The paper is devoted to the problem of classification of extremal positive linear maps acting between 𝔅(𝒦) and 𝔅(ℋ) where 𝒦 and ℋ are Hilbert spaces. It is shown that every positive map with the property that rank ϕ(P) ≤ 1 for any one-dimensional projection P is a rank 1 preserver. This allows us to characterize all decomposable extremal maps as those which satisfy the above condition. Further, we prove that every extremal positive map which is 2-positive turns out to be automatically completely...

We investigate when a C*-algebra element generates a closed ideal, and discuss Moore-Penrose and commuting generalized inverses.

Let $\tau$ be a continuous unitary representation of the locally compact group $G$ on the Hilbert space $H_{\tau }$. Let $C_{\tau }^{*}[V{N}_{\tau }]$ be the $C^{*}[W^{*}]$ algebra generated by$$(L^1\left(G\right))\text{and}{M}_{\tau }(C_{\tau }^{*})=\left\{\phi \in V{N}_{\tau };\phi C_{\tau }^{*}+C_{\tau }^{*}\phi \subset C_{\tau }^{*}\right\}.$$The main result obtained in this paper is Theorem 1:If $G$ is $\sigma$-compact and $M_{\tau }(C_{\tau }^{*})=V{N}_{\tau }$ then supp $\tau$ is discrete and each $\pi$ in supp $\tau$ in CCR.We apply this theorem to the quasiregular representation $\tau ={\pi }_H$ and obtain among other results that $M_{{\pi }_H}(C_{{\pi }_H}^{*})=V{N}_{{\pi }_H}$ implies in many cases that $G/H$ is a compact coset space.

It is shown that every almost linear Pexider mappings $f$, $g$, $h$ from a unital $C^{*}$-algebra $𝒜$ into a unital $C^{*}$-algebra $ℬ$ are homomorphisms when $f\left(2^{n}uy\right)=f\left(2^{n}u\right)f\left(y\right)$, $g\left(2^{n}uy\right)=g\left(2^{n}u\right)g\left(y\right)$ and $h\left(2^{n}uy\right)=h\left(2^{n}u\right)h\left(y\right)$ hold for all unitaries $u\in 𝒜$, all $y\in 𝒜$, and all $n\in \mathbb{Z}$, and that every almost linear continuous Pexider mappings $f$, $g$, $h$ from a unital $C^{*}$-algebra $𝒜$ of real rank zero into a unital $C^{*}$-algebra $ℬ$ are homomorphisms when $f\left(2^{n}uy\right)=f\left(2^{n}u\right)f\left(y\right)$, $g\left(2^{n}uy\right)=g\left(2^{n}u\right)g\left(y\right)$ and $h\left(2^{n}uy\right)=h\left(2^{n}u\right)h\left(y\right)$ hold for all $u\in \{v\in 𝒜\mid v=v^{*}\text{and}v\text{is}\text{invertible}\}$, all $y\in 𝒜$ and all $n\in \mathbb{Z}$. Furthermore, we prove the Cauchy-Rassias stability of $*$-homomorphisms between unital $C^{*}$-algebras, and $ℂ$-linear...

We investigate the structure of the multiplier module of a Hilbert module over a pro-C*-algebra and the relationship between the set of all adjointable operators from a Hilbert A-module E to a Hilbert A-module F and the set of all adjointable operators from the multiplier module M(E) to M(F).

We study similarity to partial isometries in C*-algebras as well as their relationship with generalized inverses. Most of the results extend some recent results regarding partial isometries on Hilbert spaces. Moreover, we describe partial isometries by means of interpolation polynomials.