A moment method for polydisperse sprays

This Note outlines a new moment method to solve the kinetic spray equation, which is the basic mathematical model used to predict the behaviour of polydisperse sprays. The method was successfully applied to the test-cases of spray-wall impingement and crossing of two spray jets that were affected by the Stokes drag force. Lagrangian computations of the same test-cases were used as reference solutions. To cite this article: L. Schneider et al., C. R. Acad. Sci. Paris, Ser. I 347 (2009).     

Uniqueness of unbounded solutions of the Lagrangian mean curvature flow equation for graphs

We observe that the comparison result of Barles–Biton–Ley for viscosity solutions of a class of nonlinear parabolic equations can be applied to a geometric fully nonlinear parabolic equation which arises from the graphic solutions for the Lagrangian mean curvature flow. To cite this article: J. Chen, C. Pang, C. R. Acad. Sci. Paris, Ser. I 347 (2009).     

Hybrid kinetic/fluid models for nonequilibrium systems

Our purpose is to derive a model describing the evolution of particles at various scales following their kinetic energy. Fast particles will be described through a collisional kinetic equation of Boltzmann-BGK type. This equation will be coupled with a fluid model (Euler equations) that describes the evolution of slower particles. The main interest of this approach is to reduce the cost of numerical simulations. To cite this article: N. Crouseilles et al., C. R. Acad. Sci. Paris, Ser. I 336 (2003).     

Representation theorems for generators of backward stochastic differential equations

It is proved that the generator g of a backward stochastic differential equation (BSDE) can be represented by the solutions of the corresponding BSDEs if and only if g is a Lebesgue generator. To cite this article: L. Jiang, C. R. Acad. Sci. Paris, Ser. I 340 (2005).     

Dérivation de modèles couplés dérive-diffusion/cinétique par une méthode de décomposition en vitesseDerivation of a kinetic/drift-diffusion model describing fast and slow particles

Our purpose is to derive a model describing the evolution of charged particles in a plasma, at various scales following their kinetic energy. Fast particles will be described through a collisional kinetic equation of Boltzmann type. This equation will be coupled with a drift-diffusion model that describes the evolution of slower particles. The main interest of this approach is to reduce the cost of numerical simulations. This gain is due to the use of a macroscopic model for slow particles instead of a kinetic model for all the particles, which would involve a larger number of variables. To cite this article: N. Crouseilles, C. R. Acad. Sci. Paris, Ser. I 334 (2002) 827–832.     

Self-similar solutions with fat tails for a coagulation equation with nonlocal drift

We investigate the existence of self-similar solutions for a coagulation equation with nonlocal drift. In addition to explicitly given exponentially decaying solutions we establish the existence of self-similar profiles with algebraic decay. To cite this article: M. Herrmann et al., C. R. Acad. Sci. Paris, Ser. I 347 (2009).     

Hölder continuity of solutions to a basic problem in the calculus of variations

For the basic problem in the calculus of variations where the Lagrangian is convex and depends only on the gradient, we establish the continuity of the solutions when the Dirichlet boundary condition is defined by a continuous function ϕ. When ϕ is Lipschitz continuous, then the solutions are Hölder continuous. To cite this article: P. Bousquet et al., C. R. Acad. Sci. Paris, Ser. I 346 (2008).     

Boundedness of the gradient of a solution to the Neumann–Laplace problem in a convex domain

It is shown that solutions of the Neumann problem for the Poisson equation in an arbitrary convex n-dimensional domain are uniformly Lipschitz. Applications of this result to some aspects of regularity of solutions to the Neumann problem on convex polyhedra are given. To cite this article: V. Maz'ya, C. R. Acad. Sci. Paris, Ser. I 347 (2009).     

Équation des ondes sur les espaces symétriques riemanniens

We prove that the solutions of the homogeneous wave equation on Riemannian symmetric spaces have dispersion properties and we deduce Strichartz type estimates for these solutions. To cite this article: A. Hassani, C. R. Acad. Sci. Paris, Ser. I 347 (2009).     

Periodic solutions for systems of forced coupled pendulum-like equations

The existence of periodic solutions for systems of forced pendulum-like equations was studied in the papers by J. A. Marlin (Internat. J. Nonlinear Mech.3 (1968), 439–447) and J. Mawhin (Internat. J. Nonlinear Mech.5 (1970), 335–339). In both works some symmetry hypotheses on the forcing terms were considered. This paper discusses the existence and multiplicity of periodic solutions of systems under consideration without any requirement on the symmetry of the forcing terms. Note that as a model example it is possible to consider the motion of N coupled pendulums (see the already mentioned paper by J. A. Marlin) or the oscillations of an N-coupled point Josephson junction with external time-dependent disturbances studied in the autonomous case by M. Levi, F. C. Hoppensteadt, and W. L. Miranker (Quart. Appl. Math.36 (1978), 167–198).     

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.     

A uniqueness result for monotone elliptic problems

We give here a short proof of the uniqueness of entropy solutions for nonlinear monotone elliptic problems with L¹-data. To cite this article: M.M. Porzio, C. R. Acad. Sci. Paris, Ser. I 337 (2003).     

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).     

Growth estimates for solutions to initial-boundary value problems in viscoelasticity

For the abstract Volterra integro-differential equation u_tt ? Nu + ∝_?∞^t K(t ? τ) u(τ) dτ = 0 in Hilbert space, with prescribed past history u(τ) = U(τ), ? ∞ < τ < 0, and associated initial data u(0) = f, u_t(0) = g, we establish conditions on K(t), ? ∞ < t < + ∞ which yield various growth estimates for solutions u(t), belonging to a certain uniformly bounded class, as well as lower bounds for the rate of decay of solutions. Our results are interpreted in terms of solutions to a class of initial-boundary value problems in isothermal linear viscoelasticity.     

Holonomic systems with solutions ramified along a cuspSystèmes holonomes avec solutions ramifiées le long d'un cusp

We classify the holonomic systems of (micro) differential equations of multiplicity one along a singular Lagrangian irreducible variety contained in an involutive submanifold of maximal codimension. We show that their solutions are related to _kF_k?1 hypergeometric functions on the Riemann sphere. To cite this article: O. Neto, P.C. Silva, C. R. Acad. Sci. Paris, Ser. I 335 (2002) 171–176.     

A new stability result for viscosity solutions of nonlinear parabolic equations with weak convergence in time

We present a new stability result for viscosity solutions of fully nonlinear parabolic equations which allows to pass to the limit when one has only weak convergence in time of the nonlinearities. To cite this article: G. Barles, C. R. Acad. Sci. Paris, Ser. I 343 (2006).     

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).     

A kinetic approximation of Hele–Shaw flow

In this Note we consider a fourth order degenerate parabolic equation modeling the evolution of the interface of a spreading droplet. The equation is approximated trough a collisional kinetic equation. This permits to derive numerical approximations that preserves positivity of the solution and the main relevant physical properties. A Monte Carlo application is also shown. To cite this article: L. Pareschi et al., C. R. Acad. Sci. Paris, Ser. I 338 (2004).     

Local gradient estimates of solutions to some conformally invariant fully nonlinear equations

We establish local gradient estimates to solutions of general conformally invariant fully nonlinear second order elliptic equations. To cite this article: Y.Y. Li, C. R. Acad. Sci. Paris, Ser. I 343 (2006).     

Équations d'Hamilton–Jacobi liées aux jeux différentiels avec coût de type supremum

In this Note we present a study of the existence and uniqueness to discontinuous viscosity solutions of Hamilton–Jacobi PDE related with differential games with supremum cost. To cite this article: O.-S. Serea, C. R. Acad. Sci. Paris, Ser. I 344 (2007).