Orientador: Valerio Ramos Batista / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Matematica, Estatistica e Computação Cientifica / Made available in DSpace on 2018-08-04T03:34:02Z (GMT). No. of bitstreams: 1 Lopes_LauriclecioFigueiredo_M.pdf: 1161319 bytes, checksum: c34f319b4252610a06e72d9b93740a89 (MD5) Previous issue date: 2005 / Resumo: Entende-se por superfícies mínimas aquelas cuja curvatura média é nula. Têm-se como exemplos clássicos o catenóide, o helicóide e a superfície de Scherk. Historicamente, elas estão relacionadas com minimização de área, porém quando realiza-se uma variação normal incluindo os bordos, a superfície original com curvatura média nula pode representar uma área localmente máxima. Em certos casos de variação com bordo fixo, tem-se realmente a minimização do funcional área. No espaço euclidiano tridimensional, o Teorema da Representação de Weierstrass expressa uma superfície mínima em termos de integrais envolvendo uma função holomorfa e uma meromorfa. A partir desta meromorfa pode-se deduzir a aplicação normal de Gauss. Conceitos como curvatura Gaussiana, curvatura total, superfícies completas e regularidade também são utilizados para deduzir propriedades das superfícies mínimas. Quando estudamos as superfícies mínimas para as quais o bordo consiste de duas circunferências disjuntas, os Teoremas de Enneper e Shiffman, o Princípio de Reflexão de Schwarz e a unicidade do Problema de Bjõrling são ferramentas importantes para a dedução das soluções, a saber, o catenóide e as superfícies de Riemann. Estas apresentam simetrias por reflexão a um plano e invariância por rotação de 180 graus em torno de uma reta. A função "P de Weierstrass" simétrica é de grande utilidade no estudo destas propriedades / Abstract: Minimal surfaces are known to be the ones with mean curvature zero. Classical exampIes are the catenoid, helicoid and the Scherk surface. Historically, they were associated with the property of minimizing area. However, they can even maximize it localIy for cases of normal variation which include the boundary. For fixed boundary, we shalI analyse when they realIy minimize the area functional. In the three-dimensional Euclidean space, the Weierstrass Representation Theorem expresses any minimal surface S by means of integraIs with a holomorphic and a meromorphic functions, usualIy denoted by f and g, respectively. The unitary normal N of S is fulIy determined by g. Concepts like "Gaussian curvature", "total curvature", "com pleteness" and "regularity" are also employed in order to read off some properties of minimal surfaces. Concerning the case for which the boundary of S consists of two disjoint circumferences, Enneper's and Shiffman's Theorems, The Schwarz's Reflection PrincipIe and the B6rling's Problem are fundamental tools to characterize the solutions, namely the catenoid and the Riemann's examples. AlI these are invariant by a reflectional symmetry in a plane, and also by a rotation of 180-degree around a straight line. The symmetric Weierstrass-Pfunction is very useful to deduce these properties / Mestrado / Matematica / Mestre em Matemática

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The Riemann Mapping Theorem is presented and proven in this essay. The theorem, first published 1851, is essential for the study of holomorphic functions on simply connected, proper subsets of C. / Uppsatsen presenterar och formulerar Riemanns avbildningssats. Satsen från 1851 är ett essentiellt resultat för studiet av holomorfa funktioner på enkelt sammanhängande, äkta delmängder av C.

Die asymptotische Entwicklung der Funktion \(Z(t)=e^{i\vartheta(t)}\zeta{(1/2+it)}\) für reelle \(t\to+\infty\) (dabei ist \(\vartheta(t)=\Im\log{\Gamma{(1/4+it/2)}}-(t\log{\pi})/2\) und \(\zeta{(1/2+it)}\) die Riemannsche Zetafunktion auf der kritischen Geraden $\Re{(s)}=1/2$ – heute allgemein als Riemann–Siegel–Formel bezeichnet – wird auf neue Weise mit Hilfe der Sattelpunktmethode aus der sogenannten Riemann–Siegel"–Integralformel hergeleitet. Die Formeln zur Berechnung der in der asymptotischen Reihe auftretenden Koeffizienten werden vereinfacht und für \(t \ge 200\) explizite Fehlerabschätzungen für die ersten 11 Partialsummen dieser Reihe angegeben. Der tabellarische Anhang enthält u. a. die exakte Darstellung der ersten 13 Koeffizienten der asymptotischen Reihe in der auf D. H. Lehmer zurückgehenden Form sowie die Potenzreihenentwicklungen und die Entwicklungen nach Tschebyscheffschen Polynomen 1. Art der ersten 11 Koeffizienten mit einer Genauigkeit von 50 Dezimalstellen.

This thesis will cover an elementary proof of the Riemann–Roch Theorem for planecurves. We will introduce the notions of divisors, which is a convenient way of com-puting multiplicities of rational function, then continuing by introducing differentials.Furthermore we will introduce the K-vector space L(D), consisting of rational func-tions which are controlled by a divisor D. This is followed by presenting some moreresults before we arrive at an elementary proof of the Riemann–Roch Theorem.

In this thesis we provide a body of knowledge that concerns Riemann zeta-function and its generalizations in a cohesive manner. In particular, we have studied and mentioned some recent results regarding Hurwitz and Lerch functions, as well as Dirichlet's L-function. We have also investigated some fundamental concepts related to these functions and their universality properties. In addition, we also discuss different formulations and approaches to the proof of the Prime Number Theorem and the Riemann Hypothesis. These two topics constitute the main theme of this thesis. For the Prime Number Theorem, we provide a thorough discussion that compares and contrasts Norbert Wiener's proof with that of Newman's short proof. We have also related them to Hadamard's and de la Vallee Poussin's original proofs written in 1896. As far as the Riemann Hypothesis is concerned, we discuss some recent results related to equivalent formulations of the Riemann Hypothesis as well as the Generalized Riemann Hypothesis.

The first part of this thesis deals with detonations in gaseous reactive mixtures. Various technological applications have been proposed involving detonations, particularly in the field of propulsion. However, it has been confirmed experimentally that detonations generally exhibit an unstable behaviour, leading to complicated flow structures. A thorough understanding of the evolution of detonation waves is needed before they can be used for propulsion purposes. Herein, we present the first detailed numerical study of three-dimensional structures in gaseous detonations. This study is based on a parallelized, unsplit, shock-capturing algorithm. We show that we can reproduce all types of detonations that have been observed experimentally. The advancements in the field of gaseous compressible reactive flows paved the way for the study of the significantly more complex phenomena that occur in the flow of two-phase, heterogeneous compressible reactive mixtures. In the second part of this thesis, we develop a new shock-capturing algorithm for the study of these flows. We first present a new numerical procedure for solving exactly the Riemann problem of compressible two-phase flow models containing non-conservative products. We then examine the accuracy and robustness of three known methods for the integration of the non-conservative products. The issue of existence and uniqueness of solutions to the Riemann problem is also discussed. Due to the ill-posedness of the Riemann problem of standard two-phase models, we present and analyze, in the third and last part of this work, a conservative approximation to reduced one-pressure one-velocity models for compressible two-phase flows that contain non-conservative products. Herein, we develop an exact Riemann solver for the proposed reduced model. Further, we investigate the structure of the steady two-phase detonation waves admitted by this model. Finally, we report on numerical simulations of the transmission of a purely gaseous detonation to heterogeneous mixtures. The effect of the solid particles on the structure of the resulting two-phase detonation is discussed in detail.

This paper is a study on some upper bounds of the Mertens function, which is often considered somewhat of a ``mysterious" function in mathematics and is closely related to the Riemann Hypothesis. We discuss some known bounds of the Mertens function, and also seek new bounds with the help of an automated conjecture-making program named CONJECTURING, which was created by C. Larson and N. Van Cleemput, and inspired by Fajtowicz's Dalmatian Heuristic. By utilizing this powerful program, we were able to form, validate, and disprove hypotheses regarding the Mertens function and how it is bounded.

L’algèbre de Witt a été intensivement étudiée. Elle est présente dans de nombreux domaines des Mathématiques. Cette thèse est l’étude de deux généralisations de l’algèbre de Witt: les algèbres de type Witt et les algèbres de Krichever-Novikov. Dans une première partie on s’intéresse aux structures Lie-admissibles sur les algèbres de type Witt. On donne toutes les structures troisième-puissance associatives et flexibles Lie-admissibles sur ces algèbres. De plus, on étudie les formes symplectiques qui induisent un produit symétrique gauche. Dans une seconde partie on étudie les algèbres automorphes. Partant d’une surface de Riemann compacte quelconque, on considère l’action d’un sous-groupe fini du groupe des automorphismes de la surface sur des algèbres d’origines géométriques comme les algèbres de Krichever-Novikov. Plus précisément nous faisons le lien entre la sous-algèbre des éléments invariants sur la surface et l’algèbre sur la surface quotient. La structure presque-gradue des algèbres de Krichever-Novikov induit une presque-graduation sur ces sous-algèbres de certaines algèbres de Krichever- Novikov / The Witt algebra has been intensively studied and arise in many research fields in Mathematics. We are interested in two generalizations of the Witt algebra: the Witt type algebras and the Krichever-Novikov algebras. In a first part we study the problem of finding Lie-admissible structures on Witt type algebras. We give all third-power associative Lie-admissible structures and flexible Lie-admissible structures on these algebras. Moreover we study the symplectic forms which induce a graded left-symmetric product. In the second part of the thesis we study the automorphic algebras. Starting from arbitrary compact Riemann surfaces we consider the action of finite subgroups of the automorphism group of the surface on certain geometrically defined Lie algebras as the Krichever-Novikov type algebras. More precisely, we relate for G a finite subgroup of automorphism acting on the Riemann surface, the invariance subalgebras living on the surface to the algebras on the quotient surface under the group action. The almost-graded Krichever-Novikov algebras structure on the quotient gives in this way a subalgebra of a certain Krichever-Novikov algebra (with almost-grading) on the original Riemann surface