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Stochastic Treatment of Adsorbate Local-Potential Effects on Surface-Ion Neutralization

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Physical Review Letters 1993年第24期71卷 4075-4075页

作者： Zoran L. Mišković Sydney G. Davison Frank O. Goodman Department of Applied Mathematics University of Waterloo Waterloo Ont. N2L 3G1 Canada Institute of Nuclear Sciences-Vinča Belgrade Department of Physics University of Waterloo Guelph-Waterloo Program for Graduate Work in Physics

The influence of a laterally inhomogeneous electrostatic potential of an adsorbate-covered surface on the resonant charge transfer in ion-surface scattering is investigated by means of the time-dependent Anderson-Newns Hamiltonian. The adsorbate-induced random modulation of the projectile orbital energy level is treated as a stochastic process, and its role in the charge transfer is evaluated analytically, in the Gaussian-process approximation, for low projectile speeds and low surface coverage by alkali atoms.

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Stochastic block models with multiple continuous attributes

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arXiv 2018年

作者： Stanley, Natalie Bonacci, Thomas Kwitt, Roland Niethammer, Marc Mucha, Peter J. Curriculum in Bioinformatics and Computational Biology University of North Carolina Chapel Hill Department of Pharmacology & Lineberger Comprehensive Cancer Center University of North Carolina Chapel Hill Department of Computer Science University of Salzburg Department of Computer Science & Biomedical Research Imaging Center University of North Carolina Chapel Hill Carolina Center for Interdisciplinary Applied Mathematics Department of Mathematics University of North Carolina Chapel Hill

The stochastic block model (SBM) is a probabilistic model for community structure in networks. Typically, only the adjacency matrix is used to perform SBM parameter inference. In this paper, we consider circumstances in which nodes have an associated vector of continuous attributes that are also used to learn the node-to-community assignments and corresponding SBM parameters. While this assumption is not realistic for every application, our model assumes that the attributes associated with the nodes in a network’s community can be described by a common multivariate Gaussian model. In this augmented, attributed SBM, the objective is to simultaneously learn the SBM connectivity probabilities with the multivariate Gaussian parameters describing each community. While there are recent examples in the literature that combine connectivity and attribute information to inform community detection, our model is the first augmented stochastic block model to handle multiple continuous attributes. This provides the flexibility in biological data to, for example, augment connectivity information with continuous measurements from multiple experimental modalities. Because the lack of labeled network data often makes community detection results difficult to validate, we highlight the usefulness of our model for two network prediction tasks: link prediction and collaborative filtering. As a result of fitting this attributed stochastic block model, one can predict the attribute vector or connectivity patterns for a new node in the event of the complementary source of information (connectivity or attributes, respectively). We also highlight two biological examples where the attributed stochastic block model provides satisfactory performance in the link prediction and collaborative filtering tasks. Copyright © 2018, The Authors. All rights reserved.

关键词： Population dynamics

A Bi-variant Variational Model for Diffeomorphic Image Registration with Relaxed Jacobian Determinant Constraints

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arXiv 2023年

作者： Li, Yanyan Chen, Ke Chen, Chong Zhang, Jianping School of Mathematics and Computational Science Xiangtan University Hunan Xiangtan411105 China Department of Mathematics and Statistics University of Strathclyde GlasgowG1 1XH United Kingdom LSEC ICMSEC Academy of Mathematics and Systems Science Chinese Academy of Sciences Beijing Beijing100190 China National Center for Applied Mathematics in Hunan Xiangtan University Hunan Xiangtan411105 China Hunan Key Laboratory for Computation and Simulation in Science and Engieering Xiangtan University Hunan Xiangtan411105 China

Diffeomorphic registration is a widely used technique for finding a smooth and invertible transformation between two coordinate systems, which are measured using template and reference images. The point-wise volume-preserving constraint det(∇φ(x)) = 1 is effective in some cases, but may be too restrictive in others, especially when local deformations are relatively large. This can result in poor matching when enforcing large local deformations. In this paper, we propose a new bi-variant diffeomorphic image registration model that introduces a soft constraint on the Jacobian equation det(∇φ(x)) = f(x) > 0. This allows local deformations to shrink and grow within a flexible range 0 M M. The Jacobian determinant of transformation is explicitly controlled by optimizing the relaxation function f(x). To prevent deformation folding and improve the smoothness of the transformation, a positive constraint is imposed on the optimization of the relaxation function f(x), and a regularizer is used to ensure the smoothness of f(x). Furthermore, the positivity constraint ensures that f(x) is as close to one as possible, which helps to achieve a volume-preserving transformation on average. We also analyze the existence of the minimizer for the variational model and propose a penalty-splitting algorithm with a multilevel strategy to solve this model. Numerical experiments demonstrate the convergence of the proposed algorithm and show that the positivity constraint can effectively control the range of relative volume without compromising the accuracy of the registration. Moreover, the proposed model generates diffeomorphic maps for large local deformations and outperforms several existing registration models in terms of *** Codes 54H30, 68U10, 94A08 Copyright © 2023, The Authors. All rights reserved.

关键词： Iterative methods

Hybrid fluid–particle modeling of shock-driven hydrodynamic instabilities in a plasma

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Matter and Radiation at Extremes 2021年第3期6卷 24-32页

作者： Hong-bo Cai Xin-xin Yan Pei-lin Yao Shao-ping Zhu 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 Department of Engineering Physics Tsinghua UniversityBeijing 100084China Graduate School China Academy of Engineering PhysicsP.O.Box 2101Beijing 100088China Science and Technology on Plasma Physics Laboratory Laser Fusion Research CenterCAEP621900 MianyangChina

Shock-driven hydrodynamic instabilities in a plasma usually lead to interfacial mixing and the generation of electromagnetic fields,which are nonequilibrium processes coupling kinetics with meso-and macroscopic *** understanding and modeling of these physical processes are very challenging tasks for single-fluid hydrodynamic *** work presents a new framework that incorporates both kinetics and hydrodynamics to simulate shock waves and hydrodynamic instabilities in high-density *** this hybrid code,ions are modeled using the standard particle-in-cell method together with a Monte Carlo description of collisions while electrons are modeled as a massless fluid,with the electron heat flux and fluid–particle energy exchange being considered in the electron pressure *** high-density plasmas,Maxwell’s equations are solved using Ohm’s law instead of Ampere’s *** hybrid algorithm retains ion kinetic effects and their consequences for plasma interpenetration,shock wave propagation,and hydrodynamic ***,we investigate the shock-induced(or gravity-induced)turbulent mixing between a light and a heavy plasma,where hydrodynamic instabilities are initiated by a shock wave(or gravity).This study reveals that self-generated electromagnetic fields play a role in the formation of baroclinic vorticity along the interface and in late-time mixing of the *** results confirm the ability of the proposed method to describe shock-driven hydrodynamic instabilities in a plasma,in particular,nonequilibrium processes that involve mixing and electromagnetic fields at the interface.

关键词： hydrodynamic shock mixing

OPERATORS ON ANTI-DUAL PAIRS: SUPREMUM AND INFIMUM OF POSITIVE OPERATORS

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arXiv 2023年

作者： Tarcsay, Zsigmond Göde, Ábel Department of Mathematics Corvinus University of Budapest IX. Fővám tér 13-15. BudapestH-1093 Hungary Department of Applied Analysis and Computational Mathematics Eötvös Loránd University Pázmány Péter sétány 1/c. BudapestH-1117 Hungary

Our purpose in this note is to investigate the order properties of positive operators from a locally convex space into its conjugate dual. We introduce a natural generalization of the Busch-Gudder strength function and we prove Kadison's anti-lattice theorem and Ando's result on the infimum of positive operators in that *** Codes 47B65, 46A20 Copyright © 2023, The Authors. All rights reserved.

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ON THE STABILITY OF POSITIVE SEMIGROUPS

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arXiv 2021年

作者： Del Moral, Pierre Horton, Emma Jasra, Ajay Centre de Recherche Inria Bordeaux Sud-Ouest Talence 33405 France Applied Mathematics and Computational Science Program Computer Electrical and Mathematical Sciences and Engineering Division King Abdullah University of Science & Technology Building 1 Thuwal23955-6900 Saudi Arabia

The stability and contraction properties of positive integral semigroups on Polish spaces are investigated. Our novel analysis is based on the extension of V -norm contraction methods, associated to functionally weighted Banach spaces for Markov semigroups, to positive semigroups. This methodology is applied to a general class of positive and possibly time-inhomogeneous bounded integral semigroups and their normalised versions. The spectral theorems that we develop are an extension of Perron-Frobenius and Krein-Rutman theorems for positive operators to a class of time-varying positive semigroups. In the context of time-homogeneous models, the regularity conditions discussed in the present article appear to be necessary and sufficient condition for the existence of leading eigenvalues. We review and illustrate the impact of these results in the context of positive semigroups arising in transport theory, physics, mathematical biology and signal processing. Copyright © 2021, The Authors. All rights reserved.

关键词： Banach spaces

Electronic and vibrational properties of Pu3Ga: A theoretical explanation for the phonon softening observed in Pu-Ga alloys

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Physical Review B 2017年第13期96卷 134102-134102页

作者： Menglei Li Yu Yang Fawei Zheng Ping Zhang Institute of Applied Physics and Computational Mathematics Beijing 100088 China Center for Fusion Energy Science and Technology CAEP Beijing 100084 China Department of Physics Capital Normal University Beijing 100048 China Beijing Computational Science Research Center Beijing 100084 China Center for Applied Physics and Technology Peking University HEDPS Beijing 100871 China Compression Science Research Center CAEP Mianyang 621900 China

By using the density functional theory plus U (DFT+U) method and taking spin-orbit coupling into account, we investigate the electronic and phonon properties of Pu3Ga. Most interestingly, we find that there is a significant phonon softening in the transverse acoustic branch at the L point in the Brillouin zone. Via bond strength analysis, we reveal that the nearest-neighboring bond strengths in the face-centered-cubic lattice are weaker around Ga atoms, which is responsible for the observed phonon softening.

关键词： Acoustic phonons Spin-orbit coupling Face-centered cubic

Publisher's Note: "The fundamental gap for a class of Schrödinger operators on path and hypercube graphs" [J. Math. Phys. 55, 052104 (2014)]

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Journal of Mathematical Physics 2014年第6期55卷

作者： Jarret, Michael Jordan, Stephen P. Department of Physics University of Maryland College Park 20742-4111 MD United States Applied and Computational Mathematics Division National Institute of Standards and Technology Gaithersburg 20899 MD United States

This article was originally published online on 29 May 2014 with an error in the placement of text on pages 3 and 4. The text should have appeared as below:

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Dependence of the correlated-momentum patterns in double ionization on the carrier-envelope phase and intensity of a few-cycle laser pulse

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Physical Review A 2010年第6期82卷 063423-063423页

作者： G. G. Xin D. F. Ye J. Liu Key Laboratory of Cluster Science and Department of Physics School of Science Beijing Institute of Technology Beijing 100081 China Science and Technology Computation Physics Laboratory Beijing Institute of Applied Physics and Computational Mathematics Beijing 100088 China Graduate School China Academy of Engineering Physics Beijing 100088 China Center for Applied Physics and Technology Peking University Beijing 100084 China

In the present paper, we investigate the correlated electron emission of atoms irradiated by a few-cycle laser pulse, with emphasis on the correlated longitudinal momentum spectra. We find that the spectra show clear v-shaped structures, in analogy to what was observed recently in long-pulse experiments. Moreover, the patterns of the spectra depend sensitively on the carrier-envelope phase as well as the laser intensity. The v-shaped structure is more pronounced at lower and higher intensities and becomes obscure at medium intensity. At a lower intensity, upon change of the phase from 0 to π/2, the v-shaped structure shifts from the first quadrant to the third quadrant and the ratios between the double ionization yields in the first and third quadrants are found to increase by a few orders of magnitude. The semiclassical rescattering model is exploited in the preceding calculations and the underlying mechanisms are uncovered by analyzing the subcycle dynamics of classical trajectories.

关键词： Electron emission