Influence of the photonuclear effect on electron-neutrino-induced electromagnetic cascades under the Landau-Pomeranchuk-Migdal regime in standard rock

The observation of earth skimming neutrinos has been proposed as a rather sensitive method to detect ultra-high energy (UHE) cosmic neutrinos. Energetic cosmic neutrinos can interact inside the rock and produce leptons via a charged current interaction. In the case of an incoming electron neutrino undergoing a charged current interaction, the produced UHE electron will induce an underground electromagnetic shower. At high energy (above 7.7 TeV in standard rock), such showers are subject to LPM (Landau, Pomeranchuk and Migdal) suppression of the radiative processes cross sections (bremsstrahlung and pair production). The consequence of this suppression is that showers are elongated. This effect will increase the detection probability of such events allowing deeper showers to emerge with detectable energies. On the other hand, the photonuclear processes which are usually neglected in electromagnetic showers with respect to radiative processes, turn out to become dominant in the LPM regime and will reduce the shower length. In this work, we have performed a complete Monte Carlo study of an underground shower induced by UHE electrons by taking into account both the LPM suppression and the photonuclear interaction. We will discuss the effects of both of these processes on the shower length and on the detectability of such events by ground arrays or fluorescence telescopes. We show that limits on neutrino fluxes that were obtained using simulations that were obviously neglecting photonuclear processes are overoptimistic and should be corrected.Comment: 6 pages, 7 figure

Seed-div: an abstract role-playing game for discussing collective management of agrobiodiversity

L'objectif principal de cette recherche est d'accompagner les paysans dans l'élaboration d'un cadre de gestion collective de la diversité de leurs variétés de céréales vivrières. La gestion semencière et son impact sur la dynamique de la biodiversité sont soumis aux choix individuels des paysans, leurs stratégies d'une part, et au fonctionnement général du système semencier d'autre part. Nous postulons que la compréhension partagée des interactions au sein de ce système complexe est un prérequis pour travailler ensemble à la construction de règles de gestion collective qui participent à la durabilité de l'agriculture via un accès à un large choix de semences. La modélisation participative conceptuelle et les jeux de rôle ont été utilisés durant différents ateliers réunissant chercheurs, ONG, organisations paysannes et agriculteurs. Le résultat de cette série d'ateliers correspond à un modèle, un système multi-agents, représentant un archétype de village malien permettant de simuler la diversité de stratégies individuelles de gestion de semences qui sont ensuite disponibles gratuitement pour la communauté villageoise. Les agents du modèle sont des agriculteurs qui choisissent les variétés à semer ce qui provoque des échanges dans la communauté en fonction de leurs stratégies individuelles ou de facteurs externes. Les paramètres utilisés ont une valeur qualitative c'est pourquoi le modèle sert de support de discussion entre paysans de différentes régions. Le modèle a été construit et validé au travers de ces ateliers avec un impact évident sur les acteurs locaux pour la construction de nouveaux scénarios de gestion de la diversité variétale. Ainsi, le modèle a pu être utilisé en termes de prospective pour simuler des scénarios à partir de nouvelles formes d'action collective. (Résumé d'auteur

A Statistical Approach to the Rupture of Brittle Materials

International audienceSince initial defects are the main cause of the failure of structures made of brittle materials, the scope of this paper is to take these defects into account in the evaluation of the failure probability of a structure. Using the weakest link theory assumption and modeling the failure probability of a single link, a general relationship between the statistical distribution of defects and the failure probability is obtained. After determining the size of the critical defect, some correlations between the defect distribution and the Weibull's parameters are deduced from either Linear Fracture Mechanics or Continuum Damage Mechanics. The effect of the statistical distribution of defects within the material is computed and studied with respect to the distribution itself, the loaded volume of the structure and the heterogeneity of the stress field

Toxicokinetics of fumonisin B1 in turkey poults and tissue persistence after exposure to a diet containing the maximum European tolerance for fumonisins in avian feeds

The kinetic of fumonisin B1 (FB1) after a single IV and oral dose, and FB1 persistence in tissue were investigated in turkey poults by HPLC after purification of samples on columns. After IV administration (single-dose: 10 mg FB1/kg bw), serum concentration–time curves were best described by a three-compartment open model. Elimination half-life and mean residence time of FB1 were 85 and 52 min, respectively. After oral administration (single-dose: 100 mg FB1/kg bw) bioavailability was 3.2%; elimination half-life and mean residence time were 214 and 408 min, respectively. Clearance of FB1 was 7.6 and 7.5 ml/min/kg for IV and oral administration respectively. Twenty four hours after the administration of FB1 by the intravenous route, liver and kidney contained the highest levels of FB1 in tissues, level in muscle was low or below the limit of detection (LD, 13 µg/kg). The persistence of FB1 in tissue was also studied after administration for nine weeks of a feed that contained 5, 10 and 20 mg FB1+FB2/kg diet. Eight hours after the last intake of 20 mg FB1+FB2/kg feed (maximum recommended concentration of fumonisins established by the EU for avian feed), hepatic and renal FB1 concentrations were 119 and 22 µg/kg, level in muscles was below the LD

Three simultaneous and independent approaches to the characterization of a new species of Labeo (Teleostei, Cyprinidae) from West Africa

Une nouvelle espèce de #Labeo (Cuvier, 1817) a été trouvée dans les hauts bassins du Niger et du Sénégal (Baoulé). Quoique reconnue comme une nouvelle espèce, certains caractères se chevauchent avec ceux de deux autres espèces sympatriques : #L. coubie et #L. senegalensis. Ce chevauchement est d'ailleurs suffisant pour ne pas écarter le fait que cette supposée nouvelle espèce ne soit en réalité qu'un hybride des deux autres. Pour vérifier l'une ou l'autre hypothèse, trois méthodes séparées ont été utilisées : une analyse morphologique/morphométrique, une analyse chromosomique/enzymologique et une étude de parasitologie comparative. Ces trois études complémentaires ont été menées simultanément mais surtout de façon indépendante afin de minimiser au mieux de tout préjugé. A partir de cela, nous avons pu montrer que chacune des trois espèces pouvait être caractérisée grâce à la combinaison de caractères morphologiques (forme de la bouche notamment) et méristiques (nombre de branchiospines essentiellement). Si les trois espèces possèdent le même nombre de chromosomes (2N = 50), le nouveau morphotype présente quatre loci homozygotes pour des allèles qui n'existent ni chez #L. coubie ni chez #L. senegalensis

Rooted maps on orientable surfaces, Riccati's equation and continued fractions

International audienceWe present a new approach in the study of rooted maps without regard to genus. We prove the existence of a new type of equation for the generating series of these maps enumerated with respect to edges and vertices. This is Riccati's equation. It seems to be the first time that such a differential equation appears in the enumeration of rooted maps. Solving this equation leads to different closed forms of the studied generating series. The most interesting consequence is a development of this generating function in a very nice continued fraction leading to a new equation generalizing the well-known Dyck equation for rooted planar trees. In a second part, we also obtain a differential equation for the generating series of rooted trees regardless of the genus, with respect to edges. This also leads to a continued fraction for the generating series of rooted genus independent trees and to an unexpected relation between both previous generating series of trees and rooted maps

Proceedings of the 6th international coral reef symposium

Two acoustic surveys have been done in the lagoon all around New Caledonia, with a digital integrator. The cruises lasting two weeks were done at six month interval. Much information has been obtained on stock biomass and spatial distribution of fish and schools. Fish are dispersed at night and stay near the surface. During the day they form schools, usually of very small size. Some species are found mostly along the coasts, on the reef flats and far inside in the bays. Some others stay in the middle of the bays or in the central part of the lagoon and occur usually in deeper water at some distance of the bottom. Aerial and diving observations have shown that the fish of coastal schools were feeding on the reef. Species schooling during the day in the middle of the bays usualy occur deep in the water, not far from the bottom where suspended organic matter is abundant. In a shallow water environment like a coral reef lagoon, the concept of pelagic fish is questionable and most species seem to have strong relations with the bottom. The small pelagic fish, preyed by larger pelagic species (jacks, scads, spanish mackerels ...), play a role of energy transfer from the benthic to the pelagic compartment. (Résumé d'auteur

Radial velocity follow-up for confirmation and characterization of transiting exoplanets

Radial Velocity follow-up is essential to establish or exclude the planetary nature of a transiting companion as well as to accurately determine its mass. Here we present some elements of an efficient Doppler follow-up strategy, based on high-resolution spectroscopy, devoted to the characterization of transiting candidates. Some aspects and results of the radial velocity follow-up of the CoRoT space mission are presented in order to illustrate the strategy used to deal with the zoo of transiting candidate