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Accurate deep potential model for the Al-Cu-Mg alloy in the full concentration space

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arXiv 2020年

作者： Jiang, Wanrun Zhang, Yuzhi Zhang, Linfeng Wang, Han Songshan Lake Materials Laboratory DongguanGuangdong523808 China Institute of Physics Chinese Academy of Sciences Beijing100190 China Beijing Institute of Big Data Research Beijing100871 China Yuanpei College Peking University Beijing100871 China Program in Applied and Computational Mathematics Princeton University PrincetonNJ08544 United States Laboratory of Computational Physics Institute of Applied Physics and Computational Mathematics Huayuan Road 6 Beijing100088 China

Combining first-principles accuracy and empirical-potential efficiency for the description of the potential energy surface (PES) is the philosopher's stone for unraveling the nature of matter via atomistic simulation. This has been particularly challenging for multi-component alloy systems due to the complex and non-linear nature of the associated PES. In this work, we develop an accurate PES model for the Al-Cu-Mg system by employing Deep Potential (DP), a neural network based representation of the PES, and DP Generator (DP-GEN), a concurrent-learning scheme that generates a compact set of ab initio data for training. The resulting DP model gives predictions consistent with first-principles calculations for various binary and ternary systems on their fundamental energetic and mechanical properties, including formation energy, equilibrium volume, equation of state, interstitial energy, vacancy and surface formation energy, as well as elastic moduli. Extensive benchmark shows that the DP model is ready and will be useful for atomistic modeling of the Al-Cu-Mg system within the full range of concentration. Copyright © 2020, The Authors. All rights reserved.

关键词： Copper alloys

Phase equilibrium of water with hexagonal and cubic ice using the SCAN functional

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arXiv 2021年

作者： Piaggi, Pablo Miguel Panagiotopoulos, Athanassios Z. Debenedetti, Pablo G. Car, Roberto Department of Chemistry Princeton University PrincetonNJ08544 United States Department of Chemical and Biological Engineering Princeton University PrincetonNJ08544 United States Princeton Institute for the Science and Technology of Materials Princeton University PrincetonNJ08544 United States Department of Physics Princeton University PrincetonNJ08544 United States Program in Applied and Computational Mathematics Princeton University PrincetonNJ08544 United States

Machine learning models are rapidly becoming widely used to simulate complex physicochemical phenomena with ab initio accuracy. Here, we use one such model as well as direct density functional theory (DFT) calculations to investigate the phase equilibrium of water, hexagonal ice (Ih), and cubic ice (Ic), with an eye towards studying ice nucleation. The machine learning model is based on deep neural networks and has been trained on DFT data obtained using the SCAN exchange and correlation functional. We use this model to drive enhanced sampling simulations aimed at calculating a number of complex properties that are out of reach of DFT-driven simulations and then employ an appropriate reweighting procedure to compute the corresponding properties for the SCAN functional. This approach allows us to calculate the melting temperature of both ice polymorphs, the driving force for nucleation, the heat of fusion, the densities at the melting temperature, the relative stability of ice Ih and Ic, and other properties. We find a correct qualitative prediction of all properties of interest. In some cases, quantitative agreement with experiment is better than for state-of-the-art semiempirical potentials for water. Our results also show that SCAN correctly predicts that ice Ih is more stable than ice Ic. Copyright © 2021, The Authors. All rights reserved.

关键词： Ice

Hyperuniformity of generalized random organization models

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Physical Review E 2019年第2期99卷 022115-022115页

作者： Zheng Ma Salvatore Torquato Department of Chemistry Department of Physics Princeton Institute for the Science and Technology of Materials and Program in Applied and Computational Mathematics Princeton University Princeton New Jersey 08544 USA

Studies of random organization models of monodisperse (i.e., identical) spherical particles have shown that a hyperuniform state is achievable when the system goes through an absorbing phase transition to a critical state. Here we investigate to what extent hyperuniformity is preserved when the model is generalized to particles with a size distribution and/or nonspherical shapes. We begin by examining binary disks in two dimensions and demonstrate that their critical states are hyperuniform as two-phase media, but not hyperuniform nor multihyperuniform as point patterns formed by the particle centroids. We further confirm the generality of our findings by studying particles with a continuous size distribution. Finally, to study the effect of rotational degrees of freedom, we extend our model to noncircular particles, namely, hard rectangles with various aspect ratios, including the hard-needle limit. Although these systems exhibit only short-range orientational order, hyperuniformity is still preserved. Our analysis reveals that the redistribution of the “mass” of the particles rather than the particle centroids is central to this dynamical process. The consideration of the “active volume fraction” of generalized random organization models may help to resolve which universality class they belong to and hence may lead to a deeper theoretical understanding of absorbing-state models. Our results suggest that general particle systems subject to random organization can be a robust way to fabricate a wide class of hyperuniform states of matter by tuning the structures via different particle-size and -shape distributions. This in turn potentially enables the creation of multifunctional hyperuniform materials with desirable optical, transport, and mechanical properties.

关键词： Classical statistical mechanics

Isostables for stochastic oscillators

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arXiv 2021年

作者： Pérez-Cervera, Alberto Lindner, Benjamin Thomas, Peter J. National Research University Higher School of Economics Moscow Russia Instituto de Matemática Interdisciplinar Universidad Complutense de Madrid Madrid28040 Spain Bernstein Center for Computational Neuroscience Berlin Berlin Germany Department of Physics Humboldt University Berlin Germany Department of Mathematics Applied Mathematics and Statistics Case Western Reserve University ClevelandOH44106 United States

Thomas and Lindner (2014, Phys. Rev. Lett.) defined an asymptotic phase for stochastic oscillators as the angle in the complex plane made by the eigenfunction, having complex eigenvalue with least negative real part, of the backward Kolmogorov (or stochastic Koopman) operator. We complete the phase-amplitude description of noisy oscillators by defining the stochastic isostable coordinate as the eigenfunction with the least negative nontrivial real eigenvalue. Our results suggest a framework for stochastic limit cycle dynamics that encompasses noise-induced oscillations. Copyright © 2021, The Authors. All rights reserved.

关键词： Eigenvalues and eigenfunctions

Understanding viscoelastic flow instabilities: Oldroyd-B and beyond

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arXiv 2022年

作者： Sánchez, Hugo A. Castillo Jovanović, Mihailo R. Kumar, Satish Morozov, Alexander Shankar, V. Subramanian, Ganesh Wilson, Helen J. Department Of Applied Mathematics And Statistics Institute Of Mathematics And Computational Sciences University Of Sao Paulo Brazil Ming Hsieh Department Of Electrical And Computer Engineering University Of Southern California Los AngelesCA90089 United States Department Of Chemical Engineering And Materials Science University Of Minnesota MinneapolisMN55455 United States SUPA School Of Physics And Astronomy The University Of Edinburgh EdinburghEH9 3FD United Kingdom Department Of Chemical Engineering Indian Institute Of Technology Kanpur208016 India Engineering Mechanics Unit Jawaharlal Nehru Center For Advanced Scientific Research Bangalore560064 India Mathematics Department University College London Gower Street LondonWC1E 6BT United Kingdom

The Oldroyd-B model has been used extensively to predict a host of instabilities in shearing flows of viscoelastic fluids, often realized experimentally using polymer solutions. The present review, written on the occasion of the birth centenary of James Oldroyd, provides an overview of instabilities found across major classes of shearing flows. These comprise (i) the canonical rectilinear shearing flows including plane Couette, plane and pipe Poiseuille flows;(ii) viscometric shearing flows with curved streamlines such as those in the TaylorCouette, cone-and-plate and parallel-plate geometries;(iii) non-viscometric shearing flows with an underlying extensional flow topology such as the flow in a cross-slot device;and (iv) multilayer shearing flows. While the underlying focus in all these cases is on results obtained using the Oldroyd-B model, we also discuss their relation to the actual instability, and as to how the shortcomings of the Oldroyd-B model may be overcome by the use of more realistic constitutive models. All the three commonly used tools of stability analysis, viz., modal linear stability, nonmodal stability, and weakly nonlinear stability analyses are discussed, with supporting evidence from experiments and numerical simulations as appropriate. Despite only accounting for a shear-rate-independent viscosity and first normal stress coefficient, the Oldroyd-B model is able to qualitatively predict the majority of instabilities in the aforementioned shearing flows. The review also highlights, where appropriate, open questions in the area of viscoelastic stability. © 2022, CC BY.

关键词： Stability

Free-space realization of tunable pin-like optical vortex beams

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arXiv 2021年

作者： Bongiovanni, Domenico Li, Denghui Goutsoulas, Mihalis Wu, Hao Hu, Yi Song, Daohong Morandotti, Roberto Efremidis, Nikolaos K. Chen, Zhigang Moe Key Laboratory of Weak-Light Nonlinear Photonics Teda Applied Physics Institute and School of Physics Nankai University Tianjin300457 China INRS-EMT 1650 Blvd. Lionel-Boulet VarennesQCJ3X 1S2 Canada Department of Applied Mathematics University of Crete Heraklion Crete71409 Greece Institute of Fundamental and Frontier Sciences University of Electronic Science and Technology of China Chengdu610054 China Institute of Applied and Computational Mathematics Forth Heraklion Crete70013 Greece Department of Physics and Astronomy San Francisco State University San FranciscoCA94132 United States

We demonstrate, both analytically and experimentally, free-space pin-like optical vortex beams (POVBs). Such angular-momentum-carrying beams feature tunable peak intensity and undergo robust anti-diffracting propagation, realized by judiciously modulating both the amplitude and the phase profile of a standard laser beam. Specifically, they are generated by superimposing a radially-symmetric power-law phase on a helical phase structure, which allows the inclusion of an orbital angular momentum term to the POVBs. During propagation in free-space, these POVBs initially exhibit autofocusing dynamics, and subsequently, their amplitude patterns morph into a high-order Bessel-like profile characterized by a hollow-core and an annular main-lobe with a constant or tunable width during propagation. In contrast with numerous previous endeavors on Bessel beams, our work represents the first demonstration of long-distance free-space generation of optical vortex "pins", with their peak intensity evolution controlled by the impressed amplitude structure. Both the Poynting vectors and the optical radiation forces associated with these beams are also numerically analyzed, revealing novel properties that may be useful for a wide range of applications. © 2021, CC BY.

关键词： Laser beams

The photometric variability of massive stars due to gravity waves excited by core convection

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arXiv 2023年

作者： Anders, Evan H. Lecoanet, Daniel Cantiello, Matteo Burns, Keaton J. Hyatt, Benjamin A. Kaufman, Emma Townsend, Richard H.D. Brown, Benjamin P. Vasil, Geoffrey M. Oishi, Jeffrey S. Jermyn, Adam S. Northwestern University 1800 Sherman Ave EvanstonIL60201 United States Department of Engineering Sciences & Applied Mathematics Northwestern University 2145 Sheridan Road EvanstonIL60208 United States Center for Computational Astrophysics Flatiron Institute 160 Fifth Avenue New YorkNY10010 United States Department of Astrophysical Sciences Princeton University 4 Ivy Lane PrincetonNJ08544 United States Department of Mathematics Massachusetts Institute of Technology 77 Massachusetts Avenue CambridgeMA02139 United States Department of Physics & Astronomy Northwestern University 2145 Sheridan Road EvanstonIL60208 United States Department of Astronomy University of Wisconsin-Madison 475 N. Charter Street MadisonWI53706 United States Department of Astrophysical & Planetary Sciences University of Colorado Boulder 391 UCB BoulderCO80309 United States School of Mathematics University of Edinburgh James Clerk Maxwell Building EdinburghEH9 3FD United Kingdom Department of Physics & Astronomy Bates College 2 Andrews Road LewistonME04240 United States

Massive stars die in catastrophic explosions, which seed the interstellar medium with heavy elements and produce neutron stars and black holes. Predictions of the explosion’s character and the remnant mass depend on models of the star’s evolutionary history. Models of massive star interiors can be empirically constrained by asteroseismic observations of gravity wave oscillations. Recent photometric observations reveal a ubiquitous red noise signal on massive main sequence stars;a hypothesized source of this noise is gravity waves driven by core convection. We present the first 3D simulations of massive star convection extending from the star’s center to near its surface, with realistic stellar luminosities. Using these simulations, we make the first prediction of photometric variability due to convectively-driven gravity waves at the surfaces of massive stars, and find that gravity waves produce photometric variability of a lower amplitude and lower characteristic frequency than the observed red noise. We infer that the photometric signal of gravity waves excited by core convection is below the noise limit of current observations, so the red noise must be generated by an alternative process. © 2023, CC BY.

关键词： Gravity waves

Bivariate collocation for computing R0in epidemic models with two structures

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arXiv 2021年

作者： Breda, Dimitri De Reggi, Simone Scarabel, Francesca Vermiglio, Rossana Wu, Jianhong CDLab-Computational Dynamics Laboratory Department of Mathematics Computer Science and Physics University of Udine Via delle Scienze 206 33100 Italy LIAM-Laboratory for Industrial and Applied Mathematics Department of Mathematics and Statistics York University 4700 Keele Street TorontoONM3J 1P3 Canada Department of Mathematics The University of Manchester Oxford Rd ManchesterM13 9PL United Kingdom Joint UNIversities Pandemic and Epidemiological Research

Structured epidemic models can be formulated as first-order hyperbolic PDEs, where the "spatial" variables represent individual traits, called structures. For models with two structures, we propose a numerical technique to approximate R0, which measures the transmissibility of an infectious disease and, rigorously, is defined as the dominant eigenvalue of a next-generation operator. Via bivariate collocation and cubature on tensor grids, the latter is approximated with a finite-dimensional matrix, so that its dominant eigenvalue can easily be computed with standard techniques. We use test examples to investigate experimentally the behavior of the approximation: the convergence order appears to be infinite when the corresponding eigenfunction is smooth, and finite for less regular eigenfunctions. To demonstrate the effectiveness of the technique for more realistic applications, we present a new epidemic model structured by demographic age and immunity, and study the approximation of R0in some particular cases of *** Codes 65J10, 65L15, 65M70, 37N25, 47A75, 92D30 © 2021, CC BY.

关键词： Matrix algebra

Inter-species spin-noise correlations in hot atomic vapors

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arXiv 2023年

作者： Mouloudakis, K. Vouzinas, F. Margaritakis, A. Koutsimpela, A. Mouloudakis, G. Koutrouli, V. Skotiniotis, M. Tsironis, G.P. Loulakis, M. Mitchell, M.W. Vasilakis, G. Kominis, I.K. Department of Physics University of Crete Heraklion71003 Greece ICFO - Institut de Ciències Fotòniques The Barcelona Institute of Science and Technology Castelldefels Barcelona08860 Spain School of Applied Mathematical and Physical Sciences National Technical University of Athens Athens15780 Greece Institute of Electronic Structure and Laser Foundation for Research and Technology Heraklion71110 Greece Física Teòrica: Informació i Fenòmens Quàntics Departament de Física Universitat Autònoma de Barcelona Bellaterra08193 Spain Departamento de Electromagnetismo y Física de la Materia Universidad de Granada Granada18010 Spain Institute of Theoretical and Computational Physics University of Crete Heraklion70013 Greece Institute of Applied and Computational Mathematics Foundation for Research and Technology Heraklion70013 Greece ICREA - Institució Catalana de Recerca i Estudis Avançats Barcelona08010 Spain Quantum Biometronics Heraklion71409 Greece

We report an experimental and theoretical study of spin noise correlations in a 87Rb-133Cs unpolarized alkali-metal vapor dominated by spin-exchange collisions. We observe strong unequal-time inter-species correlations and account for these with a first-principles theoretical model. Since the two atomic species have different spin precession frequencies, the dual-species vapor enables the use of an additional experimental handle, the applied magnetic field, for untangling various subtypes of spin correlations. In particular, the measured cross-correlation and auto-correlation spectra shed light on a number of spin-dynamic effects involving intra-atom, inter-atom, intra-species and inter-species correlations. Cross-correlation coefficients exceeding 60% have been observed at low-magnetic fields, where the two spin species couple strongly via spin-exchange collisions. The understanding of such spontaneously generated correlations can motivate the design of quantum-enhanced measurements with single or multi-species spin-polarized alkali-metal vapors used in quantum sensing applications. © 2023, CC BY.

关键词： Atoms