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Molecular dynamics simulation of thermal stability of nanocrystalline vanadium

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Science china(Technological Sciences) 2006年第4期49卷 400-407页

作者： WEI Mingzhi1, XIAO Shifang1, YUAN Xiaojian2.& HU Wangyu1,2.1. Material Science and Engineering College,{2., changsha 410082. china 2. Department of Applied Physics,{2., changsha 410082. china Material Science and Engineering College Hunan University Department of Applied Physics Hunan University

The microstructure and thermal stability of nanocrystalline vanadium with an average grain size ranging from 2.86 to 7.50 nm are calculated by means of the analytic embedded-atom method and molecular dynamics. The grain boundary and nanocrystal- line grain atoms are differentiated by the common neighbor analysis method. The results indicate that the fraction of grain boundary increases with the grain size decreasing, and the mean energy of atoms is higher than that of coarse crystals. The thermal-stable tem- peratures of nanocrystalline vanadium are determined from the evolution of atomic energy, fraction of grain boundary and radial distribution function. It is shown that the stable tem- perature decreases obviously with the grain size decreasing. In addition the reasons which cause the grain growth of nanocrystalline vanadium are discussed.

关键词： nanocrystalline, embedded-atom method, molecular dynamics, thermal stability.

Study on H atoms diffusion and adsorption properties of MgH_2.V systems

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Science china(Technological Sciences) 2008年第7期51卷 979-988页

作者： ZHOU DianWu1,2. LIU JinShui3 & PENG Ping3 1 State Key Laboratory of Advanced Design and Manufacturing for Vehicle Body, hunan university,{2. 2.College of Mechanical and Automatic Engineering, hunan university,{2. 3 College of Materials Science and Engineering, hunan university,{2. State Key Laboratory of Advanced Design and Manufacturing for Vehicle Body Hunan University College of Mechanical and Automatic Engineering Hunan University College of Materials Science and Engineering

Based on experimental results that VH0.81/MgH2.interface was found during the process of mechanically milling MgH2.5at.%V nanocomposite, H atoms diffusion and adsorption properties of MgH2.V systems have been investigated by using a first-principles plane-wave pseudopotential method based on the density functional theory. The results are as follows. When VH/MgH2.interface is formed due to V alloying MgH2.phase, the vacancy formed by H atoms near VH phase region is more stable than that without V alloying, while vacancy near MgH2.phase region is less stable than that without V alloying. During the process of H atoms diffusion after V alloying, the max migration barrier energy of H atoms in MgH2.V systems is reduced compared with that of MgH2.phase, which means that H atoms diffuse easily. When H diffuses into VH from MgH2.across VH/MgH2.interface, among three substitutions such as the replacement of H for V vacancy, or interstitial site or V atoms, the replacement of H for V vacancy has the strongest diffusion ability, next interstitial site, and finally V atoms site. As far as H adsorbed on different surfaces of VH phase is concerned, physical adsorption is carried out more easily than chemical adsorption, and the behavior of H atoms adsorbed on the surface near VH phase region can be found more easily than that near MgH2.phase region.

关键词： plane-wave pseudopotential theory magnesium hydride diffusion adsorption

Size distributions and magic number characteristics of cluster configurations formed during solidification processes of liquid metal Al

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Science china(Technological Sciences) 2006年第2期49卷 172-187页

作者： LIU Rangsu1, LIU Fengxiang1, DONG Kejun1, ZHENG Caixing1, LIU Hairong2. PENG Ping2.& LI Jiyong3 1. Department of Physics,{2., changsha 410082. china 2. Department of Material Science and Engineering,{2., changsha 410082. china 3. Department of Chemistry,{2., changsha 410082. china Department of Physics Hunan University

A molecular dynamics simulation study has been performed for a large systemconsisting of 100000 liquid metal Al atoms to investigate the formation and magic numbercharacteristics of the cluster configurations formed during the rapid solidification processes. Thecluster-type index method (CTIM) has been adopted to describe various types of clusterconfigurations. The results indicate that the icosahedral clusters (12.0 12.0) and theircombinations play the most important role in the rnicrostructure transitions during solidificationprocesses; for the cluster configurations of different levels formed by various combinations withdiffering numbers of basic clusters, their size distributions possess obvious magic number sequencewhich is in turn as 13(13), 19(2.), 2.-2.(2.), 32.33(32., 39-40, 43-44, 48..., (those in bracket arethe corresponding value in liquid state); the magic numbers correspond to the peak value positionsof the cluster numbers for corresponding level formed with various combinations by 1, 2. 3, 4, 5, 6,7, ...basic clusters, respectively. This magic number sequence is in good agreement with theexperimental results obtained by Harris et al. At the same time, this simulation study also gives ascientific and reasonable explanation to these experimental results.

关键词： liquid metal, solidification processes, cluster configuration, magic numbers, computer simulation.

Formation and evolution mechanisms of large-clusters during rapid solidification process of liquid metal Al

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Science china(Physics,Mechanics & Astronomy) 2005年第1期48卷 101-112页

作者： LIU Rangsu, DONG Kejun, LIU Fengxiang, ZHENG Caixing, LIU Hairong & LI Jiyong Department of Applied Physics, hunan university, changsha 410082. china College of Materials Science and Engineering, hunan university, changsha 410082. china College of Chemistry and Chemical Engineering, hunan university, changsha 410082. china Department of Applied Physics Hunan University Changsha 410082 China College of Materials Science and Engineering Hunan University Changsha 410082 China College of Chemistry and Chemical Engineering Hunan University Changsha 410082 China

A molecular dynamics simulation study has been performed for the formation and evolution characteristics of nano-clusters in a large-scale system consisting of 400000 atoms of liquid metal Al. The center-atom method combined with pair-bond analysis technique and cluster-type index method (CTIM) has been applied here to describe the structural configurations of various basic clusters. It is demonstrated that both the 1551 bond-type and the icosahedral cluster (12.0 12.0) constructed by 1551 bond-types are dominant among all the bond-types and cluster-types, respectively, in the system and play a critical role in the microstructure transitions of liquid metal Al. The nano-clusters (containing up to 150 atoms) are formed by the combination of some middle and small clusters with distinctly different sizes, through mutual competition by unceasing annex and evolution in a seesaw manner (in turn of obtaining and losing),which do not occur as the multi-shell structures accumulated with an atom as the center and the surrounding atoms are arranged according to a certain rule. This is the essential distinction of nano-cluster in liquid metal from those obtained by gaseous deposition, ionic spray methods, and so on. Though the nano-clusters differ from each other in shape and size, all of them possess protruding corners that could become the starting points of various dendrite structures in the solidification processes of liquid metals.

关键词： liquid metal, solidification process, large-cluster configuration, evolution mechanism, computer simulation.

Asymptotic stability for nonautonomous delay differential equations

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Chinese Science Bulletin 1997年第20期42卷 1676-1679页

作者： YU JiansheDepartment of Applied Mathematics, hunan university, changsha 410082. china Department of Applied Mathematics Hunan University Changsha China

MANY dynamic population models can be transformed to the form of delay differential equationx（t） + λx（t） + f（t,x（t-τ1）,….,x（t-τm））=0,t≥0,（1）where the biologically meaningful equilibrium of the original equation is transformed into thezero equilibriurn of （1）. Throughout this note, we assume that λ>0,τi>0（i=1,…,m ）,

关键词： delay equation stability asymptotic stability.

A new orthogonality relationship for orthotropic thin plate theory and its variational principle

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Science china(Physics,Mechanics & Astronomy) 2005年第3期48卷 371-380页

作者： LUO Jianhui 1 , LONG Yuqiu 2.& LIU Guangdong 1 1. College of Civil Engineering, hunan university,{2. 2. Department of Civil Engineering, Tsinghua {2., Beijing 100084, china College of Civil Engineering Hunan University Changsha China Department of Civil Engineering Tsinghua University Beijing China

The thought how dual vectors are constructed in a new orthogonality relationship for theory of elasticity is generalized into orthotropic thin plate bending problems by using the analogy theory between plane elasticity problems and plate bending problems. Dual differential equations are directly obtained by using a mixed variables method. A dual differential matrix to be derived possesses a peculiarity of which principal diagonal sub-matrixes are zero matrixes. Two independently and symmetrically orthogonality sub-relationships are discovered. By using the integral form for elastic bending theory of orthotropic thin plate the orthogonality relationship is demonstrated. By selecting felicitous dual vectors a new orthogonality relationship for theory of elasticity can be generalized into elastic bending theory of orthotropic thin plate. By using the integral form a variational principle which is relative to differential form and a whole function expression are proposed.

关键词： theory of elasticity, thin plate theory, dual vectors, orthogonality relationship, orthotropic, variational principle.

Research on Uncertainties in Evaluation Indicator System for Ecological Residential Community

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湖南大学学报（自然科学版） 2009年第S1期36卷 177-181页

作者： JIAO Sheng1,GUAN Chen-yin2.ZENG Guang-ming3,LIU Jian-long1,Zhou Jian-fei3(1.College of Architecture,hunan {2.,{2.,hunan 410082.china 2.Beijin School,hunan {2. of Commerce,{2.,hunan 4102.9,china 3.College of Environmental Science and Engineering,hunan {2.,{2.,hunan 410082.china) College of Architecture Hunan University Changsha 410082 China Beijin School Hunan University of Commerce Changsha 410209 China College of Environmental Science and Engineering Hunan University Changsha 410082 China

In the process of evaluating,the weights of indicators are firstly determined by AHP and Delphi methods;and the values of indicators are normalized by grey correlative coefficient method.A suit of means were put forward,by which a qualitative and quantitative evaluation indicator system suitable for the situation of china and uncertainties can be *** idiographic and operable methods and process were *** the principle of elasticity,hiberarchy and maneuverability,a three-layer evaluation indicator system was established by AHP in Jiuyi ecological residential community,which includes 5 subsystems and 2. *** weights of indicators are measured by AHP and expert estimate and their best indicators values up to par were determined by fuzzy mathematics and *** whole evaluation indicator system not only has an active and practical effect on estimating ecological residential community,but also guides ecological residential community planning.

关键词： ecological residential community evaluation indicator system ecological risk evaluation uncertainty fuzzy mathematics grey correlative coefficient

Extended Fan's Algebraic Method and Its Application to KdV and Variant Boussinesq Equations

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Communications in Theoretical Physics 2007年第7期48卷 1-6页

作者： YANG Xian-Lin TANG Jia-Shi College of Mechanics and Aerospace,hunan university,{{2. 410082.china{2.Department of Computer Science,hunan Radio and Television university,{{2. 410004,china College of Mechanics and Aerospace Hunan University Department of Computer Science Hunan Radio and Television University

An extended Fan's algebraic method is used for constructing exact traveling wave solution of nonlinearpartial differential *** key idea of this method is to introduce an auxiliary ordinary differential equationwhich is regarded as an extended elliptic equation and whose degree Υ is expanded to the case of r>*** efficiency ofthe method is demonstrated by the KdV equation and the variant Boussinesq *** results indicate that themethod not only offers all solutions obtained by using Fu's and Fan's methods,but also some new solutions.

关键词： algebraic method KdV equation variant boussinesq equations polynomial complete discrimination system

A DISCRETE CHARACTERIZATION OF HERZ-TYPE TRIEBEL-LIZORKIN SPACES AND ITS APPLICATIONS

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Acta Mathematica Scientia 2004年第3期24卷 412-420页

作者： XuJingshi DepartmentofMathematics HunanUniversityChanysha410082China

In this paper, the author establishes a discrete characterization of the Herz-type Triebel-Lizorkin spaces which is used to prove the boundedness of pseudo-differential operators on these function spaces.

关键词： Herz-type space Triebel-Lizorkin space discrete characterization pseudo-differential operator maximal operator