关于局部流代数与可微分变换群的表示(Ⅱ)(英文)

设X是一个K维的连通的C~∞流形,Diff(X)是X→X的可微分变换且在无限远附近不动的一一映照全体所成的群。本文继[5]以后,利用X上的张量丛给出一类新的既约酉表示,这种酉表示密切地联系于拟不变测度,特别是Poisson测度。     

广义指数二分性与微分方程的不变流形

用 Hadamar和 Bogoliubov的方法,在常微分方程、泛函微分方程以及半线性抛物型方程所能满足的条件下对Banach或Hilbert空间上的非自治抽象微分方程建立了不变流形理论。首先,对相应的线性方程提出了“广义指数二分性”概念并讨论了它和线性方程谱的关系,然后,我们给出了不变流形存在性结论以及强稳定(不稳定)流形、弱稳定(不稳定)流形和弱双曲流形的分类。进而,我们对这些不变流形给出了C~k光滑性、周期性、概周期性和吸斥性的结论。     

Riemann流形上的一类标准共形不变度量

任意紧Riemann面上都存在一个仅依赖于共形类且拥有常曲率的度量.Harbermann和Jost用Yamabe算子对应的Green函数在数量曲率为正的局部共形平坦流形上构造了一个标准共形不变度量.在此之后,这类标准共形不变度量被推广到了数量曲率为正的球型CR流形上.进一步的,应用相应的Yamabe算子对应的Green函数可以构造数量曲率为正的球型四元切触流形和数量曲率为正的八元切触流形上类似的标准共形不变张量.在四元切触正质量猜测和八元切触正质量猜测成立的前提下,上述共形不变张量是共形不变度量.文中利用Paneitz算子对应的Green函数在局部共形平坦流形上构造了一类上述标准共形不变张量,并且在一定条件(详见定理3.1)下,该标准共形不变张量进一步为标准共形不变度量.     

满旗流形SO(8)/T上不变爱因斯坦度量（英文）

本文研究了迷向表示分为12个不可约子空间的满旗流形SO(8)/T上不变爱因斯坦度量的问题.利用计算机计算满旗流形SO(8)/T爱因斯坦方程组的方法,得到了满旗流形SO(8)/T上有160个不变爱因斯坦度量(up to a scale)的结果,在等距情况下考虑这160个不变爱因斯坦度量,其中1个是凯莱爱因斯坦度量,4个是非凯莱爱因斯坦度量.推广了只对迷向表示分为小于等于6个不可约子空间的满旗流形上不变爱因斯坦度量的研究.     

Riemann流形上ρ-(η,d)-B不变凸的向量变分不等式及向量优化问题

该文研究了Riemann流形上的优化问题.首先,利用广义方向导数在Riemann流形上引入ρ-(η,d)-B不变凸函数、ρ-(η,d)-B伪不变凸函数和ρ-(η,d)-B拟不变凸函数.其次,讨论了变分不等式的解与Riemann流形上向量优化问题解之间的关系.最后,建立了优化问题的Kuhn-Tucker充分条件.     

Kaehler流形的Sasaki子流形

Kaehler流形是偶维微分流形,奇维微分流形中,与之媲美的是Sasaki流形。它是正规、切触度量流形。关于Sasaki流形,有判别定理(见[1]中P_(272)定理5.1) 定理A 殆切触度量流形M是Sasaki流形的充要条件为 (xφ)Y=g(X,Y)ξ-g(Y,ξ)X。 (1) 我们知道,Kaehler流形的Sasaki实超曲面是Sasaki流形,其维数也是奇数。Bejancu成功地对Kaehler流形的反全纯子流形引入Sasaki结构,定义了Sasaki反全纯子流形,其维     

流形的去核乘积

一个拓扑空间X的k重去核乘积,指的是把乘积空间X~k中全部形如(x,…,x)的点去掉后所得到的子空间.吴文俊在[1]中提出了有限可剖分空间的一个新拓扑不变量,其中包括该空间的去核乘积的伦型,即有限可剖分空间的k重去核乘积的伦型是原空间的拓扑不变量,而且一般非同伦不变.[1]还提出在流形的范畴中,这个新拓扑不变量是否有新的意义的问题.本文指出,对于某一类流形来说,它的k重去核乘积的上同调群、同调群以及同伦     

Milnor的一个定理的简单证明

一个流形W叫做是π-流形,如果它的切丛T(W)和W上的一维平凡向量丛的Whitney和是平凡丛.对π-流形,我们希望剜补后所得的流形还是π-流形。对此,有下面的Milnor的重要结果。 定理 设W是C~∞π-流形,dimW=n≥2p+1,则π_p(W)中的任一元素可使得流形X(w,f)也是π-流形的C~∞嵌入f:S~p×D~(n-p)→W表示。 定理中的x(W,f)表示由f实施剜补后所得的流形。这一定理的一个推论是任意n维π-     

迷向和为五的SO(7)/U(1)×U(2)上的不变爱因斯坦度量

本文研究了迷向和为五的广义旗流形上的不变爱因斯坦度量的问题.利用计算Grobner基的方法来研究爱因斯坦方程组的解,获得了广义旗流形SO(7)/U(1)×U(2)上的不变爱因斯坦度量的结果,推广了利用数学实验里的用Nsolve command命令来计算爱因斯坦方程组的结果.     

On the Representations of the Local Current Algebra and the Group of Diffeomorphisms(II)

设X是一个k维的连通的C^\infty流形，Diff（X)是$X\arrow X$的可微分变换且在无限远附近不动的一一映照全体所成的群。本文继[5]以后，利用X上的张量丛给出一类新的既约酉表示，这种酉表示密切地联系于拟不变测度，特别是Poisson测度。     

Harmonic Riemannian maps on locally conformal Kaehler manifolds

We study harmonic Riemannian maps on locally conformal Kaehler manifolds (lcK manifolds). We show that if a Riemannian holomorphic map between lcK manifolds is harmonic, then the Lee vector field of the domain belongs to the kernel of the Riemannian map under a condition. When the domain is Kaehler, we prove that a Riemannian holomorphic map is harmonic if and only if the lcK manifold is Kaehler. Then we find similar results for Riemannian maps between lcK manifolds and Sasakian manifolds. Finally, we check the constancy of some maps between almost complex (or almost contact) manifolds and almost product manifolds.     

Contactly geodesic transformations of almost-contact metric structures

We introduce the notion of contactly geodesic transformation of the metric of an almost-contact metric structure as a contact analog of holomorphically geodesic transformations of the metric of an almost-Hermitian structure. A series of invariants of such transformations is obtained. We prove that such transformations preserve the normality property of an almost-contact metric structure. We prove that cosymplectic and Sasakian manifolds, as well as Kenmotsu manifolds, do not admit nontrivial contactly geodesic transformations of the metric, which is a contact analog of the well-known result for Kählerian manifolds due to Westlake and Yano.     

Generalized Einstein conditions on holomorphic Riemannian manifolds

Summary At first, a necessary and sufficient condition for a K?hler-Norden manifold to be holomorphic Einstein is found. Next, it is shown that the so-called (real) generalized Einstein conditions for K?hler-Norden manifolds are not essential since the scalarcurvature of such manifolds is constant. In this context, we study generalized holomorphic Einstein conditions. Using the one-to-one correspondence between K?hler-Norden structures and holomorphic Riemannian metrics, we establish necessary and sufficient conditions for K?hler-Norden manifolds to satisfy the generalized holomorphic Einstein conditions. And a class of new examples of such manifolds is presented. Finally, in virtue of the obtained results, we mention that Theorems 1 and 2 of H. Kim and J. Kim [10] are not true in general.     

Symplectic topology on subcritical manifolds

We introduce a new class of closed symplectic manifolds called subcritical. These manifolds are closed analogues of subcritical Stein manifolds. We study symplectic and Lagrangian embeddings into such manifolds and into their hyperplane sections. Received: November 13, 2000     

On Flat Complete Causal Lorentzian Manifolds

We describe up to finite coverings causal flat affine complete Lorentzian manifolds such that the past and the future of any point are closed near this point. We say that these manifolds are strictly causal. In particular, we prove that their fundamental groups are virtually abelian. In dimension 4, there is only one, up to a scaling factor, strictly causal manifold which is not globally hyperbolic. For a generic point of this manifold, either the past or the future is not closed and contains a lightlike straight line     

CONFORMAL AND GENERALIZED CONCIRCULAR MAPPINGS OF EINSTEIN-WEYL MANIFOLDS

In this article, after giving a necessary and sufficient condition for two Einstein- Weyl manifolds to be in conformal correspondence, we prove that any conformal mapping between such manifolds is generalized concircular if and only if the covector field of the conformal mapping is locally a gradient. Using this fact we deduce that any conformal mapping between two isotropic Weyl manifolds is a generalized concircular mapping. Moreover, it is shown that a generalized concircularly flat Weyl manifold is generalized concircular to an Einstein manifold and that its scalar curvature is prolonged covariant constant.     

Conformal and generalized concircular mappings of Einstein-Weyl manifolds

In this article, after giving a necessary and sufficient condition for two Einstein-Weyl manifolds to be in conformal correspondence, we prove that any conformal mapping between such manifolds is generalized concircular if and only if the covector field of the conformal mapping is locally a gradient. Using this fact we deduce that any conformal mapping between two isotropic Weyl manifolds is a generalized concircular mapping. Moreover, it is shown that a generalized concircularly flat Weyl manifold is generalized concircular to an Einstein manifold and that its scalar curvature is prolonged covariant constant.     

Equivariant cohomology distinguishes toric manifolds

The equivariant cohomology of a space with a group action is not only a ring but also an algebra over the cohomology ring of the classifying space of the acting group. We prove that toric manifolds (i.e. compact smooth toric varieties) are isomorphic as varieties if and only if their equivariant cohomology algebras are weakly isomorphic. We also prove that quasitoric manifolds, which can be thought of as a topological counterpart to toric manifolds, are equivariantly homeomorphic if and only if their equivariant cohomology algebras are isomorphic.     

N-S方程一般近似惯性流形构造和逼近

1．引言为了用有限维常微分方程来研究Navier七lobes（N七）方程的长时间动力学行为,Foias,Sell和Temaml］引入了耗散系统惯性流形的概念．但惯性流形存在的一个相当苛刻的条件一谱间隔条件一是包括N习方程在内的很多耗散系统无法满足的．因此,Foias,Manlea和TemamZ］随后又提出了近似惯性流形的概念．近似惯性流形也是一个光滑的Lipschitz流形,所有原方程的解在时间充分大时,将被吸引进入该流形的一个三邻域中．因其存在性不需要谱间隔条件来保证,从而可证明包括N－S方程在内的一大类耗散系统存在近似惯性流形．利用近似惯性…     

On the Constant Type of Almost Hermitian Manifolds

We suggest a most natural generalization of the notion of constant type for nearly Kählerian manifolds introduced by A. Gray to arbitrary almost Hermitian manifolds. We prove that the class of almost Hermitian manifolds of zero constant type coincides with the class of Hermitian manifolds. We show that the class of G ₁-manifolds of zero constant type coincides with the class of 6-dimensional G ₁-manifolds with a non-integrable structure. Finally, we prove that the class of normal G ₂-manifolds of nonzero constant type coincides with the class of 4-dimensional G ₂-manifolds with a nonintegrable structure.