检索结果-内蒙古大学图书馆

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

学校读者我要写书评

暂无评论

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

Atomic determination of the nuclear quadrupole moment Q(209Bi) using the multi-configuration Dirac-Hartree-Fock method

学校读者我要写书评

暂无评论

arXiv 2025年

作者： Li, Jiguang Bieron, Jacek Godefroid, Michel Jönsson, Per Institute of Applied Physics and Computational Mathematics Beijing100088 China Instytut Fizyki Teoretycznej Uniwersytet Jagielloński Kraków Poland Université Libre de Bruxelles Brussels1050 Belgium Department of Materials Science and Applied Mathematics Malmö University MalmöS-20506 Sweden

The multiconfiguration Dirac-Hartree-Fock method implemented in the Grasp2018 package was employed to calculate the magnetic dipole hyperfine interaction constants and electric field gradients of levels in the ground configuration of the neutral bismuth atom. Combining the calculated electric field gradient of the ground state with the measured electric quadrupole hyperfine interaction constant, we extracted the nuclear quadrupole moment for the 209Bi isotope, Q(209Bi) = −422(22) mb. This value, together with other results obtained from atomic- and molecular-structure calculations, created the "world average" nuclear quadrupole moment of this isotope, Q(209Bi) = −420(17) mb. © 2025, CC BY.

关键词： Atoms

SWARMESH: Swarm-driven adaptive mesh for singular perturbation problems

学校读者我要写书评

暂无评论

Swarm and Evolutionary Computation 2025年 96卷

作者： Panchal, Aneesh Singh, Abhishek Kumar Kumar, Vivek Mehra, Mani Department of Computational and Data Sciences Indian Institute of Science BangaloreKarnataka-560012 India Institute of Mathematics and Computer Science Universität Greifswald Walther-Rathenau-Straße 47 Greifswald17489 Germany Department of Mathematics Indian Institute of Technology Delhi-110016 India Department of Applied Mathematics Delhi Technological University Delhi-110042 India

Convection-dominated singularly perturbed problems are a special type of differential equations that arise in various natural phenomena such as fluid dynamics. Hence, these problems need special consideration in the literature due to their singular characteristics. Solving these problems involves various challenges, including layer resolution and non-linear mesh formation. However, this paper introduces a novel algorithm for generating optimal adaptive meshes using a modified particle swarm optimization technique to solve convection-dominated singularly perturbed problems. Our proposed algorithm uses an entropy-like adaptation parameter to locate the layer positions (singular regions). Unlike the other meshes (gradient-based), the proposed algorithm requires no priori knowledge of the number of mesh points required. Hence, it works as an arbitrary method to solve the problem. Once the layer positions are known, the particle swarm optimization algorithm is implemented to find out the required adaptive mesh using parameters (N,θ). Various test problems (linear and non-linear) have been solved numerically, and the results have been discussed and compared with the previously existing algorithm. The results turn out to be better than the existing algorithm as the proposed algorithm results are more accurate, along with a lesser number of required points. This paper brings a novel and robust method to find a non-linear adaptive mesh for convection-dominated singularly perturbed problems. Also, this research bridges the literature gap by merging the capabilities of metaheuristic algorithms with the challenges of singularly perturbed problems, opening up avenues for further exploration and application in similar domains. © 2025 Elsevier B.V.

关键词： Particle swarm optimization (PSO)

Inferring System and Optimal Control Parameters of Closed-Loop Systems from Partial Observations

学校读者我要写书评

暂无评论

arXiv 2025年

作者： Geadah, Victor Arbelaiz, Juncal Ritz, Harrison Daw, Nathaniel D. Cohen, Jonathan D. Pillow, Jonathan W. Program in Applied and Computational Mathematics Princeton University PrincetonNJ United States Department of Mechanical and Aerospace Engineering Princeton University PrincetonNJ United States Princeton Neuroscience Institute Princeton University PrincetonNJ United States

We consider the joint problem of system identification and inverse optimal control for discrete-time stochastic Linear Quadratic Regulators. We analyze finite and infinite time horizons in a partially observed setting, where the state is observed noisily. To recover closed-loop system parameters, we develop inference methods based on probabilistic state-space model (SSM) techniques. First, we show that the system parameters exhibit non-identifiability in the infinite-horizon from closed-loop measurements, and we provide exact and numerical methods to disentangle the parameters. Second, to improve parameter identifiability, we show that we can further enhance recovery by either (1) incorporating additional partial measurements of the control signals or (2) moving to the finite-horizon setting. We further illustrate the performance of our methodology through numerical examples. © 2025, CC BY.

关键词： Stochastic systems

THE MANY-BODY GROUND STATE MANIFOLD OF FLAT BAND INTERACTING HAMILTONIAN FOR MAGIC ANGLE TWISTED BILAYER GRAPHENE

学校读者我要写书评

暂无评论

arXiv 2025年

作者： Stubbs, Kevin D. Ragone, Michael Macdonald, Allan H. Lin, Lin Department of Mathematics University of California BerkeleyCA94720 United States Department of Physics University of Texas at Austin AustinTX78712 United States Applied Mathematics and Computational Research Division Lawrence Berkeley National Laboratory BerkeleyCA94720 United States

At a magic relative twist angle, magic angle twisted bilayer graphene (MATBG) has an octet of flat bands that can host strong correlation physics when partially filled. A key theoretical discovery in MATBG is the existence of ferromagnetic Slater determinants as exact ground states of the corresponding flat band interacting (FBI) Hamiltonian. The FBI Hamiltonian describes the behavior of electrons that interact with each other in a high-dimensional space, and is constructed from the band structure of the non-interacting Bistritzer–MacDonald model at the chiral limit. A key property of the FBI Hamiltonian for MATBG is that it is frustration free and can be written as a sum of non-commuting terms. In this work, we provide a complete characterization of the ground state manifold of the FBI Hamiltonian, proving that it is precisely the linear span of such ferromagnetic Slater determinants. © 2025, CC BY.

关键词： Ferromagnetism

Unbiased Parameter Estimation for Bayesian Inverse Problems

学校读者我要写书评

暂无评论

arXiv 2025年

作者： Chada, Neil K. Jasra, Ajay Maama, Mohamed Tempone, Raul Department of Mathematics City University of Hong Kong China School of Data Science The Chinese University of Hong Kong Shenzhen CN Shenzhen China Applied Mathematics and Computational Science Program Computer Electrical and Mathematical Sciences and Engineering Division King Abdullah University of Science and Technology Thuwal23955-6900 Saudi Arabia

In this paper we consider the estimation of unknown parameters in Bayesian inverse problems. In most cases of practical interest, there are several barriers to performing such estimation, This includes a numerical approximation of a solution of a differential equation and, even if exact solutions are available, an analytical intractability of the marginal likelihood and its associated gradient, which is used for parameter estimation. The focus of this article is to deliver unbiased estimates of the unknown parameters, that is, stochastic estimators that, in expectation, are equal to the maximizer of the marginal likelihood, and possess no numerical approximation error. Based upon the ideas of [4] we develop a new approach for unbiased parameter estimation for Bayesian inverse problems. We prove unbiasedness and establish numerically that the associated estimation procedure is faster than the current state-of-the-art methodology for this problem. We demonstrate the performance of our methodology on a range of problems which include a PDE and ODE. Copyright © 2025, The Authors. All rights reserved.

关键词： Markov processes

Periodic propagation of singularities for heat equations with time delay

学校读者我要写书评

暂无评论

arXiv 2025年

作者： Wang, Gengsheng Yu, Huaiqiang Zhang, Yubiao Center for Applied Mathematics KL-AAGDM Tianjin University Tianjin300072 China School of Mathematics KL-AAGDM Tianjin University Tianjin300350 China Radon Institute for Computational and Applied Mathematics Austrian Academy of Sciences Altenbergerstraße 69 Upper Austria Linz4040 Austria Chair for Dynamics Control Machine Learning and Numerics Department of Mathematics Friedrich-Alexander-Universität Erlangen-Nürnberg Erlangen91058 Germany

This paper presents two remarkable phenomena associated with the heat equation with a time delay: namely, the propagation of singularities and periodicity. These are manifested through a distinctive mode of propagation of singularities in the solutions. Precisely, the singularities of the solutions propagate periodically in a bidirectional fashion along the time axis. Furthermore, this propagation occurs in a stepwise manner. More specifically, when propagating in the positive time direction, the order of the joint derivatives of the solution increases by 2 for each period;conversely, when propagating in the reverse time direction, the order of the joint derivatives decreases by 2 per period. Additionally, we elucidate the way in which the initial data and historical values impact such a propagation of singularities. The phenomena we have discerned not only corroborate the pronounced differences between heat equations with and without time delay but also vividly illustrate the substantial divergence between the heat equation with a time delay and the wave equation, especially when viewed from the point of view of singularity *** Codes 35K05 45K05 58J47 © 2025, CC BY.

关键词： Wave equations

SPECIAL ORTHOGONAL, SPECIAL UNITARY, AND SYMPLECTIC GROUPS AS PRODUCTS OF GRASSMANNIANS

学校读者我要写书评

暂无评论

arXiv 2025年

作者： Lim, Lek-Heng Lu, Xiang Ye, Ke Computational and Applied Mathematics Initiative University of Chicago ChicagoIL60637 United States Department of Statistics University of Chicago ChicagoIL60637 United States KLMM Academy of Mathematics and Systems Science Chinese Academy of Sciences Beijing100190 China

We describe a curious structure of the special orthogonal, special unitary, and symplectic groups that has not been observed, namely, they can be expressed as matrix products of their corresponding Grassmannians realized as involution matrices. We will show that SO(n) is a product of two real Grassmannians, SU(n) a product of four complex Grassmannians, and Sp(2n, R) or Sp(2n, C) a product of four symplectic Grassmannians over or ℂ *** Codes 14M15, 22E10, 22E15, 51A50 © 2025, CC BY.

关键词： Matrix algebra

Advancements on multi-fidelity random Fourier neural networks: application to hurricane modeling for offshore wind energy

学校读者我要写书评

暂无评论

Advancements on multi-fidelity random Fourier neural network...

AIAA Science and Technology Forum and Exposition, AIAA SciTech Forum 2025

作者： Davis, Owen Geraci, Gianluca Wentz, Jacqueline M. King, Ryan N. Cortiella, Alexandre Rybchuk, Alex Gomez, Miguel Sanchez Deskos, Georgios Motamed, Mohammad Optimization and Uncertainty Quantification Sandia National Laboratories AlbuquerqueNM United States Computational Data Science Sandia National Laboratories LivermoreCA United States National Wind Technology Center National Renewable Energy Laboratory GoldenCO United States Department of Applied Mathematics and Statistics University of New Mexico AlbuquerqueNM United States

ISBN: (数字)9781624107238

ISBN: (纸本)9781624107238

Multi-fidelity approaches are emerging as effective strategies in computational science to handle otherwise intractable tasks like Uncertainty Quantification (UQ), training of Machine Learning (ML) models, and optimization, for expensive high-fidelity applications in which the amount of available simulations or data is limited. The main idea is simple: large datasets generated for low-fidelity approximations of the problem at hand are fused with a much sparser dataset for the target (high-fidelity) system. In this paper, we build on our recent success in designing random Fourier Neural Networks (rFNNs) [1] to target problems arising in wind energy applications and in particular problems of interest for hurricane modeling. In this context, data for the high-fidelity models are limited and lower fidelity alternatives are needed. In this work, we introduce a novel multi-fidelity training approach for our rFNNs and demonstrate its use on a simple verification problem and on a hurricane modeling problem in which high-fidelity data are generated via Large-Eddy Simulations (LES), while low-fidelity data are given by a mesoscale model. Initial results demonstrate how the multi-fidelity training approach can improve the quality of the resulting surrogate. © 2025, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.

关键词： Large eddy simulation