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Science China Mathematics 2024年第7期67卷 1641-1664页

作者： Jinye Shen Fanhai Zeng Martin Stynes School of Mathematics Southwestern University of Finance and EconomicsChengdu611130China School of Mathematics Shandong UniversityJinan250100China Applied and computational Mathematics division Beijing Computational Science Research CenterBeijing100193China

Fractional initial-value problems(IVPs) and time-fractional initial-boundary value problems(IBVPs), each with a Caputo temporal derivative of order α ∈(0, 1), are considered. An averaged variant of the well-known L1 scheme is proved to be O(N^(-2)) convergent for IVPs on suitably graded meshes with N points, thereby improving the O(N^(-(2-α))) convergence rate of the standard L1 scheme. The analysis relies on a delicate decomposition of the temporal truncation error that yields a sharp dependence of the order of convergence on the degree of mesh grading used. This averaged L1 scheme can be combined with a finite difference or piecewise linear finite element discretization in space for IBVPs, and under a restriction on the temporal mesh width, one gets again O(N^(-2)) convergence in time, together with O(h^(2)) convergence in space,where h is the spatial mesh width. Numerical experiments support our results.

关键词： time-fractional subdiffusion averaged L1 scheme

Influences of Co-Flow and Counter-Flow Modes of Reactant Flow Arrangement on a PEMFC at Start-Up

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Computer Modeling in Engineering & Sciences 2024年第5期139卷 1337-1356页

作者： Qianqian Shao Min Wang Nuo Xu School of Petroleum Engineering Guangdong University of Petrochemical TechnologyMaoming525000China Mechanics division Beijing Computational Science Research CenterBeijing100193China

To investigate the influences of co-flowand counter-flowmodes of reactant flowarrangement on a proton exchange membrane fuel cell(PEMFC)during start-up,unsteady physical and mathematical models fully coupling the flow,heat,and electrochemical reactions in a PEMFC are established.The continuity equation and momentum equation are solved by handling pressure-velocity coupling using the SIMPLE algorithm.The electrochemical reaction rates in the catalyst layers(CLs)of the cathode and anode are calculated using the Butler-Volmer equation.The multiphase mixture model describes the multiphase transport process of gas mixtures and liquid water in the fuel cell.After validation,the influences of co-flow and counter-flow modes on the PEMFC performance are investigated,including the evolution of the current density,flow field,temperature field,and reactant concentration field during start-up,as well as the steady distribution of the current density,reactant concentration,andmembrane water content when the start-up stabilizes.Co-flow and counter-flow modes influence the current density distribution and temperature distribution.On the one hand,the co-flow mode accelerates the start-up process of the PEMFC and leads to a more evenly distributed current density than the counter-flow mode.On the other hand,the temperature difference between the inlet and outlet sections of the cell is up to 10.1℃ under the co-flow mode,much larger than the 5.0℃ observed in the counter-flow mode.Accordingly,the counter-flowmode results in a more evenly distributed temperature and a lower maximum temperature than the co-flow case.Therefore,in the flow field design of a PEMFC,the reactant flow arrangements can be considered to weigh between better heat management and higher current density distribution of the cell.

关键词： PEMFC full coupling model Butler-Volmer equation multiphase mixture model co-flow mode counter-flow mode

A scoping review of methodologies for applying artificial intelligence to physical activity interventions

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Journal of Sport and Health Science 2024年第3期13卷 428-441页

作者： Ruopeng An Jing Shen Junjie Wang Yuyi Yang Brown School Washington UniversitySt.LouisMO 63130USA Department of Physical Education China University of Geosciences BeijingBeijing 100083China School of Kinesiology and Health Promotion Dalian University of TechnologyDalian 116024China division of computational and Data Sciences Washington UniversitySt.LouisMO 63130USA

Purpose This scoping review aimed to offer researchers and practitioners an understanding of artificial intelligence(AI)applications in physical activity(PA)interventions;introduce them to prevalent machine learning(ML),deep learning(DL),and reinforcement learning(RL)algorithms;and encourage the adoption of AI methodologies.Methods A scoping review was performed in PubMed,Web of Science,Cochrane Library,and EBSCO focusing on AI applications for promoting PA or predicting related behavioral or health outcomes.AI methodologies were summarized and categorized to identify synergies,patterns,and trends informing future research.Additionally,a concise primer on predominant AI methodologies within the realm of PA was provided to bolster understanding and broader application.Results The review included 24 studies that met the predetermined eligibility criteria.AI models were found effective in detecting significant patterns of PA behavior and associations between specific factors and intervention outcomes.Most studies comparing AI models to traditional statistical approaches reported higher prediction accuracy for AI models on test data.Comparisons of different AI models yielded mixed results,likely due to model performance being highly dependent on the dataset and task.An increasing trend of adopting state-of-the-art DL and RL models over standard ML was observed,addressing complex human–machine communication,behavior modification,and decision-making tasks.Six key areas for future AI adoption in PA interventions emerged:personalized PA interventions,real-time monitoring and adaptation,integration of multimodal data sources,evaluation of intervention effectiveness,expanding access to PA interventions,and predicting and preventing injuries.Conclusion The scoping review highlights the potential of AI methodologies for advancing PA interventions.As the field progresses,staying informed and exploring emerging AI-driven strategies is essential for achieving significant improvements in PA interventions and fostering overall we

关键词： Artificial intelligence Intervention Machine learning Neural network Physical activity

The initial stages of Li_(2)O_(2) formation during oxygen reduction reaction in Li-O_(2) batteries:The significance of Li_(2)O_(2) in charge-transfer reactions within devices

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Journal of Energy Chemistry 2024年第1期88卷 223-231,I0006页

作者： Daniela M.Josepetti Bianca P.Sousa Simone A.J.Rodrigues Renato G.Freitas Gustavo Doubek Advanced Energy Storage division LABCenter for Innovation on New EnergiesSchool of Chemical EngineeringUniversity of CampinasAv Albert Einstein 50013083-852CampinasSPBrazil Institute of Physics&Department of Chemistry Laboratory of Computational MaterialsFederal University of Mato Grosso78060-900CuiabáMTBrazil

Lithium-oxygen batteries are a promising technology because they can greatly surpass the energy density of lithium-ion batteries.However,this theoretical characteristic has not yet been converted into a real device with high cyclability.Problems with air contamination,metallic lithium reactivity,and complex discharge and charge reactions are the main issues for this technology.A fast and reversible oxygen reduction reaction(ORR)is crucial for good performance of secondary batteries',but the partial knowledge of its mechanisms,especially when devices are concerned,hinders further development.From this perspective,the present work uses operando Raman experiments and electrochemical impedance spectroscopy(EIS)to assess the first stages of the discharge processes in porous carbon electrodes,following their changes cycle by cycle at initial operation.A growth kinetic formation of the discharge product signal(Li_(2)O_(2))was observed with operando Raman,indicating a first-order reaction and enabling an analysis by a microkinetic model.The solution mechanism in the evaluated system was ascribed for an equivalent circuit with three time constants.While the time constant for the anode interface reveals to remain relatively constant after the first discharge,its surface seemed to be more non-uniform.The model indicated that the reaction occurs at the Li_(2)O_(2) surface,decreasing the associated resistance during the initial discharge phase.Furthermore,the growth of Li_(2)O_(2) forms a hetero-phase between Li_(2)O_(2)/electrolyte,while creating a more compact and homogeneous on the Li_(2)O_(2)/cathode surface.The methodology here described thus offers a way of directly probing changes in surface chemistry evolution during cycling from a device through EIS analysis.

关键词： Li-O_(2)battery Operando Raman analysis Equivalent circuit modeling Time-constant distribution

Positive definiteness of real quadratic forms resulting from the variable-step L1-type approximations of convolution operators

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Science China Mathematics 2024年第2期67卷 237-252页

作者： Hong-Lin Liao Tao Tang Tao Zhou School of Mathematics Nanjing University of Aeronautics and AstronauticsNanjing 211106China division of Science and Technology BNU-HKBU United International CollegeZhuhai 519087China SUSTech International Center for Mathematics Shenzhen 518055China NCMIS&LSEC Institute of Computational Mathematics and Scientific/Engineering ComputingAcademy of Mathematics and Systems ScienceChinese Academy of SciencesBeijing 100190China

The positive definiteness of real quadratic forms with convolution structures plays an important rolein stability analysis for time-stepping schemes for nonlocal operators. In this work, we present a novel analysistool to handle discrete convolution kernels resulting from variable-step approximations for convolution operators.More precisely, for a class of discrete convolution kernels relevant to variable-step L1-type time discretizations, weshow that the associated quadratic form is positive definite under some easy-to-check algebraic conditions. Ourproof is based on an elementary constructing strategy by using the properties of discrete orthogonal convolutionkernels and discrete complementary convolution kernels. To our knowledge, this is the first general result onsimple algebraic conditions for the positive definiteness of variable-step discrete convolution kernels. Using theunified theory, we obtain the stability for some simple nonuniform time-stepping schemes straightforwardly.

关键词： discrete convolution kernels positive definiteness variable time-stepping orthogonal convolution kernels complementary convolution kernels

Review of deep learning algorithms in molecular simulations and perspective applications on petroleum engineering

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Geoscience Frontiers 2024年第2期15卷 55-67页

作者： Jie Liu Tao Zhang Shuyu Sun Physical Science and Engineering division(PSE) Computational Transport Phenomena LaboratoryKing Abdullah University of Science and Technology(KAUST)Thuwal 23955-6900Saudi Arabia

In the last few decades,deep learning(DL)has afforded solutions to macroscopic problems in petroleum engineering,but mechanistic problems at the microscale have not benefited from it.Mechanism studies have been the strong demands for the emerging projects,such as the gas storage and hydrate production,and for some problems encountered in the storage process,which are common found as the chemical interaction between injected gas and mineral,and the formation of hydrate.Emerging advances in DL technology enable solving molecular dynamics(MD)with quantum accuracy.The conventional quantum chemical method is computational expensive,whereas the classical MD method cannot guarantee high accuracy because of its empirical force field parameters.With the help of the DL force field,precision at the quantum chemistry level can be achieved in MD.Moreover,the DL force field promotes the computational speed compared with first-principles calculations.In this review,the basic knowledge of the molecular force field and deep neural network(DNN)is first introduced.Then,three representative opensource packages relevant to the DL force field are introduced.As the most common components in the development of oil and gas reservoirs,water and methane are studied from the aspects of computational efficiency and chemical reaction respectively,providing the foundation of oil and gas researches.However,in the oil and gas problems,the complex molecular topo structures and various element types set a high challenge for the DL techniques in MD.Regarding the computational efficiency,it needs improvement via GPU and parallel accelerations to compete with classical MD.Even with such difficulties,the booming of this technique in the area of petroleum engineering can be predictable.

关键词： Deep neural network Molecular dynamics Force field Petroleum engineering

力-热耦合效应对CuO氧化岛表面单原子氧的调控（英文）

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Science China Materials 2024年

作者：杨欢欢姜肖王智灏梁汉普张燮管鹏飞 Materials and Energy division Beijing Computational Science Research Center School of Materials Science and Engineering Northwestern Polytechnical University

单原子氧的扩散,是外延Cu2O氧化岛逐层生长动力学中的热力学决速步,其中力-热耦合效应会导致氧缺陷的出现.而氧缺陷在氧化岛表面的形成机制及其调控仍需进一步的研究.基于第一性原理模拟,本文以典型的金属氧化物Cu2O为研究对象,系统地...

单原子氧的扩散,是外延Cu2O氧化岛逐层生长动力学中的热力学决速步,其中力-热耦合效应会导致氧缺陷的出现.而氧缺陷在氧化岛表面的形成机制及其调控仍需进一步的研究.基于第一性原理模拟,本文以典型的金属氧化物Cu2O为研究对象,系统地研究了力-热耦合效应下,表面不同嵌入深度的本征氧缺陷的热力学形成行为.通过构建关于氧缺陷调控的热力学相图,预测了Cu表面氧化过程中Cu2O氧化岛的生长机制,其与原位环境透射电子显微镜（ETEM）的实验观测具有较好的一致性.通过引入应力调控的氧缺陷的热力学相图,实现了对氧化岛表面上氧缺陷的类型和浓度的调控.本文为理解金属表面的逐层氧化行为提供了理论支持,并为设计高性能的抗腐蚀氧化物表面提供了调控方案.

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Error Analysis of the Nonconforming P1 Finite Element Method to the Sequential Regularization Formulation for Unsteady Navier-Stokes Equations

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Annals of Applied Mathematics 2024年第1期 43-70页

作者： Yanming Lai Kewei Liang Ping Lin Xiliang Lu Qimeng Quan School of Mathematics and Statistics Wuhan University School of Mathematical Sciences Zhejiang University division of Mathematics University of Dundee School of Mathematics and Statistics and Hubei Key Laboratory of computational Science Wuhan University

In this paper we investigate the nonconforming P1finite element approximation to the sequential regularization method for unsteady Navier-Stokes equations. We provide error estimates for a full discretization scheme. Typically, conforming P1finite element methods lead to error bounds that depend inversely on the penalty parameter ?. We obtain an ?-uniform error bound by utilizing the nonconforming P1finite element method in this paper. Numerical examples are given to verify theoretical results.

关键词：

Dual-Defect Engineering Strategy Enables High-Durability Rechargeable Magnesium-Metal Batteries

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Nano-Micro Letters 2024年第9期16卷 449-461页

作者： Fuyu Chen Bai‑Qing Zhao Kaifeng Huang Xiu‑Fen Ma Hong‑Yi Li Xie Zhang Jiang Diao Jili Yue Guangsheng Huang Jingfeng Wang Fusheng Pan National Innovation Center for Lndustry‑Education Integration of Energy Storage Technology School of Materials Science and EngineeringChongqing UniversityChongqing 400044People’s Republic of China National Magnesium Alloy Material Engineering Technology Research Center Chongqing UniversityChongqing 400044People’s Republic of China Materials and Energy division Beijing Computational Science Research CenterBeijing 100193People’s Republic of China School of Materials Science and Engineering Northwestern Polytechnical UniversityXi’an 710072People’s Republic of China National Key Laboratory of Advanced Casting Technologies Chongqing UniversityChongqing 400044People’s Republic of China

Rechargeable magnesium-metal batteries(RMMBs)are promising next-generation secondary batteries;however,their development is inhibited by the low capacity and short cycle lifespan of cathodes.Although various strategies have been devised to enhance the Mg^(2+)migration kinetics and structural stability of cathodes,they fail to improve electronic conductivity,rendering the cathodes incompatible with magnesium-metal anodes.Herein,we propose a dual-defect engineering strategy,namely,the incorporation of Mg^(2+)pre-intercalation defect(P-Mgd)and oxygen defect(Od),to simultaneously improve the Mg^(2+)migration kinetics,structural stability,and electronic conductivity of the cathodes of RMMBs.Using lamellar V_(2)O_(5)·nH_(2)O as a demo cathode material,we prepare a cathode comprising Mg0.07V_(2)O_(5)·1.4H_(2)O nanobelts composited with reduced graphene oxide(MVOH/rGO)with P-Mgd and Od.The Od enlarges interlayer spacing,accelerates Mg^(2+)migration kinetics,and prevents structural collapse,while the P-Mgd stabilizes the lamellar structure and increases electronic conductivity.Consequently,the MVOH/rGO cathode exhibits a high capacity of 197 mAh g^(−1),and the developed Mg foil//MVOH/rGO full cell demonstrates an incredible lifespan of 850 cycles at 0.1 A g^(−1),capable of powering a light-emitting diode.The proposed dual-defect engineering strategy provides new insights into developing high-durability,high-capacity cathodes,advancing the practical application of RMMBs,and other new secondary batteries.

关键词： Rechargeable magnesium-metal batteries Dual-defect engineering Vanadium-based cathode High durability Lamellar structure

Modeling asymmetric fracture mechanics of Mg alloy wire in drawing process

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Journal of Magnesium and Alloys 2024年第5期12卷 2057-2069页

作者： Sunghoon Choi Jongwon Shin Joung Sik Suh Dongchoul Kim Department of Mechanical Engineering Sogang University Advanced Metals division Korea Institute of Materials Science

In this study, a numerical analysis was conducted on the ductile fracture of a 2-mm diameter Mg-1Zn-0.5Mn-0.5Sr-0.1Ca alloy wire during drawing. The hexagonally close-packed crystal structure of Mg alloys causes asymmetric fracture behavior, especially in the compression region. The aim of this study is to develop a comprehensive damage model for Mg alloy wire that accurately predicts ductile fracture, with a focus on the compression region. A novel experimental method was introduced to measure the ductile fracture of Mg alloy wires under different stress states. The wire drawing process was simulated using the Generalized Incremental Stress-State dependent damage(GISSMO)Model and the Semi-Analytical Model for Polymers(SAMP) model. The damage model's prediction and the experimental results were found to be in excellent agreement, especially in determining crack initiation. computational analysis established a safe zone diagram for die angle and reduction ratio, and experimental validation confirmed the feasibility of this approach. The proposed damage model can provide a practical and reliable analysis for optimizing the drawing process of Mg alloy wire.

关键词： Mg alloy Wire drawing Finite element method Damage model Safe zone diagram