Let н be a complex, separable, infinite dimensional Hilbert space, T ε（Ｈ）. （ｕ＋Ｋ）（T） denotes the （ｕ＋ｋ）-orbit of T, i.e., （ｕ＋ｋ）（T） = {R-1TR: R is invertible and of the form unitary plus compact}...Let н be a complex, separable, infinite dimensional Hilbert space, T ε（Ｈ）. （ｕ＋Ｋ）（T） denotes the （ｕ＋ｋ）-orbit of T, i.e., （ｕ＋ｋ）（T） = {R-1TR: R is invertible and of the form unitary plus compact}. Let be an analytic and simply connected Cauchy domain in C and n ε N. A（, n） denotes the class of operators, each of which satisfies （i） T is essentially normal; （ii） σ（T） =, ρF（T） ∩ σ（T） = ; （iii） ind （λ-T） = -n, nul （λ-T） = 0 （λ∈Ω ）. It is proved that given T1, T2 ε A（, n） and ε > 0, there exists a compact operator K with K <ε such that T1 +Kε （ｕ＋ｋ）（T2）. This result generalizes a result of P. S. Guinand and L. Marcoux [6,15]. Furthermore, the authors give a character of the norm closure of （ｕ＋Ｋ）（T）, and prove that for each T ε A（, n）, there exists a compact （SI） perturbation of T whose norm can be arbitrarily small.展开更多
Two operators A, B ∈ B（H） are said to be strongly approximatively similar, denoted by A -sas B, if （i） given ε 〉 0, there exist Ki ∈ B（H） compact with ｜｜Ki｜｜ 〈ε（i = 1,2） such that A＋K1 and B ＋ K2 a...Two operators A, B ∈ B（H） are said to be strongly approximatively similar, denoted by A -sas B, if （i） given ε 〉 0, there exist Ki ∈ B（H） compact with ｜｜Ki｜｜ 〈ε（i = 1,2） such that A＋K1 and B ＋ K2 are similar; （ii） σ0（A） = σ0（B） and dim H（λ; A） = dim H（λ; B） for each λ ∈ σ0（A）. In this paper, we prove the following result. Let S,T ∈ B（H） be quasitriangular satisfying： （i） σ（T） = σ（S） = σw（S） is connected and σe（S） = σlre（S）; （ii） ρs-F（S） ∩ σ（S） consists of at most finite components and each component Ω satisfies that Ω = int Ω, where int Ω is the interior of Ω. Then, S -sas T if and only if S and T are essentially similar.展开更多
Given an essentially normal operator T with connected spectrum and ind (λ-T)>0 for λ in ρ F(T)∩σ(T) , and a positive number ∈ ,the authors show that theree xists a compact K with ‖K‖&...Given an essentially normal operator T with connected spectrum and ind (λ-T)>0 for λ in ρ F(T)∩σ(T) , and a positive number ∈ ,the authors show that theree xists a compact K with ‖K‖<∈ such that T+K is strongly irreducible.展开更多
This paper gives characterizations for diffusion processes on the line and birth-death processes whose generators admit the empty essential spectra. Some equivalent conditions for empty essential spectra for general M...This paper gives characterizations for diffusion processes on the line and birth-death processes whose generators admit the empty essential spectra. Some equivalent conditions for empty essential spectra for general Markov generators are also discussed.展开更多
Many authors have studied the limit hehavior of the sequence of probability measureon a topological group or scmigroup.As to the description of the limit behavior of the sequence by the essential point setof the convo...Many authors have studied the limit hehavior of the sequence of probability measureon a topological group or scmigroup.As to the description of the limit behavior of the sequence by the essential point setof the convolution sequence, Maximov studied the case of compact topologica1 group. Inthis note, the problem of weak convergence for the sequence of convolution power of aprobability measure is considered on the locally compact topological semigroup. Jn particu-lar. the relation between the essential point set of the sequence and the support set of theweak limit of the sequence is studied.展开更多
文摘Let н be a complex, separable, infinite dimensional Hilbert space, T ε（Ｈ）. （ｕ＋Ｋ）（T） denotes the （ｕ＋ｋ）-orbit of T, i.e., （ｕ＋ｋ）（T） = {R-1TR: R is invertible and of the form unitary plus compact}. Let be an analytic and simply connected Cauchy domain in C and n ε N. A（, n） denotes the class of operators, each of which satisfies （i） T is essentially normal; （ii） σ（T） =, ρF（T） ∩ σ（T） = ; （iii） ind （λ-T） = -n, nul （λ-T） = 0 （λ∈Ω ）. It is proved that given T1, T2 ε A（, n） and ε > 0, there exists a compact operator K with K <ε such that T1 +Kε （ｕ＋ｋ）（T2）. This result generalizes a result of P. S. Guinand and L. Marcoux [6,15]. Furthermore, the authors give a character of the norm closure of （ｕ＋Ｋ）（T）, and prove that for each T ε A（, n）, there exists a compact （SI） perturbation of T whose norm can be arbitrarily small.
基金NCET(040296)NNSF of China(10371049)the Specialized Research Fund for the Doctoral Program of Higher Education(20050183002)
文摘Two operators A, B ∈ B（H） are said to be strongly approximatively similar, denoted by A -sas B, if （i） given ε 〉 0, there exist Ki ∈ B（H） compact with ｜｜Ki｜｜ 〈ε（i = 1,2） such that A＋K1 and B ＋ K2 are similar; （ii） σ0（A） = σ0（B） and dim H（λ; A） = dim H（λ; B） for each λ ∈ σ0（A）. In this paper, we prove the following result. Let S,T ∈ B（H） be quasitriangular satisfying： （i） σ（T） = σ（S） = σw（S） is connected and σe（S） = σlre（S）; （ii） ρs-F（S） ∩ σ（S） consists of at most finite components and each component Ω satisfies that Ω = int Ω, where int Ω is the interior of Ω. Then, S -sas T if and only if S and T are essentially similar.
文摘Given an essentially normal operator T with connected spectrum and ind (λ-T)>0 for λ in ρ F(T)∩σ(T) , and a positive number ∈ ,the authors show that theree xists a compact K with ‖K‖<∈ such that T+K is strongly irreducible.
基金Research supported in part by RFDP(No.2001002707)973 ProjectNSFC(No.10121101)
文摘This paper gives characterizations for diffusion processes on the line and birth-death processes whose generators admit the empty essential spectra. Some equivalent conditions for empty essential spectra for general Markov generators are also discussed.
基金Project supported by the Natural Science Foundation of Shandong Province.
文摘Many authors have studied the limit hehavior of the sequence of probability measureon a topological group or scmigroup.As to the description of the limit behavior of the sequence by the essential point setof the convolution sequence, Maximov studied the case of compact topologica1 group. Inthis note, the problem of weak convergence for the sequence of convolution power of aprobability measure is considered on the locally compact topological semigroup. Jn particu-lar. the relation between the essential point set of the sequence and the support set of theweak limit of the sequence is studied.
