Characterization of the precipitation in southwestern part of Greece with X-band Doppler radar, 2-D video disdrometer and rain gauges

International audienceWe document precipitation in the southwestern part of Greece with the National Observatory of Athens (NOA) X-band radar, NOA 2D video disdrometer and a network of rain gauges. The observations were collected between February and April 2004. Time evolution of the drop size distribution (DSD) is presented for the 9 March 2004 case where rain rate (computed on 1-min period) was measured up to 80 mm/h and reflectivity at the location of the disdrometer exceeded 40 dBZ. We then present the differences of DSD as function of the rain rate for the studied case as well as for the entire observations of the field experiment. It shows that higher the rain rate is, larger the range of the DSD and higher the concentration of the raindrops are

Synoptic environment related to rapid cyclogenesis in the Eastern Mediterranean

International audienceThis paper presents first results on the investigation of the synoptic conditions that led to the rapid development of a low-pressure system over the Aegean Sea. Indeed, during the period 21?22 January 2004, a very deep cyclone was observed over the Aegean Sea with a minimum central pressure of ~972 hPa, a value which is among the lowest observed over the entire Mediterranean Sea during the last 40 years. The rapid development was associated with a two-trough system that, under the influence of a very intense upper-level jet, was merged in one and then acquired a negative tilting. Additional information on the mesoscale organisation of the system is given, based on lightning data and space borne microwave and infrared observations

Acoustique en Master 2 : Les étudiants font le cours

International audienceCet article rend compte d’une expérience pédagogique menée dans le cadre d’un cours d’acoustique de deuxième année de master professionnel en ingénierie. Il s’agissait pour l’enseignant de renforcer l’engagement, l’implication et la motivation des étudiants en passant d’un enseignement magistral à un enseignement qui rende les étudiants davantage acteurs de leurs apprentissages et favorise le travail en équipe. Dans ce cadre, les étudiants ont eu à concevoir le cours pour le reste de la promotion en préparant un exposé en équipe à partir de leurs lectures, les différents exposés étant ensuite présentés à l’ensemble de la promotion. Le projet de recherche que nous présentons a été engagé pour caractériser tous les aspects de cette pédagogie utilisée, et tenter d’inférer les apprentissages réalisés. La méthodologie qualitative mise en œuvre a consisté en des entretiens avec l’enseignant et avec les étudiants. Il semble d’abord que l’exposé ne rende actif que le groupe qui le présente, et les étudiants déclarent . De plus, les étudiants, s’ils sont intéressés au départ par cette méthode qui affiche sa différence, éprouvent des difficultés à se placer eux-mêmes dans une posture d’enseignant dont ils ne pensent pas avoir les compétences. D'autre part, les étudiants conviennent avoir de bonnes connaissances concernant le thème spécifique qu’ils ont eu à étudier mais reconnaissent que s’ils avaient à traiter de problématiques relevant de la thématique des autres exposés, ils se trouveraient en difficulté. Enfin, la nature des évaluations pose problème: est-ce qu'on évalue leur capacité à enseigner, leur capacité à s’approprier un sujet et construire un exposé, ou leurs apprentissages sur ce sujet ? L’enseignant a donc redéfini ses objectifs d'apprentissage, et a mesuré l’importance de la mise en cohérence des évaluations et de leurs critères avec ceux-ci. Si les exposés peuvent être maintenus en tant qu'évaluations, des activités pédagogiques en équipe et contextualisées devraient permettre à l'avenir de garantir une meilleure acquisition des concepts de base

Detection of reinforcement bars in concrete slabs by infrared thermography and microwaves excitation

International audienceThis paper presents a NDT method by infrared thermography with a microwave excitation system applied to the detection of metallic parts: a metal ring behind a wooden plate of 1cm thick, a reinforcement bar in front of a concrete wall and the detection of reinforcement bars equally spaced in a concrete slab of 6.5 cm thick. The excitation device is based on a magnetron associated with a horn pyramidal antenna. A contrast algorithm applied to the sequences of thermograms highlights metal ring or bars location

Statistical analysis of storm electrical discharges reconstituted from a lightning mapping system, a lightning location system, and an acoustic array

International audienceIn the framework of the European Hydrological Cycle in the Mediterranean Experiment project, a field campaign devoted to the study of electrical activity during storms took place in the south of France in 2012. An acoustic station composed of four microphones and four microbarometers was deployed within the coverage of a Lightning Mapping Array network. On the 26 October 2012, a thunderstorm passed just over the acoustic station. Fifty-six natural thunder events, due to cloud-to-ground and intracloud flashes, were recorded. This paper studies the acoustic reconstruction, in the low frequency range from 1 to 40 Hz, of the recorded flashes and their comparison with detections from electromagnetic networks. Concurrent detections from the European Cooperation for Lightning Detection lightning location system were also used. Some case studies show clearly that acoustic signal from thunder comes from the return stroke but also from the horizontal discharges which occur inside the clouds. The huge amount of observation data leads to a statistical analysis of lightning discharges acoustically recorded. Especially, the distributions of altitudes of reconstructed acoustic detections are explored in detail. The impact of the distance to the source on these distributions is established. The capacity of the acoustic method to describe precisely the lower part of nearby cloud-to-ground discharges, where the Lightning Mapping Array network is not effective, is also highlighted

Hepatitis C virus (HCV) protein expression enhances hepatic fibrosis in HCV transgenic mice exposed to a fibrogenic agent.

International audienceBACKGROUND & AIMS: During chronic HCV infection, activation of fibrogenesis appears to be principally related to local inflammation. However, the direct role of hepatic HCV protein expression in fibrogenesis remains unknown. METHODS: We used transgenic mice expressing the full length HCV open reading frame exposed to a 'second hit' of the fibrogenic agent carbon tetrachloride (CCl(4)). Both acute and chronic liver injuries were induced in these mice by CCl(4) injections. Liver injury, expression of matrix re-modeling genes, reactive oxygen species (ROS), inflammation, hepatocyte proliferation, ductular reaction and hepatic progenitor cells (HPC) expansion were examined. RESULTS: After CCl(4) treatment, HCV transgenic mice exhibited enhanced liver fibrosis, significant changes in matrix re-modeling genes and increased ROS production compared to wild type littermates despite no differences in the degree of local inflammation. This increase was accompanied by a decrease in hepatocyte proliferation, which appeared to be due to delayed hepatocyte entry into the S phase. A prominent ductular reaction and hepatic progenitor cell compartment expansion were observed in transgenic animals. These observations closely mirror those previously made in HCV-infected individuals. CONCLUSIONS: Together, these results demonstrate that expression of the HCV proteins in hepatocytes contributes to the development of hepatic fibrosis in the presence of other fibrogenic agents. In the presence of CCl(4), HCV transgenic mice display an intra-hepatic re-organization of several key cellular actors in the fibrogenic process

Natalizumab affects T-cell phenotype in multiple sclerosis: implications for JCV reactivation

The anti-CD49d monoclonal antibody natalizumab is currently an effective therapy against the relapsing-remitting form of multiple sclerosis (RRMS). Natalizumab therapeutic efficacy is limited by the reactivation of the John Cunningham polyomavirus (JCV) and development of progressive multifocal leukoencephalopathy (PML). To correlate natalizumab-induced phenotypic modifications of peripheral blood T-lymphocytes with JCV reactivation, JCV-specific antibodies (serum), JCV-DNA (blood and urine), CD49d expression and relative abundance of peripheral blood T-lymphocyte subsets were longitudinally assessed in 26 natalizumab-treated RRMS patients. Statistical analyses were performed using GraphPad Prism and R. Natalizumab treatment reduced CD49d expression on memory and effector subsets of peripheral blood T-lymphocytes. Moreover, accumulation of peripheral blood CD8+ memory and effector cells was observed after 12 and 24 months of treatment. CD4+ and CD8+ T-lymphocyte immune-activation was increased after 24 months of treatment. Higher percentages of CD8+ effectors were observed in subjects with detectable JCV-DNA. Natalizumab reduces CD49d expression on CD8+ T-lymphocyte memory and effector subsets, limiting their migration to the central nervous system and determining their accumulation in peripheral blood. Impairment of central nervous system immune surveillance and reactivation of latent JCV, can explain the increased risk of PML development in natalizumab-treated RRMS subjects