An Efficient Surface Integral Equation Solution to EM Scattering by Chiral Objects Above a Lossy Half Space

In this paper, an extension of the electric-magnetic current combined-field integral equation (JMCFIE) is presented for the efficient analysis of EM scattering by an arbitrary shaped homogenous chiral object located above a lossy half space. This formulation can lead to a well tested equation system using the method of moments (MoM) solution with the vector triangular basis functions and Galerkin's method. The multilevel fast multipole algorithm (MLFMA) is then employed to reduce the memory requirement and computational complexity of the MoM solution. The inner-outer flexible generalized minimal residual (FGMRES) method is used to further speed up the convergence. The accuracy and efficiency are confirmed with a couple of numerical examples.      

粗糙面与导弹目标复合电磁散射仿真计算

提出了一种求解粗糙面和三维目标复合电磁散射问题的通用仿真方法。将描述粗糙面上电磁波反射的基尔霍夫-赫姆霍兹方程与目标表面的电场积分方程相结合,得到新型的混合方程,进而采用矩量法求解,通过数值算例验证了该方法的精度和效率。采用此方法研究了两种典型导弹目标与粗糙面的复合散射特性,分析计算结果可得:粗糙面粗糙度参数对复合散射特性有着重要的影响作用。     

Computational cost estimations and comparisons for three methods of applied electromagnetics (MoM, MAS, MMAS)

The computational costs of three numerical techniques used in electromagnetics, namely the moment method (MoM), the method of auxiliary sources (MAS), and its modified version (MMAS), are estimated for various calculation schemes and configurations. Both surface and volumetric problems are considered. The number of multiplications required for the system-matrix fill is calculated and added to the algorithmic cost of the matrix inversion. The Green's function singularity extraction is also taken into account, particularly for the MoM. The original integrals are transformed into the local (area or volume) coordinate systems, and are subsequently evaluated on the basis of standard numerical quadrature schemes. For the surface integral equation (SIE), some calculations using either the well-known Duffy transformations or some analytical-numerical integration schemes are also presented (expressions are available only for the scalar potential integral case). For the MAS and MMAS, the matrix fill is shown to be much faster, since no time-consuming integrations are involved. The analysis is applied to various objects, such as a perfectly conducting (PEC) parallelpiped, a PEC sphere, and a microstrip patch antenna, and useful conclusions are drawn on the relative efficiency of the three methods.     

PC群集系统中并行矩量法研究

目前复杂环境的EMC分析,计算量过大,耗时太长,使分析与优化遇到实质性的困难.本文研究MPI结合矩量法的并行技术,测试了在PC群集系统中并行矩量法的性能,并以此完成大型计算.与大型机和工作站相比,PC群集系统中的并行矩量法可以用较低的硬件成本有效的实现复杂环境电磁特性分析.     

Determining the equivalent impedance boundary condition forcorrugated coatings based on the genetic algorithm

A methodology based on the genetic algorithm (GA) is proposed to determine the equivalent impedance boundary condition (IBC) for corrugated material coating structures. In this approach, rigorous solutions of the reflection coefficients at a number of incident angles are first calculated using a periodic method of moments (MoM) solver. The IBC model is used to predict the reflection coefficients at the same observation angles. The model coefficients are then optimized using the GA so that the difference between the approximated and the MoM predicted reflection coefficients is minimized. The GA proves efficient in obtaining an optimal IBC model. The resulting IBC model can be readily incorporated into an existing computational electromagnetics code to assess the performance of the corrugated coating when mounted on complex platforms     

Loop-tree implementation of the adaptive integral method (AIM) for numerically-stable, broadband, fast electromagnetic modeling

The adaptive integral method (AIM) is implemented in conjunction with the loop-tree (LT) decomposition of the electric current density in the method of moments approximation of the electric field integral equation. The representation of the unknown currents in terms of its solenoidal and irrotational components allows for accurate, broadband electromagnetic (EM) simulation without low-frequency numerical instability problems, while scaling of computational complexity and memory storage with the size of the problem are of the same order as in the conventional AIM algorithm. The proposed algorithm is built as an extension to the conventional AIM formulation that utilizes roof-top expansion functions, thus providing direct and easy way for the development of the new stable formulation when the roof-top based AIM is available. A new preconditioning strategy utilizing near interactions in the system which are typically available in the implementation of fast solvers is proposed and tested. The discussed preconditioner can be used with both roof-top and LT formulations of AIM and other fast algorithms. The resulting AIM implementation is validated through its application to the broadband, EM analysis of large microstrip antennas and planar interconnect structures.     

A universal robot control system (URCS) based on the TUNISmultiprocessor

The design and development of a universal robot control system (URCS) that would enable computation-intensive control algorithms to be implemented and modified is reported. This required shifting from hardware to software, using high-performance computing platforms. In general, multiprocessing has been found to be a cost-effective method for increasing performance, especially when the control algorithm can be composed into concurrent computational tasks. The URCS was developed using the University of Toronto Multiprocessor System (TUNIS) as the computing platform. One processor reads sensors, another calculates compensation signals and commands to the motors, a third is designated for operator requests, and the last is used for the operating system. An interface that allows the URCS to control the PUMA 560 robot was designed and built     

MoM-NPO混合算法分析天线-载体系统

安装在电大尺寸平台上的天线,载体的影响不容忽视。采用同样基于电流展开的矩量物理光学混合算法,并通过NURBS物理光学法进一步降低复杂结构的建模和计算,将载体对天线的影响用物理光学电流合并到包括天线的在内较小的矩量法区,使矩量法解决天线-载体系统成为可能。通过矩量法和混合算法分析载体对天线性能的影响证明,载体对天线的影响是显著的,混合算法能够在保证精度的前提下提高运算速度,为解决电大尺寸载体上天线的特性提供了良好的途径。     

QoS-aware computational method for IoT composite service

This paper integrated the quality of service (QoS) requirements of Internet of things (IoT) composite services, and put forward effective decomposition and optimization methods of the QoS metrics. The authors break down the complex QoS calculation model into four basic models, and each model is given a computational method. Combined with the QoS technology of the composite service, the authors adopt the algorithm to find the sub-optimal service with an acceptable cost under the QoS constraints. The proposed algorithm can quickly provide QoS computing services than other two algorithms for large-scale IoT compose services.     

流量自适应的移动僵尸网络云控机制研究

僵尸网络从传统恶意代码进化而来,随着智能手机的计算能力与移动互联网接入技术的快速发展,构建移动僵尸网络已成为一种潜在的威胁。针对移动互联网,提出一种具有流量自适应性的移动僵尸网络云控机制,通过分析用户的流量使用情况,在3G和Wi-Fi不同网络环境下采取不同的流量使用策略,使用自适应的调度算法执行僵尸指令。仿真实验证明,在确保僵尸网络命令有效执行的情况下,流量自适应调度算法可有效增强移动僵尸网络的隐蔽性和实时性。     

电大尺寸物体电磁辐射与散射特性几种分析方法的比较研究

在一定的规则剖分下，矩量法中的系数矩阵为Ｔｏｅｐｌｉｔｚ矩阵或多重Ｔｏｅｐｌｉｔｚ矩阵。利用这一特征而提出的共轭梯度（ＣＧＭ）和快速付里叶变换（ＦＦＴ）算法已成为目前国际上分析电大尺寸问题的一种有效手段。虽然ＣＧＭ—ＦＦＴ将普通矩量法中正比于Ｎ２（Ｎ为系数矩阵的阶数）的存储量压缩为正比于Ｎ的存储量，但其迭代算法使所花ＣＰＵ时间仍与普通矩量法相当。本文采用基于递推的Ｌｉｖｅｎｓｏｎ算法和一种库软件处理同样的问题，所花ＣＰＵ时间和普通矩量法相比降低两个量级，而且存储量比ＣＧＭ—ＦＦＴ技术还要小。本文以直导线的辐射和散射问题为例介绍了几种算法的基本原理，并对他们的计算时间和存储空间等进行了比较研究，得出了一些重要结论。     

Electromagnetic scattering analysis of coated conductors with edgesusing the method of auxiliary sources (MAS) in conjunction with thestandard impedance boundary condition (SIBC)

A novel combination of the method of auxiliary sources (MAS) and the standard impedance boundary condition (SIBC) is employed in the analysis of transverse magnetic (TM) plane wave scattering from infinite, coated, perfectly conducting cylinders with square cross sections. The scatterer is initially modeled by a SIBC surface and the scattering mechanism is subsequently analyzed via MAS. Although SIBC as well as MAS possess theoretical limitations with regard to an edge, the numerical results show that the MAS/SIBC method provides results of high accuracy for a range of structures with edges. The SIBC modeling of coated conductors with edges has previously been investigated in the literature and thus, this work focuses on comparing MAS and the method of moments (MoM) for SIBC surfaces (MoM/SIBC). A detailed complexity analysis shows that the MAS/SIBC method is, under certain conditions, more efficient than the MoM/SIBC method, proving that the proposed novel combination is a powerful and advantageous computational tool     

Globally convergent algorithms for maximum a posterioritransmission tomography

This paper reviews and compares three maximum likelihood algorithms for transmission tomography. One of these algorithms is the EM algorithm, one is based on a convexity argument devised by De Pierro (see IEEE Trans. Med. Imaging, vol.12, p.328-333, 1993) in the context of emission tomography, and one is an ad hoc gradient algorithm. The algorithms enjoy desirable local and global convergence properties and combine gracefully with Bayesian smoothing priors. Preliminary numerical testing of the algorithms on simulated data suggest that the convex algorithm and the ad hoc gradient algorithm are computationally superior to the EM algorithm. This superiority stems from the larger number of exponentiations required by the EM algorithm. The convex and gradient algorithms are well adapted to parallel computing.     

High-performance computing for vision

The main focus of the paper is on effectively using commercial-off-the-shelf (COTS) based general purpose parallel computing platforms to realize high speed implementations of vision tasks. Due to the successful use of the COTS-based systems in a variety of high performance applications, it is attractive to consider their use for vision applications as well. However, the irregular data dependencies in vision tasks lead to large communication overheads in the HPC systems. At the University of Southern California, our research efforts have been directed toward designing scalable parallel algorithms for vision tasks on the HPC systems. In our approach, we use the message passing programming model to develop portable code. Our algorithms are specified using C and MPI. In this paper, we summarize our efforts, and illustrate our approach using several example vision tasks     

对非线性常微分方程的参数估计和局部影响分析

通过引入B样条基函数,给出非线性常微分方程中未知参数的两步估计法。然后导出基于数据删除模型的广义Cook距离的计算公式,并说明该算法降低了计算量。最终利用FitzHugh-Nagumo方程的模拟实验,检验了该算法的有效性,同时与现有算法进行比较,分析证明了其优越性。     

IP语音包的自适应编码和封装算法的研究

IP电话与传统电话相比语音质量较差，其中最主要的原因是因特网的带宽变化较大，导致丢包率较大。该文根据因特网带宽变化的特点提出了1种应用在IP电话网关中的语音自适应编码与封装策略，采用该策略的编码器能根据网络的带宽变化动态调节语音编码速率和语音包封装大小。据此，本文提出了4种算法：一种基于RTP协议语音包丢失率的计算算法、变速率编码算法，不同长度IP语音包的封装算法和根据丢包率来调整编码速率和封装的自适应算法。     

Time discretization of continuous-time filters and smoothers forHMM parameter estimation

In this paper we propose algorithms for parameter estimation of fast-sampled homogeneous Markov chains observed in white Gaussian noise. Our algorithms are obtained by the robust discretization of stochastic differential equations involved in the estimation of continuous-time hidden Markov models (HMM's) via the EM algorithm. We present two algorithms: the first is based on the robust discretization of continuous-time filters that were recently obtained by Elliott to estimate quantities used in the EM algorithm; the second is based on the discretization of continuous-time smoothers, yielding essentially the well-known Baum-Welch re-estimation equations. The smoothing formulas for continuous-time HMM's are new, and their derivation involves two-sided stochastic integrals. The choice of discretization results in equations which are identical to those obtained by deriving the results directly in discrete time. The filter-based EM algorithm has negligible memory requirements; indeed, independent of the number of observations. In comparison the smoother-based discrete-time EM algorithm requires the use of the forward-backward algorithm, which is a fixed-interval smoothing algorithm and has memory requirements proportional to the number of observations. On the other hand, the computational complexity of the filter-based EM algorithm is greater than that of the smoother-based scheme. However, the filters may be suitable for parallel implementation. Using computer simulations we compare the smoother-based and filter-based EM algorithms for HMM estimation. We provide also estimates for the discretization error     

基于遗传算法的K-means初始化EM算法及聚类应用

混合高斯模型能够有效地拟合概率密度函数,常用的混合高斯概率密度模型参数估计方法是EM迭代算法,这种算法的缺点是估计精度过分依赖于初始值,而且不能估计模型阶数。基于遗传算法的K-means初始化EM算法可以同时估计模型阶数和参数。试验结果表明,该算法具有更好的聚类效果。     

Reaction analysis in stripline circuits

In this paper, a full-wave layered-interconnect simulator (UA-FWLIS), which is capable of simulating EM effects in packaging-interconnect problems, is introduced. Standard integral-equation-based method of moment (MoM) techniques are employed in UA-FWLIS. However, instead of using standard time-consuming numerical integration techniques, we have analytically evaluated the MoM reaction elements, thereby greatly improving the computational efficiency of the simulator. This paper illustrates the application of the simulator by employing it in the studies of coupling in a stripline structure and S-parameters for an interconnect     

基于特征基函数法的一维理想导体粗糙海面电磁散射快速算法研究

针对传统矩量法在处理具有较多未知量的理想导体粗糙海面电磁散射问题时对计算机内存的需求过大, 耗时过长的缺陷, 文中引入了特征基函数法, 并根据Foldy-Lax多径散射方程构造特征基函数, 首先只考虑离散子域本身的自相互作用构造主要特征基函数, 然后考虑各离散子域间的互耦效应构造次要特征基函数, 最后由主要特征基函数和次要特征基函数的加权叠加构造特征基函数.通过与传统矩量法仿真结果的对比, 讨论了不同次要特征基函数的阶数或不同离散子域的个数对计算精度和计算效率的影响.仿真结果表明了本文所采用的算法能够在保证计算精度的前提下, 减少计算时间, 并能够通过离散子域尺寸的选取控制实际操作矩阵的维数.