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

Quantum phase transitions in three-leg spin tubes

We investigate the properties of a three-leg quantum spin tube using several techniques such as the density matrix renormalization group method, strong coupling approaches and the non linear sigma model. For integer spins S, the model proves to exhibit a particularly rich phase diagram consisting of an ensemble of 2S phase transitions. They can be accurately identified by the behavior of a non local string order parameter associated to the breaking of a hidden symmetry in the Hamiltonian. The nature of these transitions are further elucidated within the different approaches. We carry a detailed DMRG analysis in the specific cases S = 1. The numerical data confirm the existence of two Haldane phases with broken hidden symmetry separated by a trivial singlet state. The study of the gap and of the von Neumann entropy suggest a first order phase transition but at the close proximity of a tricritical point separating a gapless and a first order transition line in the phase diagram of the quantum spin tube.Comment: 20 pages, 18 figure

Results of a self-triggered prototype system for radio-detection of extensive air showers at the Pierre Auger Observatory

We describe the experimental setup and the results of RAuger, a small radio-antenna array, consisting of three fully autonomous and self-triggered radio-detection stations, installed close to the center of the Surface Detector (SD) of the Pierre Auger Observatory in Argentina. The setup has been designed for the detection of the electric field strength of air showers initiated by ultra-high energy cosmic rays, without using an auxiliary trigger from another detection system. Installed in December 2006, RAuger was terminated in May 2010 after 65 registered coincidences with the SD. The sky map in local angular coordinates (i.e., zenith and azimuth angles) of these events reveals a strong azimuthal asymmetry which is in agreement with a mechanism dominated by a geomagnetic emission process. The correlation between the electric field and the energy of the primary cosmic ray is presented for the first time, in an energy range covering two orders of magnitude between 0.1 EeV and 10 EeV. It is demonstrated that this setup is relatively more sensitive to inclined showers, with respect to the SD. In addition to these results, which underline the potential of the radio-detection technique, important information about the general behavior of self-triggering radio-detection systems has been obtained. In particular, we will discuss radio self-triggering under varying local electric-field conditions.Comment: accepted for publication in JINS

Gauge theory picture of an ordering transition in a dimer model

We study a phase transition in a 3D lattice gauge theory, a "coarse-grained" version of a classical dimer model. Duality arguments indicate that the dimer lattice theory should be dual to a XY model coupled to a gauge field with geometric frustration. The transition between a Coulomb phase with dipolar correlations and a long range ordered columnar phase is understood in terms of a Higgs mechanism. Monte Carlo simulations of the dual model indicate a continuous transition with exponents close but apparently different from those of the 3d XY model. The continuous nature of the transition is confirmed by a flowgram analysis.Comment: 4 pages, 4 figure

Evaluation of cassava (Manihot esculenta Crantz) germplasm collections using RAPD markers

Des marqueurs RAPD sont combinés avec une analyse de calcul de distance (simple matching) afin d'évaluer les relations génétiques entre les cultivars africains de manioc. Une étude préliminaire sur 3 espèces avec 20 "primers" montre clairement que ces marqueurs peuvent être très utiles. L'ADN de 19 cultivars a été amplifié en utilisant 8 primers. Les cultivars se discriminent bien et sont distribués de manière cohérente si on compare aux résultats obtenus avec les RFLP ou isoenzymes. La diversité génétique, la caractérisation des collections et les études d'introgression sont les domaines que les RAPD peuvent contribuer à améliorer pour le manioc. (Résumé d'auteur

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

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

Radio Detection of Extensive Air Showers with CODALEMA

The principle and performances of the CODALEMA experimental device, set up to study the possibility of high energy cosmic rays radio detection, are presented. Radio transient signals associated to cosmic rays have been identified, for which arrival directions and shower's electric field topologies have been extracted from the antenna signals. The measured rate, about 1 event per day, corresponds to an energy threshold around 5.10^16 eV. These results allow to determine the perspectives offered by the present experimental design for radiodetection of UHECR at a larger scale.Comment: 4 pages and 3 figures. To appear in the Proceedings of the 29th ICRC, Pune (2005

Fast Evaluation of the Fatigue Lifetime of Elastomers Based on a Heat Build-up Protocol and Micro-tomography Measurements

WOSInternational audienceThe temperature of rubber-like materials increases under cyclic loadings, due to their dissipative behaviour and low thermal conductivity. This well-known phenomenon, called heat build-up, has attracted the attention of researchers for a long time. But, to our knowledge, no published studies have tried to link this temperature rise to fatigue behaviour, as already done for many metallic materials. Two main points are discussed in this paper. The first one is dedicated to heat build-up measurements: a specific experimental protocol was developed to capture the instantaneous heat build-up and, based on this protocol, a "heat build-up test" was defined in order to link the temperature rise to the principal maximum strain, which is a commonly used variable for fatigue criterion. A discussion on the correlation between these results and the fatigue behaviour is opened. This relation is illustrated for several industrial materials by a comparison between heat build-up measurements and fatigue life duration. The second point investigates the ability to couple X-ray tomography measurements presented elsewhere [1] to the former heat build-up results in order to predict the initiation lifetime. An approach based on a critical energy criterion was proposed and the comparison to a classic Wöhler curve approach gave very good results