1,720,957 research outputs found
Análisis armónico en nilvariedades
Full text linkTesis (Doctor en Matemática)--Universidad Nacional de Córdoba, Facultad de Matemática, Astronomía, Física y Computación, 2020.Fil: Gallo, Andrea Lilén. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía, Física y Computación; Argentina.Esta tesis se encuadra en el estudio del análisis armónico en pares de Gelfand de la forma (K,N), donde N es un grupo de Lie nilpotente y K es un subgrupo de automorfismos de N. En una primera parte trabajamos con una familia de pares de Gelfand (K,N) definida previamente por Jorge Lauret. Descomponemos la acción del producto semidirecto de K y N, sobre el espacio de funciones definidas sobre N de cuadrado integrable. Para estas familias, encontramos además la medida de Plancherel y la proyección sobre cada componente mediante las funciones esféricas asociadas al par. En el caso del grupo de Heisenberg se obtienen estos resultados para los pares de Gelfand asociados a cualquier K subgrupo de automorfismos del grupo de Heisenberg. Finalmente, nos avocamos al estudio de pares de Gelfand generalizados, es decir, a pares de Gelfand donde el subgrupo K no es necesariamente compacto. Un resultado clásico garantiza que si (K,N) es un par de Gelfand donde N es un grupo de Lie nilpotente y K subgrupo compacto de automorfismos de N, entonces N es a lo sumo 2-pasos nilpotente. En esta tesis, damos un ejemplo concreto de un par de Gelfand generalizado (K,N) donde N es un grupo de Lie 3-pasos nilpotente.This thesis is part of the study of harmonic analysis in Gelfand pairs (K,N), where N is a nilpotent Lie group and K a subgroup of automorphisms of N. In the first part, we work with a family of Gelfand pairs (K,N) defined by Jorge Lauret. We decompose the action of the semidirect product of K and N in the space of square integrable functions defined on N. We also find the Plancherel measure and the projection over each component by using spherical functions associated to the pair. In the Heisenberg case we obtain similar results with every Gelfand pair associated with each automorphism subgroup of the Heisenberg group. Finally, we deal with the study of generalized Gelfand pairs, i.e when K is non-compact. A classic result assures that, if (K,N) is a Gelfand pair with N nilpotent and K compact then N is necessarily 2-step nilpotent. In this thesis, we give an explicit example of a generalized Gelfand pair (K,N) where N is a 3-step nilpotent Lie group.Fil: Gallo, Andrea Lilén. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía, Física y Computación; Argentina
A generalized Gelfand pair attached to a 3-step nilpotent Lie group
Full text linkLet N be a nilpotent Lie group and K a compact subgroup of the automorphism group Aut(N) of N. It is well-known that if (K⋉ N, K) is a Gelfand pair then N is at most 2-step nilpotent Lie group. The notion of Gelfand pair was generalized when K is a non-compact group. In this work, we give an example of a 3-step nilpotent Lie group and a non-compact subgroup K of Aut(N) such that (K⋉ N, N) is a generalized Gelfand pair.Fil: Gallo, Andrea Lilén. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigación y Estudios de Matemática. Universidad Nacional de Córdoba. Centro de Investigación y Estudios de Matemática; Argentina. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; ArgentinaFil: Saal, Linda Victoria. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentin
Some harmonic analysis on commutative nilmanifolds
No full textIn this work, we consider a family of Gelfand pairs (KnN, N) (inshort (K, N) ) where Nis a two step nilpotent Lie group, and Kis the group oforthogonal automorphisms ofN. This family has a nice analytic property: almos tall these 2-step nilpotent Lie group have square integrable representations. In these cases, following Moore-Wolf’s theory, we find an explicit expression for the inversion formula of N, and as a consequence, we decompose the regular action ofKnNonL2(N). This explicit expression for the Fourier inversion formula of N, specializedto a class of commutative nilmanifolds described by J. Lauret, sharpens the recent analysis due to J. Wolf concerning the regular action ofKnNonL2(N) . When Nis the Heisenberg group, we obtain the decomposition ofL2(N) under the action of KnN for all Ksuch that (K, N) is a Gelfand pair. Finally, we also give aparametrization for the generic spherical functions associated to the pair (K, N) ,and we give an explicit expression for these functions in some casesFil: Gallo, Andrea Lilén. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigación y Estudios de Matemática. Universidad Nacional de Córdoba. Centro de Investigación y Estudios de Matemática; Argentina. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; ArgentinaFil: Saal, Linda Victoria. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentin
Hörmander conditions for vector-valued kernels of singular integrals and their commutators
No full textWe study Coifman type estimates and weighted norm inequalities for singular integral operators and their commutators, given by the convolution with a vector-valued kernel. We define a weaker Hörmander type condition associated with Young functions for the vector-valued kernels. With this general framework we obtain as an example the result for the square operator and its commutator given in [M. Lorente, M. S. Riveros, and A. de la Torre, J. Math. Anal. Appl. 336 (2007), no. 1, 577-592].Fil: Gallo, Andrea Lilén. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigación y Estudios de Matemática. Universidad Nacional de Córdoba. Centro de Investigación y Estudios de Matemática; ArgentinaFil: Ibañez Firnkorn, Gonzalo Hugo. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigación y Estudios de Matemática. Universidad Nacional de Córdoba. Centro de Investigación y Estudios de Matemática; ArgentinaFil: Riveros, María Silvina. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigación y Estudios de Matemática. Universidad Nacional de Córdoba. Centro de Investigación y Estudios de Matemática; Argentin
Acotación de operadores integrales, dados por un núcleo a valores vectoriales que satisface una condición de tipo Hörmander y aplicaciones
Full text linkTesis (Lic. en Matemática)--Universidad Nacional de Córdoba, Facultad de Matemática, Astronomía y Física, 2015.El principio de Calderón-Zygmund “asegura” que toda integral singular está acotada en normas Lp(w), con w un cierto peso, por un operador maximal apropiado. Para integrales singulares de Calderón-Zygmund (con núcleo satisfaciendo la condición de Lipschitz) este es el resultado clásico de Coifman: el operador que controla en normas p’s es la maximal de Hardy-Littlewood. Para integrales singulares con núcleo no tan suave, por ejemplo
con núcleo en Hr, el operador maximal que controla es Mr’, que resulta mayor que el de Hardy-Littlewood.
En este trabajo se definen condiciones que debe satisfacer un núcleo K de una integral singular a valores vectoriales, es decir cuando KЄ H†A,X. y a partir de esta condición se prueba que el operador maximal que controla en normas p ´s es el MA-. Como aplicación de este resultado estudiamos el operador cuadrado
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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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