Marginally trapped surfaces in spaces of oriented geodesics

We investigate the geometric properties of marginally trapped surfaces (surfaces which have null mean curvature vector) in the spaces of oriented geodesics of Euclidean 3-space and hyperbolic 3-space, endowed with their canonical neutral Kaehler structures. We prove that every rank one surface in these four manifolds is marginally trapped. In the Euclidean case we show that Lagrangian rotationally symmetric sections are marginally trapped and construct an explicit family of marginally trapped Lagrangian tori. In the hyperbolic case we explore the relationship between marginally trapped and Weingarten surfaces, and construct examples of marginally trapped surfaces with various properties.     

Surjectivity of differential operators and the division problem in certain function and distribution spaces

We give an overview on surjectivity conditions for partial differential operators and operators defined by multiplication with polynomials on certain function and distribution spaces of Laurent Schwartz. We complement the classical results by treating the surjectivity of operators on the space of slowly increasing functions and on the space of rapidly decreasing distributions, respectively.     

Hypercyclic convolution operators on Fréchet spaces of analytic functions

A result of Godefroy and Shapiro states that the convolution operators on the space of entire functions on Cn, which are not multiples of identity, are hypercyclic. Analogues of this result have appeared for some spaces of holomorphic functions on a Banach space. In this work, we define the space holomorphic functions associated to a sequence of spaces of polynomials and determine conditions on this sequence that assure hypercyclicity of convolution operators. Some known results come out as particular cases of this setting. We also consider holomorphic functions associated to minimal ideals of polynomials and to polynomials of the Schatten-von Neumann class.     

Sampling and interpolation in large Bergman and Fock spaces

We obtain sampling and interpolation theorems in weighted spaces of analytic functions for radial weights of arbitrary (more rapid than polynomial) growth. We give an application to invariant subspaces of arbitrary index in large weighted Bergman spaces.     

Remarks on classifications and adjunctions

Jon Barwise and Jerry Seligman introduced the category of classifications and infomorphisms to model information theoretical concepts and information flow processes. This is the dual category of the category of Chu spaces introduced by Michael Barr and Peter Chu and studied extensively by Vaughan Pratt, Gordon Plotkin and others at Stanford. It is also very closely related to the theory of institutions introduced in a different context by Joseph Goguen and Rod Burstall. Here some aspects of the theory are reviewed and some adjunctions between the category of classifications and other related categories are studied from a more abstract point of view.     

Continuity envelopes and sharp embeddings in spaces of generalized smoothness

We study continuity envelopes in spaces of generalized smoothness and . The results are applied in proving sharp embedding assertions in some limiting situations.     

Weighted BMO and Carleson measures on spaces of homogeneous type

In this paper we characterize the weighted BMO(ω)(X), with X a space of homogeneous type, through an adequate weighted Carleson measure. As a byproduct we can define the weighted Triebel-Lizorkin space and obtain the identification with the above space.     

The Sharkovski? Theorem for spaces of measurable functions

We formulate a generalization of the so-called Random Sharkovski? Theorem from paper by Jan Andres, which is the randomized version of the classical Sharkovski? Theorem. We use the method of transformation to deterministic case involving the Kuratowski-Ryll-Nardzewski selection theorem, which allows us to omit the assumption of completeness of the incorporated measurable space. Moreover, we formulate an analogue of the Sharkovski? Theorem for spaces of measurable functions and for Lp-spaces.     

模糊向量空间的商空间

在史和黄重新定义的模糊向量空间的模糊基和模糊维数的基础上,讨论模糊向量空间的模糊线性映射及其性质,定义模糊向量空间(V,μ)的商空间(V/K,μK)并研究了它的性质,证明公式dim(μK)+dim (k(e)ff)=dim(μ)成立,其中k(e)ff是模糊向量空间(V,μ)关于模糊线性映射f的模糊核空间.