In the last years some results for the Laplacian on manifolds have been shown to hold also for the graph Laplacian, e.g. Courant's nodal domain theorem or Cheeger's inequality. Friedman (Some geometric aspects of graphs and their eigenfunctions, Duke Math. J. 69 (3), pp. 487-525, 1993) described the idea of a ``graph with boundary". With this concept it is possible to formulate Dirichlet and Neumann eigenvalue problems. Friedman also conjectured another ``classical" result for manifolds, the Faber-Krahn theorem, for regular bounded trees with boundary. The Faber-Krahn theorem states that among all bounded domains $D \subset R^n$ with fixed volume, a ball has lowest first Dirichlet eigenvalue. In this paper we show such a result for regular trees by using a rearrangement technique. We give restrictive conditions for trees with boundary where the first Dirichlet eigenvalue is minimized for a given "volume". Amazingly Friedman's conjecture is false, i.e. in general these trees are not ``balls". But we will show that these are similar to ``balls". (author's abstract) / Series: Preprint Series / Department of Applied Statistics and Data Processing

The Laplacian energy of a graph is the sum of the distances of the eigenvalues of the Laplacian matrix of the graph to the graph's average degree. The maximum Laplacian energy over all graphs on n nodes and m edges is conjectured to be attained for threshold graphs. We prove the conjecture to hold for graphs with the property that for each k there is a threshold graph on the same number of nodes and edges whose sum of the k largest Laplacian eigenvalues exceeds that of the k largest Laplacian eigenvalues of the graph. We call such graphs spectrally threshold dominated. These graphs include split graphs and cographs and spectral threshold dominance is preserved by disjoint unions and taking complements. We conjecture that all graphs are spectrally threshold dominated. This conjecture turns out to be equivalent to Brouwer's conjecture concerning a bound on the sum of the k largest Laplacian eigenvalues.

In this thesis we are interested in some problems regarding harmonic functions. The topics are divided into three chapters. Chapter 2 concerns singularities developed by solutions of the Cauchy problem for a holomorphic elliptic equation, especially Laplace's equation. The principal motivation is to locate the singularities of the Schwarz potential. The results have direct applications to Laplacian growth (or the Hele-Shaw problem). Chapter 3 concerns the Dirichlet problem when the boundary is an algebraic set and the data is a polynomial or a real-analytic function. We pursue some questions related to the Khavinson-Shapiro conjecture. A main topic of interest is analytic continuability of the solution outside its natural domain. Chapter 4 concerns certain complex-valued harmonic functions and their zeros. The special cases we consider apply directly in astrophysics to the study of multiple-image gravitational lenses.

In this paper we prove a Faber-Krahn-type inequality for regular trees and give a complete characterization of extremal trees. It extends a former result of the author. The main tools are rearrangements and perturbation of regular trees. (author's abstract) / Series: Preprint Series / Department of Applied Statistics and Data Processing

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Title: Symmetries of the CR sub-Laplacian Author: Zuzana Vlasáková Department: Charles University Institute of Mathematics Supervisor: Prof. RNDr. Vladimír Souček, DrSc. Author's e-mail address: zuzana.kasarova@email.cz Supervisor's e-mail address: soucek@karlin.mff.cuni.cz Abstract: The aim of this work is to characterize the vector space of symme- try operators of the CR sub-Laplacian. To do this, we define a CR structure on some distinguished submanifold of Cn+1 (it is in fact the big cell in the CR sphere) and write down the CR sub-Laplacian on it. We also define the symmetries of the CR sub-Laplacian in general and using the ambient con- struction, which we introduce in the sequel, we construct all of them. Keywords: CR geometry, CR sub-Laplacian, symmetries of differential op- erator. 1

The subject of the thesis is the derivation of non-local diffusion equations from kinetic models with heavy-tailed equilibrium in velocity. We are particularly interested in confining the kinetic equations and developing methods that allow us, from the confined kinetic models, to derive confined versions of non-local diffusion equations.

SILVA, A. K. V. Estimativas gradiente para autofunções do V-Laplaciano e métricas m-quasi-Einstein generalizadas compactas com bordo. 2017. 40 f. Tese (Doutorado em Matemática) – Centro de Ciências, Universidade Federal do Ceará, Fortaleza, 2017. / Submitted by Andrea Dantas (pgmat@mat.ufc.br) on 2017-04-18T14:49:03Z No. of bitstreams: 1 2015_tese_akvsilva.pdf: 322426 bytes, checksum: d6abc5541598409191f635ad25e1f501 (MD5) / Rejected by Rocilda Sales (rocilda@ufc.br), reason: Bom dia Andrea, Por favor repasse esse e-mail para o aluno. Estou devolvendo o trabalho pois tem alguns itens que não estão normalizados. O ano que deve constar na capa, folha de rosto e ficha catalográfica é o da entrega. E na ficha catalográfica o nome do autor e o título do trabalho não é em caixa alta. Somente as iniciais e quando necessário. Atenciosamente, Rocilda Sales on 2017-04-19T11:01:58Z (GMT) / Submitted by Andrea Dantas (pgmat@mat.ufc.br) on 2017-04-19T13:11:59Z No. of bitstreams: 1 2015_tese_akvsilva.pdf: 322367 bytes, checksum: c9bd22b4cb5917adacde8be99093e8d8 (MD5) / Rejected by Rocilda Sales (rocilda@ufc.br), reason: Alterar o ano. on 2017-04-19T14:52:13Z (GMT) / Submitted by Andrea Dantas (pgmat@mat.ufc.br) on 2017-04-19T16:22:45Z No. of bitstreams: 1 2015_tese_akvsilva.pdf: 322367 bytes, checksum: 1523e0c8bd0590358cda3a542819aa62 (MD5) / Rejected by Rocilda Sales (rocilda@ufc.br), reason: Correção na folha de aprovação. on 2017-04-19T16:39:17Z (GMT) / Submitted by Andrea Dantas (pgmat@mat.ufc.br) on 2017-04-19T17:04:43Z No. of bitstreams: 1 2015_tese_akvsilva.pdf: 322112 bytes, checksum: e3087741f0e7bb8b966418fb10253c7b (MD5) / Approved for entry into archive by Rocilda Sales (rocilda@ufc.br) on 2017-04-24T11:14:14Z (GMT) No. of bitstreams: 1 2015_tese_akvsilva.pdf: 322112 bytes, checksum: e3087741f0e7bb8b966418fb10253c7b (MD5) / Made available in DSpace on 2017-04-24T11:14:14Z (GMT). No. of bitstreams: 1 2015_tese_akvsilva.pdf: 322112 bytes, checksum: e3087741f0e7bb8b966418fb10253c7b (MD5) Previous issue date: 2015-08-17 / The main of this work was to study properties of Riemannian when subjected to conditions on Bakry-Émery-Ricci tensor. Essentially we study two cases. In the first case, motivated by the work of Barros and Ribeiro Jr. (2014), He, Petersen and Wylie (2012) and Miao and Tam (2011), was introduced generalized m-quasi-Einstein metrics compact with boundary, where we get a result that classify these metrics; more specifically, assuming that gradient field of the exponential of potential function is a conformal vector field, we obtain that this must be a geodesic ball in a simply connected space form. That we get some results that implies when these are trivial metrics. In the second case, we work the Bakry-Émery-Ricci tensor bounded bellow, initially in a compact Riemannian, with or without boundary, and later on balls in complete Riemannian. With this study, we obtain gradient estimates for eigenfunctions of V-Laplacian operator, that generalize results of (Li, 2005) and (Li, 2015). Finally, as consequence theses results, we show an Harnack’s inequality. / Este trabalho tem como principal objetivo estudar propriedades de variedades Riemannianas quando submetidas a condições sobre tensores de Ricci-Bakry-Émery. Essencialmente estudamos dois casos. No primeiro caso, motivados pelos trabalhos de Barros e Ribeiro Jr (2014), He, Petersen e Wylie (2012) e por Miao e Tam (2011), introduzimos métricas m-quasi-Einstein generalizadas compactas com bordo, donde obtemos um resultado que garante uma classificação para estas métricas; mais precisamente, assumindo que o gradiente da exponencial da função potencial é um campo conforme, obtemos que aquela deve ser uma bola geodésica de uma forma espacial simplesmente conexa. Disso, obtemos alguns resultados em que garantimos quando estas métricas são triviais. No segundo caso, trabalhos o tensor de Ricci-Bakry-Émery limitado por baixo, inicialmente, em variedades Riemannianas compactas, com bordo ou sem bordo, e posteriormente, sobre bolas em variedades Riemannianas completas. Com esse estudo, obtivemos estimativas do gradiente para autofunções do operador V-Laplaciano, generalizando resultados de (Li, 2005) e (Li, 2015). Finalmente, como consequências desses resultados, exibimos uma desigualdade de Harnack.

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CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior / Apresentamos um mÃtodo para a obtenÃÃo de limites inferiores para o primeiro autovalor de Dirichlet em termos de campos vetoriais com divergÃncia positiva. Aplicando-o ao gradiente de uma funÃÃo distante, obtemos estimativas de de autovalor em bolas geodÃsicas em cut locus e dos domÃnios de subvariedades com curvatura mÃdia localmente limitada.Para subvariedades das variedade de Hadamard com limites mÃdios de curvaturas, estes limites inferiores dependem da dimensÃo das subvariedades e limite sobre sua curvatura mÃdia. / We present a method to obtain lower bounds for first Dirichlet eigenvalue in terms of vector fields with positive divergence. Applying this to the gradient of a distance function we obtain estimates of eigenvalue of geodesic balls inside the cut locus and of domains in submanifolds with locally bounded mean curvature. For submanifolds of Hadamard manifolds with bounded mean curvature these lower bounds depend only on the dimension of the submanifold and the bound on its mean curvature.