Blue light-emitting diodes (LED's), utilizing InGaN-based multi-quantum well (MQW) active regions deposited by organometallic chemical vapor epitaxy (OMVPE), are one of the fundamental building-blocks for current solid-state lighting applications. Studies [1,2] have previously been conducted to explore the optical and physical properties of the active MQW's over a variety of different OMVPE growth conditions. However, the conclusions of these papers have often been contradictory, possibly due to a limited data set or lack of understanding of the fundamental fluid dynamics and gas-phase chemistry that occurs during the deposition process.

Multi-quantum well structures grown over a range of pressures from typical low-pressure production processes at 200 Torr, up to near-atmospheric growth conditions at 700 Torr, have been investigated in this study. At all growth pressures, clear trends of gas-phase chemical reactions are observed for increased gas residence times (lower gas speeds from the injector flange and lower rotation rates) and increased V/III ratios (higher NH3 flows).

Confocal microscopy, excitation-dependent PL (PLE), and time-resolved photo-luminescence (TRPL) have been employed on these MQW structures to investigate the carrier lifetime characteristics. Confocal emission images show spatially-separated bright and dark regions. The bright regions are red-shifted in wavelength relative to the dark regions, suggesting microscopic spatial localization of high indium content regions. As the growth pressure and gas residence times are reduced, a larger difference in band-gap between bright and dark regions, longer lifetimes, and higher average PL intensities can be obtained, indicating that higher optical quality material can be realized. Optimized MQW's grown at high pressure exhibit higher PLE slope intensities and IQE characteristics than lower pressure samples. Results on simple LED structures indicate that the improvement in MQW optical quality at high pressures translates to higher output power at a 110 A/cm2 injection current density.

Background: While smoking rates in the United States have decreased, some population subgroups have smoking rates that exceed national and state averages. These higher rates often are associated with higher incidence rates of tobacco-associated cancers. Over time, a decrease in smoking rates leads to lower cancer incidence. Methods: Using spatial modelling techniques, we identified an underserved geographic locale in South Florida with higher than expected incidence rates of tobacco-associated cancers. We then used a community-based participatory research (CBPR) design to conduct focus groups in 2011 to elicit information about the acceptability of a smoking cessation intervention delivered by trained former smokers from within peer networks. Results: A variety of smoking cessation strategies was presented and discussed in separate, gender-stratified focus groups comprised of former and current smokers (n = 39). Focus group findings consistently indicated that support groups were the preferred cessation mechanism in this community. Based on this finding, we changed our initially proposed cessation approach to one which employed support groups as a quit method. Conclusions: Currently, we are collecting pilot data to test this intervention and to reach smokers who might not otherwise be directly targeted with cessation messaging from larger tobacco control initiatives. If successful, this strategy can be adapted to effect other important changes in health behaviours in at-risk populations.

Special interest has recently attached to formulations of Boolean algebra in terms of ring operations [7], [1]. These axiomatizations have not been as brief as those reached through other modes of approach.

The present note will show that the number of axioms when ring operations are used may be as small as in any present version that is not metamathematical,that is, the number of axioms finally employed will be two.

The Unity of Science movement is directed primarily toward the further advancement of science, but a second phase is entered when the assessment of its significance for various aspects of civilization is undertaken. In this second phase would fall investigations of the utility of its resources in relation to educational problems.