Energy relaxation of an excited electron gas in quantum wires: many-body electron LO-phonon coupling

We theoretically study energy relaxation via LO-phonon emission in an excited one-dimensional electron gas confined in a GaAs quantum wire structure. We find that the inclusion of phonon renormalization effects in the theory extends the LO-phonon dominated loss regime down to substantially lower temperatures. We show that a simple plasmon-pole approximation works well for this problem, and discuss implications of our results for low temperature electron heating experiments in quantum wires.Comment: 10 pages, RevTex, 4 figures included. Also available at http://www-cmg.physics.umd.edu/~lzheng

Active Brownian Particles. From Individual to Collective Stochastic Dynamics

We review theoretical models of individual motility as well as collective dynamics and pattern formation of active particles. We focus on simple models of active dynamics with a particular emphasis on nonlinear and stochastic dynamics of such self-propelled entities in the framework of statistical mechanics. Examples of such active units in complex physico-chemical and biological systems are chemically powered nano-rods, localized patterns in reaction-diffusion system, motile cells or macroscopic animals. Based on the description of individual motion of point-like active particles by stochastic differential equations, we discuss different velocity-dependent friction functions, the impact of various types of fluctuations and calculate characteristic observables such as stationary velocity distributions or diffusion coefficients. Finally, we consider not only the free and confined individual active dynamics but also different types of interaction between active particles. The resulting collective dynamical behavior of large assemblies and aggregates of active units is discussed and an overview over some recent results on spatiotemporal pattern formation in such systems is given.Comment: 161 pages, Review, Eur Phys J Special-Topics, accepte

Factors influencing terrestriality in primates of the Americas and Madagascar

Among mammals, the order Primates is exceptional in having a high taxonomic richness in which the taxa are arboreal, semiterrestrial, or terrestrial. Although habitual terrestriality is pervasive among the apes and African and Asian monkeys (catarrhines), it is largely absent among monkeys of the Americas (platyrrhines), as well as galagos, lemurs, and lorises (strepsirrhines), which are mostly arboreal. Numerous ecological drivers and species-specific factors are suggested to set the conditions for an evolutionary shift from arboreality to terrestriality, and current environmental conditions may provide analogous scenarios to those transitional periods. Therefore, we investigated predominantly arboreal, diurnal primate genera from the Americas and Madagascar that lack fully terrestrial taxa, to determine whether ecological drivers (habitat canopy cover, predation risk, maximum temperature, precipitation, primate species richness, human population density, and distance to roads) or species-specific traits (body mass, group size, and degree of frugivory) associate with increased terrestriality. We collated 150,961 observation hours across 2,227 months from 47 species at 20 sites in Madagascar and 48 sites in the Americas. Multiple factors were associated with ground use in these otherwise arboreal species, including increased temperature, a decrease in canopy cover, a dietary shift away from frugivory, and larger group size. These factors mostly explain intraspecific differences in terrestriality. As humanity modifies habitats and causes climate change, our results suggest that species already inhabiting hot, sparsely canopied sites, and exhibiting more generalized diets, are more likely to shift toward greater ground use

Répteis em fragmentos de Cerrado e Mata Atlântica no Campo das Vertentes, Estado de Minas Gerais, Sudeste do Brasil

Os dados sobre a fauna reptiliana em Minas Gerais são pontuais e revelam carência de informações sobre esse grupo, principalmente em regiões de transição entre a Mata Atlântica e o Cerrado. A área do estudo está situada no município de Ritápolis (21° 01' 37.07" S e 44° 19' 11.84" O), microrregião Campo das Vertentes, Estado de Minas Gerais, Sudeste do Brasil. Pretendeu-se com a presente pesquisa conhecer a composição da fauna de répteis local. As observações, capturas e coletas foram realizadas quinzenalmente, durante dois dias consecutivos, de agosto de 2005 a julho de 2006. As capturas foram realizadas por meio de armadilhas de interceptação e queda, distribuídas em oito sítios, sendo quatro em área de mata de galeria e quatro em área aberta, perfazendo um esforço amostral de 6.912 horas-balde. Foi também realizada procura ativa e encontros ocasionais com registros fotográficos dos espécimes, e, no caso de serpentes, alguns exemplares foram entregues por terceiros quando encontradas mortos. Registrou-se a presença de 31 espécies de répteis, sendo duas espécies de cágados, nove de lagartos, duas de anfisbenas e 18 de serpentes. Apenas os lagartos Cercosaura ocellata, Enyalius bilineatus e Tupinambis merianae e as serpentes Leptodeira annulata e Apostolepis assimilis foram capturados nas armadilhas de queda. Os lagartos mais comuns foram Ameiva ameiva e Mabuya frenata, e as serpentes mais abundantes foram Oxyrhophus guibei e Sibynomorphus mikanii. Os lagartos estão bem representados na área, com espécies típicas de mata, como Enyalius bilineatus, e de áreas aberta de cerrado, como Ameiva ameiva e Mabuya frenata. A fauna de serpentes possui representantes típicos de áreas abertas do Cerrado, como O. guibei e Micrurus frontalis, e de regiões florestadas, como Liophis poecilogyrus e Philodryas olfersii. A diversidade de espécies de répteis e o registro prévio de Amphisbaena dubia e Hydromedusa tectifera para o Estado de Minas Gerais indicam a grande potencialidade do Campo das Vertentes em revelar a ocorrência de espécies novas ou a ampliação na distribuição de outras