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Order and information in the patterns of spinning magnetic micro-disks at the air-water interface

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arXiv 2019年

作者： Wang, Wendong Gardi, Gaurav Malgaretti, Paolo Kishore, Vimal Koens, Lyndon Son, Donghoon Gilbert, Hunter Wu, Zongyuan Harwani, Palak Lauga, Eric Holm, Christian Sitti, Metin Physical Intelligence Department Max Planck Institute for Intelligent Systems Stuttgart70569 Germany University of Michigan Shanghai Jiao Tong University Joint Institute Shanghai Jiao Tong University Dong Chuan Road 800 Minhang Shanghai 200240 China Forschungszentrum Jülich Germany Department of Physics Banaras Hindu University Varanasi221005 India Department of Mathematics and Statistics Macquarie University Australia School of Mechanical Engineering Pusan National University Busan46241 Korea Republic of Department of Mechanical and Industrial Engineering Louisiana State University United States Department of Electronics and Electrical Communication Engineering Indian Institute of Technology Kharagpur India Department of Applied Mathematics and Theoretical Physics University of Cambridge United Kingdom Institute for Computational Physics University of Stuttgart Allmandring 3 Stuttgart70569 Germany School of Medicine and School of Engineering Koç University Istanbul34450 Turkey Institute for Biomedical Engineering ETH Zurich Zurich8092 Switzerland

The application of the Shannon entropy to study the relationship between information and structures has yielded insights into molecular and material systems. However, the difficulty in directly observing and manipulating atoms and molecules hampers the ability of these systems to serve as model systems for further exploring the links between information and structures. Here, we use, as a model experimental system, hundreds of spinning magnetic micro-disks self-organizing at the air-water interface to generate various spatiotemporal patterns with varying degrees of orders. Using the neighbor distance as the information-bearing variable, we demonstrate the links among information, structure, and interactions. Most importantly, we establish a direct link between information and structure without using explicit knowledge of interactions. Finally, we show that the Shannon entropy by neighbor distances is a powerful observable in characterizing structural changes. Our findings are relevant for analyzing natural self-organizing systems and for designing collective robots. Copyright © 2019, The Authors. All rights reserved.

关键词： Air

Constructing Impactful Machine Learning Research for Astronomy: Best Practices for Researchers and Reviewers

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arXiv 2023年

作者： Huppenkothen, Daniela Ntampaka, Michelle Ho, Matthew Fouesneau, Morgan Nord, Brian Peek, J.E.G. Walmsley, Mike Wu, John F. Avestruz, C. Buck, Tobias Brescia, Massimo Finkbeiner, Douglas P. Goulding, Andy D. Kacprzak, T. Melchior, Peter Pasquato, Mario Ramachandra, Nesar Ting, Yuan-Sen van de Ven, Glenn Villar, Soledad Villar, V.A. Zinger, Elad SRON Netherlands Institute for Space Research Niels Bohrweg 4 Leiden2333CA Netherlands Anton Pannekoek Institute for Astronomy University of Amsterdam Science Park 904 Amsterdam1098 XH Netherlands Space Telescope Science Institute BaltimoreMD21218 United States Department of Physics & Astronomy Johns Hopkins University BaltimoreMD21218 United States UMR 7095 98 bis bd Arago ParisF-75014 France Königstuhl 17 HeidelbergD-69117 Germany Fermi National Accelerator Laboratory P. O. Box 500 BataviaIL60510 United States Kavli Institute for Cosmological Physics University of Chicago ChicagoIL60637 United States Department of Astronomy and Astrophysics University of Chicago ChicagoIL60637 United States Jodrell Bank Centre for Astrophysics Department of Physics & Astronomy University of Manchester ManchesterM13 9PL United Kingdom Dunlap Institute for Astronomy & Astrophysics University of Toronto 50 St. George Street TorontoONM5S 3H4 Canada Leinweber Center for Theoretical Physics University of Michigan Ann ArborMI48109 United States Department of Physics University of Michigan Ann ArborMI48109 United States Universität Heidelberg Interdisziplinäres Zentrum für Wissenschaftliches Rechnen Im Neuenheimer Feld 205 Heidelberg69120 Germany Universität Heidelberg Zentrum für Astronomie Institut für Theoretische Astrophysik Albert-Ueberle-Straße 2 Heidelberg69120 Germany Department of Physics "E. Pancini " University Federico II of Napoli Via Cinthia 21 NapoliI-80126 Italy INAF Astronomical Observatory of Capodimonte Salita Moiariello 16 NapoliI-80131 Italy Department of Physics Harvard University 17 Oxford St. CambridgeMA02138 United States Harvard-Smithsonian Center for Astrophysics 60 Garden St. CambridgeMA02138 United States Department of Astrophysical Sciences Princeton University PrincetonNJ08544 United States Swiss Data Science Center Paul Scherrer Institute Villigen5303 Switzerland Center for Statistics & Machine Learn

Machine learning has rapidly become a tool of choice for the astronomical community. It is being applied across a wide range of wavelengths and problems, from the classification of transients to neural network emulators of cosmological simulations, and is shifting paradigms about how we generate and report scientific results. At the same time, this class of method comes with its own set of best practices, challenges, and drawbacks, which, at present, are often reported on incompletely in the astrophysical literature. With this paper, we aim to provide a primer to the astronomical community, including authors, reviewers, and editors, on how to implement machine learning models and report their results in a way that ensures the accuracy of the results, reproducibility of the findings, and usefulness of the method. Copyright © 2023, The Authors. All rights reserved.

关键词： Machine learning

Parallel assimilation of observed data in the hydrodynamic model of the ocean circulation

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Moscow University computational mathematics and Cybernetics 2017年第2期41卷 58-63页

作者： Belyaev, K.P. Kuleshov, A.A. Smirnov, I.N. Tanajura, C.A.S. Shirshov Institute of Oceanology Russian Academy of Sciences Moscow 117917 Russian Federation Keldysh Institute of Applied Mathematics Russian Academy of Sciences Moscow 125047 Russian Federation Department of Computational Mathematics and Cybernetics Moscow State University Moscow 119991 Russian Federation Federal University of Bahia Salvador 40010-010 Brazil

The parallel use of the Kalman ensemble filter technique for assimilating data from observations in theHYCOMmodel of theWorldOcean is described. Data from satellite observations of the sea’s surface temperature and the sea’s surface height are assimilated both separately and conjointly. Numerical experiments on correcting model calculations using data from observations are performed. The results from the corrections are compared to model calculations without assimilation. The effectiveness of the employed parallelization algorithm is confirmed. © 2017, Allerton Press, Inc.

关键词： assimilation of observational data numerical experiments ocean circulation model parallel calculations

Anisotropic and mutable magnetization in Kondo lattice CeSb2

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Chinese Physics B 2017年第6期26卷 319-323页

作者：张云朱燮刚胡丙锋谭世勇谢东华冯卫刘琴张文刘瑜宋海峰罗丽珠张政军赖新春 Science and Technology on Surface Physics and Chemistry Laboratory Department of Engineering Physics Tsinghua University Key Laboratory of Neutron Physics Institute of Nuclear Physics and ChemistryChina Academy of Engineering Physics Laboratory of Computational Physics Institute of Applied Physics and Computational Mathematics Software Center for High Performance Numerical Simulation China Academy of Engineering Physics Key Laboratory of Advanced Materials (MOE) School of Materials Science and EngineeringTsinghua University

We have systematically studied the behaviors of the resistivity and magnetization of CeSb2 single crystals as a function of temperature and external field. Four anomalies in the resistivity/magnetization-versus-temperature curves are observed at low magnetic field. They are located at 15.5 K, 11.5 K, 9.5 K, and 6.5 K, corresponding to the paramagnetic–magnetically ordered state（MO）, MO-antiferromagnetic（AFM）, AFM–AFM, and AFM–ferromagnetic（FM） transitions, *** anomaly at 9.5 K is only visible with H‖[010] by magnetic susceptibility measurements, indicating that the AFM–AFM transition only happens along [010] direction in ab-plane. The four magnetic transitions are strongly suppressed by high external field. Finally, the field-temperature phase diagrams of CeSb2 with different orientations of the applied field in ab-plane are constructed and indicate the highly anisotropic nature of the magnetization of CeSb2.

关键词： CeSb2 electronic properties magnetic properties

Two-dimensional ferromagnetic-ferroelectric multiferroics in violation of the d0 rule

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arXiv 2019年

作者： Tan, Hengxin Li, Menglei Liu, Haitao Liu, Zhirong Li, Yuanchang Duan, Wenhui State Key Laboratory of Low-Dimensional Quantum Physics and Collaborative Innovation Center of Quantum Matter Department of Physics Tsinghua University Beijing100084 China Department of Physics Capital Normal University Beijing100084 China Institute of Applied Physics and Computational Mathematics PO Box 8009 Beijing100088 China Center for Nanochemistry College of Chemistry and Molecular Engineering Peking University Beijing100871 China Advanced Research Institute of Multidisciplinary Science Beijing Institute of Technology Beijing100081 China Institute for Advanced Study Tsinghua University Beijing100084 China

Contribution of d-electron to ferroelectricity of type-II multiferroics causes strong magneto-electric coupling and distinguishes them from the conventional type-I multiferroics. However, their therein polarization is too small because the ferroelectricity is merely a derivative from the magnetic order. Here we report a new class of multiferroic materials, monolayer VOX2 (X = Cl, Br, and I), which combine the advantages of type-I and type-II multiferroics. Both ferroelectricity and magnetism arise from the same V cation, where the filled d-orbital is perpendicular to an a priori ferroelectric polarization and thus poses no hindrance to ferroelectricity, indicating a violation of the usual d0 rule. This makes the combination of large polarizations and strong magneto-electric coupling possible. Our findings not only add new ferromagnetic-ferroelectric multiferroics, but also point to a unique mechanism to engineer multiferroics. Copyright © 2019, The Authors. All rights reserved.

关键词： Ferroelectricity

Collision cross sections of N2 by H+ impact at keV energies within time-dependent density-functional theory

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Physical Review A 2018年第3期97卷 032706-032706页

作者： W. Yu C.-Z. Gao Y. Zhang F. S. Zhang R. Hutton Y. Zou B. Wei Institute of Modern Physics Department of Nuclear Science and Technology Fudan University Shanghai 200433 China Key Laboratory of Nuclear Physics and Ion-beam Application (MOE) Fudan University Shanghai 200433 China Institute of Applied Physics and Computational Mathematics Beijing 100088 China College of Nuclear Science and Technology Beijing Normal University Beijing 100875 China

We calculate electron capture and ionization cross sections of N2 impacted by the H+ projectile at keV energies. To this end, we employ the time-dependent density-functional theory coupled nonadiabatically to molecular dynamics. To avoid the explicit treatment of the complex density matrix in the calculation of cross sections, we propose an approximate method based on the assumption of constant ionization rate over the period of the projectile passing the absorbing boundary. Our results agree reasonably well with experimental data and semi-empirical results within the measurement uncertainties in the considered energy range. The discrepancies are mainly attributed to the inadequate description of exchange-correlation functional and the crude approximation for constant ionization rate. Although the present approach does not predict the experiments quantitatively for collision energies below 10 keV, it is still helpful to calculate total cross sections of ion-molecule collisions within a certain energy range.

关键词： Atomic & molecular collisions Electronic excitation & ionization

Reactive task and motion planning for robust whole-body dynamic locomotion in constrained environments

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arXiv 2018年

作者： Zhao, Ye Li, Yinan Sentis, Luis Topcu, Ufuk Liu, Jun George W. Woodruff School Of Mechanical Engineering Georgia Tech United States Department Of Applied Mathematics University Of Waterloo Canada Department Of Aerospace Engineering And Engineering Mechanics UT Austin United States Institute For Computational Engineering And Sciences UT Austin United States

Contact-based decision and planning methods are becoming increasingly important to endow higher levels of autonomy for legged robots. Formal synthesis methods derived from symbolic systems have great potential for reasoning about high-level locomotion decisions and achieving complex maneuvering behaviors with correctness guarantees. This study takes a first step toward formally devising an architecture composed of task planning and control of whole-body dynamic locomotion behaviors in constrained and dynamically changing environments. At the high level, we formulate a two-player temporal logic game between the multi-limb locomotion planner and its dynamic environment to synthesize a winning strategy that delivers symbolic locomotion actions. These locomotion actions satisfy the desired high-level task specifications expressed in a fragment of temporal logic. Those actions are sent to a robust finite transition system that synthesizes a locomotion controller that fulfills state reachability constraints. This controller is further executed via a low-level motion planner that generates feasible locomotion trajectories. We construct a set of dynamic locomotion models for legged robots to serve as a template library for handling diverse environmental *** devise a replanning strategy that takes into consideration sudden environmental changes or large state disturbances to increase the robustness of the resulting locomotion behaviors. We formally prove the correctness of the layered locomotion framework guaranteeing a robust implementation by the motion planning layer. Simulations of reactive locomotion behaviors in diverse environments indicate that our framework has the potential to serve as a theoretical foundation for intelligent locomotion behaviors. Copyright © 2018, The Authors. All rights reserved.

关键词： Motion planning

First Sagittarius A* Event Horizon Telescope Results. V. Testing Astrophysical Models of the Galactic Center Black Hole

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arXiv 2023年

作者： Akiyama, Kazunori Alberdi, Antxon Alef, Walter Algaba, Juan Carlos Anantua, Richard Asada, Keiichi Azulay, Rebecca Bach, Uwe Baczko, Anne-Kathrin Ball, David Baloković, Mislav Barrett, John Bauböck, Michi Benson, Bradford A. Bintley, Dan Blackburn, Lindy Blundell, Raymond Bouman, Katherine L. Bower, Geoffrey C. Boyce, Hope Bremer, Michael Brinkerink, Christiaan D. Brissenden, Roger Britzen, Silke Broderick, Avery E. Broguiere, Dominique Bronzwaer, Thomas Bustamante, Sandra Byun, Do-Young Carlstrom, John E. Ceccobello, Chiara Chael, Andrew Chan, Chi-Kwan Chatterjee, Koushik Chatterjee, Shami Chen, Ming-Tang Chen, Yongjun Cheng, Xiaopeng Cho, Ilje Christian, Pierre Conroy, Nicholas S. Conway, John E. Cordes, James M. Crawford, Thomas M. Crew, Geoffrey B. Cruz-Osorio, Alejandro Cui, Yuzhu Davelaar, Jordy De Laurentis, Mariafelicia Deane, Roger Dempsey, Jessica Desvignes, Gregory Dexter, Jason Dhruv, Vedant Doeleman, Sheperd S. Dougal, Sean Dzib, Sergio A. Eatough, Ralph P. Emami, Razieh Falcke, Heino Farah, Joseph Fish, Vincent L. Fomalont, Ed. Ford, H. Alyson Fraga-Encinas, Raquel Freeman, William T. Friberg, Per Fromm, Christian M. Fuentes, Antonio Galison, Peter Gammie, Charles F. García, Roberto Gentaz, Olivier Georgiev, Boris Goddi, Ciriaco Gold, Roman Gómez-Ruiz, Arturo I. Gómez, José L. Gu, Minfeng Gurwell, Mark Hada, Kazuhiro Haggard, Daryl Haworth, Kari Hecht, Michael H. Hesper, Ronald Heumann, Dirk Ho, Luis C. Ho, Paul Honma, Mareki Huang, Chih-Wei L. Huang, Lei Hughes, David H. Ikeda, Shiro Impellizzeri, C.M. Violette Inoue, Makoto Issaoun, Sara James, David J. Jannuzi, Buell T. Janssen, Michael Jeter, Britton Jiang, Wu Jiménez-Rosales, Alejandra Johnson, Michael D. Jorstad, Svetlana Joshi, Abhishek V. Jung, Taehyun Karami, Mansour Karuppusamy, Ramesh Kawashima, Tomohisa Keating, Garrett K. Kettenis, Mark Kim, Dong-Jin Kim, Jae-Young Kim, Jongsoo Kim, Junhan Kino, Motoki Koay, Jun Yi Kocherlakota, Prashant Kofuji, Yutaro Koch, Patrick M. Koyama, Shoko Kramer, Carsten Kramer, Michael Krichbaum, Thomas P. K Massachusetts Institute of Technology Haystack Observatory 99 Millstone Road WestfordMA01886 United States National Astronomical Observatory of Japan 2-21-1 Osawa Mitaka Tokyo181-8588 Japan Black Hole Initiative Harvard University 20 Garden Street CambridgeMA02138 United States Instituto de Astrofísica de Andalucía-CSIC Glorieta de la Astronomía s/n GranadaE-18008 Spain Max-Planck-Institut für Radioastronomie Auf dem Hügel 69 BonnD-53121 Germany Department of Physics Faculty of Science Universiti Malaya Kuala Lumpur50603 Malaysia Center for Astrophysics Harvard & Smithsonian 60 Garden Street CambridgeMA02138 United States Department of Physics & Astronomy The University of Texas at San Antonio One UTSA Circle San AntonioTX78249 United States Institute of Astronomy and Astrophysics Academia Sinica 11F of Astronomy-Mathematics Building AS/NTU No. 1 Sec. 4 Roosevelt Rd Taipei10617 Taiwan Departament d’Astronomia i Astrofísica Universitat de València C. Dr. Moliner 50 Burjassot ValènciaE-46100 Spain Observatori Astronòmic Universitat de València C. Catedrático José Beltrán 2 Paterna ValènciaE-46980 Spain Steward Observatory Department of Astronomy University of Arizona 933 N. Cherry Ave. TucsonAZ85721 United States Yale Center for Astronomy & Astrophysics Yale University 52 Hillhouse Avenue New HavenCT06511 United States Department of Physics University of Illinois 1110 West Green Street UrbanaIL61801 United States Fermi National Accelerator Laboratory MS209 P.O. Box 500 BataviaIL60510 United States Department of Astronomy and Astrophysics University of Chicago 5640 South Ellis Avenue ChicagoIL60637 United States East Asian Observatory 660 N. A’ohoku Place HiloHI96720 United States 660 N. A’ohoku Place HiloHI96720 United States California Institute of Technology 1200 East California Boulevard PasadenaCA91125 United States Institute of Astronomy and Astrophysics Academia Sinica 645 N. A’ohoku Place HiloHI96

In this paper, we provide a first physical interpretation for the Event Horizon Telescope (EHT)’s 2017 observations of Sgr A∗. Our main approach is to compare resolved EHT data at 230 GHz and unresolved non-EHT observations from radio to X-ray wavelengths to predictions from a library of models based on time-dependent general relativistic magnetohydrodynamics (GRMHD) simulations, including aligned, tilted, and stellar wind-fed simulations;radiative transfer is performed assuming both thermal and non-thermal electron distribution functions. We test the models against 11 constraints drawn from EHT 230 GHz data and observations at 86 GHz, 2.2 µm, and in the X-ray. All models fail at least one constraint. Light curve variability provides a particularly severe constraint, failing nearly all strongly magnetized (MAD) models and a large fraction of weakly magnetized (SANE) models. A number of models fail only the variability constraints. We identify a promising cluster of these models, which are MAD and have inclination i ≤ 30°. They have accretion rate (5.2–9.5) × 10−9M☉ yr−1, bolometric luminosity (6.8–9.2) × 1035 erg s−1, and outflow power (1.3–4.8) × 1038 erg s−1. We also find that: all models with i ≥ 70° fail at least two constraints, as do all models with equal ion and electron temperature;exploratory, non-thermal model sets tend to have higher 2.2 µm flux density;the population of cold electrons is limited by X-ray constraints due to the risk of bremsstrahlung overproduction. Finally we discuss physical and numerical limitations of the models, highlighting the possible importance of kinetic effects and duration of the simulations. © 2023, CC BY.

关键词： Galaxies

DtN-based mixed-dimensional coupling in aerospace structures 57

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DtN-based mixed-dimensional coupling in aerospace structures

57th Israel Annual Conference on Aerospace Sciences, IACAS 2017

作者： Ofir, Yoav Rabinovich, Daniel Givoli, Dan Technion - Israel Institute of Technology Interdepartmental Program of Applied Mathematics Haifa3200003 Israel Technion - Israel Institute of Technology Department of Aerospace Engineering Haifa3200003 Israel

A new computational approach for the mixed-dimensional modeling of time-harmonic waves in elastic aerospace structures is proposed. A two-dimensional (2D) structure is considered, which includes a part that is assumed to behave in a one-dimensional (1D) way. The 2D and 1D structural regions are discretized by using 2D and 1D Finite Element (FE) formulations. The hybrid model, if designed properly, is much more efficient than the standard 2D model taken for the entire problem. One important issue related to such hybrid 2D-1D models is the way the 2D-1D coupling is done, and the coupling error generated. Here, three closely-related coupling methods are considered - the DtN method, the CML method and an Iterative DtN technique. They are all based on the Dirichlet-to-Neumann (DtN) map associated with the 1D problem, on the interface. Direct application of these three methods results in low accuracy, as a recent study shows. Therefore, these methods are used here in conjunction with a Boundary Stress Recovery (BSR) technique, originally proposed by Hughes, which provides the same order of accuracy for the stress as for the primary variable. The performance of the three methods is demonstrated and they are compared via numerical examples. Conclusions are drawn on their relative merit.

关键词： One dimensional