Banach空间上的强混合算子

1999年,L.B.Gonzalez证明了任意无限维可分Banach空间上存在拓扑传递的有界线性算子.这个结果肯定地回答了S.Rolewicz提出的问题.本文证明了由L.B.Gonzalez所给出的算子实际上是强混合的,同时,对加权移位算子的混合性利用权序列进行了刻划并指出任意无限维可分Hilbert空间上存在弱混合而非强混合的有界线性算子.     

相似不变子空间和保相似线性映射

本文给出了可分无限维Hilbert空间H上有界线性算子全体B(H)中的相似不变子空间的构造,同时给出了B(H)上双边保相似线性映射的表示.     

A-Weyl定理及其摄动

本文讨论了本质逼近点谱的一种变形,并利用该变形定义的新的谱集,研究了α-Weyl定理在紧摄动下的稳定性.同时,给出了对任意的正整数n∈N,算子T~n∈B(H)不满足α-Weyl定理的稳定性的充分条件,其中H表示无限维的复可分Hilbert空间,B(H)表示H上的有界线性算子的全体.     

Banach空间上强混合的C0-半群

证明了每个可分无限维复Banach空间上都存在一个强混合的Co-半群,在加权函数空间上给出了转移半群是强混合的一个充要条件.     

上三角算子矩阵Browder定理的稳定性

令H为无限维且复可分的Hilbert空间,B(H)为H上的有界线性算子全体.若T∈B(H)满足σ_w(T)=σ_b(T),则称T有Browder定理,其中σ_ω(T)和σ_b(T)分别表示算子T的Weyl谱和Borwder谱;对任意的紧算子K∈B(H),若T+K有Browder定理,则称T满足Browder定理的稳定性.给出了2-阶上三角算子矩阵的平方满足Borwder定理的稳定性的充要条件.     

每个算子都是两个强不可约算子的和

本文证明了可分无穷维 Hilbert空间上每个有界线性算子均可写成两个强不可约算子之和 .这回答了文献 [9]中提出一个公开问题     

Banach空间上强混合的C_0-半群

证明了每个可分无限维复Banach空间上都存在一个强混合的C_0-半群,在加权函数空间上给出了转移半群是强混合的一个充要条件.     

上三角算子矩阵的单值延拓性质的摄动

设H为无限维可分的复Hilbert空间,B(H)为H上的有界线性算子全体.算子T∈B(H)称为具有单值延拓性质,若对任意一个开集U(?)C,满足方程(T-λI)f(λ)=0(任给λ∈U)的唯一的解析函数f:U→H为零函数;T∈B(H)称为满足单值延拓性质的稳定性,若对任意一个紧算子K∈B(H),T+K都满足单值延拓性质.本文给出了2×2上三角算子矩阵在紧摄动下满足单值延拓性质的稳定性的特征.     

算子矩阵的单值扩张性质的判定

H表示无限维可分的复Hilbert空间,B(H)为H上的有界线性算子的全体.若对于复数域C中任意一个开集U,满足方程(T-λI)f(λ)=0(任给λ∈U)的唯一的解析函数f:U→H为零函数,称算子T具有单值延拓性质(简记为T∈(SVEP)).若对任意一个紧算子K,T+K都满足单值延拓性质,称T∈B(H)满足单值延拓性质的稳定性.给出了2×2上三角算子矩阵满足单值延拓性质的稳定性的特征.     

良序套张量积的代数中的强不可约算子

设Ｈ为复的可分无限维Ｈｉｌｂｅｒｔ空间，称有界线性算子Ｔ为强不可约的，如果与Ｔ可交换的幂等算子只有０和Ｉ．王宗尧、蒋春澜、纪有清等人证明了在任何一个套的套代数中都存在大量的强不可约算子，并且找到了它们的酉轨道闭包．本文考虑有限个套的张量积的代数中强不可约算子的存在性问题。证明了：对复平面上任何一个连通完备集σ、总存在一个对角算子Ｎ和它的一个范数可以任意小的紧摄动Ｔ＝Ｘ＋Ｋ，使得Ｔ是一个强不可约算子、Ｔ在有限个良序套的张量积的代数中，并且σ（Ｔ）＝σｌｒｅ（Ｔ）＝σ（Ｎ）＝σｌｒｅ（Ｎ）＝σ进一步，文章还对具有单点谱的算子和良序套与正交补为良序套的张量积的代数进行了讨论，得到了一些结果．     

Existence and nonexistence of hypercyclic semigroups

In these notes we provide a new proof of the existence of a hypercyclic uniformly continuous semigroup of operators on any separable infinite-dimensional Banach space that is very different from--and considerably shorter than--the one recently given by Bermúdez, Bonilla and Martinón. We also show the existence of a strongly dense family of topologically mixing operators on every separable infinite-dimensional Fréchet space. This complements recent results due to Bès and Chan. Moreover, we discuss the Hypercyclicity Criterion for semigroups and we give an example of a separable infinite-dimensional locally convex space which supports no supercyclic strongly continuous semigroup of operators.

     

Strongly irreducible operators on Banach spaces

This paper firstly discusses the existence of strongly irreducible operators on Banach spaces. It shows that there exist strongly irreducible operators on Banach spaces with w*-separable dual. It also gives some properties of strongly irreducible operators on Banach spaces. In particular, if T is a strongly irreducible operator on an infinite-dimensional Banach space, then T is not of finite rank and T is not an algebraic operator. On Banach spaces with subsymmetric bases, including infinite-dimensional separable Hilbert spaces, it shows that quasisimilarity does not preserve strong irreducibility. In addition, we show that the strong irreducibility of an operator does not imply the strong irreducibility of its conjugate operator, which is not the same as the property in Hilbert spaces.     

Hypercyclic subspaces in Fréchet spaces

In this note, we show that every infinite-dimensional separable Fréchet space admitting a continuous norm supports an operator for which there is an infinite-dimensional closed subspace consisting, except for zero, of hypercyclic vectors. The family of such operators is even dense in the space of bounded operators when endowed with the strong operator topology. This completes the earlier work of several authors.

     

Frequent hypercyclicity,chaos, and unconditional Schauder decompositions

We prove that if X is any complex separable infinite-dimensional Banach space with an unconditional Schauder decomposition, X supports an operator T which is chaotic and frequently hypercyclic. In contrast with the complex case, we observe that there are real Banach spaces with an unconditional basis which support no chaotic operator.     

On the complete metrisability of spaces of contractive semigroups

Archiv der Mathematik - The space of unitary $$C_{0}$$ -semigroups on a separable infinite-dimensional Hilbert space, when viewed under the topology of uniform weak operator convergence on compact...     

Sums of hypercyclic operators

Every bounded operator on a complex infinite-dimensional separable Hilbert space can be written as the sum of two hypercyclic operators, and also as the sum of two chaotic operators.     

Hypercyclic and topologically mixing cosine functions on Banach spaces

Our first aim in this paper is to give sufficient conditions for the hypercyclicity and topological mixing of a strongly continuous cosine function. We apply these results to study the cosine function associated to translation groups. We also prove that every separable infinite dimensional complex Banach space admits a topologically mixing uniformly continuous cosine family.

     

按序列分布混沌与拓扑混合

本文讨论了按序列分布混沌与拓扑混合的关系,并证明了:若X为至少两点的可分局部紧致度量空间,连续映射f:X→X是拓扑混合的,则对于任一正整数递增序列{mi},存在X的c-稠密Fσ子集D是f按{mi}的某子序列的分布混沌集.