In this paper,we study locally strongly convex affine hypersurfaces with the vanishing Weyl curvature tensor and semi-parallel cubic form relative to the Levi-Civita connection of the affine metric.As a main result,we...In this paper,we study locally strongly convex affine hypersurfaces with the vanishing Weyl curvature tensor and semi-parallel cubic form relative to the Levi-Civita connection of the affine metric.As a main result,we classify these hypersurfaces as not being of a flat affine metric.In particular,2 and 3-dimensional locally strongly convex affine hypersurfaces with semi-parallel cubic forms are completely determined.展开更多
Let N n+p be an (n+p)-dimensional locally symmetric and conformally flat Riemannian manifold and Mn be an n-dimensional compact submanifold minimally immersed in N n+p . Instead of (n+p)-dimensional unit sphere, we ge...Let N n+p be an (n+p)-dimensional locally symmetric and conformally flat Riemannian manifold and Mn be an n-dimensional compact submanifold minimally immersed in N n+p . Instead of (n+p)-dimensional unit sphere, we generalize Pinching Theorems about submanifolds in unit sphere and get theorems about submanifolds in locally symmetric and conformally flat Riemannian manifold.展开更多
The compact minimal submanifold in a locally symetric and conformally flat Riemann manifold is discussed in this paper.We get the Pinching constant for scalar curvature.The result of Li[2]is generallied,but the method...The compact minimal submanifold in a locally symetric and conformally flat Riemann manifold is discussed in this paper.We get the Pinching constant for scalar curvature.The result of Li[2]is generallied,but the method is completely different. Meanwhile,we get better conclusion than that of [3].We also research the Pinching problem for sectional curvature on compact minimal submanifolds in a unit sphere, partially improving the results of S.T.Yan[4].展开更多
The aim of this paper is to verify that the study of generic conformally flat hypersurfaces in 4-dimensional space forms is reduced to a surface theory in the standard 3-sphere.The conformal structure of generic confo...The aim of this paper is to verify that the study of generic conformally flat hypersurfaces in 4-dimensional space forms is reduced to a surface theory in the standard 3-sphere.The conformal structure of generic conformally flat(local-)hypersurfaces is characterized as conformally flat(local-)3-metrics with the Guichard condition.Then,there is a certain class of orthogonal analytic(local-)Riemannian 2-metrics with constant Gauss curvature-1 such that any 2-metric of the class gives rise to a one-parameter family of conformally flat 3-metrics with the Guichard condition.In this paper,we firstly relate 2-metrics of the class to surfaces in the 3-sphere:for a 2-metric of the class,a 5-dimensional set of(non-isometric)analytic surfaces in the 3-sphere is determined such that any surface of the set gives rise to an evolution of surfaces in the 3-sphere issuing from the surface and the evolution is the Gauss map of a generic conformally flat hypersurface in the Euclidean4-space.Secondly,we characterize analytic surfaces in the 3-sphere which give rise to generic conformally flat hypersurfaces.展开更多
We investigate n-dimensional(n≥4),conformally flat,minimal,Lagrangian submanifolds of the n-dimensional complex space form in terms of the multiplicities of the eigenvalues of the Schouten tensor and classify those t...We investigate n-dimensional(n≥4),conformally flat,minimal,Lagrangian submanifolds of the n-dimensional complex space form in terms of the multiplicities of the eigenvalues of the Schouten tensor and classify those that admit at most one eigenvalue of multiplicity one.In the case where the ambient space is Cn,the quasi umbilical case was studied in Blair(2007).However,the classification there is not complete and several examples are missing.Here,we complete(and extend) the classification and we also deal with the case where the ambient complex space form has non-vanishing holomorphic sectional curvature.展开更多
In this paper we study on gradient quasi-Einstein solitons with a fourth-order vanishing condition on the Weyl tensor.More precisely,we show that for n≥4,the Cotton tensor of any ndimensional gradient quasi-Einstein ...In this paper we study on gradient quasi-Einstein solitons with a fourth-order vanishing condition on the Weyl tensor.More precisely,we show that for n≥4,the Cotton tensor of any ndimensional gradient quasi-Einstein soliton with fourth order f-divergence free Weyl tensor is flat,if the manifold is compact,or noncompact but the potential function satisfies some growth condition.As corollaries,some local characterization results for the quasi-Einstein metrics are derived.展开更多
A gap theorem on complete noncompact n-dimensional locally conformally flat Riemannian manifold with nonnegative and bounded Ricci curvature is proved.If there holds the following condition:integral(sk(x0,s)ds= o...A gap theorem on complete noncompact n-dimensional locally conformally flat Riemannian manifold with nonnegative and bounded Ricci curvature is proved.If there holds the following condition:integral(sk(x0,s)ds= o(log r)) from n=0 to r then the manifold is flat.展开更多
基金supported by the NNSF of China (12101194,11401173).
文摘In this paper,we study locally strongly convex affine hypersurfaces with the vanishing Weyl curvature tensor and semi-parallel cubic form relative to the Levi-Civita connection of the affine metric.As a main result,we classify these hypersurfaces as not being of a flat affine metric.In particular,2 and 3-dimensional locally strongly convex affine hypersurfaces with semi-parallel cubic forms are completely determined.
文摘Let N n+p be an (n+p)-dimensional locally symmetric and conformally flat Riemannian manifold and Mn be an n-dimensional compact submanifold minimally immersed in N n+p . Instead of (n+p)-dimensional unit sphere, we generalize Pinching Theorems about submanifolds in unit sphere and get theorems about submanifolds in locally symmetric and conformally flat Riemannian manifold.
文摘The compact minimal submanifold in a locally symetric and conformally flat Riemann manifold is discussed in this paper.We get the Pinching constant for scalar curvature.The result of Li[2]is generallied,but the method is completely different. Meanwhile,we get better conclusion than that of [3].We also research the Pinching problem for sectional curvature on compact minimal submanifolds in a unit sphere, partially improving the results of S.T.Yan[4].
文摘The aim of this paper is to verify that the study of generic conformally flat hypersurfaces in 4-dimensional space forms is reduced to a surface theory in the standard 3-sphere.The conformal structure of generic conformally flat(local-)hypersurfaces is characterized as conformally flat(local-)3-metrics with the Guichard condition.Then,there is a certain class of orthogonal analytic(local-)Riemannian 2-metrics with constant Gauss curvature-1 such that any 2-metric of the class gives rise to a one-parameter family of conformally flat 3-metrics with the Guichard condition.In this paper,we firstly relate 2-metrics of the class to surfaces in the 3-sphere:for a 2-metric of the class,a 5-dimensional set of(non-isometric)analytic surfaces in the 3-sphere is determined such that any surface of the set gives rise to an evolution of surfaces in the 3-sphere issuing from the surface and the evolution is the Gauss map of a generic conformally flat hypersurface in the Euclidean4-space.Secondly,we characterize analytic surfaces in the 3-sphere which give rise to generic conformally flat hypersurfaces.
基金supported by the Ministry of Education,Science and Technological Development of the Republic of Serbia(Grant No.174012)。
文摘We investigate n-dimensional(n≥4),conformally flat,minimal,Lagrangian submanifolds of the n-dimensional complex space form in terms of the multiplicities of the eigenvalues of the Schouten tensor and classify those that admit at most one eigenvalue of multiplicity one.In the case where the ambient space is Cn,the quasi umbilical case was studied in Blair(2007).However,the classification there is not complete and several examples are missing.Here,we complete(and extend) the classification and we also deal with the case where the ambient complex space form has non-vanishing holomorphic sectional curvature.
文摘In this paper we study on gradient quasi-Einstein solitons with a fourth-order vanishing condition on the Weyl tensor.More precisely,we show that for n≥4,the Cotton tensor of any ndimensional gradient quasi-Einstein soliton with fourth order f-divergence free Weyl tensor is flat,if the manifold is compact,or noncompact but the potential function satisfies some growth condition.As corollaries,some local characterization results for the quasi-Einstein metrics are derived.
基金Supported by the National Natural Science Foundation of China (Grant No.70631003)the Natural Science Foundation of Anhui Education Department (Grant No.KJ2011A061)+1 种基金the Natural Science Foundation of Anhui Science and Technology Department (Grant No.1104606M01)the Doctor of Philosophy Foundation of Anhui University of Architecture (Grant No.2007-6-3)
文摘A gap theorem on complete noncompact n-dimensional locally conformally flat Riemannian manifold with nonnegative and bounded Ricci curvature is proved.If there holds the following condition:integral(sk(x0,s)ds= o(log r)) from n=0 to r then the manifold is flat.