Finite-element calculation of the transmission probability and theresonant-tunneling lifetime through arbitrary potential barriers

A numerical method for the calculation of the transmission probability through a potential barrier or structure and of the lifetime of a resonant state in a double- or multiple-barrier structure is presented. This method is based on a combination of the finite-element method and the analytical approach. A generalized boundary condition of the heterointerface is introduced by use of the interface matrix, and thus the method is applicable to the potential barriers made of arbitrary semiconductors. The validity of the method is confirmed by calculating the transmission probability of rectangular potential barriers and double barrier structures. Numerical results on sinusoidal barriers and voltage-applied barriers are also presented     

基于化学物质释放的五点傅里叶变换求解泊松方程的方法

在电离层化学物质释放数值模拟中,傅里叶变换是一种有效的求解泊松方程的方法,但其仿真精度有待进一步提高.文章提出一种改进的傅里叶变换求解泊松方程的方法,对泊松方程的五点差分形式做傅里叶变换,并引入误差修正项,弥补二阶差分带来的误差,模型中给出了详细推导过程,并与常用方法进行了对比分析.研究结果表明,改进方法求得电势的均方误差（Mean Square Error,MSE）相对Birdsall方法和电势求导方法小6个量级,电势空间分布更加接近解析结果.文中所提方法满足化学物质释放数值仿真的要求,为等离子体粒子模拟中泊松方程的求解提供了一种新的方法.     

Comparison of various image induction (II) methods with physicaloptics (PO) for the far-field computation of flat-sectioned segmentedreflectors

Kottler's (1923) extension of Kirchhoff's diffraction integral to electromagnetic fields yields the copolarized and cross-polarized fields of segmented reflectors. For flat sections, the Maggi-Rubinowicz (1888, 1917) potential can be used to transform Kottler's surface integral into a line integral resulting in an expression composed entirely of line integrals. Computation is simplified by the use of the Asvestas (1985) potential which eliminates the need to compute a geometrical optics term required by the original Maggi-Rubinowicz potential. In computing the far fields, a further simplification is realized by considering the antenna in reception rather than in transmission as an involved dyadic potential is then replaced by a simple vector potential. This is an exact-analysis method in the context of the image-induction model which, in theory, provides results which are very close to the physical optics (PO) model for the transmitting antenna. An approximate closed-form method is obtained by applying the Gordon (1975) transform to Silver's (1949) vector far field equations     

Electrostatic potential of impurities in quantum wells

The method of images is used to calculate the electrostatic potential of an electric charge inside a double barrier structure. This potential is important for finding impurity energy levels in the quantum structure and has never been used before in exact form. The media were modeled by assigning different dielectric constants to the barriers and to the well. The highly doped contacts were assumed to have infinite dielectric constants. This method is based on calculating the Fourier transform parallel to the interfaces of the potential. This function can be obtained in closed form. The potential is then obtained by inverse Fourier transform. This integral is computationally more efficient to evaluate than the direct sum of Coulomb image terms     

An efficient finite-element formulation without spurious modes foranisotropic waveguides

A numerically efficient finite-element formulation is presented for the analysis of lossless, inhomogeneously loaded, anisotropic waveguides of arbitrary shape. The electromagnetic field is described either by the three components of a magnetic vector potential and an electric scalar potential or by the three components of an electric vector potential and a magnetic scalar potential. The uniqueness of the potentials is ensured by the incorporation of the Coulomb gauge and by proper boundary conditions. Owing to the implementation of the solenoidality condition for the vector potential even in the case of zero wavenumber, no spurious modes appear. Variation expressions suited to the finite-element method are formulated in terms of the potentials. Standard finite-element techniques are employed for the numerical solution, leading to a generalized eigenvalue problem with symmetric, sparse matrices. This is solved by means of the bisection method with the sparsity of the matrices fully utilized. Dielectric- and ferrite-loaded waveguides with closed and open boundaries and including both isotropic and anisotropic materials are presented as examples     

A Numerical Calculation of the Capacitance for the Rectangular Coaxial Line with Offset Inner Conductor Having an Anisotropic Dielectric

The capacitances of the rectangular coaxial lines with an offset zero-thickness inner conductor having a sapphire dielectric are presented by using an expanded charge simulation method, In order to apply the method to an anisotropic region, we propose an electric potential formula for a two-dimensional system consisting of a line charge and an infinite plate conductor which are arbitrarily situated in the region. The potential formula is anatyticafly derived by means of an affine transformation, a confomal mapping technique, and the method of images. The capacitance calculated using this method is in good agreement with those of other available methods.     

基于遗传算法和人工势场法的路径规划

在移动机器人的研究中,路劲规划是一个最基本也最复杂的问题。为了得到适合于机器人行走,以及全局最优的路径,采用遗传算法与人工势场法相结合的方法进行机器人的路径规划。首先采用遗传算法规划出全局最优或近似最优的无碰撞路径;再通过改进的人工势场法优化路径,增加路径节点,使路径更平滑。仿真实验结果表明,使用该方法所规划的路径是有效的和可行的。     

紫外非均匀虚拟势场下无人机编队重构避碰算法

针对复杂电磁环境下无人机编队重构过程中的路径规划和机间避碰问题,该文在传统紫外虚拟势场基础上,利用距离因子对斥力函数进行了改进,构建了一种紫外非均匀虚拟势场来协助无人机进行机间避碰。改进的紫外非均匀虚拟势场可以使得无人机避碰路径更加平滑,相同时间内,无人机可以飞行更远的距离。此外,通过无线紫外光测距方法计算无人机机间距离,并结合紫外非均匀势场对传统的人工势场法进行改进,实现无人机编队重构。仿真结果表明,该文算法可以有效解决传统算法下路径振荡和局部最小值问题,同时避碰效率相比传统人工势场算法有明显提升,在预设环境中该文算法路程缩短6%,到达目标点的时间提前40%。最后在两种不同的队形重构场景下,对该文算法进行了验证,结果表明该文算法可以有效实现无人机队形重构中预期的机间避碰效果。     

基于分频带自相关函数的混叠语音基频分离提取新算法

混叠语音的基频分离提取问题是听觉场景分析系统的重要一环。以往的分频带自相关函数的混叠语音基频分离提取方法都是基于频带只受混叠信号之一支配的假设,而事实上,频带常常同时受两个信号影响,为此,本文提出了一种混叠语音基频分离提取新算法,算法在寻找可能的频带组时采用了闭环自适应频带选取模块,根据频带组的基频及其周期度确定两个潜在基频,提高了搜索潜在基频的鲁棒性;利用两个潜在基频重新判断频带的归属来分离信号提取基频,提高了提取基频的精度。实验结果证明新算法具有较高的有效基频提取精度。     

基于归属不确定性的变规模网络重叠社区识别

 拓扑势理论是一种新的复杂网络社区识别理论.针对该理论和方法存在的应用范围不明确和社区重叠节点数量过少等问题,提出基于归属不确定性的变规模网络重叠社区识别方法.在证明拓扑势熵最小值点存在性的基础上,该方法通过提出重叠节点社区归属不确定性测度以及变规模社区的概念和思想,实现社区的有效识别.通过实验验证了该测度的合理性和有效性.实验结果表明,该方法不但具有识别变规模重叠社区的能力,而且还可获得与拓扑势方法相当的社区识别效果.     

位积分方程组矩量法用于精确计算非均匀介质柱的电磁散射

位积分方程组的主要特点是以电磁位为未知函数,这些未知函数在具有不同电磁参数的介质分界面处是连续的,因而在矩量法的实现过程中能够非常方便地应用高阶插值基函数来展开未知函数,以便获得高精度的解。但是,经典的点匹配方案使该模型的数值稳定性较差。本文用位积分方程组矩量法模型计算任意截面非均匀介质柱的电磁散射,采用三角形离散方案和高阶插值基函数,在测试过程中应用新提出的测试方法,克服了原位方程组矩量法模型的数值不稳定性。对矩量法矩阵中自阻抗元素的奇异性处理方法也作了详细介绍。文中提供的数值结果表明,该方法是精确、稳定的。     

Calculating endocardial potentials from epicardial potentialsmeasured during external stimulation

This paper presents a boundary integral method for calculating the potential field generated by external stimulation at locations within the heart using realistic heart geometry and samples of the potential taken from the epicardial surface. This method assumes the heart is homogeneous and isotropic. To test the method we made epicardial and endocardial measurements in dogs during transthoracic pacing stimuli. From the epicardial potential measurements we predicted the endocardial potential values and compared them with the measured data. Despite the seemingly gross assumptions, the mean correlation coefficient between the measured and predicted potentials for three dogs and eleven stimulation electrode configurations was 0.985, and the mean rms error was 17%.     

Electron states in single-layer graphene containing short-range defects: The potential separable in the momentum representation

Electron states in single-layer graphene containing short-range defects are studied. A model potential concentrated on a circle and asymmetric with respect to the band number is treated. The study is carried out for the (2 + 1)-dimensional Dirac equation with a potential separable in the angular momentum representation. The characteristic equation derived in the study for bound and resonance states is compared with the equation derived previously for the same system by another method. The momentum representation used in this study provides a means for satisfactorily regularizing the Hadamard-incorrect problem with a singular potential. The method developed here is applied to regularization of the previously derived formulas for the scattering parameters and conductivity in graphene.     

Dynamic extraction of visual evoked potentials through spatialanalysis and dipole localization

The dynamic extraction of evoked potential is a problem of great interest in EEG signal processing. Here, a comprehensive method is presented which integrates spatial analysis and dipole localization to make full use of the spatial-temporal information contained in the multichannel stimulation records. A realistic double boundary head model is constructed through CT scans and a two-step method devised to overcome the ill-posed nature of the forward problem of EEG caused by the low conductivity of the skull. As a result, visual evoked potentials can be effectively extracted from only two consecutive records and the dynamic information of visual evoked potential thus procured. The efficiency of the presented method has been verified by means of computer simulation and a clinical experiment     

填充液晶的光子晶体的光控可调光子带隙

可调光子晶体由于其潜在的应用价值成为现今光子晶体研究中的一个热点。文章首次提出了通过光诱导液晶取向技术来调制光子晶体光子禁带的方法,进而采用平面波展开法分析了填充液晶的二维三角形光子晶体禁带结构的可调节性。数值模拟结果表明:通过偏振光控制空气孔中所填充的相列液晶的方向可以对光子晶体的禁带结构进行调节。与电场调制方法相比,该光控液晶取向技术具有响应速度快、结构简单的优点。这种可调光子晶体可用于制作场敏偏光片、全光光开关和可调光衰减器。     

电气化铁道地电位升对铁路通信信号的影响

本文分析了电气化铁道对铁道通信信号系统产生影响的机理,对地电位升进行了准确、严密的数学推导,得出了交流电气化铁道引起的地电位升的计算公式,提出了地电位升的防护措施,可供铁道通信工作者参考.     

Design and Testing of a Superconducting Rotating Machine

We have designed, constructed and tested an eight-pole superconducting rotating machine, based on an unconventional topology that could potentially lead to a significant increase in power density. Calculations have been carried out in two steps: estimation of the magnetic scalar potential from a Coulomb formulation using the Markov chain Monte Carlo (MCMC) method, and the calculation of the flux density by derivation of the potential using a regularization method. The use of the MCMC method enables the calculation of the magnetic scalar potential in selected regions of the discrete geometry, which is an important factor to minimize the computation time. The principle of the operation has been validated by a successful testing of the motor showing this novel configuration of an electrical motor as very promising     

Body Surface Potential Mapping Based on Cylindrical Regression

A new statistical method is proposed for evaluating the electric potentials of the human heart measured on the body surface (body surface potential mapping). The method is based on the representation of the measured values in terms of a cylindrical regression model, where the regression is set up horizontally by means of a trigonometric polynomial and vertically by means of an ordinary one. The special experimental equipment required for the optimal exploitation of the model is briefly described. The estimated potential distribution can be graphically displayed in three dimensions; the polynomial degree can be chosen in such a way as to resolve all statistical detail desired. The statistical optimality of the new approximation method is established. The method requires relatively little computational effort and, thus, is suitable for implementation on small computers.     

Determination of potential at the beveled interface between two materials

A numerical method is described to compute the electrostatic potential at the beveled interface between two different materials by solving the two-dimensional Poisson's equation. The bevel angles are discretized in such a manner that an exact expression for the normal component of the electric field can be used. Curved interfaces can be treated. This method has been employed to calculate the potential distribution in a power VMOS device.     

Use of the ventricular propagated excitation model in the magnetocardiographic inverse problem for reconstruction of electrophysiological properties

A novel magnetocardiographic inverse method for reconstructing the action potential amplitude (APA) and the activation time (AT) on the ventricular myocardium is proposed. This method is based on the propagated excitation model, in which the excitation is propagated through the ventricle with nonuniform height of action potential. Assumption of stepwise waveform on the transmembrane potential was introduced in the model. Spatial gradient of transmembrane potential, which is defined by APA and AT distributed in the ventricular wall, is used for the computation of a current source distribution. Based on this source model, the distributions of APA and AT are inversely reconstructed from the QRS interval of magnetocardiogram (MCG) utilizing a maximum a posteriori approach. The proposed reconstruction method was tested through computer simulations. Stability of the methods with respect to measurement noise was demonstrated. When reference APA was provided as a uniform distribution, root-mean-square errors of estimated APA were below 10 mV for MCG signal-to-noise ratios greater than, or equal to, 20 dB. Low-amplitude regions located at several sites in reference APA distributions were correctly reproduced in reconstructed APA distributions. The goal of our study is to develop a method for detecting myocardial ischemia through the depression of reconstructed APA distributions.