All a b c d e f g h i j k l m n o p q r s t u v w x y z Other

Previous Page 61 Next

Displaying 1201 – 1220 of 3251

Showing per page

Joint subnormality of n-tuples and C₀-semigroups of composition operators on L²-spaces, II

Piotr Budzyński, Jan Stochel (2009)

Studia Mathematica

In the previous paper, we have characterized (joint) subnormality of a C₀-semigroup of composition operators on L²-space by positive definiteness of the Radon-Nikodym derivatives attached to it at each rational point. In the present paper, we show that in the case of C₀-groups of composition operators on L²-space the positive definiteness requirement can be replaced by a kind of consistency condition which seems to be simpler to work with. It turns out that the consistency condition also characterizes...

Jordan *-derivation pairs on standard operator algebras and related results

Dilian Yang (2005)

Colloquium Mathematicae

Motivated by Problem 2 in [2], Jordan *-derivation pairs and n-Jordan *-mappings are studied. From the results on these mappings, an affirmative answer to Problem 2 in [2] is given when E = F in (1) or when 𝓐 is unital. For the general case, we prove that every Jordan *-derivation pair is automatically real-linear. Furthermore, a characterization of a non-normal prime *-ring under some mild assumptions and a representation theorem for quasi-quadratic functionals are provided.

Jordan isomorphisms and maps preserving spectra of certain operator products

Jinchuan Hou, Chi-Kwong Li, Ngai-Ching Wong (2008)

Studia Mathematica

Let ₁, ₂ be (not necessarily unital or closed) standard operator algebras on locally convex spaces X₁, X₂, respectively. For k ≥ 2, consider different products T ₁ ∗ ⋯ ∗ T k on elements in i , which covers the usual product T ₁ ∗ ⋯ ∗ T k = T ₁ ⋯ T k and the Jordan triple product T₁ ∗ T₂ = T₂T₁T₂. Let Φ: ₁ → ₂ be a (not necessarily linear) map satisfying σ ( Φ ( A ₁ ) ∗ ⋯ ∗ Φ ( A k ) ) = σ ( A ₁ ∗ ⋯ ∗ A k ) whenever any one of A i ’s has rank at most one. It is shown that if the range of Φ contains all rank one and rank two operators then Φ must be a Jordan isomorphism multiplied by a root...

Kernels of Toeplitz operators on the Bergman space

Young Joo Lee (2023)

Czechoslovak Mathematical Journal

A Coburn theorem says that a nonzero Toeplitz operator on the Hardy space is one-to-one or its adjoint operator is one-to-one. We study the corresponding problem for certain Toeplitz operators on the Bergman space.

Korovkin-type theorems and applications

Nazim Mahmudov (2009)

Open Mathematics

Let {T n} be a sequence of linear operators on C[0,1], satisfying that {T n (e i)} converge in C[0,1] (not necessarily to e i) for i = 0,1,2, where e i = t i. We prove Korovkin-type theorem and give quantitative results on C 2[0,1] and C[0,1] for such sequences. Furthermore, we define King’s type q-Bernstein operator and give quantitative results for the approximation properties of such operators.

Currently displaying 1201 – 1220 of 3251