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

Cosmological implications from some proposals in Quantum Gravity

In this thesis we present the cosmological applications of some proposals from Quantum Gravity. Namely, we will explore classical and quantum cosmological implications of the Generalized Uncertainty Principle (GUP), the Ho\v{r}ava-Lifshitz (HL) theory of gravity and the Swampland Conjectures. Furthermore, we will also present a detailed analysis of Lorentzian Vacuum Transitions in various contexts. First of all, we will present a study of the classical implications of a general form of the GUP to the standard inflationary scenario driven by a scalar field. We will then present the study of the compatibility between the dS swampland conjecture and the Ho\v{r}ava-Lifshitz $F(\bar{R})$ theories. Then we will study the effects of considering a GUP in the variables of the superspace in a model of the Wheeler-DeWitt (WDW) equation in HL gravity. Finally, we will present a general study of the Lorentzian vacuum transitions. We will present a general method to compute the transition probabilities between two minima of a scalar field potential for any model of the superspace that leads to a generic form of the Hamiltonian constraint, by solving the WDW equation with a semiclassical expansion. We will only consider up to first order in this expansion but the method provides enough information to compute the probabilities up to any desired order. We will then apply the method in different scenarios. With these studies we will approach keys aspects of cosmology that are hoped to be solved by quantum gravity, that is we will explore (at a toy model level): the origin of inflation, the viability of the swampland conjectures and a plausible model to avoid the initial singularity. This thesis encompasses six research articles where these results were presented originally.Comment: PhD Dissertation. 176 pages, 19 figure