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51.
N. S. Bakhvalov A. V. Knyazev R. R. Parashkevov 《Numerical Linear Algebra with Applications》2002,9(2):115-139
We prove extension theorems in the norms described by Stokes and Lamé operators for the three‐dimensional case with periodic boundary conditions. For the Lamé equations, we show that the extension theorem holds for nearly incompressible media, but may fail in the opposite limit, i.e. for case of absolutely compressible media. We study carefully the latter case and associate it with the Cosserat problem. Extension theorems serve as an important tool in many applications, e.g. in domain decomposition and fictitious domain methods, and in analysis of finite element methods. We consider an application of established extension theorems to an efficient iterative solution technique for the isotropic linear elasticity equations for nearly incompressible media and for the Stokes equations with highly discontinuous coefficients. The iterative method involves a special choice for an initial guess and a preconditioner based on solving a constant coefficient problem. Such preconditioner allows the use of well‐known fast algorithms for preconditioning. Under some natural assumptions on smoothness and topological properties of subdomains with small coefficients, we prove convergence of the simplest Richardson method uniform in the jump of coefficients. For the Lamé equations, the convergence is also uniform in the incompressible limit. Our preliminary numerical results for two‐dimensional diffusion problems show fast convergence uniform in the jump and in the mesh size parameter. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
52.
An active resonator designed especially for Nd: YAG lasers is proposed. The expected performance of this resonator is the generation of a laser beam with a flat-topped distribution and a divergence invariant under the thermal lensing effect, such that it could be applied to surface treatment without special optical or mechanical elements. The beam quality and efficiency of such a resonator are presented and discussed in comparison with a parallel-plane resonator as adopted by most industrial Nd: YAG lasers. 相似文献
53.
白鹏 《数学物理学报(A辑)》2005,25(5):694-709
该文将文[1]的结果推广到多元t分布的情形.结果表明, 两个多元t分布之间的Kullback Leibler距离与分布中的刻度矩阵之比的最大特征根密切相关.作为应用, 文章建立了一种在估计未知正定阵时的熵损失函数. 相似文献
54.
55.
The concept of global statistical information in the classical statistical experiment with independent exponentially distributed samples is investigated. Explicit formulas are evaluated for common exponential families. It is shown that the generalized likelihood ratio test procedure of model selection can be replaced by a generalized information procedure. Simulations in a classical regression model are used to compare this procedure with that based on the Akaike criterion. 相似文献
56.
Janne Martikainen Tuomo Rossi Jari Toivanen 《Numerical Linear Algebra with Applications》2002,9(8):629-652
A fast direct solution method for a discretized vector‐valued elliptic partial differential equation with a divergence constraint is considered. Such problems are typical in many disciplines such as fluid dynamics, elasticity and electromagnetics. The method requires the problem to be posed in a rectangle and boundary conditions to be either periodic boundary conditions or the so‐called slip boundary conditions in one co‐ordinate direction. The arising saddle‐point matrix has a separable form when bilinear finite elements are used in the discretization. Based on a result for so‐called p‐circulant matrices, the saddle‐point matrix can be transformed into a block‐diagonal form by fast Fourier transformations. Thus, the fast direct solver has the same structure as methods for scalar‐valued problems which are based on Fourier analysis and, therefore, it has the same computational cost ??(N log N). Numerical experiments demonstrate the good efficiency and accuracy of the proposed method. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
57.
本文报道板条激光器的热稳运行,在150W至10000W的泵浦功率下输出发散角基本保持不变,最大输出功率大于150W;并绘出了腔内插入柱面镜,以压缩输出激光发散角的初步结果. 相似文献
58.
In this paper, we consider the question of necessary conditions for optimality for systems governed by second-order parabolic partial delay-differential equations with first boundary conditions. All the coefficients of the system are assumed bounded measurable and contain controls and delays in their arguments. The second-order parabolic partial delay-differential equation is in divergence form. In Theorem 4.1, we present results on the existence and uniqueness of weak solutions in the sense of Ladyzhenskaya-Solonnikov-Ural'ceva for this class of systems. An integral maximum principle and its point-wise version for the corresponding controlled system are established in Theorem 5.1 and Corollary 5.1, respectively.The authors wish to thank Dr. E. Noussair for his stimulating discussion and valuable comments in the preparation of this paper. Further, they also wish to acknowledge the referee of the paper for his valuable suggestions and comments. The discussion presented in Section 6 is in response to his suggestions. 相似文献
59.
60.
G. GAT U. GOGINAVA 《数学学报(英文版)》2006,22(2):497-506
The (NSrlund) logarithmic means of the Fourier series of the integrable function f is:
1/lnn-1∑k=1Sk(f)/n-k, where ln:=n-1∑k=11/k.
In this paper we discuss some convergence and divergence properties of this logarithmic means of the Walsh-Fourier series of functions in the uniform, and in the L^1 Lebesgue norm. Among others, as an application of our divergence results we give a negative answer to a question of Móricz concerning the convergence of logarithmic means in norm. 相似文献