Melting properties of mixed Ni13-xAlx(x=0 to 13) clusters

Starting from the configuration full optimized by Genetic Algorithm (GA), the melting behaviors of Binary Ni13-xAlx(x=0 to 13) clusters have been investigated by Monte Carlo (MC) simulations with Metropolis algorithm with a n-body Gupta potential. In contrast to bulk, these clusters have smeared first order transitions occurring over a range of temperature. The melting temperature Tm calculated from Lindemanns criterion vary drastically with concentrations x. For most clusters studied, the average energy per atom E, the relative root-mean-square (rms) bond length fluchuation δ and the heat capacity C per atom related to the energy fluctuation of the system change with temperature in the transition region in manners differing from LJ and alkali metal clusters. For Ni12Al, Ni7Al6, Ni6Al7, Ni5Al8 clusters, there are behaviors characteristic of magic number in C, which do not exist in the pure TM clusters.     

浅海相干声场不确定性研究

提出一种采用随机响应面法求解浅海中含不确定参数波动方程的方法.将海洋环境不确定参数表示为标准随机变量,利用Hermite多项展开式表示相干声场的随机响应,用概率配点法求解随机多项式系数后,获得相干声场的近似表达式.通过与Monte Carlo法、声场位移法比较,表明本文方法计算精度和效率较高.     

Gruhn-Hess两体势修正模型向列相液晶微滴的Monte Carlo模拟

基于Gruhn-Hess两体势修正模型,用Monte Carlo方法模拟向列相液晶微滴.Gruhn-Hess两体势是空间各向异性的,修正模型的势参数依赖于液晶的弹性常数K₁₁、K₂₂、K₃₃及表面弹性常数K₁₃.假设向列相液晶微滴具有自由表面,在低温下计算分子二阶序参数和切向内禀强度在微滴内不同区域的变化,并与Gruhn-Hess两体势模型一作对比分析.结果表明:附加K₁₃项的修正模型在微滴表面产生内禀锚定,其大小决定了内禀易取向方向及内禀锚定强度的大小,且内禀强度的大小与K₃₃/K₁₁值有关;空间不完整的向列相液晶微滴由内层到外层有序度逐渐降低.     

Deposition pressure effect on the surface roughness scaling of microcrystalline silicon films

The scaling behaviour of surface roughness evolution of microcrystalline silicon (μc-Si:H) films prepared by very-high frequency plasma-enhanced chemical vapour deposition (VHF-PECVD) has been investigated by using a spectroscopic ellipsometry (SE) technique. The growth exponent β was analysed for the films deposited under different pressures P_g. The results suggest that films deposited at P_g = 70 Pa have a growth exponent β about 0.22, which corresponds to the definite diffusion growth. However, abnormal scaling behaviour occurs in the films deposited at P_g = 300 Pa. The exponent β is about 0.81 that is much larger than 0.5 of zero diffusion limit in the scaling theory. The growth mode of μ c-Si:H deposited at P_g= 300 Pa is clearly different from that of μc-Si:H at P_g = 70 Pa. Monte Carlo simulations indicate that the sticking process and the surface diffusion of the radicals are two key factors to affect the growth mode under different pressures. Under P_g= 300 Pa, β>0.5 is correlated with the strong shadowing effect resulting from the larger sticking coefficient.     

分子核间距对非时序双电离的影响

利用半经典再散射模型研究了激光强度在一定范围内时分子核间距对非时序双电离过程的影响.分别计算了非时序双电离率、两电子的电离能、两电子的动量相关、Coulomb和激光场的复合势随分子核间距的变化关系.研究表明,分子核间距在1.0—6.0 a.u.范围内时,非时序双电离率和两电子动量和为零的双电离事件数随着分子核间距的增大而增大.当分子核间距继续增大(大于6.0 a.u.)时,非时序双电离率和两电子动量和为零的双电离事件数却减小.     

Multiple scattering of light by water cloud droplets with external and internal mixing of black carbon aerosols

The mixture of water cloud droplets with black carbon impurities is modeled by external and internal mixing models.The internal mixing model is modeled with a two-layered sphere(water cloud droplets containing black carbon(BC) inclusions),and the single scattering and absorption characteristics are calculated at the visible wavelength of 0.55 μm by using the Lorenz-Mie theory.The external mixing model is developed assuming that the same amount of BC particles are mixed with the water droplets externally.The multiple scattering characteristics are computed by using the Monte Carlo method.The results show that when the size of the BC aerosol is small,the reflection intensity of the internal mixing model is bigger than that of the external mixing model.However,if the size of the BC aerosol is big,the absorption of the internal mixing model will be larger than that of the external mixing model.     

格子Boltzmann守恒型非平衡态的外推边界

针对非平衡态外推边界处理方法在某些条件下发生质量泄漏的问题,结合质量守恒定律对其进行修正,建立一种新的质量守恒型的边界处理格式.其基本思想是在边界处定义一个虚拟密度来修正平衡态分布函数,使得系统质量守恒.以重力作用下的密度场及磁流体模拟问题为例,利用该格式进行分析,讨论质量泄露问题的本质及各种因素的影响.通过对三种典型的流动:二维Poiseuille流、Couette流、Womersley流的模拟,验证该边界格式的计算精度和稳定性.     

Kinetic Monte Carlo simulations of three-dimensional self-assembled quantum dot islands

By three-dimensional kinetic Monte Carlo simulations, the effects of the temperature, the flux rate, the total coverage and the interruption time on the distribution and the number of self-assembled InAs/GaAs(001) quantum dot(QD) islands are studied, which shows that a higher temperature, a lower flux rate and a longer growth time correspond to a better island distribution. The relations between the number of islands and the temperature and the flux rate are also successfully simulated. It is observed that for the total coverage lower than 0.5 ML, the number of islands decreases with the temperature increasing and other growth parameters fixed and the number of islands increases with the flux rate increasing when the deposition is lower than 0.6 ML and the other parameters are fixed.     

巨正则量子Monte Carlo方法和二维Hubbard模型的研究

用巨正则量子Monte Carlo方法,计算了二维单带Hubbard模型的局域磁矩、磁化率、交错磁化率和内能等物理量.结果表明,用巨正则量子Monte Carlo方法能够统一地研究Hubbard模型的关联强度从弱至强区域的性质,它是处理强关联多体系统的有效方法.     

路径积分Monte Carlo方法与非线性随机振动

给出了一种求解非线性随机振动问题的新方法-基于路径积分表述的Monte Carlo方法。受白噪声激励的非线性系统的各响应统计值被表成路径积分形式,并采用Monte Carlo方法进行计算。讨论了应用方面的问题,并计算了两个实例。