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851.
本文从示意眼模型出发,利用自治的单透镜近似模型,根据矩阵光学原理,用计算机算出不同近视眼度数焦点的前移量以及在三种不同原因引起的近视眼的情况下角膜需要切除的数量。计算告诉我们即使1000°近视眼,角膜最大切除量也仅50μ,不到角膜总厚度的1/10。 理论上探讨了根据激光束的高斯分布经过光学系统改变光强分布来实现近视眼需要校正的曲率。 相似文献
852.
ASYMPTOTIC ERROR EXPANSION AND DEFECT CORRECTION FOR SOBOLEV AND VISCOELASTICITY TYPE EQUATIONS 总被引:10,自引:0,他引:10
1.IntroductionLetObearectangulardomain.WeareconcernedwiththeRichardsonextrapolationanddefectcorrectionofthefiniteelementapproximationstothesolutionsofthefollowingsimpleSobolevtypeequationandviscoelasticitytypeequationTheextrapolationtechniqueusedforthefin… 相似文献
853.
The Global Cauchy Problem for the Critical and Subcritical Nonlinear Schrodinger Equations in Hs 下载免费PDF全文
Baoxiang Wang 《偏微分方程(英文版)》1998,11(2):173-192
In this paper, the local and global existence of solutions for the Cauchy problem of the critical and subcritical nonlinear Schrödinger equations in H^s (s ≥ 2) is studied by using the manner of formal differentiation with respect to time. Some conjectures posed by Cazenave and Weissler in [1] are verified. 相似文献
854.
I.Intr0ductionForflndingallzerosofacomplexpolynomialofdegree;Ip(z)=zu olz'-l ..' a.-1z a.(l.l)whenzerosareal1simple,manymethodsareavailable.AmongthemaretheDurand-Kerneralgorithm,theAberthalgorithm,thesquarerootingaIg0rithmandtheirvarietiesI3'[1'141.Thecom… 相似文献
855.
高维动力系统的初值问题* 总被引:1,自引:0,他引:1
在这篇文章中,我们证明了一类包含退化情形的高维动力系统初值问题整体古典解的存在性及零解的一致稳定性。 相似文献
856.
Based on the properties of the convolution and the convolute commutation, some quasi-variational principles for the problems
of nonconservative force field in the micropolar elastodynamics are given and verified in this paper. The theorem given in
this paper can be applied to the theories of the nonlocal elastic mediums and the nonlocal micropolar elastic mediums. 相似文献
857.
858.
刘慈群 《应用数学和力学(英文版)》1988,9(6):521-252
The transient spherical flow behavior of a slightly compressible non-Newtonian, power-law fluids in porous media is studied.
A nonlinear partial differential equation of parabolic type is derived. The diffusivity equation for spherical flow is a special
case of the new equation. We obtain analytical, asymptotic and approximate solutions by using the methods of Laplace transform
and weighted mass conservation. The structures of asymptotic and approximate solutions are similar, which enriches the theory
of one-dimensional flow of non-Newtonian fluids through porous media. 相似文献
859.
Based upon the theorems of structural variations this paper derives a set of expressions for calculating partial derivatives
of internal forces, stresses and joint displacements with respect to bar areas for truss structures. Compared with the known
formulas for finding the gradients of structural behaviours the calculation effort with the proposed expressions in this paper
is usually smaller because the additional virtual loadings needed are relatively fewer. It is of practical significance to
various optimization methods in which the calculation of gradients of behaviours is widely used. Moreover, applying the derived
formulas to the fully stressed design (FSD), we obtain an improved iterative method for FSD. The numerical examples show that
the new method considerably reduces the reanalysis number required to converge to an FSD in comparison with the simple stress
ratio method. 相似文献
860.
The fixed stream-tube method widely adopted in engineering field for giving an approximate solution to the two-dimensional problems of two-phase flow through porous media is summarized and an improvement has been made in this paper. Its core part, i.e., the fluid displacement within a one-dimensional stream tube with variable cross-sectional area under a given pressure difference across the tube is thoroughly studied. The existence and uniqueness of solution are proved, the exact solution, numerical solution and its convergence, stability analyses are given in this paper. 相似文献