A NONCONFORMING ANISOTROPIC FINITE ELEMENT APPROXIMATION WITH MOVING GRIDS FOR STOKES PROBLEM

This paper is devoted to the five parameters nonconforming finite element schemes with moving grids for velocity-pressure mixed formulations of the nonstationary Stokes problem in 2-D. We show that this element has anisotropic behavior and derive anisotropic error estimations in some certain norms of the velocity and the pressure based on some novel techniques. Especially through careful analysis we get an interesting result on consistency error estimation, which has never been seen for mixed finite element methods in the previously literatures.     

Defect Diagnosis Using a Current Ratio Based Quiescent Signal Analysis Model for Commercial Power Grids

Quiescent Signal Analysis (QSA) is a novel electrical-test-based diagnostic technique that uses I _DDQ measurements made at multiple chip supply pads as a means of locating shorting defects in the layout. The use of multiple supply pads reduces the adverse effects of leakage current by scaling the total leakage current over multiple measurements. In previous work, a resistance model for QSA was developed and demonstrated on a small circuit. In this paper, the weaknesses of the original QSA model are identified, in the context of a production power grid (PPG) and probe card model, and a new model is described. The new QSA algorithm is developed from the analysis of I _DDQ contour plots. A family of hyperbola curves is shown to be a good fit to the contour curves. The parameters to the hyperbola equations are derived with the help of inserted calibration transistors. Simulation experiments are used to demonstrate the prediction accuracy of the method on a PPG.     

提高供电可靠性的措施探讨

结合珠海市配电网络系统构架、运行情况和技术管理的具体现状,从技术措施和组织措施两方面展开讨论,以尽可能缩短用户平均停电时间、提高供电可靠性为目的,实现社会各阶层可以享受到高质量的供电服务,供电企业达到不停电、多售电的营销目标,不间断供电问题圆满解决的双赢局面。     

高速集成电路电源网络的频率特性分析

提出了用一种简单模型计算随频率变化的电感。由于稠密的部分电感矩阵使得方程求解非常困难，采用二次求逆的方法对其进行处理。采用频变电感的计算方法，分析了三种类型电源网络的电感随频率变化的特性。由计算结果可知，网络的回路电感随信号频率的升高呈下降趋势，且成对分布的电源网络的回路电感最小。这为电源网络的设计和同步开关噪声的分析提供了一定的依据。     

用于扫描电镜图像放大倍率校准的三个微米级栅网图形标准样板的研究

本文是一篇有关用于扫描电镜图像放大倍率校准的三个微米级栅网图形标准样板的研究报告。这三个标准样板(G125、G250、G4)为铜质栅网网格，包含6个设计标称值分别为12．50μm(G125)、25．00μm(G250)、62．50μm、82．50μm、125．00μm、165．00μm(G4)的网格。样板已经过均匀性、稳定性检查并时栅网网格线距进行了检定。这三个标准栅网样板可有几个作用：(1)同时时两个垂直方向上的扫描电镜图像放大倍率进行检查或校准，是一组调整低倍图像放大倍率的图形标准样板；(2)对图像X、Y方向的畸变和边缘的畸变进行校验，是评价扫描电镜图像质量的一个重要工具；(3)用于同一量级物体长度的精确比对测量。     

The three-dimensional prolonged adaptive unstructured finite element multigrid method for the Navier–Stokes equations

This paper presents the development of the three- dimensional prolonged adaptive finite element equation solver for the Navier–Stokes equations. The finite element used is the tetrahedron with quadratic approximation of the velocities and linear approximation of the pressure. The equation system is formulated in the basic variables. The grid is adapted to the solution by the element Reynolds number. An element in the grid is refined when the Reynolds number of the element exceeds a preset limit. The global Reynolds number in the investigation is increased by scaling the solution for a lower Reynolds number. The grid is refined according to the scaled solution and the prolonged solution for the lower Reynolds number constitutes the start vector for the higher Reynolds number. Since the Reynolds number is the ratio of convection to diffusion, the grid refinements act as linearization and symmetrization of the equation system. The linear equation system of the Newton formulation is solved by CGSTAB with coupled node fill-in preconditioner. The test problem considered is the three-dimensional driven cavity flow. © 1997 John Wiley & Sons, Ltd.     

Partition of Unity for a Class of Nonlinear Parabolic Equation on Overlapping Non-Matching Grids

A class of nonlinear parabolic equation on a polygonal domain Ω  R2 is inves- tigated in this paper. We introduce a finite element method on overlapping non-matching grids for the nonlinear parabolic equation based on the partition of unity method. We give the construction and convergence analysis for the semi-discrete and the fully discrete finite element methods. Moreover, we prove that the error of the discrete variational problem has good approximation properties. Our results are valid for any spatial dimensions. A numerical example to illustrate the theoretical results is also given.     

分布式计算模型的分析和比较

分布式计算是近年提出的一种新的计算技术,针对当前几种主流的分布式计算技术,如Web Services,中间件、网格等进行了分析和比较,尽管各种分布式计算技术在理念、规范、应用和实现等方面有较大的差异,但每一种技术都得到了一定程度的发展和应用,解决了特定范围内的分布式计算问题。所以,多种计算技术的综合研究,不仅是分布式未来研究的方向,也是分布式计算技术发展的关键。     

Path-based distance functions in n-dimensional generalizations of the face- and body-centered cubic grids

Path-based distance functions are defined on n-dimensional generalizations of the face-centered cubic and body-centered cubic grids. The distance functions use both weights and neighborhood sequences. These distances share many properties with traditional path-based distance functions, such as the city-block distance, but are less rotational dependent. For the three-dimensional case, we introduce four different error functions which are used to find the optimal weights and neighborhood sequences that can be used to define the distance functions with low rotational dependency.     

An improvement of classical slope limiters for high‐order discontinuous Galerkin method

In this paper, we describe some existing slope limiters (Cockburn and Shu's slope limiter and Hoteit's slope limiter) for the two‐dimensional Runge–Kutta discontinuous Galerkin (RKDG) method on arbitrary unstructured triangular grids. We describe the strategies for detecting discontinuities and for limiting spurious oscillations near such discontinuities, when solving hyperbolic systems of conservation laws by high‐order discontinuous Galerkin methods. The disadvantage of these slope limiters is that they depend on a positive constant, which is, for specific hydraulic problems, difficult to estimate in order to eliminate oscillations near discontinuities without decreasing the high‐order accuracy of the scheme in the smooth regions. We introduce the idea of a simple modification of Cockburn and Shu's slope limiter to avoid the use of this constant number. This modification consists in: slopes are limited so that the solution at the integration points is in the range spanned by the neighboring solution averages. Numerical results are presented for a nonlinear system: the shallow water equations. Four hydraulic problems of discontinuous solutions of two‐dimensional shallow water are presented. The idealized dam break problem, the oblique hydraulic jump problem, flow in a channel with concave bed and the dam break problem in a converging–diverging channel are solved by using the different slope limiters. Numerical comparisons on unstructured meshes show a superior accuracy with the modified slope limiter. Moreover, it does not require the choice of any constant number for the limiter condition. Copyright © 2008 John Wiley & Sons, Ltd.