Electronic and phononic properties of the chalcopyrite CuGaS2

The availability of ab initio electronic calculations and the concomitant techniques for deriving the corresponding lattice dynamics have been profusely used for calculating thermodynamic and vibrational properties of semiconductors, as well as their dependence on isotopic masses. The latter have been compared with experimental data for elemental and binary semiconductors with different isotopic compositions. Here we present theoretical and experimental data for several vibronic and thermodynamic properties of CuGa2, a canonical ternary semiconductor of the chalcopyrite family. Among these properties are the lattice parameters, the phonon dispersion relations and densities of states (projected on the Cu, Ga, and S constituents), the specific heat and the volume thermal expansion coefficient. The calculations were performed with the ABINIT and VASP codes within the LDA approximation for exchange and correlation and the results are compared with data obtained on samples with the natural isotope composition for Cu, Ga and S, as well as for isotope enriched samples.Comment: 9 pages, 8 Figures, submitted to Phys. Rev

RELATIVE ABUNDANCE AND MICROHABITAT OF FOUR SYMPATRIC ANTPITTAS IN AN INTERANDEAN VALLEY OF SOUTHERN ECUADOR

Exploring mechanisms that determine species coexistence is a key step to understand community organization and patterns of distribution of biodiversity. Anpittas, genus Grallaria, offer a great opportunity to measure coexistence mechanisms among closely related species. Antpittas are terrestrial insectivores with a specialized foraging technique and limited dispersal abilities; these factors could produce high levels of niche overlap and consequently reduce the chances of stable coexistence. We explored niche partitioning in space among four antpitta species (Rufous Antpitta, Chesnut-crowned Antpitta, Undulated Antpitta, Tawny Antpitta) which coexist in a tropical Andean valley located in southern Ecuador. We determined the abundance of each antpitta species in mature native forest, shrub, pasture, and páramo habitats, and gathered data about the microhabitat of each species. Abundance was determined using point counts, territories were located by triangulating on individual calls, and microhabitat characteristics were measured within each territory. We found no differences in the abundance or probability of occurrence of species among habitats for Rufous Antpitta, Chesnut-crowned Antpitta, and Undulated Anpitta, but Tawny Antpitta was restricted to páramo. At the microhabitat level, Rufous and Chesnut-crowned Antpittas shared similar vegetation characteristics, with the important presence of shrubs. Undulated Antpitta occurred in a microhabitat characterized by the presence of trees and a ground cover of mosses, while Tawny Antpitta occupied microhabitats with an open vegetation. In general our results suggest that closely related birds could partition their niche at different spatial scales, which could promote the coexistence of species in the tropical Andes

Host-induced gene silencing in the necrotrophic fungal pathogen Sclerotinia sclerotiorum.

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Structure of Polyelectrolytes in Poor Solvent

We present simulations on charged polymers in poor solvent. First we investigate in detail the dilute concentration range with and without imposed extension constraints. The resulting necklace polymer conformations are analyzed in detail. We find strong fluctuations in the number of pearls and their sizes leading only to small signatures in the form factor and the force-extension relation. The scaling of the peak in the structure factor with the monomer density shows a pertinent different behavior from good solvent chains.Comment: 7 pages, 5 figures. submitted to EP

Like-charge attraction through hydrodynamic interaction

We demonstrate that the attractive interaction measured between like-charged colloidal spheres near a wall can be accounted for by a nonequilibrium hydrodynamic effect. We present both analytical results and Brownian dynamics simulations which quantitatively capture the one-wall experiments of Larsen and Grier (Nature 385, p. 230, 1997).Comment: 10 pages, 4 figure

On the nature of long-range contributions to pair interactions between charged colloids in two dimensions

We perform a detailed analysis of solutions of the inverse problem applied to experimentally measured two-dimensional radial distribution functions for highly charged latex dispersions. The experiments are carried out at high colloidal densities and under low-salt conditions. At the highest studied densities, the extracted effective pair potentials contain long-range attractive part. At the same time, we find that for the best distribution functions available the range of stability of the solutions is limited by the nearest neighbour distance between the colloidal particles. Moreover, the measured pair distribution functions can be explained by purely repulsive pair potentials contained in the stable part of the solution.Comment: 6 pages, 5 figure

Drag Prediction Using Adaptive Discontinuous Finite Elements

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/106502/1/AIAA2013-51.pd