Sur les automorphismes analytiques des variétés hyperboliques

Results of H. Cartan about holomorphic automorphisms on bounded domains are generalized to the case of hyperbolic manifolds in the sense of Kobayashi. In this setting, we give an identity theorem together with its topological version. We show also that a sequence of automorphisms which converges uniformly on some nonempty open set, has a limit on the whole space which is an automorphism. At the end of the paper, conditions are given for the sequence of iterates of a self holomorphic map in order to be an automorphism.     

Un processus effectif de détermination des systoles pour les surfaces hyperboliques

We give an effective process to discribe explicitly the systols of an hyperbolic surface depending on his Fenchel-Nielsen coordinates.      

Groupes d’automorphismes polynomiaux du plan

We study the embeddings of lattices from simple Lie groups into the group of polynomial automorphisms of the affine plane and answer a question of Dekimpe concerning cristallographic polynomial groups of the plane.      

Un raffinement du caractère hilbertien du corps K(X)

Given an infinite field K. We will show that for the elements of a hilbertian set of K(X) associated to a family of polynomials with coefficients in K, the specialized polynomials remain also primitive knowing that the starting polynomials are it. This result refines the hilbertian character of the field K(X). Moreover, by an application of this result, one obtains an analog of the famous arithmetic progression theorem.     

Un théorème de représentation des solutions de viscosité d'une équation d'Hamilton–Jacobi–Bellman ergodique dégénérée sur le tore

We consider an ergodic Hamilton–Jacobi–Bellman equation coming from a stochastic control problem in which there are exactly k points where the dynamics vanishes and the Lagrangian is minimal. Under a stabilizability assumption, we state that the solutions of the ergodic equation are uniquely determined by their value on these k points, and that the set of solutions is sup-norm isometric to a non-empty closed convex set whose dimension is less or equal to k. To cite this article: M. Akian et al., C. R. Acad. Sci. Paris, Ser. I 346 (2008).     

Un problème aux limites mixte des surfaces minimales avec une multiple projection plane et le dessin optimal des escaliers tournants

One admires rotational staircases in classical buildings since centuries. In particular, we are fascinated and inspired by the beautiful winding staircase (please, regard the picture below) in the center of the recently constructed University Library of the Brandenburgian Technical University at Cottbus by the bureau of architects Herzog & de Meuron from Basel. The sophisticated mathematician directly recognizes this staircase being a rotational minimal surface – namely the well-known helicoid – with a multiply covering projection onto the plane, solving a semi-free boundary value problem. We now ask the question, in which class of surfaces this helicoid is uniquely determined. Furthermore, we examine in how far the boundary values can be perturbed such that neighboring surfaces still exist. Both questions being affirmatively answered, we receive the stability of this boundary value problem. Finally, we investigate that our surface realizes a global minimum of area in the class of all parametric minimal surfaces solving an adequate mixed boundary value problem. Here we study one-to-one harmonic mappings onto the universal covering of the plane. This is achieved on the basis of our joint investigations with Professor Stefan Hildebrandt from the University of Bonn. Since H. Catalan was the first to classify the helicoid among ruled minimal surfaces and J. Plateau contributed, besides his inspiring experiments with soap bubbles, also his name to our central problem, I would like to present this treatise in the French language. During the construction of our University Library I got acquainted to the responsible architect for this project from the bureau Herzog & de Meuron, Frau Christine Binswanger and would like to dedicate this work to her with great respect. In her home city of Basel, classical Analysis could originally be developed by members of the Bernoulli family and Leonhard Euler.     

Le rang du systeme lineaire des racines d'une algebre de lie rigide resoluble complexe

Adams and Conway have stated without proof a result which says, roughly speaking, that the representation ring R(G) of a compact, connected Lie group G is generated as a λ-ring by elements in 1-to-1 correspondence with the branches of the Dynkin diagram. In this note we present an elementary proof of this.     

Nombre de rotation presque sûr des endomorphismes du cercle affines par morceaux

We define the almost sure rotation number for some degree one endomorphisms over the circle. It is the rotation number for almost any point of the circle. We describe it for a particular family of expanding piecewise affine endomorphisms. We show that its dependance on the parameters is H?lder for any exposant 0 < α < 1 but in general not Lipschitz. In particular the set of parameters which give an irrational almost sure rotation number has a Hausdorff dimension equal to 1. Received: 16 July 2001     

Sur la forme des composantes connexes du complémentaire de la courbe brownienne plane

Résumé Nous nous proposons d'étudier la forme des petites composantes connexes du complémentaire de la trajectoire brownienne plane. Nous montrons l'existence d'une loi limite de cette forme. De plus, nous obtenons un théorème limite qui montre que la donnée de l'ensemble des composantes connexes correspondant à une seule trajectoire suffit pour décrire cette loi.

---

Summary We study the shape of the small connected components of the complement of a 2-dimensional Brownian path. We show the existence of an asymptotic law for this shape. Moreover, we prove a limit theorem that shows that the family of all the connected components of the complement of a single path contains all the information about this law.

     

Étude du cas rationnel de la théorie des formes linéaires de logarithmes

We establish new measures of linear independence of logarithms on commutative algebraic groups in the so-called rational case. More precisely, let k be a number field and v₀ be an arbitrary place of k. Let G be a commutative algebraic group defined over k and H be a connected algebraic subgroup of G. Denote by Lie(H) its Lie algebra at the origin. Let u∈Lie(G(Cv₀)) a logarithm of a point p∈G(k). Assuming (essentially) that p is not a torsion point modulo proper connected algebraic subgroups of G, we obtain lower bounds for the distance from u to Lie(H)k_⊗Cv₀. For the most part, they generalize the measures already known when G is a linear group. The main feature of these results is to provide a better dependence in the height loga of p, removing a polynomial term in logloga. The proof relies on sharp estimates of sizes of formal subschemes associated to H (in the sense of Bost) obtained from a lemma by Raynaud as well as an absolute Siegel lemma and, in the ultrametric case, a recent interpolation lemma by Roy.     

Un procédé de réduction de la diffusion numérique des schémas à différence de flux d'ordre un pour les systèmes hyperboliques non linéairesA process of reduction of the numerical diffusion of usual order one Flux Difference Schemes for nonlinear hyperbolic systems

We present a particular process of time integration which can be applied to any classical (approximate or exact) Riemann solver. Temporary reservoirs of “fluid” empty up when the CFL number of the corresponding characteristic wave reaches one. The resulting method is both conservative and consistent. When applied to first order methods the numerical diffusion may be very small, and even zero in particular cases. We eventually give numerical results in the case of perfect gas dynamics when using the Riemann solver developed by Collela and Glaz. To cite this article: F. Alouges et al., C. R. Acad. Sci. Paris, Ser. I 335 (2002) 627–632.     

Sur la répartition des entiers premiers à un entier sans petit facteur premier

Let Mk(q;h) be the kth moment of the number of integers coprime to q in an interval of length h centered on its mean . By comparison with the kth centered moment of the binomial distribution with parameters h and P, for which we show

μk(h,P)?(ck)^k/2(k+hP(1−P)⁾k/2,     

Problèmes linéaires dans le Compendy de la praticque des nombres de Barthélemy de Romans et Mathieu Préhoude (1471): Une approche nouvelle basée sur des sources proches du Liber abbaci de Léonard de Pise

The Compendy de la praticque des nombres (1471) is one of a number of commercial arithmetics produced in southern France during the medieval period. Its interest and originality rest in its treatment of problem-solving. The author of the text limited his treatment to an in-depth analysis of only a few types of problems, not treating particular cases but rather emphasizing general methods. The sources from which he drew were very close to the Liber abbaci of Leonardo Fibonacci and many of them were new to the southern French arithmetic tradition. Thus, the Compendy sheds new light on the transmission of arithmetic thought into Europe. Copyright 2000 Academic Press.Le Compendy de la praticque des nombres (1471) est un traité qui appartient au groupe des arithmétiques commerciales du Sud de la France. L'intérêt et l'originalité du texte résident dans la partie consacrée à la résolution de problèmes. L'auteur sélectionne quelques types de problèmes seulement, auxquels il consacre une longue étude, délaissant les cas particuliers pour privilégier les méthodes. Ce faisant, il utilise de nouvelles sources, proches du “Liber abbaci” de Léonard de Pise, étrangères aux autres arithmétiques françaises de la même famille. Le Compendy nous apporte ainsi un éclairage nouveau sur la transmission de l'algorisme. Copyright 2000 Academic Press.MSC subject classifications: 01A35; 01A40.