Positively curved homogeneous metrics on spheres

We classify all homogeneous metrics on spheres with positive sectional curvature. This work was completed while W. Ziller was visiting IMPA and he would like to thank the Institute for its hospitality. L. Verdiani was supported by GNSAGA. W. Ziller was supported in part by the Francis J. Carey Term Chair, the Clay Institute and a grant from the National Science Foundation.     

Multiplicative maps on ℬ(X)

A structural feature of multiplicative maps on ℬ(X) which sends some rank-1 operator to an operator of rank not greater than 1 is given, and based on it, some characterizations of automorphism of ℬ(X) are obtained and some multiplicative preserver problems are answered. Project supported by the National Natural Science Foundation of China (Grant No.19671055) and Provincial Natural Science Foundation of Shanxi.     

On twistor Gauss maps of surfaces in 4-spheres

In this paper we study surfaces in S⁴ and their twistor Gauss maps. Some necessary and sufficient conditions that the twistor Gauss map is harmonic are given. We find many examples of nonisotropic harmonic maps from a surface to P ³.Supported by the National Natural Science Foundation of China and the Science Foundation of Zhejiang Province.     

Harmonic polynomial morphisms between Euclidean spaces

Two non-existence theorems on harmonic polynomial morphisms between Euclidean spaces have been shown. Project supported partially by the National Natural Science Foundation of China (Grant No. 19531050) and the State Education Commission Foundation of China.     

关于拟调和映射的一些注记

Several theorems on the finiteness of energy for quasi-harmonic spheres are proved,some counter-examples which state that the energy of quasi-harmonic sphere may be infinite are given. The results support some conditions of a question posed by Lin Fanghua and Wang Changyou.     

Degenerate Orbit Flip Homoclinic Bifurcations with Higher Dimensions

Bifurcations of a degenerate homoclinic orbit with orbit flip in high dimensional system are studied. By establishing a local coordinate system and a Poincaré map near the homoclinic orbit, the existence and uniqueness of 1–homoclinic orbit and 1–periodic orbit are given. Also considered is the existence of 2–homoclinic orbit and 2–periodic orbit. In additon, the corresponding bifurcation surfaces are given. Project supported by the National Natural Science Foundation of China (No: 10171044), the Natural Science Foundation of Jiangsu Province (No: BK2001024), the Foundation for University Key Teachers of the Ministry of Education of China     

Covering spheres of Banach spaces by balls

If the unit sphere of a Banach space X can be covered by countably many balls no one of which contains the origin, then, as an easy consequence of the separation theorem, X* is w*-separable. We prove the converse under suitable renorming. Moreover, the balls of the countable covering can be chosen as translates of the same ball. Research of V. P. Fonf was supported in part by Israel Science Foundation, Grant # 139/02 and by the Istituto Nazionale di Alta Matematica of Italy. Research of C. Zanco was supported in part by the Ministero dell’Università e della Ricerca Scientifica e Tecnologica of Italy and by the Center for Advanced Studies in Mathematics at the Ben-Gurion University of the Negev, Beer-Sheva, Israel.     

The isometric extension of “into” mappings on unit spheres of AL -spaces

In this paper, we show that if V ₀ is an isometric mapping from the unit sphere of an AL-space onto the unit sphere of a Banach space E, then V ₀ can be extended to a linear isometry defined on the whole space. This work was supported by the Research Foundation for Doctor Programme (Grant No. 20060055010) and the National Natural Science Foundation of China (Grant No. 10571090)     

Dyer-Lashof operations in the string topology of spheres and projective spaces

We compute the 2-primary Dyer-Lashof operations in the string topology of several families of manifolds, specifically spheres and a variety of projective spaces. These operations, while well known in the context of iterated loop spaces, give a collection of homotopy invariants of manifolds new to string topology. The computations presented here begin an exploration of these invariants.This material is based upon work supported by the National Science Foundation under agreement No. DMS-0111298.     

Linear programming with spheres and hemispheres of objective vectors

Given a linear program with a boundedp-dimensional feasible region let the objective vector range over ans-sphere, that is, ans-dimensional sphere centered at the origin wheres does not exceedp–1. If the feasible region and the sphere are in general position with respect to each other, then the corresponding set of all optimal solutions is a topologicals-sphere. Similar results are developed for unbounded feasible regions and hemispheres of objective vectors.This research is based on work supported in part by the National Science Foundation under Grant DMS-86-03232.     

Continuity of Julia sets

A sufficient and necessary condition is given for the continuity of Julia sets in the space of all rational maps with degreek>1. Project supported by the National Natural Science Foundation of China (Grant No. 19871002).     

Non-wandering points and the depth for graph maps

Let G be a graph and f:G→G be continuous.Denote by R(f) andΩ(f) the set of recurrent points and the set of non-wandering points of f respectively.LetΩ_0(f) = G andΩ_n(f)=Ω(f|_(Ω_(n-1)(f))) for all n∈N.The minimal m∈NU {∞} such thatΩ_m(f)=Ω_(m 1)(f) is called the depth of f.In this paper,we show thatΩ_2 (f)=(?) and the depth of f is at most 2.Furthermore,we obtain some properties of non-wandering points of f.     

Isovariant maps from free -manifolds to representation spheres

The isovariant version of Borsuk–Ulam type theorems has been studied by Wasserman and the first author. In this paper, first we consider the relation between the existence of C_n-isovariant maps from free C_n-manifolds to representation spheres and Borsuk–Ulam type inequalities for their dimensions. Our main result classifies the C_n-isovariant maps by C_n-isovariant homotopy types when a Borsuk–Ulam type inequality holds. For proving it, we use the multidegree of a C_n-equivariant map developed by the first author.     

Regularity for weakly Dirac-harmonic maps to hypersurfaces

We prove that a weakly Dirac-harmonic map from a Riemann spin surface to a compact hypersurface is smooth. Supported by IMPRS “Mathematics in the Sciences” and the Klaus Tschira Foundation.     

Admissible estimators of binomial probability and the inverse bayes rule map

Explicit formulae for prior distribution moments through values of the Bayes estimator of binomial probability are obtained. These are used to derive a new admissibility criterion.Research supported by National Science Foundation Grants #DMS-8702620 and #DMS-8802359.     

The Enumeration of General Rooted Planar Maps

This paper provides some functional equations satisfied by the generating functions for enumerating general rooted planar maps with up to three parameters. Furthermore, the generating functions can be obtained explicitly by employing the Lagrangian inversion. This is also an answer to an open problem in 1989.     

Maximum density space packing with parallel strings of spheres

A string of spheres is a sequence of nonoverlapping unit spheres inR ³ whose centers are collinear and such that each sphere is tangent to exactly two other spheres. We prove that if a packing with spheres inR ³ consists of parallel translates of a string of spheres, then the density of the packing is smaller than or equal to . This density is attained in the well-known densest lattice sphere packing. A long-standing conjecture is that this density is maximum among all sphere packings in space, to which our proof can be considered a partial result. The work of A. Bezdek and E. Makai was partially supported by the Hungarian National Foundation for Scientific Research under Grant Number 1238.     

Levitin–Polyak well-posedness in generalized vector variational inequality problem with functional constraints

In this paper, we study Levitin–Polyak type well-posedness for generalized vector variational inequality problems with abstract and functional constraints. Various criteria and characterizations for these types of well-posednesses are given. This research is partially supported by the National Science Foundation of China and Shanghai Pujiang Program.     

Weak monotonicity inequality and partial regularity for harmonic maps

The notion of locally weak monotonicity inequality for weakly harmonic maps is introduced and various results on this class of maps are obtained. For example, the locally weak monotonicity inequality is nearly equivalent to theε-regularity. Project supported by the National Natural Science Foundation of China (Grant No. 19571028) and the Guangdong Provincial Natural Science Foundation of China.