8,891 research outputs found
Groundnut viral diseases in West Africa
This paper describes groundnut viral diseases observed in West Africa. Six viruses are identified and their main properties are reported here: peanut Clump, groundnut rosette, groundnut eyespot, groundnut crinkle, tomato spotted wilt and groundnut chlorotic spotting viruses. Four other diseases are described in part: groundnut streak, groundnut mosaic, groundnut flecking and groundnut golden mosaic diseases. Some of them are economically very important such as the two strains of rosette, peanut clump and tomato spotted wilt diseases. Others are apparently of minor importance though they occur relatively frequently and show a wide distribution, such as groundnut eyespot, groundnut crinkle, groundnut streak and groundnut golden mosaic diseases. The others appear occasionally but are nevertheless described: some which are very infectious, as groundnut chlorotic spotting disease could become very important within a few years. (Résumé d'auteur
Quelques données préliminaires sur l'environnement et la qualité des apports du Niger au Sahel
La terrasse Mitis Ă la pointe de Mille-Vaches (pĂ©ninsule de Portneuf), rive nord de lâestuaire maritime du Saint-Laurent : nature des dĂ©pĂŽts et Ă©volution du niveau marin relatif Ă lâholocĂšne
La basse terrasse Ă lâextrĂ©mitĂ© sud-ouest de la pĂ©ninsule de Portneuf, sur la Haute CĂŽte-Nord du Saint-Laurent, correspond Ă la terrasse Mitis prĂ©sente dans quelques autres localitĂ©s de la rive nord de lâestuaire. EntiĂšrement composĂ©e de matĂ©riaux meubles dĂ©tritiques, elle comprend plusieurs unitĂ©s, la plupart sableuses, dâune Ă©paisseur supĂ©rieure Ă 3 m. Mises en place en milieu littoral et intertidal, ces unitĂ©s reposent sur un dĂ©pĂŽt de sable fin gris, infratidal, lui-mĂȘme susjacent au substrat limono-argileux dĂ©posĂ© dans la Mer de Goldthwait, il y a >9,5 ka. Un dĂ©pĂŽt de limon sableux, gris, laminĂ©, contenant des dĂ©bris de plantes en place correspondant Ă un faciĂšs de schorre infĂ©rieur, coiffe la sĂ©quence sableuse. Par endroits, ce dĂ©pĂŽt est lui-mĂȘme recouvert dâune couche de tourbe de 25â30 cm dâĂ©paisseur. LâunitĂ© Ă la base de la falaise active a Ă©tĂ© mise en place entre 1990 ± 60 et 2740 ± 70 BP. Les unitĂ©s sableuses au-dessus datent de 1570 ± 60 Ă 1880 ± 90 BP, alors que lâunitĂ© limoneuse Ă faciĂšs de schorre infĂ©rieur a donnĂ© un Ăąge au 14C allant de 1570 ± 50 Ă 1970 ± 70 BP. LâĂąge mĂ©dian de la terrasse Mitis est de 1880 ± 90 BP, alors que si on prend en compte uniquement les dates pour lâunitĂ© limoneuse Ă faciĂšs de schorre infĂ©rieur, il est de 1830 ± 60 BP. LâĂ©dification de la terrasse Mitis Ă la pointe de Mille-Vaches est donc contemporaine de la plupart des sites des deux rives de lâestuaire. Le substrat argileux de la vaste batture en face de la terrasse, qui se prolonge sous celle-ci, a Ă©tĂ© Ă©rodĂ© lors dâun bas niveau marin pendant lâHolocĂšne moyen qui fut suivi dâune remontĂ©e du niveau de quelques mĂštres. Un glissement de terrain historique, survenu vraisemblablement lors du sĂ©isme de 1663, caractĂ©rise la partie supĂ©rieure de lâestran en face de la falaise active.The low terrace at the SW extremity of the Portneuf Peninsula, on the north shore of the Lower St. Lawrence estuary, is an equivalent of the Mitis terrace occurring at a few other localities. The terrace is entirely made of detritic sediments. The various units, mostly fine to coarse sand deposited in the shore zone, are over 3 m in thickness. These sediments appear to unconformably overlie a subtidal dark grey fine sand resting on a surface eroded into a Goldthwait Sea clay deposit older than 9.5 ka. At the surface of the terrace, there is a grey, laminated sandy silt deposit with plant remains in situ (a lower marsh facies), locally covered by a thin (25â30 cm) layer of peat. The sand unit at the base of the studied exposure has been dated 1990 ± 60 to 2740 ± 70 BP. The overlying sandy units are dated 1570 ± 60 to 1880 ± 90 BP, whereas the silt unit at the surface is dated 1570 ± 50 to 1970 ± 70 BP. The median age of the terrace is 1880 ± 90 BP, whereas if we use only the 14C dates for the silt unit, it is 1830 ± 60 BP. At Pointe de Mille-Vaches, the Mitis terrace is thus contemporaneous with most localities on both shores of the estuary. The substrate of the wide tidal flat in front of the Mitis terrace (an erosion surface underlying the terrace) was cut into the marine clay during a mid-Holocene lowstand, which was followed by a rising sea level of a few meters. An historical landslide, which possibly occurred during the 1663 seismic event, characterizes the upper part of the tidal zone in front of the active cliff
Employment Outlook and Occupational Change in the Media Content Industries (2000-2005).
Abstract not availableJRC.J-Institute for Prospective Technological Studies (Seville
Human impact on erosion and sedimentation
Cet article prĂ©sente les premiers rĂ©sultats obtenus sur les transports solides en suspension de trois petits bassins versants au Mali, en zone de savane humide. Les flux annuels de matiĂšres en suspension y sont relativement faibles, compris entre 4 et 45 t km-2 an-1, et varient dans le mĂȘme sens que la pluviomĂ©trie et les Ă©coulements annuels. Les transports solides varient Ă©galement au cours de la saison des pluies, quelques crues importantes pouvant assurer l'essentiel du tonnage annuel exportĂ©. L'influence de la mise en culture sur l'Ă©rosion est Ă©tudiĂ©e au pas de temps de la crue sur les deux bassins dont les occupations du sol sont les plus contrastĂ©es. Le bassin le plus cultivĂ© s'avĂšre ĂȘtre le plus ruisselant (en terme d'intensitĂ© maximale), ce qui favorise l'exportation de matiĂšres en suspension. (RĂ©sumĂ© d’auteur
Lutte contre la dégradation des sols dans la vallée du fleuve Sénégal : essai de drainage sur le périmÚtre de Donaye 8
System-performance analysis of optimized gain-switched pulse source employed in 40-and 80-Gb/s OTDM systems
The development of ultrashort optical pulse sources, exhibiting excellent temporal and spectral profiles, will play a crucial role in the performance of future optical time division multiplexed (OTDM) systems. In this paper, we demonstrate the difference in performance in 40- and 80-Gb/s OTDM systems between optical pulse sources based on a gain-switched laser whose pulses are compressed by a nonlinearly and linearly chirped fiber Bragg grating. The results achieved show that nonlinear chirp in the wings of the pulse leads to temporal pedestals formed on either side of the pulse when using the linearly chirped grating, whereas with the nonlinearly chirped grating, pedestals are essentially eliminated. In an OTDM system, these pedestals cause coherent interaction between neighboring channels, resulting in intensity fluctuations that lead to a power penalty of 1.5 dB (40 Gb/s) and 3.5 dB (80 Gb/s) in comparison to the case where the nonlinearly chirped grating is used. Simulations carried out with the aid of Virtual Photonics Inc. verify the results achieved
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