RESUMO
In this work we demonstrate by photoluminescence studies white light emission from a monolithic InGaN/GaN single quantum well structure grown by metal organic chemical vapour deposition. As-grown and thermally annealed samples at high temperature (1000 °C, 1100 °C and 1200 °C) and high pressure (1.1 GPa) were analysed by spectroscopic techniques, and the annealing effect on the photoluminescence is deeply explored. Under laser excitation of 3.8 eV at room temperature, the as-grown structure exhibits two main emission bands: a yellow band peaked at 2.14 eV and a blue band peaked at 2.8 eV resulting in white light perception. Interestingly, the stability of the white light is preserved after annealing at the lowest temperature (1000 °C), but suppressed for higher temperatures due to a deterioration of the blue quantum well emission. Moreover, the control of the yellow/blue bands intensity ratio, responsible for the white colour coordinate temperatures, could be achieved after annealing at 1000 °C. The room temperature white emission is studied as a function of incident power density, and the correlated colour temperature values are found to be in the warm white range: 3260-4000 K.
RESUMO
AIM: To identify risk factors for cariogenic feeding practices in the first year of life. STUDY DESIGN: Cohort study. METHODS: 500 children born within the public health care system in São Leopoldo, Brazil, were recruited in a follow-up program. Anthropometric and demographic data were collected soon after birth; data on feeding practices were assessed at 12 months of age using a standardised questionnaire; clinical examination at 4 years of age allowed identification of cariogenic feeding practices in the first year of life and to quantify their relative risks. In the present study, the attributable risks of each child were summed, and the outcome was assessed for the upper quartile of scores for cariogenic feeding practices. STATISTICS: Adjusted relative risks for the outcome were estimated using robust Poisson regression models. RESULTS: A total of 327 children comprised the final study sample, i.e. were followed from birth to 4 years of age. Multivariate analysis showed that the risk of cariogenic feeding practices doubled in children from mothers with less than 5 years of education (RR 2.19, 95%CI 1.26-3.82) and was 70% higher in children from mothers with 5-8 years of education when compared with maternal education >8 years. The other independent variables were not associated with the outcome. CONCLUSIONS: Low maternal education is a risk factor for cariogenic feeding practices, independently of other factors. Mothers with low educational levels should be the focus of child health promotion interventions, especially those aimed at controlling dental caries.