共查询到20条相似文献,搜索用时 15 毫秒
1.
A. A. Borisenko 《Mathematical Notes》1996,60(1):3-7
In this paper we consider compact multidimensional surfaces of nonpositive external curvature in a Riemannian space. If the
curvature of the underlying space is ≥ 1 and the curvature of the surface is ≤ 1, then in small codimension the surface is
a totally geodesic submanifold that is locally isometric to the sphere. Under stricter restrictions on the curvature of the
underlying space, the submanifold is globally isometric to the unit sphere.
Translated fromMatematicheskie Zametki, Vol. 60, No. 1, pp. 3–10, July, 1996. 相似文献
2.
记H0 =maxx∈M|H(x) | ,其中H(x)为Sn p( 1 )的n维紧致子流形的平均曲率向量 .则其Lplace算子的第一特征值满足 :λ1≤n nH20 . 相似文献
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5.
The aim of this paper is to investigate the relations between Seifert manifolds and (1, 1)-knots. In particular, we prove that each orientable Seifert manifold with invariants has the fundamental group cyclically presented by G n ((x 1 q ...x n q l x n ?p ) and, moreover, it is the n-fold strongly-cyclic covering of the lens space L(|nlq ? p|, q) which is branched over the (1, 1)-knot K(q, q(nl ? 2), p ? 2q, p ? q) if p ≥ 2q and over the (1, 1)-knot K(p? q, 2q ? p, q(nl ? 2), p ? q) if p< 2q.
相似文献
$\{ Oo,0| - 1;\underbrace {(p,q),...,(p,q)}_{n times},(l,l - 1)\} $
6.
A finite group G is said to be a B(n, k) group if for any n-element subset {a 1,…, a n } of G, |{a i a j |1 ≤ i, j ≤ n}| ≤k. In this article, we give characterizations of the B(5, 19) 2-groups, and the B(6, k) 2-groups for 21 ≤ k ≤ 28. 相似文献
7.
In this paper, we study an important class of (α,β)-metrics in the form F = (α+β)^m+1/α^m on an n-dimensional manifold and get the conditions for such metrics to be weakly- Berwald metrics, where α = √aij(x)y^iy^j is a Riemannian metric and β = bi(x)y^i is a 1-form and m is a real number with m ≠ -1,0,-1/n. Furthermore, we also prove that this kind of (α,β)-metrics is of isotropic mean Berwald curvature if and only if it is of isotropic S-curvature. In this case, S-curvature vanishes and the metric is weakly-Berwald metric. 相似文献
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9.
Jinwoo Shin 《Annals of Global Analysis and Geometry》2017,51(4):379-399
In this paper we study four-dimensional \((m,\rho )\)-quasi-Einstein manifolds with harmonic Weyl curvature when \(m\notin \{0,\pm 1,-2,\pm \infty \}\) and \(\rho \notin \{\frac{1}{4},\frac{1}{6}\}\). We prove that a non-trivial \((m,\rho )\)-quasi-Einstein metric g (not necessarily complete) is locally isometric to one of the following: (i) \({\mathcal {B}}^2_\frac{R}{2(m+2)}\times {\mathbb {N}}^2_\frac{R(m+1)}{2(m+2)}\), where \({\mathcal {B}}^2_\frac{R}{2(m+2)}\) is the northern hemisphere in the two-dimensional (2D) sphere \({\mathbb {S}}^2_\frac{R}{2(m+2)}\), \({\mathbb {N}}_\delta \) is a 2D Riemannian manifold with constant curvature \(\delta \), and R is the constant scalar curvature of g. (ii) \({\mathcal {D}}^2_\frac{R}{2(m+2)}\times {\mathbb {N}}^2_\frac{R(m+1)}{2(m+2)}\), where \({\mathcal {D}}^2_\frac{R}{2(m+2)}\) is half (cut by a hyperbolic line) of hyperbolic plane \({\mathbb {H}}^2_\frac{R}{2(m+2)}\). (iii) \({\mathbb {H}}^2_\frac{R}{2(m+2)}\times {\mathbb {N}}^2_\frac{R(m+1)}{2(m+2)}\). (iv) A certain singular metric with \(\rho =0\). (v) A locally conformal flat metric. By applying this local classification, we obtain a classification of the complete \((m,\rho )\)-quasi-Einstein manifolds given the condition of a harmonic Weyl curvature. Our result can be viewed as a local classification of gradient Einstein-type manifolds. A corollary of our result is the classification of \((\lambda ,4+m)\)-Einstein manifolds, which can be viewed as (m, 0)-quasi-Einstein manifolds. 相似文献
10.
Nathaniel J. Schwartz 《代数通讯》2018,46(5):1912-1925
Symmetric k-varieties generalize Riemannian symmetric spaces to reductive groups defined over arbitrary fields. For most perfect fields, it is known that symmetric k-varieties are in one-to-one correspondence with isomorphy classes of k-involutions. Therefore, it is useful to have representatives of each isomorphy class in order to describe the k-varieties. Here we give matrix representatives for each isomorphy class of k-involutions of SL(n,k) in the case that k is any field of characteristic 2; we also describe fixed-point groups of each type of involution. 相似文献
11.
F.M. Dannan 《Journal of Difference Equations and Applications》2013,19(6):589-599
We established necessary and sufficient conditions for the asymptotic stability of the difference equation where the coefficients a and b are real numbers and k and l are nonnegative integers. 相似文献
12.
Xu Hongwei Zhang Wei 《高校应用数学学报(英文版)》2007,22(3):371-377
The geometric properties for Gaussian image of submanifolds in a sphere are investigated.The computation formula,geometric equalities and inequalities for the volume of Gaussian image of certain submanifolds in a sphere are obtained. 相似文献
13.
Ann Kiefer 《代数通讯》2013,41(12):4408-4418
The number of pairs of commuting involutions in Sym(n) and Alt(n) is determined up to isomorphism. It is also proven that, up to isomorphism and duality, there are exactly two abstract regular polyhedra on which the group Sym(6) acts as a regular automorphism group. 相似文献
14.
设$D$是一个非平凡的对称$(v,k,\lambda)$设计, $G$是$D$的一个自同构群.本文证明了如果$G$以二维典型群PSL$(2,q)$作为基柱且在$D$上的作用是旗传递和点本原的,那么设计$D$的参数只能为$(7, 3, 1)$, $(7, 4, 2)$, $(11, 5, 2)$, $(11, 6, 3)$或$(15, 8, 4)$. 相似文献
15.
关于f~((k))-af~n的零点 总被引:2,自引:0,他引:2
张占亮 《数学的实践与认识》2004,34(11):129-134
设 f (z) 为平面内超越亚纯函数 ,a≠ 0 为常数 ,证明了当 n≥ k+3 时 ,f( k) -afn有无穷多个零点 . 相似文献
16.
关于f~(k)f-a的零点 总被引:1,自引:0,他引:1
本文部分证明了[1]中的一个猜测:设f(z)为开平面上有穷级的超越整函数,k为非负整数,则f(k)f仅可能有的Picard例外值是0. 相似文献
17.
Wiesława T. Obuchowska 《Mathematical Methods of Operations Research》2008,68(3):445-467
In this paper we are concerned with the problem of boundedness and the existence of optimal solutions to the constrained integer
optimization problem. We present necessary and sufficient conditions for boundedness of either a faithfully convex or quasi-convex
polynomial function over the feasible set contained in , and defined by a system of faithfully convex inequality constraints and/or quasi-convex polynomial inequalities. The conditions
for boundedness are provided in the form of an implementable algorithm, terminating after a finite number of iterations, showing
that for the considered class of functions, the integer programming problem with nonempty feasible region is unbounded if
and only if the associated continuous optimization problem is unbounded. We also prove that for a broad class of objective
functions (which in particular includes polynomials with integer coefficients), an optimal solution set of the constrained
integer problem is nonempty over any subset of . 相似文献
18.
Zhanliang Zhang 《Frontiers of Mathematics in China》2006,1(4):612-619
The aim of this paper is to discuss the value distribution of the function f
(k) − af
n. Under the assumption that f(z) is a transcendental meromorphic function in the complex plane and a is a non-zero constant, it is proved that if n ⩽ k + 3, then f
(k) − af
n has infinitely many zeros. The main result is obtained by using the Nevanlinna theory and the Clunie lemma of complex functions.
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Translated from Acta Scientiarum Naturalium Universitatis NeiMongol, 2004, 35(1): 5–9 相似文献
19.
Let consist of all simple graphs on 2k vertices and edges. For a simple graph G and a positive integer , let denote the number of proper vertex colorings of G in at most colors, and let . We prove that and is the only extremal graph. We also prove that as . © 2007 Wiley Periodicals, Inc. J Graph Theory 56: 135–148, 2007 相似文献
20.
In this paper geodesically corresponding metricsg and
on a manifoldM, dim 5, under the assumption that the tensorsR andS of the metricg satisfyR.R=Q(S, R), are considered. It is stated that the corresponding tensors
and
of
not necessarily must satisfy
. Certain relations between the curvatures ofg and
are obtained.Supported by a post-doctoral fellowship of the researchcouncil of the KU Leuven; Bitnet FGBDA3O at BLEKUL11 相似文献