The Padé-Rayleigh-Ritz method for solving large hermitian eigenproblems

We make use of the Padé approximants and the Krylov sequencex, Ax,,...,A ^m–1 x in the projection methods to compute a few Ritz values of a large hermitian matrixA of ordern. This process consists in approaching the poles ofR _x()=((I–A)^–1 x,x), the mean value of the resolvant ofA, by those of [m–1/m]_Rx(), where [m–1/m]_Rx() is the Padé approximant of orderm of the functionR _x(). This is equivalent to approaching some eigenvalues ofA by the roots of the polynomial of degreem of the denominator of [m–1/m]_Rx(). This projection method, called the Padé-Rayleigh-Ritz (PRR) method, provides a simple way to determine the minimum polynomial ofx in the Krylov subspace methods for the symmetrical case. The numerical stability of the PRR method can be ensured if the projection subspacem is sufficiently small. The mainly expensive portion of this method is its projection phase, which is composed of the matrix-vector multiplications and, consequently, is well suited for parallel computing. This is also true when the matrices are sparse, as recently demonstrated, especially on massively parallel machines. This paper points out a relationship between the PRR and Lanczos methods and presents a theoretical comparison between them with regard to stability and parallelism. We then try to justify the use of this method under some assumptions.     

The asymptotic behavior of queueing systems: Large deviations theory and dominant pole approximation

This paper presents the exact asymptotics of the steady state behavior of a broad class of single-node queueing systems. First we show that the asymptotic probability functions derived using large deviations theory are consistent (in a certain sense) with the result using dominant pole approximations. Then we present an exact asymptotic formula for the cumulative probability function of the queue occupancy and relate it to the cell loss ratio, an important performance measure for service systems such as ATM networks. The analysis relies on a new generalization of the Taylor coefficients of a complex function which we call characteristic coefficients. Finally we apply our framework to obtain new results for the M/D/1 system and for a more intricate multiclass M/D/n system.     

用双标量位法计算爪极电机三维磁场

本文采用双标量法计算三维恒定磁场,给出了四面体、直三棱柱和任意六面体三种常用三维单元在双标量法中的计算格式,将此方法用于空载爪极电机的磁场计算,表明所得结果是合理的.     

晶体管脉冲调宽型放大器在同步机励磁中的应用

本文介绍了利用PWM方法进行同步发电机励磁的工作原理,分析了电路特性,给出了设计的基本方法.实验表明PWM方法比可控硅励磁具有更好的动态特性,可靠性亦较高.     

计算机在自动控制中的应用

本文介绍了计算机自动控制的概念,综述了计算机在自功控制几个主要方面的应用.     

初论改革检录工作

检录工作是田径运动会临场裁判工作的开始,与其它各裁判组有着密切的联系,与运动员、教练员接触面最广,对运动会的顺利进行有着重要影响。本文对检录工作的改革进行初步论述,提出了4点改革措施。     

选频平衡及计算机仿真在工业缝纫机降噪减振研究中的应用

本文结合GC301-01型中速平缝机及885型高速平缝机的降噪减振研究,提出了一种新的平衡方法——选频动平衡。经分析与实验验证,证明这种动平衡方法对于机构复杂的机器的降噪有明显效果。     

磁场处理纸浆料提高纸的机械强度的试验

本文总结了磁场处理纸浆料提高纸的机械强度的试验结果.通过多次重复试验,证明某一浓度、知浆度的纸浆料,在室温下以某一流速通过某一强度的磁场时切割磁力线,可使纸张的机械强度提高10—25%.这一成果若能推广到生产中,必将产生较大的经济效益.     

机床颤振的一种新的控制方法

首先评述了目前对机床颤振的各种控制方法,然后提出在线变刀具前、后角抑制颤振的方法,并讨论了这种新方法的抑振原理。试验表明,该方法效果明显。所研制的控制装置结构简单,不需对机床作任何改装,故有可能成为普通车床及数控车床上具有抑制颤振能力的一个功能部件。     

CM6125CNC型数控车床无级变速系统设计

本文通过具体实例的设计计算对机床主传动采用直流主轴电动机——机械无级变速系统时,电动机调速特性的确定、机械传动机构变速级数、传动比和公比的选取以及无级变速系统如何满足机床传动系统的要求等,进行了分析讨论,并在此基础上给出设计计算的步骤,可供设计参考。