Background levels of heavy metals in surficial sediments of the Gulf of Lions (NW Mediterranean): An approach based on 133Cs normalization and lead isotope measurements

This paper presents an attempt to reach natural background levels of heavy metals in surficial sediments of the Gulf of Lions(NW Mediterranean). To correct for the grain-size effect, normalization procedures based on a clay mineral indicator element are commonly used, after a first grain size separation by sieving. In our study, we tested the applicability of this method with respect to commonly used normalizer elements, and found that stable Cs shows the best ability to reflect the fine sediment fraction. Background levels were successfully reached for Co, Cr, Cu, Ni and Pb, compared to various literature references. Nevertheless, in the case of lead, the normalized data depicted a general enrichment in all samples, and the natural levels could only be reached when concentrations were corrected for the atmospheric contribution by analysing lead isotope ratios. Also for Zn, a general enrichment was found in our samples, although less important

Organisation socio-spatiale et structuration régionale de l’Outaouais

L'organisation socio-spatiale de l'Outaouais se caractérise par une juxtaposition d'éléments dont l'interdépendance est faible. Cette faiblesse se révèle bien à l'étude des comportements différenciés de migration. Cette réalité s'oppose aux efforts des divers organismes politico-administratifs cherchant à intégrer la région dans un ensemble cohérent. Cela impose une compréhension du dynamisme des éléments locaux qui constituent un passage obligé de toute politique d'aménagement et de développement régional.The socio-spatial organization of the Outaouais region is characterized by a juxtaposition of elements, the interdependence of which is weak. This weakness can be revealed, for example, by a study of the migration behaviour. To this reality is opposed the integration objective supported by political organisms at the regional level. However, this opposition can be resolved by a better understanding of local dynamisms at the roots of any political intervention

Replantation des cocoteraies : mythe ou réalité ?

Le constat du faible dynamisme des plantations de cocotier et de la part déclinante du coprah dans la production et les échanges mondiaux pourrait laisser craindre que les cocoteraies sont condamnées à terme. Cela n'est pas si sûr, car le cocotier dispose d'un certain nombre d'atouts, notamment en conditions villageoises, et se prête à des utilisations variées qui dépassent le strict adre du coprah : la plante dite aux mille usages est d'abord une plante vivrière. L'article passe en revue les conditions sous lesquelles de nouvelles plantations sont envisageables et présente quelques solutions alternatives à la replantation, comme la réhabilitation ou la diversification dans le cadre d'associations de culture sous cocotier adulte. (Résumé d'auteur

Finitely generated simple sharply 2-transitive groups

We construct the first examples of infinite sharply 2-transitive groups which are finitely generated. Moreover, we construct such a group that has Kazhdan property (T), is simple, has exactly four conjugacy classes, and we show that this number is as small as possible

Adaptive networks: coevolution of disease and topology

Adaptive networks have been recently introduced in the context of disease propagation on complex networks. They account for the mutual interaction between the network topology and the states of the nodes. Until now, existing models have been analyzed using low-complexity analytic formalisms, revealing nevertheless some novel dynamical features. However, current methods have failed to reproduce with accuracy the simultaneous time evolution of the disease and the underlying network topology. In the framework of the adaptive SIS model of Gross et al. [Phys. Rev. Lett. 96, 208701 (2006)], we introduce an improved compartmental formalism able to handle this coevolutionary task successfully. With this approach, we analyze the interplay and outcomes of both dynamical elements, process and structure, on adaptive networks featuring different degree distributions at the initial stage.Comment: 11 pages, 8 figures, 1 appendix. To be published in Physical Review

Exact solution of bond percolation on small arbitrary graphs

We introduce a set of iterative equations that exactly solves the size distribution of components on small arbitrary graphs after the random removal of edges. We also demonstrate how these equations can be used to predict the distribution of the node partitions (i.e., the constrained distribution of the size of each component) in undirected graphs. Besides opening the way to the theoretical prediction of percolation on arbitrary graphs of large but finite size, we show how our results find application in graph theory, epidemiology, percolation and fragmentation theory.Comment: 5 pages and 3 figure