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Approximate contact solutions for non-axisymmetric homogeneous and power-law graded elastic bodies:A practical tool for design engineers and tribologists

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Friction 2024年第2期12卷 340-355页

作者： Valentin L.POPOV Qiang LI Emanuel WILLERt Institute of Mechanics Technische Universität BerlinBerlin 10623Germany

In two recent papers,approximate solutions for compact non-axisymmetric contact problems of homogeneous and power-law graded elastic bodies have been suggested,which provide explicit analytical relations for the force–approach relation,the size and the shape of the contact area,as well as for the pressure distribution *** solutions were derived for profiles,which only slightly deviate from the axisymmetric *** the present paper,they undergo an extensive testing and validation by comparison of solutions with a great variety of profile shapes with numerical solutions obtained by the fast Fourier transform(FFt)-assisted boundary element method(BEM).Examples are given with quite significant deviations from axial symmetry and show surprisingly good agreement with numerical solutions.

关键词： normal contact non-axisymmetric indenter extremal principle generalized method of dimensionality reduction(MDR) functional elastic grading

A derived grid-based model for simulation of pedestrian flow

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Journal of Zhejiang university-Science A(Applied Physics & Engineering) 2009年第2期10卷 209-220页

作者： Günter BRWOLFF Hartmut SCHWANDt Institut für Mathematik Technische Universitt Berlin

We present a derived grid-based model for the simulation of pedestrian flow. Interactions among pedestrians are considered as the result of forces within a certain neighbourhood. Unlike the social force model,the forces here,as in Newtonian physics,are proportional to the inverse of the square of the distance. Despite the notion of neighbourhood and the underlying grid,this model differs from the existing cellular automaton(CA) models in that the pedestrians are treated as individuals. Bresenham's algorithm for line rastering is applied in the step calculation.

关键词： Bresenham's algorithm Cellular automaton (CA) Pedestrian dynamics Social force model

Developing a web-based spatial decision support system for geothermal exploration at the Olkaria geothermal field

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International Journal of Digital Earth 2017年第11期10卷 1118-1145页

作者： Daniel Mwaur Martin Kad Institute of Geodesy and Geoinformation Science Technische Universität BerlinBerlinGermany

Geothermal exploration is a complex process that spans a number of *** a decision is made to drill a geothermal well,there is need for an extensive exploration process to determine the most suitable *** process of evaluating and analyzing data from individual scientific disciplines can be complex and *** have been made at solving this problem using GIS-based tools but the uptake of these tools is often hindered by the limited knowledge of GIS by decision *** paper presents an approach for solving the geothermal exploration question through a web-based spatial decision support system(SDSS)that incorporates the various geosciences through a multi-criteria spatial decision analysis *** results reveal a decision-making gap that is to be filled using a novel,automated exploration *** approach hypothesizes an easier and faster decision-making *** research focuses on Olkaria,an active geothermal area in Kenya,East Africa and highlights a pragmatic approach to identifying priority areas for *** evaluates contributions made by many disciplines in identifying potential sites ideal for harnessing geothermal energy and the gaps that emerge in an effort to synergize the results from the different disciplines.

关键词： GIS SDSS geothermal web based multi-criteria decision analysis

Strength of adhesive contacts: Influence of contact geometry and material gradients

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Friction 2017年第3期5卷 308-325页

作者： Valentin L.POPOV Roman POHRt Qiang LI Institute of Mechanics Technische Universit(a)t Berlin Berlin 10623 GermanyNational Research Tomsk Polytechnic University Tomsk 634050 Russia Institute of Mechanics Technische Universit(a)t Berlin Berlin 10623 Germany

the strength of an adhesive contact between two bodies can strongly depend on the macroscopic and microscopic shape of the *** the past,the influence of roughness has been investigated ***,even in the presence of perfectly smooth surfaces,geometry can come into play in form of the macroscopic shape of the contacting *** we present numerical and experimental results for contacts of rigid punches with flat but oddly shaped face contacting a soft,adhesive *** it is carefully pulled off,we find that in contrast to circular shapes,detachment occurs not instantaneously but detachment fronts start at pointed comers and travel inwards,until the final configuration is reached which for macroscopically isotropic shapes is almost *** elongated indenters,the final shape resembles the original one with rounded *** describe the influence of the shape of the stamp both experimentally and *** simulations are performed using a new formulation of the boundary element method for simulation of adhesive contacts suggested by Pohrt and *** is based on a local,mesh dependent detachment criterion which is derived from the Griffith principle of balance of released elastic energy and the work of *** validation of the suggested method is made both by comparison with known analytical solutions and with *** method is applied for simulating the detachment of flat-ended indenters with square,triangle or rectangular shape of cross-section as well as shapes with various kinds of faults and to 'brushes'.the method is extended for describing power-law gradient media.

关键词： adhesion boundary element method (BEM) flat-ended indenters,gradient media

Reduction of friction by normal oscillations.Ⅱ.In-plane system dynamics

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Friction 2017年第2期5卷 534-535,536页

作者： Xinyu MAO Valentin L.POPOV Jasminka StARCEVIC Mikhail POPOV technische universit(a)t berlin Berlin 10623 GermanyTsinghua University Beijing 100084 China technische universit(a)t berlin Berlin 10623 GermanyTomsk Polytechnic University Tomsk 634050 RussiaTomsk State University Tomsk 634050 Russia technische universit(a)t berlin Berlin 10623 GermanyTomsk State University Tomsk 634050 Russia

the influence of out-of-plane oscillations on friction is a well-known phenomenon that has been studied extensively with various experimental methods,e.g.,pin-on-disk ***,existing theoretical models have yet achieved only qualitative correspondence with *** we argue that this may be due to the system dynamics (mass and tangential stiffness) of the pin or other system components being *** paper builds on the results of a previous study [19] by taking the stiffness and resulting dynamics of the system into *** main governing parameters determining macroscopic friction,including a dimensionless oscillation amplitude,a dimensionless sliding velocity and the relation between three characteristic frequencies (that of externally excited oscillation and two natural oscillation frequencies associated with the contact stiffness and the system stiffness) are *** the limiting cases of a very soft system and a very stiff system,our results reproduce the results of previous *** between these two limiting cases there is also a resonant case,which is studied here for the first *** resonant case is notable in that it lacks a critical sliding velocity,above which oscillations no longer reduce *** obtained for the resonant case are qualitatively supported by experiments.

关键词： sliding friction out-of-plane oscillation stiffness system dynamics macroscopic friction coefficient

Finding the semantic similarity in single-particle diffraction images using self-supervised contrastive projection learning

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npj Computational Materials 2023年第1期9卷 2118-2126页

作者： Julian Zimmermann Fabien Beguet Daniel Guthruf Bruno Langbehn Daniela Rupp EtH Zürich ZürichSwitzerland technische universität berlin BerlinGermany Max-Born-Institut BerlinGermany

Single-shot coherent diffraction imaging of isolated nanosized particles has seen remarkable success in recent years,yielding in-situ measurements with ultra-high spatial and temporal *** progress of high-repetition-rate sources for intense X-ray pulses has further enabled recording datasets containing millions of diffraction images,which are needed for the structure determination of specimens with greater structural variety and dynamic *** size of the datasets,however,represents a monumental problem for their ***,we present an automatized approach for finding semantic similarities in coherent diffraction images without relying on human expert *** introducing the concept of projection learning,we extend self-supervised contrastive learning to the context of coherent diffraction imaging and achieve a dimensionality reduction producing semantically meaningful embeddings that align with physical *** method yields substantial improvements compared to previous approaches,paving the way toward real-time and large-scale analysis of coherent diffraction experiments at X-ray free-electron lasers.

关键词： projection coherent similarity

Representations of molecules and materials for interpolation of quantum-mechanical simulations via machine learning

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npj Computational Materials 2022年第1期8卷 378-391页

作者： Marcel F.Langer Alex Goeßmann Matthias Rupp NOMAD Laboratory Fritz Haber Institute of the Max Planck SocietyBerlinGermany Machine Learning Group Technische Universität BerlinBerlinGermany Institute of Mathematics Technische Universität BerlinBerlinGermany Citrine Informatics Redwood CityCAUSA Department of Computer and Information Science University of KonstanzKonstanzGermany

Computational study of molecules and materials from first principles is a cornerstone of physics,chemistry,and materials science,but limited by the cost of accurate and precise *** settings involving many simulations,machine learning can reduce these costs,often by orders of magnitude,by interpolating between reference *** requires representations that describe any molecule or material and support *** comprehensively review and discuss current representations and relations between *** selected state-of-the-art representations,we compare energy predictions for organic molecules,binary alloys,and Al–Ga–In sesquioxides in numerical experiments controlled for data distribution,regression method,and hyper-parameter optimization.

关键词： alloys corners precise

Skeletal faunas from the Qiongzhusian of southern Shaanxi: biodiversity and lithofacies-biofacies links in the Lower Cambrian carbonate settings

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Progress in Natural Science:Materials International 2004年第1期14卷 92-97页

作者： Michael StEINER 13355 berlin Ackerstrasse 71～76 Germany technische universitt berlin Sekr.ACK 14

the Xiaoyang section, located in Zhenba County of Shaanxi Province, is important both for documenting the biodiversity of the Qiongzhusian Stage (Lower Cambrian) and for analyzing lithofacies biofacies links in carbonate depositing environments on the Yangtze Platform. the skeletal fossils from the Xihaoping Member, including linguloid valves, cambroclavid and chancelloriid sclerites, genal and occipital spines of polymerid trilobites, and tubular fossils, are described here as the Eoobolus Cambroclavus fauna, which mainly occurred in peritidal environments. the fossils from the argillaceous limestones of the lower Shuijingtuo Formation, containing lingulate brachiopods, eodiscoid trilobites, bivalved arthropods, microdictyoniid sclerites and siliceous sponge spicules, are regarded as the Palaeobolus Hupeidiscus Kunmingella fauna, which presumably lived in subtidal or deeper water environments. the faunal diversity in the Xihaoping Member is lower than that in the lower Shuijingtuo Formation. the investigations of the skeletal fossil assemblages from carbonate lithofacies in southern Shaanxi will significantly contribute to a detailed documentation of the biodiversity during the Qiongzhusian interval on the Yangtze Platform and add new knowledge on the Cambrian bioradiation.

关键词： skeletal fauna Xihaoping Member Shuijingtuo Formation Lower Cambrian Shaanxi

APPROXIMAtING tHE StAtIONARY BELLMAN EQUAtION BY HIERARCHICAL tENSOR PRODUCtS

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Journal of Computational Mathematics 2024年第3期42卷 638-661页

作者： Mathias Oster Leon Sallandt Reinhold Schneider technische universität berlin Strasse des 17.Juni 13510623 BerlinGermany

We treat infinite horizon optimal control problems by solving the associated stationary Bellman equation numerically to compute the value function and an optimal feedback *** dynamical systems under consideration are spatial discretizations of non linear parabolic partial differential equations(PDE),which means that the Bellman equation suffers from the curse of *** non linearity is handled by the Policy Iteration algorithm,where the problem is reduced to a sequence of linear equations,which remain the computational bottleneck due to their high *** reformulate the linearized Bellman equations via the Koopman operator into an operator equation,that is solved using a minimal residual *** the Koopman operator we identify a preconditioner for operator equation,which deems essential in our numerical *** overcome computational infeasability we use low rank hierarchical tensor product approximation/tree-based tensor formats,in particular tensor trains(tt tensors)and multi-polynomials,together with high-dimensional quadrature,*** controlling a destabilized version of viscous Burgers and a diffusion equation with unstable reaction term numerical evidence is given.

关键词： Feedback control Dynamic programming Hamilton-Jacobi-Bellman tensor product approximation Variational Monte-Carlo