Effect of local alloy disorder on the emission kinetics of deep donors (DX centers) in AlxGa1-xAs

In this paper we summarize our recent studies of the effects of local alloy disorder on the properties ofDX levels. A single emission rate is observed in GaAs where all Si-donors have identical local environments. In contrast, three discrete emission rates are observed in dilute AlGaAs alloys, suggesting that the group IV donor moves towards the interstitial site, thereby “selecting” three of the twelve surrounding group III atoms. We present evidence for an ordering of theDX levels consistent with Morgan’s model of a deepening potential well for theDX level as Al atoms are subsequently substituted for Ga atoms near the relaxed donor. These conclusions are consistent with earlier calculations of Chadi and Chang.     

Reconstruction of graphs based on random walks

The analysis of complex networks is of major interest in various fields of science. In many applications we face the challenge that the exact topology of a network is unknown but we are instead given information about distances within this network. The theoretical approaches to this problem have so far been focusing on the reconstruction of graphs from shortest path distance matrices. Often, however, movements in networks do not follow shortest paths but occur in a random fashion. In these cases an appropriate distance measure can be defined as the mean length of a random walk between two nodes — a quantity known as the mean first hitting time.In this contribution we investigate whether a graph can be reconstructed from its mean first hitting time matrix and put forward an algorithm for solving this problem. A heuristic method to reduce the computational effort is described and analyzed. In the case of trees we can even give an algorithm for reconstructing graphs from incomplete random walk distance matrices.     

Preliminary characterization and pathogenicity studies of a virus isolated from ticks (Ornithodoros coriaceus) and from tick-exposed cattle

Several viral isolates from ticks (Ornithodoros coriaceus) and from the blood of cattle which aborted after exposure to these ticks were found to be identical by reciprocal cross serum-neutralization tests. Characterization studies indicate that the virus is a member of the Togaviridae family, although specific identification is still incomplete. Whether its natural host is the tick or bovine animals is also unknown. Pregnant cows inoculated with the agent by all conventional parenteral routes, including intrafetal, delivered healthy calves at term. It was concluded, therefore, that it was not a bovine pathogen and that the abortions which occurred after tick-exposure were due to a 2nd agent in O coriaceus ticks which also harbor the virus. While several ciruses believed to be tick-borne have been isolated from cattle in various parts of the world, it is believed that the present report describes the first isolation in the Western Hemisphere for a viral agent from Argasid ticks which has been demonstrated to replicate in cattle.     

RHEED Intensity Oscillations for the Stoichiometric Growth of SrTiO3 Thin Films by Reactive Molecular Beam Epitaxy

The growth of high quality multicomponent oxide thin films by reactive molecular beam epitaxy (MBE) requires precise composition control. We report the use of in situ reflection high-energy electron diffraction (RHEED) for the stoichiometric deposition of SrTiO₃ (1 0 0) from independent strontium and titanium sources. By monitoring changes in the RHEED intensity oscillations as monolayer doses of strontium and titanium are sequentially deposited, the Sr:Ti ratio can be adjusted to within 1% of stoichiometry. Furthermore, the presence of a beat frequency in the intensity oscillation envelope allows the adjustment of the strontium and titanium fluxes so that a full monolayer of coverage is obtained with each shuttered dose of strontium or titanium. RHEED oscillations have also been employed to determine the doping concentration in barium- and lanthanum-doped SrTiO₃ films.     

Pornography and Sexist Attitudes Among Heterosexuals

Using a probability‐based sample of young Danish adults and a randomized experimental design, this study investigated effects of past pornography consumption, experimental exposure to nonviolent pornography, perceived realism of pornography, and personality (i.e., agreeableness) on sexist attitudes (i.e., attitudes toward women, hostile and benevolent sexism). Further, sexual arousal mediation was assessed. Results showed that, among men, an increased past pornography consumption was significantly associated with less egalitarian attitudes toward women and more hostile sexism. Further, lower agreeableness was found to significantly predict higher sexist attitudes. Significant effects of experimental exposure to pornography were found for hostile sexism among low in agreeableness participants and for benevolent sexism among women. These experimental exposure effects were found to be mediated by sexual arousal.     

A thermodynamic basis for evaluating environmental policy trade-offs

This paper introduces a novel thermodynamic measure of chemical change in the environment called pollution potential, which is defined as the change in exergy of mixing per mole of chemical species in the environment that may be attributed to pollutant releases – equivalent to the ideal exergy per mole required to remove a pollutant from the environment. Because all chemical pollutants may be measured in terms of pollution potential, the methodology described may provide a scientific basis for cross-comparison of disparate environmental impacts such as global warming potential (GWP) and ozone depletion potential (ODP) in a single measure. As an illustrative example, steady-state pollution potentials are calculated for several CFC replacements and a strong correlation between pollution potential and GWP is found for hydrofluorocarbons (HFCs). Although ozone depletion is found to be a significant factor in the pollution potential of CFC-11, for hydrochlorofluorocarbons (HCFCs) the contribution of ozone effects to total pollution potential is minimal. These findings suggest that policies that favor marginal reductions in ODP without regard for other environmental effects (e.g. climate change) may have unintended and detrimental consequences. Electronic Publication