Scientific Output

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

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

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  • 2022 • 275 [NiFe]-(Oxy)Sulfides Derived from NiFe2O4 for the Alkaline Hydrogen Evolution Reaction
    Tetzlaff, D. and Alagarasan, V. and Simon, C. and Siegmund, D. and Puring, K.J. and Marschall, R. and Apfel, U.-P.
    Energies 15 (2022)
    The development of noble-metal-free electrocatalysts is regarded as a key factor for realizing industrial-scale hydrogen production powered by renewable energy sources. Inspired by nature, which uses Fe-and Ni-containing enzymes for efficient hydrogen generation, Fe/Ni-containing chalcogenides, such as oxides and sulfides, received increasing attention as promising electrocatalysts to produce hydrogen. We herein present a novel synthetic procedure for mixed Fe/Ni (oxy)sulfide materials by the controlled (partial) sulfidation of NiFe2O4 (NFO) nanoparticles in H2S-containing atmospheres. The variation in H2S concentration and the temperature allows for a precise control of stoichiometry and phase composition. The obtained sulfidized materials (NFS) catalyze the hydrogen evolution reaction (HER) with increased activity in comparison to NFO, up to −10 and −100 mA cm−2 at an overpotential of approx. 250 and 450 mV, respectively. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/en15020543
  • 2022 • 274 3D atomic-scale imaging of mixed Co-Fe spinel oxide nanoparticles during oxygen evolution reaction
    Xiang, W. and Yang, N. and Li, X. and Linnemann, J. and Hagemann, U. and Ruediger, O. and Heidelmann, M. and Falk, T. and Aramini, M. and DeBeer, S. and Muhler, M. and Tschulik, K. and Li, T.
    Nature Communications 13 (2022)
    The three-dimensional (3D) distribution of individual atoms on the surface of catalyst nanoparticles plays a vital role in their activity and stability. Optimising the performance of electrocatalysts requires atomic-scale information, but it is difficult to obtain. Here, we use atom probe tomography to elucidate the 3D structure of 10 nm sized Co2FeO4 and CoFe2O4 nanoparticles during oxygen evolution reaction (OER). We reveal nanoscale spinodal decomposition in pristine Co2FeO4. The interfaces of Co-rich and Fe-rich nanodomains of Co2FeO4 become trapping sites for hydroxyl groups, contributing to a higher OER activity compared to that of CoFe2O4. However, the activity of Co2FeO4 drops considerably due to concurrent irreversible transformation towards CoIVO2 and pronounced Fe dissolution. In contrast, there is negligible elemental redistribution for CoFe2O4 after OER, except for surface structural transformation towards (FeIII, CoIII)2O3. Overall, our study provides a unique 3D compositional distribution of mixed Co-Fe spinel oxides, which gives atomic-scale insights into active sites and the deactivation of electrocatalysts during OER. © 2022, The Author(s).
    view abstractdoi: 10.1038/s41467-021-27788-2
  • 2022 • 273 3D modeling of generalized Newtonian fluid flow with data assimilation using the least-squares finite element method
    Averweg, S. and Schwarz, A. and Schwarz, C. and Schröder, J.
    Computer Methods in Applied Mechanics and Engineering 392 (2022)
    In this contribution we present a least-squares finite element formulation to model steady-state flow of incompressible, non-Newtonian fluids in three dimensions including data assimilation. The approach is based on the incompressible Navier–Stokes equations and the nonlinear viscosity is considered by means of the Carreau–Yasuda viscosity model, which can account for shear-thickening and shear-thinning behavior of generalized Newtonian fluids. We outline the procedure how to integrate given data into the numerical solution of flow problems without additional computational cost using the least-squares FEM. Assimilation of experimental data provides the opportunity to reduce model errors resulting in a solution which more closely approximates reality. Furthermore, the preprocessing of the available data using Kriging interpolation is also described briefly. The presented formulation is first validated by investigating the flow in a cube with an exact solution without data assimilation. Convergence is evaluated based on the error in velocities and pressure compared to the exact solution. Then the effect of data assimilation is shown by modeling blood flow through a carotid bifurcation model and integrating data either along lines or over entire cross-sectional areas. The improvement of the numerical solution by means of data assimilation is revealed by comparing the calculated velocity profiles with experimental and numerical reference values. © 2022
    view abstractdoi: 10.1016/j.cma.2022.114668
  • 2022 • 272 A chiral one-dimensional atom using a quantum dot in an open microcavity
    Antoniadis, N.O. and Tomm, N. and Jakubczyk, T. and Schott, R. and Valentin, S.R. and Wieck, A.D. and Ludwig, A. and Warburton, R.J. and Javadi, A.
    npj Quantum Information 8 (2022)
    In a chiral one-dimensional atom, a photon propagating in one direction interacts with the atom; a photon propagating in the other direction does not. Chiral quantum optics has applications in creating nanoscopic single-photon routers, circulators, phase-shifters, and two-photon gates. Here, we implement chiral quantum optics using a low-noise quantum dot in an open microcavity. We demonstrate the non-reciprocal absorption of single photons, a single-photon diode. The non-reciprocity, the ratio of the transmission in the forward-direction to the transmission in the reverse direction, is as high as 10.7 dB. This is achieved by tuning the photon-emitter coupling in situ to the optimal operating condition (β = 0.5). Proof that the non-reciprocity arises from a single quantum emitter lies in the photon statistics—ultralow-power laser light propagating in the diode’s reverse direction results in a highly bunched output (g(2)(0) = 101), showing that the single-photon component is largely removed. © 2022, The Author(s).
    view abstractdoi: 10.1038/s41534-022-00545-z
  • 2022 • 271 A Compact Fiber-Coupled NIR/MIR Laser Absorption Instrument for the Simultaneous Measurement of Gas-Phase Temperature and CO, CO2, and H2O Concentration
    Shi, L. and Endres, T. and Jeffries, J.B. and Dreier, T. and Schulz, C.
    Sensors 22 (2022)
    A fiber-coupled, compact, remotely operated laser absorption instrument is developed for CO, CO2, and H2O measurements in reactive flows at the elevated temperatures and pressures expected in gas turbine combustor test rigs with target pressures from 1–25 bar and temperatures of up to 2000 K. The optical engineering for solutions of the significant challenges from the ambient acoustic noise (~120 dB) and ambient test rig temperatures (60 °C) are discussed in detail. The sensor delivers wavelength-multiplexed light in a single optical fiber from a set of solid-state lasers ranging from diodes in the near-infrared (~1300 nm) to quantum cascade lasers in the mid-infrared (~4900 nm). Wavelength-multiplexing systems using a single optical fiber have not previously spanned such a wide range of laser wavelengths. Gas temperature is inferred from the ratio of two water vapor transitions. Here, the design of the sensor, the optical engineering required for simultaneous fiber delivery of a wide range of laser wavelengths on a single optical line-of-sight, the engineering required for sensor survival in the harsh ambient environment, and laboratory testing of sensor performance in the exhaust gas of a flat flame burner are presented. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/s22031286
  • 2022 • 270 A Concept for Using Road Wetness Information in an All-Wheel-Drive Control
    Warth, G. and Sieberg, P. and Unterreiner, M. and Schramm, D.
    Energies 15 (2022)
    This paper presents a concept for using road wetness information in an all-wheel-drive (AWD) control that distributes drive torques in the longitudinal direction. Driving on wet roads requires special attention. Not only does the road surface friction coefficient decrease, but driving dynamics targets must be adjusted to prevent vehicle instability under wet conditions. As an exemplary application, the otherwise generic control concept is implemented on an AWD vehicle with a torque-on-demand transfer case. Therefore, the AWD topology of a drive train with a torque-on-demand transfer case is analysed in advance in terms of occurring torques and rotational speeds. In the fol-lowing, the vehicle dynamics goals for driving in wet road conditions are described—divided into primary and secondary goals. Starting from a state-of-the art AWD control, an adaptive control strategy is derived by superimposing a wetness coordination unit. With the knowledge of occurring road wetness, this unit adapts newly introduced parameters in order to meet the target driving behaviour under wet conditions. Lastly, the derived AWD control is implemented into a 14-DOF, non-linear vehicle model in Matlab/Simulink, which is used as a virtual plant. The performance of the developed concept is assessed by the driving maneuver “Power On Cornering“ (PON), which means an acceleration out of steady-state circular motion. As its essential benefit, the AWD control enables a maximum spread between driving stability, agility and traction under combined dynamics when using wetness information. The newly introduced wetness coordination unit uses only a few additional and physically interpretable key parameters for this purpose, without significantly increasing the controller complexity. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/en15041284
  • 2022 • 269 A cracking oxygen story: A new view of stress corrosion cracking in titanium alloys
    Joseph, S. and Kontis, P. and Chang, Y. and Shi, Y. and Raabe, D. and Gault, B. and Dye, D.
    Acta Materialia 227 (2022)
    Titanium alloys can suffer from halide-associated stress corrosion cracking at elevated temperatures e.g., in jet engines, where chlorides and Ti-oxide promote the cracking of water vapour in the gas stream, depositing embrittling species at the crack tip. Here we report, using isotopically-labelled experiments, that crack tips in an industrial Ti-6Al-2Sn-4Zr-6Mo alloy are strongly enriched (>5 at.%) in oxygen from the water vapour, far greater than the amounts (0.25 at.%) required to embrittle the material. Surprisingly, relatively little hydrogen (deuterium) is measured, despite careful preparation and analysis. Therefore, we suggest that a combined effect of O and H leads to cracking, with O playing a vital role, since it is well-known to cause embrittlement of the alloy. In contrast it appears that in α + β Ti alloys, it may be that H may drain away into the bulk owing to its high solubility in β-Ti, rather than being retained in the stress field of the crack tip. Therefore, whilst hydrides may form on the fracture surface, hydrogen ingress might not be the only plausible mechanism of embrittlement of the underlying matrix. This possibility challenges decades of understanding of stress-corrosion cracking as being related solely to the hydrogen enhanced localised plasticity (HELP) mechanism, which explains why H-doped Ti alloys are embrittled. This would change the perspective on stress corrosion embrittlement away from a focus purely on hydrogen to also consider the ingress of O originating from the water vapour, insights critical for designing corrosion resistant materials. © 2022 Acta Materialia Inc.
    view abstractdoi: 10.1016/j.actamat.2022.117687
  • 2022 • 268 A CutFEM based framework for numerical simulations of machine driven tunnels with arbitrary alignments
    Bui, H.-G. and Schillinger, D. and Zendaki, Y. and Meschke, G.
    Computers and Geotechnics 144 (2022)
    We describe a novel computational framework based on the cut finite element method (CutFEM) for process-oriented simulation in mechanized tunneling. The framework incorporates all relevant components required for the simulation of the tunnel advance process, namely the ground, the staged installation of the lining support, the tail void grouting and the tunnel boring machine. We demonstrate that CutFEM concepts can significantly facilitate the modeling, discretization and coupling of the different components, while maintaining the same accuracy as the standard boundary-fitted finite element method. The proposed CutFEM technology, which is being applied and investigated in the context of advancement simulations in mechanized tunneling for the first time, enables the seamless analysis of an arbitrary number of different tunnel alignment variants on the same structured background mesh without the need to set up a new model for each variant. This is a shift of paradigm in simulation-supported tunnel design, as the CutFEM based framework considerably facilitates a direct integration of geometric, building information and simulation models in early stages of a tunnel project. The simulation model allows for the damage assessment of the buildings during tunnel advancement with regards to different excavation scenarios, as shown in the numerical examples in this paper. © 2022 Elsevier Ltd
    view abstractdoi: 10.1016/j.compgeo.2022.104637
  • 2022 • 267 A hybrid approach for the efficient computation of polycrystalline yield loci with the accuracy of the crystal plasticity finite element method
    Biswas, A. and Kalidindi, S.R. and Hartmaier, A.
    Modelling and Simulation in Materials Science and Engineering 30 (2022)
    Direct experimental evaluation of the anisotropic yield locus (YL) of a given material, representing the zeros of the material's yield function in the stress space, is arduous. It is much more practical to determine the YL by combining limited measurements of yield strengths with predictions from numerical models based on microstructural features such as the orientation distribution function (ODF; also referred to as the crystallographic texture). For the latter, several different strategies exist in the current literature. In this work, we develop and present a new hybrid method that combines the numerical efficiency and simplicity of the classical crystallographic yield locus (CYL) method with the accuracy of the computationally expensive crystal plasticity finite element method (CPFEM). The development of our hybrid approach is presented in two steps. In the first step, we demonstrate for diverse crystallographic textures that the proposed hybrid method is in good agreement with the shape of the predicted YL estimated by either CPFEM or experiments, even for pronounced plastic anisotropy. It is shown that the calibration of only two parameters of the CYL method with only two yield stresses for different load cases obtained from either CPFEM simulations or experiments produces a reliable computation of the polycrystal YL for diverse crystallographic textures. The accuracy of the hybrid approach is evaluated using the results from the previously established CPFEM method for the computation of the entire YL and also experiments. In the second step, the point cloud data of stress tensors on the YL predicted by the calibrated CYL method are interpolated within the deviatoric stress space by cubic splines such that a smooth yield function can be constructed. Since the produced YL from the hybrid approach is presented as a smooth function, this formulation can potentially be used as an anisotropic yield function for the standard continuum plasticity methods commonly used in finite element analysis. © 2022 The Author(s). Published by IOP Publishing Ltd.
    view abstractdoi: 10.1088/1361-651X/ac4a24
  • 2022 • 266 A model for lime consolidation of porous solids
    Detmann, B. and Gavioli, C. and Krejčí, P. and Lamač, J. and Namlyeyeva, Y.
    Nonlinear Analysis: Real World Applications 65 (2022)
    We propose a mathematical model describing the process of filling the pores of a building material with lime water solution with the goal to improve the consistency of the porous solid. Chemical reactions produce calcium carbonate which glues the solid particles together at some distance from the boundary and strengthens the whole structure. The model consists of a 3D convection–diffusion system with a nonlinear boundary condition for the liquid and for calcium hydroxide, coupled with the mass balance equations for the chemical reaction. The main result consists in proving that the system has a solution for each initial data from a physically relevant class. A 1D numerical test shows a qualitative agreement with experimental observations. © 2021 Elsevier Ltd
    view abstractdoi: 10.1016/j.nonrwa.2021.103483
  • 2022 • 265 A pressure-jump study on the interaction of osmolytes and crowders with cubic monoolein structures
    Surmeier, G. and Paulus, M. and Schneider, E. and Dogan, S. and Tolan, M. and Nase, J.
    Soft Matter 18 990-998 (2022)
    Many vital processes that take place in biological cells involve remodeling of lipid membranes. These processes take place in a milieu that is packed with various solutes, ranging from ions and small organic osmolytes to proteins and other macromolecules, occupying about 30% of the available volume. In this work, we investigated how molecular crowding, simulated with the polymer polyethylene glycol (PEG), and the osmolytes urea and trimethylamine-N-oxide (TMAO) affect the equilibration of cubic monoolein structures after a phase transition from a lamellar state induced by an abrupt pressure reduction. In absence of additives, swollen cubic crystallites form after the transition, releasing excess water over several hours. This process is reflected in a decreasing lattice constant and was monitored with small angle X-ray scattering. We found that the osmotic pressure exerted by PEG and TMAO, which are displaced from narrow inter-bilayer spaces, accelerates the equilibration. When the radius of gyration of the added PEG was smaller than the radius of the water channels of the cubic phase, the effect became more pronounced with increasing molecular weight of the polymers. As the release of hydration water from the cubic structures is accompanied by an increasing membrane curvature and a reduction of the interface between lipids and aqueous phase, urea, which has a slight affinity to reside near membrane surfaces, stabilized the swollen crystallites and slowed down the equilibration dynamics. Our results support the view that cellular solutes are important contributors to dynamic membrane processes, as they can accelerate dehydration of inter-bilayer spaces and promote or counteract membrane curvature. This journal is © The Royal Society of Chemistry.
    view abstractdoi: 10.1039/d1sm01425k
  • 2022 • 264 A rank-one convex, nonpolyconvex isotropic function on with compact connected sublevel sets
    Voss, J. and Ghiba, I.-D. and Martin, R.J. and Neff, P.
    Proceedings of the Royal Society of Edinburgh Section A: Mathematics (2022)
    According to a 2002 theorem by Cardaliaguet and Tahraoui, an isotropic, compact and connected subset of the group of invertible - - matrices is rank-one convex if and only if it is polyconvex. In a 2005 Journal of Convex Analysis article by Alexander Mielke, it has been conjectured that the equivalence of rank-one convexity and polyconvexity holds for isotropic functions on as well, provided their sublevel sets satisfy the corresponding requirements. We negatively answer this conjecture by giving an explicit example of a function which is not polyconvex, but rank-one convex as well as isotropic with compact and connected sublevel sets. Copyright © The Author(s), 2022. Published by Cambridge University Press on behalf of The Royal Society of Edinburgh.
    view abstractdoi: 10.1017/prm.2021.9
  • 2022 • 263 A thermodynamic framework for unified continuum models for the healing of damaged soft biological tissue
    Zuo, D. and He, Y. and Avril, S. and Yang, H. and Hackl, K.
    Journal of the Mechanics and Physics of Solids 158 (2022)
    When they are damaged or injured, soft biological tissues are able to self-repair and heal. Mechanics is critical during the healing process, as the damaged extracellular matrix (ECM) tends to be replaced with a new undamaged ECM supporting homeostatic stresses. Computational modeling has been commonly used to simulate the healing process. However, there is a pressing need to have a unified thermodynamics theory for healing. From the viewpoint of continuum damage mechanics, some key parameters related to healing processes, for instance, the volume fraction of newly grown soft tissue and the growth deformation, can be regarded as internal variables and have related evolution equations. This paper is aiming to establish this unified framework inspired by thermodynamics for continuum damage models for healing of soft biological tissues, in which we introduce for the first time the coupled description of damage/healing and growth/remodeling based on thermodynamic considerations. Therefore, this new model is more concise and offers a universal approach to simulate the healing process. Three numerical examples are provided to demonstrate the effectiveness of the proposed model, which are in good agreement with the existing works, including an application for balloon angioplasty in an arteriosclerotic artery with a fiber cap. © 2021
    view abstractdoi: 10.1016/j.jmps.2021.104662
  • 2022 • 262 A thermo-viscoplasticity model for metals over wide temperature ranges- application to case hardening steel
    Oppermann, P. and Denzer, R. and Menzel, A.
    Computational Mechanics 69 541-563 (2022)
    In this contribution, a model for the thermomechanically coupled behaviour of case hardening steel is introduced with application to 16MnCr5 (1.7131). The model is based on a decomposition of the free energy into a thermo-elastic and a plastic part. Associated viscoplasticity, in terms of a temperature-depenent Perzyna-type power law, in combination with an isotropic von Mises yield function takes respect for strain-rate dependency of the yield stress. The model covers additional temperature-related effects, like temperature-dependent elastic moduli, coefficient of thermal expansion, heat capacity, heat conductivity, yield stress and cold work hardening. The formulation fulfils the second law of thermodynamics in the form of the Clausius–Duhem inequality by exploiting the Coleman–Noll procedure. The introduced model parameters are fitted against experimental data. An implementation into a fully coupled finite element model is provided and representative numerical examples are presented showing aspects of the localisation and regularisation behaviour of the proposed model. © 2021, The Author(s).
    view abstractdoi: 10.1007/s00466-021-02103-4
  • 2022 • 261 Ab initio calculation of the magnetic Gibbs free energy of materials using magnetically constrained supercells
    Mendive-Tapia, E. and Neugebauer, J. and Hickel, T.
    Physical Review B 105 (2022)
    We present a first-principles approach for the computation of the magnetic Gibbs free energy of materials using magnetically constrained supercell calculations. Our approach is based on an adiabatic approximation of slowly varying local moment orientations, the so-called finite-temperature disordered local moment picture. It describes magnetic phase transitions and how electronic and/or magnetostructural mechanisms generate a discontinuous (first-order) character. We demonstrate that the statistical mechanics of the local moment orientations can be described by an affordable number of supercell calculations containing noncollinear magnetic configurations. The applicability of our approach is illustrated by firstly studying the ferromagnetic state in bcc Fe. We then investigate the temperature-dependent properties of a triangular antiferromagnetic state stabilizing in two antiperovskite systems Mn3AN (A=Ga, Ni). Our calculations provide the negative thermal expansion of these materials as well as the ab initio origin of the discontinuous character of the phase transitions, electronic and/or magnetostructural, in good agreement with experiment. © 2022 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the "https://creativecommons.org/licenses/by/4.0/"Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Open access publication funded by the Max Planck Society.
    view abstractdoi: 10.1103/PhysRevB.105.064425
  • 2022 • 260 Ab initio investigations of point and complex defect structures in B2-FeAl
    Sözen, H.I. and Mendive-Tapia, E. and Hickel, T. and Neugebauer, J.
    Physical Review Materials 6 (2022)
    We study single-site and two-site defect structures in B2-type Fe-Al alloys by means of density functional theory supercell calculations. The defect formation energies are calculated as functions of the chemical potential, which are used to obtain the dependence of the defect concentrations on Al content at different temperatures. We also examine the converging behavior of the formation energies with respect to the supercell size to study the corresponding limit of dilute defects. The effect of magnetism is investigated by considering nonmagnetic, ferromagnetic, and paramagnetic states, calculations for the latter showing that the magnitude of the local magnetic moments strongly impacts the defect formation energies. The methodological studies are used to provide explanations for the wide spread of defect formation energies reported by experiments and other theoretical investigations. Based on these insights, the stability of the B2-FeAl structure as a function of Al concentration is obtained and discussed. © 2022 authors. Published by the American Physical Society.published article's title, journal citation, and DOI. Open access publication funded by the Max Planck Society.
    view abstractdoi: 10.1103/PhysRevMaterials.6.023603
  • 2022 • 259 About the effectiveness of a hydrophobic surface treatment of Baumberger Sandstones
    Orlowsky, J. and Groh, M. and Braun, F.
    Environmental Earth Sciences 81 (2022)
    The Baumberger Sandstone, a sandy limestone, is used since the Middle Ages as a building material not only in the surrounding Münster region of North Rhine-Westphalia (Germany), where it is quarried since to date. To prevent the ingress of water and reduce weathering processes conservation methods, mostly in form of organosilicon compounds, were used. This study deals with the performance of applied hydrophobing agents on Baumberger Sandstone samples and their influence on the weathering processes during long-term exposure. The samples were exposed at several locations in Germany to different climatic conditions for up to 24 years. Afterwards, investigations concerning the water absorption behaviour and the degree of superficial damages were carried out. With an evaluation method on basis of NMR measurements, a very low and uneven distributed effective hydrophobic zone could be detected. This caused an ingress of water in the uppermost part and a progressive weathering of investigated natural stones. Thus the hydrophobic surface treatment did not lead to a significant decrease of weathering or damaging processes. Based on these results a hydrophobic surface treatment of Baumberger Sandstone seems not to be suitable. © 2022, The Author(s).
    view abstractdoi: 10.1007/s12665-022-10186-2
  • 2022 • 258 Adaptation of the Chemical Percolation Devolatilization Model for Low Temperature Pyrolysis in a Fluidized Bed Reactor
    Pielsticker, S. and Ontyd, C. and Kreitzberg, T. and Hatzfeld, O. and Schiemann, M. and Scherer, V. and Kneer, R.
    Combustion Science and Technology 194 417-434 (2022)
    In the present study, the CPD model originally developed based on predictions from heated grid (HGR) and entrained flow (EFR) experiments, has been adapted to analyze pyrolysis kinetics in a small-scale fluidized bed reactor. Impacts of particle feed, particle heat up as well as tar cracking reactions in the gas phase are considered. Furthermore, an optimized solver structure allows a time step independent solution and enables the use of implicit methods. A comparison with experimental results is undertaken for pulverized Rhenish lignite fuel particles in the temperature range from 673 to 973 K in N2 atmosphere. The comparison between simulated and experimentally derived volatile release rates reveals a good agreement, indicating that the high temperature derived kinetic parameters from HRG and EFR experiments can be extrapolated to lower temperatures. Nevertheless, discrepancies in the tar to light gas ratio occur with the proposed model implementation. © 2022 Taylor & Francis Group, LLC.
    view abstractdoi: 10.1080/00102202.2019.1682433
  • 2022 • 257 AI-methods for the integration of structural design knowledge in early phases of the building design process [KI-Methoden zur Integration tragwerksplanerischen Wissens in frühe Phasen des Gebäudeentwurfsprozesses]
    Schnellenbach-Held, M. and Steiner, D.
    Bautechnik 99 191-198 (2022)
    AI-methods for the integration of structural design knowledge in early phases of the building design process. The early integration of the structural design expertise in the building planning process allows an efficient support of the involved highly complex decision-making. A knowledge-based system (KBS) is developed for the supply and the usage of suitable engineering experience knowledge. This performs an evaluation of bearing structures and the proposal of design options through the application of development level dependent fuzzy knowledge bases and related inference systems. The levels of development include the assessment of structures based on the possibility theory and comprises concepts of adaptive detailing. An imitation of the human decision-making behavior is achieved by the use of an easily understandable formulation of rules following the Modus Ponens and Fuzzy Logic inference mechanisms. Acquisition of applicable knowledge is based on parametric studies covering the calculation and design of structural elements that initially are carried out for reinforced concrete components. Considerable value ranges are determined based on practical experiences. Additionally, mechanisms for the consideration of uncertain parameters are provided. The resulting (KBS) system enables an efficiency increase in the early planning process. © 2022, Ernst und Sohn. All rights reserved.
    view abstractdoi: 10.1002/bate.202000090
  • 2022 • 256 Aluminum Diethylphosphinate as a Flame Retardant for Polyethylene: Investigation of the Pyrolysis and Combustion Behavior of PE/AlPi-Mixtures
    Lau, S. and Gonchikzhapov, M. and Paletsky, A. and Shmakov, A. and Korobeinichev, O. and Kasper, T. and Atakan, B.
    Combustion and Flame 240 (2022)
    The popularity of organic polymers despite their high flammability forces the introduction of flame retardants (FR) such as metal phosphinates into the combustible material. The thermal behavior of aluminum diethylphosphinate (AlPi) as FR in the widely used polymer ultra-high molecular weight polyethylene (UHMWPE) is investigated here. The study focuses on the effect of the FR on the gas phase activity when a polymer is pyrolyzed or burned. For this purpose, the fast pyrolysis of AlPi was investigated by differential mass-spectrometric thermal analysis (DMSTA). Also, the thermal and chemical structures of diffusion flames of UHMWPE + AlPi specimens were investigated using micro thermocouples and molecular beam mass spectrometry, respectively. Small amounts of AlPi (2.5 wt.%) decrease the gas temperature significantly by a maximum of 155 K related to FR-free polymer flames, indicating a retardancy effect of the additive on the flame. From the results of subsequent limiting oxygen index (LOI) tests, it is obvious that a PE burn-up cannot be achieved in a self-sustained flame when an additive content above 10 wt.% is used as FR. In the mass-spectrometric studies, the phosphorus-containing species produced in the pyrolysis experiments (DMSTA) of the neat AlPi as well as the species which are formed in flames during combustion experiments can be detected. In the flames, the concentration of the phosphorus containing compounds peaks at low heights above the polymer surface which indicate a gas phase activity of AlPi or its pyrolysis products. Besides a charring layer on top of the burning surface could be noticed. The use of AlPi as a FR for UHMWPE shows flame retardant effects in both the condensed and the gas phase. © 2022 The Combustion Institute
    view abstractdoi: 10.1016/j.combustflame.2022.112006
  • 2022 • 255 Amphiphilic polymer conetworks with ideal and non-ideal swelling behavior demonstrated by small angle X-ray scattering
    Wilhelm, S.A. and Maricanov, M. and Brandt, V. and Katzenberg, F. and Tiller, J.C.
    Polymer 242 (2022)
    Amphiphilic polymer conetworks (APCNs) combine two incompatible properties within one material by featuring two interconnected independently swelling nanophases. To simultaneously address both properties, the APCNs need to be swellable in orthogonal solvents without changing their nanostructure. This has not been demonstrated yet. Two novel APCN families applying the macromeric cross-linker approach have been synthesized by cross-linking the hydrophilic poly(2-hydroxyethyl acrylate) (PHEA) or poly(N,N-dimethylacrylamide) (PDMA), respectively, with the hydrophobic poly(2-(1-ethylpentyl)-2-oxazoline) (PEPOx). For the first time, the APCN PHEA-l-PEPOx could be proven to swell in two orthogonal solvents, water and n-heptane, retaining its nanostructure in a broad range of compositions by using small-angle X-ray scattering (SAXS). PDMA-l-PEPOx seems to show a similar behavior according to swelling experiments, but SAXS revealed that particularly the PDMA phase reversibly changes its nanostructure upon swelling. Thus, the structural integrity of APCNs upon swelling depends on the topology as well as the chemical nature of the polymer phases. Altogether, SAXS experiments are required and well suited to judge changes in nanostructure upon swelling of APCNs. © 2022
    view abstractdoi: 10.1016/j.polymer.2022.124582
  • 2022 • 254 An investigation of the influence of integration of steel heat treatment and brazing process on the microstructure and performance of vacuum-brazed cemented carbide/steel joints
    Tillmann, W. and Ulitzka, T. and Dahl, L. and Wojarski, L. and Ulitzka, H.
    Welding in the World (2022)
    Cemented carbides are commonly brazed to transformation hardening tool steels without taking a proper and adequate steel heat treatment into account. This publication shows the limits and possibilities of integrating a steel heat treatment, including a quenching process, into a vacuum brazing process. Therefore, copper-based filler metals are selected to ensure the steel component’s high and homogenous hardness and supply a high joint quality. In this context, the aimed steel hardness was chosen in the range between 400 and 440 HV1 based on industrial experiences. This specific hardness range for the steel component was set to avoid wear of machining tools in subsequent machining steps if the steel hardness is too high and to prevent wear and deformation of the tool itself in case of a steel hardness too low. When using the transformation hardening tool steel 1.2344, the obtained shear strength values did not exceed a threshold of 20 MPa which can be attributed to the required N2-quenching from brazing respectively solution annealing temperature. However, the steel components featured a hardness of 527.1 HV1 for the specimens brazed with pure copper at 1100 °C and 494.0 HV1 for those brazed with a CuGeNi filler metal at 1040 °C. This publication also shows an alternative route to manufacture long-lasting tools with a cemented carbide/steel joint by applying the difficult to wet and not well researched, but for many other reasons very suitable precipitation hardening maraging steel. Especially, the comparable low coefficient of thermal expansion (CTE) and the capability of the lath martensite to compensate large amounts of externally imposed stresses during the austenite-to-martensite transformation as well as the cooling rate independent of the hardening mechanism of the maraging steel and a pre-applied nickel coating including the corresponding diffusion processes are responsible for a sound joint with a shear strength > 300 MPa. Moreover, the subsequent tempering process at 580 °C for 3 h provides the maraging steel joining partner with a hardness of 426.6 ± 6.0 HV1. © 2022, The Author(s).
    view abstractdoi: 10.1007/s40194-022-01266-9
  • 2022 • 253 Analysing the entropy of lithium-ion cells to trace anodic half-cell ageing
    Mertin, G.K. and Wycisk, D. and Stadler, J. and von Kessel, O. and Richter, E. and Oldenburger, M. and Wieck, A.D. and Birke, K.P.
    Journal of Energy Storage 50 (2022)
    The full-cell entropy and its temperature dependency were measured for automotive lithium-ion cells with a graphite anode in dependence of the state of charge. Resulting entropy curves can be related to certain characteristic conditions of the graphite anode. Those characteristics are induced by a certain lithium-ion concentrations within the graphite. Comparing the entropy curves of fresh to aged cells shows a shift in the characteristics of these curves at a similar charge input. Those shifts were assigned to a change in the anodic net capacity, enabling an entropy based state of health estimation of the anode. The execution of the differential voltage analysis leads to similar results. © 2022 Elsevier Ltd
    view abstractdoi: 10.1016/j.est.2022.104109
  • 2022 • 252 Analytical model of the in-plane torsion test
    Cwiekala, N. and Traphöner, H. and Haupt, P. and Clausmeyer, T. and Tekkaya, A.E.
    Acta Mechanica 233 641-663 (2022)
    In research and industry, the in-plane torsion test is applied to investigate the material behaviour at large plastic strains: a sheet is clamped in two concentric circles, the boundaries are twisted against each other applying a torque, and simple shear of the material arises. This deformation is analysed within the scope of finite elasto-plasticity. An additive decomposition of the Almansi strain tensor is derived, valid as an approximation for arbitrary large plastic strains and sufficiently small elastic strains and rotations. Constitutive assumptions are the von Mises yield criterion, an associative flow rule, isotropic hardening, and a physically linear elasticity relation. The incremental formulation of the elasticity relation applies covariant Oldroyd derivatives of the stress and the strain tensors. The assumptions combined with equilibrium conditions lead to evolution equations for the distribution of stresses and accumulated plastic strain. The nonzero circumferential stress must be determined from the equilibrium condition because no deformation is present in tangential direction. As a result, a differential-algebraic-equation (DAE) system is derived, consisting of three ordinary differential equations combined with one algebraic side condition. As an example material, properties of a dual phase steel DP600 are analysed numerically at an accumulated plastic strain of 3.0. Radial normal stresses of 3.1% and tangential normal stresses of 1.0% of the shear stresses are determined. The influence of the additional normal stresses on the determination of the flow curve is 0.024%, which is negligibly small in comparison with other experimental influences and measurement accuracies affecting the experimental flow curve determination. © 2022, The Author(s).
    view abstractdoi: 10.1007/s00707-021-03129-8
  • 2022 • 251 Application of Photogrammetric Object Reconstruction for Simulation Environments in the Context of Inland Waterways
    Jarofka, M. and Schweig, S. and Maas, N. and Kracht, F.E. and Schramm, D.
    Lecture Notes in Networks and Systems 306 1-17 (2022)
    For the automated generation of simulation environments in the context of inland waterways navigation, a toolchain for the reconstruction of roadside buildings is used for the first time in this field. It was first implemented and tested for the reconstruction of roadside buildings. The toolchain uses data of a stereo camera to automatically generate models of the surrounding objects. This contribution describes the major changes that have to be made to adapt the toolchain to the changed environment. An unmanned aerial vehicle (UAV) is used to take images of specific objects. Due to the limited space on this UAV, only the supplied camera is used. Thus, the further steps in the toolchain have to be adapted. For the evaluation of the resulting model quality images of two bridges are considered. The implemented programs Metashape and Meshroom are compared with each other in terms of quality and computational effort. It is shown that the resulting model quality is better by using the program Metashape. Regarding the computational effort, the necessary time as well as the CPU and GPU utilization are reviewed. Although the GPU utilization is similar, Metashape outperforms Meshroom in terms of CPU utilization and total processing time. Furthermore, two different image recording methods are compared. On the one hand, models are reconstructed from only the top view. On the other hand, a tilted viewing angle with images from both sides of the bridges is used. © 2022, The Author(s), under exclusive license to Springer Nature Switzerland AG.
    view abstractdoi: 10.1007/978-3-030-84811-8_1
  • 2022 • 250 Asymmetric interfaces in epitaxial off-stoichiometric Fe3+x Si1−x /Ge/Fe3+x Si1−x hybrid structures: Effect on magnetic and electric transport properties
    Tarasov, A.S. and Tarasov, I.A. and Yakovlev, I.A. and Rautskii, M.V. and Bondarev, I.A. and Lukyanenko, A.V. and Platunov, M.S. and Volochaev, M.N. and Efimov, D.D. and Goikhman, A.Yu. and Belyaev, B.A. and Baron, F.A. and Shanid...
    Nanomaterials 12 (2022)
    Three-layer iron-rich Fe3+x Si1−x /Ge/Fe3+x Si1−x (0.2 < x < 0.64) heterostructures on a Si(111) surface with Ge thicknesses of 4 nm and 7 nm were grown by molecular beam epitaxy. Systematic studies of the structural and morphological properties of the synthesized samples have shown that an increase in the Ge thickness causes a prolonged atomic diffusion through the interfaces, which significantly increases the lattice misfits in the Ge/Fe3+x Si1−x heterosystem due to the incorporation of Ge atoms into the Fe3+x Si1−x bottom layer. The resultant lowering of the total free energy caused by the development of the surface roughness results in a transition from an epitaxial to a polycrystalline growth of the upper Fe3+x Si1−x. The average lattice distortion and residual stress of the upper Fe3+x Si1−x were determined by electron diffraction and theoretical calculations to be equivalent to 0.2 GPa for the upper epitaxial layer with a volume misfit of −0.63% compared with a undistorted counterpart. The volume misfit follows the resultant interatomic misfit of |0.42|% with the bottom Ge layer, independently determined by atomic force microscopy. The variation in structural order and morphology significantly changes the magnetic properties of the upper Fe3+x Si1−x layer and leads to a subtle effect on the transport properties of the Ge layer. Both hysteresis loops and FMR spectra differ for the structures with 4 nm and 7 nm Ge layers. The FMR spectra exhibit two distinct absorption lines corresponding to two layers of ferromagnetic Fe3+x Si1−x films. At the same time, a third FMR line appears in the sample with the thicker Ge. The angular dependences of the resonance field of the FMR spectra measured in the plane of the film have a pronounced easy-axis type anisotropy, as well as an anisotropy corresponding to the cubic crystal symmetry of Fe3+x Si1−x, which implies the epitaxial orientation relationship of Fe3+x Si1−x (111)[0−11] || Ge(111)[1−10] || Fe3+x Si1−x (111)[0−11] || Si(111)[1−10]. Calculated from ferromagnetic resonance (FMR) data saturation magnetization exceeds 1000 kA/m. The temperature dependence of the electrical resistivity of a Ge layer with thicknesses of 4 nm and 7 nm is of semiconducting type, which is, however, determined by different transport mechanisms. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/nano12010131
  • 2022 • 249 Atomic cluster expansion: Completeness, efficiency and stability
    Dusson, G. and Bachmayr, M. and Csányi, G. and Drautz, R. and Etter, S. and van der Oord, C. and Ortner, C.
    Journal of Computational Physics 454 (2022)
    The Atomic Cluster Expansion (Drautz (2019) [21]) provides a framework to systematically derive polynomial basis functions for approximating isometry and permutation invariant functions, particularly with an eye to modelling properties of atomistic systems. Our presentation extends the derivation by proposing a precomputation algorithm that yields immediate guarantees that a complete basis is obtained. We provide a fast recursive algorithm for efficient evaluation and illustrate its performance in numerical tests. Finally, we discuss generalisations and open challenges, particularly from a numerical stability perspective, around basis optimisation and parameter estimation, paving the way towards a comprehensive analysis of the convergence to a high-fidelity reference model. © 2022 Elsevier Inc.
    view abstractdoi: 10.1016/j.jcp.2022.110946
  • 2022 • 248 Automated and manual classification of metallic nanoparticles with respect to size and shape by analysis of scanning electron micrographs [Automatisierte und manuelle Klassifizierung metallischer Nanopartikel nach Größe und Form aus rasterelektronenmikroskopischen Aufnahmen]
    Bals, J. and Loza, K. and Epple, P. and Kircher, T. and Epple, M.
    Materialwissenschaft und Werkstofftechnik 53 270-283 (2022)
    Automated image analysis has been applied to scanning electron micrographs (transmission mode; STEM) of metallic nanoparticles (silver and gold; about 10 nm to 20 nm). For a reliable particle identification, scanning electron microscopic images must be recorded with distinct contrast and resolution parameters. The particles were separated from the background and classified according to shape and size by machine learning (machine learning). Training images were created with model particles cut out of real electron microscopic images. The automated analysis of the particle size (expressed as area) was well possible, but overlapping particles could not be safely separated. The assignment of particle to six different shape classes (sphere, triangle, square, pentagon, hexagon, rod) by automated analysis was difficult. The fact that real particles never have an ideal geometrical shape but are always distorted or have rough edges or cropped tips is the fundamental reason of this problem. This effect also occurred with human image evaluators and poses a considerable obstacle in the training process for machine learning. Image analysis by machine learning techniques is difficult if different human evaluators disagree on the shape assignment of given particles because a proper training cannot be provided. © 2022 The Authors. Materialwissenschaft und Werkstofftechnik published by Wiley-VCH GmbH.
    view abstractdoi: 10.1002/mawe.202100285
  • 2022 • 247 Bifacial semi-transparent ultra-thin Cu(In,Ga)Se2 solar cells on ITO substrate: How ITO thickness and Na doping influence the performance
    Li, Y. and Yin, G. and Schmid, M.
    Solar Energy Materials and Solar Cells 234 (2022)
    Ultra-thin Cu(In,Ga)Se2 (CIGSe) is a promising absorber for thin-film solar cells, as it combines the advantages of low raw material consumption and high conversion efficiency. In addition, ultra-thin absorbers on transparent back contacts bring the advantage of semitransparency, which is essential for e.g. tandem or bifacial solar cells. This work optimizes ultra-thin CIGSe on In2O3:Sn (ITO) for application in bifacial semi-transparent ultra-thin (BSTUT) CIGSe solar cells. Firstly, 100–400 nm ITO were coated onto glass substrates, and it was revealed that the thickness of ITO influences its optical bandgap Eg due to the Burstein-Moss (B-M) shift. The band gap of 400 nm ITO increased by 0.14 eV compared to the 100 nm thick ITO, and the Voc of the related BSTUT CIGSe solar cells raised by 0.043 V as a result of the diminished Schottky barrier Φb at the ITO/CIGSe interface. Secondly, 0–8 mg of NaF used for post deposition treatment (PDT) of the CIGSe were applied to the BSTUT solar cells. Compared to the reference without NaF, 8 mg NaF PDT enhanced the carrier density NA from 2 × 1015cm−3 to 1.2 × 1016cm−3 and diminished the ITO/CIGSe Schottky barrier Φb by 0.21 eV. In conclusion, we found that NaF PDT can tune the carrier density of ultra-thin CIGSe on ITO, and both thicker ITO and higher NaF PDT dose can reduce the ITO/CIGSe Schottky barrier. These discoveries enable future optimization of BSTUT CIGSe solar cells. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.solmat.2021.111431
  • 2022 • 246 Bimetallic MxRu100−x nanoparticles (M = Fe, Co) on supported ionic liquid phases (MxRu100−x@SILP) as hydrogenation catalysts: Influence of M and M:Ru ratio on activity and selectivity
    Sisodiya-Amrute, S. and Van Stappen, C. and Rengshausen, S. and Han, C. and Sodreau, A. and Weidenthaler, C. and Tricard, S. and DeBeer, S. and Chaudret, B. and Bordet, A. and Leitner, W.
    Journal of Catalysis 407 141-148 (2022)
    Bimetallic iron-ruthenium and cobalt-ruthenium nanoparticles with systematic variations in the Fe:Ru and Co:Ru ratios are prepared following an organometallic approach and immobilized on an imidazolium-based supported ionic liquid phase (SILP). Resulting MxRu100-x@SILP materials are characterized by electron microscopy, X-ray diffraction and X-ray absorption spectroscopy, confirming the formation of small, well-dispersed and alloyed zero-valent bimetallic nanoparticles. A systematic comparison of the performances of FexRu100−x@SILP and CoxRu100−x@SILP catalysts is made using the hydrogenation of benzilideneacetone as model reaction. The M:Ru ratio is found to have a critical influence on activity and selectivity, with clear synergistic effects arising from the combination of the noble and 3d metals. CoxRu100−x@SILP catalysts are significantly more reactive to reach a given selectivity at a systematically higher content of the 3d metal as compared to the FexRu100−x@SILP catalysts, evidencing a remarkable influence of the nature of the “diluting” 3d metal on the overall performance of the MxRu100−x@SILP catalysts. © 2022 The Author(s)
    view abstractdoi: 10.1016/j.jcat.2022.01.030
  • 2022 • 245 Binding Methylarginines and Methyllysines as Free Amino Acids: A Comparative Study of Multiple Host Classes**
    Warmerdam, Z. and Kamba, B.E. and Le, M.-H. and Schrader, T. and Isaacs, L. and Bayer, P. and Hof, F.
    ChemBioChem 23 (2022)
    Methylated free amino acids are an important class of targets for host-guest chemistry that have recognition properties distinct from those of methylated peptides and proteins. We present comparative binding studies for three different host classes that are each studied with multiple methylated arginines and lysines to determine fundamental structure-function relationships. The hosts studied are all anionic and include three calixarenes, two acyclic cucurbiturils, and two other cleft-like hosts, a clip and a tweezer. We determined the binding association constants for a panel of methylated amino acids using indicator displacement assays. The acyclic cucurbiturils display stronger binding to the methylated amino acids, and some unique patterns of selectivity. The two other cleft-like hosts follow two different trends, shallow host (clip) following similar trends to the calixarenes, and the other more closed host (tweezer) binding certain less-methylated amino acids stronger than their methylated counterparts. Molecular modelling sheds some light on the different preferences of the various hosts. The results identify hosts with new selectivities and with affinities in a range that could be useful for biomedical applications. The overall selectivity patterns are explained by a common framework that considers the geometry, depth of binding pockets, and functional group participation across all host classes. © 2021 The Authors. ChemBioChem published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/cbic.202100502
  • 2022 • 244 Biomolecule‐Mediated Therapeutics of the Dentin–Pulp Complex: A Systematic Review
    Machla, F. and Angelopoulos, I. and Epple, M. and Chatzinikolaidou, M. and Bakopoulou, A.
    Biomolecules 12 (2022)
    The aim of this systematic review was to evaluate the application of potential therapeutic signaling molecules on complete dentin‐pulp complex and pulp tissue regeneration in orthotopic and ectopic animal studies. A search strategy was performed according to the Preferred Reporting Items for Systematic Reviews and Meta‐Analyses (PRISMA) statement in the MEDLINE/PubMed database. Animal studies evaluating the application of signaling molecules to pulpectomized teeth for pulp tissue or dentin‐pulp complex regeneration were included. From 2530 identified records, 18 fulfilled the eligibility criteria and were subjected to detailed qualitative analysis. Among the applied molecules, basic fibroblast growth factor, vascular endothelial growth factor, bone morpho-genetic factor‐7, nerve growth factor, and platelet‐derived growth factor were the most frequently studied. The clinical, radiographical and histological outcome measures included healing of peri-apical lesions, root development, and apical closure, cellular recolonization of the pulp space, in-growth of pulp‐like connective tissue (vascularization and innervation), mineralized dentin‐like tissue formation along the internal dentin walls, and odontoblast‐like cells in contact with the internal dentin walls. The results indicate that signaling molecules play an important role in dentin/pulp regeneration. However, further studies are needed to determine a more specific subset combination of molecules to achieve greater efficiency towards the desired tissue engineering applications. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/biom12020285
  • 2022 • 243 Bismuth-based halide perovskite and perovskite-inspired light absorbing materials for photovoltaics
    Ünlü, F. and Deo, M. and Mathur, S. and Kirchartz, T. and Kulkarni, A.
    Journal of Physics D: Applied Physics 55 (2022)
    The efficiency of organic-inorganic hybrid lead halide perovskite solar cells (PSCs) has increased over 25% within a frame of ten years, which is phenomenal and indicative of the promising potential of perovskite materials in impacting the next generation solar cells. Despite high technology readiness of PSCs, the presence of lead has raised concerns about the adverse effect of lead on human health and the environment that may slow down or inhibit the commercialization of PSCs. Thus, there is a dire need to identify materials with lower toxicity profile and comparable optoelectronic properties in regard to lead-halide perovskites. In comparison to tin-, germanium-, and copper-based PSCs, which suffer from stability issues under ambient operation, bismuth-based perovskite and perovskite-inspired materials have gained attention because of their enhanced stability in ambient atmospheric conditions. In this topical review, we initially discuss the background of lead and various lead-free perovskite materials and further discuss the fundamental aspects of various bismuth-based perovskite and perovskite-inspired materials having a chemical formula of A3Bi2X9, A2B'BiX6, B' aBibXa+3b (A = Cs+, MA+ and bulky organic ligands; B' = Ag+, Cu+; X = I-, Cl-, Br-) and bismuth triiodide (BiI3) semiconducting material particularly focusing on their structure, optoelectronic properties and the influence of compositional variation on the photovoltaic device performance and stability. © 2021 IOP Publishing Ltd Printed in the UK.
    view abstractdoi: 10.1088/1361-6463/ac3033
  • 2022 • 242 Bis-Phosphaketenes LM(PCO)2 (M=Ga, In): A New Class of Reactive Group 13 Metal-Phosphorus Compounds
    Sharma, M.K. and Dhawan, P. and Helling, C. and Wölper, C. and Schulz, S.
    Chemistry - A European Journal (2022)
    Phosphaketenes are versatile reagents in organophosphorus chemistry. We herein report on the synthesis of novel bis-phosphaketenes, LM(PCO)2 (M=Ga 2 a, In 2 b; L=HC[C(Me)N(Ar)]2; Ar=2,6-i-Pr2C6H3) by salt metathesis reactions and their reactions with LGa to metallaphosphenes LGa(OCP)PML (M=Ga 3 a, In 3 b). 3 b represents the first compound with significant In−P π-bonding contribution as was confirmed by DFT calculations. Compounds 3 a and 3 b selectively activate the N−H and O−H bonds of aniline and phenol at the Ga−P bond and both reactions proceed with a rearrangement of the phosphaethynolate group from Ga−OCP to M−PCO bonding. Compounds 2–5 are fully characterized by heteronuclear (1H, 13C{1H}, 31P{1H}) NMR and IR spectroscopy, elemental analysis, and single crystal X-ray diffraction (sc-XRD). © 2022 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/chem.202200444
  • 2022 • 241 Boron in Ni-Rich NCM811 Cathode Material: Impact on Atomic and Microscale Properties
    Roitzheim, C. and Kuo, L.-Y. and Sohn, Y.J. and Finsterbusch, M. and Möller, S. and Sebold, D. and Valencia, H. and Meledina, M. and Mayer, J. and Breuer, U. and Kaghazchi, P. and Guillon, O. and Fattakhova-Rohlfing, D.
    ACS Applied Energy Materials 5 524-538 (2022)
    Doping of Ni-rich cathode active materials with boron is a promising way to improve their cycling stability and mitigate their degradation, but it is still not understood how this effect is achieved and where the boron is located. To receive deeper insights into the impact of doping on atomic and microscale properties, B-doped Li[Ni0.8Co0.1Mn0.1]O2 (NCM811) cathode materials were synthesized by a hydroxide coprecipitation as a model compound to verify the presence and location of boron in B-doped, Ni-rich NCM, as well as its impact on the microstructure and electrochemical properties, by a combined experimental and theoretical approach. Besides X-ray diffraction and Rietveld refinement, DFT calculation was used to find the preferred site of boron absorption and its effect on the NCM lattice parameters. It is found that boron shows a trigonal planar and tetrahedral coordination to oxygen in the Ni layers, leading to a slight increase in lattice parameter c through an electrostatic interaction with Li ions. Therefore, B-doping of NCM811 affects the crystal structure and cation disorder and leads to a change in primary particle size and shape. To experimentally prove that the observations are caused by boron incorporated into the NCM lattice, we detected, quantified, and localized boron in 2 mol % B-doped NCM811 by ion beam analysis and TOF-SIMS. It was possible to quantify boron by NRA with a depth resolution of 2 μm. We found a boron enrichment on the agglomerate surface but also, more importantly, a significant high and constant boron concentration in the interior of the primary particles near the surface, which experimentally verifies that boron is incorporated into the NCM811 lattice. ©
    view abstractdoi: 10.1021/acsaem.1c03000
  • 2022 • 240 Bound-preserving Flux Limiting for High-Order Explicit Runge–Kutta Time Discretizations of Hyperbolic Conservation Laws
    Kuzmin, D. and Quezada de Luna, M. and Ketcheson, D.I. and Grüll, J.
    Journal of Scientific Computing 91 (2022)
    We introduce a general framework for enforcing local or global maximum principles in high-order space-time discretizations of a scalar hyperbolic conservation law. We begin with sufficient conditions for a space discretization to be bound preserving (BP) and satisfy a semi-discrete maximum principle. Next, we propose a global monolithic convex (GMC) flux limiter which has the structure of a flux-corrected transport (FCT) algorithm but is applicable to spatial semi-discretizations and ensures the BP property of the fully discrete scheme for strong stability preserving (SSP) Runge–Kutta time discretizations. To circumvent the order barrier for SSP time integrators, we constrain the intermediate stages and/or the final stage of a general high-order RK method using GMC-type limiters. In this work, our theoretical and numerical studies are restricted to explicit schemes which are provably BP for sufficiently small time steps. The new GMC limiting framework offers the possibility of relaxing the bounds of inequality constraints to achieve higher accuracy at the cost of more stringent time step restrictions. The ability of the presented limiters to recognize undershoots/overshoots, as well as smooth solutions, is verified numerically for three representative RK methods combined with weighted essentially nonoscillatory (WENO) finite volume space discretizations of linear and nonlinear test problems in 1D. In this context, we enforce global bounds and prove preservation of accuracy for the linear advection equation. © 2022, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.
    view abstractdoi: 10.1007/s10915-022-01784-0
  • 2022 • 239 CALPHAD-informed phase-field model for two-sublattice phases based on chemical potentials: η-phase precipitation in Al-Zn-Mg-Cu alloys
    Liu, C. and Davis, A. and Fellowes, J. and Prangnell, P.B. and Raabe, D. and Shanthraj, P.
    Acta Materialia 226 (2022)
    The electrochemical properties of high strength 7xxx aluminium alloys strongly depend on the substitutional occupancy of Zn by Cu and Al in the strengthening η-phase with the two-sublattice structure, and its microstructural and compositional prediction is the key to design of new generation corrosion resistant alloys. In this work, we have developed a chemical-potential-based phase-field model capable of describing multi-component and two-sublattice ordered phases, during commercial multi-stage artificial ageing treatments, by directly incorporating the compound energy CALPHAD formalism. The model developed has been employed to explore the complex compositional pathway for the formation of the η-phase in Al-Zn-Mg-Cu alloys during heat treatments. In particular, the influence of alloy composition, solute diffusivity, and heat treatment parameters on the microstructural and compositional evolution of η-phase precipitates, was systematically investigated from a thermodynamic and kinetic perspective and compared to electron probe microanalysis validation data. The simulated η-phase growth kinetics and the matrix residual solute evolution in the AA7050 alloy indicates that Zn depletion mainly controlled the η-phase growth process during the early stage of ageing, resulting in fast η-phase growth kinetics, enrichment of Zn in the η-phase, and an excess in residual Cu in the matrix. The gradual substitution of Zn by Cu atoms in the η-phase during the later ageing stage was in principle a kinetically controlled process, owing to the slower diffusivity of Cu relative to Zn in the matrix. It was also found that the higher nominal Zn content in alloys like the AA7085 alloy, compared to the AA7050 alloy, could significantly enhance the chemical potential of Zn, but this had a minor influence on Cu, which essentially led to the higher Zn content (and consequently lower Cu) seen in the η-phase. Finally, substantial depletion of Zn and supersaturation of Cu in the matrix of the AA7050 alloy was predicted after 24 h ageing at 120 ∘C, whereas the second higher-temperature ageing stage at 180 ∘C markedly enhanced the diffusion of Cu from the supersaturated matrix into the η-phase, while the matrix residual Zn content was only slightly affected. © 2021 The Author(s)
    view abstractdoi: 10.1016/j.actamat.2021.117602
  • 2022 • 238 Cementite decomposition in 100Cr6 bearing steel during high-pressure torsion: Influence of precipitate composition, size, morphology and matrix hardness
    Kiranbabu, S. and Tung, P.-Y. and Sreekala, L. and Prithiv, T.S. and Hickel, T. and Pippan, R. and Morsdorf, L. and Herbig, M.
    Materials Science and Engineering A 833 (2022)
    Premature failure of rail and bearing steels by White-Etching-Cracks leads to severe economic losses. This failure mechanism is associated with microstructure decomposition via local severe plastic deformation. The decomposition of cementite plays a key role. Due to the high hardness of this phase, it is the most difficult obstacle to overcome in the decaying microstructure. Understanding the mechanisms of carbide decomposition is essential for designing damage-resistant steels for industrial applications. We investigate cementite decomposition in the bearing steel 100Cr6 (AISI 52100) upon exposure to high-pressure torsion (maximum shear strain, Ƴmax = 50.2). Following-up on our earlier work on cementite decomposition in hardened 100Cr6 steel (Qin et al., Act. Mater. 2020 [1]), we now apply a modified heat treatment to generate a soft-annealed microstructure where spherical and lamellar cementite precipitates are embedded in a ferritic matrix. These two precipitate types differ in morphology (spherical vs. lamellar), size (spherical: 100–1000 nm diameter, lamellar: 40–100 nm thickness) and composition (Cr and Mn partitioning). We unravel the correlation between cementite type and its resistance to decomposition using multi-scale chemical and structural characterization techniques. Upon high-pressure torsion, the spherical cementite precipitates did not decompose, but the larger spherical precipitates (≥ 1 μm) deformed. In contrast, the lamellar cementite precipitates underwent thinning followed by decomposition and dissolution. Moreover, the decomposition behavior of cementite precipitates is affected by the type of matrix microstructure. We conclude that the cementite size and morphology, as well as the matrix mechanical properties are the predominating factors influencing the decomposition behavior of cementite. The compositional effects of Cr and Mn on cementite stability calculated by complementary density functional theory (DFT) calculations are minor in the current scenario. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.msea.2021.142372
  • 2022 • 237 Chapter 11: Pathways in Classification Space: Machine Learning as a Route to Predicting Kinetics of Structural Transitions in Atomic Crystals
    Rogal, J. and Tuckerman, M.E.
    RSC Theoretical and Computational Chemistry Series 2022-January 312-348 (2022)
    Machine learning methods have become increasingly central in the development of a large variety of versatile tools for molecular simulations, many of which have the potential to advance significantly the fields of computational chemistry and physics. In this chapter, we present a framework for combining machine learning for local structure classification with the definition of a global classifier space as a basis for enhanced sampling of structural transformations in condensed phase systems. The transformation is represented by a path in classifier space, and the associated path collective variable is used to drive the process derived from changes in local structural motifs. Enhanced sampling along this type of path collective variable yields insight into the physical mechanism as well as corresponding free energy barriers of the transition. The idea is generally applicable, and the approach, as outlined here, can be adapted to a wide range of systems. © The Royal Society of Chemistry 2022.
    view abstractdoi: 10.1039/9781839164668-00312
  • 2022 • 236 Characterization of the high-temperature behavior of PBF-EB/M manufactured γ titanium aluminides
    Teschke, M. and Moritz, J. and Telgheder, L. and Marquardt, A. and Leyens, C. and Walther, F.
    Progress in Additive Manufacturing (2022)
    Due to their high specific strength and temperature resistance, γ-titanium aluminides (γ-TiAl) have a growing importance for automotive and aerospace applications. However, conventional processing is very challenging due to the inherent brittleness of the material. Therefore, new manufacturing techniques and methods have to be established. Additive manufacturing techniques such as electron powder bed fusion (PBF-EB/M) are favored, since they enable near net shape manufacturing of highly complex geometries. The high preheating temperatures, which typically occur during PBF-EB/M, can significantly improve the processability of TiAl and facilitate the fabrication of complex parts. In this study, a previously optimized material condition of the β-solidifying TNM alloy TNM-B1 (Ti-43.5Al-4Nb-1Mo-0.1B) was manufactured by PBF-EB/M. The resulting microstructure, defect distribution and morphology, and mechanical properties were characterized by means of characterization methods, e.g., CT, SEM, light microscopy, hardness measurements, and tensile tests. A special focus was on the mechanical high-temperature behavior. The pronounced sensitivity of the material to defects and internal notches, e.g., due to lack of fusion defects (misconnections) which were found in the as-built condition, was identified as a main cause for premature failure below the yield point due to the low ductility. This failure was analyzed and potential improvements were identified. © 2022, The Author(s).
    view abstractdoi: 10.1007/s40964-022-00274-x
  • 2022 • 235 Charge dynamics in magnetically disordered Mott insulators
    Bleicker, P. and Hering, D.-B. and Uhrig, G.S.
    Physical Review B 105 (2022)
    With the aid of both a semianalytical and a numerically exact method, we investigate the charge dynamics in the vicinity of half-filling in the one- and two-dimensional t-J model derived from a Fermi-Hubbard model in the limit of large interaction U and hence small exchange coupling J. The spin degrees of freedom are taken to be disordered. So we consider the limit 0<J«T«W, where W is the bandwidth. We focus on evaluating the local spectral density of a single hole excitation and the charge gap that separates the upper and the lower Hubbard band. We find indications that no band edges exist if the magnetic exchange is taken into account; instead of band edges, Gaussian tails seem to appear. A discussion of the underlying physics is provided. © 2022 American Physical Society.
    view abstractdoi: 10.1103/PhysRevB.105.085121
  • 2022 • 234 Cobalt ferrite nanoparticles for tumor therapy: Effective heating versus possible toxicity
    Garanina, A.S. and Nikitin, A.A. and Abakumova, T.O. and Semkina, A.S. and Prelovskaya, A.O. and Naumenko, V.A. and Erofeev, A.S. and Gorelkin, P.V. and Majouga, A.G. and Abakumov, M.A. and Wiedwald, U.
    Nanomaterials 12 (2022)
    Magnetic nanoparticles (MNPs) are widely considered for cancer treatment, in particular for magnetic hyperthermia (MHT). Thereby, MNPs are still being optimized for lowest possible toxicity on organisms while the magnetic properties are matched for best heating capabilities. In this study, the biocompatibility of 12 nm cobalt ferrite MNPs, functionalized with citrate ions, in different dosages on mice and rats of both sexes was investigated for 30 days after intraperitoneal injection. The animals’ weight, behavior, and blood cells changes, as well as blood biochemical parameters are correlated to histological examination of organs revealing that cobalt ferrite MNPs do not have toxic effects at concentrations close to those used previously for efficient MHT. Moreover, these MNPs demonstrated high specific loss power (SLP) of about 400 W g−1. Importantly the MNPs retained their magnetic properties inside tumor tissue after intratumoral administration for several MHT cycles within three days. Thus, cobalt ferrite MNPs represent a perspective platform for tumor therapy by MHT due to their ability to provide effective heating without exerting a toxic effect on the organism. This opens up new avenues for smaller MNPs sizes while their heating efficiency is maintained. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/nano12010038
  • 2022 • 233 Combustion of Straw Pellets in an Agitated Fuel Bed: Experiments and DEM/CFD Simulations
    Buss, F. and Wirtz, S. and Scherer, V.
    Combustion Science and Technology 194 195-212 (2022)
    The influence of bed agitation during the combustion of biomass pellets was investigated experimentally and numerically. In the experiments, a bulk of straw pellets was burnt in a batch-operated reactor. The reactor allows for air staging and mixing of the fuel bed by vertically moveable mixing elements. The primary to secondary air ratio was varied and the reactor was operated either in the agitated (moving mixing elements) or the static mode (mixing elements at rest). The overall mass of the bulk was measured continuously during the combustion process. The results show a significant increase of the mass loss rate by almost 60% when the bed was agitated compared to the static case. Samples of the residual material of the pellets reveal a totally different amount of molten and agglomerated ash particles for the different operational conditions. Decreased primary to secondary air ratios as well as agitation of the fuel bed did lead to less agglomeration of the ash. The Discrete Element Method (DEM) was coupled with a Computational Fluid Dynamics (CFD) simulation. Coupled DEM/CFD simulations of the batch reactor were performed to get access to bulk internal data of the solid material and the fluid phase. Simulations identified that a reduced amount of ash exposed to the volatile flame through agitation of the fuel bed was the main reason for minimized ash agglomeration. © 2019 Taylor & Francis Group, LLC.
    view abstractdoi: 10.1080/00102202.2019.1678844
  • 2022 • 232 Compact Folded Leaky-Wave Antenna Radiating a Fixed Beam at Broadside for 5G mm-Wave Applications
    Neophytou, K. and Steeg, M. and Stöhr, A. and Antoniades, M.
    IEEE Antennas and Wireless Propagation Letters 21 292-296 (2022)
    A compact planar fixed-beam leaky-wave antenna that radiates its main beam at broadside is presented, that consists of two folded branches of periodically distributed series-fed microstrip patches. The antenna is fed from the center through a 50 Ω transmission line that subsequently feeds two constituent 100 Ω parallel branches, each consisting of eight series-fed microstrip patches. Fixed-beam operation is achieved by the combination of the two oppositely directed beams that are generated by the two branches. The proposed structure achieves a significant reduction of the longitudinal size by incorporating a 180° bend at the center of each branch, thus effectively folding the antenna in half. This results in a longitudinal size that is 1.8 times smaller than the analogous unfolded antenna. The antenna maintains a measured fixed beam at broadside over a wide zero beam-squinting bandwidth of 3 GHz in the 28 GHz band, with a radiation efficiency above 60% and a maximum measured gain of 14 dBi at 27.4 GHz, with an overall compact size of 5.8 × 1.1 cm. © 2002-2011 IEEE.
    view abstractdoi: 10.1109/LAWP.2021.3128563
  • 2022 • 231 Comparison of the Catalytic Activity of Mono- and Multinuclear Ga Complexes in the ROCOP of Epoxides and Cyclic Anhydrides
    Ghosh, S. and Glöckler, E. and Wölper, C. and Linders, J. and Janoszka, N. and Gröschel, A.H. and Schulz, S.
    European Journal of Inorganic Chemistry 2022 (2022)
    Tetranuclear Schiff-base complexes L1–32Ga4(t-Bu)8 1–3 are highly active and selective (&gt;99 %) catalyst in the alternating ring-opening copolymerization (ROCOP) of epoxides and anhydrides, yielding polyesters with high molecular weights (Mn) and narrow dispersity (Đ). The thermal properties (Tg) of the resulting polyester range from 18 °C to 124 °C and increase with increasing steric bulk or rigidity along the polymer backbone. Comparative studies using structurally related complexes L4Ga(t-Bu)2 4, [L5GaR2]2 (R=t-Bu 5, R=Me 6) and L6Ga(t-Bu)2 7 proved that the Ga2O2 core of catalyst 1 is the catalytically active species. © 2021 The Authors. European Journal of Inorganic Chemistry published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/ejic.202101017
  • 2022 • 230 Competing Effects in the Hydration Mechanism of a Garnet-Type Li7La3Zr2O12 Electrolyte
    Arinicheva, Y. and Guo, X. and Gerhards, M.-T. and Tietz, F. and Fattakhova-Rohlfing, D. and Finsterbusch, M. and Navrotsky, A. and Guillon, O.
    Chemistry of Materials 34 1473-1480 (2022)
    Li-ion conducting oxides (Li7La3Zr2O12, LLZO) with a cubic garnet-type structure are among the most promising candidates to be used as solid electrolytes in all-solid-state Li batteries. However, the environmental instability of the electrolyte, induced by interaction between the material and gas molecules commonly found in air, namely, water and carbon dioxide, poses challenges for its manufacture and application. Herein, a combined experimental kinetic and thermodynamic study was performed as a function of temperature to clarify the mechanism of hydration of a garnet-type LLZO electrolyte in moist air. It was found that the kinetics of LLZO hydration is diffusion-limited and the hydration mechanism at room temperature and at higher temperatures differs. The hydration of LLZO increases up to 200 °C. Above this temperature, stagnation of water uptake is observed due to the onset of a competing dehydration process. The dehydration of LLZO takes place up to 400 °C. The partial pressure of water significantly affects the extent of hydration. Expanding this combined kinetic and thermodynamic approach to LLZO materials with a variety of chemical compositions and morphologies would allow prediction of their reactivity in a humid atmosphere and adjustment of the processing conditions accordingly to meet the requirements of technological applications. © 2022 American Chemical Society
    view abstractdoi: 10.1021/acs.chemmater.1c02581
  • 2022 • 229 Comprehensive investigation of crystallographic, spin-electronic and magnetic structure of (Co0.2Cr0.2Fe0.2Mn0.2Ni0.2)3O4: Unraveling the suppression of configuration entropy in high entropy oxides
    Sarkar, A. and Eggert, B. and Witte, R. and Lill, J. and Velasco, L. and Wang, Q. and Sonar, J. and Ollefs, K. and Bhattacharya, S.S. and Brand, R.A. and Wende, H. and de Groot, F.M.F. and Clemens, O. and Hahn, H. and Kruk, R.
    Acta Materialia 226 (2022)
    High entropy oxides (HEOs) are a rapidly emerging class of functional materials consisting of multiple principal cations. The original paradigm of HEOs assumes cationic occupations with the highest possible configurational entropy allowed by the composition and crystallographic structure. However, the fundamental question remains on the actual degree of configurational disorder in HEOs, especially, in systems with a low enthalpy barriers for cation anti-site mixing. Considering the experimental limitations due to the presence of multiple principal cations in HEOs, here we utilize a robust and cross-referenced characterization approach using soft X-ray magnetic circular dichroism, hard X-ray absorption spectroscopy, Mössbauer spectroscopy, neutron powder diffraction and SQUID magnetometry to study the competition between crystal field stabilization energy and configurational entropy governing the cation occupation in a spinel HEO (S-HEO), (Co0.2Cr0.2Fe0.2Mn0.2Ni0.2)3O4. In contrast to the previous studies, the derived complete structural and spin-electronic model, (Co0.6Fe0.4)(Cr0.3Fe0.1Mn0.3Ni0.3)2O4, highlights a significant deviation from the hitherto assumed paradigm of entropy-driven non-preferential distribution of cations in HEOs. An immediate correlation of this result can be drawn with bulk as well as the local element specific magnetic properties, which are intrinsically dictated by cationic occupations in spinels. The real local lattice picture presented here provides an alternate viewpoint on ionic arrangement in HEOs, which is of fundamental interest for predicting and designing their structure-dependent functionalities. © 2021 Acta Materialia Inc.
    view abstractdoi: 10.1016/j.actamat.2021.117581
  • 2022 • 228 Conductivity enhancement of Al- and Ta-substituted Li7La3Zr2O7 solid electrolytes by nanoparticles
    Bauer, A. and Ali, M.Y. and Orthner, H. and Uhlenbruck, S. and Wiggers, H. and Fattakhova-Rohlfing, D. and Guillon, O.
    Journal of the European Ceramic Society 42 1033-1041 (2022)
    A nanopowder consisting of La2Zr2O7 particles with lithium containing species on their surface was prepared by spray flame synthesis and subsequently added to Li7La3Zr2O12 powder obtained by a conventional solid-state reaction. The spray flame synthesis method utilized in this work yields nanoparticles with a small size of approximately 5 nm, which is unprecedented within the scope of oxide-based ionic conductors for solid-state batteries. Remarkably, the addition of nanoparticles for sintering at a relatively low temperature of 1000 °C significantly improved the ionic conductivity by 50 %. In contrast, there was no influence of incorporating nanoparticles on the conductivity at sintering temperatures at or above 1100 °C, which is the typical temperature range applied for conventional sintering of Li7La3Zr2O12. Compared to prior published work with analogous materials, a more than twofold improvement in conductivity was demonstrated while the sintering temperature was decreased by 100 °C. © 2021 Elsevier Ltd
    view abstractdoi: 10.1016/j.jeurceramsoc.2021.11.029
  • 2022 • 227 Controlling ambidextrous mirror symmetry breaking in photosensitive supramolecular polycatenars by alkyl-chain engineering
    Alaasar, M. and Cai, X. and Kraus, F. and Giese, M. and Liu, F. and Tschierske, C.
    Journal of Molecular Liquids 351 (2022)
    Liquid crystalline (LC) photo sensitive materials capable of forming mirror-symmetry broken mesophases are of great interest to produce nano-structured materials for optical and photonic applications. Herein we report how mirror-symmetry breaking could be controlled in photo sensitive supramolecular polycatenars by alkyl chain engineering. For this purpose, three new series of supramolecular photo-switchable multi-chain complexes (polycatenars) formed by intermolecular hydrogen bonding interaction between azopyridines with one variable terminal chain as the proton-acceptors and Y-shaped or taper shaped benzoic acids having either two or three terminal chains as the hydrogen bond-donors were synthesized. The LC self-assembly of these supramolecules was characterized by differential scanning calorimetry (DSC), polarized optical microscopy (POM) and X-ray diffraction (XRD). Depending on the number and length of terminal chains spontaneously chiral isotropic liquid (Iso1[*]) as well as two different types of three dimensional (3D) bicontinous cubic phases are observed, which are either chiral (Cubbi[*]/I23) or achiral (Cubbi/Ia3¯d). Moreover, UV light irradiation leads to the first fast and reversible photoinduced transformation between chiral and achiral 3D cubic phases as well as between a chiral crystalline and a chiral cubic liquid crystalline phase. © 2022 The Authors
    view abstractdoi: 10.1016/j.molliq.2022.118597
  • 2022 • 226 Couette flow in a rectangular channel in the whole range of the gas rarefaction
    Pleskun, H. and Bode, T. and Brümmer, A.
    Physics of Fluids 34 (2022)
    The mass flow rate of a Couette flow in a long rectangular channel is calculated for constant or linear wall velocities in the whole range of the gas rarefaction and in a wide range of the width-to-height ratio. Analytical solutions for arbitrary width-to-height ratios are given for the hydrodynamic regime, the slip regime, and the free molecular regime. Therefore, both the velocity field and the mass flow rate can be calculated. In the transitional regime, simulations via direct simulation Monte Carlo method are performed. The results are provided as reduced flow rates in tabulated data, which can be used for any constant or linear increasing wall velocity (e.g., bounding walls of working chambers in positive displacement vacuum pumps). © 2022 Author(s).
    view abstractdoi: 10.1063/5.0082940
  • 2022 • 225 Covalent Allosteric Inhibitors of Akt Generated Using a Click Fragment Approach
    van der Westhuizen, L. and Weisner, J. and Taher, A. and Landel, I. and Quambusch, L. and Lindemann, M. and Uhlenbrock, N. and Müller, M.P. and Green, I.R. and Pelly, S.C. and Rauh, D. and van Otterlo, W.A.L.
    ChemMedChem (2022)
    Akt is a protein kinase that has been implicated in the progression of cancerous tumours. A number of covalent allosteric Akt inhibitors are known, and based on these scaffolds, a small library of novel potential covalent allosteric imidazopyridine-based inhibitors was designed. The envisaged compounds were synthesised, with click chemistry enabling a modular approach to a number of the target compounds. The binding modes, potencies and antiproliferative activities of these synthesised compounds were explored, thereby furthering the structure activity relationship knowledge of this class of Akt inhibitors. Three novel covalent inhibitors were identified, exhibiting moderate activity against Akt1 and various cancer cell lines, potentially paving the way for future covalent allosteric inhibitors with improved properties. © 2022 The Authors. ChemMedChem published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/cmdc.202100776
  • 2022 • 224 Creating a Ferromagnetic Ground State with Tc Above Room Temperature in a Paramagnetic Alloy through Non-Equilibrium Nanostructuring
    Ye, X. and Fortunato, N. and Sarkar, A. and Geßwein, H. and Wang, D. and Chen, X. and Eggert, B. and Wende, H. and Brand, R.A. and Zhang, H. and Hahn, H. and Kruk, R.
    Advanced Materials (2022)
    Materials with strong magnetostructural coupling have complex energy landscapes featuring multiple local ground states, thus making it possible to switch among distinct magnetic-electronic properties. However, these energy minima are rarely accessible by a mere application of an external stimuli to the system in equilibrium state. A ferromagnetic ground state, with Tc above room temperature, can be created in an initially paramagnetic alloy by nonequilibrium nanostructuring. By a dealloying process, bulk chemically disordered FeRh alloys are transformed into a nanoporous structure with the topology of a few nanometer-sized ligaments and nodes. Magnetometry and Mössbauer spectroscopy reveal the coexistence of two magnetic ground states, a conventional low-temperature spin-glass and a hitherto-unknown robust ferromagnetic phase. The emergence of the ferromagnetic phase is validated by density functional theory calculations showing that local tetragonal distortion induced by surface stress favors ferromagnetic ordering. The study provides a means for reaching conventionally inaccessible magnetic states, resulting in a complete on/off ferromagnetic–paramagnetic switching over a broad temperature range. © 2022 The Authors. Advanced Materials published by Wiley-VCH GmbH.
    view abstractdoi: 10.1002/adma.202108793
  • 2022 • 223 Cross-correlation spectra in interacting quantum dot systems
    Fischer, A. and Kleinjohann, I. and Sinitsyn, N.A. and Anders, F.B.
    Physical Review B 105 (2022)
    Two-color spin-noise spectroscopy of interacting electron spins in singly charged semiconductor quantum dots provides information on the interquantum dot interactions. We investigate the spin cross-correlation function in a quantum dot ensemble employing a modified semiclassical approach. Spin-correlation functions are calculated using a Hamilton quaternion approach that maintains local quantum mechanical properties of the spins. This method takes into account the effects of the nuclear-electric quadrupolar interactions, the randomness of the coupling constants, and the variation of the electron g factor on the spin-noise power spectra. We demonstrate that the quantum dot ensemble can be mapped on an effective two-quantum dot problem and discuss how the characteristic length scale of the interdot interaction modifies the low-frequency cross-correlation spectrum. We argue that details on the interaction strength distribution can be extracted from the cross-correlation spectrum when applying a longitudinal or a transversal external magnetic field. ©2022 American Physical Society
    view abstractdoi: 10.1103/PhysRevB.105.035303
  • 2022 • 222 Cross-relaxation interactions in ZnO:Mn2+: The ground state optical pumping
    Azamat, D.V. and Badalyan, A.G. and Romanov, N.G. and Hrabovsky, M. and Jastrabik, L. and Dejneka, A. and Yakovlev, D.R. and Bayer, M.
    Applied Physics Letters 120 (2022)
    A steady-state population inversion in the ground state of Mn2+ in ZnO was detected by application of continuous microwave and circularly polarized optical pumping in the temperature range of 3-6 K. Multiple spin-flip processes occur in view of a simultaneous saturation in the harmonically related transitions of Mn2+ spins. It is found that an additional relaxation channel arises at 2.7 K due to dynamic polarization of the 55Mn nuclei through the saturation of the first order electron-nuclear forbidden transitions. The transient populations are created between 55Mn nuclear sublevels. © 2022 Author(s).
    view abstractdoi: 10.1063/5.0078442
  • 2022 • 221 Crystal Structures of Two Titanium Phosphate-Based Proton Conductors: Ab Initio Structure Solution and Materials Properties
    Petersen, H. and Stegmann, N. and Fischer, M. and Zibrowius, B. and Radev, I. and Philippi, W. and Schmidt, W. and Weidenthaler, C.
    Inorganic Chemistry 61 2379-2390 (2022)
    Transition-metal phosphates show a wide range of chemical compositions, variations of the valence states, and crystal structures. They are commercially used as solid-state catalysts, cathode materials in rechargeable batteries, or potential candidates for proton-exchange membranes in fuel cells. Here, we report on the successful ab initio structure determination of two novel titanium pyrophosphates, Ti(III)p and Ti(IV)p, from powder X-ray diffraction (PXRD) data. The low-symmetry space groups P21/c for Ti(III)p and P1¯ for Ti(IV)p required the combination of spectroscopic and diffraction techniques for structure determination. In Ti(III)p, trivalent titanium ions occupy the center of TiO6 polyhedra, coordinated by five pyrophosphate groups, one of them as a bidentate ligand. This secondary coordination causes the formation of one-dimensional six-membered ring channels with a diameter dmax of 3.93(2) Å, which is stabilized by NH4+ ions. Annealing Ti(III)p in inert atmospheres results in the formation of a new compound, denoted as Ti(IV)p. The structure of this compound shows a similar three-dimensional framework consisting of [PO4]3- tetrahedra and TiIV+O6 octahedra and an empty one-dimensional channel with a diameter dmax of 5.07(1) Å. The in situ PXRD of the transformation of Ti(III)p to Ti(IV)p reveals a two-step mechanism, i.e., the decomposition of NH4+ ions in a first step and subsequent structure relaxation. The specific proton conductivity and activation energy of the proton migration of Ti(III)p, governed by the Grotthus mechanism, belong to the highest and lowest, respectively, ever reported for this class of materials, which reveals its potential application in electrochemical devices like fuel cells and water electrolyzers in the intermediate temperature range. © 2021 The Authors. Published by American Chemical Society.
    view abstractdoi: 10.1021/acs.inorgchem.1c02613
  • 2022 • 220 Crystallographic Analysis of Plate and Lath Martensite in Fe-Ni Alloys
    Thome, P. and Schneider, M. and Yardley, V.A. and Payton, E.J. and Eggeler, G.
    Crystals 12 (2022)
    In the present work, we use an advanced EBSD method to analyze the two prominent types of martensite microstructures that are found in the binary Fe-Ni system, lath martensite (27.5 at.% Ni) and plate martensite (29.5 at.% Ni). We modify, document, and apply an analytical EBSD procedure, which was originally proposed by Yardley and Payton, 2014. It analyzes the distributions of the three KSI-angles (ξ1, ξ2, and ξ3, KSI after Kurdjumov and Sachs), which describe small angular deviations between crystal planes in the unit cells of martensite and austenite—which are related through specific orientation relationships. The analysis of the angular distributions can be exploited to obtain high-resolution, color-coded micrographs of martensitic microstructures, which, for example, visualize the difference between lath and plate martensite and appreciate the microstructural features, like midribs in large plate martensite crystals. The differences between the two types of martensite also manifest themselves in different distributions of the KSI-angles (wider for lath and narrower for plate martensite). Finally, our experimental results prove that local distortions result in scatter, which is larger than the differences between the orientation relationships of Kurdjumov/Sachs, Nishiyama/Wassermann, and Greninger/Troiano. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/cryst12020156
  • 2022 • 219 Cutting fluid behavior under consideration of chip formation during micro single-lip deep hole drilling of Inconel 718
    Oezkaya, E. and Baumann, A. and Michel, S. and Schnabel, D. and Eberhard, P. and Biermann, D.
    International Journal of Modelling and Simulation (2022)
    When micro-single-lip deep hole drilling the efficiency of the cutting fluid supply cannot be investigated experimentally due to the inaccessibility of the cutting zone. For this reason, this paper examines the cutting fluid behavior, taking into account the chip formation and the transient chip position, with the help of various combined simulation methods. Therefore, experimentally obtained chips are digitalized and converted into a Computer-Aided Design model for the following simulations. Furthermore, for a comparison of the simulations with the experiments, the velocity of the cutting fluid in the chip flute of the tool is measured by a similar Particle Image Velocimetry method. Then, a transient coupled particle simulation of Smoothed Particle Hydrodynamics and the Discrete Element Method is performed to obtain the transient chip positions along the chip flute under the influence of the cutting fluid. Based on these chip positions, a Computational Fluid Dynamics simulation follows to derive insights about the flow field and pressure field at certain points in time. This multi-physics simulation chain allows to deal with experimental results in a simulation context to gain further insights about the deep hole drilling process, which are experimentally inaccessible and allows further connections between experiment and simulation. © 2022 Informa UK Limited, trading as Taylor & Francis Group.
    view abstractdoi: 10.1080/02286203.2022.2042057
  • 2022 • 218 Cyclophilin A Is Not Acetylated at Lysine‐82 and Lysine‐125 in Resting and Stimulated Platelets
    Rosa, A. and Butt, E. and Hopper, C.P. and Loroch, S. and Bender, M. and Schulze, H. and Sickmann, A. and Vorlova, S. and Seizer, P. and Heinzmann, D. and Zernecke, A.
    International Journal of Molecular Sciences 23 (2022)
    Cyclophilin A (CyPA) is widely expressed by all prokaryotic and eukaryotic cells. Upon activation, CyPA can be released into the extracellular space to engage in a variety of functions, such as interaction with the CD147 receptor, that contribute to the pathogenesis of cardiovascular diseases. CyPA was recently found to undergo acetylation at K82 and K125, two lysine residues conserved in most species, and these modifications are required for secretion of CyPA in response to cell activation in vascular smooth muscle cells. Herein we addressed whether acetylation at these sites is also required for the release of CyPA from platelets based on the potential for local delivery of CyPA that may exacerbate cardiovascular disease events. Western blot analyses confirmed the presence of CyPA in human and mouse platelets. Thrombin stimulation resulted in CyPA release from platelets; however, no acetylation was observed—neither in cell lysates nor in supernatants of both untreated and activated platelets, nor after immunoprecipitation of CyPA from platelets. Shotgun proteomics detected two CyPA peptide precursors in the recombinant protein, acetylated at K28, but again, no acetylation was found in CyPA derived from resting or stimulated platelets. Our findings suggest that acetylation of CyPA is not a major protein modification in platelets and that CyPA acetylation is not required for its secretion from platelets. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/ijms23031469
  • 2022 • 217 Damage Evolution of Steel Fibre-Reinforced High-Performance Concrete in Low-Cycle Flexural Fatigue: Numerical Modeling and Experimental Validation
    Gebuhr, G. and Pise, M. and Anders, S. and Brands, D. and Schröder, J.
    Materials 15 (2022)
    This contribution aims to analyze the deterioration behaviour of steel fibre-reinforced high-performance concrete (HPC) in both experiments as well as numerical simulations. For this purpose, flexural tensile tests are carried out on beams with different fibre contents and suitable damage indicators are established to describe and calibrate the damage behaviour numerically using a phase-field model approach. In addition to conventional measurement methods, the tests are equipped with acoustic emission sensors in order to obtain a more precise picture of crack evolution by observing acoustic events. It is shown that, in addition to classical damage indicators, such as stiffness degradation and absorbed energy, various acoustic indicators, such as the acoustic energy of individual crack events, can also provide information about the damage progress. For the efficient numerical analysis of the overall material behaviour of fibre-reinforced HPC, a phenomenological material model is developed. The data obtained in the experiments are used to calibrate and validate the numerical model for the simulation of three-point bending beam tests. To verify the efficiency of the presented numerical model, the numerical results are compared with the experimental data, e.g., load-CMOD curves and the degradation of residual stiffness. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/ma15031179
  • 2022 • 216 Deformation and phase transformation in polycrystalline cementite (Fe3C) during single- and multi-pass sliding wear
    Tsybenko, H. and Tian, C. and Rau, J. and Breitbach, B. and Schreiber, P. and Greiner, C. and Dehm, G. and Brinckmann, S.
    Acta Materialia 227 (2022)
    Cementite (Fe3C) plays a major role in the tribological performance of rail and bearing steels. Nonetheless, the current understanding of its deformation behavior during wear is limited because it is conventionally embedded in a matrix. Here, we investigate the deformation and chemical evolution of bulk polycrystalline cementite during single-pass sliding at a contact pressure of 31 GPa and reciprocating multi-pass sliding at 3.3 GPa. The deformation behavior of cementite was studied by electron backscatter diffraction for slip trace analysis and transmission electron microscopy. Our results demonstrate activation of several deformation mechanisms below the contact surface: dislocation slip, shear band formation, fragmentation, grain boundary sliding, and grain rotation. During sliding wear, cementite ductility is enhanced due to the confined volume, shear/compression domination, and potentially frictional heating. The microstructural alterations during multi-pass wear increase the subsurface nanoindentation hardness by up to 2.7 GPa. In addition, we report Hägg carbide (Fe5C2) formation in the uppermost deformed regions after both sliding experiments. Based on the results of electron and X-ray diffraction, as well as atom probe tomography, we propose potential sources of excess carbon and mechanisms that promote the phase transformation. © 2022 The Author(s)
    view abstractdoi: 10.1016/j.actamat.2022.117694
  • 2022 • 215 Determination and analysis of the constitutive parameters of temperature-dependent dislocation-density-based crystal plasticity models
    Sedighiani, K. and Traka, K. and Roters, F. and Raabe, D. and Sietsma, J. and Diehl, M.
    Mechanics of Materials 164 (2022)
    Physics-based crystal plasticity models rely on certain statistical assumptions about the collective behavior of dislocation populations on one slip system and their interactions with the dislocations on the other slip systems. One main advantage of using such physics-based constitutive dislocation models in crystal plasticity kinematic frameworks is their suitability for predicting the mechanical behavior of polycrystals over a wide range of deformation temperatures and strain rates with the same physics-based parameter set. In this study, the ability of a widely used temperature-dependent dislocation-density-based crystal plasticity formulation to reproduce experimental results, with a main focus on the yield stress behavior, is investigated. First, the material parameters are identified from experimental macroscopic stress–strain curves using a computationally efficient optimization methodology that uses a genetic algorithm along with the response surface methodology. For this purpose, a systematic set of compression tests on interstitial free (IF) steel samples is performed at various temperatures and strain rates. Next, the influence of the individual parameters on the observed behavior is analyzed. Based on mutual interactions between various parameters, the ability to find a unique parameter set is discussed. This allows identifying shortcomings of the constitutive law and sketch ideas for possible improvements. Particular attention is directed toward identifying possibly redundant material parameters, narrowing the acceptable range of material parameters based on physical criteria, and modifying the crystal plasticity formulation numerically for high-temperature use. © 2021 The Author(s)
    view abstractdoi: 10.1016/j.mechmat.2021.104117
  • 2022 • 214 Development and analysis of a mechatronic system for in-process monitoring and compensation of straightness deviation in BTA deep hole drilling
    Gerken, J.F. and Klages, N. and Biermann, D. and Denkena, B.
    Mechanical Systems and Signal Processing 170 (2022)
    In BTA deep hole drilling straightness deviation of the bore is a very important quality criteria. The avoidance of straightness deviation is not possible due to the many influencing variables. Currently used methods for compensation require significant additional time, as they either require the interruption of the drilling process, or require an additional boring process. By using a newly developed, manufactured and tested compensation unit, which is mounted between the drill head and the drill pipe, a targeted tilting of the drill head and thus a targeted influencing of the straightness deviation in the running process is possible with the use of a radially adjustable control pad and an innovative actuator concept. The developed measuring system offers the possibility to record the straightness deviation during the drilling process. On the basis of experimental test series, a control system was developed and applied to the BTA deep drilling process. After a drilling path of 1,000 mm, a maximum straightness deviation reduction of approx. 51 % can be realized. Compared to the process without control and compensation unit, the progressive increase of the straightness deviation was significantly reduced. © 2022 Elsevier Ltd
    view abstractdoi: 10.1016/j.ymssp.2022.108838
  • 2022 • 213 Development of Antifouling Polysulfone Membranes by Synergistic Modification with Two Different Additives in Casting Solution and Coagulation Bath: Synperonic F108 and Polyacrylic Acid
    Burts, K.S. and Plisko, T.V. and Sjölin, M. and Rodrigues, G. and Bildyukevich, A.V. and Lipnizki, F. and Ulbricht, M.
    Materials 15 (2022)
    This study deals with the development of antifouling ultrafiltration membranes based on polysulfone (PSF) for wastewater treatment and the concentration and purification of hemicellulose and lignin in the pulp and paper industry. The efficient simple and reproducible technique of PSF membrane modification to increase antifouling performance by simultaneous addition of triblock copolymer polyethylene glycol-polypropylene glycol-polyethylene glycol (Synperonic F108, Mn =14 × 103 g mol−1) to the casting solution and addition of polyacrylic acid (PAA, Mn = 250 × 103 g mol−1) to the coagulation bath is proposed for the first time. The effect of the PAA concentration in the aqueous solution on the PSF/Synperonic F108 membrane structure, surface characteristics, performance, and antifouling stability was investigated. PAA concentrations were varied from 0.35 to 2.0 wt.%. Membrane composition, structure, and topology were investigated by Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and scanning electron microscopy (SEM). The addition of PAA into the coagulation bath was revealed to cause the formation of a thicker and denser selective layer with decreasing its pore size and porosity; according to the structural characterization, an interpolymer complex of the two additives was formed on the surface of the PSF membrane. Hydrophilicity of the membrane selective layer surface was shown to increase significantly. The selective layer surface charge was found to become more negative in comparison to the reference membrane. It was shown that PSF/Synperonic F108/PAA membranes are characterized by better antifouling performance in ultrafiltration of humic acid solution and thermomechanical pulp mill (ThMP) process water. Membrane modification with PAA results in higher ThMP process water flux, fouling recovery ratio, and hemicellulose and total lignin rejection compared to the reference PSF/Synperonic F108 membrane. This suggests the possibility of applying the developed membranes for hemicellulose concentration and purification. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/ma15010359
  • 2022 • 212 Development of polysulfone ultrafiltration membranes with enhanced antifouling performance for the valorisation of side streams in the pulp and paper industry
    Burts, K.S. and Plisko, T.V. and Bildyukevich, A.V. and Rodrigues, G. and Sjölin, M. and Lipnizki, F. and Ulbricht, M.
    Colloids and Surfaces A: Physicochemical and Engineering Aspects 632 (2022)
    One-stage method of polysulfone (PSf) membrane modification by the addition of polyacrylic acid (PAA, Mn = 250 kg·mol−1) to the coagulation bath during membrane preparation via non-solvent induced phase separation (NIPS) was proposed. The effect of PAA concentration on the membrane structure, hydrophilicity, zeta potential, separation performance and antifouling stability in ultrafiltration of lysozyme, polyvinylpyrrolidone (PVP K-30, Mn = 40 kg mol−1) and humic acid model solutions as well as thermomechanical pulp mill process (ThMP) water was studied. Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), measurements of the tangential flow streaming potential and water contact angle were used for membrane characterization. It was found that addition of PAA into coagulation bath resulted in decreasing pore size and porosity of the selective layer as well as the formation of a thicker and denser selective layer. Water contact angle of the modified membranes was found to decrease significantly and zeta potential of the selective layer was shown to become more negative in the studied pH range 3–10, all compared to the reference membrane. It was revealed that pure water flux (PWF) decreased and lysozyme and PVP K-30 rejection increased with the increase in PAA concentration in the coagulation bath. It was found that membranes modified with PAA demonstrated better antifouling stability in ultrafiltration of humic acid solution and ThMP process water. Modified membranes were found to have higher flux, fouling recovery ratio and hemicelluloses rejection in ThMP process water ultrafiltration compared to the reference PSf membrane that allows application of these membranes for hemicelluloses concentration and purification. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.colsurfa.2021.127742
  • 2022 • 211 Dimethyl ether (DME) and dimethoxymethane (DMM) as reaction enhancers for methane: Combining flame experiments with model-assisted exploration of a polygeneration process
    Zhang, H. and Kaczmarek, D. and Rudolph, C. and Schmitt, S. and Gaiser, N. and Oßwald, P. and Bierkandt, T. and Kasper, T. and Atakan, B. and Kohse-Höinghaus, K.
    Combustion and Flame 237 (2022)
    The potential of dimethyl ether (DME) and dimethoxymethane (DMM), representatives of the attractive oxymethylene ether (OME) alternative fuel family, are explored here as reactivity enhancers for methane-fueled polygeneration processes. Typically, such processes that can flexibly generate power, heat, or chemicals, operate under fuel-rich conditions in gas turbines or internal combustion engines. To provide a consistent basis for the underlying reaction mechanisms, it is recognized that speciation data for the DME/CH4 fuel combination are available for such conditions while such information for the DMM/CH4 system is largely lacking. In addition, it should be noted that a detailed speciation study in flames, i.e., combustion systems involving chemistry and transport processes over a large temperature range, is still missing in spite of the potential of such systems to provide extended species information. In a systematic approach using speciation with electron ionization molecular-beam mass spectrometry (EI-MBMS), we thus report, as a first step, investigation of six fuel-rich premixed flames of DME and DMM and their blends with methane with special attention on interesting chemicals. Secondly, a comprehensive but compact DME/DMM/CH4 model (PolyMech2.1) is developed based on these data. This model is then examined against available experimental data under conditions from various facilities, focusing preferentially on elevated pressure and fuel-rich conditions. Comparison with existing literature models is also included in this evaluation. Thirdly, an analysis is given on this basis, via the extensively tested PolyMech2.1 model, for assumed polygeneration conditions in a homogeneous charge compression ignition (HCCI) engine environment. The main interest of this model-assisted exploration is to evaluate whether addition of DME or DMM in a polygeneration process can lead to potentially useful conditions for the production of syngas or other chemicals, along with work and heat. The flame results show that high syngas yields, i.e., up to ∼78% for CO and ∼35% for H2, can be obtained in their burnt gases. From the large number of intermediates detected, predominantly acetylene, ethylene, ethane, and formaldehyde show yields of 2.1−4.4% (C2 hydrocarbons) and 3.4−8.7% (CH2O), respectively. Also, methanol and methyl formate show comparably high yields of up to 0.6−6.7% in the flames with DMM, which is 1–2 orders of magnitude higher than in those with DME as the additive. In the modeling-assisted exploration of the engine process, the PolyMech2.1 model is seen to perform at significantly reduced computational costs compared to a recently validated model without sacrificing the prediction performance. Promising conditions for the assumed polygeneration process using fuel combinations in the DME/DMM/CH4 system are identified with attractive syngas yields of up to 77% together with work and heat output at exergetic efficiencies of up to 89% with DME. © 2021
    view abstractdoi: 10.1016/j.combustflame.2021.111863
  • 2022 • 210 Dislocation-enhanced electrical conductivity in rutile TiO2 accessed by room-temperature nanoindentation
    Bishara, H. and Tsybenko, H. and Nandy, S. and Muhammad, Q.K. and Frömling, T. and Fang, X. and Best, J.P. and Dehm, G.
    Scripta Materialia 212 (2022)
    Dislocation-enhanced electrical conductivity is an emerging topic for ceramic oxides. In contrast to the majority of present studies which focus on large-scale crystal deformation or thin film fabrication to introduce dislocations, we use a nanoindentation “pop-in stop” method to locally generate 〈011〉 edge-type dislocations at room temperature, without crack formation, on the (100) surface of a rutile TiO2 single-crystal. Ion beam assisted deposition of microcontacts allowed for both deformed and non-deformed zones to be locally probed by impedance spectroscopy. Compared to the dislocation-free region, a local enhancement of the electrical conductivity by 50% in the dislocation-rich regions is found. The study paves the way for local “mechanical-doping” of ceramics and oxide materials, allowing for the use of dislocations to tune the local conductivity with high spatial resolution. © 2022 The Author(s)
    view abstractdoi: 10.1016/j.scriptamat.2022.114543
  • 2022 • 209 Dislocation-mediated electronic conductivity in rutile
    Muhammad, Q.K. and Bishara, H. and Porz, L. and Dietz, C. and Ghidelli, M. and Dehm, G. and Frömling, T.
    Materials Today Nano 17 (2022)
    It has been recently shown that doping-like properties can be introduced into functional ceramics by inducing dislocations. Especially for TiO2, donor and acceptor-like behavior were observed depending on the type of introduced mesoscopic dislocation network. However, these early reports could not fully elucidate the mechanism behind it. In this work, we rationalize the electrical properties of dislocations by targeted microelectrode impedance measurements, local conductivity atomic force microscopy, and Kelvin probe force microscopy on deformed single crystals, comparing dislocation-rich and deficient regions. With the help of finite element method calculations, a semi-quantitative model for the effect of dislocations on the macroscopic electrical properties is developed. The model describes the dislocation bundles as highly conductive regions in which respective space charges overlap and induce temperature-independent, highly stable electronic conductivity. We illustrate the mechanism behind unique electrical properties tailored by introducing dislocations and believe that these results are the cornerstone in developing dislocation-tuned functionality in ceramics. © 2021 Elsevier Ltd
    view abstractdoi: 10.1016/j.mtnano.2021.100171
  • 2022 • 208 Durability assessment of differently orientated surfaces of treated long-term weathered natural stones
    Kunz, A. and Groh, M. and Braun, F. and Brüggerhoff, S. and Orlowsky, J.
    Journal of Cultural Heritage 53 176-183 (2022)
    In this study, selected natural stone prisms have been compared with each other to detect the effectiveness of the hydrophobic treatment on differently orientated surfaces. The samples have been examined after 2 and 17 years of weathering at two different locations in Germany. The examinations focused on certain criteria which are based on the research of the last four years. By measuring colour changes, not only the influence of different hydrophobing agents could be investigated, but also different stone deterioration patterns could be identified. It could be determined that the effectiveness of water repellents is significantly influenced by the penetration and distribution depth of the active substance. The results of non-destructive NMR measurements show that the durability of the stones is more influenced by the uniform distribution of the active ingredient and the penetration depth than by the surface orientation. Thus, for the Obernkirchener Sandstone, the efficiency of the applied agents was proven after 17 years of outdoor weathering. Despite determined effective hydrophobic zones, degradation of the natural stones could not be prevented. Measuring the damaged depth with NMR it was found out that water penetrates the stone within the first 500 to 1000 µm, even with an intact hydrophobic layer, and can cause surface changes, like biogenic growth and decomposition. In these degradation processes, the orientation of the samples again has a significant influence. Thus, the roof surfaces show stronger deterioration. © 2021 Elsevier Masson SAS
    view abstractdoi: 10.1016/j.culher.2021.12.001
  • 2022 • 207 Effect of Ag Doping on the Microstructure and Electrochemical Response of TiAlN Coatings Deposited by DCMS/HiPIMS Magnetron Sputtering
    Tillmann, W. and Grisales, D. and Echavarría, A.M. and Calderón, J.A. and Gaitan, G.B.
    Journal of Materials Engineering and Performance (2022)
    Incorporation of silver particles in nitride coatings has been used to improve the mechanical resistance of steels, but few details are known about the effect of the incorporation of these metals on the electrochemical behavior. In order to evaluate the corrosion resistance and the possible formation of a galvanic couple between the ceramic matrix of TiAlN and the metallic Ag, a TiAlN composite coating doped with four different contents of silver (0.8-25 at.%) was deposited on AISI H11 hot working steel, using the hybrid DCMS/HiPIMS magnetron sputtering technique. The microstructure, topography, elemental chemical, and phase composition of the coatings were determined using SEM/EDS, AFM, XRD, and XPS characterization techniques. The electrochemical behavior was evaluated by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization. The TiAlN matrix and TiAlN(Ag)-coated samples exhibit higher impedance modulus values than steel substrate, indicating better anticorrosion performance. The anodic current density of the Ag-doped coating increases with the Ag content, suggesting enhanced silver release to the surrounding electrolyte. The TiAlN coating doped with 0.8 at.% silver exhibited the highest corrosion resistance at long immersion times. Finally, it must be noted that all the coatings exhibited corrosion protection to the AISI H11 steel substrate. © 2021, ASM International.
    view abstractdoi: 10.1007/s11665-021-06467-9
  • 2022 • 206 Effect of laser shock peening without protective coating on the surface mechanical properties of NiTi alloy
    Wang, H. and Keller, S. and Chang, Y. and Kashaev, N. and Yan, K. and Gurevich, E.L. and Ostendorf, A.
    Journal of Alloys and Compounds 896 (2022)
    We study the effect of laser shock peening (LSP) without protective coating on the surface mechanical property of NiTi alloy. The Vickers microhardness and wear resistance are measured to determine the mechanical property of NiTi samples treated with different LSP parameters (3 J with 10 ns and 5 J with 20 ns). From the electron backscatter diffraction (EBSD) analysis, it can be found that the laser shock peening does not induce obvious grain refinement in the surface region of NiTi alloy. Both compressive and tensile residual stress in the top layer are determined using the hole drilling method. The results show that the LSP treatment without a protective coating increases the roughness and enhances the surface mechanical properties of NiTi alloy. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.jallcom.2021.163011
  • 2022 • 205 Effect of microstructure heterogeneity on the mechanical properties of friction stir welded reduced activation ferritic/martensitic steel
    Li, S. and Vajragupta, N. and Biswas, A. and Tang, W. and Wang, H. and Kostka, A. and Yang, X. and Hartmaier, A.
    Scripta Materialia 207 (2022)
    The microhardness distribution in the different zones of a friction stir welded reduced activation ferritic/martensitic steel has been investigated and correlated to the hierarchical martensitic microstructure in the respective zones, characterized by electron backscatter diffraction orientation analysis. It is found that the variation of prior austenite grain size, packet size, and block width in different subzones is influenced by the peak temperature and effective strain rate during the friction stir welding process. The distribution of the microhardness correlates directly with the geometrically necessary dislocation density observed in the different zones. © 2021
    view abstractdoi: 10.1016/j.scriptamat.2021.114306
  • 2022 • 204 Effect of thermal and densification processes on reaction and conventional sinterings of a hydrolyzed calcium phosphate phase
    Zyman, Z. and Epple, M. and Goncharenko, A. and Tkachenko, M. and Rokhmistrov, D. and Sofronov, D.
    Ceramics International 48 6716-6721 (2022)
    Thermal processes resulting in the densification of compacts of an uncalcined powder (UPC) and of the powder calcined at 700 °C for 1 h (CPC), obtained from a hydrolyzed powder with a primary molar ratio of Ca/P = 1:1 obtained by the nitrate synthesis were studied during heating under reaction and conventional sintering modes up to 1100 °C. Due to desorption, decomposition, crystallization and phase transformation processes, the density of the UPC increased stepwise and finally reached 95% of the theoretical density of the formed biphasic HA/β-TCP product with a 52/48 ratio compared to 67% and a 0.55/0.45 ratio in the CPC. Because the annealing time at 1100 °C was negligible (about 1 min), a proper completing sintering to produce high quality ceramics from such UPC phases seems very promising. © 2021 Elsevier Ltd and Techna Group S.r.l.
    view abstractdoi: 10.1016/j.ceramint.2021.11.222
  • 2022 • 203 Effective hyperelastic material parameters from microstructures constructed using the planar Boolean model
    Brändel, M. and Brands, D. and Maike, S. and Rheinbach, O. and Schröder, J. and Schwarz, A. and Stoyan, D.
    Computational Mechanics (2022)
    We construct two-dimensional, two-phase random heterogeneous microstructures by stochastic simulation using the planar Boolean model, which is a random collection of overlapping grains. The structures obtained are discretized using finite elements. A heterogeneous Neo-Hooke law is assumed for the phases of the microstructure, and tension tests are simulated for ensembles of microstructure samples. We determine effective material parameters, i.e., the effective Lamé moduli λ∗ and μ∗, on the macroscale by fitting a macroscopic material model to the microscopic stress data, using stress averaging over many microstructure samples. The effective parameters λ∗ and μ∗ are considered as functions of the microscale material parameters and the geometric parameters of the Boolean model including the grain shape. We also consider the size of the Representative Volume Element (RVE) given a precision and an ensemble size. We use structured and unstructured meshes and also provide a comparison with the FE2 method. © 2022, The Author(s).
    view abstractdoi: 10.1007/s00466-022-02142-5
  • 2022 • 202 Effects of aging on the stress-induced martensitic transformation and cyclic superelastic properties in Co-Ni-Ga shape memory alloy single crystals under compression
    Lauhoff, C. and Reul, A. and Langenkämper, D. and Krooß, P. and Somsen, C. and Gutmann, M.J. and Pedersen, B. and Kireeva, I.V. and Chumlyakov, Y.I. and Eggeler, G. and Schmahl, W.W. and Niendorf, T.
    Acta Materialia 226 (2022)
    Co-Ni-Ga shape memory alloys attracted scientific attention as promising candidate materials for damping applications at elevated temperatures, owing to excellent superelastic properties featuring a fully reversible stress-strain response up to temperatures as high as 500 °C. In the present work, the effect of aging treatments conducted in a wide range of aging temperatures and times, i.e. at 300–400 °C for 0.25–8.5 h, was investigated. It is shown that critical features of the martensitic transformation are strongly affected by the heat treatments. In particular, the formation of densely dispersed γ’-nanoparticles has a strong influence on the martensite variant selection and the morphology of martensite during stress-induced martensitic transformation. Relatively large, elongated particles promote irreversibility. In contrast, small spheroidal particles are associated with excellent functional stability during cyclic compression loading of 〈001〉-oriented single crystals. In addition to mechanical experiments, a detailed microstructural analysis was performed using in situ optical microscopy and neutron diffraction. Fundamental differences in microstructural evolution between various material states are documented and the relations between thermal treatment, microstructure and functional properties are explored and rationalized. © 2022 Acta Materialia Inc.
    view abstractdoi: 10.1016/j.actamat.2022.117623
  • 2022 • 201 Effects of Cr/Ni ratio on physical properties of Cr-Mn-Fe-Co-Ni high-entropy alloys
    Wagner, C. and Ferrari, A. and Schreuer, J. and Couzinié, J.-P. and Ikeda, Y. and Körmann, F. and Eggeler, G. and George, E.P. and Laplanche, G.
    Acta Materialia 227 (2022)
    Physical properties of ten single-phase FCC CrxMn20Fe20Co20Ni40-x high-entropy alloys (HEAs) were investigated for 0 ≤ x ≤ 26 at%. The lattice parameters of these alloys were nearly independent of composition while solidus temperatures increased linearly by ∼30 K as x increased from 0 to 26 at.%. For x ≥ 10 at.%, the alloys are not ferromagnetic between 100 and 673 K and the temperature dependencies of their coefficients of thermal expansion and elastic moduli are independent of composition. Magnetic transitions and associated magnetostriction were detected below ∼200 K and ∼440 K in Cr5Mn20Fe20Co20Ni35 and Mn20Fe20Co20Ni40, respectively. These composition and temperature dependencies could be qualitatively reproduced by ab initio simulations that took into account a ferrimagnetic ↔ paramagnetic transition. Transmission electron microscopy revealed that plastic deformation occurs initially by the glide of perfect dislocations dissociated into Shockley partials on {111} planes. From their separations, the stacking fault energy (SFE) was determined, which decreases linearly from 69 to 23 mJ·m−2 as x increases from 14 to 26 at.%. Ab initio simulations were performed to calculate stable and unstable SFEs and estimate the partial separation distances using the Peierls-Nabarro model. While the compositional trends were reasonably well reproduced, the calculated intrinsic SFEs were systematically lower than the experimental ones. Our ab initio simulations show that, individually, atomic relaxations, finite temperatures, and magnetism strongly increase the intrinsic SFE. If these factors can be simultaneously included in future computations, calculated SFEs will likely better match experimentally determined SFEs. © 2022
    view abstractdoi: 10.1016/j.actamat.2022.117693
  • 2022 • 200 Effects of Dispersion and Charge-Transfer Interactions on Structures of Heavy Chalcogenide Compounds: A Quantum Chemical Case Study for (Et2Bi)2Te
    van der Vight, F. and Schulz, S. and Jansen, G.
    ChemPlusChem (2022)
    The reasons for the unusually small Bi−Te−Bi bond angle of 86.6° observed in the crystal strucure of (Et2Bi)2Te are investigated by quantum chemical calculations. With the help of coupled cluster theory at the CCSD(T) level it is demonstrated that the structure of an isolated monomer should have a bond angle larger than 90°, despite a Bi−Bi distance in good agreement with the value of 4.09 Å found in the crystal structure. The discrepancy is resolved by a lengthening of the Bi−Te bond in the crystal, which is shown to be caused by partial electron transfer from neighbouring molecules to the Bi−Te σ* orbital. Through symmetry-adapted perturbation theory at the DFT-SAPT level it is shown that London dispersion interactions are highly important for the packing of molecules in the solid state and, in turn, for the small Bi−Te−Bi bond angle. © 2022 The Authors. ChemPlusChem published by Wiley-VCH GmbH.
    view abstractdoi: 10.1002/cplu.202100487
  • 2022 • 199 Effects of Microstructure Modification by Friction Surfacing on Wear Behavior of Al Alloys with Different Si Contents
    Schütte, M.R. and Ehrich, J. and Linsler, D. and Hanke, S.
    Materials 15 (2022)
    In this work, Al alloys with 6.6%, 10.4%, and 14.6% Si were deposited as thick coatings by Friction Surfacing (FS), resulting in grain refinement and spheroidization of needle-shaped eutectic Si phase. Lubricated sliding wear tests were performed on a pin-on-disc tribometer using Al-Si alloys in as-cast and FS processed states as pins and 42CrMo4 steel discs. The chemical composition of the worn surfaces was analyzed by X-ray photoelectron spectroscopy (XPS). The wear mechanisms were studied by scanning electron microscopy (SEM) and focused ion beam (FIB), and the wear was evaluated by measuring the weight loss of the samples. For the hypoeutectic alloys, spheroidization of the Si phase particles in particular leads to a significant improvement in wear resistance. The needle-shaped Si phase in as-cast state fractures during the wear test and small fragments easily detach from the surface. The spherical Si phase particles in the FS state also break away from the surface, but to a smaller extent. No reduction in wear due to FS was observed for the hypereutectic alloy. Here, large bulky primary Si phase particles are already present in the as-cast state and do not change significantly during FS, providing high wear resistance in both material states. This study highlights the mechanisms and limitations of improved wear resistance of Si-rich Al alloys deposited as thick coatings by Friction Surfacing. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/ma15051641
  • 2022 • 198 Efficient and robust numerical treatment of a gradient-enhanced damage model at large deformations
    Junker, P. and Riesselmann, J. and Balzani, D.
    International Journal for Numerical Methods in Engineering 123 774-793 (2022)
    The modeling of damage processes in materials constitutes an ill-posed mathematical problem which manifests in mesh-dependent finite element results. The loss of ellipticity of the discrete system of equations is counteracted by regularization schemes of which the gradient enhancement of the strain energy density is often used. In this contribution, we present an extension of the efficient numerical treatment, which has been proposed by Junker et al. in 2019, to materials that are subjected to large deformations. Along with the model derivation, we present a technique for element erosion in the case of severely damaged materials. Efficiency and robustness of our approach is demonstrated by two numerical examples including snapback and springback phenomena. © 2021 The Authors. International Journal for Numerical Methods in Engineering published by John Wiley & Sons Ltd.
    view abstractdoi: 10.1002/nme.6876
  • 2022 • 197 Efficient model-based bioequivalence testing
    Möllenhoff, K. and Loingeville, F. and Bertrand, J. and Nguyen, T.T. and Sharan, S. and Zhao, L. and Fang, L. and Sun, G. and Grosser, S. and Mentré, F. and Dette, H.
    Biostatistics (Oxford, England) 23 314-327 (2022)
    The classical approach to analyze pharmacokinetic (PK) data in bioequivalence studies aiming to compare two different formulations is to perform noncompartmental analysis (NCA) followed by two one-sided tests (TOST). In this regard, the PK parameters area under the curve (AUC) and $C_{\max}$ are obtained for both treatment groups and their geometric mean ratios are considered. According to current guidelines by the U.S. Food and Drug Administration and the European Medicines Agency, the formulations are declared to be sufficiently similar if the $90\%$ confidence interval for these ratios falls between $0.8$ and $1.25 $. As NCA is not a reliable approach in case of sparse designs, a model-based alternative has already been proposed for the estimation of $\rm AUC$ and $C_{\max}$ using nonlinear mixed effects models. Here we propose another, more powerful test than the TOST and demonstrate its superiority through a simulation study both for NCA and model-based approaches. For products with high variability on PK parameters, this method appears to have closer type I errors to the conventionally accepted significance level of $0.05$, suggesting its potential use in situations where conventional bioequivalence analysis is not applicable. © The Author 2020. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.
    view abstractdoi: 10.1093/biostatistics/kxaa026
  • 2022 • 196 Efficient parametrization of the atomic cluster expansion
    Bochkarev, A. and Lysogorskiy, Y. and Menon, S. and Qamar, M. and Mrovec, M. and Drautz, R.
    Physical Review Materials 6 (2022)
    The atomic cluster expansion (ACE) provides a general, local, and complete representation of atomic energies. Here we present an efficient framework for parametrization of ACE models for elements, alloys, and molecules. To this end, we first introduce general requirements for a physically meaningful description of the atomic interaction, in addition to the usual equivariance requirements. We then demonstrate that ACE can be converged systematically with respect to two fundamental characteristics—the number and complexity of basis functions and the choice of nonlinear representation. The construction of ACE parametrizations is illustrated for several representative examples with different bond chemistries, including metallic copper, covalent carbon, and several multicomponent molecular and alloy systems. We discuss the Pareto front of optimal force to energy matching contributions in the loss function, the influence of regularization, the importance of consistent and reliable reference data, and the necessity of unbiased validation. Our ACE parametrization strategy is implemented in the freely available software package pacemaker that enables largely automated and GPU accelerated training. The resulting ACE models are shown to be superior or comparable to the best currently available ML potentials and can be readily used in large-scale atomistic simulations. ©2022 American Physical Society
    view abstractdoi: 10.1103/PhysRevMaterials.6.013804
  • 2022 • 195 Elastic energy of multi-component solid solutions and strain origins of phase stability in high-entropy alloys
    Darvishi Kamachali, R. and Wang, L.
    Scripta Materialia 206 (2022)
    The elastic energy of mixing for multi-component solid solutions is derived by generalizing Eshelby's sphere-in-hole model. By surveying the dependence of the elastic energy on the chemical composition and lattice misfit, we derive a lattice strain coefficient λ*. Studying several high-entropy alloys and superalloys, we propose that most solid solution multi-component alloys are stable when λ*&lt;0.16, generalizing the Hume-Rothery atomic-size rule for binary alloys. We also reveal that the polydispersity index δ, frequently used for describing strain in multi-component alloys, directly represents the elastic energy (e) with e=qδ2, q being an elastic constant. Furthermore, the effects of (i) the number and (ii) the atomic-size distribution of constituting elements on the phase stability of high-entropy alloys were quantified. The present derivations and discussions open for richer considerations of elastic effects in high-entropy alloys, offering immediate support for quantitative assessments of their thermodynamic properties and studying related strengthening mechanisms. © 2021
    view abstractdoi: 10.1016/j.scriptamat.2021.114226
  • 2022 • 194 Electrocatalytic Conversion of Glycerol to Oxalate on Ni Oxide Nanoparticles-Modified Oxidized Multiwalled Carbon Nanotubes
    Morales, D.M. and Jambrec, D. and Kazakova, M.A. and Braun, M. and Sikdar, N. and Koul, A. and Brix, A.C. and Seisel, S. and Andronescu, C. and Schuhmann, W.
    ACS Catalysis 12 982-992 (2022)
    Electrocatalytic oxidation of glycerol (GOR) as the anode reaction in water electrolysis facilitates the production of hydrogen at the cathode at a substantially lower cell voltage compared with the oxygen evolution reaction. It simultaneously provides the basis for the production of value-added compounds at the anode. We investigate earth-abundant transition-metal oxide nanoparticles (Fe, Ni, Mn, Co) embedded in multiwalled carbon nanotubes as GOR catalysts. Out of the four investigated composites, the Ni-based catalyst exhibits the highest catalytic activity toward the GOR according to rotating disk electrode voltammetry, reaching a current density of 10 mA cm–2 already at 1.31 V vs RHE, a potential below the formation of Ni3+. Chronoamperometry conducted in a flow-through cell followed by HPLC analysis is used to identify and quantify the GOR products over time, revealing that the applied potential, electrolyte concentration, and duration of the experiment impact strongly the composition of the products’ mixture. Upon optimization, the GOR is directed toward oxalate production. Moreover, oxalate is not further converted and hence accumulates as a major organic product under the chosen conditions in a concentration ratio of 60:1 with acetate as a minor product after 48 h electrolysis in 7 M KOH, which represents a promising route for the synthesis of this highly valued product. © 2022 American Chemical Society
    view abstractdoi: 10.1021/acscatal.1c04150
  • 2022 • 193 Electrophoretic Deposition of Platinum Nanoparticles using Ethanol-Water Mixtures Significantly Reduces Neural Electrode Impedance
    Ramesh, V. and Giera, B. and Karnes, J.J. and Stratmann, N. and Schaufler, V. and Li, Y. and Rehbock, C. and Barcikowski, S.
    Journal of the Electrochemical Society 169 (2022)
    Platinum electrodes are critical components in many biomedical devices, an important example being implantable neural stimulation or recording electrodes. However, upon implantation, scar tissue forms around the electrode surface, causing unwanted deterioration of the electrical contact. We demonstrate that sub-monolayer coatings of platinum nanoparticles (PtNPs) applied to 3D neural electrodes by electrophoretic deposition (EPD) can enhance the electrode?s active surface area and significantly lower its impedance. In this work we use ethanol-water mixtures as the EPD solvent, in contrast to our previous studies carried out in water. We show that EPD coating in 30 vol.% ethanol improves the device?s electrochemical performance. Computational mesoscale multiparticle simulations were for the first time applied to PtNP-on-Pt EPD, revealing correlations between ethanol concentration, electrochemical properties, and coating homogeneity. Thereto, this optimum ethanol concentration (30 vol.%) balances two opposing trends: (i) the addition of ethanol reduces water splitting and gas bubble formation, which benefits surface coverage, and (ii) increased viscosity and reduced permittivity occur at high ethanol concentrations, which impair the coating quality and favoring clustering. A seven-fold increase in active surface area and significantly reduced in vitro impedance of the nano-modified neural stimulation electrode surfaces highlight the influence of ethanol-water mixtures in PtNP EPD. © 2022 The Electrochemical Society ("ECS"). Published on behalf of ECS by IOP Publishing Limited.
    view abstractdoi: 10.1149/1945-7111/ac51f8
  • 2022 • 192 Enhanced heterogeneous activation of peroxymonosulfate by Ruddlesden-Popper-type La2CoO4+δ nanoparticles for bisphenol A degradation
    Hammad, M. and Alkan, B. and Al-kamal, A.K. and Kim, C. and Ali, M.Y. and Angel, S. and Wiedemann, H.T.A. and Klippert, D. and Schmidt, T.C. and Kay, C.W.M. and Wiggers, H.
    Chemical Engineering Journal 429 (2022)
    The scalable synthesis of stable catalysts for environmental remediation applications remains challenging. Nonetheless, metal leaching is a serious environmental issue hindering the practical application of transition-metal based catalysts including Co-based catalysts. Herein, for the first time, we describe a facile one-step and scalable spray-flame synthesis of high surface area La2CoO4+δ nanoparticles containing excess oxygen interstitials (+δ) and use them as a stable and efficient catalyst for activating peroxymonosulfate (PMS) towards the degradation of bisphenol A. Importantly, the La2CoO4+δ catalyst exhibits higher catalytic degradation of bisphenol A (95% in 20 min) and stability than LaCoO3–x nanoparticles (60%) in the peroxymonosulfate activation system. The high content of Co2+ in the structure showed a strong impact on the catalytic performance of the La2CoO4+δ + PMS system. Despite its high specific surface area, our results showed a very low amount of leached cobalt (less than 0.04 mg/L in 30 min), distinguishing it as a material with high chemical stability. According to the radical quenching experiments and the electron paramagnetic resonance technology, SO4[rad]–, [rad]OH, and 1O2 were generated and SO4[rad]– played a dominant role in bisphenol A degradation. Moreover, the La2CoO4+δ + PMS system maintained conspicuous catalytic performance for the degradation of other organic pollutants including methyl orange, rhodamine B, and methylene blue. Overall, our results showed that we developed a new synthesis method for stable La2CoO4+δ nanoparticles that can be used as a highly active heterogeneous catalyst for PMS-assisted oxidation of organic pollutants. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.cej.2021.131447
  • 2022 • 191 Enhancement of Proton Therapy Efficiency by Noble Metal Nanoparticles Is Driven by the Number and Chemical Activity of Surface Atoms
    Zwiehoff, S. and Johny, J. and Behrends, C. and Landmann, A. and Mentzel, F. and Bäumer, C. and Kröninger, K. and Rehbock, C. and Timmermann, B. and Barcikowski, S.
    Small 18 (2022)
    Proton-based radiotherapy is a modern technique for the treatment of solid tumors with significantly reduced side effects to adjacent tissues. Biocompatible nanoparticles (NPs) with high atomic numbers are known to serve as sensitizers and to enhance treatment efficacy, which is commonly believed to be attributed to the generation of reactive oxygen species (ROS). However, little systematic knowledge is available on how either physical effects due to secondary electron generation or the particle surface chemistry affect ROS production. Thereto, ligand-free colloidal platinum (Pt) and gold (Au) NPs with well-controlled particle size distributions and defined total surface area are proton-irradiated. A fluorescence-based assay is developed to monitor the formation of ROS using terephthalic acid as a cross-effect-free dye. The findings indicate that proton irradiation (PI)-induced ROS formation sensitized by noble metal NPs is driven by the total available particle surface area rather than particle size or mass. Furthermore, a distinctive material effect with Pt being more active than Au is observed which clearly indicates that the chemical reactivity of the NP surface is a main contributor to ROS generation upon PI. These results pave the way towards an in-depth understanding of the NP-induced sensitizing effects upon PI and hence a well-controlled enhanced therapy. © 2021 The Authors. Small published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/smll.202106383
  • 2022 • 190 ERK1/2 Activity Is Critical for the Outcome of Ischemic Stroke
    Schanbacher, C. and Bieber, M. and Reinders, Y. and Cherpokova, D. and Teichert, C. and Nieswandt, B. and Sickmann, A. and Kleinschnitz, C. and Langhauser, F. and Lorenz, K.
    International Journal of Molecular Sciences 23 (2022)
    Ischemic disorders are the leading cause of death worldwide. The extracellular signal-regulated kinases 1 and 2 (ERK1/2) are thought to affect the outcome of ischemic stroke. However, it is under debate whether activation or inhibition of ERK1/2 is beneficial. In this study, we report that the ubiquitous overexpression of wild-type ERK2 in mice (ERK2wt ) is detrimental after transient occlusion of the middle cerebral artery (tMCAO), as it led to a massive increase in infarct volume and neurological deficits by increasing blood–brain barrier (BBB) leakiness, inflammation, and the number of apoptotic neurons. To compare ERK1/2 activation and inhibition side-by-side, we also used mice with ubiquitous overexpression of the Raf-kinase inhibitor protein (RKIPwt ) and its phosphorylation-deficient mutant RKIPS153A, known inhibitors of the ERK1/2 signaling cascade. RKIPwt and RKIPS153A attenuated ischemia-induced damages, in particular via anti-inflammatory signaling. Taken together, our data suggest that stimulation of the Raf/MEK/ERK1/2-cascade is severely detrimental and its inhibition is rather protective. Thus, a tight control of the ERK1/2 signaling is essential for the outcome in response to ischemic stroke. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/ijms23020706
  • 2022 • 189 Existence and uniqueness of Rayleigh waves in isotropic elastic Cosserat materials and algorithmic aspects
    Khan, H. and Ghiba, I.-D. and Madeo, A. and Neff, P.
    Wave Motion 110 (2022)
    We discuss the propagation of surface waves in an isotropic half space modelled with the linear Cosserat theory of isotropic elastic materials. To this aim we use a method based on the algebraic analysis of the surface impedance matrix and on the algebraic Riccati equation, and which is independent of the common Stroh formalism. Due to this method, a new algorithm which determines the amplitudes and the wave speed in the theory of isotropic elastic Cosserat materials is described. Moreover, this method allows us to prove the existence and uniqueness of a subsonic solution of the secular equation, a problem which remains unsolved in almost all generalized linear theories of elastic materials. Since the results are suitable to be used for numerical implementations, we propose two numerical algorithms which are viable for any elastic material. Explicit numerical calculations are made for aluminium-epoxy in the context of the Cosserat model. Since the novel form of the secular equation for isotropic elastic material has not been explicitly derived elsewhere, we establish it in this paper, too. © 2022 Elsevier B.V.
    view abstractdoi: 10.1016/j.wavemoti.2022.102898
  • 2022 • 188 Experimental and computational analysis of the coolant distribution considering the viscosity of the cutting fluid during machining with helical deep hole drills
    Oezkaya, E. and Michel, S. and Biermann, D.
    Advances in Manufacturing (2022)
    An experimental analysis regarding the distribution of the cutting fluid is very difficult due to the inaccessibility of the contact zone within the bore hole. Therefore, suitable simulation models are necessary to evaluate new tool designs and optimize drilling processes. In this paper the coolant distribution during helical deep hole drilling is analyzed with high-speed microscopy. Micro particles are added to the cutting fluid circuit by a developed high-pressure mixing vessel. After the evaluation of suitable particle size, particle concentration and coolant pressure, a computational fluid dynamics (CFD) simulation is validated with the experimental results. The comparison shows a very good model quality with a marginal difference for the flow velocity of 1.57% between simulation and experiment. The simulation considers the kinematic viscosity of the fluid. The results show that the fluid velocity in the chip flutes is low compared to the fluid velocity at the exit of the coolant channels of the tool and drops even further between the guide chamfers. The flow velocity and the flow pressure directly at the cutting edge decrease to such an extent that the fluid cannot generate a sufficient cooling or lubrication. With the CFD simulation a deeper understanding of the behavior and interactions of the cutting fluid is achieved. Based on these results further research activities to improve the coolant supply can be carried out with great potential to evaluate new tool geometries and optimize the machining process. © 2022, The Author(s).
    view abstractdoi: 10.1007/s40436-021-00383-w
  • 2022 • 187 Experimental and numerical investigations of micro-meso damage evolution for a WC/Co-type tool material
    Schneider, Y. and Weber, U. and Xu, C. and Zielke, R. and Schmauder, S. and Tillmann, W.
    Materialia 21 (2022)
    Commercial Co/WC/diamond composites with 90vol.% Co also belong to hard metals and, as a kind of tool materials, are very useful. Their deformation behavior can be both ductile and quasi-brittle, determined by the diamond portion and local morphology. Another characteristic is that submicron-sized WC particles, possessing non-negligible strengthening influence due to the size effect, cannot be fully present in a representative microstructure. This work emphasizes the local damage evolutions’ dependence on microstructural features. Rice&Tracey damage and cohesive zone model describe the ductile and quasi-brittle damage behavior. The mechanism-based strain gradient plasticity takes the size effect of submicron-sized WC particles into consideration. Both real and artificial microstructures are used. Besides homogeneous boundary conditions (BCs), the periodic BCs are also applied in a 2D damage simulation. This work proves that FE models with two phases, the homogenized Co-WC matrix and diamond particles, can correctly predict damage evolution. FE results show that the WC phase has a higher mean stress value than the diamond phase, which is proved by the nano-indentation test. From FE simulation results, local hot spots appear in the matrix closed to sharp diamond corners/edges and crossing regions of shear bands. The experimental and numerical results are compared on micro and macro scales. For the local strain distribution and the damage development, numerical predictions match the reality well, even in morphological details. Furthermore, since the published data about WC-Co type tool materials with Co>50vol.% are rare, the obtained knowledge in this work also contributes to the data collection. © 2022 The Authors
    view abstractdoi: 10.1016/j.mtla.2022.101343
  • 2022 • 186 Experimental investigation of laser surface texturing and related biocompatibility of pure titanium
    Li, H. and Wang, X. and Zhang, J. and Wang, B. and Breisch, M. and Hartmaier, A. and Rostotskyi, I. and Voznyy, V. and Liu, Y.
    International Journal of Advanced Manufacturing Technology (2022)
    While pure titanium is a material of choice for medical applications for its excellent mechanical and chemical properties, further improving its surface-related functionalities by surface texturing is also promising. In the present work, we experimentally investigate the fabrication, as well as the resulting functionalities of surface wettability and biocompatibility, of precise mesh-type surface textures on pure titanium by picosecond pulsed laser ablation operating at 1064 nm wavelength. Specifically, the dependence of microgroove morphology on average power and scanning speed is evaluated to yield optimized laser processing parameters, which are utilized to fabricate high precision mesh-type surface textures with uniform feature size and limited thermal effects on pure titanium. Subsequent performance evaluation tests demonstrate that the mesh-type surface textures induce a beneficial effect on the biocompatibility with respect to BMSC cells due to the enhanced hydrophilicity. © 2022, The Author(s), under exclusive licence to Springer-Verlag London Ltd., part of Springer Nature.
    view abstractdoi: 10.1007/s00170-022-08710-6
  • 2022 • 185 Experimental Validation of an Analytical Condensation Model for Application in Steam Turbine Design
    Lapp, F.F. and Schuster, S. and Hecker, S. and Brillert, D.
    International Journal of Turbomachinery, Propulsion and Power 7 (2022)
    This paper presents experimental data on shear-stress-driven liquid water films on a horizontal plate formed by the condensation of superheated steam. The experimental results were obtained in the Experimental Multi-phase Measurement Application (EMMA) at the University of Duisburg-Essen. The liquid film thickness was spatially and temporally investigated with an optical measurement system. Furthermore, the resulting local heat transfer coefficient in the case of film condensation was determined for a variety of steam velocities and temperatures. Subsequently, the presented data are compared to the results of an analytical condensation model for shear-stressdriven liquid films developed by Cess and Koh. Thus, the model is qualitatively validated, with explicable remaining disparities between the model and experiment that are further discussed. The presented results are an important contribution to the contemporary research into steady-state, single-component multiphase flow considering phase-change phenomena including heat transfer. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/ijtpp7010009
  • 2022 • 184 Exploring stability of a nanoscale complex solid solution thin film by in situ heating transmission electron microscopy
    Manjón, A.G. and Zhang, S. and Völker, B. and Meischein, M. and Ludwig, Al. and Scheu, C.
    MRS Bulletin (2022)
    Abstract: Combining thin film deposition with in situ heating electron microscopy allows to understand the thermal stability of complex solid solution nanomaterials. From a CrMnFeCoNi alloy target a thin film with an average thickness of ~10 nm was directly sputtered onto a heating chip for in situ transmission electron microscopy. We investigate the growth process and the thermal stability of the alloy and compare our results with other investigations on bulk alloys or bulk-like films thicker than 100 nm. For the chosen sputtering condition and SiNx substrate, the sputter process leads to the Stranski–Krastanov growth type (i.e., islands forming on the top of a continuous layer). Directly after sputtering, we detect two different phases, namely CoNi-rich nanoscale islands and a continuous CrMnFe-rich layer. In situ annealing of the thin film up to 700°C leads to Ostwald ripening of the islands, which is enhanced in the areas irradiated by the electron beam during heating. Besides Ostwald ripening, the chemical composition of the continuous layer and the islands changed during the heating process. After annealing, the islands are still CoNi-rich, but lower amounts of Fe and Cr are observed and Mn was completely absent. The continuous layer also changed its composition. Co and Ni were removed, and the amount of Cr lowered. These results confirm that the synthesis of a CrMnFeCoNi thin film with an average thickness of ~10 nm can lead to a different morphology, chemical composition, and stability compared to thicker films (>100 nm). Impact statement: Exploring stability of a complex solid solution thin film by in situ heating transmission electron microscopy is a study of the thermal stability of sputtered complex solid solution thin films with thicknesses of ~10 nm. Complex solid solution materials have a promising electrocatalytic behavior due to the interplay of multi-element active sites. In order to understand their catalytic properties, it is important to identify the different structure-composition-activity correlations. Thus, our investigation helps to clarify and to understand the stability of nanoscale complex solid solution with an average film thickness of ~10 nm. Graphic abstract: Combining sputter deposition with in situ heating transmission electron microscopy allows to understand the thermal stability of nanoscale complex solid solution thin films. [Figure not available: see fulltext.] © 2022, The Author(s).
    view abstractdoi: 10.1557/s43577-021-00217-x
  • 2022 • 183 Extrusion process simulation and layer shape prediction during 3D-concrete-printing using the Particle Finite Element Method
    Reinold, J. and Nerella, V.N. and Mechtcherine, V. and Meschke, G.
    Automation in Construction 136 (2022)
    Product quality and processing of additively manufactured concrete components strongly depend on the flow processes during material extrusion. To control layer deformations and enable purposeful design, numerical analyses with varying process and material parameters were performed to obtain a deeper understanding of flow processes and forces developing in the vicinity of the nozzle using the Lagrangian-based Particle Finite Element Method in association with a Bingham constitutive model. This model was validated by comparing the simulated layer geometries with those obtained from laboratory 3D-printing experiments. Within the investigated parameter range, the forces generated under the extrusion nozzle can be 6 times higher than those induced by self-weight and may cause deformations in substrate layers. Since the distribution of extrusion forces may change substantially under the nozzle for varying parameters, a novel indicator based on the yielding material is introduced to find optimal 3D-printing parameters to prevent plastic deformations in substrate layers. © 2022 Elsevier B.V.
    view abstractdoi: 10.1016/j.autcon.2022.104173
  • 2022 • 182 Fabrication of thin sheets of the sodium superionic conductor Na5YSi4O12 with tape casting
    Yang, A. and Ye, R. and Li, X. and Lu, Q. and Song, H. and Grüner, D. and Ma, Q. and Tietz, F. and Fattakhova-Rohlfing, D. and Guillon, O.
    Chemical Engineering Journal 435 (2022)
    All-solid-state sodium batteries (ASSNBs), which combine the benefits of high safety and low cost, are expected to be an alternative or complementary storage technology to lithium ion batteries. Herein, we developed an aqueous tape casting technique for the continuous fabrication of ceramic sheets made of silicate-based Na5YSi4O12 (NYS) Na+ ion superionic conductor for the first time. After sintering, the ceramics showed a total conductivity of 1.0 mS cm−1 at room-temperature, low total activation energy of 0.30 eV, and wide electrochemical window of over 8 V. The critical current density of NYS tape against Na-metal electrodes can reach 2.2 mA cm−2 and the galvanostatic cycling time is over 280 h under 0.8 mA cm−2 and 0.8 mAh cm−2. The obtained tape has high crystalline purity, dense microstructure, favorable mechanical properties (hardness H of 2 GPa and elastic modulus E of 45 GPa). This work not only highlights the potential of the scarcely studied silicate-based NYS ionic conductor as a functional separator, but also presents a cost-efficient and eco-friendly continuous fabrication using the aqueous tape casting technique, thus being expected to boost the practical application of NYS as solid-state electrolyte in ASSNBs. © 2022 Elsevier B.V.
    view abstractdoi: 10.1016/j.cej.2022.134774
  • 2022 • 181 Factors Influencing the Crystallization-Onset Time of Metastable ASDs
    Wolbert, F. and Fahrig, I.-K. and Gottschalk, T. and Luebbert, C. and Thommes, M. and Sadowski, G.
    Pharmaceutics 14 (2022)
    In formulation development, amorphous solid dispersions (ASD) are considered to improve the bioavailability of poorly water-soluble active pharmaceutical ingredients (APIs). However, the crystallization of APIs often limits long-term stability and thus the shelf life of ASDs. It has already been shown earlier that the long-term stability of ASDs strongly depends on the storage conditions (relative humidity, temperature), the manufacturing methods, and the resulting particle sizes. In this work, ASDs composed of the model APIs Griseofulvin (GRI) or Itraconazole (ITR) and the polymers poly (vinylpyrrolidone-co-vinyl acetate) (PVPVA) or Soluplus® were manufactured via spray drying and hot-melt extrusion. Each API/polymer combination was manufactured using the two manufacturing methods with at least two different API loads and two particle-size distributions. It was a priori known that these ASDs were metastable and would crystallize over time, even in the dry stage. The amount of water absorbed by the ASD from humid air (40◦ C/75% relative humidity), the solubility of the API in the ASD at humid conditions, and the resulting glass-transition temperature were predicted using the Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT) and the Gordon–Taylor approach, respectively. The onset of crystallization was determined via periodic powder X-ray diffraction (PXRD) measurements. It was shown that simple heuristics such as “larger particles always crystallize later than smaller particles” are correct within one manufacturing method but cannot be transferred from one manufacturing method to another. Moreover, amorphous phase separation in the ASDs was shown to also influence their crystallization kinetics. Counterintuitively, phase separation accelerated the crystallization time, which could be explained by the glass-transition temperatures of the evolving phases. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/pharmaceutics14020269
  • 2022 • 180 Fatigue Assessment of Twin Wire Arc Sprayed and Machine Hammer-Peened ZnAl4 Coatings on S355 JRC+C Substrate
    Milz, M.P. and Wirtz, A. and Abdulgader, M. and Biermann, D. and Tillmann, W. and Walther, F.
    Materials 15 (2022)
    Structural elements for applications in maritime environments, especially offshore instal-lations, are subjected to various stresses, such as mechanical loads caused by wind or waves and corrosive attacks, e.g., by seawater, mist and weather. Thermally sprayed ZnAl coatings are often used for maritime applications, mainly due to good corrosion protection properties. Machine hammer peening (MHP) has the potential to increase fatigue and corrosion fatigue resistance of ZnAl coatings by adjusting various material properties such as hardness, porosity and roughness. This study investigates the fatigue behavior of twin wire arc sprayed and MHP post-treated ZnAl4 coat-ings. Unalloyed steel (S355 JRC+C) was selected as substrate material and tested as a reference. MHP achieved the desired improvements in material properties with increased hardness, decreased roughness and uniform coating thickness. Multiple and constant amplitude tests have been carried out to evaluate the fatigue capability of coating systems. In the high cycle fatigue regime, the addi-tional MHP post-treatment led to an improvement of the lifetime in comparison to pure sandblasted specimens. The surface was identified as a crack initiation point. ZnAl coating and MHP post-treat-ment are suitable to improve the fatigue behavior in the high cycle fatigue regime compared to uncoated specimens. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/ma15031182
  • 2022 • 179 Fe3+ -hosting carbon phases in the deep Earth
    Albers, C. and Sakrowski, R. and Libon, L. and Spiekermann, G. and Winkler, B. and Schmidt, C. and Bayarjargal, L. and Cerantola, V. and Chariton, S. and Giordano, N. and Gretarsson, H. and Kaa, J. and Liermann, H.-P. and Sunderma...
    Physical Review B 105 (2022)
    Iron-bearing carbonates play an important role in Earth's carbon cycle. Owing to their stability at mantle conditions, recently discovered iron carbonates with tetrahedrally coordinated carbon atoms are candidates for carbon storage in the deep Earth. The carbonates' iron oxidation and spin state at extreme pressure and temperature conditions contribute to the redox conditions and element partitioning in the deep mantle. By laser heating FeCO3 at pressures of about 83 GPa, Fe43+C3O12 and Fe22+Fe23+C4O13 were synthesized and then investigated by x-ray emission spectroscopy to elucidate their spin state, both in situ and temperature quenched. Our experimental results show both phases in a high-spin state at all pressures and over the entire temperature range investigated, i.e., up to 3000 K. The spin state is conserved after temperature quenching. A formation path is favored where Fe43+C3O12 forms first and then reacts to Fe22+Fe23+C4O13, most likely accompanied by the formation of oxides. Density functional theory calculations of Fe22+Fe23+C4O13 at 80 GPa confirm the experimental findings with both ferric and ferrous iron in high-spin state with antiferromagnetic order at 80 GPa. As the intercrystalline cation partitioning between the Fe-bearing carbonates and the surrounding perovskite and ferropericlase depends on the spin state of the iron, an understanding of the redox conditions prevalent in subducted slab regions in the lower mantle has to take the latter into account. Especially, Fe22+Fe23+C4O13 may play a key role in subducted material in the lower mantle, potentially with a similar role as silicate perovskite. © 2022 American Physical Society.
    view abstractdoi: 10.1103/PhysRevB.105.085155
  • 2022 • 178 Feature extraction and neural network-based multi-peak analysis on time-correlated LiDAR histograms
    Chen, G. and Landmeyer, F. and Wiede, C. and Kokozinski, R.
    Journal of Optics (United Kingdom) 24 (2022)
    Time correlated single photon counting is a statistical method to generate time-correlated histograms (TC-Hists), which are based on the time-of-flight information measured by photon detectors such as single-photon avalanche diodes. With restricted measurements per histogram and the presence of high background light, it is challenging to obtain the target distance in a TC-Hist. In order to improve the data processing robustness under these conditions, the concept of machine learning is applied to the TC-Hist. Using the neural network-based multi-peak analysis (NNMPA), introduced by us, including a physics-guided feature extraction and a distance prediction process, the analysis is focused on a small number of critical features in the TC-Hist. Based on these features, possible target distances with correlated certainty values are inferred. Furthermore, two optimization approaches regarding learning ability and real-time performance are discussed. In particular, variants of the NNMPA are evaluated on both synthetic and real datasets. The proposed method not only has higher robustness in allocating the coarse position ( ±5% ) of the target distance in harsh conditions, but also is faster than the classical digital processing with an average-filter and noise suppression. Thus, it can be applied to improve the system robustness, especially in the case of high background light and middle-range detections. © 2022 The Author(s). Published by IOP Publishing Ltd.
    view abstractdoi: 10.1088/2040-8986/ac486d
  • 2022 • 177 Ferromagnetic Europium Sulfide Thin Films: Influence of Precursors on Magneto-Optical Properties
    Beer, S.M.J. and Muriqi, A. and Lindner, P. and Winter, M. and Rogalla, D. and Nolan, M. and Ney, A. and Debus, J. and Devi, A.
    Chemistry of Materials 34 152-164 (2022)
    Europium sulfide (EuS) thin films are appealing as ferromagnetic semiconductors and luminescent and optomagnetic materials owing to their unique functional properties. With the emerging field of spintronics and magneto-optical devices, chemical vapor deposition (CVD) offers a versatile platform to tune the material properties and the method to fabricate device structures needed for such applications. Herein, we report the growth of high-quality cubic EuS via a versatile CVD process where the new Eu(III) precursors employed facilitate the formation of the target EuS layers under moderated process conditions. Based on the prior evaluation of the physicochemical properties of these precursors using thermal analysis and density functional theory studies, adequate volatility, thermal stability, and sufficient reactivity toward potential co-reactants, namely, elemental sulfur, could be inferred. Thus, the use of toxic hydrogen sulfide generally needed for sulfide film depositions could be avoided, which is a significant advantage in terms of simplifying the deposition process. The as-deposited thin films were analyzed in terms of the structure, composition, and morphology, revealing highly oriented polycrystalline and stoichiometric EuS films. UV/vis measurements yielded a band gap of around 1.6 eV, and Raman spectroscopy exhibited a coupling between the phonons and electron spin systems of EuS. These findings, together with the soft ferromagnetic character of the films derived from semiconducting quantum interference device measurements, signify the potential of CVD-grown EuS for future technological applications. © 2021 American Chemical Society.
    view abstractdoi: 10.1021/acs.chemmater.1c02958
  • 2022 • 176 First evidence of crucible steel production in Medieval Anatolia, Kubadabad: A trace for possible technology exchange between Anatolia and Southern Asia
    Güder, Ü. and Çeken, M. and Yavaş, A. and Yalçın, Ü. and Raabe, D.
    Journal of Archaeological Science 137 (2022)
    In this article, we present the first archaeological evidence for crucible steel production in Anatolia uncovered in recent excavations at Kubadabad, which was built as a palace by the Anatolian Seljuks in the early 13th century AD. Along with plenty of crucible sherds recovered at the site, blades made of crucible steel, production waste-iron chunks and manganese oxide pellets also revealed remarkable information about the process of production. Based on the results of the archaeometry analysis of crucibles of a unique shape with a pointed base, it was discovered that the fabric of the crucible was tempered with finely crushed charcoal, straw and quartz-containing sand. In addition, metallography and SEM analysis conducted on the metal finds demonstrated that high-quality tools were produced from manganese alloy crucible steel ingots at the site. This study evaluates most of the finds found at Kubadabad from the end of the 13th century AD, when some of the buildings were converted into workshops for decorated ceramic tiles and metal production under Ilkhanid patronage or Turkish beyliks. Using analytical results and archaeological findings, we discuss the historical connections of crucible steel production in Kubadabad, which differs from the Central Asian and Persian traditions, but shares similarities with the Southern Asian tradition. © 2021 Elsevier Ltd
    view abstractdoi: 10.1016/j.jas.2021.105529
  • 2022 • 175 Fluid-structure interaction simulation of tissue degradation and its effects on intra-aneurysm hemodynamics
    Wang, H. and Uhlmann, K. and Vedula, V. and Balzani, D. and Varnik, F.
    Biomechanics and Modeling in Mechanobiology (2022)
    Tissue degradation plays a crucial role in vascular diseases such as atherosclerosis and aneurysms. Computational modeling of vascular hemodynamics incorporating both arterial wall mechanics and tissue degradation has been a challenging task. In this study, we propose a novel finite element method-based approach to model the microscopic degradation of arterial walls and its interaction with blood flow. The model is applied to study the combined effects of pulsatile flow and tissue degradation on the deformation and intra-aneurysm hemodynamics. Our computational analysis reveals that tissue degradation leads to a weakening of the aneurysmal wall, which manifests itself in a larger deformation and a smaller von Mises stress. Moreover, simulation results for different heart rates, blood pressures and aneurysm geometries indicate consistently that, upon tissue degradation, wall shear stress increases near the flow-impingement region and decreases away from it. These findings are discussed in the context of recent reports regarding the role of both high and low wall shear stress for the progression and rupture of aneurysms. © 2022, The Author(s).
    view abstractdoi: 10.1007/s10237-022-01556-7
  • 2022 • 174 Formation and Cleavage of a Sb−Sb Double Bond: From Carbene-Coordinated Distibenes to Stibinidenes
    Krüger, J. and Wölper, C. and Auer, A.A. and Schulz, S.
    European Journal of Inorganic Chemistry 2022 (2022)
    Reactions of L(Cl)Ga-substituted stibine [L(Cl)Ga]2SbCl (L=HC[C(Me)NAr]2; Ar=2,6-i-Pr2C6H3) with N-heterocyclic carbenes RNHCMe (RNHCMe=[C(R)NMe]2C:; R=Me, Et, iPr) gave NHC-coordinated stibinidenes L(Cl)GaSb-RNHCMe (R=Me 1 a, Et 1 b, iPr 1 c) and distibenes L(Cl)GaSbSb(RNHCMe)Ga(Cl)L (R=Me 2 a, Et 2 b, iPr 2 c). Distibenes 2 a and 2 b react with a second equivalent of RNHCMe with cleavage of the Sb−Sb double bond and formation of stibinidenes 1 a and 1 b. 1 a–2 b were spectroscopically characterized and the solid-state structures determined by single crystal X-ray diffraction (sc-XRD). Quantum chemical calculations gave a deeper insight into the electronic nature and bonding situation of 1 a–2 c and the reaction energetics were investigated in detail. © 2021 The Authors. European Journal of Inorganic Chemistry published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/ejic.202100960
  • 2022 • 173 Free standing dual phase cathode tapes-scalable fabrication and microstructure optimization of garnet-based ceramic cathodes
    Rosen, M. and Finsterbusch, M. and Guillon, O. and Fattakhova-Rohlfing, D.
    Journal of Materials Chemistry A 10 2320-2326 (2022)
    To make ceramic based all-solid-state batteries competitive for the battery market, a shift from the separator supported cell-design for lab cells to a scalable, cathode-supported one is necessary to improve the energy density. Using tape casting, we were able to demonstrate for the first time all-ceramic free-standing LiCoO2 (LCO)/Li6.45Al0.05La3Zr1.6Ta0.4O12 (LLZO) mixed cathodes with high capacities and active material utilization. Further morphology engineering by introduction of a sequential layer casting enabled us to tailor the microstructure of the mixed cathodes resulting in opposite concentration gradients for the active material and the electrolyte over the thickness of the cathode. With this optimized microstructure, we were able to increase the discharge capacity of the free-standing mixed cathodes to 2.8 mA h cm-2 utilizing 99% of the theoretical capacity. For the oxide garnet-based system, both the scalable fabrication method and the achieved electrochemical performance demonstrates industrial relevance for the first time. Additionally, the obtained free-standing cathodes have sufficient mechanical stability to allow the application of hybrid and ultra-thin separators to further increase the energy density on the full cell level. This journal is © The Royal Society of Chemistry.
    view abstractdoi: 10.1039/d1ta07194g
  • 2022 • 172 Fuel-Rich Natural Gas Conversion in HCCI Engines with Ozone and Dimethyl Ether as Ignition Promoters: A Kinetic and Exergetic Analysis
    Freund, D. and Horn, C. and Atakan, B.
    Notes on Numerical Fluid Mechanics and Multidisciplinary Design 152 47-65 (2022)
    Fuel-rich operated HCCI engines are suitable for the polygeneration of work, heat, and base chemicals like synthesis gas (CO + H2). Under favorable conditions, these engines are exergetically more efficient than separate steam reformer and cogeneration gas engines. However, to achieve ignition, reactive fuel additives like dimethyl ether or ozone must be supplied, which have some, probably negative and not yet quantified, impacts on the exergetic efficiency. Therefore, the aim of this work is to compute and evaluate the effect of DME and ozone on the exergy input and exergetic efficiency of fuel-rich operated HCCI engines, which convert natural gas at equivalence ratios of 1.5 to 2.5. Results of a single-zone-model (SZM) and a multi-zone model (MZM) are compared to analyze the influence of inhomogeneities in the cylinder on the system’s exergetic efficiency. Natural gas as fuel is compared with previous neat methane results. The single-zone model results show that natural gas is much more reactive than methane. Ethane and propane convert partially in the compression stroke and lead to ethene, propene, and OH radicals. However, the ethane and propane conversions do not favor but slightly reduce the formation of methyl hydroperoxide, which is an important buffer molecule for fuel-rich methane ignition. But in addition, further buffer molecules like ethene or ethyl hydroperoxide are intermediately formed. The product selectivities are neither influenced by the natural gas composition, nor by the chosen additive. Compared to ozone, the DME molar and mass fractions needed for ignition are up to 11 times higher, and its exergy contribution to the total mixture is even 95 times higher. Therefore, the system’s exergetic efficiency is much higher when ozone is chosen as additive: reasonable values of up to 82.8% are possible, compared to 67.7% with DME. The multi-zone model results show that the efficiency is strongly dependent on the fuel conversion and thus unconverted fuel should be recycled within the polygeneration system to maintain high efficiencies. Comparing the total exergetic efficiency, ozone is a favorable additive for fuel-rich operated HCCI polygeneration. © 2022, The Author(s), under exclusive license to Springer Nature Switzerland AG.
    view abstractdoi: 10.1007/978-3-030-90727-3_4
  • 2022 • 171 Geminal C-Cl and Si-Cl bond activation of chloromethanes and chlorosilanes by gallanediyl LGa
    Helling, C. and Ganesamoorthy, C. and Wölper, C. and Schulz, S.
    Dalton Transactions 51 2050-2058 (2022)
    The activation of relatively inert E-X σ-bonds by low-valent main group metal complexes is receiving increasing interest. We here confirm the promising potential of gallanediyl LGa (L = HC[C(Me)N(Dip)]2, Dip = 2,6-i-Pr2C6H3) to activate E-Cl (E = C, Si) σ-bonds of group 14 element compounds. Equimolar reactions of LGa with chloromethanes and chlorosilanes EHxCl4-x (E = C, x = 0-2; E = Si, x = 0, 1) occurred with E-Cl bond insertion and formation of gallylmethanes and -silanes L(Cl)GaEHxCl3-x (E = C, x = 2 (1), 1 (2), 0 (3); E = Si, x = 1 (4)). In contrast, consecutive insertion into a geminal E-Cl bond was observed with two equivalents of LGa, yielding digallyl complexes [L(Cl)Ga]2EHxCl2-x (E = C, x = 2 (5); E = Si, x = 1 (6), 0 (7)). Compounds 1-7 were characterized by heteronuclear NMR (1H, 13C, 29Si (4, 6)), IR spectroscopy and elemental analysis, and their solid-state structures were determined by single-crystal X-ray diffraction (sc-XRD). © 2022 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/d1dt04192d
  • 2022 • 170 Generation of terahertz transients from Co2Fe0.4Mn0.6Si Heusler alloy/heavy-metal bilayers
    Heidtfeld, S. and Adam, R. and Kubota, T. and Takanashi, K. and Cao, D. and Schmitz-Antoniak, C. and Bürgler, D.E. and Wang, F. and Greb, C. and Chen, G. and Komissarov, I. and Hardtdegen, H. and Mikulics, M. and Sobolewski, R. a...
    Journal of Magnetism and Magnetic Materials 547 (2022)
    We generated pulses of electromagnetic radiation with a frequency content up to three terahertz (THz) by optical excitation of Co2Fe0.4Mn0.6Si Heusler alloy/heavy metal bilayers (CFMS/HM) using fs-laser pulses. We attribute the generation process to the conversion of a spin current, generated by the illumination with a fs-laser pulse, to a charge current via the inverse spin Hall effect. We compared the THz emission efficiency in CFMS/Pt and CFMS/Ta bilayers due to their high spin–orbit coupling of Pt and Ta. Surprisingly, our data reveal that CFMS/Pt shows substantially larger THz amplitudes compared to CFMS/Ta. Both bilayers exhibit a tunability of the THz amplitude by external magnetic field both at 300 K and 100 K. Ferromagnetic resonance measurements demonstrate that CFMS/Ta has a high effective spin mixing conductance, describing the efficiency of interfacial spin transport. We observe that the efficiency of the THz radiation cannot be solely described by the spin–orbit coupling strength and the spin diffusion length in the HM material plays an important role. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.jmmm.2021.168791
  • 2022 • 169 Green steel at its crossroads: Hybrid hydrogen-based reduction of iron ores
    Souza Filho, I.R. and Springer, H. and Ma, Y. and Mahajan, A. and da Silva, C.C. and Kulse, M. and Raabe, D.
    Journal of Cleaner Production 340 (2022)
    Iron- and steelmaking cause ∼7% of the global CO2 emissions, due to the use of carbon for the reduction of iron ores. Replacing carbon by hydrogen as the reductant offers a pathway to massively reduce these emissions. However, the production of hydrogen using renewable energy will remain as one of the bottlenecks at least during the next two decades, because making the gigantic annual crude steel production of 1.8 billion tons sustainable requires a minimum stoichiometric amount of ∼97 million tons of green hydrogen per year. Another fundamental aspect to render the ironmaking sector more sustainable lies in an optimal utilization of green hydrogen and energy, thus reducing efforts for costly in-process hydrogen recycling. We therefore demonstrate here how the efficiency in hydrogen and energy consumption during iron ore reduction can be dramatically improved by the knowledge-based combination of two technologies: partially reducing the ore at low temperature via solid-state direct reduction (DR) to a kinetically defined degree, and subsequently melting and completely transforming it to iron under a reducing plasma (i.e. via hydrogen plasma reduction, HPR). Results suggest that an optimal transition point between these two technologies occurs where their efficiency in hydrogen utilization is equal. We found that the reduction of hematite through magnetite into wüstite via DR is clean and efficient, but it gets sluggish and inefficient when iron forms at the outermost layers of the iron ore pellets. Conversely, HPR starts violent and unstable with arc delocalization, but proceeds smoothly and efficiently when processing semi-reduced oxides, an effect which might be related to the material's high electrical conductivity. We performed hybrid reduction experiments by partially reducing hematite pellets via DR at 700 °C to 38% global reduction (using a standard thermogravimetry system) and subsequently transferring them to HPR, conducted with a lean gas mixture of Ar-10%H2 in an arc-melting furnace, to achieve full conversion into liquid iron. This hybrid approach allows to exploit the specific characteristics and kinetically favourable regimes of both technologies, while simultaneously showing the potential to keep the consumption of energy and hydrogen low and improve both, process stability and furnace longevity by limiting its overexposure to plasma radiation. © 2022 Elsevier Ltd
    view abstractdoi: 10.1016/j.jclepro.2022.130805
  • 2022 • 168 Halogen and structure sensitivity of halobenzene adsorption on copper surfaces
    Schunke, C. and Miller, D.P. and Zurek, E. and Morgenstern, K.
    Physical Chemistry Chemical Physics 24 4485-4492 (2022)
    The adsorption orientation of molecules on surfaces influences their reactivity, but it is still challenging to tailor the interactions that govern their orientation. Here, we investigate how the substituent and the surface structure alter the adsorption orientation of halogenated benzene molecules from parallel to tilted relative to the surface plane. The deviation of the parallel orientation of bromo-, chloro-, and fluorobenzene molecules adsorbed on Cu(111) and Cu(110) surfaces is determined, utilising the surface selection rule in reflection-absorption infrared spectroscopy. On Cu(111), all three halogenated molecules are adsorbed with their molecular plane almost parallel to the surface at low coverages. However, they are tilted at higher coverages; yet, the threshold coverages differ. On Cu(110), merely bromo- and chlorobenzene follow this trend, albeit with a lower threshold for both. In contrast, fluorobenzene molecules are tilted already at low coverages. The substantial influence of the halogen atom and the surface structure on the adsorption orientation, resulting from an interplay of molecule-molecule and molecule-surface interactions, is highly relevant for reactivity confined to two dimensions. © 2022 the Owner Societies.
    view abstractdoi: 10.1039/d1cp05660c
  • 2022 • 167 Hierarchical nature of hydrogen-based direct reduction of iron oxides
    Ma, Y. and Souza Filho, I.R. and Bai, Y. and Schenk, J. and Patisson, F. and Beck, A. and van Bokhoven, J.A. and Willinger, M.G. and Li, K. and Xie, D. and Ponge, D. and Zaefferer, S. and Gault, B. and Mianroodi, J.R. and Raabe, D.
    Scripta Materialia (2022)
    Fossil-free ironmaking is indispensable for reducing massive anthropogenic CO2 emissions in the steel industry. Hydrogen-based direct reduction (HyDR) is among the most attractive solutions for green ironmaking, with high technology readiness. The underlying mechanisms governing this process are characterized by a complex interaction of several chemical (phase transformations), physical (transport), and mechanical (stresses) phenomena. Their interplay leads to rich microstructures, characterized by a hierarchy of defects ranging across several orders of magnitude in length, including vacancies, dislocations, internal interfaces, and free surfaces in the form of cracks and pores. These defects can all act as reaction, nucleation, and diffusion sites, shaping the overall reduction kinetics. A clear understanding of the roles and interactions of these dynamically-evolving nano-/microstructure features is missing. Gaining better insights into these effects could enable improved access to the microstructure-based design of more efficient HyDR methods, with potentially high impact on the urgently needed decarbonization in the steel industry. © 2022 The Author(s)
    view abstractdoi: 10.1016/j.scriptamat.2022.114571
  • 2022 • 166 Highly dispersed Pd clusters/nanoparticles encapsulated in MOFs via in situ auto-reduction method for aqueous phenol hydrogenation
    Huang, X. and Li, X. and Xia, W. and Hu, B. and Muhler, M. and Peng, B.
    Journal of Materials Science and Technology 109 167-175 (2022)
    In this work, a novel in situ auto-reduction strategy was developed to encapsulate uniformly dispersed Pd clusters/nanoparticles in MIL-125-NH2. It is demonstrated that the amino groups in MIL-125-NH2 can react with formaldehyde to form novel reducing groups (-NH[sbnd]CH2OH), which can in situ auto-reduce the encapsulated Pd2+ ions to metallic Pd clusters/nanoparticles. As no additional reductants are required, the strategy limits the aggregation and migration of Pd clusters and the formation of large Pd nanoparticles via controlling the amount of Pd2+ precursor. When applied as catalysts in the hydrogenation of phenol in the aqueous phase, the obtained Pd(1.5)/MIL-125-NH-CH2OH catalyst with highly dispersed Pd clusters/nanoparticles with the size of around 2 nm exhibited 100% of phenol conversion and 100% of cyclohexanone selectivity at 70 °C after 5 h, as well as remarkable reusability for at least five cycles due to the large MOF surface area, the highly dispersed Pd clusters/nanoparticles and their excellent stability within the MIL-125-NH-CH2OH framework. © 2021
    view abstractdoi: 10.1016/j.jmst.2021.08.079
  • 2022 • 165 Hydrogen trapping and embrittlement in high-strength Al alloys
    Zhao, H. and Chakraborty, P. and Ponge, D. and Hickel, T. and Sun, B. and Wu, C.-H. and Gault, B. and Raabe, D.
    Nature 602 437-441 (2022)
    Ever more stringent regulations on greenhouse gas emissions from transportation motivate efforts to revisit materials used for vehicles1. High-strength aluminium alloys often used in aircrafts could help reduce the weight of automobiles, but are susceptible to environmental degradation2,3. Hydrogen ‘embrittlement’ is often indicated as the main culprit4; however, the exact mechanisms underpinning failure are not precisely known: atomic-scale analysis of H inside an alloy remains a challenge, and this prevents deploying alloy design strategies to enhance the durability of the materials. Here we performed near-atomic-scale analysis of H trapped in second-phase particles and at grain boundaries in a high-strength 7xxx Al alloy. We used these observations to guide atomistic ab initio calculations, which show that the co-segregation of alloying elements and H favours grain boundary decohesion, and the strong partitioning of H into the second-phase particles removes solute H from the matrix, hence preventing H embrittlement. Our insights further advance the mechanistic understanding of H-assisted embrittlement in Al alloys, emphasizing the role of H traps in minimizing cracking and guiding new alloy design. © 2022, The Author(s).
    view abstractdoi: 10.1038/s41586-021-04343-z
  • 2022 • 164 Identification of a novel homozygous synthesis of cytochrome c oxidase 2 variant in siblings with early-onset axonal Charcot-Marie-Tooth disease
    Gangfuß, A. and Hentschel, A. and Rademacher, N. and Sickmann, A. and Stüve, B. and Horvath, R. and Gross, C. and Kohlschmidt, N. and Förster, F. and Abicht, A. and Schänzer, A. and Schara-Schmidt, U. and Roos, A. and Della Marina, A.
    Human Mutation (2022)
    The synthesis of cytochrome c oxidase 2 (SCO2) gene encodes for a mitochondrial located metallochaperone essential for the synthesis of the cytochrome c oxidase (COX) subunit 2. Recessive mutations in SCO2 have been reported in several cases with fatal infantile cardioencephalomyopathy with COX deficiency and in only four cases with axonal neuropathy. Here, we identified a homozygous pathogenic variant (c.361G &gt; C; p.[Gly121Arg]) in SCO2 in two brothers with isolated axonal motor neuropathy. To address pathogenicity of the amino acid substitution, biochemical studies were performed and revealed increased level of the mutant SCO2-protein and dysregulation of COX subunits in leukocytes and moreover unraveled decrease of proteins involved in the manifestation of neuropathies. Hence, our combined data strengthen the concept of SCO2 being causative for a very rare form of axonal neuropathy, expand its molecular genetic spectrum and provide first biochemical insights into the underlying pathophysiology. © 2022 The Authors. Human Mutation published by Wiley Periodicals LLC.
    view abstractdoi: 10.1002/humu.24338
  • 2022 • 163 Identification of the main mixing process in the synthesis of alloy nanoparticles by laser ablation of compacted micropowder mixtures
    Waag, F. and Fares, W.I.M.A. and Li, Y. and Andronescu, C. and Gökce, B. and Barcikowski, S.
    Journal of Materials Science 57 3041-3056 (2022)
    Alloy nanoparticles offer the possibility to tune functional properties of nanoscale structures. Prominent examples of tuned properties are the local surface plasmon resonance for sensing applications and adsorption energies for applications in catalysis. Laser synthesis of colloidal nanoparticles is well suited for generating alloy nanoparticles of desired compositions. Not only bulk alloys but also compacted mixtures of single-metal micropowders can serve as ablation targets. However, it is still unknown how mixing of the individual metals transfers from the micro- to the nanoscale. This work experimentally contributes to the elucidation of the mixing processes during the laser-based synthesis of alloy nanoparticles. Key parameters, such as the initial state of mixing in the ablation target, the laser pulse duration, the laser spot size, and the ablation time, are varied. Experiments are performed on a cobalt-iron alloy, relevant for application in oxidation catalysis, in ethanol. The extent of mixing in the targets after ablation and in individual nanoparticles are studied by energy-dispersive X-ray spectroscopy and by cyclic voltammetry at relevant conditions for the oxygen evolution reaction, as model reaction. The results point at the benefits of well pre-mixed ablation targets and longer laser pulse durations for the laser-based synthesis of alloy nanoparticles. Graphical abstract: [Figure not available: see fulltext.] © 2021, The Author(s).
    view abstractdoi: 10.1007/s10853-021-06731-2
  • 2022 • 162 Impact of Climate Change on Drinking Water Safety
    Ma, B. and Hu, C. and Zhang, J. and Ulbricht, M. and Panglisch, S.
    ACS Environmental Science and Technology Water 2 259-261 (2022)
    Widespread, rapid, and intensifying climate change plays an important role in drinking water quality. By scientifically exploring the interrelated mechanisms between climate change and drinking water quality, professionals can better adapt and optimize the water management and thereby ensure drinking water safety. Here, a new concept regarding water quality under the conditions of climate change is proposed due to the potential long-time and far-reaching impacts. © 2022 American Chemical Society
    view abstractdoi: 10.1021/acsestwater.2c00004
  • 2022 • 161 Impact of cobalt content and grain growth inhibitors in laser-based powder bed fusion of WC-Co
    Schwanekamp, T. and Marginean, G. and Reuber, M. and Ostendorf, A.
    International Journal of Refractory Metals and Hard Materials 105 (2022)
    Processing of tungsten carbide‑cobalt (WC-Co) by laser-based powder bed fusion (PBF-LB) can result in characteristic microstructure defects such as cracks, pores, undesired phases and tungsten carbide (WC) grain growth, due to the heterogeneous energy input and the high thermal gradients. Besides the processing conditions, the material properties are affected by the initial powder characteristics. In this paper, the impact of powder composition on microstructure, phase formation and mechanical properties in PBF-LB of WC-Co is studied. Powders with different cobalt contents from 12 wt.-% to 25 wt.-% are tested under variation of the laser parameters. Furthermore, the impact of vanadium carbide (VC) and chromium (Cr) additives is investigated. Both are known as grain growth inhibitors for conventional sintering processes. The experiments are conducted at a pre-heating temperature of around 800 °C to prevent crack formation in the samples. Increasing laser energy input reduces porosity but leads to severe embrittlement for low cobalt content and to abnormal WC grain growth for high cobalt content. It is found that interparticular porosity at low laser energy is more severe for low cobalt content due to poor wetting of the liquid phase. Maximum bending strength of σB &gt; 1200 MPa and Vickers hardness of approx. 1000 HV3 can be measured for samples generated from WC-Co 83/17 powder with medium laser energy input. The addition of V and Cr leads to increased formation of additional phases such as Co3W3C, Co3V and Cr23C6 and to increased lateral and multi-laminar growth of the WC grains. In contrast to conventional sintering, a grain growth inhibiting effect of V and Cr in the laser molten microstructure is not achieved. © 2022 Elsevier Ltd
    view abstractdoi: 10.1016/j.ijrmhm.2022.105814
  • 2022 • 160 Impact of local arrangement of Fe and Ni on the phase stability and magnetocrystalline anisotropy in Fe-Ni-Al Heusler alloys
    Sokolovskiy, V.V. and Miroshkina, O.N. and Buchelnikov, V.D. and Gruner, M.E.
    Physical Review Materials 6 (2022)
    On the basis of density functional calculations, we report on a comprehensive study of the influences of atomic arrangement and Ni substitution for Al on the ground-state structural and magnetic properties for Fe2Ni1+xAl1-x Heusler alloys. We discuss systematically the competition between five Heusler-type structures formed by shuffles of Fe and Ni atoms and their thermodynamic stability. All Ni-rich Fe2Ni1+xAl1-x tend to decompose into a dual-phase mixture consisting of Fe2NiAl and FeNi. The successive replacement of Ni by Al leads to a change of ground-state structure and eventually an increase in magnetocrystalline anisotropy energy (MAE). We predict for stoichiometric Fe2NiAl a ground-state structure with nearly cubic lattice parameters but alternating layers of Fe and Ni possessing a uniaxial MAE that is even larger than tetragonal L10-FeNi. This opens an alternative route for improving the phase stability and magnetic properties in FeNi-based permanent magnets. © 2022 American Physical Society.
    view abstractdoi: 10.1103/PhysRevMaterials.6.025402
  • 2022 • 159 Improvement of proton conductivity of magnetically aligned phosphotungstic acid-decorated cobalt oxide embedded Nafion membrane
    Pourzare, K. and Mansourpanah, Y. and Farhadi, S. and Sadrabadi, M.M.H. and Ulbricht, M.
    Energy 239 (2022)
    The fabrication of proton exchange membranes with a short conduction pathway in the direction of membrane thickness is desirable for fuel cell applications. In this study, a new nanohybrid additive (Co3O4-NH2/H3PW12O40; CAW) is synthesized, by anchoring phosphotungstic acid (H3PW12O40; HPW) on aminopropylsiloxane-functionalized cobalt oxide, and then it is incorporated into the Nafion (NF) matrix to prepare nanocomposite membranes by film casting from CAW dispersions in NF solutions. To obtain short-pathway proton-conducting channels, through the nanocomposite membranes drying process, a magnetic field is employed to align the nanohybrid particles in transversal (thickness) direction of the NF matrix. Furthermore, the alignment of nanohybrids is observed directly by scanning electron microscopy, and estimated indirectly by proton conductivity and methanol permeability values. It is found that alignment of nanohybrids in the NF matrix elevates the conductivity of proton as well as the permeability of methanol. The aligned NF/CAW nanocomposite membrane with 1 wt% of CAW reveals the highest proton conductivity of 211 mS cm−1 at 90 °C and 95% relative humidity, which is 39% higher than that of pure NF (152 mS cm−1). Interestingly, through the orientation of CAW, 76% improvement in the selectivity of the membranes is observed. © 2021 Elsevier Ltd
    view abstractdoi: 10.1016/j.energy.2021.121940
  • 2022 • 158 In Situ Analytical Methods for the Characterization of Mechanochemical Reactions
    Weidenthaler, C.
    Crystals 12 (2022)
    The interest in mechanochemical reactions and their fields of application have increased enormously in recent times. Mechanically activated reactions offer the advantage of cost-efficiency as well as environmentally friendly syntheses routes. In contrast to thermally induced processes, the energy transfer via the milling media takes place on a local scale. This leads to unique reaction pathways, which often also result in the formation of metastable phases. For the understanding of reaction pathways on a mechanistic level, it is very important to follow the processes taking place in the grinding jar during milling. Besides the measurement of pressure and temperature changes during a mechanochemical reaction, in situ high energy synchrotron X-ray powder diffraction and Raman spectroscopy experiments have been successfully implemented over the last 10 years. This review will highlight the developments which were achieved in the field of in situ monitoring of mechanochemical reactions and their input to the understanding of mechanochemistry. © 2022 by the author. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/cryst12030345
  • 2022 • 157 In Situ Carbon Corrosion and Cu Leaching as a Strategy for Boosting Oxygen Evolution Reaction in Multimetal Electrocatalysts
    Zhang, J. and Quast, T. and He, W. and Dieckhöfer, S. and Junqueira, J.R.C. and Öhl, D. and Wilde, P. and Jambrec, D. and Chen, Y.-T. and Schuhmann, W.
    Advanced Materials (2022)
    The number of active sites and their intrinsic activity are key factors in designing high-performance catalysts for the oxygen evolution reaction (OER). The synthesis, properties, and in-depth characterization of a homogeneous CoNiFeCu catalyst are reported, demonstrating that multimetal synergistic effects improve the OER kinetics and the intrinsic activity. In situ carbon corrosion and Cu leaching during the OER lead to an enhanced electrochemically active surface area, providing favorable conditions for improved electronic interaction between the constituent metals. After activation, the catalyst exhibits excellent activity with a low overpotential of 291.5 ± 0.5 mV at 10 mA cm−2 and a Tafel slope of 43.9 mV dec−1. It shows superior stability compared to RuO2 in 1 m KOH, which is even preserved for 120 h at 500 mA cm−2 in 7 m KOH at 50 °C. Single particles of this CoNiFeCu after their placement on nanoelectrodes combined with identical location transmission electron microscopy before and after applying cyclic voltammetry are investigated. The improved catalytic performance is due to surface carbon corrosion and Cu leaching. The proposed catalyst design strategy combined with the unique single-nanoparticle technique contributes to the development and characterization of high-performance catalysts for electrochemical energy conversion. © 2022 The Authors. Advanced Materials published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/adma.202109108
  • 2022 • 156 In situ measurement of gas-borne silicon nanoparticle volume fraction and temperature by spatially and spectrally line-resolved attenuation and emission imaging
    Liu, G. and Asif, M. and Mohri, K. and Schulz, C. and Dreier, T. and Endres, T. and Menser, J.
    Powder Technology 396 535-541 (2022)
    In this study, the temperature and volume fraction distributions of liquid silicon nanoparticles in the aerosol flow in gas-phase synthesis were retrieved using tomographic reconstruction of emission and extinction spectra in the 230–700 nm range. Measurements were done in an optically accessible microwave-plasma flow reactor fed with a SiH4/H2/Ar gas mixture. Optical emission and extinction spectra in the visible spectral range were captured along a line perpendicular to the flow direction covering the entire cross-section of the Si particle stream. Particle temperature and volume fraction distributions were determined and the preferred location of the silicon particles in a 1-mm thick zone at the circumference of the cylindric flow was revealed. The combined recording of line-resolved emission/extinction spectra is a promising method for spatially-resolved detection of nanoparticles in combustion or gas-phase synthesis. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.powtec.2021.11.017
  • 2022 • 155 Incorporation of Cu/Ni in Ordered Mesoporous Co-Based Spinels to Facilitate Oxygen Evolution and Reduction Reactions in Alkaline Media and Aprotic Li−O2 Batteries
    Priamushko, T. and Budiyanto, E. and Eshraghi, N. and Weidenthaler, C. and Kahr, J. and Jahn, M. and Tüysüz, H. and Kleitz, F.
    ChemSusChem 15 (2022)
    Ordered mesoporous CuNiCo oxides were prepared via nanocasting with varied Cu/Ni ratio to establish its impact on the electrochemical performance of the catalysts. Physicochemical properties were determined along with the electrocatalytic activities toward oxygen evolution/reduction reactions (OER/ORR). Combining Cu, Ni, and Co allowed creating active and stable bifunctional electrocatalysts. CuNiCo oxide (Cu/Ni≈1 : 4) exhibited the highest current density of 411 mA cm−2 at 1.7 V vs. reversible hydrogen electrode (RHE) and required the lowest overpotential of 312 mV to reach 10 mA cm−2 in 1 m KOH after 200 cyclic voltammograms. OER measurements were also conducted in the purified 1 m KOH, where CuNiCo oxide (Cu/Ni≈1 : 4) also outperformed NiCo oxide and showed excellent chemical and catalytic stability. For ORR, Cu/Ni incorporation provided higher current density, better kinetics, and facilitated the 4e− pathway of the oxygen reduction reaction. The tests in Li−O2 cells highlighted that CuNiCo oxide can effectively promote ORR and OER at a lower overpotential. © 2021 The Authors. ChemSusChem published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/cssc.202102404
  • 2022 • 154 Increased adhesion of thermal sprayed coatings – Innovative process combination enables substitution of conventional blasting processes [Innovative Verfahrenskombination ermöglicht Substitution konventioneller Strahlprozesse Erhöhte Haftfestigkeit thermischer Spritzschichten]
    Vogel, F. and Diaz, M.R. and Biermann, D. and Möhwald, K.
    WT Werkstattstechnik 112 28-33 (2022)
    To enable thermal sprayed coatings with increased adhesion, the Institute of Machining Technology (ISF) of TU Dortmund University together with the Institute of Materials Science (IW) of Leibniz Universität Hannover developed an innovative process combination. This serves as a basis for investigating whether the coating properties can be further optimized by an additional process step to allow for the production of wear-resistant coatings in the future without substrate activation by blasting. © 2022, VDI Fachmedien GmBH & Co. KG. All rights reserved.
    view abstractdoi: 10.37544/1436-4980-2021-1-2-32
  • 2022 • 153 Indentation behavior of creep-feed grinding induced gradient microstructures in single crystal nickel-based superalloy
    Miao, Q. and Ding, W. and Kuang, W. and Fu, Y. and Yin, Z. and Dai, C. and Cao, L. and Wang, H.
    Materials Letters 306 (2022)
    The gradient microstructures of surface layer in single crystal nickel-based superalloy were produced by creep-feed grinding. The mechanical properties (i.e., hardness, elastic modulus) and room-temperature (RT) creep behavior of such structures were evaluated using a nano-indentation technique. Results show that the gradient structures along depth from ground surface consisted of nanograins, submicron grains and lamellar-shape structures, and dislocation structures. Furthermore, it was found that the hardness and elastic modulus of gradient structures were higher by 8–10% than that of bulk material on average. However, the regions containing nanograins showed a remarkable increase in creep depth compared to bulk material, implying that the creep behavior of ground layer was changed unfavorably. The obtained stress exponents of gradient structures suggested that dislocation activities were the main mechanism for indentation creep deformation. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.matlet.2021.130956
  • 2022 • 152 Indirect Electrooxidation of Methane to Methyl Bisulfate on a Boron-Doped Diamond Electrode
    Britschgi, J. and Bilke, M. and Schuhmann, W. and Schüth, F.
    ChemElectroChem 9 (2022)
    Although highly desired and studied for decades, direct methane functionalization to liquid products remains a challenge. We report an electrochemical system using a boron-doped diamond (BDD) anode in concentrated sulfuric acid that is able to convert methane to methyl bisulfate and methanesulfonic acid without the use of a catalyst by indirect electrochemical oxidation. Due to its high material stability, BDD can be operated at high current densities. High temperature (140 °C) and pressure (70 bar) support the formation of methyl bisulfate to concentrations as high as 160 mM in 3 h and methanesulfonic acid to concentrations of up to 750 mM in 8 h. We present a novel way of catalyst-free electrochemical methane oxidation and show general trends and limitations of this reaction. © 2021 The Authors. ChemElectroChem published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/celc.202101253
  • 2022 • 151 Inference of Intensity-Based Models for Load-Sharing Systems With Damage Accumulation
    Muller, C.H. and Meyer, R.
    IEEE Transactions on Reliability (2022)
    To model damage accumulation for load-sharing systems, two models given by intensity functions of self-exciting point processes are proposed: a model with additive damage accumulation and a model with multiplicative damage accumulation. Both models include the model without damage accumulation as a special case. For both models, the likelihood functions are derived and maximum likelihood estimators and likelihood ratio tests are given in a scale-invariant version and a scale-dependent version. Furthermore, a Bayesian approach using Markov chain Monte Carlo methods for posterior computation is provided. The frequentist and Bayesian methods are applied to a data set of failures of tension wires of concrete beams where a significant damage accumulation effect is confirmed by both additive and multiplicative damage accumulation models. This is all the more remarkable as a simulation study indicates that the tests for an existing damage accumulation effect are rather conservative. Moreover, prediction intervals for the failure times of the tension wires in a new experiment are given, which improve former prediction intervals derived without damage accumulation. The simulation study considers a scenario with a fixed time horizon and one with fixed numbers of failed components of the systems. IEEE
    view abstractdoi: 10.1109/TR.2022.3140483
  • 2022 • 150 Influence of laser-generated surface micro-structuring on the intrinsically bonded hybrid system CFRP-EN AW 6082-T6 on its corrosion properties
    Delp, A. and Freund, J. and Wu, S. and Scholz, R. and Löbbecke, M. and Haubrich, J. and Tröster, T. and Walther, F.
    Composite Structures 285 (2022)
    The corrosion behavior of a hybrid material consisting of intrinsically bonded carbon fiber-reinforced epoxy resin with laser-structured EN AW 6082 metal was investigated. Particular attention was paid to the effects of the laser-structuring, surface topography and the contacting. Pristine and hybridized specimens were corroded in aqueous NaCl electrolyte (0.1 mol/l) using a potentiodynamic polarization technique and subsequently analyzed using computed tomography, scanning electron-, light- and laser scanning microscopy. The results show that the corrosive reaction arises mainly from the aluminum component. Surface pretreatment of the aluminum resulted in increasing corrosion rates, but showed no influence on the hybrids corrosion properties. Optical micrographs suggest that the epoxy resin acts as a sealant preventing galvanic corrosion between the aluminum and carbon fibers by hindering the diffusion of the electrolyte into the joints. While corrosion effects were observed locally at the aluminum surface, they were, contrary to expectations, not enhanced on the hybrid interfaces. © 2022 Elsevier Ltd
    view abstractdoi: 10.1016/j.compstruct.2022.115238
  • 2022 • 149 Influence of machining on the surface integrity of high- and medium-entropy alloys
    Richter, T. and Schroepfer, D. and Rhode, M. and Boerner, A. and Neumann, R.S. and Schneider, M. and Laplanche, G.
    Materials Chemistry and Physics 275 (2022)
    High- and medium-entropy alloys (HEAs) are a quite new class of materials. They have a high potential for applications from low to high temperatures due to the excellent combination of their structural properties. Concerning their application as components; processing properties, such as machinability, have hardly been investigated so far. Hence, machinability analyses with a focus on the influence of the milling process and its basic parameters (cutting speed, feed per cutting edge) on the resulting surface integrity of specimens from an equiatomic high- (CoCrFeMnNi) and a medium- (CoCrNi) entropy alloy have been carried out. A highly innovative milling process with ultrasonic assistance (USAM) was compared to conventional milling processes. Recent studies have shown that USAM has a high potential to significantly reduce the mechanical load on the tool and workpiece surface during milling. In this study, the basic machining and ultrasonic parameters were systematically varied. After machining, the surface integrity of the alloys was analyzed in terms of topography, defects, subsurface damage, and residual stresses. It was observed that USAM reduces the cutting forces and increases the surface integrity in terms of lower tensile residual stresses and defect density near the surfaces for the CoCrFeMnNi alloy. It was shown that the cutting forces and the metallurgical influence in the sub surface region are reduced by increasing the cutting speed and reducing the feed rate per cutting edge. With the CoCrNi alloy, the tool revealed severe wear. As a result, for this alloy no influence of the parameters on the machinability could be determined. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.matchemphys.2021.125271
  • 2022 • 148 Influence of Mo/Cr ratio on the lamellar microstructure and mechanical properties of as-cast Al0.75CoCrFeNi compositionally complex alloys
    Asabre, A. and Gemagami, P. and Parsa, A.B. and Wagner, C. and Kostka, A. and Laplanche, G.
    Journal of Alloys and Compounds 899 (2022)
    The Al0.75CoCrFeNi alloy (Al16Co21Cr21Fe21Ni21 in at.%) presents a lamellar microstructure in the as-cast state consisting of a spinodally-decomposed B2/BCC matrix and Widmanstätten-type FCC plates. In this study, to retain the lamellar microstructure and improve tensile strength, Al16Co21Cr21-xFe21Ni21Mox alloys with x ≤ 10 at.% were investigated. For x = 2 at.%, the Widmanstätten microstructure changed into a vermicular one due to the stabilization of the BCC phase. With increasing the Mo/Cr ratio, the BCC phase transformed into topologically close-packed (TCP) phases, i.e., σ phase for x = 4 at.% and R phase for x ≥ 6 at.%, whose volume fractions increases with x. The as-cast alloys with x = 10 and 4 at.% presented the largest microhardness of ~600 HV0.5. The former had the highest volume fraction in TCP phases, which are hard and brittle while the latter presented the finest microstructure (enhanced phase boundary strengthening). While the alloys with x &gt; 4 at.% were too brittle to machine tensile specimens, the others were tested between 20 and 700 °C. The ultimate tensile strength increased with increasing x up to ~1460 MPa for x = 4 at.% at 400 °C. At 700 °C, the strength of all alloys significantly decreased due to the softening of the B2 phase. Most of them had limited ductility and showed intergranular fracture except for x = 4 at.% presenting pronounced necking with ~38% ductility. The latter effect was attributed to the occurrence of interfacial sliding resulting in cavitation at grain boundaries and interphase boundaries. © 2021 The Author(s)
    view abstractdoi: 10.1016/j.jallcom.2021.163183
  • 2022 • 147 Influence of surface activation on the microporosity of PE-CVD and PE-ALD SiOx thin films on PDMS
    Hoppe, C. and Mitschker, F. and Mai, L. and Liedke, M.O. and de los Arcos, T. and Awakowicz, P. and Devi, A. and Attallah, A.G. and Butterling, M. and Wagner, A. and Grundmeier, G.
    Plasma Processes and Polymers (2022)
    The microporosity, structure and permeability of SiOx thin films deposited by microwave plasma-enhanced chemical vapour deposition (PE-CVD) and plasma-enhanced atomic layer deposition (PE-ALD) on polydimethylsiloxane (PDMS) substrates were investigated by positron annihilation spectroscopy and complementary technique, such as X-ray photoelectron spectroscopy, infrared spectroscopy, time of flight mass spectroscopy and atomic force microscopy. The SiOx films were deposited onto spin-coated PDMS substrates, which were previously exposed to an oxygen plasma thus achieving the conversion of the top polymer layer into SiOx. The presence of this oxidised surface near the region led to an overall decrease in micropore density and to a shift towards smaller pore sizes within the deposited SiOx films. A correlation between the oxygen fluence during the oxygen plasma treatment and the microporosity of the PE-CVD and PE-ALD SiOx films could be established. © 2022 The Authors. Plasma Processes and Polymers published by Wiley-VCH GmbH.
    view abstractdoi: 10.1002/ppap.202100174
  • 2022 • 146 Influence of Temperature and Concentration on the Self-Assembly of Nonionic CiEj Surfactants: A Light Scattering Study
    Kroll, P. and Benke, J. and Enders, S. and Brandenbusch, C. and Sadowski, G.
    ACS Omega 7 7057-7065 (2022)
    Nonionic poly(ethylene oxide) alkyl ether (CiEj) surfactants self-assemble into aggregates of various sizes and shapes above their critical micelle concentration (CMC). Knowledge on solution attributes such as CMC as well as aggregate characteristics is crucial to choose the appropriate surfactant for a given application, e.g., as a micellar solvent system. In this work, we used static and dynamic light scattering to measure the CMC, aggregation number (Nagg), and hydrodynamic radius (Rh) of four different CiEj surfactants (C8E5, C8E6, C10E6, and C10E8). We examined the influence of temperature, concentration, and molecular structure on the self-assembly in the vicinity of the CMC. A minimum in the CMC vs temperature curve was identified for all surfactants investigated. Further, extending the hydrophilic and hydrophobic chain lengths leads to an increase and decrease of the CMC, respectively. The size of the aggregates strongly depends on temperature. Nagg and Rh increase with increasing temperature for all surfactants investigated. Additionally, Nagg and Rh both increase with increasing surfactant concentration. The data obtained in this work further improve the understanding of the influence of temperature and molecular structure on the self-assembly of CiEj surfactants and will further foster their use in micellar solvent systems. © 2022 The Authors. Published by American Chemical Society
    view abstractdoi: 10.1021/acsomega.1c06766
  • 2022 • 145 Influence of the PTFE Membrane Thickness on the CO2 Electroreduction Performance of Sputtered Cu-PTFE Gas Diffusion Electrodes
    Huq, F. and Sanjuán, I. and Baha, S. and Braun, M. and Kostka, A. and Chanda, V. and Junqueira, J.R.C. and Sikdar, N. and Ludwig, A. and Andronescu, C.
    ChemElectroChem 9 (2022)
    Gas diffusion electrodes (GDE) obtained by sputtering metal films on polytetrafluoroethylene (PTFE) membranes are among the most performant electrodes used to electrochemically reduce CO2. The present work reveals several essential aspects for fabricating performant PTFE-based gas diffusion electrodes (GDEs) for CO2 electroreduction (CO2R). We show that adding an additive layer (a mixture of carbon and Nafion™ or Nafion™ only) is required for stabilizing the metal catalyst film (Cu), deposited via sputtering on the PTFE membrane, during the CO2R experiments. We found that the PTFE membrane thickness used in the GDE fabrication plays an essential role in electrode performance. The quantification of the products formed during the CO2R conducted in a flow-cell electrolyzer revealed that on thinner membranes, CO2R is the dominant process while on thicker ones, the H2 formation is promoted. Thus, the PTFE membrane influences the CO2 transport to the catalyst layer and can be used to promote the CO2R while maintaining a minimum H2 production. © 2021 The Authors. ChemElectroChem published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/celc.202101279
  • 2022 • 144 Interfacial Properties of Deep Eutectic Solvents by Density Gradient Theory
    Cea-Klapp, E. and Gajardo-Parra, N. and Aravena, P. and Quinteros-Lama, H. and Held, C. and Canales, R.I. and Garrido, J.M.
    Industrial and Engineering Chemistry Research 61 2580-2591 (2022)
    Deep eutectic solvents (DES) are room-temperature liquid mixtures constituted of a hydrogen-bonding acceptor (HBA) and a hydrogen-bonding donor (HBD). They have high practical potential due to their versatility, quick preparation, and wide applications. Therefore, it is appropriate to have robust models to predict their properties. In this work, the density gradient theory has been combined with the perturbed-chain statistical associating fluid theory to model and understand the interfacial behavior in systems of deep eutectic solvents. DESs were modeled as mixtures of their constituents, and a methodology is proposed for estimating the chemical potential of DESs to extend their study to the interfacial properties. Available experimental data of hydrophilic and hydrophobic DESs were used to calculate the influence parameters, providing a way to linearize them in terms of the molecular parameters of HBDs and their molar ratio between HBD and HBA. This treatment has made it feasible to predict the thermal dependence of surface tension in most of the DESs analyzed with an average absolute relative deviation of 1.26%. Furthermore, density gradient theory and perturbed-chain statistical associating fluid theory were applied to predict the vapor-liquid surface tension in mixtures of organic compounds with DES. In particular, we have calculated the surface tension in mixtures of ChCl-glycerol and ChCl-lactic acid with water, ethanol, propanol, phenol, acetone, and ethyl acetate without fitting binary interaction parameters. The behavior of density profiles suggests that the surface is enriched with DES components for the DES + water mixtures. In contrast, it is enriched with diluent for the other ternary systems (ethanol, isopropanol, phenol, acetone, and ethyl acetate). © 2022 American Chemical Society
    view abstractdoi: 10.1021/acs.iecr.1c03817
  • 2022 • 143 Interplay of domain structure and phase transitions: Theory, experiment and functionality
    Grünebohm, A. and Marathe, M. and Khachaturyan, R. and Schiedung, R. and Lupascu, D.C. and Shvartsman, V.V.
    Journal of Physics Condensed Matter 34 (2022)
    Domain walls and phase boundaries are fundamental ingredients of ferroelectrics and strongly influence their functional properties. Although both interfaces have been studied for decades, often only a phenomenological macroscopic understanding has been established. The recent developments in experiments and theory allow to address the relevant time and length scales and revisit nucleation, phase propagation and the coupling of domains and phase transitions. This review attempts to specify regularities of domain formation and evolution at ferroelectric transitions and give an overview on unusual polar topological structures that appear as transient states and at the nanoscale. We survey the benefits, validity, and limitations of experimental tools as well as simulation methods to study phase and domain interfaces. We focus on the recent success of these tools in joint scale-bridging studies to solve long lasting puzzles in the field and give an outlook on recent trends in superlattices. © 2021 IOP Publishing Ltd.
    view abstractdoi: 10.1088/1361-648X/ac3607
  • 2022 • 142 Interplay of Halogen and Weak Hydrogen Bonds in the Formation of Magic Nanoclusters on Surfaces
    Bertram, C. and Miller, D.P. and Schunke, C. and Kemeny, I. and Kimura, M. and Bovensiepen, U. and Zurek, E. and Morgenstern, K.
    Journal of Physical Chemistry C 126 588-596 (2022)
    Halogen bonding has recently been recognized as an interaction whose relevance is on par with hydrogen bonding. While observed frequently in solution chemistry, the significance of halogen bonds in forming extended supramolecular structures on surfaces is less explored. Herein, we report on the self-assembly of chlorobenzene molecules adsorbed on the Cu(111) surface into nanosized clusters at submonolayer coverages, where the molecular planes are close to parallel to the surface. A comprehensive study of the role of intermolecular interactions through both halogen and weak hydrogen bonds on nanocluster formation is presented, gained by combining the results of temperature-programmed desorption, reflection-absorption infrared spectroscopy, scanning tunneling microscopy, and density functional theory calculations. Based on an unprecedented precise determination of the molecules’ orientation within the clusters, the binding motifs that lead to the formation and stability of nanoclusters with magic sizes are identified and explained. A complex and delicate interplay of halogen bonds with weak hydrogen bonds, van-der-Waals forces, and surface–adsorbate interactions leads to a preference for hexamers and tetramers with an observable propensity for halogen bonding over weak hydrogen bonding when adsorbed to the Cu(111) surface. © 2021 American Chemical Society
    view abstractdoi: 10.1021/acs.jpcc.1c08045
  • 2022 • 141 Interplay of viscosity and surface tension for ripple formation by laser melting
    Morawetz, K. and Trinschek, S. and Gurevich, E.L.
    Physical Review B 105 (2022)
    A model for ripple formation on liquid surfaces exposed to an external laser or particle beam and a variable ground is developed. The external incident beam is hereby mechanically coupled to the liquid surface due to surface roughness. Starting from the Navier-Stokes equation, the coupled equations for the velocity potential and the surface height are derived in a shallow-water approximation with special attention to viscosity. The resulting equations obey conservation laws for volume and momentum where characteristic potentials for gravitation and surface tension are identified analogously to conservative forces. The approximate solutions are discussed in the context of ripple formation in laser-materials processing involving melting of a surface by a laser beam. Linear stability analysis provides the formation of a damped wave modified by an interplay between the external beam, the viscosity, and the surface tension. The limit of small viscosity leads to damped gravitational and the limit of high viscosity to capillary waves. The resulting wavelengths are in the order of the ripples occurring in laser welding experiments, hinting at the involvement of hydrodynamic processes in their origin. By discussing the response of the system to external periodic excitations with the help of Floquet multipliers, we show that the ripple formation could be triggered by a a periodically modulated external beam, e.g., appropriate repetition rates of an incident laser beam. The weak nonlinear stability analysis provides ranges where hexagonal or stripe structures can appear. The orientation of stripe structures and ripples are shown to be dependent on the incident angle of the laser or particle beam where a minimal angle is reported. Numerical simulations confirm the findings and allow us to describe the influence of variable grounds. © 2022 American Physical Society.
    view abstractdoi: 10.1103/PhysRevB.105.035415
  • 2022 • 140 Introducing Water-Network-Assisted Proton Transfer for Boosted Electrocatalytic Hydrogen Evolution with Cobalt Corrole
    Li, X. and Lv, B. and Zhang, X.-P. and Jin, X. and Guo, K. and Zhou, D. and Bian, H. and Zhang, W. and Apfel, U.-P. and Cao, R.
    Angewandte Chemie - International Edition 61 (2022)
    Proton transfer is vital for many biological and chemical reactions. Hydrogen-bonded water-containing networks are often found in enzymes to assist proton transfer, but similar strategy has been rarely presented by synthetic catalysts. We herein report the Co corrole 1 with an appended crown ether unit and its boosted activity for the hydrogen evolution reaction (HER). Crystallographic and 1H NMR studies proved that the crown ether of 1 can grab water via hydrogen bonds. By using protic acids as proton sources, the HER activity of 1 was largely boosted with added water, while the activity of crown-ether-free analogues showed very small enhancement. Inhibition studies by adding 1) external 18-crown-6-ether to extract water molecules and 2) potassium ion or N-benzyl-n-butylamine to block the crown ether of 1 further confirmed its critical role in assisting proton transfer via grabbed water molecules. This work presents a synthetic example to boost HER through water-containing networks. © 2021 Wiley-VCH GmbH
    view abstractdoi: 10.1002/anie.202114310
  • 2022 • 139 Invariants in the paramagnetic resonance spectra of impurity-doped crystals
    Kamenskii, A.N. and Kozlov, V.O. and Kuznetsov, N.S. and Ryzhov, I.I. and Kozlov, G.G. and Bayer, M. and Greilich, A. and Zapasskii, V.S.
    Physical Review B 105 (2022)
    We show that in cubic crystals with anisotropic impurity centers the sum of squares of the magnetic resonance [electron paramagnetic resonance (EPR)] frequencies is invariant with respect to the magnetic field direction. The connection between such an invariant and the g-tensor components of the impurity is derived for different types of centers. The established regularity is confirmed experimentally for the spin-noise spectra of a cubic CaF2-Nd3+ crystal. We show how this property of the EPR spectra can be efficiently used for the assignment of paramagnetic centers in cubic crystals. © 2022 American Physical Society.
    view abstractdoi: 10.1103/PhysRevB.105.014416
  • 2022 • 138 Inverse modeling of cancellous bone using artificial neural networks
    Stieve, V. and Blaszczyk, M. and Hackl, K.
    ZAMM Zeitschrift fur Angewandte Mathematik und Mechanik (2022)
    Artificial neural networks are used to solve different tasks of daily life, engineering and medicine. In this work, we investigate its suitability for the examination of simulation results of cancellous bone with the aim to evaluate whether the bone is affected by osteoporosis. This bone disease is characterized by a reduction of the cortical bone phase, one of the two main components of the bone. The neural network predicts the simulated volume fraction in different parts of a cylinder, which models the bone. As a basis for its calculations, the neural network gets the information about the magnetic field inside the cylinder from finite element simulations. Examinations show that it is possible to train neural networks on solving that task with very high accuracies. © 2022 The Authors. ZAMM - Journal of Applied Mathematics and Mechanics published by Wiley-VCH GmbH.
    view abstractdoi: 10.1002/zamm.202100541
  • 2022 • 137 Investigation of Laser-Induced Periodic Surface Structures Using Synthetic Optical Holography
    Neutsch, K. and Gurevich, E.L. and Hofmann, M.R. and Gerhardt, N.C.
    Nanomaterials 12 (2022)
    In this paper, the investigation of laser-induced periodic surface structures (LIPSSs) on a polycrystalline diamond substrate using synthetic optical holography (SOH) is demonstrated. While many techniques for LIPSS detection operate with sample contact and/or require preparation or processing of the sample, this novel technique operates entirely non-invasively without any processing of or contact with the LIPSS sample at all. The setup provides holographic amplitude and phase images of the investigated sample with confocally enhanced and diffraction-limited lateral resolution, as well as three-dimensional surface topography images of the periodic structures via phase reconstruction with one single-layer scan only. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/nano12030505
  • 2022 • 136 Investigation of the combustion chemistry in laminar, low-pressure oxymethylene ether flames (OME0–4)
    Gaiser, N. and Zhang, H. and Bierkandt, T. and Schmitt, S. and Zinsmeister, J. and Kathrotia, T. and Hemberger, P. and Shaqiri, S. and Kasper, T. and Aigner, M. and Oßwald, P. and Köhler, M.
    Combustion and Flame (2022)
    Quantitative speciation data for alternative fuels is highly desired to assess their emission potential and to develop and validate chemical kinetic models. In terms of substitute choices for fossil diesel are oxymethylene ethers (OMEs) strongly discussed. Due to the absence of carbon-carbon bonds, soot emissions from combustion of OMEs are low, but significant emissions of unregulated pollutants such as aldehydes emerge. The combustion behavior of OME fuels with different chain lengths, OME0–4, was investigated in laminar premixed low-pressure flames using complementary molecular-beam mass spectrometry (MBMS) techniques. MBMS sampling provides an in-situ access directly into the reaction zone of the flame. Almost all chemical species involved in the oxidation process can be detected and quantified simultaneously. Neat OME0–3 flames were analyzed by electron ionization (EI) MBMS with high mass resolution (R ≈ 3900) providing exact elementary composition. To obtain isomer-specific information, an OME1-doped hydrogen flame and a stochiometric OME4 flame were studied by double-imaging photoelectron photoion coincidence (i2PEPICO) spectroscopy. Both, EI-MBMS detection and i2PEPICO spectroscopy, enables a complete overview of all intermediates. The results show a dominance of oxygenated intermediates for all measured conditions. Mole fraction profiles for the most important species are presented (i.e. formaldehyde, methanol, methyl formate and formic acid) and compared to modeling results. Hydrocarbons with more than four carbon atoms were not detected under the investigated conditions. Isomers such as ethanol/dimethyl ether (m/z = 46) and ethenol/acetaldehyde (m/z = 44) could be separated using threshold photoelectron spectra for clear identification and photoionization efficiency curves for quantification. This investigation permits the discussion and analysis of systematic trends, including intermediate species, for the combustion of the studied series of oxymethylene ether fuels. © 2022 The Combustion Institute
    view abstractdoi: 10.1016/j.combustflame.2022.112060
  • 2022 • 135 Investigation of the effect of carbon post- vs pre-coated metallic bipolar plates for PEMFCs – start-up and shut-down
    Müller, M.-V. and Giorgio, M. and Hausmann, P. and Kinlechner, L. and Heinzel, A. and Schwämmlein, J.
    International Journal of Hydrogen Energy 47 8532-8548 (2022)
    In this work, the influence of increased potentials during the start-up/shut-down process on metallic bipolar plates (316L) with the coating system Cr/a-C based on graphite-like carbon is investigated. In comparison to commonly applied post-coated bipolar plates, a new low-cost manufacturing process based on pre-coated metal sheets for bipolar plates was evaluated. By developing a vehicle near start-up/shut-down cycle, a relative humidity of 140% and anode residence time of 0.94 s show the greatest damage potential of the cycle variations. After 2000 start-up/shut-down cycles, pre-coated metallic bipolar plates show no increased voltage loss compared to conventional coatings. Nevertheless, the resistances increase for Cr/a-C post- and pre-coating at the H2 outlet. This correlates with an increased surface roughness of the bipolar plate but otherwise only minor surface changes can be observed. The coating variation has no effect on the extent of catalyst coated membrane thinning or increased content of metal ions. © 2021 Hydrogen Energy Publications LLC
    view abstractdoi: 10.1016/j.ijhydene.2021.12.179
  • 2022 • 134 Ion-induced secondary electron emission of oxidized nickel and copper studied in beam experiments
    Buschhaus, R. and Prenzel, M. and Von Keudell, A.
    Plasma Sources Science and Technology 31 (2022)
    Ion-induced secondary electron emission at a target surface is an essential mechanism for laboratory plasmas, i.e. magnetron sputtering discharges. Electron emission, however, is strongly affected by the target condition itself such as oxidation. Data of oxidized targets, however, are very sparse and prone to significant systematic errors, because they were often determined by modeling the complex behavior of the plasma. Thus, it is difficult to isolate the process of ion-induced electron emission from all other plasma-surface-interactions. By utilizing ion beams, the complex plasma environment is avoided and electron yields are determined with higher accuracy. In this study, ion-induced secondary electron emission coefficients (SEECs) of clean, untreated (air-exposed), and intentionally oxidized copper and nickel surfaces were investigated in such a particle beam experiment. Pristine and oxidized metal foils were exposed to beams of singly charged argon ions with energies of 0.2 keV-10 keV. After the ion beam treatment, the surface conditions were analyzed by ex-situ X-ray photoelectron spectroscopy measurements. Further, a model for the electron emission of a partly oxidized surface is presented, which is in agreement with the experimental data. It was found, that oxidized and untreated/air-exposed surfaces do not show the same SEEC: for intentionally oxidized targets, the electron yields were smaller by a factor of 2 than for untreated/air-exposed surfaces. SEECs of oxides were found to be between the values for clean and for untreated metal surfaces. Further, the SEEC was at maximum for untreated/air-exposed surfaces and at minimum for clean surfaces; the electron yields of untreated/air-exposed and clean surfaces were in agreement with values reported in the literature. © 2022 The Author(s). Published by IOP Publishing Ltd.
    view abstractdoi: 10.1088/1361-6595/ac4c4c
  • 2022 • 133 Kinetic model assessment for the synthesis of γ-valerolactone from n-butyl levulinate and levulinic acid hydrogenation over the synergy effect of dual catalysts Ru/C and Amberlite IR-120
    Delgado, J. and Vasquez Salcedo, W.N. and Bronzetti, G. and Casson Moreno, V. and Mignot, M. and Legros, J. and Held, C. and Grénman, H. and Leveneur, S.
    Chemical Engineering Journal 430 (2022)
    The production of platform molecules from the valorization of lignocellulosic biomass is increasing. Among these plateform molecules, γ-valerolactone (GVL) is a promising one and could be used for different industrial applications. This molecule is synthesized from levulinic acid (LA) or alkyl levulinates (AL) through a tandem hydrogenation/cyclization (lactonization) cascade. A lot of investigations have been carried out to develop the best catalyst for the hydrogenation step by using solely LA or AL. However, one should keep in mind that in the AL production via fructose alcoholysis, there is also LA production, and both are present in the product mixture during the further conversion. To the best of our knowledge, no article exists describing the hydrogenation of LA and AL simultaneously in one-pot. Also, the literature reporting the use of solid catalyst for the second cyclization step is rare. To fill this gap, the hydrogenation of levulinic acid and butyl levulinate (BL) was studied over Ru/C and Amberlite IR-120. Several kinetic models were evaluated via Bayesian inference and K-fold approach. The kinetic assessment showed that a non-competitive Langmuir-Hinshelwood with no dissociation of hydrogen where LA, BL and H2 are adsorbed on different sites (NCLH1.2) and non-competitive Langmuir-Hinshelwood with dissociation of hydrogen where LA, BL and H2 are adsorbed on different sites (NCLH2.2) are the best model to describe this system. The presence of LA and Amberlite IR-120 allows to increase the kinetics of cyclization steps, and in fine to accelerate the production of GVL. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.cej.2021.133053
  • 2022 • 132 Knowledge-Driven Data Ecosystems Toward Data Transparency
    Geisler, S. and Vidal, M.-E. and Cappiello, C. and Lóscio, B.F. and Gal, A. and Jarke, M. and Lenzerini, M. and Missier, P. and Otto, B. and Paja, E. and Pernici, B. and Rehof, J.
    Journal of Data and Information Quality 14 (2022)
    A data ecosystem (DE) offers a keystone-player or alliance-driven infrastructure that enables the interaction of different stakeholders and the resolution of interoperability issues among shared data. However, despite years of research in data governance and management, trustability is still affected by the absence of transparent and traceable data-driven pipelines. In this work, we focus on requirements and challenges that DEs face when ensuring data transparency. Requirements are derived from the data and organizational management, as well as from broader legal and ethical considerations. We propose a novel knowledge-driven DE architecture, providing the pillars for satisfying the analyzed requirements. We illustrate the potential of our proposal in a real-world scenario. Last, we discuss and rate the potential of the proposed architecture in the fulfillmentof these requirements. © 2021 Copyright held by the owner/author(s). Publication rights licensed to ACM.
    view abstractdoi: 10.1145/3467022
  • 2022 • 131 Laser pre-structure-assisted micro-milling of Ti6Al4V titanium alloy
    Hojati, F. and Azarhoushang, B. and Daneshi, A. and Biermann, D.
    International Journal of Advanced Manufacturing Technology (2022)
    High flexibility of the micro-milling process compared to nontraditional methods has led to its growing application in manufacturing complex micro-parts with tight tolerances and high accuracies. However, difficulties such as tool deflection, size effect, and tool wear limit the application of micro-milling. In this regard, the role of laser-assisted machining (LAM) is highlighted to prevent mentioned issues through reduction of machining forces and providing the possibility for using higher feeds. Ti6Al4V as a hard-to-machine material is chosen as the workpiece material. Unlike traditional LAM, Ti6Al4V parts were structured using a picosecond laser before micro-milling. The influence of laser structuring at different structure densities on the reduction of machining forces was analyzed at two feeds of 10 and 50 µm/tooth at a constant cutting speed of 35 m/min. A remarkable reduction in cutting forces was observed at both feeds. Additionally, the role of structure density in cutting force reduction is highlighted. © 2022, The Author(s).
    view abstractdoi: 10.1007/s00170-022-08774-4
  • 2022 • 130 Laser-equipped gas reaction chamber for probing environmentally sensitive materials at near atomic scale
    Khanchandani, H. and El-Zoka, A.A. and Kim, S.-H. and Tezins, U. and Vogel, D. and Sturm, A. and Raabe, D. and Gault, B. and Stephenson, L.T.
    PLoS ONE 17 (2022)
    Numerous metallurgical and materials science applications depend on quantitative atomic-scale characterizations of environmentally-sensitive materials and their transient states. Studying the effect upon materials subjected to thermochemical treatments in specific gaseous atmospheres is of central importance for specifically studying a material’s resistance to certain oxidative or hydrogen environments. It is also important for investigating catalytic materials, direct reduction of an oxide, particular surface science reactions or nanoparticle fabrication routes. This manuscript realizes such experimental protocols upon a thermochemical reaction chamber called the "Reacthub" and allows for transferring treated materials under cryogenic &amp; ultrahigh vacuum (UHV) workflow conditions for characterisation by either atom probe or scanning Xe+/electron microscopies. Two examples are discussed in the present study. One protocol was in the deuterium gas charging (25 kPa D2 at 200°C) of a high-manganese twinning-induced-plasticity (TWIP) steel and characterization of the ingress and trapping of hydrogen at various features (grain boundaries in particular) in efforts to relate this to the steel’s hydrogen embrittlement susceptibility. Deuterium was successfully detected after gas charging but most contrast originated from the complex ion FeOD+ signal and the feature may be an artefact. The second example considered the direct deuterium reduction (5 kPa D2 at 700°C) of a single crystal wüstite (FeO) sample, demonstrating that under a standard thermochemical treatment causes rapid reduction upon the nanoscale. In each case, further studies are required for complete confidence about these phenomena, but these experiments successfully demonstrate that how an ex-situ thermochemical treatment can be realised that captures environmentally-sensitive transient states that can be analysed by atomic-scale by atom probe microscope. © 2022 Khanchandani et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
    view abstractdoi: 10.1371/journal.pone.0262543
  • 2022 • 129 Laser-induced incandescence for non-soot nanoparticles: recent trends and current challenges
    Sipkens, T.A. and Menser, J. and Dreier, T. and Schulz, C. and Smallwood, G.J. and Daun, K.J.
    Applied Physics B: Lasers and Optics 128 (2022)
    Laser-induced incandescence (LII) is a widely used combustion diagnostic for in situ measurements of soot primary particle sizes and volume fractions in flames, exhaust gases, and the atmosphere. Increasingly, however, it is applied to characterize engineered nanomaterials, driven by the increasing industrial relevance of these materials and the fundamental scientific insights that may be obtained from these measurements. This review describes the state of the art as well as open research challenges and new opportunities that arise from LII measurements on non-soot nanoparticles. An overview of the basic LII model, along with statistical techniques for inferring quantities-of-interest and associated uncertainties is provided, with a review of the application of LII to various classes of materials, including elemental particles, oxide and nitride materials, and non-soot carbonaceous materials, and core–shell particles. The paper concludes with a discussion of combined and complementary diagnostics, and an outlook of future research. © 2022, The Author(s).
    view abstractdoi: 10.1007/s00340-022-07769-z
  • 2022 • 128 Lead-Dominated Hyperfine Interaction Impacting the Carrier Spin Dynamics in Halide Perovskites
    Kirstein, E. and Yakovlev, D.R. and Glazov, M.M. and Evers, E. and Zhukov, E.A. and Belykh, V.V. and Kopteva, N.E. and Kudlacik, D. and Nazarenko, O. and Dirin, D.N. and Kovalenko, M.V. and Bayer, M.
    Advanced Materials 34 (2022)
    The outstanding optical quality of lead halide perovskites inspires studies of their potential for the optical control of carrier spins as pursued in other materials. Entering largely uncharted territory, time-resolved pump–probe Kerr rotation is used to explore the coherent spin dynamics of electrons and holes in bulk formamidinium caesium lead iodine bromide (FA0.9Cs0.1PbI2.8Br0.2) and to determine key parameters characterizing interactions of their spins, such as the g-factors and relaxation times. The demonstrated long spin dynamics and narrow g-factor distribution prove the perovskites as promising competitors for conventional semiconductors in spintronics. The dynamic nuclear polarization via spin-oriented holes is realized and the identification of the lead (207Pb) isotope in optically detected nuclear magnetic resonance proves that the hole–nuclei interaction is dominated by the lead ions. A detailed theoretical analysis accounting for the specifics of the lead halide perovskite materials allows the evaluation of the underlying hyperfine interaction constants, both for electrons and holes. Recombination and spin dynamics evidence that at low temperatures, photogenerated electrons and holes are localized at different regions of the perovskite crystal, resulting in their long lifetimes up to 44 μs. The findings form the base for the tailored development of spin-optoelectronic applications for the large family of lead halide perovskites and their nanostructures. © 2021 The Authors. Advanced Materials published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/adma.202105263
  • 2022 • 127 Limit theorems for Bessel and Dunkl processes of large dimensions and free convolutions
    Voit, M. and Woerner, J.H.C.
    Stochastic Processes and their Applications 143 207-253 (2022)
    We study Bessel and Dunkl processes (Xt,k)t≥0 on RN with possibly multivariate coupling constants k≥0. These processes describe interacting particle systems of Calogero–Moser–Sutherland type with N particles. For the root systems AN−1 and BN these Bessel processes are related with β-Hermite and β-Laguerre ensembles. Moreover, for the frozen case k=∞, these processes degenerate to deterministic or pure jump processes. We use the generators for Bessel and Dunkl processes of types A and B and derive analogues of Wigner's semicircle and Marchenko–Pastur limit laws for N→∞ for the empirical distributions of the particles with arbitrary initial empirical distributions by using free convolutions. In particular, for Dunkl processes of type B new non-symmetric semicircle-type limit distributions on R appear. Our results imply that the form of the limiting measures is already completely determined by the frozen processes. Moreover, in the frozen cases, our approach leads to a new simple proof of the semicircle and Marchenko–Pastur limit laws for the empirical measures of the zeros of Hermite and Laguerre polynomials respectively. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.spa.2021.10.005
  • 2022 • 126 Limiter-based entropy stabilization of semi-discrete and fully discrete schemes for nonlinear hyperbolic problems
    Kuzmin, D. and Hajduk, H. and Rupp, A.
    Computer Methods in Applied Mechanics and Engineering 389 (2022)
    The algebraic flux correction (AFC) schemes presented in this work constrain a standard continuous finite element discretization of a nonlinear hyperbolic problem to satisfy relevant maximum principles and entropy stability conditions. The desired properties are enforced by applying a limiter to antidiffusive fluxes that represent the difference between the high-order baseline scheme and a property-preserving approximation of Lax–Friedrichs type. In the first step of the limiting procedure, the given target fluxes are adjusted in a way that guarantees preservation of local and/or global bounds. In the second step, additional limiting is performed, if necessary, to ensure the validity of fully discrete and/or semi-discrete entropy inequalities. The limiter-based entropy fixes considered in this work are applicable to finite element discretizations of scalar hyperbolic equations and systems alike. The underlying inequality constraints are formulated using Tadmor's entropy stability theory. The proposed limiters impose entropy-conservative or entropy-dissipative bounds on the rate of entropy production by antidiffusive fluxes and Runge–Kutta (RK) time discretizations. Two versions of the fully discrete entropy fix are developed for this purpose. The first one incorporates temporal entropy production into the flux constraints, which makes them more restrictive and dependent on the time step. The second algorithm interprets the final stage of a high-order AFC-RK method as a constrained antidiffusive correction of an implicit low-order scheme (algebraic Lax–Friedrichs in space + backward Euler in time). In this case, iterative flux correction is required, but the inequality constraints are less restrictive and limiting can be performed using algorithms developed for the semi-discrete problem. To motivate the use of limiter-based entropy fixes, we prove a finite element version of the Lax–Wendroff theorem and perform numerical studies for standard test problems. In our numerical experiments, entropy-dissipative schemes converge to correct weak solutions of scalar conservation laws, of the Euler equations, and of the shallow water equations. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.cma.2021.114428
  • 2022 • 125 Low Cycle Fatigue Performance of Additively Processed and Heat-Treated Ti-6Al-7Nb Alloy for Biomedical Applications
    Hein, M. and Kokalj, D. and Dias, N.F.L. and Stangier, D. and Oltmanns, H. and Pramanik, S. and Kietzmann, M. and Hoyer, K.-P. and Meißner, J. and Tillmann, W. and Schaper, M.
    Metals 12 (2022)
    In biomedical engineering, laser powder bed fusion is an advanced manufacturing technology, which enables, for example, the production of patient-customized implants with complex geometries. Ti-6Al-7Nb shows promising improvements, especially regarding biocompatibility, compared with other titanium alloys. The biocompatible features are investigated employing cytocompatibility and antibacterial examinations on Al2O3-blasted and untreated surfaces. The mechanical properties of additively manufactured Ti-6Al-7Nb are evaluated in as-built and heat-treated conditions. Recrystallization annealing (925◦C for 4 h), β annealing (1050◦C for 2 h), as well as stress relieving (600◦C for 4 h) are applied. For microstructural investigation, scanning and transmission electron microscopy are performed. The different microstructures and the mechanical properties are compared. Mechanical behavior is determined based on quasi-static tensile tests and strain-controlled low cycle fatigue tests with total strain amplitudes εA of 0.35%, 0.5%, and 0.8%. The as-built and stress-relieved conditions meet the mechanical demands for the tensile properties of the international standard ISO 5832-11. Based on the Coffin–Manson–Basquin relation, fatigue strength and ductility coefficients, as well as exponents, are determined to examine fatigue life for the different conditions. The stress-relieved condition exhibits, overall, the best properties regarding monotonic tensile and cyclic fatigue behavior. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/met12010122
  • 2022 • 124 Magnetic and structural properties of Co-Ni-Z (Z= Al, Ga, In, Sn) Heusler alloys: Effect of structural motives and chemical disorder
    Sokolovskiy, V. and Miroshkina, O.N. and Sanosyan, A. and Baigutlin, D. and Buchelnikov, V. and Gruner, M.E.
    Journal of Magnetism and Magnetic Materials 546 (2022)
    Ground state properties of Ni-excess Co2Ni1+xZ1−x (Z= Al, Ga, In, Sn) full Heusler alloys are investigated by abinitio calculations. We consider the effect of different structural motives and chemical disorder on structural stability and magnetic characteristics of these alloys. Co-Ni-(In, Sn) are found to be unstable with respect to decomposition into pure bulk elements. Co2Ni(Al, Ga) are stable, however, introducing the Ni excess destabilizes these alloys making off-stoichiometric Co2Ni1+xAl1−x and Co2Ni1+xGa1−x unstable at x&gt;0.5 and x&gt;0.25, respectively. Saturation magnetization Ms of Co2Ni(Al, Ga) is of the same order like other Co2Ni-based Heusler alloys. Our study showed that an effective way to increase Ms is the introducing of chemical disorder. For stable compounds in which a tetragonal structure with alternating planes of Co and Ni exists, we calculate the magnetocrystalline anisotropy energy (MAE) given large values about −2 MJ/m3 with in-plane favorable spin configuration. The deviation from stoichiometry reduces the MAE by a factor of two. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.jmmm.2021.168728
  • 2022 • 123 Magnetic Resonance Imaging–based biomechanical simulation of cartilage: A systematic review
    Seyedpour, S.M. and Nafisi, S. and Nabati, M. and Pierce, D.M. and Reichenbach, J.R. and Ricken, T.
    Journal of the Mechanical Behavior of Biomedical Materials 126 (2022)
    MRI-based mathematical and computational modeling studies can contribute to a better understanding of the mechanisms governing cartilage's mechanical performance and cartilage disease. In addition, distinct modeling of cartilage is needed to optimize artificial cartilage production. These studies have opened up the prospect of further deepening our understanding of cartilage function. Furthermore, these studies reveal the initiation of an engineering-level approach to how cartilage disease affects material properties and cartilage function. Aimed at researchers in the field of MRI-based cartilage simulation, research articles pertinent to MRI-based cartilage modeling were identified, reviewed, and summarized systematically. Various MRI applications for cartilage modeling are highlighted, and the limitations of different constitutive models used are addressed. In addition, the clinical application of simulations and studied diseases are discussed. The paper's quality, based on the developed questionnaire, was assessed, and out of 79 reviewed papers, 34 papers were determined as high-quality. Due to the lack of the best constitutive models for various clinical conditions, researchers may consider the effect of constitutive material models on the cartilage disease simulation. In the future, research groups may incorporate various aspects of machine learning into constitutive models and MRI data extraction to further refine the study methodology. Moreover, researchers should strive for further reproducibility and rigorous model validation and verification, such as gait analysis. © 2021
    view abstractdoi: 10.1016/j.jmbbm.2021.104963
  • 2022 • 122 Magnetic response of CoFe2O4nanoparticles confined in a PNIPAM microgel network
    Witt, M.U. and Landers, J. and Hinrichs, S. and Salamon, S. and Kopp, J. and Hankiewicz, B. and Wende, H. and Von Klitzing, R.
    Soft Matter 18 1089-1099 (2022)
    The paper addresses coupling of magnetic nanoparticles (MNPs) with the polymer matrix of temperature-sensitive microgels and their response to magnetic fields. Therefore, CoFe2O4@CA (CA = citric acid) NPs are embedded within N-isopropylacrylamid (NIPAM) based microgels. The volume phase transition (VPT) of the magnetic microgels and the respective pure microgels is studied by dynamic light scattering and electrophoretic mobility measurements. The interaction between MNPs and microgel network is studied via magnetometry and AC-susceptometry using a superconducting quantum interference device (SQUID). The data show a significant change of the magnetic properties by crossing the VPT temperature (VPTT). The change is related to the increased confinement of the MNP due to the shrinking of the microgels. Modifying the microgel with hydrophobic allyl mercaptan (AM) affects the swelling ability and the magnetic response, i.e. the coupling of MNPs with the polymer matrix. Modeling the AC-susceptibility data results in an effective size distribution. This distribution represents the varying degree of constraint in MNP rotation and motion by the microgel network. These findings help to understand the interaction between MNPs and the microgel matrix to design multi responsive systems with tunable particle matrix coupling strength for future applications. This journal is © The Royal Society of Chemistry.
    view abstractdoi: 10.1039/d1sm01597d
  • 2022 • 121 Major surgical trauma impairs the function of natural killer cells but does not affect monocyte cytokine synthesis
    Müller-Heck, R.M. and Bösken, B. and Michiels, I. and Dudda, M. and Jäger, M. and Flohé, S.B.
    Life 12 (2022)
    Major traumatic and surgical injury increase the risk for infectious complications due to immune dysregulation. Upon stimulation with interleukin (IL) 12 by monocyte/macrophages, natural killer (NK) cells release interferon (IFN) γ that supports the elimination of the pathogen. In the present study, we investigated the impact of invasive spine surgery on the relationship between monocytes and NK cells upon exposure to Staphylococcus aureus. Mononuclear cells and serum were isolated from peripheral blood of patients before and up to 8 d after surgery and stimulated with inactivated S. aureus bacteria. NK cell and monocyte function were determined by flow cytometry. NK cells continuously lost their ability to produce IFN-γ during the first week after surgery independently from monocyte-derived IL-12 secretion. IFN-γ synthesis was minimal on day 8 and was associated with decreased expression of the IL-12 receptor and activation of transcription factors required for IFNG gene transcription. Addition of recombinant IL-12 could at least partially restore NK cell function. Pre-operative levels of growth/differentiation factor (GDF) 15 in the serum corre-lated with the extent of NK cell suppression and with hospitalization. Thus, NK cell suppression after major surgery might represent a therapeutic target to improve the immune defense against opportunistic infections. © 2021 by the authors. Li-censee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/life12010013
  • 2022 • 120 Manufacturing of W/steel composites using electro-discharge sintering process
    Ganesh, V. and Leich, L. and Dorow-Gerspach, D. and Heuer, S. and Coenen, J.W. and Wirtz, M. and Pintsuk, G. and Gormann, F. and Lied, P. and Baumgärtner, S. and Theisen, W. and Linsmeier, C.
    Nuclear Materials and Energy 30 (2022)
    Tungsten-steel metal matrix composites are consolidated using electro-discharge sintering. At first steel and tungsten powders are sintered separately and then 25 vol% W, 50 vol% W and 75 vol% W mixed powders are sintered. A thorough process parametric study is carried out involving analysis of the influence of particle size distribution, sintering pressure, and discharge energy on the maximum discharge current and obtained residual porosity. Thermal expansion coefficient and the specific heat capacity of the optimized sintered composites are almost same as their theoretical values, however the thermal conductivities and the mechanical properties are lower than the expected values. © 2021 The Authors
    view abstractdoi: 10.1016/j.nme.2021.101089
  • 2022 • 119 Massive interstitial solid solution alloys achieve near-theoretical strength
    Liu, C. and Lu, W. and Xia, W. and Du, C. and Rao, Z. and Best, J.P. and Brinckmann, S. and Lu, J. and Gault, B. and Dehm, G. and Wu, G. and Li, Z. and Raabe, D.
    Nature Communications 13 (2022)
    Interstitials, e.g., C, N, and O, are attractive alloying elements as small atoms on interstitial sites create strong lattice distortions and hence substantially strengthen metals. However, brittle ceramics such as oxides and carbides usually form, instead of solid solutions, when the interstitial content exceeds a critical yet low value (e.g., 2 at.%). Here we introduce a class of massive interstitial solid solution (MISS) alloys by using a highly distorted substitutional host lattice, which enables solution of massive amounts of interstitials as an additional principal element class, without forming ceramic phases. For a TiNbZr-O-C-N MISS model system, the content of interstitial O reaches 12 at.%, with no oxides formed. The alloy reveals an ultrahigh compressive yield strength of 4.2 GPa, approaching the theoretical limit, and large deformability (65% strain) at ambient temperature, without localized shear deformation. The MISS concept thus offers a new avenue in the development of metallic materials with excellent mechanical properties. © 2022, The Author(s).
    view abstractdoi: 10.1038/s41467-022-28706-w
  • 2022 • 118 MEAM interatomic potentials of Ni, Re, and Ni-Re alloys for atomistic fracture simulations
    Alam, M. and Lymperakis, L. and Groh, S. and Neugebauer, J.
    Modelling and Simulation in Materials Science and Engineering 30 (2022)
    Second nearest neighbor modified embedded atom method (2NN-MEAM) interatomic potentials are developed for the Ni, Re, and Ni-Re binaries. To construct the potentials, density functional theory (DFT) calculations have been employed to calculate fundamental physical properties that play a dominant role in fracture. The potentials are validated to accurately reproduce material properties that correlate with material's fracture behavior. The thus constructed potentials were applied to perform large scale simulations of mode I fracture in Ni and Ni-Re binaries with low Re content. Substitutional Re did not alter the ductile nature of crack propagation, though it resulted in a monotonous increase of the critical stress intensity factor with Re content. © 2021 The Author(s). Published by IOP Publishing Ltd.
    view abstractdoi: 10.1088/1361-651X/ac3a15
  • 2022 • 117 Measuring and Modeling Water Sorption in Amorphous Indomethacin and Ritonavir
    Borrmann, D. and Danzer, A. and Sadowski, G.
    Molecular Pharmaceutics 19 998-1007 (2022)
    The amorphous state of an active pharmaceutical ingredient (API) enhances its water solubility compared to its crystalline state. However, it is well known that amorphous substances can absorb significant amounts of water therewith inducing API recrystallization. This work explores methods to obtain reliable information about water sorption in amorphous APIs and its modeling. Experimental water-sorption curves over a broad humidity range were obtained by measuring the mass increase of well-defined films of amorphous APIs. Water-sorption isotherms modeled using perturbed-chain statistical associating fluid theory (PC-SAFT) showed better accordance with the experimental data than those obtained using the Flory-Huggins model. Crank's diffusion equation was used to describe the water-sorption kinetics providing Fickian diffusion coefficients of water in indomethacin and in ritonavir. Stefan-Maxwell diffusion coefficients were obtained by converting Fickian diffusion coefficients using water activity coefficients obtained from PC-SAFT. Finally, the free-volume theory was applied to explain the persistent water concentration dependency of the Stefan-Maxwell diffusion coefficients. © 2022 American Chemical Society. All rights reserved.
    view abstractdoi: 10.1021/acs.molpharmaceut.1c00984
  • 2022 • 116 Mechanical Behaviour and Failure Mode of High Interstitially Alloyed Austenite under Combined Compression and Cyclic Torsion
    Ngeru, T. and Kurtulan, D. and Karkar, A. and Hanke, S.
    Metals 12 (2022)
    multiaxial stress states frequently occur in technical components and, due to the multitude of possible load situations and variations in behaviour of different materials, are to date not fully predictable. This is particularly the case when loads lie in the plastic range, when strain accumulation, hardening and softening play a decisive role for the material reaction. This study therefore aims at adding to the understanding of material behaviour under complex load conditions. Fatigue tests conducted under cyclic torsional angles (5°, 7.5°, 10° and 15°), with superimposed axial static compression loads (250 MPa and 350 MPa), were carried out using smooth specimens at room temperature. A high nitrogen alloyed austenitic stainless steel (nickel free), was employed to determine not only the number of cycles to failure but particularly to aid in the understanding of the mechanical material reaction to the multiaxial stresses as well as modes of crack formation and growth. Experimental test results indicate that strain hardening occurs under the compressive strain, while at the same time cyclic softening is observable in the torsional shear stresses. Furthermore, the cracks’ nature is unusual with multiple branching and presence of cracks perpendicular in direction to the surface cracks, indicative of the varying multiaxial stress states across the samples’ cross section as cross slip is activated in different directions. In addition, it is believed that the static compressive stress facilitated the Stage I (mode II) crack to change direction from the axial direction to a plane perpendicular to the specimen’s axis. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/met12010157
  • 2022 • 115 Mechanical in vitro fatigue testing of implant materials and components using advanced characterization techniques
    Wegner, N. and Klein, M. and Scholz, R. and Kotzem, D. and Macias Barrientos, M. and Walther, F.
    Journal of Biomedical Materials Research - Part B Applied Biomaterials 110 898-909 (2022)
    Implants of different material classes have been used for the reconstruction of damaged hard and soft tissue for decades. The aim is to increase and subsequently maintain the patient's quality of life through implantation. In service, most implants are subjected to cyclic loading, which must be taken particularly into consideration, since the fatigue strength is far below the yield and tensile strength. Inaccurate estimation of the structural strength of implants due to the consideration of yield or tensile strength leads to a miscalculation of the implant's fatigue strength and lifetime, and therefore, to its unexpected early fatigue failure. Thus, fatigue failure of an implant based on overestimated performance capability represents acute danger to human health. The determination of fatigue strength by corresponding tests investigating various stress amplitudes is time-consuming and cost-intensive. This study summarizes four investigation series on the fatigue behavior of different implant materials and components, following a standard and an in vitro short-time testing procedure, which evaluates the material reaction in one enhanced test set-up. The test set-up and the applied characterization methods were adapted to the respective application of the implant with the aim to simulate the surrounding of the human body with laboratory in vitro tests only. It could be shown that by using the short-time testing method the number of tests required to determine the fatigue strength can be drastically reduced. In future, therefore it will be possible to exclude unsuitable implant materials or components before further clinical investigations by using a time-efficient and application-oriented testing method. © 2021 Wiley Periodicals LLC.
    view abstractdoi: 10.1002/jbm.b.34970
  • 2022 • 114 Membrane Structure Obtained in an Experimental Evolution Process
    Dávila, M.J. and Mayer, C.
    Life 12 (2022)
    Recently, an evolution experiment was carried out in a cyclic process, which involved periodic vesicle formation in combination with peptide and vesicle selection. As an outcome, an octapeptide (KSPFPFAA) was identified which rapidly integrated into the vesicle membrane and, according to its significant accumulation, is obviously connected to a particular advantage of the corresponding functionalized vesicle. Here we report a molecular dynamics study of the structural details of the functionalized vesicle membrane, which was a product of this evolution process and is connected to several survival mechanisms. In order to elucidate the particular advantage of this structure, we performed all-atom molecular dynamics simulations to examine structural changes and interactions of the peptide (KSPFPFAA) with the given octadecanoic acid/octadecylamine (1:1) bilayer under acidic conditions. The calculations clearly demonstrate the specific interactions between the peptide and the membrane and reveal the mechanisms leading to the improved vesicle survival. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/life12020145
  • 2022 • 113 Memory effects in black phosphorus field effect transistors
    Grillo, A. and Pelella, A. and Faella, E. and Giubileo, F. and Sleziona, S. and Kharsah, O. and Schleberger, M. and Di Bartolomeo, A.
    2D Materials 9 (2022)
    We report the fabrication and the electrical characterization of back-gated field effect transistors with a black phosphorus (BP) channel. We show that the hysteresis of the transfer characteristic, due to intrinsic defects, can be exploited to realize non-volatile memories. We demonstrate that gate voltage pulses allow to trap and store charge inside the defect states, which enable memory devices with endurance over 200 cycles and retention longer than 30 min. We show that the use of a protective poly(methyl methacrylate) layer, positioned on top of the BP channel, does not affect the electrical properties of the device but avoids the degradation caused by the exposure to air. © 2021 IOP Publishing Ltd.
    view abstractdoi: 10.1088/2053-1583/ac3f45
  • 2022 • 112 Microfiltration of polymeric microgels as soft model colloids through sterile filter membranes
    Büning, D. and Ennen-Roth, F. and Netke, T. and Schumacher, J. and Ulbricht, M.
    Journal of Membrane Science 649 (2022)
    In this work, filtration studies were performed with particles of soft or super-soft nature, made from polyacrylamide copolymers, and hard polystyrene reference particles, all having average diameters between 180 and 200 nm, at relatively high particle concentrations and different transmembrane pressures under stirred and non-stirred dead-end filtration conditions in order to evaluate the separation and fouling behavior of a commercially available high-flux microfiltration membrane (experimentally determined barrier pore diameter 210 nm). In order to identify the underlying fouling processes the dependencies of the flux on cumulative volume or time were analyzed in the frame of established models. It was found that low transmembrane pressures of 0.1 bar lead to immediate filter cake formation, that facilitates a high retention of the particles and leads to less fouling that cannot be removed by external washing. Medium to high pressures (0.5–2.0 bar) resulted in a pronounced penetration of microgel particles into the membrane structure and pore blocking in the first phase (I) of the filtration, before entering the cake formation phase (II); the particle rejection in phase I was lower and the extent of fouling remaining after washing was larger. Super-soft microgels showed a significantly more pronounced pore blocking phase (I), compared to their soft counterparts or the hard sphere reference particles. The results of the study yield deeper insights into retention and blocking mechanisms during filtrations of deformable microgels as model colloids with a benchmark sterile filtration membrane. This is relevant for purification of such polymeric materials after their synthesis or for the development of test systems mimicking the removal of microorganisms by sterile filtration. © 2022 Elsevier B.V.
    view abstractdoi: 10.1016/j.memsci.2022.120364
  • 2022 • 111 Microstructure and residual stress evolution in nanocrystalline Cu-Zr thin films
    Chakraborty, J. and Oellers, T. and Raghavan, R. and Ludwig, A. and Dehm, G.
    Journal of Alloys and Compounds 896 (2022)
    Grazing incidence X-ray diffraction (GIXRD) and scanning transmission electron microscopy (STEM) combined with energy dispersive X-ray spectroscopy (EDS) were employed to study the microstructure evolution and stress development in the nanocrystalline Cu100−X-ZrX (2.5 at% ≤ x ≤ 5.5 at%) alloy thin films. Small Zr additions to Cu led to significant lattice parameter anisotropy in the as-deposited Cu-Zr thin films both due to macroscopic lattice strain and stacking faults in the Cu matrix. Strain free lattice parameters obtained after the XRD stress analysis of Cu-Zr thin films confirmed formation of a supersaturated substitutional Cu-Zr solid solution. For the first time, the study of film microstructure by XRD line profile analysis (XLPA) confirmed progressive generation of dislocations and planar faults with increasing Zr composition in Cu-Zr alloy films. These microstructural changes led to the generation of tensile stresses in the thin films along with considerable stress gradients across the films thicknesses which are quantified by the traditional dψhkl−Sin2ψ and GIXRD stress measurement methods. The origin of tensile stresses and stress gradients in the Cu-Zr film are discussed on the basis of film growth and heterogeneous microstructure with changing Zr composition. © 2021
    view abstractdoi: 10.1016/j.jallcom.2021.162799
  • 2022 • 110 Microstructure property classification of nickel-based superalloys using deep learning
    Nwachukwu, U. and Obaied, A. and Horst, O.M. and Ali, M.A. and Steinbach, I. and Roslyakova, I.
    Modelling and Simulation in Materials Science and Engineering 30 (2022)
    Nickel-based superalloys have a wide range of applications in high temperature and stress domains due to their unique mechanical properties. Under mechanical loading at high temperatures, rafting occurs, which reduces the service life of these materials. Rafting is heavily affected by the loading conditions associated with plastic strain; therefore, understanding plastic strain evolution can help understand these material's service life. This research classifies nickel-based superalloys with respect to creep strain with deep learning techniques, a technique that eliminates the need for manual feature extraction of complex microstructures. Phase-field simulation data that displayed similar results to experiments were used to build a model with pre-trained neural networks with several convolutional neural network architectures and hyper-parameters. The optimized hyper-parameters were transferred to scanning electron microscopy images of nickel-based superalloys to build a new model. This fine-tuning process helped mitigate the effect of a small experimental dataset. The built models achieved a classification accuracy of 97.74% on phase-field data and 100% accuracy on experimental data after fine-tuning. © 2022 The Author(s). Published by IOP Publishing Ltd.
    view abstractdoi: 10.1088/1361-651X/ac3217
  • 2022 • 109 Mixing and segregation of spheres of three different sizes on a batch stoker grate: Experiments and discrete element simulation
    Hilse, N. and Kriegeskorte, M. and Illana, E. and Wirtz, S. and Scherer, V.
    Powder Technology 400 (2022)
    Mixing and segregation in a tri-disperse granular assembly of polyoxymethylene (POM) spheres induced by the moveable stoking bars of a generic batch grate system are examined. Each particle size class features a separate colour. Stroke bar velocity and stroke length are varied. Different moving modes of the bars are analysed. Optically transparent walls of the grate allow for the localization of the visible particles. Based on the visible particle positions a segregation index is calculated. The initial arrangement of the particles in the experiments, which exhibits small statistical differences introduced by the grate filling procedure, has an influence on the progression of the segregation index. The experiments are compared with discrete element (DEM) simulations employing an in-house DEM code. Experiments are in good general agreement with the simulations. The particle rearrangement during bar movement is characterized by an initially fast mixing on short time-scales and a slow process to reach a final state of segregation. These two processes are influenced by the penetration depth of the bars into the bed and the specific movement mode. Three modes predominantly showed segregation in the direction of bar movement, whereas two modes showed large-scale spatial particle rearrangement. Two moving modes show bridging at the beginning of the experiments, an effect that could be reproduced by the DEM simulations. The influence of the modes and their specific parameters on segregation indices, a mixing rate and a segregation efficiency are discussed in detail. © 2022 Elsevier B.V.
    view abstractdoi: 10.1016/j.powtec.2022.117258
  • 2022 • 108 Modeling of the Split-Hopkinson-Pressure-Bar experiment with the explicit material point method
    Maassen, S.F. and Niekamp, R. and Bergmann, J.A. and Pöhl, F. and Schröder, J. and Wiederkehr, P.
    Computational Particle Mechanics 9 153-166 (2022)
    The material point method (MPM) represents an alternative discretization method for numerical simulations. It aims to combine the benefits of a Lagrangian representation of bodies and an Eulerian numerical solution approach. Therefore, especially at high material deformations the method is not prone to mesh distortions such as the finite element method (FEM). For this reason, the MPM is used to a great extent for modeling granular materials as in geo-mechanics. However, high deformations occur in many industrial processes on metallic materials. The Split-Hopkinson-Pressure-Bar (SHPB) experiment is used to characterize material properties at high deformation rates. Although widely used, this experiment is not yet standardized and shows a variety of sensitivities, e.g. to friction. Inter alia for this reason, simulations are conducted with the experiment to allow for a better evaluation of the measured data. The purpose of this work from an engineering point of view is to analyze the performance of the MPM on an SHPB experiment. In order to validate the experimental results for the material characterization under dynamic loading conditions we introduce frictional contact. We use arbitrary tri-linear brick domains in a 3D CPDI1 scheme, instead of originally used parallelepipeds. This allows for a more flexible geometry approximation using standard meshes. The results of the method are analyzed with respect to discretization sensitivity and discussed in the context of the experimental results for a 42CrMo4 steel. We were able to show that the method is capable to reproduce the SHPB experiment. Additionally the method shows convergency in the results with finer discretizations. Thus, the MPM has underlined its importance as an alternative simulation technique for problems with high deformation. © 2021, The Author(s).
    view abstractdoi: 10.1007/s40571-021-00399-w
  • 2022 • 107 Molecular Emissions from Stretched Excitation Pulse in Nanosecond Phase-Selective Laser-Induced Breakdown Spectroscopy of TiO2 Nanoaerosols
    Xiong, G. and Zhang, Y. and Schulz, C. and Tse, S.D.
    Applied Spectroscopy (2022)
    In phase-selective laser-induced breakdown spectroscopy (PS-LIBS), gas-borne nanoparticles are irradiated with laser pulses (∼2.4 GW/cm2) resulting in breakdown of the nanoparticle phase but not the surrounding gas phase. In this work, the effect of excitation laser-pulse duration and energy on the intensity and duration of TiO2–nanoparticle PS-LIBS emission signal is investigated. Laser pulses from a frequency-doubled neodymium-doped yttrium aluminum garnet (Nd:YAG) laser (532 nm) are stretched from 8 ns (full width at half maximum, FWHM) up to ∼30 ns at fixed pulse energy using combinations of two optical cavities. The intensity of the titanium atomic emissions at around 500 nm wavelength increases by ∼60%, with the stretched pulse and emissions at around 482 nm, attributed to TiO, enhanced over 10 times. While the atomic emissions rise with the stretched laser pulse and decay around 20 ns after the end of the laser pulse, the TiO emissions reach their peak intensity at about 20 ns later and last longer. At low laser energy (i.e., 1 mJ/pulse, or 80 MW/cm2), the TiO emissions dominate, but their increase with laser energy is lower compared to the atomic emissions. The origin of the 482 nm emission is explored by examining several different aerosol setups, including Ti–O, Ti–N, and Ti–O–N from a spark particle generator and Ti–O–N–C–H aerosol from flame synthesis. The 482 nm emissions are attributed to electronically excited TiO, likely resulting from the reaction of excited titanium atoms with surrounding oxidizing (carbonaceous and/or radical) species. The effects of pulse length are attributed to the shift of absorption from the initial interaction with the particle to the prolonged interaction with the plasma through inverse bremsstrahlung. © The Author(s) 2022.
    view abstractdoi: 10.1177/00037028211072583
  • 2022 • 106 Molecular Permeation in Freestanding Bilayer Silica
    Naberezhnyi, D. and Mai, L. and Doudin, N. and Ennen, I. and Hütten, A. and Altman, E.I. and Devi, A. and Dementyev, P.
    Nano Letters 22 1287-1293 (2022)
    Graphene and other single-layer structures are pursued as high-flux separation membranes, although imparting porosity endangers their crystalline integrity. In contrast, bilayer silica composed of corner-sharing (SiO4) units is foreseen to be permeable for small molecules due to its intrinsic lattice openings. This study sheds light on the mass transport properties of freestanding 2D SiO2 upon using atomic layer deposition (ALD) to grow large-area films on Au/mica substrates followed by transfer onto Si3N4 windows. Permeation experiments with gaseous and vaporous substances reveal the suspended material to be porous, but the membrane selectivity appears to diverge from the size exclusion principle. Whereas the passage of inert gas molecules is hindered with a permeance below 10-7 mol·s-1·m-2·Pa-1, condensable species like water are found to cross vitreous bilayer silica a thousand times faster in accordance with their superficial affinity. This work paves the way for bilayer oxides to be addressed as inherent 2D membranes. © 2022 American Chemical Society.
    view abstractdoi: 10.1021/acs.nanolett.1c04535
  • 2022 • 105 Molecular tweezers - a new class of potent broad-spectrum antivirals against enveloped viruses
    Le, M.-H. and Taghuo K., E.S. and Schrader, T.
    Chemical Communications 58 2954-2966 (2022)
    A new supramolecular approach to broad spectrum antivirals utilizes host guest chemistry between molecular tweezers and lysine/arginine as well as choline. Basic amino acids in amyloid-forming SEVI peptides (semen-derived enhancers of viral infection) are included inside the tweezer cavity leading to disaggregation and neutralization of the fibrils, which lose their ability to enhance HIV-1/HIV-2 infection. Lipid head groups contain the trimethylammonium cation of choline; this is likewise bound by molecular tweezers, which dock onto viral membranes and thus greatly enhance their surface tension. Disruption of the envelope in turn leads to total loss of infectiosity (ZIKA, Ebola, Influenza). This complexation event also seems to be the structural basis for an effective inihibition of cell-to-cell spread in Herpes viruses. The article describes the discovery of novel molecular recognition motifs and the development of powerful antiviral agents based on these host guest systems. It explains the general underlying mechanisms of antiviral action and points to future optimization and application as therapeutic agents. This journal is © The Royal Society of Chemistry
    view abstractdoi: 10.1039/d1cc06737k
  • 2022 • 104 Mono-ADP-ribosylation sites of human CD73 inhibit its adenosine-generating enzymatic activity
    Hesse, J. and Rosse, M.K. and Steckel, B. and Blank-Landeshammer, B. and Idel, S. and Reinders, Y. and Sickmann, A. and Sträter, N. and Schrader, J.
    Purinergic Signalling 18 115-121 (2022)
    CD73-derived adenosine plays a major role in damage-induced tissue responses by inhibiting inflammation. Damage-associated stimuli, such as hypoxia and mechanical stress, induce the cellular release of ATP and NAD+ and upregulate the expression of the nucleotide-degrading purinergic ectoenzyme cascade, including adenosine-generating CD73. Extracellular NAD+ also serves as substrate for mono-ADP-ribosylation of cell surface proteins, which in human cells is mediated by ecto-ADP-ribosyltransferase 1 (ARTC1). Here we explored, whether human CD73 enzymatic activity is regulated by mono-ADP-ribosylation, using recombinant human CD73 in the presence of ARTC1 with etheno-labelled NAD+ as substrate. Multi-colour immunoblotting with an anti-etheno-adenosine antibody showed ARTC1-mediated transfer of ADP-ribose together with the etheno label to CD73. HPLC analysis of the enzymatic activity of in vitro-ribosylated CD73 revealed strong inhibition of adenosine generation in comparison to non-ribosylated CD73. Mass spectrometry of in vitro-ribosylated CD73 identified six ribosylation sites. 3D model analysis indicated that three of them (R328, R354, R545) can interfere with CD73 enzymatic activity. Our study identifies human CD73 as target for ARTC1-mediated mono-ADP-ribosylation, which can profoundly modulate its adenosine-generating activity. Thus, in settings with enhanced release of NAD+ as substrate for ARTC1, assessment of CD73 protein expression in human tissues may not be predictive of adenosine formation resulting in anti-inflammatory activity. © 2021, The Author(s).
    view abstractdoi: 10.1007/s11302-021-09832-4
  • 2022 • 103 Multilevel Picard approximations for McKean-Vlasov stochastic differential equations
    Hutzenthaler, M. and Kruse, T. and Nguyen, T.A.
    Journal of Mathematical Analysis and Applications 507 (2022)
    In the literature there exist approximation methods for McKean-Vlasov stochastic differential equations which have a computational effort of order 3. In this article we introduce full-history recursive multilevel Picard approximations for McKean-Vlasov stochastic differential equations. We prove that these MLP approximations have computational effort of order 2+ which is essentially optimal in high dimensions. © 2021 Elsevier Inc.
    view abstractdoi: 10.1016/j.jmaa.2021.125761
  • 2022 • 102 Nanoparticles Carrying NF-κB p65-Specific siRNA Alleviate Colitis in Mice by Attenuating NF-κB-Related Protein Expression and Pro-Inflammatory Cellular Mediator Secretion
    Müller, E.K. and Białas, N. and Epple, M. and Hilger, I.
    Pharmaceutics 14 (2022)
    Ulcerative colitis is a disease that causes inflammation and ulcers in the colon and which is typically recurrent, and NF-κB proteins are important players during disease progression. Here, we assess the impact of silica-coated calcium phosphate nanoparticles carrying encapsulated siRNA against NF-κB p65 on a murine model of colitis. To this end, nanoparticles were injected intravenously (2.0 mg siRNA/kg body weight) into mice after colitis induction with dextran sulfate sodium or healthy ones. The disease activity index, the histopathological impact on the colon, the protein expression of several NF-κB-associated players, and the mediator secretion (colon tissue, blood) were analyzed. We found that the nanoparticles effectively alleviated the clinical and histopathological features of colitis. They further suppressed the expression of NF-κB proteins (e.g., p65, p50, p52, p100, etc.) in the colon. They finally attenuated the local (colon) or systemic (blood) pro-inflammatory mediator secretion (e.g., TNF-α, IFN-β, MCP-1, interleukins, etc.) as well as the leucocyte load of the spleen and mesenteric lymph nodes. The nanoparticle biodistribution in diseased animals was seen to pinpoint organs containing lymphoid entities (appendix, intestine, lung, etc.). Taken together, the nanoparticle-related silencing of p65 NF-κB protein expression could well be used for the treatment of ulcerative colitis in the future. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/pharmaceutics14020419
  • 2022 • 101 Noncontact reception of ultrasound from soft magnetic mild steel with zero applied bias field EMATs
    Rieger, K. and Erni, D. and Rueter, D.
    NDT and E International 125 (2022)
    Electromagnetic acoustic transducers (EMATs) without added magnets or bias currents receive ultrasound as bulk or Lamb waves from soft magnetic iron or mild steels. EMATs typically include bulky permanent or electromagnets for biasing magnetic fields in ultrasound reception. New compact-coils-only EMATs without additional magnets excite bias fields with pulsed strong coil currents, limiting detection time. Here, short premagnetization pulses in a simple EMAT coil allowed longer ultrasound reception from mild steel and virtually zero externally applied bias field. An unexpected long-lasting magnetic imprint inside the metal was clearly responsible and not normally expected with soft magnetic ferrous materials. Suggestions are made for mechanisms of electroacoustic coupling and permanent magnetization, even of transformer irons, after the termination of an exciting field. This contributes to novel applications of compact-coils-only EMATs without added magnets. © 2021 Elsevier Ltd
    view abstractdoi: 10.1016/j.ndteint.2021.102569
  • 2022 • 100 Noncovalent Intra- and Intermolecular Interactions in Peri-Substituted Pnicta Naphthalene and Acenaphthalene Complexes
    Gehlhaar, A. and Wölper, C. and van der Vight, F. and Jansen, G. and Schulz, S.
    European Journal of Inorganic Chemistry 2022 (2022)
    Five peri-substituted naphthalene and acenaphthalene complexes (Ph2Pn)2Naph (E=Sb 1, Bi 3), (Ph2Sb)2Acenaph (2), (Ph2Bi)(Me3Sn)Naph (4) and (PhBiNaph)2 (5) were synthesized and characterized in solution (1H, 13C NMR, IR) and in the solid-state (sc-XRD). 1–5 show different types of noncovalent intermolecular interactions in the solid-state including Naph−H⋅⋅⋅π, π⋅⋅⋅π and Bi⋅⋅⋅π (5) contacts, which were exemplarily (5) quantified by use of density functional theory and local coupled cluster electronic structure theory calculations, demonstrating that the Bi⋅⋅⋅π contact provides the main stabilizing contribution. Symmetry-adapted intermolecular perturbation theory calculations showed that this and other contacts are dominated by London dispersion interactions. © 2021 The Authors. European Journal of Inorganic Chemistry published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/ejic.202100883
  • 2022 • 99 Non-gradient full waveform inversion approaches for exploration during mechanized tunneling applied to surrogate laboratory measurements
    Trapp, M. and Nestorović, T.
    Tunnelling and Underground Space Technology 120 (2022)
    Drilling into unknown soil during mechanized tunneling may cause damage of the tunnel boring machine or delays in the construction process. A full waveform inversion can prevent these issues supplying a detailed image of the subsoil, but claims several challenges like the need for an adequate method or the need for an appropriate utilization of seismic sources and receivers. In this research, a small-scale surrogate model is constructed in order to create representative tunneling field data in a laser laboratory. With the experimental model, ultrasonic data is generated. After constructing an adequate forward model, two non-gradient full waveform inversion methods based on parameter identification are applied to the measurement data in order to determine the inner structure of the model out of seismic waveforms. Furthermore, the positioning of seismic sources and receivers is investigated. The algorithms are found to perform well on the acquired measurement data, with different precisions dependent on the utilized method and on the source-receiver configuration. The comparability of the ultrasonic data to tunneling field data is analyzed. © 2021 Elsevier Ltd
    view abstractdoi: 10.1016/j.tust.2021.104252
  • 2022 • 98 Non-uniform He bubble formation in W/W2C composite: Experimental and ab-initio study
    Šestan, A. and Sreekala, L. and Markelj, S. and Kelemen, M. and Zavašnik, J. and Liebscher, C.H. and Dehm, G. and Hickel, T. and Čeh, M. and Novak, S. and Jenuš, P.
    Acta Materialia 226 (2022)
    Tungsten-tungsten carbide (W/W2C) composites are considered as possible structural materials for future nuclear fusion reactors. Here, we report on the effect of helium (He) implantation on microstructure evolution of polycrystalline W/W2C composite consolidated by field-assisted sintering technique (FAST), homogenously implanted at room temperature with 1 MeV 4He+ ions at the fluence of 8 × 1016 ions cm−2 and annealed at 1873 K for 20 minutes. Samples were analysed by scanning and transmission electron microscopy to study the presence and size of He bubbles. Monomodal He bubbles in W (30-80 nm) are limited to point defects and grain boundaries, with a considerable void denuded zone (150 nm). Bubbles do not form in W2C, but at the W|W2C interface and are considerably larger (200-400 nm). The experimental observations on He behaviour and migration in W and W2C were assessed by density functional theory (DFT) calculations, suggesting He migration and accumulation in the composite are determined by the effective He-He binding in clusters, which will give rise to decohesion. In the presence of He clusters, the decohesion of bulk W into free surfaces is energetically highly favourable but not sufficient in the W2C; hence bubbles are only observed in W grains and interfaces and not within bulk W2C. © 2022
    view abstractdoi: 10.1016/j.actamat.2021.117608
  • 2022 • 97 Novel insights into PORCN mutations, associated phenotypes and pathophysiological aspects
    Arlt, A. and Kohlschmidt, N. and Hentschel, A. and Bartels, E. and Groß, C. and Töpf, A. and Edem, P. and Szabo, N. and Sickmann, A. and Meyer, N. and Schara-Schmidt, U. and Lau, J. and Lochmüller, H. and Horvath, R. and Oktay,...
    Orphanet Journal of Rare Diseases 17 (2022)
    Background: Goltz syndrome (GS) is a X-linked disorder defined by defects of mesodermal- and ectodermal-derived structures and caused by PORCN mutations. Features include striated skin-pigmentation, ocular and skeletal malformations and supernumerary or hypoplastic nipples. Generally, GS is associated with in utero lethality in males and most of the reported male patients show mosaicism (only three non-mosaic surviving males have been described so far). Also, precise descriptions of neurological deficits in GS are rare and less severe phenotypes might not only be caused by mosaicism but also by less pathogenic mutations suggesting the need of a molecular genetics and functional work-up of these rare variants. Results: We report two cases: one girl suffering from typical skin and skeletal abnormalities, developmental delay, microcephaly, thin corpus callosum, periventricular gliosis and drug-resistant epilepsy caused by a PORCN nonsense-mutation (c.283C > T, p.Arg95Ter). Presence of these combined neurological features indicates that CNS-vulnerability might be a guiding symptom in the diagnosis of GS patients. The other patient is a boy with a supernumerary nipple and skeletal anomalies but also, developmental delay, microcephaly, cerebral atrophy with delayed myelination and drug-resistant epilepsy as predominant features. Skin abnormalities were not observed. Genotyping revealed a novel PORCN missense-mutation (c.847G > C, p.Asp283His) absent in the Genome Aggregation Database (gnomAD) but also identified in his asymptomatic mother. Given that non-random X-chromosome inactivation was excluded in the mother, fibroblasts of the index had been analyzed for PORCN protein-abundance and -distribution, vulnerability against additional ER-stress burden as well as for protein secretion revealing changes. Conclusions: Our combined findings may suggest incomplete penetrance for the p.Asp283His variant and provide novel insights into the molecular etiology of GS by adding impaired ER-function and altered protein secretion to the list of pathophysiological processes resulting in the clinical manifestation of GS. © 2022, The Author(s).
    view abstractdoi: 10.1186/s13023-021-02068-w
  • 2022 • 96 Numerical Investigation of Hydroelastic Effects on Floating Structures
    Jiang, C. and el Moctar, O. and Schellin, T.E. and Qi, Y.
    Lecture Notes in Civil Engineering 158 309-330 (2022)
    Hydroelasticity effects of an offshore floating structure comprise the combined motions and deformations of the floating body responding to environmental excitations. The review of research on hydroelasticity of very large floating structure shows that understanding the physical phenomenon has increased, but discussions of practical implications of hydroelasticity on offshore structure design are rare. Conventionally, floating structure designs are based on a rigid quasi-static analysis, meaning that the hydrodynamic loads are estimated under rigid assumption and then applied to the elastic structure regardless of structural inertia. Here, the hydroelastic behavior of a standard floating module designed within the scope of the Space@Sea project was numerically investigated, and the role of hydroelasticity in the practical assessment of a large floating structure was demonstrated. The fluid dynamics relied on a Computational Fluid Dynamics (CFD) code, and the structural responses were computed by a Computational Structural Dynamics (CSD) solver. The CFD-CSD solver was coupled using an implicit two-way coupling approach, computing the nonlinear 6-DoF rigid body motion separately from linear elastic structural deformations. First, the numerical model was validated against benchmark test data, and then a standard floating module in waves was assessed in terms of structural integrity and motions. Maximum stresses and bending moments obtained by the coupled CFD-CSD approach and the traditional rigid-quasi-static approach were compared, and the implication of hydroelasticity on the floating module was assessed. The hydroelastic criterion and the validity of a rigid a quasi-static analysis determined the effects on dynamic responses. © 2022, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.
    view abstractdoi: 10.1007/978-981-16-2256-4_19
  • 2022 • 95 Numerical Multi-level Model for Fibre Reinforced Concrete: Validation and Comparison with Fib Model Code
    Neu, G.E. and Gudžulić, V. and Meschke, G.
    RILEM Bookseries 36 365-376 (2022)
    In this contribution, a Finite Element modelling scheme for steel-fibre reinforced concrete (SFRC) is proposed with which the post-cracking response of fibre reinforced structural members can be predicted. In contrast to the common guidelines, the post-cracking response of SFRC is derived from the actual fibre properties instead of indirectly from bending tests. The numerical model is designed to directly track the influence of design parameters such as fibre type, fibre orientation, fibre content and concrete strength on the structural response. For this purpose, sub models on the single fibre level are combined into a crack bridging model, considering the fibre orientation and the fibre content, and are integrated into a finite element model for the purpose of numerical structural analysis. The predictive capability of the proposed numerical multi-level model for SFRC is systematically validated by means of test series performed on the fibre, crack and the structural level. The experimental study comprises pull-out tests of Dramix 3D fibres, uniaxial tension tests involving different fibre contents and fibre types as well as three-point bending tests on notched beams with 23 and 57 kg/m3 Dramix 3D fibres. Furthermore, the results are compared to the modelling approach presented in the fib model code 2010 and an inverse analysis approach. © 2022, RILEM.
    view abstractdoi: 10.1007/978-3-030-83719-8_32
  • 2022 • 94 Numerical Simulation of Tube Manufacturing Consisting of Roll Forming and High-Frequency Induction Welding
    Egger, C. and Lüchinger, M. and Schreiner, M. and Tillmann, W.
    Materials 15 (2022)
    This paper presents a fully coupled three-dimensional finite element model for the simulation of a tube manufacturing process consisting of roll forming and high-frequency induction welding. The multiphysics model is based on the dual mesh method. Thus, the electromagnetic field, the temperature field, the elasto-plastic deformation of the weld bead, and the phase transformations within the material can be simulated for a moving tube without remeshing. A comparison with mea-surements shows that the geometry of the welded tube and the weld bead, the force on the squeeze rolls, the temperature along the band edges, and the hardness distribution within the heat-affected zone can be simulated realistically. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/ma15031270
  • 2022 • 93 Obtaining different orientation relationships for Cu films grown on (0001) α-Al2O3substrates by magnetron sputtering
    Dehm, G. and Edongué, H. and Wagner, T. and Oh, S.H. and Arzt, E.
    International Journal of Materials Research 96 249-254 (2022)
    Cu films were grown on (0001) α-Al2O3 single-crystals by magnetron sputtering. The growth behavior was manipulated by Ar+-ion sputter cleaning of the substrates at kinetic energies between 100 and 500 eV, changing the sputter rate from 0.75 to 1.1 nm/s, and using nominal substrate temperatures of 100 and 200 °C, respectively. Polycrystalline Cu films formed on α-Al2O3 substrates after an Ar+-ion bombardment at 500 eV, while epitaxial Cu films evolved when Ar+-ion energies of 100 and 200 eV were used. The epitaxial Cu films always consisted of two twin-related growth variants. However, two different orientation relationships emerged which differ by a 30° in-plane rotation of the (111) oriented Cu films when the deposition rate is changed from 0.75 to 1.1 nm/s. The results will be discussed on the basis of differences in the growth process. © 2005 Carl Hanser Verlag, München.
    view abstractdoi: 10.3139/ijmr-2005-0045
  • 2022 • 92 Olfactory Stem Cells for the Treatment of Spinal Cord Injury—A New Pathway to the Cure?
    Rövekamp, M. and von Glinski, A. and Volkenstein, S. and Dazert, S. and Sengstock, C. and Schildhauer, T.A. and Breisch, M.
    World Neurosurgery (2022)
    Objective: Because full functional recovery after spinal cord injury (SCI) remains a major challenge, stem cell therapies represent promising strategies to improve neurologic functions after SCI. The olfactory mucosa (OM) displays an attractive source of multipotent cells for regenerative approaches and is easily accessible by biopsies because of its exposed location. The regenerative capacity of the resident olfactory stem cells (OSCs) has been demonstrated in animal as well as clinical studies. This study aims to demonstrate the feasibility of isolation, purification and cultivation of OSCs. Methods: OM specimens were taken dorso-posterior from nasal middle turbinate. OSCs were isolated and purified using the neurosphere assay. Differentiation capacity of the OSCs in neural lineage and their behavior in a plasma clot matrix were investigated. Results: Our study demonstrated that OSCs differentiated into neural lineage and were positive for GFAP as well as β-III tubulin. Furthermore, OSCs were viable and proliferated in a plasma clot matrix. Conclusions: Because there are no standard methods for purification, characterization, and delivery of OSCs to the injury site, which is a prerequisite for the clinical approval, this study focuses on the establishment of appropriate methods and underlines the high potential of the OM for autologous cell therapeutic approaches. © 2022 Elsevier Inc.
    view abstractdoi: 10.1016/j.wneu.2022.02.019
  • 2022 • 91 Operando electrochemical SERS monitors nanoparticle reactions by capping agent fingerprints
    Wonner, K. and Murke, S. and Alfarano, S.R. and Hosseini, P. and Havenith, M. and Tschulik, K.
    Nano Research (2022)
    Nanomaterials are frequently employed in daily life goods, including health, textile, and food industry. A comprehensive picture is lacking on the role of the capping agents, added ligand molecules, in case of nanoparticle reactions and degradation in aqueous solutions, like surface waters or biofluids. Here, we aim to elucidate the capping agent influence on nanoparticle reactivity probing two commonly employed capping agents citrate and polyvinylpyrrolidone (PVP). Their influence on silver nanoparticle (AgNP) transformation is studied, which is particularly important due to its application as an antimicrobial agent. We induce oxidation and reduction processes of AgNPs in halide solutions and we monitor the associated transformations of particles and capping agents by spectro-electrochemical surface-enhanced Raman spectroscopy (SERS). Raman bands of the capping agents are used here to track chemical changes of the nanoparticles under operando conditions. The sparingly soluble and non-plasmon active silver salts (AgBr and AgCl) are formed under potential bias. In addition, we spectroscopically observe plasmon-mediated structural changes of citrate to cis- or trans-aconitate, while PVP is unaltered. The different behavior of the capping agents implies a change in the physical properties on the surface of AgNPs, in particular with respect to the surface accessibility. Moreover, we showcase that reactions of the capping agents induced by different external stimuli, such as applied bias or laser irradiation, can be assessed. Our results demonstrate how SERS of capping agents can be exploited to operando track nanoparticle conversions in liquid media. This approach is envisaged to provide a more comprehensive understanding of nanoparticle fates in complex liquid environments and varied redox conditions. [Figure not available: see fulltext.] © 2021, The Author(s).
    view abstractdoi: 10.1007/s12274-021-3999-2
  • 2022 • 90 Optical absorption spectroscopy of reactive oxygen and nitrogen species in a surface dielectric barrier discharge
    Schücke, L. and Bodnar, A. and Friedrichs, N. and Böddecker, A. and Peters, N. and Ollegott, K. and Oberste-Beulmann, C. and Wirth, P. and Nguyen-Smith, R.T. and Korolov, I. and Gibson, A.R. and Muhler, M. and Awakowicz, P.
    Journal of Physics D: Applied Physics 55 (2022)
    A twin surface dielectric barrier discharge (SDBD) ignited in a dry synthetic air gas stream is studied regarding the formation of reactive oxygen and nitrogen species (RONS) and their impact on the conversion of admixed n-butane. The discharge is driven by a damped sinusoidal voltage waveform at peak-to-peak amplitudes of 8 kVpp-13 kVpp and pulse repetition frequencies of 250 Hz-4000 Hz. Absolute densities of O3, NO2, NO3, as well as estimates of the sum of the densities of N2O4 and N2O5 are determined temporally resolved by means of optical absorption spectroscopy using a laser driven broadband light source, suitable interference filters, and a photodiode detector. The measured densities are acquired across the center of the reactor chamber as well as at the outlet of the chamber. The temporal and spatial evolution of the species' densities is correlated to the conversion of n-butane at concentrations of 50 ppm and 400 ppm, measured by means of flame ionization detectors. The n-butane is admixed either before or after the reactor chamber, in order to separate the impact of short- and long-lived reactive species on the conversion process. It is found that, despite the stationary conversion at the selected operating points, at higher voltages and repetition frequencies the densities of the measured species are not in steady state. Based on the produced results it is presumed that the presence of n-butane modifies the formation and consumption pathways of O3. At the same time, there is no significant impact on the formation of dinitrogen oxides (N2O4 and N2O5). Furthermore, a comparatively high conversion of n-butane, when admixed at the outlet of the reactor chamber is observed. These findings are discussed together with known rate coefficients for the reactions of n-butane with selected RONS. © 2022 The Author(s). Published by IOP Publishing Ltd
    view abstractdoi: 10.1088/1361-6463/ac5661
  • 2022 • 89 Optical and structural properties of ZnO NPs and ZnO–Bi2O3 nanocomposites
    Dhahri, I. and Ellouze, M. and Labidi, S. and Al-Bataineh, Q.M. and Etzkorn, J. and Guermazi, H. and Telfah, A. and Tavares, C.J. and Hergenröder, R. and Appel, T.
    Ceramics International 48 266-277 (2022)
    Pure ZnO and ZnO–Bi2O3 nanocomposites with 5 wt% and 10 wt% of Bi2O3 content were synthesized using the co-precipitation method. Optical properties such as refractive index (n), extinction coefficient (k), bandgap (Eg), and Urbach energies, as well as the band structure, were determined by modeling the experimental transmittance and reflectance UV–Vis spectra. The deduced bandgap and Urbach energies for pure ZnO (3.758 eV) increase with the increase of the doping degree of Bi2O3 in ZnO–Bi2O3 nanocomposite films. X-ray diffraction and scanning electron microscopy (SEM) was used to study the structural and morphological properties of these nanocomposite films. Pure ZnO and nanocomposites with Bi2O3 exhibit crystalline domains with wurtzite hexagonal structures, and as the doping degree of Bi2O3 increases, the crystallite size decreases. Based on SEM micrographs, the ZnO nanoparticles (NPs) structure shows the presence of aggregation. Moreover, Bi2O3 NPs in the nanocomposite film led to the further aggregation in the form of large rods. The elemental and chemical properties of the nanocomposites were investigated using infrared and energy-dispersive X-ray spectroscopy. The charge transfer process in the studied system is between ZnO and Bi2O3 conduction bands. Density-functional theory (DFT) calculations were performed for ZnO, Bi2O3, and ZnO-Bi2O3 compounds to investigate structural, optical, and electronic properties, being in agreement with the experimental results. © 2021 Elsevier Ltd and Techna Group S.r.l.
    view abstractdoi: 10.1016/j.ceramint.2021.09.101
  • 2022 • 88 Optical Optimization Potential of Transparent-Passivated Contacts in Silicon Solar Cells
    Eberst, A. and Zamchiy, A. and Qiu, K. and Winkel, P. and Gebrewold, H.T. and Lambertz, A. and Duan, W. and Li, S. and Bittkau, K. and Kirchartz, T. and Rau, U. and Ding, K.
    Solar RRL (2022)
    Herein, an optical loss analysis of the recently introduced silicon carbide–based transparent passivating contact (TPC) for silicon heterojunction solar cells is presented, the most dominant losses are identified, and the potential for reducing these losses is discussed. Magnesium fluoride is applied as an antireflective coating to reduce the reflective losses by up to 0.8 mA cm−2. When applying the magnesium fluoride, the passivation quality of the layer stack degrades, but is restored after annealing on a hot plate in ambient air. Afterwards, a road map for TPC solar cells toward an efficiency of 25% is presented and discussed. The largest part in efficiency gain is achieved by reducing the finger width and by increasing the passivation quality. Furthermore, it is shown that TPC solar cells have the potential to achieve short-circuit current densities above 42 mA cm−2 if the finger width is reduced and the front-side indium tin oxide (ITO) layer can be replaced by an ITO silicon nitride double layer. © 2022 The Authors. Solar RRL published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/solr.202101050
  • 2022 • 87 Origins of the hydrogen signal in atom probe tomography: Case studies of alkali and noble metals
    Yoo, S.-H. and Kim, S.-H. and Woods, E. and Gault, B. and Todorova, M. and Neugebauer, J.
    New Journal of Physics 24 (2022)
    Atom probe tomography (APT) analysis is being actively used to provide near-atomic-scale information on the composition of complex materials in three-dimensions. In recent years, there has been a surge of interest in the technique to investigate the distribution of hydrogen in metals. However, the presence of hydrogen in the analysis of almost all specimens from nearly all material systems has caused numerous debates as to its origins and impact on the quantitativeness of the measurement. It is often perceived that most H arises from residual gas ionization, therefore affecting primarily materials with a relatively low evaporation field. In this work, we perform systematic investigations to identify the origin of H residuals in APT experiments by combining density-functional theory (DFT) calculations and APT measurements on an alkali and a noble metal, namely Na and Pt, respectively. We report that no H residual is found in Na metal samples, but in Pt, which has a higher evaporation field, a relatively high signal of H is detected. These results contradict the hypothesis of the H signal being due to direct ionization of residual H2 without much interaction with the specimen's surface. Based on DFT, we demonstrate that alkali metals are thermodynamically less likely to be subject to H contamination under APT-operating conditions compared to transition or noble metals. These insights indicate that the detected H-signal is not only from ionization of residual gaseous H2 alone, but is strongly influenced by material-specific physical properties. The origin of H residuals is elucidated by considering different conditions encountered during APT experiments, specifically, specimen-preparation, transportation, and APT-operating conditions by taking thermodynamic and kinetic aspects into account. © 2022 The Author(s). Published by IOP Publishing Ltd on behalf of the Institute of Physics and Deutsche Physikalische Gesellschaft.
    view abstractdoi: 10.1088/1367-2630/ac40cd
  • 2022 • 86 Oxidation of oxymethylene ether (OME0−5): An experimental systematic study by mass spectrometry and photoelectron photoion coincidence spectroscopy
    Gaiser, N. and Bierkandt, T. and Oßwald, P. and Zinsmeister, J. and Kathrotia, T. and Shaqiri, S. and Hemberger, P. and Kasper, T. and Aigner, M. and Köhler, M.
    Fuel 313 (2022)
    This paper presents a systematic study of oxymethylene ethers (OMEs) oxidation in an atmospheric laminar flow reactor setup. Oxymethylene ethers with different number of oxymethylene ether groups (n = 0–5) have been investigated under lean and rich conditions (750–1250 K). The flow reactor is coupled to an electron ionization molecular-beam mass spectrometer (EI-MBMS) with high mass resolution to measure speciation data. Additional isomer-selective speciation analysis was performed using a novel atmospheric laminar flow reactor combined with double-imaging photoelectron photoion coincidence (i2PEPICO) spectroscopy at the vacuum ultraviolet radiation (VUV) beamline of the Swiss Light Source. The results show a dominance of oxygenated intermediates during the combustion of all OMEs in the investigated temperature regime. The observed species pool is thereby nearly independent of the OME's chain length. In particular the presence of significant fractions of ethanol is remarkable and indicates unknown or underestimated reaction pathways to form C–C bonds from OME structures. Formation of combustion intermediates during oxidation of longer OMEs occurs at lower temperatures and correlates with the ignition delay time. No hydrocarbons with more than four carbon atoms are detected. The combination of high mass resolution provided by EI-MBMS detection and isomer-selective analysis by i2PEPICO enables a complete overview of all intermediates. This allows for in-depth discussion and analysis of systematic trends for several intermediate species. © 2021 Elsevier Ltd
    view abstractdoi: 10.1016/j.fuel.2021.122650
  • 2022 • 85 Oxygen vacancies-enriched Ta-doped Bi2WO6 with Pt as cocatalyst for boosting the dehydrogenation of benzyl alcohol in water
    Shen, Z. and Hu, Y. and Pan, Q. and Huang, C. and Zhu, B. and Xia, W. and Wang, H. and Yue, J. and Muhler, M. and Zhao, G. and Wang, X. and Huang, X.
    Applied Surface Science 571 (2022)
    Selective photocatalytic oxidation of alcohols into value-added aldehydes or ketones is a promising alternative for alcohol oxidation concerning the mild reaction conditions and the controllable selectivity. To increase the activity, defective Bi2WO6 with abundant oxygen vacancies (OVs) was synthesized via substitution of W by Ta. The resulting Ta-doped Bi2WO6 loaded with Pt nanoparticles as co-catalyst efficiently converted aromatic and aliphatic alcohols into the corresponding carbonyl compounds with high selectivity (&gt;99%) in aqueous solution under visible-light irradiation and anaerobic conditions, with equivalent H2 as a coupled product. The optimal amount of benzyl alcohol converted by the Ta-doped catalyst was two times higher than that of the undoped catalyst. Surface OVs were found to favor the dissociative adsorption of the alcohols and to prolong the life time of the charge carriers. More importantly, isotopic labelling experiments confirmed that over Pt-loaded pristine undoped Bi2WO6, the coupled H2 product results from water reduction, while over Pt-loaded Ta-doped Bi2WO6, the produced H2 originates from benzyl alcohol, implying that benzyl alcohol can be photo-oxidized via a complete dehydrogenation pathway. Thus, enriched surface OVs in photocatalysts can activate α-C-H bonds in alcohols, boosting the photocatalytic oxidation performance. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.apsusc.2021.151370
  • 2022 • 84 Pair-amplitude dynamics in strongly coupled superconductor-quantum dot hybrids
    Heckschen, M. and Sothmann, B.
    Physical Review B 105 (2022)
    We consider a three-terminal system consisting of a quantum dot strongly coupled to two superconducting reservoirs in the infinite-gap limit and weakly coupled to a normal metal. Using a real-time diagrammatic approach, we calculate the dynamics of the proximity-induced pair amplitude on the quantum dot. We find that after a quench the pair amplitude shows pronounced oscillations with a frequency determined by the coupling to the superconductors. In addition, it decays exponentially on a timescale set by the coupling to the normal metal. Strong oscillations of the pair amplitude occur also when the system is periodically driven both in the adiabatic and fast-driving limit. We relate the dynamics of the pair amplitude to the Josephson and Andreev current through the dot to demonstrate that it is an experimentally accessible quantity. © 2022 American Physical Society.
    view abstractdoi: 10.1103/PhysRevB.105.045420
  • 2022 • 83 Parallel shape divergence between ecotypes of the limpet Nacella concinna along the Antarctic Peninsula: a new model species for parallel evolution?
    de Aranzamendi, M.C. and Martínez, J.J. and Held, C. and Sahade, R.
    Zoology 150 (2022)
    Parallel phenotypic divergence is the independent differentiation between phenotypes of the same lineage or species occupying ecologically similar environments in different populations. We tested in the Antarctic limpet Nacella concinna the extent of parallel morphological divergence in littoral and sublittoral ecotypes throughout its distribution range. These ecotypes differ in morphological, behavioural and physiological characteristics. We studied the lateral and dorsal outlines of shells and the genetic variation of the mitochondrial gene Cytochrome Oxidase subunit I from both ecotypes in 17 sample sites along more than 2,000 km. The genetic data indicate that both ecotypes belong to a single evolutionary lineage. The magnitude and direction of phenotypic variation differ between ecotypes across sample sites; completely parallel ecotype-pairs (i.e., they diverge in the same magnitude and in the same direction) were detected in 84.85% of lateral and 65.15% in dorsal view comparisons. Besides, specific traits (relative shell height, position of shell apex, and elliptical/pear-shape outline variation) showed high parallelism. We observed weak morphological covariation between the two shape shell views, indicating that distinct evolutionary forces and environmental pressures could be acting on this limpet shell shape. Our results demonstrate there is a strong parallel morphological divergence pattern in N. concinna along its distribution, making this Antarctic species a suitable model for the study of different evolutionary forces shaping the shell evolution of this limpet. © 2021 Elsevier GmbH
    view abstractdoi: 10.1016/j.zool.2021.125983
  • 2022 • 82 Pedestrian Counting Based on Piezoelectric Vibration Sensor
    Yu, Y. and Qin, X. and Hussain, S. and Hou, W. and Weis, T.
    Applied Sciences (Switzerland) 12 (2022)
    Pedestrian counting has attracted much interest of the academic and industry communities for its widespread application in many real-world scenarios. While many recent studies have focused on computer vision-based solutions for the problem, the deployment of cameras brings up concerns about privacy invasion. This paper proposes a novel indoor pedestrian counting approach, based on footstep-induced structural vibration signals with piezoelectric sensors. The approach is privacy-protecting because no audio or video data is acquired. Our approach analyzes the space-differential features from the vibration signals caused by pedestrian footsteps and outputs the number of pedestrians. The proposed approach supports multiple pedestrians walking together with signal mixture. Moreover, it makes no requirement about the number of groups of walking people in the detection area. The experimental results show that the averaged F1-score of our approach is over 0.98, which is better than the vibration signal-based state-of-the-art methods. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/app12041920
  • 2022 • 81 Performance and characteristics of modified PES-based membranes upon exposure to harsh cleaning conditions by sodium hypochlorite
    Abdel-Karim, A. and El-Kalliny, A.S. and Ahmed, S.I.A. and Souaya, E.R. and Badawy, M.I. and Ulbricht, M. and Gad-Allah, T.A.
    Egyptian Journal of Chemistry 65 315-325 (2022)
    Overcoming the increased protein fouling of polymeric polyethersulfone-based membranes (e.g. PES-PVP, PES-pluronic, and PES-Tetronic) is an essential target for wider ultrafiltration-based applications of such fabricated membranes. Hence, this study has been actively devoted to trace both performance and characteristics changes of modified PES-based membranes upon exposure to harsh cleaning conditions by sodium hypochlorite (400 ppm for 10 days). Simultaneously, different characterization tools have been adopted to study such purposes as SEM, FTIR, tensile strength, performance patterns. SEM analysis has proved the increment in pore size after contacting the fabricated membranes with NaOCl agent. However, tensile strength, contact angle, and overall porosity criteria showed a slight change. For instance, overall porosity ranged between 70-80 %, contact angle difference was about 3-4 deg, and tensile strength decrement was negligible. Further, AFM data proved that the relative roughness of all membranes did not dramatically. what is more, performance patterns in terms of pure water permeability is boosted two-three fold compared to untreated membranes with preserving BSA rejection ability (e.g. maximum BSA rejection loss is recorded for PES-T904 membrane; decrease from 70 % to about 55 %; about 21 % loss). Such preserved ultrafiltration behaviour may be ascribed to the more formed negative charge, and preservation hydrophilic nature even after NaOCl exposure. to end with, the fabricated modified PES membranes showed a preserved ultrafiltration performance after such harsh cleaning conditions. ©2022 National Information and Documentation Center (NIDOC)
    view abstractdoi: 10.21608/EJCHEM.2021.86400.4180
  • 2022 • 80 Photochemical Sandmeyer-type Halogenation of Arenediazonium Salts
    Sivendran, N. and Belitz, F. and Sowa Prendes, D. and Manu Martínez, Á. and Schmid, R. and Gooßen, L.J.
    Chemistry - A European Journal 28 (2022)
    Trihalide salts were found to efficiently promote photochemical dediazotizing halogenations of diazonium salts. In contrast to classical Sandmeyer reactions, no metal catalysts are required to achieve high yields and outstanding selectivities for halogenation over competing hydridodediazotization. Convenient protocols are disclosed for synthetically meaningful brominations, iodinations, and chlorinations of diversely functionalized derivatives. © 2021 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/chem.202103669
  • 2022 • 79 Photon Echo Polarimetry of Excitons and Biexcitons in a CH3NH3PbI3Perovskite Single Crystal
    Trifonov, A.V. and Grisard, S. and Kosarev, A.N. and Akimov, I.A. and Yakovlev, D.R. and Höcker, J. and Dyakonov, V. and Bayer, M.
    ACS Photonics 9 621-629 (2022)
    Lead halide perovskites show remarkable performance when used in photovoltaic and optoelectronic devices. However, the peculiarities of light-matter interactions in these materials in general are far from being fully explored experimentally and theoretically. Herein, we specifically address the energy level order of optical transitions and demonstrate photon echoes in a methylammonium lead triiodide single crystal, thereby determining the optical coherence times (T2) for excitons and biexcitons at cryogenic temperature to be 0.79 and 0.67 ps, respectively. Most importantly, we have developed an experimental photon-echo polarimetry method that not only identifies the contributions from exciton and biexciton complexes but also allows accurate determination of the biexciton binding energy of 2.4 meV, even though the period of quantum beats between excitons and biexcitons is much longer than the coherence times of the resonances. Our experimental and theoretical analysis methods contribute to the understanding of the complex mechanism of quasiparticle interactions at moderate pump density and show that even in high-quality perovskite crystals and at very low temperatures, inhomogeneous broadening of excitonic transitions due to local crystal potential fluctuations is a source of optical dephasing. ©
    view abstractdoi: 10.1021/acsphotonics.1c01603
  • 2022 • 78 Photostability of polylactide with respect to blue LED radiation at very high irradiance and ambient temperature
    Hemmerich, M. and Scholz, R. and Meyer, J. and Walther, F.
    Materials Today Communications 31 (2022)
    For an overall sustainable development of lighting systems, it is crucial to establish alternatives to fossil based optical plastics. One biodegradable plastic alternative, based exclusively on renewable raw materials and having outstanding optical properties, could be the bioplastic polylactide (PLA). In order to evaluate the stability of PLA under the influence of extreme levels of optical LED radiation (λmax = 450 nm, FWHM = 16.3 nm), aging experiments were carried out over a period of 5000 h (~ 7 months) using an innovative self-developed test setup. As a reference the widely used optical plastic polycarbonate (PC) was aged under the same conditions. The novel test setup allowed aging tests at low temperatures of 23.0 and 36.1 °C (below the crystallization temperature of PLA) with irradiances of 7.9 and 16.1 kW/m2, respectively. Photodegradation tests in which temperature can be varied virtually independent of radiant flux were performed. To the best of our knowledge this is a first in degradation experiments. By this, aging can be attributed to more radiation- or temperature-related phenomena. Before, during, and after aging, optical, mechanical and chromatographic methods were used to analyze the samples. PLA was found to be largely resistant to visible blue LED radiation under the selected aging conditions. Only an increase in surface hardness and stiffness, indicating embrittlement, was observed. In contrast, even at the low temperatures used in these experiments, PC shows a significant decrease in transmission in the short-wavelength range of up to 17.0% after prolonged aging. Moreover, known degradation products (by FTIR spectroscopy), a decrease in molar mass (5.1%) and a trend increase in Martens hardness and indentation modulus, were detected for all PC of samples. © 2022 Elsevier Ltd
    view abstractdoi: 10.1016/j.mtcomm.2022.103307
  • 2022 • 77 Polyconvex anisotropic hyperelasticity with neural networks
    Klein, D.K. and Fernández, M. and Martin, R.J. and Neff, P. and Weeger, O.
    Journal of the Mechanics and Physics of Solids 159 (2022)
    In the present work, two machine learning based constitutive models for finite deformations are proposed. Using input convex neural networks, the models are hyperelastic, anisotropic and fulfill the polyconvexity condition, which implies ellipticity and thus ensures material stability. The first constitutive model is based on a set of polyconvex, anisotropic and objective invariants. The second approach is formulated in terms of the deformation gradient, its cofactor and determinant, uses group symmetrization to fulfill the material symmetry condition, and data augmentation to fulfill objectivity approximately. The extension of the dataset for the data augmentation approach is based on mechanical considerations and does not require additional experimental or simulation data. The models are calibrated with highly challenging simulation data of cubic lattice metamaterials, including finite deformations and lattice instabilities. A moderate amount of calibration data is used, based on deformations which are commonly applied in experimental investigations. While the invariant-based model shows drawbacks for several deformation modes, the model based on the deformation gradient alone is able to reproduce and predict the effective material behavior very well and exhibits excellent generalization capabilities. In addition, the models are calibrated with transversely isotropic data, generated with an analytical polyconvex potential. For this case, both models show excellent results, demonstrating the straightforward applicability of the polyconvex neural network constitutive models to other symmetry groups. © 2021 Elsevier Ltd
    view abstractdoi: 10.1016/j.jmps.2021.104703
  • 2022 • 76 Polyurea Thickened Lubricating Grease—The Effect of Degree of Polymerization on Rheological and Tribological Properties
    Jopen, M. and Degen, P. and Henzler, S. and Grabe, B. and Hiller, W. and Weberskirch, R.
    Polymers 14 (2022)
    Lubricating greases based on urea thickeners are frequently used in high-performance applications since their invention in 1954. One property that has so far been neglected in the further development of these systems due to their low solubility and the resulting difficulty of analysis, is to better understand how the degree of polymerization affect such polyurea lubricating systems. In this work, we prepared three different oligoor polyurea systemswith different degrees of polymerization (DP) and investigated the influence of DP on rheological and tribological properties. The results showed that the DP has an influence on the flow limit in rheology as well as on the extreme pressure (EP) and anti-wear (AW) properties as examined by tribology measurements. By optimizing the DP for a thickener system, comparable EP and AW properties can be achieved through the use of additives. The DP showed an increasing influence on the flow limit. This could reduce damage to rolling bearings due to lateral loading at rest. Therefore, modifying the DP of the polyurea systems shows similar effects as the addition of external additives. Overall, this would reduce the use of additives in industrial applications. © 2022 by the authors.Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/polym14040795
  • 2022 • 75 Predicting Solvent Effects on Homogeneity and Kinetics of the Hydroaminomethylation: A Thermodynamic Approach Using PC-SAFT
    Huxoll, F. and Kampwerth, A. and Seidensticker, T. and Vogt, D. and Sadowski, G.
    Industrial and Engineering Chemistry Research 61 2323-2332 (2022)
    Solvents may significantly affect the phase behavior and kinetics of chemical reactions. Especially for complex reactions performed in mixtures of different solvents, it requires a high experimental effort to quantify these effects. This work focuses on a novel thermodynamic approach to predict solvent effects on both reaction rates and phase behavior. We applied this method to the homogeneously catalyzed hydroaminomethylation of 1-decene in a thermomorphic multiphase system of methanol and n-dodecane. For that purpose, the thermodynamic activities of the reactants and the liquid-liquid equilibrium of the multicomponent reaction system were successfully modeled using the Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT). An increasing concentration of n-dodecane in the solvent mixture was predicted not only to limit the working space for the reaction due to unwanted phase separation but also to massively reduce the reaction rate. These results were in good agreement with batch experiments and homogeneity tests performed in this work. The approach is applicable to a wide variety of liquid-phase reactions and thus is a valuable tool for reducing the experimental effort to a minimum. © 2022 The Authors. Published by American Chemical Society
    view abstractdoi: 10.1021/acs.iecr.1c03891
  • 2022 • 74 Preparation of Practical High-Performance Electrodes for Acidic and Alkaline Media Water Electrolysis
    Moon, G.-H. and Wang, Y. and Kim, S. and Budiyanto, E. and Tüysüz, H.
    ChemSusChem 15 (2022)
    The synthesis of electrocatalyst and the electrode preparation were merged into a one-step process and proved to be a versatile method to synthesize metal oxide electrocatalysts on the conductive carbon paper (CP). Very simply, the metal precursor deposited on the CP was thermally treated by a torch-gun for just 6 s, resulting in the formation of RuO2, Co3O4, and mixed oxide nanoparticles. The material could be directly used as working electrode for oxygen evolution reaction (OER). Compared with commercial and other state-of-the-art electrocatalysts, the fabricated electrode showed a superior electrocatalytic activity for OER in 1 m HClO4 and 1 m KOH in terms of not only a low overpotential to reach 10 mA cm−2 but also a high current density at 1.6 VRHE with satisfying a long-term stability. The novel strategy without requiring time-consuming and uneconomical steps could be expanded to the preparation of various metal oxides on conductive substrates towards diverse electrocatalytic applications. © 2021 The Authors. ChemSusChem published by Wiley-VCH GmbH.
    view abstractdoi: 10.1002/cssc.202102114
  • 2022 • 73 Prevention of Caries and Dental Erosion by Fluorides—A Critical Discussion Based on Physico-Chemical Data and Principles
    Epple, M. and Enax, J. and Meyer, F.
    Dentistry Journal 10 (2022)
    Dental erosion is a common problem in dentistry. It is defined as the loss of tooth mineral by the attack of acids that do not result from caries. From a physico-chemical point of view, the nature of the corroding acids only plays a minor role. A protective effect of fluorides, to prevent caries and dental erosion, is frequently claimed in the literature. The proposed modes of action of fluorides include, for example, the formation of an acid-resistant fluoride-rich surface layer and a fluoride-induced surface hardening of the tooth surface. We performed a comprehensive literature study on the available data on the interaction between fluoride and tooth surfaces (e.g., by toothpastes or mouthwashes). These data are discussed in the light of general chemical considerations on fluoride incorporation and the acid solubility of teeth. The analytical techniques available to address this question are presented and discussed with respect to their capabilities. In summary, the amount of fluoride that is incorporated into teeth is very low (a few µg mm−2), and is unlikely to protect a tooth against an attack by acids, be it from acidic agents (erosion) or from acid-producing cariogenic bacteria. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/dj10010006
  • 2022 • 72 Probabilistic-based fatigue reliability assessment of carbon steel coil spring from random strain loading excitation
    Chin, C.H. and Abdullah, S. and Singh, S.S.K. and Ariffin, A.K. and Schramm, D.
    Journal of Mechanical Science and Technology 36 109-118 (2022)
    This paper aims to assess the fatigue reliability of random loading signals of a suspension coil spring using probabilistic approaches. Strain time histories were acquired while the car was travelling on different road conditions (i.e., in a rural area, in an industrial area, on a university campus, on a highway and on a newly constructed road). Fatigue lives were predicted from the strain histories and fitted into probability density functions. Lognormal distribution was found to be an appropriate way to represent fatigue data. Next, the reliability function and mean-cycles-to-failure (MCTF) were determined. The results indicated that fatigue reliability rapidly deteriorated under rural road conditions, which resulted in a short MCTF of 104 cycles. Meanwhile, the new road signals had the longest MCTF of about 108 cycles. Accordingly, this is due to the rural road having the most surface irregularities, which caused more severe fatigue damage to the coil spring. This study contributed to a greater in-depth understanding of the effect of loading signals on fatigue reliability. This is essential in determining the appropriate service life of the coil spring during its production to ensure vehicle safety and reduce maintenance costs. © 2021, The Korean Society of Mechanical Engineers and Springer-Verlag GmbH Germany, part of Springer Nature.
    view abstractdoi: 10.1007/s12206-021-1209-5
  • 2022 • 71 Process Diagnostics and Control in Thermal Spray
    Mauer, G. and Moreau, C.
    Journal of Thermal Spray Technology (2022)
    This perspective paper summarizes the authors’ view on how process diagnostics and control can help to gain a deeper insight into thermal spray processes and to better understand the underlying mechanisms. The current situation in terms of available process control strategies and suitable sensors is described. In perspective, it is assumed that with suitable models, sensors and machine learning tools, it will be possible to perform a smaller number of experiments to develop coatings with specific target characteristics. In addition, trained machine learning tools can be used to implement an efficient control strategy to produce coatings with high reproducibility and reliability. The corresponding existing knowledge gaps are analyzed to identify needs for future research. © 2022, The Author(s).
    view abstractdoi: 10.1007/s11666-022-01341-z
  • 2022 • 70 Process-Related Characterization of the Influence of the Die Design on the Microstructure and the Mechanical Properties of Profiles Made from Directly Recycled Hot Extruded EN AW-6060 Aluminum Chips
    Koch, A. and Laskowski, S. and Walther, F.
    Minerals, Metals and Materials Series 1021-1028 (2022)
    Solid-state-recycling processes for aluminum chips are promising alternatives to energy-intensive re-melting. In order to directly recycle aluminum chips without the necessity of re-melting, these are pre-compacted and further processed into profiles in a hot extrusion process. The quality of the so-produced profiles depends on the quality of the interface between the single chips, which are linked by microstructural welding. In order to enable a successful welding process, the pathways during the extrusion process have to be long enough in order to transfer enough energy and the encasing oxide layers have to be broken up successfully. Parameters like pressure, shear strain, and temperature influence the quality of the oxide layer breakup. Especially the shear strain can be varied by the material flow and the die. Therefore, this study examines the effects of different extrusion dies on the microstructure and the mechanical properties. The microstructure was characterized using metallographic investigations and could found to form within four different zones depending on the conditions during the extrusion process. The mechanical properties were investigated by means of tensile tests and fatigue tests and could be correlated well with the microstructure, since two different damage mechanisms depending on the specimen position can be distinguished. © 2022, The Minerals, Metals & Materials Society.
    view abstractdoi: 10.1007/978-3-030-92529-1_133
  • 2022 • 69 Progress and Challenges of InGaN/GaN-Based Core–Shell Microrod LEDs
    Meier, J. and Bacher, G.
    Materials 15 (2022)
    LEDs based on planar InGaN/GaN heterostructures define an important standard for solid-state lighting. However, one drawback is the polarization field of the wurtzite heterostructure impacting both electron–hole overlap and emission energy. Three-dimensional core–shell microrods offer field-free sidewalls, thus improving radiative recombination rates while simultaneously increasing the light-emitting area per substrate size. Despite those promises, microrods have still not replaced planar devices. In this review, we discuss the progress in device processing and analysis of microrod LEDs and emphasize the perspectives related to the 3D device architecture from an applications point of view. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/ma15051626
  • 2022 • 68 Pseudoelastic cycling of ultra-fine-grained NiTi shape-memory wires
    Yawny, A. and Sade, M. and Eggeler, G.
    International Journal of Materials Research 96 608-618 (2022)
    In the present study, we investigate pseudoelastic pull-pull cycling of ultra-fine-grained (40 nm) Ni-rich (50.9 at.% Ni) NiTi shape-memory wires at temperatures ranging from 301 to 323 K. Strain-controlled experiments were performed using incremental strain steps and different constant maximum strains. Pull-pull cycling results in decreasing/increasing plateau stresses characterizing the forward/reverse transformations and an accumulation of non-recoverable strain. Saturation is reached after 30 cycles. We interpret our results in terms of a microstructural scenario where dislocations, which are introduced during the martensitic transformation (lattice invariant shear) and during pull-pull cycling (dislocation plasticity), interact with the stress-induced formation of martensite. We show that the slopes of stress-strain curves naturally depend on the total strain imposed in strain-controlled testing. We also provide a dislocation-based explanation for the evolving stress levels of the loading and unloading plateaus during pseudoelastic cycling. And most importantly, we show how dislocations act as microstructural markers which allow the material to remember its previous stress-strain history. © 2005 Carl Hanser Verlag, München.
    view abstractdoi: 10.3139/ijmr-2005-0108
  • 2022 • 67 Pushing the Limits in Real-Time Measurements of Quantum Dynamics
    Kleinherbers, E. and Stegmann, P. and Kurzmann, A. and Geller, M. and Lorke, A. and König, J.
    Physical Review Letters 128 (2022)
    Time-resolved studies of quantum systems are the key to understanding quantum dynamics at its core. The real-time measurement of individual quantum numbers as they switch between certain discrete values, well known as a "random telegraph signal,"is expected to yield maximal physical insight. However, the signal suffers from both systematic errors, such as a limited time resolution and noise from the measurement apparatus, as well as statistical errors due to a limited amount of data. Here we demonstrate that an evaluation scheme based on factorial cumulants can reduce the influence of such errors by orders of magnitude. The error resilience is supported by a general theory for the detection errors as well as experimental data of single-electron tunneling through a self-assembled quantum dot. Thus, factorial cumulants push the limits in the analysis of random telegraph data, which represent a wide class of experiments in physics, chemistry, engineering, and life sciences. © 2022 American Physical Society.
    view abstractdoi: 10.1103/PhysRevLett.128.087701
  • 2022 • 66 Qualification of the Low-pressure Cold Gas Spraying for the Additive Manufacturing of Copper–Nickel–Diamond Grinding Wheels
    Tillmann, W. and Zajaczkowski, J. and Baumann, I. and Kipp, M. and Biermann, D.
    Journal of Thermal Spray Technology 31 206-216 (2022)
    Grinding wheels are usually manufactured by powder metallurgical processes, i.e., by molding and sintering. Since this requires the production of special molds and the sintering is typically carried out in a continuous furnace, this process is time-consuming and cost-intensive. Therefore, it is only worthwhile for medium and large batches. Another influencing factor of the powder metallurgical process route is the high thermal load during the sintering process. Due to their high thermal sensitivity, superabrasives such as diamond or cubic boron nitride are very difficult to process in this way. In this study, a novel and innovative approach is presented, in which superabrasive grinding wheels are manufactured by thermal spraying. For this purpose, flat samples as well as grinding wheel bodies were coated by low-pressure (LP) cold gas spraying with a blend of a commercial Cu-Al2O3 cold gas spraying powder and nickel-coated diamonds. The coatings were examined metallographically in terms of their composition. A well-embedded superabrasive content of 12 % was achieved. After the spraying process, the grinding wheels were conditioned and tested for the grinding application of cemented carbides and the topographies of both the grinding wheel and the cemented carbide were evaluated. Surface qualities of the ground surface that are comparable to those of other finishing processes were reached. This novel process route offers great flexibility in the combination of binder and hard material as well as a cost-effective single-part and small-batch production. © 2021, The Author(s).
    view abstractdoi: 10.1007/s11666-021-01291-y
  • 2022 • 65 Quantification of the Influence of ConcreteWidth per Fiber Strand on the Splitting Crack Failure of Textile Reinforced Concrete (TRC)
    Beßling, M. and Orlowsky, J.
    Polymers 14 (2022)
    The composite material textile reinforced concrete (TRC) requires a high bond performance between the fiber strand and the concrete matrix. While the influence of the textile on bond behavior is well known, in this publication the influence of the concrete matrix is investigated by means of single-sided pull-out tests. The results of the presented study show dependence between the concrete strength and bond performance of the composite material. When a concrete of a higher-strength class is used, the bond-flow–pull-out distance curve shifts upward independent of the textile geometry and the yarn impregnation. A simplified model is presented to predict the occurrence of a crack along the fiber strand. This model serves as a basis to investigate the correlation between concrete width per fiber strand and resistance against a splitting crack. The effective concrete tensile strength decreases to about 35% when the concrete width is increased from 10 mm to 50 mm. To quantify the decrease, a mathematical relationship, which describes the test results independent of textile and concrete type, is proposed. © 2022 by the authors.
    view abstractdoi: 10.3390/polym14030489
  • 2022 • 64 Quantitative analysis of grain boundary diffusion, segregation and precipitation at a sub-nanometer scale
    Peng, Z. and Meiners, T. and Lu, Y. and Liebscher, C.H. and Kostka, A. and Raabe, D. and Gault, B.
    Acta Materialia 225 (2022)
    Grain boundaries are intrinsic and omnipresent microstructural imperfections in polycrystalline and nanocrystalline materials. They are short-circuit diffusion paths and preferential locations for alloying elements, dopants, and impurities segregation. They also facilitate heterogeneous nucleation and the growth of secondary phases. Therefore, grain boundaries strongly influence many materials' properties and their stabilities during application. Here, we propose an approach to measure diffusion, segregation, and segregation-induced precipitation at grain boundaries at a sub-nanometer scale by combining atom probe tomography and scanning transmission electron microscopy. Nanocrystalline multilayer thin films with columnar grain structure were used as a model system as they offer a large area of random high-angle grain boundaries and inherent short diffusion distance. Our results show that the fast diffusion flux proceeds primarily through the core region of the grain boundary, which is around 1 nm. While the spatial range that the segregated solute atoms occupied is larger: below the saturation level, it is 1,2 nm; as the segregation saturates, it is 2–3.4 nm in most grain boundary areas. Above 3.4 nm, secondary phase nuclei seem to form. The observed distributions of the solutes at the matrix grain boundaries evidence that even at a single grain boundary, different regions accommodate different amounts of solute atoms and promote secondary phase nuclei with different compositions, which is caused by its complex three-dimensional topology. © 2021 Acta Materialia Inc.
    view abstractdoi: 10.1016/j.actamat.2021.117522
  • 2022 • 63 Rapid Water Diffusion at Cryogenic Temperatures through an Inchworm-like Mechanism
    Fang, W. and Meyer auf der Heide, K.M. and Zaum, C. and Michaelides, A. and Morgenstern, K.
    Nano Letters 22 340-346 (2022)
    Water diffusion across the surfaces of materials is of importance to disparate processes such as water purification, ice formation, and more. Despite reports of rapid water diffusion on surfaces the molecular level, details of such processes remain unclear. Here, with scanning tunneling microscopy, we observe structural rearrangements and diffusion of water trimers at unexpectedly low temperatures (<10 K) on a copper surface, temperatures at which water monomers or other clusters do not diffuse. Density functional theory calculations reveal a facile trimer diffusion process involving transformations between elongated and almost cyclic conformers in an inchworm-like manner. These subtle intermolecular reorientations maintain an optimal balance of hydrogen-bonding and water–surface interactions throughout the process. This work shows that the diffusion of hydrogen-bonded clusters can occur at exceedingly low temperatures without the need for hydrogen bond breakage or exchange; findings that will influence Ostwald ripening of ice nanoclusters and hydrogen bonded clusters in general. © 2021 American Chemical Society
    view abstractdoi: 10.1021/acs.nanolett.1c03894
  • 2022 • 62 Rare-earth modified amorphous carbon films: Effects of erbium and gadolinium on the structural evolution and mechanical properties
    Tillmann, W. and Lopes Dias, N.F. and Stangier, D. and Berndt, J. and Klemme, S. and Kesper, L. and Berges, U. and Westphal, C. and Thomann, C.A. and Debus, J.
    Diamond and Related Materials 123 (2022)
    Modifying amorphous carbon (a-C) with rare-earth elements is a highly auspicious concept to synthetize functional films with unique characteristics. Among the rare earth elements, Er and Gd demonstrate abundant physicochemical properties and, hence, are of remarkable interest for the element modification of a-C films. Therefore, Er-containing a-C:Er and Gd-containing a-C:Gd films are prepared in a reactive-free magnetron sputtering process. The a-C:Er and a-C:Gd films have an amount of up to 5 at.-% Er and 4.8 at.-% Gd. High-resolution x-ray photoelectron spectroscopy analyses show the formation of Er[sbnd]C and Gd[sbnd]C components, which rise proportionally with increasing amount of the rare-earth element. The addition of Er and Gd lowers the sp3 content of C bonds. At the highest concentrations of the respective rare-earth elements, the a-C:Er and a-C:Gd films exhibit a reduced sp3 content of 8%. The number and size of sp2‑carbon clusters in the amorphous network are enhanced with increasing amount of Er and Gd which is evaluated by Raman scattering measurements. X-ray diffraction analyses reveal Er and Gd carbide phases, indicating the formation of a nanocomposite structure consisting of carbidic nanocrystallites and an a-C network. In nanoindentation tests, the non-modified a-C demonstrates a hardness of (21.7 ± 1.6) GPa and an elastic modulus of (232 ± 10) GPa. With increasing Er and Gd contents, the hardness linearly decreases to (16.7 ± 0.9) GPa and (14.8 ± 0.9) GPa, respectively. An analogous behavior is also identified for the elastic modulus. The reduced hardness and elastic modulus are attributed to the lower sp3 content and the larger number and size of the sp2-hybridized carbon atoms. Additionally, the adhesion was slightly improved by the addition of Er and Gd in comparison to non-modified a-C. © 2022 Elsevier B.V.
    view abstractdoi: 10.1016/j.diamond.2022.108898
  • 2022 • 61 Rate-Independent Systems and Their Viscous Regularizations: Analysis, Simulation, and Optimal Control
    Herzog, R. and Knees, D. and Meyer, C. and Sievers, M. and Stötzner, A. and Thomas, S.
    International Series of Numerical Mathematics 172 121-144 (2022)
    This chapter provides a survey on the analysis, simulation, and optimal control of a class of non-smooth evolution systems that appears in the modeling of dissipative solids. Our focus is on models that include internal constraints, such as a flow rule in plasticity, and that account for the temperature dependence of the respective materials. We discuss here two cases, namely purely rate-independent models and viscously regularized models coupled to the temperature equation. © 2022, Springer Nature Switzerland AG.
    view abstractdoi: 10.1007/978-3-030-79393-7_6
  • 2022 • 60 Reactivity of NK Cells Against Ovarian Cancer Cells Is Maintained in the Presence of Calcium Phosphate Nanoparticles
    Hrvat, A. and Schmidt, M. and Obholzer, M. and Benders, S. and Kollenda, S. and Horn, P.A. and Epple, M. and Brandau, S. and Mallmann-Gottschalk, N.
    Frontiers in Immunology 13 (2022)
    Calcium phosphate nanoparticles (CaP-NPs) are biodegradable carriers that can be functionalized with biologically active molecules. As such, they are potential candidates for delivery of therapeutic molecules in cancer therapies. In this context, it is important to explore whether CaP-NPs impair the natural or therapy-induced immune cell activity against cancer cells. Therefore, in this study, we have investigated the effects of different CaP-NPs on the anti-tumor activity of natural killer (NK) cells using different ovarian cancer (OC) cell line models. We explored these interactions in coculture systems consisting of NK cells, OC cells, CaP-NPs, and therapeutic Cetuximab antibodies (anti-EGFR, ADCC-inducing antibody). Our experiments revealed that aggregated CaP-NPs can serve as artificial targets, which activate NK cell degranulation and impair ADCC directed against tumor targets. However, when CaP-NPs were properly dissolved by sonication, they did not cause substantial activation. CaP-NPs with SiO2-SH-shell induced some activation of NK cells that was not observed with polyethyleneimine-coated CaP-NPs. Addition of CaP-NPs to NK killing assays did not impair conjugation of NK with OC and subsequent tumor cytolytic NK degranulation. Therapeutic antibody coupled to functionalized CaP-NPs maintained substantial levels of antibody-dependent cellular cytotoxic activity. Our study provides a cell biological basis for the application of functionalized CaP-NPs in immunologic anti-cancer therapies. Copyright © 2022 Hrvat, Schmidt, Obholzer, Benders, Kollenda, Horn, Epple, Brandau and Mallmann-Gottschalk.
    view abstractdoi: 10.3389/fimmu.2022.830938
  • 2022 • 59 Real-Time Risk Assessment of Tunneling-Induced Building Damage Considering Polymorphic Uncertainty
    Cao, B.T. and Obel, M. and Freitag, S. and Heußner, L. and Meschke, G. and Mark, P.
    ASCE-ASME Journal of Risk and Uncertainty in Engineering Systems, Part A: Civil Engineering 8 (2022)
    The risk assessment of tunneling-induced damage in buildings is a challenging task in geotechnical and structural engineering. It is important to consider the soil-structure interaction during the tunnel construction process. In this paper, finite-element (FE) simulation models of mechanized tunneling processes are combined with FE models of buildings to predict tunneling-induced damage. The soil-structure interaction is taken into account by considering the building stiffness in the tunneling process simulation model and by applying the computed foundation settlements as boundary conditions of the building model. The building damage risk is assessed by means of strains in the structural members and a corresponding category of damage is determined. Uncertainties of the geotechnical parameters and the structural parameters are quantified as random variables and intervals in the framework of polymorphic uncertainty modeling. For real-time predictions, the FE simulation models are approximated by artificial neural networks. This makes it possible to predict the structural damage risk according to scenarios of the operational tunneling process parameters in order to assist machine drivers during tunnel construction. © 2021 American Society of Civil Engineers.
    view abstractdoi: 10.1061/AJRUA6.0001192
  • 2022 • 58 Recrystallization in non-conventional microstructures of 316L stainless steel produced via laser powder-bed fusion: effect of particle coarsening kinetics
    Pinto, F.C. and Aota, L.S. and Souza Filho, I.R. and Raabe, D. and Sandim, H.R.Z.
    Journal of Materials Science (2022)
    Abstract: Alloys processed by laser powder-bed fusion show distinct microstructures composed of dislocation cells, dispersed nanoparticles, and columnar grains. Upon post-build annealing, such alloys show sluggish recrystallization kinetics compared to the conventionally processed counterpart. To understand this behavior, AISI 316L stainless steel samples were constructed using the island scan strategy. Rhodonite-like (MnSiO3) nanoparticles and dislocation cells are found within weakly-textured grains in the as-built condition. Upon isothermal annealing at 1150 °C (up to 2880 min), the nucleation of recrystallization occurs along the center of the melt pool, where nuclei sites, high stored elastic energy, and local large misorientation are found in the as-built condition. The low value of the Avrami coefficient (n = 1.16) can be explained based on the non-random distribution of nucleation sites. The local interaction of the recrystallization front with nanoparticles speeds up their coarsening causing the decrease of the Zener-Smith pinning force. This allows the progression of recrystallization in LPBF alloys, although sluggish. These results allow us to understand the progress of recrystallization in LPBF 316L stainless steel, shedding light on the nucleation mechanisms and on the competition between driving and dragging pressures in non-conventional microstructures. They also help to understand the most relevant microstructural aspects applicable for tuning microstructures and designing new LPBF alloys. Graphical abstract: [Figure not available: see fulltext.] © 2022, The Author(s).
    view abstractdoi: 10.1007/s10853-021-06859-1
  • 2022 • 57 Redox Replacement of Silver on MOF-Derived Cu/C Nanoparticles on Gas Diffusion Electrodes for Electrocatalytic CO2 Reduction
    Sikdar, N. and Junqueira, J.R.C. and Öhl, D. and Dieckhöfer, S. and Quast, T. and Braun, M. and Aiyappa, H.B. and Seisel, S. and Andronescu, C. and Schuhmann, W.
    Chemistry - A European Journal 28 (2022)
    Bimetallic tandem catalysts have emerged as a promising strategy to locally increase the CO flux during electrochemical CO2 reduction, so as to maximize the rate of conversion to C−C-coupled products. Considering this, a novel Cu/C−Ag nanostructured catalyst has been prepared by a redox replacement process, in which the ratio of the two metals can be tuned by the replacement time. An optimum Cu/Ag composition with similarly sized particles showed the highest CO2 conversion to C2+ products compared to non-Ag-modified gas-diffusion electrodes. Gas chromatography and in-situ Raman measurements in a CO2 gas diffusion cell suggest the formation of top-bound linear adsorbed *CO followed by consumption of CO in the successive cascade steps, as evidenced by the increasingνC−H bands. These findings suggest that two mechanisms operate simultaneously towards the production of HCO2H and C−C-coupled products on the Cu/Ag bimetallic surface. © 2022 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.
    view abstractdoi: 10.1002/chem.202104249
  • 2022 • 56 Reduction of biofilm accumulation by constant and alternating potentials in static and dynamic field experiments
    Schwarze, J. and Koc, J. and Koschitzki, F. and Gardner, H. and Hunsucker, K.Z. and Swain, G.W. and Rosenhahn, A.
    Biofouling (2022)
    The application of electric fields to conductive coatings is an environmentally friendly way to reduce biofilm formation. In particular alternating potentials (APs) have received increasing attention in recent studies. Here, an electrochemical rotating disk setup for dynamic field exposure experiments was developed to study how APs alter the attachment of fouling organisms in a multispecies ocean environment. A specific focus of the device design was proper integration of the potentiostat in the strongly corroding saltwater environment. The effect of APs on the accumulation of fouling organisms in short term field exposures was studied. Potentials on conductive gold surfaces were periodically switched between −0.3 V and 0.3 V or between −0.8 V and 0.6 V at a frequency of 0.5 Hz. APs were capable of significantly reducing the attachment of marine fouling organisms compared with the conductive samples immersed at open circuit potentials. © 2022 Informa UK Limited, trading as Taylor & Francis Group.
    view abstractdoi: 10.1080/08927014.2022.2027923
  • 2022 • 55 Rejuvenation in Deep Thermal Cycling of a Generic Model Glass: A Study of Per-Particle Energy Distribution
    Bruns, M. and Varnik, F.
    Materials 15 (2022)
    We investigate the effect of low temperature (cryogenic) thermal cycling on a generic model glass and observe signature of rejuvenation in terms of per-particle potential energy distributions. Most importantly, these distributions become broader and its average values successively increase when applying consecutive thermal cycles. We show that linear dimension plays a key role for these effects to become visible, since we do only observe a weak effect for a cubic system of roughly one hundred particle diameter but observe strong changes for a rule-type geometry with the longest length being two thousand particle diameters. A consistent interpretation of this new finding is provided in terms of a competition between relaxation processes, which are inherent to glassy systems, and excitation due to thermal treatment. In line with our previous report (Bruns et al., PRR 3, 013234 (2021)), it is shown that, depending on the parameters of thermal cycling, rejuvenation can be either too weak to be detected or strong enough for a clear observation. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/ma15030829
  • 2022 • 54 Reliability based optimization of steel-fibre segmental tunnel linings subjected to thrust jack loadings
    Neu, G.E. and Edler, P. and Freitag, S. and Gudžulić, V. and Meschke, G.
    Engineering Structures 254 (2022)
    The circular lining in mechanized tunnelling consists of concrete segments, which are exposed to different loading cases during tunnel construction. One of the most critical loading condition is the thrust jack force, which is induced to the lining segments by the Tunnel Boring Machine (TBM) during construction. Experimental campaigns showed that steel fibre reinforced concrete is suitable for bearing such loads and could replace conventional reinforcement schemes. In this contribution, a numerical model is presented, which allows to directly track the influence of important design parameters such as fibre type, fibre orientation, fibre content and concrete strength on the structural response of steel-fibre reinforced segments. For this purpose, submodels on the single fibre level are combined into a crack bridging model considering the fibre orientation and the fibre content. The submodels are integrated into a finite element model to perform numerical structural analyses. Two validation examples demonstrate that the modelling approach is capable to predict the failure loads as well as the crack development of fibre reinforced specimens subjected to localized loads. Finally, an optimization procedure is carried out to determine a robust and cost-effective design of a fibre reinforced segmental linings. A hybrid reinforcement scheme consisting of two layers of fibre reinforced concrete is employed in order to provide an improved material utilization. The thickness of the segment and the fibre content are optimized taking uncertainties of the material parameters and construction tolerances as uncertain a priori parameters into account. A sufficient load bearing capacity and serviceability performance under all possible conditions is ensured by the consideration of accepted failure probabilities as constraints in the optimization task. © 2022 Elsevier Ltd
    view abstractdoi: 10.1016/j.engstruct.2021.113752
  • 2022 • 53 Revealing in-plane grain boundary composition features through machine learning from atom probe tomography data
    Zhou, X. and Wei, Y. and Kühbach, M. and Zhao, H. and Vogel, F. and Darvishi Kamachali, R. and Thompson, G.B. and Raabe, D. and Gault, B.
    Acta Materialia 226 (2022)
    Grain boundaries (GBs) are planar lattice defects that govern the properties of many types of polycrystalline materials. Hence, their structures have been investigated in great detail. However, much less is known about their chemical features, owing to the experimental difficulties to probe these features at the atomic length scale inside bulk material specimens. Atom probe tomography (APT) is a tool capable of accomplishing this task, with an ability to quantify chemical characteristics at near-atomic scale. Using APT data sets, we present here a machine-learning-based approach for the automated quantification of chemical features of GBs. We trained a convolutional neural network (CNN) using twenty thousand synthesized images of grain interiors, GBs, or triple junctions. Such a trained CNN automatically detects the locations of GBs from APT data. Those GBs are then subjected to compositional mapping and analysis, including revealing their in-plane chemical decoration patterns. We applied this approach to experimentally obtained APT data sets pertaining to three case studies, namely, Ni-P, Pt-Au, and Al-Zn-Mg-Cu alloys. In the first case, we extracted GB specific segregation features as a function of misorientation and coincidence site lattice character. Secondly, we revealed interfacial excesses and in-plane chemical features that could not have been found by standard compositional analyses. Lastly, we tracked the temporal evolution of chemical decoration from early-stage solute GB segregation in the dilute limit to interfacial phase separation, characterized by the evolution of complex composition patterns. This machine-learning-based approach provides quantitative, unbiased, and automated access to GB chemical analyses, serving as an enabling tool for new discoveries related to interface thermodynamics, kinetics, and the associated chemistry-structure-property relations. © 2022 The Authors
    view abstractdoi: 10.1016/j.actamat.2022.117633
  • 2022 • 52 Revealing the influence of Mo addition on interphase precipitation in Ti-bearing low carbon steels
    Dong, H. and Chen, H. and Riyahi khorasgani, A. and Zhang, B. and Zhang, Y. and Wang, Z. and Zhou, X. and Wang, W. and Wang, H. and Li, T. and Yang, Z. and van der Zwaag, S.
    Acta Materialia 223 (2022)
    Mo is widely used as an effective microalloying element to improve mechanical performance of interphase precipitation steels, but the precise role of Mo in interphase precipitation behavior is not fully understood. In this contribution, interphase precipitation behavior in a series of Ti-Mo-bearing low carbon steels is systematically studied, and the role of Mo in interphase precipitates and its coarsening behavior is revisited. It is found that (Ti, Mo)C precipitates instead of TiC are formed in the Mo-containing alloys, and the average site fraction of Mo in (Ti, Mo)C is almost independent of the bulk Mo content. Moreover, the number density of interphase precipitates can be substantially enhanced by a minor addition of Mo, albeit it does not further rise with increasing the bulk Mo content. This is because the Mo fraction in (Ti, Mo)C rather than the bulk Mo content governs the driving force for precipitation nucleation and the interfacial energy of the (Ti, Mo)C/α and (Ti, Mo)C/γ interfaces. In addition to the reduced interfacial energy, decrease of Ti trans-interface diffusivity has been identified as another key reason for the enhanced carbide coarsening resistance in Mo-containing alloys. © 2021 Acta Materialia Inc.
    view abstractdoi: 10.1016/j.actamat.2021.117475
  • 2022 • 51 Robust optimization in nanoparticle technology: A proof of principle by quantum dot growth in a residence time reactor
    Dienstbier, J. and Aigner, K.-M. and Rolfes, J. and Peukert, W. and Segets, D. and Pflug, L. and Liers, F.
    Computers and Chemical Engineering 157 (2022)
    Knowledge-based determination of the best-possible experimental setups for nanoparticle design is highly challenging. Additionally, such processes are accompanied by noticeable uncertainties. Therefore, protection against those is needed. Robust optimization helps determining optimal processes. The latter guarantees quality requirements regardless of how uncertainties e.g., in raw materials, particle size distributions (PSD), heat and mass transport characteristics, and (growth) rates, manifest within predefined ranges. To approach this task, we exemplarily model a particle synthesis process with seeded growth by population balance equations and study different growth kinetics. We determine the mean residence time maximizing the product mass subject to a guaranteed yield. Additionally, we hedge against uncertain growth rates and derive an algorithmically tractable reformulation for the robustified problem. This reformulation can be applied if both the objective and the constraint functions are quasiconcave in the uncertainty which is a natural assumption in this context. We also show that the approach extends to higher-dimensional uncertainties if the uncertain parameters do not influence each other. We evaluate our approach for seeded growth synthesis of zinc oxide quantum dots and demonstrate computationally that a guaranteed yield is met for all growth rates within predefined regions. The protection against uncertainties only reduces the maximum amount of product that can be obtained by a negligible margin. © 2021
    view abstractdoi: 10.1016/j.compchemeng.2021.107618
  • 2022 • 50 Role of Anionic Backbone in NHC-Stabilized Coinage Metal Complexes: New Precursors for Atomic Layer Deposition**
    Boysen, N. and Philip, A. and Rogalla, D. and Karppinen, M. and Devi, A.
    Chemistry - A European Journal (2022)
    Cu and Ag precursors that are volatile, reactive, and thermally stable are currently of high interest for their application in atomic-layer deposition (ALD) of thin metal films. In pursuit of new precursors for coinage metals, namely Cu and Ag, a series of new N-heterocyclic carbene (NHC)-based CuI and AgI complexes were synthesized. Modifications in the substitution pattern of diketonate-based anionic backbones led to five monomeric Cu complexes and four closely related Ag complexes with the general formula [M(tBuNHC)(R)] (M=Cu, Ag; tBuNHC=1,3-di-tert-butyl-imidazolin-2-ylidene; R=diketonate). Thermal analysis indicated that most of the Cu complexes are thermally stable and volatile compared to the more fragile Ag analogs. One of the promising Cu precursors was evaluated for the ALD of nanoparticulate Cu metal deposits by using hydroquinone as the reducing agent at appreciably low deposition temperatures (145–160 °C). This study highlights the considerable impact of the employed ligand sphere on the structural and thermal properties of metal complexes that are relevant for vapor-phase processing of thin films. © 2022 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.
    view abstractdoi: 10.1002/chem.202103798
  • 2022 • 49 Role of geochemical protoenzymes (geozymes) in primordial metabolism: specific abiotic hydride transfer by metals to the biological redox cofactor NAD+
    Henriques Pereira, D.P. and Leethaus, J. and Beyazay, T. and do Nascimento Vieira, A. and Kleinermanns, K. and Tüysüz, H. and Martin, W.F. and Preiner, M.
    FEBS Journal (2022)
    Hydrogen gas, H2, is generated in serpentinizing hydrothermal systems, where it has supplied electrons and energy for microbial communities since there was liquid water on Earth. In modern metabolism, H2 is converted by hydrogenases into organically bound hydrides (H–), for example, the cofactor NADH. It transfers hydrides among molecules, serving as an activated and biologically harnessed form of H2. In serpentinizing systems, minerals can also bind hydrides and could, in principle, have acted as inorganic hydride donors—possibly as a geochemical protoenzyme, a ‘geozyme’— at the origin of metabolism. To test this idea, we investigated the ability of H2 to reduce NAD+ in the presence of iron (Fe), cobalt (Co) and nickel (Ni), metals that occur in serpentinizing systems. In the presence of H2, all three metals specifically reduce NAD+ to the biologically relevant form, 1,4-NADH, with up to 100% conversion rates within a few hours under alkaline aqueous conditions at 40 °C. Using Henry's law, the partial pressure of H2 in our reactions corresponds to 3.6 mm, a concentration observed in many modern serpentinizing systems. While the reduction of NAD+ by Ni is strictly H2-dependent, experiments in heavy water (2H2O) indicate that native Fe can reduce NAD+ both with and without H2. The results establish a mechanistic connection between abiotic and biotic hydride donors, indicating that geochemically catalysed, H2-dependent NAD+ reduction could have preceded the hydrogenase-dependent reaction in evolution. © 2022 The Authors. The FEBS Journal published by John Wiley & Sons Ltd on behalf of Federation of European Biochemical Societies
    view abstractdoi: 10.1111/febs.16329
  • 2022 • 48 Scrutinizing the Debye plasma model: Rydberg excitons unravel the properties of low-density plasmas in semiconductors
    Stolz, H. and Semkat, D. and Schwartz, R. and Heckötter, J. and Aßmann, M. and Kraeft, W.-D. and Fehske, H. and Bayer, M.
    Physical Review B 105 (2022)
    For low-density plasmas, the classical limit described by the Debye-Hückel theory is still considered as an appropriate description even though a clear experimental proof of this paradigm is lacking due to the problems in determining the plasma-induced shift of single-particle energies in atomic systems. We show that Rydberg excitons in states with a high principal quantum number are highly sensitive probes for their surrounding making it possible to unravel accurately the basic properties of low-density nondegenerate electron-hole plasmas. To this end, we accurately measure the parameters of Rydberg excitons such as energies and linewidths in absorption spectra of bulk cuprous oxide crystals in which a tailored electron-hole plasma has been generated optically. Since from the absorption spectra exciton energies, as well as the shift of the single-particle energies given by the band edge, can be directly derived, the measurements allow us to determine the plasma density and temperature independently, which has been a notoriously hard problem in semiconductor physics. Our analysis shows unambiguously that the impact of the plasma cannot be described by the classical Debye model, but requires a quantum many-body theory, not only for the semiconductor plasma investigated here, but in general. Furthermore, it reveals an exciton scattering mechanism with coupled plasmon-phonon modes becoming important even at very low plasma densities. © 2022 American Physical Society.
    view abstractdoi: 10.1103/PhysRevB.105.075204
  • 2022 • 47 Selective 1,2 addition of polar X–H bonds to the Ga–P double bond of gallaphosphene L(Cl)GaPGaL
    Sharma, M.K. and Wölper, C. and Schulz, S.
    Dalton Transactions 51 1612-1616 (2022)
    Gallaphosphene L(Cl)GaPGaL 1 (L = HC[C(Me)N(2,6-i-Pr2-C6H3)]2) reacts at ambient temperature with a series of polar X–H bonds, i.e. ammonia, primary amines, water, phenol, thiophenol, and selenophenol, selectively with 1,2 addition at the polar Ga–P double bond. The gallium atom serves as electrophile and the phosphorous atom is protonated in all reactions. The resulting complexes L(Cl)GaP(H)Ga(X)L (X = NH22, NHi-Pr 3, NHPh 4, OH 5, OXyl 6, SPh 7, SePh 8) were characterized by IR and heteronuclear (1H, 13C{1H}, 31P{1H}) NMR spectroscopy, elemental analysis, and single-crystal X-ray diffraction. This journal is © The Royal Society of Chemistry
    view abstractdoi: 10.1039/d1dt04299h
  • 2022 • 46 Selective Anodic Oxidation of Solketal as Acetal-Protected Glycerol over Nickel Boride in Alkaline Media to Glyceric Acid**
    Cychy, S. and Lechler, S. and Muhler, M.
    ChemElectroChem 9 (2022)
    Alkaline anodic oxidation of glycerol suffers from facile C−C bond cleavage, especially when using non-precious metal electrocatalysts, which limits the yield of more valuable C3 oxygenates. Usually, a high C3 selectivity is a tradeoff with conversion for most catalysts. Thus, we used solketal as the reactant, which is acetal-protected glycerol with acetone. CV experiments showed that solketal is oxidized over nickel boride (NixB) at potentials where NiOOH is formed. Electrolysis over NixB in a thin-film spectroelectrochemical flow cell at 1.58 V vs. RHE to avoid pronounced oxygen evolution showed a stable current density of ca. 6 mA cm−2. Simultaneously recorded ATR-FTIR spectra revealed solketal conversion to solketalate and formate. Indeed, 59 % conversion and 77 % selectivity to glyceric acid were determined by HPLC after acidic cleavage of the acetal, resulting in a yield of 45 %. Therefore, solketal is a promising reactant for the selective electrosynthesis of glyceric acid. © 2021 The Authors. ChemElectroChem published by Wiley-VCH GmbH.
    view abstractdoi: 10.1002/celc.202101214
  • 2022 • 45 Selective Disruption of Survivin's Protein-Protein Interactions: A Supramolecular Approach Based on Guanidiniocarbonylpyrrole
    Aschmann, D. and Vallet, C. and Tripathi, S.K. and Ruiz-Blanco, Y.B. and Brabender, M. and Schmuck, C. and Sanchez-Garcia, E. and Knauer, S.K. and Giese, M.
    ChemBioChem 23 (2022)
    Targeting specific protein binding sites to interfere with protein-protein interactions (PPIs) is crucial for the rational modulation of biologically relevant processes. Survivin, which is highly overexpressed in most cancer cells and considered to be a key player of carcinogenesis, features two functionally relevant binding sites. Here, we demonstrate selective disruption of the Survivin/Histone H3 or the Survivin/Crm1 interaction using a supramolecular approach. By rational design we identified two structurally related ligands (LNES and LHIS), capable of selectively inhibiting these PPIs, leading to a reduction in cancer cell proliferation. © 2022 The Authors. ChemBioChem published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/cbic.202100618
  • 2022 • 44 Silicon- and tungsten-containing hydrogen-free and hydrogenated amorphous carbon films for friction-reducing applications
    Tillmann, W. and Wittig, A. and Dias, N.F.L. and Stangier, D. and Thomann, C.A. and Moldenhauer, H. and Debus, J.
    Diamond and Related Materials 123 (2022)
    For tribological applications, adding Si or W to hydrogen-free a-C or hydrogenated a-C:H is highly beneficial to tailor the film properties. Hence, a direct comparison between Si- and W-containing a-C and a-C:H considerably enhances the understanding of both the interaction between Si or W and the hydrogenation state as well as its effect on the structure and tribo-mechanical properties of these films. Therefore, non-modified a-C(:H), Si-containing a-C(:H):Si, and W-containing a-C(:H):W films were systematically grown in a mid-frequency magnetron sputtering process. The formation of W-based nanocrystallites within a-C(:H):W is identified by x-ray diffraction, whereas a-C(:H):Si still possesses an amorphous character. Raman scattering spectra show higher I(D)/I(G) ratios for hydrogen-free a-C(:X) films compared to the respective a-C(:H):X, indicating a higher number and larger sizes of sp2 clusters in the carbon network. For the hydrogenated a-C:H:X films, the reduced number of sp2 clusters is related to the presence of terminating C[sbnd]H bonds, which were detected as stretching modes. Among the different films, a-C:W has the highest I(D)/I(G) ratio, while a-C:H and a-C:H:Si exhibit the lowest I(D)/I(G) values. While a-C:Si and a-C:H:Si are characterized by comparable hardness values of (18.7 ± 1.3) and (18.4 ± 1.1) GPa, a-C:W has a lower hardness of (13.8 ± 1.0) GPa compared to a-C:H:W with (17.5 ± 0.9) GPa. Among all modified a-C(:H):X films, a-C:Si and a-C:H:Si reveal the lowest coefficients of friction, but show highest wear rates in dry sliding against 100Cr6 steel. Contrarily, a-C:W has higher friction and wear than a-C:H:W. Consequently, the Si-containing a-C(:H):Si films demonstrate comparable tribo-mechanical properties, while the hydrogenation state leads to different tribo-mechanical properties of a-C(:H):W. © 2022
    view abstractdoi: 10.1016/j.diamond.2022.108866
  • 2022 • 43 Simulation of crack propagation based on eigenerosion in brittle and ductile materials subject to finite strains
    Wingender, D. and Balzani, D.
    Archive of Applied Mechanics (2022)
    In this paper, a framework for the simulation of crack propagation in brittle and ductile materials is proposed. The framework is derived by extending the eigenerosion approach of Pandolfi and Ortiz (Int J Numer Methods Eng 92(8):694–714, 2012. https://doi.org/10.1002/nme.4352) to finite strains and by connecting it with a generalized energy-based, Griffith-type failure criterion for ductile fracture. To model the elasto-plastic response, a classical finite strain formulation is extended by viscous regularization to account for the shear band localization prior to fracture. The compression–tension asymmetry, which becomes particularly important during crack propagation under cyclic loading, is incorporated by splitting the strain energy density into a tensile and compression part. In a comparative study based on benchmark problems, it is shown that the unified approach is indeed able to represent brittle and ductile fracture at finite strains and to ensure converging, mesh-independent solutions. Furthermore, the proposed approach is analyzed for cyclic loading, and it is shown that classical Wöhler curves can be represented. © 2022, The Author(s).
    view abstractdoi: 10.1007/s00419-021-02101-1
  • 2022 • 42 Simulation of Powder Flow Behavior in an Artificial Feed Frame Using an Euler-Euler Model
    Zimmermann, M. and Raffel, C. and Bartsch, J. and Thommes, M.
    Chemical Engineering and Technology (2022)
    The Eulerian approach is an alternative numerical method to the traditionally used discreet particle techniques for modeling powder flow, avoiding limitations on particle number and diameter. The feasibility of an Euler-Euler simulation in a pharmaceutical application was investigated. In two- and three-dimensional flow simulations, computational fluid dynamics models and parameters were determined and verified based on comparison with experiments. Residence time distributions were calculated to show the applicability of the Eulerian model with two granular phases under the constraint of a continuous setup. Finally, this model was implemented to improve the process understanding of the powder flow in an artificial feed frame of a rotary tablet press. © 2022 The Authors. Chemical Engineering & Technology published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/ceat.202100580
  • 2022 • 41 Simulation, analysis and control of a self-propelling heat removal system using supercritical CO2 under varying boundary conditions
    Hofer, M. and Ren, H. and Hecker, F. and Buck, M. and Brillert, D. and Starflinger, J.
    Energy 247 (2022)
    The supercritical carbon dioxide (sCO21) heat removal system, which is based on a closed Brayton cycle with sCO2 as a working fluid, is an innovative heat removal system for existing and future nuclear power plants. This paper provides the design, layout and control of the system based on assumptions developed in the project sCO2-4-NPP. A self-propelling operational readiness state enables a fast start-up and consumes only 12% of the design thermal power input. The system is analysed over a wide range of ambient and steam-side conditions in ATHLET, using performance maps for the turbomachinery, which were designed recently. The performance analysis suggests that it is a good option to operate the system at the design compressor inlet temperature of 55 °C at any boundary condition. With decreasing thermal power input, the rotational speed of the turbomachinery must be decreased to keep the system self-propelling. Moreover, the turbomachinery design with a higher surge margin is preferred. By controlling the compressor inlet temperature via the air mass flow rate and turbine inlet temperature via the turbomachinery speed, the heat removal system is successfully operated in interaction with a pressurized water reactor. © 2022 The Authors
    view abstractdoi: 10.1016/j.energy.2022.123500
  • 2022 • 40 Spin Crossover in a Cobalt Complex on Ag(111)
    Johannsen, S. and Ossinger, S. and Grunwald, J. and Herman, A. and Wende, H. and Tuczek, F. and Gruber, M. and Berndt, R.
    Angewandte Chemie - International Edition 61 (2022)
    The Co-based complex [Co(H2B(pz)(pypz))2] (py=pyridine, pz=pyrazole) deposited on Ag(111) was investigated with scanning tunneling microscopy at ≈5 K. Due to a bis(tridentate) coordination sphere the molecules aggregate mainly into tetramers. Individual complexes in these tetramers undergo reversible transitions between two states with characteristic image contrasts when current is passed through them or one of their neighbors. Two molecules exhibit this bistability while the other two molecules are stable. The transition rates vary linearly with the tunneling current and exhibit an intriguing dependence on the bias voltage and its polarity. We interpret the states as being due to S=1/2 and 3/2 spin states of the Co2+ complex. The image contrast and the orders-of-magnitude variations of the switching yields can be tentatively understood from the calculated orbital structures of the two spin states, thus providing first insights into the mechanism of electron-induced excited spin-state trapping (ELIESST). © 2022 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/anie.202115892
  • 2022 • 39 Splicing the active phases of copper/cobalt-based catalysts achieves high-rate tandem electroreduction of nitrate to ammonia
    He, W. and Zhang, J. and Dieckhöfer, S. and Varhade, S. and Brix, A.C. and Lielpetere, A. and Seisel, S. and Junqueira, J.R.C. and Schuhmann, W.
    Nature Communications 13 (2022)
    Electrocatalytic recycling of waste nitrate (NO3−) to valuable ammonia (NH3) at ambient conditions is a green and appealing alternative to the Haber−Bosch process. However, the reaction requires multi-step electron and proton transfer, making it a grand challenge to drive high-rate NH3 synthesis in an energy-efficient way. Herein, we present a design concept of tandem catalysts, which involves coupling intermediate phases of different transition metals, existing at low applied overpotentials, as cooperative active sites that enable cascade NO3−-to-NH3 conversion, in turn avoiding the generally encountered scaling relations. We implement the concept by electrochemical transformation of Cu−Co binary sulfides into potential-dependent core−shell Cu/CuOx and Co/CoO phases. Electrochemical evaluation, kinetic studies, and in−situ Raman spectra reveal that the inner Cu/CuOx phases preferentially catalyze NO3− reduction to NO2−, which is rapidly reduced to NH3 at the nearby Co/CoO shell. This unique tandem catalyst system leads to a NO3−-to-NH3 Faradaic efficiency of 93.3 ± 2.1% in a wide range of NO3− concentrations at pH 13, a high NH3 yield rate of 1.17 mmol cm−2 h−1 in 0.1 M NO3− at −0.175 V vs. RHE, and a half-cell energy efficiency of ~36%, surpassing most previous reports. © 2022, The Author(s).
    view abstractdoi: 10.1038/s41467-022-28728-4
  • 2022 • 38 Strain rate dependent deformation behavior of BCC-structured Ti29Zr24Nb23Hf24 high entropy alloy at elevated temperatures
    Cao, T. and Guo, W. and Lu, W. and Xue, Y. and Lu, W. and Su, J. and Liebscher, C.H. and Li, C. and Dehm, G.
    Journal of Alloys and Compounds 891 (2022)
    The mechanical behavior and deformation mechanisms of a body-centered cubic (BCC) Ti29Zr24Nb23Hf24 (at%) high entropy alloy (HEA) was investigated in temperatures and strain rates from 700° to 1100 °C and 10−3 to 10 s−1, respectively. The HEA exhibits a substantial increase in yield stress with increasing strain rate. The strain rate sensitivity (SRS) coefficient is ~3 times that of BCC alloy Nb-1Zr and even ~3.5 times that of pure Nb. This high SRS is attributed to the high Peierls stress of the HEA, which is about twice the Peierls stress of pure Nb. On the other hand, the flow stress exhibits a tendency from strain softening to strain hardening with the increase of strain rate especially at the relatively low temperatures. This behavior is explained by a change in dislocation motion from climbing to multiple slip with the increase of strain rate. Taking the specimen subjected to 800 ºC for example, dislocation walls formed at the early stage of deformation and at low strain rate of 10−3 s−1. In this case there is sufficient time to activate dislocations climb, which results in discontinuous dynamic recrystallization, and strain softening. However, when the strain rate amounts to 1 s−1, thermally activated processes such as dislocation climb are too sluggish. As a consequence, multiple slip systems are activated, and the dislocation interactions lead to the evolution of deformation bands, leading to strain hardening. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.jallcom.2021.161859
  • 2022 • 37 Strategies for damage tolerance enhancement in metal/ceramic thin films: Lessons learned from Ti/TiN
    Mishra, A.K. and Gopalan, H. and Hans, M. and Kirchlechner, C. and Schneider, J.M. and Dehm, G. and Jaya, B.N.
    Acta Materialia 228 (2022)
    Most functional microelectronic devices as well as hard coatings use brittle ceramics like Titanium Nitride (TiN) in nanostructured, thin film form. Damage tolerance is critical to their deployment in service, and life extension. In this study, we explore multilayering to enhance the damage tolerance of such material systems. Ti/TiN is a model metal/ceramic system with a strong interface, where elastic-plastic mismatch could potentially be used to modify the crack driving force. We carry out systematic numerical simulations of crack driving force in Ti/TiN multilayers with changing layer spacing. Micro-cantilever experiments are then carried out on a selected set of multilayers to determine the fracture toughness as a function of the number of interfaces. The 50 layer multilayer exhibits a fracture toughness that is 82% higher than the single layer TiN while maintaining a comparable hardness to the latter. The weak intercolumnar boundaries of sputtered films are found to be a limitation in fully exploiting the advantage of the shielding effect due to alternating stiff and compliant layers. The results are discussed in the context of design parameters for multilayering in metal/ceramic thin film systems in general. © 2022 Acta Materialia Inc.
    view abstractdoi: 10.1016/j.actamat.2022.117777
  • 2022 • 36 Stress-Based Methods for Quasi-Variational Inequalities Associated with Frictional Contact
    Kober, B. and Starke, G. and Krause, R. and Rovi, G.
    International Series of Numerical Mathematics 172 445-466 (2022)
    The stress-based formulation of elastic contact with Coulomb friction in the form of a quasi-variational inequality is investigated. Weakly symmetric stress approximations are constructed using a finite element combination on the basis of Raviart–Thomas spaces of next-to-lowest order. An error estimator is derived based on a displacement reconstruction and proved to be reliable under certain assumptions on the solution formulated in terms of a norm equivalence in the trace space H1∕2(Γ). Numerical results illustrate the effectiveness of the adaptive refinement strategy for a Hertzian frictional contact problem in the compressible as well as in the incompressible case. © 2022, Springer Nature Switzerland AG.
    view abstractdoi: 10.1007/978-3-030-79393-7_18
  • 2022 • 35 Strong magnetoelectric coupling at an atomic nonmagnetic electromagnetic probe in bismuth ferrite
    Schell, J. and Schmuck, M. and Efe, İ. and Dang, T.T. and Gonçalves, J.N. and Lewin, D. and Castillo, M.E. and Shvartsman, V.V. and Costa, Â.R.G. and Köster, U. and Vianden, R. and Noll, C. and Lupascu, D.C.
    Physical Review B 105 (2022)
    Isolated nonmagnetic substitutional defect ions experience huge coupled electric magnetic interaction in the single-phase multiferroic BiFeO3. In the ferroelectric state above the magnetic Néel temperature TN, the electric environment generates a single symmetric electric field gradient (EFG) parallel to the electric polarization direction. Below TN, a distinct magnetic interaction arises, monitored by the probe nuclei via their magnetic moment. Two magnetic environments arise, given by the relative angle of the local magnetic moment within its easy magnetic plane with respect to the EFG orientation. The angle between field gradient orientation and magnetic field direction is the most stable fitting parameter. The magnetic interaction concomitantly increases the EFG dramatically which reflects an outstandingly large local magnetoelectric coupling. In the set of best fits, two different electric environments form concurrently with two distinctly different local magnetic fields. The magnetic ordering in BiFeO3 thus completely distorts the electric environment of the nonmagnetic probe nucleus. The implications for the local effect of dopants in BiFeO3 are discussed. A third probe environment arising independent of temperature is identified and associated with an iron vacancy. © 2022 American Physical Society.
    view abstractdoi: 10.1103/PhysRevB.105.094102
  • 2022 • 34 Strong Stationarity for Optimal Control of Variational Inequalities of the Second Kind
    Christof, C. and Meyer, C. and Schweizer, B. and Turek, S.
    International Series of Numerical Mathematics 172 307-327 (2022)
    This chapter is concerned with necessary optimality conditions for optimal control problems governed by variational inequalities of the second kind. The so-called strong stationarity conditions are derived in an abstract framework. Strong stationarity conditions are regarded as the most rigorous ones, since they imply all other types of stationarity concepts and are equivalent to purely primal optimality conditions. The abstract framework is afterward applied to four application-driven examples. © 2022, Springer Nature Switzerland AG.
    view abstractdoi: 10.1007/978-3-030-79393-7_12
  • 2022 • 33 Structural Insights into Hysteretic Spin-Crossover in a Set of Iron(II)-2,6-bis(1H-Pyrazol-1-yl)Pyridine) Complexes
    Suryadevara, N. and Mizuno, A. and Spieker, L. and Salamon, S. and Sleziona, S. and Maas, A. and Pollmann, E. and Heinrich, B. and Schleberger, M. and Wende, H. and Kuppusamy, S.K. and Ruben, M.
    Chemistry - A European Journal 28 (2022)
    Bistable spin-crossover (SCO) complexes that undergo abrupt and hysteretic (ΔT1/2) spin-state switching are desirable for molecule-based switching and memory applications. In this study, we report on structural facets governing hysteretic SCO in a set of iron(II)-2,6-bis(1H-pyrazol-1-yl)pyridine) (bpp) complexes – [Fe(bpp−COOEt)2](X)2⋅CH3NO2 (X=ClO4, 1; X=BF4, 2). Stable spin-state switching – T1/2=288 K; ΔT1/2=62 K – is observed for 1, whereas 2 undergoes above-room-temperature lattice-solvent content-dependent SCO – T1/2=331 K; ΔT1/2=43 K. Variable-temperature single-crystal X-ray diffraction studies of the complexes revealed pronounced molecular reorganizations – from the Jahn-Teller-distorted HS state to the less distorted LS state – and conformation switching of the ethyl group of the COOEt substituent upon SCO. Consequently, we propose that the large structural reorganizations rendered SCO hysteretic in 1 and 2. Such insights shedding light on the molecular origin of thermal hysteresis might enable the design of technologically relevant molecule-based switching and memory elements. © 2021 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/chem.202103853
  • 2022 • 32 Structure-Performance Relationship of LaFe1-xCoxO3 Electrocatalysts for Oxygen Evolution, Isopropanol Oxidation, and Glycerol Oxidation
    Brix, A.C. and Dreyer, M. and Koul, A. and Krebs, M. and Rabe, A. and Hagemann, U. and Varhade, S. and Andronescu, C. and Behrens, M. and Schuhmann, W. and Morales, D.M.
    ChemElectroChem 9 (2022)
    Mitigating high energy costs related to sustainable H2 production via water electrolysis is important to make this process commercially viable. Possible approaches are the investigation of low-cost, highly active oxygen evolution reaction (OER) catalysts and the exploration of alternative anode reactions, such as the electrocatalytic isopropanol oxidation reaction (iPOR) or the glycerol oxidation reaction (GOR), offering the possibility of simultaneously lowering the anodic overpotential and generating value-added products. A suitable class of catalysts are non-noble metal-based perovskites with the general formula ABO3, featuring rare-earth metal cations at the A- and transition metals at the B-site. We synthesised a series of LaFe1-xCoxO3 materials with x=0–0.70 by automated co-precipitation at constant pH and subsequent calcination at 800 °C. X-ray diffraction studies revealed that the phase purity was preserved in samples with x≤0.3. The activity towards the OER, iPOR, and GOR was investigated by rotating disk electrode voltammetry, showing a relation between structure and metal composition with the activity trends observed for the three reactions. Additionally, GOR product analysis via high-performance liquid chromatography (HPLC) was conducted after 24 and 48 h electrolysis in a circular flow-through cell setup, pointing out a trade-off between activity and selectivity. © 2022 The Authors. ChemElectroChem published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/celc.202200092
  • 2022 • 31 Switching from Heteronuclear Allyl Cations to Vinyl Cations by Using a Chemical Charge Trap
    Krüger, J. and Wölper, C. and Haberhauer, G. and Schulz, S.
    Inorganic Chemistry 61 597-604 (2022)
    Halide abstraction of the carbene-coordinated pnictinidenes (MecAAC)EGa(Cl)L (E = As 1, Sb 2, Bi 3, MecAAC = [H2C(CMe2)2NDipp]C; L = HC[C(Me)NDipp]2; Dipp = 2,6-i-Pr2C6H3) yielded the series of cationic group 15 compounds [(MecAAC)EGaL][Al(ORF)4] (E = As 4, Sb 5; Al(ORF)4 = Al(OC(CF3)3)4) and [(MecAAC)EGaL][B(ArF)4] (E = Sb 6, Bi 7; B(ArF)4 = B[C6H3(CF3)2]4), which were characterized by heteronuclear NMR spectroscopy and sc-XRD. The electronic nature of the cations [(MecAAC)EGaL]+ is controlled by the central pnictogen atom, according to quantum chemical calculations. The calculations furthermore demonstrated that compounds containing the lighter pnictogens (E = N, P) are best described as heteronuclear allyl cations, whereas heavier pnictogen atoms (E = As, Sb, Bi) serve as a trap for the positive charge, resulting in carbene-stabilized heterovinyl-type structures. © 2021 The Authors. Published by American Chemical Society.
    view abstractdoi: 10.1021/acs.inorgchem.1c03279
  • 2022 • 30 Synthesis and Characterization of Cationic Hydrogels from Thiolated Copolymers for Independent Manipulation of Mechanical and Chemical Properties of Cell Substrates
    Pätzold, F. and Stamm, N. and Kamps, D. and Specht, M. and Bolduan, P. and Dehmelt, L. and Weberskirch, R.
    Macromolecular Bioscience (2022)
    Cells sense both mechanical and chemical properties in their environment and respond to these inputs with altered phenotypes. Precise and selective experimental manipulations of these environmental cues require biocompatible synthetic materials, for which multiple properties can be fine-tuned independently from each other. For example, cells typically show critical thresholds for cell adhesion as a function of substrate parameters such as stiffness and the degree of functionalization. However, the choice of tailor-made, defined materials to produce such cell adhesion substrates is still very limited. Here, a platform of synthetic hydrogels based on well-defined thiolated copolymers is presented. Therefore, four disulfide crosslinked hydrogels of different composition by free radical polymerization are prepared. After cleavage with dithiothreitol, four soluble copolymers P1–P4 with 0–96% cationic monomer content are obtained. P1 and P4 are then combined with PEGDA3500 as a crosslinker, to fabricate 12 hydrogels with variable elasticity, ranging from 8.1 to 26.3 kPa and cationic group concentrations of up to 350 µmol cm−3. Systematic analysis using COS7 cells shows that all of these hydrogels are nontoxic. However, successful cell adhesion requires both a minimal elasticity and a minimal cationic group concentration. © 2022 The Authors. Macromolecular Bioscience published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/mabi.202100453
  • 2022 • 29 Synthesis of freestanding few-layer graphene in microwave plasma: The role of oxygen
    Fortugno, P. and Musikhin, S. and Shi, X. and Wang, H. and Wiggers, H. and Schulz, C.
    Carbon 186 560-573 (2022)
    We systematically studied the role of oxygen in gas-phase synthesis of graphene in atmospheric hydrocarbon-fed microwave plasmas. Oxygen is introduced through the use of alcohols, and mixtures of ethylene and water. These reactants were contrasted with oxygen-free hydrocarbon reactants, including ethylene and toluene. Solid materials were collected at the plasma reactor exit and characterized. Gas-phase temperature and key species concentrations were measured using in situ Fourier-transform infrared absorption and emission spectroscopy inside the reactors. Ethanol resulted in pure few-layer graphene formation, in agreement with previous studies. In contrast, ethylene fed at the same flow rate produced a mixture of carbon allotropes. A shift towards graphene formation is observed when water is added to ethylene, or when the flow rate of ethylene is cut to half. Simulations suggest that reactants undergo rapid chemical reactions in the plasma front and the mixture composition in and immediately after the plasma is in chemical equilibrium. The primary factor that controls graphene growth appears to be the total amount of carbon available in the growth region. Oxygen, through CO formation, modulates the amount of acetylene and other growth species, while other factors require further study. © 2021 The Authors
    view abstractdoi: 10.1016/j.carbon.2021.10.047
  • 2022 • 28 Systematic in-depth study on material constitutive parameter identification for numerical cutting simulation on 16MnCr5 comparing temperature-coupled and uncoupled Split Hopkinson pressure bars
    Saelzer, J. and Thimm, B. and Zabel, A.
    Journal of Materials Processing Technology 302 (2022)
    A comprehensive systematic comparative study on high-strain-rate tests (Split Hopkinson Pressure Bar), with and without in-situ heating of the specimens and their respective influence on the quality of empirical material models is presented. The determination of material constitutive model parameters is one of the most challenging aspects of the modelling and simulation of machining processes. Chip formation and process forces show a significant dependence on the actual constitutive model and its parameters as well as on the testing method. Typically, the influences of strain, strain rate, and temperature are investigated in separate experiments of quasi-static compression tests and tests, because the most widespread phenomenological constitutive material models (e.g. Johnson–Cook model) neglect interactions between temperature and strain rate. In contrast, the presented work demonstrates, that a coupled experimental approach of strain rate and temperature in the same test increases the quality of such uncoupled material models as well. The authors compared both approaches (separated and in situ temperature-dependent experiments) by determining the constitutive model parameters for AISI 5115 steel samples taken from a single material batch. The parameters are calculated based on a covariance matrix adaptation evolution strategy and applied in identical two-dimensional orthogonal FEM cutting simulations. Process forces and chip thickness values were used for comparison with the machining experiments. The work therefore gives new aspects to decide for a suitable experimental approach when calibrating a constitutive equation. © 2022 Elsevier B.V.
    view abstractdoi: 10.1016/j.jmatprotec.2021.117478
  • 2022 • 27 Targeting early stages of cardiotoxicity from anti-PD1 immune checkpoint inhibitor therapy
    Michel, L. and Helfrich, I. and Hendgen-Cotta, U.B. and Mincu, R.-I. and Korste, S. and Mrotzek, S.M. and Spomer, A. and Odersky, A. and Rischpler, C. and Herrmann, K. and Umutlu, L. and Coman, C. and Ahrends, R. and Sickmann, A. ...
    European heart journal 43 316-329 (2022)
    AIMS: Cardiac immune-related adverse events (irAEs) from immune checkpoint inhibition (ICI) targeting programmed death 1 (PD1) are of growing concern. Once cardiac irAEs become clinically manifest, fatality rates are high. Cardio-oncology aims to prevent detrimental effects before manifestation of severe complications by targeting early pathological changes. We therefore aimed to investigate early consequences of PD1 inhibition for cardiac integrity to prevent the development of overt cardiac disease. METHODS AND RESULTS: We investigated cardiac-specific consequences from anti-PD1 therapy in a combined biochemical and in vivo phenotyping approach. Mouse hearts showed broad expression of the ligand PDL1 on cardiac endothelial cells as a main mediator of immune-crosstalk. Using a novel melanoma mouse model, we assessed that anti-PD1 therapy promoted myocardial infiltration with CD4+ and CD8+ T cells, the latter being markedly activated. Left ventricular (LV) function was impaired during pharmacological stress, as shown by pressure-volume catheterization. This was associated with a dysregulated myocardial metabolism, including the proteome and the lipidome. Analogous to the experimental approach, in patients with metastatic melanoma (n = 7) receiving anti-PD1 therapy, LV function in response to stress was impaired under therapy. Finally, we identified that blockade of tumour necrosis factor alpha (TNFα) preserved LV function without attenuating the anti-cancer efficacy of anti-PD1 therapy. CONCLUSIONS: Anti-PD1 therapy induces a disruption of cardiac immune homeostasis leading to early impairment of myocardial functional integrity, with potential prognostic effects on the growing number of treated patients. Blockade of TNFα may serve as an approach to prevent the manifestation of ICI-related cardiotoxicity. Published on behalf of the European Society of Cardiology. All rights reserved. © The Author(s) 2021. For permissions, please email: journals.permissions@oup.com.
    view abstractdoi: 10.1093/eurheartj/ehab430
  • 2022 • 26 Temperature dependence of Fano resonances in CrPS4
    Riesner, M. and Fainblat, R. and Budniak, A.K. and Amouyal, Y. and Lifshitz, E. and Bacher, G.
    Journal of Chemical Physics 156 (2022)
    A Fano resonance, as often observed in scattering, absorption, or transmission experiments, arises from quantum interference between a discrete optical transition and a continuous background. Here, we present a temperature-dependent study on Fano resonances observed in photoluminescence from flakes of the layered semiconductor antiferromagnet chromium thiophosphate (CrPS4). Two Fano resonances with a distinctly different temperature dependence were identified. The continuous background that is responsible for the Fano resonances is attributed to the d–d transition of the optically active Cr3+ center, predominantly the spin-forbidden 2Eg → 4A2g transition with contributions of the broad-band 4T2g → 4A2g transition. The discrete states that interfere with this continuous background are suggested to arise from localized atomic phosphorus. A model idea for explaining the individual temperature dependence of the Fano resonances is presented. © 2022 Author(s).
    view abstractdoi: 10.1063/5.0079298
  • 2022 • 25 The dual role of martensitic transformation in fatigue crack growth
    Wang, X. and Liu, C. and Sun, B. and Ponge, D. and Jiang, C. and Raabe, D.
    Proceedings of the National Academy of Sciences of the United States of America 119 (2022)
    Deformation-induced martensitic transformation (DIMT) has been used for designing high-performance alloys to prevent structural failure under static loads. Its effectiveness against fatigue, however, is unclear. This limits the application of DIMT for parts that are exposed to variable loads, although such scenarios are the rule and not the exception for structural failure. Here we reveal the dual role of DIMT in fatigue crack growth through in situ observations. Two antagonistic fatigue mechanisms mediated by DIMT are identified, namely, transformation-mediated crack arresting, which prevents crack growth, and transformation-mediated crack coalescence, which promotes crack growth. Both mechanisms are due to the hardness and brittleness of martensite as a transformation product, rather than to the actual transformation process itself. In fatigue crack growth, the prevalence of one mechanism over the other critically depends on the crack size and the mechanical stability of the parent austenite phase. Elucidating the two mechanisms and their interplay allows for the microstructure design and safe use of metastable alloys that experience fatigue loads. The findings also generally reveal how metastable alloy microstructures must be designed for materials to be fatigue-resistant. © 2022 National Academy of Sciences. All rights reserved.
    view abstractdoi: 10.1073/pnas.2110139119
  • 2022 • 24 The effect of argon as atomization gas on the microstructure, machine hammer peening post-treatment, and corrosion behavior of twin wire arc sprayed (Twas) znal4 coatings
    Tillmann, W. and Abdulgader, M. and Wirtz, A. and Milz, M.P. and Biermann, D. and Walther, F.
    Coatings 12 (2022)
    In the twin wire arc spraying (TWAS) process, it is common to use compressed air as atomizing gas. Nitrogen or argon also are used to reduce oxidation and improve coating performance. The heat required to melt the feedstock material depends on the electrical conductivity of the wires used and the ionization energy of both the feedstock material and atomization gas. In the case of ZnAl4, no phase changes were recorded in the obtained coatings by using either compressed air or argon as atomization gas. This fact has led to the assumption that the melting behavior of ZnAl4 with its low melting and evaporating temperature is different from materials with a higher melting point, such as Fe and Ni, which also explains the unexpected compressive residual stresses in the as-sprayed conditions. The heavier atomization gas, argon, led to slightly higher compressive stresses and oxide content. Compressed air as atomization gas led to lower porosity, decreased surface roughness, and better corrosion resistance. In the case of argon, Al precipitated in the form of small particles. The post-treatment machine hammer peening (MHP) has induced horizontal cracks in compressed air sprayed coatings. These cracks were mainly initiated in the oxidized Al phase. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/coatings12010032
  • 2022 • 23 The effect of deviations from precise [001] tensile direction on creep of Ni-base single crystal superalloys
    Heep, L. and Bürger, D. and Bonnekoh, C. and Wollgramm, P. and Dlouhy, A. and Eggeler, G.
    Scripta Materialia 207 (2022)
    Low temperature (1023 K) high stress (800 MPa) tensile creep behavior of the superalloy single crystal ERBO-1 (CMSX-4 type) is investigated. Three loading directions are compared: precise [001] and 15 ° deviations from [001] towards [111] and [011]. It is found that creep rates ε˙ scale as ε˙[001]→[111]&gt;ε˙[001]&gt;ε˙[001]→[011]already in the early stages of creep (ε≤1%), where dislocation network formation and planar fault intersections cannot rationalize the observed rate effects. An analysis based on Peach-Köhler force calculations suggests, that fast creep rates are observed, when dislocations from two octahedral systems, which are required to react and form the leading part of a planar fault ribbon in the γ’-phase, experience similar driving forces. Creep data, micromechanical calculations and TEM results are in good qualitative agreement. From a technological point of view, the results show that while 15 ° deviations from [001] towards [011] can be tolerated, deviations towards [111] must be avoided. © 2021
    view abstractdoi: 10.1016/j.scriptamat.2021.114274
  • 2022 • 22 The effects of the driving frequencies on micro atmospheric pressure He/N2plasma jets driven by tailored voltage waveforms
    Hübner, G. and Bischoff, L. and Korolov, I. and Donkó, Z. and Leimkühler, M. and Liu, Y. and Böke, M. and Schulz-Von Der Gathen, V. and Mussenbrock, T. and Schulze, J.
    Journal of Physics D: Applied Physics 55 (2022)
    Capacitively coupled micro atmospheric pressure plasma jets are important tools for the generation of radicals at room temperature for various applications. Voltage waveform tailoring (VWT), which is based on the simultaneous use of a set of excitation frequencies, has been demonstrated to provide an efficient control of the electron energy probability function (EEPF) in such plasmas and, thus, allows optimizing the electron impact driven excitation and dissociation processes as compared to the classical single-frequency operation mode. In this work, the effects of changing the driving frequencies on the spatio-temporally resolved electron power absorption dynamics, the generation of helium metastables and the dissociation of nitrogen molecules are investigated in He/N2 plasmas based on experiments and simulations. We find that under a single-frequency excitation, the plasma and helium metastable densities are enhanced as a function of the driving frequency at a fixed voltage. When using valleys-type driving voltage waveforms synthesized based on consecutive harmonics of the fundamental driving frequency, the spatial symmetry of the electron power absorption dynamics and of the metastable density profile is broken. Increasing the fundamental frequency at a constant voltage is found to drastically enhance the plasma and metastable densities, which is a consequence of the change of the EEPF. Finally, we compare the energy efficiency of the formation of radicals under single-frequency and VWT operation at different driving frequencies. For a given power dissipated in the plasma, VWT yields a higher helium metastable as well as electron density and a higher dissociation rate of N2. © 2021 IOP Publishing Ltd.
    view abstractdoi: 10.1088/1361-6463/ac3791
  • 2022 • 21 The Journal of Chemical & Engineering Data: Introduction of Topical Sections and Updates from the Editorial Team
    Siepmann, J.I. and Gardas, R. and Kofke, D.A. and Nieto De Castro, C. and Paulechka, E. and Pini, R. and Sadowski, G. and Schwarz, C.E.
    Journal of Chemical and Engineering Data 67 1-2 (2022)
    doi: 10.1021/acs.jced.1c00969
  • 2022 • 20 The orthorhombic-tetragonal morphotropic phase boundary in high-pressure synthesized BiMg0.5Ti0.5O3–BiZn0.5Ti0.5O3 perovskite solid solutions
    Salak, A.N. and Shvartsman, V.V. and Cardoso, J.P. and Pushkarev, A.V. and Radyush, Y.V. and Olekhnovich, N.M. and Khalyavin, D.D. and Vieira, J.M. and Čižmár, E. and Feher, A.
    Journal of Physics and Chemistry of Solids 161 (2022)
    (1–x)BiMg0.5Ti0.5O3−xBiZn0.5Ti0.5O3 [(1−x)BMT–xBZT] ceramics of perovskite solid solutions, in which BMT and BZT are lead-free structural analogs of PbZrO3 and PbTiO3, respectively, have been synthesized under high pressure. It was found that the as-prepared compositions with a relative BZT content of &lt;75 mol% are orthorhombic (space group Pnnm), while those with a BZT content above this value are tetragonal (P4mm). In the solution with x = 0.75, both phases coexist forming a morphotropic phase boundary (MPB). The compositional dependence of the normalized unit cell volume exhibits a ∼5% jump at x = 0.75. At the same time, the microstructure of the obtained (1–x)BMT−xBZT ceramics shows no particular variation with the chemical composition over MPB. Piezoresponse force microscopy measurements indicate the ferroelectric state of the studied materials and allowed one to estimate their intrinsic piezoelectric coefficients. © 2021 Elsevier Ltd
    view abstractdoi: 10.1016/j.jpcs.2021.110392
  • 2022 • 19 The role of DNA nanostructures in the catalytic properties of an allosterically regulated protease
    Kosinski, R. and Perez, J.M. and Schöneweiß, E.-C. and Ruiz-Blanco, Y.B. and Ponzo, I. and Bravo-Rodriguez, K. and Erkelenz, M. and Schlücker, S. and Uhlenbrock, G. and Sanchez-Garcia, E. and Saccà, B.
    Science Advances 8 (2022)
    DNA-scaffolded enzymes typically show altered kinetic properties; however, the mechanism behind this phenomenon is still poorly understood. We address this question using thrombin, a model of allosterically regulated serine proteases, encaged into DNA origami cavities with distinct structural and electrostatic features. We compare the hydrolysis of substrates that differ only in their net charge due to a terminal residue far from the cleavage site and presumably involved in the allosteric activation of thrombin. Our data show that the reaction rate is affected by DNA/substrate electrostatic interactions, proportionally to the degree of DNA/enzyme tethering. For substrates of opposite net charge, this leads to an inversion of the catalytic response of the DNA-scaffolded thrombin when compared to its freely diffusing counterpart. Hence, by altering the electrostatic environment nearby the encaged enzyme, DNA nanostructures interfere with charge-dependent mechanisms of enzyme-substrate recognition and may offer an alternative tool to regulate allosteric processes through spatial confinement. © 2022 The Authors.
    view abstractdoi: 10.1126/sciadv.abk0425
  • 2022 • 18 The value of (private) investor relations during the COVID-19 crisis
    Neukirchen, D. and Engelhardt, N. and Krause, M. and Posch, P.N.
    Journal of Banking and Finance (2022)
    We investigate the value of investor relations (IR) and find firms with strong IR to experience between five and eight percentage points higher stock returns than those with weak IR during the COVID-19 crisis. Firms with better-quality IR are also associated with higher investor loyalty and appear to have attracted significantly more institutional investors over the crisis period. This suggests that a firm's IR contributes to value generation by enhancing credibility with shareholders and by diversifying its shareholder base. After decomposing IR into public and private transmission channels, we find the private IR function to be the main driver of our results. © 2022 Elsevier B.V.
    view abstractdoi: 10.1016/j.jbankfin.2022.106450
  • 2022 • 17 Theoretical formulation and computational aspects of a two-scale homogenization scheme combining the TPM and FE2 method for poro-elastic fluid-saturated porous media
    Ricken, T. and Schröder, J. and Bluhm, J. and Bartel, F.
    International Journal of Solids and Structures 241 (2022)
    The focus of this investigation lies on the development of a two-scale homogenization scheme for poro-elastic fluid-saturated porous media. For this purpose, the general concepts of the Theory of Porous Media (TPM) are combined with the FE2 method. After an introduction of the basics of TPM, the weak forms for the macroscopic and the microscopic scale will be formulated and the averaged macroscopic tangent moduli considering the microscale will be derived. Additionally, the formulation of lower level boundary conditions, which refer to the quantities that will be transmitted from the macro- to the microscale, in strict compliance with the Hill–Mandel homogeneity condition, is derived. Finally, a numerical example will be presented, pointing out the gained features of the methodology. © 2021
    view abstractdoi: 10.1016/j.ijsolstr.2021.111412
  • 2022 • 16 Theoretical simulation and experimental verification of dynamic caustic manipulation using a deformable mirror for laser material processing
    Smarra, M. and Gurevich, E.L. and Ostendorf, A.
    Optics and Laser Technology 149 (2022)
    The influence of a deformable mirror on spatial light modulation in ultrafast lasers processing is demonstrated. The deformable mirror was integrated into an optical setup which contains an additional lens for generating a nearly linear focus shift in the focal plane behind the f-theta lens. The deformation of the mirror surface can be described by the Zernike terms Defocus, Astigmatism, and a combination of both, resulting in a cylindric lens behavior. The influence of the mirror surface deformation in this optical setup on the intensity distribution in the focal plane was simulated. From the simulation results, the caustic in the focal plane was calculated. The simulation results were compared to experiments using a picosecond laser with a maximum pulse energy of about 60 µJ. We demonstrate that the initial astigmatism of the raw beam can be reduced using the deformable mirror. A linear focus shift (R2=98.7%) and the generation of elliptical/ line intensity distributions are shown. Line intensity distribution was used to demonstrate slit drilling application in thin metal foils. © 2021
    view abstractdoi: 10.1016/j.optlastec.2021.107814
  • 2022 • 15 Thermoelastic fracture analysis of functionally graded materials using the scaled boundary finite element method
    Iqbal, M.D. and Birk, C. and Ooi, E.T. and Pramod, A.L.N. and Natarajan, S. and Gravenkamp, H. and Song, C.
    Engineering Fracture Mechanics 264 (2022)
    The scaled boundary finite element method is extended to model fracture in functionally graded materials (FGM) under coupled thermo-mechanical loads. The governing equations of coupled thermo-mechanical equilibrium are discretized using scaled boundary shape functions enriched with the thermal load terms. The material gradient is modeled as a series of power functions, and the stiffness matrix is calculated semi-analytically. Stress intensity factors and T−stress are directly calculated from their definition without any need for additional post-processing techniques. Arbitrary-sided polygon elements are employed for flexible mesh generation. Several numerical examples for isotropic and orthotropic FGMs are presented to validate the proposed technique. © 2022 Elsevier Ltd
    view abstractdoi: 10.1016/j.engfracmech.2022.108305
  • 2022 • 14 Tool type and macrostructure for magnetic abrasive finishing of flat surfaces on CNC machine tools
    Zelinko, A. and Welzel, F. and Biermann, D. and Maiboroda, V.
    Production Engineering (2022)
    Magnetic abrasive finishing (MAF) can be used on CNC machine tools as a final machining step to finish workpieces after the milling process. This paper presents a new tool system for the magnetic abrasive finishing of flat surfaces on traditional CNC machine tools using permanent magnets and a paramagnetic adapter without magnetizing the spindle. Five MAF-tool types with variated dimensions, quantity and arrangement of the permanent magnets were developed and tested for machining ferromagnetic materials at different feed rate and equivalent cutting speed. The magnetic flux density was measured for all MAF-tool types with a Hall sensor and the distribution is presented graphically. The benefits of a novel top cover structure for MAF-tools are presented and 20 types of structures were tested as well as divided into three groups. Optimal top cover structures lead to a significant increase in the process capability and a surface roughness reduction for MAF of flat surfaces of ferromagnetic workpieces. Furthermore, the significant influence of the top cover material on the process capability was discovered and a total of seven metal and plastic materials were tested, which were milled from solid material or additively manufactured. © 2022, The Author(s) under exclusive licence to German Academic Society for Production Engineering (WGP).
    view abstractdoi: 10.1007/s11740-021-01097-5
  • 2022 • 13 Transverse magnetic routing of light emission in hybrid plasmonic-semiconductor nanostructures: Towards operation at room temperature
    Klompmaker, L. and Poddubny, A.N. and Yalcin, E. and Litvin, L.V. and Jede, R. and Karczewski, G. and Chusnutdinow, S. and Wojtowicz, T. and Yakovlev, D.R. and Bayer, M. and Akimov, I.A.
    Physical Review Research 4 (2022)
    We study experimentally and theoretically the temperature dependence of transverse magnetic routing of light emission from hybrid plasmonic-semiconductor quantum well structures where the exciton emission from the quantum well is routed into surface plasmon polaritons propagating along a nearby semiconductor-metal interface. In II-VI and III-V direct-band semiconductors the magnitude of routing is governed by the circular polarization of exciton optical transitions, that is induced by a magnetic field. For structures comprising a (Cd,Mn)Te/(Cd,Mg)Te diluted magnetic semiconductor quantum well we observe a strong directionality of the emission up to 15% at low temperature of 20K and magnetic field of 485mT due to giant Zeeman splitting of holes mediated via the strong exchange interaction with Mn2+ ions. For increasing temperatures towards room temperature the magnetic susceptibility decreases and the directionality strongly drops to 4% at about 65 K. We also propose an alternative design based on a nonmagnetic (In,Ga)As/(In,Al)As quantum well structure, suitable for higher temperatures. According to our calculations, such structure can demonstrate emission directionality up to 5% for temperatures below 200 K and moderate magnetic fields of 1 T. © 2022 authors. Published by the American Physical Society.
    view abstractdoi: 10.1103/PhysRevResearch.4.013058
  • 2022 • 12 Tuning the magnetic phase diagram of Ni-Mn-Ga by Cr and Co substitution
    Schröter, M. and Herper, H.C. and Grünebohm, A.
    Journal of Physics D: Applied Physics 55 (2022)
    Ni-Mn-based Heusler alloys have a high technical potential related to a large change of magnetization at the structural phase transition. These alloys show a subtle dependence of magnetic properties and structural phase stability on composition and substitution by 3d elements and although they have been extensively investigated, there are still ambiguities in the published results and their interpretation. To shed light on the large spread of reported properties, we perform a comprehensive study by means of density functional theory calculations. We focus on Cr and Co co-substitution whose benefit has been predicted previously for the expensive Ni-Mn-In-based alloy and study the more abundant iso-electronic counterpart Ni-Mn-Ga. We observe that substituting Ni partially by Co and/or Cr enhances the magnetization of the Heusler alloy and at the same time reduces the structural transition temperature. Thereby, Cr turns out to be more efficient to stabilize the ferromagnetic alignment of the Mn spins by strong antiferromagnetic interactions between Mn and Cr atoms. In a second step, we study Cr on the other sublattices and observe that an increase in the structural transition temperature is possible, but depends critically on the short-range order of Mn and Cr atoms. Based on our results, we are able to estimate composition dependent magnetic phase diagrams. In particular, we demonstrate that neither the atomic configuration with the lowest energy nor the results based on the coherent potential approximation are representative for materials with a homogeneous distribution of atoms and we also predict a simple method for fast screening of different concentrations which can be viewed as a blueprint for the study of high entropy alloys. Our results help to explain the large variation of experimentally found materials properties. © 2021 The Author(s). Published by IOP Publishing Ltd.
    view abstractdoi: 10.1088/1361-6463/ac2a66
  • 2022 • 11 Understanding Alkali Contamination in Colloidal Nanomaterials to Unlock Grain Boundary Impurity Engineering
    Kim, S.-H. and Yoo, S.-H. and Chakraborty, P. and Jeong, J. and Lim, J. and El-Zoka, A.A. and Zhou, X. and Stephenson, L.T. and Hickel, T. and Neugebauer, J. and Scheu, C. and Todorova, M. and Gault, B.
    Journal of the American Chemical Society 144 987-994 (2022)
    Metal nanogels combine a large surface area, a high structural stability, and a high catalytic activity toward a variety of chemical reactions. Their performance is underpinned by the atomic-level distribution of their constituents, yet analyzing their subnanoscale structure and composition to guide property optimization remains extremely challenging. Here, we synthesized Pd nanogels using a conventional wet chemistry route, and a near-atomic-scale analysis reveals that impurities from the reactants (Na and K) are integrated into the grain boundaries of the poly crystalline gel, typically loci of high catalytic activity. We demonstrate that the level of impurities is controlled by the reaction condition. Based on ab initio calculations, we provide a detailed mechanism to explain how surface-bound impurities become trapped at grain boundaries that form as the particles coalesce during synthesis, possibly facilitating their decohesion. If controlled, impurity integration into grain boundaries may offer opportunities for designing new nanogels. © 2022 The Authors. Published by American Chemical Society
    view abstractdoi: 10.1021/jacs.1c11680
  • 2022 • 10 Unexpectedly High Capacitance of the Metal Nanoparticle/Water Interface: Molecular-Level Insights into the Electrical Double Layer
    Azimzadeh Sani, M. and Pavlopoulos, N.G. and Pezzotti, S. and Serva, A. and Cignoni, P. and Linnemann, J. and Salanne, M. and Gaigeot, M.-P. and Tschulik, K.
    Angewandte Chemie - International Edition 61 (2022)
    The electrical double-layer plays a key role in important interfacial electrochemical processes from catalysis to energy storage and corrosion. Therefore, understanding its structure is crucial for the progress of sustainable technologies. We extract new physico-chemical information on the capacitance and structure of the electrical double-layer of platinum and gold nanoparticles at the molecular level, employing single nanoparticle electrochemistry. The charge storage ability of the solid/liquid interface is larger by one order-of-magnitude than predicted by the traditional mean-field models of the double-layer such as the Gouy–Chapman–Stern model. Performing molecular dynamics simulations, we investigate the possible relationship between the measured high capacitance and adsorption strength of the water adlayer formed at the metal surface. These insights may launch the active tuning of solid–solvent and solvent–solvent interactions as an innovative design strategy to transform energy technologies towards superior performance and sustainability. © 2021 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/anie.202112679
  • 2022 • 9 Uniaxially Aligned 1D Sandwich-Molecular Wires: Electronic Structure and Magnetism
    Kraus, S. and Herman, A. and Huttmann, F. and Bianchi, M. and Stan, R.-M. and Holt, A.J. and Tsukamoto, S. and Rothenbach, N. and Ollefs, K. and Dreiser, J. and Bischof, K. and Wende, H. and Hofmann, P. and Atodiresei, N. and Michely, T.
    Journal of Physical Chemistry C 126 3140-3150 (2022)
    Sandwich-molecular wires consisting of europium and cyclooctatetraene (Cot) were grown in situ on the moiré of graphene with Ir(110). The moiré templates a uniaxial alignment of monolayer EuCot nanowire carpets and multilayer films with the EuCot wire axis along the [001] direction of the Ir substrate. Using angle-resolved photoemission spectroscopy, we investigate the band structure of the wire carpet films. While π-derived bands were not observed experimentally, we find a flat band 1.85 eV below the Fermi energy. Using density-functional theory and X-ray photoelectron spectroscopy and replacing europium through barium in the sandwich-molecular wires, it is concluded that the flat band is derived from Eu 4f states weakly mixed with Eu 5d states and slightly overlapping with Cot π states. X-ray magnetic circular dichroism is employed to characterize the magnetic properties of the EuCot wire carpet films at low temperatures. Clear evidence for an easy-axis magnetization along the wires is found. © 2022 American Chemical Society
    view abstractdoi: 10.1021/acs.jpcc.1c10625
  • 2022 • 8 Unravelling Anion Solvation in Water-Alcohol Mixtures by Single Entity Electrochemistry
    Saw, E.N. and Kanokkanchana, K. and Amin, H.M.A. and Tschulik, K.
    ChemElectroChem (2022)
    Single entity electrochemistry is employed to gain insights into ion solvation in solvent mixtures. To this end, the time required for the oxidation of individual indicator nanoparticles to sparingly soluble products is used to probe ionic diffusion, and hence gain new insights into the solvation properties of solvent mixtures. Herein, water-ethanol or water-methanol mixtures of different compositions are analyzed following this new approach, using silver nanoparticle oxidation in the presence of chloride and iodide as a complementary indicator reaction. For increasing concentrations of the bulkier alcohol molecules in the mixtures with water, an increasing content of alcohol molecules in the halide's solvation shell is detected by the observation of hindered halide diffusion. The extent of this solvent replacement is shown to scale with the charge density of the ions and the experimental results are rationalized with respect to literature-derived thermodynamic data, highlighting the ability of single entity electrochemistry to explore solvation in solvent mixtures. © 2022 The Authors. ChemElectroChem published by Wiley-VCH GmbH.
    view abstractdoi: 10.1002/celc.202101435
  • 2022 • 7 Unravelling Composition–Activity–Stability Trends in High Entropy Alloy Electrocatalysts by Using a Data-Guided Combinatorial Synthesis Strategy and Computational Modeling
    Banko, L. and Krysiak, O.A. and Pedersen, J.K. and Xiao, B. and Savan, A. and Löffler, T. and Baha, S. and Rossmeisl, J. and Schuhmann, W. and Ludwig, Al.
    Advanced Energy Materials 12 (2022)
    High entropy alloys (HEA) comprise a huge search space for new electrocatalysts. Next to element combinations, the optimization of the chemical composition is essential for tuning HEA to specific catalytic processes. Simulations of electrocatalytic activity can guide experimental efforts. Yet, the currently available underlying model assumptions do not necessarily align with experimental evidence. To study deviations of theoretical models and experimental data requires statistically relevant datasets. Here, a combinatorial strategy for acquiring large experimental datasets of multi-dimensional composition spaces is presented. Ru–Rh–Pd–Ir–Pt is studied as an exemplary, highly relevant HEA system. Systematic comparison with computed electrochemical activity enables the study of deviations from theoretical model assumptions for compositionally complex solid solutions in the experiment. The results suggest that the experimentally obtained distribution of surface atoms deviates from the ideal distribution of atoms in the model. Leveraging both advanced simulation and large experimental data enables the estimation of electrocatalytic activity and solid-solution stability trends in the 5D composition space of the HEA system. A perspective on future directions for the development of active and stable HEA catalysts is outlined. © 2022 The Authors. Advanced Energy Materials published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/aenm.202103312
  • 2022 • 6 Unravelling the lamellar size-dependent fracture behavior of fully lamellar intermetallic γ-TiAl
    Neogi, A. and Janisch, R.
    Acta Materialia 227 (2022)
    Strengthening of metals by incorporating nano-scale coherent twin boundaries is one of the important breakthroughs of recent years in overcoming the strength-ductility trade-off. To this effect, also twin boundaries in nano-lamellar lightweight Ti-Al alloys promise a great potential, but their contribution to the deformation and fracture behavior needs to be better understood for designing optimal microstructures. To this end, we carry out linear elastic fracture mechanics informed large-scale atomistic simulations of fully lamellar microstructures consisting of the so-called ”true twin” boundaries in γ-TiAl. We find that nano-scale lamellae are not only effective in improving the fracture toughness and crack growth resistance, but also that the lamellar size controls the crack tip mechanisms. We identify a critical lamella thickness in the region between 1.64 and 3.04 nm, above which the crack tip events are primarily dislocation-based plasticity and the critical fracture initiation toughness exhibits an increasing trend with decreasing lamella size. Below the critical thickness, a decline in fracture toughness is observed and the crack tip propagation mechanisms are quasi-brittle in nature, i.e. the cleavage of atomic bonds at the crack tip is accompanied by plasticity events, such as twin-boundary migration and dislocation nucleation. A layer-wise analysis of the unstable stacking fault energy, the energy barrier for dislocation nucleation, that the critical thickness is of a similar value as the distance from the twin boundary at which bulk properties are restored. © 2022
    view abstractdoi: 10.1016/j.actamat.2022.117698
  • 2022 • 5 Unveiling nonmonotonic chemical trends in the solubility of H in complex Fe-Cr-Mn carbides by means of ab initio based approaches
    Sreekala, L. and Dey, P. and Hickel, T. and Neugebauer, J.
    Physical Review Materials 6 (2022)
    The microstructure of advanced high-strength steels often shows a sensitive dependence on alloying. For example, adding Cr to improve the corrosion resistance of medium-Mn steels also enhances the precipitation of carbides. The current study focuses on the behavior of H in such complex multicomponent carbides by employing different methodological strategies. We systematically analyze the impact of Cr, Mn, and Fe using density functional theory (DFT) for two prototype precipitate phases, M3C and M23C6, where M represents the metal sublattice. Our results show that the addition of these alloying elements yields strong nonmonotonic chemical trends for the H solubility. We identify magnetovolume effects as the origin for this behavior, which depend on the considered system, the sites occupied by H, and short- vs long-range interactions between H and the alloying elements. We further show that the H solubility is directly correlated with the occupation of its nearest-neighbor shells by Cr and Mn. Based on these insights, DFT data from H containing binary-metal carbides are used to design a ridge regression based model that predicts the solubility of H in the ternary-metal carbides (Fe-Cr-Mn-C). © 2022 authors. Published by the American Physical Society.
    view abstractdoi: 10.1103/PhysRevMaterials.6.014403
  • 2022 • 4 Use of twin girder auxiliary bridges in the course of an emergency project for crossing the BAB 40 [Einsatz von Zwillingsträgerhilfsbrücken im Zuge einer Notmaßnahme zur Querung der BAB 40]
    Kosky, T. and Zillinger, W. and Shahnazian, A. and Ay, Y. and Stranghöner, N. and Afzali, N. and Makevičius, L. and Ungermann, D. and Kalameya, J.
    Stahlbau 91 72-83 (2022)
    Use of twin girder auxiliary bridges in the course of an emergency project for crossing the BAB 40. On 2020/09/17 a damaged fuel tanker completely burnt-out under a railway bridge over the German motorway A 40 between Duisburg and Mülheim a. d. R. Three out of five bridges had been damaged by the extremely high temperature that the structural and transport safety could no longer be ensured. Therefore the affected railway tracks of the DB Netz AG had to be shut. Immediately after the recording of damages, one bridge structure had been demolished. Due to the immediate detailed design for the replacement and the DB-internal as well as the governmental approvals the erection of the complete structure, including foundations, auxiliary bridges and rail system could be realized in a minimum amount of time. The initial operation of the bridges took place on 2020/12/28 (bridge 3) and 2012/09/06 (bridges 2, 4). Only by the use of twin-girder-auxiliary-bridges type ZH26 of the DB Netz AG the short-term replacement of the damaged bridges could be realized. Subsequent the whole building process is described. The available auxiliary-bridge-systems of the DB Netz AG and their limitations of use are summarized additionally. The use of the auxiliary-bridges as a structural chain as well as the use as permanent makeshift require DB-internal approvals. The required verifications, especially fatigue design, and the therefore required expertise for the durability of the bolted connections are described as well. © 2022, Ernst und Sohn. All rights reserved.
    view abstractdoi: 10.1002/stab.202100103
  • 2022 • 3 WC Decomposition Phenomena in ID-HVOF-Sprayed WC-CoCr Coatings Using Fine Powder Feedstock
    Tillmann, W. and Hagen, L. and Baumann, I. and Paulus, M.
    Coatings 12 (2022)
    Over the last few decades, the high velocity oxygen fuel (HVOF) spraying of WC-CoCr for internal diameter (ID) coating has attracted much interest for hard chrome replacement. Current demands for the ID coating of small cylindrical parts necessitates the use of specialized spray gun equipment and powder feedstocks with small particle size fractions. Due to the limited spray distance inside cylindrical parts with small IDs, the process control, spraying fine WC-CoCr powders, meets new challenges to avoid significant WC decomposition, which increases the risk of mechanical degradation. Within the scope of this study, ID-HVOF spraying using a fine-structured WC-CoCr (−15 + 5 µm) feedstock with a mean WC particle size of 400 nm is examined with respect to the WC decomposition phenomena using X-ray diffraction (XRD). Hence, a statistical design of experiments (DoE) is utilized to systematically analyze various spray parameter settings along with their interaction as part of the WC to W2C conversion. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/coatings12020124
  • 2022 • 2 X-ray Absorption Near-Edge Structure (XANES) at the O K-Edge of Bulk Co3 O4: Experimental and Theoretical Studies
    Kenmoe, S. and Douma, D.H. and Raji, A.T. and M’passi-Mabiala, B. and Götsch, T. and Girgsdies, F. and Knop-Gericke, A. and Schlögl, R. and Spohr, E.
    Nanomaterials 12 (2022)
    We combine theoretical and experimental X-ray absorption near-edge spectroscopy (XANES) to probe the local environment around cationic sites of bulk spinel cobalt tetraoxide (Co3 O4 ). Specifically, we analyse the oxygen K-edge spectrum. We find an excellent agreement between our calculated spectra based on the density functional theory and the projector augmented wave method, previous calculations as well as with the experiment. The oxygen K-edge spectrum shows a strong pre-edge peak which can be ascribed to dipole transitions from O 1s to O 2p states hybridized with the unoccupied 3d states of cobalt atoms. Also, since Co3 O4 contains two types of Co atoms, i.e., Co3+ and Co2+, we find that contribution of Co2+ ions to the pre-edge peak is solely due to single spin-polarized t2g orbitals (dxz, dyz, and dxy ) while that of Co3+ ions is due to spin-up and spin-down polarized eg orbitals (dx2 −y2 andd z2 ). Furthermore, we deduce the magnetic moments on the Co3+ and Co2+ to be zero and 3.00 µB respectively. This is consistent with an earlier experimental study which found that the magnetic structure of Co3 O4 consists of antiferromagnetically ordered Co2+ spins, each of which is surrounded by four nearest neighbours of oppositely directed spins. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/nano12060921
  • 2022 • 1 Zeeman and Davydov splitting of Frenkel excitons in the antiferromagnet CuB2 O4
    Kopteva, N.E. and Kudlacik, D. and Yakovlev, D.R. and Eremin, M.V. and Nurmukhametov, A.R. and Bayer, M. and Pisarev, R.V.
    Physical Review B 105 (2022)
    The optical spectra of antiferromagnetic copper metaborate CuB2O4 are characterized by an exceptionally rich structure of narrow absorption lines due to electronic transitions within the magnetic Cu2+ ions, but their unambiguous identification and behavior in magnetic fields have remained far from being fully understood. We study the polarized magnetoabsorption spectra of this tetragonal antiferromagnet with high spectral resolution across the energy range of 1.4055-1.4065 eV in magnetic fields up to 9.5 T for temperatures from 1.6 up to the Néel temperature TN=20 K. We observe a set of eight absorption lines at T=1.6 K in magnetic fields exceeding 1.4 T, which we identify as arising from Frenkel excitons related to the ground and first excited states of the Cu2+ ions. The number of these excitons is defined by the presence of the four Cu2+ ions with doubly degenerate spin state S=1/2 at the 4b positions in the crystallographic unit cell. The energies of these excitons are determined by the exchange interaction of 0.5 meV of the Cu2+ ions in the excited state with the surrounding ions and by the Davydov splitting of 0.12 meV. In large magnetic field the observed Zeeman splitting is controlled by the anisotropic g-factors of both the ground and excited states. We develop a theoretical model of Frenkel excitons in the magnetic field that accounts for specific features of the spin structure and exchange interactions in CuB2O4. The model is used for fitting the experimental data and evaluation of the Frenkel exciton parameters, such as the Davydov splitting, the molecular exchange energy, and the g-factors of the ground and excited states of the Cu2+ ions. © 2022 American Physical Society.
    view abstractdoi: 10.1103/PhysRevB.105.024421