空间形式中紧致超曲面的刚性

设(M~n,g)是一个黎曼流形,f:M~n→Q~(n+1)(c)是一个等距浸入,其中Q~(n+1)(c)是n+1维的空间形式.如果对于任一个等距浸入f:M~n→Q~(n+1)(c),都存在等距变换φ:Q~(n+1)(c)→Q~(n+1)(c),使得φ·f=f,则称f(M~n)具有刚性.本文证明:如果超曲面是紧致的,(1)当c≤0时,如果紧致超曲面的维数大于或等于3,则紧致超曲面具有刚性;(2)当c0时,如果紧致超曲面的维数大于或等于5,则空间形式中紧致超曲面具有刚性;这推广了经典的Cohn-Vossen定理.     

关于伪脐子流形的一个整体定理

设 M~n 是截面曲率为 c 的(n+p)维黎曼空间 M~(n+p)(c)中 n 维子流形。如在 M~n 上存在函数λ使得:〈h(x,y),H〉=λ〈x,y〉成立,其中λ=H~2,则称 M~n是 M~(n+p)(c)的伪脐子流形。本文得到常曲率空间中紧致伪脐子流形的一个整体定理(定理2.1)。     

常曲率空间中具正Ricci曲率的子流形

设S~(n+p)(1)是一单位球面,M~n是浸入S~(n+p)(1)的具有非零平行平均曲率向量的n维紧致子流形.证明了当n≥4,p≥2时,如果M~n的Ricci曲率不小于(n-2)(1+H~2),则M~n是全脐的或者M~n的Ricci曲率等于(n-2)(1+H~2),进而M~n的几何分类被完全给出.     

关于可三角剖分的紧致流形的模2示嵌类

<正> 引言 关于复合形或更一般的空間在欧氏空間中的实現問題,Whitney和Thom分別有下面的結果: 定理.(Whitney)n維紧致微分流形M~n可微分实現于R~N中的必要条件为 W~k(M~n)=0,k≥N-n.(1) 定理.(Thom)一个有可数基而局部可縮的紧致Hausdorff空間X可以拓扑实現     

从n维微分流形到p(≥2)维欧氏空间的可微映射的一个性质

本文讨论了从n维微分流形M~n到p(≥2)维欧氏空间R~p的可微映射的一个基本性质,即定理1.指出使得秩处处不为零的所有可微映射M~n→R~p形成C~∞(M~n,R~p)中的一个开的稠密子集,其中C~∞(M~n,R~p)表示具有Whitney拓扑结构的一切可微映射M~n→R~p所组成的空间。最后讨论了一类特殊的可微映射的芽(R~n,0)→(R~n,0),n≥2,指出几乎每一个这样的可微芽在恰当的坐标系下,其代表具有某种简便的表达形式。     

紧黎曼流形上Hardy-Littlewood-Sobolev不等式的极值问题:次临界逼近法

令(M~n,g)为n维无边紧黎曼流形,0αn,qn/n-α,该文研究了下列HardyLittlewood-Sobolev (HLS)不等式‖I_αf‖_L~q(M~n)≤C‖f‖L~p(M~n),■的极值问题.首先,利用算子I_α:L~p(M~n)→L~q(M~n)在次临界情形(即p(nq)/(n+αq))时的紧致性,证明p(nq)/(n+αq)时极值函数f_p∈L~p(M~n)的存在性;进而证明函数列{f_p}为临界情形时HLS不等式的最佳常数的极值列;最后,结合极值列{f_p}在L((nq)/(n+αq))(M~n)中的一致有界性,利用文献[32]建立的集中列紧原理证明{f_p}在L((nq)/(n+αq))(M~n)中存在收敛子列,从而给出临界情形(即p=((nq)/(n+αq)))时极值函数的存在性.     

常曲率黎曼流形的极小子流形

本文目的在于建立下述定理:常曲率 a 的黎曼流形 V~(n p)中的紧致无边极小子流形M~n 常满足∫_(Mn){p∑R_(ijkl)~2 2p∑R_(ij)~2-R~2 n(3p-2n 2)aR}*1≥n~2(n-1)(n-p-1)a~2Vol(M~n),其中∑R_(ijkl)~2是M~n 的黎曼曲率张量的模长平方,∑R_(ij)~2是 M~n 的李齐(Ricci)曲率张量的模长平方,R 是 M~n 的数量曲率.上述积分不等式是 M~n 的内在性质.     

局部对称共形平坦黎曼流形的极小子流形

设M~(n+2)是■+■维局部对称的共形平坦■曼流形,M~n是它的紧致的n维极小子流形(n≥4).本文证明,若M~n的每点各方向的(?)曲率的下确界Q>(n-2)K,其中K是M~(n+p)在该点的截面曲率的上确界,则M~n是全测地的,且有正常数截面曲率.     

在射影平面、Klein 瓶上推广的 C~r 封闭引理

<正> 设 M~n 是 n 维紧致 C~∞流形.用(?)(M~n)表示在 M~n 上全体 C~r 向量场赋予 C~r 范数‖·‖_r后所形成的 Banach 空间.用 X~t 表示由 X∈(?)(M~n)导出的流.     

正曲率空间形式中超曲面的全脐性与高阶平均曲率

本文研究正曲率空间形式S~(n+1)(c)(c0)中紧致的闭的等距浸入超曲面M~n的全脐性质和高阶平均曲率,所得结果改进和推广了这方面最近有关定理.     

Dubins’ problem on surfaces. I. nonnegative curvature

Let M be a complete, connected, two-dimensional Riemannian manifold. Consider the following question: Given any (p₁,v₁) and (p₂, v₂) in T M, is it possible to connect p₁ to P₂ by a curve y in M with arbitrary small geodesic curvature such that, for i = 1, 2, y is equal to v_i at p_i? In this article, we bring a positive answer to the question if M verifies one of the following three conditions: (a) M is compact, (b) M is asymptotically flat, and (c) M has bounded nonnegative curvature outside a compact subset.     

Kähler-Ricci soliton typed equations on compact complex manifolds withC 1(M) > 0

As a generalization of Calabi’s conjecture for Kähler-Ricci forms, which was solved by Yau in 1977, we discuss the existence of Kähler-Ricci soliton typed equation on a compact Kähler manifold (M, g) with positive first Chem C₁ (M) > 0 as well as the uniqueness. For a given positively definite (1,1)-form Ω ∈ C₁ (M) of M and a holomorphic vector field X on M, we prove that there is a Kähler form ω in the Kähler class [ω_g] solving the Kähler-Ricci soliton typed equation if and only if, i) X is belonged to a reductive subalgebra of holomorphic vector fields and the imaginary part of X generates a compact one-parameter transformations subgroup of M; and ii) L_X Ω is a real-valued (1,1)-form. Moreover, the solution ω is unique in the class [ω_g].     

Closure of the set of classical Riemannian spaces

The basic result of the paper is a theorem asserting that the closure of the set of compact Riemannian spaces in the set of all compact metric spaces with inner metric consists precisely of the set of compact metric spaces with bilaterally bounded curvature in the sense of A. D. Aleksandrov. Here the convergence of a sequence of Riemannian spaces in the topology we consider means its Lipschitz convergence to a limit metric space and the uniform bilateral boundedness of the sectional curvatures of the spaces of the sequence. The results obtained are considered in application to the compactness theorem of M. Gromov.Translated from Itogi Nauki i Tekhniki, Seriya Problemy Geometrii, Vol. 21, pp. 43–66, 1989.     

半单复形IMv(M,Q)

设M ,V ,Q是李普希茨流形 ,M是V的局部LIP平坦的紧子流形 ,V是开流形且dimV =dimQ .设U是M在V中的某开邻域且Δn 是Rn 中n维标准单形 .如f:Δn×U→Δn×Q是一个LIP浸入且P1f =P1,称f是一个n维单形 .令 (IMV(m ,Q) ) n 是上面所定义的所有n维单形的集合且令IMV(m ,Q) ={ (IMV(M ,Q) ) n} n 0 .本文证明了IMV(M ,Q)在我们所定义的面运算 i和退化运算Si下是一个半单复形 .     

On holomorphic immersions into K(a)hler manifolds of constant holomorphic sectional curvature

We study holomorphic immersions f: X → M from a complex manifold X into a Kahler manifold of constant holomorphic sectional curvature M, i.e. a complex hyperbolic space form, a complex Euclidean space form, or the complex projective space equipped with the Fubini-Study metric. For X compact we show that the tangent sequence splits holomorphically if and only if f is a totally geodesic immersion. For X not necessarily compact we relate an intrinsic cohomological invariant p(X) on X, viz. the invariant defined by Gunning measuring the obstruction to the existence of holomorphic projective connections, to an extrinsic cohomological invariant v(f)measuring the obstruction to the holomorphic splitting of the tangent sequence. The two invariants p(X) and v(f) are related by a linear map on cohomology groups induced by the second fundamental form.In some cases, especially when X is a complex surface and M is of complex dimension 4, under the assumption that X admits a holomorphic projective connection we obtain a sufficient condition for the holomorphic splitting of the tangent sequence in terms of the second fundamental form.     

紧致超曲面上的谱

设Ｍ是Ｓ^n 1(1)上的紧致极小超曲面,Ｍ１,n-1是Ｓ^(n 1)(1)上的Ｃlifford极小超曲面。若它们的谱相同,则它们是墙虎的。对于Ｓ^(n 1)(1)上的紧致常平均曲率超曲面和Ｈ（r)－环,在某些条件下等谱可推出等距。     

C~k(M)类函数集列紧的充要条件

本文讨论了 Rn中紧集 M上 Ck类函数 ,用构造 ε-网的方法给出了这类函数集列紧的一个充要条件 ,从而推广了著名的 Ascoli-Arzela定理     

On the complex structure of symplectic quotients

Science China Mathematics - Let K be a compact group. For a symplectic quotient Mλ of a compact Hamiltonian Kähler K-manifold, we show that the induced complex structure on Mλ is...     

On an exotic pseudo-interior in the hyperspace of convex compact sets

We study the geometry of the distribution of the subspace L formed by the convex solids with everywhere dense skeleton in the hyper space. M of convex compact solids (homeomorphic to the Hilbert cube Q). It is proved that the pair (M, L) is homeomorphic to the pair (Q,s), where s is the pseudo-interior of the Hilbert cube.Translated fromMatematicheskie Melody i Fiziko-Mekhanicheskie Polya, Issue 34, 1991, pp. 15–18.     

关于双曲空间形式的一个注记

本文主要证明一个具有光滑边界的紧黎曼流形,如果有非平凡解,则就等度量同构与双曲空间形式 会的紧区域,这里Ｄ～２■是■的Ｈｅｓｓｉａｎ与ｇ是Ｍ上的黎曼度量． 还证明关于上述方程的边值问题,只有混合边值问题,而且当ｃ＜－１时有解．