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.

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  • 2020 • 789 Effective Description of Anisotropic Wave Dispersion in Mechanical Band-Gap Metamaterials via the Relaxed Micromorphic Model
    d’Agostino, M.V. and Barbagallo, G. and Ghiba, I.-D. and Eidel, B. and Neff, P. and Madeo, A.
    Journal of Elasticity 139 299-329 (2020)
    In this paper the relaxed micromorphic material model for anisotropic elasticity is used to describe the dynamical behavior of a band-gap metamaterial with tetragonal symmetry. Unlike other continuum models (Cauchy, Cosserat, second gradient, classical Mindlin–Eringen micromorphic etc.), the relaxed micromorphic model is endowed to capture the main microscopic and macroscopic characteristics of the targeted metamaterial, namely, stiffness, anisotropy, dispersion and band-gaps. The simple structure of our material model, which simultaneously lives on a micro-, a meso- and a macroscopic scale, requires only the identification of a limited number of frequency-independent and thus truly constitutive parameters, valid for both static and wave-propagation analyses in the plane. The static macro- and micro-parameters are identified by numerical homogenization in static tests on the unit-cell level in Neff et al. (J. Elast.,, 2019, in this volume). The remaining inertia parameters for dynamical analyses are calibrated on the dispersion curves of the same metamaterial as obtained by a classical Bloch–Floquet analysis for two wave directions. We demonstrate via polar plots that the obtained material parameters describe very well the response of the structural material for all wave directions in the plane, thus covering the complete panorama of anisotropy of the targeted metamaterial. © 2019, Springer Nature B.V.
    view abstractdoi: 10.1007/s10659-019-09753-9
  • 2020 • 788 Metallic reflectors with notched RCS spectral signature using dielectric resonators
    Abbas, A.A. and El-Absi, M. and Abuelhaija, A. and Solbach, K. and Kaiser, T.
    Electronics Letters 56 273-276 (2020)
    Dielectric resonators are placed in front of the metallic plane plate and corner reflectors. Excitation of the resonant mode produces strong scattering of an incident plane wave which shows up as narrow notch in the mono-static radar cross section (RCS) spectral signature at the resonance frequency. Experimental proof at V-band is given with a corner reflector of centimetre size with spherical dielectric resonators of 0.8 mm diameter showing a notch at 64 GHz. © The Institution of Engineering and Technology 2020.
    view abstractdoi: 10.1049/el.2019.2942
  • 2020 • 787 Nanoparticle Formation and Behavior in Turbulent Spray Flames Investigated by DNS
    Abdelsamie, A. and Kruis, F.E. and Wiggers, H. and Thévenin, D.
    Flow, Turbulence and Combustion 105 497-516 (2020)
    This work is a first direct numerical simulation of a configuration closely related to the SpraySyn burner (Schneider et al. in Rev Sci Instrum 90:085108, 2019). This burner has been recently developed at the University of Duisburg-Essen to investigate experimentally nanoparticle synthesis in spray flames for a variety of materials. The present simulations are performed for ethanol and titanium tetraisopropoxide as a solvent and precursor, respectively, in order to produce titanium dioxide nanoparticles. In the direct numerical simulations, the complete scenario leading to the production of well-defined nanoparticles is taken into account, including evaporation of the liquid mixture (solvent and precursor) injected as a spray, multi-step kinetics for gas-phase combustion, and finally nanoparticle synthesis. The employed models are described in this article. Additionally, the impact of the inlet velocity of the pilot flame on the nanoparticle synthesis is investigated. It has been found that increasing this speed delays spray flame ignition, decreases nanoparticle concentration, but leads to a narrower size distribution at early stage. © 2020, The Author(s).
    view abstractdoi: 10.1007/s10494-020-00144-y
  • 2020 • 786 Consistent management and evaluation of building models in the early design stages
    Abualdenien, J. and Schneider-Marin, P. and Zahedi, A. and Harter, H. and Exner, H. and Steiner, D. and Singh, M.M. and Borrmann, A. and Lang, W. and Petzold, F. and König, M. and Geyer, P. and Schnellenbach-Held, M.
    Journal of Information Technology in Construction 25 212-232 (2020)
    The early stages of building design involve the consideration of different design variants and their assessment regarding various performance criteria including energy consumption and costs. During the design process, the involved experts from different disciplines frequently exchange building information to develop a design that satisfies the project's requirements and objectives. In the course of this iterative process, the building design evolves throughout multiple refinement stages. At the same time, different variants are developed. In BIM-based projects, the maturity of the design information provided by the model is expressed by the notion of Level of development (LOD). So far, however, there is no method to formally define the information requirements of a LOD. In particular, there are no means for expressing the uncertainty involved with the provided information. By contrast, despite the insufficient information available in early design stages, a BIM model appears precise and certain. This situation leads to false assumptions and model evaluations, for example, in the case of energy efficiency calculations or structural analysis. Hence, this paper presents an overview of a set of approaches that were developed to alleviate and preserve the consistency of the designed solutions. The approach includes the development of a multi-LOD meta-model, which allows one to explicitly describe the LOD requirements of each building component type incorporating the possible uncertainties, e.g. concerning the building dimensions. On the basis of this multi-LOD model, methods for evaluating a building design's performance regarding the building's structure and life cycle energy performance are proposed that take the defined uncertainties into account. To support the management of design variants in one consistent model, a graph-based approach is introduced. Finally, a minimized communication protocol is described to facilitate the workflow and communicate the evaluation results for supporting the decision-making process. © 2020 The author(s). This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International (, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
    view abstractdoi: 10.36680/j.itcon.2020.013
  • 2020 • 785 Enhanced antibacterial performance of ultrathin silver/platinum nanopatches by a sacrificial anode mechanism
    Abuayyash, A. and Ziegler, N. and Meyer, H. and Meischein, M. and Sengstock, C. and Moellenhoff, J. and Rurainsky, C. and Heggen, M. and Garzón-Manjón, A. and Scheu, C. and Tschulik, K. and Ludwig, Al. and Köller, M.
    Nanomedicine: Nanotechnology, Biology, and Medicine 24 (2020)
    The development of antibacterial implant surfaces is a challenging task in biomaterial research. We fabricated a highly antibacterial bimetallic platinum (Pt)/silver(Ag) nanopatch surface by short time sputtering of Pt and Ag on titanium. The sputter process led to a patch-like distribution with crystalline areas in the nanometer-size range (1.3–3.9 nm thickness, 3–60 nm extension). Structural analyses of Pt/Ag samples showed Ag- and Pt-rich areas containing nanoparticle-like Pt deposits of 1–2 nm. The adhesion and proliferation properties of S. aureus on the nanopatch samples were analyzed. Consecutively sputtered Ag/Pt nanopatches (Pt followed by Ag) induced enhanced antimicrobial activity compared to co-sputtered Pt/Ag samples or pure Ag patches of similar Ag amounts. The underlying sacrificial anode mechanism was proved by linear sweep voltammetry. The advantages of this nanopatch coating are the enhanced antimicrobial activity despite a reduced total amount of Ag/Pt and a self-limited effect due the rapid Ag dissolution. © 2019 Elsevier Inc.
    view abstractdoi: 10.1016/j.nano.2019.102126
  • 2020 • 784 Time-resolved diffraction with an optimized short pulse laser plasma X-ray source
    Afshari, M. and Krumey, P. and Menn, D. and Nicoul, M. and Brinks, F. and Tarasevitch, A. and Sokolowski-Tinten, K.
    Structural Dynamics 7 (2020)
    We present a setup for time-resolved X-ray diffraction based on a short pulse, laser-driven plasma X-ray source. The employed modular design provides high flexibility to adapt the setup to the specific requirements (e.g., X-ray optics and sample environment) of particular applications. The configuration discussed here has been optimized toward high angular/momentum resolution and uses Kα-radiation (4.51 keV) from a Ti wire-target in combination with a toroidally bent crystal for collection, monochromatization, and focusing of the emitted radiation. 2 × 10 5 Ti-Kα1 photons per pulse with 10 - 4 relative bandwidth are delivered to the sample at a repetition rate of 10 Hz. This allows for the high dynamic range (104) measurements of transient changes in the rocking curves of materials as for example induced by laser-triggered strain waves. © 2020 Author(s).
    view abstractdoi: 10.1063/1.5126316
  • 2020 • 783 Modeling the residual stresses induced in the metastable austenitic stainless steel disc springs manufactured by incremental sheet forming by a combined hardening model with phase transformation
    Afzal, M.J. and Maqbool, F. and Hajavifard, R. and Buhl, J. and Walther, F. and Bambach, M.
    Procedia Manufacturing 47 1410-1415 (2020)
    A numerical model for predicting the beneficial residual stress induced in metastable austenitic stainless steel (MASS) disc springs through incremental sheet forming (ISF) is developed. An important input for the numerical model is the phase-specific flow curves of the MASS constituents, i.e., austenite γ and martensite α' phase. These curves are determined by using an available CP-FEM framework. The cyclic plasticity effects introduced by the bending/unbending deformation mechanism of the ISF are modeled by using a combined non-linear isotropic/kinematic hardening model. The kinetics of the strain-induced martensite transformation is modeled by using the Olson-Cohen model, whereas the stresses in the whole material are approximated by a mixture rule. The combined non-linear isotropic/kinematic hardening along with Olson-Cohen model and the mixture rule is integrated as a user-material routine (UMAT). The model parameters are calibrated by tensile tests with online Feritscope measurements and tension-compression tests. Afterward, the incremental forming simulations of disc spring manufacturing are performed and the numerically determined residual stress values are compared to the experimental values. The comparison indicates a good match. Hence, the developed numerical strategy provides accurate residual stresses prediction and can be utilized to design the disc spring properties through adjusting residual stresses, which is possible by varying process parameters of the ISF process. © 2020 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license ( Peer-review under responsibility of the scientific committee of the 23rd International Conference on Material Forming.
    view abstractdoi: 10.1016/j.promfg.2020.04.300
  • 2020 • 782 Preparation of antibiofouling nanocomposite PVDF/Ag-SiO2 membrane and long-term performance evaluation in the MBR system fed by real pharmaceutical wastewater
    Ahsani, M. and Hazrati, H. and Javadi, M. and Ulbricht, M. and Yegani, R.
    Separation and Purification Technology 249 (2020)
    In this work, the Ag-SiO2 nanoparticles were successfully synthesized and their antibacterial property was confirmed using the plate colony counting method. The SiO2 and Ag-SiO2 nanoparticles were used to prepare the PVDF/SiO2 and PVDF/Ag-SiO2 nanocomposite membranes, respectively. Pure water flux, contact angle and mechanical strength measurement analyses were conducted to characterize and compare the performance of the neat and nanocomposite membranes. Moreover, in order to investigate the structure of the prepared membranes scanning electron microscope (SEM) was used to obtain surface and cross-section images. A long-term filtration test was carried out in a bench scale submerged membrane bioreactor (MBR) system, fed by real pharmaceutical wastewater, to evaluate the antibiofouling performance of the prepared neat and nanocomposite membranes. In comparison to the neat PVDF, the pure water flux of the nanocomposite PVDF membrane (PVDF/Ag-SiO2; 0.6 wt%) increased about 60% and the water contact angle decreased from about 99° to 89°. The obtained results showed that the nanocomposite PVDF/Ag-SiO2 membrane exhibits considerable antibiofouling properties such that the accumulated dried biofilm as well as the extra cellular polymeric substances (EPSs) collected from the cake layer decreased considerably for the nanocomposite membrane. Moreover, the flux recovery ratio increased from 58% for the neat PVDF membrane to 76% for the nanocomposite PVDF/Ag-SiO2 membrane. The excitation and emission matrix (EEM) fluorescence spectroscopy analysis revealed that the accumulated protein on the surface of nanocomposite membranes decreased considerably in a way that the peak corresponding to tryptophan protein-like substances diminished completely, indicating the high antibiofouling potential of nanocomposite membranes. The chemical oxygen demand (COD) and ammonium removal efficiencies of the neat and nanocomposite membranes were higher than 90% and 95%, respectively, indicating negligible impact of the membrane modification on the effluents’ quality. © 2020
    view abstractdoi: 10.1016/j.seppur.2020.116938
  • 2020 • 781 Frequency- and angle-dependent scattering of a finite-sized meta-structure via the relaxed micromorphic model
    Aivaliotis, A. and Tallarico, D. and d’Agostino, M.-V. and Daouadji, A. and Neff, P. and Madeo, A.
    Archive of Applied Mechanics 90 1073-1096 (2020)
    In this paper, we explore the use of micromorphic-type interface conditions for the modeling of a finite-sized metamaterial. We show how finite-domain boundary value problems can be approached in the framework of enriched continuum mechanics (relaxed micromorphic model) by imposing continuity of macroscopic displacement and of generalized tractions, as well as additional conditions on the micro-distortion tensor and on the double-traction. The case of a metamaterial slab of finite width is presented, its scattering properties are studied via a semi-analytical solution of the relaxed micromorphic model and compared to a direct finite-element simulation encoding all details of the selected microstructure. The reflection and transmission coefficients obtained via the two methods are presented as a function of the frequency and of the direction of propagation of the incident wave. We find excellent agreement for a large range of frequencies going from the long-wave limit to frequencies beyond the first band-gap and for angles of incidence ranging from normal to near-parallel incidence. The present paper sets the basis for a new viewpoint on finite-size metamaterial modeling enabling the exploration of meta-structures at large scales. © 2020, Springer-Verlag GmbH Germany, part of Springer Nature.
    view abstractdoi: 10.1007/s00419-019-01651-9
  • 2020 • 780 Numerical Study and Optimization of Post-Wall Waveguides and Filters for Millimeter Waves
    Akopian, A. and Burduli, G. and Jandieri, V. and Maeda, H. and Hong, W. and Yasumoto, K. and Erni, D.
    GeMIC 2020 - Proceedings of the 2020 German Microwave Conference 212-215 (2020)
    Functional post-wall waveguides and waveguide based compact passive circuits-namely bandpass filters-that are formed by introducing additional metallic or dielectric posts inside the post-wall waveguide are analyzed. The propagation constant of a post-wall waveguide is experimentally measured and compared with the results obtained using the originally developed numerical method. A good agreement is observed in the whole frequency range. The S-parameters of the waveguide-based bandpass filters are calculated using the image theory combined with the lattice sums technique. The developed formulation is numerically fast, hence it can be considered as one of the best-suited approach for structural topological optimization. Finally, a breeder genetic algorithm is used as a global search heuristic in order to track down the optimal geometrical parameters for the introduced posts yielding a bandpass filter characteristic in the desired frequency bands. © 2020 IMA-Institut fur Mikrowellen-und Antennentechnik e.V.
    view abstract
  • 2020 • 779 Frequency-coded chipless RFID tags: Notch model, detection, angular orientation, and coverage measurements
    Alam, J. and Khaliel, M. and Fawky, A. and El-Awamry, A. and Kaiser, T.
    Sensors (Switzerland) 20 (2020)
    This paper focuses on the frequency coded chipless Radio Frequency Identification (RFID) wherein the tag’s information bits are physically encoded by the resonators’ notch position which has an effect on the frequency spectrum of the backscattered or retransmitted signal of the tag. In this regard, the notch analytical model is developed to consider the notch position and quality factor. Besides, the radar cross section (RCS) mathematical representation of the tag is introduced to consider the incident wave’s polarization and orientation angles. Hence, the influences of the incident wave’s orientation and polarization mismatches on the detection performance are quantified. After that, the tag measurement errors and limitations are comprehensively explained. Therefore, approaches to measureing RCS-and retransmission-based tags are introduced. Furthermore, the maximum reading range is theoretically calculated and practically verified considering the Federal Communications Commission (FCC) Ultra Wideband (UWB) regulations. In all simulations and experiments conducted, a mono-static configuration is considered, in which one antenna is utilized for transmission and reception. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/s20071843
  • 2020 • 778 In situ melt pool monitoring and the correlation to part density of Inconel® 718 for quality assurance in selective laser melting
    Alberts, D. and Schwarze, D. and Witt, G.
    Solid Freeform Fabrication 2017: Proceedings of the 28th Annual International Solid Freeform Fabrication Symposium - An Additive Manufacturing Conference, SFF 2017 1481-1494 (2020)
    Additive Manufacturing looks back on a history of about two decades and today SLM® technology keeps moving as an integral element in industrial production environments. Sensitive markets such as energy, medical or aerospace have the highest quality standards for complex, safety-related and highly stressed components which are to be met at competitive costs for each build job and single part. In this context process monitoring is necessary for documentation, qualification and at the same time it is expected to be able to detect process anomalies during the process. In addition to surface roughness, part density which mostly depends on volume energy, changing with laser power, scan velocity etc., is a distinctive quality feature of every component. This paper presents a method for a real time melt pool monitoring system based on photodiodes and the correlation between thermal emission and part density of Inconel® 718 with respect to volume energy deviation. Copyright © SFF 2017.All rights reserved.
    view abstract
  • 2020 • 777 Combinatorial synthesis of Ni–Mn–Ga-(Fe,Co,Cu) high temperature ferromagnetic shape memory alloys thin films
    Alexandrakis, V. and Barandiaran, J.M. and Pérez-Checa, A. and Lázpita, P. and Decker, P. and Salomon, S. and Feuchtwanger, J. and Ludwig, Al. and Chernenko, V.
    Scripta Materialia 178 104-107 (2020)
    High temperature ferromagnetic shape memory alloys (HT-FSMAs) in form of a thin film materials library of Ni–Mn–Ga, alloyed with Fe, Co and Cu has been fabricated by co-sputtering and characterized by high-throughput screening techniques. The weak dependence of martensitic transformation temperature and tetragonal ratio of the martensitic lattice on the doping composition and their irregular variation are ascribed to the competitive influence of the alloying elements Fe, Co and Cu. © 2019 Acta Materialia Inc.
    view abstractdoi: 10.1016/j.scriptamat.2019.10.043
  • 2020 • 776 Wide-Angle RCS Enhanced Tag Based on Dielectric Resonator - Lens Combination
    Alhaj Abbas, A. and El-Absi, M. and Abuelhaija, A. and Solbach, K. and Kaiser, T.
    Frequenz 74 1-8 (2020)
    In a novel mm-wave localization system, dielectric resonators (DR) have been proposed as passive chipless RFID tags to mark fixed reference nodes. To counter clutter and improve the limited read range due to the low RCS level of a DR at millimeter-wave frequencies we propose a combination of several DRs with a dielectric spherical lens which allows improvement of up to 30 dB. The paper presents the design principle and shows simulation results and experimental verification of a scaled tag operating in the 10-12 GHz range and covering a range of incidence angle of the reader signal of ± 50°. A frequency sweeping RF reader can identify the tag (information) by the peak of the RCS level at its DR resonant frequency. For a multiple-tag scenario we can realize up to 12 different tags which can be discriminated unambiguously by their resonant frequencies in a 1: 1.2 frequency bandwidth. © 2020 Walter de Gruyter GmbH, Berlin/Boston.
    view abstractdoi: 10.1515/freq-2019-0068
  • 2020 • 775 Combinatorial Synthesis and High-Throughput Characterization of Microstructure and Phase Transformation in Ni–Ti–Cu–V Quaternary Thin-Film Library
    Al Hasan, N.M. and Hou, H. and Sarkar, S. and Thienhaus, S. and Mehta, A. and Ludwig, Al. and Takeuchi, I.
    Engineering 6 637-643 (2020)
    Ni–Ti–based shape memory alloys (SMAs) have found widespread use in the last 70 years, but improving their functional stability remains a key quest for more robust and advanced applications. Named for their ability to retain their processed shape as a result of a reversible martensitic transformation, SMAs are highly sensitive to compositional variations. Alloying with ternary and quaternary elements to fine-tune the lattice parameters and the thermal hysteresis of an SMA, therefore, becomes a challenge in materials exploration. Combinatorial materials science allows streamlining of the synthesis process and data management from multiple characterization techniques. In this study, a composition spread of Ni–Ti–Cu–V thin-film library was synthesized by magnetron co-sputtering on a thermally oxidized Si wafer. Composition-dependent phase transformation temperature and microstructure were investigated and determined using high-throughput wavelength dispersive spectroscopy, synchrotron X-ray diffraction, and temperature-dependent resistance measurements. Of the 177 compositions in the materials library, 32 were observed to have shape memory effect, of which five had zero or near-zero thermal hysteresis. These compositions provide flexibility in the operating temperature regimes that they can be used in. A phase map for the quaternary system and correlations of functional properties are discussed with respect to the local microstructure and composition of the thin-film library. © 2020 THE AUTHORS
    view abstractdoi: 10.1016/j.eng.2020.05.003
  • 2020 • 774 Role of coherency loss on rafting behavior of Ni-based superalloys
    Ali, M.A. and Görler, J.V. and Steinbach, I.
    Computational Materials Science 171 (2020)
    The role of coherency loss on rafting of superalloys under high temperature low stress creep conditions is investigated by phase-field crystal plasticity simulations. It is demonstrated that coalescence, critically depending on the state of coherency between precipitate and matrix is crucial to understand the rafting behavior of superalloys. An explicit mechanisms is developed predicting coherency loss based on the plastic activity in the matrix. The simulations are verified using experimental creep test results. © 2019 Elsevier B.V.
    view abstractdoi: 10.1016/j.commatsci.2019.109279
  • 2020 • 773 Effect of γ′ precipitate size on hardness and creep properties of Ni-base single crystal superalloys: Experiment and simulation
    Ali, M.A. and López-Galilea, I. and Gao, S. and Ruttert, B. and Amin, W. and Shchyglo, O. and Hartmaier, A. and Theisen, W. and Steinbach, I.
    Materialia 12 (2020)
    The role and effect of γ′ precipitate size on the mechanical properties of Ni-base single crystal superalloy is investigated. The underlying mechanisms are analyzed on the one hand with the help of experiments including hardness and creep tests, and on the other hand with the help of two different simulation approaches by taking the typical γ/γ′ microstructure into account. Simulations, based on the crystal plasticity finite element method (CPFEM) are carried out for the hardness tests, whereas simulations, based on the crystal plasticity coupled phase-field method (CPPFM) are carried out for the creep tests. The hardness test simulation results show that the hardness of material varies inversely with the size of γ′ precipitates for a given γ′ phase volume fraction and it varies directly with the volume fraction of γ′ precipitates for a given precipitate size. These results are qualitatively consistent with the experimental observations. The creep simulation results show that the refinement of γ′ precipitates with a certain volume fraction of precipitates leads to an improvement of creep resistance by delaying the plastic activity in the material. © 2020 Acta Materialia Inc.
    view abstractdoi: 10.1016/j.mtla.2020.100692
  • 2020 • 772 45-degree rafting in Ni-based superalloys: A combined phase-field and strain gradient crystal plasticity study
    Ali, M.A. and Amin, W. and Shchyglo, O. and Steinbach, I.
    International Journal of Plasticity 128 (2020)
    45° rafting of Ni-based superalloys has been investigated with the help of creep test simulations applying a strain gradient crystal plasticity model coupled to the multi-phase field method. This mode of rafting lies in between P- A nd N-type rafting modes. The model parameters are calibrated against experimental data for N-type rafting under high temperature and low stress creep condition. By increasing the stress level, the mixed-mode rafting of precipitates with a clear tendency toward formation of 45° rafts is observed. We show that the key factor for the occurrence of this type of rafting is the generation of highly localized creep strain of more than 10% due to non-homogeneous creep deformation in the form of slip bands. We have successfully captured the evolution of microstructure under high stress leading to production of localized shear bands. © 2020 Elsevier Ltd.
    view abstractdoi: 10.1016/j.ijplas.2020.102659
  • 2020 • 771 Spray-Flame-Prepared LaCo1–xFexO3 Perovskite Nanoparticles as Active OER Catalysts: Influence of Fe Content and Low-Temperature Heating
    Alkan, B. and Medina, D. and Landers, J. and Heidelmann, M. and Hagemann, U. and Salamon, S. and Andronescu, C. and Wende, H. and Schulz, C. and Schuhmann, W. and Wiggers, H.
    ChemElectroChem 7 2564-2574 (2020)
    Spray-flame synthesis was used to produce high-surface-area perovskite electrocatalysts with high phase purity, minimum surface contamination, and high electrochemical stability. In this study, as-prepared LaCo1–xFexO3 perovskite nanoparticles (x=0.2, 0.3, and 0.4) were found to contain a high degree of combustion residuals, and mostly consist of both, stoichiometric and oxygen-deficient perovskite phases. Heating them at moderate temperature (250 °C) in oxygen could remove combustion residuals and increases the content of stoichiometric perovskite while preventing particle growth. A higher surface crystallinity was observed with increasing iron content coming along with a rise in oxygen deficient phases. With heat treatment, OER activity and stability of perovskites improved at 30 and 40 at.% Fe while deteriorating at 20 at.% Fe. This study highlights spray-flame synthesis as a promising technique to synthesize highly active nanoscale perovskite catalysts with improved OER activity. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
    view abstractdoi: 10.1002/celc.201902051
  • 2020 • 770 Self-mode-locking and chirp compensation in an external cavity diode laser at 1550 nm
    Alloush, A. and Bassal, A. and Brenner, C. and Fortin, C. and Mekhazni, K. and Gamarra, P. and Calò, C. and Hofmann, M.R.
    Proceedings of SPIE - The International Society for Optical Engineering 11356 (2020)
    In this work, self-mode-locking of 100 GHz mode-locked pulses from a single-section InP quantum-dash-based laser chip whilst employed in external cavity geometry at 1550nm is investigated. The chip is operated at a forward current marginally above its monolithic operation's lasing threshold. Ultrashort pulses with 1 ps pulse- width were obtained by compensating the chirp by a single mode fiber (SMF). © 2020 SPIE.
    view abstractdoi: 10.1117/12.2555946
  • 2020 • 769 Comparison of self-mode-locking in monolithic and external cavity diode laser at 1550 nm
    Alloush, M.A. and Bassal, A. and Brenner, C. and Fortin, C. and Mekhazni, K. and Gamarra, P. and Calo, C. and Hofmann, M.R.
    Proceedings of SPIE - The International Society for Optical Engineering 11301 (2020)
    In this work, a comparison of self-mode-locking of a 100 GHz repetition-rate monolithic diode as a stand-alone laser source and whilst employed in an external cavity arrangement at 1550 nm is reported. We operated our chip at a forward current slightly above the monolithic chip's lasing threshold and compensated the chirp by a single mode fiber. Ultrashort pulses with 1 ps pulse-width were generated. Changes in the dispersion compensation parameters due to the changed cavity dispersion were analyzed. © 2020 SPIE.
    view abstractdoi: 10.1117/12.2545780
  • 2020 • 768 Integrated BIM-to-FEM approach in mechanised tunnelling
    Alsahly, A. and Hegemann, F. and König, M. and Meschke, G.
    Geomechanik und Tunnelbau 13 212-220 (2020)
    In current tunnelling practice, Finite Element (FE) simulations form an integral element in the planning and the design phase of mechanised tunnelling projects. The generation of adequate computational models is often time consuming and requires data from many different sources, in particular, when manually generated using 2D-CAD drawings. Incorporating Building Information Modelling (BIM) concepts offers opportunities to simplify this process by using geometrical BIM sub-models as a basis for structural analyses. This paper presents a Tunnel Information Model (TIM) as a BIM specifically tailored to fit the needs of mechanised tunnelling projects and a ”BIM-to-FEM“ technology, that automatically extracts relevant information (geology, alignment, lining, material and process parameters) needed for FE simulations from BIM sub-models and subsequently performs FE analysis of the tunnel drive. The results of the analysis are stored centrally on a data server to which the user has continuous access. A case study from the Wehrhahn-Metro line project in Düsseldorf, Germany, is presented and discussed to demonstrate the efficiency and the applicability of the proposed BIM-to-FEM workflow. © 2020, Ernst und Sohn. All rights reserved.
    view abstractdoi: 10.1002/geot.202000002
  • 2020 • 767 Porous ultra-thin films from photocleavable block copolymers: In-situ degradation kinetics study of pore material
    Altinpinar, S. and Ali, W. and Schuchardt, P. and Yildiz, P. and Zhao, H. and Theato, P. and Gutmann, J.S.
    Polymers 12 (2020)
    On the basis of the major application for block copolymers to use them as separation membranes, lithographic mask, and as templates, the preparation of highly oriented nanoporous thin films requires the selective removal of the minor phase from the pores. In the scope of this study, thin film of polystyrene-block-poly(ethylene oxide) block copolymer with a photocleavable junction groups based on ortho-nitrobenzylester (ONB) (PS-h-PEO) was papered via the spin coating technique followed by solvent annealing to obtain highly-ordered cylindrical domains. The polymer blocks are cleaved by means of a mild UV exposure and then the pore material is washed out of the polymer film by ultra-pure water resulting in arrays of nanoporous thin films to remove one block. The removal of the PEO materials from the pores was proven using the grazing-incidence small-angle X-ray scattering (GISAXS) technique. The treatment of the polymer film during the washing process was observed in real time after two different UV exposure time (1 and 4 h) in order to draw conclusions regarding the dynamics of the removal process. In-situ X-ray reflectivity measurements provide statistically significant information about the change in the layer thickness as well as the roughness and electron density of the polymer film during pore formation. 4 H UV exposure was found to be more efficient for PEO cleavage. By in-situ SFM measurements, the structure of the ultra-thin block copolymer films was also analysed and, thus, the kinetics of the washing process was elaborated. The results from both measurements confirmed that the washing procedure induces irreversible change in morphology to the surface of the thin film. © 2020 by the authors.
    view abstractdoi: 10.3390/POLYM12040781
  • 2020 • 766 Response to Comment on "high-surface-area corundum by mechanochemically induced phase transformation of boehmite"
    Amrute, A.P. and Lodziana, Z. and Schreyer, H. and Weidenthaler, C. and Schüth, F.
    Science 368 (2020)
    Li et al. commented that our report claims that methods reported thus far cannot enable the production of high-purity corundum with surface areas greater than 100 m2g-1, and that our obtained material could be porous aggregates rather than nanoparticles. We disagree with both of these suggestions. © 2020 American Association for the Advancement of Science. All rights reserved.
    view abstractdoi: 10.1126/science.abb0948
  • 2020 • 765 Hydrothermal Stability of High-Surface-Area α-Al2O3and Its Use as a Support for Hydrothermally Stable Fischer-Tropsch Synthesis Catalysts
    Amrute, A.P. and Jeske, K. and Łodziana, Z. and Prieto, G. and Schüth, F.
    Chemistry of Materials 32 4369-4374 (2020)
    Nanocrystalline corundum synthesized by ball milling of boehmite is found to be exceptionally robust toward chemical weathering, a common problem of transition aluminas in different applications, most notably in the case of supported catalysts, which are exposed to hydrothermal reaction environments. Detailed characterization and surface cation coordination analysis indicate that the absence of tetrahedral Al species on corundum makes it stable toward chemical weathering. A cobalt catalyst developed using nano-α-Al2O3 as the support showed Fischer-Tropsch synthesis activity and selectivity comparable to the benchmark Co/γ-Al2O3 and remained stable over 250 h on-stream. Copyright © 2020 American Chemical Society.
    view abstractdoi: 10.1021/acs.chemmater.0c01587
  • 2020 • 764 Spray-flame synthesis of La(Fe, Co)O3 nano-perovskites from metal nitrates
    Angel, S. and Neises, J. and Dreyer, M. and Friedel Ortega, K. and Behrens, M. and Wang, Y. and Arandiyan, H. and Schulz, C. and Wiggers, H.
    AIChE Journal 66 (2020)
    Nano-sized perovskites were synthesized in a spray flame from nitrate precursors dissolved in ethanol and in ethanol/2-ethylhexanoic acid (2-EHA) mixtures. Experiments with ethanol led to a broad particle-size distribution and to the formation of undesired phases such as La2CoO4, La2O3, and Co3O4. The addition of 2-EHA can initiate micro explosions of the burning droplets and has been systematically investigated toward the formation of single-phase, high-surface-area LaCoO3 and LaFeO3 with a narrow size distribution. To investigate the effect of 2-EHA, temperature-dependent changes of the chemical composition of the precursor solutions were analyzed with ATR-FTIR between 23 and 70°C. In all cases, the formation of esters was identified while in the solutions containing iron, additional formation of carboxylates was observed. The synthesized materials were characterized by BET SSA, XRD, SAED and EDX-TEM and their catalytic activity was analyzed, reaching 50% CO conversion at temperatures below 160 and 300°C for LaCoO3 and LaFeO3, respectively. © 2019 The Authors. AIChE Journal published by Wiley Periodicals, Inc. on behalf of American Institute of Chemical Engineers.
    view abstractdoi: 10.1002/aic.16748
  • 2020 • 763 Spin-locked transport in a two-dimensional electron gas
    Anghel, S. and Passmann, F. and Schiller, K.J. and Moore, J.N. and Yusa, G. and Mano, T. and Noda, T. and Betz, M. and Bristow, A.D.
    Physical Review B 101 (2020)
    Spin-orbit interactions in solids have inspired innovative physics for spin-based technologies. One such example is the persistent spin helix, where spin-orbit interactions from the semiconductor lattice are balanced with those in asymmetric quantum wells, to create long-lived spin textures. Spin transport in the presence of the momentum-dependent spin-orbit interactions lead to Larmor precession and subsequent dephasing that challenges the design of current spin-based information processing devices. We demonstrate that external magnetic fields can be applied to overcome this issue for spin-polarized charge carriers transported by in-plane electric fields. A frame of reference picture is introduced to describe the emergence and dynamics of the polarization-locked spin-wave packet after optical excitation. Applying well-matched magnetic fields maintains the persistent spin-helix profile regardless of whether the frame of reference is in motion or not. Monte Carlo simulations allow this traveling persistent spin-helix concept to be extended to a proposed spin Hall-effect transistor to ease design requirements. © 2020 American Physical Society.
    view abstractdoi: 10.1103/PhysRevB.101.155414
  • 2020 • 762 On the reversible deactivation of cobalt ferrite spinel nanoparticles applied in selective 2-propanol oxidation
    Anke, S. and Falk, T. and Bendt, G. and Sinev, I. and Hävecker, M. and Antoni, H. and Zegkinoglou, I. and Jeon, H. and Knop-Gericke, A. and Schlögl, R. and Roldan Cuenya, B. and Schulz, S. and Muhler, M.
    Journal of Catalysis 382 57-68 (2020)
    CoFe2O4 nanoparticles (NPs) were synthesized by using a colloidal one-pot synthesis method based on the decomposition of metal acetylacetonates in the presence of oleyl amine. The characterization by X-ray diffraction, transmission electron microscopy and N2 physisorption revealed non-porous spinel phase CoFe2O4 NPs with an average particle size of 4 nm. The unsupported metal oxide NPs were applied in the selective oxidation of 2-propanol in a continuously operated fixed-bed reactor under quasi steady-state conditions using a heating rate of 0.5 k min−1. 2-Propanol was found to be oxidatively dehydrogenated over CoFe2O4 yielding acetone and H2O with high selectivity. Only to a minor extent dehydration to propene and total oxidation to CO2 was observed at higher temperatures. The detected low-temperature reaction pathway with maxima at 430 and 510 K was inhibited after the initial 2-propanol oxidation up to 573 K, but an oxidative treatment in O2 or N2O atmosphere led to full regeneration. No correlation between the desorbing amount or the surface oxygen species investigated by O2 temperature-programmed desorption experiments and the low-temperature activity was observed. The amounts of evolving CO2 during the TPO experiments indicate deactivation due to formation of carbonaceous species. Inhibition experiments with pre-adsorbed reaction intermediates and infrared spectroscopy identified acetate species as reversible poison, whereas carbonates are rather spectators. In addition, carbon deposition was detected by X-ray photoelectron spectroscopy, which also revealed a minor influence of cobalt reduction during the deactivation process as confirmed by X-ray absorption spectroscopy studies. © 2019 Elsevier Inc.
    view abstractdoi: 10.1016/j.jcat.2019.12.007
  • 2020 • 761 Numerical analysis of dielectric post-wall waveguides
    Archemashvili, E. and Yasumoto, K. and Jandieri, V. and Pistora, J. and Maeda, H. and Erni, D.
    2020 International Workshop on Antenna Technology, iWAT 2020 (2020)
    Functional post-wall waveguides that are formed by periodically distributed dielectric posts are numerically analyzed. In this preliminary study, the propagation constant and attenuation constant of the dielectric post-wall waveguide is rigorously calculated using our originally developed numerical method. The developed formulation is accurate and numerically very fast. Structural parameters of the dielectric post-wall waveguide are properly chosen in order to achieve the confinement of the field in the guiding region as strong as possible even in case of one-layered dielectric structure. The final goal of our investigations is to realize the functional dielectric post-wall waveguide-based filters, which are expected to have a practical application in THz region, where the metallic (PEC) rods are losing their properties. © 2020 IEEE.
    view abstractdoi: 10.1109/iWAT48004.2020.1570608549
  • 2020 • 760 Subharmonic Injection Locking for Phase and Frequency Control of RTD-Based THz Oscillator
    Arzi, K. and Suzuki, S. and Rennings, A. and Erni, D. and Weimann, N. and Asada, M. and Prost, W.
    IEEE Transactions on Terahertz Science and Technology 10 221-224 (2020)
    Phase and frequency control of resonant tunneling diode (RTD) based terahertz oscillators are major challenges in realizing coherent signal sources for arrayed applications, such as spatial power combining, beam steering, or multi-in multi-out systems. In this letter, we demonstrate frequency locking and control of an RTD oscillating at f0 ∼ 550 GHz, via radiative injection of a weak sinusoidal subharmonic signal at f0/2. Precise frequency control, within the locking range of around 2 GHz, is demonstrated. A peak output power enhancement of 14 dB in the whole locking range, compared to the free running oscillator, is achieved. Furthermore, occurrence of phase locking is identified by the spectral linewidth reduction, quantifiable in the full-width at half-maximum parameter. A signal linewidth of 490 Hz was achieved in locked operation. © 2011-2012 IEEE.
    view abstractdoi: 10.1109/TTHZ.2019.2959411
  • 2020 • 759 Ab initio Description of Bond Breaking in Large Electric Fields
    Ashton, M. and Mishra, A. and Neugebauer, J. and Freysoldt, C.
    Physical Review Letters 124 (2020)
    Strong (1010 V/m) electric fields capable of inducing atomic bond breaking represent a powerful tool for surface chemistry. However, their exact effects are difficult to predict due to a lack of suitable tools to probe their associated atomic-scale mechanisms. Here we introduce a generalized dipole correction for charged repeated-slab models that controls the electric field on both sides of the slab, thereby enabling direct theoretical treatment of field-induced bond-breaking events. As a prototype application, we consider field evaporation from a kinked W surface. We reveal two qualitatively different desorption mechanisms that can be selected by the magnitude of the applied field. © 2020 authors. Published by the American Physical Society.
    view abstractdoi: 10.1103/PhysRevLett.124.176801
  • 2020 • 758 Implicit time discretization schemes for mixed least-squares finite element formulations
    Averweg, S. and Schwarz, A. and Nisters, C. and Schröder, J.
    Computer Methods in Applied Mechanics and Engineering 368 (2020)
    This work is an extension of the ideas in Averweg et al. (2019) with the focus on a detailed investigation of implicit time discretization schemes to model instationary fluid flow, based on the incompressible Navier–Stokes equations, and linear elastodynamic structural behavior. The variational approaches for fluid and solid mechanics are based on a mixed least-squares finite element method. The L2-norm minimization of the residuals of the constructed first-order systems of the governing differential equations is based on two-field stress–velocity (SV) functionals. For the time discretization of the SV-fluid formulation, four different types of implicit integration schemes are investigated, namely the Houbolt method, the Crank–Nicolson method and two explicit, singly diagonally implicit Runge–Kutta methods (ESDIRK). The SV-formulation for the solid is discretized applying the Houbolt method. The presented time integration schemes are validated investigating an unsteady fluid flow and an elastodynamic structural benchmark. Since both (fluid and solid) SV formulations are discretized using conforming finite element spaces in H(div) and H1, respectively, the inherent fulfillment of coupling conditions, when modeling fluid–structure interaction problems, is given a priori. Therefore, the applicability is also examined by two simplified FSI problems for small deformations, in order to represent the main characteristics of the presented approach. © 2020 Elsevier B.V.
    view abstractdoi: 10.1016/j.cma.2020.113111
  • 2020 • 757 Towards deterministic computation of internal stresses in additively manufactured materials under fatigue loading: Part I
    Awd, M. and Labanie, M.F. and Moehring, K. and Fatemi, A. and Walther, F.
    Materials 13 (2020)
    The ongoing studies of the influence of internal defects on fatigue strength of additively manufactured metals adopted an internal crack or notch-like model at which the threshold stress intensity factor is the driving mechanism of fatigue failure. The current article highlights a shortcoming of this approach and offers an alternative based on X-ray microcomputed tomography and cyclic plasticity with a hybrid formulation of Chaboche and Armstrong-Frederick material laws. The presented tessellation and geometrical transformation scheme enabled a significantly more realistic morphological representation of internal defects that yielded a cyclic strain within 2% of the experimental values. This means that cyclic plasticity models have an accurate prediction of mechanical properties without repeating a full set of experiments for additively manufactured arbitrary microstructures. The coupling with a material law that is oriented towards the treatment of cyclic hardening and softening enabled more accurate computation of internal stresses under cyclic loading than ever before owing to the maturity of tessellation and numerical tools since then. The resulting stress-strain distributions were used as input to the Fatemi-Socie damage model, based on which a successful calculation of fatigue lifetime became possible. Furthermore, acting stresses on the internal pores were shown to be more than 450% concerning the applied remote stress amplitude. The results are a pretext to a scale bridging numerical solution that accounts for the short crack formation stage based on microstructural damage. © 2020 by the authors.
    view abstractdoi: 10.3390/ma13102318
  • 2020 • 756 Microstructural damage and fracture mechanisms of selective laser melted Al-Si alloys under fatigue loading
    Awd, M. and Siddique, S. and Walther, F.
    Theoretical and Applied Fracture Mechanics 106 (2020)
    Employment of selective laser melted materials for industrial applications has grown in the recent years owing to improvements in machine systems and scanning techniques to result in near full-density parts; however, there are still limitations when their industrial application, particularly under cyclic loading, is concerned. This study investigates the chain from processing to post-process stress-relief to structural investigations in terms of microstructure and three-dimensional defect analysis by micro-computed tomography, and their corresponding behavior under quasi-static, high-cycle fatigue as well as very high-cycle fatigue for AlSi12 and AlSi10Mg alloys. Microstructure and damage mechanisms have been investigated as a function of in-process and post-process thermal treatments. Their corresponding influence on mechanical behavior revealed that there do exist differences in damage mechanisms in high-cycle fatigue and very high-cycle fatigue where the role of microstructure and small porosity respectively determines the damage mechanism in the two regions. The process parameters determining the required set of material behavior under quasi-static and cyclic loading have been identified. © 2020
    view abstractdoi: 10.1016/j.tafmec.2020.102483
  • 2020 • 755 Improvement of Fatigue Strength in Lightweight Selective Laser Melted Alloys by In-Situ and Ex-Situ Composition and Heat Treatment
    Awd, M. and Johannsen, J. and Chan, T. and Merghany, M. and Emmelmann, C. and Walther, F.
    Minerals, Metals and Materials Series 115-126 (2020)
    Selective laser melting is a powder-bed-fusion process that is applied to different alloys. Thus, it is essential to study what are the different process variables that affect the static, quasi-static, and cyclic mechanical properties. In this contribution, two examples of alloys are introduced: AlSi (AlSi12, AlSi10Mg) and Ti-6Al-4V. The influence of controlled cooling and degassing mechanisms of residual gases is investigated by structural analysis in electron microscopy and X-ray computed tomography. Controlled cooling through platform heating or multi-exposure treatments increased the dendritic width in AlSi alloys and decomposed alpha prime in Ti-6Al-4V. The alteration was a cause for enhanced ductility and slowing of crack propagation. The cyclic deformation is tracked during mechanical testing and is simulated in FE software using a high-throughput methodology to calculate Woehler curves based on Fatemi-Socie damage parameters. The cyclic deformation simulation is in agreement with the experimental data and quantified cyclic damage using Fatemi-Socie parameters. © 2020, The Minerals, Metals & Materials Society.
    view abstractdoi: 10.1007/978-3-030-36296-6_11
  • 2020 • 754 Continuum mechanical modeling of strain-induced crystallization in polymers
    Aygün, S. and Klinge, S.
    International Journal of Solids and Structures 196-197 129-139 (2020)
    The present contribution focuses on the thermodynamically consistent mechanical modeling of the strain-induced crystallization in unfilled polymers. This phenomenon is of particular importance for the mechanical properties of polymers as well as for their manufacturing and the application. The model developed uses the principle of the minimum of dissipation potential and assumes two internal variables: the deformations due to crystallization and the regularity of the network. In addition to the dissipation potential necessary for the derivation of evolution equations, the well-established Arruda-Boyce model is chosen to depict the elastic behavior of the polymer. Two special features of the model are the evolution direction depending on the stress state and the distinction of crystallization during the loading and unloading phase. The model has been implemented into the finite element method and applied for numerical simulation of the growth and shrinkage of the crystal regions during a cyclic tension test for samples with different initial configurations. The concept enables the visualization of the microstructure evolution, yielding information that is still inaccessible by experimental techniques. © 2020 Elsevier Ltd
    view abstractdoi: 10.1016/j.ijsolstr.2020.04.017
  • 2020 • 753 Overcoming the Limitations of Transient Photovoltage Measurements for Studying Recombination in Organic Solar Cells
    Azzouzi, M. and Calado, P. and Telford, A.M. and Eisner, F. and Hou, X. and Kirchartz, T. and Barnes, P.R.F. and Nelson, J.
    Solar RRL 4 (2020)
    Transient photovoltage (TPV) measurements are frequently used to study recombination processes in thin-film solar cells by probing the decay of a small optically induced voltage perturbation to infer the charge carrier dynamics of devices at open circuit. However, the validity of this method to probe organic semiconductors has recently come into doubt due to large discrepancies in the reported carrier lifetime values for the same systems and the reporting of unrealistic reaction order values. Herein, the validity of TPV to extract reliable charge carrier lifetimes in thin-film solar cells is explored through the use of time-dependent drift-diffusion simulations and measurements. It is found that in low-mobility materials, TPV serves primarily as a probe of charge carrier redistribution in the bulk rather than bulk recombination dynamics and that the extracted time constant is highly mobility dependent. To address this shortcoming, transient photocharge, a new technique to measure the charge carrier density during photovoltage decay, is introduced and applied to study the recombination dynamics in a series of (fullerene and nonfullerene) organic solar cell systems. It is shown that using this technique the charge carrier recombination lifetime in the active layer is more accurately determined. © 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/solr.201900581
  • 2020 • 752 Steels in additive manufacturing: A review of their microstructure and properties
    Bajaj, P. and Hariharan, A. and Kini, A. and Kürnsteiner, P. and Raabe, D. and Jägle, E.A.
    Materials Science and Engineering A 772 (2020)
    Today, a large number of different steels are being processed by Additive Manufacturing (AM) methods. The different matrix microstructure components and phases (austenite, ferrite, martensite) and the various precipitation phases (intermetallic precipitates, carbides) lend a huge variability in microstructure and properties to this class of alloys. This is true for AM-produced steels just as it is for conventionally-produced steels. However, steels are subjected during AM processing to time-temperature profiles which are very different from the ones encountered in conventional process routes, and hence the resulting microstructures differ strongly as well. This includes a very fine and highly morphologically and crystallographically textured microstructure as a result of high solidification rates as well as non-equilibrium phases in the as-processed state. Such a microstructure, in turn, necessitates additional or adapted post-AM heat treatments and alloy design adjustments. In this review, we give an overview over the different kinds of steels in use in fusion-based AM processes and present their microstructures, their mechanical and corrosion properties, their heat treatments and their intended applications. This includes austenitic, duplex, martensitic and precipitation-hardening stainless steels, TRIP/TWIP steels, maraging and carbon-bearing tool steels and ODS steels. We identify areas with missing information in the literature and assess which properties of AM steels exceed those of conventionally-produced ones, or, conversely, which properties fall behind. We close our review with a short summary of iron-base alloys with functional properties and their application perspectives in Additive Manufacturing. © 2019 Elsevier B.V.
    view abstractdoi: 10.1016/j.msea.2019.138633
  • 2020 • 751 High-velocity water vapor corrosion of Yb-silicate: Sprayed vs. sintered body
    Bakan, E. and Kindelmann, M. and Kunz, W. and Klemm, H. and Vaßen, R.
    Scripta Materialia 178 468-471 (2020)
    The water vapor corrosion of Yb-silicates is of interest to their application as environmental barrier coatings in gas turbine technology. In this study, densified samples from the Yb-silicate powder, as well as plasma-sprayed free-standing Yb-silicate coating were tested at a high-velocity steam rig (T = 1400 °C, v = 90 m/s, PH2O = 0.19 atm) for microstructural comparison. After the test, the measured weight losses of the coatings were larger than that of the densified sample. At the same time, the thicknesses of the corroded scales at the coating surfaces were found to be thicker than that of the sintered sample by a factor of two. © 2019
    view abstractdoi: 10.1016/j.scriptamat.2019.12.019
  • 2020 • 750 An investigation on burner rig testing of environmental barrier coatings for aerospace applications
    Bakan, E. and Mack, D.E. and Lobe, S. and Koch, D. and Vaßen, R.
    Journal of the European Ceramic Society (2020)
    In this study, burner rig testing of Si/Yb2Si2O7 environmental barrier coating protected SiC-based ceramic matrix composites was conducted. Tests were performed at standard conditions as well as with liquid water injection to the flame. Furthermore, the influence of the impingement angle of the flame (45° vs. 90°) on water vapor corrosion was explored. Gas flow rates were adapted in each test to adjust 1250 °C at the sample surface. The comparison of test results showed that water injection advances the corrosion of the Yb2Si2O7 topcoat and the impingement angle affects the size and shape of the corroded area on the sample surface. © 2020 Elsevier Ltd
    view abstractdoi: 10.1016/j.jeurceramsoc.2020.06.016
  • 2020 • 749 A 3D particle finite element model for the simulation of soft soil excavation using hypoplasticity
    Bal, A.R.L. and Dang, T.S. and Meschke, G.
    Computational Particle Mechanics 7 151-172 (2020)
    A numerical model based on the particle finite element method (PFEM) combined with a hypoplastic constitutive model is proposed for the analysis of soft soil excavations by means of single and multiple excavation tools. The PFEM allows to efficiently account for large deformations of the excavated soil material and free surfaces characterizing the simulation of tool–soil interaction during excavation. The utilization of a hypoplastic model, formulated in rate form, allows for a straightforward coupling with the standard velocity-based PFEM. Furthermore, effects such as pressure and density dependency of the soil stiffness are consistently incorporated into the formulation. The solution of the governing equations is performed implicitly, while an adaptive sub-stepping scheme is employed for the explicit time integration of the constitutive equation. Thus, the accuracy of the solution is improved at both global and local (constitutive) levels. The performance of the method is evaluated by means of the numerical re-analysis of selected geotechnical benchmark examples and soft soil excavations in 2D and 3D setups. © 2019, OWZ.
    view abstractdoi: 10.1007/s40571-019-00271-y
  • 2020 • 748 Atomic Scale Origin of Metal Ion Release from Hip Implant Taper Junctions
    Balachandran, S. and Zachariah, Z. and Fischer, A. and Mayweg, D. and Wimmer, M.A. and Raabe, D. and Herbig, M.
    Advanced Science 7 (2020)
    Millions worldwide suffer from arthritis of the hips, and total hip replacement is a clinically successful treatment for end-stage arthritis patients. Typical hip implants incorporate a cobalt alloy (Co–Cr–Mo) femoral head fixed on a titanium alloy (Ti-6Al-4V) femoral stem via a Morse taper junction. However, fretting and corrosion at this junction can cause release of wear particles and metal ions from the metallic implant, leading to local and systemic toxicity in patients. This study is a multiscale structural-chemical investigation, ranging from the micrometer down to the atomic scale, of the underlying mechanisms leading to metal ion release from such taper junctions. Correlative transmission electron microscopy and atom probe tomography reveals microstructural and compositional alterations in the subsurface of the titanium alloy subjected to in vitro gross-slip fretting against the cobalt alloy. Even though the cobalt alloy is comparatively more wear-resistant, changes in the titanium alloy promote tribocorrosion and subsequent degradation of the cobalt alloy. These observations regarding the concurrent occurrence of electrochemical and tribological phenomena are vital to further improve the design and performance of taper junctions in similar environments. © 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/advs.201903008
  • 2020 • 747 Degradation, bone regeneration and tissue response of an innovative volume stable magnesium-supported GBR/GTR barrier membrane
    Barbeck, M. and Kühnel, L. and Witte, F. and Pissarek, J. and Precht, C. and Xiong, X. and Krastev, R. and Wegner, N. and Walther, F. and Jung, O.
    International Journal of Molecular Sciences 21 (2020)
    Introduction: Bioresorbable collagenous barrier membranes are used to prevent premature soft tissue ingrowth and to allow bone regeneration. For volume stable indications, only non-absorbable synthetic materials are available. This study investigates a new bioresorbable hydrofluoric acid (HF)-treated magnesium (Mg) mesh in a native collagen membrane for volume stable situations. Materials and Methods: HF-treated and untreated Mg were compared in direct and indirect cytocompatibility assays. In vivo, 18 New Zealand White Rabbits received each four 8 mm calvarial defects and were divided into four groups: (a) HF-treated Mg mesh/collagen membrane, (b) untreated Mg mesh/collagen membrane (c) collagen membrane and (d) sham operation. After 6, 12 and 18 weeks, Mg degradation and bone regeneration was measured using radiological and histological methods. Results: In vitro, HF-treated Mg showed higher cytocompatibility. Histopathologically, HF-Mg prevented gas cavities and was degraded by mononuclear cells via phagocytosis up to 12 weeks. Untreated Mg showed partially significant more gas cavities and a fibrous tissue reaction. Bone regeneration was not significantly different between all groups. Discussion and Conclusions: HF-Mg meshes embedded in native collagen membranes represent a volume stable and biocompatible alternative to the non-absorbable synthetic materials. HF-Mg shows less corrosion and is degraded by phagocytosis. However, the application of membranes did not result in higher bone regeneration. © 2020 by the authors.
    view abstractdoi: 10.3390/ijms21093098
  • 2020 • 746 Symmetric single-impurity Kondo model on a tight-binding chain: Comparison of analytical and numerical ground-state approaches
    Barcza, G. and Bauerbach, K. and Eickhoff, F. and Anders, F.B. and Gebhard, F. and Legeza, Ö.
    Physical Review B 101 (2020)
    We analyze the ground-state energy, local spin correlation, impurity spin polarization, impurity-induced magnetization, and corresponding zero-field susceptibilities of the symmetric single-impurity Kondo model on a tight-binding chain with bandwidth W=2D where a spin-12 impurity at the chain center interacts with coupling strength JK with the local spin of the bath electrons. We compare perturbative results and variational upper bounds from Yosida, Gutzwiller, and first-order Lanczos wave functions to the numerically exact extrapolations obtained from the density-matrix renormalization group (DMRG) method and from the numerical renormalization group (NRG) method performed with respect to the inverse system size and Wilson parameter, respectively. In contrast to the Lanczos and Yosida wave functions, the Gutzwiller variational approach becomes exact in the strong-coupling limit JK≫W, and reproduces the ground-state properties from DMRG and NRG for large couplings JKâ‰W, with a high accuracy. For weak coupling, the Gutzwiller wave function describes a symmetry-broken state with an oriented local moment, in contrast to the exact solution. We calculate the impurity spin polarization and its susceptibility in the presence of magnetic fields that are applied globally or only locally to the impurity spin. The Yosida wave function provides qualitatively correct results in the weak-coupling limit. In DMRG, chains with about 103 sites are large enough to describe the susceptibilities down to JK/D≈0.6. For smaller Kondo couplings, only the NRG provides reliable results for a general host-electron density of states ρ0(ϵ). To compare with results from Bethe ansatz that become exact in the wide-band limit, we study the impurity-induced magnetization and zero-field susceptibility. For small Kondo couplings, the zero-field susceptibilities at zero temperature approach χ0(JK≪D)/(gμB)2≈exp[1/(ρ0(0)JK)]/[2CDπeρ0(0)JK], where ln(C) is the regularized first inverse moment of the density of states. Using NRG, we determine the universal subleading corrections up to second order in ρ0(0)JK. © 2020 American Physical Society.
    view abstractdoi: 10.1103/PhysRevB.101.075132
  • 2020 • 745 Design and Evaluation of a Passive Frequency-Coded Reflector using W-Band FMCW Radar
    Barowski, J. and Abbas, A.A. and El-Absi, M. and Piotrowsky, L. and Pohl, N. and Rolfes, I. and Solbach, K.
    GeMIC 2020 - Proceedings of the 2020 German Microwave Conference 92-95 (2020)
    This paper presents results to validate the passive frequency coding capability of dielectric resonators in chipless reflector tags. For this purpose, two measurement setups are used. First, the general functionality is proven by using a vector network analyzer. Secondly, a FMCW radar is used to measure the frequency dependent target response, since it achieves a much higher mobility and can be used as a tag-reader in real operation. Furthermore, both measurement systems are compared regarding their stability and dynamic range. © 2020 IMA-Institut fur Mikrowellen-und Antennentechnik e.V.
    view abstract
  • 2020 • 744 An energy-relaxation-based framework for the modelling of magnetic shape memory alloys—Simulation of key response features under homogeneous loading conditions
    Bartel, T. and Kiefer, B. and Buckmann, K. and Menzel, A.
    International Journal of Solids and Structures 182-183 162-178 (2020)
    In this contribution we present a constitutive modelling framework for magnetic shape memory alloys (MSMA) that builds on a global variational principle. The approach relies on concepts of energy relaxation and generalised notions of convexity to compute effective energy hulls to the non-convex energy landscape associated with the underlying multi-phase solid, from which the prediction of microstructure evolution results. In this sense it fundamentally distinguishes itself from MSMA models that essentially follow phenomenological concepts of classical plasticity (Kiefer and Lagoudas, 2005; 2009). The microstructure is not spatially resolved, but micro-scale quantities are taken into account in an effective sense by additional state variables—such as volume fractions or interface orientations—and appropriate mixture rules. The model allows all mechanisms central to MSMA behaviour—i.e. variant switching, magnetisation rotation away from easy axes, and magnetic domain evolution—to occur simultaneously. The authors have previously been able to demonstrate that such a modelling approach can quantitatively capture the key characteristics of single-crystalline MSMA response under standard loading scenarios (Kiefer et al., 2015). The modelling framework presented here is now further able to predict much more general response features, such as variant switching diagrams, magnetic field-biased pseudo-elasticity and the influence of specimen shape anisotropy. Moreover, the global variational framework is formulated in a manner that lends itself to finite element implementation. In this work, however, numerical examples are considered in which the nonlocal nature of the demagnetisation field is taken into account in an approximate sense through appropriate shape factors. © 2019 Elsevier Ltd
    view abstractdoi: 10.1016/j.ijsolstr.2019.07.016
  • 2020 • 743 Fatigue of brazed joints made of X5CrNi18-10 and Cu110 and derivation of reliable assessment approaches
    Baumgartner, J. and Tillmann, W. and Bobzin, K. and Öte, M. and Wiesner, S. and Sievers, N.
    Welding in the World 64 707-719 (2020)
    Brazing in a continuous belt furnace is a quite cost-effective way of joining components consisting of many individual parts. It is extensively used in many industrial sectors like the automotive or in the energy industry. Even though many components are cyclically loaded during service up to now, no approaches to assess the lifetime under in-service loads are available. In order to assess the fatigue strength of brazed joints, three different specimen types have been investigated: peel and shear as well as a component-like specimens. The specimens were characterized and tested under load control using constant and variable amplitudes. Subsequently, the fatigue life of these joints was assessed by linear-elastic notch stresses. A reference S-N curve and characteristic damage sums were derived that enable to perform a reliable fatigue assessment. Further parameters which seem to have a strong influence on the fatigue life, the surface topology, and the overall quality of the braze were identified. Their influence is discussed. © 2020, The Author(s).
    view abstractdoi: 10.1007/s40194-020-00850-1
  • 2020 • 742 In Situ X-ray Microscopy Reveals Particle Dynamics in a NiCo Dry Methane Reforming Catalyst under Operating Conditions
    Beheshti Askari, A. and Al Samarai, M. and Morana, B. and Tillmann, L. and Pfänder, N. and Wandzilak, A. and Watts, B. and Belkhou, R. and Muhler, M. and Muhler, M. and Debeer, S.
    ACS Catalysis 10 6223-6230 (2020)
    Herein, we report the synthesis of a γ-Al2O3-supported NiCo catalyst for dry methane reforming (DMR) and study the catalyst using in situ scanning transmission X-ray microscopy (STXM) during the reduction (activation step) and under reaction conditions. During the reduction process, the NiCo alloy particles undergo elemental segregation with Co migrating toward the center of the catalyst particles and Ni migrating to the outer surfaces. Under DMR conditions, the segregated structure is maintained, thus hinting at the importance of this structure to optimal catalytic functions. Finally, the formation of Ni-rich branches on the surface of the particles is observed during DMR, suggesting that the loss of Ni from the outer shell may play a role in the reduced stability and hence catalyst deactivation. These findings provide insights into the morphological and electronic structural changes that occur in a NiCo-based catalyst during DMR. Further, this study emphasizes the need to study catalysts under operating conditions in order to elucidate material dynamics during the reaction. © 2020 American Chemical Society.
    view abstractdoi: 10.1021/acscatal.9b05517
  • 2020 • 741 Static and oscillation superimposed ring compression tests with structured and coated tools for Sheet-Bulk Metal Forming
    Behrens, B.-A. and Meijer, A. and Stangier, D. and Hübner, S. and Biermann, D. and Tillmann, W. and Rosenbusch, D. and Müller, P.
    Journal of Manufacturing Processes 55 78-86 (2020)
    Forming tools with tailored surfaces or functional surface modifications offer great potential for the adaption and optimization of forming processes. However, the interaction of the resulting tribological conditions with additional process oscillations and lubricants has not yet been sufficiently investigated. In the field of sheet-bulk metal forming the superimposition of oscillations is a new, highly promising approach for optimizing the forming of metallic materials. The aim of this study is therefore to investigate the forming behavior of metallic materials with an oscillation superimposition in combination with structured tool surfaces. In order to examine to what extend the friction factor and the forming force can be influenced by structured surfaces and PVD-coatings ring compression tests were conducted to re-create the real process conditions. The experiments were carried out statically and with an oscillation superimposition in the main force flow of the machine under lubrication and dry conditions. Occurring interactions between surface applications, lubrication and oscillation superimposition are identified and analyzed within the context of this work. Thereby, three different deterministic surface structures of the ring compression tools were considered. A radial and tangential arrangement of a wave-like structure as well as an isotropic honeycomb structure were applied on the forming tools by means of micromilling. For a lubricated and vibration superimposed process, especially the isotropic honeycomb structure caused a significant decrease in friction. This was attributed to the formation of lubrication pockets. Despite the reduced friction, in some cases no reduction of the forming force occurred by using an oscillation superimposed forming process. This behavior was attributed to damping effects caused by the lubricating pockets. © 2020 The Society of Manufacturing Engineers
    view abstractdoi: 10.1016/j.jmapro.2020.04.007
  • 2020 • 740 Influence of tailored surfaces and superimposed-oscillation on sheet-bulk metal forming operations
    Behrens, B.-A. and Tillmann, W. and Biermann, D. and Hübner, S. and Stangier, D. and Freiburg, D. and Meijer, A. and Koch, S. and Rosenbusch, D. and Müller, P.
    Journal of Manufacturing and Materials Processing 4 (2020)
    Producing complex sheet metal components in fewer process steps motivated the development of the innovative forming process called sheet-bulk metal forming (SBMF). In this process, sheet metal forming and bulk-metal forming are combined to create a unique forming process in which a component with external and internal gearing is produced in three production steps. However, the high degrees of deformation that occur using high-strength steels and the number of different process steps result in high process forces, strongly limiting the service life of tools. To reduce the forming force during SBMF processes, tool and process modifications were investigated. Therefore, plane-strain compression tests were conducted to examine the influence of a CrAlN PVD coating and tailored surfaces produced by high-feed milling (HF) of tool-active elements on the material flow of the specimens. In addition to the tool-sided modifications, the influence of an oscillation overlay during the forming process was investigated. Based on the results of the compression tests, the surfaces of the active tool elements of the SBMF process were modified in order to transfer the basic experimental results to the production of a functional component. The friction is thus adapted locally in the SBMF process. © 2020 by the authors.
    view abstractdoi: 10.3390/jmmp4020041
  • 2020 • 739 Artificial Signal Transduction
    Bekus, R. and Schrader, T.
    ChemistryOpen 9 667-682 (2020)
    Communication between and inside cells as well as their response to external stimuli relies on elaborated systems of signal transduction. They all require a directional transmission across membranes, often realized by primary messenger docking onto external receptor units and subsequent internalization of the signal in form of a released second messenger. This in turn starts a cascade of events which ultimately control all functions of the living cell. Although signal transduction is a fundamental biological process realized by supramolecular recognition and multiplication events with small molecules, chemists have just begun to invent artificial models which allow to study the underlying rules, and one day perhaps to rescue damaged transduction systems in nature. This review summarizes the exciting pioneering efforts of chemists to create simple models for the basic principles of signal transduction across a membrane. It starts with first attempts to establish molecular recognition events on liposomes with embedded receptor amphiphiles and moves on to simple transmembrane signaling across lipid bilayers. More elaborated systems step by step incorporate more elements of cell signaling, such as primary and secondary messenger or a useful cellular response such as cargo release. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
    view abstractdoi: 10.1002/open.201900367
  • 2020 • 738 Morphology, microstructure, coordinative unsaturation, and hydrogenation activity of unsupported MoS2: How idealized models fail to describe a real sulfide material
    Bekx-Schürmann, S. and Mangelsen, S. and Breuninger, P. and Antoni, H. and Schürmann, U. and Kienle, L. and Muhler, M. and Bensch, W. and Grünert, W.
    Applied Catalysis B: Environmental 266 (2020)
    Polycrystalline MoS2 from (NH4)2MoS4 thermolysis was activated in dilute H2 at 523 K < TR < 873 K and studied by XRD, total scattering analysis, XPS, HRTEM, and chemisorption to explain, why coordinative unsaturation decreases with growing TR contrary to expectations from the MoS2 structure. Hydrogenation rates were measured for identifying active sites. With increasing TR, activity and chemisorption peaked at different TR,peak. Below TR,peak, increasing activity was not paralleled by changes in MoS2 microstructure. Decreasing chemisorption above TR,peak was assigned to saturation of vacancies by sulfide from internal defects and to inclusion of vacancies in the interior of aggregates. Upon high-temperature reduction, stacks grew anisotropically (basal planes extended), retaining defects like bending, turbostratic disorder. Preferential exposure of stack bases in aggregate surfaces resulted in enhanced decrease of chemisorption. Correlations between activity, edge area and (b)rim length estimated from a morphological model localized active sites in the (b)rim region. © 2020 Elsevier B.V.
    view abstractdoi: 10.1016/j.apcatb.2020.118623
  • 2020 • 737 Towards Reliable and Quantitative Surface-Enhanced Raman Scattering (SERS): From Key Parameters to Good Analytical Practice
    Bell, S.E.J. and Charron, G. and Cortés, E. and Kneipp, J. and de la Chapelle, M.L. and Langer, J. and Procházka, M. and Tran, V. and Schlücker, S.
    Angewandte Chemie - International Edition 59 5454-5462 (2020)
    Experimental results obtained in different laboratories world-wide by researchers using surface-enhanced Raman scattering (SERS) can differ significantly. We, an international team of scientists with long-standing expertise in SERS, address this issue from our perspective by presenting considerations on reliable and quantitative SERS. The central idea of this joint effort is to highlight key parameters and pitfalls that are often encountered in the literature. To that end, we provide here a series of recommendations on: a) the characterization of solid and colloidal SERS substrates by correlative electron and optical microscopy and spectroscopy, b) on the determination of the SERS enhancement factor (EF), including suitable Raman reporter/probe molecules, and finally on c) good analytical practice. We hope that both newcomers and specialists will benefit from these recommendations to increase the inter-laboratory comparability of experimental SERS results and further establish SERS as an analytical tool. © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
    view abstractdoi: 10.1002/anie.201908154
  • 2020 • 736 Impact of electron solvation on ice structures at the molecular scale
    Bertram, C. and Auburger, P. and Bockstedte, M. and Stähler, J. and Bovensiepen, U. and Morgenstern, K.
    Journal of Physical Chemistry Letters 11 1310-1316 (2020)
    Electron attachment and solvation at ice structures are well-known phenomena. The energy liberated in such events is commonly understood to cause temporary changes at such ice structures, but it may also trigger permanent modifications to a yet unknown extent. We determine the impact of electron solvation on D2O structures adsorbed on Cu(111) with low-Temperature scanning tunneling microscopy, two-photon photoemission, and ab initio theory. Solvated electrons, generated by ultraviolet photons, lead not only to transient but also to permanent structural changes through the rearrangement of individual molecules. The persistent changes occur near sites with a high density of dangling OD groups that facilitate electron solvation. We conclude that energy dissipation during solvation triggers permanent molecular rearrangement via vibrational excitation. Copyright © 2020 American Chemical Society.
    view abstractdoi: 10.1021/acs.jpclett.9b03723
  • 2020 • 735 Weakly symmetric stress equilibration for hyperelastic material models
    Bertrand, F. and Moldenhauer, M. and Starke, G.
    GAMM Mitteilungen 43 (2020)
    A stress equilibration procedure for hyperelastic material models is proposed and analyzed in this paper. Based on the displacement-pressure approximation computed with a stable finite element pair, it constructs, in a vertex-patch-wise manner, an H(div)-conforming approximation to the first Piola-Kirchhoff stress. This is done in such a way that its associated Cauchy stress is weakly symmetric in the sense that its antisymmetric part is zero tested against continuous piecewise linear functions. Our main result is the identification of the subspace of test functions perpendicular to the range of the local equilibration system on each patch which turn out to be rigid body modes associated with the current configuration. Momentum balance properties are investigated analytically and numerically and the resulting stress reconstruction is shown to provide improved results for surface traction forces by computational experiments. © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/gamm.202000007
  • 2020 • 734 Asymptotically Exact A Posteriori Error Analysis for the Mixed Laplace Eigenvalue Problem
    Bertrand, F. and Boffi, D. and Stenberg, R.
    Computational Methods in Applied Mathematics 20 215-225 (2020)
    This paper derives a posteriori error estimates for the mixed numerical approximation of the Laplace eigenvalue problem. We discuss a reconstruction in the standard H 0 1 -conforming space for the primal variable of the mixed Laplace eigenvalue problem and compare it with analogous approaches present in the literature for the corresponding source problem. In the case of Raviart-Thomas finite elements of arbitrary polynomial degree, the resulting error estimator constitutes a guaranteed upper bound for the error and is shown to be local efficient. Our reconstruction is performed locally on a set of vertex patches. © 2020 Walter de Gruyter GmbH, Berlin/Boston 2020.
    view abstractdoi: 10.1515/cmam-2019-0099
  • 2020 • 733 Equilibrated Stress Reconstruction and a Posteriori Error Estimation for Linear Elasticity
    Bertrand, F. and Kober, B. and Moldenhauer, M. and Starke, G.
    CISM International Centre for Mechanical Sciences, Courses and Lectures 597 69-106 (2020)
    Based on the displacement–pressure approximation computed with a stable finite element pair, a stress equilibration procedure for linear elasticity is proposed. Our focus is on the Taylor–Hood finite element space, with emphasis on the behavior for (nearly) incompressible materials. From a combination of displacement in the standard continuous finite element spaces of polynomial degrees k+1 and pressure in the standard continuous finite element spaces of polynomial degrees k, we construct an H(div)-conforming, weakly symmetric stress reconstruction. Explicit formulas are first given for a flux reconstruction and then for the stress reconstruction. © 2020, CISM International Centre for Mechanical Sciences.
    view abstractdoi: 10.1007/978-3-030-33520-5_3
  • 2020 • 732 Digital holography for evaluation of the refractive index distribution externally induced in semiconductors
    Besaga, V.R. and Gerhardt, N.C. and Hofmann, M.R.
    Proceedings of SPIE - The International Society for Optical Engineering 11306 (2020)
    In this paper, we analyse the capabilities of the digital holographic approach for evaluation of the refractive index distribution appearing in semiconductor materials due to external optical excitation. The study is based on a modified transmission Mach-Zehnder holographic microscope operating in the near-infrared spectral range. Practical considerations for holographic characterization of semiconductor samples are discussed. Experimentally measured data are compared with simulations as well as approaches to interpretation of the retrieved data are covered. © COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only.
    view abstractdoi: 10.1117/12.2544160
  • 2020 • 731 Inspection of semiconductor-based planar wave-guiding structures with a near-infrared transmission digital holographic microscopy
    Besaga, V.R. and Gerhardt, N.C. and Hofmann, M.R.
    Proceedings of SPIE - The International Society for Optical Engineering 11369 (2020)
    In this paper we report on practical investigations aimed at failure detection of the integrated optical circuits (IOC) on Silicon substrate during the control measurements of the items in use. Experiments are performed with a near-infrared (1064 nm) digital holographic microscope (≈90×magnification) in transmission mode. The instrument provides non-destructive and fast (<380 ms reconstruction time for 4112×3008 pixels images) data analysis at the diffraction-limited accuracy (lateral resolution of 760 nm). High quality of the instrument performance is shown on example of topography reconstruction of a standard glass-substrate test target. Practical applicability of the approach was proven on example of diffractive input elements of the IOCs designed for sensing purposes. © COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only.
    view abstractdoi: 10.1117/12.2553911
  • 2020 • 730 α-Aminoisobutyric acid-stabilized peptide sams with low nonspecific protein adsorption and resistance against marine biofouling
    Beyer, C.D. and Reback, M.L. and Gopal, S.M. and Nolte, K.A. and Finlay, J.A. and Clare, A.S. and Schäfer, L.V. and Metzler-Nolte, N. and Rosenhahn, A.
    ACS Sustainable Chemistry and Engineering 8 2665-2671 (2020)
    A series of low fouling peptide self-assembled monolayers (SAMs) was developed to understand how the effects of subtle sequence alterations determine the properties of peptide-terminated SAMs and settlement and adhesion of two model fouling organisms, the green alga Ulva linza and the diatom Navicula perminuta, and adsorption of two different proteins, fibrinogen and lysozyme. Insertion of the bulky, nonproteinogenic amino acid α-aminoisobutyric acid (Aib) was examined for how it affects the peptide surfaces and performance in the assays. By exchanging the serine (S) of the sequence (SGKGSSGSS) with alanine (A), we slightly altered the hydrophilicity and found reduced fouling by N. perminuta. The inclusion of Aib residues resulted in surface structural changes of the peptides from a mixture of β-sheet/random coil to strictly random coil and a decrease in the overall packing density by about 17-37%. Notably, these changes had little effect on the ability of the surface to resist nonspecific adsorption of fibrinogen and lysozyme and attachment of N. perminuta. The sequences containing Aib were 50-84% better than without Aib against the settlement of the zoospore of U. linza. Furthermore, the inclusion of Aib helped to create peptides that were 100% resistant against enzymatic degradation by trypsin, whereas the peptides without Aib were 95% degraded after 4 h. © 2020 American Chemical Society.
    view abstractdoi: 10.1021/acssuschemeng.9b05889
  • 2020 • 729 Process control even for deep boreholes - development of a mechatronic tool system for BTA deep hole drilling for compensation of straightness deviation [Entwicklung eines mechatronischen werkzeugsystems für das BTA-tiefbohren zur kompensation des mittenverlaufs: Prozesskontrolle auch bei tiefen bohrungen]
    Biermann, D. and Iovkov, I. and Gerken, J.F. and Denkena, B. and Bergmann, B. and Klages, N.
    WT Werkstattstechnik 110 50-53 (2020)
    Even though deep hole drilling methods can produce boreholes of higher quality than conventional drilling methods, the straightness deviation of the bore hole represents a quality problem, particularly with increasing drilling depth. Process control in industrial applications is currently performed manually and very time-consuming by the machine operator using a mobile ultrasonic system. In order to ensure a high quality of the components and to save costs, a mechatronic system for process-parallel measurement and influencing of the straightness deviation is being developed. © 2020, VDI Fachmedien GmBbH & Co. KG Unternehmen fur Fachinformationen. All rights reserved.
    view abstract
  • 2020 • 728 FEM simulation of consolidation and microstructure development during PM-hip of cold work tool steel D7
    Birke, C. and Deng, Y. and Riehm, S. and Rajaei, A. and Kaletsch, A. and Broeckmann, C. and Bohrt, S. and Pfeifer, H. and Wulbieter, N. and Theisen, W.
    Euro PM 2018 Congress and Exhibition (2020)
    Hot Isostatic Pressing (HIP) with integrated heat treatment is an innovative technology, as it saves time and energy by combining the densification and heat treatment in a single step. However, qualified final products still require traditional expensive and time-consuming trial-and-error tests. To save this, a numerical model was developed to predict the component shrinkage, metallurgical phase transformations and development of internal stresses during the whole process chain. This contribution presents a numerical simulation of the densification and the cooling of D7 cold work steel in a HIP unit. Simulation results are compared to experiments. Measured dimensions of the final component after HIP, as well as the phase fractions obtained by X-ray diffraction (XRD), are compared to the corresponding numerically predicted data. © European Powder Metallurgy Association (EPMA).
    view abstract
  • 2020 • 727 Effect of Grain Statistics on Micromechanical Modeling: The Example of Additively Manufactured Materials Examined by Electron Backscatter Diffraction
    Biswas, A. and Prasad, M.R.G. and Vajragupta, N. and Kostka, A. and Niendorf, T. and Hartmaier, A.
    Advanced Engineering Materials 22 (2020)
    Micromechanical modeling is one of the prominent numerical tools for the prediction of mechanical properties and the understanding of deformation mechanisms of metals. As input parameters, it uses data obtained from microstructure characterization techniques, among which the electron backscatter diffraction (EBSD) technique allows us to understand the nature of microstructural features, that are usually described by statistics. Because of these advantages, the EBSD dataset is widely used for synthetic microstructure generation. However, for the statistical description of microstructural features, the population of input data must be considered. Preferably, the EBSD measurement area must be sufficiently large to cover an adequate number of grains. However, a comprehensive study of this measurement area with a crystal plasticity finite element method (CPFEM) framework is still missing although it would considerably facilitate information exchange between experimentalists and simulation experts. Herein, the influence of the EBSD measurement area and the number of grains on the statistical description of the microstructural features and studying the corresponding micromechanical simulation results for 316L stainless steel samples produced by selective laser melting is investigated. © 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/adem.201901416
  • 2020 • 726 Optimized reconstruction of the crystallographic orientation density function based on a reduced set of orientations Reconstruction of the orientation density function
    Biswas, A. and Vajragupta, N. and Hielscher, R. and Hartmaier, A.
    Journal of Applied Crystallography 53 178-187 (2020)
    Crystallographic textures, as they develop for example during cold forming, can have a significant influence on the mechanical properties of metals, such as plastic anisotropy. Textures are typically characterized by a non-uniform distribution of crystallographic orientations that can be measured by diffraction experiments like electron backscatter diffraction (EBSD). Such experimental data usually contain a large number of data points, which must be significantly reduced to be used for numerical modeling. However, the challenge in such data reduction is to preserve the important characteristics of the experimental data, while reducing the volume and preserving the computational efficiency of the numerical model. For example, in micromechanical modeling, representative volume elements (RVEs) of the real microstructure are generated and the mechanical properties of these RVEs are studied by the crystal plasticity finite element method. In this work, a new method is developed for extracting a reduced set of orientations from EBSD data containing a large number of orientations. This approach is based on the established integer approximation method and it minimizes its shortcomings. Furthermore, the L 1 norm is applied as an error function; this is commonly used in texture analysis for quantitative assessment of the degree of approximation and can be used to control the convergence behavior. The method is tested on four experimental data sets to demonstrate its capabilities. This new method for the purposeful reduction of a set of orientations into equally weighted orientations is not only suitable for numerical simulation but also shows improvement in results in comparison with other available methods. © 2020 Abhishek Biswas et al.
    view abstractdoi: 10.1107/S1600576719017138
  • 2020 • 725 Experimental Evidence for the Incorporation of Two Metals at Equivalent Lattice Positions in Mixed-Metal Metal–Organic Frameworks
    Bitzer, J. and Otterbach, S. and Thangavel, K. and Kultaeva, A. and Schmid, R. and Pöppl, A. and Kleist, W.
    Chemistry - A European Journal 26 5667-5675 (2020)
    Metal–organic frameworks containing multiple metals distributed over crystallographically equivalent framework positions (mixed-metal MOFs) represent an interesting class of materials, since the close vicinity of isolated metal centers often gives rise to synergistic effects. However, appropriate characterization techniques for detailed investigations of these mixed-metal metal–organic framework materials, particularly addressing the distribution of metals within the lattice, are rarely available. The synthesis of mixed-metal FeCuBTC materials in direct syntheses proved to be difficult and only a thorough characterization using various techniques, like powder X-ray diffraction, X-ray absorption spectroscopy and electron paramagnetic resonance spectroscopy, unambiguously evidenced the formation of a mixed-metal FeCuBTC material with HKUST-1 structure, which contained bimetallic Fe−Cu paddlewheels as well as monometallic Cu−Cu and Fe−Fe units under optimized synthesis conditions. The in-depth characterization showed that other synthetic procedures led to impurities, which contained the majority of the applied iron and were impossible or difficult to identify using solely standard characterization techniques. Therefore, this study shows the necessity to characterize mixed-metal MOFs extensively to unambiguously prove the incorporation of both metals at the desired positions. The controlled positioning of metal centers in mixed-metal metal–organic framework materials and the thorough characterization thereof is particularly important to derive structure–property or structure–activity correlations. © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
    view abstractdoi: 10.1002/chem.201905596
  • 2020 • 724 A study on the load-dependent enthalpy of adsorption and interactions in adsorption of C5 and C6 hydrocarbons on zeolites 13X and ZSM-5 and an activated carbon
    Bläker, C. and Pasel, C. and Luckas, M. and Dreisbach, F. and Bathen, D.
    Microporous and Mesoporous Materials 302 (2020)
    In a systematic experimental work, the adsorption of linear, branched and cyclic C5 and C6 hydrocarbons on the zeolites 13X-APG and HiSiv 3000 and the activated carbon Norit R1 Extra is studied. By simultaneous measurement of adsorption capacities and load-dependent enthalpies of adsorption using a self-developed sensor gas calorimeter a deep knowledge about the energetic strength of interactions in adsorption is gained. A special focus is laid on the discussion of the influence of pore geometry and surface chemistry of the adsorbents as well as the molecular structure and binding types of the adsorptives used. Depending on the pore geometry and the surface chemistry of the adsorbents, the load-dependent enthalpies of adsorption show different shapes. While the enthalpies of adsorption on the Faujasite zeolite increase with loading, they are independent of loading on the ZSM-5 zeolite and decrease on the activated carbon. On both zeolites the cyclic and branched adsorptive molecules show lower enthalpies of adsorption compared to the linear molecules due to a less favorable arrangement on the surface. On activated carbon, the enthalpies of adsorption of linear and cyclic hydrocarbons are comparable and significantly higher than those of branched hydrocarbons. For molecules with C=C double bonds only 13X-APG showed higher enthalpies of adsorption and thus stronger interactions. © 2020 Elsevier Inc.
    view abstractdoi: 10.1016/j.micromeso.2020.110205
  • 2020 • 723 Photo-switching and -cyclisation of hydrogen bonded liquid crystals based on resveratrol
    Blanke, M. and Balszuweit, J. and Saccone, M. and Wölper, C. and Doblas Jiménez, D. and Mezger, M. and Voskuhl, J. and Giese, M.
    Chemical Communications 56 1105-1108 (2020)
    A series of hydrogen-bonded liquid crystals based on resveratrol and resveratrone is reported and investigated with respect to their photo-switchability (at 405 nm) and photo-cyclisation (at 300 nm). © 2020 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c9cc07721a
  • 2020 • 722 Spatially controlled VLS epitaxy of gallium arsenide nanowires on gallium nitride layers
    Blumberg, C. and Liborius, L. and Ackermann, J. and Tegude, F.-J. and Poloczek, A. and Prost, W. and Weimann, N.
    CrystEngComm 22 1239-1250 (2020)
    We present Au catalyzed p-GaAs nanowire growth on n-GaN layers as a possible method to grow an arsenide on a nitride compound semiconductor by metal organic vapor phase epitaxy. The GaAs growth position, the nanowire density and the nanowire growth direction are controlled by a combination of vapor-liquid-solid growth and selective area epitaxy. Thus, a spatially controlled nanowire growth is attained, which is mandatory for device fabrication. The growth position is defined by lithographically positioned Au discs on n-GaN. By adapting the growth conditions (QTBAs, presaturation) the nanowire density is optimized. Lateral and vertical anisotropic nanowire growth is attained through VLS growth in structured SiOx openings. Critical technological parameters for successful control of the growth direction are the positioning of the Au catalyst in relation to the SiOx mask, the size of the eutectic in relation to the opening dimensions, and the SiOx thickness. These results lead to distinct pn-junction positions and adjustable nanowire growth dimensions and directions. This journal is © The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c9ce01926j
  • 2020 • 721 Design of an automated reagent-dispensing system for reaction screening and validation with dna-tagged substrates
    Bobers, J. and Škopić, M.K. and Dinter, R. and Sakthithasan, P. and Neukirch, L. and Gramse, C. and Weberskirch, R. and Brunschweiger, A. and Kockmann, N.
    ACS Combinatorial Science 22 101-108 (2020)
    Laboratory automation strategies have vast potential for accelerating discovery processes. They enable higher efficiency and throughput for time-consuming screening procedures and reduce error-prone manual steps. Automating repetitive procedures can for instance support chemists in optimizing chemical reactions. Particularly, the technology of DNA-encoded libraries (DELs) may benefit from automation techniques, since translation of chemical reactions to DNA-tagged reactants often requires screening of multiple reaction parameters and evaluation of large numbers of reactants. Here, we describe a portable, automated system for reagent dispensing that was designed from open source materials. The system was validated by performing amide coupling of carboxylic acids to DNA-linked amine and a micelle-mediated Povarov reaction to DNA-tagged hexahydropyrroloquinolines. The latter reaction required accurate pipetting of multiple components including different solvents and a surface-active reagent. Analysis of reactions demonstrated that the robotic system achieved high accuracy comparable to experimentation by an experienced chemist with the potential of higher throughput. © 2020 American Chemical Society.
    view abstractdoi: 10.1021/acscombsci.9b00207
  • 2020 • 720 Scalable Fabrication of Biophotoelectrodes by Means of Automated Airbrush Spray-Coating
    Bobrowski, T. and Conzuelo, F. and Ruff, A. and Hartmann, V. and Frank, A. and Erichsen, T. and Nowaczyk, M.M. and Schuhmann, W.
    ChemPlusChem 85 1396-1400 (2020)
    The fabrication and electrochemical evaluation of transparent photoelectrodes consisting of Photosystem I (PSI) or Photosystem II (PSII) is described, which are embedded and electrically wired by a redox polymer. The fabrication process is performed by an automated airbrush-type spray coating system, which ensures controlled and scalable electrode preparation. As proof of concept, electrodes with a surface area of up to 25 cm2 were prepared. The macro-porous structure of the indium tin oxide electrodes allows a high loading of the photoactive protein complexes leading to enhanced photocurrents, which are essential for potentially technologically relevant solar-powered devices. In addition, we show that unpurified crude PSII extracts, which can be provided in comparatively high yields for electrode modification, are suitable for photoelectrode fabrication with comparable photocurrent densities. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
    view abstractdoi: 10.1002/cplu.202000291
  • 2020 • 719 Synthesis of graphene-related carbon nanoparticles from a liquid isopropanol precursor by a one-step atmospheric plasma process
    Bodnar, W. and Schiorlin, M. and Frank, A. and Schulz, T. and Wöhrl, N. and Miron, C. and Scheu, C. and Kolb, J.F. and Kruth, A.
    Applied Surface Science 514 (2020)
    This study presents a cost-efficient single-step-method to synthesize nanographite from isopropanol by bipolar pulsed electric discharges. The influence of pulse width within the nanosecond range, repetition frequency within the kilohertz range and processing time on the product was systematically investigated by Raman spectroscopy, high-resolution transmission electron microscopy and gas chromatography - mass spectrometry. It was found that long pulses in the microsecond range promote the creation of amorphous and oxidic carbon structures. Although, hydrocarbon cracking and subsequent graphitization do occur, these process conditions are not suitable to drive intermediate reduction processes. In contrast, applying short pulses in the nanosecond regime ensures fast reduction processes and formation of graphene-related nanostructures. The number of observed nanographite layers lies in the range of 3–13 with an average interlayer spacing of 3.4(0.3) Å and an average distance between defects of 11.5(6.0) nm meaning that the produced nanographite is in the area of small defect density. Furthermore, no significant influence of process times on the product properties over a period up to 15 min was observed, indicating good process homogeneity. © 2020 Elsevier B.V.
    view abstractdoi: 10.1016/j.apsusc.2020.145926
  • 2020 • 718 Efficient OER Catalyst with Low Ir Volume Density Obtained by Homogeneous Deposition of Iridium Oxide Nanoparticles on Macroporous Antimony-Doped Tin Oxide Support
    Böhm, D. and Beetz, M. and Schuster, M. and Peters, K. and Hufnagel, A.G. and Döblinger, M. and Böller, B. and Bein, T. and Fattakhova-Rohlfing, D.
    Advanced Functional Materials 30 (2020)
    A multistep synthesis procedure for the homogeneous coating of a complex porous conductive oxide with small Ir nanoparticles is introduced to obtain a highly active electrocatalyst for water oxidation. At first, inverse opal macroporous Sb doped SnO2 (ATO) microparticles with defined pore size, composition, and open-porous morphology are synthesized that reach a conductivity of ≈3.6 S cm−1 and are further used as catalyst support. ATO-supported iridium catalysts with a controlled amount of active material are prepared by solvothermal reduction of an IrOx colloid in the presence of the porous ATO particles, whereby homogeneous coating of the complete outer and inner surface of the particles with nanodispersed metallic Ir is achieved. Thermal oxidation leads to the formation of ATO-supported IrO2 nanoparticles with a void volume fraction of ≈89% calculated for catalyst thin films based on scanning transmission electron microscope tomography data and microparticle size distribution. A remarkably low Ir bulk density of ≈0.08 g cm−3 for this supported oxide catalyst architecture with 25 wt% Ir is determined. This highly efficient oxygen evolution reaction catalyst reaches a current density of 63 A gIr −1 at an overpotential of 300 mV versus reversible hydrogen electrode, significantly exceeding a commercial TiO2-supported IrO2 reference catalyst under the same measurement conditions. © 2019 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/adfm.201906670
  • 2020 • 717 Chirality in the plane
    Böhmer, C.G. and Lee, Y. and Neff, P.
    Journal of the Mechanics and Physics of Solids 134 (2020)
    It is well-known that many three-dimensional chiral material models become non-chiral when reduced to two dimensions. Chiral properties of the two-dimensional model can then be restored by adding appropriate two-dimensional chiral terms. In this paper we show how to construct a three-dimensional chiral energy function which can achieve two-dimensional chirality induced already by a chiral three-dimensional model. The key ingredient to this approach is the consideration of a nonlinear chiral energy containing only rotational parts. After formulating an appropriate energy functional, we study the equations of motion and find explicit soliton solutions displaying two-dimensional chiral properties. © 2019
    view abstractdoi: 10.1016/j.jmps.2019.103753
  • 2020 • 716 Gas atomization and laser additive manufacturing of nitrogen-alloyed martensitic stainless steel
    Boes, J. and Röttger, A. and Theisen, W. and Cui, C. and Uhlenwinkel, V. and Schulz, A. and Zoch, H.-W. and Stern, F. and Tenkamp, J. and Walther, F.
    Additive Manufacturing 34 (2020)
    Nitrogen as an alloying element can improve the corrosion resistance and the mechanical properties of stainless steels. Therefore, nitrogen-alloyed martensitic stainless steels, such as X30CrMoN151, have been developed in recent decades and conventional processing of this steel by casting or powder metallurgy is well understood. However, only very few attempts to process nitrogen-alloyed martensitically hardenable stainless steels containing more than 0.2 mass-% of carbon by laser powder bed fusion (L-PBF) have been reported so far. In this study, X30CrMoN15-1 steel powder has been produced from quasi nitrogen-free X30CrMo15-1 steel by gas atomization using N2 as the process gas to introduce nitrogen into the steel. The gas-atomized powder was characterized in terms of nitrogen content, particle size distribution, particle morphology, and flow properties. The powder was then processed by L-PBF under an N2 gas atmosphere, and microstructural investigations were performed on the L-PBF-built samples using scanning electron microscopy and X-ray computed tomography. Additionally, a first impression of the mechanical properties of the L-PBF-built steel in the as-built and quenched and tempered condition was obtained by means of fatigue tests. It was shown that a nitrogen content of 0.16 mass-% could be introduced into the steel during gas atomization. The resulting powder was successfully processed by means of L-PBF, and specimens with a high density were produced. During fatigue testing, a large amount of retained austenite in the as-built condition resulted in a greater damage tolerance of the specimens compared to the heat-treated condition. © 2020 Elsevier B.V.
    view abstractdoi: 10.1016/j.addma.2020.101379
  • 2020 • 715 Processing of X65MoCrWV3-2 Cold Work Tool Steel by Laser Powder Bed Fusion
    Boes, J. and Röttger, A. and Theisen, W.
    Steel Research International 91 (2020)
    Laser powder bed fusion (L-PBF) of forming tools has become of major interest in the tooling industry because of the high geometrical flexibility of this process. During L-PBF, a metallic powder bed is melted selectively by a laser beam, enabling the layer-wise manufacturing of parts from 3D computer-aided design data. The process is characterized by a locally and temporally unsteady heat flow in the solidified part and in the melt pool, causing nonequilibrium solidification and phase transformations. In addition, rapid heating and cooling occur, promoting the formation of microstructural defects, cold cracks, and distortion. Because of the high tendency to form cold cracks, processing of martensitic tool steels is still a challenging task. Tool steel X65MoCrWV3-2 is processed by L-PBF and the resulting microstructure and the associated local properties are investigated by microhardness measurements, nanoindentation, and scanning electron microscopy. It is gathered from the investigations that regions of different microstructures and mechanical properties on both micro- and macroscale are present in the L-PBF-densified steel. The different microstructures and properties are the result of the alternating heat insert at different temperature regimes, forming heat-affected zones in which the tempering processes are triggered and strongly varying properties are generated. © 2019 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/srin.201900445
  • 2020 • 714 Microstructure and properties of high-strength C + N austenitic stainless steel processed by laser powder bed fusion
    Boes, J. and Röttger, A. and Theisen, W.
    Additive Manufacturing 32 (2020)
    In the developing field of laser powder bed fusion (L-PBF), austenitic stainless steels, such as AISI 316L, have gained great importance owing to their excellent processability. However, the moderate strength of these steels limits their applicability. This can be counteracted by the use of nitrogen as an alloying element to improve both strength and corrosion resistance. In this work, nitrogen-alloyed high-strength austenitic stainless steel X40MnCrMoN19-18-1 was processed by L-PBF, and the resulting microstructural and mechanical properties were investigated. The same material was also processed by hot isostatic pressing (HIP), which was used as a reference state. In the L-PBF process, argon and nitrogen were used as process gases to investigate the influence of process atmosphere on the microstructure and on changes in the chemical composition during processing. The results show a minor decrease in the nitrogen content of the steel after L-PBF, independently of the process gas, whereby argon resulted in a slightly higher specimen density. The microstructure after L-PBF processing contained small precipitates that could be removed by a short solution-annealing treatment. The tensile properties of the L-PBF-built steel are comparable to those of the steel produced by hot isostatic pressing in terms of ultimate tensile strength, but had lower elongation to fracture values. The ductility of the material was enhanced by solution annealing without significant impairment of the ultimate tensile strength. This work demonstrates that nitrogen-alloyed stainless steels can be processed by means of L-PBF and can extend the variety of appropriate steels towards applications with high requirements for the material strength and chemical resistance. © 2020 Elsevier B.V.
    view abstractdoi: 10.1016/j.addma.2020.101081
  • 2020 • 713 Drifting inwards in protoplanetary discs i Sticking of chondritic dust at increasing temperatures
    Bogdan, T. and Pillich, C. and Landers, J. and Wende, H. and Wurm, G.
    Astronomy and Astrophysics 638 (2020)
    Sticking properties rule the early phases of pebble growth in protoplanetary discs in which grains regularly travel from cold, water-rich regions to the warm inner part. This drift affects composition, grain size, morphology, and water content as grains experience ever higher temperatures. In this study we tempered chondritic dust under vacuum up to 1400 K. Afterwards, we measured the splitting tensile strength of millimetre-sized dust aggregates. The deduced effective surface energy starts out as γe = 0.07 J m-2. This value is dominated by abundant iron-oxides as measured by Mössbauer spectroscopy. Up to 1250 K, γe continuously decreases by up to a factor five. Olivines dominate at higher temperature. Beyond 1300 K dust grains significantly grow in size. The γe no longer decreases but the large grain size restricts the capability of growing aggregates. Beyond 1400 K aggregation is no longer possible. Overall, under the conditions probed, the stability of dust pebbles would decrease towards the star. In view of a minimum aggregate size required to trigger drag instabilities it becomes increasingly harder to seed planetesimal formation closer to a star. © ESO 2020.
    view abstractdoi: 10.1051/0004-6361/202038120
  • 2020 • 712 Performance of wear resistant MCrAlY coatings with oxide dispersion strengthening
    Bolelli, G. and Vorkötter, C. and Lusvarghi, L. and Morelli, S. and Testa, V. and Vaßen, R.
    Wear 444-445 (2020)
    Aiming to devise suitable materials for sliding wear protection at high temperature, aluminium oxide-dispersion strengthened (ODS) CoNiCrAlY coatings were manufactured by vacuum plasma spraying (VPS). Feedstock materials were ball-milled powders with 2, 10 and 30 wt% Al2O3 content. The ball-on-disc sliding wear behaviour of the coatings was tested at 750 °C against an Al2O3 counterpart, and compared to a pure CoNiCrAlY coating (obtained from a commercial feedstock not subjected to ball milling) and to an uncoated Ni-base superalloy. Sliding wear rates decrease from the uncoated superalloy (≈3 × 10−5 mm3/(N·m)) to the pure CoNiCrAlY coating (≈2 × 10−5 mm3/(N·m)) and to the ODS ones, with the notable exception of the 10 wt% Al2O3-containing sample. Analyses of worn samples indicate that pure CoNiCrAlY is subject to severe adhesive wear, mitigated by the formation of a thick (&gt;1 μm) “glaze” layer via compaction and (probable) sintering of tribo-oxidized debris particles. Addition of Al2O3 particles to the CoNiCrAlY matrix can either enhance or worsen the “glaze” stability. Specifically, a coating strengthened with 30 wt% Al2O3 provides an especially good mechanical support to the “glaze”. This produces beneficial effects resulting in a particularly low wear rate of ≈3 × 10−6 mm3/(N·m). © 2019 Elsevier B.V.
    view abstractdoi: 10.1016/j.wear.2019.203116
  • 2020 • 711 The brittle-to-ductile transition in cold-rolled tungsten sheets: the rate-limiting mechanism of plasticity controlling the BDT in ultrafine-grained tungsten
    Bonnekoh, C. and Reiser, J. and Hartmaier, A. and Bonk, S. and Hoffmann, A. and Rieth, M.
    Journal of Materials Science 55 12314-12337 (2020)
    Conventionally produced tungsten (W) sheets are brittle at room temperature. In contrast to that, severe deformation by cold rolling transforms W into a material exhibiting room-temperature ductility with a brittle-to-ductile transition (BDT) temperature far below room temperature. For such ultrafine-grained (UFG) and dislocation-rich materials, the mechanism controlling the BDT is still the subject of ongoing debates. In order to identify the mechanism controlling the BDT in room-temperature ductile W sheets with UFG microstructure, we conducted campaigns of fracture toughness tests accompanied by a thermodynamic analysis deducing Arrhenius BDT activation energies. Here, we show that plastic deformation induced by rolling reduces the BDT temperature and also the BDT activation energy. A comparison of BDT activation energies with the trend of Gibbs energy of kink-pair formation revealed a strong correlation between both quantities. This demonstrates that out of the three basic processes, nucleation, glide, and annihilation, crack tip plasticity in UFG W is still controlled by the glide of dislocations. The glide is dictated by the mobility of the screw segments and therefore by the underlying process of kink-pair formation. Reflecting this result, a change of the rate-limiting mechanism for plasticity of UFG W seems unlikely, even at deformation temperatures well below room temperature. As a result, kink-pair formation controls the BDT in W over a wide range of microstructural length scales, from single crystals and coarse-grained specimens down to UFG microstructures. © 2020, The Author(s).
    view abstractdoi: 10.1007/s10853-020-04801-5
  • 2020 • 710 Silicon Nanoparticle Films Infilled with Al2O3Using Atomic Layer Deposition for Photosensor, Light Emission, and Photovoltaic Applications
    Botas, A.M.P. and Leitão, J.P. and Falcão, B.P. and Wiesinger, M. and Eckmann, F. and Teixeira, J.P. and Wiggers, H. and Stutzmann, M. and Ferreira, R.A.S. and Pereira, R.N.
    ACS Applied Nano Materials 3 5033-5044 (2020)
    Solution-processed thin films of crystalline silicon nanoparticles (Si NPs) have a great potential for a wide variety of electronic and optoelectronic applications. However, such films are inherently unstable due to their huge surface-to-volume ratios and high surface energies, making them prone to degradation associated with spontaneous oxidation in ambient conditions. In this work, we explore the use of atomic layer deposition (ALD) as a means to stabilize and potentially functionalize solution-processed thin films of Si NPs for (opto)electronics, e.g., thin-film transistors, photosensors, light-emitting devices, and photovoltaics. We prepared films of randomly distributed Si NPs with ultrashort surface ligands (Si-H termination) using wet chemistry and spray-coating and then use ALD to infill the films with Al2O3. Through microscopy and optical structural/morphological analysis, we demonstrate the achievability of ALD infilling of films of Si NPs and probe the stability of these films against oxidation. Moreover, we show that the ALD infilling leads to changes in the light emission properties of the Si NP films, including a relative quenching of disorder-related emission features and variations in surface-related dielectric confinement effects. Our studies reveal ALD as a relevant technique toward manufacturing de facto robust, functional nanomaterials based on Si NPs and on nanoscale silicon materials more generally. © 2020 American Chemical Society.
    view abstractdoi: 10.1021/acsanm.0c00116
  • 2020 • 709 Vibration-Driven Self-Doping of Dangling-Bond Wires on Si(553)-Au Surfaces
    Braun, C. and Neufeld, S. and Gerstmann, U. and Sanna, S. and Plaickner, J. and Speiser, E. and Esser, N. and Schmidt, W.G.
    Physical Review Letters 124 (2020)
    Density-functional theory is used to explore the Si(553)-Au surface dynamics. Our study (i) reveals a complex two-stage order-disorder phase transition where with rising temperature first the ×3 order along the Si step edges and, subsequently, the ×2 order of the Au chains is lost, (ii) identifies the transient modification of the electron chemical potential during soft Au chain vibrations as instrumental for disorder at the step edge, and (iii) shows that the transition leads to a self-doping of the Si dangling-bond wire at the step edge. The calculations are corroborated by Raman measurements of surface phonon modes and explain previous electron diffraction, scanning tunneling microscopy, and surface transport data. © 2020 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the "" 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.124.146802
  • 2020 • 708 Non-destructive detection of the efficiency of long-term weathered hydrophobic natural stones using single-sided NMR
    Braun, F. and Orlowsky, J.
    Journal of Cultural Heritage 41 51-60 (2020)
    Conservation methods on buildings and monuments made out of natural stone aim on preventing weathering processes, reducing their impact on site and consequently improving the long-term durability of building stones. For this purpose, nowadays particularly organosilicon compounds are used for the application on natural stones. In this study, single-sided NMR has been used to non-destructively detect the long-term efficiency of hydrophobing agents (silanes, siloxanes and silicone resins) applied on different porous natural stones (Baumberger and Obernkirchener Sandstone), which were naturally weathered for over 24 years on different sites in Germany. An evaluation system is presented, based on non-destructive NMR measurements, to assess the hydrophobic properties and the long-term stability of the treated stone surfaces. It could be shown, that the mineralogical composition as well as the type of hydrophobing agent and its active ingredient content have a significant influence on the long-term hydrophobic effect. © 2019 Elsevier Masson SAS
    view abstractdoi: 10.1016/j.culher.2019.07.005
  • 2020 • 707 Solute hydrogen and deuterium observed at the near atomic scale in high-strength steel
    Breen, A.J. and Stephenson, L.T. and Sun, B. and Li, Y. and Kasian, O. and Raabe, D. and Herbig, M. and Gault, B.
    Acta Materialia 188 108-120 (2020)
    Observing solute hydrogen (H) in matter is a formidable challenge, yet, enabling quantitative imaging of H at the atomic-scale is critical to understand its deleterious influence on the mechanical strength of many metallic alloys that has resulted in many catastrophic failures of engineering parts and structures. Here, we report on the APT analysis of hydrogen (H) and deuterium (D) within the nanostructure of an ultra-high strength steel with high resistance to hydrogen embrittlement. Cold drawn, severely deformed pearlitic steel wires (Fe–0.98C–0.31Mn–0.20Si–0.20Cr–0.01Cu–0.006P–0.007S wt%, ε=3.1) contains cementite decomposed during the pre-deformation of the alloy and ferrite. We find H and D within the decomposed cementite, and at some interfaces with the surrounding ferrite. To ascertain the origin of the H/D signal obtained in APT, we explored a series of experimental workflows including cryogenic specimen preparation and cryogenic-vacuum transfer from the preparation into a state-of-the-art atom probe. Our study points to the critical role of the preparation, i.e. the possible saturation of H-trapping sites during electrochemical polishing, how these can be alleviated by the use of an outgassing treatment, cryogenic preparation and transfer prior to charging. Accommodation of large amounts of H in the under-stoichiometric carbide likely explains the resistance of pearlite against hydrogen embrittlement. © 2020 Acta Materialia Inc.
    view abstractdoi: 10.1016/j.actamat.2020.02.004
  • 2020 • 706 Enhanced dissolution of silver nanoparticles in a physical mixture with platinum nanoparticles based on the sacrificial anode effect
    Breisch, M. and Loza, K. and Pappert, K. and Rostek, A. and Rurainsky, C. and Tschulik, K. and Heggen, M. and Epple, M. and Tiller, J.C. and Schildhauer, T.A. and Köller, M. and Sengstock, C.
    Nanotechnology 31 (2020)
    A strategy to reduce implant-related infections is the inhibition of the initial bacterial implant colonization by biomaterials containing silver (Ag). The antimicrobial efficacy of such biomaterials can be increased by surface enhancement (nanosilver) or by creating a sacrificial anode system for Ag. Such a system will lead to an electrochemically driven enhanced Ag ion release due to the presence of a more noble metal. Here we combined the enlarged surface of nanoparticles (NP) with a possible sacrificial anode effect for Ag induced by the presence of the electrochemically more noble platinum (Pt) in physical mixtures of Ag NP and Pt NP dispersions. These Ag NP/Pt NP mixtures were compared to the same amounts of pure Ag NP in terms of cell biological responses, i.e. the antimicrobial activity against Staphylococcus aureus and Escherichia coli as well as the viability of human mesenchymal stem cells (hMSC). In addition, Ag NP was analyzed by ultraviolet-visible (UV-vis) spectroscopy, cyclic voltammetry, and atomic absorption spectroscopy. It was found that the dissolution rate of Ag NP was enhanced in the presence of Pt NP within the physical mixture compared to a dispersion of pure Ag NP. Dissolution experiments revealed a fourfold increased Ag ion release from physical mixtures due to enhanced electrochemical activity, which resulted in a significantly increased toxicity towards both bacteria and hMSC. Thus, our results provide evidence for an underlying sacrificial anode mechanism induced by the presence of Pt NP within physical mixtures with Ag NP. Such physical mixtures have a high potential for various applications, for example as antimicrobial implant coatings in the biomedicine or as bactericidal systems for water and surface purification in the technical area. © 2019 IOP Publishing Ltd.
    view abstractdoi: 10.1088/1361-6528/ab4e48
  • 2020 • 705 Solubility of Pharmaceutical Ingredients in Natural Edible Oils
    Brinkmann, J. and Rest, F. and Luebbert, C. and Sadowski, G.
    Molecular Pharmaceutics 17 2499-2507 (2020)
    Natural edible oils (NEOs) are common excipients for lipid-based formulations. Many of them are complex mixtures comprising hundreds of different triglycerides (TGs). One major challenge in developing lipid-based formulations is the variety in NEO compositions affecting the solubility of active pharmaceutical ingredients. In this work, solubilities of indomethacin (IND), ibuprofen (IBU), and fenofibrate (FFB) in soybean oil and in coconut oil were measured via differential scanning calorimetry, high-performance liquid chromatography, and Raman spectroscopy. Furthermore, this work proposes an approach that mimics NEOs using one key TG and models the API solubilities in these NEOs based on perturbed-chain statistical associating fluid theory (PC-SAFT). Key TGs were determined using the 1,2,3-random hypothesis, and PC-SAFT parameters were estimated via a group-contribution method. Using the proposed approach, the solubility of IBU and FFB was modeled in soybean oil and coconut oil. Furthermore, the solubilities of five more APIs (IND, cinnarizine, naproxen, griseofulvin, and felodipine) were modeled in soybean oil. All modeling results were found in very good agreement with the experimental data. The influence of different NEO kinds on API solubility was examined by comparing FFB and IBU solubilities in soybean oil and refined coconut oil. PC-SAFT was thus found to allow assessing the batch-to-batch consistency of NEO batches in silico. Copyright © 2020 American Chemical Society.
    view abstractdoi: 10.1021/acs.molpharmaceut.0c00215
  • 2020 • 704 Detecting deviations from second-order stationarity in locally stationary functional time series
    Bücher, A. and Dette, H. and Heinrichs, F.
    Annals of the Institute of Statistical Mathematics 72 1055-1094 (2020)
    A time-domain test for the assumption of second-order stationarity of a functional time series is proposed. The test is based on combining individual cumulative sum tests which are designed to be sensitive to changes in the mean, variance and autocovariance operators, respectively. The combination of their dependent p values relies on a joint-dependent block multiplier bootstrap of the individual test statistics. Conditions under which the proposed combined testing procedure is asymptotically valid under stationarity are provided. A procedure is proposed to automatically choose the block length parameter needed for the construction of the bootstrap. The finite-sample behavior of the proposed test is investigated in Monte Carlo experiments, and an illustration on a real data set is provided. © 2019, The Institute of Statistical Mathematics, Tokyo.
    view abstractdoi: 10.1007/s10463-019-00721-7
  • 2020 • 703 β-Cyclodextrin-based star polymers for membrane surface functionalization: Covalent grafting via “click” chemistry and enhancement of ultrafiltration properties
    Büning, J. and Frost, I. and Okuyama, H. and Lempke, L. and Ulbricht, M.
    Journal of Membrane Science 596 (2020)
    This work provides the proof-of-concept that surface functionalization of porous membranes with well-defined star-like polymers of varied number of arms and arm length leads to a tunable effective thickness of grafted layers and a specific influence on size-selective sieving through ultrafilter pores. Alkyl-brominated β-cyclodextrine with either 7 or 21 initiator sites per molecule was synthesized and further used for controlled atom transfer radical polymerization of copolymers of 2-dimethylamino(ethyl) methacrylate (DMAEMA) and propargyl methacrylate (PgMA), leading to star polymers with either 7 or 21 arms. Alkyne-containing PgMA segments enable the “click” coupling while DMAEMA segments provide the bulk of the polymer. Star polymers were characterized with respect to chemical structure and molecular weight (M). During ultrafiltration (UF) through cellulose membranes with different molecular weight cut-off, rejection was not simply correlated with star polymer M but was governed by macromolecular architecture, i.e. the smaller colloidal diameter for macromolecules of same M but 21 instead of 7 arms. Azide-functionalized poly(ethylene terephthalate) (PET) track-etched (TE) membranes and cellulose UF membranes were prepared by polymer-analogous surface functionalization so that the alkyne-substituted star polymers could be “click”-grafted. Isoporous PET TE membranes with a nominal pore diameter of 200 nm were used as model system to study the grafting and its effects onto pore size via the reduction of hydraulic permeability. Effective grafted layer thickness in the range of 10–50 nm correlated with macromolecular structure and architecture. For “click”-functionalized cellulose UF membranes, the effective pore size in the barrier layer was influenced by grafted star polymers, and a pronounced additional influence of the architecture and arm length of the grafted star polymer on macromolecular sieving was observed. Of particular interest are results with the more flexible 7-armed star polymers (compared to 21-armed counterparts); their grafting at the UF membrane pores of similar dimension leads to a large increase of test solute rejection at very low reduction of convective water flux, both compared to the unmodified membrane. © 2019 Elsevier B.V.
    view abstractdoi: 10.1016/j.memsci.2019.117610
  • 2020 • 702 How nanoscale dislocation reactions govern low-temperature and high-stress creep of ni-base single crystal superalloys
    Bürger, D. and Dlouhý, A. and Yoshimi, K. and Eggeler, G.
    Crystals 10 (2020)
    The present work investigates γ-channel dislocation reactions, which govern low-temperature (T = 750◦C) and high-stress (resolved shear stress: 300 MPa) creep of Ni-base single crystal superalloys (SX). It is well known that two dislocation families with different b-vectors are required to form planar faults, which can shear the ordered γ’-phase. However, so far, no direct mechanical and microstructural evidence has been presented which clearly proves the importance of these reactions. In the mechanical part of the present work, we perform shear creep tests and we compare the deformation behavior of two macroscopic crystallographic shear systems [011](111) and [112](111). These two shear systems share the same glide plane but differ in loading direction. The [112](111) shear system, where the two dislocation families required to form a planar fault ribbon experience the same resolved shear stresses, deforms significantly faster than the [011](111) shear system, where only one of the two required dislocation families is strongly promoted. Diffraction contrast transmission electron microscopy (TEM) analysis identifies the dislocation reactions, which rationalize this macroscopic behavior. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/cryst10020134
  • 2020 • 701 Investigation and equalisation of the flow distribution in a fuel cell stack
    Bürkle, F. and Moyon, F. and Feierabend, L. and Wartmann, J. and Heinzel, A. and Czarske, J. and Büttner, L.
    Journal of Power Sources 448 (2020)
    The possibility to use fuel cells as an electrical power source makes them interesting for a wide range of applications. In this work, computational fluid dynamics (CFD) simulations and optical measurements are performed to predict the flow distribution in a flow setup resembling the parallel flow circuits in fuel cell stacks. For the first time it is shown that by an adaptation of the port sizes in the inlet manifold to the individual fuel cells, the average global deviation between the flow rates can be reduced from 10.1% to 4.0% by means of a model experiment. The measurements are performed with a high resolution laser Doppler velocity profile sensor (LD-PS) specifically developed for measurements in small-scale channels, in this work 4×1 mm2, allowing for a spatial resolution below 2 μm and relative velocity uncertainties below 0.1%, helping to resolve installation effects possibly occurring in fuel cells to improve their efficiency. The presented results can be used by manufacturers to increase the efficiency of their fuel cell stacks. © 2019 Elsevier B.V.
    view abstractdoi: 10.1016/j.jpowsour.2019.227546
  • 2020 • 700 Efficient cut-cell quadrature based on moment fitting for materially nonlinear analysis
    Bui, H.-G. and Schillinger, D. and Meschke, G.
    Computer Methods in Applied Mechanics and Engineering 366 (2020)
    Cut-cell quadrature based on the moment fitting scheme generates an accurate numerical integration rule for each cut element with the same small number of point evaluations as a standard Gauss quadrature rule. It therefore significantly increases the efficiency of unfitted finite element schemes such as the finite cell method that have often relied on cut-cell integration with prohibitively many quadrature points. Moment fitting, however, does not directly apply to inhomogeneous integrands as they result from nonlinear material behavior. In this article, we describe a novel modification of moment fitting approach that opens the door for its application in materially nonlinear analysis. The basic idea is the decomposition of each cut cell into material subdomains, each of which can be assigned a physically valid location where constitutive integration and the update of local history variables can be performed. We formulate a moment fitting scheme for each material subdomain using the same quadrature points, such that the resulting weights from all material subdomains can be added and the total number of point evaluations remains the same as in standard Gauss quadrature. We discuss numerical details of the modified scheme, including its ramifications for consistent linearization, and demonstrate its optimal performance in the context of the finite cell method and elastoplasticity. © 2020 Elsevier B.V.
    view abstractdoi: 10.1016/j.cma.2020.113050
  • 2020 • 699 A parallelization strategy for hydro-mechanically coupled mechanized tunneling simulations
    Bui, H.-G. and Meschke, G.
    Computers and Geotechnics 120 (2020)
    3D computational simulations of the tunnel advancement in mechanized tunneling usually demand high computational resources. This paper addresses strategies to enable large scale simulations of the advancement process by means of iterative, parallel solvers, considering frictional contact between the tunnel boring machine and the soil, fully saturated soil with different permeabilities and a number of additional features inherently connected with tunnel simulations, which require special attention in regards to robustness. To improve the computational performance of mechanized tunnel simulations a solution strategy based on domain decomposition is proposed to solve the resulting discretized linear system in parallel using an appropriately accelerated iterative solver. The interaction between the TBM and the ground is modeled by means of robust contact algorithm based on penalty method. The domain decomposition scheme accounts for contact treatment in parallel, which becomes relevant when the TBM traverses through different domains in the mesh. Different variants of block preconditioners are investigated in regards to their performance to speed-up the convergence of the iterative solver for the block linear system arising from simulations of tunnel advancement in saturated soft soil, considering different permeabilities. A validation of the computational model and selected numerical examples to showcase the efficiency of the proposed method and to verify the applicability of this strategy to high performance tunneling simulations are presented. © 2019 Elsevier Ltd
    view abstractdoi: 10.1016/j.compgeo.2019.103378
  • 2020 • 698 Biomimetic scaffold fabricated with a mammalian trabecular bone template
    Bulygina, I. and Senatov, F. and Choudhary, R. and Kolesnikov, E. and Kaloshkin, S. and Scholz, R. and Knyazeva, M. and Walther, F. and Anisimova, N. and Kiselevskiy, M.
    Polymer Degradation and Stability 172 (2020)
    This study proposes the method of ultra-high molecular weight polyethylene (UHMWPE) biomimetic scaffold fabrication. Anisotropy is considered to be a distinctive feature of native bone but basically only a 3D-fabricated scaffold structure may be anisotropic, while 3D-printing is not applicable to UHMWPE. We proposed a novel method that suggested a template of native mammalian bone to be used as a negative for UHMWPE scaffold fabrication. This method allows direct replication of the bone's structural features on the micro- and macro-scale. Bone scaffolds obtained using the specified method showed anisotropic structure; the pores' average proportions for scaffold and bone were 770 and 470, and 700 and 500 μm, respectively. According to SEM and CT investigations, the scaffolds' macro- and microstructure mimicked the native bone architecture; this feature distinguishes the proposed method from the other UHMWPE scaffold fabrication techniques. The combination of the hydrophilic surface and the nanorelief affected the adhesion and proliferation of cells: the adhesion of multipotent mesenchymal stromal cells (MMSC) amounted to 40% after 4 h; the proliferation of MMSC was 75% after 48 h. The proposed novel method of fabricating biomimetic scaffolds can be used to obtain bone implants of the complex microstructure and anisotropy from high-melt viscosity polymers which cannot be 3D-printed to be further applied in bone reconstruction. The FT-IR analysis confirmed the occurrence of carboxyl oxidation when the surface of UHMWPE sample was treated with chromic acid. The oxidation index (OI) of the samples was found in the order of etching in chromic acid > sterilization > hot moulding respectively. It can be suggested that the oxidative degradation of UHMWPE can be reduced by optimizing manufacturing conditions and further selection of an appropriate processing method. © 2020 Elsevier Ltd
    view abstractdoi: 10.1016/j.polymdegradstab.2020.109076
  • 2020 • 697 Towards credible CFD simulations for floating offshore wind turbines
    Burmester, S. and Vaz, G. and el Moctar, O.
    Ocean Engineering 209 (2020)
    The credibility in the results needs to be demonstrated in order to be able to use computational fluid dynamics (CFD) as an engineering tool. This may be obtained by sufficient verification and validation studies involving error and uncertainty quantification. This study investigates how to perform credible CFD simulations of floating offshore wind turbines (FOWTs). Three methods to estimate discretisation errors were compared for three different problems related to FOWTs: wave propagation in 2D, wave loads on a circular cylinder, and surge decay of a semi-submersible FOWT. The three discretisation error estimation methods are a least-squares formulation using the observed order of convergence in combination with a data quality measure for different spatial and temporal refinement, another least-squares fit method using the theoretical order of convergence for constant Courant number grid refinement studies, and the factor of safety method applying a ratio between observed and theoretical order of convergence. We compared the final results to an analytical solution of the 2D wave signal, and to experimental data for the wave loads and surge decay motions, for validation purposes. The results of this work show the advantages and disadvantages of the three error estimation methods. The uncertainty bars for the discretisation uncertainty of the numerical simulations were mostly larger than the comparison error with the model test data and analytical solution. © 2020 Elsevier Ltd
    view abstractdoi: 10.1016/j.oceaneng.2020.107237
  • 2020 • 696 Investigation of a semi-submersible floating wind turbine in surge decay using CFD
    Burmester, S. and Vaz, G. and Gueydon, S. and el Moctar, O.
    Ship Technology Research 67 2-14 (2020)
    The hydrodynamic damping estimation of the surge motion and the flow characteristics of a moored semi-submersible floating offshore wind turbine is the focus of this paper. The numerical surge decay tests were investigated using a Reynolds-Averaged Navier–Stokes solver. Solution verification on the numerical simulations was performed by estimation of the numerical errors and uncertainties. A linear stiffness matrix and a non-linear quasi-static mooring model were used in the equations of motion. Several surge decay simulations were performed to understand the effects of wave radiation, coupled motions and non-linear moorings on the hydrodynamic damping and the flow field around the floater. The numerical results were compared with experimental data. The free surface had major effects on the hydrodynamic damping and the flow field. © 2018, © University of Duisburg-Essen 2018.
    view abstractdoi: 10.1080/09377255.2018.1555987
  • 2020 • 695 Synovial bone sialoprotein indicates aseptic failure in total joint arthroplasty
    Busch, A. and Jäger, M. and Dittrich, F. and Wegner, A. and Landgraeber, S. and Haversath, M.
    Journal of Orthopaedic Surgery and Research 15 (2020)
    Background: Until today, a reliable diagnostic discrimination between periprosthetic joint infections (PJI) and aseptic failure (AF) after total joint arthroplasty (TJA) remains challenging. Nearly all recent research focused on synovial markers to be elevated in PJI rather than in AF patients. In this study, synovial bone sialoprotein (sBSP) was investigated in PJI and AF arthroplasty patients before revision surgery. Methods: sBSP and C-reactive protein (CRP) were determined in synovial fluid samples of PJI (n = 13) patients fulfilling the MSIS criteria and AF (n = 25) patients. Beside descriptive analysis and comparison, computed statistics determined the area under the receiver operating characteristics curve (AUC) to evaluate the discrimination ability of the tested synovial markers. Results: In patients with PJI according to the MSIS criteria, mean sBSP was significantly lower: 14.8 ng/ml (95% CI 5.5-24.1) vs. 38.2 ng/ml in the AF group (95% CI 31.1-45.3), p ≤ 0.001. Conversely, mean sCRP was significantly higher in PJI patients: 8.4 μg/ml (95% CI 0-17.2) vs. 1.8 μg/ml in the AF group (95% CI 0.9-2.8), p = 0.032. The AUC of sCRP in PJI patients was 0.71. The AUC of sBSP in AF revision arthroplasty patients was 0.83. The detection of osteolyses was not associated with higher sBSP concentrations. Conclusions: Considering the MSIS criteria, significantly higher sBSP concentrations were found in synovial fluid samples of AF compared to PJI patients. sCRP showed only fair, sBSP good discrimination potential. If it is not clear whether PJI is present or not, sBSP may be considered as an add-on synovial marker. © 2020 The Author(s).
    view abstractdoi: 10.1186/s13018-020-01718-2
  • 2020 • 694 Is Procalcitonin (PCT) a reliable biomarker for preoperative diagnosing of low grade periprosthetic joint infection? A prospective study
    Busch, A. and Jäger, M. and Engler, H. and Haversath, M. and Bielefeld, C. and Landgraeber, S. and Wegner, A.
    BMC Musculoskeletal Disorders 21 (2020)
    Background: Since a "gold-standard" is missing, diagnosing periprosthetic joint infection (PJI) remains a challenge in orthopedic surgery. The purpose of this study was to evaluate the accuracy of serum and synovial fluid Procalcitonin (S-PCT and SF-PCT) as a diagnostic parameter and to compare it to the biomarkers recommended in the 2018 Definition of periprosthetic hip and knee infection. Methods: Between August 2018 and July 2019, a prospective cohort study was conducted in 70 patients with painful hip, shoulder and knee arthroplasty. Besides medical history, clinical and laboratory data was gathered. PJI was diagnosed based on the 2018 Definition of periprosthetic hip and knee infection. Preoperative blood and synovial joint fluid were taken for PCT measurement. S-PCT and SF-PCT levels were measured using standard quantitative PCT enzyme immunoassays. Results: Twenty three patients (33%) were classified as the PJI group and fourty seven patient (67%) as the aseptic group. The mean levels of S-PCT were significantly (p < 0.001) higher in the PJI group than those in the aseptic group (PJI 0.05 ± 0.21 ng/mL (0.0-1.03) vs. aseptic 0.02 ± 0.03 ng/mL (0.0-0.18)). In synovial fluid, the mean PCT values in the aseptic group were significantly higher (p < 0.001) than those of PJI group (PJI 2.7 ± 1.4 ng/mL (0.53-9.7) vs. aseptic 8.7 ± 2.5 ng/mL (0.25-87.9)). S- PCT, with a cut-off level of 0.5 ng/mL, had a sensitivity of 13.0% and a specificity of 91.0%. SF-PCT, with a cut-off level of 5.0 ng/mL, had a sensitivity of 13.0% and a specificity of 52.0%. Conclusion: S-PCT and SF-PCT appeared to be no reliable biomarkers in the differential diagnosis of PJI from aseptic loosening in total joint arthroplasty. © 2020 The Author(s).
    view abstractdoi: 10.1186/s12891-020-03266-6
  • 2020 • 693 Corrigendum to: SiO 2 microstructure evolution during plasma deposition analyzed via ellipsometric porosimetry (Plasma Processes and Polymers, (2019), 16, 9, (1900015), 10.1002/ppap.201900015)
    Buschhaus, R. and von Keudell, A.
    Plasma Processes and Polymers 17 (2020)
    The paper by Rahel Buschhaus and Achim von Keudell, published online on 2 April 2019 and in issue 9, 2019, e1900015 (, contains some errors the authors wish to correct. These errors were: (i)The substrate holder was not placed at the opposing end of the plasma line, instead the holder was surrounding the plasma line concentrically. The sample was placed on the substrate holder at a distance of 3.7 cm from the plasma line. (ii)The pressure in the MW process was 25 Pa instead of 100 Pa. This implies different values in Table 1 and a four times larger mean free path in the MW process. (iii)The SEI values in Table 1 are changed because the flow was improperly used in the calculation. The correct Table 1 is as follows: (Table presented.) These errors do not affect significantly the reasoning in the manuscript and the main conclusions remain valid. The authors apologize for any inconvenience caused. © 2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/ppap.202000036
  • 2020 • 692 Transport properties of shell-ferromagnetic Heusler precipitates in decomposed Ni49.8Mn45.1Sn5.1 and decomposition limit for Ni50Mn50−xSnx alloys
    Çakır, A. and Koyun, H.N. and Acet, M. and Farle, M.
    Journal of Magnetism and Magnetic Materials 499 (2020)
    Shell-ferromagnetism is observed in Mn-rich NiMn-based Heusler alloys as a result of phase-separation. Off-stoichiometric NiMn-based Heusler alloys decompose into a dual-phase composite when annealed under a magnetic field. As a result of this process, an initially anti-ferromagnetic Heusler alloy gains hard-ferromagnetic properties with a nearly 10 Tesla coercive field of a core/shell structured precipitate. In the present study, Ni50.1Mn42.1Sn7.8 and Ni50.4Mn36.6Sn13.0 alloys are investigated for magnetic and structural instabilities and shell-ferromagnetic decomposition to obtain information on the compositional limits of the decomposition. Furthermore, we investigate the magneto-transport properties of shell-ferromagnets obtained by annealing Ni49.8Mn45.1Sn5.1 in a magnetic-field. © 2019 Elsevier B.V.
    view abstractdoi: 10.1016/j.jmmm.2019.166265
  • 2020 • 691 Targeted Approach to Distinguish and Determine Absolute Levels of GDF8 and GDF11 in Mouse Serum
    Camparini, L. and Kollipara, L. and Sinagra, G. and Loffredo, F.S. and Sickmann, A. and Shevchuk, O.
    Proteomics 20 (2020)
    Growth differentiation factor 11 (GDF11) is a TGF-β superfamily circulating factor that regulates cardiomyocyte size in rodents, sharing 90% amino acid sequence identity in the active domains with myostatin (GDF8)—the major determinant of skeletal muscle mass. Conflicting data on age-related changes in circulating levels have been reported mainly due to the lack of specific detection methods. More recently, liquid chromatography tandem mass spectrometry (LC-MS/MS) based assay showed that the circulating levels of GDF11 do not change significantly throughout human lifespan, but GDF8 levels decrease with aging in men. Here a novel detection method is demonstrated based on parallel reaction monitoring LC-MS/MS assay combined with immunoprecipitation to reliably distinguish GDF11 and GDF8 as well as determine their endogenous levels in mouse serum. The data indicate that both GDF11 and GDF8 circulating levels significantly decline with aging in female mice. © 2020 The Authors. Proteomics published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/pmic.201900104
  • 2020 • 690 A six-compound, high performance gasoline surrogate for internal combustion engines: Experimental and numerical study of autoignition using high-pressure shock tubes
    Cancino, L.R. and da Silva, A., Jr. and De Toni, A.R. and Fikri, M. and Oliveira, A.A.M. and Schulz, C. and Curran, H.J.
    Fuel 261 (2020)
    This paper presents experimental and modeling data for the autoignition of a novel, six-component, high performance gasoline surrogate fuel comprising ethanol, n-heptane, i-octane, 1-hexene, methylcyclohexane, and toluene (AL-P-I-O-N-A). Experimental tests are conducted in two high-pressure shock tubes to determine the ignition delay time as a function of pressure, temperature and equivalence ratio. Ignition delay times were measured at 10 and 30 bar in the temperature range from 749 to 1204 K and equivalence ratios ranging from 0.35 to 1.30. A modified Arrhenius equation is defined to mathematically describe the ignition delay time of the proposed surrogate. For experimental data with temperatures higher than 900 K, a multiple linear regression identified the pressure dependence exponent of 0.72 and stoichiometry dependence exponent of 0.62, as well as a global activation energy of ≈109 kJ/mol. A simplistic approach to mechanism reduction based on the elimination of reactions with no relevant rate of progress was used in order to reduce an extensive detailed kinetics model (hierarchically constructed with more than 17800 reactions). The reduced detailed kinetics model with 4885 elementary reactions among 326 chemical species was used for numerical simulations. Comparisons between the experimental and numerical data are favorable, with the predictions using the reduced kinetics model differing by less than 0.056% when compared to the complete mechanism. It was observed that for low temperatures the proposed reduced kinetics model agrees only qualitatively with the measurements. In order to understand the likely cause of this discrepancy a brute force sensitivity analysis on IDT was performed, elucidating the more influencing reactions on the ignition delay times. The experimental data obtained in this research was compared to available data in the literature in terms of anti-knock index (AKI) and for a scaled pressure of 30 bar (τ30) at a stoichiometric composition. A modified Arrhenius equation was then fitted and an AKI dependence exponent of -1.11 was obtained, inferring that the higher the AKI the higher the IDT, independent of fuel composition at temperatures lower than the NTC region. This trend should be confirmed by further studies. © 2019 Elsevier Ltd
    view abstractdoi: 10.1016/j.fuel.2019.116439
  • 2020 • 689 On the influence of crystallography on creep of circular notched single crystal superalloy specimens
    Cao, L. and Thome, P. and Agudo Jácome, L. and Somsen, C. and Cailletaud, G. and Eggeler, G.
    Materials Science and Engineering A 782 (2020)
    The present work contributes to a better understanding of the effect of stress multiaxiality on the creep behavior of single crystal Ni-base superalloys. For this purpose we studied the creep deformation and rupture behavior of double notched miniature creep tensile specimens loaded in three crystallographic directions [100], [110] and [111] (creep conditions: 950 °C and 400 MPa net section stress). Crystal plasticity finite element method (CPFEM) was used to analyze the creep stress and strain distributions during creep. Double notched specimens have the advantage that when one notch fails, the other is still intact and allows to study a material state which is close to rupture. No notch root cracking was observed, while microstructural damage (pores and micro cracks) were frequently observed in the center of the notch root region. This is in agreement with the FEM results (high axial stress and high hydrostatic stress in the center of the notched specimen). Twinning was observed in the notch regions of [110] and [111] specimens, and <112> {111} twins were detected and analyzed using orientation imaging scanning electron microscopy. The present work shows that high lattice rotations can be detected in SXs after creep fracture, but they are associated with the high strains accumulated in the final rupture event. © 2020 The Authors
    view abstractdoi: 10.1016/j.msea.2020.139255
  • 2020 • 688 Low temperature dehydrogenation properties of ammonia borane within carbon nanotube arrays: a synergistic effect of nanoconfinement and alane
    Cao, Z. and Ouyang, L. and Felderhoff, M. and Zhu, M.
    RSC Advances 10 19027-19033 (2020)
    Ammonia borane (AB, NH3BH3) is considered as one of the most promising hydrogen storage materials for proton exchange membrane fuel cells due to its high theoretical hydrogen capacity under moderate temperatures. Unfortunately, its on-board application is hampered by the sluggish kinetics, volatile byproducts and harsh conditions for reversibility. In this work, AB and AlH3were simultaneously infiltrated into a carbon nanotube array (CMK-5) to combine the synergistic effect of alane with nanoconfinement for improving the dehydrogenation properties of AB. Results showed that the transformation from AB to DADB started at room temperature, which promoted AB to release 9.4 wt% H2within 10 min at a low temperature of 95 °C. Moreover, the entire suppression of all harmful byproducts was observed. © The Royal Society of Chemistry 2020.
    view abstractdoi: 10.1039/d0ra02283g
  • 2020 • 687 Artificial neural network surrogate modelling for real-time predictions and control of building damage during mechanised tunnelling
    Cao, B.T. and Obel, M. and Freitag, S. and Mark, P. and Meschke, G.
    Advances in Engineering Software 149 (2020)
    Tunnelling induced surface settlements can cause damage in buildings located in the vicinity of the tunnel. Currently, surface settlements and associated building damage risks usually are estimated based on empirical equations, e.g. by assuming Gaussian curves for the settlement trough and by applying the Limit Tensile Strain Method or the tilt-based method to evaluate and categorise the expected building damage. In this paper, finite element simulations are used to predict the soil-structure interaction in mechanised tunnelling during the tunnel advancement. The time variant surface settlement field and the corresponding tunnelling induced strains in the facade of a building are computed by two independent finite element models. Coupling both models allows predicting the expected category of damage (cod) for the building, given the operational parameters of the tunnel drive. Based upon this coupled approach, a method is proposed in the paper, which provides optimised operational parameters (e.g. tail void grouting pressure and face support pressure) during the advancement of tunnel boring machines below vulnerable buildings, such that the risk of damage for existing buildings is minimised. For real-time applicability of this method two different types of Artificial Neural Networks in combination with the Proper Orthogonal Decomposition approach are generated as surrogate models of the finite element simulations. The surrogate models are finally linked and implemented into a user-friendly application, which can be used as an assistant tool to adjust the operational parameters of the tunnel boring machine at the construction site. © 2020 Elsevier Ltd
    view abstractdoi: 10.1016/j.advengsoft.2020.102869
  • 2020 • 686 Phase Transitions in the Metastable Perovskite Multiferroics BiCrO3and BiCr0.9Sc0.1O3: A Comparative Study
    Cardoso, J.P. and Delmonte, D. and Gilioli, E. and Fertman, E.L. and Fedorchenko, A.V. and Shvartsman, V.V. and Paukšta, V. and Grigalaitis, R. and Banys, J.R. and Khalyavin, D.D. and Vieira, J.M. and Salak, A.N.
    Inorganic Chemistry 59 8727-8735 (2020)
    The temperature behavior of the crystal structure as well as dielectric and magnetic properties of the perovskite bismuth chromate ceramics with the 10 mol % Cr3+-to-Sc3+ substitution were studied and compared with those of the unmodified compound. Using a high-pressure synthesis, BiCrO3 and BiCr0.9Sc0.1O3 were obtained as metastable perovskite phases which are monoclinic C2/c with the 6ap × 2ap × 6ap superstructure (where ap is the primitive perovskite unit-cell parameter) under ambient conditions. At room temperature, the unit cell volume of BiCr0.9Sc0.1O3 is ∼1.3% larger than that of BiCrO3. Both perovskites undergo a reversible structural transition into a nonpolar GdFeO3-type phase (orthorhombic Pnma, 2ap × 2ap × 2ap) in the temperature ranges of 410-420 K (BiCrO3) and 470-520 K (BiCr0.9Sc0.1O3) with a relative jump of the primitive perovskite unit cell volume of about -1.6 and -2.0%, respectively. Temperature dependences of the complex dielectric permittivity demonstrate anomalies in the phase transition ranges. The Pnma-to-C2/c crossover in BiCrO3 is accompanied by a decrease in the direct current (dc) conductivity, while in BiCr0.9Sc0.1O3 the conductivity increases. The onset of an antiferromagnetic order in BiCr0.9Sc0.1O3 is observed at the Néel temperature (TN) of about 85 K as compared with TN = 110 K in BiCrO3. In contrast to BiCrO3, which exhibits a spin reorientation at Tsr ∼72 K, no such a transition occurs in BiCr0.9Sc0.1O3. Copyright © 2020 American Chemical Society.
    view abstractdoi: 10.1021/acs.inorgchem.0c00338
  • 2020 • 685 High-resolution in vivo imaging of peripheral nerves using optical coherence tomography: A feasibility study
    Carolus, A.E. and Lenz, M. and Hofmann, M. and Welp, H. and Schmieder, K. and Brenke, C.
    Journal of Neurosurgery 132 1907-1913 (2020)
    Objective: Because of their complex topography, long courses, and small diameters, peripheral nerves are challenging structures for radiological diagnostics. However, imaging techniques in the area of peripheral nerve diseases have undergone unexpected development in recent decades. They include MRI and high-resolution sonography (HRS). Yet none of those imaging techniques reaches a resolution comparable to that of histological sections. Fascicles are the smallest discernable structure. Optical coherence tomography (OCT) is the first imaging technique that is able to depict a nerve's ultrastructure at micrometer resolution. In the current study, the authors present an in vivo assessment of human peripheral nerves using OCT. Methods: OCT measurement was performed in 34 patients with different peripheral nerve pathologies, i.e., nerve compression syndromes. The nerves were examined during surgery after their exposure. Only the sural nerve was twice examined ex vivo. The Thorlabs OCT systems Callisto and Ganymede were used. For intraoperative use, a hand probe was covered with a sterile foil. Different postprocessing imaging techniques were applied and evaluated. In order to highlight certain structures, five texture parameters based on gray-level co-occurrence matrices were calculated according to Haralick. Results: The intraoperative use of OCT is easy and intuitive. Image artifacts are mainly caused by motion and the sterile foil. If the artifacts are kept at a low level, the hyporeflecting bundles of nerve fascicles and their inner parts can be displayed. In the Haralick evaluation, the second angular moment is most suitable to depict the connective tissue. Conclusions: OCT is a new imaging technique that has shown promise in peripheral nerve surgery for particular questions. Its resolution exceeds that provided by recent radiological possibilities such as MRI and HRS. Since its field of view is relatively small, faster acquisition times would be highly desirable and have already been demonstrated by other groups. Currently, the method resembles an optical biopsy and can be a supplement to intraoperative sonography, giving high-resolution insight into a suspect area that has been located by sonography in advance. © AANS 2020, except where prohibited by US copyright law.
    view abstractdoi: 10.3171/2019.2.JNS183542
  • 2020 • 684 Effect of Spray Parameters in a Spray Flame Reactor During FexOy Nanoparticles Synthesis
    Carvajal, L. and Buitrago-Sierra, R. and Santamaría, A. and Angel, S. and Wiggers, H. and Gallego, J.
    Journal of Thermal Spray Technology 29 368-383 (2020)
    Abstract: Synthesis and characterization of FexOy nanoparticles were carried out in order to study reaction parameters influence in a spray flame reactor. FexOy powders were prepared with three different precursors aiming to understand how the reactor conditions, dispersion gas flow, and precursor solution flow affect morphology, shape, particle size distribution, crystalline phases, and residue content of the obtained materials. Thermogravimetric analysis, scanning electron microscopy, transmission electron microscopy (TEM), x-ray diffraction (XRD), and Raman spectroscopy were employed to characterize the materials. In addition, magnetic behavior of the obtained samples was evaluated. It was found that the evaluated parameters influenced the residue contents obtaining weight changes from 10 to 35%. Particle size distribution centers also showed differences between 17 and 24 nm. By XRD, Raman, and TEM, the presence of hematite (a-Fe2O3), maghemite (γ-Fe2O3), and magnetite (Fe3O4) was evidenced and explained based on the gas and liquid content in the flame. Additionally, the saturation magnetization was measured for selected samples, obtaining values between 26 and 32 emu g−1. These magnetic measurements were correlated with the crystalline phase composition and particle size distributions. Graphic Abstract: [Figure not available: see fulltext.] © 2020, ASM International.
    view abstractdoi: 10.1007/s11666-020-00991-1
  • 2020 • 683 Self-organization of silicates on different length scales exemplified by amorphous mesoporous silica and mesoporous zeolite beta using multiammonium surfactants
    Castro, M. and Losch, P. and Farès, C. and Haouas, M. and Taulelle, F. and Breynaert, E. and Kirschhock, C. and Park, W. and Ryoo, R. and Schmidt, W.
    RSC Advances 10 20928-20938 (2020)
    In this study the structure directing effect of a gemini-type piperidine-based multi-ammonium surfactant during hydrothermal zeolite synthesis was investigated for two cases: with and without a source of aluminum. The absence of an aluminum source led to the formation of an amorphous mesoporous MCM-48 type silica material, while the presence of aluminum guaranteed the formation of zeolite beta with a hierarchical pore system. The two opposing cases were studied in a time and temperature-dependent manner. The mobility and through space interaction of these large surfactant molecules were studied by liquid state nuclear magnetic resonance (NMR) at a temperature relevant to hydrothermal synthesis (363 K) in pure water and upon addition of an aluminum and silicon source. In the gel state, at different stages of aging and hydrothermal synthesis, low angle X-ray diffraction (XRD) and solid state magic angle spinning nuclear magnetic resonance (1H MAS NMR) spectrometry determined the developing order within the system. At each of these different synthesis steps the respective intermediate materials were calcined. Transmission electron microscopy then allowed closer inspection of the locally developing mesoscopic order, while N2physisorption was used to follow the evolution of porosity. © The Royal Society of Chemistry 2020.
    view abstractdoi: 10.1039/d0ra03828h
  • 2020 • 682 Could face-centered cubic titanium in cold-rolled commercially-pure titanium only be a Ti-hydride?
    Chang, Y. and Zhang, S. and Liebscher, C.H. and Dye, D. and Ponge, D. and Scheu, C. and Dehm, G. and Raabe, D. and Gault, B. and Lu, W.
    Scripta Materialia 178 39-43 (2020)
    A face-centered cubic (FCC) phase in electro-polished specimens for transmission electron microscopy of commercially pure titanium has sometimes been reported. Here, a combination of atom-probe tomography, scanning transmission electron microscopy and low-loss electron energy loss spectroscopy is employed to study both the crystal structural and chemical composition of this FCC phase. Our results prove that the FCC phase is actually a TiHx (x ≥ 1) hydride, and not a new allotrope of Ti, in agreement with previous reports. The formation of the hydride is discussed. © 2019 Acta Materialia Inc.
    view abstractdoi: 10.1016/j.scriptamat.2019.11.010
  • 2020 • 681 Chemistry in nanosecond plasmas in water
    Chauvet, L. and Nenbangkaeo, C. and Grosse, K. and von Keudell, A.
    Plasma Processes and Polymers 17 (2020)
    Discharges in liquids are the basis of a range of applications in electrochemistry, wastewater treatment, or plasma medicine. One advantage of discharges in water is their ability to produce radicals and molecules directly inside liquid with a high conversion efficiency. In this study, H2O2 production in a 10 ns pulsed discharge in water is investigated. The dynamic of these discharges is based on plasma ignition directly inside liquid followed by the formation of a bubble that expands in time before it eventually collapses. This sequence can be well described by cavitation theory. H2O2 is produced using different plasma conditions varying the treatment time, the pulse frequency between 1 and 100 Hz, and the applied voltage in a range from 15–30 kV. The resulting H2O2 concentration is measured using absorption spectroscopy ex situ based on a colorimetry method. The results indicate that the main parameter controlling the H2O2 production constitutes the applied voltage. The measured concentrations are compared with a global chemistry model simulating the chemistry involved during a single pulse using pressures and temperatures from the cavitation model. In addition, a global chemical equilibrium model for H2O2 creation is evaluated as well. The models show a good agreement with the data. The energy efficiency for the production of H2O2 reaches values up to 2 g/kWh. © 2020 The Authors. Plasma Processes and Polymers published by Wiley-VCH Verlag GmbH & Co. KGaA
    view abstractdoi: 10.1002/ppap.201900192
  • 2020 • 680 Effect of corrosion and surface finishing on fatigue behavior of friction stir welded EN AW-5754 aluminum alloy using various tool configurations
    Chehreh, A.B. and Grätzel, M. and Bergmann, J.P. and Walther, F.
    Materials 13 (2020)
    In this study, fatigue behavior of surface finished and precorroded friction stir welded (FSW) specimens using various tool configurations were comparatively investigated by the load increase method. The FSW using conventional, stationary shoulder and dual-rotational configurations was carried out by a robotized tool setup on 2 mm EN AW-5754 aluminum sheets in butt joint formation. After extraction of the specimens, their weld seam and root surfaces were milled to two different depths of 200 μm and 400 μm to remove the surface and the FSW tool shoulder effects. This surface finishing process was performed to investigate the effect of the surface defects on the fatigue behavior of the FSW EN AW-5754 aluminum alloy sheets. It was found that material removal from the weld and root surfaces of the specimens, increased the fracture stresses of conventional and dual-rotational FSW from 204 to 229 MPa and 196 to 226 MPa, respectively. However, this increase could not be detected in stationary shoulder FSW. Specimens with finished surfaces, which showed superior properties, were used in salt spray and cyclic climate change test to investigate the effect of corrosion on the fatigue behavior of FSW specimens. It was shown that cyclic climate change test reduced the fatigue properties of the base material, conventional, stationary shoulder and dual-rotational FSW approximately 1%-7%. This decrease in the fatigue properties was greater in the case of the salt spray test, which was 7% to 21%. © 2020 by the authors.
    view abstractdoi: 10.3390/ma13143121
  • 2020 • 679 Sintering and biocompatibility of blended elemental Ti-xNb alloys
    Chen, Y. and Han, P. and Dehghan-Manshadi, A. and Kent, D. and Ehtemam-Haghighi, S. and Jowers, C. and Bermingham, M. and Li, T. and Cooper-White, J. and Dargusch, M.S.
    Journal of the Mechanical Behavior of Biomedical Materials 104 (2020)
    Titanium-niobium (Ti–Nb) alloys have great potential for biomedical applications due to their superior biocompatibility and mechanical properties that match closely to human bone. Powder metallurgy is an ideal technology for efficient manufacture of titanium alloys to generate net-shape, intricately featured and porous components. This work reports on the effects of Nb concentrations on sintered Ti-xNb alloys with the aim to establish an optimal composition in respect to mechanical and biological performances. Ti-xNb alloys with 33, 40, 56 and 66 wt% Nb were fabricated from elemental powders and the sintering response, mechanical properties, microstructures and biocompatibility assessed and compared to conventional commercial purity titanium (CPTi). The sintered densities for all Ti-xNb compositions were around 95%, reducing slightly with increasing Nb due to increasing open porosity. Higher Nb levels retarded sintering leading to more inhomogeneous phase and pore distributions. The compressive strength decreased with increasing Nb, while all Ti-xNb alloys displayed higher strengths than CPTi except the Ti–66Nb alloy. The Young's moduli of the Ti-xNb alloys with ≥40 wt% Nb were substantially lower (30–50%) than CPTi. In-vitro cell culture testing revealed excellent biocompatibility for all Ti-xNb alloys comparable or better than tissue culture plate and CPTi controls, with the Ti–40Nb alloy exhibiting superior cell-material interactions. In view of its mechanical and biological performance, the Ti–40Nb composition is most promising for hard tissue engineering applications. © 2020
    view abstractdoi: 10.1016/j.jmbbm.2020.103691
  • 2020 • 678 Dictionary learning in Fourier-transform scanning tunneling spectroscopy
    Cheung, S.C. and Shin, J.Y. and Lau, Y. and Chen, Z. and Sun, J. and Zhang, Y. and Müller, M.A. and Eremin, I.M. and Wright, J.N. and Pasupathy, A.N.
    Nature Communications 11 (2020)
    Modern high-resolution microscopes are commonly used to study specimens that have dense and aperiodic spatial structure. Extracting meaningful information from images obtained from such microscopes remains a formidable challenge. Fourier analysis is commonly used to analyze the structure of such images. However, the Fourier transform fundamentally suffers from severe phase noise when applied to aperiodic images. Here, we report the development of an algorithm based on nonconvex optimization that directly uncovers the fundamental motifs present in a real-space image. Apart from being quantitatively superior to traditional Fourier analysis, we show that this algorithm also uncovers phase sensitive information about the underlying motif structure. We demonstrate its usefulness by studying scanning tunneling microscopy images of a Co-doped iron arsenide superconductor and prove that the application of the algorithm allows for the complete recovery of quasiparticle interference in this material. © 2020, The Author(s).
    view abstractdoi: 10.1038/s41467-020-14633-1
  • 2020 • 677 Durability assessment of suspension coil spring considering the multifractality of road excitations
    Chin, C.H. and Abdullah, S. and Singh, S.S.K. and Ariffin, A.K. and Schramm, D.
    Measurement: Journal of the International Measurement Confederation 158 (2020)
    This study presents the characterisation of multifractality of road excitation time series under different road conditions for prediction of the durability of a suspension coil spring. Road excitation acceleration signals and strain signals were acquired from the suspension system of a vehicle travelling under different road conditions. Multifractal analysis revealed a higher tendency to multifractality in road excitations with more surface irregularities. With the fatigue lives predicted by different strain-life models (Coffin-Manson, Morrow, and Smith-Watson-Topper), fatigue life prediction linear models based on road multifractality were established. It was found that the Morrow-based linear model gave the most accurate estimation of fatigue life, with the highest R2 of 0.8762. In conclusion, the models for the prediction of coil springs’ fatigue life based on road multifractality provide an accurate and faster alternative for durability assessment of coil springs. This can significantly facilitate the design process of coil springs to meet industry requirements. © 2020 Elsevier Ltd
    view abstractdoi: 10.1016/j.measurement.2020.107697
  • 2020 • 676 Bump energy for durability prediction of coil spring based on local regularity analysis
    Chin, C.H. and Abdullah, S. and Singh, S.S.K. and Ariffin, A.K. and Schramm, D.
    International Journal of Integrated Engineering 12 12-19 (2020)
    This paper aims to study the identification of bumps in vibrational signals and develop bump-energybased durability predictive models for a suspension coil spring. The bump energy of the loading signal is affected by high frequency noises and can lead to inaccurate results. Therefore, it is necessary to eliminate high frequency noise during bump identification. Local regularity analysis was employed to determine the singular points in road signals. Bump signals were then reconstructed from these singular points. Subsequently, bump-energy-based models were developed by correlating with the fatigue lives estimated using the Coffin-Manson, Morrow and Smith-Watson-Topper strain-life models. The results show that the bump signals extracted from the road excitations had a frequency band within 0-50 Hz, indicating that the high frequency noises had been successfully removed during extraction of the bumps. The bump-energy-based models predicted a fatigue life ranging from 3.98x104 to 4x109 cycles within a 95% confidence interval, where the Coffin-Manson-based model showed the highest fatigue life. This is because the Coffin-Manson model did not consider the mean stress effects. When compared with the experimental results, the Coffin-Manson-based model indicates the highest accuracy, given its highest R2 of 0.948. The bump-energy-based models developed in this study contributed an accurate durability prediction of coil springs. © Universiti Tun Hussein Onn Malaysia Publisher's Office.
    view abstractdoi: 10.30880/ijie.2020.12.05.002
  • 2020 • 675 Peel-back controlled lithospheric convergence explains the secular transitions in Archean metamorphism and magmatism
    Chowdhury, P. and Chakraborty, S. and Gerya, T.V. and Cawood, P.A. and Capitanio, F.A.
    Earth and Planetary Science Letters 538 (2020)
    The preserved archive of continental crust suggests that various secular geologic and geochemical transitions took place during the Mesoarchean and Neoarchean (∼3.2–2.5 Ga). These transitions, which are imprinted in the metamorphic and magmatic rock-record, include the emergence of paired metamorphism, an increasing depth of tonalite-trondhjemite-granodiorite (TTG) formation, the widespread appearance of granites and changes in the composition of mafic rock. Previous studies have argued that these secular transitions reflect secular cooling of the mantle and herald a gradual transition from pre-plate tectonic to plate tectonic regimes. However, their tectonic driver remains elusive, in part due to a lack of detailed understanding of lithospheric dynamics prevalent during this transitional period when the mantle was warmer compared to the present-day. Here, we demonstrate that lithospheric convergence driven by peel-back (/peeling) process under warmer mantle conditions – termed as peel-back convergence – may explain the late Archean secular transitions. This tectonic phenomena features large-scale peeling (a form of delamination, but not dripping) of the mantle lithosphere with or without lower crustal rocks during convergence. We simulated numerical models of peel-back convergence under Archean crust-mantle conditions and predicted the pressure-temperature (P-T) conditions of crustal metamorphism and melting. The evolution of peel-back convergent setting features juxtaposition of a colder, compressional regime with thickened crust that forms at the site of peeling, and a warmer, extensional regime with thinned crust forming behind it. The metamorphic and magmatic P-T conditions prevalent in these two tectonothermal sites replicate the features of the late Archean rock record, including the: appearance of coeval high-T/P and intermediate-T/P metamorphic rocks; greater abundance of high-T/P relative to intermediate-T/P metamorphic rocks; dominant formation of TTGs at higher pressures where garnet ± rutile is stable in the residue; reworking of pre-existing felsic rocks/sediments to produce potassic granites; and interaction of crustal melts and mantle to form hybrid granitoids. Thus, peel-back convergence can explain the thermobaric bimodality of late Archean rocks within an asymmetric tectono-thermal framework. However, unlike modern convergent plate boundaries, the asymmetry is controlled by lithospheric peeling. © 2020 Elsevier B.V.
    view abstractdoi: 10.1016/j.epsl.2020.116224
  • 2020 • 674 Optimal control problems with control complementarity constraints: existence results, optimality conditions, and a penalty method
    Clason, C. and Deng, Y. and Mehlitz, P. and Prüfert, U.
    Optimization Methods and Software 35 142-170 (2020)
    A special class of optimal control problems with complementarity constraints on the control functions is studied. It is shown that such problems possess optimal solutions whenever the underlying control space is a first-order Sobolev space. After deriving necessary optimality conditions of strong stationarity-type, a penalty method based on the Fischer–Burmeister function is suggested and its theoretical properties are analyzed. Finally, the numerical treatment of the problem is discussed and results of computational experiments are presented. © 2019, © 2019 Informa UK Limited, trading as Taylor & Francis Group.
    view abstractdoi: 10.1080/10556788.2019.1604705
  • 2020 • 673 Testing of formed gear wheels at quasi-static and elevated strain rates
    Clausmeyer, T. and Gutknecht, F. and Gerstein, G. and Nürnberger, F.
    Procedia Manufacturing 47 623-628 (2020)
    Geared components can be manufactured from sheet metals by sheet-bulk metal forming. One relevant load case in service are overload events, which might induce elevated strain rates. To determine the characteristic hardening and fracture behavior, specimens manufactured from the deep-drawing steel DC04 were tested with strain rates ranging from 0.0001 to 5 s−1. The gear wheels manufactured by sheet-bulk metal forming are tested at crosshead velocities of 0.08 mm/s and 175 mm/s. The tests are analyzed by measuring deformed geometry and hardness. While the tensile tests results show obvious strain-rate dependency, the hardness measurements show no strain-rate depended effect. The analyses are complemented by finite-element-simulations, which assess the homogeneity of deformation and point out the mechanisms of failure. Both coupled and uncoupled ductile damage models are able to predict the critical areas for crack initiation. The coupled damage model has slight advantages regarding deformed shape prediction. © 2020 The Authors. Published by Elsevier Ltd.
    view abstractdoi: 10.1016/j.promfg.2020.04.191
  • 2020 • 672 Prediction of ductile damage in the process chain of caliber rolling and forward rod extrusion
    Clausmeyer, T. and Schowtjak, A. and Wang, S. and Gitschel, R. and Hering, O. and Pavliuchenko, P. and Lohmar, J. and Ostwald, R. and Hirt, G. and Erman Tekkaya, A.
    Procedia Manufacturing 47 649-655 (2020)
    Many metal forming processes involve several steps, which influence the shape and properties of the final component. The previous manufacturing process of the semi-finished component influences the properties of extruded components. The authors analyze the evolution of damage and voids in the sequence of caliber rolling to cold forward rod extrusion. The analysis is performed with the help of a variant of the Lemaitre model, microstructural analysis of the void area fraction and density measurements. The numerical analysis of this process chain makes use of a fully three-dimensional simulation approach. Even though the damage distribution is non-axisymmetric in caliber rolling, the distribution is almost axisymmetric after cold forward extrusion. The shoulder opening angle in extrusion is varied to compare model predictions with experiments. The decrease in density is largest for the largest shoulder opening angle and smallest for the smallest shoulder opening angle. The simulations agree qualitatively well with the experiments in term of the measured void area fraction and the density changes. The quantitative comparison reveals differences of one to two orders of magnitude. © 2020 The Authors. Published by Elsevier Ltd.
    view abstractdoi: 10.1016/j.promfg.2020.04.201
  • 2020 • 671 Evaluation of molecular orbital symmetry via oxygen-induced charge transfer quenching at a metal-organic interface
    Cojocariu, I. and Sturmeit, H.M. and Zamborlini, G. and Cossaro, A. and Verdini, A. and Floreano, L. and D'Incecco, E. and Stredansky, M. and Vesselli, E. and Jugovac, M. and Cinchetti, M. and Feyer, V. and Schneider, C.M.
    Applied Surface Science 504 (2020)
    Thin molecular films under model conditions are often exploited as benchmarks and case studies to investigate the electronic and structural changes occurring on the surface of metallic electrodes. Here we show that the modification of a metallic surface induced by oxygen adsorption allows the preservation of the geometry of a molecular adlayer, giving access to the determination of molecular orbital symmetries by means of near-edge X-ray absorption fine structure spectroscopy, NEXAFS. As a prototypical example, we exploited nickel tetraphenylporphyrin molecules deposited on a bare and on an oxygen pre-covered Cu(1 0 0) surface. We find that adsorbed atomic oxygen quenches the charge transfer at the metal-organic interface but, in contrast to a thin film sample, maintains the ordered adsorption geometry of the organic molecules. In this way, it is possible to disentangle π* and σ* symmetry orbitals, hence estimate the relative oscillator strength of core level transitions directly from the experimental data, as well as to evaluate and localize the degree of charge transfer in a coupled system. In particular, we neatly single out the σ* contribution associated with the N 1s transition to the mixed N 2px,y-Ni 3dx 2 -y 2 orbital, which falls close to the leading π*-symmetry LUMO resonance. © 2019
    view abstractdoi: 10.1016/j.apsusc.2019.144343
  • 2020 • 670 Chemical instability at chalcogenide surfaces impacts chalcopyrite devices well beyond the surface
    Colombara, D. and Elanzeery, H. and Nicoara, N. and Sharma, D. and Claro, M. and Schwarz, T. and Koprek, A. and Wolter, M.H. and Melchiorre, M. and Sood, M. and Valle, N. and Bondarchuk, O. and Babbe, F. and Spindler, C. and Cojoc...
    Nature Communications 11 (2020)
    The electrical and optoelectronic properties of materials are determined by the chemical potentials of their constituents. The relative density of point defects is thus controlled, allowing to craft microstructure, trap densities and doping levels. Here, we show that the chemical potentials of chalcogenide materials near the edge of their existence region are not only determined during growth but also at room temperature by post-processing. In particular, we study the generation of anion vacancies, which are critical defects in chalcogenide semiconductors and topological insulators. The example of CuInSe2 photovoltaic semiconductor reveals that single phase material crosses the phase boundary and forms surface secondary phases upon oxidation, thereby creating anion vacancies. The arising metastable point defect population explains a common root cause of performance losses. This study shows how selective defect annihilation is attained with tailored chemical treatments that mitigate anion vacancy formation and improve the performance of CuInSe2 solar cells. © 2020, The Author(s).
    view abstractdoi: 10.1038/s41467-020-17434-8
  • 2020 • 669 A simple finite element for the geometrically exact analysis of Bernoulli–Euler rods
    da Costa e Silva, C. and Maassen, S.F. and Pimenta, P.M. and Schröder, J.
    Computational Mechanics 65 905-923 (2020)
    This work develops a simple finite element for the geometrically exact analysis of Bernoulli–Euler rods. Transversal shear deformation is not accounted for. Energetically conjugated cross-sectional stresses and strains are defined. A straight reference configuration is assumed for the rod. The cross-section undergoes a rigid body motion. A rotation tensor with the Rodrigues formula is used to describe the rotation, which makes the updating of the rotational variables very simple. A formula for the Rodrigues parameters in function of the displacements derivative and the torsion angle is for the first time settled down. The consistent connection between elements is thoroughly discussed, and an appropriate approach is developed. Cubic Hermitian interpolation for the displacements together with linear Lagrange interpolation for the torsion incremental angle were employed within the usual Finite Element Method, leading to adequate C1 continuity. A set of numerical benchmark examples illustrates the usefulness of the formulation and numerical implementation. © 2019, Springer-Verlag GmbH Germany, part of Springer Nature.
    view abstractdoi: 10.1007/s00466-019-01800-5
  • 2020 • 668 Tunable two-dimensional electron system at the (110) surface of SnO2
    Dai, J. and Frantzeskakis, E. and Fortuna, F. and Lömker, P. and Yukawa, R. and Thees, M. and Sengupta, S. and Le Fèvre, P. and Bertran, F. and Rault, J.E. and Horiba, K. and Müller, M. and Kumigashira, H. and Santander-Syro, A.F.
    Physical Review B 101 (2020)
    We report the observation of a two-dimensional electron system (2DES) at the (110) surface of the transparent bulk insulator SnO2 and the tunability of its carrier density by means of temperature or Eu deposition. The 2DES is insensitive to surface reconstructions and, surprisingly, it survives even after exposure to ambient conditions- A n extraordinary fact recalling the well known catalytic properties SnO2. Our data show that surface oxygen vacancies are at the origin of such 2DES, providing key information about the long-debated origin of n-type conductivity in SnO2, at the basis of a wide range of applications. Furthermore, our study shows that the emergence of a 2DES in a given oxide depends on a delicate interplay between its crystal structure and the orbital character of its conduction band. © 2020 American Physical Society.
    view abstractdoi: 10.1103/PhysRevB.101.085121
  • 2020 • 667 A Supported Bismuth Halide Perovskite Photocatalyst for Selective Aliphatic and Aromatic C–H Bond Activation
    Dai, Y. and Poidevin, C. and Ochoa-Hernández, C. and Auer, A.A. and Tüysüz, H.
    Angewandte Chemie - International Edition 59 5788-5796 (2020)
    Direct selective oxidation of hydrocarbons to oxygenates by O2 is challenging. Catalysts are limited by the low activity and narrow application scope, and the main focus is on active C−H bonds at benzylic positions. In this work, stable, lead-free, Cs3Bi2Br9 halide perovskites are integrated within the pore channels of mesoporous SBA-15 silica and demonstrate their photocatalytic potentials for C−H bond activation. The composite photocatalysts can effectively oxidize hydrocarbons (C5 to C16 including aromatic and aliphatic alkanes) with a conversion rate up to 32900 μmol gcat−1 h−1 and excellent selectivity (&gt;99 %) towards aldehydes and ketones under visible-light irradiation. Isotopic labeling, in situ spectroscopic studies, and DFT calculations reveal that well-dispersed small perovskite nanoparticles (2–5 nm) possess enhanced electron–hole separation and a close contact with hydrocarbons that facilitates C(sp3)−H bond activation by photoinduced charges. © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
    view abstractdoi: 10.1002/anie.201915034
  • 2020 • 666 Influence of muck properties and chamber design on pressure distribution in EPB pressure chambers – Insights from computational flow simulations
    Dang, T.S. and Meschke, G.
    Tunnelling and Underground Space Technology 99 (2020)
    Earth Pressure Balance (EPB) shield machines are widely used in mechanized tunneling operations in soft grounds. In contrast to slurry shield machines, the pressure distribution in EPB excavation chambers is not well undersood, as it is influenced by the muck properties and the chamber design. A computational model specifically developed in Dang and Meschke (2018) for the numerical simulation of material transport in EPB pressure chambers is employed to investigate the pressure distribution in two different types of EPB chambers, characterized by a different design of the mixing components, the rotators and the screw conveyor. The numerical model allows for the description of all rotating and fixed components of the EPB chambers including the screw conveyor and considers adequately the compressibility and the consistency of the soil paste. The spatio-temporal pressure distribution is investigated with respect to the influence of chamber design and the properties of the soil paste. Essential characteristics of the pressure distribution, such as the pressure unbalance between the left and right side and pressure fluctuations observed in in situ measurements are captured by the numerical analyses. The key factors influencing the pressure unbalance and pressure fluctuations are identified by parametric studies for two different EPB chamber designs. © 2020 Elsevier Ltd
    view abstractdoi: 10.1016/j.tust.2020.103333
  • 2020 • 665 Material Characterization of Additively Manufactured Metals by Laser Speckle Photometry
    Dang, D. and Elspas, A. and Cikalova, U. and Kleszczynski, S. and Bendjus, B. and Witt, G.
    Proceedings of the International Spring Seminar on Electronics Technology 2020-May (2020)
    In contrast to traditional time-consuming and costly manufacturing processes, additive manufacturing offers an effective production of prototypes. In addition to the numerous process developments of recent years, quality assurance as well as the testing of material properties afterward have now become one of the main requirements. Previous research approaches such as thermography or optical imaging have essential disadvantages, why there is a need for simple and effective solutions. For this purpose, the Laser Speckle Photometry (LSP) as a novel nondestructive approach for evaluating the material quality manufactured by Laser Powder Bed Fusion of Metals (LPBF-M) is presented. For the validation of this testing method exactly defined defective samples were reproducibly fabricated by specific adaptation in the building process. Voids were introduced into the structure, which are not visible on the surface. The simple LSP setup and the adjusted evaluation algorithm, based on the correlation function, are decisive for characterizing different material density states. This paper presents the potential of LSP for the use in LPBF-M processes stated with the first results of the validation. © 2020 IEEE.
    view abstractdoi: 10.1109/ISSE49702.2020.9120869
  • 2020 • 664 What is a deep defect? Combining Shockley-Read-Hall statistics with multiphonon recombination theory
    Das, B. and Aguilera, I. and Rau, U. and Kirchartz, T.
    Physical Review Materials 4 (2020)
    Slow nonradiative recombination is a key factor in achieving high open-circuit voltages or high luminescence yields in any optoelectronic material. Whether a defect is contributing substantially to nonradiative recombination is often estimated by defect statistics based on the model by Shockley, Read, and Hall. However, defect statistics are agnostic to the origin of the capture coefficients and therefore conclude that essentially every defect between the two quasi-Fermi levels is equally likely to be a recombination-active defect. Here, we combine Shockley-Read-Hall statistics with microscopic models for defect-assisted recombination to study how the microscopic properties of a material affect how recombination active a defect is depending on its energy level. We then use material parameters representative of typical photovoltaic absorber materials (CH3NH3PbI3, Si, and GaAs) to illustrate the relevance, but also the limitations of our model. © 2020 American Physical Society.
    view abstractdoi: 10.1103/PhysRevMaterials.4.024602
  • 2020 • 663 Plasma-assisted gas-phase synthesis and in-line coating of silicon nanoparticles
    Dasgupta, M. and Fortugno, P. and Wiggers, H.
    Plasma Processes and Polymers 17 (2020)
    This study investigates the feasibility of plasma-supported in-line functionalization of silicon nanoparticles (NPs) in an atmospheric pressure gas-phase reactor. The approach utilizes the synthesis of core silicon NPs and their subsequent coating downstream of the particle formation zone. In-line coating is accomplished with a cylindrical coating nozzle to achieve homogenous mixing of coating precursor vapors with in-coming NPs. Multiple siloxanes were tested for their coating suitability and their ability towards coating homogeneity. It was found that tetraethyl orthosilicate is favored for thin layers consisting of almost pure silica while hexamethyldisiloxane and octamethylcyclotetrasiloxane (OMCTS) coatings contained reasonable amounts of hydrocarbons. Moreover, OMCTS showed a pronounced tendency towards homogeneous nucleation, thus leading to the additional formation of silica NPs due to homogeneous nucleation. © 2020 The Authors. Plasma Processes and Polymers published by WILEY-VCH Verlag GmbH & Co. KGaA
    view abstractdoi: 10.1002/ppap.201900245
  • 2020 • 662 Tunable and switchable nanoparticle separation with thermo-responsive track-etched membranes prepared by controlled surface-initiated polymerization of poly(N-isopropylacrylamide)
    Daumann, K. and Frost, S. and Ulbricht, M.
    RSC Advances 10 21028-21038 (2020)
    This work describes how the control of grafting density and grafted chain length of a thermo-responsive polymer in membrane pores can be utilized to tune the pore size and the switchability of size-based selectivity in the ultrafiltration range. Using a previously established methodology for controlled synthesis, surface-initiated atom transfer polymerization (ATRP) of poly(N-isopropylacrylamide) (PNIPAAm) to the pore walls of poly(ethylene terephthalate) track-etched membranes with experimentally determined pore diameters of 35 nm (PET30) and 110 nm (PET80) is performed. Characterization in this study is mainly done with filtration experiments, making use of the well-defined pore structure of the base membranes. It is demonstrated that both the gravimetrically determined degree of functionalization and the effective pore size determined from water permeability are a linear function of ATRP time. For the grafted PET30 membranes, it is shown that the rejection of lysozyme (diameter ∼ 4 nm) can be switched between 99% at 23 °C and 65% at 45 °C for the membrane with the highest degree of functionalization. For the grafted PET80 membranes, it is found that two different types of membranes can be obtained. Membranes with long grafted chains at low grafting density show very large changes of water permeability as a function of temperature (effective pore size switching ratio of up to 10) and, for example, rejection for 20 nm silica particles of 95% and 23% at 23 °C and 45 °C, respectively. Membranes with PNIPAAm at high grafting density show much lower switching ratios (as low as 1.4, for long enough grafted chains). Effective pore size and thermo-responsive change of pore size can therefore be tuned by the combination of both synthesis parameters, initiator density and ATRP time. The switchable thermo-responsive separation of two colloids with a tailored membrane is demonstrated for mixtures of bovine serum albumin (BSA; ∼7 nm) and silica nanoparticles (20 nm); at 23 °C silica is completely rejected and only BSA is in the permeate; at 40 °C both colloids permeate through the membrane. © The Royal Society of Chemistry 2020.
    view abstractdoi: 10.1039/d0ra03418e
  • 2020 • 661 Ultrafast vector imaging of plasmonic skyrmion dynamics with deep subwavelength resolution
    Davis, T.J. and Janoschka, D. and Dreher, P. and Frank, B. and Meyer zu Heringdorf, F.J. and Giessen, H.
    Science 368 (2020)
    Plasmonic skyrmions are an optical manifestation of topological defects in a continuous vector field. Identifying them requires characterization of the vector structure of the electromagnetic near field on thin metal films. Here we introduce time-resolved vector microscopy that creates movies of the electric field vectors of surface plasmons with subfemtosecond time steps and a 10-nanometer spatial scale. We image complete time sequences of propagating surface plasmons as well as plasmonic skyrmions, resolving all vector components of the electric field and their time dynamics, thus demonstrating dynamic spin-momentum coupling as well as the time-varying skyrmion number. The ability to image linear optical effects in the spin and phase structures of light in the single-nanometer range will allow for entirely novel microscopy and metrology applications. © 2020 American Association for the Advancement of Science. All rights reserved.
    view abstractdoi: 10.1126/science.aba6415
  • 2020 • 660 The role of microscale solid matrix compressibility on the mechanical behaviour of poroelastic materials
    Dehghani, H. and Noll, I. and Penta, R. and Menzel, A. and Merodio, J.
    European Journal of Mechanics, A/Solids 83 (2020)
    We present the macroscale three-dimensional numerical solution of anisotropic Biot's poroelasticity, with coefficients derived from a micromechanical analysis as prescribed by the asymptotic homogenisation technique. The system of partial differential equations (PDEs) is discretised by finite elements, exploiting a formal analogy with the fully coupled thermal displacement systems of PDEs implemented in the commercial software Abaqus. The robustness of our computational framework is confirmed by comparison with the well-known analytical solution of the one-dimensional Therzaghi's consolidation problem. We then perform three-dimensional numerical simulations of the model in a sphere (representing a biological tissue) by applying a given constant pressure in the cavity. We investigate how the macroscale radial displacements (as well as pressures) profiles are affected by the microscale solid matrix compressibility (MSMC). Our results suggest that the role of the MSMC on the macroscale displacements becomes more and more prominent by increasing the length of the time interval during which the constant pressure is applied. As such, we suggest that parameter estimation based on techniques such as poroelastography (which are commonly used in the context of biological tissues, such as the brain, as well as solid tumours) should allow for a sufficiently long time in order to give a more accurate estimation of the mechanical properties of tissues. © 2020 The Authors
    view abstractdoi: 10.1016/j.euromechsol.2020.103996
  • 2020 • 659 Are the Global Raw Material Markets in a State of Renewed Change? [Befinden sich die globalen Rohstoffmärkte in einem erneuten Wandel?]
    Deike, R.
    Chemie-Ingenieur-Technik 92 331-340 (2020)
    The growth of global population is no longer exponential, but there is still a growth. Are stronger raw materials consumptions automatically the effects? Markets for listed commodities are very much influenced by futures in their pricing, and in a time of comprehensive, extremely fast communication trends and hypes are generated. At the end of the day, markets are determined by the real relationship between supply and demand from a medium- and long-term perspective. What will be the effects in future developments of global commodity markets when China's economy will perform the transformation from an industrial into a service society?. © 2020, Wiley-VCH Verlag. All rights reserved.
    view abstractdoi: 10.1002/cite.201900136
  • 2020 • 658 Multiscale simulation system determines topographies of workpiece surfaces: Process optimization for internal cylindrical peel grinding [Prozessoptimierung für das innenrundschälschleifen]
    Dereli, T.T. and Biermann, D. and Menzel, A. and Schmidt, N. and Furlan, T. and Holtermann, R.
    VDI-Z Integrierte Produktion 162 25-27 (2020)
  • 2020 • 657 Optimal designs for estimating individual coefficients in polynomial regression with no intercept
    Dette, H. and Melas, V.B. and Shpilev, P.
    Statistics and Probability Letters 158 (2020)
    We identify optimal designs for estimating individual coefficients in a polynomial regression with no intercept. Here the regression functions do not form a Chebyshev system such that the seminal results of Studden (1968) characterizing c-optimal designs are not applicable. © 2019
    view abstractdoi: 10.1016/j.spl.2019.108636
  • 2020 • 656 Likelihood ratio tests for many groups in high dimensions
    Dette, H. and Dörnemann, N.
    Journal of Multivariate Analysis 178 (2020)
    In this paper, we investigate the asymptotic distribution of likelihood ratio tests in models with several groups, when the number of groups converges with the dimension and sample size to infinity. We derive central limit theorems for the logarithm of various test statistics and compare our results with the approximations obtained from a central limit theorem where the number of groups is fixed. © 2020 Elsevier Inc.
    view abstractdoi: 10.1016/j.jmva.2020.104605
  • 2020 • 655 Testing relevant hypotheses in functional time series via self-normalization
    Dette, H. and Kokot, K. and Volgushev, S.
    Journal of the Royal Statistical Society. Series B: Statistical Methodology 82 629-660 (2020)
    We develop methodology for testing relevant hypotheses about functional time series in a tuning-free way. Instead of testing for exact equality, e.g. for the equality of two mean functions from two independent time series, we propose to test the null hypothesis of no relevant deviation. In the two-sample problem this means that an L2-distance between the two mean functions is smaller than a prespecified threshold. For such hypotheses self-normalization, which was introduced in 2010 by Shao, and Shao and Zhang and is commonly used to avoid the estimation of nuisance parameters, is not directly applicable. We develop new self-normalized procedures for testing relevant hypotheses in the one-sample, two-sample and change point problem and investigate their asymptotic properties. Finite sample properties of the tests proposed are illustrated by means of a simulation study and data examples. Our main focus is on functional time series, but extensions to other settings are also briefly discussed. © 2020 Royal Statistical Society
    view abstractdoi: 10.1111/rssb.12370
  • 2020 • 654 The influence of oxygen on the chemical composition and mechanical properties of Ti-6Al-4V during laser powder bed fusion (L-PBF)
    Dietrich, K. and Diller, J. and Dubiez-Le Goff, S. and Bauer, D. and Forêt, P. and Witt, G.
    Additive Manufacturing 32 (2020)
    In Laser powder bed fusion (L-PBF), metal powders, sensitive to humidity and oxygen, like AlSi10Mg or Ti-6Al-4 V are used as starting material. Titanium-based materials are influenced by oxygen and nitrogen due to the formation of oxides and nitrides, respectively. During this research, the oxygen concentration in the build chamber was controlled from 2 ppm to 1000 ppm using an external measurement device. Built Ti-6Al-4 V specimens were evaluated regarding their microstructure, hardness, tensile strength, notch toughness, chemical composition and porosity, demonstrating the importance of a stable atmospheric control. It could be shown that an increased oxygen concentration in the shielding gas atmosphere leads to an increase of the ultimate tensile strength by 30 MPa and an increased (188.3 ppm) oxygen concentration in the bulk material. These results were compared to hot isostatic pressed (HIPed) samples to prevent the influence of porosity. In addition, the fatigue behavior was investigated, revealing increasingly resistant samples when oxygen levels in the atmosphere are lower. © 2019
    view abstractdoi: 10.1016/j.addma.2019.100980
  • 2020 • 653 How porosity is affected by different residual oxygen concentrations in the building chamber during laser powder bed fusion (L-PBF)
    Dietrich, K. and Krumova, V. and Bauer, D. and Forêt, P. and Witt, G.
    Euro PM 2018 Congress and Exhibition (2020)
    L-PBF (Laser powder bed fusion) is a layer by layer 3D manufacturing technique similar to the laser welding process where it is common knowledge that the interaction between material, laser and gas is of great importance. Used metals like aluminum or titanium tend to form oxides or nitrides in the presence of the corresponding gas influencing the chemical and mechanical properties. In L-PBF, establishing process conditions means purging the process chamber with an inert gas (nitrogen or argon) to an oxygen concentration of around 1000 ppm replacing the air inside. To understand the effect of residual oxygen on aluminum based alloy AlSi10Mg parts this paper will show a parameter study at 100 ppm oxygen in the process chamber compared with 1000 ppm. Finally, it will be investigated how oxygen affects final parts regarding porosity and microstructure. By reducing the oxygen concentration during a build job, lower porosity could be reached at higher laser speed. © European Powder Metallurgy Association (EPMA).
    view abstract
  • 2020 • 652 Chemical boundary engineering: A new route toward lean, ultrastrong yet ductile steels
    Ding, R. and Yao, Y. and Sun, B. and Liu, G. and He, J. and Li, T. and Wan, X. and Dai, Z. and Ponge, D. and Raabe, D. and Zhang, C. and Godfrey, A. and Miyamoto, G. and Furuhara, T. and Yang, Z. and van der Zwaag, S. and Chen, H.
    Science Advances 6 (2020)
    For decades, grain boundary engineering has proven to be one of the most effective approaches for tailoring the mechanical properties of metallic materials, although there are limits to the fineness and types of microstructures achievable, due to the rapid increase in grain size once being exposed to thermal loads (low thermal stability of crystallographic boundaries). Here, we deploy a unique chemical boundary engineering (CBE) approach, augmenting the variety in available alloy design strategies, which enables us to create a material with an ultrafine hierarchically heterogeneous microstructure even after heating to high temperatures. When applied to plain steels with carbon content of only up to 0.2 weight %, this approach yields ultimate strength levels beyond 2.0 GPa in combination with good ductility (>20%). Although demonstrated here for plain carbon steels, the CBE design approach is, in principle, applicable also to other alloys. Copyright © 2020 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works. Distributed under a Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC).
    view abstractdoi: 10.1126/sciadv.aay1430
  • 2020 • 651 Shifting value stream patterns along the product lifecycle with digital twins
    Dittrich, M.-A. and Schleich, B. and Clausmeyer, T. and Damgrave, R. and Erkoyuncu, J.A. and Haefner, B. and de Lange, J. and Plakhotnik, D. and Scheidel, W. and Wuest, T.
    Procedia CIRP 86 3-11 (2020)
    The concept of digital twins promises high potentials for product design, manufacturing, user experience and recycling. Thus, digital twins have received increasing interest in academia and industry. However, the actual benefits of digital twins remain in many cases unclear. This article aims to summarize selected recent developments in this field and demonstrate use cases from different phases of the product lifecycle. For that purpose, examples from the design, manufacturing, use and recycling phase are presented. In a subsequent discussion, ideas for new value stream patterns using digital twins are envisioned and research questions are derived. © 2019 The Authors. Published by Elsevier B.V.
    view abstractdoi: 10.1016/j.procir.2020.01.049
  • 2020 • 650 A possible mobile health solution in orthopedics and trauma surgery: Development protocol and user evaluation of the ankle joint app
    Dittrich, F. and Back, D.A. and Harren, A.K. and Jäger, M. and Landgraeber, S. and Reinecke, F. and Beck, S.
    JMIR mHealth and uHealth 8 (2020)
    Background: Ankle sprains are one of the most frequent sports injuries. With respect to the high prevalence of ankle ligament injuries and patients' young age, optimizing treatment and rehabilitation is mandatory to prevent future complications such as chronic ankle instability or osteoarthritis. Objective: In modern times, an increasing amount of smartphone usage in patient care is evident. Studies investigating mobile health (mHealth)-based rehabilitation programs after ankle sprains are rare. The aim of this study was to expose any issues present in the development process of a medical app as well as associated risks and chances. Methods: The development process of the Ankle Joint App was defined in chronological order using a protocol. The app's quality was evaluated using the (user) German Mobile App Rating Scale (MARS-G) by voluntary foot and ankle surgeons (n=20) and voluntary athletes (n=20). Results: A multidisciplinary development team built a hybrid app with a corresponding backend structure. The app's content provides actual medical literature, training videos, and a log function. Excellent interrater reliability (interrater reliability=0.92; 95% CI 0.86-0.96) was obtained. The mean overall score for the Ankle Joint App was 4.4 (SD 0.5). The mean subjective quality scores were 3.6 (surgeons: SD 0.7) and 3.8 (athletes: SD 0.5). Behavioral change had mean scores of 4.1 (surgeons: SD 0.7) and 4.3 (athletes: SD 0.7). The medical gain value, rated by the surgeons only, was 3.9 (SD 0.6). Conclusions: The data obtained demonstrate that mHealth-based rehabilitation programs might be a useful tool for patient education and collection of personal data. The achieved (user) MARS-G scores support a high quality of the tested app. Medical app development with an a priori defined target group and a precisely intended purpose, in a multidisciplinary team, is highly promising. Follow-up studies are required to obtain funded evidence for the ankle joints app's effects on economical and medical aspects in comparison with established nondigital therapy paths. © 2020 JMIR Publications. All rights reserved.
    view abstractdoi: 10.2196/16403
  • 2020 • 649 Thermodynamic Modeling of Solvent-Impact on Phase Separation in Amorphous Solid Dispersions during Drying
    Dohrn, S. and Reimer, P. and Luebbert, C. and Lehmkemper, K. and Kyeremateng, S.O. and Degenhardt, M. and Sadowski, G.
    Molecular Pharmaceutics 17 2721-2733 (2020)
    Understanding and prevention of unwanted changes of a pharmaceutical formulation during the production process is part of the critical requirements for the successful approval of a new drug product. Polymer-based formulations, so-called amorphous solid dispersions (ASDs), are often produced via solvent-based processes. In such processes, active pharmaceutical ingredients (APIs) and polymers are first dissolved in a solvent or solvent mixture, then the solvent is evaporated, for example, via spray drying or rotary evaporation. During the drying step, unwanted liquid-liquid phase separation may occur, leading to polymer-rich and API-rich regions with crystallization potential, and thus, heterogeneities and a two-phasic system in the final ASD. Phase separation in ASDs may impact their bioperformance because of the locally higher degree of API supersaturation. Although it is known that the choice of the solvent plays an important role in the formation of heterogeneities, solvent-impact on ASD drying and eventual product quality is often neglected in the process design. This study aims to investigate for the first time the phase behavior and drying process of API/polymer/solvents systems from a thermodynamic perspective. Unwanted phase changes during the drying process of the ASD containing hydroxypropyl methylcellulose acetate succinate and naproxen prepared from acetone/water or ethanol/water solvent mixtures were predicted using the thermodynamic model PC-SAFT. The predicted phase behavior and drying curves were successfully validated by confocal Raman spectroscopy. Copyright © 2020 American Chemical Society.
    view abstractdoi: 10.1021/acs.molpharmaceut.0c00418
  • 2020 • 648 Phase behavior of pharmaceutically relevant polymer/solvent mixtures
    Dohrn, S. and Luebbert, C. and Lehmkemper, K. and Kyeremateng, S.O. and Degenhardt, M. and Sadowski, G.
    International Journal of Pharmaceutics 577 (2020)
    In the pharmaceutical industry, polymers are used as excipients for formulating poorly water-soluble active pharmaceutical ingredients (APIs) in so-called “amorphous solid dispersions” (ASDs). ASDs can be produced via solvent-based processes, where API and polymer are both dissolved in a solvent, followed by a solvent evaporation step (e.g. spray drying). Aiming at a homogeneous API/polymer formulation, phase separation of the components (API, polymer, solvent) during solvent evaporation must be avoided. The latter is often determined by the phase behavior of polymer/solvent mixtures used for ASD processing. Therefore, this work investigates the polymer-solvent interactions in these mixtures. Suitable polymer/solvent combinations investigated in this work comprise the pharmaceutically relevant polymers poly(vinylpyrrolidone) (PVP), poly(vinylpyrrolidone-co-vinyl acetate) (PVPVA64), and hydroxyppropyl methylcellulose acetate succinate 126G (HPMCAS) as well as the solvents acetone, dichloromethane (DCM), ethanol, ethyl acetate, methanol, and water. Based on vapor-sorption experiments demixing of solvents and polymers were predicted using the Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT). These were found to be correct for all investigated solvent/polymer mixtures. Acetone, DCM, ethanol, methanol, and water were found to be completely miscible with PVPVA64. DCM, ethanol, methanol, and water were found to be completely miscible with PVP K90, while none of the investigated solvents was appropriate for avoiding immiscibility with HPMCAS. In addition, the impact of temperature, polymer molecular weight, and solvent-mixture composition on miscibility was successfully predicted using PC-SAFT. Thus, the proposed methodology allows identifying suitable solvents or solvent mixtures relevant for solvent-based preparations of pharmaceutical ASD formulations with low experimental effort. © 2020 Elsevier B.V.
    view abstractdoi: 10.1016/j.ijpharm.2020.119065
  • 2020 • 647 Development of a 3D Printing Technique for PVDF Thin Films for Sensor Elements of Electronic Devices
    Dubkov, S.V. and Silibin, M.V. and Lebedev, S.V. and Ryazanov, R.I. and Shvartsman, V.V.
    Proceedings of the 2020 IEEE Conference of Russian Young Researchers in Electrical and Electronic Engineering, EIConRus 2020 2587-2590 (2020)
    The paper proposes a method for forming thin films of polyvinylidene fluoride using a 3D printer. The extrusion parameters of a filament based on PVDF with a diameter of 1.75 were established and the optimal characteristics for printing by 3D printer were selected (nozzle temperature, table temperature, feed rate). Studies have shown that the local polarization of a thin PVDF film is stable for 20 hours. © 2020 IEEE.
    view abstractdoi: 10.1109/EIConRus49466.2020.9039127
  • 2020 • 646 Establishing structure-sensitivity of ceria reducibility: Real-Time observations of surface-hydrogen interactions
    Duchoň, T. and Hackl, J. and Mueller, D.N. and Kullgren, J. and Du, D. and Senanayake, S.D. and Mouls, C. and Gottlob, D.M. and Khan, M.I. and Cramm, S. and Veltruská, K. and Matolín, V. and Nemšák, S. and Schneider, C.M.
    Journal of Materials Chemistry A 8 5501-5507 (2020)
    The first layer of atoms on an oxide catalyst provides the first sites for adsorption of reactants and the last sites before products or oxygen are desorbed. We employ a unique combination of morphological, structural, and chemical analyses of a model ceria catalyst with different surface terminations under an H2 environment to unequivocally establish the effect of the last layer of atoms on surface reduction. (111) and (100) terminated epitaxial islands of ceria are simultaneously studied in situ allowing for a direct investigation of the structure-reducibility relationship under identical conditions. Kinetic rate constants of Ce4+ to Ce3+ transformation and equilibrium concentrations are extracted for both surface terminations. Unlike the kinetic rate constants, which are practically the same for both types of islands, more pronounced oxygen release, and overall higher reducibility were observed for (100) islands compared to (111) ones. The findings are in agreement with coordination-limited oxygen vacancy formation energies calculated by density functional theory. The results point out the important aspect of surface terminations in redox processes, with particular impact on the catalytic reactions of a variety of catalysts. This journal is © The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c9ta11784a
  • 2020 • 645 Interdiffusion in Cr–Fe–Co–Ni medium-entropy alloys
    Durand, A. and Peng, L. and Laplanche, G. and Morris, J.R. and George, E.P. and Eggeler, G.
    Intermetallics 122 (2020)
    Diffusion in multi-component alloys is attracting renewed attention because of the worldwide interest in high- and medium-entropy alloys (HEAs/MEAs). In the present work, we used diffusion multiples made from MEAs of the quaternary Cr–Fe–Co–Ni system arranged as six distinct pseudo-binary diffusion couples (Cr29Fe13Co29Ni29–Cr29Fe29Co29Ni13, Cr29Fe29Co13Ni29–Cr29Fe29Co29Ni13, and so on, where the interdiffusing elements are italicized for clarity). In the two halves of each couple, the starting concentrations of the interdiffusing elements (Fe,Ni and Co,Ni in the above examples) were different while those of the background elements (Cr,Co and Cr,Fe in the above examples) were the same. The diffusion multiples were annealed at temperatures between 1153 and 1355 K at times from 100 to 900 h, after which the concentrations of the different elements were measured as a function of distance across each couple. Interdiffusion coefficients were derived from such concentration profiles using the standard Sauer-Freise method and compared with literature data as well as with published tracer diffusion coefficients. Although the background elements were homogeneously distributed initially, some of them developed distinct sine-wave shaped concentration gradients near the interfaces after annealing, implying that uphill diffusion of these elements had occurred. We show using a kinetic model for substitutional diffusion via vacancy hopping that such uphill diffusion can occur even in the absence of thermodynamic interactions, i.e. in ideal solid solutions in which the thermodynamic factor Φ of each element is equal to one (Φi=1+∂lnfi/∂lnci where fi and ci are the activity coefficient and mole fraction of element i, respectively). The model accounts for all elemental fluxes and also rationalizes the diffusion profiles of the major interdiffusing elements. © 2020
    view abstractdoi: 10.1016/j.intermet.2020.106789
  • 2020 • 644 Microscopic model for the stacking-fault potential and the exciton wave function in GaAs
    Durnev, M.V. and Glazov, M.M. and Linpeng, X. and Viitaniemi, M.L.K. and Matthews, B. and Spurgeon, S.R. and Sushko, P.V. and Wieck, A.D. and Ludwig, Ar. and Fu, K.-M.C.
    Physical Review B 101 (2020)
    Two-dimensional stacking fault defects embedded in a bulk crystal can provide a homogeneous trapping potential for carriers and excitons. Here we utilize state-of-The-Art structural imaging coupled with density-functional and effective-mass theory to build a microscopic model of the stacking-fault exciton. The diamagnetic shift and exciton dipole moment at different magnetic fields are calculated and compared with the experimental photoluminescence of excitons bound to a single stacking fault in GaAs. The model is used to further provide insight into the properties of excitons bound to the double-well potential formed by stacking fault pairs. This microscopic exciton model can be used as an input into models which include exciton-exciton interactions to determine the excitonic phases accessible in this system. © 2020 American Physical Society.
    view abstractdoi: 10.1103/PhysRevB.101.125420
  • 2020 • 643 Phonons in magnetically disordered materials: Magnetic versus phononic time scales
    Dutta, B. and Körmann, F. and Ghosh, S. and Sanyal, B. and Neugebauer, J. and Hickel, T.
    Physical Review B 101 (2020)
    The lattice dynamics in magnetic materials, such as Fe depends on the degree of disorder of the atomic magnetic moments and the time scale of spin fluctuations. Using first-principles methods, we have studied this effect by determining the force constant matrix in two limits: (i) When spin fluctuations are much faster than the atom vibrations, their combined impact is captured by a spin-space averaged force constant matrix, (ii) when individual spin fluctuations are sufficiently slow to scatter the phonon modes, the itinerant coherent potential approximation with spin-pair resolved force constants (i.e., φ↑↑,φ↓↓, and φ↑↓) is employed in this paper. The physical consequences for the vibrational spectral functions are analyzed by systematically modifying the input parameters (magnetization and ratio of force constants betweens atoms with equal and opposite spin directions) and by deriving them for the prototype material system bcc Fe from first-principles calculations. In the paramagnetic regime, the two limits yield identical phonon spectra. Below the Curie temperature, however, there are regions in the parametric study that show qualitative differences, including a broadening of the phonon peaks. For bcc Fe, however, the quantitative modifications of phonon frequencies turn out to be small. © 2020 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the 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. Open access publication funded by the Max Planck Society.
    view abstractdoi: 10.1103/PhysRevB.101.094201
  • 2020 • 642 Biocompatible magnetic fluids of co-doped iron oxide nanoparticles with tunable magnetic properties
    Dutz, S. and Buske, N. and Landers, J. and Gräfe, C. and Wende, H. and Clement, J.H.
    Nanomaterials 10 (2020)
    Magnetite (Fe3O4) particles with a diameter around 10 nm have a very low coercivity (Hc) and relative remnant magnetization (Mr/Ms), which is unfavorable for magnetic fluid hyperthermia. In contrast, cobalt ferrite (CoFe2O4) particles of the same size have a very high Hc and Mr/Ms, which is magnetically too hard to obtain suitable specific heating power (SHP) in hyperthermia. For the optimization of the magnetic properties, the Fe2+ ions of magnetite were substituted by Co2+ step by step, which results in a Co doped iron oxide inverse spinel with an adjustable Fe2+ substitution degree in the full range of pure iron oxide up to pure cobalt ferrite. The obtained magnetic nanoparticles were characterized regarding their structural and magnetic properties as well as their cell toxicity. The pure iron oxide particles showed an average size of 8 nm, which increased up to 12 nm for the cobalt ferrite. For ferrofluids containing the prepared particles, only a limited dependence of Hc and Mr/Ms on the Co content in the particles was found, which confirms a stable dispersion of the particles within the ferrofluid. For dry particles, a strong correlation between the Co content and the resulting Hc and Mr/Ms was detected. For small substitution degrees, only a slight increase in Hc was found for the increasing Co content, whereas for a substitution of more than 10% of the Fe atoms by Co, a strong linear increase in Hc and Mr/Ms was obtained. Mössbauer spectroscopy revealed predominantly Fe3+ in all samples, while also verifying an ordered magnetic structure with a low to moderate surface spin canting. Relative spectral areas of Mössbauer subspectra indicated a mainly random distribution of Co2+ ions rather than the more pronounced octahedral site-preference of bulk CoFe2O4. Cell vitality studies confirmed no increased toxicity of the Co-doped iron oxide nanoparticles compared to the pure iron oxide ones. Magnetic heating performance was confirmed to be a function of coercivity as well. The here presented non-toxic magnetic nanoparticle system enables the tuning of the magnetic properties of the particles without a remarkable change in particles size. The found heating performance is suitable for magnetic hyperthermia application. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/nano10061019
  • 2020 • 641 Tautomeric Equilibria of Nucleobases in the Hachimoji Expanded Genetic Alphabet
    Eberlein, L. and Beierlein, F.R. and Van Eikema Hommes, N.J.R. and Radadiya, A. and Heil, J. and Benner, S.A. and Clark, T. and Kast, S.M. and Richards, N.G.J.
    Journal of Chemical Theory and Computation 16 2766-2777 (2020)
    Evolution has yielded biopolymers that are constructed from exactly four building blocks and are able to support Darwinian evolution. Synthetic biology aims to extend this alphabet, and we recently showed that 8-letter (hachimoji) DNA can support rule-based information encoding. One source of replicative error in non-natural DNA-like systems, however, is the occurrence of alternative tautomeric forms, which pair differently. Unfortunately, little is known about how structural modifications impact free-energy differences between tautomers of the non-natural nucleobases used in the hachimoji expanded genetic alphabet. Determining experimental tautomer ratios is technically difficult, and so, strategies for improving hachimoji DNA replication efficiency will benefit from accurate computational predictions of equilibrium tautomeric ratios. We now report that high-level quantum-chemical calculations in aqueous solution by the embedded cluster reference interaction site model, benchmarked against free-energy molecular simulations for solvation thermodynamics, provide useful quantitative information on the tautomer ratios of both Watson-Crick and hachimoji nucleobases. In agreement with previous computational studies, all four Watson-Crick nucleobases adopt essentially only one tautomer in water. This is not the case, however, for non-natural nucleobases and their analogues. For example, although the enols of isoguanine and a series of related purines are not populated in water, these heterocycles possess N1-H and N3-H keto tautomers that are similar in energy, thereby adversely impacting accurate nucleobase pairing. These robust computational strategies offer a firm basis for improving experimental measurements of tautomeric ratios, which are currently limited to studying molecules that exist only as two tautomers in solution. Copyright © 2020 American Chemical Society.
    view abstractdoi: 10.1021/acs.jctc.9b01079
  • 2020 • 640 Electrical detection of excitonic states by time-resolved conductance measurements
    Ebler, C. and Labud, P.A. and Rai, A.K. and Reuter, D. and Wieck, A.D. and Ludwig, Ar.
    Physical Review B 101 (2020)
    We present time-resolved conductance measurements and charge spectra for the conduction-band states of InAs quantum dots after creating metastable holes by illumination. We demonstrate an electrical way of measuring the conduction-band energy offset and inverse tunnel rates of electrons from a two-dimensional electron gas into neutral (X0), single positively (X1+), and double positively (X2+) charged exciton states. The experiment also gives information about the metastable hole storage time and discharge dynamics. © 2020 American Physical Society.
    view abstractdoi: 10.1103/PhysRevB.101.125303
  • 2020 • 639 A fourth-order gauge-invariant gradient plasticity model for polycrystals based on Kröner’s incompatibility tensor
    Ebobisse, F. and Neff, P.
    Mathematics and Mechanics of Solids 25 129-159 (2020)
    In this paper we derive a novel fourth-order gauge-invariant phenomenological model of infinitesimal rate-independent gradient plasticity with isotropic hardening and Kröner’s incompatibility tensor inc(εp):=Curl[(Curl εp)T], where εp is the symmetric plastic strain tensor. Here, gauge-invariance denotes invariance under diffeomorphic reparametrizations of the reference configuration, suitably adapted to the geometrically linear setting. The model features a defect energy contribution that is quadratic in the tensor inc(εp) and it contains isotropic hardening based on the rate of the plastic strain tensor (Formula presented.). We motivate the new model by introducing a novel rotational invariance requirement in gradient plasticity, which we call micro-randomness, suitable for the description of polycrystalline aggregates on a mesoscopic scale and not coinciding with classical isotropy requirements. This new condition effectively reduces the increments of the non-symmetric plastic distortion (Formula presented.) to their symmetric counterpart (Formula presented.). In the polycrystalline case, this condition is a statement about insensitivity to arbitrary superposed grain rotations. We formulate a mathematical existence result for a suitably regularized non-gauge-invariant model. The regularized model is rather invariant under reparametrizations of the reference configuration including infinitesimal conformal mappings. © The Author(s) 2019.
    view abstractdoi: 10.1177/1081286519845026
  • 2020 • 638 Simultaneous analysis of light gases and heavy pyrolyzates evolved from lignite and hard coal by pyrolysis–GC/MS–GC/TCD
    Eckhard, T. and Wütscher, A. and Muhler, M.
    Journal of Analytical and Applied Pyrolysis 149 (2020)
    The pyrolysis of solid fossil fuels and biomass is of great relevance, because it influences the combustion kinetics of these fuels, and the pyrolysis products are potential raw materials for further chemical processing. The aim of this work was to develop a pyrolysis system able to separate the whole variety of pyrolysis products during one pyrolysis experiment without the need to replace GC columns for improved resolution. A conventional pyrolysis system equipped with a coupled gas chromatography (GC)/mass spectrometry (MS) detector was extended by a second GC with a fused-silica capillary column and a thermal conductivity detector (TCD). The coupled pyrolysis–GC/MS–GC/TCD system was used to investigate the evolved pyrolysis products of two lignites and a hard coal enabling the qualitative detection of pyrolyzates (GC/MS) while simultaneously quantifying the light gases (TCD). Benzofuran, catechol, and a preference for even-numbered hydrocarbon pyrolyzates in addition to a higher pristene/heptadecane ratio were found to be characteristic for the two studied German lignites in comparison to the Columbian hard coal as well as a higher release of especially oxygen-containing light gases. © 2020 Elsevier B.V.
    view abstractdoi: 10.1016/j.jaap.2020.104833
  • 2020 • 637 Use of poly(ethylene naphthalate) as a self-vetoing structural material
    Efremenko, Y. and Fajt, L. and Febbraro, M. and Fischer, F. and Guitart, M. and Hackett, B. and Hayward, C. and Hodák, R. and Majorovits, B. and Manzanillas, L. and Muenstermann, D. and Oz, E. and Pjatkan, R. and Pohl, M. and Rad...
    Journal of Physics: Conference Series 1468 (2020)
    Poly(ethylene naphthalate), PEN, is an industrial polyester which has been shown to scintillate in the blue wavelength region. Combined with measurements of a high intrinsic radiopurity, this has sparked interest in the material for use in low-background experiments. © 2020 Published under licence by IOP Publishing Ltd.
    view abstractdoi: 10.1088/1742-6596/1468/1/012225
  • 2020 • 636 A Computational Approach to the Microstructural Design of High-Speed Steels
    Egels, G. and Wulbieter, N. and Weber, S. and Theisen, W.
    Steel Research International 91 (2020)
    Increasing requirements concerning the operational conditions and durability of tools create a demand for the optimization of tool steels. High-speed steels (HSSs), for example, contain high amounts of carbides embedded in a secondary hardenable martensitic matrix. The wear behavior and the mechanical properties of HSS can be optimized for a certain application by adjusting the type and amount of carbides, as well as their compositions and the composition of the matrix. Computational thermodynamics based on the calculation of phase diagrams method allow the estimation of arising phases as well as phase compositions during the solidification or the heat treatment of a steel. However, in complex alloy systems, for example, HSS, the relationships between the content of alloying elements and the stability and the composition of phases can be complicated and nonlinear. Therefore, it can be difficult to find alloy compositions that are suitable to achieve a desired microstructure with iterative calculations. To handle this difficulty, a computational tool is developed, which determines compositions to obtain predefined HSS microstructures. The computational tool is based on a neural network that was previously trained with a thermodynamically calculated database. The efficiency of this approach is experimentally verified by producing and investigating laboratory melts of different HSS. © 2019 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/srin.201900455
  • 2020 • 635 Interface-related magnetic and vibrational properties in Fe/MgO heterostructures from nuclear resonant spectroscopy and first-principles calculations
    Eggert, B. and Gruner, M.E. and Ollefs, K. and Schuster, E. and Rothenbach, N. and Hu, M.Y. and Zhao, J. and Toellner, T.S. and Sturhahn, W. and Pentcheva, R. and Cuenya, B.R. and Alp, E.E. and Wende, H. and Keune, W.
    Physical Review Materials 4 (2020)
    We combine Fe57 Mössbauer spectroscopy and Fe57 nuclear resonant inelastic x-ray scattering (NRIXS) on nanoscale polycrystalline [bcc-Fe57/MgO] multilayers with various Fe-layer thicknesses and layer-resolved density-functional-theory (DFT)-based first-principles calculations of a (001)-oriented [Fe(8 ML)/MgO(8 ML)](001) heterostructure (where ML denotes monolayer) to unravel the interface-related atomic vibrational properties of a multilayer system. Being consistent in theory and experiment, we observe enhanced hyperfine magnetic fields Bhf in the multilayers as compared to Bhf in bulk bcc Fe; this effect is associated with the Fe/MgO interface layers. NRIXS and DFT both reveal a strong reduction of the longitudinal acoustic phonon peak in combination with an enhancement of the low-energy vibrational density of states (VDOS) suggesting that the presence of interfaces and the associated increase in the layer-resolved magnetic moments results in drastic changes in the Fe-partial VDOS. From the experimental and calculated VDOS, vibrational thermodynamic properties have been determined as a function of Fe thickness and were found to be in excellent agreement. © 2020 American Physical Society.
    view abstractdoi: 10.1103/PhysRevMaterials.4.044402
  • 2020 • 634 Magnetic response of FeRh to static and dynamic disorder
    Eggert, B. and Schmeink, A. and Lill, J. and Liedke, M.O. and Kentsch, U. and Butterling, M. and Wagner, A. and Pascarelli, S. and Potzger, K. and Lindner, J. and Thomson, T. and Fassbender, J. and Ollefs, K. and Keune, W. and Bal...
    RSC Advances 10 14386-14395 (2020)
    Atomic scale defects generated using focused ion as well as laser beams can activate ferromagnetism in initially non-ferromagnetic B2 ordered alloy thin film templates. Such defects can be induced locally, confining the ferromagnetic objects within well-defined nanoscale regions. The characterization of these atomic scale defects is challenging, and the mechanism for the emergence of ferromagnetism due to sensitive lattice disordering is unclear. Here we directly probe a variety of microscopic defects in systematically disordered B2 FeRh thin films that are initially antiferromagnetic and undergo a thermally-driven isostructural phase transition to a volatile ferromagnetic state. We show that the presence of static disorder i.e., the slight deviations of atoms from their equilibrium sites is sufficient to induce a non-volatile ferromagnetic state at room temperature. A static mean square relative displacement of 9 × 10-4 Å-2 is associated with the occurrence of non-volatile ferromagnetism and replicates a snapshot of the dynamic disorder observed in the thermally-driven ferromagnetic state. The equivalence of static and dynamic disorder with respect to the ferromagnetic behavior can provide insights into the emergence of ferromagnetic coupling as well as achieving tunable magnetic properties through defect manipulations in alloys. This journal is © The Royal Society of Chemistry.
    view abstractdoi: 10.1039/d0ra01410a
  • 2020 • 633 Inelastic electron tunneling spectroscopy for probing strongly correlated many-body systems by scanning tunneling microscopy
    Eickhoff, F. and Kolodzeiski, E. and Esat, T. and Fournier, N. and Wagner, C. and Deilmann, T. and Temirov, R. and Rohlfing, M. and Tautz, F.S. and Anders, F.B.
    Physical Review B 101 (2020)
    We present an extension of the tunneling theory for scanning tunneling microscopy (STM) to include different types of electron-vibrational couplings responsible for inelastic contributions to the tunnel current in the strong-coupling limit. It allows for a better understanding of more complex scanning tunneling spectra of molecules on a metallic substrate in separating elastic and inelastic contributions. The starting point is the exact solution of the spectral functions for the electronically active local orbitals in the absence of the STM tip. This includes electron-phonon coupling in the coupled system comprising the molecule and the substrate to arbitrary order including the antiadiabatic strong-coupling regime as well as the Kondo effect on a free-electron spin of the molecule. The tunneling current is derived in second order of the tunneling matrix element which is expanded in powers of the relevant vibrational displacements. We use the results of an ab initio calculation for the single-particle electronic properties as an adapted material-specific input for a numerical renormalization group approach for accurately determining the electronic properties of a 1,4,5,8-naphthalene-Tetracarboxylic acid dianhydride molecule on Ag(111) as a challenging sample system for our theory. Our analysis shows that the mismatch between the ab initio many-body calculation of the tunnel current in the absence of any electron-phonon coupling to the experimental scanning tunneling spectra can be resolved by including two mechanisms: (i) a strong unconventional Holstein term on the local substrate orbital leads to the reduction of the Kondo temperature and (ii) a further electron-vibrational coupling to the tunneling matrix element is responsible for inelastic steps in the dI/dV curve at finite frequencies. © 2020 American Physical Society.
    view abstractdoi: 10.1103/PhysRevB.101.125405
  • 2020 • 632 Studies on ultra-short pulsed laser shock peening of stainless-steel in different confinement media
    Elango, K. and Hoppius, J.S. and Kukreja, L.M. and Ostendorf, A. and Gurevich, E.L.
    Surface and Coatings Technology 397 (2020)
    We investigate the role of liquid confinement media on ultra-short pulsed Laser Shock Peening (LSP). The LSP of stainless-steel 316 and 316 L was studied using Ti: Sapphire laser pulses of about 2 ps duration, maximum energy of about 1 mJ and pulse repetition rate of 5 kHz in different liquid confinement media of Ethanol, Deionized water and separate aqueous solutions of NaCl and Glycerol. It is found that the laser fluence and/or energy attenuating mechanisms like self-focusing, filamentation, plasma breakdown in the confinement media are less significant with ps laser pulses than those with sub-ps or fs pulse durations. It is shown that the resulting surface hardness of the peened steel as a function of laser fluence depends significantly on the confinement media and the relative increase in the hardness increases monotonically with the acoustic impedance of the liquid of the confinement medium used during LSP. © 2020 Elsevier B.V.
    view abstractdoi: 10.1016/j.surfcoat.2020.125988
  • 2020 • 631 Pressure stability of the first hydration shell of yttrium in aqueous YCl3 solution
    Elbers, M. and Sternemann, C. and Julius, K. and Paulus, M. and Surmeier, G. and König, N. and Nase, J. and Bolle, J. and Wagner, R. and Irifune, T. and Tolan, M.
    High Pressure Research (2020)
    The pressure stability of the first hydration shell of Y3+ ions in aqueous solution has been investigated by means of extended x-ray absorption fine-structure spectroscopy at the yttrium K-edge for hydrostatic pressures up to 4.5 kbar and concentrations between 1 M and 2.5 M. We find approximately 8.4 water molecules surrounding the yttrium cation at a mean distance of 2.370 Å at ambient conditions, independent on the concentration. The yttrium hydration shell has a low compressibility in the order of (-3.8 ± 0.7)×10-4 Å kbar-1 emphasizing its pressure stability in the kbar range. At the studied conditions, no indication for chloride complexation was observed. © 2020, © 2020 Informa UK Limited, trading as Taylor & Francis Group.
    view abstractdoi: 10.1080/08957959.2020.1724998
  • 2020 • 630 Tailored CNTs buckypaper membranes for the removal of humic acid and separation of oil-in- water emulsions
    Elnabawy, E. and Elsherbiny, I.M.A. and Abdelsamad, A.M.A. and Anis, B. and Hassan, A. and Ulbricht, M. and Khalil, A.S.G.
    Membranes 10 (2020)
    Carbon nanotubes (CNTs) are a robust material and proven as a promising candidate for a wide range of electronic, optoelectronic and environmental applications. In this work, two different methods were utilized for the preparation of CNTs exhibiting different aspect ratios via chemical vapor deposition (CVD). The as-prepared CNTs were analyzed using scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2 adsorption isotherms, thermogravimetric analysis and Raman spectroscopy in order to investigate their morphological and structural properties. Free-standing CNTs “buckypaper” membranes were fabricated, characterized and tailored to meet the requirements of two applications, i.e., (1) the removal of humic acid (HA) from water and (2) separation of oil-in-water emulsions. It was revealed that the hydrophobic buckypapers showed high separation performance for Shell oil-in-water emulsions filtration, with up to 98% through the accumulation of oil droplets onto the membrane surface. The absorption capacity of buckypaper membranes for various organic liquids (oil, chloroform and toluene) was evaluated over 10 absorption cycles to investigate their recyclability and robustness. Moreover, surface modification was introduced to the pristine CNTs to increase their surface hydrophilicity and improve the pure water permeability of buckypapers. These modified buckypapers showed high flux for HA solutions and excellent HA rejection efficiency up to 95%via size exclusion and electrostatic repulsion mechanisms. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/membranes10050097
  • 2020 • 629 ConvNet Transfer Learning for GPR Images Classification
    Elsaadouny, M. and Barowski, J. and Rolfes, I.
    GeMIC 2020 - Proceedings of the 2020 German Microwave Conference 21-24 (2020)
    The ground penetrating radar (GPR) is an important tool for detecting and defining buried objects. One of the main problems facing this method is the high probability of false alarms, therefor proper signal processing has to be considered. In this paper, the matched filter algorithm has been implemented to process the GPR data. After processing the data and detecting the underground reflections, further processing is mandatory to classify these reflections, therefore, a convolutional neural network (ConvNet) is presented for classifying these responses. The ConvNets are considered as the best artificial intelligence algorithms for image classification problems. Generally, a ConvNet requires a very large number of images to be trained well and to achieve the best results. To overcome the problem of having a limited amount of the GPR data, the ConvNet has been trained on another popular dataset, which is the Fashion-MNIST, and then transfer learning is applied to use the learned features of the network with the limited GPR dataset. The network performance has been monitored and the classification results show a high degree of precision and accuracy. © 2020 IMA-Institut fur Mikrowellen-und Antennentechnik e.V.
    view abstract
  • 2020 • 628 Selective Hydrogenation of Benzofurans Using Ruthenium Nanoparticles in Lewis Acid-Modified Ruthenium-Supported Ionic Liquid Phases
    El Sayed, S. and Bordet, A. and Weidenthaler, C. and Hetaba, W. and Luska, K.L. and Leitner, W.
    ACS Catalysis 10 2124-2130 (2020)
    Ruthenium nanoparticles immobilized on a Lewis-acid-functionalized supported ionic liquid phase (Ru@SILP-LA) act as effective catalysts for the selective hydrogenation of benzofuran derivatives to dihydrobenzofurans. The individual components (nanoparticles, chlorozincate-based Lewis-acid, ionic liquid, support) of the catalytic system are assembled using a molecular approach to bring metal and acid sites in close contact on the support material, allowing the hydrogenation of O-containing heteroaromatic rings while keeping the aromaticity of C6-rings intact. The chlorozincate species were identified to be predominantly [ZnCl4]2- anions using X-ray photoelectron spectroscopy and are in close interaction with the metal nanoparticles. The Ru@SILP-[ZnCl4]2- catalyst exhibited high activity, selectivity, and stability for the catalytic hydrogenation of a variety of substituted benzofurans, providing easy access to biologically relevant dihydrobenzofuran motifs under continuous flow conditions. Copyright © 2020 American Chemical Society.
    view abstractdoi: 10.1021/acscatal.9b05124
  • 2020 • 627 Thermal fatigue behavior of functionally graded W/EUROFER-layer systems using a new test apparatus
    Emmerich, T. and Vaßen, R. and Aktaa, J.
    Fusion Engineering and Design 154 (2020)
    In future fusion reactors tungsten coatings shall protect First Wall components, made of reduced activation ferritic martensitic steel, against the plasma, because of tungsten's favourable thermo-mechanical properties and low sputtering yield. Functionally graded material layers implemented between the coating and the steel substrate, compensate the difference in the coefficient of thermal expansion. By using the vacuum plasma spraying technique several layer systems were successfully produced and tested, among other aspects, in regard to their thermal fatigue behaviour up to 500 thermal cycles in a vacuum furnace. However, higher numbers of thermal cycles are anticipated for future fusion reactors and, therefore, a less time consuming approach for thermal fatigue testing is required. Hence, a new testing apparatus with induction heating and inert gas cooling was built and first thermal fatigue experiments with up to 5000 cycles were carried out on different functionally graded tungsten/steel layers systems. The subsequent investigations of these samples show that the layer systems are stable for the applied number of thermal cycles and their properties are solely determined during their respective coating processes. © 2020
    view abstractdoi: 10.1016/j.fusengdes.2020.111550
  • 2020 • 626 What drives stocks during the corona-crash? News attention vs. rational expectation
    Engelhardt, N. and Krause, M. and Neukirchen, D. and Posch, P.
    Sustainability (Switzerland) 12 (2020)
    We explore if the corona-crash 2020 was driven by news attention or rational expectations about the pandemic's economic impact. Using a sample of 64 national stock markets covering 94% of the world's GDP, we find the stock markets' decline to be mainly associated with higher news attention and less with rational expectation. We estimate the economic cost from the news hype to amount to USD 3.5 trillion for the US and USD 200 billion on average for the rest of the G8 countries. © 2020 by the authors.
    view abstractdoi: 10.3390/su12125014
  • 2020 • 625 Diffusion, defects and understanding the growth of a multicomponent interdiffusion zone between Pt-modified B2 NiAl bond coat and single crystal superalloy
    Esakkiraja, N. and Gupta, A. and Jayaram, V. and Hickel, T. and Divinski, S.V. and Paul, A.
    Acta Materialia 195 35-49 (2020)
    Composition-dependent diffusion coefficients are determined in B2-Ni(CoPt)Al system following the pseudo-binary and pseudo-ternary diffusion couple methods, which would not be possible otherwise in a quaternary inhomogeneous material fulfilling the conditions to solve the equations developed based on the Onsager formalism. The end-member compositions to produce ideal/near-ideal diffusion profiles are chosen based on thermodynamic details. The pseudo-binary interdiffusion coefficients of Ni and Al decrease in the presence of Co but increase in the presence of Pt. The pseudo-ternary interdiffusion coefficients indicate that the main interdiffusion coefficients increase significantly in the presence of Pt. Marginal changes of the cross interdiffusion coefficients substantiate a minor change of the diffusional interactions between the components. The thermodynamic driving forces show opposite trends with respect to composition as compared to the changes of the interdiffusion coefficients advocating a dominating role of the Pt(Co)-induced modifications of point defect concentrations. DFT-based calculations revealed that Pt alloying increases the Ni vacancy concentration and decreases the activation energy for the triple defect diffusion mechanism. These findings explain the increase in the thickness of the interdiffusion zone between the B2-Ni(Pt)Al bond coat and the single crystal superalloy René N5 because of Pt addition. Furthermore, the EPMA and TEM analyses reveal the growth of refractory elements-enriched precipitates. © 2020 Acta Materialia Inc.
    view abstractdoi: 10.1016/j.actamat.2020.04.016
  • 2020 • 624 Fabrication of a novel and highly selective ion-imprinted PES-based porous adsorber membrane for the removal of mercury(II) from water
    Esmali, F. and Mansourpanah, Y. and Farhadi, K. and Amani, S. and Rasoulifard, A. and Ulbricht, M.
    Separation and Purification Technology 250 (2020)
    Herein, poly(ether sulfone) based ion imprinted membranes (IIM) were prepared through phase inversion, using ion imprinted polymer (IIP) particles obtained by radical copolymerization of acrylamide, acrylonitrile and ethyleneglycoldimethacrylate along with a template of Hg(II) complexed with bathophenanthroline (BPh). Optimization of the ability for Hg(II) removal from water and pure water flux of the IIM were investigated through Central Composite Design (CCD) combined with Response Surface Methodology (RSM). Accordingly, the optimized factors were obtained as IIP percentage of 2.5 wt% used in membrane preparation, as well as trans-membrane pressure of 0.19 bar, pH 7.95 and Hg(II) concentration of 4 ppm during filtration through the membrane. Using the optimum parameters, the removal percentage and flux of IIM were about 98.1% and 37.5 kg/m2 h, respectively. The maximum adsorption capacity of IIM was 432 mg/m2 (or 21.6 mg/g), almost four times higher than that of non-imprinted membrane (NIM; 105 mg/m2) (or 5.25 mg/g) which was prepared using copolymer particles prepared without the Hg(II) template. The IIM showed a high selectivity toward Hg(II) ions compared to other metal ions and could be effectively recycled for at least 6 times without any major loss of adsorption capacity. The synthesized imprinted membranes have demonstrated considerable potentials to selectively separate mercury(II) from simulated industrial wastewater. © 2020 Elsevier B.V.
    view abstractdoi: 10.1016/j.seppur.2020.117183
  • 2020 • 623 Temperature-independent giant dielectric response in transitional BaTiO3 thin films
    Everhardt, A.S. and Denneulin, T. and Grünebohm, A. and Shao, Y.-T. and Ondrejkovic, P. and Zhou, S. and Domingo, N. and Catalan, G. and Hlinka, J. and Zuo, J.-M. and Matzen, S. and Noheda, B.
    Applied Physics Reviews 7 (2020)
    Ferroelectric materials exhibit the largest dielectric permittivities and piezoelectric responses in nature, making them invaluable in applications from supercapacitors or sensors to actuators or electromechanical transducers. The origin of this behavior is their proximity to phase transitions. However, the largest possible responses are most often not utilized due to the impracticality of using temperature as a control parameter and to operate at phase transitions. This has motivated the design of solid solutions with morphotropic phase boundaries between different polar phases that are tuned by composition and that are weakly dependent on temperature. Thus far, the best piezoelectrics have been achieved in materials with intermediate (bridging or adaptive) phases. But so far, complex chemistry or an intricate microstructure has been required to achieve temperature-independent phase-transition boundaries. Here, we report such a temperature-independent bridging state in thin films of chemically simple BaTiO3. A coexistence among tetragonal, orthorhombic, and their bridging low-symmetry phases are shown to induce continuous vertical polarization rotation, which recreates a smear in-transition state and leads to a giant temperature-independent dielectric response. The current material contains a ferroelectric state that is distinct from those at morphotropic phase boundaries and cannot be considered as ferroelectric crystals. We believe that other materials can be engineered in a similar way to contain a ferroelectric state with gradual change of structure, forming a class of transitional ferroelectrics. Similar mechanisms could be utilized in other materials to design low-power ferroelectrics, piezoelectrics, dielectrics, or shape-memory alloys, as well as efficient electro- and magnetocalorics. © 2020 Author(s).
    view abstractdoi: 10.1063/1.5122954
  • 2020 • 622 Electronic structure based design of thin film metallic glasses with superior fracture toughness
    Evertz, S. and Kirchlechner, I. and Soler, R. and Kirchlechner, C. and Kontis, P. and Bednarcik, J. and Gault, B. and Dehm, G. and Raabe, D. and Schneider, J.M.
    Materials and Design 186 (2020)
    High fracture toughness is crucial for the application of metallic glasses as structural materials to avoid catastrophic failure of the material in a brittle manner. One fingerprint for fracture toughness in metallic glasses is the fraction of hybridized bonds, which is affected by alloying Pd57.4Al23.5Y7.8M11.3 with M = Fe, Ni, Co, Cu, Os, Ir, Pt, and Au. It is shown that experimental fracture toughness data is correlated to the fraction of hybridized bonds which scale with the localized bonds at the Fermi level. Thus, the localized bonds at the Fermi level are utilized quantitatively as a measure for fracture toughness. Based on ab initio calculations, the minimum fraction of hybridized bonds was identified for Pd57.4Al23.5Y7.8Ni11.3. According to the ansatz that the crystal orbital overlap population at the Fermi level scales with fracture toughness, for Pd57.4Al23.5Y7.8Ni11.3 a value of around 95 ± 20 MPa·m0.5 is predicted quantitatively for the first time. Consistent with this prediction, in micro-mechanical beam bending experiments Pd57.4Al23.5Y7.8Ni11.3 thin films show pronounced plasticity and absence of crack growth. © 2018 The Authors
    view abstractdoi: 10.1016/j.matdes.2019.108327
  • 2020 • 621 Review on Quantum Mechanically Guided Design of Ultra-Strong Metallic Glasses
    Evertz, S. and Schnabel, V. and Köhler, M. and Kirchlechner, I. and Kontis, P. and Chen, Y.-T. and Soler, R. and Jaya, B.N. and Kirchlechner, C. and Music, D. and Gault, B. and Schneider, J.M. and Raabe, D. and Dehm, G.
    Frontiers in Materials 7 (2020)
    Quantum mechanically guided materials design has been used to predict the mechanical property trends in crystalline materials. Thereby, the identification of composition-structure-property relationships is enabled. However, quantum mechanics based design guidelines and material selection criteria for ultra-strong metallic glasses have been lacking. Hence, based on an ab initio model for metallic glasses in conjunction with an experimental high-throughput methodology geared toward revealing the relationship between chemistry, topology and mechanical properties, we propose principles for the design of tough as well as stiff metallic glasses. The main design notion is that a low fraction of hybridized bonds compared to the overall bonding in a metallic glass can be used as a criterion for the identification of damage-tolerant metallic glass systems. To enhance the stiffness of metallic glasses, the bond energy density must be increased as the bond energy density is the origin of stiffness in metallic glasses. The thermal expansion, which is an important glass-forming identifier, can be predicted based on the Debye-Grüneisen model. © Copyright © 2020 Evertz, Schnabel, Köhler, Kirchlechner, Kontis, Chen, Soler, Jaya, Kirchlechner, Music, Gault, Schneider, Raabe and Dehm.
    view abstractdoi: 10.3389/fmats.2020.00089
  • 2020 • 620 Hydrodynamic optimisation of a multi-purpose wind offshore supply vessel
    Feng, Y. and Moctar, O.E. and Schellin, T.E.
    Ship Technology Research 67 69-83 (2020)
    The aim of this study was to reduce the total resistance of a multi-purpose wind offshore supply vessel by optimising its hull. Resistance was computed using a potential flow boundary element method and a Reynolds-averaged Navier–Stokes equations solver. Optimised hull forms were obtained for the ship advancing at different ship speeds under calm water conditions, employing the two multi-objective optimisation algorithms, Non-dominated Sorting Genetic Algorithm II (NSGA-II) and Multi-Objective Simulated Annealing (MOSA). Using NSGA-II yielded slightly larger reductions of total resistances than MOSA. The greatest reductions were achieved at ship speeds between 11 and 14knots. At these speeds, a thinner and longer bulbous bow reduced resistance. At speeds greater than 15knots, a bloated bulbous bow was more helpful to reduce resistance. © 2019, © University of Duisburg-Essen 2019.
    view abstractdoi: 10.1080/09377255.2019.1602976
  • 2020 • 619 Exchange bias effect in bulk multiferroic BiFe0.5Sc0.5O3
    Fertman, E.L. and Fedorchenko, A.V. and Desnenko, V.A. and Shvartsman, V.V. and Lupascu, D.C. and Salamon, S. and Wende, H. and Vaisburd, A.I. and Stanulis, A. and Ramanauskas, R. and Olekhnovich, N.M. and Pushkarev, A.V. and Rady...
    AIP Advances 10 (2020)
    Below the Néel temperature, TN ∼220 K, at least two nano-scale antiferromagnetic (AFM) phases coexist in the polar polymorph of the BiFe0.5Sc0.5O3 perovskite; one of these phases is a weak ferromagnetic. Non-uniform structure distortions induced by high-pressure synthesis lead to competing AFM orders and a nano-scale spontaneous magnetic phase separated state of the compound. Interface exchange coupling between the AFM domains and the weak ferromagnetic domains causes unidirectional anisotropy of magnetization, resulting in the exchange bias (EB) effect. The EB field, HEB, and the coercive field strongly depend on temperature and the strength of the cooling magnetic field. HEB increases with an increase in the cooling magnetic field and reaches a maximum value of about 1 kOe at 5 K. The exchange field vanishes above TN with the disappearance of long-range magnetic ordering. The effect is promising for applications in electronics as it is large enough and as it is tunable by temperature and the magnetic field applied during cooling. © 2020 Author(s).
    view abstractdoi: 10.1063/1.5135586
  • 2020 • 618 Slicing parameter optimization for 3D printing of biodegradable drug-eluting tracheal stents
    Feuerbach, T. and Kock, S. and Thommes, M.
    Pharmaceutical Development and Technology 25 650-658 (2020)
    In 3D printing, the schematic representation of an object must be converted into machine commands. This process is called slicing. Depending on the slicing parameters, products with different properties are obtained. In this work, biodegradable drug-eluting tracheal stents consisting of a medical grade poly(lactic-co-glycolic acid) and a drug were printed by fused deposition modeling. A slicing parameter optimization method was proposed with the aim of obtaining a particularly low stent porosity and high mechanical strength while maintaining the stent dimensions, which is essential regarding patient-tailored implants. Depending on the three slicing parameters printing pattern, lateral strand distance and spatial fill, porosities of approximately 2–5% were obtained. The tensile strength was used as a measure for the mechanical strength of the implants and was found to be dependent on the porosity as well as the strand orientation relative to the load direction. Strand orientations in load direction yielded the highest tensile strengths of 40–46 MPa and the bonding between individual layers yielded the lowest tensile strengths of 20–24 MPa. In vitro dissolution tests of successfully printed stents were used to predict sustained release of the drug over several months. © 2020, © 2020 Informa UK Limited, trading as Taylor & Francis Group.
    view abstractdoi: 10.1080/10837450.2020.1727921
  • 2020 • 617 Second harmonic generation as a probe of broken mirror symmetry
    Fichera, B.T. and Kogar, A. and Ye, L. and Gökce, B. and Zong, A. and Checkelsky, J.G. and Gedik, N.
    Physical Review B 101 (2020)
    The notion of spontaneous symmetry breaking has been used to describe phase transitions in a variety of physical systems. In crystalline solids, the breaking of certain symmetries, such as mirror symmetry, is difficult to detect unambiguously. Using 1T-TaS2, we demonstrate here that rotational-anisotropy second harmonic generation (RA-SHG) is not only a sensitive technique for the detection of broken mirror symmetry, but also that it can differentiate between mirror symmetry-broken structures of opposite planar chirality. We also show that our analysis is applicable to a wide class of different materials with mirror symmetry-breaking transitions. Lastly, we find evidence for bulk mirror symmetry-breaking in the incommensurate charge density wave phase of 1T-TaS2. Our results pave the way for RA-SHG to probe candidate materials where broken mirror symmetry may play a pivotal role. © 2020 American Physical Society.
    view abstractdoi: 10.1103/PhysRevB.101.241106
  • 2020 • 616 Thermal Spray Processes for the Repair of Gas Turbine Components
    Fiebig, J. and Bakan, E. and Kalfhaus, T. and Mauer, G. and Guillon, O. and Vaßen, R.
    Advanced Engineering Materials 22 (2020)
    Gas turbine components are often operated in harsh conditions, which can lead to severe damage. As it is highly desirable from both an economical and an ecological point of view to restore these worn areas instead of manufacturing new components, repair technologies are of huge interest for companies supplying maintenance and overhaul of gas turbines. In this article, two thermal techniques are described that can be used for this application: cold gas spraying (CGS) and vacuum plasma spraying (VPS). The CGS process allows the deposition of metallic coatings with excellent mechanical properties; several examples including γ-TiAl, Inconel (IN) 718, and IN 738 are given. Essential for the deposition of high-performance coatings in CGS is to exceed the so-called critical velocity. This is discussed also with experimental findings. As a final topic, experiments that use VPS for the repair of single-crystal alloys are described. © 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/adem.201901237
  • 2020 • 615 A simple Peltier cold trap aperture for protection of vacuum UV optics against hydrocarbons and reliable calibration of VUV spectrometers using D2 lamps
    Fiebrandt, M. and Awakowicz, P.
    Measurement Science and Technology 31 (2020)
    A simple Peltier cooled cold trap aperture is presented to minimize the flux of hydrocarbons on optics in vacuum UV systems. The system can be cooled down to -40 °C under vacuum. To test the effect of the cold trap, the aperture is placed in front of a high-intensity D2 lamp used for calibration in the range of 116 nm to 300 nm which is flanged to a VUV spectrometer. The influence of the aperture temperature is monitored by measuring the intensity loss rate of the Lyman-alpha emission line at 121.6 nm due to the formation of carbon contamination on the MgF2 window of the lamp depending on the Peltier temperature. The application of the aperture significantly reduced the intensity loss from approx. 20% h-1 to less than 2% h-1 and enables the reliable use of a D2 lamp for the relative intensity calibration of the spectrometer. © 2020 IOP Publishing Ltd.
    view abstractdoi: 10.1088/1361-6501/ab7f7a
  • 2020 • 614 Determination of atomic oxygen state densities in a double inductively coupled plasma using optical emission and absorption spectroscopy and probe measurements
    Fiebrandt, M. and Bibinov, N. and Awakowicz, P.
    Plasma Sources Science and Technology 29 (2020)
    A collisional radiative model for fast estimation and monitoring of atomic oxygen ground and excited state densities and fluxes in varying Ar:O2 mixtures is developed and applied in a double inductively coupled plasma source at a pressure of 5 Pa and incident power of 500 W. The model takes into account measured line intensities of 130.4 nm, 135.6 nm, 557.7 nm, and 777.5 nm, the electron densities and electron energy distribution functions determined using a Langmuir probe and multipole resonance probe as well as the state densities of the first four excited states of argon measured with the branching fraction method and compared to tunable diode laser absorption spectroscopy. The influence of cascading and self absorption is included and the validity of the used cross sections and reaction rates is discussed in detail. The determined atomic oxygen state densities are discussed for their plausibility, sources of error, and compared to other measurements. Furthermore, the results of the model are analyzed to identify the application regimes of much simpler models, which could be used more easily for process control, e.g. actinometry. © 2020 The Author(s). Published by IOP Publishing Ltd.
    view abstractdoi: 10.1088/1361-6595/ab7cbe
  • 2020 • 613 Optimization of adhesively joined laser-sintered parts
    Fieger, T. and Nugara, D. and Huebner, J. and Witt, G.
    Solid Freeform Fabrication 2017: Proceedings of the 28th Annual International Solid Freeform Fabrication Symposium - An Additive Manufacturing Conference, SFF 2017 567-577 (2020)
    As additive manufacturing technologies are advancing in quality and economic feasibility, joining and assembly is becoming increasingly important for industrial users. In this study, the performance of four adhesives for polyamide 12 specimens is analyzed. Testing of bonding relevant factors, such as the surface energy of the solid substrates, is conducted. Tensile shear tests of plain polyamide 12 specimens glued together, show an early adhesive failure of the joint. To increase the polar bonding forces and the surface energy of the solid substrate, pretreatments such as atmospheric plasma, chemical, corona and flame treatment are applied. An increase up to 81% of the original binding strength can be achieved with flame treatment. As an alternative to increase the bonding strength of the joints, the effects of design changes of the bonding area are looked at. The research shows that micro tubes on the surface of a substrate can increase the bonding strength up to 49%. A summary of the impact of all pretreatments and design changes is given and the suitability of each application is assessed. Copyright © SFF 2017.All rights reserved.
    view abstract
  • 2020 • 612 Real-time prediction of process forces in milling operations using synchronized data fusion of simulation and sensor data
    Finkeldey, F. and Saadallah, A. and Wiederkehr, P. and Morik, K.
    Engineering Applications of Artificial Intelligence 94 (2020)
    To prevent undesirable effects during milling processes, online predictions of upcoming events can be used. Process simulations enable the capability to retrieve additional knowledge about the process, since their application allows the generation of data about characteristics, which cannot be measured during the process and can be incorporated as pre-calculated features into the analysis. Furthermore, sensor technologies were used as reasonable data sources for analyzing different monitoring scopes of milling processes. Machine learning-based models utilize data, acquired by various available data sources, to generate predictions of upcoming events in real-time. In this paper, we propose a novel approach for combining simulation data with sensor data to generate online predictions of process forces, which are influenced by tool wear, using an ensemble-based machine learning method. In addition, a methodology was developed in order to synchronize pre-calculated simulation data and streaming sensor measurements in real time. Milling experiments using ball-end milling tools with varying cutting speeds and tooth feeds showed the robustness of the approach in enhancing the prediction accuracy compared to only using one of each data source. © 2020 Elsevier Ltd
    view abstractdoi: 10.1016/j.engappai.2020.103753
  • 2020 • 611 Enhancing Electrogenerated Chemiluminescence on Platinum Electrodes through Surface Modification
    Fiorani, A. and Eßmann, V. and Santos, C.S. and Schuhmann, W.
    ChemElectroChem 7 1256-1260 (2020)
    Increasing the light emission of electrogenerated chemiluminescence is an important goal for enhancing the sensitivity for potential practical applications. Electrogenerated chemiluminescence is primarily triggered by a heterogeneous electron transfer reaction, for which the electrode material plays a pivotal role. We investigated how a platinum electrode, one of the most used but poorly efficient noble metal electrode materials in electrogenerated chemiluminescence, can be modified to enhance light emission. A polypyrrole layer was deposited on the platinum electrode through electrochemically induced polymerization, and subsequently pyrolyzed with the formation of a carbonaceous film. Electrochemiluminescence of the [Ru(bpy)3]2+/tri-n-propylamine system on such carbon film electrodes showed an enhancement of up to a 4 times increase, as compared with the bare platinum electrode. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
    view abstractdoi: 10.1002/celc.202000103
  • 2020 • 610 Impact of structural relaxation on mechanical properties of amorphous polymers
    Flügel, K. and Hennig, R. and Thommes, M.
    European Journal of Pharmaceutics and Biopharmaceutics 154 214-221 (2020)
    Fusion based methods, such as hot-melt extrusion, are a common way of preparing amorphous solid dispersions. Since the amorphous glass, however, is not in a configurational equilibrium, the molecular arrangement of the obtained material can differ in dependence of the preparation conditions. Although the changes in the configuration of an amorphous material, which are commonly referred to as structural relaxation or physical aging, are well investigated, the impact on mechanical properties of amorphous solid dispersions have widely been neglected so far. The presented study investigated copovidone as a model polymer commonly used in amorphous solid dispersions and revealed that structural relaxation was already introduced into the polymer during hot-melt extrusion while its degree was cooling rate dependent. The degree of structural relaxation significantly affected the mechanical properties of copovidone as assessed by diametral compression tests, macroindentation and nanoindentation. An increase in Young's modulus and indentation hardness was observable with a higher degree of structural relaxation, which, during tablet compression, translated into tablets with significantly lower tensile strength. Furthermore, evaluation of the force-displacement curves during tablet compression revealed a decreased proportion of irreversible deformation with higher degree of structural relaxation correlating well with the increased indentation hardness during macroindentation. Thus, understanding structural relaxation and its impact on material properties is of utmost importance to assess the processability and compaction performance of amorphous solid dispersions in dependence of their preparation conditions and thermal history. © 2020 Elsevier B.V.
    view abstractdoi: 10.1016/j.ejpb.2020.07.016
  • 2020 • 609 Bound-preserving flux limiting schemes for DG discretizations of conservation laws with applications to the Cahn–Hilliard equation
    Frank, F. and Rupp, A. and Kuzmin, D.
    Computer Methods in Applied Mechanics and Engineering 359 (2020)
    Many mathematical models of computational fluid dynamics involve transport of conserved quantities, which must lie in a certain range to be physically meaningful. The analytical or numerical solution [Formula presented] of a scalar conservation law is said to be bound-preserving if global bounds u∗ and u∗ exist such that [Formula presented] holds in the domain of definition. These bounds must be known a priori. To enforce such inequality constraints at least for element averages in the context of discontinuous Galerkin (DG) methods, the numerical fluxes must be defined and constrained in an appropriate manner. In this work, we introduce a general framework for calculating fluxes that produce non-oscillatory DG approximations and preserve relevant global bounds for element averages even if the analytical solution of the PDE violates them due to modeling errors. The proposed methodology is based on a combination of flux and slope limiting. The (optional) slope limiter adjusts the gradients to impose local bounds on pointwise values of the high-order DG solution, which is used to calculate the fluxes. The flux limiter constrains changes of element averages so as to prevent violations of global bounds. Since manipulations of the target flux may introduce a consistency error, it is essential to guarantee that physically admissible fluxes remain unchanged. We propose two kinds of flux limiters, which meet this requirement. The first one is of monolithic type and its time-implicit version requires the iterative solution of a nonlinear problem. Only a fully converged solution is provably bound-preserving. The time-explicit version of this limiter is subject to a time step restriction, which we derive in this article. The second limiter is an iterative version of the multidimensional flux-corrected transport (FCT) algorithm and works as postprocessed correction scheme. This fractional step limiting approach guarantees that each iterate is bound-preserving but avoidable consistency errors may occur if the iterative process is terminated too early. Each iterate depends only on local information of the previous iterate. This concept of limiting the numerical fluxes is also applicable to finite volume methods. Practical applicability of the proposed flux limiters as well as the benefits of using an optional slope limiter are demonstrated by numerical studies for the advection equation (hyperbolic, linear) and the Cahn–Hilliard equation (parabolic, nonlinear) for first-order polynomials. While both flux limiters work for arbitrary order polynomials, we discuss the construction of bound-preserving slope limiters, and show numerical studies only for first-order polynomials. © 2019 Elsevier B.V.
    view abstractdoi: 10.1016/j.cma.2019.112665
  • 2020 • 608 Image-based size analysis of agglomerated and partially sintered particles via convolutional neural networks
    Frei, M. and Kruis, F.E.
    Powder Technology 360 324-336 (2020)
    There is a high demand for fully automated methods for the analysis of primary particle size distributions of agglomerated, sintered or occluded primary particles, due to their impact on material properties. Therefore, a novel, deep learning-based, method for the detection of such primary particles was proposed and tested, which renders a manual tuning of analysis parameters unnecessary. As a specialty, the training of the utilized convolutional neural networks was carried out using only synthetic images, thereby avoiding the laborious task of manual annotation and increasing the ground truth quality. Nevertheless, the proposed method performs excellent on real world samples of sintered silica nanoparticles with various sintering degrees and varying image conditions. In a direct comparison, the proposed method clearly outperforms two state-of-the-art methods for automated image-based particle size analysis (Hough transformation and the ImageJ ParticleSizer plug-in), thereby attaining human-like performance. © 2019 Elsevier B.V.
    view abstractdoi: 10.1016/j.powtec.2019.10.020
  • 2020 • 607 Multilevel surrogate modeling approach for optimization problems with polymorphic uncertain parameters
    Freitag, S. and Edler, P. and Kremer, K. and Meschke, G.
    International Journal of Approximate Reasoning 119 81-91 (2020)
    The solution of optimization problems with polymorphic uncertain data requires combining stochastic and non-stochastic approaches. The concept of uncertain a priori parameters and uncertain design parameters quantified by random variables and intervals is presented in this paper. Multiple runs of the nonlinear finite element model solving the structural mechanics with varying a priori and design parameters are needed to obtain a solution by means of iterative optimization algorithms (e.g. particle swarm optimization). The combination of interval analysis and Monte Carlo simulation is required for each design to be optimized. This can only be realized by substituting the nonlinear finite element model by numerically efficient surrogate models. In this paper, a multilevel strategy for neural network based surrogate modeling is presented. The deterministic finite element simulation, the stochastic analysis as well as the interval analysis are approximated by sequentially trained artificial neural networks. The approach is verified and applied to optimize the concrete cover of a reinforced concrete structure, taking the variability of material parameters and the structural load as well as construction imprecision into account. © 2019 Elsevier Inc.
    view abstractdoi: 10.1016/j.ijar.2019.12.015
  • 2020 • 606 On the Importance of Structural and Functional Fatigue in Shape Memory Technology
    Frenzel, J.
    Shape Memory and Superelasticity (2020)
    The present work provides a brief overview on structural and functional fatigue in shape memory alloys (SMAs). Both degenerative processes are of utmost technological importance because they limit service lives of shape memory components. While our fundamental understanding of these two phenomena has improved during the last two decades, there are still fields which require scientific attention. NiTi SMAs are prone to the formation of small cracks, which nucleate and grow in the early stages of structural fatigue. It is important to find out how these micro-cracks evolve into engineering macro-cracks, which can be accounted for by conventional crack growth laws. The present work provides examples for the complexity of short crack growth in pseudoelastic SMAs. The importance of functional fatigue has also been highlighted. Functional fatigue is related to the degeneration of specific functional characteristics, such as actuator stroke, recoverable strain, plateau stresses, hysteresis width, or transformation temperatures. It is caused by the accumulation of transformation-induced defects in the microstructure. The functional stability of SMAs can be improved by (1) making phase transformations processes smoother and (2) by improving the material’s resistance to irreversible processes like dislocation plasticity. Areas in need of further research are discussed. © 2020, The Author(s).
    view abstractdoi: 10.1007/s40830-020-00281-3
  • 2020 • 605 Conductive films prepared from inks based on copper nanoparticles synthesized by transferred arc discharge
    Fu, Q. and Stein, M. and Li, W. and Zheng, J. and Kruis, F.E.
    Nanotechnology 31 (2020)
    Copper nanoparticles (NPs) are considered as a promising alternative for silver and gold NPs in conductive inks for the application of printing electronics, since copper shows a high electrical conductivity but is significantly cheaper than silver and gold. In this study, copper NPs were synthesized in the gas phase by transferred arc discharge, which has demonstrated scale-up potential. Depending on the production parameters, copper NPs can be continuously synthesized at a production rate of 1.2-5.5 g h-1, while their Brunauer-Emmett-Teller sizes were maintained below 100 nm. To investigate the suitability in electronic printing, we use ball milling technique to produce copper conductive inks. The effect of ball milling parameters on ink stability was discussed. In addition, the electrical resistivity of copper films sintered at 300 °C in reducing atmosphere was measured to be 5.4 ± 0.6 μΩ cm which is about three times higher than that of bulk copper (1.7 μΩ cm). This indicates that conductive inks prepared from gas-phase synthesized copper NPs are competitive to the conductive inks prepared from chemically synthesized copper NPs. © 2019 IOP Publishing Ltd.
    view abstractdoi: 10.1088/1361-6528/ab4524
  • 2020 • 604 Synergistic Effect of Molybdenum and Tungsten in Highly Mixed Carbide Nanoparticles as Effective Catalysts in the Hydrogen Evolution Reaction under Alkaline and Acidic Conditions
    Fu, Q. and Peng, B. and Masa, J. and Chen, Y.-T. and Xia, W. and Schuhmann, W. and Muhler, M.
    ChemElectroChem 7 983-988 (2020)
    Monometallic Mo and W carbides as well as highly mixed (Mo,W) carbides with various Mo/W ratios were synthesized directly on oxygen-functionalized carbon nanotubes (OCNTs), and used as noble-metal-free electrocatalysts in the hydrogen evolution reaction (HER) under both acidic and alkaline conditions. A purely orthorhombic structure was found in both monometallic and mixed carbide samples by X-ray diffraction. Transmission electron microscopy images showed that the carbide particles were highly dispersed on the OCNTs with well-controlled particle size. The homogeneous distribution of Mo and W in the carbides was confirmed by elemental mapping. (Mo,W)2C/OCNT with a Mo/W ratio of 3 : 1 showed the lowest overpotential to reach a current density of 10 mA/cm2 (87 mV in 0.1 M KOH and 92 mV in 0.5 M H2SO4), and the smallest Tafel slope of 34 mV/dec. Long-term stability under both alkaline and acidic conditions was demonstrated for 24 h. Our results revealed that an optimal amount of W in the mixed carbide can significantly improve its performance in the HER following the Tafel reaction pathway, most likely due to the weakened Mo−Hads bond. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
    view abstractdoi: 10.1002/celc.202000047
  • 2020 • 603 Walter Thiel (1949-2019)
    Fürstner, A. and List, B. and Ritter, T. and Schüth, F. and Neese, F.
    Angewandte Chemie (International ed. in English) 59 1382-1383 (2020)
    On August 23, 2019 Walter Thiel passed away suddenly and unexpectedly. Thiel was a giant in the field of Theoretical Chemistry and has left deep marks as an outstanding scientist and as a wonderful human being. With Walter Thiel, the scientific community has lost a visionary scientific leader and an important voice of reason. © 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/anie.201915463
  • 2020 • 602 A silicon–carbonyl complex stable at room temperature
    Ganesamoorthy, C. and Schoening, J. and Wölper, C. and Song, L. and Schreiner, P.R. and Schulz, S.
    Nature Chemistry 12 608-614 (2020)
    Main-group-element compounds with energetically high-lying donor and low-lying acceptor orbitals are able to mimic chemical bonding motifs and reactivity patterns known in transition metal chemistry, including small-molecule activation and catalytic reactions. Monovalent group 13 compounds and divalent group 14 compounds, particularly silylenes, have been shown to be excellent candidates for this purpose. However, one of the most common reactions of transition metal complexes, the direct reaction with carbon monoxide and formation of room-temperature isolable carbonyl complexes, is virtually unknown in main-group-element chemistry. Here, we show the synthesis, single-crystal X-ray structure, and density functional theory computations of a room-temperature-stable silylene carbonyl complex [L(Br)Ga]2Si:–CO (L = HC[C(Me)N(2,6-iPr2-C6H3)]2), which was obtained by direct carbonylation of the electron-rich silylene intermediate [L(Br)Ga]2Si:. Furthermore, [L(Br)Ga]2Si:–CO reacts with H2 and PBr3 with bond activation, whereas the reaction with cyclohexyl isocyanide proceeds with CO substitution. [Figure not available: see fulltext.] © 2020, The Author(s), under exclusive licence to Springer Nature Limited.
    view abstractdoi: 10.1038/s41557-020-0456-x
  • 2020 • 601 Influence of rafted microstructures on creep in Ni-base single crystal superalloys: A 3D discrete dislocation dynamics study
    Gao, S. and Ali, M.A. and Hartmaier, A.
    Modelling and Simulation in Materials Science and Engineering 28 (2020)
    Ni-base single-crystal superalloys exhibit a dynamic evolution of their microstructure during operation at elevated temperatures. The rafting of γ′ precipitates changes the mechanical behavior in a way that was understood insufficiently. In this work, we combine a phase-field method with a discrete dislocation dynamics model to clarify the influence of different rafted microstructures with the same initial dislocation density and configuration on creep behavior. The unrafted and rafted microstructures of Ni-base single crystal superalloys are simulated by a phase-field crystal plasticity method. By introducing these microstructures into a 3D discrete dislocation dynamics (DDD) model, the creep behavior under uniaxial loads of 350 and 250 MPa along [100] direction at 950 °C is studied. Due to the negative lattice mismatch of Ni-base superalloys, the N-type rafting with the formation of plate-like γ′ precipitates occurs under uniaxial tensile loads along {100} direction at high temperatures, while the P-type rafting with the formation of rod-like γ′ precipitates occurs under compressive loads. Taking the cuboidal, N-type rafted and P-type rafted microstructures as the initial and fixed microstructures for the same loading conditions, it is found from DDD simulations that the rafted microstructures result in smaller creep deformation than the cuboidal microstructure. The reason for this is that the coalescence of γ′ precipitates during the rafting diminishes the width of some γ channels, so as to increase the local Orowan stresses which retard the dislocation glide. For tensile loads, the N-type rafted microstructure has the best creep resistance. For a low compressive load, the P-type rafting shows a better creep resistance than N-type rafting. © 2019 IOP Publishing Ltd.
    view abstractdoi: 10.1088/1361-651X/ab5e40
  • 2020 • 600 Temperature-controlled magnetic nanoparticles hyperthermia inhibits primary tumor growth and metastases dissemination
    Garanina, A.S. and Naumenko, V.A. and Nikitin, A.A. and Myrovali, E. and Petukhova, A.Y. and Klimyuk, S.V. and Nalench, Y.A. and Ilyasov, A.R. and Vodopyanov, S.S. and Erofeev, A.S. and Gorelkin, P.V. and Angelakeris, M. and Savch...
    Nanomedicine: Nanotechnology, Biology, and Medicine 25 (2020)
    Magnetic hyperthermia (MHT) is a promising approach for cancer therapy. However, a systematic MHT characterization as function of temperature on the therapeutic efficiency is barely analyzed. Here, we first perform comparative temperature-dependent analysis of the cobalt ferrite nanoparticles-mediated MHT effectiveness in two murine tumors models – breast (4T1) and colon (CT26) cancer in vitro and in vivo. The overall MHT killing capacity in vitro increased with the temperature and CT26 cells were more sensitive than 4T1 when heated to 43 °C. Well in line with the in vitro data, such heating cured non-metastatic CT26 tumors in vivo, while only inhibiting metastatic 4T1 tumor growth without improving the overall survival. High-temperature MHT (>47 °C) resulted in complete 4T1 primary tumor clearance, 25–40% long-term survival rates, and, importantly, more effective prevention of metastasis comparing to surgical extraction. Thus, the specific MHT temperature must be defined for each tumor individually to ensure a successful antitumor therapy. © 2020 Elsevier Inc.
    view abstractdoi: 10.1016/j.nano.2020.102171
  • 2020 • 599 An: In situ SAXS investigation of the formation of silver nanoparticles and bimetallic silver-gold nanoparticles in controlled wet-chemical reduction synthesis
    Garcia, P.R.A.F. and Prymak, O. and Grasmik, V. and Pappert, K. and Wlysses, W. and Otubo, L. and Epple, M. and Oliveira, C.L.P.
    Nanoscale Advances 2 225-238 (2020)
    We present a study on the formation of silver (Ag) and bimetallic silver-gold (AgAu) nanoparticles monitored by in situ SAXS as well as by ex situ TEM, XRD and UV-vis analysis in a flow reactor at controlled reaction temperature. The formation mechanism of the nanoparticles is derived from the structural parameters obtained from the experimental data. The evolution of the average particle size of pure and alloyed nanoparticles shows that the particle growth occurs initially by a coalescence mechanism. The later growth of pure silver nanoparticles is well described by Ostwald ripening and for the alloyed nanoparticles by a process with a significantly slower growth rate. Additionally, the SAXS data of pure silver nanoparticles revealed two major populations of nanoparticles, the first one with a continuous crystal growth to a saturation plateau, and the second one probably with a continuous emergence of small new crystals. The particle sizes obtained by SAXS agree well with the results from transmission electron microscopy and X-ray diffraction. The present study demonstrates the capability of an in situ investigation of synthesis processes using a laboratory based SAXS instrument. Online monitoring of the synthesis permitted a detailed investigation of the structural evolution of the system. This journal is © The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c9na00569b
  • 2020 • 598 Prospects of Value-Added Chemicals and Hydrogen via Electrolysis
    Garlyyev, B. and Xue, S. and Fichtner, J. and Bandarenka, A.S. and Andronescu, C.
    ChemSusChem 13 2513-2521 (2020)
    Cost is a major drawback that limits the industrial-scale hydrogen production through water electrolysis. The overall cost of this technology can be decreased by coupling the electrosynthesis of value-added chemicals at the anode side with electrolytic hydrogen generation at the cathode. This Minireview provides a directory of anodic oxidation reactions that can be combined with cathodic hydrogen generation. The important parameters for selecting the anodic reactions, such as choice of catalyst material and its selectivity towards specific products are elaborated in detail. Furthermore, various novel electrolysis cell architectures for effortless separation of value-added products from hydrogen gas are described. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
    view abstractdoi: 10.1002/cssc.202000339
  • 2020 • 597 Simulation and optimization of the design of focusing dielectric lenses based on cartesian ovals with physical optics
    Garten, O. and Barowski, J. and Rolfes, I.
    2020 International Workshop on Antenna Technology, iWAT 2020 (2020)
    This paper presents the design of a focusing dielectric lens, which is described by a so-called Cartesian oval. The mathematical model of Cartesian ovals is introduced briefly. Next, a physical optics (PO) approach for the simulation of the electric field outside of the antenna is presented. Simulation results at 80 GHz are shown. The agreement between a full wave reference method and the proposed method is good, especially in the focal region. The simulation time is decreased significantly by the asymptotic PO approach compared to the finite integration technique. Eventually, a lens design is optimized with the PO to achieve the desired focal point. © 2020 IEEE.
    view abstractdoi: 10.1109/iWAT48004.2020.1570609732
  • 2020 • 596 Improved Adhesion of Different Environmental Barrier Coatings on Al2O3/Al2O3-Ceramic Matrix Composites
    Gatzen, C. and Mack, D.E. and Guillon, O. and Vaßen, R.
    Advanced Engineering Materials 22 (2020)
    In high-temperature combustion atmospheres, well-adhering environmental barrier coatings (EBCs) are required to protect the underlying ceramic matrix composites (CMCs) from corrosion. Herein the adhesion mechanisms of three different coatings produced by atmospheric plasma spraying (APS) on an Al2O3/Al2O3-CMC are investigated. In particular, the influence of surface structuring by laser ablation prior to coating production is investigated. Y2O3, yttria-stabilized zirconia (YSZ), and Gd2Zr2O7 are chosen as potential EBCs. The coating adhesion on CMC-substrates with and without surface structuring is analyzed by furnace cycling, pull-adhesion tests, and burner-rig tests with gradient. Special interest is paid to the interactions at the coating–substrate interface before and after heat treatment and their effect on the coating adhesion and lifetime. Two different adhesion mechanisms are found: adhesion promoted by chemical reaction and adhesion promoted by mechanical interlocking. © 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/adem.202000087
  • 2020 • 595 Electrostatic potential shape of gate-defined quantum point contacts
    Geier, M. and Freudenfeld, J. and Silva, J.T. and Umansky, V. and Reuter, D. and Wieck, A.D. and Brouwer, P.W. and Ludwig, S.
    Physical Review B 101 (2020)
    Quantum point contacts (QPCs) are fundamental building blocks of nanoelectronic circuits. For their emission dynamics as well as for interaction effects such as the 0.7 anomaly the details of the electrostatic potential are important, but the precise potential shapes are usually unknown. Here, we measure the one-dimensional subband spacings of various QPCs as a function of their conductance and compare our findings with models of lateral parabolic versus hard-wall confinement. We find that a gate-defined QPC near pinch-off is compatible with the parabolic saddle-point scenario. However, as the number of populated subbands is increased, Coulomb screening flattens the potential bottom and a description in terms of a finite hard-wall potential becomes more realistic. © 2020 American Physical Society.
    view abstractdoi: 10.1103/PhysRevB.101.165429
  • 2020 • 594 Competition of defect ordering and site disproportionation in strained LaCoO3 on SrTiO3 (001)
    Geisler, B. and Pentcheva, R.
    Physical Review B 101 (2020)
    The origin of the 3×1 reconstruction observed in epitaxial LaCoO3 films on SrTiO3(001) is assessed by first-principles calculations including a Coulomb repulsion term. We compile a phase diagram as a function of the oxygen pressure, which shows that (3×1)-ordered oxygen vacancies (LaCoO2.67) are favored under commonly used growth conditions, while stoichiometric films emerge under oxygen-rich conditions. Growth of further reduced LaCoO2.5 brownmillerite films is impeded by phase separation. We report two competing ground-state candidates for stoichiometric films: a semimetallic phase with 3×1 low-spin/intermediate-spin/intermediate-spin (LS/IS/IS) magnetic order and a semiconducting phase with IS/IS/IS magnetic order. This demonstrates that tensile strain induces ferromagnetism even in the absence of oxygen vacancies. Both phases exhibit an intriguing (3×1)-reconstructed octahedral rotation pattern and accordingly modulated La-La distances. In particular, charge and bond disproportionation and concomitant orbital order of the t2g hole emerge at the Co sites that are also observed for unstrained bulk LaCoO3 in the IS state and explain structural data obtained by x-ray diffraction at elevated temperature. Site disproportionation drives a metal-to-semiconductor transition that reconciles the IS state with the experimentally observed low conductivity during spin-state crossover without the presence of Jahn-Teller distortions. © 2020 American Physical Society. ©2020 American Physical Society.
    view abstractdoi: 10.1103/PhysRevB.101.165108
  • 2020 • 593 Electrochemical CO2 Reduction-The Effect of Chalcogenide Exchange in Ni-Isocyclam Complexes
    Gerschel, P. and Battistella, B. and Siegmund, D. and Ray, K. and Apfel, U.-P.
    Organometallics 39 1497-1510 (2020)
    Among the numerous homogeneous electrochemical CO2 reduction catalysts, [Ni(cyclam)]2+ is known as one of the most potent catalysts. Likewise, [Ni(isocyclam)]2+ was reported to enable electrochemical CO2 conversion but has received significantly less attention. However, for both catalysts, a purposeful substitution of a single nitrogen donor group by chalcogen atoms was never reported. In this work, we report a series of isocyclam-based Ni complexes with {ON3}, {SN3}, {SeN3}, and {N4} moieties and investigated the influence of nitrogen/chalcogen substitution on electrochemical CO2 reduction. While [Ni(isocyclam)]2+ showed the highest selectivity toward CO2 reduction within this series with a Faradaic efficiency of 86% for the generation of CO at an overpotential of-1.20 V and acts as a homogeneous catalyst, the O-and S-containing Ni complexes revealed comparable catalytic activities at ca. 0.3 V milder overpotential but tend to form deposits on the electrode, acting as precursors for a heterogeneous catalysis. Moreover, the heterogeneous species generated from the O-and S-containing complexes enable a catalytic hydride transfer to acetonitrile, resulting in the generation of acetaldehyde. The incorporation of selenium, however, resulted in loss of CO2 reduction activity, mainly leading to hydrogen generation that is also catalyzed by a heterogeneous electrodeposit. Copyright © 2020 American Chemical Society.
    view abstractdoi: 10.1021/acs.organomet.0c00129
  • 2020 • 592 High-performance positively charged hollow fiber nanofiltration membranes fabricated via green approach towards polyethyleneimine layer assembly
    Ghiasi, S. and Behboudi, A. and Mohammadi, T. and Ulbricht, M.
    Separation and Purification Technology 251 (2020)
    In this study, high performance positively charged hyper-branched polyethyleneimine (PEI) nanofiltration (NF) layer was assembled successfully on negatively charged polyethersulfone/polyimide (PES/PI) hollow fiber ultrafiltration (UF) membranes under different conditions. In accordance with principles of green chemistry, glutaraldehyde (GA) as cross-linker and purely aqueous solutions were used as a less hazardous alternative compared to, e.g. trimesoyl chloride in an organic solvent. The effects of the surface roughness and charge of the substrate UF membranes, due to the presence of PI, and various fabrication conditions, such as pH of PEI aqueous solution, GA/PEI ratio and crosslinking reaction time, were investigated and discussed. Electron microscopy images revealed the successful assembly of the PEI NF layer at uniform coverage of the PES/PI UF membranes. It was found that the varied preparation conditions drastically affect the membrane surface hydrophilicity, surface zeta potential, permeation flux, and salt rejection. The membrane fabricated at optimum conditions had a molecular weight cut-off of ≤ 400 Da; steric hindrance and Donnan exclusion resulted to achieve salt rejections of 94.2% and 87.4% for MgCl2 and MgSO4, respectively. Moreover, fabricated membranes were tested through three cycles of six-hour filtrations and over 95% flux recovery after the filtration of salts via the backwashing process was recorded. © 2020 Elsevier B.V.
    view abstractdoi: 10.1016/j.seppur.2020.117313
  • 2020 • 591 Understanding Mono- And Bivalent Ion Selectivities of Nanoporous Graphene Using Ionic and Bi-ionic Potentials
    Ghosh, M. and Madauß, L. and Schleberger, M. and Lebius, H. and Benyagoub, A. and Wood, J.A. and Lammertink, R.G.H.
    Langmuir 36 7400-7407 (2020)
    Nanoporous graphene displays salt-dependent ion permeation. In this work, we investigate the differences in Donnan potentials arising between reservoirs, separated by a perforated graphene membrane, containing different cations. We compare the case of monovalent cations interacting with nanoporous graphene with the case of bivalent cations. This is accomplished through both measurements of membrane potential arising between two salt reservoirs at different concentrations involving a single cation (ionic potential) and between two reservoirs containing different cations at the same concentration (bi-ionic potential). In our present study, Donnan dialysis experiments involve bivalent MgCl2, CaCl2, and CuCl2 as well as monovalent KCl and NH4Cl salts. For all salts, except CuCl2, clear Donnan and diffusion potential plateaus were observed at low and high salt concentrations, respectively. Our observations show that the membrane potential scaled to the Nernst potential for bivalent cations has a lower value (≈50%) than for monovalent cations (≈72%) in the Donnan exclusion regime. This is likely due to the adsorption of these bivalent cations on monolayer graphene. For bivalent cations, the diffusion regime is reached at a lower ionic strength compared to the monovalent cations. For Mg2+ and Ca2+, the membrane potential does not seem to depend upon the type of ions in the entire ionic strength range. A similar behavior is observed for the KCl and NH4Cl membrane potential curves. For CuCl2, the membrane potential curve is shifted toward lower ionic strength compared to the other two bivalent salts and the Donnan plateau is not observed at the lowest ionic strength. Bi-ionic potential measurements give further insight into the strength of specific interactions, allowing for the estimation of the relative ionic selectivities of different cations based on comparing their bi-ionic potentials. This effect of possible ion adsorption on graphene can be removed through ion exchange with monovalent salts. © 2020 American Chemical Society.
    view abstractdoi: 10.1021/acs.langmuir.0c00924
  • 2020 • 590 Syntheses, structures and catalytic activity of tetranuclear Mg complexes in the ROP of cyclic esters under industrially relevant conditions
    Ghosh, S. and Wölper, C. and Tjaberings, A. and Gröschel, A.H. and Schulz, S.
    Dalton Transactions 49 375-387 (2020)
    Four tetranuclear magnesium complexes were synthesized and fully characterized. They are excellent catalysts for the ring-opening polymerization (ROP) of bulk racemic-lactide (rac-LA) and ϵ-caprolactone (ϵ-CL) even with low catalyst loading under industrially relevant conditions without additional co-initiators, yielding polymers with high molecular weight (Mn) and moderately controlled molecular weight distribution (MWD). The polymerization activity depends on the steric and electronic properties of the imino(phenolate) ligands. Kinetic studies of the most active catalyst 1 confirmed that the ROP of rac-LA and ϵ-CL has a first order dependence on monomer concentration. The ROP of rac-LA and ϵ-CL using 1-4 with BnOH gave polymers with narrow MWD and a close correlation between Mobsn and Mtheon values. Catalyst 1 was also capable of polymerizing technical-grade rac-LA and ϵ-CL even with large monomer-to-catalyst ratios ([M]0/[C]0) of up to 10 000 : 1 and without any additional co-initiator. The very high turnover frequencies (TOF) of 9600 h-1 (rac-LA) and 24 000 h-1 (ϵ-CL) prove that 1 belongs to the most active biocompatible, sustainable and nontoxic ROP catalysts under industrially relevant conditions. © 2020 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c9dt04359d
  • 2020 • 589 Guanidiniocarbonyl-Pyrroles (GCP) – 20 Years of the Schmuck Binding Motif
    Giese, M. and Niemeyer, J. and Voskuhl, J.
    ChemPlusChem 85 985-997 (2020)
    In this Minireview, an overview about the past 20 years of the guanidiniocarbonyl-pyrrole (GCP) binding motif, which was designed, investigated and applied by Prof. Dr. Carsten Schmuck, is presented. Here we highlight the first steps from design and discovery, initial binding studies, applications in material science to advanced biomedical use in protein modulation and delivery of genetic material. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
    view abstractdoi: 10.1002/cplu.202000142
  • 2020 • 588 Alkyl-Alkyl Interactions in the Periphery of Supramolecular Entities: From the Evaluation of Weak Forces to Applications
    Giese, M. and Albrecht, M.
    ChemPlusChem 85 715-724 (2020)
    Supramolecular chemistry is based on weak intermolecular forces which nevertheless are of importance for chemical processes. In this report the relevance of alkyl-alkyl interactions in supramolecular assemblies is discussed. We show how hierarchically formed helicates can be used to evaluate weak interactions of alkyl groups based on solvent-supported London dispersion. In addition, the role of nano-segregation of alkyl groups in the periphery of supramolecular assemblies is described, as well as how this can be used to improve the properties of liquid-crystalline materials by controlling the alkyl-chain-mediated aggregation process. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
    view abstractdoi: 10.1002/cplu.202000077
  • 2020 • 587 Diffusion of Gold Nanoparticles in Inverse Opals Probed by Heterodyne Dynamic Light Scattering
    Giraudet, C. and Knoll, M.S.G. and Galvan, Y. and Süß, S. and Segets, D. and Vogel, N. and Rausch, M.H. and Fröba, A.P.
    Transport in Porous Media 131 723-737 (2020)
    The diffusive behavior of nanoparticles inside porous materials is attracting a lot of interest in the context of understanding, modeling, and optimization of many technical processes. A very powerful technique for characterizing the diffusive behavior of particles in free media is dynamic light scattering (DLS). The applicability of the method in porous media is considered, however, to be rather difficult due to the presence of multiple sources of scattering. In contrast to most of the previous approaches, the DLS method was applied without ensuring matching refractive indices of solvent and porous matrix in the present study. To test the capabilities of the method, the diffusion of spherical gold nanoparticles within the interconnected, periodic nanopores of inverse opals was analyzed. Despite the complexity of this system, which involves many interfaces and different refractive indices, a clear signal related to the motion of particles inside the porous media was obtained. As expected, the diffusive process inside the porous sample slowed down compared to the particle diffusion in free media. The obtained effective diffusion coefficients were found to be wave vector-dependent. They increased linearly with increasing spatial extension of the probed particle concentration fluctuations. On average, the slowing-down factor measured in this work agrees within combined uncertainties with literature data. © 2019, Springer Nature B.V.
    view abstractdoi: 10.1007/s11242-019-01364-1
  • 2020 • 586 Hydrogels Derivatized With Cationic Moieties or Functional Peptides as Efficient Supports for Neural Stem Cells
    Glotzbach, K. and Stamm, N. and Weberskirch, R. and Faissner, A.
    Frontiers in Neuroscience 14 (2020)
    The increasing incidence of neurodegenerative diseases such as Alzheimer’s or Parkinson’s disease represents a significant burden for patients and national health systems. The conditions are primarily caused by the death of neurons and other neural cell types. One important aim of current stem cell research is to find a way to replace the lost cells. In this perspective, neural stem cells (NSCs) have been considered as a promising tool in the field of regenerative medicine. The behavior of NSCs is modulated by environmental influences, for example hormones, growth factors, cytokines, and extracellular matrix molecules or biomechanics. These factors can be studied by using well-defined hydrogels, which are polymeric networks of synthetic or natural origin with the ability to swell in water. These gels can be modified with a variety of molecules and optimized with regard to their mechanical properties to mimic the natural extracellular environment. In particular modifications applying distinct units such as functional domains and peptides can modulate the development of NSCs with regard to proliferation, differentiation and migration. One well-known peptide sequence that affects the behavior of NSCs is the integrin recognition sequence RGD that has originally been derived from fibronectin. In the present review we provide an overview concerning the applications of modified hydrogels with an emphasis on synthetic hydrogels based on poly(acrylamides), as modified with either cationic moieties or the peptide sequence RGD. This knowledge might be used in tissue engineering and regenerative medicine for the therapy of spinal cord injuries, neurodegenerative diseases and traumata. © Copyright © 2020 Glotzbach, Stamm, Weberskirch and Faissner.
    view abstractdoi: 10.3389/fnins.2020.00475
  • 2020 • 585 Structural evolution of bimetallic Co-Cu catalysts in CO hydrogenation to higher alcohols at high pressure
    Göbel, C. and Schmidt, S. and Froese, C. and Fu, Q. and Chen, Y.-T. and Pan, Q. and Muhler, M.
    Journal of Catalysis 383 33-41 (2020)
    Bimetallic Co-Cu catalysts are widely applied in higher alcohol synthesis (HAS), but the formation of the final active structure has not yet been fully clarified, especially for Co-rich catalysts. We investigated the structural evolution of a Co-Cu catalyst (Co:Cu = 2) from the hydrotalcite precursor containing additional Al3+ and Zn2+ to the final active state after 80 h under reaction conditions at 280 °C and 60 bar. The reconstruction of the bimetallic Co-Cu nanoparticles obtained by H2 reduction was induced by the feed gas consisting of an equimolar H2 and CO syngas mixture resulting in fast phase separation and sintering of metallic Cu0 and Co0 in the first 2 h time on stream (TOS) and a continuous carbidization of Co0 forming Co2C and its sintering until steady state was reached after 40 h TOS. An intergrowth of metallic Cu0 nanoparticles with Co2C nanoparticles was observed to occur under reaction conditions. The high selectivity to oxygenates amounting to 41% compared with 29% to hydrocarbons is ascribed to the multi-functional Co2C/Cu0 interface enabling dissociative CO adsorption, hydrogenation and CO insertion. The formation of hydrogenated carbon species (CxHy) originating from dissociative CO chemisorption is assumed to be favored by hydrogen spillover from Cu0 to Co2C. The adsorption sites for molecular CO provided by both Cu0 and Co2C facilitate its insertion into the CxHy intermediates thus leading to a higher selectivity to alcohols following the Anderson-Schulz-Flory distribution. © 2020 Elsevier Inc.
    view abstractdoi: 10.1016/j.jcat.2020.01.004
  • 2020 • 584 Recent progress in laser materials processing and synthesis
    Gökce, B. and Filipescu, M. and Barcikowski, S.
    Applied Surface Science 513 (2020)
    doi: 10.1016/j.apsusc.2020.145762
  • 2020 • 583 Quantitative estimates for bending energies and applications to non-local variational problems
    Goldman, M. and Novaga, M. and Röger, M.
    Proceedings of the Royal Society of Edinburgh Section A: Mathematics 150 131-169 (2020)
    We discuss a variational model, given by a weighted sum of perimeter, bending and Riesz interaction energies, that could be considered as a toy model for charged elastic drops. The different contributions have competing preferences for strongly localized and maximally dispersed structures. We investigate the energy landscape in dependence of the size of the 'charge', that is, the weight of the Riesz interaction energy. In the two-dimensional case, we first prove that for simply connected sets of small elastica energy, the elastica deficit controls the isoperimetric deficit. Building on this result, we show that for small charge the only minimizers of the full variational model are either balls or centred annuli. We complement these statements by a non-existence result for large charge. In three dimensions, we prove area and diameter bounds for configurations with small Willmore energy and show that balls are the unique minimizers of our variational model for sufficiently small charge. © Copyright 2019 Royal Society of Edinburgh.
    view abstractdoi: 10.1017/prm.2018.149
  • 2020 • 582 Decomposition Reactions of Fe(CO)5, Fe(C5H5)2, and TTIP as Precursors for the Spray-Flame Synthesis of Nanoparticles in Partial Spray Evaporation at Low Temperatures
    Gonchikzhapov, M. and Kasper, T.
    Industrial and Engineering Chemistry Research 59 8551-8561 (2020)
    Flame spray pyrolysis is an important method of nanoparticle manufacturing. Reactions of the precursor and the solvent determine which intermediates can contribute to particle formation. To investigate the chemical interaction between the solvent and the precursor during the partial evaporation of the spray preceding ignition, precursor solutions were sprayed into an externally heated flow reactor. The thermal decomposition of the precursors Fe(CO)5, Fe(C5H5)2, and Ti(i-OC3H7)4 in solutions of xylene and ethanol was investigated. Decomposition products were analyzed by mass spectrometry. The relevance of reactions at these low temperatures for the spray-flame process is substantiated by measurements of the spatial temperature distribution of the spray flame. Depending on the relative thermal stabilities of the precursor and the solvent, the less stable component can initiate decomposition of the more stable component, resulting in different reaction patterns of the solutions. The results are discussed with regard to their potential influence on particle formation pathways. © 2020 American Chemical Society.
    view abstractdoi: 10.1021/acs.iecr.9b06667
  • 2020 • 581 Cr2AlC MAX phase as bond coat for thermal barrier coatings: Processing, testing under thermal gradient loading, and future challenges
    Gonzalez-Julian, J. and Mauer, G. and Sebold, D. and Mack, D.E. and Vassen, R.
    Journal of the American Ceramic Society 103 2362-2375 (2020)
    Cr2AlC layers with thickness up to 100 µm were deposited by high-velocity-atmospheric plasma spray (HV-APS) on Inconel 738 substrates to analyze the potential of MAX phases as bond coat in thermal barrier coating systems (TBCs). The deposited Cr2AlC layers showed high purity with theoretical densities up to 93%, although some secondary phases were detected after the deposition process. On top of this MAX phase layer, a porous yttria-stabilized zirconia (YSZ) was deposited by atmospheric plasma spraying. The system was tested under realistic thermal loading conditions using a burner rig facility, achieving surface and substrate temperatures of 1400°C and 1050°C, respectively. The system failed after 745 cycles mainly for three reasons: (i) open porosity of the bond coat layer, (ii) oxidation of secondary phases, and (iii) inter-diffusion. Nevertheless, these results show a high potential of Cr2AlC and other Al-based MAX phases as bond coat material for high-temperature applications. Furthermore, future challenges to transfer MAX phases as eventual bond coat or protective layer are discussed. © 2019 The Authors. Journal of the American Ceramic Society published by Wiley Periodicals, Inc. on behalf of American Ceramic Society (ACERS)
    view abstractdoi: 10.1111/jace.16935
  • 2020 • 580 Standard Gibbs energy of metabolic reactions: VI. Glyceraldehyde 3-phosphate dehydrogenase reaction
    Greinert, T. and Vogel, K. and Mühlenweg, J.-K. and Sadowski, G. and Maskow, T. and Held, C.
    Fluid Phase Equilibria 517 (2020)
    Glycolysis is a very central metabolic pathway for many organisms because it represents a key component in their energy production. For this reason, it has always been an extensively studied pathway. The glyceraldehyde 3-phosphate dehydrogenase (GDH) reaction is an important reaction of glycolysis yielding nicotinamide adenine dinucleotide (NADH). The aim of this work is to investigate the thermodynamics of the GDH reaction and determine the standard Gibbs energy of reaction ΔRg'0 and standard enthalpy of reaction ΔRh'0. Currently, so-called ‘standard’ data exist in the literature that depend on the conditions they were measured at. In this work, ΔRg'0 and ΔRh'0 values were determined that are independent from reaction conditions by accounting for the activity coefficients of the reacting substances. Therefore, the equation of state electrolyte Perturbed-Chain Statistical Associating Fluid Theory (ePC-SAFT) was used. The required ePC-SAFT parameters were taken from literature or fitted to new experimental osmotic coefficients. A value of ΔRg'0 = 51.5 ± 0.4 kJ mol−1 was determined at 298.15 K. This value deviates by up to 10 kJ mol−1 from existing literature values, caused by activity coefficients in the reaction medium. It can be used to determine the Gibbs energy of reaction ΔRg', which will allow statements concerning the feasibility of the GDH reaction. Further, a method is presented to predict influences of pH, initial substrate concentration and Mg2+ concentration on the reaction equilibrium. Finally, we measured the standard reaction enthalpy for the GDH reaction ΔRh'0 by titration calorimetric measurements (ΔRh'0 = 4.6 ± 0.1 kJ mol−1). This value was within van ’t Hoff evaluated ΔRh'0 (9 ± 16 kJ mol−1) using temperature-dependent equilibrium constants from equilibrium measurements corrected by ePC-SAFT predicted activity coefficients. © 2020 Elsevier B.V.
    view abstractdoi: 10.1016/j.fluid.2020.112597
  • 2020 • 579 Standard Gibbs energy of metabolic reactions: V. Enolase reaction
    Greinert, T. and Vogel, K. and Seifert, A.I. and Siewert, R. and Andreeva, I.V. and Verevkin, S.P. and Maskow, T. and Sadowski, G. and Held, C.
    Biochimica et Biophysica Acta - Proteins and Proteomics 1868 (2020)
    The glycolytic pathway is one of the most important pathways for living organisms, due to its role in energy production and as supplier of precursors for biosynthesis in living cells. This work focuses on determination of the standard Gibbs energy of reaction ΔRg′0 of the enolase reaction, the ninth reaction in the glycolysis pathway. Exact ΔRg′0 values are required to predict the thermodynamic feasibility of single metabolic reactions or even of metabolic reaction sequences under cytosolic conditions. So-called “apparent” standard data from literature are only valid at specific conditions. Nevertheless, such data are often used in pathway analyses, which might lead to misinterpretation of the results. In this work, equilibrium measurements were combined with activity coefficients in order to obtain new standard values ΔRg′0 for the enolase reaction that are independent of the cytosolic conditions. Reaction equilibria were measured at different initial substrate concentrations and temperatures of 298.15 K, 305.15 K and 310.15 K at pH 7. The activity coefficients were predicted using the equation of state electrolyte Perturbed-Chain Statistical Associating Fluid Theory (ePC-SAFT). The ePC-SAFT parameters were taken from literature or fitted to new experimentally determined osmotic coefficients and densities. At 298.15 K and pH 7, a ΔRg′0(298.15 K, pH 7) value of −2.8 ± 0.2 kJ mol− 1 was obtained. This value differs by up to 5 kJ mol− 1 from literature data. Reasons are the poorly defined “standard” conditions and partly undefined reaction conditions of literature works. Finally, using temperature-dependent equilibrium constants and the van ‘t Hoff equation, the standard enthalpy of reaction of ΔRh′0(298.15 K, pH 7) = 27 ± 10 kJ mol− 1 was determined, and a similar value was found by quantum-chemistry calculations. © 2020 Elsevier B.V.
    view abstractdoi: 10.1016/j.bbapap.2020.140365
  • 2020 • 578 Standard Gibbs energy of metabolic reactions: IV. Triosephosphate isomerase reaction
    Greinert, T. and Baumhove, K. and Sadowski, G. and Held, C.
    Biophysical Chemistry 258 (2020)
    The glycolytic pathway is present in most organisms and represents a central part of the energy production mechanism in a cell. For a general understanding of glycolysis, the investigation from a thermodynamic point of view is essential and allows realising thermodynamic feasibility analyses under in vivo conditions. However, available literature standard Gibbs energies of reaction, ΔRg′0, are calculated using equilibrium-molality ratios Km′, which might lead to a misinterpretation of the glycolytic pathway. It was the aim of this work to thermodynamically investigate the triosephosphate isomerase (TPI) reaction to provide new activity-based reaction data. In vitro equilibrium experiments were performed, and activity coefficients were predicted with the equation of state electrolyte PC-SAFT (ePC-SAFT). The combination of experimental concentrations and predicted activity coefficients yielded the thermodynamic equilibrium constant Ka and a new value for ΔRg′0(298.15 K, pH 7) = 7.1 ± 0.3 kJ mol‑1. The availability of the new ΔRg′0 value allowed predicting influences of the reaction medium on the reaction equilibrium of the TPI reaction. In this work, influences of the initial substrate concentration, pH and Mg2+ concentration on the reaction equilibrium were investigated and a method is presented to predict these influences. The higher the substrate concentration and the higher the temperature, the stronger the reaction equilibrium is shifted on the product side. While the pH did not have a significant influence on the reaction equilibrium, Mg2+ yielded a shift of the reaction equilibrium to the substrate side. All these effects were predicted correctly with ePC-SAFT. Based on the ePC-SAFT predictions we concluded that a charge-reduction of the product by complexation of the product with Mg2+ was responsible for the strong influence of Mg2+ on the reaction equilibrium. Finally, the standard enthalpy of reaction of ΔRh′0(pH 7) = 18 ± 7 kJ mol‑1 was determined with the equilibrium constants Ka at 298.15 K, 304.15 K and 310.15 K using the van ‘t Hoff equation. © 2020 Elsevier B.V.
    view abstractdoi: 10.1016/j.bpc.2020.106330
  • 2020 • 577 Characterization of a transient spark micro-discharge in nitrogen using simultaneous two-wavelength diagnostics
    Gröger, S. and Fiebrandt, M. and Hamme, M. and Bibinov, N. and Awakowicz, P.
    Measurement Science and Technology 31 (2020)
    A transient spark micro-discharge in nitrogen is investigated between two sharpened electrodes at a pressure of 0.5 bar. The plasma parameters (gas temperature, electron density and reduced electric field) are determined using optical emission spectroscopy (OES) and numerical simulations. The gas temperature of 3500 ± 100 K is determined by the comparison of the measured and simulated rotational distributions of the photoemission spectra of neutral molecular nitrogen N2(C-B,0-0). Both direct and stepwise electron impact excitation are considered in the collision-radiative model. The rate constants for electron impact excitation processes are calculated for different electric field values using the electron velocity distribution function, which is simulated by solving the Boltzmann equation. The applied broadband echelle spectrometer is absolutely calibrated in a spectral range of 200 nm to 800 nm, using two standard light sources, a deuterium lamp and a tungsten ribbon lamp, which are certificated by the Physikalisch-Technische Bundesanstalt (PTB), Germany. With the aid of this absolutely calibrated echelle spectrometer and a microwave atmospheric plasma source operated in a nitrogen flow, the intensified charge-coupled device (ICCD) camera, provided with an in-house made optical arrangement for simultaneous two-wavelength diagnostic is calibrated. The spatial resolution of this diagnostic system under the studied plasma conditions amounts to 13 m. The accurate examination of the experimental results allows determining the dominant process of electron impact excitation of molecular nitrogen ion from ionic ground state. Applying the chosen excitation model of the nitrogen photoemission, the spatially resolved reduced electric field and the electron density are determined. This is done by using the inverse Abel transformation of the absolute intensities of molecular nitrogen bands N2(C-B,0-0) and N2 + (B-X,0-0), which were measured with the calibrated ICCD camera. The measured electric current of the micro-discharge is compared with the calculated one using the measured plasma parameters and a good coincidence is established. © 2020 The Author(s). Published by IOP Publishing Ltd.
    view abstractdoi: 10.1088/1361-6501/ab7e69
  • 2020 • 576 Contact Behavior of Microcrystalline Cellulose Pellets Depending on their Water Content
    Grohn, P. and Weis, D. and Thommes, M. and Heinrich, S. and Antonyuk, S.
    Chemical Engineering and Technology 43 887-895 (2020)
    Microcrystalline cellulose pellets for oral drug delivery are often produced by a combined wet extrusion-spheronization process. During the entire process, the cylindrical as well as the spherical pellets are exposed to various stresses resulting in a change of their shape and size due to plastic deformation and breakage. In this work, the effect of moisture content of pellets on their mechanical behavior is studied. In static compression tests, the strong influence of water content on deformation behavior of pellets is confirmed. Moreover, impact tests are performed using a setup consisting of three high-speed cameras to record pellet-wall collisions. Material properties, such as stiffness, restitution coefficient, breakage force, and displacement, were analyzed depending on the water content. © 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/ceat.201900517
  • 2020 • 575 Hydrophilic poly(phenylene sulfone) membranes for ultrafiltration
    Gronwald, O. and Frost, I. and Ulbricht, M. and Kouchaki Shalmani, A. and Panglisch, S. and Grünig, L. and Handge, U.A. and Abetz, V. and Heijnen, M. and Weber, M.
    Separation and Purification Technology 250 (2020)
    Poly(alkylene oxide) based tri- and multiblock oligomers with hydrophobic poly(phenylene sulfone) blocks were evaluated as dope solution additives used for preparation of improved poly(phenylene sulfone) (PPSU) flat sheet (FS) and single bore (SB) ultrafiltration membranes by non-solvent induced phase separation (NIPS). Identical polymer dope recipes were used in both of FS membrane preparation and SB fiber spinning processes. PPSU membranes modified with 9.2 wt % Pluronic® F127 based additive, M2 (7.5 kDa PPSU/ Pluronic® F127), or Lutensol® AT80 based additive, T2 (7.5 kDa PPSU/ Lutensol® AT80), displayed compared to pristine PPSU membranes elevated hydraulic permeance ranging from 485 to 674 kg m−2 bar-1h−1 (pristine PPSU: 310 – 464 kg m−2 bar-1h−1), higher molecular weight cut-off values from 37.0 to 53.5 kDa (pristine PPSU: 21.4 – 23.7 kDa), lower contact angles of 46.4° and 49.8° (pristine PPSU: 86.7°) and reduced fouling propensity with irreversible fouling values of 10 % (pristine PPSU: 15 %) for diluted potting soil extract as model substance. The combined analysis methods of X-ray photoelectron spectroscopy (XPS) and proton nuclear magnetic resonance spectroscopy (1H NMR) indicated modest surface enrichment of the additives in the filtration layer. Consequently, PPSU ultrafiltration membranes modified with additives T2 and M2 provide interesting alternatives to poly(ether sulfone) (PESU) and poly(vinylidene fluoride) (PVDF) based membranes for surface water filtration combining both excellent filtration characteristics with a long lifetime due to its higher chemical resistance. © 2020 Elsevier B.V.
    view abstractdoi: 10.1016/j.seppur.2020.117107
  • 2020 • 574 Carbon Supported Phosphoric Acid Catalysts for Gas-Phase Synthesis of Diesel Additives
    Grünert, A. and Schmidt, W. and Schüth, F.
    Catalysis Letters (2020)
    Abstract: Carbon supported phosphoric acid (H3PO4/C) was found to be a more productive catalyst for the gas-phase synthesis of the diesel fuel additive/substitute oxymethylene ethers (OME) as compared to benchmark zeolite catalysts. In this contribution, the performance of catalysts H3PO4/C and related H2PO4 −/C and HPO4 2−/C materials in OME synthesis from methanol and formaldehyde is described. Graphic Abstract: [Figure not available: see fulltext.]. © 2020, The Author(s).
    view abstractdoi: 10.1007/s10562-020-03200-4
  • 2020 • 573 In situ investigation of atmospheric plasma-sprayed Mn–Co–Fe–O by synchrotron X-ray nano-tomography
    Grünwald, N. and Lhuissier, P. and Salvo, L. and Villanova, J. and Menzler, N.H. and Guillon, O. and Martin, C.L. and Vaßen, R.
    Journal of Materials Science 55 12725-12736 (2020)
    Applying atmospherically plasma-sprayed (APS) Mn1.0Co1.9Fe0.1O4 (MCF) protective coatings on interconnector steels minimized the chromium-related degradation within solid oxide fuel cell stack-tests successfully. Post-test characterization of the coatings disclosed a severe microstructural and phase evolution. A self-healing of micro-cracks, the formation and agglomeration of small pores, the occurrence of a dense spinel layer at the surface and a strong elemental de-mixing were reported in ex situ experiments. In the present publication, we prove for the first time these mechanisms by tracking the microstructure in situ at a single APS coating using synchrotron X-ray nano-tomography at the European Synchrotron Radiation Facility. Therefore, a 100-µm-long cylindrical sample with a diameter of 123 µm was cut from an APS-MCF free-standing layer and measured within a high-temperature furnace. All microstructural changes mentioned above could be verified. Porosity measurements reveal a decrease in the porosity from 9 to 3% during the annealing, which is in good accordance with the literature. Additionally, a partial detachment of an approximately 5-µm-thick layer at the sample surface is observed. The layer is dense and does not exhibit any cracks which are penetrating the layer. This kind of shell is assumed to be gastight and thus protecting the bulk from further oxidation. © 2020, The Author(s).
    view abstractdoi: 10.1007/s10853-020-04916-9
  • 2020 • 572 Numerical multi-level model for fiber-reinforced concrete - Multi-level validation based on an experimental study on high-strength concrete [Numerisches Mehrebenen-Modell für Stahlfaserbeton: Von der Faser- zur Bauteilebene: Mehrstufige Validierung anhand einer experimentellen Studie an hochfestem Faserbeton]
    Gudžulic, V. and Neu, G.E. and Gebuhr, G. and Anders, S. and Meschke, G.
    Beton- und Stahlbetonbau 115 146-157 (2020)
    Numerical multi-level model for fiber-reinforced concrete – Multi-level validation based on an experimental study on high-strength concrete. The contribution systematically examines the predictive capability of a numerical multi-level model for steel fiber reinforced concrete made of high-strength concrete by means of test series performed on the fiber as well as the structure level. The experimental study comprises pull-out tests of Dramix 3D fibers in high-strength concrete with different embedment lengths and inclinations to the crack surface as well as three-point bending tests on notched beams with three significantly different fiber contents. The numerical model is designed to directly track the influence of design parameters such as fiber type, fiber orientation, fiber content and concrete strength on the structural response. For this purpose, submodels on the single fiber level are combined into a crack bridging model, considering the fiber orientation and the fiber content, and are integrated into a finite element model for the purpose of numerical structural analysis. The validation of the models for hooked-end steel fibers shows that the interaction mechanisms between fiber and high-strength concrete are realistically captured for all investigated cases (fiber inclinations, embedment lengths). On the structural level, the load-displacement diagrams from the numerical simulations show a good agreement of the peak load as well as the post-peak behavior for all fiber contents. © 2020, Ernst und Sohn. All rights reserved.
    view abstractdoi: 10.1002/best.201900067
  • 2020 • 571 Computational shape optimisation for a gradient-enhanced continuum damage model
    Guhr, F. and Sprave, L. and Barthold, F.-J. and Menzel, A.
    Computational Mechanics 65 1105-1124 (2020)
    An isotropic gradient-enhanced damage model is applied to shape optimisation in order to establish a computational optimal design framework in view of optimal damage distributions. The model is derived from a free Helmholtz energy density enriched by the damage gradient contribution. The Karush–Kuhn–Tucker conditions are solved on a global finite element level by means of a Fischer–Burmeister function. This approach eliminates the necessity of introducing a local variable, leaving only the global set of equations to be iteratively solved. The necessary steps for the numerical implementation in the sense of the finite element method are established. The underlying theory as well as the algorithmic treatment of shape optimisation are derived in the context of a variational framework. Based on a particular finite deformation constitutive model, representative numerical examples are discussed with a focus on and application to damage optimised designs. © 2020, The Author(s).
    view abstractdoi: 10.1007/s00466-019-01810-3
  • 2020 • 570 Homolytic versus Heterolytic Hydrogen Evolution Reaction Steered by a Steric Effect
    Guo, X. and Wang, N. and Li, X. and Zhang, Z. and Zhao, J. and Ren, W. and Ding, S. and Xu, G. and Li, J. and Apfel, U.-P. and Zhang, W. and Cao, R.
    Angewandte Chemie - International Edition 59 8941-8946 (2020)
    Several H−H bond forming pathways have been proposed for the hydrogen evolution reaction (HER). Revealing these HER mechanisms is of fundamental importance for the rational design of catalysts and is also extremely challenging. Now, an unparalleled example of switching between homolytic and heterolytic HER mechanisms is reported. Three nickel(II) porphyrins were designed and synthesized with distinct steric effects by introducing bulky amido moieties to ortho- or para-positions of the meso-phenyl groups. These porphyrins exhibited different catalytic HER behaviors. For these Ni porphyrins, although their 1e-reduced forms are active to reduce trifluoroacetic acid, the resulting Ni hydrides (depending on the steric effects of porphyrin rings) have different pathways to make H2. Understanding HER processes, especially controllable switching between homolytic and heterolytic H−H bond formation pathways through molecular engineering, is unprecedented in electrocatalysis. © 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/anie.202002311
  • 2020 • 569 Dislocation-induced breakthrough of strength and ductility trade-off in a non-equiatomic high-entropy alloy
    Guo, W. and Su, J. and Lu, W. and Liebscher, C.H. and Kirchlechner, C. and Ikeda, Y. and Körmann, F. and Liu, X. and Xue, Y. and Dehm, G.
    Acta Materialia 185 45-54 (2020)
    In conventional metallic materials, strength and ductility are mutually exclusive, referred to as strength-ductility trade-off. Here, we demonstrate an approach to improve the strength and ductility simultaneously by introducing micro-banding and the accumulation of a high density of dislocations in single-phase high-entropy alloys (HEAs). We prepare two compositions (Cr10Mn50Fe20Co10Ni10 and Cr10Mn10Fe60Co10Ni10) with distinctive different stacking fault energies (SFEs) as experimental materials. The strength and ductility of the Cr10Mn50Fe20Co10Ni10 HEA are improved concurrently by grain refinement from 347.5 ± 216.1 µm to 18.3 ± 9.3 µm. The ultimate tensile strength increases from 543 ± 4 MPa to 621 ± 8 MPa and the elongation to failure enhances from 43±2% to 55±1%. To reveal the underlying deformation mechanisms responsible for such a strength-ductility synergy, the microstructural evolution upon loading is investigated by electron microscopy techniques. The dominant deformation mechanism observed for the Cr10Mn50Fe20Co10Ni10 HEA is the activation of micro-bands, which act both as dislocation sources and dislocation barriers, eventually, leading to the formation of dislocation cell structures. By decreasing grain size, much finer dislocation cell structures develop, which are responsible for the improvement in work hardening rate at higher strains (&gt;7%) and thus for the increase in both strength and ductility. In order to drive guidelines for designing advanced HEAs by tailoring their SFE and grain size, we compute the SFEs of Cr10MnxFe70–xCo10Ni10 (10 ≤ x ≤ 60) based on first principles calculations. Based on these results the overall changes on deformation mechanism can be explained by the influence of Mn on the SFE. © 2019 Acta Materialia Inc.
    view abstractdoi: 10.1016/j.actamat.2019.11.055
  • 2020 • 568 Continuous Wave THz System Based on an Electrically Tunable Monolithic Dual Wavelength Y-Branch DBR Diode Laser
    Gwaro, J.O. and Brenner, C. and Theurer, L.S. and Maiwald, M. and Sumpf, B. and Hofmann, M.R.
    Journal of Infrared, Millimeter, and Terahertz Waves 41 568-575 (2020)
    We analyse the use of a tunable dual wavelength Y-branch DBR laser diode for THz applications. The laser generates electrically tunable THz difference frequencies in the range between 100 and 300 GHz. The optical beats are tuned via current injection into a micro-resistor heater integrated on top of one of the distributed Bragg reflector (DBR) section of the diode. The laser is integrated in a homodyne THz system employing fiber coupled ion-implanted LT-GaAs log spiral antennas. The applicability of the developed system in THz spectroscopy is demonstrated by evaluating the spectral resonances of a THz filter as well as in THz metrology in thickness determination of a polyethylene sample. © 2020, The Author(s).
    view abstractdoi: 10.1007/s10762-020-00676-4
  • 2020 • 567 Signatures of an atomic crystal in the band structure of a C60 thin film
    Haag, N. and Lüftner, D. and Haag, F. and Seidel, J. and Kelly, L.L. and Zamborlini, G. and Jugovac, M. and Feyer, V. and Aeschlimann, M. and Puschnig, P. and Cinchetti, M. and Stadtmüller, B.
    Physical Review B 101 (2020)
    Transport phenomena in molecular materials are intrinsically linked to the orbital character and the degree of localization of the valence states. Here we combine angle-resolved photoemission with photoemission tomography to determine the spatial distribution of all molecular states of the valence band structure of a C60 thin film. While the two most frontier valence states exhibit a strong band dispersion, the states at larger binding energies are characterized by distinct emission patterns in energy and momentum space. Our findings demonstrate the formation of an atomic crystal-like band structure in a molecular solid with delocalized π-like valence states and strongly localized σ states at larger binding energies. © 2020 American Physical Society.
    view abstractdoi: 10.1103/PhysRevB.101.165422
  • 2020 • 566 Modeling of Interfacial Tensions of Long-Chain Molecules and Related Mixtures Using Perturbed Chain-Statistical Associating Fluid Theory and the Density Gradient Theory
    Haarmann, N. and Reinhardt, A. and Danzer, A. and Sadowski, G. and Enders, S.
    Journal of Chemical and Engineering Data 65 1005-1018 (2020)
    Long-chain compounds such as fatty-acid methyl esters and fatty alcohols are often based on renewable sources and are widely used in soaps and as surfactants. Hence, the knowledge of their pure-component surface tensions and interfacial tensions against water is indispensable. As experimental data of these systems are scarce, a simultaneous and preferentially predictive thermodynamic modeling of phase equilibria and interfacial properties is desirable. In our previous works (Haarmann et al., Ind. Eng. Chem. Res. 2019, 58 (7), 2551-2574 and Haarmann et al., Ind. Eng. Chem. Res. 2019, 58 (11), 4625-4643), the focus was on the description of the phase equilibria of pure long-chain compounds and their binary mixtures with water using a homosegmental as well as a newly introduced heterosegmental approach of the Perturbed Chain Statistical Associating Fluid Theory. Here, both approaches were combined with the Density Gradient Theory in order to obtain interfacial properties. When the combined models were applied, the pure-component surface tensions of polar and self-associating long-chain compounds could be represented in very good agreement with the experimental data. Furthermore, the interfacial tensions of the binary mixtures long-chain compound (n-hexanol, methyl hexanoate, and n-hexanoic acid) + water were investigated. Copyright © 2019 American Chemical Society.
    view abstractdoi: 10.1021/acs.jced.9b00339
  • 2020 • 565 Measurement concept to reduce environmental impact in direct time-of-flight LiDAR sensors
    Haase, J.F. and Buchner, A. and Grollius, S. and Ruskowski, J. and Vogt, H.
    Proceedings of SPIE - The International Society for Optical Engineering 11288 (2020)
    For some applications, a reliable detection of the distance of objects is necessary, even under strong environmental conditions. Commonly this includes sunlight, but fog, rain and snow cause interferences as well. For fast and reliable threedimensional monitoring of the environment, LiDAR is a key sensor technology. A light source, often in the near-infrared, emits a short light pulse and the time-of-flight of the photons reflected by an object is measured. This allows to calculate the distance by using the speed of light. In order to be able to ensure reliable detection despite possible interferences, we have set up a new measurement concept based on the existing time-gating. Thus, an area is covered by step-wise shifting of the measuring window. By accumulating different delays, the true distance to the object can be determined. An advantage of the method is that no information about the approximate position of the object has to be known in advance. In this paper we present measurement results with this method, which were taken in different environmental conditions. The method can be implemented in addition to already existing concepts and can therefore supplement them. © 2020 SPIE.
    view abstractdoi: 10.1117/12.2546021
  • 2020 • 564 Are Onsager's reciprocal relations necessary to apply Thermodynamic Extremal Principles?
    Hackl, K. and Fischer, F.D. and Zickler, G.A. and Svoboda, J.
    Journal of the Mechanics and Physics of Solids 135 (2020)
    Onsager's Reciprocal Relations between thermodynamic forces and fluxes, for which Onsager was awarded the Nobel Prize, automatically follow from Thermodynamic Extremal Principles. Thus, the Principles are up to now non-applicable for the treatment of experimentally determined or theoretically modeled non-reciprocal systems as e.g. those in the magnetic field. However, we can demonstrate that adding of a certain barrier constraint as bilinear form of thermodynamic forces and fluxes accounted by the Thermodynamic Extremal Principles provides to non-reciprocal relations between the thermodynamic forces and fluxes. Such a novel idea may contribute to a better understanding of physics behind non-reciprocal systems. © 2019 Elsevier Ltd
    view abstractdoi: 10.1016/j.jmps.2019.103780
  • 2020 • 563 Magnetic Properties and Mössbauer Spectroscopy of Fe3O4/CoFe2O4 Nanorods
    Hähsler, M. and Landers, J. and Nowack, T. and Salamon, S. and Zimmermann, M. and Heißler, S. and Wende, H. and Behrens, S.
    Inorganic Chemistry 59 3677-3685 (2020)
    Fe3O4/CoFe2O4 nanorods were obtained via a simple seed-mediated synthesis. Nanorods were used as seeds to grow CoFe2O4 by thermal codecomposition of the cobalt(II) and iron(III) acetylacetonate precursors. The growth process was monitored by electron microscopy (SEM, TEM), and the resulting nanorods were characterized by powder X-ray diffraction analysis and IR and Raman spectroscopy. Magnetometry and AC susceptometry studies revealed a distribution of Néel relaxation times with an average blocking temperature of 140 K and a high-field magnetization of 42 Am2/kg. Complementarily recorded 57Fe-Mössbauer spectra were consistent with the Fe3O4/CoFe2O4 spinel structure and exhibited considerable signs of spin frustration, which was correlated to the internal and surface structure of the nanorods. © 2020 American Chemical Society.
    view abstractdoi: 10.1021/acs.inorgchem.9b03267
  • 2020 • 562 Thermally Induced Crossover from 2D to 1D Behavior in an Array of Atomic Wires: Silicon Dangling-Bond Solitons in Si(553)-Au
    Hafke, B. and Brand, C. and Witte, T. and Sothmann, B. and Horn-Von Hoegen, M. and Erwin, S.C.
    Physical Review Letters 124 (2020)
    The self-assembly of submonolayer amounts of Au on the densely stepped Si(553) surface creates an array of closely spaced "atomic wires" separated by 1.5 nm. At low temperature, charge transfer between the terraces and the row of silicon dangling bonds at the step edges leads to a charge-ordered state within the row of dangling bonds with ×3 periodicity. Interactions between the dangling bonds lead to their ordering into a fully two-dimensional (2D) array with centered registry between adjacent steps. We show that as the temperature is raised, soliton defects are created within each step edge. The concentration of solitons rises with increasing temperature and eventually destroys the 2D order by decoupling the step edges, reducing the effective dimensionality of the system to 1D. This crossover from higher to lower dimensionality is unexpected and, indeed, opposite to the behavior in other systems. © 2020 American Physical Society.
    view abstractdoi: 10.1103/PhysRevLett.124.016102
  • 2020 • 561 Matrix-free subcell residual distribution for Bernstein finite elements: Monolithic limiting
    Hajduk, H. and Kuzmin, D. and Kolev, T. and Tomov, V. and Tomas, I. and Shadid, J.N.
    Computers and Fluids 200 (2020)
    This paper is focused on the aspects of limiting in residual distribution (RD) schemes for high-order finite element approximations to advection problems. Both continuous and discontinuous Galerkin methods are considered in this work. Discrete maximum principles are enforced using algebraic manipulations of element contributions to the global nonlinear system. The required modifications can be carried out without calculating the element matrices and assembling their global counterparts. The components of element vectors associated with the standard Galerkin discretization are manipulated directly using localized subcell weights to achieve optimal accuracy. Low-order nonlinear RD schemes of this kind were originally developed to calculate local extremum diminishing predictors for flux-corrected transport (FCT) algorithms. In the present paper, we incorporate limiters directly into the residual distribution procedure, which makes it applicable to stationary problems and leads to well-posed nonlinear discrete problems. To circumvent the second-order accuracy barrier, the correction factors of monolithic limiting approaches and FCT schemes are adjusted using smoothness sensors based on second derivatives. The convergence behavior of presented methods is illustrated by numerical studies for two-dimensional test problems. © 2020 Elsevier Ltd
    view abstractdoi: 10.1016/j.compfluid.2020.104451
  • 2020 • 560 Matrix-free subcell residual distribution for Bernstein finite element discretizations of linear advection equations
    Hajduk, H. and Kuzmin, D. and Kolev, T. and Abgrall, R.
    Computer Methods in Applied Mechanics and Engineering 359 (2020)
    In this work, we introduce a new residual distribution (RD) framework for the design of bound-preserving high-resolution finite element schemes. The continuous and discontinuous Galerkin discretizations of the linear advection equation are modified to construct local extremum diminishing (LED) approximations. To that end, we perform mass lumping and redistribute the element residuals in a manner which guarantees the LED property. The hierarchical correction procedure for high-order Bernstein finite element discretizations involves localization to subcells and definition of bound-preserving weights for subcell contributions. Using strong stability preserving (SSP) Runge–Kutta methods for time integration, we prove the validity of discrete maximum principles under CFL-like time step restrictions. The low-order version of our method has roughly the same accuracy as the one derived from a piecewise (multi)-linear approximation on a submesh with the same nodal points. In high-order extensions, we use an element-based flux-corrected transport (FCT) algorithm which can be interpreted as a nonlinear RD scheme. The proposed LED corrections are tailor-made for matrix-free implementations which avoid the rapidly growing cost of matrix assembly for high-order Bernstein elements. The results for 1D, 2D, and 3D test problems compare favorably to those obtained with the best matrix-based approaches. © 2019 Elsevier B.V.
    view abstractdoi: 10.1016/j.cma.2019.112658
  • 2020 • 559 Bathymetry Reconstruction Using Inverse ShallowWater Models: Finite Element Discretization and Regularization
    Hajduk, H. and Kuzmin, D. and Aizinger, V.
    Lecture Notes in Computational Science and Engineering 132 223-230 (2020)
    In the present paper, we use modified shallow water equations (SWE) to reconstruct the bottom topography (also called bathymetry) of a flow domain without resorting to traditional inverse modeling techniques such as adjoint methods. The discretization in space is performed using a piecewise linear discontinuous Galerkin (DG) approximation of the free surface elevation and (linear) continuous finite elements for the bathymetry. Our approach guarantees compatibility of the discrete forward and inverse problems: for a given DG solution of the forward SWE problem, the underlying continuous bathymetry can be recovered exactly. To ensure well-posedness of the modified SWE and reduce sensitivity of the results to noisy data, a regularization term is added to the equation for the water height. A numerical study is performed to demonstrate the ability of the proposed method to recover bathymetry in a robust and accurate manner. © Springer Nature Switzerland AG 2020.
    view abstractdoi: 10.1007/978-3-030-30705-9_20
  • 2020 • 558 Influence of 3 d, 4 d, and 5 d dopants on the oxygen evolution reaction at α-Fe2O3(0001) under dark and illumination conditions
    Hajiyani, H. and Pentcheva, R.
    Journal of Chemical Physics 152 (2020)
    Using density functional theory+U (DFT+U) calculations, we explore the effect of dopants on the performance of α-Fe2O3(0001) as an anode material for the oxygen evolution reaction (OER). Systematic screening of 3d, 4d, and 5d transition metal dopants indicates general trends with dopant band filling and allows us to identify the most efficient dopants with respect to the overpotential and relate those to the solution energy and electronic properties. Different conditions (electrochemical vs photoelectrochemical) are accounted for by considering hydroxylated, hydrated, and oxygenated terminations. Based on the DFT+U results, we identify Rh as the most promising dopant that can reduce the overpotential both under dark and illumination conditions: from 0.56 V to 0.48 V for the hydroxylated surface and quite substantially from 1.12 V to 0.31 V for the hydrated termination and from 0.81 V to 0.56 V for the oxygenated surface. The origin of this improvement is attributed to the modification of the binding energy of chemisorbed species to the Fe2O3(0001) surface. Investigation of the spin density of intermediate steps during the OER shows that surface iron ions adopt a wide range of oxidation states (+2, +3, and +4) in pure hematite, depending on the termination and chemisorbed species on the surface, but a Fe+3 state is stabilized predominantly upon doping. While Rh is in the +3 state in the bulk, it transforms to +4 at the surface and acquires a finite magnetic moment in several intermediate steps. © 2020 Author(s).
    view abstractdoi: 10.1063/1.5143236
  • 2020 • 557 Kokkos implementation of an Ewald Coulomb solver and analysis of performance portability
    Halver, R. and Meinke, J.H. and Sutmann, G.
    Journal of Parallel and Distributed Computing 138 48-54 (2020)
    We have implemented the computation of Coulomb interactions in particle systems using the performance portable C++ framework Kokkos. For the computation of the electrostatic interactions in particle systems we used an Ewald summation. This implementation we consider as a basis for a performance portability study. As target architectures we used Intel CPUs, including Intel Xeon Phi, as well as Nvidia GPUs. To provide a measure for performance portability we compute the number of needed operations and required cycles, i.e. runtime, and compare these with the measured runtime. Results indicate a similar quality of performance portability on all investigated architectures. © 2019 Elsevier Inc.
    view abstractdoi: 10.1016/j.jpdc.2019.12.003
  • 2020 • 556 Examining Performance Portability with Kokkos for an Ewald Sum Coulomb Solver
    Halver, R. and Meinke, J.H. and Sutmann, G.
    Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) 12044 LNCS 35-45 (2020)
    We have implemented the computation of Coulomb interactions in particle systems using the performance portable C++ framework Kokkos. Coulomb interactions are evaluated with an Ewald-sum-based solver, where the interactions are split into long- and short-range contributions. The short-range contributions are calculated using pair-wise contributions of particles while long-range interactions are calculated using Fourier sums. We evaluate the performance portability of the implementation on Intel CPUs, including Intel Xeon Phi, and Nvidia GPUs. © 2020, Springer Nature Switzerland AG.
    view abstractdoi: 10.1007/978-3-030-43222-5_4
  • 2020 • 555 Thermal phase design of ultrathin magnetic iron oxide films: From Fe3O4 to γ-Fe2O3 and FeO
    Hamed, M.H. and Mueller, D.N. and Müller, M.
    Journal of Materials Chemistry C 8 1335-1343 (2020)
    We demonstrate the thermally induced phase transformations between Fe3O4, γ-Fe2O3 and FeO ultrathin iron oxide films, which are part of all-oxide heterostructures, and present a comprehensive thermodynamic analysis of the emerging interfacial redox processes. We thereby reveal the essential-but mostly underrated-role of oxide substrates, which can completely alter the standard FexOy temperature-pressure phase diagram as an additional oxygen supplier or scavenger. We introduce an adjusted phase diagram specifically for FexOy/Nb:SrTiO3 and FexOy/YSZ heterostructures based on a total effective oxygen activity. This novel approach opens up the route towards tuning physical functionalities in all-oxide heterostructures by a controlled thermal phase design. This journal is © The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c9tc05921k
  • 2020 • 554 Gas-phase synthesis of iron oxide nanoparticles for improved magnetic hyperthermia performance
    Hammad, M. and Hardt, S. and Mues, B. and Salamon, S. and Landers, J. and Slabu, I. and Wende, H. and Schulz, C. and Wiggers, H.
    Journal of Alloys and Compounds 824 (2020)
    Magnetic nanoparticle-mediated hyperthermia has shown great potential in cancer therapy. However, upscaling of the synthesis of iron oxide nanoparticle with the required narrow size distribution remains challenging. This paper describes the reproducible and scalable synthesis of citric acid-functionalized iron oxide nanoparticles optimized for hyperthermia treatment. Iron oxide nanoparticles were synthesized by a spray flame method, which is eco-friendly and cost-effective. To the best of our knowledge, this is the first study reporting spray-flame synthesis of small iron oxide nanoparticles (approx. 7 nm) with narrow size distribution (polydispersity index ≪ 0.1). The citric acid-coated iron oxide nanoparticles revealed a hydrodynamic size of approx. 37 nm and a high magnetic saturation of 69 Am2/kg at room temperature. The magnetic hyperthermia study showed a significantly enhanced value of the intrinsic loss power (4.8 nHm2/kg), which is 1.5-fold higher than the best commercially available equivalents. The improved heating efficiency and small hydrodynamic size of citric acid-coated iron oxide nanoparticles demonstrate that the system could potentially be used as a nanoplatform for hyperthermia treatment. © 2020 Elsevier B.V.
    view abstractdoi: 10.1016/j.jallcom.2020.153814
  • 2020 • 553 Using spectral-based representative volume element crystal plasticity simulations to predict yield surface evolution during large scale forming simulations
    Han, F. and Diehl, M. and Roters, F. and Raabe, D.
    Journal of Materials Processing Technology 277 (2020)
    We present a new approach to predict the evolution of anisotropic yield functions by coupling large scale forming simulations with crystal plasticity-spectral based virtual experiments, realizing a multi-scale model for metal forming. Employing a fast spectral method solver enables us to conduct on-the-fly full-field virtual experiments to evolve the yield surface at each integration point of the macroscopic finite element model. As illustrative example, two advanced anisotropic yield functions, namely Yld2000-2D and Yld2004-18p, are used in finite element simulations of deep drawing for a 2090-T3 aluminum alloy sheet. The simulated earing profiles are compared to the experimental ones as well as to simulations with non-evolving yield functions. It is found that the prediction of the earing is improved for the case of the evolving Yld2000-2D yield function. The evolution of the plastic anisotropy during cup drawing is systematically analyzed, showing that the evolution of anisotropy can have considerable effect on the prediction accuracy of the macroscopic simulations. © 2019 Elsevier B.V.
    view abstractdoi: 10.1016/j.jmatprotec.2019.116449
  • 2020 • 552 Microstructure-based multiscale modeling of large strain plastic deformation by coupling a full-field crystal plasticity-spectral solver with an implicit finite element solver
    Han, F. and Roters, F. and Raabe, D.
    International Journal of Plasticity 125 97-117 (2020)
    We present a fully embedded implementation of a full-field crystal plasticity model in an implicit finite element (FE) framework, a combination which realizes a multiscale approach for the simulation of large strain plastic deformation. At each integration point of the macroscopic FE model a spectral solver, based on Fast Fourier Transforms (FFTs), feeds-in the homogenized response from an underlying full-field polycrystalline representative volume element (RVE) model which is solved by using a crystal plasticity constitutive formulation. Both, a phenomenological hardening law and a dislocation density based hardening model, implemented in the open source software DAMASK, have been employed to provide the constitutive response at the mesoscale. The accuracy of the FE-FFT model has been benchmarked by one-element tests of several loading scenarios for an FCC polycrystal including simple tension, simple compression, and simple shear. The multiscale model is applied to simulate four application cases, i.e., plane strain deformation of an FCC plate, compression of an FCC cylinder, four-point bending of HCP bars, and beam bending of a dual-phase steel. The excellent capabilities of the model to predict the microstructure evolution at the mesoscale and the mechanical responses at both macroscale and mesoscale are demonstrated. © 2019 Elsevier Ltd.
    view abstractdoi: 10.1016/j.ijplas.2019.09.004
  • 2020 • 551 Data-oriented constitutive modeling of plasticity in metals
    Hartmaier, A.
    Materials 13 (2020)
    Constitutive models for plastic deformation of metals are typically based on flow rules determining the transition from elastic to plastic response of a material as function of the applied mechanical load. These flow rules are commonly formulated as a yield function, based on the equivalent stress and the yield strength of the material, and its derivatives. In this work, a novel mathematical formulation is developed that allows the efficient use of machine learning algorithms describing the elastic-plastic deformation of a solid under arbitrary mechanical loads and that can replace the standard yield functions with more flexible algorithms. By exploiting basic physical principles of elastic-plastic deformation, the dimensionality of the problem is reduced without loss of generality. The data-oriented approach inherently offers a great flexibility to handle different kinds of material anisotropy without the need for explicitly calculating a large number of model parameters. The applicability of this formulation in finite element analysis is demonstrated, and the results are compared to formulations based on Hill-like anisotropic plasticity as reference model. In future applications, the machine learning algorithm can be trained by hybrid experimental and numerical data, as for example obtained from fundamental micromechanical simulations based on crystal plasticity models. In this way, data-oriented constitutive modeling will also provide a new way to homogenize numerical results in a scale-bridging approach. © 2020 by the authors.
    view abstractdoi: 10.3390/ma13071600
  • 2020 • 550 Evaluation of Different Phased Array Approaches for Orbital Angular Momentum Beam Steering
    Hassan, M.H. and Al-Mulla, M. and Sievert, B. and Rennings, A. and Erni, D.
    GeMIC 2020 - Proceedings of the 2020 German Microwave Conference 44-47 (2020)
    This paper presents several approaches for beam steering of vortex waves that are generated by a Uniform Circular Patch Array (UCA) operating at 10 GHz. Firstly, we design and evaluate a uniform circular patch array with 8 patch antennas. For the beam steering of Orbital Angular Momentum (OAM) waves two different types of phasing are necessary, firstly the azimuthal OAM phasing of the UCA elements, and secondly the global circular array phasing for beam steering. The steering works well up to the steering angle of 20°, where the gain difference between the two lobes is less than 3 dB. Secondly, we use the same UCA but with 4 elements instead of 8 elements. Each antenna element will be replaced with 3 different subarrays of 4 antennas (linear, rectangular and circular). These 4 approaches are compared to each other. Here, there is an additional phase shift, which will be called local subarray phasing. The rectangular array shows a better performance compared to the other forms. The advantage of using an array is, that the steering is working good up to an angle of 30°. © 2020 IMA-Institut fur Mikrowellen-und Antennentechnik e.V.
    view abstract
  • 2020 • 549 A crossover in spatio-temporal correlations of strain fluctuations in glass forming liquids
    Hassani, M. and Bruns, M. and Varnik, F.
    Journal of Statistical Mechanics: Theory and Experiment 2020 (2020)
    Via molecular dynamics simulations of a generic glass former in the supercooled and normal liquid states, it is shown that spatial correlations of strain fluctuations exhibit a crossover from the well-established power-law ∼1/r 3-decay at long wavelengths to an exponential behavior, ∼&amp;esp(-r/lc) at intermediate distances. The characteristic length of the exponential decay grows both with temperature and time via, l2 c ∝ D(T)t, with D(T) being the temperature-dependent diffusion coefficient. This suggests that the crossover between the power-law and exponential decays is governed by a diffusion process. © 2020 IOP Publishing Ltd and SISSA Medialab srl.
    view abstractdoi: 10.1088/1742-5468/ab5366
  • 2020 • 548 Multi-Stimuli-Responsive Supramolecular Polymers Based on Noncovalent and Dynamic Covalent Bonds
    Hatai, J. and Hirschhäuser, C. and Niemeyer, J. and Schmuck, C.
    ACS Applied Materials and Interfaces 12 2107-2115 (2020)
    Several modes of supramolecular assembly relying on noncovalent as well as dynamic covalent interactions were combined in a single molecule. The supramolecular self-assembly of 1 can be controlled by three stimuli, namely light, pH, and addition of metal ions, in both organic and aqueous media. The multi-stimuli-responsive nature of 1 was used successfully for the controlled encapsulation and on-demand release of hydrophobic molecules, such as dyes and drugs. © 2019 American Chemical Society.
    view abstractdoi: 10.1021/acsami.9b19279
  • 2020 • 547 Elastic properties of single crystal Bi12SiO20 as a function of pressure and temperature and acoustic attenuation effects in Bi12 MO20 (M = Si, Ge and Ti)
    Haussühl, E. and Reichmann, H.J. and Schreuer, J. and Friedrich, A. and Hirschle, C. and Bayarjargal, L. and Winkler, B. and Alencar, I. and Wiehl, L. and Ganschow, S.
    Materials Research Express 7 (2020)
    A comprehensive study of sillenite Bi12SiO20 single-crystal properties, including elastic stiffness and piezoelectric coefficients, dielectric permittivity, thermal expansion and molar heat capacity, is presented. Brillouin-interferometry measurements (up to 27 GPa), which were performed at high pressures for the first time, and ab initio calculations based on density functional theory (up to 50 GPa) show the stability of the sillenite structure in the investigated pressure range, in agreement with previous studies. Elastic stiffness coefficients c 11 and c 12 are found to increase continuously with pressure while c 44 increases slightly for lower pressures and remains nearly constant above 15 GPa. Heat-capacity measurements were performed with a quasi-adiabatic calorimeter employing the relaxation method between 2 K and 395 K. No phase transition could be observed in this temperature interval. Standard molar entropy, enthalpy change and Debye temperature are extracted from the data. The results are found to be roughly half of the previous values reported in the literature. The discrepancy is attributed to the overestimation of the Debye temperature which was extracted from high-temperature data. Additionally, Debye temperatures obtained from mean sound velocities derived by Voigt-Reuss averaging are in agreement with our heat-capacity results. Finally, a complete set of electromechanical coefficients was deduced from the application of resonant ultrasound spectroscopy between 103 K and 733 K. No discontinuities in the temperature dependence of the coefficients are observed. High-temperature (up to 1100 K) resonant ultrasound spectra recorded for Bi12 MO20 crystals revealed strong and reversible acoustic dissipation effects at 870 K, 960 K and 550 K for M = Si, Ge and Ti, respectively. Resonances with small contributions from the elastic shear stiffness c 44 and the piezoelectric stress coefficient e 123 are almost unaffected by this dissipation. © 2020 The Author(s). Published by IOP Publishing Ltd.
    view abstractdoi: 10.1088/2053-1591/ab6ad6
  • 2020 • 546 The effect of downstream laser fragmentation on the specific surface area and photoelectrochemical performance of barium tantalum oxynitride
    Haydous, F. and Waag, F. and Si, W. and Li, F. and Barcikowski, S. and Gökce, B. and Lippert, T.
    Applied Surface Science 510 (2020)
    One approach to improve the photoelectrochemical solar water splitting performance of photoanodes based on oxynitride perovskite particles is through increasing the active surface area which allows the generation of more electron-hole pairs that contribute in the water reduction and oxidation reactions. In this study, we explore the pros and cons of downstream laser fragmentation as a method to increase the specific surface area of oxynitride particles and highlight the important issues that must be considered for effective solar water splitting. The synthesis of particles with a high surface area of up to 32.4 m2 g−1 is demonstrated. Furthermore, the fragmented oxynitrides revealed lower absorbance values, a blue shift in the absorption edge and a higher background absorbance. These observations, in addition to the lower crystalline quality of the fragmented oxynitrides, were attributed to the loss of N content during fragmentation and the formation of secondary phases. The photoanodes based on the fragmented particles showed lower photocurrents than those prepared from the un-fragmented particles even though the surface area was increased. The decrease in photoactivity was ascribed to the presence of more grain boundaries in the fragmented oxynitride photoanodes which leads to more recombinations of the photogenerated carriers. Interestingly, after seven fragmentation passages, the photocurrent starts to increase again due to the formation of an amorphous layer which improves the transport of the photogenerated carriers. © 2020
    view abstractdoi: 10.1016/j.apsusc.2020.145429
  • 2020 • 545 On the atomic solute diffusional mechanisms during compressive creep deformation of a Co-Al-W-Ta single crystal superalloy
    He, J. and Zenk, C.H. and Zhou, X. and Neumeier, S. and Raabe, D. and Gault, B. and Makineni, S.K.
    Acta Materialia 184 86-99 (2020)
    We investigated the solute diffusional behavior active during compressive creep deformation at 150 MPa / 975 °C of a Co-Al-W-Ta single crystal superalloy in the [001] orientation. We report the formation of shear-bands that involves re-orientation of γ/γʹ rafts to {111} from {001} planes, referring to as γ/γ′ raft-rotation. In the shear-band regions, we observed abundant micro-twins, stacking faults (SFs), disordered zones within the γʹ termed as ‘γ pockets’ and also few geometrically-close-packed (GCP) phases. We used a correlative approach blending electron microscopy and atom probe tomography to characterize the structure and composition of these features. The SFs were identified as intrinsic and exhibit a W enrichment up to 14.5 at.% and an Al deficiency down to 5.1 at.%, with respect to the surrounding γʹ phase. The micro-twin boundaries show a solute enrichment similar to the SFs with a distinct W compositional profile gradients perpendicular from the boundaries into the twin interior, indicating solute diffusion within the micro-twins. The γ-pockets have a composition close to that of γ but richer in W/Ta. Based on these observations, we propose (i) a solute diffusion mechanism taking place during micro-twinning, (ii) a mechanism for the γ/γʹ raft-rotation process and evaluate their influence on the overall creep deformation of the present Co-based superalloy. © 2019
    view abstractdoi: 10.1016/j.actamat.2019.11.035
  • 2020 • 544 On the rhenium segregation at the low angle grain boundary in a single crystal Ni-base superalloy
    He, J. and Scholz, F. and Horst, O.M. and Thome, P. and Frenzel, J. and Eggeler, G. and Gault, B.
    Scripta Materialia 185 88-93 (2020)
    Industrial scale single crystal (SX) Ni-base superalloys contain numerous low angle grain boundaries inherited from the solidification process. Here, we demonstrate that low angle grain boundaries in a fully heat-treated SX model Ni-base superalloy are strongly segregated with up to 12 at% Re. Some Re-rich dislocations forming this grain boundary are found located inside γ, others close to a γ/γ′ interface. Although these segregated Re atoms lose their solid-solution strengthening effect, they may enhance the creep resistance by pinning the low angle grain boundaries and slowing down dislocation reactions. © 2020 Acta Materialia Inc.
    view abstractdoi: 10.1016/j.scriptamat.2020.03.063
  • 2020 • 543 Corrigendum to ‘On the Re segregation at the low angle grain boundary in a single crystal Ni-base superalloy’ Scripta Materialia Volume 185, August 2020, Pages 88-93 (Scripta Materialia (2020) 185 (88–93), (S1359646220302475), (10.1016/j.scriptamat.2020.03.063))
    He, J. and Scholz, F. and Horst, O.M. and Thome, P. and Frenzel, J. and Eggeler, G. and Gault, B.
    Scripta Materialia 187 309 (2020)
    The authors regret that the acknowledgement for the funding in the initially version of the article was incomplete and should read “All authors acknowledge the financial support from DFG SFB TR 103 through project A1, A2, A4, B7”. The authors would like to apologise for any inconvenience caused. © 2020 Acta Materialia Inc.
    view abstractdoi: 10.1016/j.scriptamat.2020.06.039
  • 2020 • 542 Dual pH-Induced Reversible Self-Assembly of Gold Nanoparticles by Surface Functionalization with Zwitterionic Ligands
    He, H. and Ostwaldt, J.-E. and Hirschhäuser, C. and Schmuck, C. and Niemeyer, J.
    Small 16 (2020)
    The dual pH-induced reversible self-assembly (PIRSA) of Au-nanoparticles (Au NPs) is reported, based on their decoration with the self-complementary guanidiniocarbonyl pyrrole carboxylate zwitterion (GCPZ). The assembly of such functionalized Au NPs is found at neutral pH, based on supramolecular pairing of the GCPZ groups. The resulting self-assembled system can be switched back to the disassembled state by addition of base or acid. Two predominant effects that contribute to the dual-PIRSA of Au NPs are identified, namely the ionic hydrogen bonding between the GCPZ groups, but also a strong hydrophobic effect. The contribution of each interaction is depending on the concentration of GCPZ on NPs, which allows to control the self-assembly state over a wide range of different water/solvent ratios. © 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/smll.202001044
  • 2020 • 541 CO-concentration and temperature measurements in reacting CH4/O2 mixtures doped with diethyl ether behind reflected shock waves
    He, D. and Shi, L. and Nativel, D. and Herzler, J. and Fikri, M. and Schulz, C.
    Combustion and Flame 216 194-205 (2020)
    The oxidation of CH4/diethyl ether mixtures was studied with laser absorption-based time-resolved temperature and CO concentration measurements behind reflected shock waves. Fuel-rich (equivalence ratio ϕ = 2.0) mixtures were studied because of their relevance for mechanism development for partial oxidation reactions in the context of polygeneration processes and measurements at ϕ = 0.5 and 1.0 were used to verify the mechanism performance in an extended range of equivalence ratios. Temperature and CO concentration were measured via absorption using two fundamental vibrations of CO (ν" = 0, P20 and ν" = 1, R21) with two mid-IR quantum-cascade lasers near 4.8546 and 4.5631 µm. Interference from broadband absorption of CO2 in the region near 4.56 µm was quantified based on measured temperature-dependent CO2 absorption cross-sections and mechanism-based prediction of CO2 concentrations. The measured temporal CO-concentration and temperature profiles were compared with simulations based on two mechanisms (Fikri et al., 2017; Yasunaga et al., 2010). For mixtures with ϕ = 0.5, the two mechanisms show similar results, and well reproduce the experimental data. At ϕ = 1.0 and 2.0, the Fikri et al. mechanism shows very good agreement with the experiments whereas the Yasunaga et al. mechanism predicts a too fast CO-concentration and temperature rise. © 2020 The Combustion Institute
    view abstractdoi: 10.1016/j.combustflame.2020.02.024
  • 2020 • 540 Reduced dimension GDSW coarse spaces for monolithic Schwarz domain decomposition methods for incompressible fluid flow problems
    Heinlein, A. and Hochmuth, C. and Klawonn, A.
    International Journal for Numerical Methods in Engineering 121 1101-1119 (2020)
    Monolithic preconditioners for incompressible fluid flow problems can significantly improve the convergence speed compared with preconditioners based on incomplete block factorizations. However, the computational costs for the setup and the application of monolithic preconditioners are typically higher. In this article, several techniques are applied to monolithic two-level generalized Dryja-Smith-Widlund (GDSW) preconditioners to further improve the convergence speed and the computing time. In particular, reduced dimension GDSW coarse spaces, restricted and scaled versions of the first level, hybrid, and parallel coupling of the levels, and recycling strategies are investigated. Using a combination of all these improvements, for a small time-dependent Navier-Stokes problem on 240 message passing interface (MPI) ranks, a reduction of 86% of the time-to-solution can be obtained. Even without applying recycling strategies, the time-to-solution can be reduced by more than 50% for a larger steady Stokes problem on 4608 MPI ranks. For the largest problems with 11 979 MPI ranks, the scalability deteriorates drastically for the monolithic GDSW coarse space. On the other hand, using the reduced dimension coarse spaces, good scalability up to 11 979 MPI ranks, which corresponds to the largest problem configuration fitting on the employed supercomputer, could be achieved. © 2019 The Authors. International Journal for Numerical Methods in Engineering published by John Wiley & Sons, Ltd.
    view abstractdoi: 10.1002/nme.6258
  • 2020 • 539 Pattern Formation in High Power Impulse Magnetron Sputtering (HiPIMS) Plasmas
    Held, J. and von Keudell, A.
    Plasma Chemistry and Plasma Processing 40 643-660 (2020)
    High power impulse magnetron sputtering (HiPIMS) plasmas produce a very energetic growth flux for the synthesis of thin films with superior properties. High power densities in the range of a few kW / cm 2 are applied to a metal target electrode in short pulses with a length of 10–400μs and duty cycles of a few percent or less in an argon plasma gas. Fast camera and probe measurements revealed the formation of very characteristic plasma patterns that become visible as rotating localized ionization zones, so called spokes. The appearance of these spokes at high plasma powers is believed to be essential for the good performance of HiPIMS plasmas. The rotation direction of the spokes is in E→ × B→ direction at high plasma powers, but in retrograde E→ × B→ direction at low plasma powers. This characteristic behavior is explained by applying a simple drift wave model from literature and comparing the dispersion relation of those waves with measured data. The pronounced rotation reversal is explained by either a change in the governing density gradient in the plasma or by the change in the direction of the streaming ions during the transition from an argon dominated regime at low powers to a metal dominated regime at high powers. © 2019, Springer Science+Business Media, LLC, part of Springer Nature.
    view abstractdoi: 10.1007/s11090-019-10052-3
  • 2020 • 538 Ligand Effects on the Electronic Structure of Heteroleptic Antimony-Centered Radicals
    Helling, C. and Cutsail, G.E., III and Weinert, H. and Wölper, C. and Schulz, S.
    Angewandte Chemie - International Edition 59 7561-7568 (2020)
    We report on the structures of three unprecedented heteroleptic Sb-centered radicals [L(Cl)Ga](R)Sb. (2-R, R=B[N(Dip)CH]2 2-B, 2,6-Mes2C6H3 2-C, N(SiMe3)Dip 2-N) stabilized by one electropositive metal fragment [L(Cl)Ga] (L=HC[C(Me)N(Dip)]2, Dip=2,6-i-Pr2C6H3) and one bulky B- (2-B), C- (2-C), or N-based (2-N) substituent. Compounds 2-R are predominantly metal-centered radicals. Their electronic properties are largely influenced by the electronic nature of the ligands R, and significant delocalization of unpaired-spin density onto the ligands was observed in 2-B and 2-N. Cyclic voltammetry (CV) studies showed that 2-B undergoes a quasi-reversible one-electron reduction, which was confirmed by the synthesis of [K([2.2.2]crypt)][L(Cl)GaSbB[N(Dip)CH]2] ([K([2.2.2]crypt)][2-B]) containing the stibanyl anion [2-B]−, which was shown to possess significant Sb−B multiple-bonding character. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
    view abstractdoi: 10.1002/anie.202000586
  • 2020 • 537 Damage-induced performance variations of cold forged parts
    Hering, O. and Tekkaya, A.E.
    Journal of Materials Processing Technology 279 (2020)
    Forming processes play a key role in the manufacturing of metal components. They allow for the economical production of geometrical shapes with reproducibly high quality. Strain hardening and residual stresses affect the performance of the produced parts. These factors are controllable and can even be utilized to increase the performance of the component. This, however, does not apply to damage. Damage in metals describes the decrease of the load-bearing capacity due to the appearance and evolution of voids. The aim is to analyse, predict, and control the evolution of damage in cold forging, to allow for a production of cold forged components with a defined, load-adapted performance. It was investigated numerically to what extent the load path, which is responsible for the damage evolution, is affected in cold forging. Subsequently, the effect of load path changes on the product performance was determined experimentally in the region of the central axis where the load path is affected most by the extrusion parameters. Hereby, a correlation between the occurring triaxiality during forming and the product performance by means of number of cycles to failure in multi-step fatigue tests, impact energy and Young's modulus was observed. © 2019 Elsevier B.V.
    view abstractdoi: 10.1016/j.jmatprotec.2019.116556
  • 2020 • 536 Influence of ligands
    Herper, H.C. and Brena, B. and Puglia, C. and Bhandary, S. and Wende, H. and Eriksson, O. and Sanyal, B.
    SpringerBriefs in Applied Sciences and Technology 65-67 (2020)
    The adsorption of small molecules on the metal center of 3d metal phthalocyanines alters the bonding scheme of the molecule and can induce different spin states and magnetic moments, as well as trigger more exotic effects like Kondo resonance. Soft X-ray spectroscopy studies and computational studies have highlighted this kind of effects in magnetic molecules like FePc, CoPc and MnPc by adsorption of for example CO, NO, O&#x0024;&#x0024;:2&#x0024;&#x0024; molecules. © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2020.
    view abstractdoi: 10.1007/978-981-15-3719-6_7
  • 2020 • 535 Electron correlation and spin transition
    Herper, H.C. and Brena, B. and Puglia, C. and Bhandary, S. and Wende, H. and Eriksson, O. and Sanyal, B.
    SpringerBriefs in Applied Sciences and Technology 35-43 (2020)
    Theoretical treatment of functional metalorganics is non-trivial for the metal centers with narrow bands (3d, 4d of transition metals or 4f bands of rare-earth metals), featuring a sizeable Coulomb interaction. An interplay between crystal field, spin-orbit coupling and Coulomb interaction expresses the properties of the molecule. Correlated metal centers, immersed in the electron bath of organic ring makes it ideal to treat with Anderson’s impurity model. In this chapter, we will focus on the description of electron correlation in functional metalorganics with the aid of density functional theory, combined with a many body approach. For most of the illustrative purposes, we will consider iron porphyrin (FeP) molecule. The chapter will reveal the importance of the treatment of explicit electron correlation in order to accurately identify the spin transition, magnetic anisotropy, Kondo effect etc., which are key ingredients for molecular spintronics and electronics. © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2020.
    view abstractdoi: 10.1007/978-981-15-3719-6_5
  • 2020 • 534 Theoretical methods
    Herper, H.C. and Brena, B. and Puglia, C. and Bhandary, S. and Wende, H. and Eriksson, O. and Sanyal, B.
    SpringerBriefs in Applied Sciences and Technology 19-24 (2020)
    In this chapter, the theoretical methods required for the description of structure, electronic structure and magnetism of magnetic molecules in the gas phase and in the adsorbed configurations will be discussed. The main workhorse of the theoretical methods is the density functional theory that provides a materials-specific description of electronic structure, which is quite sufficient for many of the materials. However, in the present context of magnetic molecules, one needs to go beyond standard approximations in density functional theory. In this regard, some of the crucial characteristics in the electronic structure and magnetism will be discussed such as electron correlation, van der Waals interaction, band gaps, magnetic anisotropy and spin-dipole moments. © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2020.
    view abstractdoi: 10.1007/978-981-15-3719-6_3
  • 2020 • 533 Interaction with substrates
    Herper, H.C. and Brena, B. and Puglia, C. and Bhandary, S. and Wende, H. and Eriksson, O. and Sanyal, B.
    SpringerBriefs in Applied Sciences and Technology 45-64 (2020)
    Organometallic molecules have attracted interest because their properties can be varied by changing ligands, metal center, end groups etc. which makes them candidates for various applications. Special attention has been paid to hybrid systems of molecules and substrates as possible building blocks for future electronic and magnetic devices. In view of such devices phthalocyanine molecules are advantageous because they can adsorb flat on metallic or semiconducting substrates. Aiming to understand the magnetic properties of the molecules and their interplay with substrates and ligands the focus will be on the paramagnetic Pc molecules i.e. Mn, Fe, Co and CuPc and their interaction with (metallic) substrates and nonmagnetic TMPCs such as NiPc and ZnPc are only briefly mentioned. © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2020.
    view abstractdoi: 10.1007/978-981-15-3719-6_6
  • 2020 • 532 Applications
    Herper, H.C. and Brena, B. and Puglia, C. and Bhandary, S. and Wende, H. and Eriksson, O. and Sanyal, B.
    SpringerBriefs in Applied Sciences and Technology 69-73 (2020)
    In this chapter, a short introduction to possible applications utilizing organic molecules interacting with ferromagnetic substrates will be given. By explaining the spin filtering concept, studies with Cu-phthalocyanine as well as zinc methyl phenalenyl molecules will be reviewed. The hybridization of the electronic states of the molecules at the interface to those of substrates is a crucial point to realize functional hybrid metalorganic interfaces. A large magnetic anisotropy is found for the hybridized phenalenyl layer, which is important for the interface magnetoresistance effect used in this spin filter concept study. © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2020.
    view abstractdoi: 10.1007/978-981-15-3719-6_8
  • 2020 • 531 Electronic structure of isolated molecules
    Herper, H.C. and Brena, B. and Puglia, C. and Bhandary, S. and Wende, H. and Eriksson, O. and Sanyal, B.
    SpringerBriefs in Applied Sciences and Technology 25-34 (2020)
    Phthalocyanine molecules with a 3d transition metal in the center, like MnPc, FePc, CoPc, NiPc and CuPc, have attracted a huge interest in the last decades due to the large number of possible applications. Experimental and theoretical gas phase studies are an important reference to understand the properties of the molecules, as well as how they can be modified and manipulated upon deposition on substrates or in supramolecular conformations. However, in several 3d metal phthalocyanines the electronic structure of the single molecule is still under debate even after several spectroscopical studies and computational works have been performed. This is mostly due to the highly correlated 3d electrons of the metal atoms, which pose a challenge for the theory. In addition, the experiments to determine the electronic structure are often carried out in different conditions (on thick films or in gas phase for example), and this can lead to different results. The following chapter provides an overview of the theoretical and experimental results and debates related to the electronic structure of gas phase MnPc, FePc, CoPc, NiPc and CuPc. © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2020.
    view abstractdoi: 10.1007/978-981-15-3719-6_4
  • 2020 • 530 Experimental techniques
    Herper, H.C. and Brena, B. and Puglia, C. and Bhandary, S. and Wende, H. and Eriksson, O. and Sanyal, B.
    SpringerBriefs in Applied Sciences and Technology 5-17 (2020)
    Different spectroscopic methods can be used to characterize the electronic structure of a system of interest, i.e. molecular, solid or adsorbate samples. The different techniques give complementary information about the geometric and electronic structure of the system. By Photoelectron Spectroscopy (PES), Auger and resonant photoemission (RPES) the occupied electronic levels can be studied, whereas X-ray Absorption Spectroscopy (XAS) gives information about the unoccupied valence states of the system in presence, however, of a core hole. Magnetic information can be obtained from X-ray Magnetic Circular Dichroism (XMCD). © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2020.
    view abstractdoi: 10.1007/978-981-15-3719-6_2
  • 2020 • 529 Introduction
    Herper, H.C. and Brena, B. and Puglia, C. and Bhandary, S. and Wende, H. and Eriksson, O. and Sanyal, B.
    SpringerBriefs in Applied Sciences and Technology 1-4 (2020)
    Phthalocyanine molecules with a 3d transition metal in the centre, like MnPc, FePc, CoPc, NiPc and CuPc, have attracted a huge interest in the last decades due to the large number of possible applications. Experimental and theoretical gas phase studies are an important reference to understand the properties of the molecules, as well as how they can be modified and manipulated upon deposition on substrates or in supramolecular conformations. However, in several 3d metal phthalocyanines, the electronic structure of the single molecule is still under debate even after several spectroscopic studies and computational works have been performed. This is mostly due to the highly correlated 3d electrons of the metal atoms, which pose a challenge for the theory. In addition, the experiments to determine the electronic structure are often carried out in different conditions (on thick films or in gas phase for example), and this can lead to different results. The following chapter provides an overview of the theoretical and experimental results and debates related to the electronic structure of gas phase MnPc, FePc, CoPc, NiPc and CuPc. © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2020.
    view abstractdoi: 10.1007/978-981-15-3719-6_1
  • 2020 • 528 High-pressure shock-tube study of the ignition and product formation of fuel-rich dimethoxymethane (DMM)/air and CH4/DMM/air mixtures
    Herzler, J. and Fikri, M. and Schulz, C.
    Combustion and Flame 216 293-299 (2020)
    Ignition delay times (IDTs) of fuel-rich CH4/dimethoxymethane (DMM)/air mixtures (ϕ = 2 and 10) were measured in a high-pressure shock tube at a pressure of 30 bar and compared to simulations based on reaction mechanisms for DMM from literature. Additionally, IDT of DMM/air mixtures were measured at similar conditions in a wide range of equivalence ratios (ϕ = 0.5, 1, and 2). Those mechanisms that predict the IDTs of DMM within the experimental uncertainties also predict the IDTs of the fuel-rich CH4/DMM/air mixtures very well although they were not designed for these conditions. For the measurements at ϕ = 10, product gas samples were extracted from the shock tube test section at around 14–24 ms after arrival of the reflected shock wave by a fast-opening valve and analyzed with gas chromatography. Besides CO, H2, and H2O, ethane, ethylene, acetylene, benzene, propene and toluene were observed as main reaction products. © 2020 The Combustion Institute
    view abstractdoi: 10.1016/j.combustflame.2020.03.008
  • 2020 • 527 Investigation of process control influence on tribological properties of FLM-manufactured components
    Hesse, D. and Stanko, M. and Hohenberg, P. and Stommel, M.
    Journal of Manufacturing and Materials Processing 4 (2020)
    In recent years, additive manufacturing methods such as Fused Layer Modeling have been continuously improved by industry and research institutions. In many cases, the influence of process control on the mechanical component properties is being investigated. Influencing parameters include the infill and its orientation as well as patterns. Extrusion parameters such as the volume flow, which can be influenced by the speed, the line width, and the layer thickness, and the temperatures, which determine the interlaminar bonding between the lines and layers, are relevant as well. In this contribution, the influence of process control on the tribological properties of cylindrical tribo-test specimens made of polybutylene terephthalate is investigated. Using a reciprocating pin-on-plate tribo-tester, the static and dynamic friction forces as well as the linear wear is determined. The results show a significant influence of the orientation and density of the infill on the tribological properties. Due to the process-specific large degrees of freedom, the advantage of a load-compatible individualisation and consequently the optimisation of tribologically exposed components is given compared to conventional manufacturing processes. © 2020 by the authors.
    view abstractdoi: 10.3390/jmmp4020037
  • 2020 • 526 Poly(2-oxazoline)s with a 2,2′-Iminodiacetate End Group Inhibit and Stabilize Laccase
    Hijazi, M. and Türkmen, E. and Tiller, J.C.
    ChemBioChem 21 874-882 (2020)
    Poly(2-oxazoline)s (POxs) with 2,2′-iminodiacetate (IDA) end groups were investigated as inhibitors for laccase. The polymers with the IDA end groups are reversible, competitive inhibitors for this enzyme. The IC50 values were found to be in a range of 1–3 mm. Compared with IDA alone, the activity was increased by a factor of more than 30; thus indicating that attaching a polymer chain to an inhibitor can already improve the activity of the former. The enzyme activity drops to practically zero upon increasing the concentration of the most active telechelic inhibitor, IDA-PEtOx30-IDA (PEtOx: poly(2-ethyl-2-oxazoline)), from 5 to 8 mm. This unusual behavior was investigated by means of dynamic light scattering, which showed specific aggregation above 5 mm. Furthermore, the laccase could be stabilized in the presence of POx-IDA, upon addition at a concentration of 20 mm and higher. Whereas laccase becomes completely inactive at room temperature after one week, the stabilized laccase is fully active for at least a month in aqueous solution. © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
    view abstractdoi: 10.1002/cbic.201900561
  • 2020 • 525 Toward Mobile Integrated Electronic Systems at THz Frequencies
    Hillger, P. and van Delden, M. and Thanthrige, U.S.M. and Ahmed, A.M. and Wittemeier, J. and Arzi, K. and Andree, M. and Sievert, B. and Prost, W. and Rennings, A. and Erni, D. and Musch, T. and Weimann, N. and Sezgin, A. and Pohl...
    Journal of Infrared, Millimeter, and Terahertz Waves (2020)
    This paper discusses advances related to the integration of future mobile electronic THz systems. Without claiming to provide a comprehensive review of this surging research area, the authors gathered research on selected topics that are expected to be of relevance for the future exploration of components for practical mobile THz imaging and sensing applications. First, a brief technology review of integrated mobile THz components is given. Advances in III-V technology, silicon technology, and resonant-tunneling diodes (RTD) are discussed. Based on an RTD source and a SiGe-HBT direct detector, low-cost and compact computed tomography is presented for volumetric continuous-wave imaging at around 300 GHz. Moreover, aspects of system integration of mobile THz MIMO radars are discussed. Thereby, a novel phase-locked loop concept utilizing a high-stability yttrium-iron-garnet-tuned oscillator to synthesize ultra-stable reference mmWave signals is shown, and an adaptive self-interference cancellation algorithm for THz MIMO in the digital domain based on Kalman filter theory is proposed. © 2020, Springer Science+Business Media, LLC, part of Springer Nature.
    view abstractdoi: 10.1007/s10762-020-00699-x
  • 2020 • 524 Pattern-forming nanoprecipitates in NiTi-related high entropy shape memory alloys
    Hinte, C. and Barienti, K. and Steinbrücker, J. and Gerstein, G. and Swider, M.A. and Herbst, S. and Eggeler, G. and Maier, H.J.
    Scripta Materialia 186 132-135 (2020)
    The microstructure and the fracture behavior of TiZrHfCoNiCu high entropy shape memory alloys with two different compositions were investigated. An unusual microstructure featuring pattern-forming nanoprecipitates was observed in dendritic and the interdendritic regions of both alloys. The unique higher-level order of these precipitates does not follow concentration gradients but is influenced by homogeneity and mechanical stress. The results also demonstrate that high entropy alloys are not necessarily homogeneous single-phase solid solutions. Moreover, it appears that solid solution strengthening as the primary mechanism also has to be questioned. © 2020 Acta Materialia Inc.
    view abstractdoi: 10.1016/j.scriptamat.2020.05.007
  • 2020 • 523 Materials for hydrogen-based energy storage – past, recent progress and future outlook
    Hirscher, M. and Yartys, V.A. and Baricco, M. and Bellosta von Colbe, J. and Blanchard, D. and Bowman, R.C., Jr. and Broom, D.P. and Buckley, C.E. and Chang, F. and Chen, P. and Cho, Y.W. and Crivello, J.-C. and Cuevas, F. and Dav...
    Journal of Alloys and Compounds 827 (2020)
    Globally, the accelerating use of renewable energy sources, enabled by increased efficiencies and reduced costs, and driven by the need to mitigate the effects of climate change, has significantly increased research in the areas of renewable energy production, storage, distribution and end-use. Central to this discussion is the use of hydrogen, as a clean, efficient energy vector for energy storage. This review, by experts of Task 32, “Hydrogen-based Energy Storage” of the International Energy Agency, Hydrogen TCP, reports on the development over the last 6 years of hydrogen storage materials, methods and techniques, including electrochemical and thermal storage systems. An overview is given on the background to the various methods, the current state of development and the future prospects. The following areas are covered; porous materials, liquid hydrogen carriers, complex hydrides, intermetallic hydrides, electrochemical storage of energy, thermal energy storage, hydrogen energy systems and an outlook is presented for future prospects and research on hydrogen-based energy storage. © 2020 The Authors
    view abstractdoi: 10.1016/j.jallcom.2019.153548
  • 2020 • 522 Thermoelastic anisotropy in NdScO3 and NdGaO3 perovskites
    Hirschle, C. and Schreuer, J. and Ganschow, S. and Peters, L.
    Materials Chemistry and Physics 254 (2020)
    Single crystal thermal expansion and elastic stiffness of NdGaO3 and NdScO3 were investigated by inductive gauge dilatometry and resonant ultrasound spectroscopy between 103K and 1673K, as they are used extensively as perovskite-type substrates for epitaxial crystal growth. Thermal expansion of NdGaO3 is in agreement with literature data and has very similar magnitude and anisotropy compared to NdScO3. The anisotropy of the elastic stiffness of NdGaO3 is more pronounced and qualitatively different from what is found for NdScO3. It is explained in terms of structural instabilities, which lead to known phase transitions in other perovskites. The anisotropy of the elastic stiffness of NdGaO3 is compatible with what is found for other orthorhombic perovskites that undergo a transition to a rhombohedral structure at high temperatures. The elastic properties of NdScO3 directly follow from the properties of other REScO3. The samples were characterized with regards to their compositions and lattice parameters using electron probe microanalysis and X-ray powder diffraction. © 2020 Elsevier B.V.
    view abstractdoi: 10.1016/j.matchemphys.2020.123528
  • 2020 • 521 Potential and status of damage controlled forming processes
    Hirt, G. and Tekkaya, A.E. and Clausmeyer, T. and Lohmar, J.
    Production Engineering 14 (2020)
    In modern process design of metallic components, the influence of the metal forming process on the component properties can be taken into account. However, damage occurring concurrent to forming cannot be accounted for yet. Due to the complex multi-scale, multi-mechanism nature of damage, it is very challenging to predict its evolution through any metal forming process chain. In order to enable such damage controlled forming processes in the future three research questions need to be addressed in detail: How are the mechanisms governing the damage initiation and evolution in metals best characterized? How can the damage mechanisms be described and the damage evolution be predicted using models? How do forming processes influence the damage evolution? Answering these questions and considering damage during process design will in the long term lead to improved lightweight components that do not require conventional safety factors, as their performance is already fully known. © 2020, The Author(s).
    view abstractdoi: 10.1007/s11740-019-00948-6
  • 2020 • 520 A generalized micromorphic approach accounting for variation and dispersion of preferred material directions
    von Hoegen, M. and Skatulla, S. and Schröder, J.
    Computers and Structures 232 (2020)
    Materials exhibiting a heterogeneous and non-uniform composition in terms of elastic and anisotropic properties such as biological tissues require special efforts to accurately describe their constitutive behavior. In contrast to classical models, micromorphic formulations can predict the macroscopically observable material response as originated from distinct scale-dependent micro-structural deformation mechanisms. This is facilitated by additional independent degrees of freedom and associated additional strain and stress quantities. Here, a generalized continuum is mathematically constructed from a macro-continuum and a micro-continuum which are both adequately coupled on kinematics and constitutive levels as well as by micro-boundary conditions. In view of biomechanical modeling, the potential of the formulation is studied for a number of academic examples characterized by an anisotropic material composition to elucidate the micromorphic material response as compared with the one obtained using a classical continuum mechanics approach. The results demonstrate the ability of the generalized continuum approach to address non-affine elastic reorientation of the preferred material direction in the macro-space and its dispersion in the micro-space as affecting deformation, strain and stress on the macroscopic level. In particular, if the anisotropy in the micromorphic formulation is solely linked to the extra degrees of freedom and associated strain and stress measures, the deformation for small and large strains is shown to be distinctly different to the classical response. Together with the ability to implicitly account for scale-dependent higher-order deformation effects in the constitutive law the proposed generalized micromorphic formulation provides an advanced description, especially for fibrous biological materials. © 2017 Elsevier Ltd
    view abstractdoi: 10.1016/j.compstruc.2017.11.013
  • 2020 • 519 A pressurized flow reactor combustion experiment interfaced with synchrotron double imaging photoelectron photoion coincidence spectroscopy
    Hoener, M. and Kaczmarek, D. and Bierkandt, T. and Bodi, A. and Hemberger, P. and Kasper, T.
    Review of Scientific Instruments 91 (2020)
    A new pressurized low-temperature combustion experiment has been commissioned at the Swiss Light Source, Paul Scherrer Institute. The experiment uses photoionization with tunable synchrotron radiation and double imaging photoelectron photoion coincidence (i2PEPICO) detection at the vacuum ultraviolet beamline. The experimental setup is described, including the high-pressure reactor experiment, sampling interface, and reactant delivery system. The CRF-PEPICO (Combustion Reactions Followed by Photoelectron Photoion Coincidence) endstation and VUV beamline are briefly elaborated. The novel aspects of the apparatus and the new components are elucidated in detail, such as the fluid supply system to the reactor and the reactor integration into the endstation. We also present a system overview of the experimental setup. The technical details are followed by a description of the experimental procedure used to operate the pressurized flow reactor setup. Finally, first experimental results demonstrating the capability of the setup are provided and analyzed. A major advantage of this new experiment is that the excellent isomer resolution capabilities of the i2PEPICO technique can be transferred to the investigation of reactions at elevated pressures of several bars. This enables the investigation of pressure effects on the reactivity of fuel mixtures and covers more realistic conditions found in technical combustors. The capability to obtain quantitative oxidation data is confirmed, and the main and certain intermediate species are quantified for a selected condition. The results show excellent agreement with a chemical kinetics model and previously published reference measurements performed with a gas chromatography setup. © 2020 Author(s).
    view abstractdoi: 10.1063/1.5141168
  • 2020 • 518 Reorientational dynamics of trimethoxyboroxine: A molecular glass former studied by dielectric spectroscopy and 11B nuclear magnetic resonance
    Hoffmann, L. and Beerwerth, J. and Greim, D. and Senker, J. and Sternemann, C. and Hiller, W. and Böhmer, R.
    Journal of Chemical Physics 152 (2020)
    In this work, trimethoxyboroxine (TMB) is identified as a small-molecule glass former. In its viscous liquid as well as glassy states, static and dynamic properties of TMB are explored using various techniques. It is found that, on average, the structure of the condensed TMB molecules deviates from threefold symmetry so that TMB's electric dipole moment is nonzero, thus rendering broadband dielectric spectroscopy applicable. This method reveals the super-Arrhenius dynamics that characterizes TMB above its glass transition, which occurs at about 204 K. To extend the temperature range in which the molecular dynamics can be studied, 11B nuclear magnetic resonance experiments are additionally carried out on rotating and stationary samples: Exploiting dynamic second-order shifts, spin-relaxation times, line shape effects, as well as stimulated-echo and two-dimensional exchange spectroscopy, a coherent picture regarding the dynamics of this glass former is gained. © 2020 Author(s).
    view abstractdoi: 10.1063/1.5129769
  • 2020 • 517 Ultrafast optically induced spin transfer in ferromagnetic alloys
    Hofherr, M. and Häuser, S. and Dewhurst, J.K. and Tengdin, P. and Sakshath, S. and Nembach, H.T. and Weber, S.T. and Shaw, J.M. and Silva, T.J. and Kapteyn, H.C. and Cinchetti, M. and Rethfeld, B. and Murnane, M.M. and Steil, D. ...
    Science Advances 6 (2020)
    The vision of using light to manipulate electronic and spin excitations in materials on their fundamental time and length scales requires new approaches in experiment and theory to observe and understand these excitations. The ultimate speed limit for all-optical manipulation requires control schemes for which the electronic or magnetic subsystems of the materials are coherently manipulated on the time scale of the laser excitation pulse. In our work, we provide experimental evidence of such a direct, ultrafast, and coherent spin transfer between two magnetic subsystems of an alloy of Fe and Ni. Our experimental findings are fully supported by time-dependent density functional theory simulations and, hence, suggest the possibility of coherently controlling spin dynamics on subfemtosecond time scales, i.e., the birth of the research area of attomagnetism. Copyright © 2020 The Authors,
    view abstractdoi: 10.1126/sciadv.aay8717
  • 2020 • 516 Study on machinability of additively manufactured and conventional titanium alloys in micro-milling process
    Hojati, F. and Daneshi, A. and Soltani, B. and Azarhoushang, B. and Biermann, D.
    Precision Engineering 62 1-9 (2020)
    Capability of Additive Manufacturing (AM) technology in the production of complex parts with high flexibility has led to the growing interest in their application as an alternative for conventional manufacturing processes. Despite the outstanding benefits of the AM process, due to their poor surface quality, the precision parts produced by this method generally need to be machined, ground, or polished. This paper addresses the machinability of AM Ti6Al4V titanium alloy parts in the micro-milling process with a specific focus on cutting forces, specific cutting energy, burr formation, and surface quality. Additive parts were produced by Electron Beam Melting (EBM) technique and were compared with the extruded Ti6Al4V parts in the micro-milling process. No significant difference could be observed in the cutting forces of both materials at chip thicknesses between 7.4 and 37.3 μm, despite the higher hardness of the EBM Ti6Al4V compared to the extruded Ti6Al4V. However, micro-milling of the EBM parts produced finer surfaces. Cutting forces and specific cutting energies of EBM parts were less than those of extruded parts at minimal chip thicknesses (lower than 7.4 μm). Continuous wavy-type burrs were formed in micro-milling of the EBM Ti6Al4V and were larger than those of extruded Ti6Al4V. © 2019 Elsevier Inc.
    view abstractdoi: 10.1016/j.precisioneng.2019.11.002
  • 2020 • 515 Analysis of incremental die bending of wires and tubes
    Holstein, V. and Hermes, M. and Tekkaya, A.E.
    Production Engineering 14 265-274 (2020)
    The use of bent wires, tubes, and profiles has a broad application in the industry as it is based on a great number of possible applications. Both structures with a high light-weight construction potential as well as functional and aesthetic geometry can be realised expediently. Known processes are often limited in case of tight radii and complex bending contours that cut each other or that are similar to a loop. The so called incremental die bending provides the remedy. It is an innovative process for the production of complexly shaped workpieces in the form of bent wires, tubes, or profiles. The bending process in case of incremental die bending is different to conventional processes, since a die is reshaped. With this process the semi-product is put into a hard bending shape by a moving feeding unit. The process is very accurate and at the same time cost-effective, since almost any bending contours can be produced form-based in one working stage. Furthermore, the die geometry enables the manufacture of contours that were previously very work-intensive or not producible at all. © 2020, The Author(s).
    view abstractdoi: 10.1007/s11740-020-00952-1
  • 2020 • 514 Extreme tensile strain states in La0.7Ca0.3MnO3 membranes
    Hong, S.S. and Gu, M. and Verma, M. and Harbola, V. and Wang, B.Y. and Lu, D. and Vailionis, A. and Hikita, Y. and Pentcheva, R. and Rondinelli, J.M. and Hwang, H.Y.
    Science 368 (2020)
    A defining feature of emergent phenomena in complex oxides is the competition and cooperation between ground states. In manganites, the balance between metallic and insulating phases can be tuned by the lattice; extending the range of lattice control would enhance the ability to access other phases. We stabilized uniform extreme tensile strain in nanoscale La0.7Ca0.3MnO3 membranes, exceeding 8% uniaxially and 5% biaxially. Uniaxial and biaxial strain suppresses the ferromagnetic metal at distinctly different strain values, inducing an insulator that can be extinguished by a magnetic field. Electronic structure calculations indicate that the insulator consists of charge-ordered Mn4+ and Mn3+ with staggered strain-enhanced Jahn-Teller distortions within the plane. This highly tunable strained membrane approach provides a broad opportunity to design and manipulate correlated electron states. © 2020 American Association for the Advancement of Science. All rights reserved.
    view abstractdoi: 10.1126/science.aax9753
  • 2020 • 513 A biphasic model for full cycle simulation of the human heart aimed at rheumatic heart disease
    Hopkins, G. and Skatulla, S. and Moj, L. and Ricken, T. and Ntusi, N. and Meintjes, E.
    Computers and Structures 232 (2020)
    Rheumatic heart disease (RHD) is identified as a serious health concern in developing countries, specifically amongst young individuals, accounting for between 250 000 and 1.4 million deaths annually. As such, attention is initially placed on the importance of the development of a cardiac analysis toolbox with functionality for pathophysiological analysis of the disease. Subsequently, in order to develop a toolbox to further the understanding of the mechanisms of the disease as linked to changes in the cytoskeletal architecture and hypertrophy of cardiac myocytes, a continuum bi-phasic model applicable to cardiac tissue is formulated based on the theory of porous media (TPM). This makes it possible to account for interactions and contributions of multiple phases of constituent materials as well as concentrations of solved components, which in computational cardiac modelling are the solid phase – the cardiac tissue – and the liquid phase – blood and interstitial fluid. Therefore, subsequent attention is paid to the cardiac model development in order to implement a sound base on which to add strain- and nutrient-driven phase transition, in addition to a nutrient phase contained within the liquid phase. To this end, based on thermodynamical restrictions, constitutive relations are proposed for stress, permeability, seepage velocity and interaction forces. The approach is implemented in the in-house computational cardiac mechanics toolbox SESKA which supports finite element as well as Element-free Galerkin-based approximations. This paper considers the passive and active non-linear elastic material behaviour of the myocardium of the left ventricle coupled with porous media theory, along with an additional coupling to the haemodynamics of the circulatory system, facilitating modelling of the full cardiac cycle. In order to illustrate the potential and efficacy of the approach with qualitative results, a human heart affected by RHD is investigated, making use of cardiovascular magnetic resonance scans taken over a period of two years to generate realistic 3D computer models. © 2018 Elsevier Ltd
    view abstractdoi: 10.1016/j.compstruc.2018.02.012
  • 2020 • 512 Experimental investigation on influence of engagement angle and tool geometry on plunge milling
    Huang, N. and Krebs, E. and Baumann, J. and Zhou, Y. and Wu, S. and Biermann, D.
    International Journal of Advanced Manufacturing Technology 108 1973-1981 (2020)
    Taking advantage of the superior cutter axial stiffness, plunge milling provides a higher material removal rate in rough milling for components with deep cavities. Tool wear depending on cutting parameters of radial cutting width, axial cutting depth, step interval, feedrate, and spindle speed has been studied by several researchers. For a more comprehensive understanding of the wear mechanism, this study investigates the influences of tool engagement angle and tool geometry on tool wear based on multiple sets of machining tests. The development of tool wear during plunge milling is monitored. Results show that tool wear of insert with large engagement angle mainly exists on minor edge, which is caused by increased tool deflection. When the radial distance equals to tool radius, optimal engagement angle can be achieved while considering both tool life and machining efficiency. The experimental results show that tool life of insert with rake angle of 22° is 6.5% higher than rake angle of 15°. Smaller corner radius has positive influences on tool life improvement. Surprisingly, tool life of insert without cutting edge chamfer is 3.6 times than insert with cutting edge chamfer. The best tool geometric parameters of plunge insert can then be identified among a variety of inserts. This work is useful for cutting tool producers and manufacturers to optimize tool geometry and machining parameters. © 2020, Springer-Verlag London Ltd., part of Springer Nature.
    view abstractdoi: 10.1007/s00170-020-05480-x
  • 2020 • 511 Development of an energy-based approach for optimized frequency selection for fatigue testing on polymers – Exemplified on polyamide 6
    Hülsbusch, D. and Kohl, A. and Striemann, P. and Niedermeier, M. and Strauch, J. and Walther, F.
    Polymer Testing 81 (2020)
    Polymers and composite materials show temperature-dependent material properties. Therefore, the frequency resembles a critical part in fatigue testing, due to its influence on the self-heating of the polymeric material and thereby on the number of cycles to failure. The aim of this paper is the development of a testing method, which allows comparable results with varying frequencies. To minimize the self-heating effect on the fatigue behavior, a model was established for selecting optimized frequencies regarding the load-specific temperature increase of the specimen. A new energy-parameter, the induced energy-rate, was introduced and correlated to the load-specific increase in temperature in multiple and constant amplitude tests at ambient conditions. With this approach, it was possible to determine a threshold value for the newly defined induced energy-rate. A stress-specific model was developed and a limit frequency was calculated. The results were verified in multiple and constant amplitude tests and S/N-curves. © 2019
    view abstractdoi: 10.1016/j.polymertesting.2019.106260
  • 2020 • 510 Manipulation of the size and phase composition of yttrium iron garnet nanoparticles by pulsed laser post-processing in liquid
    Hupfeld, T. and Stein, F. and Barcikowski, S. and Gökce, B. and Wiedwald, U.
    Molecules 25 (2020)
    Modification of the size and phase composition of magnetic oxide nanomaterials dispersed in liquids by laser synthesis and processing of colloids has high implications for applications in biomedicine, catalysis and for nanoparticle-polymer composites. Controlling these properties for ternary oxides, however, is challenging with typical additives like salts and ligands and can lead to unwanted byproducts and various phases. In our study, we demonstrate how additive-free pulsed laser post-processing (LPP) of colloidal yttrium iron oxide nanoparticles using high repetition rates and power at 355 nm laser wavelength can be used for phase transformation and phase purification of the garnet structure by variation of the laser fluence as well as the applied energy dose. Furthermore, LPP allows particle size modification between 5 nm (ps laser) and 20 nm (ns laser) and significant increase of the monodispersity. Resulting colloidal nanoparticles are investigated regarding their size, structure and temperature-dependent magnetic properties. © 2020 by the authors.
    view abstractdoi: 10.3390/molecules25081869
  • 2020 • 509 Dynamics of laser-induced cavitation bubbles at a solid-liquid interface in high viscosity and high capillary number regimes
    Hupfeld, T. and Laurens, G. and Merabia, S. and Barcikowski, S. and Gökce, B. and Amans, D.
    Journal of Applied Physics 127 (2020)
    No unified model is available yet to explain the dynamics of laser-induced cavitation bubbles during laser ablation of solid targets in liquids, when an extremely high capillary number is achieved (>100), i.e., when the viscous forces strongly contribute to the friction. By investigating laser-induced bubbles on gold and yttrium-iron-garnet targets as a function of the liquid viscosity, using a nanosecond laser and an ultrafast shadowgraph imaging setup, we give a deeper insight into what determines the bubble dynamics. We find that the competition between the viscous forces and the surface tension (capillary number Ca), on the one hand, and the competition between the viscous forces and inertia (Reynolds number Re), on the other hand, are both key factors. Increasing the viscous forces, and hereby Ca up to 100 has an impact on the bubble shape and results in a very pronounced rim, which separates the bubble in a spherical cap driven by inertia and an interlayer. The temporal evolution of the footprint radius of the interlayer can be addressed in the framework of the inertiocapillary regime. For an intermediate viscosity, the thickness of the interlayer is consistent with a boundary layer equation. Interestingly, our data cannot be interpreted with simplified hydrodynamic (Cox-Voinov) or molecular-kinetic theory models, highlighting the originality of the dynamics reported when extremely high capillary numbers are achieved. Upon bubble collapse, spherical persistent microbubbles are created and partly dispersed in water, whereas the high-viscous polyalphaolefines lead to long-standing oblate persistent bubbles sticking to the target's surface, independent of the ablated target. Overall, liquid's viscosity determines laser ablation-induced cavitation. © 2020 Author(s).
    view abstractdoi: 10.1063/1.5116111
  • 2020 • 508 Pitfalls and prospects of optical spectroscopy to characterize perovskite-transport layer interfaces
    Hutter, E.M. and Kirchartz, T. and Ehrler, B. and Cahen, D. and Von Hauff, E.
    Applied Physics Letters 116 (2020)
    Perovskite photovoltaics has witnessed an unprecedented increase in power conversion efficiency over the last decade. The choice of transport layers, through which photo-generated electrons and holes are transported to electrodes, is a crucial factor for further improving both the device performance and stability. In this perspective, we critically examine the application of optical spectroscopy to characterize the quality of the transport layer-perovskite interface. We highlight the power of complementary studies that use both continuous wave and time-resolved photoluminescence to understand non-radiative losses and additional transient spectroscopies for characterizing the potential for loss-less carrier extraction at the solar cell interfaces. Based on this discussion, we make recommendations on how to extrapolate results from optical measurements to assess the quality of a transport layer and its impact on solar cell efficiency. © 2020 Author(s).
    view abstractdoi: 10.1063/1.5143121
  • 2020 • 507 On a perturbation theory and on strong convergence rates for stochastic ordinary and partial differential equations with nonglobally monotone coefficients
    Hutzenthaler, M. and Jentzen, A.
    Annals of Probability 48 53-93 (2020)
    We develop a perturbation theory for stochastic differential equations (SDEs) by which we mean both stochastic ordinary differential equations (SODEs) and stochastic partial differential equations (SPDEs). In particular, we estimate the Lp-distance between the solution process of an SDE and an arbitrary Ito process, which we view as a perturbation of the solution process of the SDE, by the Lp-distances of the differences of the local characteristics for suitable p, q &gt; 0. As one application of the developed perturbation theory, we establish strong convergence rates for numerical approximations of a class of SODEs with nonglobally monotone coefficients. As another application of the developed perturbation theory, we prove strong convergence rates for spatial spectral Galerkin approximations of solutions of semilinear SPDEs with nonglobally monotone nonlinearities including Cahn-Hilliard-Cook-type equations and stochastic Burgers equations. Further applications of the developed perturbation theory include regularity analyses of solutions of SDEs with respect to their initial values as well as small-noise analyses for ordinary and partial differential equations. © Institute of Mathematical Statistics, 2020.
    view abstractdoi: 10.1214/19-AOP1345
  • 2020 • 506 Multilevel picard approximations of high-dimensional semilinear parabolic differential equations with gradient-dependent nonlinearities
    Hutzenthaler, M. and Kruse, T.
    SIAM Journal on Numerical Analysis 58 929-961 (2020)
    Parabolic partial differential equations (PDEs) and backward stochastic differential equations have a wide range of applications. In particular, high-dimensional PDEs with gradient-dependent nonlinearities appear often in the state-of-the-art pricing and hedging of financial derivatives. In this article we prove that semilinear heat equations with gradient-dependent nonlinearities can be approximated under suitable assumptions with computational complexity that grows polynomially both in the dimension and the reciprocal of the accuracy. © 2020 Martin Hutzenthaler and Thomas Kruse
    view abstractdoi: 10.1137/17M1157015
  • 2020 • 505 Elasto-plastic large deformation analysis of multi-patch thin shells by isogeometric approach
    Huynh, G.D. and Zhuang, X. and Bui, H.G. and Meschke, G. and Nguyen-Xuan, H.
    Finite Elements in Analysis and Design 173 (2020)
    This paper studies elasto-plastic large deformation behaviour of thin shell structures using the isogeometric computational approach with the main focus on the efficiency in modelling the multi-patches and arbitrary material formulation. In terms of modelling, we employ the bending strip method to connect the patches in the structure. The incorporation of bending strips allows to eliminate the strict demand of the C1 continuity condition, which is postulated in the Kirchhoff-Love theory for thin shell, and therefore it enables us to use the standard multi-patch structure even with C0 continuity along the patch boundaries. Furthermore, arbitrary nonlinear material models such as hyperelasticity and finite strain plasticity are embedded in the shell formulation, from which a unified thin shell formulation can be achieved. In terms of analysis, the Bézier decomposition concept is used to retain the local support of the traditional finite element. The performance of the presented approach is verified through several numerical benchmarks. © 2020
    view abstractdoi: 10.1016/j.finel.2020.103389
  • 2020 • 504 Phase-coherent caloritronics with ordinary and topological Josephson junctions
    Hwang, S.-Y. and Sothmann, B.
    European Physical Journal: Special Topics 229 683-705 (2020)
    We provide a brief and comprehensive overview over recent developments in the field of phase-coherent caloritronics in ordinary and topological Josephson junctions. We start from the simple case of a short, one-dimensional superconductor-normal metal-superconductor (S-N-S) Josephson junction and derive the phase-dependent thermal conductance within the Bogoliubov-de Gennes formalism. Then, we review the key experimental breakthroughs that have triggered the recent growing interest into phase-coherent heat transport. They include the realization of thermal interferometers, diffractors, modulators and routers based on superconducting tunnel junctions. Finally, we discuss very recent theoretical findings based on superconductor-topological insulator-superconductor (S-TI-S) Josephson junctions that show interesting heat transport properties due to the interplay between topological band structures and superconductivity. © 2020, The Author(s).
    view abstractdoi: 10.1140/epjst/e2019-900094-y
  • 2020 • 503 A mixed least-squares finite element formulation with explicit consideration of the balance of moment of momentum, a numerical study
    Igelbüscher, M. and Schröder, J. and Schwarz, A.
    GAMM Mitteilungen 43 (2020)
    Important conditions in structural analysis are the fulfillment of the balance of linear momentum (vanishing resultant forces) and the balance of angular momentum (vanishing resultant moment), which is not a priori satisfied for arbitrary element formulations. In this contribution, we analyze a mixed least-squares (LS) finite element formulation for linear elasticity with explicit consideration of the balance of angular momentum. The considered stress-displacement (σ − u) formulation is based on the squared L2(ℬ)-norm minimization of the residuals of a first-order system of differential equations. The formulation is constructed by means of two residuals, that is, the balance of linear momentum and the constitutive equation. Motivated by the crucial point of weighting factors within LS formulations, a scale independent formulation is constructed. The displacement approximation is performed by standard Lagrange polynomials and the stress approximation with Raviart-Thomas functions. The latter ansatz functions do not a priori fulfill the symmetry of the Cauchy stress tensor. Therefore, a redundant residual, the balance of angular momentum ((x − x0) × (divσ + f) + axl[σ − σT]), is introduced and the results are discussed from the engineering point of view, especially for coarse mesh discretizations. However, this formulation shows an improvement compared to standard LS σ − u formulations, which is considered here in a numerical study. © 2019 The Authors. GAMM - Mitteilungen published by Wiley-VCH Verlag GmbH & Co. KGaA on behalf of Gesellschaft für Angewandte Mathematik und Mechanik
    view abstractdoi: 10.1002/gamm.202000009
  • 2020 • 502 Ultraviolet/vacuum-ultraviolet emission from a high power magnetron sputtering plasma with an aluminum target
    Iglesias, E.J. and Hecimovic, A. and Mitschker, F. and Fiebrandt, M. and Bibinov, N. and Awakowicz, P.
    Journal of Physics D: Applied Physics 53 (2020)
    We report the in situ measurement of the ultraviolet/vacuum-ultraviolet (UV/VUV) emission from a plasma produced by high power impulse magnetron sputtering with aluminum target, using argon as background gas. The UV/VUV detection system is based upon the quantification of the re-emitted fluorescence from a sodium salicylate layer that is placed in a housing inside the vacuum chamber, at 11 cm from the center of the cathode. The detector is equipped with filters that allow for differentiating various spectral regions, and with a front collimating tube that provides a spatial resolution ≈ 0.5 cm. Using various views of the plasma, the measured absolutely calibrated photon rates enable to calculate emissivities and irradiances based on a model of the ionization region. We present results that demonstrate that Al+ ions are responsible for most of the VUV irradiance. We also discuss the photoelectric emission due to irradiances on the target ∼ 2 × 1018 s-1 . cm-2 produced by high energy photons from resonance lines of Ar+. © 2019 IOP Publishing Ltd.
    view abstractdoi: 10.1088/1361-6463/ab52f8
  • 2020 • 501 Analysis of mixture stratification effects on unstrained laminar flames
    Inanc, E. and Chakraborty, N. and Kempf, A.M.
    Combustion and Flame 219 339-348 (2020)
    Detailed one-dimensional computations of unsteady unstrained laminar flames subjected to sinusoidal equivalence ratio perturbations are presented. The responses of the flame thickness, flame speeds, species concentrations and the species reaction rates to equivalence ratio variations are investigated. The effect of stratification is quantified by comparing the structure of a stratified flame to that of an equivalent homogeneous mixture flame at an equivalence ratio that the stratified flame experiences. The difference between a flame burning into a leaner mixture or a richer mixture yields hysteresis for consumption speed and flame thickness in the equivalence ratio space, which becomes more prominent with stronger stratification, especially when the flame propagates towards a negative equivalence ratio gradient under fuel-lean conditions. The displacement speed and its components are analysed, with the diffusion, reaction rate and cross-dissipation components all showing a strong hysteresis, but with different signs, partially cancelling each other. The phase space responses of the scalars are compared and the different phase shifts are evaluated. Interestingly, these observations were not affected by the choice of the reaction mechanism. The effects of equal and mixture-average diffusivity assumptions on the results are tested, where the latter caused two times stronger hysteresis effects: the thermo-diffusive effects of heat and products behind the flame were found to play a significant role for laminar flame propagation in stratified mixtures, even for unstrained flames. The stratified flame shows significant alteration in the species concentrations and reaction rates, especially for the minor and product species. The response of the sinusoidal oscillations is compared against cases with linear mixture stratification. Even with the absence of the compressible strain, it is demonstrated that the stratification effects heavily influence the flame properties and the treatment of thermo-physical transport properties has been demonstrated to be pivotal to the accurate prediction of this behaviour. © 2020 The Combustion Institute
    view abstractdoi: 10.1016/j.combustflame.2020.06.009
  • 2020 • 500 Correlation analysis of strongly fluctuating atomic volumes, charges, and stresses in body-centered cubic refractory high-entropy alloys
    Ishibashi, S. and Ikeda, Y. and Körmann, F. and Grabowski, B. and Neugebauer, J.
    Physical Review Materials 4 (2020)
    Local lattice distortions in a series of body-centered cubic alloys, including refractory high-entropy alloys, are investigated by means of atomic volumes, atomic charges, and atomic stresses defined by the Bader charge analysis based on first-principles calculations. Analyzing the extensive data sets, we find large distributions of these atomic properties for each element in each alloy, indicating a large impact of the varying local chemical environments. We show that these local-environment effects can be well understood and captured already by the first and the second nearest neighbor shells. Based on this insight, we employ linear regression models up to the second nearest neighbor shell to accurately predict these atomic properties. Finally, we find that the elementwise-averaged values of the atomic properties correlate linearly with the averaged valence-electron concentration of the considered alloys. © 2020 authors. Published by the American Physical Society.
    view abstractdoi: 10.1103/PhysRevMaterials.4.023608
  • 2020 • 499 Cellulose Nanocrystal-Templated Tin Dioxide Thin Films for Gas Sensing
    Ivanova, A. and Frka-Petesic, B. and Paul, A. and Wagner, T. and Jumabekov, A.N. and Vilk, Y. and Weber, J. and Schmedt Auf Der Günne, J. and Vignolini, S. and Tiemann, M. and Fattakhova-Rohlfing, D. and Bein, T.
    ACS Applied Materials and Interfaces 12 12639-12647 (2020)
    Porous tin dioxide is an important low-cost semiconductor applied in electronics, gas sensors, and biosensors. Here, we present a versatile template-assisted synthesis of nanostructured tin dioxide thin films using cellulose nanocrystals (CNCs). We demonstrate that the structural features of CNC-templated tin dioxide films strongly depend on the precursor composition. The precursor properties were studied by using low-temperature nuclear magnetic resonance spectroscopy of tin tetrachloride in solution. We demonstrate that it is possible to optimize the precursor conditions to obtain homogeneous precursor mixtures and therefore highly porous thin films with pore dimensions in the range of 10-20 nm (ABET = 46-64 m2 g-1, measured on powder). Finally, by exploiting the high surface area of the material, we developed a resistive gas sensor based on CNC-templated tin dioxide. The sensor shows high sensitivity to carbon monoxide (CO) in ppm concentrations and low cross-sensitivity to humidity. Most importantly, the sensing kinetics are remarkably fast; both the response to the analyte gas and the signal decay after gas exposure occur within a few seconds, faster than in standard SnO2-based CO sensors. This is attributed to the high gas accessibility of the very thin porous film. © 2020 American Chemical Society.
    view abstractdoi: 10.1021/acsami.9b11891
  • 2020 • 498 Elevated region area measurement for quantitative analysis of laser beam melting process stability
    zur Jacobsmühlen, J. and Kleszczynski, S. and Witt, G. and Merhof, D.
    Proceedings - 26th Annual International Solid Freeform Fabrication Symposium - An Additive Manufacturing Conference, SFF 2015 549-559 (2020)
    Laser beam melting (LBM) processes enable layer-based production of geometrically complex metallic parts with very good mechanical properties for Rapid Manufacturing. Collisions between powder coating mechanism and elevated part regions pose a major risk to process stability, which is crucial for industrial application. Minimizing elevated region area usually involves parameter tuning in a trial-and-error approach, as the process outcome is the only measure of stability. One published approach to quantifying elevated region area utilizes an imaging system, which acquires layer images of the powder bed after powder deposition and detects elevated regions using image analysis. We extend the image-based analysis to each part region, create quantitative visualizations of elevated region area for quick assessment/comparison and compute a figure of merit. In experimental build jobs with overhanging structures and different support junction parameters we gain insight into problematic part regions, which can be used as feedback in job design. The presented method helps to improve LBM process stability, which is strongly linked to process efficiency. © SFF 2015.All rights reserved.
    view abstract
  • 2020 • 497 Pseudarthroses [Pseudarthrosen]
    Jäger, M. and Wassenaar, D. and Busch, A. and Haversath, M.
    Orthopade 49 547-560 (2020)
    Fractures and osteotomies are characterized by a structural discontinuity of the affected bone with formation of a gap. If bone healing does not lead to an osseous bridging of the fragments within a time period of 6 months a nonunion (pseudarthrosis) occurs. In this stage spontaneous bone healing is unlikely in the future without any intervention. Pseudarthrosis is classified into hypertrophic and atrophic types. Moreover, the differentiation between aseptic and septic conditions, the size of the defect, the local blood supply and the mechanical stability are crucial for treatment planning. The type of pseudarthrosis and the accompanying comorbidities can be classified in scoring systems and influence the selection of the treatment procedure. The operative principles aim at the vitalization of atrophic bone parts, achieving sufficient stabilization and cures the infection, whereas nonoperative measures are primarily supportive measures. The foundation of successful treatment is the minimization of individual risk profiles and sufficient patient compliance. © 2020, Springer Medizin Verlag GmbH, ein Teil von Springer Nature.
    view abstractdoi: 10.1007/s00132-020-03920-w
  • 2020 • 496 Thermodynamic modelling of the Ni–Zr system
    Jana, A. and Sridar, S. and Fries, S.G. and Hammerschmidt, T. and Kumar, K.C.H.
    Intermetallics 116 (2020)
    In this work, we report the thermodynamic modelling of the Ni–Zr system using the Calphad method combined with ab initio calculations. Density functional theory (DFT) is employed to calculate the enthalpy of formation of the intermediate phases. The calculated enthalpies of formation are in close agreement with the experimental data. An approach based on special quasirandom structures (SQS) was used for calculating the enthalpy of mixing of the fcc solid solution. The vibrational contribution to the heat capacities of NiZr, NiZr2, Ni3Zr and Ni7Zr2 phases were calculated using the quasiharmonic approximation (QHA) and the corresponding electronic contribution was obtained using an approach based on Mermin statistics. The total heat capacities for these phases were fitted to appropriate expressions and integrated to obtain the Gibbs energy functions valid down to 0 K. The calculated thermochemical properties along with critically selected experimental constitutional and thermochemical data served as input for the thermodynamic optimisation of the system. The calculated phase equilibria and the thermodynamic properties using the optimised Gibbs energy functions are in good agreement with the input data. The calculated congruent melting points of NiZr and NiZr2 phases are close to the recent experimental data. The Ni10Z7 phase forms by a peritectic reaction, which is also in agreement with the experimental data. © 2019 Elsevier Ltd
    view abstractdoi: 10.1016/j.intermet.2019.106640
  • 2020 • 495 Functional all-optical logic gates for true time-domain signal processing in nonlinear photonic crystal waveguides
    Jandieri, V. and Khomeriki, R. and Onoprishvili, T. and Werner, D.H. and Berakdar, J. and Erni, D.
    Optics Express 28 18317-18331 (2020)
    We present a conceptual study on the realization of functional and easily scalable all-optical NOT, AND and NAND logic gates using bandgap solitons in coupled photonic crystal waveguides. The underlying structure consists of a planar air-hole type photonic crystal with a hexagonal lattice of air holes in crystalline silicon (c-Si) as the nonlinear background material. The remaining logical operations can be performed using combinations of these three logic gates. A unique feature of the proposed working scheme is that it operates in the true time-domain, enabling temporal solitons to maintain 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 all-optical logic gates for ultrafast full-optical digital signal processing. In the suggested setup, 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 feasibility and efficiency of the proposed logic gates as well as their scalability is demonstrated using our original rigorous theoretical formalism together with full-wave computational electromagnetics. © 2020 Optical Society of America.
    view abstractdoi: 10.1364/OE.395015
  • 2020 • 494 What is the role of acid-acid interactions in asymmetric phosphoric acid organocatalysis? A detailed mechanistic study using interlocked and non-interlocked catalysts
    Jansen, D. and Gramüller, J. and Niemeyer, F. and Schaller, T. and Letzel, M.C. and Grimme, S. and Zhu, H. and Gschwind, R.M. and Niemeyer, J.
    Chemical Science 11 4381-4390 (2020)
    Organocatalysis has revolutionized asymmetric synthesis. However, the supramolecular interactions of organocatalysts in solution are often neglected, although the formation of catalyst aggregates can have a strong impact on the catalytic reaction. For phosphoric acid based organocatalysts, we have now established that catalyst-catalyst interactions can be suppressed by using macrocyclic catalysts, which react predominantly in a monomeric fashion, while they can be favored by integration into a bifunctional catenane, which reacts mainly as phosphoric acid dimers. For acyclic phosphoric acids, we found a strongly concentration dependent behavior, involving both monomeric and dimeric catalytic pathways. Based on a detailed experimental analysis, DFT-calculations and direct NMR-based observation of the catalyst aggregates, we could demonstrate that intermolecular acid-acid interactions have a drastic influence on the reaction rate and stereoselectivity of asymmetric transfer-hydrogenation catalyzed by chiral phosphoric acids. © The Royal Society of Chemistry 2020.
    view abstractdoi: 10.1039/d0sc01026j
  • 2020 • 493 Topology optimization with anisotropic materials, including a filter to smooth fiber pathways
    Jantos, D.R. and Hackl, K. and Junker, P.
    Structural and Multidisciplinary Optimization 61 2135-2154 (2020)
    In a recent publication, an approach to optimize the orientation of anisotropic materials was presented. This strategy was embedded into the thermodynamic topology optimization based on growth. In this paper, we show that the thermodynamic orientation optimization can also be used in more classical approaches to topology optimization. We furthermore enhance the approach by a novel filtering technique to provide control over the smoothness of the pathway of principal material directions, i.e., the curvature of fibers. The filter is based on a convolution operator and is applied to the material stiffness tensor, so that the filtering technique is not directly bounded to the actual parameterization for the design variables. To this end, the topology is defined by a continuous density approach with penalization of intermediate densities (SIMP) solved via the optimality criteria method (OCM). A set of three continuous Euler angles is used as additional design variables to describe the local material rotation of the anisotropic base material. The thermodynamic optimization of the material orientation is performed by evolution of the Euler angles to minimize the elastic energy. The related evolution equations are derived by means of the Hamilton principle, well-known from material modeling. © 2020, Springer-Verlag GmbH Germany, part of Springer Nature.
    view abstractdoi: 10.1007/s00158-019-02461-x
  • 2020 • 492 Comparative study of the residual stress development in HMDSN-based organosilicon and silicon oxide coatings
    Jaritz, M. and Hopmann, C. and Wilski, S. and Kleines, L. and Banko, L. and Grochla, D. and Ludwig, Al. and Dahlmann, R.
    Journal of Physics D: Applied Physics 53 (2020)
    To investigate the stress formation mechanisms in thin plasma polymers, a comparative study of organosilicon (SiNOCH) and silicon oxide (SiOx) coatings in dependence of power input for deposition was conducted. Both coating types were produced in a low-pressure (15 Pa) microwave excited hexamethyldilisazane (HMDSN) plasma. Residual stress values were obtained using a high-throughput, time resolved and in-situ measurement method, including a CCD-camera, a line laser and micro-machined cantilever sensor chips. Both plasma polymer types were shown to form residual stresses with opposite signs. The stress evolution in the coatings revealed a strong dependency on the variation of power input for deposition. The SiOx coating exhibits mostly compressive stresses. Higher power inputs constitute higher ion momentums as well as a higher degree of fragmentation of the monomer. The SiOx coatings were deposited with a high oxygen flow and with a higher average energy of the plasma for all investigated parameter sets than the SiNOCH coating. Therefore, it is conceivable that ion peening is mostly responsible for the compressive stress formation in the SiOx coatings. In contrast to the SiOx coating, the SiNOCH coating can be applied without residual stress. For higher excitation powers, tensile stresses are predominant, most likely due to attractive forces between island or column boundaries and crosslinking. © 2020 IOP Publishing Ltd.
    view abstractdoi: 10.1088/1361-6463/ab8ceb
  • 2020 • 491 Characterization of low-resistance ohmic contacts to a two-dimensional electron gas in a GaAs/AlGaAs heterostructure
    Javaid Iqbal, M. and Reuter, D. and Wieck, A.D. and Van Der Wal, C.
    EPJ Applied Physics 89 (2020)
    The study of electron transport in low-dimensional systems is of importance, not only from a fundamental point of view, but also for future electronic and spintronic devices. In this context heterostructures containing a two-dimensional electron gas (2DEG) are a key technology. In particular GaAs/AlGaAs heterostructures, with a 2DEG at typically 100 nm below the surface, are widely studied. In order to explore electron transport in such systems, low-resistance ohmic contacts are required that connect the 2DEG to macroscopic measurement leads at the surface. Here we report on designing and measuring a dedicated device for unraveling the various resistance contributions in such contacts, which include pristine 2DEG series resistance, the 2DEG resistance under a contact, the contact resistance itself, and the influence of pressing a bonding wire onto a contact. We also report here a recipe for contacts with very low resistance values that remain below 10 ω for annealing times between 20 and 350 s, hence providing the flexibility to use this method for materials with different 2DEG depths. The type of heating, temperature ramp rate and gas forming used for annealing is found to strongly influence the annealing process and hence the quality of the resulting contacts. © EDP Sciences, 2020.
    view abstractdoi: 10.1051/epjap/2020190202
  • 2020 • 490 Millimeterwave Radar Systems for In-Line Thickness Monitoring in Pipe Extrusion Production Lines
    Jebramcik, J. and Rolfes, I. and Pohl, N. and Barowski, J.
    IEEE Sensors Letters 4 (2020)
    This letter presents algorithms and considerations for the applicability of millimeter wave radar systems as monitoring sensors in the field of plastic pipe extrusion. Since a constant wall thickness of the pipe is a major quality factor of the product, monitoring systems that in-line measure the thickness during the extrusion process are commonly used. Modern ultrawideband radar systems achieve target resolutions in the range of millimeters, allowing competition with well-established methods, such as ultrasound sensors, and even expensive photonic Terahertz devices. The authors describe a novel accurate and efficient method to measure the pipe-wall's thickness based on frequency domain evaluation of the material reflection. The general feasibility of W-band radar sensors, as well as the accuracy of the proposed method, is demonstrated by measurements using a moderate size polyvinyl chloride pipe. © 2017 IEEE.
    view abstractdoi: 10.1109/LSENS.2020.2991778
  • 2020 • 489 Validation of a dynamic mooring model coupled with a RANS solver
    Jiang, C. and el Moctar, O. and Moura Paredes, G. and Schellin, T.E.
    Marine Structures 72 (2020)
    Standard design procedures and simulation tools for marine structures are aimed primarily for use by the offshore oil and gas. Mooring system restoring forces acting on floating offshore structures are obtained from a quasi-static mooring model alone or from a coupled analysis based on potential flow solvers that do not always consider nonlinear mooring-induced restoring forces, fluid structure interactions, and associated hydrodynamic damping effects. This paper presents the validation of a dynamic mooring system analysis technique that couples the dynamic mooring model with a Reynolds-averaged Navier-Stokes (RANS) equations solver. We coupled a dynamic mooring model with a RANS equations solver, and analyzed a moored floating buoy in calm water, regular and irregular waves and validated our motion and mooring force predictions against experimental measurements. The mooring system consisted of three catenary chains. The analyzed response comprised decaying oscillating buoy motions, linear and quadratic damping characteristics, and tensile forces in mooring lines. The generally favorable comparison of predicted buoy motions and mooring forces to experimental data confirmed the reliability of our implemented coupling technique to predict system response. Additional comparative results from a potential flow solver demonstrated the benefits of the coupled dynamic mooring model with RANS equations. The successful validated tool of coupling the dynamic mooring model with the RANS solver is available as open source, and it shows the potential of the coupled methodology to be used for analyzing the moored offshore structures. © 2020 Elsevier Ltd
    view abstractdoi: 10.1016/j.marstruc.2020.102783
  • 2020 • 488 Frequency Selective Surface Coded Retroreflectors for Chipless Indoor Localization Tag Landmarks
    Jimenez-Saez, A. and Schusler, M. and El-Absi, M. and Abbas, A.A. and Solbach, K. and Kaiser, T. and Jakoby, R.
    IEEE Antennas and Wireless Propagation Letters 19 726-730 (2020)
    This letter presents the integration of frequency selective surfaces (FSSs) with retroreflectors for the realization of chipless wireless indoor localization tag landmarks. As an example, the high radar cross section (RCS) of a trihedral corner reflector is signed with an FSS-based stopband filter, so that the backscattered power from several corner reflectors can be distinguished by a mobile reader according to the frequency response of the FSS. Measurement results with a 3 × 3 × 3 cm3 trihedral corner reflector and a stopband FSS in a Rogers RT/Duroid 5880 high-frequency laminate at 90 GHz shows an RCS above -25 dBsqm for 90° coverage in the TM plane. Due to the high RCS, measurements at distances up to 4 m with a standard 25 dBi gain horn antenna and a vector network analyzer as a reader are shown. These preliminary results show the potential of the concept for applications such as indoor localization with sub-mm accuracy, where high bandwidths, but only a low number of bits, are needed for the identification of the tag landmarks. © 2002-2011 IEEE.
    view abstractdoi: 10.1109/LAWP.2020.2975143
  • 2020 • 487 Element-specific displacements in defect-enriched TiO2: Indication of a flash sintering mechanism
    Jongmanns, M. and Wolf, D.E.
    Journal of the American Ceramic Society 103 589-596 (2020)
    Flash sintering experiments of ceramics indicate the formation of a state far from equilibrium. It is hypothesized that this state is enriched by Frenkel defects. The possibility is investigated that such lattice defects are being generated by a proliferation of lattice vibrations that lie close to the Brillouin zone edge. We show by means of Molecular Dynamics simulations of rutile TiO2 that this mechanism generates Frenkel defects in concentrations far beyond equilibrium. These defects deform the whole lattice in a way that the mean-square displacements of the vibration amplitudes of the Ti and O atoms are specifically enhanced. This finding compares well to atomic displacement data of flash sintered rutile TiO2 reported recently. © 2019 The Authors. Journal of the American Ceramic Society published by Wiley Periodicals, Inc. on behalf of American Ceramic Society (ACERS)
    view abstractdoi: 10.1111/jace.16696
  • 2020 • 486 Dynamic unidirectional anisotropy in cubic FeGe with antisymmetric spin-spin-coupling
    Josten, N. and Feggeler, T. and Meckenstock, R. and Spoddig, D. and Spasova, M. and Chai, K. and Radulov, I. and Li, Z.-A. and Gutfleisch, O. and Farle, M. and Zingsem, B.
    Scientific Reports 10 (2020)
    Strong unidirectional anisotropy in bulk polycrystalline B20 FeGe has been measured by ferromagnetic resonance spectroscopy. Such anisotropy is not present in static magnetometry measurements. B20 FeGe exhibits inherent Dzyaloshinskii-Moriya interaction, resulting in a nonreciprocal spin-wave dispersion. Bulk and micron sized samples were produced and characterized. By X-band ferromagnetic resonance spectroscopy at 276 K ± 1 K, near the Curie temperature, a distribution of resonance modes was observed in accordance with the cubic anisotropy of FeGe. This distribution exhibits a unidirectional anisotropy, i.e. shift of the resonance field under field inversion, of KUD = 960 J/m3 ± 10 J/m3, previously unknown in bulk ferromagnets. Additionally, more than 25 small amplitude standing spin wave modes were observed inside a micron sized FeGe wedge, measured at 293 K ± 2 K. These modes also exhibit unidirectional anisotropy. This effect, only dynamically measurable and not detectable in static magnetometry measurements, may open new possibilities for directed spin transport in chiral magnetic systems. © 2020, The Author(s).
    view abstractdoi: 10.1038/s41598-020-59208-8
  • 2020 • 485 Tunable coupling by means of oxygen intercalation and removal at the strongly interacting graphene/cobalt interface
    Jugovac, M. and Genuzio, F. and Menteş, T.O. and Locatelli, A. and Zamborlini, G. and Feyer, V. and Schneider, C.M.
    Carbon 163 341-347 (2020)
    It is well known that intercalated species can strongly affect the graphene-substrate interaction. As repeatedly shown by experiment and theory, the intercalation of atomic species may establish a free-standing character in chemisorbed graphene systems. Here, we focus on graphene grown on a strongly interacting support, cobalt, and demonstrate that the film electronic structure and doping can be tuned via the intercalation/removal of interfacial oxygen. Importantly, cathode lens microscopy reveals the main mechanism of oxygen intercalation, and in particular how microscopic openings in the mesh enable oxygen accumulation at the graphene-cobalt interface. Our experiments show that this process can be carefully controlled through temperature, without affecting the film morphology and crystalline quality. The presence of oxygen at the interface induces an upward shift of the graphene π band, moving its crossing above the Fermi level, accompanied by an increased Fermi velocity and reduced momentum width. Control on the graphene coupling to cobalt may enable one to alter the induced spin polarization in graphene's electronic states. © 2020 Elsevier Ltd
    view abstractdoi: 10.1016/j.carbon.2020.03.034
  • 2020 • 484 Bulk nanostructured AlCoCrFeMnNi chemically complex alloy synthesized by laser-powder bed fusion
    Jung, H.Y. and Peter, N.J. and Gärtner, E. and Dehm, G. and Uhlenwinkel, V. and Jägle, E.A.
    Additive Manufacturing 35 (2020)
    We report the synthesis of a bulk nanostructured alloy using laser-powder bed fusion. The equiatomic AlCoCrFeMnNi chemically complex alloy forms a nanoscale modulated structure, which is homogeneously distributed in the as-built condition. The nanostructure consists of Al & Ni-rich ordered and Cr & Fe-rich disordered BCC phases. The two phases form an interconnected phase network with coherent interface boundaries. Atom probe tomography and aberration-corrected scanning transmission electron microscopy analysis of the spatial distribution of the modulated structure suggests the occurrence of nano-scale spinodal decomposition. These results introduce a direct synthesis of bulk nanostructured alloys with promising geometric flexibility. © 2020 Elsevier B.V.
    view abstractdoi: 10.1016/j.addma.2020.101337
  • 2020 • 483 Investigation of the polarization state in spin-VCSELs with thermally tuned birefringence
    Jung, N. and Lindemann, M. and Stadler, P. and Pusch, T. and Michalzik, R. and Hofmann, M.R. and Gerhardt, N.C.
    Proceedings of SPIE - The International Society for Optical Engineering 11356 (2020)
    Vertical-cavity surface-emitting lasers (VCSELs) are commonly used in optical data communication mainly for short-haul transmissions in data centers. Spin-VCSELs can be a promising solution in order to overcome the bandwidth limitations of conventional VCSELs by utilizing the spin and polarization instead of current and intensity. Recently, their polarization dynamics have been enhanced to resonance frequencies of more than 200 GHz by implementing a large amount of birefringence into the laser cavity. For future applications onchip solutions to control the birefringence are preferred. For this purpose, a keyhole-shaped mesa-structure on standard wafer material for an 850nm oxide-confined AlGaAs-VCSEL is used. A variable heating current is driven into the semiconductor ridge connected to the mesa at a constant pump current. This creates an asymmetrical heat gradient. Here we investigate the polarization behaviour in a spin-VCSEL with thermally induced birefringence. We analyze the hysteresis in the heating and pump current of the sample to identify optimized working points near the polarization switching points. © 2020 SPIE.
    view abstractdoi: 10.1117/12.2555395
  • 2020 • 482 Femto- To Microsecond Dynamics of Excited Electrons in a Quadruple Cation Perovskite
    Jung, E. and Budzinauskas, K. and Öz, S. and Ünlü, F. and Kuhn, H. and Wagner, J. and Grabowski, D. and Klingebiel, B. and Cherasse, M. and Dong, J. and Aversa, P. and Vivo, P. and Kirchartz, T. and Miyasaka, T. and Van Loosdre...
    ACS Energy Letters 5 785-792 (2020)
    Quadruple cation mixed halide perovskite, GA0.015Cs0.046MA0.152FA0.787Pb(I0.815Br0.185)3, single crystals were grown for the first time using an inverse temperature crystallization process. Solar cell devices in n-i-p stack configuration using thin films of the same materials showed power conversion efficiency above 20%. Complementary time-resolved spectroscopy confirmed that polycrystalline thin films and single crystals identically composed exhibit similar carrier dynamics in the picosecond range. Cooling of excited carriers and bandgap renormalization occur on the same time scale of 200-300 fs. The radiative recombination coefficient (1.2 × 10-9 cm3/s) is comparable to values reported for a GaAs semiconductor. At low excitation density, a long carrier lifetime of 3.2 μs was recorded possibly due to the passivation of recombination centers. This study clarifies discrepancies about the lifetime of hot carriers, the impact of radiative recombination, and the role of recombination centers on solar cell performance. The quadruple cation perovskites displayed short time dynamics with slow recombination of charge carriers. Copyright © 2020 American Chemical Society.
    view abstractdoi: 10.1021/acsenergylett.9b02684
  • 2020 • 481 Modeling of viscoelastic structures with random material properties using time-separated stochastic mechanics
    Junker, P. and Nagel, J.
    International Journal for Numerical Methods in Engineering 121 308-333 (2020)
    Modeling and simulation of materials with stochastic properties is an emerging field in both mathematics and mechanics. The most important goal is to compute the stochastic characteristics of the random stress, such as the expectation value and the standard deviation. An accurate approach are Monte Carlo simulations; however, they consume drastic computational power due to the large number of stochastic realizations that have to be simulated before convergence is achieved. In this paper, we show that a recently published approach for accurate modeling of viscoelastic materials with stochastic material properties at the material point level in the work of Junker and Nagel is also valid for macroscopic bodies. The method is based on a separation of random but time-invariant variables and time-dependent but deterministic variables for the strain response at the material point (time-separated stochastic mechanics [TSM]). We recall the governing equations, derive a simplified form, and discuss the numerical implementation into a finite element routine. To validate our approach, we compare the TSM simulations with Monte Carlo simulations, which provide the “true” answer but at unaffordable computational costs. In contrast, the numerical effort of our approach is in the same range as for deterministic viscoelastic simulations. © 2019 The Authors. International Journal for Numerical Methods in Engineering Published by John Wiley & Sons, Ltd.
    view abstractdoi: 10.1002/nme.6210
  • 2020 • 480 Chemisorption and Physisorption at the Metal/Organic Interface: Bond Energies of Naphthalene and Azulene on Coinage Metal Surfaces
    Kachel, S.R. and Klein, B.P. and Morbec, J.M. and Schöniger, M. and Hutter, M. and Schmid, M. and Kratzer, P. and Meyer, B. and Tonner, R. and Gottfried, J.M.
    Journal of Physical Chemistry C 124 8257-8268 (2020)
    Organic/inorganic hybrid interfaces play a prominent role in organic (opto)electronics, heterogeneous catalysis, sensors, and other current fields of technology. The performance of the related devices and processes depends critically on the nature and strength of interfacial interaction. Here, we use the molecular isomers naphthalene (Nt) and azulene (Az) on the Ag(111) and Cu(111) surfaces as model systems that cover different bonding regimes from physisorption to chemisorption. Az also serves as a model for nonalternant molecular electronic materials and for topological 5-7 defects in graphene. The interaction energies are determined from the quantitative analysis of temperature-programmed desorption data. On both surfaces, Az binds more strongly than Nt, with zero-coverage desorption energies (in kJ/mol) of 120 for Az/Ag and 179 for Az/Cu, compared to 103 for Nt/Ag and 114 for Nt/Cu. The integrated experimental energies are compared with adsorption energies from density-functional theory (DFT) calculations, which include van der Waals contributions using four different correction schemes for the PBE functional: (1) the DFT-D3 scheme with Becke-Johnson damping, (2) the vdWsurf correction based on DFT-TS, (3) a many-body dispersion correction scheme, and (4) the D3surf scheme. Differences in the performance of these methods are discussed. Periodic energy decomposition analysis reveals details of the surface chemical bond and confirms that Az/Cu forms a chemisorptive bond, while the other systems are physisorbed. The variation of the adsorbate-substrate interaction with the topology of the Ï-electron system and the type of surface can be employed to modify the interface properties in graphene-based and organic electronic devices. © 2020 American Chemical Society.
    view abstractdoi: 10.1021/acs.jpcc.0c00915
  • 2020 • 479 A covariant formulation of finite plasticity with plasticity-induced evolution of anisotropy: Modeling, algorithmics, simulation, and comparison to experiments
    Kaiser, T. and Lu, J. and Menzel, A. and Papadopoulos, P.
    International Journal of Solids and Structures 185-186 116-142 (2020)
    Motivated by experimental findings on sheet-metal forming, this article concerns the modeling of evolving anisotropies in finite plasticity. A covariant formulation of plasticity is employed in conjunction with evolution equations for the structural tensors that characterize the symmetry group of the yield function. A specific model is implemented into a finite element code to simulate tension and torsion tests. The results are then compared to experiments. © 2019 Elsevier Ltd
    view abstractdoi: 10.1016/j.ijsolstr.2019.08.005
  • 2020 • 478 Metal Complexes of Donor-functionalized Fluorinated β-Ketoiminates – Synthesis, Structure, and CVD Application
    Kaiser, K. and Ganesamoorthy, C. and Wölper, C. and Schulz, S.
    Zeitschrift fur Anorganische und Allgemeine Chemie 646 681-691 (2020)
    Six alkali metal complexes of partly-fluorinated, donor-functionalized β-ketoiminate ligands [L1Li (1), L1Na (2), L1K (3), L1Cs (4), L1 = OC(CF3)CHC(CH3)NCH2CH2OCH3; L2Li (5), L2Na (6), L2 = OC(CF3)CHC(CH3)NCH2CH2N(CH3)2] were prepared and structurally characterized. Reactions of L1Li with PtCl2 gave the homoleptic Pt complex L12Pt (7), which was characterized spectroscopically and by single-crystal X-ray diffraction and whose promising application as CVD precursor (chemical vapor deposition) is shown. Polycrystalline, pure Pt films were grown at 500 °C on SiO2@Si(100) substrates at 10–3 mbar and characterized by XRD, SEM, AFM, EDX and XPS. © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
    view abstractdoi: 10.1002/zaac.201900239
  • 2020 • 477 Detection and amplification of spin noise using scattered laser light in a quantum-dot microcavity
    Kamenskii, A.N. and Petrov, M.Y. and Kozlov, G.G. and Zapasskii, V.S. and Scholz, S.E. and Sgroi, C. and Ludwig, Ar. and Wieck, A.D. and Bayer, M. and Greilich, A.
    Physical Review B 101 (2020)
    Fundamental properties of the spin-noise signal formation in a quantum-dot microcavity are studied by measuring the angular characteristics of the scattered light intensity. A distributed Bragg reflector microcavity was used to enhance the light-matter interaction with an ensemble of n-doped (In,Ga)As/GaAs quantum dots, which allowed us to study subtle effects of coherent scattering at the quantum dot ensemble. Detecting the scattered light outside of the aperture of the transmitted light, we measured the basic electron spin properties, such as g factor and spin dephasing time. Further, we investigated the influence of the microcavity on the scattering distribution and possibilities of signal amplification by additional resonant excitation. © 2020 American Physical Society.
    view abstractdoi: 10.1103/PhysRevB.101.041401
  • 2020 • 476 How photocorrosion can trick you: A detailed study on low-bandgap Li doped CuO photocathodes for solar hydrogen production
    Kampmann, J. and Betzler, S. and Hajiyani, H. and Häringer, S. and Beetz, M. and Harzer, T. and Kraus, J. and Lotsch, B.V. and Scheu, C. and Pentcheva, R. and Fattakhova-Rohlfing, D. and Bein, T.
    Nanoscale 12 7766-7775 (2020)
    The efficiency of photoelectrochemical tandem cells is still limited by the availability of stable low band gap electrodes. In this work, we report a photocathode based on lithium doped copper(ii) oxide, a black p-type semiconductor. Density functional theory calculations with a Hubbard U term show that low concentrations of Li (Li0.03Cu0.97O) lead to an upward shift of the valence band maximum that crosses the Fermi level and results in a p-type semiconductor. Therefore, Li doping emerged as a suitable approach to manipulate the electronic structure of copper oxide based photocathodes. As this material class suffers from instability in water under operating conditions, the recorded photocurrents are repeatedly misinterpreted as hydrogen evolution evidence. We investigated the photocorrosion behavior of LixCu1-xO cathodes in detail and give the first mechanistic study of the fundamental physical process. The reduced copper oxide species were localized by electron energy loss spectroscopy mapping. Cu2O grows as distinct crystallites on the surface of LixCu1-xO instead of forming a dense layer. Additionally, there is no obvious Cu2O gradient inside the films, as Cu2O seems to form on all LixCu1-xO nanocrystals exposed to water. The application of a thin Ti0.8Nb0.2Ox coating by atomic layer deposition and the deposition of a platinum co-catalyst increased the stability of LixCu1-xO against decomposition. These devices showed a stable hydrogen evolution for 15 minutes. © The Royal Society of Chemistry .
    view abstractdoi: 10.1039/c9nr10250g
  • 2020 • 475 Analysis of the wear behaviour of diamond impregnated tools used for the core drilling of concrete with statistical lifetime prediction
    Kansteiner, M. and Biermann, D. and Malevich, N. and Horn, M. and Müller, C.H. and Ferreira, M. and Tillmann, W.
    Euro PM 2018 Congress and Exhibition (2020)
    At the EUROPM 2017 a first approach for the analysis of the wear in core drilling processes of concrete based on statistical features was presented. Due to promising results of this first approach, and to increase the data basis, further experiments with the same tools were conducted. Beside a conventional concrete (C20/25), a second concrete (C100/115), with different composition and properties, was machined. Like before, the presented analysis is based on process force measurements and a microscopic analysis of the segments to detect diamond breakouts. Statistical methods were used to detect such certain events. Additionally, a lifetime estimation for single diamonds is carried out, which allows to forecast the breakout of single diamonds. Hence, the time when half or all of the diamonds visible in the beginning are broken out can be forecast. © European Powder Metallurgy Association (EPMA).
    view abstract
  • 2020 • 474 Following the motion of a charged conducting sphere by electrostatic induction in a parallel plate capacitor
    Kaponig, M. and Mölleken, A. and Tarasevitch, D. and Utzat, D. and Nienhaus, H. and Möller, R.
    Journal of Electrostatics 103 (2020)
    The charges induced in the plates of a parallel plate capacitor due to a conducting charged moving sphere have been measured up to the mechanical contact. For larger distances the induced charge scales linearly with the distance. However, when the sphere approaches the plate further the charges on the sphere are attracted by the induced charges in the plate and move on the surface of the sphere towards the plate. This leads to a further increase of the induced charge. The experimental results compare well to an approximate formula which will be discussed in detail. © 2019
    view abstractdoi: 10.1016/j.elstat.2019.103411
  • 2020 • 473 Evidence for an Fulde-Ferrell-Larkin-Ovchinnikov State with Segmented Vortices in the BCS-BEC-Crossover Superconductor FeSe
    Kasahara, S. and Sato, Y. and Licciardello, S. and Čulo, M. and Arsenijević, S. and Ottenbros, T. and Tominaga, T. and Böker, J. and Eremin, I. and Shibauchi, T. and Wosnitza, J. and Hussey, N.E. and Matsuda, Y.
    Physical Review Letters 124 (2020)
    We present resistivity and thermal-conductivity measurements of superconducting FeSe in intense magnetic fields up to 35 T applied parallel to the ab plane. At low temperatures, the upper critical field μ0Hc2ab shows an anomalous upturn, while thermal conductivity exhibits a discontinuous jump at μ0H∗≈24 T well below μ0Hc2ab, indicating a first-order phase transition in the superconducting state. This demonstrates the emergence of a distinct field-induced superconducting phase. Moreover, the broad resistive transition at high temperatures abruptly becomes sharp upon entering the high-field phase, indicating a dramatic change of the magnetic-flux properties. We attribute the high-field phase to the Fulde-Ferrel-Larkin-Ovchinnikov (FFLO) state, where the formation of planar nodes gives rise to a segmentation of the flux-line lattice. We point out that strongly orbital-dependent pairing as well as spin-orbit interactions, the multiband nature, and the extremely small Fermi energy are important for the formation of the FFLO state in FeSe. © 2020 American Physical Society.
    view abstractdoi: 10.1103/PhysRevLett.124.107001
  • 2020 • 472 Functionalized Macrocycles in Supramolecular Organocatalysis
    Kauerhof, D. and Niemeyer, J.
    ChemPlusChem 85 889-899 (2020)
    Supramolecular organocatalysis has emerged as a novel research field in the context of homogeneous catalysis. In particular, the use of functionalized macrocycles as supramolecular catalysts is highly promising, as these systems are oftentimes easily accessible and offer distinct advantages in catalysis. Macrocyclic catalysts can provide defined binding pockets, such as hydrophobic cavities, and can thus create a reaction microenvironment for catalysis. In addition, macrocycles can offer a preorganized arrangement of functional groups, such as binding sites or catalytically active groups, thus enabling a defined and possibly multivalent binding and activation of substrates. The aim of this Minireview is to provide an overview of recent advances in the area of supramolecular organocatalysis based on functionalized macrocycles (including cyclodextrins, calixarenes, and resorcinarenes), with a focus on those examples where certain catalytically active groups (such as hydrogen bond donors/acceptors, Brønsted acid or base groups, or nucleophilic units) are present in or have been installed on the macrocycles. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
    view abstractdoi: 10.1002/cplu.202000152
  • 2020 • 471 Modeling the Noise of Transferred-Substrate InP DHBTs at Highest Frequencies
    Kaule, E. and Doerner, R. and Weimann, N. and Rudolph, M.
    GeMIC 2020 - Proceedings of the 2020 German Microwave Conference 52-55 (2020)
    This paper investigates noise modeling of transferred-substrate indium phosphide double heterobipolar transistors (InP DUBTs). It is shown that the shot noise of these devices exhibits a pronounced correlation which allows for a reliable extrapolation of the noise performance based on standard noise measurement at lower frequencies, or even on the knowledge of small-signal model parameters alone. © 2020 IMA-Institut fur Mikrowellen-und Antennentechnik e.V.
    view abstract
  • 2020 • 470 Rational design of thiolated polyenes as trifunctional Raman reporter molecules in surface-enhanced Raman scattering nanotags for cytokine detection in a lateral flow assay
    Keller, T. and Brem, S. and Tran, V. and Sritharan, O. and Schäfer, D. and Schlücker, S.
    Journal of Biophotonics 13 (2020)
    The characteristic vibrational spectroscopic fingerprint of Raman reporter molecules adsorbed on noble metal nanoparticles is employed for the identification of target proteins by the corresponding surface-enhanced Raman scattering (SERS) nanotag-labeled antibodies. Here, we present the modular synthesis of thiolated polyenes with two to five C═C double bonds introduced via stepwise Wittig reactions. The experimental characterization of their electronic and vibrational properties is complemented by density functional theory calculations. Highly SERS-active nanotags are generated by using the thiolated polyenes as Raman reporter molecules in Au/Au core/satellite supraparticles with multiple hot spots. The cytokines IL-1β and IFN-γ are detected in a duplex SERS-based lateral flow assay on a nitrocellulose test strip by Raman microscopy. The thiolated polyenes are suitable for use in immuno-SERS applications such as point-of-care testing as well as cellular and tissue imaging. © 2020 The Authors. Journal of Biophotonics published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/jbio.201960126
  • 2020 • 469 Thermophysical Properties of Mixtures of Titanium(IV) Isopropoxide (TTIP) and p-Xylene
    Keller, A. and Wlokas, I. and Kohns, M. and Hasse, H.
    Journal of Chemical and Engineering Data 65 869-876 (2020)
    Titanium(IV) isopropoxide (TTIP) is an important precursor for the production of nanoparticles by spray flame processes. In these processes, the precursor is provided in a solution in a combustible solvent, which is p-xylene here. As no thermophysical data for solutions of TTIP in p-xylene were available in the literature, they were measured in the present work. The vapor-liquid equilibrium was measured at pressures ranging from 20 to 80 kPa. The specific density, viscosity, thermal conductivity, molar isobaric heat capacity, and self-diffusion coefficients were determined experimentally at 101.3 kPa at temperatures between 293.15 and 373.15 K. Sample compositions cover the range from pure TTIP to pure p-xylene. Chemical reactions in the studied system were considered. The experiments were carried out in such a way that they do not compromise the results for the thermophysical properties. The vapor-liquid equilibrium data were correlated using the NRTL model. Empirical correlations were established for the other properties. The results provide a rational basis for spray flame process design. © 2020 American Chemical Society.
    view abstractdoi: 10.1021/acs.jced.9b01059
  • 2020 • 468 Effect of electric current on the optical orientation of interface electrons in AlGaAs/GaAs heterostructures
    Ken, O.S. and Zhukov, E.A. and Akimov, I.A. and Korenev, V.L. and Kopteva, N.E. and Kalitukha, I.V. and Sapega, V.F. and Wieck, A.D. and Ludwig, Ar. and Schott, R. and Kusrayev, Y.G. and Yakovlev, D.R. and Bayer, M.
    Physical Review B 102 (2020)
    The effect of a lateral electric current on the photoluminescence H band of an AlGaAs/GaAs heterostructure is investigated. The photoluminescence intensity and optical orientation of electrons contributing to the H band are studied by means of continuous-wave and time-resolved photoluminescence spectroscopy and time-resolved Kerr rotation. It is shown that the H band is due to recombination of the heavy holes localized at the heterointerface with photoexcited electrons attracted to the heterointerface from the GaAs layer. Two lines with significantly different decay times constitute the H band: a short-lived high-energy one and a long-lived low-energy one. The high-energy line originates from recombination of electrons freely moving along the structure plane, while the low-energy one is due to recombination of donor-bound electrons near the interface. Application of a lateral electric field of ∼100-200 V/cm results in a quenching of both lines. This quenching is due to a decrease of electron concentration near the heterointerface as a result of a photocurrent-induced heating of electrons in the GaAs layer. On the contrary, electrons near the heterointerface are effectively cooled, so the donors near the interface are not completely empty up to ∼100 V/cm, which is in stark contrast with the case of bulk materials. The optical spin polarization of the donor-bound electrons near the heterointerface weakly depends on the electric field. Their polarization kinetics is determined by the spin dephasing in the hyperfine fields of the lattice nuclei. The long spin memory time (>40 ns) can be associated with suppression of the Bir-Aronov-Pikus mechanism of spin relaxation for electrons. © 2020 American Physical Society.
    view abstractdoi: 10.1103/PhysRevB.102.045302
  • 2020 • 467 Computer modeling of semiconductor nanotubes for water splitting
    Kenmoe, S. and Spohr, E.
    Current Opinion in Electrochemistry 19 88-95 (2020)
    One-dimensional nanostructures such as nanorods and nanotubes (NTs) are regarded as promising materials for photoelectrochemical water splitting. Modeling the electronic properties of oxidic NTs with diameters in the range of 3–30 nm in contact with liquid water is challenging owing to the fact that the systems are too large for direct ab initio molecular dynamics simulations. Here we summarize recent efforts to develop strained two-dimensional model systems for pristine and doped titania NTs. We have studied their structural, optical and photoelectrochemical properties by a number of different techniques attributable to quantum mechanical density functional theory. © 2019 Elsevier B.V.
    view abstractdoi: 10.1016/j.coelec.2019.10.013
  • 2020 • 466 The impact of post manufacturing treatment of functionally graded Ti6Al4V scaffolds on their surface morphology and mechanical strength
    Khrapov, D. and Koptyug, A. and Manabaev, K. and Léonard, F. and Mishurova, T. and Bruno, G. and Cheneler, D. and Loza, K. and Epple, M. and Surmenev, R. and Surmeneva, M.
    Journal of Materials Research and Technology 9 1866-1881 (2020)
    An ultrasonic vibration post-treatment procedure was suggested for additively manufactured lattices. The aim of the present research was to investigate mechanical properties and the differences in mechanical behavior and fracture modes of Ti6Al4V scaffolds treated with traditional powder recovery system (PRS) and ultrasound vibration (USV). Scanning electron microscopy (SEM) was used to investigate the strut surface and the fracture surface morphology. X-ray computed tomography (CT) was employed to evaluate the inner structure, strut dimensions, pore size, as well as the surface morphology of additively manufactured porous scaffolds. Uniaxial compression tests were conducted to obtain elastic modulus, compressive ultimate strength and yield stress. Finite element analysis was performed for a body-centered cubic (BCC) element-based model and for CT-based reconstruction data, as well as for a two-zone scaffold model to evaluate stress distribution during elastic deformation. The scaffold with PRS post treatment displayed ductile behavior, while USV treated scaffold displayed fragile behavior. Double barrel formation of PRS treated scaffold was observed during deformation. Finite element analysis for the CT-based reconstruction revealed the strong impact of surface morphology on the stress distribution in comparison with BCC cell model because of partially molten metal particles on the surface of struts, which usually remain unstressed. © 2019 The Authors.
    view abstractdoi: 10.1016/j.jmrt.2019.12.019
  • 2020 • 465 On the dispersion of waves for the linear thermoelastic relaxed micromorphic model
    Khurana, A. and Bala, S. and Khan, H. and Tomar, S.K. and Neff, P.
    Journal of Thermal Stresses 43 3-20 (2020)
    We present the complete set of constitutive relations and field equations for the linear thermoelastic relaxed micromorphic continuum and investigate its variants for wave propagation. It is found that the additional thermal effects give rise to new waves and generate couplings with longitudinal waves which are not existing in the relaxed micromorphic continuum without thermal effects. However, transverse waves go unaffected by the thermal properties. Thermal effects do not create any band gap in the dispersion curves of the model with three curvature parameters. The dispersion curves have been computed numerically for a particular model and compared with those presented in earlier studies. © 2019, © 2019 Taylor & Francis Group, LLC.
    view abstractdoi: 10.1080/01495739.2019.1679056
  • 2020 • 464 Sensitivity analysis as a tool for optimal material design
    Kijanski, W. and Barthold, F.-J.
    Proceedings of the 6th European Conference on Computational Mechanics: Solids, Structures and Coupled Problems, ECCM 2018 and 7th European Conference on Computational Fluid Dynamics, ECFD 2018 1808-1819 (2020)
    The presented contribution discusses the derivation of design sensitivity information of physical reaction forces arising in mechanical systems. The obtained gradient information can be used for the design of support areas within problems stated on single scales as well as for the design of microstructures in terms of representative volume elements (RVE) within numerical homogenisation techniques. Especially, FE2 approaches based on Langrange multiplier methods, where the Lagrange multiplier itself can be connected to some force or traction values on the surface of the RVE, can benefit from introduced and presented relations. copyright © Crown copyright (2018).All right reserved.
    view abstract
  • 2020 • 463 Efficient Area Matched Converter Aided Solar Charging of Lithium Ion Batteries Using High Voltage Perovskite Solar Cells
    Kin, L.-C. and Liu, Z. and Astakhov, O. and Agbo, S.N. and Tempel, H. and Yu, S. and Kungl, H. and Eichel, R.-A. and Rau, U. and Kirchartz, T. and Merdzhanova, T.
    ACS Applied Energy Materials 3 431-439 (2020)
    Efficient solar charging of a battery has been demonstrated in the past by sizing batteries many times that of a solar cell to reduce the effective current density experienced by the battery. Although efficient, such a strategy of coupling a battery up to 10 times larger with a solar cell will make solar-battery integration more challenging and limit the size, and thus maximum power output, of an integrated device. Area matched LFP-LTO (lithium iron phosphate, lithium titanate) battery solar charging using high voltage lead halide perovskite solar cells with a boost converter gave a maximum overall efficiency of 9.9% and a high 14.9% solar to battery charging efficiency. Two differently sized systems were compared using the same converter, and an exergy analysis was performed, showing limitations of converter usage in solar-powered internet of things (IoT) devices and size dependent battery losses. © 2019 American Chemical Society.
    view abstractdoi: 10.1021/acsaem.9b01672
  • 2020 • 462 Size dependent strength, slip transfer and slip compatibility in nanotwinned silver
    Kini, M.K. and Dehm, G. and Kirchlechner, C.
    Acta Materialia 184 120-131 (2020)
    Perfect slip transfer through single coherent Σ3 twin boundaries is known to be a cross-slip-like mechanism occurring at low stresses, which is expected to strongly depend on material properties like stacking fault energy. In the present study, we extend the argument of perfect slip transfer to (i) multiple closely spaced coherent twin boundaries in a nanotwinned thin film and (ii) to materials with very low stacking fault energy. The slip transfer is indicated by the continuity of slip steps and observed across up to 100 coherent Σ3 boundaries. The study addresses size scaling due to multiple weak obstacles for dislocation motion and discusses the underlying deformation mechanisms. The importance of strain compatibility is further extended to incoherent twin boundaries. © 2019
    view abstractdoi: 10.1016/j.actamat.2019.11.042
  • 2020 • 461 Parallel adaptive FETI-DP using lightweight asynchronous dynamic load balancing
    Klawonn, A. and Kühn, M.J. and Rheinbach, O.
    International Journal for Numerical Methods in Engineering 121 621-643 (2020)
    A parallel FETI-DP domain decomposition method using an adaptive coarse space is presented. The implementation builds on a recently introduced adaptive FETI-DP approach for elliptic problems in three dimensions and uses small, local eigenvalue problems for faces and, additionally, for a small number of edges. The condition number of the preconditioned operator then satisfies a bound that is independent of coefficient heterogeneities in the problem. The computational cost of the local eigenvalue problems is not negligible, and also a significant load imbalance can be introduced. As a remedy, certain eigenvalue problems are discarded by a theory-guided heuristic strategy, based on the diagonal entries of the stiffness matrices. Additionally, a lightweight pairwise dynamic load balancing strategy is implemented for the eigenvalue problems. The load balancing is supervised by an orchestrating rank using asynchronous point-to-point communication. The resulting method shows good weak and strong scalability up to thousands of cores while fast convergence is obtained even for heterogeneous problems. © 2019 John Wiley & Sons, Ltd.
    view abstractdoi: 10.1002/nme.6237
  • 2020 • 460 Coarse spaces for feti-DP and BDDC methods for heterogeneous problems: Connections of deflation and a generalized transformation-of-basis approach
    Klawonn, A. and Klawonn, A. and Kuhn, M. and Rheinbach, O.
    Electronic Transactions on Numerical Analysis 52 43-76 (2020)
    In FETI-DP (Finite Element Tearing and Interconnecting) and BDDC (Balancing Domain Decomposition by Constraints) domain decomposition methods, the convergence behavior of the iterative scheme can be improved by implementing a coarse space using a transformation of basis and local assembly. This is an alternative to coarse spaces implemented by deflation or balancing. The transformation-of-basis approaches are more robust with respect to inexact solvers than deflation and therefore more suitable for multilevel extensions. In this paper, we show a correspondence of FETI-DP or BDDC methods using a generalized transformation-of-basis approach and of FETI-DP methods using deflation or balancing, where the deflation vectors are obtained from the transformation of basis. These methods then have essentially the same eigenvalues. As opposed to existing theory, this result also applies to general scalings and highly heterogeneous problems. We note that the new methods differ slightly from the classic FETI-DP and BDDC methods using a transformation of basis and that the classic theory has to be replaced. An important application for the theory presented in this paper are FETI-DP and BDDC methods with adaptive coarse spaces, i.e., where deflation vectors are obtained from approximating local eigenvectors. These methods have recently gained considerable interest. © 2020 Kent State University.
    view abstractdoi: 10.1553/etna_vol52s43
  • 2020 • 459 Computational homogenization with million-way parallelism using domain decomposition methods
    Klawonn, A. and Köhler, S. and Lanser, M. and Rheinbach, O.
    Computational Mechanics 65 (2020)
    Parallel computational homogenization using the well-knwon FE 2 approach is described and combined with domain decomposition and algebraic multigrid solvers. It is the purpose of this paper to show that and how the FE 2 method can take advantage of the largest supercomputers available and those of the upcoming exascale era for virtual material testing of micro-heterogeneous materials such as advanced steel. The FE 2 method is a computational micro-macro homogenization approach where at each Gauss integration point of the macroscopic finite element problem a microscopic finite element problem, defined on a representative volume element (RVE), is attached. Note that the FE 2 method is not embarrassingly parallel since the RVE problems are coupled through the macroscopic problem. Numerical results considering different grids on both, the macroscopic and microscopic level as well as weak scaling results for up to a million parallel processes are presented. © 2019, Springer-Verlag GmbH Germany, part of Springer Nature.
    view abstractdoi: 10.1007/s00466-019-01749-5
  • 2020 • 458 Regularized, parameter free scale similarity type models for Large Eddy Simulation
    Klein, M. and Ketterl, S. and Engelmann, L. and Kempf, A. and Kobayashi, H.
    International Journal of Heat and Fluid Flow 81 (2020)
    The fidelity of Large Eddy Simulations (LES) depends strongly on the closures of the sub-grid scale (SGS) stress tensor. Although it is well known that the SGS stresses in LES are not aligned with the strain rate tensor, the most widely used models are still of eddy viscosity type, due to their robust behavior in LES and reasonable performance in a posteriori testing. The unstable behavior of more advanced anisotropic models, that is typically found in LES, has been attributed to either the fact that these models provide backscatter or to the fact that they do not provide a sufficient amount of dissipation. Based on recent advances in the field, an alternative modeling strategy is suggested, which can be used to regularize an arbitrary anisotropic (e.g. scale similarity type) model. The resulting model is easy to implement, can be written in compact form and is free of model parameters. The model has been tested a-posteriori and results are presented for a Taylor-Green-Vortex, a free plane jet and a turbulent channel flow of friction Reynolds numbers 395, 590 and 934. The results are compared to well-known eddy viscosity models and when applicable, to simulations without explicit LES model. The new model exhibits good performance for a variety of mesh resolutions and for all configurations. Furthermore, a-priori analysis results in the context of liquid atomization indicate that the model might be suitable as well in more complex physical scenarios. The a-priori analysis performance of the model is found to be nearly equivalent to the underlying structural anisotropic model in terms of its correlation coefficient, but the model is free of backscatter and provides good stability in LES. © 2019 Elsevier Inc.
    view abstractdoi: 10.1016/j.ijheatfluidflow.2019.108496
  • 2020 • 457 Relaxation dynamics in a Hubbard dimer coupled to fermionic baths: Phenomenological description and its microscopic foundation
    Kleinherbers, E. and Szpak, N. and König, J. and Schützhold, R.
    Physical Review B 101 (2020)
    We study relaxation dynamics in a strongly interacting two-site Fermi-Hubbard model that is induced by coupling each site to a local fermionic bath. To derive the proper form of the Lindblad operators that enter an effective description of the system-bath coupling in different temperature regimes, we employ a diagrammatic real-time technique for the time evolution of the reduced density matrix. In spite of a local coupling to the baths, the found Lindblad operators are nonlocal in space. We compare with the local approximation, where those nonlocal effects are neglected. Furthermore, we propose an improvement on the commonly used secular approximation (rotating-wave approximation), referred to as coherent approximation, which turns out superior in all studied parameter regimes (and equivalent otherwise). We look at the relaxation dynamics for several important observables and compare the methods for early and late times in various temperature regimes. © 2020 American Physical Society.
    view abstractdoi: 10.1103/PhysRevB.101.125131
  • 2020 • 456 Position dependency of surface roughness in parts from laser beam melting systems
    Kleszczynski, S. and Ladewig, A. and Friedberger, K. and zur Jacobsmühlen, J. and Merhof, D. and Witt, G.
    Proceedings - 26th Annual International Solid Freeform Fabrication Symposium - An Additive Manufacturing Conference, SFF 2015 360-370 (2020)
    Laser Beam Melting is a promising Additive Manufacturing technology for the production of complex metal components. During batch production of multiple identical parts in a single build job, we observed parts with deviating surface roughness in certain areas, which all faced away from the laser. This suggests a dependency of surface roughness on the part position in the build chamber. In this work we systematically reproduce and analyze this effect. We place hollow pyramids with twelve faces and two different overhanging angles at nine positions on the substrate plate and build this setup twice, using an imaging setup for process documentation. Surface roughness is measured by contact profilometry on three lines for each pyramid face. Our experiments reproduce the effect. Based on these findings we present a hypothesis for the cause and show metallographic images to support our theory. As a consequence, the position relative to the laser should be considered in the design phase for parts with high surface quality requirements. © SFF 2015.All rights reserved.
    view abstract
  • 2020 • 455 The role of molecular interactions on Michaelis constants of α-chymotrypsin catalyzed peptide hydrolyses
    Knierbein, M. and Held, C. and Sadowski, G.
    Journal of Chemical Thermodynamics 148 (2020)
    In this work, the effects of co-solvent and pressure on Michaelis constants at ambient temperature were analyzed for the enzymatic peptide hydrolyses of L-phenylalanine-p-nitroanilide (HPNA) and of N-succinyl-L-phenylalanine-p-nitroanilide (SPNA). These two substrates resemble each other in their molecular structure. That is, at the position of SPNA's succinyl-group (S), HPNA possesses a hydrogen atom (H). Two co-solvents were considered: trimethylamine N-oxide and dimethyl sulfoxide. The thermodynamic model Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT) was used to predict the activity of HPNA and SPNA under different reaction conditions regarding solvent composition and pressure. The PC-SAFT parameters (pure-component parameters and one binary parameter between substrate and solvent) were fitted to solubility data of HPNA in different solvents (water, ethanol, ethyl acetate, dimethyl sulfoxide), which were measured in this work at 30 °C and 1 bar. The resulting PC-SAFT predicted Michaelis constants were validated by experimental literature data. Results show that pressure decreased the Michaelis constants of both reactions, HPNA hydrolysis and SPNA hydrolysis. In spite of that, co-solvent effects on the Michaelis constants were predicted to be contrary for the two hydrolysis reactions. For the hydrolysis of HPNA, the co-solvents under investigation decreased the Michaelis constant while the co-solvents increased the Michaelis constant for the hydrolysis of SPNA. These PC-SAFT predictions were in qualitative agreement with the experimental literature data. This shows that molecular interactions are the key to understand the effects of co-solvents on Michaelis constants for the considered reactions. Applying the thermodynamic model PC-SAFT allowed predicting the observed combined effects of co-solvent and pressure on enzymatic reaction kinetics, which opens the door for solvent design of enzymatic reactions in the future. © 2020 Elsevier Ltd
    view abstractdoi: 10.1016/j.jct.2020.106142
  • 2020 • 454 Volatility forecasting accuracy for Bitcoin
    Köchling, G. and Schmidtke, P. and Posch, P.N.
    Economics Letters 191 (2020)
    We analyze the quality of Bitcoin volatility forecasting of GARCH-type models applying different volatility proxies and loss functions. We construct model confidence sets and find them to be systematically smaller for asymmetric loss functions and a jump robust proxy. © 2019 Elsevier B.V.
    view abstractdoi: 10.1016/j.econlet.2019.108836
  • 2020 • 453 The role of humidity and UV-C emission in the inactivation of B. subtilis spores during atmospheric-pressure dielectric barrier discharge treatment
    Kogelheide, F. and Voigt, F. and Hillebrand, B. and Moeller, R. and Fuchs, F. and Gibson, A.R. and Awakowicz, P. and Stapelmann, K. and Fiebrandt, M.
    Journal of Physics D: Applied Physics 53 (2020)
    Experiments are performed to assess the inactivation of Bacillus subtilis spores using a non-thermal atmospheric-pressure dielectric barrier discharge. The plasma source used in this study is mounted inside a vacuum vessel and operated in controlled gas mixtures. In this context, spore inactivation is measured under varying nitrogen/oxygen and humidity content and compared to spore inactivation using ambient air. Operating the dielectric barrier discharge in a sealed vessel offers the ability to distinguish between possible spore inactivation mechanisms since different process gas mixtures lead to the formation of distinct reactive species. The UV irradiance and the ozone density within the plasma volume are determined applying spectroscopic diagnostics with neither found to fully correlate with spore inactivation. It is found that spore inactivation is most strongly correlated with the humidity content in the feed gas, implying that reactive species formed, either directly or indirectly, from water molecules are strong mediators of spore inactivation. © 2020 The Author(s). Published by IOP Publishing Ltd.
    view abstractdoi: 10.1088/1361-6463/ab77cc
  • 2020 • 452 Characterisation of volume and surface dielectric barrier discharges in N2–O2 mixtures using optical emission spectroscopy
    Kogelheide, F. and Offerhaus, B. and Bibinov, N. and Krajinski, P. and Schücke, L. and Schulze, J. and Stapelmann, K. and Awakowicz, P.
    Plasma Processes and Polymers 17 (2020)
    A volume and a twin surface dielectric barrier discharge (VDBD and SDBD) are generated in different nitrogen–oxygen mixtures at atmospheric pressure by applying damped sinusoidal voltage waveforms with oscillation periods in the microsecond time scale. Both electrode configurations are located inside vacuum vessels and operated in a controlled atmosphere to exclude the influence of surrounding air. The discharges are characterised with different spatial and temporal resolution by applying absolutely calibrated optical emission spectroscopy in conjunction with numerical simulations and current–voltage measurements. Plasma parameters, namely the electron density and the reduced electric field, and the dissipated power are found to depend strongly on the oxygen content in the working gas mixture. Different spatial and temporal distributions of plasma parameters and dissipated power are explained by surface and residual volume charges for different O2 admixtures due to their effects on the electron recombination rate. Thus, the oxygen admixture is found to strongly influence the breakdown process and plasma conditions of a VDBD and a SDBD. © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/ppap.201900126
  • 2020 • 451 Optimization of Transparent Passivating Contact for Crystalline Silicon Solar Cells
    Kohler, M. and Finger, F. and Rau, U. and Ding, K. and Pomaska, M. and Zamchiy, A. and Lambertz, A. and Duan, W. and Lentz, F. and Li, S. and Smirnov, V. and Kirchartz, T.
    IEEE Journal of Photovoltaics 10 46-53 (2020)
    A highly transparent front contact layer system for crystalline silicon (c-Si) solar cells is investigated and optimized. This contact system consists of a wet-chemically grown silicon tunnel oxide, a hydrogenated microcrystalline silicon carbide [SiO2/μc-SiC:H(n)] prepared by hot-wire chemical vapor deposition (HWCVD), and a sputter-deposited indium doped tin oxide. Because of the exclusive use of very high bandgap materials, this system is more transparent for the solar light than state of the art amorphous (a-Si:H) or polycrystalline silicon contacts. By investigating the electrical conductivity of the μc-SiC:H(n) and the influence of the hot-wire filament temperature on the contact properties, we find that the electrical conductivity of μc-SiC:H(n) can be increased by 12 orders of magnitude to a maximum of 0.9 S/cm due to an increased doping density and crystallite size. This optimization of the electrical conductivity leads to a strong decrease in contact resistivity. Applying this SiO2/μc-SiC:H(n) transparent passivating front side contact to crystalline solar cells with an a-Si:H/c-Si heterojunction back contact we achieve a maximum power conversion efficiency of 21.6% and a short-circuit current density of 39.6 mA/cm2. All devices show superior quantum efficiency in the short wavelength region compared to the reference cells with a-Si:H/c-Si heterojunction front contacts. Furthermore, these transparent passivating contacts operate without any post processing treatments, e.g., forming gas annealing or high-temperature recrystallization. © 2011-2012 IEEE.
    view abstractdoi: 10.1109/JPHOTOV.2019.2947131
  • 2020 • 450 Synthesis of Bis-BINOL Derivatives: Linking via the 3-, 4-, or 5-Position by Generation of Suitable C 1 -Symmetric Precursors
    Kohlhaas, M. and Lutz, F. and Paransothy, N. and Octa-Smolin, F. and Wölper, C. and Niemeyer, J.
    Synthesis (Germany) 52 853-860 (2020)
    Bis-BINOL derivatives have proven highly useful in applications such as chemosensing or organocatalysis. In this account, we describe strategies for the linking of BINOL units via the 3-, 4-, or 5-positions, showing that unique synthetic strategies are necessary to address each position. We report the synthesis of suitable C 1 -symmetric precursors, which are generated either by monohalogenation or by monodeprotection of C 2 -symmetric starting materials, and their subsequent coupling to give linked bis-BINOL derivatives. © 2020 American Institute of Physics Inc.. All rights reserved.
    view abstractdoi: 10.1055/s-0039-1690763
  • 2020 • 449 Effective size separation of laser-generated, surfactant-free nanoparticles by continuous centrifugation
    Kohsakowski, S. and Seiser, F. and Wiederrecht, J.-P. and Reichenberger, S. and Vinnay, T. and Barcikowski, S. and Marzun, G.
    Nanotechnology 31 (2020)
    High-power, nanosecond, pulsed-laser ablation in liquids enables the continuous synthesis of highly pure colloidal nanoparticles (NPs) at an application-relevant scale. The gained mass-weighted particle size distribution is however often reported to be broad, requiring post treatment like centrifugation to remove undesired particle size fractions. To date, available centrifugation techniques are generally discontinuous, limiting the throughput and hindering economic upscaling. Hence, throughout this paper, a scalable, continuously operating centrifugation of laser-generated platinum NPs in a tubular bowl centrifuge is reported for the first time. To that end, using a 121 W ns-laser, the continuous production of a colloidal suspension of NPs, yet with broad particle size distribution has been employed, yielding productivities of 1-2 g h-1 for gold, silver, and platinum. The power-specific productivities (Au: 18 mg h-1 W-1, Pt: 13 mg h-1 W-1, Ag: 8 mg h-1 W-1, Ni: 6 mg h-1 W-1) are far higher than reported before. Subsequent downstream integration of a continuously operating tubular bowl centrifuge was successfully achieved for Pt NPs allowing the removal of undesired particle size with high throughput. By means of a systematic study of relevant centrifugation parameters involved, effective size optimization and respective size sharpness parameters for a maximum Pt NP diameter of 10 nm are reported. The results of the experimental centrifugation of laser-generated Pt NPs were in excellent agreement with the theoretically calculated cut-off diameter. After centrifugation with optimized parameters (residence time of 5 min; g-force of 38,454 g), the polydispersity indices of the Pt NPs size distributions were reduced by a factor of six, and high monodispersity was observed. © 2019 IOP Publishing Ltd.
    view abstractdoi: 10.1088/1361-6528/ab55bd
  • 2020 • 448 In vivo biodistribution of calcium phosphate nanoparticles after intravascular, intramuscular, intratumoral, and soft tissue administration in mice investigated by small animal PET/CT
    Kollenda, S.A. and Klose, J. and Knuschke, T. and Sokolova, V. and Schmitz, J. and Staniszewska, M. and Costa, P.F. and Herrmann, K. and Westendorf, A.M. and Fendler, W.P. and Epple, M.
    Acta Biomaterialia 109 244-253 (2020)
    Calcium phosphate nanoparticles were covalently surface-functionalized with the ligand DOTA and loaded with the radioisotope 68Ga. The biodistribution of such 68Ga-labelled nanoparticles was followed in vivo in mice by positron emission tomography in combination with computer tomography (PET-CT). The biodistribution of 68Ga-labelled nanoparticles was compared for different application routes: intravenous, intramuscular, intratumoral, and into soft tissue. The particle distribution was measured in vivo by PET-CT after 5 min, 15 min, 30 min, 1 h, 2 h, and 4 h, and ex vivo after 5 h. After intravenous injection (tail vein), the nanoparticles rapidly entered the lungs with later redistribution into liver and spleen. The nanoparticles remained mostly at the injection site following intramuscular, intratumoral, or soft tissue application, with less than 10 percent being mobilized into the blood stream. Statement of Significance: The in vivo biodistribution of DOTA-terminated calcium phosphate nanoparticles was followed by PET/CT. To our knowledge, this is the first study of this kind. Four different application routes of clinical relevance were pursued: Intravascular, intramuscular, intratumoral, and into soft tissue. Given the high importance of calcium phosphate as biomaterial and for nanoparticular drug delivery and immunization, this is most important to assess the biofate of calcium phosphate nanoparticles for therapeutic application and also judge biodistribution of nanoscopic calcium phosphate ceramics, including debris from endoprostheses and related implants. © 2020
    view abstractdoi: 10.1016/j.actbio.2020.03.031
  • 2020 • 447 Correlation of Uniaxial and Multiaxial Fatigue Models for Automobile Spring Life Assessment
    Kong, Y.S. and Abdullah, S. and Schramm, D. and Omar, M.Z. and Haris, S.M.
    Experimental Techniques 44 197-215 (2020)
    This paper presents a regression analysis of uniaxial and multiaxial fatigue life for automobile coil spring under various road excitations. Coil spring is a suspension component with complex geometry and shear loading which is applied during operating conditions. Hence, uniaxial strain measurement for durability assessment of coil spring is insufficient because the loadings are non-proportional. Rosette strain signals of coil spring under five different road conditions were obtained and used as input to uniaxial strain-life and multiaxial critical plane models to predict the spring fatigue life. During the multiaxial fatigue analysis, the strain biaxiality ratio of range 0.3 to 0.5 indicates the loadings as out-of-phase. Through a simple linear regression method, a linear regression model between uniaxial and multiaxial fatigue life were obtained with coefficient of determination value as high as 0.8696. This model provides significant contribution through correlating uniaxial to multiaxial fatigue life. Hence, uniaxial fatigue life predictions could be approximated to multiaxial for more conservative analysis through the application of generated linear models. © 2019, The Society for Experimental Mechanics, Inc.
    view abstractdoi: 10.1007/s40799-019-00344-w
  • 2020 • 446 Multi-Criteria Optimization in the Production of Lithium-Ion Batteries
    Kornas, T. and Wittmann, D. and Daub, R. and Meyer, O. and Weihs, C. and Thiede, S. and Herrmann, C.
    Procedia Manufacturing 43 720-727 (2020)
    Lithium-ion-batteries (LIBs) play a key role in determining the environmental impacts of future mobility technologies. In particular, the production of LIBs has a strong environmental impact as it is characterized by high scrap rates. In addition to existing expert-based approaches for the identification of quality drivers in production, a trend towards data-driven methods is discernible. Nevertheless, most approaches show shortcomings in the involvement of multi-criteria optimization. Therefore, this paper uses desirability functions to jointly optimize several quality parameters. Validation was conducted based on the data of an assembly line for prismatic LIBs. © 2020 The Authors. Published by Elsevier B.V.
    view abstractdoi: 10.1016/j.promfg.2020.02.113
  • 2020 • 445 Electron tunneling dynamics between two-dimensional and zero-dimensional quantum systems: Contributions of momentum matching, higher subbands, and phonon-assisted processes
    Korsch, A.R. and Ebler, C. and Nguyen, G.N. and Scholz, S. and Wieck, A.D. and Ludwig, Ar.
    Physical Review B 102 (2020)
    We investigate tunneling dynamics of electrons from an ensemble of self-assembled InAs quantum dots into the subbands of a two-dimensional electron gas (2DEG). LO-phonon-assisted tunneling processes and tunneling into higher subbands of the 2DEG electronic structure cause distinct resonances in the evolution of the tunneling rate as a function of the energy detuning between quantum dot and 2DEG ground state. By devising a semiquantitative model, we identify the momentum mismatch between the quantum dot and 2DEG wave function as the crucial quantity governing the evolution of the tunneling rate. In particular, we demonstrate that this mechanism along with the availability of tunneling into the second 2DEG subband allows for tuning of the tunneling rate by more than two orders of magnitude. © 2020 American Physical Society.
    view abstractdoi: 10.1103/PhysRevB.102.035413
  • 2020 • 444 Effect of miniaturization and surface roughness on the mechanical properties of the electron beam melted superalloy Inconel®718
    Kotzem, D. and Dumke, P. and Sepehri, P. and Tenkamp, J. and Walther, F.
    Progress in Additive Manufacturing 5 267-276 (2020)
    In this work, the Ni-based super alloy Inconel 718 manufactured via electron beam melting is investigated. Typical microstructure of Inconel 718, which was processed by electron beam melting, consists of columnar oriented dendritic structure with strong texture along building direction in hatch region, whereas microstructure differs in contour region, which is supposed to influence mechanical properties in the as-built state. As highly complex geometries are possible to manufacture with additive manufacturing techniques, the influence of miniaturization and surface roughness on microstructural and mechanical properties has to be understood in detail. Therefore, samples were processed with different initial sizes and subsequently tested in as-built and polished condition. Before performing mechanical tests, process-induced microstructure was determined by scanning electron microscope as well as distribution of defects and geometrical deviations by microfocused computed tomography. To characterize the mechanical properties, different testing methods, both tensile and fatigue tests, were carried out. Present investigations show almost similar microstructures in large-scale and small-scale Inconel 718 volumes. However, small-scale volumes show higher number of defects in the form of surface and near-surface defects. Furthermore, as-built specimens show geometrical deviations when compared to initial CAD diameter, which makes the implementation of an average equivalent diameter mandatory. It can be demonstrated that small-scale as-built volumes have reduced mechanical properties, whereby ultimate tensile strength is reduced by 60% and fatigue strength is reduced by 75%, showing that increased defect density and as-built surface roughness have a higher impact on fatigue properties and are the dominating reason for early failure in the as-built state due to multiple crack initiation. © 2019, Springer Nature Switzerland AG.
    view abstractdoi: 10.1007/s40964-019-00101-w
  • 2020 • 443 Influence of specimen position on the build platform on the mechanical properties of as-built direct aged electron beam melted Inconel 718 alloy
    Kotzem, D. and Arold, T. and Niendorf, T. and Walther, F.
    Materials Science and Engineering A 772 (2020)
    Electron powder bed fusion (E-PBF) allows for manufacturing of near-net-shape components of unprecedented complexity. In order to transfer specific benefits into industrial environments, equal properties of any volume built are mandatory. The main objective of this work is to investigate the process-induced material properties in arbitrary build envelope positions. Microstructure, hardness, relative density and fatigue behavior are in focus and thoroughly studied for E-PBF manufactured Inconel 718 alloy. In particular, it can be stated that all specimens have an effective diameter below dimensions set in the initial CAD data. Furthermore, it could be demonstrated that the relative density varies at different positions of the building platform, even for specimens built in direct vicinity. In terms of hardness, specimens at the outer perimeter of the building platform show increased values indicating a higher fraction of strengthening phases. Based on the cyclic tests, a relationship between building platform position and fatigue behavior can be derived. Specimens located in the front of the building platform show superior cyclic properties as compared to specimens in the back of building platform. Notch effects, i.e. process induced topography, are revealed to be the most detrimental influencing factor in the condition tested. © 2019
    view abstractdoi: 10.1016/j.msea.2019.138785
  • 2020 • 442 Damage tolerance evaluation of E-PBF-manufactured inconel 718 strut geometries by advanced characterization techniques
    Kotzem, D. and Arold, T. and Niendorf, T. and Walther, F.
    Materials 13 247 (2020)
    By means of electron beam powder bed fusion (E-PBF), highly complex lightweight structures can be manufactured within short process times. Due to the increasing complexity of producible components and the entangled interplay of damage mechanisms, common bulk material properties such as ultimate tensile or fatigue strength are not sufficient to guarantee safe and reliable use in demanding applications. Within this work, the damage tolerance of E-PBF-manufactured Ni-based alloy Inconel 718 (IN 718) strut geometries under uniaxial cyclic loading was investigated supported by several advanced measurement techniques. Based on thermal and electrical measurements, the failure of single struts could reliably be detected, revealing that continuous monitoring is applicable for such complex geometries. Process-induced surface roughness was found to be the main reason for early failure during cyclic loading. Thus, adequate post-processing steps have to be established for complex geometries to significantly improve damage tolerance and, eventually, in-service properties. © 2020 by the authors.
    view abstractdoi: 10.3390/ma13010247
  • 2020 • 441 Real-Time Capable Calculation of Reaction Forces of Multibody Systems Using Optimized Bushings on the Example of a Vehicle Wheel Suspension
    Kracht, F.E. and Schramm, D.
    Computational Methods in Applied Sciences 53 409-416 (2020)
    This paper presents an object-oriented modeling method capable of simulating the dynamics including the reaction forces of multibody systems with kinematic loops in hard real-time, called RTOOM. The modeling method describes the system by explicit equations, which can be solved numerically stable with a standard explicit numerical integrator with fixed step size. By knowing the application and the desired accuracy, the model can be adapted to fit the problem. Algebraic loops are resolved with low-pass filters parameterized for the frequency range of the application. Bushings with optimized spring and damping constants are used to avoid iterative methods for solving kinematics loops. For the optimization, a high accurate, non-manipulated and non-real-time multibody model is used. The optimization targets are stability, computing time and accuracy. The double wishbone suspension of the Formula Student racing car A40-02 of the University of Duisburg-Essen is used as an example. It has been successfully proven that a simulation up to 30 Hz with a required step size of 1 ms can be achieved. The simulation results show a very good accuracy up to 15 Hz with a deviation of the force below 4% and the acceleration below 7%. If the parameterization of the bushings remains the same, the accuracy is still acceptable even at higher frequencies. © 2020, Springer Nature Switzerland AG.
    view abstractdoi: 10.1007/978-3-030-23132-3_49
  • 2020 • 440 Influence of precipitation hardening on the high-temperature sliding wear resistance of an aluminium alloyed iron-nickel base alloy
    Krell, J. and Röttger, A. and Ziesing, U. and Theisen, W.
    Tribology International 148 (2020)
    This work investigates the effects of precipitation hardening on hot hardness and high-temperature sliding wear resistance of an iron-nickel base alloy. Three variants of a carbide rich alloy containing 0, 2 and 3 wt.-% aluminium were manufactured and aged for 24 h at 650, 700 and 750 °C. Hot hardness (20–800 °C) and sliding wear tests (600 °C) were conducted for each condition. The addition of aluminium has little effect on the type or volume content of the carbides. Ageing caused the precipitation of NiAl in the aluminium-containing alloys. The precipitation-hardened samples show higher hot hardness and better hot wear resistance. The lower wear loss can mainly be attributed to the improved support of the carbides by the precipitation strengthened matrix. © 2020
    view abstractdoi: 10.1016/j.triboint.2020.106342
  • 2020 • 439 Comprehensive investigation of the microstructure-property relationship of differently manufactured Co–Cr–C alloys at room and elevated temperature
    Krell, J. and Röttger, A. and Theisen, W.
    Wear 444-445 (2020)
    The purpose of this study was to investigate the influence of the microstructure on sliding wear and hardness of four different Co–Cr–C alloys at room and elevated temperature. Different microstructures were produced by applying three different processes. The hardness, hot hardness and wear loss at room temperature of these alloys correlate strongly with the carbide volume content. In sliding wear tests against an Al2O3 ball, abrasive wear occurs at room temperature. The size or geometric arrangement of the carbides or metal matrix plays a minor role at room temperature. At 600 °C the wear behaviour changes due to the softening matrix. In alloys with small free matrix path lengths, the highest wear rates occur due to micro-fatigue and micro-cracking. In hypoeutectic alloys with a high free matrix path length, the carbides lose their effectiveness due to the lack of support by the matrix. In these alloys, wear is dominated by the properties of the matrix. A hypereutectic casting alloy with large primary carbides shows the best wear results, as the carbides support themselves due to their size and retain their wear-reducing effect. © 2019 Elsevier B.V.
    view abstractdoi: 10.1016/j.wear.2019.203138
  • 2020 • 438 Tensor Spines - A Hyperstreamlines Variant Suitable for Indefinite Symmetric Second-Order Tensors
    Kretzschmar, V. and Gunther, F. and Stommel, M. and Scheuermann, G.
    IEEE Pacific Visualization Symposium 2020-June 106-110 (2020)
    Modern engineering uses optimization to design long-living and robust components. One part of this process is to find the optimal stress-aware design under given geometric constraints and loading conditions. Tensor visualization provides techniques to show and evaluate the stress distribution based on finite element method simulations. One such technique are hyperstreamlines. They allow us to explore the stress along a line following one principal stress direction while showing the other principal stress directions and their values. In this paper, we show shortcomings of this approach from an engineer's point of view and propose a variant called tensor spines. It provides an improved perception of the relation between the principal stresses helping engineers to optimize their designs further. © 2020 IEEE.
    view abstractdoi: 10.1109/PacificVis48177.2020.1008
  • 2020 • 437 Arduino-based slider setup for gas–liquid mass transfer investigations: Experiments and CFD simulations
    Krieger, W. and Bayraktar, E. and Mierka, O. and Kaiser, L. and Dinter, R. and Hennekes, J. and Turek, S. and Kockmann, N.
    AIChE Journal 66 (2020)
    The implementation of traditional sensors is a drawback when investigating mass transfer phenomena within microstructured devices, since they disturb the flow and reactor characteristics. An Arduino based slider setup is developed, which is equipped with a computer-vision system to track gas–liquid slug flow. This setup is combined with an optical analytical method allowing to compare experimental results against CFD simulations and investigate the entire lifetime of a single liquid slug with high spatial and temporal resolution. Volumetric mass transfer coefficients are measured and compared with data from literature and the mass transfer contribution of the liquid film is discussed. © 2020 The Authors. AIChE Journal published by Wiley Periodicals, Inc. on behalf of American Institute of Chemical Engineers.
    view abstractdoi: 10.1002/aic.16953
  • 2020 • 436 Fast-Acting Antibacterial, Self-Deactivating Polyionene Esters
    Krumm, C. and Trump, S. and Benski, L. and Wilken, J. and Oberhaus, F. and Köller, M. and Tiller, J.C.
    ACS Applied Materials and Interfaces 12 21201-21209 (2020)
    Biocidal compounds that quickly kill bacterial cells and are then deactivated in the surrounding without causing environmental problems are of great current interest. Here, we present new biodegradable antibacterial polymers based on polyionenes with inserted ester functions (PBI esters). The polymers are prepared by polycondensation reaction of 1,4-dibromobutene and different tertiary diaminodiesters. The resulting PBI esters are antibacterially active against a wide range of bacterial strains and were found to quickly kill these cells within 1 to 10 min. Because of hydrolysis of the ester groups, the PBI esters are degraded and deactivated in aqueous media. The degradation rate depends on the backbone structure and the pH. The structure of the polymers also controls the deactivation mechanism. While the more hydrophilic polymers require hydrolyses of only 19 to 30% of the ester groups to become practically inactive, the more hydrophobic PBI esters require up to 85% hydrolysis to achieve the same result. Thus, depending on the environmental conditions and the chemical nature, the PBI esters can be active for only 20 min or for at least one week. © 2020 American Chemical Society.
    view abstractdoi: 10.1021/acsami.9b19313
  • 2020 • 435 Tuning Light-Driven Water Oxidation Efficiency of Molybdenum-Doped BiVO4 by Means of Multicomposite Catalysts Containing Nickel, Iron, and Chromium Oxides
    Krysiak, O.A. and Junqueira, J.R.C. and Conzuelo, F. and Bobrowski, T. and Wilde, P. and Wysmolek, A. and Schuhmann, W.
    ChemPlusChem 85 327-333 (2020)
    Mo-doped BiVO4 has emerged as a promising material for photoelectrodes for photoelectrochemical water splitting, however, still shows a limited efficiency for light-driven water oxidation. We present the influence of an oxygen-evolution catalyst composed of Ni, Fe, and Cr oxides on the activity of Mo:BiVO4 photoanodes. The photoanodes are prepared by spray-coating, enabling compositional and thickness gradients of the incorporated catalyst. Two different configurations are evaluated, namely with the catalyst embedded into the Mo:BiVO4 film or deposited on top of it. Both configurations provide a significantly different impact on the photoelectrocatalytic efficiency. Structural characterisation of the materials by means of SEM, TEM and XRD as well as the photoelectrocatalytic activity investigated by means of an optical scanning droplet cell and in situ detection of oxygen using scanning photoelectrochemical microscopy are presented. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
    view abstractdoi: 10.1002/cplu.201900701
  • 2020 • 434 Asymmetric spin transitions of nonthermalized Mn2+ ions in (Zn,Mn)Se-based quantum wells
    Kudlacik, D. and Kavokin, K.V. and Lüders, C. and Barthelmi, K. and Schindler, J.J. and Moldenhauer, H. and Waldkirch, P. and Sapega, V.F. and Yakovlev, D.R. and Waag, A. and Bayer, M. and Debus, J.
    Physical Review B 101 (2020)
    In Zn1-xMnxSe/(Zn,Be)Se quantum wells with x<0.035, nonthermalized Mn2+ ions demonstrate in spin-flip scattering spectra multiple Stokes and anti-Stokes transitions whose absolute energies deviate by up to 20% from each other. This asymmetry is tuned significantly by the optical power density, magnetic field direction, and Mn ion concentration. The nonequidistant Mn2+ spin transitions are modeled by the Zeeman splitting and quadrupolar crystal-field components taking values of up to 7 GHz. We suggest that nonequilibrium carriers dynamically polarize the Mn-ion spins so that they occupy levels with positive and negative spin projection numbers giving rise to asymmetric spin transitions. © 2020 American Physical Society.
    view abstractdoi: 10.1103/PhysRevB.101.155432
  • 2020 • 433 WS2 monolayer based light emitting devices fabricated by scalable deposition techniques
    Kümmell, T. and Andrzejewski, D. and Beckmann, Y. and Abdelbaky, M. and Yeow, T. and Grundmann, A. and Heuken, M. and Kalisch, H. and Vescan, A. and Musselman, K. and Bacher, G.
    Proceedings of SPIE - The International Society for Optical Engineering 11302 (2020)
    Transition metal dichalcogenides (TMDC) have become attractive candidates for 2D electronics and optoelectronics. While several concepts for light emitting devices have been reported, many of them realized using exfoliated TMDC flakes of micrometer size, only few approaches tackle the challenge of upscaling to relevant device sizes. We demonstrate a light emitting diode based on WS2 monolayers in a scalable design. The devices are fabricated by combining two industrially relevant deposition processes in a vertical p-n architecture: Metal organic CVD (MOCVD) is used to realize the optically active WS2 monolayers, while ZnO deposited by spatial atomic layer deposition (sALD) is employed as an electron injection layer on the cathode side. Organic layers spin-coated on an ITO covered glass substrate provide hole injection and transport. The resulting devices exhibit rectifying behavior and red electroluminescence from an area of 6 mm2. © COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only.
    view abstractdoi: 10.1117/12.2544926
  • 2020 • 432 High-strength Damascus steel by additive manufacturing
    Kürnsteiner, P. and Wilms, M.B. and Weisheit, A. and Gault, B. and Jägle, E.A. and Raabe, D.
    Nature 582 515-519 (2020)
    Laser additive manufacturing is attractive for the production of complex, three-dimensional parts from metallic powder using a computer-aided design model1–3. The approach enables the digital control of the processing parameters and thus the resulting alloy’s microstructure, for example, by using high cooling rates and cyclic re-heating4–10. We recently showed that this cyclic re-heating, the so-called intrinsic heat treatment, can trigger nickel-aluminium precipitation in an iron–nickel–aluminium alloy in situ during laser additive manufacturing9. Here we report a Fe19Ni5Ti (weight per cent) steel tailor-designed for laser additive manufacturing. This steel is hardened in situ by nickel-titanium nanoprecipitation, and martensite is also formed in situ, starting at a readily accessible temperature of 200 degrees Celsius. Local control of both the nanoprecipitation and the martensitic transformation during the fabrication leads to complex microstructure hierarchies across multiple length scales, from approximately 100-micrometre-thick layers down to nanoscale precipitates. Inspired by ancient Damascus steels11–14—which have hard and soft layers, originally introduced via the folding and forging techniques of skilled blacksmiths—we produced a material consisting of alternating soft and hard layers. Our material has a tensile strength of 1,300 megapascals and 10 per cent elongation, showing superior mechanical properties to those of ancient Damascus steel12. The principles of in situ precipitation strengthening and local microstructure control used here can be applied to a wide range of precipitation-hardened alloys and different additive manufacturing processes. © 2020, The Author(s), under exclusive licence to Springer Nature Limited.
    view abstractdoi: 10.1038/s41586-020-2409-3
  • 2020 • 431 Control of thermally stable core-shell nano-precipitates in additively manufactured Al-Sc-Zr alloys
    Kürnsteiner, P. and Bajaj, P. and Gupta, A. and Wilms, M.B. and Weisheit, A. and Li, X. and Leinenbach, C. and Gault, B. and Jägle, E.A. and Raabe, D.
    Additive Manufacturing 32 (2020)
    Laser Additive Manufacturing (LAM) of light metals such as high-strength Al-based alloys offers tremendous potential for e.g. weight reduction and associated reduced fuel consumptions for the transportation industry. Typically, commercial Sc-containing alloys, such as Scalmalloy®, rely on precipitation hardening to increase their strength. Conventional processing involves controlled ageing during which ordered and coherent Al3Sc precipitates form from a Sc-supersaturated solid solution. Here we show how the intrinsic heat treatment (IHT) of directed energy deposition (DED) can be used to trigger the precipitation of Al3Sc already during the LAM process. High number densities of 1023 nano-precipitates per m3 can be realized through solid-state phase transformation from the supersaturated Al-Sc matrix that results from the fast cooling rate in LAM. Yet, the IHT causes precipitates to coarsen, hence reducing their strengthening effect. We implement alternative solidification conditions to exploit the IHT to form a Zr-rich shell around the Al3Sc precipitates that prevents coarsening. Our approach is applicable to a wide range of precipitation-hardened alloys to trigger in-situ precipitation during LAM. © 2019 Elsevier B.V.
    view abstractdoi: 10.1016/j.addma.2019.100910
  • 2020 • 430 High-throughput characterization of Ag–V–O nanostructured thin-film materials libraries for photoelectrochemical solar water splitting
    Kumari, S. and Helt, L. and Junqueira, J.R.C. and Kostka, A. and Zhang, S. and Sarker, S. and Mehta, A. and Scheu, C. and Schuhmann, W. and Ludwig, Ar.
    International Journal of Hydrogen Energy 45 12037-12047 (2020)
    Ag–V–O thin-film materials libraries, with both composition (Ag22-77V23-78Ox) and thickness (123–714 nm) gradients were fabricated using combinatorial reactive magnetron co-sputtering aiming on establishing relations between composition, structure, and functional properties. As-deposited libraries were annealed in air at 300 °C for 10 h. High-throughput characterization methods of composition, structure and functional properties were used to identify photoelectrochemically active regions. The phases AgV6O15, Ag2V4O11, AgVO3, and Ag4V2O7 were observed throughout the composition gradient. The photoelectrochemical properties of Ag–V–O films are dependent on composition and morphology. An enhanced photocurrent density (~300–554 μA/cm2) was obtained at 30 to 45 at.% Ag along the thickness gradient. Thin films of these compositions show a nanowire morphology, which is an important factor for the enhancement of photoelectrochemical performance. The photoelectrochemically active regions were further investigated by high-throughput synchrotron-X-ray diffraction and transmission electron microscopy (Ag32V68Ox) which confirmed the presence of Ag2V4O11 as the dominating phase along with the minor phases AgV6O15 and AgVO3. This enhanced photoactive region shows bandgap values of ~2.30 eV for the direct and ~1.87 eV for the indirect bandgap energies. The porous nanostructured films improve charge transport and are hence of interest for photoelectrochemical water splitting. © 2020 Hydrogen Energy Publications LLC
    view abstractdoi: 10.1016/j.ijhydene.2020.02.154
  • 2020 • 429 Structural and photoelectrochemical properties in the thin film system Cu-Fe-V-O and its ternary subsystems Fe-V-O and Cu-V-O
    Kumari, S. and Junqueira, J.R.C. and Sarker, S. and Mehta, A. and Schuhmann, W. and Ludwig, Al.
    Journal of Chemical Physics 153 (2020)
    Thin-film material libraries in the ternary and quaternary metal oxide systems Fe-V-O, Cu-V-O, and Cu-Fe-V-O were synthesized using combinatorial reactive co-sputtering with subsequent annealing in air. Their compositional, structural, and functional properties were assessed using high-throughput characterization methods. Prior to the investigation of the quaternary system Cu-Fe-V-O, the compositions (Fe61V39)Ox and (Cu52V48)Ox with promising photoactivity were identified from their ternary subsystems Fe-V-O and Cu-V-O, respectively. Two Cu-Fe-V-O material libraries with (Cu29-72Fe4-27V22-57)Ox and (Cu11-55Fe27-73V12-34)Ox composition spread were investigated. Seven mixed ternary and quaternary phase regions were identified: I (α-Cu3FeV6O26/FeVO4), II (Cu5V2O10/FeVO4/α-Cu3Fe4V6O26), III (Cu5V2O10), IV (Cu5V2O10/FeVO4, V (FeVO4/γ-Cu2V2O7/α-Cu3Fe4V6O26), VI (β-Cu2V2O7/α-Cu3Fe4V6O26/FeVO4), and VII (β-Cu3Fe4V6O26/FeVO4). In the investigated composition range, two photoactive regions, (Cu53Fe7V40)Ox and (Cu45Fe21V34)Ox, were identified, exhibiting 103 μA/cm2 and 108 μA/cm2 photocurrent density for the oxygen evolution reaction at 1.63 V vs reversible hydrogen electrode, respectively. The highest photoactive region (Cu45Fe21V34)Ox comprises the dominant α-Cu3Fe4V6O24 phase and minor FeVO4 phase. This photoactive region corresponds to having an indirect bandgap of 1.87 eV and a direct bandgap of 2.58 eV with an incident photon-to-current efficiency of 30% at a wavelength of 310 nm. © 2020 Author(s).
    view abstractdoi: 10.1063/5.0009512
  • 2020 • 428 Combinatorial Search for New Solar Water Splitting Photoanode Materials in the Thin-Film System Fe-Ti-W-O
    Kumari, S. and Khare, C. and Xi, F. and Nowak, M. and Sliozberg, K. and Gutkowski, R. and Bassi, P.S. and Fiechter, S. and Schuhmann, W. and Ludwig, Al .
    Zeitschrift fur Physikalische Chemie 234 867-885 (2020)
    In order to identify new solar water splitting photoanodes, Fe-Ti-W-O materials libraries were fabricated by combinatorial reactive co-sputtering and investigated by high-throughput characterization methods to elucidate compositional, thickness, and structural properties. In addition, photoelectrochemical measurements such as potentiodynamic photocurrent determination and open circuit potential measurements were performed using an automated scanning droplet cell. In the thin-film library, a quaternary photoactive region Fe30-49Ti29-55W13-22Ox was identified as a hit composition region, comprising binary and ternary phases. The identified region shows a distinct surface morphology with larger grains (∼200 nm) being embedded into a matrix of smaller grains (∼80-100 nm). A maximum photocurrent density of 117 μA/cm2 at a bias potential of 1.45 V vs. RHE in NaClO4 as an electrolyte under standard solar simulating conditions was recorded. Additional samples with compositions from the hit region were fabricated by reactive co-sputtering and spin coating followed by annealing. Synchrotron X-ray diffraction of sputtered Fe32Ti52W16Ox thin-films, annealed in air (600 °C, 700 °C, 800 °C) revealed the presence of the phases FeTiO3 and Ti0.54W0.46O2. The composition Fe48Ti30W22Ox from the hit region was fabricated by spin coating and subsequent annealing for a detailed investigation of its structure and photoactivity. After annealing the spin-coated sample at 650 °C for 6 h, X-ray diffraction results showed a dominant pattern with narrow diffraction lines belonging to a distorted FeWO4 (ferberite) phase along with broad diffraction lines addressed as Fe2TiO5 and in a small fraction also, Fe1.7Ti0.23O3. In hematite, Fe can be substituted by Ti, therefore we suggest that in the newfound ferberite-type phase, Ti partially substitutes for Fe leading to a small lattice distortion and a doubling of the monoclinic unit cell. In addition, Na from the substrate stabilizes the new phase: its tentative chemical formula is NaxFe0.33Ti0.67W2O8. A maximum photocurrent density of around 0.43 mA/cm2 at 1.45 V vs. RHE in 1M NaOH (pH ∼13.6) as an electrolyte was measured. Different aspects of the dependence of annealing and precursor solution concentration on phase transformation and photoactivity are discussed. © 2020 Alfred Ludwig et al., published by De Gruyter, Berlin/Boston 2020.
    view abstractdoi: 10.1515/zpch-2019-1462
  • 2020 • 427 Quantum-phase-field: From de broglie-bohm double-solution program to doublon networks
    Kundin, J. and Steinbach, I.
    Zeitschrift fur Naturforschung - Section A Journal of Physical Sciences 75 155-170 (2020)
    Different forms of linear and non-linear field equations, so-called 'phase-field' equations, are studied in relation to the de Broglie-Bohm double-solution program. This defines a framework in which elementary particles are described by localised non-linear wave solutions moving by the guidance of a pilot wave, defined by the solution of a Schrödinger-type equation. First, we consider the phase-field order parameter as the phase for the linear pilot wave, second as the pilot wave itself, and third as a moving soliton interpreted as a massive particle. In the last case, we introduce the equation for a superwave, the amplitude of which can be considered as a particle moving in accordance to the de Broglie-Bohm theory. Lax pairs for the coupled problems are constructed in order to discover possible non-linear equations that can describe the moving particle and to propose a framework for investigating coupled solutions. Finally, doublons in 1 + 1 dimensions are constructed as self-similar solutions of a non-linear phase-field equation forming a finite space object. Vacuum quantum oscillations within the doublon determine the evolution of the coupled system. Applying a conservation constraint and using general symmetry considerations, the doublons are arranged as a network in 1 + 1 + 2 dimensions, where nodes are interpreted as elementary particles. A canonical procedure is proposed to treat charge and electromagnetic exchange. © 2020 I. Steinbach et al., published by De Gruyter, Berlin/Boston 2020.
    view abstractdoi: 10.1515/zna-2019-0343
  • 2020 • 426 Subcell flux limiting for high-order Bernstein finite element discretizations of scalar hyperbolic conservation laws
    Kuzmin, D. and Quezada de Luna, M.
    Journal of Computational Physics 411 (2020)
    This work extends the concepts of algebraic flux correction and convex limiting to continuous high-order Bernstein finite element discretizations of scalar hyperbolic problems. Using an array of adjustable diffusive fluxes, the standard Galerkin approximation is transformed into a nonlinear high-resolution scheme which has the compact sparsity pattern of the piecewise-linear or multilinear subcell discretization. The representation of this scheme in terms of invariant domain preserving states makes it possible to prove the validity of local discrete maximum principles under CFL-like conditions. In contrast to predictor-corrector approaches based on the flux-corrected transport methodology, the proposed flux limiting strategy is monolithic, i.e., limited antidiffusive terms are incorporated into the well-defined residual of a nonlinear (semi-)discrete problem. A stabilized high-order Galerkin discretization is recovered if no limiting is performed. In the limited version, the compact stencil property prevents direct mass exchange between nodes that are not nearest neighbors. A formal proof of sparsity is provided for simplicial and box elements. The involved element contributions can be calculated efficiently making use of matrix-free algorithms and precomputed element matrices of the reference element. Numerical studies for Q2 discretizations of linear and nonlinear two-dimensional test problems illustrate the virtues of monolithic convex limiting based on subcell flux decompositions. © 2020 Elsevier Inc.
    view abstractdoi: 10.1016/
  • 2020 • 425 Locally bound-preserving enriched Galerkin methods for the linear advection equation
    Kuzmin, D. and Hajduk, H. and Rupp, A.
    Computers and Fluids 205 (2020)
    In this work, we introduce algebraic flux correction schemes for enriched (P1⊕P0 and Q1⊕P0) Galerkin discretizations of the linear advection equation. The piecewise-constant component stabilizes the continuous Galerkin approximation without introducing free parameters. However, violations of discrete maximum principles are possible in the neighborhood of discontinuities and steep fronts. To keep the cell averages and the degrees of freedom of the continuous P1/Q1 component in the admissible range, we limit the fluxes and element contributions, the complete removal of which would correspond to first-order upwinding. The first limiting procedure that we consider in this paper is based on the flux-corrected transport (FCT) paradigm. It belongs to the family of predictor-corrector algorithms and requires the use of small time steps. The second limiting strategy is monolithic and produces nonlinear problems with well-defined residuals. This kind of limiting is well suited for stationary and time-dependent problems alike. The need for inverting consistent mass matrices in explicit strong stability preserving Runge–Kutta time integrators is avoided by reconstructing nodal time derivatives from cell averages. Numerical studies are performed for standard 2D test problems. © 2020 Elsevier Ltd
    view abstractdoi: 10.1016/j.compfluid.2020.104525
  • 2020 • 424 Limiting and divergence cleaning for continuous finite element discretizations of the MHD equations
    Kuzmin, D. and Klyushnev, N.
    Journal of Computational Physics 407 (2020)
    This work introduces a new type of constrained algebraic stabilization for continuous piecewise-linear finite element approximations to the equations of ideal magnetohydrodynamics (MHD). At the first step of the proposed flux-corrected transport (FCT) algorithm, the Galerkin element matrices are modified by adding graph viscosity proportional to the fastest characteristic wave speed. At the second step, limited antidiffusive corrections are applied and divergence cleaning is performed for the magnetic field. The limiting procedure developed for this stage is designed to enforce local maximum principles, as well as positivity preservation for the density and thermodynamic pressure. Additionally, it adjusts the magnetic field in a way which penalizes divergence errors without violating conservation laws or positivity constraints. Numerical studies for 2D test problems are performed to demonstrate the ability of the proposed algorithms to accomplish this task in applications to ideal MHD benchmarks. © 2020 Elsevier Inc.
    view abstractdoi: 10.1016/
  • 2020 • 423 Monolithic convex limiting for continuous finite element discretizations of hyperbolic conservation laws
    Kuzmin, D.
    Computer Methods in Applied Mechanics and Engineering 361 (2020)
    Using the theoretical framework of algebraic flux correction and invariant domain preserving schemes, we introduce a monolithic approach to convex limiting in continuous finite element schemes for linear advection equations, nonlinear scalar conservation laws, and hyperbolic systems. In contrast to flux-corrected transport (FCT) algorithms that apply limited antidiffusive corrections to bound-preserving low-order solutions, our new limiting strategy exploits the fact that these solutions can be expressed as convex combinations of bar states belonging to a convex invariant set of physically admissible solutions. Each antidiffusive flux is limited in a way which guarantees that the associated bar state remains in the invariant set and preserves appropriate local bounds. There is no free parameter and no need for limit fluxes associated with the consistent mass matrix of time derivative term separately. Moreover, the steady-state limit of the nonlinear discrete problem is well defined and independent of the pseudo-time step. In the case study for the Euler equations, the components of the bar states are constrained sequentially to satisfy local maximum principles for the density, velocity, and specific total energy in addition to positivity preservation for the density and pressure. The results of numerical experiments for standard test problems illustrate the ability of built-in convex limiters to resolve steep fronts in a sharp and nonoscillatory manner. © 2019 Elsevier B.V.
    view abstractdoi: 10.1016/j.cma.2019.112804
  • 2020 • 422 Gradient-Based Limiting and Stabilization of Continuous Galerkin Methods
    Kuzmin, D.
    Lecture Notes in Computational Science and Engineering 132 331-339 (2020)
    In this paper, we stabilize and limit continuous Galerkin discretizations of a linear transport equation using an algebraic approach to derivation of artificial diffusion operators. Building on recent advances in the analysis and design of edge-based algebraic flux correction schemes for singularly perturbed convection-diffusion problems, we derive algebraic stabilization operators that generate nonlinear high-order stabilization in smooth regions and enforce discrete maximum principles everywhere. The correction factors for antidiffusive element or edge contributions are defined in terms of nodal gradients that vanish at local extrema. The proposed limiting strategy is linearity-preserving and provides Lipschitz continuity of constrained terms. Numerical examples are presented for two-dimensional test problems. © Springer Nature Switzerland AG 2020.
    view abstractdoi: 10.1007/978-3-030-30705-9_29
  • 2020 • 421 Vibrational Energy Redistribution between CH Stretching Modes in Alkyl Chain Monolayers Revealed by Time-Resolved Two-Color Pump-Probe Sum Frequency Spectroscopy
    Lackner, M. and Hille, M. and Hasselbrink, E.
    Journal of Physical Chemistry Letters 11 108-112 (2020)
    The vibrational dynamics of the various CH stretching modes in a fatty acid Langmuir-Blodgett film was studied using a resonant narrowband infrared (IR) laser pulse for pumping and a broadband femtosecond IR visible pulse pair for detection in a sum frequency spectroscopy setup. The resulting two-dimensional spectra indicate that pumping either the antisymmetric methyl or methylene stretch results in the transfer of energy to the other modes on a time scale faster than 2 ps. This rapid process is followed by energy redistribution to other modes, presumably the bending and internal rotational modes, with a time constant of approximately 85 ps. The formation of gauche defects is not observed within the first 250 ps. The whole spectrum recovers on a time scale of several nanoseconds, indicating dissipation of the excitation energy into the substrate. Copyright © 2019 American Chemical Society.
    view abstractdoi: 10.1021/acs.jpclett.9b03386
  • 2020 • 420 BOPcat software package for the construction and testing of tight-binding models and bond-order potentials
    Ladines, A.N. and Hammerschmidt, T. and Drautz, R.
    Computational Materials Science 173 (2020)
    Atomistic models like tight-binding (TB), bond-order potentials (BOP) and classical potentials describe the interatomic interaction in terms of mathematical functions with parameters that need to be adjusted for a particular material. The procedures for constructing TB/BOP models differ from the ones for classical potentials. We developed the BOPcat software package as a modular python code for the construction and testing of TB/BOP parameterizations. It makes use of atomic energies, forces and stresses obtained by TB/BOP calculations with the BOPfox software package. It provides a graphical user interface and flexible control of raw reference data, of derived reference data like defect energies, of automated construction and testing protocols, and of parallel execution in queuing systems. We demonstrate the concepts and usage of the BOPcat software and illustrate its key capabilities by exemplary constructing and testing a parameterization of a magnetic BOP for Fe. We provide a parameterization protocol with a successively increasing set of reference data that leads to good transferability to a variety of properties of the ferromagnetic bcc groundstate and to crystal structures which were not part of the training set. © 2019 Elsevier B.V.
    view abstractdoi: 10.1016/j.commatsci.2019.109455
  • 2020 • 419 A systematic literature review of ecosystems: An approach to introduce logistics ecosystems into academia
    Lamberjohann, M. and Otto, B.
    Interconnected Supply Chains in an Era of Innovation - Proceedings of the 8th International Conference on Information Systems, Logistics and Supply Chain, ILS 2020 29-36 (2020)
    The term ecosystem experiences a peak in academic attention, however, its usage varies as well as its application in certain industries. In the world of logistics, the usage of the term ecosystem is not common within academia. Hence, a systematic literature review has been performed by scanning 146 studies out of an original dataset of 2264 results. This systematic literature review has got the goal to create a methodological overview of the term ecosystem, create types of ecosystems, and merge them with similar studies out of the supply chain management research area. Finally, this paper identifies a commonality that justifies a merge of supply chain management collaboration approaches and the general research of ecosystems and sets a foundation for future research. © Interconnected Supply Chains in an Era of Innovation - Proceedings of the 8th International Conference on Information Systems, Logistics and Supply Chain, ILS 2020. All rights reserved.
    view abstract
  • 2020 • 418 Spotlight on AKT: Current Therapeutic Challenges
    Landel, I. and Quambusch, L. and Depta, L. and Rauh, D.
    ACS Medicinal Chemistry Letters 11 225-227 (2020)
    The protein kinase B (Akt) exemplifies an important switch of cell death and survival within the PI3K/Akt signaling pathway, which renders Akt a valuable target in diseases such as cancer. Herein, we give a short overview of clinical applications involving Akt, outline promising and innovative approaches to investigate the role of this kinase in diseases, and highlight the current challenges that require thorough investigation to set the groundwork for successful therapeutic strategies. © 2020 American Chemical Society.
    view abstractdoi: 10.1021/acsmedchemlett.9b00548
  • 2020 • 417 Modified advanced core decompression (mACD) [Modifizierte „advanced core decompression“ (mACD)]
    Landgraeber, S. and Jäger, M.
    Operative Orthopadie und Traumatologie 32 96-106 (2020)
    Objective: The modified advanced core decompression (mACD) combines the advantages of a low invasive core decompression with maximal removal of osteonecrotic bone and a biologic reconstruction of the resulting bone defect. Indications: Avascular (atraumatic) osteonecrosis of the femoral head (ARCO stage II). Contraindications: Subchondral fractures (ARCO stage III); advanced osteoarthritis (e.g., ACRO stage IV); persisting risk factors such as high-dose corticoid therapy, chemotherapy, alcohol abuse; open growth plates; history of side effects or intolerance to components of the applied bone substitute; lack of patient compliance; osteomyelitis or other septic conditions. Surgical technique: Supine positioning on the operation table, skin disinfection, and sterile draping. Skin incision and core decompression using a 3.2 mm guide wire. Removal of a bone cylinder from a nonaffected area of the femoral neck using a hollow trephine. Drilling of the osteonecrotic area over the applied wire up to 5 mm to the subchondral bone under fluoroscopy, insertion of an expandable bone knife and removal of the osteonecrotic bone supported by a curette. Bone grafting of the autologous bone into the subchondral defect zone and filling of the drill canal by resorbable bone substitute. Postoperative management: Bed rest for 24 h, then partial weight bearing (20 kg) on crutches for 2–6 weeks depending on the bone quality in the defect zone and the applied bone substitute. Results: Midterm superiority (2 years) in hip survival of the mACD over advanced core depression and core depression, especially in ARCO stage II. © 2020, Springer Medizin Verlag GmbH, ein Teil von Springer Nature.
    view abstractdoi: 10.1007/s00064-020-00653-z
  • 2020 • 416 Influence of anisotropic damage evolution on cold forging
    Langenfeld, K. and Schowtjak, A. and Schulte, R. and Hering, O. and Möhring, K. and Clausmeyer, T. and Ostwald, R. and Walther, F. and Tekkaya, A.E. and Mosler, J.
    Production Engineering 14 115-121 (2020)
    This contribution deals with the influence of anisotropic material degradation (damage) within numerical simulations of cold forging. For that purpose, two constitutive frameworks for modeling ductile damage are presented: an isotropic and an anisotropic model. In a first step, both models are calibrated based on a uniaxial tensile test. Then, the forward rod extrusion process is simulated with the isotropic model. The deformation of a characteristic element is transferred to the anisotropic model and the local response is investigated. Both models are compared to one another in terms of the process induced ductile damage. It will be shown, that the magnitude of the induced damage agrees reasonably well, but that the orientation of ductile damage is of major importance. © 2020, German Academic Society for Production Engineering (WGP).
    view abstractdoi: 10.1007/s11740-019-00942-y
  • 2020 • 415 A micromorphic approach for gradient-enhanced anisotropic ductile damage
    Langenfeld, K. and Mosler, J.
    Computer Methods in Applied Mechanics and Engineering 360 (2020)
    This paper deals with the numerically effective modeling of anisotropic material degradation caused by ductile damage. Although standard local anisotropic damage models are relatively well-developed nowadays, their regularization which is required in order to eliminate their mathematical ill-posedness is far from being straightforward. It bears emphasis that this regularization is not only required from a mathematical point of view, since the aforementioned ill-posedness is known to be the source for the pathological mesh dependence as far as the finite element method is concerned. Within this paper, a general local framework for capturing anisotropic material degradation caused by ductile damage is extended to a non-local model by means of a gradient-enhancement. However, in order to achieve a numerically effective implementation, the gradient-enhancement is not implemented in a direct manner, but by means of a micromorphic approximation. By doing so, the implementation of the underlying local model is almost unaffected. Particularly the inequalities resulting from the yield function can be restricted to the local integration point level. Since a naive micromorphic implementation turns out to be unsuitable for regularizing the underlying local model, a novel adaption of the yield function is proposed. It is shown that the resulting single-surface-model is indeed able to capture anisotropic material degradation caused by ductile damage and, furthermore, that the finite element implementation is mesh objective. © 2019 Elsevier B.V.
    view abstractdoi: 10.1016/j.cma.2019.112717
  • 2020 • 414 Present and future of surface-enhanced Raman scattering
    Langer, J. and de Aberasturi, D.J. and Aizpurua, J. and Alvarez-Puebla, R.A. and Auguié, B. and Baumberg, J.J. and Bazan, G.C. and Bell, S.E.J. and Boisen, A. and Brolo, A.G. and Choo, J. and Cialla-May, D. and Deckert, V. and Fa...
    ACS Nano 14 28-117 (2020)
    The discovery of the enhancement of Raman scattering by molecules adsorbed on nanostructured metal surfaces is a landmark in the history of spectroscopic and analytical techniques. Significant experimental and theoretical effort has been directed toward understanding the surface-enhanced Raman scattering (SERS) effect and demonstrating its potential in various types of ultrasensitive sensing applications in a wide variety of fields. In the 45 years since its discovery, SERS has blossomed into a rich area of research and technology, but additional efforts are still needed before it can be routinely used analytically and in commercial products. In this Review, prominent authors from around the world joined together to summarize the state of the art in understanding and using SERS and to predict what can be expected in the near future in terms of research, applications, and technological development. This Review is dedicated to SERS pioneer and our coauthor, the late Prof. Richard Van Duyne, whom we lost during the preparation of this article. © 2020 American Chemical Society. All rights reserved.
    view abstractdoi: 10.1021/acsnano.9b04224
  • 2020 • 413 Processing of a single-crystalline CrCoNi medium-entropy alloy and evolution of its thermal expansion and elastic stiffness coefficients with temperature
    Laplanche, G. and Schneider, M. and Scholz, F. and Frenzel, J. and Eggeler, G. and Schreuer, J.
    Scripta Materialia 177 44-48 (2020)
    The equiatomic CrCoNi alloy is regarded as a model single-phase face-centered cubic medium-entropy alloy. A CrCoNi single crystal was grown by a Bridgman technique using a Ni-base superalloy seed. The elastic stiffnesses and thermal expansion coefficient were determined between 100 K and 673 K employing resonant ultrasound spectroscopy and dilatometry, respectively. All data were found to be in excellent agreement with those reported for polycrystalline CrCoNi. A comparison of the normalized Cauchy pressure of CrCoNi with those of other alloys indicates that interatomic bonds become more directional with increasing Cr-concentration while Co and Ni promote a metallic character. © 2019 Acta Materialia Inc.
    view abstractdoi: 10.1016/j.scriptamat.2019.09.020
  • 2020 • 412 Combined Thermogravimetric Determination of Activity Coefficients and Binary Diffusion Coefficients - A New Approach Applied to Ferrocene/ n-Tetracosane Mixtures
    Lau, S. and Atakan, B.
    Journal of Chemical and Engineering Data 65 1211-1221 (2020)
    The use of isothermal thermogravimetry is investigated for combined measurements of activity coefficients and diffusion coefficients in binary mixtures, where the vapor pressure is dominated by one compound. The coupling of evaporation with gas phase and condensed phase diffusion leads to an unsteady mass loss, which depends on the activity coefficient and both, gas phase and condensed phase, diffusion coefficients, as is explained. This can be used to measure two of these properties, if the remaining parameters are known. This concept is evaluated for the ferrocene/n-tetracosane system. The former is a flame-retardant, and the latter was regarded as a substitute for a polymer, with simpler behavior. Between 341 and 399 K, the activity coefficient for ferrocene is measured to drop from above 3 to values near 1, while the diffusion coefficients are weakly temperature dependent, with values around 2 × 10-9/m2·s-1. In addition, the vapor pressures of the two pure substances were re-evaluated for this temperature range. This relatively simple method seems to be useful for the determination of such properties of other flame-retardant-related systems. Copyright © 2019 American Chemical Society.
    view abstractdoi: 10.1021/acs.jced.9b00578
  • 2020 • 411 Behavioral Analysis of Human-Machine Interaction in the Context of Demand Planning Decisions
    Lauer, T. and Welsch, R. and Ramlah Abbas, S. and Henke, M.
    Advances in Intelligent Systems and Computing 965 130-141 (2020)
    The trend of digitalization has led to disruptive changes in production and supply chain planning, where autonomous machines and artificial intelligence gain competitive advantages. Besides, the satisfaction of customers’ wishes has reached top priority for demand-driven companies. Consequently, companies implement digital applications, for instance neural networks for accurate demand forecasting and optimized decision-making tools, to cope with nervous operational planning activities. Since planning tasks require human-machine interaction to increase performance and efficiency of planning decisions, this analysis focuses on forms of interaction to determine the right level of collaboration. The paper outlines various levels of interaction and analyses the impact of human reactions in the context of an industrial demand planning algorithm use case at Infineon Technologies AG conducting a behavioral experiment. The results show that a variance in the levels of human-machine interaction has influence on human acceptance of algorithms, but further experiments need to be conducted to outline an overall framework. © 2020, Springer Nature Switzerland AG.
    view abstractdoi: 10.1007/978-3-030-20454-9_13
  • 2020 • 410 Dislocation plasticity in FeCoCrMnNi high-entropy alloy: quantitative insights from in situ transmission electron microscopy deformation
    Lee, S. and Duarte, M.J. and Feuerbacher, M. and Soler, R. and Kirchlechner, C. and Liebscher, C.H. and Oh, S.H. and Dehm, G.
    Materials Research Letters 8 216-224 (2020)
    The mechanical properties of high-entropy alloys (HEAs) are still not deeply understood. Detailed knowledge of the strengthening mechanism, especially, the atomistic origin of solid solution hardening and its interplay with dislocation plasticity is needed. Here, we report on the dislocation glide behavior of a FeCoCrNiMn face-centered cubic (FCC) single crystal studied by in situ deformation in a transmission electron microscope (TEM). The threshold shear stress for dislocation glide in a thin foil is measured from dislocation curvature as exceeding 400 MPa. Interestingly, dislocations are prevented from straightening upon unloading due to high frictional stresses. IMPACT STATEMENT: The fiction stress for dislocation glide in a FeCoCrMnNi HEA is assessed by direct measurement of dislocation line curvature during in situ TEM deformation, which is higher compared to other FCC metals, explaining the outstanding yield and flow stress of the HEA. © 2020, © 2020 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group.
    view abstractdoi: 10.1080/21663831.2020.1741469
  • 2020 • 409 Effects of filter structure, flow velocity, particle concentration and fouling on the retention efficiency of ultrafiltration for sub-20 nm gold nanoparticles
    Lee, H. and Segets, D. and Süß, S. and Peukert, W. and Chen, S.-C. and Pui, D.Y.H.
    Separation and Purification Technology 241 (2020)
    Ultrafiltration techniques with membranes of pore sizes under 100 nm have been widely applied in drinking water, wastewater, semiconductor and pharmaceutical process water treatments for nanoparticle (NP) and pathogen removal. The most direct way to evaluate the membrane performance is to experimentally obtain the size fractional retention efficiency. However, the real-life performance of the membrane in terms of fouling (or loading) characteristics and the effects of the concentration of challenging particles and rate of flux (or filtration velocities) on the filtration efficiency during fouling have not been well understood. In this study, systematic filtration experiments for filtration efficiency at clean and loaded conditions were conducted for three different 50 nm rated membrane filters, including PTFE (Polytetrafluoroethylene), PCTE (Polycarbonate Track-Etched) and MCE (Mixed Cellulose Ester) membranes, against 5, 10 and 20 nm Au NPs at different feed concentrations and fluxes. The results showed that the effects of feed concentration and flux are significant. This study provides important insights of retention mechanisms and efficiency for different ultrafiltration membrane structures at varied filtration velocities and fouling characteristics giving clear directions of future NP ultrafiltration research. © 2020 Elsevier B.V.
    view abstractdoi: 10.1016/j.seppur.2020.116689
  • 2020 • 408 Accumulating design knowledge with reference models: Insights from 12 years’ research into data management
    Legner, C. and Pentek, T. and Otto, B.
    Journal of the Association for Information Systems 21 735-770 (2020)
    Over the past several decades, digital technologies have evolved from supporting business processes and decision-making to becoming an integral part of business strategies. Although the IS discipline has extensive experience with digitalization and designing sociotechnical artifacts, the underlying design knowledge is seldom systematically accumulated across different settings and projects, and thus cannot be transferred and reused in new contexts. Motivated by this gap in the research, we turn to the data management field, where reference models have become important sources of descriptive and prescriptive domain knowledge. To study knowledge accumulation in reference models, we analyze the revelatory and extreme case of a longitudinal DSR process involving more than 30 European companies and 15 researchers from three universities over 12 years. The insights into reference model development allow us to theorize about knowledge accumulation mechanisms from both a process perspective and an artifact perspective: First, we observe that knowledge accumulation occurs in stages in response to technology’s evolving roles in business (problem space) and as a result of maturing design knowledge (solution space). Second, we find that reference models act as design boundary objects; they explicate and integrate knowledge from different disciplines and allow for the development of design knowledge over time—from descriptive (conceptual) models to prescriptive (capability or maturity) ones. To cope with fundamental changes in the problem space, these models require continuous updating as well as transfer/exaptation to new problem spaces. Our findings inform the IS community about the fundamental logic of knowledge accumulation in longitudinal DSR processes. © 2020 by the Association for Information Systems.
    view abstractdoi: 10.17705/1jais.00618
  • 2020 • 407 Snoek-type damping performance in strong and ductile high-entropy alloys
    Lei, Z. and Wu, Y. and He, J. and Liu, X. and Wang, H. and Jiang, S. and Gu, L. and Zhang, Q. and Gault, B. and Raabe, D. and Lu, Z.
    Science Advances 6 (2020)
    Noise and mechanical vibrations not only cause damage to devices, but also present major public health hazards. High-damping alloys that eliminate noise and mechanical vibrations are therefore required. Yet, low operating temperatures and insufficient strength/ductility ratios in currently available high-damping alloys limit their applicability. Using the concept of high-entropy alloy (HEA), we present a class of high-damping materials. The design is based on refractory HEAs, solid-solutions doped with either 2.0 atomic % oxygen or nitrogen, (Ta0.5Nb0.5HfZrTi)98O2 and (Ta0.5Nb0.5HfZrTi)98N2. Via Snoek relaxation and ordered interstitial complexes mediated strain hardening, the damping capacity of these HEAs is as high as 0.030, and the damping peak reaches up to 800 K. The model HEAs also exhibit a high tensile yield strength of ~1400 MPa combined with a large ductility of ~20%. The high-temperature damping properties, together with superb mechanical properties make these HEAs attractive for applications where noise and vibrations must be reduced. © 2020 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works. Distributed under a Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC).
    view abstractdoi: 10.1126/sciadv.aba7802
  • 2020 • 406 Uniaxial tensile tests in textile reinforced concretes with inorganic impregnated carbon fibres [Einaxiale Zugversuche an textilbewehrten Betonen mit anorganisch getränkten Carbonfasern]
    Lenting, M. and Orlowsky, J.
    Beton- und Stahlbetonbau 115 495-503 (2020)
    Uniaxial tensile tests in textile reinforced concretes with inorganic impregnated carbon fibres. The composite material textile reinforced concrete is being increasingly used in building construction. In particular carbon textiles are used with different impregnation materials, which are bound in mortar or concrete. Numerous research and practical projects have led to individual approvals for specific cases being granted and first directives for designing and using textile reinforced concrete being developed. The development and optimization of these materials still have huge improvement potential. Until now, most textiles have been impregnated with epoxy resin, styrene-butadiene or acrylates. Beside the introduction of a polymer in the composite material, these polymers can cause load-bearing capacity losses under temperature stresses above 80 °C. Mineral impregnation materials have hardly been researched, but are particularly interesting for use in drinking water structures in order to avoid polymer-based materials. This publication shows that a very fine crack pattern can be achieved with inorganic impregnations of carbon rovings. Very small crack widths are particularly necessary in the repair sector, for example in the rehabilitation of drinking water reservoirs. In addition, mineral impregnations are less susceptible to temperature stresses. © 2020, Ernst und Sohn. All rights reserved.
    view abstractdoi: 10.1002/best.201900062
  • 2020 • 405 Microstructures, Heat Treatment, and Properties of Boron-Alloyed Tool Steels
    Lentz, J. and Röttger, A. and Theisen, W.
    Steel Research International 91 (2020)
    To enable the development of novel Fe–C–B–Cr and Fe–C–B–Cr–Mo cold work tool steels, the microstructures and hardness-tempering behaviors of hypoeutectic laboratory melts are investigated. The results show that increasing Cr content enhances the thermodynamic stability of the ultrahard M2B borides. The formation of carboborides is suppressed by adjusting the B/(C + B) ratio, Cr content, and austenitization temperature. A secondary hardenability at 500 °C is achieved by Mo addition. In addition, Mo stabilizes the M23(C,B)6 phase and at higher contents the M3B2 boride. Based on these investigations, Fe0.4C1B–Cr alloys are designed which, inspired by the microstructure of the steel X153CrMoV12-1, feature a α′-Fe hardenable matrix but 15 vol% of eutectic M2B borides instead of M7C3 for wear protection. The Fe0.4C1B–Cr steels are produced by casting and hot rolling as well as powder metallurgy and hot isostatic pressing. The (tribo-) mechanical properties are investigated and compared with X153CrMoV12-1. Fracture toughness, bending strength, wear resistance, and hardness of the novel Fe0.4C1B–Cr alloys are found to be similar or superior to the steel X153CrMoV12-1, at decreased material cost. © 2019 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/srin.201900416
  • 2020 • 404 Correlative chemical and structural investigations of accelerated phase evolution in a nanocrystalline high entropy alloy
    Li, Y.J. and Kostka, A. and Savan, A. and Ludwig, Al.
    Scripta Materialia 183 122-126 (2020)
    Based on our recently-developed combinatorial processing platforms for accelerated investigations of phase evolution in multinary alloys, a novel correlative atom probe tomography and transmission electron microscopy approach is proposed to study phase stability in a nanocrystalline CrMnFeCoNi alloy. We observed that the material can decompose at 250 °C for 5 h or 300 °C for 1 h, having the same decomposed products as in its coarse-grained counterpart after annealing at 500 °C for 500 days. A low apparent activation energy for the diffusion of Ni in the nanocrystalline alloy is derived and explains the fast kinetics of phase decomposition in nanocrystalline alloys. © 2020 Acta Materialia Inc.
    view abstractdoi: 10.1016/j.scriptamat.2020.03.016
  • 2020 • 403 Single-layer Janus black arsenic-phosphorus (b-AsP): Optical dichroism, anisotropic vibrational, thermal, and elastic properties
    Li, L.L. and Bacaksiz, C. and Nakhaee, M. and Pentcheva, R. and Peeters, F.M. and Yagmurcukardes, M.
    Physical Review B 101 (2020)
    By using density functional theory (DFT) calculations, we predict a puckered, dynamically stable Janus single-layer black arsenic-phosphorus (b-AsP), which is composed of two different atomic sublayers, arsenic and phosphorus atoms. The calculated phonon spectrum reveals that Janus single-layer b-AsP is dynamically stable with either pure or coupled optical phonon branches arising from As and P atoms. The calculated Raman spectrum indicates that due to the relatively strong P-P bonds, As atoms have no contribution to the high-frequency optical vibrations. In addition, the orientation-dependent isovolume heat capacity reveals anisotropic contributions of LA and TA phonon branches to the low-temperature thermal properties. Unlike pristine single layers of b-As and b-P, Janus single-layer b-AsP exhibits additional out-of-plane asymmetry which leads to important consequences for its electronic, optical, and elastic properties. In contrast to single-layer b-As, Janus single-layer b-AsP is found to possess a direct band gap dominated by the P atoms. Moreover, real and imaginary parts of the dynamical dielectric function, including excitonic effects, reveal the highly anisotropic optical feature of the Janus single-layer. A tight-binding (TB) model is also presented for Janus single-layer b-AsP, and it is shown that, with up to seven nearest hoppings, the TB model reproduces well the DFT band structure in the low-energy region around the band gap. This TB model can be used in combination with the Green's function approach to study, e.g., quantum transport in finite systems based on Janus single-layer b-AsP. Furthermore, the linear-elastic properties of Janus single-layer b-AsP are investigated, and the orientation-dependent in-plane stiffness and Poisson ratio are calculated. It is found that the Janus single layer exhibits strong in-plane anisotropy in its Poisson ratio much larger than that of single-layer b-P. This Janus single layer is relevant for promising applications in optical dichroism and anisotropic nanoelasticity. © 2020 American Physical Society.
    view abstractdoi: 10.1103/PhysRevB.101.134102
  • 2020 • 402 Compatible deformation and extra strengthening by heterogeneous nanolayer composites
    Li, J. and Lu, W. and Gibson, J. and Zhang, S. and Korte-Kerzel, S. and Raabe, D.
    Scripta Materialia 179 30-35 (2020)
    A topologically heterogeneous microstructure design is introduced in a Cu/Zr nanolayered composite, in which each soft 100 nm Cu or Zr layer is surrounded on both sides by several hard 10 nm Cu/Zr bilayers. This design aims to impose a full geometrical constraint on all of the soft layers. Micropillar compression tests demonstrate that the composite deforms in a compatible fashion among the layers, in which no extrusion of the soft layers occurs. An elevated strength of 730 MPa is achieved in the composite compared with the strength prediction based on the linear rule of mixtures. © 2020
    view abstractdoi: 10.1016/j.scriptamat.2020.01.006
  • 2020 • 401 Application Progress of Annealing Treatment Process in the Study of Nano-multilayer Films [退火处理工艺在纳米多层膜材料研究中的应用进展]
    Li, H. and Xing, Z. and Hodúlová, E. and Hu, A. and Tillmann, W.
    Cailiao Daobao/Materials Reports 34 03099-03105 (2020)
    Compared with traditional bulk materials, nano-multilayer films exhibit unique optical, magnetic, electrical, mechanical and thermal properties due to their small-size effects, surface effects, quantum size effects, and quantum tunneling effects. Therefore, nano-multilayer films have been widely used in the areas of optical devices, semiconductors, electromagnetic protection, processing and manufacturing, surface protection and electronic packaging as optical absorbing materials, electromagnetic absorbing materials, magnetic recording materials, photovoltaic materials and low-temperature joining materials. There exists intrinsic size dependence in the physical and mechanical properties with the microstructure of nano-multilayer films. Due to the limitation of the preparation process, defects such as vacancies and dislocations can cause difficulty in fully meeting the requirements of heat resistance, wear resistance and corrosion resistance in the complex service environment, which limits the further development of nano-multilayer films. In the field of concentrating circuits and chip fabrication, nano-multilayer films devices are often working in a severe environment deviating from the normal temperature. However, metastable nano-multilayer films with high surface free energy tend to reach a state of low-energy and form a stable structure by interdiffusion of immiscible dual phases, interlayer detachment and interface evolution under heat. It might result in the extinction of melting point depression property, superhardness property and so on due to the destructions of the nano-multilayer structure. Therefore, studying on the microstructure evolution, thermal stability and failure mechanism of nano-multilayer films is particularly important for increasing the service life and reliability of nano-multilayer systems. As a common heat treatment method, the annealing process is widely used to eliminate defects in metals, so as to achieve to modify the properties. For nano-multilayer films operating at high temperatures, the annealing process is also an effective means of extending its service life. At present, the main directions of annealing process in nano-multilayer films research and application are: (i) improving nano-multilayer film performance by adopting different annealing temperature, holding time and cooling rate; (ii) investigating the effect of annealing temperature on the thermal stability of nano-multilayer films by increasing the annealing upper limit temperature and obtain a critical temperature that maintains stability of the interface of nano-multilayer. It is found that the appropriate annealing process can refine the nano-multilayer films grain structure, increase the density, decrease the defect density, induce the formation of special structures, reinforcing the interaction of atoms and dislocations. Therefore, the light transmittance of the film is increased with improvement of optical properties, as well as the magnetic, electrical and mechanical properties are significantly improved; (iii) in addition, the nano-multilayer film is annealed in a certain temperature range to observe the bilayer interface evolution, atomic diffusion and new phase formation using TEM, XRD and other means. Thus the structural stability, chemical stability and mechanical stability of nano-multilayer film can be studied. In this paper, the current progress and challenges of annealing process in nano-multilayer films modification and thermal stability research are reviewed. The influence of annealing parameters on the enhancement of nano-multilayer properties including optical properties, magnetic properties, electrical properties, mechanical properties is elaborated. Furthermore, it mainly focuses on the influencing mechanism of elevated temperature annealing on the thermal stability and microstructure evolution of immiscible nano-multilayer system. At last, the further development of annealing process for designing and preparing of high-strength and thermally stable nano-multilayer films are prospected, which has important theoretical significance and application value in materials welding/joining, integrated circuits, cutting tools, absorbing coatings, etc. © 2020, Materials Review Magazine. All right reserved.
    view abstractdoi: 10.11896/cldb.19010159
  • 2020 • 400 Phase decomposition in a nanocrystalline CrCoNi alloy
    Li, Y.J. and Kostka, A. and Savan, A. and Ludwig, Al.
    Scripta Materialia 188 259-263 (2020)
    Phase stability of a nanocrystalline CrCoNi alloy is investigated using the combinatorial processing platform approach, which enables synthesis, processing and direct atomic-scale characterizations of alloys by atom probe tomography and transmission electron microscopy. Phase decomposition with formation of CoNi-rich phase occurs faster in the smaller (10 nm) grain-sized region than the larger one (20 nm), both being present in the same sample. Chemical analyses indicate that diffusion of Co and Cr plays an important role in phase decomposition. Comparison of phase stability between CrMnFeCoNi and CrCoNi implies that elemental segregation may promote phase decomposition by providing an additional chemical driving force for it. © 2020 Acta Materialia Inc.
    view abstractdoi: 10.1016/j.scriptamat.2020.07.054
  • 2020 • 399 Identification of a multi-dimensional reaction coordinate for crystal nucleation in Ni3Al
    Liang, Y. and Díaz Leines, G. and Drautz, R. and Rogal, J.
    The Journal of chemical physics 152 224504 (2020)
    Nucleation during solidification in multi-component alloys is a complex process that comprises competition between different crystalline phases as well as chemical composition and ordering. Here, we combine transition interface sampling with an extensive committor analysis to investigate the atomistic mechanisms during the initial stages of nucleation in Ni3Al. The formation and growth of crystalline clusters from the melt are strongly influenced by the interplay between three descriptors: the size, crystallinity, and chemical short-range order of the emerging nuclei. We demonstrate that it is essential to include all three features in a multi-dimensional reaction coordinate to correctly describe the nucleation mechanism, where, in particular, the chemical short-range order plays a crucial role in the stability of small clusters. The necessity of identifying multi-dimensional reaction coordinates is expected to be of key importance for the atomistic characterization of nucleation processes in complex, multi-component systems.
    view abstractdoi: 10.1063/5.0010074
  • 2020 • 398 n-Doped InGaP Nanowire Shells in GaAs/InGaP Core–Shell p–n Junctions
    Liborius, L. and Bieniek, J. and Nägelein, A. and Tegude, F.-J. and Prost, W. and Hannappel, T. and Poloczek, A. and Weimann, N.
    Physica Status Solidi (B) Basic Research 257 (2020)
    Herein, the characterization of n-doped InGaP:Si shells in coaxial not-intentionally doped (nid)-GaAs/n-InGaP as well as n–p–n core–multishell nanowires grown by metalorganic vapor-phase epitaxy is reported. The multi-tip scanning tunneling microscopy technique is used for contact-independent resistance profiling along the tapered nid-GaAs/n-InGaP core–shell nanowires to estimate the established emitter shell doping concentration to ND ≈ 3 · 1018 cm−3. Contacts on these shells are demonstrated and exhibit ohmic current–voltage characteristics after annealing. Application potential is demonstrated by the growth and processing of coaxial p-GaAs/n-InGaP junctions in n–p–n core–multishell nanowires, with n-InGaP being the electron-supplying emitter material. Current–voltage characteristics and temperature-dependent electroluminescence measurements substantiate successful doping of the n-InGaP shell. A tunneling-assisted contribution to the leakage currents of the investigated p–n junctions is verified by the sub-bandgap luminescence at low temperatures and is attributed to radiative tunneling processes. © 2019 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/pssb.201900358
  • 2020 • 397 Investigation on the influence of damage on the fatigue strength of hot rolled sheet metal
    Liebsch, C. and Möhring, K. and Lohmar, J. and Walther, F. and Hirt, G.
    Production Engineering 14 65-75 (2020)
    Continuous casting leads to the formation of voids, which can be considered as an initial state of damage. During hot rolling these voids shall be closed, reducing this initial damage and avoiding its negative influence on the mechanical properties and performance of the produced material. However, hot rolling also influences the microstructure, which in turn affects the performance e.g. the fatigue strength. So far, little research has been published on the separation of those influencing factors. This paper is a first attempt to separate the influence of damage from the microstructure in hot rolling. Numerical simulation is utilized to study void closure throughout the multi-pass process while the evolution of microstructure and damage is investigated experimentally using numerous characterization methods. Two process routes with a large and a small pass reduction have been investigated and comparable microstructures have been achieved. A continuous damage reduction throughout the rolling process has been observed by means of void distribution and density measurements. The large pass reduction showed a slightly reduced damage and an increased fatigue strength in all considered thicknesses, however this could not be traced back to the damage reduction exclusively. © 2019, German Academic Society for Production Engineering (WGP).
    view abstractdoi: 10.1007/s11740-019-00933-z
  • 2020 • 396 Sensitivity analysis of elastoplastic structural response regarding geometry and external loads
    Liedmann, J. and Barthold, F.-J.
    Proceedings of the 6th European Conference on Computational Mechanics: Solids, Structures and Coupled Problems, ECCM 2018 and 7th European Conference on Computational Fluid Dynamics, ECFD 2018 1308-1319 (2020)
    This paper is concerned with the determination of design sensitivity information of structures with elastoplastic material behavior in the context of shape optimization. Incidentally, design means geometry and external load parameters. Sensitivity information is provided by a variational approach based on an enhanced kinematic concept that allows a strict separation of geometry and physics. Continuous equations are first derived and subsequently discretized to compute structural response and response sensitivities simultaneously within a finite element framework, which results in a very efficient algorithm to obtain gradient information compared to other numerical methods. The obtained gradients can be used to solve inverse problems utilizing gradient based mathematical optimization, such as Sequential Quadratic Programming (SQP). Copyright © Crown copyright (2018).All right reserved.
    view abstract
  • 2020 • 395 Irreversible Structural Changes of Copper Hexacyanoferrate Used as a Cathode in Zn-Ion Batteries
    Lim, J. and Kasiri, G. and Sahu, R. and Schweinar, K. and Hengge, K. and Raabe, D. and La Mantia, F. and Scheu, C.
    Chemistry - A European Journal 26 4917-4922 (2020)
    The structural changes of copper hexacyanoferrate (CuHCF), a Prussian blue analogue, which occur when used as a cathode in an aqueous Zn-ion battery, are investigated using electron microscopy techniques. The evolution of ZnxCu1−xHCF phases possessing wire and cubic morphologies from initial CuHCF nanoparticles are monitored after hundreds of cycles. Irreversible introduction of Zn ions to CuHCF is revealed locally using scanning transmission electron microscopy. A substitution mechanism is proposed to explain the increasing Zn content within the cathode material while simultaneously the Cu content is lowered during Zn-ion battery cycling. The present study demonstrates that the irreversible introduction of Zn ions is responsible for the decreasing Zn ion capacity of the CuHCF cathode in high electrolyte concentration. © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
    view abstractdoi: 10.1002/chem.201905384
  • 2020 • 394 Bias current and temperature dependence of polarization dynamics in spin-lasers with electrically tunable birefringence
    Lindemann, M. and Jung, N. and Stadler, P. and Pusch, T. and Michalzik, R. and Hofmann, M.R. and Gerhardt, N.C.
    AIP Advances 10 (2020)
    We investigate and compare the intensity and polarization dynamics in a vertical-cavity surface-emitting laser (VCSEL) with a monolithically integrated, electrically controlled birefringence tuning mechanism. The influence of the bias current on the polarization dynamics is investigated over a large range of birefringence values. Bias current tuning toward low values and simultaneous maximization of the resonance frequency is an important strategy to optimize the spin-VCSEL toward energy-efficient operation. A polarization dynamics resonance tuning range from a few GHz up to the maximum frequency of 36 GHz was achieved, and polarization dynamics at maximum frequency are demonstrated at minimum bias current and at high temperatures of approximately 70 °C. We propose a strategy for data communication with low energy consumption and low cooling effort. © 2020 Author(s).
    view abstractdoi: 10.1063/1.5139199
  • 2020 • 393 Control of secondary structure and morphology of peptide–guanidiniocarbonylpyrrole conjugates by variation of the chain length
    Liu, X. and Wang, K. and Externbrink, M. and Niemeyer, J. and Giese, M. and Hu, X.-Y.
    Chinese Chemical Letters 31 1239-1242 (2020)
    Peptide amphiphiles with well-organized secondary structure are an important family of molecules that are known to assemble into a variety of nanostructures. In this work, we present three guanidiniocarbonylpyrrole (GCP) containing peptide amphiphiles, which show versatile morphology and secondary structure changes as a result of different chain lengths and in different concentration regimes. The random coil conformation, α-helix, and β-sheet are obtained for peptide 1, peptide 2, and peptide 3, respectively under neutral aqueous conditions. Furthermore, all peptide amphiphiles can aggregate to form nanoparticles at low concentrations. However, at high concentrations, peptide 1 self-assembles into left-handed twisted helical fibers, while longer bamboo-like morphology can be observed exclusively for peptide 2. For peptide 3, freshly prepared samples show uniform spherical morphology, whereas an obvious morphological transition from original nanoparticles to disordered fibers was realized after incubating for one week. These fascinating morphology changes were determined by the combination of circular dichroism, dynamic light scattering, transmission electron microscopy, atomic force microscopy, and theoretical calculations. © 2020 The Author
    view abstractdoi: 10.1016/j.cclet.2019.10.036
  • 2020 • 392 Terahertz beam steering concept based on a MEMS-reconfigurable reflection grating
    Liu, X. and Samfaß, L. and Kolpatzeck, K. and Häring, L. and Balzer, J.C. and Hoffmann, M. and Czylwik, A.
    Sensors (Switzerland) 20 (2020)
    With an increasing number of applications of terahertz systems in industrial fields and communications, terahertz beamforming and beam steering techniques are required for high-speed, large-area scanning. As a promising means for beam steering, micro-electro-mechanical system (MEMS)-based reflection gratings have been successfully implemented for terahertz beam control. So far, the diffraction grating efficiency is relatively low due to the limited vertical displacement range of the reflectors. In this paper, we propose a design for a reconfigurable MEMS-based reflection grating consisting of multiple subwavelength reflectors which are driven by 5-bit, high-throw electrostatic actuators. We vary the number of the reflectors per grating period and configure the throw of individual reflectors so that the reflection grating is shaped as a blazed grating to steer the terahertz beam with maximum diffraction grating efficiency. Furthermore, we provide a mathematical model for calculating the radiation pattern of the terahertz wave reflected by general reflection gratings consisting of subwavelength reflectors. The calculated and simulated radiation patterns of the designed grating show that we can steer the angle of the terahertz waves in a range of up to ± 56.4∘ with a maximum sidelobe level of −10 dB at frequencies from 0.3 THz to 1 THz. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/s20102874
  • 2020 • 391 Real-Time Detection of Single Auger Recombination Events in a Self-Assembled Quantum Dot
    Lochner, P. and Kurzmann, A. and Kerski, J. and Stegmann, P. and König, J. and Wieck, A.D. and Ludwig, Ar. and Lorke, A. and Geller, M.
    Nano Letters 20 1631-1636 (2020)
    Auger recombination is a nonradiative process, where the recombination energy of an electron-hole pair is transferred to a third charge carrier. It is a common effect in colloidal quantum dots that quenches the radiative emission with an Auger recombination time below nanoseconds. In self-assembled QDs, the Auger recombination has been observed with a much longer recombination time on the order of microseconds. Here, we use two-color laser excitation on the exciton and trion transition in resonance fluorescence on a single self-assembled quantum dot to monitor in real-time single quantum events of the Auger process. Full counting statistics on the random telegraph signal give access to the cumulants and demonstrate the tunability of the Fano factor from a Poissonian to a sub-Poissonian distribution by Auger-mediated electron emission from the dot. Therefore, the Auger process can be used to tune optically the charge carrier occupation of the dot by the incident laser intensity, independently from the electron tunneling from the reservoir by the gate voltage. Our findings are not only highly relevant for the understanding of the Auger process but also demonstrate the perspective of the Auger effect for controlling precisely the charge state in a quantum system by optical means. © 2020 American Chemical Society.
    view abstractdoi: 10.1021/acs.nanolett.9b04650
  • 2020 • 390 Radiative Auger process in the single-photon limit
    Löbl, M.C. and Spinnler, C. and Javadi, A. and Zhai, L. and Nguyen, G.N. and Ritzmann, J. and Midolo, L. and Lodahl, P. and Wieck, A.D. and Ludwig, Ar. and Warburton, R.J.
    Nature Nanotechnology 15 558-562 (2020)
    In a multi-electron atom, an excited electron can decay by emitting a photon. Typically, the leftover electrons are in their ground state. In a radiative Auger process, the leftover electrons are in an excited state and a redshifted photon is created1–4. In a semiconductor quantum dot, radiative Auger is predicted for charged excitons5. Here we report the observation of radiative Auger on trions in single quantum dots. For a trion, a photon is created on electron–hole recombination, leaving behind a single electron. The radiative Auger process promotes this additional (Auger) electron to a higher shell of the quantum dot. We show that the radiative Auger effect is a powerful probe of this single electron: the energy separations between the resonance fluorescence and the radiative Auger emission directly measure the single-particle splittings of the electronic states in the quantum dot with high precision. In semiconductors, these single-particle splittings are otherwise hard to access by optical means as particles are excited typically in pairs, as excitons. After the radiative Auger emission, the Auger carrier relaxes back to the lowest shell. Going beyond the original theoretical proposals, we show how applying quantum optics techniques to the radiative Auger photons gives access to the single-electron dynamics, notably relaxation and tunnelling. This is also hard to access by optical means: even for quasi-resonant p-shell excitation, electron relaxation takes place in the presence of a hole, complicating the relaxation dynamics. The radiative Auger effect can be exploited in other semiconductor nanostructures and quantum emitters in the solid state to determine the energy levels and the dynamics of a single carrier. © 2020, The Author(s), under exclusive licence to Springer Nature Limited.
    view abstractdoi: 10.1038/s41565-020-0697-2
  • 2020 • 389 Design of Complex Solid-Solution Electrocatalysts by Correlating Configuration, Adsorption Energy Distribution Patterns, and Activity Curves
    Löffler, T. and Savan, A. and Meyer, H. and Meischein, M. and Strotkötter, V. and Ludwig, Al. and Schuhmann, W.
    Angewandte Chemie - International Edition 59 5844-5850 (2020)
    Complex solid-solution electrocatalysts (also referred to as high-entropy alloy) are gaining increasing interest owing to their promising properties which were only recently discovered. With the capability of forming complex single-phase solid solutions from five or more constituents, they offer unique capabilities of fine-tuning adsorption energies. However, the elemental complexity within the crystal structure and its effect on electrocatalytic properties is poorly understood. We discuss how addition or replacement of elements affect the adsorption energy distribution pattern and how this impacts the shape and activity of catalytic response curves. We highlight the implications of these conceptual findings on improved screening of new catalyst configurations and illustrate this strategy based on the discovery and experimental evaluation of several highly active complex solid solution nanoparticle catalysts for the oxygen reduction reaction in alkaline media. © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
    view abstractdoi: 10.1002/anie.201914666
  • 2020 • 388 Ionic Liquid-Based Low-Temperature Synthesis of Phase-Pure Tetradymite-Type Materials and Their Thermoelectric Properties
    Loor, M. and Salloum, S. and Kawulok, P. and Izadi, S. and Bendt, G. and Guschlbauer, J. and Sundermeyer, J. and Perez, N. and Nielsch, K. and Schierning, G. and Schulz, S.
    Inorganic Chemistry 59 3428-3436 (2020)
    Phase-pure crystalline Bi2Se3 and Bi2Te3 nanoparticles are formed in reactions of [C4C1Im]3[Bi3I12] (C4C1Im = 1-butyl-3-methylimidazolium) with [C4C1Pyr][ESiMe3] (E = Se or Te; C4C1Pyr = 1-butyl-1-methylpyrrolidinium) in the ionic liquid (IL) [C4C1Im]I. The resulting crystalline tetradymite-type nanoparticles exhibit stoichiometric Bi:E (E = Se or Te) molar ratios (2:3). Because all synthetic steps were performed under strict inert gas conditions, the surfaces of the Bi2Se3 and Bi2Te3 nanoparticles are free of metal oxide species. As proven by infrared and X-ray photoelectron spectroscopy analyses, the nanoparticle surfaces reveal only minor organic contamination from solvent residues ([C4C1Im]I). The nanomaterials show high Seebeck coefficients of -124 μV K-1 (Bi2Se3) and -155 μV K-1 (Bi2Te3) and feature high electrical conductivities (328 and 946 S cm-1, respectively) at the highest tested temperature (240 °C). The corresponding thermal conductivities (0.8 and 2.3 W m-1 K-1, respectively, at 30 °C) are comparable to those of single crystals and recently reported ab initio calculations, which is in remarkable contrast to typical findings of nanograined bulk materials obtained from compacted nanoparticles. These findings emphasize the low level of impurities, surface contamination, and, in general, defects produced by the synthetic approach reported here. The figure of merit in the in-plane direction of the compacted pellets reached peak values 0.45 for Bi2Se3 and 0.4 for Bi2Te3. © 2020 American Chemical Society.
    view abstractdoi: 10.1021/acs.inorgchem.9b03060
  • 2020 • 387 Integrated HIP-heat treatment of Ni-base superalloys fabricated by SLM
    Lopez-Galilea, I. and Ruttert, B. and Theisen, W.
    Euro PM 2018 Congress and Exhibition (2020)
    The selective laser melting (SLM) technique provides an economic approach to manufacture Ni-base superalloy components for high-pressure gas turbines as well as to repair damaged blades during operation. In this study, two advanced processing routes are combined: SLM, to fabricate small specimens of CMSX-4 and Hot Isostatic Pressing (HIP) with rapid cooling rate as post-processing. First, a parametric study is carried out to investigate the influence of the SLM process parameters on the microstructure and defects occurring during SLM. Then, an integrated HIP-heat treatment (homogenization and first step of the aging heat treatment in one single step) is performed to obtain dense materials with the required γ/γ'-microstructure to achieve excellent mechanical properties. The used rapid cooling rate provided by the HIP, has a strong impact on the γ'-particle size and shape whereas the combination of temperature and pressure during the HIP-treatment mainly affects the reduction of porosity and cracks. © European Powder Metallurgy Association (EPMA).
    view abstract
  • 2020 • 386 Shedding Light on Proton and Electron Dynamics in [FeFe] Hydrogenases
    Lorent, C. and Katz, S. and Duan, J. and Kulka, C.J. and Caserta, G. and Teutloff, C. and Yadav, S. and Apfel, U.-P. and Winkler, M. and Happe, T. and Horch, M. and Zebger, I.
    Journal of the American Chemical Society 142 5493-5497 (2020)
    [FeFe] hydrogenases are highly efficient catalysts for reversible dihydrogen evolution. H2 turnover involves different catalytic intermediates including a recently characterized hydride state of the active site (H-cluster). Applying cryogenic infrared and electron paramagnetic resonance spectroscopy to an [FeFe] model hydrogenase from Chlamydomonas reinhardtii (CrHydA1), we have discovered two new hydride intermediates and spectroscopic evidence for a bridging CO ligand in two reduced H-cluster states. Our study provides novel insights into these key intermediates, their relevance for the catalytic cycle of [FeFe] hydrogenase, and novel strategies for exploring these aspects in detail. Copyright © 2020 American Chemical Society.
    view abstractdoi: 10.1021/jacs.9b13075
  • 2020 • 385 Directed Exciton Magnetic Polaron Formation in a Single Colloidal Mn2+:CdSe/CdS Quantum Dot
    Lorenz, S. and Erickson, C.S. and Riesner, M. and Gamelin, D.R. and Fainblat, R. and Bacher, G.
    Nano Letters 20 1896-1906 (2020)
    One of the most prominent signatures of transition-metal doping in colloidal nanocrystals is the formation of charge carrier-induced magnetization of the dopant spin sublattice, called exciton magnetic polaron (EMP). Understanding the direction of EMP formation, however, is still a major obstacle. Here, we present a series of temperature-dependent photoluminescence studies on single colloidal Mn2+:CdSe/CdS core/shell quantum dots (QDs) performed in a vector magnetic field providing a unique insight into the interaction between individual excitons and numerous magnetic impurities. The energy of the QD emission and its full width at half-maximum are controlled by the interplay of EMP formation and statistical magnetic fluctuations, in excellent agreement with theory. Most important, we give the first direct demonstration that anisotropy effects - hypothesized for more than a decade - dominate the direction of EMP formation. Our findings reveal a pathway for directing the orientation of optically induced magnetization in colloidal nanocrystals. © 2020 American Chemical Society.
    view abstractdoi: 10.1021/acs.nanolett.9b05136
  • 2020 • 384 Coulometric Titration of Active Sites at Mesostructured Cobalt Oxide Spinel by Surface Interrogation Mode of Scanning Electrochemical Microscopy
    Lorenz, J. and Yu, M. and Tuÿsüz, H. and Harms, C. and Dyck, A. and Wittstock, G.
    Journal of Physical Chemistry C 124 7737-7748 (2020)
    Cobalt-based transition-metal oxides are promising candidates for the oxygen evolution reaction (OER). However, a complex interplay between the catalyst crystal structures and material morphologies as well as the surface reactions hampers a comprehensive understanding of the electrocatalytic OER at those materials. Here, we investigate the amount and reactivity of specific surface sites of a mesostructured cobalt oxide spinel powder by surface interrogation mode of scanning electrochemical microscopy (SI-SECM). The powder material was supplied in cavity microelectrodes and efficiently titrated with an Fe(II)-triethanolamine redox mediator generated at a gold microelectrode in an alkaline electrolyte. Thus, quantification of different surface sites was achieved, and their reactivity showed dependence on the cobalt oxidation state. Titration experiments after adjustable time delays with respect to the generation of the different surface sites indicated that these surface sites are active for the OER. Kinetic analysis revealed two pseudo-first-order decay constants that were related to fast and slow surface sites for the OER. Rate constants were determined for potentials where predominantly a mixed-valence CoIII/IV state might be present as the most active species. These results expand the great potential of the surface interrogation mode on studying the reaction kinetics of distinct surface sites for practically relevant powdered, nonprecious metal catalysts to address a highly relevant challenge in electrocatalysis. Copyright © 2020 American Chemical Society.
    view abstractdoi: 10.1021/acs.jpcc.9b11114
  • 2020 • 383 Tuning the density of zwitterionic polymer brushes on PET fabrics by aminolysis: Effect on antifouling performances
    Lorusso, E. and Ali, W. and Leniart, M. and Gebert, B. and Oberthür, M. and Gutmann, J.S.
    Polymers 12 (2020)
    Here, we synthesize zwitterionic polymer brushes on polyester fabrics by atom transfer radical polymerization (ATRP) after a prefunctionalization step involving an aminolysis reaction with ethylenediamine. Aminolysis is an easy method to achieve homogeneous distributions of functional groups on polyester fibers (PET) fabrics. Varying the polymerization time and the prefunctionalization conditions of the reaction, it is possible to tune the amount of water retained over the surface and study its effect on protein adhesion. This study revealed that the polymerization time plays a major role in preventing protein adhesion on the PET surface. © 2019 by the authors.
    view abstractdoi: 10.3390/polym12010006
  • 2020 • 382 Synthesis, Structure, Properties, and Applications of Bimetallic Nanoparticles of Noble Metals
    Loza, K. and Heggen, M. and Epple, M.
    Advanced Functional Materials 30 (2020)
    Bimetallic nanoparticles of noble metals are of high interest in imaging, biomedical devices, including nanomedicine, and heterogeneous catalysis. Synthesis, properties, characterization, biological properties, and practical applicability of nanoparticles on the basis of platinum group metals and the coin metals Ag and Au are discussed, also in comparison with the corresponding monometallic nanoparticles. In addition to the parameters that are required to characterize monometallic nanoparticles (mainly size, size distribution, shape, crystallographic nature, surface functionalization, charge), further information is required for a full characterization of bimetallic nanoparticles. This concerns the overall elemental composition of a bimetallic nanoparticle population (ratio of the two metals) and the internal distribution of the elements in individual nanoparticles (e.g., the presence of homogeneous alloys, core–shell systems, and possible intermediate stages). It is also important to ensure that all particles are identical in terms of elemental composition, that is, that the homogeneity of the particle population is given. Macroscopic properties like light absorption, antibacterial effects, and catalytic activity depend on these properties. The currently available methods for a full characterization of bimetallic nanoparticles are discussed, and future developments in this field are outlined. © 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/adfm.201909260
  • 2020 • 381 Interfacial nanophases stabilize nanotwins in high-entropy alloys
    Lu, W. and Liebscher, C.H. and Yan, F. and Fang, X. and Li, L. and Li, J. and Guo, W. and Dehm, G. and Raabe, D. and Li, Z.
    Acta Materialia 185 218-232 (2020)
    Nanostructuring metals through nanograins and nanotwins is an efficient strategy for strength increase as the mean free path of dislocations is reduced. Yet, nanostructures are thermally often not stable, so that the material properties deteriorate upon processing or during service. Here, we introduce a new strategy to stabilize nanotwins by an interfacial nanophase design and realize it in an interstitial high-entropy alloy (iHEA). We show that nanotwins in a carbon-containing FeMnCoCrNi iHEA can remain stable up to 900 °C. This is enabled by co-segregation of Cr and C to nanoscale 9R structures adjacent to incoherent nanotwin boundaries, transforming the 9R structures into elongated nano-carbides in equilibrium with the nanotwin boundaries. This nanoscale 9R structures assisted nano-carbide formation leads to an unprecedented thermal stability of nanotwins, enabling excellent combination of yield strength (~1.1 GPa) and ductility (~21%) after exposure to high temperature. Stimulating the formation of nanosized 9R phases by deformation together with interstitial doping establishes a novel interfacial-nanophase design strategy. The resulting formation of nano-carbides at twin boundaries enables the development of strong, ductile and thermally stable bulk nanotwinned materials. © 2019 Acta Materialia Inc.
    view abstractdoi: 10.1016/j.actamat.2019.12.010
  • 2020 • 380 Acoustic response of a laser-excited polycrystalline Au-film studied by ultrafast Debye-Scherrer diffraction at a table-top short-pulse x-ray source
    Lu, W. and Nicoul, M. and Shymanovich, U. and Brinks, F. and Afshari, M. and Tarasevitch, A. and Von Der Linde, D. and Sokolowski-Tinten, K.
    AIP Advances 10 (2020)
    The transient acoustic response of a free-standing, polycrystalline thin Au-film upon femtosecond optical excitation has been studied by time-resolved Debye-Scherrer x-ray diffraction using ultrashort Cu Kα x-ray pulses from a laser-driven plasma x-ray source. The temporal strain evolution has been determined from the transient shifts of multiple Bragg diffraction peaks. The experimental data are in good agreement with the results of calculations based on the two-temperature model and an acoustic model assuming uniaxial strain propagation in the laser-excited thin film. © 2020 Author(s).
    view abstractdoi: 10.1063/1.5142220
  • 2020 • 379 Joining dissimilar thin-walled tubes by Magnetic Pulse Welding
    Lueg-Althoff, J. and Bellmann, J. and Hahn, M. and Schulze, S. and Gies, S. and Tekkaya, A.E. and Beyer, E.
    Journal of Materials Processing Technology 279 (2020)
    Welding dissimilar metal tubes attracts interest for a wide range of automotive, aeronautical, and plant engineering applications as well as other consumables. Hybrid driveshafts or structural elements can meet mechanical requirements at a reduced weight. However, joining materials with strongly different thermo-physical properties is a challenge for conventional fusion welding processes. In Magnetic Pulse Welding (MPW), the weld formation is based on the high-velocity collision between the joining partners, without additional heat input. This allows for the fabrication of sound “cold” welds. MPW of tubular parts is usually realized by the radial electromagnetic compression of the outer “flyer” part and the subsequent impact on the inner “parent” part. This impact represents a harsh loading for the parent, which therefore is usually designed as a thick-walled or solid part to avoid damage or unwanted deformations. To further increase the lightweight potential, the objective of the present manuscript is the comprehensive analysis of MPW with thin-walled parent parts. Experimental and analytical investigations are presented, which enable to reduce the parent thickness without affecting the joint strength. The approaches comprise the observation of the impact and deformation behavior by inline laser-based measurement technology as well as the development of adequate, re-usable mandrels to support the parent parts. The focus is on aluminum flyer parts, which are welded to steel and copper parent parts. Critical values for the parent wall thickness are deduced and recommendations for the process design of MPW with thin-walled tubes are given. © 2019 Elsevier B.V.
    view abstractdoi: 10.1016/j.jmatprotec.2019.116562
  • 2020 • 378 Nanocrystalline Ga-Zn Oxynitride Materials: Minimized Defect Density for Improved Photocatalytic Activity?
    Lukic, S. and Busser, G.W. and Zhang, S. and Menze, J. and Muhler, M. and Scheu, C. and Winterer, M.
    Zeitschrift fur Physikalische Chemie 234 1133-1153 (2020)
    We present an alternative synthesis strategy for developing nanocrystalline (Ga1-xZnx)(N1-xOx) semiconductors known to be very efficient photoabsorbers. In a first step we produce mixtures of highly crystalline β-Ga2O3 and wurtzite-type ZnO nanoparticles by chemical vapor synthesis. (Ga1-xZnx)(N1-xOx) nanoparticles of wurtzite structure are then formed by reaction of these precursor materials with ammonia. Microstructure as well as composition (zinc loss) changes with nitridation time: band gap energy, crystallite size and crystallinity increase, while defect density decreases with increasing nitridation time. Crystallite growth results in a corresponding decrease in specific surface area. In the UV regime photocatalytic activity for overall water splitting can be monitored for samples both before and after nitridation. We find a significantly lower photocatalytic activity in the nitrided samples, even though the crystallinity is significantly higher and the defect density is significantly lower after nitridation. Both properties should have led to a lower probability for charge carrier recombination, and, consequently, to a higher photocatalytic activity. © 2019 Walter de Gruyter GmbH, Berlin/Boston 2019.
    view abstractdoi: 10.1515/zpch-2019-1432
  • 2020 • 377 Crystal structure and composition dependence of mechanical properties of single-crystalline NbCo2 Laves phase
    Luo, W. and Kirchlechner, C. and Zavašnik, J. and Lu, W. and Dehm, G. and Stein, F.
    Acta Materialia 184 151-163 (2020)
    Extended diffusion layers of the cubic C15 and hexagonal C14 and C36 NbCo2 Laves phases with concentration gradients covering their entire homogeneity ranges were produced by the diffusion couple technique. Single-phase and single-crystalline micropillars of the cubic and hexagonal NbCo2 Laves phases were prepared in the diffusion layers by focused ion beam (FIB) milling. The influence of chemical composition, structure type, orientation and pillar size on the deformation behavior and the critical resolved shear stress (CRSS) was studied by micropillar compression tests. The pillar orientation influences the activated slip systems, but the deformation behavior and the CRSS are independent of orientation. The deformation of the smallest NbCo2 micropillars (0.8 µm in top diameter) appears to be dislocation nucleation controlled and the CRSS approaches the theoretical shear stress for dislocation nucleation. The CRSS of the 0.8 µm-sized NbCo2 micropillars is nearly constant from 26 to 34 at.% Nb where the C15 structure is stable. It decreases as the composition approaches the Co-rich and Nb-rich boundaries of the homogeneity range where the C15 structure transforms to the C36 and the C14 structure, respectively. The decrease in the CRSS at these compositions is related to the reduction of shear modulus and stacking fault energy. As the pillar size increases, stochastic deformation behavior and large scatter in the CRSS values occur and obscure the composition effect on the CRSS. © 2019
    view abstractdoi: 10.1016/j.actamat.2019.11.036
  • 2020 • 376 Composition dependence of hardness and elastic modulus of the cubic and hexagonal NbCo2 Laves phase polytypes studied by nanoindentation
    Luo, W. and Kirchlechner, C. and Li, J. and Dehm, G. and Stein, F.
    Journal of Materials Research 35 185-195 (2020)
    Regarding the effect of composition on the mechanical properties of intermetallic phases such as Laves phases, there is conflicting information in the literature. Some authors observed defect hardening when deviating from stoichiometric Laves phase composition, whereas others find defect softening. Here, we present a systematic investigation of the defect state, hardness, and elastic modulus of cubic and hexagonal NbCo2 Laves phases as a function of crystal structure and composition. For this purpose, diffusion couples were prepared which exhibit diffusion layers of the cubic C15 and hexagonal C14 and C36 NbCo2 Laves phases, with concentration gradients covering their entire homogeneity ranges from 24 to 37 at.% Nb. Direct observations of dislocations and stacking faults in the diffusion layers as a function of composition were performed by electron channeling contrast imaging, and the hardness and elastic modulus were probed in the diffusion layers along the concentration gradients by nanoindentation. © 2020 Materials Research Society.
    view abstractdoi: 10.1557/jmr.2019.384
  • 2020 • 375 Author Correction: A strong and ductile medium-entropy alloy resists hydrogen embrittlement and corrosion (Nature Communications, (2020), 11, 1, (3081), 10.1038/s41467-020-16791-8)
    Luo, H. and Sohn, S.S. and Lu, W. and Li, L. and Li, X. and Soundararajan, C.K. and Krieger, W. and Li, Z. and Raabe, D.
    Nature Communications 11 (2020)
    The original version of this Article contained an error in the author affiliations. The affiliation of Hong Luo and Xiaogang Li with Beijing Advanced Innovation Center for Materials Genome Engineering, Beijing 100083, China was inadvertently omitted. This has now been corrected in both the PDF and HTML versions of the Article. © 2020, The Author(s).
    view abstractdoi: 10.1038/s41467-020-17295-1
  • 2020 • 374 A strong and ductile medium-entropy alloy resists hydrogen embrittlement and corrosion
    Luo, H. and Sohn, S.S. and Lu, W. and Li, L. and Li, X. and Soundararajan, C.K. and Krieger, W. and Li, Z. and Raabe, D.
    Nature Communications 11 (2020)
    Strong and ductile materials that have high resistance to corrosion and hydrogen embrittlement are rare and yet essential for realizing safety-critical energy infrastructures, hydrogen-based industries, and transportation solutions. Here we report how we reconcile these constraints in the form of a strong and ductile CoNiV medium-entropy alloy with face-centered cubic structure. It shows high resistance to hydrogen embrittlement at ambient temperature at a strain rate of 10−4 s−1, due to its low hydrogen diffusivity and the deformation twinning that impedes crack propagation. Moreover, a dense oxide film formed on the alloy’s surface reduces the hydrogen uptake rate, and provides high corrosion resistance in dilute sulfuric acid with a corrosion current density below 7 μA cm−2. The combination of load carrying capacity and resistance to harsh environmental conditions may qualify this multi-component alloy as a potential candidate material for sustainable and safe infrastructures and devices. © 2020, The Author(s).
    view abstractdoi: 10.1038/s41467-020-16791-8
  • 2020 • 373 Black phosphorus–arsenic alloys for lithium ion batteries
    Luxa, J. and Bouša, D. and Zoller, F. and Fattakhova-Rohlfing, D. and Sofer, Z.
    FlatChem 19 (2020)
    Phosphorus and arsenic belong to the 5th group of elements – so-called pnictogens. These materials are among the most intensively studied nanomaterials with layered structure. In this contribution we report the synthesis of arsenic – black phosphorus alloys. Two samples with various black phosphorus and arsenic content together with pure black phosphorus were exfoliated using shear force milling. Extensive analyses have revealed the successful synthesis of AsP alloys with good crystallinity and composition close to that of the intended value. Testing these materials for lithium ion batteries (LIBs) shows that there is a huge capacity loss after the initial charge/discharge cycles. Such a drop was attributed to a delithiation of the lithium rich phase and a loss of proper electrical contact. After the initial capacity loss, the Coulombic efficiencies in the subsequent cycles reached 90–99%. Moreover, both of the alloys exhibited higher capacity than pure black phosphorus sample, indicating that alloying with arsenic is an advantageous technique. The results of this work show the fundamental charge storage capabilities of AsP alloys a can serve as a starting point for the synthesis of advanced materials based on AsP alloys. © 2019 Elsevier B.V.
    view abstractdoi: 10.1016/j.flatc.2019.100143
  • 2020 • 372 Realization of all-optical vortex switching in exciton-polariton condensates
    Ma, X. and Berger, B. and Aßmann, M. and Driben, R. and Meier, T. and Schneider, C. and Höfling, S. and Schumacher, S.
    Nature Communications 11 (2020)
    Vortices are topological objects representing the circular motion of a fluid. With their additional degree of freedom, the vorticity, they have been widely investigated in many physical systems and different materials for fundamental interest and for applications in data storage and information processing. Vortices have also been observed in non-equilibrium exciton-polariton condensates in planar semiconductor microcavities. There they appear spontaneously or can be created and pinned in space using ring-shaped optical excitation profiles. However, using the vortex state for information processing not only requires creation of a vortex but also efficient control over the vortex after its creation. Here we demonstrate a simple approach to control and switch a localized polariton vortex between opposite states. In our scheme, both the optical control of vorticity and its detection through the orbital angular momentum of the emitted light are implemented in a robust and practical manner. © 2020, The Author(s).
    view abstractdoi: 10.1038/s41467-020-14702-5
  • 2020 • 371 Interaction of process parameters, forming mechanisms, and residual stresses in single point incremental forming
    Maaß, F. and Hahn, M. and Tekkaya, A.E.
    Metals 10 (2020)
    The residual stress state of a sheet metal component manufactured by metal forming has a significant influence on the mechanical properties, and thus determines the time until the component fails, especially for dynamic loads. The origin of the resulting residual stress state of incrementally formed parts with regard to the forming mechanisms of shearing, bending, and the normal stress component is still under investigation. The relationship between the process parameters, the forming mechanisms, and the resulting residual stress state for a complex part geometry manufactured by single point incremental forming (SPIF) is presented in this publication. For this purpose, a validated numerical process model is used to analyze the influence of the step-down increment ∆z for truncated cones on the characteristics of the forming mechanisms and the resulting residual stress state. For the first time the forming mechanisms are evaluated numerically on both sides of the formed component. A relationship between the process parameters, forming mechanisms, residual stresses, and the mechanical properties of an incrementally formed component is shown. Shearing-induced hardening is identified as a relevant influence on the residual stress state of cones. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/met10050656
  • 2020 • 370 A linearity preserving nodal variation limiting algorithm for continuous Galerkin discretization of ideal MHD equations
    Mabuza, S. and Shadid, J.N. and Cyr, E.C. and Pawlowski, R.P. and Kuzmin, D.
    Journal of Computational Physics 410 (2020)
    In this work, a stabilized continuous Galerkin (CG) method for magnetohydrodynamics (MHD) is presented. Ideal, compressible inviscid MHD equations are discretized in space on unstructured meshes using piecewise linear or bilinear finite element bases to get a semi-discrete scheme. Stabilization is then introduced to the semi-discrete method in a strategy that follows the algebraic flux correction paradigm. This involves adding some artificial diffusion to the high order, semi-discrete method and mass lumping in the time derivative term. The result is a low order method that provides local extremum diminishing properties for hyperbolic systems. The difference between the low order method and the high order method is scaled element-wise using a limiter and added to the low order scheme. The limiter is solution dependent and computed via an iterative linearity preserving nodal variation limiting strategy. The stabilization also involves an optional consistent background high order dissipation that reduces phase errors. The resulting stabilized scheme is a semi-discrete method that can be applied to inviscid shock MHD problems and may be even extended to resistive and viscous MHD problems. To satisfy the divergence free constraint of the MHD equations, we add parabolic divergence cleaning to the system. Various time integration methods can be used to discretize the scheme in time. We demonstrate the robustness of the scheme by solving several shock MHD problems. © 2020 Elsevier Inc.
    view abstractdoi: 10.1016/
  • 2020 • 369 A swift technique to hydrophobize graphene and increase its mechanical stability and charge carrier density
    Madauß, L. and Pollmann, E. and Foller, T. and Schumacher, J. and Hagemann, U. and Heckhoff, T. and Herder, M. and Skopinski, L. and Breuer, L. and Hierzenberger, A. and Wittmar, A. and Lebius, H. and Benyagoub, A. and Ulbricht, ...
    npj 2D Materials and Applications 4 (2020)
    Despite the improvement of the quality of CVD grown single-layer graphene on copper substrates, transferring the two-dimensional layer without introducing any unintentional defects still poses a challenge. While many approaches focus on optimizing the transfer itself or on necessary post-transfer cleaning steps, we have focused on developing a pre-treatment of the monolayer graphene on copper to improve the quality and reproducibility of the transfer process. By pressing an ethylene-vinyl acetate copolymer foil onto the monolayer graphene on copper using a commercially available vacuum bag sealer graphene is stabilized by the attachment of functional carbon groups. As a result, we are able to transfer graphene without the need of any supporting layer in an all-H2O wet-chemical transfer step. Despite the general belief that the crumbling of graphene without a support layer in a H2O environment is caused due to differences in surface energy, we will show that this assumption is false and that this behavior is caused rather by the polar interactions between graphene and water. Suppressing these interactions protects graphene from ripping and results in extremely clean, highly crystalline graphene with a coverage close to 100%. © 2020, The Author(s).
    view abstractdoi: 10.1038/s41699-020-0148-9
  • 2020 • 368 Phosphoproteomic analysis of STRIPAK mutants identifies a conserved serine phosphorylation site in PAK kinase CLA4 to be important in fungal sexual development and polarized growth
    Märker, R. and Blank-Landeshammer, B. and Beier-Rosberger, A. and Sickmann, A. and Kück, U.
    Molecular Microbiology 113 1053-1069 (2020)
    The highly conserved striatin-interacting phosphatases and kinases (STRIPAK) complex regulates phosphorylation/dephosphorylation of developmental proteins in eukaryotic microorganisms, animals and humans. To first identify potential targets of STRIPAK, we performed extensive isobaric tags for relative and absolute quantification-based proteomic and phosphoproteomic analyses in the filamentous fungus Sordaria macrospora. In total, we identified 4,193 proteins and 2,489 phosphoproteins, which are represented by 10,635 phosphopeptides. By comparing phosphorylation data from wild type and mutants, we identified 228 phosphoproteins to be regulated in all three STRIPAK mutants, thus representing potential targets of STRIPAK. To provide an exemplarily functional analysis of a STRIPAK-dependent phosphorylated protein, we selected CLA4, a member of the conserved p21-activated kinase family. Functional characterization of the ∆cla4 deletion strain showed that CLA4 controls sexual development and polarized growth. To determine the functional relevance of CLA4 phosphorylation and the impact of specific phosphorylation sites on development, we next generated phosphomimetic and -deficient variants of CLA4. This analysis identified (de)phosphorylation of a highly conserved serine (S685) residue in the catalytic domain of CLA4 as being important for fungal cellular development. Collectively, these analyses significantly contribute to the understanding of the mechanistic function of STRIPAK as a phosphatase and kinase signaling complex. © 2020 The Authors. Molecular Microbiology published by John Wiley & Sons Ltd
    view abstractdoi: 10.1111/mmi.14475
  • 2020 • 367 From Precursor Chemistry to Gas Sensors: Plasma-Enhanced Atomic Layer Deposition Process Engineering for Zinc Oxide Layers from a Nonpyrophoric Zinc Precursor for Gas Barrier and Sensor Applications
    Mai, L. and Mitschker, F. and Bock, C. and Niesen, A. and Ciftyurek, E. and Rogalla, D. and Mickler, J. and Erig, M. and Li, Z. and Awakowicz, P. and Schierbaum, K. and Devi, A.
    Small 16 (2020)
    The identification of bis-3-(N,N-dimethylamino)propyl zinc ([Zn(DMP)2], BDMPZ) as a safe and potential alternative to the highly pyrophoric diethyl zinc (DEZ) as atomic layer deposition (ALD) precursor for ZnO thin films is reported. Owing to the intramolecular stabilization, BDMPZ is a thermally stable, volatile, nonpyrophoric solid compound, however, it possesses a high reactivity due to the presence of Zn-C and Zn-N bonds in this complex. Employing this precursor, a new oxygen plasma enhanced (PE)ALD process in the deposition temperature range of 60 and 160 °C is developed. The resulting ZnO thin films are uniform, smooth, stoichiometric, and highly transparent. The deposition on polyethylene terephthalate (PET) at 60 °C results in dense and compact ZnO layers for a thickness as low as 7.5 nm with encouraging oxygen transmission rates (OTR) compared to the bare PET substrates. As a representative application of the ZnO layers, the gas sensing properties are investigated. A high response toward NO2 is observed without cross-sensitivities against NH3 and CO. Thus, the new PEALD process employing BDMPZ has the potential to be a safe substitute to the commonly used DEZ processes. © 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/smll.201907506
  • 2020 • 366 Soft X-ray diffraction patterns measured by a LiF detector with sub-micrometre resolution and an ultimate dynamic range
    Makarov, S. and Pikuz, S. and Ryazantsev, S. and Pikuz, T. and Buzmakov, A. and Rose, M. and Lazarev, S. and Senkbeil, T. and Von Gundlach, A. and Stuhr, S. and Rumancev, C. and Dzhigaev, D. and Skopintsev, P. and Zaluzhnyy, I. an...
    Journal of Synchrotron Radiation 27 625-632 (2020)
    The unique diagnostic possibilities of X-ray diffraction, small X-ray scattering and phase-contrast imaging techniques applied with high-intensity coherent X-ray synchrotron and X-ray free-electron laser radiation can only be fully realized if a sufficient dynamic range and/or spatial resolution of the detector is available. In this work, it is demonstrated that the use of lithium fluoride (LiF) as a photoluminescence (PL) imaging detector allows measuring of an X-ray diffraction image with a dynamic range of ∼107 within the sub-micrometre spatial resolution. At the PETRA III facility, the diffraction pattern created behind a circular aperture with a diameter of 5μm irradiated by a beam with a photon energy of 500eV was recorded on a LiF crystal. In the diffraction pattern, the accumulated dose was varied from 1.7 × 105Jcm-3 in the central maximum to 2 × 10-2Jcm-3 in the 16th maximum of diffraction fringes. The period of the last fringe was measured with 0.8μm width. The PL response of the LiF crystal being used as a detector on the irradiation dose of 500eV photons was evaluated. For the particular model of laser-scanning confocal microscope Carl Zeiss LSM700, used for the readout of the PL signal, the calibration dependencies on the intensity of photopumping (excitation) radiation (λ = 488nm) and the gain have been obtained. © 2020. J. Synchrotron Rad.
    view abstractdoi: 10.1107/S1600577520002192
  • 2020 • 365 Improving identification of in-organello protein-protein interactions using an affinityenrichable, isotopically coded, and mass spectrometry-cleavable chemical crosslinker
    Makepeace, K.A.T. and Mohammed, Y. and Rudashevskaya, E.L. and Petrotchenko, E.V. and Vögtle, F.-N. and Meisinger, C. and Sickmann, A. and Borchers, C.H.
    Molecular and Cellular Proteomics 19 624-639 (2020)
    An experimental and computational approach for identification of protein-protein interactions by ex vivo chemical crosslinking and mass spectrometry (CLMS) has been developed that takes advantage of the specific characteristics of cyanurbiotindipropionylsuccinimide (CBDPS), an affinity-tagged isotopically coded mass spectrometry (MS)-cleavable crosslinking reagent. Utilizing this reagent in combination with a crosslinker-specific data-dependent acquisition strategy based on MS2 scans, and a software pipeline designed for integrating crosslinker-specific mass spectral information led to demonstrated improvements in the application of the CLMS technique, in terms of the detection, acquisition, and identification of crosslinker-modified peptides. This approach was evaluated on intact yeast mitochondria, and the results showed that hundreds of unique protein-protein interactions could be identified on an organelle proteome-wide scale. Both known and previously unknown protein-protein interactions were identified. These interactions were assessed based on their known sub-compartmental localizations. Additionally, the identified crosslinking distance constraints are in good agreement with existing structural models of protein complexes involved in the mitochondrial electron transport chain. © 2020 Makepeace et al.
    view abstractdoi: 10.1074/mcp.RA119.001839
  • 2020 • 364 Tracking the ultrafast nonequilibrium energy flow between electronic and lattice degrees of freedom in crystalline nickel
    Maldonado, P. and Chase, T. and Reid, A.H. and Shen, X. and Li, R.K. and Carva, K. and Payer, T. and Horn Von Hoegen, M. and Sokolowski-Tinten, K. and Wang, X.J. and Oppeneer, P.M. and Dürr, H.A.
    Physical Review B 101 (2020)
    Femtosecond laser excitation of solid-state systems creates out-of-equilibrium hot electrons that cool down by transferring their energy to other degrees of freedom and ultimately to lattice vibrations of the solid. By combining ab initio calculations with ultrafast diffuse electron scattering, we gain a detailed understanding of the complex nonequilibrium energy transfer between electrons and phonons in laser-excited Ni metal. Our experimental results show that the wave-vector-resolved population dynamics of phonon modes is distinctly different throughout the Brillouin zone and are in remarkable agreement with our theoretical results. We find that zone-boundary phonon modes become occupied first. As soon as the energy in these modes becomes larger than the average electron energy, a backflow of energy from lattice to electronic degrees of freedom occurs. Subsequent excitation of lower-energy phonon modes drives the thermalization of the whole system on the picosecond time scale. We determine the evolving nonequilibrium phonon occupations, which we find to deviate markedly from thermal occupations. © 2020 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the "" 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. Funded by "" Bibsam.
    view abstractdoi: 10.1103/PhysRevB.101.100302
  • 2020 • 363 Tunable signal velocity in the integer quantum hall effect of tailored graphene
    Malki, M. and Uhrig, G.S.
    Journal of the Physical Society of Japan 89 (2020)
    Topological properties in condensed matter physics are often claimed to be a fruitful resource for technical applications, but so far they only play a minor role in applications. Here we propose to put topological edge states to use in tailored graphene for Fermi velocity engineering. By tuning external control parameters such as gate voltages, the dispersions of the edge states regime are modified in a controllable way. This enables the realizations of devices such as tunable delay lines and interferometers with switchable delays. © 2020 The Physical Society of Japan.
    view abstractdoi: 10.7566/JPSJ.89.054705
  • 2020 • 362 Influence of defects on structural colours generated by laser-induced ripples
    Maragkaki, S. and Skaradzinski, C.A. and Nett, R. and Gurevich, E.L.
    Scientific Reports 10 (2020)
    The colourisation of metallic surface which appears due to periodic surface patterns induced by ultrashort laser pulses is studied. Ripples due to the sub-micrometer size of their period act as a diffraction grating, generating structural colours. Carefully chosen strategy of the laser spot scanning allows us to mimic the nanostructures responsible for structural colours of some flowers on the metal substrate. We investigate the correlation between the colourising effects and the artificially-induced defects in the ripples structure and show that these defects can make the colours observable in a larger range of viewing angles. Further we address the influence of the processing parameters on the spectral profile of the reflected light. © 2020, The Author(s).
    view abstractdoi: 10.1038/s41598-019-56638-x
  • 2020 • 361 Needle-type organic electrochemical transistor for spatially resolved detection of dopamine
    Mariani, F. and Quast, T. and Andronescu, C. and Gualandi, I. and Fraboni, B. and Tonelli, D. and Scavetta, E. and Schuhmann, W.
    Microchimica Acta 187 (2020)
    In this work, the advantages of carbon nanoelectrodes (CNEs) and orgonic electrochemical transistors (OECTs) were merged to realise nanometre-sized, spearhead OECTs based on single- and double-barrel CNEs functionalised with a conducting polymer film. The needle-type OECT shows a high aspect ratio that allows its precise positioning by means of a macroscopic handle and its size is compatible with single-cell analysis. The device was characterised with respect to its electrolyte-gated behaviour and was employed as electrochemical sensor for the proof-of-concept detection of dopamine (DA) over a wide concentration range (10−12—10−6 M). Upon application of fixed drain and gate voltages (Vd = − 0.3 V, Vg = − 0.9 V, respectively), the nano-sized needle-type OECT sensor exhibited a linear response in the low pM range and from 0.002 to 7 μM DA, with a detection limit of 1 × 10−12 M. [Figure not available: see fulltext.]. © 2020, The Author(s).
    view abstractdoi: 10.1007/s00604-020-04352-1
  • 2020 • 360 Polymer/enzyme-modified HF-etched carbon nanoelectrodes for single-cell analysis
    Marquitan, M. and Ruff, A. and Bramini, M. and Herlitze, S. and Mark, M.D. and Schuhmann, W.
    Bioelectrochemistry 133 (2020)
    Carbon-based nanoelectrodes fabricated by means of pyrolysis of an alkane precursor gas purged through a glass capillary and subsequently etched with HF were modified with redox polymer/enzyme films for the detection of glucose at the single-cell level. Glucose oxidase (GOx) was immobilized and electrically wired by means of an Os-complex-modified redox polymer in a sequential dip coating process. For the synthesis of the redox polymer matrix, a poly(1-vinylimidazole-co-acrylamide)-based backbone was used that was first modified with the electron transfer mediator [Os(bpy)2Cl]+ (bpy = 2,2′-bipyridine) followed by the conversion of the amide groups within the acrylamide monomer into hydrazide groups in a polymer-analogue reaction. The hydrazide groups react readily with bifunctional epoxide-based crosslinkers ensuring high film stability. Insertion of the nanometre-sized polymer/enzyme modified electrodes into adherently growing single NG108-15 cells resulted in a positive current response correlating with the intracellular glucose concentration. Moreover, the nanosensors showed a stable current output without significant loss in performance after intracellular measurements. © 2020
    view abstractdoi: 10.1016/j.bioelechem.2020.107487
  • 2020 • 359 Glutamate detection at the cellular level by means of polymer/enzyme multilayer modified carbon nanoelectrodes
    Marquitan, M. and Mark, M.D. and Ernst, A. and Muhs, A. and Herlitze, S. and Ruff, A. and Schuhmann, W.
    Journal of Materials Chemistry B 8 3631-3639 (2020)
    Carbon nanoelectrodes in the sub-micron range were modified with an enzyme cascade immobilized in a spatially separated polymer double layer system for the detection of glutamate at the cellular level. The enzyme cascade consists of glutamate oxidase (GlutOx) that was immobilized in a hydrophilic redox silent polymer on top of a horseradish peroxidase (HRP)/redox polymer layer. In the presence of O2, glutamate was oxidized under concomitant reduction of O2to H2O2at GlutOx. H2O2is further reduced to water by means of HRP and electrons are shuttledviathe redox polymer matrix that wires the HRP to the electrode surface, hence delivering a current response proportional to the glutamate concentration. The nanometer-sized sensors could be successfully used to measure glutamate release from primary mouse astrocytes in 10 mM HEPES buffer. © The Royal Society of Chemistry 2020.
    view abstractdoi: 10.1039/c9tb02461a
  • 2020 • 358 An in vitro comparison of flow dynamics of the Magna Ease and the Trifecta prostheses
    Marx, P. and Kowalczyk, W. and Demircioglu, A. and Shehada, S.-E. and Wendta, H. and Mourad, F. and Thielmann, M. and Jakob, H. and Wendt, D.
    Minimally Invasive Therapy and Allied Technologies 29 78-85 (2020)
    Objectives: We aimed to compare the in vitro flow dynamics of the Perimount Magna Ease™ (PME) and the Trifecta™ (TF) bioprostheses. Material and methods: A new flow chamber was designed to compare the flow patterns of the PME (Edwards Lifesciences, Irvine, CA, USA) and the TF (SJM, St. Paul, MN, USA) aortic valve prostheses. This new channel offered the possibility of 2D-particle-image-velocimetry (2D-PIV) to completely evaluate the flow field downstream from the aortic valve to the middle of the aortic arch. Maximum average velocities, vorticity, shear strength, maximum orifice diameters and jet flow diameters were analyzed. Valve sizes of 21, 23 and 25 mm were evaluated. Results: Average velocity values, shear strength and vorticities were smaller in the flow field of the TF (maximum average velocity: 0.81 ± 0.03m/s, PME 23 mm vs. 0.7 ± 0.02m/s TF 23 mm, P <.001) under pulsatile flow conditions (70 Hz, 70 mL stroke volume). The evaluation of the upper orifice area revealed bigger maximum diameters during the peak flow phase for the TF, but more leaflet-flutter. Conclusions: Our flow chamber allowed a precise and highly sensitive characterization and comparison of complex fluid dynamics of different aortic valve prostheses. Both the Trifecta™ and the Perimount Magna Ease™ showed a good performance on a high level. © 2019, © 2019 Society of Medical Innovation and Technology.
    view abstractdoi: 10.1080/13645706.2019.1586732
  • 2020 • 357 Equivalent Mid-Term Results of Open vs Endoscopic Gluteal Tendon Tear Repair Using Suture Anchors in Forty-Five Patients
    Maslaris, A. and Vail, T.P. and Zhang, A.L. and Patel, R. and Jäger, M. and Bini, S.A.
    Journal of Arthroplasty 35 S352-S358 (2020)
    Background: Little is known about the relative efficacy of open (OGR) vs endoscopic (EGR) gluteal tendon repair of gluteal tendon tears in minimizing pain and restoring function. Our aim is to compare these 2 surgical techniques and quantify their impact on clinical outcomes. Methods: All patients undergoing gluteal tendon tear repair at our institution between 2015 and 2018 were retrospectively reviewed. Pain scores, limp, hip abduction strength, and the use of analgesics were recorded preoperatively and at last follow-up. The Hip disability and Osteoarthritis Outcome Score Junior and Harris Hip Score Section1 were obtained at last follow-up. Fatty degeneration was quantified using the Goutallier-Fuchs Classification (GFC). Statistical analysis was conducted using one-way analysis of variance and t-tests. Results: Forty-five patients (mean age 66, 87% females) met inclusion criteria. Average follow-up was 20.3 months. None of the 10 patients (22%) undergoing EGR had prior surgery. Of 35 patients (78%) undergoing OGR, 12 (27%) had prior hip replacement (75% via lateral approach). The OGRs had more patients with GFC ≥2 (50% vs 11%, P = .02) and used more anchors (P = .03). Both groups showed statistical improvement (P ≤ .01) for all outcomes measured. GFC >2 was independently associated with a worst limp and Harris Hip Score Section 1 score (P = .05). EGR had a statistically higher opioid use reduction (P < .05) than OGR. Other comparisons between EGR and OGR did not reach statistical significance. Conclusion: In this series, open vs endoscopic operative approach did not impact clinical outcomes. More complex tears were treated open and with more anchors. Fatty degeneration adversely impacted outcomes. Although further evaluation of the efficacy of EGR in complex tears is indicated, both approaches can be used successfully. © 2020 Elsevier Inc.
    view abstractdoi: 10.1016/j.arth.2020.03.013
  • 2020 • 356 Effect of size and domain orientation on strength of Barium Titanate
    Mathews, N.G. and Saxena, A.K. and Kirchlechner, C. and Dehm, G. and Jaya, B.N.
    Scripta Materialia 182 68-73 (2020)
    Microscale mechanical behaviour of single crystalline Barium Titanate (BaTiO3), a ferroelectric ceramic was studied by uniaxial in situ micropillar compression and nanoindentation. It was observed that pillars below 1 µm diameter reached the theoretical strength of BaTiO3 whereas larger pillars yielded at lower stress values with multiple stress drops confirming slip activity. A size scaling exponent of 0.96 ± 0.09 was estimated for BaTiO3 which is close to one of the soft fcc metals. The material's strength, hardness and deformation behaviour did not show any dependence on the character of the ferroelectric domain, within our error bars. © 2020
    view abstractdoi: 10.1016/j.scriptamat.2020.02.039
  • 2020 • 355 A Fully Nonlinear Beam Model of Bernoulli–Euler Type
    de Mattos Pimenta, P. and Maassen, S. and da Costa e Silva, C. and Schröder, J.
    CISM International Centre for Mechanical Sciences, Courses and Lectures 597 127-151 (2020)
    This work presents a geometrically exact Bernoulli–Euler rod model. In contrast to Pimenta (1993b), Pimenta and Yojo (1993), Pimenta (1996), Pimenta and Campello (2001), where the hypothesis considered was Timoshenko’s, this approach is based on the Bernoulli–Euler theory for rods, so that transversal shear deformation is not accounted for. Energetically conjugated cross-sectional stresses and strains are defined. The fact that both the first Piola–Kirchhoff stress tensor and the deformation gradient appear again as primary variables is also appealing. A straight reference configuration is assumed for the rod, but, in the same way, as in Pimenta (1996), Pimenta and Campello (2009), initially curved rods can be accomplished, if one regards the initial configuration as a stress-free deformed state from the straight position. Consequently, the use of convective non-Cartesian coordinate systems is not necessary, and only components on orthogonal frames are employed. A cross section is considered to undergo a rigid body motion and parameterization of the rotation field is done by the rotation tensor with the Rodrigues formula that makes the updating of the rotational variables very simple. This parametrization can be seen in Pimenta et al. (2008), Campello et al. (2011). A simple formula for the incremental Rodrigues parameters in function of the displacements derivative and the torsion angle is also settled down. A 2-node finite element with Cubic Hermitian interpolation for the displacements, together with a linear approximation for the torsion angle, is displayed within the usual Finite Element Method, leading to adequate C1 continuity. © 2020, CISM International Centre for Mechanical Sciences.
    view abstractdoi: 10.1007/978-3-030-33520-5_5
  • 2020 • 354 Coatings with Columnar Microstructures for Thermal Barrier Applications
    Mauer, G. and Vaßen, R.
    Advanced Engineering Materials 22 (2020)
    Columnar-structured thermal barrier coatings (TBCs) manufactured by electron beam-physical vapor deposition (EB-PVD) are well known to exhibit high strain tolerance. However, as EB-PVD is a high-vacuum process, it is expensive. Suspension plasma spraying (SPS) and plasma spray-physical vapor deposition (PS-PVD) are alternatives for the manufacture of similar microstructures. Herein, the state of the art of manufacturing columnar-structured TBCs by SPS and PS-PVD is outlined. Both processes have been investigated and further developed at Forschungszentrum Jülich for many years. The mechanisms leading to the formation of columnar-structured coatings are described and differentiated from EB-PVD. Examples are given for SPS and PS-PVD columnar microstructures and their life performance. © 2019 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/adem.201900988
  • 2020 • 353 The learning curve of patient-specific unikondylar arthroplasty may be advantageous to off-the-shelf implants: A preliminary study
    Mayer, C. and Bittersohl, B. and Haversath, M. and Franz, A. and Krauspe, R. and Jäger, M. and Zilkens, C.
    Journal of Orthopaedics 22 256-260 (2020)
    Introduction: Introducing a new arthroplasty system into clinical routine is challenging and could have an effect on early results. Since UKA are known to have failure mechanisms related to technical factors, reliable results and easy adoption are ideal. The question remains whether there are differences in objective procedure parameters in the early learning curve of different UKA systems. Methods: two different UKA implants (Biomet Oxford[BO] followed by Conformis iuni[CI]) were introduced consecutively into clinical routine. We retrospectively analyzed the first 20 cases of each implant for one arthroplasty surgeon regarding operating time, correction of the mechanical axis, learning curve parameters, and revision rate of implants for 1.5 years postoperatively. Results: Operating time (BO:98.3 ± 26.3min, CI:83.85 ± 21.8min (p < 0.078)), and tourniquet time differed in favor of the CI implant (BO:97.5 ± 29.5min; CI:73.5 ± 33.2 min; p < 0.017)). Mechanical alignment was restored in boths (preop:BO:mean 2.9°varus, CI:2.7°varus, postop:BOmean1.3°varus, CI:1°varus), while one BO patient and two CI patients were overcorrected. Operating time decreased from the first five implants to implants 16–20 for CI (95.2 ± 18.5min to 69 ± 21.5min, p < 0.076) and BO (130.6 ± 27.6min to 78 ± 17.3min, p < 0.009). Within 18 months of follow-up, 2 BO and 1 CI implants were revised. Conclusion: The introduction of an UKA implant was associated with longer surgery in both implants. Procedure time seems to differ between implants, while a learning curve was observed regarding instrumentation. CI implants seem to be reliable and adaptable in a medium-volume practice. The early results of this retrospective single-surgeon study were in favor of the individualized implant. Certainly, further studies encompassing larger cohorts with various implants are needed. © 2020 Professor P K Surendran Memorial Education Foundation
    view abstractdoi: 10.1016/j.jor.2020.05.005
  • 2020 • 352 Herbivores coprolites from chehrabad salt mine of zanjan, iran (Sassanid era, 224-651 ad) reveals eggs of strongylidae and anoplocephalidae helminths
    Meigouni, M. and Makki, M. and Haniloo, A. and Askari, Z. and Mobedi, I. and Naddaf, S.R. and Boenke, N. and Stollner, T. and Aali, A. and Heidari, Z. and Mowlavi, G.
    Iranian Journal of Parasitology 15 109-114 (2020)
    Background: The ancient Chehrabad Salt mine, a well-known archaeological site in Iran, has recently received increasing interest from Iranian and international archeologists. Also, the biological remains from this site have provided valuable sources for studying the pathogenic agents of ancient times. This study aimed to identify the parasitic helminth eggs preserved in the herbivores coprolites. Methods: From 2011 to 2015, we received three coprolites belonging to herbivorous animals recovered during excavations in Chehrabad Salt mine of Zanjan, Iran. The coprolites were dated back to the Sassanid era (224-651 AD) by using radiocarbon accelerator mass spectrometry (AMS) and archeological stratigraphy methods. Following rehydration of the specimens in a 0.5% trisodium phosphate solution, the suspensions were mounted in glycerin jelly on glass slides and examined by a light microscope with 100x and 400x magnifications. Results: Two coprolites belonged to donkeys and one to an unknown herbivore species. The recovered eggs belonged to members of two helminths families, Strongylidae, and Anoplocephalidae. Also, within the two coprolites, some mites, presumably of the order Oribatida, were observed. Conclusion: The presence of two different nematodes in the equids coprolites provide clues of the burden of helminths infection on working animal at the Sassanid time and demonstrates the appropriate preservation condition of biological remains in the ancient salt mine of Chehrabad as well. © 2020, Tehran University of Medical Sciences (TUMS). All rights reserved.
    view abstractdoi: 10.18502/ijpa.v15i1.2533
  • 2020 • 351 Tantalum and zirconium induced structural transitions at complex [111] tilt grain boundaries in copper
    Meiners, T. and Duarte, J.M. and Richter, G. and Dehm, G. and Liebscher, C.H.
    Acta Materialia 190 93-104 (2020)
    Alloying nanocrystalline copper (Cu) with immiscible elements, such as tantalum (Ta) and zirconium (Zr), is a promising technique to manipulate grain boundary properties and by this suppress grain growth at elevated temperatures. However, insights on the atomistic origins on the influence of impurity elements on grain boundaries are lacking. In this study, the atomistic effects of Ta and Zr on [111] tilt grain boundaries in Cu are investigated by high resolution scanning transmission electron microscopy techniques. In case of Ta, the formation of spherical, nano-scale precipitates in close vicinity to the grain boundaries is observed, but no sign of segregation. The particles induce a repelling force to migrating boundaries and act as local pinning points. The segregation of Zr is observed to occur either at confined grain boundary steps or homogeneously along the boundaries without steps. In both cases a strong disordering of the defect or grain boundary structure is revealed. Furthermore, at low Zr concentrations it induces structural grain boundary transitions and partial atomic reordering of the grain boundary structural units. © 2020 Acta Materialia Inc.
    view abstractdoi: 10.1016/j.actamat.2020.02.064
  • 2020 • 350 Observations of grain-boundary phase transformations in an elemental metal
    Meiners, T. and Frolov, T. and Rudd, R.E. and Dehm, G. and Liebscher, C.H.
    Nature 579 375-378 (2020)
    The theory of grain boundary (the interface between crystallites, GB) structure has a long history1 and the concept of GBs undergoing phase transformations was proposed 50 years ago2,3. The underlying assumption was that multiple stable and metastable states exist for different GB orientations4–6. The terminology ‘complexion’ was recently proposed to distinguish between interfacial states that differ in any equilibrium thermodynamic property7. Different types of complexion and transitions between complexions have been characterized, mostly in binary or multicomponent systems8–19. Simulations have provided insight into the phase behaviour of interfaces and shown that GB transitions can occur in many material systems20–24. However, the direct experimental observation and transformation kinetics of GBs in an elemental metal have remained elusive. Here we demonstrate atomic-scale GB phase coexistence and transformations at symmetric and asymmetric [11 1 ¯] tilt GBs in elemental copper. Atomic-resolution imaging reveals the coexistence of two different structures at Σ19b GBs (where Σ19 is the density of coincident sites and b is a GB variant), in agreement with evolutionary GB structure search and clustering analysis21,25,26. We also use finite-temperature molecular dynamics simulations to explore the coexistence and transformation kinetics of these GB phases. Our results demonstrate how GB phases can be kinetically trapped, enabling atomic-scale room-temperature observations. Our work paves the way for atomic-scale in situ studies of metallic GB phase transformations, which were previously detected only indirectly9,15,27–29, through their influence on abnormal grain growth, non-Arrhenius-type diffusion or liquid metal embrittlement. © 2020, The Author(s), under exclusive licence to Springer Nature Limited.
    view abstractdoi: 10.1038/s41586-020-2082-6
  • 2020 • 349 On the effects of diluted and mixed ionic liquids as liquid substrates for the sputter synthesis of nanoparticles
    Meischein, M. and Fork, M. and Ludwig, Al.
    Nanomaterials 10 (2020)
    The synthesis of nanoparticles by combinatorial sputtering in ionic liquids is a versatile approach for discovering new materials. Whereas the influence on nanoparticle formation of different pure ionic liquids has been addressed, the influence of (I) dilution of ionic liquid with solvents and (II) different mixtures of ionic liquids is less known. Therefore, mixtures of the ionic liquid [Bmim][(Tf)2N] with the organic solvent anisole and other ionic liquids ([Bmim][(Pf)2N], [BmPyr][(Tf)2N]) were used as liquid substrates for the sputter synthesis of nanoparticles, in order to investigate the influence of these mixtures on the size of the nanoparticles. First, mixtures of anisole with a suspension of sputtered Ag nanoparticles in [Bmim][(Tf)2N] were prepared in different volumetric steps to investigate if the stabilization of the NPs by the ionic liquid could be reduced by the solvent. However, a continuous reduction in nanoparticle size and amount with increasing anisole volume was observed. Second, Ag, Au and Cu were sputtered on ionic liquid mixtures. Ag nanoparticles in [Bmim][(Tf)2N]/[Bmim][(Pf)2N] mixtures showed a decrease in size with the increasing volumetric fraction of [Bmim][(Tf)2N], whereas all nanoparticles obtained from [Bmim][(Tf)2N]/[BmPyr][(Tf)2N] mixtures showed increasing size and broadening of the size distribution. Maximum sizes of sputtered Ag and Au NPs were reached in mixtures of [Bmim][(Tf)2N] with 20 vol.% and 40 vol.% [BmPyr][(Tf)2N]. The results indicate that ionic liquid mixtures with different portions of cations and anions have the capability of influencing the ionic liquid stabilization characteristics with respect to, e.g., nanoparticle size and size distribution. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/nano10030525
  • 2020 • 348 Continuum Damage Mechanics—Modelling and Simulation
    Menzel, A. and Sprave, L.
    Solid Mechanics and its Applications 262 231-256 (2020)
    Continuum damage mechanics elaborates the continuum mechanics-based modelling and simulation of mechanical degradation effects. The objective of this contribution is to briefly review different aspects of continuum damage mechanics of solid continua with a focus on general modelling concepts and application to isotropic as well as anisotropic damage approaches on the one hand, and to discuss possible solution strategies in the context of finite element simulations on the other. In particular, viscous regularisation and gradient-enhanced regularisation—as a reduced form of general non-local theories—are considered. Several numerical examples including ductile damage, i.e. the coupling of damage with plasticity related phenomena, are addressed which show the applicability of the particular modelling and simulation frameworks highlighted. © 2020, Springer Nature Switzerland AG.
    view abstractdoi: 10.1007/978-3-030-31547-4_8
  • 2020 • 347 Development and Implementation of Statistical Methods for Quality Optimization in the Large-Format Lithium-Ion Cells Production
    Meyer, O. and Weihs, C. and Mähr, S. and Tran, H.-Y. and Kirchhof, M. and Schnackenberg, S. and Neuhaus-Stern, J. and Rößler, S. and Braunwarth, W.
    Energy Technology 8 (2020)
    Herein, two techniques to optimize the production process of large-format lithium-ion cells for plug-in hybrid electric vehicles using data-driven methods are introduced and demonstrated. The first approach uses standard settings of the quality influencing factors to maximize the number of produced electrode sheets that meet predefined quality specifications. The second approach uses statistical methods to determine the levels of the quality influencing factors of a certain process that optimizes all quality parameters of the corresponding product jointly. © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/ente.201900244
  • 2020 • 346 Investigation of the track width-dependent melt pool characteristics during laser-sintering of polyamide 12 in correlation to various focus diameters
    Meyer, L. and Witt, G.
    Progress in Additive Manufacturing 5 19-25 (2020)
    Factors such as not only costs, production time, reproducibility, but also the quality of the components are decisive factors in assessing the economic efficiency of a manufacturing process. With additive manufacturing processes, component production is made possible directly from a 3D CAD model. This means that small series and prototypes can already be produced economically today. In this area, the laser-sintering process, in particular, offers great potential for series production due to its high strength values and ductility. With laser-sintering systems that allow an optical widening of the laser focus, a faster exposure of the component and thus a shortening of the building time is possible. We developed a laser-sintering system whose laser focus diameter is adjustable in its cross-sectional area from 0.47 to 2 mm. The goal for the future is to produce large-area components significantly faster by widening the focus diameter, thus making laser-sintering more productive. In this paper, the focus-dependent melt pool formation is examined in correlation to different hatch distances during the laser-sintering of polyamide 12. For this purpose, a test specimen was developed which can display single tracks as well as a multitude of different track widths for all feasible focus level variations. This knowledge is required to determine and investigate the track width-dependent melt pool formation as a function of the focal diameter of the component cross sections. © 2020, The Author(s).
    view abstractdoi: 10.1007/s40964-020-00126-6
  • 2020 • 345 Influence of the ratio between the translation and contra-rotating coating mechanism on different laser sintering materials and their packing density
    Meyer, L. and Wegner, A. and Witt, G.
    Solid Freeform Fabrication 2017: Proceedings of the 28th Annual International Solid Freeform Fabrication Symposium - An Additive Manufacturing Conference, SFF 2017 1432-1447 (2020)
    An initial study about the advanced machine parameters and their impact on the packing density of different laser sintering materials was conducted on a self-developed laser sintering machine. Usually, on commercial machines, the ratio between the translational and contra-rotatory movement of the roller is fixed. The standard ratio is established for polyamide 12, but new materials, such as polyamide 6 or polybutylene terephthalate, need adjustable parameters to find optimized composition coating results. In the testing machine, the contra rotating roller can be replaced by a coating blade to generate the powder layers. In Addition to the tests with the roller, two different shapes of coating blades were tested. This allows a comparison between both commercial coating systems in laser sintering machines. Copyright © SFF 2017.All rights reserved.
    view abstract
  • 2020 • 344 Forming amorphous calcium carbonate within hydrogels by enzyme-induced mineralization in the presence of N-(phosphonomethyl)glycine
    Milovanovic, M. and Unruh, M.T. and Brandt, V. and Tiller, J.C.
    Journal of Colloid and Interface Science 579 357-368 (2020)
    Amorphous inorganic materials have a great potential in material science. Amorphous calcium carbonate (ACC) is a widely useable system, however, its stabilization often turns out to be difficult and the synthesis is mostly limited to precipitation in solution as nanoparticles. Stable ACC in bulk phases would create new composite materials. Previous work described the enzyme-induced mineralization of hydrogels with crystalline calcium carbonate by entrapping urease into a hydrogel and treating this with an aqueous mineralization solution containing urea und calcium chloride. Here, this method was modified using a variety of crystallization inhibitors attached to the hydrogel matrix or added to the surrounding mineralization solution. It was found that only N-(phosphonomethyl)glycine (PMGly) in solution completely inhibits the crystallization of ACC in the hydrogel matrix. The stability of the homogeneously precipitated ACC could be accounted to the combination of stabilizing effects of the additive and stabilization through confinement. The crystallization could be accelerated at higher temperatures up to 60 °C. Here, a combination of Mg ions and PMGly was required to stabilize ACC in the hydrogel. Variation of these two compounds can be used to control a number of different calcium carbonate morphologies within the hydrogel. While the ACC nanoparticles within the hydrogel are stable over weeks even in water, a calcite layer grows on the surface of the hydrogel, which might be used as self-hardening mechanism of a surface. © 2020 Elsevier Inc.
    view abstractdoi: 10.1016/j.jcis.2020.06.047
  • 2020 • 343 Direct growth of graphene on GaN via plasma-enhanced chemical vapor deposition under N2 atmosphere
    Mischke, J. and Pennings, J. and Weisenseel, E. and Kerger, P. and Rohwerder, M. and Mertin, W. and Bacher, G.
    2D Materials 7 (2020)
    One of the bottlenecks in the implementation of graphene as a transparent electrode in modern opto-electronic devices is the need for complicated and damaging transfer processes of high-quality graphene sheets onto the desired target substrates. Here, we study the direct, plasma-enhanced chemical vapor deposition (PECVD) growth of graphene on GaN-based light-emitting diodes (LEDs). By replacing the commonly used hydrogen (H2) process gas with nitrogen (N2), we were able to suppress GaN surface decomposition while simultaneously enabling graphene deposition at &lt;800 °C in a single-step growth process. Optimizing the methane (CH4) flow and varying the growth time between 0.5 h and 8 h, the electro-optical properties of the graphene layers could be tuned to sheet resistances as low as ∼1 kΩ/D with a maximum transparency loss of ∼12%. The resulting high-quality graphene electrodes show an enhanced current spreading effect and an increase of the emission area by a factor of ∼8 in operating LEDs. © 2020 The Author(s).
    view abstractdoi: 10.1088/2053-1583/ab8969
  • 2020 • 342 Load direction-dependent influence of forming-induced initial damage on the fatigue performance of 16MnCrS5 steel
    Moehring, K. and Walther, F.
    Materials 13 1-19 (2020)
    Forming processes influence the mechanical properties of manufactured workpieces in general and by means of forming-induced initial damage in particular. The effect of the latter on performance capability is the underlying research aspect for the investigations conducted. In order to address this aspect, fatigue tests under compressive, tensile and compressive-tensile loads were set-up with discrete block-by-block increased amplitudes and constant amplitudes, and performed up to fracture or distinct lifetimes. Aiming at the correlation of the macroscale mechanical testing results at the mesoscale, intensive metallographic investigations of cross-sections using the microscopical methods of secondary electron analysis, energy dispersive spectroscopy and electron backscatter diffraction were performed. Thereby, the correlation of forming-induced initial damage and fatigue performance was determined, the relevance of compressive loads for the cyclic damage evolution was shown, and material anisotropy under compressive loads was indicated. Finally, the need was addressed to perform further investigations regarding crack propagations and crack arrest investigations in order to clarify the mechanism by which initial damage affects cyclic damage evolution. The relevance of the principal stress axis relative to the extrusion direction was emphasized and used as the basis of an argument for investigations under load paths with different stress directions. © 2020 by the authors.
    view abstractdoi: 10.3390/ma13122680
  • 2020 • 341 Equivalence of regression curves sharing common parameters
    Möllenhoff, K. and Bretz, F. and Dette, H.
    Biometrics 76 518-529 (2020)
    In clinical trials, the comparison of two different populations is a common problem. Nonlinear (parametric) regression models are commonly used to describe the relationship between covariates, such as concentration or dose, and a response variable in the two groups. In some situations, it is reasonable to assume some model parameters to be the same, for instance, the placebo effect or the maximum treatment effect. In this paper, we develop a (parametric) bootstrap test to establish the similarity of two regression curves sharing some common parameters. We show by theoretical arguments and by means of a simulation study that the new test controls its significance level and achieves a reasonable power. Moreover, it is demonstrated that under the assumption of common parameters, a considerably more powerful test can be constructed compared with the test that does not use this assumption. Finally, we illustrate the potential applications of the new methodology by a clinical trial example. © 2019 The Authors. Biometrics published by Wiley Periodicals, Inc. on behalf of International Biometric Society
    view abstractdoi: 10.1111/biom.13149
  • 2020 • 340 In vivo imaging of human peripheral nerves using optical coherence tomography compared to histopathology slices
    Möller, J. and Carolus, A.E. and Van De Nes, J.A.P. and Lenz, M. and Brenke, C. and Schmieder, K. and Welp, H. and Gerhardt, N.C. and Hofmann, M.R.
    Progress in Biomedical Optics and Imaging - Proceedings of SPIE 11228 (2020)
    In this work we demonstrate the ability of in vivo optical coherence tomography (OCT) images to resolve all relevant structures of human peripheral nerves. Measurements have been acquired in more than 30 peripheral nerve surgeries using a commercial OCT system (Thorlabs Ganymede) with a hand probe, which can be directly placed on the nerve, covered by a sterile foil. The resulting 3D OCT images were processed using texture analysis to highlight structural tissue features of the nerve. A comparison of OCT images and corresponding histopathology slices was performed in order to confirm the visualization of the nerve's structures by OCT. © COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only.
    view abstractdoi: 10.1117/12.2544801
  • 2020 • 339 Archetypes of digital business models in logistics start-ups
    Möller, F. and Bauhaus, H. and Hoffmann, C. and Niess, C. and Otto, B.
    27th European Conference on Information Systems - Information Systems for a Sharing Society, ECIS 2019 (2020)
    Our work develops an archetypical representation of current digital business models of Start-Ups in the logistics sector. In order to achieve our goal, we analyze the business models of 125 Start-Ups. We draw our sample from the Start-Up database AngelList and focus on platform-driven businesses. We chose Start-Ups as they often are at the forefront of innovation and thus have a high likelihood of operating digital business models. Following well-established methodological guidelines, we construct a taxonomy of digital business models in multiple iterations. We employ different algorithms for cluster analysis to find and generate clusters based on commonalities between the business models across the dimensions and characteristics of the taxonomy. Ultimately, we use the dominant features of the emerging patterns within the clusters to derive archetypes. © 27th European Conference on Information Systems - Information Systems for a Sharing Society, ECIS 2019. All rights reserved.
    view abstract
  • 2020 • 338 Differentiation between Carbon Corrosion and Oxygen Evolution Catalyzed by NixB/C Hybrid Electrocatalysts in Alkaline Solution using Differential Electrochemical Mass Spectrometry
    Möller, S. and Barwe, S. and Dieckhöfer, S. and Masa, J. and Andronescu, C. and Schuhmann, W.
    ChemElectroChem 7 2680-2686 (2020)
    Carbon is a frequently used electrode material and an important additive in catalyst films. Its corrosion is often reported during electrocatalysis at high anodic potentials, especially in acidic electrolyte. Investigation of the carbon corrosion in alkaline environment is difficult due to the CO2/CO32− equilibrium. We report the on-line determination of electrolysis products generated on NixB/C hybrid electrocatalysts in alkaline electrolyte at anodic potentials using differential electrochemical mass spectrometry (DEMS). NixB/C catalyst films were obtained from mixtures containing different ratios of NiXB and benzoxazine monomers followed by polymerization and pyrolysis. The impact of the composition of the electrocatalyst on the dominant electrolysis process allows to distinguish between the oxygen evolution reaction and carbon corrosion using DEMS results as well as the catalyst surface composition evaluated from X-ray photoelectron spectra. At the imposed highly oxidative conditions, an increasing amount of NixB in the electrocatalyst leads to a suppression of carbon corrosion. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
    view abstractdoi: 10.1002/celc.202000697
  • 2020 • 337 Online Monitoring of Electrochemical Carbon Corrosion in Alkaline Electrolytes by Differential Electrochemical Mass Spectrometry
    Möller, S. and Barwe, S. and Masa, J. and Wintrich, D. and Seisel, S. and Baltruschat, H. and Schuhmann, W.
    Angewandte Chemie - International Edition 59 1585-1589 (2020)
    Carbon corrosion at high anodic potentials is a major source of instability, especially in acidic electrolytes and impairs the long-term functionality of electrodes. In-depth investigation of carbon corrosion in alkaline environment by means of differential electrochemical mass spectrometry (DEMS) is prevented by the conversion of CO2 into CO3 2−. We report the adaptation of a DEMS system for online CO2 detection as the product of carbon corrosion in alkaline electrolytes. A new cell design allows for in situ acidification of the electrolyte to release initially dissolved CO3 2− as CO2 in front of the DEMS membrane and its subsequent detection by mass spectrometry. DEMS studies of a carbon-supported nickel boride (NixB/C) catalyst and Vulcan XC 72 at high anodic potentials suggest protection of carbon in the presence of highly active oxygen evolution electrocatalysts. Most importantly, carbon corrosion is decreased in alkaline solution. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
    view abstractdoi: 10.1002/anie.201909475
  • 2020 • 336 The Amyloid Inhibitor CLR01 Relieves Autophagy and Ameliorates Neuropathology in a Severe Lysosomal Storage Disease
    Monaco, A. and Maffia, V. and Sorrentino, N.C. and Sambri, I. and Ezhova, Y. and Giuliano, T. and Cacace, V. and Nusco, E. and De Risi, M. and De Leonibus, E. and Schrader, T. and Klärner, F.-G. and Bitan, G. and Fraldi, A.
    Molecular Therapy 28 1167-1176 (2020)
    Fraldi and colleagues demonstrated that multiple amyloid proteins progressively aggregate in neurons of a severe lysosomal storage disease, impairing autophagy degradation and triggering neurodegeneration. They also showed that inhibiting amyloid deposition protects against neurodegeneration, thus providing evidence that amyloid aggregation is a new attractive target for the treatment of LSDs. © 2020 The Author(s) Lysosomal storage diseases (LSDs) are inherited disorders caused by lysosomal deficiencies and characterized by dysfunction of the autophagy-lysosomal pathway (ALP) often associated with neurodegeneration. No cure is currently available to treat neuropathology in LSDs. By studying a mouse model of mucopolysaccharidosis (MPS) type IIIA, one of the most common and severe forms of LSDs, we found that multiple amyloid proteins including α-synuclein, prion protein (PrP), Tau, and amyloid β progressively aggregate in the brain. The amyloid deposits mostly build up in neuronal cell bodies concomitantly with neurodegeneration. Treating MPS-IIIA mice with CLR01, a “molecular tweezer” that acts as a broad-spectrum inhibitor of amyloid protein self-assembly reduced lysosomal enlargement and re-activates autophagy flux. Restoration of the ALP was associated with reduced neuroinflammation and amelioration of memory deficits. Together, these data provide evidence that brain deposition of amyloid proteins plays a gain of neurotoxic function in a severe LSD by affecting the ALP and identify CLR01 as new potent drug candidate for MPS-IIIA and likely for other LSDs. © 2020 The Author(s)
    view abstractdoi: 10.1016/j.ymthe.2020.02.005
  • 2020 • 335 Trimetallic Mn-Fe-Ni Oxide Nanoparticles Supported on Multi-Walled Carbon Nanotubes as High-Performance Bifunctional ORR/OER Electrocatalyst in Alkaline Media
    Morales, D.M. and Kazakova, M.A. and Dieckhöfer, S. and Selyutin, A.G. and Golubtsov, G.V. and Schuhmann, W. and Masa, J.
    Advanced Functional Materials 30 (2020)
    Discovering precious metal-free electrocatalysts exhibiting high activity and stability toward both the oxygen reduction (ORR) and the oxygen evolution (OER) reactions remains one of the main challenges for the development of reversible oxygen electrodes in rechargeable metal–air batteries and reversible electrolyzer/fuel cell systems. Herein, a highly active OER catalyst, Fe0.3Ni0.7OX supported on oxygen-functionalized multi-walled carbon nanotubes, is substantially activated into a bifunctional ORR/OER catalyst by means of additional incorporation of MnOX. The carbon nanotube-supported trimetallic (Mn-Ni-Fe) oxide catalyst achieves remarkably low ORR and OER overpotentials with a low reversible ORR/OER overvoltage of only 0.73 V, as well as selective reduction of O2 predominantly to OH−. It is shown by means of rotating disk electrode and rotating ring disk electrode voltammetry that the combination of earth-abundant transition metal oxides leads to strong synergistic interactions modulating catalytic activity. The applicability of the prepared catalyst for reversible ORR/OER electrocatalysis is evaluated by means of a four-electrode configuration cell assembly comprising an integrated two-layer bifunctional ORR/OER electrode system with the individual layers dedicated for the ORR and the OER to prevent deactivation of the ORR activity as commonly observed in single-layer bifunctional ORR/OER electrodes after OER polarization. © 2019 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/adfm.201905992
  • 2020 • 334 Interstitial doping enhances the strength-ductility synergy in a CoCrNi medium entropy alloy
    Moravcik, I. and Hornik, V. and Minárik, P. and Li, L. and Dlouhy, I. and Janovska, M. and Raabe, D. and Li, Z.
    Materials Science and Engineering A 781 (2020)
    An equiatomic CoCrNi medium entropy alloy (MEA) with face-centered cubic (FCC) structure exhibits excellent combination of strength and ductility. Here we employ interstitial doping to enhance its mechanical performance. Interstitial CoCrNi MEAs with two different carbon contents, i.e., 0.5 at. % and 1 at. %, as well as a carbon-free CoCrNi reference MEA have been studied. The results show that up to 1 at. % carbon can be fully dissolved into the homogenized plus water-quenched FCC solid solution structure. Subsequent annealing leads to precipitation of nano-sized M23C6 type carbides which provide dispersion strengthening and enhanced strain hardening. The best combination of ultimate tensile strength of 1180 MPa at an elongation above 60% was obtained in fine grained CoCrNi doped with 0.5 at. % of carbon. Carbon alloying is also shown to significantly increase the lattice friction stress. Dislocation glide and mechanical twinning act as main deformation mechanisms. Thus, the joint contribution of multiple deformation mechanisms in the carbon-doped MEAs leads to significantly enhanced strength-ductility combinations compared to the carbon-free reference alloy, demonstrating that interstitial alloying can enhance the mechanical properties of MEAs. © 2020 Elsevier B.V.
    view abstractdoi: 10.1016/j.msea.2020.139242
  • 2020 • 333 Yield strength increase of a CoCrNi medium entropy alloy by interstitial nitrogen doping at maintained ductility
    Moravcik, I. and Hadraba, H. and Li, L. and Dlouhy, I. and Raabe, D. and Li, Z.
    Scripta Materialia 178 391-397 (2020)
    We show that interstitial nitrogen doping improves the tensile properties of a CoCrNi alloy. A material with 0.5 at% interstitial nitrogen was compared to a nitrogen-free CoCrNi alloy. The nitrogen-doped variant has a stable, single-phase face-centered cubic (FCC) lattice structure without nitrides, also after different annealing treatments (800–900 °C, 10 and 30 min). The nitrogen caused an increase in yield strength by 24–33% at identical ductility compared to the nitrogen-free material with similar grain size. The strengthening effect of nitrogen was explained in terms of the simultaneous increase of the lattice friction stress and of the Hall-Petch coefficient. © 2019
    view abstractdoi: 10.1016/j.scriptamat.2019.12.007
  • 2020 • 332 Moving cracks form white etching areas during rolling contact fatigue in bearings
    Morsdorf, L. and Mayweg, D. and Li, Y. and Diederichs, A. and Raabe, D. and Herbig, M.
    Materials Science and Engineering A 771 (2020)
    White etching cracks (WECs) and the associated white etching areas (WEAs) are responsible for failure of widely spread engineering applications such as bearings and railways. Although the phenomenon is known for more than 100 years, the underlying mechanisms are still a matter of debate. In this work, we thoroughly investigate a 100Cr6 wind turbine gearbox bearing after failure in service operation. Based on our findings from detailed microstructure characterization on multiple length scales we formulate a new consistent explanation for the formation of WEAs during rolling contact fatigue. We propose a mechanism of moving WECs - not only in terms of conventional crack propagation but also as a movement of the crack normal to its plane. During cyclic loading the crack continuously changes its position and leaves behind a severely plastically deformed area consisting of ferritic nano-grains, i.e. the WEAs. The atomic-scale delocalization of the crack plane in a single loading cycle adds up to micron-sized WEAs during repetitive loading/unloading. After the initial formation of a fatigue crack around inclusions, crack face rubbing occurs during compressive loading cycles. This leads to the formation of WEA by local severe plastic deformation. It also leads to partial cohesion of the abutting crack faces and material transport between them. As a result, the WEC opens at a slightly shifted position with respect to its former location during unloading. © 2019 Elsevier B.V.
    view abstractdoi: 10.1016/j.msea.2019.138659
  • 2020 • 331 Influence of aluminum surface treatment on tensile and fatigue behavior of thermoplastic-based hybrid laminates
    Mrzljak, S. and Trautmann, M. and Wagner, G. and Walther, F.
    Materials 13 (2020)
    Hybrid laminates consist of layers of different materials, which determine the mechanical properties of the laminate itself. Furthermore, the structure and interfacial properties between the layers play a key role regarding the performance under load and therefore need to be investigated in respect to industrial applicability. In this regard, a hybrid laminate comprised of AA6082 aluminum alloy sheets and glass and carbon fiber-reinforced thermoplastic (polyamide 6) is investigated in this study with a focus on the influence of aluminum surface treatment application on tensile and fatigue behavior. Four different aluminum surface treatments are discussed (adhesion promoter, mechanical blasting, phosphating, and anodizing), which were characterized by Laser Scanning Microscopy. After the thermal consolidation of the hybrid laminate under defined pressure, double notch shear tests and tensile tests were performed and correlated to determine the resulting interfacial strength between the aluminum sheet surface and the fiber-reinforced plastic, and its impact on tensile performance. To investigate the performance of the laminate under fatigue load in LCF and HCF regimes, a short-time procedure was applied consisting of resource-efficient instrumented multiple and constant amplitude tests. Digital image correlation, thermography, and hysteresis measurement methods were utilized to gain information about the aluminum surface treatment influence on fatigue damage initiation and development. The results show that fatigue-induced damage initiation, development, and mechanisms differ significantly depending on the applied aluminum surface treatment. The used measurement technologies proved to be suitable for this application and enabled correlations in between, showing that the hybrid laminates damage state, in particular regarding the interfacial bonding of the layers, can be monitored not just through visual recordings of local strain and temperature development, but also through stress-displacement hysteresis analysis. © 2020 by the authors.
    view abstractdoi: 10.3390/ma13143080
  • 2020 • 330 Unfolding the complexity of phonon quasi-particle physics in disordered materials
    Mu, S. and Olsen, R.J. and Dutta, B. and Lindsay, L. and Samolyuk, G.D. and Berlijn, T. and Specht, E.D. and Jin, K. and Bei, H. and Hickel, T. and Larson, B.C. and Stocks, G.M.
    npj Computational Materials 6 (2020)
    The concept of quasi-particles forms the theoretical basis of our microscopic understanding of emergent phenomena associated with quantum-mechanical many-body interactions. However, the quasi-particle theory in disordered materials has proven difficult, resulting in the predominance of mean-field solutions. Here, we report first-principles phonon calculations and inelastic X-ray and neutron-scattering measurements on equiatomic alloys (NiCo, NiFe, AgPd, and NiFeCo) with force-constant dominant disorder—confronting a key 50-year-old assumption in the Hamiltonian of all mean-field quasi-particle solutions for off-diagonal disorder. Our results have revealed the presence of a large, and heretofore unrecognized, impact of local chemical environments on the distribution of the species-pair-resolved force-constant disorder that can dominate phonon scattering. This discovery not only identifies a critical analysis issue that has broad implications for other elementary excitations, such as magnons and skyrmions in magnetic alloys, but also provides an important tool for the design of materials with ultralow thermal conductivities. © 2020, The Author(s).
    view abstractdoi: 10.1038/s41524-020-0271-3
  • 2020 • 329 Experimental investigation on a hole edge supported slab with punching shear reinforcement [Experimentelle Untersuchungen zu lochrandgestützten Flachdecken mit Durchstanzbewehrung]
    Mucha, R. and Welsch, T. and Schnellenbach-Held, M.
    Beton- und Stahlbetonbau 115 290-299 (2020)
    Experimental investigation on a hole edge supported slab with punching shear reinforcement. In order to prevent the punching of conventional flat slabs, various design concepts resting upon numerous experiments have been developed and enshrined in design codes. Hole edge supported flat slabs with a small load application area have not been considered in these design codes. Previous experimental and numerical investigations showed the different load bearing behavior of conventional flat slabs and hole edge supported flat slabs with a small load application area. It was found that, resulting from these differences and depending on the kind of hole edge support, the punching shear capacity of hole edge supported flat slabs is possibly overestimated when using existing design codes. Linked to this the question raised how the use of punching shear reinforcement will lead to an increased punching shear capacity of hole edge supported slabs. In order to answer this question, a tentative test analogous to previous experiments was carried out on a flat slab specimen with punching shear reinforcement in the form of stud rails. In the following, the results of this test are reported and compared to the findings of the previous investigations. © 2020, Ernst und Sohn. All rights reserved.
    view abstractdoi: 10.1002/best.201900095
  • 2020 • 328 Confinement of a three-dimensional organic molecule to two dimensions on a surface
    Müller, M. and Henzl, J. and Morgenstern, K.
    Chemical Physics Letters 738 (2020)
    We investigate the adsorption geometry of a three-dimensional organic molecule, anilino-nitro azobenzene, within hydrogen-bonded supramolecular structures on Au(111) by low temperature scanning tunneling microscopy. Therein, three conformational isomers exist, completely planar trans and cis-isomers and a non-planar, but surface adapted cis-isomer. The anilino-end of the molecule is planar for all isomers. In contrast, the nitro-end of the cis-isomer is only planar, if the nitro-end of the molecule forms hydrogen bonds. Our study pinpoints the subtle balance between molecule-substrate and molecule-molecule interaction in adsorption-induced bond-angle distortion that drive partial or full planarization of the molecule. © 2019 Elsevier B.V.
    view abstractdoi: 10.1016/j.cplett.2019.136906
  • 2020 • 327 Herpesviruses induce aggregation and selective autophagy of host signalling proteins NEMO and RIPK1 as an immune-evasion mechanism
    Muscolino, E. and Schmitz, R. and Loroch, S. and Caragliano, E. and Schneider, C. and Rizzato, M. and Kim, Y.-H. and Krause, E. and Juranić Lisnić, V. and Sickmann, A. and Reimer, R. and Ostermann, E. and Brune, W.
    Nature Microbiology 5 331-342 (2020)
    Viruses manipulate cellular signalling by inducing the degradation of crucial signal transducers, usually via the ubiquitin–proteasome pathway. Here, we show that the murine cytomegalovirus (Murid herpesvirus 1) M45 protein induces the degradation of two cellular signalling proteins, the nuclear factor κ-light-chain-enhancer of activated B cells (NF-κB) essential modulator (NEMO) and the receptor-interacting protein kinase 1 (RIPK1), via a different mechanism: it induces their sequestration as insoluble protein aggregates and subsequently facilitates their degradation by autophagy. Aggregation of target proteins requires a distinct sequence motif in M45, which we termed ‘induced protein aggregation motif’. In a second step, M45 recruits the retromer component vacuolar protein sorting 26B (VPS26B) and the microtubule-associated protein light chain 3 (LC3)-interacting adaptor protein TBC1D5 to facilitate degradation of aggregates by selective autophagy. The induced protein aggregation motif is conserved in M45-homologous proteins of several human herpesviruses, including herpes simplex virus, Epstein–Barr virus and Kaposi’s sarcoma-associated herpesvirus, but is only partially conserved in the human cytomegalovirus UL45 protein. We further show that the HSV-1 ICP6 protein induces RIPK1 aggregation and degradation in a similar fashion to M45. These data suggest that induced protein aggregation combined with selective autophagy of aggregates (aggrephagy) represents a conserved viral immune-evasion mechanism. © 2019, The Author(s), under exclusive licence to Springer Nature Limited.
    view abstractdoi: 10.1038/s41564-019-0624-1
  • 2020 • 326 Characterization of few-layer graphene aerosols by laser-induced incandescence
    Musikhin, S. and Fortugno, P. and Corbin, J.C. and Smallwood, G.J. and Dreier, T. and Daun, K.J. and Schulz, C.
    Carbon 167 870-880 (2020)
    Gas-phase synthesis is a promising route for producing large amounts of high quality few-layer graphene (FLG) nanoparticles economically, but optimizing these processes requires a detailed understanding of the formation kinetics, which in turn demands diagnostics for characterizing this material in situ. This work reports the first laser-induced incandescence measurements on FLG aerosols. Temporally- and spectrally-resolved incandescence signals from FLG particles are measured and used to calculate pyrometric temperatures. Differences between incandescence signals and pyrometric temperatures obtained from FLG and aerosolized soot nanoaggregates are attributed to the larger absorption cross-section and specific surface area of FLG compared to soot. LII signal intensity is found to vary linearly with particle number concentration measured independently by a condensation particle counter. Overall, these results demonstrate the potential for laser-induced incandescence to measure FLG nanoparticle mass (volume) fraction and active surface area in situ, as well as to differentiate graphene from other types of carbonaceous nanomaterials online. © 2020 Elsevier Ltd
    view abstractdoi: 10.1016/j.carbon.2020.05.052
  • 2020 • 325 Picosecond laser-induced surface structures on alloys in liquids and their influence on nanoparticle productivity during laser ablation
    Nadarajah, R. and Barcikowski, S. and Gökce, B.
    Optics Express 28 2909-2924 (2020)
    The productivity of nanoparticles formed by laser ablation of gold-silver and iron-gold alloy as well as copper and iron-nickel alloy targets in water is correlated with the formation of laser-induced surface structures. At a laser fluence optimized for maximum nanoparticle productivity, it is found that a binary alloy with an equimolar ratio forms laser-induced periodic surface structures (LIPSS) after ablation, if one of the constituent metals also form LIPSS. The ablation rate of nanoparticles linearly depends on the laser fluence if LIPSS is not formed, while a logarithmic trend and a decrease in productivity is evident when LIPSS is formed. To cancel LIPSS formation and recover from this decrease, a change to circularly polarized light is performed and an increase in nanoparticle productivity of more than 30% is observed. © 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
    view abstractdoi: 10.1364/OE.28.002909
  • 2020 • 324 Hungry for charge - How a beryllium scorpionate complex "eats" a weakly coordinating anion
    Naglav-Hansen, D. and Dzialkowski, K. and Tobey, B. and Wölper, C. and Jansen, G. and Schulz, S.
    Zeitschrift fur Naturforschung - Section B Journal of Chemical Sciences 75 503-508 (2020)
    We present the reaction of a tris(pyrazolyl) beryllium scorpionate (TpBe) complex with a weakly coordinating anion (WCA), which yields the heteroleptic complex TpBeOC(CF3)3 1 (TpBeORF). The product 1 has been characterized by multinuclear NMR spectroscopy (1H, 9Be, 13C) and single-crystal X-ray diffraction (scXRD). Quantum chemical calculations (DFT, NPA, LOL) were performed to study the bonding nature in 1. © 2020 Walter de Gruyter GmbH, Berlin/Boston 2020.
    view abstractdoi: 10.1515/znb-2020-0034
  • 2020 • 323 Coherence of a Driven Electron Spin Qubit Actively Decoupled from Quasistatic Noise
    Nakajima, T. and Noiri, A. and Kawasaki, K. and Yoneda, J. and Stano, P. and Amaha, S. and Otsuka, T. and Takeda, K. and Delbecq, M.R. and Allison, G. and Ludwig, Ar. and Wieck, A.D. and Loss, D. and Tarucha, S.
    Physical Review X 10 (2020)
    The coherence of electron spin qubits in semiconductor quantum dots suffers mostly from low-frequency noise. During the past decade, efforts have been devoted to mitigate such noise by material engineering, leading to substantial enhancement of the spin dephasing time for an idling qubit. However, the role of the environmental noise during spin manipulation, which determines the control fidelity, is less understood. We demonstrate an electron spin qubit whose coherence in the driven evolution is limited by high-frequency charge noise rather than the quasistatic noise inherent to any semiconductor device. We employ a feedback-control technique to actively suppress the latter, demonstrating a π-flip gate fidelity as high as 99.04±0.23% in a gallium arsenide quantum dot. We show that the driven-evolution coherence is limited by the longitudinal noise at the Rabi frequency, whose spectrum resembles the 1/f noise observed in isotopically purified silicon qubits. © 2020 authors. Published by the American Physical Society.
    view abstractdoi: 10.1103/PhysRevX.10.011060
  • 2020 • 322 Unravelling the nucleation, growth, and faceting of magnetite-gold nanohybrids
    Nalench, Y.A. and Shchetinin, I.V. and Skorikov, A.S. and Mogilnikov, P.S. and Farle, M. and Savchenko, A.G. and Majouga, A.G. and Abakumov, M.A. and Wiedwald, U.
    Journal of Materials Chemistry B 8 3886-3895 (2020)
    The chemical synthesis of nanoparticles with a preassigned size and shape is important for an optimized performance in any application. Therefore, systematic monitoring of the synthesis is required for the control and detailed understanding of the nucleation and growth of the nanoparticles. Here, we study Fe3O4-Au hybrid nanoparticles in detail using probes of the reaction mixture during synthesis and their thorough characterization. The proposed approach eliminates the problem of repeatability and reproducibility of the chemical synthesis and was carried out using laboratory equipment (standard transmission electron microscopy, X-ray diffraction, and magnetometry) for typically 10 μL samples instead of, for example, a dedicated synthesis and inspection at a synchrotron radiation facility. From the three independent experimental techniques we extract the nanoparticle size at 12 stages of the synthesis. These diameters show identical trends and good quantitative agreement. Two consecutive processes occur during the synthesis of Fe3O4-Au nanoparticles, the nucleation and the growth of spherical Fe3O4nanoparticles on the surface of Au seeds during the heating stage and their faceting towards octahedral shape during reflux. The final nanoparticles with sizes of 15 nm Fe3O4and 4 nm Au exhibit superparamagnetic behavior at ambient temperature. These are high-quality, close to stoichiometric Fe3O4nanocrystals with nearly volumetric magnetic behavior as confirmed by the presence of the Verwey transition. Understanding the processes occurring during the synthesis allows the nanoparticle size and shape to be adjusted, improving their capabilities in biomedical applications. © The Royal Society of Chemistry 2020.
    view abstractdoi: 10.1039/c9tb02721a
  • 2020 • 321 Impact of shock-tube facility-dependent effects on incident- and reflected-shock conditions over a wide range of pressures and Mach numbers
    Nativel, D. and Cooper, S.P. and Lipkowicz, T. and Fikri, M. and Petersen, E.L. and Schulz, C.
    Combustion and Flame 217 200-211 (2020)
    In real shock tubes, deviations from the ideal gas-dynamic behavior can affect experiments and complicate data analysis and interpretation. These non-ideal effects depend on the shock-tube geometry and therefore, results (e.g., ignition delay times) may vary between different experimental facilities. To clarify the influence of geometry and operating procedures, these effects were investigated in four geometrically different shock tubes located in two laboratories, Texas A&amp;M University and the University of Duisburg-Essen. Incident shock-wave attenuation and pressure rise (dp*/dt) were measured behind reflected shock waves over a 2.1–4.1 Mach number and a 0.1–3.0 MPa post-reflected-shock pressure range. A strong influence of the Mach number on dp*/dt was observed for all facilities and conditions, whereas only a slight influence was found for shock-wave attenuation. Both dp*/dt and attenuation were higher by about a factor of two for the shock tubes with approximately half the inner diameter (8.0 vs. 16.2 cm). These findings are analyzed through correlations with initial pressure, inner diameter, Mach number, and specific heat ratio. The implication of non-ideal effects on experiments with reactive mixtures and related combustion experiments is discussed. Extreme conditions of dp*/dt were derived from the correlations and used to understand the effects of an equivalent dT*/dt on simulated ignition delay times of two reactive systems (CH4/air and C7H16/air). It was found that smaller shock-tube diameters with respectively larger dp*/dt show shorter ignition delay times (especially at temperatures below 1000 K for the C7H16/air case). Therefore, the geometry constraints must be considered in simulations through dp*/dt inputs in the chemical kinetics simulation for the extreme cases to account for non-ideal effects. © 2020
    view abstractdoi: 10.1016/j.combustflame.2020.03.023
  • 2020 • 320 Experimental and Theoretical Investigation on Phase Formation and Mechanical Properties in Cr-Co-Ni Alloys Processed Using a Novel Thin-Film Quenching Technique
    Naujoks, D. and Schneider, M. and Salomon, S. and Pfetzing-Micklich, J. and Subramanyam, A.P.A. and Hammerschmidt, T. and Drautz, R. and Frenzel, J. and Kostka, A. and Eggeler, G. and Laplanche, G. and Ludwig, Al.
    ACS Combinatorial Science 22 232-247 (2020)
    The Cr-Co-Ni system was studied by combining experimental and computational methods to investigate phase stability and mechanical properties. Thin-film materials libraries were prepared and quenched from high temperatures up to 700 °C using a novel quenching technique. It could be shown that a wide A1 solid solution region exists in the Cr-Co-Ni system. To validate the results obtained using thin-film materials libraries, bulk samples of selected compositions were prepared by arc melting, and the experimental data were additionally compared to results from DFT calculations. The computational results are in good agreement with the measured lattice parameters and elastic moduli. The lattice parameters increase with the addition of Co and Cr, with a more pronounced effect for the latter. The addition of ∼20 atom % Cr results in a similar hardening effect to that of the addition of ∼40 atom % Co. Copyright © 2020 American Chemical Society.
    view abstractdoi: 10.1021/acscombsci.9b00170
  • 2020 • 319 Corrigendum to ‘Strong converse magnetoelectric effect in (Ba,Ca)(Zr,Ti)O3-NiFe2O4 multiferroics: A relationship between phase-connectivity and interface coupling’ (Acta Materialia (2018) 144 (305–313), (S1359645417309072), (10.1016/j.actamat.2017.10.048))
    Naveed-Ul-Haq, M. and Shvartsman, V.V. and Trivedi, H. and Salamon, S. and Webers, S. and Wende, H. and Hagemann, U. and Schröder, J. and Lupascu, D.C.
    Acta Materialia 187 91-92 (2020)
    The authors regret to inform the readers of Acta Materialia that Figure 10 of the article contains mistakes, none of which change the overall interpretation of the data nor the main point of the paper, but which should be rectified, nonetheless. 1. There was a calculation error during the conversion from applied voltage to the electric field and finally to the converse ME coupling coefficient. This was amended, with the correct data being shown in Table 1, to more clearly show the composition-dependent change to the reader. The overall interpretation remains unaffected, with the sample BCZTNFO30 displaying the highest ME coefficient.2. The value of the ME coefficient for the BCZTNFO50 sample was recorded at a different frequency (1.7 Hz) than the other compositions (8 Hz), which lead to a strongly deviating result for this sample. In order to obtain a dataset with consistent parameters, a single data point from the magnetic field dependent measurement regime was used, the results of which are shown in Figure 11 of the original manuscript. The slope and thus the converse ME coupling coefficient were calculated from a linear function between this point and the point of origin, which is justified by the fact that our measurement values show high stability and precision, making it highly unlikely for significant deviations to result from this approximation. The combination of parameters (magnetic field, temperature, electric field) represents the optimum for this sample, as also used for the original measurement, in addition to the now matching frequency of 8 Hz. This updated data point has also been included in Table 1 and Figure 1.3. Furthermore, the dataset of the BCZTNFO20 sample currently shown in Figure 10 of the manuscript is not the correct one, evident by the lower point density, higher amount of noise and the deviating frequency of 11 Hz. This dataset was replaced with the correct one for this sample, as shown in Figure 2, recorded at the same point density and frequency (8 Hz) as all the other samples of this set.From this updated set of data, new values of ME coefficients were calculated: 16.9(6) ps/m for BCZTNFO20, 90.1(6) ps/m for BCZTNFO30, 34.9(2) ps/m for BCZTNFO40 and 25.4 ps/m for BCZTNFO50. This does not change the conclusions that were drawn in the manuscript, as sample BCTNFO30 still has the highest value of the converse ME coupling coefficient. However, all of the values are increased at least twofold due to the corrected voltage conversion, clearly showing that this NFO-based sample set exhibits greatly improved ME response compared to previously used CFO-based materials. Furthermore, thanks to the now correct coefficient for BCZTNFO50, the composition dependent peak is much clearer, with the coupling coefficient consistently dropping when we move away from the optimum BCZTNFO30 composition to either side (see Figure 1), giving more merit to our original interpretation. The significant change of the measurement signal for BCZTNFO50 we observed when going from 1.7 Hz to 8 Hz is most probably caused by the fact that this sample has a lower resistivity of only 1 GΩ compared to the 30 GΩ of BCZTNFO30 (see Figure 3). This presumably induces a strong increase of frequency-dependence of the ME coefficient through Maxwell-Wagner relaxation due to the different dielectric permittivities of the two constituents that make up the sample, further exacerbated by the higher temperature at which this measurement was performed. These findings were discussed in greater detail in the dissertation of one of the co-authors [1]. Another minor correction needs to be made regarding Figure 1 of the original manuscript: There are typo mistakes on all four panels of Figure 1, where the phase of BCZT was incorrectly labeled as P4/mmm, which should be labeled as P4/mm. The same should be understood for Table 1 and wherever P4/mmm is mentioned in the text. The authors would like to apologise for any inconvenience caused. © 2020 Acta Materialia Inc.
    view abstractdoi: 10.1016/j.actamat.2020.01.054
  • 2020 • 318 Experimental and analytical analysis on the stacking sequence of composite pressure vessels
    Nebe, M. and Asijee, T.J. and Braun, C. and van Campen, J.M.J.F. and Walther, F.
    Composite Structures 247 (2020)
    The industrialization of fuel cell electric vehicles demands cost efficient storage solutions for hydrogen. While gaseous storage in type IV pressure vessels is currently the most mature technology, further structure optimization needs to be undertaken in order to meet cost requirements. This research investigates the effects of stacking sequence of composite pressure vessels regarding laminate quality, structural deformation and finally burst pressure. Therefore, a known laminate is studied on a subscale vessel geometry with changing stacking sequences. The specimens are pressurized in a specially designed chamber up to burst pressures of 166.11 MPa. Through a multisensor arrangement of stereometric systems, the deformation is tracked up to burst by using 3D digital image correlation. The experimental results show a difference of 67% in burst pressure between the investigated stacking sequences. Experimental cylinder strains and burst pressures are compared to results derived from 3D elasticity theory with implemented first ply failure criterion. Additionally, using X-ray computed tomography and acid digestion tests, insights about the distribution of fiber volume fraction and porosity are provided. For the investigated sequences in this research, the results show the considerable influence of stacking sequence on the laminate quality, the structural deformation and finally the burst pressure of composite pressure vessels. Moreover, it is shown that while the used 3D elasticity approach proved to be a useful tool for the prediction of strains and failure in the cylindrical section, discrepancies between prediction and experiment can arise based on preliminary failure occuring at the cylinder-dome transition. The results therefore emphasize the need for analytical and numerical analysis strategies to consider transition-related effects between cylinder and dome. © 2020 Elsevier Ltd
    view abstractdoi: 10.1016/j.compstruct.2020.112429
  • 2020 • 317 The axiomatic introduction of arbitrary strain tensors by Hans Richter – a commented translation of ‘Strain tensor, strain deviator and stress tensor for finite deformations’
    Neff, P. and Graban, K. and Schweickert, E. and Martin, R.J.
    Mathematics and Mechanics of Solids 25 1060-1080 (2020)
    We provide a faithful translation of Hans Richter’s important 1949 paper ‘Verzerrungstensor, Verzerrungsdeviator und Spannungstensor bei endlichen Formänderungen’ from its original German version into English, complemented by an introduction summarizing Richter’s achievements. © The Author(s) 2020.
    view abstractdoi: 10.1177/1081286519880594
  • 2020 • 316 Identification of Scale-Independent Material Parameters in the Relaxed Micromorphic Model Through Model-Adapted First Order Homogenization
    Neff, P. and Eidel, B. and d’Agostino, M.V. and Madeo, A.
    Journal of Elasticity 139 269-298 (2020)
    We rigorously determine the scale-independent short range elastic parameters in the relaxed micromorphic generalized continuum model for a given periodic microstructure. This is done using both classical periodic homogenization and a new procedure involving the concept of apparent material stiffness of a unit-cell under affine Dirichlet boundary conditions and Neumann’s principle on the overall representation of anisotropy. We explain our idea of “maximal” stiffness of the unit-cell and use state of the art first order numerical homogenization methods to obtain the needed parameters for a given tetragonal unit-cell. These results are used in the accompanying paper (d’Agostino et al. in J. Elast. 2019. Accepted in this volume) to describe the wave propagation including band-gaps in the same tetragonal metamaterial. © 2019, Springer Nature B.V.
    view abstractdoi: 10.1007/s10659-019-09752-w
  • 2020 • 315 A Stochastic Large-Signal Model for Printed High-Frequency Rectifiers Used for Efficient Generation of Higher Harmonics
    Neumann, K. and Kuhnel, L. and Langer, F. and Rennings, A. and Benson, N. and Schmechel, R. and Erni, D.
    IEEE Transactions on Microwave Theory and Techniques 68 2151-2160 (2020)
    This article investigates the stochastic Schottky barrier variations of printed distributed Schottky diodes consisting of a self-assembled arrangement of crystalline silicon microcones onto a metal layer. The microcone formation emerges from an inkjet printed Si nanoparticle film after laser sintering, yielding a Schottky diode when a corresponding top metallization is applied. The I - V characteristic and the voltage-dependent impedance of such diode is measured. By using the simulation software Advanced Design System (ADS), we develop a new scalable circuit model consisting of many different elementary diodes, which can explain the measured behavior. The elementary microcone diodes differ electrically in their barrier height, which is modeled as a stochastic process with a Gaussian distribution. A comparison between this model and a single diode model based on the thermionic field emission theory is conducted. We show that the distributed model outperforms the single-diode model in every regard and allows a prediction of the power levels of the harmonic frequency generation. Through more in-depth research, we find that a distributed barrier height leads to a smoother I - V curve, which in turn can lead to higher second and third harmonic power levels. By adjusting the barrier height distribution, the desired harmonics can be increased. © 1963-2012 IEEE.
    view abstractdoi: 10.1109/TMTT.2020.2990561
  • 2020 • 314 Microstructure characteristics of non-monodisperse quantum dots: On the potential of transmission electron microscopy combined with X-ray diffraction
    Neumann, S. and Menter, C. and Mahmoud, A.S. and Segets, D. and Rafaja, D.
    CrystEngComm 22 3644-3655 (2020)
    Although the concept of quantum confinement was introduced more than thirty years ago, a wide application of quantum dots is still limited by the fact that monodisperse quantum dots with controlled optoelectronic properties are typically synthesized on a relatively small scale. Larger scale synthesis techniques are usually not able to produce monodisperse nanoparticles yet. In this contribution, we illustrate the capability of the combination of transmission electron microscopy and X-ray diffraction to reveal detailed and scale-bridging information about the complex microstructure of non-monodisperse quantum dots, which is the first step towards further upscaling of the techniques for production of quantum dots with controlled properties. As a model system, CdSe quantum dots synthesized using an automated robotic hot-injection method at different temperatures were chosen. The combined microstructure analytics revealed the size and shape of the CdSe nanocrystals and the kind, density and arrangement of planar defects. The role of the planar defects in the particle coarsening by oriented attachment and the effect of the planar fault arrangement on the phase constitution, on the crystallographic coherence of the counterparts and on the optoelectronic properties are discussed. © The Royal Society of Chemistry 2020.
    view abstractdoi: 10.1039/d0ce00312c
  • 2020 • 313 In-depth particle localization with common-path digital holographic microscopy
    Neutsch, K. and Schnitzler, L. and Sun, J. and Tranelis, M.J. and Hofmann, M.R. and Gerhardt, N.C.
    Proceedings of SPIE - The International Society for Optical Engineering 11306 (2020)
    Three-dimensional particle tracking and localization has various applications in biology and medicine, where it may be used to analyze contrast agents, or in flow analysis, e.g. for localizing dust particles in a gas stream or to analyze turbulence in a flow. Moreover, particle localization finds applications in IT-security, where a random arrangement of particles in a transparent environment may represent a Physically Unclonable Function (PUF), which is interesting for individual labeling of high value goods. In conventional systems, such as bright field microscopy, a three-dimensional representation of particles is rather difficult, as it is challenging to acquire depth information about the sample. Quantitative phase imaging techniques provide phase and amplitude and thus in-depth information. Furthermore, they offer single shot measurements while providing images from multiple focal planes. Concerning the stability, which is an important aspect in localizing particles of diffraction limited size, common-path digital holographic microscopy is a reliable tool in particular in combination with a self-referencing system. In this article, we show a common-path digital holographic microscope for particle localization. Firstly, the setup is characterized with a test chart in order to evaluate lateral and axial resolution properties. Afterwards a sample with particles distributed in a three-dimensional medium is analyzed. For reconstruction of the holograms, we use the angular spectrum method, numerical phase unwrapping as well as Zernike polynomials for aberration correction. All in all, the system is able to achieve stable particle localization in 3D with lateral resolution in the sub-micrometer range and an axial sensitivity of at least 100 nm. © COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only.
    view abstractdoi: 10.1117/12.2545925
  • 2020 • 312 Numerical investigation of damage in single-step, two-step, and reverse deep drawing of rotationally symmetric cups from DP800 dual phase steel
    Nick, M. and Feuerhack, A. and Bergs, T. and Clausmeyer, T.
    Procedia Manufacturing 47 636-642 (2020)
    Damage evolution in deep drawing processes has an influence on the service properties of manufactured components. Knowledge and control of the damage state will therefore allow a reduction in safety factors and, consequently, in sheet thickness. To investigate the damage after deep drawing of rotationally symmetric cups, a LEMAITRE type damage model calibrated in previous works was used in the Finite Element (FE) simulation of the deep drawing process. Three process variants were investigated: single-step deep drawing, two-step deep drawing, and reverse deep drawing. The single-step deep drawing process was used as a reference to evaluate the damage evolution in two-step and reverse deep drawing. In both two-step and reverse deep drawing, the overall damage values did not decrease when compared to single-step deep drawing. However, in reverse deep drawing specifically, the location of maximum damage in the cup wall was moved from an area near the cup floor towards the edge of the cup. In real-life components, this control over the location of maximum damage will allow a tailoring of the damage state in the component to the expected service loads, thereby increasing service life or allowing a reduction in sheet thickness, respectively. © 2020 The Authors. Published by Elsevier Ltd.
    view abstractdoi: 10.1016/j.promfg.2020.04.195
  • 2020 • 311 Influence of the Feed Rate in the Single-Lip Deep Hole Drilling Process on the Surface Integrity of Steel Components
    Nickel, J. and Baak, N. and Walther, F. and Biermann, D.
    Lecture Notes in Mechanical Engineering 198-212 (2020)
    High strength steels like AISI 4140 are commonly used in many technical areas in which the mechanical properties of materials have to meet special requirements, for example, in the case of dynamically loaded parts. In the automotive industry increasing requirements due to lightweight design or energy efficiency lead to increasing demands on the mechanical and dynamic material strength. In response to this development, optimized machining processes are capable of improving the mechanical properties like fatigue performance by influencing the surface integrity of the machined components. In this paper, the influence of the single-lip deep hole drilling process on the surface integrity of quenched and tempered AISI 4140 specimens is analyzed in detail. Under variation of one of the main process parameters, the feed rate, the process output parameters such as cutting forces and the resulting condition of the machined surface and subsurface are determined. In combination with the analysis of the resulting hardness, microstructure and surface conditions of the machined surface, a magnetic Barkhausen noise (MBN) analysis with a custom-built sensor is applied and further developed. With this non-destructive technique, the surface integrity of the bore wall and the fatigue damage over the lifecycle of the part can be analyzed. The correlation of the surface integrity produced by the single-lip deep hole drilling process with the results from the micro-magnetic measurements are used to improve the possibility of predicting a components fatigue performance. © 2020, Springer Nature Singapore Pte Ltd.
    view abstractdoi: 10.1007/978-981-15-0054-1_21
  • 2020 • 310 Structure Defines Function: Clinically Relevant Mutations in ErbB Kinases
    Niggenaber, J. and Hardick, J. and Lategahn, J. and Rauh, D.
    Journal of Medicinal Chemistry 63 40-51 (2020)
    The ErbB receptor tyrosine kinase family members EGFR (epidermal growth factor receptor) and Her2 are among the prominent mutated oncogenic drivers of non-small cell lung cancer (NSCLC). Their importance in proliferation, apoptosis, and cell death ultimately renders them hot targets in cancer therapy. Small-molecule tyrosine kinase inhibitors seem well suited to be tailor-made therapeutics for EGFR mutant NSCLC; however, drug resistance mutations limit their success. Against this background, the elucidation and visualization of the three-dimensional structure of cancer-related kinases provide valuable insights into their molecular functions. This field has undergone a revolution because X-ray crystal structure determinations aided structure-based drug design approaches and clarified the effect of activating and resistance-conferring mutations. Here, we present an overview of important mutations affecting EGFR and Her2 and highlight their influence on the kinase domain conformations and active site accessibility. © 2019 American Chemical Society.
    view abstractdoi: 10.1021/acs.jmedchem.9b00964
  • 2020 • 309 An aminotetracyanocyclopentadienide system: Light-induced formation of a thermally stable cyclopentadienyl radical
    Nimax, P.R. and Zoller, F. and Blockhaus, T. and Küblböck, T. and Fattakhova-Rohlfing, D. and Sünkel, K.
    New Journal of Chemistry 44 72-78 (2020)
    Crystals of the aminotetracyanocyclopentadienyl radical were obtained from the reaction of CaCl2 with Ag[C5(CN)4(NH2)] and recrystallization in MeOH, performed in sunlight. The radical was characterized by X-ray diffraction, EPR and UV Vis spectroscopy as well as by cyclovoltammetry and DFT calculations. © 2019 The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.
    view abstractdoi: 10.1039/c9nj04354c
  • 2020 • 308 Random walk methods for Monte Carlo simulations of Brownian diffusion on a sphere
    Novikov, A. and Kuzmin, D. and Ahmadi, O.
    Applied Mathematics and Computation 364 (2020)
    This paper is focused on efficient Monte Carlo simulations of Brownian diffusion effects in particle-based numerical methods for solving transport equations on a sphere (or a circle). Using the heat equation as a model problem, random walks are designed to emulate the action of the Laplace–Beltrami operator without evolving or reconstructing the probability density function. The intensity of perturbations is fitted to the value of the rotary diffusion coefficient in the deterministic model. Simplified forms of Brownian motion generators are derived for rotated reference frames, and several practical approaches to generating random walks on a sphere are discussed. The alternatives considered in this work include projections of Cartesian random walks, as well as polar random walks on the tangential plane. In addition, we explore the possibility of using look-up tables for the exact cumulative probability of perturbations. Numerical studies are performed to assess the practical utility of the methods under investigation. © 2019 Elsevier Inc.
    view abstractdoi: 10.1016/j.amc.2019.124670
  • 2020 • 307 High-Throughput Characterization of Structural and Photoelectrochemical Properties of a Bi-Mo-W-O Thin-Film Materials Library
    Nowak, M. and Gutkowski, R. and Junqueira, J. and Schuhmann, W. and Ludwig, Al
    Zeitschrift fur Physikalische Chemie 234 835-845 (2020)
    A Bi-W-Mo-O thin-film materials library was fabricated by combinatorial reactive magnetron sputtering. The composition spread was investigated using high-throughput methods to determine crystalline phases, composition, morphology, optical properties, and photoelectrochemical performance. The aurivillius phase (Bi2O2)2+ (BiM(W1-NMoN)M-1O3M+1)2- is the predominantly observed crystal structure, indicating that the thin films in the library are solid solutions. With increasing amounts of Mo ≙ 7-22% the diffraction peak at 2θ = 28° ≙ [131] shifts due to lattice distortion, the photoelectrochemical activity is increasing up to a wavelength of 460 nm with an incident photon to current efficiency (IPCE) of 4.5%, and the bandgap decreases. A maximum photocurrent density of 31 μA/cm2 was measured for Bi31W62Mo7Oz at a bias potential of 1.23 V vs. RHE (0.1 M Na2SO4). © 2020 Wolfgang Schuhmann, Alfred Ludwig et al., published by De Gruyter, Berlin/Boston 2020.
    view abstractdoi: 10.1515/zpch-2019-1439
  • 2020 • 306 Thinking the future of membranes: Perspectives for advanced and new membrane materials and manufacturing processes
    Nunes, S.P. and Culfaz-Emecen, P.Z. and Ramon, G.Z. and Visser, T. and Koops, G.H. and Jin, W. and Ulbricht, M.
    Journal of Membrane Science 598 (2020)
    The state-of-the-art of membrane technology is characterized by a number of mature applications such as sterile filtration, hemodialysis, water purification and gas separation, as well as many more niche applications of successful membrane-based separation and processing of fluid mixtures. The membrane industry is currently employing a portfolio of established materials, mostly standard polymers or inorganic materials (not originally developed for membranes), and easily scalable manufacturing processes such as phase inversion, interfacial polymerization and coating. Innovations in membranes and their manufacturing processes must meet the desired intrinsic properties that determine selectivity and flux, for specific applications. However, tunable and stable performance, as well as sustainability over the entire life cycle of membrane products are becoming increasingly important. Membrane manufacturers are progressively required to share the carbon footprint of their membrane modules with their customers. Environmental awareness among the world's population is a growing phenomenon and finds its reflection in product development and manufacturing processes. In membrane technology one can see initial steps in this direction with the replacement of hazardous solvents, the utilization of renewable materials for membrane production and the reuse of membrane modules. Other examples include increasing the stability of organic membrane polymers and lowering the cost of inorganic membranes. In a long-term perspective, many more developments in materials science will be required for making new, advanced membranes. These include “tools” such as self-assembly or micro- and nano-fabrication, and “building blocks”, e.g. tailored block copolymers or 1D, 2D and 3D materials. Such membranes must be fabricated in a simpler manner and be more versatile than existing ones. In this perspective paper, a vision of such LEGO®-like membranes with precisely adjustable properties will be illustrated with, where possible, examples that already demonstrate feasibility. These include the possibility to switch properties using an external stimulus, adapting a membrane's selectivity to a given separation, or providing the ability to assemble, disassemble and reassemble the membrane on a suitable support as scaffold, in situ, in place and on-demand. Overall, it is foreseen that the scope of future membrane applications will become much wider, based on improved existing membrane materials and manufacturing processes, as well as the combination of novel, tailor-made “building blocks” and “tools” for the fabrication of next-generation membranes tuned to specific applications. © 2020 Elsevier B.V.
    view abstractdoi: 10.1016/j.memsci.2019.117761
  • 2020 • 305 Investigation of the influence of exposure time on the dual-curing reaction of RPU 70 during the DLS process and the resulting mechanical part properties
    Obst, P. and Riedelbauch, J. and Oehlmann, P. and Rietzel, D. and Launhardt, M. and Schmölzer, S. and Osswald, T.A. and Witt, G.
    Additive Manufacturing 32 (2020)
    Photo-differential scanning calorimetry (Photo-DSC), standard DSC and tensile testing are used in order to investigate the influence of different exposure times on the dual-curing reaction and mechanical properties of RPU 70 specimens produced by the additive manufacturing technology Digital Light Synthesis (DLS). A comparison of reaction enthalpies measured with a Photo-DSC of different exposure times followed by thermal curing and DSC experiments with different exposed DLS green products shows that the degree of thermal cross-linking of the two-component resin RPU 70 is determined by the preceding cross-linking reaction during photo-polymerization. A shorter exposure time of UV-light enhances the subsequent thermal cross-linking, while increased exposure reduces the effect of thermal curing in the second process step. Tensile testing results of specimen produced with custom-made print profiles on the DLS Carbon M2 with different exposure times show that mechanical characteristics such as tensile strength and elongation at break are strongly dependent on the degree of UV-cross-linking. The mechanical characteristics of DLS parts produced with the RPU 70 resin system can therefore be adapted to specific requirements and applications using these customized print profiles with different exposure times. © 2019 Elsevier B.V.
    view abstractdoi: 10.1016/j.addma.2019.101002
  • 2020 • 304 Thin-Film Microtensile-Test Structures for High-Throughput Characterization of Mechanical Properties
    Oellers, T. and Arigela, V.G. and Kirchlechner, C. and Dehm, G. and Ludwig, Al.
    ACS Combinatorial Science 22 142-149 (2020)
    A photolithographic process for the rapid fabrication of thin-film tensile-test structures is presented. The process is applicable to various physical vapor deposition techniques and can be used for the combinatorial fabrication of thin-film tensile-test structure materials libraries for the high-throughput characterization of mechanical properties. The functionality of the fabrication process and the feasibility of performing high-quality measurements with these structures are demonstrated with Cu tensile-test structures. In addition, the scalability from unary structures to libraries with compositional variations is demonstrated. Copyright © 2020 American Chemical Society.
    view abstractdoi: 10.1021/acscombsci.9b00182
  • 2020 • 303 Simulative analyses focused on the changes in cutting fluid supply of twist drills with a modified flank face geometry
    Oezkaya, E. and Bücker, M. and Biermann, D.
    International Journal of Mechanical Sciences 180 (2020)
    In this paper, a combination of Finite Element Method (FEM) and Computational Fluid Dynamics (CFD) simulations is presented. They were performed in order to develop an optimised flank face design for twist drills used for machining Inconel 718. This modification consists of a retraction behind the cutting edge which is ground into the tool flank face. It results in an increased free volume behind the cutting edge which can then be filled with cutting fluid, but in consequence, there also is a decrease in cutting material stabilising the cutting edge. Therefore, sufficient mechanical strength of the remaining cutting edge had to be ensured. At the same time, the increase in cutting fluid flow behind the cutting edge also helps to protect the remaining cutting material from the high temperatures which occur when machining nickel-based alloys such as Inconel 718. After the simulation-based findings had been transferred to real tools modified by grinding, subsequent experimental investigations could show that twist drills with a modified flank face reached tool life up to five times longer compared to standard tools. © 2020
    view abstractdoi: 10.1016/j.ijmecsci.2020.105650
  • 2020 • 302 Mathematical analysis of transmission properties of electromagnetic meta-materials
    Ohlberger, M. and Schweizer, B. and Urban, M. and Verfurth, B.
    Networks and Heterogeneous Media 15 29-56 (2020)
    We study time-harmonic Maxwell's equations in meta-materials that use either perfect conductors or high-contrast materials. Based on known effective equations for perfectly conducting inclusions, we calculate the transmission and re ection coecients for four different geometries. For highcontrast materials and essentially two-dimensional geometries, we analyze parallel electric and parallel magnetic elds and discuss their potential to exhibit transmission through a sample of meta-material. For a numerical study, one often needs a method that is adapted to heterogeneous media; we consider here a Heterogeneous Multiscale Method for high contrast materials. The qualitative transmission properties, as predicted by the analysis, are conrmed with numerical experiments. The numerical results also underline the applicability of the multiscale method. © 2020 American Institute of Mathematical Sciences.
    view abstractdoi: 10.3934/nhm.2020002
  • 2020 • 301 Defect spectroscopy on the dielectric material aluminum oxide
    Oing, D. and Geller, M. and Stahl, L. and Kerski, J. and Lorke, A. and Wöhrl, N.
    Scientific Reports 10 (2020)
    A method for defect characterization is presented that allows to measure the activation energy, capture cross-section, and defect density in dielectric materials. This is exemplarily performed on aluminum oxide thin films deposited on hydrogen-terminated diamond. During the measurement, samples were illuminated using a 405 nm laser, charging the defects while simultaneously measuring the surface conductivity of the diamond at different temperatures. By applying the standard boxcar evaluation known from deep-level transient spectroscopy, we found five different defect levels in Al 2O 3. One can be identified as substitutional silicon in aluminum oxide, while the others are most likely connected to either aluminum interstitials or carbon and nitrogen impurities. © 2020, The Author(s).
    view abstractdoi: 10.1038/s41598-020-69240-3
  • 2020 • 300 The influence of 30 years outdoor weathering on the durability of hydrophobic agents applied on obernkirchener sandstones
    Orlowsky, J. and Braun, F. and Groh, M.
    Buildings 10 (2020)
    The durability of eleven different water repellents applied on one sandstone type was studied after a long-term weathering at seven different locations in Germany. By measuring colour changes, it could be shown that the formation of black crusts, the deposition of particles and biogenic growth caused a gradual darkening as well as significant changes in total colour over time. Additionally, the water absorption behaviour was investigated with two different methods: applying a low pressure using the pipe method and capillary water absorption measurements from a wet underlay. Afterwards, the test results were analysed with four different evaluation methods: calculation of the protection degree from pipe method and capillary water absorption, determination of the velocity of water uptake during capillary water absorption and calculation of the damaged depth of the stone surface using single-sided NMR technique. The growing damaged depth leads to an increase of the water uptake velocity and to a decrease of the protection degree of the applied hydrophobing agents. Three protective agents based on isobutyltrimethoxysilane showed already after two years of outdoor weathering a clear loss of performance, which significantly increased after 30 years of exposure. © 2020 by the authors.
    view abstractdoi: 10.3390/buildings10010018
  • 2020 • 299 Analysis of elastic rolling stand deformation and interstand tension effects on section faults of hot rolled wire rod and bars Untersuchung der Einflüsse der elastischen Gerüstauffederung und der Längsspannungen auf die Querschnittsabweichungen beim Warmwalzen von Draht und Stabstahl
    Overhagen, C. and Braun, R. and Deike, R.
    Technisches Messen 87 343-348 (2020)
    The present work aims at the modelling and simulation of the hot rolling process for wire rod and bars. After the fundamentals of plasticity, which are essential for the understanding of the process characteristics have been described, typical section deviations that can be expected in wire rod and bar mills are calculated with help of a numerical simulation model. The model allows the calculation of section shapes under the influence of elastic rolling stand deformations and interstand tensions. From this computational assessment of section faults, the necessity of inline measurement and process control for wire rod and bar mills is shown. This work is part of the PIREF project which incorporates the development of sensors, control systems and process models in order to control the dimensional accuracy of hot rolled wire rod and bars. The metal forming process model, as described here is used internally as a model for the static and kinematic interactions in the rolling process inside of the control model. © 2020 Walter de Gruyter GmbH, Berlin/Boston.
    view abstractdoi: 10.1515/teme-2019-0130
  • 2020 • 298 Heterobifunctional Rotaxanes for Asymmetric Catalysis
    Pairault, N. and Zhu, H. and Jansen, D. and Huber, A. and Daniliuc, C.G. and Grimme, S. and Niemeyer, J.
    Angewandte Chemie - International Edition 59 5102-5107 (2020)
    Heterobifunctional rotaxanes serve as efficient catalysts for the addition of malonates to Michael acceptors. We report a series of four different heterobifunctional rotaxanes, featuring an amine-based thread and a chiral 1,1′-binaphthyl-phosphoric-acid-based macrocycle. High-level DFT calculations provided mechanistic insights and enabled rational catalyst improvements, leading to interlocked catalysts that surpass their non-interlocked counterparts in terms of reaction rates and stereoselectivities. © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
    view abstractdoi: 10.1002/anie.201913781
  • 2020 • 297 Grain boundary segregation, phase formation, and their influence on the coercivity of rapidly solidified SmF e11Ti hard magnetic alloys
    Palanisamy, D. and Ener, S. and Maccari, F. and Schäfer, L. and Skokov, K.P. and Gutfleisch, O. and Raabe, D. and Gault, B.
    Physical Review Materials 4 (2020)
    SmFe11Ti-based alloys have potential as permanent magnet materials; however, until now, crystallographically textured bulk permanent magnets have not yet been produced from this alloy system. This is partly due to the lack of information on the morphology and composition of grain boundary phases present in the Fe-rich Sm-Fe-Ti alloys. Here we investigated the microstructure of a Sm1.25Fe11Ti alloy by using correlative transmission electron microscopy and atom-probe tomography, combined with magneto-optical Kerr effect (MOKE) probing to relate the material's micro- and nanostructure to its properties. The grains of the Sm(Fe,Ti)12 matrix phase are separated by grain boundaries exhibiting a different composition over 3-4 nm width. They contain >75at% of the ferromagnetic element Fe, with an enrichment of Sm of up to 16.6 at% and a depletion in Ti, down to approx. 3.4 at%. We believe that the grain boundary is ferromagnetic at room temperature, which makes the magnetic decoupling of the grains practically impossible, which, in turn, leads to a low coercivity of SmFe11Ti-based alloys. MOKE measurements reveal the strong ferromagnetic coupling across the grain boundary, causing the nucleation of reversal magnetic domains when exposed to low magnetic fields. In a triple-junction area we identified three other ferromagnetic phases: Sm3(Fe,Ti)29,SmFe2, and Fe2Ti. These details bring out the scope of further adjustment of the coercivity in the Sm-Fe-Ti alloy system by grain boundary segregation engineering through the reduction of the presence of ferromagnetic phases to ensure a magnetic decoupling of the micrometer-sized Sm(Fe,Ti)12 grains. © 2020 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the ""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. Open access publication funded by the Max Planck Society.
    view abstractdoi: 10.1103/PhysRevMaterials.4.054404
  • 2020 • 296 Transferability of process parameters in laser powder bed fusion processes for an energy and cost efficient manufacturing
    Pannitz, O. and Sehrt, J.T.
    Sustainability (Switzerland) 12 1-14 (2020)
    In the past decade, the sales of metal additive manufacturing systems have increased intensely. In particular, PBF-LB/M systems (powder bed fusion of metals using a laser-based system) represent a technology of great industrial interest, in which metallic powders are molten and solidified layer upon layer by a focused laser beam. This leads to a simultaneous increase in demand for metallic powder materials. Due to adjusted process parameters of PBF-LB/M systems, the powder is usually procured by the system's manufacturer. The requirement and freedom to process different feedstocks in a reproducible quality and the economic and ecological factors involved are reasons to have a closer look at the differences between the quality of the provided metallic powders. Besides, different feedstock materials require different energy inputs, allowing a sustainable process control to be established. In this work, powder quality of stainless steel 1.4404 and the effects during the processing of metallic powders that are nominally the same were analyzed and the influence on the build process followed by the final part quality was investigated. Thus, a correlation between morphology, particle size distribution, absorptivity, flowability, and densification depending on process parameters was demonstrated. Optimized exposure parameters to ensure a more sustainable and energy and cost-efficient manufacturing process were determined. © 2020 by the authors.
    view abstractdoi: 10.3390/su12041565
  • 2020 • 295 Poling and annealing of piezoelectric Poly(Vinylidene fluoride) micropillar arrays
    Pariy, I.O. and Ivanova, A.A. and Shvartsman, V.V. and Lupascu, D.C. and Sukhorukov, G.B. and Surmeneva, M.A. and Surmenev, R.A.
    Materials Chemistry and Physics 239 (2020)
    This work reports on the effect of calcination and poling processes on the crystalline phase and piezoresponse of poly(vinylidene fluoride) (PVDF) micropillar arrays. PVDF micropillars were prepared by the imprinting method, heated and treated with high-voltage poling. The effect of the treatment conditions on the crystallization behaviour and the piezoelectric properties of the patterned PVDF films was investigated by piezoresponse force microscopy (PFM), Fourier transform infrared spectroscopy (FTIR), and differential scanning calorimetry (DSC). DSC data show that poling of the PVDF micropillars increases the crystallinity of the polymer from 12% to 22.7%. FTIR measurements of PVDF films show that the calcination and poling processes affect the γ to β phase transformation. In the imprinted and annealed samples, the γ phase was predominant (58% and 46%, respectively). For the poled samples, up to 42% of the β phase was found. Piezoelectric measurements using PFM showed that the poled PVDF micropillars possess a much higher piezoelectric coefficient (29 pm/V) compared to the annealed sample (10 pm/V). The piezoresponse of the PVDF micropillar arrays is thus substantially enhanced by poling. © 2019 Elsevier B.V.
    view abstractdoi: 10.1016/j.matchemphys.2019.122035
  • 2020 • 294 Laser-induced surface relief nanocrowns as a manifestation of nanoscale Rayleigh-Plateau hydrodynamic instability
    Pavlov, D.V. and Gurbatov, S.O. and Kudryashov, S.I. and Gurevich, E.L. and Kuchmizhak, A.A.
    Applied Surface Science 511 (2020)
    Nanoscale hydrodynamic instability of ring-like molten rims around ablative microholes produced in nanometer-thick silver and gold films by tightly focused nanosecond (ns) laser pulses was experimentally explored in terms of laser pulse energy and film thickness. These parametric dependencies of basic instability characteristics - order and period of the resulting nanocrowns - were analyzed, revealing its apparently Rayleigh-Plateau character, as compared to much less consistent possible van der Waals and impact origins. Along with fundamental importance, these findings will put forward ns pulsed laser ablation as an alternative facile inexpensive table-top approach to study such hydrodynamic instabilities developing at ns temporal and nanometer spatial scales as well as to produce unique plasmon-active hierarchical surface morphologies applicable for chemo- and biosensing. © 2020 Elsevier B.V.
    view abstractdoi: 10.1016/j.apsusc.2020.145463
  • 2020 • 293 An approach to evaluate the strengthening requirement of concrete bridges - Evaluation of structural and damage data using methods of the risk assessment [Ein Ansatz zur Bewertung des Verstärkungsbedarfs von Massivbrücken: Auswertung von Bauwerks- und Schadensdaten mit Methoden der Risikobewertung]
    Peeters, M. and Schnellenbach-Held, M.
    Beton- und Stahlbetonbau 115 280-289 (2020)
    An approach to evaluate the strengthening requirement of concrete bridges – Evaluation of structural and damage data using methods of the risk assessment. Due to the condition of the bridges and the constantly increasing traffic load, there is an enormous need for bridge strengthening relevant to bearing capacity in addition to the replacement construction. Therefore, the available financial resources for the maintenance of the bridge stock and for the maintenance of a functioning infrastructure must be used efficiently and effectively within the maintenance management. The presented approach to determine the basic strengthening requirement of concrete bridges provides a further feature for the decision-making which bridge categories require a strengthening and which bridges can be considered as rather uncritical with regard to a strengthening. The determination is made on the basis of risk assessment methods and on the basis of real damage data on superstructures of about 1,240 concrete bridges in the course of federal trunk roads. The risk assessment was carried out on the one hand by using level-frequency diagrams, considering the risk matrices, and on the other hand by using risk numbers, each separately for the assessment attribute of stability and durability. © 2020, Ernst und Sohn. All rights reserved.
    view abstractdoi: 10.1002/best.201900096
  • 2020 • 292 Design of a 1000 L pilot-scale airlift bioreactor for nitrification with application of a three-phase hydrodynamic mathematical model and prediction of a low liquid circulation velocity
    Pelivanoski, B. and Detmann, B. and Ooms, K. and Winkler, M. and Vasyukova, E. and Denecke, M.
    Chemical Engineering Research and Design 153 257-262 (2020)
    In this study, a 1000 L pilot scale internal loop airlift bioreactor was operated and compared to a mathematical model to determine the best design for optimal supply of oxygen for nitrification and sufficient air for biomass fluidization. The design model is based on parameters such as geometry, carrier density, and airflow of the 1000 L pilot scale bioreactor. The model predicts a range of superficial air velocities (0.009–0.013 m/s) under which the airlift bioreactor was fluidized. Three superficial air velocities (0.009 m/s, 0.011 m/s and 0.013 m/s) were experimentally tested in the pilot plant and the obtained circulation velocities were compared with the predicted design scenarios. The predicted velocity was in agreement with the measured velocity. The aim of the mathematical model and the calculations of different geometry scenarios was to define the optimal geometry design for the physical model. The results show that the ratio of the cross-sectional area between the riser and the downcomer of 1.33 resulted in the lowest superficial liquid velocity of 0.076 m/s in the riser at a relative low superficial air velocity of 0.011 m/s and a carrier density of 1030 kg/m3. This bioreactor design enabled longest retention time of particles in the oxygenated riser. © 2019 Institution of Chemical Engineers
    view abstractdoi: 10.1016/j.cherd.2019.10.018
  • 2020 • 291 Interactive online modules - Impacting the individual learning success in engineering mechanics?
    Pelz, M. and Lang, M. and Özmen, Y. and Schröder, J. and Walker, F. and Müller, R.
    SEFI 47th Annual Conference: Varietas Delectat... Complexity is the New Normality, Proceedings 862-870 (2020)
    The collaborative research project FUNDAMENT (Improvement of individual learning success by the use of digital media in civil engineering) of the University of Duisburg-Essen and the Technical University of Kaiserslautern, which is funded by the German Federal Ministry of Education and Research (BMBF), has developed and evaluated so-called interactive online modules (IOM) for the introductory phase of the civil engineering studies (EM), more precise in the courses of engineering mechanics. The IOM consists of learning videos, online exercises and online forums. These IOM have the objective of increasing the individual learning success of civil engineering students and therefore to minimize the high drop-out rates in engineering sciences in the long term. In this paper the effectiveness of the IOM will be determined on the basis of a longitudinal study in a classic experimental and control group design in the EM 1 course in the first semester. Paper and pencil tests (multiple-choice-single-select test design - multi-matrix) are applied at two measuring points (MP): beginning (MP 1) and end of the first semester (MP 2). Initial analyses of the data are presenting an increase of the mean person ability (dichotomous Rasch model) regarding the achieved scores at both MP. The cause of this increase cannot be defined exactly, an allocation to the IOM is currently not possible due to a small number of participants in the control group. © 2020 SEFI 47th Annual Conference: Varietas Delectat... Complexity is the New Normality, Proceedings. All rights reserved.
    view abstract
  • 2020 • 290 Early stage phase separation of AlCoCr0.75Cu0.5FeNi high-entropy powder at the nanoscale
    Peter, N.J. and Duarte, M.J. and Liebscher, C.H. and Srivastava, V.C. and Uhlenwinkel, V. and Jägle, E.A. and Dehm, G.
    Journal of Alloys and Compounds 820 (2020)
    High entropy alloys are generally considered to be single phase material. This state is, however, typically a non-equilibrium state after fabrication at high cooling rates. Phase constitution after fabrication or heat treatment is mostly known for isothermal annealing only and for casts as well as rapidly quenched alloys. Knowledge on early phase separation stages of high entropy alloys and their mechanisms are missing so far. Here, we present results on phase separation at intermediate cooling rates, by characterization of gas atomized powder of the AlCoCr0.75Cu0.5FeNi alloy. Although investigation by X-ray diffraction and Electron Backscatter Diffraction indicates a single-phase nature of the powder particles, aberration-corrected scanning transmission electron microscopy and atom probe tomography reveal a nanoscale phase separation into Ni–Al-rich B2 and Fe–Cr-rich A2 regions as well as a high number density of 3.1 × 1024 Cu-rich clusters per m3 in the B2 matrix. The observed phase separation and cluster formation are linked to spinodal decomposition and nucleation processes, respectively. The study highlights that adequate characterization techniques need to be chosen when making statements about phase stability and structural evolution in compositionally complex alloys. © 2019 The Authors
    view abstractdoi: 10.1016/j.jallcom.2019.153149
  • 2020 • 289 Multitask-learning for the extraction of avascular necrosis of the femoral head in MRI
    Pham, D.D. and Dovletov, G. and Serong, S. and Landgraeber, S. and Jäger, M. and Pauli, J.
    Informatik aktuell 150-155 (2020)
    In this paper, we present a 2D deep multitask learning approach for the segmentation of small structures on the example of avascular necrosis of the femoral head (AVNFH) in MRI. It consists of one joint encoder and three separate decoder branches, each assigned to its own objective. We propose using a reconstruction task to initially pre-train the encoder and shift the objective towards a second necrosis segmentation task in a reconstruction-dependent loss adaptation manner. The third branch deals with the rough localization of the topographical neighborhood of possible femoral necrosis areas. Its output is used to emphasize the roughly approximated location of the segmentation branch’s output. The evaluation of the segmentation performance of our architecture on coronal T1-weighted MRI volumes shows promising improvements compared to a standard U-Net implementation. © Springer Fachmedien Wiesbaden GmbH, ein Teil von Springer Nature 2020.
    view abstractdoi: 10.1007/978-3-658-29267-6_31
  • 2020 • 288 U-net in constraint few-shot settings: enforcing few-sample-fitting for faster convergence of u-net for femur segmentation in X-ray
    Pham, D.D. and Lausen, M. and Dovletov, G. and Serong, S. and Landgraeber, S. and Jäger, M. and Pauli, J.
    Informatik aktuell 280-285 (2020)
    In this paper, we investigate the feasibility of using a standard U-Net for Few-Shot segmentation tasks in very constraint settings. We demonstrate on the example of femur segmentation in X-ray images, that a U-Net architecture only needs few samples to generate accurate segmentations, if the images and the structure of interest only show little variance in appearance and perspective. This is often the case in medical imaging. We also present a novel training strategy for the UNet, leveraging U-Net’s Few-Shot capability for inter-patient consistent protocols. We propose repeatedly enforcing Few-Sample-Fitting the network for faster convergence. The results of our experiments indicate that incrementally fitting the network to an increasing sample set can lead to faster network convergence in constraint few-shot settings. © Springer Fachmedien Wiesbaden GmbH, ein Teil von Springer Nature 2020.
    view abstractdoi: 10.1007/978-3-658-29267-6_62
  • 2020 • 287 Burst-like reverse martensitic transformation during heating, cooling and under isothermal conditions in stabilized Ni-Ti-Nb
    Picornell, C. and Pons, J. and Paulsen, A. and Frenzel, J. and Kaminskii, V. and Sapozhnikov, K. and Van Humbeeck, J. and Kustov, S.
    Scripta Materialia 180 23-28 (2020)
    To reveal mechanisms of martensite stabilization by prestrain in shape memory alloys, details of reverse martensitic transformation (MT) in prestrained Ni45Ti46Nb9 alloy were studied using calorimetry, dilatometry and resistivity. The first reverse MT is burst-like and is shifted to higher temperatures by ~120 K as compared to the nominal MT. During thermal cycling approaching the first reverse MT, stabilized martensite shows “forbidden” behaviours like burst-like reverse MT not during heating, but during cooling and under isothermal conditions. These unusual effects are attributed to non-thermoelastic nature of the first reverse MT in stabilized martensite under high chemical driving force. © 2020 Acta Materialia Inc.
    view abstractdoi: 10.1016/j.scriptamat.2020.01.018
  • 2020 • 286 Non-standing spin-waves in confined micrometer-sized ferromagnetic structures under uniform excitation
    Pile, S. and Feggeler, T. and Schaffers, T. and Meckenstock, R. and Buchner, M. and Spoddig, D. and Zingsem, B. and Ney, V. and Farle, M. and Wende, H. and Ohldag, H. and Ney, A. and Ollefs, K.
    Applied Physics Letters 116 (2020)
    A non-standing characteristic of directly imaged spin-waves in confined micrometer-sized ultrathin Permalloy (Ni 80 Fe 20) structures is reported along with evidence of the possibility to alter the observed state by modifications to the sample geometry. Using micromagnetic simulations, the presence of the spin-wave modes excited in the Permalloy stripes along with the quasi-uniform modes was observed. The predicted spin-waves were imaged in direct space using time resolved scanning transmission X-ray microscopy, combined with a ferromagnetic resonance excitation scheme (STXM-FMR). STXM-FMR measurements revealed a non-standing characteristic of the spin-waves. Also, it was shown by micromagnetic simulations and confirmed using STXM-FMR results that the observed characteristic of the spin-waves can be influenced by the local magnetic fields in different sample geometries. © 2020 Author(s).
    view abstractdoi: 10.1063/1.5139881
  • 2020 • 285 Chemical complexity, microstructure and martensitic transformation in high entropy shape memory alloys
    Piorunek, D. and Frenzel, J. and Jöns, N. and Somsen, C. and Eggeler, G.
    Intermetallics 122 (2020)
    High entropy shape memory alloys (HESMAs) represent a relatively young class of functional materials. They show a reversible martensitic phase transformation which allows to exploit shape memory effects at relatively high temperatures. HESMAs represent ordered complex solid-solutions. Their high temperature phase is of B2 type, and various elements (e.g. Ni, Cu, Ti, Zr, Hf) occupy sites in specific sub-lattices. In the present work, we study the processing and the functional properties of HESMAs. We study effects of chemical complexity on solidification microstructures and martensitic transformations. Binary, ternary, quaternary, quinary and senary model alloys were investigated using advanced microstructural and thermal characterization methods. The results show that element partitioning during solidification results in a redistribution of individual alloy elements in dendritic/interdendritic regions. Surprisingly, the atomic ratios of the two groups of elements which occupy the Ni- (first group: Ni, Cu and Pd) and Ti-sub-lattice (second group: Ti, Zr, Hf) are maintained. This allows the material to form martensite throughout its heterogeneous microstructure. The effect of chemical complexity/composition on martensite start temperatures, MS, is discussed on the basis of valence electron concentrations, cV. Some of the alloys fall into MS(cV)-regimes which are uncommon for classical Ni-Ti-based shape memory alloys. In the present work, a new HESMA of type NiCuPdTiZrHf was identified which has the potential to provide maximum shape memory strains close to 15%. © 2020
    view abstractdoi: 10.1016/j.intermet.2020.106792
  • 2020 • 284 Adsorption of toluene-3,4-dithiol on silver islands investigated by surface-enhanced Raman spectroscopy
    Plaickner, J. and Speiser, E. and Chandola, S. and Esser, N. and Singh, D.K.
    Journal of Raman Spectroscopy 51 788-794 (2020)
    The adsorbtion of toluene-3,4-dithiol (TDT) molecules on Ag islands was investigated with surface-enhanced Raman spectroscopy (SERS). The SERS spectrum was compared with the ordinary Raman spectrum of TDT, and differences in spectral features were discussed with the support of density functional theory calculations. The disappearance of all the S–H-related bands in the SERS spectrum indicates that TDT adsorbs on Ag via both thiol groups, as supported by the emergence of a weak band at 223 cm−1 attributed to Ag–S stretching. Signatures of Ag–S–C complexes suggest that the adsorption is partially disordered. The observation of all the vibrational modes involving the methyl group indicates that the methyl group is exposed, offering new functionalization possibilities of the surface. © 2020 John Wiley & Sons, Ltd.
    view abstractdoi: 10.1002/jrs.5843
  • 2020 • 283 Conduction-based thermally assisted micromilling process for cutting difficult-to-machine materials
    Platt, T. and Meijer, A. and Biermann, D.
    Journal of Manufacturing and Materials Processing 4 (2020)
    The increasing demand for complex and wear-resistant forming tools made of difficult-to-machine materials requires efficient manufacturing processes. In terms of high-strength materials; highly suitable processes such as micromilling are limited in their potential due to the increased tool loads and the resulting tool wear. This promotes hybrid manufacturing processes that offer approaches to increase the performance. In this paper; conduction-based thermally assisted micromilling using a prototype device to homogeneously heat the entire workpiece is investigated. By varying the workpiece temperature by 20 °C < TW < 500 °C; a highly durable high-speed steel (HSS) AISI M3:2 (63 HRC) and a hot-work steel (HWS) AISI H11 (53 HRC) were machined using PVD-TiAlN coated micro-end milling tools (d = 1 mm). The influence of the workpiece temperature on central process conditions; such as tool wear and achievable surface quality; are determined. As expected; the temporary thermal softening of the materials leads to a reduction in the cutting forces and; thus; in the resulting tool wear for specific configurations of the thermal assistance. While only minor effects are detected regarding the surface topography; a significant reduction in the burr height is achieved. © 2020 by the authors.
    view abstractdoi: 10.3390/jmmp4020034
  • 2020 • 282 One-step preparation of antifouling polysulfone ultrafiltration membranes via modification by a cationic polyelectrolyte based on polyacrylamide
    Plisko, T.V. and Bildyukevich, A.V. and Burts, K.S. and Ermakov, S.S. and Penkova, A.V. and Kuzminova, A.I. and Dmitrenko, M.E. and Hliavitskaya, T.A. and Ulbricht, M.
    Polymers 12 (2020)
    A novel method for one-step preparation of antifouling ultrafiltration membranes via a non-solvent induced phase separation (NIPS) technique is proposed. It involves using aqueous 0.05-0.3 wt. % solutions of cationic polyelectrolyte based on a copolymer of acrylamide and 2-acryloxyethyltrimethylammonium chloride (Praestol 859) as a coagulant in NIPS. Asystematic study of the effect of the cationic polyelectrolyte addition to the coagulant on the structure, performance and antifouling stability of polysulfone membranes was carried out. The methods for membrane characterization involved scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), contact angle and zeta-potential measurements and evaluation of the permeability, rejection and antifouling performance in human serum albumin solution and surface water ultrafiltration. It was revealed that in the presence of cationic polyelectrolyte in the coagulation bath, its concentration has a major influence on the rate of &quo