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Particle In Cell Simulations of Mildly Relativistic Outflows in Kilonova Emissions

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arXiv 2023年

作者： Rassel, Mohira Kilian, Patrick Aberham, Vito Spanier, Felix Lloyd-Ronning, Nicole Fryer, Chris L. Center for Theoretical Astrophysics Los Alamos National Laboratory Los AlamosNM87545 United States Center for Non Linear Studies Los Alamos National Laboratory Los AlamosNM87545 United States Space Science Institute 4765 Walnut St Suite B BoulderCO80301 United States Institut für Theoretische Astrophysik Universität Heidelberg Heidelberg69120 Germany Computational Physics and Methods Group Los Alamos National Laboratory Los AlamosNM87545 United States Department of Math Engineering & Science University of New Mexico Los AlamosNM87545 United States Computer Computational and Statistical Sciences Division 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

The electromagnetic emission from neutron star mergers is comprised of multiple components. Synchrotron emission from the disk-powered jet as well as thermal emission from the merger ejecta (powered by a variety of sources) are among the most studied sources. The low masses and high velocities of the merger ejecta quickly develop conditions where emission from collisionless shocks becomes critical and synchrotron emission from the merger ejecta constitutes a third component to the observed signal. The aim of this project is to examine shock development, magnetic field generation and particle acceleration in the case of mildly relativistic shocks, which are expected when the tidal ejecta of neutron star mergers drive a shock into the external medium. Using LANL’s VPIC (vector particle-in-cell) code, we have run simulations of such mildly-relativistic, collisionless, weakly-magnetized plasmas and compute the resultant magnetic fields and particle energy spectra. We show the effects of varying plasma conditions, as well as explore the validity of using different proton to electron mass ratios in VPIC. Our results have implications for observing late-time electromagnetic counterparts to gravitational wave detections of neutron star mergers. Copyright © 2023, The Authors. All rights reserved.

关键词： Merging

Active learning with multifidelity modeling for efficient rare event simulation

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arXiv 2021年

作者： Dhulipala, Somayajulu L.N. Shields, Michael D. Spencer, Benjamin W. Bolisetti, Chandrakanth Slaughter, Andrew E. Labouré, Vincent M. Chakroborty, Promit Computational Mechanics and Materials Idaho National Laboratory Idaho FallsID83402 United States Department of Civil and Systems Engineering Johns Hopkins University BaltimoreMD21218 United States Advanced Reactor Technology and Design Idaho National Laboratory Idaho FallsID83402 United States Computational Frameworks Idaho National Laboratory Idaho FallsID83402 United States Reactor Physics Methods and Analysis Idaho National Laboratory Idaho FallsID83402 United States

While multifidelity modeling provides a cost-effective way to conduct uncertainty quantification with computationally expensive models, much greater efficiency can be achieved by adaptively deciding the number of required high-fidelity (HF) simulations, depending on the type and complexity of the problem and the desired accuracy in the results. We propose a framework for active learning with multifidelity modeling emphasizing the efficient estimation of rare events. Our framework works by fusing a low-fidelity (LF) prediction with an HF-inferred correction, filtering the corrected LF prediction to decide whether to call the high-fidelity model, and for enhanced subsequent accuracy, adapting the correction for the LF prediction after every HF model call. The framework does not make any assumptions as to the LF model type or its correlations with the HF model. In addition, for improved robustness when estimating smaller failure probabilities, we propose using dynamic active learning functions that decide when to call the HF model. We demonstrate our framework using several academic case studies and two finite element (FE) model case studies: estimating Navier-Stokes velocities using the Stokes approximation and estimating stresses in a transversely isotropic model subjected to displacements via a coarsely meshed isotropic model. Across these case studies, not only did the proposed framework estimate the failure probabilities accurately, but compared with either Monte Carlo or a standard variance reduction method, it also required only a small fraction of the calls to the HF model. © 2021, CC BY-NC-ND.

关键词： Uncertainty analysis

Would the occurrence of a Maunder-like solar minimum reverse the observed climate change?

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Evolving Earth

Evolving Earth 2025年 3卷

作者： Marcio Cataldi Rafael Rangel Vitor Luiz Victalino Galves Sonia Jerez Juan Pedro Montávez Amar Halifa-Marín Luiz Landau Regional Atmospheric Modelling Group (MAR) Physics of the Earth Department of Physics Regional Campus of International Excellence (CEIR) “Campus Mare Nostrum” University of Murcia Spain Climate System Monitoring and Modelling Laboratory (LAMMOC) Water Resources and Environmental Engineering Federal Fluminense University Brazil Laboratory of Computational Methods in Engineering (LAMCE) Civil Engineering Program Alberto Luiz Coimbra Institute for Graduate Studies and Research in Engineering Federal University of Rio de Janeiro Rio de Janeiro Brazil

This study examines a scenario combining a prolonged solar minimum, like the historical Maunder Minimum, with the increased CO2 emissions characteristic of the industrial era. Two scenarios were developed in NCAR/CESM 2.0 implemented at LAMMOC/UFF to create simulations from 1850 to 2000, it contrasts differing radiative forcings from 1950 onward—one reflecting actual observed changes, including rising CO2 levels, and the other simulating a decrease in solar output like that during the Maunder Minimum but with continued CO2 growth. The results were validated against ERA5 data and 20th-century reanalysis. By calculating meridional averages at 30-degree latitude intervals, distinct regional impacts of the Maunder Minimum were identified. Notably the simulated Maunder Minimum reduced global warming by and even mitigated 70 % in HS in the last decade of the 20th century. However, this attenuation was lower in the HN, especially in the 30–60N region where no attenuation was observed.

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Inferring Type II-P Supernova Progenitor Masses from Plateau Luminosities

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arXiv 2022年

作者： Barker, Brandon L. O’Connor, Evan P. Couch, Sean M. Department of Physics and Astronomy Michigan State University East LansingMI48824 United States Department of Computational Mathematics Science and Engineering Michigan State University East LansingMI48824 United States Computational Physics and Methods Los Alamos National Laboratory Los AlamosNM87545 United States Center for Nonlinear Studies Los Alamos National Laboratory Los AlamosNM87545 United States Center for Theoretical Astrophysics Los Alamos National Laboratory Los AlamosNM87545 United States The Oskar Klein Centre Department of Astronomy Stockholm University AlbaNova StockholmSE-106 91 Sweden Facility for Rare Isotope Beams Michigan State University East LansingMI48824 United States

Connecting observations of core-collapse supernova explosions to the properties of their massive star progenitors is a long-sought, and challenging, goal of supernova science. Recently, Barker et al. (2022) presented bolometric light curves for a landscape of progenitors from spherically symmetric neutrino-driven core-collapse supernova (CCSN) simulations using an effective model. They find a tight relationship between the plateau luminosity of the Type II-P CCSN light curve and the terminal iron core mass of the progenitor. Remarkably, this allows us to constrain progenitor properties with photometry alone. We analyze a large observational sample of Type II-P CCSN light curves and estimate a distribution of iron core masses using the relationship of Barker et al. (2022). The inferred distribution matches extremely well with the distribution of iron core masses from stellar evolutionary models, and namely, contains high-mass iron cores that suggest contributions from very massive progenitors in the observational data. We use this distribution of iron core masses to infer minimum and maximum mass of progenitors in the observational data. Using Bayesian inference methods to locate optimal initial mass function parameters, we find (formula presented)solar masses for the observational data. Copyright © 2022, The Authors. All rights reserved.

关键词： Supernovae

AN ADAPTIVE FINITE ELEMENT METHOD FOR TWO-DIMENSIONAL ELLIPTIC EQUATIONS WITH LINE DIRAC SOURCES

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arXiv 2021年

作者： Cao, Huihui Li, Hengguang Yi, Nianyu Yin, Peimeng Hunan Key Laboratory for Computation and Simulation in Science and Engineering School of Mathematics and Computational Science Xiangtan University Hunan Xiangtan411105 China Wayne State University Department of Mathematics DetroitMI48202 United States Multiscale Methods and Dynamics Group Computer Science and Mathematics Division Oak Ridge National Laboratory Oak RidgeTN37831 United States

In this paper, we propose a novel adaptive finite element method for an elliptic equation with line Dirac delta functions as a source term. We first study the well-posedness and global regularity of the solution in the whole domain. Instead of regularizing the singular source term and using the classical residual-based a posteriori error estimator, we propose a novel a posteriori estimator based on an equivalent transmission problem with zero source term and nonzero flux jumps on line fractures. The transmission problem is defined in the same domain as the original problem excluding on line fractures, and the solution is therefore shown to be more regular. The estimator relies on meshes conforming to the line fractures and its edge jump residual essentially uses the flux jumps of the transmission problem on line fractures. The error estimator is proven to be both reliable and efficient, an adaptive finite element algorithm is proposed based on the error estimator and the bisection refinement method. Numerical tests show that quasi-optimal convergence rates are achieved even for high order approximations and the adaptive meshes are only locally refined at singular points. © 2021, CC BY-NC-ND.

关键词： Fracture

The origin of the anomalous expansion of the first peak in the radial distribution function during the rapid solidification of tantalum metal

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Physical Chemistry Chemical Physics 2025年 2025 May 27页

作者： Jiang, Yuanqi Wen, Dadong Xu, Qiang Lv, Jian Zhao, Rui Peng, Ping College of Physics & Electronic Information Key Laboratory of Atomic and Molecular Physics Nanchang Normal University Nanchang330032 China School of Computational Science and Electronics Hunan Institute of Engineering Xiangtan411104 China Key Laboratory of Material Simulation Methods and Software of Ministry of Education College of Physics Jilin University Changchun130012 China School of Mechanical and Electrical Engineering Xinyu University Xinyu338004 China School of Material Science & Engineering Hunan University Changsha410082 China

The cause of the anomalous shift in the first maximum peak of radial distribution functions (RDFs) with decreasing temperature in metallic melts and glasses remains highly controversial. In this study, we show that the first RDF peak exhibits anomalous expansion as the temperature decreases during the non-equilibrium solidification (γ1 = 1 × 1010 K s−1 and γ2 = 1 × 1011 K s−1) of liquid tantalum. This behavior is primarily due to alterations in both the geometric and electronic structures of the system. In terms of geometric structure, for example, at the cooling rate of γ1, the system forms a significant number of cage-like icositetrahedral Voronoi polyhedra (0,0,12,2) and standard icosahedral Voronoi polyhedra (0,0,12,0) at low temperatures. These Voronoi polyhedra have longer bond lengths and lower binding energies compared to their high-temperature counterparts. Furthermore, these Voronoi polyhedra nest together, forming a stable Ta26-C2v atomic configuration with minimal changes in bond lengths. This unique geometric arrangement contributes fundamentally to the anomalous expansion of the first peak of the RDF. Regarding the electronic structure, the temperature influences the interactions between Ta atoms. At higher temperatures, the electronic localization functions (ELFs) and the Mulliken bond overlap populations (Qi-j) are significantly increased, leading to stronger electronic interactions and a denser arrangement of nearest-neighbor atoms with shorter bond lengths. Consequently, the combined effects of geometric and electronic structural changes during non-equilibrium solidification could explain the anomalous expansion of the first peak of the RDF. © 2025 The Royal Society of Chemistry.

关键词： Rapid solidification

Rapid generation of parametric aircraft structural models

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Rapid generation of parametric aircraft structural models

AIAA Scitech Forum, 2019

作者： Joe, John Gandhi, Viraj Dannenhoffer, John F. Dalir, Hamid Advanced Composite Structures Engineering Laboratory Department of Mechanical and Energy Engineering Purdue School of Engineering and Technology IUPUI IndianapolisIN46202 United States Aerospace Computational Methods Laboratory Department of Mechanical and Energy Engineering Syracuse University SyracuseNY13244 United States

ISBN: (数字)9781624105784

ISBN: (纸本)9781624105784

Within the aerospace design, analysis and optimization community, there is an increasing demand for automatic generation of parametric feature tree (build recipe) attributed multidisciplinary models. Currently, this is mainly done by creating separate models for different disciplines such as mid-surface model for aeroelasticity, outer-mold line for aerodynamics and CFD, and built-up element model for structural analysis. Since all of these models are built independently, any changes in design parameters require updates on all the models which is inefficient, time-consuming and prone to deficiencies. Here a browser-based system, called the engineering Sketch Pad (ESP), is used. It provides the user with the ability to interact with a configuration by building and/or modifying the design parameters and feature tree that define the configuration. ESP is based an open-source constructive solid modeler, named OpenCSM, which is built upon the OpenCASCADE geometry kernel and the EGADS geometry generation system. The use of OpenCSM as part of the AFRL’s CAPS project on computational Aircraft Prototype Syntheses for automatic commercial and fighter jet models is demonstrated. The rapid generation of parametric aircraft structural models proposed and developed in this work will benefit the aerospace industry with coming up with efficient, fast and robust multidisciplinary design standardization of aircraft structures. © 2019, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.

关键词： Aircraft manufacture

Physics-based modeling and predictive simulation of powder bed fusion additive manufacturing across length scales

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GAMM Mitteilungen 2021年第3期44卷 e202100014-e202100014页

作者： Meier, Christoph Fuchs, Sebastian L. Much, Nils Nitzler, Jonas Penny, Ryan W. Praegla, Patrick M. Proell, Sebastian D. Sun, Yushen Weissbach, Reimar Schreter, Magdalena Hodge, Neil E. John Hart, A. Wall, Wolfgang A. Institute for Computational Mechanics Technical University of Munich Munich Germany Institute for Continuum and Material Mechanics Hamburg University of Technology Hamburg Germany Department of Mechanical Engineering Massachusetts Institute of Technology Cambridge United States Unit of Strength of Materials and Structural Analysis University of Innsbruck Innsbruck Austria Methods Development Group Lawrence Livermore National Laboratory Livermore United States

Powder bed fusion additive manufacturing (PBFAM) of metals has the potential to enable new paradigms of product design, manufacturing and supply chains while accelerating the realization of new technologies in the medical, aerospace, and other industries. Currently, wider adoption of PBFAM is held back by difficulty in part qualification, high production costs and low production rates, as extensive process tuning, post-processing, and inspection are required before a final part can be produced and deployed. Physics-based modeling and predictive simulation of PBFAM offers the potential to advance fundamental understanding of physical mechanisms that initiate process instabilities and cause defects. In turn, these insights can help link process and feedstock parameters with resulting part and material properties, thereby predicting optimal processing conditions and inspiring the development of improved processing hardware, strategies and materials. This work presents recent developments of our research team in the modeling of metal PBFAM processes spanning length scales, namely mesoscale powder modeling, mesoscale melt pool modeling, macroscale thermo-solid-mechanical modeling and microstructure modeling. Ongoing work in experimental validation of these models is also summarized. In conclusion, we discuss the interplay of these individual submodels within an integrated overall modeling approach, along with future research directions. © 2021 The Authors. GAMM - Mitteilungen published by Wiley-VCH GmbH.

关键词： Microstructure

Observation of non-superconducting phase changes in LuH2±xNy

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arXiv 2023年

作者： Xing, Xiangzhuo Wang, Chao Yu, Linchao Xu, Jie Zhang, Chutong Zhang, Mengge Huang, Song Zhang, Xiaoran Yang, Bingchao Chen, Xin Zhang, Yongsheng Guo, Jian-Gang Shi, Zhixiang Ma, Yanming Chen, Changfeng Liu, Xiaobing School of Physics and Physical Engineering Qufu Normal University Qufu273165 China Advanced Research Institute of Multidisciplinary Sciences Qufu Normal University Qufu273165 China Beijing National Laboratory for Condensed Matter Physics Institute of Physics Chinese Academy of Sciences Beijing100190 China School of Physics Southeast University Nanjing211189 China Innovation Center for Computational Methods & Software College of Physics Jilin University Changchun130012 China State Key Laboratory of Superhard Materials Jilin University Changchun130012 China International Center of Future Science Jilin University Changchun130012 China Department of Physics and Astronomy University of Nevada Las VegasNV89154 United States

The recent report of near-ambient superconductivity in nitrogen doped lutetium hydride1 has triggered a worldwide fanaticism and raised major questions about the latest claims. An intriguing phenomenon of color changes in pressurized samples from blue to pink to red was observed and correlated with the claimed superconducting transition, but the origin and underlying physics of these color changes have yet to be elucidated2-7. Here we report synthesis and characterization of high-purity nitrogen doped lutetium hydride LuH2±xNy with the same structure and composition as in the main phase of near-ambient superconductor1. We find a new purple phase of LuH2±xNy between blue and pink phase, and reveal that the sample color changes likely stem from pressure-driven redistribution of nitrogen and its interaction with the LuH2 framework. No superconducting transition is found in all blue, purple, pink and red phases at temperatures 1.8-300 K and pressures 0-30 GPa. Instead, we identify a notable temperature-induced resistance anomaly of structural and/or electronic origin in LuH2±xNy, which is most pronounced in the pink phase and may have been erroneously interpreted as a sign of superconducting transition. This work establishes key benchmarks for nitrogen doped lutetium hydrides, allowing an in-depth understanding of the novel pressure-induced phase changes. © 2023, CC BY.

关键词： Electric resistance