A note on the crossed product R(A, α) associated with PSL_2(R)

Given the hyperbolic measure dxdy/y2 on the upper half plane H, the rational actions of PSL2(R) on H induces a continuous unitary representation α of this group on the Hilbert space L2(H, dxdy/y2). Supposing that A = {Mf : f ∈ L∞(H, dxdy/y2)}, we show that the crossed product R(A,α) is of type I. In fact, the crossed product R(A,α) is *-isomorphic to the von Neumann algebra B(L2(P,ν))■LK, where LK is the abelian group von Neumann algebra generated by the left regular representation of K.     

(0,1)-矩阵类u(R,S)的基数函数f(R,S)及其非零集

Let R and S be two vectors with m and n nonnegative integers as conponents respectively. Let u(R, S) be the class consisting of all m×n (0,1) - matrices with row sum vector R and column sum vector S. Suppose that A is the maximal mrixat with row sum vector R. Let S he the column sum vector of A. (of. H. J. Ryser, Combinatorial Mathematics, Carcus Math. Monograph 14 (1963)). Let L(S)={S=(s₁,…,s_m),S-1≥s₂≥…≥s_n}, and let F(R, S) be the cardinal function of u(R,S), i. e.. f(R, S) = |u(R, S) |. Then L(S) is the nonzero-point set of f(R,S). In this paper our principal result is the following.     

Some Remarks on the Graph Γ I (R)

Let R be a commutative ring with nonzero identity and Z(R) its set of zero-divisors. The zero-divisor graph of R is Γ(R), with vertices Z(R)?{0} and distinct vertices x and y are adjacent if and only if xy = 0. For a proper ideal I of R, the ideal-based zero-divisor graph of R is Γ _I (R), with vertices {x ∈ R?I | xy ∈ I for some y ∈ R?I} and distinct vertices x and y are adjacent if and only if xy ∈ I. In this article, we study the relationship between the two graphs Γ(R) and Γ _I (R). We also determine when Γ _I (R) is either a complete graph or a complete bipartite graph and investigate when Γ _I (R) ? Γ(S) for some commutative ring S.     

k-smooth Points of m(Ω,R)

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(0,1)-矩阵类■(R,S)的基数函数f(R,S)及其非零集

Gale和Ryser曾独立地得到了(0,1)-矩阵类(R,S)非空的充要条件。然而,正如Ryser所宣称的,(R,S)的基数f(R,S)是R与S的一个极端复杂的函数,确定f(R,S)的值是一个远为困难的问题。魏万迪给出了|(R,S)|的一个下界,接着我们在文[6]中研究了(R,S)的结构与基数,并得到了比[5]更好的|(R,S)|的下界。本文先研究f(R,S)的非零集的结构与基数,然后研究f(R,S)的递减性,并求出它的极值     

(0,1)-矩阵类(?)(R,S)

我们把元素全部是1或0的矩阵称为(0,1)-矩阵。设A是一个m×n阶(0,1)-矩阵,其第ⅰ行全部元素之和为r_i(1≤i≤m),第j列全部元素之和为s_j(1≤j≤n)。那么称向量R=(r_1,r_2,…,r_m)为A的行和向量;S=(s_1,s_2,…,s_n)为A的列和向量。所谓具有行和向量R,列和向量S的(0,1)-矩阵类(R,S)是指:     

Gaussian Property of the Rings R(X) and R〈X〉

The content of a polynomial f over a commutative ring R is the ideal c(f) of R generated by the coefficients of f. A commutative ring R is said to be Gaussian if c(fg) = c(f)c(g) for every polynomials f and g in R[X]. A number of authors have formulated necessary and sufficient conditions for R(X) (respectively, R?X?) to be semihereditary, have weak global dimension at most one, be arithmetical, or be Prüfer. An open question raised by Glaz is to formulate necessary and sufficient conditions that R(X) (respectively, R?X?) have the Gaussian property. We give a necessary and sufficient condition for the rings R(X) and R?X? in terms of the ring R in case the square of the nilradical of R is zero.     

SL(2,R)和Ernst方程

近年来,利用孤子理论的方法从不同角度对Ernst方程进行的研究,取得了不少进展我们将指出,基于作者们在Wahlquist和Estabrook工作的基础上提出的延拓结构理论,可以全面而系统地概括这些成果,并推进这方面的研究. 我们将以Harrison曾讨论过的情形为例,通过求解延拓结构的基本方程,得到Ernst方程的一个SL(2,R)×R′(l)延拓结构,这是Harrison 所没有完成的.我     

Reuse,Recycle, Reduce (3R) – strategies for the calculation of transient magnetic fields

The discretization of transient magneto-dynamic field problems with geometric discretization schemes such as the Finite Integration Technique or the Finite-Element Method based on Whitney form functions results in nonlinear differential-algebraic systems of equations of index 1. Their time integration with embedded s-stage singly diagonal implicit Runge–Kutta methods requires the solution of s nonlinear systems within one time step. Accelerated solution of these schemes is achieved with techniques following so-called 3R-strategies (“reuse, recycle, reduce”). This involves e.g. the solution of the linear(-ized) equations in each time step where the solution process of the iterative preconditioned conjugate gradient method reuses and recycles spectral information of linear systems from previous stages. Additionally, a combination of an error controlled spatial adaptivity and an error controlled implicit Runge–Kutta scheme is used to reduce the number of unknowns for the algebraic problems effectively and to avoid unnecessary fine grid resolutions both in space and time. First numerical results for 2D nonlinear magneto-dynamic problems validate the presented approach and its implementation. The space discretization in the numerical examples is done by Lagrangian nodal finite elements but the presented algorithms also work in combination with other discretization schemes for the Maxwell equations such as the Whitney vector finite elements.     

Average width and optimal recovery of the anisotropic classesW r H α (R d ) in the metricC k (R d )

This paper concerns the problems of the average widths and the optimal recovery of the anisotropic Hölder classesW ^r H ^α (R ^d ) of smooth functions defined on the Euclidean spaceR ^d in the metricC ^k (R ^d ). The weak asymptotic behavior is established for the corresponding quantities.     

On the efficiency of some supplemented (α1,α2,…,αR)-resolvable block designs

Statistical properties of designs with two kinds of treatments: basic and supplementary, are examined. The basic treatments are arranged randomly in an (α₁,α₂,…,α_R)-resolvable block design. This basic design is orthogonally supplemented by some orthogonal addition of the supplementary treatments.Mixed linear models of observations following two- or three-step randomizations are considered. The final design under these models is generally balanced and that allows obtaining its stratum efficiency factors for both cases.     

THE PLANCHEREL FORMULA FOR THE LINE BUNDLES ON SL(n + 1, R)/S(GL(1, R) × GL(n,R))

In this paper we obtain the Plancherel formula for the spaces of L~2-sections of the line bundles over the pseudo-Riemannian symmetric space G/H where G = SL(n + 1, R)and H = S(GL(1, R) × GL(n, R)). The Plancherel formula is given in an explicit form by means of spherical distributions associated with the character χ——λof the subgroup H. We follow the method of Faraut, Kosters and van Dijk.     

与群PSL2(R)相关的交叉积R(A,α)的一点注记

在上半复平面H上给定双曲测度dxdy/y2,群G=PSL2(R)在H上的分式线性作用导出了G在Hilbert空间L2(H,dxdy/y2)上的酉表示α.证明了交叉积R(A,α)是Ⅰ型von Neumann代数,其中A={Mf:f∈L∞(H,dxdy/y2)}.具体地,交叉积代数R(A,α)与von Neumann代数B(L2(P,v))-(×)LK是*-同构的,其中LK是G中子群K的左正则表示生成的群von Neumann代数.     

Characteristic Foliations of Spheres Embedded in the Standard Overtwisted Structure (R3, ζ1)

The characteristic foliation of a sphere embedded in the standard tight contact structure (R³, ₀) is unique up to isotopy. We show that any Morse-Smale foliation on the sphere with null Euler class, is, up to isotopy, the characteristic foliation of a sphere embedded in the standard overtwisted contact structure (R³, ₁). We thus have a new way of looking at the two standard structures as opposites in the world of contact structures.     

SL(n+1,R)/S(GL(1,R)×GL(n,R))上线丛的一个超几何方程（英文）

本文研究了伪黎曼对称空间SL(n+1,R)/S(GL(1,R)×GL(n,R))线丛上的微分方程.利用李代数方法,即Casimir算子得到这个微分算子.这个微分算子是一个超几何方程,这个结论推广了文献[1,3,5]中的微分方程.     

On the invariants of Möbius groupsM(R n )

Suppose that $$\operatorname{Re} (a + d^ * ) \in \left\{ {\begin{array}{*{20}c} {( - 2,2),if g(x) is f.p.f. or elliptic,} \\ {\left[ { - 2,2} \right], if g(x) is parabolic,} \\ {( - \infty ,\infty ), if g(x) is loxodromic.} \\ \end{array} } \right.$$ is a Clifford matrix of dimensionn, g(x)=(ax+b)(cx+d) ^?1. We study the invariant balls and the more careful classifications of the loxodromic and parabolic elements inM(R ⁿ ), prove that the loxodromic elements inM(R ^2k+1 ) certainly have an invariant ball, expound the geometric meaning of Ahlfors' hyperbolic elements, and introduce the uniformly hyperbolic and parabolic elements and give their identifications. We prove that $$\operatorname{Re} (a + d^ * ) \in \left\{ {\begin{array}{*{20}c} {( - 2,2),if g(x) is f.p.f. or elliptic,} \\ {\left[ { - 2,2} \right], if g(x) is parabolic,} \\ {( - \infty ,\infty ), if g(x) is loxodromic.} \\ \end{array} } \right.$$ These results are fundamental in the higher dimensional Möbius groups, especially in Fuchs groups.     

On the Evaluation of the Tutte Polynomial at the Points (1, –1) and (2, –1)

Motivated by the identity t (K _n+2; 1, –1) = t (K _n ; 2, –1), where t(G; x, y) is the Tutte polynomial of a graph G, we search for graphs G having the property that there is a pair of vertices u, v such that t(G; 1, –1) = t(G – {u, v}; 2, –1). Our main result gives a sufficient condition for a graph to have this property; moreover, it describes the graphs for which the property still holds when each vertex is replaced by a clique or a coclique of arbitrary order. In particular, we show that the property holds for the class of threshold graphs, a well-studied class of perfect graphs.