ON HOLOMORPHIC CURVES OF CONSTANT CURVATURE IN THE COMPLEX GRASSMANN MANIFOLD G（2,5）

In this article, it is proved that there doesn’t exist any nonsingular holomorphic sphere in complex Grassmann manifold G(2, 5) with constant curvature k = 4/7, 1/2, 4/9. Thus, from [7] it follows that if φ : S2 → G(2, 5) is a nonsingular holomorphic curve with constant curvature K, then, K = 4, 2, 4/3, 1 or 4/5.     

On All Fractional （a,b, k）-Critical Graphs

Let a,b,k,r be nonnegative integers with 1≤a≤b and r≥2.LetG be a graph of order n with n(a+b)(r(a+b)-2)+ak/a.In this paper,we first show a characterization for all fractional(a,b,k)-critical graphs.Then using the result,we prove that G is all fractional(a,b,k)-critical if δ(G)≥(r-1)b2/a+k and |NG(x1)∪NG(x2)∪···∪NG(xr)|≥bn+ak/a+b for any independent subset {x1,x2,...,xr} in G.Furthermore,it is shown that the lower bound on the condition|NG(x1)∪NG(x2)∪···∪NG(xr)|≥bn+ak/a+b is best possible in some sense,and it is an extension of Lu's previous result.     

Pseudo-holomorphic curves in complex Grassmann manifolds

It is proved that the Kähler angle of the pseudo-holomorphic sphere of constant curvature in complex Grassmannians is constant. At the same time we also prove several pinching theorems for the curvature and the Kähler angle of the pseudo-holomorphic spheres in complex Grassmannians with non-degenerate associated harmonic sequence.

     

Holomorphic two-spheres in complex Grassmann manifold <Emphasis Type="Italic">G</Emphasis>(2, 4)

In this paper, we use the harmonic sequence to study the linearly full holomorphic two-spheres in complex Grassmann manifold G(2, 4). We show that if the Gaussian curvature K (with respect to the induced metric) of a non-degenerate holomorphic two-sphere satisfies K ≤ 2 (or K ≥ 2), then K must be equal to 2. Simultaneously, we show that one class of the holomorphic two-spheres with constant curvature 2 is totally geodesic. Concerning the degenerate holomorphic two-spheres, if its Gaussian curvature K ≤ 1 (or K ≥ 1), then K = 1. Moreover, we prove that all holomorphic two-spheres with constant curvature 1 in G(2, 4) must be U (4)-equivalent.     

关于球面到CPN中的共形极小浸入

本文证明一个关于球面Ｓ~２ 到ＣＰ~Ｎ中的共形极小浸入的曲率ｐｉｎｃｈｉｎｇ定理．     

关于球面到CPN中的共形极小浸入

本文证明一个关于球面Ｓ² 到ＣＰ^N中的共形极小浸入的曲率ｐｉｎｃｈｉｎｇ定理．     

Construction of homogeneous minimal 2-spheres in complex Grassmannians

In this paper, we construct a class of homogeneous minimal 2-spheres in complex Grassmann manifolds by applying the irreducible unitary representations of SU (2). Furthermore, we compute induced metrics, Gaussian curvatures, Khler angles and the square lengths of the second fundamental forms of these homogeneous minimal 2-spheres in G(2, n + 1) by making use of Veronese sequence.     

Projecting 4-folds from G(1, 5) to G(1, 4)

 We study 4-dimensional subvarieties of the Grassmannian G(1,5) with singular locus of dimension at most 1 that can be isomorphically projected to G(1,4). Received: 26 July 2001     

GEOMETRIC PROPERTIES FOR GAUSSIAN IMAGE OF SUBMANIFOLDS IN S^n＋p（1）

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.