Electron transport in semiconductors in the presence of impact ionization

The development of impact ionization in semiconductors has been considered. A transport equation for the electron distribution function in the presence of impact ionization has been derived. It has been found that the collison integral of this equation is nonlinear with respect to the distribution function. The relation between the solutions of this equation and the usual Boltzmann equation have been determined. A Monte Carlo method for numerical calculations in the presence of impact ionization has been developed. The results of numerical calculations carried out using a simplified model of indium antimonide are presented.     

Resonance in the polarization spectrum of a two-level atom in a polychromatic field

A numerical solution has been obtained for a two-level atomic system interacting with a 101-component polychromatic field. The analytical method of recurrence relations has confirmed the numerical calculations. The resonance in the polarization spectrum follows the transition frequency.     

高斯激光场中穿进轨道电子横向动量的阈值

采用数值模拟计算的方法,分析了强激光场中电子的动力学特性,发现穿进轨道电子的入射动量存在一定的阈值.通过研究穿进轨道电子的动力学特征,探讨了电子入射动量的阈值条件,发现与阈值相关的两个因素:激光强度和光束腰宽,推导了阈值的定标关系,结果显示:定标式与数值计算结果基本相符合.     

Explicit and implicit finite difference schemes for fractional Cattaneo equation

In this paper, the numerical solution of fractional (non-integer)-order Cattaneo equation for describing anomalous diffusion has been investigated. Two finite difference schemes namely an explicit predictor–corrector and totally implicit schemes have been developed. In developing each scheme, a separate formulation approach for the governing equations has been considered. The explicit predictor–corrector scheme is the fractional generalization of well-known MacCormack scheme and has been called Generalized MacCormack scheme. This scheme solves two coupled low-order equations and simultaneously computes the flux term with the main variable. Fully implicit scheme however solves a single high-order undecomposed equation. For Generalized MacCormack scheme, stability analysis has been studied through Fourier method. Through a numerical test, the experimental order of convergency of both schemes has been found. Then, the domain of applicability and some numerical properties of each scheme have been discussed.     

Comparison of image characteristics in projection photolithography

The characteristics of images formed by some typical photomasks have been compared using numerical simulation. The technique for estimating the critical dimensions of image elements has been considered. The dependences of the critical dimensions on the numerical aperture and coherence parameter for a light source with a circular aperture and for different types of photomasks have been analyzed.     

化学工程中分形问题的正交配置法

将欧氏空间中的正交配置法扩展到分数维的情况,并将它应用于化学工程中具有分形结构的反应扩散问题的计算.并将计算结果与理论解的相应结果作了对比.     

Simulation of transmission coefficient through a triangular potential barrier

An analytical expression of the transmission coefficient for the electron transport through a triangular potential barrier has been modified for solution using the method of numerical simulation. The triangular potential barrier has been modelled as a staircase function. The performance of this numerical simulation method is briefly described. The simulation has been developed for personal computer IBM PC AT.     

Enhancement of charging and discharging rates in a latent heat storage system by use of PCM with different melting temperatures

A latent heat storage module with rapid charging and discharging rates has been developed. The heat storage module consisted of horizontal cylindrical capsules filled with three types of PCM with different melting temperatures. A numerical model has been developed to predict the transient behavior of the heat storage module. Both the experimental and numerical results showed some improvements in charging and discharging rates by use of a “three-type” PCM     

Computation of the Reflection Coefficient of a Triangular Semiconductor Prism in a Rectangular Waveguide

In this paper we present a method to solve Maxwell's equations that enables to compute waveguide structure containing a semiconductor triangular prism. The numerical study has showed that the triangular prism in the waveguide has a wider frequency band in comparison with a square rod under equal conditions. The reflection coefficient dependencies on frequency, prism size and its permittivity have been computed. The algorithm and computer programme have been tested and compared with the numerical results and experimental data of the paper [1] with good agreement.     

船型体煤粉燃烧器流场的数值模拟

本文将贴体坐标用于具有复杂形状的船型体煤粉燃烧器的三维流场数值模拟中，建立了在贴体坐标下的总体质量校正方程。计算结果令人满意。同时，对存在的问题作了进一步讨论。     

Work hardening and recovery in fully lamellar TiAl: relative activity of deformation systems

The relative activity of deformation systems during work hardening and thermal recovery has been investigated in fully lamellar TiAl. This has been done by a combination of a series of deformation/static recovery experiments and numerical simulations based on a defect density-based crystal plasticity model. Firstly, active deformation systems in differently oriented polysynthetically twinned crystals/single lamellar colonies have been studied. Subsequently, numerical experiments on a polycolony microstructure have been used to investigate the inhomogeneous microplasticity (i.e. the typical microyield) in fully lamellar TiAl. From this, it has been possible to analyse how changes in the lamella thickness, domain size and colony size influence the onset of macroscopic yield. Based on static recovery experiments with differently oriented polysynthetically twinned crystals, numerical studies have revealed trends in the recovery of work hardening in both polysynthetically twinned crystals and polycolony microstructures.     

Spinpolarized OPW-band structure of magnetic semiconductors with application to EuO. Part II

The OPW-method has been generalized for the calculation of spinpolarized energy bands in magnetic semiconductors and applied to the ferromagnetic semiconductor EuO. Part II describes the numerical methods used in the application to EuO together with a careful consideration of numerical problems involved. Finally the results of the calculations are presented. With the aid of selection rules and Van Hove-singularities a list of allowed optical transitions has been deduced. These results compare favorably with recent experiments.     

Simulation of a High Harmonic Gyrotron with Axis-Encircling Electron Beam and Permanent Magnet

A computer code for simulation of beam-field interaction in a resonant cavity of a gyrotron has been developed. It is based on a self-consistent, time-independent, single-mode physical model. The code has been applied to the analysis of the electrodynamical system of a novel high-harmonic gyrotron with axis-encircling beam and a permanent magnet. In this paper both the physical model and numerical techniques used are outlined. Some results of the numerical experiments are presented and discussed.     

Non-linear response of a gyrostabilized platform to transient input

In this paper the response of a gyrostabilized platform subjected to a transient torque has been analyzed by deliberately introducing non-linearity into the command of the servomotor. The resulting third-order non-linear differential equation has been solved by using a transformation technique involving the displacement variable. The condition under which platform oscillations may grow with time or die with time are important from the point of view of platform stabilization. The effect of deliberate addition of non-linearity with a view to achieving the ideal response—that is, to bring the platform back to its equilibrium position with as few oscillations as possible—has been investigated. The conditions under which instability may set in on account of the small transient input and small non-linearity has also been discussed. The analysis is illustrated by means of a numerical example. The results of analysis are compared with numerical solutions obtained on a digital computer.     

The mutual synchronization of coupled delayed feedback klystron oscillators

We report on the results of a numerical investigation of the synchronization of two coupled klystron oscillators with an external feedback circuit. Simulation has been carried out using the particle-in-cell method. We have also considered the results of a numerical analysis of an amplifier klystron and an isolated klystron oscillator, which make it possible to choose the optimal values of parameters of coupled klystrons. The structure of the synchronization domain for various parameters has been analyzed. The possibility of increasing the total output power with an appropriate choice of parameter of coupling between the oscillators has been revealed.     

Three-dimensional simulation of nonlinear dynamics of domain walls in films with perpendicular anisotropy

A three-dimensional computer simulation of static magnetization configurations and dynamic processes occurring in a domain wall moving in a uniaxial magnetic film with perpendicular anisotropy has been performed based on the numerical solution of Landau–Lifshitz–Gilbert equations. The calculated static states correspond to a domain wall containing Bloch lines with a surface magnetization distribution that depends on the thickness of the film. It has been shown that these structures can be characterized by particular values of the homotopy index. It has been found that the vortex and antivortex structures existing in the bulk of the film form vortex filaments. A method has been proposed for visualization of the joint motion of vortex filaments and Bloch points, which is based on the numerical calculation of the homotopy index and the winding number.     

A Novel Formulation of the Fourier Model Method in S-Matrix Form for Arbitrary Shaped Gratings

A new formula has been proposed for analyzing arbitrary shaped-gratings. The formula is in very simple form, is always suitable for all the gratings of arbitrary profiles, any depth, and any permittivity. The new formula has a character of satisfying rigorously the energy-flux conservation. The effectiveness and its characters have been confirmed by numerical examples. The numerical examples have shown that the new formula is superior to the classical formulas with Fourier series technique in convergence, computing precision, and stability.     

Numerical Analysis of Emission Line Broadening under Coulomb Interaction in an Electron–Hole System

A numerical analysis of the energy spectrum of an ensemble of interacting particles in a two-dimensional system has been performed by means of direct solution of the microparticle Schröedinger equation. Comparison of the numerical calculations of the form factor of the homogeneous broadening of spectral lines with the results obtained according to perturbation theory has been made. The range of applicability of the universal relation between the amplification and emission spectra is discussed.     

贝塞耳函数调制的高斯光束通过有光阑ABCD光学系统的传输

基于惠更斯菲涅尔广义衍射积分,对变量为径向平方的贝塞耳函数调制的高斯光束(QBG光束)通过有圆孔光阑限制的一阶ABCD光学系统的传输进行了研究.采用将圆域函数可表示为复高斯函数叠加的方法,推导出了普适的场分布解析公式,以QBG光束通过有圆孔光阑限制的薄透镜系统为例进行了分析与讨论,数值计算结果证明了本文所用方法的优点,所得结果与直接用广义衍射积分公式进行复杂的数值计算结果完全一致 关键词： QBG光束 光阑 ABCD光学系统 传输特性     

多重网格法在燃烧室内流场数值模拟中的应用

多重网格法在燃烧室内流场数值模拟中的应用林文漪，杨彬，周力行（清华大学工程力学系北京１０００８４）关键词：多重网格，数值模拟，湍流一、前言现代燃烧设备多具有复杂的流场结构、多级燃烧的特点及庞大的几何尺寸，无疑地为其数值模拟带来了困难。为了保证计算精度...