Results 31 to 40 of about 468 (41)

On the triviality of domains of powers and adjoints of closed operators

, 2018
The paper is devoted to counterexamples involving the triviality of domains of products and/or adjoints of densely defined ...
Mortad, Mohammed Hichem
core   +1 more source

Elliptic operators and their symbols

Demonstratio Mathematica, 2019
We consider special elliptic operators in functional spaces on manifolds with a boundary which has some singular points. Such an operator can be represented by a sum of operators, and for a Fredholm property of an initial operator one needs a Fredholm ...
Vasilyev Vladimir
doaj   +1 more source

Unbounded Hankel operators and moment problems

, 2019
We find simple conditions for a non-negative Hankel quadratic form to be closable. Under some mild a priori assumption on the associated moments these sufficient conditions turn out to be also necessary.
Yafaev, D. R.
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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.
doaj   +1 more source

On semibounded Toeplitz operators

, 2016
We show that a semibounded Toeplitz quadratic form is closable in the space $\ell^2({\Bbb Z}_{+})$ if and only if its matrix elemens are Fourier coefficients of an absolutely continuous measure.
Yafaev, D. R.
core   +2 more sources

A distance formula related to a family of projections orthogonal to their symmetries

, 2017
Let u be a hermitian involution, and e an orthogonal projection, acting on the same Hilbert space. We establish the exact formula, in terms of the norm of eue, for the distance from e to the set of all orthogonal projections q from the algebra generated ...
Spitkovsky, Ilya M.
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Nilpotent perturbations of m-isometric and m-symmetric tensor products of commuting d-tuples of operators

Demonstratio Mathematica
If T1{{\mathbb{T}}}_{1} and T2{{\mathbb{T}}}_{2} are commuting dd-tuples of Hilbert space operators in B(ℋ)dB{\left({\mathcal{ {\mathcal H} }})}^{d} such that (T1*⊗I+I⊗T2*,T1⊗I+I⊗T2)\left({{\mathbb{T}}}_{1}^{* }\otimes I+I\otimes {{\mathbb{T}}}_{2}^{* },{
Duggal Bhagwati Prashad, Kim In Hyoun
doaj   +1 more source

Quantum injectivity of G-frames in Hilbert spaces

Demonstratio Mathematica
Inspired by some recent work on the quantum detection problem by discrete frames and continuous frames, in this article, we examine the quantum detection problem with G-frames.
Hong Guoqing, Wan Linbin, Zhang Jianxia
doaj   +1 more source

A new extended Mulholland's inequality involving one partial sum

Open Mathematics
By using the weight coefficients and the techniques of real analysis, a new extended Mulholland’s inequality with multi-parameters involving one partial sum is given. The equivalent statements of the best value related to several parameters are provided.
Peng Ling, Yang Bicheng
doaj   +1 more source

Full operators and algebras generated by invertible operators

, 2009
In the present work we characterized full operators and we showed some properties that have nonfull injectives operators. With the results developed for full operators, we affirmatively respond two questions formulated by Bravo and Feintuch on when the ...
R, Wilson R. Pacheco
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