检索结果-内蒙古大学图书馆

arXiv 2021年

作者： Fornasier, Massimo Klock, Timo Riedl, Konstantin Technical University of Munich School of Computation Information and Technology Department of Mathematics Munich Germany Munich Center for Machine Learning Munich Germany Munich Data Science Institute Munich Germany Simula Research Laboratory Department of Numerical Analysis and Scientific Computing Oslo Norway University of San Diego Department of Mathematics San DiegoCA United States

In this paper, we study consensus-based optimization (CBO), which is a multi-agent metaheuristic derivative-free optimization method that can globally minimize nonconvex nonsmooth functions and is amenable to theoretical analysis. Based on an experimentally supported intuition that, on average, CBO performs a gradient descent of the squared Euclidean distance to the global minimizer, we devise a novel technique for proving the convergence to the global minimizer in mean-field law for a rich class of objective functions. The result unveils internal mechanisms of CBO that are responsible for the success of the method. In particular, we prove that CBO performs a convexification of a large class of optimization problems as the number of optimizing agents goes to infinity. Furthermore, we improve prior analyses by requiring mild assumptions about the initialization of the method and by covering objectives that are merely locally Lipschitz continuous. As a core component of this analysis, we establish a quantitative nonasymptotic Laplace principle, which may be of independent interest. From the result of CBO convergence in mean-field law, it becomes apparent that the hardness of any global optimization problem is necessarily encoded in the rate of the mean-field approximation, for which we provide a novel probabilistic quantitative estimate. The combination of these results allows to obtain probabilistic global convergence guarantees of the numerical CBO *** Codes 65K10, 90C26, 90C56, 35Q90, 35Q84 Copyright © 2021, The Authors. All rights reserved.

关键词： Fokker Planck equation

来源：评论

学校读者我要写书评

暂无评论

Virtual Excitations and Quantum Correlations in Ultra-Strongly Coupled Harmonicoscillators Under Intrinsic Decoherence

SSRN

引用

SSRN 2022年

作者： Jellal, Ahmed Hab-Arrih, Radouan Chnafa, Hasna El Kinani, El Hassan Laboratory of Theoretical Physics Faculty of Sciences Chouaïb Doukkali University PO Box 20 El Jadida24000 Morocco Canadian Quantum Research Center 204-3002 32 Ave VernonBCV1T 2L7 Canada Mathematical Modeling and Scientific Computing Team Department of Mathematics Faculty of Sciences Moulay Ismail University Meknes Morocco

We study the intrinsic decoherence of coupled harmonic oscillators. The Milburn master equation is solved exactly, and the dynamics of virtual ground state excitations are investigated. The interaction of quantum correlations and virtual excitation was then studied. The following is a summary of our major findings. (i) The damped oscillatory profile of all three quantities is the same. (ii) Ultra-strong coupling combined with huge anisotropy values results in the reemergence of entanglement and steering. (iii) To sustain entanglement and steering, virtual excitations are required. (iv) The quantum correlations are amplified in the quantum synchronous regime. (v) Ultra-strong couplings cause inherent decoherence to be avoided. © 2022, The Authors. All rights reserved.

关键词： Anisotropy

来源：评论

学校读者我要写书评

暂无评论

Gravitational tuning forks and hierarchical triple systems

arXiv

引用

arXiv 2021年

作者： Cardoso, Vitor Duque, Francisco Khanna, Gaurav CENTRA Departamento de Física Instituto Superior Técnico – IST Universidade de Lisboa – UL Avenida Rovisco Pais 1 Lisboa1049 Portugal Department of Physics Center for Scientific Computing and Visualization Research University of Massachusetts DarthmouthMA02747 United States Department of Physics University of Rhode Island KingstonRI02881 United States

We study gravitational wave (GW) emission in the strong-field regime by a hierarchical triple system composed of a binary system placed in the vicinity of a supermassive black hole (SMBH). The LIGO-Virgo collaboration recently reported evidence for coalescences with this dynamical origin. These systems are common in galactic centers and thus are a target for the space-based LISA mission as well as other advanced detectors. Doppler shifts, aberration, lensing and strong amplitude modulations are features present in the GW signal from these systems, built into our framework and with no need for phenomenological patches. We find that the binary can resonantly excite the quasinormal modes of the SMBH, as in the resonant excitation of two tuning forks with matching frequencies. The flux of energy crossing the SMBH horizon can be significant, when compared with that from standard extreme-mass-ratio inspirals. Therefore, these triple systems are excellent probes of strong-field physics and of the BH nature of compact objects. © 2021, CC BY.

关键词： Hierarchical systems

来源：评论

学校读者我要写书评

暂无评论

Virtual excitations and quantum correlations in ultra-strongly coupled harmonic oscillators under intrinsic decoherence

arXiv

引用

arXiv 2022年

作者： Hab-Arrih, Radouan Jellal, Ahmed El Kinani, El Hassan Laboratory of Theoretical Physics Faculty of Sciences Chouaïb Doukkali University PO Box 20 El Jadida24000 Morocco Canadian Quantum Research Center 204-3002 32 Ave VernonBCV1T 2L7 Canada Mathematical Modeling and Scientific Computing Team Department of Mathematics Faculty of Sciences Moulay Ismail University Meknes Morocco

关键词： Ground state

来源：评论

学校读者我要写书评

暂无评论

Temperature-dependent micromagnetic model of the antiferromagnet Mn2Au: A multiscale approach

引用

Physical Review B 2022年第9期106卷 094402-094402页

作者： Joel Hirst Unai Atxitia Sergiu Ruta Jerome Jackson Leon Petit Thomas Ostler Materials & Engineering Research Institute Sheffield Hallam University Sheffield S1 1WB United Kingdom Dahlem Center for Complex Quantum Systems and Fachbereich Physik Freie Universitat Berlin 14195 Berlin Germany Instituto de Ciencia de Materiales de Madrid CSIC Cantoblanco 28049 Madrid Spain Scientific Computing Department STFC Daresbury Laboratory Warrington WA4 4AD United Kingdom Department of Physics & Mathematics University of Hull Hull HU6 7RX United Kingdom Department of Engineering and Mathematics Sheffield Hallam University Sheffield S1 1WB United Kingdom

Antiferromagnets (AFMs) are strong candidates for the future spintronic and memory applications largely because of their inherently fast dynamics and lack of stray fields, with Mn2Au being one of the most promising. For the numerical modeling of magnetic material properties, it is common to use ab initio methods, atomistic models, and micromagnetics. However, each method alone describes the physics within certain limits. Multiscale methods bridging the gap between these three approaches have been already proposed for ferromagnetic materials. Here we present a complete multiscale model of the AFM Mn2Au as an exemplar material, starting with results from ab initio methods going via atomistic spin dynamics (ASD) to an AFM Landau-Lifshitz-Bloch (AFM-LLB) model. First, bulk Mn2Au is modelled using a classical spin Hamiltonian constructed based on earlier first-principles calculations. Second, this spin model is used in the stochastic Landau-Lifshitz-Gilbert to calculate temperature-dependent equilibrium properties, such as magnetization and magnetic susceptibilities. Third, the temperature-dependent micromagnetic parameters are used in the AFM-LLB. We validate our approach by comparing the ASD and AFM-LLB models for three paradigmatic cases: (i) damped magnetic oscillations, (ii) magnetization dynamics following a heat pulse resembling pump-probe experiments, and (iii) magnetic domain wall motion under thermal gradients.

关键词： Antiferromagnetism Domain walls Micromagnetism Spin dynamics Ultrafast magnetic effects

来源：评论

学校读者我要写书评

暂无评论

Democratizing Uncertainty Quantification

arXiv

引用

arXiv 2024年

作者： Seelinger, Linus Reinarz, Anne Lykkegaard, Mikkel B. Akers, Robert Alghamdi, Amal M.A. Aristoff, David Bangerth, Wolfgang Bénézech, Jean Diez, Matteo Frey, Kurt Jakeman, John D. Jørgensen, Jakob S. Kim, Ki-Tae Kent, Benjamin M. Martinelli, Massimiliano Parno, Matthew Pellegrini, Riccardo Petra, Noemi Riis, Nicolai A.B. Rosenfeld, Katherine Serani, Andrea Tamellini, Lorenzo Villa, Umberto Dodwell, Tim J. Scheichl, Robert Scientific Computing Center Karlsruhe Institute of Technology Karlsruhe Germany Department of Computer Science Durham University Durham United Kingdom digiLab Exeter United Kingdom UK Atomic Energy Authority Oxford United Kingdom Lyngby Denmark Department of Mathematics Colorado State University Fort CollinsCO United States Department of Mathematics Department of Geosciences Colorado State University Fort CollinsCO United States Centre for Integrated Materials Processes and Structures Department of Mechanical Engineering University of Bath Bath United Kingdom National Research Council Institute of Marine Engineering Rome Italy Institute for Disease Modeling Global Health Division Bill & Melinda Gates Foundation United States Optimization and Uncertainty Quantification Sandia National Laboratories AlbuquerqueNM United States University of California Merced United States National Research Council-Institute for Applied Mathematics and Information Technologies "E. Magenes" Pavia Italy Solea Energy ThetfordVT United States Copenhagen Imaging ApS Herlev Denmark The University of Texas Austin United States Heidelberg University Germany

Uncertainty Quantification (UQ) is vital to safety-critical model-based analyses, but the widespread adoption of sophisticated UQ methods is limited by technical complexity. In this paper, we introduce UM-Bridge (the UQ and Modeling Bridge), a high-level abstraction and software protocol that facilitates universal interoperability of UQ software with simulation codes. It breaks down the technical complexity of advanced UQ applications and enables separation of concerns between experts. UM-Bridge democratizes UQ by allowing effective interdisciplinary collaboration, accelerating the development of advanced UQ methods, and making it easy to perform UQ analyses from prototype to High Performance computing (HPC) scale. In addition, we present a library of ready-to-run UQ benchmark problems, all easily accessible through UM-Bridge. These benchmarks support UQ methodology research, enabling reproducible performance comparisons. We demonstrate UM-Bridge with several scientific applications, harnessing HPC resources even using UQ codes not designed with HPC support. © 2024, CC BY-NC-ND.

关键词： Application programs

来源：评论

学校读者我要写书评

暂无评论

GW190521: Tracing imprints of spin-precession on the most massive black hole binary

arXiv

引用

arXiv 2023年

作者： Miller, Simona J. Isi, Maximiliano Chatziioannou, Katerina Varma, Vijay Mandel, Ilya Department of Physics California Institute of Technology PasadenaCA91125 United States LIGO Laboratory California Institute of Technology PasadenaCA91125 United States Center for Computational Astrophysics Flatiron Institute New YorkNY10010 United States Department of Mathematics Center for Scientific Computing and Data Science Research University of Massachusetts DartmouthMA02747 United States Max Planck Institute for Gravitational Physics Albert Einstein Institute PotsdamD-14476 Germany School of Physics Astronomy Monash University ClaytonVIC3800 Australia OzGrav: The ARC Centre of Excellence for Gravitational Wave Discovery ClaytonVIC3800 Australia

GW190521 is a remarkable gravitational-wave signal on multiple fronts: its source is the most massive black hole binary identified to date and could have spins misaligned with its orbit, leading to spin-induced precession;an astrophysically consequential property linked to the binary's origin. However, due to its large mass, GW190521 was only observed during its final 3-4 cycles, making precession constraints puzzling and giving rise to alternative interpretations, such as eccentricity. Motivated by these complications, we trace the observational imprints of precession on GW190521 by dissecting the data with a novel time domain technique, allowing us to explore the morphology and interplay of the few observed cycles. We find that precession inference hinges on a quiet portion of the pre-merger data that is suppressed relative to the merger-ringdown. Neither pre-merger nor post-merger data alone are the sole driver of inference, but rather their combination;in the quasi-circular scenario, precession emerges as a mechanism to accommodate the lack of a stronger pre-merger signal in light of the observed post-merger. In terms of source dynamics, the pre-merger suppression arises from a tilting of the binary with respect to the observer. Establishing such a consistent picture between the source dynamics and the observed data is crucial for characterizing the growing number of massive binary observations and bolstering the robustness of ensuing astrophysical claims. © 2023, CC BY.

关键词： Stars

来源：评论

学校读者我要写书评

暂无评论

Brain solute transport is more rapid in periarterial than perivenous spaces

Research Square

引用

research Square 2021年

作者： Vinje, Vegard Bakker, Erik Nicolaas Theodorus Petrus Rognes, Marie E. Department of Scientific Computing and Numerical Analysis Simula Research Laboratory Martin Linges vei 25 Fornebu 1364 Norway Amsterdam University Medical Center Dept. of Biomedical Engineering and Physics Meibergdreef 9 Amsterdam1105 AZ Netherlands University of Bergen Department of Mathematics Bergen Norway

Background: Perivascular fluid flow, of cerebrospinal or interstitial fluid in spaces surrounding brain blood vessels, is recognized as a key component underlying brain transport and clearance. An important open question is how and to what extent differences in vessel type or geometry affect perivascular fluid flow and transport. Methods: Using computational modelling in both idealized and image-based geometries, we study and compare fluid flow and solute transport in pial (surface) periarterial and perivenous spaces. Results: Our findings demonstrate that differences in geometry between arterial and venous pial perivascular spaces (PVSs) lead to higher net CSF flow, more rapid tracer transport and earlier arrival times of injected tracers in periarterial spaces compared to perivenous spaces. Conclusions: These findings can explain the experimentally observed rapid appearance of tracers around arteries, and the delayed appearance around veins without the need of a circulation through the parenchyma, but rather by direct transport along the PVSs. © 2021, CC BY.

关键词： Blood vessels

来源：评论

学校读者我要写书评

暂无评论

Numerical simulations of black hole–neutron star mergers in scalar-tensor gravity

arXiv

引用

arXiv 2023年

作者： Ma, Sizheng Varma, Vijay Stein, Leo C. Foucart, Francois Duez, Matthew D. Kidder, Lawrence E. Pfeiffer, Harald P. Scheel, Mark A. TAPIR 350-17 California Institute of Technology 1200 E California Boulevard PasadenaCA91125 United States PotsdamD-14476 Germany Department of Physics Cornell University IthacaNY14853 United States Cornell Center for Astrophysics and Planetary Science Cornell University IthacaNY14853 United States Department of Mathematics Center for Scientific Computing and Data Science Research University of Massachusetts DartmouthMA02747 United States Department of Physics & Astronomy The University of Mississippi UniversityMS38677 United States Department of Physics & Astronomy University of New Hampshire 9 Library Way DurhamNH03824 United States Department of Physics & Astronomy Washington State University PullmanWA99164 United States

We present a numerical-relativity simulation of a black hole - neutron star merger in scalar-tensor (ST) gravity with binary parameters consistent with the gravitational wave event GW200115. In this exploratory simulation, we consider the Damour-Esposito-Farèse extension to Brans-Dicke theory, and maximize the effect of spontaneous scalarization by choosing a soft equation of state and ST theory parameters at the edge of known constraints. We extrapolate the gravitational waves, including tensor and scalar (breathing) modes, to future null-infinity. The numerical waveforms undergo ∼ 22 wave cycles before the merger, and are in good agreement with predictions from post-Newtonian theory during the inspiral. We find the ST system evolves faster than its general-relativity (GR) counterpart due to dipole radiation, merging a full gravitational-wave cycle before the GR counterpart. This enables easy differentiation between the ST waveforms and GR in the context of parameter estimation. However, we find that dipole radiation’s effect may be partially degenerate with the NS tidal deformability during the late inspiral stage, and a full Bayesian analysis is necessary to fully understand the degeneracies between ST and binary parameters in GR. Copyright © 2023, The Authors. All rights reserved.

关键词： Tensors

来源：评论

学校读者我要写书评

暂无评论

Combined influences of Soret effect and horizontal magnetic field on dynamics of vertical convection in binary fluids

引用

Physical Review Fluids 2025年第5期10卷 053503-053503页

作者： Chao-Nan Zhang Lai-yun Zheng Xu-Long Li Juan-Juan Qin Bing-Xin Zhao Don Liu School of Mathematics and Statistics Ningxia University Yinchuan 750021 China School of Mechanical Engineering Ningxia University Yinchuan 750021 China Ningxia Key Laboratory of Interdisciplinary Mechanics and Scientific Computing Yinchuan 750021 China Ningxia Basic Science Research Center of Mathematics Yinchuan 750021 China Department of Mathematics and Mechanical Engineering Louisiana Tech University Ruston Louisiana 71270 USA

The influence of the Soret effect and a uniform magnetic field on the dynamic behavior of vertical convection are investigated using a high-accuracy numerical method. The effects of the Soret number (Sr, which quantifies the direction and magnitude of species migration relative to the temperature gradient; positive Sr denotes migration toward hotter regions, negative toward cooler regions) on flow, heat and mass transfer, and flow transition in the presence of a magnetic field are analyzed. The results reveal that, for a given magnetic field strength, positive and negative Soret effects have significantly different influences on heat and mass transfer as well as on flow structure. For a high Rayleigh number (Ra, vigor of the buoyancy) and a small magnetic field, the heat transfer initially decreases and then increases with increasing Soret number, while the mass transfer consistently decreases. In cases where temperature is dominant, heat transfer for Sr=−1 exceeds that for Sr=0 by 24%, while mass transfer with Sr=−1 exceeds that for Sr=0 by 85%. When concentration is dominant, heat transfer reaches a minimum at Sr=0, whereas mass transfer peaks at Sr=−1, corresponding to an approximate 71% increase over heat transfer at Sr=0, and around a 210% increase in mass transfer. Additionally, the flow exhibits greater complexity when the Soret number is negative than when it is positive. When the magnetic field is weak, the temperature-dominated flow changes from chaotic to periodic with increasing Soret number and eventually returns to a chaotic state. When the magnetic field is strong, the flow transitions from chaotic to periodic and finally to a steady state. The transition route involves two types of periodic flow: a simple periodic flow with an integer multiple of the fundamental frequency, and a complex periodic flow with multiple lower-frequency subharmonic waves. Furthermore, as the strength of the magnetic field increases, the flow in the rectangular enclosure is

关键词： Diffusion in solids

来源：评论

学校读者我要写书评

暂无评论

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

请选择保存的检索档案：

请选择收藏分类：

通借通还

建议与咨询 留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

请选择保存的检索档案： 新增检索档案 确定 取消

请选择收藏分类： 新增自定义分类 确定 取消

通借通还

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

请选择保存的检索档案：

请选择收藏分类：