Spatial diffusion in a periodic optical lattice: revisiting the Sisyphus effect

We numerically study the spatial diffusion of an atomic cloud experiencing Sisyphus cooling in a three-dimensional lin$\bot$lin optical lattice in a broad range of lattice parameters. In particular, we investigate the dependence on the size of the lattice sites which changes with the angle between the laser beams. We show that the steady-state temperature is largely independent of the lattice angle, but that the spatial diffusion changes significantly. It is shown that the numerical results fulfil the Einstein relations of Brownian motion in the jumping regime as well as in the oscillating regime. We finally derive an effective Brownian motion model from first principles which gives good agreement with the simulations.Comment: accepted for publication in Eur. Phys. J.

Dielectric resonances in disordered media

Binary disordered systems are usually obtained by mixing two ingredients in variable proportions: conductor and insulator, or conductor and super-conductor. and are naturally modeled by regular bi-dimensional or tri-dimensional lattices, on which sites or bonds are chosen randomly with given probabilities. In this article, we calculate the impedance of the composite by two independent methods: the so-called spectral method, which diagonalises Kirchhoff's Laws via a Green function formalism, and the Exact Numerical Renormalization method (ENR). These methods are applied to mixtures of resistors and capacitors (R-C systems), simulating e.g. ionic conductor-insulator systems, and to composites consituted of resistive inductances and capacitors (LR-C systems), representing metal inclusions in a dielectric bulk. The frequency dependent impedances of the latter composites present very intricate structures in the vicinity of the percolation threshold. We analyse the LR-C behavior of compounds formed by the inclusion of small conducting clusters (``$n$-legged animals'') in a dielectric medium. We investigate in particular their absorption spectra who present a pattern of sharp lines at very specific frequencies of the incident electromagnetic field, the goal being to identify the signature of each animal. This enables us to make suggestions of how to build compounds with specific absorption or transmission properties in a given frequency domain.Comment: 10 pages, 6 figures, LaTeX document class EP

Impact de l’autoroute sur le milieu. Étude bibliographique et propositions de recherche au Québec

L'impact sur le milieu des autoroutes construites au Québec depuis 1960 préoccupe peu de chercheurs. Face à cette lacune, un survol de la littérature en la matière s'imposait avant de dégager quelques avenues de recherche à explorer.The impact of highways built in Québec since 1960 has never been evaluated. A preliminary analysis of the literature is necessary before formulating research proposals

Credit constraints and the cyclicality of R&D investment: Evidence from France

We use a French firm-level data set containing 13,000 firms over the period 1993-2004 to analyze the relationship between credit constraints and firms' R&D behavior over the business cycle. Our main results can be summarized as follows: (i) the share of R&D investment over total investment is countercyclical without credit constraints, but it becomes less countercyclical as firms face tighter credit constraints; (ii) this result is magnified for firms in sectors that depend more heavily upon external finance, or that are characterized by a low degree of asset tangibility ; (iii) in more credit constrained firms, R&D investment share plummets during recessions but does not increase proportionally during upturns; (iv) average R&D investment and productivity growth are more negatively correlated with sales volatility in more credit constrained firms.business cycles ; R&D ; credit constraints ; volatility

How do the grains slide in fine-grained zirconia polycrystals at high temperature?

Degradation of mechanical properties of zirconia polycrystals is hardly discussed in terms of solution-precipitation grain-boundary sliding due to experimental controversies over imaging of intergranular amorphous phases at high and room temperatures. Here, the authors applied the techniques of mechanical spectroscopy and transmission electron microscopy (TEM) to shed light on the amorphization of grain interfaces at high temperature where the interface-reaction determines the behaviour of fine-grained zirconia polycrystals. They present mechanical spectroscopy results, which yield evidences of an intergranular amorphous phase in silica doped and high-purity zirconia at high temperature. Quenching of zirconia polycrystals reveals an intergranular amorphous phase on TEM images at room temperature.Comment: 12 pages, 3 figure

Searching for variable stars in Galactic Open Clusters

A long-term project, aiming at systematic search for variable stars in Galactic Open Clusters, was started at the Geneva Observatory in 2002. We have been observing regularly a sample of twenty-seven Galactic Open Clusters in the U, B, V Geneva filters. The goal is to identify and to study their variable stars, as well as the connection between the variable stars in a cluster and the cluster properties. We present the status of this work in progress, and show preliminary results for one of these clusters, IC 4651.Comment: To appear in the proceedings of Stellar Pulsation: Challenges for theory and observations Conference, Santa Fe, NM, US

Méthodologie pour la détermination rapide de conditions opératoires optimales : application au réacteur discontinu

BOOK ABSTRACT : Les évolutions fondamentales du génie des procédés soustendent la plupart des progrès dans le domaine des industries de transformation de la matière et de production d'énergie. Diminuer la consommation d'énergie et les impacts sur l'environnement, accroître la qualité des produits, assurer la sécurité des installations, préserver la rentabilité économique sont autant de défis qui imposent au génie des procédés de développer des méthodes toujours plus efficaces. À travers l'étude de cas concrets, l'ouvrage propose une immersion dans la discipline. Le lecteur pourra acquérir une idée précise des possibilités actuelles du génie des procédés, cerner le type de problèmes qui peuvent être résolus, s'approprier les stratégies et prendre connaissance des méthodes en percevant les avantages et les limites de chacune d'elles. Bien plus qu'un ensemble de méthodes, c'est une façon d'aborder les problèmes concrets et de les résoudre que l'ouvrage souhaite transmettre. Le Laboratoire de Génie Chimique de Toulouse (LGC), fondé en 1965 sous sa forme actuelle, sur la base de l'Institut de Génie Chimique créé en 1949, a eu un rôle historique prépondérant dans l'implantation du génie chimique en Europe, et reste l'un des acteurs majeurs de la recherche en génie des procédés. Cet ouvrage est le résultat d'une réflexion collective menée au sein du LGC. Chaque chapitre a été rédigé par des chercheurs et enseignants-chercheurs directement impliqués dans l'obtention des résultats présentés