Itération de pliages de quadrilatères

Iteration of quadrilateral foldings. Starting with a quadrilateral q₀=(A₁,A₂,A₃,A₄) of ², one constructs a sequence of quadrilaterals q_n=(A_4n+1,...,A_4n+4) by iteration of foldings: q_n=₄°₃°₂°₁(q_n-1) where the folding _j replaces the vertex number j by its symmetric with respect to the opposite diagonal (see Fig. 1).We study the dynamical behavior of this sequence. In particular, we prove that:– The drift exists.– When none of the q_n is isometric to q₀, then the drift v is zero if and only if one has maxa_j+mina_j1/2a_j where a₁,...,a₄ are the sidelengths of q₀.– For Lebesgue almost all q₀ the sequence (q_n-nv)_n1 is dense on a bounded analytic curve with a center or an axis of symmetry. However, for Baire generic q₀, the sequence (q_n-nv)_n1 is unbounded (see Figs. 2 to 7).      

Un théorème de dualité

Sans résumé Herrn H. Hopf zum sechzigsten Geburtstag gewidmet     

Algèbres de Poisson et Algèbres de Lie Résolubles

Let 𝔤 be a solvable Lie algebra and Q an (ad 𝔤)-stable prime ideal of the symmetric algebra S(𝔤) of 𝔤. If E denotes the set of nonzero elements of S(𝔤)/Q which are eigenvectors for the adjoint action of 𝔤 on S(𝔤)/Q, then the localization (S(𝔤)/Q) _E has a natural structure of Poisson algebra. We study this algebra here.

Soient 𝔤 une algèbre de Lie résoluble et Q un idéal premier (ad 𝔤)-stable de l'algèbre symétrique S(𝔤) de 𝔤. Si E est l'ensemble des éléments non nuls de S(𝔤)/Q qui sont vecteurs propres pour l'action adjointe de 𝔤 dans S(𝔤)/Q, l'algèbre localisée (S(𝔤)/Q) _E a une structure naturelle d'algèbre de Poisson. On étudie ici cette algèbre.     

Un phénomène de concentration de genre

We show that the main part of the genus of the preimages of a projective line by a generic holomorphic endomorphism of goes to the support of the Green measure.

---

Résumé Nous montrons que le genre des préimages dune droite projective par un endomorphisme holomorphe générique de se concentre sur le support de la mesure de Green.A phenomenon of concentration of genus

---

---

Mathematics Subject Classification (2000): 32H50, 32U40, 32Q45     

Algèbres de Sobolev Généralisées

We examine the structure of a generalized Sobolev spaces. We also exhibit a class of locally uniformlyA-convex algebras, the unitization of which are not the same type.

     

Homogénéisation d'un problème de capillarité

We study the behavior of the height of a liquid contained in a vertical cylindrical tube where are immerged a periodic distribution (period ɛ) of cylindrical fibers with radius r < ɛ and whose material-liquid coefficient is λ. It is showed that the homogenized problem depends on the limit of λr/ɛ² as (ɛ, λ, r) → (0,0, 0). The second problem is when the border is made of two alternate periodic bands, the first of length r being incrusted in the second of length ɛ − r. Here, the homogenized problem depends on the limit of r/ɛ as (, r) → (0, 0). For this, we use epi-convergence techniques.     

Deux théorèmes de non-annulation de valeurs spéciales de fonctions L

In answer to questions recently raised by Merel [Mer], we prove two non-vanishing theorems for the central value of automorphic L-functions: let p be prime and let χ be a primitive character modulo p. Then for all p large enough 1. If χ is not quadratic and even, there exists a primitive weight 2 form f of level p with . 2. If χ is quadratic and even, then there exists a primitive weight 2 form f of level p with . Received: 12 March 2000 / Revised version: 26 September 2000     

Couplage de deux milieux hétérogènes multiplicateurs de neutrons

Summary The object of several studies has been the analyzing of heterogeneous mediums which multiply neutrons, and which cannot be assimilated in homogeneous ones.These studies always postulate that the isolated medium is infinite, and never permit treating a multimedium assembly. We resolve this problem by the intermediary of a simplified model, equivalent to the real one. Considering successively all the isolated medium and using the calculating method of heterogeneous mediums, the equivalent conditions are established. A safety calculation, for the exponential experiment of the EPUL, shows the use of this method.

---

---

Subside du Fonds National Suisse de la Recherche Scientifique, N° A 183.     

Déformations d'algèbres de Weyl

We study here the rigidity of algebras which are the completion of the Weyl algebra A or the universal enveloping algebra A′ of the Lie algebra of the 2k+1 dimensional Heisenberg group. We define a canonical completion A_* of A and of A and prove that A_* does not does not have any continuous, Sp(k)-invariant deformation. Finally, we study the cohomology group associated to the problem of deformation of A′ and its completion. The invariant cohomology is one dimensional.     

Convergence de modèles moléculaires vers des modèles de mécanique des milieux continus

The work we present here is focused on the justification of continuum mechanics as a natural asymptotic of molecular theories when the interatomic distance goes to zero. We give a sound theoretical ground to existing models, and derive and next study (apparently) new ones.     

Inégalités de Morse Holomorphes Singulières

We generalize Demailly’s holomorphic Morse inequalities to the case of a line bundle E equipped with a singular metric on an arbitrary compact complex manifold X. Our inequalities give an estimate of the cohomology groups with values in the tensor power E^⊗k twisted by the corresponding sequence of multiplier ideal sheaves introduced by Nadel. The allowed singularities are of the following type: the metric is locally given by a weight exp(−φ) where with holomorphic f_j. As a consequence, we obtain a necessary and sufficient analytic condition, invariant by bimeromorphism, for a manifold X to be Moishezon. This characterization improves a result given by Ji and Shiffman. We finally recall and improve some results of Kollár in order to show that the corresponding sufficient conditions obtained by Siu and Demailly in the smooth case are not necessary.      

Modèles semi-factoriels et modèles de Néron

Let S be the spectrum of a discrete valuation ring with function field K. Let X be a scheme over S. We will say that X is semi-factorial over S if any invertible sheaf on the generic fiber X _K can be extended to an invertible sheaf on X. Here we show that any proper geometrically normal scheme over K admits a proper, flat, normal and semi-factorial model over S. We also construct some semi-factorial compactifications of regular S-schemes, such as Néron models of abelian varieties. The semi-factoriality property for a scheme X/S corresponds to the Néron property of its Picard functor. In particular, one can recover the Néron model of the Picard variety ${{\rm Pic}_{X_K/K,{\rm red}}^0}$ of X _K from the Picard functor Pic _X/S , as in the known case of curves. This provides some information on the relative algebraic equivalence on the S-scheme X.     

Une Neutralisation Explicite de L'algèbre de Weyl Quantique Complétée

Soit p un nombre premier. Nous établissons l'existence de neutralisations de divers complétés de l'algèbre de Weyl quantique spécialisée en une racine de l'unité primitive d'ordre p (qui est “génériquement” une algèbre d'Azumaya) et donnons en particulier un énoncé de neutralisation explicite relevant celui construit en caractéristique p dans [3 Gros , M. , Le Stum , B. , Quiros , A. ( 2010 ). A Simpson correspondence in positive characteristic . Publ. RIMS Kyoto Univ. 46 : 1 – 35 .[Crossref], [Web of Science ®] , [Google Scholar]].

Let p be a prime number. We establish the existence of neutralizations of various completions of the quantum Weyl algebra specialized at a primitive root of unity of prime order p (which is “generically” an Azumaya algebra) and, in particular, we give a statement of explicit neutralization similar to the one built in characteristic p in [3 Gros , M. , Le Stum , B. , Quiros , A. ( 2010 ). A Simpson correspondence in positive characteristic . Publ. RIMS Kyoto Univ. 46 : 1 – 35 .[Crossref], [Web of Science ®] , [Google Scholar]].     

Une version feuilletée du théorème de translation de Brouwer

The Brouwers plane translation theorem asserts that for a fixed point free orientation preserving homeomorphism f of the plane, every point belongs to a proper topological imbedding C of R, disjoint from its image and separating $f(C)$ and $f^{-1}(C)$. Such a curve is called a Brouwer line. We prove that we can construct a foliation of the plane by Brouwer lines.      

Paramètres algébriques de groupes formels et critères d'isogénie

We generalise G. and D. Chudnovsky's isogeny criterion for elliptic curves over Q to the case of Abelian varieties of dimension g. The proof is bused on an explicit construction of algebraic parameters of their formal groups.