MacPherson-Srolovitz晶粒长大速率方程的仿真验证

2007年MacPherson和Srolovitz联合推导出一个三维个体晶粒长大的准确速率方程,但并未给出实验或计算机仿真的验证.采用Potts模型Monte Carlo方法对该速率方程进行了大尺度仿真验证.结果表明,仿真数据与MacPherson-Srolovitz速率方程符合很好,从而初步证实了该速率方程,即三维晶粒长大速率是晶粒棱长和晶粒平均宽度的函数. 关键词： 三维晶粒长大 速率方程 Monte Carlo仿真     

基于检测光纤的漫射高光谱采集的Monte Carlo仿真

从漫射高光谱中可以获得被测物体成分、结构及其分布等信息。采用光纤光谱仪获取漫射高光谱是一种常用的方法。Monte Carlo方法在研究光在浑浊介质的传播方面得到了广泛的应用。然而,使用Monte Carlo方法研究漫射高光谱时,必须考虑实际的检测条件对信号采集的影响。将光纤参数引入到Monte Carlo模型中,研究了光纤参数对被检测光学信号的影响。仿真结果表明,孔径角和半径增大,检测的漫射高光谱随之增大,而光纤与被测物质表面的距离小于1 mm时对漫射高光谱的影响在一定程度上可以忽略。进一步研究发现存在固定的修正系数使不同孔径角的光纤所采集的漫射高光谱转化为孔径角为π/2的光纤对应的信号。同时,得到了实际光纤孔径角范围内的修正系数拟合曲线。不同半径的光纤通过面积归一化可以得到很好的一致性。研究检测光纤参数对漫射高光谱的影响对实际测量有重要的指导意义,而且不同光纤所对应的检测结果可以通过修正系数和面积归一化进行移植。     

薄膜生长的理论模型与Monte Carlo模拟

用Monte Carlo方法模拟了薄膜的二维生长.引入Morse作用势描述粒子间的相互作用情况,研究了相互作用范围α对薄膜生长初期形貌的影响.薄膜的生长经历了由临界核的形成、团的长大、形成迷津结构到连续成膜4个阶段.模拟结果表明,随着沉积粒子数的增加,成团粒子所占百分比下降.这与实际情况相符. 关键词： 薄膜生长 Monte Carlo方法 Morse势     

材料中He深度分布演化的Monte Carlo模拟研究

基于He泡生长的迁移-合并机理,用Monte Carlo方法模拟了对材料进行等温退火过程中He深度分布的演化,探讨了不同参数对这一演化的影响.研究表明:材料中He泡的初始浓度和尺寸将影响He深度分布的变化,而退火温度则对演化速率起重要作用但对最终的He深度分布影响较小;随着反应的进行,整个系统的演化是逐渐趋缓的. 关键词： He 深度分布 Monte Carlo模拟     

多分散高浓度介质偏振光后向扩散散射的Monte Carlo仿真

建立了针对多分散高浓度介质偏振光后向扩散散射的Monte Carlo仿真模型，导出了多分散 系统的有效自由程分布函数. 给出了半径为50nm与550nm及其三种不同体积浓度比混合的聚 苯乙烯微球作为散射粒子的高浓度介质的仿真结果. 定性地分析了多分散介质偏振光后向扩 散散射的光强空间分布特征与粒子的体积浓度比的关系. 关键词： 后向扩散散射 偏振光 多分散高浓度介质 Monte Carlo仿真     

τ质量测量方案的Monte Carlo研究

在τ质量实验测量之前对多种测量方案进行了细致的Monte Carlo研究,并进行了比较.确定τ质量测量实验采用最大似然法,并给出可能的测量精度.研究了包括探测效率、束流能散等诸多因素对实验的影响,同时对实验的实现提出要求.     

偏振光在非球形气溶胶中传输特性的Monte Carlo仿真

非球形气溶胶是影响辐射传输的重要因素. 系统给出了矢量辐射传输Monte Carlo模型, 并验证了其准确度; 考虑入射光偏振态, 讨论了不同方向漫射光Stokes矢量对气溶胶形状的敏感性; 分析了气溶胶形状、入射光偏振状态对光波退偏振度、透过率及反射率的影响. 模拟仿真结果表明, 对于不同偏振态的入射光, 不同方向的Stokes矢量对气溶胶形状变化的灵敏程度并不一致, 而在天顶角0°方向区域,Q, U及V分量对形状的灵敏程度普遍不高; 气溶胶形状对反射漫射光退偏程度的影响强于透射漫射光, 入射光偏振态不同, 漫射光退偏程度也存在较大差异. 气溶胶形状对光波整体透过率与反射率影响显著, 且该影响随传播距离增大而增大; 入射光偏振态对透过率与反射率影响相对较小, 与自然光相比, 水平偏振光透过率略偏小, 反射率略偏大, 垂直偏振光反之, 圆偏振光与自然光的模拟结果相当.     

TEXONO中微子实验屏蔽效果的Monte Carlo研究

TEXONO实验采用CsI (T1)晶体量能器测量反应堆低能中微子的能谱和通量,确定中微子ν_e的反常磁矩并为中微子振荡实验做技术准备.详细描述了屏蔽体的安排,本底的主要来源,基于GEANT3软件包做了Monte Carlo研究,得到屏蔽体对本底的屏蔽效果.     

微空心阴极放电的Monte Carlo模拟研究

基于MATLAB与VC++混合语言，采用Monte Carlo模拟对高气压下亚毫米级微空心阴极放电（MHCD）中电子的运动过程进行了研究，计算出不同气压下的稳态时场向电子密度分布，电子能量分布以及对各种碰撞的统计等.分析表明：高气压下微空心阴极放电更能反映空心阴极效应——“来回振荡”的本质.通过模拟得到，电子在阴极间来回振荡的过程中，仍以前向散射为主.随着气压的升高，侧向散射效应逐渐体现出来. 关键词： 微空心阴极 Monte Carlo 负辉区 碰撞截面     

超薄膜生长的Monte Carlo模拟研究

利用Monte Carlo(MC)方法模拟研究了薄膜生长的初始阶段岛的形貌和岛的尺寸与基底温度和入射粒子剩余能量之间的关系.模型中考虑了粒子的沉积、吸附粒子的扩散和蒸发等过程.结果表明当基底温度从200K变化到260K时,岛的形貌经历了一个从分散生长逐渐过渡到分形生长的过程,并且在较低温度(200K)下,随入射粒子剩余能量的增加,岛的形貌也经历了同样的变化过程.进一步研究证明,随着基底温度的升高或入射粒子剩余能量的增加,沉积粒子的扩散能力显著增强,从而使岛的形貌发生了改变.     

Monte Carlo simulation of electron avalanches and avalanche size distributions in methane

The simulation of electron avalanches and avalanche size distributions in methane is presented in this paper. A model for electron transport under the influence of a constant electric field based on the Monte Carlo method is described in detail. The model is verified and then used to simulate the avalanche development, to calculate the number of electrons in the avalanche (avalanche size), and to determine the avalanche size distribution. The simulated avalanche size distributions in methane are compared with the experimental results, and a good agreement is observed. The influence of inter‐electrode distance, pressure, and reduced electric field on the shape of the avalanche size distribution is discussed. The assumption from the literature that for a constant reduced electric field the shape of the reduced avalanche size distribution is independent of the mean size of the avalanche is confirmed for a wide range of experimental conditions. The simulations have shown that avalanche size distributions depend only on the reduced electric field, confirming the similarity principle.     

Kinetic-diffusion asymptotic-preserving Monte Carlo algorithms for plasma edge neutral simulation

We developed novel Monte Carlo simulation strategies for the neutral model in plasma edge simulations where both low-collisional and high-collisional regimes are present. To maintain accuracy and reduce simulation costs in high-collisional regimes, we use hybridized particles that exhibit both kinetic and diffusive behaviour depending on the local collisionality. The method maintains an asymptotically correct distribution and a correct mean, variance, and time correlation for all values of the collisionality. We apply this scheme to a fusion case with a strongly heterogeneous background, prompting the inclusion of a diffusion-induced drift. Our numerical results show a large increase in efficiency at the expense of a minor bias.     

Monte Carlo simulation of grain growth in polycrystalline materials

Understanding the kinetics of grain growth, under the influence of second phase (such as impurities, voids and bubbles) is fundamental to advances in the control of microstructural evolution. As a precursor to this objective, we have investigated the grain growth kinetics in a polycrystalline material using a standard Q-state Potts’ model under Monte Carlo settings. Based on physical reasoning, new modifications are suggested to circumvent some of the disadvantages in the basic Potts model. The efficacy of these modifications vis-à-vis the basic model is verified. The influence of second phase particles on the impurity loaded grain boundaries is investigated for the study of grain growth kinetics.     

Monte Carlo simulation of the enantioseparation process

By means of Monte Carlo simulation, a study of enantioseparation by capillary electrophoresis has been carried out. A simplified system consisting of two enantiomers S (R) and a selector chiral C, which reacts with the enantiomers to form complexes RC (SC), has been considered. The dependence of Δμ$\Delta \mu$ (enantioseparation) with the concentration of chiral selector and with temperature have been analyzed by simulation. The effect of the binding constant and the charge of the complexes are also analyzed. The results are qualitatively satisfactory, despite the simplicity of the model.     

Monte Carlo simulation for temperature dependence of Ga diffusion length on GaAs(0 0 1)

Diffusion length of Ga on the GaAs(0 0 1)-(2×4)β2 is investigated by a newly developed Monte Carlo-based computational method. The new computational method incorporates chemical potential of Ga in the vapor phase and Ga migration potential on the reconstructed surface obtained by ab initio calculations; therefore we can investigate the adsorption, diffusion and desorption kinetics of adsorbate atoms on the surface. The calculated results imply that Ga diffusion length before desorption decreases exponentially with temperature because Ga surface lifetime decreases exponentially. Furthermore, Ga diffusion length L along and [1 1 0] on the GaAs(0 0 1)-(2×4)β2 are estimated to be and L_[110]200 nm, respectively, at the incorporation–desorption transition temperature (T860 K).     

Monte Carlo simulation of hydrogen adsorption on Ni surfaces

In the present paper the adsorption kinetics of the hydrogen molecule on the (111) and (100) surfaces have been studied with the model proposed by Panczyk and the grand canonical Monte Carlo simulation method. The equilibrium adsorption isotherms are calculated at five different temperatures ranging from 314 K to 376 K and compared with the experimental equilibrium adsorption isotherms. The effects of temperature and pressure on coverage are also analyzed.      

Monte Carlo simulation of metal deposition on foreign substrates

The deposition of a metal on a foreign substrate is studied by means of grand canonical Monte Carlo simulations and a lattice-gas model with pair potential interactions between nearest neighbors. The influence of temperature and surface defects on adsorption isotherms and differential heat of adsorption is considered. The general trends can be explained in terms of the relative interactions between adsorbate atoms and substrate atoms. The systems Ag/Au(1 0 0), Ag/Pt(1 0 0), Au/Ag(1 0 0) and Pt/Ag(1 0 0) are analyzed as examples.     

硅纳米薄膜中声子弹道扩散导热的蒙特卡罗模拟

通过建立声子散射概率函数描述声子在输运过程中的散射,提出了一种模拟声子弹道扩散导热的蒙特卡罗方法,并将其应用于硅纳米薄膜中的稳态和瞬态弹道扩散导热过程的研究. 提出的蒙特卡罗方法对边界发射的声子束进行跟踪,根据散射概率函数模拟声子束在传播区域内经历的散射过程,并通过统计声子束的分布得到温度分布. 稳态导热过程的模拟发现,尺寸效应会引起边界温度跳跃,其值随着Knudsen数的增大而增大;计算的硅纳米薄膜的热导率随着厚度的增大而增大,与文献中的实验数据和理论模型相符. 通过瞬态导热过程的模拟得到了纳米薄膜内的温度分布随时间的变化,发现瞬态导热过程中的热波现象与空间尺度相关,材料尺寸越小,弹道输运越强,薄膜中的热波现象也越显著. 关键词： 纳米薄膜 弹道扩散导热 蒙特卡罗模拟 尺寸效应     

Monte Carlo simulation of magnetic nanostructured thin films

Using Monte Carlo simulation, we have compared the magnetic properties between nanostructured thin films and two-dimensional crystalline solids. The dependence of nanostructured properties on the interaction between particles that constitute the nanostructured thin films is also studied. The result shows that the parameters in the interaction potential have an important effect on the properties of nanostructured thin films at the transition temperatures.