1,720,964 research outputs found
Spherical analysis on homogeneous vector bundles of the 3-dimensional euclidean motion group
Get PDFArtículo finalmente publicado en: Díaz Martín, R. y Levstein, F. (2018). Spherical analysis on homogeneous vector bundles of the 3-dimensional euclidean motion group. Monatshefte fur Mathematik, 185 (4), 621-649. https://doi.org/10.1007/s00605-017-1123-1Fil: Díaz Martín, Rocío Patricia. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía, Física y Computación; Argentina.Fil: Levstein, Fernando. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía, Física y Computación; Argentina.We consider R3 as a homogeneous manifold for the action of the motion group given by rotations and translations. For an arbitrary τ∈SO(3)ˆ, let Eτ be the homogeneous vector bundle over R3 associated with τ. An interesting problem consists in studying the set of bounded linear operators over the sections of Eτ that are invariant under the action of SO(3)⋉R3. Such operators are in correspondence with the End(Vτ)-valued, bi-τ-equivariant, integrable functions on R3 and they form a commutative algebra with the convolution product. We develop the spherical analysis on that algebra, explicitly computing the τ-spherical functions. We first present a set of generators of the algebra of SO(3)⋉R3-invariant differential operators on Eτ. We also give an explicit form for the τ-spherical Fourier transform, we deduce an inversion formula and we use it to give a characterization of End(Vτ)-valued, bi-τ-equivariant, functions on R3.This work has been supported by a fellowship from Consejo Nacional de Investigaciones Cientı́ficas y Técnicas and
reserch grants from Secretarı́a de Ciencia y Tecnologı́a, Universidad Nacional de Córdoba and Consejo Nacional de
Investigaciones Cientı́ficas y Técnicas (Argentina).info:eu-repo/semantics/submittedVersionFil: Díaz Martín, Rocío Patricia. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía, Física y Computación; Argentina.Fil: Levstein, Fernando. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía, Física y Computación; Argentina.Matemática Pur
Harmonic analysis on some generalized Gelfand pairs attached to Heisenberg groups
Get PDFLet H_n be the 2n + 1-dimensional Heisenberg group. We consider thegeneralized Gelfand pairs (R*xH_1,R) and ((R_{>0} ×SO(n))xH_n, R_?>0? ×SO(n)) for n ≥ 2.We describe the spherical distributions corresponding to these pairs and we obtain inversionformulæ in terms of them for the spaces of Schwartz functions on R^{2n}and H_n. We use theTengstrand transform to compute the spherical distributions for n = 1 explicitly.Fil: Levstein, Fernando. 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: Saal, Linda Victoria. 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
Nilpotency degree of the nilradical of a solvable Lie algebra on two generators and uniserial modules associated to free nilpotent Lie algebras
No full textGiven a sequence d~ = (d1, . . . , dk) of natural numbers, we consider
the Lie subalgebra h of gl(d, F), where d = d1 + · · · + dk and F is a field of
characteristic 0, generated by two block upper triangular matrices D and E
partitioned according to d~, and study the problem of computing the nilpotency
degree m of the nilradical n of h. We obtain a complete answer when D and E
belong to a certain family of matrices that arises naturally when attempting
to classify the indecomposable modules of certain solvable Lie algebras.
Our determination of m depends in an essential manner on the symmetry of
E with respect to an outer automorphism of sl(d). The proof that m depends
solely on this symmetry is long and delicate.
As a direct application of our investigations on h and n we give a full
classification of all uniserial modules of an extension of the free ℓ-step nilpotent
Lie algebra on n generators when F is algebraically closed.Fil: Cagliero, Leandro Roberto. 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: Levstein, Fernando. 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: Szechtman, Fernando. University Of Regina; Canad
Spherical analysis on homogeneous vector bundles of the 3-dimensional euclidean motion group
Get PDFWe consider R3 as a homogeneous manifold for the action of the motion group given by rotations and translations. For an arbitrary τ∈ SO(3) ^ , let Eτ be the homogeneous vector bundle over R3 associated with τ. An interesting problem consists in studying the set of bounded linear operators over the sections of Eτ that are invariant under the action of SO(3) ⋉ R3. Such operators are in correspondence with the End(Vτ) -valued, bi-τ-equivariant, integrable functions on R3 and they form a commutative algebra with the convolution product. We develop the spherical analysis on that algebra, explicitly computing the τ-spherical functions. We first present a set of generators of the algebra of SO(3) ⋉ R3-invariant differential operators non Eτ. We also give an explicit form for the τ-spherical Fourier transform, we deduce an inversion formula and we use it to give a characterization of End(Vτ) -valued, bi-τ-equivariant, functions on R3.Fil: Díaz Martín, Rocío Patricia. Universidad Nacional de Córdoba; 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: Levstein, Fernando. Universidad Nacional de Córdoba; 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
Generalized quadrangles and subconstituent algebra ¹
Get PDFThe point graph of a generalized quadrangle GQ(s, t) is a strongly regular graph Γ = srg(ν, κ, λ, µ) whose parameters depend on s and t. By a detailed analysis of the adjacency matrix we compute the Terwilliger algebra of this kind of graphs (and denoted it by T ). We find that there are only two non-isomorphic Terwilliger algebras for all the generalized quadrangles. The two classes correspond to wether s 2 = t or not. We decompose the algebra into direct sum of simple ideals. Considering the action T × CX −→ CX we find the decomposition into irreducible T -submodules of CX (where X is the set of vertices of the Γ).Fil: Levstein, Fernando. 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: Maldonado, Ana Carolina. Universidade Federal de Pernambuco; Brasil. 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
Hamming Graph based Image Compression with variable Threshold
Get PDFIn this paper a lossy image compression methodusing the adjacency matrix of a graph is proposed.We instantiate the method using the Hamming graph,which gives rise to an image compression algorithmthat uses a Hadamard Matrix together with a thresholdapproach. In threshold methods, selection of thecorrect (static) threshold value is difficult. In our approachwe use a new threshold determination thatchanges from block to block obtaining an algorithmthat uses only integer and modular operations andobtains good results in some standard images. Thenew method has better stability under recompressioniteration than jpg.Fil: Levstein, Fernando. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Lezama, Javier Hérnan. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; Argentina. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; ArgentinaFil: Maldonado, Ana Carolina. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; ArgentinaFil: Penazzi, Daniel Eduardo. Universidad Nacional de Córdoba; ArgentinaFil: Schilman, Mauro. Universidad Nacional de Córdoba; Argentin
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Cuadrángulos generalizados esquemas de Johnson y álgebras de Terwilliger
Get PDFTesis (Doctor en Matemática)--Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física, 2004.El trabajo de tesis se enmarca dentro de la Combinatoria Algebraica. Estudiamos dos casos particulares de esquemas de asociación: los provenientes de cuadrángulos generalizados y los esquemas de Johnson. Descomponemos en ideales simples las álgebras de Terwilliger asociadas (T-álgebras) y describimos en forma explícita los T-módulos irreducibles. Los cálculos realizados para los esquemas de Johnson pueden ser aplicados para describir explicítamente la T-álgebra de los hipercubos (recientemente estudiada por Go)
Variations on the Author
Get PDF“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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