Le rôle du couvert ligneux sur le bilan hydrique d'une steppe (nord du Sénégal)

L'évapotranspiration de deux bosquets de ligneux (Acacia tortilis et Balanites aegyptiaca possédant leur strate herbacée) et d'une zone herbacée hors couvert de la steppe sahélienne (Ferlo sénégalais) a été étudiée de 1989 à 1992. L'évapotranspiration a été estimée à partir de l'équation du bilan (mesures à la sonde à neutrons). La steppe a évapotranspiré en moyenne 1,92 mm/j en saison des pluies (période n° 1), 1,62 mm/j en saison dite "différée" (période n° 2), 0,62 mm/j en saison sèche fraîche (période n° 3) et 0,09 mm/j en saison sèche chaude (période n° 4). L'ETR maximale journalière des deux bosquets de ligneux est supérieure à celle de la zone herbacée toute l'année, l'ETR du bosquet d'Acacia tortilis étant supérieure à celle du bosquet de Balanites aegyptiaca, soit respectivement pour Acacia tortilis, Balanites aegyptiaca et la zone herbacée : 5,04-4,15 et 3,98 mm/j (période n° 1), 4,28-3,76 et 2,89 mm/j (période n° 2), 1,73-1,79 et 1,34 mm/j (période n° 3), 0,93-0,46 et 0,36 mm/j (période n° 4). En fin de saison sèche, après un cycle de végétation, il subsiste dans le sol de la zone herbacée un stock d'eau de 20 mm : cette steppe aurait pu produire 13,7 à 20,8 kg MS/ha/année de bois en plus. (Résumé d'auteur

Adaptation au niveau de disponibilité en azote, en communautés herbacées : deux exemples : Anthroxanthum odoratum L. et Arrhenatherum elatius (L.) J. et C. Prest var. vulgare Koch

Les relations entre la croissance et la disponibilité en azote de trois populations d'#A. odoratum# et de trois populations d'#A. elatius# sont étudiés en conditions naturelles et semi-controlées. Les deux espéces et leurs populations diffèrent par leur efficacité d'utilisation de l'azote pour la croissance et par leur tolérance à l'ombrage. Les résultats sont interprétés en termes d'avantages adaptatifs des deux espéces dans leurs milieux respectifs. (Résumé d'auteur

Combining the Estimated Date of HIV Infection with a Phylogenetic Cluster Study to Better Understand HIV Spread: Application in a Paris Neighbourhood

International audienceObjectivesTo relate socio-demographic and virological information to phylogenetic clustering in HIV infected patients in a limited geographical area and to evaluate the role of recently infected individuals in the spread of HIV.MethodsHIV-1 pol sequences from newly diagnosed and treatment-naive patients receiving follow-up between 2008 and 2011 by physicians belonging to a health network in Paris were used to build a phylogenetic tree using neighbour-joining analysis. Time since infection was estimated by immunoassay to define recently infected patients (very early infected presenters, VEP). Data on socio-demographic, clinical and biological features in clustered and non-clustered patients were compared. Chains of infection structure was also analysed.Results547 patients were included, 49 chains of infection containing 108 (20%) patients were identified by phylogenetic analysis. analysis. Eighty individuals formed pairs and 28 individuals were belonging to larger clusters. The median time between two successive HIV diagnoses in the same chain of infection was 248 days [CI = 176–320]. 34.7% of individuals were considered as VEP, and 27% of them were included in chains of infection. Multivariable analysis showed that belonging to a cluster was more frequent in VEP and those under 30 years old (OR: 3.65, 95 CI 1.49–8.95, p = 0.005 and OR: 2.42, 95% CI 1.05–5.85, p = 0.04 respectively). The prevalence of drug resistance was not associated with belonging to a pair or a cluster. Within chains, VEP were not grouped together more than chance predicted (p = 0.97).ConclusionsMost newly diagnosed patients did not belong to a chain of infection, confirming the importance of undiagnosed or untreated HIV infected individuals in transmission. Furthermore, clusters involving both recently infected individuals and longstanding infected individuals support a substantial role in transmission of the latter before diagnosis

Prevalence of HIV-1 drug resistance in treated patients with viral load >50 copies/mL in 2009: a French nationwide study

Background Surveillance of HIV-1 drug resistance in treated patients with plasma viral load (VL) >50 copies/mL. Methods The protease and reverse transcriptase (RT) genes were systematically sequenced in samples from 756 patients with VL >50 copies/mL in 2009. The genotyping results were interpreted for each antiretroviral drug (ARV) by using the ANRS algorithm v21. Weighted analyses were used to derive representative estimates of percentages of patients. Prevalence rates were compared with those obtained in 2004 among patients with VL >1000 copies/mL. Results Sequences were obtained for 506 patients. Sequencing was successful in 45%, 80% and 96% of samples with VL of 51-500, 501-1000 and >1000 copies/mL, respectively. Resistance or possible resistance to at least one ARV was observed in 59% of samples. Overall, 0.9% of samples contained viruses resistant to all drugs belonging to at least three drug classes. All resistance prevalence rates were significantly lower in 2009 than in 2004. Conclusion In France, where 86% of patients were receiving combination antiretroviral therapy in 2009, only 15.0% of patients had a VL >50 copies/mL, suggesting that only 8.9% of treated patients could potentially transmit resistant viruses. Only 0.08% of patients harboured viruses fully resistant to at least three antiretroviral drug classes. Further studies are needed to determine whether resistance continues to decline over tim

IRIM at TRECVID 2010: Semantic Indexing and Instance Search

International audienceThe IRIM group is a consortium of French teams working on Multimedia Indexing and Retrieval. This paper describes our participation to the TRECVID 2010 semantic indexing and instance search tasks. For the semantic indexing task, we evaluated a number of different descriptors and tried different fusion strategies, in particular hierarchical fusion. The best IRIM run has a Mean Inferred Average Precision of 0.0442, which is above the task median performance. We found that fusion of the classification scores from different classifier types improves the performance and that even with a quite low individual performance, audio descriptors can help. For the instance search task, we used only one of the example images in our queries. The rank is nearly in the middle of the list of participants. The experiment showed that HSV features outperform the concatenation of HSV and Edge histograms or the Wavelet features