Threshold Behavior Of (gaal)as-gaas Lasers At Low Temperatures

The temperature dependence of the threshold current, differential quantum efficiency, and internal loss have been measured in the temperature range 10-293°K. The threshold current increases relatively slowly with temperature above 100°K and is independent of the impurity concentration. Theoretical calculation shows that this behavior is to be expected for a band-to-band transition that follows k selection. The threshold behavior at low temperatures (≤ 80°K) depends strongly on the type and concentration of the impurity. The relatively fast decrease in threshold below 100°K shows saturation for an active layer with n-type impurities or with high-concentration p-type impurities. The saturation is attributed to the carrier diffusion length becoming smaller than the active-layer thickness. The internal differential quantum efficiency is near unity and is independent of temperature. The internal loss, however, decreases with temperature due to reduction in free-carrier absorption.491293

Distribution of Major Health Risks: Findings from the Global Burden of Disease Study

BACKGROUND: Most analyses of risks to health focus on the total burden of their aggregate effects. The distribution of risk-factor-attributable disease burden, for example by age or exposure level, can inform the selection and targeting of specific interventions and programs, and increase cost-effectiveness. METHODS AND FINDINGS: For 26 selected risk factors, expert working groups conducted comprehensive reviews of data on risk-factor exposure and hazard for 14 epidemiological subregions of the world, by age and sex. Age-sex-subregion-population attributable fractions were estimated and applied to the mortality and burden of disease estimates from the World Health Organization Global Burden of Disease database. Where possible, exposure levels were assessed as continuous measures, or as multiple categories. The proportion of risk-factor-attributable burden in different population subgroups, defined by age, sex, and exposure level, was estimated. For major cardiovascular risk factors (blood pressure, cholesterol, tobacco use, fruit and vegetable intake, body mass index, and physical inactivity) 43%–61% of attributable disease burden occurred between the ages of 15 and 59 y, and 87% of alcohol-attributable burden occurred in this age group. Most of the disease burden for continuous risks occurred in those with only moderately raised levels, not among those with levels above commonly used cut-points, such as those with hypertension or obesity. Of all disease burden attributable to being underweight during childhood, 55% occurred among children 1–3 standard deviations below the reference population median, and the remainder occurred among severely malnourished children, who were three or more standard deviations below median. CONCLUSIONS: Many major global risks are widely spread in a population, rather than restricted to a minority. Population-based strategies that seek to shift the whole distribution of risk factors often have the potential to produce substantial reductions in disease burden

Um pouco de história, desenvolvimentos recentes e perspectivas para a pesquisa em atividade física e saúde no Brasil A short history, recent developments, and perspectives for research in physical activity and health in Brazil

As grandes transformações mundiais das últimas décadas provocaram mudanças sociais e na saúde, individual e coletiva, jamais imaginadas. O perfil dos problemas de saúde atuais faz com que a promoção de estilos de vida saudáveis (e ativos fisicamente) seja valorizada e colocada como uma das prioridades em saúde pública no planeta. A Educação Física Brasileira está atenta a essas evoluções nas ciências e nas práticas que envolvem a atividade física relacionada à saúde, e precisa responder aos anseios da sociedade em termos de formação profissional competente e produção científica de qualidade nesta área. Este artigo discute desenvolvimentos recentes e perspectivas na pesquisa em atividade física e saúde, com repercussões para a Educação Física no Brasil.<br>The tremendous modifications observed in the world during the past few decades caused unthinkable changes in social and health (both individual and collective). Current health problems turned lifestyle characteristics as public health matter all over the world, specially the promotion of healthy (and active lifestyles). The area of Physical Education in Brazil is aware of that global movement related to the promotion of health enhancing physical activity, and needs to respond to the society's needs in terms of professional preparation, and quality research in this area. This paper discusses recent developments and perspectives for physical activity and health research, and it's consequences for Physical Education in Brazil