Etude expérimentale du ruissellement sur des sols à végétation contrastée du Mont Lozère

Les conditions d'apparition du ruissellement de surface, et les valeurs limites que peut atteindre l'infiltration sont étudiés expérimentalement par simulation de pluie sur des sols à végétation contrastée du Mont Lozère (Sud du Massif Central, France), développés sur arène granitique peu profonde. Les résultats mettent en évidence la forte capacité d'infiltration du milieu naturel, mais aussi la grande variabilité spatiale de cette capacité d'infiltration, pour aboutir à un schéma de fonctionnement dans lequel, si la circulation hypodermique, à la limite de la roche saine, demeure le processus essentiel de transfert de l'eau entre son point de chute et le cours d'eau, le ruissellement sur les versants n'est pas exclu et peut jouer un rôle important dans la formation des crues. Par ailleurs il semblerait qu'une pelouse en bon état, couvrant parfaitement le sol, présente une aussi bonne protection contre le ruissellement et l'érosion que les litières forestières testées. (Résumé d'auteur

Bonding of gold nanoclusters to oxygen vacancies on rutile TiO2(110)

Through an interplay between scanning tunneling microscopy (STM) and density functional theory (DFT) calculations, we show that bridging oxygen vacancies are the active nucleation sites for Au clusters on the rutile TiO2(110) surface. We find that a direct correlation exists between a decrease in density of vacancies and the amount of Au deposited. From the DFT calculations we find that the oxygen vacancy is indeed the strongest Au binding site. We show both experimentally and theoretically that a single oxygen vacancy can bind 3 Au atoms on average. In view of the presented results, a new growth model for the TiO2(110) system involving vacancy-cluster complex diffusion is presented

Au/TiO2(110) interfacial reconstruction stability from ab initio

We determine the stability and properties of interfaces of low-index Au surfaces adhered to TiO2(110), using density functional theory energy density calculations. We consider Au(100) and Au(111) epitaxies on rutile TiO2(110) surface, as observed in experiments. For each epitaxy, we consider several different interfaces: Au(111)//TiO2(110) and Au(100)//TiO2(110), with and without bridging oxygen, Au(111) on 1x2 added-row TiO2(110) reconstruction, and Au(111) on a proposed 1x2 TiO reconstruction. The density functional theory energy density method computes the energy changes on each of the atoms while forming the interface, and evaluates the work of adhesion to determine the equilibrium interfacial structure.Comment: 20 pages, 11 figure

Global Diversity Hotspots and Conservation Priorities for Sharks

Sharks are one of the most threatened groups of marine animals, as high exploitation rates coupled with low resilience to fishing pressure have resulted in population declines worldwide. Designing conservation strategies for this group depends on basic knowledge of the geographic distribution and diversity of known species. So far, this information has been fragmented and incomplete. Here, we have synthesized the first global shark diversity pattern from a new database of published sources, including all 507 species described at present, and have identified hotspots of shark species richness, functional diversity and endemicity from these data. We have evaluated the congruence of these diversity measures and demonstrate their potential use in setting priority areas for shark conservation. Our results show that shark diversity across all species peaks on the continental shelves and at mid-latitudes (30–40 degrees N and S). Global hotspots of species richness, functional diversity and endemicity were found off Japan, Taiwan, the East and West coasts of Australia, Southeast Africa, Southeast Brazil and Southeast USA. Moreover, some areas with low to moderate species richness such as Southern Australia, Angola, North Chile and Western Continental Europe stood out as places of high functional diversity. Finally, species affected by shark finning showed different patterns of diversity, with peaks closer to the Equator and a more oceanic distribution overall. Our results show that the global pattern of shark diversity is uniquely different from land, and other well-studied marine taxa, and may provide guidance for spatial approaches to shark conservation. However, similar to terrestrial ecosystems, protected areas based on hotspots of diversity and endemism alone would provide insufficient means for safeguarding the diverse functional roles that sharks play in marine ecosystems

GRAIN BOUNDARY INTERNAL FRICTION AND RELATIONSHIP TO INTERGRANULAR FRACTURE

Creep rate, stress rupture and fracture mode have been measured on Ni-20 W/0 Cr alloys containing 0 and 180 at. ppm Ce. Grain boundary viscosity and anelastic relaxation phenomena have been determined by high temperature internal friction measurements and results correlated to fracture behavior