Nouvelles inégalités intégrales et applications à la stabilisation des systèmes distribués non dissipatifs

First we prove some new integral inequalities to obtain an estimate on behavior at infinity of a positive and non necessarly decreasing function. This extends some integral inequalities due to A. Haraux, V. Komornik and P. Martinez concerning decreasing functions. Then we give applications to (internal or boundary) stabilization of certain nondissipative distributed systems. To cite this article: A. Guesmia, C. R. Acad. Sci. Paris, Ser. I 336 (2003).     

Moment identities for Poisson–Skorohod integrals and application to measure invariance

We present a moment identity on the Poisson space that extends the Skorohod isometry to arbitrary powers of the Skorohod integral. Applications of this identity are given to the invariance of Poisson measures under intensity preserving random transformations. To cite this article: N. Privault, C. R. Acad. Sci. Paris, Ser. I 347 (2009).     

Invertibility of functional Galois connectionsInversibilité des correspondances de Galois fonctionnelles

We consider equations of the form Bf=g, where B is a Galois connection between lattices of functions. This includes the case where B is the Fenchel transform, or more generally a Moreau conjugacy. We characterize the existence and uniqueness of a solution f in terms of generalized subdifferentials, which extends K. Zimmermann's covering theorem for max-plus linear equations. To cite this article: M. Akian et al., C. R. Acad. Sci. Paris, Ser. I 335 (2002) 883–888.     

Une généralisation de l'intégrale stochastique de Wick–Itô

The covariance of the fractional Brownian motion belongs to a family of positive functions introduced by Schoenberg in the 1930s. We show that one can define a stochastic integral for a large sub-family of the corresponding Gaussian second order stochastic processes. To cite this article: D. Alpay et al., C. R. Acad. Sci. Paris, Ser. I 346 (2008).     

A simplified variational model for the bidimensional coupled evolution equations of a nematic liquid crystal

In Dias (C. R. Acad. Sci. Paris Sér. A. 285 (1977)) we have deduced, from Leslie's model (Arch. Rat. Mech. Anal. 28 (1968)), a weak formulation for the bidimensional coupled evolution equations of an incompressible nematic liquid crystal submitted to an homogeneous magnetic field. In this paper we prove some results about the existence, regularity and uniqueness of their solutions. This study extends the special case developed in Dias (J. Mécanique15 (1976)), where we assumed that the director field depends on time only.     

Coupling of a multilevel fast multipole method and a microlocal discretization for the 3-D integral equations of electromagnetism

The aim of this work is to propose an accurate and efficient numerical approximation for high frequency diffraction of electromagnetic waves. In the context of the boundary integral equations presented in F. Collino and B. Després, to be published in J. Comput. Appl. Math., the strategy we propose combines the microlocal discretization (T. Abboud et al., in: Third International Conference on Mathematical Aspects of Wave Propagation Phenomena, SIAM, 1995, pp. 178–187) and the multilevel fast multipole method (J.M. Song, W.C. Chew, Microw. Opt. Tech. Lett. 10 (1) (1995) 14–19). This leads to a numerical method with a reduced complexity, of order O(N^4/3ln(N)+N_iterN^2/3), instead of the complexity O(N_iterN²) for a classical numerical iterative solution of integral equations. Computations on an academic geometry show that the new method improves the efficiency, for a solution with a good level of accuracy. To cite this article: A. Bachelot et al., C. R. Acad. Sci. Paris, Ser. I 336 (2003).     

On simultaneous uniformization and local nonuniformizabilitySur uniformisation simultanée et nonuniformisabilité locale

We prove existence of a one-dimensional holomorphic foliation (with isolated irremovable singularities) tangent to a rational vector field on appropriate affine algebraic surface of dimension 2 such that the family of leaves intersecting arbitrary given cross-section does not admit a uniformization holomorphic in the parameter by a family of simply connected domains in $\text{C}$. We show that such a foliation can be chosen transversally affine, having a Liouvillian first integral, with dense and hyperbolic leaves and an attracting cycle. This extends the author's result [4] giving a negative answer to Ilyashenko's simultaneous uniformization conjecture and answers negatively to the local version of this conjecture recently proposed by Shcherbakov. To cite this article: A. Glutsyuk, C. R. Acad. Sci. Paris, Ser. I 334 (2002) 489–494.     

A level-set method for shape optimization

We study a level-set method for numerical shape optimization of elastic structures. Our approach combines the level-set algorithm of Osher and Sethian with the classical shape gradient. Although this method is not specifically designed for topology optimization, it can easily handle topology changes for a very large class of objective functions. Its cost is moderate since the shape is captured on a fixed Eulerian mesh. To cite this article: G. Allaire et al., C. R. Acad. Sci. Paris, Ser. I 334 (2002) 1125–1130.     

Amplitude des oscillations d'ondes solitaires généralisées

Various physical systems of dispersive waves admit solutions in the form of generalized solitary waves. Such waves result from the resonance between a long localized wave and short periodic oscillations. Many estimates (rigorous and numerical) have been given for the amplitude of the ripples in the tail of the generalized solitary wave when its central part has a sech² shape. This Note provides estimates (not yet rigorous) for the ripple amplitude when the central part is flat and wide. To cite this article: C. Fochesato, F. Dias, C. R. Acad. Sci. Paris, Ser. I 337 (2003).     

Integral Equation Method for the First and Second Problems of the Stokes System

Using the integral equation method we study solutions of boundary value problems for the Stokes system in Sobolev space H ¹(G) in a bounded Lipschitz domain G with connected boundary. A solution of the second problem with the boundary condition $\partial {\bf u}/\partial {\bf n} -p{\bf n}={\bf g}$ is studied both by the indirect and the direct boundary integral equation method. It is shown that we can obtain a solution of the corresponding integral equation using the successive approximation method. Nevertheless, the integral equation is not uniquely solvable. To overcome this problem we modify this integral equation. We obtain a uniquely solvable integral equation on the boundary of the domain. If the second problem for the Stokes system is solvable then the solution of the modified integral equation is a solution of the original integral equation. Moreover, the modified integral equation has a form f?+?S f?=?g, where S is a contractive operator. So, the modified integral equation can be solved by the successive approximation. Then we study the first problem for the Stokes system by the direct integral equation method. We obtain an integral equation with an unknown ${\bf g}=\partial {\bf u}/\partial {\bf n} -p{\bf n}$ . But this integral equation is not uniquely solvable. We construct another uniquely solvable integral equation such that the solution of the new eqution is a solution of the original integral equation provided the first problem has a solution. Moreover, the new integral equation has a form ${\bf g}+\tilde S{\bf g}={\bf f}$ , where $\tilde S$ is a contractive operator, and we can solve it by the successive approximation.     

Bianchi–Euler system for relativistic fluids and Bel–Robinson type energySystème de Bianchi–Euler pour un fluide relativiste,et énergie de type Bel–Robinson

We write a first order symmetric hyperbolic system coupling the Riemann tensor with the dynamical acceleration of a prefect relativistic fluid. We determine the associated, coupled, Bel–Robinson type energy, and the integral equality that it satisfies. To cite this article: Y. Choquet-Bruhat, J.W. York, C. R. Acad. Sci. Paris, Ser. I 335 (2002) 711–716.     

Generalized infinite-dimensional Fresnel integrals

A generalized infinite dimensional oscillatory integral with a polynomially growing phase function is defined and explicitly computed in terms of an absolutely convergent Gaussian integral. The results are applied to the Feynman path integral representation for the solution of the Schrödinger equation with an anharmonic oscillator potential. To cite this article: S. Albeverio, S. Mazzucchi, C. R. Acad. Sci. Paris, Ser. I 338 (2004).     

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).     

Extension du filtre de Chandrasekhar au cas des modèles espace d'état périodiques

This Note extends the Chandrasekhar-type recursions due to Morf, Sidhu, and Kailath (1974) to the case of periodic time-varying state-space models. We show that the S-lagged increments of the one-step prediction error covariance satisfy certain recursions from which we derive some algorithms for linear least squares estimation for periodic state-space models. The proposed recursions have potential computational advantages over the Kalman Filter and, in particular, the periodic Riccati difference equation. To cite this article: A. Aknouche, F. Hamdi, C. R. Acad. Sci. Paris, Ser. I 346 (2008).     

Interior error estimate for periodic homogenization

The aim of this Note is to give interior error estimates for problems in periodic homogenization, by using the periodic unfolding method. The interior error estimates are obtained by transposition without any supplementary hypothesis of regularity on correctors. This error is of order ?. To cite this article: G. Griso, C. R. Acad. Sci. Paris, Ser. I 340 (2005).     

On the exceptional series,and its descendantsLa série exceptionnelle,et sa descendance

Many of the striking similarities which occur for the adjoint representation of groups in the exceptional series (cf. [1–3]) also occur for certain representations of specific reductive subgroups. The tensor algebras on these representations are easier to describe (cf. [4,5,7]), and may offer clues to the original situation.The subgroups which occur form a Magic Triangle, which extends Freudenthal's Magic Square of Lie algebras. We describe these groups from the perspective of dual pairs, and their representations from the action of the dual pair on an exceptional Lie algebra. To cite this article: P. Deligne, B.H. Gross, C. R. Acad. Sci. Paris, Ser. I 335 (2002) 877–881.     

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).     

Anti symmetric solutions of non-linear laminar flow between parallel permeable disks

The equations describing similarity solutions for flow between infinite parallel permeable disks with equal rates of suction or injection at the walls is derived using the stream function. This leads to a fourth order non-linear Ordinary Differential Equation. This equation is shown to admit anti-symmetric solutions using the moving plane method. To cite this article: Adimurthi, A. Karthik, C. R. Acad. Sci. Paris, Ser. I 346 (2008).     

On one-homogeneous solutions to elliptic systems in two dimensionsSur les solutions un-homogènes des systèmes elliptiques en dimension deux

In this Note we consider a class of nonlinear second order elliptic systems in divergence form and two independent variables. We prove that all Lipschitz continuous one-homogeneous weak solutions are linear. To cite this article: D. Phillips, C. R. Acad. Sci. Paris, Ser. I 335 (2002) 39–42.     

On Dirichlet Type Problems of Polynomial Dirac Equations with Boundary Conditions

Let ${{\bf D}_{\bf x} := \sum_{i=1}^n \frac{\partial}{\partial x_i} e_i}$ be the Euclidean Dirac operator in ${\mathbb{R}^n}$ and let P(X) = a _m X ^m + . . . + a ₁ X +  a ₀ be a polynomial with real coefficients. Differential equations of the form P(D _x )u(x) = 0 are called homogeneous polynomial Dirac equations with real coefficients. In this paper we treat Dirichlet type problems of the a slightly less general form P(D _x )u(x) = f(x) (where the roots are exclusively real) with prescribed boundary conditions that avoid blow-ups inside the domain. We set up analytic representation formulas for the solutions in terms of hypercomplex integral operators and give exact formulas for the integral kernels in the particular cases dealing with spherical and concentric annular domains. The Maxwell and the Klein–Gordon equation are included as special subcases in this context.