Tesi sul tema "Conjectures mathématiques"
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Vanden, Wyngaerd Anna. "Delta conjectures and Theta refinements". Doctoral thesis, Universite Libre de Bruxelles, 2020. https://dipot.ulb.ac.be/dspace/bitstream/2013/314077/4/toc.pdf.
Testo completoDoctorat en Sciences
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Cheukam, Ngouonou Jovial. "Apprentissage automatique de cartes d’invariants d’objets combinatoires avec une application pour la synthèse d’algorithmes de filtrage". Electronic Thesis or Diss., Ecole nationale supérieure Mines-Télécom Atlantique Bretagne Pays de la Loire, 2024. http://www.theses.fr/2024IMTA0418.
Testo completoTo improve the efficiency of solution methods for many combinatorial optimisation problems in our daily lives, we use constraints programming to automatically generate conjectures. These conjectures characterise combinatorial objects used to model these optimisation problems. These include graphs, trees, forests, partitions and Boolean sequences. Unlike the state of the art, the system, called Bound Seeker, that we have developed not only generates conjectures independently, but it also points to links between conjectures. Thus, it groups the conjectures in the form of bounds of the same variable characterising the same combinatorial object. This grouping is called a bounds map of the combinatorial object considered. Then, a study consisting of establishing links between generated maps is carried out. The goal of this study is to deepen knowledge on combinatorial objects and to develop the beginnings of automatic proofs of conjectures. Then, to show the consistency of the maps and the Bound Seeker, we develop some manual proofs of the conjectures discovered by the Bound Seeker. This allows us to demonstrate the usefulness of some new bound theorems that we have established. To illustrate one of its concrete applications, we introduce a method for semi-automatic generation of filtering algorithms that reduce the search space for solutions to a combinatorial optimisation problem. This reduction is made thanks to the new bound theorems that we established after having automatically selected them from the conjectures generated by the Bound Seeker. To show the effectiveness of this technique, we successfully apply it to the problem of developing balanced academic courses for students
Charles, François. "Cycles algébriques et cohomologie de certaines variétés projectives complexes". Phd thesis, Université Pierre et Marie Curie - Paris VI, 2010. http://tel.archives-ouvertes.fr/tel-00472932.
Testo completoPaperman, Charles. "Circuits booléens, prédicats modulaires et langages réguliers". Paris 7, 2014. http://www.theses.fr/2014PA077258.
Testo completoThe Straubing conjecture, stated in his book published in 1994, suggest that a regular language definable by a fragment of logic and equipped with an arbitrary numerical signature is definable using the same fragment of logic using only regular predicates. The considered fragments of logic are classed of formulas of monadic second order logic over finite words. This thesis is a contribution to the study of the Straubing conjecture. To prove such a conjecture, it seems necessary to obtain two results of two distinct types: 1. Algebraic characterizations of classes of regular languages defined by fragments of logics equipped with regular predicates, 2. Undefinability results of regular languages in fragments of logics equipped with arbitrary numerical predicates. The first part of this thesis is dedicated to the operation of adding regular predicates to a given fragment of logic, with a particular focus on modular predicates in the case where logical fragments have some algebraic structure. The second par of this thesis is dedicated to undefinability results with a particular focus on two-variable first order logic
Balzin, Eduard. "Les fibrations de Grothendieck et l’algèbre homotopique". Thesis, Nice, 2016. http://www.theses.fr/2016NICE4032/document.
Testo completoThis thesis is devoted to the study of families of categories equipped with a homotopical structure. The principal results comprising this work are:i. A generalisation of the Reedy model structure, which, in this work, is constructed for sections of a suitable family of model categories over a Reedy category. Unlike previous considerations, such as Hirschowitz-Simpson, we require as little as possible from the family, so that our result may be applied in situations when the transition functors in the family are non-linear in nature. ii. An extension of Segal formalism for algebraic structures to the setting of monoidal categories over an operator category in the sense of Barwick. We do this by treating monoidal structures using the language of Grothendieck opfibrations, and introduce derived sections of the latter using the simplicial replacements of Bousfield-Kan. Our Reedy structure result then permits to work with derived sections. iii. A proof of a certain homotopy descent result, which gives sufficient conditions on when an inverse image functor is an equivalence between suitable categories of derived sections. We show this result for functors which satisfy a technical ``Quillen Theorem A''-type property, called resolutions. One example of a resolution is given by a functor from the category of planar marked trees of Kontsevich-Soibelman, to the stratified fundamental groupoid of the Ran space of the $2$-disc. An application of the homotopy descent result to this functor gives us a new proof of Deligne conjecture, providing an alternative to the use of operads
Fuser, Alain. "Autour de la conjecture d'Alexandru". Nancy 1, 1997. http://www.theses.fr/1997NAN10289.
Testo completoViguié, Stéphane. "Contribution à l'étude de la conjecture de Gras et de la conjecture principale d'Iwasawa, par les systèmes d'Euler". Phd thesis, Université de Franche-Comté, 2011. http://tel.archives-ouvertes.fr/tel-00839919.
Testo completoHeistercamp, Muriel. "The Weinstein conjecture with multiplicities on spherizations". Doctoral thesis, Universite Libre de Bruxelles, 2011. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/209882.
Testo completoL'existence d'une orbite orbite fermée du flot de Reeb sur S fut annoncée par Weinstein dans sa conjecture en 1978. Indépendamment, Weinstein et Rabinowitz ont montré l'existence d'une orbite fermée sur les hypersurfaces de type étoilées dans l'espace réel de dimension 2n. Sous les hypothèses précédentes, l'existence d'une orbite fermée fut démontrée par Hofer et Viterbo. Dans le cas particulier du flot géodésique, l'existence de plusieurs orbites fermées fut notamment étudiée par Gromov, Paternain et Paternain-Petean. Dans cette thèse, ces résultats sont généralisés.
Les résultats principaux de cette thèse montrent que la structure topologique de la variété M implique, pour toute hypersurface étoilée fibre par fibre, l'existence de beaucoup d'orbites fermées du flot de Reeb. Plus précisément, une borne inférieure de la croissance du nombre d'orbites fermées du flot de Reeb en fonction de leur période est mise en évidence. /
Let M be a smooth closed manifold and denote by T*M the cotangent bundle over M endowed with its usual symplectic structure induced by the Liouville form. A hypersurface S of T*M is said to be fiberwise starshaped if for each point q in M the intersection Sq of S with the fiber at q bounds a domain starshaped with respect to the origin 0q in T*qM. There is a flow naturally associated to S, generated by the unique Reeb vector field R along S ,the Reeb flow.
The existence of one closed orbit was conjectured by Weinstein in 1978 in a more general setting. Independently, Weinstein and Rabinowitz established the existence of a closed orbit on star-like hypersurfaces in the 2n-dimensional real space. In our setting the Weinstein conjecture without the assumption was proved in 1988 by Hofer and Viterbo. The existence of many closed orbits has already been well studied in the special case of the geodesic flow, for example by Gromov, Paternain and Paternain-Petean. In this thesis we will generalize their results.
The main result of this thesis is to prove that the topological structure of $M$ forces, for all fiberwise starshaped hypersurfaces S, the existence of many closed orbits of the Reeb flow on S. More precisely, we shall give a lower bound of the growth rate of the number of closed Reeb-orbits in terms of their periods.
Doctorat en Sciences
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Wang, Zhengfang. "Equivalence singulière à la Morita et la cohomologie de Hochschild singulière". Thesis, Sorbonne Paris Cité, 2016. http://www.theses.fr/2016USPCC203/document.
Testo completoIn this thesis, we are concerned with some aspects of singular categories of unitalassociative k-algebras over a commutative ring k. First, we develop a Morita theory for singular categories. Analogous to the classical Morita theory, we propose a definition of singular equivalence of Morita type with level. This follows and generalizes a definition of stable equivalence of Morita type introduced by Michel Broué. A derived equivalence of standard type induces a singular equivalence of Morita type with level. Second, we study the Hom-space from A to A[i] in the singular category Dsg(AkAop) of the enveloping algebra AkAop, where A is an associative k-projective k-algebra and i is any integer. Recall that the i-th Hochschild cohomology group HHi(A,A) can be realized as the Hom-space from A to A[i] in the bounded derived category Db(A k Aop). From this motivation, we call HomDsg(AkAop)(A,A[i]) the i-th singular Hochschild cohomology group and denote this group by HHi sg(A,A). Analogous to the Hochschild cohomology ring HH_(A,A), we prove that there is a Gerstenhaber algebra structure on the singular Hochschild ring HH_sg(A,A) and provide an interpretation of the Lie bracket from the point of view of PROP theory. We also associate a cochain complex, which we call singular Hochschild cochain complex, C_sg(A,A) to the singular Hochschild cohomology. Thenwe study the higher algebraic structures (e.g. B1-algebra) on C_sg(A,A) and propose asingular version of the Deligne conjecture. Following Keller’s approach which was developed for derived equivalences, we establish the invariance of the Gerstenhaber algebra structure which we defined on the singular Hochschild cohomology under singular equivalence of Morita type with level. In this proof, we define the singular derived Picard group sgDPic(A) of an associative algebra A and develop what we call a singular infinitesimal deformation theory. Then we realize HH_sg(A,A) as the graded Lie algebra of the ‘graded algebraic group’ associated to sgDPic(A)
Brandin, Karen. "Autour d'une conjecture de Gross pour les corps de fonctions". Bordeaux 1, 2006. http://www.theses.fr/2006BOR13341.
Testo completoShi, Ruxi. "Étude sur la conjecture de Fuglede et les suites oscillantes". Thesis, Amiens, 2018. http://www.theses.fr/2018AMIE0026/document.
Testo completoIn this thesis, we solve Fuglede's conjecture on the field of p-adic numbers, and study some randomness and the oscillating properties of sequences related to Sarnak's conjecture. In the first part, we first prove Fuglede's conjecture for compact open sets in the field Q_p which states that a compact open set in Q_p is a spectral set if and only if it tiles Q_p by translation. It is also proved that a compact open set is a spectral set (or a tile) if and only if it is p-homogeneous. We characterize spectral sets in Z/p^n Z (p>1 prime, n>0 integer) by tiling property and also by homogeneity. Finally, we prove Fuglede's conjecture in Q_p without the assumption of compact open sets and also show that the spectral sets (or tiles) are the sets which differ by null sets from compact open sets. In the second part, we first give several equivalent definitions of oscillating sequences in terms of their disjointness from different dynamical systems on tori. Then we define Chowla property and Sarnak property for numerical sequences taking values 0 or complex numbers of modulus 1. We prove that Chowla property implies Sarnak property. It is also proved that for Lebesgue almost every b>1, the sequence (e^{2 pi b^n})_{n in N} shares Chowla property and consequently is orthogonal to all topological dynamical systems of zero entropy. We also discuss whether the samples of a given random sequence have almost surely Chowla property. Some dependent random sequences having almost surely Chowla property are constructed
Lagoutte, Aurélie. "Interactions entre les Cliques et les Stables dans un Graphe". Thesis, Lyon, École normale supérieure, 2015. http://www.theses.fr/2015ENSL1012/document.
Testo completoThis thesis is concerned with different types of interactions between cliques and stable sets, two very important objects in graph theory, as well as with the connections between these interactions. At first, we study the classical problem of graph coloring, which can be stated in terms of partioning the vertices of the graph into stable sets. We present a coloring result for graphs with no triangle and no induced cycle of even length at least six. Secondly, we study the Erdös-Hajnal property, which asserts that the maximum size of a clique or a stable set is polynomial (instead of logarithmic in random graphs). We prove that the property holds for graphs with no induced path on k vertices and its complement.Then, we study the Clique-Stable Set Separation, which is a less known problem. The question is about the order of magnitude of the number of cuts needed to separate all the cliques from all the stable sets. This notion was introduced by Yannakakis when he studied extended formulations of the stable set polytope in perfect graphs. He proved that a quasi-polynomial number of cuts is always enough, and he asked if a polynomial number of cuts could suffice. Göös has just given a negative answer, but the question is open for restricted classes of graphs, in particular for perfect graphs. We prove that a polynomial number of cuts is enough for random graphs, and in several hereditary classes. To this end, some tools developed in the study of the Erdös-Hajnal property appear to be very helpful. We also establish the equivalence between the Clique-Stable set Separation problem and two other statements: the generalized Alon-Saks-Seymour conjecture and the Stubborn Problem, a Constraint Satisfaction Problem
Chen, Ke. "Special subvarieties of mixed shimura varieties". Paris 11, 2009. http://www.theses.fr/2009PA112177.
Testo completoThis thesis studies the André-Oort conjecture for mixed Shimura varieties. The main result is: let M be a mixed Shimura variety defined by a mixed Shimura datum (P,Y), C a fixed Q-torus of P, and Z an arbitrary closed subvariety in M, then the set of maximal C-special subvarieties of M contained in Z is finite. The proof follows the strategy applied by L. Clozel, E. Ullmo, and A. Yafaev in the pure case, which relies on Ratner's theory on ergodic properties of unipotent flows on homogeneous spaces. Besides, a minoration on the degree of the Galois orbit of a special subvariety is proved in the mixed case, adapted from the pure case established by E. Ullmo and A. Yafaev. Finally, a relative version of the Manin-Mumford conjecture is proved in characteristic zero: let A be an abelian S-scheme of characteristic zero, then the Zariski closure of a sequence of torsion subschemes in A remains a finite union of torsion subschemes
Macho-Stadler, Marta. "Isomorphisme de Thom pour les feuilletages presque sans holonomie". Lyon 1, 1996. http://www.theses.fr/1996LYO10094.
Testo completoDarondeau, Lionel. "Sur la conjecture de Green-Griffiths logarithmique". Thesis, Paris 11, 2014. http://www.theses.fr/2014PA112134/document.
Testo completoThe topic of this memoir is the geometry of holomorphic entire curves with values in the complement of generic hypersurfaces of the complex projective space. The well-known conjectures of Kobayashi and of Green-Griffiths assert that for such hypersurfaces, having large degree, the images of these curves shall fulfill algebraic constraints. By adapting the jet techniques developed notably by Bloch, Green-Griffiths, Demailly, Siu, Diverio-Merker-Rousseau, in the case of curves with values in projective hypersurfaces (so-called compact case), we obtain the algebraic degeneracy of entire curves f : ℂ→Pⁿ∖Xd (so called logarithmic case), for generic hypersurfaces Xd in Pⁿ of degree d ≥ (5n)² nⁿ. As in the compact case, our proof essentially relies on the algebraic elimination of all derivatives in differential equations that are satisfied by every nonconstant entire curve. The existence of such differential equations is obtained thanks to the holomorphic Morse inequalities and a simplified variant of a residue formula firstly developed by Bérczi from the Atiyah-Bott equivariant localization formula. The effective lower bound d ≥ (5n)² nⁿ is obtained by radically simplifying a huge iterated residue computation. Next, the deformation of these differential equations by derivation along slanted vector fields, the existence of which is here generalized and clarified, allows us to generate sufficiently many new differential equations in order to realize the final algebraic elimination mentioned above
Chavli, Eirini. "The Broué-Malle-Rouquier conjecture for the exceptional groups of rank 2". Sorbonne Paris Cité, 2016. http://www.theses.fr/2016USPCC022.
Testo completoBetween 1994 and 1998, the work of M. Broué. G. Malle, and R. Rouquier generalized in a natural way the definition of the Hecke algebra associated to a finite Coxeter group, for the case of an arbitrary complex relleetion group. Attempting to also generalize the properties of the Coxeter case, they stated a number of conjectures concerning these Hecke algebras. One specific example of importance regarding those yet unsolved conjectures is the so-called BMR freeness conjecture. This conjecture is known to be true apart from 17 cases, that are almost aIl the exceptional groups of rank 2. These exceptional groups of rank 2 fall in to three familles : The tetrahedral, octahedral and icosahcdral family. We prove the validity of the BMR freeness conjecture for the exceptional groups belonging to the first Iwo families, using a case-by-case analysis and we give a vice description of the hasis, similar to the classical case of the finite Coxeter groups. We also give a new consequence of this conjecture, by obtaining the classification of irreducible representations of the braid group on 3 strands in dimension at most 5, recovering results of Tuba and Wenzl
Djament, Aurélien. "Représentations génériques des groupes linéaires : catégories de foncteurs en grassmaniennes, avec applications à la conjecture artinienne". Paris 13, 2006. http://www.theses.fr/2006PA132034.
Testo completoRaouj, Abdelaziz. "Sur la densité de certains ensembles de multiples : résolution d'une conjecture d'Erdös". Nancy 1, 1992. http://docnum.univ-lorraine.fr/public/SCD_T_1992_0120_RAOUJ.pdf.
Testo completoLazzarini, Laurent. "Courbes pseudo-holomorphes et transversalité : la conjecture d'Arnold pour les sous-variétés lagrangiennes fortement négatives". Nancy 1, 1999. http://www.theses.fr/1999NAN10202.
Testo completoThe main object of this work is to examine how in an almost complex manifold of any dimension a pseudo-holomorphie curve can be factorized through a somewhere injective curve, in order to get some smooth moduli space of curves. One first deals with the easy case of the closed curves, then with curves with boundary in a totally real submanifold. Contrary to a closed curve, a curve with boundary may be neither somewhere injective nor multi-covered. However it is possible to extract from its image another curve somewhere injective but still with boundary in the totally real submanifold. Moreover, if the initial curve is a disc, then the extracted disc can be 50 as weIl. As an application, one proves a special case of the Arnold conjecture for the intersection of a Lagrangian submanifold and its Hamiltonian isotopies in a symplectie manifold
Debouzy, Nathalie. "Nombres presque premiers jumeaux sous une conjecture d'Elliott-Halberstam". Thesis, Aix-Marseille, 2018. http://www.theses.fr/2018AIXM0188/document.
Testo completoWe improve Bombieri’s asymptotic sieve to localise the variables. As a consequence, we prove, under a Elliott-Halberstam conjecture, that there exists an infinity of twins almost prime. Those are prime numbers p such that for all ε > 0, p −2 is either a prime number or can be written as p1p2 where p1 and p2 are prime and p1 < Xε, and we give the explicit asymptotic. In addition to this main work, there are two other chapters: the first one gives an asymptotic of prime numbers p such p−2is either a prime number or a product of three primes without using a preliminary sieve and so a stronger conjecture was needed. Hence this part shows the strength of the preliminary sieve and presents a few detailed sommations, most of them involving the Möbius fonction, that could be useful. The second one presents an easy and explicit method to calculate an average order of multiplicative functions
Dejou, Gaëlle. "Conjecture de brumer-stark non abélienne". Phd thesis, Université Claude Bernard - Lyon I, 2011. http://tel.archives-ouvertes.fr/tel-00618624.
Testo completoPéringuey, Paul. "Conjecture d’Artin sur les racines primitives généralisées parmi les entiers avec peu de facteurs premiers". Electronic Thesis or Diss., Université de Lorraine, 2022. http://www.theses.fr/2022LORR0218.
Testo completoIn this thesis we are interested in a generalization of the notion of primitive root proposed by Carmichael: an integer a is a generalized primitive root modulo a positive integer n if it generates a subgroup of maximal size in “mathbb{Z}/nmathbb{Z}”. More precisely, we study an analogue of Artin's conjecture for primitive roots in this framework. Artin's conjecture states that the proportion of primes smaller than x, for which a given integer a is a primitive root, converges to a nonzero limit as long as a is neither -1 nor a square. This conjecture was proved conditionally on the generalized Riemann hypothesis for certain numbers fields by Hooley in 1967.By analogy with Artin's conjecture we count the number of elements of a subset of positive integers A smaller than x for which a given integer a is a generalized primitive root. The case where the set A is the set of all positive integers has already been treated by Li and Pomerance in various papers. In the first chapter of this thesis we introduce a characterization of generalized primitive roots modulo an integer n in terms of the prime factorization of n, and then we describe a heuristic approach to the problem. The second chapter is devoted to the case where the set A is the set of ell almost primes, i.e. the integers having at most ell prime factors. Using sieve methods, results from algebraic number theory, the Selberg-Delange method and some combinatorial arguments we prove, conditionally on the generalized Riemann hypothesis, results similar to those obtained by Hooley for the Artin conjecture. Moreover, we show unconditionally an upper bound for the proportion of almost primes for which a is a generalized primitive root. Finally, we show that in the special case where ell=2, a better error term can be obtained by replacing the Selberg-Delange method by the hyperbola method. In the third and last chapter we consider the case where A is the set of sifted “x^heta” integers, i.e. the integers having no prime factor smaller than “x^heta”, for 0
Viguié, Stéphane. "Contribution à l’étude de la conjecture de Gras et de la conjecture principale d’Iwasawa, par les systèmes d’Euler". Thesis, Besançon, 2011. http://www.theses.fr/2011BESA2026/document.
Testo completoThe goal of this work is to show how Euler systems allows us to compare, for some abelian extensions, the Galois module of global units modulo Stark units with the Galois module of ideal p-classes. We restricts ourselves to abelian extensions over a base field k which can be an imaginary quadratic field or a global field of positive characteristic. The Gras conjecture predicts that for all finite abelian extension K/k, all prime number p not dividing [K : k], and all irreducible and nontrivial Qp-character ψ of Gal (K/k), the ψ-part of the p-class group of K and the ψ-part of the group of global units modulo Stark units have the same cardinal. First we prove a weak form of the conjecture, and then we use Euler systems to extend the results obtained among others by Rubin, Xu et Zhao. Then we assume that k is an imaginary quadratic field, and we consider a special Zp-extension k∞ of k, where p is a prime number different from 2 and 3, decomposed in k. We prove that for all finite extension K∞ of k∞ abelian over k, and for all irreducible Cp-character χ of the torsion subgroup of Gal(K∞/k), the characteristic ideal of the χ-quotients of the module of p-classes and the characteristic ideal of the module of global units modulo Stark units are the same. It is one of the versions of the main conjecture in Iwasawa theory, which extends a result of Rubin and Bley. It is also a step for a further work, where we extend a result of Rubin on the two variables main conjecture
Fu, Lie. "Sous-structure de Hodge, anneaux de Chow et action de certains automorphismes". Paris 6, 2013. http://www.theses.fr/2013PA066299.
Testo completoMotion estimation is a major challenge in the field of image sequenceprocessing. The thesis is a study of the dynamics of geophysical flowsvisualized by satellite imagery. Satellite image sequences are currentlyunderused for the task of dynamics estimation. A good understanding ofgeophysical flows allows a better analysis and forecast of phenomena indomains such as oceanography and meteorology. Data assimilation provides anexcellent framework for achieving a compromise between heteorogenous data,especially numerical models and observations. Hence, in this thesis we set outto apply variational data assimilation methods, such as 4D-Var, to estimatemotion in image sequences. Asmajor drawbacks of applying 4D-Var are theconsiderable computation time and memory required, we define and use a modelreduction method in order to significantly decrease the necessary computationtime and memory. We then explore the possibilities that reduced models providefor motion estimation, particularly the possibility of strictly imposing someknown constraints on the computed solutions. Different kinds of reductions arediscussed, using a proper orthogonal decomposition, a sine basis fordivergence-free motion and a basis dedicated to a particular spatialdomain. In each case, results are presented on both synthetic and satelittedata
Ghazal, Salman. "Étude de la conjecture de Seymour sur le second voisinage". Phd thesis, Université Claude Bernard - Lyon I, 2011. http://tel.archives-ouvertes.fr/tel-00744560.
Testo completoMoussaoui, Ahmed. "Centre de Bernstein stable et conjecture d'Aubert-Baum-Plymen-Solleveld". Thesis, Paris 6, 2015. http://www.theses.fr/2015PA066108/document.
Testo completoThis thesis focus on links between the local Langlands correspondence and the Bernstein center. A framework was introduced by Vogan and developed by Haines : the stable Bernstein center. We start by extending the generalized Springer correspondence to the orthogonal group (which is disconnected). Then we state a conjecture about (complete) Langlands parameters of supercuspidal representations of a p-adic split group and we prove it for classical and linear groups thanks to the work of M\oe glin, Henniart and Harris and Taylor. Based on the work of Lusztig on generalized Springer correspondence, we define a cuspidal support map for complete Langlands parameters. Referring to some results of Heiermann, we get a Langlands parametrization of the smooth dual of classical groups. Moreover, we state "Galois" version of the Aubert-Baum-Plymen-Solleveld conjecture and we prove that with the previous results. It gives a new proof of the validity of the ABPS conjecture for classical groups and it provides explicit relations with Langlands correspondence. As a corrolary, we obtain the compatibility of the Langlands correspondence with parabolic induction for classical groups
Orr, Martin. "La conjecture d'André-Pink : orbites de Hecke et sous-variétés faiblement spéciales". Phd thesis, Université Paris Sud - Paris XI, 2013. http://tel.archives-ouvertes.fr/tel-00879010.
Testo completoMawfik, Nadia. "Effet du logiciel "geometric supposer" sur l'habileté à conjecturer et l'habileté à argumenter d'élèves-professeurs marocains". Master's thesis, Université Laval, 1987. http://hdl.handle.net/20.500.11794/29319.
Testo completoKuzzay, Denis. "Investigations on the relevance of Onsager's conjecture in real incompressible turbulence". Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLS405/document.
Testo completoThe zeroth law of turbulence states that fully developed turbulent incompressible flows dissipatetheir kinetic energy independently of the Reynolds number. Since its discovery by Taylor in 1935, thislaw has had many experimental and numerical confirmations, and is at the heart of our understandingof turbulence. In the following years, Taylor proposed a mechanism for the zeroth law, based onviscosity and the idea of a cascade of energy through scales. In 1949, Onsager realized that energydissipation could occur without the final assistance by viscosity at small scales if the velocity fieldbecomes sufficiently irregular, and conjectured the minimum regularity condition above which energyconservation is ensured in the absence of viscosity. In 2000, two french mathematicians, Jean Duchonand Raoul Robert, were able to derive the analytical expression for the inertial dissipation in termsof velocity increments, along with the corresponding energy balance. However, the relevance of theseideas for real turbulence has never been studied.In this thesis, we present the first tests of Onsager’s idea from experimental data, based on thework of Duchon and Robert. We enter the framework of von Kármán flows for which the regularity ofNavier-Stokes equations is unknown. We use particle image velocimetry measurements which provideus with the three components of the velocity field on a meridional plane, and allows for the computationof velocity increments at the resolution scale of our measurement set-up. In this work, we point out thenon-trivial character of turbulent flows at the Kolmogorov scale, where we observe irregular
Gardes, Marie-Line. "Étude de processus de recherche de chercheurs, élèves et étudiants, engagés dans la recherche d’un problème non résolu en théorie des nombres". Thesis, Lyon 1, 2013. http://www.theses.fr/2013LYO10231/document.
Testo completoOur thesis deals with the transposition of mathematician’s reserach activity in mathematical classroom, in the domain of number theory. Our research focuses on the study of a research process for researchers, pupils and students involved in the research of an unsolved problem: the Erdös-Straus conjecture. Our mathematical and epistemological analyses allow us to identify different aspects of the mathematician’s work and the elements for progress in his research. The notion of “gesture” is developed to describe, analyze and contextualize different research processes. This analysis reveals the potentiality of this problem to create a research situation in classroom, where pupils are in a position similar to the mathematician’s one. Didactical analyses are based on the construction of such a situation and its experimentation in laboratory. We study the research process of the students with the methodological tools developed in mathematical and epistemological analyses. This analysis shows several potentiality of this situation: a wealth of procedures implemented, effective work on the dialectical aspects of the mathematical research activity and implementation of experimental approach. The notion of “gesture” is relevant to consider the question of the transposition of mathematician’s work
Rousseau, Erwan. "Sur la conjecture de Kobayashi et l'hyperbolicité des hypersurfaces projectives en dimension 2 et 3". Phd thesis, Université de Bretagne occidentale - Brest, 2004. http://tel.archives-ouvertes.fr/tel-00007896.
Testo completoMoutot, Etienne. "Autour du problème du Domino - Structures combinatoires et outils algébriques". Thesis, Lyon, 2020. http://www.theses.fr/2020LYSEN027.
Testo completoGiven a finite set of square tiles, the domino problem is the question of whether is it possible ta tile the plane using these tiles.This problem is known to be undecidable in the planar case, and is strongly linked ta the question of the periodicity of the tiling.ln this thesis we look at this problem in two different ways: we look at the particular case of low complexity tilings and we generalize it to more general structures than the plane: groups.A tiling of the plane is sa id of low complexity if there are at most mn rectangles of size m x n appearing in it. Nivat conjectured in 1997 that any such tiling must be periodic, with the consequence that the domino problem would be decidable for low complexity tilings. Using algebraic tools introduced by Kari and Szabados, we prove a generalized version of Nivat's conjecture for a particular class of tilings (a subclass of what is called of algebraic subshifts). We also manage to prove that Nivat's conjecture holds for uniformly recurrent tilings, with the consequence that the domino problem is indeed decidable for low-complexity tilings.The domino problem can be formulated in the more general context of Cayley graphs of groups. ln this thesis, we develop new techniques allowing to relate the Cayley graph of some groups with graphs of substitutions on words.A first technique allows us to show that there exists bath strongly periodic and weakly-but-not strongly a periodic tilings of the Baumslag-Solitar groups BS(l,n).A second technique is used to show that the domino problem is undecidable for surface groups. Which provides yet another class of groups verifying the conjecture saying that the domino problem of a group is decidable if and only if the group is virtually free
Ancona, Giuseppe. "Décomposition du motif d'un schéma abélien universel". Paris 13, 2012. http://scbd-sto.univ-paris13.fr/intranet/edgalilee_th_2012_ancona.pdf.
Testo completoLet S = Sk(G, x) be a Shimura variety of PEL type and A the universal abelian scheme over S. Let ƒ : Ar → S be the fiber product of A over S. The relative cohomology Rⁱ ƒ*ℚ Ar is canonically identified with the image, via an additive functor, of an explicit representation Wi,r de G, in such a way that each decomposition of Wi,r into subrepresentations induces a decomposition of Rⁱ ƒ*ℚ Ar into subvariations of Hodge structures. Our main result is that every such decomposition lifts canonically to a decomposition of the motive of Ar in the category CHM(S)ℚ of relative Chow motives. For some PEL varieties, such as the Siegel one, this means that we lift to motives all decompositions of Rⁱ ƒ*ℚAr into subvariations of Hodge structures. We also obtain a refinement of the Hodge conjecture for abelian varieties which are generic amongst those which satisfy a certain moduli problem
Nguyen, thi bich Thuy. "Etude de certains ensembles singuliers associés à une application polynomiale". Thesis, Aix-Marseille, 2013. http://www.theses.fr/2013AIXM4054.
Testo completoThere are two parts in the present work. The first part concerns the asymptotic set of a polynomial mapping $F: C^n to C^n$. In the 90s, Zbigniew Jelonek showed that this set is a $(n-1)$ - (complex) dimensional singular variety. We give a method, called {it m'ethode des fa{c c}ons}, for stratifying this set. We obtain a Thom-Mather stratification. Moreover, there exists a Whitney stratification such that the set of possible fa{c c}ons is constant on every stratum. By using the fa{c c}ons, we give an algorithm for expliciting the asymptotic sets of a dominant quadratic polynomial mapping in three variables. As a result, we have a complete list of the asymptotic sets in this case. The second part concerns the set called Valette set $V_F$. In 2010, Anna and Guillaume Valette constructed a real pseudomanifold $V_F subset R^{2n + p}$, where $p > 0$, associated to a polynomial mapping $F: C^n to C^n$. In the case $n = 2$, they proved that if $F$ is a polynomial mapping with nowhere vanishing Jacobian, then $F$ is not proper if and only if the homology (or intersection homology) of $V_F$ is not trivial in dimension 2. We give a generalization of this result, in the case of a polynomial mapping $F : C^n to C^n$ with nowhere vanishing Jacobian. We give also a method for stratifying the set $V_F$. As applications, we have the stratifications of the set of asymptotic critical values of $F$ and the set of bifurcation points of $F$
Hillion, Erwan. "Analyse et géométrie dans les espaces métriques mesurés : inégalités de Borell-Brascamp-Lieb et conjecture de Olkin-Shepp". Toulouse 3, 2010. http://thesesups.ups-tlse.fr/1592/.
Testo completoThe work done during this PhD thesis is based on the theory of Ricci curvature bounds in measured length spaces, developed by Sturm, Lott and Villani, using deep results coming from the optimal transportation theory. In a first part, we study two families of functional inequalities, called Prékopa-Leindler and Borell-Brascamp-Lieb inequalities, and show that they allows us to give an alternate definition to Ricci curvature bounds, satisfying a "wishlist" similar to the one fulfilled by the Sturm-Lott- Villani condition CD(K,N). The second part is about a possible generalization of Sturm-Lott-Villani definition in a discrete setting. We emphasise the case of the translation of probability measures on a linear graph, and study the convexity of entropy along such a translation. The expression of this translation as a binomial convolution enlightens a conjecture stated by Olkin and Shepp about the entropy of sums of idependent Bernoulli random variables, for which we give a partial proof
Noël, Pierre-André. "Dynamiques stochastiques sur réseaux complexes". Thesis, Université Laval, 2012. http://www.theses.ulaval.ca/2012/29319/29319.pdf.
Testo completoThe goal of this thesis is to develop and study mathematical models reproducing the behaviour of systems composed of numerous elements whose interactions make a complex network structure. The body of the document is divided in three parts; an introductory chapter and a recapitulative conclusion complete the thesis. Part I pertains to a specific dynamics (susceptible-infectious-removed propagation, SIR) on a class of networks that is also specific (configuration model). This problem has already been studied, among other ways, as a branching process in the infinite system size limit, providing a probabilistic solution for the final state of this stochastic process. The principal original contribution of part I consists of modifying this model in order to introduce finite-size effects and to allow the study of its (discrete) time evolution while preserving the probabilistic nature of the solution. Part II, containing the principal contributions of this thesis, is interested in the general problem of stochastic processes on complex networks. The state of the system (including the interaction structure) is partially represented through motifs, then the (continuous) time evolution is studied with a Markov process. Although the state is only partially represented, satisfactory results are often possible. In the particular case of the problem studied in part I, the results are exact. The approach turns out to be very general, and simple approximation methods allow one to obtain a solution for cases of considerable complexity. Part III searches for a closed form exact analytical solution to the the model developed in part II for the problem initially studied in part I. The system is re-expressed in terms of operators and different relations are used in an attempt to solve it. Despite the failure of this enterprise, some results deserve mention, notably a generalization of Sack's relationship, a special case of the Zassenhaus relationship.
Gao, Ziyang. "The mixed Ax-Lindemann theorem and its applications to the Zilber-Pink conjecture". Thesis, Paris 11, 2014. http://www.theses.fr/2014PA112347/document.
Testo completoThe Zilber-Pink conjecture is a diophantine conjecture concerning unlikely intersections in mixed Shimura varieties. It is a common generalization of the André-Oort conjecture and the Mordell-Lang conjecture. This dissertation is aimed to study the Zilber-Pink conjecture. More concretely, we will study the André-Oort conjecture, which predicts that a subvariety of a mixed Shimura variety having dense intersection with the set of special points is special, and the André-Pink-Zannier conjecture which predicts that a subvariety of a mixed Shimura variety having dense intersection with a generalized Hecke orbit is weakly special. The latter conjecture generalizes the Mordell-Lang conjecture as explained by Pink.In the Pila-Zannier method, a key point to study the Zilber-Pink conjec- ture is to prove the Ax-Lindemann theorem, which is a generalization of the functional analogue of the classical Lindemann-Weierstrass theorem. One of the main results of this dissertation is to prove the Ax-Lindemann theorem in its most general form, i.e. the mixed Ax-Lindemann theorem. This generalizes results of Pila, Pila-Tsimerman, Ullmo-Yafaev and Klingler-Ullmo-Yafaev concerning the Ax-Lindemann theorem for pure Shimura varieties.Another main result of this dissertation is to prove the André-Oort conjecture for a large class of mixed Shimura varieties: unconditionally for any mixed Shimura variety whose pure part is a subvariety of AN6 (e.g. products of universal families of abelian varieties of dimension 6 and the Poincaré bundle over A6) and under GRH for all mixed Shimura varieties of abelian type. This generalizes existing theorems of Klinger-Ullmo-Yafaev, Pila, Pila-Tsimerman and Ullmo concerning pure Shimura varieties.As for the André-Pink-Zannier conjecture, we prove several cases when the ambient mixed Shimura variety is the universal family of abelian varieties. First we prove the overlap of André-Oort and André-Pink-Zannier, i.e. we study the generalized Hecke orbit of a special point. This generalizes results of Edixhoven-Yafaev and Klingler-Ullmo-Yafaev for Ag. Secondly we prove the conjecture in the following case: a subvariety of an abelian scheme over a curve is weakly special if its intersection with the generalized Hecke orbit of a torsion point of a non CM fiber is Zariski dense. Finally for the generalized Hecke orbit of an arbitrary algebraic point, we prove the conjecture for curves. These generalize existing results of Habegger-Pila and Orr for Ag.In all these proofs, the o-minimal theory, in particular the Pila-Wilkie counting theorems, plays an important role
Merlin, Louis. "Entropie minimale des espaces localement symétriques". Thesis, Bordeaux, 2014. http://www.theses.fr/2014BORD0110/document.
Testo completoIn this thesis we give an overview of the volume entropy rigidity problem. A conjecture by Gromov and Katok states that, on a locally symmetric space (M; g0), the symmetric metric g0 has minimal volume entropy among metrices with the same total volume. The text is self-contained, assuming a basic knowledge in differential geometry. Therefore we discuss in the first chapter some background material used in the sequel. The case of compact quotients of H2 _ H2 was unknown before this work ; we give a fully detailled proof. The key-point is to build a calibrating form as in [BCG95]. As a by-product, we present some applications provided by the proof of the volume entropy rigidity conjecture. We conclude by an informal section explaining the motivations of the problem to a non-mathematical reader
Fu, Lie. "Sous-structures de Hodge, anneaux de Chow et action de certains automorphismes". Phd thesis, Ecole Normale Supérieure de Paris - ENS Paris, 2013. http://tel.archives-ouvertes.fr/tel-01001733.
Testo completoNguyen, Huu Kien. "La rationalité uniforme de la série Poincaré de relations d'équivalence p-adiques et la conjecture d'Igusa sur des sommes exponentielles". Thesis, Lille 1, 2018. http://www.theses.fr/2018LIL1I020/document.
Testo completoThe results in the rationality of Poincaré series associated with definable family of equivalence relations over valued fields was researched by Denef. This problem has relation with the existence of elimination of imaginaries theorem for theories of valued fields (see the result of Hrushovski, Martin and Rideau). Motivic integration theory was born helps us to show the uniform dependence of the rationality of Poincaré series on p-adic local fields. In the chapter 1 of this thesis, I extend the result on p-uniform rationality of Poincaré series associated with definable family of equivalence relations in some theories of valued field in which elimination of imaginaries has not been proved yet, for example theories on analytic structures. My method is that I extend the motivic integration theory for constructible motivic functions in two papers of Cluckers and Loeser to rational constructible motivic functions. Another classical problem of number theory is estimation of exponential sums. Exponential sums modulo pm was studied by Igusa, and for a fixed prime p, he gave a deep relation between estimation of exponential sums modulo pm and poles of Igusa local zeta function. Igusa also showed that a uniform estimation in p and m of exponential sums modulo pm could give an Poisson summation formula of Siegel-Weil type. By this motivation, many researches tried to give the best uniform upper bound of exponential sums modulo pm. In the chapters 2, 3, 4, we will try to obtain some uniform versions for upper bound of exponential sums modulo pm given by log-canonical threshold or Newton polyhedron due to Igusa's, Denef-Sperber's and Cluckers-Veys's conjectures
Rechtman, Ana. "Pièges dans la théorie des feuilletages : exemples et contre-exemples". Phd thesis, Ecole normale supérieure de lyon - ENS LYON, 2009. http://tel.archives-ouvertes.fr/tel-00361633.
Testo completoDans le premier chapitre nous abordons la première question. On dit qu'un champ de vecteurs non singulier est géodésible s'il existe une métrique riemannienne sur la variété ambiante pour laquelle toutes les orbites sont des géodésiques. Soit X un tel champ de vecteurs sur une variété fermée de dimension trois. Supposons que la variété est difféomorphe à la sphère ou son deuxième groupe d'homotopie est non trivial. Pour ces variétés, on montre que si X est analytique réel ou s'il préserve une forme volume, il possède une orbite périodique.
Le deuxième chapitre est dédié à la seconde question. En 1983, R. Brooks avait annoncé qu'un feuilletage dont presque toutes les feuilles sont Folner est moyennable. A l'aide d'un piège, on va construire un contre-exemple à cette affirmation, c'est-à-dire un feuilletage non moyennable dont toutes les feuilles sont Folner.
Nous cherchons ensuite des conditions suffisantes sur le feuilletage pour que l'énoncé de R. Brooks soit valable. Comme suggéré par V. A. Kaimanovich, une possibilité est supposer que le feuilletage soit minimal. On montre que cette hypothèse est suffisante en utilisant un théorème de D. Cass que décrit les feuilles minimales.
Motte, François. "De la géométrie à l’arithmétique en théorie inverse de Galois". Thesis, Lille 1, 2019. http://www.theses.fr/2019LIL1I049/document.
Testo completoWe contribute to the Malle conjecture on the number of finite Galois extensions E of some number field K of Galois group G and of discriminant of norm bounded by y. We establish a lower bound for every group G and every number field K containing a certain number field K'. To achieve this goal, we start from a regular Galois extension F/K(T) that we specialize. We prove a strong version of the Hilbert Irreducibility Theorem which counts the number of specialized extensions and not only the specialization points. We can also prescribe the local behaviour of the specialized extensions at some primes. Consequently, we deduce new results on the local-global Grunwald problem, in particular for some non-solvable groups. To reach our goals, we prove some results in diophantine geometry about the number of integral points on an algebraic curve
Fonseca, Tiago. "Matrices à signes alternants, boucles denses et partitions planes". Phd thesis, Université Pierre et Marie Curie - Paris VI, 2010. http://tel.archives-ouvertes.fr/tel-00521884.
Testo completoKebbab, Eric Franck Idir. "Aspects géométriques des principes locaux-globaux dans la théorie abstraite des formes quadratiques". Phd thesis, Université Pierre et Marie Curie - Paris VI, 2014. http://tel.archives-ouvertes.fr/tel-00990237.
Testo completoMüllner, Clemens. "Exponential sum estimates and Fourier analytic methods for digitally based dynamical systems". Thesis, Aix-Marseille, 2017. http://www.theses.fr/2017AIXM0042/document.
Testo completoThe present dissertation was inspired by two conjectures, one by Gelfond and one of Sarnak.In 1968 Gelfond proved that the sum of digits modulo m is asymptotically equally distributed along arithmetic progressions.Furthermore, he stated three problems which are nowadays called Gelfond problems.The second and third questions are concerned with the sum of digits of prime numbers and polynomial subsequences.Mauduit and Rivat were able to solve these problems for primes and squares in 2010 and 2009 respectively.Drmota, Mauduit and Rivat generalized the result concerning the sequence of the sum of digits of squares.They showed that each block appears asymptotically equally frequently.Sarnak conjectured in 2010 that the Mobius function does not correlate with deterministic functions.This dissertation deals with the distribution of automatic sequences along special subsequences and other properties of automatic sequences.A main result of this thesis is that all automatic sequences satisfy the Sarnak conjecture.Through a slightly modified approach, we also deal with the distribution of automatic sequences along the subsequence of primes.In the course of the treatment of general automatic sequences, a new structure for deterministic finite automata is developed,which allows a new view for automata or automatic sequences.We extend the result of Drmota, Mauduit and Rivat to digital sequences.This is also a generalization of the third Gelfond problem
Weiss, Nicolas. "Cohomologie de Gl2(Z[i,1/2]) à coefficients dans F2". Strasbourg 1, 2007. https://publication-theses.unistra.fr/public/theses_doctorat/2007/WEISS_Nicolas_2007.pdf.
Testo completoThe aim of this Phd thesis was to compute H*(BGL_2(Z[i,1/2]),F_2). This cohomology ring appears in a certain version of the conjecture of Lichtenbaum and Quillen, asserting that the cohomology modulo 2 of the classifying space of a general linear group over Z[1/2] should be detected by the cohomology of its subgroup of diagonal matrices. The original idea was to show that this conjecture fails in the special case of the general linear group of rank 4 over Z[1/2], and the cohomology of BGL_2(Z[i,1/2]) should have been the main argument. By computing H*(BGL_2(Z[i,1/2]),F_2), we proved that the conjecture is true in the case of GL_2(Z[i,1/2]). The calculation of H*(BGL_2(Z[i,1/2]),F_2) depends on the analysis of a certain space Z on which PSL_2(Z[i]) acts in a good way, and the as well as on calculation of H*(BPSL_2(Z[i]),F_2) and H*(BGo,F_2) where Go is a suitable subgroup of PSL_2(Z[i]) such that PSL_2(Z[i,1/2]) is isomorphic to the amalgamated sum PSL_2(Z[i])*_Go PSL_2(Z[i])
Abdelaziz, Youssef. "Diagonals of rational functions in physics". Thesis, Sorbonne université, 2020. http://www.theses.fr/2020SORUS012.
Testo completoWe study integer coefficient series that are solution of linear differential equations. We focus on diagonals of rational functions related to theoretical physics and enumerative combinatorics. These diagonals correspond to hypergeometric functions or Heun functions. These hypergeometric and Heun functions, are obtained using the method of creative telescoping. We show that these hypergeometric and Heun functions are in fact modular forms, or squares of modular forms, and in some cases derivatives of modular forms. Using algebraic geometry, we were able to understand some of the reasons behind the emergence of these functions, in the context of diagonals of rational functions. The creative telescoping method also allowed us also to understand better the validity of the conjecture advanced by Christol in the 80's. In particular, we were able to show several potential counter-examples to this conjecture corresponded in fact to diagonals of rational functions
Gardes, Marie-Line. "Étude de processus de recherche de chercheurs, élèves et étudiants, engagés dans la recherche d'un problème non résolu en théorie des nombres". Phd thesis, Université Claude Bernard - Lyon I, 2013. http://tel.archives-ouvertes.fr/tel-00948332.
Testo completoWang, Juanyong. "Positivity of direct images and projective varieties with nonnegative curvature". Thesis, Institut polytechnique de Paris, 2020. http://www.theses.fr/2020IPPAX048.
Testo completoThe birational classification of algebraic varieties is a central problem in algebraic geometry. Recently great progress has been made towards the establishment of the MMP and the Abundance and by these works, smooth (or mildly singular) projective varieties can be birationally divided into two categories: 1. varieties with pseudoeffective canonical divisor, which are shown to reach a minimal model under the MMP; 2. uniruled varieties, which are covered by rational curves. In this thesis refined studies of these two categories of varieties are carried out respectively, by following the philosophy of studying the canonical fibrations associated to them.For any variety X in the first category, the most important canonical fibration associated to X is the Iitaka-Kodaira fibration whose base variety is of dimension equal to the Kodaira dimension of X. This thesis tacles an important corollary of the Abundance conjecture, namely, the Iitaka conjecture C_{n,m}, which states the supadditivity of the Kodaira dimension with respect to algebraic fibre spaces. In this thesis the Kähler version of C_{n,m} is proved under the assumption that the base variety of the fibre space is a complex torus by further developping the positivity theorem of direct images and the pluricanonical version of the Green-Lazarsfeld-Simpson type theorem on cohomology jumping loci. This generalizes the main result of Cao-Păun (2017).As for varieties in the second category, one studies the Albanese map and the MRC fibration, instead of the Iitaka-Kodaira fibration. A philosophy in this investigation is that when the tangent bundle or the anticanonical divisor admits certain positivity, the aforementioned two fibrations of the variety should have a rigid structure. In this thesis I study in this thesis the structure of (mildly singular) projective varieties with nef anticanonical divisor. By again applying the positivity of direct images and by applying results from the foliation theory, I manage to prove that the Albanese map of such variety is a locally constant fibration and that if its smooth locus is simply connected then the MRC fibration induces a splitting into a product. These generalize the corresponding results for smooth projective varieties in Cao (2019) and Cao-Höring (2019)
Hu, Yining. "Quelques Résultats Arithmétiques Impliquant des Suites Engendrées par Automates". Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066333.
Testo completoThis thesis comprises one part concerning the union-closed sets conjecture and four other chapters dedicated to subjects related to automatic sequences. In the first part, we give a sufficient condition for a weaker version of the conjecture ($\varepsilon$-union closed sets conjecture) to hold. We also give an upper bound of the minimal maximal frequency for a family of size $n$. In Chapter 3 we prove that the coefficient extraction formula for algebraic series known for fields of characteristic $0$ is a consequence of a theorem of Furstenberg that says certains algebraic series can be written as the diagonals of a rational fractions in two variables. As the theorem is true for all fields, so is the formula. In Chapter 4 we give a generalization of the result of J.-P. Allouche and J. Shallit concerning certain infinite products and block-counting functions. In Chapter 5 we give an explicit construction based on $p$-adic valuation of an infinite word with subword complexity $\Theta(n^t)$. In Chapter 6 we give a new proof of the transcendence of the power series $L(1,\chi_s)/\Pi$, where $L$ is an analogue in positive characteristics of Dirichlet $L$ functions defined by D. Goss and $\Pi$ the analogue of $\pi$ defined by L. Carlitz