Solutions concentrating at curves for some singularly perturbed elliptic problems

We study positive solutions of the equation ?ε²Δu+u=u^p, where p>1 and ε>0 is small, with Neumann boundary conditions in a three-dimensional domain $\text{Ω}$. We prove the existence of solutions concentrating along some closed curve on $\text{?Ω}$. To cite this article: A. Malchiodi, C. R. Acad. Sci. Paris, Ser. I 338 (2004).     

Positive solutions for slightly super-critical elliptic equations in contractible domainsSolutions positives pour l'équation Δu+u(n+2)/(n−2)+ε=0 en ouverts contractibles

We give examples of bounded domains $\text{Ω}$, even contractible, having the following property: there exists $\text{k}\text{?}\text{(Ω)}$ such that, for every integer $\text{k?}\text{k}\text{?}\text{(Ω)}$, problem $\text{P(ε,Ω)}$ below, for ε>0 small enough, has at least one solution blowing up as ε→0 at exactly k points. We also prove that the blow-up points tend to some points of $\text{?Ω}$ as k→∞. To cite this article: R. Molle, D. Passaseo, C. R. Acad. Sci. Paris, Ser. I 335 (2002) 459–462.     

On the recovery of a manifold with boundary in Rn

If the Riemann curvature tensor associated with a smooth field $\text{C}$ of positive-definite symmetric matrices of order n vanishes in a simply-connected open subset $\text{Ω?}\text{R}{}^{\mathrm{n}}$, then $\text{C}$ is the metric tensor field of a manifold isometrically immersed in $\text{R}{}^{\mathrm{n}}$.In this Note, we first show how, under a mild smoothness assumption on the boundary of $\text{Ω}$, this classical result can be extended “up to the boundary”. When $\text{Ω}$ is bounded, we also establish the continuity of the manifold with boundary obtained in this fashion as a function of its metric tensor field, the topologies being those of the Banach spaces $\text{C}{}^{\mathrm{?}}\text{(}\text{Ω}\text{)}$. To cite this article: P.G. Ciarlet, C. Mardare, C. R. Acad. Sci. Paris, Ser. I 338 (2004).     

Capacitary estimates of solutions of a class of nonlinear elliptic equations

Let $\text{Ω}$ be a smooth bounded domain in $\text{R}{}^{\mathrm{N}}$ and K a compact subset of $\text{?Ω}$. Assume that q?(N+1)/(N?1) and denote by U_K the maximal solution of ?Δu+u^q=0 in $\text{Ω}$ which vanishes on $\text{?Ω?K}$. We obtain sharp upper and lower estimates for U_K in terms of the Bessel capacity C_2/q,q′ and prove that U_K is σ-moderate. In addition we relate the strong ‘blow-up’ points of U_K on $\text{?Ω}$ to the ‘thick’ points of K in the fine topology associated with C_2/q,q′ and characterize these points by a path integral condition on U_K. To cite this article: M. Marcus, L. Véron, C. R. Acad. Sci. Paris, Ser. I 336 (2003).     

Lifting of BV functions with values in S1

We show that for every $\text{u∈}\text{BV}\text{(Ω;S}{}^1\text{)}$, there exists a bounded variation function $\text{?∈}\text{BV}\text{(Ω;}\text{R}\text{)}$ such that u=e^i? a.e. on $\text{Ω}$ and |?|_BV?2|u|_BV. The constant 2 is optimal in dimension n>1. To cite this article: J. Dávila, R. Ignat, C. R. Acad. Sci. Paris, Ser. I 337 (2003).     

Bifurcation for a class of singular elliptic problems with quadratic convection term

We study the bifurcation problem ?Δu=g(u)+λ|?u|²+μ in $\text{Ω,}\text{u=0}$ on $\text{?Ω}$, where λ,μ?0 and $\text{Ω}$ is a smooth bounded domain in $\text{R}{}^{\mathrm{N}}$. The singular character of the problem is given by the nonlinearity g which is assumed to be decreasing and unbounded around the origin. In this Note we prove that the above problem has a positive classical solution (which is unique) if and only if λ(a+μ)<λ₁, where a=lim_t→+∞g(t) and λ₁ is the first eigenvalue of the Laplace operator in $\text{H}{}^1{}_0\text{(Ω)}$. We also describe the decay rate of this solution, as well as a blow-up result around the bifurcation parameter. To cite this article: M. Ghergu, V. R?dulescu, C. R. Acad. Sci. Paris, Ser. I 338 (2004).     

Uniqueness of the blow-up boundary solution of logistic equations with absorbtion

Let $\text{Ω}$ be a smooth bounded domain in $\text{R}{}^{\mathrm{N}}$. Assume f∈C¹[0,∞) is a non-negative function such that f(u)/u is increasing on (0,∞). Let a be a real number and let b?0, $\text{b}\text{/≡0}$ be a continuous function such that b≡0 on $\text{?Ω}$. We study the logistic equation Δu+au=b(x)f(u) in $\text{Ω}$. The special feature of this work is the uniqueness of positive solutions blowing-up on $\text{?Ω}$, in a general setting that arises in probability theory. To cite this article: F.-C. C??rstea, V. R?dulescu, C. R. Acad. Sci. Paris, Ser. I 335 (2002) 447–452.     

The effect of perturbations on the first eigenvalue of the p-LaplacianL'éffet des pérturbations sur la première valeur propre du p-Laplacien

Let $\text{Ω}$ be a domain with Lipschitzian boundary of a compact Riemannian manifold (M,g) and p>1. We prove that we can make the volume of M arbitrarily close to the volume of $\text{(Ω,g)}$ while the first eigenvalue of the p-Laplacian on M remains uniformly bounded from below in terms of the the first eigenvalue of the Neumann problem for the p-Laplacian on $\text{(Ω,g)}$. To cite this article: A.-M. Matei, C. R. Acad. Sci. Paris, Ser. I 335 (2002) 255–258.     

Détermination du potentiel dans l'équation de Schrödinger à partir de mesures sur une partie du bordDetermination of potential in Schrödinger equation from measurements on a part of the boundary

We study the Schrödinger equation iy′+Δy+qy=0 on $\text{Ω×(0,T)}$ with Dirichlet boundary data $\text{y|}{}_{\mathrm{?\Omega \times (0,T)}}$ and initial condition $\text{y|}{}_{\mathrm{\Omega \times \{0\}}}$ and we consider the inverse problem of determining the potential q(x), $\text{x∈Ω}$ when is given, where Γ₀ is an open subset of $\text{?Ω}$ satisfying an appropriate geometrical condition. The detailed proof will be given in [1]. To cite this article: L. Baudouin, J.-P. Puel, C. R. Acad. Sci. Paris, Ser. I 334 (2002) 967–972.     

On the horizontal distribution of zeros of linear combinations of Euler products

We investigate the behavior of the zero counting function of certain natural Dirichlet series with functional equation in the immediate vicinity of the critical line $\text{{}\text{Re}\text{(s)=}\text{1}\text{2}\text{}}$. To cite this article: D.A. Hejhal, C. R. Acad. Sci. Paris, Ser. I 338 (2004).     

On the nondegeneracy of the critical points of the Robin function in symmetric domainsSur le non-dégénérescence des points critiques de la fonction de Robin dans les domaines symétriques

Let $\text{Ω}$ be a smooth bounded domain of $\text{R}{}^{\mathrm{N}}$, N?2, which is symmetric with respect to the origin. In this Note we prove that, under some geometrical condition on $\text{Ω}$ (for example convexity in the directions x₁,…,x_N), the Hessian matrix of the Robin function computed at zero is diagonal and strictly negative definite. To cite this article: M. Grossi, C. R. Acad. Sci. Paris, Ser. I 335 (2002) 157–160.     

Monotonicity in integrodifferential equations

We study the behavior of positive solutions of the Dirichlet problem Lu=f(u) in $\text{Ω}$ with $\text{Ω=(a,+∞)}$, where a can be ?∞, and L is an abstract operator which is non-increasing under translation and satisfies a strong maximum principle property. This covers the case of many integral operators. Under some assumptions on f (e.g., bistable, monostable), we show that any solution exhibits a monotone behavior. To cite this article: J. Coville, C. R. Acad. Sci. Paris, Ser. I 337 (2003).     

Asymptotics for the blow-up boundary solution of the logistic equation with absorption

Let $\text{Ω}$ be a smooth bounded domain in $\text{R}{}^{\mathrm{N}}$. Assume that f?0 is a C¹-function on [0,∞) such that f(u)/u is increasing on (0,+∞). Let a be a real number and let b?0, b?0 be a continuous function such that b≡0 on $\text{?Ω}$. The purpose of this Note is to establish the asymptotic behaviour of the unique positive solution of the logistic problem Δu+au=b(x)f(u) in $\text{Ω}$, subject to the singular boundary condition u(x)→+∞ as $\text{dist}\text{(x,?Ω)→0}$. Our analysis is based on the Karamata regular variation theory. To cite this article: F.-C. Cîrstea, V. R?dulescu, C. R. Acad. Sci. Paris, Ser. I 336 (2003).     

Le cocycle du verger

We define and prove uniqueness of a natural homomorphism (called the Orchard morphism) from some groups associated naturally to a finite set E to the group $\text{E}\text{(E)}$ of two-partitions of E representing equivalence relations having at most two classes on E. As an application, given a finite generic configuration $\text{C}\text{?}\text{R}{}^{\mathrm{d}}$, we exhibit a natural partition of $\text{C}$ in two sets. To cite this article: R. Bacher, C. R. Acad. Sci. Paris, Ser. I 338 (2004).     

Bifurcation and asymptotics for the Lane–Emden–Fowler equation

We are concerned with the Lane–Emden–Fowler equation ?Δu=λf(u)+a(x)g(u) in $\text{Ω}$, subject to the Dirichlet boundary condition u=0 on $\text{?Ω,}$ where $\text{Ω?}\text{R}{}^{\mathrm{N}}$ is a smooth bounded domain, λ is a positive parameter, $\text{a}\text{:}\text{Ω}\text{→[0,∞)}$ is a Hölder function, and f is a positive nondecreasing continuous function such that f(s)/s is nonincreasing in (0,∞). The singular character of the problem is given by the nonlinearity g which is assumed to be unbounded around the origin. In this Note we discuss the existence and the uniqueness of a positive solution of this problem and we also describe the precise decay rate of this solution near the boundary. The proofs rely essentially on the maximum principle and on elliptic estimates. To cite this article: M. Ghergu, V.D. R?dulescu, C. R. Acad. Sci. Paris, Ser. I 337 (2003).     

On a generalized X-ray transform and a new method for defect detection using the medium electronic density

We consider a generalization of the X-ray transform which maps a function $\text{f(}\text{V}\text{)}$ defined in $\text{R}{}^3$ onto its integrals over a pair of parallel straight lines and not over a single straight line as in a conventional X-ray transform. This new transformation arises from the image formation by double Compton-scattered radiation in transmission imaging. The problem of reconstructing $\text{f(}\text{V}\text{)}$ from its line pair integrals is formulated as an inverse problem for this generalized X-ray transform. Exploiting the line duality in the new transformation, we derive an equivalent nonlinear integral equation for $\text{f(}\text{V}\text{)}$. Special classes of solutions can be constructed. They may serve as basis for a new method of defect detection, using the medium electronic density, in non-destructive inspection. To cite this article: M.K. Nguyen, T.T. Truong, C. R. Acad. Sci. Paris, Ser. I 336 (2003).     

Une note sur les lemmes div–curl

Let $\text{Ω}$ be a strongly Lipschitz domain of $\text{R}{}^{\mathrm{n}}$ (n?2). We give endpoint versions of div–curl lemmata on $\text{Ω}$, for a given function f on $\text{Ω}$ whose gradient belongs to a Hardy space on $\text{Ω}$. To cite this article: P. Auscher et al., C. R. Acad. Sci. Paris, Ser. I 337 (2003).     

Problème de Gleason et interpolation pour les fonctions hyper-analytiquesGleason's problem and interpolation for hyperholomorphic functions

We prove a Gleason type theorem in the setting of functions hyperholomorphic in the unit ball of $\text{R}{}^4$. We give an interpretation of the result in terms of pairs of functions defined in the unit ball of $\text{C}{}^2$. Finally we use the theorem to study the homogeneous interpolation problem in the setting of hyperholomorphic functions. To cite this article: D. Alpay, M. Shapiro, C. R. Acad. Sci. Paris, Ser. I 335 (2002) 889–894.     

Extension of a Riemannian metric with vanishing curvature

Let $\text{Ω}$ be a connected and simply-connected open subset of $\text{R}{}^{\mathrm{n}}$ such that the geodesic distance in $\text{Ω}$ is equivalent to the Euclidean distance. Let there be given a Riemannian metric (g_ij) of class $\text{C}{}^2$ and of vanishing curvature in $\text{Ω}$, such that the functions g_ij and their partial derivatives of order $\text{?}\text{2}$ have continuous extensions to $\text{Ω}$. Then there exists a connected open subset $\text{Ω}$ of $\text{R}{}^{\mathrm{n}}$ containing $\text{Ω}$ and a Riemannian metric $\text{(}\text{g}\text{?}{}_{\mathrm{ij}}\text{)}$ of class $\text{C}{}^2$ and of vanishing curvature in $\text{Ω}$ that extends the metric (g_ij). To cite this article: P.G. Ciarlet, C. Mardare, C. R. Acad. Sci. Paris, Ser. I 338 (2004).     

Up to isometries,a deformation is a continuous function of its metric tensorAux isométries près,une déformation est une fonction continue de son tenseur métrique

If the Riemann–Christoffel tensor associated with a field of class $\text{C}{}^2$ of positive definite symmetric matrices of order three vanishes in a connected and simply connected open subset $\text{Ω?}\text{R}{}^3$, then this field is the metric tensor field associated with a deformation of class $\text{C}{}^3$ of the set $\text{Ω}$, uniquely determined up to isometries of $\text{R}{}^3$. We establish here that the mapping defined in this fashion is continuous, for ad hoc metrizable topologies. To cite this article: P.G. Ciarlet, F. Laurent, C. R. Acad. Sci. Paris, Ser. I 335 (2002) 489–493.