Sobolev extension property for tree-shaped domains with self-contacting fractal boundary

International audienceIn this paper, we investigate the existence of extension operators fromW1,p( ) toW1,p(R2) (1 < p < 1) for a class of tree-shaped domains with a self-similar fractal boundary pre- viously studied by Mandelbrot and Frame. When the fractal boundary has no self-contact, the results of Jones imply that there exist such extension operators for all p 2 [1,1]. In the case when the fractal boundary self-intersects, this result does not hold. Here, we prove however that extension operators exist for p < p? where p? depends only on the dimension of the self-intersection of the boundary. The construction of these operators mainly relies on the self-similar properties of the domains

JLip versus Sobolev Spaces on a Class of Self-Similar Fractal Foliages

International audienceFor a class of self-similar sets $\Gamma^\infty$ in $\R^2$, supplied with a probability measure $\mu$ called the self-similar measure, we investigate if the $B_s^{q,q}(\Gamma^\infty)$ regularity of a function can be characterized using the coefficients of its expansion in the Haar wavelet basis. Using the the Lipschitz spaces with jumps recently introduced by Jonsson, the question can be rephrased: when does $B_s^{q,q}(\Gamma^\infty)$ coincide with $JLip(s,q,q;0;\Gamma^\infty)$? When $\Gamma^\infty$ is totally disconnected, this question has been positively answered by Jonsson for all $s,q$, $00$, $1\le p,q<\infty$, using possibly higher degree Haar wavelets coefficients). Here, we fully answer the question in the case when $

Comparison of Different Definitions of Traces for a Class of Ramified Domains with Self-Similar Fractal Boundaries

International audienceWe consider a class of ramified bidimensional domains with a self-similar boundary, which is supplied with the self-similar probability measure. Emphasis is put on the case when the domain is not an epsilon-delta domain as defined by Jones and the fractal is not totally disconnected.We compare two notions of trace on the fractal boundary for functions in some Sobolev space, the classical one ( the strict definition ) and another one proposed in 2007 and heavily relying on self-similarity. We prove that the two traces coincide almost everywhere with respect to the self similar probability measure

Contributions à l'étude d'espaces de fonctions et d'EDP dans une classe de domaines à frontière fractale auto-similaire

Cette thèse est consacrée à des questions d'analyse en amont de la modélisation de structures arborescentes, comme le poumon humain. Plus particulièrement, nous portons notre intérêt sur une classe de domaines ramifiés du plan, dont la frontière comporte une partie fractale auto-similaire. Nous commençons par une étude d'espaces de fonctions dans cette classe de domaines. Nous étudions d'abord la régularité Sobolev de la trace sur la partie fractale de la frontière de fonctions appartenant à des espaces de Sobolev dans les domaines considérés. Nous étudions ensuite l'existence d'opérateurs de prolongement sur la classe de domaines ramifiés. Nous comparons finalement la notion de trace auto-similaire sur la partie fractale du bord à des définitions plus classiques de trace. Nous nous intéressons enfin à un problème de transmission mixte entre le domaine ramifié et le domaine extérieur. L'interface du problème est la partie fractale du bord du domaine. Nous proposons ici une approche numérique, en approchant l'interface fractale par une interface préfractale. La stratégie proposée ici est basée sur le couplage d'une méthode auto-similaire pour la résolution du problème intérieur et d'une méthode intégrale pour la résolution du problème extérieur.We study some questions of analysis in view of the modeling of tree-like structures, such as the human lungs. More particularly, we focus on a class of planar ramified domains whose boundary contains a fractal self-similar part. We start by studying some function spaces defined for this class of domains. We first study the Sobolev regularity of the traces on the fractal part of the boundary of functions in some Sobolev spaces of the ramified domains. Then, we study the existence of Sobolev extension operators for the ramified domains we consider. Finally, we compare the notion of self-similar trace on the fractal part of the boundary with more classical definitions of trace. In the last part, we focus on a mixed transmission problem between the ramified domain and the exterior domain. The fractal part of the boundary is the interface of the problem. We propose a numerical approach where we approximate the self-similar interface by a prefractal interface. The proposed strategy is based on a self-similar method for the resolution of the inner problem coupled with an integral method for the resolution of the outer problem.RENNES1-Bibl. électronique (352382106) / SudocSudocFranceF

A transmission problem across a fractal self-similar interface

We consider a transmission problem in which the interior domain has infinitely ramified structures. Transmission between the interior and exterior domains occurs only at the fractal component of the interface between the interior and exterior domains. We also consider the sequence of the transmission problems in which the interior domain is obtained by stopping the self-similar construction after a finite number of steps; the transmission condition is then posed on a prefractal approximation of the fractal interface. We prove the convergence in the sense of Mosco of the energy forms associated with these problems to the energy form of the limit problem. In particular, this implies the convergence of the solutions of the approximated problems to the solution of the problem with fractal interface. The proof relies in particular on an extension property. Emphasis is put on the geometry of the ramified domain. The convergence result is obtained when the fractal interface has no self-contact, and in a particular geometry with self-contacts, for which an extension result is proved

Contributions to the study of function spaces and PDE for a class of domains with fractal self-similar boundary

Cette thèse est consacrée à des questions d'analyse en amont de la modélisation de structures arborescentes, comme le poumon humain. Plus particulièrement, nous portons notre intérêt sur une classe de domaines ramifiés du plan, dont la frontière comporte une partie fractale auto-similaire. Nous commençons par une étude d'espaces de fonctions dans cette classe de domaines. Nous étudions d'abord la régularité Sobolev de la trace sur la partie fractale de la frontière de fonctions appartenant à des espaces de Sobolev dans les domaines considérés. Nous étudions ensuite l'existence d'opérateurs de prolongement sur la classe de domaines ramifiés. Nous comparons finalement la notion de trace auto-similaire sur la partie fractale du bord à des définitions plus classiques de trace. Nous nous intéressons enfin à un problème de transmission mixte entre le domaine ramifié et le domaine extérieur. L'interface du problème est la partie fractale du bord du domaine. Nous proposons ici une approche numérique, en approchant l'interface fractale par une interface préfractale. La stratégie proposée ici est basée sur le couplage d'une méthode auto-similaire pour la résolution du problème intérieur et d'une méthode intégrale pour la résolution du problème extérieur.We study some questions of analysis in view of the modeling of tree-like structures, such as the human lungs. More particularly, we focus on a class of planar ramified domains whose boundary contains a fractal self-similar part. We start by studying some function spaces defined for this class of domains. We first study the Sobolev regularity of the traces on the fractal part of the boundary of functions in some Sobolev spaces of the ramified domains. Then, we study the existence of Sobolev extension operators for the ramified domains we consider. Finally, we compare the notion of self-similar trace on the fractal part of the boundary with more classical definitions of trace. In the last part, we focus on a mixed transmission problem between the ramified domain and the exterior domain. The fractal part of the boundary is the interface of the problem. We propose a numerical approach where we approximate the self-similar interface by a prefractal interface. The proposed strategy is based on a self-similar method for the resolution of the inner problem coupled with an integral method for the resolution of the outer problem

Contributions à l'étude d'espaces de fonctions et d'EDP dans une classe de domaines à frontière fractale auto-similaire

We study some questions of analysis in view of the modeling of tree-like structures, such as the human lungs. More particularly, we focus on a class of planar ramified domains whose boundary contains a fractal self-similar part. We start by studying some function spaces defined for this class of domains. We first study the Sobolev regularity of the traces on the fractal part of the boundary of functions in some Sobolev spaces of the ramified domains. Then, we study the existence of Sobolev extension operators for the ramified domains we consider. Finally, we compare the notion of self-similar trace on the fractal part of the boundary with more classical definitions of trace. In the last part, we focus on a mixed transmission problem between the ramified domain and the exterior domain. The fractal part of the boundary is the interface of the problem. We propose a numerical approach where we approximate the self-similar interface by a prefractal interface. The proposed strategy is based on a self-similar method for the resolution of the inner problem coupled with an integral method for the resolution of the outer problem.Cette thèse est consacrée à des questions d'analyse en amont de la modélisation de structures arborescentes, comme le poumon humain. Plus particulièrement, nous portons notre intérêt sur une classe de domaines ramifiés du plan, dont la frontière comporte une partie fractale auto-similaire. Nous commençons par une étude d'espaces de fonctions dans cette classe de domaines. Nous étudions d'abord la régularité Sobolev de la trace sur la partie fractale de la frontière de fonctions appartenant à des espaces de Sobolev dans les domaines considérés. Nous étudions ensuite l'existence d'opérateurs de prolongement sur la classe de domaines ramifiés. Nous comparons finalement la notion de trace auto-similaire sur la partie fractale du bord à des définitions plus classiques de trace. Nous nous intéressons enfin à un problème de transmission mixte entre le domaine ramifié et le domaine extérieur. L'interface du problème est la partie fractale du bord du domaine. Nous proposons ici une approche numérique, en approchant l'interface fractale par une interface préfractale. La stratégie proposée ici est basée sur le couplage d'une méthode auto-similaire pour la résolution du problème intérieur et d'une méthode intégrale pour la résolution du problème extérieur

Optimal location of resources for biased movement of species: the 1D case

International audienceIn this paper, we investigate an optimal design problem motivated by some issues arising in population dynamics. In a nutshell, we aim at determining the optimal shape of a region occupied by resources for maximizing the survival ability of a species in a given box and we consider the general case of Robin boundary conditions on its boundary. Mathematically, this issue can be modeled with the help of an extremal indefinite weight linear eigenvalue problem. The optimal spatial arrangement is obtained by minimizing the positive principal eigenvalue with respect to the weight, under a L 1 constraint standing for limitation of the total amount of resources. The specificity of such a problem rests upon the presence of nonlinear functions of the weight both in the numerator and denominator of the Rayleigh quotient. By using adapted symmetrization procedures, a well-chosen change of variable, as well as necessary optimality conditions, we completely solve this optimization problem in the unidimensional case by showing first that every minimizer is unimodal and bang-bang. This leads to investigate a finite dimensional optimization problem. This allows to show in particular that every minimizer is (up to additive constants) the characteristic function of three possible domains: an interval that sticks on the boundary of the box, an interval that is symmetrically located at the middle of the box, or, for a precise value of the Robin coefficient, all intervals of a given fixed length