École Polytechnique

About: École Polytechnique is a education organization based out in Palaiseau, France. It is known for research contribution in the topics: Laser & Plasma. The organization has 18995 authors who have published 39265 publications receiving 1225163 citations. The organization is also known as: Ecole Polytechnique & Polytechnique.

Stochastic Burgers and KPZ equations from particle systems

Abstract: We consider two strictly related models: a solid on solid interface growth model and the weakly asymmetric exclusion process, both on the one dimensional lattice. It has been proven that, in the diffusive scaling limit, the density field of the weakly asymmetric exclusion process evolves according to the Burgers equation and the fluctuation field converges to a generalized Ornstein-Uhlenbeck process. We analyze instead the density fluctuations beyond the hydrodynamical scale and prove that their limiting distribution solves the (non linear) Burgers equation with a random noise on the density current. For the solid on solid model, we prove that the fluctuation field of the interface profile, if suitably rescaled, converges to the Kardar–Parisi–Zhang equation. This provides a microscopic justification of the so called kinetic roughening, i.e. the non Gaussian fluctuations in some non-equilibrium processes. Our main tool is the Cole-Hopf transformation and its microscopic version. We also develop a mathematical theory for the macroscopic equations.

Germs of arcs on singular algebraic varieties and motivic integration

Abstract: We study the scheme of formal arcs on a singular algebraic variety and its images under truncations. We prove a rationality result for the Poincare series of these images which is an analogue of the rationality of the Poincare series associated to p-adic points on a p-adic variety. The main tools which are used are semi-algebraic geometry in spaces of power series and motivic integration (a notion introduced by M. Kontsevich). In particular we develop the theory of motivic integration for semi-algebraic sets of formal arcs on singular algebraic varieties, we prove a change of variable formula for birational morphisms and we prove a geometric analogue of a result of Oesterle.

A frequency domain approach to registration of aliased images with application to super-resolution

Abstract: Super-resolution algorithms reconstruct a high-resolution image from a set of low-resolution images of a scene. Precise alignment of the input images is an essential part of such algorithms. If the low-resolution images are undersampled and have aliasing artifacts, the performance of standard registration algorithms decreases. We propose a frequency domain technique to precisely register a set of aliased images, based on their low-frequency, aliasing-free part. A high-resolution image is then reconstructed using cubic interpolation. Our algorithm is compared to other algorithms in simulations and practical experiments using real aliased images. Both show very good visual results and prove the attractivity of our approach in the case of aliased input images. A possible application is to digital cameras where a set of rapidly acquired images can be used to recover a higher-resolution final image.

Imaging lipid bodies in cells and tissues using third-harmonic generation microscopy

Abstract: Lipid bodies have an important role in energy storage and lipid regulation. Here we show that lipid bodies are a major source of contrast in third-harmonic generation (THG) microscopy of cells and tissues. In hepatocytes, micrometer-sized lipid bodies produce a THG signal 1-2 orders of magnitude larger than other structures, which allows one to image them with high specificity. THG microscopy with approximately 1,200 nm excitation can be used to follow the distribution of lipid bodies in a variety of unstained samples including insect embryos, plant seeds and intact mammalian tissue (liver, lung). We found that epi-THG imaging is possible in weakly absorbing tissues because bulk scattering redirects a substantial fraction of the forward-generated harmonic light toward the objective. Finally, we show that the combination of THG microscopy with two-photon and second-harmonic imaging provides a new tool for exploring the interactions between lipid bodies, extracellular matrix and fluorescent compounds (vitamin A, NADH and others) in tissues.

Hydrogen Evolution from Water by Visible Light, a Homogeneous Three Component Test System for Redox Catalysis

Abstract: Reference LPI-ARTICLE-1978-012doi:10.1002/hlca.19780610740View record in Web of Science Record created on 2006-02-21, modified on 2017-05-12