检索结果-内蒙古大学图书馆

Investigation of Langdon effect on the nonlinear evolution of SRS from the early-stage inflation to the late-stage development of secondary instabilities

学校读者我要写书评

暂无评论

arXiv 2022年

作者： Qiu, Jie Hao, Liang Cao, Lihua Zou, Shiyang Institute of Applied Physics and Computational Mathematics Beijing100094 China

In a laser-irradiated plasma, the Langdon effect can result in a super-Gaussian electron energy distribution function (EEDF), imposing significant influences on the stimulated backward Raman scattering (SRS). In this work, the influence of a super-Gaussian EEDF on the nonlinear evolution of SRS is investigated by three wave model simulation and Vlasov-Maxwell simulation for plasma parameters covering a wide range of kλDe from 0.19 to 0.48 at both high and low intensity laser drives. In the early-stage of SRS evolution, it is found that besides the kinetic effects due to electron trapping [Phys. Plasmas 25, 100702 (2018)], the Langdon effect can also significantly widen the parameter range for the absolute growth of SRS, and the time for the absolute SRS to reach saturation is greatly shorten by Langdon effect within certain parameter region. In the late-stage of SRS, when secondary instabilities such as decay of the electron plasma wave to beam acoustic modes, rescattering, and Langmuir decay instability become important, the Langdon effect can influence the reflectivity of SRS by affecting the secondary processes. The comprehension of Langdon effect on nonlinear evolution and saturation of SRS would contribute to a better understanding and prediction of SRS in inertial confinement fusion. © 2022, CC BY-NC-SA.

关键词： Distribution functions

Discontinuity Computing Using physics-Informed Neural Network

学校读者我要写书评

暂无评论

arXiv 2022年

作者： Liu, Li Liu, Shengping Xie, Hui Xiong, Fansheng Yu, Tengchao Xiao, Mengjuan Liu, Lufeng Yong, Heng Institute of Applied Physics and Computational Mathematics Beijing100094 China

Simulating discontinuities is a long standing problem especially for shock waves with strong nonlinear feather. Despite being a promising method, the recently developed physics-informed neural network (PINN) is still weak for calculating discontinuities compared with traditional shock-capturing methods. In this paper, we intend to improve the shock-capturing ability of the PINN. The primary strategy of this work is to weaken the expression of the network near discontinuities by adding a gradient-weight into the governing equations locally at each residual point. This strategy allows the network to focus on training smooth parts of the solutions. Then, automatically affected by the compressible property near shock waves, a sharp discontinuity appears with wrong inside shock transition-points compressed into well-trained smooth regions as passive particles. We study the solutions of one-dimensional Burgers equation and one- and two-dimensional Euler equations. Compared with the traditional high-order WENO-Z method in numerical examples, the proposed method can substantially improve discontinuity computing. Copyright © 2022, The Authors. All rights reserved.

关键词： Euler equations

Discontinuity Computing Using physics-Informed Neural Networks

学校读者我要写书评

暂无评论

SSRN

SSRN 2022年

作者： Liu, Li Liu, Shengping Xie, Hui Xiong, Fansheng Yu, Tengchao Xiao, Mengjuan Liu, Lufeng Yong, Heng Institute of Applied Physics and Computational Mathematics Beijing100094 China

Simulating discontinuities is a long standing problem particularly for shock waves with strong nonlinear features. Despite being a promising method, the recently developed physics-informed neural networks (PINNs) are still not fully effective for calculating discontinuities compared with those of traditional shock-capturing methods. In this study, we first reveal that the training of PINNs may fall into paradoxical phenomenon when simulating problems with strong discontinuities. Intend to break the paradox and improve the shock-capturing ability of the PINNs, we propose a strategy to weaken the expression of the neural network (NN) near discontinuities by adding a physics-dependent weight into the governing equations locally at each residual point. Correspondingly, the NN will focus on training the smooth parts of the solutions. Then, automatically affected by the compressible property, a sharp discontinuity appears with transition points inside the shock waves compressed into well-trained smooth regions as passive particles. To demonstrate the effect of the new method, we study one-dimensional Burgers equation and one- and two-dimensional Euler equations. Compared with a traditional high-order weighted essential non-oscillatory (WENO) method in the numerical examples, the proposed weighted-equations PINNs (PINNs-WE) method can substantially improve discontinuity computing. © 2022, The Authors. All rights reserved.

关键词： Euler equations

Prediction of a kagome topological superconducting family: XB3 (X=Ni, Pd)

学校读者我要写书评

暂无评论

Physical Review B 2024年第5期109卷 054506-054506页

作者： Peng-Cheng Xiao Liu Yang Hong-Yan Lu Ning Hao Ping Zhang School of Physics and Physical Engineering Qufu Normal University Qufu 273165 China Anhui Province Key Laboratory of Low-Energy Quantum Materials and Devices High Magnetic Field Laboratory HFIPS Chinese Academy of Sciences Hefei Anhui 230031 China Institute of Applied Physics and Computational Mathematics Beijing 100088 China

Materials featuring the kagome configuration hold significant research potential following their discovery. Drawing inspiration from MgB2, we introduce a kagome topological superconducting family: XB3 (X=Ni, Pd). This prediction is based on first-principles calculations and an analysis of bulk-edge correspondence. In this family, the boron atoms transition from their original honeycomb arrangement to form a stable kagome lattice, as confirmed by the phonon spectrum analysis. Through the calculations of the topological invariant and surface states, we establish that these materials belong to the Z2 Dirac metal category with nodal surface characteristics. Employing the Allen-Dynes modified McMillan formula, we anticipate superconducting critical temperatures, denoted as Tc, of 14.5 K for NiB3 and 19.1 K for PdB3. These values surpass most of both conventional topological superconductors' candidates and kagome superconductors due to the relatively robust electron-phonon coupling. Moreover, the spin texture analysis of the Dirac cone at the high symmetry point K lends further support to their status as topological superconductors. Consequently, the XB3 family presents an exciting platform for experimental investigations into topological superconductors and their potential applications in fault-tolerant quantum computation.

关键词： First-principles calculations Superconductivity Topological materials Topological superconductors Kagome lattice BCS theory

Preface Special Issues in Honor of Professor Zhong-Ci Shi(Part Ⅰ)

学校读者我要写书评

暂无评论

Annals of applied mathematics 2023年第3期39卷 I0001-I0002页

作者： Weinan E Song Jiang Tao Tang Pingwen Zhang Peking University Institute of Applied Physics and Computational Mathematics BNU-HKBU United International College Wuhan University&Peking University

Professor Zhong-Ci Shi, a professor of Chinese Academy of Sciences(CAS) and world-renowned computational mathematician, passed away on 13 February, 2023. Annals of applied mathematics will devote a few special issues ... 详细信息

关键词： devote passed outstanding

Equations Describing the Direct Relation between Laser Phase and Stokes Light for Sbs Pumped by Phase-Modulated Laser in Optical Fibers

学校读者我要写书评

暂无评论

SSRN

SSRN 2022年

作者： Ke, Wei-Wei Institute of Applied Physics and Computational Mathematics Beijing100088 China

Undepleted pump approximation is applied to the transient three-wave coupling model of SBS in optical fibers with phase-modulated laser injection. Equations describing the evolution of the Stokes light in both time domain and frequency domain are derived. They establish a direct relation between the laser phase and Stokes light. The equations are validated numerically by comparing with the original coupling model as well. © 2022, The Authors. All rights reserved.

关键词： Stimulated Brillouin scattering

Comparison of numerical treatments for the pseudo-differential term in the Wigner equation

学校读者我要写书评

暂无评论

arXiv 2022年

作者： Chen, Zhenzhu Institute of Applied Physics and Computational Mathematics Beijing100094 China

Effectively handling the nonlocal pseudo-differential term plays an important role in solving the Wigner equation with high accuracy. This paper systematically analyzes and compares numerical treatments of the pseudo-differential term under different types of potentials. Copyright © 2022, The Authors. All rights reserved.

关键词：

Topology Modification Based Rezoning Strategies for Ale Method on Unstructured Hexahedral Meshes

学校读者我要写书评

暂无评论

SSRN

SSRN 2022年

作者： Liu, Lufeng Zhou, Xuan Guo, Shaodong Chen, Yibing Zhou, Haibing Institute of Applied Physics and Computational Mathematics Beijing100094 China

The Arbitrary Lagrangian-Eulerian (ALE) simulation of multi-material flows with large deformation often suffers from the tangled mesh which are difficult to rezone. This work presents a novel hexahedral mesh rezoning method with topology modification for computational meshes with complex boundaries. In order to adapt the computational mesh to the deformed or moved boundaries, the element connectivity is changed by the coarsening, refinement and reconnection methods, which are designed based on the basic sheet operations. Meanwhile, the geometric features of complex boundaries are preserved via refining the boundary nodes and generating the boundary layered meshes. We incorporate the proposed rezoning method into the Arbitrary Lagrangian Eulerian method to improve the simulation ability. To our knowledge, this is the first time the hexahedral topology-modification method has been used as a rezoning method in ALE simulations. Examples show that the topology-modification mesh rezoning method can simultaneously improve the element quality and size distribution for the deformed meshes with preserving the geometric features of boundaries. The accuracy and efficiency of the ALE simulation with large deformation are improved by using the topology-modification rezoning method. © 2022, The Authors. All rights reserved.

关键词： Coarsening

Electron Beam Weibel Instability in the Collisionless Shock with Low Mach Number

学校读者我要写书评

暂无评论

arXiv 2022年

作者： Yao, Jiansheng Zhao, Yingkui Ouyang, Biyao Ye, Difa Institute of Applied Physics and Computational Mathematics Beijing100088 China

The electron beam Weibel instability in the electrostatic collisionless shock is studied via particle in cell simulation. When the non-relativistic incoming plasmas collide with cold dilute plasmas, an electrostatic shock forms near the interface. Following that, a filamentary out-of-plane magnetic field is formed as a result of the Weibel instability. It is demonstrated that the anisotropy of incoming hot electrons is insufficient to trigger the Weibel instability. And the Weibel instability is excited by cold electrons in dilute plasmas. After being accelerated to relativistic velocities by the shock electric field into the dense plasmas, electrons in the dilute plasma have considerable anisotropy and can trigger the Weibel instability © 2022, CC BY.

关键词： Electron beams