1,721,002 research outputs found
Álgebras aproximadamente finitas /
Full text linkDissertação (Mestrado) - Universidade Federal de Santa Catarina, Centro de Ciências Físicas e Matemáticas
Produtos Cruzados
Full text linkDissertação (mestrado) - Universidade Federal de Santa Catarina, Centro de Ciências Físicas e Matemáticas.Dado (A,G,a) um C* sistema dinâmico, estudaremos o produto cruzado da C*-algebra A pelo grupo discreto G pela ação a de G em A. Como dada uma ação parcial de G em um espaço de Hausdorff localmente compacto X, existe uma ação parcial de G na C*-algebra C0(X) associada, e a recíproca também vale, vamos provar que se uma ação parcial é topologicamente livre e minimal em X, então o produto cruzado reduzido associado é simples, [1]. É claro que antes disto precisamos introduzir as noções de produto cruzado por ações parciais e produto cruzado reduzido. Por último, aplicaremos este resultado para alguns exemplos
A new look at the crossed product of a C*-algebra by a semigroup of endomorphisms
Full text linkLet G be a group and let P ⊆ G be a subsemigroup. In order to describe the crossed product of a C * -algebra A by an action of P by unital endomorphisms we find that we must extend the action to the whole group G. This extension fits into a broader notion of interaction groups which consists of an assignment of a positive operator V g on A for each g in G, obeying a partial group law, and such that (V g , V g −1 ) is an interaction for every g, as defined in a previous paper by the author. We then develop a theory of crossed products by interaction groups and compare it to other endomorphism crossed product constructions
O produto cruzado por endomorfismo parcial
Full text linkOrientadores: Ruy Exel Filho, Jorge Tulio Mujica AscuiTese (Doutorado) - Universidade Estadual de Campinas, Instituto de Matematica, Estatistica e Computação CientificaDoutoradoMatematicaDoutor em Matemátic
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
PARTIAL REPRESENTATIONS AND AMENABLE FELL BUNDLES OVER FREE GROUPS
No full textWe show that a Fell bundle B = {Bt}t∈F, over an arbitrary free group F, is amenable, whenever it is orthogonal (in the sense that B ∗ x By = 0, if x and y are distinct generators of F) and semi-saturated (in the sense that Bts coincides with the closed linear span of BtBs, when the multiplication “ts” involves no cancelation). In this work we continue the study of the phenomena of amenability for Fell bundles over discrete groups, initiated in [E3]. By definition, a Fell bundle is said to be amenable if the left regular representation of its cross-sectional C ∗-algebra is faithful. This property is also equivalent to the faithfulness of the standard conditional expectation. The reader is referred to [E3] for more information, but we also offer a very brief survey containing some of the most relevant definitions, in our section on preliminaries below. The starting point for our work is Theorem 6.7 of [E3], where it is shown that a certain grading of the Cuntz–Krieger algebra gives rise to an amenable Fell bundle over a free group. Our main goal is to further pursue the argument leading to this result, in order to obtain a large class of amenable Fell bundles. We find that the crucial properties implying the amenability of a Fell bundle, over a free group F, are orthogonality and semi-saturatedness. A Fell bundle B = {Bt}t∈F is said to be orthogonal if the fibers Bx and By, corresponding to two distinct generators x and y of F, are orthogonal in the sense that B ∗ xBy = 0. On the other hand, B is said to be semi-saturated when each fiber Bt is “built up ” from the fibers corresponding to the generators appearing in the reduced decomposition of t. More precisely, if t = x1x2 ···xn is in reduced form, then one requires that Bt = Bx1 Bx2 ···Bxn (meaning closed linear span). This property makes sense for any group G, which, like the free group, is equipped with a length function |·|. A Fell bundle over such a group is said to be semi-saturated if Bts = BtBs (closed linear span), whenever t and s satisfy |ts | = |t | + |s|. Our main result, Theorem 6.3, states, precisely, that any Fell bundle over F, which is orthogonal, semi-saturated, and has separable fibers, must be amenable
A Fredholm operator approach to Morita equivalence, K-Theory
No full textAbstract. Given C * -algebras A and B and an imprimitivity A-B-bimodule X, we construct an explicit isomorphism X * : where K i denote the complex K-theory functors for i = 0, 1. Our techniques do not require separability nor existence of countable approximate identities. We thus extend, to general C * -algebras, the result of Brown, Green and Rieffel according to which strongly Morita equivalent C * -algebras have isomorphic K-groups. The method employed includes a study of Fredholm operators on Hilbert modules
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