On unbounded hyponormal operators III
J. Janas (1994)
Studia Mathematica
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The paper deals mostly with spectral properties of unbounded hyponormal operators. Some nontrivial examples of such operators are given.
J. Janas (1994)
Studia Mathematica
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The paper deals mostly with spectral properties of unbounded hyponormal operators. Some nontrivial examples of such operators are given.
Mecheri, Salah (2005)
Revista Colombiana de Matemáticas
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Mohammed Hichem Mortad (2011)
Colloquium Mathematicae
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We present a new approach to the question of when the commutativity of operator exponentials implies that of the operators. This is proved in the setting of bounded normal operators on a complex Hilbert space. The proofs are based on some results on similarities by Berberian and Embry as well as the celebrated Fuglede theorem.
Chun Guang Li, Ting Ting Zhou (2014)
Studia Mathematica
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A bounded linear operator T acting on a Hilbert space is said to be polaroid if each isolated point in the spectrum is a pole of the resolvent of T. There are several generalizations of the polaroid property. We investigate compact perturbations of polaroid type operators. We prove that, given an operator T and ε > 0, there exists a compact operator K with ||K|| < ε such that T + K is polaroid. Moreover, we characterize those operators for which a certain polaroid type property...
C. Benhida, E. H. Zerouali (2009)
Studia Mathematica
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Let R and S be two operators on a Hilbert space. We discuss the link between the subscalarity of RS and SR. As an application, we show that backward Aluthge iterates of hyponormal operators and p-quasihyponormal operators are subscalar.
S.C. Arora, Ramesh Kumar (1981)
Publications de l'Institut Mathématique
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Nathan S. Feldman (2002)
Studia Mathematica
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We show that there are linear operators on Hilbert space that have n-dimensional subspaces with dense orbit, but no (n-1)-dimensional subspaces with dense orbit. This leads to a new class of operators, called the n-supercyclic operators. We show that many cohyponormal operators are n-supercyclic. Furthermore, we prove that for an n-supercyclic operator, there are n circles centered at the origin such that every component of the spectrum must intersect one of these circles.
M. R. Dostanić (1989)
Matematički Vesnik
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Galakhov, E. (1997)
Memoirs on Differential Equations and Mathematical Physics
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Ryotaro Sato (1976)
Colloquium Mathematicae
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Ryotaro Sato (1976)
Colloquium Mathematicae
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Sungeun Jung, Yoenha Kim, Eungil Ko, Ji Eun Lee (2012)
Studia Mathematica
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We give several conditions for (A,m)-expansive operators to have the single-valued extension property. We also provide some spectral properties of such operators. Moreover, we prove that the A-covariance of any (A,2)-expansive operator T ∈ ℒ(ℋ ) is positive, showing that there exists a reducing subspace ℳ on which T is (A,2)-isometric. In addition, we verify that Weyl's theorem holds for an operator T ∈ ℒ(ℋ ) provided that T is (T*T,2)-expansive. We next study (A,m)-isometric operators...
Abdelkader Benali, Mohammed Hichem Mortad (2014)
Bulletin of the Polish Academy of Sciences. Mathematics
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We are mainly concerned with the result of Kaplansky on the composition of two normal operators in the case in which at least one of the operators is unbounded.
Beatriz Margolis (1972)
Annales Polonici Mathematici
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Prykarpatsky, Yarema A., Samoilenko, Anatoliy M., Prykarpatsky, Anatoliy K. (2005)
Applied Mathematics E-Notes [electronic only]
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