QEPAS based ppb-level detection of CO and N2O using a high power CW DFB-QCL

An ultra-sensitive and selective quartz-enhanced photoacoustic spectroscopy (QEPAS) sensor platform was demonstrated for detection of carbon monoxide (CO) and nitrous oxide (N2O). This sensor used a stateof- the art 4.61 μm high power, continuous wave (CW), distributed feedback quantum cascade laser (DFB-QCL) operating at 10°C as the excitation source. For the R(6) CO absorption line, located at 2169.2 cm−1, a minimum detection limit (MDL) of 1.5 parts per billion by volume (ppbv) at atmospheric pressure was achieved with a 1 sec acquisition time and the addition of 2.6% water vapor concentration in the analyzed gas mixture. For the N2O detection, a MDL of 23 ppbv was obtained at an optimum gas pressure of 100 Torr and with the same water vapor content of 2.6%. In both cases the presence of water vapor increases the detected CO and N2O QEPAS signal levels as a result of enhancing the vibrational-translational relaxation rate of both target gases. Allan deviation analyses were performed to investigate the long term performance of the CO and N2O QEPAS sensor systems. For the optimum data acquisition time of 500 sec a MDL of 340 pptv and 4 ppbv was obtained for CO and N2O detection, respectively. To demonstrate reliable and robust operation of the QEPAS sensor a continuous monitoring of atmospheric CO and N2O concentration levels for a period of 5 hours were performed

INVESTIGATION Physiological and lifestyle factors contributing to risk and severity of peri-orbital dark circles in the Brazilian population*

Abstract: BACKGROUND: Peri-orbital dark circles are a cosmetic concern worldwide, and have been attributed to hyperpigmentation from allergy or atopic dermatitis, blood stasis, structural shadowing effects, and a thin epidermis/dermis under the eye. It is of interest to better understand lifestyle and demographic risk factors and the relative impact of melanin, blood and epidermal/dermal factors on the severity of Peri-orbital dark circles. OBJECTIVE: To compare by non-invasive imaging the impact of biological factors to a visual grading scale for Peri-orbital dark circles, and test the correlation of various demographic factors with Peri-orbital dark circles. METHODS: Subjects completed a lifestyle and health survey, and Peri-orbital dark circles severity was evaluated using standardized photographs. Hyperspectral image analysis was used to assess the contributions of melanin, blood volume, degree of blood oxygen saturation, and dermal scattering. RESULTS: Family history was the most signifi cant risk factor for Peri-orbital dark circles. The average age of onset was 24 years, and earlier onset correlated with higher severity scores. Asthma was signifi cantly associated with Peri-orbital dark circles scores, but self-reported allergy was not. In this study, sleep was not correlated with Peri-orbital dark circles scores. Hyperspectral imaging indicated that melanin was the dominant correlate for Peri-orbital dark circles severity, while oxygen saturation was secondary. The difference between under-eye and cheek measurements for ∆L*and ∆E* were the most signifi cant instrumental parameters correlated with visual assessment of Peri-orbital dark circles severity. CONCLUSION: Although typically associated with lack of sleep, risk of Peri-orbital dark circles is primarily hereditary. The main factors contributing to the appearance of Peri-orbital dark circles are melanin and (deoxygenated) blood

A mid-infrared laser absorption sensor for carbon monoxide and temperature measurements

May 2010School of EngineeringPh

A Shock Tube Study of the Ignition of n-Heptane, n-Decane, n-Dodecane, and n-Tetradecane at Elevated Pressures

The ignition of n-heptane, n-decane, n-dodecane, and n-tetradecane has been investigated in a heated shock tube. n-Alkane/air mixtures at Φ = 0.25, 0.5, and 1.0 were studied in reflected shock experiments at 9−58 atm and 786−1396 K. Ignition times were measured using a combination of endwall electronically excited OH emission and sidewall pressure measurements. The measured ignition times are compared to previous data, where available, with good agreement and to several kinetic modeling predictions. The current data and the combination of the current data with previous shock tube and rapid compression machine measurements show that any differences in reactivity for C₇ and larger n-alkanes is slight, within the experimental uncertainties, for n-alkane/air mixtures with common carbon content at a large range of temperatures (650−1400 K) and elevated pressures. To our knowledge, the n-tetradecane measurements presented here are the first ignition measurements to be reported for this compound. The complete data set greatly extends the kinetic modeling targets available for large n-alkanes at elevated-pressure conditions relevant to practical combustion devices