SUMMARYTo evaluate the prevalence of antibody against hepatitis A in two socioecono¬ mically distinct populations of a developing country, 540 serum specimens from children and adults living in São Paulo, Brazil, were tested for IgG antiHAV by a commercial radioimunoassay (Havab, Abbott Laboratories). The prevalence of anti-HAV in low socioeconomic level subjects was 75.0% in children 2-11 years old and 100.0% in adults, whereas in middle socioeconomic level significantly lower prevalences were observed (40.3% in chidren 2-11 years old and 91.9% in adults). Voluntary blood donors of middle socioeconomic level showed a prevalence of 90.4%. These data suggest that hepatitis A infection remains a highly endemic disease in São Paulo, Brazil.

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This paper presents the project and implementation results of a digital PM demodulator system for processing LEO satellite signals from Brazilian Data Collecting System. The demodulator was implemented on the Altera Cyclone II DSP Development Kit equipped with FPGA EP2C70. Demodulation is done with a second order Digital Phase Locked Loop (DPLL) with -π to π linear phase detector realized by a CORDIC algorithm operating on vectoring mode. The parameters of the DPLL were calculated using control system theory.

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Summary The Brazilian Environmental Data Collection System (SBCDA) is an asynchronous multiuser message forwarding system based on low earth orbit (LEO) satellites with applications restricted to environmental monitoring and human life protection. This work presents a multiuser SBCDA decoder with low data memory and computational load. The decoder uses spectrum analysis to detect signal presences and upon every signal detection starts a signal decoding process with single‐user bit detection. Simulations considering an Additive White Gaussian Noise (AWGN) scenario with signal's time‐frequency positions uniformly and independently distributed and signal's powers uniformly distributed in dB within a dynamic range of 24 dB are present for different densities of user signals. Those show a frame error rate (FER) of approximately 25% for an average of six coexisting signals at every time instant, in which a missed signal was considered as a frame error. Finally, there are considerations on how to improve the performance maintaining a single‐input and single‐user bit detection strategy.

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