La Extension De Caratheodory Para Medidas Con Valores En Operadores Positivos.
Lie algebras generated by Jordan operators
It is proved that if is a Jordan operator on a Hilbert space with the Jordan decomposition , where is normal and is compact and quasinilpotent, i = 1,2, and the Lie algebra generated by J₁,J₂ is an Engel Lie algebra, then the Banach algebra generated by J₁,J₂ is an Engel algebra. Some results for normal operators and Jordan operators on Banach spaces are given.
Limacons, normal operators and polar factorizations.
Local spectrum and Kaplansky's theorem on algebraic operators
Using elementary arguments we improve former results of P. Vrbová concerning local spectrum. As a consequence, we obtain a new proof of Kaplansky’s theorem on algebraic operators on a Banach space.
Logarithmic concavity, unitarity and selfadjointness
Isometric automorphisms of normed linear spaces are characterized by suitable concavity properties of powers of operators. Bounded selfadjoint operators in Hilbert spaces are described by parallel concavity properties of the exponential group. Unbounded infinitesimal generators of 𝓒₀-groups of Hilbert space operators having concavity properties are characterized as well.