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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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Stability of three-dimensional icosahedral quasicrystals in multi-component systems

arXiv

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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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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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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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Elliptical characteristics and numerical simulation of the PSEs of ferrofluid

Elliptical characteristics and numerical simulation of the P...

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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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Svgd: A Virtual Gradients Descent Method for Stochastic Optimization

arXiv

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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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The ecotoxicological effects of thiamethoxam on photosynthesis and nitrogen fixation in cyanobacteria: From inhibition to recovery

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Journal of Environmental sciences 2025年

作者： Jiale Zhang Shiye Zhu Xiyan Xu Youzheng Chai Jihai Shao Gen Lu Jianhua Zeng Ma Bai Anwei Chen College of Environment and Ecology Hunan Agricultural University Changsha 410128 China School of Chemistry and Chemical Engineering Beijing Institute of Technology Beijing 100081 China Center for Water and Ecology State Key Joint Laboratory of Environment Simulation and Pollution Control School of Environment Tsinghua University Beijing 100084 China Institute of Resource Biology and Biotechnology Department of Biotechnology College of Life Science and Technology Huazhong University of Science and Technology Wuhan 430074 China School of Food Engineering Anhui Science and Technology University Fengyang AnHui 233100 China College of Chemistry & Pharmacy Northwest A&F University Yangling Shaanxi 712100 China

Thiamethoxam (THX) is a highly efficacious, broad-spectrum neonicotinoid insecticide that is prevalently detected in contemporary environmental settings. Although considerable research has been conducted on the adverse effects of THX on non-target organisms, there is a paucity of knowledge regarding its impact on nitrogen (N)-fixing cyanobacteria, which play a crucial role in the N-cycle. This study examined the impact of the neonicotinoid pesticide THX on N-fixing cyanobacteria Nostoc sp. PCC7120. It combined biochemical and molecular data to clarify the toxicity and recovery mechanism of Nostoc sp. PCC7120 exposed to THX. The results show that at low THX concentrations, cyanobacteria exhibited hormetic responses and then enter recovery phases, whereas at high concentrations, they showed toxicity phases before entering recovery phases. The main changes were in cell growth, antioxidant system, photosynthetic performance and N-fixation. The starch granules and vacuoles of Nostoc sp. PCC7120 became larger after THX treatment, indicating a shift in resources from growth to storage. Additionally, molecular stimulations indicated that THX could bind to molybdenum-iron cofactor sites of nitrogenase to destroy N-fixation, and also bind to Q A and Q B sites of photosynthetic proteins (D1 and D2) to affect photosynthesis. These findings provide a valuable reference for the ecological risks of THX and biogeochemical N-cycle.

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Error analysis of SAV finite element method to phase field crystal model

arXiv

引用

arXiv 2019年

作者： Wang, Liupeng Huang, Yunqing Jiang, Kai School of Mathematics and Computational Science Xiangtan University Xiangtan Hunan411105 China Hunan Key Laboratory for Computation and Simulation in Science and Engineering Xiangtan Hunan411105 China Key Laboratory of Ministry of Education for Intelligent Computing and Information Processing Xiangtan University Xiangtan Hunan411105 China

In this paper, we construct and analyze an energy stable scheme by combining the latest developed scalar auxiliary variable (SAV) approach and linear finite element method (FEM) for phase field crystal (PFC) model, and show rigorously that the scheme is first-order in time and second-order in space for the L2and H1 gradient ow equations. To reduce eficiently computational cost and capture accurately the phase interface, we give a simple adaptive strategy, equipped with a posteriori gradient estimator, i.e. L2norm of the recovered gradient. Extensive numerical experiments are presented to verify our theoretical results and to demonstrate the efiectiveness and accuracy of our proposed method. Copyright © 2019, The Authors. All rights reserved.

关键词： Finite element method

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Jacobi Spectral Collocation Method Based on Lagrange Interpolation Polynomials for Solving Nonlinear Fractional Integro-Differential Equations

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Advances in Applied Mathematics and Mechanics 2018年第6期10卷 1440-1458页

作者： Xingfa Yang Yin Yang Yanping Chen Jie Liu State Key Laboratory of Advanced Design and Manufacturing for Vehicle Body Hunan UniversityChangsha 410082HunanChina Hunan Key Laboratory for Computation and Simulation in Science and Engineering Key Laboratory of Intelligent Computing&Information Processing of Ministry of EducationSchool of Mathematics and Computational ScienceXiangtan UniversityXiangtan 411105HunanChina School of Mathematical Sciences South China Normal UniversityGuangzhou 510631GuangdongChina Center for Research on Leading Technology of Special Equipment School of Mechanical and Electric EngineeringGuangzhou UniversityGuangzhou 510006GuangdongChina

In this paper,we study a class of nonlinear fractional integro-differential equations,the fractional derivative is described in the Caputo *** the properties of the Caputo derivative,we convert the fractional integro-differential equations into equivalent integral-differential equations of Volterra type with singular kernel,then we propose and analyze a spectral Jacobi-collocation approximation for nonlinear integro-differential equations of Volterra *** provide a rigorous error analysis for the spectral methods,which shows that both the errors of approximate solutions and the errors of approximate fractional derivatives of the solutions decay exponentially in L^(∞)-norm and weighted L^(2)-norm.

关键词： Spectral method nonlinear fractional derivative Volterra integro-differential equations Caputo derivative

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Error Estimates for the Iterative Discontinuous Galerkin Method to the Nonlinear Poisson-Boltzmann Equation

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Communications in Computational Physics 2018年第1期23卷 168-197页

作者： Peimeng Yin Yunqing Huang Hailiang Liu Mathematics Department Iowa State UniversityAmesIA 50011USA Key Laboratory of Intelligent Computing&Information Processing of Ministry of Education Hunan Key Laboratory for Computation and Simulation in Science and EngineeringSchool of Mathematics and Computational ScienceXiangtan UniversityXiangtan411105P.R.China

This paper is devoted to the error estimate for the iterative discontinuous Galerkin(IDG)method introduced in[***,*** and ***.16:491-515,2014]to the nonlinear Poisson-Boltzmann *** total error includes both the iteration error and the discretization error of the direct DG method to linear elliptic *** the DDG method,the energy error is obtained by a constructive approach through an explicit global projection satisfying interface conditions dictated by the choice of numerical *** L^(2) error of order O(h^(m+1))for polynomials of degree m is further *** bounding constant is also shown to be independent of the iteration *** tests are given to validate the established convergence theory.

关键词： Poisson-Boltzmann equation DG methods global projection energy error estimates L^(2)error estimates

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