In this paper,we present a necessary and sufficient condition for hyponormal block Toeplitz operators T on the vector-valued weighted Bergman space with symbolsΦ(z)=G*(z)+F(z),where F(z)=∑Ni=1 Aiziand...In this paper,we present a necessary and sufficient condition for hyponormal block Toeplitz operators T on the vector-valued weighted Bergman space with symbolsΦ(z)=G*(z)+F(z),where F(z)=∑Ni=1 Aiziand G(z)=∑Ni=1 A−izi,Aiae culants.展开更多
We consider the hyponormality of the block dual Toeplitz operator SΦacting on the orthogonal complement of the vector valued weighted Bergman space (Aα2(D,Cn))⊥.We provide a necessary and sufficient ...We consider the hyponormality of the block dual Toeplitz operator SΦacting on the orthogonal complement of the vector valued weighted Bergman space (Aα2(D,Cn))⊥.We provide a necessary and sufficient condition for the hyponormality of SΦwith matrix valued bounded harmonic symbol.In this process,we introduce a function gw,s∈(Aα2(D))⊥,which is similar to the reproducing kernel of the weighted Bergman space Aα2(D).We also give some additional applications of the function gw,s∈(Aα2(D))⊥.展开更多
In this article, we give an operator transform T (*) from class A operator to the class of hyponormal operators. It is different from the operator transform T defined by M. Ch and T. Yamazaki. Then, we show that...In this article, we give an operator transform T (*) from class A operator to the class of hyponormal operators. It is different from the operator transform T defined by M. Ch and T. Yamazaki. Then, we show that σ(T ) = σ( T (*)) and σa(T )/{0} = σa( T (*))/{0}, in case T belongs to class A. Next, we obtain some relations between T and T (9).展开更多
In this paper we consider the block Toeplitz operators TФ on the weighted Bergman space A2α(D, Cn) and we give a necessary and sufficient condition for the hyponor-mality of block Toeplitz operators with symbol in...In this paper we consider the block Toeplitz operators TФ on the weighted Bergman space A2α(D, Cn) and we give a necessary and sufficient condition for the hyponor-mality of block Toeplitz operators with symbol in the class of functions Ф=F + G* withmatrix-valued polynomial functions F and G with degree 2.展开更多
In this paper,cohyponormal weighted composition operators on the Fock space over CNare characterized completely.We also consider a class of weighted composition operators on the Fock space over CNwhich are both ...In this paper,cohyponormal weighted composition operators on the Fock space over CNare characterized completely.We also consider a class of weighted composition operators on the Fock space over CNwhich are both posinormal and coposinormal.As an application,we obtain the characterization of hyponormal,cohyponormal,posinormal and coposinormal composition operators on the Fock space over CN.展开更多
The complete characterizations of the spectra and their various parts of hyponormal unilateral and bilateral weighted shifts are presented respectively in this paper. The results obtained here generalize the correspon...The complete characterizations of the spectra and their various parts of hyponormal unilateral and bilateral weighted shifts are presented respectively in this paper. The results obtained here generalize the corresponding work of the references.展开更多
By an elementary proof, we use a result of Conway and Dudziak to show that if A is a hyponormal operator with spectral radius r(A) such that its spectrum is the closed disc {z:|z| ≤ r(A)} then A is reflexive. ...By an elementary proof, we use a result of Conway and Dudziak to show that if A is a hyponormal operator with spectral radius r(A) such that its spectrum is the closed disc {z:|z| ≤ r(A)} then A is reflexive. Using this result, we give a simple proof of a result of Bercovici, Foias, and Pearcy on reflexivity of shift operators. Also, it is shown that every power of an invertible bilateral weighted shift is reflexive.展开更多
We introduce the notion of weak k-hyponormality and polynomial hyponormality for commuting operator pairs on a Hilbert space and investigate their relationship with k-hyponormality and subnormality.We provide examples...We introduce the notion of weak k-hyponormality and polynomial hyponormality for commuting operator pairs on a Hilbert space and investigate their relationship with k-hyponormality and subnormality.We provide examples of 2-variable weighted shifts which are weakly 1-hyponormal but not hyponormal.By relating the weak k-hyponormality and k-hyponormality of a commuting operator pair to positivity of restriction of some linear functionals to corresponding cones of functions,we prove that there is an operator pair that is polynomially hyponormal but not 2-hyponormal,generalizing Curto and Putinar’s result(1991,1993)to the two-variable case.展开更多
By bounded vector-valued functions and block matrix representations of Hankel operators, we completely characterize the hyponormality of Toeplitz operators on the Hardy space of the polydisk.
For a hyponormal operator T if there is a polynomial p(·) such that σ(p(T))= {0}, then p(T) =0. In general, it is proved in this way: from σ(p(T)) =0, we know that σ(T) consists of finite points, and therefore...For a hyponormal operator T if there is a polynomial p(·) such that σ(p(T))= {0}, then p(T) =0. In general, it is proved in this way: from σ(p(T)) =0, we know that σ(T) consists of finite points, and therefore T must be normal and so is p(T), hence p(T) =0.展开更多
In this paper,we mainly study the hyponormality of dual Toeplitz operators on the orthogonal complement of the harmonic Bergman space.First we show that the dual Toeplitz operator with the bounded symbol is hyponormal...In this paper,we mainly study the hyponormality of dual Toeplitz operators on the orthogonal complement of the harmonic Bergman space.First we show that the dual Toeplitz operator with the bounded symbol is hyponormal if and only if it is normal.Then we obtain a necessary and sufficient condition for the dual Toeplitz operator Sφ with the symbol φ(z)=azn1zm1+bzn2zm2(n1,n2,m1,m2∈N and a,b∈C)to be hyponormal.Finally,we show that the rank of the commutator of two dual Toeplitz operators must be an even number if the commutator has a finite rank.展开更多
In this paper,we prove that the necessary and sufficient condition for a Toeplitz operator Tu on the Dirichlet space to be hyponormal is that the symbol u is constant for the case that the projection of u in the Diric...In this paper,we prove that the necessary and sufficient condition for a Toeplitz operator Tu on the Dirichlet space to be hyponormal is that the symbol u is constant for the case that the projection of u in the Dirichlet space is a polynomial and for the case that u is a class of special symbols,respectively.We also prove that a Toeplitz operator with harmonic polynomial symbol on the harmonic Dirichlet space is hyponormal if and only if its symbol is constant.展开更多
It is shown in[6]and[7]that a necessary and sufficient condition for a hyponormal weightedunilateral shift to be unitarily equivalent to a Toeplitz operator is that its weights satisfy(1-|an|2)=(1-|a0|2)(1-|an-1|2)n≥...It is shown in[6]and[7]that a necessary and sufficient condition for a hyponormal weightedunilateral shift to be unitarily equivalent to a Toeplitz operator is that its weights satisfy(1-|an|2)=(1-|a0|2)(1-|an-1|2)n≥1,where ansatisfiesan=1.In[8],the author obtainedsimilar result for the hyponormal weighted unilateral shift of multiplicity 2.The aim of this展开更多
Let H^2(M) be a noncommutative Hardy space associated with semifinite von Neumann algebra M, we get the connection between numerical spectrum and the spectrum of Toeplitz operator Tt acting on H^2(M), and the norm...Let H^2(M) be a noncommutative Hardy space associated with semifinite von Neumann algebra M, we get the connection between numerical spectrum and the spectrum of Toeplitz operator Tt acting on H^2(M), and the norm of Toeplitz operator Tt is equivalent to ||t|| when t is hyponormal operator in M.展开更多
This paper presents a discussion on a problem suggested by N.Salinas(J.Operator Theory,Vol.10,1983),i.e.,if T=(T1,T2,…,Tn)is a commuting n-tuple ofhyponormal operators on a complex Hilbert space,do we have(1)(...This paper presents a discussion on a problem suggested by N.Salinas(J.Operator Theory,Vol.10,1983),i.e.,if T=(T1,T2,…,Tn)is a commuting n-tuple ofhyponormal operators on a complex Hilbert space,do we have(1)(2)δ(T-μ)=dist(μ,σl(T)),μ∈Cn?It is proved that the problems(1)and(2)are both true for some commuting n-tuples ofsemihyponormal operators.In general case,problem(1)has a negative answer.As an ap-plication,we point out that there exists a commuting n-tuple of hyponormal operatorsT(n≥2),such that|λ|【,where σT(T)denotes J.L.Taylor’sjoint spectra of T,even if the condition of Taylor’s joint spectra of T is given.展开更多
In this paper, necessary and sufficient conditions are obtained for unilateral weighted shifts to be near subnormal. As an application of the main results, many answers to the Hilbert space problem 160 are presented a...In this paper, necessary and sufficient conditions are obtained for unilateral weighted shifts to be near subnormal. As an application of the main results, many answers to the Hilbert space problem 160 are presented at the end of the paper.展开更多
In this paper,we describe the eigenvalues of an operator weighted Shift and give some sufficient conditions for an operator weighted shift to be reflexive.We also show that every hyponomal operator weighted shift is r...In this paper,we describe the eigenvalues of an operator weighted Shift and give some sufficient conditions for an operator weighted shift to be reflexive.We also show that every hyponomal operator weighted shift is reflexive.展开更多
In this paper,a generalized Toeplitz operator is defined and some of results about the classical Toeplitz operator are generalized.In particular,we obtain the necessary and sufficient condition for the product of two ...In this paper,a generalized Toeplitz operator is defined and some of results about the classical Toeplitz operator are generalized.In particular,we obtain the necessary and sufficient condition for the product of two such Toeplitz operators to still be Toeplitz operator and the necessary and sufficient condition for such Toeplitz operator to be normal operator.Finally,a necessary condition for two such Toeplitz operators to be commutative is established.展开更多
In this paper, we show that the hyponormal Toeplitz operator Tφ with trigonometric polynomial symbol φ is either normal or completely non-normal. Moreover, if Tφ is non-normal, then Tφ has a dense set of cyclic ve...In this paper, we show that the hyponormal Toeplitz operator Tφ with trigonometric polynomial symbol φ is either normal or completely non-normal. Moreover, if Tφ is non-normal, then Tφ has a dense set of cyclic vectors. Some general conditions are also considered.展开更多
摘要In this paper,we present a necessary and sufficient condition for hyponormal block Toeplitz operators T on the vector-valued weighted Bergman space with symbolsΦ(z)=G*(z)+F(z),where F(z)=∑Ni=1 Aiziand G(z)=∑Ni=1 A−izi,Aiae culants.
基金Supported by the Scientific Research Fund of Liaoning Provincial Education Department of China (Grant No.LJKMZ20221405)the National Natural Science Foundation of China (Grant No.12031002)。
摘要We consider the hyponormality of the block dual Toeplitz operator SΦacting on the orthogonal complement of the vector valued weighted Bergman space (Aα2(D,Cn))⊥.We provide a necessary and sufficient condition for the hyponormality of SΦwith matrix valued bounded harmonic symbol.In this process,we introduce a function gw,s∈(Aα2(D))⊥,which is similar to the reproducing kernel of the weighted Bergman space Aα2(D).We also give some additional applications of the function gw,s∈(Aα2(D))⊥.
基金supported by Science Foundation of Ministry of Education of China (208081)Technology and pioneering project in Henan Provice (102300410012)Education Foundation of Henan Province (2007110016, 2008B110006)
摘要In this article, we give an operator transform T (*) from class A operator to the class of hyponormal operators. It is different from the operator transform T defined by M. Ch and T. Yamazaki. Then, we show that σ(T ) = σ( T (*)) and σa(T )/{0} = σa( T (*))/{0}, in case T belongs to class A. Next, we obtain some relations between T and T (9).
基金supported by Basic Science Research Program through the National Research Foundation of Korea(NRF)funded by the Ministry of Education(2009-0093827)
摘要In this paper we consider the block Toeplitz operators TФ on the weighted Bergman space A2α(D, Cn) and we give a necessary and sufficient condition for the hyponor-mality of block Toeplitz operators with symbol in the class of functions Ф=F + G* withmatrix-valued polynomial functions F and G with degree 2.
基金Supported by the National Natural Science Foundation of China(Grant No.12271134)Shanxi Scholarship Council of China(Grant No.2020-089)Program of Graduate Bilingual Curriculum Construction in Shanxi Normal University(Grant No.YJSSY201903).
摘要In this paper,cohyponormal weighted composition operators on the Fock space over CNare characterized completely.We also consider a class of weighted composition operators on the Fock space over CNwhich are both posinormal and coposinormal.As an application,we obtain the characterization of hyponormal,cohyponormal,posinormal and coposinormal composition operators on the Fock space over CN.
摘要The complete characterizations of the spectra and their various parts of hyponormal unilateral and bilateral weighted shifts are presented respectively in this paper. The results obtained here generalize the corresponding work of the references.
基金supported by a grant (No.86-GR-SC-27) from Shiraz University Research Council
摘要By an elementary proof, we use a result of Conway and Dudziak to show that if A is a hyponormal operator with spectral radius r(A) such that its spectrum is the closed disc {z:|z| ≤ r(A)} then A is reflexive. Using this result, we give a simple proof of a result of Bercovici, Foias, and Pearcy on reflexivity of shift operators. Also, it is shown that every power of an invertible bilateral weighted shift is reflexive.
基金supported by National Natural Science Foundation of China(GrantNos.10801028 and 11271075)Science and Technology Development Planning Program of Jilin Province(GrantNo.201215008)Specialized Research Fund for the Doctoral Program of Higher Education(Grant No.20120043120003)
摘要We introduce the notion of weak k-hyponormality and polynomial hyponormality for commuting operator pairs on a Hilbert space and investigate their relationship with k-hyponormality and subnormality.We provide examples of 2-variable weighted shifts which are weakly 1-hyponormal but not hyponormal.By relating the weak k-hyponormality and k-hyponormality of a commuting operator pair to positivity of restriction of some linear functionals to corresponding cones of functions,we prove that there is an operator pair that is polynomially hyponormal but not 2-hyponormal,generalizing Curto and Putinar’s result(1991,1993)to the two-variable case.
基金Supported by National Natural Science Foundation of China(Grant No.10971020)
摘要By bounded vector-valued functions and block matrix representations of Hankel operators, we completely characterize the hyponormality of Toeplitz operators on the Hardy space of the polydisk.
基金Project supported by the National Natural Science Foundation of China
摘要For a hyponormal operator T if there is a polynomial p(·) such that σ(p(T))= {0}, then p(T) =0. In general, it is proved in this way: from σ(p(T)) =0, we know that σ(T) consists of finite points, and therefore T must be normal and so is p(T), hence p(T) =0.
基金Partially supported by NSFC(Grant No.11701052)the second author was partially supported by the Fundamental Research Funds for the Central Universities(Grant Nos.2020CDJQY-A039 and 2020CDJ-LHSS-003)。
摘要In this paper,we mainly study the hyponormality of dual Toeplitz operators on the orthogonal complement of the harmonic Bergman space.First we show that the dual Toeplitz operator with the bounded symbol is hyponormal if and only if it is normal.Then we obtain a necessary and sufficient condition for the dual Toeplitz operator Sφ with the symbol φ(z)=azn1zm1+bzn2zm2(n1,n2,m1,m2∈N and a,b∈C)to be hyponormal.Finally,we show that the rank of the commutator of two dual Toeplitz operators must be an even number if the commutator has a finite rank.
基金Supported by the National Natural Science Foundation of China (Grant No.10971195)the Natural Science Foundation of Zhejiang Province (Grant Nos.Y6090689 Y6110260)
摘要In this paper,we prove that the necessary and sufficient condition for a Toeplitz operator Tu on the Dirichlet space to be hyponormal is that the symbol u is constant for the case that the projection of u in the Dirichlet space is a polynomial and for the case that u is a class of special symbols,respectively.We also prove that a Toeplitz operator with harmonic polynomial symbol on the harmonic Dirichlet space is hyponormal if and only if its symbol is constant.
基金This research was supported in part by a Foundation from Academy of Sciences of China.
摘要It is shown in[6]and[7]that a necessary and sufficient condition for a hyponormal weightedunilateral shift to be unitarily equivalent to a Toeplitz operator is that its weights satisfy(1-|an|2)=(1-|a0|2)(1-|an-1|2)n≥1,where ansatisfiesan=1.In[8],the author obtainedsimilar result for the hyponormal weighted unilateral shift of multiplicity 2.The aim of this
基金partly supported by Natural Science Foundation of the Xinjiang Uygur Autonomous Region(2013211A001)
摘要Let H^2(M) be a noncommutative Hardy space associated with semifinite von Neumann algebra M, we get the connection between numerical spectrum and the spectrum of Toeplitz operator Tt acting on H^2(M), and the norm of Toeplitz operator Tt is equivalent to ||t|| when t is hyponormal operator in M.
摘要This paper presents a discussion on a problem suggested by N.Salinas(J.Operator Theory,Vol.10,1983),i.e.,if T=(T1,T2,…,Tn)is a commuting n-tuple ofhyponormal operators on a complex Hilbert space,do we have(1)(2)δ(T-μ)=dist(μ,σl(T)),μ∈Cn?It is proved that the problems(1)and(2)are both true for some commuting n-tuples ofsemihyponormal operators.In general case,problem(1)has a negative answer.As an ap-plication,we point out that there exists a commuting n-tuple of hyponormal operatorsT(n≥2),such that|λ|【,where σT(T)denotes J.L.Taylor’sjoint spectra of T,even if the condition of Taylor’s joint spectra of T is given.
摘要In this paper, necessary and sufficient conditions are obtained for unilateral weighted shifts to be near subnormal. As an application of the main results, many answers to the Hilbert space problem 160 are presented at the end of the paper.
基金Project supported by thc Scicncc Foundation for the Young of Liaoning Univcrsiry.
摘要In this paper,we describe the eigenvalues of an operator weighted Shift and give some sufficient conditions for an operator weighted shift to be reflexive.We also show that every hyponomal operator weighted shift is reflexive.
基金Foundation item: the Natural Science Foundation of Jiangxi Province (No. 2007GZS0371)
摘要In this paper,a generalized Toeplitz operator is defined and some of results about the classical Toeplitz operator are generalized.In particular,we obtain the necessary and sufficient condition for the product of two such Toeplitz operators to still be Toeplitz operator and the necessary and sufficient condition for such Toeplitz operator to be normal operator.Finally,a necessary condition for two such Toeplitz operators to be commutative is established.
基金Supported by the National Natural Science Foundation of China (Grant Nos.1097102010671028)
摘要In this paper, we show that the hyponormal Toeplitz operator Tφ with trigonometric polynomial symbol φ is either normal or completely non-normal. Moreover, if Tφ is non-normal, then Tφ has a dense set of cyclic vectors. Some general conditions are also considered.