Hypernovae as possible sources of Galactic positrons

INTEGRAL/SPI has recently observed a strong and extended emission resulting from electron-positron annihilation located in the Galactic center region, consistent with the Galactic bulge geometry, without any counterpart at high gamma-ray energies, nor in the 1809 keV $^{26}$Al decay line. In order to explain the rate of positron injection in the Galactic bulge, estimated to more than 10$^{43}$ s$^{-1}$, the most commonly considered positron injection sources are type Ia supernovae. However, SN Ia rate estimations show that those sources fall short to explain the observed positron production rate, raising a challenging question about the nature of the Galactic positron source. In this context, a possible source of Galactic positrons could be supernova events of a new type, as the recently observed SN2003dh/GRB030329, an exploding Wolf-Rayet star (type Ic supernova) associated with a hypernova/gamma-ray burst; the question about the rate of this kind of events remains open, but could be problematically low. In this paper, we explore the possibility of positron production and escape by such an event in the framework of an asymmetric model, in which a huge amount of $^{56}$Ni is ejected in a cone with a very high velocity; the ejected material becomes quickly transparent to positrons, which spread out in the interstellar medium.Comment: 8 pages, 2 figures. To appear in the Proceedings of the 5th INTEGRAL Workshop: "The INTEGRAL Universe", February 16-20, 2004, Munich, German

Characterization of a Multi-User Indoor Positioning System Based on Low Cost Depth Vision (Kinect) for Monitoring Human Activity in a Smart Home

An increasing number of systems use indoor positioning for many scenarios such as asset tracking, health care, games, manufacturing, logistics, shopping, and security. Many technologies are available and the use of depth cameras is becoming more and more attractive as this kind of device becomes affordable and easy to handle. This paper contributes to the effort of creating an indoor positioning system based on low cost depth cameras (Kinect). A method is proposed to optimize the calibration of the depth cameras, to describe the multi-camera data fusion and to specify a global positioning projection to maintain the compatibility with outdoor positioning systems. The monitoring of the people trajectories at home is intended for the early detection of a shift in daily activities which highlights disabilities and loss of autonomy. This system is meant to improve homecare health management at home for a better end of life at a sustainable cost for the community

Poissons récoltés par dragages dans le lagon de Nouvelle-Calédonie

Au cours de l'échantillonnage à la drague des lagons de Nouvelle-Calédonie, 73 familles de poissons ont été récoltées; 4 d'entre elles sont signalées pour la première fois de la région. 323 espèces ont été recensées dont 49 pour la première fois de Nouvelle-Calédonie. Les familles et les espèces sont présentées avec leur pourcentage d'occurence dans les dragages. Des remarques biogéographiques sont faites par rapport aux régions environnantes et malgré de nombreuses lacunes dans les connaissances entre les faunes de Nouvelle-Calédonie et de la Grande Barrière Australienne. (Résumé d'auteur

Curvature based corner detector for discrete, noisy and multi-scale contours

International audienceEstimating curvature on digital shapes is known to be a difficult problem even in high resolution images 10,19. Moreover the presence of noise contributes to the insta- bility of the estimators and limits their use in many computer vision applications like corner detection. Several recent curvature estimators 16,13,15, which come from the dis- crete geometry community, can now process damaged data and integrate the amount of noise in their analysis. In this paper, we propose a comparative evaluation of these estimators, testing their accuracy, efficiency, and robustness with respect to several type of degradations. We further compare the best one with the visual curvature proposed by Liu et al. 14, a recently published method from the computer vision community. We finally propose a novel corner detector, which is based on curvature estimation, and we provide a comprehensive set of experiments to compare it with many other classical cor- ner detectors. Our study shows that this corner detector has most of the time a better behavior than the others, while requiring only one parameter to take into account the noise level. It is also promising for multi-scale shape description

Infiltration processes in karst using an event-based conceptual model of flow and transport of dissolved organic carbon

International audienceThe aim of this study is to characterize karst infiltration processes during flood events using a rainfall-discharge model coupled with a transport model for non-conservative solutes. The modelling approach is based on a classical karst devoted model with three connected reservoirs: SOIL (and epikarst) that feeds the aquifer partitioned into DIFFUSE and CONDUIT. Solute transport is modelled using mixing equations, including an empirical retardation factor in SOIL, as well as a first order solute decay. In order to take into account some specificities commonly observed in karst systems, three parameters are added to simulate overflows, piston-type flows in conduits, and a variation of the recharge area according to the initial hydrological conditions. To validate our approach, we used the dissolved organic carbon (DOC) as tracer, which is a non- conservative compound derived from the enrichment of infiltrated water into soil humic substances. The model was applied on a small karst system at Fertans in the French Jura mountains, where discharge and continuous measurements of DOC fluorescence are recorded. The model was calibrated and validated on a set of 19 flood events, showing that the model adequately simulated hydrographs and delayed chemographs during flood events with various rainfall intensities. A large variability of the recharge area was highlighted according to low and high groundwater level periods, and was attributed to the state of hydraulic connectivity in the unsaturated zone. The model simulate the contributions of pre-event and event waters during flood events and allow to better quantify the available resource considering the mixing effect of DOC. It shows, in particular, that total discharge of some flood events during dry periods are mainly composed by pre-event water via piston flow-type processes. Finally, this study show the ability of mixing model to properly simulate solute transport taking into account degradation and retardation processes

Meaningful Thickness Detection on Polygonal Curve

International audienceThe notion of meaningful scale was recently introduced to detect the amount of noise present along a digital contour. It relies on the asymptotic properties of the maximal digital straight segment primitive. Even though very useful, the method is restricted to digital contour data and is not able to process other types of geometric data like disconnected set of points. In this work, we propose a solution to overcome this limitation. It exploits another primitive called the Blurred Segment which controls the straight segment recognition precision of disconnected sets of points. The resulting noise detection provides precise results and is also simpler to implement. A first application of contour smoothing demonstrates the efficiency of the proposed method. The algorithms can also be tested online

Relations entre la production d'huile et le nombre de régimes chez le palmier à huile (Elaeis guineensis Jacq.). Conséquences pour la pollinisation dans les jeunes plantations

A l'aide de résultats expérimentaux et de données génétiques, cet article illustre la prépondérance du nombre de régimes sur le poids moyen d'un régime dans l'amélioration du poids total. L'amélioration génétique du palmier à huile par sélection clonale ou sexuée, directe ou indirecte, aboutit à une augmentation du nombre de régimes et donc à un sex-ratio élevé. Dans des conditions écologiques favorables, celui-ci atteint des valeurs telles que la production de pollen est très souvent insuffisante à l'entrée en production. Si des apports de pollen extérieur sont effectués, la situation évolue très vite vers une diminution du sex-ratio, ce qui rend alors la pollinisation naturelle tout à fait efficace. La pollinisation assistée est actuellement la technique la plus utilisée pour faire face avec succès aux carences en pollen observées dans les jeunes plantations. Du fait des contraintes qu'elle impose, d'autres solutions sont recherchées dans le domaine des techniques culturales : introduction de sources de pollen dans la plantation, ou dans le domaine de la génétique : sélection de matériel plus masculin, amélioration du taux d'extraction de l'huil

Approche hydrochimique de la dégradation mécanique du versant instable de Séchilienne

National audienceLa chimie des eaux est un signal très fin qui permet la localisation dans le temps et dans l'espace de l'arrivée des eaux d'infiltration à l'origine des impulsions mécaniques des instabilités de versant. Il s'agit de comprendre comment s'organise la relation complexe entre altération chimique, modifications hydromécaniques et fragilisation/mouvements du versant rocheux instable. Pour cela, un suivi hydrogéochimique des eaux souterraines a été mis en place depuis 2010 sur le site de Séchilienne (France). La conductivité électrique est représentative du signal chimique engendré par la dégradation du massif. L'acquisition en continu de ce paramètre est pertinente pour le site de Séchilienne et peut se substituer au suivi chimique. L'avantage de l'acquisition de cette donnée est triple, ce qui peut en faire un outil pour la gestion du risque : mesure en temps réel, avec un pas de temps très fin et mise en œuvre peu coûteuse

Unstable rock slope hydrogeology: insights from the large-scale study of western Argentera-Mercantour hillslopes (South-East France)

International audienceInventory of unstable hillslopes, hydrogeological mapping and hydrochemical characteristics of natural spring waters were used to determine the long-term relationships between groundwater and gravitational instabilities in the Upper Tinée Valley (South-East French Alps). Water chemistry and flow records allow to propose a conceptual model of water flow within unstable rocky slopes and to back-calculate the volume of infiltrated water and the flow velocity in the aquifers for different deformation states of the slopes. An increase in infiltrated yield, flow velocity and porosity is observed and linked to collapsed and toppled structures in the upper parts of the hillslopes. In these areas, perched aquifers take place in the reworked media. When a large landslide occurs, it modifies the geometry of the slope and bypasses the perched flows down to the foot of the slope. With long-term continuous slope deformation, the associated effect between water flows and slope destabilization changes. In the fractured rock, the coupled effect corresponds to rising water pressures with limited volumes of infiltrated water; in the more fractured and permeable collapsed and toppled areas, the volumes of infiltrated water increase with a lower variation of water pressures