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arXiv 2024年

作者： Wollaeger, Ryan T. Fryer, Chris L. Chiodi, Robert Brady, Peter T. Korobkin, Oleg Harnish, Cale Fontes, Christopher J. Haack, Jeffrey R. Chapurin, Oleksandr Koshkarov, Oleksandr Delzanno, Gian Luca Livescu, Daniel Center for Theoretical Astrophysics Los Alamos National Laboratory Los AlamosNM87545 United States Computer Computational and Statistical Sciences Division Los Alamos National Laboratory Los AlamosNM87545 United States Center for Nonlinear Studies Los Alamos National Laboratory Los AlamosNM87545 United States The University of Arizona TucsonAZ85721 United States Department of Physics and Astronomy The University of New Mexico AlbuquerqueNM87131 United States The George Washington University WashingtonDC20052 United States T-5 Applied Mathematics and Plasma Physics Group Los Alamos National Laboratory Los AlamosNM87545 United States Computational Physics Division Los Alamos National Laboratory Los AlamosNM87545 United States

The interaction of β-particles with the weakly ionized plasma background is an important mechanism for powering the kilonova transient signal from neutron star mergers. For this purpose, we present an implementation of the approximate fast-particle collision kernel, described by Inokuti (1971) following the seminal formulation of Bethe (1930), in a spectral solver of the Vlasov-Maxwell-Boltzmann equations. In particular, we expand the fast-particle plane-wave atomic excitation kernel into coefficients of the Hermite basis, and derive the relevant discrete spectral system. In this fast-particle limit, the approach permits the direct use of atomic data, including optical oscillator strengths, normally applied to photon-matter interaction. The resulting spectral matrix is implemented in the MASS-APP spectral solver framework, in a way that avoids full matrix storage per spatial zone. We numerically verify aspects of the matrix construction, and present a proof-of-principle 3D simulation of a 2D axisymmetric kilonova ejecta snapshot. Our preliminary numerical results indicate that a reasonable choice of Hermite basis parameters for β-particles in the kilonova are a bulk velocity parameter u⃗ = 0, a thermal velocity parameter α⃗ = 0.5c, and a 9x9x9 mode velocity basis set (Hermite orders 0 to 8 in each dimension). For ejecta-interior sample zones, we estimate the ratio of thermalization from large-angle ( 2.5◦) bound excitation scattering to total thermalization is ∼0.002-0.003. © 2024, CC BY.

关键词： Boltzmann equation

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A new covariant formalism for kinetic plasma simulations in curved spacetimes

arXiv

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arXiv 2023年

作者： Trent, Tyler Christian, Pierre Chan, Chi-Kwan Psaltis, Dimitrios Özel, Feryal School of Physics Georgia Institute of Technology 837 State St NW AtlantaGA30332 United States Departments of Astronomy and Physics University of Arizona 933 N. Cherry Ave. TucsonAZ85721 United States Physics Department Fairfield University 1073 N Benson Rd FairfieldCT06824 United States Data Science Institute and Program in Applied Mathematics University of Arizona 1230 N. Cherry Ave. TucsonAZ85721 United States

Low density plasmas are characterized by a large scale separation between the gyromotion of particles around local magnetic fields and the macroscopic scales of the system, often making global kinetic simulations computationally intractable. The guiding center formalism has been proposed as a powerful tool to bridge the gap between these scales. Despite its usefulness, the guiding center approach has been formulated successfully only in flat spacetimes, limiting its applicability in astrophysical settings. Here, we present a new covariant formalism that leads to kinetic equations in the guiding center limit that are valid in arbitrary spacetimes. Through a variety of experiments, we demonstrate that our equations capture all known gyro-center drifts while overcoming one severe limitation imposed on numerical algorithms by the fast timescales of the particle gyromotion. This formalism will enable explorations of a variety of global plasma kinetic phenomena in the curved spacetimes around black holes and neutron stars. © 2023, CC BY.

关键词： Integral equations

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Measuring the Substructure Mass Power Spectrum of 23 SLACS Strong Galaxy-Galaxy Lenses with Convolutional Neural Networks

arXiv

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arXiv 2024年

作者： Fagin, Joshua Vernardos, Georgios Tsagkatakis, Grigorios Pantazis, Yannis Shajib, Anowar J. O’Dowd, Matthew The Graduate Center The City University of New York 365 Fifth Avenue New YorkNY10016 United States Department of Astrophysics American Museum of Natural History Central Park West and 79th Street NY10024-5192 United States Department of Physics and Astronomy Lehman College The CUNY BronxNY10468 United States Institute of Computer Science FORTH HeraklionGR-70013 Greece Institute of Applied and Computational Mathematics FORTH HeraklionGR-70013 Greece Department of Astronomy & Astrophysics University of Chicago ChicagoIL606374 United States Kavli Institute for Cosmological Physics University of Chicago ChicagoIL60637 United States

Strong gravitational lensing can be used as a tool for constraining the substructure in the mass distribution of galaxies. In this study we investigate the power spectrum of dark matter perturbations in a population of 23 Hubble Space Telescope images of strong galaxy-galaxy lenses selected from The Sloan Lens ACS (SLACS) survey. We model the dark matter substructure as a Gaussian Random Field perturbation on a smooth lens mass potential, characterized by power-law statistics. We expand upon the previously developed machine learning framework to predict the power-law statistics by using a convolutional neural network (CNN) that accounts for both epistemic and aleatoric uncertainties. For the training sets, we use the smooth lens mass potentials and reconstructed source galaxies that have been previously modelled through traditional fits of analytical and shapelet profiles as a starting point. We train three CNNs with different training set: the first using standard data augmentation on the best-fitting reconstructed sources, the second using different reconstructed sources spaced throughout the posterior distribution, and the third using a combination of the two data sets. We apply the trained CNNs to the SLACS data and find agreement in their predictions. Our results suggest a significant substructure perturbation favoring a high frequency power spectrum across our lens population. © 2024, CC BY.

关键词： Convolutional neural networks

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Chiral Quasi-Bound States in the Continuum

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Physical Review Letters 2021年第7期126卷 073001-073001页

作者： Adam Overvig Nanfang Yu Andrea Alù Photonics Initiative Advanced Science Research Center at the Graduate Center of the City University of New York New York New York 10031 USA Department of Applied Physics and Applied Mathematics Columbia University New York New York 10027 USA Physics Program Graduate Center City University of New York New York New York 10016 USA

Quasi-bound states in the continuum (QBICs) are Fano resonant states with long optical lifetimes controlled by symmetry-breaking perturbations. While conventional Fano responses are limited to linear polarizations and do not support tailored phase control, here we introduce QBICs born of chiral perturbations that encode arbitrary elliptical polarization states and enable geometric phase engineering. We thereby design metasurfaces with ultrasharp spectral features that shape the impinging wave front with near-unity efficiency. Our findings extend Fano resonances beyond their conventional limits, opening opportunities for nanophotonics, classical and quantum optics, and acoustics.

关键词： Metamaterials Photonic crystals

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Measuring 3D Chemistry at 1 nm Resolution with Fused Multi-Modal Electron Tomography

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Microscopy and microanalysis : the official journal of Microscopy Society of America, Microbeam Analysis Society, Microscopical Society of Canada 2023年第1期29卷 1394-1395页

作者： Schwartz, Jonathan Di, Zichao Wendy Jiang, Yi Cho, Min Gee Qian, Yiwen Gu, Junsi Rozeveld, Steve Ercius, Peter Fessler, Jeffrey A. Xu, Ting Scott, Mary Hovden, Robert Department of Materials Science and Engineering University of Michigan Ann Arbor MI United States Mathematics and Computer Science Division Argonne National Laboratory Lemont IL United States Advanced Photon Source Argonne National Laboratory Lemont IL United States Department of Materials Science and Engineering University of California at Berkeley Berkeley CA United States National Center for Electron Microscopy Lawrence Berkeley National Laboratory Berkeley CA United States Dow Chemical Co. Midland MI United States Department of Electrical Engineering and Computer Science University of Michigan Ann Arbor MI United States Materials Science Division Lawrence Berkeley National Laboratory Berkeley CA United States Applied Physics Program University of Michigan Ann Arbor MI United States

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Reduced order models from computed states of physical systems using non-local calculus on finite weighted graphs

arXiv

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arXiv 2021年

作者： Duschenes, Matthew Garikipati, Krishna Department of Mechanical Engineering University of Michigan United States Applied Physics University of Michigan United States Department of Mathematics University of Michigan United States Michigan Institute for Computational Discovery & Engineering University of Michigan United States

Partial differential equation-based numerical solution frameworks for initial and boundary value problems have attained a high degree of complexity. applied to a wide range of physics with the ultimate goal of enabling engineering solutions, these approaches encompass a spectrum of spatiotemporal discretization techniques that leverage solver technology and high performance computing. While high-fidelity solutions can be achieved using these approaches, they come at a high computational expense and complexity. Systems with billions of solution unknowns are now routine. The expense and complexity do not lend themselves to typical engineering design and decision-making, which must instead rely on reduced-order models. Here we present an approach to reduced-order modelling that builds off of recent graph theoretic work for representation, exploration, and analysis on computed states of physical systems (Banerjee et al., Comp. Meth. App. Mech. Eng., 351, 501-530, 2019). We extend a non-local calculus on finite weighted graphs to build such models by exploiting first order dynamics, polynomial expansions, and Taylor series. Some aspects of the non-local calculus related to consistency of the models are explored. Details on the numerical implementations and the software library that has been developed for non-local calculus on graphs are described. Finally, we present examples of applications to various quantities of interest in mechano-chemical systems. © 2021, CC BY-NC-SA.

关键词： Graphic methods

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BPS2025 - Engineering turbulence in cryo-plunging for deeper vitrification

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Biophysical Journal 2025年第3期124卷 494a-494a页

作者： Arvind Srinivasan Yue Sun Simon Merminod Christopher Rycroft Maxim B. Prigozhin Applied Physics Program Harvard University Cambridge MA USA Department of Mathematics University of Wisconsin Madison Madison WI USA Department of Molecular and Cellular Biology Harvard University Cambridge MA USA

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Kinetic study of transverse electron-scale interface instability in relativistic shear flows

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Matter and Radiation at Extremes 2020年第5期5卷 12-19页

作者： Peilin Yao Hongbo Cai Xinxin Yan Wenshuai Zhang Bao Du Jianmin Tian Enhao Zhang Xuewu Wang Shaoping Zhu Department of Engineering Physics Tsinghua UniversityBeijing 100084China Institute of Applied Physics and Computational Mathematics Beijing 100094China Center for Applied Physics and Technology HEDPSand College of EngineeringPeking UniversityBeijing 100871China Center for Applied Physics and Technology HEDPSSchool of Physicsand College of EngineeringPeking UniversityBeijing 100871China Graduate School China Academy of Engineering PhysicsBeijing 100088China

Interfacial magnetic field structures induced by transverse electron-scale shear instability(mushroom instability)are found to be strongly associated with electron and ion dynamics,which in turn will influence the development of the instability *** find that high-frequency electron oscillations are excited normal to the shear ***,on a larger time scale,the bulk of the ions are gradually separated under the influence of local magnetic fields,eventually reaching an equilibrium related to the initial shear *** a theoretical model of this *** separation on the scale of the electron skin depth will prevent different ions from mixing and will thereafter restrain the growth of higher-order *** also analyze the role of electron thermal motion in the generation of the magnetic field,and we find an increase in the instability growth rate with increasing plasma *** results have potential for providing a more realistic description of relativistic plasma flows.

关键词： temperature. relativistic transverse

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The Role of Heterogeneity in Autonomous Perimeter Defense Problems

arXiv

引用

arXiv 2022年

作者： Adler, Aviv Mickelin, Oscar Ramachandran, K. Sukhatme, Gaurav S. Karaman, Sertac Department of Electrical Engineering and Computer Science Massachusetts Institute of Technology CambridgeMA United States Program in Applied and Computational Mathematics Princeton University Princeton NJ08544 United States Department of Computer Science University of Southern California Los AngelesCA90089 United States Department of Aeronautics and Astronautics Massachusetts Institute of Technology CambridgeMA02139 United States

When is heterogeneity in the composition of an autonomous robotic team beneficial and when is it detrimental? We investigate and answer this question in the context of a minimally viable model that examines the role of heterogeneous speeds in perimeter defense problems, where defenders share a total allocated speed budget. We consider two distinct problem settings and develop strategies based on dynamic programming and on local interaction rules. We present a theoretical analysis of both approaches and our results are extensively validated using simulations. Interestingly, our results demonstrate that the viability of heterogeneous teams depends on the amount of information available to the defenders. Moreover, our results suggest a universality property: across a wide range of problem parameters the optimal ratio of the speeds of the defenders remains nearly constant. Copyright © 2022, The Authors. All rights reserved.

关键词： Dynamic programming

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Symmetry-based phenomenological model for magnon transport in a multiferroic

arXiv

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arXiv 2024年

作者： Harris, Isaac A. Husain, Sajid Meisenheimer, Peter Ramesh, Maya Park, Hyeon Woo Caretta, Lucas Schlom, Darrell Yao, Zhi Martin, Lane W. Íñiguez-González, Jorge Kim, Se Kwon Ramesh, Ramamoorthy Department of Physics University of California BerkeleyCA United States Materials Science Division Lawrence Berkeley National Laboratory BerkeleyCA United States Department of Materials Science and Engineering University of California BerkeleyCA United States Department of Materials Science and Engineering Cornell University Ithaca United States Department of Physics Korea Advanced Institute of Science and Technology Daejon Korea Republic of School of Engineering Brown University ProvidenceRI United States Applied Mathematics and Computational Research Division Lawrence Berkeley National Laboratory BerkeleyCA94720 United States Department of Materials Science and NanoEngineering Rice University HoustonTX United States Department of Physics and Astronomy Rice University HoustonTX United States Department of Chemistry Rice University HoustonTX United States Rice Advanced Materials Institute Rice University HoustonTX United States Materials Research and Technology Department Luxembourg Institute of Science and Technology Esch-Sur-Alzette Luxembourg Department of Physics and Materials Science University of Luxembourg Belvaux Luxembourg

Magnons – carriers of spin information – can be controlled by electric fields in the multiferroic BiFeO3 (BFO), a milestone that brings magnons closer to application in future devices. The origin of magnon-spin currents in BFO, however, is not fully understood due to BFO’s complicated magnetic texture. In this letter, we present a phenomenological model to elucidate the existence of magnon spin currents in generalized multiferroics by examining the symmetries inherent to their magnetic and polar structures. This model is grounded in experimental data obtained from BFO and its derivatives, which informs the symmetry operations and resultant magnon behavior. By doing so, we address the issue of symmetry-allowed, switchable magnon spin transport in multiferroics, thereby establishing a critical framework for comprehending magnon transport within complex magnetic textures. © 2024, CC BY.

关键词： Spin waves

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