Treating some solid state problems with the Dirac equation

The ambiguity involved in the definition of effective-mass Hamiltonians for nonrelativistic models is resolved using the Dirac equation. The multistep approximation is extended for relativistic cases allowing the treatment of arbitrary potential and effective-mass profiles without ordering problems. On the other hand, if the Schrodinger equation is supposed to be used, our relativistic approach demonstrate that both results are coincidents if the BenDaniel and Duke prescription for the kinetic-energy operator is implemented. Applications for semiconductor heterostructures are discussed.Comment: 06 pages, 5 figure

Quantifying the Drivers of Star Formation on Galactic Scales. I. The Small Magellanic Cloud

We use the star formation history of the Small Magellanic Cloud (SMC) to place quantitative limits on the effect of tidal interactions and gas infall on the star formation and chemical enrichment history of the SMC. The coincident timing of two recent (< 4 Gyr) increases in the star formation rate and SMC/Milky Way(MW) pericenter passages suggests that global star formation in the SMC is driven at least in part by tidal forces due to the MW. The Large Magellanic Cloud (LMC) is the other potential driver of star formation, but is only near the SMC during the most recent burst. The poorly constrained LMC-SMC orbit is our principal uncertainty. To explore the correspondence between bursts and MW pericenter passages further, we model star formation in the SMC using a combination of continuous and tidally-triggered star formation. The behavior of the tidally-triggered mode is a strong inverse function of the SMC-MW separation (preferred behavior ~ r^-5, resulting in a factor of ~100 difference in the rate of tidally-triggered star formation at pericenter and apocenter). Despite the success of these closed-box evolutionary models in reproducing the recent SMC star formation history and current chemical abundance, they have some systematic shortcomings that are remedied by postulating that a sizable infall event (~ 50% of the total gas mass) occured about 4 Gyr ago. Regardless of whether this infall event is included, the fraction of stars in the SMC that formed via a tidally triggered mode is > 10% and could be as large as 70%.Comment: Accepted for publication in Ap

Co-evolution of strategy and structure in complex networks with dynamical linking

Here we introduce a model in which individuals differ in the rate at which they seek new interactions with others, making rational decisions modeled as general symmetric two-player games. Once a link between two individuals has formed, the productivity of this link is evaluated. Links can be broken off at different rates. We provide analytic results for the limiting cases where linking dynamics is much faster than evolutionary dynamics and vice-versa, and show how the individual capacity of forming new links or severing inconvenient ones maps into the problem of strategy evolution in a well-mixed population under a different game. For intermediate ranges, we investigate numerically the detailed interplay determined by these two time-scales and show that the scope of validity of the analytical results extends to a much wider ratio of time scales than expected

Avaliação da fermentação de caldo de sorgo sacarino empregando leveduras comerciais.

Visando explorar o potencial deste material, empregando o caldo de sorgo sacarino BRS 511, foi avaliado o comportamento de três leveduras comerciais (CAT-1, PE-2 e SA-1) em quatro ciclos fermentativos

Aplicação de celulases imobilizadas nahidrólise de Brachiaria brizantha.

O objetivo deste trabalho foi desenvolver um biocatalisador para aplicação na hidrólise de holocelulose de braquiária

Between old broadcast media and new networked media: materiality and media consumption practices

Past tensions between content and materiality have prevented communication researchers from forming a deeper conceptualization of the role played by the material character of communication technologies in shaping social arrangements and cultural forms of expression. Drawing on the findings of a comparative research project on European audiences, we examine the interrelation between material facets of media technologies and the practices they afford on the audience side. Relations between "old" mass media, such as television, and "new" networked and individualized media, such as the Internet, are discussed, focusing on the transitions between different media technologies and the processes of substitution or supplementation occurring in these transitions.info:eu-repo/semantics/publishedVersio