Thermodynamics of solutions in liquid methane

Imperial Users onl

Formaldehyde sensor using non-dispersive UV spectroscopy at 340nm

Formaldehyde is a volatile organic compound that exists as a gas at room temperature. It is hazardous to human health causing irritation of the eyes, nose and throat, headaches, limited pulmonary function and is a potential human carcinogen. Sources include incomplete combustion, numerous modern building materials and vehicle fumes. Here we describe a simple method for detecting formaldehyde using low resolution non-dispersive UV absorption spectroscopy for the first time. A two channel system has been developed, making use of a strong absorption peak at 339nm and a neighbouring region of negligible absorption at 336nm as a reference. Using a modulated UV LED as a light source and narrowband filters to select the desired spectral bands, a simple detection system was constructed that was specifically targeted at formaldehyde. A minimum detectable absorbance of 4.5 × 10-5 AU was estimated (as ΔI/I0), corresponding to a limit of detection of approximately 6.6 ppm for a 195mm gas cell, with a response time of 20s. However, thermally-induced drift in the LED spectral output caused this to deteriorate over longer time periods to around 30 ppm or 2 × 10-4 A

Noise analysis for CCD-based ultraviolet and visible spectrophotometry

Full-text not yet available due to publisher embargo.We present the results of a detailed analysis of the noise behavior of two CCD spectrometers in common use, an AvaSpec-3648 CCD UV spectrometer and an Ocean Optics S2000 Vis spectrometer. Light sources used include a deuterium UV/Vis lamp and UV and visible LEDs. Common noise phenomena include source fluctuation noise, photoresponse nonuniformity, dark current noise, fixed pattern noise, and read noise. These were identified and characterized by varying light source, spectrometer settings, or temperature. A number of noise-limiting techniques are proposed, demonstrating a best-case spectroscopic noise equivalent absorbance of 3.5×10−4  AU for the AvaSpec-3648 and 5.6×10−4  AU for the Ocean Optics S2000 over a 30 s integration period. These techniques can be used on other CCD spectrometers to optimize performance

A measurement strategy for non-dispersive ultra-violet detection of formaldehyde in indoor air: Spectral analysis and interferent gases

We have conducted an extensive review of published spectra in order to identify a region with potential for detection of formaldehyde in indoor air. 85 chemicals and chemical groups common to the indoor environment were identified, 32 of which had absorption spectra in the UV-vis region. Of these, 11 were found to overlap with the formaldehyde UV region. It was found that the region between 320 to 360 nm is relatively free from interference from indoor gases, with NO being the only major interferent. A method is proposed for a low resolution (3 nm) spectroscopic detection method, specifically targeted at formaldehyde absorption features at 327 nm with a reference at 334 nm. 32 ppb of NO was found to have a cross-sensitivity with equivalent magnitude to 100 ppb of formaldehyde. A second reference at 348 nm would reduce this cross-sensitivity.This work was funded by the Engineering and Physics Science Research Council (EPSRC) under grants GR/T18424, EP/P504880 and EP/H02252X. Enquiries for access to the data referred to in this article should be directed to [email protected]

Crying a river: how much salt-laden jelly can a leatherback turtle really eat?

Leatherback turtles (Dermochelys coriacea) are capital breeders that accumulate blubber (33 kJ g−1 wet mass) by hyperphagia on a gelatinous diet at high latitudes; they breed in the tropics. A jellyfish diet is energy poor (0.1–0.2 kJ g−1 wet mass) so leatherbacks must ingest large quantities. Two published estimates of feeding rate [50% body mass day−1 (on Rhizostoma pulmo) and 73% body mass day−1 (on Cyanea capillata)] have been criticised as too high. Jellyfish have high salt and water contents that must be removed to access organic material and energy. Most salt is removed (as NaCl) by paired lachrymal salt glands. Divalent ions are lost via the gut. In this study, the size of adult salt glands (0.622 kg for a 450 kg turtle; relatively three times the size of salt glands in cheloniid turtles) was measured for the first time by computed tomography scanning. Various published values for leatherback field metabolic rate, body fluid composition and likely blubber accumulation rates are combined with known jellyfish salt, water and organic compositions to calculate feasible salt gland secretion rates and feeding rates. The results indicate that leatherbacks can produce about 10–15 ml secretion g−1 salt gland mass h−1 (tear osmolality 1800 mOsm kg−1). This will permit consumption of 80% body mass day−1 of C. capillata. Calculations suggest that leatherbacks will find it difficult/impossible to accumulate sufficient blubber for reproduction in a single feeding season. Rapid jellyfish digestion and short gut transit times are essential

X-ray microcalorimetry for space

The X-ray microcalorimeter is an X-ray detector of potentially high energy resolution and quantum efficiency. The energy of incident X-rays is determined by measuring the resultant change in the resistance of a cooled semiconductor as an X-ray is incident on it. The history of X-ray microcalorimetry is reviewed, the current state of the art is placed in the context of contemporary X-ray detectors, and new X-ray detectors in the development stages. The performance of X-ray microcalorimeters is compared to other detectors. The principles of operation of microcalorimeters are discussed, and the relations between operating parameters established. The system devised and operated by the University of London microcalorimetry collaboration is described, and the future development of X-ray microcalorimetry considered. The design and implementation of a suite of computer programmes to analyse the data generated by the detector is described, and a space-based processing system defined. Results obtained with the detector operating at 100 mK in 1991 facing a Fe source are presented and analysed. A resolution of 316 eV is shown at 200mK, and 276 eV at 100mK. The absence of the expected improvement in resolution at the lower temperature is investigated. The microcalorimeter as an observational tool will require a space platform at a low temperature. Various low-temperature techniques are described, and the design and operation of the adiabatic demagnetisation refrigerator (ADR) used is described and modelled. The ADR is appraised as a means of cooling a space-based detector to 100mK, and a hypothetical system involving a 2-stage ADR is devised and modelled. One ADR operates between 100 mK and 1.0 K, and a second operates between 1.0 K and 4.0 K. The complete cooling system maintains a 100mK stage for 59 hours, with a recycle time of 17 hours. Replacing the high temperature ADR with a pumped helium tank cooling to 2.0 K increases the hold time to 80 hours, recycling in 3 minutes