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Copyright of Canadian Journal of Physics is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Journal of Physics is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Abstract. Tunable diode laser absorption spectroscopy has been employed by our group at the National Center tot Atmospheric Research to study a number of important trace atmospheric gases and processes over the past 10 years. This paper presents an overview of these studies along with details on instrument hardware and software features implemented for high sensitivity. The merits of four different approaches in assessing instrument performance are presented with formaldehyde (CH[sub 2]O) used as the target gas. One method utilizes the Allan variance. When our present aircraft system is operated in the laboratory, the Allan variance indicates a CH[sub 2]O detection limit of 0.031 ppbv for integration times of 25 s. This sensitivity corresponds to a minimum detectable absorbance of 1.0 x 10[sup -6], and this is within a factor of two of that reported by Werle et al. who used high-frequency modulation spectroscopy. The present instrument utilizes conventional low-frequency (2f = 100 kHz) wavelength modulation. Instrument performance, obtained from replicate measurements of CH[sub 2]O standards acquired over time periods as long as 1.5 hours, on average resulted in a factor of two poorer precision than indicated by the Allan variance. Since replicate measurements precisely simulate the acquisition procedures... [ABSTRACT FROM AUTHOR]

Presents letter from readers of the periodical 'British Dental Journal' concerning dentistry in Great Britain. Prescription of fluoride mouthwash; Protection from needle stick injury; Community dental care.

Using a difference frequency spectrometer we have measured the Q(2) to Q(38) 20[sup 0]0←01[sup 1]0,Σ←Π transitions of carbon dioxide at 296 K and pressures up to 15 kPa. These low pressure spectra were analyzed using both the Voigt model, and an empirical line shape that blends together a hard collision model and a speed dependent Lorentzian profile. The broadening coefficients were obtained with an accuracy of 1% or better. The low density or first order low pressure line mixing parameters were also determined. We have compared both our measured low pressure line-mixing parameters and the complete band spectrum at high pressures with those predicted by a relaxation matrix calculated from an EPG fitting law. Spectra at the highest pressures were recorded using both the difference frequency spectrometer and an FTIR spectrometer, the temperature for the latter experiments being 303 K. The vibrational band intensity and linear pressure shift of the branch as a whole were also measured. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]