A community-based cross-sectional study among 554 Kolkata city street children assessed nontobacco substance use and sexual abuses along with human immunodeficiency virus (HIV)/ sexually transmitted infections (STIs) during 2007, using conventional cluster sampling technique for "hard-to-reach population" with a field-tested questionnaire and the collection of a blood sample for HIV and syphilis serology testing as a composite indicator of STIs. The reported prevalence of nontobacco substance use was 30%; 9% reported having been sexually abused. Some factors (age, lack of contact with family, orphan children, night stay at public place, etc.) were documented to be associated with substance use and sexual abuses. Seroprevalence of HIV was found to be 1% and that of STIs was 4%. This 1% HIV seroprevalence in street children is a matter of concern. Community-based intervention is necessary for them. The study's limitations are noted.

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Any nonuniformity in the flatness of a crystal element used in an ultrasonic transducer may lead to significant variations in transducer response. An accurate estimation of such variations could obviously be a measure of the nonuniformity involved, whatever its extent may be. Studies are reported on the effect of nonparallelism between two major plane surfaces of the crystal element on transducer response by studying the normal displacement amplitude pattern and its distribution over one of the vibrating ͑plane͒ surfaces at resonance. Measurements are carried out in air using a phase-locked laser interferometry technique where the effect of tapering in disk thickness on the transducer performance is manifested through the variation in vibrational patterns. Results of these measurements are compared with those obtained from electrical ͑conductance͒ response to highlight the importance of the former. Other comparison measurements, such as the conventional method of determination of acoustic response and pulse waveforms of the radiated signals in water, are also reported as a function of tapering in disk thickness. A correlation is discussed between results obtained from different measurements.

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