6 citations · 26 across the 19 of their papers we have counts for
19 papers
Non-stable subnormal contractions have nontrivial hyperinvariant subspaces
Maria F. Gamal'
A contraction on a (complex, separable) Hilbert space is stable, or of class , if in the strong operator topology. It is proved that for a non-stable pur…
Some relationships with subnormal operators and existence of hyperinvariant subspaces
Maria F. Gamal'
If is a polynomially bounded operator, is an invariant subspace of , is a unilateral shift and is subnormal, then $T…
Examples of cyclic polynomially bounded operators that are not similar to contractions
Maria F. Gamal'
A question if a polynomially bounded operator is similar to a contraction was posed by Halmos and was answered in the negative by Pisier. His counterexample is an operator of infin…
On similarity to contractions of class with finite defects
Maria F. Gamal'
A criterion on the similarity of a (bounded, linear) operator on a (complex, separable) Hilbert space in terms of shift-type invariant subspaces of to a contra…
On existence of hyperinvariant subspaces for quasinilpotent operators with a nonsymmetry in the growth of the resolvent
Maria F. Gamal'
Let be a quasinilpotent operator on a Banach space. Under assumptions of a certain nonsymmetry in the growth of the resolvent of , it is proved that every operator in the co…
On expansive operators that are quasisimilar to the unilateral shift of finite multiplicity
Maria F. Gamal'
An operator on a Hilbert space is called expansive, if (). Expansive operators quasisimilar to the unilateral shift of…
On isometric asymptotes of operators quasisimilar to isometries
Maria F. Gamal'
The notion of isometric and unitary asymptotes was introduced for power bounded operators in 1989 and was generalized in 2016--2019 by Kérchy. In particular, it was shown that ther…
Example of quasianalytic contraction whose spectrum is a proper subarc of the unit circle
Maria F. Gamal'
A partial answer on [KS2, Question 2] is given. Namely, an operator similar to a quasianalytic contraction whose quasianalytic spectral set is equal to its spectrum and is a pr…
On power bounded operators with holomorphic eigenvectors, II
Maria F. Gamal'
In [U] (among other results), M. Uchiyama gave the necessary and sufficient conditions for contractions to be similar to the unilateral shift of multiplicity in terms of no…
Invertibility of functions of operators and existence of hyperinvariant subspaces
Maria F. Gamal'
Let be an absolutely continuous polynomially bounded operator, and let be a singular inner function. It is shown that if is invertible and some additional conditions…
On existence of shift-type invariant subspaces for polynomially bounded operator
Maria F. Gamal'
A particular case of results from [K2] is as follows. Let the unitary asymptote of a contraction contain the bilateral shift (of finite or infinite multiplicity). Then there ex…
On polynomially bounded operators with shift-type invariant subspaces
Maria F. Gamal'
A particular case of [07] was generalized from contractions to polynomially bounded operators in [G19]. Namely, it is proved in [G19] that if the unitary asymptote of a polynomiall…
On contractions that are quasiaffine transforms of unilateral shifts
M. F. Gamal'
It is known that if is a contraction of class and is of trace class, then is a quasiaffine transform of a unilateral shift. Also it is known that if t…
Notes on the codimension one conjecture in the operator corona theorem
M. F. Gamal'
Answering on the question of S.R.Treil [23], for every , , examples of contractions are constructed such that their characteristic functions $F\in H^\infty(\mathcal E\to\…
On power bounded operators that are quasiaffine tranforms of singular unitaries
Maria F. Gamal'
In [9] a question is raised: if a power bounded operator is quasisimilar to a singular unitary operator, is it similar to this unitary operator? For polynomially bounded operators,…
A sufficient condition for the similarity of a polynomially bounded operator to a contraction
Maria Gamal'
Let be a polynomially bounded operator, and let be its invariant subspace. Suppose that is similar to a contraction, wh…
Examples of cyclic polynomially bounded operators that are not similar to contractions, II
Maria Gamal'
The question if polynomially bounded operator is similar to a contraction was posed by Halmos and was answered in the negative by Pisier. His counterexample is an operator of infin…
Some sufficient conditions for existence of hyperinvariant subspaces for operators intertwined with unitaries
Maria F. Gamal'
For a power bounded or polynomially bounded operator sufficient conditions for the existence of a nontrivial hyperinvariant subspace are given. The obtained hyperinvariant subs…
One dimensional perturbations of unitaries that are quasiaffine transforms of singular unitaries, and multipliers between model spaces
Maria F. Gamal'
It is shown that, under some natural additional conditions, an operator which intertwines one cyclic singular unitary operator with one dimensional perturbation of another cyclic s…