An Efficient High-Order Extrapolation Procedure for Multiaspect Electromagnetic Scattering Analysis

This paper presents a new high-order extrapolation procedure for computing multiaspect electromagnetic scattering characteristics for arbitrarily shaped 3-D conducting targets. The method aims to reduce the number of simulation angles required to resolve a monostatic radar cross section when the method of moments is used for perfect electrically conducting targets. The methodology developed in this contribution employs a novel procedure for automatically computing the higher order moments required for the implementation of the asymptotic waveform evaluation extrapolation technique. The method uses the Leibnitz theorem and the Faa di Bruno formula for computing higher derivatives of the incident electric field, with respect to the angles of incidence. Three numerical case studies are provided to demonstrate the validity and efficacy of the new method.     

An Efficient Procedure for Implementing a Dual Simplex Network Flow Algorithm

This paper shows that for linear programming formulations of network flow problems, the nonzero components of rows of the basis inverse are identical. A simple algorithm for identifying these nonzero components is given along with a suggested data structure for implementation. The algorithm requires only one bit of storage for each node plus one additional bit. Finally we indicate how these ideas may be used in the development of a dual simplex code for network flow problems.     

An Efficient Algorithm for Global Path Optimization in MPLS Networks

This paper proposes an algorithm to solve the optimization of label switched paths (LSPs) in multiprotocol label switching (MPLS) networks. The underlying optimization problem in this task is the well-known unsplittable multicommodity flow problem equipped with practically relevant objective functions and specialized with hard technical requirements.The proposed heuristic algorithm is based on network flow theory. It incorporates iterative shortest path search and performs adaptive edge weight adjustments in order to successfully satisfy all the required traffic demands and to maximize user-defined objectives. The robust algorithm facilitates the incorporation of several strategic and optimization objectives and the fulfillment of certain hard technical requirements of the target problem domain as well. Novel features of the approach include a new adaptive path allocation/deallocation strategy based on the identification of bottleneck links, demand ordering and preprocessing phases, and a systematic path allocation control method.The efficiency of the method is empirically shown on randomly generated networks with practical sizes and topologies, and on a real-world IP (Internet Protocol) backbone network. The algorithm is able to successfully solve difficult problem instances comprising very large instances with 1000 nodes, 3500 edges and 999000 traffic demands. The computational tests demonstrate that the proposed approach can be efficiently applied to solve problem instances that embed MPLS specific hard technical requirements. Furthermore, it is shown that our algorithm offers significantly better performance than the straightforward adaptations of existing methods that were developed for related network optimization problems. Namely, our algorithm produces acceptable results quicker, it can solve problems that were not previously solvable, and it yields better results than the alternative methods. The extensive empirical tests demonstrate the combinatorial properties of the target problem and the performance aspects of the algorithm and its components as well.     

An Efficient and Stable Spectral-Element Method for Acoustic Scattering by an Obstacle

A spectral-element method is developed to solve the scattering problem for time-harmonic sound waves due to an obstacle in an homogeneous compressible fluid. The method is based on a boundary perturbation technique coupled with an efficient spectral-element solver. Extensive numerical results are presented, in order to show the accuracy and stability of the method.     

结构凝聚动刚度的有效简化方案

本文提出一种基于模态展开和幂级数展开的混合方案,用于简化结构凝聚动刚度的计算.本方案的收敛性较好,并且它的误差易于估计,因此较实用方便.     

WPERF+:一种有效的分布式查询处理优化算法

分布式查询是一种网络通信成本较大的查询过程,设计和开发出有效的查询策略和技术是分布式查询面临的挑战。本文展示了一种新的分布式查询的算法。即WPERF 连接算法,它结合了W算法和PERF算法的特点。进一步强化了W算法和PERF的性能。文章从理论上证明了WPERF 算法具有有效降低分布式查询处理成本的效能。     

An Efficient Algorithm for Software Generation of Binary Linear Recurrences

We describe a method for efficient software generation of binary linear sequences. Suppose that a machine sized word can hold an unsigned integer between 0 and 2^w–1 and a binary linear sequence (s^(t))_t0 has a characteristic polynomial of degree n having l nonzero coefficients. Then given nw initial bits of the sequence, it is possible to generate successive blocks of (s^(t))_t0 of length w bits each. The time required to generate each block is equal to the time required to perform l bitwise XOR operations on machine sized words. Compared to the basic method of sequence generation, this provides a w-fold increase in speed.Acknowledgement We would like to thank Subhamoy Maitra, Sandeepan Choudhury and Kishan Chand Gupta for discussions and helpful comments. We would also like to thank Professor Harald Niederreiter for pointing out that Lemma 2 can be easily derived from Corollary 1 of [4]. Finally, we thank the reviewers for pointing out several typos in the paper.     

基于图像纹理特征的目标快速检索

在讨论共生矩阵的基础上,提出了一个通过图像分割获取目标图像纹理特征,进而实现图像快速检索的方法。试验表明,该方法检索目标图像的可靠性较高,具有良好的应用价值。     

An Efficient Algorithm for the Single Machine Total Tardiness Problem

This paper presents an exact algorithm for the single machine total tardiness problem (1// Σ T_i). We present a new synthesis of various results from the literature which leads to a compact and concise representation of job precedences, a simple optimality check, new decomposition theory, a new lower bound, and a check for presolved subproblems. These are integrated through the use of an equivalence concept that permits a continuous reformation of the data to permit early detection of optimality at the nodes of an enumeration tree. The overall effect is a significant reduction in the size of the search tree, CPU times, and storage requirements. The algorithm is capable of handling much larger problems (e.g., 500 jobs) than its predecessors in the literature (≤ 150). In addition, a simple modification of the algorithm gives a new heuristic which significantly outperforms the best known heuristics in the literature.     

An Efficient Algebraic Algorithm for the Geometric Completion to Involution

 We describe an adaption of a differential algebraic completion algorithm for linear systems of partial differential equations that allows us to deduce intrinsic differential geometric information like the number of prolongations and projections needed for the completion. This new hybrid algorithm represents a much more efficient realisation of the classical Cartan–Kuranishi completion than previous purely geometric ones. A classical problem in geometric completion theory is the existence of δ-singular coordinate systems in which the algorithms do not terminate. We develop a new and a very simple criterion for δ-singularity based on a comparison of the Janet and the Pommaret division. This criterion can also be used for the direct construction of δ-regular coordinates. Received: July 28, 2000; revised version: October 16, 2001     

广义Vandermonde方程组的有效快速算法

基于求解Vandermonde方程组的Bjorck-Pereyra算法,本文给出了求解广义Vandermonde方程组的有效快速算法,所需的计算量为O(n2)。数值算例表明,与求解Vandermonde方程组的Gohberg-Kailath-Koltracht算法和Gauss消元法相比,本文的算法具有更高的计算精度。     

An Application of DHW Algorithm for the Solution of Inverse Heat Conduction Problem

A damped heat wave (DHW) algorithm is applied for the temperature distribution calculation in a solution of a linear inverse heat conduction problem (IHCP). A nonlinear least squares algorithm is used for calculation of the unknown boundary heat flux history in a one-dimensional medium. The solution is based on the assumption that the temperature measurements are available, at least, at one point of the medium over the whole time domain. Sample calculations, for a comparison between exact heat sources and estimated ones, are made to confirm the validity of the proposed method. The close agreement between the exact and estimated values calculated for both exact and noisy data shows the potential of the proposed method for finding a relatively accurate heat source distribution in a one-dimensional homogeneous finite medium. The proposed method of solving inverse heat conduction problems is very simple and easy to implement.Paper presented at the Seventeenth European Conference on Thermophysical Properties, September 5–8, 2005, Bratislava, Slovak Republic.M. L?ffler: Deceased     

Microscopic Structure in Liquid Hydrogen and Deuterium: An X-Ray Scattering Study

The static structure factors S(Q) of liquid normal H₂ and D₂ have been measured in the wave-vector region 5 nm^–1<Q<30 nm^–1 through X-ray scattering using two independent sets of data. While the first set has been derived using a standard liquid diffraction geometry, the second has been worked out integrating the dynamic structure factors S(Q, ), measured through inelastic X-ray scattering spectroscopy. In the latter case the first spectral-moment sum rule has been used to obtain directly absolute static structure factor values. A comparison with quantum and classical Monte Carlo simulations shows that a quantitative agreement with the experimental data for both H₂ and D₂ can be obtained only if quantum effects are properly taken into account.     

一种有效降低红外预警系统虚警率的检测算法

为了解决红外预警系统在受到地物、云层、飞鸟等干扰点的影响下,目标探测虚警率高的问题,提出一种基于目标点角坐标变化的检测算法.该算法是先通过分析系统扫描到的目标点角速度变化情况,将可能的目标点从含有噪声的背景中分离出来;然后利用内点惩罚函数及最速下降法相结合的最优值算法求出每个目标点的航路;最后,对航路的真实性进行判断,从而检测出运动目标.通过实验证明了该算法抗噪声干扰能力强,易于硬件实现,能够有效地降低红外预警系统的虚警率.     

An Efficient Algorithm to Construct an Orthonormal Basis for the Extended Krylov Subspace

Subspace projection methods based on the Krylov subspace using powers of a matrix $A$ have often been standard for solving large matrix computations in many areas of application. Recently, projection methods based on the extended Krylov subspace using powers of $A$ and $A^{−1}$ have attracted attention, particularly for functions of a matrix times a vector and matrix equations. In this article, we propose an efficient algorithm for constructing an orthonormal basis for the extended Krylov subspace. Numerical experiments indicate that this algorithm has less computational cost and approximately the same accuracy as the traditional algorithm.     

An Annular Crack in a Magnetoelectroelastic Layer

A flat annular crack in a magnetoelectroelastic layer subjected to mechanical, electric and magnetic loadings is investigated under magnetoelectrically impermeable boundary condition on the crack surface. Using Hankel transform technique, the mixed boundary value problem is reduced to a system of singular integral equations. With the aid of Gauss-Chebyshev integration technique, the integral equations are further reduced to a system of algebraic equations. The field intensity factor and energy release rate are determined. Numerical results reveal the effects of electric and magnetic loadings and crack configuration on crack propagation and growth.     

An Efficient Algorithm for Analysis of Transfer Lines With Unreliable Machines and Finite Buffers

In a recent paper [3], Gershwin proposed a decomposition method for the approximate analysis of transfer lines with unreliable machines and finite buffers. The method is based on a decomposition of the line into a set of two-machine lines. It leads to a set of equations which are solved using an iterative algorithm. Experimental results have shown that this technique is very accurate. However, it may happen that the algorithm fails to converge. In this paper, we propose to replace the original set of equations by an equivalent one, which is again solved using an iterative procedure. This new algorithm is simpler than the previous one, and its computational complexity is lower. Moreover, on all examples we tested, the algorithm always converged.