De l'inefficacité du réseau social : des liens sociaux non mobilisés chez les patients atteints de cancer

International audienceDe nombreuses études sur les réseaux sociaux portent sur la question des ressources auxquelles un individu peut avoir accès à travers ses relations sociales. En s'intéressant aux réseaux qui ont « fonctionné », elles tentent alors de spécifier les facteurs ayant permis l'accès aux ressources. Mais peu de travaux se sont penchés sur les réseaux ayant échoué à fournir à l'individu le bien ou le service qu'il recherchait. Cet article se propose de discuter de ces réseaux « inefficaces » à travers le cas de patients atteints de cancer recherchant des informations relatives à leur pathologie. Les résultats indiquent que les causes de l'inefficacité du réseau sont à rechercher dans la non mobilisation des liens de la part des malades rencontrés. Un certain nombre de contraintes pèsent sur ces liens empêchant ainsi leur mobilisation

On the asymptotic theory of localized structures in a thin two-dimensional Harris current sheet: plasmoids, multiplasmoids and X points

We develop a new asymptotic method of resolution of the two-dimensional equilibrium equation of collisionless plasmas described by the Maxwell–Vlasov equations. This method differs from the classical one proposed by K. Schindler [Earth's Magnetospheric Processes (ed. B. M. McCormac). Norwood, MA: Reidel, 1972, pp. 200–209.] since we consider free-boundary plasmas. Our method is a generalization of the usual multiscale asymptotic developments. The first-approximation asymptotic solutions are found from the elimination of increasing and singular terms in the next approximation. We apply the method to the mathematical description of nonlinear structures that may form in neutral sheets. Particular solutions describing localized plasmoids (O-point configuration) as well as X-point magnetic configurations are obtained. We also find more general solutions describing a finite number of ‘magnetic islands' (multiplasmoid solutions) separated by X points

Avoidance threshold to oil water soluble fraction by a juvenile marine teleost fish

When oil spills occur, behavior is the first line of defense for a fish to avoid being contaminated. Here, we determined the avoidance threshold of the European seabass (Dicentrarchus labrax) to the water-soluble fraction (WSF) of oil using a dual flow choice box. Our experiment revealed that a plume of 20%-diluted WSF (total PAH concentration: 8.54 μg L-1) triggered a significant avoidance response that was detected within 7.5 minutes of introducing WSF-contaminated water in the experimental set-up. However, the ecological relevance of seabass capacity to detect and avoid WSF remains to be established. In the short term, such response is indeed liable to reduce sea bass contact time with oil-contaminated water and thus preserve their functional integrity. In the long term, however, this may contribute to displace a population into a possibly less auspicious environment, with very similar consequences than contaminant exposure i.e., disturbed population dynamics and demography