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We obtain partial affirmative answers to the question whether isomorphism of the unitary groups of two C*-algebras, either as topological groups or as discrete groups, implies isomorphism of the C*-algebras as real C*-algebras.

Operator Algebras · Mathematics 2023-06-29 Lionel Fogang Takoutsing , Leonel Robert

We develop the theory of central ideals on commutative rings. We introduce and study the central seminormalization of a ring in another one. This seminormalization is related to the theory of regulous functions on real algebraic varieties.…

Algebraic Geometry · Mathematics 2021-03-18 Jean-Philippe Monnier

As a generalization of the Exel-Pardo's notion of self-similar graph, we introduce self-similar group actions on ultragraphs and their $C^*$-algebras. We then approach to the $C^*$-algebras by inverse semigroup and tight groupoid models.

Operator Algebras · Mathematics 2025-05-20 Hossein Larki , Najmeh Rajabzadeh-Hasiri

Groupoid actions on C*-bundles and inverse semigroup actions on C*-algebras are closely related when the groupoid is r-discrete.

Operator Algebras · Mathematics 2007-05-23 John Quigg , Nandor Sieben

The paper presents a construction of the crossed product of a C*-algebra by a semigroup of endomorphisms generated by partial isometries.

Operator Algebras · Mathematics 2014-11-27 B. K. Kwasniewski , A. V. Lebedev

We construct reduced and full semigroup C*-algebras for left cancellative semigroups. Our new construction covers particular cases already considered by A. Nica and also Toeplitz algebras attached to rings of integers in number fields due…

Operator Algebras · Mathematics 2012-02-23 Xin Li

The relation between representations and positive definite functions is a key concept in harmonic analysis on topological groups. Recently this relation has been studied on topological groupoids. This is the first in a series of papers in…

Operator Algebras · Mathematics 2007-05-23 Massoud Amini , Alireza Medghalchi

In this paper, we prove that unital homomorphisms from continuous functions on a compact metric space to matrices over a C*-algebra with tracial rank at most one are approximately diagonalizable. We also consider some generalizations of…

Operator Algebras · Mathematics 2017-03-13 Min Ro

We study groupoids and semigroup C*-algebras arising from graphs of monoids, in the setting of right LCM monoids. First, we establish a general criterion when a graph of monoids gives rise to a submonoid of the fundamental group which is…

Operator Algebras · Mathematics 2022-12-06 Cheng Chen , Xin Li

We investigate ideal-semisimple and congruence-semisimple semirings. We give several new characterizations of such semirings using e-projective and e-injective semimodules. We extend several characterizations of semisimple rings to (not…

Rings and Algebras · Mathematics 2019-08-02 Jawad Y. Abuhlail , Rangga Ganzar Noegraha

We give a new construction of a C*-algebra from a cancellative semigroup $P$ via partial isometric representations, generalising the construction from the second named author's thesis. We then study our construction in detail for the…

Operator Algebras · Mathematics 2022-08-10 Charles Starling , Ilija Tolich

We introduce quasi-homomorphisms of cluster algebras, a flexible notion of a map between cluster algebras of the same type (but with different coefficients). The definition is given in terms of seed orbits, the smallest equivalence classes…

Rings and Algebras · Mathematics 2016-01-18 Chris Fraser

In the present paper we study the structure of C*-$algebras generated by a certain *-algebra A and a partial isometry inducing an endomorphism of A.

Operator Algebras · Mathematics 2007-05-23 A. Lebedev , A. Odzijewicz

This is a survey of work in which the author was involved in recent years. We consider C*-algebras constructed from representations of one or several algebraic endomorphisms of a compact abelian group - or, dually, of a discrete abelian…

Operator Algebras · Mathematics 2015-12-04 Joachim Cuntz

In this paper we propose a semiring-theoretic approach to MV-algebras based on the connection between such algebras and idempotent semirings - such an approach naturally imposing the introduction and study of a suitable corresponding class…

Rings and Algebras · Mathematics 2017-06-02 Antonio Di Nola , Ciro Russo

We prove a complete analog of the Borsuk Homotopy Extension Theorem for arbitrary semiprojective C*-algebras. We also obtain some other results about semiprojective C*-algebras: a partial lifting theorem with specified quotient, a lifting…

Operator Algebras · Mathematics 2015-05-05 Bruce Blackadar

We present the results of computation of cohomology for some Lie (super)algebras of Hamiltonian vector fields and related algebras. At present, the full cohomology rings for these algebras are not known even for the low dimensional vector…

Numerical Analysis · Mathematics 2007-05-23 Vladimir V. Kornyak

In this paper, we initiate the study of higher rank Baumslag-Solitar semigroups and their related C*-algebras. We focus on two extreme, but interesting, classes - one is related to products of odometers and the other is related to…

Operator Algebras · Mathematics 2025-04-25 Robert Valente , Dilian Yang

We study partial homology and cohomology from ring theoretic point of view via the partial group algebra $\mathbb{K}_{par}G$. In particular, we link the partial homology and cohomology of a group $G$ with coefficients in an irreducible…

Group Theory · Mathematics 2023-11-10 Marcelo Muniz Alves , Mikhailo Dokuchaev , Dessislava H. Kochloukova

We characterize locally injective semialgebraic maps between two semialgebraic sets in terms of the induced homomorphism between their rings of (continuous) semialgebraic functions.

Algebraic Geometry · Mathematics 2025-04-17 E. Baro , J. F. Fernando , J. M. Gamboa