Accroissement et diversification de l'offre de produits laitiers au Sénégal : la bataille industrielle du lait en poudre à Dakar et des minilaiteries à la conquête des marchés des villes secondaires

Les travaux d'analyse de l'évolution de l'offre de produits laitiers au Sénégal, entre 2000 et 2005, ont mis en évidence un certain cloisonnement géographique des marchés avec une tendance à la diversification de l'offre de produits sur le marché de Dakar. Cette évolution est liée à la croissance des importations de lait en poudre et au développement d'un tissu d'industries, et de petites et moyennes entreprises / industries. La bataille commerciale que se livrent les importateurs et transformateurs industriels révèle la croissance de la demande et l'enjeu économique du marché dakarois. La filière locale, caractérisée par un accroissement du nombre de petites unités de transformation, se développe surtout dans les régions. Cependant, le dynamisme de ce secteur échappe aux décideurs politiques à Dakar du fait du confinement des minilaiteries sur les marchés des villes secondaires où elles sont implantées. L'Etat a privilégié la couverture des besoins des consommateurs dakarois avec des tarifs douaniers particulièrement bas pour la poudre de lait transformée qui bénéficie, de plus, de subventions dans les pays producteurs. Ses interventions sur la filière locale, basées sur l'intensification (insémination artificielle), n'ont pas permis de lever les multiples contraintes (santé animale, alimentation, eau, gestion de la qualité, collecte du lait de brousse...). Il semble dès lors nécessaire dans l'élaboration des politiques laitières d'examiner la filière de manière plus globale et de favoriser une concertation avec l'ensemble des acteurs des deux sous-filières pour accroître l'impact des décisions politiques, notamment en termes de sécurité alimentaire et de lutte contre la pauvreté en milieu rural. (Résumé d'auteur

The Permian-Triassic boundary and Early Triassic sedimentation in Western European basins: an overview

At the scale of the peri-Tethyan basins of western Europe, the “Buntsandstein” continental lithostratigraphic units are frequently attributed to the “Permian-Triassic” because, in most cases, the lack of any “Scythian” (i.e. Early Triassic) biochronological evidence makes it very difficult to attribute the basal beds of the cycle to the Permian or to the Triassic. A careful recognition of unconformities and sedimentary indications of clearly arid climate provide powerful tools for correlation within non-marine successions that are devoid of any biostratigraphic markers, at least on the scale of the West European Plate. From a review of the “Buntsandstein” series of several basins we can characterize the Permian-Triassic boundary and the beginning of Triassic sedimentation at the scale of Western Europe. We clearly show that, except for the Central Germanic Basin, an unconformity can be observed between the Permian and the Triassic. Apart from the Germanic Basin, there is a total lack of typically “Scythian” fossils in the rest of West European basins, and the oldest biochronological markers yielded by these units are palynomorphs allowing to assign an Anisian age generally to the upper part of the “Buntsandstein”, but also its lowermost in a few cases. In the peri-Tethyan basins of western Europe, the Permian-Triassic boundary corresponds to an unconformity overlain by conglomerates containing ventifacts (followed by fluvial sandstones, sometimes rich in paleosols and sometimes totally devoid), which are attributed mainly to the lower Olenekian, i.e. Smithian. Alternatively, the succession passes up directly into fluvial sandstones containing the first paleosols, and then plant debris and palynomorphs attributed to the Anisian. In this way, the lack of typically Early Triassic fossils in most of the peri-Tethyan basins, at the scale of the west European Plate, can be explained by a true stratigraphic hiatus in the earliest Triassic (i.e. Induan) and by arid conditions unfavourable for the development of flora and fauna and their preservation during the Olenekian.En las cuencas peritéthicas de Europa occidental, la unidad litoestratigráfi ca continental “Buntsandstein” es frecuentemente atribuida al “Pérmico-Triásico”, porque, en la mayoría de los casos, la falta de elementos biocronológicos “scythienses” complica la atribución de los niveles basales al Pérmico o al Triásico. Un cuidadoso examen de las discordancias, y el uso de indicadores sedimentarios de climas claramente áridos constituyen herramientas fundamentales para la correlación de estas unidades no marinas, desprovistas de cualquier marcador bioestratigráfi co, al menos en el Oeste de la Placa Europea. La revisión de las series “Buntsandstein” de varias cuencas nos ha permitido caracterizar el límite Pérmico-Triásico y el comienzo de la sedimentación durante el Triásico inferior en el oeste de Europa, demostrando claramente que, excepto en la Cuenca Germánica Central, se puede observar una discordancia entre las series pérmicas y triásicas. Excepto en esta Cuenca Germánica, existe una falta total de fósiles típicamente “scythienses”, y los elementos bioestratigráfi cos más antiguos encontrados son conjuntos de palinomorfos que permiten asignar a los niveles superiores de las series “Buntsandstein” una edad Anisiense, en algunos cortes los niveles inferiores. En las cuencas peritéthicas de Europa occidental, el límite Pérmico-Triásico se corresponde con una discordancia que se recubre por conglomerados con ventifactos (seguidos por areniscas fl uviales, a veces ricas en paleosuelos y a veces totalmente desprovistas de ellos), atribuidos principalmente al Olenekiense inferior (Smithiense), o directamente areniscas fluviales donde aparecen los primeros paleosuelos, así como restos de plantas y palinomorfos, atribuidos al Anisiense. De esta forma en el Oeste de la Placa Europea, la falta de fósiles característicos del Triásico Inferior, en la mayoría de las cuencas perithéticas, puede explicarse por un importante hiato estratigráfi co durante el Triásico Inferior (Induense) y por unas condiciones áridas, desfavorables para la vida y la preservación de fósiles durante el Olenekiense

Méthode d'évaluation de l'action de conseil en irrigation IRRIPARC en régions Nord-Pas-de-Calais et Picardie

Parmi les nombreuses actions de conseil en irrigation développées en France, trop peu d'entre elles sont évaluées pour apprécier leur impact sur les pratiques d'irrigation et les bénéfices pour la ressource. Dans cet article, nous proposons une méthode d'évaluation de l'une d'entre elles, sur l'étude d'un cas concret : l'action IRRIPARC. Dans les régions Nord-Pas-de-Calais et Picardie, des fiches de réglages de canons enrouleurs ont été diffusées aux agriculteurs, pour limiter les effets du vent sur l'uniformité de la répartition de l'eau d'irrigation. La méthode d'évaluation proposée repose sur l'étude de trois critères : l'efficacité, la pertinence et la cohérence de l'action. La collecte des données se fait par enquêtes quantitatives et qualitatives auprès de différents acteurs : les agriculteurs, public cible de l'action, et les partenaires impliqués dans l'action IRRIPARC. L'analyse débouche sur des perspectives d'évolution et fournit des recommandations pour l'action. / Several technical support actions in irrigation have been carried out in France. However, very few have been evaluated to determine their actual impact on irrigation practices and their water saving benefits. In this paper, an assessment method of a technical support action is presented on a concrete case: the IRRIPARC action. The action was carried in the Nord Pas-de-Calais region of France. It aims at providing to farmers technical forms to help them to set their irrigation guns according to the wind speed in order to improve water distribution uniformity. The method depends on three criteria based on the effectiveness, the relevance and the consistency of the action. The data have been collected through quantitative and qualitative enquiries to different stakeholders: farmers to which the action was intended, and other partners which were involved in the action. The analysis results in evolution perspective of IRRIPARC action

Long and short paths in uniform random recursive dags

In a uniform random recursive k-dag, there is a root, 0, and each node in turn, from 1 to n, chooses k uniform random parents from among the nodes of smaller index. If S_n is the shortest path distance from node n to the root, then we determine the constant \sigma such that S_n/log(n) tends to \sigma in probability as n tends to infinity. We also show that max_{1 \le i \le n} S_i/log(n) tends to \sigma in probability.Comment: 16 page

New data on the Silurian-Devonian paleontology and biostratigraphy of Bolivia

P. 269-314In order to precisely establish the bio- and chronostratigraphic position of several levels of the Silurian–Devonian succession of Bolivia, with respect to the International Time Scale, additional Silurian and Devonian localities belonging to the Eastern Cordillera and the Interandean Zone areas have been recently revised and sampled, both for macrofossils and palynomorphs. Specifically, the localities are Ñuñumayani, and Muruhuta from the late Silurian–early Devonian time interval. Correlations with other fossiliferous localities are discussed, namely Huacallani and Rumicorral.S

Coil conversion to β-strand induced by dimerisation

Most molecular processes in living organisms rely on protein–protein interactions, many of which are mediated by β-sheet interfaces; this study investigates the formation of β-sheet interfaces through the conversion of coils into β-strands. Following an exhaustive search in the Protein Data Bank, the corresponding structural dimorphic fragments were extracted, characterised and analysed. Their short strand lengths and specific amino acid profiles indicate that dimorphic β-strand interfaces are likely to be less stable than standard ones and could even convert to coil interfaces if their environment changes. Moreover, the construction of a simple classifier able to discriminate between the sequences of dimorphic and standard β-strand interfaces suggests that the nature of those dimorphic sequences could be predicted, providing a novel means of identifying proteins capable of forming dimers

Immune Boosting Explains Regime-Shifts in Prevaccine-Era Pertussis Dynamics

Understanding the biological mechanisms underlying episodic outbreaks of infectious diseases is one of mathematical epidemiology’s major goals. Historic records are an invaluable source of information in this enterprise. Pertussis (whooping cough) is a re-emerging infection whose intermittent bouts of large multiannual epidemics interspersed between periods of smaller-amplitude cycles remain an enigma. It has been suggested that recent increases in pertussis incidence and shifts in the age-distribution of cases may be due to diminished natural immune boosting. Here we show that a model that incorporates this mechanism can account for a unique set of pre-vaccine-era data from Copenhagen. Under this model, immune boosting induces transient bursts of large amplitude outbreaks. In the face of mass vaccination, the boosting model predicts larger and more frequent outbreaks than do models with permanent or passively-waning immunity. Our results emphasize the importance of understanding the mechanisms responsible for maintaining immune memory fo

Search for the standard model Higgs boson in the H to ZZ to 2l 2nu channel in pp collisions at sqrt(s) = 7 TeV

A search for the standard model Higgs boson in the H to ZZ to 2l 2nu decay channel, where l = e or mu, in pp collisions at a center-of-mass energy of 7 TeV is presented. The data were collected at the LHC, with the CMS detector, and correspond to an integrated luminosity of 4.6 inverse femtobarns. No significant excess is observed above the background expectation, and upper limits are set on the Higgs boson production cross section. The presence of the standard model Higgs boson with a mass in the 270-440 GeV range is excluded at 95% confidence level.Comment: Submitted to JHE

Search for anomalous t t-bar production in the highly-boosted all-hadronic final state

A search is presented for a massive particle, generically referred to as a Z', decaying into a t t-bar pair. The search focuses on Z' resonances that are sufficiently massive to produce highly Lorentz-boosted top quarks, which yield collimated decay products that are partially or fully merged into single jets. The analysis uses new methods to analyze jet substructure, providing suppression of the non-top multijet backgrounds. The analysis is based on a data sample of proton-proton collisions at a center-of-mass energy of 7 TeV, corresponding to an integrated luminosity of 5 inverse femtobarns. Upper limits in the range of 1 pb are set on the product of the production cross section and branching fraction for a topcolor Z' modeled for several widths, as well as for a Randall--Sundrum Kaluza--Klein gluon. In addition, the results constrain any enhancement in t t-bar production beyond expectations of the standard model for t t-bar invariant masses larger than 1 TeV.Comment: Submitted to the Journal of High Energy Physics; this version includes a minor typo correction that will be submitted as an erratu