1,721,044 research outputs found
Projections and isolated points of parts of the spectrum
No full textIn this paper, we relate the existence of certain projections, commuting with a bounded linear operator T ∈ L(X) acting on Banach space X, with the generalized Kato decomposition of T. We also relate the existence of these projections with some properties of the quasi-nilpotent part H0(T) and the analytic core K(T). Further results are given for the isolated points of some parts of the spectrum
Further Properties of an Operator Commuting with an Injective Quasi-Nilpotent Operator
Full text linkIn (Aiena et al., Math. Proc. R. Irish Acad. 122A(2):101–116,
2022), it has been shown that a bounded linear operator T ∈ L(X),
defined on an infinite-dimensional complex Banach space X, for which
there exists an injective quasi-nilpotent operator that commutes with it,
has a very special structure of the spectrum. In this paper, we show that
we have much more: if a such quasi-nilpotent operator does exist, then
some of the spectra of T originating from B-Fredholm theory coalesce.
Further, the spectral mapping theorem holds for all the B-Weyl spectra.
Finally, the generalized version of Weyl type theorems hold for T
assuming that T is of polaroid type. Our results apply to the operators
that belong to the commutant of Volterra operators
Weyl-Type Theorems on Banach Spaces Under Compact Perturbations
No full textIn this paper, we study Browder-type and Weyl-type theorems for operators T+ K defined on a Banach space X, where K is (a non necessarily commuting) compact operator on X. In the last part, the theory is exemplified in the case of isometries, analytic Toeplitz operators, semi-shift operators, and weighted right shifts
A unifying approach to Weyl type theorems for Banach space operators
Full text linkWeyl type theorems have been proved for a considerably large number of classes of operators. In this paper, by introducing the class of quasi totally hereditarily normaloid operators, we obtain a theoretical and general framework from which Weyl type theorems may be promptly established for many of these classes of operators. This framework also entails Weyl type theorems for perturbations f(T+K), where K is algebraic and commutes with T, and f is an analytic function, defined on an open neighborhood of the spectrum of $T+K, such that f is non constant on each of the components of its domain
Riesz operators and perturbation ideals
Full text linkThis paper is a general survey on Riesz operator theory on infinite dimensional complex Banach spaces.We also outline a new approach to the study of the containment relationships which exists between some well-known perturbation ideals starting from some recent characterizations, due to the author of the class of all Riesz operators and of the ideal of all inessential operators
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
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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