Utilisation des modules de Drinfeld en cryptologie

We present in this Note a new and efficient public-key cryptosystem based on Drinfeld modules. The details will appear elsewhere. To cite this article: R. Gillard et al., C. R. Acad. Sci. Paris, Ser. I 336 (2003).     

Braids on surfaces and finite type invariants

We prove that there is no functorial universal finite type invariant for braids in Σ×I if the genus of Σ is positive. To cite this article: P. Bellingeri, L. Funar, C. R. Acad. Sci. Paris, Ser. I 338 (2004).     

Explicit Plancherel formula for the p-adic group GL(n)

We provide an explicit Plancherel formula for the p-adic group GL(n). We determine explicitly the Bernstein decomposition of Plancherel measure, including all numerical constants. We also prove a transfer-of-measure formula for GL(n). To cite this article: A.-M. Aubert, R. Plymen, C. R. Acad. Sci. Paris, Ser. I 338 (2004).     

Test d'adéquation en régression non-linéaire,cas des fonctions monotones

We propose a goodness-of-fit test for monotonous nonlinear regression models. The test is based on an adaptation, to the regression context, of the smooth test paradigm of Neyman (1937) for testing the distribution of a sample. We complete his approach with a data-driven criterion for the test's parameters. To cite this article: B. Fontez, G.R. Ducharme, C. R. Acad. Sci. Paris, Ser. I 338 (2004).     

Comment établir des conditions nécessaires d'optimalité dans les problèmes de contrôle dont certains arguments sont déviés ?

We give a general idea to state necessary optimality conditions for problems of variational calculus or optimal control problems with deviating arguments. To cite this article: L. Samassi, R. Tahraoui, C. R. Acad. Sci. Paris, Ser. I 338 (2004).     

On bounds for total absolute curvature of surfaces in hyperbolic 3-space

We construct examples of surfaces in hyperbolic space which do not satisfy the Chern–Lashof inequality (which holds for immersed surfaces in Euclidean space). To cite this article: R. Langevin, G. Solanes, C. R. Acad. Sci. Paris, Ser. I 336 (2003).     

On the contact boundaries of normal surface singularities

The abstract boundary M of a normal complex-analytic surface singularity is canonically equipped with a contact structure. We show that if M is a rational homology sphere, then this contact structure is uniquely determined by the topological type of M. An essential tool is the notion of open book carrying a contact structure, defined by E. Giroux. To cite this article: C. Caubel, P. Popescu-Pampu, C. R. Acad. Sci. Paris, Ser. I 339 (2004).     

Actions moyennables et fonctions harmoniquesAmeanable actions and harmonic functions

We prove that the action of a countable discrete group on a locally compact invariant space of minimal harmonic functions is ameanable. To cite this article: P. Biane, E. Germain, C. R. Acad. Sci. Paris, Ser. I 334 (2002) 355–358.     

Weak convergence results for inhomogeneous rotating fluid equations

We consider the equations governing incompressible, viscous fluids in three space dimensions, rotating around an inhomogeneous vector B(x): this is a generalization of the usual rotating fluid model (where B is constant). We prove the weak convergence of Leray-type solutions towards a vector field which satisfies the usual 2D Navier–Stokes equation in the regions of space where B is constant, with Dirichlet boundary conditions, and a heat–type equation elsewhere. The method of proof uses weak compactness arguments. To cite this article: I. Gallagher, L. Saint-Raymond, C. R. Acad. Sci. Paris, Ser. I 336 (2003).     

The extended mapping class group is generated by 3 symmetries

We prove that for g?1 the extended mapping class group is generated by three orientation reversing involutions. To cite this article: M. Stukow, C. R. Acad. Sci. Paris, Ser. I 338 (2004).     

Basis conversions among univariate polynomial representations

In this Note we provide a family of conversion algorithms relating Bernstein polynomials, monomials and the classical families of orthogonal polynomials, such as Jacobi, Gegenbauer, Legendre, Chebyshev, Laguerre and Hermite polynomials. To cite this article: R. Barrio, J.M. Peña, C. R. Acad. Sci. Paris, Ser. I 339 (2004).     

A simple proof of an inequality of Bourgain,Brezis and Mironescu

A simpler proof of a recent inequality of Bourgain, Brezis and Mironescu is given. To cite this article: J. Van Schaftingen, C. R. Acad. Sci. Paris, Ser. I 338 (2004).     

Sur la forme de Seifert entière des germes de courbe plane à deux branches

Two plane curve germs with two branches, which are isomeric, are shown to have isomorphic integral Seifert forms. The weight filtration on the integral homology of the Milnor fiber is the key ingredient of the proof. To cite this article: P. du Bois, C. R. Acad. Sci. Paris, Ser. I 336 (2003).     

Dynamical shape gradient for the Navier–Stokes system

This Note deals with the sensitivity analysis of a newtonian incompressible fluid driven by the Navier–Stokes equations with respect to the dynamic of the fluid domain boundary. The structure of the gradient with respect to the velocity of the domain for a given cost function is established. This result is obtained using new shape derivation tools for Eulerian functionals and the Min–Max derivation principle. To cite this article: R. Dziri et al., C. R. Acad. Sci. Paris, Ser. I 338 (2004).     

Modélisation de structures électromagnétiques périodiques – matériaux bianisotropes avec mémoire

In this Note we propose a rigorous justification of the limit constitutive law of a periodic bi-anisotropic electromagnetic structure with memory. This study is based on the periodic unfolding method, introduced by D. Cioranescu, A. Damlamian and G. Griso, and is applied on the time domain and on the frequency domain. To cite this article: A. Bossavit et al., C. R. Acad. Sci. Paris, Ser. I 338 (2004).     

A null series with small anti-analytic part

We show that it is possible for an L² function on the circle, which is a sum of an almost everywhere convergent series of exponentials with positive frequencies, to not belong to the Hardy space H². A consequence in the uniqueness theory is obtained. To cite this article: G. Kozma, A. Olevskiǐ, C. R. Acad. Sci. Paris, Ser. I 336 (2003).     

Estimates for L1-vector fields

A simple proof of an integral inequality involving L¹-vector fields is provided. This gives a short proof of estimates of Bourgain and Brezis for elliptic and div–curl systems. To cite this article: J. Van Schaftingen, C. R. Acad. Sci. Paris, Ser. I 339 (2004).     

Sur les opérateurs précompacts positifs

We characterize complete Hausdorff locally convex solid lattices (E,τ) satisfying the following property: for all operators $\text{S,T}\text{:E→E}$ such that 0?S?T and T precompact, the operator S² is precompact. To cite this article: B. Aqzzouz, R. Nouira, C. R. Acad. Sci. Paris, Ser. I 337 (2003).     

Limiting laws associated with Brownian motion perturbated by normalized exponential weights

We perturb Brownian motion on the time interval [0,t] by an exponential weight; we show that for a large class of these weights the corresponding probability laws converge weakly as t→∞. To cite this article: B. Roynette et al., C. R. Acad. Sci. Paris, Ser. I 337 (2003).     

Hypersurfaces compactes d'un fibré vectoriel riemannien à courbure moyenne prescriteCompact hypersurfaces of a Riemannian vector bundle with prescribed mean curvature

Let M be a compact Riemannian manifold, E a Riemannian vector bundle on M and Σ the sphere subbundle of E. We look for embeddings of Σ into E admitting prescribed mean curvatures of various types. To cite this article: P. Cherrier, A. Hanani, C. R. Acad. Sci. Paris, Ser. I 335 (2002) 525–528.