Applications of Kalman filtering to real-time trace gas concentration measurements.

A Kalman filtering technique is applied to the simultaneous detection of NH3 and CO2 with a diode-laser-based sensor operating at 1.53 micrometers. This technique is developed for improving the sensitivity and precision of trace gas concentration levels based on direct overtone laser absorption spectroscopy in the presence of various sensor noise sources. Filter performance is demonstrated to be adaptive to real-time noise and data statistics. Additionally, filter operation is successfully performed with dynamic ranges differing by three orders of magnitude. Details of Kalman filter theory applied to the acquired spectroscopic data are discussed. The effectiveness of this technique is evaluated by performing NH3 and CO2 concentration measurements and utilizing it to monitor varying ammonia and carbon dioxide levels in a bioreactor for water reprocessing, located at the NASA-Johnson Space Center. Results indicate a sensitivity enhancement of six times, in terms of improved minimum detectable absorption by the gas sensor.

Ammonia Detection by use of Near-Infrared Diode-Laser-Based Overtone Spectroscopy.

We describe a portable diode-laser-based sensor for NH(3) detection using vibrational overtone absorption spectroscopy at 1.53 mum. Use of fiber-coupled optical elements makes such a trace gas sensor rugged and easy to align. On-line data acquisition and processing requiring <30 s can be performed with a laptop PC running LabVIEW software. The gas sensor was used primarily for NH(3) concentration measurements with a sensitivity of 0.7 parts per million (signal-to-noise ratio of 3) over a two-week period in a bioreactor being developed at the NASA Johnson Space Center for water treatment technologies to support long-duration space missions. The feasibility of simultaneous, real-time measurements of NH(3) and CO(2) concentrations is also reported.

Ambient formaldehyde detection with a laser spectrometer based on difference-frequency generation in PPLN.

A laser spectrometer based on difference-frequency generation in periodically poled LiNbO3 (PPLN) has been used to quantify atmospheric formaldehyde with a detection limit of 0.32 parts per billion in a given volume (ppbV) using specifically developed data-processing techniques. With state-of-the-art fiber-coupled diode-laser pump sources at 1083 nm and 1561 nm, difference-frequency radiation has been generated in the 3.53-micrometers (2832-cm-1) spectral region. Formaldehyde in ambient air in the 1- to 10-ppb V range has been detected continuously for nine and five days at two separate field sites in the Greater Houston area operated by the Texas Natural Resource Conservation Commission (TNRCC) and the Houston Regional Monitoring Corporation (HRM). The acquired spectroscopic data are compared with results obtained by a well-established wet-chemical o-(2,3,4,5,6-pentafluorobenzyl) hydroxylamine (PFBHA) technique.

Field intercomparison of a novel optical sensor for formaldehyde quantification.

A one-week in situ intercomparison campaign was completed on the Rice University campus for measuring HCHO using three different techniques, including a novel optical sensor based on difference frequency generation (DFG) operating at room temperature. Two chemical derivatization methods, 2,4-dinitrophenylhydrazine (DNPH) and o-(2,3,4,5,6-pentafluorobenzyl) hydroxylamine (PFBHA), were deployed during the daylight hours for three- to four-hour time-integrated samples. A real-time optical sensor based on laser absorption spectroscopy was operated simultaneously, including nighttime hours. This tunable spectroscopic source based on difference frequency mixing of two fiber-amplified diode lasers in periodically poled LiNb03 (PPLN) was operated at 3.5315 micrometers (2831.64 cm 1) to access a strong HCHO ro-vibrational transition free of interferences from other species. The results showed a bias of -1.7 and -1.2 ppbv and a gross error of 2.6 and 1.5 ppbv for DNPH and PFBHA measurements, respectively, compared with DFG measurements. These results validate the DFG sensor for time-resolved measurements of HCHO in urban areas.

Bromocriptine compared to long-acting estrogens in lactation prevention: clinical efficacy, prolactin secretion and coagulation parameters.

Sixty-eight mothers who did not want to breast-feed their babies were submitted to one of the following regimes: an intramuscular injection of estrogen (25 mg) within 1 h after delivery (n = 24) or the administration of bromocriptine for 15 or 23 days (n = 21 and 23, respectively). A careful clinical evaluation was performed every day by the same examiner during the first 7 days postpartum; blood samples were collected on days 0, 3 and 5 for human prolactin (hPRL) and estradiol, also in some cases on day 17; assays were measured by radioimmunoassay. An evaluation of the coagulation parameters was performed on day 5 in 9 estrogen-treated patients and in 25 bromocriptine-treated patients. Only 5 (11%) out of the 44 patients treated with bromocriptine experienced at least one undesirable effect of breast engorgement, in contrast to 16 (67%) out of the 24 estrogen-treated patients; this difference was statistically highly significant (P less than 0.001). Dizziness was a significant side-effect of bromocriptine treatment, occurring in 20% of the cases. In the patients in whom the administration of bromocriptine was withdrawn after 15 days, a significant mean rebound elevation of hPRL levels above the normal range occurred on the 17th day. The latter observation gives some support to earlier proposals to continue bromocriptine for up to a total 3 wk in order to avoid rebound lactation. There was no significant alteration of fibrinogen, Howell time, activated partial thromblastin time (APTT), prothrombin time (PT), thrombin time and coagulation time; mean plasminogen levels were comparable in both treated groups, while mean antithrombin III levels were increased in the bromocriptine-treated group. The significance of the latter finding requires further evaluation.