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Quelques aspects géométriques et analytiques des domaines bornés symétriques réels / Some geometric and analytic aspects of real bounded symmetric domainsOliveira Da Costa, Fernando de 19 October 2011 (has links)
Dans cette thèse, nous étudions quelques problèmes géométriques liés aux domaines bornés symétriques réels. Ces espaces sont des espaces D=G/K riemanniens symétriques non compacts, obtenus à partir de domaines bornés hermitiens symétriques. Lorsque le domaine D=G/K est de type Cr ou Dr, G opère transitivement sur chaque composante connexe de l'ensemble [sigma] des tripotents maximaux du système triple de Jordan réel positif T0D. Dans le cas complexe, cet ensemble est connexe et est appelé frontière de Shilov du domaine. Dans le cas réel, [sigma] n'est en général pas connexe. Nous fixons donc une composante connexe S de [sigma]. Alors l'action de G sur S x S possède un nombre fini d'orbites et nous donnons un système explicite de représentants. Si le domaine est de type Cs ou D2s, alors parmi ces orbites, il y a celle des couples d'éléments transverses. Sous ces hypothèses, nous pouvons alors définir l'ensemble des triplets d'éléments de S transverses deux à deux, sur lequel G opère. Là encore, nous déterminons les orbites de cette action. Enfin, nous nous intéressons à un problème analytique concernant un système de Hua. Nous montrons que pour toute fonction continue [phi] sur S, la transformée de poisson f=P[sigma phi]:=[intégrale]SP(.,u)[sigma phi](u)du est solution du système de Hua Hf(x)=(2n-/r)2[sigma]([sigma]-1)f(x)Id, où P(.,.) est le noyau de Poisson sur D x S et où n- désigne la dimension de V-. / In this thesis, we are interested in geometric problems related with \emph{real bounded symmetric domains}. These spaces are Riemannian symmetric spaces $\mathcal{D}=G/K$ of noncompact type, constructed from \emph{hermitian bounded symmetric domains}. When $\mathcal{D}=G/K$ is of type $C_r$ or $D_r$, we prove that $G$ acts transitively on each connected component of the set $\Sigma$ of \emph{maximal tripotents} in the \emph{compact Jordan triple system} $T_0\mathcal{D}$. In the hermitian case, this set is connected and is called \emph{the Shilov boundary}. In the real case, $\Sigma$ is not necessarily connected, thus we choose a connected component $\mathcal{S}$ of $\Sigma$. Then the action of $G$ in $\mathcal{S}\times\mathcal{S}$ as a finite number of orbits for wich we give representative elements. If $\mathcal{D}$ is of type $C_s$ or $D_{2s}$, then the set of couples of transversal elements of $\mathcal{S}$ is a $G$-orbit in $\mathcal{S}\times\mathcal{S}$. Under these assumptions, $G$ acts on the set of transversal triples in $\mathcal{S}\times\mathcal{S}\times\mathcal{S}$ and we determine the orbits for this action. Finally, we are interested in Hua differential systems. We prove that for any continuous function $\varphi$ on $\mathcal{S}$, the Poisson transform $f=\mathcal{P}_\sigma\varphi:=\int_\mathcal{S}\mathcal{P}(\cdot,u)^\sigma\varphi(u)du$ is a solution of the Hua system $\mathcal{H}f(x)=(\frac{2n^-}{r})^2\sigma(\sigma-1)f(x)\textnormal{Id}$, where $\mathcal{P}(\cdot,\cdot)$ is the Poisson kernel on $\mathcal{D}\times\mathcal{S}$ and $n^-$ is the dimension of $V^-$.
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The C*-algebras of certain Lie groups / Les C*-algèbres de certains groupes de LieGünther, Janne-Kathrin 22 September 2016 (has links)
Dans la présente thèse de doctorat, les C*-algèbres des groupes de Lie connexes réels nilpotents de pas deux et du groupe de Lie SL(2,R) sont caractérisées. En outre, comme préparation à une analyse de sa C*-algèbre, la topologie du spectre du produit semi-direct U(n) x H_n est décrite, où H_n dénote le groupe de Lie de Heisenberg et U(n) le groupe unitaire qui agit sur H_n par automorphismes. Pour la détermination des C*-algèbres de groupes, la transformation de Fourier à valeurs opérationnelles est utilisée pour appliquer chaque C*-algèbre dans l'algèbre de tous les champs d'opérateurs bornés sur son spectre. On doit trouver les conditions que satisfait l'image de cette C*-algèbre sous la transformation de Fourier et l'objectif est de la caractériser par ces conditions. Dans cette thèse, il est démontré que les C*-algèbres des groupes de Lie connexes réels nilpotents de pas deux et la C*-algèbre de SL(2,R) satisfont les mêmes conditions, des conditions appelées «limites duales sous contrôle normique». De cette manière, ces C*-algèbres sont décrites dans ce travail et les conditions «limites duales sous contrôle normique» sont explicitement calculées dans les deux cas. Les méthodes utilisées pour les groupes de Lie nilpotents de pas deux et pour le groupe SL(2,R) sont très différentes l'une de l'autre. Pour les groupes de Lie nilpotents de pas deux, on regarde leurs orbites coadjointes et on utilise la théorie de Kirillov, alors que pour le groupe SL(2,R), on peut mener les calculs plus directement / In this doctoral thesis, the C*-algebras of the connected real two-step nilpotent Lie groups and the Lie group SL(2,R) are characterized. Furthermore, as a preparation for an analysis of its C*-algebra, the topology of the spectrum of the semidirect product U(n) x H_n is described, where H_n denotes the Heisenberg Lie group and U(n) the unitary group acting by automorphisms on H_n. For the determination of the group C*-algebras, the operator valued Fourier transform is used in order to map the respective C*-algebra into the algebra of all bounded operator fields over its spectrum. One has to find the conditions that are satisfied by the image of this C*-algebra under the Fourier transform and the aim is to characterize it through these conditions. In the present thesis, it is proved that both the C*-algebras of the connected real two-step nilpotent Lie groups and the C*-algebra of SL(2,R) fulfill the same conditions, namely the “norm controlled dual limit” conditions. Thereby, these C*-algebras are described in this work and the “norm controlled dual limit” conditions are explicitly computed in both cases. The methods used for the two-step nilpotent Lie groups and the group SL(2,R) are completely different from each other. For the two-step nilpotent Lie groups, one regards their coadjoint orbits and uses the Kirillov theory, while for the group SL(2,R) one can accomplish the calculations more directly
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Geometric Steiner minimal treesDe Wet, Pieter Oloff 31 January 2008 (has links)
In 1992 Du and Hwang published a paper confirming the correctness of a well
known 1968 conjecture of Gilbert and Pollak suggesting that the Euclidean
Steiner ratio for the plane is 2/3. The original objective of this thesis was to
adapt the technique used in this proof to obtain results for other Minkowski
spaces. In an attempt to create a rigorous and complete version of the proof,
some known results were given new proofs (results for hexagonal trees and
for the rectilinear Steiner ratio) and some new results were obtained (on
approximation of Steiner ratios and on transforming Steiner trees).
The most surprising result, however, was the discovery of a fundamental
gap in the proof of Du and Hwang. We give counter examples demonstrating
that a statement made about inner spanning trees, which plays an important
role in the proof, is not correct. There seems to be no simple way out of
this dilemma, and whether the Gilbert-Pollak conjecture is true or not for
any number of points seems once again to be an open question. Finally we
consider the question of whether Du and Hwang's strategy can be used for
cases where the number of points is restricted. After introducing some extra
lemmas, we are able to show that the Gilbert-Pollak conjecture is true for 7
or fewer points. This is an improvement on the 1991 proof for 6 points of
Rubinstein and Thomas. / Mathematical Sciences / Ph. D. (Mathematics)
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Compactness in categories and its application in different categoriesThulapersad, Sarah 12 1900 (has links)
In the paper [HSS] Herrlich, Salicrup and Strecker were able to show that Kuratowski / Mrowka's Theorem concerning compactness for topological spaces could be applied to a wider setting. In this dissertation, which is based on the paper [F subscript 1], we interpret Kuratowski / Mrowka's result in the category R-Mod. Chapter One deals mainly with the preliminary definitions and results and we also show that there is a 1-1 correspondence between torsion theories and standard factorisation systems. In Chapter Two we, obtain for every torsion theory T, a theory of T-compactness which is an extension of the definition of compactness found in [HSS]. We then obtain a characterisation of T-compactness under certain conditions on the ring R and torsion theory T. In Chapter Three we examine the class of T-compact R-modules more closely when the ring R is T-hereditary and T-noetherian. We also obtain further characterisation of T-compactness under these additional conditions. In Chapter Four we show that many topological results have analogues in R-Mod. / Mathematical Sciences / M. Sc. (Mathematics)
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Ordered spaces of continuous functions and bitopological spacesNailana, Koena Rufus 11 1900 (has links)
This thesis is divided into two parts: Ordered spaces of Continuous Functions and
the algebras associated with the topology of pointwise convergence of the associated
construct, and Strictly completely regular bitopological spaces.
The Motivation for part of the first part (Chapters 2, 3 and 4) comes from the
recent study of function spaces for bitopological spaces in [44] and [45]. In these
papers we see a clear generalisation of classical results in function spaces ( [14] and
[55]) to bi-topological spaces. The well known definitions of the pointwise topology and
the compact open topology in function spaces are generalized to bitopological spaces,
and then familiar results such as Arens' theorem are generalised. We will use the same
approach in chapters 2, 3 and 4 to formulate analogous definitions in the setting of
ordered spaces. Well known results, including Arens' theorem, are also generalised
to ordered spaces. In these chapters we will also compare function spaces in the
category of topological spaces and continuous functions, the category of bi topological
spaces and bicontinuous functions, and the category of ordered topological spaces and
continuous order-preserving functions. This work has resulted in the publication of
[30] and [31].
Continuing our study of Function Spaces, we oonsider in Chapters 5 and 6 some
Categorical aspects of the construction, motivated by a series of papers which includes
[39], [40], [41] and [50]. In these papers the Eilenberg-Moore Category of algebras of
the monad induced by the Hom-functor on the categories of sets and categories of
topological spaces are classified. Instead of looking at the whole product topology we
will restrict ourselves to the pointwise topology and give examples of the EilenbergMoore Algebras arising from this restriction. We first start by way of motivation, with
the discussion of the monad when the range space is the real line with the usual topology.
We then restrict our range space to the two point Sierpinski space, with the aim
of discovering a topological analogue of the well known characterization of Frames as
the Eilenberg-Moore Category of algebras associated with the Hom-F\mctor of maps
into the Sierpinski space [11]. In this case the order structure features prominently, resulting in the category Frames with a special property called "balanced" and Frame
homomorphisms as the Eilenberg-Moore category of M-algebras. This has resulted
in [34].
The Motivation for the second part comes from [20] and [15]. In [20], J. D. Lawson
introduced the notion of strict complete regularity in ordered spaces. A detailed study
of this notion was done by H-P. A. Kiinzi in [15]. We shall introduce an analogous
notion for bitopological spaces, and then shall also compare the two notions in the categories
of bi topological spaces and bicontinuous functions, and of ordered topological
spaces and continuous order-preserving functions via the natural functors considered
in the previous chapters. We further study the Stone-Cech bicompactification and
Stone-Cech ordered compactification in the two categories. This has resulted in [32] and [33] / Mathematical Sciences / D. Phil. (Mathematics)
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