Laser-induced nucleation of carbon dioxide bubbles.

A detailed experimental study of laser-induced nucleation (LIN) of carbon dioxide (CO2) gas bubbles is presented. Water and aqueous sucrose solutions supersaturated with CO2 were exposed to single nanosecond pulses (5 ns, 532 nm, 2.4-14.5 MW cm(-2)) and femtosecond pulses (110 fs, 800 nm, 0.028-11 GW cm(-2)) of laser light. No bubbles were observed with the femtosecond pulses, even at high peak power densities (11 GW cm(-2)). For the nanosecond pulses, the number of bubbles produced per pulse showed a quadratic dependence on laser power, with a distinct power threshold below which no bubbles were observed. The number of bubbles observed increases linearly with sucrose concentration. It was found that filtering of solutions reduces the number of bubbles significantly. Although the femtosecond pulses have higher peak power densities than the nanosecond pulses, they have lower energy densities per pulse. A simple model for LIN of CO2 is presented, based on heating of nanoparticles to produce vapor bubbles that must expand to reach a critical bubble radius to continue growth. The results suggest that non-photochemical laser-induced nucleation of crystals could also be caused by heating of nanoparticles.

Recall rates and caries experience of patients undergoing general anesthesia for dental treatment.

PURPOSE: The purpose of this study was to evaluate the recall rate and caries experience of children seen under general anesthesia (GA) at The University of Iowa Hospitals and Clinics. METHODS: After a retrospective chart review, information from 217ASA (American Society of Anesthesiologists) 1 patients undergoing GA between 1998 and 2002 was gleaned regarding: (1) date of GA; (2) age at time of GA; (3) follow-up (recall) visits; (4) referral status; (5) new caries experience; and (6) treatment of new/recurrent lesions. A 19-question survey was also mailed to parents/legal guardians for satisfaction. RESULTS: Survey data were not reported in this study due to the poor (25%) return rate after several attempts: 41% of the patients were referrals; 54% returned for a 2 week postoperative visit, but only 13% returned for a 6-month recall, with subsequent recoils being even lower; 72% were insured by Medicaid; and 25% had recurrent or new lesions at follow-up appointments. CONCLUSION: Recall rates after general anesthesia for dental treatment at a university hospital are very low, and new or recurrent caries experience is high.