Dans cette thèse nous nous sommes intéressés de trois types de problèmes : 1 -Existence et unicité d’une fonction harmonique strictement positive associée à une marche aléatoire inhomogène confinée dans un orthant. 2 -Etude de la convergence en loi des arbres de Galton Watson critiques conditionnés à avoir un nombre assez grand de noeuds protégés. 3 -Etude de la convergence en loi des arbres de Galton Watson conditionnés à avoir une génération anormalement grande. / In this thesis we are interested in three types of problems: 1-Existence and uniqueness of a positive harmonic function associated with an inhomogeneous random walk confined in an orthant. 2-Study of convergence in distribution of critical Galton Watson trees conditioned to have a large enoughnumber of protected nodes. 3-Study of the convergence in distribution of Galton Watson trees conditioned to have a large generation.

Title: Baire and Harmonic Functions Author: Petr Pošta Department: Department of Mathematical Analysis Supervisor: prof. RNDr. Jaroslav Lukeš, DrSc., Department of Mathematical Analysis Abstract: The present thesis consists of six research papers. The first four articles deal with topics related to potential theory, Baire-one functions and its important subclasses, in particular differences of semicontinuous functions. The first paper is devoted to the stability of the Dirichlet problem for which a new criterion in terms of Poisson equation is provided. The second paper improves the recent result obtained by Lukeš et al. It shows that the classical Dirichlet solution belongs to the B1/2 subclass of Baire-one functions. A generalization of this result to the abstract context of the Choquet theory on functions spaces is provided. Finally, an abstract Dirichlet problem for the boundary condition belonging to the class of differences of semincontinuous functions is discussed. The third paper concentrates on the Lusin-Menshov property and the approximation of Baire- one and finely continuous functions by differences of semicontinuous and finely continuous functions. It provides an exposition of topologies (various density topologies as well as the fine topologies in both linear and non-linear potential...

Submitted by Marlene Santos (marlene.bc.ufg@gmail.com) on 2016-08-04T19:38:03Z No. of bitstreams: 2 Mestrado - Edwin Oswaldo Salinas Reyes - 2016.pdf: 1254340 bytes, checksum: f20230521814efa37f16e24f8d80f74e (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Approved for entry into archive by Luciana Ferreira (lucgeral@gmail.com) on 2016-08-05T12:33:56Z (GMT) No. of bitstreams: 2 Mestrado - Edwin Oswaldo Salinas Reyes - 2016.pdf: 1254340 bytes, checksum: f20230521814efa37f16e24f8d80f74e (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Made available in DSpace on 2016-08-05T12:33:56Z (GMT). No. of bitstreams: 2 Mestrado - Edwin Oswaldo Salinas Reyes - 2016.pdf: 1254340 bytes, checksum: f20230521814efa37f16e24f8d80f74e (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Previous issue date: 2016-02-29 / Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq / In this work we refer to the study of a new method and simple approach to minimal surface Laguerre in isotropic model of Laguerre geometry as the bi-harmonic function graph. We developed the isotropic geometry which studies the geometric properties invariant under certain affine transformations in Euclidean space, and the fundamental elements of Laguerre geometry which are spheres orienteds and plans orienteds, and properties which are invariant on the transformation of Laguerre. In addition, we will show a close relationship between minimal surfaces Laguerre spherical type and isotropic minimal surfaces which are given by the graph of harmonic functions and minimal Euclidean surfaces. Finally, the duality metric in the isotropic space is used to develop an isotropic exchange for minimal surfaces Laguerre in certain Lie transformation of Laguerre minimal surfaces in Euclidean space. / Neste trabalho nos referimos ao estudo de um novo método de desenvolvimento de superfícies mínimas de Laguerre vista no modelo isotrópico da geometria de Laguerre como o gráfico de funções bi-harmônicas. Desenvolvemos a geometria isotrópica a qual estuda as propriedades geométricas invariantes por certas transformações afines no espaço Euclidiano, os elementos fundamentais da geometria de Laguerre as quais são esferas e planos orientados e as propriedades as quais são invariantes sobre as transformações de Laguerre. Além disso, mostraremos uma relação fechada entre superfícies mínimas de Laguerre do tipo esférico e superfícies mínimas isotrópicas as quais são dadas pelo gráfico de funções harmônicas e superfícies mínimas Euclidianas. Finalmente, a métrica dual no espaço isotrópico é utilizada para desenvolver uma contrapartida isotrópica de superfícies mínimas de Laguerre em certas transformações de Lie de superfícies mínimas de Laguerre no espaço Euclidiano.

Après une présentation des notations usuelles de la théorie des graphes, on étudie l'ensemble des fonctions harmoniques sur les graphes, c'est à dire des fonctions dont le laplacien est nul. Ces fonctions forment un espace vectoriel et sur un graphe uniformément localement fini, on montre que cet espace vectoriel est soit de dimension un, soit de dimension infinie. Lorsque le graphe comporte une infinité de cycles, ce résultat tombe en défaut et on exhibe des exemples qui montrent qu'il existe un graphe sur lequel les harmoniques forment un espace vectoriel de dimension n, pour tout n. Un exemple de graphe périodique est également traité. Ensuite, toujours pour le laplacien, on étudie plus précisément sur les arbres uniformément localement finis les valeurs propres dont l'espace propre est de dimension infini. Dans ce cas, il est montré que l'espace propre contient un sous-espace isomorphe à l'ensemble des suites réelles bornées. Une inégalité concernant le spectre est donnée dans le cas spécial où les arêtes sont de longueur un. Des exemples montrent que ces inclusions sont optimales. Dans le chapitre suivant, on étudie le comportement asymptotique des valeurs propres pour des opérateurs elliptiques d'ordre 2 quelconques sous des conditions de Kirchhoff dynamiques. Après réécriture du problème sous la forme d'un opérateur de Sturm-Liouville, on écrit le problème de façon matricielle. Puis on trouve une équation caractéristique dont les zéros correspondent aux valeurs propres. On en déduit une formule pour l'asymptotique des valeurs propres. Dans le dernier chapitre, on étudie la stabilité de solutions stationnaires pour certains problèmes de réaction-diffusion où le terme de non linéarité est polynomial. / After a quick presentation of usual notations for the graph theory, we study the set of harmonic functions on graphs, that is, the functions whose laplacian is zero. These functions form a vectorial space. On a uniformly locally finite tree, we shaw that this space has dimension one or infinity. When the graph has an infinite number of cycles, this result change and we describe some examples showing that there exists a graph on which the harmonic functions form a vectorial space of dimension n, for all n. We also treat the case of a particular periodic graph. Then, we study more precisely the eigenvalues of infinite dimension. In this case, the eigenspace contains a subspace isomorphic to the set of bounded sequences. An inequality concerning the spectral is given when edges length is equal to one. Examples show that these inclusions are optimal. We also study the asymptotic behavior of eigenvalues for elliptic operators under dynamical Kirchhoff node conditions. We write the problem as a Sturm-Liouville operator and we transform it in a matrix problem. Then we find a characteristic equation whose zeroes correspond to eigenvalues. We deduce a formula for the asymptotic behavior. In the last chapter, we study the stability of stationary solutions for some reaction-diffusion problem whose the non-linear term is polynomial.