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Deep Variational Free Energy Approach to Dense Hydrogen

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Physical Review Letters 2023年第12期131卷 126501-126501页

作者： Hao Xie Zi-Hang Li Han Wang Linfeng Zhang Lei Wang Beijing National Laboratory for Condensed Matter Physics and Institute of Physics Chinese Academy of Sciences Beijing 100190 China School of Physical Sciences University of Chinese Academy of Sciences Beijing 100190 China Laboratory of Computational Physics Institute of Applied Physics and Computational Mathematics Fenghao East Road 2 Beijing 100094 China DP Technology Beijing 100080 China AI for Science Institute Beijing 100080 China Songshan Lake Materials Laboratory Dongguan Guangdong 523808 China

We developed a deep generative model-based variational free energy approach to the equations of state of dense hydrogen. We employ a normalizing flow network to model the proton Boltzmann distribution and a fermionic neural network to model the electron wave function at given proton positions. By jointly optimizing the two neural networks we reached a comparable variational free energy to the previous coupled electron-ion Monte Carlo calculation. The predicted equation of state of dense hydrogen under planetary conditions is denser than the findings of ab initio molecular dynamics calculation and empirical chemical model. Moreover, direct access to the entropy and free energy of dense hydrogen opens new opportunities in planetary modeling and high-pressure physics research.

关键词： Strongly correlated systems Warm-dense matter Machine learning Quantum Monte Carlo

Dispersive blow-up for solutions to three dimensional generalized Zakharov-Kuznetsov equations

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arXiv 2024年

作者： Ban, Yingzhe Shan, Minjie Institute of Applied Physics and Computational Mathematics Beijing100088 China College of Science Minzu University of China Beijing100081 China

We illustrate the dispersive blow up phenomena of the solutions of three dimensional generalized Zakharov-Kuznetsov equations. In particular, we construct smooth initial data such that, the associated global solutions fail to be C1 at time t in a null set containing all rational numbers, but are C1 at all times t which are generic irrational numbers. The key ingredient are to construct linear solutions which exhibit such phenomena and to prove nonlinear smoothing estimates for the full nonlinear *** Codes 35Q53, 35B44 Copyright © 2024, The Authors. All rights reserved.

关键词： Sobolev spaces

Unified Gas-Kinetic Particle Method for Frequency-dependent Radiation Transport

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arXiv 2023年

作者： Li, Weiming Liu, Chang Song, Peng Institute of Applied Physics and Computational Mathematics Beijing China HEDPS Center for Applied Physics and Technology College of Engineering Peking University Beijing China

This paper proposes a unified gas-kinetic particle (UGKP) method for the frequency-dependent photon transport process. The photon transport is a typical multiscale process governed by the nonlinear radiative transfer equations (RTE). The flow regime of photon transport varies from the ballistic regime to the diffusive regime with respect to optical depth and photon frequency. The UGKP method is an asymptotic preserving (AP) scheme and a regime adaptive scheme. The teleportation error is significantly reduced, and the computational efficiency is remarkably improved in the diffusive regime. Distinguished from the standard multigroup treatment, the proposed UGKP method solves the frequency space in a non-discretized way. Therefore the Rosseland diffusion system can be precisely preserved in the optically thick regime. Taking advantage of the local integral solution of RTE, the distribution of the emitted photon can be constructed from its macroscopic moments. The Monte Carlo particles in the UGKP method need only be tracked before their first collision events, and a re-sampling process is performed to close the photon distribution for each time step. The large computational cost of excessive scattering events can be saved, especially in the optically thick regime. The proposed UGKP method is implicit and removes the light speed constraint on the time step. The particle tracking approach combining the implicit formulation makes the proposed UGKP method an efficient solution algorithm for frequency-dependent radiative transfer problems. We demonstrate with numerical examples the capability of the proposed multi-frequency UGKP method. Copyright © 2023, The Authors. All rights reserved.

关键词： Radiative transfer

Two-plasmon-decay instability stimulated by dual laser beams in inertial confinement fusion

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Matter and Radiation at Extremes 2025年第1期10卷 48-56页

作者： C.-W.Lian Y.Ji R.Yan J.Li L.-F.Wang Y.-K.Ding J.Zheng Department of Modern Mechanics University of Science and Technology of ChinaHefeiAnhui 230026China Collaborative Innovation Center of IFSA Shanghai Jiao Tong UniversityShanghai 200240China Department of Plasma Physics and Fusion Engineering University of Science and Technology of ChinaHefei 230026China Institute of Applied Physics and Computational Mathematics Beijing 100088China

Two-plasmon-decay instability(TPD)poses a critical target preheating risk in direct-drive inertial confinement *** this paper,TPD collectively driven by dual laser beams consisting of a normal-incidence laser beam(Beam-N)and a large-angle-incidence laser beam(Beam-L)is investigated via particle-in-cell *** is found that significant TPD growth can develop in this regime at previously unexpected low laser intensities if the intensity of Beam-L exceeds the large-angle-incidence *** beams contribute to the growth of TPD in a“seed-amplification”manner in which the absolute instability driven by Beam-L provides the seeds that are convectively amplified by Beam-N,making TPD energetically important and causing significant pump depletion and hot-electron generation.

关键词： laser pump decay

An Efficient Numerical Method for High Energy Α Particle Transport Based on a Hybrid Collision Model and Machine Learning

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SSRN

SSRN 2023年

作者： Liu, Chang Du, Bao Song, Peng Institute of Applied Physics and Computational Mathematics Beijing China HEDPS Center for Applied Physics and Technology College of Engineering Peking University Beijing China

The plasma heating by the α particle transport is a main self-heating source in inertial confinement fusion (ICF) that determines the capsule implosion performance. Due to the high energy of α particle and the high temperature in the ICF capsule hot spot, significant non-equilibrium effect exists and the continuum mechanics breaks down. For the numerical simulation of implosion and charged particle transport, the Boltzmann equation needs to be solved to capture the kinetic effects. However, the 7-dimensional Boltzmann equation, the highly frequent Coulomb collision, and the multi-folded integral stopping power formulation greatly limits the computational efficiency and challenges the computational power. To overcome the high computational cost of high-frequent coulomb collisions, we propose a hybrid collision model according to which the collisions are categorized into low frequent large-angle collisions and high frequent small-angle grazing collisions. The large-angle collision process is precisely solved based on the Coulomb cross-section. For the highly frequent small-angle grazing, a statistic model is constructed with second-order accuracy in time. The hybrid collision model reduces the computational cost of scattering calculation by two magnitudes. For the multi-folded integral stopping power formulation, a neural network is used to improve computational efficiency. Based on the proposed algorithm, we develop one-dimensional to three-dimensional module code to directly solve the the α particle transport Boltzmann equation. The α transport module code is integrated into the multi-physics LARED-S program. The MC version ICF software is verified by a simulation study of the N191110 experiment. © 2023, The Authors. All rights reserved.

关键词： Monte Carlo methods

Stabilizing oxygen vacancies and promoting electrostrain in leadfree potassium niobate-based piezoelectrics over wide temperature ranges

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Journal of Advanced Ceramics 2024年第12期13卷 1965-1973页

作者： Bingcheng Luo Wei Feng Suwei Dai Hongzhou Song Yunyi Wu Jie Zhang College of Science China Agricultural UniversityBeijing 100083China State Key Laboratory of New Ceramics and Fine Processing School of Materials Science and EngineeringTsinghua UniversityBeijing 100084China School of Materials Science and Technology China University of Geosciences BeijingBeijing 100083China Institute of Applied Physics and Computational Mathematics Beijing 100094China Research Center for Comprehensive Energy Technology CTG Science and Technology Research InstituteBeijing 100038China Research Center for Metamaterials Wuzhen LaboratoryJiaxing 314500China

Piezoelectric ceramics provide high strain and large driving forces in actuators.A large electrostrain can be realized by the introduction of point defects such as vacancies,interstitial defects,and substitution *** Mn doping,a significant increase in the reversible electrostrain from 0.05%to 0.17%could be achieved in potassium niobite lead-free piezoelectric *** origins of the large electrostrain were analyzed via in situ X-ray diffraction(XRD)under an electric *** electrostrain and other typical electrical properties of the samples were measured at various temperatures,which enabled the ceramics to perform under a very wide temperature range,such as−80–130℃ for the 0.5 mol%Mn-doped sample with low dielectric loss(≤0.02).More importantly,combined with characterizations of the defect behavior by thermally stimulated depolarization current(TSDC),the failure mechanisms of electrostrain in a hightemperature environment could be revealed,which was associated with synergistic damage to the defects caused by the electric field and high *** results can provide good ideas and a basis for the design of piezoelectric materials with good electrostrain stability over a wide temperature range.

关键词： piezoelectric ceramic lead-free point defect electrostrain thermally stimulated depolarization current(TSDC)

Unified Gas-Kinetic Particle Method for Frequency-Dependent Radiation Transport

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SSRN

SSRN 2023年

We propose a unified gas-kinetic particle (UGKP) method for the frequency-dependent photon transport process. The photon transport is a typical multiscale process governed by the nonlinear radiative transfer equations (RTE). The flow regime of photon transport varies from the ballistic regime to the diffusive regime with respect to optical depth and photon frequency. The UGKP method is an asymptotic preserving (AP) scheme and a regime adaptive scheme. The teleportation error is significantly reduced, and the computational efficiency is remarkably improved in the diffusive regime. Distinguished from the standard multigroup treatment, the proposed UGKP method solves the frequency space analytically in a non-discretized way. Therefore the Rosseland diffusion system can be precisely preserved in the optically thick regime. Taking advantage of the local integral solution of RTE, the distribution of the emitted photon can be constructed from its macroscopic moments. The Monte Carlo particles in the UGKP method will only be tracked before their first collision events, and a re-sampling process is performed to close the photon distribution for each time step. The large computational cost of excessive scattering events can be saved, especially in the optically thick regime. The proposed UGKP method is implicit and removes the light speed constraint on the time step. The particle tracking approach combining the implicit formulation makes the proposed UGKP method an efficient solution algorithm for frequency-dependent radiative transfer problems. We demonstrate with numerical examples the capability of the proposed multifrequency UGKP method. © 2023, The Authors. All rights reserved.

关键词： Monte Carlo methods

Shock consolidation and the corresponding plasticity in nanopowdered Mg

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arXiv 2024年

作者： He, D.B. Wang, M.Y. Bi, W.B. Shang, M. Cai, Y. Deng, L. Zhang, X.M. Tang, J.F. Wang, L. College of Science Hunan Agricultural University Changsha410128 China Laboratoroy of Computational Physics Institute of Applied Physics and Computational Mathematics PO Box 8009 Beijing100088 China The Peac Institute of Multiscale Sciences Sichuan Chengdu610207 China

Nanopowder consolidation under high strain rate shock compression is a potential method for synthesizing and processing bulk nanomaterials. A thorough investigation of the shock deformation of powder materials is of great engineering signicance. Deformation twinning plays a vital role in accommodating plastic deformation of np-Mg which is hexagonal close packed (hcp) metals, but its mechanisms are still unsettled under high strain rate shock compression. Here we combine nonequilibrium molecular dynamics (NEMD) simulations and X-ray diffraction (XRD) simulation methods to investigate the deformation twinning and pore compaction in shock-compressed np-Mg. Significant anisotropy and strong dependence on crystallographic orientation are presented during shock-induced deformation twinning. During the shock stage, three typical types of twins were firstly induced, namely {112¯1} twin (T1), {112¯2} twin (T2) and {101¯2} twin (T3). Most of them were generated in grains with a larger angle between the impact direction and the c-axis of the lattice. With the increase of strain rate, the types and quantities of twins continued to enrich, but they did not occur when the strain rate (up ≥ 2.0 kms−1) was too high. We also discussed the deformation mechanisms of the three types of twins and found that the coupling of slip and shuffle dominated twin deformation. In addition, void filling occurred due to the interaction of twinning and other plastic deformations, leading to the densification of np-Mg. During the release stage, an interesting reverse change was observed, where the twins produced by the impact receded, and twins were produced in grains that were previously difficult to produce. Copyright © 2024, The Authors. All rights reserved.

关键词： Plastic deformation

On the global stability and large time behavior of solutions of the Boussinesq equations

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arXiv 2025年

作者： Jiang, Song Wang, Quan LCP Institute of Applied Physics and Computational Mathematics Huayuan Road 6 Beijing100088 China College of Mathematics Sichuan University Sichuan Chengdu610065 China

We study the two-dimensional viscous Boussinesq equations, which model the motion of stratified flows in a circular domain influenced by a general gravitational potential f. First, we demonstrate that the Boussinesq equations admit steady-state solutions only in the form of hydrostatic equilibria, given by (u, ρ, p) = (0, ρs, ps), where the pressure gradient satisfies ∇ps = −ρs∇f. Subsequently, we establish that any hydrostatic equilibrium satisfying the condition ∇ρs = δ(x, y)∇f is linearly unstable if δ(x, y) is positive at some point (x, y) = (x0, y0), This instability corresponds to the well-known Rayleigh-Taylor instability. Thirdly, by employing a series of regularity estimates, we reveal that although the presence of the Rayleigh-Taylor instability increases the velocity, the system ultimately converges to a state of hydrostatic equilibrium. This result is achieved by analyzing perturbations around any state of hydrostatic equilibrium, including both stable and unstable configurations. Specifically, the state of hydrostatic equilibrium can be expressed as ρ = −γf + β,where γ and β are positive constants, provided that the global perturbation satisfies additional conditions. This highlights the system’s tendency to stabilize into a hydrostatic state despite the presence of instabilities. Keywords— Boussinesq equations;global stability;large time behavior. Copyright © 2025, The Authors. All rights reserved.

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