Evaluation of a photoacoustic detector for water vapor measurements under simulated tropospheric/lower stratospheric conditions.

Although water vapor is one of the most important and certainly the most variable minor constituent of the atmosphere, accurate measurements of p(H20) with high time resolution are difficult, particularly in the cold upper troposphere/lower stratosphere. This work demonstrates that a diode laser-based photoacoustic (PA) water vapor detector is a viable alternative to current water vapor sensors for airborne measurements. The PA system was compared with a high-quality frost point hygrometer (FPH) and with a Lyman-alpha hygrometer in the pressure range of 1000-100 hPa at frost point temperatures between 202 and 216 K. These conditions were simulated in a large environmental chamberfor 14 h. Simultaneous measurements with the three instruments agreed within 6%. Nitric acid vapor interferes with the FPH measurements at low frost point temperatures but does not affect the other instruments. The sensitivity of the PA system is already sufficient for measurements in the upper troposphere, and straightforward improvements can extend its useful range above the tropopause. Rugged construction, extreme simplicity, small size, and potential for long-term automatic operation make the PA system potentially suitable for airborne measurements.

Screening of pentachlorophenol-contaminated wood by thermodesorption sampling and photoacoustic detection.

The still-remaining high amounts of pentachlorophenol (PCP), used as wood preservative, in buildings and in waste wood are a potential risk for humans and the environment. To ensure a fast and selective measurement of PCP, a screening tool was developed, which is not only sensitive, but, unlike conventional methods, it requires no added chemicals, is simple, cost-effective, mobile, and capable of on-site operation. The instrument combines light-induced thermodesorption sampling followed by an external cavity diode laser based photoacoustic detector. Measurements on wood samples proved that the system can determine PCP to as low as a concentration of 10 microg/cm2 within minutes without destruction of the sample. The system was calibrated with reference to the concentration of PCP impregnated on the wood surface. It is demonstrated that measurements are not influenced by moisture content of the wood samples.

Digital communication with fetal monitors.

BACKGROUND: Fetal heart rate (FHR) values in the averaged format that are provided by commercial computed cardiotocography analysis systems may be unsuitable for special analysis purposes. METHOD: I developed a communication software program to obtain any measured values of fetal monitors for individual analysis of computed cardiotocography. EXPERIENCE: The software program was used to study the data continuity of beat-to-beat FHR values as an experiment for chaos theory and power spectrum analysis. The results indicated that the signal loss was recognized at a precision of 95%. CONCLUSION: The described method of digital communication with fetal monitors was found to be useful for individual purposes in the field of computed cardiotocography analysis.

Chaos theory and power spectrum analysis in computerized cardiotocography.

Power spectrum and chaos theory analysis, methods recently applied to fetal surveillance, may offer an effective tool for recognising fetal hypoxia and consequential collapse of fetal homeostasis earlier than at present. However, strict continuity and high precision of input data is an indispensable prerequisite. If one overlooks this requirement the results may be misleading. The aim of the present work was to find a method that provides strictly continuous and highly precise beat-to-beat FHR data values. It was found that only the determination of heart beat intervals between successive R peaks, using the digital FECG recording technique developed here, meets the necessary requirements for power spectrum and chaos theory analysis.

Pulsed-laser excitation of acoustic modes in open high-Q photoacoustic resonators for trace gas monitoring: results for C(2)H(4).

The pulsed excitation of acoustic resonances was studied with a continuously monitoring photoacoustic detector system. Acoustic waves were generated in C(2)H(4)/N(2) gas mixtures by light absorption of the pulses from a transversely excited atmospheric CO(2) laser. The photoacoustic part consisted of high-Q cylindrical resonators (Q factor 820 for the first radial mode in N(2)) and two adjoining variable acoustic filter systems. The time-resolved signal was Fourier transformed to a frequency spectrum of high resolution. For the first radial mode a Lorentzian profile was fitted to the measured data. The outside noise suppression and the signal-to-noise ratio were investigated in a normal laboratory environment in the flow-through mode. The acoustic and electric filter system combined with the averaging of the photoacoustic signal in the time domain suppressed the outside noise by a factor of 4500 (73 dB). The detection limit for trace gas analysis of ethylene in pure N(2) was 2.0 parts in 10(9) by volume (ppbV) (minimal absorption coefficient α(min) = 6.1 × 10(-8) cm(-1), pulse energy 20 mJ, 1-bar N(2)), and in environmental air, in which the absorption of other gas components produces a high background signal, we can detect C(2)H(4) to ~180 ppbV. In addition, an alternative experimental technique, in which the maximum signal of the second azimuthal mode was monitored, was tested. To synchronize the sampling rate at the resonance frequency, a resonance tracking system was applied. The detection limit for ethylene measurements was α(min) = 9.1 × 10(-8) cm(-1) for this system.

No evidence of the existence of beta adrenoceptors in human sperm using radioligand binding technique.

The investigations were carried out on 20 freshly ejaculated and pooled samples of human semen with normozoospermia and motility of 70-80%. In the present study no difference was found between total and non-specific binding to semen membranes using [3H]-dihydroalprenolol (DHA) as a radioligand. Our results suggest that beta adrenoceptors could not be found in human sperm.