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IEEE International Conference on Plasma Science (ICOPS)

作者： L. Huang D. Xiao Graduate School of China Academy of Engineering Physics Beijing China Institute of Applied Physics and Computational Mathematics Beijing China

ISBN: (数字)9798350360912

ISBN: (纸本)9798350360929

Magneto-Rayleigh-Taylor (MRT) instability is one of the most important questions that affect the quality of Z-pinch implosions. In this paper, the effect of finite resistivity on the MRT instability in the linear development stage is theoretically investigated. A three-region slab model based on resistive MHD equations under the incompressible approximation, is used to obtain the dispersion relation of the MRT instability in two cases, where the skin depth is smaller and is comparable to the characteristic wavelength. The resistivity in the full range from zero to infinity is covered and its role on the MRT instability can be numerically examined by these two models. It is shown that the axial magnetic field will be diffused from the perturbed plasma due to the resistivity, and its role on stabilizing the MRT instability especially for short wavelength perturbations will then be weakened, i.e., the resistivity has a destabilizing effect on the MRT instability in the linear stage. The larger the resistivity is, the stronger the magnetic diffusion becomes, and the greater the destabilizing effect is. For the actual resistivity in Z-pinches, an axial magnetic field of tens of Tesla has no remarkable stabilizing effect on the MRT instability in the linear stage in magnetized liner inertial fusion, and it still has certain stabilizing effect on the linear MRT instability for wire-array Z-pinch implosions. In addition, it is impossible to completely stabilize MRT perturbations for any wavelengths with tens of Telsa magnetic field due to magnetic diffusion.

关键词： Magnetohydrodynamics Perturbation methods Conductivity Mathematical models Skin Plasmas Numerical models

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ANALYSIS ON A NUMERICAL SCHEME WITH SECOND-ORDER TIME ACCURACY FOR NONLINEAR DIFFUSION EQUATIONS

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Journal of computational mathematics 2021年第5期39卷 777-800页

作者： Xia Cui Guangwei Yuan Fei Zhao Laboratory of Computational Physics Institute of Applied Physics and Computational MathematicsP.O.Box 8009-26Beijing 100088China College of Science North China University of TechnologyBeijing 1OO144China Graduate School of China Academy of Engineering Physics Beijing 100088China

A nonlinear fully implicit finite difference scheme with second-order time evolution for nonlinear diffusion problem is *** scheme is constructed with two-layer coupled discretization(TLCD)at each time *** does not stir numerical oscillation,while permits large time step length,and produces more accurate numerical solutions than the other two well-known second-order time evolution nonlinear schemes,the Crank-Nicolson(CN)scheme and the backward difference formula second-order(BDF2)*** developing a new reasoning technique,we overcome the difficulties caused by the coupled nonlinear discrete diffusion operators at different time layers,and prove rigorously the TLCD scheme is uniquely solvable,unconditionally stable,and has second-order convergence in both s-pace and *** tests verify the theoretical results,and illustrate its superiority over the CN and BDF2 schemes.

关键词： Nonlinear diffusion problem Nonlinear two-layer coupled discrete scheme Second-order time accuracy Property analysis Unique existence Convergence

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Phonon vibrational and transport properties of SnSe/SnS superlattice at finite temperatures

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Physical Review B 2025年第14期111卷 144314-144314页

作者： Feng-ning Xue Wei Li Zi Li Yong Lu College of Mathematics and Physics Beijing University of Chemical Technology Beijing 100029 People's Republic of China State Key Laboratory of Explosion Science and Technology Beijing Institute of Technology Beijing 100081 People's Republic of China School of Electronic Information Engineering Lanzhou Institute of Technology Lanzhou 730050 People's Republic of China Institute of Applied Physics and Computational Mathematics and National Key Laboratory of Computational Physics Beijing 100088 People's Republic of China

The structural stability and phonon properties of SnSe/SnS superlattices at finite temperatures have been studied using machine learning force field molecular dynamics and the anharmonic phonon approach. The vertical SnSe/SnS superlattice undergoes a phase transition from the Pnma phase to a P4/nmm phase at finite temperatures, which is different from the high-temperature Cmcm phase of the SnSe and SnS systems. The stability of P4/nmm phase is determined by molecular dynamics trajectories and anharmonic phonon dispersion relations. The TO modes at the q=Γ(0,0,0) and q=M(1/2,1/2,0) points in the P4/nmm phase exhibit imaginary frequencies in the harmonic approximation but stabilize at elevated temperatures. An analysis of phonon power spectra upon temperature also confirms the dynamic stabilization. The P4/nmm phase has higher symmetry than the Pnma phase, and the phase transition between them is accompanied by competition between the Jahn-Teller effect and phonon anharmonicity. Unlike the anisotropic distribution of Sn-Se/S bonds in the Pnma phase, the P4/nmm phase forms chemical bonds with similar bond lengths both in plane and interlayer, and their resonance effect can significantly enhance phonon scattering. The calculated phonon density of states and lifetime are strongly temperature dependent, demonstrating the heavy anharmonicity in the SnSe/SnS system. The P4/nmm phase has an extremely low lattice thermal conductivity, close to the experimental values of SnSe and SnS. Moreover, with the reduction of band gap and the enhancement of band degeneracy near the Fermi level, the P4/nmm phase exhibits superior electronic transport properties and significantly enhanced response to infrared and visible light. This makes it show great potential in thermoelectric and photovoltaic applications.

关键词： Bond length

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Photoionization process of the hydrogenlike carbon ion embedded in warm and hot dense plasmas

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Physical Review E 2024年第5期109卷 055205-055205页

作者： S. M. Lu F. Y. Zhou L. Y. Xie Y. L. Ma G. P. Zhao X. Gao Y. Wu J. G. Wang Institute of Modern Physics National Key Laboratory of Computational Physics Key Laboratory of Atomic and Molecular Physics and Functional Materials of Gansu Province and College of Physics and Electronic Engineering College of Data Science School of Physics and Information Technology Center for Applied Physics and Technology College of Engineering

Complicated many-body interactions between ions and surrounding particles exist in warm and hot dense plasmas. It will significantly alter the atomic structures and dynamic properties of the embedded ions. Recently, the atomic-state-dependent (ASD) screening model has been proposed and shown to be valid for investigating the screening effect in warm and hot dense plasmas over a wide range of electron densities and temperatures. By employing the ASD model, we investigate the photoionization process for the hydrogenlike carbon ion embedded in warm and hot dense plasmas with corresponding Coulomb coupling parameter ranges of 0.05 ≤ Γ ≤ 1.16, where Γ characterizes the ratio of the average potential to thermal energy. It is found that there are stronger plasma screening effects on the ionization energy and photoionization cross section due to the negative-energy electron distributions considered in the ASD model compared to those considering only free electrons. The present results from the ASD model show reasonable agreement with the classical Debye-Hückel (DH) model in weakly coupled plasmas. However, significant deviations of the ionization energy and cross section between these two models are observed in moderately and strongly coupled plasmas, due to the approximate treatment of the plasma-electron density distribution of the DH model. In the region of low photoelectron energies, the positions of the shape resonance peaks of the cross sections obtained from the ASD model differ significantly from those of the DH model due to the different screening effects.

关键词： Atomic & molecular collisions Single- and few-photon ionization & excitation Hot dense plasma Ions

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An Extendable Cloud-Native Alloy Property Explorer

arXiv

引用

arXiv 2024年

作者： Li, Zhuoyuan Wen, Tongqi Zhang, Yuzhi Liu, Xinzijian Zhang, Chengqian Pattamatta, A.S.L. Subrahmanyam Gong, Xiaoguo Ye, Beilin Wang, Han Zhang, Linfeng Srolovitz, David J. Department of Mechanical Engineering The University of Hong Kong Hong Kong AI for Science Institute Beijing China DP Technology Beijing China Laboratory of Computational Physics Institute of Applied Physics and Computational Mathematics Beijing China

The ability to rapidly evaluate materials properties through atomistic simulation approaches is the foundation of many new artificial intelligence-based approaches to materials identification and design. This depends on the availability of accurate descriptions of atomic bonding through various forms of interatomic potentials. We present an efficient, robust platform for calculating materials properties, i.e., APEX, the Alloy Property Explorer. APEX enables the rapid evolution of interatomic potential development and optimization, which is of particular importance in fine-tuning new classes of general AI-based foundation models to forms that are readily applicable to impacting materials development. APEX is an open-source, extendable, and cloud-native platform for material property calculations using a range of atomistic simulation methodologies that effectively manages diverse computational resources and is built upon user-friendly features including automatic results visualization, web-based platforms and NoSQL database client. It is designed for expert and non-specialist users, lowers the barrier to entry for interdisciplinary research within the "AI for Materials" framework. We describe the foundation and use of APEX, as well as provide an example of its application to properties of titanium for a wide-range of bonding descriptions. Copyright © 2024, The Authors. All rights reserved.

关键词： Materials properties

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Phase evolution of Ce-based heavy-fermion superconductors under compression: a combined first-principle and effective-model study

arXiv

引用

arXiv 2023年

作者： Ma, Hao-Tian Tian, Peng-Fei Guo, Da-Liang Ming, Xing Zheng, Xiao-Jun Liu, Yu Li, Huan College of Physics and Electronic Information Engineering Guilin University of Technology Guilin541004 China Laboratory of Computational Physics Institute of Applied Physics and Computational Mathematics Beijing100088 China

In many Ce-based superconductors, superconducting (SC) phases emerge or can be tuned in proximity to the antiferromagnetic (AF) quantum critical point (QCP), but so far the explicit phase evolution near the QCP lack theoretical understanding. Here, by combing the density functional theory plus dynamical mean-field theory (DFT+DMFT) with effective-model calculations, we provide a theoretical description for Ce-based superconductors under compression. DFT+DMFT calculations for the normal states reveal that the Kondo hybridizations are significantly enhanced under compression, while the initially localized f electrons become fully itinerant via localized-itinerant crossover. We then construct an effective model and show that with the extracted Kondo coupling and RKKY exchange strengths from first-principle calculations, the ground-state phases of these materials can be properly predicted. We also show that the coexistence of magnetic correlation and Kondo hybridization can drive AF+SC coexisting state in narrow compression region. Under compression, competition between Kondo and RKKY interactions can drive successive transitions, from AF phase to AF+SC coexisting phase, then to paramagnetic SC phase via an AF transition which generates the QCP, and finally to normal Kondo paramagnetic (KP) phase through an SC-KP transition induced by the localized-itinerant crossover. Our study gives proper explanation to the pressure-induced QCP and SC-KP transition, and to the phase evolution in pressured Ce-based superconductors, and can help to understand the SC states around the ferromagnetic quantum transition points in uranium-based superconductors. © 2023, CC BY.

关键词： Density functional theory

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Ultrastrong Coupling between Polar Distortion and Optical Properties in Ferroelectric MoBr2O2 (vol 146, pg 15411, 2024)

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JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 2024年第32期146卷 22860-22860页

作者： Li, Zhaojun Varrassi, Lorenzo Yang, Yali Franchini, Cesare Bellaiche, Laurent He, Jiangang School of Mathematics and Physics University of Science and Technology Beijing Beijing 100083 China Department of Physics and Astronomy “Augusto Righi” Alma Mater Studiorum Università di Bologna Bologna 40127 Italy Faculty of Physics and Center for Computational Materials Science University of Vienna Kolingasse 14-16 Vienna 1090 Austria Smart Ferroic Materials Center Physics Department and Institute for Nanoscience and Engineering University of Arkansas Fayetteville Arkansas 72701 United States Key Laboratory of Advanced Materials and Devices for Post-Moore Chips Ministry of Education University of Science and Technology Beijing Beijing 100083 China

Tuning the properties of materials by using external stimuli is crucial for developing versatile smart materials. Strong coupling among the order parameters within a single-phase material constitutes a potent foundation for achieving precise property control. However, cross-coupling is fairly weak in most single materials. Leveraging first-principles calculations, we demonstrate a layered mixed anion compound MoBr2O2 that exhibits electric-field switchable spontaneous polarization and ultrastrong coupling between polar distortion and electronic structures as well as optical properties. It offers feasible avenues of achieving tunable Rashba spin-splitting, electrochromism, thermochromism, photochromism, and nonlinear optics by applying an external electric field to a single domain sample and heating, as well as intense light illumination. Additionally, it exhibits an exceptionally large photostrictive effect. These findings not only showcase the feasibility of achieving multiple order parameter coupling within a single material but also pave the way for comprehensive applications based on property control, such as energy harvesting, information processing, and ultrafast control.

关键词： Chemical structure Light Materials Phase transitions Polarization

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A Fast and Robust MUSIC Algorithm for Estimating Multiple Coherent Signals

A Fast and Robust MUSIC Algorithm for Estimating Multiple Co...

引用

Communication, Image and Signal Processing (CCISP), International Conference on

作者： Mingyang Zhang Lihai Ji Pengyan Jia Shanghai Zhangjiang Institute of Mathematics Shanghai China Institute of Applied Physics and Computational Mathematics and Shanghai Zhangjiang Institute of Mathematics Beijing China

ISBN: (数字)9798350356656

ISBN: (纸本)9798350356663

The conventional MUSIC algorithm demonstrates subpar performance in estimating coherent signals from multiple targets and yields unreliable results. Moreover, it suffers from high computational complexity and sluggish processing speed when applied to extensive datasets involving multiple sensors. In order to tackle these challenges, this paper presents an enhanced and expedient version of the MUSIC algorithm for estimating multiple coherent signals. Drawing upon the ROOT-MUSIC algorithm, which is based on the propagation operator, this algorithm introduces a spatial smoothing technique by substituting the original covariance matrix with the average of subarray covariance matrices. Simulation results demonstrate that the proposed algorithm not only resolves the issue of estimating multiple coherent signals but also achieves exceptional performance in terms of robustness and computational speed, even under low signal-to-noise ratio conditions.

关键词： Smoothing methods Simulation Signal processing algorithms Robustness Multiple signal classification Sensors Covariance matrices Spatial resolution Signal resolution Signal to noise ratio

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Effects of thermophoresis on Brownian coagulation of spherical particles over the entire particle size regime

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Particuology 2022年第8期20卷 8-17页

作者： Kaiyuan Wang Pei Wang Suyuan Yu Institute of Applied Physics and Computational Mathematics Bejing 100094.China Center forCombustionEergy.Key Laboratory for Thermal Science and Power Engineering of Ministry of Education Department of Energyand PowerEngineeringTsinghua UniversityBejing 100084.China Smoore International Holdings Ltd.Shenzhen 518102 China

In many energy and combustion *** experience large temperature gradients,which can affect the coagulation process due to *** study presents a rigorous theory of thermophoretically modified Brownian coagulation in the entire particle size *** theoretical derivations are based on the kinetictheory forthe free-molecular regime and the harmonic mean method for the transition *** coagulation kernels in different size regimes can be expressed as the basic Brownian coagulation kernel times an enhancement factor,The enhancement factor represents the coagulationrate enhancement induced by thermophoresis and is a function of specific dimensionless *** on the enhancement factor,the thermophoretic enhancement effects on particle coagulation are further analyzed under a wide range of gas and particle *** results show that thermophoretic enhancement effects are ignorable in the free-molecular regime,but need to be considered in the continuum regime and the transition *** addition,the enhancement effects increase significantly with increase of gas temperature and temperature gradient while decrease with increase of gas *** present study can improve understanding ofthermophoretic effects on Brownian coagulation in the entire size regime and provide a useful tool to calculate the coagulation rates in presence of thermophoresis.

关键词： Thermophoresis Brownian coagulation Enhancement factor Knudsen number

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Subspace method based on neural networks for solving the partial differential equation in weak form

arXiv

引用

arXiv 2024年

作者： Liu, Pengyuan Xu, Zhaodong Sheng, Zhiqiang National Key Laboratory of Computational Physics Institute of Applied Physics and Computational Mathematics Beijing100088 China HEDPS Center for Applied Physics and Technology College of Engineering Peking University Beijing100871 China Graduate School China Academy of Engineering Physics Beijing100088 China

We present a subspace method based on neural networks for solving the partial differential equation in weak form with high accuracy. The basic idea of our method is to use some functions based on neural networks as base functions to span a subspace, then find an approximate solution in this subspace. Training base functions and finding an approximate solution can be separated, that is different methods can be used to train these base functions, and different methods can also be used to find an approximate solution. In this paper, we find an approximate solution of the partial differential equation in the weak form. Our method can achieve high accuracy with low cost of training. Numerical examples show that the cost of training these base functions is low, and only one hundred to two thousand epochs are needed for most tests. The error of our method can fall below the level of 10−7 for some tests. The proposed method has the better performance in terms of the accuracy and computational cost. Copyright © 2024, The Authors. All rights reserved.

关键词： Partial differential equations

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