On problems in the calculus of variations in increasingly elongated domains

We consider minimization problems in the calculus of variations set in a sequence of domains the size of which tends to infinity in certain directions and such that the data only depend on the coordinates in the directions that remain constant. We study the asymptotic behavior of minimizers in various situations and show that they converge in an appropriate sense toward minimizers of a related energy functional in the constant directions

A Lagrangian formulation for the Oldroyd B fluid and the second principle of thermodynamics

We show that the Oldroyd B fluid model is the Eulerian form of a Lagrangian model with an internal variable that satisfies the second principle of thermodynamics under some conditions on the initial value of the internal variable. We similarly derive a compressible version of the Oldroyd B model and several nonlinear versions thereof. We also derive Lagrangian formulations of the Zaremba-Jaumann and Oldroyd A fluid models. We discuss whether or not these new models satisfy the second principle

Homogenization of hexagonal lattices

International audienceWe characterize the macroscopic e ffective behavior of a graphene sheet modeled by a hexagonal lattice of elastic bars, using Gamma-convergence

Nonlinear elliptic partial differential equations: an introduction

This textbook presents the essential parts of the modern theory of nonlinear partial differential equations, including the calculus of variations. After a short review of results in real and functional analysis, the author introduces the main mathematical techniques for solving both semilinear and quasilinear elliptic PDEs, and the associated boundary value problems. Key topics include infinite dimensional fixed point methods, the Galerkin method, the maximum principle, elliptic regularity, and the calculus of variations. Aimed at graduate students and researchers, this textbook contains numerous examples and exercises and provides several comments and suggestions for further study