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arXiv 2019年

作者： Jiang, Kai Si, Wei School of Mathematics and Computational Science Hunan Key Laboratory for Computation and Simulation in Science and Engineering Xiangtan University 411105 China

The relative stability of three-dimensional icosahedral quasicrystals in multi-component systems has been investigated based on a phenomenological coupled-mode Swift-Hohenberg model with two-length-scales. A recently developed projection method, Which provides a unified numerical framework to study periodic crystals and quasicrystals, Is used to compute free energy to high accuracy. Compared with traditional approaches, the advantage of the projection method has also been discussed in detail. A rigorous and systematic computation demonstrates that threedimensional icosahedral quasicrystal and two-dimensional decagonal quasicrystal are both stable phases in such a simple multi-component coupled-mode Swift-Hohenberg model. The result extends the two length-scales interaction mechanism of stabilizing quasicrystals from single-component to multi-component systems. Copyright © 2019, The Authors. All rights reserved.

关键词： Quasicrystals

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Algebraic multigrid block preconditioning for multi-group radiation diffusion equations

arXiv

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arXiv 2020年

作者： Yue, Xiaoqiang Zhang, Shulei Xu, Xiaowen Shu, Shi Shi, Weidong School of Mathematics and Computational Science Hunan Key Laboratory for Computation and Simulation in Science and Engineering Key Laboratory of Intelligent Computing & Information Processing of Ministry of Education Xiangtan University Xiangtan411105 China Laboratory of Computational Physics Institute of Applied Physics and Computational Mathematics Beijing100088 China School of Applied Mathematics Shanxi University of Finance and Economics Taiyuan030006 China

The paper focuses on developing and studying efficient block preconditioners based on classical algebraic multigrid for the large-scale sparse linear systems arising from the fully coupled and implicitly cell-centered finite volume discretization of multi-group radiation diffusion equations, whose coefficient matrices can be rearranged into the (G + 2) × (G + 2) block form, where G is the number of energy groups. The preconditioning techniques are based on the monolithic classical algebraic multigrid method, physical-variable based coarsening two-level algorithm and two types of block Schur complement preconditioners. The classical algebraic multigrid is applied to solve the subsystems that arise in the last three block preconditioners. The coupling strength and diagonal dominance are further explored to improve performance. We use representative one-group and twenty-group linear systems from capsule implosion simulations to test the robustness, efficiency, strong and weak parallel scaling properties of the proposed methods. Numerical results demonstrate that block preconditioners lead to mesh- and problem-independent convergence, and scale well both algorithmically and in parallel. Copyright © 2020, The Authors. All rights reserved.

关键词： Finite volume method

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Doubling Algorithm for Nonsymmetric Algebraic Riccati Equations Based on a Generalized Transformation

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Advances in Applied Mathematics and Mechanics 2018年第6期10卷 1327-1343页

作者： Bo Tang Yunqing Huang Ning Dong School of Mathematics and Computational Science Hunan Key Laboratory for Computation and Simulation in Science and EngineeringKey Laboratory of Intelligent Computing and Information Processing of Ministry of EducationXiangtan UniversityXiangtan 411105HunanChina School of Science Hunan City UniversityYiyang 413000HunanChina School of Science Hunan University of TechnologyZhuzhou 412000HunanChina

We consider computing the minimal nonnegative solution of the nonsymmetric algebraic Riccati equation with *** is well known that such equations can be efficiently solved via the structure-preserving doubling algorithm(SDA)with the shift-and-shrink transformation or the generalized Cayley *** this paper,we propose a more generalized transformation of which the shift-and-shrink transformation and the generalized Cayley transformation could be viewed as two special ***,the doubling algorithm based on the proposed generalized transformation is presented and shown to be ***,the convergence result and the comparison theorem on convergent rate are *** numerical experiments show that the doubling algorithm with the generalized transformation is efficient to derive the minimal nonnegative solution of nonsymmetric algebraic Riccati equation with M-matrix.

关键词： Shift-and-shrink transformation generalized Cayley transformation doubling algorithm nonsymmetric algebraic Riccati equation

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Optical Remote Sensing Image Understanding with Weak Supervision: Concepts, Methods, and Perspectives

arXiv

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arXiv 2022年

作者： Yue, Jun Fang, Leyuan Ghamisi, Pedram Xie, Weiying Li, Jun Chanussot, Jocelyn Plaza, Antonio The Department of Geomatics Engineering Changsha University of Science and Technology Changsha410114 China The College of Electrical and Information Engineering Hunan University Changsha410082 China The Peng Cheng Laboratory Shenzhen518000 China Helmholtz Institute Freiberg for Resource Technology Freiberg09599 Germany Vienna1030 Austria The State Key Laboratory of Integrated Services Networks Xidian University Xi'An710071 China The Guangdong Provincial Key Laboratory of Urbanization and Geo-Simulation School of Geography and Planning Sun Yat-Sen University Guangzhou510275 China Université Grenoble Alpes Inria CNRS Grenoble INP LJK Grenoble38000 France The Hyperspectral Computing Laboratory Department of Technology of Computers and Communications University of Extremadura Cáceres10003 Spain

In recent years, supervised learning has been widely used in various tasks of optical remote sensing image understanding, including remote sensing image classification, pixel-wise segmentation, change detection, and object detection. The methods based on supervised learning need a large amount of high-quality training data and their performance highly depends on the quality of the labels. However, in practical remote sensing applications, it is often expensive and time-consuming to obtain large-scale data sets with high-quality labels, which leads to a lack of sufficient supervised information. In some cases, only coarse-grained labels can be obtained, resulting in the lack of exact supervision. In addition, the supervised information obtained manually may be wrong, resulting in a lack of accurate supervision. Therefore, remote sensing image understanding often faces the problems of incomplete, inexact, and inaccurate supervised information, which will affect the breadth and depth of remote sensing applications. In order to solve the above-mentioned problems, researchers have explored various tasks in remote sensing image understanding under weak supervision. This paper summarizes the research progress of weakly supervised learning in the field of remote sensing, including three typical weakly supervised paradigms: 1) Incomplete supervision, where only a subset of training data is labeled;2) Inexact supervision, where only coarse-grained labels of training data are given;3) Inaccurate supervision, where the labels given are not always true on the ground. Copyright © 2022, The Authors. All rights reserved.

关键词： Object detection

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Multifractal temporally weighted detrended partial cross-correlation analysis of two non-stationary time series affected by common external factors

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Physica A: Statistical Mechanics and its Applications 2021年 573卷

作者： Bao-Gen Li Dian-Yi Ling Zu-Guo Yu Hunan Key Laboratory for Computation and Simulation in Science and Engineering and Key Laboratory of Intelligent Computing and Information Processing of Ministry of Education Xiangtan University Xiangtan Hunan 411105 China School of Electrical Engineering and Computer Science Queensland University of Technology GPO Box 2434 Brisbane Q4001 Australia

When common factors strongly influence two cross-correlated time series recorded in complex natural and social systems, the results will be biased if we use multifractal detrended cross-correlation analysis (MF-DXA) without considering these common factors. In order to better study the time series of such cases, we extend the multifractal temporally weighted detrended cross-correlation analysis (MF-TWXDFA) proposed by our group (Wei et al., 2017) and propose multifractal temporally weighted detrended partial cross-correlation analysis (MF-TWDPCCA) to quantify intrinsic power-law cross-correlation of two non-stationary time series affected by common external factors in this paper. To test the performance of MF-TWDPCCA, we apply it and multifractal partial cross-correlation analysis (MF-DPXA) proposed by Qian et al. (2015) on simulated series. Numerical tests on artificially simulated series demonstrate that MF-TWDPCCA can more accurately detect the intrinsic cross-correlations for two simultaneously recorded series than MF-DPXA and MF-TWXDFA. To further show the utility of MF-TWDPCCA, we apply it on time series from stock markets and find that there exists significantly multifractal power-law cross-correlation between stock returns. In addition, a new partial cross-correlation coefficient is defined to quantify the level of intrinsic cross-correlation between two time series.

关键词： Partial cross-correlation Multifractal temporally weighted detrended partial cross-correlation analysis Partial cross-correlation coefficient

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Elliptical characteristics and numerical simulation of the PSEs of ferrofluid

Elliptical characteristics and numerical simulation of the P...

引用

中国力学大会（CCTAM2019）

作者： Li Mingjun Tang Shujiang Hiroshi Yamaguchi Jie Wu School of Mathematics and Computational Science Xiangtan University Hunan Key Laboratory for Computation and Simulation in Science and Engineering Xiangtan University Department of Mechanical Engineering Doshisha University

Ferrofluid is a colloidal suspension system with magnetic nanoparticles, the overall field of study in ferrofluid has a highly interdisciplinary character in practical applications. In this paper a set of parabolized stability equations(PSEs)of ferrofluid is represented by Rosensweig equations. The characteristic analysis show that in subsonic region the nonlinear PSEs of ferrofluid are parabolical, and in supersonic region are elliptical. The PSEs of ferrofluid is solved numerically for heat conduction process and RT instability problem, respectively. The results of characteristic analysis and numerical simulation all verify that the basic characteristic of ferrofluid are not influenced by the external magnetic field, and the viscosity is the only reason for the variation of ellipticity of PSEs of ferrofluid. That is to say, the external magnetic field and the viscosity are essentially different.

关键词： Ferrofluid Magnetic nanoparticles Parabolized stability equations Ellipticity

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Weak localization and crossover from Lifshitz transition in two dimensions

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Physical Review B 2021年第15期104卷 155135-155135页

作者： Kai-He Ding Zhen-Gang Zhu Yong-Le Hu Gang Su Department of Physics and Electronic Science Changsha University of Science and Technology Changsha 410076 China Hunan Provincial Key Laboratory of Flexible Electronic Materials Genome Engineering Changsha University of Science and Technology Changsha 410076 China School of Electronic Electrical and Communication Engineering University of Chinese Academy of Sciences Beijing 100049 China Theoretical Condensed Matter Physics and Computational Materials Physics Laboratory College of Physical Sciences University of Chinese Academy of Sciences Beijing 100049 China CAS Center for Excellence in Topological Quantum Computation University of Chinese Academy of Sciences Beijing 100190 China College of Automobile and Mechanical Engineering Changsha University of Science and Technology Changsha 410076 China Kavli Institute of Theoretical Sciences University of Chinese Academy of Sciences Beijing 100049 China

Dirac point plays a crucial role in regulating electronic properties of topological semimetals. In two dimensions, the manipulation of Dirac points can spur a transition from Dirac semimetal through semi-Dirac phase to a gapped phase. Across such a so-called Lifshitz transition, we find that the quantum interference corrections to the conductivity δσxx and δσyy are always negative, giving rise to a weak localization behavior. The ratio δσxx/δσyy undergoes a transition from linear to parabolic dependence on the merging parameter across the Lifshitz transition, which leads to a crossover of the temperature dependence of the inverse inelastic scattering time 1/τɛ from ∼T to ∼Tln(T0/T). This fingerprint behavior can be readily tested experimentally through merging Dirac points in two-dimensional lattices. This work presents an alternative perspective to understand weak localization through Lifshitz transition.

关键词： Topological phases of matter Weak localization Dirac semimetal Disordered systems Two-dimensional electron system

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Svgd: A Virtual Gradients Descent Method for Stochastic Optimization

arXiv

引用

arXiv 2019年

作者： Li, Zheng Shu, Shi School of Mathematics and Computational Science Xiangtan University Xiangtan Hunan411105 China Hunan Key Laboratory for Computation and Simulation in Science and Engineering Xiangtan University Xiangtan411105 China

Inspired by dynamic programming, we propose Stochastic Virtual Gradient Descent (SVGD) algorithm where the Virtual Gradient is defined by computational graph and automatic differentiation. The method is computationally efficient and has little memory requirements. We also analyze the theoretical convergence properties and implementation of the algorithm. Experimental results on multiple datasets and network models show that SVGD has advantages over other stochastic optimization methods. Copyright © 2019, The Authors. All rights reserved.

关键词： Machine learning

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Enforced Freedom: Electric-Field-Induced Declustering of Ionic-Liquid Ions in the Electrical Double Layer

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Energy & Environmental Materials 2020年第3期3卷 414-420页

作者： Yufan Zhang Ting Ye Ming Chen Zachary A.H.Goodwin Guang Feng Jun Huang Alexei A.Kornyshev IEK-13 Institute of Energy and Climate ResearchForschungszentrum Jülich GmbHJülich 52425Germany State Key Laboratory of Coal Combustion School of Energy and Power EngineeringHuazhong University of Science and Technology(HUST)Wuhan 430074China Department of Chemistry Imperial College LondonMolecular Sciences Research HubWhite City CampusLondon W120BZUK Department of Physics Imperial College LondonSouth Kensington CampusLondon SW72AZUK Thomas Young Centre for Theory and Simulation of Materials Imperial College LondonSouth Kensington CampusLondon SW72AZUK Hunan Provincial Key Laboratory of Chemical Power Sources College of Chemistry and Chemical EngineeringCentral South UniversityChangsha 410083China

Ions in the bulk of solvent-free ionic liquids bind into ion pairs and *** competition between the propensity of ions to stay in a bound state,and the reduction of the energy when unbinding in electric field,determines the portion of free ions in the electrical double *** present the simplest possible mean-field theory to study this effect."Cracking"of ion pairs into free ions in electric field is accompanied by the change of the dielectric response of the ionic *** predictions from the theory are verified and further explored by molecular dynamics simulations.A particular finding of the theory is that the differential capacitance vs potential curve displays a bell shape,despite the low concentration of free charge carriers,because the dielectric response reduces the threshold concentration for the bell-to camelshape *** presented theory does not take into account overscreening and oscillating charge distributions in the electrical double *** in spite of the simplicity of the model,its findings demonstrate a clear physical effect:a preference to be a charged monopole rather than a dipole(or higher order multipole)in strong electric field.

关键词： differential capacitance ion pairs ionic liquids unbinding

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A two-dimensional GeSe/SnSe heterostructure for high performance thin-film solar cells

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Journal of Materials Chemistry A 2019年第18期7卷 11265-11271页

作者： Yuliang Mao Congsheng Xu Jianmei Yuan Hongquan Zhao Hunan Key Laboratory for Micro-Nano Energy Materials and Devices School of Physics and Optoelectronics Xiangtan University Hunan 411105 China Hunan Key Laboratory for Computation and Simulation in Science and Engineering School of Mathematics and Computational Science Xiangtan University Hunan 411105 China Chongqing Institute of Green and Intelligent Technology Chinese Academy of Sciences Chongqing 401120 China

Based on the first-principles calculations, we demonstrated that a GeSe/SnSe heterostructure has type-II band alignment and a direct band gap, which can effectively prevent the recombination of photogenerated electron–hole pairs. Moreover, the GeSe/SnSe heterostructure also exhibits strong optical absorption intensity, which can reach the order of 10⁵ cm⁻¹. Our predicted photoelectric conversion efficiency (PCE) for the GeSe/SnSe heterostructure reaches 21.47%. We also found that the hole carrier mobility of the GeSe/SnSe heterostructure along the x direction has been significantly improved to 6.42 × 10⁴ cm² V⁻¹ s⁻¹, which is higher than that of black phosphorus (1 × 10⁴ cm² V⁻¹ s⁻¹). By applying a vertical external electric field, we found that the band gap and band offset of the GeSe/SnSe heterojunction can be effectively tuned. The revealed type-II band alignment, strong optical absorption, superior PCE and superior hole carrier mobility of the GeSe/SnSe heterostructure imply that this new proposed material has broad application prospects in solar cells.

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