Les agricultures irriguées face à de nouveaux défis

L'irrigation concerne 18 % des terres cultivées et assure plus de 40 % de l'alimentation mondiale. Si la productivité à l'hectare de l'agriculture irriguée est plus élevée et plus régulière que celle de l'agriculture pluviale, l'irrigation est cependant plus contraignante à bien des égards : investissements élevés, charges de fonctionnement et de maintenance importantes, systèmes de cultures intensifs très dépendants des filières en amont (agrofournitures) et en aval (mise en marché), gestion collective souvent obligatoire, partage de l'eau devant être négocié avec les autres usagers. Ce numéro thématique fait état, de manière non exhaustive, des nouvelles problématiques de l'irrigation, des grandes évolutions en cours, de leurs enjeux et des problèmes qu'elles posent. A partir d'études de situations agraires localisées en Europe, en Asie, au Maghreb et en Afrique subsaharienne, trois grandes problématiques sont abordées : (i) l'innovation technique et l'amélioration des performances de l'agriculture irriguée ; (ii) les nouvelles formes de gestion de l'eau et des terres au sein des périmètres collectifs ; et (iii) les tensions autour de l'irrigation dans les territoires. (Résumé d'auteur

Estimation bayésienne du paramètre de multifractalité

National audienceL’analyse multifractale est largement utilisée pour caractériser et interpréter les propriétés d’invariance d’échelle de données expérimentales issues de multiples et diverses applications. Cependant, l'estimation du paramètre dit de multifractalité, qui permet de discriminer entre grandes classes de processus modèles pour l’invariance d’échelle, est délicate. Quand la taille des données est limitée notamment, la performance des estimateurs classiques, reposant principalement sur des régressions linéaires, est souvent trop faible, limitant ainsi la possibilité d’une véritable utilisation pratique de ce paramètre. Dans cette contribution, nous envisageons une procédure dont l’originalité est double. D’une part, nous construisons un modèle semi-paramétrique générique pour décrire la statistique du logarithme des coefficients dominants de processus multifractals, construits à partir de cascades multiplicatives (une déclinaison adaptée à l’analyse multifractale des coefficients d’ondelettes classiquement utilisés). D’autre part, nous élaborons une formulation bayésienne adaptée à ce problème ainsi qu’un algorithme MCMC pour approcher la loi a posteriori et les estimateurs bayésiens. La pertinence du modèle semi-paramétrique proposé et l’intérêt et la qualité des estimateurs bayésiens construits sont évalués au moyen de simulations numériques. Nous montrons la réelle amélioration des performances d'estimation obtenues à partir du schéma bayésien

Bayesian estimation for the multifractality parameter

International audienceMultifractal analysis has matured into a widely used signal and image processing tool. Due to the statistical nature of multifractal processes (strongly non-Gaussian and intricate dependence) the accurate estimation of multifractal parameters is very challenging in situations where the sample size is small (notably including a range of biomedical applications) and currently available estimators need to be improved. To overcome such limitations, the present contribution proposes a Bayesian estimation procedure for the multifractality (or intermittence) parameter. Its originality is threefold: First, the use of wavelet leaders, a recently introduced multiresolution quantity that has been shown to yield significant benefits for multifractal analysis; Second, the construction of a simple yet generic semi-parametric model for the marginals and covariance structure of wavelet leaders for the large class of multiplicative cascade based multifractal processes; Third, the construction of original Bayesian estimators associated with the model and the constraints imposed by multifractal theory. Performance are numerically assessed and illustrated for synthetic multifractal processes for a range of multifractal parameter values. The proposed procedure yields significantly improved estimation performance for small sample sizes

Parameter estimation for sums of correlated gamma random variables. Application to anomaly detection in Internet Traffic

International audienceA new family of distributions, constructed by summing correlated gamma random variables, is studied. First, a simple closed-form expression for their density is derived. Second, the three parameters characterizing such a density are estimated by using the maximum likelihood (ML) principle. Numerical simulation are conducted to compare the performance of the ML estimator against those of the conventional estimator of moments. Finally, a multiresolution multivariate gamma based modeling of Internet traffic illustrate the potential interest of the proposed distributions for the detection of anomalies. Aggregated times series of IP packet counts are split into adjacent non overlapping time blocks. The distribution of these series are modeled by the proposed multivariate gamma based distributions, over a collection of different aggregation levels. The anomaly detection strategy is based on tracking changes along time of the corresponding multiresolution parameters

Measurements and calibration method for WLAN indoor path loss modelling

International audienceFor indoor Wireless LAN systems planning, an accurate propagation modelling is required. Semi-empirical models represent an efficient approach to the coverage prediction. Based on measurement results, the model parameters are derived. In this paper we present the influence of the measurement point choice on the accuracy of the parameters estimation and thus on the model robustness

Impact of a marine protected area to fishery profitability and income distribution. Some evidence from the Gulf of Thailand (Mu Ko Chumphon National Park versus Chumphon Province )

International audienceMethodological difficulties, particularly when multifleet-multispecies fisheries are active, explain pro parte a weak research effort on the socio-economic impact of fishery activities after the implementation of a marine protected area. Two components of the socio-economic impact have been prioritized : the fishing unit profitability and the fishery household income distribution by comparing a marine protected area (Mu Ko Chumpon National Park) and an unprotected area (Chumphon Province) in Thailand. One can distinguish three phases : a bibliographical analysis, the carrying out of fishers village monographs and of a sample-based survey of fishery households. The sampling unit was the fishery household forming one or several fishing units defined by a métier (an association of a fleet, a main fishing gear, target species): 126 households forming 225 fishing units have been surveyed. The positive impact of the MPA on fishery profitability is shown by a principal component analysis which indicates that there is a lower proportion of fishing units harvesting inside or in adjacent areas of the MPA (insiders who are benefitting from implicit access rights) which face negative profit than those fishing remote from the MPA but in Chumphon Province (outsiders). This positive impact is confirmed by the performance of Chi-square tests : the insiders have relatively higher profit per fishing day than outsiders and Chi-square tests show a greater homogeneity of profits per fishing day and a lower variability for the insiders. A steady social impact from the MPA on fishery income distribution is revealed by the measure of concentration using an Herfindhal index and Lorenz curves which show the more egalitarian structure of insiders regarding the operating profit and the income per fishery household

Rapid polymyxin NP test for the detection of polymyxin resistance mediated by the MCR-1/MCR-2 genes

The Rapid Polymyxin NP test has been recently developed to rapidly detect polymyxin resistance in Enterobacteriaceae. Here we evaluated this test for detecting MCR- 1/MCR-2-producing Enterobacteriaceae using a collection of 70 non-redundant strains either recovered from the environment, animals, or humans. Sensitivity and specificity were found to be 100%