Frequency comb metrology with an optical parametric oscillator

We report on the first demonstration of absolute frequency comb metrology with an optical parametric oscillator (OPO) frequency comb. The synchronously-pumped OPO operated in the 1.5-μm spectral region and was referenced to an H-maser atomic clock. Using different techniques, we thoroughly characterized the frequency noise power spectral density (PSD) of the repetition rate frep, of the carrier-envelope offset frequency fCEO, and of an optical comb line νN. The comb mode optical linewidth at 1557 nm was determined to be ~70 kHz for an observation time of 1 s from the measured frequency noise PSD, and was limited by the stability of the microwave frequency standard available for the stabilization of the comb repetition rate. We achieved a tight lock of the carrier envelope offset frequency with only ~300 mrad residual integrated phase noise, which makes its contribution to the optical linewidth negligible. The OPO comb was used to measure the absolute optical frequency of a near-infrared laser whose second-harmonic component was locked to the F = 2→3 transition of the 87Rb D2 line at 780 nm, leading to a measured transition frequency of νRb = 384,228,115,346 ± 16 kHz. We performed the same measurement with a commercial fiber-laser comb operating in the 1.5-μm region. Both the OPO comb and the commercial fiber comb achieved similar performance. The measurement accuracy was limited by interferometric noise in the fibered setup of the Rb-stabilized laser

Acid inhibition on the first day of dosing: comparison of four proton pump inhibitors

BACKGROUND: Rapid and consistent acid suppression on the first day of dosing may be important in treating acid-related disorders. AIM: To compare the antisecretory activity and onset of action of single doses of rabeprazole, lansoprazole, pantoprazole, omeprazole capsule, omeprazole multiple unit pellet system (MUPS) tablet and placebo in healthy Helicobacter pylori-negative subjects. METHODS: This cross-over, double-blind, randomized study was performed in 18 H. pylori-negative subjects. Twenty-four-hour intragastric pH monitoring was performed on the day of treatment (once-daily dose of rabeprazole 20 mg, lansoprazole 30 mg, pantoprazole 40 mg, omeprazole capsule 20 mg, omeprazole MUPS tablet 20 mg or placebo). RESULTS: The intragastric pH (3.4) and time at pH > 4 during the 24 h post-dose (8.0 h) were significantly greater with rabeprazole than with lansoprazole, pantoprazole, omeprazole capsule, omeprazole MUPS tablet or placebo (P <or= 0.04 for rabeprazole vs. the others). Daytime and night-time pH values were higher with rabeprazole and lansoprazole than with pantoprazole, omeprazole capsule and omeprazole MUPS tablet (P </= 0.04). CONCLUSION: Rabeprazole was the most potent acid inhibitor of all the proton pump inhibitors tested during the first day of dosing

Antibiotic prophylaxis of infective endocarditis during digestive endoscopy: over- and underuse in Switzerland despite professed adherence to guidelines

BACKGROUND AND STUDY AIMS: Guidelines for antibiotic prophylaxis of infective endocarditis associated with gastrointestinal endoscopy are not uniform. Though based on weak scientific evidence, they do represent an attempt to unify the management of antibiotic prophylaxis. We investigated whether physicians who profess to adhere to these guidelines actually do apply them correctly. MATERIALS AND METHODS: A questionnaire was sent to all 195 Swiss gastroenterologists asking whether they adhered to antibiotic prophylaxis guidelines and under what conditions did they apply antibiotic prophylaxis in gastrointestinal endoscopy. We analysed whether the Swiss gastroenterologists who claim to adhere to these guidelines actually do so in practice. RESULTS: The response rate to our questionnaire was 95%. Of the Swiss gastroenterologists, 60% correctly employ antibiotic prophylaxis guidelines in gastroscopy, as do 47% in colonoscopy. In therapeutic endoscopy, the percentage of correct antibiotic prophylaxis use depends upon the type of intervention and varies between 21 and 58%. Overuse of antibiotic prophylaxis is at least twice as frequent in colonoscopy and therapeutic endoscopy than in gastroscopy. CONCLUSIONS: Guidelines for antibiotic prophylaxis are not well applied and do not lead to uniform management despite a high degree of professed adherence to them. This phenomenon can be explained by "cognitive dissonance" and "reactance." We conclude that guidelines based on unconvincing data may even prove harmful