Universal metamaterial absorbe

We propose a design for an universal absorber, characterized by a resonance frequency that can be tuned from visible to microwave frequencies independently of the choice of the metal and the dielectrics involved. An almost resonant perfect absorption up to 99.8 % is demonstrated at resonance for all polarization states of light and for a very wide angular aperture. These properties originate from a magnetic Fabry-Perot mode that is confined in a dielectric spacer of $\lambda/100$ thickness by a metamaterial layer and a mirror. An extraordinary large funneling through nano-slits explains how light can be trapped in the structure. Simple scaling laws can be used as a recipe to design ultra-thin perfect absorbers whatever the materials and the desired resonance wavelength, making our design truly universal

Large negative lateral shifts due to negative refraction

When a thin structure in which negative refraction occurs (a metallo-dielectric or a photonic crystal) is illuminated by a beam, the reflected and transmitted beam can undergo a large negative lateral shift. This phenomenon can be seen as an interferential enhancement of the geometrical shift and can be considered as a signature of negative refraction

X-Band Polarimetric & Doppler radar observations of heavy precipitation events over the Mediterranean region (France).

Numerous heavy precipitations take place over the western Mediterranean Sea especially during summer and in some case lead to severe floods over the continent (Vaison la Romaine in 1992, Draguignan the 15-16 June 2010, Antibes 30 October-1 November 2010...). Since the Mediterranean is surrounded by mountain barriers, and strong contrasts between sea and continent exist, local forcing is important. The present work aims at examining the environmental conditions and precipitation structures of storms observed in these regions and at improving our knowledge about the life-cycle of the more intense events and processes that govern their evolution. It uses observations gathered by the X band polarimetric & Doppler weather Radar HYDRIX. This radar, owned by the LATMOS/CNRS, developed and operated by NOVIMET, collects in an operational way since 2008 reflectivity, Doppler and polarimetric data with a time step and a spatial resolution of 5 minutes and 1 km respectively. In addition to these data, derived products such as instantaneous rainfall, cumulated rain, cell displacement and hydrometeor classification are obtained in real time. It also provides Doppler information in clear air region. All these data can be used to document the low level environment and the internal dynamics, microphysics and the interaction-mechanisms (wind shear, ...) leading to high-accumulated surface rainfall. The presentation focus on the first step of this work devoted to the temporal and spatial characterisation of the precipitation that affects the Provencal and Ligurian region. A statistical and a spectral analysis are performed to construct a climatology and to document the life cycle and the dynamical-microphysical characteristics of a few representative high-impact events

Joint diffusivity and source estimation in tokamak plasma heat transport

International audienceIn this work, we focus on the diffusivity and source identification in the electron heat transport model. This phenomenon is described by a second-order parabolic differential equation with distributed diffusion parameter and input. Once existence and uniqueness conditions of the heat model solution are established, a spectral Galerkin method is used to express this solution in the finite dimensional framework. The time-space separation and the Kalman filter are combined to simultaneously estimate the distributed variables (diffusion coefficient and the input). Computer simulations on both simulated and real data are provided to illustrate the performance of the proposed technique

Adaptive Distributed Parameter and Input Estimation in Plasma Tokamak Heat Transport

International audienceIn this paper, the adaptive estimation of spatially varying diffusion and source term coefficients for a linear parabolic partial differential equation describing tokamak plasma heat transport is considered. An estimator is defined in the infinite-dimensional framework having the system state and the parameters' estimate as its states. Our scheme allows to estimate constant, spatially distributed and spatio-temporally distributed parameters as well as input with known upper bounds in time. While the parameters convergence depends on the plant signal richness assumption, the state convergence is established using the Lyapunov approach. Since the estimator is infinite-dimensional, the Galerkin finite-dimensional technique is used to implement it. In silico simulations are provided to illustrate the performance of the proposed approach

Optically optimal wavelength-scale patterned ITO/ZnO composite coatings for thin film solar cells

International audienceA methodology is proposed for finding structures that are, optically speaking, locally optimal : a physical analysis of much simpler structures is used to constrain the optimization process. The obtained designs are based on a flat amorphous silicon layer (to minimize recombination) with a patterned anti-reflective coating made of ITO or ZnO, or a composite ITO/ZnO coating. These latter structures are realistic and present good performances despite very thin active layers

Estimation de la diffusion thermique dans les plasmas de Tokamak

6 pagesInternational audienceCe travail concerne l'étude du profil de transport de la température des électrons du plasma. Une approximation numérique basée sur la méthode de Galerkin est proposée. Le coefficient de diffusion est estimé grâce à la projection spatiale qui réduit le problème à une dimension finie. Le filtre de Kalman étendu est proposé pour cette identification. Le travail est accompagné par un ensemble de simulations et de comparaisons avec les données expérimentales

Adaptive Distributed Parameter and Input Estimation in Plasma Tokamak Heat Transport

International audienceIn this paper, the adaptive estimation of spatially varying diffusion and source term coefficients for a linear parabolic partial differential equation describing tokamak plasma heat transport is considered. An estimator is defined in the infinite-dimensional framework having the system state and the parameters' estimate as its states. Our scheme allows to estimate constant, spatially distributed and spatio-temporally distributed parameters as well as input with known upper bounds in time. While the parameters convergence depends on the plant signal richness assumption, the state convergence is established using the Lyapunov approach. Since the estimator is infinite-dimensional, the Galerkin finite-dimensional technique is used to implement it. In silico simulations are provided to illustrate the performance of the proposed approach