in liquid technique to fabricate colloidal Co?Au CSNPs with core?shell yields up to 78% in mass. An in-depth analysis of the CSNPs down to single-particle levels revealed the presence of a unique nested core?shell structure with a very thin gold-rich shell, a nanocrystalline ϵ-cobalt sublayer, and a nested gold-rich core. The generated Co?Au CSNPs feature soft magnetic properties, while all gold-rich phases (thin shells and nested cores) exhibit a face-centered cubic solid solution with substantial cobalt substitution. The experimental findings are backed by refined thermodynamic surface energy calculations, which more accurately predict the predominance of solid solution and core?shell phase structures in correlation with particle size and nominal composition. Based on the Co?Au bulk phase diagram and in conjunction with previously reported results on the Fe?Au core?shell system as well as Co? Pt controls, we deduce four general rules for core?shell formation in non-or partially miscible laser-generated bimetallic nanosystems. ©2021 American Chemical Society.
    view abstractdoi: 10.1021/acs.jpcc.1c02138
  • 2021 • 559 Forward: Information modelling of tunnelling and underground infrastructure: Technology and applications
    Fang, Y. and Ninic, J. and Meschke, G. and König, M. and Zhang, Q.
    Tunnelling and Underground Space Technology 116 (2021)
    doi: 10.1016/j.tust.2021.104067
  • 2021 • 558 Frazil ice in the antarctic marginal ice zone
    Paul, F. and Mielke, T. and Schwarz, C. and Schröder, J. and Rampai, T. and Skatulla, S. and Audh, R.R. and Hepworth, E. and Vichi, M. and Lupascu, D.C.
    Journal of Marine Science and Engineering 9 (2021)
    Frazil ice, consisting of loose disc-shaped ice crystals, is the first ice that forms in the annual cycle in the marginal ice zone (MIZ) of the Antarctic. A sufficient number of frazil ice crystals form the surface “grease ice” layer, playing a fundamental role in the freezing processes in the MIZ. As soon as the ocean waves are sufficiently damped by a frazil ice cover, a closed ice cover can form. In this article, we investigate the rheological properties of frazil ice, which has a crucial influence on the growth of sea ice in the MIZ. An in situ test setup for measuring temperature and rheological properties was developed. Frazil ice shows shear thinning flow behavior. The presented measurements enable real-data-founded modelling of the annual ice cycle in the MIZ. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/jmse9060647
  • 2021 • 557 Free Molecule Studies by Perturbed γ-γ Angular Correlation: A New Path to Accurate Nuclear Quadrupole Moments
    Haas, H. and Röder, J. and Correia, J.G. and Schell, J. and Fenta, A.S. and Vianden, R. and Larsen, E.M.H. and Aggelund, P.A. and Fromsejer, R. and Hemmingsen, L.B.S. and Sauer, S.P.A. and Lupascu, D.C. and Amaral, V.S.
    Physical Review Letters 126 (2021)
    Accurate nuclear quadrupole moment values are essential as benchmarks for nuclear structure models and for the interpretation of experimentally determined nuclear quadrupole interactions in terms of electronic and molecular structure. Here, we present a novel route to such data by combining perturbed γ-γ angular correlation measurements on free small linear molecules, realized for the first time within this work, with state-of-the-art ab initio electronic structure calculations of the electric field gradient at the probe site. This approach, also feasible for a series of other cases, is applied to Hg and Cd halides, resulting in Q(Hg199,5/2-)=+0.674(17) b and Q(Cd111,5/2+)=+0.664(7) b. © 2021 authors. Published by the American Physical Society.
    view abstractdoi: 10.1103/PhysRevLett.126.103001
  • 2021 • 556 Frenkel pairs cause elastic softening in zirconia: Theory and experiments
    Kathiria, R. and Wolf, D.E. and Raj, R. and Jongmanns, M.
    New Journal of Physics 23 (2021)
    Recent results from molecular dynamics simulations have shown that significant concentrations of Frenkel pairs can be introduced by the proliferation of phonons lying at the edge of the Brillouin zone and when above the Debye temperature. Following the work of Granato (2014 Eur. Phys. J. B 87 18) we extend those calculations to the influence of Frenkels on the elastic modulus. Significant softening is predicted which is confirmed by in situ measurements of the elastic modulus during flash. Frenkel pairs have been proposed to play a central role in the flash phenomena. © 2021 The Author(s). Published by IOP Publishing Ltd on behalf of the Institute of Physics and Deutsche Physikalische Gesellschaft.
    view abstractdoi: 10.1088/1367-2630/abf704
  • 2021 • 555 From diffusive mass transfer in Stokes flow to low Reynolds number Marangoni boats
    Ender, H. and Kierfeld, J.
    European Physical Journal E 44 (2021)
    We present a theory for the self-propulsion of symmetric, half-spherical Marangoni boats (soap or camphor boats) at low Reynolds numbers. Propulsion is generated by release (diffusive emission or dissolution) of water-soluble surfactant molecules, which modulate the air–water interfacial tension. Propulsion either requires asymmetric release or spontaneous symmetry breaking by coupling to advection for a perfectly symmetrical swimmer. We study the diffusion–advection problem for a sphere in Stokes flow analytically and numerically both for constant concentration and constant flux boundary conditions. We derive novel results for concentration profiles under constant flux boundary conditions and for the Nusselt number (the dimensionless ratio of total emitted flux and diffusive flux). Based on these results, we analyze the Marangoni boat for small Marangoni propulsion (low Peclet number) and show that two swimming regimes exist, a diffusive regime at low velocities and an advection-dominated regime at high swimmer velocities. We describe both the limit of large Marangoni propulsion (high Peclet number) and the effects from evaporation by approximative analytical theories. The swimming velocity is determined by force balance, and we obtain a general expression for the Marangoni forces, which comprises both direct Marangoni forces from the surface tension gradient along the air–water–swimmer contact line and Marangoni flow forces. We unravel whether the Marangoni flow contribution is exerting a forward or backward force during propulsion. Our main result is the relation between Peclet number and swimming velocity. Spontaneous symmetry breaking and, thus, swimming occur for a perfectly symmetrical swimmer above a critical Peclet number, which becomes small for large system sizes. We find a supercritical swimming bifurcation for a symmetric swimmer and an avoided bifurcation in the presence of an asymmetry. © 2021, The Author(s).
    view abstractdoi: 10.1140/epje/s10189-021-00034-9
  • 2021 • 554 From digital models to numerical analysis for mechanised tunnelling: A fully automated design-through-analysis workflow
    Ninic, J. and Alsahly, A. and Vonthron, A. and Bui, H.-G. and Koch, C. and König, M. and Meschke, G.
    Tunnelling and Underground Space Technology 107 (2021)
    Large infrastructure projects involving the construction of tunnels in urban areas constitute complex, integrated and multi-disciplinary systems, which require building and construction information modelling as well as computational design assessment tools for decision making during all project phases and during their complete life cycle. Even if the underlying information needed for computational analysis is stored in an information model, the translation to computational models is still cumbersome and requires significant manual work for model generation and set-up as well as excessive computing resources and time. To address these shortcomings, this paper presents a systematic summary of concepts for integrated information modelling, numerical analysis and visualisation for urban mechanized tunnelling. Our first approach “BIM-to-FEM” is characterised by a fully automated link for error-free data exchange between a standalone Tunnelling Information Model and the process-oriented simulation model for mechanized tunnelling “ekate”. In the second approach “SATBIM”, a fully automated data exchange workflow is established between a parametric multi-level information model for tunnelling and multi-level numerical models based on both Finite Element and Isogeometric Analysis, where meta models are employed for real-time design assessment. We discuss the different applications of these concepts, such as scenario-based exploration of design alternatives, real-time design assessment within a TIM based on meta-models, and the potentials of using these models for the process control during construction. Furthermore, we present two case studies where real project data has been used for the integration of information and numerical modelling. The examples in this paper indicate clear advantages of this approach compared to traditional approaches in terms of efficiency of modelling achieved by reduced user interactions and error-free information exchange, and show the benefits of multi-level model representation and real-time analysis tasks. © 2020 Elsevier Ltd
    view abstractdoi: 10.1016/j.tust.2020.103622
  • 2021 • 553 From volatility to solubility: Thermodynamics of imidazolium-based ionic liquids containing chloride and bromide anions
    Zaitsau, D.H. and Siewert, R. and Pimerzin, A.A. and Bülow, M. and Held, C. and Loor, M. and Schulz, S. and Verevkin, S.P.
    Journal of Molecular Liquids 323 (2021)
    Ionic liquids (ILs) are effectively used for tuning the composition and the morphology of nanoparticles or stabilizing agents for nanoparticles for catalytic dehydrogenation. Thermodynamic properties of ionic liquids, e.g. vapor pressures and vaporization enthalpies help optimise these processes. Vapor pressures and vaporization enthalpies of the series of 1-alkyl-3-methylimidazolium ionic liquids with chloride and bromide anions have been measured by using quartz-crystal microbalance (QCM). Possible thermal decomposition pathways of [C2C1Im][Br] during vaporization were analyzed by using high-level quantum-chemical methods. These theoretical results explained and supported the absence of decomposition in QCM experimental conditions. According to the measured vapor pressures the [CnC1Im][Cl] and [CnC1Im][Br] series are very suitable for catalytic applications, taking also into account their sufficient thermal stability at the level of 523–543 K. Solubility parameters of ILs and practically relevant solutes were assessed with help of experimental vaporization enthalpies. © 2020 Elsevier B.V.
    view abstractdoi: 10.1016/j.molliq.2020.114998
  • 2021 • 552 From π-Bonded Gallapnictenes to Nucleophilic, Redox-Active Metal-Coordinated Pnictanides
    Krüger, J. and Wölper, C. and Schulz, S.
    Angewandte Chemie - International Edition 60 3572-3575 (2021)
    A comprehensive reactivity study of gallapnictenes LGaEGa(Cl)L (E=As, Sb; L=HC[C(Me)N(Ar)]2, Ar=Dip=2,6-i-Pr2C6H3) proved the nucleophilic character of the pnictogen and the electrophilic nature of the Ga atom. Reactions of LGaEGa(Cl)L with imidazolium chloride [IPrH][Cl] yielded {[LGa(Cl)]2E−}{IPrH+} (E=As 1, Sb 2), and those with HCl and MeI gave pnictanes [LGa(Cl)]2EH (E=As 5, Sb 6) and L(I)GaE(Me)Ga(Cl)L (E=As 7, Sb 8). Pnictanides 1 and 2 also react with [H(OEt2)2][BArF4] (BArF4=B(C6F5)4) to 5 and 6, while reactions with MeI yielded [LGa(Cl)]2EMe (E=As 9, Sb 10). Single electron oxidation reactions of pnictanides 1 and 2 gave the corresponding radicals [LGa(Cl)]2E. (E=As, Sb). © 2020 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/anie.202013618
  • 2021 • 551 Frustrated flexibility in metal-organic frameworks
    Pallach, R. and Keupp, J. and Terlinden, K. and Frentzel-Beyme, L. and Kloß, M. and Machalica, A. and Kotschy, J. and Vasa, S.K. and Chater, P.A. and Sternemann, C. and Wharmby, M.T. and Linser, R. and Schmid, R. and Henke, S.
    Nature Communications 12 (2021)
    Stimuli-responsive flexible metal-organic frameworks (MOFs) remain at the forefront of porous materials research due to their enormous potential for various technological applications. Here, we introduce the concept of frustrated flexibility in MOFs, which arises from an incompatibility of intra-framework dispersion forces with the geometrical constraints of the inorganic building units. Controlled by appropriate linker functionalization with dispersion energy donating alkoxy groups, this approach results in a series of MOFs exhibiting a new type of guest- and temperature-responsive structural flexibility characterized by reversible loss and recovery of crystalline order under full retention of framework connectivity and topology. The stimuli-dependent phase change of the frustrated MOFs involves non-correlated deformations of their inorganic building unit, as probed by a combination of global and local structure techniques together with computer simulations. Frustrated flexibility may be a common phenomenon in MOF structures, which are commonly regarded as rigid, and thus may be of crucial importance for the performance of these materials in various applications. © 2021, The Author(s).
    view abstractdoi: 10.1038/s41467-021-24188-4
  • 2021 • 550 Fully Algebraic Two-Level Overlapping Schwarz Preconditioners for Elasticity Problems
    Heinlein, A. and Hochmuth, C. and Klawonn, A.
    Lecture Notes in Computational Science and Engineering 139 531-539 (2021)
    Different parallel two-level overlapping Schwarz preconditioners with Generalized Dryja–Smith–Widlund (GDSW) and Reduced dimension GDSW (RGDSW) coarse spaces for elasticity problems are considered. GDSW type coarse spaces can be constructed from the fully assembled system matrix, but they additionally need the index set of the interface of the corresponding nonoverlapping domain decomposition and the null space of the elasticity operator, i.e., the rigid body motions. In this paper, fully algebraic variants, which are constructed solely from the uniquely distributed system matrix, are compared to the classical variants which make use of this additional information; the fully algebraic variants use an approximation of the interface and an incomplete algebraic null space. Nevertheless, the parallel performance of the fully algebraic variants is competitive compared to the classical variants for a stationary homogeneous model problem and a dynamic heterogenous model problem with coefficient jumps in the shear modulus; the largest parallel computations were performed on 4096 MPI (Message Passing Interface) ranks. The parallel implementations are based on the Trilinos package FROSch. © 2021, Springer Nature Switzerland AG.
    view abstractdoi: 10.1007/978-3-030-55874-1_52
  • 2021 • 549 Functional central limit theorems for multivariate Bessel processes in the freezing regime
    Voit, M. and Woerner, J.H.C.
    Stochastic Analysis and Applications 39 136-156 (2021)
    Multivariate Bessel processes (Formula presented.) describe interacting particle systems of Calogero-Moser-Sutherland type and are related with β-Hermite and β-Laguerre ensembles. They depend on a root system and a multiplicity k. Recently, several limit theorems were derived for (Formula presented.) with fixed starting point. Moreover, the SDEs of (Formula presented.) were used to derive strong laws of large numbers for (Formula presented.) with starting points of the form (Formula presented.) with x in the interior of the Weyl chambers. Here we provide associated almost sure functional central limit theorems which are locally uniform in t. The Gaussian limit processes admit explicit representations in terms of the solutions of associated deterministic ODEs. © 2020 Taylor & Francis Group, LLC.
    view abstractdoi: 10.1080/07362994.2020.1786402
  • 2021 • 548 Functional Rotaxanes in Catalysis
    Kwamen, C. and Niemeyer, J.
    Chemistry - A European Journal 27 175-186 (2021)
    Mechanically interlocked molecules (MIMs) have gained attention in the field of catalysis due to their unique molecular properties. Central to MIMs, rotaxanes are highly promising and attractive supramolecular catalysts due to their unique three-dimensional structures and the flexibility of their subcomponents. This Minireview discusses the use of rotaxanes in organocatalysis and transition-metal catalysis. © 2020 The Authors. Published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/chem.202002876
  • 2021 • 547 Functionalization of textiles by deposition of UV-cured organic thin layers with charge storage properties for electronic and environmental technology
    Bahners, T. and Tsarkova, L. and Gebert, B. and Gutmann, J.S.
    Progress in Organic Coatings 157 (2021)
    Charge storing concepts receive an increasing interest in a view of the fast development of flexible textile electronics. The paper reports on initial charging capacity and charge conservation properties of technical textiles modified with UV-cured organic thin films. The results have been evaluated for three types of textile substrates and two types of monomers, an acrylic and allylic, with differing UV-absorption spectral characteristics. The most pronounced increase of the decay time from a few minutes to several hours has been found for polyethylene terephthalate (PET) fibers coated with thin layers of UV-cured tetraallyloxyethane monomer, representing ca 1 wt-% add-on. The mechanisms behind the measured effects could be rationalized along the concepts of “grafting to” and “grafting from” polymerization, which defines the tethering density, layer thickness and the degree of cross-linking. The behavior proved to be stable both under normal conditions and under elevated temperature/humidity conditions. The reported results provide design strategies for thin organic coatings with regards to targeted applications. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.porgcoat.2021.106332
  • 2021 • 546 Fundamental investigations on wear evolution of machining Inconel 718
    Potthoff, N. and Wiederkehr, P.
    Procedia CIRP 99 171-176 (2021)
    Nickel-based superalloys are often used in aerospace industry for different applications, e.g., blisks or turbine blades. Due to its high strength and corrosion resistance, materials like Inconel 718 lead to a poor machinability and, thus, to a high amount of tool wear. In this paper, the influence of different process parameter values on the tool wear is analyzed. For the fundamental investigations, the tool wear evolution was examined for two different path strategies with and without coolant. To identify suitable process parameter values, the width of flank wear land and process forces were analyzed based on a screening design of experiments. © 2021 The Authors. Published by Elsevier B.V.
    view abstractdoi: 10.1016/j.procir.2021.03.024
  • 2021 • 545 Fundamentals of electro-mechanically coupled cohesive zone formulations for electrical conductors
    Kaiser, T. and Menzel, A.
    Computational Mechanics 68 51-67 (2021)
    Motivated by the influence of (micro-)cracks on the effective electrical properties of material systems and components, this contribution deals with fundamental developments on electro-mechanically coupled cohesive zone formulations for electrical conductors. For the quasi-stationary problems considered, Maxwell’s equations of electromagnetism reduce to the continuity equation for the electric current and to Faraday’s law of induction, for which non-standard jump conditions at the interface are derived. In addition, electrical interface contributions to the balance equation of energy are discussed and the restrictions posed by the dissipation inequality are studied. Together with well-established cohesive zone formulations for purely mechanical problems, the present developments provide the basis to study the influence of mechanically-induced interface damage processes on effective electrical properties of conductors. This is further illustrated by a study of representative boundary value problems based on a multi-field finite element implementation. © 2021, The Author(s).
    view abstractdoi: 10.1007/s00466-021-02019-z
  • 2021 • 544 Future perspectives on in-vitro diagnosis of drug allergy by the lymphocyte transformation test
    Fatangare, A. and Glässner, A. and Sachs, B. and Sickmann, A.
    Journal of Immunological Methods 495 (2021)
    This article aims to envisage future perspectives of the lymphocyte transformation test (LTT). We describe the select innovative techniques, which can be integrated at different stages of the LTT to potentially improve the sensitivity, specificity, or practicability of the LTT. We first focus upon the cell sorting techniques comprising immunomagnetic cell separation and flow cytometry, which can be implemented prior and after the LTT culturing step to concentrate and quantify specific immune cell types. Further, we elaborate upon three important omics techniques such as transcriptomics, proteomics, and metabolomics, which can be integrated downstream of the LTT to analyze molecular changes in specific immune cells following drug induced activation and proliferation. We also develop visions, how state of the art techniques used in other scientific fields, can be transferred and applied in the context of in-vitro detection of drug allergy. © 2021
    view abstractdoi: 10.1016/j.jim.2021.113072
  • 2021 • 543 Future research directions in the machining of Inconel 718
    De Bartolomeis, A. and Newman, S.T. and Jawahir, I.S. and Biermann, D. and Shokrani, A.
    Journal of Materials Processing Technology 297 (2021)
    Inconel 718 is the most popular nickel-based superalloy, extensively used in aerospace, automotive and energy industries owing to its extraordinary thermomechanical properties. It is also notoriously a difficult-to-cut material, due to its short tool life and low productivity in machining operations. Despite significant progress in cutting tool technologies, the machining of Inconel 718 is still considered a grand challenge. This paper provides a comprehensive review of recent advances in machining Inconel 718. The progress in cutting tools’ materials, coatings, geometries and surface texturing for machining Inconel 718 is reviewed. The investigation is focused on the most adopted tool materials for machining of Inconel 718, namely Cubic Boron Nitrides (CBNs), ceramics and coated carbides. The thermal conductivity of cutting tool materials has been identified as a major parameter of interest. Process control, based on sensor data for monitoring the machining of Inconel 718 alloy and detecting surface anomalies and tool wear are reviewed and discussed. This has been identified as the major step towards realising real-time control for machining safety critical Inconel 718 components. Recent advances in various processes, e.g. turning, milling and drilling for machining Inconel 718 are investigated and discussed. Recent studies related to machining additively manufactured Inconel 718 are also discussed and compared with the wrought alloy. Finally, the state of current research is established, and future research directions proposed. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.jmatprotec.2021.117260
  • 2021 • 542 Gas-Phase Synthesis of Silicon-Rich Silicon Nitride Nanoparticles for High Performance Lithium–Ion Batteries
    Kilian, S.O. and Wiggers, H.
    Particle and Particle Systems Characterization 38 (2021)
    The practical application of silicon-based anodes is severely hindered by continuous capacity fade during cycling. A very promising way to stabilize silicon in lithium–ion battery (LIB) anodes is the utilization of nanostructured silicon-rich silicon nitride (SiNx), a conversion-type anode material. Here, SiNx with structure sizes in the sub-micrometer range have been synthesized in a hot-wall reactor by pyrolysis of monosilane and ammonia. This work focusses on understanding process parameter–particle property correlations. Further, a model for the growth of SiNx nanoparticles in this hot–wall–reactor design is proposed. This synthesis concept is of specific interest regarding simplicity, flexibility, and scalability: A way utilizing any mixtures of precursor gases to build multi-functional nanoparticles that can be directly used for LIBs instead of focusing on modification of nanostructures after they have been formed. Lab-scale production rates as high as 30 g h−1 can be easily achieved and further scaled. SiN0.7 nanoparticles provide a first cycle coulombic efficiency of 54%, a specific discharge capacity of 1367 mAh g−1, and a capacity retention over 80% after 300 cycles at 0.5 C (j = 0.68 mA cm−2). These results imply that silicon-rich silicon nitrides are promising candidates for high-performance LIBs with very high durability. © 2021 The Authors. Particle & Particle Systems Characterization published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/ppsc.202100007
  • 2021 • 541 Gate voltage dependence of noise distribution in radio-frequency reflectometry in gallium arsenide quantum dots
    Shinozaki, M. and Muto, Y. and Kitada, T. and Nakajima, T. and Delbecq, M.R. and Yoneda, J. and Takeda, K. and Noiri, A. and Ito, T. and Ludwig, Ar. and Wieck, A.D. and Tarucha, S. and Otsuka, T.
    Applied Physics Express 14 (2021)
    We investigate gate voltage dependence of electrical readout noise in high-speed rf reflectometry using gallium arsenide quantum dots. The fast Fourier transform spectrum from the real time measurement reflects build-in device noise and circuit noise including the resonator and the amplifier. We separate their noise spectral components by model analysis. Detail of gate voltage dependence of the flicker noise is investigated and compared to the charge sensor sensitivity. We point out that the dominant component of the readout noise changes by the measurement integration time. © 2021 The Japan Society of Applied Physics
    view abstractdoi: 10.35848/1882-0786/abe41f
  • 2021 • 540 Gate-Controlled Field Emission Current from MoS2 Nanosheets
    Pelella, A. and Grillo, A. and Urban, F. and Giubileo, F. and Passacantando, M. and Pollmann, E. and Sleziona, S. and Schleberger, M. and Di Bartolomeo, A.
    Advanced Electronic Materials 7 (2021)
    Monolayer molybdenum disulfide (MoS2) nanosheets, obtained via chemical vapor deposition onto SiO2/Si substrates, are exploited to fabricate field-effect transistors with n-type conduction, high on/off ratio, steep subthreshold slope, and good mobility. The transistor channel conductance increases with the reducing air pressure due to oxygen and water desorption. Local field emission measurements from the edges of the MoS2 nanosheets are performed in high vacuum using a tip-shaped anode. It is demonstrated that the voltage applied to the Si substrate back-gate modulates the field emission current. Such a finding, that it is attributed to gate-bias lowering of the MoS2 electron affinity, enables a new field-effect transistor based on field emission. © 2020 Wiley-VCH GmbH
    view abstractdoi: 10.1002/aelm.202000838
  • 2021 • 539 Gd-Ru Nanoparticles Supported on Zr0.5Ce0.5O2Nanorods for Dry Methane Reforming
    Das, S. and Sengupta, M. and Bag, A. and Saini, A. and Muhler, M. and Bordoloi, A.
    ACS Applied Nano Materials 4 2547-2557 (2021)
    Dry reforming of methane is considered a potential reaction for the utilization of waste greenhouse gases to generate valuable chemicals. However, catalyst deactivation under a harsh reaction condition appears as the main obstacle toward its commercialization. In the present work, a facile hydrothermal synthesis procedure was adopted to prepare a robust Ru-based catalyst. Among the various combinations, a 1% Ru supported over Zr0.5Ce0.5O2 nanorod catalyst showed enhanced coke resistance and almost stable activity during 200 h activity analysis. Promotion of Ru/Zr0.5Ce0.5O2 with an optimum amount of Gd2O3 improved catalyst stability, which was attributed to the strong interaction of Ru with Gd2O3 leading to smaller Ru particle size (∼5 nm) and an improved OSC was inhibiting coke deposition. Promotion with 0.5% Gd2O3 further lowered the apparent activation energy of methane conversion to ∼20.6 kcal/mol without changing the reaction orders significantly. DFT calculation confirmed, due to the orbital similarity, methane cracking is preferred over Ru atoms and CO2 activation occurred on Gd atoms. ©
    view abstractdoi: 10.1021/acsanm.0c03140
  • 2021 • 538 Gene transfection achieved by utilizing antibacterial calcium phosphate nanoparticles for enhanced regenerative therapy
    Xiang, C. and Tenkumo, T. and Ogawa, T. and Kanda, Y. and Nakamura, K. and Shirato, M. and Sokolova, V. and Epple, M. and Kamano, Y. and Egusa, H. and Sasaki, K.
    Acta Biomaterialia 119 375-389 (2021)
    Protamine-coated multi-shell calcium phosphate (CaP) was developed as a non-viral vector for tissue regeneration therapy. CaP nanoparticles loaded with different amounts of plasmid DNA encoding bone morphogenetic protein 2 (BMP-2) and insulin-like growth factor 1 (IGF-1) were used to treat MC3T3E1 cells, and the yield of the released BMP-2 or IGF-1 was measured using ELISA 3 days later. Collagen scaffolds containing CaP nanoparticles were implanted into rat cranial bone defects, and BMP-2 and IGF-1 yields, bone formation, and bone mineral density enhancement were evaluated 28 days after gene transfer. The antibacterial effects of CaP nanoparticles against Streptococcus mutans and Aggregatibacter actinomycetemcomitans increased with an increase in the protamine dose, while they were lower for Staphylococcus aureus and Porphyromonas gingivalis. In the combination treatment with BMP-2 and IGF-1, the concentration ratio of BMP-2 and IGF-1 is an important factor affecting bone formation activity. The calcification activity and OCN mRNA of MC3T3E1 cells subjected to a BMP-2:IGF-1 concentration ratio of 1:4 was higher at 14 days. During gene transfection treatment, BMP-2 and IGF-1 were released simultaneously after gene transfer; the loaded dose of the plasmid DNA encoding IGF-1 did not impact the BMP-2 or IGF-1 yield or new bone formation ratio in vitro and in vivo. In conclusion, two growth factor-releasing systems were developed using an antibacterial gene transfer vector, and the relationship between the loaded plasmid DNA dose and resultant growth factor yield was determined in vitro and in vivo. © 2020
    view abstractdoi: 10.1016/j.actbio.2020.11.003
  • 2021 • 537 Generation of ultrashort keV Ar+ ion pulses via femtosecond laser photoionization
    Golombek, A. and Breuer, L. and Danzig, L. and Kucharczyk, P. and Schleberger, M. and Sokolowski-Tinten, K. and Wucher, A.
    New Journal of Physics 23 (2021)
    Ion beams with energies in the keV regime are widely utilized in solid-state physics, but the ultrafast dynamics triggered by an ion impact onto a solid surface is to date exclusively accessible via simulations based on many untested assumptions and model parameters. A possible experimental access rests on the availability of a laser-synchronized ion source delivering sufficiently short ion pulses for time resolved pump-probe experiments. Here, we demonstrate a new miniaturized ion optical bunching setup for the creation of rare gas ion pulses using strong-field femtosecond laser photoionization. Neutral Ar gas atoms at room temperature are intercepted by a 50 fs, 800 nm laser pulse focused to ∼10 μm spot size. We demonstrate the generation of monoenergetic 2 keV Ar+ ion pulses with 180 ps duration (FWHM) at laser peak intensities around 1014 W cm−2 and of multiply charged Arq+ ions (q = 1-5) at higher laser intensities. The results are in good agreement with detailed ion trajectory simulations, which show that the temporal resolution is essentially limited by the initial (thermal) velocity spread of the generated photo-ions, indicating the possibility to achieve even better time resolution by cooling the gas prior to ionization. © 2021 The Author(s). Published by IOP Publishing Ltd on behalf of the Institute of Physics and Deutsche Physikalische Gesellschaft
    view abstractdoi: 10.1088/1367-2630/abe443
  • 2021 • 536 Generation of Vortex Waves Using Crossed 2λ-Dipole Antennas
    Hassan, M.H. and Sievert, B. and Rennings, A. and Erni, D.
    15th European Conference on Antennas and Propagation, EuCAP 2021 (2021)
    In this paper, a simple and novel method is presented to generate Orbital Angular Momentum (OAM) waves for the first OAM mode order with radial polarization. This approach consists of two crossed 2λ-dipole antennas (CDA) where each antenna is fed in the center with identical amplitude but with a 90° phase shift to radiate vortex waves. Further, in order to enhance the gain, the number of crossed dipoles can be increased. Therefore, the simulation of two and four CDA is performed with the full-wave simulator FEKO. Moreover, a two and four crossed 2λ-dipole phased array of two elements can increase the directivity of the radiation in the broadside direction. A reflector of 100 mm × 100 mm is also added for two and four crossed 2λ-dipole antennas to improve the gain in the same direction. © 2021 EurAAP.
    view abstractdoi: 10.23919/EuCAP51087.2021.9411239
  • 2021 • 535 Global kinome profiling reveals DYRK1A as critical activator of the human mitochondrial import machinery
    Walter, C. and Marada, A. and Suhm, T. and Ernsberger, R. and Muders, V. and Kücükköse, C. and Sánchez-Martín, P. and Hu, Z. and Aich, A. and Loroch, S. and Solari, F.A. and Poveda-Huertes, D. and Schwierzok, A. and Pommereni...
    Nature Communications 12 (2021)
    The translocase of the outer mitochondrial membrane TOM constitutes the organellar entry gate for nearly all precursor proteins synthesized on cytosolic ribosomes. Thus, TOM presents the ideal target to adjust the mitochondrial proteome upon changing cellular demands. Here, we identify that the import receptor TOM70 is targeted by the kinase DYRK1A and that this modification plays a critical role in the activation of the carrier import pathway. Phosphorylation of TOM70Ser91 by DYRK1A stimulates interaction of TOM70 with the core TOM translocase. This enables transfer of receptor-bound precursors to the translocation pore and initiates their import. Consequently, loss of TOM70Ser91 phosphorylation results in a strong decrease in import capacity of metabolite carriers. Inhibition of DYRK1A impairs mitochondrial structure and function and elicits a protective transcriptional response to maintain a functional import machinery. The DYRK1A-TOM70 axis will enable insights into disease mechanisms caused by dysfunctional DYRK1A, including autism spectrum disorder, microcephaly and Down syndrome. © 2021, The Author(s).
    view abstractdoi: 10.1038/s41467-021-24426-9
  • 2021 • 534 Grain boundary energy landscape from the shape analysis of synthetically stabilized embedded grains
    Schratt, A.A. and Steinbach, I. and Mohles, V.
    Computational Materials Science 193 (2021)
    The Gibbs free energy of grain boundaries (GBs) in Al bicrystals has been investigated by Molecular Dynamics (MD) simulations. In our novel approach, one grain is fully embedded in a large matrix grain with fixed misorientation. Hence all inclinations are considered simultaneously since the boundary covers the full orientation subspace. A synthetical driving force is employed to counteract the shrinkage of the embedded grain by the capillary forces. Hence, the number of atoms of the embedded grain is kept constant, but its shape adjusts itself at elevated temperatures in order to minimize the total GB energy. The quasi-equilibrium shapes are used to derive the GB energy γ(n) as functions of the GB plane normal n. For GBs with the misorientations Σ5〈001〉 and Σ7〈111〉, analytical functions were derived and validated in a mesoscopic front-tracking simulation: the latter simulations recovered the grain shapes observed in MD simulations. For the Σ5〈001〉 misorientation it is shown that the anisotropy of γ(n) varies quite strongly with temperature. For a Σ9〈110〉 misorientation, the derived numerical energy function was found to be rather complex, showing pronounced energy minima for mixed tilt/twist GBs parallel to 111 crystal planes. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.commatsci.2021.110384
  • 2021 • 533 Heteroternary cucurbit[8]uril complexes as supramolecular scaffolds for self-assembled bifunctional photoredoxcatalysts
    Lutz, F. and Lorenzo-Parodi, N. and Schmidt, T.C. and Niemeyer, J.
    Chemical Communications 57 2887-2890 (2021)
    The self-assembly of bifunctional photoredoxcatalysts is reported. A series of photosensitizers and water-reducing catalysts were functionalized with viologen- and naphthol-units, respectively. Subsequent formation of the heteroternary cucurbit[8]uril-viologen-naphthol complexes was used for the constitution of bifunctional photoredoxcatalysts for hydrogen generation. © The Royal Society of Chemistry 2021.
    view abstractdoi: 10.1039/d0cc08025j
  • 2021 • 532 Higgs-like pair amplitude dynamics in superconductor-quantum-dot hybrids
    Kamp, M. and Sothmann, B.
    Physical Review B 103 (2021)
    We consider a quantum dot weakly tunnel coupled to superconducting reservoirs. A finite superconducting pair amplitude can be induced on the dot via the proximity effect. We investigate the dynamics of the induced pair amplitude after a quench and under periodic driving of the system by means of a real-time diagrammatic approach. We find that the quench dynamics is dominated by an exponential decay towards equilibrium. In contrast, the periodically driven system can sustain coherent oscillations of both the amplitude and the phase of the induced pair amplitude in analogy to Higgs and Nambu-Goldstone modes in driven bulk superconductors. © 2021 American Physical Society.
    view abstractdoi: 10.1103/PhysRevB.103.045414
  • 2021 • 531 Highly Efficient and Selective Aerobic Oxidation of Cinnamyl Alcohol under Visible Light over Pt-Loaded NaNbO3Enriched with Oxygen Vacancies by Ni Doping
    Zhao, G. and Bonke, S.A. and Schmidt, S. and Wang, Z. and Hu, B. and Falk, T. and Hu, Y. and Rath, T. and Xia, W. and Peng, B. and Schnegg, A. and Weng, Y. and Muhler, M.
    ACS Sustainable Chemistry and Engineering 9 5422-5429 (2021)
    NaNbO3 enriched with oxygen vacancies by Ni doping was successfully synthesized via a polymerized complex method and applied as a photocatalyst in the oxidation of cinnamyl alcohol (CA) to cinnamaldehyde in air. Reaction rates as high as 45 μmol h-1 were achieved under visible light with a high apparent quantum efficiency of 67.2% and excellent chemoselectivity larger than 99%. UV-vis, electron paramagnetic resonance, and attenuated total reflectance infrared spectroscopy results indicate that the CA molecules preferentially adsorb at the oxygen vacancies, thus enabling electron transfer between coordinatively bound CA and NaNbO3 under visible light, inducing CA oxidation. The photocatalytic aerobic oxidation of CA is assumed to proceed via the one-photon pathway with H2O2 as the coupled product. The photodeposited Pt nanoparticles on the surface not only enhanced the oxidation rate but also improved the selectivity to cinnamaldehyde substantially because of the fast decomposition of formed H2O2, in this way avoiding its consecutive oxidation by H2O2. The oxygen vacancies on the surface generated by Ni doping are identified to play a decisive role in the chemisorption of cinnamyl alcohol and the interface charge transfer. © 2021 American Chemical Society. All rights reserved.
    view abstractdoi: 10.1021/acssuschemeng.1c00460
  • 2021 • 530 Highly Ordered Mesoporous Co3O4 Electrocatalyst for Efficient, Selective, and Stable Oxidation of 5-Hydroxymethylfurfural to 2,5-Furandicarboxylic Acid
    Wang, C. and Bongard, H.-J. and Yu, M. and Schüth, F.
    ChemSusChem (2021)
    Electrochemical oxidation of biomass substrates to valuable bio-chemicals is highly attractive. However, the design of efficient, selective, stable, and inexpensive electrocatalysts remains challenging. Here it is reported how a 3D highly ordered mesoporous Co3O4/nickel foam (om-Co3O4/NF) electrode fulfils those criteria in the electrochemical oxidation of 5-hydroxymethylfurfural (HMF) to value-added 2,5-furandicarboxylic acid (FDCA). Full conversion of HMF and an FDCA yield of &gt;99.8 % are achieved with a faradaic efficiency close to 100 % at a potential of 1.457 V vs. reversible hydrogen electrode. Such activity and selectivity to FDCA are attributed to the fast electron transfer, high electrochemical surface area, and reduced charge transfer resistance. More impressively, remarkable catalyst stability under long-term testing is obtained with 17 catalytic cycles. This work highlights the rational design of metal oxides with ordered meso-structures for electrochemical biomass conversion. © 2021 The Authors. ChemSusChem published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/cssc.202002762
  • 2021 • 529 Highly Selective Guiding Springs for Large Displacements in Surface MEMS
    Schmitt, P. and Schmitt, L. and Tsivin, N. and Hoffmann, M.
    Journal of Microelectromechanical Systems 30 597-611 (2021)
    In this paper we introduce the concept, modelling and analysis of triangular and sinusoidal springs intended for large in-plane translational displacements for MEMS-guiding applications. The proposed spring systems combine the advantages of minimal space requirement, low stiffness in the axial direction and high mechanical resistance in off-axis directions. An analytical model for the description of the force-displacement characteristic of triangular springs is derived considering typical mechanical constraints. Based on the model, geometrical parameters of the springs influencing linearity and selectivity with respect to the in- and off-axis stiffness are analyzed. The validity of the models is demonstrated by finite element analysis and experimental verification realized by silicon-on-insulator demonstrators. [2020-0360] © 1992-2012 IEEE.
    view abstractdoi: 10.1109/JMEMS.2021.3074822
  • 2021 • 528 High-Power Lensless THz Imaging of Hidden Objects
    Mansourzadeh, S. and Damyanov, D. and Vogel, T. and Wulf, F. and Kohlhaas, R.B. and Globisch, B. and Schultze, T. and Hoffmann, M. and Balzer, J.C. and Saraceno, C.J.
    IEEE Access 9 6268-6276 (2021)
    The potential of pulsed THz radiation for time-of-flight imaging applications is well recognized. However, advances in this field are currently severely limited by the low average power of ultrafast THz sources. Typically, this results in impractically long acquisition times and a loss in resolution and contrast. These limitations make imaging of the objects in real-life scenarios impossible. Here, conclusively, the potential of state-of-the-art high-average power THz time-domain spectrometer (TDS), driven by a 100-W class, one-box ultrafast oscillator for imaging applications is shown by demonstrating lensless THz imaging in reflection mode of a dielectric sample with low reflectivity. Images obtained with our home-built 20-mW average power THz-TDS system show a significant contrast enhancement compared to a state-of-the-art commercial THz-TDS with less than 200~mu text{W} of average power. Our unique setup even allows us to obtain images of such an object with high-contrast hidden inside a medium-density fiberboard (MDF) box. This opens the door to THz time-of-flight imaging of concealed objects of unknown shape and orientation in various real-life scenarios which were so far impossible to realize. © 2013 IEEE.
    view abstractdoi: 10.1109/ACCESS.2020.3048781
  • 2021 • 527 High-Temperature Oxidation in Dry and Humid Atmospheres of the Equiatomic CrMnFeCoNi and CrCoNi High- and Medium-Entropy Alloys
    Stephan-Scherb, C. and Schulz, W. and Schneider, M. and Karafiludis, S. and Laplanche, G.
    Oxidation of Metals 95 105-133 (2021)
    Abstract: Surface degradation phenomena of two model equiatomic alloys from the CrMnFeCoNi alloy system were investigated in 2% O2 and 10% H2O (pO2 = 0.02 and 10−7 atm, respectively) at 800 °C for times up to 96 h. The crystallographic structures, morphologies, and chemical compositions of the corrosion layers developing on CrMnFeCoNi and CrCoNi were comparatively analyzed by mass gain analysis, X-ray diffraction, and scanning electron microscopy combined with energy-dispersive X-ray spectroscopy and electron backscatter diffraction. The oxidation resistance of CrMnFeCoNi is relatively poor due to the fast growth of porous Mn-oxide(s). CrCoNi forms an external chromia layer that is dense and continuous in a dry 2% O2 atmosphere. This layer buckles and spalls off after exposure to 10% H2O atmosphere. Beneath the chromia layer, a Cr-depleted zone forms in the CrCoNi alloy in both environments. As the oxide scale spalls off in the H2O-containing atmosphere, a secondary chromia layer was observed and correspondingly enlarges the Cr-depleted zone. In contrast, as the chromia layer remains without significant spallation when CrCoNi is exposed to a dry oxidizing atmosphere, the region depleted in Cr is narrower. Graphic Abstract: [Figure not available: see fulltext.]. © 2020, The Author(s).
    view abstractdoi: 10.1007/s11085-020-10014-7
  • 2021 • 526 Historical Perspective of the Journal of Chemical & Engineering Data's Published Topics, 1956-2020
    Gardas, R.L. and Kofke, D.A. and Pini, R. and Sadowski, G. and Schwarz, C.E. and Siepmann, J.I. and Wu, J.
    Journal of Chemical and Engineering Data 66 1555-1556 (2021)
    doi: 10.1021/acs.jced.1c00193
  • 2021 • 525 Holistic View on Materials Development: Water Electrolysis as a Case Study
    Klemenz, S. and Stegmüller, A. and Yoon, S. and Felser, C. and Tüysüz, H. and Weidenkaff, A.
    Angewandte Chemie - International Edition (2021)
    In view of rising ecological awareness, materials development is primarily aimed at improving the performance and efficiency of innovative and more elaborate materials. However, a materials performance figure of merit should include essential aspects of materials: environmental impact, economic constraints, technical feasibility, etc. Thus, we promote the inclusion of sustainability criteria already during the materials design process. With such a holistic design approach, new products may be more likely to meet the circular economy requirements than when traditional development strategies are pursued. Using catalysts for water electrolysis as an example, we present a modelling method based on experimental data to holistically evaluate processes. © 2021 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/anie.202105324
  • 2021 • 524 Hollow CeO2@Co2N Nanosheets Derived from Co-ZIF-L for Boosting the Oxygen Evolution Reaction
    Zhang, J. and He, W. and Aiyappa, H.B. and Quast, T. and Dieckhöfer, S. and Öhl, D. and Junqueira, J.R.C. and Chen, Y.-T. and Masa, J. and Schuhmann, W.
    Advanced Materials Interfaces 8 (2021)
    Rational design of highly active electrocatalysts for the oxygen evolution reaction (OER) is critical to improving overall electrochemical water splitting efficiency. This study suggests hollow CeO2@Co2N nanosheets synthesized using Co-ZIF-L as a precursor, followed by a hydrothermal reaction and a nitridation process as very attractive OER catalysts. The increased activity is supposed to be due to nitridation and strong electronic interaction between CeO2 and Co2N that contribute to the formation of active CoOOH phase. The synthesized CeO2@Co2N exhibits low overpotentials of 219 and 345 mV at OER current densities of 10 and 100 mA cm–2, respectively, as well as a long-term durability of 30 h at a comparatively high current density of 100 mA cm−2. © 2021 The Authors. Advanced Materials Interfaces published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/admi.202100041
  • 2021 • 523 How Hydrogen Admixture Changes Plasma Jet Characteristics in Spray Processes at Low Pressure
    Mauer, G.
    Plasma Chemistry and Plasma Processing 41 109-132 (2021)
    In plasma spraying, hydrogen is widely used as a secondary working gas besides argon. In particular under low pressure, there are strong effects on the plasma jet characteristics even by small hydrogen percentages. Under such conditions, fundamental mechanisms like diffusion and recombination are affected while this is less relevant under atmospheric conditions. This was investigated for argon–hydrogen mixtures by optical emission spectroscopy (OES). The small electron densities under the investigated low pressure conditions implied specific difficulties in the application of several OES-based methods which are discussed in detail. Adding hydrogen to the plasma gas effected an increased plasma enthalpy. Moreover, the jet expanded radially as the reactive part of the thermal conductivity was enhanced by recombination of atomic hydrogen so that the shock waves were less reflected at the cold jet rims. In the jet cores, the lowest temperatures were found for the highest hydrogen admixture because the energy consumption due to the dissociation of molecular hydrogen outbalanced the increase of the plasma enthalpy. Variations in the radial temperature profiles were related to the jet structure and radial thermal conductivity. The local hydrogen–argon concentration ratios revealed an accumulation of hydrogen atoms at the jet rims. Clear indications were found, that higher hydrogen contents promoted the fast recombination of electrons and ions. However, it is assumed that the transport properties of the plasma were hardly affected by this, since the electron densities and thus the ionization degrees were generally small due to the low pressure conditions. © 2020, The Author(s).
    view abstractdoi: 10.1007/s11090-020-10143-6
  • 2021 • 522 How the Physicochemical Properties of the Bulk Material Affect the Ablation Crater Profile, Mass Balance, and Bubble Dynamics During Single-Pulse, Nanosecond Laser Ablation in Water
    Kalus, M.-R. and Barcikowski, S. and Gökce, B.
    Chemistry - A European Journal 27 5978-5991 (2021)
    Understanding the key steps that drive the laser-based synthesis of colloids is a prerequisite for learning how to optimize the ablation process in terms of nanoparticle output and functional design of the nanomaterials. Even though many studies focus on cavitation bubble formation using single-pulse ablation conditions, the ablation efficiency and nanoparticle properties are typically investigated under prolonged ablation conditions with repetition rate lasers. Linking single-pulse and multiple-pulse ablation is difficult due to limitations induced by gas formation cross-effects, which occur on longer timescales and depend on the target materials’ oxidation-sensitivity. Therefore, this study investigates the ablation and cavitation bubble dynamics under nanosecond, single laser pulse conditions for six different bulk materials (Au, Ag, Cu, Fe, Ti, and Al). Also, the effective threshold fluences, ablation volumes, and penetration depths are quantified for these materials. The thermal and chemical properties of the corresponding bulk materials not only favor the formation of larger spot sizes but also lead to the highest molar ablation efficiencies for low melting materials such as aluminum. Furthermore, the concept of the cavitation bubble growth linked with the oxidation sensitivity of the ablated material is discussed. With this, evidence is provided that intensive chemical reactions occurring during the very early timescale of ablation are significantly enhanced by the bubble collapse. © 2021 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/chem.202005087
  • 2021 • 521 How to Design Digitalized Laboratories?: Lessons Learned from Implementing Virtual and Remote Labs
    Strenger, N. and Frerich, S.
    Advances in Intelligent Systems and Computing 1231 AISC 103-111 (2021)
    This contribution is showing ways to overcome issues on the way to digitalized laboratories in engineering education. The results presented in this paper were gained throughout a long-term study: 10 different laboratories were surveyed over a time period of 8 years. A non-standardized survey method was chosen for this evaluation, including a semi-structured guideline with open questions developed during several phases of pre-testing. The didactics and technical concepts of the laboratories are addressed, as well as challenges encountered during implementation and operation. Key findings of the whole study were identified by looking at didactical set-ups, technical aspects, and project managing topics. Although some aspects of hands-on experiments on-site were easily conveyed into virtual or remote laboratories, others needed to overcome severe impairments. However, personal commitment and financial support were identified as important success factors. By addressing original learning objectives as well as technical challenges that arose during set-up and digitalization of the laboratories, the results of this contribution clearly emphasize the connection between didactical purposes and technical realization. In some cases, both virtual and remote laboratories needed additional assistance in rephrasing learning objectives and adapting them throughout the process. © 2021, Springer Nature Switzerland AG.
    view abstractdoi: 10.1007/978-3-030-52575-0_8
  • 2021 • 520 How to get from static to dynamic electromagnetism
    König, J.
    European Journal of Physics 42 (2021)
    We demonstrate how to derive Maxwell’s equations, including Faraday’s law and Maxwell’s correction to Ampère’s law, by generalizing the description of static electromagnetism to dynamical situations. Thereby, Faraday’s law is introduced as a consequence of the relativity principle rather than an experimental fact, in contrast to the historical course and common textbook presentations. As a by-product, this procedure yields explicit expressions for the infinitesimal Lorentz and, upon integration, the finite Lorentz transformation. The proposed approach helps to elucidate the relation between Galilei and Lorentz transformations and provides an alternative derivation of the Lorentz transformation without explicitly referring to the speed of light. © 2021 European Physical Society
    view abstractdoi: 10.1088/1361-6404/abee60
  • 2021 • 519 Hybrid chitosan/gelatin/nanohydroxyapatite scaffolds promote odontogenic differentiation of dental pulp stem cells and in vitro biomineralization
    Vagropoulou, G. and Trentsiou, M. and Georgopoulou, A. and Papachristou, E. and Prymak, O. and Kritis, A. and Epple, M. and Chatzinikolaidou, M. and Bakopoulou, A. and Koidis, P.
    Dental Materials 37 e23-e36 (2021)
    Objective: Hybrid chitosan/gelatin/nanohydroxyapatite (CS/Gel/nHA) scaffolds have attracted considerable interest in tissue engineering (TE) of mineralized tissues. The present study aimed to investigate the potential of CS/Gel/nHA scaffolds loaded with dental pulp stem cells (DPSCs) to induce odontogenic differentiation and in vitro biomineralization. Methods: CS/Gel/nHA scaffolds were synthesized by freeze-drying, seeded with DPSCs, and characterized with flow cytometry. Scanning Electron Microscopy (SEM), live/dead staining, and MTT assays were used to evaluate cell morphology and viability; real-time PCR for odontogenesis-related gene expression analysis; SEM-EDS (Energy Dispersive X-ray spectroscopy), and X-ray Diffraction analysis (XRD) for structural and chemical characterization of the mineralized constructs, respectively. Results: CS/Gel/nHA scaffolds supported viability and proliferation of DPSCs over 14 days in culture. Gene expression patterns indicated pronounced odontogenic shift of DPSCs, evidenced by upregulation of DSPP, BMP-2, ALP, and the transcription factors RunX2 and Osterix. SEM-EDS showed the production of a nanocrystalline mineralized matrix inside the cell-based and - to a lesser extent - the cell-free constructs, with a time-dependent production of net-like nanocrystals (appr. 25−30 nm in diameter). XRD analysis gave the crystallite size (D = 50 nm) but could not distinguish between the initially incorporated and the biologically produced nHA. Significance: This is the first study validating the potential of CS/Gel/nHA scaffolds to support viability and proliferation of DPSCs, and to provide a biomimetic microenvironment favoring odontogenic differentiation and in vitro biomineralization without the addition of any inductive factors, including dexamethasone and/or growth/morphogenetic factors. These results reveal a promising strategy towards TE of mineralized dental tissues. © 2020 The Academy of Dental Materials
    view abstractdoi: 10.1016/j.dental.2020.09.021
  • 2021 • 518 Hybrid State Estimation-A Contribution Towards Reliability Enhancement of Artificial Neural Network Estimators
    Sieberg, P.M. and Blume, S. and Reicherts, S. and Maas, N. and Schramm, D.
    IEEE Transactions on Intelligent Transportation Systems (2021)
    Data-driven models are obtained purely from data without complex theoretical modeling and without explicit model knowledge. This results in black box models whose traceability and reliability constitute a major challenge. This contribution addressed this issue and presents a novel hybrid estimation method, which enhances the reliability of artificial neural networks. Within this method, a simple model based on physical knowledge secures a model based on an artificial neural network. An unscented Kalman filter realizes the interaction of the two individual models. Thereby, a confidence level determines which model is trusted to a greater extent or even entirely. As part of the method for adjusting this confidence level, the input variables of the artificial neural network are related to the data used in training. The more often the artificial neural network has encountered a situation in the training process, the greater the confidence level will be. Finally, the confidence level is used to set the covariances of the unscented Kalman filter. In this contribution, the method is presented using the application of roll angle estimation for passenger cars. By using the hybrid method the reliability of the estimation is increased in comparison to the artificial neural network. For this purpose, sensor malfunctions as well as a sensor failure are simulated. These disturbances are compensated by the introduced method. In addition, the hybrid state estimator increases the estimation quality compared to the individual estimators. The proposed method can be applied to any problem, where knowledge-based models are available to secure data-driven models. IEEE
    view abstractdoi: 10.1109/TITS.2021.3055800
  • 2021 • 517 -Hydrogenases: Maturation and reactivity of enzymatic systems and overview of biomimetic models
    Kleinhaus, J.T. and Wittkamp, F. and Yadav, S. and Siegmund, D. and Apfel, U.-P.
    Chemical Society Reviews 50 1668-1784 (2021)
    While hydrogen plays an ever-increasing role in modern society, nature has utilized hydrogen since a very long time as an energy carrier and storage molecule. Among the enzymatic systems that metabolise hydrogen, [FeFe]-hydrogenases are one of the most powerful systems to perform this conversion. In this light, we will herein present an overview on developments in [FeFe]-hydrogenase research with a strong focus on synthetic mimics and their application within the native enzymatic environment. This review spans from the biological assembly of the natural enzyme and the highly controversial discussed mechanism for the hydrogen generation to the synthesis of multiple mimic platforms as well as their electrochemical behaviour. © The Royal Society of Chemistry.
    view abstractdoi: 10.1039/d0cs01089h
  • 2021 • 516 Identification of Active Sites in the Catalytic Oxidation of 2-Propanol over Co1+xFe2–xO4 Spinel Oxides at Solid/Liquid and Solid/Gas Interfaces
    Falk, T. and Budiyanto, E. and Dreyer, M. and Pflieger, C. and Waffel, D. and Büker, J. and Weidenthaler, C. and Ortega, K.F. and Behrens, M. and Tüysüz, H. and Muhler, M. and Peng, B.
    ChemCatChem 13 2942-2951 (2021)
    A series of Co1+xFe2–xO4 (0≤x≤2) spinel nanowires was synthesized by nanocasting using SBA-15 silica as hard template, which was characterized by X-ray powder diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy. The Co1+xFe2–xO4 spinels were applied in the aerobic oxidation of aqueous 2-propanol solutions to systematically study the influence of exposed Co and Fe cations on the catalytic properties. The activity of the catalysts was found to depend strongly on the Co content, showing an exponential increase of the reaction rate with increasing Co content. Ensembles of Co3+cus (coordinatively unsaturated) sites were identified as the active sites for selective 2-propanol oxidation, which are assumed to consist of more than six Co ions. In addition, gas-phase oxidation with and without water vapor co-feeding was performed to achieve a comparison with liquid-phase oxidation kinetics. An apparent activation energy of 94 kJ mol−1 was determined for 2-propanol oxidation over Co3O4 in the liquid phase, which is in good agreement with the gas-phase oxidation in the presence of water vapor. In contrast to gas-phase conditions, the catalysts showed high stability and reusability in the aqueous phase with constant conversion in three consecutive runs. © 2021 The Authors. ChemCatChem published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/cctc.202100352
  • 2021 • 515 Identification of thermal material parameters for thermo-mechanically coupled material models: Verification and model dependency
    Rose, L. and Menzel, A.
    Meccanica (2021)
    The possibility of accurately identifying thermal material parameters on the basis of a simple tension test is presented, using a parameter identification framework for thermo-mechanically coupled material models on the basis of full field displacement and temperature field measurements. Main objective is to show the impact of the material model formulation on the results of such an identification with respect to accuracy and uniqueness of the result. To do so, and as a proof of concept, the data of two different experiments is used. One experiment including cooling of the specimen, due to ambient temperature, and one without specimen cooling. The main constitutive relations of two basic material models are summarised (associated and non-associated plasticity), whereas both models are extended so as to introduce an additional material parameter for the thermodynamically consistent scaling of dissipated energy. The chosen models are subjected to two parameter identifications each, using the data of either experiment and focusing on the determination of thermal material parameters. The influence of the predicted dissipated energy of the models on the identification process is investigated showing that a specific material model formulation must be chosen carefully. The material model with associated evolution equations used within this work does neither allow a unique identification result, nor is any of the solutions for the underlying material parameters close to literature values. In contrast to that, a stable, that is locally unique, re-identification of the literature values is possible for the boundary problem at hand if the model with non-associated evolution equation is used and if cooling is included in the experimental data. © 2021, The Author(s).
    view abstractdoi: 10.1007/s11012-020-01267-2
  • 2021 • 514 Identifying shifts between two regression curves
    Dette, H. and Dhar, S.S. and Wu, W.
    Annals of the Institute of Statistical Mathematics (2021)
    This article studies the problem whether two convex (concave) regression functions modelling the relation between a response and covariate in two samples differ by a shift in the horizontal and/or vertical axis. We consider a nonparametric situation assuming only smoothness of the regression functions. A graphical tool based on the derivatives of the regression functions and their inverses is proposed to answer this question and studied in several examples. We also formalize this question in a corresponding hypothesis and develop a statistical test. The asymptotic properties of the corresponding test statistic are investigated under the null hypothesis and local alternatives. In contrast to most of the literature on comparing shape invariant models, which requires independent data the procedure is applicable for dependent and non-stationary data. We also illustrate the finite sample properties of the new test by means of a small simulation study and two real data examples. © 2021, The Institute of Statistical Mathematics, Tokyo.
    view abstractdoi: 10.1007/s10463-020-00771-2
  • 2021 • 513 Identifying the Bottleneck for Heat Transport in Metal–Organic Frameworks
    Wieser, S. and Kamencek, T. and Dürholt, J.P. and Schmid, R. and Bedoya-Martínez, N. and Zojer, E.
    Advanced Theory and Simulations 4 (2021)
    Controlling the transport of thermal energy is key to most applications of metal–organic frameworks (MOFs). Analyzing the evolution of the effective local temperature, the interfaces between the metal nodes and the organic linkers are identified as the primary bottlenecks for heat conduction. Consequently, changing the bonding strength at that node–linker interface and the mass of the metal atoms can be exploited to tune the thermal conductivity. This insight is generated employing molecular dynamics simulations in conjunction with advanced, ab initio parameterized force fields. The focus of the present study is on MOF-5 as a prototypical example of an isoreticular MOF. However, the key findings prevail for different node structures and node–linker bonding chemistries. The presented results lay the foundation for developing detailed structure-to-property relationships for thermal transport in MOFs with the goal of devising strategies for the application-specific optimization of heat conduction. © 2020 The Authors. Advanced Theory and Simulations published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/adts.202000211
  • 2021 • 512 Ignition and propagation of nanosecond pulsed plasmas in distilled water - Negative vs positive polarity applied to a pin electrode
    Grosse, K. and Falke, M. and Von Keudell, A.
    Journal of Applied Physics 129 (2021)
    Nanosecond plasmas in liquids are being used for water treatment, electrolysis, or biomedical applications. The exact nature of these very dynamic plasmas and, most importantly, their ignition physics are strongly debated. The ignition itself may be explained by two competing hypotheses: ignition in water may occur (i) via field effects at the tip of the electrode followed by tunneling of electrons in between water molecules causing field ionization or (ii) via gaseous processes of electron multiplication in nanovoids that are created from liquid ruptures due to the strong electric field gradients. Both hypotheses are supported by theory, but experimental data are very sparse due to the difficulty in monitoring the very fast processes in space and time. In this paper, we analyze nanosecond plasmas in water that are created by applying a positive and a negative polarity to a sharp tungsten electrode. The main diagnostics are fast camera measurements and fast emission spectroscopy. It is shown that plasma ignition is dominated by field effects at the electrode-liquid interface either as field ionization for positive polarity or as field emission for negative polarity. This leads to a hot tungsten surface at a temperature of 7000 K for positive polarity, whereas the surface temperature is much lower for negative polarity. At ignition, the electron density reaches 4 × 10 25 m - 3 for the positive and 2 × 10 25 m - 3 for the negative polarity. At the same time, the emission of the H α light for the positive polarity is four times higher than that for the negative polarity. During plasma propagation, the electron densities are almost identical of the order of 1- 2 × 10 25 m - 3 followed by a decay after the end of the pulse over 15 ns. It is concluded that plasma propagation is governed by field effects in a low density region that is created either by nanovoids or by density fluctuations in supercritical water surrounding the electrode that is created by the pressure and temperature at the moment of plasma ignition. © 2021 Author(s).
    view abstractdoi: 10.1063/5.0045697
  • 2021 • 511 Immobilization of peroxidase on textile carrier materials and their application in the bleaching of colored whey
    Courth, K. and Binsch, M. and Ali, W. and Ingenbosch, K. and Zorn, H. and Hoffmann-Jacobsen, K. and Gutmann, J.S. and Opwis, K.
    Journal of Dairy Science 104 1548-1559 (2021)
    Textiles represent promising support materials for enzymes. The goal of the present work was to investigate the immobilization of commercial peroxidase on a polyester needle felt and the repeated use in the gentle degradation of norbixin in whey from dairy cheese as a practical application. High enzyme loads were obtained by a 2-step immobilization procedure. First, the number of functional groups on the textile surface was increased by a modification with amino-functional polyvinylamine. Second, the enzyme was immobilized by using 2 types of crosslinking agents. Due to the iron content of peroxidase, inductively coupled plasma–optical emission spectrometry was used for the quantitative determination of the enzyme load on the textile. The enzyme activity was evaluated using common 2,2'-azino-di-(3-ethylbenzthiazoline-6-sulfonic acid) assay for peroxidases. By the variation of enzyme input and crosslinker concentration, a maximal enzyme load of 80 mg/g of textile was achieved, and a maximum specific activity of 57 U/g of textile. For the visualization of the enzyme on the fiber surface, fluorescence microscopy as well as scanning probe microscopy were used. The immobilized peroxidase showed significant activity, even after 50 reuse cycles. In addition, the potential of the new support and enzyme combination in commercial whey bleaching was demonstrated successfully on a 10-L scale. © 2021 American Dairy Science Association
    view abstractdoi: 10.3168/jds.2019-17110
  • 2021 • 510 Impact of incorporated drugs on material properties of amorphous solid dispersions
    Flügel, K. and Schmidt, K. and Mareczek, L. and Gäbe, M. and Hennig, R. and Thommes, M.
    European Journal of Pharmaceutics and Biopharmaceutics 159 88-98 (2021)
    Formulation development of amorphous solid dispersions (ASD) still is challenging although several poorly water-soluble drugs have been marketed using this technique. During development of novel drugs, the selection of the preparation technique and polymer matrix is commonly performed for the certain drug via screening tools. However, if general trends regarding material properties are to be investigated, this approach is not beneficial, although often utilized in literature. The main component of the ASD usually is the polymer and thus it predominantly determines the material properties of the system. Therefore, to study the impact of different drugs and their drug loads on mechanical properties and wettability, three poorly soluble model drugs with drug loads ranging from 10% to 40% were incorporated into copovidone via hot-melt extrusion. The obtained extrudates were subsequently characterized regarding mechanical properties by applying diametral compression test and nanoindentation and the results were compared to the performance during tablet compression. Incorporation of all tested drugs resulted in a similar increase in brittleness of the ASDs, whereas the Young's modulus and hardness changed differently in dependence of the incorporated drug. These observations correlated well with the performance during tablet compression and it was concluded, that the brittleness seemed to be the predominant factor influencing the compression behavior of copovidone-based ASDs. Furthermore, the degree of water absorption and wettability was assessed by applying dynamic vapor sorption experiments and contact angle measurements. Here, the incorporated drugs impacted the contact angle to different degrees and a strong correlation between the contact angle and disintegration time was observable. These results highlight the importance of thorough characterization of the ASDs as it helps to predict their performance during tablet compression and thus facilitates the optimal selection of excipients. © 2020 Elsevier B.V.
    view abstractdoi: 10.1016/j.ejpb.2020.12.017
  • 2021 • 509 Impact of Ligands on Structural and Optical Properties of Ag29 Nanoclusters
    Zeng, Y. and Havenridge, S. and Gharib, M. and Baksi, A. and Weerawardene, K.L.D.M. and Ziefuß, A.R. and Strelow, C. and Rehbock, C. and Mews, A. and Barcikowski, S. and Kappes, M.M. and Parak, W.J. and Aikens, C.M. and Chakraborty, I.
    Journal of the American Chemical Society (2021)
    A ligand exchange strategy has been employed to understand the role of ligands on the structural and optical properties of atomically precise 29 atom silver nanoclusters (NCs). By ligand optimization,∼44-fold quantum yield (QY) enhancement of Ag29(BDT)12-x(DHLA)x NCs (x = 1-6) was achieved, where BDT and DHLA refer to 1,3-benzene-dithiol and dihydrolipoic acid, respectively. High-resolution mass spectrometry was used to monitor ligand exchange, and structures of the different NCs were obtained through density functional theory (DFT). The DFT results from Ag29(BDT)11(DHLA) NCs were further experimentally verified through collisional cross-section (CCS) analysis using ion mobility mass spectrometry (IM MS). An excellent match in predicted CCS values and optical properties with the respective experimental data led to a likely structure of Ag29(DHLA)12 NCs consisting of an icosahedral core with an Ag16S24 shell. Combining the experimental observation with DFT structural analysis of a series of atomically precise NCs, Ag29-yAuy(BDT)12-x(DHLA)x (where y, x = 0,0; 0,1; 0,12 and 1,12; respectively), it was found that while the metal core is responsible for the origin of photoluminescence (PL), ligands play vital roles in determining their resultant PLQY. © 2021 American Chemical Society.
    view abstractdoi: 10.1021/jacs.1c01799
  • 2021 • 508 Impact of Na+and Ca2+ Cations on the Adsorption of H2S on Binder-Free LTA Zeolites
    Starke, A. and Pasel, C. and Bläker, C. and Eckardt, T. and Zimmermann, J. and Bathen, D.
    Adsorption Science and Technology 2021 (2021)
    Hydrogen sulfide is removed from natural gas via adsorption on zeolites. The process operates very effectively, but there is still potential for improvement. Therefore, in this article, the adsorption of hydrogen sulfide was investigated on eight LTA zeolites with different cation compositions. Starting with the zeolite NaA (4 A), which contains only Na+ cations, the Ca2+ cation content was gradually increased by ion exchange. Equilibrium isotherms from cumulative breakthrough curve experiments in a fixed-bed adsorber at 25°C and 85°C at 1.3 bar (abs.) were determined in the trace range up to a concentration of 2000 ppmmol. From a comparison of the isotherms of the different materials, a mechanistic proposal for the adsorption is developed, taking into account the specific positions of the cations in the zeolite lattice when the degree of exchange is increased. The shape of the isotherms indicates two energetically different types of adsorption sites. It is assumed that two mechanisms are superimposed: a chemisorptive mechanism with dissociation of hydrogen sulfide and covalent bonding of the proton and the hydrogen sulfide ion to the zeolite lattice and a physisorptive mechanism by electrostatic interaction with the cations in the lattice. As the degree of exchange increases, the proportion of chemisorption sites seems to decrease. Above an exchange degree of 50%, only evidence of physisorption can be found. It is shown that this finding points to the involvement of weakly bound sodium cations at cation position III in the chemisorption of hydrogen sulfide. © 2021 Annika Starke et al.
    view abstractdoi: 10.1155/2021/5531974
  • 2021 • 507 Impact of single structural voids on fatigue properties of AISI 316L manufactured by laser powder bed fusion
    Kotzem, D. and Kleszczynski, S. and Stern, F. and Elspaß, A. and Tenkamp, J. and Witt, G. and Walther, F.
    International Journal of Fatigue 148 (2021)
    The laser powder bed fusion of metals (PBF-LB/M) process is already exploited in several industrial applications. The process itself allows to introduce artificial defects which can later be characterized by their influence on the resulting mechanical properties. In this study, the influence of isolated single structural defects (0.3 mm ≤ √area ≤ 1.5 mm) on the fatigue properties is discussed and the √area-parameter model is applied. The obtained results show that the investigated material is highly defect tolerant as artificial defects with √area = 0.3 mm are not crack initiating. Specimens with a defect of √area = 1.0–1.5 mm clearly show crack initiation and propagation starting from the defect, and a fatigue strength estimation tends to be more conservative. © 2021 Elsevier Ltd
    view abstractdoi: 10.1016/j.ijfatigue.2021.106207
  • 2021 • 506 Impact of structure on mechanical properties and oxidation behavior of magnetron sputtered cubic and hexagonal MoNx thin films
    Tillmann, W. and Kokalj, D. and Stangier, D.
    Applied Surface Science Advances 5 (2021)
    Molybdenum nitride films exhibit superior tribological properties, due to the possibility to form Magnéli phases when exposed to elevated temperatures. MoNx thin films were deposited by means of DC magnetron sputtering, while varying the bias-voltage and substrate temperature in regard to control the crystalline structure of the thin films. XRD experiments reveal a two-phase structure consisting of over stoichiometric cubic B1-NaCl and hexagonal MoNx phases for a high bias-voltage, whereas for lower bias-voltages the metastable cubic MoN phase was observed. Enhanced mechanical properties, obtained by means of nanoindentation, were analyzed for the thin films exhibiting the two-phase composite structure. The influence of the phase composition on the oxidation behavior, like oxidation state and formed oxide phases, was studied by means of in-situ XRD and XAS experiments using synchrotron radiation up to 700 °C. The oxidation processes start at 400 °C, forming oxides in amorphous state. Thin films composed of hexagonal MoN reveal a higher oxidation state up to 400 °C compared to cubic structured thin films, which changes above 400 °C. MoO2 and MoO3 were formed as primary oxides, independent from the crystalline structure of the deposited film. With an increase of temperature to 550 °C and 700 °C, the Magnéli-phases Mo9O26/Mo8O23 and Mo4O11 were formed. © 2021 The Author(s)
    view abstractdoi: 10.1016/j.apsadv.2021.100119
  • 2021 • 505 Impact of test temperature on functional degradation in Fe-Ni-Co-Al-Ta shape memory alloy single crystals
    Sobrero, C. and Lauhoff, C. and Langenkämper, D. and Somsen, C. and Eggeler, G. and Chumlyakov, Y.I. and Niendorf, T. and Krooß, P.
    Materials Letters 291 (2021)
    The present paper focuses on the analysis of functional fatigue properties in 〈001〉-oriented single crystalline Fe-Ni-Co-Al-Ta shape memory alloys. Superelastic cycling experiments up to 4.5% at different temperatures were conducted and revealed excellent cyclic stability at lower testing temperatures. Transmission electron microscopy observations shed light on the influence of precipitation and dislocation activity on functional stability. © 2021
    view abstractdoi: 10.1016/j.matlet.2021.129430
  • 2021 • 504 Impact of Water Coadsorption on the Electrode Potential of H-Pt(1 1 1)-Liquid Water Interfaces
    Surendralal, S. and Todorova, M. and Neugebauer, J.
    Physical Review Letters 126 (2021)
    Density functional theory molecular dynamics simulations of H-covered Pt(111)-H2O interfaces reveal that, in contrast to common understanding, H2O coadsorption has a significant impact on the electrode potential of and plays a major role in determining the stability of H adsorbates under electrochemical conditions. Based on these insights, we explain the origin behind the experimentally observed upper limit of H coverage well below one monolayer and derive a chemically intuitive model for metal-water bonding that explains an unexpectedly large interaction between coadsorbed water and adsorbates. © 2021 authors.
    view abstractdoi: 10.1103/PhysRevLett.126.166802
  • 2021 • 503 Implementation and operation of a fiber-coupled CMOS detector in a low energy electron Microscope
    Janoschka, D. and Dreher, P. and Rödl, A. and Franz, T. and Schaff, O. and Horn-von Hoegen, M. and Meyer zu Heringdorf, F.-J.
    Ultramicroscopy 221 (2021)
    The intrinsically weak signals in ultrafast electron microscopy experiments demand an improvement in the signal-to noise ratio of suitable electron detectors. We provide an experience report describing the installation and operation of a fiber-coupled CMOS based detector in a low energy electron microscope. We compare the detector performance to the traditional multi-channel-plate-based setup. The high dynamic range CMOS detector is capable of imaging spatially localized large intensity variations with low noise. The detector is blooming-free and overexposure appears uncritical. Overall, we find dramatic improvements in the imaging with the fiber-coupled CMOS detector compared to imaging with our previously used multi-channel-plate detector. © 2020 Elsevier B.V.
    view abstractdoi: 10.1016/j.ultramic.2020.113180
  • 2021 • 502 Implementation of formation mechanisms in DEM simulation of the spheronization process of pharmaceutical pellets
    Weis, D. and Grohn, P. and Evers, M. and Thommes, M. and García, E. and Antonyuk, S.
    Powder Technology 378 667-679 (2021)
    In the production process of pharmaceutical pellets with a narrow size distribution and a high sphericity, a combined extrusion-spheronization technique is frequently used. The rounding of the wet cylindrical extrudates in the spheronizer after the extrusion step is influenced by various interfering mechanisms, in particular plastic deformation, breakage, attrition and coalescence. Due to the complexity of these mechanisms which depend on the particle dynamics, there is no sufficient description of the particle rounding process in the spheronizer. In this study, the Discrete Element Method (DEM) which runs on the micro scale is coupled with a Particle Shape Evolution (PSE) model on the macro scale to describe how the particle shape changes due to collisions. For the DEM simulation a new contact model was used which was developed to capture the cyclic, dominant visco plastic deformation behaviour. Based on the DEM collision data, the changing particle shape was described in the PSE model by applying the proposed submodels for the different formation mechanisms. The resulting particle shapes obtained with this simulation framework are in a good agreement with experimental data. © 2020
    view abstractdoi: 10.1016/j.powtec.2020.09.013
  • 2021 • 501 Importance of catalyst–photoabsorber interface design configuration on the performance of Mo-doped BiVO4 water splitting photoanodes
    Krysiak, O.A. and Junqueira, J.R.C. and Conzuelo, F. and Bobrowski, T. and Masa, J. and Wysmolek, A. and Schuhmann, W.
    Journal of Solid State Electrochemistry 25 173-185 (2021)
    Photoelectrochemical water splitting is mostly impeded by the slow kinetics of the oxygen evolution reaction. The construction of photoanodes that appreciably enhance the efficiency of this process is of vital technological importance towards solar fuel synthesis. In this work, Mo-modified BiVO4 (Mo:BiVO4), a promising water splitting photoanode, was modified with various oxygen evolution catalysts in two distinct configurations, with the catalysts either deposited on the surface of Mo:BiVO4 or embedded inside a Mo:BiVO4 film. The investigated catalysts included monometallic, bimetallic, and trimetallic oxides with spinel and layered structures, and nickel boride (NixB). In order to follow the influence of the incorporated catalysts and their respective properties, as well as the photoanode architecture on photoelectrochemical water oxidation, the fabricated photoanodes were characterised for their optical, morphological, and structural properties, photoelectrocatalytic activity with respect to evolved oxygen, and recombination rates of the photogenerated charge carriers. The architecture of the catalyst-modified Mo:BiVO4 photoanode was found to play a more decisive role than the nature of the catalyst on the performance of the photoanode in photoelectrocatalytic water oxidation. Differences in the photoelectrocatalytic activity of the various catalyst-modified Mo:BiVO4 photoanodes are attributed to the electronic structure of the materials revealed through differences in the Fermi energy levels. This work thus expands on the current knowledge towards the design of future practical photoanodes for photoelectrocatalytic water oxidation. © 2020, The Author(s).
    view abstractdoi: 10.1007/s10008-020-04636-9
  • 2021 • 500 Improved process efficiency in laser-based powder bed fusion of nanoparticle coated maraging tool steel powder
    Pannitz, O. and Großwendt, F. and Lüddecke, A. and Kwade, A. and Röttger, A. and Sehrt, J.T.
    Materials 14 (2021)
    Research and development in the field of metal-based additive manufacturing are advancing steadily every year. In order to increase the efficiency of powder bed fusion of metals using a laser beam system (PBF LB/M), machine manufacturers have implemented extensive optimizations with regard to the laser systems and build volumes. However, the optimization of metallic powder materials using nanoparticle additives enables an additional improvement of the laser–material interaction. In this work, tool steel 1.2709 powder was coated with silicon carbide (SiC), few-layer graphene (FLG), and iron oxide black (IOB) on a nanometer scale. Subsequently, the feedstock material and the modified powder materials were analyzed concerning the reflectance of the laser radiation and processed by PBF-LB/M in a systematic and consistent procedure to evaluate the impact of the nano-additivation on the process efficiency and mechanical properties. As a result, an increased build rate is achieved, exhibiting a relative density of 99.9% for FLG/1.2709 due to a decreased reflectance of this modified powder material. Furthermore, FLG/1.2709 provides hardness values after precipitation hardening with only aging comparable to the original 1.2709 material and is higher than the SiC- and IOB-coated material. Additionally, the IOB coating tends to promote oxide‐formation and lack‐of‐fusion defects. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/ma14133465
  • 2021 • 499 In situ characterization of polycaprolactone fiber response to quasi-static tensile loading in scanning electron microscopy
    Delp, A. and Becker, A. and Hülsbusch, D. and Scholz, R. and Müller, M. and Glasmacher, B. and Walther, F.
    Polymers 13 (2021)
    Microstructural responses to the mechanical load of polymers used in tissue engineering is notably important for qualification at in vivo testing, although insufficiently studied, especially regarding promising polycaprolactone (PCL). For further investigations, electrospun PCL scaffolds with different degrees of fiber alignment were produced, using two discrete relative drum collector velocities. Development and preparation of an adjusted sample geometry enabled in situ tensile testing in scanning electron microscopy. By analyzing the microstructure and the use of selected tracking techniques, it was possible to visualize and quantify fiber/fiber area displacements as well as local fractures of single PCL fibers, considering quasi-static tensile load and fiber alignment. The possibility of displacement determination using in situ scanning electron microscopy techniques for testing fibrous PCL scaffolds was introduced and quantified. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/polym13132090
  • 2021 • 498 In Situ Characterization of the Damage Initiation and Evolution in Sustainable Cellulose-Based Cottonid
    Scholz, R. and Delp, A. and Walther, F.
    Minerals, Metals and Materials Series 5 867-878 (2021)
    The usage of environmentally friendly materials based on sustainable resources is nowadays more important than ever, especially in technical applications. Cottonid is based 100% on cellulose, therefore sutainable and due to its excellent properties a promising alternative material in terms of eco-friendliness. Within this study, the deformation and damage behavior of two Cottonid variants, an industrial standard as well as the structurally optimized variant M60Z50, is characterized for the first time using innovative in situ testing techniques. Quasi-static tensile tests were comparatively performed in a scanning electron microscope as well as a microfocus computer tomograph, and the development of defects present in the initial condition of the materials were investigated on surface and in volume. In general, in the elastic region, no visible damage initiation on the surface and a decrease of overall void volume within the gauge length could be detected for Cottonid. When reaching the yield strength, cracks initiate on the surface at critical areas, like pores and microcracks, which propagate and assemble until total loss of structural integrity. Further, in the plastic region, an increase in void volume could be shown in the gauge length until final failure. Compared to an industrial standard, M60Z50 exhibits a clearly lower percentage in overall void volume and shows increased mechanical properties, like yield strength and ultimate tensile strength. The structural optimization of M60Z50 seems to result in a more sufficient bonding of the paper layers during the manufacturing process, which improves the deformation and damage behavior under quasi-static loading. © 2021, The Minerals, Metals & Materials Society.
    view abstractdoi: 10.1007/978-3-030-65261-6_77
  • 2021 • 497 In situ investigation of nanometric cutting of 3C-SiC using scanning electron microscope
    Tian, D. and Xu, Z. and Liu, L. and Zhou, Z. and Zhang, J. and Zhao, X. and Hartmaier, A. and Liu, B. and Song, L. and Luo, X.
    International Journal of Advanced Manufacturing Technology (2021)
    Experimentally revealing the nanometric deformation behavior of 3C-SiC is challenging due to its ultra-small feature size for brittle-to-ductile transition. In the present work, we elucidated the nanometric cutting mechanisms of 3C-SiC by performing in situ nanometric cutting experiments under scanning electron microscope (SEM), as well as post-characterization by electron back-scattered diffraction (EBSD) and transmission electron microscopy (TEM). In particular, a new method based on the combination of image processing technology and SEM online observation was proposed to achieve in situ measurement of cutting force with an uncertainty less than 1 mN. Furthermore, the cutting cross-section was characterized by atomic force microscope (AFM) to access the specific cutting energy. The results revealed that the specific cutting energy increase non-linearly with the decrease of cutting depth due to the size effect of cutting tool in nanometric cutting. The high-pressure phase transformation (HPPT) may play the major role in 3C-SiC ductile machining under the parameters of this experiment. © 2021, The Author(s), under exclusive licence to Springer-Verlag London Ltd., part of Springer Nature.
    view abstractdoi: 10.1007/s00170-021-07278-x
  • 2021 • 496 In situ nanoindentation during electrochemical hydrogen charging: a comparison between front-side and a novel back-side charging approach
    Duarte, M.J. and Fang, X. and Rao, J. and Krieger, W. and Brinckmann, S. and Dehm, G.
    Journal of Materials Science 56 8732-8744 (2021)
    The effects of hydrogen in metals are a pressing issue causing severe economic losses due to material deterioration by hydrogen embrittlement. A crucial understanding of the interactions of hydrogen with different microstructure features can be reached by nanoindentation due to the small volumes probed. Even more, in situ testing while charging the sample with hydrogen prevents the formation of concentration gradients due to hydrogen desorption. Two custom electrochemical cells for in situ testing were built in-house to charge the sample with hydrogen during nanoindentation: “front-side” charging with the sample and the indenter tip immersed into the electrolyte, and “back-side” charging where the analyzed region is never in contact with the solution. During front-side charging, surface degradation often occurs which also negatively influences analyses after hydrogen charging. The back-side charging approach proposed in this work is a promising technique for studying in situ the effects of hydrogen in alloys under mechanical loads, while completely excluding the influence of the electrolyte on the nanoindented surface. Hydrogen diffusion from the charged back-side toward the testing surface is here demonstrated by Kelvin probe measurements in ferritic FeCr alloys, used as a case study due to the high mobility of hydrogen in the bcc lattice. During nanoindentation, a reduction on the shear stress necessary for dislocations nucleation due to hydrogen was observed using both setups; however, the quantitative data differs and a contradictory behavior was found in hardness measurements. Finally, some guidelines for the use of both approaches and a summary of their advantages and disadvantages are presented. Graphical abstract: [Figure not available: see fulltext.] © 2021, The Author(s).
    view abstractdoi: 10.1007/s10853-020-05749-2
  • 2021 • 495 In situ photothermal response of single gold nanoparticles through hyperspectral imaging anti-stokes thermometry
    Gargiulo, J. and Cortes, E. and Stefani, F.D. and Barella, M. and Violi, I.L. and Martinez, L.P. and Goschin, F. and Guglielmotti, V. and Pallarola, D. and Schlücker, S. and Pilo-Pais, M. and Acuna, G.P. and Maier, S.A.
    ACS Nano 15 2458-2467 (2021)
    Several fields of applications require a reliable characterization of the photothermal response and heat dissipation of nanoscopic systems, which remains a challenging task for both modeling and experimental measurements. Here, we present an implementation of anti-Stokes thermometry that enables the in situ photothermal characterization of individual nanoparticles (NPs) from a single hyperspectral photoluminescence confocal image. The method is label-free, potentially applicable to any NP with detectable anti-Stokes emission, and does not require any prior information about the NP itself or the surrounding media. With it, we first studied the photothermal response of spherical gold NPs of different sizes on glass substrates, immersed in water, and found that heat dissipation is mainly dominated by the water for NPs larger than 50 nm. Then, the role of the substrate was studied by comparing the photothermal response of 80 nm gold NPs on glass with sapphire and graphene, two materials with high thermal conductivity. For a given irradiance level, the NPs reach temperatures 18% lower on sapphire and 24% higher on graphene than on bare glass. The fact that the presence of a highly conductive material such as graphene leads to a poorer thermal dissipation demonstrates that interfacial thermal resistances play a very significant role in nanoscopic systems and emphasize the need for in situ experimental thermometry techniques. The developed method will allow addressing several open questions about the role of temperature in plasmon-assisted applications, especially ones where NPs of arbitrary shapes are present in complex matrixes and environments. © 2021 American Chemical Society. All rights reserved.
    view abstractdoi: 10.1021/acsnano.0c06185
  • 2021 • 494 In Situ Synchrotron X-ray Diffraction Studies of the Mechanochemical Synthesis of ZnS from its Elements
    Petersen, H. and Reichle, S. and Leiting, S. and Losch, P. and Kersten, W. and Rathmann, T. and Tseng, J. and Etter, M. and Schmidt, W. and Weidenthaler, C.
    Chemistry - A European Journal (2021)
    Mechanochemistry, as a synthesis tool for inorganic materials, became an ever-growing field in material chemistry. The direct energy transfer by collision of the educts with the milling media gives the possibility to design environmental-friendly reactions. Nevertheless, the underlying process of energy transfer and hence the kinetics of mechanosynthesis remain unclear. Herein, we present in situ synchrotron X-ray diffraction studies coupled with pressure measurements performed during the formation of ZnS and the subsequent phase transition (PT) from the hexagonal to the cubic modification. Milling Zn and S8 results in the sublimation of S8, observed by a sudden pressure increase. Simultaneously, the hexagonal metastable ZnS-modification (wurtzite) forms. Via detection of the pressure maximum, the exact start of the wurtzite formation can be determined. Immediately after the formation of wurtzite, the structural PT to the thermodynamic stable cubic modification sphalerite takes place. This PT can be described by the Prout-Tompkins equation for autocatalytic reactions, similar to thermally induced PT in sulfur vapor at high temperatures (T&gt;1133 K). The increase in the reactivity of the wurtzite formation is explained by the reaction in sulfur vapor and the induction of defect structures by the collisions with the milling media. © 2021 The Authors. Published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/chem.202101260
  • 2021 • 493 In situ total scattering experiments of nucleation and crystallisation of tantalum-based oxides: From highly dilute solutions via cluster formation to nanoparticles
    Onur Şahin, E. and Tüysüz, H. and Chan, C.K. and Moon, G.-H. and Dai, Y. and Schmidt, W. and Lim, J. and Scheu, C. and Weidenthaler, C.
    Nanoscale 13 150-162 (2021)
    The exact formation mechanism of tantalum oxides (and in general, metal/mixed metal oxides) from alkoxide precursors is still not fully understood, particularly when forming cluster-like or amorphous materials. The structural evolution of Ta-based oxides was studied in detail using X-ray total scattering experiments along with subsequent pair distribution function (PDF) analyses. Starting from a tantalum alkoxide precursor (Ta2(OEt)10), the formation of hydrolysed TaxOyHz clusters in highly diluted aqueous solution was analysed. From the PDF data, the connectivity and arrangement of TaxOy octahedra in the cluster could be deduced as well as the approximate size of the clusters (<1 nm). Construction of cluster models allowed for identification of common structural motifs in the TaxOyHz clusters, ruling out the formation of chain- or ring-like clusters. More likely, bulky clusters with a high number of corner-sharing octahedra are formed. After separation of the amorphous solid from the liquid, temperature-induced crystallisation processes were monitored via in situ total scattering experiments. Between room temperature and 600 °C, only small rearrangements of the amorphous structure are observed. At about 610 °C, amorphous TaxOyHz transforms directly into crystalline orthorhombic L-Ta2O5 without formation of any crystalline intermediate structures. © 2021 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/d0nr07871a
  • 2021 • 492 Increased space-parallelism via time-simultaneous Newton-multigrid methods for nonstationary nonlinear PDE problems
    Dünnebacke, J. and Turek, S. and Lohmann, C. and Sokolov, A. and Zajac, P.
    International Journal of High Performance Computing Applications 35 211-225 (2021)
    We discuss how “parallel-in-space & simultaneous-in-time” Newton-multigrid approaches can be designed which improve the scaling behavior of the spatial parallelism by reducing the latency costs. The idea is to solve many time steps at once and therefore solving fewer but larger systems. These large systems are reordered and interpreted as a space-only problem leading to multigrid algorithm with semi-coarsening in space and line smoothing in time direction. The smoother is further improved by embedding it as a preconditioner in a Krylov subspace method. As a prototypical application, we concentrate on scalar partial differential equations (PDEs) with up to many thousands of time steps which are discretized in time, resp., space by finite difference, resp., finite element methods. For linear PDEs, the resulting method is closely related to multigrid waveform relaxation and its theoretical framework. In our parabolic test problems the numerical behavior of this multigrid approach is robust w.r.t. the spatial and temporal grid size and the number of simultaneously treated time steps. Moreover, we illustrate how corresponding time-simultaneous fixed-point and Newton-type solvers can be derived for nonlinear nonstationary problems that require the described solution of linearized problems in each outer nonlinear step. As the main result, we are able to generate much larger problem sizes to be treated by a large number of cores so that the combination of the robustly scaling multigrid solvers together with a larger degree of parallelism allows a faster solution procedure for nonstationary problems. © The Author(s) 2021.
    view abstractdoi: 10.1177/10943420211001940
  • 2021 • 491 Increasing the Complexity in the MIL-53 Structure: The Combination of the Mixed-Metal and the Mixed-Linker Concepts
    Bitzer, J. and Teubnerová, M. and Kleist, W.
    Chemistry - A European Journal 27 1724-1735 (2021)
    The isoreticular mixed-component concept is a promising approach to tailor the material properties of metal–organic frameworks. While isoreticular mixed-metal or mixed-linker materials are commonly synthesized, the combination of both concepts for the development of isoreticular materials featuring both two metals and two linkers is still rarely investigated. Herein, we present the development of mixed-metal/mixed-linker MIL-53 materials that contain different metal combinations (Al/Sc, Al/V, Al/Cr, Al/Fe) and different linker ratios (terephthalate/2-aminoterephthalate). The possibility of changing the metal combination and the linker ratio independently from each other enables a large variety of modifications. A thorough characterization (PXRD, ATR-IR, TGA, 1H NMR, ICP-OES) confirmed that all components were incorporated into the framework structure with a statistical distribution. Nitrogen physisorption measurements showed that the breathing behavior can be tailored by adjusting the linker ratio for all metal combinations. All materials were successfully used for post-synthetic modification reactions with maleic anhydride. © 2020 The Authors. Published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/chem.202003304
  • 2021 • 490 Increasing the lightweight potential of composite cold forging by utilizing magnesium and granular cores
    Gitschel, R. and Kolpak, F. and Hering, O. and Erman Tekkaya, A.
    Metals 11 1-16 (2021)
    In this paper a process sequence, that uses forward rod extrusion with cold forged C15 steel cup billets to produce lightweight shafts, is presented. The steel cup billets feature either a lightweight magnesium alloy core or a granular medium core that is removed after forming to obtain hollow shafts without the need of complex tools and highly loaded mandrels. It is shown that composite shafts featuring magnesium cores can be produced for a wide range of extrusion strains. Due to high hydrostic pressures in forward rod extrusion, the forming limit of magnesium at room temperature can be expanded. The observed bond strength between core and sheath is below the shear yield strength of utilized magnesium AZ31 alloy. Hollow shafts are successfully produced with the presented process route by utilizing zirconium oxide beads or quartz sand as a lost core. As the law of constant volume in metal forming is violated by compressible granular media, a simulation approach using a modified Drucker-Prager yield surface to model these materials is validated to provide a tool for efficient process design. Granular cores and magnesium alloy cores offer new possibilities in production of lightweight shafts by means of composite cold forging. Both process variants allow for higher weight savings than composite shafts based on aluminum cores. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/met11010032
  • 2021 • 489 In-Depth Comparative Study of the Cathode Interfacial Layer for a Stable Inverted Perovskite Solar Cell
    Lee, J. and Tüysüz, H.
    ChemSusChem 14 2393-2400 (2021)
    Achieving long-term device stability is one of the most challenging issues that impede the commercialization of perovskite solar cells (PSCs). Recent studies have emphasized the significant role of the cathode interfacial layer (CIL) in determining the stability of inverted p-i-n PSCs. However, experimental investigations focusing on the influence of the CIL on PSC degradation have not been systematically carried out to date. In this study, a comparative analysis was performed on the PSC device stability by using four different CILs including practical oxides like ZnO and TiOx. A new implemented co-doping approach was found to results in high device performance and enhanced device stability. The PSC with a thick film configuration of chemically modified TiOx CIL preserves over 77 % of its initial efficiencies of 17.24 % for 300 h under operational conditions without any encapsulation. The PSCs developed are among the most stable reported for methylammonium lead iodide (MAPbI3) perovskite compositions. © 2021 The Authors. ChemSusChem published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/cssc.202100585
  • 2021 • 488 Inference for fractional Ornstein-Uhlenbeck type processes with periodic mean in the non-ergodic case
    Shevchenko, R. and Woerner, J.H.C.
    Stochastic Analysis and Applications (2021)
    In the paper we consider the problem of estimating parameters entering the drift of a fractional Ornstein-Uhlenbeck type process in the non-ergodic case, when the underlying stochastic integral is of Young type. We consider the sampling scheme that the process is observed continuously on (Formula presented.) and (Formula presented.) For known Hurst parameter (Formula presented.) i.e. the long range dependent case, we construct a least-squares type estimator and establish strong consistency. Furthermore, we prove a second order limit theorem which provides asymptotic normality for the parameters of the periodic function with a rate depending on H and a non-central Cauchy limit result for the mean reverting parameter with exponential rate. For the special case that the periodicity parameter is the weight of a periodic function, which integrates to zero over the period, we can even improve the rate to (Formula presented.). © 2021 Taylor & Francis Group, LLC.
    view abstractdoi: 10.1080/07362994.2021.1942916
  • 2021 • 487 Influence of a discontinuous process strategy on microstructure and microhardness in drilling inconel 718
    Wolf, T. and Iovkov, I. and Biermann, D.
    Journal of Manufacturing and Materials Processing 5 (2021)
    Nickel-base alloys are proven materials in the fields of the aerospace and oil industry, which is due to their characteristic material properties of high temperature strength, high toughness and good oxidation resistance. These properties are beneficial to applications in technical components in general. However, they also represent challenges for machining. Especially while drilling Inconel 718, high temperatures occur in the chip-formation zone that implicate high thermal load in the material and thus, influence the surface integrity, for example, by causing white layers. Hence, the development of strategies to improve the ability to supply cutting edges with cooling lubricant is becoming increasingly important. In this context, an alternative process design, the discontinuous drilling, takes place, characterized by a periodic interruption of feed motion and thus, chip formation. A minor retraction movement from the contact zone enables the cooling lubricant to reach the cutting edges and to reduce their thermal load. In comparison to the conventional process of drilling Inconel 718, the effects of discontinuous drilling with varying numbers of interruptions on the resulting surface integrity and further parameters of drilling qualities are analyzed. Thereby, the prevention of process-related phase transformations due to thermal impact was discovered when a discontinuous drilling strategy was implemented. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/jmmp5020043
  • 2021 • 486 Influence of calcination and sintering temperatures on dielectric and magnetic properties of Pb(Fe0.5Nb0.5)O3 ceramics synthesized by the solid state method
    Bartek, N. and Shvartsman, V.V. and Salamon, S. and Wende, H. and Lupascu, D.C.
    Ceramics International 47 23396-23403 (2021)
    Lead iron niobate, Pb(Fe0.5Nb0.5)O3 (PFN), belongs to the family of multiferroic materials combining ferroelectric and antiferromagnetic ordering. Its properties to a large extent depend on the synthesis conditions. For applications it is important to obtain materials with large polarization and low electric leakage. In this paper we investigate the effect of processing parameters on the structural, electrical and magnetic behaviour of PFN ceramics prepared by the solid state method. The optimal calcination and sintering temperatures are found, which enable us to obtain ceramics with a large polarization Pmax = 28 μC/cm2 and dielectric permittivity εMax ≈ 55 000. We also find that increasing the calcination and sintering temperatures decreases diffuseness of the ferroelectric phase transition and shifts the Néel temperature to lower values, which might be due to a change of the distribution of Fe3+ and Nb5+ across the B-sites of the perovskite towards a more ordered structure. © 2021
    view abstractdoi: 10.1016/j.ceramint.2021.05.055
  • 2021 • 485 Influence of crystalline defects on magnetic nanodomains in a rare-earth-free magnetocrystalline anisotropic alloy
    Palanisamy, D. and Kovács, A. and Hegde, O. and Dunin-Borkowski, R.E. and Raabe, D. and Hickel, T. and Gault, B.
    Physical Review Materials 5 (2021)
    A complex interplay between magnetic domain structure and crystalline imperfections, here twins, is revealed in a rare-earth-free MnAl bulk magnet. The magnetic domains are observed to be in the nanometer range for a large part of the magnetic structure and to scale with the number density of twins formed during thermal processing. We explain this phenomenon by a reduction in domain-wall energy at the twinned regions as proven by ab initio calculations. In addition, our atomic-scale analysis reveals that the twin boundaries contain excess Mn atoms that reduce the local magnetization, serving as an obstacle for domain wall motion. These insights can help guide the strategic design of magnetic materials by controlling the initial phase distribution to tailor the twin density and hence, the distribution of domains. © 2021 authors.
    view abstractdoi: 10.1103/PhysRevMaterials.5.064403
  • 2021 • 484 Influence of Direct Splat-Affecting Parameters on the Splat-Type Distribution, Porosity, and Density of Segmentation Cracks in Plasma-Sprayed YSZ Coatings
    Tillmann, W. and Khalil, O. and Baumann, I.
    Journal of Thermal Spray Technology 30 1015-1027 (2021)
    The integrity and properties of ceramic coatings produced by atmospheric plasma spraying are highly controlled by the splat morphology and splat interconnection. In this study, the influence of selected parameters (spray angle, surface velocity of the spray gun, and substrate temperature) on splat morphology and coating microstructure was investigated. A favorite set of spray gun parameters, of which their effects on splat morphology and coating microstructure have been verified by previous experiments, were used to conduct the experiments for the present work. It was found that depositing fully molten particles on a hot substrate increases the fraction of disk-like splats by about 60% at the expense of the fraction of irregular splats. Preheating the substrate also increases the pore count and level of coating porosity, while it does not influence the density of segmentation cracks. In contrast, the surface velocity of the spray gun does not affect the splat morphology while a slow speed decreases the coating porosity and plays a significant role in generating segmentation cracks. Shifting the spray angle by 15° distorts up to 20% of disk-like splats and slightly decreases the porosity level. However, changing the spray angle does not affect the generation of segmentation cracks. © 2021, The Author(s).
    view abstractdoi: 10.1007/s11666-021-01180-4
  • 2021 • 483 Influence of fe and ni doping on the oer performance at the co3o4(001) surface: Insights from DFT+u calculations
    Peng, Y. and Hajiyani, H. and Pentcheva, R.
    ACS Catalysis 11 5601-5613 (2021)
    Using density functional theory calculations with an on-site Hubbard U term, we study the oxygen evolution reaction (OER) at the Co3O4(001) surface. The stability of different surface terminations as a function of oxygen partial pressure as well as pH and applied voltage is compiled in a Pourbaix diagram. The termination with octahedral Co and O ions (B-layer) is found to have the lowest overpotential of 0.46 V for an octahedral Co reaction site, associated with its p-type conducting character and the higher oxidation state of the active site (+4) during OER. Furthermore, we systematically investigated the effect of Fe and Ni doping on the overpotential. Our results indicate that Ni doping at an octahedral site in the surface layer reduces the overpotential from 0.46 to 0.34 V. Likewise, Fe doping at an octahedral site at the tetrahedral Co termination (A-layer) lowers η from 0.63 to 0.37 V with octahedral Co remaining in the active site. We note that the potential determining step changes from ∗OH (B-layer) to ∗OOH formation (A-layer). While implicit solvation increases the overpotential by 0.2 V (B-layer) and 0.4 V (A-layer), which is attributed to enhanced binding energies of the intermediates, the general trends with respect to doping remain unchanged. The scaling relationship of the binding energies of ∗OOH and ∗OH is overall satisfied, with the doped systems lying close to the top of the volcano plot of the overpotential versus (ΔG∗O b-ΔG∗OH b ). A further insight into the origin of this behavior is gained by analyzing the changes in oxidation states of surface ions and, in particular, the Co active site during OER. © 2021 American Chemical Society. All rights reserved.
    view abstractdoi: 10.1021/acscatal.1c00214
  • 2021 • 482 Influence of flexible side-chains on the breathing phase transition of pillared layer MOFs: A force field investigation
    Keupp, J. and Dürholt, J.P. and Schmid, R.
    Faraday Discussions 225 324-340 (2021)
    The prototypical pillared layer MOFs, formed by a square lattice of paddle-wheel units and connected by dinitrogen pillars, can undergo a breathing phase transition by a "wine-rack"type motion of the square lattice. We studied this behavior, which is not yet fully understood, using an accurate first principles parameterized force field (MOF-FF) for larger nanocrystallites on the example of Zn2(bdc)2(dabco) [bdc: benzenedicarboxylate, dabco: (1,4-diazabicyclo[2.2.2]octane)], and found clear indications for an interface between a closed and an open pore phase traveling through the system during the phase transformation [J. Keupp and R. Schmid, Adv. Theory Simul., 2019, 2, 1900117]. In conventional simulations in small supercells this mechanism is prevented by periodic boundary conditions (PBCs), enforcing a synchronous transformation of the entire crystal. Here, we extend this investigation to pillared layer MOFs with flexible side-chains, attached to the linker. Such functionalized (fu-)MOFs are experimentally known to have different properties with the side-chains acting as fixed guest molecules. First, in order to extend the parameterization for such flexible groups, a new parameterization strategy for MOF-FF had to be developed, using a multi-structure force based fit method. The resulting parameterization for a library of fu-MOFs is then validated with respect to a set of reference systems and shows very good accuracy. In the second step, a series of fu-MOFs with increasing side-chain length is studied with respect to the influence of the side-chains on the breathing behavior. For small supercells in PBCs a systematic trend of the closed pore volume with the chain length is observed. However, for a nanocrystallite model a distinct interface between a closed and an open pore phase is visible only for the short chain length, whereas for longer chains the interface broadens and a nearly concerted transformation is observed. Only by molecular dynamics simulations using accurate force fields can such complex phenomena can be studied on a molecular level. © 2021 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/d0fd00017e
  • 2021 • 481 Influence of low Bi contents on phase transformation properties of VO2studied in a VO2:Bi thin film library
    Wang, X. and Rogalla, D. and Kostka, A. and Ludwig, Al.
    RSC Advances 11 7231-7237 (2021)
    A thin-film materials library in the system V-Bi-O was fabricated by reactive co-sputtering. The composition of Bi relative to V was determined by Rutherford backscattering spectroscopy, ranging from 0.06 to 0.84 at% along the library. The VO2phase M1 was detected by X-ray diffraction over the whole library, however a second phase was observed in the microstructure of films with Bi contents &gt; 0.29 at%. The second phase was determined by electron diffraction to be BiVO4, which suggests that the solubility limit of Bi in VO2is only ∼0.29 at%. For Bi contents from 0.08 to 0.29 at%, the phase transformation temperatures of VO2:Bi increase from 74.7 to 76.4 °C by 8 K per at% Bi. With X-ray photoemission spectroscopy, the oxidation state of Bi was determined to be 3+. The V5+/V4+ratio increases with increasing Bi content from 0.10 to 0.84 at%. The similarly increasing tendency of the V5+/V4+ratio andTcwith Bi content suggests that although the ionic radius of Bi3+is much larger than that of V4+, the charge doping effect and the resulting V5+are more prominent in regulating the phase transformation behavior of Bi-doped VO2 © The Royal Society of Chemistry 2021.
    view abstractdoi: 10.1039/d0ra09654g
  • 2021 • 480 Influence of Mg content in Al alloys on processing characteristics and dynamically recrystallized microstructure of friction surfacing deposits
    Ehrich, J. and Roos, A. and Klusemann, B. and Hanke, S.
    Materials Science and Engineering A 819 (2021)
    Friction Surfacing (FS) coatings are deposited by severe plastic deformation at elevated temperatures (≈0.8*Tliquidus), requiring different process parameters for alloys of even small composition variations. For Al alloys it is known that with increasing Mg content the thermal softening rate decreases, i.e. the material retains higher flow strength under thermomechanical processing. Further, the stacking fault energy (SFE) decreases with increasing Mg content, which influences gliding characteristics of dislocations, and also deformation and recrystallization behavior. To elucidate the influence of such known properties on FS process parameters and resulting coatings, three Al alloys differing only in Mg content (0.27, 2 and 3.5 wt.%) were processed by FS in this study. Pronounced shear flow localization was observed for increasing Mg content, yielding thin and narrow coatings and requiring a reduction of process speeds. Further, the decrease in SFE with increasing Mg content resulted in lower recrystallized grain size and higher grain orientation differences, due to a lower tendency for dislocation annihilation by recovery. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.msea.2021.141407
  • 2021 • 479 Influence of Nanoparticle Processing on the Thermoelectric Properties of (BixSb1−X)2Te3 Ternary Alloys
    Salloum, S. and Bendt, G. and Heidelmann, M. and Loza, K. and Bayesteh, S. and Sepideh Izadi, M. and Kawulok, P. and He, R. and Schlörb, H. and Perez, N. and Reith, H. and Nielsch, K. and Schierning, G. and Schulz, S.
    ChemistryOpen (2021)
    The synthesis of phase-pure ternary solutions of tetradymite-type materials (BixSb1−x)2Te3 (x=0.25; 0.50; 0.75) in an ionic liquid approach has been carried out. The nanoparticles are characterized by means of energy-dispersive X-ray spectroscopy (EDX), powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), and transmission electron microscopy. In addition, the role of different processing approaches on the thermoelectric properties - Seebeck coefficient as well as electrical and thermal conductivity - is demonstrated. © 2021 The Authors. Published by The Chemical Society of Japan & Wiley-VCH GmbH
    view abstractdoi: 10.1002/open.202000257
  • 2021 • 478 Influence of Nb as Microalloying Element on the Recovery and Recrystallization of Fe–25Mn–12Cr–C–N Twinning-Induced Plasticity Steels
    Suárez Sierra, A. and Rodríguez Baracaldo, R. and Mujica Roncery, L. and Egels, G. and Theisen, W.
    Steel Research International (2021)
    The influence of Nb on the microstructure during annealing at 950, 1000, and 1100 °C is analyzed in two types of twinning-induced plasticity (TWIP) steels, Fe–25Mn–12Cr–C–N (TWIP-0) and Fe–25Mn–12Cr–C–N–Nb (TWIP-Nb). The addition of Nb as a microalloying element affects various phenomena taking place during annealing, namely, recrystallization, grain coarsening, and recovery processes. Microstructural characterization is conducted via light microscopy, scanning electron microscopy, and electron back scattering diffraction (EBSD). Recovery takes place after annealing at 950 °C, where remaining deformation and grain nucleation can be seen. Microstructural analyses indicate that the location of the recrystallization nuclei in the recovered structure is associated with the local chemical segregation of Mn and Cr, which leads to differences in the driving force for the martensitic transformation at microscale, and therefore local deformation mechanisms. The presence of Nb as a microalloying element decelerates recovery and recrystallization kinetics. At 1100 °C/10 min, both steels exhibit complete recrystallization; moreover, abnormal grain growth starts. © 2021 Wiley-VCH GmbH
    view abstractdoi: 10.1002/srin.202000417
  • 2021 • 477 Influence of powder characteristics on the structural and the mechanical properties of additively manufactured Zr-based bulk metallic glass
    Wegner, J. and Frey, M. and Piechotta, M. and Neuber, N. and Adam, B. and Platt, S. and Ruschel, L. and Schnell, N. and Riegler, S.S. and Jiang, H.-R. and Witt, G. and Busch, R. and Kleszczynski, S.
    Materials and Design 209 (2021)
    Additive manufacturing of Zr-based bulk metallic glasses (BMGs) is subject to growing scientific and industrial attention. Laser-based powder bed fusion of metals (PBF-LB/M) becomes a key technology to overcome current restrictions of size and geometry in the manufacturing of BMGs. For industrial application, further knowledge about defect formation, such as porosity and crystallization, is mandatory to develop processing strategies and suitable quality assurance. In this context, the influence of the particle size distribution, oxygen contamination, and applied process parameters during the PBF-LB/M of the glass-forming alloy AMZ4 (in at.% Zr59.3Cu28.8Al10.4Nb1.5) on the structural and mechanical properties were evaluated. It was found that the addition of SiO2 flow aid to the feedstock is suitable to increase flowability without impeding fabrication of the amorphous material. Furthermore, the processing of partially crystalline powder particles into amorphous samples is demonstrated. It indicates that today's high effort producing amorphous powders and thus the production costs can be reduced. Flexural bending tests and high-energy synchrotron X-ray diffraction reveal that the powder feedstock's oxygen content is crucial for the amorphization, embrittlement, and flexural strength of PBF-LB/M processed Zr-based BMGs. © 2021
    view abstractdoi: 10.1016/j.matdes.2021.109976
  • 2021 • 476 Influence of process parameters on the residual stress state and properties in disc springs made by incremental sheet forming (ISF) [Einfluss der Prozessparameter auf den Eigenspannungszustand und die Eigenschaften von Tellerfedern, hergestellt durch inkrementelle Blechumformung (IBU)]
    Afzal, M.J. and Hajavifard, R. and Buhl, J. and Walther, F. and Bambach, M.
    Forschung im Ingenieurwesen/Engineering Research (2021)
    Disc springs are machine elements that are used when high forces need to be supplied and in limited installation space. They need to fulfil high demands on the stability of the spring characteristics, reliability and lifetime. In corrosive environments, metastable austenitic stainless steels (MASS) disc springs are often used. Tensile stresses that occur during service limit the lifetime of disc springs. Usually, their durability is enhanced by generating favorable compressive residual stresses using shot peening operations. Such operations lead to extra efforts and additional production costs. In this study, the adaptive and targeted generation of residual stresses via incremental sheet forming (ISF) is investigated as alternative to shot peening focusing on EN 1.4310 and EN 1.4401 stainless steel. Previous work has shown that ISF is capable of controlling the radial and tangential stresses in the springs. However, no analysis of the influence of the residual stress state in the rolled sheet strips and the ISF process parameters was performed. The goal of the current work is to analyze the evolution of residual stress during rolling and subsequent incremental forming of disc springs. In order to examine the role of dissipation and temperature increases in the rolling process, sheet blanks rolled at room and elevated temperature are analyzed. The characteristics of the compressive residual stresses induced by ISF are studied for different process parameters. X‑ray diffraction is used to investigate the buildup of these stresses. Using ISF, the generation of compressive residual stresses can be integrated into the forming process of disc springs, and further post-treatment may be skipped. The results show that the residual stress state in the rolled material is crucial, which requires tight control of the rolling temperature. Another result is that ISF is able to yield high compressive residual stresses and improved spring characteristics when small tool diameters and step-down values are used. © 2021, The Author(s).
    view abstractdoi: 10.1007/s10010-021-00491-w
  • 2021 • 475 Influence of spray gun parameters on inflight particle's characteristics, the splat-type distribution, and microstructure of plasma-sprayed YSZ coatings
    Tillmann, W. and Khalil, O. and Baumann, I.
    Surface and Coatings Technology 406 (2021)
    Ceramic coatings, fabricated with specific properties using the atmospheric plasma spray (APS) process, are widely used for many applications in which the porosity and splat interfaces are the main factors affecting the performance. Since the coating microstructure is composed of large numbers of molten and semi-molten particles impinged successfully at the substrate (known as splats), the produced coatings are characterized by the melting degree of these particles and their relative splat-type fractions. In the present work, the effect of process parameters settings has been studied systematically, relating the characteristics of impinging particles to splat formation and eventually to microstructure development and properties of the coating. Therefore, individual splats were collected on mirror-polished substrates and observed using image analysis (IA). These were evaluated and categorized into different splat types, based on their melting degree and morphology, under each combination of spray conditions. It was found that gun current and standoff distance have a profound effect on the characteristics of impinging particles. These, in turn, determine the relative fractions of splat types, layered structure, and final properties of the deposit. The effect of splat-type distribution on the bonding strength between layers, lamellar structure, and coating porosity was investigated. © 2020 Elsevier B.V.
    view abstractdoi: 10.1016/j.surfcoat.2020.126705
  • 2021 • 474 Influence of strain rate on the activation of {110}, {112}, {123} slip in ferrite of DP800
    Tian, C. and Dehm, G. and Kirchlechner, C.
    Materialia 15 (2021)
    We have performed micro pillar compression to investigate the influence of strain rate on the activation of three slip plane families, namely {110}, {112} and {123}, in ferrite of a dual phase steel. The critical resolved shear stress of all three slip plane families rises with increased strain rate. The strain rate sensitivity drops with increasing strain. Increasing strain rate does not reduce the number of activated slip systems, instead resulting in slip plane activation outside of that predicted by Schmid´s law. The activation volume of 13b³ to 16b³ suggests that the Peierl's process is the rate controlling mechanism in ferrite of DP800. © 2020
    view abstractdoi: 10.1016/j.mtla.2020.100983
  • 2021 • 473 Influence of sub-monolayer quantities of carbon nanoparticles on the melting and crystallization behavior of polyamide 12 powders for additive manufacturing
    Sommereyns, A. and Hupfeld, T. and Gann, S. and Wang, T. and Wu, C. and Zhuravlev, E. and Lüddecke, A. and Baumann, S. and Rudloff, J. and Lang, M. and Gökce, B. and Barcikowski, S. and Schmidt, M.
    Materials and Design 201 (2021)
    In this paper, the influence of 0.005 vol% and 0.05 vol% of carbon nanoparticles on the surface of polyamide 12 powder particles by dry coating and colloidal additivation is evaluated in great detail concerning thermal and microstructural properties. The dispersion of the nanoparticles on the polymer surface influences the flowability of the feedstock powder already during the additivation process. When analyzing the composite powders dynamically and isothermally with fast scanning and differential scanning calorimetry, carbon nanoparticles influence the crystallization behavior of the feedstock material significantly by acting as nucleation seeds, already at a few percent of a monolayer coating, while showing no effect on the fast heating process. The difference in calorimetric properties and crystallization behavior between the additivation methods of different abrasive forces is discussed. The surface-additivated carbon nanoparticles significantly increase the crystalline area by up to a threefold and the crystallization rate by up to a hundredfold. Furthermore, they change the crystal growth from a typical two- to three-dimensional growth of spherulites to a one- to two-dimensional growth of ellipsoidal impinged lamellar structures. Between 0.005 vol% and 0.05 vol% of well-dispersed carbon nanoparticles should be added to polyamide 12 to trigger an anisotropic heterogeneous nucleation while avoiding agglomerates. © 2021 The Authors
    view abstractdoi: 10.1016/j.matdes.2021.109487
  • 2021 • 472 Influence of substrate removal method on the properties of free-standing ysz coatings
    Vaßen, R. and Bakan, E. and Schwartz-Lückge, S.
    Coatings 11 (2021)
    Thermally sprayed ceramic coatings are often tested as free-standing layers to investigate different properties such as thermal expansion coefficient, thermal conductivity, sintering, mechanical behavior, corrosion resistance, gas tightness, or electrical properties. In this paper, four different substrate removal methods were used to obtain free-standing YSZ coatings. At first, spraying on a steel substrate and subsequent dissolution of the substrate-coating interface by hydrochloric acid (HCl) was used. Second, the steel substrate was removed by applying an electrical field via electrochemical corrosion of the surface of the substrate. In a third method, the coating was sprayed on a salt (NaCI) interlayer, which was removed later by dissolution in water. At last, the coating was sprayed on a graphite substrate and the substrate was removed by heat treatment. After the preparation of free-standing coatings, these were characterized using scanning electron microscopy, mercury porosimetry, indentation tests, and room temperature three-point bending tests, which allowed the determination of Young’s modulus and viscosity. The results revealed measurable differences in coating properties as a result of the substrate removal methods, i.e., HCl method led to higher porosity and lower modulus in the YSZ coating. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/coatings11040449
  • 2021 • 471 Influence of substrates and e-beam evaporation parameters on the microstructure of nanocrystalline and epitaxially grown Ti thin films
    Devulapalli, V. and Bishara, H. and Ghidelli, M. and Dehm, G. and Liebscher, C.H.
    Applied Surface Science 562 (2021)
    Titanium thin films were deposited on silicon nitride (SiNx) coated Si, NaCl, and sapphire substrates varying the deposition conditions using e-beam evaporation to investigate thin film growth modes. The microstructure and texture evolution in dependence of substrate, deposition rate, film thickness, and substrate temperature were studied using X-ray diffraction, electron backscatter diffraction, and transmission electron microscopy. Thin films obtained on SiNx and NaCl substrates were nanocrystalline, while the films deposited on sapphire transformed from nanocrystalline to single crystalline at deposition temperatures above 200 °C. Predominantly, a surface plane orientation of (0002) was observed for the single crystalline films due to the minimization of surface energy. The orientation relationship of epitaxial single crystalline films grown on C-plane sapphire substrate is found to be (0002)Ti ‖ (0006)Sapphire,〈112¯0〉Ti ‖ 〈033¯0〉Sapphire. In this orientation relationship, both the total surface and strain energy of the film are minimized. The results were complemented by resistivity measurements using the four-point probe method reporting an increase from ~60 μ Ω cm to ~95 μΩ cm for single crystalline and nanocrystalline films, respectively. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.apsusc.2021.150194
  • 2021 • 470 Influence of temperature on void collapse in single crystal nickel under hydrostatic compression
    Prasad, M.R.G. and Neogi, A. and Vajragupta, N. and Janisch, R. and Hartmaier, A.
    Materials 14 (2021)
    Employing atomistic simulations, we investigated the void collapse mechanisms in single crystal Ni during hydrostatic compression and explored how the atomistic mechanisms of void collapse are influenced by temperature. Our results suggest that the emission and associated mutual interactions of dislocation loops around the void is the primary mechanism of void collapse, irrespective of the temperature. The rate of void collapse is almost insensitive to the temperature, and the process is not thermally activated until a high temperature (1200-1500 K) is reached. Our simulations reveal that, at elevated temperatures, dislocation motion is assisted by vacancy diffusion and consequently the void is observed to collapse continuously without showing appreciable strain hardening around it. In contrast, at low and ambient temperatures (1 and 300 K), void collapse is delayed after an initial stage of closure due to significant strain hardening around the void. Furthermore, we observe that the dislocation network produced during void collapse remains the sample even after complete void collapse, as was observed in a recent experiment of nickel-base superalloy after hot isostatic pressing. © 2021 by the authors.
    view abstractdoi: 10.3390/ma14092369
  • 2021 • 469 Influence of the Brazing Paste Composition on the Wetting Behavior of Reactive Air Brazed Metal–Ceramic Joints
    Waetzig, K. and Schilm, J. and Mosch, S. and Tillmann, W. and Eilers, A. and Wojarski, L.
    Advanced Engineering Materials 23 (2021)
    Reactive air brazing (RAB) is a cost-effective way to produce ceramic–ceramic or ceramic–metal brazed joints in air, without applying a protective gas atmosphere or a vacuum. In addition to conventional furnace technology, the brazing with induction heating can also be used effectively. Within the scope of this study the shrinkage and wetting behavior of self-developed brazing pastes with different CuO contents and two qualities of silver powders with coarse and fine particle size are investigated by optical dilatometry on alumina (Al2O3, 99.7% purity). Thereby, the fine silver powder quality reveals a significant swelling effect at high temperatures, leading to an expansion of densified powder compacts caused by evolving gases. Joining tests are performed on ceramic–steel brazed joints using a muffle furnace and induction heating for short brazing cycles. The brazing seams and interfaces of the joints are investigated using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). As a result, correlations between the brazing filler metal composition, the steel, and the brazing conditions are obtained. © 2020 The Authors. Published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/adem.202000711
  • 2021 • 468 Influence of the PVD process conditions on the incorporation of TiN nanoparticles into magnetron sputtered CrN thin films
    Tillmann, W. and Kokalj, D. and Stangier, D. and Fu, Q. and Kruis, F.E.
    Surface and Coatings Technology 409 (2021)
    CrTiN thin films are known to form a solid solution independent from the Ti content. Using a novel spatially separated synthesis approach, consisting of magnetron sputtering and atmospheric-pressure arc evaporation, artificial CrTiN nanocomposites were deposited. For the nanocomposite formation, TiN nanoparticles were synthesized using a transferred arc reactor and directly injected into growing CrN thin films using an aerodynamic lens system. The CrN and CrTiN thin films were deposited using various deposition conditions, such as heating power, substrate rotation velocity, nanoparticle injection distance, and cathode setup. The deposited thin films were analyzed regarding their physical structure, microstructure and mechanical properties. Based on the investigations, between 0.02 and 0.11 at.-% of TiN nanoparticles are embedded in the CrN matrix dependent on the deposition parameters. 2D GI-XRD experiments using synchrotron radiation confirm the nanocomposite structure for the two thin films with the highest TiN nanoparticle content. The crystallite size of the CrN thin film decreases from 9.4 ± 2.3 nm to 5.3 ± 1.2 nm due to the embedding of the nanoparticles. Concerning the physical structure, the nanoparticle injection leads to a change of the texture, as shown by the Debbye-Scherrer rings. Based on TEM-investigations, TiN nanoparticle agglomerates lead to a coarser microstructure of the CrN matrix. The hardness of the thin films is not significantly affected by the nanoparticle embedment. The nanoparticle injection distance and cathode setup reveal the highest impact on the film properties. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.surfcoat.2021.126935
  • 2021 • 467 Influence of the sampling probe on flame temperature, species, residence times and on the interpretation of ion signals of methane/oxygen flames in molecular beam mass spectrometry measurements
    Karakaya, Y. and Sellmann, J. and Wlokas, I. and Kasper, T.
    Combustion and Flame 229 (2021)
    Laminar flames are widely used to analyze the fundamentals of combustion processes using molecular beam mass spectrometry. The extraction of a representative sample from a flame by an intrusive sampling technique is challenging because of two main issues. First, the sampling probe itself perturbs the flow and temperature field, affecting the species profiles. These effects need to be characterized by 2-D fluid dynamic simulations to reveal sources of perturbations that are in particular suction and flame cooling. Second, some intermediate species interact with the sampling probe and are removed from the gas sample before analysis. The concentrations of these intermediates in the flames are often low and close to the detection limit. Naturally occurring ions can also be extracted from the flame by molecular beam sampling. Coupled with modern ion optical devices for ion transfer to the mass analyzer very high sensitivity can be reached in the detection of ionic species in flames. Similarities in the shape of measured relative concentration profiles indicate a connection between neutrals and the corresponding protonated molecules by proton transfer reactions. A quantification method of neutral flame species based on signals of the flame-sampled ions is presented and evaluated for the intermediate methanol in methane/oxygen/argon flames. The proposed method is based on equilibrium calculations that depend on temperature. To characterize the sampling process and demonstrate the validity of the quantification approach for ion measurements, the influence of the sampling probe on flame temperature and mole fraction profiles of the main species and the intermediate methanol are investigated by a combined experimental and simulation study. A comparison of the methanol profiles measured by conventional molecular beam sampling and the novel ion sampling technique reveal acceptable agreement. This work shows that if all aspects of sampling are considered as well as possible, the ion sampling technique allows access to kinetic data of neutral intermediates. © 2021
    view abstractdoi: 10.1016/j.combustflame.2021.02.034
  • 2021 • 466 Injection molding and near-complete densification of monolithic and al2o3 fiber-reinforced ti2alc max phase composites
    Badie, S. and Gabriel, R. and Sebold, D. and Vaßen, R. and Guillon, O. and Gonzalez-Julian, J.
    Materials 14 (2021)
    Near-net shape components composed of monolithic Ti2AlC and composites thereof, containing up to 20 vol.% Al2O3 fibers, were fabricated by powder injection molding. Fibers were homogeneously dispersed and preferentially oriented, due to flow constriction and shear-induced velocity gradients. After a two-stage debinding procedure, the injection-molded parts were sintered by pressureless sintering at 1250 °C and 1400 °C under argon, leading to relative densities of up to 70% and 92%, respectively. In order to achieve near-complete densification, field assisted sintering technology/spark plasma sintering in a graphite powder bed was used, yielding final relative densities of up to 98.6% and 97.2% for monolithic and composite parts, respectively. While the monolithic parts shrank isotropically, composite assemblies underwent anisotropic densification due to constrained sintering, on account of the ceramic fibers and their specific orientation. No significant increase, either in hardness or in toughness, upon the incorporation of Al2O3 fibers was observed. The 20 vol.% Al2O3 fiber-reinforced specimen accommodated deformation by producing neat and well-defined pyramidal indents at every load up to a 30 kgf (~294 N). © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/ma14133632
  • 2021 • 465 Innovations for the optimal use of weathering steel in steel and composite bridge construction [Innovationen zum optimalen Einsatz des wetterfesten Baustahls im Stahl- und Verbundbrückenbau]
    Ungermann, D. and Hatke, P. and Knyazeva, M. and Walther, F. and Lebelt, P. and Gehrke, J.
    Stahlbau 90 106-115 (2021)
    Innovations for the optimal use of weathering steel in steel and composite bridge construction. The research project “Innovations for the optimal use of weathering steel in steel and composite bridge construction” investigated essential aspects for the optimal use of weathering steel in steel and composite bridge construction. In addition to current investigations on the formation of the corrosion-inhibiting surface layer in the current atmosphere, the qualification of two geometry-independent and non-destructive measuring techniques for crack detection underneath the compact surface layer and their verification on real bridge structures was carried out. Furthermore, tests for the optimization of the slip factor of slip-resistant prestressed connections of weathering steel were carried out. Basically, the use of weathering steel offers both economic and ecological advantages compared to organically coated structural steel by the formation of its firmly adhering and corrosion-inhibiting surface layer, especially with regard to the present service life in bridge construction. This article summarises the main research findings to demonstrate the sustainable use and advantages of weathering steel in steel and composite bridge construction under the conditions of use in the current natural atmosphere. © 2021, Ernst und Sohn. All rights reserved.
    view abstractdoi: 10.1002/stab.202000090
  • 2021 • 464 InP-Based THz Beam Steering Leaky-Wave Antenna
    Lu, P. and Haddad, T. and Sievert, B. and Khani, B. and Makhlouf, S. and Dülme, S. and Estévez, J.F. and Rennings, A. and Erni, D. and Pfeiffer, U. and Stöhr, A.
    IEEE Transactions on Terahertz Science and Technology 11 218-230 (2021)
    For mobile THz applications, integrated beam steering THz transmitters are essential. Beam steering approaches using leaky-wave antennas (LWAs) are attractive in that regard since they do not require complex feeding control circuits and beam steering is simply accomplished by sweeping the operating frequency. To date, only a few THz LWAs have been reported. These LWAs are based on polymer or graphene substrates and thus, it is quite impossible to monolithically integrate these antennas with state-of-the-art indium phosphide (InP)-based photonic or electronic THz sources and receivers. Therefore, in this article, we report on an InP-based THz LWA for the first time. The developed and fabricated THz LWA consists of a periodic leaking microstrip line integrated with a grounded coplanar waveguide to microstrip line (GCPW-MSL) transition for future integration with InP-based photodiodes. For fabrication, a substrate-transfer process using silicon as carrier substrate for a 50-μm thin InP THz antenna chip has been established. By changing the operating frequency from 230 to 330 GHz, the fabricated antenna allows to sweep the beam direction quasi-linearly from-46° to 42°, i.e., the total scanning angle is 88°. The measured average realized gain and 3-dB beam width of a 1.5-mm wide InP LWA are ∼11 dBi and 10°. This article furthermore discusses the use of the fabricated LWA for THz interconnects. © 2011-2012 IEEE.
    view abstractdoi: 10.1109/TTHZ.2020.3039460
  • 2021 • 463 Insight into intramolecular chemical structure modifications by on-surface reaction using photoemission tomography
    Cojocariu, I. and Feyersinger, F. and Puschnig, P. and Schio, L. and Floreano, L. and Feyer, V. and Schneider, C.M.
    Chemical Communications 57 3050-3053 (2021)
    The sensitivity of photoemission tomography (PT) to directly probe single molecule on-surface intramolecular reactions will be shown here. PT application in the study of molecules possessing peripheral ligands and structural flexibility is tested on the temperature-induced dehydrogenation intramolecular reaction on Ag(100), leading from CoOEP to the final product CoTBP. Along with the ring-closure reaction, the electronic occupancy and energy level alignment of the frontier orbitals, as well as the oxidation state of the metal ion, are elucidated for both the CoOEP and CoTBP systems. © The Royal Society of Chemistry 2021.
    view abstractdoi: 10.1039/d1cc00311a
  • 2021 • 462 Insights in the Thermal Volume Transition of Poly(2-oxazoline) Hydrogels
    Segiet, D. and Stockmann, A. and Sadowski, J. and Katzenberg, F. and Tiller, J.C.
    Macromolecular Chemistry and Physics (2021)
    Polymers with a lower or an upper critical solution temperature (LCST or UCST) can precipitate in a very narrow temperature range. Cross-linking of such polymers and adding them to suited solvent results in smart gels that are capable of greatly changing their dimensions with changing temperature. This transition occurs very often in a broad temperature range, which limits the applicability of smart materials. To shed some light into the design of thermo-responsive hydrogels with a narrow phase transition, poly(2-ethyl-2-oxazoline) (PEtOx), poly(2-isopropyl-2-oxazoline), and statistical copolymers of 2-butyl-2-oxazoline and 2-ethyl-2-oxazoline, respectively, are synthesized and the concentration-dependent cloud point temperatures (Tcp) of the free polymers in aqueous media are determined in relation to the thermo-responsive swelling behavior of the respective hydrogels. A narrow thermal transition of the hydrogels can only be achieved when the Tcp of the free polymers in water is independent on the concentration. Aqueous salt solutions can render even PEtOx into a concentration independent LCST polymer. However, this salt effect does not work for hydrogels. © 2021 The Authors. Macromolecular Chemistry and Physics published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/macp.202100157
  • 2021 • 461 Insights into the mechanism of combustion synthesis of iron oxide nanoparticles gained by laser diagnostics, mass spectrometry, and numerical simulations: A mini-review
    Rahinov, I. and Sellmann, J. and Lalanne, M.R. and Nanjaiah, M. and Dreier, T. and Cheskis, S. and Wlokas, I.
    Energy and Fuels (2021)
    To fully master a scaled-up combustion synthesis of nanoparticles toward a wide library of materials with tailored functionalities, a detailed understanding of the underlying kinetic mechanism is required. In this respect, flame synthesis of iron oxide nanoparticles is a model case, being one of the better understood systems and guiding the way how other material synthesis systems could be advanced. In this mini-review, we highlight, on the example of an iron oxide system, an approach combining laser spectroscopy and mass spectrometry with detailed simulations. The experiments deliver information on time-temperature history and concentration field data for gas-phase species and condensable matter under well-defined conditions. The simulations, which can be considered as in silico experiments, combining detailed kinetic modeling with computational fluid dynamics, serve both for mechanism validation via comparison to experimental observables as well as for shedding light on quantities inaccessible by experiments. This approach shed light on precursor decomposition, initial stages of iron oxide particle formation, and precursor role in flame inhibition and provided insights into the effect of temperature-residence time history on nanoparticle formation, properties, and flame structure. © XXXX American Chemical Society.
    view abstractdoi: 10.1021/acs.energyfuels.0c03561
  • 2021 • 460 Intercritical annealing to achieve a positive strain-rate sensitivity of mechanical properties and suppression of macroscopic plastic instabilities in multi-phase medium-Mn steels
    Benzing, J.T. and Luecke, W.E. and Mates, S.P. and Ponge, D. and Raabe, D. and Wittig, J.E.
    Materials Science and Engineering A 803 (2021)
    This study investigates the high strain-rate tensile properties of a cold-rolled medium-Mn steel (Fe–12Mn–3Al-0.05C % in mass fraction) designed to have a multi-phase microstructure and positive strain-rate sensitivity. At the intercritical annealing temperature of 585 °C, increasing the annealing time from 0.5 h to 8 h increased the phase volume fraction of ultrafine-grained (UFG) austenite from 2% to 35% by reversion. The remainder of the microstructure was composed of UFG ferrite and recovered α′-martensite (the latter resembles the cold-rolled state). Servo hydraulic tension testing and Kolsky-bar tension testing were used to measure the tensile properties from quasi-static strain rates to dynamic strain rates (ε˙ = 10-4 s-1 to ε˙ = 103 s-1). The strain-rate sensitivities of the yield strength (YS) and ultimate tensile strength (UTS) were positive for both annealing times. Tensile properties and all non-contact imaging modalities (infrared imaging and digital image correlation) indicated an advantageous suppression of Lüders bands and Portevin Le Chatelier (PLC) bands (a critical challenge in multi-phase medium-Mn steel design) due to the unique combination of microstructural constituents and overall composition. Fracture surfaces of specimens annealed for 0.5 h showed some instances of localized cleavage fracture (approximately 30 μm wide areas and lath-like ridges). Specimens annealed for 8 h maintained a greater product of strength and elongation by at least 2.5 GPa % (on average for each strain rate). The relevant processing-structure-property relationships are discussed in the context of recommendations for design strategies concerning multi-phase steels such that homogeneous deformation behavior and positive strain-rate sensitivities can be achieved. © 2020
    view abstractdoi: 10.1016/j.msea.2020.140469
  • 2021 • 459 Interface Optimization via Fullerene Blends Enables Open-Circuit Voltages of 1.35 V in CH3NH3Pb(I0.8Br0.2)3 Solar Cells
    Liu, Z. and Siekmann, J. and Klingebiel, B. and Rau, U. and Kirchartz, T.
    Advanced Energy Materials (2021)
    Nonradiative recombination processes are the biggest hindrance to approaching the radiative limit of the open-circuit voltage for wide bandgap perovskite solar cells. In addition to high bulk quality, good interfaces and good energy level alignment for majority carriers at charge transport layer-absorber interfaces are crucial to minimize nonradiative recombination pathways. By tuning the lowest-unoccupied molecular-orbital of electron transport layers via the use of different fullerenes and fullerene blends, open-circuit voltages exceeding 1.35 V in CH3NH3Pb(I0.8Br0.2)3 device are demonstrated. Further optimization of mobility in binary fullerenes electron transport layers can boost the power conversion efficiency as high as 18.9%. It is noted in particular that the Voc fill factor product is &gt;1.096 V, which is the highest value reported for halide perovskites with this bandgap. © 2021 The Authors. Advanced Energy Materials published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/aenm.202003386
  • 2021 • 458 Interlayer bonding capability of additively manufactured polymer structures under high strain rate tensile and shear loading
    Striemann, P. and Gerdes, L. and Huelsbusch, D. and Niedermeier, M. and Walther, F.
    Polymers 13 (2021)
    Additive manufacturing of polymers via material extrusion and its future applications are gaining interest. Supporting the evolution from prototype to serial applications, additional testing conditions are needed. The additively manufactured and anisotropic polymers often show a weak point in the interlayer contact area in the manufacturing direction. Different process parameters, such as layer height, play a key role for generating the interlayer contact area. Since the manufacturing productivity depends on the layer height as well, a special focus is placed on this process parameter. A small layer height has the objective of achieving better material performance, whereas a larger layer height is characterized by better economy. Therefore, the capability‐ and economy‐oriented variation was investigated for strain rates between 2.5 and 250 s−1 under tensile and shear load conditions. The test series with dynamic loadings were designed monitoring future applications. The interlayer tensile tests were performed with a special specimen geometry, which enables a correction of the force measurement. By using a small specimen geometry with a force measurement directly on the specimen, the influence of travelling stress waves, which occur due to the impact at high strain rates, is reduced. The interlayer tensile tests indicate a strain rate dependency of additively manufactured polymers. The capability‐oriented variation achieves a higher ultimate tensile and shear strength compared to the economy‐oriented variation. The external and internal quality assessment indicates an increasing primary surface profile and void volume content for increasing the layer height. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/polym13081301
  • 2021 • 457 Internal Diameter Coating by Warm Spraying of Fine WC-12Co Powders (− 10 + 2 µm) with Very Short Spray Distances up to 10 mm
    Baumann, I. and Tillmann, W. and Schaak, C. and Schmidt, K. and Hagen, L. and Zajaczkowski, J. and Schmidtmann, G. and Matthäus, G. and Luo, W.
    Journal of Thermal Spray Technology (2021)
    The internal diameter (ID) coating by means of thermal spraying is currently experiencing growing interest in science and industry. In contrast to the well-established plasma- and arc-based spray techniques, there is a lack of knowledge concerning kinetic processes such as HVOF, HVAF and warm spray (WS). A major challenge represents the necessity of short spray distances and the compact design of novel ID spray guns with reduced combustion power. Conventional WC-Co powders (− 45 + 15 µm) are not able to achieve a sufficient heat and momentum transfer. The use of fine powders &lt; 15 µm offers an approach to overcome this drawback as they feature a larger surface-to-volume ratio and a lower mass. However, the processing of fine powders requires suitable spray equipment and a sensitive parameter adjustment. In this study, warm spraying of fine WC-12Co powders (− 10 + 2 µm) with a novel ID spray gun (HVOF + N2) “ID RED” (Thermico Engineering GmbH, Germany) was investigated. First, the flame profile as well as the in-flight behavior of the particles along the spray jet (spray distances SD = 10-80 mm) was analyzed at different nitrogen flows NF = 15-115 L/min to find suitable spray parameter intervals. Subsequently, planar steel samples were coated with SD = 10-50 mm and constant NF = 90 L/min. Analyses regarding the microstructure, the mechanical properties and the phase evolution of the coatings were performed. The aim was to study spraying with the novel ID gun and to scrutinize shortest feasible spray distances. Finally, steel tubes (internal diameter of 81.6 mm and a wall thickness of 10.0 mm) were coated with SD = 20 mm and NF = 90 L/min to investigate in how far the results can be transferred to ID parts. Correlations between the particle behavior, the microstructure and the coating properties were made. © 2021, The Author(s).
    view abstractdoi: 10.1007/s11666-021-01195-x
  • 2021 • 456 Internal photoeffect from a single quantum emitter
    Lochner, P. and Kerski, J. and Kurzmann, A. and Wieck, A.D. and Ludwig, A. and Geller, M. and Lorke, A.
    Physical Review B 103 (2021)
    We demonstrate by time-resolved resonance fluorescence measurements on a single self-assembled quantum dot an internal photoeffect that emits electrons from the dot by an intraband excitation. We find a linear dependence of the optically generated emission rate on the excitation intensity and use a rate equation model to deduce the involved rates. The emission rate is tunable over several orders of magnitude by adjusting the excitation intensity. Our findings show that a process that is well known in single atom spectroscopy (i.e., photoionization) can also be observed in the solid state. The results also quantify an important, but mostly neglected, mechanism that may fundamentally limit the coherence times in solid-state quantum optical devices. © 2021 American Physical Society.
    view abstractdoi: 10.1103/PhysRevB.103.075426
  • 2021 • 455 Interplay between nematicity and Bardasis-Schrieffer modes in the short-time dynamics of unconventional superconductors
    Müller, M.A. and Volkov, P.A. and Paul, I. and Eremin, I.M.
    Physical Review B 103 (2021)
    Motivated by the recent experiments suggesting the importance of nematicity in the phase diagrams of iron-based and cuprate high-Tc superconductors, we study the influence of nematicity on the collective modes inside the superconducting state in a nonequilibrium. In particular, we consider the signatures of collective modes in short-time dynamics of a system with competing nematic and s- and d-wave superconducting orders. In the rotationally symmetric state, we show that the Bardasis-Schrieffer mode, corresponding to the subdominant pairing, hybridizes with the nematic collective mode and merges into a single in-gap mode, with the mixing vanishing only close to the phase boundaries. For the d-wave ground state, we find that nematic interaction suppresses the damping of the collective oscillations in the short-time dynamics. Additionally, we find that even inside the nematic s+d-wave superconducting state, a Bardasis-Schrieffer-like mode leads to order parameter oscillations that strongly depend on the competition between the two pairing symmetries. We discuss the connection of our results to the recent pump-probe experiments on high-Tc superconductors. © 2021 American Physical Society.
    view abstractdoi: 10.1103/PhysRevB.103.024519
  • 2021 • 454 Interrogating Gas-Borne Nanoparticles Using Laser-Based Diagnostics and Bayesian Data Fusion
    Menser, J. and Daun, K. and Schulz, C.
    Journal of Physical Chemistry C 125 8382-8390 (2021)
    We demonstrate how the evaporation properties of gas-borne nanoscale materials, here liquid silicon and germanium nanoparticles, can be obtained through a novel combination of in situ time-resolved laser-induced incandescence (TiRe-LII) and phase-selective laser-induced breakdown spectroscopy (PS-LIBS) based on Bayesian data fusion. This approach reduces the uncertainty in the parameters describing evaporation and condensation by more than a factor of 2 compared to the conventional path and has the capability to provide much needed particle-size-dependent information on nanomaterial phase transitions at high temperature. The inferred parameters are generally consistent with those repeated in the literature but with reduced uncertainty and an extended temperature range. © 2021 American Chemical Society.
    view abstractdoi: 10.1021/acs.jpcc.0c10026
  • 2021 • 453 Intersection-distribution-based remapping between arbitrary meshes for staggered multi-material arbitrary Lagrangian-Eulerian hydrodynamics
    Kenamond, M. and Kuzmin, D. and Shashkov, M.
    Journal of Computational Physics 429 (2021)
    We present a new intersection-distribution-based remapping method between arbitrary polygonal meshes for indirect staggered multi-material arbitrary Lagrangian-Eulerian hydrodynamics. All cell-centered material quantities are conservatively remapped using intersections between the Lagrangian (old, source) mesh and the rezoned (new, target) mesh. The new nodal masses are obtained by conservative distribution of all material masses in each new cell to the cell's corners and then collecting those corner masses at new nodes. This distribution is done using a local constrained optimization approach for each cell in the new mesh. In order to remap nodal momentum we first define cell-centered momentum for each cell in the old mesh, conservatively remap this to the new mesh and then conservatively distribute the new zonal momentum to each cell's bounding nodes, again using local constrained optimization. Our method also conserves total energy by applying a new nodal kinetic energy correction that relies on a process similar to that used for remapping nodal mass and momentum. Cell-centered kinetic energy is computed, conservatively remapped and then distributed to nodes. The discrepancy between this conservatively remapped and actual nodal kinetic energy is then conservatively distributed to the internal energies of the materials in the cells surrounding each node. Unlike conventional cell-based corrections of this type, this new nodal kinetic energy correction has not been observed to drive material internal energy negative in any of our testing. Unlike flux based remapping, our new intersection-distribution method can be applied to remapping between source and target meshes that are arbitrarily different, which provides superior flexibility in the rezoning strategy. Our method is accurate, essentially conservative and essentially bounds preserving. © 2020 Elsevier Inc.
    view abstractdoi: 10.1016/j.jcp.2020.110014
  • 2021 • 452 Investigation of an atomic-layer-deposited Al2O3 diffusion barrier between Pt and Si for the use in atomic scale atom probe tomography studies on a combinatorial processing platform
    Li, Y. and Zanders, D. and Meischein, M. and Devi, A. and Ludwig, A.
    Surface and Interface Analysis 53 727-733 (2021)
    In order to enable the application of atomic probe tomography combinatorial processing platforms for atomic-scale investigations of phase evolution at elevated temperatures, the pre-sharpened Si tip of 10–20 nm in diameter must be protected against interdiffusion and reaction of the reactive Si with a film of interest by a conformal coating on the Si tip. It is shown that unwanted reactions can be suppressed by introducing a 20-nm-thick intermediate Al2O3 layer grown by atomic layer deposition (ALD). As a representative case, Pt is chosen as a film of interest, as it easily forms silicides. Whereas without the ALD coating diffusion/reactions occur, with the protective film, this is prevented for temperatures up to at least 600°C. The effectiveness of the Al2O3 layer serving as a diffusion barrier is not limited to a sharpened Si tip but works generally for all cases where a Si substrate is used. © 2021 The Authors. Surface and Interface Analysis published by John Wiley & Sons Ltd.
    view abstractdoi: 10.1002/sia.6955
  • 2021 • 451 Investigation of coolant distribution of bottle boring systems with computational fluid dynamics simulation
    Oezkaya, E. and Fuss, M. and Metzger, M. and Biermann, D.
    CIRP Journal of Manufacturing Science and Technology 35 259-267 (2021)
    For new developments of manufacturing processes in which cooling lubricants are used, the design of cutting tools plays an important role in achieving effective coolant flow behaviour. In this work, new bottle boring systems for profiling and finishing the ground and the wall of a bore, as well as a novel bottle boring system for the machining of non-circular bore profiles are simulative investigated, because both systems are too complex and costly to carry out experimental studies in the design stage. Since no established measuring equipment can be used due to the inaccessibility, a detailed flow analysis is carried out in this study using computational fluid dynamics (CFD) simulation. Since the two systems consist of numerous components with very complex geometries, a multi-body system has to be processed in order to create the respective fluid models. Subsequently, the fluid models could be generated and a meshing strategy adapted to the geometries and physical properties selected. The shear stress transport (k-ω-SST) turbulence model, which combines the advantages of wall-bounded and free-shear layer flow, was used to resolve the flow areas. The results show that both bottle boring system prototypes have an inadequate coolant supply and the importance of CFD usage in the development process in order to save development costs and to exploit the improvement potential for tool and process is emphasized. Based on the multi-body modelling the CFD simulation model, which considered the chip formation and the different engagement positions of the tool systems, are to be taken into account in further research work and corresponding optimizations are to be carried out. © 2021 CIRP
    view abstractdoi: 10.1016/j.cirpj.2021.05.012
  • 2021 • 450 Investigation of Cyclam Based Re-Complexes as Potential Electrocatalysts for the CO2 Reduction Reaction
    Gerschel, P. and Cordes, A.L. and Bimmermann, S. and Siegmund, D. and Metzler-Nolte, N. and Apfel, U.-P.
    Zeitschrift fur Anorganische und Allgemeine Chemie 647 968-977 (2021)
    Among the various homogenous electrocatalysts, especially Re(bpy)(CO)3Cl and [Ni(cyclam)]2+ were shown to be highly efficient for the selective conversion of CO2 to CO at moderate potentials. However, a purposeful combination of a ReI tricarbonyl unit with a cyclam ligand hitherto received no attention. Herein, we report on a series of cyclam based Re complexes comprising the original {N4} as well as heteroatom-altered ligand frameworks, describe their synthesis, reveal their coordination behavior and furthermore investigate their performance towards the electrochemical CO2 reduction. © 2021 The Authors. Zeitschrift für anorganische und allgemeine Chemie published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/zaac.202000450
  • 2021 • 449 Investigation of electrical power consumption of an additive process chain and empirical modelling as feature selection for machine learning algorithms
    Ravisankar, B. and Jaeger, E. and Meißner, M. and Wirtz, A. and Wiederkehr, P. and Rehtanz, C.
    Procedia CIRP 99 358-363 (2021)
    The focus on the fourth industrial revolution and advancements in 3D printing has reignited the need for energy efficient manufacturing. In particular, Selective Laser Melting (SLM), an additive manufacturing process, has garnered wide attention owing to its adaptability in producing lightweight components for metal industries. Reasonable material demand along with environmental and methodical capabilities of SLM machines has opened up an intriguing possibility to examine its power consumption as well as to determine its suitability for energy efficient manufacturing. In addition, the energy demand of SLM machines along with its occupancy time in a factory floor poses challenges to energy supply grid and subsequent effects on energy flexibility. Hence, it is necessary to determine energy demand of SLM process chain. This paper provides an empirical power consumption analysis of an additive process chain and interprets the power utilized by various process steps of an SLM machine. © 2021 The Authors. Published by Elsevier B.V.
    view abstractdoi: 10.1016/j.procir.2021.03.103
  • 2021 • 448 Investigation of joints from laser powder fusion processed and conventional material grades of 18MAR300 nickel maraging steel
    Tillmann, W. and Wojarski, L. and Henning, T.
    Welding in the World 65 1323-1331 (2021)
    Even though the buildup rate of laser powder bed fusion processes (LPBF) has steadily increased in recent years by using more and more powerful laser systems, the production of large-volume parts is still extremely cost-intensive. Joining of an additively manufactured complex part to a high-volume part made of conventional material is a promising technology to enhance economics. Today, constructors have to select the most economical joining process with respect to the individual field of application. The aim of this research was to investigate the hybrid joint properties of LBPF and conventionally casted 18MAR300 nickel maraging steel depending on the manufacturing process and the heat treatment condition. Therefore, the microstructure and the strength of the hybrid joints manufactured by LPBF or vacuum brazing were examined and compared to solid material and joints of similar material. It was found that the vacuum-brazed hybrid joints using a 50.8-μm-thick AuNi18 foil provide a high tensile strength of 904 MPa which is sufficient for a broad field of application. Furthermore, the additively manufactured hybrid samples offered with 1998 MPa a tensile strength more than twice as high but showed a considerable impact of buildup failures to the strength in general. © 2021, The Author(s).
    view abstractdoi: 10.1007/s40194-021-01096-1
  • 2021 • 447 Investigation of natural gas/hydrogen mixtures for exergy storage in a piston engine
    Rudolph, C. and Atakan, B.
    Energy 218 (2021)
    The conversion of mechanical to chemical energy offers an option for long-term and versatile energy storage. It was already proven that piston engines can be used as flexible reactors for energy conversion. Here, a novel method for energy conversion in piston engines is investigated, the pyrolysis of natural gas/hydrogen mixtures for energy storage. The supplied energy is stored by chemical conversion into hydrogen and higher energy hydrocarbons. The storage efficiency and the product composition are addressed here. To reach sufficiently high temperatures after compression, a dilution with 85–99% argon is used. The main products are hydrogen, acetylene, ethylene and benzene but also soot precursors are formed. The piston engine is simulated as a time-dependent four-stroke single-zone model with detailed chemical kinetics. The intake pressure is kept constant at 2 bar, while intake temperature, intake argon mole fraction and the hydrogen/natural gas ratio is varied. The hydrogen addition allows a reduction of the intake temperature and argon dilution but also reduces the storage power and efficiency. Yields of acetylene or ethylene are increased and the formation of soot precursors is suppressed. A storage power of 1.59 kW is reached with an efficiency of 52%. © 2020 Elsevier Ltd
    view abstractdoi: 10.1016/j.energy.2020.119375
  • 2021 • 446 Investigation of Structural Changes of Cu(I) and Ag(I) Complexes Utilizing a Flexible, Yet Sterically Demanding Multidentate Phosphine Oxide Ligand
    Kirst, C. and Zoller, F. and Bräuniger, T. and Mayer, P. and Fattakhova-Rohlfing, D. and Karaghiosoff, K.
    Inorganic Chemistry 60 2437-2445 (2021)
    The syntheses of a sterically demanding, multidentate bis(quinaldinyl)phenylphosphine oxide ligand and some Cu(I) and Ag(I) complexes thereof are described. By introducing a methylene group between the quinoline unit and phosphorus, the phosphine oxide ligand gains additional flexibility. This specific ligand design induces not only a versatile coordination chemistry but also a rarely observed and investigated behavior in solution. The flexibility of the birdlike ligand offers the unexpected opportunity of open-wing and closed-wing coordination to the metal. In fact, the determined crystal structures of these complexes show both orientations. Investigations of the ligand in solution show a strong dependency of the chemical shift of the CH2 protons on the solvent used. Variable-temperature, multinuclear NMR spectroscopy was carried out, and an interesting dynamic behavior of the complexes is observed. Due to the introduced flexibility, the quinaldinyl substituents change their arrangements from open-wing to closed-wing upon cooling, while still staying coordinated to the metal. This change in conformation is completely reversible when warming up the sample. Based on 2D NMR spectra measured at -80 °C, an assignment of the signals corresponding to the different arrangements was possible. Additionally, the copper(I) complex shows reversible redox activity in solution. The combination of structural flexibility of a multidentate ligand and the positive redox properties of the resulting complexes comprises key factors for a possible application of such compounds in transition-metal catalysis. Via a reorganization of the ligand, occurring transition states could be stabilized, and selectivity might be enhanced. © 2021 The Authors. Published by American Chemical Society.
    view abstractdoi: 10.1021/acs.inorgchem.0c03334
  • 2021 • 445 Investigation of the combustion of iron pentacarbonyl and the formation of key intermediates in iron oxide synthesis flames
    Karakaya, Y. and Kluge, S. and Wiggers, H. and Schulz, C. and Kasper, T.
    Chemical Engineering Science 230 (2021)
    The information of the gas phase kinetics are relevant for the development of detailed reaction mechanisms as well as for process design and control in flame synthesis. In this study, the decomposition of iron pentacarbonyl and the reaction pathways towards iron oxide clusters and particles in laminar H2/O2/Ar low-pressure synthesis flames are investigated. Gas-phase species are analyzed by photoionization and electron ionization mass spectrometry. The extraction of a representative sample from the particle-laden flow of a synthesis flame by an intrusive sampling technique for the analysis is challenging, because iron-intermediate species can condense easily. Cations can be extracted from the flame with a high efficient ion sampling technique that results in high sensitivity. Iron-containing cations provide evidence of the presence of key intermediates, e.g., Fe(OH)2, Fe(OH)3, Fe2O3, and larger Fe-O-clusters which are the dominant intermediates with respect to particle formation and need to be considered in future gas-phase reaction mechanisms. © 2020 Elsevier Ltd
    view abstractdoi: 10.1016/j.ces.2020.116169
  • 2021 • 444 Investigation of the effect of residual stresses in the subsurface on process forces for consecutive orthogonal cuts
    Wöste, F. and Kimm, J. and Bergmann, J.A. and Theisen, W. and Wiederkehr, P.
    Production Engineering (2021)
    The quality and surface integrity of machined parts is influenced by residual stresses in the subsurface resulting from cutting operations. These stress characteristics can not only affect functional properties such as fatigue life, but also the process forces during machining. Especially for orthogonal cutting as an appropriate experimental analogy setup for machining operations like milling, different undeformed chip thicknesses cause specific residual stress formations in the subsurface area. In this work, the process-related depth profile of the residual stress in AISI 4140 was investigated and correlated to the resulting cutting forces. Furthermore, an analysis of the microstructure of the cut material was performed, using additional characterization techniques such as electron backscatter diffraction and nanoindentation to account for subsurface alterations. On this basis, the influence of process-related stress profiles on the process forces for consecutive orthogonal cutting strategies is evaluated and compared to the results of a numerical model. The insights obtained provide a basis for future investigations on, e. g., empirical modeling of process forces including the influence of process-specific characteristics such as residual stress. © 2021, The Author(s).
    view abstractdoi: 10.1007/s11740-021-01058-y
  • 2021 • 443 Investigation of the frequency dependent spatio-temporal dynamics and controllability of microdischarges in unipolar pulsed plasma electrolytic oxidation
    Hermanns, P. and Boeddeker, S. and Bracht, V. and Bibinov, N. and Grundmeier, G. and Awakowicz, P.
    Journal of Physics D: Applied Physics 54 (2021)
    The unipolar pulsed-plasma electrolytic oxidation (PEO) of aluminum has been replaced by bipolar pulsed methods that use a so-called 'soft-sparking'mode. This method results in an effective reduction of intense microdischarges, which are detrimental to the oxide layer. In a previous publication, we developed an in-situ multivariable microdischarge control scheme using unipolar pulsing. Using this method, it is possible to restrict the mean microdischarge size to well-defined limits, while at the same time influencing the mean microdischarge energy, number density or spectral emission behaviour. This method operates well inside a frequency range of f = 1-20 kHz. Although this method shows highly desirable plasma control properties, the mechanisms defining this frequency-dependent controllability are unclear. The aim of this study is to visualize the spatio-temporal behavior of microdischarges in higher frequency ranges. First, a wavelet transform was performed to estimate the temporal evolution of microdischarge lifetimes. Ceramic coatings were then deposited on aluminum alloy substrates in an aqueous solution using unipolar pulsed galvanostatic PEO. The aluminum samples were coated for 30 min at frequencies of f1 = 50 Hz, f2 = 5 kHz and f3 = 100 kHz. High-speed imaging was carried out utilizing four synchronized intensified charge-coupled device (ICCD) cameras, each with a 500 ns exposure time. At f2 = 5 kHz, the microdischarges were still able to follow the electrical pulses. In this regime, the process can be divided into two stages, an initial charging of the substrate surface without plasma emission and a subsequent slower evolution of microdischarges. Equivalent circuit model descriptions are given for both processes. At f3 = 100 kHz, microdischarges were not able to follow the pulse frequency, as the lifetimes and risetimes of the microdischarge characteristics were longer than the pulse length. Reignition at the same spatial location, clustering and permanent ignition through pulse periods were observed. © 2020 IOP Publishing Ltd.
    view abstractdoi: 10.1088/1361-6463/abbde4
  • 2021 • 442 Investigation of the in situ thermal conductivity and absorption behavior of nanocomposite powder materials in laser powder bed fusion processes
    Pannitz, O. and Lüddecke, A. and Kwade, A. and Sehrt, J.T.
    Materials and Design 201 (2021)
    One of the AM processes for direct manufacturing of metallic components is powder bed fusion of metals using a laser beam system (PBF-LB/M), in which metallic powders are molten and solidified in a layer upon layer manner by a focused laser beam. In recent years, the focus has initially been on increasing the efficiency of the systems itself. However, the modification of standard AM metal alloys using nanoparticles offers the possibility to improve the PBF-LB/M-process concerning its process efficiency and actual densification and thermal conductivity. In this work, a methodology for an in-situ investigation of the thermal conductivity as well as the reflectance behavior of metallic powder materials during the PBF-LB/M-process is established. The powder material stainless steel 1.4404 was coated with different nanoparticles (few-layer graphene (FLG), silicon carbide (SiC)) and processed in a standardized build process. As a result, the reflectance rate of all modified materials could be increased. Besides, the thermal conductivity of the material is attested to be a decisive and influencing factor for the quality of the final component. Thus, an improved relative density was achieved using the FLG/1.4404 and SiC/1.4404 (1 vol%) due to the increased thermal conductivity of the material. Also significant defects in the cross section were visible at SiC/1.4404 (4 vol%). © 2021 The Authors
    view abstractdoi: 10.1016/j.matdes.2021.109530
  • 2021 • 441 Investigation of the orientation relationship between nano-sized G-phase precipitates and austenite with scanning nano-beam electron diffraction using a pixelated detector
    Cautaerts, N. and Rauch, E.F. and Jeong, J. and Dehm, G. and Liebscher, C.H.
    Scripta Materialia 201 (2021)
    Scanning nano-beam electron diffraction with a pixelated detector was employed to investigate the orientation relationship of nanometer sized, irradiation induced G-phase (M6Ni16Si7) precipitates in an austenite matrix. Using this detector, the faint diffraction spots originating from the small G-phase particles could be resolved simultaneously as the intense matrix reflections. The diffraction patterns were analyzed using a two-stage template matching scheme, whereby the matrix is indexed first and the precipitates are indexed second after subtraction of the matrix contribution to the diffraction patterns. The results show that G-phase forms with orientation relationships relative to austenite that are characteristic of face-centered cubic (FCC) to body-centered cubic (BCC) transformations. This work demonstrates that nano-beam electron diffraction with a pixelated detector is a promising technique to investigate orientation relationships of nano-sized precipitates with complex crystal structures in other material systems with relative ease. © 2021 The Author(s)
    view abstractdoi: 10.1016/j.scriptamat.2021.113930
  • 2021 • 440 Investigation of the stress corrosion cracking behavior on T24 material under the operational conditions in the water wall
    Ullrich, C. and Tillmann, W. and Rademacher, H.-G. and Zielke, R. and Körner, P.
    International Journal of Pressure Vessels and Piping 190 (2021)
    The requirements for materials and their strength significantly increased with the new generation of coal fired power plants operating at steam temperatures of up to 620 °C. Therefore, new materials were introduced to fulfill the defined needs. During the commissioning process of the first plant many cracks occurred in welds of T24 material. The cracks showed clear characteristics of stress corrosion cracking (SCC). Not knowing the exact parameters that lead to cracking, experiments in high temperature water were carried out. Slow tensile tests in a controlled environment are extremely well suited to generate information about material's SCC sensitivity. In the present paper, the influence of the temperature, the oxygen concentration of water, the pre-treatment of the specimen and the heat treatment to the SCC are investigated. Furthermore critical limits for the cracking are defined where possible. © 2021
    view abstractdoi: 10.1016/j.ijpvp.2021.104317
  • 2021 • 439 Investigation of Turbulent Pulverized Solid Fuel Combustion with Detailed Homogeneous and Heterogeneous Kinetics
    Wang, B. and Shamooni, A. and Stein, O.T. and Kronenburg, A. and Kempf, A.M. and Debiagi, P. and Hasse, C.
    Energy and Fuels (2021)
    A comprehensive Euler-Lagrange framework for pulverized coal combustion using detailed multi-step heterogeneous kinetics is presented. The heterogeneous kinetics employ the POLIMI model that involves 37 species (22 solid species and 15 gas species) and 49 reactions to describe detailed pyrolysis as well as char oxidation, gasification, and annealing for a wide range of coals. The porous structure of the coal particles is considered, and the heterogeneous reactions are assumed to occur throughout the entire particle in a volume-based approach. The ordinary differential equations of the heterogeneous kinetics are integrated on each Lagrangian coal particle and predict the conversion of the raw coal components to light volatile hydrocarbons, heavy tar species, and char off-gases. Hence, the composition of the solid fuel components and the released gas changes dynamically in space and time, providing high-fidelity predictions of solid fuel combustion. The chemical conversion of the released species in the gas phase is described by a homogeneous kinetic mechanism with 76 species and 973 reactions that was reduced from the comprehensive CRECK-G-1407 kinetic mechanism. The new modeling framework is employed within carrier-phase direct numerical simulations (CP-DNS) of pulverized coal combustion in a three-dimensional turbulent mixing layer. This configuration includes the additional physics of turbulence and particle group combustion by mixing solid fuel particles suspended in a primary oxidizer stream with the products from lean volatile combustion in a secondary stream. The CP-DNS results are analyzed with and without the available set of 14 char conversion reactions, and a low degree of char conversion indicated by an increased rate of CO production is captured for particles with temperatures higher than 1800 K. The CP-DNS results from the detailed POLIMI approach feature a distinct bimodal shape of the volatile release curve and multi-regime combustion. The POLIMI data are used to evaluate the predictive capability of simpler pyrolysis models. The original competing two-step model (C2SM) by Kobayashi is investigated and shown to predict heavily delayed ignition. A new competing two-step devolatilization approach is proposed as an alternative model reduction suitable for fitting bimodal volatile release rates, such as that predicted by POLIMI. The CP-DNS using the alternative pyrolysis model faithfully captures the onset of ignition and multi-regime flame branches. Differences arise in the local tar species compositions in the gas phase as a result of the time-varying (POLIMI) and fixed (new C2SM) volatile compositions for the respective models. The flame structure is further analyzed by chemical explosive mode analysis (CEMA), and the occurrence of premixed and non-premixed flames zones is confirmed, whereas a simpler flame index analysis fails to correctly indicate the multi-regime nature of the flame. This recognition of multi-regime combustion serves as a guidance for selecting suitable conditioning variables for flamelet and other combustion submodels in large eddy simulation. © 2021 American Chemical Society.
    view abstractdoi: 10.1021/acs.energyfuels.0c03479
  • 2021 • 438 Investigations of electron-electron and interlayer electron-phonon coupling in van der Waals hBN/WSe2/hBN heterostructures by photoluminescence excitation experiments
    Jadczak, J. and Kutrowska-Girzycka, J. and Schindler, J.J. and Debus, J. and Watanabe, K. and Taniguchi, T. and Ho, C.-H. and Bryja, L.
    Materials 14 1-12 (2021)
    Monolayers of transition metal dichalcogenides (TMDs) with their unique physical properties are very promising for future applications in novel electronic devices. In TMDs monolayers, strong and opposite spin splittings of the energy gaps at the K points allow for exciting carriers with various combinations of valley and spin indices using circularly polarized light, which can further be used in spintronics and valleytronics. The physical properties of van der Waals heterostructures composed of TMDs monolayers and hexagonal boron nitride (hBN) layers significantly depend on different kinds of interactions. Here, we report on observing both a strong increase in the emission intensity as well as a preservation of the helicity of the excitation light in the emission from hBN/WSe2/hBN heterostructures related to interlayer electron-phonon coupling. In combined low-temperature (T = 7 K) reflectivity contrast and photoluminescence excitation experiments, we find that the increase in the emission intensity is attributed to a double resonance, where the laser excitation and the combined Raman mode A′ 1 (WSe2) + ZO (hBN) are in resonance with the excited (2s) and ground (1s) states of the A exciton in a WSe2 monolayer. In reference to the 2s state, our interpretation is in contrast with previous reports, in which this state has been attributed to the hybrid exciton state existing only in the hBN-encapsulated WSe2 monolayer. Moreover, we observe that the electron-phonon coupling also enhances the helicity preservation of the exciting light in the emission of all observed excitonic complexes. The highest helicity preservation of more than 60% is obtained in the emission of the neutral biexciton and negatively charged exciton (trion) in its triplet state. Additionally, to the best of our knowledge, the strongly intensified emission of the neutral biexciton XX0 at double resonance condition is observed for the first time. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/ma14020399
  • 2021 • 437 Investigations on polarization dynamics of birefringent spin-VCSELs
    Jung, N. and Lindemann, M. and Pusch, T. and Hashib, M.F. and Hoti, P. and Debernardi, P. and Michalzik, R. and Hofmann, M.R. and Gerhardt, N.C.
    Proceedings of SPIE - The International Society for Optical Engineering 11704 (2021)
    Vertical-cavity surface-emitting lasers (VCSELs) are widely used in optical data communication mainly in data centers for short-haul transmissions. However, their intensity modulation resonance frequency does not exceed 40 GHz which also limits the achievable modulation bandwidth and data rate. In contrast, spin-VCSELs can overcome these bandwidth limitations by modulating spin and polarization instead of current and intensity. In spin-VCSELs, the birefringence determines the resonance frequency of the polarization dynamics as well as the modulation bandwidth. We control the birefringence and thus the polarization dynamics via the elasto-optic effect by mechanically or thermally induced strain providing polarization oscillation frequencies up to more than 200 GHz. Detailed analysis shows that spin-VCSELs offer polarization dynamics with good signal strength even when operating close to threshold and at high temperatures. Here, we analyze devices with integrated surface gratings. VCSELs with different grating periods as well as mesa diameters and resulting different oxide apertures were investigated. &copy; 2021 SPIE. © 2021 SPIE. All rights reserved.
    view abstractdoi: 10.1117/12.2577488
  • 2021 • 436 Ion association in hydrothermal aqueous NaCl solutions: implications for the microscopic structure of supercritical water
    Elbers, M. and Schmidt, C. and Sternemann, C. and Sahle, C.J. and Jahn, S. and Albers, C. and Sakrowski, R. and Gretarsson, H. and Sundermann, M. and Tolan, M. and Wilke, M.
    Physical Chemistry Chemical Physics 23 14845-14856 (2021)
    Knowledge of the microscopic structure of fluids and changes thereof with pressure and temperature is important for the understanding of chemistry and geochemical processes. In this work we investigate the influence of sodium chloride on the hydrogen-bond network in aqueous solution up to supercritical conditions. A combination ofin situX-ray Raman scattering andab initiomolecular dynamics simulations is used to probe the oxygen K-edge of the alkali halide aqueous solution in order to obtain unique information about the oxygen's local coordination around the ions,e.g.solvation-shell structure and the influence of ion pairing. The measured spectra exhibit systematic temperature dependent changes, which are entirely reproduced by calculations on the basis of structural snapshots obtainedvia ab initiomolecular dynamics simulations. Analysis of the simulated trajectories allowed us to extract detailed structural information. This combined analysis reveals a net destabilizing effect of the dissolved ions which is reduced with rising temperature. The observed increased formation of contact ion pairs and occurrence of larger polyatomic clusters at higher temperatures can be identified as a driving force behind the increasing structural similarity between the salt solution and pure water at elevated temperatures and pressures with drawback on the role of hydrogen bonding in the hot fluid. We discuss our findings in view of recent results on hot NaOH and HCl aqueous fluids and emphasize the importance of ion pairing in the interpretation of the microscopic structure of water. © the Owner Societies 2021.
    view abstractdoi: 10.1039/d1cp01490k
  • 2021 • 435 Ion dynamics in capacitively coupled argon-xenon discharges
    Klich, M. and Wilczek, S. and Janssen, J.F.J. and Brinkmann, R.P. and Mussenbrock, T. and Trieschmann, J.
    Plasma Sources Science and Technology 30 (2021)
    An argon-xenon (Ar/Xe) plasma is used as a model system for complex plasmas. Based on this system, symmetric low-pressure capacitively coupled radiofrequency discharges are examined utilizing particle-in-cell/Monte Carlo collisions simulations. In addition to the simulation, an analytical energy balance model fed with the simulation data is applied to analyze the findings further. This work focuses on investigating the ion dynamics in a plasma with two ion species and a gas mixture as background. By varying the gas composition and driving voltage of the single-frequency discharge, fundamental mechanics of the discharge, such as the evolution of the plasma density and the energy dispersion, are discussed. Thereby, close attention is paid to these measures' influence on the ion energy distribution functions at the electrode surfaces. The results show that both the gas composition and the driving voltage can significantly impact the ion dynamics. The mixing ratio of argon to xenon allows for shifting the distribution function for one ion species from collisionless to collision dominated. The mixing ratio serves as a control parameter for the ion flux and the impingement energy of ions at the surfaces. Additionally, a synergy effect between the ionization of argon and the ionization of xenon is found and discussed. © 2021 The Author(s). Published by IOP Publishing Ltd.
    view abstractdoi: 10.1088/1361-6595/ac02b0
  • 2021 • 434 Is Cu instability during the CO2reduction reaction governed by the applied potential or the local CO concentration?
    Wilde, P. and O'Mara, P.B. and Junqueira, J.R.C. and Tarnev, T. and Benedetti, T.M. and Andronescu, C. and Chen, Y.-T. and Tilley, R.D. and Schuhmann, W. and Gooding, J.J.
    Chemical Science 12 4028-4033 (2021)
    Cu-based catalysts have shown structural instability during the electrochemical CO2reduction reaction (CO2RR). However, studies on monometallic Cu catalysts do not allow a nuanced differentiation between the contribution of the applied potential and the local concentration of CO as the reaction intermediate since both are inevitably linked. We first use bimetallic Ag-core/porous Cu-shell nanoparticles, which utilise nanoconfinement to generate high local CO concentrations at the Ag core at potentials at which the Cu shell is still inactive for the CO2RR. Usingoperandoliquid cell TEM in combination withex situTEM, we can unequivocally confirm that the local CO concentration is the main source for the Cu instability. The local CO concentration is then modulated by replacing the Ag-core with a Pd-core which further confirms the role of high local CO concentrations. Product quantification during CO2RR reveals an inherent trade-off between stability, selectivity and activity in both systems. © The Royal Society of Chemistry 2021.
    view abstractdoi: 10.1039/d0sc05990k
  • 2021 • 433 Journal of Chemical & Engineering Data: An Update from the Editorial Team
    Siepmann, J.I. and Gardas, R.L. and Kofke, D.A. and Pini, R. and Sadowski, G. and Schwarz, C.E. and Wu, J.
    Journal of Chemical and Engineering Data 66 1-2 (2021)
    doi: 10.1021/acs.jced.0c01080
  • 2021 • 432 Journal of chemical & engineering data: Why change the cover page?
    Siepmann, J.I. and Gardas, R.L. and Kofke, D.A. and Pini, R. and Sadowski, G. and Schwarz, C.E. and Wu, J.
    Journal of Chemical and Engineering Data 66 859-860 (2021)
    doi: 10.1021/acs.jced.1c00048
  • 2021 • 431 Journal of Power Sources Modelling electro-chemical induced stresses in all-solid-state batteries: Anisotropy effects in cathodes and cell design optimisation
    Mücke, R. and Finsterbusch, M. and Kaghazchi, P. and Fattakhova-Rohlfing, D. and Guillon, O.
    Journal of Power Sources 489 (2021)
    All-solid-state lithium batteries offer promising advantages in energy density and safety compared to conventional lithium ion batteries. However, the majority of this type of batteries suffers from a low cycling stability, which might originate from mechanical fatigue caused by mechanical stresses and strains in the rigid structure. We introduce a general approach to model and analyse the stresses in rigid cathode/electrolyte electrodes on a cell level, which enables to develop optimised cell designs with an improved mechanical stability. We apply this approach on composite cathodes with a Li7La3Zr2O12 (LLZO) ceramic electrolyte and LiCoO2 (LCO) active material. Using the 3D microstructure of a real cathode, the stresses inside a free-standing electrode and model cells with a thin and a thick LLZO separator are calculated for the charging cycle considering isotropic and anisotropic material properties of LCO as well as non-textured and textured crystallographic alignment. Compared to randomly oriented crystals, the textured crystallographic alignment of LCO grains, introduced by the manufacturing process, has a significant effect and yields considerably better stress distributions in all cell configurations investigated. The design of optimised all-solid-state cells with reduced separator thickness leads to a significantly more favourable stress state than a typical lab scale separator-supported cell. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.jpowsour.2020.229430
  • 2021 • 430 Kinetics of the Thermal Decomposition of Ethylsilane: Shock-Tube and Modeling Study
    Sela, P. and Peukert, S. and Somnitz, H. and Janbazi, H. and Wlokas, I. and Herzler, J. and Fikri, M. and Schulz, C.
    Energy and Fuels (2021)
    The thermal decomposition of ethylsilane (H3SiC2H5, EtSiH3) is investigated behind reflected shock waves and the gas composition is analyzed by gas chromatography/mass spectrometry (GC/MS) and high-repetition-rate time-of-flight mass spectrometry (HRR-TOF-MS) in a temperature range of 990-1330 K and pressure range of 1-2.5 bar. The unimolecular decomposition of EtSiH3 is considered to be initiated via a molecular elimination of H2 (H3SiC2H5 → H2 + HSiC2H5) followed by reactions of cyclic silicon-containing species. The main observed stable products were ethylene (C2H4) and silane (SiH4). Measurements are performed with a large excess of a silylene scavenger (C2H2) to suppress bimolecular reactions caused by silylene (SiH2) and to extract unimolecular rate constants. A kinetics mechanism accounting for the gas-phase chemistry of EtSiH3 is developed, which consists of 24 Si-containing species, 31 reactions of Si-containing species, and a set of new thermochemical data. The derived unimolecular rate constant is represented by the Arrhenius expression kuni(T) = 1.96 × 1012 s-1 exp(-205 kJ mol-1/RT). The experimental data is reproduced very well by simulations based on the mechanism of this work and is in very good agreement with literature values. It is shown that EtSiH3 is a promising precursor for the synthesis of SiC nanoparticles. © 2021 American Chemical Society.
    view abstractdoi: 10.1021/acs.energyfuels.0c03425
  • 2021 • 429 Kondo holes in strongly correlated impurity arrays: RKKY-driven Kondo screening and hole-hole interactions
    Eickhoff, F. and Anders, F.B.
    Physical Review B 104 (2021)
    The emerging and screening of local magnetic moments in solids have been investigated for more than 60 years. Local vacancies as in graphene or in heavy fermions can induce decoupled bound states that lead to the formation of local moments. In this paper, we address the puzzling question how these local moments can be screened and what determines the additionally emerging low-temperature scale. We review the initial problem for half-filled conduction bands from two complementary perspectives: By a single-particle supercell analysis in the uncorrelated limit and by the Lieb-Mathis theorem for systems with a large Coulomb interaction U. Applying Wilson's numerical renormalization group approach to a recently developed mapping of the problem onto an effective low-energy description of a Kondo hole with up to Nf=7 correlated impurities as background, we proof that the stable local moments are subject to screening by three different mechanisms. Firstly the local moments are delocalized by a finite U beyond the single-particle bound state. We find a Kosterlitz-Thouless type transition governed by an exponentially suppressed low-energy scale of a counterintuitive Kondo form with Jeff∝Un for small U, where n>1 depends on the precise model. Secondly, we show that away from half-filling the local moment phase becomes unstable and is replaced by two types of singlet phases that are adiabatically connected. At a critical value for the band center, the physics is governed by an exponentially suppressed Kondo scale approaching the strong coupling phase that is replaced by a singlet formation via antiferromagnetic RKKY interaction for large deviation from the critical values. Thirdly, we show that the local magnetic moment can be screened by a Kondo hole orbital at finite energy, even though the orbital occupation is negligible: An additional low-energy scale emerges below which the localized moment is quenched. Similarities to the experimental findings in Ce1-xLaxPd3 are pointed out. © 2021 American Physical Society.
    view abstractdoi: 10.1103/PhysRevB.104.045115
  • 2021 • 428 Korn inequalities for incompatible tensor fields in three space dimensions with conformally invariant dislocation energy
    Lewintan, P. and Müller, S. and Neff, P.
    Calculus of Variations and Partial Differential Equations 60 (2021)
    Let Ω ⊂ R3 be an open and bounded set with Lipschitz boundary and outward unit normal ν. For 1 &lt; p&lt; ∞ we establish an improved version of the generalized Lp-Korn inequality for incompatible tensor fields P in the new Banach space W01,p,r(devsymCurl;Ω,R3×3)={P∈Lp(Ω;R3×3)∣devsymCurlP∈Lr(Ω;R3×3),devsym(P×ν)=0on∂Ω}where r∈[1,∞),1r≤1p+13,r&gt;1ifp=32.Specifically, there exists a constant c= c(p, Ω , r) &gt; 0 such that the inequality ‖P‖Lp(Ω,R3×3)≤c(‖symP‖Lp(Ω,R3×3)+‖devsymCurlP‖Lr(Ω,R3×3))holds for all tensor fields P∈W01,p,r(devsymCurl;Ω,R3×3). Here, devX:=X-13tr(X)1 denotes the deviatoric (trace-free) part of a 3 × 3 matrix X and the boundary condition is understood in a suitable weak sense. This estimate also holds true if the boundary condition is only satisfied on a relatively open, non-empty subset Γ ⊂ ∂Ω. If no boundary conditions are imposed then the estimate holds after taking the quotient with the finite-dimensional space KS,dSC which is determined by the conditions symP=0 and devsymCurlP=0. In that case one can replace ‖devsymCurlP‖Lr(Ω,R3×3) by ‖devsymCurlP‖W-1,p(Ω,R3×3). The new Lp-estimate implies a classical Korn’s inequality with weak boundary conditions by choosing P= D u and a deviatoric-symmetric generalization of Poincaré’s inequality by choosing P=A∈so(3). The proof relies on a representation of the third derivatives D 3P in terms of D2devsymCurlP combined with the Lions lemma and the Nečas estimate. We also discuss applications of the new inequality to the relaxed micromorphic model, to Cosserat models with the weakest form of the curvature energy, to gradient plasticity with plastic spin and to incompatible linear elasticity. © 2021, The Author(s).
    view abstractdoi: 10.1007/s00526-021-02000-x
  • 2021 • 427 K-sign depth: From asymptotics to efficient implementation
    Malcherczyk, D. and Leckey, K. and Müller, C.H.
    Journal of Statistical Planning and Inference 215 344-355 (2021)
    The K-sign depth (K-depth) of a model parameter θ in a data set is the relative number of K-tuples among its residual vector that have alternating signs. The K-depth test based on K-depth, recently proposed by Leckey et al. (2020), is equivalent to the classical residual-based sign test for K=2, but is much more powerful for K≥3. This test has two major drawbacks. First, the computation of the K-depth is fairly time consuming having a polynomial time complexity of degree K, and second, the test requires knowledge about the quantiles of the test statistic which previously had to be obtained by simulation for each sample size individually. We tackle both of these drawbacks by presenting a limit theorem for the distribution of the test statistic and deriving an (asymptotically equivalent) form of the K-depth which can be computed efficiently. For K=3, such a limit theorem was already derived in Kustosz et al. (2016a) by mimicking the proof for U-statistics. We provide here a much shorter proof based on Donsker's theorem and extend it to any K≥3. As part of the proof, we derive an asymptotically equivalent form of the K-depth which can be computed in linear time. This alternative and the original implementation of the K-depth are compared with respect to their runtimes and absolute difference. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.jspi.2021.04.006
  • 2021 • 426 Laboratory Investigations on the Installation of Fasteners in Fiber Reinforced Concrete
    Spyridis, P. and Walter, L. and Dreier, J. and Biermann, D.
    RILEM Bookseries 30 801-812 (2021)
    A significant aspect regarding the use of post-installed anchors in concrete is related to constructability, and mainly the characteristics of possible geometrical configurations. Specifically for fibre reinforced concrete (FRC), as fibre strengths or dosages increase, these configurations may change. One of the critical parameters is the minimum allowable distance from the edge, which can significantly influence the flexibility of using post-installed anchors, or even the possibility to install them in the first place. This geometrical parameter strongly depends on the drilling and anchoring procedure, as various technologies are available. This paper will present and compare the various available technologies for fastenings, and it will focus on setting experiments in fibre reinforced concrete by use of challenging means for drilling and setting, i.e. hammer drilling, mortar injection and expansion anchors. The influence of fibres in the installation and tightening of post-installed anchors is particularly analysed. The results of the study reveal the possibilities for extended applications of fastenings in fibre reinforced concrete, as compared to plain concrete. © 2021, RILEM.
    view abstractdoi: 10.1007/978-3-030-58482-5_71
  • 2021 • 425 Large strain flow curves of sheet metals by sheet extrusion
    Kolpak, F. and Traphöner, H. and Hering, O. and Tekkaya, A.E., (1)
    CIRP Annals 70 247-250 (2021)
    Metal sheets are forward extruded at large plastic strains up to 1.6. The sheet specimens are placed between two half-cylindrical billets and cold-extruded collectively. While extruding the sheets, their central zone is plastically deformed nearly homogeneously under a deviatoric stress state equivalent to simple tension. Tensile test specimens are extracted from the extruded sheets at various extrusion strains delivering flow stresses at discrete large plastic strains of the flow curve. Sheet thicknesses as thin as 0.2 mm could be tested successfully. Steel and aluminum alloys with different strengths were investigated. Results were compared with in-plane torsion test measurements. © 2021 CIRP
    view abstractdoi: 10.1016/j.cirp.2021.03.023
  • 2021 • 424 Large-Area, Two-Dimensional MoS2Exfoliated on Gold: Direct Experimental Access to the Metal-Semiconductor Interface
    Pollmann, E. and Sleziona, S. and Foller, T. and Hagemann, U. and Gorynski, C. and Petri, O. and Madauß, L. and Breuer, L. and Schleberger, M.
    ACS Omega 6 15929-15939 (2021)
    Two-dimensional semiconductors such as MoS2 are promising for future electrical devices. The interface to metals is a crucial and critical aspect for these devices because undesirably high resistances due to Fermi level pinning are present, resulting in unwanted energy losses. To date, experimental information on such junctions has been obtained mainly indirectly by evaluating transistor characteristics. The fact that the metal-semiconductor interface is typically embedded, further complicates the investigation of the underlying physical mechanisms at the interface. Here, we present a method to provide access to a realistic metal-semiconductor interface by large-area exfoliation of single-layer MoS2 on clean polycrystalline gold surfaces. This approach allows us to measure the relative charge neutrality level at the MoS2-gold interface and its spatial variation almost directly using Kelvin probe force microscopy even under ambient conditions. By bringing together hitherto unconnected findings about the MoS2-gold interface, we can explain the anomalous Raman signature of MoS2 in contact to metals [ACS Nano. 7, 2013, 11350] which has been the subject of intense recent discussions. In detail, we identify the unusual Raman mode as the A1g mode with a reduced Raman shift (397 cm-1) due to the weakening of the Mo-S bond. Combined with our X-ray photoelectron spectroscopy data and the measured charge neutrality level, this is in good agreement with a previously predicted mechanism for Fermi level pinning at the MoS2-gold interface [Nano Lett. 14, 2014, 1714]. As a consequence, the strength of the MoS2-gold contact can be determined from the intensity ratio between the reduced A1greduced mode and the unperturbed A1g mode. © 2021 The Authors. Published by American Chemical Society.
    view abstractdoi: 10.1021/acsomega.1c01570
  • 2021 • 423 Large-Eddy Simulation of a Lifted High-Pressure Jet-Flame with Direct Chemistry
    Gruhlke, P. and Janbazi, H. and Wollny, P. and Wlokas, I. and Beck, C. and Janus, B. and Kempf, A.M.
    Combustion Science and Technology (2021)
    A large-eddy simulation is presented of a challenging high-pressure jet flame case that is representative of state of the art, dry low-NO x and low-CO real gas turbine combustion. A reaction scheme is developed for lifted lean premixed high pressure methane jet flames, and tested by three-dimensional large-eddy simulation of an experiment, for which very detailed data are available. Auto-ignition-delay times of different mixtures of fresh gas and products have been introduced as a novel optimization criterion for the mechanism development. The new mechanism has been developed by a genetic algorithm-based reduction and optimization, and consists of 15 species and 18 reactions. The large-eddy simulations are performed using a finite rate chemistry (FRC) approach and the dynamic thickened flame (DTF) model to investigate a lifted jet flame at high pressure in a gas turbine model combustor. In the simulations, the novel mechanism is compared to a similar mechanism that was generated without this criterion, and the well-established Lu19 mechanism. With the new mechanism, the LES predicts the flame as accurately as with Lu19, at a significantly lower cost. Further post processing with Lagrangian tracer particles confirmed that ignition events occur in the region corresponding to the liftoff height estimated in the experiment, which is corroborated by a chemical explosive mode analysis (CEMA). Overall, the newly developed mechanism with the novel optimization criterion was found to provide a better agreement with the experiments than previous mechanisms of similar cost, or a comparable agreement to a mechanism of significantly higher cost. © 2021 Taylor & Francis Group, LLC.
    view abstractdoi: 10.1080/00102202.2021.1903886
  • 2021 • 422 Large-Scale Production of Carbon-Supported Cobalt-Based Functional Nanoparticles for Oxygen Evolution Reaction
    Bähr, A. and Petersen, H. and Tüysüz, H.
    ChemCatChem (2021)
    A series of Co-based nanoparticles supported on activated carbon was synthesized by using waste tea leaves as a template as well as a sustainable carbon source. The crystal structure of the Co particles was adjusted by post-treatments with H2O2, ethanol vapor, and H2, which result in Co3O4, CoO, and metallic Co phases, respectively. After these different treatments, the composite materials consist of small Co-based nanoparticles with an average crystallite size of 6–14 nm supported on activated carbon with apparent specific surface areas up to 1065 m2 g−1. Correlations between the structure of the materials and their activity for the oxygen evolution reaction (OER) were established, whereby the post-treatment with ethanol vapor was found to yield the most effective electrocatalyst. The material shows good stability at 10 mA cm−2 over 10 h and reaches a mass activity of 2.9 A mgCo−1, which is even higher than pristine ordered mesoporous Co3O4. The superior electrocatalytic performance is ascribed to a high dispersion of Co-based nanoparticles and the conductivity of the activated carbon that facilitate the charge transport. © 2021 The Authors. ChemCatChem published by Wiley-VCH GmbH.
    view abstractdoi: 10.1002/cctc.202100594
  • 2021 • 421 Large-scale synthesis of iron oxide/graphene hybrid materials as highly efficient photo-Fenton catalyst for water remediation
    Hammad, M. and Fortugno, P. and Hardt, S. and Kim, C. and Salamon, S. and Schmidt, T.C. and Wende, H. and Schulz, C. and Wiggers, H.
    Environmental Technology and Innovation 21 (2021)
    The Photo-Fenton reaction is an advanced oxidation process to break down organic pollutants in aqueous systems. Moreover, the scalable synthesis and engineering of stable catalysts with a high specific surface area is extremely important for the practical application of the Photo-Fenton process. In the current study, we developed a low-cost method for large-scale production of iron oxide/graphene nanostructures with a controllable graphene loading for the photo-Fenton reaction. Under optimal condition, high efficiencies of degradation (&gt;99%) of methylene blue, rhodamine B, acid orange 7, and phenol at a concentration (60 mg/mL) were reached in 60 min under UV-A irradiation (1.6 mW/cm2) with mineralization of 72, 77, 82, and 48%, respectively. More importantly, the iron oxide/graphene nanocomposites exhibited good stability over a wide range of pH (from 3 to 9) and can be magnetically separated from the solution and repeatedly used with consistent photocatalytic performance. This enhanced removal efficiency of the iron oxide/graphene nanostructure compared to iron oxide nanoparticles is attributed to the accelerated transfer of photo-generated electrons between iron oxide and graphene and its relatively large surface area. The results demonstrate that the iron oxide/graphene system could be potentially utilized for many environmental treatment processes. © 2020 Elsevier B.V.
    view abstractdoi: 10.1016/j.eti.2020.101239
  • 2021 • 420 Laser- and Ion-Induced Defect Engineering in WS2 Monolayers
    Asaithambi, A. and Kozubek, R. and Prinz, G.M. and Reale, F. and Pollmann, E. and Ney, M. and Mattevi, C. and Schleberger, M. and Lorke, A.
    Physica Status Solidi - Rapid Research Letters 15 (2021)
    Tungsten disulfide is one of the prominent transition metal dichalcogenide materials, which shows a transition from an indirect to a direct bandgap as the layer thickness is reduced down to a monolayer. To use (Formula presented.) monolayers in devices, detailed knowledge about the luminescence properties regarding not only the excitonic but also the defect-induced contributions is needed. Herein, (Formula presented.) monolayers are irradiated with (Formula presented.) ions with different fluences to create different defect densities. Apart from the excitonic contributions, two additional emission bands are observed at low temperatures. These bands can be reduced or even suppressed, if the flakes are exposed to laser light with powers up to 1.5 mW. Increasing the temperature up to room temperature leads to recovery of this emission, so that the luminescence properties can be modified using laser excitation and temperature. The defect bands emerging after ion irradiation are attributed to vacancy defects together with physisorbed adsorbates at different defect sites. © 2020 The Authors. Physica Status Solidi (RRL) – Rapid Research Letters published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/pssr.202000466
  • 2021 • 419 Laser metal deposition of Al0.6CoCrFeNi with Ti & C additions using elemental powder blends
    Asabre, A. and Wilms, M.B. and Kostka, A. and Gemagami, P. and Weisheit, A. and Laplanche, G.
    Surface and Coatings Technology 418 (2021)
    Laser metal deposition (LMD) was used to in-situ alloy a crack-free Al0.6CoCrFeNi compositionally complex alloy (CCA) with 3 at.% Ti and 0.25 at.% C additions on an initially ferritic H10 tool steel from an elemental powder blend. After LMD, the material was annealed at 900 °C for 30 min to induce martensitic hardening in the substrate. The CCA in both as-deposited and annealed states exhibited a lamellar microstructure consisting of four phases: a matrix of interwoven disordered and ordered body-centered cubic phases, titanium carbides distributed randomly within the microstructure, and disordered face-centered cubic (FCC) plates that precipitated at the grain boundaries and grew towards the center of the grains. Chemical analyses along the build-up direction of the coating revealed a compositional gradient, similar in both as-deposited and annealed states, due to the intermixing between the substrate and the CCA. Despite a strong variation of the Fe-content, the hardness and the microstructure remain roughly constant in the major part of the as-deposited coating, which contains a large fraction of FCC plates that are beneficial to increase ductility and ensure a good compatibility with the substrate. In contrast, the upper part of the as-deposited coating, corresponding to the last solidified melt pool after LMD, has a much lower FCC fraction with an enhanced hardness. After annealing, the hardness of the tool steel substrate significantly increased and the FCC volume fraction in the coating increased from ~16% (as-deposited) to ~58%. Overall the microstructure of the coating became more homogeneous while its hardness decreased only by 10–15%. These results demonstrate that the CCA can be employed as a protective coating on a less expensive tool steel to improve its lifetime during service. © 2021 The Author(s)
    view abstractdoi: 10.1016/j.surfcoat.2021.127233
  • 2021 • 418 Laser powder bed fusion of polymers: Quantitative research direction indices
    Kusoglu, I.M. and Doñate‐buendía, C. and Barcikowski, S. and Gökce, B.
    Materials 14 1-26 (2021)
    Research on Laser Powder Bed Fusion (L‐PBF) of polymer powder feedstocks has raised over the last decade due to the increased utilization of the fabricated parts in aerospace, automotive, electronics, and healthcare applications. A total of 600 Science Citation Indexed articles were published on the topic of L‐PBF of polymer powder feedstocks in the last decade, being cited more than 10,000 times leading to an h‐index of 46. This study statistically evaluates the 100 most cited articles to extract reported material, process, and as‐built part properties to analyze the research trends. PA12, PEEK, and TPU are the most employed polymer powder feedstocks, while size, flowability, and thermal behavior are the standardly reported material properties. Likewise, process properties such as laser power, scanning speed, hatch spacing, powder layer thickness, volumetric energy density, and areal energy density are extracted and evaluated. In addition, material and process properties of the as‐built parts such as tensile test, flexural test, and volumetric porosity contents are analyzed. The incorporation of additives is found to be an effective route to enhance mechanical and functional properties. Carbon‐based additives are typically employed in applications where mechanical properties are essential. Carbon fibers, Ca‐phosphates, and SiO2 are the most reported additives in the evaluated SCI‐expanded articles for L‐PBF of polymer powder feedstocks. A comprehensive data matrix is extracted from the evaluated SCI‐index publications, and a principal component analysis (PCA) is performed to explore correlations between reported material, process, and as‐built parts. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/ma14051169
  • 2021 • 417 Lattice-shifted nematic quantum critical point in FeSe1−xSx
    Chibani, S. and Farina, D. and Massat, P. and Cazayous, M. and Sacuto, A. and Urata, T. and Tanabe, Y. and Tanigaki, K. and Böhmer, A.E. and Canfield, P.C. and Merz, M. and Karlsson, S. and Strobel, P. and Toulemonde, P. and Paul...
    npj Quantum Materials 6 (2021)
    We report the evolution of nematic fluctuations in FeSe1−xSx single crystals as a function of Sulfur content x across the nematic quantum critical point (QCP) xc ~ 0.17 via Raman scattering. The Raman spectra in the B1g nematic channel consist of two components, but only the low energy one displays clear fingerprints of critical behavior and is attributed to itinerant carriers. Curie–Weiss analysis of the associated nematic susceptibility indicates a substantial effect of nemato-elastic coupling, which shifts the location of the nematic QCP. We argue that this lattice-induced shift likely explains the absence of any enhancement of the superconducting transition temperature at the QCP. The presence of two components in the nematic fluctuations spectrum is attributed to the dual aspect of electronic degrees of freedom in Hund’s metals, with both itinerant carriers and local moments contributing to the nematic susceptibility. © 2021, The Author(s).
    view abstractdoi: 10.1038/s41535-021-00336-3
  • 2021 • 416 Layer-by-Layer Deposited Hybrid Polymer Coatings Based on Polysaccharides and Zwitterionic Silanes with Marine Antifouling Properties
    Yu, W. and Wang, Y. and Gnutt, P. and Wanka, R. and Krause, L.M.K. and Finlay, J.A. and Clare, A.S. and Rosenhahn, A.
    ACS Applied Bio Materials 4 2385-2397 (2021)
    Polyelectrolyte multilayer (PEM) assembly is a versatile tool to construct low-fouling coatings. For application in the marine environment, their structure needs to be stabilized by covalent linkage. Here, we introduce an approach for spin coating of silane-based sol-gel chemistries using layer-by-layer assembly of polysaccharide-based hybrid polymer coatings (LBLHPs). The silane sol-gel chemistry allows the films to be cross-linked under water-based and mild reaction conditions. Two different silanes were used for this purpose, a conventional triethoxymethyl silane and a de novo synthesized zwitterionic silane. The polysaccharide-silane hybrid polymer coatings were thoroughly characterized with spectroscopic ellipsometry, water contact angle (WCA) goniometry, attenuated total reflection-Fourier transform infrared spectroscopy, and atomic force microscopy. The coatings showed good stability in seawater, smooth surfaces, a high degree of hydration, and WCAs below or close to the Berg limit. LBLHPs showed low-fouling properties in biological assays against nonspecific protein adsorption, attachment of the diatom Navicula perminuta, and settlement of zoospores of the macroalga Ulva linza. © 2021 American Chemical Society.
    view abstractdoi: 10.1021/acsabm.0c01253
  • 2021 • 415 Least-squares finite element method for a meso-scale model of the spread of covid-19
    Bertrand, F. and Pirch, E.
    Computation 9 1-22 (2021)
    This paper investigates numerical properties of a flux-based finite element method for the discretization of a SEIQRD (susceptible-exposed-infected-quarantined-recovered-deceased) model for the spread of COVID-19. The model is largely based on the SEIRD (susceptible-exposed-infected-recovered-deceased) models developed in recent works, with additional extension by a quarantined compartment of the living population and the resulting first-order system of coupled PDEs is solved by a Least-Squares meso-scale method. We incorporate several data on political measures for the containment of the spread gathered during the course of the year 2020 and develop an indicator that influences the predictions calculated by the method. The numerical experiments conducted show a promising accuracy of predictions of the space-time behavior of the virus compared to the real disease spreading data. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/computation9020018
  • 2021 • 414 Least-squares formulations for eigenvalue problems associated with linear elasticity
    Bertrand, F. and Boffi, D.
    Computers and Mathematics with Applications 95 19-27 (2021)
    We study the approximation of the spectrum of least-squares operators arising from linear elasticity. We consider a two-field (stress/displacement) and a three-field (stress/displacement/vorticity) formulation; other formulations might be analyzed with similar techniques. We prove a priori estimates and we confirm the theoretical results with simple two-dimensional numerical experiments. © 2021 The Author(s)
    view abstractdoi: 10.1016/j.camwa.2020.12.013
  • 2021 • 413 Lensless digital holographic microscopy as an efficient method to monitor enzymatic plastic degradation
    Schnitzler, L. and Zarzycki, J. and Gerhard, M. and Konde, S. and Rexer, K.-H. and Erb, T.J. and Maier, U.G. and Koch, M. and Hofmann, M.R. and Moog, D.
    Marine Pollution Bulletin 163 (2021)
    A big challenge of the 21st century is to cope with the huge amounts of plastic waste on Earth. Especially the oceans are heavily polluted with plastics. To counteract this issue, biological (enzymatic) plastic decomposition is increasingly gaining attention. Recently it was shown that polyethylene terephthalate (PET) can be degraded in a saltwater-based environment using bacterial PETase produced by a marine diatom. At moderate temperatures, plastic biodegradation is slow and requires sensitive methods for detection, at least at initial stages. However, conventional methods for verifying the plastic degradation are either complex, expensive, time-consuming or they interfere with the degradation process. Here, we adapt lensless digital holographic microscopy (LDHM) as a new application for efficiently monitoring enzymatic degradation of a PET glycol copolymer (PETG). LDHM is a cost-effective, compact and sensitive optical method. We demonstrate enzymatic PETG degradation over a time course of 43 days employing numerical analysis of LDHM images. © 2020 Elsevier Ltd
    view abstractdoi: 10.1016/j.marpolbul.2020.111950
  • 2021 • 412 Limited Elemental Mixing in Nanoparticles Generated by Ultrashort Pulse Laser Ablation of AgCu Bilayer Thin Films in a Liquid Environment: Atomistic Modeling and Experiments
    Shih, C.-Y. and Chen, C. and Rehbock, C. and Tymoczko, A. and Wiedwald, U. and Kamp, M. and Schuermann, U. and Kienle, L. and Barcikowski, S. and Zhigilei, L.V.
    Journal of Physical Chemistry C (2021)
    Pulsed laser ablation in liquids (PLAL) is a promising technique for the generation of colloidal alloy nanoparticles that are of high demand in a broad range of fields, including catalysis, additive manufacturing, and biomedicine. Many of the applications have stringent requirements on the nanoparticle composition and size distributions, which can only be met through innovations in the PLAL technique guided by a clear understanding of the nanoparticle formation mechanisms. In this work, we undertake a combined computational and experimental study of the nanoparticle formation mechanisms in ultrashort PLAL of Ag/Cu and Cu/Ag bilayer thin films. Experimental probing of the composition of individual nanoparticles and predictions from large-scale atomistic simulations provide consistent evidence of limited mixing between the two components from bilayer films by PLAL. The simulated and experimental distributions of nanoparticle compositions exhibit an enhanced abundance of Ag-rich and Cu-rich nanoparticles, as well as a strongly depressed population of well-mixed alloy nanoparticles. The surprising observation that the nanoscale phase separation of the two components in the bilayer films manifests itself in the sharp departure from the complete quantitative mixing in the colloidal nanoparticles is explained by the complex dynamic interaction between the ablation plume and liquid environment revealed in the simulations of the initial stage of the ablation process. The simulations predict that rapid deceleration of the ablation plume by the liquid environment results in the formation of a transient hot and dense metal region at the front of the plume, which hampers the mixing of the two components and, at the same time, contributes to the stratification of the plume in the emerging cavitation bubble. As a result, nanoparticles of different sizes and compositions are produced in different parts of the emerging cavitation bubble during the first nanoseconds of the ablation process. Notably, the diameters of the largest nanoparticles generated in the simulations of the initial stage of the ablation process are more than twice larger than the thickness of the original bilayer films. This observation provides a plausible scenario for the formation of large nanoparticles observed in the experiments. The conclusion on limited elemental mixing in the nanoparticles is validated in simulations of bilayers with different spatial order of Cu and Ag layers, even though the two systems exhibit some notable quantitative differences mainly related to the different strength of electron-phonon coupling in Cu and Ag. Overall, the results of this study provide new insights into the formation mechanism of bimetallic nanoparticles in ultrashort PLAL from thin bilayer targets and suggest that the formation of alloy nanoparticles from immiscible elements may be hampered for targets featuring distinctive elemental segregation. © 2021 American Chemical Society.
    view abstractdoi: 10.1021/acs.jpcc.0c09970
  • 2021 • 411 Link between plasma properties with morphological, structural and mechanical properties of thin Ti films deposited by high power impulse magnetron sputtering
    Moskovkin, P. and Maszl, C. and Schierholz, R. and Breilmann, W. and Petersen, J. and Pflug, A. and Muller, J. and Raza, M. and Konstantinidis, S. and von Keudell, A. and Lucas, S.
    Surface and Coatings Technology 418 (2021)
    The main focus of this work is to correlate the basic plasma properties with morphological, structural and mechanical properties of thin films to bridge the gap between the energy source, the plasma and materials. For this purpose, the deposition and growth of thin titanium films deposited by high power impulse magnetron sputtering (HiPIMS) at various discharge power densities, from 0.17 kW/cm2 to 3.5 kW/cm2 were studied, both experimentally and by kinetic Monte Carlo simulation. Simulations of film growth were performed with a three-dimensional kinetic Monte Carlo code (NASCAM) with ion fraction and species energy determined experimentally by mass spectroscopy. Our approach, which is not purely empirically driven, intends to reveal some insights of the mechanisms underlying the synthesis process, which determine the intrinsic material properties. In order to link HiPIMS plasma parameters and Ti film properties, we used different techniques to analyse Ti films. TEM, X-ray diffraction and AFM were used to evaluate the structural and morphological properties of the films, and nano indention was used to evaluate their mechanical properties. We observed that the orientation of micro-crystals, which constitute the films, changes when the discharge power density increases. At the same time, we show that the films nano hardness changes non-monotonically with the increase of the discharge power density; it decreases first, then increases. The surface roughness behaviour is also non-monotonic; first increasing, then decreasing with the further increase of the discharge power density. 3D modelling helped to reveal that these non-monotonic evolutions are due to a transition between thermally-driven to ballistically-driven Ti atom mobility. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.surfcoat.2021.127235
  • 2021 • 410 Link between Structural and Optical Properties of CoxFe3- xO4Nanoparticles and Thin Films with Different Co/Fe Ratios
    Kampermann, L. and Klein, J. and Korte, J. and Kowollik, O. and Pfingsten, O. and Smola, T. and Saddeler, S. and Piotrowiak, T.H. and Salamon, S. and Landers, J. and Wende, H. and Ludwig, A. and Schulz, S. and Bacher, G.
    Journal of Physical Chemistry C (2021)
    CoxFe3-xO4 nanoparticles (x = 0.4 to x = 2.5) and thin films (x = 0.9 to x = 2.2) are analyzed by Raman, absorption, and photoluminescence spectroscopy to link structural and optical properties to different cobalt to iron (Co/Fe) ratios. Raman spectroscopy shows that with decreasing Co content, the crystal structure changes from a predominantly normal cubic spinel phase to a mixed inverse spinel phase. This finding is supported by absorption spectroscopy that points out that inter valence charge transfer (IVCT) processes between octahedrally coordinated Co2+ and Fe3+ cations become more prominent with increasing Fe content. Independent of the Co/Fe ratio, CoxFe3-xO4 nanoparticles show a broad photoluminescence (PL) band with a maximum at around 510 nm. Time-resolved photoluminescence spectroscopy shows subnanosecond lifetimes and temperature-resolved photoluminescence experiments reveal that the green PL increases with decreasing temperature (300 to 10 K) while showing no temperature-dependent shift in energy. It is proposed that this green PL originates from OH-groups on the particles' surface. © 2021 The Authors. Published by American Chemical Society.
    view abstractdoi: 10.1021/acs.jpcc.0c11277
  • 2021 • 409 Long-Range Ordering Effects in Magnetic Nanoparticles
    Myrovali, E. and Papadopoulos, K. and Iglesias, I. and Spasova, M. and Farle, M. and Wiedwald, U. and Angelakeris, M.
    ACS Applied Materials and Interfaces 13 21602-21612 (2021)
    The challenge for synthesizing magnetic nanoparticle chains may be achieved under the application of fixation fields, which are the externally applied fields, enhancing collective magnetic features due to adequate control of dipolar interactions among magnetic nanoparticles. However, relatively little attention has been devoted to how size, concentration of magnetic nanoparticles, and intensity of an external magnetic field affect the evolution of chain structures and collective magnetic features. Here, iron oxide nanoparticles are developed by the coprecipitation method at diameters below (10 and 20 nm) and above (50 and 80 nm) their superparamagnetic limit (at about 25 nm) and then are subjected to a tunable fixation field (40-400 mT). Eventually, the fixation field dictates smaller particles to form chain structures in two steps, first forming clusters and then guiding chain formation via "cluster-cluster"interactions, whereas larger particles readily form chains via "particle-particle"interactions. In both cases, dipolar interactions between the neighboring nanoparticles augment, leading to a substantial increase in their collective magnetic features which in turn results in magnetic particle hyperthermia efficiency enhancement of up to one order of magnitude. This study provides new perspectives for magnetic nanoparticles by arranging them in chain formulations as enhanced performance magnetic actors in magnetically driven magnetic applications. ©
    view abstractdoi: 10.1021/acsami.1c01820
  • 2021 • 408 Low temperature sintering of fully inorganic all-solid-state batteries – Impact of interfaces on full cell performance
    Ihrig, M. and Finsterbusch, M. and Tsai, C.-L. and Laptev, A.M. and Tu, C.-H. and Bram, M. and Sohn, Y.J. and Ye, R. and Sevinc, S. and Lin, S.-K. and Fattakhova-Rohlfing, D. and Guillon, O.
    Journal of Power Sources 482 (2021)
    One of the necessary prerequisites to advance the electrochemical performance of Li7La3Zr2O12 (LLZ) based all-solid-state lithium batteries is the manufacturing of dense composite cathodes from cathode active material (CAM) and the LLZ ceramic solid electrolyte. However, free co-sintering of LLZ and CAM mixtures requires temperatures above 1000 °C which often leads to decomposition and secondary phase formation, especially for high energy CAMs. In our study we present a completely dry processing route which is fast, free of any sintering additives and coatings and suitable to fabricate dense mixed cathodes, pure LLZ separators and multilayers of the two. Through application of high mechanical pressure during Field-Assisted Sintering we were able to reduce the sintering temperature down to 675–750 °C with dwell times as low as 10 min, while still obtaining 95% theoretical density for LCO/LLZ mixtures. The low sintering temperature is suitable for high energy CAMs, but leads to a significant effect of surface impurities, especially from powder handling in air, and affects the crystallinity of the CAM/LLZ interface. In the present paper we investigate the impact of resulting interfaces on the ionic conductivity, the interfacial impedance and the cycling stability of produced cells and propose the optimization strategy. © 2020 Elsevier B.V.
    view abstractdoi: 10.1016/j.jpowsour.2020.228905
  • 2021 • 407 Low-noise Yb:CALGO optical frequency comb
    Molteni, L.M. and Canella, F. and Pirzio, F. and Betz, M. and Vicentini, E. and Coluccelli, N. and Piccinno, G. and Agnesi, A. and Laporta, P. and Galzerano, G.
    Optics Express 29 19495-19505 (2021)
    We report on a compact optical frequency comb, operating in the wavelength range from 670 to 1500 nm, based on diode-pumped low-noise femtosecond Yb:CALGO amplified laser system. Both the carrier-envelope offset and repetition rate are phase-locked to reference synthesizers. A full characterization of the frequency comb, in terms of frequency stability, phase noise analysis, and optical beating against a single-frequency non-planar ring oscillator Nd:YAG laser, is presented, showing the excellent properties of the Yb:CALGO comb. © 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
    view abstractdoi: 10.1364/OE.428603
  • 2021 • 406 Low-temperature and low-pressure effective fluorescence lifetimes and spectra of gaseous anisole and toluene
    Beuting, M. and Dreier, T. and Schulz, C. and Endres, T.
    Applied Physics B: Lasers and Optics 127 (2021)
    Fluorescence spectra and lifetimes of anisole and toluene vapor in nitrogen have been measured at conditions below ambient (257–293 K and 100–2000 mbar) upon excitation with 266-nm laser light to expand the applicable range of anisole and toluene laser-induced fluorescence (LIF) for conditions below room temperature that occur in expanding flows and cases with strong evaporative cooling. Anisole fluorescence spectra broaden with decreasing pressure while fluorescence lifetimes decrease simultaneously. This is consistent with a more pronounced effect of internal vibrational redistribution on the overall fluorescence signal and can be explained by significantly reduced collision rates. In the case of toluene, the transition from photo-induced heating to photo-induced cooling was observed for the first time for 266 nm. The data confirm predictions of earlier work and is particularly important for the advancement of the available photo-physical (step-ladder) models: since those transitions mark points where the molecules are already thermalized after excitation (i.e., no vibrational relaxation occurs during deactivation), they are important support points for fitting empirical parameters and allow analytical determination of the ground state energy transferred to the excited state. The data enable temperature and/or pressure sensing, e.g., in accelerating cold flows using laser-induced fluorescence of both tracers. © 2021, The Author(s).
    view abstractdoi: 10.1007/s00340-021-07605-w
  • 2021 • 405 Lp -trace-free version of the generalized Korn inequality for incompatible tensor fields in arbitrary dimensions
    Lewintan, P. and Neff, P.
    Zeitschrift fur Angewandte Mathematik und Physik 72 (2021)
    For n≥ 3 and 1 &lt; p&lt; ∞, we prove an Lp-version of the generalized trace-free Korn-type inequality for incompatible, p-integrable tensor fields P: Ω → Rn×n having p-integrable generalized Curl n and generalized vanishing tangential trace Pτl=0 on ∂Ω , denoting by {τl}l=1,…,n-1 a moving tangent frame on ∂Ω. More precisely, there exists a constant c= c(n, p, Ω) such that ‖P‖Lp(Ω,Rn×n)≤c(‖devnsymP‖Lp(Ω,Rn×n)+‖CurlnP‖Lp(Ω,Rn×n(n-1)2)),where the generalized Curl n is given by (CurlnP)ijk:=∂iPkj-∂jPki and [InlineEquation not available: see fulltext.] denotes the deviatoric (trace-free) part of the square matrix X. The improvement towards the three-dimensional case comes from a novel matrix representation of the generalized cross product. © 2021, The Author(s).
    view abstractdoi: 10.1007/s00033-021-01550-6
  • 2021 • 404 Lymphocyte transformation test: History and current approaches
    Sachs, B. and Fatangare, A. and Sickmann, A. and Glässner, A.
    Journal of Immunological Methods 493 (2021)
    Drug-induced hypersensitivity reactions encompass a variety of different clinical phenotypes ranging from harmless rashes to fatal reactions. They can be classified into allergic (i.e. drug allergy) and non-allergic reactions (i.e. non-allergic hypersensitivity). Drug allergies in turn can either be antibody (e.g. IgE) or T cell-mediated. One of the diagnostic tools for the in vitro detection of drug allergy is the lymphocyte transformation test (LTT) which is based on the activation and expansion of the drug-specific memory T cells following co-incubation of the patient's peripheral mononuclear cells (PMBC) with the suspected drug in vitro. The read-out parameter in the classical LTT is T cell proliferation which can be measured as counts per minute following the addition of radiolabeled thymidine to the cell culture. However, in the course of time different modifications of the classical LTT with regard to the read-out parameters and methods have been proposed. Likewise, variations of the LTT platform itself have been described in the literature. This review article describes the development of the classical LTT and its use in the context of drug allergy detection and summarizes the modifications which have been published over time. © 2021 The Authors
    view abstractdoi: 10.1016/j.jim.2021.113036
  • 2021 • 403 Machine Learning in Adaptive FETI-DP: Reducing the Effort in Sampling
    Heinlein, A. and Klawonn, A. and Lanser, M. and Weber, J.
    Lecture Notes in Computational Science and Engineering 139 593-603 (2021)
    The convergence rate of classic domain decomposition methods in general deteriorates severely for large discontinuities in the coefficient functions of the considered partial differential equation. To retain the robustness for such highly heterogeneous problems, the coarse space can be enriched by additional coarse basis functions. These can be obtained by solving local generalized eigenvalue problems on subdomain edges. In order to reduce the number of eigenvalue problems and thus the computational cost, we use a neural network to predict the geometric location of critical edges, i.e., edges where the eigenvalue problem is indispensable. As input data for the neural network, we use function evaluations of the coefficient function within the two subdomains adjacent to an edge. In the present article, we examine the effect of computing the input data only in a neighborhood of the edge, i.e., on slabs next to the edge. We show numerical results for both the training data as well as for a concrete test problem in form of a microsection subsection for linear elasticity problems. We observe that computing the sampling points only in one half or one quarter of each subdomain still provides robust algorithms. © 2021, Springer Nature Switzerland AG.
    view abstractdoi: 10.1007/978-3-030-55874-1_58
  • 2021 • 402 Machine-learning-enhanced time-of-flight mass spectrometry analysis
    Wei, Y. and Varanasi, R.S. and Schwarz, T. and Gomell, L. and Zhao, H. and Larson, D.J. and Sun, B. and Liu, G. and Chen, H. and Raabe, D. and Gault, B.
    Patterns 2 (2021)
    Mass spectrometry is a widespread approach used to work out what the constituents of a material are. Atoms and molecules are removed from the material and collected, and subsequently, a critical step is to infer their correct identities based on patterns formed in their mass-to-charge ratios and relative isotopic abundances. However, this identification step still mainly relies on individual users' expertise, making its standardization challenging, and hindering efficient data processing. Here, we introduce an approach that leverages modern machine learning technique to identify peak patterns in time-of-flight mass spectra within microseconds, outperforming human users without loss of accuracy. Our approach is cross-validated on mass spectra generated from different time-of-flight mass spectrometry (ToF-MS) techniques, offering the ToF-MS community an open-source, intelligent mass spectra analysis. Time-of-flight mass spectrometry (ToF-MS) is a mainstream analytical technique widely used in biology, chemistry, and materials science. ToF-MS provides quantitative compositional analysis with high sensitivity across a wide dynamic range of mass-to-charge ratios. A critical step in ToF-MS is to infer the identity of the detected ions. Here, we introduce a machine-learning-enhanced algorithm to provide a user-independent approach to performing this identification using patterns from the natural isotopic abundances of individual atomic and molecular ions, without human labeling or prior knowledge of composition. Results from several materials and techniques are compared with those obtained by field experts. Our open-source, easy-to-implement, reliable analytic method accelerates this identification process. A wide range of ToF-MS-based applications can benefit from our approach, e.g., hunting for patterns of biomarkers or for contamination on solid surfaces in high-throughput data. A machine-learning application for the accelerated data processing and interpretation of time-of-flight mass spectrometry is presented. The machine learns patterns in a human-label-free manner, making the process easy to implement and the result highly reproducible. © 2020 The Authors
    view abstractdoi: 10.1016/j.patter.2020.100192
  • 2021 • 401 Magnetic exchange interactions in bilayer CrX3 (X=Cl,Br,and I): A critical assessment of the DFT+U approach MAGNETIC EXCHANGE INTERACTIONS in BILAYER ... SOUMYAJIT SARKAR and PETER KRATZER
    Sarkar, S. and Kratzer, P.
    Physical Review B 103 (2021)
    We perform calculations with the DFT+U approach for the three Cr trihalides CrI3, CrBr3, and CrCl3 with the aim to determine magnetic exchange interactions and magnetic ordering temperatures. A comprehensive investigation is carried out to assess the role of the Hubbard parameter U as well as of the schemes used to correct for the double counting (DC) of the Coulomb interaction. For the bilayer systems, both with low-temperature (LT) or high-temperature (HT) stacking, magnetic exchange parameters and ordering temperatures are calculated within the random-phase approximation for spin waves. Our results show that the most commonly used DC scheme, the "fully localized limit"(FLL) of DFT+U, erroneously favors ferromagnetic coupling between the layers of a bilayer structure, and yields Curie temperatures in excess of the experimental values. With the help of a perturbative model for superexchange, we are able to trace the source of this error back to the too small band gap in the majority spin channel in the FLL calculations. In contrast, when using the "around-mean-field"(AMF) DC scheme and a realistic value of U=1.7 eV for the Cr-3d orbitals, we find that the magnetic interlayer coupling is antiferromagnetic (AFM) in all three materials, in agreement with recent experiments for CrI3. We calculate the antiferromagnetic ordering temperature for both LT and HT stacking to be 22 K and 29 K for bilayer CrI3. Thus, according to our calculations, the AFM order can be observed independently of the crystal structure of the film, while the LT structure remains to be the ground state. Bilayer CrBr3 films are predicted to have a Néel temperature similar to that of CrI3, whereas the CrCl3 films prefer antiparallel in-plane magnetization. © 2021 American Physical Society.
    view abstractdoi: 10.1103/PhysRevB.103.224421
  • 2021 • 400 Magnetic field dependence of the in-plane hole g factor in ZnSe- And CdTe-based quantum wells
    Zhukov, E.A. and Mantsevich, V.N. and Yakovlev, D.R. and Krivenko, I.S. and Nedelea, V.V. and Kowski, D. and Waag, A. and Karczewski, G. and Wojtowicz, T. and Bayer, M.
    Physical Review B 103 (2021)
    The effective g factor of holes is measured in modulation-doped ZnSe/(Zn,Mg)(S,Se) quantum wells and from surface-state p-doped CdTe/(Cd,Mg)Te quantum wells by time-resolved pump-probe Kerr rotation. The measurements are performed at a temperature of 1.7 K and in magnetic fields up to 5 T applied in the Voigt geometry with orientation perpendicular to the quantum-well growth axis. The absolute value of the in-plane hole g factor increases with growing magnetic field in both studied heterostructures. A theoretical model is developed that considers the influence of magnetic field and interface mixing of heavy-hole and light-hole states on the g factor. The model results are in good agreement with the experimental data. © 2021 American Physical Society.
    view abstractdoi: 10.1103/PhysRevB.103.125305
  • 2021 • 399 Magnetic Nanoparticles as a Tool for Remote DNA Manipulations at a Single-Molecule Level
    Nikitin, A.A. and Yurenya, A.Y. and Zatsepin, T.S. and Aparin, I.O. and Chekhonin, V.P. and Majouga, A.G. and Farle, M. and Wiedwald, U. and Abakumov, M.A.
    ACS Applied Materials and Interfaces 13 14458-14469 (2021)
    Remote control of cells and single molecules by magnetic nanoparticles in nonheating external magnetic fields is a perspective approach for many applications such as cancer treatment and enzyme activity regulation. However, the possibility and mechanisms of direct effects of small individual magnetic nanoparticles on such processes in magneto-mechanical experiments still remain unclear. In this work, we have shown remote-controlled mechanical dissociation of short DNA duplexes (18-60 bp) under the influence of nonheating low-frequency alternating magnetic fields using individual 11 nm magnetic nanoparticles. The developed technique allows (1) simultaneous manipulation of millions of individual DNA molecules and (2) evaluation of energies of intermolecular interactions in short DNA duplexes or in other molecules. Finally, we have shown that DNA duplexes dissociation is mediated by mechanical stress and produced by the movement of magnetic nanoparticles in magnetic fields, but not by local overheating. The presented technique opens a new avenue for high-precision manipulation of DNA and generation of biosensors for quantification of energies of intermolecular interaction. ©
    view abstractdoi: 10.1021/acsami.0c21002
  • 2021 • 398 Magnetoelectric Tuning of Pinning-Type Permanent Magnets through Atomic-Scale Engineering of Grain Boundaries
    Ye, X. and Yan, F. and Schäfer, L. and Wang, D. and Geßwein, H. and Wang, W. and Chellali, M.R. and Stephenson, L.T. and Skokov, K. and Gutfleisch, O. and Raabe, D. and Hahn, H. and Gault, B. and Kruk, R.
    Advanced Materials 33 (2021)
    Pinning-type magnets with high coercivity at high temperatures are at the core of thriving clean-energy technologies. Among these, Sm2Co17-based magnets are excellent candidates owing to their high-temperature stability. However, despite intensive efforts to optimize the intragranular microstructure, the coercivity currently only reaches 20–30% of the theoretical limits. Here, the roles of the grain-interior nanostructure and the grain boundaries in controlling coercivity are disentangled by an emerging magnetoelectric approach. Through hydrogen charging/discharging by applying voltages of only ≈1 V, the coercivity is reversibly tuned by an unprecedented value of ≈1.3 T. In situ magneto-structural characterization and atomic-scale tracking of hydrogen atoms reveal that the segregation of hydrogen atoms at the grain boundaries, rather than the change of the crystal structure, dominates the reversible and substantial change of coercivity. Hydrogen reduces the local magnetocrystalline anisotropy and facilitates the magnetization reversal starting from the grain boundaries. This study opens a way to achieve the giant magnetoelectric effect in permanent magnets by engineering grain boundaries with hydrogen atoms. Furthermore, it reveals the so far neglected critical role of grain boundaries in the conventional magnetization-switching paradigm of pinning-type magnets, suggesting a critical reconsideration of engineering strategies to overcome the coercivity limits. © 2020 The Authors. Advanced Materials published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/adma.202006853
  • 2021 • 397 Managerial behavior in fund tournaments—the impact of TrueSkill
    Swade, A. and Köchling, G. and Posch, P.N.
    Journal of Asset Management 22 62-75 (2021)
    Measuring mutual fund managers’ skills by Microsoft’s TrueSkill algorithm, we find highly skilled managers to behave self-confident resulting in higher risk-taking in the second half of the year compared to less skilled managers. Introducing the TrueSkill algorithm, which is widely used in the e-sports community, to this branch of literature, we can replicate previous findings and theories suggesting overconfidence for mid-years winners. © 2021, The Author(s).
    view abstractdoi: 10.1057/s41260-020-00198-7
  • 2021 • 396 Material defects detection based on in-process measurements in milling of Ti6246 alloy
    Pfirrmann, D. and Baumann, J. and Krebs, E. and Biermann, D. and Wiederkehr, P.
    Procedia CIRP 99 165-170 (2021)
    An increasing demand for products and services in the aviation industry is attended by a rising demand for aircraft engines. This requires an increased productivity combined with highest quality and safety standards. In this paper, a new approach of material defect detection is presented which is based on force and acoustic-emission measurements during machining processes. Representative synthetic defects in titanium alloy Ti6246 were investigated. In order to use scale effects, the experiments were conducted in micro-milling processes. This approach could be used for an automated, non-destructive evaluation of the manufactured components in the future and thus for reducing testing effort and related auxiliary times. © 2021 The Authors. Published by Elsevier B.V.
    view abstractdoi: 10.1016/j.procir.2021.03.023
  • 2021 • 395 Materials breaking the rules: General discussion
    Addicoat, M. and Bennett, T.D. and Brammer, L. and Craig, G. and Das, C. and Dichtel, W. and Doan, H. and Evans, A.M. and Evans, J. and Goodwin, A. and Horike, S. and Jiang, J. and Kaskel, S. and Kato, M. and Kitagawa, S. and Koba...
    Faraday Discussions 225 255-270 (2021)
    doi: 10.1039/D0FD90033H
  • 2021 • 394 Maximize mixing in highly polyelemental solid solution alloy nanoparticles
    Ludwig, Al.
    Matter 4 2100-2101 (2021)
    In this issue of Matter, Yao et al. report on advanced non-equilibrium high-temperature entropy-controlled synthesis of polyelemental nanoparticles. They achieve extreme mixing of 15 metals, some of them previously immiscible, in the form of a single phase solid solution. The compositionally tunable properties of such atomic scale mixtures within a simple crystal structure makes them highly interesting for the design of new materials, e.g., electrocatalysts. © 2021 Elsevier Inc.
    view abstractdoi: 10.1016/j.matt.2021.06.015
  • 2021 • 393 Maxwell relation, giant (negative) electrocaloric effect, and polarization hysteresis
    Chen, X. and Li, S. and Jian, X. and Hambal, Y. and Lu, S.-G. and Shvartsman, V.V. and Lupascu, D.C. and Zhang, Q.M.
    Applied Physics Letters 118 (2021)
    The electrocaloric effect (ECE) in dielectrics is characterized by the isothermal entropy change ΔS and adiabatic temperature change ΔT induced by changes of external electric fields. The Maxwell relation, which relates changes of polarization P with temperature T (pyroelectric coefficient) under a fixed electric field E to ΔS for finite intervals in E, provides a convenient way to deduce the ECE from polarization data P(T, E). Hence, this method, known as the indirect method, is widely used in ECE studies in ferroelectrics. Here, we first present the thermodynamic consideration for the Maxwell relation. We then use the indirect method and P(T, E) from bipolar and unipolar polarization curves to deduce the ECE in the normal ferroelectric phase of a P(VDF-TrFE) copolymer. The deduced ECE using the P(T, E) from bipolar polarization curves exhibits a giant negative ECE. In contrast, the directly measured ECE in the same polymer shows the weak and normal ECE. We discuss the constraints of the indirect method and its relation to the polarization-electric field curves measured in practical ferroelectric materials. © 2021 Author(s).
    view abstractdoi: 10.1063/5.0042333
  • 2021 • 392 MD simulation study on defect evolution and doping efficiency of p-type doping of 3C-SiC by Al ion implantation with subsequent annealing
    Wu, J. and Xu, Z. and Liu, L. and Hartmaier, A. and Rommel, M. and Nordlund, K. and Wang, T. and Janisch, R. and Zhao, J.
    Journal of Materials Chemistry C 9 2258-2275 (2021)
    We use molecular dynamics (MD) simulation with numerical characterisation and statistical analysis to study the mechanisms of damage evolution and p-type doping efficiency by aluminum (Al) ion implantation into 3C silicon carbide (SiC) with subsequent annealing. By incorporating the electronic stopping power for implantation, a more accurate description of the atomic-scale mechanisms of damage evolution and distribution in SiC can be obtained. The simulation results show a novel observation that the recrystallization process occurs in the region below the subsurface layer, and develops from amorphous-crystalline interface to the damage center region, which is a new insight into previously published studies. During surface recrystallization, significant compressive stress concentration occurs, and more structural phase transition atoms and dislocations formed at the damage-rich-crystalline interface. Another point of interest is that for low-dose implantation, more implantation-induced defects hamper the doping efficiency. Correspondingly, the correlation between lattice damage and doping efficiency becomes weaker as the implant dose increases under the same annealing conditions. Our simulation also predicts that annealing after high temperature (HT) implantation is more likely to lead to the formation of carbon vacancies (VC). © The Royal Society of Chemistry 2021.
    view abstractdoi: 10.1039/d0tc05374k
  • 2021 • 391 Measurement and modelling solubility of amino acids and peptides in aqueous 2-propanol solutions
    Do, H.T. and Franke, P. and Volpert, S. and Klinksiek, M. and Thome, M. and Held, C.
    Physical Chemistry Chemical Physics 23 10852-10863 (2021)
    Amino acids and peptides are essential components in the biochemical industry. The final products are employed in a wide range of applications and are often synthesized by fermentation and purified in a complex downstream process. One possible separation step is using an additional solvent to lower the solubility of the desired product and, thus, promote the crystallization of the particular component. Therefore, it is crucial to have accurate knowledge of the solubility of these components. In this work, the solubilities of 20 proteinogenic amino acids and 21 peptides in aqueous 2-propanol solutions were gravimetrically determined. Additionally, the pH values of the saturated liquid phases were measured and the crystal structures of solid crystals were analysed using X-ray diffraction. The anti-solvent 2-propanol caused a decrease in the solubilities of the amino acids and peptides upon increasing its mass fraction. Exceptions were found for amino acids with aromatic substituents, l-phenylalanine and l-tyrosine. The solubility of 15 amino acids and 18 peptides was successfully modelled using the equation of state PC-SAFT that used recently determined melting properties of the amino acids and peptides as input data. This journal is © the Owner Societies.
    view abstractdoi: 10.1039/d1cp00005e
  • 2021 • 390 Measurement and PC-SAFT Modeling of the Solubility of Gallic Acid in Aqueous Mixtures of Deep Eutectic Solvents
    Sepúlveda-Orellana, B. and Gajardo-Parra, N.F. and Do, H.T. and Pérez-Correa, J.R. and Held, C. and Sadowski, G. and Canales, R.I.
    Journal of Chemical and Engineering Data (2021)
    Deep eutectic solvents have appeared as potential solvents for improving the extraction of polyphenols from vegetable or fruit matrixes. Since gallic acid is abundant in these sources, it is considered as a typical standard for quantifying their total polyphenol content after extraction with solvents. However, there are no extensive studies on the solubility behavior of gallic acid in different solvents or deep eutectic solvents. Thus, in this work, the solubility of gallic acid is measured in pure water; aqueous solutions of different hydrogen bond donors such as ethylene glycol, levulinic acid, and glycerol; and aqueous mixtures of deep eutectic solvents using choline chloride as the hydrogen bond acceptor and ethylene glycol, levulinic acid, and glycerol as the hydrogen bond donors. All of the measurements were performed at 293.15, 303.15, and 313.15 K and at 101.3 kPa and were validated by comparing the solubility of gallic acid in water from the literature. Results suggest that a 50 wt % aqueous solution of deep eutectic solvent based on ethylene glycol or glycerol improves the gallic acid solubility compared with a 50 wt % aqueous solution of its corresponding hydrogen bond donor. The deep eutectic solvent containing levulinic acid acts as the best aqueous mixture for gallic acid dissolution. Nondissolved gallic acid was measured after equilibrium using powder X-ray diffraction, showing that its structure does not change upon mixing with all of the liquid mixtures. All of the solid-liquid equilibrium results were accurately modeled with perturbed-chain statistical associating fluid theory (PC-SAFT). © 2021 American Chemical Society.
    view abstractdoi: 10.1021/acs.jced.0c00784
  • 2021 • 389 Mechanical milling to foster the solid solution formation and densification in Cr-W-Si for hot-pressing of PVD target materials
    Tillmann, W. and Fehr, A. and Heringhaus, M.
    Advanced Powder Technology 32 1927-1934 (2021)
    Based on the significantly different melting points and high oxygen affinities, the fabrication of chromium-based tungsten silicides is restricted to powder metallurgical production routes. To foster particle contacts and diffusion processes between chromium and tungsten, which are known to necessitate long sintering times, mechanical alloying or milling processes prior to sintering are established. Nonetheless, due to spinodal decomposition of Cr and W, the solid solution formation is complex and yet little understood. For this reason, the influence of the mechanical milling time (0–24 h) on the crystal structure and the microstructural properties of hot-pressed 60Cr30W10Si (wt.–%) is examined. In this context, two different powders containing a different tungsten particle size (0.8 and 3 µm) were mechanically alloyed to analyze the impact on the phase formation and the particle distribution in the microstructure. It was shown that mechanical milling supported the mechanical clamping between the particles. However, the increased milling times significantly decreased the crystallite sizes of the particles and fostered the tungsten solubility in the Cr-rich (Cr, W) solid solution formed during sintering, thus supporting the densification. © 2021 The Society of Powder Technology Japan
    view abstractdoi: 10.1016/j.apt.2021.04.001
  • 2021 • 388 Mechanical properties and adhesion behavior of amorphous carbon films with bias voltage controlled TixCy interlayers on Ti6Al4V
    Tillmann, W. and Lopes Dias, N.F. and Franke, C. and Kokalj, D. and Stangier, D. and Thomann, C.A. and Debus, J.
    Diamond and Related Materials 115 (2021)
    Amorphous carbon is a promising functional film material to enhance the surface properties of Ti-based alloys for orthopaedic applications. However, high adhesion of the amorphous carbon film on the orthopaedic implants is essential to fully exploit its potential under high load bearings. Interlayer films are generally employed to improve the adhesion. The applied bias voltage is a decisive deposition parameter and significantly influences the structure and mechanical properties during the interlayer growth, which in turn affect the properties of the amorphous carbon film. Therefore, chemically graded titanium carbide (TixCy) interlayers were deposited using bias voltages of −50, −100, and −150 V with a subsequent hydrogen-free amorphous carbon (a-C) top layer on Ti6Al4V by magnetron sputtering. The mechanical properties and adhesion behavior of single TixCy interlayers were evaluated to analyze the interaction effect of TixCy on bilayered TixCy/a-C structures. A high bias voltage generates dense TixCy of a more disordered and defected structure with high stresses, high hardness of ~16 GPa, and high elastic modulus of ~170 GPa. However, high compressive stresses provoke a low adhesion strength, while low compressive stresses ensure a good adhesion behavior of TixCy. Highly stressed TixCy interlayers lead to overall higher stresses for the entire TixCy/a-C film. Independently of TixCy, the a-C top layer exhibits hardness and elastic modulus values of ~16 and ~160 GPa, respectively. The TixCy/a-C films with TixCy interlayers deposited at high bias voltages possess a low adhesion strength, while a lower bias voltage favors a good adhesion of TixCy/a-C on Ti6Al4V. Therefore, a moderate bias voltage is crucial to deposit lowly stressed TixCy interlayers, which ensure a high adhesion of TixCy/a-C on Ti6Al4V. Consequently, the bias voltage allows controlling the mechanical properties and adhesion behavior of the interlayer and, hence, the adhesion strength of the entire amorphous carbon film structure on Ti-based alloys for orthopaedic applications. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.diamond.2021.108361
  • 2021 • 387 Mechanism for breakaway oxidation of the Ti2AlC MAX phase
    Badie, S. and Sebold, D. and Vaßen, R. and Guillon, O. and Gonzalez-Julian, J.
    Acta Materialia 215 (2021)
    The good oxidation resistance of MAX phases up to temperatures around 1200 °C can be compromised for long exposure due to the breakaway of the protective alumina layer. Herein, we unveil a mechanism of breakaway oxidation of the Ti2AlC MAX phase, identifying the main trigger and the solutions to avoid it. It is caused by excessive rumpling of the oxide scale on surfaces with arithmetical mean roughness (Ra) &gt; 3 µm and constitutes a key factor in subsequent consumption of Ti2AlC. First, the oxide scale experienced rumpling due to significant radial stresses generated at the Ti2AlC/oxide interface. Second, scale blistering resulted from substantial buckling due to the evolution of in-plane stresses and lateral lengthening. Third, blister collapse and exposure of the underlying Al-depleted Ti2AlC surface led to rapid ingress of oxygen and oxide/substrate interface recession. The self-healing ability of Ti2AlC has been restrained and breakaway oxidation kinetics following a linear trend have been initiated. Similarly, breakaway oxidation was observed on micro-damaged surfaces. A mixed oxide layer with high porosity mainly composed of rutile titanium dioxide (TiO2) promptly formed on these surfaces, gradually consuming the base Ti2AlC material. © 2021
    view abstractdoi: 10.1016/j.actamat.2021.117025
  • 2021 • 386 Mechanism of magnetization reduction in iron oxide nanoparticles
    Köhler, T. and Feoktystov, A. and Petracic, O. and Kentzinger, E. and Bhatnagar-Schöffmann, T. and Feygenson, M. and Nandakumaran, N. and Landers, J. and Wende, H. and Cervellino, A. and Rücker, U. and Kovács, A. and Dunin-Bor...
    Nanoscale 13 6965-6976 (2021)
    Iron oxide nanoparticles are presently considered as main work horses for various applications including targeted drug delivery and magnetic hyperthermia. Several questions remain unsolved regarding the effect of size onto their overall magnetic behavior. One aspect is the reduction of magnetization compared to bulk samples. A detailed understanding of the underlying mechanisms of this reduction could improve the particle performance in applications. Here we use a number of complementary experimental techniques including neutron scattering and synchrotron X-ray diffraction to arrive at a consistent conclusion. We confirm the observation from previous studies of a reduced saturation magnetization and argue that this reduction is mainly associated with the presence of antiphase boundaries, which are observed directly using high-resolution transmission electron microscopy and indirectly via an anisotropic peak broadening in X-ray diffraction patterns. Additionally small-angle neutron scattering with polarized neutrons revealed a small non-magnetic surface layer, that is, however, not sufficient to explain the observed loss in magnetization alone. © The Royal Society of Chemistry.
    view abstractdoi: 10.1039/d0nr08615k
  • 2021 • 385 Mechanism-oriented characterization of the anisotropy of extruded profiles based on solid-state recycled EN AW-6060 aluminum chips
    Koch, A. and Henkel, T. and Walther, F.
    Engineering Failure Analysis 121 (2021)
    Because of the great potential to reduce the amount of energy, the direct recycling of scrap like aluminum chips by hot extrusion is a hopeful alternative to the usual remelting process. Previous investigations showed that the chips, which are encased by oxide layers, are elongated due to the extrusion process. Therefore, the aim of this study is to test to what extend anisotropic properties, in analogy to fiber-reinforced materials, can be determined. The mechanical properties of cast-based and chip-based specimens with orientations of 0°, 30° and 90° to extrusion direction were characterized by means of mechanical quasistatic and cyclic experiments. It could be shown that quasistatic properties of the 0° orientation are highest for chip-based specimens, whereby the differences to the other orientations are slight. On the other hand, large differences in cyclic creep behavior between the orientations as well as in damage behavior could be determined. © 2020 Elsevier Ltd
    view abstractdoi: 10.1016/j.engfailanal.2020.105099
  • 2021 • 384 Mechanochemical synthesis and dehydrogenation properties of Yb(AlH4)3
    Cao, Z. and Felderhoff, M.
    International Journal of Hydrogen Energy 46 26437-26444 (2021)
    The facile synthesis of ytterbium tetrahydroaluminate Yb(AlH4)3 is conducted by a mechanochemical procedure under hydrogen atmosphere for the first time. Results show that the synthesized Yb(AlH4)3 remains as an amorphous state. The thermal decomposition of Yb(AlH4)3 goes through a four-stage pathway with several amorphous intermediate phases during the process. The first dehydrogenation step of Yb(AlH4)3 presents a relatively low apparent activation energy of 99.6 kJ mol−1, and ninety percent of the hydrogen from this stage can be liberated within 20 min at 160 °C. Rehydrogenation tests above 160 °C and 14 MPa hydrogen pressure demonstrate the unsuccessful rehydrogenations of the first decomposition step due to the formation of a thermodynamically more stable compound YbHCl. © 2021 Hydrogen Energy Publications LLC
    view abstractdoi: 10.1016/j.ijhydene.2021.05.132
  • 2021 • 383 Mechanochemical Synthesis of Catalytic Materials
    Amrute, A.P. and De Bellis, J. and Felderhoff, M. and Schüth, F.
    Chemistry - A European Journal (2021)
    The mechanochemical synthesis of nanomaterials for catalytic applications is a growing research field due to its simplicity, scalability, and eco-friendliness. Besides, it provides materials with distinct features, such as nanocrystallinity, high defect concentration, and close interaction of the components in a system, which are, in most cases, unattainable by conventional routes. Consequently, this research field has recently become highly popular, particularly for the preparation of catalytic materials for various applications, ranging from chemical production over energy conversion catalysis to environmental protection. In this Review, recent studies on mechanochemistry for the synthesis of catalytic materials are discussed. Emphasis is placed on the straightforwardness of the mechanochemical route—in contrast to more conventional synthesis—in fabricating the materials, which otherwise often require harsh conditions. Distinct material properties achieved by mechanochemistry are related to their improved catalytic performance. © 2021 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/chem.202004583
  • 2021 • 382 Mechanochemical Synthesis of Supported Bimetallic Catalysts
    De Bellis, J. and Felderhoff, M. and Schüth, F.
    Chemistry of Materials 33 2037-2045 (2021)
    In a previous publication, ball milling was introduced as an effective method for the preparation of supported metal catalysts, simply from the coarse powders of the metal and metal oxide support. In this follow-up study, we demonstrate that mixing multiple metal sources can result in supported alloyed nanoparticles, extending the field of application of the method to the synthesis of supported bimetallic catalysts. Ball milling Au and Pd or Au and Cu in a high-energy regime (shaker mill) indeed led to the formation of Au-Pd and Au-Cu nanoparticles, supported on MgO or yttria-stabilized zirconia (YSZ), which were explored as model systems. Powder X-ray diffraction and electron microscopy were the primary means to investigate as-synthesized materials. The catalytic performance in CO oxidation was also investigated to understand better how the synthetic method could affect the features of the final materials as catalysts. © 2021 The Authors. Published by American Chemical Society.
    view abstractdoi: 10.1021/acs.chemmater.0c04134
  • 2021 • 381 Melt milling as manufacturing method for solid crystalline suspensions
    da Igreja, P. and Erve, A. and Thommes, M.
    European journal of pharmaceutics and biopharmaceutics : official journal of Arbeitsgemeinschaft fur Pharmazeutische Verfahrenstechnik e.V 158 245-253 (2021)
    Production of submicron particles (0.1-1 μm) has been identified by the pharmaceutical industry as a key technology to enhance the bioavailability of poorly water-soluble drugs. However, nanosuspensions derived from commonly applied wet milling suffer from long-term stability issues, making further downstream processing necessary. In previous works, the formulation as a long-term stable solid crystalline suspension (SCS) was introduced, for which the crystalline drug is ground in a (molten) hydrophilic carrier matrix. The model formulation of the antimycotic Griseofulvin and the sugar alcohol Xylitol was reused for comparative purposes. Due to process limitations regarding the degree of comminution, the present work demonstrates the application of fine grinding in the framework of SCS manufacturing. A custom-built mill with annular gap geometry successfully yielded particles in the targeted submicron range. A process optimization study lead to improved energy utilization during grinding, which reduced the necessary grinding time and, thereby, the thermal exposition of the drug. Investigation of solid-state properties of the SCS, via differential scanning calorimetry and x-ray powder diffraction, showed no alteration even for extended grinding times. In dissolution experiments, the melt-milled SCS outperformed its predecessors, although mostly agglomerates were found by SEM imaging in the solidified product. In conclusion, melt milling is a valuable tool to overcome low aqueous solubility. Copyright © 2020. Published by Elsevier B.V.
    view abstractdoi: 10.1016/j.ejpb.2020.11.020
  • 2021 • 380 Melting Properties of Peptides and Their Solubility in Water. Part 2: Di- And Tripeptides Based on Glycine, Alanine, Leucine, Proline, and Serine
    Do, H.T. and Chua, Y.Z. and Habicht, J. and Klinksiek, M. and Volpert, S. and Hallermann, M. and Thome, M. and Pabsch, D. and Zaitsau, D. and Schick, C. and Held, C.
    Industrial and Engineering Chemistry Research 60 4693-4704 (2021)
    In downstream processes for peptides, crystallization is still used as the state-of-the-art separation step for which the knowledge about the solubility of each single compound is mandatory. Since the determination of experimental temperature-dependent solubility data is time-consuming and expensive, modeling solubility based on physical properties such as melting properties is highly desired. Unfortunately, the direct determination of melting properties for biomolecules using conventional differential scanning calorimetry is not possible due to the decomposition of the peptides before their melting. In this work, fast scanning calorimetry (FSC) with heating rates up to 20,000 K s-1 was applied to measure the melting properties of 22 peptides with focus on isomeric dipeptides and tripeptides based on glycine, l-alanine, l-leucine, l-proline, and l-serine. The experimental determination of the aqueous solubility of these peptides was performed using the photometric method (UV/Vis spectrometer) and the gravimetric method of supersaturated solutions. Additionally, the pH value and the crystal structure of peptides were determined in order to ensure the neutral species in solution and to exclude crystal structure changes in the solid phase. The experimental FSC-measured melting properties were used as input data in the thermodynamic modeling framework PC-SAFT to model the peptide solubility in water. The PC-SAFT pure-component parameters of the peptides were determined following a weighted joint-parameter method introduced in this work. This approach allows determining the pure-component parameters of a peptide by joining the pure-component parameters of the parent amino acids. The binary interactions parameter between peptide and water was fitted to solubility-independent properties such as osmotic coefficients and mixture densities of aqueous peptide solutions. The modeled peptide solubility was in good agreement with the experimental solubility. © 2021 American Chemical Society. All rights reserved.
    view abstractdoi: 10.1021/acs.iecr.0c05652
  • 2021 • 379 Mesoporous NiFe2O4 with Tunable Pore Morphology for Electrocatalytic Water Oxidation
    Simon, C. and Timm, J. and Tetzlaff, D. and Jungmann, J. and Apfel, U.-P. and Marschall, R.
    ChemElectroChem 8 227-239 (2021)
    Mesoporous NiFe2O4 for electrocatalytic water splitting was prepared via soft-templating using citric-acid-complexed metal nitrates as precursors. The mesopore evolution during thermal treatment was examined systematically giving insights into the formation process of mesoporous NiFe2O4. Detailed nitrogen physisorption analysis including desorption scanning experiments reveal the presence of highly accessible mesopores generating surface areas of up to 200 m2/g. The ability of the NiFe2O4 powders to perform electrocatalytic oxygen evolution reaction under alkaline conditions was investigated, highlighting the advantages of mesopore insertion. The most active samples reach a current density of 10 mA cm−2 at an overpotential of 410 mV with a small Tafel slope of 50 mV dec−1, indicating an enhanced activity that originated from the increased catalyst surface. © 2020 The Authors. ChemElectroChem published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/celc.202001280
  • 2021 • 378 Metal Forming
    Tekkaya, A.E.
    Springer Handbooks 357-408 (2021)
    Metal formingmetal forming processes do not only shape workpieces but also set their properties over the whole volume including the surface. They improve the physical properties such as mechanical, electrical, acoustical, etc. of workpieces and hence increase their capabilities in service. Besides the hardness, ductility, residual stresses also the ductile damage level of the formed components can be controlled during forming. Formed metallic components have low imbedded energy per mass thanks the minimal or even none scrap. Hence, metal forming is among the most environmentally friendly manufacturing processes. This chapter starts with an overview of various processes of metal forming. There are over 250 different forming processes and every year new ones are invented showing the vitality of the technology. The metallurgical fundamentals relevant for metal forming processes are described next covering the mechanisms of plastic deformation, strain hardening and heat treatment. The basic concepts of elementary plasticity including the true stress, true strain, flow stress, flow condition and flow rules are followed by simple analytical methods necessary to understand the process mechanics effectively. The technological processes are covered in two groups: Bulk and sheet forming processes. Upsetting, forging, cold extrusion, rollingrolling and shear forming is discussed in detail as bulk forming representatives. Emphasis is placed on the process description, process windows, stress states in the forming region and force displacement curves. Where necessary, tools are included as well. An introduction to sheet metal forming is given through the analytical models (such as membrane theory) and the material characterization for formability. Bending as a basic sheet forming process is studied in detail. This is followed by stretch- and deep drawing processes including hydroforming. The chapter concludes with a summary of typical forming machines including energy-, force- and displacement-controlled machines. © 2021, Springer Nature Switzerland AG.
    view abstractdoi: 10.1007/978-3-030-47035-7_11
  • 2021 • 377 Metal-Ligand Interface and Internal Structure of Ultrasmall Silver Nanoparticles (2 nm)
    Wetzel, O. and Hosseini, S. and Loza, K. and Heggen, M. and Prymak, O. and Bayer, P. and Beuck, C. and Schaller, T. and Niemeyer, F. and Weidenthaler, C. and Epple, M.
    Journal of Physical Chemistry B 125 5645-5659 (2021)
    Ultrasmall silver nanoparticles were prepared by reduction with NaBH4 and surface-terminated with glutathione (GSH). The particles had a solid core diameter of 2 nm as shown by transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS). NMR-DOSY gave a hydrodynamic diameter of 2 to 2.8 nm. X-ray photoelectron spectroscopy (XPS) showed that silver is bound to the thiol group of the central cysteine in glutathione under partial oxidation to silver(+I). In turn, the thiol group is deprotonated to thiolate. X-ray powder diffraction (XRD) together with Rietveld refinement confirmed a twinned (polycrystalline) fcc structure of ultrasmall silver nanoparticles with a lattice compression of about 0.9% compared to bulk silver metal. By NMR spectroscopy, the interaction between the glutathione ligand and the silver surface was analyzed, also with 13C-labeled glutathione. The adsorbed glutathione is fully intact and binds to the silver surface via cysteine. In situ 1H NMR spectroscopy up to 85 °C in dispersion showed that the glutathione ligand did not detach from the surface of the silver nanoparticle, i.e. the silver-sulfur bond is remarkably strong. The ultrasmall nanoparticles had a higher cytotoxicity than bigger particles in in vitro cell culture with HeLa cells with a cytotoxic concentration of about 1 μg mL-1 after 24 h incubation. The overall stoichiometry of the nanoparticles was about Ag∼250GSH∼155. © 2021 The Authors. Published by American Chemical Society.
    view abstractdoi: 10.1021/acs.jpcb.1c02512
  • 2021 • 376 Metal–Organic-Framework-Supported Molecular Electrocatalysis for the Oxygen Reduction Reaction
    Liang, Z. and Guo, H. and Zhou, G. and Guo, K. and Wang, B. and Lei, H. and Zhang, W. and Zheng, H. and Apfel, U.-P. and Cao, R.
    Angewandte Chemie - International Edition 60 8472-8476 (2021)
    Synthesizing molecule@support hybrids is appealing to improve molecular electrocatalysis. We report herein metal–organic framework (MOF)-supported Co porphyrins for the oxygen reduction reaction (ORR) with improved activity and selectivity. Co porphyrins can be grafted on MOF surfaces through ligand exchange. A variety of porphyrin@MOF hybrids were made using this method. Grafted Co porphyrins showed boosted ORR activity with large (&gt;70 mV) anodic shift of the half-wave potential compared to ungrafted porphyrins. By using active MOFs for peroxide reduction, the number of electrons transferred per O2 increased from 2.65 to 3.70, showing significantly improved selectivity for the 4e ORR. It is demonstrated that H2O2 generated from O2 reduction at Co porphyrins is further reduced at MOF surfaces, leading to improved 4e ORR. As a practical demonstration, these hybrids were used as air electrode catalysts in Zn-air batteries, which exhibited equal performance to that with Pt-based materials. © 2021 Wiley-VCH GmbH
    view abstractdoi: 10.1002/anie.202016024
  • 2021 • 375 Methodology Based on the Theory of Information to Describe the Representation Ability of the DMC + Alkane Behavior
    Sosa, A. and Ortega, J. and Fernández, L. and Haarmann, N. and Sadowski, G.
    Industrial and Engineering Chemistry Research 60 1036-1054 (2021)
    An information theory-based methodology has been applied to the multiproperty modeling of solution properties. Under this framework, a practical application on a set of binary solutions formed by dimethyl carbonate and six even saturated hydrocarbons (from C6 to C16) is carried out. A dense experimental database is generated composed of volumetric and energetic properties (from mixing processes), and phase equilibria, in order to disambiguate some discrepancies showed by the literature data, mainly for the binary with dodecane. The experimental information is modeled with a semiempirical equation for gE, and with the PCP-SAFT equation of state, which presents a solid theoretical basis. The optimal parameterizations are sought using the precision-complexity binomial whose aim is to increase the validity range of the set of parameters obtained. The Akaike Information Criterion is used to search the best parameterizations, that is, the appropriate number of parameters (complexity) and their best values (precision). With regard to the suitability of the precision-complexity methodology on the models tested, the following is concluded: with PCP-SAFT, precise and reliable estimates are obtained; for the gE model, the proposed approach is essential to control the number of free parameters and to preserve the stable numerical behavior in a wide range of conditions. © 2021 American Chemical Society.
    view abstractdoi: 10.1021/acs.iecr.0c05301
  • 2021 • 374 Methods for measuring large shear strains in in-plane torsion tests
    Traphöner, H. and Clausmeyer, T. and Tekkaya, A.E.
    Journal of Materials Processing Technology 287 (2021)
    The in-plane torsion test achieves true strains far beyond 1.0 for sheet metals, especially using specimens with circular grooves. The accurate measurement of these high strains is a challenge for the conventional digital image correlation (DIC). Thus, the determination of flow curves is limited and fracture strains for very ductile materials cannot be measured. A new grooved specimen is introduced to avoid strain localization. Shear stress and shear strain along a defined area in the groove are constant so that strains can be measured independently of the DIC system setting without error due to strain localization. Furthermore, three methods for the measurement of very high shear strains in the in-plane torsion test are presented: Firstly, the limit of the optical strain measurement is extended by m