Polynomial identification in uniform and operator algebras.
Polynomially bounded operators.
Polynomially compact derivations on Banach algebras
We consider a continuous derivation D on a Banach algebra 𝓐 such that p(D) is a compact operator for some polynomial p. It is shown that either 𝓐 has a nonzero finite-dimensional ideal not contained in the radical rad(𝓐) of 𝓐 or there exists another polynomial p̃ such that p̃(D) maps 𝓐 into rad(𝓐). A special case where Dⁿ is compact is discussed in greater detail.
Polynomially compact elements of Banach algebras
Polynomials in the Volterra and Ritt operators
We continue the paper [Ts] on the boundedness of polynomials in the Volterra operator. This provides new ways of constructing power-bounded operators. It seems interesting to point out that a similar procedure applies to the operators satisfying the Ritt resolvent condition: compare Theorem 5 and Theorem 9 below.
Pontryagin duality for convergence groups of unimodular continuous functions
Porous medium equation and fast diffusion equation as gradient systems
We show that the Porous Medium Equation and the Fast Diffusion Equation, , with , can be modeled as a gradient system in the Hilbert space , and we obtain existence and uniqueness of solutions in this framework. We deal with bounded and certain unbounded open sets and do not require any boundary regularity. Moreover, the approach is used to discuss the asymptotic behaviour and order preservation of solutions.
Positive almost periodic solutions of non-autonomous delay competitive systems with weak allee effect.
Positive Approximate Identities and Lattice-Ordered Dual spaces.
Positive Compact Operators on Banach Lattices.
Positive Contractions of L2-Spaces.
Positive C...-semigroups on C*-algebras.
Positive definite diagonal sequences
Positive fixed point of strict set contraction operators on ordered Banach spaces and applications.
Positive L¹ operators associated with nonsingular mappings and an example of E. Hille
E. Hille [Hi1] gave an example of an operator in L¹[0,1] satisfying the mean ergodic theorem (MET) and such that supₙ||Tⁿ|| = ∞ (actually, ). This was the first example of a non-power bounded mean ergodic L¹ operator. In this note, the possible rates of growth (in n) of the norms of Tⁿ for such operators are studied. We show that, for every γ > 0, there are positive L¹ operators T satisfying the MET with lim supn→ ∞ ||Tⁿ||/n1-γ₀ = 0A class of numerical sequences αₙ, intimately related to the...
Positive linear maps of matrix algebras
A characterization of the structure of positive maps is presented. This sheds some more light on the old open problem studied both in Quantum Information and Operator Algebras. Our arguments are based on the concept of exposed points, links between tensor products and mapping spaces and convex analysis.
Positive Matrix Functions on the Bitorus with Prescribed Fourier Coefficients in a Band.
Positive multiplication preserves dissipativity in commutative -algebras.
Positive operator bimeasures and a noncommutative generalization
For C*-algebras A and B and a Hilbert space H, a class of bilinear maps Φ: A× B → L(H), analogous to completely positive linear maps, is studied. A Stinespring type representation theorem is proved, and in case A and B are commutative, the class is shown to coincide with that of positive bilinear maps. As an application, the extendibility of a positive operator bimeasure to a positive operator measure is shown to be equivalent to various conditions involving positive scalar bimeasures, pairs of...
Positive operators and approximation in function spaces on completely regular spaces.