A radiation-hydrodynamics scheme valid from the transport to the diffusion limit

We present in this paper the numerical treatment of the coupling between hydrodynamics and radiative transfer. The fluid is modeled by classical conservation laws (mass, momentum and energy) and the radiation by the grey moment $M_1$ system. The scheme introduced is able to compute accurate numerical solution over a broad class of regimes from the transport to the diffusive limits. We propose an asymptotic preserving modification of the HLLE scheme in order to treat correctly the diffusion limit. Several numerical results are presented, which show that this approach is robust and have the correct behavior in both the diffusive and free-streaming limits. In the last numerical example we test this approach on a complex physical case by considering the collapse of a gas cloud leading to a proto-stellar structure which, among other features, exhibits very steep opacity gradients.Comment: 29 pages, submitted to Journal of Computational physic

Convergence of monotone finite volume schemes for hyperbolic scalar conservation laws with multiplicative noise

We study here the discretization by monotone finite volume schemes of multi-dimensional nonlinear scalar conservation laws forced by a multiplicative noise with a time and space dependent flux-function and a given initial data in $L^{2}(\R^d)$. After establishing the well-posedness theory for solutions of such kind of stochastic problems, we prove under a stability condition on the time step the convergence of the finite volume approximation towards the unique stochastic entropy solution of the equation

A hierarchy of models related to nanoflows and surface diffusion

In last years a great interest was brought to molecular transport problems at nanoscales, such as surface diffusion or molecular flows in nano or sub-nano-channels. In a series of papers V. D. Borman, S. Y. Krylov, A. V. Prosyanov and J. J. M. Beenakker proposed to use kinetic theory in order to analyze the mechanisms that determine mobility of molecules in nanoscale channels. This approach proved to be remarkably useful to give new insight on these issues, such as density dependence of the diffusion coefficient. In this paper we revisit these works to derive the kinetic and diffusion models introduced by V. D. Borman, S. Y. Krylov, A. V. Prosyanov and J. J. M. Beenakker by using classical tools of kinetic theory such as scaling and systematic asymptotic analysis. Some results are extended to less restrictive hypothesis

Reprise de l'embryogenèse adventive à partir d'embryons somatiques de caféier (Coffea arabica L.) après leur congélation dans l'azote liquide

Des embryons somatiques de caféiers (#C. arabica$ L.), obtenus à partir d'explants foliaires, survivent à une congélation à -196°C. Les jeunes embryons sont isolés puis cultivés pendant 24 heures sur un milieu enrichi en saccharose (0,75 M). Ils sont ensuite mis à incuber pendant 2 heures dans une solution cryoprotectrice contenant la même concentration en saccharose et 5 % de diméthysulfoxyde. Placés dans des ampoules cryobiologiques, ils sont alors congelés lentement, jusqu'à -40°C, avant d'être plongés et conservés dans de l'azote liquide. Après un réchauffement rapide dans un bain-marie à 40°C, les embryons sont repiqués chaque jour sur des milieux dont la concentration en saccharose est progressivement abaissée jusqu'à la valeur standard de 0,1 M. Le taux de reprise de l'embryogenèse adventive atteint 50 %, 17 semaines après le réchauffement. Les premières plantules, obtenues in vitro à partir de matériel congelé, ont un développement apparemment normal. Dans un proche avenir, la technique mise au point pourrait être élargie à d'autres espèces actuellement entretenues en champ par les stations de recherche caféière. (Résumé d'auteur

Propuesta para la enseñanza y el aprendizaje de la relación sociedad naturaleza en el nivel universitario. un ejemplo concreto en una cuenca hidrográfica en el sudeste de la provincia de Buenos Aires

La presente propuesta es para la enseñaza y el aprendizaje de la relación sociedad-naturaleza. Los destinatarios son los alumnos de la carrera de profesorado en ciencia de la Universidad Nacional de Mar del Plata. A través de ella los estudiantes podrán distinguir las diferencias presentes en los procesos tanto ecológicos como sociales, en base al concepto de articulación sociedad-naturaleza en una realidad integral. Permite explicar los fenómenos relativos a las acciones de los hombres organizados socialmente en relación a un entorno determinado, en un tiempo y espacio específico y con una tecnología definida. La propuesta de enseñanza se basa en el modelo planteado por Gallopin (1986) el cual examina la relación sociedad-naturaleza como resultado de la interacción de dos esferas la “Sociedad” y los "Sistemas Ecológicos" y se lleva a cabo en una cuenca hidrográfica

Quit Smoking and Run For Your Life!

To The Editor: The World Health Organization promotes the World No Tobacco Day on May 31

Radio Detection of Cosmic Ray Air Showers with Codalema

Studies of the radio detection of Extensive Air Showers is the goal of the demonstrative experiment CODALEMA. Previous analysis have demonstrated that detection around $5.10^{16}$ eV was achieved with this set-up. New results allow for the first time to study the topology of the electric field associated to EAS events on a event by event basis.Comment: 6 pages, 4 figures Proceedings of the Rencontres de Moriond, Very High Energy Phenomena in the Universe, La Thuile, Italy (March 12-19, 2005

Decay resistance against Coriolus versicolor in Sessile oak ( Quercus petraea Liebl.): analysis of the between-tree variability and correlations with extractives, tree growth and other basic wood properties

Abstract : Weight loss due to fungus Coriolus versicolor has been measured on 614 samples according to the NF EN 113 norm. Up to eight samples were cut at breast height (two opposite radii×four radial positions in heartwood) from 82 mature sessile oaks ( Quercus petraea Liebl.) originating from contrasting regions, silvicultural schedules and site qualities in France. The following points are addressed in the paper: (i) contribution to the total variability for weight loss of the effects "tree”, "position in the tree”, as well as their interaction; (ii) percentage of wood samples and trees in each of the five classes of natural durability defined by the norm NF EN 350-2; (iii) test of the effects of region, silvicultural schedule and site quality on weight loss and evaluating their contribution to the total variation; and (iv) correlations at tree level between weight loss and several traits related to tree growth and basic wood properties (density, swelling, grain angle, multiseriate wood rays characteristics, extractives content). The results are discussed with a view to aid the forest manager as well as the log/wood user to take advantage of the high level of between-tree variability observed as natural durability against C. versicolo