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Submitted by Johnny Rodrigues (johnnyrodrigues@ufcg.edu.br) on 2018-07-22T14:49:45Z No. of bitstreams: 1 CARLOS DAVID DE CARVALHO LOBÃO - DISSERTAÇÃO PPGMAT 2009..pdf: 418073 bytes, checksum: b2deb42599e396408cd91ddf1721d8eb (MD5) / Made available in DSpace on 2018-07-22T14:49:45Z (GMT). No. of bitstreams: 1 CARLOS DAVID DE CARVALHO LOBÃO - DISSERTAÇÃO PPGMAT 2009..pdf: 418073 bytes, checksum: b2deb42599e396408cd91ddf1721d8eb (MD5) Previous issue date: 2009-03 / As álgebras verbalmente primas são bem conhecidas em característica 0. Já sobre corpos de característica p > 2 pouco sabemos sobre elas. Apresentamos modelos genéricos e calcularemos a dimensão de Gelfand-kirillov para as álgebras E⊗E, Aa,b, Ma,b(E)⊗E e Ma,b(E)⊗E. Como consequência, obteremos a prova de não PI-equivalência entre álgebras importantes para PI-Teoria em características positiva. / The verbally prime algebras are well understood in characteristic 0 while over a field of characteristic p > 2 little is known about them. In this work we discuss some sharp differents between these two generics cases for the characteristc. We exhibit constructions of generic models. By using these models we compute the Gelfand-Kirillov dimension of the relatively free algebras of rank m in the varieties generated by E⊗E, Aa,b, Ma,b(E)⊗E e Ma,b(E)⊗E. As consequence we obtain the PI non equivalence of important algebras for the PI theory in positive characteristic.

Submitted by Leonardo Cavalcante (leo.ocavalcante@gmail.com) on 2018-04-23T20:47:31Z No. of bitstreams: 1 Arquivototal.pdf: 1433584 bytes, checksum: fb8978802ac3b768c50f569bc4124e5e (MD5) / Made available in DSpace on 2018-04-23T20:47:31Z (GMT). No. of bitstreams: 1 Arquivototal.pdf: 1433584 bytes, checksum: fb8978802ac3b768c50f569bc4124e5e (MD5) Previous issue date: 2014-03-20 / Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq / In this dissertation we develop a rst contact with the theory of Banach Algebras and C*-algebras. As usual of a rst contact, we build the Spectral Theory in Banach algebras with unit. We present the characterization theorems of C *-algebras of Gelfand-Naimark and Gelfand-Naimark-Segal, including the GNS construction. Moreover, we prove a theorem which characterizes all complex homomorphisms in the C*-algebra C(X), as point-evaluation homomorphisms. We also present, as a curiosity, a proof of the Fundamental Theorem of Algebra using the Gelfand-Mazur Theorem. As a prerequisite to the Gelfand-Naimark-Segal's characterization of C *-algebras, we further develop, in the background, the theory of the direct sum of any family of Hilbert spaces. . / Nesta dissertação desenvolveremos um primeiro contato com a Teoria de Álgebras de Banach e C*-álgebras. Como tópico de um primeiro contato, construiremos a Teoria Espectral em Álgebras de Banach com unidade. Apresentaremos os Teoremas de Caracterização de C*-álgebras de Gelfand-Naimark, e Gelfand-Naimark-Segal, incluindo a constru c~ao GNS. Al em disso, provamos um teorema que caracteriza todos os homomor smos complexos na C*-álgebra C(X) como sendo homomor smos de avaliação. Apresentaremos também, como curiosidade, uma prova do Teorema Fundamental da Álgebra a partir do Teorema de Gelfand-Mazur. Como um pré requisito a Caracterização de Gelfand-Naimark-Segal de C*-álgebras, desenvolvemos ainda, em segundo plano, a teoria da soma direta de uma familia qualquer de espaços de Hilbert.

Nous démontrons une version d'un théorème d'Heckman permettant de préciser le lien qui unit la théorie des représentations des groupes compacts à celle des matrices aléatoires à valeurs dans l'algèbre de Lie du groupe compact connexe K et dont la loi est K-invariante.<br />Les groupes de Lie classiques, qu'on note K(n), sont les ensembles de matrices unitaires de taille n*n à entrées dans le corps des réels, des complexes ou des quaternions. Pour chacun d'eux, nous étudions plus précisément deux types d'ensembles invariants. Le premier est l'ensemble k(n) - algèbre de Lie de K(n) - muni de la mesure gaussienne. Les règles de branchement classiques nous permettent de calculer la loi des mineurs principaux des matrices de ces ensembles. Le deuxième est une généralisation de l'ensemble unitaire de Laguerre (LUE). Au sein de la théorie des représentations, celle des cristaux de Kashiwara nous permet d'étudier cet ensemble. <br />Pickrell a montré que dans le cas complexe la limite d'une famille consistante de mesures K(n)-invariantes sur k(n) est ergodique si et seulement si elle est la loi d'une combinaison linéaire de matrices indépendantes de type Gaussien ou Laguerre. Nous montrons que son résultat reste vrai pour les autres groupes de Lie classiques.<br />La généralisation du LUE que nous proposons est obtenue en considérant des sommes de matrices aléatoires de rang un. L'étude de ces perturbations et des mineurs principaux fait apparaître des processus entrelacés. Nous montrons qu'une large classe d'entre eux sont déterminantaux et donnons leur noyau de corrélation.

<p>Let $\mathbf{G}$ be a connected reductive algebraic group defined over an algebraic closure of the finite field of prime order $p>0$, which we assume to be good for $\mathbf{G}$. We denote by $F : \mathbf{G} \to \mathbf{G}$ a Frobenius endomorphism of $\mathbf{G}$ and by $G$ the corresponding $\mathbb{F}_q$-rational structure. If $\operatorname{Irr}(G)$ denotes the set of ordinary irreducible characters of $G$ then by work of Lusztig and Geck we have a well defined map $\Phi_{\mathbf{G}} : \operatorname{Irr}(G) \to \{F\text{-stable unipotent conjugacy classes of }\mathbf{G}\}$ where $\Phi_{\mathbf{G}}(\chi)$ is the unipotent support of $\chi$.</p> <p>Lusztig has given a classification of the irreducible characters of $G$ and obtained their degrees. In particular he has shown that for each $\chi \in \operatorname{Irr}(G)$ there exists an integer $n_{\chi}$ such that $n_{\chi}\cdot\chi(1)$ is a monic polynomial in $q$. Given a unipotent class $\mathcal{O}$ of $\mathbf{G}$ with representative $u \in \mathbf{G}$ we may define $A_{\mathbf{G}}(u)$ to be the finite quotient group $C_{\mathbf{G}}(u)/C_{\mathbf{G}}(u)^{\circ}$. If the centre $Z(\mathbf{G})$ is connected and $\mathbf{G}/Z(\mathbf{G})$ is simple then Lusztig and H\'zard have independently shown that for each $F$-stable unipotent class $\mathcal$ of $\mathbf$ there exists $\chi \in \operatorname(G)$ such that $\Phi_(\chi)=\mathcal$ and $n_ = |A_(u)|$, (in particular the map $\Phi_$ is surjective).</p> <p>The main result of this thesis extends this result to the case where $\mathbf$ is any simple algebraic group, (hence removing the assumption that $Z(\mathbf)$ is connected). In particular if $\mathbf$ is simple we show that for each $F$-stable unipotent class $\mathcal$ of $\mathbf$ there exists $\chi \in \operatorname(G)$ such that $\Phi_(\chi) = \mathcal$ and $n_ = |A_(u)^F|$ where $u \in \mathcal^F$ is a well-chosen representative. We then apply this result to prove, (for most simple groups), a conjecture of Kawanaka's on generalised Gelfand--Graev representations (GGGRs). Namely that the GGGRs of $G$ form a $\mathbf{Z}$-basis for the $\mathbf{Z}$-module of all unipotently supported class functions of $G$. Finally we obtain an expression for a certain fourth root of unity associated to GGGRs in the case where $\mathbf{G}$ is a symplectic or special orthogonal group.</p>

Source coding and channel coding are two important problems in communications. Although side information exists in everyday scenario, the e&#64256;ect of side information is not taken into account in the conventional setups. In this thesis, we focus on the practical designs of two interesting coding problems with side information: Wyner-Ziv coding (source coding with side information at the decoder) and Gel??fand-Pinsker coding (channel coding with side information at the encoder). For WZC, we split the design problem into the two cases when the distortion of the reconstructed source is zero and when it is not. We review that the &#64257;rst case, which is commonly called Slepian-Wolf coding (SWC), can be implemented using conventional channel coding. Then, we detail the SWC design using the low-density parity-check (LDPC) code. To facilitate SWC design, we justify a necessary requirement that the SWC performance should be independent of the input source. We show that a su&#64259;cient condition of this requirement is that the hypothetical channel between the source and the side information satis&#64257;es a symmetry condition dubbed dual symmetry. Furthermore, under that dual symmetry condition, SWC design problem can be simply treated as LDPC coding design over the hypothetical channel. When the distortion of the reconstructed source is non-zero, we propose a practical WZC paradigm called Slepian-Wolf coded quantization (SWCQ) by combining SWC and nested lattice quantization. We point out an interesting analogy between SWCQ and entropy coded quantization in classic source coding. Furthermore, a practical scheme of SWCQ using 1-D nested lattice quantization and LDPC is implemented. For GPC, since the actual design procedure relies on the more precise setting of the problem, we choose to investigate the design of GPC as the form of a digital watermarking problem as digital watermarking is the precise dual of WZC. We then introduce an enhanced version of the well-known spread spectrum watermarking technique. Two applications related to digital watermarking are presented.

Soit G un groupe algébrique réductif connexe de centre connexe défini sur un corps fini de caractéristique p>0. On munit cette structure d'un endomorphisme de Frobenius F et l'on note G^F l'ensemble des points de G fixes pour l'action de F : G^F est un groupe fini. On suppose que la caractéristique p est bonne pour G.<br /><br />On définit alors une application Phi_G de l'ensemble des classes de conjugaison spéciales de G^* dans l'ensemble des classes unipotentes de G. Cette application décrit le support unipotent des différentes classes de faisceaux-caractères définis sur G.<br /><br />Parallèlement à cela, via la correspondance de Springer, on définit différents invariants, dont les d-invariants, pour les caractères d'un groupe de Weyl W. Nous avons étudié le lien entre l'induction de caractères spéciaux de certains sous groupes de W et les d-invariants. A l'aide de ceci, on démontre que Phi_G, restreinte à certaines classes spéciales particulières de G^* est surjective. On a montré que la stabilité vis-à-vis du Frobenius pouvait être introduite dans ce résultat.<br /><br />On en déduit deux résultats. Le premier est un lien étroit entre les restrictions aux éléments unipotents de faisceaux-caractères de certaines classes et différents systèmes locaux irréductibles et G-équivariants sur les classes unipotentes de G.<br /><br />Le second est une preuve d'une conjecture de Kawanaka sur les caractères de Gelfand-Graev généralisés de G : ils forment une base du Z-module des caractères virtuels de G^F à support unipotent.

On considère des équations elliptiques semilinéaires simples de la forme Lu = F(x,u), où L est le Laplacien usuel avec condition de Dirichlet sur un ouvert borné régulier de R^n et où F peut être singulière en la variable x. On obtient notemment un critère exact pour l'existence de solutions, qui se traduit par l'apparition d'un nouvel exposant critique dans les applications.

La Tesis Doctoral está dedicada al estudio de ciertas propiedades de los radios sucesivos de los cuerpos convexos (funcionales definidos a partir de circunradios e inradios de proyecciones o secciones del cuerpo). Comenzamos estableciendo las nociones básicas necesarias para el desarrollo de los contenidos. A continuación calculamos los radios sucesivos de familias particulares de conjuntos (p-bolas, anchura constante, cuerpos tangenciales), y estudiamos la conexión existente entre estos funcionales y los números de Gelfand y Kolmogorov. En el tercer capítulo consideramos el problema de Pukhov-Perel'man sobre la mejor cota superior para un cierto cociente de radios, determinando desigualdades para problemas de este tipo que van a permitir mejorar los resultados existentes en ciertos casos. Finalmente, estudiamos cómo se relacionan los radios sucesivos de la suma de Minkowski (Firey) de dos cuerpos convexos con los correspondientes funcionales de los conjuntos, obteniendo los resultados óptimos en todos los casos. / The Doctoral Thesis is focused in the study of some properties of the successive radii of convex bodies (functionals defined by means of circumradii and inradii of projections or sections of the set). We start establishing the basic notions that will be needed further on. Next, we compute the successive radii of particular families of sets (p-balls, constant width sets and tangential bodies), and study the connection between these functionals and the Gelfand and Kolmogorov numbers. In the third chapter we consider the Pukhov-Perel'man problem on the best upper bound for a particular ratio of radii, determining inequalities for some problems of this type which will allow to improve the known results in particular cases. Finally we study how the successive radii of the (Firey)-Minkowski addition of two convex bodies are related with the corresponding functionals of the sets, obtaining the optimal results in all cases.