RESUMO
High-quality amorphous Silicon Nitride (a-Si(1-x)N(x):H) Fabry-Pérot microcavities can show resonant surface Second Harmonic Generation (SHG) effect. We consider two different layouts of planar microcavities with almost identical linear reflectance and show how the structure geometry can strongly affect SHG yield. In particular, a difference of more than one order of magnitude in the SHG intensity is observed when the fundamental beam is tuned at the cavity resonance frequency. We explain this finding on the basis of a theoretical model taking into account the spatial distribution of the electric fields of the pump and harmonic frequencies inside the structure. A satisfactory matching of experimental data with the theoretical model is obtained by considering the source of second-order nonlinearity as limited to surface contributions.
RESUMO
A cross-sectional study on knowledge, attitude and practice on high risk factors for human immunodeficiency virus (HIV) infection and acquired immunodeficiency syndrome (AIDS) was carried out among rural males of Dembia district, north Gonder Administrative Zone in January 1993. A random sample of 89(92.8%) males were interviewed by six senior medical students. A total of 66(74.2%) people reported to have heard something about AIDS. Eighty (89.9%) males did not know anything about condoms. The most common sources of information on AIDS were close friends, health workers, school teachers and the radio. Favourable attitude was observed. Fifty-four (60.7%) were afraid of getting AIDS; 7.5% had practised extramarital sex in the past three months. Higher knowledge was not associated with high risk behaviour (p > 0.05). Higher knowledge and favourable attitude were strongly correlated, (r = 0.83, 95% CI = 0.76-0.89). Strengthening risk perception, condom promotion and larger or detailed studies were recommended.