Issued in English in 1937 as Thesis (Ph. D.)--Cincinnati. / From Annales scientifiques de l'Ecole normale supérieure. 3. sér., t. LVI, fasc. 1. Bibliography: p. 70.

No description available.

This thesis is primarily concerned in studying the relationship between different exponents of Diophantine approximation, which are quantities arising naturally in the study of rational approximation to a fixed n-tuple of real irrational numbers. As Khinchin observed, these exponents are not independent of each other, spurring interest in the study of the spectrum of a given family of exponents, which is the set of all possible values that can be taken by said family of exponents. Introduced in 2009-2013 by Schmidt and Summerer and completed by Roy in 2015, the parametric geometry of numbers provides strong tools with regards to the study of exponents of Diophantine approximation and their associated spectra by the introduction of combinatorial objects called n-systems. Roy proved the very surprising result that the study of spectra of exponents is equivalent to the study of certain quantities attached to n-systems. Thus, the study of rational approximation can be replaced by the study of n-systems when attempting to determine such spectra. Recently, Roy proved two new results for the case n=3, the first being that spectra are semi-algebraic sets, and the second being that spectra are stable under the minimum with respect to the product ordering. In this thesis, it is shown that both of these results do not hold in general for n>3, and examples are given. This thesis also provides non-trivial examples for n=4 where the spectra is stable under the minimum. An alternate and much simpler proof of a recent result of Marnat-Moshchevitin proving an important conjecture of Schmidt-Summerer is also given, relying only on the parametric geometry of numbers instead. Further, a conjecture which generalizes this result is also established, and some partial results are given towards its validity. Among these results, the simplest, but non-trivial, new case is also proven to be true. In a different vein, this thesis considers certain generalizations theta(q) of the classical theta q-series. We show under conditions on the coefficients of the series that theta(q) is neither rational nor quadratic irrational for each integer q>1.

This thesis contains four papers, where the first two are in the area of geometry of numbers, the third is about class group statistics and the fourth is about free path lengths. A general theme throughout the thesis is lattice points and convex bodies. In Paper A we give an asymptotic expression for the number of integer matrices with primitive row vectors and a given nonzero determinant, such that the Euclidean matrix norm is less than a given large number. We also investigate the density of matrices with primitive rows in the space of matrices with a given determinant, and determine its asymptotics for large determinants. In Paper B we prove a sharp bound for the remainder term of the number of lattice points inside a ball, when averaging over a compact set of (not necessarily unimodular) lattices, in dimensions two and three. We also prove that such a bound cannot hold if one averages over the space of all lattices. In Paper C, we give a conjectural asymptotic formula for the number of imaginary quadratic fields with class number h, for any odd h, and a conjectural asymptotic formula for the number of imaginary quadratic fields with class group isomorphic to G, for any finite abelian p-group G where p is an odd prime. In support of our conjectures we have computed these quantities, assuming the generalized Riemann hypothesis and with the aid of a supercomputer, for all odd h up to a million and all abelian p-groups of order up to a million, thus producing a large list of “missing class groups.” The numerical evidence matches quite well with our conjectures. In Paper D, we consider the distribution of free path lengths, or the distance between consecutive bounces of random particles in a rectangular box. If each particle travels a distance R, then, as R → ∞ the free path lengths coincides with the distribution of the length of the intersection of a random line with the box (for a natural ensemble of random lines) and we determine the mean value of the path lengths. Moreover, we give an explicit formula for the probability density function in dimension two and three. In dimension two we also consider a closely related model where each particle is allowed to bounce N times, as N → ∞, and give an explicit formula for its probability density function. / <p>QC 20151204</p>

Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico / Este trabalho à baseado no artigo Finiteness of the class group of a number field via lattice packings. Daremos aqui uma prova alternativa da finitude do grupo das classes de um corpo de nÃmeros de grau n. Ela à baseada apenas no fato de que a densidade de centro de um empacotamento reticulado n-dimensional à limitado fora do infinito. / This work is based on the article Finiteness of the class group of a number field via lattice packings. An alternative proof of the finiteness of the class group of a number field of the degree n is presented. It is based solely on the fact that the center density of an n-dimensional lattice packing is bounded away from infinity.

Orientadores: Sueli Irene Rodrigues Costa, Patricia Helena Araujo da Silva Nogueira / Dissertação (mestrado profissional) - Universidade Estadual de Campinas, Instituto de Matematica, Estatistica e Computação Cientifica / Made available in DSpace on 2018-08-15T04:07:16Z (GMT). No. of bitstreams: 1 Naves_LigiaRodriguesBernabe_M.pdf: 1248780 bytes, checksum: a87e22d1d349ffc57557fdb83454f7d3 (MD5) Previous issue date: 2009 / Resumo: Neste trabalho, estudamos a teoria de reticulados com foco na densidade de empacotamento, a qual possui várias aplicações e possibilita estabelecer interessantes conexões entre tópicos de álgebra linear, cálculo de várias variáveis e geometria discreta. No primeiro capítulo, introduzimos conceitos fundamentais sobre reticulados. No segundo capítulo, abordamos a densidade de empacotamentos esféricos e analisamos a importância e a dificuldade de se conhecer os empacotamentos mais densos. Discutimos também exemplos de reticulados com densidade máxima em suas dimensões. No terceiro capítulo, detalhamos a demonstração do teorema de Minkowski - Hlawka, que fornece um limitante inferior para a densidade de empacotamentos reticulados. Apresentamos também o problema dos fat struts, que tem origem em teoria de comunicação e que se relaciona com a busca de reticulados-projeção de densidade máxima / Abstract: This dissertation addresses the lattice theory with focus on packing density, which has many applications and allows to establish interesting connections between topics of linear algebra, calculus of several variables and discrete geometry. The first chapter is an introduction to the main concepts and properties of lattices. In the second chapter we discuss the sphere packing density problem, its importance and the difficulty in finding denser packings. Examples of lattices with maximum density are analyzed for lower dimensions. In the third chapter we detail the proof of the theorem of Min-kowski - Hlawka which provides a lower bound for lattice packing density of lattices in any dimension. We also present the problem of the fat struts which comes from communication theory and is related to the search for denser projection lattices / Mestrado / Geometria Topologia / Mestre em Matemática

Pour un n-uplet de nombres réels, vu comme un point de l'espace projectif, on définit pour chaqueindice d entre 0 et n-1 deux exposants d'approximation diophantienne (un ordinaire et un uniforme)qui mesurent l'approximabilité de celui-ci par des sous-espaces rationnels de dimension d dansl'espace projectif. Il se trouve que ces 2n exposants ne sont pas indépendants les uns des autres.Cette thèse s'inscrit dans l'étude du spectre de tout ou partie de ces exposants, qui a fait l'objet denombreux travaux récents. On utilise notamment les outils récents de la géométrie paramétriquedes nombres pour étudier le spectre des exposants uniforme, et on traite un cas pondéré endimension 2. / Given a n-tuple of real numbers, seen as a point in the projective space, one can define for eachindex d between 0 and n-1 two exponents of diophantine approximation (an ordinary and auniform) which measure the approximability of this n-tuple by rational subspaces of dimension d inthe projective space. These 2n exponents are not independant. This thesis is part of the study fromthe spectrum of all or part of these exponents, which have been much studied recently. We userecent tools coming from the parametric geometry of numbers to study the spectrum of the uniformexponents, and deal with a twisted case in dimension two.

Pour un réel ξ qui n’est pas algébrique de degré ≤ 2, on peut définir plusieurs exposants diophantiens qui mesurent la qualité d’approximation du vecteur (1, ξ, ξ² ) par des sous-espaces de ℝ³ définis sur ℚ de dimension donnée. Cette thèse s’inscrit dans l’étude de ces exposants diophantiens et des questions relatives à la détermination de leur spectre. En utilisant notamment les outils modernes de la géométrie paramétrique des nombres, nous construisons une nouvelle famille de réels – appelés nombres de type sturmien – et nous déterminons presque complètement le 3-système qui leur est associé. Comme conséquence, nous en déduisons la valeur de leurs exposants diophantiens et certaines informations sur les spectres. Nous considérons également le problème plus général de l’allure d’un 3-système associé à un vecteur de la forme (1, ξ, ξ ²), en formulant entre autres certaines contraintes qui n’existent pas pour un vecteur (1, ξ, η) quelconque, et en explicitant les liens qu’il entretient avec la suite des points minimaux associée à ξ. Sous certaines conditions de récurrence sur la suite des points minimaux nous montrons que nous retrouvons les 3-systèmes associés aux nombres de type sturmien. / Given a real number ξ which is not algebraic of degree ≤ 2 one may defineseveral diophantine exponents which measure how “well” the vector (1, ξ, ξ ²) can be approximated by subspaces of fixed dimension defined over ℚ. This thesis is part of the study of these diophantine exponents and their spectra. Using the parametric geometry of numbers, we construct a new family of numbers – called numbers of sturmian type – and we provide an almost complete description of the associated 3-system. As a consequence, we determine the value of the classical exponents for numbers of sturmian type, and we obtain new information on their joint spectra. We also take into consideration a more general problem consisting in describing a 3-system associated with a vector (1, ξ, ξ²). For instance we formulate special constraints which do not exist for a general vector (1, ξ, η) and we also clarify connections between a 3-system which represents ξ and the sequence of minimal points associated to ξ. Under a specific recurrence relation hypothesis on the sequence of minimal points, we show that the previous 3-system has the shape of a 3-system associated to a number of sturmian type.

No description available.