Constants Related to Operators of Class Cp.
T. Ando, K. Okubo (1975)
Manuscripta mathematica
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T. Ando, K. Okubo (1975)
Manuscripta mathematica
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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.
M.H. Protter (1979)
Manuscripta mathematica
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Michael Neumann (1978/79)
Manuscripta mathematica
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L. Boccardo, B. Dacorogna (1989)
Manuscripta mathematica
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Elmar Schrohe, Hans-Gern Leopold (1993)
Manuscripta mathematica
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Herbert Leinfelder (1979)
Mathematische Annalen
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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.
Klaus-Jürgen Eckardt (1973/74)
Manuscripta mathematica
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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...
Hans Triebel, Hans-Gerd Leopold (1994)
Manuscripta mathematica
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Vladimir G. Maz'ja, Alois Kufner (1986)
Manuscripta mathematica
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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.
John B. Conway, Gabriel Prǎjiturǎ (2005)
Studia Mathematica
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For a scalar λ, two operators T and S are said to λ-commute if TS = λST. In this note we explore the pervasiveness of the operators that λ-commute with a compact operator by characterizing the closure and the interior of the set of operators with this property.
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.
J. Janas (1984)
Annales Polonici Mathematici
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M. R. Dostanić (1989)
Matematički Vesnik
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