Modulus hyperinvariant ideals for a finitely quasinilpotent operators

Let X be a Banach space with an unconditional basis, and let C ? {0} be a collection of continuous linear operators with modulus on X that is finitely modulus-quasinilpotent at a non-zero positive vector. Then C and its right modulus sub-commutant C'm have a common non-trivial invariant closed ideal.

On the Roughness of Quasinilpotency Property of One-parameter Semigroups

Let S := {S(t)}t≥0 be a C0-semigroup of quasinilpotent operators (i.e., σ(S(t)) = {0} for eacht> 0). In dynamical systems theory the above quasinilpotency property is equivalent to a very strong concept of stability for the solutions of autonomous systems. This concept is frequently called superstability and weakens the classical ûnite time extinction property (roughly speaking, disappearing solutions). We show that under some assumptions, the quasinilpotency, or equivalently, the superstability property of a C0-semigroup is preserved under the perturbations of its infinitesimal generator.