Hypercyclic Semigroups Generated by Ornstein-Uhlenbeck Operators

The chaotic and hypercyclic behavior of the C ₀-semigroups of operators generated by a perturbation of the Ornstein-Uhlenbeck operator with a multiple of the identity in L²(\mathbb R^N){L^2(\mathbb {R}^N)} is investigated. Negative and positive results are presented, depending on the signs of the real parts of the eigenvalues of the matrix appearing in the drift of the operator.     

On Finite Presentability of Direct Products of Semigroups

A finite semigroup S is said to preserve finite generation (resp., presentability) in direct products, provided that, for every infinite semigroup T, the direct product S × T is finitely generated (resp., finitely presented) if and only if T is finitely generated (resp., finitely presented). The main result of this paper is a constructive necessary and sufficient condition for S to preserve both finite generation and presentability in direct products. The condition is that certain graphs, (s), one for each s S, are all connected. The main result is illustrated in three examples, one of which exhibits a 4-element semigroup that preserves finite generation but not finite presentability in direct products.1991 Mathematics Subject Classification: 20M05, 05C25The first author is financially supported by the Sub-Programa Ciência e Tecnologia do 2° Quadro Comunitário de Apoio (grant number BD/ 15623/98). The author also acknowledges the support of the Centro de Álgebra da Universidade de Lisboa and of the Projecto Praxis 2/2.1/MAT/73/94. The second author acknowledges partial financial support from the Nuffield Foundation.     

某些半群子范畴中的张量积

半群范畴S中张量积首先在中引入。T∈ob S称为A,B∈ob S的张量积(记为AB),如果存在双同态t:A×B→T(相当于中线性平衡映射),且对于任意双同态s:A×B→C∈ob S总存在唯一的同态μ:T→C,使s-ut。确认了张量积的存在唯一。等引入交换半群、半格等子范畴中的张量积,其定义与上述基本相同,仅将S改为该子范畴,此外该划了一些半群类的张量积。本文在§1从任意半群簇V中张量积与其在S中     

On a Class of Subdirect Products of Left and Right Clifford Semigroups

Abstract

Regular semigroups S with the property eS ? Se or Se ? eS for all idempotents e ∈ S include all left and right Clifford semigroups. Characterizations of such semigroups are given and their structure investigated, in particular in terms of spined products of left and right Clifford semigroups with respect to Clifford semigroups.     

Convolution Products in Naturally Ordered Semigroups

In this paper new equalities between two different convolution products in cancellative naturally ordered semigroups (but not in groups) are given. We also give several applications in particular cases and      

Hypercyclic algebras

We prove the existence of algebras of hypercyclic vectors in three cases: convolution operators, composition operators, and backward shift operators.     

Equations on Semidirect Products of Commutative Semigroups

This material is based upon work supported by the National Science Foundation under Grant No. CCR-9300738. Many thanks to the referee of a preliminary version of this paper for his very valuable comments and suggestions.     

On Finite Semigroups Embeddable in Inverse Semigroups

No Abstract. October 29, 1998     

关于半环半群

This paper characterizes the multiplication operator semigroup of semiring semigroup by using the tensor product of semigroups, and by using the endomorphism semigroup, and considers some properties of the multiplication operator semigroup of semiring semigroup.     

On Perfect Semigroups

It is shown that in order to characterize perfect semigroups in general, it suffices to characterize perfect semigroups among semigroups S such that S is a subsemigroup of a rational vector space, carries the identical involution, and has an archimedean component H such that S = H {0}.     

On Quasi-Separative Semigroups

We present some congruences on semigroups and use them to obtain a decomposition of quasi-separative semigroups.     

On Legal Semigroups

A new class of semigroups with a two variable regularity law is introduced. These semigroups are non-regular semigroups but they are closely related to regular semigroups. The local and global structures of this class of semigroups are investigated.AMS Subject Classification (2000): 20M10Partially supported by a Chinese University of Hong Kong Direct Research grant, Hong Kong (98/99) # 2060152.Partially supported by a grant of the National Science Foundation, China.     

Hypercyclic Toeplitz Operators

We study hypercyclicity of the Toeplitz operators in the Hardy space \({H^{2}(\mathbb{D})}\) with symbols of the form \({p(\overline{z}) + \varphi(z)}\), where \({p}\) is a polynomial and \({\varphi \in H^{\infty}(\mathbb{D})}\). We find both necessary and sufficient conditions for hypercyclicity which almost coincide in the case when deg \({p =1}\).     

直觉模糊变换半群的积与覆盖关系

提出了直觉模糊变换半群的(全)直积,圈积,直觉模糊变换半群的覆盖的定义,利用代数的手段讨论了直觉模糊变换半群的积的结合性质,研究了直觉模糊变换半群的积的覆盖关系.     

Hypercyclic Conjugate Operators

We prove that for any weighted backward shift B = B_w on an infinite dimensional separable Hilbert space H whose weight sequence w = (w_n) satisfies , the conjugate operator is hypercyclic on the space S(H) of self-adjoint operators on H provided with the topology of uniform convergence on compact sets. That is, there exists an such that is dense in S(H). We generalize the result to more general conjugate maps , and establish similar results for other operator classes in the algebra B(H) of bounded operators, such as the ideals K(H) and N(H) of compact and nuclear operators respectively.     

Numerically Hypercyclic Operators

An operator T acting on a normed space E is numerically hypercyclic if, for some \({(x, x^*)\in \Pi(E)}\), the numerical orbit \({\{x^*(T^n(x)):n\geq 0\}}\) is dense in \({\mathbb{C}}\). We prove that finite dimensional Banach spaces with dimension at least two support numerically hypercyclic operators. We also characterize the numerically hypercyclic weighted shifts on classical sequence spaces.     

Embedding Semigroups with Associate Subgroups into Semidirect Products

A semigroup S is said to have an associate subgroup G if, for each s ∈ S, there is a unique s* ∈ G such that ss*s = s. If the identity 1 _G of G is medial, i.e., c1 _G c = c holds for each c being a product of idempotents, we show that S is isomorphic to a certain subsemigroup of a semidirect product of an idempotent generated semigroup C by G. If additionally S is orthodox, we may choose C to be a band, belonging to the band variety, generated by the band of idempotents of S.     

E-酉正则半群

本文定义了PO-六元组的概念,给出了E-酉正则半群的一种结构.     

On Super Hamiltonian Semigroups

The concept of super hamiltonian semigroup is introduced. As a result, the structure theorems obtained by A. Cherubini and A. Varisco on quasi commutative semi-groups and quasi hamiltonian semigroups respectively are extended to super hamiltonian semigroups.