Scientific Output

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

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

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  • 2021 • 1358 Retrodirective Dielectric Resonator Tag With Polarization Twist Signature for Clutter Suppression in Self-Localization System
    Abbas, A.A. and Hassan, M.H. and Abuelhaija, A. and Erni, D. and Solbach, K. and Kaiser, T.
    IEEE Transactions on Microwave Theory and Techniques (2021)
    In a recently proposed indoor self-localization system, we excite dielectric resonators (DRs) in linear polarization (LP) as retrodirective passive tags, either as single DR, small array of DRs, or in combination with a spherical dielectric lens. DR tags mounted close to a reflecting wall suffer from large clutter return, which can supercede the DR tag signatures. To separate both into orthogonal polarizations, we design a polarization twist tag with two DRs tilted by ±45° and spaced by λ/4. In the EM simulation and experiment, we show that this tag design allows efficient retrodirective scattering in cross polarization. The realized cross-polarization radar cross section (RCS) is equal to the scattering of a single DR in LP and 6 dB better than the RCS from a polarization splitting single DR with 45° tilt. This polarization signature is shown to allow separation of the DR signature from the high scattering level of a flat plate reflector placed behind the polarization twist DR tag. The potential of improving lens-DR combinations by using the polarization twist DR tag with circular polarization is also discussed. IEEE
    view abstractdoi: 10.1109/TMTT.2021.3108151
  • 2021 • 1357 Frequency-coded lens by photonic crystal resonator for mm-wave chipless RFID applications
    Abbas, A.A. and Zantah, Y. and Solbach, K. and Kaiser, T.
    2021 4th International Workshop on Mobile Terahertz Systems, IWMTS 2021 (2021)
    One-dimensional Photonic Crystal (1D PhC) resonator is recently introduced as a good nominee to replace conventional tags at mm-wave and THz bands. For a use of such tags as landmarks in mm-wave indoor self-localization systems, an augmentation of their RCS is required to improve the reading range. As a solution, we propose the integration of a 1D PhC resonator with a dielectric lens (i.e. frequency coded lenses). This concept is demonstrated by locating a 1D PhC resonator in the focal area of a spherical dielectric lens made of PolyPropylene (PP) material with a relative permittivity of 2.0. On the other hand, the PhC resonator is designed by introducing a defect layer between two quarter-wave Bragg mirrors in order to produce a notch signature in the backscattering. Two frequency coded lenses of 24 mm and 40 mm diameter are simulated, fabricated, and experimentally examined. Results show that these coded lenses can achieve 9 dB and 14 dB improvement in RCS, respectively. © 2021 IEEE.
    view abstractdoi: 10.1109/IWMTS51331.2021.9486828
  • 2021 • 1356 Parallel Dislocation Networks and Cottrell Atmospheres Reduce Thermal Conductivity of PbTe Thermoelectrics
    Abdellaoui, L. and Chen, Z. and Yu, Y. and Luo, T. and Hanus, R. and Schwarz, T. and Bueno Villoro, R. and Cojocaru-Mirédin, O. and Snyder, G.J. and Raabe, D. and Pei, Y. and Scheu, C. and Zhang, S.
    Advanced Functional Materials 31 (2021)
    Dislocations play an important role in thermal transport by scattering phonons. Nevertheless, for materials with intrinsically low thermal conductivity, such as thermoelectrics, classical models require exceedingly high numbers of dislocations (>1012 cm–2) to further impede thermal transport. In this work, a significant reduction in thermal conductivity of Na0.025Eu0.03Pb0.945Te is demonstrated at a moderate dislocation density of 1 × 1010 cm–2. Further characteristics of dislocations, including their arrangement, orientation, and local chemistry are shown to be crucial to their phonon-scattering effect and are characterized by correlative microscopy techniques. Electron channeling contrast imaging reveals a uniform distribution of dislocations within individual grains, with parallel lines along four <111> directions. Transmission electron microscopy (TEM) shows the parallel networks are edge-type and share the same Burgers vectors within each group. Atom probe tomography reveals the enrichment of dopant Na at dislocation cores, forming Cottrell atmospheres. The dislocation network is demonstrated to be stable during in situ heating in the TEM. Using the Callaway transport model, it is demonstrated that both parallel arrangement of dislocations and Cottrell atmospheres make dislocations more efficient in phonon scattering. These two mechanisms provide new avenues to lower the thermal conductivity in materials for thermal-insulating applications. © 2021 The Authors. Advanced Functional Materials published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/adfm.202101214
  • 2021 • 1355 Automated assessment of a kinetic database for fcc Co-Cr-Fe-Mn-Ni high entropy alloys
    Abrahams, K. and Zomorodpoosh, S. and Khorasgani, A.R. and Roslyakova, I. and Steinbach, I. and Kundin, J.
    Modelling and Simulation in Materials Science and Engineering 29 (2021)
    The development of accurate kinetic databases by parametrizing the composition and temperature dependence of elemental atomic mobilities, is essential for correct multicomponent calculations and simulations. In this work the automated assessment procedure for the establishment of CALPHAD-type kinetic databases is proposed, including the storage of raw data and assessment results, automatic weighting of data, parameter selection and automated reassessments. This allows the establishment of reproducible up-to-date databases. The proposed software, written in python, is applied to the assessment of a kinetic database for the fcc Co-Cr-Fe-Mn-Ni high entropy alloy using only tracer diffusion data for a sharp separation of thermodynamic and kinetic data. The established database is valid for the whole composition range of the five-component high entropy alloy. © 2021 The Author(s). Published by IOP Publishing Ltd Printed in the UK
    view abstractdoi: 10.1088/1361-651X/abf62b
  • 2021 • 1354 Materials breaking the rules: General discussion
    Addicoat, M. and Bennett, T.D. and Brammer, L. and Craig, G. and Das, C. and Dichtel, W. and Doan, H. and Evans, A.M. and Evans, J. and Goodwin, A. and Horike, S. and Jiang, J. and Kaskel, S. and Kato, M. and Kitagawa, S. and Koba...
    Faraday Discussions 225 255-270 (2021)
    doi: 10.1039/D0FD90033H
  • 2021 • 1353 Positive magnetoresistance and chiral anomaly in exfoliated type-ii weyl semimetal td-wte2
    Adhikari, R. and Adhikari, S. and Faina, B. and Terschanski, M. and Bork, S. and Leimhofer, C. and Cinchetti, M. and Bonanni, A.
    Nanomaterials 11 (2021)
    Layered van der Waals semimetallic Td-WTe2, exhibiting intriguing properties which include non-saturating extreme positive magnetoresistance (MR) and tunable chiral anomaly, has emerged as a model topological type-II Weyl semimetal system. Here, ∼45 nm thick mechanically exfoliated flakes of Td-WTe2 are studied via atomic force microscopy, Raman spectroscopy, low-T/high-µ0 H magnetotransport measurements and optical reflectivity. The contribution of anisotropy of the Fermi liquid state to the origin of the large positive transverse MR⊥ and the signature of chiral anomaly of the type-II Weyl Fermions are reported. The samples are found to be stable in air and no oxidation or degradation of the electronic properties is observed. A transverse MR⊥ ∼1200 % and an average carrier mobility of 5000 cm2 V−1 s−1 at T = 5 K for an applied perpendicular field µ0 H⊥ = 7 T are established. The system follows a Fermi liquid model for T ≤ 50 K and the anisotropy of the Fermi surface is concluded to be at the origin of the observed positive MR. Optical reflectivity measurements confirm the anisotropy of the electronic behaviour. The relative orientation of the crystal axes and of the applied electric and magnetic fields is proven to determine the observed chiral anomaly in the in-plane magnetotransport. The observed chiral anomaly in the WTe2 flakes is found to persist up to T = 120 K, a temperature at least four times higher than the ones reported to date. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/nano11102755
  • 2021 • 1352 A numerical-experimental study on orthogonal cutting of aisi 1045 steel and ti6al4v alloy: Sph and fem modeling with newly identified friction coefficients
    Afrasiabi, M. and Saelzer, J. and Berger, S. and Iovkov, I. and Klippel, H. and Röthlin, M. and Zabel, A. and Biermann, D. and Wegener, K.
    Metals 11 (2021)
    Numerical simulation of metal cutting with rigorous experimental validation is a profitable approach that facilitates process optimization and better productivity. In this work, we apply the Smoothed Particle Hydrodynamics (SPH) and Finite Element Method (FEM) to simulate the chip formation process within a thermo-mechanically coupled framework. A series of cutting experiments on two widely-used workpiece materials, i.e., AISI 1045 steel and Ti6Al4V titanium alloy, is conducted for validation purposes. Furthermore, we present a novel technique to measure the rake face temperature without manipulating the chip flow within the experimental framework, which offers a new quality of the experimental validation of thermal loads in orthogonal metal cutting. All material parameters and friction coefficients are identified in-situ, proposing new values for temperature-dependent and velocity-dependent friction coefficients of AISI 1045 and Ti6Al4V under the cutting conditions. Simulation results show that the choice of friction coefficient has a higher impact on SPH forces than FEM. Average errors of force prediction for SPH and FEM were in the range of 33% and 23%, respectively. Except for the rake face temperature of Ti6Al4V, both SPH and FEM provide accurate predictions of thermal loads with 5–20% error. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/met11111683
  • 2021 • 1351 Influence of process parameters on the residual stress state and properties in disc springs made by incremental sheet forming (ISF) [Einfluss der Prozessparameter auf den Eigenspannungszustand und die Eigenschaften von Tellerfedern, hergestellt durch inkrementelle Blechumformung (IBU)]
    Afzal, M.J. and Hajavifard, R. and Buhl, J. and Walther, F. and Bambach, M.
    Forschung im Ingenieurwesen/Engineering Research (2021)
    Disc springs are machine elements that are used when high forces need to be supplied and in limited installation space. They need to fulfil high demands on the stability of the spring characteristics, reliability and lifetime. In corrosive environments, metastable austenitic stainless steels (MASS) disc springs are often used. Tensile stresses that occur during service limit the lifetime of disc springs. Usually, their durability is enhanced by generating favorable compressive residual stresses using shot peening operations. Such operations lead to extra efforts and additional production costs. In this study, the adaptive and targeted generation of residual stresses via incremental sheet forming (ISF) is investigated as alternative to shot peening focusing on EN 1.4310 and EN 1.4401 stainless steel. Previous work has shown that ISF is capable of controlling the radial and tangential stresses in the springs. However, no analysis of the influence of the residual stress state in the rolled sheet strips and the ISF process parameters was performed. The goal of the current work is to analyze the evolution of residual stress during rolling and subsequent incremental forming of disc springs. In order to examine the role of dissipation and temperature increases in the rolling process, sheet blanks rolled at room and elevated temperature are analyzed. The characteristics of the compressive residual stresses induced by ISF are studied for different process parameters. X‑ray diffraction is used to investigate the buildup of these stresses. Using ISF, the generation of compressive residual stresses can be integrated into the forming process of disc springs, and further post-treatment may be skipped. The results show that the residual stress state in the rolled material is crucial, which requires tight control of the rolling temperature. Another result is that ISF is able to yield high compressive residual stresses and improved spring characteristics when small tool diameters and step-down values are used. © 2021, The Author(s).
    view abstractdoi: 10.1007/s10010-021-00491-w
  • 2021 • 1350 The relationship between charge and molecular dynamics in viscous acid hydrates
    Ahlmann, S. and Münzner, P. and Moch, K. and Sokolov, A.P. and Böhmer, R. and Gainaru, C.
    Journal of Chemical Physics 155 (2021)
    Oscillatory shear rheology has been employed to access the structural rearrangements of deeply supercooled sulfuric acid tetrahydrate (SA4H) and phosphoric acid monohydrate, the latter in protonated (PA1H) and deuterated (PA1D) forms. Their viscoelastic responses are analyzed in relation to their previously investigated electric conductivity. The comparison of the also presently reported dielectric response of deuterated sulfuric acid tetrahydrate (SA4D) and that of its protonated analog SA4H reveals an absence of isotope effects for the charge transport in this hydrate. This finding clearly contrasts with the situation known for PA1H and PA1D. Our analyses also demonstrate that the conductivity relaxation profiles of acid hydrides closely resemble those exhibited by classical ionic electrolytes, even though the charge transport in phosphoric acid hydrates is dominated by proton transfer processes. At variance with this dielectric simplicity, the viscoelastic responses of these materials depend on their structural compositions. While SA4H displays a “simple liquid”-like viscoelastic behavior, the mechanical responses of PA1H and PA1D are more complex, revealing relaxation modes, which are faster than their ubiquitous structural rearrangements. Interestingly, the characteristic rates of these fast mechanical relaxations agree well with the characteristic frequencies of the charge rearrangements probed in the dielectric investigations, suggesting appearance of a proton transfer in mechanical relaxation of phosphoric acid hydrates. These findings open the exciting perspective of exploiting shear rheology to access not only the dynamics of the matrix but also that of the charge carriers in highly viscous decoupled conductors. © 2021 Author(s).
    view abstractdoi: 10.1063/5.0055179
  • 2021 • 1349 Aluminum depletion induced by co-segregation of carbon and boron in a bcc-iron grain boundary
    Ahmadian, A. and Scheiber, D. and Zhou, X. and Gault, B. and Liebscher, C.H. and Romaner, L. and Dehm, G.
    Nature Communications 12 (2021)
    The local variation of grain boundary atomic structure and chemistry caused by segregation of impurities influences the macroscopic properties of polycrystalline materials. Here, the effect of co-segregation of carbon and boron on the depletion of aluminum at a Σ5 (3 1 0)[0 0 1] tilt grain boundary in a α − Fe-4 at%Al bicrystal is studied by combining atomic resolution scanning transmission electron microscopy, atom probe tomography and density functional theory calculations. The atomic grain boundary structural units mostly resemble kite-type motifs and the structure appears disrupted by atomic scale defects. Atom probe tomography reveals that carbon and boron impurities are co-segregating to the grain boundary reaching levels of >1.5 at%, whereas aluminum is locally depleted by approx. 2 at.%. First-principles calculations indicate that carbon and boron exhibit the strongest segregation tendency and their repulsive interaction with aluminum promotes its depletion from the grain boundary. It is also predicted that substitutional segregation of boron atoms may contribute to local distortions of the kite-type structural units. These results suggest that the co-segregation and interaction of interstitial impurities with substitutional solutes strongly influences grain boundary composition and with this the properties of the interface. © 2021, The Author(s).
    view abstractdoi: 10.1038/s41467-021-26197-9
  • 2021 • 1348 Observability of Coulomb-assisted quantum vacuum birefringence
    Ahmadiniaz, N. and Bussmann, M. and Cowan, T.E. and Debus, A. and Kluge, T. and Schützhold, R.
    Physical Review D 104 (2021)
    We consider the scattering of an x-ray free-electron laser (XFEL) beam on the superposition of a strong magnetic field with the Coulomb field of a nucleus with charge number . In contrast to Delbrück scattering (Coulomb field only), the magnetic field introduces an asymmetry (i.e., polarization dependence) and renders the effective interaction volume quite large, while the nuclear Coulomb field facilitates a significant momentum transfer . For a field strength of (corresponding to an intensity of order ) and an XFEL frequency of 24 keV, we find a differential cross section in forward direction for one nucleus. Thus, this effect might be observable in the near future at facilities such as the Helmholtz International Beamline for Extreme Fields at the European XFEL. © 2021 Published by the American Physical Society
    view abstractdoi: 10.1103/PhysRevD.104.L011902
  • 2021 • 1347 Automated image analysis for quantification of materials microstructure evolution
    Ahmed, M. and Horst, O.M. and Obaied, A. and Steinbach, I. and Roslyakova, I.
    Modelling and Simulation in Materials Science and Engineering 29 (2021)
    In this work, an automated image analysis procedure for the quantification of microstructure evolution during creep is proposed for evaluating scanning electron microscopy micrographs of a single crystal Ni-based superalloy before and after creep at 950 °C and 350 MPa. scanning electron microscopy-micrographs of γ/γ′ microstructures are transformed into binary images. Image analysis, which involves pixel by pixel classification and feature extraction, is then combined with a supervised machine learning algorithm to improve the binarization and the quality of the results. The binarization of the gray scale images is not always straight forward, especially when the difference in gray levels between the γ-channels and the γ′-phase is small. To optimize feature extraction, we utilized a series of bilateral filters as well as a machine learning algorithm, known as the gradient boosting method, that was used for training and classifying the micrograph pixels. After testing the two methods, the gradient boosting method was identified as the most effective. Subsequently, a Python routine was written and implemented for the automated quantification of the γ′ area fraction and the γ channel width. Our machine learning method is documented and the results of the automatic procedure are discussed based on results which we previously reported in the literature. © 2021 The Author(s). Published by IOP Publishing Ltd.
    view abstractdoi: 10.1088/1361-651X/abfd1a
  • 2021 • 1346 Preparation and characterization of hydrophilic and antibacterial silver decorated silica-grafted-poly(vinylpyrrolidone) (Ag-SiO2-PVP) nanoparticles for polymeric nanocomposites
    Ahsani, M. and Sabouri, R. and Ulbricht, M. and Hazrati, H. and Jafarizad, A. and Yegani, R.
    Journal of Applied Polymer Science (2021)
    Hydrophilic antibacterial silver decorated silica-grafted-poly(vinylpyrrolidone) (Ag-SiO2-PVP) nanoparticles were successfully synthesized in multiple steps. In this regard, silanization of the silica nanoparticles was performed with different concentrations of vinyltrimethoxysilane (VTS) to generate vinyl groups onto the nanoparticles surface. Obtained results showed that by increasing the VTS concentration the amount of vinyl groups on the surface of the silica nanoparticles increased while nanoparticles agglomeration did not occur. Then, poly(vinylpyrrolidone) PVP brushes were grafted onto the silanized silica nanoparticles (SiO2-VTS) via grafting-through polymerization method to obtain PVP-grafted silica nanoparticles (SiO2-PVP). Fourier transform infrared spectroscopy, thermal gravimetric analysis, and dynamic light scattering confirmed the successful generation of the vinyl groups and PVP brushes onto the silica nanoparticles. Finally, Ag-SiO2-PVP nanoparticles were prepared by synthesizing silver nanoparticles onto the SiO2-PVP nanoparticles to render them antibacterial. Energy dispersive X-ray spectroscopy showed that highest grafting of silver nanoparticles onto the SiO2-PVP nanoparticles was obtained for the nanoparticles with highest content of vinyl groups. X-ray photoelectron spectroscopy was used to identify the elements and their chemical structure for the synthesized nanoparticles. Plate colony counting method was applied to assess the antibacterial effects of the Ag-SiO2-PVP nanoparticles which revealed outstanding bactericidal properties of them. © 2021 Wiley Periodicals LLC.
    view abstractdoi: 10.1002/app.50977
  • 2021 • 1345 Feasibility of graphene-polymer composite membranes for forward osmosis applications
    Akca, S. and Arpaçay, Pi. and McEvoy, N. and Prymak, O. and Blau, W.J. and Ulbricht, M.
    Materials Advances 2 6439-6454 (2021)
    This paper assesses the feasibility of fabricating thin-film composite membranes from stacked graphene nanosheets in combination with a polymer as a selective layer on a macroporous support membrane for utilization in osmosis applications. Reproducible dispersion procedures based on the liquid-phase exfoliation technique have been established to fabricate multi-layer graphene from graphite with the assistance of the high boiling point solvent N-methylpyrrolidone (NMP) or the low boiling point solvent ethanol. A high graphene yield of up to 7.2% with a concentration of 0.36 mg mL-1 was achieved in the NMP-based dispersions. Membrane fabrication toward a graphene-polymer sandwich architecture has been developed, in which graphene laminates modified with or without a chemical cross-linker are placed in between two polyethyleneimine (PEI layers) laminated onto the support membrane (either nylon or polyethersulfone microfiltration membranes). Graphene-polymer composite membranes were successfully fabricated via the pressure-assisted filtration technique and the performance of the membranes was studied in terms of pure water permeability and dextran rejection. The best performing membranes had water permeability varying from 33-77 L m-2 h-1 bar-1 and rejection of dextran 2000 kDa up to 96%; the selective layer has a thickness of ∼1 μm. Forward osmosis experiments with polyacrylic acid sodium salt as draw agent demonstrate the feasibility of using the established graphene-polymer composite membranes for such applications. This journal is © The Royal Society of Chemistry.
    view abstractdoi: 10.1039/d1ma00424g
  • 2021 • 1344 Plasmon-to-exciton spin conversion in semiconductor-metal hybrid nanostructures
    Akimov, I.A. and Poddubny, A.N. and Vondran, J. and Vorobyov, Yu.V. and Litvin, L.V. and Jede, R. and Karczewski, G. and Chusnutdinow, S. and Wojtowicz, T. and Bayer, M.
    Physical Review B 103 (2021)
    Optical spin control is the basis for ultrafast spintronics: circularly polarized light in combination with spin-orbit coupling enables spin manipulation of electronic states in condensed matter. However, the conventional approach is limited to longitudinal spin initialization along one particular axis that is dictated by the direction of light propagation. Here, plasmonics opens new possibilities, allowing one to tailor light polarization at the nanoscale. We demonstrate ultrafast optical excitation of electron spin on femtosecond timescales via plasmon-to-exciton spin conversion. By time resolving the THz spin dynamics in a hybrid (Cd,Mn)Te quantum-well structure covered with a metallic grating, we unambiguously determine the orientation of the photoexcited electron spins which is locked to the propagation direction of the optically excited surface plasmon polaritons. Using the spin of the incident photons as an additional degree of freedom, one can adjust not only the longitudinal, but also the transverse electron spin components normal to the light propagation at will. © 2021 American Physical Society.
    view abstractdoi: 10.1103/PhysRevB.103.085425
  • 2021 • 1343 Finite element modeling of brittle and ductile modes in cutting of 3c-sic
    Alam, M. and Zhao, L. and Vajragupta, N. and Zhang, J. and Hartmaier, A.
    Crystals 11 (2021)
    Machining of brittle ceramics is a challenging task because the requirements on the cutting tools are extremely high and the quality of the machined surface strongly depends on the chosen process parameters. Typically, the efficiency of a machining process increases with the depth of cut or the feed rate of the tool. However, for brittle ceramics, this easily results in very rough surfaces or even in crack formation. The transition from a smooth surface obtained for small depths of cut to a rough surface for larger depths of cut is called a brittle-to-ductile transition in machining. In this work, we investigate the mechanisms of this brittle-to-ductile transition for diamond cutting of an intrinsically brittle 3C-SiC ceramic with finite element modeling. The Drucker–Prager model has been used to describe plastic deformation of the material and the material parameters have been determined by an inverse method to match the deformation behavior of the material under nanoindentation, which is a similar loading state as the one occurring during cutting. Furthermore, a damage model has been introduced to describe material separation during the machining process and also crack initiation in subsurface regions. With this model, grooving simulations of 3C-SiC with a diamond tool have been performed and the deformation and damage mechanisms have been analyzed. Our results reveal a distinct transition between ductile and brittle cutting modes as a function of the depth of cut. The critical depth of cut for this transition is found to be independent of rake angle; however, the surface roughness strongly depends on the rake angle of the tool. © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// 4.0/).
    view abstractdoi: 10.3390/cryst11111286
  • 2021 • 1342 Adhesion area estimation using backscatter image gray level masking of uncoated tungsten carbide tools
    Alammari, Y. and Iovkov, I. and Berger, S. and Saelzer, J. and Biermann, D.
    Wear 476 (2021)
    Machining tribology research reveals that adhesion of the workpiece material to the cutting tool is an important aspect that governs a number of physical parameters within the tool-chip interface. Adhesion is especially a concern during machining difficult-to-cut materials such as nickel-based alloys. Adhesion may cause tool wear that leads to premature tool failure, or it may trigger other wear modes, hindering machinability and reducing product quality. Many researchers are investigating adhesion fundamentals, adhesion quantification being an indispensable tool. The research suggests strategies to reduce adhesion's undesirable effects. However, when many experimental trials are required, time-consuming adhesion quantification may cause a bottleneck. This study proposes an efficient adhesion area quantification method using image processing of discrete gray intensities on backscatter images of uncoated tungsten carbide inserts, revealed by scanning inserts through an electron microscope. The obtained images are analyzed statistically from their gray-level intensity distribution. A recognizable gray-level range, located around a peak in the histogram, corresponds to adhered material and can easily be distinguished from the background tool material. Hence, adhesion pixels are masked and counted in a statistically controlled manner. The total adhesion area is subsequently quantified by summing the total number of adhesion pixel areas. This method is applied to quantify the resulting adhesion for a variation of the cutting speed, based on a number of orthogonal machining trials carried out on nickel-based superalloy NiCr19Fe19Nb5Mo3 (2.4668), using uncoated tungsten carbide inserts. K-means clustering algorithm is applied for image segmentation, and elemental mapping is obtained by energy dispersive x-ray spectroscopy; both are used to evaluate the effectiveness of the proposed method. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.wear.2021.203666
  • 2021 • 1341 Adhesion of Inconel 718 on Uncoated Tungsten Carbide Inserts in Interrupted Orthogonal Machining under MQL
    Alammari, Y. and Iovkov, I. and Saelzer, J. and Wolf, T. and Biermann, D.
    Procedia CIRP 103 194-199 (2021)
    Nickel-base super-alloys such as Inconel 718 are used for demanding applications in the industry. Their superior corrosion resistance and mechanical properties, especially under high heat and pressure, make them very attractive for highly stressed components. In contrast, their low thermal conductivity, work hardening tendency and high strength impose challenges for machining. In particular, occurring adhesion of the workpiece material on tungsten carbide (WC) inserts and tools is common hindering their life. In order to counteract this undesirable effect, cutting fluids are usually implemented. However, due to increased awareness of cutting fluids negative impact on the operator's health and the environment, minimum quantity lubrication (MQL) is getting more attention among researchers and in the industry. In this study, the adhesion on the rake face of uncoated WC inserts under the application of MQL is observed. Inconel 718 workpieces prepared for orthogonal cutting trials are interrupted at variable intervals to allow more access for MQL to reach chip-tool interface. Mechanical load, coefficient of friction, adhesion area and chip-tool contact length on the rake face are investigated. It has been observed that interrupted machining can positively influence adhesion area and chip-tool contact length. © 2021 The Authors. Published by Elsevier B.V.
    view abstractdoi: 10.1016/j.procir.2021.10.031
  • 2021 • 1340 CHAPTER 6: Molecular Tweezers and Clips that Modify Protein Function
    Alavijeh, N.S. and Kirupakaran, A. and Klärner, F.-G. and Schrader, T.
    Monographs in Supramolecular Chemistry 2021-January 161-198 (2021)
    Protein recognition by designed protein ligands is highly challenging, but bears great opportunities. Supramolecular chemists have recently been able to synthesize tailored ligands with remarkable protein recognition properties which are absent in the natural binding partners, and which lead to synergistic effects, positive cooperativity and exquisite selectivity. Thus, the combination of powerful charged interactions with hydrophobic forces has recently led to new prototypes of protein surface binders. This review summarizes the development of molecular tweezers (part 1) and clips (part 2) as unique tools for protein recognition. The parts begin with molecular tweezers for basic amino acid inclusion and the discovery of diphosphate clips for efficient cofactor binding, respectively. Gratifyingly, both host molecules complement each other due to their different molecular shapes. Molecular tweezers will be presented first in their interaction with amino acids and small disordered peptides, where they generally complex each Lys and Arg; then the review will proceed to tweezer complexation with protein surfaces, elucidating the preference for well-accessible basic residues and various examples of protein targeting and interference with protein-protein interactions. Finally, we discuss the advantages of additional recognition elements on the tweezer skeleton, which opens the door to numerous advanced applications in chemical biology and drug discovery. For the clips, we describe in detail the inclusion of two important cationic cofactors, followed by applications on cofactor-mediated enzymatic processes. © The Royal Society of Chemistry 2021.
    view abstractdoi: 10.1039/9781788019798-00161
  • 2021 • 1339 Analysis and Modelling of the Antenna Mode and Structural Mode Scattering of a Dielectric Resonator
    Alhaj Abbas, A. and Khaliel, M. and Abuelhaija, A. and El-Absi, M. and Alam, J. and Solbach, K. and Kaiser, T.
    15th European Conference on Antennas and Propagation, EuCAP 2021 (2021)
    This paper presents an analysis of the backscattering of a dielectric resonator (DR) due to the antenna mode and the structural mode. More specifically, we focus on the structural mode scattering since the discussion of the RCS of DRs in the past has concentrated on analyzing the 'Eigenmodes' only. Therefore, we present evidence for its existence and provide a qualitative and quantitative approximation. It is found that the structural scattering of a DR with high rel. permittivity can be approximated by the scattering of a metal body of the same dimensions as the DR. Furthermore, a mathematical model of the antenna mode scattering is provided using the multipole expansion and with the aid of filter theory. As a result of the superposition of both scattering modes, it is found that the structural mode scattering slightly alters the appearance of the 'Eigenmodes' in frequency position, scattering level, quality factor, and shape. © 2021 EurAAP.
    view abstractdoi: 10.23919/EuCAP51087.2021.9411078
  • 2021 • 1338 Corner reflector tag with RCS frequency coding by dielectric resonators
    Alhaj Abbas, A. and El-Absi, M. and Abuelhaija, A. and Solbach, K. and Kaiser, T.
    IET Microwaves, Antennas and Propagation 15 560-570 (2021)
    For a novel indoor-localization system, chipless tags with high retro-directive radar cross-section (RCS) under wide-angle incidence are required as fixed landmarks. Tags based on dielectric resonators (DRs) were proposed to provide identification by resonance frequency coding. To achieve a satisfactory read range for the localization system, the low RCS levels of these tags require a major boost. A solution was found by adopting the metallic corner reflector which is known for high RCS levels over a wide bandwidth and over a wide angle of incidence. The study presents a novel corner reflector design where notches in the RCS spectral signature are created by the attachment of arrays of dielectric resonators to the metallic surfaces of corner reflectors. It is shown that notches appear due to the increased scattering of the resonators at resonance and by the power loss due to grating lobes formed in addition to the specular reflection from the arrays and from the metallic surfaces. Results from electromagnetic simulations are verified by measurements of an example dihedral corner reflector of 100 × 100 mm2 plate size with two arrays of 3 × 3 DRs producing a notch signature at about 7 GHz. © 2021 The Authors. IET Microwaves, Antennas & Propagation published by John Wiley & Sons Ltd on behalf of The Institution of Engineering and Technology.
    view abstractdoi: 10.1049/mia2.12067
  • 2021 • 1337 Optimal Designs for Model Averaging in non-nested Models
    Alhorn, K. and Dette, H. and Schorning, K.
    Sankhya A (2021)
    In this paper we construct optimal designs for frequentist model averaging estimation. We derive the asymptotic distribution of the model averaging estimate with fixed weights in the case where the competing models are non-nested. A Bayesian optimal design minimizes an expectation of the asymptotic mean squared error of the model averaging estimate calculated with respect to a suitable prior distribution. We derive a necessary condition for the optimality of a given design with respect to this new criterion. We demonstrate that Bayesian optimal designs can improve the accuracy of model averaging substantially. Moreover, the derived designs also improve the accuracy of estimation in a model selected by model selection and model averaging estimates with random weights. © 2021, The Author(s).
    view abstractdoi: 10.1007/s13171-020-00238-9
  • 2021 • 1336 Optimal designs for model averaging in non-nested models
    Alhorn, K. and Schorning, K. and Dette, H.
    Sankhya: The Indian Journal of Statistics 83 745-778 (2021)
    In this paper we construct optimal designs for frequentist model averaging estimation. We derive the asymptotic distribution of the model averaging estimate with fixed weights in the case where the competing models are non-nested. A Bayesian optimal design minimizes an expectation of the asymptotic mean squared error of the model averaging estimate calculated with respect to a suitable prior distribution. We derive a necessary condi-tion for the optimality of a given design with respect to this new criterion. We demonstrate that Bayesian optimal designs can improve the accuracy of model averaging substantially. Moreover, the derived designs also improve the accuracy of estimation in a model selected by model selection and model averaging estimates with random weights. © 2021, The Author(s).
    view abstract
  • 2021 • 1335 Nitrogen and phosphorous modified compounds for sol-gel-based flame retardants
    Ali, W. and Shabani, V. and Gutmann, J.S. and Mayer-Call, T. and Etemad-Parishanadeh, O. and Salma, A. and Textor, T.
    Melliand International 27 37-39 (2021)
    In the IGF project No. 19617 N, nitrogen and phosphorus substituted alkoxysilanes were prepared and their ability to inhibit fire growth and spread for fabrics was explored. To this end, a series of flame retardants were synthesized using different strategies including click chemistry and nucleophilic substitution of commercial organophosphorus compounds with amino-based trialkoxysilanes and/or cyanuric chloride. The new halogen-free and aldehyde-free flame retardants were applied to different fabrics such as cotton (CO), polyethylene terephthalate (PET), polyamide (PA) and their blends using the well-known industrial pad-dry-cure technique and sol-gel method. The flame-retarding efficiencies were evaluated by EN ISO 15025 test methods (protective clothing-protection against heat and flame method of test for limited flame spread). Good flame retardancy of the hybrid organic-inorganic materials was achieved with addition of as small amount as 3-5 wt.°/o for cotton fabrics. Moreover, the water solubility and the washing resistance could be controlled through the functional groups attached to the phosphor atom or through the optimization of the curing temperature. Overall, the research project demonstrated that N-P-silanes are very good permanent flame retardants for textiles. © 2021 Deutscher Fachverlag GmbH. All rights reserved.
    view abstract
  • 2021 • 1334 Spray flame synthesis (Sfs) of lithium lanthanum zirconate (llzo) solid electrolyte
    Ali, M.Y. and Orthner, H. and Wiggers, H.
    Materials 14 (2021)
    A spray-flame reaction step followed by a short 1-h sintering step under O2 atmosphere was used to synthesize nanocrystalline cubic Al-doped Li7La3Zr2O12 (LLZO). The as-synthesized nanoparticles from spray-flame synthesis consisted of the crystalline La2Zr2O7 (LZO) pyrochlore phase while Li was present on the nanoparticles’ surface as amorphous carbonate. However, a short annealing step was sufficient to obtain phase pure cubic LLZO. To investigate whether the initial mixing of all cations is mandatory for synthesizing nanoparticulate cubic LLZO, we also synthesized Li free LZO and subsequently added different solid Li precursors before the annealing step. The resulting materials were all tetragonal LLZO (I41 /acd) instead of the intended cubic phase, suggesting that an intimate intermixing of the Li precursor during the spray-flame synthesis is mandatory to form a nanoscale product. Based on these results, we propose a model to describe the spray-flame based synthesis process, considering the precipitation of LZO and the subsequent condensation of lithium carbonate on the particles’ surface. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/ma14133472
  • 2021 • 1333 RF Analysis of a Sub-GHz InP-Based 1550 nm Monolithic Mode-Locked Laser Chip
    Ali Alloush, M. and Van Delden, M. and Bassal, A. and Kleemann, N. and Brenner, C. and Lo, M. and Augustin, L. and Guzman, R. and Musch, T. and Carpintero, G. and Hofmann, M.R.
    IEEE Photonics Technology Letters (2021)
    We report a monolithic sub-GHz repetition rate mode-locked laser with record low pulse-to-pulse RMS timing jitter of 3.65 ps in the passive mode locking regime. We analyse the optical pulse generation in passive and hybrid mode-locking operating regimes, finding narrower RF tone linewidth in the passive regime, attributed to the improved contact structure of the gain sections. The noise performance is also characterized in passive and hybrid regimes, showing RMS integrated timing jitter of approximately 600 fs. For hybrid modelocking, the repetition rate can be varied over a large range from 880 to 990 MHz. We observe broad pulse widths of few hundred picoseconds attributed to the (long folded) waveguide architecture and on-chip multimode interference mirrors. This device subjects a stand-alone, ultra-compact, mode-locking based clock source to realize frequency synthesizers operating over a frequency range from sub-GHz up to approximately 15 GHz. IEEE
    view abstractdoi: 10.1109/LPT.2021.3083096
  • 2021 • 1332 Femtosecond pulse generation from external cavity diode laser based on self-mode-locking
    Alloush, M.A. and Brenner, C. and Calò, C. and Hofmann, M.R.
    Optics letters 46 344-347 (2021)
    In this Letter, we report optical pulse generation from a single-section diode gain chip, employed in an external cavity geometry based on the self-mode-locking regime. The gain chip emits light at 1550 nm wavelength range. The external cavity is operated at various repetition rates, ranging from 1 to 2.5 GHz. An optical pulse width of approximately 650 fs is obtained by fitting a Lorentzian distribution. A low RF spectral width of 78.875 kHz is measured corresponding to a low pulse-to-pulse RMS timing jitter of 1.273 ps. This system paves the way towards ultra-compact, cost-effective, and chirp-compensated femtosecond laser pulse sources with adjustable repetition rates.
    view abstractdoi: 10.1364/OL.415336
  • 2021 • 1331 Quantifying the Absorption Onset in the Quantum Efficiency of Emerging Photovoltaic Devices
    Almora, O. and Cabrera, C.I. and Garcia-Cerrillo, J. and Kirchartz, T. and Rau, U. and Brabec, C.J.
    Advanced Energy Materials 11 (2021)
    The external quantum efficiency (EQE), also known as incident-photon-to-collected-electron spectra are typically used to access the energy dependent photocurrent losses for photovoltaic devices. The integral over the EQE spectrum results in the theoretical short-circuit current under a given incident illumination spectrum. Additionally, one can also estimate the photovoltaic bandgap energy (Eg) from the inflection point in the absorption threshold region. The latter has recently been implemented in the “Emerging PV reports,” where the highest power conversion efficiencies are listed for different application categories, as a function of Eg. Furthermore, the device performance is put into perspective thereby relating it to the corresponding theoretical limit in the Shockley–Queisser (SQ) model. Here, the evaluation of the EQE spectrum through the sigmoid function is discussed and proven to effectively report the Eg value and the sigmoid wavelength range λs, which quantifies the steepness of the absorption onset. It is also shown how EQE spectra with large λs indicate significant photovoltage losses and present the corresponding implications on the photocurrent SQ model. Similarly, the difference between the photovoltaic and optical bandgap is analyzed in terms of λs. © 2021 The Authors. Advanced Energy Materials published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/aenm.202100022
  • 2021 • 1330 Soil-Building Interaction and Risk Assessment of Existing Structures During Mechanized Tunneling
    Alsahly, A. and Marwan, A. and Obel, M. and Mark, P. and Meschke, G.
    Lecture Notes in Civil Engineering 126 139-147 (2021)
    During the planning phase of tunneling projects, in particular in urban areas, it is crucial to assess the likely extent of structural damage caused by the tunnel construction in close vicinity to existing surface structures. Tunneling inevitably causes ground movements which in turn may have an impact on deformations and stresses of the above-ground structures. For this reason, a reliable estimate of the soil-structure interactions due to tunnelling-induced settlements is essential. In this contribution, various approaches that differ in precision and complexity are employed to predict the magnitude of expected settlements and the vulnerability of structures with regard to tunneling induced damage. In addition, a three-step damage assessment concept adjustable to the necessary level of detail is suggested. Firstly, ground movements are predicted using analytical or numerical approaches. Secondly, the above-ground structures are idealized by means of surrogate beam-, slab- or 3D-models. Finally, structural damage is assessed according to the computed strain pattern or the tilt of the building. This method enables the evaluation of the potential damage to above ground structures associated with planned tunnel alignment. When developing 3D numerical models, the main focus will be to ensure that the building and the soil-structure interactions are represented with an appropriate level of detail. To this end, this paper aims to provide recommendations for a sufficient level of detail (LOD) of surface structures for the assessment of tunneling induced damage in computational simulations in mechanized tunneling. © 2021, The Author(s), under exclusive license to Springer Nature Switzerland AG.
    view abstractdoi: 10.1007/978-3-030-64518-2_17
  • 2021 • 1329 Single-Particle Hyperspectral Imaging Reveals Kinetics of Silver Ion Leaching from Alloy Nanoparticles
    Al-Zubeidi, A. and Stein, F. and Flatebo, C. and Rehbock, C. and Hosseini Jebeli, S.A. and Landes, C.F. and Barcikowski, S. and Link, S.
    ACS Nano 15 8363-8375 (2021)
    Gold-silver alloy nanoparticles are interesting for multiple applications, including heterogeneous catalysis, optical sensing, and antimicrobial properties. The inert element gold acts as a stabilizer for silver to prevent particle corrosion, or conversely, to control the release kinetics of antimicrobial silver ions for long-term efficiency at minimum cytotoxicity. However, little is known about the kinetics of silver ion leaching from bimetallic nanoparticles and how it is correlated with silver content, especially not on a single-particle level. To characterize the kinetics of silver ion release from gold-silver alloy nanoparticles, we employed a combination of electron microscopy and single-particle hyperspectral imaging with an acquisition speed fast enough to capture the irreversible silver ion leaching. Single-particle leaching profiles revealed a reduction in silver ion leaching rate due to the alloying with gold as well as two leaching stages, with a large heterogeneity in rate constants. We modeled the initial leaching stage as a shrinking-particle with a rate constant that exponentially depends on the silver content. The second, slower leaching stage is controlled by the electrochemical oxidation potential of the alloy being steadily increased by the change in relative gold content and diffusion of silver atoms through the lattice. Interestingly, individual nanoparticles with similar sizes and compositions exhibited completely different silver ion leaching yields. Most nanoparticles released silver completely, but 25% of them appeared to arrest leaching. Additionally, nanoparticles became slightly porous. Alloy nanoparticles, produced by scalable laser ablation in liquid, together with kinetic studies of silver ion leaching, provide an approach to design the durability or bioactivity of alloy nanoparticles. ©
    view abstractdoi: 10.1021/acsnano.0c10150
  • 2021 • 1328 Simulative investigation of the application of nonimpregnated activated carbon in a multilayer adsorber for the separation of Hg0 from discontinuous waste gas streams
    Ambrosy, J.M. and Steinhaus, J. and Pasel, C. and Bläker, C. and Bittig, M. and Bathen, D.
    Industrial and Engineering Chemistry Research 60 4097-4109 (2021)
    In technical processes, fixed-bed adsorbers with impregnated activated carbon are used for chemisorptive mercury separation. In the case of discontinuous waste gas streams with strongly varying mercury concentrations (e.g., in crematories or metal-recycling plants), mercury may quickly break through the impregnated activated carbon layer due to the slow kinetics of chemisorptive adsorption. Under these conditions a promising purification concept is a multilayer adsorber. In the first layer, strongly fluctuating mercury concentrations should first be smoothed by physical adsorption and desorption on nonimpregnated activated carbon before the mercury is completely separated in the second layer of impregnated activated carbon by chemisorption. In this paper, experimentally validated dynamic simulations are used to show that, under suitable operating conditions and design parameters, effective smoothing of fluctuating mercury concentrations is possible in the first layer of a multilayer adsorber with nonimpregnated activated carbons. © 2021 The Authors. Published by American Chemical Society.
    view abstractdoi: 10.1021/acs.iecr.0c06149
  • 2021 • 1327 Tailoring the Electrocatalytic Activity of Pentlandite FexNi9-XS8 Nanoparticles via Variation of the Fe : Ni Ratio for Enhanced Water Oxidation
    Amin, H.M.A. and Attia, M. and Tetzlaff, D. and Apfel, U.-P.
    ChemElectroChem 8 3863-3874 (2021)
    The development of efficient and cost-effective electrocatalytic materials is an important part in scaling up sustainable electrochemical energy devices such as electrolyzers and fuel cells. In particular, the sluggish kinetics of the oxygen evolution reaction (OER) during water splitting renders the need of a catalyst indispensable. However, the development of catalysts is often based on laboratorial trial-and-error approaches and complex synthetic routes. Herein, the facile and systematic synthesis of pentlandite-like FexNi9-xS8 (x=0–9) nanosized particles from its elements with distinct Fe: Ni ratios was achieved using a mechanochemical method. The OER performance is optimized through tailoring the surface properties via altering the catalyst composition. The catalytic activity increases with higher nickel content in the structure, accomplishing an overpotential of 354 and 420 mV for ‘Ni9S8’ to drive 10 and 100 mA cm−2, respectively, with high stability. The in-situ formed nickel oxide/hydroxide species concurrent with sulphur depletion from the pentlandite structure upon OER are more active than NiS, inferring the crucial role of the pentlandite structure in activity. The herein reported simple synthetic approach could bring significant progress in the catalyst material development via rationally screening pentlandites with desired properties for modern energy systems. © 2021 The Authors. ChemElectroChem published by Wiley-VCH GmbH.
    view abstractdoi: 10.1002/celc.202100713
  • 2021 • 1326 Mechanochemical Synthesis of Catalytic Materials
    Amrute, A.P. and De Bellis, J. and Felderhoff, M. and Schüth, F.
    Chemistry - A European Journal (2021)
    The mechanochemical synthesis of nanomaterials for catalytic applications is a growing research field due to its simplicity, scalability, and eco-friendliness. Besides, it provides materials with distinct features, such as nanocrystallinity, high defect concentration, and close interaction of the components in a system, which are, in most cases, unattainable by conventional routes. Consequently, this research field has recently become highly popular, particularly for the preparation of catalytic materials for various applications, ranging from chemical production over energy conversion catalysis to environmental protection. In this Review, recent studies on mechanochemistry for the synthesis of catalytic materials are discussed. Emphasis is placed on the straightforwardness of the mechanochemical route—in contrast to more conventional synthesis—in fabricating the materials, which otherwise often require harsh conditions. Distinct material properties achieved by mechanochemistry are related to their improved catalytic performance. © 2021 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/chem.202004583
  • 2021 • 1325 Catalytic reactions in ball mills
    Amrute, A.P. and Schüth, F.
    Catalysis 33 307-346 (2021)
    Over the past two decades mechanochemistry has emerged as an important tool in catalysis research. It has not only shown promise for catalyst synthesis, resulting in properties that are often unattainable by conventional methods, but is also a very effective tool for performing catalytic reactions with exceptional selectivities. Besides, in several instances, it allows reactions under much milder conditions compared to thermochemical methods. In this chapter, we attempt to give an overview of these efforts with a focus on catalytic reactions in ball mills. Through the selection of prominent examples from the literature, from early mentions in 300 B.C. to recent times, we try to analyze how mechanical forces lead to chemical reactions and what effect they cause to materials or chemical reactions. We also discuss the state-of-the-art milling devices, and then cover broadly chemical reactions in ball mills. The latter part briefly tackles materials synthesis, but mainly focuses on chemical reactions of solid-solid and gas-solid nature from both organic synthesis and heterogeneous catalysis. The chapter also touches on the aspects of in situ analysis and scale-up with relevant literature. The latter areas are currently in the focus of attention to develop deeper understanding and to eventually find ways to make mechanocatalysis industrially applicable. © The Royal Society of Chemistry 2021.
    view abstractdoi: 10.1039/9781839163128-00307
  • 2021 • 1324 Evolution of the magnetic hyperfine field profiles in an ion-irradiated Fe60Al40film measured by nuclear resonant reflectivity
    Andreeva, M. and Smekhova, A. and Baulin, R. and Repchenko, Y. and Bali, R. and Schmitz-Antoniak, C. and Wende, H. and Sergueev, I. and Schlage, K. and Wille, H.-C.
    Journal of Synchrotron Radiation 28 1535-1543 (2021)
    Nuclear resonant reflectivity (NRR) from an Fe60zAl40film was measured using synchrotron radiation at several grazing angles near the critical angle of total external reflection. Using laterally resolved measurements after irradiation with 20keV Ne+ions of gradually varying fluence of 0-3.0×1014ionscm-2, the progressive creation of the ferromagnetic A2 phase with increasing ion fluence was confirmed. The observed depth selectivity of the method has been explained by application of the standing wave approach. From the time spectra of the nuclear resonant scattering in several reflection directions the depth profiles for different hyperfine fields were extracted. The results show that the highest magnetic hyperfine fields (∼18-23 T) are initially created in the central part of the film and partially at the bottom interface with the SiO2 substrate. The evolution of the ferromagnetic onset, commencing at a fixed depth within the film and propagating towards the interfaces, has been directly observed. At higher fluence (3.0 × 1014ions cm-2) the depth distribution of the ferro­magnetic fractions became more homogeneous across the film depth, in accordance with previous results. © 2021 International Union of Crystallography. All rights reserved.
    view abstractdoi: 10.1107/S1600577521007694
  • 2021 • 1323 Electrocatalysis in confined space
    Andronescu, C. and Masa, J. and Tilley, R.D. and Gooding, J.J. and Schuhmann, W.
    Current Opinion in Electrochemistry 25 (2021)
    The complex interplay of restricted mass transport leading to local accumulation or depletion of educts, intermediates, products, counterions and co-ions influences the reactions at the active sites of electrocatalysts when electrodes are rough, three-dimensionally mesoporous or nanoporous. This influence is important with regard to activity, and even more to selectivity, of electrocatalytic reactions. The underlying principles are discussed based on the growing awareness of these considerations over recent years. © 2020 Elsevier B.V.
    view abstractdoi: 10.1016/j.coelec.2020.100644
  • 2021 • 1322 Celebrating Wolfgang Schuhmann's 65th Birthday
    Andronescu, C. and Masa, J. and Gooding, J.J.
    ChemElectroChem (2021)
    doi: 10.1002/celc.202101368
  • 2021 • 1321 Spray-Flame Synthesis of LaMnO3+δNanoparticles for Selective CO Oxidation (SELOX)
    Angel, S. and Tapia, J.D. and Gallego, J. and Hagemann, U. and Wiggers, H.
    Energy and Fuels (2021)
    LaMnO3+δ nanoperovskites were prepared via the continuous and scalable spray-flame synthesis (SFS) technique from metal nitrate-based solutions by using either ethanol (EtOH) as solvent or a mixture of ethanol (50 vol %) and 2-ethylhexanoic acid (50 vol %) (EtOH/2-EHA). Solutions based on pure EtOH generated a mixture of several phases and a broad and multimodal particle size distribution, which is attributed to a combination of gas-to-particle and droplet-to particle formation of particles. The product contained a bimodal distribution of the orthorhombic (Pnma II) LaMnO3 perovskite-like phase and additional, unwanted phases such as La2O3 and sub-20 nm Mn-rich amorphous/poorly crystalline particles. The incorporation of 2-EHA led to high surface area (>100 m2 g-1), small, and crystalline LaMnO3+δ nanoparticles with sizes ranging between 4 and 15 nm in the presence of few sub-200 nm particles (<10 wt %). This sample is mainly composed of the orthorhombic Mn4+ rich (Pnma I) LaMnO3+δ phase, and it counts with a very high specific surface area that makes it highly promising for catalytic applications. FTIR and UV-VIS spectroscopy of the precursor solutions revealed the oxidation of the Mn2+ precursor in advance of the particle formation process along with the esterification of the solvent mixture. It is assumed that the observed liquid-phase oxidation supports the formation of Mn4+-rich perovskites. According to O2-TPD and H2-TPR measurements, the EtOH/2-EHA sample presented a much higher formation of adsorbed active oxygen species and higher reducibility than the EtOH-made material, leading to a superior performance for both the catalytic oxidation of CO and the selective oxidation (SELOX) of CO. © 2021 American Chemical Society.
    view abstractdoi: 10.1021/acs.energyfuels.0c03659
  • 2021 • 1320 Spray-flame synthesis of LaMO3(M = Mn, Fe, Co) perovskite nanomaterials: Effect of spray droplet size and esterification on particle size distribution
    Angel, S. and Schneider, F. and Apazeller, S. and Kaziur-Cegla, W. and Schmidt, T.C. and Schulz, C. and Wiggers, H.
    Proceedings of the Combustion Institute 38 1279-1287 (2021)
    Perovskite nanomaterials such as LaMnO3, LaFeO3, and LaCoO3were synthesized in a spray flame from metal nitrates dissolved in combustible liquids. The addition of low-boiling solvents such as 2-ethylhexanoic acid (2-EHA) to the ethanol-based solutions supports the formation of phase-pure particles with unimodal particle-size distribution in the 10-nm range attributed to enhanced evaporation through micro-explosions. Nevertheless, in many cases, a second particle mode with sizes of a few hundred nanometers is formed. In this paper, we investigate two possible reasons for the appearance of large particles. Firstly, we analyze the effect of the oxygen dispersion gas flow applied in the two-fluid nozzle on the droplet size distributions of burning sprays using phase Doppler anemometry. We identified that an increase of the dispersion gas flow significantly decreases the number concentration of large droplets (&gt;30 μm), which causes a significant increase of the BET surface area of as-synthesized LaMnO3and LaCoO3with increasing dispersion gas flow from 60 m2/g (5 slm dispersion gas) to 100 m2/g (8 slm). Secondly, the esterification in the mixture of solvents towards ethyl-2-ethylhexanoate, which is associated with the release of water as a byproduct, was analyzed by GC/MS. The ester concentration in the iron-containing solution was found to be up to nine times higher than in cobalt or manganese precursor solutions. Simultaneously, the produced LaFeO3materials show lower BET surface areas and the increasing dispersion gas flow has a minor effect on this material than on the cobalt and manganese perovskite cases. We attribute this to the fact that water formed during esterification forces the hydrolysis of iron nitrate and the formation of large particles within the droplets. © 2021 Elsevier Ltd. All rights reserved.
    view abstractdoi: 10.1016/j.proci.2020.07.116
  • 2021 • 1319 Anisotropic expansion of drifting spin helices in GaAs quantum wells
    Anghel, S. and Poshakinskiy, A.V. and Schiller, K. and Passmann, F. and Ruppert, C. and Tarasenko, S.A. and Yusa, G. and Mano, T. and Noda, T. and Betz, M.
    Physical Review B 103 (2021)
    The drift of electron spin helices in an external in-plane electric field in GaAs quantum wells is studied by means of time-resolved magneto-optical Kerr microscopy. The evolution of the spin distribution measured for different excitation powers reveals that, for short delay times and higher excitation powers, the spin helix drift slows down while its envelope becomes anisotropic. The effect is understood as a local decrease of the electron gas mobility due to electron collisions with nonequilibrium holes within the excitation spot and is reproduced well in the kinetic theory framework. For larger delay times, when the electrons constituting the spin helix and nonequilibrium holes are separated by an electric field, the spin helix drift accelerates and the mobility reaches its unperturbed value again. © 2021 American Physical Society.
    view abstractdoi: 10.1103/PhysRevB.103.035429
  • 2021 • 1318 Nucleation and growth of α phase in a metastable β-Titanium Ti-5Al-5Mo-5V-3Cr alloy: Influence from the nano-scale, ordered-orthorhombic O″ phase and α compositional evolution
    Antonov, S. and Shi, R. and Li, D. and Kloenne, Z. and Zheng, Y. and Fraser, H.L. and Raabe, D. and Gault, B.
    Scripta Materialia 194 (2021)
    We investigated the nucleation and growth of α precipitates in the presence of nano-scale, titanium-rich, ordered-orthorhombic O″ precipitates formed during heating at 5 °C/min to 400 °C in a metastable β-Ti alloy, Ti-5Al-5Mo-5V-3Cr. The Oʺ precipitates are found to assist α nucleation by serving as preferential nucleation sites. In the very initial stages of its precipitation, the α phase is found to have formed via a coupled diffusional-displacive mode as titanium-rich plates. At this stage, aluminum partitions equally between the β matrix and the growing α precipitates, but slowly diffuses up-hill into the α phase during isothermal aging at 400 °C for 15 h. The interplay between such pre-formed metastable phases and α can be exploited to tailor the microstructure, by refining the α distribution, and consequently improve the mechanical properties of β-Ti alloys. Our work paves the way for exploiting this cascade of metastable phases for further microstructural engineering of β-Ti alloys. © 2020
    view abstractdoi: 10.1016/j.scriptamat.2020.113672
  • 2021 • 1317 Devitrification of thin film Cu–Zr metallic glass via ultrashort pulsed laser annealing
    Antonowicz, J. and Zalden, P. and Sokolowski-Tinten, K. and Georgarakis, K. and Minikayev, R. and Pietnoczka, A. and Bertram, F. and Chaika, M. and Chojnacki, M. and Dłużewski, P. and Fronc, K. and Greer, A.L. and Jastrzębski, ...
    Journal of Alloys and Compounds 887 (2021)
    In this work we report on an ultrashort pulsed laser annealing-driven devitrification of thin film Cu67Zr33 metallic glass characterized by micro-beam X-ray diffraction and electron microscopy techniques. The essential feature of ultrashort pulsed laser annealing is ultrafast heating (1014 K/s) by femtosecond optical excitation followed by extremely rapid cooling (1010–12 K/s) due to heat dissipation into the film substrate. During repetitive optical excitation, we take X-ray diffraction snapshots of the intermediate, frozen-in stages of the glass-crystal transformation to study its kinetics. A quantitative analysis of the diffraction patterns supported by electron microscopy result shows that the glass-crystal transformation proceeds by a rapid formation of an energetically favourable layer of crystalline ZrO2 on the free surface of the glassy film accompanied by nucleation and growth of fcc-Cu in the residual amorphous matrix. We demonstrate that at low effective annealing temperatures the devitrification kinetics of both products is correlated, while at high temperatures they decouple and ZrO2 forms an order of magnitude faster than Cu. © 2021 The Authors
    view abstractdoi: 10.1016/j.jallcom.2021.161437
  • 2021 • 1316 Recrystallization kinetics, mechanisms, and topology in alloys processed by laser powder-bed fusion: AISI 316L stainless steel as example
    Aota, L.S. and Bajaj, P. and Zilnyk, K.D. and Jägle, E.A. and Ponge, D. and Sandim, H.R.Z. and Raabe, D.
    Materialia 20 (2021)
    Alloys manufactured by laser powder-bed fusion have intrinsic and hierarchical microstructural features inherited from the fast solidification (up to 104 K/s) and subsequent thermal cycles. This creates epitaxed grains, dislocation cell structures, and second-phase oxide nanoparticles. Epitaxed grains follow a pattern where finer grains are found in the melt pool centerline along the laser track. Upon further annealing, this characteristic microstructure has pronounced consequences on the recrystallization mechanisms and thus on grain topology. By changing the scanning strategy, we control the emerging grain patterns in a representative alloy (AISI 316L austenitic stainless steel) by creating linear strings for unidirectional scans, while a chessboard grain pattern arises by applying a 90°-rotation between layers. Upon post-processing annealing (at 1150 °C from 15 min to 8 h), we study the relationship between the as-built and recrystallized microstructures. Recrystallization starts with fine nuclei in regions with high dislocation density along the melt pool centerlines, resulting in early-stage linear impingement (linearly clustered nucleation), as revealed by microstructural path analysis. Recrystallization is sluggish, due to dynamic Zener-Smith pinning. This effect leads to jerky boundary motion due to periodic pinning and depinning from oxide particles, caused by their gradual coarsening. Lower nuclei number density slows kinetics for the case of unidirectional scanning, while twinning aids in the nucleation of grains with mobile grain boundaries. Our findings show that changes in the laser scanning strategy are a suitable design tool for tailoring recrystallization and thus microstructure. © 2021
    view abstractdoi: 10.1016/j.mtla.2021.101236
  • 2021 • 1315 Coherent Spin-Photon Interface with Waveguide Induced Cycling Transitions
    Appel, M.H. and Tiranov, A. and Javadi, A. and Löbl, M.C. and Wang, Y. and Scholz, S. and Wieck, A.D. and Ludwig, Ar. and Warburton, R.J. and Lodahl, P.
    Physical Review Letters 126 (2021)
    Solid-state quantum dots are promising candidates for efficient light-matter interfaces connecting internal spin degrees of freedom to the states of emitted photons. However, selection rules prevent the combination of efficient spin control and optical cyclicity in this platform. By utilizing a photonic crystal waveguide we here experimentally demonstrate optical cyclicity up to ≈15 through photonic state engineering while achieving high fidelity spin initialization and coherent optical spin control. These capabilities pave the way towards scalable multiphoton entanglement generation and on-chip spin-photon gates. © 2021 American Physical Society. All rights reserved.
    view abstractdoi: 10.1103/PhysRevLett.126.013602
  • 2021 • 1314 Model order reduction for deformable porous materials in thin domains via asymptotic analysis
    Armiti-Juber, A. and Ricken, T.
    Archive of Applied Mechanics (2021)
    We study fluid-saturated porous materials that undergo poro-elastic deformations in thin domains. The mechanics in such materials are described using a biphasic model based on the theory of porous media (TPM) and consisting of a system of differential equations for material’s displacement and fluid’s pressure. These equations are in general strongly coupled and nonlinear, such that exact solutions are hard to obtain and numerical solutions are computationally expensive. This paper reduces the complexity of the biphasic model in thin domains with a scale separation between domain’s width and length. Based on standard asymptotic analysis, we derive a reduced model that combines two sub-models. Firstly, a limit model consists of averaged equations that describe the fluid pore pressure and displacement in the longitudinal direction of the domain. Secondly, a corrector model re-captures the mechanics in the transverse direction. The validity of the reduced model is finally tested using a set of numerical examples. These demonstrate the computational efficiency of the reduced model, while maintaining reliable solutions in comparison with original biphasic TPM model in thin domain. © 2021, The Author(s).
    view abstractdoi: 10.1007/s00419-021-01907-3
  • 2021 • 1313 Laser metal deposition of Al0.6CoCrFeNi with Ti & C additions using elemental powder blends
    Asabre, A. and Wilms, M.B. and Kostka, A. and Gemagami, P. and Weisheit, A. and Laplanche, G.
    Surface and Coatings Technology 418 (2021)
    Laser metal deposition (LMD) was used to in-situ alloy a crack-free Al0.6CoCrFeNi compositionally complex alloy (CCA) with 3 at.% Ti and 0.25 at.% C additions on an initially ferritic H10 tool steel from an elemental powder blend. After LMD, the material was annealed at 900 °C for 30 min to induce martensitic hardening in the substrate. The CCA in both as-deposited and annealed states exhibited a lamellar microstructure consisting of four phases: a matrix of interwoven disordered and ordered body-centered cubic phases, titanium carbides distributed randomly within the microstructure, and disordered face-centered cubic (FCC) plates that precipitated at the grain boundaries and grew towards the center of the grains. Chemical analyses along the build-up direction of the coating revealed a compositional gradient, similar in both as-deposited and annealed states, due to the intermixing between the substrate and the CCA. Despite a strong variation of the Fe-content, the hardness and the microstructure remain roughly constant in the major part of the as-deposited coating, which contains a large fraction of FCC plates that are beneficial to increase ductility and ensure a good compatibility with the substrate. In contrast, the upper part of the as-deposited coating, corresponding to the last solidified melt pool after LMD, has a much lower FCC fraction with an enhanced hardness. After annealing, the hardness of the tool steel substrate significantly increased and the FCC volume fraction in the coating increased from ~16% (as-deposited) to ~58%. Overall the microstructure of the coating became more homogeneous while its hardness decreased only by 10–15%. These results demonstrate that the CCA can be employed as a protective coating on a less expensive tool steel to improve its lifetime during service. © 2021 The Author(s)
    view abstractdoi: 10.1016/j.surfcoat.2021.127233
  • 2021 • 1312 Water influence on the uniaxial tensile behavior of polytetrafluoroethylene-coated glass fiber fabric
    Asadi, H. and Uhlemann, J. and Stranghoener, N. and Ulbricht, M.
    Materials 14 1-23 (2021)
    Polytetrafluoroethylene (PTFE)-coated glass fiber fabrics are used for long-lasting membrane structures due to their outstanding mechanical properties, chemical stabilities, and satisfying service life. During their operation time, different environmental impacts might influence their per-formance, especially regarding the mechanical properties. In this contribution, the impact of water on the tensile strength deterioration was assessed experimentally, providing evidence of consider-able but partially reversible loss of strength by up to 20% among the various types of investigated industrially established fabrics. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/ma14040846
  • 2021 • 1311 Artificial weathering mechanisms of uncoated structural polyethylene terephthalate fabrics with focus on tensile strength degradation
    Asadi, H. and Uhlemann, J. and Stranghoener, N. and Ulbricht, M.
    Materials 14 1-24 (2021)
    In the past five decades, reinforced coated textile membranes have been used increasingly as building materials, which are environmentally exposed. Thus, their weathering degradation over the service life must be taken into account in design, fabrication, and construction. Regarding such structural membranes, PVC (polyvinylchloride)-coated PET (polyethylene terephthalate) fabric is one of the most common commercially available types. This paper focuses on the backbone of it, i.e., the woven PET fabric. Herein, weathering of uncoated PET, as the load-bearing component of the composite PET-PVC, was studied. This study assessed the uniaxial tensile strength degradation mechanisms of uncoated PET fabric during artificial accelerated weathering tests. For this purpose, exploratory data analysis was carried out to analyze the chemical and physical changes which were traced by Fourier transform infrared spectroscopy and molecular weight measurements. Finally, with the help of degradation mechanisms determined from the aforementioned evaluations, a degradation pathway network model was constructed. With that, the relationship between applied stress, mecha-nistic variables, structural changes, and performance level responses (tensile strength degradation) was assessed. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/ma14030618
  • 2021 • 1310 Laser- and Ion-Induced Defect Engineering in WS2 Monolayers
    Asaithambi, A. and Kozubek, R. and Prinz, G.M. and Reale, F. and Pollmann, E. and Ney, M. and Mattevi, C. and Schleberger, M. and Lorke, A.
    Physica Status Solidi - Rapid Research Letters 15 (2021)
    Tungsten disulfide is one of the prominent transition metal dichalcogenide materials, which shows a transition from an indirect to a direct bandgap as the layer thickness is reduced down to a monolayer. To use (Formula presented.) monolayers in devices, detailed knowledge about the luminescence properties regarding not only the excitonic but also the defect-induced contributions is needed. Herein, (Formula presented.) monolayers are irradiated with (Formula presented.) ions with different fluences to create different defect densities. Apart from the excitonic contributions, two additional emission bands are observed at low temperatures. These bands can be reduced or even suppressed, if the flakes are exposed to laser light with powers up to 1.5 mW. Increasing the temperature up to room temperature leads to recovery of this emission, so that the luminescence properties can be modified using laser excitation and temperature. The defect bands emerging after ion irradiation are attributed to vacancy defects together with physisorbed adsorbates at different defect sites. © 2020 The Authors. Physica Status Solidi (RRL) – Rapid Research Letters published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/pssr.202000466
  • 2021 • 1309 Prediction of salting-out in liquid-liquid two-phase systems with ePC-SAFT: Effect of the Born term and of a concentration-dependent dielectric constant
    Ascani, M. and Held, C.
    Zeitschrift fur Anorganische und Allgemeine Chemie 647 1305-1314 (2021)
    Knowledge on phase equilibria is of crucial importance in designing industrial processes. However, modeling phase equilibria in liquid-liquid two-phase systems (LLTPS) containing electrolytes is still a challenge for electrolyte thermodynamic models and modeling still requires a lot of experimental input data. Further, modeling electrolyte solutions requires accounting for different physical effects in the electrolyte theory, especially the change of the dielectric properties of the medium at different compositions and the related change of solvation free energy of the dissolved ions. In a previous work, the Born term was altered by combining it with a concentration-dependent dielectric constant within the framework of electrolyte Perturbed-Chain Statistical Associating Fluid Theory (ePC-SAFT), and hence called ‘ePC-SAFT advanced’. In the present work, ePC-SAFT advanced was validated against liquid-liquid equilibria (LLE) of LLTPS water+organic solvents+alkali halides as well as aqueous two-phase systems containing the phase formers poly (propylene glycol) and an ionic liquid. All the ePC-SAFT parameters were used as published in the literature, and each binary interaction parameter between ion-solvent was set to zero. ePC-SAFT advanced allowed quantitatively predicting the salt effect on LLTPS without adjusting binary interaction parameters, while classical ePC-SAFT or meaningless mixing rules for the dielectric constant term failed in predicting the phase behavior of the LLTPS. © 2021 The Authors. Zeitschrift für anorganische und allgemeine Chemie published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/zaac.202100032
  • 2021 • 1308 Ultra-Shallow All-Epitaxial Aluminum Gate GaAs/AlxGa1−xAs Transistors with High Electron Mobility
    Ashlea Alava, Y. and Wang, D.Q. and Chen, C. and Ritchie, D.A. and Ludwig, A. and Ritzmann, J. and Wieck, A.D. and Klochan, O. and Hamilton, A.R.
    Advanced Functional Materials (2021)
    The electron mobility in shallow GaAs/AlxGa1−xAs heterostructures is strongly suppressed by charge wafer surface, which arises from native surface oxide layers formed when the wafer is removed from the crystal growth system. Here an in situ epitaxial aluminum gate, grown as part of the wafer, is used to eliminate surface charge scattering. Transmission electron microscope characterization shows that the in situ epitaxial aluminum is crystalline, and the wafer surface is free of native oxide. The influence of Al thickness and the use of different semiconductor wetting layers at the semiconductor-aluminum interface are examined and correlated with electron mobility. The electron mobility is found to strongly depend on aluminum thickness. For 8 nm thick aluminum, the electron mobility is also influenced by the wetting layer, with aluminum grown on GaAs producing higher mobility compared to AlAs or Al0.33Ga0.67As wetting layers. The suppression of surface charge scattering in these all-epitaxial devices allows for high mobilities across a wide density range despite the shallow conduction channel (35 nm below the gate). These measurements also provide a uniquely sensitive method of determining the electrical quality of the semiconductor–metal interface, relevant to the formation of hybrid semiconductor–superconductor devices. © 2021 Wiley-VCH GmbH
    view abstractdoi: 10.1002/adfm.202104213
  • 2021 • 1307 Phase-sensitive detection of gas-borne Si nanoparticles via line-of-sight UV/VIS attenuation
    Asif, M. and Menser, J. and Endres, T. and Dreier, T. and Daun, K. and Schulz, C.
    Optics Express 29 21795-21809 (2021)
    The distinct optical properties of solid and liquid silicon nanoparticles are exploited to determine the distribution of gas-borne solid and liquid particles in situ using line-of-sight attenuation measurements carried out across a microwave plasma reactor operated at 100 mbar. The ratio between liquid and solid particles detected downstream of the plasma varied with measurement location, microwave power, and flow rate. Temperatures of the liquid particles were pyrometrically-inferred using a spectroscopic model based on Drude theory. The phase-sensitive measurement supports the understanding of nanoparticle formation and interaction and thus the overall gas-phase synthesis process. © 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
    view abstractdoi: 10.1364/OE.426528
  • 2021 • 1306 Are sustainable companies more likely to default? Evidence from the dynamics between credit and ESG ratings
    Aslan, A. and Poppe, L. and Posch, P.
    Sustainability (Switzerland) 13 (2021)
    We investigate the relationship between environmental, social and governance (ESG) performance and the probability of corporate credit default. By using a sample of 902 publicly-listed firms in the US from 2002 to 2017 and by converting Standard & Poor’s credit ratings into default probabilities from rating transition matrices, we find the probability of corporate credit default to be significantly lower for firms with high ESG performance. Furthermore, by expanding the time window in our regression analysis, we observe that the influence of ESG and its constituents strongly varies over time. We argue that these dynamics may be due to financial and regulatory shocks. In a sector decomposition, we additionally find that the energy sector is most influenced by ESG regarding the probability of corporate credit default. We expect an increasing availability of ESG data in the future to reduce possible survivorship bias and to enhance the comparison between ESG-rated and non-ESG-rated firms. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/su13158568
  • 2021 • 1305 MoS2-Dünnschichten für unsynchronisierte, trockenlaufende Schraubenmaschinen: Umweltfreundliche und nachhaltige Schmierungskonzepte als Herausforderung und Chance
    Aurich, D. and Wittig, A. and Stangier, D. and Debus, J. and Thomann, C.-A. and Tillmann, W. and Brümmer, A.
    Vakuum in Forschung und Praxis 33 40-44 (2021)
    MoS2 thin films for unsynchronized, dry-running screw machines. Unsynchronized, dry-running screw machines have great potential to provide a resource-saving alternative to conventional screw machine designs. By saving external synchronization and the absence of a liquid lubricant, there are economic and ecological advantages. The use of materials and energy are reduced and the purity of the process gas is increased, the impact on the environment is minimized. Vacuum coating processes are one of the key technologies for realizing an unsynchronized, dry-running screw machine. The synthesized thin films can be optimally conditioned thanks to the near-net-shape coating and the possibility of changing the structural properties of the coating in a targeted manner. MoS2 thin films as solid lubricant exhibit improved friction properties. As a result there is also a great potential to reduce friction and thus the use of energy. © 2021, John Wiley and Sons Inc. All rights reserved.
    view abstractdoi: 10.1002/vipr.202100763
  • 2021 • 1304 Co-production of industrial services [Ko-Produktion industrieller Dienstleistungen]
    Austerjost, M. and Kreyenborg, A. and Kiklhorn, D. and Azkan, C. and Graefenstein, J. and Hefft, D. and Henke, M.
    ZWF Zeitschrift fuer Wirtschaftlichen Fabrikbetrieb 116 153-156 (2021)
    The co-production of industrial services offers enormous potential, especially for German medium-sized companies. However, up to now there is a lack of a common language that guarantees efficient and secure work-cooperation of different companies at network level. The SealedServices research project is therefore developing a cooperative value creation network with which Internet-based services can be realized independently by SMEs. © 2021 Walter de Gruyter GmbH, Berlin/Boston, Germany.
    view abstractdoi: 10.1515/zwf-2021-0030
  • 2021 • 1303 Microstructure and Fatigue Damage Evolution in Additive-Manufactured Metals Using Enhanced Measurement Techniques and Modeling Approaches
    Awd, M. and Walther, F. and Siddique, S. and Fatemi, A.
    Minerals, Metals and Materials Series 5 753-762 (2021)
    Process-induced microstructures have a high impact on the fatigue strength of engineering materials. Advanced materials testing builds the base for the design and manufacturing of reliable, high-performance products for various technical applications. Combining modern analytical and intermittent testing strategies with applied enhanced measurement techniques, i.e., physical instrumentation of testing specimens during loading, allows the characterization of process-structure-property relationships in various fatigue damage stages. Further, in situ mechanical testing in analytical devices like micro-computed tomography (µ-CT) enables the immediate correlation of material’s physical reactions with the applied loading conditions. The focus of the presented studies. Using the proposed technique, the characterization of fatigue damage evolution and progression before failure depending on environmental as well as material specific microstructural characteristics is carried out. Investigations on additively manufactured Al alloys revealed the interaction between porosity and microstructure under very high-cycle fatigue (VHCF) loading conditions. Measurement-based fatigue damage tracking during testing of SLM aluminum alloys revealed the interaction between porosity and microstructure under loading in the very high-cycle fatigue (VHCF) regime. The grain boundary strengthening of the microstructure increased VHCF strength by 33%. © 2021, The Minerals, Metals & Materials Society.
    view abstractdoi: 10.1007/978-3-030-65261-6_68
  • 2021 • 1302 Coupling of the phase field approach to the Armstrong-Frederick model for the simulation of ductile damage under cyclic load
    Aygün, S. and Wiegold, T. and Klinge, S.
    International Journal of Plasticity 143 (2021)
    The present contribution proposes a thermodynamically consistent model for the simulation of the ductile damage. The model couples the phase field method of fracture to the Armstrong-Frederick plasticity model with kinematic hardening. The latter is particularly suitable for simulating the material behavior under a cyclic load. The model relies on the minimum principle of the dissipation potential. However, the application of this approach is challenging since potentials of coupled methods are defined in different spaces: The dissipation potential of the phase field model is expressed in terms of rates of internal variables, whereas the Armstrong-Frederick model proposes a formulation depending on thermodynamic forces. For this reason, a unique formulation requires the Legendre transformation of one of the potentials. The present work performs the transformation of the Armstrong-Frederick potential, such that final formulation is only expressed in the space of rates of internal variables. With the assumption for the free energy and the joint dissipation potential at hand, the derivation of evolution equations is straightforward. The application of the model is illustrated by selected numerical examples studying the material response for different load cases and sample geometries. The paper provides a comparison with the experimental results as well. © 2021 Elsevier Ltd
    view abstractdoi: 10.1016/j.ijplas.2021.103021
  • 2021 • 1301 Nanoparticle impact electrochemistry
    Azimzadeh Sani, M. and Tschulik, K.
    Frontiers of Nanoscience 18 203-252 (2021)
    This chapter presents recent developments in the use of nanoparticle impact techniques to detect and characterize individual nanoparticles. We initially present the four major nanoparticle impact techniques utilized to date: blocking impacts of electrochemically inactive nanoparticles on an ultramicroelectrode (UME); capacitive impacts of nanoparticles on a potentiostated UME; transformative electrochemical conversion of nanoparticles at a polarized UME; and catalytic nanoparticle impacts through amplification of a faradaic current. Some key uses of nanoparticle impacts are reviewed, including nanoparticle detection; characterization of various metallic, metal oxide, metal halide, polymer, and organic nanoparticles; and electrocatalysis investigations. Practical instrumentation and analysis considerations for nanoparticle impact experiments are summarized. Hereafter, recent, novel experimental configurations used for nanoparticle impact electrochemistry are highlighted, including microjet systems, fast-scan cyclic voltammetry, and the combination of impact experiments with optical methods as well as nanopipette and nanogap systems. © 2021 Elsevier Ltd
    view abstractdoi: 10.1016/B978-0-12-820055-1.00007-1
  • 2021 • 1300 Towards design principles for data-driven services in industrial environments
    Azkan, C. and Iggena, L. and Möller, F. and Otto, B.
    Proceedings of the Annual Hawaii International Conference on System Sciences 2020-January 1789-1798 (2021)
    The ever-growing amounts of data offer companies many opportunities to exploit them. Resulting data-driven services hold great potential for creating unique value for customers and the achievement of competitive advantages. Nevertheless, especially companies in the industrial environment struggle to implement successful data-driven service innovations. Surprisingly, there is a lack of scientific research addressing this issue. Thus, our research generates design principles for data-driven services to aid in their development. For this purpose, we present a qualitative interview study with experts in different lines of businesses among the industry sector, holding varying positions and roles in service systems. Through practical examples, we show which challenges exist in the development and use of data-driven services. On this basis, we derive design principles to help understanding data-driven services and to overcome difficulties identified in practice, notably, that allows practitioners to develop new services or re-design existing ones. © 2021 IEEE Computer Society. All rights reserved.
    view abstract
  • 2021 • 1299 Charge tunable gaas quantum dots in a photonic n-i-p diode
    Babin, H.G. and Ritzmann, J. and Bart, N. and Schmidt, M. and Kruck, T. and Zhai, L. and Löbl, M.C. and Nguyen, G.N. and Spinnler, C. and Ranasinghe, L. and Warburton, R.J. and Heyn, C. and Wieck, A.D. and Ludwig, Ar .
    Nanomaterials 11 (2021)
    In this submission, we discuss the growth of charge-controllable GaAs quantum dots embedded in an n-i-p diode structure, from the perspective of a molecular beam epitaxy grower. The QDs show no blinking and narrow linewidths. We show that the parameters used led to a bimodal growth mode of QDs resulting from low arsenic surface coverage. We identify one of the modes as that showing good properties found in previous work. As the morphology of the fabricated QDs does not hint at outstanding properties, we attribute the good performance of this sample to the low impurity levels in the matrix material and the ability of n-and p-doped contact regions to stabilize the charge state. We present the challenges met in characterizing the sample with ensemble photoluminescence spectroscopy caused by the photonic structure used. We show two straightforward methods to overcome this hurdle and gain insight into QD emission properties. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/nano11102703
  • 2021 • 1298 Nanocrystals form a superfluorescent lattice mimicking the atomic structure of perovskite materials
    Bacher, G.
    Nature 593 513-514 (2021)
    doi: 10.1038/d41586-021-01331-1
  • 2021 • 1297 Synthesis, sintering, and effect of surface roughness on oxidation of submicron Ti2AlC ceramics
    Badie, S. and Dash, A. and Sohn, Y.J. and Vaßen, R. and Guillon, O. and Gonzalez-Julian, J.
    Journal of the American Ceramic Society 104 1669-1688 (2021)
    Submicron Ti2AlC MAX phase powder was synthesized by molten salt shielded synthesis (MS3) using a Ti:Al:C molar ratio of 2:1:0.9 at a process temperature of 1000°C for 5 hours. The synthesized powder presented a mean particle size of ~0.9 µm and a purity of 91 wt. % Ti2AlC, containing 6 wt. % Ti3AlC2. The Ti2AlC powder was sintered by pressureless sintering, achieving a maximal relative density of 90%, hence field-assisted sintering technology/spark plasma sintering was used to enhance densification. The fine-grained microstructure was preserved, and phase purity of Ti2AlC was unaltered in the latter case, with a relative density of 98.5%. Oxidation was performed at 1200°C for 50 hours in static air of dense monolithic Ti2AlC with different surface finish, (polished, ground and sandblasted) which resulted in the formation of an approx. 8 µm thin aluminum oxide (Al2O3) layer decorated with titanium dioxide (rutile, TiO2) colonies. Surface quality had no influence on Al2O3 scale thickness, but the amount and size of TiO2 crystals increased with surface roughness. A phenomenon of rumpling of the thermally grown oxide (TGO) was observed and a model to estimate the extent of deformation is proposed. © 2020 The Authors. Journal of the American Ceramic Society published by Wiley Periodicals LLC on behalf of American
    view abstractdoi: 10.1111/jace.17582
  • 2021 • 1296 Mechanism for breakaway oxidation of the Ti2AlC MAX phase
    Badie, S. and Sebold, D. and Vaßen, R. and Guillon, O. and Gonzalez-Julian, J.
    Acta Materialia 215 (2021)
    The good oxidation resistance of MAX phases up to temperatures around 1200 °C can be compromised for long exposure due to the breakaway of the protective alumina layer. Herein, we unveil a mechanism of breakaway oxidation of the Ti2AlC MAX phase, identifying the main trigger and the solutions to avoid it. It is caused by excessive rumpling of the oxide scale on surfaces with arithmetical mean roughness (Ra) &gt; 3 µm and constitutes a key factor in subsequent consumption of Ti2AlC. First, the oxide scale experienced rumpling due to significant radial stresses generated at the Ti2AlC/oxide interface. Second, scale blistering resulted from substantial buckling due to the evolution of in-plane stresses and lateral lengthening. Third, blister collapse and exposure of the underlying Al-depleted Ti2AlC surface led to rapid ingress of oxygen and oxide/substrate interface recession. The self-healing ability of Ti2AlC has been restrained and breakaway oxidation kinetics following a linear trend have been initiated. Similarly, breakaway oxidation was observed on micro-damaged surfaces. A mixed oxide layer with high porosity mainly composed of rutile titanium dioxide (TiO2) promptly formed on these surfaces, gradually consuming the base Ti2AlC material. © 2021
    view abstractdoi: 10.1016/j.actamat.2021.117025
  • 2021 • 1295 Injection molding and near-complete densification of monolithic and al2o3 fiber-reinforced ti2alc max phase composites
    Badie, S. and Gabriel, R. and Sebold, D. and Vaßen, R. and Guillon, O. and Gonzalez-Julian, J.
    Materials 14 (2021)
    Near-net shape components composed of monolithic Ti2AlC and composites thereof, containing up to 20 vol.% Al2O3 fibers, were fabricated by powder injection molding. Fibers were homogeneously dispersed and preferentially oriented, due to flow constriction and shear-induced velocity gradients. After a two-stage debinding procedure, the injection-molded parts were sintered by pressureless sintering at 1250 °C and 1400 °C under argon, leading to relative densities of up to 70% and 92%, respectively. In order to achieve near-complete densification, field assisted sintering technology/spark plasma sintering in a graphite powder bed was used, yielding final relative densities of up to 98.6% and 97.2% for monolithic and composite parts, respectively. While the monolithic parts shrank isotropically, composite assemblies underwent anisotropic densification due to constrained sintering, on account of the ceramic fibers and their specific orientation. No significant increase, either in hardness or in toughness, upon the incorporation of Al2O3 fibers was observed. The 20 vol.% Al2O3 fiber-reinforced specimen accommodated deformation by producing neat and well-defined pyramidal indents at every load up to a 30 kgf (~294 N). © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/ma14133632
  • 2021 • 1294 Large-Scale Production of Carbon-Supported Cobalt-Based Functional Nanoparticles for Oxygen Evolution Reaction
    Bähr, A. and Petersen, H. and Tüysüz, H.
    ChemCatChem (2021)
    A series of Co-based nanoparticles supported on activated carbon was synthesized by using waste tea leaves as a template as well as a sustainable carbon source. The crystal structure of the Co particles was adjusted by post-treatments with H2O2, ethanol vapor, and H2, which result in Co3O4, CoO, and metallic Co phases, respectively. After these different treatments, the composite materials consist of small Co-based nanoparticles with an average crystallite size of 6–14 nm supported on activated carbon with apparent specific surface areas up to 1065 m2 g−1. Correlations between the structure of the materials and their activity for the oxygen evolution reaction (OER) were established, whereby the post-treatment with ethanol vapor was found to yield the most effective electrocatalyst. The material shows good stability at 10 mA cm−2 over 10 h and reaches a mass activity of 2.9 A mgCo−1, which is even higher than pristine ordered mesoporous Co3O4. The superior electrocatalytic performance is ascribed to a high dispersion of Co-based nanoparticles and the conductivity of the activated carbon that facilitate the charge transport. © 2021 The Authors. ChemCatChem published by Wiley-VCH GmbH.
    view abstractdoi: 10.1002/cctc.202100594
  • 2021 • 1293 Nanoconfinement-Controlled Synthesis of Highly Active, Multinary Nanoplatelet Catalysts from Lamellar Magic-Sized Nanocluster Templates
    Baek, W. and Bootharaju, M.S. and Lorenz, S. and Lee, S. and Stolte, S. and Fainblat, R. and Bacher, G. and Hyeon, T.
    Advanced Functional Materials (2021)
    Magic-sized semiconductor nanoclusters (MSCs) possessing intermediate stability are promising precursors for synthesizing low-dimensional nanostructures that cannot be achieved by direct methods. However, uncontrolled diffusion of MSCs in their colloidal-state poses challenges in utilizing them as precursors and/or templates for the controlled synthesis of nanomaterials. Herein, a nanoconfined diffusion-limited strategy to synthesize large CdSe nanoplatelets through the solid-state transformation of (CdSe)13 MSCs is designed, wherein MSCs serve as both precursors and lamellar bilayer templates. In sharp contrast, in the colloidal-state, these MSCs are grown to CdSe nanoribbons or nanorods. Furthermore, the nanoconfined route is used not only to transform (CdSe)13, Mn2+:(CdSe)13, and Mn2+:(Cd1−xZnxSe)13 MSCs but also to dope Cu+, producing Cu+:CdSe, Mn2+/Cu+:CdSe, Mn2+/Cu+:Cd1−xZnxSe nanoplatelets, respectively. The resulting multinary nanoplatelets with controlled compositions exhibit unique optical and magneto-optical properties through characteristic exciton transfer mechanisms. Furthermore, synergistic effects have made quinary Mn2+/Cu+:Cd0.5Zn0.5Se nanoplatelets efficient and reusable catalysts for chemical fixation of CO2 with epoxide (turnover frequency: ≈200/h) under mild conditions. This nanoconfined synthetic strategy paves the way to synthesize diverse shape-controlled multi-component nanostructures for optoelectronic and other catalytic applications. © 2021 Wiley-VCH GmbH
    view abstractdoi: 10.1002/adfm.202107447
  • 2021 • 1292 Functionalization of textiles by deposition of UV-cured organic thin layers with charge storage properties for electronic and environmental technology
    Bahners, T. and Tsarkova, L. and Gebert, B. and Gutmann, J.S.
    Progress in Organic Coatings 157 (2021)
    Charge storing concepts receive an increasing interest in a view of the fast development of flexible textile electronics. The paper reports on initial charging capacity and charge conservation properties of technical textiles modified with UV-cured organic thin films. The results have been evaluated for three types of textile substrates and two types of monomers, an acrylic and allylic, with differing UV-absorption spectral characteristics. The most pronounced increase of the decay time from a few minutes to several hours has been found for polyethylene terephthalate (PET) fibers coated with thin layers of UV-cured tetraallyloxyethane monomer, representing ca 1 wt-% add-on. The mechanisms behind the measured effects could be rationalized along the concepts of “grafting to” and “grafting from” polymerization, which defines the tethering density, layer thickness and the degree of cross-linking. The behavior proved to be stable both under normal conditions and under elevated temperature/humidity conditions. The reported results provide design strategies for thin organic coatings with regards to targeted applications. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.porgcoat.2021.106332
  • 2021 • 1291 Application of artificial neural networks for active roll control based on actor-critic reinforcement learning
    Bahr, M. and Reicherts, S. and Sieberg, P. and Morss, L. and Schramm, D.
    Advances in Intelligent Systems and Computing 1260 AISC 61-82 (2021)
    This work shows the application of artificial neural networks for the control task of the roll angle in passenger cars. The training of the artificial neural network is based on the specific actor-critic reinforcement learning training algorithm. It is implemented and trained utilizing the Python API for TensorFlow and set up in a co-simulation with the vehicle simulation realized in IPG CarMaker via MATLAB/Simulink to enable online learning. Subsequently it is validated in different representative driving maneuvers. For showing the practicability of the resulting neural controller it is also validated for different vehicle classes with respect to their corresponding structure, geometries and components. An analytical approach to adjust the resulting controller to various vehicle bodies dependent on physical correlations is presented. © Springer Nature Switzerland AG 2021.
    view abstractdoi: 10.1007/978-3-030-55867-3_4
  • 2021 • 1290 Life cycle strengthening of high-strength steels by nanosecond laser shock
    Bai, Y. and Wang, H. and Wang, S. and Huang, Y. and Chen, Y. and Zhang, W. and Ostendorf, A. and Zhou, X.
    Applied Surface Science 569 (2021)
    Laser shock peening is a surface treatment technology inducing high-pressure shock waves on metallic materials and structures. In this study, the life cycle performance improvement in high-strength steel by nanosecond laser shock peening is investigated. It is found that microstructures formed by laser shock peening lead to higher microhardness, corrosion resistance, and fatigue life, which are significantly beneficial for preventing life cycle failure of mega-scale engineering structures in critical environments. The residual stress is also measured on the surface of samples, which shows that the compressive residual stress can be found in the treated area. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.apsusc.2021.151118
  • 2021 • 1289 Microstructure and phase composition evolution of silicon-hafnia feedstock during plasma spraying and following cyclic oxidation
    Bakan, E. and Sohn, Y.J. and Vaßen, R.
    Acta Materialia 214 (2021)
    In this work, silicon–hafnia (Si-HfO2, 80/20 mol. %) feedstock was plasma sprayed for Environmental Barrier Coating bond coat application. In the as-sprayed coating, hafnium disilicide (HfSi2), HfO2 tetragonal (t), and cubic (c) phases with a total volume of ~20 % were detected together with Si and HfO2 monoclinic (m). The temperature-dependent evolution of these phases was analyzed and paired with microstructural observations. It was found that above 700 °C, HfSi2 oxidizes and HfO2 (t) and (c) transforms into (m) polymorph. Up to this temperature, as-sprayed coating showed a non-linear expansion behavior. Estimated volume expansion at ~750 °C was 3.6 % based on dilatometry measurement. The primary and secondary mechanisms leading to the expansion in the coating were identified as oxidation of HfSi2 and polymorphic phase transitions in HfO2, respectively. As a consequence of the volume expansion, the coating was extensively cracked during cyclic oxidation and hence not protective anymore. After 100 h at 1300 °C, the volume fraction of oxidation product SiO2 was significant in the coating (0.34), while HfO2 was largely consumed (0.1) in the formation of HfSiO4 (0.56). This result suggested that reversible α↔β phase transitions in SiO2-cristobalite could be another factor contributing to the cracking in the coating during cyclic oxidation. © 2021 Acta Materialia Inc.
    view abstractdoi: 10.1016/j.actamat.2021.117007
  • 2021 • 1288 Direct Detection of Surface Species Formed on Iridium Electrocatalysts during the Oxygen Evolution Reaction
    BalaKrishnan, A. and Blanc, N. and Hagemann, U. and Gemagami, P. and Wonner, K. and Tschulik, K. and Li, T.
    Angewandte Chemie - International Edition 60 21396-21403 (2021)
    The effect of surface orientations on the formation of iridium oxide species during the oxygen evolution reaction (OER) remains yet unknown. Herein, we use a needle-shaped iridium atom probe specimen as a nanosized working electrode to ascertain the role of the surface orientations in the formation of oxide species during OER. At the beginning of electrolysis, the top 2–3 nm of (024), (026), (113), and (115) planes are covered by IrO−OH, which activates all surfaces towards OER. A thick subsurface oxide layer consisting of sub-stoichiometric Ir−O species is formed on the open (024) planes as OER proceeds. Such metastable Ir−O species are thought to provide an additional contribution to the OER activity. Overall, this study sheds light on the importance of the morphological effects of iridium electrocatalysts for OER. It also provides an innovative approach that can directly reveal surface species on electrocatalysts at atomic scale. © 2021 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/anie.202106790
  • 2021 • 1287 Visible light-induced controlled surface grafting polymerization of hydroxyethyl methacrylate from isopropylthioxanthone semipinacol-terminated organic monolayers
    Balasubramaniam, A. and Manderfeld, E. and Krause, L.M.K. and Wanka, R. and Schwarze, J. and Beyer, C.D. and Rosenhahn, A.
    Polymer Chemistry 12 618-628 (2021)
    A visible light-induced living polymerization of a hydrophilic model monomer was initiated on organic silane monolayers using isopropylthioxanthone (ITX). The type II photoinitiator ITX was covalently introduced to the octadecyltrichlorosilane monolayers by UV-induced (254 nm) hydrogen abstraction and a subsequent coupling step through recombination. The resulting dormant isopropylthioxanthone semi-pinacol (ITXSP) groups can be reactivated by irradiation with visible light to initiate a controlled surface grafting polymerization. Using this surface-initiated polymerization approach, hydroxyethyl methacrylate (HEMA) was polymerized under visible light irradiation (385 nm) at room temperature. The polymer layer thickness depends linearly on the irradiation time, which is in good agreement with previous reports on the living characteristics of the polymerization reactions. It is possible to accurately control the thickness of the grafted layer by simply altering the irradiation time. © The Royal Society of Chemistry 2021.
    view abstractdoi: 10.1039/d0py01410a
  • 2021 • 1286 Naturally occurring polyphenols as building blocks for supramolecular liquid crystals-substitution pattern dominates mesomorphism
    Balszuweit, J. and Blanke, M. and Saccone, M. and Mezger, M. and Daniliuc, C.G. and Wölper, C. and Giese, M. and Voskuhl, J.
    Molecular Systems Design and Engineering 6 390-397 (2021)
    A modular supramolecular approach towards hydrogen-bonded liquid crystalline assemblies based on naturally occurring polyphenols is reported. The combination of experimental observations, crystallographic studies and semi-empirical analyses of the assemblies provides insight into the structure-property relationships of these materials. Here a direct correlation of the number of donor OH-groups as well as their orientation with the mesomorphic behavior is reported. We discovered that the number and orientation of the OH-groups have a stronger influence on the mesomorphic behavior of the supramolecular assemblies than the connectivity (e.g. stilbenoid or chalconoid) of the hydrogen bond donors. Furthermore, the photo-switching behavior of selected complexes containing azopyridine ligands was investigated. This study will help future scientists to gain a deeper understanding of the underlying mechanisms and structure-property relationships of supramolecular assemblies with mesomorphic behavior, which is still one of the major challenges in current science. This journal is © The Royal Society of Chemistry.
    view abstractdoi: 10.1039/d0me00171f
  • 2021 • 1285 Editorial
    Bambach, M. and Beese, A.M. and Lin, F. and Tekkaya, A.E.
    Journal of Materials Processing Technology 294 (2021)
    doi: 10.1016/j.jmatprotec.2021.117103
  • 2021 • 1284 Deep learning for visualization and novelty detection in large X-ray diffraction datasets
    Banko, L. and Maffettone, P.M. and Naujoks, D. and Olds, D. and Ludwig, Al.
    npj Computational Materials 7 (2021)
    We apply variational autoencoders (VAE) to X-ray diffraction (XRD) data analysis on both simulated and experimental thin-film data. We show that crystal structure representations learned by a VAE reveal latent information, such as the structural similarity of textured diffraction patterns. While other artificial intelligence (AI) agents are effective at classifying XRD data into known phases, a similarly conditioned VAE is uniquely effective at knowing what it doesn’t know: it can rapidly identify data outside the distribution it was trained on, such as novel phases and mixtures. These capabilities demonstrate that a VAE is a valuable AI agent for aiding materials discovery and understanding XRD measurements both ‘on-the-fly’ and during post hoc analysis. © 2021, The Author(s).
    view abstractdoi: 10.1038/s41524-021-00575-9
  • 2021 • 1283 Evaluation of antithrombogenic pHPC on CoCr substrates for biomedical applications
    Bannewitz, C. and Lenz-Habijan, T. and Lentz, J. and Peters, M. and Trösken, V. and Siebert, S. and Weber, S. and Theisen, W. and Henkes, H. and Monstadt, H.
    Coatings 11 1-12 (2021)
    Bare metal endovascular implants pose a significant risk of causing thrombogenic complications. Antithrombogenic surface modifications, such as phenox’s “Hydrophilic Polymer Coating” (pHPC), which was originally developed for NiTi implants, decrease the thrombogenicity of metal surfaces. In this study, the transferability of pHPC onto biomedical CoCr-based alloys is examined. Coated surfaces were characterized via contact-angle measurement and atomic force microscopy. The equivalence of the antithrombogenic effect in contact with whole human blood was demonstrated in vitro for CoCr plates compared to NiTi plates on a platform shaker and for braided devices in a Chandler loop. Platelet adhesion was assessed via scanning electron microscopy and fluorescence microscopy. The coating efficiency of pHPC on CoCr plates was confirmed by a reduction of the contact angle from 84.4° ± 5.1° to 36.2° - 5.2°. The surface roughness was not affected by the application of pHPC. Platelet adhesion was significantly reduced on pHPC-coated specimens. The platelet covered area was reduced by 85% for coated CoCr plates compared to uncoated samples. Uncoated braided devices were completely covered by platelets, while on the pHPC-coated samples, very few platelets were visible. In conclusion, the antithrombogenic effect of pHPC coating can be successfully applied on CoCr plates as well as stent-like CoCr braids. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/coatings11010093
  • 2021 • 1282 A Career in Catalysis: Robert Schlögl
    Bao, X. and Behrens, M. and Ertl, G. and Fu, Q. and Knop-Gericke, A. and Lunkenbein, T. and Muhler, M. and Schmidt, C.M. and Trunschke, A.
    ACS Catalysis 11 6243-6260 (2021)
    "Why?"is the question that initiates science. "Why?"is also the answer that maintains science. This interrogative adverb fuels the scientific career of Robert Schlögl. Robert is a dedicated solid-state chemist who has found his specialization in untangling the working principles of heterogeneous catalysts under realistic conditions. As such he combines the full complexity of real catalysts with tailor-made operando experiments to overcome pressure, material, and complexity gaps. His ability to quickly abstract the meaning of spectroscopic and microscopic data, his talent to ask the right question paired with curiosity, diligence, and creativity have made him a world-leading expert in heterogeneous catalysis and energy science. His scientific passion is focused on untangling chemical dynamics as well as working principles and understanding the important interplay of geometric and electronic structures in functional materials. Thereby his research interests involve ammonia and methanol synthesis, carbon materials in catalysis, hydrogenation, and dehydrogenation, selective oxidation, and the development of operando setups for microscopy and spectroscopy. He also has a strong commitment to society in scientifically accelerating the energy transition ("Energiewende") in Europe, where he focuses on CO2 utilization and hydrogen as an energy carrier. This is manifested in three recent large Germany-wide projects: Carbon2Chem, CatLab, and TransHyDe. ©
    view abstractdoi: 10.1021/acscatal.1c01165
  • 2021 • 1281 On the state and stability of fuel cell catalyst inks
    Bapat, S. and Giehl, C. and Kohsakowski, S. and Peinecke, V. and Schäffler, M. and Segets, D.
    Advanced Powder Technology 32 3845-3859 (2021)
    Catalyst layers (CL), as an active component of the catalyst coated membrane (CCM), form the heart of the polymer electrolyte membrane fuel cell (PEMFC). For optimum performance of the fuel cell, obtaining suitable structural and functional characteristics for the CL is crucial. Direct tuning of the microstructure and morphology of the CL is non-trivial; hence catalyst inks as CL precursors need to be modulated, which are then applied onto a membrane to form the CCM. Obtaining favorable dispersion characteristics forms an important prerequisite in engineering catalyst inks for large scale manufacturing. In order to facilitate a knowledge-based approach for developing fuel cell inks, this work introduces new tools and methods to study both the dispersion state and stability characteristics, simultaneously. Catalyst inks were prepared using different processing methods, which include stirring and ultrasonication. The proposed tools are used to characterize and elucidate the effects of the processing method. Structural characterization of the dispersed particles and their assemblages was carried out by means of transmission electron microscopy. Analytical centrifugation (AC) was used to study the state and stability of the inks. Herein, we introduce new concepts, S score, and stability trajectory, for a time-resolved assessment of inks in their native state using AC. The findings were validated and rationalized using transmittograms as a direct visualization technique. The flowability of inks was investigated by rheological measurements. It was found that probe sonication only up to an optimum amplitude leads to a highly stable colloidal ink. © 2021 The Society of Powder Technology Japan
    view abstractdoi: 10.1016/j.apt.2021.08.030
  • 2021 • 1280 Towards a framework for evaluating and reporting Hansen solubility parameters: applications to particle dispersions
    Bapat, S. and Kilian, S.O. and Wiggers, H. and Segets, D.
    Nanoscale Advances 3 4400-4410 (2021)
    A thorough understanding of complex interactions within particulate systems is a key for knowledge-based formulations. Hansen solubility parameters (HSP) are widely used to assess the compatibility of the dispersed phase with the continuous phase. At present, the determination of HSP is often based on a liquid ranking list obtained by evaluating a pertinent dispersion parameter using only one pre-selected characterization method. Furthermore, one cannot rule out the possibility of subjective judgment especially for liquids for which it is difficult to decipher the compatibility or underlying interactions. As a result, the end value of HSP might be of little or no information. To overcome these issues, we introduce a generalized and technology-agnostic combinatorics-based procedure. We discuss the principles of the procedure and the implications of evaluating and reporting particle HSP values. We demonstrate the procedure by using SiNxparticles synthesized in the gas phase. We leverage the analytical centrifugation data to evaluate stability trajectories of SiNxdispersions in various liquids to deduce particle-liquid compatibility. © The Royal Society of Chemistry 2021.
    view abstractdoi: 10.1039/d1na00405k
  • 2021 • 1279 Experimental damping behavior of strongly coupled structure and acoustic modes of a rotating disk with side cavities
    Barabas, B. and Benra, F.-K. and Petry, N. and Brillert, D.
    Proceedings of the ASME Turbo Expo 9A-2021 (2021)
    High cycle fatigue is a continuous research topic within the turbomachine community. One field of the investigations is the fluid-structure interaction of 2-D impellers, which can be simplified as disks with their surrounding side cavities. In modern machines the pressure ratios tend to increase along with pressure fluctuations and the excitation potential on the impellers. The vibrational interactions between side cavities, filled with high pressure fluid, and the disk structure play an important role in machine design. However, they are not fully understood, yet. Vibrations at frequencies that have been uncritical at lower pressure levels could become critical at higher pressure levels. Additionally, coupling effects between fluid and structure are becoming stronger at higher fluid densities. For a safe and reliable design, the excitation and the damping mechanism of coupled modes has to be better understood. This paper summarizes the test rig setup and focuses on one of the main findings of an extensive experimental research project, which investigated the fluid-structure interaction of a disk with side cavities, at the University of Duisburg-Essen. The focus lays on the damping behavior of strongly coupled acoustic and structure modes. Measurement results gathered at the aeroacoustic test rig are presented. The results show the influence of fluid pressure variations on the damping behavior of acoustic modes. Therefore, the response functions of some selected acoustic modes are evaluated with the half-width method. Compared to the weakly coupled structure mode, the damping of the strongly coupled structure mode is some orders higher at atmospheric pressure conditions. The damping ratio decreases with an increasing pressure level, however still remains some orders higher, than the damping of weakly coupled structure modes. © 2021 by Siemens Energy Global GmbH & Co. KG.
    view abstractdoi: 10.1115/GT2021-58782
  • 2021 • 1278 The 2021 Magnonics Roadmap
    Barman, A. and Gubbiotti, G. and Ladak, S. and Adeyeye, A.O. and Krawczyk, M. and Grafe, J. and Adelmann, C. and Cotofana, S. and Naeemi, A. and Vasyuchka, V.I. and Hillebrands, B. and Nikitov, S.A. and Yu, H. and Grundler, D. and...
    Journal of Physics Condensed Matter 33 (2021)
    Magnonics is a budding research field in nanomagnetism and nanoscience that addresses the use of spin waves (magnons) to transmit, store, and process information. The rapid advancements of this field during last one decade in terms of upsurge in research papers, review articles, citations, proposals of devices as well as introduction of new sub-topics prompted us to present the first roadmap on magnonics. This is a collection of 22 sections written by leading experts in this field who review and discuss the current status besides presenting their vision of future perspectives. Today, the principal challenges in applied magnonics are the excitation of sub-100 nm wavelength magnons, their manipulation on the nanoscale and the creation of sub-micrometre devices using low-Gilbert damping magnetic materials and its interconnections to standard electronics. To this end, magnonics offers lower energy consumption, easier integrability and compatibility with CMOS structure, reprogrammability, shorter wavelength, smaller device features, anisotropic properties, negative group velocity, non-reciprocity and efficient tunability by various external stimuli to name a few. Hence, despite being a young research field, magnonics has come a long way since its early inception. This roadmap asserts a milestone for future emerging research directions in magnonics, and hopefully, it will inspire a series of exciting new articles on the same topic in the coming years. © 2021 The Author(s). Published by IOP Publishing Ltd.
    view abstractdoi: 10.1088/1361-648X/abec1a
  • 2021 • 1277 Correction to: Societal importance of Antarctic negative feedbacks on climate change: blue carbon gains from sea ice, ice shelf and glacier losses (The Science of Nature, (2021), 108, 5, (43), 10.1007/s00114-021-01748-8)
    Barnes, D.K.A. and Sands, C.J. and Paulsen, M.L. and Moreno, B. and Moreau, C. and Held, C. and Downey, R. and Bax, N. and Stark, J.S. and Zwerschke, N.
    Science of Nature 108 (2021)
    In this article, all of the authors have a “2” by their name affiliating them to Australian Antarctic Division. Only J. S. Stark should however be affiliated to this institution. Also, J. Stark’s middle initial was added to his name making it now read as “J. S. Stark”. The original article has been corrected. © Springer-Verlag GmbH Germany, part of Springer Nature 2021.
    view abstractdoi: 10.1007/s00114-021-01759-5
  • 2021 • 1276 Societal importance of Antarctic negative feedbacks on climate change: blue carbon gains from sea ice, ice shelf and glacier losses
    Barnes, D.K.A. and Sands, C.J. and Paulsen, M.L. and Moreno, B. and Moreau, C. and Held, C. and Downey, R. and Bax, N. and Stark, J. and Zwerschke, N.
    Science of Nature 108 (2021)
    Diminishing prospects for environmental preservation under climate change are intensifying efforts to boost capture, storage and sequestration (long-term burial) of carbon. However, as Earth’s biological carbon sinks also shrink, remediation has become a key part of the narrative for terrestrial ecosystems. In contrast, blue carbon on polar continental shelves have stronger pathways to sequestration and have increased with climate-forced marine ice losses—becoming the largest known natural negative feedback on climate change. Here we explore the size and complex dynamics of blue carbon gains with spatiotemporal changes in sea ice (60–100 MtCyear−1), ice shelves (4–40 MtCyear−1 = giant iceberg generation) and glacier retreat (&lt; 1 MtCyear−1). Estimates suggest that, amongst these, reduced duration of seasonal sea ice is most important. Decreasing sea ice extent drives longer (not necessarily larger biomass) smaller cell-sized phytoplankton blooms, increasing growth of many primary consumers and benthic carbon storage—where sequestration chances are maximal. However, sea ice losses also create positive feedbacks in shallow waters through increased iceberg movement and scouring of benthos. Unlike loss of sea ice, which enhances existing sinks, ice shelf losses generate brand new carbon sinks both where giant icebergs were, and in their wake. These also generate small positive feedbacks from scouring, minimised by repeat scouring at biodiversity hotspots. Blue carbon change from glacier retreat has been least well quantified, and although emerging fjords are small areas, they have high storage-sequestration conversion efficiencies, whilst blue carbon in polar waters faces many diverse and complex stressors. The identity of these are known (e.g. fishing, warming, ocean acidification, non-indigenous species and plastic pollution) but not their magnitude of impact. In order to mediate multiple stressors, research should focus on wider verification of blue carbon gains, projecting future change, and the broader environmental and economic benefits to safeguard blue carbon ecosystems through law. © 2021, Crown.
    view abstractdoi: 10.1007/s00114-021-01748-8
  • 2021 • 1275 Influence of calcination and sintering temperatures on dielectric and magnetic properties of Pb(Fe0.5Nb0.5)O3 ceramics synthesized by the solid state method
    Bartek, N. and Shvartsman, V.V. and Salamon, S. and Wende, H. and Lupascu, D.C.
    Ceramics International 47 23396-23403 (2021)
    Lead iron niobate, Pb(Fe0.5Nb0.5)O3 (PFN), belongs to the family of multiferroic materials combining ferroelectric and antiferromagnetic ordering. Its properties to a large extent depend on the synthesis conditions. For applications it is important to obtain materials with large polarization and low electric leakage. In this paper we investigate the effect of processing parameters on the structural, electrical and magnetic behaviour of PFN ceramics prepared by the solid state method. The optimal calcination and sintering temperatures are found, which enable us to obtain ceramics with a large polarization Pmax = 28 μC/cm2 and dielectric permittivity εMax ≈ 55 000. We also find that increasing the calcination and sintering temperatures decreases diffuseness of the ferroelectric phase transition and shifts the Néel temperature to lower values, which might be due to a change of the distribution of Fe3+ and Nb5+ across the B-sites of the perovskite towards a more ordered structure. © 2021
    view abstractdoi: 10.1016/j.ceramint.2021.05.055
  • 2021 • 1274 Band gap of pb(Fe0.5nb0.5)o3 thin films prepared by pulsed laser deposition
    Bartek, N. and Shvartsman, V.V. and Bouyanfif, H. and Schmitz, A. and Bacher, G. and Olthof, S. and Sirotinskaya, S. and Benson, N. and Lupascu, D.C.
    Materials 14 (2021)
    Ferroelectric materials have gained high interest for photovoltaic applications due to their open-circuit voltage not being limited to the band gap of the material. In the past, different lead-based ferroelectric perovskite thin films such as Pb(Zr,Ti)O3 (Pb,La)(Zr,Ti)O3 and PbTiO3 were investigated with respect to their photovoltaic efficiency. Nevertheless, due to their high band gaps they only absorb photons in the UV spectral range. The well-known ferroelectric PbFe0.5Nb0.5O3 (PFN), which is in a structure similar to the other three, has not been considered as a possible candidate until now. We found that the band gap of PFN is around 2.75 eV and that the conductivity can be increased from 23 S/µm to 35 S/µm during illumination. The relatively low band gap value makes PFN a promising candidate as an absorber material. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/ma14226841
  • 2021 • 1273 An energy-relaxation-based framework for the modeling of magnetic shape memory alloys—Simulation of three-dimensional effects under homogeneous loading conditions
    Bartel, T. and Kiefer, B. and Menzel, A.
    International Journal of Solids and Structures 208-209 221-234 (2021)
    It is known from experimental findings that three-dimensional effects can have a strong influence on magnetic shape memory behavior. Such phenomena are, however, often neglected in MSMA constitutive models, as they only become meaningful under complex loading conditions. The extensions of our original modeling framework, cf. Bartel et al. (2020), to include 3D-effects is threefold: (i) vector-valued microstructural variables are now elements in R3, i.e. no longer parameterizable in polar coordinates, (ii) a third tetragonal martensite variant may form/vanish by switching from/back into both other variants, and (iii) a more general and robust algorithmic treatment is necessary. The latter includes the implementation of a staggered Augmented Lagrangian scheme to handle the now much larger and numerically more advanced sets of equality and inequality constraints. In this context, two extended model formulations are presented. The first considers a first-order, two-variant laminate approach (rank-one convexification), in which domain magnetizations, interface orientations etc. are now three-dimensional vectors. The second model is based on a convexification approach, for which the incorporation of the third martensitic variant is quite natural. Numerical examples are investigated to test the generalized modeling framework. Firstly, it is confirmed that both extended models recover the solution of the previously established two-dimensional model for a simple loading case. Secondly, response predictions for more complex loading scenarios (non-proportional bi-axial stresses, orthogonal magnetic field), motivated by experiments, are investigated. It is found that capturing the formation, elimination and mutual interaction of all martensitic variants as well as general three-dimensional magnetization vector orientations is of key importance under these conditions. The extended convexification model and modified algorithmic formulation are shown to reliably handle even such general cases. © 2020 Elsevier Ltd
    view abstractdoi: 10.1016/j.ijsolstr.2020.10.024
  • 2021 • 1272 A thermodynamically consistent modelling framework for strongly time-dependent bainitic phase transitions
    Bartel, T. and Geuken, G.-L. and Menzel, A.
    International Journal of Solids and Structures 232 (2021)
    In this work, a thermodynamically consistent constitutive framework is introduced that is capable of reproducing the significant time-dependent behaviour of austenite-to-bainite phase transformations. In particular, the aim is to incorporate the effect of these diffusion-controlled processes by plasticity-like evolution equations instead of incorporating related global diffusion equations. To this end, a variational principle for inelastic solids is adopted and enhanced by an additional term. This term essentially contributes to the evolution equations for the phase volume fractions of several crystallography-based bainite variants. Due to the specific modifications, special attention has to be paid with respect to the fulfilment of thermodynamical consistency, which can be shown to be unconditionally satisfied for the newly proposed modelling framework. The phase transformation model itself is based on the convexification of a multi-well energy density landscape in order to provide the effective material response for possible phase mixtures. Several material parameters are determined via parameter identification based on available experimental results for 51CrV4, which also allow the quantitative evaluation of the predicted results. © 2021 The Authors
    view abstractdoi: 10.1016/j.ijsolstr.2021.111172
  • 2021 • 1271 Preface on mechanics of additive manufacturing—Part II
    Bartel, T. and Kästner, M. and Kiefer, B. and Menzel, A.
    GAMM Mitteilungen 44 (2021)
    doi: 10.1002/gamm.202100020
  • 2021 • 1270 Cahn–Hilliard phase field theory coupled to mechanics: Fundamentals, numerical implementation and application to topology optimization
    Bartels, A. and Kurzeja, P. and Mosler, J.
    Computer Methods in Applied Mechanics and Engineering 383 (2021)
    The presented framework couples the Cahn–Hilliard phase field theory to continuum mechanics using a variational principle. All equations follow consistently from stationary of a rate potential and yield a physically sound homogenization. Static and kinematic compatibility at the material interfaces are naturally guaranteed. In order to enforce admissibility of the phase field parameter, nonlinear complementary conditions are considered and embedded into the algorithmic formulation. Eventually, the variationally consistent framework also features topology optimization automatically. In contrast to other approaches that start from the optimization problem, the present formulation starts from a more comprehensive energy potential. This perspective allows to explore the natural physical mechanisms that control the system's compliance (e.g., interface evolution) and that drive maximum structural performance (changing the direction of the evolution equation with respect to the phase field parameter). Furthermore, this perspective efficiently couples the physical constraints (e.g., mass and momentum conservation). Energetically optimized microstructures and an optimized beam structure illustrate the applicability as well as the numerical performance of the elaborated framework. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.cma.2021.113918
  • 2021 • 1269 State-of-the-art cooling and lubrication for machining inconel 718
    de Bartolomeis, A. and Newman, S.T. and Biermann, D. and Shokrani, A.
    Journal of Manufacturing Science and Engineering, Transactions of the ASME 143 (2021)
    Inconel 718 is the most used nickel superalloys with applications in aerospace, oil and gas, nuclear, and chemical industries. It is mostly used for safety-critical components where the condition of the surface is a significant concern. The combination of mechanical, thermal, and chemical properties of Inconel 718 has made it a difficult-to-machine material. Despite recent advances in machining Inconel 718, achieving desired surface integrity with prescribed properties is still not possible. Different machining environments have been investigated for improving the machinability of Inconel 718 and enhance the surface integrity of machined components. This paper provides a new investigation and classification into recent advances in the machining of Inconel 718 regarding surface integrity, mostly concentrated on turning applications. The major findings and conclusions provide a critique of the state-of-the-art in machining environments for Inconel 718 together with future directions for research. Surface integrity has been evaluated in terms of surface topology as well as mechanical and microstructural properties. The impact of various cooling and lubrication methods has been investigated. It has been found that surface integrity is affected by the thermomechanical conditions at the cutting zone which are influenced by the cutting parameters, cutting tool, tool wear, and cooling/lubrication condition. The current technologies are incapable of delivering both productivity and sustainability while meeting surface integrity requirements for machining Inconel 718. High-pressure cooling has shown the potential to enhance tool wear at the expense of higher power consumption. Copyright © 2020 by ASME
    view abstractdoi: 10.1115/1.4047842
  • 2021 • 1268 Complex-Solid-Solution Electrocatalyst Discovery by Computational Prediction and High-Throughput Experimentation**
    Batchelor, T.A.A. and Löffler, T. and Xiao, B. and Krysiak, O.A. and Strotkötter, V. and Pedersen, J.K. and Clausen, C.M. and Savan, A. and Li, Y. and Schuhmann, W. and Rossmeisl, J. and Ludwig, Al.
    Angewandte Chemie - International Edition (2021)
    Complex solid solutions (“high entropy alloys”), comprising five or more principal elements, promise a paradigm change in electrocatalysis due to the availability of millions of different active sites with unique arrangements of multiple elements directly neighbouring a binding site. Thus, strong electronic and geometric effects are induced, which are known as effective tools to tune activity. With the example of the oxygen reduction reaction, we show that by utilising a data-driven discovery cycle, the multidimensionality challenge raised by this catalyst class can be mastered. Iteratively refined computational models predict activity trends around which continuous composition-spread thin-film libraries are synthesised. High-throughput characterisation datasets are then used as input for refinement of the model. The refined model correctly predicts activity maxima of the exemplary model system Ag-Ir-Pd-Pt-Ru. The method can identify optimal complex-solid-solution materials for electrocatalytic reactions in an unprecedented manner. © 2021 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/anie.202014374
  • 2021 • 1267 FPGA-based acceleration of THz SAR imaging
    Batra, A. and Kamaleldin, A. and Zhen, L.Y. and Wiemeler, M. and Gohringer, D. and Kaiser, T.
    2021 4th International Workshop on Mobile Terahertz Systems, IWMTS 2021 (2021)
    Terahertz (THz) Synthetic Aperture Radar (SAR) is an emerging domain as it provides high spatial resolution in the range of sub-mm compared to the conventional lower frequency spectrum SAR. Despite the limited propagation range at the THz spectrum, it is suitable for short-range applications. One primary potential application could be unmanned aerial vehicle (UAV) based THz SAR for environment mapping and profiling. To address real-time mapping/profiling, a Field-Programmable Gate Array (FPGA) based signal processing platform seems to be promising. Firstly, due to energy efficiency in comparison to CPU and GPU. Secondly, it provides massive parallelism data processing. Therefore, in this paper, a hardware-accelerated 2D THz SAR imaging is presented. The time-domain image reconstruction algorithm Backprojection is implemented using hardware description language (HDL) for the FPGA platform and in consideration of measured data for the 220-330 GHz spectrum. Further, the paper presents the estimation of accuracy in comparison to CPU-based results and hardware resource utilization. Besides, the analysis on execution time and speed-up is provided. The proposed SAR imaging accelerator is implemented and evaluated on Xilinx Zynq Ultrascale+ ZCU102 FPGA board. © 2021 IEEE.
    view abstractdoi: 10.1109/IWMTS51331.2021.9486819
  • 2021 • 1266 Sub-mm resolution 3D SAR imaging at 1.5 THz
    Batra, A. and Wiemeler, M. and Gohringer, D. and Kaiser, T.
    2021 4th International Workshop on Mobile Terahertz Systems, IWMTS 2021 (2021)
    The frequency range of synthetic aperture radar is being extended to the promising THz spectrum as it provides high spatial resolution. The spectrum broadens the SAR applications to sub-mm resolution imaging and localization, non-destructive testing, and material characterization. Although the spectrum suffers from high atmospheric attenuation and free space path loss limiting the sensing range, it has emerging short-range applications. State-of-the-art THz SAR imaging is demonstrated primarily up to 1.1 THz with electronic transceiver modules. This paper presents one of the first demonstrations of 3D SAR imaging at 1.5 THz. The frequency band of 1.1-1.5 THz is considered for imaging a metallic target at a reference range of approx. 40 cm. The enhancement in terms of imaging quality compared to SAR image for the frequency band, 0.85-1.1 THz, is also presented. © 2021 IEEE.
    view abstractdoi: 10.1109/IWMTS51331.2021.9486780
  • 2021 • 1265 Process characteristics, particle behavior and coating properties during HVOF spraying of conventional, fine and nanostructured WC-12Co powders
    Baumann, I. and Hagen, L. and Tillmann, W. and Hollingsworth, P. and Stangier, D. and Schmidtmann, G. and Tolan, M. and Paulus, M. and Sternemann, C.
    Surface and Coatings Technology 405 (2021)
    In recent years, great effort has been taken in science and industry to find novel material-related solutions, which provide improved properties for future technological applications. One of these approaches is the use of fine structured and nanostructured materials. Within the field of wear protection, the use of fine or nanostructured WC-Co powder feedstock in the thermal spray process enables the application of highly wear resistant, thin near net-shape coatings on parts with complex geometries. In this study, the processing of WC-12Co powders by means of High Velocity Oxy-Fuel (HVOF) flame spraying is fundamentally investigated and the results are compared to those obtained with conventional powders. The influence of process parameter and scaling effects on the spray process and the thermo-kinetic particle behavior in the flame, the heating of the substrate as well as on the coating properties, the microstructure, the behavior of elements and phases and the residual stress is discussed comprehensively. The investigations of this work have shown that HVOF spraying of fine and nanostructured WC-12Co powders instead of conventional ones leads to a significant alteration of the thermo-kinetic spray conditions. Under optimized spray conditions, achieved by the use of special spray equipment and statistical design of experiments (DoE), improvements in terms of the economy of the spray process (higher deposition efficiencies) and the mechanical properties (higher microhardness and fracture toughness, lower porosity and roughness) can be achieved. © 2020
    view abstractdoi: 10.1016/j.surfcoat.2020.126716
  • 2021 • 1264 Cutting-fluid flow with chip evacuation during deep-hole drilling with twist drills
    Baumann, A. and Oezkaya, E. and Schnabel, D. and Biermann, D. and Eberhard, P.
    European Journal of Mechanics, B/Fluids 89 473-484 (2021)
    In this study the important aspects of cutting fluid distribution and the chip evacuation during micro twist deep-hole drilling are investigated using 3D multi-physics simulation methods. A coupled particle simulation is performed to analyze the chip transport by combining Smoothed Particle Hydrodynamics and the Discrete Element Method. Therefore, the transient transport of the chips is compared to a simulation scenario without chips. The coupled particle approach is capable to deal with free surfaces and fluid–solid interactions, that are subject to major topological changes over time. The chip positions resulting from the coupled particle simulation are used to carry out a Computational Fluid Dynamics simulation which considers the physical boundary conditions of the fluid and the process parameters to perform in-depth flow analyses. The results show good qualitative agreement between both simulation methods. Furthermore, the results show that large dead-zones with no fluid or almost zero fluid velocity exist in the flutes and that the chips there only experience a small evacuation force from the cutting fluid. The presented coupled approach of combining CFD and SPH–DEM simulation provide a significant support for future investigations to research the chip transport and to improve the tools and the process further. © 2021 The Authors
    view abstractdoi: 10.1016/j.euromechflu.2021.07.003
  • 2021 • 1263 Internal Diameter Coating by Warm Spraying of Fine WC-12Co Powders (− 10 + 2 µm) with Very Short Spray Distances up to 10 mm
    Baumann, I. and Tillmann, W. and Schaak, C. and Schmidt, K. and Hagen, L. and Zajaczkowski, J. and Schmidtmann, G. and Matthäus, G. and Luo, W.
    Journal of Thermal Spray Technology (2021)
    The internal diameter (ID) coating by means of thermal spraying is currently experiencing growing interest in science and industry. In contrast to the well-established plasma- and arc-based spray techniques, there is a lack of knowledge concerning kinetic processes such as HVOF, HVAF and warm spray (WS). A major challenge represents the necessity of short spray distances and the compact design of novel ID spray guns with reduced combustion power. Conventional WC-Co powders (− 45 + 15 µm) are not able to achieve a sufficient heat and momentum transfer. The use of fine powders &lt; 15 µm offers an approach to overcome this drawback as they feature a larger surface-to-volume ratio and a lower mass. However, the processing of fine powders requires suitable spray equipment and a sensitive parameter adjustment. In this study, warm spraying of fine WC-12Co powders (− 10 + 2 µm) with a novel ID spray gun (HVOF + N2) “ID RED” (Thermico Engineering GmbH, Germany) was investigated. First, the flame profile as well as the in-flight behavior of the particles along the spray jet (spray distances SD = 10-80 mm) was analyzed at different nitrogen flows NF = 15-115 L/min to find suitable spray parameter intervals. Subsequently, planar steel samples were coated with SD = 10-50 mm and constant NF = 90 L/min. Analyses regarding the microstructure, the mechanical properties and the phase evolution of the coatings were performed. The aim was to study spraying with the novel ID gun and to scrutinize shortest feasible spray distances. Finally, steel tubes (internal diameter of 81.6 mm and a wall thickness of 10.0 mm) were coated with SD = 20 mm and NF = 90 L/min to investigate in how far the results can be transferred to ID parts. Correlations between the particle behavior, the microstructure and the coating properties were made. © 2021, The Author(s).
    view abstractdoi: 10.1007/s11666-021-01195-x
  • 2021 • 1262 Perspective: Increasing blue carbon around Antarctica is an ecosystem service of considerable societal and economic value worth protecting
    Bax, N. and Sands, C.J. and Gogarty, B. and Downey, R.V. and Moreau, C.V.E. and Moreno, B. and Held, C. and Paulsen, M.L. and McGee, J. and Haward, M. and Barnes, D.K.A.
    Global Change Biology 27 5-12 (2021)
    Precautionary conservation and cooperative global governance are needed to protect Antarctic blue carbon: the world's largest increasing natural form of carbon storage with high sequestration potential. As patterns of ice loss around Antarctica become more uniform, there is an underlying increase in carbon capture-to-storage-to-sequestration on the seafloor. The amount of carbon captured per unit area is increasing and the area available to blue carbon is also increasing. Carbon sequestration could further increase under moderate (+1°C) ocean warming, contrary to decreasing global blue carbon stocks elsewhere. For example, in warmer waters, mangroves and seagrasses are in decline and benthic organisms are close to their physiological limits, so a 1°C increase in water temperature could push them above their thermal tolerance (e.g. bleaching of coral reefs). In contrast, on the basis of past change and current research, we expect that Antarctic blue carbon could increase by orders of magnitude. The Antarctic seafloor is biophysically unique and the site of carbon sequestration, the benthos, faces less anthropogenic disturbance than any other ocean continental shelf environment. This isolation imparts both vulnerability to change, and an avenue to conserve one of the world's last biodiversity refuges. In economic terms, the value of Antarctic blue carbon is estimated at between £0.65 and £1.76 billion (~2.27 billion USD) for sequestered carbon in the benthos around the continental shelf. To balance biodiversity protection against society's economic objectives, this paper builds on a proposal incentivising protection by building a ‘non-market framework’ via the 2015 Paris Agreement to the United Nations Framework Convention on Climate Change. This could be connected and coordinated through the Antarctic Treaty System to promote and motivate member states to value Antarctic blue carbon and maintain scientific integrity and conservation for the positive societal values ingrained in the Antarctic Treaty System. © 2020 John Wiley & Sons Ltd
    view abstractdoi: 10.1111/gcb.15392
  • 2021 • 1261 On existence and uniqueness properties for solutions of stochastic fixed point equations
    Beck, C. and Gonon, L. and Hutzenthaler, M. and Jentzen, A.
    Discrete and Continuous Dynamical Systems - Series B 26 4927-4962 (2021)
    The Feynman-Kac formula implies that every suitable classical solution of a semilinear Kolmogorov partial differential equation (PDE) is also a solution of a certain stochastic fixed point equation (SFPE). In this article we study such and related SFPEs. In particular, the main result of this work proves existence of unique solutions of certain SFPEs in a general setting. As an application of this main result we establish the existence of unique solutions of SFPEs associated with semilinear Kolmogorov PDEs with Lipschitz continuous nonlinearities even in the case where the associated semilinear Kolmogorov PDE does not possess a classical solution. © 2021 American Institute of Mathematical Sciences. All rights reserved.
    view abstractdoi: 10.3934/dcdsb.2020320
  • 2021 • 1260 On nonlinear Feynman-Kac formulas for viscosity solutions of semilinear parabolic partial differential equations
    Beck, C. and Hutzenthaler, M. and Jentzen, A.
    Stochastics and Dynamics (2021)
    The classical Feynman-Kac identity builds a bridge between stochastic analysis and partial differential equations (PDEs) by providing stochastic representations for classical solutions of linear Kolmogorov PDEs. This opens the door for the derivation of sampling based Monte Carlo approximation methods, which can be meshfree and thereby stand a chance to approximate solutions of PDEs without suffering from the curse of dimensionality. In this paper, we extend the classical Feynman-Kac formula to certain semilinear Kolmogorov PDEs. More specifically, we identify suitable solutions of stochastic fixed point equations (SFPEs), which arise when the classical Feynman-Kac identity is formally applied to semilinear Kolmorogov PDEs, as viscosity solutions of the corresponding PDEs. This justifies, in particular, employing full-history recursive multilevel Picard (MLP) approximation algorithms, which have recently been shown to overcome the curse of dimensionality in the numerical approximation of solutions of SFPEs, in the numerical approximation of semilinear Kolmogorov PDEs. © 2021 World Scientific Publishing Company.
    view abstractdoi: 10.1142/S0219493721500489
  • 2021 • 1259 Long-Term Radiographic Changes in Stemless Press-Fit Total Shoulder Arthroplasty
    Beck, S. and Patsalis, T. and Busch, A. and Dittrich, F. and Wegner, A. and Landgraeber, S. and Jäger, M.
    Zeitschrift fur Orthopadie und Unfallchirurgie 159 274-280 (2021)
    Introduction Stemmed humeral implants have represented the gold standard in total shoulder arthroplasty (TSA) for decades. Like many other joints, the latest trends in TSA designs aim at bone preservation. Current studies have demonstrated that native proximal humeral bone stresses are most closely mimicked by stemless implants. Nevertheless, there are concerns about the long-term performance of stemless designs. The aim of the present study was to evaluate the long-term radiographic changes at the proximal humerus in anatomical stemless press-fit TSA. Materials and Methods Between 2008 and 2010, 48 shoulders in 43 patients were resurfaced using an anatomic stemless shoulder prosthesis (TESS, Biomet). Thirty shoulders in twenty-five patients who were aged 65.7 ± 9.9 (34 to 82) years were available for clinical and radiographic review at a mean follow-up of 94.0 ± 8.9 (78 to 110) months. Results Radiographic changes of the proximal humerus due to stress shielding were found in 38.4% of the stemless TESS implants. Mild stress shielding accounted for 80% of the observed radiographic changes. Radiographs exhibited stable fixation of the stemless humeral press-fit implant at early and late follow-up. In contrast, radiolucent lines at the glenoid implant were found in 96.1% of the cases. Irrespective of the degree of radiographic changes, clinical scores (VAS, Quick-DASH, Constant score) significantly improved at follow-up. Conclusions The anatomic stemless press-fit implant seems to be favorable in terms of implant-related stress shielding. Clinical outcome was not affected by radiographic changes, demonstrating an 8-year clinical performance that seems to be comparable to conventional stemmed TSA. © 2020. Thieme. All rights reserved.
    view abstractdoi: 10.1055/a-1079-6549
  • 2021 • 1258 Generation of a humanized FXII knock-in mouse—A powerful model system to test novel anti-thrombotic agents
    Beck, S. and Stegner, D. and Loroch, S. and Baig, A.A. and Göb, V. and Schumbrutzki, C. and Eilers, E. and Sickmann, A. and May, F. and Nolte, M.W. and Panousis, C. and Nieswandt, B.
    Journal of Thrombosis and Haemostasis 19 2835-2840 (2021)
    Background: Effective inhibition of thrombosis without generating bleeding risks is a major challenge in medicine. Accumulating evidence suggests that this can be achieved by inhibition of coagulation factor XII (FXII), as either its knock-out or inhibition in animal models efficiently reduced thrombosis without affecting normal hemostasis. Based on these findings, highly specific inhibitors for human FXII(a) are under development. However, currently, in vivo studies on their efficacy and safety are impeded by the lack of an optimized animal model expressing the specific target, that is, human FXII. Objective: The primary objective of this study is to develop and functionally characterize a humanized FXII mouse model. Methods: A humanized FXII mouse model was generated by replacing the murine with the human F12 gene (genetic knock-in) and tested it in in vitro coagulation assays and in in vivo thrombosis models. Results: These hF12KI mice were indistinguishable from wild-type mice in all tested assays of coagulation and platelet function in vitro and in vivo, except for reduced expression levels of hFXII compared to human plasma. Targeting FXII by the anti-human FXIIa antibody 3F7 increased activated partial thromboplastin time dose-dependently and protected hF12KI mice in an arterial thrombosis model without affecting bleeding times. Conclusion: These data establish the newly generated hF12KI mouse as a powerful and unique model system for in vivo studies on anti-FXII(a) biologics, supporting the development of efficient and safe human FXII(a) inhibitors. © 2021 The Authors. Journal of Thrombosis and Haemostasis published by Wiley Periodicals LLC on behalf of International Society on Thrombosis and Haemostasis.
    view abstractdoi: 10.1111/jth.15488
  • 2021 • 1257 Reduction of surface morphology influence on THz reflection time domain spectroscopy for material classification by using multiple observation angles
    Becke, L. and Gerling, A. and Hofmann, M.R. and Brenner, C.
    Proceedings of SPIE - The International Society for Optical Engineering 11685 (2021)
    Material classification with THz radiation is typically done in transmission geometry.1 However, in many situations a reflection based classification is highly desirable. For a reflection based classification scheme, it is necessary to compensate the impact of the surface morphology on the reflection signal.2 As the surface morphology will mainly change the frequency dependent reflection pattern of the beam, we use different observation angles to improve classification based on THz reflection data. We use a THz TDS reflection setup measuring at several input and output angles. While the sample can be rotated, the transmitter can be moved on a semi-arc (see Fig. 1). We measure the reflection spectrum at different input-/output- A ngle configurations, which can be retrieved by an Euler transform of transmitter angle and sample angle. A measurement of a grating structure can be seen in Fig. 1. To reduce measuring time while maintaining a sufficient signal to noise ratio, we measure small angle variations around the main specular reflection. For classification we use a supervised machine learning approach based on principal component analysis for feature reduction and a support vector machine for classification.3 In this paper we present the impact of different observation angles on the classification accuracy in contrast to single-observation-angle classification, to check on the hypothesis that an increase in observation angle helps to classify a set of known materials by THz TDS reflection spectroscopy. In consequence we can estimate requirements on the observation angle and identify surface structures which will prevent classification. © COPYRIGHT SPIE.
    view abstractdoi: 10.1117/12.2577607
  • 2021 • 1256 Processing of a newly developed nitrogen-alloyed ferritic-austenitic stainless steel by laser powder bed fusion – Microstructure and properties
    Becker, L. and Röttger, A. and Boes, J. and Weber, S. and Theisen, W.
    Additive Manufacturing 46 (2021)
    In this work, a novel alloy design of a stainless steel with a ferritic-austenitic microstructure is derived for PBF-LB/M (powder bed fusion-laser beam/metal). The alloy was developed based on X2CrNiMo17-12-2 steel, for which an austenite volume content of approx. 54 vol% in the PBF-LB/M state was achieved using a reduced Ni equivalent. Partial substitution of Ni by Mn increases the N solubility of the alloy. By melting and further gas-atomizing this melt in an N2 atmosphere, an N content of 0.27 mass% was set in the produced steel powder. This leads to both high strength and high corrosion resistance of the PBF-LB/M-processed steel. However, microstructural investigations in the PBF-LB/M state confirm a microstructure consisting of ferrite, austenite, and Mo- and Cr-rich nitrides of M2N type. The nitrides were not completely eliminated by a subsequent heat treatment of the PBF-LB/M samples. As a result of the solution annealing, the microstructure approaches the thermodynamic equilibrium so that the austenite volume content increases from 54.2 vol% to 92.7 vol%. The higher Cr and N contents result in a higher corrosion resistance of the investigated steel compared to PBF-LB/M-processed X2CrNiMo17-12-2, regarded as the reference material. In addition, the measured strengths are significantly higher due to the larger amounts of austenite/ferrite interfaces and the N-induced solid-solution strengthening effect compared to X2CrNiMo17-12-2. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.addma.2021.102185
  • 2021 • 1255 MARCKS affects cell motility and response to BTK inhibitors in CLL
    Beckmann, L. and Berg, V. and Dickhut, C. and Sun, C. and Merkel, O. and Bloehdorn, J. and Robrecht, S. and Seifert, M. and da Palma Guerreiro, A. and Claasen, J. and Loroch, S. and Oliverio, M. and Underbayev, C. and Vaughn, L. a...
    Blood 138 544-556 (2021)
    Bruton tyrosine kinase (BTK) inhibitors are highly active drugs for the treatment of chronic lymphocytic leukemia (CLL). To understand the response to BTK inhibitors on a molecular level, we performed (phospho)proteomic analyses under ibrutinib treatment. We identified 3466 proteins and 9184 phosphopeptides (representing 2854 proteins) in CLL cells exhibiting a physiological ratio of phosphorylated serines (pS), threonines (pT), and tyrosines (pY) (pS:pT:pY). Expression of 83 proteins differed between unmutated immunoglobulin heavy-chain variable region (IGHV) CLL (UM-CLL) and mutated IGHV CLL (M-CLL). Strikingly, UM-CLL cells showed higher basal phosphorylation levels than M-CLL samples. Effects of ibrutinib on protein phosphorylation levels were stronger in UM-CLL, especially on phosphorylated tyrosines. The differentially regulated phosphopeptides and proteins clustered in pathways regulating cell migration, motility, cytoskeleton composition, and survival. One protein, myristoylated alanine-rich C-kinase substrate (MARCKS), showed striking differences in expression and phosphorylation level in UM-CLL vs M-CLL. MARCKS sequesters phosphatidylinositol-4,5-bisphosphate, thereby affecting central signaling pathways and clustering of the B-cell receptor (BCR). Genetically induced loss of MARCKS significantly increased AKT signaling and migratory capacity. CD40L stimulation increased expression of MARCKS. BCR stimulation induced phosphorylation of MARCKS, which was reduced by BTK inhibitors. In line with our in vitro findings, low MARCKS expression is associated with significantly higher treatment-induced leukocytosis and more pronounced decrease of nodal disease in patients with CLL treated with acalabrutinib. © 2021 American Society of Hematology
    view abstractdoi: 10.1182/blood.2020009165
  • 2021 • 1254 A study on the influence of ligand variation on formamidinate complexes of yttrium: New precursors for atomic layer deposition of yttrium oxide
    Beer, S.M.J. and Boysen, N. and Muriqi, A. and Zanders, D. and Berning, T. and Rogalla, D. and Bock, C. and Nolan, M. and Devi, A.
    Dalton Transactions 50 12944-12956 (2021)
    The synthesis and characterization of a series of closely related Y(iii) compounds comprising the formamidinate ligands (RNCHNR) (R = alkyl) is reported, with the scope of using them as prospective precursors for atomic layer deposition (ALD) of yttrium oxide (Y2O3) thin films. The influence of the side chain variation on the thermal properties of the resulting complexes is studied and benchmarked by thermal analysis and vapor pressure measurements. Density functional theory (DFT) studies give theoretical insights into the reactivity of the compounds towards water, which was targeted as a co-reactant for the deposition of Y2O3via thermal ALD in the next step. Among the four complexes analyzed, tris(N,N′-di-tert-butyl-formamidinato)yttrium(iii) [Y(tBu2-famd)3] 1 was found to possess enhanced thermal stability and was selected for Y2O3 ALD process development. A broad ALD window ranging from 200 °C to 325 °C was obtained, yielding films of high compositional quality. Furthermore, with a film density of (4.95 ± 0.05) g cm-1 close to the bulk value, polycrystalline fcc Y2O3 layers with a smooth topography resulted in promising dielectric properties when implemented in metal insulator semiconductor (MIS) capacitor structures. © 2021 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/d1dt01634b
  • 2021 • 1253 Theoretical description of optical and X-ray absorption spectra of MgO including many-body effects
    Begum, V. and Gruner, M.E. and Vorwerk, C. and Draxl, C. and Pentcheva, R.
    Physical Review B 103 (2021)
    Here we report the optical and X-ray absorption spectra of the wide-band-gap oxide MgO using density functional theory and many-body perturbation theory (MBPT). Our comprehensive study of the electronic structure shows that while the band gap is underestimated with the exchange-correlation functional PBEsol (4.58 eV) and the hybrid functional HSE06 (6.58 eV) compared to the experimental value (7.7 eV), it is significantly improved (7.52 eV) and even overcompensated (8.53 eV) when quasiparticle corrections are considered. Inclusion of excitonic effects by solving the Bethe-Salpeter equation (BSE) yields the optical spectrum in excellent agreement with experiment. Excellent agreement is observed also for the O and Mg K-edge absorption spectra, demonstrating the importance of the electron-hole interaction within MBPT. Projection of the electron-hole coupling coefficients from the BSE eigenvectors on the band structure allows us to determine the origin of prominent peaks and identify the orbital character of the relevant contributions. The real-space projection of the lowest energy exciton wave function of the optical spectrum indicates a Wannier-Mott type, whereas the first exciton in the O K edge is more localized. © 2021 American Physical Society.
    view abstractdoi: 10.1103/PhysRevB.103.195128
  • 2021 • 1252 Preparation and characterization of asymmetric hollow fiber polyvinyl chloride (PVC) membrane for forward osmosis application
    Behboudi, A. and Ghiasi, S. and Mohammadi, T. and Ulbricht, M.
    Separation and Purification Technology 270 (2021)
    PVC hollow fiber (HF) membrane for forward osmosis (FO) application as a potential candidate for water desalination was fabricated by altering the spinning conditions. High molecular weight polyvinylpyrrolidone (PVP) was used as a blending additive to control the phase inversion process by increasing viscosity leading to delayed demixing as observed on the ternary phase diagram and confirmed by the simulation results, and forming dense barrier layer structure by providing chain entanglements with the PVC matrix. PVP/PVC ratio of 5/100 was proved to offer suited membrane morphology and selective layer. Different air gap distances and bore fluid flow rates were investigated to achieve proper fabrication parameters. The prepared membranes presented high flux and salt rejection in nanofiltration (NF) and FO tests. The best-suited membrane demonstrated the structural parameter of 389 µm with a narrow pore size distribution and a molecular weight cut-off of 490 Da. In different draw solution (DS) concentrations, it was observed that the membranes perform well in all conditions. Considering the PVC-PVP chain entanglements and mobility and the possibility of PVP being washed away, the membranes’ performance at different temperatures indicated that 25–45 °C would be the safe operating range for the fabricated membranes with stable values of 31.0–33.4 LMH and 0.17–0.18 (FO mode) and 33.0–33.4 LMH and 0.23–0.24 (PRO mode) for water flux and specific reverse salt flux. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.seppur.2021.118801
  • 2021 • 1251 Numerical process design for targeted residual stress adjustment in hot bulk formed components taking into account macro- and microscale [Numerische Prozessauslegung zur gezielten Eigenspannungseinstellung in warmmassivumgeformten Bauteilen unter Berücksichtigung von Makro- und Mikroskala]
    Behrens, B.-A. and Schröder, J. and Brands, D. and Brunotte, K. and Wester, H. and Scheunemann, L. and Uebing, S. and Kock, C.
    Forschung im Ingenieurwesen/Engineering Research (2021)
    The aim of this work is the adjustment of an advantageous compressive residual stress profile in hot-formed components by intelligent process control with tailored cooling from the forging heat. The feasibility and potential are demonstrated in a hot forming process in which cylindrical specimen with an eccentric hole are formed at 1000 °C and subsequently cooled in water from the forging heat. Previous work shows that tensile residual stresses occur in the specimen formed in this way from the material 1.3505. Using the presented multi-scale FE models, an alternative process variant is analysed in this work, where advantageous compressive residual stresses can be generated instead of tensile residual stresses through tailored cooling from the forming heat in the specimen. The tailored cooling is achieved by partially exposing the specimen to a water-air spray. In this way, the local plastification can be influenced by inhomogeneous strains due to thermal and transformation-induced effects in order to customise the resulting residual stress distribution. The scientific challenge of this work is to generate different residual stresses in the surface of the specimen without changing the geometrical and microstructural properties. It is demonstrated that influencing the residual stresses and even reversing the stress sign is possible using smart process control during cooling. © 2021, The Author(s).
    view abstractdoi: 10.1007/s10010-021-00482-x
  • 2021 • 1250 Experimental and Numerical Investigations on the Development and Stability of Residual Stresses Arising from Hot Forming Processes
    Behrens, B.-A. and Schröder, J. and Wester, H. and Brands, D. and Uebing, S. and Kock, C.
    Minerals, Metals and Materials Series 2289-2301 (2021)
    Residual stresses are an important issue as they affect both the manufacturing process as well as the performance of the final parts. Taking the whole process chain of hot forming into account, the integrated heat treatment provided by a defined temperature profile during cooling of the parts offers a great potential for the targeted adjustment of the desired residual stress state. The aim of this work is the investigation of technological reproducibility and stability of residual stresses arising from the thermomechanical forming process. For this purpose, a long-term study of residual stresses on hot-formed components is conducted. In order to develop finite element models for hot forming, a comprehensive thermomechanical material characterisation with special focus on phase transformation effects is performed. The numerical model is validated by means of a comparison between residual stress states determined with X-ray diffraction on experimentally processed components and predicted residual stresses from the simulations. © 2021, The Minerals, Metals & Materials Society.
    view abstractdoi: 10.1007/978-3-030-75381-8_192
  • 2021 • 1249 Establishment of a rotary print head to effect residual stresses and interlayer bonding in an flm-process
    Bengfort, P. and Stracke, D. and Künne, B.
    Journal of Manufacturing and Materials Processing 5 (2021)
    In fused layer modeling (FLM) manufacturing technology, there is an increased demand for semi-crystalline materials due to their favorable mechanical properties, such as high strength and toughness. The reasons for their limited use are process-related residual stresses and reduced interlayer bonding, resulting in component distortion, warping and poor strength. Addressing these problems, this paper presents the development and implementation of a rotary print head that enables local laser pre-deposition heating and forced air cooling in the 2.5-dimensional FLM process. Samples of polypropylene are fabricated to investigate the effects of the modified process on residual stresses and interlayer bonding. The investigations show that local laser pre-deposition heating can positively influence the interlayer bonding. In combination with a reduction of the extrusion temperature and additional cooling, it is possible to considerably reduce the residual stresses. The results of this research show that pre-deposition heating and forced air cooling significantly improve the processability of semi-crystalline thermoplastics in the FLM process. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/jmmp5030082
  • 2021 • 1248 Uncovering process-structure relationships associated to the hot isostatic pressing of the high-speed steel PMHS 3-3-4 through novel microstructural characterization methods
    Benito, S. and Boes, J. and Matsuo, M. and Weber, S. and Theisen, W.
    Materials and Design 208 (2021)
    Gaining insight into the many agents that determine the underlying material microstructure is essential to engineer new and efficient solutions. Tool steels resistant to abrasive wear are particularly interesting because it is possible to tailor their macroscopic properties by adjusting some of the primary carbide phase features: micromechanical properties, volume fraction, size, and shape. For many popular ledeburitic cold-work and high-speed tool steel alloys, there is a generally good understanding of the effects of the HIP temperature, pressure, and holding time on these traits. Nevertheless, there is still no thorough investigation on the influence of powder size distribution on the primary carbide phase. To that end, we employ in this work novel microstructural characterization methods that shed light on the nature and extent of its influence. We show that powder size has an enduring effect on primary carbide geometric features associated with the solidification process during powder atomization. This work contributes significant process-structure links, which uncover new opportunities for microstructural design. © 2021 The Author(s)
    view abstractdoi: 10.1016/j.matdes.2021.109925
  • 2021 • 1247 Topical issue scientific machine learning (2/2)
    Benner, P. and Klawonn, A. and Stoll, M.
    GAMM Mitteilungen 44 (2021)
    doi: 10.1002/gamm.202100010
  • 2021 • 1246 Novel computational tools: General discussion
    Bennett, T.D. and Brammer, L. and Coudert, F.-X. and Evans, J.D. and Fischer, M. and Goodwin, A.L. and Jiang, J. and Kaskel, S. and Kitagawa, S. and Krause, S. and Lee, J.-S.M. and Matsuda, R. and Rogge, S.M.J. and Ryder, M.R. and...
    Faraday Discussions 225 341-357 (2021)
    doi: 10.1039/D0FD90034F
  • 2021 • 1245 Small-Angle X-Ray Scattering Measurements on Amphiphilic Polymer Conetworks Swollen in Orthogonal Solvents
    Benski, L. and Viran, I. and Katzenberg, F. and Tiller, J.C.
    Macromolecular Chemistry and Physics 222 (2021)
    Amphiphilic polymer conetworks (APCNs), which combine two different polymer nanophases, have a broad range of applications that involve their unique potential to separately swell one of these nanophases in a selective solvent. Little is known about the structural changes of such APCNs upon swelling in dependence on the topology. Here, conetworks composed of poly(2-ethylhexyl acrylate) crosslinked by poly(2-methyl-2-oxazoline) (PMOx) are investigated with small-angle X-ray scattering in dry and swollen state using the orthogonal solvents water and toluene. The data clearly show that the structural changes induced by swelling are strongly dependent on the topology of the APCNs. While water leads to fusion of PMOx phases resulting in larger structures than found in the dry APCN, toluene is only swelling the hydrophobic phases without structural changes. © 2020 The Authors. Macromolecular Chemistry and Physics published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/macp.202000292
  • 2021 • 1244 Intercritical annealing to achieve a positive strain-rate sensitivity of mechanical properties and suppression of macroscopic plastic instabilities in multi-phase medium-Mn steels
    Benzing, J.T. and Luecke, W.E. and Mates, S.P. and Ponge, D. and Raabe, D. and Wittig, J.E.
    Materials Science and Engineering A 803 (2021)
    This study investigates the high strain-rate tensile properties of a cold-rolled medium-Mn steel (Fe–12Mn–3Al-0.05C % in mass fraction) designed to have a multi-phase microstructure and positive strain-rate sensitivity. At the intercritical annealing temperature of 585 °C, increasing the annealing time from 0.5 h to 8 h increased the phase volume fraction of ultrafine-grained (UFG) austenite from 2% to 35% by reversion. The remainder of the microstructure was composed of UFG ferrite and recovered α′-martensite (the latter resembles the cold-rolled state). Servo hydraulic tension testing and Kolsky-bar tension testing were used to measure the tensile properties from quasi-static strain rates to dynamic strain rates (ε˙ = 10-4 s-1 to ε˙ = 103 s-1). The strain-rate sensitivities of the yield strength (YS) and ultimate tensile strength (UTS) were positive for both annealing times. Tensile properties and all non-contact imaging modalities (infrared imaging and digital image correlation) indicated an advantageous suppression of Lüders bands and Portevin Le Chatelier (PLC) bands (a critical challenge in multi-phase medium-Mn steel design) due to the unique combination of microstructural constituents and overall composition. Fracture surfaces of specimens annealed for 0.5 h showed some instances of localized cleavage fracture (approximately 30 μm wide areas and lath-like ridges). Specimens annealed for 8 h maintained a greater product of strength and elongation by at least 2.5 GPa % (on average for each strain rate). The relevant processing-structure-property relationships are discussed in the context of recommendations for design strategies concerning multi-phase steels such that homogeneous deformation behavior and positive strain-rate sensitivities can be achieved. © 2020
    view abstractdoi: 10.1016/j.msea.2020.140469
  • 2021 • 1243 Vibrational Sum Frequency Spectroscopy Study of Alcohol Adsorption on Thin-Film TiO2at Ambient Pressure and Temperature
    Bera, A. and Bullert, D. and Linke, M. and Hasselbrink, E.
    Journal of Physical Chemistry C 125 7721-7727 (2021)
    Surface-sensitive vibrational sum frequency spectroscopy (vSFS) has been utilized to study the adsorption chemistry of small alcohols, namely, methanol, ethanol, 1-propanol, and 2-propanol on TiO2 thin films under near-ambient conditions. The vSF spectra in the C-H region reveal that methanol and ethanol adsorb both molecularly and dissociatively, while 1-propanol and 2-propanol are solely detected in the molecular form. The different adsorption behavior suggests that the extent of dissociation decreases from methanol to propanol. Moreover, polarization analysis of the spectra reveals that the methyl groups are preferentially oriented with their symmetry axis pointing in a direction close to the surface normal for methanol, ethanol, and 1-propanol. However, for 2-propanol, the methyl groups exhibit a larger tilt angle. © 2021 American Chemical Society.
    view abstractdoi: 10.1021/acs.jpcc.1c01603
  • 2021 • 1242 Promising Membrane for Polymer Electrolyte Fuel Cells Shows Remarkable Proton Conduction over Wide Temperature and Humidity Ranges
    Berber, M.R. and Ismail, M.S. and Pourkashanian, M. and Zakaria Hegazy, M.B. and Apfel, U.-P.
    ACS Applied Polymer Materials 3 4275-4286 (2021)
    A step in the direction of the real-life application of fuel cells (FCs) has been realized through the fabrication of a promising proton conductive membrane comprising a perfluorosulfonic-acid ionomer and nitrogen-rich poly[2,2′-(4,4′-bipyridine)-5,5′-bibenzimidazole] (BiPyPBI). The BiPyPBI-perfluorosulfonic acid membranes displayed remarkable oxidative and mechanical stabilities with significant proton conduction over wide ranges of temperatures (40 to 140 °C) and humidities (30 to 90% RH). A 0.5 molar BiPyPBI feed ratio increased the proton conduction of perfluorosulfonic acid by 2.6- and 1.5-fold at 40 and 80 °C, respectively, due to the enhancement in the ion-exchange capacity (1.9 mmol/g, which was twofold higher than that of bare Nafion). The protonic conductivity reached 0.171 S/cm at 140 °C. Using a BiPyPBI feed increased the stability of the Nafion membrane, corresponding to a 3.5-fold increase in the mechanical stress (9.6 MPa) and a 2.2-fold decrease in the elongation at break. In addition, the oxidation stability of the Nafion membrane increased by 26%. The measured activation energy suggested that the presence of BiPyPBI created an easier proton transport pathway (by the Grotthuss mechanism) because of a stronger hydrogen-bonding network than in bare Nafion. Compared to the power density of a perfluorosulfonic-based MEA, the power density of the BiPyPBI-perfluorosulfonic-based membrane electrode assembly (MEA) at 140 °C increased by approximately 20-fold to 175 mW cm-1 at 30% RH and by approximately 5-fold to 201 mW cm-1 at 90% RH. Impedance spectra confirmed the improvement of the FC performance of the BiPyPBI-perfluorosulfonic-based MEA, indicating enhanced charge transfer. After 10,000 cycles of relative humidity stress testing, the BiPyPBI-perfluorosulfonic-based MEA showed a power density of 146 mW cm-1 (corresponding to a 16% loss in the initial power density measured at 30% RH). The MEA lost only 26% of its initial power density upon relative humidity stress cycling. © 2021 American Chemical Society.
    view abstractdoi: 10.1021/acsapm.1c00869
  • 2021 • 1241 Evaluation of log P, pK a, and log D predictions from the SAMPL7 blind challenge
    Bergazin, T.D. and Tielker, N. and Zhang, Y. and Mao, J. and Gunner, M.R. and Francisco, K. and Ballatore, C. and Kast, S.M. and Mobley, D.L.
    Journal of Computer-Aided Molecular Design (2021)
    The Statistical Assessment of Modeling of Proteins and Ligands (SAMPL) challenges focuses the computational modeling community on areas in need of improvement for rational drug design. The SAMPL7 physical property challenge dealt with prediction of octanol-water partition coefficients and pKa for 22 compounds. The dataset was composed of a series of N-acylsulfonamides and related bioisosteres. 17 research groups participated in the log P challenge, submitting 33 blind submissions total. For the pKa challenge, 7 different groups participated, submitting 9 blind submissions in total. Overall, the accuracy of octanol-water log P predictions in the SAMPL7 challenge was lower than octanol-water log P predictions in SAMPL6, likely due to a more diverse dataset. Compared to the SAMPL6 pKa challenge, accuracy remains unchanged in SAMPL7. Interestingly, here, though macroscopic pKa values were often predicted with reasonable accuracy, there was dramatically more disagreement among participants as to which microscopic transitions produced these values (with methods often disagreeing even as to the sign of the free energy change associated with certain transitions), indicating far more work needs to be done on pKa prediction methods. © 2021, The Author(s).
    view abstractdoi: 10.1007/s10822-021-00397-3
  • 2021 • 1240 Simulative design of constraints for targeted restriction of chip thickness deviations when machining titanium alloy Ti6Al4V
    Berger, S. and Brock, G. and Biermann, D.
    Procedia CIRP 102 85-90 (2021)
    When machining the titanium alloy Ti6Al4V, segmented chip formation is a major challenge as it leads to chatter-vibrations of the tool-machine-system. In this paper a counter element to suppress segmentation, the constraint, is designed by simulations. Therefore, the segmented chip formation of Ti6Al4V has been modelled in a finite element simulation using different approaches for flow stress modelling. The simulation results were validated with the help of orthogonal cutting experiments. Based on a suitable choice of a flow stress model, different geometries and positions of the constraint are analysed and discussed in this paper. © 2021 Elsevier B.V.. All rights reserved.
    view abstractdoi: 10.1016/j.procir.2021.09.015
  • 2021 • 1239 Prediction of vibration caused by dynamic compactors considering soil-dependent force emission [Erschütterungsprognose für dynamische verdichtungsgeräte unter berücksichtigung der bodenabhängigen kraftemission]
    Berg-Jahnke, R. and Meschke, G. and Heiland, D.
    Bauingenieur 96 143-155 (2021)
    Until now, vibration immissions caused by dynamically excited compactors are usually predicted using empirical formulas, whose uncertainties come from lack of knowledge about the influences of machine parameters and soil properties. A novel predictive method is presented, which is based on the individual force emission of the machine depending on the machine-soil interaction and the measured transfer mobility. The transfer mobility, which is examined by artificial vibration excitation with an impulse generator, is the transfer function between force excitation and received vibration velocity. Emitted spectral forces, which can be used for prognosis, are previously determined by extensive measurements. The developed method provides vibration values in the frequency and time domain taking into account statistical variations of influencing parameters. The comparison of predicted and measured values shows an enhanced accuracy of the new method. © 2021, VDI Fachmedien GmBbH & Co.. All rights reserved.
    view abstractdoi: 10.37544/0005-6650-2021-05-27
  • 2021 • 1238 Correction to: Modeling of cutting forces in trochoidal milling with respect to wear-dependent topographic changes (Production Engineering, (2021), 10.1007/s11740-021-01060-4)
    Bergmann, J.A. and Potthoff, N. and Rickhoff, T. and Wiederkehr, P.
    Production Engineering (2021)
    Due to technical problems, section 2.1 contained a misplaced symbol after publication of the paper. The description of workpiece dimensions has been corrected for the missing symbol. Original article corrected. © 2021, © The Author(s).
    view abstractdoi: 10.1007/s11740-021-01065-z
  • 2021 • 1237 Modeling of cutting forces in trochoidal milling with respect to wear-dependent topographic changes
    Bergmann, J.A. and Potthoff, N. and Rickhoff, T. and Wiederkehr, P.
    Production Engineering (2021)
    The aerospace industry utilizes nickel-based super-alloys due to its high level of strength and corrosion resistance. To evaluate milling strategies regarding tool wear, the prediction of forces during these cutting operations is essential. This comprises the determination of the undeformed chip thickness. Due to the complex interdependencies of tool engagements, the determination of these thicknesses is challenging. A geometric physically-based simulation system was extended by a novel time-discrete envelope model to increase the precision of the calculated undeformed chip thicknesses. In order to take tool wear into account, digitized topographies of cutting inserts in different states of tool wear were modelled. © 2021, The Author(s).
    view abstractdoi: 10.1007/s11740-021-01060-4
  • 2021 • 1236 Weakly symmetric stress equilibration and a posteriori error estimation for linear elasticity
    Bertrand, F. and Kober, B. and Moldenhauer, M. and Starke, G.
    Numerical Methods for Partial Differential Equations (2021)
    This paper proposes and analyzes a posteriori error estimator based on stress equilibration for linear elasticity with emphasis on the behavior for (nearly) incompressible materials. It is based on an H(div)-conforming, weakly symmetric stress reconstruction from the displacement-pressure approximation computed with a stable finite element pair. Our focus is on the Taylor-Hood combination of continuous finite element spaces of polynomial degrees k + 1 and k for the displacement and the pressure, respectively. This weak symmetry allows us to prove that the resulting error estimator constitutes a guaranteed upper bound for the error with a constant that depends only on local constants associated with the patches and thus on the shape regularity of the triangulation. It does not involve global constants like those from Korn's in equality which may become very large depending on the location and type of the boundary conditions. Local efficiency, also uniformly in the incompressible limit, is deduced from the upper bound by the residual error estimator. Numerical results for the popular Cook's membrane test problem confirm the theoretical predictions. © 2021 The Authors. Numerical Methods for Partial Differential Equations published by Wiley Periodicals LLC.
    view abstractdoi: 10.1002/num.22741
  • 2021 • 1235 Recent Advances in Least-Squares and Discontinuous Petrov–Galerkin Finite Element Methods
    Bertrand, F. and Demkowicz, L. and Gopalakrishnan, J.
    Computers and Mathematics with Applications 95 1-3 (2021)
    doi: 10.1016/j.camwa.2021.05.029
  • 2021 • 1234 Least-squares formulations for eigenvalue problems associated with linear elasticity
    Bertrand, F. and Boffi, D.
    Computers and Mathematics with Applications 95 19-27 (2021)
    We study the approximation of the spectrum of least-squares operators arising from linear elasticity. We consider a two-field (stress/displacement) and a three-field (stress/displacement/vorticity) formulation; other formulations might be analyzed with similar techniques. We prove a priori estimates and we confirm the theoretical results with simple two-dimensional numerical experiments. © 2021 The Author(s)
    view abstractdoi: 10.1016/j.camwa.2020.12.013
  • 2021 • 1233 An Adaptive Finite Element Scheme for the Hellinger-Reissner Elasticity Mixed Eigenvalue Problem
    Bertrand, F. and Boffi, D. and Ma, R.
    Computational Methods in Applied Mathematics 21 501-512 (2021)
    In this paper, we study the approximation of eigenvalues arising from the mixed Hellinger-Reissner elasticity problem by using a simple finite element introduced recently by one of the authors. We prove that the method converges when a residual type error estimator is considered and that the estimator decays optimally with respect to the number of degrees of freedom. A postprocessing technique originally proposed in a different context is discussed and tested numerically. © 2021 Walter de Gruyter GmbH, Berlin/Boston 2021.
    view abstractdoi: 10.1515/cmam-2020-0034
  • 2021 • 1232 Robust and reliable finite element methods in poromechanics
    Bertrand, F. and Ern, A. and Radu, F.A.
    Computers and Mathematics with Applications 91 1-2 (2021)
    doi: 10.1016/j.camwa.2021.04.012
  • 2021 • 1231 Convergence analysis of the scaled boundary finite element method for the Laplace equation
    Bertrand, F. and Boffi, D. and G. de Diego, G.
    Advances in Computational Mathematics 47 (2021)
    The scaled boundary finite element method (SBFEM) is a relatively recent boundary element method that allows the approximation of solutions to partial differential equations (PDEs) without the need of a fundamental solution. A theoretical framework for the convergence analysis of SBFEM is proposed here. This is achieved by defining a space of semi-discrete functions and constructing an interpolation operator onto this space. We prove error estimates for this interpolation operator and show that optimal convergence to the solution can be obtained in SBFEM. These theoretical results are backed by two numerical examples. © 2021, The Author(s).
    view abstractdoi: 10.1007/s10444-021-09852-z
  • 2021 • 1230 Least-squares finite element method for a meso-scale model of the spread of covid-19
    Bertrand, F. and Pirch, E.
    Computation 9 1-22 (2021)
    This paper investigates numerical properties of a flux-based finite element method for the discretization of a SEIQRD (susceptible-exposed-infected-quarantined-recovered-deceased) model for the spread of COVID-19. The model is largely based on the SEIRD (susceptible-exposed-infected-recovered-deceased) models developed in recent works, with additional extension by a quarantined compartment of the living population and the resulting first-order system of coupled PDEs is solved by a Least-Squares meso-scale method. We incorporate several data on political measures for the containment of the spread gathered during the course of the year 2020 and develop an indicator that influences the predictions calculated by the method. The numerical experiments conducted show a promising accuracy of predictions of the space-time behavior of the virus compared to the real disease spreading data. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/computation9020018
  • 2021 • 1229 Digital holography for spatially resolved analysis of the semiconductor optical response
    Besaga, V.R. and Gerhardt, N.C. and Hofmann, M.R.
    Applied Optics 60 A15-A20 (2021)
    We present spatially resolved measurements of the below-band-gap carrier-induced absorption and concurrent phase change in a semiconductor with the help of transmission digital holography. The application is demonstrated for a bulk GaAs sample, while the holograms are recorded with a conventional CMOS sensor. We show that the phase information enables spatially resolved monitoring of excess carrier distributions. Based on that, we discuss a phase-based approach for separation of carrier and heat related effects in the semiconductor optical response. © 2020 Optical Society of America.
    view abstractdoi: 10.1364/AO.402488
  • 2021 • 1228 Prestressing effect of shape memory alloy reinforcements under serviceability tensile loads
    Beßling, M. and Czaderski, C. and Orlowsky, J.
    Buildings 11 (2021)
    Repairing and strengthening of existing aged steel-reinforced concrete structures is a ma-jor challenge. Today, much of the repair work completed is insufficient and brittle. A promising new solution for repair and strengthening tasks is the use of iron-based shape memory alloy (Fe-SMA). The pre-strained Fe-SMA components enable the pre-stressing of existing building components due to the heat-triggered contraction of the steel. Thus, deflections can be reduced or even recovered. In addition, the cracking process can be adapted, and an improvement in the load, under which the first crack appears, is possible. In this paper, the effects of pre-stress generated by activated Fe-SMA rebars, which were centrally embedded inside of a concrete specimen, are shown. The objective of the study is to quantify the improvement in the loads of the first crack and show the influences of the pre-stressing on the load-bearing behavior and the cracking process. For this purpose, axial tensile tests were performed on concrete bars with height, width, and length of 50 mm, 70 mm, and 900 mm, respectively. These were compared to usual construction steel rebars, pre-strained but nonactivated Fe-SMA rebars, and activated Fe-SMA steel rebars. The evaluation of crack patterns and openings was done using digital image correlation (DIC). The pre-stressing of the concrete causes an increase in the first crack loads of more than 150%, which indicates a clear improvement in the state of serviceability limit. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/buildings11030101
  • 2021 • 1227 The Influence of Photo-Induced Space Charge and Energetic Disorder on the Indoor and Outdoor Performance of Organic Solar Cells
    Beuel, S. and Hartnagel, P. and Kirchartz, T.
    Advanced Theory and Simulations 4 (2021)
    Apart from traditional large-scale outdoor application, organic solar cells are also of interest for powering small, off-grid electronic devices indoors. For operation under the low light intensities that are typical for indoor application, a high shunt resistance is required calling for thick active layers in industrial processing to ensure maximum coverage. However, the thickness of an organic solar cell based on energetically disordered semiconductors is limited by space-charge effects from charged shallow defects under nonuniform generation. While other sources of space charge such as doping and asymmetric transport have been extensively discussed in previous studies, this work offers a theoretical analysis of this photo-induced space charge in shallow defects and visualizes how the space charge builds up with increasing light intensity with drift-diffusion simulations. It is shown that the effect particularly deteriorates the performance of an organic solar cell with high active-layer thickness and substantial energetic disorder. However, the simulations reveal that solar cells are less sensitive to these parameters under low light intensities due to a reduced density of photo-induced space charge. Therefore, a wider range of material systems and absorber thicknesses can be viable for indoor applications than one may initially expect from testing under 1 sun illumination. © 2021 The Authors. Advanced Theory and Simulations published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/adts.202000319
  • 2021 • 1226 Low-temperature and low-pressure effective fluorescence lifetimes and spectra of gaseous anisole and toluene
    Beuting, M. and Dreier, T. and Schulz, C. and Endres, T.
    Applied Physics B: Lasers and Optics 127 (2021)
    Fluorescence spectra and lifetimes of anisole and toluene vapor in nitrogen have been measured at conditions below ambient (257–293 K and 100–2000 mbar) upon excitation with 266-nm laser light to expand the applicable range of anisole and toluene laser-induced fluorescence (LIF) for conditions below room temperature that occur in expanding flows and cases with strong evaporative cooling. Anisole fluorescence spectra broaden with decreasing pressure while fluorescence lifetimes decrease simultaneously. This is consistent with a more pronounced effect of internal vibrational redistribution on the overall fluorescence signal and can be explained by significantly reduced collision rates. In the case of toluene, the transition from photo-induced heating to photo-induced cooling was observed for the first time for 266 nm. The data confirm predictions of earlier work and is particularly important for the advancement of the available photo-physical (step-ladder) models: since those transitions mark points where the molecules are already thermalized after excitation (i.e., no vibrational relaxation occurs during deactivation), they are important support points for fitting empirical parameters and allow analytical determination of the ground state energy transferred to the excited state. The data enable temperature and/or pressure sensing, e.g., in accelerating cold flows using laser-induced fluorescence of both tracers. © 2021, The Author(s).
    view abstractdoi: 10.1007/s00340-021-07605-w
  • 2021 • 1225 Zwitterionic Peptides Reduce Accumulation of Marine and Freshwater Biofilm Formers
    Beyer, C.D. and Thavalingam, S. and Guseva, T. and Schardt, L. and Zimmermann, R. and Werner, C. and Dietze, P. and Bandow, J.E. and Metzler-Nolte, N. and Rosenhahn, A.
    ACS Applied Materials and Interfaces 13 49682-49691 (2021)
    Zwitterionic peptides are facile low-fouling compounds for environmental applications as they are biocompatible and fully biodegradable as their degradation products are just amino acids. Here, a set of histidine (H) and glutamic acid (E), as well as lysine (K) and glutamic acid (E) based peptide sequences with zwitterionic properties were synthesized. Both oligopeptides (KE)4K and (HE)4H were synthesized in d and l configurations to test their ability to resist the nonspecific adsorption of the proteins lysozyme and fibrinogen. The coatings were additionally tested against the attachment of the marine organisms Navicula perminuta and Cobetia marina as well as the freshwater bacterium Pseudomonas fluorescens on the developed coatings. While the peptides containing lysine performed better in protein resistance assays and against freshwater bacteria, the sequences containing histidine were generally more resistant against marine organisms. The contribution of amino acid-intrinsic properties such as side chain pKa values and hydrophobicity, as well as external parameters such as pH and salinity of fresh water and seawater on the resistance of the coatings is discussed. In this way, a detailed picture emerges as to which zwitterionic sequences show advantages in future generations of biocompatible, sustainable, and nontoxic fouling release coatings. © 2021 The Authors. Published by American Chemical Society.
    view abstractdoi: 10.1021/acsami.1c13459
  • 2021 • 1224 Asymmetric pressure distribution in EPB shields: Evaluation of measurements and numerical simulations
    Bezuijen, A. and Dang, T.S. and Meschke, G.
    Geotechnical Aspects of Underground Construction in Soft Ground - Proceedings of the 10th International Symposium on Geotechnical Aspects of Underground Construction in Soft Ground, IS-CAMBRIDGE 2022 226-233 (2021)
    Measurements have shown that the pressure distribution at the front of an EPB shield drilling in saturated granular material is not symmetric with respect to the vertical plane. This was confirmed recently by computational simulations of the material flow within different EPB pressure chambers. The fluid pressure is higher in the part where the cutting wheel is moving upwards, compared to the pressure in the part where the movement is downward. This unbalance may influence both the steering of the TBM and the stability of the tunnel face. The pressure distribution as measured with pore pressure gauges at the cutting wheel are used to calculate the centre of gravity of the muck in an EPB and the measured pressure differences are compared with theoretical calculations. The pore pressure distribution in the mixing chamber along lines parallel to the tunnel axis is discussed. © 2021 ISSMGE, London, UK
    view abstractdoi: 10.1201/9780429321559-29
  • 2021 • 1223 A literature review on large intestinal hyperelastic constitutive modeling
    Bhattarai, A. and Kowalczyk, W. and Tran, T.N.
    Clinical Biomechanics 88 (2021)
    Impacts, traumas and strokes are spontaneously life-threatening, but chronic symptoms strangle patient every day. Colorectal tissue mechanics in such chronic situations not only regulates the physio-psychological well-being of the patient, but also confirms the level of comfort and post-operative clinical outcomes. Numerous uniaxial and multiaxial tensile experiments on healthy and affected samples have evidenced significant differences in tissue mechanical behavior and strong colorectal anisotropy across each layer in thickness direction and along the length. Furthermore, this study reviewed various forms of passive constitutive models for the highly fibrous colorectal tissue ranging from the simplest linearly elastic and the conventional isotropic hyperelastic to the most sophisticated second harmonic generation image based anisotropic mathematical formulation. Under large deformation, the isotropic description of tissue mechanics is unequivocally ineffective which demands a microstructural based tissue definition. Therefore, the information collected in this review paper would present the current state-of-the-art in colorectal biomechanics and profoundly serve as updated computational resources to develop a sophisticated characterization of colorectal tissues. © 2021 Elsevier Ltd
    view abstractdoi: 10.1016/j.clinbiomech.2021.105445
  • 2021 • 1222 Silica-coated calcium phosphate nanoparticles for gene silencing of NF-κB p65 by siRNA and their impact on cellular players of inflammation
    Białas, N. and Müller, E.K. and Epple, M. and Hilger, I.
    Biomaterials 276 (2021)
    The transcription factor NF-κB and its signaling cascade both play key roles in all inflammatory processes. The most critical member of the NF-κB transcription factor family is p65. We investigated the role of cationic silica-coated calcium phosphate nanoparticles (spherical, diameter by SEM 50–60 nm; zeta potential about +26 mV; stabilized by polyethyleneimine) carrying encapsulated siRNA against NF-κB p65 and their influence on inflamed cells. The nanoparticles were taken up by cells of the blood compartment involved in the inflammatory response, particularly by monocytes, and to a lesser extent by endothelial cells and B-cells, but not by T-cells. The particles were found in endolysosomes where they were dissolved at low pH and released the siRNA into the cytoplasm. This was confirmed by dissolution experiments of model nanoparticles in simulated endolysosomal medium (pH 4.7) and by intracellular co-localization studies of double-labeled nanoparticles (using a negatively charged model peptide for siRNA). The encapsulated functional siRNA reverted the p65 gene and protein expression in inflamed monocytes, the main cells in immune response and surveillance, almost back to the non-inflammatory condition. Additionally, the nanoparticles suppressed the pro-inflammatory cytokine expression profiles (TNF-α, IL-6, IFN-β) in inflamed J774A.1 monocytes. Taken together, such nanoparticles can be applied for the treatment of inflammatory diseases. © 2021 Elsevier Ltd
    view abstractdoi: 10.1016/j.biomaterials.2021.121013
  • 2021 • 1221 Teeth of Past and Present Elephants: Microstructure and Composition of Enamel in Fossilized Proboscidean Molars and Implications for Diagenesis
    Białas, N. and Prymak, O. and Singh, N.P. and Paul, D. and Patnaik, R. and Epple, M.
    Geochemistry, Geophysics, Geosystems 22 (2021)
    Enamel as hardest biological tissue remains unaltered for millions of years and is therefore an excellent archive for studies on paleodiet, paleoecology, paleoclimate, paleoenvironment, biomechanical, and evolutionary studies. However, diagenetic alterations can influence such interpretations and therefore we analyzed the microstructure and composition (elemental and stable isotopic) of fossil and extant proboscidean teeth to study the extent of diagenesis in them. We report for the first time on the enamel microstructure data of the Indian elephantiformes Anancus, Stegodon, Elephas, and Palaeoloxodon besides analyzing Gomphotherium and Deinotherium from new formations. Furthermore, we compare their microstructure with those of the primitive African taxa of Moeritherium and Palaeomastodon. Our results from depth-related elemental composition and oxygen isotope ratios of enamel phosphate and carbonate indicate no or only negligible modification. There is also a lack of age-dependency of these minor alterations within the fossils collected from Siwaliks of the Himalayan Foreland Basin. Overall, our study indicates that diagenesis has not played any significant role on the samples studied here and are therefore well suited for chemical and paleontological studies and proxy for paleoclimate and paleoenvironment reconstruction. © 2021. The Authors.
    view abstractdoi: 10.1029/2020GC009557
  • 2021 • 1220 Synovial alpha-defensin at reimplantation in two-stage revision arthroplasty to rule out persistent infection
    Bielefeld, C. and Engler, H. and Jäger, M. and Wegner, A. and Wassenaar, D. and Busch, A.
    In Vivo 35 1073-1081 (2021)
    Background/Aim: Owing to the lack of a diagnostic gold standard, ruling out persistent periprosthetic joint infection (PJI) before second-stage surgery in the setting of two-stage revision arthroplasty constitutes a major challenge. We evaluated if the alpha-defensin-1 (AD-1) test could predict successful infection eradication before reimplantation of a new prosthesis. Patients and Methods: Our prospective study included 20 patients who underwent two-stage revision arthroplasty for treatment of PJI. A standard quantitative enzyme AD-1 immunoassay of synovial fluid, the synovial leukocyte esterase test and routine laboratory blood testing were performed prior to explantation and reimplantation. Treatment failure was defined according to the Delphi-based consensus criteria after a minimum follow-up of 1 year. Results: A 15% of our patients met the Delphi Criteria within 1 year. None of the markers investigated were significantly different in patients with and without reinfection. Conclusion: Further research is necessary to identify biomarkers more suitable for indicating persistent infection before reimplantation. © 2021 International Institute of Anticancer Research. All rights reserved.
    view abstractdoi: 10.21873/INVIVO.12352
  • 2021 • 1219 Observation of low-temperature chemistry products in laminar premixed low-pressure flames by molecular-beam mass spectrometry
    Bierkandt, T. and Oßwald, P. and Gaiser, N. and Krüger, D. and Köhler, M. and Hoener, M. and Shaqiri, S. and Kaczmarek, D. and Karakaya, Y. and Hemberger, P. and Kasper, T.
    International Journal of Chemical Kinetics (2021)
    The formation of typical low-temperature oxidation products is observed in laminar premixed low-pressure flames investigated by photoionization molecular-beam mass spectrometry at the Swiss Light Source. The C1–C4 alkyl hydroperoxides can be identified in n-butane- and 2-butene-doped hydrogen flames by their photoionization efficiency spectra at m/z 48, 62, 76, and 90. C1–C3 alkyl hydroperoxides are also observed in a propane-doped hydrogen flame and in a neat propane flame. In addition, threshold photoelectron spectra reveal the presence of the alkyl hydroperoxides. In the 2-butene/H2 flame, the photoionization spectrum at m/z 88 also enables the identification of butenyl hydroperoxides by comparison with calculated ionization energies of the alkenyl hydroperoxides and a literature spectrum. The low-temperature species are formed close to the burner surface with maximum mole fractions at 0.25–0.75 mm above the burner. At 0.5 mm, even the methylperoxy radical (CH3OO) is measured for the first time in a laminar premixed flame. The rate of production analyses show that consumption of the hydroperoxyalkyl radicals results in the formation of cyclic ethers. In the n-butane/H2 flame, ethylene oxide, oxetane, and methyloxirane are identified. Besides expected small oxygenated species, for example, formaldehyde or acetaldehyde, the larger C4 oxygenates butanone (C2H5COCH3) and 2,3-butanedione (C4H6O2) are formed in the two C4 hydrocarbon-doped hydrogen flames. Quantification of alkyl hydroperoxides with estimated photoionization cross sections based on the corresponding alcohols, which have similar photoelectron structures to the alkyl hydroperoxides, shows that mole fractions are on the order of 10−5–10−6 in the n-butane/H2 flame. Measurements are corroborated by simulations, which also predict the presence of some peroxides in detectable concentrations, that is, mole fractions larger than 10−7, under the investigated conditions. The observation of peroxide species and cyclic ethers in the investigated laminar premixed flames give new insights into the contribution of low-temperature combustion chemistry in a flame. © 2021 The Authors. International Journal of Chemical Kinetics published by Wiley Periodicals LLC
    view abstractdoi: 10.1002/kin.21503
  • 2021 • 1218 Understanding Grain Boundary Electrical Resistivity in Cu: The Effect of Boundary Structure
    Bishara, H. and Lee, S. and Brink, T. and Ghidelli, M. and Dehm, G.
    ACS Nano 15 16607-16615 (2021)
    Grain boundaries (GBs) in metals usually increase electrical resistivity due to their distinct atomic arrangement compared to the grain interior. While the GB structure has a crucial influence on the electrical properties, its relationship with resistivity is poorly understood. Here, we perform a systematic study on the resistivity-structure relationship in Cu tilt GBs, employing high-resolution in situ electrical measurements coupled with atomic structure analysis of the GBs. Excess volume and energies of selected GBs are calculated using molecular dynamics simulations. We find a consistent relation between the coincidence site lattice (CSL) type of the GB and its resistivity. The most resistive GBs are in the high range of low-angle GBs (14°-18°) with twice the resistivity of high angle tilt GBs, due to the high dislocation density and corresponding strain fields. Regarding the atomistic structure, GB resistivity approximately correlates with the GB excess volume. Moreover, we show that GB curvature increases resistivity by ∼80%, while phase variations and defects within the same CSL type do not considerably change it. © 2021 The Authors. Published by American Chemical Society.
    view abstractdoi: 10.1021/acsnano.1c06367
  • 2021 • 1217 Novel approach to study diffusion of hydrogen bearing species in silicate glasses at low temperatures
    Bissbort, T. and Becker, H.-W. and Fanara, S. and Chakraborty, S.
    Chemical Geology 562 (2021)
    Diffusion of hydrogen bearing species in glasses plays a significant role in numerous applications in commercial as well as scientific domains. The investigation of diffusion of water in glasses at low temperatures led to experimental and analytical difficulties in the past. We present a new approach that lets us overcome these complications. Diffusion couples of An50Di50 glass (mol %, NBO/T = 0.67) were produced by coating anhydrous glass substrates with thin films of hydrated glass (~200 nm, ~2 wt% H2O) using pulsed laser deposition (PLD). Bonding the diffusant to the glass matrix of the thin film instead of using free water at the interface during experiments precludes other glass altering processes such as dissolution and precipitation. This allows us to confidently interpret the measured profiles to be a result of diffusion only. Nanoscale concentration profiles that result from diffusion at low temperatures on experimentally feasible time scales were measured with the Nuclear Resonance Reaction Analysis (NRRA, 1H(15N,αγ)12C). The non-destructive nature of NRRA enables us to observe and better understand the evolution of diffusion profiles with time within one sample. Evaluation of the sample quality by EPMA, SEM, optical microscopy, Rutherford backscattering spectroscopy (RBS), and NRRA was performed and confirmed the suitability of the samples for diffusion studies. Experiments at 1 atm in a box furnace and at 2 kbar in a CSPV (pressure medium = water) and an IHPV (pressure medium = Argon) prove that the diffusion couples can be used under various experimental conditions. We present diffusion profiles that were measured in experiments carried out in these devices and discuss the distinct features of each that result from different boundary conditions in the experiments. © 2020 Elsevier B.V.
    view abstractdoi: 10.1016/j.chemgeo.2020.120037
  • 2021 • 1216 Increasing the Complexity in the MIL-53 Structure: The Combination of the Mixed-Metal and the Mixed-Linker Concepts
    Bitzer, J. and Teubnerová, M. and Kleist, W.
    Chemistry - A European Journal 27 1724-1735 (2021)
    The isoreticular mixed-component concept is a promising approach to tailor the material properties of metal–organic frameworks. While isoreticular mixed-metal or mixed-linker materials are commonly synthesized, the combination of both concepts for the development of isoreticular materials featuring both two metals and two linkers is still rarely investigated. Herein, we present the development of mixed-metal/mixed-linker MIL-53 materials that contain different metal combinations (Al/Sc, Al/V, Al/Cr, Al/Fe) and different linker ratios (terephthalate/2-aminoterephthalate). The possibility of changing the metal combination and the linker ratio independently from each other enables a large variety of modifications. A thorough characterization (PXRD, ATR-IR, TGA, 1H NMR, ICP-OES) confirmed that all components were incorporated into the framework structure with a statistical distribution. Nitrogen physisorption measurements showed that the breathing behavior can be tailored by adjusting the linker ratio for all metal combinations. All materials were successfully used for post-synthetic modification reactions with maleic anhydride. © 2020 The Authors. Published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/chem.202003304
  • 2021 • 1215 One-Step Synthesis of Core-Shell-Structured Mixed-Metal CPO-27(Cu,Co) and Investigations on Its Controlled Thermal Transformation
    Bitzer, J. and Göbel, C. and Muhamad Ismail, A. and Fu, Q. and Muhler, M. and Kleist, W.
    European Journal of Inorganic Chemistry 2021 2257-2261 (2021)
    Using the mixed-metal approach, a direct synthesis route at ambient pressure was developed for a new type of bimetallic metal-organic framework based on the CPO-27 structure. The structural characterization of CPO-27(Cu0.6−CS−Co0.4) using X-ray diffraction, transmission electron microscopy, energy-dispersive X-ray mapping and X-ray absorption spectroscopy revealed that the Cu2+ and Co2+ ions were exclusively incorporated at the metal positions of the CPO-27 lattice, but with a core-shell distribution within the crystallites. The parent framework material was then utilized as a precursor for the generation of novel bimetallic carbon-supported materials using the controlled thermal decomposition in a reducing atmosphere. During this decomposition process, the distribution of the two metals remained the same, which resulted in unique needle-shaped particles with a high dispersion of cobalt at the periphery of the amorphous carbon and agglomerated copper particles in the inside. © 2021 The Authors. European Journal of Inorganic Chemistry published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/ejic.202100227
  • 2021 • 1214 The effective equations for the ultrasonic response of wet cortical bone
    Blaszczyk, M. and Pertsch Gilbert, R. and Hackl, K.
    Mathematical Methods in the Applied Sciences 44 9096-9109 (2021)
    We outline the mathematical model of the ultrasonic response of wet cortical bone and its time-harmonic formulation. We employ an energetic approach based on the Reuss bound of the free energy of a porous material consisting of a piezo-electric solid and a conducting fluid part. Magnetic effects are taken into consideration. Corresponding boundary value problems are stated, and associated theorems are established. A conclusion is included concerning future developments of this formulation. © 2021 John Wiley & Sons, Ltd.
    view abstractdoi: 10.1002/mma.7337
  • 2021 • 1213 Multiscale modeling of cancellous bone considering full coupling of mechanical, electric and magnetic effects
    Blaszczyk, M. and Hackl, K.
    Biomechanics and Modeling in Mechanobiology (2021)
    Modeling of cancellous bone has important applications in the detection and treatment of fatigue fractures and diseases like osteoporosis. In this paper, we present a fully coupled multiscale approach considering mechanical, electric and magnetic effects by using the multiscale finite element method and a two-phase material model on the microscale. We show numerical results for both scales, including calculations for a femur bone, comparing a healthy bone to ones affected by different stages of osteoporosis. Here, the magnetic field strength resulting from a small mechanical impact decreases drastically for later stages of the disease, confirming experimental research. © 2021, The Author(s).
    view abstractdoi: 10.1007/s10237-021-01525-6
  • 2021 • 1212 An effective model for cancellous bone with a viscous interstitial fluid *
    Blaszczyk, M. and Pertsch Gilbert, R. and Hackl, K.
    Applicable Analysis (2021)
    We outline the mathematical model of the ultrasonic response of cancellous bone and its time harmonic formulation. In contrast to the Biot model, the fluid is not inviscid. Our fluid is viscous, but does not interact with the solid components. © 2021 Informa UK Limited, trading as Taylor & Francis Group.
    view abstractdoi: 10.1080/00036811.2021.1979221
  • 2021 • 1211 Amino−Organolithium Compounds and their Aggregation for the Synthesis of Amino−Organoaluminium Compounds
    Bodach, A. and Ortmeyer, J. and Herrmann, B. and Felderhoff, M.
    European Journal of Inorganic Chemistry 2021 2248-2256 (2021)
    Here, we present a thorough structural study of small, easily accessible amino−organolithium compounds with bridging phenyl and naphthyl moieties. Their crystal structures most likely represent their aggregation as tetramers and dimers in both hydrocarbon and ethereal solvents. These amino−organolithium compounds were further used to generate their corresponding aluminium compounds as a model system. Their crystal structures are reported too. All structures are discussed with a focus on the different steric demands and bridging moieties. Additionally, the crystal structures of neophyllithium and decomposition products of some of the compounds mentioned above are reported. This study provides additional data for the future design and synthesis of amine stabilised organolithium and -aluminium compounds. © 2021 The Authors. European Journal of Inorganic Chemistry published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/ejic.202100224
  • 2021 • 1210 Activation of Molecular Hydrogen by Inter- and Intramolecular Al−N Lewis Pairs
    Bodach, A. and Nöthling, N. and Felderhoff, M.
    European Journal of Inorganic Chemistry 2021 1240-1243 (2021)
    The field of frustrated Lewis pair chemistry offers many opportunities to activate molecular hydrogen, but Al−N systems have not been established yet. In this work, we describe several intermolecular classical Al−N Lewis pairs and an intramolecular ortho-ala-aminoarene for the activation of molecular hydrogen. Their ability was investigated using the isotope exchange reaction from HD to H2 and D2. The herein studied intermolecular Lewis pairs were based on alkylalanes and N-methyldiphenylamine, while the intramolecular Lewis pair was (o-TMP−C6H4)AlH2 ((2-(2,2,6,6-tetramethyl-piperidin-1-yl)phenyl)-aluminium dihydride). The activation of molecular hydrogen was carried out in toluene under mild conditions and monitored by 1H and 2H NMR spectroscopy. Furthermore, the Al−N interaction has been probed by 27Al NMR and crystallographic studies. Additionally, the crystal structure of pure AliBu3 was determined. These studies may attribute the pronounced reactivities of these Al−N compounds to elongated Al−N bond lengths. © 2021 The Authors. European Journal of Inorganic Chemistry published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/ejic.202001152
  • 2021 • 1209 Polymorphism of dimethylaminoborane N(CH3)2-BH2
    Bodach, A. and Bernert, T. and Fischer, M. and Leya, M.B. and Weidenthaler, C.
    Acta Crystallographica Section B: Structural Science, Crystal Engineering and Materials 77 299-306 (2021)
    Dehydrocoupling of the adduct of dimethylamine and borane, NH(CH3)2-BH3 leads to dimethylaminoborane with formal composition N(CH3)2-BH2. The structure of this product depends on the conditions of the synthesis; it may crystallize either as a dimer in a triclinic space group forming a four-membered ring [N(CH3)2-BH2]2 or as a trimer forming a six-membered ring [N(CH3)2-BH2]3 in an orthorhombic space group. Due to the denser packing, the six-membered ring in the trimer structure should be energetically more stable than the four-membered ring. The triclinic structure is stable at low temperatures. Heating the triclinic phase above 290K leads to a second-order phase transition to a new monoclinic polymorph. While the crystal structures of the triclinic and orthorhombic phases were already known in the literature, the monoclinic crystal structure was determined from powder diffraction data in this study. Monoclinic dimethylaminoborane crystallizes in space group C2/m with the boron and nitrogen atoms located on the mirror plane, Wyckoff position 4i, while the carbon and hydrogen atoms are on the general position 8j. © 2021.
    view abstractdoi: 10.1107/S2052520621001979
  • 2021 • 1208 Corrigendum to: Activation of Molecular Hydrogen by Inter- and Intramolecular Al−N Lewis Pairs (European Journal of Inorganic Chemistry, (2021), 2021, 13, (1240-1243), 10.1002/ejic.202001152)
    Bodach, A. and Nöthling, N. and Felderhoff, M.
    European Journal of Inorganic Chemistry (2021)
    On page 2 (1241), top right, the authors reported “In an equilibrium H2, HD and D2 exist in equimolar amounts.” This sentence should be replaced by: “In an equilibrium H2, HD, and D2 exist in a mixture corresponding to the equilibrium constant of the reaction H2 + D22 HD, which is reported to be 3.25 by H. Niki et al.[1] at 25 °C, i.e. all three types of molecules exist in appreciable amounts.” The authors con"rm that this change does not a#ect the results or conclusions of their paper and they apologize for any inconvenience caused. [1] H. Niki, Y. Rousseau, G. J. Mains, J. Chem. Phys. 1965, 69, 45--52. Corrigendum © 2021 Wiley-VCH GmbH.
    view abstractdoi: 10.1002/ejic.202100875
  • 2021 • 1207 Sampling distributions of optimal portfolio weights and characteristics in small and large dimensions
    Bodnar, T. and Dette, H. and Parolya, N. and Thorsén, E.
    Random Matrices: Theory and Application (2021)
    Optimal portfolio selection problems are determined by the (unknown) parameters of the data generating process. If an investor wants to realize the position suggested by the optimal portfolios, he/she needs to estimate the unknown parameters and to account for the parameter uncertainty in the decision process. Most often, the parameters of interest are the population mean vector and the population covariance matrix of the asset return distribution. In this paper, we characterize the exact sampling distribution of the estimated optimal portfolio weights and their characteristics. This is done by deriving their sampling distribution by its stochastic representation. This approach possesses several advantages, e.g. (i) it determines the sampling distribution of the estimated optimal portfolio weights by expressions, which could be used to draw samples from this distribution efficiently; (ii) the application of the derived stochastic representation provides an easy way to obtain the asymptotic approximation of the sampling distribution. The later property is used to show that the high-dimensional asymptotic distribution of optimal portfolio weights is a multivariate normal and to determine its parameters. Moreover, a consistent estimator of optimal portfolio weights and their characteristics is derived under the high-dimensional settings. Via an extensive simulation study, we investigate the finite-sample performance of the derived asymptotic approximation and study its robustness to the violation of the model assumptions used in the derivation of the theoretical results. © 2022 World Scientific Publishing Company.
    view abstractdoi: 10.1142/S2010326322500083
  • 2021 • 1206 Highly conductive titania supported iridium oxide nanoparticles with low overall iridium density as OER catalyst for large-scale PEM electrolysis
    Böhm, D. and Beetz, M. and Gebauer, C. and Bernt, M. and Schröter, J. and Kornherr, M. and Zoller, F. and Bein, T. and Fattakhova-Rohlfing, D.
    Applied Materials Today 24 (2021)
    To enable future large-scale generation of hydrogen via proton exchange membrane (PEM) electrolysis, utilization of scarce iridium-based catalysts required for the oxygen evolution reaction (OER) has to be significantly lowered. To address this question, the facile synthesis of a highly active TiO2 supported iridium oxide based OER catalyst with reduced noble metal content and an Ir-density of the catalyst powder as low as 0.05–0.08 gIr cm-3 is described in this work. A high surface area corrosion-resistant titania catalyst support homogeneously coated with a 1-2 nm thin layer of amorphous IrOOHx is oxidized in molten NaNO3 between 350-375°C. This procedure allows for a controllable phase transformation and crystallization to form a layer of interconnected IrO2 nanoparticles of ≈2 nm on the surface of the TiO2 support. The increase in crystallinity is thereby accompanied by a significant increase in conductivity of up to 11 S cm-1 for a 30 wt% Ir loaded catalyst. Oxidized samples further display a significantly increased stability with less detectable Ir dissolution under OER conditions. With a mass-based activity of 59 A g-1 at an overpotential of 300 mV, the electrocatalytic activity is maintained at the level of the highly active amorphous IrOOHx phase used as precursor and outperforms it at higher current densities through the increased conductivity. MEA measurements with catalyst loadings of 0.2-0.3 mg cm-2 further confirm the high catalytic activity and initial stability at industrially relevant current densities. The introduced synthesis approach therefore shows a path for the fabrication of novel highly active and atom-efficient oxide supported catalysts with complex nanostructures and thin homogenous nanoparticle coatings that allows a future large-scale application of PEM electrolysis technology without restrictions by the natural abundance of iridium. © 2021 Elsevier Ltd
    view abstractdoi: 10.1016/j.apmt.2021.101134
  • 2021 • 1205 Local Latin hypercube refinement for multi-objective design uncertainty optimization[Formula presented]
    Bogoclu, C. and Roos, D. and Nestorović, T.
    Applied Soft Computing 112 (2021)
    Optimizing the reliability and the robustness of a design is important but often unaffordable due to high sample requirements. Surrogate models based on statistical and machine learning methods are used to increase the sample efficiency. However, for higher dimensional or multi-modal systems, surrogate models may also require a large amount of samples to achieve good results. We propose a sequential sampling strategy for the surrogate based solution of multi-objective reliability based robust design optimization problems. Proposed local Latin hypercube refinement (LoLHR) strategy is model-agnostic and can be combined with any surrogate model because there is no free lunch but possibly a budget one. The proposed method is compared to stationary sampling as well as other proposed strategies from the literature. Gaussian process and support vector regression are both used as surrogate models. Empirical evidence is presented, showing that LoLHR achieves on average better results compared to other surrogate based strategies on the tested examples. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.asoc.2021.107807
  • 2021 • 1204 Isomeric effects in structure formation and dielectric dynamics of different octanols
    Bolle, J. and Bierwirth, S.P. and Požar, M. and Perera, A. and Paulus, M. and Münzner, P. and Albers, C. and Dogan, S. and Elbers, M. and Sakrowski, R. and Surmeier, G. and Böhmer, R. and Tolan, M. and Sternemann, C.
    Physical Chemistry Chemical Physics 23 24211-24221 (2021)
    The understanding of the microstructure of associated liquids promoted by hydrogen-bonding and constrained by steric hindrance is highly relevant in chemistry, physics, biology and for many aspects of daily life. In this study we use a combination of X-ray diffraction, dielectric spectroscopy and molecular dynamics simulations to reveal temperature induced changes in the microstructure of different octanol isomers,i.e., linear 1-octanol and branched 2-, 3- and 4-octanol. In all octanols, the hydroxyl groups form the basis of chain-, cyclic- or loop-like bonded structures that are separated by outwardly directed alkyl chains. This clustering is analyzed through the scattering pre-peaks observed from X-ray scattering and simulations. The charge ordering which pilots OH aggregation can be linked to the strength of the Debye process observed in dielectric spectroscopy. Interestingly, all methods used here converge to the same interpretation: as one moves from 1-octanol to the branched octanols, the cluster structure evolves from loose large aggregates to a larger number of smaller, tighter aggregates. All alcohols exhibit a peculiar temperature dependence of both the pre-peak and Debye process, which can be understood as a change in microstructure promoted by chain association with increased chain length possibly assisted by ring-opening effects. All these results tend to support the intuitive picture of the entropic constraint provided by branching through the alkyl tails and highlight its capital entropic role in supramolecular assembly. © the Owner Societies 2021.
    view abstractdoi: 10.1039/d1cp02468j
  • 2021 • 1203 Spin polarization and magnetotransport properties of systematically disordered Fe60Al40 thin films
    Borisov, K. and Ehrler, J. and Fowley, C. and Eggert, B. and Wende, H. and Cornelius, S. and Potzger, K. and Lindner, J. and Fassbender, J. and Bali, R. and Stamenov, P.
    Physical Review B 104 (2021)
    We investigate the evolution of spin polarization, spontaneous Hall angle (SHA), saturation magnetization, and Curie temperature of B2-ordered Fe60Al40 thin films under varying antisite disorder, induced by Ne+-ion irradiation. The spin polarization increases monotonically as a function of ion fluence. A relatively high polarization of 46% and a SHA of 3.1% are achieved on 40 nm films irradiated with 2×1016 ions/cm2 at 30 keV. An interesting divergence in the trends of the magnetization and SHA is observed for low disorder concentrations. The high spin polarization and its broad tunability range make ion-irradiated Fe60Al40 a promising material for application in spin electronic devices. © 2021 American Physical Society.
    view abstractdoi: 10.1103/PhysRevB.104.134417
  • 2021 • 1202 Deep Subwavelength Laser-Induced Periodic Surface Structures on Silicon as a Novel Multifunctional Biosensing Platform
    Borodaenko, Y. and Syubaev, S. and Gurbatov, S. and Zhizhchenko, A. and Porfirev, A. and Khonina, S. and Mitsai, E. and Gerasimenko, A.V. and Shevlyagin, A. and Modin, E. and Juodkazis, S. and Gurevich, E.L. and Kuchmizhak, A.A.
    ACS Applied Materials and Interfaces (2021)
    Strong light localization inside the nanoscale gaps provides remarkable opportunities for creation of various medical and biosensing platforms stimulating an active search for inexpensive and easily scalable fabrication at a sub-100 nm resolution. In this paper, self-organized laser-induced periodic surface structures (LIPSSs) with the shortest ever reported periodicity of 70 ± 10 nm were directly imprinted on the crystalline Si wafer upon its direct femtosecond-laser ablation in isopropanol. Appearance of such a nanoscale morphology was explained by the formation of a periodic topography on the surface of photoexcited Si driven by interference phenomena as well as subsequent down-scaling of the imprinted grating period via Rayleigh-Taylor hydrodynamic instability. The produced deep subwavelength LIPSSs demonstrate strong anisotropic anti-reflection performance, ensuring efficient delivery of the incident far-field radiation to the electromagnetic "hot spots"localized in the Si nanogaps. This allows realization of various optical biosensing platforms operating via strong interactions of quantum emitters with nanoscale light fields. The demonstrated 80-fold enhancement of spontaneous emission from the attached nanolayer of organic dye molecules and in situ optical tracing of catalytic molecular transformations substantiate bare and metal-capped deep subwavelength Si LIPSSs as a promising inexpensive multifunctional biosensing platform. ©
    view abstractdoi: 10.1021/acsami.1c16249
  • 2021 • 1201 Generalized Diffusion-Relaxation Model for Solvent Sorption in Polymers
    Borrmann, D. and Danzer, A. and Sadowski, G.
    Industrial and Engineering Chemistry Research (2021)
    Solvent sorption in polymers is of general interest for a wide variety of applications. It is well known that solvent sorption in polymers depends on both solvent diffusion and the slow rearrangement of the polymer, also known as polymer relaxation. This study provides a physically meaningful model approach for describing solvent diffusion in polymers, while considering relaxation in its most generalized form. A diffusion-relaxation model was created by combining the Stefan-Maxwell equations with multiple Maxwell elements. Parameter studies reveal the capability of the developed approach to describe anomalous solvent sorption behavior in polymers like sigmoidal, two-stage, pseudo-Fickian, case II, and super case II behavior. These parameter studies also provide detailed insights into the physical reasonings behind these phenomena. Moreover, to the best of our knowledge, this is the first time that first-principles modeling of multistage sorption curves is reported. ©
    view abstractdoi: 10.1021/acs.iecr.1c02359
  • 2021 • 1200 Ultrafast Amplification and Nonlinear Magnetoelastic Coupling of Coherent Magnon Modes in an Antiferromagnet
    Bossini, D. and Pancaldi, M. and Soumah, L. and Basini, M. and Mertens, F. and Cinchetti, M. and Satoh, T. and Gomonay, O. and Bonetti, S.
    Physical Review Letters 127 (2021)
    We investigate the role of domain walls in the ultrafast magnon dynamics of an antiferromagnetic NiO single crystal in a pump-probe experiment with variable pump photon energy. Analyzing the amplitude of the energy-dependent photoinduced ultrafast spin dynamics, we detect a yet unreported coupling between the material's characteristic terahertz- and gigahertz-magnon modes. We explain this unexpected coupling between two orthogonal eigenstates of the corresponding Hamiltonian by modeling the magnetoelastic interaction between spins in different domains. We find that such interaction, in the nonlinear regime, couples the two different magnon modes via the domain walls and it can be optically exploited via the exciton-magnon resonance. © 2021 American Physical Society.
    view abstractdoi: 10.1103/PhysRevLett.127.077202
  • 2021 • 1199 Atomic layer deposition of dielectric Y2O3thin films from a homoleptic yttrium formamidinate precursor and water
    Boysen, N. and Zanders, D. and Berning, T. and Beer, S.M.J. and Rogalla, D. and Bock, C. and Devi, A.
    RSC Advances 11 2565-2574 (2021)
    We report the application of tris(N,N′-diisopropyl-formamidinato)yttrium(iii) [Y(DPfAMD)3] as a promising precursor in a water-assisted thermal atomic layer deposition (ALD) process for the fabrication of high quality Y2O3 thin films in a wide temperature range of 150 °C to 325 °C. This precursor exhibits distinct advantages such as improved chemical and thermal stability over the existing Y2O3 ALD precursors including the homoleptic and closely related yttrium tris-amidinate [Y(DPAMD)3] and tris-guanidinate [Y(DPDMG)3], leading to excellent thin film characteristics. Smooth, homogeneous, and polycrystalline (fcc) Y2O3 thin films were deposited at 300 °C with a growth rate of 1.36 Å per cycle. At this temperature, contamination levels of C and N were under the detectable limits of nuclear reaction analysis (NRA), while X-ray photoelectron spectroscopy (XPS) measurements confirmed the high purity and stoichiometry of the thin films. From the electrical characterization of metal-insulator-semiconductor (MIS) devices, a permittivity of 13.9 at 1 MHz could be obtained, while the electric breakdown field is in the range of 4.2 and 6.1 MV cm-1. Furthermore, an interface trap density of 1.25 × 1011 cm-2 and low leakage current density around 10-7 A cm-2 at 2 MV cm-1 are determined, which satisfies the requirements of gate oxides for complementary metal-oxide-semiconductor (CMOS) based applications. © 2021 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/d0ra09876k
  • 2021 • 1198 Modifications of an electrolytic aluminum oxide film under the treatment with microdischarges during plasma electrolytic oxidation, a self-organized dielectric barrier discharge (DBD) and a DBD-like plasma jet
    Bracht, V. and Kogelheide, F. and Gröger, S. and Hermanns, P. and Böddeker, S. and Bibinov, N. and Awakowicz, P.
    Plasma Research Express 3 (2021)
    A key to the understanding of mechanisms during plasma electrolytic oxidation (PEO) is the interaction between microdischarges and an amorphous oxide film. The PEO microdischarges, which are randomly distributed on the surface of a treated lightweight metal substrate (Al, Ti, Mg), cause material extraction and support the formation of hard and dense crystalline oxide films. Characterization of these microdischarges is a complicated task under PEO conditions, because of the stochastically temporal and spatial behavior as well as the small dimension of the microdischarges. Microdischarges at atmospheric pressure conditions can leave similar erosion traces on metallic films (Al, Ti) as PEO microdischarges on oxide films, and possibly can support a better understanding of the plasma-solid-interactions as well as microdischarge characteristics during PEO. A porous aluminum oxide film is deposited on aluminum substrates by pre-anodizing at a voltage of 250 V and is treated afterwards with a relative short (duration of 1 min) PEO process at a voltage of about 500 V or filamentary dielectric barrier discharges, namely a self-organized Dielectric Barrier Discharge (DBD) and a DBD-like plasma jet operated both with a He/N2 (95%/5%) gas flow. The gas temperature at DBD plasma conditions, measured using the rotational distribution in the emission spectra of molecular nitrogen, is low and amounts to about 400 K. Erosion traces on the surface of the oxide film caused by PEO and plasma spots of both atmospheric pressure discharges are studied by scanning electron microscopy and energy dispersed x-ray spectroscopy. Form and dimensions of erosion traces and established modifications of the material composition generated by the treatment with these DBD microdischarges under atmospheric pressure conditions are similar to those ones generated by the PEO process. Hence, a similar mechanism of these processes is supposed. For stronger evidences of the assumed PEO mechanism additional experimental studies are needed. © 2021 IOP Publishing Ltd
    view abstractdoi: 10.1088/2516-1067/ac2e0f
  • 2021 • 1197 Subcritical crack growth in hard alloys under cyclic loading
    Brackmann, L. and Röttger, A. and Weber, S. and Theisen, W.
    Fatigue and Fracture of Engineering Materials and Structures 44 349-365 (2021)
    In this work, the subcritical crack growth in Fe-, Ni- and Co-base hard alloys was investigated. Specimens were cyclically loaded in the pressure threshold range until a ring crack resulted as a failure criterion. Crack propagation along with the individual microstructural constituents and the associated resistance of the individual materials to crack propagation was investigated by scanning electron microscopy and by the methods adapted to it. For the Ni-base alloys, the formation of a closed ring fracture occurred after the lowest load cycle number, followed by the Co- and Fe-base alloys. Almost no crack deflection by the hard phases was detected in the Ni-base alloys. The higher number of loading cycles to produce a closed crack ring in the Fe-base alloys is attributed to the pronounced crack deflection by the hard phases and to the higher matrix strength. Besides, phase transformations were registered in front of the crack tip of the Co- and the partially austenitic Fe-base alloy. This phase transformation counteracts crack formation in the case of the Fe-base matrix but promotes crack propagation in the Co-base alloy. © 2020 The Authors. Fatigue & Fracture of Engineering Materials & Structures published by John Wiley & Sons Ltd
    view abstractdoi: 10.1111/ffe.13363
  • 2021 • 1196 Advanced characterisation techniques: Multi-scale,: In situ, and time-resolved: General discussion
    Brammer, L. and Burrows, A.D. and Chong, S.Y.-L. and Craig, G. and Evans, J. and Farha, O. and Farrusseng, D. and Fischer, M. and Goodwin, A. and Huang, Z. and Johnson, B. and Kaskel, S. and Kitagawa, S. and Lavenn, C. and Lee, A....
    Faraday Discussions 225 152-167 (2021)
    doi: 10.1039/D0FD90032J
  • 2021 • 1195 Sterically constrained tricyclic phosphine: Redox behaviour, reductive and oxidative cleavage of P-C bonds, generation of a dilithium phosphaindole as a promising synthon in phosphine chemistry
    Brand, A. and Schulz, S. and Hepp, A. and Weigand, J.J. and Uhl, W.
    Chemical Science 12 3460-3474 (2021)
    The redox behaviour of sterically constrained tricyclic phosphine 3a was investigated by spectroelectrochemistry. The data suggested a highly negative reduction potential with the reversible formation of a dianionic species. Accordingly, 3a reacted with two equivalents of Li/naphthalene by reductive cleavage of a P-C bond of one of the PC4 heterocycles. The resulting dilithium compound 5 represents a phosphaindole derivative with annulated aromatic C6 and PC4 rings. It is an interesting starting material for the synthesis of new heterocyclic molecules, as was shown by treatment with Me2SiCl2 and PhPCl2. The structures of the products (6 and 7) formally reflect ring expansion by insertion of silylen or phosphinidene fragments into a P-C bond of 3a. Treatment of 3a with H2O2 did not result in the usually observed transfer of a single O atom to phosphorus, but oxidative cleavage of a strained PC4 ring afforded a bicyclic phosphinic acid, R2PO2H. © 2021 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/d0sc06155g
  • 2021 • 1194 Muscular and molecular pathology associated with SPATA5 deficiency in a child with EHLMRS
    Braun, F. and Hentschel, A. and Sickmann, A. and Marteau, T. and Hertel, S. and Förster, F. and Prokisch, H. and Wagner, M. and Wortmann, S. and Della Marina, A. and Kölbel, H. and Roos, A. and Schara‐schmidt, U.
    International Journal of Molecular Sciences 22 (2021)
    Mutations in the SPATA5 gene are associated with epilepsy, hearing loss and mental retardation syndrome (EHLMRS). While SPATA5 is ubiquitously expressed and is attributed a role within mitochondrial morphogenesis during spermatogenesis, there is only limited knowledge about the associated muscular and molecular pathology. This study reports on a comprehensive workup of muscular pathology, including proteomic profiling and microscopic studies, performed on an 8‐year‐old girl with typical clinical presentation of EHLMRS, where exome analysis revealed two clinically relevant, compound‐heterozygous variants in SPATA5. Proteomic profiling of a quadriceps biopsy showed the dysregulation of 82 proteins, out of which 15 were localized in the mitochondrion, while 19 were associated with diseases presenting with phenotypical overlap to EHLMRS. Histological staining of our patient’s muscle biopsy hints towards mitochondrial pathology, while the identification of dysregulated proteins attested to the vulnerability of the cell beyond the mitochondria. Through our study we provide insights into the molecular etiology of EHLMRS and provide further evidence for a muscle pathology associated with SPATA5 deficiency, including a pathological histochemical pattern accompanied by dysregulated protein expression. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/ijms22157835
  • 2021 • 1193 Prediction of short fiber composite properties by an artificial neural network trained on an rve database
    Breuer, K. and Stommel, M.
    Fibers 9 1-14 (2021)
    In this study, an artificial neural network is designed and trained to predict the elastic properties of short fiber reinforced plastics. The results of finite element simulations of three-dimensional representative volume elements are used as a data basis for the neural network. The fiber volume fraction, fiber length, matrix-phase properties, and fiber orientation are varied so that the neural network can be used within a very wide range of parameters. A comparison of the predictions of the neural network with additional finite element simulations shows that the stiffnesses of short fiber reinforced plastics can be predicted very well by the neural network. The average prediction accuracy is equal or better than by a two-step homogenization using the classical method of Mori and Tanaka. Moreover, it is shown that the training of the neural network on an extended data set works well and that particularly calculation-intensive data points can be avoided without loss of prediction quality. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/fib9020008
  • 2021 • 1192 Predicting the API partitioning between lipid-based drug delivery systems and water
    Brinkmann, J. and Becker, I. and Kroll, P. and Luebbert, C. and Sadowski, G.
    International Journal of Pharmaceutics 595 (2021)
    Partitioning tests in water are early-stage standard experiments during the development of pharmaceutical formulations, e.g. of lipid-based drug delivery system (LBDDS). The partitioning behavior of the active pharmaceutical ingredient (API) between the fatty phase and the aqueous phase is a key property, which is supposed to be determined by those tests. In this work, we investigated the API partitioning between LBDDS and water by in-silico predictions applying the Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT) and validated these predictions experimentally. The API partitioning was investigated for LBDDS comprising up to four components (cinnarizine or ibuprofen with tricaprylin, caprylic acid, and ethanol). The influence of LBDDS/water mixing ratios from 1/1 up to 1/200 (w/w) as well as the influence of excipients on the API partitioning was studied. Moreover, possible API crystallization upon mixing the LBDDS with water was predicted. This work showed that PC-SAFT is a strong tool for predicting the API partitioning behavior during in-vitro tests. Thus, it allows rapidly assessing whether or not a specific LBDDS might be a promising candidate for further in-vitro tests and identifying the API load up to which API crystallization can be avoided. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.ijpharm.2021.120266
  • 2021 • 1191 Electrocatalytic Oxidation of Glycerol Using Solid-State Synthesised Nickel Boride: Impact of Key Electrolysis Parameters on Product Selectivity
    Brix, A.C. and Morales, D.M. and Braun, M. and Jambrec, D. and Junqueira, J.R.C. and Cychy, S. and Seisel, S. and Masa, J. and Muhler, M. and Andronescu, C. and Schuhmann, W.
    ChemElectroChem 8 2336-2342 (2021)
    Water electrolysis is a promising technology for sustainable hydrogen production; however, its commercialisation is limited by sluggish kinetics of the oxygen evolution reaction (OER). A potential alternative to the OER is hence required and is seen in the electrocatalytic glycerol oxidation reaction (GOR) as it offers concomitant value-added product generation from a cheap and abundant feedstock. Here, we show a facile solid-state synthesis method to obtain Ni-boride, a non-noble metal-based catalyst subsequently used in an in-depth study of the GOR product distribution as a function of key electrolysis parameters. Highly crystalline, mixed-phase Ni borides were obtained, and their synthesis was successfully optimised regarding GOR activity. Long-term chronoamperometry was conducted in a circular flow-through cell and samples were analysed by HPLC. It is shown that the formation of lactic acid, one of the most valuable GOR products, can be enhanced by optimising the electrolyte composition and the applied potential. © 2021 The Authors. ChemElectroChem published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/celc.202100739
  • 2021 • 1190 Evolution and phylogeny of the deep-sea isopod families Desmosomatidae Sars, 1897 and Nannoniscidae Hansen, 1916 (Isopoda: Asellota)
    Brix, S. and Held, C. and Kaiser, S. and Jennings, R.M. and Driskell, A. and Brandt, A.
    Organisms Diversity and Evolution (2021)
    In the deep sea, the phylogeny and biogeography of only a few taxa have been well studied. Although more than 200 species in 32 genera have been described for the asellote isopod families Desmosomatidae Sars, 1897 and Nannoniscidae Hansen, 1916 from all ocean basins, their phylogenetic relationships are not completely understood. There is little doubt about the close relationship of these families, but the taxonomic position of a number of genera is so far unknown. Based on a combined morphological phylogeny using the Hennigian method with a dataset of 107 described species and a molecular phylogeny based on three markers (COI, 16S, and 18S) with 75 species (most new to science), we could separate Desmosomatidae and Nannoniscidae as separate families. However, we could not support the concept of the subfamilies Eugerdellatinae Hessler, 1970 and Desmosomatinae Hessler, 1970. Most genera of both families were well supported, but several genera appear as para- or even polyphyletic. Within both families, convergent evolution and analogies caused difficulty in defining apomorphies for phylogenetic reconstructions and this is reflected in the results of the concatenated molecular tree. There is no biogeographic pattern in the distribution as the genera occur over the entire Atlantic and Pacific Ocean, showing no specific phylogeographical pattern. Poor resolution at deep desmosomatid nodes may reflect the long evolutionary history of the family and rapid evolutionary radiations. © 2021, The Author(s).
    view abstractdoi: 10.1007/s13127-021-00509-9
  • 2021 • 1189 Integrated Whispering-Gallery-Mode Resonator for Solid-State Coherent Quantum Photonics
    Brooks, A. and Chu, X.-L. and Liu, Z. and Schott, R. and Ludwig, Ar. and Wieck, A.D. and Midolo, L. and Lodahl, P. and Rotenberg, N.
    Nano Letters 21 8707-8714 (2021)
    Tailored photonics cavities enhance light-matter interactions, ultimately enabling a fully coherent quantum interface. Here, we report an integrated microdisk cavity containing self-assembled quantum dots to coherently route photons between different access waveguides. We measure a Purcell factor of Fexp = 6.9 ± 0.9 for a cavity quality factor of about 10,000, allowing us to observe clear signatures of coherent scattering of photons by the quantum dots. We show how this integrated system can coherently reroute photons between the drop and bus ports and how this routing is controlled by detuning the quantum dot and resonator or through the strength of the excitation beam, where a critical photon number less than one photon per lifetime is required. We discuss the strengths and limitations of this approach, focusing on how the coherent scattering and single-photon nonlinearity can be used to increase the efficiency of quantum devices such as routers or Bell-state analyzers. © 2021 American Chemical Society.
    view abstractdoi: 10.1021/acs.nanolett.1c02818
  • 2021 • 1188 Studying the mechanism of phase separation in aqueous solutions of globular proteins via molecular dynamics computer simulations
    Brudar, S. and Gujt, J. and Spohr, E. and Hribar-Lee, B.
    Physical chemistry chemical physics : PCCP 23 415-424 (2021)
    Proteins are the most abundant biomacromolecules in living cells, where they perform vital roles in virtually every biological process. To maintain their function, proteins need to remain in a stable (native) state. Inter- and intramolecular interactions in aqueous protein solutions govern the fate of proteins, as they can provoke their unfolding or association into aggregates. The initial steps of protein aggregation are difficult to capture experimentally, therefore we used molecular dynamics simulations in this study. We investigated the initial phase of aggregation of two different lysozymes, hen egg-white (HEWL) and T4 WT* lysozyme and also human lens γ-D crystallin by using atomistic simulations. We monitored the phase stability of their aqueous solutions by calculating time-dependent density fluctuations. We found that all proteins remained in their compact form despite aggregation. With an extensive analysis of intermolecular residue-residue interactions we discovered that arginine is of paramount importance in the initial stage of aggregation of HEWL and γ-D crystallin, meanwhile lysine was found to be the most involved amino acid in forming initial contacts between T4 WT* molecules.
    view abstractdoi: 10.1039/d0cp05160h
  • 2021 • 1187 Decelerated aging in metallic glasses by low temperature thermal cycling
    Bruns, M. and Hassani, M. and Varnik, F. and Hassanpour, A. and Divinski, S. and Wilde, G.
    Physical Review Research 3 (2021)
    Differential scanning calorimetry measurements on different bulk metallic glasses show no measurable rejuvenation upon deeply cooled (cryogenic) thermal cycling. This applies both to as-quenched and well-annealed samples. Extensive molecular dynamics simulations of a generic model glass former corroborate these observations. We disentangle the effects of aging from those of thermal treatment and show that aging is slowed down but not stopped - neither reversed - during thermal cycling. These observations are corroborated further by a survey of energy distribution, which continues narrowing, albeit with a smaller rate. © 2021 authors.
    view abstractdoi: 10.1103/PhysRevResearch.3.013234
  • 2021 • 1186 Analytical evaluation of signal‐to‐noise ratios for avalanche-and single‐photon avalanche diodes
    Buchner, A. and Hadrath, S. and Burkard, R. and Kolb, F.M. and Ruskowski, J. and Ligges, M. and Grabmaier, A.
    Sensors 21 (2021)
    Performance of systems for optical detection depends on the choice of the right detector for the right application. Designers of optical systems for ranging applications can choose from a variety of highly sensitive photodetectors, of which the two most prominent ones are linear mode avalanche photodiodes (LM‐APDs or APDs) and Geiger‐mode APDs or single‐photon avalanche diodes (SPADs). Both achieve high responsivity and fast optical response, while maintaining low noise characteristics, which is crucial in low‐light applications such as fluorescence lifetime measurements or high intensity measurements, for example, Light Detection and Ranging (LiDAR), in outdoor scenarios. The signal‐to‐noise ratio (SNR) of detectors is used as an analytical, scenario-dependent tool to simplify detector choice for optical system designers depending on technologi-cally achievable photodiode parameters. In this article, analytical methods are used to obtain a uni-versal SNR comparison of APDs and SPADs for the first time. Different signal and ambient light power levels are evaluated. The low noise characteristic of a typical SPAD leads to high SNR in scenarios with overall low signal power, but high background illumination can saturate the detec-tor. LM‐APDs achieve higher SNR in systems with higher signal and noise power but compromise signals with low power because of the noise characteristic of the diode and its readout electronics. Besides pure differentiation of signal levels without time information, ranging performance in LiDAR with time‐dependent signals is discussed for a reference distance of 100 m. This evaluation should support LiDAR system designers in choosing a matching photodiode and allows for further discussion regarding future technological development and multi pixel detector designs in a com-mon framework. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/s21082887
  • 2021 • 1185 Impact of single-pulse, low-intensity laser post-processing on structure and activity of mesostructured cobalt oxide for the oxygen evolution reaction
    Budiyanto, E. and Zerebecki, S. and Weidenthaler, C. and Kox, T. and Kenmoe, S. and Spohr, E. and Debeer, S. and Rüdiger, O. and Reichenberger, S. and Barcikowski, S. and Tüysüz, H.
    ACS Applied Materials and Interfaces (2021)
    Herein, we report nanosecond, single-pulse laser post-processing (PLPP) in a liquid flat jet with precise control of the applied laser intensity to tune structure, defect sites, and the oxygen evolution reaction (OER) activity of mesostructured Co3O4. High-resolution X-ray diffraction (XRD), Raman, and X-ray photoelectron spectroscopy (XPS) are consistent with the formation of cobalt vacancies at tetrahedral sites and an increase in the lattice parameter of Co3O4 after the laser treatment. X-ray absorption spectroscopy (XAS) and X-ray emission spectroscopy (XES) further reveal increased disorder in the structure and a slight decrease in the average oxidation state of the cobalt oxide. Molecular dynamics simulation confirms the surface restructuring upon laser post-treatment on Co3O4. Importantly, the defect-induced PLPP was shown to lower the charge transfer resistance and boost the oxygen evolution activity of Co3O4. For the optimized sample, a 2-fold increment of current density at 1.7 V vs RHE is obtained and the overpotential at 10 mA/cm2 decreases remarkably from 405 to 357 mV compared to pristine Co3O4. Post-mortem characterization reveals that the material retains its activity, morphology, and phase structure after a prolonged stability test. © XXX The Authors.
    view abstractdoi: 10.1021/acsami.1c08034
  • 2021 • 1184 Synthesis of Cu Single Atoms Supported on Mesoporous Graphitic Carbon Nitride and Their Application in Liquid-Phase Aerobic Oxidation of Cyclohexene
    Büker, J. and Huang, X. and Bitzer, J. and Kleist, W. and Muhler, M. and Peng, B.
    ACS Catalysis 11 7863-7875 (2021)
    Different loadings of Cu single atoms were anchored on a graphitic carbon nitride (g-C3N4) matrix using a two-step thermal synthesis method and applied in liquid-phase cyclohexene oxidation under mild conditions using molecular O2 as the oxidizing agent. The oxidation state of Cu was determined to be Cu+, which is in linear coordination with two neighboring nitrogen atoms at a distance of 1.9 Å. The catalyst with 0.9 wt % Cu pyrolyzed at 380 °C was found to exhibit the best catalytic performance with the highest conversion up to 82% with an allylic selectivity of 55%. It also showed high reusability over four catalytic runs without any detectable Cu leaching. Cyclohexene oxidation followed first-order kinetics with an apparent activation energy of 66.2 kJ mol-1. The addition of hydroquinone as a radical scavenger confirmed that cyclohexene oxidation proceeds via a radical mechanism. Time-resolved in situ attenuated total reflection infrared (ATR-IR) spectroscopy was carried out to qualitatively monitor the cyclohexene oxidation pathways. The comparison with the homogeneous analogue Cu(I) iodide indirectly verified the linearly N-coordinated single Cu(I) species to be the active sites for cyclohexene oxidation. © 2021 American Chemical Society.
    view abstractdoi: 10.1021/acscatal.1c01468
  • 2021 • 1183 Liquid-Phase Cyclohexene Oxidation with O2 over Spray-Flame-Synthesized La1−xSrxCoO3 Perovskite Nanoparticles
    Büker, J. and Alkan, B. and Chabbra, S. and Kochetov, N. and Falk, T. and Schnegg, A. and Schulz, C. and Wiggers, H. and Muhler, M. and Peng, B.
    Chemistry - A European Journal (2021)
    La1−xSrxCoO3 (x=0, 0.1, 0.2, 0.3, 0.4) nanoparticles were prepared by spray-flame synthesis and applied in the liquid-phase oxidation of cyclohexene with molecular O2 as oxidant under mild conditions. The catalysts were systematically characterized by state-of-the-art techniques. With increasing Sr content, the concentration of surface oxygen vacancy defects increases, which is beneficial for cyclohexene oxidation, but the surface concentration of less active Co2+ was also increased. However, Co2+ cations have a superior activity towards peroxide decomposition, which also plays an important role in cyclohexene oxidation. A Sr doping of 20 at. % was found to be the optimum in terms of activity and product selectivity. The catalyst also showed excellent reusability over three catalytic runs; this can be attributed to its highly stable particle size and morphology. Kinetic investigations revealed first-order reaction kinetics for temperatures between 60 and 100 °C and an apparent activation energy of 68 kJ mol−1 for cyclohexene oxidation. Moreover, the reaction was not affected by the applied O2 pressure in the range from 10 to 20 bar. In situ attenuated total reflection infrared spectroscopy was used to monitor the conversion of cyclohexene and the formation of reaction products including the key intermediate cyclohex-2-ene-1-hydroperoxide; spin trap electron paramagnetic resonance spectroscopy provided strong evidence for a radical reaction pathway by identifying the cyclohexenyl alkoxyl radical. © 2021 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/chem.202103381
  • 2021 • 1182 Extremely Low Vapor-Pressure Data as Access to PC-SAFT Parameter Estimation for Ionic Liquids and Modeling of Precursor Solubility in Ionic Liquids
    Bülow, M. and Greive, M. and Zaitsau, D.H. and Verevkin, S.P. and Held, C.
    ChemistryOpen (2021)
    Precursor solubility is a crucial factor in industrial applications, dominating the outcome of reactions and purification steps. The outcome and success of thermodynamic modelling of this industrially important property with equations of states, such as Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT), vastly depends on the quality of the pure-component parameters. The pure-component parameters for low-volatile compounds such as ionic liquids (ILs) have been commonly estimated using mixture properties, e. g. the osmotic pressure of aqueous solutions. This leads to parameters that depend on the solvent, and transferability to other mixtures often causes poor modeling results. Mixture-independent experimental properties would be a more suitable basis for the parameter estimation offering a way to universal parameter sets. Model parameters for ILs are available in the literature [10.1016/j.fluid.2012.05.029], but they were estimated using pure-IL density data. The present work focuses on a step towards a more universal estimation strategy that includes new experimental vapor-pressure data of the pure IL. ILs exhibit an almost negligible vapor pressure in magnitude of usually 10−5 Pa even at elevated temperatures. In this work, such vapor-pressure data of a series of 1-ethyl-3-methyl-imidazolium-based [C2mim]-ILs with various IL-anions (e. g. tetrafluoroborate [BF4]−, hexafluorophosphate [PF6]−, bis(trifluoromethylsulfonyl)imide [NTf2]−) were experimentally determined and subsequently used for PC-SAFT parameter estimation. The so-determined parameters were used to predict experimental molecular precursor solubility in ILs and infinitely diluted activity coefficients of various solvents in ILs. The parameters were further compared to modeling results using classical parametrization methods (use of liquid-density data only for the molecular PC-SAFT and the ion-based electrolyte PC-SAFT). As a result, the modeled precursor solubilities using the new approach are much more precise than using the classical parametrization methods, and required binary parameters were found to be much smaller (if needed). In sum, including the pure-component vapor-pressure data of ILs opens the door towards parameter estimation that is not biased by mixture data. This procedure might be suitable also for polymers and for all kind of ionic species but needs extension to ion-specific parametrization in the long term. © 2021 The Authors. Published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/open.202000258
  • 2021 • 1181 ePC-SAFT advanced – Part II: Application to Salt Solubility in Ionic and Organic Solvents and the Impact of Ion Pairing
    Bülow, M. and Ascani, M. and Held, C.
    Fluid Phase Equilibria 537 (2021)
    The applications of electrolyte thermodynamic models to non-aqueous systems is of great value to reduce experimental effort and gain inside into molecular interactions. A large-scale application is for example the design of advanced battery electrolytes. For non-aqueous electrolyte systems, the Born term was found to be important, as it accounts for the transfer of ions from water into non-aqueous medium. In part one of this study [Bülow et al., Fluid Phase Equilibria 2021, 112967] the Born term was combined with a concentration-dependent dielectric constant within the ePC-SAFT framework (electrolyte Perturbed-Chain Statistical Associating Fluid Theory). In the present work, the Bjerrum treatment for ion pairing was included in the Debye-Hückel framework within ePC-SAFT. The approach was validated by experimental data for the dissociation of salts in organic solvents derived from conductivity measurements. Further, solubility was modeled of alkali halides in organic solvents and in ionic liquids. Modeling solubility required access to the solubility product KSP, which does not depend on the solvent. The approach within this work was to first determine KSP using experimental solubility data in water and the respective ePC-SAFT predicted activity coefficients prior to predict activity coefficients in non-aqueous medium, finally yielding solubility. The so-determined solubility values were found to be in reasonable agreement with the experimental data without fitting model parameters to any data of the non-aqueous solutions. The solubility product requires the solid form of the precipitating salt to be equal for all solvents; as alkali salts precipitate from aqueous solutions as hydrates, the method cannot be applied. Therefore, a methodology is presented to extrapolate the high-temperature KSP of anhydrates to lower temperature. Using the so-extrapolated KSP allowed predicting solubility of non-solvates in other solvents. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.fluid.2021.112989
  • 2021 • 1180 Predicting vapor−liquid equilibria for sour-gas absorption in aqueous mixtures of chemical and physical solvents or ionic liquids with EPC-SAFT
    Bülow, M. and Ince, N.G. and Hirohama, S. and Sadowski, G. and Held, C.
    Industrial and Engineering Chemistry Research 60 6327-6336 (2021)
    Sour-gas absorption is the main unit operation used in refineries and petrochemical and natural gas processing plants for the effective reduction of climate-wrecking gases, mainly CO2 and H2S. Absorption is typically accomplished in an aqueous solvent mixture. The solvent mixture is vastly dependent on the application range; it might contain chemical solvents (amines), activators, and physical solvents. In this work, the vapor−liquid equilibria for absorption of the sour gases CO2 and H2S was investigated in systems containing the chemical solvent methyl diethanolamine (MDEA) and the physical solvents tetrahydrothiophene-1,1-dioxide (sulfolane) or the ionic liquid 1-butyl-3-methylimidazolium acetate. The solubilities of CO2 and H2S were predicted and validated using experimental literature data in a broad range of temperature (313−373 K), sour-gas loading (up to 2 moles gas per moles of MDEA), and pressure (up to 180 bar) at constant MDEA weight fraction (20.9 wt %) and sulfolane weight fraction (30.5 wt %). The equation-of-state electrolyte perturbed-chain statistical associating fluid theory (ePC-SAFT) was utilized in this work for the predictions combined with the Born term to physically correctly describe the Gibbs energy of solvation of ions in the aqueous mixture of chemical and physical solvents; this was introduced in a recent work [Bülow, M. et al. Fluid Phase Equilib. 2021, 535, 112967]. Using this approach allowed reducing the total number of binary interaction parameters in these systems of maximum 11 species to a minimum; these parameters were fitted exclusively to data of binary mixtures. The ePC-SAFT predictions of the gas solubility were most accurate at low sour-gas loadings and high temperatures. This work provides a thermodynamic framework for the solvent selection for sour-gas absorption in a broad range of conditions. This enables a realistic decrease in experimental effort for solvent selection in sour-gas absorption. © 2021 American Chemical Society
    view abstractdoi: 10.1021/acs.iecr.1c00176
  • 2021 • 1179 ePC-SAFT advanced - Part I: Physical meaning of including a concentration-dependent dielectric constant in the born term and in the Debye-Hückel theory
    Bülow, M. and Ascani, M. and Held, C.
    Fluid Phase Equilibria 535 (2021)
    The transition from aqueous electrolyte systems to non-aqueous electrolyte systems is highly demanded in industrial applications and especially challenging for physics-based thermodynamic models. Electrolyte thermodynamics is a complex matter, and still not all physico-chemical effects are accounted for in state-of-the-art equations of state. The dielectric constant of non-aqueous electrolyte systems changes drastically compared to aqueous systems. One main consequence is that ions are very differently solvated in non-aqueous medium compared to aqueous medium. The Born term represents a methodology to account for the influence of solvation energies of ions, which is based on influences of solvent and salt on the dielectric constant. Utilizing the Born term in electrolyte models is extensively debated, and it is often reasonably neglected in predominantly aqueous systems. Yet, it has a significant influence on transferability from aqueous to non-aqueous media i.e., systems with a large difference in polarity or permittivity compared to aqueous systems. In this work, a modified Born term was combined with electrolyte Perturbed-Chain Statistical Associating Fluid Theory (ePC-SAFT) by introducing additionally a salt concentration-dependent dielectric constant, henceforth called altered Born contribution. The new methodology was validated against infinite dilution properties for ion-solvent interactions: Gibbs energy of hydration and Gibbs energy of transfer of alkali halides from water to alcoholic solvents. Further, mean ionic activity coefficients (MIACs) of alkali halides in alcoholic solvents were quantitatively correct predicted with the advanced ePC-SAFT approach. Original ePC-SAFT parameters were applied for all predictions, and no further binary parameters were adjusted. Based on the success of the model predictions, the transferability of pure-ion ePC-SAFT parameters to organic solvents was verified and the incorporation of concentration-dependent dielectric constant into the altered Born contribution and Debye-Hückel theory was proven to be meaningful methods for the transfer of electrolyte thermodynamic models from aqueous to non-aqueous systems. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.fluid.2021.112967
  • 2021 • 1178 Corrigendum to ‘ePC-SAFT advanced - Part I: Physical Meaning of Including a concentration dependent dielectric constant in the Born term and in the Debye-Hückel theory’ [Fluid Phase Equilibria, Volume 535 (2021), 112967] (Fluid Phase Equilibria (2021) 535, (S0378381221000297), (10.1016/j.fluid.2021.112967))
    Bülow, M. and Ascani, M. and Held, C.
    Fluid Phase Equilibria 548 (2021)
    The authors regret a parameter issue that occurred in the predictions of the mean ionic activity coefficients (MIACs). This has a minor impact on some of the shown systems compared to the original publication. The corrected Figs. 6 and 7 are presented here for clarification. The overall statements of the original paper remain unchanged. A corrected comparison of the ePC-SAFT advanced model to ePC-SAFT revised is presented in Fig. 7. The authors would like to apologise for any inconvenience caused. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.fluid.2021.113184
  • 2021 • 1177 Corrigendum to ‘ePC-SAFT advanced – Part II: Application to Salt Solubility in Ionic and Organic Solvents and the Impact of Ion Pairing’ [Fluid Phase Equilibria, Volume 537 (2021), 112989] (Fluid Phase Equilibria (2021) 535, (S0378381221000297), (10.1016/j.fluid.2021.112967))
    Bülow, M. and Ascani, M. and Held, C.
    Fluid Phase Equilibria 548 (2021)
    The authors regret a parameter issue that occurred in the predictions of the solvent's activity coefficients. Therefore, Fig. 4 was slightly misrepresented and the corrected version is now shown below. In the supporting information, the corrected activity coefficients of ethanol with the concentration of LiCl are presented below in Figure S1. The authors would like to apologize for any inconvenience caused. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.fluid.2021.113183
  • 2021 • 1176 Soft synthetic microgels as mimics of mycoplasma
    Büning, D. and Schumacher, J. and Helling, A. and Chakroun, R. and Ennen-Roth, F. and Gröschel, A.H. and Thom, V. and Ulbricht, M.
    Soft Matter 17 6445-6460 (2021)
    Artificial model colloids are of special interest in the development of advanced sterile filters, as they are able to efficiently separate pleomorphic, highly deformable and infectious bacteria such as mycoplasma, which, until now, has been considered rather challenging and laborious. This study presents a full range of different soft to super soft synthetic polymeric microgels, including two types with similar hydrodynamic mean diameter,i.e., 180 nm, and zeta potential,i.e., −25 ± 10 mV, but different deformability, synthesized by inverse miniemulsion terpolymerization of acrylamide, sodium acrylate andN,N′-methylenebisacrylamide. These microgels were characterized by means of dynamic, electrophoretic and static light scattering techniques. In addition, the deformability of the colloids was investigated by filter cake compressibility studies during ultrafiltration in dead-end mode, analogously to a study of real mycoplasma,i.e.,Acholeplasma laidlawii, to allow for a direct comparison. The results indicate that the variation of the synthesis parameters,i.e., crosslinker content, polymeric solid content and content of sodium acrylate, has a significant impact on the swelling behavior of the microgels in aqueous solution as well as on their deformability under filtration conditions. A higher density of chemical crosslinking points results in less swollen and more rigid microgels. Furthermore, these parameters determine electrokinetic properties of the more or less permeable colloids. Overall, it is shown that these soft synthetic microgels can be obtained with tailor-made properties, covering the size of smallest species of and otherwise similar to real mycoplasma. This is a relevant first step towards the future use of synthetic microgels as mimics for mycoplasma. © The Royal Society of Chemistry 2021.
    view abstractdoi: 10.1039/d1sm00379h
  • 2021 • 1175 Production of polylactic acid aerogels via phase separation and supercritical CO2 drying: thermodynamic analysis of the gelation and drying process
    Bueno, A. and Luebbert, C. and Enders, S. and Sadowski, G. and Smirnova, I.
    Journal of Materials Science 56 18926-18945 (2021)
    The application range of aerogels, especially in the life-science sector, can be extended by utilizing biocompatible polymers such as polylactic acid (PLA). However, the low glass transition temperature (Tg) of PLA and the challenging gelation techniques limit the application of supercritical CO2 (scCO2) drying and thus the PLA-aerogel production. The aim of this work is to overcome this challenge and to provide a better understanding of the thermodynamics of the process. Therefore, the gelation of amorphous PLA (PDLLA) and semicrystalline PLA (PLLA) via thermal-induced phase separation (TIPS) was studied. To identify polymer/solvent/antisolvent ratios suitable for gelation, thermodynamic modeling (PC-SAFT) was used to describe the corresponding ternary phase diagrams. scCO2 drying was used to preserve the mesoporous gel structure formed during the gelation. Due to the decrease in the Tg of PLA in the presence of CO2, this could not be applied to all gels. It was found that the critical parameter to enable the scCO2 drying of low Tg polymers is the crystallinity degree (Xc) of the polymer. Based on these results, some guidelines for producing aerogels from polymers with low Tg are formulated. Graphical abstract: [Figure not available: see fulltext.] © 2021, The Author(s).
    view abstractdoi: 10.1007/s10853-021-06501-0
  • 2021 • 1174 A variationally consistent hyperstatic reaction method for tunnel lining design
    Bui, H.-G. and Ninić, J. and Do, N.-A. and Dias, D. and Meschke, G.
    International Journal for Numerical and Analytical Methods in Geomechanics (2021)
    In this technical note, a consistent finite element formulation of the Hyperstatic Reaction Method (HRM) for tunnel linings design is proposed by introducing a variational consistently linearized formulation. It permits to consider a nonlinear interaction between a lining structure and the surrounding ground. Recent advances of the HRM in regard to the consideration of the nonlinear response of the segmented tunnel lining exposed to design loads use an iterative algorithm for solving the nonlinear system of equations. In the proposed Variationally consistent Hyperstatic Reaction Method (VHRM), a distributed nonlinear spring model representing the interaction between the lining and the ground soils is considered in a variationally consistent format. Computing the tangential spring stiffness via consistent linearization, and using Newton-Raphson iteration, requires significantly smaller number of iterations as compared to the original HRM model based on nodal springs. Furthermore, the method is applicable for simulations using solid finite elements (2D and 3D), as well as beam or finite shell elements, respectively. © 2021 The Authors. International Journal for Numerical and Analytical Methods in Geomechanics published by John Wiley & Sons Ltd.
    view abstractdoi: 10.1002/nag.3288
  • 2021 • 1173 Generalized comparison of the accessible emission limits of flash- And scanning LiDAR-systems
    Burkard, R. and Viga, R. and Ruskowski, J. and Grabmaier, A.
    SMACD / PRIME 2021 - International Conference on Synthesis, Modeling, Analysis and Simulation Methods and Applications to Circuit Design and 16th Conference on PhD Research in Microelectronics and Electronics 292-295 (2021)
    In the field of autonomous driving and human-robot collaboration applications the demand for three-dimensional imaging systems, that are reliable, small and low-cost, is rising. A promising technology to satisfy these demands are scanning- or flash-based light detection and ranging (LiDAR)-systems, which differ mainly in the illumination of the field-of-view. A scanning LiDAR-system illuminates the field-of-view sequentially by deflecting a laser beam. In a flash LiDAR-system the laser beam is extended to illuminate the whole field-of-view with every emitted laser pulse. Both illumination principles are extensively treated in the recent literature separately and without the inclusion of the limits defined by the laser safety standard IEC 60825-1:2014. In this work a generalized model is derived from the standard. This model is able to determine the emission limits of the standard for both LiDAR-systems at the same time and it is used to compare the maximum output power and the intensities in the field-of-view for both LiDAR-systems. © VDE VERLAG GMBH.
    view abstract
  • 2021 • 1172 An extended model of the ISO-2631 standard to objectify the ride comfort in autonomous driving
    Burkhard, G. and Berger, T. and Enders, E. and Schramm, D.
    Work 68 S37-S45 (2021)
    BACKGROUND: With the development of autonomous driving, the occupants' comfort perception and their activities during the drive are becoming increasingly the focus of research. Especially in one of the first applications, a drive on a motorway, vertical dynamics play a major role. OBJECTIVE: To be able to robustly objectify ride comfort, better models need to be developed. Initial studies have shown, that the current ISO-2631 standard creates good results in the objectification and can be regarded as benchmark. METHODS: To increase the accuracy in objectification, an extended model with the occupants' head as additional measuring point is introduced. Instead of the known frequency filters, weighting (k-factors) is used to differentiate possible excitations. For comparing the model with the ISO-2631, a simulator study with 5 excitations and 50 inattentive subjects is carried out. RESULTS: Evaluating the study with the ISO-2631, 3 out of 5 excitations indicate a significant difference between the occupant's impression and the calculated comfort value. In comparison the extended model has no significant difference. CONCLUSION: The results further show, that inattentive occupants move their heads significantly more. By measuring accelerations of the head, the extended model creates equivalent or more accurate comfort values than the ISO-2631. © 2021 - IOS Press. All rights reserved.
    view abstractdoi: 10.3233/WOR-208004
  • 2021 • 1171 Chipless frequency-coded RFID tags integrating high-Q resonators and dielectric rod antennas
    Burmeister, T. and Jimenez-Saez, A. and Sakaki, M. and Schusler, M. and Sanchez-Pastor, J. and Benson, N. and Jakoby, R.
    15th European Conference on Antennas and Propagation, EuCAP 2021 (2021)
    A possible passive infrastructure for mm-wave self localization systems is proposed in this paper. W-band photonic crystal based high-Q resonators coupled to free space by a dielectric rod antenna are employed. Q-factors of approximately 300 and wireless tag readout over 10 cm can be achieved using Rogers RT/duroid® 6010.2LM. The maximum readout range increases to 40 cm when lower-loss additively manufactured Alumina tags are used. Development of a 3 bit prototype tag is successful, demonstrating the possibility to increase the number of resonators per tag using the presented approach. © 2021 EurAAP.
    view abstractdoi: 10.23919/EuCAP51087.2021.9410915
  • 2021 • 1170 Bone Substitutes in Orthopaedic Surgery: Current Status and Future Perspectives
    Busch, A. and Wegner, A. and Haversath, M. and Jäger, M.
    Zeitschrift fur Orthopadie und Unfallchirurgie 159 304-313 (2021)
    Bone replacement materials have been successfully supplied for a long time. But there are cases, especially in critical sized bone defects, in which the therapy is not sufficient. Nowadays, there are multiple bone substitutes available. Autologous bone grafts remain the gold standard in bone regeneration. Yet, donor-site morbidity and the available amount of sufficient material are limitations for autologous bone grafting. This study aimed to provide information about the current status in research regarding bone substitutes. We report on the advantages and drawbacks of several bone substitutes. At the end, we discuss the current developments of combining ceramic substitutes with osteoinductive substances. © 2020. Thieme. All rights reserved.
    view abstractdoi: 10.1055/a-1073-8473
  • 2021 • 1169 Functionalization of synthetic bone substitutes
    Busch, A. and Jäger, M. and Mayer, C. and Sowislok, A.
    International Journal of Molecular Sciences 22 (2021)
    Bone substitutes have been applied to treat osseous defects for a long time. To prevent implant related infection (IRI) and enhance bone healing functionalized biomaterials, antibiotics and osteoinductive substances have been introduced. This study gives an overview of the current available surface-coated bone substitutes and provides an outlook for future perspectives. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/ijms22094412
  • 2021 • 1168 A bicentric approach evaluating the combination of a hemispheric cup with a novel ceramic head in total hip arthroplasty
    Busch, A. and Wassenaar, D. and Zinser, W. and Jäger, M.
    Orthopedic Reviews 13 (2021)
    Medical ceramics are frequently used biomaterials as a liner in total hip arthroplasty. Strong efforts have been made to improve material properties over the last decades. Alumina toughened zirconia ceramics seem to be promising alternatives to further reduce fracture rates and squeaking phenomena. To answer the question if alumina toughened zirconia ceramic liners in combination with a cementless, hemispheric cup are able to reduce squeaking phenomena and fracture rates, we initiated a bicentric, mid-term trial. Noise phenomena will be recorded using MONA Score (Melbourne Orthopaedic Noise Assessment). Functional outcome (Harris Hip Score, University of California-Los Angeles, Forgotten Joint Score, EQ-5D Score, Visual Analogue Scale) and radiographic parameters will serve as secondary parameters. The study has been set up for 5 years, with follow-ups after 6-14 weeks, 12, 24 and 60 months. © the Author(s), 2021.
    view abstractdoi: 10.4081/or.2021.8794
  • 2021 • 1167 Peridynamic analysis of dynamic fracture: influence of peridynamic horizon, dimensionality and specimen size
    Butt, S.N. and Meschke, G.
    Computational Mechanics 67 1719-1745 (2021)
    In peridynamic models for fracture, the dissipated fracture energy is regularized over a non-local region denoted as the peridynamic horizon. This paper investigates the influence of this parameter on the dynamic fracture process in brittle solids, using two as well as three dimensional simulations of dynamic fracture propagation in a notched plate for two loading cases. The predicted crack speed for the various scenarios of the initially stored energy, also known as the velocity toughening behavior as well as characteristics of the crack surface topology obtained in different crack propagation regimes in 3D computational simulations are compared with the experimentally observed crack velocity and fracture surfaces for Polymethyl Methacrylate (PMMA) specimens. In addition, we investigate the influence of the specimen size on the dynamic fracture process using two dimensional peridynamic simulations. The fracture strengths and the velocity toughening relationship obtained from different specimen sizes are compared with the Linear Elastic Fracture Mechanics (LEFM) size effect relationship and with results from experiments, respectively. © 2021, The Author(s).
    view abstractdoi: 10.1007/s00466-021-02017-1
  • 2021 • 1166 Non-ideal mixing behavior in dibutyl phosphate-propylamine binary liquids: Dielectric and nuclear magnetic resonance investigations
    Calandra, P. and Turco Liveri, V. and Proietti, N. and Capitani, D. and Lombardo, D. and Gainaru, C. and Böhmer, R. and Kozak, M. and Dobies, M. and Fojud, Z. and Pochylski, M.
    Journal of Molecular Liquids 323 (2021)
    Owing to the amphiphilic nature of their constituent molecules, binary mixtures of pure liquid surfactants are usually characterized by enhanced nano-segregation and thus can exhibit interesting transport properties and complex macroscopic behavior. In this ambit it was recently shown by Turco Liveri et al. (J. Mol. Liq. 263 (2018) 274–281) at room temperature that mixtures of short aliphatic chains compounds, such as dibutyl phosphate (DBP) and n-propylamine (PA) liquids, due to their ability to allow for phosphate-to-amine proton transfer, display ionic liquid–like behavior with composition-dependent enhanced conductivity, viscosity, and magnetically-induced birefringence. To understand the molecular mechanisms at the basis of this behavior, in the present study a combination of nuclear magnetic resonance (NMR) and dielectric spectroscopy investigations has been carried out for the same materials for different amine molar ratios. It was found that at certain compositions all studied dynamical processes (conformational changes, local hopping of “free” protons among neighboring polar headgroups, long-range charge migration) exhibit significant deviations from ideal mixing behavior. The microscopic origin of these deviations is discussed. © 2020
    view abstractdoi: 10.1016/j.molliq.2020.114963
  • 2021 • 1165 Flexibilization of Biorefineries: Tuning Lignin Hydrogenation by Hydrogen Partial Pressure
    Cao, Z. and Xu, Y. and Lyu, P. and Dierks, M. and Morales-García, Á. and Schrader, W. and Nachtigall, P. and Schüth, F.
    ChemSusChem 14 373-378 (2021)
    The present study describes an interesting and practical catalytic system that allows flexible conversion of lignin into aromatic or aliphatic hydrocarbons, depending on the hydrogen partial pressure. A combination of experiment and theory shows that the product distribution between aromatics and aliphatics can be simply tuned by controlling the availability of hydrogen on the catalyst surface. Noticeably, these pathways lead to almost complete oxygen removal from lignin biomass, yielding high-quality hydrocarbons. Thus, hydrogen–lignin co-refining by using this catalytic system provides high flexibility in hydrogen storage/consumption towards meeting different regional and temporal demands. © 2020 The Authors. ChemSusChem published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/cssc.202002248
  • 2021 • 1164 Mechanochemical synthesis and dehydrogenation properties of Yb(AlH4)3
    Cao, Z. and Felderhoff, M.
    International Journal of Hydrogen Energy 46 26437-26444 (2021)
    The facile synthesis of ytterbium tetrahydroaluminate Yb(AlH4)3 is conducted by a mechanochemical procedure under hydrogen atmosphere for the first time. Results show that the synthesized Yb(AlH4)3 remains as an amorphous state. The thermal decomposition of Yb(AlH4)3 goes through a four-stage pathway with several amorphous intermediate phases during the process. The first dehydrogenation step of Yb(AlH4)3 presents a relatively low apparent activation energy of 99.6 kJ mol−1, and ninety percent of the hydrogen from this stage can be liberated within 20 min at 160 °C. Rehydrogenation tests above 160 °C and 14 MPa hydrogen pressure demonstrate the unsuccessful rehydrogenations of the first decomposition step due to the formation of a thermodynamically more stable compound YbHCl. © 2021 Hydrogen Energy Publications LLC
    view abstractdoi: 10.1016/j.ijhydene.2021.05.132
  • 2021 • 1163 Online Geological Anomaly Detection Using Machine Learning in Mechanized Tunneling
    Cao, B.-T. and Saadallah, A. and Egorov, A. and Freitag, S. and Meschke, G. and Morik, K.
    Lecture Notes in Civil Engineering 125 323-330 (2021)
    In the case of a sudden change in the geology in front of the Tunnel Boring Machine (TBM) during mechanized tunneling processes, non-appropriate investigation and process adaptation may result in non-desirable situations that can induce construction and machine defects. Therefore, subsurface anomalies detection is necessary to trigger alarm to update the process. This paper presents an approach for geological anomaly detection using data produced by the TBM. The data observations are continuously produced at a motion of 10 to 15 s from hundreds of sensors around the TBM. Unsupervised machine learning techniques are applied to analyze the online streaming data. As a result, a model, which is able to learn the system characteristics from normal operational condition and to flag any unanticipated or unexpected behavior, is established. The proposed approach has been tested on the data of the Wehrhahn-Linie metro project in Düsseldorf in Germany. The model can accurately detect the presence of concrete walls in the ground domain with a distance up to around one meter before the TBM approaches the walls. The developed method can thus be used as a monitoring system for ground risks detection to ensure safe and sustainable constructions in mechanized tunneling. © 2021, The Author(s), under exclusive license to Springer Nature Switzerland AG.
    view abstractdoi: 10.1007/978-3-030-64514-4_28
  • 2021 • 1162 Coherent GHz lattice and magnetization excitations in thin epitaxial Ag/Fe/Cr/Fe films
    Cao, D. and Adam, R. and Bürgler, D.E. and Wang, F. and Song, C. and Li, S. and Mikulics, M. and Hardtdegen, H. and Heidtfeld, S. and Greb, C. and Schneider, C.M.
    Physical Review B 104 (2021)
    We excited an epitaxial magnetic Ag/Fe/Cr/Fe multilayer nonthermally and nonoptically with very short (<1 ps) electromagnetic pulses. We detected the synchronous phononic-magnetic response by time-resolved magneto-optical Kerr effect measurements. The Ag/Fe/Cr/Fe multilayer was patterned into a coplanar waveguide transmission line, and the electromagnetic pulses were generated by pulsed-laser illumination of an integrated GaAs photoconductive switch (PCS). The detected magnetic excitations comprise up to four narrow-band high-order modes with the highest frequency reaching 30 GHz. The mode frequencies are independent of both temperature in the range from 16 to 300 K and the applied external magnetic field up to 120 mT. Our analysis shows that the origin of the rigidity of these high-frequency modes is the strong coupling of the magnetic subsystem with the lattice of the Ag/Fe/Cr/Fe multilayer. The exciting electromagnetic pulse generated by the PCS induces, via magnetoelastic coupling, long-lived (ns) standing GHz acoustic waves normal to the Ag/Fe/Cr/Fe film plane. These lattice oscillations in turn couple back and drive the magnetization oscillations via the magnetoelastic coupling. The temperature and field dependence of the damping of the oscillations can be described by inelastic phonon-phonon and phonon-magnon scattering. Our study opens up a possibility of using coherent lattice and magnetization dynamics in ferromagnetic films for spintronic devices at GHz clock rates. © 2021 American Physical Society.
    view abstractdoi: 10.1103/PhysRevB.104.054430
  • 2021 • 1161 Solvent effect on the kinetics of the hydrogenation of n-butyl levulinate to γ-valerolactone
    Capecci, S. and Wang, Y. and Casson Moreno, V. and Held, C. and Leveneur, S.
    Chemical Engineering Science 231 (2021)
    The use of lignocellulosic biomass in the chemical industry can significantly contribute to respect the various international agreements on climate change. One of the most promising platform molecules issued from the lignocellulosic biomass hydrolysis is γ-valerolactone (GVL). GVL can be upgraded to valuable chemicals and produced by the hydrogenation of alkyl levulinates. Although these reactions are widely studied, seldom research focused on the solvent effect. To fill this gap, the effect of three different reaction mixtures with an excess of butyl levulinate (BL), of butanol and GVL was studied on the kinetics of BL hydrogenation to GVL over Ru/C. PC-SAFT (Perturbed-Chain Statistical Associating Fluid Theory) shows that the solubility of hydrogen is not constant during the reaction progress, and it was taken into account. To allow a fair comparison, kinetic models were developed using Bayesian statistics for each reaction mixture. The best performances were obtained when the reaction mixture has an excess of GVL. © 2020 Elsevier Ltd
    view abstractdoi: 10.1016/j.ces.2020.116315
  • 2021 • 1160 Comparison between optical coherence tomography imaging and histological sections of peripheral nerves
    Carolus, A.E. and Möller, J. and Hofmann, M.R. and van de Nes, J.A.P. and Welp, H. and Schmieder, K. and Brenke, C.
    Journal of Neurosurgery 134 270-277 (2021)
    OBJECTIVE Optical coherence tomography (OCT) is an imaging technique that uses the light-backscattering properties of different tissue types to generate an image. In an earlier feasibility study the authors showed that it can be applied to visualize human peripheral nerves. As a follow-up, this paper focuses on the interpretation of the images obtained. METHODS Ten different short peripheral nerve specimens were retained following surgery. In a first step they were examined by OCT during, or directly after, surgery. In a second step the nerve specimens were subjected to histological examination. Various steps of image processing were applied to the OCT raw data acquired. The improved OCT images were compared with the sections stained by H & E. The authors assigned the structures in the images to the various nerve components including perineurium, fascicles, and intrafascicular microstructures. RESULTS The results show that OCT is able to resolve the myelinated axons. A weighted averaging filter helps in identifying the borders of structural features and reduces artifacts at the same time. Tissue-remodeling processes due to injury (perineural fibrosis or neuroma) led to more homogeneous light backscattering. Anterograde axonal degeneration due to sharp injury led to a loss of visible axons and to an increase of light-backscattering tissue as well. However, the depth of light penetration is too small to allow generation of a complete picture of the nerve. CONCLUSIONS OCT is the first in vivo imaging technique that is able to resolve a nerve’s structures down to the level of myelinated axons. It can yield information about focal and segmental pathologies. © AANS 2021, except where prohibited by US copyright law
    view abstractdoi: 10.3171/2019.8.JNS191278
  • 2021 • 1159 Numerical approximation of control problems of non-monotone and non-coercive semilinear elliptic equations
    Casas, E. and Mateos, M. and Rösch, A.
    Numerische Mathematik 149 305-340 (2021)
    We analyze the numerical approximation of a control problem governed by a non-monotone and non-coercive semilinear elliptic equation. The lack of monotonicity and coercivity is due to the presence of a convection term. First, we study the finite element approximation of the partial differential equation. While we can prove existence of a solution for the discrete equation when the discretization parameter is small enough, the uniqueness is an open problem for us if the nonlinearity is not globally Lipschitz. Nevertheless, we prove the existence and uniqueness of a sequence of solutions bounded in L∞(Ω) and converging to the solution of the continuous problem. Error estimates for these solutions are obtained. Next, we discretize the control problem. Existence of discrete optimal controls is proved, as well as their convergence to solutions of the continuous problem. The analysis of error estimates is quite involved due to the possible non-uniqueness of the discrete state for a given control. To overcome this difficulty we define an appropriate discrete control-to-state mapping in a neighbourhood of a strict solution of the continuous control problem. This allows us to introduce a reduced functional and obtain first order optimality conditions as well as error estimates. Some numerical experiments are included to illustrate the theoretical results. © 2021, The Author(s).
    view abstractdoi: 10.1007/s00211-021-01222-7
  • 2021 • 1158 Cryo-EM photosystem I structure reveals adaptation mechanisms to extreme high light in Chlorella ohadii
    Caspy, I. and Neumann, E. and Fadeeva, M. and Liveanu, V. and Savitsky, A. and Frank, A. and Kalisman, Y.L. and Shkolnisky, Y. and Murik, O. and Treves, H. and Hartmann, V. and Nowaczyk, M.M. and Schuhmann, W. and Rögner, M. and ...
    Nature Plants 7 1314-1322 (2021)
    Photosynthesis in deserts is challenging since it requires fast adaptation to rapid night-to-day changes, that is, from dawn’s low light (LL) to extreme high light (HL) intensities during the daytime. To understand these adaptation mechanisms, we purified photosystem I (PSI) from Chlorella ohadii, a green alga that was isolated from a desert soil crust, and identified the essential functional and structural changes that enable the photosystem to perform photosynthesis under extreme high light conditions. The cryo-electron microscopy structures of PSI from cells grown under low light (PSILL) and high light (PSIHL), obtained at 2.70 and 2.71 Å, respectively, show that part of light-harvesting antenna complex I (LHCI) and the core complex subunit (PsaO) are eliminated from PSIHL to minimize the photodamage. An additional change is in the pigment composition and their number in LHCIHL; about 50% of chlorophyll b is replaced by chlorophyll a. This leads to higher electron transfer rates in PSIHL and might enable C. ohadii PSI to act as a natural photosynthesiser in photobiocatalytic systems. PSIHL or PSILL were attached to an electrode and their induced photocurrent was determined. To obtain photocurrents comparable with PSIHL, 25 times the amount of PSILL was required, demonstrating the high efficiency of PSIHL. Hence, we suggest that C. ohadii PSIHL is an ideal candidate for the design of desert artificial photobiocatalytic systems. © 2021, The Author(s), under exclusive licence to Springer Nature Limited.
    view abstractdoi: 10.1038/s41477-021-00983-1
  • 2021 • 1157 Investigation of the orientation relationship between nano-sized G-phase precipitates and austenite with scanning nano-beam electron diffraction using a pixelated detector
    Cautaerts, N. and Rauch, E.F. and Jeong, J. and Dehm, G. and Liebscher, C.H.
    Scripta Materialia 201 (2021)
    Scanning nano-beam electron diffraction with a pixelated detector was employed to investigate the orientation relationship of nanometer sized, irradiation induced G-phase (M6Ni16Si7) precipitates in an austenite matrix. Using this detector, the faint diffraction spots originating from the small G-phase particles could be resolved simultaneously as the intense matrix reflections. The diffraction patterns were analyzed using a two-stage template matching scheme, whereby the matrix is indexed first and the precipitates are indexed second after subtraction of the matrix contribution to the diffraction patterns. The results show that G-phase forms with orientation relationships relative to austenite that are characteristic of face-centered cubic (FCC) to body-centered cubic (BCC) transformations. This work demonstrates that nano-beam electron diffraction with a pixelated detector is a promising technique to investigate orientation relationships of nano-sized precipitates with complex crystal structures in other material systems with relative ease. © 2021 The Author(s)
    view abstractdoi: 10.1016/j.scriptamat.2021.113930
  • 2021 • 1156 Presentation of the Dana Medal of the Mineralogical Society of America for 2020 to Daniela Rubatto
    Chakraborty, S.
    American Mineralogist 106 843 (2021)
    doi: 10.2138/am-2021-AP10653
  • 2021 • 1155 Phase decomposition in nanocrystalline Cr0.8Cu0.2 thin films
    Chakraborty, J. and Harzer, T.P. and Duarte, M.J. and Dehm, G.
    Journal of Alloys and Compounds 888 (2021)
    Metastable Cr0.8Cu0.2 alloy thin films with nominal thickness of 360 nm have been deposited on Si(100) substrate by co-evaporation of Cu and Cr using molecular beam epitaxy (MBE). Phase evolution, microstructure, stress development, and crystallographic texture in Cr0.8Cu0.2 thin films have been investigated by X-ray diffraction (XRD), atom probe tomography (APT) and transmission electron microscopy (TEM) combined with energy dispersive X-ray spectroscopy (EDS) during annealing of the films in the temperature range 200–450 °C. X-ray diffraction of the as-deposited thin film shows single phase bcc crystal structure of the film whereas APT observation of fine precipitates in the film matrix due to inherent compositional fluctuation indicates onset of phase separation via spinodal decomposition regime. XRD (in-situ) and APT investigation of 300 °C annealed film reveals that the early stage of phase separation involves localized formation of metastable intermediate bcc precipitate phase having 60 at% Cr and 40 at% Cu approximately (~Cr0.6Cu0.4). For longer duration of annealing at temperature ≥350 °C, such metastable bcc precipitates act as heterogeneous nucleation sites for the onset of precipitation of Cu rich fcc Cu(Cr) phase which indicates a change of phase separation mechanism from ‘spinodal decomposition’ to ‘nucleation and growth’. Annealing of the film at temperature ≥400 °C for longer duration leads to the formation of a two phase structure with Cu rich fcc precipitate phase in a Cr rich bcc matrix. Observed phase decomposition is accompanied by significant changes in the microstructure, residual stress and crystallographic texture in the Cr rich bcc film matrix which leads to the minimization of both surface and strain energies and thereby a reduction of total Gibbs free energy of the thin film. Thermodynamic model calculation has been presented in order to understand the nucleation pathway of Cu rich stable fcc Cu(Cr) precipitates via non-classical nucleation of metastable intermediate bcc Cr0.6Cu0.4 phase. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.jallcom.2021.161391
  • 2021 • 1154 Real-Time Measurement of Cellobiose and Glucose Formation during Enzymatic Biomass Hydrolysis
    Chang, H. and Wohlschlager, L. and Csarman, F. and Ruff, A. and Schuhmann, W. and Scheiblbrandner, S. and Ludwig, R.
    Analytical Chemistry 93 7732-7738 (2021)
    Enzymatic hydrolysis of lignocellulosic biomass for biofuel production relies on complex multi-enzyme ensembles. Continuous and accurate measurement of the released key products is crucial in optimizing the industrial degradation process and also investigating the activity and interaction between the involved enzymes and the insoluble substrate. Amperometric biosensors have been applied to perform continuous cellobiose measurements during the enzymatic hydrolysis of pure cellulose powders. The oxygen-sensitive mediators used in these biosensors restricted their function under physiological or industrial conditions. Also, the combined measurements of the hydrolysis products cellobiose and glucose require a high selectivity of the biorecognition elements. We employed an [Os(2,2′-bipyridine)2Cl]Cl-modified polymer and cellobiose dehydrogenase to fabricate a cellobiose biosensor, which can accurately and specifically detect cellobiose even in the presence of oxygen and the other main product glucose. Additionally, a glucose biosensor was fabricated to simultaneously measure glucose produced from cellobiose by β-glucosidases. The cellobiose and glucose biosensors work at applied potentials of +0.25 and +0.45 V versus Ag|AgCl (3 M KCl), respectively, and can selectively detect their substrate. Both biosensors were used in combination to monitor the hydrolysis of pure cellulose of low crystallinity or industrial corncob samples. The obtained results correlate with the high-performance liquid chromatography pulsed amperometric detection analysis and demonstrate that neither oxygen nor the presence of redox-active compounds from the lignin fraction of the corncob interferes with the measurements. © 2021 The Authors. Published by American Chemical Society.
    view abstractdoi: 10.1021/acs.analchem.1c01182
  • 2021 • 1153 On the role of pre-existing defects in influencing hardness in nanoscale indentations — Insights from atomistic simulations
    Chauniyal, A. and Dehm, G. and Janisch, R.
    Journal of the Mechanics and Physics of Solids 154 (2021)
    Using in-situ nanoindentation experiments it is possible to study the dislocation mechanisms which unfold under an indenter.Large-scale atomistic simulations of the same are possible due to similarities in length scale, provided that defects can be included in the simulation. Yet, nanoindentation simulations have so far been mostly undertaken on defect free samples, while studies with pre-existing defects are few. The latter show that the average hardness is not affected by the presence of pre-existing defects, which justifies the use of ideal crystals in such simulations. However, this observation is counter-intuitive, as indenter-defect interactions should lead to work hardening and manifest themselves in hardness calculations. Our simulations along with a new look at the evolution of dislocations under the indenter, show for the first time, that hardness in atomistic simulations is influenced by pre-existing defects in the sample. Utilizing a face-centred tetragonal TiAl bicrystal with misfit dislocations at the interface, to populate the sample with defects, we correlate the contact-pressure variations to defect-indenter interactions. We show that the measured contact-pressure is affected by the presence and nature of defects under the indenter. Dislocation pile ups lead to intermittent rise in contact pressure, while seamless growth leads to steady convergence. The sensitivity to detect such defect interactions depends upon indenter size while convergence to average hardness is a result of curvature accommodation near the surface. Our findings prove that pre-existing defects have a profound influence on calculated hardness in indentation simulations which also corroborates with experimental observations in the literature. © 2021 Elsevier Ltd
    view abstractdoi: 10.1016/j.jmps.2021.104511
  • 2021 • 1152 Oxygenated PAH Formation Chemistry Investigation in Anisole Jet Stirred Reactor Oxidation by a Thermodynamic Approach
    Chen, B. and Kruse, S. and Schmid, R. and Cai, L. and Hansen, N. and Pitsch, H.
    Energy and Fuels 35 1535-1545 (2021)
    Oxygenated poly aromatic hydrocarbons (OPAH) are widely produced in biomass combustion. Recent studies suggest significantly higher toxicity for OPAH in comparison to PAH and soot. However, the present understanding of OPAH formation chemistry is rudimentary. Hence, fundamental knowledge on the formation pathways of OPAH is urgently required to develop predictive models for adequate emission control strategies on OPAH emission in biomass combustion. In this work, the OPAH formation from oxidation of anisole, a representative biomass surrogate, was studied in a jet stirred reactor (JSR). The reaction products were in-situ sampled by molecular beam (MB) and analyzed by time-of-flight mass spectrometry (TOF-MS) using synchrotron radiation as a photon ionization source. The unique experimental setup allows direct detection and identification of large OPAH molecules. Over 40 sum formula of OPAH species were detected and identified by experiments, and a computational thermodynamic approach was applied to deduce possible isomers of OPAH species. The thermodynamic modeling approach assumes that isomers with relatively lower Gibbs free energies are more likely to be present due to possible lower activation energies in the formation pathways. Furthermore, the formation pathways of elucidated OPAH structures are proposed by analogy to the literature based on the intermediate information. The joint study of OPAH by experiments and quantum chemistry advances the understanding of OPAH formation chemistry. © 2020 American Chemical Society.
    view abstractdoi: 10.1021/acs.energyfuels.0c03829
  • 2021 • 1151 Scalable and Recyclable All-Organic Colloidal Cascade Catalysts
    Chen, C. and Janoszka, N. and Wong, C.K. and Gramse, C. and Weberskirch, R. and Gröschel, A.H.
    Angewandte Chemie - International Edition 60 237-241 (2021)
    We report on the synthesis of core–shell microparticles (CSMs) with an acid catalyst in the core and a base catalyst in the shell by surfactant-free emulsion polymerization (SFEP). The organocatalytic monomers were separately copolymerized in three synthetic steps allowing the spatial separation of incompatible acid and base catalysts within the CSMs. Importantly, a protected and thermo-decomposable sulfonate monomer was used as acid source to circumvent the neutralization of the base catalyst during shell formation, which was key to obtain stable, catalytically active CSMs. The catalysts showed excellent performance in an established one-pot model cascade reaction in various solvents (including water), which involved an acid-catalyzed deacetalization followed by a base-catalyzed Knoevenagel condensation. The CSMs are easily recycled, modified, and their synthesis is scalable, making them promising candidates for organocatalytic applications. © 2020 The Authors. Published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/anie.202008104
  • 2021 • 1150 A unified description of non-radiative voltage losses in organic solar cells
    Chen, X.-K. and Qian, D. and Wang, Y. and Kirchartz, T. and Tress, W. and Yao, H. and Yuan, J. and Hülsbeck, M. and Zhang, M. and Zou, Y. and Sun, Y. and Li, Y. and Hou, J. and Inganäs, O. and Coropceanu, V. and Bredas, J.-L. and Gao, F.
    Nature Energy (2021)
    Recent advances in organic solar cells based on non-fullerene acceptors (NFAs) come with reduced non-radiative voltage losses (ΔVnr). Here we show that, in contrast to the energy-gap-law dependence observed in conventional donor:fullerene blends, the ΔVnr values in state-of-the-art donor:NFA organic solar cells show no correlation with the energies of charge-transfer electronic states at donor:acceptor interfaces. By combining temperature-dependent electroluminescence experiments and dynamic vibronic simulations, we provide a unified description of ΔVnr for both fullerene- and NFA-based devices. We highlight the critical role that the thermal population of local exciton states plays in low-ΔVnr systems. An important finding is that the photoluminescence yield of the pristine materials defines the lower limit of ΔVnr. We also demonstrate that the reduction in ΔVnr (for example, &lt;0.2 V) can be obtained without sacrificing charge generation efficiency. Our work suggests designing donor and acceptor materials with high luminescence efficiency and complementary optical absorption bands extending into the near-infrared region. © 2021, The Author(s), under exclusive licence to Springer Nature Limited.
    view abstractdoi: 10.1038/s41560-021-00843-4
  • 2021 • 1149 Maxwell relation, giant (negative) electrocaloric effect, and polarization hysteresis
    Chen, X. and Li, S. and Jian, X. and Hambal, Y. and Lu, S.-G. and Shvartsman, V.V. and Lupascu, D.C. and Zhang, Q.M.
    Applied Physics Letters 118 (2021)
    The electrocaloric effect (ECE) in dielectrics is characterized by the isothermal entropy change ΔS and adiabatic temperature change ΔT induced by changes of external electric fields. The Maxwell relation, which relates changes of polarization P with temperature T (pyroelectric coefficient) under a fixed electric field E to ΔS for finite intervals in E, provides a convenient way to deduce the ECE from polarization data P(T, E). Hence, this method, known as the indirect method, is widely used in ECE studies in ferroelectrics. Here, we first present the thermodynamic consideration for the Maxwell relation. We then use the indirect method and P(T, E) from bipolar and unipolar polarization curves to deduce the ECE in the normal ferroelectric phase of a P(VDF-TrFE) copolymer. The deduced ECE using the P(T, E) from bipolar polarization curves exhibits a giant negative ECE. In contrast, the directly measured ECE in the same polymer shows the weak and normal ECE. We discuss the constraints of the indirect method and its relation to the polarization-electric field curves measured in practical ferroelectric materials. © 2021 Author(s).
    view abstractdoi: 10.1063/5.0042333
  • 2021 • 1148 Feature extraction and neural network-based analysis on time-correlated LiDAR histograms
    Chen, G. and Gembaczka, P. and Wiede, C. and Kokozinski, R.
    PHOTOPTICS 2021 - Proceedings of the 9th International Conference on Photonics, Optics and Laser Technology 17-22 (2021)
    Time correlated single photon counting (TCSPC) is used to obtain the time-of-flight (TOF) information generated by single-photon avalanche diodes. With restricted measurements per histogram and the presence of high background light, it is challenging to obtain the TOF information in the statistical histogram. In order to improve the robustness under these conditions, the concept of machine learning is applied to the statistical histogram. Using the multi-peak extraction method, introduced by us, followed by the neural-network-based multi-peak analysis, the analysis and resources can be focused on a small amount of critical information in the histogram. Multiple possible TOF positions are evaluated and the correlated soft-decisions are assigned. The proposed method has higher robustness in allocating the coarse position (± 5 %) of TOF in harsh conditions than the case using classical digital processing. Thus, it can be applied to improve the system robustness, especially in the case of high background light. Copyright © 2021 by SCITEPRESS – Science and Technology Publications, Lda. All rights reserved.
    view abstract
  • 2021 • 1147 Comment on "giant pyroelectric energy harvesting and a negative electrocaloric effect in multilayered nanostructures" by G. Vats, A. Kumar, N. Ortega, C. R. Bowen and R. S. Katiyar,: Energy Environ. Sci., 2016, 9, 1335
    Chen, X. and Shvartsman, V. and Lupascu, D.C. and Zhang, Q.M.
    Energy and Environmental Science 14 1612-1614 (2021)
    Vats et al. (2016) reported a giant negative electrocaloric effect in multi-ferroic layers. The results were deduced using the polarization from partially switched polarization loops and the Maxwell relation on the electrocaloric effect. First of all, fundamentally, the change of these polarizations with temperature, as presented in their Fig. 5, has no relation with the electrocaloric effect and hence cannot be used to deduce the ECE using the Maxwell relation. Moreover, we are troubled by the data presented in their Fig. 6, which were, as claimed by authors, deduced from the polarization data in their Fig. 5 and the Maxwell relation. We find that the ECE results presented in their Fig. 6 have no direct relation with the polarization-temperature data in their Fig. 5. © 2021 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/d0ee02548h
  • 2021 • 1146 Quantum spin mixing in Dirac materials
    Chen, Y.-J. and Hoffmann, M. and Zimmermann, B. and Bihlmayer, G. and Blügel, S. and Schneider, C.M. and Tusche, C.
    Communications Physics 4 (2021)
    The spin of the electron is nowadays replacing the charge as basic carrier of information not only in spintronics applications, but also in the emerging field of quantum information. Topological quantum materials, where spin-momentum locking is believed to lead to particularly long spin lifetimes, are regarded as a promising platform for such applications. However, spin-orbit coupling, that is essential to all topological matter, at the same time gives rise to spin mixing and decoherence as a major obstacle for quantum computing. Here, we give experimental evidence that hot-spots of spin-mixing and spin-conserving contributions of the spin-orbit operator coexist in an archetypal topological Dirac metal, and that these hot spots can have a strongly anisotropic distribution of their respective wave vectors with respect to the spin quantization direction. Our results can be understood within a theory that takes into account the decomposition of the spin-orbit Hamiltonian into spin-conserving and spin-flip terms, contributing to a better understanding of quantum decoherence in topological materials, in general. © 2021, The Author(s).
    view abstractdoi: 10.1038/s42005-021-00682-5
  • 2021 • 1145 Dispersion relation of nutation surface spin waves in ferromagnets
    Cherkasskii, M. and Farle, M. and Semisalova, A.
    Physical Review B 103 (2021)
    Inertia effects in magnetization dynamics are theoretically shown to result in a different type of spin waves, i.e., nutation surface spin waves, which propagate at terahertz frequencies in in-plane magnetized ferromagnetic thin films. Considering the magnetostatic limit, i.e., neglecting exchange coupling, we calculate dispersion relation and group velocity, which we find to be slower than the velocity of conventional (precession) spin waves. In addition, we find that the nutation surface spin waves are backward spin waves. Furthermore, we show that inertia causes a decrease of the frequency of the precession spin waves, namely magnetostatic surface spin waves and backward volume magnetostatic spin waves. The magnitude of the decrease depends on the magnetic properties of the film and its geometry. © 2021 authors.
    view abstractdoi: 10.1103/PhysRevB.103.174435
  • 2021 • 1144 A new water-soluble thermosensitive star-like copolymer as a promising carrier of the chemotherapeutic drug doxorubicin
    Chernykh, M. and Zavalny, D. and Sokolova, V. and Ponomarenko, S. and Prylutska, S. and Kuziv, Y. and Chumachenko, V. and Marynin, A. and Kutsevol, N. and Epple, M. and Ritter, U. and Piosik, J. and Prylutskyy, Y.
    Materials 14 (2021)
    A new water-soluble thermosensitive star-like copolymer, dextran-graft-poly-N-iso-propilacrylamide (D-g-PNIPAM), was created and characterized by various techniques (size-exclusion chromatography, differential scanning calorimetry, Fourier-transform infrared (FTIR) spectroscopy, and dynamic light scattering (DLS) spectroscopy). The viability of cancer cell lines (human transformed cervix epithelial cells, HeLa) as a model for cancer cells was studied using MTT and Live/Dead assays after incubation with a D-g-PNIPAM copolymer as a carrier for the drug doxorubicin (Dox) as well as a D-g-PNIPAM + Dox mixture as a function of the concentration. FTIR spectroscopy clearly indicated the complex formation of Dox with the D-g-PNIPAM copolymer. The size distribution of particles in Hank’s solution was determined by the DLS technique at different temperatures. The in vitro uptake of the studied D-g-PNIPAM + Dox nanoparticles into cancer cells was demonstrated by confocal laser scanning microscopy. It was found that D-g-PNIPAM + Dox nanoparticles in contrast to Dox alone showed higher toxicity toward cancer cells. All of the aforementioned facts indicate a possibility of further preclinical studies of the water-soluble D-g-PNIPAM particles’ behavior in animal tumor models in vivo as promising carriers of anticancer agents. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/ma14133517
  • 2021 • 1143 Targeted Phosphoinositides Analysis Using High-Performance Ion Chromatography-Coupled Selected Reaction Monitoring Mass Spectrometry
    Cheung, H.Y.F. and Coman, C. and Westhoff, P. and Manke, M. and Sickmann, A. and Borst, O. and Gawaz, M. and Watson, S.P. and Heemskerk, J.W.M. and Ahrends, R.
    Journal of Proteome Research 20 3114-3123 (2021)
    Phosphoinositides are minor components of cell membranes, but play crucial roles in numerous signal transduction pathways. To obtain quantitative measures of phosphoinositides, sensitive, accurate, and comprehensive methods are needed. Here, we present a quantitative targeted ion chromatography-mass spectrometry-based workflow that separates phosphoinositide isomers and increases the quantitative accuracy of measured phosphoinositides. Besides testing different analytical characteristics such as extraction and separation efficiency, the reproducibility of the developed workflow was also investigated. The workflow was verified in resting and stimulated human platelets, fat cells, and rat hippocampal brain tissue, where the LOD and LOQ for phosphoinositides were at 312.5 and 625 fmol, respectively. The robustness of the workflow is shown with different applications that confirms its suitability to analyze multiple less-abundant phosphoinositides. © 2021 American Chemical Society.
    view abstractdoi: 10.1021/acs.jproteome.1c00017
  • 2021 • 1142 Lattice-shifted nematic quantum critical point in FeSe1−xSx
    Chibani, S. and Farina, D. and Massat, P. and Cazayous, M. and Sacuto, A. and Urata, T. and Tanabe, Y. and Tanigaki, K. and Böhmer, A.E. and Canfield, P.C. and Merz, M. and Karlsson, S. and Strobel, P. and Toulemonde, P. and Paul...
    npj Quantum Materials 6 (2021)
    We report the evolution of nematic fluctuations in FeSe1−xSx single crystals as a function of Sulfur content x across the nematic quantum critical point (QCP) xc ~ 0.17 via Raman scattering. The Raman spectra in the B1g nematic channel consist of two components, but only the low energy one displays clear fingerprints of critical behavior and is attributed to itinerant carriers. Curie–Weiss analysis of the associated nematic susceptibility indicates a substantial effect of nemato-elastic coupling, which shifts the location of the nematic QCP. We argue that this lattice-induced shift likely explains the absence of any enhancement of the superconducting transition temperature at the QCP. The presence of two components in the nematic fluctuations spectrum is attributed to the dual aspect of electronic degrees of freedom in Hund’s metals, with both itinerant carriers and local moments contributing to the nematic susceptibility. © 2021, The Author(s).
    view abstractdoi: 10.1038/s41535-021-00336-3
  • 2021 • 1141 Durability prediction of coil spring through multibody-dynamics-based strain generation
    Chin, C.H. and Abdullah, S. and Singh, S.S.K. and Schramm, D. and Ariffin, A.K.
    Mechanical Systems and Signal Processing 154 (2021)
    The purpose of this study is to develop an acceleration-strain conversion model that considers torsional strain and spring curvature effects in inducing strain for a suspension coil spring. Measurements of strain–time histories at the coil spring are limited by complex geometry and insufficient workspace. This condition increases the demand for strain signal generation through multibody dynamics (MBD) simulation, reducing the need for real strain measurement of coil spring. Road tests were conducted to obtain the unsprung mass acceleration and strain signals of a coil spring under four road conditions (rural, industrial, highway, and campus road). Quarter-car suspension MBD simulation was modelled to simulate the deflection of a spring excited under unsprung mass acceleration. By using this model, simulated strain data with similar properties as the experimental data were generated for fatigue life prediction. The predicted fatigue life from the generated strain indicated a good correlation with the experimental fatigue life within the boundary and showed very low normalised root-mean-square error (NRMSE) between 4 × 10−6 and 2 × 10−4. Finally, it is suggested that the acceleration-strain conversion model showed an enhanced performance for producing realistic strain signals in accurately predicting the durability of coil spring. This can, therefore, further reduce the need for real strain measurement at the coil spring that can result in an erroneous signal. © 2020
    view abstractdoi: 10.1016/j.ymssp.2020.107580
  • 2021 • 1140 Neuro-fuzzy fatigue life assessment using the wavelet-based multifractality parameters
    Chin, C.H. and Abdullah, S. and Singh, S.S.K. and Ariffin, A.K. and Schramm, D.
    Journal of Mechanical Science and Technology 35 439-447 (2021)
    This study aims to establish a fatigue life predictive model based on multifractality of road excitations using neuro-fuzzy method to assess the durability of suspension spring. Traditional durability analysis in time domain is complicated and time-consuming due to the needs of large data amount. Thus, it is an idea to adopt an adaptive neuro-fuzzy inference system (ANFIS) for relating the performance of coil spring to the multifractal properties of road excitations, giving a meaningful fatigue life prediction. Different membership function numbers were tested to obtain the optimum membership function number. During the data training process, the checking data was used to test the trained model each Epoch of training for overfitting detection. As a result, the Morrow-based fatigue life prediction model was found to give the most suitable result with three membership functions. The SWT-based model needed five membership functions due to nonlinear properties in the SWT-based fatigue life data. Training process of Morrow-based-ANFIS was stopped at Epoch 8 given its lowest checking root-mean-square-error of 0.6953. SWT-based model recorded a higher error of 0.7940. The neuro-fuzzy models gave accurate fatigue life predictions with 96 % of the data distributed within the acceptance boundary, hence, contributing to an acceptable assessment of coil spring fatigue life based on load multifractality. This study had shown a nonlinear relationship between road multifractality and durability performance of coil spring. Multifractality had been proven an important feature to characterise various road excitations for durability prediction. © 2021, The Korean Society of Mechanical Engineers and Springer-Verlag GmbH Germany, part of Springer Nature.
    view abstractdoi: 10.1007/s12206-021-0102-6
  • 2021 • 1139 Computing low-frequency vibration energy with Hölder singularities as durability predictive criterion of random road excitation
    Chin, C.H. and Abdullah, S. and Singh, S.S.K. and Ariffin, A.K. and Schramm, D.
    Soft Computing (2021)
    This study aims to compute low-frequency energy with Hölder singularities in vibration signals of suspension system to predict the durability of coil spring. High frequencies in vibrations often had minimal contribution towards fatigue damage due to low amplitude range and thus induce errors in energy analysis of vibration signals. Since traditional low-pass method had not only been ineffective in reducing high frequencies, it also resulted in the loss of signal information. This study had therefore proposed characterising low-frequency energy for road excitations using Hölder singularities and power spectral analyses. Singularities and low-frequency energy of road vibration signals would first be identified through Hölder local regularity analysis. This was then followed by fatigue life prediction using the strain-life approaches (i.e. Coffin-Manson, Morrow and Smith–Watson–Topper models). The energy-based fatigue life prediction models had not only shown good fit with R2 values higher than 0.8, but had also demonstrated an accurate prediction of fatigue life with more than 95% of the data being within the acceptance boundary. The Morrow-based model provided the highest accuracy in fatigue life prediction because of its highest R2 value of 0.8625 and 100% data survival in the fatigue life correlation study. This showed that energy-based fatigue life prediction models provide an accurate and effective prediction of the durability performance. This study proposed a more precise energy characterisation method for energy-based durability prediction of suspension coil spring under random loading conditions. © 2021, The Author(s), under exclusive licence to Springer-Verlag GmbH, DE part of Springer Nature.
    view abstractdoi: 10.1007/s00500-021-05640-5
  • 2021 • 1138 CrMnFeCoNi high entropy alloys with carbon and nitrogen: mechanical properties, wear and corrosion resistance
    Chmielak, L. and Mujica Roncery, L. and Niederhofer, P. and Weber, S. and Theisen, W.
    SN Applied Sciences 3 (2021)
    The use of interstitial elements has been a key factor for the development of different kinds of steels. However, this aspect has been little explored in the field of high entropy alloys (HEAs). In this investigation, the effect of carbon and nitrogen in a near-equiatomic CrMnFeCoNi HEA is studied, analyzing their impact on the microstructure, and mechanical properties from 77K to 673K, as well as wear, and corrosion resistance. Carbon and nitrogen are part of the FCC solid solution and contribute to the formation of precipitates. An increase in the yield and ultimate tensile strength accompanied with a decrease in the ductility are the main effects of C and N. The impact toughness of the interstitial-free material is higher than that of C and C+N alloyed systems. Compared to CrNi and CrMn austenitic steels, the wear resistance of the alloys at room temperature is rather low. The surface corrosion resistance of HEAs is comparable to austenitic steels; nevertheless HEAs are more susceptible to pitting in chloride containing solutions. © 2021, The Author(s).
    view abstractdoi: 10.1007/s42452-021-04814-y
  • 2021 • 1137 Orientation-dependent plastic deformation mechanisms and competition with stress-induced phase transformation in microscale NiTi
    Choi, W.S. and Pang, E.L. and Ko, W.-S. and Jun, H. and Bong, H.J. and Kirchlechner, C. and Raabe, D. and Choi, P.-P.
    Acta Materialia 208 (2021)
    Understanding the orientation-dependent deformation behavior of NiTi shape-memory alloys at small length scales is of importance for designing nano- and micro-electromechanical systems. However, a complete understanding of the orientation- and size-dependent competition between the various modes of slip, deformation twinning, and martensitic transformation in NiTi shape-memory alloys is still lacking, especially in micron-scale specimens. In the present study, we perform micro-compression tests on [001]- and [112]-oriented micro-pillars of a solutionized Ti-49.9at.% Ni alloy. Post-mortem TEM analysis of the deformed pillars reveal that the operating plastic deformation modes are {011}&lt;100&gt; slip and {114}&lt;221¯&gt; deformation twinning, which compete with the martensitic transformation, depending on the crystal orientation. Furthermore, in both experiments and molecular dynamics simulations, we consistently find residual B19′ martensite in a herringbone microstructure composed of finely spaced (001)B19′ compound twins instead of the generally assumed [011]B19′ type II twins common in bulk samples, suggesting that the operative martensitic transformation mode may be size-dependent. Schmid factors in compression are calculated for all commonly reported slip, deformation twinning, and martensitic transformation modes as a function of crystallographic orientation, which rationalize the orientation-dependent competition between these deformation modes. © 2021 Acta Materialia Inc.
    view abstractdoi: 10.1016/j.actamat.2021.116731
  • 2021 • 1136 Electronic theory for scanning tunneling microscopy spectra in infinite-layer nickelate superconductors
    Choubey, P. and Eremin, I.M.
    Physical Review B 104 (2021)
    The recent scanning tunneling microscopy (STM) observation of -shaped and -shaped spectra (and their mixture) in superconducting thin films has been interpreted as the presence of two distinct gap symmetries in this nickelate superconductor [Gu, Nat. Commun.11, 6027 (2020)10.1038/s41467-020-19908-1]. Here, using a two-band model of nickelates capturing dominant contributions from Ni- and rare-earth (R)- orbitals, we show that the experimental observation can be simply explained within a pairing scenario characterized by a conventional -wave gap structure with the lowest harmonic on the Ni band and a -wave gap with higher harmonics on the R band. We perform realistic simulations of STM spectra employing first-principles Wannier functions to properly account for the tunneling processes and obtain and mixed spectral line shapes depending on the position of the STM tip within the unit cell. The - and -shaped spectra are contributed by Ni and R bands, respectively, and Wannier functions, in essence, provide position-dependent weighting factors, determining the spectral line shape at a given intra-unit-cell position. We propose a phase-sensitive experiment to distinguish between the proposed -wave gap structure and the time-reversal symmetry-breaking gap which yields very similar intra-unit-cell spectra. © 2021 American Physical Society
    view abstractdoi: 10.1103/PhysRevB.104.144504
  • 2021 • 1135 Biomineralization, dissolution and cellular studies of silicate bioceramics prepared from eggshell and rice husk
    Choudhary, R. and Venkatraman, S.K. and Bulygina, I. and Senatov, F. and Kaloshkin, S. and Anisimova, N. and Kiselevskiy, M. and Knyazeva, M. and Kukui, D. and Walther, F. and Swamiappan, S.
    Materials Science and Engineering C 118 (2021)
    The current investigation aims to replace the synthetic starting materials with biowaste to synthesize and explore three different silicate bioceramics. Pure silica from rice husk was extracted by decomposition of rice husk in muffle furnace followed by alkali treatment and acid precipitation. Raw eggshell and extracted silica were utilized for the preparation of wollastonite, diopside and forsterite by the solid-state method. The TG-DSC analysis shows that the crystallization temperature of wollastonite, diopside and forsterite was found to be 883 °C, 870 °C and 980 °C, respectively. The phase purity of wollastonite was attained at 1100 °C whereas diopside and forsterite were composed of secondary phases even after calcination at 1250 °C and 1300 °C respectively. All three materials behaved differently when exposed to the physiological environment, as wollastonite exhibited remarkable apatite deposition within 3 days whereas a distinct apatite phase was noticed on the surface of diopside after 2 weeks and forsterite shows the formation of apatite phase after five weeks of immersion. The rapid dissolution of Mg2+ ion from forsterite lowered the leaching of silicate ions into the simulated body fluid leading to poor apatite deposition over its surface. Chemical composition was found to plays a key role in the biomineralization ability of these bioceramics. Hemolysis and Lactate Dehydrogenase (LDH) release assays were performed to evaluate the hemocompatibility of silicate ceramics cultured at different concentrations (62.5, 125, and 250 μg/mL) with red blood cells and mononuclear leucocytes (MLs) of mice. The hemolytic activity of all the tested bioceramics was insignificant (less than 1%). The interaction between diopside and mouse multipotent mesenchymal stromal cells (MMSCs) caused a negligible increase in the number of apoptosis-associated Annexin V-binding cells whereas forsterite and wollastonite induced an increase in the number of the apoptotic cells only at the concentration of 250 μg/mL. The LDH assay did not show statistically significant changes in the proliferation of MMSCs after treatment with the bioceramics at the tested concentrations when compared to control (p &gt; 0.05). This finding showed that the death of a part of cells during the first 24 h of incubation did not prevent the proliferation of MMSCs incubated with diopside, forsterite and wollastonite for 72 h. © 2020 Elsevier B.V.
    view abstractdoi: 10.1016/j.msec.2020.111456
  • 2021 • 1134 Time will tell: Secular change in metamorphic timescales and the tectonic implications
    Chowdhury, P. and Chakraborty, S. and Gerya, T.V.
    Gondwana Research 93 291-310 (2021)
    The pressure-temperature-time (P-T-t) evolution of metamorphic rocks is directly related to geodynamics as different tectonic settings vary in their thermal architecture. The shapes of P-T paths and thermobaric ratios (T/P) of metamorphic rocks have been extensively used to distinguish different tectonic domains. However, the role of metamorphic timescales in constraining tectonic settings remains underutilized. This is because of the poorly understood relationship between them, and the difficulty in accurately constraining the onset and end of a particular metamorphic event. Here, we show why and how the intrinsic relationship between thermal regime, rheology and rate of motion controlled by the heat, mass and momentum conservation laws translate to differences in heating, cooling, burial, exhumation rates of metamorphic rocks and thereby, to the duration of metamorphism. We compare the P-T-t paths of the orogenic metamorphic rocks of different ages and in particular, analyse their retrograde cooling rates and durations. The results show that cooling rates of the metamorphic rocks are variable but are dominantly <50 °C/Ma during most of the Precambrian before increasing by an order of magnitude (>100 °C/Ma) during the late Neoproterozoic to Phanerozoic. To seek what controlled this secular change in metamorphic cooling rates, we use thermomechanical modelling to calculate the P-T-t paths of crustal rocks in different types of continental orogenic settings and compare them with the rock record. The modelled P-T-t paths show that lithospheric peel-back driven orogenic settings, which are postulated as an orogenic mode operating under the hotter mantle conditions of late Archean to early Proterozoic, are characterised by longer durations of metamorphism and slower cooling rates (a few 10s of °C/Ma) as compared to the modern orogenic settings (a few 100s of °C/Ma) operating under relatively colder mantle conditions. This is because peel-back orogens feature: (1) hot lithospheres with very high crustal geotherms being sustained by high mantle heat-flow and profuse magmatism, and (2) distributed deformation patterns that limit vertical extrusion (exhumation) of the metamorphic rocks along localized deformation zones and instead, trap them in the orogenic core for a long time. In contrast, modern orogens mostly involve colder lithospheres and allow rapid exhumation through localized deformation, which facilitates faster cooling of hot, exhumed metamorphic rocks in a colder ambience. Thus, we propose that the secular change in metamorphic cooling rates indicates a changing regime of orogenesis and thereby, of plate tectonics through time. Predominance of the slower metamorphic cooling rates before the Neoproterozoic indicate the occurrences of peel-back orogenesis and truncated hot (collisional) orogenesis during that time, while the appearance of faster cooling rates since the late Neoproterozoic indicates the transition to modern style of orogenesis. A transition between these orogenic styles also accounts for the prolonged longevity (>100 million years) of many Precambrian orogenic belts as compared to the Phanerozoic ones. This study underscores the strength of timescales in combination with P-T paths to distinguish tectonic settings of different styles and ages. © 2021 International Association for Gondwana Research
    view abstractdoi: 10.1016/
  • 2021 • 1133 Functionalization of additive-manufactured Ti6Al4V scaffolds with poly(allylamine hydrochloride)/poly(styrene sulfonate) bilayer microcapsule system containing dexamethasone
    Chudinova, E. and Koptyug, A. and Mukhortova, Y. and Pryadko, A. and Volkova, A. and Ivanov, A. and Plotnikov, E. and Khan, Y. and Epple, M. and Sokolova, V. and Prymak, O. and Douglas, T. and Surmenev, R. and Surmeneva, M.
    Materials Chemistry and Physics 273 (2021)
    Porous titanium alloy Ti6Al4V scaffolds manufactured via electron beam melting (EBM®) reveal broad prospects for applications in bone tissue engineering. However, local inflammation and even implant failure may occur while placing an implant into the body. Thus, the application of drug carriers to the surface of a metallic implant can provide treatment at the inflammation site. In this study, we propose to use polyelectrolyte (PE) microcapsules formed by layer-by-layer (LbL) synthesis loaded with both porous calcium carbonate (CaCO3) microparticles and the anti-inflammatory drug dexamethasone (DEX) to functionalize implant surfaces and achieve controlled drug release. Scanning electron microscopy indicated that the CaCO3 microparticles coated with PE bilayers loaded with DEX had a spherical shape with a diameter of 2.3 ± 0.2 μm and that the entire scaffold surface was evenly coated with the microcapsules. UV spectroscopy showed that LbL synthesis allows the manufacturing of microcapsules with 40% DEX. According to high performance liquid chromatography (HPLC) analysis, 80% of the drug was released within 24 h from the capsules consisting of three bilayers of polystyrene sulfonate (PSS) and poly(allylamine)hydrochloride (PAH). The prepared scaffolds functionalized with CaCO3 microparticles loaded with DEX and coated with PE bilayers showed hydrophilic surface properties with a water contact angle below 5°. Mouse embryonic fibroblast cells were seeded on Ti6Al4V scaffolds with and without LbL surface modification. The surface modification with LbL PE microcapsules with CaCO3 core affected cell morphology in vitro. The results confirmed that DEX had no toxic effect and did not prevent cell adhesion and spreading, thus no cytotoxic effect was observed, which will be further studied in vivo. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.matchemphys.2021.125099
  • 2021 • 1132 Entropic regularization of continuous optimal transport problems
    Clason, C. and Lorenz, D.A. and Mahler, H. and Wirth, B.
    Journal of Mathematical Analysis and Applications 494 (2021)
    We analyze continuous optimal transport problems in the so-called Kantorovich form, where we seek a transport plan between two marginals that are probability measures on compact subsets of Euclidean space. We consider the case of regularization with the negative entropy with respect to the Lebesgue measure, which has attracted attention because it can be solved by the very simple Sinkhorn algorithm. We first analyze the regularized problem in the context of classical Fenchel duality and derive a strong duality result for a predual problem in the space of continuous functions. However, this problem may not admit a minimizer, which prevents obtaining primal-dual optimality conditions. We then show that the primal problem is naturally analyzed in the Orlicz space of functions with finite entropy in the sense that the entropically regularized problem admits a minimizer if and only if the marginals have finite entropy. We then derive a dual problem in the corresponding dual space, for which existence can be shown by purely variational arguments and primal-dual optimality conditions can be derived. For marginals that do not have finite entropy, we finally show Gamma-convergence of the regularized problem with smoothed marginals to the original Kantorovich problem. © 2020 Elsevier Inc.
    view abstractdoi: 10.1016/j.jmaa.2020.124432
  • 2021 • 1131 No-gap second-order optimality conditions for optimal control of a non-smooth quasilinear elliptic equation
    Clason, C. and Nhu, V.H. and Rösch, A.
    ESAIM - Control, Optimisation and Calculus of Variations 27 (2021)
    This paper deals with second-order optimality conditions for a quasilinear elliptic control problem with a nonlinear coefficient in the principal part that is finitely PC2 (continuous and C2 apart from finitely many points). We prove that the control-To-state operator is continuously differentiable even though the nonlinear coefficient is non-smooth. This enables us to establish "no-gap"second-order necessary and sufficient optimality conditions in terms of an abstract curvature functional, i.e., for which the sufficient condition only differs from the necessary one in the fact that the inequality is strict. A condition that is equivalent to the second-order sufficient optimality condition and could be useful for error estimates in, e.g., finite element discretizations is also provided. © EDP Sciences, SMAI 2021.
    view abstractdoi: 10.1051/cocv/2020092
  • 2021 • 1130 Broadband THz detection using InP triple-barrier resonant tunneling diode with integrated antenna
    Clochiatti, S. and Mutlu, E. and Preuss, C. and Kress, R. and Prost, W. and Weimann, N.
    2021 4th International Workshop on Mobile Terahertz Systems, IWMTS 2021 (2021)
    A broadband THz detector consisting of a triple-barrier InP Resonant Tunneling Diode (RTD) with a monolithically integrated circularly polarized spiral antenna is designed, fabricated, and measured at room temperature. A free space measurement setup is utilized for far-field characterization. The detector (evaluated at zero-bias) is illuminated by a chopped continuous wave signal in the 220-330 GHz band, and the direct detection scheme consists of a lock-in amplifier in voltage mode readout. The measured average responsivity RV is in the range of 750 V/W with a peak of 900 V/W at 257.5 GHz, with the lowest calculated NEP of 2.5 pW/√Hz. © 2021 IEEE.
    view abstractdoi: 10.1109/IWMTS51331.2021.9486794
  • 2021 • 1129 Ferrous to Ferric Transition in Fe-Phthalocyanine Driven by NO2 Exposure
    Cojocariu, I. and Carlotto, S. and Sturmeit, H.M. and Zamborlini, G. and Cinchetti, M. and Cossaro, A. and Verdini, A. and Floreano, L. and Jugovac, M. and Puschnig, P. and Piamonteze, C. and Casarin, M. and Feyer, V. and Schneider, C.M.
    Chemistry - A European Journal 27 3526-3535 (2021)
    Due to its unique magnetic properties offered by the open-shell electronic structure of the central metal ion, and for being an effective catalyst in a wide variety of reactions, iron phthalocyanine has drawn significant interest from the scientific community. Nevertheless, upon surface deposition, the magnetic properties of the molecular layer can be significantly affected by the coupling occurring at the interface, and the more reactive the surface, the stronger is the impact on the spin state. Here, we show that on Cu(100), indeed, the strong hybridization between the Fe d-states of FePc and the sp-band of the copper substrate modifies the charge distribution in the molecule, significantly influencing the magnetic properties of the iron ion. The FeII ion is stabilized in the low singlet spin state (S=0), leading to the complete quenching of the molecule magnetic moment. By exploiting the FePc/Cu(100) interface, we demonstrate that NO2 dissociation can be used to gradually change the magnetic properties of the iron ion, by trimming the gas dosage. For lower doses, the FePc film is decoupled from the copper substrate, restoring the gas phase triplet spin state (S=1). A higher dose induces the transition from ferrous to ferric phthalocyanine, in its intermediate spin state, with enhanced magnetic moment due to the interaction with the atomic ligands. Remarkably, in this way, three different spin configurations have been observed within the same metalorganic/metal interface by exposing it to different doses of NO2 at room temperature. © 2020 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/chem.202004932
  • 2021 • 1128 Insight into intramolecular chemical structure modifications by on-surface reaction using photoemission tomography
    Cojocariu, I. and Feyersinger, F. and Puschnig, P. and Schio, L. and Floreano, L. and Feyer, V. and Schneider, C.M.
    Chemical Communications 57 3050-3053 (2021)
    The sensitivity of photoemission tomography (PT) to directly probe single molecule on-surface intramolecular reactions will be shown here. PT application in the study of molecules possessing peripheral ligands and structural flexibility is tested on the temperature-induced dehydrogenation intramolecular reaction on Ag(100), leading from CoOEP to the final product CoTBP. Along with the ring-closure reaction, the electronic occupancy and energy level alignment of the frontier orbitals, as well as the oxidation state of the metal ion, are elucidated for both the CoOEP and CoTBP systems. © The Royal Society of Chemistry 2021.
    view abstractdoi: 10.1039/d1cc00311a
  • 2021 • 1127 Reversible redox reactions in metal-supported porphyrin: The role of spin and oxidation state
    Cojocariu, I. and Carlotto, S. and Zamborlini, G. and Jugovac, M. and Schio, L. and Floreano, L. and Casarin, M. and Feyer, V. and Schneider, C.M.
    Journal of Materials Chemistry C 9 12559-12565 (2021)
    On-surface molecular functionalization paved the way for the stabilization of chelated ions in different oxidation and spin states, allowing for the fine control of catalytic and magnetic properties of metalorganic networks. Considering two model systems, a reduced Co(i) and an open-shell Co(ii) metal-supported 2D molecular array, we investigate the interplay between the low valence oxidation and unpaired spin state in the molecular reactivity. We show that the redox reaction taking place at the cobalt tetraphenylporphyrin/Cu(100) interface, stabilizing the low-spin Co(i) state with no unpaired electrons in its valence shell, plays a pivotal role in changing the reactivity. This goes beyond the sole presence of unpaired electrons in the valence state of the Co(ii) metal-organic species, often designated as being responsible for the reactivity towards small molecules like NO and NO2. The reversible Co-NO2interaction, established with the Co(i) leads to the stabilization of the Co(iii) oxidation state. © The Royal Society of Chemistry 2021.
    view abstractdoi: 10.1039/d1tc02222a
  • 2021 • 1126 A consistent view on cooperative multistage electrostatic actuation
    Conrad, P. and Hoffmann, M.
    GMM-Fachberichte 2021-February 431-434 (2021)
    Electrostatic fields between electrodes of different potentials induce actuating forces in many different ways. A key question for the design of complex interacting multi-actuator systems is the consistent description of all these electrostatic effects in a way that all forces can be controlled from given and varying electrode potentials. A joining principle to describe all electrostatic effects on solids and liquids in this multiactuator system could be an electrostatic pressure. This should allow a unified simulation of forces between electrodes and forces on elastomers or liquids at once. In this work we investigate this method in a first step for uncoupled simplified electrostatic systems by Finite Element Method (FEM). For these uncoupled systems, this method yields realistic values, as comparison with force calculation via Energy minimization and literature shows. © VDE VERLAG GMBH · Berlin · Offenbach.
    view abstract
  • 2021 • 1125 On the simultaneous use of simple geometrically exact shear-rigid rod and shell finite elements
    Costa e Silva, C. and Maassen, S.F. and Pimenta, P.M. and Schröder, J.
    Computational Mechanics (2021)
    This work addresses simultaneous use of geometrically exact shear-rigid rod and shell finite elements and describes both models within the same framework. Parameterization of the rotation field is performed by Rodrigues rotation vector, which makes the incremental updating of the rotational variables remarkably simple. For the rod element, cubic Hermitian interpolation for the displacements together with quadratic Lagrange interpolation for the incremental torsion angle were employed, while, for the triangular shell element, a complete quadratic Lagrange interpolation was used. The internal incremental torsion angle resulting from the displacement field within the shell element is then made compatible with the boundary incremental torsion angle of the shell element by an internal Lagrange multiplier. The compatibility between contiguous shell elements as well rod elements is mastered in the standard way by simply connecting nodes. This technique is an important contribution of the work, whose performance is illustrated by several numerical examples. © 2021, The Author(s), under exclusive licence to Springer-Verlag GmbH, DE part of Springer Nature.
    view abstractdoi: 10.1007/s00466-020-01967-2
  • 2021 • 1124 Immobilization of peroxidase on textile carrier materials and their application in the bleaching of colored whey
    Courth, K. and Binsch, M. and Ali, W. and Ingenbosch, K. and Zorn, H. and Hoffmann-Jacobsen, K. and Gutmann, J.S. and Opwis, K.
    Journal of Dairy Science 104 1548-1559 (2021)
    Textiles represent promising support materials for enzymes. The goal of the present work was to investigate the immobilization of commercial peroxidase on a polyester needle felt and the repeated use in the gentle degradation of norbixin in whey from dairy cheese as a practical application. High enzyme loads were obtained by a 2-step immobilization procedure. First, the number of functional groups on the textile surface was increased by a modification with amino-functional polyvinylamine. Second, the enzyme was immobilized by using 2 types of crosslinking agents. Due to the iron content of peroxidase, inductively coupled plasma–optical emission spectrometry was used for the quantitative determination of the enzyme load on the textile. The enzyme activity was evaluated using common 2,2'-azino-di-(3-ethylbenzthiazoline-6-sulfonic acid) assay for peroxidases. By the variation of enzyme input and crosslinker concentration, a maximal enzyme load of 80 mg/g of textile was achieved, and a maximum specific activity of 57 U/g of textile. For the visualization of the enzyme on the fiber surface, fluorescence microscopy as well as scanning probe microscopy were used. The immobilized peroxidase showed significant activity, even after 50 reuse cycles. In addition, the potential of the new support and enzyme combination in commercial whey bleaching was demonstrated successfully on a 10-L scale. © 2021 American Dairy Science Association
    view abstractdoi: 10.3168/jds.2019-17110
  • 2021 • 1123 Convergence in Hölder norms with applications to Monte Carlo methods in infinite dimensions
    Cox, S. and Hutzenthaler, M. and Jentzen, A. and Van Neerven, J. and Welti, T.
    IMA Journal of Numerical Analysis 41 493-548 (2021)
    We show that if a sequence of piecewise affine linear processes converges in the strong sense with a positive rate to a stochastic process that is strongly Hölder continuous in time, then this sequence converges in the strong sense even with respect to much stronger Hölder norms and the convergence rate is essentially reduced by the Hölder exponent. Our first application hereof establishes pathwise convergence rates for spectral Galerkin approximations of stochastic partial differential equations. Our second application derives strong convergence rates of multilevel Monte Carlo approximations of expectations of Banach-space-valued stochastic processes. © 2020 The Author(s) 2018. Published by Oxford University Press on behalf of the Institute of Mathematics and its Applications. All rights reserved.
    view abstractdoi: 10.1093/imanum/drz063
  • 2021 • 1122 Mineral-bonded composites for enhanced structural impact safety: Material level investigations [Impaktsicherheit von Baukonstruktionen durch mineralisch gebundene Komposite: Materialebene]
    Curosu, I. and Mechtcherine, V. and Vo, D.M.P. and Sennewald, C. and Cherif, C. and Wölfel, E. and Scheffler, C. and Gong, T. and Heravi, A.A. and Tamsen, E. and Balzani, D. and Shehni, A. and Häußler-Combe, U. and Fuchs, A. an...
    Beton- und Stahlbetonbau 116 45-57 (2021)
    Mineral-bonded composites for enhanced structural impact safety: material level investigations. The Research Training Group GRK 2250/1 „Mineral-bonded composites for enhanced structural impact safety“ aims at the development of novel strengthening materials with various types of fiber reinforcement for enhancing the impact resistance of the critical infrastructure. Adequate testing methods and evaluation protocols are developed for a fundamental material characterization including the rate effects. The experimental results form an important basis for formulating numerical models for simulations of the composites, strengthening layers and concrete elements by linking different space and time scales. Finally, methods for evaluating the sustainability and resilience of the developed strengthening solutions and materials are developed. © 2021, Ernst und Sohn. All rights reserved.
    view abstractdoi: 10.1002/best.202000074
  • 2021 • 1121 Optimizing the nickel boride layer thickness in a spectroelectrochemical ATR-FTIR thin-film flow cell applied in glycerol oxidation
    Cychy, S. and Lechler, S. and Huang, Z. and Braun, M. and Brix, A.C. and Blümler, P. and Andronescu, C. and Schmid, F. and Schuhmann, W. and Muhler, M.
    Chinese Journal of Catalysis 42 2206-2215 (2021)
    The influence of the drop-casted nickel boride catalyst loading on glassy carbon electrodes was investigated in a spectroelectrochemical ATR-FTIR thin-film flow cell applied in alkaline glycerol electrooxidation. The continuously operated radial flow cell consisted of a borehole electrode positioned 50 µm above an internal reflection element enabling operando FTIR spectroscopy. It is identified as a suitable tool for facile and reproducible screening of electrocatalysts under well-defined conditions, additionally providing access to the selectivities in complex reaction networks such as glycerol oxidation. The fast product identification by ATR-IR spectroscopy was validated by the more time-consuming quantitative HPLC analysis of the pumped electrolyte. High degrees of glycerol conversion were achieved under the applied laminar flow conditions using 0.1 M glycerol and 1 M KOH in water and a flow rate of 5 µL min−1. Conversion and selectivity were found to depend on the catalyst loading, which determined the catalyst layer thickness and roughness. The highest loading of 210 µg cm−2 resulted in 73% conversion and a higher formate selectivity of almost 80%, which is ascribed to longer residence times in rougher films favoring readsorption and C–C bond scission. The lowest loading of 13 µg cm−2 was sufficient to reach 63% conversion, a lower formate selectivity of 60%, and, correspondingly, higher selectivities of C2 species such as glycolate amounting to 8%. Thus, only low catalyst loadings resulting in very thin films in the few μm thickness range are suitable for reliable catalyst screening. © 2021 Dalian Institute of Chemical Physics, the Chinese Academy of Sciences
    view abstractdoi: 10.1016/S1872-2067(20)63766-4
  • 2021 • 1120 Rapid Acidic Media Growth of Cs3Bi2Br9 Halide Perovskite Platelets for Photocatalytic Toluene Oxidation
    Dai, Y. and Tüysüz, H.
    Solar RRL 5 (2021)
    Organic ligands with long carbon chains have been widely utilized to mediate the growth of halide perovskite crystals with tunable morphologies. However, the presence of these surfactants on the surface of halide perovskites limits their performance in photocatalytic conversion applications. Herein, a rapid synthetic protocol to prepare Cs3Bi2Br9 platelets with clean surfaces and controllable thickness in a dilute H2SO4 solution after a quick cooling process in liquid nitrogen or mixtures of dry ice is reported. Electron microscopy and X-ray diffraction reveal the preferential exposure of (00l) facets in Cs3Bi2Br9 platelets with variable thickness from 100 to 500 nm. Infrared spectroscopy hints that the selective chemisorption of ethyl acetoacetate on (00l) facets of bismuth perovskites regulates the growth of the crystals. These novel lead-free halide perovskite platelets can drive the photo-oxidation of toluene to benzaldehyde with high selectivity (≥88%) and stability over 36 h. © 2021 The Authors. Solar RRL published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/solr.202100265
  • 2021 • 1119 Investigation of the Roughness Influence on the Absorption Behavior of additively manufactured Metals by the Laser Speckle Photometry
    Dang, D. and Elspas, A. and Cikalova, U. and Kleszczynski, S. and Bendjus, B. and Witt, G.
    Proceedings of the International Spring Seminar on Electronics Technology 2021-May (2021)
    The Laser Powder Bed Fusion of Metals (LPBF-M) is one of the most important methods in the additive manufacturing. This process can be used to produce components with a high degree of complexity and design freedom as well as with material density. Unfortunately, hundreds of factors influence the quality of the processes and thus the material characteristics which limits the reproducibility and the economic viability. Therefore, quality control during process, as well as the testing of material properties afterward, is one of the key development fields. This paper presents the applicability of the Laser Speckle Photometry (LSP) for determination of the surface topology in additive manufacturing of metals. The LSP is a non-destructive testing method which examines optical interference patterns bases on the speckle phenomena for the defect detection on surfaces. For this purpose, samples with a specific pore structure in the near-surface zone which influences the surface characteristics were manufactured. With the LSP, the surfaces were measured to verify a correlation between the roughness and the LSP signal. Depended on the surface roughness different absorption behaviors of the fabricated specimens were determined during external laser excitation as a part of LSP measurement and simultaneously measured temperature. © 2021 IEEE.
    view abstractdoi: 10.1109/ISSE51996.2021.9467607
  • 2021 • 1118 Defect tolerant device geometries for lead-halide perovskites
    Das, B. and Liu, Z. and Aguilera, I. and Rau, U. and Kirchartz, T.
    Materials Advances 2 3655-3670 (2021)
    The term "defect tolerance"is widely used in the literature to describe materials such as lead-halides perovskites, where solution-processed polycrystalline thin films exhibit long non-radiative lifetimes of microseconds or longer. Studies on defect tolerance of materials mostly look at the properties of the host material and/or the chemical nature of defects that affect their capture coefficients. However, the recombination activity of a defect is not only a function of its capture coefficients but also depends on the electrostatics and the design of the layer stack of a photovoltaic device. Here we study the influence of device geometry on defect tolerance by combining calculations of capture coefficients with device simulations. We derive generic device design principles which can inhibit recombination inside a photovoltaic device for a given set of capture coefficients based on the idea of slowing down the slower of the two processes (electron and hole capture) even further by modifying electron and hole injection into the absorber layer. We use the material parameters and typical p-i-n device geometry representing methylammonium lead halide perovskites solar cells to illustrate the application of our generic design principles to improve specific devices. © 2021 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/d0ma00902d
  • 2021 • 1117 Gd-Ru Nanoparticles Supported on Zr0.5Ce0.5O2Nanorods for Dry Methane Reforming
    Das, S. and Sengupta, M. and Bag, A. and Saini, A. and Muhler, M. and Bordoloi, A.
    ACS Applied Nano Materials 4 2547-2557 (2021)
    Dry reforming of methane is considered a potential reaction for the utilization of waste greenhouse gases to generate valuable chemicals. However, catalyst deactivation under a harsh reaction condition appears as the main obstacle toward its commercialization. In the present work, a facile hydrothermal synthesis procedure was adopted to prepare a robust Ru-based catalyst. Among the various combinations, a 1% Ru supported over Zr0.5Ce0.5O2 nanorod catalyst showed enhanced coke resistance and almost stable activity during 200 h activity analysis. Promotion of Ru/Zr0.5Ce0.5O2 with an optimum amount of Gd2O3 improved catalyst stability, which was attributed to the strong interaction of Ru with Gd2O3 leading to smaller Ru particle size (∼5 nm) and an improved OSC was inhibiting coke deposition. Promotion with 0.5% Gd2O3 further lowered the apparent activation energy of methane conversion to ∼20.6 kcal/mol without changing the reaction orders significantly. DFT calculation confirmed, due to the orbital similarity, methane cracking is preferred over Ru atoms and CO2 activation occurred on Gd atoms. ©
    view abstractdoi: 10.1021/acsanm.0c03140
  • 2021 • 1116 Designing of low Pt electrocatalyst through immobilization on metal@C support for efficient hydrogen evolution reaction in acidic media
    Davodi, F. and Cilpa-Karhu, G. and Sainio, J. and Tavakkoli, M. and Jiang, H. and Mühlhausen, E. and Marzun, G. and Gökce, B. and Laasonen, K. and Kallio, T.
    Journal of Electroanalytical Chemistry 896 (2021)
    Nanoparticles comprising of transition metals encapsulated in an ultrathin graphene layer (NiFe@UTG) are utilized to anchor very low amount of finely dispersed pseudo-atomic Pt to function as a durable and active electrocatalyst (Pt/NiFe@UTG) for the hydrogen evolution reaction (HER) in acidic media. Our experiments show the vital role of the carbon shell thickness for efficient utilization of Pt. Furthermore, density functional theory calculations suggest that the metal-core has a crucial role in achieving promising electrocatalytic properties. The thin carbon shell allows the desired access of Pt atoms to the vicinity of the NiFe core while protecting the metallic core from oxidation in the harsh acidic media. In acidic media, the performance of this Pt/NiFe@UTG catalyst with 0.02 at% Pt is the same as that of commercial Pt/C (10 and 200 mV overpotential to reach 10 and 200 mA cm−2, respectively) with promising durability (5000 HER cycles). Our electrochemical characterization (cyclic voltammetry) shows no Pt specific peaks, indicating the existence of a very low Pt loading on the surface of the catalyst. Hence, this conductive core-shell catalyst support enables efficient utilization of Pt for electrocatalysis. © 2021 The Authors
    view abstractdoi: 10.1016/j.jelechem.2021.115076
  • 2021 • 1115 Future research directions in the machining of Inconel 718
    De Bartolomeis, A. and Newman, S.T. and Jawahir, I.S. and Biermann, D. and Shokrani, A.
    Journal of Materials Processing Technology 297 (2021)
    Inconel 718 is the most popular nickel-based superalloy, extensively used in aerospace, automotive and energy industries owing to its extraordinary thermomechanical properties. It is also notoriously a difficult-to-cut material, due to its short tool life and low productivity in machining operations. Despite significant progress in cutting tool technologies, the machining of Inconel 718 is still considered a grand challenge. This paper provides a comprehensive review of recent advances in machining Inconel 718. The progress in cutting tools’ materials, coatings, geometries and surface texturing for machining Inconel 718 is reviewed. The investigation is focused on the most adopted tool materials for machining of Inconel 718, namely Cubic Boron Nitrides (CBNs), ceramics and coated carbides. The thermal conductivity of cutting tool materials has been identified as a major parameter of interest. Process control, based on sensor data for monitoring the machining of Inconel 718 alloy and detecting surface anomalies and tool wear are reviewed and discussed. This has been identified as the major step towards realising real-time control for machining safety critical Inconel 718 components. Recent advances in various processes, e.g. turning, milling and drilling for machining Inconel 718 are investigated and discussed. Recent studies related to machining additively manufactured Inconel 718 are also discussed and compared with the wrought alloy. Finally, the state of current research is established, and future research directions proposed. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.jmatprotec.2021.117260
  • 2021 • 1114 Mechanochemical Synthesis of Supported Bimetallic Catalysts
    De Bellis, J. and Felderhoff, M. and Schüth, F.
    Chemistry of Materials 33 2037-2045 (2021)
    In a previous publication, ball milling was introduced as an effective method for the preparation of supported metal catalysts, simply from the coarse powders of the metal and metal oxide support. In this follow-up study, we demonstrate that mixing multiple metal sources can result in supported alloyed nanoparticles, extending the field of application of the method to the synthesis of supported bimetallic catalysts. Ball milling Au and Pd or Au and Cu in a high-energy regime (shaker mill) indeed led to the formation of Au-Pd and Au-Cu nanoparticles, supported on MgO or yttria-stabilized zirconia (YSZ), which were explored as model systems. Powder X-ray diffraction and electron microscopy were the primary means to investigate as-synthesized materials. The catalytic performance in CO oxidation was also investigated to understand better how the synthetic method could affect the features of the final materials as catalysts. © 2021 The Authors. Published by American Chemical Society.
    view abstractdoi: 10.1021/acs.chemmater.0c04134
  • 2021 • 1113 Presence of male mitochondria in somatic tissues and their functional importance at the whole animal level in the marine bivalve Arctica islandica
    Dégletagne, C. and Abele, D. and Glöckner, G. and Alric, B. and Gruber, H. and Held, C.
    Communications Biology 4 (2021)
    Metazoans normally possess a single lineage of mitochondria inherited from the mother (♀-type mitochondria) while paternal mitochondria are absent or eliminated in fertilized eggs. In doubly uniparental inheritance (DUI), which is specific to the bivalve clade including the ocean quahog, Arctica islandica, ♂-type mitochondria are retained in male gonads and, in a few species, small proportions of ♂-type mitochondria co-exist with ♀-type in somatic tissues. To the best of our knowledge, we report, for the first time in metazoan, the natural occurrence of male and female individuals with exclusively ♂-type mitochondria in somatic tissues of the bivalve A. islandica. Mitochondrial genomes differ by ~5.5% at DNA sequence level. Exclusive presence of ♂-type mitochondria affects mitochondrial complexes partially encoded by mitochondrial genes and leads to a sharp drop in respiratory capacity. Through a combination of whole mitochondrial genome sequencing and molecular assays (gene presence and expression), we demonstrate that 1) 11% of individuals of an Icelandic population appear homoplasmic for ♂-type mitochondria in somatic tissues, 2) ♂-type mitochondrial genes are transcribed and 3) individuals with ♂-type mitochondria in somatic cells lose 30% of their wild-type respiratory capacity. This mitochondrial pattern in A. islandica is a special case of DUI, highlighted in individuals from both sexes with functional consequences at cellular and conceivably whole animal level. © 2021, The Author(s).
    view abstractdoi: 10.1038/s42003-021-02593-1
  • 2021 • 1112 Dielectric Properties of Nanoconfined Water: A Canonical Thermopotentiostat Approach
    Deißenbeck, F. and Freysoldt, C. and Todorova, M. and Neugebauer, J. and Wippermann, S.
    Physical Review Letters 126 (2021)
    We introduce a novel approach to sample the canonical ensemble at constant temperature and applied electric potential. Our approach can be straightforwardly implemented into any density-functional theory code. Using thermopotentiostat molecular dynamics simulations allows us to compute the dielectric constant of nanoconfined water without any assumptions for the dielectric volume. Compared to the commonly used approach of calculating dielectric properties from polarization fluctuations, our thermopotentiostat technique reduces the required computational time by 2 orders of magnitude. © 2021 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the ""Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.
    view abstractdoi: 10.1103/PhysRevLett.126.136803
  • 2021 • 1111 A similarity measure for second order properties of non-stationary functional time series with applications to clustering and testing
    van Delft, A. and Dette, H.
    Bernoulli 27 469-501 (2021)
    Due to the surge of data storage techniques, the need for the development of appropriate techniques to identify patterns and to extract knowledge from the resulting enormous data sets, which can be viewed as collections of dependent functional data, is of increasing interest in many scientific areas. We develop a similarity measure for spectral density operators of a collection of functional time series, which is based on the aggregation of Hilbert–Schmidt differences of the individual time-varying spectral density operators. Under fairly general conditions, the asymptotic properties of the corresponding estimator are derived and asymptotic normality is established. The introduced statistic lends itself naturally to quantify (dis)-similarity between functional time series, which we subsequently exploit in order to build a spectral clustering algorithm. Our algorithm is the first of its kind in the analysis of non-stationary (functional) time series and enables to discover particular patterns by grouping together ‘similar’ series into clusters, thereby reducing the complexity of the analysis considerably. The algorithm is simple to implement and computationally feasible. As a further application, we provide a simple test for the hypothesis that the second order properties of two non-stationary functional time series coincide. © 2021 ISI/BS.
    view abstractdoi: 10.3150/20-BEJ1246
  • 2021 • 1110 A nonparametric test for stationarity in functional time series
    van Delft, A. and Characiejus, V. and Dette, H.
    Statistica Sinica 31 1375-1395 (2021)
    We propose a new measure for stationarity in functional time series that is based on an explicit representation of the L2-distance between the spectral density operator of a nonstationary process and its best (L2-)approximation by a spectral density operator corresponding to a stationary process. This distance can be estimated by the sum of the Hilbert-Schmidt inner products of the periodogram operators (evaluated at different frequencies). Furthermore, the asymptotic normality of an appropriately standardized version of the estimator can be established for the corresponding estimator under the null and alternative hypotheses. As a result, we obtain a simple asymptotic frequency-domain level α-test (using the quantiles of the normal distribution) to test for the hypothesis of stationarity of a functional time series. We also briefly discuss other applications, such as asymptotic confidence intervals for the measure of stationarity, or the construction of tests for “relevant deviations from stationarity”. We demonstrate in a small simulation study that the new method has very good finite-sample properties. Moreover, we apply our test to annual temperature curves. © 2021 Institute of Statistical Science. All rights reserved.
    view abstractdoi: 10.5705/ss.202018.0320
  • 2021 • 1109 In situ characterization of polycaprolactone fiber response to quasi-static tensile loading in scanning electron microscopy
    Delp, A. and Becker, A. and Hülsbusch, D. and Scholz, R. and Müller, M. and Glasmacher, B. and Walther, F.
    Polymers 13 (2021)
    Microstructural responses to the mechanical load of polymers used in tissue engineering is notably important for qualification at in vivo testing, although insufficiently studied, especially regarding promising polycaprolactone (PCL). For further investigations, electrospun PCL scaffolds with different degrees of fiber alignment were produced, using two discrete relative drum collector velocities. Development and preparation of an adjusted sample geometry enabled in situ tensile testing in scanning electron microscopy. By analyzing the microstructure and the use of selected tracking techniques, it was possible to visualize and quantify fiber/fiber area displacements as well as local fractures of single PCL fibers, considering quasi-static tensile load and fiber alignment. The possibility of displacement determination using in situ scanning electron microscopy techniques for testing fibrous PCL scaffolds was introduced and quantified. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/polym13132090
  • 2021 • 1108 Adaptation of cluster analysis methods to optimize a biomechanical motion model of humans in a nursing bed
    Demmer, J. and Kitzig, A. and Stockmanns, G. and Naroska, E. and Viga, R. and Grabmaier, A.
    European Signal Processing Conference 2021-January 1323-1327 (2021)
    The paper considers the optimization of a Hidden-Markov Model (HMM) based method for the generation of averaged motion sequences. To create averaged motion sequences, motion sequences of different test persons were originally recorded with a motion capture system (MoCap system) and then averaged using an HMM approach. The resulting averaged data sets, however, partly showed serious motion artifacts and uncoordinated intermediate movements, especially in the extremities. The aim of this work was to combine only movements with similar courses in the extremities by a suitable cluster analysis. For each test person, model body descriptions of 21 body elements are available, each of which is represented in three-dimensional time series. For optimization, the MoCap data are first compared using time warp edit distance (TWED) and clustered using an agglomerative hierarchical procedure. Finally, the data of the resulting clusters are used to generate new averaged motion sequences using the HMM approach. The resulting averaged data can be used, for example, in a simulation in a multilevel biomechanical model. © 2021 European Signal Processing Conference, EUSIPCO. All rights reserved.
    view abstractdoi: 10.23919/Eusipco47968.2020.9287503
  • 2021 • 1107 Studying Fluid Characteristics Atop Surface Patterned Membranes via Particle Image Velocimetry
    Denizer, D. and ElSherbiny, I.A.M. and Ulbricht, M. and Panglisch, S.
    Chemie-Ingenieur-Technik (2021)
    Surface patterning is a recent promising approach to promote performance of pressure-driven membranes in water treatment and desalination. Nevertheless, knowledge about foulant deposition mechanisms, especially at early stage of filtration, is still lacking. The applicability of particle imaging velocimetry to study fluid characteristics atop surface patterned thin-film composite membranes was investigated at different operating conditions. This work is an important first step toward reliable understanding of the impacts of topographical membrane surface modification on hydrodynamic conditions and foulant deposition mechanisms. © 2021 The Authors. Chemie Ingenieur Technik published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/cite.202100043
  • 2021 • 1106 Modeling chemical reactions in porous media: a review
    Detmann, B.
    Continuum Mechanics and Thermodynamics 33 2279-2300 (2021)
    First, different porous media theories are presented. Some approaches are based on the classical mixture theory for fluids introduced in the 1960s by Truesdell and Coworkers. One of the first researchers who extended the theory to porous media (thus mixtures containing at least one solid constituent) and also accounting for chemical reactions was Bowen. Another important branch of porous media theory goes back to Biot. In the beginning, he dealt with classical geotechnical problems and set up his model empirically. Mathematicians often use reaction–diffusion equations which are limited in comparison with continuum models by several restrictive assumptions and very often only applicable to special problems. In this paper, the focus lies on approaches based on the mixture theory which incorporate chemical reactions. Different strategies to describe the chemical potential for mixtures are presented, and different opinions about the exploitation of the second law of thermodynamics for mixtures are put forward. Finally, several works of different types including chemical reactions in porous media are summarized. © 2021, The Author(s).
    view abstractdoi: 10.1007/s00161-021-01049-5
  • 2021 • 1105 A note on optimal designs for estimating the slope of a polynomial regression
    Dette, H. and Melas, V.B. and Shpilev, P.
    Statistics and Probability Letters 170 (2021)
    In this note we consider the optimal design problem for estimating the slope of a polynomial regression with no intercept at a given point, say z. In contrast to previous work, we investigate the model on the non-symmetric interval. © 2020 Elsevier B.V.
    view abstractdoi: 10.1016/j.spl.2020.108992
  • 2021 • 1104 Identifying shifts between two regression curves
    Dette, H. and Dhar, S.S. and Wu, W.
    Annals of the Institute of Statistical Mathematics (2021)
    This article studies the problem whether two convex (concave) regression functions modelling the relation between a response and covariate in two samples differ by a shift in the horizontal and/or vertical axis. We consider a nonparametric situation assuming only smoothness of the regression functions. A graphical tool based on the derivatives of the regression functions and their inverses is proposed to answer this question and studied in several examples. We also formalize this question in a corresponding hypothesis and develop a statistical test. The asymptotic properties of the corresponding test statistic are investigated under the null hypothesis and local alternatives. In contrast to most of the literature on comparing shape invariant models, which requires independent data the procedure is applicable for dependent and non-stationary data. We also illustrate the finite sample properties of the new test by means of a small simulation study and two real data examples. © 2021, The Institute of Statistical Mathematics, Tokyo.
    view abstractdoi: 10.1007/s10463-020-00771-2
  • 2021 • 1103 Detecting relevant differences in the covariance operators of functional time series: a sup-norm approach
    Dette, H. and Kokot, K.
    Annals of the Institute of Statistical Mathematics (2021)
    In this paper we propose statistical inference tools for the covariance operators of functional time series in the two sample and change point problem. In contrast to most of the literature, the focus of our approach is not testing the null hypothesis of exact equality of the covariance operators. Instead, we propose to formulate the null hypotheses in the form that “the distance between the operators is small”, where we measure deviations by the sup-norm. We provide powerful bootstrap tests for these type of hypotheses, investigate their asymptotic properties and study their finite sample properties by means of a simulation study. © 2021, The Institute of Statistical Mathematics, Tokyo.
    view abstractdoi: 10.1007/s10463-021-00795-2
  • 2021 • 1102 Detecting structural breaks in eigensystems of functional time series
    Dette, H. and Kutta, T.
    Electronic Journal of Statistics 15 944-983 (2021)
    Detecting structural changes in functional data is a prominent topic in statistical literature. However not all trends in the data are important in applications, but only those of large enough influence. In this paper we address the problem of identifying relevant changes in the eigenfunctions and eigenvalues of covariance kernels of L2[0, 1]-valued time series. By selfnormalization techniques we derive pivotal, asymptotically consistent tests for relevant changes in these characteristics of the second order structure and investigate their finite sample properties in a simulation study. The applicability of our approach is demonstrated analyzing German annual temperature data. © 2021, Institute of Mathematical Statistics. All rights reserved.
    view abstractdoi: 10.1214/20-EJS1796
  • 2021 • 1101 Correcting Intraday Periodicity Bias in Realized Volatility Measures
    Dette, H. and Golosnoy, V. and Kellermann, J.
    Econometrics and Statistics (2021)
    Diurnal fluctuations in volatility are a well-documented stylized fact of intraday price data. This warrants an investigation how this intraday periodicity (IP) affects both finite sample as well as asymptotic properties of several popular realized estimators of daily integrated volatility which are based on functionals of a finite number of intraday returns. It turns out that most of the estimators considered in this study exhibit a finite-sample bias due to IP, which can however get negligible when the number of intraday returns diverges to infinity. The appropriate correction factors for this bias are derived based on estimates of the IP. The adequacy of the new corrections is evaluated by means of a Monte Carlo simulation study and an empirical example. © 2021 EcoSta Econometrics and Statistics
    view abstractdoi: 10.1016/j.ecosta.2021.03.002
  • 2021 • 1100 A bioinspired oxoiron(iv) motif supported on a N2S2macrocyclic ligand
    Deutscher, J. and Gerschel, P. and Warm, K. and Kuhlmann, U. and Mebs, S. and Haumann, M. and Dau, H. and Hildebrandt, P. and Apfel, U.-P. and Ray, K.
    Chemical Communications 57 2947-2950 (2021)
    A mononuclear oxoiron(iv) complex1-transbearing two equatorial sulfur ligations is synthesized and characterized as an active-site model of the elusive sulfur-ligated FeIVO intermediates in non-heme iron oxygenases. The introduction of sulfur ligands weakens the Fe-O bond and enhances the oxidative reactivity of the FeIVO unit with a diminished deuterium kinetic isotope effect, thereby providing a compelling rationale for nature's use of thecis-thiolate ligated oxoiron(iv) motif in key metabolic transformations. © The Royal Society of Chemistry 2021.
    view abstractdoi: 10.1039/d1cc00250c
  • 2021 • 1099 Influence of substrates and e-beam evaporation parameters on the microstructure of nanocrystalline and epitaxially grown Ti thin films
    Devulapalli, V. and Bishara, H. and Ghidelli, M. and Dehm, G. and Liebscher, C.H.
    Applied Surface Science 562 (2021)
    Titanium thin films were deposited on silicon nitride (SiNx) coated Si, NaCl, and sapphire substrates varying the deposition conditions using e-beam evaporation to investigate thin film growth modes. The microstructure and texture evolution in dependence of substrate, deposition rate, film thickness, and substrate temperature were studied using X-ray diffraction, electron backscatter diffraction, and transmission electron microscopy. Thin films obtained on SiNx and NaCl substrates were nanocrystalline, while the films deposited on sapphire transformed from nanocrystalline to single crystalline at deposition temperatures above 200 °C. Predominantly, a surface plane orientation of (0002) was observed for the single crystalline films due to the minimization of surface energy. The orientation relationship of epitaxial single crystalline films grown on C-plane sapphire substrate is found to be (0002)Ti ‖ (0006)Sapphire,〈112¯0〉Ti ‖ 〈033¯0〉Sapphire. In this orientation relationship, both the total surface and strain energy of the film are minimized. The results were complemented by resistivity measurements using the four-point probe method reporting an increase from ~60 μ Ω cm to ~95 μΩ cm for single crystalline and nanocrystalline films, respectively. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.apsusc.2021.150194
  • 2021 • 1098 Pseudocapacitive Redox Polymers as Battery Materials: A Proof-of-Concept All-Polymer Aqueous Battery
    Dieckhöfer, S. and Medina, D. and Ruff, A. and Conzuelo, F. and Schuhmann, W.
    ChemElectroChem 8 2308-2314 (2021)
    Redox polymers with distinct redox units have been long recognized for their pseudocapacitive and reversible charge storage behaviour. Many systems investigated so far have utilized organic electrolytes and/or have coupled a redox polymer half-cell to a non-polymer counter electrode. However, due to safety and sustainability considerations, aqueous electrolyte based charge storage in all-polymer configurations is considered a promising option for possible future applications. We present a strategy based on pseudocapacitive charge storage in Osmium-complex and viologen-modified redox polymers with specifically designed poly(vinylimidazole)- and poly(vinylpyridine)-based backbones. We couple both redox polymers in an aqueous battery configuration, demonstrating Nernst-potential driven energy storage. Electrochemical characterization in a concentric three-electrode Swagelok cell and coin cells reveals stable reversible capacities over more than 1800 cycles, with nearly quantitative coulombic efficiencies (>99.4 %) for the coin cells. © 2021 The Authors. ChemElectroChem published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/celc.202100450
  • 2021 • 1097 Probing the Local Reaction Environment During High Turnover Carbon Dioxide Reduction with Ag-Based Gas Diffusion Electrodes
    Dieckhöfer, S. and Öhl, D. and Junqueira, J.R.C. and Quast, T. and Turek, T. and Schuhmann, W.
    Chemistry - A European Journal 27 5906-5912 (2021)
    Discerning the influence of electrochemical reactions on the electrode microenvironment is an unavoidable topic for electrochemical reactions that involve the production of OH− and the consumption of water. That is particularly true for the carbon dioxide reduction reaction (CO2RR), which together with the competing hydrogen evolution reaction (HER) exert changes in the local OH− and H2O activity that in turn can possibly affect activity, stability, and selectivity of the CO2RR. We determine the local OH− and H2O activity in close proximity to a CO2-converting Ag-based gas diffusion electrode (GDE) with product analysis using gas chromatography. A Pt nanosensor is positioned in the vicinity of the working GDE using shear-force-based scanning electrochemical microscopy (SECM) approach curves, which allows monitoring changes invoked by reactions proceeding within an otherwise inaccessible porous GDE by potentiodynamic measurements at the Pt-tip nanosensor. We show that high turnover HER/CO2RR at a GDE lead to modulations of the alkalinity of the local electrolyte, that resemble a 16 m KOH solution, variations that are in turn linked to the reaction selectivity. © 2021 The Authors. Published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/chem.202100387
  • 2021 • 1096 Accelerated Electrochemical Investigation of Li Plating Efficiency as Key Parameter for Li Metal Batteries Utilizing a Scanning Droplet Cell
    Dieckhöfer, S. and Schuhmann, W. and Ventosa, E.
    ChemElectroChem 8 3143-3149 (2021)
    The scanning droplet cell (SDC) allows for automatized electrochemical experiments leading to time-saving and reproducible experimental conditions. Its implementation for non-aqueous battery research is discussed, and the necessary adaptations to be operated inside an Ar-filled glovebox in complete absence of oxygen and moisture are described. Due to the importance of the use of Li metal electrodes for next-generation high-energy batteries, the complex multi-parameter optimisation of the Li plating/stripping processes are investigated by means of the SDC. In particular, the influence of pulsed Li plating protocols on the coulombic efficiency is evaluated. The results clearly show that fine tuning of the parameters of pulsed Li plating protocols, i. e. the relaxation period and Li plating duration, is required to improve Li plating efficiencies at high current densities. © 2021 The Authors. ChemElectroChem published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/celc.202100733
  • 2021 • 1095 Pathways toward 30% Efficient Single-Junction Perovskite Solar Cells and the Role of Mobile Ions
    Diekmann, J. and Caprioglio, P. and Futscher, M.H. and Le Corre, V.M. and Reichert, S. and Jaiser, F. and Arvind, M. and Toro, L.P. and Gutierrez-Partida, E. and Peña-Camargo, F. and Deibel, C. and Ehrler, B. and Unold, T. and Ki...
    Solar RRL (2021)
    Perovskite semiconductors have demonstrated outstanding external luminescence quantum yields, enabling high power conversion efficiencies (PCEs). However, the precise conditions to advance to an efficiency regime above monocrystalline silicon cells are not well understood. Herein, a simulation model that describes efficient p–i–n-type perovskite solar cells well and a range of different experiments is established. Then, important device and material parameters are studied and it is found that an efficiency regime of 30% can be unlocked by optimizing the built-in voltage across the perovskite layer using either highly doped (1019 cm−3) transport layers (TLs), doped interlayers or ultrathin self-assembled monolayers. Importantly, only parameters that have been reported in recent literature are considered, that is, a bulk lifetime of 10 μs, interfacial recombination velocities of 10 cm s−1, a perovskite bandgap ((Formula presented.)) of 1.5 eV, and an external quantum efficiency (EQE) of 95%. A maximum efficiency of 31% is predicted for a bandgap of 1.4 eV. Finally, it is demonstrated that the relatively high mobile ion density does not represent a significant barrier to reach this efficiency regime. The results of this study suggest continuous PCE improvements until perovskites may become the most efficient single-junction solar cell technology in the near future. © 2021 The Authors. Solar RRL published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/solr.202100219
  • 2021 • 1094 Plasma and nanoparticle shielding during pulsed laser ablation in liquids cause ablation efficiency decrease
    Dittrich, S. and Barcikowski, S. and Gökce, B.
    Opto-Electronic Advances 4 1-13 (2021)
    Understanding shielding cross-effects is a prerequisite for maximal power-specific nanosecond laser ablation in liquids (LAL). However, discrimination between cavitation bubble (CB), nanoparticle (NP), and shielding, e.g., by the plasma or a transient vapor layer, is challenging. Therefore, CB imaging by shadowgraphy is performed to better understand the plasma and laser beam-NP interaction during LAL. By comparing the fluence-dependent CB volume for ablations performed with 1 ns pulses with reports from the literature, we find larger energy-specific CB volumes for 7 ns-ablation. The increased CB for laser ablation with higher ns pulse durations could be a first explanation of the efficiency decrease reported for these laser systems having higher pulse durations. Consequently, 1 ns-LAL shows superior ablation efficiency. Moreover, a CB cascade occurs when the focal plane is shifted into the liquid. This effect is enhanced when NPs are present in the fluid. Even minute amounts of NPs trapped in a stationary layer decrease the laser energy significantly, even under liquid flow. However, this local concentration in the sticking film has so far not been considered. It presents an essential obstacle in high-yield LAL, shielding already the second laser pulse that arrives and presenting a source of satellite bubbles. Hence, measures to lower the NP concentration on the target must be investigated in the future. © 2021 Institute of Optics and Electronics, Chinese Academy of Sciences.
    view abstractdoi: 10.29026/oea.2021.200072
  • 2021 • 1093 Modeling solubility of amino acids and peptides in water and in water+2-propanol mixtures: PC-SAFT vs. gE models
    Do, H.T. and Chakrabarty, S. and Held, C.
    Fluid Phase Equilibria 542-543 (2021)
    Amino acids and peptides are essential components for many industrial branches. Knowledge on the solubility behavior is required in purification processes, which often involve crystallization as main unit operation. Since the determination of experimental solubility data is expensive, thermodynamic modeling is meaningful towards reducing the experimental effort. Modeling is usually based on a solid-liquid equilibrium condition that requires the melting properties of the solids. For amino acids and peptides such data is now available, and three gE models (Wilson, NRTL, UNIQUAC) were applied in this work to model solubility in water as well as in water + 2-propanol. The new melting properties were used as input data and binary parameters for each model were fitted to experimental solubility data of the amino acids and peptides in water. Modeling solubility in water + 2-propanol required additional parameters. Binary parameters between water and 2-propanol were fitted to vapor-liquid-equilibrium data, and binary parameters between amino acid and 2-propanol as well as between peptide and 2-propanol were fitted to solubility data in water + 2-propanol mixtures. In general, the gE models allowed describing the solubility in water, while some inaccuracies were observed for the temperature dependence of the modeled solubility. Further, the decrease of solubility upon 2-propanol addition was modeled qualitatively correct using the gE models. The Wilson model was less accurate than NRTL and UNIQUAC, where the latter yielded similar results. The results were finally compared to PC-SAFT, which shows a dramatically improved modeling accuracy while using less binary parameters. © 2021
    view abstractdoi: 10.1016/j.fluid.2021.113087
  • 2021 • 1092 Measurement and modelling solubility of amino acids and peptides in aqueous 2-propanol solutions
    Do, H.T. and Franke, P. and Volpert, S. and Klinksiek, M. and Thome, M. and Held, C.
    Physical Chemistry Chemical Physics 23 10852-10863 (2021)
    Amino acids and peptides are essential components in the biochemical industry. The final products are employed in a wide range of applications and are often synthesized by fermentation and purified in a complex downstream process. One possible separation step is using an additional solvent to lower the solubility of the desired product and, thus, promote the crystallization of the particular component. Therefore, it is crucial to have accurate knowledge of the solubility of these components. In this work, the solubilities of 20 proteinogenic amino acids and 21 peptides in aqueous 2-propanol solutions were gravimetrically determined. Additionally, the pH values of the saturated liquid phases were measured and the crystal structures of solid crystals were analysed using X-ray diffraction. The anti-solvent 2-propanol caused a decrease in the solubilities of the amino acids and peptides upon increasing its mass fraction. Exceptions were found for amino acids with aromatic substituents, l-phenylalanine and l-tyrosine. The solubility of 15 amino acids and 18 peptides was successfully modelled using the equation of state PC-SAFT that used recently determined melting properties of the amino acids and peptides as input data. This journal is © the Owner Societies.
    view abstractdoi: 10.1039/d1cp00005e
  • 2021 • 1091 Melting Properties of Peptides and Their Solubility in Water. Part 2: Di- And Tripeptides Based on Glycine, Alanine, Leucine, Proline, and Serine
    Do, H.T. and Chua, Y.Z. and Habicht, J. and Klinksiek, M. and Volpert, S. and Hallermann, M. and Thome, M. and Pabsch, D. and Zaitsau, D. and Schick, C. and Held, C.
    Industrial and Engineering Chemistry Research 60 4693-4704 (2021)
    In downstream processes for peptides, crystallization is still used as the state-of-the-art separation step for which the knowledge about the solubility of each single compound is mandatory. Since the determination of experimental temperature-dependent solubility data is time-consuming and expensive, modeling solubility based on physical properties such as melting properties is highly desired. Unfortunately, the direct determination of melting properties for biomolecules using conventional differential scanning calorimetry is not possible due to the decomposition of the peptides before their melting. In this work, fast scanning calorimetry (FSC) with heating rates up to 20,000 K s-1 was applied to measure the melting properties of 22 peptides with focus on isomeric dipeptides and tripeptides based on glycine, l-alanine, l-leucine, l-proline, and l-serine. The experimental determination of the aqueous solubility of these peptides was performed using the photometric method (UV/Vis spectrometer) and the gravimetric method of supersaturated solutions. Additionally, the pH value and the crystal structure of peptides were determined in order to ensure the neutral species in solution and to exclude crystal structure changes in the solid phase. The experimental FSC-measured melting properties were used as input data in the thermodynamic modeling framework PC-SAFT to model the peptide solubility in water. The PC-SAFT pure-component parameters of the peptides were determined following a weighted joint-parameter method introduced in this work. This approach allows determining the pure-component parameters of a peptide by joining the pure-component parameters of the parent amino acids. The binary interactions parameter between peptide and water was fitted to solubility-independent properties such as osmotic coefficients and mixture densities of aqueous peptide solutions. The modeled peptide solubility was in good agreement with the experimental solubility. © 2021 American Chemical Society. All rights reserved.
    view abstractdoi: 10.1021/acs.iecr.0c05652
  • 2021 • 1090 Proof of concept for a novel interstage injection design in axial compressors
    Doerr, T. and Braun, S. and Schuster, S. and Brillert, D.
    Journal of Engineering for Gas Turbines and Power 143 (2021)
    A common technique to increase the thermal efficiency and the power output of gas turbines is to inject water upstream of the compressor section. Through the evaporation of the water throughout the compressor, an isothermal process is approached. A recently developed technology for this enhanced process is interstage injection in which water is injected directly between the stages. One advantage of this over wet compression is the avoidance of icing, since the local temperatures at the injection positions are already above melting point. Moreover, stage characteristics and load distribution can be rearranged within the compressor by individually adjusting the injection amount in different stages. However, there is little practical understanding of this process, and suitable injection methods have still to be found. This paper therefore demonstrates the implementation of a novel technology of interstage injection in an axial compressor test rig whereby twin jet nozzles are integrated directly into the trailing edge of the first stator row to deliver a homogenous spray over the entire radial span. Due to the resultant blade complexity, blades are manufactured by selective laser melting (SLM) and subsequently installed in an enhanced four-stage axial compressor. The installed control and measurement principles of the test rig are presented and results demonstrate the functionality of the innovative design. Copyright © 2021 by ASME.
    view abstractdoi: 10.1115/1.4049306
  • 2021 • 1089 Evaluation of performance gain by interstage injection in a four-stage axial compressor
    Doerr, T. and Schuster, S. and Brillert, D.
    Proceedings of the ASME Turbo Expo 7 (2021)
    Recently, the energy market has seen a shift towards renewable energies due to changing demands. Gas turbines are used as a transitional technology to cope with grid fluctuations. The changing conditions have increased the interest in applying Wet Compression in order to increase the power output during peak demands. The novelty of this paper arises from the experimental results of Interstage Injection by analysing the stage and overall pressure ratios at different operating points in the four stage axial compressor "eco.MAC"("evaporative cooling Multiphase Axial Compressor"). An innovative injection design is realized with twin jet nozzles in the trailing edge of SLM printed stator blades. A variation of water mass fraction, inlet temperature and rotational speed is performed and shows a gain in pressure ratio up to 1.5 %. Moreover, a polynomial approach is used for the dry data to compare wet and dry results at equal air mass flow rates. For the first time, a linear dependency of the pressure gain on the compressor's gas temperature is experimentally found. It can be concluded that Interstage Injection is an effective technology to be applied in later stages of axial compressors due to the strong influence of local gas temperatures on the evaporation rate and thus the pressure gain. Furthermore, reducing the local injection rate decreases aerodynamic losses between the liquid and gas phase. Hence, a multiple injection and reduced local injection rates should be targeted. Copyright © 2021 by ASME.
    view abstractdoi: 10.1115/GT2021-58560
  • 2021 • 1088 Tuneable material properties of Organosolv lignin biocomposites in response to heat and shear forces
    Dörrstein, J. and Schwarz, D. and Scholz, R. and Walther, F. and Zollfrank, C.
    European Polymer Journal 148 (2021)
    Lignin as a renewable biomacromolecule is considered as a sustainable feedstock for the generation of bioplastics and bioplastic composites. However, during thermoplastic processing, high temperature and mechanical forces are known to promote destructive bond-cleavage in a vast majority of macromolecules due to overheating and internal friction between molecular constituents. This study demonstrates that several material properties (e.g. thermal stability, mechanical properties) of biocomposites with a high Organosolv lignin content (≥50 w%) can be tuned by carefully selecting thermal and mechanical energy input during compounding. Organosolv lignin obtained from ensiled grass was shown to undergo in-situ coupling reactions at temperatures below the main degradation point (&lt;200 °C) resulting in an up to 6-fold increase in molecular weight (Mw). The results from Fourier Transform Infrared (FTIR) spectroscopy suggested the formation of ester bonds, which was ascribed to direct esterification reactions, which occur due to energy transfer in the melt phase. When subjecting the extracted lignin to prolonged compounding times, it was shown that higher coupling degrees resulted in a lignin biocomposite with increased stiffness and ultimate tensile stress of about 1800% and 40%, respectively. Temperature was shown to have the highest effect on coupling reactions, whereas the energy transfer by mechanical forces during compounding was lower and followed a non-linear behaviour. In tensile stress–strain curves, biocomposites with high energy input revealed a distinct yield point (16 MPa). Ultra-micro-hardness tests confirmed that the biocomposite became significantly stiffer in response to shear and thermal forces with a reduction in indentation creep Cit of 2.0% to a value of up to 8.5%. Organosolv lignin biocomposites obtained at higher specific energy input (EIN) through thermal energy input and shear forces showed an increased dynamic stiffness Cdyn up to 100%, which was observed by multiple step tests (MST). © 2021 Elsevier Ltd
    view abstractdoi: 10.1016/j.eurpolymj.2021.110359
  • 2021 • 1087 Towards Explainability of non-Convolutional Neural Networks
    Doese, J. and Weis, T.
    UbiComp/ISWC 2021 - Adjunct Proceedings of the 2021 ACM International Joint Conference on Pervasive and Ubiquitous Computing and Proceedings of the 2021 ACM International Symposium on Wearable Computers 100-103 (2021)
    Artificial intelligence has risen in popularity in research and applications in the past years. Explainability is a topic that has been proven to work on human interpretable data like images or sentences, but the research is narrow whenever such data is missing. Creating trust through explainability on raw data processing neural networks of any kind will become necessary in the future as networks are evolving further towards artificial general intelligence. This research is focused to visualize parts of the hidden layers instead of focusing explainability on the input data and is independent of the neural network's size. We create a model that represents the neural network in a way that neurons that are activating on similar features are grouped together in structures. This model will be analyzed in a machine-learning equivalent process to identify parts of the network being responsible for a decision. In a further step we use the model to test the processing of raw sensor-data versus an approach of heatmapped explainability with a convolutional neural network. Relevant data points in the input are visualized by a common heatmap approach while the hidden layers are analyzed in this research and should point to structures that have a comparable function in the network. For example, if the heatmap highlights peaks of values, the model will be highlighted in the area that is observed as the activation of the neural network on peaks. We will provide the research of artificial general intelligence with a solution for explainability which is necessary for advanced research and the operation of such applications in complex or dangerous scenarios. © 2021 ACM.
    view abstractdoi: 10.1145/3460418.3479313
  • 2021 • 1086 Solvent influence on the phase behavior and glass transition of Amorphous Solid Dispersions
    Dohrn, S. and Luebbert, C. and Lehmkemper, K. and Kyeremateng, S.O. and Degenhardt, M. and Sadowski, G.
    European Journal of Pharmaceutics and Biopharmaceutics 158 132-142 (2021)
    Understanding the long-term stability of amorphous solid dispersions (ASDs) is important for their successful approval for market. ASD stability does not only depend on the interplay between the active pharmaceutical ingredient (API) and the polymer in the final formulation but may already be disadvantageously influenced by process steps during the production (e.g. selection of inappropriate solvent for spray drying). Residual solvent can affect the API solubility in the polymer, molecular mobility (by influencing the glass-transition temperature) and induce liquid-liquid phase separation. Enhanced mobility in the ASD due to residual solvent can promote recrystallization in ASDs. The removal of residual solvent can be expensive, time-consuming, and usually requires secondary drying procedures to fulfil the regulatory requirements. The aim of this work is to predict the API solubility in polymer-solvent mixtures, solvent influence on the glass transition, and the occurrence of liquid-liquid phase separation of solvent-loaded ASDs using the thermodynamic model PC-SAFT and to experimentally validate these predictions. ASDs containing the APIs ritonavir or naproxen and the polymers poly (vinylpyrrolidone), poly (vinylpyrrolidone-co-vinyl acetate), or hydroxypropyl methylcellulose acetate succinate were spray-dried using the solvents acetone, ethanol, and dichloromethane. API solubility, sorption behavior, liquid-liquid phase separation and glass transition in the ternary API/polymer/solvent mixtures were predicted based on the binary phase behavior between API/solvent, API/polymer, and polymer/solvent and successfully validated experimentally using dynamic vapor sorption (DVS), and Raman spectroscopy. Thus, the presented methodology allows for an in-silico selection of appropriate solvent systems for solvent-based ASD preparation based on a limited amount of experimental data for binary systems only. © 2020 The Authors
    view abstractdoi: 10.1016/j.ejpb.2020.11.002
  • 2021 • 1085 Predicting process design spaces for spray drying amorphous solid dispersions
    Dohrn, S. and Rawal, P. and Luebbert, C. and Lehmkemper, K. and Kyeremateng, S.O. and Degenhardt, M. and Sadowski, G.
    International Journal of Pharmaceutics: X 3 (2021)
    Amorphous solid dispersions (ASDs) are commonly manufactured using spray-drying processes. The product quality can be decisively influenced by the choice of process parameters. Following the quality-by-design approach, the identification of the spray-drying process design space is thus an integral task in drug product development. Aiming a solvent-free and homogeneous ASD, API crystallization and amorphous phase separation needs to be avoided during drying. This publication provides a predictive approach for determining spray-drying process conditions via considering thermodynamic driving forces for solvent drying as well as ASD-specific API/polymer/solvent interactions and glass transitions. The ternary API/polymer/solvent phase behavior was calculated using the Perturbed-Chain Statistical Associating Theory (PC-SAFT) and combined with mass and energy balances to find appropriate spray-drying conditions. A process design space was identified for the ASDs of ritonavir and naproxen with either poly(vinylpyrrolidone) or poly(vinylpyrrolidone-co-vinylacetate) spray dried from the solvents acetone, dichloromethane, or ethanol. © 2021 The Author(s)
    view abstractdoi: 10.1016/j.ijpx.2021.100072
  • 2021 • 1084 Solvent mixtures in pharmaceutical development: Maximizing the API solubility and avoiding phase separation
    Dohrn, S. and Luebbert, C. and Lehmkemper, K. and Kyeremateng, S.O. and Degenhardt, M. and Sadowski, G.
    Fluid Phase Equilibria 548 (2021)
    Knowing the solubilities of active pharmaceutical ingredients (APIs) in pure solvents and solvent mixtures is essential for several manufacturing aspects of pharmaceutical product development. In this paper, we demonstrate that time-consuming and costly experiments can be reduced to a minimum using the thermodynamic model Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT) that can simultaneously predict API solubilities in pure solvents and solvent mixtures as well as unwanted liquid-liquid phase separation (LLPS). We investigated the temperature-dependent solubility of naproxen, ritonavir, and indomethacin in the solvents acetone, dichloromethane, ethanol, ethyl acetate, methanol, 2-propanol, tetrahydrofuran, and water, and mixtures thereof. Solvent mixtures with predicted enhanced API solvation properties (cosolvency) were validated by experiments. Moreover, concentration regions in which LLPS was predicted to occur were also found to be in perfect agreement with the experimental data. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.fluid.2021.113200
  • 2021 • 1083 Microstructure formation and mechanical properties of ODS steels built by laser additive manufacturing of nanoparticle coated iron-chromium powders
    Doñate-Buendia, C. and Kürnsteiner, P. and Stern, F. and Wilms, M.B. and Streubel, R. and Kusoglu, I.M. and Tenkamp, J. and Bruder, E. and Pirch, N. and Barcikowski, S. and Durst, K. and Schleifenbaum, J.H. and Walther, F. and G...
    Acta Materialia 206 (2021)
    Oxide dispersion strengthened (ODS) steels are known for their enhanced mechanical performance at high temperatures or under radiation exposure. Their microstructure depends on the manufacturing process, from the nanoparticle addition to the base steel powder, to the processing of the nanoparticle enriched powder. The optimization and control of the processing steps still represent a challenge to establish a clear methodology for the additive manufacturing of ODS steels. Here, we evaluate the microstructure, nanoparticle evolution, and mechanical properties of ODS steels prepared by dielectrophoretic controlled adsorption of 0.08 wt% laser-synthesized yttrium oxide (Y2O3) on an iron-chromium ferritic steel powder (PM2000). The influence of the ODS steel fabrication technique is studied for two standard additive manufacturing techniques, directed energy deposition (DED) and laser powder bed fusion (LPBF). The compressive strength of the ODS steels at 600 °C is increased by 21% and 29% for the DED and LPBF samples, respectively, compared to the DED and LPBF steels manufactured without Y2O3 nanoparticle addition. The Martens hardness is enhanced by 9% for the LPBF ODS steel while no significant change is observed in the DED ODS steel. The microstructure and nanoparticle composition and distribution are evaluated by electron backscatter diffraction, scanning electron microscopy–energy-dispersive X-ray spectroscopy, and atom probe tomography, to compare the microstructural features of DED and LPBF manufactured parts. Smaller grain size and more homogeneous distribution with lower agglomeration of Y-O nanoparticles in the LPBF sample are found to be key factors for enhanced mechanical response at 600 °C. The enhanced mechanical properties of the LPBF-processed sample and the more homogeneous nanoparticle dispersion can be linked to results obtained by finite element methods simulations of the melt pool that show two orders of magnitude faster cooling rates for LPBF than for DED. Therefore, this work presents and validates a complete laser-based methodology for the preparation and processing of an ODS steel, proving the modification of the microstructure and enhancement of the high-temperature strength of the as-built parts. © 2020
    view abstractdoi: 10.1016/j.actamat.2020.116566
  • 2021 • 1082 On the selection and design of powder materials for laser additive manufacturing
    Doñate-Buendía, C. and Gu, D. and Schmidt, M. and Barcikowski, S. and Korsunsky, A.M. and Gökce, B.
    Materials and Design 204 (2021)
    doi: 10.1016/j.matdes.2021.109653
  • 2021 • 1081 The effect of co incorporation on the co oxidation activity of lafe1−xcoxo3 perovskites
    Dreyer, M. and Krebs, M. and Najafishirtari, S. and Rabe, A. and Ortega, K.F. and Behrens, M.
    Catalysts 11 (2021)
    Perovskite oxides are versatile materials due to their wide variety of compositions of-fering promising catalytic properties, especially in oxidation reactions. In the presented study, LaFe1−xCoxO3 perovskites were synthesized by hydroxycarbonate precursor co-precipitation and thermal decomposition thereof. Precursor and calcined materials were studied by scanning electron microscopy (SEM), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), thermogravimetric analysis (TG), and X-ray powder diffraction (XRD). The calcined catalysts were in addition studied by transmission electron microscopy (TEM) and N2 physisorption. The obtained perovskites were applied as catalysts in transient CO oxidation, and in operando studies of CO oxidation in diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). A pronounced increase in activity was already observed by incorporating 5% cobalt into the structure, which contin-ued, though not linearly, at higher loadings. This could be most likely due to the enhanced redox properties as inferred by H2-temperature programmed reduction (H2-TPR). Catalysts with higher Co contents showing higher activities suffered less from surface deactivation related to carbonate poisoning. Despite the similarity in the crystalline structures upon Co incorporation, we observed a different promotion or suppression of various carbonate-related bands, which could indicate different surface properties of the catalysts, subsequently resulting in the observed non-linear CO oxidation activity trend at higher Co contents. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/catal11050550
  • 2021 • 1080 Dynamics of reactive oxygen species on cobalt-containing spinel oxides in cyclic co oxidation
    Dreyer, M. and Rabe, A. and Budiyanto, E. and Ortega, K.F. and Najafishirtari, S. and Tüysüz, H. and Behrens, M.
    Catalysts 11 (2021)
    Reactive oxygen species (ROS) are considered to be responsible for the high catalytic activity of transition metal oxides like Co3-xFexO4 in oxidation reactions, but the detailed influences of catalyst composition and morphology on the formation of these reactive oxygen species are not fully understood. In the presented study, Co3O4 spinels of different mesostructures, i.e., particle size, crystallinity, and specific surface area, are characterized by powder X-ray diffraction, scanning electron microscopy, and physisorption. The materials were tested in CO oxidation performed in consecutive runs and compared to a Co3-xFexO4 composition series with a similar mesostructure to study the effects of catalyst morphology and composition on ROS formation. In the first run, the CO conversion was observed to be dominated by the exposed surface area for the pure Co-spinels, while a negative effect of Fe content in the spinels was seen. In the following oxidation run, a U-shaped conversion curve was observed for materials with high surface area, which indicated the in situ formation of ROS on those materials that were responsible for the new activity at low temperature. This activation was not stable at the higher reaction temperature but was confirmed after temperature-programmed oxidation (TPO). However, no activation after the first run was observed for low-surface-area and highly crystalline materials, and the lowest surface-area material was not even activated after TPO. Among the catalyst series studied here, a correlation of small particle size and large surface area with the ability for ROS formation is presented, and the benefit of a nanoscaled catalyst is discussed. Despite the generally negative effect of Fe, the highest relative activation was observed at intermediate Fe contents suggesting that Fe may be involved in ROS formation. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/catal11111312
  • 2021 • 1079 The Effect of Water on the 2-Propanol Oxidation Activity of Co-Substituted LaFe1−CoxO3 Perovskites
    Dreyer, M. and Cruz, D. and Hagemann, U. and Zeller, P. and Heidelmann, M. and Salamon, S. and Landers, J. and Rabe, A. and Ortega, K.F. and Najafishirtari, S. and Wende, H. and Hartmann, N. and Knop-Gericke, A. and Schlögl, R. a...
    Chemistry - A European Journal (2021)
    Perovskites are interesting oxidation catalysts due to their chemical flexibility enabling the tuning of several properties. In this work, we synthesized LaFe1−xCoxO3 catalysts by co-precipitation and thermal decomposition, characterized them thoroughly and studied their 2-propanol oxidation activity under dry and wet conditions to bridge the knowledge gap between gas and liquid phase reactions. Transient tests showed a highly active, unstable low-temperature (LT) reaction channel in conversion profiles and a stable, less-active high-temperature (HT) channel. Cobalt incorporation had a positive effect on the activity. The effect of water was negative on the LT channel, whereas the HT channel activity was boosted for x&gt;0.15. The boost may originate from a slower deactivation rate of the Co3+ sites under wet conditions and a higher amount of hydroxide species on the surface comparing wet to dry feeds. Water addition resulted in a slower deactivation for Co-rich catalysts and higher activity in the HT channel state. © 2021 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/chem.202102791
  • 2021 • 1078 Experimental Investigation of Ethanol Oxidation and Development of a Reduced Reaction Mechanism for a Wide Temperature Range
    Drost, S. and Kaczmarek, D. and Eckart, S. and Herzler, J. and Schießl, R. and Fritsche, C. and Fikri, M. and Atakan, B. and Kasper, T. and Krause, H. and Schulz, C. and Maas, U.
    Energy and Fuels 35 14780-14792 (2021)
    Rapid compression machine, shock-tube, plug-flow reactor, and heat-flux burner experiments were performed for stoichiometric and fuel-rich ethanol/air mixtures. The experimental ignition delay time conditions included temperatures from 801 to 1313 K at pressures of approximately 10, 20, and 40 bar. Species concentration profiles are measured in a range from 423 to 973 K at a pressure of 6 bar, and laminar burning velocities are measured in a range of 358-388 K at a pressure of 1 bar. The experimental results were simulated using the detailed reaction mechanism AramcoMech 3.0, showing that this mechanism is well suited even for the large range of experimental conditions covered in our work. Furthermore, a reduced mechanism was developed and validated with our experimental data. The sarting point for the reduced mechanism is an already existing reduced reaction mechanism (UCB Chen) for methane, ethane, and propane oxidations. Additional reactions for the ethanol subsystem were taken from AramcoMech 3.0. They were chosen according to their importance in representing the experimental data in simulations with the detailed AramcoMech 3.0, resulting in four additional species and 27 additional reactions. The performance of the reduced mechanism was compared against experimental results from this work, from the literature, and against simulations based on the detailed reaction mechanism. The reduced mechanism shows only minor differences in the results compared to the detailed AramcoMech 3.0. It reproduces very well experimentally with determined ignition delay times of ethanol/argon/nitrogen/oxygen mixtures with inert gas/oxygen ratios between 3.76 and 7.52 (molar), equivalence ratios between 1 and 2 in a temperature range from 848 to 1313 K, and pressures from 10 to 40 bar. Furthermore, it can also predict with a high accuracy laminar burning velocities and species profiles in plug-flow reactors. © 2021 The Authors. Published by American Chemical Society
    view abstractdoi: 10.1021/acs.energyfuels.1c01993
  • 2021 • 1077 Delivery of toll-like receptor 3 ligand poly(I:C) to the liver by calcium phosphate nanoparticles conjugated with an F4/80 antibody exerts an anti-hepatitis B virus effect in a mouse model
    Du, Y. and Yang, X. and Li, J. and Sokolova, V. and Zou, S. and Han, M. and Yan, H. and Wey, K. and Lu, M. and Dittmer, U. and Yang, D. and Epple, M. and Wu, J.
    Acta Biomaterialia (2021)
    Hepatitis B virus (HBV) is a global health issue, but currently available anti-HBV drugs have limited success. Previously, introduction of the Toll-like receptor (TLR)-3 ligand poly(I:C) to the liver via hydrodynamic injection (HI) was shown to effectively suppress HBV replication in a chronic HBV replication mouse model. However, this method cannot be applied in human beings. To improve the liver targeting of poly(I:C) via intravenous injection, calcium phosphate nanoparticles (CPNs) carrying poly(I:C) with or without antibodies were constructed, and their anti-HBV effects were investigated. We found that significantly more anti-F4/80-conjugated and IgG2α-conjugated nanoparticles were taken up in liver cells both in vivo and in vitro. In addition, these nanoparticles produced pronounced immunostimulatory effects in vitro in primary liver cells. Importantly, treatment with nanoparticles carrying poly(I:C) increased the production of intrahepatic cytokines and chemokines and enhanced T cell responses, significantly reducing HBsAg, HBeAg and HBV DNA levels in the mice. Compared to nonconjugated and isotype-antibody-conjugated nanoparticles, the anti-F4/80-conjugated nanoparticles demonstrated the strongest anti-HBV effects. In summary, nanoparticles carrying poly(I:C) conjugated with an F4/80 antibody promoted liver targeting, and they may represent a suitable alternative to HI for future anti-HBV treatment. Statement of Significance: HBV chronically infects approximately 250 million individuals worldwide but current anti-HBV drugs have limited success. Introduction of toll-like receptor 3 ligand poly(I:C) into liver by hydrodynamic injection has been proven to promote HBV clearance in mouse model. However, this technique is not clinically suitable for human patients. We have constructed calcium phosphate nanoparticles carrying poly(I:C) with specific antibody targeting liver nonparenchymal cells. The uptake into relevant liver cells and the anti-HBV effects were studied. After intravenous injection into mice, the uptake rate of anti-F4/80-conjugated nanoparticels was enhanced in liver, and these nanoparticles exert effective anti-HBV effects in vivo. This may provide important insight into future HBV immunotherapy based on nanoparticle-mediated drug delivery. © 2021 Acta Materialia Inc.
    view abstractdoi: 10.1016/j.actbio.2021.01.045
  • 2021 • 1076 In situ nanoindentation during electrochemical hydrogen charging: a comparison between front-side and a novel back-side charging approach
    Duarte, M.J. and Fang, X. and Rao, J. and Krieger, W. and Brinckmann, S. and Dehm, G.
    Journal of Materials Science 56 8732-8744 (2021)
    The effects of hydrogen in metals are a pressing issue causing severe economic losses due to material deterioration by hydrogen embrittlement. A crucial understanding of the interactions of hydrogen with different microstructure features can be reached by nanoindentation due to the small volumes probed. Even more, in situ testing while charging the sample with hydrogen prevents the formation of concentration gradients due to hydrogen desorption. Two custom electrochemical cells for in situ testing were built in-house to charge the sample with hydrogen during nanoindentation: “front-side” charging with the sample and the indenter tip immersed into the electrolyte, and “back-side” charging where the analyzed region is never in contact with the solution. During front-side charging, surface degradation often occurs which also negatively influences analyses after hydrogen charging. The back-side charging approach proposed in this work is a promising technique for studying in situ the effects of hydrogen in alloys under mechanical loads, while completely excluding the influence of the electrolyte on the nanoindented surface. Hydrogen diffusion from the charged back-side toward the testing surface is here demonstrated by Kelvin probe measurements in ferritic FeCr alloys, used as a case study due to the high mobility of hydrogen in the bcc lattice. During nanoindentation, a reduction on the shear stress necessary for dislocations nucleation due to hydrogen was observed using both setups; however, the quantitative data differs and a contradictory behavior was found in hardness measurements. Finally, some guidelines for the use of both approaches and a summary of their advantages and disadvantages are presented. Graphical abstract: [Figure not available: see fulltext.] © 2021, The Author(s).
    view abstractdoi: 10.1007/s10853-020-05749-2
  • 2021 • 1075 Role of cooperative factors in the photocatalytic activity of Ba and Mn doped BiFeO3nanoparticles
    Dubey, A. and Schmitz, A. and Shvartsman, V.V. and Bacher, G. and Lupascu, D.C. and Castillo, M.E.
    Nanoscale Advances 3 5830-5840 (2021)
    The escalated photocatalytic (PC) efficiency of the visible light absorber Ba-doped BiFe0.95Mn0.05O3(BFM) nanoparticles (NPs) as compared to BiFeO3(BFO) NPs is reported for the degradation of the organic pollutants rhodamine B and methyl orange. 1 mol% Ba-doped-BFM NPs degrade both dyes within 60 and 25 minutes under UV + visible illumination, respectively. The Ba and Mn co-doping up to 5 mol% in BFO NPs increases the specific surface area, energy of d-d transitions, and PC efficiency of the BFO NPs. The maximum PC efficiency found in 1 mol% Ba doped BFM NPs is attributed to a cooperative effect of factors like its increased light absorption ability, large surface area, active surface, reduced recombination of charge carriers, and spontaneous polarization to induce charge carrier separation. The 1 mol% Ba and 5 mol% Mn co-incorporation is found to be the optimum dopant concentration for photocatalytic applications. These properties of co-doped BFO NPs can,e.g., be exploited in the field of water splitting. © The Royal Society of Chemistry 2021.
    view abstractdoi: 10.1039/d1na00420d
  • 2021 • 1074 Co-Sintering Study of Na0.67[Ni0.1Fe0.1Mn0.8]O2 and NaSICON Electrolyte–Paving the way to High Energy Density All-Solid-State Batteries
    Dück, G. and Naqash, S. and Finsterbusch, M. and Breuer, U. and Guillon, O. and Fattakhova-Rohlfing, D.
    Frontiers in Energy Research 9 (2021)
    Sodium is a promising candidate for stationary storage applications, especially when the demand for lithium-ion batteries increases due to electromobility applications. Even though its energy density is lower, Na-ion technology is estimated to lead to a cost reduction of 30% compared to Li-ion technology. To improve safety as well as energy density, Na-based all-solid-state-batteries featuring solid electrolytes such as beta-alumina and sodium superionic conductors and cathode materials such as Na3V2(PO4)3 and NaxCoO2 have been developed over the past years. However, the biggest challenge are mixed cathodes with highly conductive interfaces, especially when co-sintering the materials. For example, a promising sodium superionic conductor type Na3Zr2Si2PO12 electrolyte sinters at 1,250°C, whereas the corresponding Na3V2PO12 cathode decomposes at temperatures higher than 900°C, posing a bottleneck. Thus in this paper, we synthesized Na0.62 [Ni0.10Fe0.10Mn0.80]O2 as cathode material for all-solid-state sodium-ion batteries via a relatively cheap and easy solution-assisted solid state reaction processing route. The thermal investigations of the pure cathode material found no degradation up to 1,260°C, making it a perfect match for Na3.4Zr2Si2.4P0.6O12 electrolyte. In our aim to produce a co-sintered mixed cathode, electron microscopy investigation showed a highly dense microstructure and the elemental mapping performed via energy dispersive X-ray spectroscopy and secondary ion mass spectrometry confirm that Na3.4Zr2Si2.4P0.6O12 and Na0.62 [Ni0.10Fe0.10Mn0.80]O2 do not react during sintering. However, the active cathode material forms a sodium rich and a sodium deficient phase which needs further investigation to understand the origin and its impact on the electrochemical performance. © Copyright © 2021 Dück, Naqash, Finsterbusch, Breuer, Guillon and Fattakhova-Rohlfing.
    view abstractdoi: 10.3389/fenrg.2021.689416
  • 2021 • 1073 Increased space-parallelism via time-simultaneous Newton-multigrid methods for nonstationary nonlinear PDE problems
    Dünnebacke, J. and Turek, S. and Lohmann, C. and Sokolov, A. and Zajac, P.
    International Journal of High Performance Computing Applications 35 211-225 (2021)
    We discuss how “parallel-in-space & simultaneous-in-time” Newton-multigrid approaches can be designed which improve the scaling behavior of the spatial parallelism by reducing the latency costs. The idea is to solve many time steps at once and therefore solving fewer but larger systems. These large systems are reordered and interpreted as a space-only problem leading to multigrid algorithm with semi-coarsening in space and line smoothing in time direction. The smoother is further improved by embedding it as a preconditioner in a Krylov subspace method. As a prototypical application, we concentrate on scalar partial differential equations (PDEs) with up to many thousands of time steps which are discretized in time, resp., space by finite difference, resp., finite element methods. For linear PDEs, the resulting method is closely related to multigrid waveform relaxation and its theoretical framework. In our parabolic test problems the numerical behavior of this multigrid approach is robust w.r.t. the spatial and temporal grid size and the number of simultaneously treated time steps. Moreover, we illustrate how corresponding time-simultaneous fixed-point and Newton-type solvers can be derived for nonlinear nonstationary problems that require the described solution of linearized problems in each outer nonlinear step. As the main result, we are able to generate much larger problem sizes to be treated by a large number of cores so that the combination of the robustly scaling multigrid solvers together with a larger degree of parallelism allows a faster solution procedure for nonstationary problems. © The Author(s) 2021.
    view abstractdoi: 10.1177/10943420211001940
  • 2021 • 1072 A Time-Simultaneous Multigrid Method for Parabolic Evolution Equations
    Dünnebacke, J. and Turek, S. and Zajac, P. and Sokolov, A.
    Lecture Notes in Computational Science and Engineering 139 333-342 (2021)
    We present a time-simultaneous multigrid scheme for parabolic equations that is motivated by blocking multiple time steps together. The resulting method is closely related to multigrid waveform relaxation and is robust with respect to the spatial and temporal grid size and the number of simultaneously computed time steps. We give an intuitive understanding of the convergence behavior and briefly discuss how the theory for multigrid waveform relaxation can be applied in some special cases. Finally, some numerical results for linear and also nonlinear test cases are shown. © 2021, Springer Nature Switzerland AG.
    view abstractdoi: 10.1007/978-3-030-55874-1_32
  • 2021 • 1071 A mechanical analysis of chemically stimulated linear shape memory polymer actuation
    Dumlu, H. and Marquardt, A. and Zirdehi, E.M. and Varnik, F. and Shen, Y. and Neuking, K. and Eggeler, G.
    Materials 14 1-21 (2021)
    In the present work, we study the role of programming strain (50% and 100%), end loads (0, 0.5, 1.0, and 1.5 MPa), and chemical environments (acetone, ethanol, and water) on the exploitable stroke of linear shape memory polymer (SMP) actuators made from ESTANE ETE 75DT3 (SMP-E). Dynamic mechanical thermal analysis (DMTA) shows how the uptake of solvents results in a decrease in the glass temperature of the molecular switch component of SMP-E. A novel in situ technique allows chemically studying triggered shape recovery as a function of time. It is found that the velocity of actuation decreases in the order acetone > ethanol > water, while the exploitable strokes shows the inverse tendency and increases in the order water > ethanol > acetone. The results are interpreted on the basis of the underlying chemical (how solvents affect thermophysical properties) and micromechanical processes (the phenomenological spring dashpot model of Lethersich type rationalizes the behavior). The study provides initial data which can be used for micromechanical modeling of chemically triggered actuation of SMPs. The results are discussed in the light of underlying chemical and mechanical elementary processes, and areas in need of further work are highlighted. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/ma14030481
  • 2021 • 1070 Reinforcing bars modelling using a rod–solid interface element without the need for mesh compatibility
    Durand, R. and Farias, M.M. and Pedroso, D.M. and Meschke, G.
    Finite Elements in Analysis and Design 197 (2021)
    This paper presents a finite element methodology for modelling solid media with any number of straight or curved reinforcing bars (rebars). The formulation can handle rebars arbitrarily located within a 2D or 3D finite element mesh without the need for nodal compatibility. A new continuous rod–solid interface (or joint) element is developed to connect bulk elements to the rebars, including a method that directly considers the relative displacements. An arbitrary constitutive model can be used in conjunction with the proposed interface element to represent slip behaviour. In this regard, we also present a cyclic nonlinear constitutive model. Unlike existing embedded approaches, the proposed method allows for the direct application of boundary conditions at reinforcements’ endpoints, including tip bearing. The formulation is verified by comparing with literature examples and analytical solutions. In all cases, excellent agreement is observed. The approach can be conveniently applied to the study of complex reinforced concrete structures or any solid medium where reinforcing bars improve its mechanical properties. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.finel.2021.103634
  • 2021 • 1069 Achieving a high Short Circuit Current Density of 40.9 mA/cm2 for Two-Side Contacted Silicon Heterojunction Solar Cells by using SiC-based Transparent Passivating Contacts
    Eberst, A. and Zamchiy, A. and Qiu, K. and Lambertz, A. and Duan, W. and Li, S. and Bittkau, K. and Haas, S. and Finger, F. and Kirchartz, T. and Rau, U. and Ding, K.
    Conference Record of the IEEE Photovoltaic Specialists Conference 300-302 (2021)
    A silicon heterojunction solar cell using silicon carbide as front contact is presented, which features the main advantage of high transparency. To enhance this advantage, an optical loss analysis is performed. It is found that reflection losses play an important role for the solar cell, which can easily be reduced by applying an additional MgF2 coating. The deposition of the coating degrades the passivation quality of the contact but can be cured, eventually leading to a certified short circuit current density of 40.9 mA/cm2 and efficiency of 23.99%. Afterwards, a roadmap to a theoretical efficiency of 25% is presented. © 2021 IEEE.
    view abstractdoi: 10.1109/PVSC43889.2021.9518496
  • 2021 • 1068 In-flight distribution of an electron within a surface acoustic wave
    Edlbauer, H. and Wang, J. and Ota, S. and Richard, A. and Jadot, B. and Mortemousque, P.-A. and Okazaki, Y. and Nakamura, S. and Kodera, T. and Kaneko, N.-H. and Ludwig, A. and Wieck, A.D. and Urdampilleta, M. and Meunier, T. and ...
    Applied Physics Letters 119 (2021)
    Surface acoustic waves (SAWs) have large potential to realize quantum-optics-like experiments with single flying electrons employing their spin or charge degree of freedom. For such quantum applications, highly efficient trapping of the electron in a specific moving quantum dot (QD) of a SAW train plays a key role. Probabilistic transport over multiple moving minima would cause uncertainty in synchronization that is detrimental for coherence of entangled flying electrons and in-flight quantum operations. It is thus of central importance to identify the device parameters enabling electron transport within a single SAW minimum. A detailed experimental investigation of this aspect is so far missing. Here, we fill this gap by demonstrating time-of-flight measurements for a single electron that is transported via a SAW train between distant stationary QDs. Our measurements reveal the in-flight distribution of the electron within the moving acousto-electric quantum dots of the SAW train. Increasing the acousto-electric amplitude, we observe the threshold necessary to confine the flying electron at a specific, deliberately chosen SAW minimum. Investigating the effect of a barrier along the transport channel, we also benchmark the robustness of SAW-driven electron transport against stationary potential variations. Our results pave the way for highly controlled transport of electron qubits in a SAW-driven platform for quantum experiments. © 2021 Author(s).
    view abstractdoi: 10.1063/5.0062491
  • 2021 • 1067 Room temperature synthesized solid solution AuFe nanoparticles and their transformation into Au/Fe Janus nanocrystals
    Efremova, M.V. and Spasova, M. and Heidelmann, M. and Grebennikov, I.S. and Li, Z.-A. and Garanina, A.S. and Tcareva, I.O. and Savchenko, A.G. and Farle, M. and Klyachko, N.L. and Majouga, A.G. and Wiedwald, U.
    Nanoscale 13 10402-10413 (2021)
    Solid solution AuFe nanoparticles were synthesized for the first time under ambient conditions by an adapted method previously established for the Fe3O4-Au core-shell morphology. These AuFe particles preserved the fcc structure of Au incorporated with paramagnetic Fe atoms. The metastable AuFe can be segregated by transformation into Janus Au/Fe particles with bcc Fe and fcc Au upon annealing. The ferromagnetic Fe was epitaxially grown on low index fcc Au planes. This preparation route delivers new perspective materials for magnetoplasmonics and biomedical applications and suggests the reconsideration of existing protocols for magnetite-gold core-shell synthesis. © The Royal Society of Chemistry.
    view abstractdoi: 10.1039/d1nr00383f
  • 2021 • 1066 Influence of Mg content in Al alloys on processing characteristics and dynamically recrystallized microstructure of friction surfacing deposits
    Ehrich, J. and Roos, A. and Klusemann, B. and Hanke, S.
    Materials Science and Engineering A 819 (2021)
    Friction Surfacing (FS) coatings are deposited by severe plastic deformation at elevated temperatures (≈0.8*Tliquidus), requiring different process parameters for alloys of even small composition variations. For Al alloys it is known that with increasing Mg content the thermal softening rate decreases, i.e. the material retains higher flow strength under thermomechanical processing. Further, the stacking fault energy (SFE) decreases with increasing Mg content, which influences gliding characteristics of dislocations, and also deformation and recrystallization behavior. To elucidate the influence of such known properties on FS process parameters and resulting coatings, three Al alloys differing only in Mg content (0.27, 2 and 3.5 wt.%) were processed by FS in this study. Pronounced shear flow localization was observed for increasing Mg content, yielding thin and narrow coatings and requiring a reduction of process speeds. Further, the decrease in SFE with increasing Mg content resulted in lower recrystallized grain size and higher grain orientation differences, due to a lower tendency for dislocation annihilation by recovery. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.msea.2021.141407
  • 2021 • 1065 Stationary Flow Predictions Using Convolutional Neural Networks
    Eichinger, M. and Heinlein, A. and Klawonn, A.
    Lecture Notes in Computational Science and Engineering 139 541-549 (2021)
    Computational Fluid Dynamics (CFD) simulations are a numerical tool to model and analyze the behavior of fluid flow. However, accurate simulations are generally very costly because they require high grid resolutions. In this paper, an alternative approach for computing flow predictions using Convolutional Neural Networks (CNNs) is described; in particular, a classical CNN as well as the U-Net architecture are used. First, the networks are trained in an expensive offline phase using flow fields computed by CFD simulations. Afterwards, the evaluation of the trained neural networks is very cheap. Here, the focus is on the dependence of the stationary flow in a channel on variations of the shape and the location of an obstacle. CNNs perform very well on validation data, where the averaged error for the best networks is below 3%. In addition to that, they also generalize very well to new data, with an averaged error below 10%. © 2021, Springer Nature Switzerland AG.
    view abstractdoi: 10.1007/978-3-030-55874-1_53
  • 2021 • 1064 Kondo holes in strongly correlated impurity arrays: RKKY-driven Kondo screening and hole-hole interactions
    Eickhoff, F. and Anders, F.B.
    Physical Review B 104 (2021)
    The emerging and screening of local magnetic moments in solids have been investigated for more than 60 years. Local vacancies as in graphene or in heavy fermions can induce decoupled bound states that lead to the formation of local moments. In this paper, we address the puzzling question how these local moments can be screened and what determines the additionally emerging low-temperature scale. We review the initial problem for half-filled conduction bands from two complementary perspectives: By a single-particle supercell analysis in the uncorrelated limit and by the Lieb-Mathis theorem for systems with a large Coulomb interaction U. Applying Wilson's numerical renormalization group approach to a recently developed mapping of the problem onto an effective low-energy description of a Kondo hole with up to Nf=7 correlated impurities as background, we proof that the stable local moments are subject to screening by three different mechanisms. Firstly the local moments are delocalized by a finite U beyond the single-particle bound state. We find a Kosterlitz-Thouless type transition governed by an exponentially suppressed low-energy scale of a counterintuitive Kondo form with Jeff∝Un for small U, where n>1 depends on the precise model. Secondly, we show that away from half-filling the local moment phase becomes unstable and is replaced by two types of singlet phases that are adiabatically connected. At a critical value for the band center, the physics is governed by an exponentially suppressed Kondo scale approaching the strong coupling phase that is replaced by a singlet formation via antiferromagnetic RKKY interaction for large deviation from the critical values. Thirdly, we show that the local magnetic moment can be screened by a Kondo hole orbital at finite energy, even though the orbital occupation is negligible: An additional low-energy scale emerges below which the localized moment is quenched. Similarities to the experimental findings in Ce1-xLaxPd3 are pointed out. © 2021 American Physical Society.
    view abstractdoi: 10.1103/PhysRevB.104.045115
  • 2021 • 1063 Spectral properties of strongly correlated multi-impurity models in the Kondo insulator regime: Emergent coherence, metallic surface states, and quantum phase transitions
    Eickhoff, F. and Anders, F.B.
    Physical Review B 104 (2021)
    We investigate the real-space spectral properties of strongly correlated multi-impurity arrays in the Kondo insulator regime. Employing a recently developed mapping onto an effective correlated cluster problem makes the problem accessible to the numerical renormalization group. The evolution of the spectrum as a function of cluster size and cluster site is studied. We applied the extended Lieb-Mattis theorem to predict whether the spectral function must vanish at the Fermi energy developing a true pseudogap or whether the spectral function remains finite at . Our numerical renormalization group spectra confirm the predictions of the theorem and shows a metallic behavior at the surface of a cluster prevailing in arbitrary spatial dimensions. We present a conventional minimal extension of a particle-hole symmetric Anderson lattice model at that leads to a gapped bulk band but a surface band with mainly -orbital character for weak and moderate hybridization strength. The change in the site-dependent spectra upon introducing a Kondo hole in the center of the cluster is presented as a function of the hole-orbital energy. In particular, the spectral signatures across the Kosterlitz-Thouless-type quantum phase transition from a singlet to a local moment fixed point are discussed. © 2021 American Physical Society
    view abstractdoi: 10.1103/PhysRevB.104.165105
  • 2021 • 1062 Ion association in hydrothermal aqueous NaCl solutions: implications for the microscopic structure of supercritical water
    Elbers, M. and Schmidt, C. and Sternemann, C. and Sahle, C.J. and Jahn, S. and Albers, C. and Sakrowski, R. and Gretarsson, H. and Sundermann, M. and Tolan, M. and Wilke, M.
    Physical Chemistry Chemical Physics 23 14845-14856 (2021)
    Knowledge of the microscopic structure of fluids and changes thereof with pressure and temperature is important for the understanding of chemistry and geochemical processes. In this work we investigate the influence of sodium chloride on the hydrogen-bond network in aqueous solution up to supercritical conditions. A combination ofin situX-ray Raman scattering andab initiomolecular dynamics simulations is used to probe the oxygen K-edge of the alkali halide aqueous solution in order to obtain unique information about the oxygen's local coordination around the ions,e.g.solvation-shell structure and the influence of ion pairing. The measured spectra exhibit systematic temperature dependent changes, which are entirely reproduced by calculations on the basis of structural snapshots obtainedvia ab initiomolecular dynamics simulations. Analysis of the simulated trajectories allowed us to extract detailed structural information. This combined analysis reveals a net destabilizing effect of the dissolved ions which is reduced with rising temperature. The observed increased formation of contact ion pairs and occurrence of larger polyatomic clusters at higher temperatures can be identified as a driving force behind the increasing structural similarity between the salt solution and pure water at elevated temperatures and pressures with drawback on the role of hydrogen bonding in the hot fluid. We discuss our findings in view of recent results on hot NaOH and HCl aqueous fluids and emphasize the importance of ion pairing in the interpretation of the microscopic structure of water. © the Owner Societies 2021.
    view abstractdoi: 10.1039/d1cp01490k
  • 2021 • 1061 ConvNet Fine-Tuning Investigation for GPR Images Classification
    Elsaadouny, M. and Barowski, J. and Rolfes, I.
    2021 34th General Assembly and Scientific Symposium of the International Union of Radio Science, URSI GASS 2021 (2021)
    Deep learning has been widely implemented as a new classification platform during the past few years. One of the main problems facing deep learning is the problem of data dependency as it requires a very large amount of data for training. Therefore, transfer learning (TL) has been introduced as a solution to this problem. This study focuses on the fine-tuning strategy of the transfer learning and how it can be implemented to classify the ground-penetrating radar (GPR) images. The GPR data has been collected and processed using the matched filter algorithm and further clutter reduction techniques. The resultant GPR images compromises of a limited number of samples, therefore, the deployed convolutional neural network (ConvNet) has been trained first using another larger dataset, then fine-tuned using the GPR dataset. The obtained results are promising and show a high degree of precision and accuracy compared to previously conducted researches. © 2021 URSI.
    view abstractdoi: 10.23919/URSIGASS51995.2021.9560298
  • 2021 • 1060 Unsupervised Learning Implementation for SAR Images Clustering
    Elsaadouny, M. and Barowski, J. and Rolfes, I.
    2021 International Conference on Electromagnetics in Advanced Applications, ICEAA 2021 104 (2021)
    Unsupervised learning algorithms play a major role and participate in different applications. These algorithms work mainly on defining the hidden patterns within the dataset and clustering the data points into different groups. Unlike supervised learning, unsupervised learning works without any supervision from human, therefore, it is mainly used with unknown data to discover the underlying structure of it. In this research, two of the main unsupervised learning algorithms are implemented and evaluated in clustering of the synthetic aperture radar (SAR) images. © 2021 IEEE.
    view abstractdoi: 10.1109/ICEAA52647.2021.9539661
  • 2021 • 1059 Experimental and numerical investigation of vortex-induced vibration for a fully submerged oscillating circular cylinder in a circulating water channel
    El Sheshtawy, H. and Youssef, M. and Tödter, S. and Neugebauer, J. and El Moctar, O. and Schellin, T.E.
    Proceedings of the International Offshore and Polar Engineering Conference 2029-2034 (2021)
    Investigated was the lock-in case of the vortex-induced vibration of an oscillating circular cylinder in a circulating water channel subjected to a reduced velocity flow of 5.18 at a Reynolds number of 5 × 104. The coupled dynamic inline and transverse response of the cylinder was measured and compared to numerical simulations. The discretization errors and the effect of different y+ values on the solution were analyzed. The numerically simulated cylinder displacements acting on the cylinder were validated against experimental measurements. The presented experiment and numerical results provided reliable benchmark data suitable for numerical validation of vortex-induced vibration for a circular cylinder oscillating in two degrees-of-freedom. © 2021 by the International Society of Offshore and Polar Engineers (ISOPE).
    view abstract
  • 2021 • 1058 Ultrafast charge carrier dynamics in potassium-doped endohedral metallofullerene Sc3N@C80 thin films
    Emmerich, S. and Hedwig, S. and Cinchetti, M. and Stadtmüller, B. and Aeschlimann, M.
    Journal of Electron Spectroscopy and Related Phenomena 252 (2021)
    Molecular materials have emerged as highly flexible platform for photovoltaic and light-harvesting applications. One of the most important challenges for this class of materials is the trapping of charge carriers in bound electron–hole pairs, which severely limits the free charge carrier generation. Here, we demonstrate a significant modification of the exciton dynamics in thin films of endohedral metallofullerene complexes upon alkali metal doping. For the exemplary case of Sc3N@C80 thin films, we show that potassium doping results in an additional relaxation channel for the optically excited charge-transfer excitons that prevents the trapping of excitons in a long-lived Frenkel exciton-like state. Instead, potassium doping leads to an ultrafast exciton dissociation and most likely to the generation of free charge carriers. In this way, we propose alkali metal doping of molecular films as a novel approach to enhance the light-to-charge carrier conversion efficiency in photovoltaic molecular materials. © 2021 The Authors
    view abstractdoi: 10.1016/j.elspec.2021.147110
  • 2021 • 1057 Surfactant-loaded capsules as Marangoni microswimmers at the air–water interface: Symmetry breaking and spontaneous propulsion by surfactant diffusion and advection
    Ender, H. and Froin, A.-K. and Rehage, H. and Kierfeld, J.
    European Physical Journal E 44 (2021)
    Abstract: We present a realization of a fast interfacial Marangoni microswimmer by a half-spherical alginate capsule at the air–water interface, which diffusively releases water-soluble spreading molecules (weak surfactants such as polyethylene glycol (PEG)), which act as “fuel” by modulating the air–water interfacial tension. For a number of different fuels, we can observe symmetry breaking and spontaneous propulsion although the alginate particle and emission are isotropic. The propulsion mechanism is similar to soap or camphor boats, which are, however, typically asymmetric in shape or emission to select a swimming direction. We develop a theory of Marangoni boat propulsion starting from low Reynolds numbers by analyzing the coupled problems of surfactant diffusion and advection and fluid flow, which includes surfactant-induced fluid Marangoni flow, and surfactant adsorption at the air–water interface; we also include a possible evaporation of surfactant. The swimming velocity is determined by the balance of drag and Marangoni forces. We show that spontaneous symmetry breaking resulting in propulsion is possible above a critical dimensionless surfactant emission rate (Peclet number). We derive the relation between Peclet number and swimming speed and generalize to higher Reynolds numbers utilizing the concept of the Nusselt number. The theory explains the observed swimming speeds for PEG–alginate capsules, and we unravel the differences to other Marangoni boat systems based on camphor, which are mainly caused by surfactant evaporation from the liquid–air interface. The capsule Marangoni microswimmers also exhibit surfactant-mediated repulsive interactions with walls, which can be qualitatively explained by surfactant accumulation at the wall. Graphic Abstract: [Figure not available: see fulltext.]. © 2021, The Author(s).
    view abstractdoi: 10.1140/epje/s10189-021-00035-8
  • 2021 • 1056 From diffusive mass transfer in Stokes flow to low Reynolds number Marangoni boats
    Ender, H. and Kierfeld, J.
    European Physical Journal E 44 (2021)
    We present a theory for the self-propulsion of symmetric, half-spherical Marangoni boats (soap or camphor boats) at low Reynolds numbers. Propulsion is generated by release (diffusive emission or dissolution) of water-soluble surfactant molecules, which modulate the air–water interfacial tension. Propulsion either requires asymmetric release or spontaneous symmetry breaking by coupling to advection for a perfectly symmetrical swimmer. We study the diffusion–advection problem for a sphere in Stokes flow analytically and numerically both for constant concentration and constant flux boundary conditions. We derive novel results for concentration profiles under constant flux boundary conditions and for the Nusselt number (the dimensionless ratio of total emitted flux and diffusive flux). Based on these results, we analyze the Marangoni boat for small Marangoni propulsion (low Peclet number) and show that two swimming regimes exist, a diffusive regime at low velocities and an advection-dominated regime at high swimmer velocities. We describe both the limit of large Marangoni propulsion (high Peclet number) and the effects from evaporation by approximative analytical theories. The swimming velocity is determined by force balance, and we obtain a general expression for the Marangoni forces, which comprises both direct Marangoni forces from the surface tension gradient along the air–water–swimmer contact line and Marangoni flow forces. We unravel whether the Marangoni flow contribution is exerting a forward or backward force during propulsion. Our main result is the relation between Peclet number and swimming velocity. Spontaneous symmetry breaking and, thus, swimming occur for a perfectly symmetrical swimmer above a critical Peclet number, which becomes small for large system sizes. We find a supercritical swimming bifurcation for a symmetric swimmer and an avoided bifurcation in the presence of an asymmetry. © 2021, The Author(s).
    view abstractdoi: 10.1140/epje/s10189-021-00034-9
  • 2021 • 1055 Twins – A weak link in the magnetic hardening of ThMn12-type permanent magnets
    Ener, S. and Skokov, K.P. and Palanisamy, D. and Devillers, T. and Fischbacher, J. and Eslava, G.G. and Maccari, F. and Schäfer, L. and Diop, L.V.B. and Radulov, I. and Gault, B. and Hrkac, G. and Dempsey, N.M. and Schrefl, T. an...
    Acta Materialia 214 (2021)
    Nd2Fe14B-type materials exhibit the highest energy product around room temperature and hence dominate the high-performance permanent magnet market. Intensive research efforts aim at alternative material systems containing less critical elements with similar or better magnetic properties. Nd- and Sm-based compounds with a ThMn12-type structure exhibit intrinsic properties comparable or even superior to Nd2Fe14B. However, it has not been possible to achieve technically relevant coercivity and remanent magnetization in ThMn12-based bulk sintered magnets. Using SmFe11Ti as a prototypical representative, we demonstrate that one important reason for the poor performance is the formation of twins inside micro-crystalline grains. The nature of the twins in SmFe11Ti was investigated in twinned “single crystals” and both bulk and thin film poly-crystalline samples, using advanced electron microscopy and atom probe tomography as well as simulations and compared with benchmark Nd2Fe14B. Both micro-twins and nano-twins show a twin orientation of 57±2° and an enrichment in Sm, which could affect domain wall motion in this material. Micromagnetic simulations indicate that twins act as nucleation centers, representing the magnetically weakest link in the microstructure. The relation between twin formation energies and geometrical features are briefly discussed using molecular dynamic simulations. © 2021
    view abstractdoi: 10.1016/j.actamat.2021.116968
  • 2021 • 1054 Trust and stock market volatility during the COVID-19 crisis
    Engelhardt, N. and Krause, M. and Neukirchen, D. and Posch, P.N.
    Finance Research Letters 38 (2021)
    We investigate if trust affects global stock market volatility during the COVID-19 pandemic. Using a sample of 47 national stock markets, we find the stock markets’ volatility to be significantly lower in high-trust countries (in reaction to COVID-19 case announcements). Both trust in fellow citizens as well as in the countries’ governments are of significant importance. © 2020 Elsevier Inc.
    view abstractdoi: 10.1016/
  • 2021 • 1053 Esg ratings and stock performance during the covid-19 crisis
    Engelhardt, N. and Ekkenga, J. and Posch, P.
    Sustainability (Switzerland) 13 (2021)
    We investigate the association between Environmental, Social, and Governance (ESG) ratings and stock performance during the COVID-19 crisis. Although there is mixed evidence in the literature whether ESG is valuable in times of crisis, we find high ESG-rated European firms to be associated with higher abnormal returns and lower stock volatility. After decomposing ESG into its separate components, we find the social score to be the predominant driver of our results. Further, we argue that ESG is value-enhancing in low-trust countries, and in countries with poorer security regulations and where lower disclosure standards prevail. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/su13137133
  • 2021 • 1052 A-posteriori LES assessment of subgrid-scale closures for bounded passive scalars
    Engelmann, L. and Klein, M. and Kempf, A.M.
    Computers and Fluids 218 (2021)
    Scale similarity or gradient models represent attractive, functionally simple expressions for large eddy simulation (LES) subgridscale (SGS) models, showing excellent behaviour in a-priori LES studies for small to moderate filter sizes. However, when applied a-posteriori to real LES calculations, they frequently suffer from numerically unstable behavior. A recent regularization approach revealed promising results for both wall-bounded and free turbulent flows. One attractive feature of this modelling strategy is that it can potentially be applied in many different contexts, such as momentum transport in single or two phase flows, different fluids such as non-Newtonian fluids, etc. The aim of the present study is to test the application of this regularisation technique to turbulent transport of bounded passive scalars. The performance of the model together with suitable discretization strategies will be assessed for turbulent plane free jet simulations. LES results will be benchmarked against DNS calculations of the same configuration obtained with the same code. The new model exhibits good results for momentum and scalar transport, outperforming standard eddy-viscosity models particularly with respect to the prediction of second order moments. Further, they provide good stability and are easy to implement. While the influence of the SGS model for scalar transport is not negligible, it is shown that an appropriate momentum SGS-closure is likely to be more important. © 2021
    view abstractdoi: 10.1016/j.compfluid.2021.104840
  • 2021 • 1051 Towards the Suitability of Information Entropy as an LES Quality Indicator
    Engelmann, L. and Ihme, M. and Wlokas, I. and Kempf, A.
    Flow, Turbulence and Combustion (2021)
    The Shannon entropy is a rigorous measure to evaluate the complexity in dynamical systems. Shannon entropy can be directly calculated from any set of experimental or numerical data and yields the uncertainty of a given dataset. Originating from information theory, the concept can be generalized from assessing the uncertainty in a message to any dynamical system. Following the concept of ergodicity, turbulence forms another class of dynamical systems, which is generally assessed using statistical measures. The quantification of resolution quality is a crucial aspect in assessing turbulent-flow simulations. While a vast variety of statistical measures for the evaluation of resolution is available, measures closer representing the dynamics of a turbulent systems, such as the Wasserstein metric or the Ljapunov exponent become popular. This study investigates how the Shannon entropy can lead to useful insights in the quality of turbulent-flow simulations. The Shannon entropy is calculated based on distributions, which enables the direct evaluation from unsteady flow simulations or by post-processing. A turbulent channel flow and a planar turbulent jet are used as validation tests. The Shannon entropy is calculated for turbulent velocity- and scalar-fields and correlations with physical quantities, such as turbulent kinetic energy and passive scalars, are investigated. It is shown that the spatial structure of the Shannon entropy can be related to flow phenomena. This is illustrated by the investigation of the entropy of the velocity fluctuations, passive scalars and turbulent kinetic energy. Grid studies reveal the Shannon entropy as a converging measure. It is demonstrated, that classical turbulent-kinetic-energy-based quality measures struggle with the identification of insufficient resolution, while the Shannon entropy has demonstrated potential to form a solid basis for LES quality assessment. © 2021, The Author(s).
    view abstractdoi: 10.1007/s10494-021-00277-8
  • 2021 • 1050 Refinement and Experimental Validation of a Vacancy Model of Pore Annihilation in Single-Crystal Nickel-Base Superalloys during Hot Isostatic Pressing
    Epishin, A. and Camin, B. and Hansen, L. and Heuser, M. and Lopez-Galilea, I. and Ruttert, B. and Theisen, W. and Fedelich, B.
    Advanced Engineering Materials 23 (2021)
    Initially, as-cast and homogenized single crystals of nickel-base superalloy CMSX-4 are subjected to hot isostatic pressing at 1288 °C. Two series of experiments are conducted: under the same pressure of 103 MPa but with different durations, between 0.5 and 6 h, and under different pressures, between 15 and 150 MPa, but for the same time of 0.5 h. The porosity annihilation is investigated metallographically and by high-resolution synchrotron X-ray tomography. The obtained experimental results are compared with the predictions of the vacancy model proposed recently in the group. Herein, the model is further refined by coupling with X-ray tomography. The model describes the evolution of the pore arrays enclosed in the 3D synchrotron tomograms during hot isostatic pressing and properly predicts the time and stress dependences of the pore annihilation kinetics. The validated model and the obtained experimental results are used for selecting the optimal technological parameters such as applied pressure and processing time. © 2021 The Authors. Advanced Engineering Materials published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/adem.202100211
  • 2021 • 1049 Site-specific facet protection of gold nanoparticles inside a 3D DNA origami box: a tool for molecular plasmonics
    Erkelenz, M. and Kosinski, R. and Sritharan, O. and Giesler, H. and Saccà, B. and Schlücker, S.
    Chemical Communications 57 3151-3153 (2021)
    Bare gold nanocubes and nanospheres with different sizes are incorporated into a rationally designed 3D DNA origami box. The encaged particles expose a gold surface accessible for subsequent site-specific functionalization, for example, for applications in molecular plasmonics such as SERS or SEF. © The Royal Society of Chemistry 2021.
    view abstractdoi: 10.1039/d0cc07712g
  • 2021 • 1048 Angular dependence of Hall effect and magnetoresistance in SrRuO3- SrIrO3 heterostructures
    Esser, S. and Wu, J. and Esser, S. and Gruhl, R. and Jesche, A. and Roddatis, V. and Moshnyaga, V. and Pentcheva, R. and Gegenwart, P.
    Physical Review B 103 (2021)
    The perovskite SrRuO3 is a prototypical itinerant ferromagnet which allows interface engineering of its electronic and magnetic properties. We report the synthesis and investigation of atomically flat artificial multilayers of SrRuO3 with the spin-orbit semimetal SrIrO3 in combination with band-structure calculations with a Hubbard U term and topological analysis. The latter reveal an electronic reconstruction and emergence of flat Ru-4dxz bands near the interface, ferromagnetic interlayer coupling, and a negative Berry-curvature contribution to the anomalous Hall effect. We analyze the Hall effect and magnetoresistance measurements as a function of the field angle from an out-of-plane towards an in-plane orientation (either parallel or perpendicular to the current direction) by a two-channel model. The magnetic easy direction is tilted by about 20∘ from the sample normal for low magnetic fields, rotating towards the out-of-plane direction by increasing fields. Fully strained epitaxial growth enables a strong anisotropy of magnetoresistance. An additional Hall effect contribution, not accounted for by the two-channel model, is compatible with stable skyrmions only up to a critical angle of roughly 45∘ from the sample normal. Within about 20∘ from the thin film plane an additional peaklike contribution to the Hall effect suggests the formation of a nontrivial spin structure. © 2021 American Physical Society.
    view abstractdoi: 10.1103/PhysRevB.103.214430
  • 2021 • 1047 Elucidation of mass transfer mechanisms in pellet formation by spheronization
    Evers, M. and Mattusch, A. and Weis, D. and Garcia, E. and Antonyuk, S. and Thommes, M.
    European Journal of Pharmaceutics and Biopharmaceutics 160 92-99 (2021)
    Previously published mechanisms of pellet formation during extrusion-spheronization include a transfer of material between different granules. This research aimed to specify the origin of this transfered mass, enabling further insight into the extrusion-spheronization process. Granules of various diameters were rounded simultaniously in a spheronizer to ascertain if mass transfer between smaller and larger granules is truly in balance, or if mass transfer from smaller to larger granules is preferred. Granules were also marked with a fluorescent tracer to enable quantification of mass transfer. By using differently sized and shaped granules as starting material, different modes of mass transfer were investigated. Samples were taken after various process durations to investigate the kinetics of the tranfer mechanism. It was found that both small and large granules dispense and receive mass during spheronization. In general, small granules increase their size, while large granules maintain their size or show a slight size decrease, resulting in the particularly narrow monomodal size distribution. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.ejpb.2021.01.013
  • 2021 • 1046 Suppression of nuclear spin fluctuations in an InGaAs quantum dot ensemble by GHz-pulsed optical excitation
    Evers, E. and Kopteva, N.E. and Yugova, I.A. and Yakovlev, D.R. and Reuter, D. and Wieck, A.D. and Bayer, M. and Greilich, A.
    npj Quantum Information 7 (2021)
    The coherent electron spin dynamics of an ensemble of singly charged (In,Ga)As/GaAs quantum dots in a transverse magnetic field is driven by periodic optical excitation at 1 GHz repetition frequency. Despite the strong inhomogeneity of the electron g factor, the spectral spread of optical transitions, and the broad distribution of nuclear spin fluctuations, we are able to push the whole ensemble of excited spins into a single Larmor precession mode that is commensurate with the laser repetition frequency. Furthermore, we demonstrate that an optical detuning of the pump pulses from the probed optical transitions induces a directed dynamic nuclear polarization and leads to a discretization of the total magnetic field acting on the electron ensemble. Finally, we show that the highly periodic optical excitation can be used as universal tool for strongly reducing the nuclear spin fluctuations and preparation of a robust nuclear environment for subsequent manipulation of the electron spins, also at varying operation frequencies. © 2021, The Author(s).
    view abstractdoi: 10.1038/s41534-021-00395-1
  • 2021 • 1045 Shielding of external magnetic field by dynamic nuclear polarization in (In,Ga)As quantum dots
    Evers, E. and Kopteva, N.E. and Yugova, I.A. and Yakovlev, D.R. and Bayer, M. and Greilich, A.
    Physical Review B 104 (2021)
    The dynamics of the coupled electron-nuclear spin system is studied in an ensemble of singly charged (In,Ga)As/GaAs quantum dots (QDs) using periodic optical excitation at 1 GHz repetition rate. In combination with the electron-nuclei interaction, the highly repetitive excitation allows us to lock the electron spins into magnetic resonance in a transverse external magnetic field. Sweeping the field to higher values, the locking leads to an effective "diamagnetic"response of significant strength due to dynamic nuclear polarization, which shields the QD electrons at least partly from the external field and can even keep the internal magnetic field constant up to 1.3 T field variation. We model the effect through a magnetic field-dependent polarization rate of the nuclei, from which we suggest a strategy for adjusting the nuclear polarization through the detuning between optical excitation and electronic transition, in addition to tuning the magnetic field. © 2021 American Physical Society.
    view abstractdoi: 10.1103/PhysRevB.104.075302
  • 2021 • 1044 Identification of Active Sites in the Catalytic Oxidation of 2-Propanol over Co1+xFe2–xO4 Spinel Oxides at Solid/Liquid and Solid/Gas Interfaces
    Falk, T. and Budiyanto, E. and Dreyer, M. and Pflieger, C. and Waffel, D. and Büker, J. and Weidenthaler, C. and Ortega, K.F. and Behrens, M. and Tüysüz, H. and Muhler, M. and Peng, B.
    ChemCatChem 13 2942-2951 (2021)
    A series of Co1+xFe2–xO4 (0≤x≤2) spinel nanowires was synthesized by nanocasting using SBA-15 silica as hard template, which was characterized by X-ray powder diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy. The Co1+xFe2–xO4 spinels were applied in the aerobic oxidation of aqueous 2-propanol solutions to systematically study the influence of exposed Co and Fe cations on the catalytic properties. The activity of the catalysts was found to depend strongly on the Co content, showing an exponential increase of the reaction rate with increasing Co content. Ensembles of Co3+cus (coordinatively unsaturated) sites were identified as the active sites for selective 2-propanol oxidation, which are assumed to consist of more than six Co ions. In addition, gas-phase oxidation with and without water vapor co-feeding was performed to achieve a comparison with liquid-phase oxidation kinetics. An apparent activation energy of 94 kJ mol−1 was determined for 2-propanol oxidation over Co3O4 in the liquid phase, which is in good agreement with the gas-phase oxidation in the presence of water vapor. In contrast to gas-phase conditions, the catalysts showed high stability and reusability in the aqueous phase with constant conversion in three consecutive runs. © 2021 The Authors. ChemCatChem published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/cctc.202100352
  • 2021 • 1043 Wavelet neural network modeling for the retention efficiency of sub-15 nm nanoparticles in ultrafiltration under small particle to pore diameter ratio
    Fan, Z. and Ji, P.-P. and Zhang, J. and Segets, D. and Chen, D.-R. and Chen, S.-C.
    Journal of Membrane Science 635 (2021)
    Ultrafiltration (UF) using membranes with a small ratio of particle to pore diameter (PPD) would be very desirable for energy saving. The nanoparticle (NP) retention efficiency of membranes with a small PPD ratio depends on various physical and chemical properties of NPs, membranes and solutions as well as the filtration conditions. Until now, no simple model is available for the calculation of NP retention efficiency in UF membranes, besides, it is unlikely to conduct experiments covering all conditions for obtaining the efficiency. The artificial neural network (ANN) has been attracting much attention for studying the performance of a highly nonlinear system. In this study, a wavelet ANN model was developed to predict the NP retentions in membranes for the dead-ended UFs under different conditions. A total of 13 parameters, including the membrane features, particle properties, water solution characteristics, operating conditions, etc., are considered as ANN inputs and the NP retention efficiency as the output. A total of 200 datasets with high quality from literature were selected, in which 50% were for the model training, 30% for the model validation and the remaining 20% for the model testing. A high correlation between the output and inputs was obtained and the significance of the 13 parameters on the NP retention was ranked. A case study was performed to further validate the trained ANN model in the prediction of the retention efficiency of 10 nm gold NPs in a 50 nm pore sized polycarbonate track etched (PCTE) membrane at different pH conditions (5–9). Focusing on the variation of pH, an excellent agreement between the model prediction and the calculation by the modified extended Derjaguin Landau Verwey Overbeek-Maxwell (MEDLVO-Maxwell) model originating from classical and extended DLVO theory was obtained. The interaction energy in the MEDLVO-Maxwell model was based on the separation distance calculated by a quench molecular dynamics (MD) simulation. This study illustrates and validates the application of ANN modeling on the NP retention efficiency prediction in the UF with small PPD ratios. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.memsci.2021.119503
  • 2021 • 1042 Author Correction: Strain rate dependency of dislocation plasticity (Nature Communications, (2021), 12, 1, (1845), 10.1038/s41467-021-21939-1)
    Fan, H. and Wang, Q. and El-Awady, J.A. and Raabe, D. and Zaiser, M.
    Nature Communications 12 (2021)
    The original version of this Article contained an error in Figs. 3 and 8. In the original version of Fig. 3, the references reported in panels a and c are not correct. © 2021, The Author(s).
    view abstractdoi: 10.1038/s41467-021-22963-x
  • 2021 • 1041 Strain rate dependency of dislocation plasticity
    Fan, H. and Wang, Q. and El-Awady, J.A. and Raabe, D. and Zaiser, M.
    Nature Communications 12 (2021)
    Dislocation glide is a general deformation mode, governing the strength of metals. Via discrete dislocation dynamics and molecular dynamics simulations, we investigate the strain rate and dislocation density dependence of the strength of bulk copper and aluminum single crystals. An analytical relationship between material strength, dislocation density, strain rate and dislocation mobility is proposed, which agrees well with current simulations and published experiments. Results show that material strength displays a decreasing regime (strain rate hardening) and then increasing regime (classical forest hardening) as the dislocation density increases. Accordingly, the strength displays universally, as the strain rate increases, a strain rate-independent regime followed by a strain rate hardening regime. All results are captured by a single scaling function, which relates the scaled strength to a coupling parameter between dislocation density and strain rate. Such coupling parameter also controls the localization of plasticity, fluctuations of dislocation flow and distribution of dislocation velocity. © 2021, The Author(s).
    view abstractdoi: 10.1038/s41467-021-21939-1
  • 2021 • 1040 Nanoindentation pop-in in oxides at room temperature: Dislocation activation or crack formation?
    Fang, X. and Bishara, H. and Ding, K. and Tsybenko, H. and Porz, L. and Höfling, M. and Bruder, E. and Li, Y. and Dehm, G. and Durst, K.
    Journal of the American Ceramic Society (2021)
    Most oxide ceramics are known to be brittle macroscopically at room temperature with little or no dislocation-based plasticity prior to crack propagation. Here, we demonstrate the size-dependent brittle to ductile transition in SrTiO3 at room temperature using nanoindentation pop-in events visible as a sudden increase in displacement at nominally constant load. We identify that the indentation pop-in event in SrTiO3 at room temperature, below a critical indenter tip radius, is dominated by dislocation-mediated plasticity. When the tip radius increases to a critical size, concurrent dislocation activation and crack formation, with the latter being the dominating process, occur during the pop-in event. Beyond the experimental examination and theoretical justification presented on SrTiO3 as a model system, further validation on α-Al2O3, BaTiO3, and TiO2 are briefly presented and discussed. A new indentation size effect, mainly for brittle ceramics, is suggested by the competition between the dislocation-based plasticity and crack formation at small scale. Our finding complements the deformation mechanism in the nano-/microscale deformation regime involving plasticity and cracking in ceramics at room temperature to pave the road for dislocation-based mechanics and functionalities study in these materials. © 2021 The Authors. Journal of the American Ceramic Society published by Wiley Periodicals LLC on behalf of American Ceramic Society (ACERS)
    view abstractdoi: 10.1111/jace.17806
  • 2021 • 1039 Forward: Information modelling of tunnelling and underground infrastructure: Technology and applications
    Fang, Y. and Ninic, J. and Meschke, G. and König, M. and Zhang, Q.
    Tunnelling and Underground Space Technology 116 (2021)
    doi: 10.1016/j.tust.2021.104067
  • 2021 • 1038 Photodegradation of Triple-Cation Perovskite Solar Cells: The Role of Spectrum and Bias Conditions
    Farooq, A. and Khan, M.R. and Abzieher, T. and Voigt, A. and Lupascu, D.C. and Lemmer, U. and Richards, B.S. and Paetzold, U.W.
    ACS Applied Energy Materials 4 3083-3092 (2021)
    Despite promising power conversion efficiencies, a key barrier for the future commercialization of perovskite-based solar cells (PSCs) is their lack of stability when exposed to sunlight for extended periods. This work investigates the phenomenon of light-induced degradation in triple-cation PSCs held at a constant voltage near the maximum power point and exposed to different regions of the solar spectrum. This light-induced degradation is expected to exhibit a strong wavelength dependence with a significant performance deterioration caused by high-energy photons. The challenging wavelengths are found to span over the range 300-500 nm, while longer wavelength light is found to be the least harmful for a mixed-cation perovskite composition when tested for a period of 250 h. The analyses of perovskite layers undergoing light-induced degradation indicate that the performance deterioration is directly linked to the decomposition of the perovskite absorber into lead iodide. The decomposition occurring in the bulk of the absorber material generates trap states with activation energies of 0.26 and 0.42 eV, determined using thermally stimulated current measurements. Apart from the spectral dependence of the degradation, bias conditions-such as open-circuit, short-circuit, or maximum power point-are found to have pronounced effects on light stability. These findings allow identifying strategies to improve the lifetime of PSCs. © 2021 The Authors. Published by American Chemical Society.
    view abstractdoi: 10.1021/acsaem.0c02813
  • 2021 • 1037 Future perspectives on in-vitro diagnosis of drug allergy by the lymphocyte transformation test
    Fatangare, A. and Glässner, A. and Sachs, B. and Sickmann, A.
    Journal of Immunological Methods 495 (2021)
    This article aims to envisage future perspectives of the lymphocyte transformation test (LTT). We describe the select innovative techniques, which can be integrated at different stages of the LTT to potentially improve the sensitivity, specificity, or practicability of the LTT. We first focus upon the cell sorting techniques comprising immunomagnetic cell separation and flow cytometry, which can be implemented prior and after the LTT culturing step to concentrate and quantify specific immune cell types. Further, we elaborate upon three important omics techniques such as transcriptomics, proteomics, and metabolomics, which can be integrated downstream of the LTT to analyze molecular changes in specific immune cells following drug induced activation and proliferation. We also develop visions, how state of the art techniques used in other scientific fields, can be transferred and applied in the context of in-vitro detection of drug allergy. © 2021
    view abstractdoi: 10.1016/j.jim.2021.113072
  • 2021 • 1036 Does needle design affect the regenerative potential of bone marrow aspirate? An in vitro study
    Feddahi, N. and Herten, M. and Tassemeier, T. and Rekasi, H. and Hackel, A. and Haversath, M. and Jäger, M.
    Life 11 (2021)
    While autologous bone is still the gold standard for treatment of bone defects, its availability is limited. Sufficient numbers of mesenchymal stroma cells (MSC) may be an alternative. Small volumes of bone marrow aspirate (BMA) were harvested with two different needle systems comparing the yield and regenerative potency of the MSCs. BMA (10 mL) was aspirated from the posterior iliac crest of 12 patients with degenerative spinal disc disease using both needle systems in each patient: the Jamshidi needle (JAM) and on the contralateral side the Marrow Cellution® Needle (AMC). Number of mononuclear cells (MNCs) and regeneration capacity (colony-forming unit/CFU) were determined. MSCs were characterized for surface markers and their differentiation into trilineages. There was no significant difference between the two harvesting needles regarding the quantity of MNCs in BMA: 5.2 ± 1.8 × 109 MNC/mL for AMC vs. 4.8 ± 2.5 × 109 MNC/mL for JAM, p = 0.182. The quantity of CFUs per ml BMA was similar for both groups: 3717 ± 5556 for AMC and 4305 ± 5507 for JAM (p = 0.695). The potency of MSCs expressed as colony-forming potential per 106 MNC resulted in 0.98 ± 1.51 for AMC and 1.00 ± 0.96 for JAM (p = 0.666). Regardless of the needle design, 10 mL bone marrow aspirate contains a sufficient number of about 40,000 MSCs that can be used to enhance bone healing. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/life11080748
  • 2021 • 1035 Spatially resolved GHz magnetization dynamics of a magnetite nano-particle chain inside a magnetotactic bacterium
    Feggeler, T. and Meckenstock, R. and Spoddig, D. and Zingsem, B.W. and Ohldag, H. and Wende, H. and Farle, M. and Winklhofer, M. and Ollefs, K.J.
    Physical Review Research 3 (2021)
    Understanding magnonic properties of nonperiodic magnetic nanostructures requires real-space imaging of ferromagnetic resonance modes with spatial resolution well below the optical diffraction limit and sampling rates in the 5-100 GHz range. Here, we demonstrate element-specific scanning transmission x-ray microscopy-detected ferromagnetic resonance (STXM-FMR) applied to a chain of dipolarly coupled nano-particles (40-50 nm particle size) inside a single cell of a magnetotactic bacterium Magnetospirillum magnetotacticum. The ferromagnetic resonance mode of the nano-particle chain driven at 6.748 GHz and probed with 50 nm x-ray focus size was found to have a uniform phase response but non-uniform amplitude response along the chain segments due to the superposition of dipolar coupled modes of chain segments and individual particles, in agreement with micromagnetic simulations. © 2021 Published by the American Physical Society
    view abstractdoi: 10.1103/PhysRevResearch.3.033036
  • 2021 • 1034 Ammonia Synthesis and Mechanochemistry
    Felderhoff, M.
    Joule 5 297-299 (2021)
    Ammonia synthesis is one of the world's largest chemical processes and therefore also one of the world's largest CO2 emitters. New developments that operate under milder reaction conditions and environmentally friendly methods for supplying the feedstock for ammonia can significantly reduce these emissions. Mechanochemical processes have been in the focus of chemist for several years. Consequently, mechanochemical processes for the synthesis of ammonia are under development. © 2021 Elsevier Inc. Ammonia synthesis is one of the world's largest chemical processes and therefore also one of the world's largest CO2 emitters. New developments that operate under milder reaction conditions and environmentally friendly methods for supplying the feedstock for ammonia can significantly reduce these emissions. Mechanochemical processes have been in the focus of chemist for several years. Consequently, mechanochemical processes for the synthesis of ammonia are under development. © 2021 Elsevier Inc.
    view abstractdoi: 10.1016/j.joule.2021.01.009
  • 2021 • 1033 Adapted Process Strategies in Front Face Flow Drilling and Thread Forming of Lightweight Casting Materials
    Felinks, N. and Overberg, T. and Sarafraz, Y. and Walther, F. and Biermann, D.
    Procedia CIRP 103 213-218 (2021)
    By using modern technologies to produce detachable joints in lightweight components, it is possible to reduce material consumption and manufacturing times. By front face flow drilling of lightweight cast materials, expanded bore walls are formed into thin-walled profiles, which are used as core holes for internal threads. The flow drilling process has to be adapted to the specific properties of the regarded materials AZ91 and AlSi10Mg. Thus, enhanced adjustments make it possible to increase the bore qualities significantly. Particularly in order to improve the roundness of the holes, the influence of decreased feed rates on the shape of the flow-drilled holes is analysed. Furthermore, this paper deals with the influence of the process temperature during flow drilling. By varying the predrilling diameter as well as the peripheral speed, the friction between the tool and the workpiece can be significantly influenced. This directly affects the thermally induced formability of the lightweight alloys. In order to produce high strength threads, cold forming is used instead of conventional tapping. In particular, in the context of the adapted flow drilling strategies, the surface qualities and the threads profiles are investigated in detail. Finally, continuous load increase tests were conducted to evaluate the fatigue properties of the formed internal threads using various strategies. © 2021 The Authors. Published by Elsevier B.V.
    view abstractdoi: 10.1016/j.procir.2021.10.034
  • 2021 • 1032 Investigation into deep hole drilling of austenitic steel with advanced tool solutions
    Felinks, N. and Rinschede, T. and Biermann, D. and Stangier, D. and Tillmann, W. and Fuß, M. and Abrahams, H.
    International Journal of Advanced Manufacturing Technology (2021)
    Deep hole drilling processes for high-alloyed materials are characterised by worn guide pads and chatter vibrations. In order to increase feed rates, process stability and bore quality in STS deep hole drilling, various investigations were carried out with adjustments to the tool. First, a new process chain for the production of tribologically optimised guide pads and their effects on the guide pad shape is described in detail. The results of these studies show that the shape change in the area of the axial run-in chamfer through a micro finishing process leads to a better bore hole quality. Furthermore, the influence of guide pad coating and cooling lubricant on the deep hole drilling process was investigated. In addition, the machining of the austenitic steel AISI 304 is analysed by using a conventional steel boring bar and an innovative carbon fibre reinforced plastic (CFRP)-boring bar. While the conventional drill tube oscillates with different eigenfrequencies, the CFRP-boring bar damps chatter vibrations of the drill head and stabilises the process. Even at higher feed rates up to f = 0.3 mm, it is possible to machine austenitic, difficult-to-cut-materials with significantly reduced vibrations. © 2021, The Author(s).
    view abstractdoi: 10.1007/s00170-021-07989-1
  • 2021 • 1031 Capsules from synthetic diblock-peptides as potential artificial oxygen carriers
    Feng, H. and Linders, J. and Myszkowska, S. and Mayer, C.
    Journal of Microencapsulation 38 276-284 (2021)
    The design of an encapsulation system consisting of a synthetic peptide which is fully biodegradable into non-toxic constituents. This system should be capable of encapsulating perfluorinated hydrocarbons and should be a promising basis for oxygen carriers to be used as artificial blood replacement. A diblock-peptide is synthesised following a phosgene-free method and characterised by 1H-NMR. Subsequently, this diblock-peptide is self-assembled with perfluorodecalin (PFD) to form PFD-filled capsules as potential artificial oxygen carriers allowing for rapid oxygen uptake and release. The diblock-peptide Bu-PAsp10-PPhe10 is successfully synthesised and used to encapsulate PFD. The capsules have a spherical shape with an average diameter of 360 nm in stable aqueous dispersion. NMR measurements prove their physical capability for reversible uptake and release of oxygen. The resulting capsules are expected to be fully biodegradable and possibly could act as oxygen carriers for artificial blood replacement. © 2021 Informa UK Limited, trading as Taylor & Francis Group.
    view abstractdoi: 10.1080/02652048.2021.1903594
  • 2021 • 1030 A semi-analytical method to simulate hydroelastic slamming of 2D structural sections by coupling Wagner theory with the finite element method
    Feng, S. and Zhang, G. and Moctar, O.E. and Sun, Z. and Zhang, Z.
    Ocean Engineering 240 (2021)
    A semi-analytical method based on coupling Wagner theory with the finite element method is applied to numerically simulate hydroelastic slamming of arbitrary symmetric 2D structural sections subject to a constant impact velocity or to free fall motion. The averaged elastic velocity method is adopted to consider the influence of the elastic response on the distribution of the slamming load. A coupled dynamic equation is established to govern the fluid-structural interaction. The nonlinear pressure term improves accuracy. To validate the method, numerically predicted structural deformations and the associated strains during impact for several wedge-shaped sections and a cylindrical shell are compared with published results. The results show that the averaged elastic velocity method is efficient in estimating the structure dynamics. The effect of the nonlinear pressure term on hydroelastic structural dynamics is parametrically studied by considering wedge sections with different deadrise angles and with the elastic bottom plating under different end constraints. This nonlinear pressure term ensures reliably predicted hydroelastic structural responses, especially for wedges of larger deadrise angles and smaller hydroelastic properties. The proposed method provides an efficient tool to estimate structural strength under slamming during the initial design stage of the marine or aerospace structure. © 2021 Elsevier Ltd
    view abstractdoi: 10.1016/j.oceaneng.2021.109998
  • 2021 • 1029 Design of refractory compositionally complex alloys with optimal mechanical properties
    Ferrari, A. and Lysogorskiy, Y. and Drautz, R.
    Physical Review Materials 5 (2021)
    We use an analytical model to propose candidate compositionally complex alloys of the Mo-Nb-Ta-W family with optimal yield stress. We then introduce a computationally tractable method based on first-principles calculations to model phase equilibria in complex alloys at arbitrary concentrations. We utilize this method to predict the phase diagram at the optimized compositions and observe a tendency towards ordering for some of the proposed alloys. By combining yield stress data and thermodynamic equilibria, we suggest two alloy compositions with optimal mechanical properties and a strong solid solution forming ability for further experimental validation. © 2021 American Physical Society.
    view abstractdoi: 10.1103/PhysRevMaterials.5.063606
  • 2021 • 1028 Design and Characterization of a Screw Extrusion Hot-End for Fused Deposition Modeling
    Feuerbach, T. and Thommes, M.
    Molecules (Basel, Switzerland) 26 (2021)
    The filament is the most widespread feedstock material form used for fused deposition modeling printers. Filaments must be manufactured with tight dimensional tolerances, both to be processable in the hot-end and to obtain printed objects of high quality. The ability to successfully feed the filament into the printer is also related to the mechanical properties of the filament, which are often insufficient for pharmaceutically relevant excipients. In the scope of this work, an 8 mm single screw hot-end was designed and characterized, which allows direct printing of materials from their powder form and does not require an intermediate filament. The capability of the hot-end to increase the range of applicable excipients to fused deposition modeling was demonstrated by processing and printing several excipients that are not suitable for fused deposition modeling in their filament forms, such as ethylene vinyl acetate and poly(1-vinylpyrrolidone-co-vinyl acetate). The conveying characteristic of the screw was investigated experimentally with all materials and was in agreement with an established model from literature. The complete design information, such as the screw geometry and the hot-end dimensions, is provided in this work.
    view abstractdoi: 10.3390/molecules26030590
  • 2021 • 1027 Sensitivity of ultrasonic coda wave interferometry to material damage-observations from a virtual concrete lab
    Finger, C. and Saydak, L. and Vu, G. and Timothy, J.J. and Meschke, G. and Saenger, E.H.
    Materials 14 (2021)
    Ultrasonic measurements are used in civil engineering for structural health monitoring of concrete infrastructures. The late portion of the ultrasonic wavefield, the coda, is sensitive to small changes in the elastic moduli of the material. Coda Wave Interferometry (CWI) correlates these small changes in the coda with the wavefield recorded in intact, or unperturbed, concrete specimen to reveal the amount of velocity change that occurred. CWI has the potential to detect localized damages and global velocity reductions alike. In this study, the sensitivity of CWI to different types of concrete mesostructures and their damage levels is investigated numerically. Realistic numerical concrete models of concrete specimen are generated, and damage evolution is simulated using the discrete element method. In the virtual concrete lab, the simulated ultrasonic wavefield is propagated from one transducer using a realistic source signal and recorded at a second transducer. Different damage scenarios reveal a different slope in the decorrelation of waveforms with the observed reduction in velocities in the material. Finally, the impact and possible generalizations of the findings are discussed, and recommendations are given for a potential application of CWI in concrete at structural scale. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/ma14144033
  • 2021 • 1026 Room-temperature Fe:ZnSe laser tunable in the spectral range of 3.7–5.3 µm applied for intracavity absorption spectroscopy of CO2 isotopes, CO and N2O
    Fjodorow, P. and Frolov, M.P. and Korostelin, Y.V. and Kozlovsky, V.I. and Schulz, C. and Leonov, S.O. and Skasyrsky, Y.K.
    Optics Express 29 12033-12048 (2021)
    We demonstrate an intracavity absorption spectroscopy system based on a broadband single-crystal pulsed Fe:ZnSe laser. The laser operates at room-temperature and is continuously tunable in the spectral range of 3.76–5.29 µm. The long-wavelength emission up to 5.29 µm is a record achievement for Fe:ZnSe lasers, to the best of our knowledge. The developed laser system is applied for measurements of gaseous absorption inside the laser resonator. We demonstrate sensitive detection of (i) CO2 isotopes in the atmosphere and in human breath, (ii) CO in breath (after cigarette smoking) and in the smoke of a smoldering paper, and (iii) N2O in a gas flow. The achieved detection limits are: 0.1 ppm for 12CO2 and 13CO2, 3 ppm for CO, and 1 ppm for N2O. The sensitivity of the current system is primarily limited by the short pump-pulse duration of 40 ns. Possibilities for sensitivity enhancement by up to a factor of 107 are discussed. © 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
    view abstractdoi: 10.1364/OE.422926
  • 2021 • 1025 Impact of incorporated drugs on material properties of amorphous solid dispersions
    Flügel, K. and Schmidt, K. and Mareczek, L. and Gäbe, M. and Hennig, R. and Thommes, M.
    European Journal of Pharmaceutics and Biopharmaceutics 159 88-98 (2021)
    Formulation development of amorphous solid dispersions (ASD) still is challenging although several poorly water-soluble drugs have been marketed using this technique. During development of novel drugs, the selection of the preparation technique and polymer matrix is commonly performed for the certain drug via screening tools. However, if general trends regarding material properties are to be investigated, this approach is not beneficial, although often utilized in literature. The main component of the ASD usually is the polymer and thus it predominantly determines the material properties of the system. Therefore, to study the impact of different drugs and their drug loads on mechanical properties and wettability, three poorly soluble model drugs with drug loads ranging from 10% to 40% were incorporated into copovidone via hot-melt extrusion. The obtained extrudates were subsequently characterized regarding mechanical properties by applying diametral compression test and nanoindentation and the results were compared to the performance during tablet compression. Incorporation of all tested drugs resulted in a similar increase in brittleness of the ASDs, whereas the Young's modulus and hardness changed differently in dependence of the incorporated drug. These observations correlated well with the performance during tablet compression and it was concluded, that the brittleness seemed to be the predominant factor influencing the compression behavior of copovidone-based ASDs. Furthermore, the degree of water absorption and wettability was assessed by applying dynamic vapor sorption experiments and contact angle measurements. Here, the incorporated drugs impacted the contact angle to different degrees and a strong correlation between the contact angle and disintegration time was observable. These results highlight the importance of thorough characterization of the ASDs as it helps to predict their performance during tablet compression and thus facilitates the optimal selection of excipients. © 2020 Elsevier B.V.
    view abstractdoi: 10.1016/j.ejpb.2020.12.017
  • 2021 • 1024 A High-Pressure High-Temperature Column for the Simulation of Hydrothermal Water Circulation at Laboratory Scale
    Frank, S. and Zuber, P. and Pollak, S. and Heinze, T. and Schreuer, J. and Wohnlich, S.
    Geotechnical Testing Journal 44 (2021)
    Modeling the geothermal energy production cycle of a deep geothermal system at laboratory scale is challenging because of high-temperature and pressure conditions. In this work, a high-pressure high-temperature column to simulate production, heat transfer, and reinjection of a geothermal fluid in a fractured rock system is presented. The column includes two independently heated pressure vessels, a heat exchanger, and sensors for temperatures, pressures, flow rate, electric conductivity, and pH value of the circulating fluid at different locations. The presented column enables the quantitative analysis of coupled hydro-thermo-chemical processes in fractured rock cores close to in situ geothermal conditions. Heat extraction and reinjection of geothermal fluids into fractured reservoirs can be reproduced because of the possibility of heating and cooling of the circulating fluid. Further, it is possible to inject a second fluid phase into the column to investigate additional processes, such as mineral precipitation during reinjection. In this work, we present the experimental setup of the column and first results showing the capability of the system. © 2021 ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959.
    view abstractdoi: 10.1520/GTJ20200020
  • 2021 • 1023 Controlled growth of ordered monolayers of N-heterocyclic carbenes on silicon
    Franz, M. and Chandola, S. and Koy, M. and Zielinski, R. and Aldahhak, H. and Das, M. and Freitag, M. and Gerstmann, U. and Liebig, D. and Hoffmann, A.K. and Rosin, M. and Schmidt, W.G. and Hogan, C. and Glorius, F. and Esser, N. ...
    Nature Chemistry (2021)
    N-Heterocyclic carbenes (NHCs) are promising modifiers and anchors for surface functionalization and offer some advantages over thiol-based systems. Because of their strong binding affinity and high electron donation, NHCs can dramatically change the properties of the surfaces to which they are bonded. Highly ordered NHC monolayers have so far been limited to metal surfaces. Silicon, however, remains the element of choice in semiconductor devices and its modification is therefore of utmost importance for electronic industries. Here, a comprehensive study on the adsorption of NHCs on silicon is presented. We find covalently bound NHC molecules in an upright adsorption geometry and demonstrate the formation of highly ordered monolayers exhibiting good thermal stability and strong work function reductions. The structure and ordering of the monolayers is controlled by the substrate geometry and reactivity and in particular by the NHC side groups. These findings pave the way towards a tailor-made organic functionalization of silicon surfaces and, thanks to the high modularity of NHCs, new electronic and optoelectronic applications. [Figure not available: see fulltext.] © 2021, The Author(s), under exclusive licence to Springer Nature Limited.
    view abstractdoi: 10.1038/s41557-021-00721-2
  • 2021 • 1022 FibeR-CNN: Expanding Mask R-CNN to improve image-based fiber analysis
    Frei, M. and Kruis, F.E.
    Powder Technology 377 974-991 (2021)
    Fiber-shaped materials (e.g. carbon nano tubes) are of great relevance, due to their unique properties but also the health risk they can impose. Unfortunately, image-based analysis of fibers still involves manual annotation, which is a time-consuming and costly process. We therefore propose the use of region-based convolutional neural networks (R-CNNs) to automate this task. Mask R-CNN, the most widely used R-CNN for semantic segmentation tasks, is prone to errors when it comes to the analysis of fiber-shaped objects. Hence, a new architecture – FibeR-CNN – is introduced and validated. FibeR-CNN combines two established R-CNN architectures (Mask and Keypoint R-CNN) and adds additional network heads for the prediction of fiber widths and lengths. As a result, FibeR-CNN is able to surpass the mean average precision of Mask R-CNN by 33% (11 percentage points) on a novel test data set of fiber images. © 2020 Elsevier B.V.
    view abstractdoi: 10.1016/j.powtec.2020.08.034
  • 2021 • 1021 Virtualization of Process Engineering – Experimental Technology in Teaching [Virtualisierung verfahrenstechnischer Prozesse – Experimentiertechnik in der Lehre]
    Frerich, S.C.
    Chemie-Ingenieur-Technik (2021)
    In this article, junior professor Sulamith C. Frerich from the Ruhr University Bochum (RUB) introduces herself. She provides insight into current research issues and shows how she combines university tasks with non-university research. She reports from plastics characterization and processing as well as numerical simulation and process optimization. She gives two examples for application-oriented composite production from polymers and active ingredients and describes how she designs the transfer. In addition, she explains how online teaching works in process engineering. © 2021 The Authors. Chemie Ingenieur Technik published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/cite.202100169
  • 2021 • 1020 Nonlinear Bicolor Holography Using Plasmonic Metasurfaces
    Frese, D. and Wei, Q. and Wang, Y. and Cinchetti, M. and Huang, L. and Zentgraf, T.
    ACS Photonics 8 1013-1019 (2021)
    Nonlinear metasurface holography shows the great potential of metasurfaces to control the phase, amplitude, and polarization of light while simultaneously converting the frequency of the light. The possibility of tailoring the scattering properties of a coherent beam, as well as the scattering properties of nonlinear signals originating from the meta-atoms, facilitates a huge degree of freedom in beam shaping application. Recently, several approaches showed that virtual objects or any kind of optical information can be generated at a wavelength different from the laser input beam. Here, we demonstrate a single-layer nonlinear geometric-phase metasurface made of plasmonic nanostructures for a simultaneous second- and third-harmonic generation. Different from previous works, we demonstrate a two-color hologram with dissimilar types of nanostructures that generate the color information by different nonlinear optical processes. The amplitude ratio of both harmonic signals can be adapted depending on the nanostructures' resonance as well as the power and the wavelength of the incident laser beam. The two-color holographic image is reconstructed in the Fourier space at visible wavelengths with equal amplitudes using a single near-infrared wavelength. Nonlinear holography using multiple nonlinear processes simultaneously provides an alternative path to holographic color display applications, enhanced optical encryption schemes, and multiplexed optical data storage. © 2021 The Authors. Published by American Chemical Society.
    view abstractdoi: 10.1021/acsphotonics.1c00028
  • 2021 • 1019 Thermoplastic forming of additively manufactured Zr-based bulk metallic glass: A processing route for surface finishing of complex structures
    Frey, M. and Wegner, J. and Neuber, N. and Reiplinger, B. and Bochtler, B. and Adam, B. and Ruschel, L. and Riegler, S.S. and Jiang, H.-R. and Kleszczynski, S. and Witt, G. and Busch, R.
    Materials and Design 198 (2021)
    Additive manufacturing of bulk metallic glasses (BMGs) through laser powder bed fusion (LPBF) has drawn growing interest in the last years, especially concerning industry-relevant alloys based on iron or zirconium. The process-inherent high cooling rates and localized melting pools allow to overcome geometrical restrictions given for the production of BMGs by classical casting routes. Yet, the achievable surface qualities are still limited, making an adequate post-processing necessary. In this work, we report on applying thermoplastic forming on LPBF-formed parts for the first time to decrease surface roughness and imprint finely structured surface patterns without the need for complex abrasive machining. This BMG-specific post-processing approach allows to functionalize surface areas on highly complex LPBF-formed specimens, which could be of interest especially for medical or jewelry applications. © 2020 The Authors
    view abstractdoi: 10.1016/j.matdes.2020.109368
  • 2021 • 1018 Synergistic Effects of Co and Fe on the Oxygen Evolution Reaction Activity of LaCoxFe1−xO3
    Füngerlings, A. and Koul, A. and Dreyer, M. and Rabe, A. and Morales, D.M. and Schuhmann, W. and Behrens, M. and Pentcheva, R.
    Chemistry - A European Journal (2021)
    In a combined experimental and theoretical study we assess the role of Co incorporation on the OER activity of LaCoxFe1−xO3. Phase pure perovskites were synthesized up to (Formula presented.) in 0.025/0.050 steps. HAADF STEM and EDX analysis points towards FeO2-terminated (001)-facets in LaFeO3, in accordance with the stability diagram obtained from density functional theory calculations with a Hubbard U term (DFT+U). Linear sweep voltammetry conducted in a rotating disk electrode setup shows a reduction of the OER overpotential and a nonmonotonic trend with x, with double layer capacitance measurements indicating an intrinsic nature of activity. This is supported by DFT+U results that show reduced overpotentials for both Fe and Co reaction sites with the latter reaching values of 0.32–0.40 V, ∼0.3 V lower than for Fe. This correlates with a stronger reduction of the binding energy difference of the *O and *OH intermediates towards an optimum value of 1.6 eV for (Formula presented.), the OH deprotonation being the potential limiting step in most cases. Significant variations of the magnetic moments of both surface and subsurface Co and Fe during OER demonstrate that the beneficial effect is a result of a concerted action involving many surrounding ions, which extends the concept of the active site. © 2021 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/chem.202102829
  • 2021 • 1017 Distinguishing persistent effects in an undoped GaAs/AlGaAs quantum well by top-gate-dependent illumination
    Fujita, T. and Hayashi, R. and Kohda, M. and Ritzmann, J. and Ludwig, Ar. and Nitta, J. and Wieck, A.D. and Oiwa, A.
    Journal of Applied Physics 129 (2021)
    Persistent photoconductivity of GaAs/AlGaAs heterostructures has hampered the measurement of charge- and spin-related quantum effects in gate-defined quantum devices and integrated charge sensors due to Si-dopant-related deep donor levels (DX centers). In this study, this effect is overcome by using an undoped GaAs/AlGaAs heterostructure for photonic purposes. We also measure the electron transport before and after LED illumination at low temperatures. In addition to a regular rapid saturation showing the increased carrier density, a slow accumulation of illumination effects appeared when different top-gate voltages were applied during illumination, which indicated the redistribution of charge at the oxide-GaAs interface. This study provides interesting insights into the development of optically stable devices for efficient semiconductor quantum interfaces. © 2021 Author(s).
    view abstractdoi: 10.1063/5.0047558
  • 2021 • 1016 Characterization of a surface plasmon antenna fabricated on a gate-defined lateral quantum dot
    Fukai, R. and Sakai, Y. and Nakagawa, T. and Fujita, T. and Kiyama, H. and Ludwig, Ar. and Wieck, A.D. and Oiwa, A.
    Japanese Journal of Applied Physics 60 (2021)
    Quantum repeater composed of a quantum memory and an interface between photon qubits and memory qubits is indispensable for long-distance quantum communication. Gate-defined lateral quantum dots (QDs) can be a suitable platform for such quantum repeaters because of its aptitude for spin qubit and feasibility of quantum state transfer from photon polarization to electron spin. So far, the reported photoelectron excitation probabilities in such a QD are not high enough to implement practical repeater protocols. To improve the photoexcitation probability, we combine a surface plasmon antenna (SPA) with QDs. We fabricated a SPA designed to enhance the optical transmission to the QDs in a practical illumination setup in a refrigerator and characterized the fabricated antenna by measuring photocurrents at room temperature. © 2021 The Japan Society of Applied Physics
    view abstractdoi: 10.35848/1347-4065/abd533
  • 2021 • 1015 Stacking fault energy in relation to hydrogen environment embrittlement of metastable austenitic stainless crni‐steels
    Fussik, R. and Egels, G. and Theisen, W. and Weber, S.
    Metals 11 (2021)
    Metastable austenitic steels react to plastic deformation with a thermally and/or mechan-ically induced martensitic phase transformation. The martensitic transformation to α’‐martensite can take place directly or indirectly via the intermediate stage of ε‐martensite from the single‐phase austenite. This effect is influenced by the stacking fault energy (SFE) of austenitic steels. An SFE &lt; 20 mJ/m2 is known to promote indirect conversion, while an SFE &gt; 20 mJ/m2 promotes the direct conversion of austenite into α’‐martensite. This relationship has thus far not been considered in relation to the hydrogen environment embrittlement (HEE) of metastable austenitic CrNi steels. To gain new insights into HEE under consideration of the SFE and martensite formation of metastable CrNi steels, tensile tests were carried out in this study at room temperature in an air environment and in a hydrogen gas atmosphere with a pressure of p = 10 MPa. These tests were conducted on a conventionally produced alloy AISI 304L and a laboratory‐scale modification of this alloy. In terms of metal physics, the steels under consideration differed in the value of the experimentally deter-mined SFE. The SFE of the AISI 304L was 22.7 ± 0.8 mJ/m2 and the SFE of the 304 mod alloy was 18.7 ± 0.4 mJ/m2. The tensile specimens tested in air revealed a direct γ→α’ conversion for AISI 304L and an indirect γ→ε→α’ conversion for 304mod. From the results it could be deduced that the indirect phase transformation is responsible for a significant increase in the content of deformation‐induced α’‐martensite due to a reduction of the SFE value below 20 mJ/m2 in hydrogen gas atmosphere. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/met11081170
  • 2021 • 1014 Asymmetric Interplay Between K+ and Blocker and Atomistic Parameters From Physiological Experiments Quantify K+ Channel Blocker Release
    Gabriel, T.S. and Hansen, U.-P. and Urban, M. and Drexler, N. and Winterstein, T. and Rauh, O. and Thiel, G. and Kast, S.M. and Schroeder, I.
    Frontiers in Physiology 12 (2021)
    Modulating the activity of ion channels by blockers yields information on both the mode of drug action and on the biophysics of ion transport. Here we investigate the interplay between ions in the selectivity filter (SF) of K+ channels and the release kinetics of the blocker tetrapropylammonium in the model channel KcvNTS. A quantitative expression calculates blocker release rate constants directly from voltage-dependent ion occupation probabilities in the SF. The latter are obtained by a kinetic model of single-channel currents recorded in the absence of the blocker. The resulting model contains only two adjustable parameters of ion-blocker interaction and holds for both symmetric and asymmetric ionic conditions. This data-derived model is corroborated by 3D reference interaction site model (3D RISM) calculations on several model systems, which show that the K+ occupation probability is unaffected by the blocker, a direct consequence of the strength of the ion-carbonyl attraction in the SF, independent of the specific protein background. Hence, KcvNTS channel blocker release kinetics can be reduced to a small number of system-specific parameters. The pore-independent asymmetric interplay between K+ and blocker ions potentially allows for generalizing these results to similar potassium channels. Copyright © 2021 Gabriel, Hansen, Urban, Drexler, Winterstein, Rauh, Thiel, Kast and Schroeder.
    view abstractdoi: 10.3389/fphys.2021.737834
  • 2021 • 1013 Reducing cohesion of metal powders for additive manufacturing by nanoparticle dry-coating
    Gärtner, E. and Jung, H.Y. and Peter, N.J. and Dehm, G. and Jägle, E.A. and Uhlenwinkel, V. and Mädler, L.
    Powder Technology 379 585-595 (2021)
    Additive manufacturing processes, such as laser powder bed fusion, require steady powder processing but often exhibit poor flowability and low powder bed densities. Reducing the attractive Van-der-Waals force through nanoparticle coating can enhance initially poor flowability. We investigated the effect of dry-coating nanosized SiO2 on gas-atomized CoCrFeNi powders containing different amounts of particles &lt; 20 μm with respect to nanoparticle concentration and mixing time. The dynamic angle of repose of a 0–90 μm powder reduced 50% and bulk powder density increased 30% with nanoparticle concentrations up to 0.153 wt.-%. The granular Bond-number was correlated with the powder flowability and porosity. The effect of mixing time was investigated with mixing two fractions 20–90 μm and 0–90 μm at a constant nominal nanoparticle surface area coverage of 128% for 2 to 1440 min. Short mixing times improved the flowability, while extensive mixing resulted in nanoparticle reagglomeration and deteriorated flow. © 2020
    view abstractdoi: 10.1016/j.powtec.2020.10.065
  • 2021 • 1012 Experimental multi-scale approach to determine the local mechanical properties of foam base material in polyisocyanurate metal panels
    Gahlen, P. and Fröbel, S. and Karbach, A. and Gabriel, D. and Stommel, M.
    Polymer Testing 93 (2021)
    Polyisocyanurate (PIR) foams were examined regarding their local chemical composition using ATR-IR spectroscopy. As a special parameter the PIR: Amide III intensity ratio is to be mentioned, which represents the quantity of the formed PIR groups. Based on the local PIR: Amide III intensity ratio, the mechanical properties (Young's modulus) of the foam base material were analyzed at defined positions by AFM and Nanoindentation. It turned out that the AFM method is only suitable for qualitative analysis, because the values differ strongly from macroscopic measurements. For the measurements using nanoindentation, a new embedding method was developed, which achieves significantly more realistic and reproducible results compared to the embedding method used in the literature and shows a very good agreement with the macroscopic values. In general, it has been shown that a higher PIR: Amide III intensity ratio tends to lead to a higher Young's modulus. Nevertheless, there are other, currently unknown characteristic values which also influence the Young's modulus. © 2020 The Author(s)
    view abstractdoi: 10.1016/j.polymertesting.2020.106965
  • 2021 • 1011 Rheology based estimates of self- And collective diffusivities in viscous liquids
    Gainaru, C. and Ahlmann, S. and Röwekamp, L.S. and Moch, K. and Bierwirth, S.P. and Böhmer, R.
    Journal of Chemical Physics 155 (2021)
    The self-diffusion coefficient of viscous liquids is estimated on the basis of a simple analysis of their rheological shear spectra. To this end, the Almond-West approach, previously employed to access single-particle diffusivities in ionic conductors, is generalized for application to molecular dynamics in supercooled liquids. Rheology based estimates, presented for indomethacin, ortho-terphenyl, and trinaphthylbenzene, reveal relatively small, yet systematic differences when compared with diffusivity data directly measured for these highly viscous liquids. These deviations are discussed in terms of mechanical Haven ratios, introduced to quantify the magnitude of collective translational effects that have an impact on the viscous flow. © 2021 Author(s).
    view abstractdoi: 10.1063/5.0055811
  • 2021 • 1010 Impact of deep eutectic solvents and their constituents on the aqueous solubility of phloroglucinol dihydrate
    Gajardo-Parra, N.F. and Do, H.T. and Yang, M. and Pérez-Correa, J.R. and Garrido, J.M. and Sadowski, G. and Held, C. and Canales, R.I.
    Journal of Molecular Liquids 344 (2021)
    Phlorotannins are highly bioactive phenolic compounds mainly found in brown algae. Phloroglucinol is the basic unit from which phlorotannins polymerize. Deep eutectic solvents (DES) are potentially beneficial for increasing phenolics solubility, therefore good solvent candidates for phlorotannins extraction processes. Solubility measurements were performed for phloroglucinol in pure water and aqueous mixtures of DES or their constituents, i.e., different hydrogen bond donors (HBD) and choline chloride (ChCl). The stable crystal form of the phenolic in equilibrium was phloroglucinol dihydrate within the studied temperature range (293.15–313.15 K) and water weight fractions (≥0.25). The water + ChCl + HBD mixtures yielded higher solubility for phloroglucinol dihydrate than the corresponding water + HBD or water + ChCl mixtures. Solubility predicted with PC-SAFT was in quantitative agreement with the experimental data. The solubility behavior of phloroglucinol dihydrate in the different mixtures was related to the hydrogen bonds formed using molecular dynamics and PC-SAFT. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.molliq.2021.117932
  • 2021 • 1009 Parallel hybrid Monte Carlo / Molecular Statics for Simulation of Solute Segregation in Solids
    Ganesan, H. and Longsworth, M. and Sutmann, G.
    Journal of Physics: Conference Series 1740 (2021)
    A parallel hybrid Monte Carlo/molecular statics method is presented for studying segregation of interstitial atoms in the solid state. The method is based on the efficient use of virtual atoms as placeholders to find energetically favorable sites for interstitials in a distorted environment. MC trial moves perform an exchange between a randomly chosen virtual atom with a carbon atom followed by a short energy minimization via MS to relax the lattice distortion. The proposed hybrid method is capable of modeling solute segregation in deformed crystalline metallic materials with a moderate MC efficiency. To improve sampling efficiency, the scheme is extended towards a biased MC approach, which takes into account the history of successful trial moves in the system. Parallelization of the hybrid MC/MS method is achieved by a Manager-Worker model which applies a speculative execution of trial moves, which are asynchronously executed on the cores. The technique is applied to an Fe-C system including a dislocation as a symmetry breaking perturbation in the system. © Published under licence by IOP Publishing Ltd.
    view abstractdoi: 10.1088/1742-6596/1740/1/012001
  • 2021 • 1008 Manufacturing of W-steel joint using plasma sprayed graded W/steel-interlayer with current assisted diffusion bonding
    Ganesh, V. and Dorow-Gerspach, D. and Heuer, S. and Matejicek, J. and Vilemova, M. and Bram, M. and Coenen, J.W. and Wirtz, M. and Pintsuk, G. and Theisen, W. and Linsmeier, C.
    Fusion Engineering and Design 172 (2021)
    The differences in the thermophysical properties between tungsten and steel create thermal stress peaks at its interface when joined directly for the breeding blanket of a fusion reactor. In order to solve this problem, a graded interlayer made of several layers of W/steel-composites is considered to reduce these stress peaks. Plasma spraying under an argon shrouded chamber was employed as a cost efficient manufacturing technique for such composites and field assisted sintering technology/spark plasma sintering was used to diffusion bond them with bulk-W and bulk-steel. Firstly, thermophysical characterizations were performed on these composites. Secondly, two approaches have been investigated to join bulk-W and 75 vol% W composite: direct joining and using a vanadium foil. Only vanadium foil resulted in successful bond formation at all the three bonding temperatures of 800 °C, 900 °C and 1000 °C. Thirdly, investigation of diffusion bonding parameters (temperature and time) for the joining of 25 vol% W, 50 vol% W, 75 vol% W and bulk-steel were studied and optimum process parameter were identified. Finally, this optimized parameter (1000 °C; 30 min) was employed to manufacture a complete 12 mm x 12 mm W-steel joint consisting of this graded interlayer. © 2021
    view abstractdoi: 10.1016/j.fusengdes.2021.112896
  • 2021 • 1007 Homozygous WASHC4 variant in two sisters causes a syndromic phenotype defined by dysmorphisms, intellectual disability, profound developmental disorder, and skeletal muscle involvement
    Gangfuß, A. and Czech, A. and Hentschel, A. and Münchberg, U. and Horvath, R. and Töpf, A. and O'Heir, E. and Lochmüller, H. and Stehling, F. and Kiewert, C. and Sickmann, A. and Kuechler, A. and Kaiser, F.J. and Kölbel, H. a...
    Journal of Pathology (2021)
    Recessive variants in WASHC4 are linked to intellectual disability complicated by poor language skills, short stature, and dysmorphic features. The protein encoded by WASHC4 is part of the Wiskott–Aldrich syndrome protein and SCAR homolog family, co-localizes with actin in cells, and promotes Arp2/3-dependent actin polymerization in vitro. Functional studies in a zebrafish model suggested that WASHC4 knockdown may also affect skeletal muscles by perturbing protein clearance. However, skeletal muscle involvement has not been reported so far in patients, and precise biochemical studies allowing a deeper understanding of the molecular etiology of the disease are still lacking. Here, we report two siblings with a homozygous WASHC4 variant expanding the clinical spectrum of the disease and provide a phenotypical comparison with cases reported in the literature. Proteomic profiling of fibroblasts of the WASHC4-deficient patient revealed dysregulation of proteins relevant for the maintenance of the neuromuscular axis. Immunostaining on a muscle biopsy derived from the same patient confirmed dysregulation of proteins relevant for proper muscle function, thus highlighting an affliction of muscle cells upon loss of functional WASHC4. The results of histological and coherent anti-Stokes Raman scattering microscopic studies support the concept of a functional role of the WASHC4 protein in humans by altering protein processing and clearance. The proteomic analysis confirmed key molecular players in vitro and highlighted, for the first time, the involvement of skeletal muscle in patients. © 2021 The Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd. © 2021 The Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.
    view abstractdoi: 10.1002/path.5812
  • 2021 • 1006 Historical Perspective of the Journal of Chemical & Engineering Data's Published Topics, 1956-2020
    Gardas, R.L. and Kofke, D.A. and Pini, R. and Sadowski, G. and Schwarz, C.E. and Siepmann, J.I. and Wu, J.
    Journal of Chemical and Engineering Data 66 1555-1556 (2021)
    doi: 10.1021/acs.jced.1c00193
  • 2021 • 1005 In situ photothermal response of single gold nanoparticles through hyperspectral imaging anti-stokes thermometry
    Gargiulo, J. and Cortes, E. and Stefani, F.D. and Barella, M. and Violi, I.L. and Martinez, L.P. and Goschin, F. and Guglielmotti, V. and Pallarola, D. and Schlücker, S. and Pilo-Pais, M. and Acuna, G.P. and Maier, S.A.
    ACS Nano 15 2458-2467 (2021)
    Several fields of applications require a reliable characterization of the photothermal response and heat dissipation of nanoscopic systems, which remains a challenging task for both modeling and experimental measurements. Here, we present an implementation of anti-Stokes thermometry that enables the in situ photothermal characterization of individual nanoparticles (NPs) from a single hyperspectral photoluminescence confocal image. The method is label-free, potentially applicable to any NP with detectable anti-Stokes emission, and does not require any prior information about the NP itself or the surrounding media. With it, we first studied the photothermal response of spherical gold NPs of different sizes on glass substrates, immersed in water, and found that heat dissipation is mainly dominated by the water for NPs larger than 50 nm. Then, the role of the substrate was studied by comparing the photothermal response of 80 nm gold NPs on glass with sapphire and graphene, two materials with high thermal conductivity. For a given irradiance level, the NPs reach temperatures 18% lower on sapphire and 24% higher on graphene than on bare glass. The fact that the presence of a highly conductive material such as graphene leads to a poorer thermal dissipation demonstrates that interfacial thermal resistances play a very significant role in nanoscopic systems and emphasize the need for in situ experimental thermometry techniques. The developed method will allow addressing several open questions about the role of temperature in plasmon-assisted applications, especially ones where NPs of arbitrary shapes are present in complex matrixes and environments. © 2021 American Chemical Society. All rights reserved.
    view abstractdoi: 10.1021/acsnano.0c06185
  • 2021 • 1004 Considering Non-Surface Scattering in Physical Optics Approximations
    Garten, O. and Statz, C. and Gerling, S. and Jebramcik, J. and Barowski, J. and Plettemeier, D. and Rolfes, I.
    IEEE Transactions on Antennas and Propagation (2021)
    This work addresses the issue of volume scattering effects within the context of the physical optics (PO) approach. This decreases the modeling and computational effort to simulate scattering from complex material compositions. It is shown that there is a natural progression from the classical PO for perfect electric conductors over the PO for dielectric scatterers towards the proposed formulation Four specializations of the general algorithm are presented to emphasize the versatility of this approach. Details regarding the implementation of the proposed examples are described. Results for each of the special cases are shown and compared to commercially available full-wave solvers of CST and FEKO. CCBY
    view abstractdoi: 10.1109/TAP.2021.3060043
  • 2021 • 1003 Correlation between pre- and post-treatments of additively manufactured 316L parts and the resulting low cycle fatigue behavior
    Garthe, K.-U. and Hoyer, K.-P. and Hagen, L. and Tillmann, W. and Schaper, M.
    Rapid Prototyping Journal (2021)
    Purpose: The currently existing restrictions regarding the deployment of additively manufactured components because of poor surface roughness, porosity and residual stresses as well as their influence on the low-cycle fatigue (LCF) strength are addressed in this paper. Design/methodology/approach: This study aims to evaluating the effect of different pre- and post-treatments on the LCF strength of additively manufactured 316L parts. Therefore, 316L specimens manufactured by laser powder bed fusion were examined in their as-built state as well as after grinding, or coating with regard to the surface roughness, residual stresses and LCF strength. To differentiate between topographical effects and residual stress-related phenomena, stress-relieved 316L specimens served as a reference throughout the investigations. To enable an alumina coating of the 316L components, atmospheric plasma spraying was used, and the near-surface residual stresses and the surface roughness are measured and investigated. Findings: The results have shown that the applied pre- and post-treatments such as stress-relief heat treatment, grinding and alumina coating have each led to an increase in LCF strength of the 316L specimens. In contrast, the non-heat-treated specimens predominantly exhibited coating delamination. Originality/value: To the best of the authors’ knowledge, this is the first study of the correlation between the LCF behavior of additively manufactured uncoated 316L specimens in comparison with additively manufactured 316L specimens with an alumina coating. © 2021, Emerald Publishing Limited.
    view abstractdoi: 10.1108/RPJ-01-2021-0017
  • 2021 • 1002 Introduction of a New Method for Continuous Aluminum Hot Extrusion
    Gebhard, J. and Kotzyba, P. and Hering, O. and Tekkaya, A.E.
    Minerals, Metals and Materials Series 1021-1032 (2021)
    The new extrusion process combines the conventional methods of direct and indirect aluminum hot extrusion by an innovative container and die setup with a moving or stationary valve. The process enables the continuous extrusion of aluminum profiles without any interruptions. With both variants, moving or stationary valves, the usual dead cycle times can be used for a continuous extrusion process. Furthermore, due to the continuous material flow, a stationary profile exit temperature can be achieved, which leads to constant material properties. As of now, a continuous extrusion press for aluminum is not available. The new process concept is analyzed on the basis of scaled experimental models using the model material plasticine and numerical simulations. The similarity of the model material was validated by aluminum extrusion experiments. Various model material colors were investigated, and the resulting material flow and process forces of the new process were analyzed. © 2021, The Minerals, Metals & Materials Society.
    view abstractdoi: 10.1007/978-3-030-75381-8_85
  • 2021 • 1001 Tuning the Thermoelectric Properties of Transition Metal Oxide Thin Films and Superlattices on the Quantum Scale
    Geisler, B. and Yordanov, P. and Gruner, M.E. and Keimer, B. and Pentcheva, R.
    Physica Status Solidi (B) Basic Research (2021)
    Combining advanced growth and characterization techniques with state-of-the-art first-principles simulations in the frameworks of density functional theory and Boltzmann transport theory, recent advances in the field of transition metal oxide films and superlattices (SLs) as thermoelectric materials are discussed, with particular focus on a selection of quantum-scale approaches to tune their thermoelectric performance. Specifically, (Formula presented.) films grown on regular and miscut substrates have enabled experimental confirmation of the large predicted out-of-plane Seebeck coefficient of this anisotropic material and also reveal the necessity of a Hubbard-U parameter on the Co (Formula presented.) states. Furthermore, oxygen diffusion and incorporation from the (Formula presented.) substrate lead to a significant enhancement of the high-temperature Seebeck coefficient in (Formula presented.) SLs. Next, it is shown how n- and p-type materials can be achieved either by exploiting interface polarity in a (Formula presented.) SL or using epitaxial strain to shift orbital-dependent transport resonances across the Fermi level in (Formula presented.) SLs. Moreover, confinement- and strain-induced metal-to-insulator transitions induce high Seebeck coefficients and power factors in short-period (Formula presented.) and (Formula presented.) SLs ((Formula presented.) V, Cr, Mn). Finally, a relation between the topologically nontrivial Chern insulating behavior and enhanced thermoelectric response in (Formula presented.) SLs is established. The article concludes with a discussion of challenges and future topics of research in oxide thermoelectrics. © 2021 The Authors. physica status solidi (b) basic solid state physics published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/pssb.202100270
  • 2021 • 1000 Correlated interface electron gas in infinite-layer nickelate versus cuprate films on SrTiO3(001)
    Geisler, B. and Pentcheva, R.
    Physical Review Research 3 (2021)
    Based on first-principles calculations including a Coulomb repulsion term, we identify trends in the electronic reconstruction of ANiO2/SrTiO3(001) (A=Pr, La) and ACuO2/SrTiO3(001) (A=Ca, Sr). Common to all cases is the emergence of a quasi-two-dimensional electron gas (q2DEG) in SrTiO3(001), albeit the higher polarity mismatch at the interface of nickelates versus cuprates to the nonpolar SrTiO3(001) substrate (3+/0 versus 2+/0) results in an enhanced q2DEG carrier density. The simulations reveal a significant dependence of the interfacial Ti 3dxy band bending on the rare-earth-metal ion in the nickelate films, being 20-30% larger for PrNiO2 and NdNiO2 than for LaNiO2. Contrary to expectations from the formal polarity mismatch, the electrostatic doping in the films is twice as strong in cuprates as in nickelates. We demonstrate that the depletion of the self-doping rare-earth-metal 5d states enhances the similarity of nickelate and cuprate Fermi surfaces in film geometry, reflecting a single hole in the Ni and Cu 3dx2-y2 orbitals. Finally, we show that NdNiO2 films grown on a polar NdGaO3(001) substrate feature a simultaneous suppression of q2DEG formation as well as Nd 5d self-doping. © 2021 authors.
    view abstractdoi: 10.1103/PhysRevResearch.3.013261
  • 2021 • 999 A taxonomy for data ecosystems
    Gelhaar, J. and Groß, T. and Otto, B.
    Proceedings of the Annual Hawaii International Conference on System Sciences 2020-January 6113-6122 (2021)
    In the increasingly interconnected business world, economic value is less and less created by one company alone but rather through the combination and enrichment of data by various actors in so-called data ecosystems. The research field around data ecosystems is, however, still in its infancy. With this study, we want to address this issue and contribute to a deeper understanding of data ecosystems. Therefore, we develop a taxonomy for data ecosystems which is grounded both theoretically through the linkage to the scientific knowledge base and empirically through the analyses of data ecosystem use cases. The resulting taxonomy consists of key dimensions and characteristics of data ecosystems and contributes to a better scientific understanding of this concept. Practitioners can use the taxonomy as an instrument to further understand, design and manage the data ecosystems their organizations are involved in. © 2021 IEEE Computer Society. All rights reserved.
    view abstract
  • 2021 • 998 Generalized Method for Charge-Transfer Equilibration in Reactive Molecular Dynamics
    Gergs, T. and Schmidt, F. and Mussenbrock, T. and Trieschmann, J.
    Journal of Chemical Theory and Computation (2021)
    Variable charge models (e.g., electronegativity equalization method (EEM), charge equilibration (QEq), electrostatic plus (ES+)) used in reactive molecular dynamics simulations often inherently impose a global charge transfer between atoms (approximating each system as an ideal metal). Consequently, most surface processes (e.g., adsorption, desorption, deposition, sputtering) are affected, potentially causing dubious dynamics. This issue has been addressed by certain split charge variants (i.e., split charge equilibration (SQE), redoxSQE) through a distance-dependent bond hardness, by the atomic charge ACKS2 and QTPIE models, which are based on the Kohn-Sham density functional theory, as well as by an electronegativity screening extension to the QEq model (approximating each system as an ideal insulator). In a brief review of the QEq and the QTPIE model, their applicability for studying surface interactions is assessed in this work. Following this evaluation, a revised generalization of the QEq and QTPIE models is proposed and formulated, called the charge-transfer equilibration model or in short the QTE model. This method is based on the equilibration of charge-transfer variables, which locally constrain the split charge transfer per unit time (i.e., due to overlapping orbitals) without any kind of bond hardness specification. Furthermore, a formalism relying solely on atomic charges is obtained by a respective transformation, employing an extended Lagrangian method. We moreover propose a mirror boundary condition and its implementation to accelerate surface investigations. The models proposed in this work facilitate reactive molecular dynamics simulations, which describe various materials and surface phenomena appropriately. © 2021 The Authors. Published by American Chemical Society.
    view abstractdoi: 10.1021/acs.jctc.1c00382
  • 2021 • 997 Investigation of Cyclam Based Re-Complexes as Potential Electrocatalysts for the CO2 Reduction Reaction
    Gerschel, P. and Cordes, A.L. and Bimmermann, S. and Siegmund, D. and Metzler-Nolte, N. and Apfel, U.-P.
    Zeitschrift fur Anorganische und Allgemeine Chemie 647 968-977 (2021)
    Among the various homogenous electrocatalysts, especially Re(bpy)(CO)3Cl and [Ni(cyclam)]2+ were shown to be highly efficient for the selective conversion of CO2 to CO at moderate potentials. However, a purposeful combination of a ReI tricarbonyl unit with a cyclam ligand hitherto received no attention. Herein, we report on a series of cyclam based Re complexes comprising the original {N4} as well as heteroatom-altered ligand frameworks, describe their synthesis, reveal their coordination behavior and furthermore investigate their performance towards the electrochemical CO2 reduction. © 2021 The Authors. Zeitschrift für anorganische und allgemeine Chemie published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/zaac.202000450
  • 2021 • 996 Existence results for non-homogeneous boundary conditions in the relaxed micromorphic model
    Ghiba, I.-D. and Neff, P. and Owczarek, S.
    Mathematical Methods in the Applied Sciences 44 2040-2049 (2021)
    In this paper, we notice a property of the extension operator from the space of tangential traces of H(curl; Ω) in the context of the linear relaxed micromorphic model, a theory that is recently used to describe the behavior of some metamaterials showing unorthodox behaviors with respect to elastic wave propagation. We show that the new property is important for existence results of strong solution for non-homogeneous boundary condition in both the dynamic and the static case. © 2020 John Wiley & Sons, Ltd.
    view abstractdoi: 10.1002/mma.6913
  • 2021 • 995 A Constrained Cosserat Shell Model up to Order O(h5) : Modelling, Existence of Minimizers, Relations to Classical Shell Models and Scaling Invariance of the Bending Tensor
    Ghiba, I.-D. and Bîrsan, M. and Lewintan, P. and Neff, P.
    Journal of Elasticity 146 83-141 (2021)
    We consider a recently introduced geometrically nonlinear elastic Cosserat shell model incorporating effects up to order O(h5) in the shell thickness h. We develop the corresponding geometrically nonlinear constrained Cosserat shell model, we show the existence of minimizers for the O(h5) and O(h3) case and we draw some connections to existing models and classical shell strain measures. Notably, the role of the appearing new bending tensor is highlighted and investigated with respect to an invariance condition of Acharya (Int. J. Solids Struct. 37(39):5517–5528, 2000) which will be further strengthened. © 2021, The Author(s), under exclusive licence to Springer Nature B.V.
    view abstractdoi: 10.1007/s10659-021-09851-7
  • 2021 • 994 Charge Regulation at a Nanoporous Two-Dimensional Interface
    Ghosh, M. and Junker, M.A. and Van Lent, R.T.M. and Madauß, L. and Schleberger, M. and Lebius, H. and Benyagoub, A. and Wood, J.A. and Lammertink, R.G.H.
    ACS Omega 6 2487-2493 (2021)
    In this work, we have studied the pH-dependent surface charge nature of nanoporous graphene. This has been investigated by membrane potential and by streaming current measurements, both with varying pH. We observed a lowering of the membrane potential with decreasing pH for a fixed concentration gradient of potassium chloride (KCl) in the Donnan dominated regime. Interestingly, the potential reverses its sign close to pH 4. The fitted value of effective fixed ion concentration (C¯ R) in the membrane also follows the same trend. The streaming current measurements show a similar trend with sign reversal around pH 4.2. The zeta potential data from the streaming current measurement is further analyzed using a 1-pK model. The model is used to determine a representative pK (acid-base equilibrium constant) of 4.2 for the surface of these perforated graphene membranes. In addition, we have also theoretically investigated the effect of the PET support in our membrane potential measurement using numerical simulations. Our results indicate that the concentration drop inside the PET support can be a major contributor (up to 85%) for a significant deviation of the membrane potential from the ideal Nernst potential. © 2021 The Authors. Published by American Chemical Society.
    view abstractdoi: 10.1021/acsomega.0c03958
  • 2021 • 993 Fluorinated β-Ketoiminate Zinc Complexes: Synthesis, Structure and Catalytic Activity in Ring Opening Polymerization of Lactide
    Ghosh, S. and Huse, K. and Wölper, C. and Tjaberings, A. and Gröschel, A.H. and Schulz, S.
    Zeitschrift fur Anorganische und Allgemeine Chemie 647 1744-1750 (2021)
    Complexes LZnR (L=C6F5NC(CF3)C(H)C(CF3)O; R=Me 1; Et 2) and L2Zn(thf)2 (3) were synthesized and analyzed by NMR (1H, 13C, 19F) and IR spectroscopy, elemental analysis, and single crystal X-ray diffraction. Complexes 1 and 2 are dinuclear in the solid state but monomeric in toluene solution according to diffusion-ordered spectroscopy (DOSY-NMR). They showed poor activity in the ring opening polymerization (ROP) of lactide (LA) but moderate activity in the presence of benzyl alcohol (BnOH), yielding polymers with high number average molecular weight (Mn) and moderately controlled molecular weight distribution (PDI). Homonuclear-decoupled 1H NMR analysis of polylactic acid (PLA) obtained from rac-LA showed isotactic enrichment of the polymer microstructure, and kinetic studies of the ROP of L-LA with complex 2 showed a first order dependence of the monomer concentration. Analyses of low molecular weight polymers by 1H NMR and MALDI-ToF mass spectrometry demonstrated the coordination-insertion mechanism (CIM). © 2021 The Authors. Zeitschrift für anorganische und allgemeine Chemie published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/zaac.202100133
  • 2021 • 992 Synthesis and Catalytic Activity of Gallium Schiff-base Complexes in the Ring-Opening Homo- and Copolymerization of Cyclic Esters
    Ghosh, S. and Glöckler, E. and Wölper, C. and Tjaberings, A. and Gröschel, A.H. and Schulz, S.
    Zeitschrift fur Anorganische und Allgemeine Chemie 647 1594-1601 (2021)
    Tetranuclear Ga(III) complexes L1–32Ga4(t-Bu)8 1–3 are synthesized and characterized (elemental analysis, IR, 1H, 13C, DOSY NMR spectroscopy, XRD) and their activity in the ring-opening polymerization (ROP) of lactide (LA) and ϵ-caprolactone (ϵ-CL) is reported. Complex 1 is the most active homopolymerization catalyst in the presence of benzyl alcohol (BnOH), yielding isotactic-enriched polylactides (PLAs) with Pm (probably of mesomerism) values up to 0.72 by a first order kinetic with respect to the monomer concentration. The living character of the polymerization process was confirmed by a polymerization resumption experiment. Complexes 1–3 are also active catalysts in the copolymerization of LA and ϵ-CL, and sequential addition of both monomers gave well-defined block copolymers with narrow Đ values (distributions of molecular weight). © 2021 The Authors. Zeitschrift für anorganische und allgemeine Chemie published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/zaac.202100183
  • 2021 • 991 Pressure-deformation relations of elasto-capillary drops (droploons) on capillaries
    Ginot, G. and Kratz, F.S. and Walzel, F. and Farago, J. and Kierfeld, J. and Höhler, R. and Drenckhan, W.
    Soft Matter 17 9131-9153 (2021)
    An increasing number of multi-phase systems exploit complex interfaces in which capillary stresses are coupled with solid-like elastic stresses. Despite growing efforts, simple and reliable experimental characterisation of these interfaces remains a challenge, especially of their dilational properties. Pendant drop techniques are convenient, but suffer from complex shape changes and associated fitting procedures with multiple parameters. Here we show that simple analytical relationships can be derived to describe reliably the pressure-deformation relations of nearly spherical elasto-capillary droplets (“droploons”) attached to a capillary. We consider a model interface in which stresses arising from a constant interfacial tension are superimposed with mechanical extra-stresses arising from the deformation of a solid-like, incompressible interfacial layer of finite thickness described by a neo-Hookean material law. We compare some standard models of liquid-like (Gibbs) and solid-like (Hookean and neo-Hookean elasticity) elastic interfaces which may be used to describe the pressure-deformation relations when the presence of the capillary can be considered negligible. Combining Surface Evolver simulations and direct numerical integration of the drop shape equations, we analyse in depth the influence of the anisotropic deformation imposed by the capillary on the pressure-deformation relation and show that in many experimentally relevant circumstances either the analytical relations of the perfect sphere may be used or a slightly modified relation which takes into account the geometrical change imposed by the capillary. Using the analogy with the stress concentration around a rigid inclusion in an elastic membrane, we provide simple non-dimensional criteria to predict under which conditions the simple analytical expressions can be used to fit pressure-deformation relations to analyse the elastic properties of the interfacesvia“Capillary Pressure Elastometry”. We show that these criteria depend essentially on the drop geometry and deformation, but not on the interfacial elasticity. Moreover, this benchmark case shows for the first time that Surface Evolver is a reliable tool for predictive simulations of elastocapillary interfaces. This opens doors to the treatment of more complex geometries/conditions, where theory is not available for comparison. Our Surface Evolver code is available for download in the ESI. © The Royal Society of Chemistry 2021.
    view abstractdoi: 10.1039/d1sm01109j
  • 2021 • 990 Increasing the lightweight potential of composite cold forging by utilizing magnesium and granular cores
    Gitschel, R. and Kolpak, F. and Hering, O. and Erman Tekkaya, A.
    Metals 11 1-16 (2021)
    In this paper a process sequence, that uses forward rod extrusion with cold forged C15 steel cup billets to produce lightweight shafts, is presented. The steel cup billets feature either a lightweight magnesium alloy core or a granular medium core that is removed after forming to obtain hollow shafts without the need of complex tools and highly loaded mandrels. It is shown that composite shafts featuring magnesium cores can be produced for a wide range of extrusion strains. Due to high hydrostic pressures in forward rod extrusion, the forming limit of magnesium at room temperature can be expanded. The observed bond strength between core and sheath is below the shear yield strength of utilized magnesium AZ31 alloy. Hollow shafts are successfully produced with the presented process route by utilizing zirconium oxide beads or quartz sand as a lost core. As the law of constant volume in metal forming is violated by compressible granular media, a simulation approach using a modified Drucker-Prager yield surface to model these materials is validated to provide a tool for efficient process design. Granular cores and magnesium alloy cores offer new possibilities in production of lightweight shafts by means of composite cold forging. Both process variants allow for higher weight savings than composite shafts based on aluminum cores. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/met11010032
  • 2021 • 989 Effect of Multilayer Termination on Nonspecific Protein Adsorption and Antifouling Activity of Alginate-Based Layer-by-Layer Coatings
    Gnanasampanthan, T. and Beyer, C.D. and Yu, W. and Karthäuser, J.F. and Wanka, R. and Spöllmann, S. and Becker, H.-W. and Aldred, N. and Clare, A.S. and Rosenhahn, A.
    Langmuir 37 5950-5963 (2021)
    Layer-by-layer (LbL) assembly is a versatile platform for applying coatings and studying the properties of promising compounds for antifouling applications. Here, alginate-based LbL coatings were fabricated by alternating the deposition of alginic acid and chitosan or polyethylenimine to form multilayer coatings. Films were prepared with either odd or even bilayer numbers to investigate if the termination of the LbL coatings affects the physicochemical properties, resistance against the nonspecific adsorption (NSA) of proteins, and antifouling efficacy. The hydrophilic films, which were characterized using spectroscopic ellipsometry, water contact angle goniometry, ATR-FTIR spectroscopy, AFM, XPS, and SPR spectroscopy, revealed high swelling in water and strongly reduced the NSA of proteins compared to the hydrophobic reference. While the choice of the polycation was important for the protein resistance of the LbL coatings, the termination mattered less. The attachment of diatoms and settling of barnacle cypris larvae revealed good antifouling properties that were controlled by the termination and the charge density of the LbL films. ©
    view abstractdoi: 10.1021/acs.langmuir.1c00491
  • 2021 • 988 Processing and oxidation response of Cr2AlC MAX-phase composites containing ceramic fibers
    Go, T. and Vaßen, R. and Guillon, O. and Gonzalez-Julian, J.
    Open Ceramics 6 (2021)
    Three different ceramic matrix composites (CMCs) were produced using Cr2AlC as a matrix, and carbon, SiC and Al2O3 short fibers as a secondary phase. Cr2AlC powders were synthesized by solid-state reaction, followed by mixing with the fibers, and full densification using a field-assisted sintering technique. Of the three different fiber types, Carbon fibers reacted strongly with Cr2AlC, while the reaction with SiC fibers was more limited and alumina fibers didn't show any reaction. Oxidation tests of the monolithic Cr2AlC and the composites were performed by thermogravimetric analysis. An alumina layer formed at 1000 ​°C on every sample, well attached and worked as a good oxidation barrier. Under realistic conditions using a burner rig for cyclic oxidation at 1200 ​°C for 500 cycles, the oxidation resistance of the alumina fiber CMC is good, as no defects or degradation are visible and the alumina layer is well attached. © 2021 The Author(s)
    view abstractdoi: 10.1016/j.oceram.2021.100090
  • 2021 • 987 Surface reactions during temperature-programmed desorption and reduction experiments with oxygen-functionalized carbon blacks
    Göckeler, M. and Berger, C.M. and Purcel, M. and Bergsträßer, R. and Schinkel, A.-P. and Muhler, M.
    Applied Surface Science 561 (2021)
    Carbon black was functionalized by gas-phase oxidation using nitric acid vapor at 150 °C, and temperature-programmed desorption (TPD) and temperature-programmed reduction (TPR) experiments were performed in a plug-flow reactor to analyze the decomposition mechanisms of oxygen-containing surface groups by monitoring evolved H2O, CO2, and CO quantitatively. Subsequent TPD measurements detected an enrichment of acidic surface groups with increasing duration of the HNO3 functionalization from 2 h to 24 h. A significant amount of H2O was released during the TPD experiments, yielding H2O evolution profiles which were deconvoluted into two Gaussian peaks at 162 °C and 228 °C. The combined analysis of the CO2 and H2O profiles indicates that desorbed H2O originates from chemisorbed water bound to carboxylic acid groups and from condensation reactions of carboxylic acids and phenols. Phenols and carbonyls were found to be reduced selectively by H2 during TPR, generating a pronounced H2O peak at 650 °C. A new peak in the CO2 evolution profile appeared at 575 °C in reducing atmosphere, which is assigned to the hydrolysis of anhydrides and lactones with subsequent decomposition. Thus, taking H2O into account is mandatory for a complete quantitative analysis of the decomposition mechanisms occurring during TPD and TPR experiments. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.apsusc.2021.150044
  • 2021 • 986 Nickel nanoparticles supported on nitrogen–doped carbon nanotubes are a highly active, selective and stable CO2 methanation catalyst
    Gödde, J. and Merko, M. and Xia, W. and Muhler, M.
    Journal of Energy Chemistry 54 323-331 (2021)
    CO2 methanation using nickel-based catalysts has attracted large interest as a promising power-to-gas route. Ni nanoparticles supported on nitrogen-doped CNTs with Ni loadings in the range from 10 wt% to 50 wt% were synthesized by impregnation, calcination and reduction and characterized by elemental analysis, X-ray powder diffraction, H2 temperature-programmed reduction, CO pulse chemisorption and transmission electron microscopy. The Ni/NCNT catalysts were highly active in CO2 methanation at atmospheric pressure, reaching over 50% CO2 conversion and over 95% CH4 selectivity at 340 °C and a GHSV of 50,000 mL g−1 h−1 under kinetically controlled conditions. The small Ni particle sizes below 10 nm despite the high Ni loading is ascribed to the efficient anchoring on the N-doped CNTs. The optimum loading of 30 wt%–40 wt% Ni was found to result in the highest Ni surface area, the highest degree of conversion and the highest selectivity to methane. A constant TOF of 0.3 s−1 was obtained indicating similar catalytic properties of the Ni nanoparticles in the range from 10 wt% to 50 wt% Ni loading. Long-term experiments showed that the Ni/NCNT catalyst with 30 wt% Ni was highly stable for 100 h time on stream. © 2020 Science Press
    view abstractdoi: 10.1016/j.jechem.2020.06.007
  • 2021 • 985 A new approach for open-end sequential change point monitoring
    Gösmann, J. and Kley, T. and Dette, H.
    Journal of Time Series Analysis 42 63-84 (2021)
    We propose a new sequential monitoring scheme for changes in the parameters of a multivariate time series. In contrast to procedures proposed in the literature which compare an estimator from the training sample with an estimator calculated from the remaining data, we suggest to divide the sample at each time point after the training sample. Estimators from the sample before and after all separation points are then continuously compared calculating a maximum of norms of their differences. For open-end scenarios our approach yields an asymptotic level (Formula presented.) procedure, which is consistent under the alternative of a change in the parameter. By means of a simulation study it is demonstrated that the new method outperforms the commonly used procedures with respect to power and the feasibility of our approach is illustrated by analyzing two data examples. © 2020 The Authors. Journal of Time Series Analysis published by John Wiley & Sons Ltd.
    view abstractdoi: 10.1111/jtsa.12555
  • 2021 • 984 Generation of ultrashort keV Ar+ ion pulses via femtosecond laser photoionization
    Golombek, A. and Breuer, L. and Danzig, L. and Kucharczyk, P. and Schleberger, M. and Sokolowski-Tinten, K. and Wucher, A.
    New Journal of Physics 23 (2021)
    Ion beams with energies in the keV regime are widely utilized in solid-state physics, but the ultrafast dynamics triggered by an ion impact onto a solid surface is to date exclusively accessible via simulations based on many untested assumptions and model parameters. A possible experimental access rests on the availability of a laser-synchronized ion source delivering sufficiently short ion pulses for time resolved pump-probe experiments. Here, we demonstrate a new miniaturized ion optical bunching setup for the creation of rare gas ion pulses using strong-field femtosecond laser photoionization. Neutral Ar gas atoms at room temperature are intercepted by a 50 fs, 800 nm laser pulse focused to ∼10 μm spot size. We demonstrate the generation of monoenergetic 2 keV Ar+ ion pulses with 180 ps duration (FWHM) at laser peak intensities around 1014 W cm−2 and of multiply charged Arq+ ions (q = 1-5) at higher laser intensities. The results are in good agreement with detailed ion trajectory simulations, which show that the temporal resolution is essentially limited by the initial (thermal) velocity spread of the generated photo-ions, indicating the possibility to achieve even better time resolution by cooling the gas prior to ionization. © 2021 The Author(s). Published by IOP Publishing Ltd on behalf of the Institute of Physics and Deutsche Physikalische Gesellschaft
    view abstractdoi: 10.1088/1367-2630/abe443
  • 2021 • 983 Multistate current-induced magnetization switching in Au/Fe/MgO(001) epitaxial heterostructures
    Gospodarič, P. and Młyńczak, E. and Soldatov, I. and Kákay, A. and Bürgler, D.E. and Plucinski, L. and Schäfer, R. and Fassbender, J. and Schneider, C.M.
    Physical Review Research 3 (2021)
    Magnetization switching using in-plane charge current recently has been widely investigated in heavy metal/ferromagnet bilayers with the switching mechanism usually attributed to the action of the spin-orbit coupling. Here we study in-plane current induced magnetization switching in model epitaxial bilayers that consist of Au(001) and Fe(001) grown on MgO(001). We use the planar Hall effect combined with magnetooptical Kerr effect (MOKE) microscopy to investigate magnetic properties of the bilayers and current-induced switching. We show that a current density beyond 1.4×107 A/cm2 can be employed for reproducible electrical switching of the magnetization between multiple stable states that correspond to different arrangements of magnetic domains with magnetization direction along one of the in-plane easy magnetization axes of the Fe(001) film. Lower current densities result in stable intermediate transversal resistances which are interpreted based on MOKE-microscopy investigations as resulting from the current-induced magnetic domain structure that is formed in the area of the Hall cross. We find that the physical mechanism of the current-induced magnetization switching of the Au/Fe/MgO(001) system at room temperature can be fully explained by the Oersted field, which is generated by the charge current flowing mostly through the Au layer. © 2021 authors. Published by the American Physical Society.
    view abstractdoi: 10.1103/PhysRevResearch.3.023089
  • 2021 • 982 Analysis of proximity consequences of coil windings in electromagnetic forming
    Goyal, S.P. and Lashkari, M. and Elsayed, A. and Hahn, M. and Tekkaya, A.E.
    Journal of Manufacturing and Materials Processing 5 (2021)
    Multiturn coils are required for manufacturing sheet metal parts with varying depths and special geometrical features using electromagnetic forming (EMF). Due to close coil turns, the physical phenomena of the proximity effect and Lorentz forces between the parallel coil windings are observed. This work attempts to investigate the mechanical consequences of these phenomena using numerical and experimental methods. A numerical model was developed in LS-DYNA. It was validated using experimental post-mortem strain and laser-based velocity measurements after and during the experiments, respectively. It was observed that the proximity effect in the parallel conductors led to current density localization at the closest or furthest ends of the conductor cross-section and high local curvature of the formed sheet. Further analysis of the forces between two coil windings explained the departure from the “inverse-distance” rule observed in the literature. Finally, some measures to prevent or reduce undesired coil deformation are provided. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/jmmp5020045
  • 2021 • 981 Prehistoric salt mining in Hallstatt, Austria. New chronologies out of small wooden fragments
    Grabner, M. and Wächter, E. and Nicolussi, K. and Bolka, M. and Sormaz, T. and Steier, P. and Wild, E.M. and Barth, F.E. and Kern, A. and Rudorfer, J. and Kowarik, K. and Stöllner, T. and Reschreiter, H.
    Dendrochronologia 66 (2021)
    The prehistoric salt mine of Hallstatt together with its burial ground is one of the most prominent archaeological sites in the world, and has given its name to the “Hallstatt period”, an epoch of European prehistory (800 to 400 BCE). Due to the perfect conservation in rock salt a high number of organic materials have been found, including mostly wooden artefacts and structural timber. More than 2000 samples were taken from various archaeological sites in the mines as well as at the surface. It was possible to date 763 samples by the means of dendrochronology and by 14C wiggle matching. The dendrochronological dating was possible due to crossdating with various available chronologies (like Villingen-Magdalenenberg or Dachstein/Schwarzer See). The fir (Abies alba Mill.) chronologies span the periods: -1232 to -1063; -819 to -425 and -371 to-129. The spruce (Picea abies L. Karst.) chronologies span the periods: -1228 to -1063; -813 to -669 and -342 to -123. The larch (Larix decidua Mill.) chronologies span the periods: -1393 ± 18 to-1286 ± 18 based on wiggle matching data and -252 to -164. A beech (Fagus sylvatica L.) chronology span the time -1182 to -1062. © 2021 The Author(s)
    view abstractdoi: 10.1016/j.dendro.2021.125814
  • 2021 • 980 Application of Neural Networks to External Parameter Estimation for Nonlinear Vehicle Models
    Gräber, T. and Schäfer, M. and Unterreiner, M. and Schramm, D.
    SAE International Journal of Connected and Automated Vehicles 4 297-312 (2021)
    In this article, we propose a method of combining neural networks (NN) with nonlinear state-space models (SSM). Such model parts that are well understood can be integrated into the state space, while the NN can estimate such parts that are uncertain or hard to model. We apply the method to vehicle state estimation on a race track. Therefore, we derive a nonlinear two-track model with a scaled magic formula and adaptively estimate the tire parameters - stiffnesses and maximum friction potential - with the NN. The results show that the NN is able to reach an excellent estimation performance and generalizes over different model parameters, such as tire type, tread depth, surfaces conditions, and maneuvers. The trained model is furthermore integrated into an Extended Kalman Filter (EKF) to estimate the longitudinal speed, lateral speed, and yaw rate of the vehicle. ©
    view abstractdoi: 10.4271/12-04-03-0024
  • 2021 • 979 New thermodynamic activity-based approach allows predicting the feasibility of glycolysis
    Greinert, T. and Vogel, K. and Maskow, T. and Held, C.
    Scientific Reports 11 (2021)
    Thermodynamic feasibility analyses help evaluating the feasibility of metabolic pathways. This is an important information used to develop new biotechnological processes and to understand metabolic processes in cells. However, literature standard data are uncertain for most biochemical reactions yielding wrong statements concerning their feasibility. In this article we present activity-based equilibrium constants for all the ten glycolytic reactions, accompanied by the standard reaction data (standard Gibbs energy of reaction and standard enthalpy of reaction). We further developed a thermodynamic activity-based approach that allows to correctly determine the feasibility of glycolysis under different chosen conditions. The results show for the first time that the feasibility of glycolysis can be explained by thermodynamics only if (1) correct standard data are used and if (2) the conditions in the cell at non-equilibrium states are accounted for in the analyses. The results here will help to determine the feasibility of other metabolisms and to understand metabolic processes in cells in the future. © 2021, The Author(s).
    view abstractdoi: 10.1038/s41598-021-85594-8
  • 2021 • 978 (tBuN)SiMe2NMe2-A new N,N ′-κ 2-monoanionic ligand for atomic layer deposition precursors
    Griffiths, M.B.E. and Zanders, D. and Land, M.A. and Masuda, J.D. and Devi, A. and Barry, S.T.
    Journal of Vacuum Science and Technology A: Vacuum, Surfaces and Films 39 (2021)
    Eight new atomic layer deposition (ALD) precursors were synthesized using a ligand that is new to the field of ALD: (tBuNH)SiMe2NMe2. Complexes containing Mg, V, Mn, Fe, Co, Ni, and Zn were found to be tetrahedral, and Li complexes form more complex structures. These compounds performed exceptionally well by thermogravimetric analysis (TGA). All compounds except for one Li species and the Fe complex left residual masses below 5%, similar or better than the analogous amidinate complexes. In particular, the Co(II) complex is very thermally robust and performs very well during a TGA stress test, surpassing temperatures above 200 °C. These compounds are the first of a family of precursors containing this type of monoanionic N-Si-N ligand and are prime candidates for ALD process development. © 2021 Author(s).
    view abstractdoi: 10.1116/6.0000795
  • 2021 • 977 Gas-phase aluminium acetylacetonate decomposition: revision of the current mechanism by VUV synchrotron radiation
    Grimm, S. and Baik, S.-J. and Hemberger, P. and Bodi, A. and Kempf, A.M. and Kasper, T. and Atakan, B.
    Physical Chemistry Chemical Physics 23 15059-15075 (2021)
    Although aluminium acetylacetonate, Al(C5H7O2)3, is a common precursor for chemical vapor deposition (CVD) of aluminium oxide, its gas-phase decomposition is not well-known. Here, we studied its thermal decomposition in a microreactor by double imaging photoelectron photoion coincidence spectroscopy (i2PEPICO) between 325 and 1273 K. The reactor flow field was characterized by CFD. Quantum chemical calculations were used for the assignment of certain species. The dissociative ionization of the room temperature precursor molecule starts at a photon energy of 8.5 eV by the rupture of the bond to an acetylacetonate ligand leading to the formation of the Al(C5H7O2)2+ion. In pyrolysis experiments, up to 49 species were detected and identified in the gas-phase, including reactive intermediates and isomeric/isobaric hydrocarbons, oxygenated species as well as aluminium containing molecules. We detected aluminium bis(diketo)acetylacetonate-H, Al(C5H7O2)C5H6O2, atm/z224 together with acetylacetone (C5H8O2) as the major initial products formed at temperatures above 600 K. A second decomposition channel affords Al(OH)2(C5H7O2) along with the formation of a substituted pentalene ring species (C10H12O2) as assigned by Franck-Condon simulations and quantum chemical calculations. Acetylallene (C5H6O), acetone (C3H6O) and ketene (C2H2O) were major secondary decomposition products, formed upon decomposition of the primary products. Three gas-phase aromatic hydrocarbons were also detected and partially assigned for the first time:m/z210,m/z186 (C14H18or C12H10O2) andm/z146 (C11H14or C9H6O2) and their formation mechanism is discussed. Finally, Arrhenius parameters are presented on the gas-phase decomposition kinetics of Al(C5H7O2)3, aided by numerical simulation of the flow field. © the Owner Societies 2021.
    view abstractdoi: 10.1039/d1cp00720c
  • 2021 • 976 Macroscopic process simulation of surface and profile grinding processes estimating forces for the production of turbine blades
    Grimmert, A. and Wiederkehr, P.
    Procedia CIRP 102 126-131 (2021)
    In aerospace industry surface and profile grinding processes are widely used for the manufacturing of turbine blades. Maximizing the productivity is a key factor for industry, which can be achieved by reducing the number of cuts necessary in order to remove the remaining millimeters of stock material after casting. This leads to high depth of cut values and, therefore, considerably high process forces. Turbine blades are highly flexible workpieces resulting in process induced deflections. In order to avoid mechanical damages of the workpiece during the process, a macroscopic grinding simulation is used, which is presented in this paper. For this process simulation a coupled multiphysics FE model was created using the software COMSOL Multiphysics. First, the material removal was evaluated using the deformed geometry module of the software. Based on the current material removal the process forces were calculated using an experimentally calibrated grinding force model. The forces were subsequently applied onto the grinding area allowing for a calculation of the resulting stresses and deflections. Further, the simulation was extended for profile grinding processes using an inclined grinding wheel and a fir tree profile of a turbine blade. The simulated forces were validated based on experimentally conducted grinding processes. © 2021 Elsevier B.V.. All rights reserved.
    view abstractdoi: 10.1016/j.procir.2021.09.022
  • 2021 • 975 Ignition and propagation of nanosecond pulsed plasmas in distilled water - Negative vs positive polarity applied to a pin electrode
    Grosse, K. and Falke, M. and Von Keudell, A.
    Journal of Applied Physics 129 (2021)
    Nanosecond plasmas in liquids are being used for water treatment, electrolysis, or biomedical applications. The exact nature of these very dynamic plasmas and, most importantly, their ignition physics are strongly debated. The ignition itself may be explained by two competing hypotheses: ignition in water may occur (i) via field effects at the tip of the electrode followed by tunneling of electrons in between water molecules causing field ionization or (ii) via gaseous processes of electron multiplication in nanovoids that are created from liquid ruptures due to the strong electric field gradients. Both hypotheses are supported by theory, but experimental data are very sparse due to the difficulty in monitoring the very fast processes in space and time. In this paper, we analyze nanosecond plasmas in water that are created by applying a positive and a negative polarity to a sharp tungsten electrode. The main diagnostics are fast camera measurements and fast emission spectroscopy. It is shown that plasma ignition is dominated by field effects at the electrode-liquid interface either as field ionization for positive polarity or as field emission for negative polarity. This leads to a hot tungsten surface at a temperature of 7000 K for positive polarity, whereas the surface temperature is much lower for negative polarity. At ignition, the electron density reaches 4 × 10 25 m - 3 for the positive and 2 × 10 25 m - 3 for the negative polarity. At the same time, the emission of the H α light for the positive polarity is four times higher than that for the negative polarity. During plasma propagation, the electron densities are almost identical of the order of 1- 2 × 10 25 m - 3 followed by a decay after the end of the pulse over 15 ns. It is concluded that plasma propagation is governed by field effects in a low density region that is created either by nanovoids or by density fluctuations in supercritical water surrounding the electrode that is created by the pressure and temperature at the moment of plasma ignition. © 2021 Author(s).
    view abstractdoi: 10.1063/5.0045697
  • 2021 • 974 Additive manufacturing of a carbon-martensitic hot-work tool steel using a powder mixture – Microstructure, post-processing, mechanical properties
    Großwendt, F. and Röttger, A. and Strauch, A. and Chehreh, A. and Uhlenwinkel, V. and Fechte-Heinen, R. and Walther, F. and Weber, S. and Theisen, W.
    Materials Science and Engineering A 827 (2021)
    This work examines the processing of a hot-work tool steel using laser-based powder bed fusion of metals (PBF-LB/M). The hot-work tool steel was produced using a low-cost powder mixture consisting of pure iron and other elemental powders as well as ferroalloys. Furthermore, a prealloyed starting powder with the same nominal chemical composition as the powder mixture was produced by inert-gas atomization. Besides, a reference steel was produced by casting to compare the microstructures and mechanical properties resulting from the different processing routes. The first step examined the application of a chemically homogeneous and dense layer of the powder mixture prior to PBF-LB/M densification. In addition to evaluate suitable process parameters for PBF-LB/M processing of the starting materials, the microstructure formation was comprehensively examined using electron microscopy and the processes adapted to it. To eliminate defects (cracks, pores) and chemical inhomogeneities, thermal posttreatments, namely supersolidus liquid phase heat-treatment (SLPHT) and hot isostatic pressing (HIP) were performed. Suitable heat-treatment parameters were evaluated. Finally, the obtained microstructures and the associated properties of the post-processed PBF-LB/M samples were compared with those in the reference states. As a main result, it was possible to achieve full redensification and simultaneous chemical homogenization of the PBF-LB/M-processed powder mixture by SLPHT post-processing. The hardness of the additively manufactured and SLPHT-post-processed specimens exceeds that of the cast reference. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.msea.2021.142038
  • 2021 • 973 Impact of the allowed compositional range of additively manufactured 316l stainless steel on processability and material properties
    Großwendt, F. and Becker, L. and Röttger, A. and Chehreh, A.B. and Strauch, A.L. and Uhlenwinkel, V. and Lentz, J. and Walther, F. and Fechte-Heinen, R. and Weber, S. and Theisen, W.
    Materials 14 (2021)
    This work aims to show the impact of the allowed chemical composition range of AISI 316L stainless steel on its processability in additive manufacturing and on the resulting part properties. ASTM A276 allows the chromium and nickel contents in 316L stainless steel to be set between 16 and 18 mass%, respectively, 10 and 14 mass%. Nevertheless, the allowed compositional range impacts the microstructure formation in additive manufacturing and thus the properties of the manufactured components. Therefore, this influence is analyzed using three different starting powders. Two starting powders are laboratory alloys, one containing the maximum allowed chromium content and the other one containing the maximum nickel content. The third material is a commercial powder with the chemical composition set in the middle ground of the allowed compositional range. The materials were processed by laser-based powder bed fusion (PBF-LB/M). The powder characteristics, the microstructure and defect formation, the corrosion resistance, and the mechanical properties were investigated as a function of the chemical composition of the powders used. As a main result, solid-state cracking could be observed in samples additively manufactured from the starting powder containing the maximum nickel content. This is related to a fully austenitic solidification, which occurs because of the low chromium to nickel equivalent ratio. These cracks reduce the corrosion resistance as well as the elongation at fracture of the additively manufactured material that possesses a low chromium to nickel equivalent ratio of 1.0. A limitation of the nickel equivalent of the 316L type steel is suggested for PBF-LB/M production. Based on the knowledge obtained, a more detailed specification of the chemical composition of the type 316L stainless steel is recommended so that this steel can be PBF-LB/M processed to defect-free components with the desired mechanical and chemical properties. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/ma14154074
  • 2021 • 972 Large-Eddy Simulation of a Lifted High-Pressure Jet-Flame with Direct Chemistry
    Gruhlke, P. and Janbazi, H. and Wollny, P. and Wlokas, I. and Beck, C. and Janus, B. and Kempf, A.M.
    Combustion Science and Technology (2021)
    A large-eddy simulation is presented of a challenging high-pressure jet flame case that is representative of state of the art, dry low-NO x and low-CO real gas turbine combustion. A reaction scheme is developed for lifted lean premixed high pressure methane jet flames, and tested by three-dimensional large-eddy simulation of an experiment, for which very detailed data are available. Auto-ignition-delay times of different mixtures of fresh gas and products have been introduced as a novel optimization criterion for the mechanism development. The new mechanism has been developed by a genetic algorithm-based reduction and optimization, and consists of 15 species and 18 reactions. The large-eddy simulations are performed using a finite rate chemistry (FRC) approach and the dynamic thickened flame (DTF) model to investigate a lifted jet flame at high pressure in a gas turbine model combustor. In the simulations, the novel mechanism is compared to a similar mechanism that was generated without this criterion, and the well-established Lu19 mechanism. With the new mechanism, the LES predicts the flame as accurately as with Lu19, at a significantly lower cost. Further post processing with Lagrangian tracer particles confirmed that ignition events occur in the region corresponding to the liftoff height estimated in the experiment, which is corroborated by a chemical explosive mode analysis (CEMA). Overall, the newly developed mechanism with the novel optimization criterion was found to provide a better agreement with the experiments than previous mechanisms of similar cost, or a comparable agreement to a mechanism of significantly higher cost. © 2021 Taylor & Francis Group, LLC.
    view abstractdoi: 10.1080/00102202.2021.1903886
  • 2021 • 971 Resistance to avapritinib in pdgfra-driven gist is caused by secondary mutations in the pdgfra kinase domain
    Grunewald, S. and Klug, L.R. and Mühlenberg, T. and Lategahn, J. and Falkenhorst, J. and Town, A. and Ehrt, C. and Wardelmann, E. and Hartmann, W. and Schildhaus, H.-U. and Treckmann, J. and Fletcher, J.A. and Jung, S. and Czodro...
    Cancer Discovery 11 108-125 (2021)
    Gastrointestinal stromal tumors (GIST) harboring activating mutations of PDGFRA respond to imatinib, with the notable exception of the most common mutation, D842V. Avapritinib is a novel, potent KIT/PDGFRA inhibitor with substantial clinical activity in patients with the D842V genotype. To date, only a minority of PDGFRA-mutant patients treated with avapri-tinib have developed secondary resistance. Tumor and plasma biopsies in 6 of 7 patients with PDGFRA primary mutations who progressed on avapritinib or imatinib had secondary resistance mutations within PDGFRA exons 13, 14, and 15 that interfere with avapritinib binding. Secondary PDGFRA mutations causing V658A, N659K, Y676C, and G680R substitutions were found in 2 or more patients each, representing recurrent mechanisms of PDGFRA GIST drug resistance. Notably, most PDGFRA-mutant GISTs refractory to avapritinib remain dependent on the PDGFRA oncogenic signal. Inhibitors that target PDGFRA protein stability or inhibition of PDGFRA-dependent signaling pathways may overcome avapritinib resistance. © 2020 American Association for Cancer Research.
    view abstractdoi: 10.1158/2159-8290.CD-20-0487
  • 2021 • 970 Finite-temperature interplay of structural stability, chemical complexity, and elastic properties of bcc multicomponent alloys from ab initio trained machine-learning potentials
    Gubaev, K. and Ikeda, Y. and Tasnádi, F. and Neugebauer, J. and Shapeev, A.V. and Grabowski, B. and Körmann, F.
    Physical Review Materials 5 (2021)
    An active learning approach to train machine-learning interatomic potentials (moment tensor potentials) for multicomponent alloys to ab initio data is presented. Employing this approach, the disordered body-centered cubic (bcc) TiZrHfTax system with varying Ta concentration is investigated via molecular dynamics simulations. Our results show a strong interplay between elastic properties and the structural ω phase stability, strongly affecting the mechanical properties. Based on these insights we systematically screen composition space for regimes where elastic constants show little or no temperature dependence (elinvar effect). © 2021 American Physical Society.
    view abstractdoi: 10.1103/PhysRevMaterials.5.073801
  • 2021 • 969 Data Strategy Development: A Taxonomy for Data Strategy Tools and Methodologies in the Economy
    Gür, I. and Spiekermann, M. and Arbter, M. and Otto, B.
    Lecture Notes in Information Systems and Organisation 46 448-461 (2021)
    Data are a key driver of the digital era. They shift the strategic landscape of organizations and change how companies approach their business. Nevertheless, existing approaches on data strategies vary vastly and little common ground is visible. Therefore, we develop a comprehensive taxonomy for data strategy tools and methodologies in order to identify characteristics and relevant properties of data strategy. We derived the taxonomy inductively by analyzing existing data strategy tools and methodologies offered in the current economy and deductively by conducting a structured literature review on the existing body of knowledge in the scientific literature. It serves as a scientific instrument to profoundly assess and create data strategies and work towards a consensus in the respective research field. © 2021, The Author(s), under exclusive license to Springer Nature Switzerland AG.
    view abstractdoi: 10.1007/978-3-030-86790-4_30
  • 2021 • 968 Reply to ‘Ideal solar cell efficiencies’
    Guillemoles, J.-F. and Kirchartz, T. and Cahen, D. and Rau, U.
    Nature Photonics 15 165-166 (2021)
    doi: 10.1038/s41566-021-00775-1
  • 2021 • 967 Modelling of microstructure formation in metal additive manufacturing: Recent progress, research gaps and perspectives
    Gunasegaram, D.R. and Steinbach, I.
    Metals 11 (2021)
    Microstructures encountered in the various metal additive manufacturing (AM) processes are unique because these form under rapid solidification conditions not frequently experienced elsewhere. Some of these highly nonequilibrium microstructures are subject to self-tempering or even forced to undergo recrystallisation when extra energy is supplied in the form of heat as adjacent layers are deposited. Further complexity arises from the fact that the same microstructure may be attained via more than one route—since many permutations and combinations available in terms of AM process parameters give rise to multiple phase transformation pathways. There are additional difficulties in obtaining insights into the underlying phenomena. For instance, the unstable, rapid and dynamic nature of the powder-based AM processes and the microscopic scale of the melt pool behaviour make it difficult to gather crucial information through in-situ observations of the process. Therefore, it is unsurprising that many of the mechanisms responsible for the final microstructures—including defects—found in AM parts are yet to be fully understood. Fortunately, however, computational modelling provides a means for recreating these processes in the virtual domain for testing theories—thereby discovering and rationalising the potential influences of various process parameters on microstructure formation mechanisms. In what is expected to be fertile ground for research and development for some time to come, modelling and experimental efforts that go hand in glove are likely to provide the fastest route to uncovering the unique and complex physical phenomena that determine metal AM microstructures. In this short Editorial, we summarise the status quo and identify research opportunities for modelling microstructures in AM. The vital role that will be played by machine learning (ML) models is also discussed. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/met11091425
  • 2021 • 966 A combined experimental and first-principles based assessment of finite-temperature thermodynamic properties of intermetallic al3sc
    Gupta, A. and Tas, B. and Korbmacher, D. and Dutta, B. and Neitzel, Y. and Grabowski, B. and Hickel, T. and Esin, V. and Divinski, S.V. and Wilde, G. and Neugebauer, J.
    Materials 14 (2021)
    We present a first-principles assessment of the finite-temperature thermodynamic properties of the intermetallic Al3Sc phase including the complete spectrum of excitations and compare the theoretical findings with our dilatometric and calorimetric measurements. While significant electronic contributions to the heat capacity and thermal expansion are observed near the melting temperature, anharmonic contributions, and electron–phonon coupling effects are found to be relatively small. On the one hand, these accurate methods are used to demonstrate shortcomings of empirical predictions of phase stabilities such as the Neumann–Kopp rule. On the other hand, their combination with elasticity theory was found to provide an upper limit for the size of Al3Sc nanoprecipitates needed to maintain coherency with the host matrix. The chemo-mechanical coupling being responsible for the coherency loss of strengthening precipitates is revealed by a combination of state-of-the-art simulations and dedicated experiments. These findings can be exploited to fine-tune the microstructure of Al-Sc-based alloys to approach optimum mechanical properties. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/ma14081837
  • 2021 • 965 Characterization of Flow Induced Anisotropy in Sheet Metal at Large Strain
    Gutknecht, F. and Traphöner, H. and Clausmeyer, T. and Tekkaya, A.E.
    Experimental Mechanics (2021)
    Background: Many metals exhibit a stress overshoot, the so-called cross-hardening when subjected to a specific strain-path change. Existing tests for sheet metals are limited to an equivalent prestrain of 0.2 and show varying levels of cross-hardening for identical grades. Objective: The aim is to determine cross-hardening at large strains, relevant for forming processes. Mild steel grades (DC04, DC06, DX56) and high strength steel grades (BS600, DP600, ZE800) are investigated to quantify the level of cross-hardening between different grades and reveal which grades exhibit cross-hardening at all. Method: A novel test setup for large prestrain using hydraulic bulge test and torsion of curved sheets is developed to achieve an orthogonal strain-path change, i.e. the strain rate tensors for two subsequent loadings are orthogonal. The influence of strain rate differences between the tests and clamping of curved sheets on the determined cross-hardening are evaluated. The results are compared to experiments in literature. Results: Cross-hardening for sheet metal at prestrains up to 0.6 true plastic strain are obtained for the first time. For DX56 grade the maximum cross-hardening for all prestrains have a constant level of approximately 6%, while the maximum cross-hardening for DC04 and DC06 grades increases, with levels between 7 and 11%. The high strength grades BS600 and ZE800 do not show cross-hardening behavior, while, differencing from previous publications, cross-hardening is observed for dual phase steel DP600. Conclusion: Depending on the microstructure of the steel grade the cross-hardening increases with large prestrain or remains constant. © 2021, The Author(s).
    view abstractdoi: 10.1007/s11340-021-00776-9
  • 2021 • 964 Momentum and energy dissipation of hot electrons in a Pb/Ag(111) quantum well system
    Haag, F. and Eul, T. and Grad, L. and Haag, N. and Knippertz, J. and Mathias, S. and Cinchetti, M. and Aeschlimann, M. and Stadtmüller, B.
    Physical Review B 104 (2021)
    The band structure of multilayer systems plays a crucial role for the ultrafast hot carrier dynamics at interfaces. Here, we study the energy- and momentum-dependent quasiparticle lifetimes of excited electrons in a highly ordered Pb monolayer film on Ag(111) prior and after the adsorption of a monolayer of 3,4,9,10-perylene-tetracarboxylic dianhydride (PTCDA). Using time-resolved two-photon momentum microscopy with femtosecond visible light pulses, we show that the electron dynamics of the Pb/Ag(111) quantum well system is largely dominated by two types of scattering processes: (i) isotropic intraband scattering processes within the quantum well state (QWS) and (ii) isotropic interband scattering processes from the -like QWS into the Pb band. In the latter case, the Pb QWS acts as an electron source for the momentum space refilling process of the Pb band. This conclusion is confirmed by the modification of the band structure and the quasiparticle dynamics of the Pb/Ag(111) bilayer film after the adsorption of PTCDA. We find both an adsorption-induced suppression of the QWS itself as well as of the refilling process into the Pb band. Our study hence demonstrates the isotropic nature of the momentum-dependent scattering processes of metallic bilayer systems and uncovers a new possibility to selectively tune and control scattering processes occurring in quantum (well) materials by the adsorption of organic molecules. ©2021 American Physical Society
    view abstractdoi: 10.1103/PhysRevB.104.104308
  • 2021 • 963 Free Molecule Studies by Perturbed γ-γ Angular Correlation: A New Path to Accurate Nuclear Quadrupole Moments
    Haas, H. and Röder, J. and Correia, J.G. and Schell, J. and Fenta, A.S. and Vianden, R. and Larsen, E.M.H. and Aggelund, P.A. and Fromsejer, R. and Hemmingsen, L.B.S. and Sauer, S.P.A. and Lupascu, D.C. and Amaral, V.S.
    Physical Review Letters 126 (2021)
    Accurate nuclear quadrupole moment values are essential as benchmarks for nuclear structure models and for the interpretation of experimentally determined nuclear quadrupole interactions in terms of electronic and molecular structure. Here, we present a novel route to such data by combining perturbed γ-γ angular correlation measurements on free small linear molecules, realized for the first time within this work, with state-of-the-art ab initio electronic structure calculations of the electric field gradient at the probe site. This approach, also feasible for a series of other cases, is applied to Hg and Cd halides, resulting in Q(Hg199,5/2-)=+0.674(17) b and Q(Cd111,5/2+)=+0.664(7) b. © 2021 authors. Published by the American Physical Society.
    view abstractdoi: 10.1103/PhysRevLett.126.103001
  • 2021 • 962 A 32x24 pixel SPAD detector system for LiDAR and quantum imaging
    Haase, J.F. and Grollius, S. and Grosse, S. and Buchner, A. and Ligges, M.
    Proceedings of SPIE - The International Society for Optical Engineering 11693 (2021)
    We have developed a 32x24 pixel sensor array based on single-photon avalanche diodes (SPADs). Beside conventional 2-dimensional imaging, this sensor allows for precise timing of single-photon arrival times which can be exploited in a variety of technical and scientific approaches like 3D image acquisition, quantum imaging and quantum random number generation. Thus, such a sensor is eligible for many fields of application such as autonomous driving, remote and non-lineof-sight sensing, safety, robotics and more recently random number generation for statistical applications or data encryption. The novel sensor contains CMOS integrated backside illuminated SPADs which are connected to an underlying read-out IC by wafer-to-wafer bonding. Their single-photon sensitivity (quantum efficiency QE=60 % @ 580 nm) and high-speed performance (readout frequency o '"= 25 kHz, temporal resolution tTDC = 312.5 ps) make the sensor a promising choice for, e.g. quantum imaging with photon-pairs where a 2-dimensional spatial and temporal resolution are as crucial as a low noise level. SPADs also offer exciting opportunities for random number generation by using the randomness of photon generation paired with time-resolved detection and post-processing. Another potential application of the sensor is light detection and ranging for which we integrated the sensor into a demonstrator system for direct time-of-flight measurements. It is capable of coincidence detection using 4 SPADs in each pixel, which allows for background light suppression in outdoor situations. This combination of single-photon sensitivity, precise photon arrival timing and our recent developments in wafer-to-wafer bonding technology gives access to a new generation of optical sensors for a variety of applications. © 2021 SPIE.
    view abstractdoi: 10.1117/12.2578775
  • 2021 • 961 Deformation and damage assessments of two dp1000 steels using a micromechanical modelling method
    Habibi, N. and Vajragupta, N. and Münstermann, S.
    Crystals 11 (2021)
    Damage characterization and micromechanical modelling in dual-phase (DP) steels have recently drawn attention, since any changes in the alloying elements or process route strongly influence the microstructural features, deformation behavior of the phases, and damage to the micro-mechanisms, and subsequently the particular mechanical properties of the material. This approach can be used to stablish microstructure–properties relationships. For instance, the effects of local damage from shear cutting on edge crack sensitivity in the following deformation process can be studied. This work evaluated the deformation and damage behaviors of two DP1000 steels using a microstructure-based approach to estimate the edge cracking resistance. Phase fraction, grain size, phase distribution, and texture were analyzed using electron backscatter diffraction and secondary electron detectors of a scanning electron microscope and employed in 3D representative volume elements. The deformation behavior of the ferrite phase was defined using a crystal plasticity model, which was calibrated through nanoindentation tests. Various loading conditions, including uniaxial tension, equi-biaxial tension, plane strain tension, and shearing, along with the maximum shear stress criterion were applied to investigate the damage initiation and describe the edge cracking sensitivity of the studied steels. The results revealed that a homogenous microstructure leads to homogenous stress–strain partitioning, delayed damage initiation, and high edge cracking resistance. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/cryst11070805
  • 2021 • 960 Plasticity induced by nanoindentation in a CrCoNi medium-entropy alloy studied by accurate electron channeling contrast imaging revealing dislocation-low angle grain boundary interactions
    Habiyaremye, F. and Guitton, A. and Schäfer, F. and Scholz, F. and Schneider, M. and Frenzel, J. and Laplanche, G. and Maloufi, N.
    Materials Science and Engineering A 817 (2021)
    In the present work, interactions of nanoindentation-induced dislocations (NIDs) with a low-angle grain boundary (LAGB) are investigated in a single-crystalline CrCoNi medium-entropy alloy (MEA). Microstructural evolutions before and after nanoindentation were examined using accurate electron channeling contrast imaging (A-ECCI). In the as-grown state, the alloy microstructure consists of subgrains separated by LAGBs. After nanoindentation on the (001) plane far away from LAGBs, the load-displacement curves exhibit the typical behavior of metals and alloys with a pop-in marking the elastic-plastic transition. This pop-in is related to the nucleation of NIDs that are observed to form pile-ups on {111} planes. In contrast, when indents are performed in the vicinity of a LAGB with a low misorientation angle of 0.24° and consisting of dislocations spaced ~60 nm apart, different micromechanical responses and deformation mechanisms are observed depending on the distance between the LAGB and the nanoindenter tip. When the distance between the LAGB and the nanoindenter tip is larger than four times the size of the indent (corresponding ratio: R > 4), the LAGB does not affect the micromechanical response nor interact with NIDs. In contrast, when the indenter comes in direct or indirect contact with the LAGB (R < 1), the load-displacement curve deviates at low loads from the elastic stage, and pop-ins are not observed. In this case, the continuous deformation is accommodated by the movement of the pre-existing LAGB dislocations. For intermediate cases with 1 < R < 4, the load of the initial pop-in is dependent on the local defect density. In this latter case, the pile-ups of NIDs directly impinge on the LAGB. Microstructural analyses reveal that the LAGB accommodates plasticity by blocking the NIDs, activating a dislocation nucleation site in the adjacent subgrain/emission of dislocation from the LAGB, and inducing slight motions of its constituent dislocations. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.msea.2021.141364
  • 2021 • 959 Triazole groups as biomimetic amide groups in peptides can trigger racemization
    Hättasch, T. and Schmuck, C. and Niemeyer, J.
    Arkivoc 2021 185-196 (2021)
    Amino acids are key building blocks for the synthesis of chiral organic materials. In this context, α-azido amino acids are interesting starting materials which allow the construction of functionalized, amino-acid based compounds by copper-catalyzed alkyne-azide click reactions. We have now employed this strategy for the synthesis of arginine-derivatives and found that the formation of the azide and the click reaction can be carried out in good yields and with almost no loss of stereopurity. However, further transformation by saponification/amide-formation led to significant racemization at the α-carbon. This process was investigated in detail, showing that the triazole-moiety seems to be responsible for the facile racemization. Thus, the highly useful modification of α-azido amino acids by the CuAAC-reaction needs to be used with caution when stereopure materials are desired. ©AUTHOR(S)
    view abstractdoi: 10.24820/ARK.5550190.P011.484
  • 2021 • 958 Polarity-controlled AlN/Si templates by in situ oxide desorption for variably arrayed MOVPE-GaN nanowires
    Häuser, P. and Blumberg, C. and Liborius, L. and Prost, W. and Weimann, N.
    Journal of Crystal Growth 566-567 (2021)
    In this paper, we present a comprehensive study of position-defined Al-polar AlN nucleation on lithographically patterned Si(1 1 1) substrates as a method to obtain ordered Ga-polar GaN nanowire arrays, with possible application in future nanowire-based devices such as LEDs and photoelectrochemical water-splitting cells. In a hydrogen processing step, ex situ prepared oxide on pre-structured Si-pillars could be selectively removed. This enabled Al-polar AlN nucleation on the Si-pillar's sidewalls during the following metal–organic vapor phase epitaxy, while dominant N-polar AlN layer growth was observed on the still oxidized Si(1 1 1) horizontal substrate surface neighboring the pillars. 100% of the Ga-polar GaN wires are emerging on the Al-polar AlN growth sites, thus selective area epitaxy without any mask material could be realized. To gain a precise understanding of the growth mechanisms, the attainable Ga-adatom collection area per NW was varied by changing the Si-pillars’ placement pattern. The wire length and diameter increase with extended pitch. At a constant pitch, the size of the wires is adjustable by variation of the Si-pillars’ diameter, therefore growth of GaN wires of controllable dimension and pitch could be attained. Additionally, parasitic NW growth was completely suppressed for any pitch < 3.5 µm, while an increased pitch resulted in additional parasitic growth. Based on these results a model was derived, which includes the site-controlled removal of the oxide, the thus achieved local polarity control of AlN growth, and the influence of the collection area of each NW with respect to their size, whereas the collection area could be set in the experiment by adjustment of the lithographically controlled pitch and growth-parameter dependent Ga-adatom diffusion length. The mask-less polarity- and site-controlled growth of NWs with a height of 5.3 µm ± 0,33 µm and a diameter of 800 nm ± 160 nm at a pitch of 2.5 µm could be attained. Hence, a deep understanding of the growth mechanisms and the geometrical control of polarity- and site-controlled GaN NWs could be achieved, forming the base for development of NW-based devices on a conductive AlN/Si-template. © 2021
    view abstractdoi: 10.1016/j.jcrysgro.2021.126162
  • 2021 • 957 Part-optimized forming by spatially distributed vaporizing foil actuators
    Hahn, M. and Tekkaya, A.E.
    International Journal of Material Forming (2021)
    Electrically vaporizing foil actuators are employed as an innovative high speed sheet metal forming technology, which has the potential to lower tool costs. To reduce experimental try-outs, a predictive physics-based process design procedure is developed for the first time. It consists of a mathematical optimization utilizing numerical forming simulations followed by analytical computations for the forming-impulse generation through the rapid Joule heating of the foils. The proposed method is demonstrated for an exemplary steel sheet part. The resulting process design provides a part-specific impulse distribution, corresponding parallel actuator geometries, and the pulse generator’s charging energy, so that all process parameters are available before the first experiment. The experimental validation is then performed for the example part. Formed parts indicate that the introduced method yields a good starting point for actual testing, as it only requires adjustments in the form of a minor charging energy augmentation. This was expectable due to the conservative nature of the underlying modeling. The part geometry obtained with the most suitable charging energy is finally compared to the target geometry. © 2021, The Author(s).
    view abstractdoi: 10.1007/s12289-021-01634-8
  • 2021 • 956 Extremely low-energy ARPES of quantum well states in cubic-GaN/AlN and GaAs/AlGaAs heterostructures
    Hajlaoui, M. and Ponzoni, S. and Deppe, M. and Henksmeier, T. and As, D.J. and Reuter, D. and Zentgraf, T. and Springholz, G. and Schneider, C.M. and Cramm, S. and Cinchetti, M.
    Scientific Reports 11 (2021)
    Quantum well (QW) heterostructures have been extensively used for the realization of a wide range of optical and electronic devices. Exploiting their potential for further improvement and development requires a fundamental understanding of their electronic structure. So far, the most commonly used experimental techniques for this purpose have been all-optical spectroscopy methods that, however, are generally averaging in momentum space. Additional information can be gained by angle-resolved photoelectron spectroscopy (ARPES), which measures the electronic structure with momentum resolution. Here we report on the use of extremely low-energy ARPES (photon energy ~ 7 eV) to increase depth sensitivity and access buried QW states, located at 3 nm and 6 nm below the surface of cubic-GaN/AlN and GaAs/AlGaAs heterostructures, respectively. We find that the QW states in cubic-GaN/AlN can indeed be observed, but not their energy dispersion, because of the high surface roughness. The GaAs/AlGaAs QW states, on the other hand, are buried too deep to be detected by extremely low-energy ARPES. Since the sample surface is much flatter, the ARPES spectra of the GaAs/AlGaAs show distinct features in momentum space, which can be reconducted to the band structure of the topmost surface layer of the QW structure. Our results provide important information about the samples’ properties required to perform extremely low-energy ARPES experiments on electronic states buried in semiconductor heterostructures. © 2021, The Author(s).
    view abstractdoi: 10.1038/s41598-021-98569-6
  • 2021 • 955 Effect of composition on polarization hysteresis and energy storage ability of p(Vdf-trfe-cfe) relaxor terpolymers
    Hambal, Y. and Shvartsman, V.V. and Lewin, D. and Huat, C.H. and Chen, X. and Michiels, I. and Zhang, Q. and Lupascu, D.C.
    Polymers 13 (2021)
    The temperature dependence of the dielectric permittivity and polarization hysteresis loops of P(VDF-TrFE-CFE) polymer films with different compositions are studied. Among them, the three compositions, 51.3/48.7/6.2, 59.8/40.2/7.3, and 70/30/8.1, are characterized for the first time. Relaxor behavior is confirmed for all studied samples. Increasing the CFE content results in lowering the freezing temperature and stabilizes the ergodic relaxor state. The observed double hysteresis loops are related to the field-induced transition to a ferroelectric state. The critical field corresponding to this transition varies with the composition and temperature; it becomes larger for temperatures far from the freezing temperature. The energy storage performance is evaluated from the analysis of unipolar polarization hysteresis loops. P(VDF-TrFE-CFE) 59.8/40.2/7.3 shows the largest energy density of about 5 J·cm−3 (at the field of 200 MV·m−1) and a charge–discharge efficiency of 63%, which iscomparable with the best literature data for the neat terpolymers. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/polym13081343
  • 2021 • 954 Directly Measured Electrocaloric Effect in Relaxor Polymer Nanocomposites
    Hambal, Y. and Menze, K.-H. and Shvartsman, V.V. and Lupascu, D.C.
    IEEE International Symposium on Applications of Feeroelectric, ISAF 2021, International Symposium on Integrated Functionalities, ISIF 2021 and Piezoresponse Force Microscopy Workshop, PFM 2021 - Proceedings (2021)
    Composites of electroactive polymers and ferroelectric nanoparticles are promising for energy storage and electrocaloric applications. In this paper we report on synthesis and electrocaloric properties of P(VDF-TrFE-CFE)/ BaZr0.20Ti0.80O3 nanocomposites. BaZr0.20Ti0.80O3 (BZT) nanoparticles were synthesized via the hydrothermal route. The P(VDF-TrFE-CFE)/BZT composite films with varying amount (1.25 vol.% to 5 vol.%) of the nanoparticles were prepared by the solution casting method. The nanocomposite films showed a significant increase in the dielectric permittivity with the amount of nanoparticles. An increase in the polarization as well as in hysteresis losses with the amount of nanoparticles was observed. The direct electrocaloric effect was measured using a custom built quasi-Adiabatic calorimeter. The P(VDF-TrFE-CFE)/BZT nanocomposite film with 5 vol.% BZT showed an electrocaloric temperature change of ~ 1.8 K at room temperature and an electric field of 50 MV/m, which is comparable to literature values. © 2021 IEEE.
    view abstractdoi: 10.1109/ISAF51943.2021.9477327
  • 2021 • 953 Large-scale synthesis of iron oxide/graphene hybrid materials as highly efficient photo-Fenton catalyst for water remediation
    Hammad, M. and Fortugno, P. and Hardt, S. and Kim, C. and Salamon, S. and Schmidt, T.C. and Wende, H. and Schulz, C. and Wiggers, H.
    Environmental Technology and Innovation 21 (2021)
    The Photo-Fenton reaction is an advanced oxidation process to break down organic pollutants in aqueous systems. Moreover, the scalable synthesis and engineering of stable catalysts with a high specific surface area is extremely important for the practical application of the Photo-Fenton process. In the current study, we developed a low-cost method for large-scale production of iron oxide/graphene nanostructures with a controllable graphene loading for the photo-Fenton reaction. Under optimal condition, high efficiencies of degradation (&gt;99%) of methylene blue, rhodamine B, acid orange 7, and phenol at a concentration (60 mg/mL) were reached in 60 min under UV-A irradiation (1.6 mW/cm2) with mineralization of 72, 77, 82, and 48%, respectively. More importantly, the iron oxide/graphene nanocomposites exhibited good stability over a wide range of pH (from 3 to 9) and can be magnetically separated from the solution and repeatedly used with consistent photocatalytic performance. This enhanced removal efficiency of the iron oxide/graphene nanostructure compared to iron oxide nanoparticles is attributed to the accelerated transfer of photo-generated electrons between iron oxide and graphene and its relatively large surface area. The results demonstrate that the iron oxide/graphene system could be potentially utilized for many environmental treatment processes. © 2020 Elsevier B.V.
    view abstractdoi: 10.1016/j.eti.2020.101239
  • 2021 • 952 Ultrastrong and Ductile Soft Magnetic High-Entropy Alloys via Coherent Ordered Nanoprecipitates
    Han, L. and Rao, Z. and Souza Filho, I.R. and Maccari, F. and Wei, Y. and Wu, G. and Ahmadian, A. and Zhou, X. and Gutfleisch, O. and Ponge, D. and Raabe, D. and Li, Z.
    Advanced Materials 33 (2021)
    The lack of strength and damage tolerance can limit the applications of conventional soft magnetic materials (SMMs), particularly in mechanically loaded functional devices. Therefore, strengthening and toughening of SMMs is critically important. However, conventional strengthening concepts usually significantly deteriorate soft magnetic properties, due to Bloch wall interactions with the defects used for hardening. Here a novel concept to overcome this dilemma is proposed, by developing bulk SMMs with excellent mechanical and attractive soft magnetic properties through coherent and ordered nanoprecipitates (<15 nm) dispersed homogeneously within a face-centered cubic matrix of a non-equiatomic CoFeNiTaAl high-entropy alloy (HEA). Compared to the alloy in precipitate-free state, the alloy variant with a large volume fraction (>42%) of nanoprecipitates achieves significantly enhanced strength (≈1526 MPa) at good ductility (≈15%), while the coercivity is only marginally increased (<10.7 Oe). The ordered nanoprecipitates and the resulting dynamic microband refinement in the matrix significantly strengthen the HEAs, while full coherency between the nanoprecipitates and the matrix leads at the same time to the desired insignificant pinning of the magnetic domain walls. The findings provide guidance for developing new high-performance materials with an excellent combination of mechanical and soft magnetic properties as needed for the electrification of transport and industry. © 2021 The Authors. Advanced Materials published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/adma.202102139
  • 2021 • 951 Violation of Boltzmann Equipartition Theorem in Angular Phonon Phase Space Slows down Nanoscale Heat Transfer in Ultrathin Heterofilms
    Hanisch-Blicharski, A. and Tinnemann, V. and Wall, S. and Thiemann, F. and Groven, T. and Fortmann, J. and Tajik, M. and Brand, C. and Frost, B.-O. and Von Hoegen, A. and Horn-von Hoegen, M.
    Nano Letters 21 7145-7151 (2021)
    Heat transfer through heterointerfaces is intrinsically hampered by a thermal boundary resistance originating from the discontinuity of the elastic properties. Here, we show that with shrinking dimensions the heat flow from an ultrathin epitaxial film through atomically flat interfaces into a single crystalline substrate is significantly reduced due to violation of Boltzmann equipartition theorem in the angular phonon phase space. For films thinner than the phonons mean free path, we find phonons trapped in the film by total internal reflection, thus suppressing heat transfer. Repopulation of those phonon states, which can escape the film through the interface by transmission and refraction, becomes the bottleneck for cooling. The resulting nonequipartition in the angular phonon phase space slows down the cooling by more than a factor of 2 compared to films governed by phonons diffuse scattering. These allow tailoring of the thermal interface conductance via manipulation of the interface. © 2021 The Authors. Published by American Chemical Society.
    view abstractdoi: 10.1021/acs.nanolett.1c01665
  • 2021 • 950 Comparison of damage mechanisms: Acoustic cavitation versus series of single laser-induced bubbles
    Hanke, S. and Kaiser, S.A.
    Wear 476 (2021)
    Cavitation is the formation and collapse of bubbles due to pressure changes in fluids. In the vicinity of a solid surface, shock waves, an impinging water jet, and other effects of collapsing bubbles may cause severe damage. Cavitation erosion is extensively studied using techniques generating clouds of bubbles, e.g. flow channels or ultrasonic oscillations. Single bubbles can be generated in a highly controlled manner by evaporating fluid by a short laser pulse. This technique is typically used to study bubble dynamics and the damage from one single bubble on very soft materials. In the present study, two austenitic steels and a NiAl-bronze are exposed to standard acoustic cavitation and repeated laser-induced single bubbles. The evolution of surface damage and the underlying mechanisms are investigated. Surface changes are not observed before 200 single bubbles. After 50,000 bubbles the three alloys are still within the incubation phase. Comparable damage mechanisms act on the materials under both testing techniques. Since the surface area affected by repeated single bubbles is relatively small (≈500 μm diameter), the weight loss could not be measured and correlations are based on surface roughening and the mechanisms of damage specific for each material. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.wear.2021.203641
  • 2021 • 949 Toward tailoring the degradation rate of magnesium-based biomaterials for various medical applications: Assessing corrosion, cytocompatibility and immunological effects
    Hartjen, P. and Wegner, N. and Ahmadi, P. and Matthies, L. and Nada, O. and Fuest, S. and Yan, M. and Knipfer, C. and Gosau, M. and Walther, F. and Smeets, R.
    International Journal of Molecular Sciences 22 1-13 (2021)
    Magnesium (Mg)-based biomaterials hold considerable promise for applications in regenerative medicine. However, the degradation of Mg needs to be reduced to control toxicity caused by its rapid natural corrosion. In the process of developing new Mg alloys with various surface modifications, an efficient assessment of the relevant properties is essential. In the present study, a WE43 Mg alloy with a plasma electrolytic oxidation (PEO)-generated surface was investigated. Surface microstructure, hydrogen gas evolution in immersion tests and cytocompatibility were assessed. In addition, a novel in vitro immunological test using primary human lymphocytes was introduced. On PEO-treated WE43, a larger number of pores and microcracks, as well as increased roughness, were observed compared to untreated WE43. Hydrogen gas evolution after two weeks was reduced by 40.7% through PEO treatment, indicating a significantly reduced corrosion rate. In contrast to untreated WE43, PEO-treated WE43 exhibited excellent cytocompatibility. After incubation for three days, untreated WE43 killed over 90% of lymphocytes while more than 80% of the cells were still vital after incubation with the PEO-treated WE43. PEO-treated WE43 slightly stimulated the activation, proliferation and toxin (perforin and granzyme B) expression of CD8+ T cells. This study demonstrates that the combined assessment of corrosion, cytocompatibility and immunological effects on primary human lymphocytes provide a comprehensive and effective procedure for characterizing Mg variants with tailorable degradation and other features. PEO-treated WE43 is a promising candidate for further development as a degradable biomaterial. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/ijms22020971
  • 2021 • 948 Control of electron velocity distributions at the wafer by tailored voltage waveforms in capacitively coupled plasmas to compensate surface charging in high-aspect ratio etch features
    Hartmann, P. and Wang, L. and Nösges, K. and Berger, B. and Wilczek, S. and Brinkmann, R.P. and Mussenbrock, T. and Juhasz, Z. and Donkó, Z. and Derzsi, A. and Lee, E. and Schulze, J.
    Journal of Physics D: Applied Physics 54 (2021)
    Low pressure single- or dual-frequency capacitively coupled radio frequency (RF) plasmas are frequently used for high-aspect ratio (HAR) dielectric etching due to their capability to generate vertical ion bombardment of the wafer at high energies. Electrons typically reach the wafer at low energies and with a wide angular distribution during the local sheath collapse. Thus, in contrast to positive ions, electrons cannot propagate deeply into HAR etch features and the bottom as well as the sidewalls of such trenches can charge up positively, while the mask charges negatively. This causes etch stops and distortion of profile shapes. Here, we investigate low pressure, high voltage capacitively coupled RF argon gas discharges by Particle-In-Cell/Monte Carlo collisions simulations and demonstrate that this problem can be solved by Voltage Waveform Tailoring, i.e. the velocity and angular distribution of electrons impacting on the electrodes can be tuned towards high velocities and small angles to the surface-normal, while keeping the energies of the impacting ions high. The applied voltage waveforms consist of a base frequency of 400 kHz with 10 kV amplitude and a series of higher harmonics. A high frequency component at 40 or 60 MHz is used additionally. Square voltage waveforms with different rise-times are examined as well. We show that high fluxes of electrons towards the wafer at normal velocities of up to 2.2 × 107 m s-1 (corresponding to 1.4 keV energy) can be realized. © 2021 The Author(s). Published by IOP Publishing Ltd.
    view abstractdoi: 10.1088/1361-6463/abf229
  • 2021 • 947 Numerical analysis of the impact of cytoskeletal actin filament density alterations onto the diffusive vesicle-mediated cell transport
    Haspinger, D.C. and Klinge, S. and Holzapfel, G.A.
    PLoS Computational Biology 17 (2021)
    The interior of a eukaryotic cell is a highly complex composite material which consists of water, structural scaffoldings, organelles, and various biomolecular solutes. All these components serve as obstacles that impede the motion of vesicles. Hence, it is hypothesized that any alteration of the cytoskeletal network may directly impact or even disrupt the vesicle transport. A disruption of the vesicle-mediate cell transport is thought to contribute to several severe diseases and disorders, such as diabetes, Parkinson's and Alzheimer's disease, emphasizing the clinical relevance. To address the outlined objective, a multiscale finite element model of the diffusive vesicle transport is proposed on the basis of the concept of homogenization, owed to the complexity of the cytoskeletal network. In order to study the microscopic effects of specific nanoscopic actin filament network alterations onto the vesicle transport, a parametrized three-dimensional geometrical model of the actin filament network was generated on the basis of experimentally observed filament densities and network geometries in an adenocarcinomic human alveolar basal epithelial cell. Numerical analyzes of the obtained effective diffusion properties within two-dimensional sampling domains of the whole cell model revealed that the computed homogenized diffusion coefficients can be predicted statistically accurate by a simple two-parameter power law as soon as the inaccessible area fraction, due to the obstacle geometries and the finite size of the vesicles, is known. This relationship, in turn, leads to a massive reduction in computation time and allows to study the impact of a variety of different cytoskeletal alterations onto the vesicle transport. Hence, the numerical simulations predicted a 35% increase in transport time due to a uniformly distributed four-fold increase of the total filament amount. On the other hand, a hypothetically reduced expression of filament cross-linking proteins led to sparser filament networks and, thus, a speed up of the vesicle transport. © 2021 Public Library of Science. All rights reserved.
    view abstractdoi: 10.1371/journal.pcbi.1008784
  • 2021 • 946 Beam divergence reduction of vortex waves with a tailored lens and a tailored reflector
    Hassan, M.H. and Sievert, B. and Svejda, J.T. and Ahmed, A.M. and Barowski, J. and Rennings, A. and Rolfes, I. and Sezgin, A. and Erni, D.
    IEEE Access 9 9800-9811 (2021)
    Reducing the strong beam divergence inherent to Orbital Angular Momentum waves (also known as OAM waves or vortex waves), a tailored lens and a tailored reflector are presented in this study. The generation of the OAM waves is accomplished by a Uniform Circular Patch Antenna Array (UCA) operating at 10 GHz. Here, the tailored lens and reflector are set up by two correspondingly designed shape functions rotated around the antenna's center axis in broadside direction (i.e. body of revolution approach). Initially, the tailored lens is introduced to be compared to the UCA in the presence and absence of the conventional lens separately. Upon the usage of the tailored lens, a gain improvement of 5.8 dB has been obtained in the simulation compared to a gain of 4.8 dB in the measurement. On the other hand, the tailored reflector is set under the same procedure to be compared also to the UCA with and without a conventional reflector. Both of the reflectors are simulated under idealized conditions with the aid of an OAM impressed field source used as an emitter for a meaningful comparison. The simulated gain has shown a better performance accomplished by the tailored reflector as the height r0 reaches a level less than 1.5 λ as well as the opening angle θ is less than 38° (given an UCA with an element separation distance d=λ/2). Furthermore, three different ground plane shapes with realistic UCA are applied for the simulation procedure where each of them is perturbing the radiation of the reflector. All of the lenses and the reflectors are manufactured and later measured in an anechoic chamber to undergo a comparison with the simulated results. This article demonstrates that the vortex waves need a tailored lens or a tailored reflector to decrease the beam divergence effectively especially when the radius of the UCA becomes increasingly large. © 2013 IEEE.
    view abstractdoi: 10.1109/ACCESS.2021.3050043
  • 2021 • 945 Generation of Vortex Waves Using Crossed 2λ-Dipole Antennas
    Hassan, M.H. and Sievert, B. and Rennings, A. and Erni, D.
    15th European Conference on Antennas and Propagation, EuCAP 2021 (2021)
    In this paper, a simple and novel method is presented to generate Orbital Angular Momentum (OAM) waves for the first OAM mode order with radial polarization. This approach consists of two crossed 2λ-dipole antennas (CDA) where each antenna is fed in the center with identical amplitude but with a 90° phase shift to radiate vortex waves. Further, in order to enhance the gain, the number of crossed dipoles can be increased. Therefore, the simulation of two and four CDA is performed with the full-wave simulator FEKO. Moreover, a two and four crossed 2λ-dipole phased array of two elements can increase the directivity of the radiation in the broadside direction. A reflector of 100 mm × 100 mm is also added for two and four crossed 2λ-dipole antennas to improve the gain in the same direction. © 2021 EurAAP.
    view abstractdoi: 10.23919/EuCAP51087.2021.9411239
  • 2021 • 944 Transition from elastic to plastic strain release in core−shell nanowires revealed by in-plane x-ray diffraction
    Hassan, A.A. and Salehi, W.A. and Lewis, R.B. and Anjum, T. and Sternemann, C. and Geelhaar, L. and Pietsch, U.
    Nanotechnology 32 (2021)
    We investigate the strain evolution and relaxation process as function of increasing lattice mismatch between the GaAs core and surrounding InxGa1−xAs shell in core-shell nanowire heterostructures grown on Si(111) substrates. The dimensions of the core and shell are kept constant whereas the indium concentration inside the shell is varied. Measuring the 224¯ and 220 ¯ in-plane Bragg reflections normal to the nanowire side edges and side facets, we observe a transition from elastic to plastic strain release for a shell indium content x &gt; 0.5. Above the onset of plastic strain relaxation, indium rich mounds and an indium poor coherent shell grow simultaneously around the GaAs core. Mound formation was observed for indium contents x = 0.5 and 0.6 by scanning electron microscopy. Considering both the measured radial reflections and the axial 111 Bragg reflection, the 3D strain variation was extracted separately for the core and the InxGa1−xAs shell. © 2021 The Author(s). Published by IOP Publishing Ltd Printed in the UK
    view abstractdoi: 10.1088/1361-6528/abe5db
  • 2021 • 943 Study on the Austemperability of Thin-wall Ductile Cast Iron Produced by High-Pressure Die-casting
    van gen Hassend, F. and Ninnemann, L. and Töberich, F. and Breuckmann, M. and Röttger, A. and Weber, S.
    Journal of Materials Engineering and Performance (2021)
    The production of thin-wall ductile iron (TWDI) by high-pressure die-casting (HPDC) is complex because of several metallurgical and microstructural challenges. The present work aims to evaluate the austemperability of components (4 mm thickness) produced by HPDC process. The graphitization kinetics, the pearlite formation during continuous cooling, and the effect of austempering on the evolution of the ausferritic microstructure were investigated using dilatometric tests, microstructural analysis as well as Vickers hardness tests and tensile tests. Results show that components exhibit a brittle behavior because of white structures, small shrinkage cavities, and microporosity in the as-cast condition. Graphitization at 1100 °C allows rapid formation of small graphite particles within a short time (40 s). The critical cooling time (t8/5) to avoid the formation of pearlite upon cooling was found to be 5 s at a martensite start temperature of 193 ± 14 °C. Austempering at 360 °C for 40 min results in an ausferritic microstructure with stable carbon-enriched austenite which provides a high hardness (355 ± 4 HV10) and tensile strength (Rm = 709 ± 65 MPa). The results represent main criteria regarding the producibility of die-casted TWDI, which are helpful for future alloy and heat treatment design. © 2021, The Author(s).
    view abstractdoi: 10.1007/s11665-021-06252-8
  • 2021 • 942 Robust dynamic adaptation of the Smagorinsky model based on a sub-grid activity sensor
    Hasslberger, J. and Engelmann, L. and Kempf, A. and Klein, M.
    Physics of Fluids 33 (2021)
    The present study deals with the application of a sub-grid activity sensor to an eddy viscosity type base model in the context of Large Eddy Simulation (LES). The coherent structure function is used to build this sensor in combination with explicit test filtering. The proposed sensor features two main advantages: First, it attenuates the sub-grid scale dissipation of the base model for transitional flows. Depending on local conditions, the sensor is essentially blending the eddy viscosity between zero and the value resulting from the standard Smagorinsky model. Second, the sensor rectifies the incorrect near-wall scaling of the standard Smagorinsky model. Application of the sensor requires no averaging (in the homogeneous direction) and is easy to implement, and the additional computational cost is insignificant. In order to assess the model, three different configurations have been examined: laminar-to-turbulent transition in the Taylor-Green vortex, wall-dominated channel flows, and a free planar jet flow including passive scalar mixing. Based on a posteriori LES, it has been found that the new sensor-enhanced Smagorinsky model often outperforms established eddy viscosity models from the literature, such as the standard Smagorinsky model and the sigma model, as well as the LES without the explicit sub-grid model. © 2021 Author(s).
    view abstractdoi: 10.1063/5.0032117
  • 2021 • 941 Correlating the Synthesis, Structure, and Catalytic Performance of Pt-Re/TiO2for the Aqueous-Phase Hydrogenation of Carboxylic Acid Derivatives
    Haus, M.O. and Meledin, A. and Leiting, S. and Louven, Y. and Roubicek, N.C. and Moos, S. and Weidenthaler, C. and Weirich, T.E. and Palkovits, R.
    ACS Catalysis 11 5119-5134 (2021)
    Pt-Re bimetallic catalysts have many applications, ranging from catalytic reforming to the reduction of carboxylic acid derivatives. However, the exact role of Re in these systems has remained a matter of discussion, partly due to the plethora of suggested synthesis protocols and analysis conditions. This study presents an extensive comparison of such literature protocols and the resulting materials. In detail, characterization by N2 physisorption, X-ray diffraction, temperature-programmed reduction, CO pulse chemisorption, Fourier-transform infrared spectroscopy of adsorbed CO, scanning transmission electron microscopy, energy-dispersive X-ray spectroscopy, and in situ X-ray photoelectron spectroscopy is combined with catalytic testing to yield synthesis-structure-activity correlations. Accordingly, the investigated catalysts share common features, such as Pt0 nanoparticles (1-4 nm) decorated with partially reduced Re species (ReOx-y). The remaining rhenium oxide is spread over the TiO2 support and enhances Pt dispersion in sequential impregnation protocols. While differences in the number of active sites (Pt0/ReOx-y) mostly explain catalytic results, small variations in the extent of Re reduction and site composition cause additional modulations. The optimal bimetallic catalyst outperforms Ru/C (previous benchmark) in the reduction of N-(2-hydroxyethyl)succinimide, an important step in the production of a bio-based polyvinylpyrrolidone polymer. © 2021 American Chemical Society. All rights reserved.
    view abstractdoi: 10.1021/acscatal.0c05612
  • 2021 • 940 Effect of interface dislocations on mass flow during high temperature and low stress creep of single crystal Ni-base superalloys
    He, J. and Cao, L. and Makineni, S.K. and Gault, B. and Eggeler, G.
    Scripta Materialia 191 23-28 (2021)
    In this work, the nanometer-scale mass flow coupled to dislocation processes near the γ/γ′-interface during high temperature and low stress creep of a model Ni-base single crystal superalloy is investigated. In the early creep stages, the dislocation networks in the γ-phase at γ/γ′-interfaces attract γ-stabilizing elements like Cr, Co and in particular Re, resulting in compositional gradients close to the interface. At larger strains, where dislocations frequently cut into the γ′-phase, this local interfacial enrichment in these elements is no longer observed. The cutting dislocations take part of the segregated atoms away, whilst the remaining atoms are released and diffuse back into the γ-channels. © 2020
    view abstractdoi: 10.1016/j.scriptamat.2020.09.016
  • 2021 • 939 Correlation of load drop and crack initiation criteria in fatigue life experiments of metallic materials
    Heckmann, K. and Sievers, J. and Schopf, T. and Lücker, L. and Schmiedt-Kalenborn, A. and Walther, F. and Starke, P. and Acosta, R. and Boller, C.
    Engineering Fracture Mechanics 251 (2021)
    The simulation and assessment of fatigue damage of metallic materials are strongly dependent on the definition of critical damage initiation, i.e. the formation of a crack after a certain number of cycles under fatigue loading. To get this described in an appropriate way classical fatigue analysis needs to be combined with fracture mechanics to obtain a realistic size of an initiating macro crack in a component in the end. Ultimately, this size depends on the procedure of how fatigue life curves are generated from the fatigue tests performed. In this paper strain-controlled fatigue tests and fractographic results have been combined with a computational assessment to better understand the relationship between a traditional load drop criterion characterizing the size of a crack being initiated. It is stated that the location of an initiating crack versus the location of an extensometer applied to the specimen can have an influence on the crack size being initiated and thus the fatigue life for a load drop criterion being fixed. A relationship is proposed to link a crack size dependent on the fatigue test evaluation scheme with the fatigue life, which can be used in engineering assessments. The relevance of practical application cases is discussed. © 2021 Elsevier Ltd
    view abstractdoi: 10.1016/j.engfracmech.2021.107785
  • 2021 • 938 Asymmetric Rydberg blockade of giant excitons in Cuprous Oxide
    Heckötter, J. and Walther, V. and Scheel, S. and Bayer, M. and Pohl, T. and Aßmann, M.
    Nature Communications 12 (2021)
    The ability to generate and control strong long-range interactions via highly excited electronic states has been the foundation for recent breakthroughs in a host of areas, from atomic and molecular physics to quantum optics and technology. Rydberg excitons provide a promising solid-state realization of such highly excited states, for which record-breaking orbital sizes of up to a micrometer have indeed been observed in cuprous oxide semiconductors. Here, we demonstrate the generation and control of strong exciton interactions in this material by optically producing two distinct quantum states of Rydberg excitons. This is made possible by two-color pump-probe experiments that allow for a detailed probing of the interactions. Our experiments reveal the emergence of strong spatial correlations and an inter-state Rydberg blockade that extends over remarkably large distances of several micrometers. The generated many-body states of semiconductor excitons exhibit universal properties that only depend on the shape of the interaction potential and yield clear evidence for its vastly extended-range and power-law character. © 2021, The Author(s).
    view abstractdoi: 10.1038/s41467-021-23852-z
  • 2021 • 937 Analysis of the Fine Structure of the D-Exciton Shell in Cuprous Oxide
    Heckötter, J. and Rommel, P. and Main, J. and Aßmann, M. and Bayer, M.
    Physica Status Solidi - Rapid Research Letters 15 (2021)
    The exciton states in cuprous oxide show a pronounced fine structure splitting associated with the crystal environment and the resulting electronic band structure. High-resolution spectroscopy reveals an especially pronounced splitting of the yellow D excitons with one state pushed above any other state with the same principal quantum number. This large splitting offset is related to a strong mixing of these D states with the 1S exciton of the green series, as suggested by previously published calculations. Here, a detailed comparison of this theory with experimental data is given, which leads to a complete reassignment of the experimentally observed D exciton lines. The origin of different amounts of green admixture to D-envelope states is deduced by analyzing the different terms of the Hamiltonian. The yellow–green mixing leads to level repulsion and induces an exchange interaction splitting to D-envelope states, from which one of them becomes the highest state within each multiplet. Furthermore, the assignment of D exciton states according to their total angular momentum F is given and corrects an earlier description given in a former study. © 2021 The Authors. physica status solidi (RRL) Rapid Research Letters published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/pssr.202100335
  • 2021 • 936 Elemental segregation to lattice defects in the CrMnFeCoNi high-entropy alloy during high temperature exposures
    Heczko, M. and Mazánová, V. and Gröger, R. and Záležák, T. and Hooshmand, M.S. and George, E.P. and Mills, M.J. and Dlouhý, A.
    Acta Materialia 208 (2021)
    The influence of small plastic pre-strains on the elevated-temperature stability and microstructure of the equiatomic CrMnFeCoNi FCC solid solution is investigated. Particular attention is given to whether any of the alloy elements segregate to individual dislocations. To that end, CrMnFeCoNi samples were first deformed in tension at room temperature to plastic strains of 0.2 and 2.3%, and subsequently annealed at 973 K for 800 hours. The pre-strains activated planar slip of 1/2&lt;110&gt;-type dislocations on {111}-type glide planes. Interactions of this planar slip with special Σ3 grain boundaries formed a large number of dislocation segments with a &lt;110&gt;-type crystallographic orientation suitable for a credible end-on analysis of dislocation cores in HR-STEM. The cores of the 1/2&lt;110&gt; dislocations pushed up against the investigated grain boundaries were found to be close to the compact configuration. Within the sensitivity of the Super-X EDS mapping, no concentration gradient was detected near dislocations that would indicate enrichment at dislocation cores of any of the elemental constituents of the alloy after the pre-deformation and annealing. However, a Cr-rich tetragonal sigma phase nucleated and grew at grain boundary triple junctions during this anneal, processes that were not accelerated by the enhanced dislocation density present after pre-strain. A clear chromium gradient was observed in the Cr-depleted zones near grain boundaries suggesting that Cr transport occurred by relatively slow diffusion from the bulk to the grain boundaries and then by relatively fast diffusion along the grain boundaries to the precipitates. Accompanying the Cr depletion near grain boundaries is a simultaneous Ni and Mn enrichment, which promotes formation of the L10 NiMn phase that is observed on the grain boundaries after prolonged annealing. © 2021
    view abstractdoi: 10.1016/j.actamat.2021.116719
  • 2021 • 935 Vascular Network Formation on Macroporous Polydioxanone Scaffolds
    Heene, S. and Thoms, S. and Kalies, S. and Wegner, N. and Peppermüller, P. and Born, N. and Walther, F. and Scheper, T. and Blume, C.A.
    Tissue Engineering - Part A 27 1239-1249 (2021)
    In this study, microvascular network structures for tissue engineering were generated on newly developed macroporous polydioxanone (PDO) scaffolds. PDO represents a polymer biodegradable within months and offers optimal material properties such as elasticity and nontoxic degradation products. PDO scaffolds prepared by porogen leaching and cryo-dried to achieve pore sizes of 326 ± 149.67 μm remained stable with equivalent values for Young's modulus after 4 weeks. Scaffolds were coated with fibrin for optimal cell adherence. To exclude interindividual differences, autologous fibrin was prepared out of human plasma-derived fibrinogen and proved a comparable quality to nonautologous commercially available fibrinogen. Fibrin-coated scaffolds were seeded with recombinant human umbilical vein endothelial cells expressing GFP (GFP-HUVECs) in coculture with adipose tissue-derived mesenchymal stem cells (AD-hMSCs) to form vascular networks. The growth factor content in culture media was optimized according its effect on network formation, quantified and assessed by AngioTool®. A ratio of 2:3 GFP-HUVECs/AD-hMSCs in medium enriched with 20 ng/mL vascular endothelial growth factor, basic fibroblast growth factor, and hydrocortisone was found to be optimal. Network structures appeared after 2 days of cultivation and stabilized until day 7. The resulting networks were lumenized that could be verified by dextran staining. This new approach might be suitable for microvascular tissue patches as a useful template to be used in diverse vascularized tissue constructs. We consider this work as important for the current research in the field of tissue engineering and the development of new and functional tissue. The approach for the production of vascularized tissue patches, consisting of the biodegradable synthetic polymer polydioxanone and of the physiological, autologous, and patient-specific polymer fibrin, and seeded with endothelial cells and mesenchymal stem cells, displayed within this work, could be useful for the sustaining development of diverse and more complex tissue constructs. Therefore, these scaffolds could be used as a cornerstone for future tissue engineering approaches. © 2021 Mary Ann Liebert Inc.
    view abstractdoi: 10.1089/ten.tea.2020.0232
  • 2021 • 934 Dislocation networks in gamma/gamma’-microstructures formed during selective laser melting of a Ni-base superalloy
    Heep, L. and Schwalbe, C. and Heinze, C. and Dlouhy, A. and Rae, C.M.F. and Eggeler, G.
    Scripta Materialia 190 121-125 (2021)
    A dislocation network which formed during selective laser melting (SLM) of a Ni-base superalloy was analyzed using scanning transmission electron microscopy (STEM). This network traverses an ordered Gamma'-phase domain, in between two adjacent Gamma-solid solution regions. The Gamma’-phase region has formed when two Gamma’-phase particles have started to coalesce, trapping the dislocation network in this ordered region so that it formed two dislocation families with pairs of anti-phase boundary (APB) coupled super partial dislocations. The network features are presented and unusual features (twist character and low APB energies), not previously reported, are discussed. © 2020
    view abstractdoi: 10.1016/j.scriptamat.2020.08.019
  • 2021 • 933 Challenges in the Application of Manganese Oxide Powders as OER Electrocatalysts: Synthesis, Characterization, Activity and Stability of Nine Different MnxOy Compounds
    Heese-Gärtlein, J. and Rabe, A. and Behrens, M.
    Zeitschrift fur Anorganische und Allgemeine Chemie 647 1363-1372 (2021)
    Manganese oxides are seen as potential electrocatalysts for the alkaline oxygen evolution reaction (OER). To find the most suitable OER catalyst among the large number of known manganese oxide compounds, several comparative studies of selected MnxOy materials in water oxidation catalysis were reported in recent years with, in some cases, conflicting results. In this study, nine different manganese oxide powders differing in structure and/or composition were synthesized, characterized and compared regarding their OER activity and stability using a consistent set of experimental parameters. It turned out that the activity generally depends strongly on the manganese oxide compound. α-MnO2 manganese oxides of the hollandite-type were found to be more active than those with a lower oxidation state or other crystal structures. The most active catalyst cryptomelane, α-(K)MnO2, reached a current density of 10 mA/cm2 at 1.77±0.02 V in LSV measurements. At a potential of 1.8 V, the current density was approximately 15 mA cm−2. In contrast, the samples with the lowest activity exhibited values less than 1 mA cm−2 at the same potential. The stability experiments revealed a fast decrease in activity of all samples within the first minutes of measurement and an almost complete activity loss after 60 min. Conductivity differences are discussed as a likely reason for the observed differences in performance. © 2021 The Authors. Zeitschrift für anorganische und allgemeine Chemie published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/zaac.202000180
  • 2021 • 932 Identification of the factor XII contact activation site enables sensitive coagulation diagnostics
    Heestermans, M. and Naudin, C. and Mailer, R.K. and Konrath, S. and Klaetschke, K. and Jämsä, A. and Frye, M. and Deppermann, C. and Pula, G. and Kuta, P. and Friese, M.A. and Gelderblom, M. and Sickmann, A. and Preston, R.J.S. ...
    Nature Communications 12 (2021)
    Contact activation refers to the process of surface-induced activation of factor XII (FXII), which initiates blood coagulation and is captured by the activated partial thromboplastin time (aPTT) assay. Here, we show the mechanism and diagnostic implications of FXII contact activation. Screening of recombinant FXII mutants identified a continuous stretch of residues Gln317–Ser339 that was essential for FXII surface binding and activation, thrombin generation and coagulation. Peptides spanning these 23 residues competed with surface-induced FXII activation. Although FXII mutants lacking residues Gln317–Ser339 were susceptible to activation by plasmin and plasma kallikrein, they were ineffective in supporting arterial and venous thrombus formation in mice. Antibodies raised against the Gln317–Ser339 region induced FXII activation and triggered controllable contact activation in solution leading to thrombin generation by the intrinsic pathway of coagulation. The antibody-activated aPTT allows for standardization of particulate aPTT reagents and for sensitive monitoring of coagulation factors VIII, IX, XI. © 2021, The Author(s).
    view abstractdoi: 10.1038/s41467-021-25888-7
  • 2021 • 931 Synergistic Electrocatalytic Hydrogen Evolution in Ni/NiS Nanoparticles Wrapped in Multi-Heteroatom-Doped Reduced Graphene Oxide Nanosheets
    Hegazy, M.B.Z. and Berber, M.R. and Yamauchi, Y. and Pakdel, A. and Cao, R. and Apfel, U.-P.
    ACS Applied Materials and Interfaces 13 34043-34052 (2021)
    Hydrogen production is a key driver for sustainable and clean fuels used to generate electricity, which can be achieved through electrochemical splitting of water in alkaline solutions. However, the hydrogen evolution reaction (HER) is kinetically sluggish in alkaline media. Therefore, it has become imperative to develop inexpensive and highly efficient electrocatalysts that can replace the existing expensive and scarce noble-metal-based catalysts. Herein, we report on the rational design of nonprecious heterostructured electrocatalysts comprising a highly conductive face-centered cubic nickel metal, a nickel sulfide (NiS) phase, and a reduced graphene oxide (rGO) doped with phosphorous (P), sulfur (S), and nitrogen (N) in one ordered heteromaterial named Ni/NiS/P,N,S-rGO. The Ni/NiS/P,N,S-rGO electrode shows the best performance toward HER in 1.0 M KOH media among all materials tested with an overpotential of 155 mV at 10.0 mA cm-2 and a Tafel slope of 135 mV dec-1. The performance is comparable to the herein used Pt/C-20% benchmark catalyst examined under the same experimental conditions. The chronoamperometry and chronopotentiometry measurements have reflected the high durability of the Ni/NiS/P,N,S-rGO electrode for technological applications. At the same time, the current catalyst showed a high robustness and structure retention after long-term HER performance, which is reflected by SEM, XRD, and XPS measurements. ©
    view abstractdoi: 10.1021/acsami.1c05888
  • 2021 • 930 Impact of magnetic transition on Mn diffusion in α -iron: Correlative state-of-the-art theoretical and experimental study
    Hegde, O. and Kulitckii, V. and Schneider, A. and Soisson, F. and Hickel, T. and Neugebauer, J. and Wilde, G. and Divinski, S. and Fu, C.-C.
    Physical Review B 104 (2021)
    An accurate prediction of atomic diffusion in Fe alloys is challenging due to thermal magnetic excitations and magnetic transitions. We investigate the diffusion of Mn in bcc Fe using an effective interaction model and first-principles based spin-space averaged relaxations in magnetically disordered systems. The theoretical results are compared with the dedicated radiotracer measurements of Mn54 diffusion in a wide temperature range of 773 to 1173 K, performed by combining the precision grinding (higher temperatures) and ion-beam sputtering (low temperatures) sectioning techniques. The temperature evolution of Mn diffusion coefficients in bcc iron in theory and experiment agree very well and consistently reveal a reduced acceleration of Mn solute diffusion around the Curie point. By analyzing the temperature dependencies of the ratio of Mn diffusion coefficients to self-diffusion coefficients we observe a dominance of magnetic disorder over chemical effects on high-temperature diffusion. Therefore, the missing acceleration mainly reflects an anomalous behavior of the Mn solute in the magnetically ordered low-temperature state of the Fe host, as compared to other transition metals. © 2021 authors. Published by the American Physical Society.
    view abstractdoi: 10.1103/PhysRevB.104.184107
  • 2021 • 929 Generation of terahertz transients from Co2Fe0.4 M0.6 Si-Heusler-alloy/normal-metal nanobilayers excited by femtosecond optical pulses
    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...
    Physical Review Research 3 (2021)
    We generated pulses of electromagnetic radiation in the terahertz (THz) frequency range by optical excitation of (CFMS)/normal-metal (NM) bilayer structures. The CFMS is a Heusler alloy showing a band gap in one spin channel and is therefore a half metal. We compared the THz emission efficiency in a systematic manner for four different CFMS/NM bilayers, where NM was either Pt, Ta, Cr, or Al. Our measurements show that the THz intensity is highest for a Pt capping. We also demonstrate the tunability of the THz amplitude by varying the magnetic field for all four bilayers. We attribute the THz generation to the inverse spin Hall effect. In order to investigate the role of the interface in THz generation, we measured the spin mixing conductance for each CFMS/NM bilayer using a ferromagnetic resonance method. We found that the spin-orbit coupling cannot completely describe the THz generation in the bilayers and that the spin transmission efficiency of the CFMS/NM interface and the spin diffusion length, as well as the oxidation of the NM layer, play crucial roles in the THz emission process. © 2021 Published by the American Physical Society
    view abstractdoi: 10.1103/PhysRevResearch.3.043025
  • 2021 • 928 Dipolar-stabilized first and second-order antiskyrmions in ferrimagnetic multilayers
    Heigl, M. and Koraltan, S. and Vaňatka, M. and Kraft, R. and Abert, C. and Vogler, C. and Semisalova, A. and Che, P. and Ullrich, A. and Schmidt, T. and Hintermayr, J. and Grundler, D. and Farle, M. and Urbánek, M. and Suess, D....
    Nature Communications 12 (2021)
    Skyrmions and antiskyrmions are topologically protected spin structures with opposite vorticities. Particularly in coexisting phases, these two types of magnetic quasi-particles may show fascinating physics and potential for spintronic devices. While skyrmions are observed in a wide range of materials, until now antiskyrmions were exclusive to materials with D2d symmetry. In this work, we show first and second-order antiskyrmions stabilized by magnetic dipole–dipole interaction in Fe/Gd-based multilayers. We modify the magnetic properties of the multilayers by Ir insertion layers. Using Lorentz transmission electron microscopy imaging, we observe coexisting antiskyrmions, Bloch skyrmions, and type-2 bubbles and determine the range of material properties and magnetic fields where the different spin objects form and dissipate. We perform micromagnetic simulations to obtain more insight into the studied system and conclude that the reduction of saturation magnetization and uniaxial magnetic anisotropy leads to the existence of this zoo of different spin objects and that they are primarily stabilized by dipolar interaction. © 2021, The Author(s).
    view abstractdoi: 10.1038/s41467-021-22600-7
  • 2021 • 927 Combining machine learning and domain decomposition methods for the solution of partial differential equations—A review
    Heinlein, A. and Klawonn, A. and Lanser, M. and Weber, J.
    GAMM Mitteilungen 44 (2021)
    Scientific machine learning (SciML), an area of research where techniques from machine learning and scientific computing are combined, has become of increasing importance and receives growing attention. Here, our focus is on a very specific area within SciML given by the combination of domain decomposition methods (DDMs) with machine learning techniques for the solution of partial differential equations. The aim of the present work is to make an attempt of providing a review of existing and also new approaches within this field as well as to present some known results in a unified framework; no claim of completeness is made. As a concrete example of machine learning enhanced DDMs, an approach is presented which uses neural networks to reduce the computational effort in adaptive DDMs while retaining their robustness. More precisely, deep neural networks are used to predict the geometric location of constraints which are needed to define a robust coarse space. Additionally, two recently published deep domain decomposition approaches are presented in a unified framework. Both approaches use physics-constrained neural networks to replace the discretization and solution of the subdomain problems of a given decomposition of the computational domain. Finally, a brief overview is given of several further approaches which combine machine learning with ideas from DDMs to either increase the performance of already existing algorithms or to create completely new methods. © 2021 The Authors. GAMM - Mitteilungen published by Wiley-VCH GmbH.
    view abstractdoi: 10.1002/gamm.202100001
  • 2021 • 926 Fully Algebraic Two-Level Overlapping Schwarz Preconditioners for Elasticity Problems
    Heinlein, A. and Hochmuth, C. and Klawonn, A.
    Lecture Notes in Computational Science and Engineering 139 531-539 (2021)
    Different parallel two-level overlapping Schwarz preconditioners with Generalized Dryja–Smith–Widlund (GDSW) and Reduced dimension GDSW (RGDSW) coarse spaces for elasticity problems are considered. GDSW type coarse spaces can be constructed from the fully assembled system matrix, but they additionally need the index set of the interface of the corresponding nonoverlapping domain decomposition and the null space of the elasticity operator, i.e., the rigid body motions. In this paper, fully algebraic variants, which are constructed solely from the uniquely distributed system matrix, are compared to the classical variants which make use of this additional information; the fully algebraic variants use an approximation of the interface and an incomplete algebraic null space. Nevertheless, the parallel performance of the fully algebraic variants is competitive compared to the classical variants for a stationary homogeneous model problem and a dynamic heterogenous model problem with coefficient jumps in the shear modulus; the largest parallel computations were performed on 4096 MPI (Message Passing Interface) ranks. The parallel implementations are based on the Trilinos package FROSch. © 2021, Springer Nature Switzerland AG.
    view abstractdoi: 10.1007/978-3-030-55874-1_52
  • 2021 • 925 Machine Learning in Adaptive FETI-DP: Reducing the Effort in Sampling
    Heinlein, A. and Klawonn, A. and Lanser, M. and Weber, J.
    Lecture Notes in Computational Science and Engineering 139 593-603 (2021)
    The convergence rate of classic domain decomposition methods in general deteriorates severely for large discontinuities in the coefficient functions of the considered partial differential equation. To retain the robustness for such highly heterogeneous problems, the coarse space can be enriched by additional coarse basis functions. These can be obtained by solving local generalized eigenvalue problems on subdomain edges. In order to reduce the number of eigenvalue problems and thus the computational cost, we use a neural network to predict the geometric location of critical edges, i.e., edges where the eigenvalue problem is indispensable. As input data for the neural network, we use function evaluations of the coefficient function within the two subdomains adjacent to an edge. In the present article, we examine the effect of computing the input data only in a neighborhood of the edge, i.e., on slabs next to the edge. We show numerical results for both the training data as well as for a concrete test problem in form of a microsection subsection for linear elasticity problems. We observe that computing the sampling points only in one half or one quarter of each subdomain still provides robust algorithms. © 2021, Springer Nature Switzerland AG.
    view abstractdoi: 10.1007/978-3-030-55874-1_58
  • 2021 • 924 Detection of fatigue induced fracture of prestressing steel by means of monitoring of experiment and structure [Detektieren ermüdungsbedingter spannstahlbrüche mittels rissmonitoring im versuch und am bauwerk]
    Heinrich, J. and Maurer, R. and Leckey, K. and Müller, C.H. and Ickstadt, K.
    Bauingenieur 96 92-101 (2021)
    On a prestressed concrete bridge in the region of the point of zero moment due to permanent load systematic crack formations with crack widths up to 0.5 mm were de-tected. These cracks were a consequence of the restraint mo-ments due to temperature (∆TM), which have not been considered at that time. As a result of the cracks, the tendons were endangered by fatigue. Even with more refined methods, it was not possible to verify sufficient fatigue resistance. In addi-tion, the overall structural condition was in a poor state. There-fore, the road authority decided to build a new bridge as repla-cement as soon as possible. Up to that point the structural safety of the bridge had to be ensured. For this purpose, conti-nuous crack monitoring was carried out for the critical areas. Fatigue tests on prestressed concrete components at TU Dortmund University formed the basis for its evaluation. These tests succeeded in reliably identifying individual wire breaks during the ongoing test and in developing a prognosis method for the remaining service life. The experiences and difficulties of transferring these methods to a real structure are reported. © 2021, VDI Fachmedien GmBbH & Co. All rights reserved.
    view abstractdoi: 10.37544/0005-6650-2021-03-60
  • 2021 • 923 Surrogate models for the prediction of damping ratios in coupled acoustoelastic rotor-cavity systems
    Heinrich, C.R. and Unglaube, T. and Beirow, B. and Brillert, D. and Steff, K. and Petry, N.
    Proceedings of the ASME Turbo Expo 9B-2021 (2021)
    Centrifugal compressors are versatile machines that many industries employ for a wide range of different applications, including the production of highly compressed gases. During the last decades, comprehensive research was conducted on the impact of high-pressure operating conditions on the vibrational behavior of radial compressors. In various studies, acoustic modes building up in the side cavities were found to be a potential source of high cycle fatigue. Nowadays, it is well-known that an increase in gas pressure levels leads to a more pronounced fluid-structure interaction between the side cavities and the impeller resulting in a frequency shift of the acoustic and structural modes. In a recently published paper, the authors presented a generalized model which can predict this behavior. As it is not always possible to avoid operating close to or accelerating through a resonance, it is crucial to know the damping present within the system. Currently, only a few publications concentrate on the damping of radial impellers. Therefore, the authors present measurement data acquired from a test rig at the University of Duisburg-Essen, which reveals the damping behavior of a disk under varying operating conditions. Two surrogate models are proposed to predict the identified damping behavior. The first one is based solely on a one-dimensional piston model and the second approach uses an enhanced version of the generalized method. Finally, the measurement data is used to validate both surrogate systems. © 2021 American Society of Mechanical Engineers (ASME). All rights reserved.
    view abstractdoi: 10.1115/GT2021-58835
  • 2021 • 922 A distribution free test for changes in the trend function of locally stationary processes∗
    Heinrichs, F. and Dette, H.
    Electronic Journal of Statistics 15 3762-3797 (2021)
    In the common time series model Xi,n = μ(i/n) +εi,n with non-stationary errors we consider the problem of detecting a significant deviation of the mean function μ from a benchmark g(μ) (suchastheini-tial value μ(0) or the average trend∫ 1 0 μ(t)dt). The problem is motivated by a more realistic modelling of change point analysis, where one is inter-ested in identifying relevant deviations in a smoothly varying sequence of means (μ(i/n))i=1,…,n and cannot assume that the sequence is piecewise constant. A test for this type of hypotheses is developed using an appro-priate estimator for the integrated squared deviation of the mean function and the threshold. By a new concept of self-normalization adapted to non-stationary processes an asymptotically pivotal test for the hypothesis of a relevant deviation is constructed. The results are illustrated by means of a simulation study and a data example. © 2021, Institute of Mathematical Statistics. All rights reserved.
    view abstractdoi: 10.1214/21-EJS1871
  • 2021 • 921 On general imperfect interfaces with spatially non-constant displacement jumps
    Heitbreder, T. and Kurzeja, P. and Mosler, J.
    International Journal of Solids and Structures 232 (2021)
    A novel constitutive framework suitable for material interfaces undergoing large deformations is presented. In contrast to previous works, it accounts for spatially non-constant displacement jumps in the Helmholtz energy by employing their gradient along the interface. This first-order generalization encompasses classic cohesive zone models and surface elasticity theory as special cases. Based on a unifying variational ansatz, all balance laws are derived in a natural manner. Balance of angular momentum is enforced pointwise by designing energies that are material frame indifferent. It is shown that for quadratic energies already existing interface models can predict the same features as the novel framework. However, for higher-order energies, this analogy is lost and the generalized, gradient-based framework indeed allows to capture additional effects. An exemplary experiment highlights such effects for a 3d-printed specimen with a soft interface. © 2021 Elsevier Ltd
    view abstractdoi: 10.1016/j.ijsolstr.2021.111068
  • 2021 • 920 A fresh look at the structure of aromatic thiols on Au surfaces from theory and experiment
    Hekele, J. and Linke, M. and Keller, T. and Jose, J. and Hille, M. and Hasselbrink, E. and Schlücker, S. and Kratzer, P.
    Journal of Chemical Physics 155 (2021)
    A detailed study of the adsorption structure of self-assembled monolayers of 4-nitrothiophenol on the Au(111) surface was performed from a theoretical perspective via first-principles density functional theory calculations and experimentally by Raman and vibrational sum frequency spectroscopy (vSFS) with an emphasis on the molecular orientation. Simulations—including an explicit van der Waals (vdW) description—for different adsorbate structures, namely, for (3×3), (2 × 2), and (3 × 3) surface unit cells, reveal a significant tilting of the molecules toward the surface with decreasing coverage from 75° down to 32° tilt angle. vSFS suggests a tilt angle of 50°, which agrees well with the one calculated for a structure with a coverage of 0.25. Furthermore, calculated vibrational eigenvectors and spectra allowed us to identify characteristic in-plane (NO2 scissoring) and out-of-plane (C-H wagging) modes and to predict their strength in the spectrum in dependence of the adsorption geometry. We additionally performed calculations for biphenylthiol and terphenylthiol to assess the impact of multiple aromatic rings and found that vdW interactions are significantly increasing with this number, as evidenced by the absorption energy and the molecule adopting a more upright-standing geometry. © 2021 Author(s).
    view abstractdoi: 10.1063/5.0053493
  • 2021 • 919 All-electron real-time and imaginary-time time-dependent density functional theory within a numeric atom-centered basis function framework
    Hekele, J. and Yao, Y. and Kanai, Y. and Blum, V. and Kratzer, P.
    Journal of Chemical Physics 155 (2021)
    Real-time time-dependent density functional theory (RT-TDDFT) is an attractive tool to model quantum dynamics by real-time propagation without the linear response approximation. Sharing the same technical framework of RT-TDDFT, imaginary-time time-dependent density functional theory (it-TDDFT) is a recently developed robust-convergence ground state method. Presented here are high-precision all-electron RT-TDDFT and it-TDDFT implementations within a numerical atom-centered orbital (NAO) basis function framework in the FHI-aims code. We discuss the theoretical background and technical choices in our implementation. First, RT-TDDFT results are validated against linear-response TDDFT results. Specifically, we analyze the NAO basis sets’ convergence for Thiel’s test set of small molecules and confirm the importance of the augmentation basis functions for adequate convergence. Adopting a velocity-gauge formalism, we next demonstrate applications for systems with periodic boundary conditions. Taking advantage of the all-electron full-potential implementation, we present applications for core level spectra. For it-TDDFT, we confirm that within the all-electron NAO formalism, it-TDDFT can successfully converge systems that are difficult to converge in the standard self-consistent field method. We finally benchmark our implementation for systems up to ∼500 atoms. The implementation exhibits almost linear weak and strong scaling behavior. © 2021 Author(s).
    view abstractdoi: 10.1063/5.0066753
  • 2021 • 918 Photoelectron Photoion Coincidence Spectroscopy Provides Mechanistic Insights in Fuel Synthesis and Conversion
    Hemberger, P. and Bodi, A. and Bierkandt, T. and Köhler, M. and Kaczmarek, D. and Kasper, T.
    Energy and Fuels 35 16265-16302 (2021)
    Clean combustion, i.e., the reduction of NOx and soot emissions, and carbon neutrality, achieved in part by biofuel synthesis, are major milestones in the transition to a sustainable future. To overcome empiric and time-consuming process optimization steps, we need detailed reaction mechanistic and chemical insights on these processes. Be it in combustion or in catalysis, highly reactive intermediates, such as radicals, carbenes, and ketenes drive chemical reactions. Knowing the fate of these species helps develop strategies to optimize chemical energy conversion processes. This calls for advanced mass spectrometric tools, which enable the detection of transient species. In this review, we report on the application of state-of-the-art photoelectron photoion coincidence (PEPICO) spectroscopy with vacuum ultraviolet (VUV) synchrotron radiation as advanced diagnostic tools in catalysis and combustion research. We discuss reaction mechanisms in biomass conversion to sustainable fuels, where we report on the pyrolysis of wood samples probed using VUV photoionization mass spectrometry (PIMS) and obtain deep mechanistic insights in the (non)catalytic pyrolysis of lignin model compounds with PEPICO detection. PEPICO is also shown to contribute to the mechanistic understanding of catalysis by unveiling catalytic alkane valorization mechanisms. We discuss how PEPICO detection advances combustion diagnostics, thanks to the application of photoelectron spectroscopy and velocity map imaging. We report on mechanistic aspects of ignition, such as fuel radical formation and oxidation to peroxy species, and discuss reaction pathways of pollutant formation. In addition, we zoom into the elementary reactions of combustion and discuss isomer-selective kinetics experiments on radical oxidation. Newly revealed reaction pathways to polycyclic aromatic hydrocarbon (PAH) formation are also detailed. Finally, we describe current instrumental developments to improve PEPICO detection and report on innovative sources, reactors, and reaction sampling approaches to be combined with this technique. © 2021 American Chemical Society.
    view abstractdoi: 10.1021/acs.energyfuels.1c01712
  • 2021 • 917 Protein signature of human skin fibroblasts allows the study of the molecular etiology of rare neurological diseases
    Hentschel, A. and Czech, A. and Münchberg, U. and Freier, E. and Schara-Schmidt, U. and Sickmann, A. and Reimann, J. and Roos, A.
    Orphanet Journal of Rare Diseases 16 (2021)
    Background: The elucidation of pathomechanisms leading to the manifestation of rare (genetically caused) neurological diseases including neuromuscular diseases (NMD) represents an important step toward the understanding of the genesis of the respective disease and might help to define starting points for (new) therapeutic intervention concepts. However, these “discovery studies” are often limited by the availability of human biomaterial. Moreover, given that results of next-generation-sequencing approaches frequently result in the identification of ambiguous variants, testing of their pathogenicity is crucial but also depending on patient-derived material. Methods: Human skin fibroblasts were used to generate a spectral library using pH8-fractionation of followed by nano LC-MS/MS. Afterwards, Allgrove-patient derived fibroblasts were subjected to a data independent acquisition approach. In addition, proteomic signature of an enriched nuclear protein fraction was studied. Proteomic findings were confirmed by immunofluorescence in a muscle biopsy derived from the same patient and cellular lipid homeostasis in the cause of Allgrove syndrome was analysed by fluorescence (BODIPY-staining) and coherent anti-Stokes Raman scattering (CARS) microscopy. Results: To systematically address the question if human skin fibroblasts might serve as valuable biomaterial for (molecular) studies of NMD, we generated a protein library cataloguing 8280 proteins including a variety of such linked to genetic forms of motoneuron diseases, congenital myasthenic syndromes, neuropathies and muscle disorders. In silico-based pathway analyses revealed expression of a diversity of proteins involved in muscle contraction and such decisive for neuronal function and maintenance suggesting the suitability of human skin fibroblasts to study the etiology of NMD. Based on these findings, next we aimed to further demonstrate the suitability of this in vitro model to study NMD by a use case: the proteomic signature of fibroblasts derived from an Allgrove-patient was studied. Dysregulation of paradigmatic proteins could be confirmed in muscle biopsy of the patient and protein-functions could be linked to neurological symptoms known for this disease. Moreover, proteomic investigation of nuclear protein composition allowed the identification of protein-dysregulations according with structural perturbations observed in the muscle biopsy. BODIPY-staining on fibroblasts and CARS microscopy on muscle biopsy suggest altered lipid storage as part of the underlying disease etiology. Conclusions: Our combined data reveal that human fibroblasts may serve as an in vitro system to study the molecular etiology of rare neurological diseases exemplified on Allgrove syndrome in an unbiased fashion. © 2021, The Author(s).
    view abstractdoi: 10.1186/s13023-020-01669-1
  • 2021 • 916 Investigation of the frequency dependent spatio-temporal dynamics and controllability of microdischarges in unipolar pulsed plasma electrolytic oxidation
    Hermanns, P. and Boeddeker, S. and Bracht, V. and Bibinov, N. and Grundmeier, G. and Awakowicz, P.
    Journal of Physics D: Applied Physics 54 (2021)
    The unipolar pulsed-plasma electrolytic oxidation (PEO) of aluminum has been replaced by bipolar pulsed methods that use a so-called 'soft-sparking'mode. This method results in an effective reduction of intense microdischarges, which are detrimental to the oxide layer. In a previous publication, we developed an in-situ multivariable microdischarge control scheme using unipolar pulsing. Using this method, it is possible to restrict the mean microdischarge size to well-defined limits, while at the same time influencing the mean microdischarge energy, number density or spectral emission behaviour. This method operates well inside a frequency range of f = 1-20 kHz. Although this method shows highly desirable plasma control properties, the mechanisms defining this frequency-dependent controllability are unclear. The aim of this study is to visualize the spatio-temporal behavior of microdischarges in higher frequency ranges. First, a wavelet transform was performed to estimate the temporal evolution of microdischarge lifetimes. Ceramic coatings were then deposited on aluminum alloy substrates in an aqueous solution using unipolar pulsed galvanostatic PEO. The aluminum samples were coated for 30 min at frequencies of f1 = 50 Hz, f2 = 5 kHz and f3 = 100 kHz. High-speed imaging was carried out utilizing four synchronized intensified charge-coupled device (ICCD) cameras, each with a 500 ns exposure time. At f2 = 5 kHz, the microdischarges were still able to follow the electrical pulses. In this regime, the process can be divided into two stages, an initial charging of the substrate surface without plasma emission and a subsequent slower evolution of microdischarges. Equivalent circuit model descriptions are given for both processes. At f3 = 100 kHz, microdischarges were not able to follow the pulse frequency, as the lifetimes and risetimes of the microdischarge characteristics were longer than the pulse length. Reignition at the same spatial location, clustering and permanent ignition through pulse periods were observed. © 2020 IOP Publishing Ltd.
    view abstractdoi: 10.1088/1361-6463/abbde4
  • 2021 • 915 In-field detection method for imidacloprid by surface enhanced Raman spectroscopy
    Hermsen, A. and Lamers, D. and Schoettl, J. and Mayer, C. and Jaeger, M.
    Toxicological and Environmental Chemistry (2021)
    Neonicotinoids such as imidacloprid are used in agriculture worldwide. Due to their hazardous potential, their occurrence is monitored. For pesticide identification in environmental samples, the major tool, high performance liquid chromatography coupled with mass spectrometry, is not fit for field monitoring due to instrument size and technical requirements. To overcome this disadvantage, a method for fast on-site identification of imidacloprid was developed using a handheld Raman spectrometer and surface enhanced Raman spectroscopy. As enhancing agents, gold nanoparticles in solution and on textile support were compared for easy, fast and sensitive monitoring. Agglomeration of nanoparticles led to further signal enhancement. Several agglomeration reagents, filter paper and non-woven polylactide as substrates were tested for optimum enhancement. Addition of hydrochloric acid provided best amplification of imidacloprid signals in solution, while PLA as solid support yielded best sensitivity. Both the solution and solid support methods were estimated to be sufficiently sensitive for fieldable pesticide identification, which may precede standard laboratory analysis. Based on spectral analysis, a proposal for the imidacloprid-gold surface geometry was derived. © 2021 Informa UK Limited, trading as Taylor & Francis Group.
    view abstractdoi: 10.1080/02772248.2021.1991929
  • 2021 • 914 Tissue differentiation using optical emission spectroscopy for gastric mucosal devitalisation
    Hillebrand, B. and Jurjut, O. and Schuhmann, T. and Schürmann, M. and Neugebauer, A. and Kemen, M. and Awakowicz, P. and Enderle, M.
    Journal of Physics D: Applied Physics 54 (2021)
    Argon plasma coagulation is a promising new approach to combat obesity. During the procedure, a large area of the gastric lamina mucosae and the parietal cells that are located in this layer are ablated. This reduces the secretion of the hormone ghreline, which is known to play a major role in inducing appetite. One hypothesis is that this procedure partly suppresses the feeling of hunger which lowers the food-intake and body weight effectively. To rule out side effects, the treatment of other structures of the gastric wall that are much more sensitive to thermal injury, such as the tela submucosa and the lamina muscularis propria, needs to be avoided. The possibility of layer specific tissue differentiation is explored in this work using optical emission spectroscopy on ex vivo human stomach tissue. The optical emission generated during the plasma treatment of each layer is measured with two different spectrometers. The three main layers of the gastric wall can be differentiated by specific emissions lines of electrolytic ions and trace elements. In order to evaluate the diagnostic quality of this method a linear support vector classifier is used to differentiate the three layers against each other on the basis of these emission lines of these elements. This differentiation between 'mucosa' and 'submucosa' results in a sensitivity of up to 82% and specificity of up to 92%. However, a lower sensitivity and specificity is found for a classification between 'submucosa' and 'muscularis' which implies that a classification between 'mucosa' and 'not mucosa' would be a much more suitable classification for a later clinical application. © 2021 The Author(s). Published by IOP Publishing Ltd.
    view abstractdoi: 10.1088/1361-6463/abf400
  • 2021 • 913 Characterisation of an artesian groundwater system in the Valle de Iglesia in the Central Andes of Argentina
    Hinzer, I. and Altherr, M. and Christiansen, R. and Schreuer, J. and Wohnlich, S.
    International Journal of Earth Sciences (2021)
    Despite its location in the “Arid Diagonal” of South America, the Valle de Iglesia contains a number of artesian springs, the most important of which are the Baños Pismanta thermal springs, which release water at ~ 45 °C. Despite the scarcity of water resources in the Valle de Iglesia, there have been few attempts to study these springs in any detail. In this study, &gt; 50 springs are described, each characterised by small volcano-like mud structures up to 15 m tall. Hydrogeological and hydrochemical analyses of the groundwater system in the Valle de Iglesia were performed to improve our understanding of the subsurface water flow and of the connections between the subsurface water and the associated systems of faults and springs. Site measurements were made, and the concentrations of the main ions and trace elements were also determined by laboratory analysis of water samples. The samples obtained from the spring were rich in Na–HCO3–SO4 and Na–SO4–HCO3, but the surface water samples from the Agua Negra River were rich in Ca–SO4–HCO3. The temperature of the springs was in the range 20–45 °C. Both the temperatures and the ionic ratios are compatible with the presence of a deep hydraulic circulation system. The oxidation of sulphide minerals nearby the magmatic rocks and volcanic edifices causes the mobilisation of arsenic, which accumulates in the groundwater due to the low annual rainfall. The concentrations of arsenic in the spring water samples were therefore higher than the current limit set by the World Health Organisation, meaning that the water is not suitable for human consumption. © 2021, The Author(s).
    view abstractdoi: 10.1007/s00531-021-02058-0
  • 2021 • 912 On the relation of structural disorder and thermoelastic properties in ZnGa2O4 and Zn1−xMgxGa2O4 (x ≈ 0.33)
    Hirschle, C. and Schreuer, J. and Galazka, Z. and Ritter, C.
    Journal of Alloys and Compounds 886 (2021)
    The cation distribution at room temperature, as well as elastic properties and thermal expansion of single crystal ZnGa2O4 (ZGO) and Zn1−xMgxGa2O4 (x ≈ 0.33; ZMGO) with spinel-type structure were studied in a wide temperature range using single crystal X-ray diffraction, neutron powder diffraction, inductive gauge dilatometry and resonant ultrasound spectroscopy. ZGO adopts an almost normal spinel structure, whereas ZMGO is significantly disordered. At room temperature, the elastic properties of ZMGO mostly fall between those of ZGO and MgGa2O4 (MGO). The temperature dependences of the thermoelastic properties of ZGO and ZMGO, as well as thermal expansion of ZGO reveal distinct signatures of glass-like transitions, which separate states in which the cation dynamics are fast enough to relax the cation order in response to temperature change in laboratory timescales from those in which they are not. In equilibrium, thermal expansion is increased in ZMGO, whereas the thermoelastic coefficients are decreased in both ZGO and ZMGO. The temperature range of the transition is significantly larger in ZGO compared to ZMGO and MGO. Trends within the elastic properties, thermoelastic properties, thermal expansion and the glass-like transition in the (Zn,Mg)Ga2O4 solid solution series are discussed based on the impact of inversion, structural disorder, bond character and in comparison to other spinels. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.jallcom.2021.161214
  • 2021 • 911 Threshold photoionization shows no sign of nitryl hydride in methane oxidation with nitric oxide
    Hoener, M. and Bodi, A. and Hemberger, P. and Endres, T. and Kasper, T.
    Physical Chemistry Chemical Physics 23 1265-1272 (2021)
    Methane was doped with nitric oxide and oxidized in a high-pressure flow reactor. The nitrogen chemistry during partial oxidation was studied using photoelectron photoion coincidence spectroscopy with vacuum ultraviolet synchrotron radiation. The adiabatic ionization energy of nitrous acid, HONO, has been determined as 10.95 ± 0.03 eV. The HONO breakdown diagram was plotted based solely on the measured parent signal and the computed Franck-Condon envelope of trans-HONO, confirming the trans-HONO dissociative photoionization threshold to NO+ + OH at 11.34 eV. The spectra show strong indication for the presence of cis-HONO. We expected the m/z 47 photoion mass selected threshold photoelectron signal to rebound near 12 eV, i.e., at the ionization energy of nitryl hydride, the third HNO2 isomer. Recent computational studies suggest nitryl hydride is formed at a rate similar to trans-HONO, is more thermally stable than nitrous acid, its cation is bound, and its photoelectron spectrum is predicted to exhibit a strong origin band near 12 eV. The absence of its mass selected threshold photoelectron signal shows that nitryl hydride is either not formed in measurable amounts or is consumed faster than nitrous acid, for instance by isomerization to trans-HONO. This journal is © the Owner Societies.
    view abstractdoi: 10.1039/d0cp04924g
  • 2021 • 910 Reduction of warping in kinematic l-profile bending using local heating
    Hoffmann, E. and Meya, R. and Tekkaya, A.E.
    Metals 11 (2021)
    Kinematic bending of profiles allows to manufacture parts with high flexibility concerning the geometry. Still, the production of profiles with asymmetric cross-sections regarding the force application axis using kinematic bending processes offers challenges regarding springback and warping. These geometric deviations can be reduced by partial, cross-sectional heating during the process as it lowers the flow stress locally. In this work, the influence of partial, cross-sectional heating during a three-roll push-bending process on the warping and springback of L-profiles is investigated. Numerical and experimental methods reveal the influence of temperature on warping and springback. A newly developed analytical model predicts the warping and bending moment in the design phase and assists to understand the effect of warping reduction through partial heating during plastic bending. With increasing temperature of the heated profile area, the warping is reduced up to 76% and the springback of the bend profiles is decreased up to 44%. The warping reduction is attributed to a shift in stress free fiber due to the temperature gradient between heated and room temperature areas. The shift of stress-free fiber leads to an adapted shear center position, resulting in an approximated “quasi-symmetric” bending case. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/met11071146
  • 2021 • 909 Process enhancement of the 3-roll bending reduces twisting of L profiles: Twist-free bending thanks to cross-section heating [Verfahrenserweiterung des drei-rollen-schubbiegens reduziert verdrillung von l-profilen verdrillungsfreies biegen dank querschnittserwärmung]
    Hoffmann, E. and Meya, R. and Tekkaya, A.E.
    VDI-Z Integrierte Produktion 163 52-54 (2021)
  • 2021 • 908 Experimental Analysis on Granular Media-Based Tube Forming with Active Axial Feed
    Hoffmann, E. and Löbbe, C. and Tekkaya, A.E.
    Minerals, Metals and Materials Series 2661-2670 (2021)
    Production of high strength, high stiffness, and safety-relevant profile parts is feasible through the sequence of media-based forming and in-die quenching. As forming media, solid granular media have been recently introduced. In this work, the granular media tube press hardening process with additional axial feeding is investigated in order to enhance the tube thickness distribution and to enlarge the process window. The experiments show that, compared to the process with frictional feed, the limits for insufficient forming and wrinkling are unaffected by the change of the feeding system, while the area for intolerable thinning is reduced. Additionally, through the new feeding system, a higher degree of design freedom could be achieved, e.g., shoulder angles of 90° are possible. Furthermore, for the design of the process, an advanced FEM simulation has been developed, which is based on the Drucker–Prager cap model and covers also the thermal interactions. © 2021, The Minerals, Metals & Materials Society.
    view abstractdoi: 10.1007/978-3-030-75381-8_220
  • 2021 • 907 Computational generation of virtual concrete mesostructures
    Holla, V. and Vu, G. and Timothy, J.J. and Diewald, F. and Gehlen, C. and Meschke, G.
    Materials 14 (2021)
    Concrete is a heterogeneous material with a disordered material morphology that strongly governs the behaviour of the material. In this contribution, we present a computational tool called the Concrete Mesostructure Generator (CMG) for the generation of ultra-realistic virtual concrete morphologies for mesoscale and multiscale computational modelling and the simulation of concrete. Given an aggregate size distribution, realistic generic concrete aggregates are generated by a sequential reduction of a cuboid to generate a polyhedron with multiple faces. Thereafter, concave depressions are introduced in the polyhedron using Gaussian surfaces. The generated aggregates are assembled into the mesostructure using a hierarchic random sequential adsorption algorithm. The virtual mesostructures are first calibrated using laboratory measurements of aggregate distributions. The model is validated by comparing the elastic properties obtained from laboratory testing of concrete specimens with the elastic properties obtained using computational homogenisation of virtual concrete mesostructures. Finally, a 3D-convolutional neural network is trained to directly generate elastic properties from voxel data. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/ma14143782
  • 2021 • 906 A priori error estimates for the finite element approximation of a nonsmooth optimal control problem governed by a coupled semilinear pde-ode system
    Holtmannspotter, M. and Rösch, A.
    SIAM Journal on Control and Optimization 59 3329-3358 (2021)
    In this paper we investigate a priori error estimates for finite element discretization of a simplified semilinear gradient enhanced damage model. The model equations are of a special structure as the state equation consists of an elliptic PDE which has to be fulfilled at almost all times coupled with a nonsmooth, semilinear ODE that has to hold true in almost all points in space. The system is discretized by a constant discontinuous Galerkin method in time and usual conforming linear finite elements in space. For the uncontrolled equation, we prove linear convergence in time and an order of O (h 3 2 e) for the discretization error in space. Our main result regarding the optimal control problem is the uniform convergence of dG(0)cG(1)-discrete controls to l in H1 { 0} (0, T;L2(Ω). Error estimates for the controls are established via a quadratic growth condition. Numerical experiments are added to illustrate the proven rates of convergence. © 2021 Society for Industrial and Applied Mathematics Publications. All rights reserved.
    view abstractdoi: 10.1137/20M1331263
  • 2021 • 905 Ultraviolet resonance Raman spectroscopy of anthracene: Experiment and theory
    Holtum, T. and Bloino, J. and Pappas, C. and Kumar, V. and Barone, V. and Schlücker, S.
    Journal of Raman Spectroscopy (2021)
    Ultraviolet resonance Raman (UVRR) scattering is a highly sensitive and selective vibrational spectroscopic technique with a broad range of applications from polyaromatic hydrocarbons (PAHs) to biomolecular systems (peptides/proteins and nucleic acids) and catalysts. The interpretation of experimental UVRR spectra is not as straightforward as in purely vibrational Raman scattering (Placzek approximation) due to the involvement of higher lying electronic states and vibronic coupling. This necessitates the comparison with theoretical UVRR spectra computed by electronic structure calculations. Anthracene is an ideal model system for such a comparison between experiment and theory because it is rigid, symmetric, and of moderate size. By taking into account Herzberg–Teller contributions including Duschinsky effects, bulk solvent effects, and anharmonic contributions, a good qualitative agreement close to the resonance condition is achieved. The present study shows that within the framework of time-dependent density functional theory (TD-DFT), a general and robust approach for the analysis and interpretation of resonance Raman spectra of medium- to large-size molecules is available. © 2021 The Authors. Journal of Raman Spectroscopy published by John Wiley & Sons Ltd.
    view abstractdoi: 10.1002/jrs.6223
  • 2021 • 904 Thermoelastic properties and γ’-solvus temperatures of single-crystal Ni-base superalloys
    Horst, O.M. and Schmitz, D. and Schreuer, J. and Git, P. and Wang, H. and Körner, C. and Eggeler, G.
    Journal of Materials Science 56 7637-7658 (2021)
    Abstract: The present work shows that thermal expansion experiments can be used to measure the γʼ-solvus temperatures of four Ni-base single-crystal superalloys (SX), one with Re and three Re-free variants. In the case of CMSX-4, experimental results are in good agreement with numerical thermodynamic results obtained using ThermoCalc. For three experimental Re-free alloys, the experimental and calculated results are close. Transmission electron microscopy shows that the chemical compositions of the γ- and the γʼ-phases can be reasonably well predicted. We also use resonant ultrasound spectroscopy (RUS) to show how elastic coefficients depend on chemical composition and temperature. The results are discussed in the light of previous results reported in the literature. Areas in need of further work are highlighted. Graphical abstract: [Figure not available: see fulltext.] © 2021, The Author(s).
    view abstractdoi: 10.1007/s10853-020-05628-w
  • 2021 • 903 A W-Band Transceiver Chip for Future 5G Communications in InP-DHBT Technology
    Hossain, M. and Shivan, T. and Hrobak, M. and Al-Sawaf, T. and Stoppel, D. and Yacoub, H. and Weimann, N. and Heinrich, W. and Krozer, V.
    EuMIC 2020 - 2020 15th European Microwave Integrated Circuits Conference 193-196 (2021)
    This paper presents a W-band transceiver chip using InP-DHBT technology for future 5G application. It consists of a transceiver switch, a medium power amplifier (MPA) and a low noise amplifier (LNA) in 0.8 µm InP-DHBT technology. The switch operates from 75 GHz to 110 GHz and simulation results show more than 20 dB isolation and 1 dB output power (P1dBout) of 15 dBm. The measured MPA exhibits 16 dBm saturated output power (Psat) with 18 % power added efficiency (PAE) at 90 GHz. The measured LNA small signal gain is higher than 30 dB from 75 to 110 GHz and the measured noise figure values are below 9 dB. After integrating individual components (switch, LNA and PA), the entire transceiver chip achieves a measured isolation of more than 15 dB. The entire circuit consumes total 280 mW DC power. The chip area is only 2.5x1.5 mm2, To the knowledge of the authors, this is the first monolithically integrated transceiver covering the W-band for future 5G communication reported so far. © 2021 EuMA.
    view abstract
  • 2021 • 902 Pathways for oral and rectal delivery of gold nanoparticles (1.7 nm) and gold nanoclusters into the colon: Enteric-coated capsules and suppositories
    Hosseini, S. and Wetzel, O. and Kostka, K. and Heggen, M. and Loza, K. and Epple, M.
    Molecules 26 (2021)
    Two ways to deliver ultrasmall gold nanoparticles and gold-bovine serum albumin (BSA) nanoclusters to the colon were developed. First, oral administration is possible by incorporation into gelatin capsules that were coated with an enteric polymer. These permit the transfer across the stomach whose acidic environment damages many drugs. The enteric coating dissolves due to the neutral pH of the colon and releases the capsule’s cargo. Second, rectal administration is possible by incorporation into hard-fat suppositories that melt in the colon and then release the nanocarriers. The feasibility of the two concepts was demonstrated by in-vitro release studies and cell culture studies that showed the easy redispersibility after dissolution of the respective transport system. This clears a pathway for therapeutic applications of drug-loaded nanoparticles to address colon diseases, such as chronic inflammation and cancer. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/molecules26165069
  • 2021 • 901 Current Trends in Metal–Organic and Covalent Organic Framework Membrane Materials
    Hosseini Monjezi, B. and Kutonova, K. and Tsotsalas, M. and Henke, S. and Knebel, A.
    Angewandte Chemie - International Edition (2021)
    Metal–organic frameworks (MOFs) and covalent organic frameworks (COFs) have been thoroughly investigated with regards to applications in gas separation membranes in the past years. More recently, new preparation methods for MOFs and COFs as particles and thin-film membranes, as well as for mixed-matrix membranes (MMMs) have been developed. We will highlight novel processes and highly functional materials: Zeolitic imidazolate frameworks (ZIFs) can be transformed into glasses and we will give an insight into their use for membranes. In addition, liquids with permanent porosity offer solution processability for the manufacture of extremely potent MMMs. Also, MOF materials influenced by external stimuli give new directions for the enhancement of performance by in situ techniques. Presently, COFs with their large pores are useful in quantum sieving applications, and by exploiting the stacking behavior also molecular sieving COF membranes are possible. Similarly, porous polymers can be constructed using MOF templates, which then find use in gas separation membranes. © 2020 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/anie.202015790
  • 2021 • 900 Study on the Fuel Consumptions Using Traffic Simulation with Example of City Duisburg
    Hu, X. and Ma, X. and Schramm, D.
    Mechanisms and Machine Science 88 488-495 (2021)
    With the development of microscopic traffic simulation and computer performance, traffic simulation is no longer limited to solving problems in the field of transportation. Microscopic traffic simulation can provide massive details, which can provide more possibilities for many studies. For studying traffic emissions, fuel consumptions and how the vehicle dynamic characteristics will affect traffic flow, a series of driver model and vehicle model for traffic simulation were built in this work. A traffic scenario of part of City Duisburg was also built in Simulation of Urban MObility (SUMO), which took advantage of the road network from Open Street Map (OSM) and traffic counter data provided by the municipality of Duisburg. As the vehicle models in SUMO are quite abstract and simplified, more detailed driver model and vehicle models were developed and applied in the simulation. The driver model is a fuzzy logic model based on behavior data of human drivers collected from driving simulator. In the vehicle models the characteristics of powertrains, braking systems, and the changes of driving resistances are all considered. These models make the simulated vehicles more similar to human drivers and realistic vehicles. The average fuel consumptions in this scenario was studied and the results with different models were also compared. © 2020, The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG.
    view abstractdoi: 10.1007/978-3-030-60076-1_44
  • 2021 • 899 Simulation with car-following model considering vehicle dynamic features
    Hu, X. and Ma, X. and Schramm, D.
    International Journal of Advanced Mechatronic Systems 9 3-10 (2021)
    Microscopic traffic simulation has been applied not only for traffic prediction but also in more and more research fields. The typical car-following models widely used in simulation always need massive traffic observation data. By mathematical abstraction from traffic data, some important characteristics of vehicles and drivers will be inevitably abandoned. In this article, a modelling method of car-following behaviour has been proposed, in which the dynamic features of different vehicles have been considered. As an example, an internal combustion engine vehicle model and electric vehicle model were implemented in the traffic simulation. The simulation results of using typical car-following models were also compared with the results using new model. From the result, the new model can display during simulation corresponding dynamic features. The internal combustion engine vehicle model also presented different dynamic characteristics from electric vehicle model, which caused a different simulation result. © 2021 Inderscience Publishers. All rights reserved.
    view abstract
  • 2021 • 898 The Role of Nitrogen-doping in the Catalytic Transfer Hydrogenation of Phenol to Cyclohexanone with Formic Acid over Pd supported on Carbon Nanotubes
    Hu, B. and Li, X. and Busser, W. and Schmidt, S. and Xia, W. and Li, G. and Li, X. and Peng, B.
    Chemistry - A European Journal 27 10948-10956 (2021)
    Highly selective one-step hydrogenation of phenol to cyclohexanone, an important intermediate in the production of nylon 6 and nylon 66, is desirable but remains a challenge. Pd nanoparticles supported on nitrogen- and oxygen-functionalized carbon nanotubes (NCNTs, OCNTs) were prepared, characterized, and applied in the hydrogenation of phenol to cyclohexanone to study the effect of N-doping. Almost full conversion of phenol with high selectivity to cyclohexanone was achieved over Pd/NCNT under mild reaction conditions using either H2 or formic acid (FA) as a hydrogen source. The effects of reaction temperature and FA/phenol ratio and the reusability were investigated. Separate FA decomposition experiments without and with the addition of phenol were performed to investigate the reaction mechanism, especially the deactivation behavior. Deactivation was observed for both catalysts during the FA decomposition, while only Pd/OCNT rather than Pd/NCNT was deactivated in the transfer hydrogenation with FA and the FA decomposition in the presence of phenol, indicating the unique role of N-doping. Therefore, we assume that deactivation is caused by the strongly bound formates on the active Pd sites, suppressing further FA decomposition and/or transfer hydrogenation on Pd. The nonplanar adsorption of phenol on NCNTs via weak O−H⋅⋅⋅N interactions enables the occurrence of the subsequent hydrogenation by adsorbed formate on Pd. © 2021 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/chem.202100981
  • 2021 • 897 Solvent Effects on Photocatalytic Anaerobic Oxidation of Benzyl Alcohol over Pt-Loaded Defective SrTiO3Nanoparticles
    Hu, Y. and Shen, Z. and Li, B. and Li, S. and Yue, J. and Zhao, G. and Muhler, M. and Wang, X.
    ACS Applied Nano Materials 4 9254-9264 (2021)
    Photocatalytic selective oxidation of alcohols under mild conditions is an emerging technique to encounter the global challenges of energy source shortages and the green synthesis perspective. Herein, we investigate the solvent effects on heterogeneous photocatalytic anaerobic oxidation of benzyl alcohol with Pt-loaded defective SrTiO3nanoparticles. It is found that the optimal solvent is water mixed with a small amount of dimethylformamide (DMF) or acetonitrile, while the solvent effects on the oxidation of benzyl alcohol are related to the adsorption of benzyl alcohol and benzaldehyde on the photocatalysts in different solvents, in which the adsorption of benzyl alcohol plays a major role, while such positive effect can be significantly offset in case the adsorption of benzaldehyde is leading the effort. This work offers the avenue to improve the photocatalytic oxidation of alcohols by optimizing the reaction solvents in addition to the well-known structure engineering of the photocatalysts. © 2021 American Chemical Society
    view abstractdoi: 10.1021/acsanm.1c01750
  • 2021 • 896 Determination of residual dimethyl sulfoxide by high-resolution continuum source graphite furnace molecular absorption spectrometry
    Huang, M.D. and Esser, N. and Hinrichs, K. and Tan, Q. and Rappich, J. and Nickel, N.H. and Dittrich, T.
    Spectrochimica Acta - Part B Atomic Spectroscopy 177 (2021)
    High-resolution continuum source molecular absorption spectrometry (HR-CSMAS) has been extended to the determination of sulfur-containing organic molecule, on the example of dimethyl sulfoxide (DMSO) as a residual solvent in CH3NH3PbI3 perovskite thin films. For this purpose, DMSO molecules were converted into CS molecules by pyrolysis in a graphite furnace at low temperature and the sulfur content was determined by measuring molecular absorption of CS at 258.055 nm. An aqueous solution of DMSO was used for calibration. A characteristic mass of 17 ng was achieved for S after pyrolysis at 160 °C by using Pd as a chemical modifier. Furthermore, the content of DMSO was normalized to that of Pb whereas the content of Pb was determined by reducing the Pb in the perovskite to metallic Pb with Zn powder and measuring absorption of the weak Pb line at 261.418 nm by high-resolution continuum source atomic absorption spectrometry (HR-CSAAS). The Pb content remained constant whereas the S/Pb molar ratio decreased with increasing annealing time. Our results open new opportunities for the characterization of residual DMSO in wide classes of materials. © 2020 Elsevier B.V.
    view abstractdoi: 10.1016/j.sab.2020.106050
  • 2021 • 895 Assessment of a complete and classified platelet proteome from genome-wide transcripts of human platelets and megakaryocytes covering platelet functions
    Huang, J. and Swieringa, F. and Solari, F.A. and Provenzale, I. and Grassi, L. and De Simone, I. and Baaten, C.C.F.M.J. and Cavill, R. and Sickmann, A. and Frontini, M. and Heemskerk, J.W.M.
    Scientific Reports 11 (2021)
    Novel platelet and megakaryocyte transcriptome analysis allows prediction of the full or theoretical proteome of a representative human platelet. Here, we integrated the established platelet proteomes from six cohorts of healthy subjects, encompassing 5.2 k proteins, with two novel genome-wide transcriptomes (57.8 k mRNAs). For 14.8 k protein-coding transcripts, we assigned the proteins to 21 UniProt-based classes, based on their preferential intracellular localization and presumed function. This classified transcriptome-proteome profile of platelets revealed: (i) Absence of 37.2 k genome-wide transcripts. (ii) High quantitative similarity of platelet and megakaryocyte transcriptomes (R = 0.75) for 14.8 k protein-coding genes, but not for 3.8 k RNA genes or 1.9 k pseudogenes (R = 0.43–0.54), suggesting redistribution of mRNAs upon platelet shedding from megakaryocytes. (iii) Copy numbers of 3.5 k proteins that were restricted in size by the corresponding transcript levels (iv) Near complete coverage of identified proteins in the relevant transcriptome (log2fpkm > 0.20) except for plasma-derived secretory proteins, pointing to adhesion and uptake of such proteins. (v) Underrepresentation in the identified proteome of nuclear-related, membrane and signaling proteins, as well proteins with low-level transcripts. We then constructed a prediction model, based on protein function, transcript level and (peri)nuclear localization, and calculated the achievable proteome at ~ 10 k proteins. Model validation identified 1.0 k additional proteins in the predicted classes. Network and database analysis revealed the presence of 2.4 k proteins with a possible role in thrombosis and hemostasis, and 138 proteins linked to platelet-related disorders. This genome-wide platelet transcriptome and (non)identified proteome database thus provides a scaffold for discovering the roles of unknown platelet proteins in health and disease. © 2021, The Author(s).
    view abstractdoi: 10.1038/s41598-021-91661-x
  • 2021 • 894 Simulation and modeling of the residual stress state in the sub-surface zone of BTA deep-hole drilled specimens with eigenstrain theory
    Huang, X. and Schmidt, R. and Strodick, S. and Walther, F. and Biermann, D. and Zabel, A.
    Procedia CIRP 102 150-155 (2021)
    The BTA (Boring and Trepanning Association) deep-hole drilling process is used to machine bores with large diameters (D > 40 mm) and a bore-length (l) to diameter ratio lager than ten (l/D >10). The resulting bore surface and its sub-surface zone are influenced by the cutting action and the self-guiding effect of the tool. The Guide pads support the asymmetric tool on the bore surface while burnishing the surface. The mechanical/thermal loads induced by the process lead to hardening, microstructure alteration and substantial residual stresses in the sub-surface. Particularly the residual stress state influences the fatigue strength and reliability of the machined part. To predict the residual stress in BTA deep-hole drilling, for the first time a novel analytical modeling approach is developed based on eigenstrain theory, integrating the machining process of cutting insert and the burnishing process of guide pad. A semi-analytical 3D contact model is built for the cycling incremental plasticity due to the equivalent mechanical/thermal loading of cutting process. Furthermore, an approximate estimation is provided for the contact condition between the inclined guide pad and bore hole, which facilitates the incremental contact analysis in the burnishing process. With the induced inelastic deformation known, residual stress distribution in the machined surface is constructed based on the eigenstrain theory. The results of the model are compared to X-Ray-Diffraction (XRD) measurements of BTA deep-hole drilled specimens. © 2021 The Author(s).
    view abstractdoi: 10.1016/j.procir.2021.09.026
  • 2021 • 893 Ceria-Based Materials for Thermocatalytic and Photocatalytic Organic Synthesis
    Huang, X. and Zhang, K. and Peng, B. and Wang, G. and Muhler, M. and Wang, F.
    ACS Catalysis 11 9618-9678 (2021)
    Value-added chemicals, fuels, and pharmaceuticals synthesized by organic transformation from raw materials via catalytic techniques have attracted enormous attention in the past few decades. Heterogeneous catalysts with high stability, long cycling life, good environmental-friendliness, and economic efficiency are greatly desired to accomplish the catalytic organic transformations. With the advantages of reversible Ce3+/Ce4+ redox pairs, tailorable oxygen vacancies, and surface acid-base properties, ceria-based catalysts have been actively investigated in the fields of catalytic organic synthesis. In this Review, we summarize the fundamentals and latest applications of ceria-based heterogeneous catalysts for organic transformations via thermocatalytic and photocatalytic routes. The fabricating approaches of various ceria and ceria-based catalysts and their structure/composition-activity relationship are discussed and prospected. The advanced characterization techniques and theoretical methods for reaction mechanism studies over CeO2-based catalysts are summarized and discussed. This comprehensive Review provides a basic understanding of the structure-performance relationships of ceria-based catalysts for organic synthesis. In addition, it also provides some insights and outlooks in the design and research direction in the ceria-based catalysts with better performance. © 2021 American Chemical Society.
    view abstractdoi: 10.1021/acscatal.1c02443
  • 2021 • 892 Molecular proteomics and signalling of human platelets in health and disease
    Huang, J. and Zhang, P. and Solari, F.A. and Sickmann, A. and Garcia, A. and Jurk, K. and Heemskerk, J.W.M.
    International Journal of Molecular Sciences 22 (2021)
    Platelets are small anucleate blood cells that play vital roles in haemostasis and thrombosis, besides other physiological and pathophysiological processes. These roles are tightly regulated by a complex network of signalling pathways. Mass spectrometry-based proteomic techniques are contributing not only to the identification and quantification of new platelet proteins, but also reveal post-translational modifications of these molecules, such as acetylation, glycosylation and phosphorylation. Moreover, target proteomic analysis of platelets can provide molecular biomarkers for genetic aberrations with established or non-established links to platelet dysfunctions. In this report, we review 67 reports regarding platelet proteomic analysis and signalling on a molecular base. Collectively, these provide detailed insight into the: (i) technical developments and limitations of the assessment of platelet (sub)proteomes; (ii) molecular protein changes upon ageing of platelets; (iii) complexity of platelet signalling pathways and functions in response to collagen, rhodocytin, thrombin, thromboxane A2 and ADP; (iv) proteomic effects of endothelial-derived mediators such as prostacyclin and the anti-platelet drug aspirin; and (v) molecular protein changes in platelets from patients with congenital disorders or cardiovascular disease. However, sample sizes are still low and the roles of differentially expressed proteins are often unknown. Based on the practical and technical possibilities and limitations, we provide a perspective for further improvements of the platelet proteomic field. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/ijms22189860
  • 2021 • 891 A stochastic Gronwall inequality and applications to moments, strong completeness, strong local Lipschitz continuity, and perturbations
    Hudde, A. and Hutzenthaler, M. and Mazzonetto, S.
    Annales de l'institut Henri Poincare (B) Probability and Statistics 57 603-626 (2021)
    There are numerous applications of the classical (deterministic) Gronwall inequality. Recently, Michael Scheutzow discovered a stochastic Gronwall inequality which provides upper bounds for p-th moments, p ∈ (0, 1), of the supremum of nonnegative scalar continuous processes which satisfy a linear integral inequality. In this article we complement this with upper bounds for p-th moments, p ∈ [2,∞), of the supremum of general Itô processes which satisfy a suitable one-sided affine-linear growth condition. As example applications, we improve known results on strong local Lipschitz continuity in the starting point of solutions of stochastic differential equations (SDEs), on (exponential) moment estimates for SDEs, on strong completeness of SDEs, and on perturbation estimates for SDEs. © 2021 Institute of Mathematical Statistics. All rights reserved.
    view abstractdoi: 10.1214/20-AIHP1064
  • 2021 • 890 New signatures of the spin gap in quantum point contacts
    Hudson, K.L. and Srinivasan, A. and Goulko, O. and Adam, J. and Wang, Q. and Yeoh, L.A. and Klochan, O. and Farrer, I. and Ritchie, D.A. and Ludwig, Ar. and Wieck, A.D. and von Delft, J. and Hamilton, A.R.
    Nature Communications 12 (2021)
    One dimensional semiconductor systems with strong spin-orbit interaction are both of fundamental interest and have potential applications to topological quantum computing. Applying a magnetic field can open a spin gap, a pre-requisite for Majorana zero modes. The spin gap is predicted to manifest as a field dependent dip on the first 1D conductance plateau. However, disorder and interaction effects make identifying spin gap signatures challenging. Here we study experimentally and numerically the 1D channel in a series of low disorder p-type GaAs quantum point contacts, where spin-orbit and hole-hole interactions are strong. We demonstrate an alternative signature for probing spin gaps, which is insensitive to disorder, based on the linear and non-linear response to the orientation of the applied magnetic field, and extract a spin-orbit gap ΔE ≈ 500 μeV. This approach could enable one-dimensional hole systems to be developed as a scalable and reproducible platform for topological quantum applications. © 2021, The Author(s).
    view abstractdoi: 10.1038/s41467-020-19895-3
  • 2021 • 889 Dielectric Junction: Electrostatic Design for Charge Carrier Collection in Solar Cells
    Hüpkes, J. and Rau, U. and Kirchartz, T.
    Solar RRL (2021)
    Conventional solar cells typically use doping of the involved semiconducting layers and work function differences between highly conductive contacts for the electrostatic design and the charge selectivity of the junction. In some halide perovskite solar cells, however, substantial variations in the permittivity of different organic and inorganic semiconducting layers strongly affect the electrostatic potential and thereby indirectly also the carrier concentrations, recombination rates, and eventually efficiencies of the device. Here, numerical simulations are used to study the implications of electrostatics on device performance for classical p−n junctions and p−i−n junctions, and for device geometries as observed in perovskite photovoltaics, where high-permittivity absorber layers are surrounded by low-permittivity and often also low-conductivity charge transport layers. The key principle of device design in materials with sufficiently high mobilities that are still dominated by defect-assisted recombination is the minimization of volume with similar densities of electrons and holes. In classical solar cells this is achieved by doping. For perovskites, the concept of a dielectric junction is proposed by the selection of charge transport layers with adapted permittivity if doping is not sufficient. © 2021 The Authors. Solar RRL published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/solr.202100720
  • 2021 • 888 Martingale estimation functions for Bessel processes
    Hufnagel, N. and Woerner, J.H.C.
    Statistical Inference for Stochastic Processes (2021)
    In this paper we derive martingale estimating functions for the dimensionality parameter of a Bessel process based on the eigenfunctions of the diffusion operator. Since a Bessel process is non-ergodic and the theory of martingale estimating functions is developed for ergodic diffusions, we use the space-time transformation of the Bessel process and formulate our results for a modified Bessel process. We deduce consistency, asymptotic normality and discuss optimality. It turns out that the martingale estimating function based of the first eigenfunction of the modified Bessel process coincides with the linear martingale estimating function for the Cox Ingersoll Ross process. Furthermore, our results may also be applied to estimating the multiplicity parameter of a one-dimensional Dunkl process and some related polynomial processes. © 2021, The Author(s).
    view abstractdoi: 10.1007/s11203-021-09250-8
  • 2021 • 887 Design of a new wrought CrCoNi-based medium-entropy superalloy C-264 for high-temperature applications
    Hunfeld, J. and Sommer, H. and Kiese, J. and Wang, H. and Riyahi khorasgani, A. and Li, T. and Somsen, C. and Kostka, A. and Laplanche, G.
    Materials and Design 211 (2021)
    A new wrought CrCoNi-based medium-entropy superalloy (MESA) was designed by changing the composition of a commercial superalloy of type C-263, which is used for stationary components in gas turbines. ∼5 at.% Cr and 0.85 at.% Ti + Al were added at the expense of Ni while the Ti/Al ratio was decreased. Owing to these modifications, the brittle η phase, which is stable in C-263 below 900 °C is no longer observed in C-264. Besides, the solvus temperature and volume fraction of the γ′ phase in the peak-aged state are larger in C-264 (∼935 °C, 13.5%) compared to C-263 (∼890 °C, 12.8%), resulting in superior tensile and creep properties. The stress and temperature dependencies of the creep rates were described by power-law and Arrhenius relationships. The stress exponents were between 4 and 5, while the apparent activation energies were 550 and 400 kJ/mol for C-264 and C-263, respectively. During creep at 880 °C in air, internal nitridation in both MESAs resulted in the formation of TiN precipitates, with C-264 being slightly more affected due to its higher nitrogen solubility. Due to its superior creep resistance, good malleability and machinability, the C-264 MESA is currently commercially available from VDM Metals International. © 2021 The Authors
    view abstractdoi: 10.1016/j.matdes.2021.110174
  • 2021 • 886 What is a data-driven organization?
    Hupperz, M.J. and Gür, I. and Möller, F. and Otto, B.
    27th Annual Americas Conference on Information Systems, AMCIS 2021 (2021)
    Modern businesses rely on efficient management of their data assets. Data management and analytics have become decisive success factors for enterprises and companies during the last decades. However, the different aspects of transforming an organization into a data-driven one leave a lot of room for scientific inquiry. There are various aspects to consider in the transition to a data-driven organization. The paper investigates key elements and corresponding requirements of data-driven organizations to foster consensual definition in the research field. The work is grounded in the theory of organizational design and presents deductively generated results collected in a literature review. Key contributions of the paper are a shared understanding and a proposition for key elements of data-driven organizations. © AMCIS 2021.
    view abstract
  • 2021 • 885 Synthesis, Reactivity, and Lewis Acidity of Cationic Zinc Complexes
    Huse, K. and Wölper, C. and Schulz, S.
    Organometallics 40 1907-1913 (2021)
    Reactions of Rnac2ZnEt (R = Mes, Dipp) and 16Fnac2ZnEt with [Ph3C][B(C6F5)4] simultaneously proceed with β-hydride elimination and ethyl abstraction and formation of the corresponding zinc cations [Rnac2Zn]+ and [16Fnac2Zn]+. While [Rnac2Zn]+ cations undergo additional side reactions but do not react with the [B(C6F5)4]- anion, [16Fnac2Zn]+ activates the borate anion with formation of 16Fnac2ZnC6F5 (1). In contrast, [16Fnac2Zn][SbF6] (2) was formed in the reaction of 16Fnac2ZnEt with [Ph3C][SbF6] in SO2. 2 reacts with OPEt3 with formation of [16Fnac2Zn(OPEt3)][SbF6]2 (3) and with B(C6F5)3 with formation of 1. [16Fnac2Zn][SbF6] is slightly less Lewis acidic in comparison to B(C6F5)3 according to the Gutmann-Beckett method. ©
    view abstractdoi: 10.1021/acs.organomet.1c00227
  • 2021 • 884 Transfer-free, scalable photodetectors based on MOCVD-grown 2D-heterostructures
    Hutten, U. and Daniel, L. and Grundmann, A. and Stracke, N. and Abdelbaky, M. and Beckmann, Y. and Heuken, M. and Mertin, W. and Kalisch, H. and Vescan, A. and Bacher, G. and Kümmell, T.
    2D Materials 8 (2021)
    2D semiconductors based on transition metal dichalcogenides are highly promising for ultrathin photodetectors due to their thickness in the nanometer range and their exceptional light absorption properties. To enable efficient separation of optically generated electron-hole pairs heterostructures have to be implemented, which are usually prepared by poorly controlled mechanical steps such as exfoliation, transfer and stacking processes that prevent industrial upscaling. Here, semitransparent photodetectors in the mm2 range based on MoS2/WS2 heterostructures are presented that are realized without any transfer step by a scalable metal-organic chemical vapor deposition process on a sapphire substrate in a continuous growth run. The heterostructure device exhibits a responsivity, which is enhanced by about 5-6 orders of magnitude with respect to reference devices based on either MoS2 or WS2 monolayers only. The large gain enhancement is attributed to efficient charge carrier separation at the MoS2/WS2 heterointerface combined with hole trapping, leading to an improved electron transport in the heterostructure under illumination. © 2021 The Author(s).
    view abstractdoi: 10.1088/2053-1583/ac186d
  • 2021 • 883 Differentiability of semigroups of stochastic differential equations with Hölder-continuous diffusion coefficients
    Hutzenthaler, M. and Pieper, D.
    Alea (Rio de Janeiro) 18 309-324 (2021)
    Differentiability of semigroups is useful for many applications. Here we focus on stochastic differential equations whose diffusion coefficient is the square root of a differentiable function but not differentiable itself. For every m ∈ {0, 1, 2} we establish an upper bound for a Cm-norm of the semigroup of such a diffusion in terms of the Cm-norms of the drift coefficient and of the squared diffusion coefficient. The constants in our upper bound are often bounded in the dimension. Our estimates are thus suitable for analyzing certain high-dimensional and infinitedimensional degenerate stochastic differential equations. © 2021,Alea (Rio de Janeiro) All Rights Reserved
    view abstractdoi: 10.30757/ALEA.V18-14
  • 2021 • 882 Overcoming the Curse of Dimensionality in the Numerical Approximation of Parabolic Partial Differential Equations with Gradient-Dependent Nonlinearities
    Hutzenthaler, M. and Jentzen, A. and Kruse, T.
    Foundations of Computational Mathematics (2021)
    Partial differential equations (PDEs) are a fundamental tool in the modeling of many real-world phenomena. In a number of such real-world phenomena the PDEs under consideration contain gradient-dependent nonlinearities and are high-dimensional. Such high-dimensional nonlinear PDEs can in nearly all cases not be solved explicitly, and it is one of the most challenging tasks in applied mathematics to solve high-dimensional nonlinear PDEs approximately. It is especially very challenging to design approximation algorithms for nonlinear PDEs for which one can rigorously prove that they do overcome the so-called curse of dimensionality in the sense that the number of computational operations of the approximation algorithm needed to achieve an approximation precision of size ε> 0 grows at most polynomially in both the PDE dimension d∈ N and the reciprocal of the prescribed approximation accuracy ε. In particular, to the best of our knowledge there exists no approximation algorithm in the scientific literature which has been proven to overcome the curse of dimensionality in the case of a class of nonlinear PDEs with general time horizons and gradient-dependent nonlinearities. It is the key contribution of this article to overcome this difficulty. More specifically, it is the key contribution of this article (i) to propose a new full-history recursive multilevel Picard approximation algorithm for high-dimensional nonlinear heat equations with general time horizons and gradient-dependent nonlinearities and (ii) to rigorously prove that this full-history recursive multilevel Picard approximation algorithm does indeed overcome the curse of dimensionality in the case of such nonlinear heat equations with gradient-dependent nonlinearities. © 2021, The Author(s).
    view abstractdoi: 10.1007/s10208-021-09514-y
  • 2021 • 881 Solvent Selection in Homogeneous Catalysis - Optimization of Kinetics and Reaction Performance
    Huxoll, F. and Jameel, F. and Bianga, J. and Seidensticker, T. and Stein, M. and Sadowski, G. and Vogt, D.
    ACS Catalysis 11 590-594 (2021)
    Solvents have an enormous impact on yield and turnover of chemical reactions in complex media. There is, however, a lack of consistent model-based tools to a priori identify the appropriate solvent for homogeneously catalyzed reactions. Here, a thermodynamically consistent approach for a reductive amination reaction is presented. It combines solvent screening using a thermodynamic-activity model and quantum chemical calculations. The optimization of activity coefficient-based predicted kinetics gives a suitable list of candidate solvents. The results were confirmed by batch experiments in selected solvents. This approach allows reducing time and lab resources for solvent selection to a minimum. ©
    view abstractdoi: 10.1021/acscatal.0c04431
  • 2021 • 880 Thermodynamic Properties of Biogenic Amines and Their Solutions
    Huxoll, F. and Heyng, M. and Andreeva, I.V. and Verevkin, S.P. and Sadowski, G.
    Journal of Chemical and Engineering Data (2021)
    Vapor pressures of the biologically and industrially relevant amines 2-phenylethan-1-amine, 2-amino-1-phenylethanol, α-(methylaminomethyl)benzyl alcohol, 1-phenylmethanamine, and N,N-diethylundecan-1-amine were measured via the transpiration method. Pure-component parameters for the thermodynamic model PC-SAFT were fitted to these vapor pressures and to liquid densities. The pure-component parameters were validated with measured liquid densities of binary mixtures dimethylsulfoxid + 4-(2-aminoethyl)phenol, dimethylsulfoxid + 2-amino-1-phenylethanol, dimethylsulfoxid + α-(methylaminomethyl)benzyl alcohol, and dimethylsulfoxid + 1-phenylmethanamine at 0.102 MPa and temperatures from 298.15 to 343.15 K at different amine mass fractions. Solid-liquid equilibria at 0.1 MPa were measured in binary mixtures of α-(methylaminomethyl)benzyl alcohol + water and 4-(2-aminoethyl)phenol + water at 298.15 and 308.15 K. Finally, the presence of liquid-liquid phase separation for these systems was qualitatively predicted using PC-SAFT based on the solid-liquid equilibria only and validated for the system α-(methylaminomethyl)benzyl alcohol + water by experiments at 293.15 and 323 K at 0.1 MPa. © 2021 American Chemical Society.
    view abstractdoi: 10.1021/acs.jced.1c00202
  • 2021 • 879 Phase Equilibria for the Hydroaminomethylation of 1-Decene
    Huxoll, F. and Schlüter, S. and Budde, R. and Skiborowski, M. and Petzold, M. and Böhm, L. and Kraume, M. and Sadowski, G.
    Journal of Chemical and Engineering Data (2021)
    This work focuses on the measuring and modeling of phase equilibria of interest for the hydroaminomethylation of 1-decene with syngas (CO/H2) and diethylamine to N,N-diethylundecan-1-amine and water in a solvent system of methanol and n-dodecane. H2 solubilities were measured in undecanal and N,N-dimethyldodecan-1-amine at 343 and 363 K between 2 and 4 MPa via the isochoric saturation method. Vapor-Liquid equilibrium data were measured for the binary systems methanol/N,N-diethylundecan-1-amine, 1-decene/diethylamine, and 1-decene/N,N-diethylundecan-1-amine at temperatures between 299 and 372 K and at pressures of 0.005, 0.018, 0.025, or 0.030 MPa. Liquid-Liquid equilibria were measured in the ternary systems methanol/n-dodecane/diethylamine, methanol/n-dodecane/undecanal, and methanol/n-dodecane/N,N-diethylundecan-1-amine at 0.1 MPa and at temperatures ranging from 278.15 to 308.15 K. Measured and available phase-equilibrium data from literature were modeled using perturbed-chain polar statistical associating fluid theory. This then allowed for modeling the Henry's law constant for H2 and CO in the liquid components (methanol, n-dodecane, 1-decene, diethylamine, undecanal, N,N-diethylundecan-1-amine, and water) at 373.15 and 393.15 K. © 2021 The Authors. Published by American Chemical Society.
    view abstractdoi: 10.1021/acs.jced.1c00561
  • 2021 • 878 Li and Ta-modified KNN piezoceramic fibers for vibrational energy harvesters
    Ichangi, A. and Shvartsman, V.V. and Lupascu, D.C. and Lê, K. and Grosch, M. and Kathrin Schmidt-Verma, A. and Bohr, C. and Verma, A. and Fischer, T. and Mathur, S.
    Journal of the European Ceramic Society 41 7662-7669 (2021)
    Piezoelectric energy harvesters (PEH) hold enormous potential for converting mechanical energy from our surrounding environment into electrical energy that can be used for powering portable electronics. Potassium sodium niobate (KNN) is one of the promising alternatives to replace lead-based piezoelectric materials. This work presents a cutting-edge demonstration of synthesis-function-device integration of piezoelectric nanofibers, where the morphology and the composition are engineered towards achieving high device output. We report a flexible nanogenerator based on electrospun Li and Ta-modified lead-free KNN nanofibers yielding a high voltage output of 5.6 V, which is around 9-fold higher than for the Mn-doped KNN nanofibers reported previously. The influence of Li and Ta-incorporation into the KNN lattice on the electromechanical coupling and the effect of a nanofiber morphology are investigated. The net-shaped KNN and Li and Ta-modified KNN nanofibers, synthesized by electrospinning of appropriate sols, maintain their structural integrity upon calcination and firing steps. The phase analysis (XRD) confirms the formation of single-phase (KNN) material. Li and Ta are found to be incorporated on the A and B-sites of the perovskite lattice, respectively. Piezo force microscopy data show the heat-treated nanofibers to exhibit multi-domain ferroelectric properties. © 2021 Elsevier Ltd
    view abstractdoi: 10.1016/j.jeurceramsoc.2021.08.010
  • 2021 • 877 Surface Modification of Ready-to-Use Hollow Fiber Ultrafiltration Modules for Oil/Water Separation
    Idrees, H. and ElSherbiny, I.M.A. and Hecket, M. and Ke, Q. and Staaks, C. and Khalil, A.S.G. and Ulbricht, M. and Panglisch, S.
    Chemie-Ingenieur-Technik (2021)
    Reusing wastewater from oil-related industries is becoming increasingly important, especially in water-stressed oil-producing countries. Before oily wastewater can be discharged or reused, it must be properly treated, e.g., by membrane-based processes like ultrafiltration. A major issue of the applied membranes is their high fouling propensity. This paper reports on mitigating fouling inside ready-to-use ultrafiltration hollow-fiber modules used in a polishing step in oil/water separation. For this purpose, in-situ polyzwitterionic hydrogel coating was applied. The membrane performance was tested with oil nano-emulsions using a mini-plant system. The main factors influencing fouling were systematically investigated using statistical design of experiments. © 2021 The Authors. Chemie Ingenieur Technik published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/cite.202100044
  • 2021 • 876 Melt milling as manufacturing method for solid crystalline suspensions
    da Igreja, P. and Erve, A. and Thommes, M.
    European journal of pharmaceutics and biopharmaceutics : official journal of Arbeitsgemeinschaft fur Pharmazeutische Verfahrenstechnik e.V 158 245-253 (2021)
    Production of submicron particles (0.1-1 μm) has been identified by the pharmaceutical industry as a key technology to enhance the bioavailability of poorly water-soluble drugs. However, nanosuspensions derived from commonly applied wet milling suffer from long-term stability issues, making further downstream processing necessary. In previous works, the formulation as a long-term stable solid crystalline suspension (SCS) was introduced, for which the crystalline drug is ground in a (molten) hydrophilic carrier matrix. The model formulation of the antimycotic Griseofulvin and the sugar alcohol Xylitol was reused for comparative purposes. Due to process limitations regarding the degree of comminution, the present work demonstrates the application of fine grinding in the framework of SCS manufacturing. A custom-built mill with annular gap geometry successfully yielded particles in the targeted submicron range. A process optimization study lead to improved energy utilization during grinding, which reduced the necessary grinding time and, thereby, the thermal exposition of the drug. Investigation of solid-state properties of the SCS, via differential scanning calorimetry and x-ray powder diffraction, showed no alteration even for extended grinding times. In dissolution experiments, the melt-milled SCS outperformed its predecessors, although mostly agglomerates were found by SEM imaging in the solidified product. In conclusion, melt milling is a valuable tool to overcome low aqueous solubility. Copyright © 2020. Published by Elsevier B.V.
    view abstractdoi: 10.1016/j.ejpb.2020.11.020
  • 2021 • 875 Low temperature sintering of fully inorganic all-solid-state batteries – Impact of interfaces on full cell performance
    Ihrig, M. and Finsterbusch, M. and Tsai, C.-L. and Laptev, A.M. and Tu, C.-H. and Bram, M. and Sohn, Y.J. and Ye, R. and Sevinc, S. and Lin, S.-K. and Fattakhova-Rohlfing, D. and Guillon, O.
    Journal of Power Sources 482 (2021)
    One of the necessary prerequisites to advance the electrochemical performance of Li7La3Zr2O12 (LLZ) based all-solid-state lithium batteries is the manufacturing of dense composite cathodes from cathode active material (CAM) and the LLZ ceramic solid electrolyte. However, free co-sintering of LLZ and CAM mixtures requires temperatures above 1000 °C which often leads to decomposition and secondary phase formation, especially for high energy CAMs. In our study we present a completely dry processing route which is fast, free of any sintering additives and coatings and suitable to fabricate dense mixed cathodes, pure LLZ separators and multilayers of the two. Through application of high mechanical pressure during Field-Assisted Sintering we were able to reduce the sintering temperature down to 675–750 °C with dwell times as low as 10 min, while still obtaining 95% theoretical density for LCO/LLZ mixtures. The low sintering temperature is suitable for high energy CAMs, but leads to a significant effect of surface impurities, especially from powder handling in air, and affects the crystallinity of the CAM/LLZ interface. In the present paper we investigate the impact of resulting interfaces on the ionic conductivity, the interfacial impedance and the cycling stability of produced cells and propose the optimization strategy. © 2020 Elsevier B.V.
    view abstractdoi: 10.1016/j.jpowsour.2020.228905
  • 2021 • 874 Polymer-Ceramic Composite Cathode with Enhanced Storage Capacity Manufactured by Field-Assisted Sintering and Infiltration
    Ihrig, M. and Ye, R. and Laptev, A.M. and Grüner, D. and Guerdelli, R. and Scheld, W.S. and Finsterbusch, M. and Wiemhöfer, H.-D. and Fattakhova-Rohlfing, D. and Guillon, O.
    ACS Applied Energy Materials 4 10428-10432 (2021)
    Polymer-ceramic all-solid-state Li batteries (ASSLBs) combine the advantages of fully inorganic and polymer-based ASSLBs. In particular, the application of proposed polymer-ceramic composite cathodes could be essential for the enhancement of the energy storage capacity of ASSLBs. The use of a modified field-assisted sintering technique with adjustable pressure and with alternative mica foil enables the fabrication of porous cathodes at a reduced sintering temperature and without side phase formation. This allows sintering of a porous LiCoO2/Li7La3Zr2O12:Ta composite network suitable for polymer infiltration and assembly in an ASSLB from the cathode side. The ceramic LiCoO2/Li7La3Zr2O12:Ta composite cathodes infiltrated with an ion-conducting polymer have shown an enhanced areal storage capacity. © 2021 The Authors. Published by American Chemical Society.
    view abstractdoi: 10.1021/acsaem.1c02667
  • 2021 • 873 Chemically induced local lattice distortions versus structural phase transformations in compositionally complex alloys
    Ikeda, Y. and Gubaev, K. and Neugebauer, J. and Grabowski, B. and Körmann, F.
    npj Computational Materials 7 (2021)
    Recent experiments show that the chemical composition of body-centered cubic (bcc) refractory high entropy alloys (HEAs) can be tuned to enable transformation-induced plasticity (TRIP), which significantly improves the ductility of these alloys. This calls for an accurate and efficient method to map the structural stability as a function of composition. A key challenge for atomistic simulations is to separate the structural transformation between the bcc and the ω phases from the intrinsic local lattice distortions in such chemically disordered alloys. To solve this issue, we develop a method that utilizes a symmetry analysis to detect differences in the crystal structures. Utilizing this method in combination with ab initio calculations, we demonstrate that local lattice distortions largely affect the phase stability of Ti–Zr–Hf–Ta and Ti–Zr–Nb–Hf–Ta HEAs. If relaxation effects are properly taken into account, the predicted compositions near the bcc–hcp energetic equilibrium are close to the experimental compositions, for which good strength and ductility due to the TRIP effect are observed. © 2021, The Author(s).
    view abstractdoi: 10.1038/s41524-021-00502-y
  • 2021 • 872 Detailed simulations of the DLR auto-igniting pulsed jet experiment
    Inanc, E. and Lipkowicz, J.T. and Kempf, A.M.
    Fuel 284 (2021)
    Numerical simulations of an auto-igniting pulsed jet in a vitiated co-flow experiment by DLR (German Aerospace Center) are conducted by highly-resolved large-eddy simulations using direct chemistry with an augmented reduced mechanism. The experiments consist of two operation modes: continuous injection used for code-verification and pulsed injection utilized for fundamental investigation of auto-ignition dynamics. Initially, reference one-dimensional self-igniting counter-flow flames are investigated. Then, a grid convergence study has been performed. It is shown that even a coarser grid would be sufficient to describe the ignition chemistry since the ignition kernel appears at low velocities and fuel-lean conditions in zones of low scalar dissipation rates. For the statistically steady jet, numerical predictions are in a very good agreement with the experiments, giving confidence in the applied models. For the pulsed jet, all of the predicted ignition delay times and locations are in the range of the experimental observations. Time-resolved statistics reveal that thermochemical properties of the gas in a pulsed jet achieve states that are impossible to reproduce in laminar conditions. For further analysis, hydroxyl and formaldehyde are chosen as a marker for the established flame and for the ignition, respectively. In laminar conditions, these two species are perfectly correlated. However, the unsteady dynamics of the pulsed jet invalidates the correlation between the minor species chemistry prior to ignition. This yields the discrepancy in the auto-ignition delay time and the location of the ignition kernel between different pulses, as the thermochemical state needed for the ignition occurs in a random manner. © 2020 Elsevier Ltd
    view abstractdoi: 10.1016/j.fuel.2020.118947
  • 2021 • 871 Effect of sub-grid wrinkling factor modelling on the large eddy simulation of turbulent stratified combustion
    Inanc, E. and Kempf, A.M. and Chakraborty, N.
    Combustion Theory and Modelling 25 911-939 (2021)
    Different flame efficiency function (wrinkling factor) models are compared and tested for the Cambridge stratified flame using Large Eddy Simulations (LES) with an artificially thickened flame approach. Different numerical discretisations and definitions of the outer cut-off length are tested, as different practices exist that can have a strong impact on the results. The Cambridge experiment is chosen since it exhibits a Reynolds number of more than 11,500 and the stratified flame is strongly wrinkled further downstream, making it a challenging configuration for the turbulent (stratified) combustion modelling. The sub-grid level physics have been modelled by four wrinkling factor closures, which rely explicitly on algebraic functions of resolved variables, to analyse the influence of wrinkling factor modelling on the predictions of LES. Many such models have been proposed and were tested successfully–but typically for perfectly premixed flames, using specific discretisations and definitions of the cut-off length or filter width. The present paper shows that the models tested perform well even for stratified combustion, provided that the correct definition for the cut-off length is used, and to a lesser extent, suitable discretisation methodologies are employed. © 2021 Informa UK Limited, trading as Taylor & Francis Group.
    view abstractdoi: 10.1080/13647830.2021.1962546
  • 2021 • 870 Effect of Organic Solvents on the Structure and Activity of a Minimal Lipase
    Ingenbosch, K.N. and Vieyto-Nuñez, J.C. and Ruiz-Blanco, Y.B. and Mayer, C. and Hoffmann-Jacobsen, K. and Sanchez-Garcia, E.
    Journal of Organic Chemistry (2021)
    Lipases are ubiquitously used in chemo-enzymatic synthesis and industrial applications. Nevertheless, the modulation of the activity of lipases by organic solvents still is not fully understood at the molecular level. We systematically investigated the activity and structure of lipase A from Bacillus subtilis in binary water-organic solvent mixtures of dimethyl sulfoxide (DMSO), acetonitrile (ACN), and isopropyl alcohol (IPA) using activity assays, fluorescence spectroscopy, molecular dynamics (MD) simulations, and FRET/MD analysis. The enzymatic activity strongly depended on the type and amount of organic solvent in the reaction media. Whereas IPA and ACN reduced the activity of the enzyme, small concentrations of DMSO led to lipase activation via an uncompetitive mechanism. DMSO molecules did not directly interfere with the binding of the substrate in the active site, contrary to what is known for other solvents and enzymes. We propose that the His156-Asp133 interaction, the binding of organic molecules to the active site, and the water accessibility of the substrate are key factors modulating the catalytic activity. Furthermore, we rationalized the role of solvent descriptors on the regulation of enzymatic activity in mixtures with low concentrations of the organic molecule, with prospective implications for the optimization of biocatalytic processes via solvent tuning. © 2021 The Authors. Published by American Chemical Society.
    view abstractdoi: 10.1021/acs.joc.1c01136
  • 2021 • 869 A modified tool design for the drilling of high-performance aerospace materials
    Iovkov, I. and Bücker, M. and Biermann, D.
    CIRP Annals 70 83-86 (2021)
    High-performance Ni- and Ti-based materials are generally difficult to machine. Drilling in particular is highly demanding for the applied tools due to challenging thermal stress. This paper describes a novel modification for twist drills which significantly improves the cooling and lubrication of the main and secondary cutting edges and leads to an enhancement in process productivity. Within the scope of this work, the achievable improvements with regard to wear progress, cutting edge temperature and cutting fluid flow when machining Inconel 718 are analysed. The solution developed could also prove its efficiency in the machining of titanium-based alloy Ti6Al4V. © 2021 The Author(s)
    view abstractdoi: 10.1016/j.cirp.2021.04.024
  • 2021 • 868 Development of the scaled boundary finite element method for crack propagation modeling of elastic solids subjected to coupled thermo-mechanical loads
    Iqbal, M.D. and Birk, C. and Ooi, E.T. and Gravenkamp, H.
    Computer Methods in Applied Mechanics and Engineering 387 (2021)
    This study presents the development of the scaled boundary finite element method to model discrete crack propagation induced by thermal loads. The SBFEM excels in modeling stress singularities at sharp crack tips with high accuracy. Polygon meshes are used so that a robust local re-meshing algorithm can be utilized to propagate the crack. The scaled boundary finite element formulation for steady-state thermal stress analysis is presented. Following a scaled boundary finite element analysis of a given thermal problem, the effect of initial strains due to temperature is taken into account semi-analytically in a subsequent stress analysis. Several numerical examples are presented to validate the technique and illustrate its salient features. © 2021
    view abstractdoi: 10.1016/j.cma.2021.114106
  • 2021 • 867 Deterioration of concrete due to ASR: Experiments and multiscale modeling
    Iskhakov, T. and Giebson, C. and Timothy, J.J. and Ludwig, H.M. and Meschke, G.
    Cement and Concrete Research 149 (2021)
    The process of ASR (Alkali-Silica Reaction) induced expansion and damage in pavement concrete specimens is investigated using laboratory experiments and computational modeling. In the experimental program, the concrete specimens are subject to CS-CPT (climate simulation concrete prism test) to obtain ASR induced expansion with and without external supply of alkali. The dissolution rates of the granodiorite used in the concrete mix and the gel formation rates are determined under concrete-like conditions (pH 13.8, with/without Ca(OH)2 and NaCl) at different temperatures. A micromechanics based computational model with aggregate-scale diffusion and reaction kinetics coupled to an Eigenstrain based micromechanics damage model is developed for the simulation of ASR induced expansion and damage. Data from the experimental program are used to calibrate and validate the computational model. Model predictions show that for the given concrete mixture, ASR induced expansion in the specimen exposed to water is predominantly governed by microcracking in the aggregate, while the expansion in the specimen subjected to external alkali supply is governed by microcracking in both the aggregates and the cement paste. © 2021 Elsevier Ltd
    view abstractdoi: 10.1016/j.cemconres.2021.106575
  • 2021 • 866 Specific heat and gap structure of a nematic superconductor: Application to FeSe
    Islam, K.R. and Böker, J. and Eremin, I.M. and Chubukov, A.V.
    Physical Review B 104 (2021)
    We report the results of our in-depth analysis of spectroscopic and thermodynamic properties of a multiorbital metal, like FeSe, which first develops a nematic order and then undergoes a transition into a superconducting state, which coexists with nematicity. We analyze the angular dependence of the gap function and specific heat of such a nematic superconductor. We specifically address three issues: (i) the angular dependence of the gap in light of the competition between the nematicity-induced mixture and the orbital transmutation of low-energy excitations in the nematic state, (ii) the effect of nematicity on the magnitude of the jump of the specific heat at and the temperature dependence of below , and (iii) a potential transition at from an state to an state that breaks time-reversal symmetry. We consider two scenarios for a nematic order: scenario A, in which this order develops between and orbitals on hole and electron pockets, and scenario B, in which there is an additional component of the nematic order for fermions on the two electron pockets. ©2021 American Physical Society
    view abstractdoi: 10.1103/PhysRevB.104.094522
  • 2021 • 865 Coherent Beam Splitting of Flying Electrons Driven by a Surface Acoustic Wave
    Ito, R. and Takada, S. and Ludwig, Ar. and Wieck, A.D. and Tarucha, S. and Yamamoto, M.
    Physical Review Letters 126 (2021)
    We develop a coherent beam splitter for single electrons driven through two tunnel-coupled quantum wires by surface acoustic waves (SAWs). The output current through each wire oscillates with gate voltages to tune the tunnel coupling and potential difference between the wires. This oscillation is assigned to coherent electron tunneling motion that can be used to encode a flying qubit and is well reproduced by numerical calculations of time evolution of the SAW-driven single electrons. The oscillation visibility is currently limited to about 3%, but robust against decoherence, indicating that the SAW electron can serve as a novel platform for a solid-state flying qubit. © 2021 American Physical Society.
    view abstractdoi: 10.1103/PhysRevLett.126.070501
  • 2021 • 864 Interface-Dominated Topological Transport in Nanograined Bulk Bi2Te3
    Izadi, S. and Han, J.W. and Salloum, S. and Wolff, U. and Schnatmann, L. and Asaithambi, A. and Matschy, S. and Schlörb, H. and Reith, H. and Perez, N. and Nielsch, K. and Schulz, S. and Mittendorff, M. and Schierning, G.
    Small 17 (2021)
    3D topological insulators (TI) host surface carriers with extremely high mobility. However, their transport properties are typically dominated by bulk carriers that outnumber the surface carriers by orders of magnitude. A strategy is herein presented to overcome the problem of bulk carrier domination by using 3D TI nanoparticles, which are compacted by hot pressing to macroscopic nanograined bulk samples. Bi2Te3 nanoparticles well known for their excellent thermoelectric and 3D TI properties serve as the model system. As key enabler for this approach, a specific synthesis is applied that creates nanoparticles with a low level of impurities and surface contamination. The compacted nanograined bulk contains a high number of interfaces and grain boundaries. Here it is shown that these samples exhibit metallic-like electrical transport properties and a distinct weak antilocalization. A downward trend in the electrical resistivity at temperatures below 5 K is attributed to an increase in the coherence length by applying the Hikami–Larkin–Nagaoka model. THz time-domain spectroscopy reveals a dominance of the surface transport at low frequencies with a mobility of above 103 cm2 V−1 s−1 even at room temperature. These findings clearly demonstrate that nanograined bulk Bi2Te3 features surface carrier properties that are of importance for technical applications. © 2021 The Authors. Small published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/smll.202103281
  • 2021 • 863 Probing negatively charged and neutral excitons in MoS2/hBN and hBN/MoS2/hBN van der Waals heterostructures
    Jadczak, J. and Kutrowska-Girzycka, J. and Bieniek, M. and Kazimierczuk, T. and Kossacki, P. and Schindler, J.J. and Debus, J. and Watanabe, K. and Taniguchi, T. and Ho, C.H. and Wójs, A. and Hawrylak, P. and Bryja, L.
    Nanotechnology 32 (2021)
    High-quality van der Waals heterostructures assembled from hBN-encapsulated monolayer transition metal dichalcogenides enable observations of subtle optical and spin-valley properties whose identification was beyond the reach of structures exfoliated directly on standard SiO2/Si substrates. Here, we describe different van der Waals heterostructures based on uncapped singlelayer MoS2stacked onto hBN layers of different thicknesses and hBN-encapsulated monolayers. Depending on the doping level, they reveal the fine structure of excitonic complexes, i.e. neutral and charged excitons. In the emission spectra of a particular MoS2/hBN heterostructure without an hBN cap we resolve two trion peaks, T1and T2, energetically split by about 10 meV, resembling the pair of singlet and triplet trion peaks (TSand TT) in tungsten-based materials. The existence of these trion features suggests that monolayer MoS2has a dark excitonic ground state, despite having a 'bright' single-particle arrangement of spin-polarized conduction bands. In addition, we show that the effective excitonic g-factor significantly depends on the electron concentration and reaches the lowest value of -2.47 for hBN-encapsulated structures, which reveals a nearly neutral doping regime. In the uncapped MoS2structures, the excitonic g-factor varies from -1.15 to -1.39 depending on the thickness of the bottom hBN layer and decreases as a function of rising temperature. © 2021 Institute of Physics Publishing. All rights reserved.
    view abstractdoi: 10.1088/1361-6528/abd507
  • 2021 • 862 Investigations of electron-electron and interlayer electron-phonon coupling in van der Waals hBN/WSe2/hBN heterostructures by photoluminescence excitation experiments
    Jadczak, J. and Kutrowska-Girzycka, J. and Schindler, J.J. and Debus, J. and Watanabe, K. and Taniguchi, T. and Ho, C.-H. and Bryja, L.
    Materials 14 1-12 (2021)
    Monolayers of transition metal dichalcogenides (TMDs) with their unique physical properties are very promising for future applications in novel electronic devices. In TMDs monolayers, strong and opposite spin splittings of the energy gaps at the K points allow for exciting carriers with various combinations of valley and spin indices using circularly polarized light, which can further be used in spintronics and valleytronics. The physical properties of van der Waals heterostructures composed of TMDs monolayers and hexagonal boron nitride (hBN) layers significantly depend on different kinds of interactions. Here, we report on observing both a strong increase in the emission intensity as well as a preservation of the helicity of the excitation light in the emission from hBN/WSe2/hBN heterostructures related to interlayer electron-phonon coupling. In combined low-temperature (T = 7 K) reflectivity contrast and photoluminescence excitation experiments, we find that the increase in the emission intensity is attributed to a double resonance, where the laser excitation and the combined Raman mode A′ 1 (WSe2) + ZO (hBN) are in resonance with the excited (2s) and ground (1s) states of the A exciton in a WSe2 monolayer. In reference to the 2s state, our interpretation is in contrast with previous reports, in which this state has been attributed to the hybrid exciton state existing only in the hBN-encapsulated WSe2 monolayer. Moreover, we observe that the electron-phonon coupling also enhances the helicity preservation of the exciting light in the emission of all observed excitonic complexes. The highest helicity preservation of more than 60% is obtained in the emission of the neutral biexciton and negatively charged exciton (trion) in its triplet state. Additionally, to the best of our knowledge, the strongly intensified emission of the neutral biexciton XX0 at double resonance condition is observed for the first time. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/ma14020399
  • 2021 • 861 Upconversion of Light into Bright Intravalley Excitons via Dark Intervalley Excitons in hBN-Encapsulated WSe2Monolayers
    Jadczak, J. and Glazov, M. and Kutrowska-Girzycka, J. and Schindler, J.J. and Debus, J. and Ho, C.-H. and Watanabe, K. and Taniguchi, T. and Bayer, M. and Bryja, L.
    ACS Nano (2021)
    Semiconducting monolayers of transition-metal dichalcogenides are outstanding platforms to study both electronic and phononic interactions as well as intra- and intervalley excitons and trions. These excitonic complexes are optically either active (bright) or inactive (dark) due to selection rules from spin or momentum conservation. Exploring ways of brightening dark excitons and trions has strongly been pursued in semiconductor physics. Here, we report on a mechanism in which a dark intervalley exciton upconverts light into a bright intravalley exciton in hBN-encapsulated WSe2 monolayers. Excitation spectra of upconverted photoluminescence reveals resonances at energies 34.5 and 46.0 meV below the neutral exciton in the nominal WSe2 transparency range. The required energy gains are theoretically explained by cooling of resident electrons or by exciton scattering with D- or K-valley phonons. Accordingly, an elevated temperature and a moderate concentration of resident electrons are necessary for observing the upconversion resonances. The interaction process observed between the inter- and intravalley excitons elucidates the importance of dark excitons for the optics of two-dimensional materials. ©
    view abstractdoi: 10.1021/acsnano.1c08286
  • 2021 • 860 Distant spin entanglement via fast and coherent electron shuttling
    Jadot, B. and Mortemousque, P.-A. and Chanrion, E. and Thiney, V. and Ludwig, Ar. and Wieck, A.D. and Urdampilleta, M. and Bäuerle, C. and Meunier, T.
    Nature Nanotechnology 16 570-575 (2021)
    In the quest for large-scale quantum computing, networked quantum computers offer a natural path towards scalability. While recent experiments have demonstrated nearest neighbour entanglement for electron spin qubits in semiconductors, on-chip long-distance entanglement could bring more versatility to connect quantum core units. Here, we employ the moving trapping potential of a surface acoustic wave to realize the controlled and coherent transfer of a pair of entangled electron spins between two distant quantum dots. The subsequent electron displacement induces coherent spin rotations, which drives spin quantum interferences. We observe high-contrast interference as a signature of the preservation of the entanglement all along the displacement procedure, which includes a separation of the two spins by a distance of 6 μm. This work opens the route towards fast on-chip deterministic interconnection of remote quantum bits in semiconductor quantum circuits. © 2021, The Author(s), under exclusive licence to Springer Nature Limited.
    view abstractdoi: 10.1038/s41565-021-00846-y
  • 2021 • 859 Simulation-based analysis of the energy demand within an additive subtractive process chain
    Jaeger, E. and Ravisankar, B. and Wirtz, A. and Meißner, M. and Rehtanz, C. and Biermann, D. and Wiederkehr, P.
    Procedia CIRP 99 352-357 (2021)
    Additive manufacturing processes, such as Selective Laser Melting (SLM), has become increasingly established in metal-processing industry offering versatile possibilities for producing individualised components or lightweight structures. SLM machines offer ecological and economical potentials due to comparatively low power and material demand. Required pre-and post-processes as sieving and milling, which are used to ensure a stable process and fulfil demands on surface quality and tolerances, are often neglected. Differentiating from this, an approach for analysing the energy demand of an additive-subtractive process chain is presented based on exemplary processes using a combination of empirical models and a geometric physically-based simulation. © 2021 The Authors. Published by Elsevier B.V.
    view abstractdoi: 10.1016/j.procir.2021.03.051
  • 2021 • 858 Osteonecrosis [Osteonekrosen]
    Jäger, M.
    Orthopade 50 798-801 (2021)
    doi: 10.1007/s00132-021-04147-z
  • 2021 • 857 The Impact of Antimony on the Performance of Antimony Doped Tin Oxide Supported Platinum for the Oxygen Reduction Reaction
    Jalalpoor, D. and Göhl, D. and Paciok, P. and Heggen, M. and Knossalla, J. and Radev, I. and Peinecke, V. and Weidenthaler, C. and Mayrhofer, K.J.J. and Ledendecker, M. and Schüth, F.
    Journal of the Electrochemical Society 168 (2021)
    Antimony doped tin oxide (ATO) supported platinum nanoparticles are considered a more stable replacement for conventional carbon supported platinum materials for the oxygen reduction reaction. However, the interplay of antimony, tin and platinum and its impact on the catalytic activity and durability has only received minor attention. This is partly due to difficulties in the preparation of morphology- and surface-area-controlled antimony-doped tin oxide materials. The presented study sheds light onto catalyst-support interaction on a fundamental level, specifically between platinum as a catalyst and ATO as a support material. By using a previously described hard-templating method, a series of morphology controlled ATO support materials for platinum nanoparticles with different antimony doping concentrations were prepared. Compositional and morphological changes before and during accelerated stress tests are monitored, and underlying principles of deactivation, dissolution and catalytic performance are elaborated. We demonstrate that mobilized antimony species and strong metal support interactions lead to Pt/Sb alloy formation as well as partially blocking of active sites. This has adverse consequences on the accessible platinum surface area, and affects negatively the catalytic performance of platinum. Operando time-resolved dissolution experiments uncover the potential boundary conditions at which antimony dissolution can be effectively suppressed and how platinum influences the dissolution behavior of the support. © 2021 The Author(s). Published on behalf of The Electrochemical Society by IOP Publishing Limited.
    view abstractdoi: 10.1149/1945-7111/abd830
  • 2021 • 856 Thermochemistry of Oxygen-Containing Organosilane Radicals and Uncertainty Estimations of Organosilane Group-Additivity Values
    Janbazi, H. and Schulz, C. and Wlokas, I. and Peukert, S.
    Journal of Physical Chemistry A 125 8699-8711 (2021)
    Si-C-H-O-containing radicals are important intermediates during the combustion and pyrolysis of precursors applied for the gas-phase synthesis of silica nanoparticles. Despite the industrial importance of silica nanoparticles, a comprehensive thermodynamics database of organosilane species is still missing. This work presents thermochemical data of 91 Si-C-H-O radical species. Quantum-chemical calculations and isodesmic reaction schemes are used to determine the standard enthalpy of formation, entropy, and heat capacities covering the 298-2000 K temperature range. In addition, 90 group-additivity values (GAVs) are calculated, which cover all relevant group increments. A combinatorial approach is used to ensure that all possible group increments are considered. The theoretically calculated species are used as a training set to derive 90 GAVs of Si-C-H-O radical species for the first time. In addition, uncertainty contributions of GAVs were estimated. These uncertainty estimates also comprise GAVs that were previously derived to compute thermochemical data of stable Si-C-H species and radicals as well as stable Si-C-H-O compounds. Therefore, uncertainty contributions of GAVs for a whole set of 243 group increments used to predict thermochemical data of Si-organic species are reported. © 2021 The Authors. Published by American Chemical Society
    view abstractdoi: 10.1021/acs.jpca.1c06941
  • 2021 • 855 Band-gap solitons in nonlinear photonic crystal waveguides and their application for functional all-optical logic gating