ZERO-TEMPERATURE 2D STOCHASTIC ISING MODEL AND ANISOTROPIC CURVE-SHORTENING FLOW

International audienceLet D be a simply connected, smooth enough domain of R2. For L > 0 consider the continuous time, zero-temperature heat bath dynamics for the nearest-neighbor Ising model on Z2 with initial condition such that σx = −1 if x ∈ LD and σx = +1 otherwise. It is conjectured [24] that, in the diffusive limit where space is rescaled by L, time by L2 and L → ∞, the boundary of the droplet of "−" spins follows a deterministic anisotropic curve-shortening flow, where the normal velocity at a point of its boundary is given by the local curvature times an explicit function of the local slope. The behavior should be similar at finite temperature T < Tc, with a different temperature-dependent anisotropy function. We prove this conjecture (at zero temperature) when D is convex. Existence and regularity of the solution of the deterministic curve-shortening flow is not obvious a priori and is part of our result. To our knowledge, this is the first proof of mean curvature-type droplet shrinking for a model with genuine microscopic dynamics

PLACE DU CAFE DANS LES SYSTEMES DE PRODUCTION DU SUD-OUEST ETHIOPIEN ET IMPACT PREVISIONNEL DES OUTILS DE CERTIFICATION

N° ISBN - 978-2-7380-1284-5International audienceThe role of coffee in southwest Ethiopia's production systems and the forecasted impact of certification projects. Southwest Ethiopia, the genetic cradle of Arabica coffee, is characterized by the progressive transformation of its forests, based on an enrichment of the last on coffee plants and on a lightening and speciesbased modification of the tree strata. The gathering and/or production of coffee, which is almost always combined with cereal cultivation with yoke in open fields and hand tool-based gardening in houses nearby within the very complex local production systems, is nowadays promoted as “forest coffee” or “wild coffee”, appellations that are nowadays used in some certification projects. Also, as a part of the current policies of development of this original product and protection of the forested areas, government allocates big forestry concessions to national and foreign investors. The aim of this communication is to analyse the role of coffee within the diversified production systems of southwest Ethiopia, and the possible effects of “forest coffee” certification projects on farmers' practices, income and socioeconomic differentiation evolution. Forestry concessions evolving into more and more of a capitalistic farming model – based on employment of precarious daily workers – this research work also poses the problem of the absence of fairness in this type of development. It also underlines the risks of the certification process cited above, which includes in the same chain value very different ways of producing coffee – both in terms of the production process and the associated social and production relations – and, in that sense, could create some confusion and, at the same time, could deprive the Ethiopian peasantry of a part of its patrimony

Nouvelles données sur le peuplement ancien de la Nouvelle-Calédonie : la vallée de la Koumac (Grande-Terre)

Les premières fouilles préhistoriques et datations réalisées dans la vallée de la Koumac montrent que l'occupation des vallées de Nouvelle-Calédonie est aussi ancienne que les premiers sites "Lapita" de la côte (ca. 3000 BP). Les vallées permettent également une étude interdisciplinaire de l'ensemble des activités humaines, y compris la production d'industrie lithique, peu étudiée jusqu'alors. (Résumé d'auteur