Results 21 to 30 of about 44 (44)
Strongly exposed points in the unit ball of trace‐class operators
International Journal of Mathematics and Mathematical Sciences, Volume 30, Issue 7, Page 393-397, 2002., 2002 A theorem of Arazy shows that every extreme point of the unit ball of trace‐class operators is strongly exposed. We give this result a simpler and direct proof here.
Kourosh Nourouzi
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Proper contractions and invariant subspaces
International Journal of Mathematics and Mathematical Sciences, Volume 28, Issue 4, Page 223-230, 2001., 2001 Let T be a contraction and A the strong limit of {T∗nTn}n ≥ 1. We prove the following theorem: if a hyponormal contraction T does not have a nontrivial invariant subspace, then T is either a proper contraction of class 𝒞00 or a nonstrict proper contraction of class 𝒞10 for which A is a completely nonprojective nonstrict proper contraction.
C. S. Kubrusly, N. Levan
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Some remarks on the invariant subspace problem for hyponormal operators
International Journal of Mathematics and Mathematical Sciences, Volume 28, Issue 6, Page 359-365, 2001., 2001 We make some remarks concerning the invariant subspace problem for hyponormal operators. In particular, we bring together various hypotheses that must hold for a hyponormal operator without nontrivial invariant subspaces, and we discuss the existence of such operators.
Vasile Lauric
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Berezin number inequalities for operators
Concrete Operators, 2019 The Berezin transform à of an operator A, acting on the reproducing kernel Hilbert space ℋ = ℋ (Ω) over some (non-empty) set Ω, is defined by Ã(λ) = 〉Aǩ λ, ǩ λ〈 (λ ∈ Ω), where k⌢λ=kλ‖kλ‖${\mathord{\buildrel{\lower3pt\hbox{$\scriptscriptstyle\frown ...
Bakherad Mojtaba, Garayev Mubariz T.
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On the projection constants of some topological spaces and some applications
Abstract and Applied Analysis, Volume 6, Issue 5, Page 299-308, 2001., 2001 We find a lower estimation for the projection constant of the projective tensor product X⊗ ∧Y and the injective tensor product X⊗ ∨Y, we apply this estimation on some previous results, and we also introduce a new concept of the projection constants of operators rather than that defined for Banach spaces.
Entisarat El-Shobaky +2 more
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Product and factorization of hypo-EP operators
Special Matrices, 2018 In this article, we derive some necessary and sufficient conditions for the product of hypo-EP operators to be hypo-EP and we characterize hypo-EP operators through factorizations.
Johnson P. Sam, Vinoth A.
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Some results on dominant operators
International Journal of Mathematics and Mathematical Sciences, Volume 21, Issue 2, Page 217-220, 1998., 1997 We show that the Weyl spectrum of a dominant operator satisfies the spectral mapping theorem for analytic functions and then answer a question of Oberai.
Youngoh Yang
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Factorization of k‐quasihyponormal operators
International Journal of Mathematics and Mathematical Sciences, Volume 14, Issue 3, Page 439-442, 1991., 1989 Let A be the class of all operators T on a Hilbert space H such that R(T*kT), the range space of T*KT, is contained in R(T*k+1), for a positive integer k. It has been shown that if T ϵ A, there exists a unique operator CT on H such that The main objective of this paper is to characterize k‐quasihyponormal; normal, and self‐adjoint operators T in A in ...
S. C. Arora, J. K. Thukral
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Cohyponormal operators with the single valued extension property
International Journal of Mathematics and Mathematical Sciences, Volume 9, Issue 4, Page 659-663, 1986., 1986 It is proved that in order to find a nontrivial hyperinvariant subspace for a cohyponormal operator it suffices to make the further assumption that the operator have the single‐valued extension property.
Ridgley Lange, Shengwang Wang
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Absolute continuity and hyponormal operators
International Journal of Mathematics and Mathematical Sciences, Volume 4, Issue 2, Page 321-335, 1981., 1981 Let T be a completely hyponormal operator, with the rectangular representation T = A + iB, on a separable Hilbert space. If 0 is not an eigenvalue of T* then T also has a polar factorization T = UP, with U unitary. It is known that A, B and U are all absolutely continuous operators.
C. R. Putnam
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