The DCN/HCN abundance ratio in hot molecular cores

We have observed the 3-2 transitions of DCN and (HCN)-N-15 in a number of hot molecular cores previously surveyed by us with the interesting result that the DCN/HCN ratio is low, a few times 10(-3), in the hot cores. The abundance ratio of DCN/HCN is derived both 'on-core' and 'off-core' and, in general is larger at the 'off-core' positions. Comparision with chemical models of these sources indicates that DCN liberated from evaporated ices can be destroyed rapidly in the hot gas by reaction with atomic hydrogen, which works to reset the the initial DCN/HCN ratio in the ice to the gas-phase atomic D/H ratio. The low DCN/HCN abundance ratio we measure can be reached in less than 10(4) years, consistent with previous estimates of the core ages, if the activation energy of the reaction is less than 500 K.

Molecular abundances in the Magellanic Clouds .2. Deuterated species in the LMC

The first definite discoveries of extragalactic deuterium are reported. DCO+ has been detected in three and DCN has been measured in one star-forming region of the Large Magellanic Cloud (LMC). While the HCO+/DCO+ abundance ratios are found to be 19 +/- 3, 24 +/- 4, and 67 +/- 18 for N113, N44BC and N159HW, respectively, a HCN/DCN abundance ratio of 23 +/- 5 is obtained for N113. These results are consistent with a gas temperature of about 20 K and a D/H ratio of about 1.5 x 10(-5), consistent with that observed in the Galaxy. If the cloud temperature is closer to 30 K, then a D/H ratio is required to be up to an order of magnitude larger. Because this ratio provides a lower limit to the primordial D/H ratio, it indicates that the baryon mass density alone is unable to close the universe.

DENSE GAS IN NEARBY GALAXIES .6. A LARGE C-12/C-13 RATIO IN A NUCLEAR STARBURST ENVIRONMENT

Toward the starburst nucleus of NGC 253, C-12/C-13 line intensity ratios from six carbon bearing molecules (CO, CN, CS, HCN, HCO+, and HNC) are used to confine the possible range of carbon and oxygen isotope ratios. A detailed analysis yields C-12/C-13 approximately 40 and O-16/O-18 approximately 200. Also reported are first detections of (CS)-C-13 and of the 0(0) - 1(-1) E line of methanol (CH3OH) in an extragalactic source.

A high C/O ratio and weak thermal inversion in the atmosphere of exoplanet WASP-12b

The carbon-to-oxygen ratio (C/O) in a planet provides critical information about its primordial origins and subsequent evolution. A primordial C/O greater than 0.8 causes a carbide-dominated interior, as opposed to the silicate-dominated composition found on Earth; the atmosphere can also differ from those in the Solar System. The solar C/O is 0.54 (ref. 3). Here we report an analysis of dayside multi-wavelength photometry of the transiting hot-Jupiter WASP-12b (ref. 6) that reveals C/O>=1 in its atmosphere. The atmosphere is abundant in CO. It is depleted in water vapour and enhanced in methane, each by more than two orders of magnitude compared to a solar-abundance chemical-equilibrium model at the expected temperatures. We also find that the extremely irradiated atmosphere (T>2,500K) of WASP-12b lacks a prominent thermal inversion (or stratosphere) and has very efficient day-night energy circulation. The absence of a strong thermal inversion is in stark contrast to theoretical predictions for the most highly irradiated hot-Jupiter atmospheres.

EXPERIMENTAL STUDIES OF LINE INTENSITY RATIO AS A DIAGNOSTIC OF RECOMBINING PLASMAS

Double slits have been incorporated in a flat field spectrometer to record spatially resolved and integrated spectra simultaneously. Variation of the absorbed irradiance and ionisation stage along the fibre plasmas has been monitored. By comparison of the spatially resolved and integrated resonance line ratios, it is found that the spatially integrated values deviated significantly from the real experimental circumstances due to nonuniformity along the plasmas.

Cooking rice in a high water to rice ratio reduces inorganic arsenic content

Total arsenic and arsenic speciation was performed on different rice types (basmati, long-grain, polished ([white] and wholegrain [brown]) that had undergone various forms of cooking. The effect of rinse washing, low volume (2.5 : 1 water : rice) and high volume (6 : 1 water : rice) cooking, as well as steaming, were investigated. Rinse washing was effective at removing circa. 10% of the total and inorganic arsenic from basmati rice, but was less effective for other rice types. While steaming reduced total and inorganic arsenic rice content, it did not do so consistently across all rice types investigated. Low volume water cooking did not remove arsenic. High volume water : rice cooking did effectively remove both total and inorganic arsenic for the long-grain and basmati rice (parboiled was not investigated in high volume cooking water experiment), by 35% and 45% for total and inorganic arsenic content, respectively, compared to uncooked (raw) rice. To reduce arsenic content of cooked rice, specifically the inorganic component, rinse washing and high volume of cooking water are effective.

Arsenic mobilization from iron oxyhydroxides is regulated by organic matter carbon to nitrogen (C:N) ratio

Arsenic (As) is mobilized from delta and floodplain aquifer sediments throughout S.E. Asia via reductive dissolution of As bound to iron (Fe) oxyhydroxides. The reductive driving force is organic carbon, but its source and constitution is uncertain. Here batch incubation experiments were conducted to investigate the role of organic matter (OM) carbon:nitrogen (C:N) ratio on the mobilization of arsenic, Fe and N from As dosed, Fe oxyhydroxide coated sands. As mobilization into pore waters from the sand was strongly regulated by the C:N ratio of the OM, and also the concentration of OM present. The lower the C:N, the more As released. Fe and ammonium release were similarly dependent on the quality and quantity of OM, but Fe mobilization was more rapid and ammonium release slower than As suggesting that the mobilization of these 3 moieties although interdependent, were not directly linked. It was concluded that low C:N ratios for OM responsible for reducing aquifers were As in groundwater is observed were likely.