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Coarse-grained computations of demixing in dense gas-fluidized beds

Physical Review E 2007年第5期75卷 051309-051309页

作者： Sung Joon Moon S. Sundaresan I. G. Kevrekidis []Department of Chemical Engineering & Program in Applied and Computational Mathematics Princeton University Princeton New Jersey 08544 USA

We use an “equation-free,” coarse-grained computational approach to accelerate molecular dynamics-based computations of demixing (segregation) of dissimilar particles subject to an upward gas flow (gas-fluidized beds). We explore the coarse-grained dynamics of these phenomena in gently fluidized beds of solid mixtures of different densities, typically a slow process for which reasonable continuum models are currently unavailable.

关键词： DISCRETE PARTICLE SIMULATION EQUATION-FREE MIXTURES DYNAMICS SYSTEMS POWDERS MODEL

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Inertially driven buckling and overturning of jets in a Hele-Shaw cell

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Physical Review E 2003年第5期68卷 056305-056305页

作者： Adriana I. Pesci Martin A. Porter Raymond E. Goldstein Department of Physics and Program in Applied Mathematics University of Arizona Tucson Arizona 85721 USA

We study a fluid jet descending through stratified surroundings at low Reynolds number in Hele-Shaw flow. The jet buckles and overturns inside a conduit of entrained fluid which supports smooth or unstable traveling waves. A model of the recirculating flow within the conduit shows that buckling and waves arise from Kelvin-Helmholtz instabilities and quantitatively accounts for the main experimental observations. Beyond the onset of the instability, a damped, forced Burgers’ equation obtained from corrections to Darcy’s law for small Reynolds number governs the interface dynamics and supports singularities corresponding to the observed jet overturning and unstable waves.

关键词： Jets

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Alternating direction finite element method for a class of moving boundary problems

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1st International Symposium on computational and Information Science, CIS 2004

作者： Liu, Xu-Zheng Cui, Xia Yong, Jun-Hai Sun, Jia-Guang Department of Computer Science and Technology Tsinghua University Beijing100084 China Laboratory of Computational Physics Institute of Applied Physics Computational Mathematics Beijing100088 China School of Software Tsinghua University Beijing100084 China

ISBN: (纸本)9783540241270

An alternating direction finite element scheme for a class of moving boundary problems is studied. Using coordinate transformations of the spatial variants, a new domain independent of the time is obtained and an ADFE scheme on the new domain is proposed. Then the unique solvability of the approximation scheme is proved, and optimal H1 and L2 norm space estimates and O((∆t)2) estimate for the temporal variant are obtained. © Springer-Verlag Berlin Heidelberg 2004.

关键词： Finite element method

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Ab initio multi-scale modeling of ferroelectrics: The case of PbTiO3

arXiv

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arXiv 2022年

作者： Xie, Pinchen Chen, Yixiao Weinan, E. Car, Roberto Program in Applied and Computational Mathematics Princeton University PrincetonNJ08544 United States Department of Mathematics and Program in Applied and Computational Mathematics Princeton University PrincetonNJ08544 United States Department of Chemistry Department of Physics Program in Applied and Computational Mathematics Princeton Institute for the Science and Technology of Materials Princeton University PrincetonNJ08544 United States

We report an ab initio multi-scale study of lead titanate using the Deep Potential (DP) models, a family of machine learning-based atomistic models, trained on first-principles density functional theory data, to represent potential and polarization surfaces. Our approach includes anharmonic effects beyond the limitations of reduced models and of the linear approximation for the polarization. The calculated enthalpy, spontaneous polarization, specific heat and dielectric susceptibility agree well with experiments on single crystals. In addition, we study how the free energy depends on the polarization with enhanced sampling methods, further supporting the first-order and order-disorder character of the transition. The latter is evidenced by persistence of local dipoles above the transition temperature. The simulated free energy surface as a function of the global polarization leads to a Landau-Devonshire theory of the single domain crystal. © 2022, CC BY.

关键词： Free energy

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Low Back Muscle Electrical Activity in Pregnant Women of the Second and Third Trimesters 1

Low Back Muscle Electrical Activity in Pregnant Women of the...

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1st International Conference on Computer, Science, Engineering and Technology, ICComSET 2018

作者： Purnamasari, K.D. Widyawati, M.N. Suryono, S. Postgraduate Applied Science Midwifery Program Poltekkes Kemenkes Semarang Indonesia Department of Physics Faculty of Science and Mathematics Diponegoro University Semarang Indonesia

Low back pain during pregnancy causes axial or parasagittal discomfort. These problems are experienced by more than two-thirds of pregnancies. Clinically the measurement of pain was carried out using the Visual Analogue Scale (VAS) method. Unfortunately, the method has low accuracy and is subjective. This paper proposes a method of measuring pain by using electromyography tools so that pain level measurement has a high level of accuracy and is non-invasive to patients. The study was carried out by installing electromyography electrodes on L4 and L5 muscles. The signal is recorded on a digital storage oscilloscope to find out the electrical activity. The results of the recording were evaluated for the action potential and frequency *** study was conducted on 15 respondents with lower back muscle pain in mothers monitored for 1 minute with electromyography. The monitoring results are calculated on average frequency and action potential and then presented in the form of trends. The results of the analysis of pain level measurement were compared with the results of VAS measurements. From the results of this study indicate that the trend of the action potential and signal frequency using electromyography shows different results when respondents experience the same pain scale on VAS. The value generated in the measurement using VAS is only a pain number scale that is felt by the respondent where the value is subjective. © 2019 IOP Publishing Ltd. All rights reserved.

关键词： Cathode ray oscilloscopes

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Optimizing the Vertebrate Vestibular Semicircular Canal: Could We Balance Any Better?

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Physical Review Letters 2004年第19期93卷 198106-198106页

作者： Todd M. Squires Department of Physics and Department of Applied and Computational Mathematics California Institute of Technology 114-36 Pasadena California 91125 USA

The fluid-filled semicircular canals (SCCs) of the vestibular system are used by all vertebrates to sense angular rotation. Despite masses spanning seven decades, all mammalian SCCs are nearly the same size. We propose that the SCC represents a sensory organ that evolution has “optimally designed.” Four geometric parameters characterize the SCC, and “building materials” of given physical properties are assumed. Identifying physical and physiological constraints on SCC operation, we find the most sensitive SCC has dimensions consistent with available data. Since natural selection involves optimization, this approach may find broader use in understanding biological structures.

关键词： .semicircular Building Materials SCCs

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Charge transfer and excitation processes in low energy collisions of He ions with Li atoms

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Research in Astronomy and Astrophysics 2021年第8期21卷 275-284页

作者： Xiao-Xia Wang Kun Wang Yi-Geng Peng Chun-Hua Liu Ling Liu Yong Wu Heinz-Peter Liebermann Robert J.Buenker Yi-Zhi Qu College of Material Sciences and Optoelectronic Technology University of Chinese Academy of SciencesBeijing 100049China Institute of Environmental Science Shanxi UniversityTaiyuan 030006China Department of Applied Physics Nanjing University of Science and TechnologyNanjing 210094China School of Physics Southeast UniversityNanjing 210094China Data Center for High Energy Density Physics Institute of Applied Physics and Computational MathematicsBeijing 100088China Fachbereich C-Mathematik und Naturwissenschaften Bergische Universitat WuppertalD-42097 WuppertalGermany

Electron capture between solar wind ions and neutral species has contributed to the understanding of X-ray production from solar system *** charge transfer and excitation processes in solar wind ions of He^(+)(1 s) colliding with Li(1 s^(2)2 s) atoms are studied by utilizing the full quantum-mechanical molecular-orbital close-coupling(QMOCC) method with impact energies of 0.003-2 keV *** of cross sections from single-and multi-configurational calculations for a selfconsistent field(SCF and MCSCF) process are carried *** show that the dominant reaction channels are He(1 s2 l ^(1,3) L)+Li^(+)(1 s^(2) ^(1) S).Good consistency is found among present total and state-selective charge transfer and excitation cross sections with other theoretical and experimental data in the same energy *** to the differences between coupling matrix elements in high-energy states,the charge transfer cross sections calculated from SCF and MCSCF split slightly as E> 0.4 keV *** Stueckelberg oscillations for charge transfer appear in the present *** addition,the differences of cross sections for electron excitation to Li(ls^(2)2 p) in the singlet/triplet molecular states with He+(1 s) are much smaller than those of charge transfer processes because of the similar energy gaps from Li(ls^(2)2 p) to the ground state in singlet/triplet states in the large R region.

关键词： Sun:solar wind ISM:molecules ISM:kinematics and dynamics molecular processes

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The impact of cosmic ray feedback during the epoch of reionisation

arXiv

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arXiv 2025年

作者： Farcy, Marion Rosdahl, Joakim Dubois, Yohan Blaizot, Jérémy Martin-Alvarez, Sergio Haehnelt, Martin Kimm, Taysun Teyssier, Romain Institute for Physics Laboratory for Galaxy Evolution and Spectral Modelling EPFL Observatoire de Sauverny Chemin Pegasi 51 Versoix1290 Switzerland Centre de Recherche Astrophysique de Lyon CNRS UMR 5574 Univ. Lyon Ens de Lyon 9 avenue Charles André Saint-Genis-LavalF-69230 France Institut d’Astrophysique de Paris CNRS UMR 7095 Sorbonne Université 98 bis bd Arago Paris75014 France Stanford University StanfordCA94305 United States Kavli Institute for Cosmology Institute of Astronomy Madingley Road CambridgeCB3 0HA United Kingdom Department of Astronomy Yonsei University 50 Yonsei-ro Seodaemun-gu Seoul03722 Korea Republic of Department of Astrophysical Sciences Princeton University Peyton Hall PrincetonNJ08544 United States Program in Applied and Computational Mathematics Princeton University Fine Hall Washington Road PrincetonNJ08544-1000 United States

Galaxies form and evolve via a multitude of complex physics. In this work, we investigate the role of cosmic ray (CR) feedback in galaxy evolution and reionisation, by examining its impact on the escape of ionising radiation from galaxies. For this purpose, we present two sphinx cosmological radiation-magneto-hydrodynamics simulations, allowing for the first time a study of the impact of CR feedback on thousands of resolved galaxies during the Epoch of Reionisation (EoR). The simulations differ in their feedback prescriptions: one adopts a calibrated strong supernova (SN) feedback, while the other simulation reduces the strength of SN feedback and includes CR feedback instead. We show that both comparably regulate star formation, reasonably match observations of high-redshift UV luminosity functions, and produce a similar amount of hydrogen ionising photons. In contrast to the model with strong SN feedback, the model with CRs lead to incomplete reionisation, which is in strong disagreement with observational estimates of the reionisation history. This is due to CR feedback shaping the ISM differently, filling with gas the low density cavities otherwise carved by SN explosions. As a result, this reduces the escape of ionising photons, at any halo mass, and primarily in the close vicinity of the stars. Our study indicates that CR feedback regulates galaxy growth during the EoR, but negatively affects reionisation, a tension which paves the way for further exploration and refinement of existing galaxy formation and feedback models. Such improvements are crucial in order to capture and understand the process of reionisation and the underlying evolution of galaxies through cosmic time. © 2025, CC BY.

关键词： Cosmic rays

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Continuously heterogeneous hyper-objects in cryo-EM and 3-D movies of many temporal dimensions

arXiv

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arXiv 2017年

作者： Lederman, Roy R. Singer, Amit Program in Applied and Computational Mathematics Princeton University PrincetonNJ United States Department of Mathematics Program in Applied and Computational Mathematics Princeton University PrincetonNJ United States

Single particle cryo-electron microscopy (EM) is an increasingly popular method for determining the 3-D structure of macromolecules from noisy 2-D images of single macromolecules whose orientations and positions are random and unknown. One of the great opportunities in cryo-EM is to recover the structure of macromolecules in heterogeneous samples, where multiple types or multiple conformations are mixed together. Indeed, in recent years, many tools have been introduced for the analysis of multiple discrete classes of molecules mixed together in a cryo-EM experiment. However, many interesting structures have a continuum of conformations which do not fit discrete models nicely;the analysis of such continuously heterogeneous models has remained a more elusive goal. In this manuscript we propose to represent heterogeneous molecules and similar structures as higher dimensional objects. We generalize the basic operations used in many existing reconstruction algorithms, making our approach generic in the sense that, in principle, existing algorithms can be adapted to reconstruct those higher dimensional objects. As proof of concept, we present a prototype of a new algorithm which we use to solve simulated reconstruction problems. Copyright © 2017, The Authors. All rights reserved.

关键词： Inverse problems

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End-to-end symmetry preserving inter-atomic potential energy model for finite and extended systems 18

End-to-end symmetry preserving inter-atomic potential energy...

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Proceedings of the 32nd International Conference on Neural Information Processing Systems

作者： Linfeng Zhang Jiequn Han Han Wang Wissam A. Saidi Roberto Car E. Weinan Program in Applied and Computational Mathematics Princeton University Institute of Applied Physics and Computational Mathematics China and CAEP Software Center for High Performance Numerical Simulation China Department of Mechanical Engineering and Materials Science University of Pittsburgh Program in Applied and Computational Mathematics Princeton University and Department of Chemistry and Department of Physics Princeton University and Princeton Institute for the Science and Technology of Materials Princeton University Program in Applied and Computational Mathematics Princeton University and Department of Mathematics Princeton University and Beijing Institute of Big Data Research China

Machine learning models are changing the paradigm of molecular modeling, which is a fundamental tool for material science, chemistry, and computational biology. Of particular interest is the inter-atomic potential energy surface (PES). Here we develop Deep Potential - Smooth Edition (DeepPot-SE), an end-to-end machine learning-based PES model, which is able to efficiently represent the PES of a wide variety of systems with the accuracy of ab initio quantum mechanics models. By construction, DeepPot-SE is extensive and continuously differentiable, scales linearly with system size, and preserves all the natural symmetries of the system. Further, we show that DeepPot-SE describes finite and extended systems including organic molecules, metals, semiconductors, and insulators with high fidelity.

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