Results 51 to 60 of about 332 (118)

Negative Powers of Contractions Having a Strong AA+ Spectrum

Moroccan Journal of Pure and Applied Analysis, 2023
Zarrabi proved in 1993 that if the spectrum of a contraction T on a Banach space is a countable subset of the unit circle 𝕋, and if limn→+∞log(‖T−n‖)n=0{\lim _{n \to + \infty }}{{\log \left( {\left\| {{T^{ - n}}} \right\|} \right)} \over {\sqrt n ...
Esterle Jean
doaj   +1 more source

A Modified Regularization Method for Inverse Problems of Nonhomogeneous Differential Operator Equation

Journal of Mathematics, Volume 2025, Issue 1, 2025.
This paper investigates an abstract nonhomogeneous backward Cauchy problem governed by an unbounded linear operator in a Hilbert space H. The coefficient operator in the equation is assumed to be unbounded, self‐adjoint, positive, and to possess a discrete spectrum, with data prescribed at the final time t = T.
Nihed Teniou, Xian-Ming Gu
wiley   +1 more source

On some properties of Banach operators

International Journal of Mathematics and Mathematical Sciences, Volume 27, Issue 3, Page 149-153, 2001., 2001
A mapping α from a normed space X into itself is called a Banach operator if there is a constant k such that 0 ≤ k < 1 and ‖α2(x) − α(x)‖ ≤ k‖α(x) − x‖ for all x ∈ X. In this note we study some properties of Banach operators. Among other results we show that if α is a linear Banach operator on a normed space X, then N(α − 1) = N((α−1)2), N(α − 1)∩R(α −
A. B. Thaheem, AbdulRahim Khan
wiley   +1 more source

On the spectrum of ψ‐contracting operators

International Journal of Stochastic Analysis, Volume 14, Issue 3, Page 303-308, 2001., 2001
The spectrum σ(A) of a continuous linear operator A : E → E defined on a Banach space E, which is contracting with respect to the Hausdorff measure of noncompactness, is investigated.
Anwar A. Al-Nayef
wiley   +1 more source

An introduction to the distorted Fourier transform

Advanced Nonlinear Studies
This article is intended as an introduction to the distorted Fourier transform associated with a Schrödinger operator on the line or the half-line. This versatile tool has seen numerous applications in nonlinear PDE in recent years.
Ko Haram, Schlag Wilhelm
doaj   +1 more source

Schrödinger operators with potential waveguides on periodic graphs

, 2020
We consider discrete Schrödinger operators with periodic potentials on periodic graphs perturbed by guided positive potentials, which are periodic in some directions and finitely supported in other ones.
O. Post, N. Saburova
semanticscholar   +1 more source

Joint numerical ranges: recent advances and applications minicourse by V. Müller and Yu. Tomilov

Concrete Operators, 2020
We present a survey of some recent results concerning joint numerical ranges of n-tuples of Hilbert space operators, accompanied with several new observations and remarks.
Müller V., Tomilov Yu.
doaj   +1 more source

Operators with minimal pseudospectra and connections to normality

, 2020
This paper mainly studies the class of bounded linear operators A with minimal pseudospectra σε (A) = σ(A)+Dε for some ε > 0 , where σ(A) denotes the spectrum of A , and Dε denotes the open disk of radius ε centered at the origin.
Samir Raouafi
semanticscholar   +1 more source

Peripheral local spectrum preservers and maps increasing the local spectral radius

, 2016
We address two long standing problems in the context of local spectral radius preservers. First, we completely describe the form of maps preserving the peripheral local spectrum of product or triple product of operators.
A. Bourhim, Tarik Jari, J. Mashreghi
semanticscholar   +1 more source

Topological properties of the block numerical range of operator matrices

, 2020
We show that the block numerical range of an n×n -operator matrix A corresponding to an operator A on the Banach space X with respect to a decomposition X = ∏Xj has at most n connected components.
Agnes Radl, M. Wolff
semanticscholar   +1 more source