29,103 research outputs found

    HCO, c-C3H and CF+ : three new molecules in diffuse, translucent and "spiral-arm'' clouds

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    %methods {We used the EMIR receiver and FTS spectrometer at the IRAM 30m to construct absorption spectra toward bright extra-galactic background sources at 195 kHz spectral resolution (≈\approx 0.6 \kms). We used the IRAM Plateau de Bure interferometer to synthesize absorption spectra of \hthcop\ and HCO toward the galactic HII region W49.} %results {HCO, \cc3h\ and CF\p\ were detected toward the blazars \bll\ and 3C111 having \EBV\ = 0.32 and 1.65 mag. HCO was observed in absorption from ``spiral-arm'' clouds in the galactic plane occulting W49. The complement of detectable molecular species in the 85 - 110 GHz absorption spectrum of diffuse/translucent gas is now fully determined at rms noise level Ύτ≈0.002\delta_\tau \approx 0.002 at \EBV\ = 0.32 mag (\AV\ = 1 mag) and ÎŽÏ„\delta_\tau/\EBV\ ≈ 0.003\approx\ 0.003 mag−1^{-1} overall.} %conclusions {As with OH, \hcop\ and \cch, the relative abundance of \cc3h\ varies little between diffuse and dense molecular gas, with N(\cc3h)/N({\it o-c}-\c3h2) ≈\approx 0.1. We find N(CF\p)/N(H13^{13}CO\p) ≈5\approx 5, N(CF\p)/N(\cch) ≈\approx 0.005-0.01 and because N(CF\p) increases with \EBV\ and with the column densities of other molecules we infer that fluorine remains in the gas phase as HF well beyond \AV\ = 1 mag. We find N(HCO)/N(H13^{13}CO\p) = 16 toward \bll, 3C111 and the 40 km/s spiral arm cloud toward W49, implying X(HCO) ≈10−9\approx 10^{-9}, about 10 times higher than in dark clouds. The behaviour of HCO is consistent with previous suggestions that it forms from C\p\ and \HH, even when \AV\ is well above 1 mag. The survey can be used to place useful upper limits on some species, for instance N(\hhco)/N(\HH CS) >> 32 toward 3C111, compared to 7 toward TMC-1, confirming the possibility of a gas phase formation route to \hhco.}Comment: A\%A in pres

    A radial mode ultrasonic horn for the inactivation of <i>Escherichia coli</i> K12

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    Tuned cylindrical radial mode ultrasonic horns offer advantages over ultrasonic probes in the design of flow-through devices for bacterial inactivation. This study presents a comparison of the effectiveness of a radial horn and probe in the inactivation of Escherichia coli K12. The radial horn is designed using finite element analysis and the predicted modal parameters are validated using experimental modal analysis. A validated finite element model of the probe is also presented. Visual studies of the cavitation fields produced by the radial horn and probe are carried out using luminol and also backlighting to demonstrate the advantages of radial horns in producing a more focused cavitation field with widely dispersed streamers. Microbiological studies show that, for the same power density, better inactivation of E. coli K12 is achieved using the radial horn and, also, the radial horn offers greater achievable power density resulting in further improvements in bacterial inactivation. The radial horn is shown to be more effective than the probe device and offers opportunities to design in-line flow-through devices for processing applications

    Integrating effects of species composition and soil properties to predict shifts in montane forest carbon-water relations.

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    This study was designed to address a major source of uncertainty pertaining to coupled carbon-water cycles in montane forest ecosystems. The Sierra Nevada of California was used as a model system to investigate connections between the physiological performance of trees and landscape patterns of forest carbon and water use. The intrinsic water-use efficiency (iWUE)-an index of CO2 fixed per unit of potential water lost via transpiration-of nine dominant species was determined in replicated transects along an ∌1,500-m elevation gradient, spanning a broad range of climatic conditions and soils derived from three different parent materials. Stable isotope ratios of carbon and oxygen measured at the leaf level were combined with field-based and remotely sensed metrics of stand productivity, revealing that variation in iWUE depends primarily on leaf traits (∌24% of the variability), followed by stand productivity (∌16% of the variability), climatic regime (∌13% of the variability), and soil development (∌12% of the variability). Significant interactions between species composition and soil properties proved useful to predict changes in forest carbon-water relations. On the basis of observed shifts in tree species composition, ongoing since the 1950s and intensified in recent years, an increase in water loss through transpiration (ranging from 10 to 60% depending on parent material) is now expected in mixed conifer forests throughout the region

    Study of thermal insulation for airborne liquid hydrogen fuel tanks

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    A concept for a fail-safe thermal protection system was developed. From screening tests, approximately 30 foams, adhesives, and reinforcing fibers using 0.3-meter square liquid nitrogen cold plate, CPR 452 and Stafoam AA1602, both reinforced with 10 percent by weight of 1/16 inch milled OCF Style 701 Fiberglas, were selected for further tests. Cyclic tests with these materials in 2-inch thicknesses bonded on a 0.6-meter square cold plate with Crest 7410 adhesive systems, were successful. Zero permeability gas barriers were identified and found to be compatible with the insulating concept

    A Submillimeter HCN Laser in IRC+10216

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    We report the detection of a strong submillimeter wavelength HCN laser line at a frequency near 805 GHz toward the carbon star IRC+10216. This line, the J=9-8 rotational transition within the (04(0)0) vibrationally excited state, is one of a series of HCN laser lines that were first detected in the laboratory in the early days of laser spectroscopy. Since its lower energy level is 4200 K above the ground state, the laser emission must arise from the inner part of IRC+10216's circumstellar envelope. To better characterize this environment, we observed other, thermally emitting, vibrationally excited HCN lines and find that they, like the laser line, arise in a region of temperature approximately 1000 K that is located within the dust formation radius; this conclusion is supported by the linewidth of the laser. The (04(0)0), J=9-8 laser might be chemically pumped and may be the only known laser (or maser) that is excited both in the laboratory and in space by a similar mechanism.Comment: 11 pages, 3 figure
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