de Sitter 空间中的常平均曲率完备类空超曲面

设Ｍ是常曲率ｃ的ｄｅ Ｓｉｔｔｅｒ空间Ｓ１＾ｎ＋１（ｃ）的常平均曲率的完备类空超曲面,Ｓ表示第二形式的范数平方。本文证明：差Ｓ〈２√ｎ－１ｃ,则Ｍ是全脐的和等距于一球面。     

Some Theorems for Hypersurface of Randers Spaces

In this paper, we consider the hypersurfaces of Randers space with constant flag curvature. (1) Let (Mⁿ⁺¹, F) be a Randers-Minkowski space. If (Mⁿ, F) is a hypersurface of (Mⁿ⁺¹, F) with constant flag curvature K=1, then we can prove that M is Riemannian. (2) Let (Mⁿ⁺¹, F) be a Randers space with constant flag curvature. Assume (M, F) is a compact hypersurface of (Mⁿ⁺¹, F) with constant mean curvature|H|. Then a pinching theorem is established, which generalizes the result of[Proc. Amer. Math. Soc., 120, 1223-1229 (1994)] from the Riemannian case to the Randers space.     

de Sitter空间中法联络平坦的完备类空子流形

该文证明了de Sitter空间中具有平行平均曲率向量的常数量曲率完备类空子流形,如果其法联络是平坦的,且M的截面曲率小于0,或M的第二基本形式模长平方‖σ‖相似文献   

ON COMPLETE SPACE-LIKE SUBMANIFOLDS WITH PARALLEL MEAN CURVATURE VECTOR

§１．ＩｎｔｒｏｄｕｃｔｉｏｎＬｅｔＮｎ＋ｐｐｂｅａｎ（ｎ＋ｐ）－ｄｉｍｅｎｓｉｏｎａｌｃｏｎｎｅｃｔｅｄｐｓｅｕｄｏ－Ｒｉｅｍａｎｎｉａｎｍａｎｉｆｏｌｄｏｆｉｎｄｅｘｐ．ＩｆＮｎ＋ｐｐｉｓｃｏｍｐｌｅｔｅａｎｄｈａｓｃｏｎｓｔａｎｔｓｅｃｔｉｏｎ...     

四元空间形式中具有常数Khler角的浸入曲面

对四元Khler流形中的浸入曲面引入了Khler角的概念,同时讨论Khler角是常数的情形.主要结果是:若x:M→N(c)是具有常数Q-截面曲率c的实四维四元空间形式N(c)中具有常数Khler角θ(sinθ≠0)的等距浸入曲面,则必有c=0.     

De Sitter空间中具有非负截曲率的常平均曲率完备类空超曲面

设M为de Sitter空间S1^n 1（1）中的完备（非紧）类空超曲面，具有常平均曲率和非负截曲率，在适当条件下，我们证明了它与欧式空间或者双曲柱面等距。     

S4中等参超曲面的谱刻画

本文证明了如果Ｓ⁴中的具常平均曲率ｈ的超曲面Ｍ与其具平均曲率ｈ的等参超曲面Ｍ_０（强）等谱，则Ｍ＝Ｍ_０．     

Sn+1中具有调和M(o)bius曲率张量的超曲面

设x:Mn→Sn 1是(n 1)维单位球面Sn 1中的无脐点的超曲面.Sn 1中超曲面x有两个基本的共形不变量:M(o)bius度量g和M(o)bius第二基本形式B.当超曲面维数大于3时,在相差一个M(o)bius变换下这两个不变量完全决定了超曲面.另外M(o)bius形式Ф也是一个重要的不变量,在一些分类定理中Ф=0条件的假定是必要的.本文考虑了Sn 1(n≥3)中具有消失M(o)bius形式Ф的超曲面:对具有调和曲率张量的超曲面进行分类,进而,在M(o)bius度量的意义下,对Einstein超曲面和具有常截面曲率的超曲面也进行了分类.     

Constant Mean Curvature Surfaces in $${\mathbb {M}}^2(c)\times \mathbb {R}$$ and Finite Total Curvature

We consider surfaces with parallel mean curvature vector field and finite total curvature in product spaces of type \({\mathbb {M}}^n(c)\times {\mathbb {R}}\), where \({\mathbb {M}}^n(c)\) is a space form and characterize certain of these surfaces. When \(n=2\), our results are similar to those obtained in Bérard et al. (Ann Glob Anal Geom 16(3):273–290, 1998) for surfaces with constant mean curvature in space forms.     

Geometric realizations of curvature models by manifolds with constant scalar curvature

We show any pseudo-Riemannian curvature model can be geometrically realized by a manifold with constant scalar curvature. We also show that any pseudo-Hermitian curvature model, para-Hermitian curvature model, hyper-pseudo-Hermitian curvature model, or hyper-para-Hermitian curvature model can be realized by a manifold with constant scalar and -scalar curvature.     

A Geometric Problem and the Hopf Lemma. Ⅱ

A classical result of A. D. Alexandrov states that a connected compact smooth n-dimensional manifold without boundary, embedded in Rn+1, and such that its mean curvature is constant, is a sphere. Here we study the problem of symmetry of M in a hyperplane Xn+1 =constant in case M satisfies: for any two points (X′, Xn+1), (X′, ^Xn+1)on M, with Xn+1 ＞ ^Hn+1, the mean curvature at the first is not greater than that at the second. Symmetry need not always hold, but in this paper, we establish it under some additional conditions. Some variations of the Hopf Lemma are also presented. Several open problems are described. Part Ⅰ dealt with corresponding one dimensional problems.     

Hypersurfaces of the hyperbolic space with constant scalar curvature

We classify hypersurfaces of the hyperbolic space ?ⁿ⁺¹(c) with constant scalar curvature and with two distinct principal curvatures. Moreover, we prove that if Mⁿ is a complete hypersurfaces with constant scalar curvature n(n ? 1) R and with two distinct principal curvatures such that the multiplicity of one of the principal curvatures is n? 1, then R ≥ c. Additionally, we prove two rigidity theorems for such hypersurfaces.     

Kenmotsu–Bryant Type Representation Formulas for Constant Mean Curvature Surfaces in ” 3(-c2) and S 3 1(c2)

Let c be a positive constant and H a constant satisfying |H| > c. Our primary object of this paper is to give representation formulas for branched CMC H (constant mean curvature H) surfaces in the hyperbolic 3-space ³(-c²) of constant curvature c², and for spacelike CMC H surfaces in the de Sitter 3-space S ³ ₁(c²) of constant curvature c². These formulas imply, for example, that every CMC H surface in ³(-c²) can be represented locally by a harmonic map to the unit 2-sphere S².     

Quasi—conformally Flat Manifolds with Constant Scalar Curvature

§１．　ＩｎｔｒｏｄｕｃｔｉｏｎＬｅｔＭｂｅａｎｎ－ｄｉｍｅｎｓｉｏｎａｌｃｏｎｆｏｒｍａｌｌｙｆｌａｔｍａｎｉｆｏｌｄｗｉｔｈｃｏｎｓｔａｎｔｓｃａｌａｒｃｕｒｖａｔｕｒｅρ（ｎ≥３）．ＷｈｅｎｔｈｅＲｉｃｃｉｃｕｒｖａｔｕｒｅＳｏｆＭｉｓｏｆｂｏｕｎｄｅｄｂｅｌｏｗａｎｄｙＳｙ２＜ρ２／（ｎ－１），Ｇｏｌｄ－ｂｅｒｇｐｒｏｖｅｄｔｈａｔＭｉｓｏｆｃｏｎｓｔａｎｔｃｕｒｖａｔｕｒｅ［１］．ＷｈｅｎＭｉｓａｃｏｍｐａｃｔｍａｎｉｆｏｌｄｗｉｔｈｐｏｓｉｔｉｖｅＲｉｃｃｉｃｕｒｖａｔｕｒｅ，ＷｕＢ…     

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.     

Almost hermitian manifolds and Osserman condition

Let(M, g, J) be an almost Hermitian manifold. In this paper we study holomorphically nonnegatively(δ,Δ)-pinched almost Hermitian manifolds. In [3] it was shown that for such Kahler manifolds a plane with maximal sectional curvature has to be a holomorphic plane(J-invariant). Here we generalize this result to arbitrary almost Hermitian manifolds with respect to the holomorphic curvature tensorH R and toRK-manifolds of a constant type λ(p). In the proof some estimates of the sectional curvature are established. The results obtained are used to characterize almost Hermitian manifolds of constant holomorphic sectional curvature (with respect to holomorphic and Riemannian curvature tensor) in terms of the eigenvalues of the Jacobi-type operators, i.e. to establish partial cases of the Osserman conjecture. Some examples are studied. The first author is partially supported by SFS, Project #04M03.     

Dupin超曲面的主曲率的重数

作者证明了如下结果 :设M是空间形式的闭定向Dupin超曲面 ,其截面曲率为正 ,M至少有两个不同主曲率 .如果除最小 (或最大 )主曲率外 ,M的其余主曲率均为常数 ,则最小 (或最大 )主曲率的重数大于 2 .     

紧流形上的Schrodinger算子的谱间隙估计

M是一个n维紧黎曼流形,具有严格凸边界,且Ricci曲率不小于(n-1)K(其中K≥0为某个常数).假定Schrodinger算子的Dirichlet (或Robin)特征值问题的第一特征函数f1在M上是对数凹的,该文得到了此类Schrodinger算子的前两个Dirichlet(或Robin)特征值之差的下界估计,这推广了最近Andrews等人在R^n中有界凸区域上关于Laplace算子的一个相应结果[4].     

Lie Superalgebras Associated with Constant Sectional Curvature

This note describes an observation connecting Riemannian manifolds of constant sectional curvature with a particular class of Lie superalgebras. Specifically, it is shown that the structural equations of a space M with constant sectional curvature, of one variety or another, nearly coincide with some identities satisfied by tensors which can be used to construct some specific families of Lie superalgebras. In particular, one obtains either osp(n,2), spl(n,2), or osp(4,2n) if the Riemannian manifold has constant curvature, constant holomorphic curvature or constant quaternion-holomorphic curvature, respectively.Mathematics Subject Classiffications (2000). 17A70, 53C29, 53C99, 57Rxx     

On the generalized Chern conjecture for hypersurfaces with constant mean curvature in a sphere

Let M be a compact hypersurface with constant mean curvature in Denote by H and S the mean curvature and the squared norm of the second fundamental form of M,respectively.We verify that there exists a positive constant γ(n) depending only on n such that if |H| ≤γ(n) and β(n,H)≤S ≤β(n,H)+n/18,then S≡β(n,H) and M is a Clifford torus.Here,β(n,H)=n+n~3/2(n-1)H~2+n(n-2)/2(n-1)(1/2)n~2H~4+4(n-1)H~2.