Prisoner＇s Dilemma Game with Nonlinear Attractive Effect on Regular Small-World Networks

We investigate a spatial Prisoner＇s Dilemma game with nonlinear attractive effect on regular small-world networks. The players located on the sites of networks can either cooperate with their neighbours or defect. In every generation, each player updates its strategy by firstly choosing one of the neighbours with a probability proportional to .A^α denoting the attractiveness of the neighbour, where .4 is the collected payoff and ^α （-〉0） is a free parameter characterizing the extent of nonlinear effect. Then each player adopts its strategy with a probability dependent on their payoff difference. Using Monte Carlo simulations, we investigate the density pc of cooperators in the stationary state for various values of α and the rewiring probability q of the network. It is shown that the introduction of such attractive effect remarkably promotes the emergence and persistence of cooperation over a wide range of the temptation to defect for the same network structures. We also point out that long-range connections either enhance or inhibit the cooperation, which depends on the value of α and the payoff parameter b.     

High-temperature Raman spectroscopic study of vanadoborate Na_3VO_2B_6O_(11)

Raman spectra of a vanadoborate(Na3VO2B6O11) crystal from room temperature up to the melting point have been recorded. The main internal vibrational modes of the crystal have been assigned. It was found that all the Raman bands exhibit decreases in frequency and the widths of the Raman bands increase with the increase of temperature. However,no phase transition was observed under 525℃. The micro-structure of its melt was studied by quantum chemistry ab initio calculation. The continuous three-dimensional network of the crystal collapsed and transformed into VO_4 and VBO_6 clusters during the melting process with an isomerization reaction from four-coordinated boron to a three-coordinated species.     

Theoretical study of a melting curve for tin

The melting curve of Sn has been calculated using the dislocation-mediated melting model with the `zone-linking method'. The results are in good agreement with the experimental data. According to our calculation, the melting temperature of γ -Sn at zero pressure is about 436~K obtained by the extrapolation of the method from the triple point of Sn. The results show that this calculation method is better than other theoretical methods for predicting the melting curve of polymorphic material Sn.     

Phase Transition and Melting Curves of Calcium Fluoride via Molecular Dynamics Simulations

The phase transition and melting curves of CaF2 are investigated by using the general utility lattice programme （CULP） via the shell model with molecular dynamics method. By calculating the entropy H （at OK） and Cibbs free energy G^＊ （at 30OK）, we find that the phase transition pressure from the face-centred cubic （fee） structure to the orthorhombic structure is 11.40 CPa and 9.33 CPa at OK and 300K, respectively. The modified melting point of the fee CaF2 is in the range of 1650-1733K at OCPa. All these results are well consistent with the available experimental data and other theoretical results. We also obtain that the melting temperature of high pressure phase is 990-1073 K at 10 CPa. Moreover, the temperature dependences of the elastic constants Cij, bulk module B and shear module G are also predicted.     

Effect of Intense Laser Irradiation on the Lattice Stability of Al_2Au

The structural, electronic and lattice-dynamical properties of the intermetallic Al 2 Au at different electronic temperatures have been investigated via density functional calculations. The results of electronic density of state indicate that, although its value changes considerably, Al2Au is still of metal with the increasing of electronic temperature. The acoustic mode of Al2Au gets negative which leads to lattice dynamical instability when the electronic temperature is beyond 1.44 eV. Moreover, with the increasing of the electronic temperature, the vibrational frequencies of the T1u optical mode (triply degenerate) of Al2Au at Γ point decrease first and increase then, the turning point is at Te = 1.40 eV. T2g optical mode at Γ point has a similar situation, but the turning point is at Te = 1.80 eV. The predicted melting temperatures of Al2Au undergo a sharp decrease from 1333K at normal temperature to 1172 K at Te = 1.8 eV after intense laser irradiation.     

Surface-Induced Melting of Metal Nanoclusters

We investigate the size effect on melting of metal nanoclusters by molecular dynamics simulation and thermodynamic theory based on Kofman‘s melt model. By the minimization of the free energy of metal nanoclusters with respect to the thickness of the surface liquid layer, it has been found that the nanoclusters of the same metal have the same premelting temperature Tpre = To - To(γsu - γlu - γsl)/(ρLξ) (To is the melting point of bulk metal, γsu the solid-vapour interracial free energy: γlu the liquid-vapour interracial free energy, γsl the solid-liquid interracial free energy, p the density of metal, L the latent heat of bulk metal, and ξ the characteristic length of surface-interface interaction) to be independent of the size of nanoclusters, so that the characteristic length ξ of a metal can be obtained easily by Tpre, which can be obtained by experiments or molecular dynamics (MD) simulations. The premelting temperature Tpre of Cu is obtained by MD simulations, then ξ is obtained.The melting point Tcm is further predicted by free energy analysis and is in good agreement with the result of our MD simulations. We also predict the maximum premelting-liquid width of Cu nanoclusters with various sizes and the critical size, below which there is no premelting.     

Stochastic bounded consensus tracking of leader-follower multi-agent systems with measurement noises and sampled-data

<正>This paper is concerned with the stochastic bounded consensus tracking problems of leader-follower multi-agent systems,where the control input of an agent can only use the information measured at the sampling instants from its neighbours or the virtual leader with a time-varying reference state,and the measurements are corrupted by random noises.The probability limit theory and the algebra graph theory are employed to derive the necessary and sufficient conditions guaranteeing the mean square bounded consensus tracking.It is shown that the maximum allowable upper boundary of the sampling period simultaneously depends on the constant feedback gains and the network topology. Furthermore,the effects of the sampling period on the tracking performance are analysed.It turns out that from the view point of the sampling period,there is a trade-off between the tracking speed and the static tracking error. Simulations are provided to demonstrate the effectiveness of the theoretical results.     

EXAFS study on the local atomic strucures around iron in glycosylated haemoglobin

Samples with 5.1%9.8% and 15.3% HbA1c were extracted from normal subjects and patients with slight and serious diabetes respectively.Extended x-ray absorption fine structure spectra of Fe K absorption were collected at the EXAFS experimental station of the Beijing Synchrotron Radiation Facility.The step-by-step fluorescent mode was employed with a count time of 10s per point.Several independent scans were averageed to eliminate the statistical nosie.Reference backscattering amplitudes and phaseshifts were calculated using the curve wave theory (FEFF code) of EXAFS.Apart from the nitrogen neighbors around the central iron atom,oxygen neighbours are also found.The Fe-Nbond length increases by about 0.02A for the sample with 15.3% HbAlc Compared with the others,but the Fe-Obond length is almost unchanged.With increasing of HbAlc concentration,the content of Hb increases and the content of HbO2 decreases.This demonstrates that the glycosylation of haemoglobin will decrease its ability to carry oxygen.     

Structural and thermal stabilities of Au@Ag core-shell nanoparticles and their arrays:A molecular dynamics simulation

Thermal stability of core-shell nanoparticles(CSNPs)is crucial to their fabrication processes,chemical and physical properties,and applications.Here we systematically investigate the structural and thermal stabilities of single Au@Ag CSNPs with different sizes and their arrays by means of all-atom molecular dynamics simulations.The formation energies of all Au@Ag CSNPs we reported are all negative,indicating that Au@Ag CSNPs are energetically favorable to be formed.For Au@Ag CSNPs with the same core size,their melting points increase with increasing shell thickness.If we keep the shell thickness unchanged,the melting points increase as the core sizes increase except for the CSNP with the smallest core size and a bilayer Ag shell.The melting points of Au@Ag CSNPs show a feature of non-monotonicity with increasing core size at a fixed NP size.Further simulations on the Au@Ag CSNP arrays with 923 atoms reveal that their melting points decrease dramatically compared with single Au@Ag CSNPs.We find that the premelting processes start from the surface region for both the single NPs and their arrays.     

Atomic and Electronic Structures of Zr Atomic Chains

The atomic, binding and electronic structures of very thin Zr chains are studied by the first-principles density functional method. The present calculations reveal that zirconium can form planar chains in zigzag, dimer and ladder structures. The zigzag geometry has two minima. The most stable geometry is the zigzag one with a unitcell rather close to equilateral triangles with four nearest neighbours. The other stable zigzag structure has awide bond angle and allows for two nearest neighbours. An intermediary structure has the ladder geometry andis formed by two strands. The dimer structure is also found to be more stable than the truly linear chain. Allthese planar geometries are more favourable energetically than the linear chain. We also show that by going fromZr bulk to a Zr chain, the characters of bonding do not change significantly.     

Test of universality in anisotropic 3D Ising model

Chen and Dohm predicted theoretically in 2004 that the widely believed universality principle is violated in the Ising model on the simple cubic lattice with more than only six nearest neighbours. Schulte and Drope by Monte Carlo simulations found such violation, but not in the predicted direction. Selke and Shchur tested the square lattice. Here, we check only this universality for the susceptibility ratio near the critical point. For this purpose we study first the standard Ising model on a simple cubic lattice with six nearest neighbours, then with six nearest and 12 next-nearest neighbours, and compare the results with the Chen–Dohm lattice of six nearest neighbours and only half of the 12 next-nearest neighbours. We do not confirm the violation of universality found by Schulte and Drope in the susceptibility ratio.     

小尺寸铝纳米团簇的相变行为

采用分子动力学方法模拟了半径从0.3–1.3 nm变化的小尺寸铝纳米团簇的熔化、凝固行为. 基于势能-温度曲线、热容-温度曲线分析, 获得了熔点、凝固点与尺寸的依变关系, 并利用表面能理论、小尺寸效应开展了现象分析.研究表明, 铝团簇原子数小于80时, 熔点和凝固点的尺寸依赖性出现无规律的异常变化; 而大于该原子数, 熔、凝固点则随着团簇尺寸的减小而单调下降; 当原子数为27时, 团簇熔点高于块材熔点近40 K. 同时, 铝纳米团簇呈现出凝固滞后现象, 即凝固点低于熔点. 关键词： 纳米团簇 熔点 凝固点 分子动力学     

纳米团簇熔化过程的分子动力学模拟

本文采用分子动力学结合嵌入原子多体势,模拟了不同半径的Ni纳米团簇的升温熔化过程,研究团簇尺寸对熔点和表面能的影响.模拟结果表明:团簇的熔点显著低于体材料的熔点.团簇熔化的过程首先是在团簇的表面出现预熔,然后向团簇内部扩展,直到整个团簇完全熔为液态.在模拟的纳米尺度范围内,团簇的熔点与团簇尺寸基本成线性关系.团簇的表面能随着团簇尺寸的增大而减小,而且表面能均高于体材料的表面能.     

Molecular dynamics simulations on the melting of gold nanoparticles

Molecular dynamics is employed to study the melting of bulk gold and gold nanoparticles. PCFF, Sutton-Chen and COMPASS force fields are adopted to study the melting point of bulk gold and we find out that the Sutton-Chen force field is the most accurate model in predicting the melting point of bulk gold. Consequently, the Sutton-Chen force field is applied to study the melting points of spherical gold nanoparticles with different diameters. Variations of diffusion coefficient, potential energy and translational order parameter with temperature are analyzed. The simulated melting points of gold nanoparticles are between 615～1115 K, which are much lower than that of bulk gold (1336 K). As the diameter of gold nanoparticle drops, the melting point also descends. The melting mechanism is also analyzed for gold nanoparticles.     

应变效应对金属Cu表面熔化影响的分子动力学模拟

采用Mishin镶嵌原子势，通过分子动力学方法模拟了金属Cu 的(110)表面在不同应变下的熔 化行为，分析了表面熔化过程中系统结构组态和能量的变化以及固液界面迁移情况.金属Cu 的(110)表面在低于热力学熔点的温度下发生预熔化，准液体层的厚度随温度升高而增加.当 温度高于热力学熔点时，固液界面的移动速度与温度成正比，外推得到热力学熔点为1380K ，与实验结果1358K吻合良好.应变效应（包括拉伸和压缩）导致热力学熔点降低，并促进表 面预熔化进程.在相同温度条件下，准液体层的厚度随应变绝对值的增加而增大.应变效应导 致的固相自由能增加是金属Cu(110)表面热稳定性下降的主要因素，且表面应力和应变方向 的异同也会影响表面预熔化的进程. 关键词： 表面预熔化 热力学熔点 表面应力 分子动力学     

Thermal transport in melting and recrystallization of amorphous and polycrystalline Si thin films

The liquid-solid interface motion and temperature history of thin Si films during excimer laser annealing are observed by in situ experiments combining time-resolved (~1 ns) electrical conductance, optical reflectance/transmittance at visible and near-IR wavelengths and thermal emission measurements. For laser energy densities causing partial melting, the maximum temperature remains close to the melting point of amorphous silicon (a-Si). When complete melting occurs, substantial supercooling is observed, followed by spontaneous nucleation. These phase transformations are consistent with the recrystallized poly-Si morphologies. It is also found that the melting of poly-Si occurs close to the melting point of crystalline silicon. This temperature is higher than the melting point of a-Si by about 100-150 K.     

MEAM势与Tersoff势比较研究——碳化硅熔化与凝固行为

运用分子动力学方法对比模拟研究了碳化硅的体熔化、表面熔化和晶体生长过程.分别采用MEAM 势和Tersoff势两种势函数描述碳化硅.结果表明:体熔化时,两种势函数描述的SiC的原子平均能量、 Lindemann指数和结构有序参数与温度的变化关系相似,但MEAM势对应的体熔点(4250 K)比Tersoff势(4750 K) 的要高.表面熔化时,两种势函数描述的SiC在相同的过热度下熔化速度相近;而在相同的温度条件下,MEAM 作用的SiC表面熔化速度更快.这是由于MEAM势SiC的热力学熔点(3338 K)低于Tersoff势SiC的热力学熔点 (3430 K)的缘故.两种势函数作用的SiC在晶体生长方面差异很大.MEAM势SiC的晶体生长速度与过冷度有关, 过冷度约为400 K时晶体生长速度最快.但Tersoff势SiC晶体却在过冷度为0—1000 K的范围内均不能生长. 综合考虑,MEAM势比Tersoff势能更好地描述碳化硅的熔化和凝固行为.     

铜原子纳米团簇热力学性质的分子动力学模拟研究

利用分子动力学模拟方法,研究了CuN(N=80,140,216,312,408,500,628和736)纳米团簇在热化和冷凝过程中结构和热力学性质的变化,模型采用的是Johnson的EAM作用势.模拟结果表明:铜团簇的熔点和凝固点随其尺寸线性增加,并逐渐向大块晶体靠拢;所有团簇的凝固点都低于熔点,出现凝固过程中的滞后现象;在熔点和凝固点附近,团簇都具有负热容特性,负热容是由相变前后团簇内部结构突变引起的.     

The pre-melting absorption of sound by In2Bi

Longitudinal ultrasound sets mobile dislocations into oscillation relative to the small liquid domains that develop near the melting point. The resultant attenuation goes inversely as the temperature displacement somewhat below the melting point, in agreement with the observations of Saunders and his colleagues.     

铂纳米粒子热稳定性的原子级模拟研究

本文采用分子动力学结合嵌入原子多体势,模拟了铂纳米粒子在升温过程中的热稳定性和熔化机制,并利用共近邻分析方法分析了它的微结构演化过程。模拟的结果表明：铂纳米粒子的熔点明显低于体材料的熔点;由于表面层原子的结合力较弱,在升温过程中表面会首先出现预熔;纳米粒子的熔化是从表面层开始的,并随着温度的升高,熔化的表面层会逐渐向内部扩展,最终导致纳米粒子整体转变为液态结构;当温度低于表面预熔温度时,纳米粒子保持良好的晶态结构。