胶体中排空作用的耦合效应

通过Monte Carlo模拟和接受率方法研究了限制在圆柱形管道中大胶球之间以及大胶球与管壁之间排空作用的耦合效应.研究发现,当两个大胶球靠近时,大胶球之间的排空作用因与大胶球与管道壁之间的排空作用耦合而得到加强,同样当大胶球与管道壁靠近时,大胶球与管道壁之间的排空作用也因与另一大胶球之间排空作用的耦合而得到了加强.此外,研究还发现,随着圆柱形管道直径的减小,胶球之间、胶球与管道壁之间的排空作用的耦合效应是增强的. 关键词： 排空作用的耦合效应 接受率方法 Monte Carlo模拟     

约束条件下胶球间排空力的研究

用MonteCarlo方法对处于两平行硬板约束下三个浓度的大小胶球系统进行了模拟,通过对大胶球表面小胶球密度的统计,由密度积分公式获得了大胶球所受的排空力.研究结果显示,因为平行硬板的存在或当改变两平行硬板的距离时,同浓度下,排空力在硬板距离小的时候最明显;三个浓度中,浓度高的,排空力受硬板距离影响最大;有硬板约束比无该约束的时候,排空力效果更显著.     

描述离散系统动力学演变的Monte Carlo方法分析

通用动力学方程通过描述离散系统中颗粒尺度分布的演变过程来量化颗粒动力学演变过程,而Monte Carlo(MC)算法是求解通用动力学方程的重要方法.目前几种主流的MC算法为Liffman的直接模拟Monte Carlo算法(DSMC)、阶梯式常体积法、常数目法和多重Monte Carlo(MMC)算法.利用这些MC算法描述理想的纯凝并工况和纯破碎工况,发现:由于避免了多个动力学事件之间的解耦过程,基于事件驱动的MC算法比基于时间驱动的MC算法具有更高的计算精度和更低的计算代价;由于尽量减少对整体系统的扰动,阶梯式恢复模拟颗粒数目的MC算法比连续式恢复模拟颗粒数目的MC算法具有更高的精度;由于始终保持计算区域体积,多重Monte Carlo算法具有更友好的扩展性.     

相干介观系统中散粒噪声的Monte Carlo模拟方法研究

根据电荷通过低温量子导体时具有的二项分布导致散粒噪声这一结论,结合Landauer电流公式的物理内涵建立了相干介观系统中的散粒噪声模型,并通过Monte Carlo模拟方法产生了散粒噪声时间序列.介观系统中散粒噪声的抑制来源于电子输运时的相关性,传输本征值双峰分布导致量子混沌腔和无序金属中的散粒噪声抑制.根据这两个结论,通过Monte Carlo模拟定性地分析了传输本征值分布与电子输运相关性之间的关系. 关键词： 散粒噪声 Landauer公式 介观系统     

6H-SiC电子输运的Monte Carlo模拟

从实际测量和单粒子Monte Carlo模拟两个方面研究了6H-SiC的电子输运规律,在模拟中考 虑了6H-SiC主要的散射机理,模拟的结果体现了6H-SiC具有良好的高温和高场特性以及迁移 率的各向异性,其横向迁移率和纵向迁移率相差近5倍.模拟结果和实验数据的对比说明了对 6H-SiC输运特性的模拟是正确的. 关键词： 6H-SiC Monte Carlo模拟 迁移率 散射机理     

任意入射辐射条件下介质特性对瞬态辐射传递的影响

用基于Monte Carlo法的DRESOR法在平行平板系统内具有吸收、无发射介质中研究不同波形入射、壁面反射、介质散射率、光学厚度、各向异性散射等条件对瞬态辐射传递的影响.任意连续波形入射辐射是目前大多数数值方法很难处理的瞬态辐射问题,而DRESOR法通过在系统内计算一单位入射辐射能对介质的DRESOR数分布,就能计算任意连续波形入射辐射条件下高方向分辨率的瞬态辐射强度结果.DRESOR法和Monte Carlo法计算的结果进行了比较验证,两者吻合较好,证明了DRESOR法处理瞬态入射辐射问题的正确性和有效性.     

变分累积展开方法中确定相变点的新方法

在计算有限温度SU(2)格点规范模型Polyakov线的过程中,考虑到变分累积展开法中有限距离相互作用效应与Monte Carlo中的有限体积效应的相似性,采用了新的方法来确定相变点.与已有的方法以及Monte Carlo模拟给出的结果比较,新方法给出的结果更接近Monte Carlo结果.     

可见光在CsI:Na转换屏中传输的模拟研究

本文用Monte Carlo方法模拟了X射线与转换屏作用产生的可见光子在无晶柱和理想晶柱转换屏中的传输过程,给出了可见光子在转换屏中的点扩展函数,并计算了其MTF.结果表明,晶柱结构的转换屏能有效地改善转换屏的空间分辨特性.同时,本文还给出了转换屏的转换效率及传输效率与球管电压、转换屏厚度之间关系的模拟结果.     

SU(2) Group Space Decimation有效作用量的Monte Carlo研究

我们在4⁴周期性正方格点对SU(2)-Y(120)群Group Space Decimation有效近似作用量进行了Monte Carlo模拟, 发现有效作用量系统在β≤9没有凝固点, 但有效作用量系统的内能曲线与SU(2) Wilson作用量的内能曲线有差别. 这说明, 虽然Group Space Decimation方法原则上可使分立子群代替连续群进行Monte Carlo模拟, 但就减少计算机模拟时间来说不是非常有效.     

光学应用 光学医学应用

R318.51 2005010798 散射介质中时间分辨漫反射的Monte Carlo模拟及其前瞻 =Monte Carlo simulation of time-resolved diffuse reflectance in turbid media[刊,中]／徐兰青(福建师范大学物理与光电信息科技学院.福建．福州(350007)),李晖…∥福光接术.-2004,26(1)．-60-63 综述了Monte Carlo方法在时间分辨漫反射法中的应用,介绍了时间分辨漫反射法测量组织光学特性参数的几种较为有效的时域Monte Carlo模拟算法,并对发展现状和趋势作了评价。图2参13(于晓光)     

Effects of unsymmetrical geometric confinements on depletion interactions in colloidal suspensions

The depletion interactions between two large-spheres immersed in a fluid of small spheres under unsymmetrical geometrical confinement are studied through the acceptance ratio method. The numerical results show that no matter whether the volume fraction is large or small, both the depletion potential and depletion force are affected by the presence of the two plates; the closer the two large spheres are to the plate, the larger the effects of the unsymmetrical confinements.     

Effects of electrostatic interactions and geometrical confinements on depletion interactions in charged colloidal system

In a charged colloidal system, the influence on depletion interaction between two like-charged macro-ions is studied through Monte Carlo simulation in this paper. The numerical results show that this depletion force is affected by both the electrostatic interactions between charged spheres and charged plates and by the geometrical factor of the two charged plates, and they further indicate that the influence of geometrical confinement on the depletion interaction is larger than that of electrostatic potential.     

Grand Canonical Ensemble Monte Carlo Simulation of Depletion Interactions in Colloidal Suspensions

Depletion interactions in colloidal suspensions confined between two parallel plates are investigated by using acceptance ratio method with grand canonical ensemble Monte Carlo simulation. The numerical results show that both the depletion potential and depletion force are affected by the confinement from the two parallel plates. Furthermore, it is found that in the grand canonical ensemble Monte Carlo simulation, the depletion interactions are strongly affected by the generalized chemical potential.     

One class of electrostatic fields perfectly conserving the parallelism of planar homogeneous beams of charged particles

Electrostatic systems whose field is a superposition of two two-dimensional fields with the plane of symmetry (midplane) in common are considered. It is assumed that these fields overlap in the region through which a charged particle beam passes. The basic property of these systems is that they perfectly (without angular aberrations) conserve the parallelism of charged particle beams that are homogeneous in terms of energy-to-charge ratio and pass in the midplane of the field. A four-electrode system where each of the electrodes consists of two plates symmetric with respect to the midplane is an example of the new-class electrostatic systems.     

Depletion interactions in cylindric pipeline

In a colloidal system confined by a small cylindric pipeline, the depletion interaction between two large spheres is different to the system confined by two plates, and the influence on depletion interaction from the pipeline is related to both the size and shape of it. In this paper, the depletion interactions in the systems confined by pipelines of different sizes or different shapes are studied by Monte Carlo simulations. The numerical results show that the influence on depletion force from the cylindric pipeline is stronger than that from two parallel plates, and the depletion force will be strengthened when the diameter of the cylinder is decreased. In addition, we also find that the depletion interaction is rather affected if the shape change of the pipeline is slightly changed, and the influence on depletion force from the shape change is stronger than that from the size change.     

Effective interactions in the charged colloidal system

In the charged colloidal system, with the aid of the hyper-sphere method, the effective interactions between two like-charged macro-ions are studied through Monte Carlo simulations. Numerical results show that the depletion interactions dominate the total Coulomb interactions in the region while the two macro-ions are near.     

Closed-form solution of mid-potential between two parallel charged plates with more extensive application

Efficient calculation of the electrostatic interactions including repulsive force between charged molecules in a biomolecule system or charged particles in a colloidal system is necessary for the molecular scale or particle scale mechanical analyses of these systems. The electrostatic repulsive force depends on the mid-plane potential between two charged particles. Previous analytical solutions of the mid-plane potential, including those based on simplified assumptions and modern mathematic methods, are reviewed. It is shown that none of these solutions applies to wide ranges of interparticle distance from 0 to 10 and surface potential from 1 to 10. Three previous analytical solutions are chosen to develop a semi-analytical solution which is proven to have more extensive applications. Furthermore, an empirical closed-form expression of mid-plane potential is proposed based on plenty of numerical solutions. This empirical solution has extensive applications, as well as high computational efficiency.     

A new constituent of electrostatic energy in semiconductors

The concept of electric energy is revisited in detail for semiconductors. We come to the conclusion that the main relationship used to calculate the energy related to the penetration of the electric field in semiconductors is missing a fundamental term. For instance, spatial derivate of the electrostatic energy using the traditional formula fails at giving the correct electrostatic force between semiconductor based capacitor plates, and reveals unambiguously the existence of an extra contribution to the standard electrostatic free energy. The additional term is found to be related to the generation of space charge regions which are predicted when combining electrostatics with semiconductor physics laws, such as for accumulation and inversion layers. On the contrary, no such energy is needed when relying on electrostatics only, as for instance when adopting the so-called full depletion approximation. The same holds for neutral and charged insulators that are still consistent with the customary definition, but these two examples are in fact singular cases. In semiconductors for instance, this additional energy can largely exceed the energy gained by the dipoles, thus becoming the dominant term. This unexpected result clearly asks for a generalization of electrostatic energy in matter in order to reconcile basic concepts of electrostatic energy in the framework of classical physics.     

二维情况下两组分带电囊泡形变耦合相分离的理论模拟研究

结合离散空间变分方法和耗散动力学研究了二维两组分带电囊泡的形变耦合相分离,系统地考察了囊泡带电量组分含量、带电组分的电荷密度、两组分间的相容性和温度等因素对形变耦合相分离动力学的影响.模拟结果表明电荷引入可增加不同组分间的表观相溶性.当温度较高时,静电相互作用可直接抑制囊泡相分离,避免了同种组分的团聚;当温度较低时,静电相互作用则可明显增加分相相区数目,使其呈微观相分离,从而避免了同种组分大范围的团聚.