A study on the distribution of adsorbed nanoparticles

We use Monte Carlo simulation to calculate the distributions of particles under adsorption force near planar and cylindrical surfaces, respectively. Both hard sphere interaction and repulsive Yukawa (screened coulomb) interaction are employed in our simulations. We study the influence of the inter-particle potentials. The difference between the MC simulation results and the analytical results of ideal gas model shows that the interaction between particles plays an important role in the density distribution under external fields. Moreover, the 2-dimensional constructions of particles close to the surface are studied and show relations of the interaction between particles. These results may indicate us how to improve the methods of building nanoparticle coatings and nano-scale patterns.     

全尺度方法对颗粒与流体之间相交换量研究

本文采用了内嵌边界多重直接力算法全尺度计算研究了三维空间中颗粒群在重力作用下沉降时,颗粒群与流体之间的相互作用过程。结合多相流的欧拉-欧拉双流体模型方法中对颗粒群与流体之间相互作用力的处理方式,分析了颗粒与流体之间的相交换量。并把全尺度计算得到的颗粒群与流体之间的相交换量与本文中提到的单颗粒受力模型(SPM)和颗粒群受力模型(GPM)对相互作用力进行了比较分析。     

Brownian dynamics simulations of a cubic haematite particle suspension with a more effective treatment of steric layer interactions

We have proposed a new repulsive layer model for describing the interaction between steric layers of coated cubic particles. This approach is an effective technique applicable to particle-based simulations such as a Brownian dynamics simulation of a suspension composed of cubic particles. 3D Brownian dynamics simulations employing this repulsive interaction model have been performed in order to investigate the equilibrium aggregate structures of a suspension composed of cubic haematite particles. It has been verified that Brownian dynamics employing the present steric interaction model are in good agreement with Monte Carlo results with respect to particle aggregate structures and particle orientational characteristics. From the viewpoint of developing a surface modification technology, we have also investigated a regime change in the aggregate structure of cubic particle in a quasi-2D system by means of Brownian dynamics simulations. If the magnetic particle–particle interaction strength is relatively strong, in zero applied magnetic field the particles aggregate in an offset face-to-face configuration. As the magnetic field strength is increased, the offset face-to-face structure is transformed into a more direct face-to-face contact configuration that extends throughout the whole simulation region.     

Two-dimensional Monte Carlo simulations of a suspension comprised of magnetic and nonmagnetic particles in gradient magnetic fields

Distributions of particles in a suspension comprised of magnetic particles (MPs) and nonmagnetic particles (NPs) under gradient magnetic fields are vitally important for the preparation of magnetic-nonmagnetic functionally graded materials (FGMs). In the present study, the effects of magnetic field gradient, magnetic interaction between MPs and concentration of NPs on the distributions of particles in the suspension are investigated using a two-dimensional Monte Carlo simulation. The results show that a gradient distribution of MPs is formed under gradient magnetic fields and increases with increasing the field gradient. However, as the interaction between MPs increases, the distribution gradient decreases, accompanied by the formation of chain-like MP clusters. Moreover, NPs are found to hinder the translation of MPs along the field direction. As the NP concentration increases, the translation of MPs becomes difficult.     

Friction coefficients and directed motion of asymmetric test particles

The behavior of a test particle in a rarefied gas of classical particles is investigated. considering different interaction mechanisms (specular and diffuse reflection, respectively). For large mass ratio between test and gas particles, analytical expressions for the linear friction coefficient are derived. Moreover, the existence of directed motion of asymmetric test particles with distinct initial conditions (but in the absence of any gradients) is shown. The analytical results are supported by a numerical simulation technique applicable to systems with any mass ratio, which is described here in detail.     

Computer simulation of the collision frequency of two particles in optical tweezers

Optical tweezers have been successfully used in the study of colloid science. In most applications people are concerned with the behaviour of a single particle held in the optical tweezers. Recently, the ability of the optical tweezers to simultaneously hold two particles has been used to determine the stability ratio of colloidal dispersion. This new development stimulates the efforts to explore the characteristics of a two-particle system in the optical tweezers.An infinite spherical potential well has been used to estimate the collision frequency for two particles in the optical trap based on a Monte Carlo simulation. In this article, a more reasonable harmonic potential, commonly accepted for the optical tweezers, is adopted in a Monte Carlo simulation of the collision frequency. The effect of hydrodynamic interaction of particles in the trap is also considered. The simulation results based on this improved model show quantitatively that the collision frequency drops down sharply at first and then decreases slowly as the distance between the two particles increases. The simulation also shows how the collision frequency is related to the stiffness of the optical tweezers.     

Particle Simulation of a 35-GHz Third-Harmonic Low-Voltage Complex Cavity Gyrotron

A self-consistent particle simulation code has been developed for the research of a 35-GHz third-harmonic Low-voltage complex cavity gyrotron. Aided with microcomputer we use FORTRAN to simulate the process of interaction between electron beam and electromagnetic field. About 7000 macro particles are included at the same time. In the program many useful physical graphs are accessible for the further research of this kind of gyrotron such as the field profile, electrons distribution in various spaces, output power, efficiency and et al. Such simulation results may be helpful to the optimization of devices operation parameters     

Verifying the reciprocity of interparticle interaction forces in strongly coupled systems

We propose a simple criterion for revealing the breaking of pair interaction symmetry in strongly coupled dissipative systems. The criterion is based on the analysis of correlations between the velocities of strongly interacting particles, which can be measured relatively easily in experiments with macroparticles in various media. We derive analytic relations that make it possible to calculate the derivatives of the interaction force between a pair of particles from the data on the correlations of their velocities and coordinates. The proposed criterion and relations are verified using the results of numerical simulation of the dynamics of dust particles in a plasma.     

Liquid–liquid phase transition and anomalous diffusion in simulated liquid GeO2

We perform molecular dynamics (MD) simulation of diffusion in liquid GeO₂ at the temperatures ranged from 3000 to 5000 K and densities ranged from 3.65 to 7.90 g/cm³. Simulations were done in a model containing 3000 particles with the new interatomic potentials for liquid and amorphous GeO₂, which have weak Coulomb interaction and Morse-type short-range interaction. We found a liquid–liquid phase transition in simulated liquid GeO₂ from a tetrahedral to an octahedral network structure upon compression. Moreover, such phase transition accompanied with an anomalous diffusion of particles in liquid GeO₂ that the diffusion constant of both Ge and O particles strongly increases with increasing density (e.g. with increasing pressure) and it shows a maximum at the density around 4.95 g/cm³. The possible relation between anomalous diffusion of particles and structural phase transition in the system has been discussed.     

Amplitude modulation and soliton formation of an intense laser beam interacting with dense quantum plasma: Symbolic simulation analysis

In this theoretical study, we investigate the amplitude modulation and envelop soliton formation in a dense plasma when such a plasma interacts with a strong laser beam. We have made use of the symbolic simulation technique to find the modulation instability of an electrostatic wave with higher orders of non-linearity. We identified the range of wavenumber in which such non-linearity is important. Furthermore, we have analysed the formation of envelope soliton of waves localized in space. The results obtained here will be helpful in interpreting different phenomena that arise in laser plasma interaction. The importance of the relativistic contribution of streaming particles is discussed alongside the parametric influences experienced by the plasma particles.     

活性Janus粒子体系中的定向运动涌现行为

本文使用过阻尼郎之万方程动力学模拟方法模拟了二维体系中活性Janus粒子的群体动力学行为. 体系随着粒子密度的增加,存在一个活性粒子的定向运动涌现行为. 此现象在无各向异性相互作用或者无活性驱动的体系中无法观察到. 另外涌现行为发生的临界转变密度会随着活性大小和各向异性相互作用强度的增大而减小,且通过调节活性大小和各向异性相互作用强度大小可以控制体系不同状态的转变. 最后借助动力学理论分析,重复出了模拟结果的基本特征. 结果论证了单个粒子层次上的各向异性相互作用足以导致活性体系进入稳定的群体定向运动.     

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.     

宇宙线高能族事例中簇射粒子的横向分布

对甘巴拉山铅乳胶室实验所获取的总观测能为100TeV至400TeV的高能族事例中簇射粒子的横向分布进行了分析,并与相应的Monte Carlo模拟计算进行了比较.模拟计算采用的是CORSIKA程序,其中的强相互作用采用QGSJET模型.结果表明:采用CORSIKA(QGSJET)程序进行模拟所给出的族事例中簇射粒子的横向分布以及族事例能量集中率分布的整体趋势均与相应的实验数据基本相符.     

Monte Carlo simulation of light scattering from size distributed sub-micron spherical CdS particles in a volume element

Simulation of polarized light scattering by spherical particles having modal radius of 180 nm is presented in this paper. A Monte Carlo method which is based on the Stokes-Mueller formalism developed in ANSI Standard C-language is used for simulation. Single scattering is considered in our program with monodispersed sub-micron sized spherical CdS particles. We have considered only θ dependent scattering as described by Mie theory for spherical CdS particles. The experiments for studying light scattering properties of these particles were conducted in a designed and developed laser based light scattering studies setup. The simulation results were compared with experimental results and theoretical results obtained purely from Mie theory. The closeness of agreement or disagreement between these results is discussed in this paper.     

驻波声场中单分散细颗粒的相互作用特性

利用外加声场促进悬浮在气相中的细颗粒发生相互作用,进而引起颗粒的碰撞和凝并,使得颗粒平均粒径增大、数目浓度降低,是控制细颗粒排放的重要技术途径.为探究驻波声场中单分散细颗粒的相互作用,建立包含曳力、重力、声尾流效应的颗粒相互作用模型,采用四阶经典龙格-库塔算法和二阶隐式亚当斯插值算法对模型进行求解.将数值模拟得到的颗粒声波夹带速度和相互作用过程与相应的解析解和实验结果进行对比,验证模型的准确性.进而研究颗粒初始条件和直径对相互作用特性的影响.结果表明,初始时刻颗粒中心连线越接近声波波动方向、颗粒位置越接近波腹点,颗粒间的声尾流效应就越强,颗粒发生碰撞所需要的时间就越短.研究还发现,颗粒直径对颗粒相互作用的影响取决于初始时刻颗粒中心连线偏离声波波动方向的程度.当偏离较小时,颗粒直径越大,颗粒发生碰撞所需要的时间越短;当偏离很大时,直径较小的颗粒能够发生碰撞,而直径较大的颗粒则无法发生碰撞.     

Two-dimensional Monte Carlo simulations of structures of a suspension comprised of magnetic and nonmagnetic particles in uniform magnetic fields

The structures of suspensions comprised of magnetic and nonmagnetic particles in magnetic fields are studied using two-dimensional Monte Carlo simulations. The magnetic interaction among magnetic particles, magnetic field strength, and concentrations of both magnetic and nonmagnetic particles are considered as key influencing factors in the present work. The results show that chain-like clusters of magnetic particles are formed along the field direction. The size of the clusters increases with increasing magnetic interaction between magnetic particles, while it keeps nearly unchanged as the field strength increases. As the concentration of magnetic particles increases, both the number and size of the clusters increase. Moreover, nonmagnetic particles are found to hinder the migration of magnetic ones. As the concentration of nonmagnetic particles increases, the hindrance on migration of magnetic particles is enhanced.     

梯度场中荧光关联谱测量的Monte Carlo模拟

荧光关联谱（FCS）利用少量分子的荧光涨落获得分子运动和反应信息,是一种探测活细胞内生物过程的有力工具。本文利用Monte Carlo方法模拟激光梯度场下瑞利粒子的布郎运动,分析梯度场对FCS测量得到的扩散时间、粒子数等参数的影响,模拟与初步实验结果定性吻合。文中还讨论了Monte Carlo模拟预测的一些实验现象。     

LES-DSMC方法研究超细颗粒气固两相流动过程

采用考虑颗粒脉动流动对气相湍流流动影响的大涡模拟(LES)研究气相湍流,采用直接模拟蒙特卡罗方法(DSMC)模拟颗粒间的碰撞。单颗粒运动满足牛顿第二定律,颗粒相和气相相间作用的双向耦合由牛顿第三定律确定,考虑超细颗粒间的van der Waals作用力。数值模拟垂直管内超细颗粒气固两相流动,对颗粒相速度、浓度以及团聚物流动过程进行分析。     

A numerical simulation of the backward Raman amplifying in plasma

This paper describe a numerical simulation method for the interaction between laser pulses and low density plasmas based on hydrodynamic approximation. We investigate Backward Raman Amplifying （BRA） experiments and their variants. The numerical results are in good agreement with experiments.     

Mesoscale simulation of aggregation of imogolite nanotubes from potential of mean force interactions

The aggregation of colloidal clay mineral particles plays an important role in controlling the mechanical and transport properties of soils. Interactions and aggregation of plate-like montmorillonite particles were previously studied with the help of Molecular Dynamics (MD) simulation. This paper investigates the aggregation of cylindrical imogolite-like phyllosilicate nanotubes. Nano-scale MD simulations are carried out to find the potential of mean force between two nanotubes. This PMF is then used in a mesoscale simulation that represents interactions between elemental nanotubes through coarse-graining. We investigate the distribution of water molecules around the curved surfaces, and the effects of the surface charge density and tube length on aggregation. Shorter nanotubes were found to form larger stacks.