Efficient optical frequency-comb generator.

We have demonstrated a method that efficiently transfers the power from a single-frequency laser into a wideband frequency comb. The comb was produced by a 2.7-GHz electro-optic modulator in a resonant optical cavity. A coupled cavity technique was used to transfer 8.5% of the laser power into a comb with a span of 400 modes, or more than 1 THz.

Hepatitis B control in Toronto classrooms for the mentally retarded: a seroprevalence survey.

A seroepidemiologic hepatitis B survey of students and staff at schools for the mentally retarded in the City of Toronto found 2.5% of students to be carriers, 5% to be immune without being immunized, 11.3% to have immunization underway or complete, and 81.2% to be susceptible. The first two groups were older and more likely to have been born in countries with intermediate or high hepatitis B marker prevalence. Among staff tested, 4.1% were immune without immunization while all others were susceptible. Because hepatitis B control recommendations could not be made on the basis of these results alone, local Medical Officers of Health also considered other studies and practical experience to recommend the following: (1) Use Ontario Ministry of Health Guidelines for mentally retarded hepatitis B carriers in regular schools; (2) Offer hepatitis B vaccine to all susceptible students and staff in schools specifically for the mentally retarded.