Stiefel-Whitney classes and the conormal cycle of a singular variety

A geometric construction of Sullivan's Stiefel-Whitney homology classes of a real analytic variety is given by means of the conormal cycle of an embedding of in a smooth variety. We prove that the Stiefel-Whitney classes define additive natural transformations from certain constructible functions to homology. We also show that, for a complex analytic variety, these classes are the mod 2 reductions of the Chern-MacPherson classes.

     

格序群的极小扭类,准素扭类和极扭类

本文给出了格序群的扭类是准素扭类的一个充分必要条件，证明了任一非零扭类至少包含一个极小扭类，从而将文〔１〕和〔２〕中在有限制条件情况下的有关结论推广到无任何限制条件的情形。本文还给出了一个扭类是极扭类的几个充分必要条件，并得到了格序群的极扭类、准素扭类和极小扭类之间的关系。     

巧用体力与面力的变换求解非常体力弹性力学问题

在弹性力学问题的求解中,考虑体力的计算比考虑面力的计算要复杂很多,而且在力学实验中模拟体力的载荷条件通常也比较困难。因此,将体力转化为面力,可以简化弹性力学问题的求解,并且对于实验设计,也可提供极大的方便。本文以两个典型平面问题为例,分别探讨了在直角坐标系和极坐标系下对非常体力的处理方法,为实验的设计提供了新的思路,有助于学生灵活运用弹性力学理论解决实际工程问题,具有一定的工程应用价值和教学实践意义。

     

s-乘数收敛及Orlicz-Pettis型定理

本文给出了在局部凸空间中与弱拓扑具有相同的ｓ－乘数收敛点列的最强的可允许极拓扑Ｆ（μ_ｓ）的刻划．并给出Ｆ（μｓ）＝β（Ｘ,Ｘ＇）的充分条件和必要条件,由此证明了ｃ０（或ｌｐ,０＜ｐ＜∞）－乘数收敛性是对可允许极拓扑全体而言的不变性,     

Homogeneity Rank and Atoms of Actions

We introduce two related concepts for smooth actions of compact Lie groups:The homogeneity rank is a simple numerical invariant of the action.As one of our results we determine the precise range of this invariantfor isometric actions on compact Riemannian manifolds with positivesectional curvature and exhibit special properties of the actionswith maximal homogeneity rank.Atoms are special components of fixed point sets. They inherit actionswith the same cohomogenity and homogeneity rank as the original action,but with trivial principal isotropy group. Other properties of the originalaction like polarity are reflected in the atoms.We determine the atoms in some interesting concrete cases.Not only for this purpose we give a detailed treatise on the structureof fixed point sets, in particular in cohomogeneity one manifolds.     

Stability estimates for h-p spectral element methods for elliptic problems

In a series of papers of which this is the first we study how to solve elliptic problems on polygonal domains using spectral methods on parallel computers. To overcome the singularities that arise in a neighborhood of the corners we use a geometrical mesh. With this mesh we seek a solution which minimizes a weighted squared norm of the residuals in the partial differential equation and a fractional Sobolev norm of the residuals in the boundary conditions and enforce continuity by adding a term which measures the jump in the function and its derivatives at inter-element boundaries, in an appropriate fractional Sobolev norm, to the functional being minimized. Since the second derivatives of the actual solution are not square integrable in a neighborhood of the corners we have to multiply the residuals in the partial differential equation by an appropriate power of r_k, where r_k measures the distance between the pointP and the vertexA _k in a sectoral neighborhood of each of these vertices. In each of these sectoral neighborhoods we use a local coordinate system (τ_k, θ_k) where τ_k = lnr_k and (r_k, θ_k) are polar coordinates with origin at A_k, as first proposed by Kondratiev. We then derive differentiability estimates with respect to these new variables and a stability estimate for the functional we minimize. In [6] we will show that we can use the stability estimate to obtain parallel preconditioners and error estimates for the solution of the minimization problem which are nearly optimal as the condition number of the preconditioned system is polylogarithmic inN, the number of processors and the number of degrees of freedom in each variable on each element. Moreover if the data is analytic then the error is exponentially small inN.     

体锥与满足角性质锥之间的关系

本文证明：当锥Λ的极锥是尖锥或由不含θ点的闭球体张成时，Λ是体锥；拟多面体锥Λ和极锥Λ*弱*内部非空锥类是一致的并指出了P．Q．Khanh（1992年）的一个错误．     

Analysis of FDTD to UPML for Maxwell equations in polar coordinates

An FDTD system associated with uniaxial perfectly matched layer(UPML) for an electromagnetic scattering problem in two-dimensional space in polar coordinates is considered.Particularly the FDTD system of an initial-boundary value problems of the transverse magnetic(TM) mode to Maxwell’s equations is obtained by Yee’s algorithm,and the open domain of the scattering problem is truncated by a circle with a UPML.Besides,an artificial boundary condition is imposed on the outer boundary of the UPML.Afterwards,stability of the FDTD system on the truncated domain is established through energy estimates by the Gronwall inequality.Numerical experiments are designed to approve the theoretical analysis.     

Small Point Sets that Meet All Generators of W(2n+1,q)

Let W(2n+1,q), n1, be the symplectic polar space of finite order q and (projective) rank n. We investigate the smallest cardinality of a set of points that meets every generator of W(2n+1,q). For q even, we show that this cardinality is q ⁿ⁺¹+q ^{n–1, and we characterize all sets of this cardinality. For q odd, better bounds are known.