Simulation of microchannel flow using the lattice Boltzmann method

For microchannel flow simulation, the slip boundary model is very important to guarantee the accuracy of the solution. In this paper, a new slip model, the Langmuir slip model, instead of the popularly used Maxwell slip model, is incorporated into the lattice Boltzmann (LB) method through the non-equilibrium extrapolation scheme to simulate the rarefied gas flow. Its feasibility and accuracy are examined by simulations of microchannel flow. Although, for simplicity, in this paper our recently developed LB model is used to solve the flow field, this does not prevent the present boundary scheme from easily incorporating other LB models, for example the more advanced collision model with multiple relaxation times. In addition, the existing non-equilibrium extrapolation LB boundary scheme for macroscopic flows can be recovered naturally from the present scheme when the Knudsen number .     

Modeling of wave dispersion along cylindrical structures using the spectral method

Algorithm and code are presented that solve dispersion equations for cylindrically layered media consisting of an arbitrary number of elastic and fluid layers. The algorithm is based on the spectral method which discretizes the underlying wave equations with the help of spectral differentiation matrices and solves the corresponding equations as a generalized eigenvalue problem. For a given frequency the eigenvalues correspond to the wave numbers of different modes. The advantage of this technique is that it is easy to implement, especially for cases where traditional root-finding methods are strongly limited or hard to realize, i.e., for attenuative, anisotropic, and poroelastic media. The application of the new approach is illustrated using models of an elastic cylinder and a fluid-filled tube. The dispersion curves so produced are in good agreement with analytical results, which confirms the accuracy of the method. Particle displacement profiles of the fundamental mode in a free solid cylinder are computed for a range of frequencies.     

色散周期结构的辅助场时域有限差分法分析

利用辅助场时域有限差分(FDTD)方法分析色散周期结构的斜入射问题. 主要基于Floquet定理, 在FDTD迭代式中引入辅助场量, 结合变换的周期及吸收边界条件,解决了周期结构斜入射问题的电磁特性仿真. 进一步将辅助场FDTD方法引入至色散周期结构的模拟, 结合Z变换方法,给出了基于Drude色散模型的具体迭代公式. 数值计算结果表明所构建方法的有效性及普适应.     

相场晶体法模拟过冷熔体中的晶体生长

利用相场晶体(phase-field crystal)模型,采用有限差分法,模拟了过冷熔体中晶体生长过程,研究了不同相区、不同过冷度对晶体生长过程的影响.结果表明,在共存区中,随着演化的进行,晶体生长被抑制,液-晶边界层逐渐变厚;在单相区中,随着过冷度的增大,晶态区面积显著增加,液-晶边界层逐渐变薄.晶体生长速度和过冷度成近似线性的关系. 关键词： 相场晶体 自由能函数 过冷熔体 晶体生长     

Antireflection subwavelength structures analyzed by using the finite difference time domain method

Antireflection subwavelength structures (ASSs) are analyzed by using the finite difference time domain (FDTD) method in the visible light spectrum. Low reflectance can be obtained by both the conical and pyramidal shapes over a broadband range. Comparing the reflectance of different structure shapes and aspect ratios by the FDTD method, it shows that the antireflection efficiencies of the pyramidal structures are better than that of the conical structures when the aspect ratio is up to 0.8. It is found that, for the conical structure surface, the average transmittance increases gradually with the aspect ratio and the average transmittance is about 99.6% with the aspect ratio of 2.0. However, for the pyramidal structure with the aspect ratio ranging from 1.0 to 2.0, the average transmittance is up to 99.7%.     

Pulsed method for measuring the capacitance of semiconductor structures using a ballast capacitor

An easily implemented method for measuring the capacitance of semiconductor structures using small-amplitude current pulses is described. It is shown that the accuracy of the method described can be improved significantly when a ballast capacitor is employed and, in addition, a calibration procedure is performed. The influence of the ballast capacitor on the measurement process is analyzed in detail. Zh. Tekh. Fiz. 69, 82–84 (March 1999)     

Analysis of flow structures in supersonic plane mixing layers using the POD method

The proper orthogonal decomposition (POD) method was applied to analyzing the database obtained from the direct numerical simulation (DNS) of supersonic plane mixing layers. The effect of different forms of the inner products in the POD method was investigated. It was observed that the mean flow contributes to a predominant part of the total flow energy, and the energy spectrum of the turbulence fluctuations covers a wide range of POD modes. The patterns of leading (high energy) POD modes reveal that the flow structures exhibit spanwise counter rotating rolls, as well as oblique vortices. These flow patterns are insensitive to the velocity of the observer. As the convective Mach number increases, the energy spectrum becomes wider, the leading POD modes contain more complicated structures, and the flow becomes more chaotic.     

光学相干层析信号的模拟分析与计算

对传统的模拟介质散射响应函数的蒙特卡罗算法的计算过程进行了改进，提出光子不可分割的假设，这样可以避免人为选定光子被吸收阈值的不确定性；同时采用双曲线法模拟入射高斯光束，解决了对表面为非平面介质的传输信号进行模拟的问题.通过对盖玻片（平面）与眼角膜（曲面）的光学相干层析探测信号及层析图的数值模拟，并与相应实验结果进行比较，证实了该方法与假设的可行性. 关键词： 光学相干层析 蒙特卡罗法模拟 散射     

Simulation of the formation of porous-silicon structures

The formation of porous silicon is investigated by the Monte Carlo method in a model that takes account of the nonuniformity of the charge distribution over the silicon-electrolyte interface, hole diffusion, generation, and recombination processes, and size quantization. The structures obtained in a computer simulation for various doping levels of the crystalline substrate, temperatures, HF concentrations, and anode current densities are presented. Analysis of nanoporous structures shows that the porosity depends on the depth and reveals the presence of a fractal dimensionality on scales of less than 10 nm. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 9, 685–690 (10 May 1997)     

Simulation of the nonlinear vibration of a string using the cellular automation method

In this study, the nonlinear dynamic responses of a string were simulated using the cellular automaton (CA) method. The local rules were set for the amplitude of vibration and the decay rate of amplitude. In the case of nonlinear systems, the velocity of wave propagation is not constant and depends on the amplitude. Thus, a new treatment of the time step was proposed, i.e., the time step in the CA method is adjusted to real time by considering the effect of the propagation velocity. As numerical examples, first, the dynamic responses of a string with linear characteristic were simulated and a typical resonance curve could be obtained. Secondly the dynamic responses of a string with nonlinear characteristic were simulated. Some characteristic types of vibration could be obtained. It was concluded that the linear and nonlinear dynamic responses of a string could be simulated using the CA method.     

Simulation of plasma doping process by using the localized molecular dynamics method

Plasma doping is the candidate for semiconductor doping. Accurate simulation of the doping technology is needed for the advanced integrated circuit manufacturing. In this paper, the plasma doping process simulation is performed by using the localized molecular dynamics method. Models that involve the statistics of the implanted compositions, angles and energies are developed. The effect of the model on simulation results is studied. The simulation results about the doping concentration profile are supported by experimental data.     

相场法模拟多元合金过冷熔体中的枝晶生长

在二元合金相场模型研究的基础上，进行扩展获得了多元合金相场模型.以Al-Si-Mg三元合金为例，采用该相场模型实现了逼真地模拟多元合金凝固过程的等轴枝晶生长，得到了二次或更高次晶臂生长等复杂的枝晶形貌.随着第三组元Mg含量的减少，枝晶的二次枝晶越发达，枝晶中溶质的偏析越严重，枝晶尖端的生长速率和半径越大，与丁二腈-丙酮体系中枝晶尖端生长速率、半径随溶质浓度变化关系的理论计算和实验结果相符合.另外，枝晶初生晶臂中心的溶质浓度最低，在被二次晶臂包围的界面区域的溶质浓度最高；固液界面区域具有较大的浓度梯度，其中枝晶尖端前沿的梯度最大. 关键词： 相场法 多元合金 凝固过程 枝晶生长     

Passive and active interior noise control of box structures using the structural intensity method

This paper presents passive and active vibro-acoustic noise control methods for attenuating the interior noise level in box structures which can be an analogy of cabins of vehicle and aircraft. The structural intensity (SI) approach is adopted to identify the predominant vibration panels and interior noise sources for box structures. In the study, the finite element method is used to determine the structural vibration and structural intensity in the box surfaces. According to structural intensity vectors plot and structural intensity stream lines presentation, the possible effective control positions where the dampers may be attached and the active control forces may act to reduce vibration and interior noise, are identified. From the study, it can be demonstrated that the structural intensity approach and stream line presentation are possible methods for identifying the vibro-acoustic interior noise source and predominant panels which may be modified to reduce the interior noise level. The structural intensity methodology, passive and active noise control results can be extended to the further study of the vibration and interior noise control of actual cabins of vehicles and aircraft.     

平行束缪子透射成像蒙特卡罗模拟

使用蒙特卡罗程序Geant4,模拟平行束缪子垂直于理想探测器平面入射法国试验客体（FTO）模型,在模型的上方和下方各放置三块理想探测器,用以输出缪子位置信息,从而确定入射与出射缪子径迹。通过三种方法统计缪子穿过模型前后的透射比,对模型进行透射成像,得到不同的成像结果。统计方法一和方法二分辨力可达2 mm2 mm,统计方法三可达1 mm1 mm,Cu与W区分较为明显,而且可显示出FTO模型中心的空气球,FTO模型与模型周围空气的边界十分清晰。模拟结果表明,平行束入射缪子可以进行透射成像。     

一种主动浮标阵的定位解算方法仿真分析

在研究单枚主动定向浮标定位原理的基础上,推导出一种利用最小二乘法解算多枚浮标的定位结果的方法,并针对圆阵就阵元个数、圆阵半径以及测距误差对该解算方法的性能影响进行了数值仿真分析。仿真结果表明,该算法在测向均方误差较大或者目标在距离圆内的情况下,性能远优于单枚主动定向浮标;圆阵半径2 km左右,阵元个数在6左右时,该解算方法的性能达到最佳。此外,该解算算法很容易被扩展至三维定位问题,因此有一定的理论和应用价值。     

Deformation study of bicrystalline and nano-polycrystalline structures using phase field crystal method

Deformation behaviors of bicrystalline and nano-polycrystalline structures of various tilt angles and inclination angles in two dimensions are investigated in detail using a two-mode phase field crystal model.The interaction between grain boundary(GB)and dislocation is also examined in bicrystals and nano-polycrystals that both contain asymmetric and symmetric tilt GBs,with energy analysis being carried out to analyze these processes.During deformation simulations,we assume the volume of each simulation cell at every time step is coincident with that of the initial state just before deformation.Our simulation results show that the behaviors of symmetric and asymmetric GBs in bicrystals and nano-polycrystals differ from each other depending on tilt angle and inclination angle.A new dislocation emission mechanism of interest is observed in bicrystals which contain low angle symmetric tilt GBs.Low angle GB has a higher mobility relative to high angle GB in both bicrystalline and nano-polycrystalline structures,as does asymmetric GB to symmetric GB.The generation,motion,pileup and annihilation of dislocations,grain rotation and grain coalescence are observed,which is consistent with the simulation results obtained by molecular dynamics.These simulation results can provide strong guidelines for experimentation.     

Study of the stable structures of Ga6As6 cluster using FP-LMTO MD method

We have investigated the structures and energies of a Ga₆As₆ cluster using full-potential linear-muffin-tin-orbital molecular-dynamics calculations. 9 stable structures were obtained for a Ga₆As₆ cluster, including the structure, a cube with two capped Ga–As pairs considered by Yi (Chem. Phys. Lett. 325 (2000) 269), who used the Car–Parrinello method based on the pseudopotential method and the local density functional formalism. However, the ground state we obtained is a distorted structure of a bicapped pentaprism, the energy of which is lower than that of Yi. Furthermore, we found the structure a1 presented semiconductor-like properties through the calculation of the density of states.     

大粒子数二维硬核玻色子系统的量子蒙特卡罗模拟

采用随机级数展开的量子蒙特卡罗方法研究二维硬核的玻色-赫伯德模型的热力学性质. 首先通过算符变换将模型映射成为二维反铁磁准海森伯模型. 变换后的模型比通常的海森伯模型多一项, 该项正比于系统的格点总数 N, 对于大粒子数的系统, 该项使模拟耗时指数增加, 所以难以计算大粒子数系统.采用非局域操作循环更新后, 这个困难可以得到很好的解决, 可使粒子数总数增大到几千个.研究结果表明, 粒子数密度在0-0.5范围内增大时, 能量呈递减趋势, 并趋于某一定值, 随着正方晶格系统尺度增大, 能量也随之增大;正方晶格系统尺度一定时, 能量和磁化强度随着温度的升高而增大, 化学势的变化对能量和磁化强度没有影响, 能量随着正方晶格系统尺度增大而增大, 磁化强度却随之减小;正方晶格系统尺度一定时, 化学势的增大对比热没有影响, 随着温度的升高比热出现先增大后减小的趋势, 最后趋于某个值, 达到平衡, 而正方晶格系统尺度越大, 比热曲线增大部分的趋势越大, 减小部分的趋势也更明显, 参照朗道超流理论, 本文模拟的能量和比热曲线趋势与朗道二流体模型下He II的理论研究一致; 不同正方晶格系统尺度的影响不大, 均匀磁化率倒数在0-0.5(J/k_B)的低温范围内有很小的波动, J为耦合能, k_B为玻尔兹曼常数, 温度在0.5-2 (J/k_B)的范围内, 均匀磁化率的倒数随着温度的升高而增大, 且曲线的趋势显示了一种类似近藤行为.