Rice pathogens intercepted on seeds originating from 11 African countries and from the USA

1,916 rice seed samples from 11 African countries and the USA were tested for the presence of pathogenic microorganisms or those affecting seed quality. Bacillus spp., Pantoea spp., Sphingomonas sp. and the fungi Acremoniella sp., Alternaria sp., Aspergillus flavus, A. fumigatus, A. niger, Chaetomium sp., Curvularia sp., Fusarium oxysporum, F. solani, Fusarium sp., Helminthosporium sp., Microdochium oryzae, Nigrospora oryzae, Penicillium sp., Pestalotia sp., Phoma sp., Magnaporthe oryzae, Rhizopus sp., Sarocladium sp. and Tilletia barclayana were isolated. The highest incidence values were obtained with Curvularia sp., Microdochium oryzae, A. flavus, F. solani and Nigropora sp. In contrast, these fungi were not isolated from seeds of many countries with Togo having the least affected seeds (nine out of the 24 potential organisms diagnosed). The highest frequencies of these organisms were found on seed samples from Benin (20/22), Burundi and Tanzania (19/24), and Senegal (18/24). Across countries, A. flavus, A. fumigatus, Curvularia sp., F. solani, Nigropora sp., Rhizopus sp. and Microdochium oryzae were the most frequently isolated organisms. Concerning the major diseases, blast was diagnosed only once despite the high number of samples tested

Efficient slow-light coupling in a photonic crystal waveguide without transition region

We consider the coupling into a slow mode that appears near an inflection point in the band structure of a photonic crystal waveguide. Remarkably, the coupling into this slow mode, which has a group index n(g) > 1000, can be essentially perfect without any transition region. We show that this efficient coupling occurs thanks to an evanescent mode in the slow medium, which has appreciable amplitude and helps satisfy the boundary conditions but does not transport any energy. (C) 2008 Optical Society of AmericaPublisher PDFPeer reviewe

Supermodes of Hexagonal Lattice Waveguide Arrays

We present a semi-analytical formulation for calculating the supermodes and corresponding Bloch factors of light in hexagonal lattice photonic crystal waveguide arrays. We then use this formulation to easily calculate dispersion curves and predict propagation in systems too large to calculate using standard numerical methods.Comment: Accepted by J. Opt. Soc. Am. B, DocID:160522. http://www.opticsinfobase.org/abstract.cfm?msid=16052

Relations entre eleveurs et agriculteurs dans un contexte de changements climatiques dans le bassin de l’oueme superieur au Benin : Entre cooperation et conflit

Au Bénin, comme dans tous les pays de l’Afrique de l’Ouest, la transhumance permet aux éleveurs d’exploiter non seulement les ressources fourragères et hydriques dispersées mais également de développer de multiples interactions notamment coopératives et conflictuelles entre éleveurs et entre éleveurs et agriculteurs. La présente étude à pour objectif d’analyser les différentes formes d’interactions entre les éleveurs d’une part, et entre les éleveurs et agriculteurs d’autre part dans les zones pastorales du bassin de l’Ouémé Supérieur au Bénin. L’approche méthodologique adoptée repose sur la collecte des données socio-anthropologiques issues d’enquêtes de terrain. Des entretiens individuels et des discussions de groupe ont été réalisés dans les zones pastorales du milieu d’étude auprès de 300 individus. Les méthodes d’analyse de discours et fréquentielles ont permis d’analyser les différentes formes de relations entre éleveurs et agriculteurs, les facteurs de risques et les mesures d’atténuation. Les résultats de terrain révèlent que les éleveurs développent entre eux diverses formes d’interactions non conflictuelles basées essentiellement sur les aides mutuelles et le partage de connaissances (90,4 %). Les relations coopératives entre éleveurs et agriculteurs portent essentiellement sur les échanges des sous-produits animaux contre les sous-produits agricoles (49,4 %), les aides mutuelles lors de la récolte contre les résidus (25,3 %) et les échanges du lait contre les produits agricoles (10,3 %). Malgré ces multiples formes d’interactions coopératives entre acteurs, l’accès aux ressources pastorales (51,9 %) et l’attribution des dégâts dans les champs causés par les transhumants aux sédentaires (16,2 %) dégradent les interactions pacifiques entre éleveurs. Les interactions conflictuelles entre éleveurs et agriculteurs sont liées principalement aux dégâts dans les champs (66,9 %). La prise en compte de ces résultats dans une politique sectorielle de développement durable du secteur agropastoral, permettrait un réel décollage dudit secteur et la consolidation des interactions pacifiques entre éleveurs et agriculteurs.   English title: Relations between herders and farmers in a context of climate change in the upper Oueme Basin in Benin: Between cooperation and conflict In Benin, as in all West African countries, transhumance allows herders to exploit not only the scattered fodder and water resources but also to develop multiple interactions, particularly cooperative and conflictual interactions between herders and between herders and farmers. This study aims to analyze the different forms of cooperative and conflictual interactions between herders on the one hand, and between herders and farmers on the other hand in the pastoral areas of the Upper Ouémé in Benin. The methodological approach adopted is based on the collection of socio-anthropological data from field surveys. Individual interviews and focus group discussions were conducted in pastoral areas of the study area with 300 individuals. Discourse and frequency analysis methods made it possible to analyze the different forms of interactions between herders and farmers, risk factors and mitigation measures. The field results reveal that herders develop various forms of non-conflictual interactions among themselves based essentially on mutual aid and knowledge sharing (90.4%). Cooperative interactions between breeders and farmers mainly concern trade of animal by-products against agricultural by-products (49.4%), mutual aid at harvest time against residues (25.3%) and trade of milkagainst agricultural products (10.3%). Despite these multiple forms of cooperative interactions between actors, access to pastoral resources (51.9%) and the attribution of field damage caused by transhumant herders to sedentary ones (16.2%) degrade peaceful interactions between herders. Conflictual interactions between herders and farmers are mainly related to field damage (66.9%). Taking these results into account in a sectoral policy for sustainable development of the agropastoral sector would allow a real take-off of the sector and the consolidation of peaceful interactions between herders and farmers

Some discrete exponential dispersion models : poisson-tweedie and hinde-demétrio classes

In this paper we investigate two classes of exponential dispersion models (EDMs) for overdispersed count data with respect to the Poisson distribution. The first is a class of Poisson mixture with positive Tweedie mixing distributions. As an approximation (in terms of unit variance function) of the first, the second is a new class of EDMs characterized by their unit variance functions of the form µ + µp, where p is a real index related to a precise model. These two classes provide some alternatives to the negative binomial distribution (p = 2) which is classically used in the framework of regression models for count data when overdispersion results in a lack of fit of the Poisson regression model. Some properties are then studied and the practical usefulness is also discussed

Absorption enhancing proximity effects in aperiodic nanowire arrays

Aperiodic Nanowire (NW) arrays have higher absorption than equivalent periodic arrays, making them of interest for photovoltaic applications. An inevitable property of aperiodic arrays is the clustering of some NWs into closer proximity than in the equivalent periodic array. We focus on the modes of such clusters and show that the reduced symmetry associated with cluster formation allows external coupling into modes which are dark in periodic arrays, thus increasing absorption. To exploit such modes fully, arrays must include tightly clustered NWs that are unlikely to arise from fabrication variations but must be created intentionally.Comment: Accepted by Optics Expres