Grippes aviaires en Afrique. Cibler la vigilance

En 2006, la détection du virus de l'influenza (grippe) aviaire H5N1 en Afrique suscite une grande inquiétude : le virus pourrait se propager à l'ensemble du continent, puis être réintroduit en Europe par les oiseaux migrateurs. Des programmes de surveillance épidémiologique et de renforcement des dispositifs nationaux sont mis en place, appuyés par des organismes internationaux. En parallèle, des programmes de recherche sont lancés pour décrire et comprendre les processus de transmission de ce virus en Afrique, et évaluer les risques. Parmi eux, le projet Gripavi vise à caractériser la circulation des virus d'influenza aviaire et de la maladie de Newcastle à la fois dans l'avifaune sauvage et la volaille domestique. Il montre que le continent africain n'est pas exempt de risques et que la vigilance doit rester de mise. En précisant les modes de persistance du virus en Afrique et en identifiant des situations à risque, il met au jour des pistes pour cibler les stratégies de surveillance et de contrôle, et en améliorer ainsi l'efficacité

Numerical and experimental analyses of resin infusion manufacturing processes of composite materials

Liquid resin infusion (LRI) processes are promising manufacturing routes to produce large, thick, or complex structural parts. They are based on the resin flow induced, across its thickness, by a pressure applied onto a preform/resin stacking. However, both thickness and fiber volume fraction of the final piece are not well controlled since they result from complex mechanisms which drive the transient mechanical equilibrium leading to the final geometrical configuration. In order to optimize both design and manufacturing parameters, but also to monitor the LRI process, an isothermal numerical model has been developed which describes the mechanical interaction between the deformations of the porous medium and the resin flow during infusion.1, 2 With this numerical model, it is possible to investigate the LRI process of classical industrial part shapes. To validate the numerical model, first in 2D, and to improve the knowledge of the LRI process, this study details a comparison between numerical simulations and an experimental study of a plate infusion test carried out by LRI process under industrial conditions. From the numerical prediction, the filling time, the resin mass and the thickness of the preform can be determined. On another hand, the resin flow and the preform response can be monitored by experimental methods during the filling stage. One key issue of this research study is to highlight the changes in major process parameters during the resin infusion stage, such as the temperature of the preform and resin, and the variations of both thickness and fiber volume fraction of the preform. Moreover, this numerical/experimental approach is the best way to improve our knowledge on the resin infusion processes, and finally, to develop simulation tools for the design of advanced composite parts

Les conditions de travail et la santé des immigrés : Seraient- ils plus résistants à la pénibilité au travail que les natifs

L'objectif de ce papier est d'évaluer l'impact de la pénibilité du travail sur l'état de santé des travailleurs de façon générale, et plus particulièrement des travailleurs immigrés. Nous utilisons les données de l'Enquête Santé 2002‐2003 de l'INSEE et nous construisons un ensemble d'indicateurs de pénibilité qui nous permettent de distinguer entre les effets de la pénibilité physique, dite objective, et les effets de la pénibilité vécue, qui s'apparente plus à une pression psychologique ou à une faible latitude décisionnelle dans l'emploi. Après une étude descriptive, nous estimons des équations de santé qui intègrent les variable s de pénibilité. Les premiers résultats indiquent que malgré u ne surreprésentation des immigrés dans les emplois aux conditions de travail difficiles, ces travailleurs se révèlent plus résistants face à la pénibilité professionnelle, aussi bien physique que psych

Immigration and its dependence on the welfare system: the case of France

In this paper, we bring to light the link between immigration in France and the appeal to its welfare system: familial assistance, retirement, health, housing assistance, unemployment benefits and RMI (the French Minimum Guaranteed Income). Our results show that when we control for differences in characteristics between natives and immigrants, the over representation of mi grants among the beneficiaries of social protection is noticed only for unemployment benefits and for the RMI (in addition to an over representation also on housing assistance, in particular for the populations born in North Africa

An experimental assessment of the saturated transverse permeability of Non Crimp New Concept (NC2) multiaxial fabrics.

Over the past few years some manufacturing processes involving resin impregnation in dry preforms prior to cure, and more specifically resin infusion across the fabric thickness (the so-called Resin Infusion Processes) have been developed. In these increasingly used processes, the transverse permeability of the fabric controls both manufacturing cycles and dimensions, and consequently the mechanical properties of the final composites. A big effort has been realized to obtain reliable experimental techniques for measuring the transverse permeability. Since the distinction between saturated and effective permeabilities is still being discussed, and the flow-front is hardly defined in such small dimensions (of the order of 1 mm), our measurements on some so-called Non-Crimped New Concept (NC2) are carried out for saturated flow, i.e., the fiber network is completely impregnated right from the onset of the experiment. In our case [1], these measures rely on the measurements of the pressure drop induced by the flow of a controlled fluid across the fabric, easily converted into transverse permeability through Darcy's law. One of the main results of these measurements is that the low NC2 transverse permeability depends on the face of the fabric receiving the fluid. This original behavior may, in turn, be translated into manufacturing guidelines to achieve optimal processing configuration. An attempt to relate this differential to the stitching hole surface is proposed which appears to explain some minor phenomena. On the contrary, the 3D shape of the stitching hole reconstruction from polishings could yield some appropriate explanation

Influence of the stitching density on the transverse permeability of Non-Crimped New Concept (NC2) multiaxial reinforcements : measurements and predictions

International audienceNew manufacturing processes arise for polymer-based composites which involve resin infusion through dry pre-forms. Modelling approaches of these processes require to assess new physical characteristics of the materials. In this paper, the transverse permeability of new multiaxial stitched materials, referred to as NC2, is investigated. First, in the framework of Darcy's flows, this permeability is assessed for various biaxial NC2 using a specific device. Through this approach it is shown that the transverse permeability depends strongly on the stitching density. Then, the results from a simplified FE study carried out at the blanket scale are shown to correlate quite well the experimental measurements and evidences established in the first part

Mechanical investigation of compression stockings and of their effects on the human leg. Étude mécanique des articles de contention et de leurs effets sur la jambe humaine.

Ce papier est une synthèse de différentes études apportant un regard scientifique sur la contention qui consiste à exercer des pressions sur la jambe humaine au moyen de chaussettes ou de bas afin de faciliter le reflux veineux. Il paraît évident que la répartition des pressions sur la jambe affecte le débit sanguin dans les veines. Néanmoins, la répartition conduisant à un débit veineux optimal est non triviale, et diffère en fonction de l'application : traitement médical ou récupération chez les sportifs. Afin d'améliorer les connaissances à ce sujet, un modèle numérique 2D a été mis en place pour calculer les champs de contraintes dans la jambe en prenant en compte le comportement mécanique réel des articles de contention et des tissus de la jambe. Des méthodes d'identification appropriées, basées soit sur le recalage de modèle et la corrélation d'images numériques (pour les articles de contention), soit sur le recalage de modèle par mise en correspondance locale non linéaire d'images fournies par l'IRM (pour les tissus internes de la jambe), ont été développées pour identifier ces paramètres de comportement. This paper presents a synthesis of different studies willing to bring a scientific insight into leg compression, which is the process of applying external compression forces onto the human leg with stockings or socks, for enhancing the venous flow. It seems obvious that the pressure distribution on the leg affects the blood flow in the veins. However, the pressure distribution that leads to the optimal blood flow is not trivial, and it is different with regard to the application: medical treatment or recovering after an effort in sports. In order to improve the scientific knowledge about this topic, a numerical 2D model was set up for computing stress fields inside the leg, accounting for the actual material properties of both the compression stocking and of the leg biological tissues. Suitable identification methods, based either on model updating from digital image correlation (for the compression stockings), or on image warping and model updating from MRI scans (for the internal leg tissues), were developed for retrieving these material properties