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ROBUSTNESS OF AN UPWIND FINITE DIFFERENCE SCHEME FOR SEMILINEAR CONVECTION-DIFFUSION PROBLEMS WITH BOUNDARY TURNING POINTS

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Journal of Computational Mathematics 2003年第4期21卷 401-410页

作者： Torsten Linfi (Institut fur Numerische Mathematik, technische universitdt Dresden, D-01062 Dresden, Germany) Institut fiir Nwnerisclie Mathematik Technische Universitdt Dresden 德国 D-01062 Dresden

We consider a singularly perturbed semilinear convection-diffusion problem with a boundary layer of attractive turning-point type. It is shown that its solution can be decomposed into a regular solution component and a layer component. This decomposition is used to analyse the convergence of an upwinded finite difference scheme on Shishkin meshes.

关键词： Convection-diffusion Singular perturbation Solution decomposition Shishkin mesh.

Constrained crystals deep convolutional generative adversarial network for the inverse design of crystal structures

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npj Computational Materials 2021年第1期7卷 588-594页

作者： Teng Long Nuno M.Fortunato Ingo Opahle Yixuan Zhang Ilias Samathrakis Chen Shen Oliver Gutfleisch Hongbin Zhang Institute of Materials Science Technische Universität DarmstadtDarmstadtGermany

Autonomous materials discovery with desired properties is one of the ultimate goals for materials science,and the current studies have been focusing mostly on high-throughput screening based on density functional theory calculations and forward modeling of physical properties using machine *** the deep learning techniques,we have developed a generative model,which can predict distinct stable crystal structures by optimizing the formation energy in the latent *** is demonstrated that the optimization of physical properties can be integrated into the generative model as on-top screening or backward propagator,both with their own *** the generative models on the binary Bi-Se system reveals that distinct crystal structures can be obtained covering the whole composition range,and the phases on the convex hull can be reproduced after the generated structures are fully relaxed to the *** method can be extended to multicomponent systems for multi-objective optimization,which paves the way to achieve the inverse design of materials with optimal properties.

关键词： properties crystal inverse

Cathodic activated stainless steel mesh as a highly active electrocatalyst for the oxygen evolution reaction with self-healing possibility

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Journal of Energy Chemistry 2020年第10期29卷 153-160页

作者： Gui-Rong Zhang Liu-Liu Shen Patrick Schmatz Konrad Krois Bastian J.M.Etzold Ernst-Berl-Institut für technische und Makromolekulare Chemie Technische Universit鋞Darmstadt64287 DarmstadtGermany

The oxygen evolution reaction(OER)represents one of the major bottlenecks for broad-based applications of many clean energy storage/conversion *** key to solving this problem lies in developing high-performing,cost effective and stable catalysts for the ***,we demonstrate that ubiquitous stainless steel mesh(SSM)materials activated by a facile cathodization treatment can be employed as a high performing OER catalyst,as showcased by the impressively low overpotentials of 275 and 319 mV to reach the benchmark current densities of 10 and 100 mA cm^−2(1.0 M KOH),*** SSM also exhibits excellent performance in a two-electrode water electrolyzer,which requires a low cell voltage of 1.58 at 10 mA cm^−2 and outperforms many of water electrolyzers using earth-abundant OER ***,cathodized SSM with minor performance degradation after the stability test can also be readily healed by subjecting it to an additional cathodization *** is disclosed that the superior performance of cathodized SSMs stems from the surface enrichment of OER active Ni(oxy)hydroxide,facile gas-bubble removal and transportation over the unique mesh-structured surfaces,while the abundant reservoir of nickel in the bulk allows healing of the catalyst by a facile cathodization.

关键词： Oxygen evolution reaction Water splitting Stainless steel mesh Cathodization Mass transfer limitation Self-healing

A MULTIGRID SEMISMOOTH NEWTON METHOD FOR SEMILINEAR CONTACT PROBLEMS

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Journal of Computational Mathematics 2017年第4期35卷 486-528页

作者： Michael Ulbrich Stefan Ulbrich Daniela Bratzke technische Universitat Miinchen Department of Mathematics Garching b. Munchen Germany technische Universitiit darmstadt Department of Mathematics Darmstadt Germany technische Universitat darmstadt Department of Mathematics Darmstadt Germany

This paper develops and analyzes multigrid semismooth Newton methods for a class of inequality-constrained optimization problems in function space which are motivated by and include linear elastic contact problems of Signorini type. We show that after a suitable Moreau-Yosida type regularization of the problem superlinear local convergence is obtained for a class of semismooth Newton methods. In addition, estimates for the order of tile error introduced by the regularization are derived. The main part of the paper is devoted to the analysis of a multilevel preconditioner for the semismooth Newton system. We prove a rigorous bound for the contraction rate of the multigrid cycle which is robust with respect to sufficiently small regularization parameters and the number of grid levels. Moreover, it applies to adaptively refined grids. The paper concludes with numerical results.

关键词： Contact problems Semismooth Newton methods Multigrid methods Errorestimates.

Voltage-driven charge-mediated fast 180 degree magnetization switching in nanoheterostructure at room temperature

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npj Computational Materials 2017年第1期3卷 137-145页

作者： Min Yi Hongbin Zhang Bai-Xiang Xu Department of Materials and Earth Sciences Technische Universitat Darmstadt64287 DarmstadtGermany

Voltage-driven 180°magnetization switching without electric current provides the possibility for revolutionizing the *** demonstrated the voltage-driven charge-mediated 180°magnetization switching at room temperature by combining firstprinciples calculations and temperature-dependent magnetization dynamics *** electric field(E)-induced interface charge is found to allow a giant modulation of the magnetic anisotropy(K)of the *** K is revealed to vary linearly with respect to E and the epitaxial *** dynamics simulations using the so-obtained K show that both inplane and perpendicular 180°switching can be achieved by E *** temperature effect renders the 180°switching as probability *** analysis indicates a fast(around 4 ns)and low-error-probability 180°switching achievable at room temperature by controlling the magnitude of E and the pulse *** study inspires the rational design of miniaturized nanoscale spintronic devices where thermal fluctuation has a great impact.

关键词： magnetization charge render

Experimental study on the tribo-chemical smoothening process between self-mated silicon carbide in a water-lubricated surfacecontact reciprocating test

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Friction 2019年第2期7卷 181-191页

作者： Le JIN Herbert SCHEERER Georg ANDERSOHN Matthias OECHSNER Dieter HELLMANN Center for Structural Materials Technische Universit?t Darmstadt KSB

Silicon carbide(SiC) can be tribo-chemically smoothened during a self-mated sliding procedure in the aqueous environment. As well reported in the point-contact tests, this smoothening process works well due to the abundant water as oxidant. After this smoothening process, the tribo-surface is well polished, a closely mated tribo-gap naturally forms, and an ultra-low friction state is built. However, water in the tribo-gap could be insufficient in industrial applications, e.g., the seal gap in mechanical seals. In this study, the tribo-chemical smoothening behavior in such environment was researched. A surface-contact reciprocating test was used to simulate the aqueous environment where water was insufficient. After tests, compared to the published results from the point-contact tests, the same ultra-low friction state was achieved. A part of the tribo-surface was tribo-chemically smoothened. The obtained smoothened surface microstructure was consistent with the published information. Meanwhile, severe abrasive wear occurred. A porous oxygen-rich layer was found existing beneath the abrasion-induced grooves, in which numerous smashed wear debris adhered on the worn surfaces. We concluded that the shortage of water initiated the severe abrasion, meanwhile the generated wear debris aggravated the wear condition. This understanding is instructive for developing new methods to avoid the severe abrasion in the same water insufficient environment.

关键词： silicon carbide surface-contact sliding friction tribo-chemical smoothening abrasion ultra-low friction mechanical seal

Surface area-volume ratios in insects

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Insect Science 2017年第5期24卷 829-841页

作者： Sara Kuhsel Adrian Bruckner Sebastian Schmelzle Michael Heethoff Nico Bluthgen Department of Biology Technische Universitat Darmstadt Schnittspahnstrasse 3 D-64287 Darmstadt Germany

Body mass, volume and surface area are important for many aspects of the physiology and performance of species. Whereas body mass scaling received a lot of attention in the literature, surface areas of animals have not been measured explicitly in this context. We quantified surface area-volume （SA/V） ratios for the first time using 3D surface models based on a structured light scanning method for 126 species of pollinating insects from 4 orders （Diptera, Hymenoptera, Lepidoptera, and Coleoptera）. Water loss of 67 species was measured gravimetrically at very dry conditions for 2 h at 15 and 30 ℃ to demonstrate the applicability of the new 3D surface measurements and relevance for predicting the performance of insects. Quantified SA/V ratios significantly explained the variation in water loss across species, both directly or after accounting for isometric scaling （residuals of the SA/V - mass2/3 relationship）. Small insects with a proportionally larger surface area had the highest water loss rates. Surface scans of insects to quantify allometric SA/Vratios thus provide a promising method to predict physiological responses, improving the potential of body mass isometry alone that assume geometric similarity.

关键词： body size body shape 3D surface imaging sphericity structured light water loss

Influence of High-Speed Milling Process on Mechanical and Microstructural Properties of Ultrafine Grained Profiles Produced by Linear Flow Splitting

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Transactions of Nanjing University of Aeronautics and Astronautics 2017年第4期34卷 349-356页

作者： Abele Eberhard Müller Clemens Turan Emrah Niehuesbernd Joern Bruder Enrico Falk Florian Institute of Production Management Technology and Machine Tools(PTW)Technische Universitt Darmstadt Physical Metallurgy(PhM) Technische Universitt Darmstadt

The effects of milling parameters on the surface quality,microstructures and mechanical properties of machined parts with ultrafine grained(UFG)gradient microstructures are *** effects of the cutting speed,feed per tooth,cutting tool geometry and cooling strategy are *** has been found that the surface quality of machined grooves can be improved by increasing the cutting ***,cryogenic cooling with CO_2 exhibits no significant improvement of surface *** and hardness investigations revealed similar microstructure and hardness variations near the machined groove walls for both utilized tool ***,cryogenic cooling can decrease more far-ranging hardness reductions due to high process temperatures,especially in the UFG regions of the machined parts,whilst it cannot prevent the drop in hardness directly at the groove walls.

关键词： high-speed milling ultrafine grained microstructure linear flow splitting hardness

Effect of Different Calcination Temperatures and Post Annealing on the Properties of Acetic Acid Based Sol-Gel (Na_(0.5)K_(0.5))NbO_3(NKN) Thin Films

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Journal of Materials Science & Technology 2013年第2期29卷 142-148页

作者： Sebastian Wiegand Stefan Flege Olaf Baake Wolfgang Ensinger Materials Analysis Group Department of Materials and Geosciences Technische Universitt Darmstadt Petersenstrasse 23 64287 Darmstadt Germany

（Na0.5K0.5）NbO3 （NKN） lead free thin films were synthesized by means of an acetic acid based sol-gel process on Pt/Ti/SiO2/Si substrates. Na-acetate, K-acetate and Nb-pentaethoxide were used as metal precursors and acetic acid as the solvent. The effect of different calcination temperatures on the properties of the NKN films was investigated by X-ray diffraction, scanning electron microscopy, leakage current and hysteresis measurements. Low calcination temperatures led to low currents at high electric fields whereas high calcination temperatures led to low currents at low electric fields. Based on these findings calcination at low temperature was combined with a post annealing treatment. Low leakage currents of 4×10^-4 A/cm2 at 150 kV/cm and 2Pr and 2Ec values of 28 μC/cm2 and 150 kV/cm, respectively, could be obtained. All films were single phase NKN with random crystal orientations and no crack or pore formation was visible on the surface.

关键词： Sol-gel process (Na0.5K0.5)NbO3 Thin film Perovskite Lead-free Piezo material