A note on the spectral mapping theorem
A note on the stability of linear combinations of algebraic operators.
A Note on Time Dependent Scattering Theory for P2 - P2 + (1 + |Q|) - 1 ... and P1 P2 + (1 + |Q|) - 1 - ... on L2 (R2).
A note on weak estimates for oscillating kernels
A notion of analytic generator for groups of unbounded operators
We introduce a notion of analytic generator for groups of unbounded operators, on Banach modules, arising from Esterle’s quasimultiplier theory. Characterizations of analytic generators are given in terms of the existence of certain functional calculi. This extends recent results about C₀ groups of bounded operators. The theory is applicable to sectorial operators, representations of , and integrated groups.
A numerical radius inequality and an estimate for the numerical radius of the Frobenius companion matrix
It is shown that if A is a bounded linear operator on a complex Hilbert space, then , where w(A) and ||A|| are the numerical radius and the usual operator norm of A, respectively. An application of this inequality is given to obtain a new estimate for the numerical radius of the Frobenius companion matrix. Bounds for the zeros of polynomials are also given.
A numerical radius inequality involving the generalized Aluthge transform
A spectral radius inequality is given. An application of this inequality to prove a numerical radius inequality that involves the generalized Aluthge transform is also provided. Our results improve earlier results by Kittaneh and Yamazaki.
A perturbation characterization of compactness of self-adjoint operators
A characterization of compactness of a given self-adjoint bounded operator A on a separable infinite-dimensional Hilbert space is established in terms of the spectrum of perturbations. An example is presented to show that without separability, the perturbation condition, which is always necessary, is not sufficient. For non-separable spaces, another condition on the self-adjoint operator A, which is necessary and sufficient for the perturbation, is given.
A perturbation of Lomonosov's theorem
A perturbation problem in the presence of affine symmetries
An approach to a local analysis of solutions of a perturbation problem is proposed when the unperturbed operator has affine symmetries. The main result is a local theorem on existence, uniqueness, and analytic dependence on a parameter.
A perturbation theorem for semigroups of linear operators
A Perturbation Theorem for the Essential Spectral Radius of Strongly Continuous Semigroups.
A perturbation theory of resonances
A posteriori estimations of approximate solutions for some types of boundary value problems
A potential operator and some ergodic properties of a positive contraction
A probabilistic version of the Frequent Hypercyclicity Criterion
For a bounded operator T on a separable infinite-dimensional Banach space X, we give a "random" criterion not involving ergodic theory which implies that T is frequently hypercyclic: there exists a vector x such that for every non-empty open subset U of X, the set of integers n such that Tⁿx belongs to U, has positive lower density. This gives a connection between two different methods for obtaining the frequent hypercyclicity of operators.
A problem in Rayleigh-Taylor instability
A Problem of Mixed Interpolation.
A product integral representation of the generalized inverse
A proof of Nehari's theorem through the coefficient of a matricial measure.