Role of Self-Interaction Effects in the Geometry Optimization of Small Metal Clusters

By combining the Self-Interaction Correction (SIC) with pseudopotential perturbation theory, the role of self-interaction errors inherent to the Local Density Approximation (LDA) to Density Functional Theory is estimated in the determination of ground state and low energy isomeric structures of small metallic clusters. Its application to neutral sodium clusters with 8 and 20 atoms shows that the SIC provides sizeable effects in Na_8, leading to a different ordering of the low lying isomeric states compared with ab-initio LDA predictions, whereas for Na_20, the SIC effects are less pronounced, such that a quantitative agreement is achieved between the present method and ab-initio LDA calculations.Comment: RevTeX, 4 pages, 1 figure available from [email protected]

The role of elasticity in slab bending

International audiencePrevious studies showed that plate rheology exerts a dominant control on the shape and velocity of subducting plates. Here, we perform a systematic investigation of the role of elasticity in slab bending, using fully dynamic 2-D models where an elastic, viscoelastic, or viscoelastoplastic plate subducts freely into a purely viscous mantle. We derive a scaling relationship between the bending radius of viscoelastic slabs and the Deborah number, De, which is the ratio of Maxwell time over deformation time. We show that De controls the ratio of elastically stored energy over viscously dissipated energy and find that at De>10-2, substantially less energy is required to bend a viscoelastic slab to the same shape as a purely viscous slab with the same intrinsic viscosity. Elastically stored energy at higher De favors retreating modes of subduction via unbending, while trench advance only occurs for some cases with De 1, where most zones have low De 0.1. Slabs with De<10-2 either have very low viscosities or they may be yielding, in which case our De estimates may be underestimated by up to an order of magnitude, potentially pointing towards a significant role of elasticity in ∼60% of the subduction zones. In support of such a role of elasticity in subduction, we find that increasing De correlates with increasing proportion of larger seismic events in both instrumental and historic catalogues

Evolution of Supermassive Black Holes from Cosmological Simulations

The correlations between the mass of supermassive black holes and properties of their host galaxies are investigated through cosmological simulations. Black holes grow from seeds of 100 solar masses inserted into density peaks present in the redshift range 12-15. Seeds grow essentially by accreting matter from a nuclear disk and also by coalescences resulting from merger episodes. At z=0, our simulations reproduce the black hole mass function and the correlations of the black hole mass both with stellar velocity dispersion and host dark halo mass. Moreover, the evolution of the black hole mass density derived from the present simulations agrees with that derived from the bolometric luminosity function of quasars, indicating that the average accretion history of seeds is adequately reproduced . However, our simulations are unable to form black holes with masses above $10^9 M_{\odot}$ at $z\sim 6$, whose existence is inferred from the bright quasars detected by the Sloan survey in this redshift range.Comment: Talk given at the International Workshop on Astronomy and Relativistic Astrophysics (IWARA 2009), Maresias, Brazil. to be published in the International Journal of Modern Physics

THE HABITAT OF EUROPEAN BROWN BEARS IN NORTHERN SPAIN: MAPPING HABITAT FRAGMENTATION AND POTENTIAL CONNECTIVITY

The European brown bear in northern Spain is considered to be an endangered species whose habitat has been fragmented into two subpopulations due to habitat loss and lack of connectivity. The importance of improving connectivity and preventing more habitat destruction is vital to recover the species in this region. This research looks at spatial and temporal variations of brown bear habitat by mapping the conditions of habitat fragmentation and potential connectivity at a regional extent. This research examines net changes of brown bear habitat fragmentation between 1990-2000, 2000-2006, and overall 1990-2006; and the degree of brown bear habitat connectivity between subpopulations and at a landscape level for 2006. The purpose of this research is to use fragmentation and connectivity geospatial tools to map the spatial relationships among habitat, potential linkages and barriers, and to identify gaps in managed habitats to assist with restoring habitat connectivity. Based on the fragmentation results, high fragmentation occurred in core habitat between 2000-2006. Habitat connectivity is a measure of how diverse the landscape is based on movement resistance and multiple pathways. It’s important to analyze connectivity at different scales to determine critical areas of concern. The results showed that connectivity is most constrained by human infrastructure, and this can be viewed as a challenge for brown bear recovery in the study area

Multi-Scale Spatio-Temporal Analysis of Brown Bear Habitat in Northern Iberia: A Large Landscape Conservation Planning Perspective

Problem Statement The distributions of brown bears in northern Iberia are mainly found in protected areas but they also extend beyond protected boundaries. Since brown bears need large continuous areas of habitat with sufficient availability of preferred foods, escape cover and den sites; it’s important to map brown bear habitats at a landscape level to further examine their connectivity and fragmented habitats. The major problems for brown bear recovery and management in the northern Iberian Peninsula is the lack of identified linkages (one means of achieving connectivity) between subpopulations, and barriers (fragmentation-natural or anthropogenic) that divide them. Brown bear habitats in northern Iberia are highly fragmented as a result of previous and ongoing developments and land-use land cover changes. Improvement of connectivity and prevention of more habitat destruction is vital to recovering the species in this region. To help understand the spatial and temporal variations of brown bear habitat connectivity and fragmentation, there is a need for maps which both accurately represent the condition of habitat and comparable at multiple scales (Soulé and Terborgh 1999 & FOP 2014). Brown bears in the study area are endangered in large part due to a loss of connectivity in their habitat. Planning must be sustainable in order to maintain ecosystems in which brown bear habitats reside. In addition, these ecosystems provide clean water, air, and genetic resources-the basic resources people need to survive (Servheen et al. 1999). The essential goal of maintaining connectivity in large landscape conservation is addressed via the spatial configuration of habitat that is important to satisfy the demands of the species. This research will quantify change of brown bear habitat fragmentation by applying post-classification change mapping techniques to remote sensing-derived, multi-temporal land cover maps. Spatio-temporal change analyses will be conducted to evaluate brown bear habitat fragmentation identified by the Morphological Spatial Pattern Analysis (MSPA) and potential connectivity using Circuit Theory (Circuitscape). In terms of analyzing connectivity, geographic extent and scale are important; therefore, broader landscapes should be considered for effective bear management conservation planning (Hilty et al. 2006). The questions driving my research are: What are the net changes of brown bear habitat fragmentation at multiple scales for 1990, 2000, and 2006? What is the degree of brown bear habitat connectivity at multiple scales in 2006? When did brown bear conservation policies take effect and should large landscape conservation planning be implemented? Study Area & Methods The research setting for this study is located in a mountain range in northern Spain, the Cantabrian Cordillera. The Cantabrian Cordillera has three geographic distinct regions: Western (the Asturian Massif in Galicia, Asturias, Leon, and Cantabria); Central (the Cantabrian Massif, in Cantabria); and the Eastern (Monte Vascos or Basque Mountains in the Basque Country). MSPA will map land cover maps that will be reclassified into binary classes of foreground (habitat: core and links) and background (non-habitat). MSPA will utilize the binary map and convert the foreground (area of interest) into seven spatial pattern elements: core, islet, bridge, loop, branch, edge, and perforation. MSPA maps will be compared to evaluate changes in brown bear habitat structure for 1990, 2000, & 2006. IDRISI Selva provides an excellent tool for comparing categorical maps based on cross-tabulation at the pixel level. The Land Change Modeler (LCM) will evaluate gains/losses and net change of brown bear habitat fragmentation using MSPA categories. Circuitscape (an open-source program that uses circuit theory) will help to predict potential connectivity of brown bear habitats within and between subpopulations in northern Spain. A raster habitat map will be coded for resistances (high values denote greater resistance to movement) or conductances (reciprocal of resistance; higher values indicate greater ease of movement). The purpose of this research is to use MSPA and Circuit Theory to map and understand the spatial relationships among habitat, potential linkages and barriers, and to identify gaps in managed habitats to assist with restoring connectivity. Bibliography Soulé, M.E. & J. Terborgh. 1999. Conserving Nature at Regional and Continental Scales: A Scientific Approach for North America. Bioscience 29(10): 809-817 Fundacion Oso Pardo (FOP). http://www.fundacionosopardo.org/index.php/the-brown-bear/?lang=en (last accessed 15 October 2014) Hilty, J.A., W.Z. Lidicker & A.M. Merenlender. 2006. Corridor Ecology: The Science and Practice of Linking Landscapes for Biodiversity Conservation. Washington: Island Press Servheen, C., S. Herrero & B. Peyton. 1999. Status Survey and Conservation Action Plan. Bears. IUCN 1-32