Oxygen diffusion and reactivity at low temperature on bare amorphous olivine-type silicate

The mobility of O atoms at very low temperatures is not generally taken into account, despite O diffusion would add to a series of processes leading to the observed rich molecular diversity in space. We present a study of the mobility and reactivity of O atoms on an amorphous silicate surface. Our results are in the form of RAIRS and temperature-programmed desorption spectra of O2 and O3 produced via two pathways: O + O and O2 + O, investigated in a submonolayer regime and in the range of temperature between 6.5 and 30 K. All the experiments show that ozone is formed efficiently on silicate at any surface temperature between 6.5 and 30 K. The derived upper limit for the activation barriers of O + O and O2 + O reactions is 150 K/kb. Ozone formation at low temperatures indicates that fast diffusion of O atoms is at play even at 6.5 K. Through a series of rate equations included in our model, we also address the reaction mechanisms and show that neither the Eley Rideal nor the Hot atom mechanisms alone can explain the experimental values. The rate of diffusion of O atoms, based on modeling results, is much higher than the one generally expected, and the diffusive process proceeds via the Langmuir-Hinshelwood mechanism enhanced by tunnelling. In fact, quantum effects turn out to be a key factor that cannot be neglected in our simulations. Astrophysically, efficient O3 formation on interstellar dust grains would imply the presence of huge reservoirs of oxygen atoms. Since O3 is a reservoir of elementary oxygen, and also of OH via its hydrogenation, it could explain the observed concomitance of CO2 and H2O in the ices.Comment: 28 pages, 14 figure

A Keck/DEIMOS spectroscopic survey of the faint M31 satellites And IX, And XI, And XII, and And XIII

We present the first spectroscopic analysis of the faint M31 satellite galaxies, AndXI and AndXIII, and a reanalysis of existing spectroscopic data for two further faint companions, And IX and AndXII. By combining data obtained using the DEIMOS spectrograph mounted on the Keck II telescope with deep photometry from the Suprime-Cam instrument on Subaru, we have calculated global properties for the dwarfs, such as systemic velocities, metallicites and half-light radii.We find each dwarf to be very metal poor ([Fe/H] -2 both photometrically and spectroscopically, from their stacked spectrum), and as such, they continue to follow the luminosity-metallicity relationship established with brighter dwarfs. We are unable to resolve a dispersion for And XI due to small sample size and low S/N, but we set a one sigma upper limit of sigma-v <5 km/s. For And IX, And XII and And XIII we resolve velocity dispersions of v=4.5 (+3.4,-3.2), 2.6(+5.1,-2.6) and 9.7(+8.9,-4.5) km/s, and derive masses within the half light radii of 6.2(+5.3,-5.1)x10^6 Msun, 2.4 (+6.5,-2.4)x10^6 Msun and 1.1(+1.4,-0.7)x10^7 Msun respectively. We discuss each satellite in the context of the Mateo relations for dwarf spheroidal galaxies, and the Universal halo profiles established for Milky Way dwarfs (Walker et al. 2009). For both galaxies, this sees them fall below the Universal halo profiles of Walker et al. (2009). When combined with the findings of McConnachie & Irwin (2006a), which reveal that the M31 satellites are twice as extended (in terms of both half-light and tidal radii) as their Milky Way counterparts, these results suggest that the satellite population of the Andromeda system could inhabit halos that are significantly different from those of the Milky Way in terms of their central densities (abridged).Comment: 26 pages, 18 figures, MNRAS submitte

Draco, a flawless dwarf galaxy

The Draco dwarf spheroidal galaxy (dSph), with its apparent immense mass to light ratio and compact size, holds many clues to the nature of the enigmatic dark matter. Here we present deep photometric studies of this dwarf galaxy, undertaken with the MegaCam Camera at the Canada-France-hawaii Telescope, the Wide Field Camera at the Isaac Newton Telescope and the Wide-Field and Planetary Camera on board the Hubble Space Telescope. The new photometric data cover the entirety of the galaxy, and reach i=24.5 at 50% completeness, significantly deeper than previous panoramic studies, allowing searches for tidal disturbances of much lower surface brightness than has been possible before. With these improved statistics, we find no evidence for asymmetric disturbances or tidal tails that possess more than 3% of the stars found within the centre of the galaxy. We find that the central stellar density, as probed by the HST data, rises into the central 0.5'. Uncertainties in the position of the centroid of the galaxy do not allow us to determine whether the apparent flattening of the profile interior to 0.5' is reliable or not. Draco is therefore a flawless dwarf galaxy, featureless and apparently unaffected by Galactic tides.Comment: 13 pages, 16 figures, accepted for publication in MNRA

A Keck/DEIMOS spectroscopic survey of faint Galactic satellites: searching for the least massive dwarf galaxies

[abridged] We present the results of a spectroscopic survey of the recently discovered faint Milky Way satellites Boo, UMaI, UMaII and Wil1. Using the DEIMOS spectrograph on Keck, we have obtained samples that contain from 15 to 85 probable members of these satellites for which we derive radial velocities precise to a few km/s down to i~21-22. About half of these stars are observed with a high enough S/N to estimate their metallicity to within \pm0.2 dex. From this dataset, we show that UMaII is the only object that does not show a clear radial velocity peak. However, the measured systemic radial velocity (v_r=115\pm5 km/s) is in good agreement with recent simulations in which this object is the progenitor of the recently discovered Orphan Stream. The three other satellites show velocity dispersions that make them highly dark-matter dominated systems. In particular the Willman 1 object is not a globular cluster given its metallicity scatter over -2.0<[Fe/H]<-1.0 and is therefore almost certainly a dwarf galaxy or dwarf galaxy remnant. We measure a radial velocity dispersion of only 4.3_{-1.3}^{+2.3} km/s around a systemic velocity of -12.3\pm2.3 km/s which implies a mass-to-light ratio of ~700 and a total mass of ~5x10^5 Msun for this satellite, making it the least massive satellite galaxy known to date. Such a low mass could mean that the 10^7 Msun limit that had until now never been crossed for Milky Way and Andromeda satellite galaxies may only be an observational limit and that fainter, less massive systems exist within the Local Group. However, more modeling and an extended search for potential extra-tidal stars are required to rule out the possibility that these systems have not been significantly heated by tidal interaction.Comment: 24 pages, 11 figures, MNRAS accepte

Dynamics of Dipolar Spinor Condensates

We study the semiclassical dynamics of a spinor condensate with the magnetic dipole-dipole interaction included. The time evolution of the population imbalance and the relative phase among different spin components depends greatly on the relative strength of interactions as well as on the initial conditions. The interplay of spin exchange and dipole-dipole interaction makes it possible to manipulate the atomic population on different components, leading to the phenomena of spontaneous magnetization and Macroscopic Quantum Self Trapping. Simple estimate demonstrates that these effects are accessible and controllable by modifying the geometry of the trapping potential.Comment: 13 pages,3 figure

Predicting enhanced absorption of light gases in polyethylene using simplified PC-SAFT and SAFT-VR

International audienceAbsorption of light gases in polyethylene (PE) is studied using two versions of the Statistical Associating Fluid Theory (SAFT): SAFT for chain molecules with attractive potentials of variable range (VR) and simplified perturbed-chain (PC) SAFT. Emphasis is placed on the light gases typically present during ethylene polymerisation in the gas-phase reactor (GPR) process. The two approaches are validated using experimental binary-mixture data for gas absorbed in PE, and predictions are made for mixtures of more components. For most cases studied both SAFT versions perform equally well. For the case of ternary mixtures of two gases with PE, it is predicted that the less-volatile of the two gases acts to enhance the absorption of the more-volatile gas, while the more-volatile gas inhibits the absorption of the less-volatile gas. This general behaviour is also predicted in mixtures containing more gases, such as typical reactor mixtures. The magnitude of the effect may vary considerably, depending on the relative proximity of the gas-mixture saturation pressure to the reactor pressure; for example it is predicted that the absorption of ethylene may be approximately doubled if diluent gases, propane or nitrogen, are partially or completely replaced by less-volatile butane or pentane for a reactor pressure similar to 2 MPa. In the case of a co-polymerisation reaction, it is predicted that increases in absorption of both co-monomers may be obtained in roughly equal proportion. Our findings cast light on the so-called co-monomer effect, in which substantial increases in the rate of ethylene polymerisation are observed in the presence of hexene co-monomer, while suggesting that the effect is more general and not restricted to co-monomer. For example, similar rate increases may be expected in the presence of, e.g., pentane instead of hexene, but without the change in the branch structure of the produced polymer that is inevitable when the amount of co-monomer is increased

Improvement in the pre-hospital care of recreational drug users through the development of club specific ambulance referral guidelines

<p>Abstract</p> <p>Background</p> <p>Previously developed 'club guidelines' developed for club owners and promoters have tended to focus more on the legislative aspects of clubs, rather than the medical management of unwell clubbers within club environments. Despite this lack of guidance on the management of unwell clubbers, a significant proportion of clubs have 'club medic' rooms for managing these individuals. However, due to the lack of specific guidance on the training of staff working in these rooms and guidelines on when an ambulance should be called for an unwell clubber, there have been instances previously where clubbers have been inappropriately managed within the club environment, and often referred to hospital only after significant physiological derangement has occurred, thereby leading to an increased risk of morbidity and mortality.</p> <p>Methods</p> <p>We identified owners and promoters of local club venues within the catchment area of our Emergency Department and working jointly with them and other key stakeholders, in particular the London Ambulance Service and Metropolitan Police, identified strategies to improve pre-hospital care for clubbers who become unwell as a result of recreational drug use. These included developing guidelines detailing indications for ambulance transfer to hospital for clubbers with recreational drug toxicity and the training of club medic staff to use the guidelines</p> <p>Results</p> <p>Following the initial development of a pilot set of guidelines, an audit of their use identified training needed relating to the assessment of unwell clubbers with recreational drug toxicity and revisions required to the pilot version of the guidelines. After training related to the revised guidelines, all the club medic staff were confident in their ability to assess unwell clubbers with recreational drug toxicity, the use of the guidelines and also when to call an ambulance.</p> <p>Conclusion</p> <p>Working with key stakeholders in the local community, we have developed guidelines that can be used to improve the pre-hospital care of clubber unwell with recreational drug toxicity, and demonstrated that individuals with a variety of medical knowledge can be trained to use these guidelines. Wider dissemination of these guidelines, both regionally, nationally and potentially internationally, may help to reduce the pre-hospital morbidity and mortality associated with recreational drug toxicity encountered in club environments.</p

Suicidal Behavior and Depression in Smoking Cessation Treatments

BACKGROUND: Two treatments for smoking cessation--varenicline and bupropion--carry Boxed Warnings from the U.S. Food and Drug Administration (FDA) about suicidal/self-injurious behavior and depression. However, some epidemiological studies report an increased risk in smoking or smoking cessation independent of treatment, and differences between drugs are unknown. METHODOLOGY: From the FDA's Adverse Event Reporting System (AERS) database from 1998 through September 2010 we selected domestic, serious case reports for varenicline (n = 9,575), bupropion for smoking cessation (n = 1,751), and nicotine replacement products (n = 1,917). A composite endpoint of suicidal/self-injurious behavior or depression was defined as a case with one or more Preferred Terms in Standardized MedDRA Query (SMQ) for those adverse effects. The main outcome measure was the ratio of reported suicide/self-injury or depression cases for each drug compared to all other serious events for that drug. RESULTS: Overall we identified 3,249 reported cases of suicidal/self-injurious behavior or depression, 2,925 (90%) for varenicline, 229 (7%) for bupropion, and 95 (3%) for nicotine replacement. Compared to nicotine replacement, the disproportionality results (OR (95% CI)) were varenicline 8.4 (6.8-10.4), and bupropion 2.9 (2.3-3.7). The disproportionality persisted after excluding reports indicating concomitant therapy with any of 58 drugs with suicidal behavior warnings or precautions in the prescribing information. An additional antibiotic comparison group showed that adverse event reports of suicidal/self-injurious behavior or depression were otherwise rare in a healthy population receiving short-term drug treatment. CONCLUSIONS: Varenicline shows a substantial, statistically significant increased risk of reported depression and suicidal/self-injurious behavior. Bupropion for smoking cessation had smaller increased risks. The findings for varenicline, combined with other problems with its safety profile, render it unsuitable for first-line use in smoking cessation

Seasonal patterns and controls on net ecosystem CO2 exchange in a boreal peatland complex

We measured seasonal patterns of net ecosystem exchange (NEE) of CO2 in a diverse peatland complex underlain by discontinuous permafrost in northern Manitoba, Canada, as part of the Boreal Ecosystems Atmosphere Study (BOREAS). Study sites spanned the full range of peatland trophic and moisture gradients found in boreal environments from bog (pH 3.9) to rich fen (pH 7.2). During midseason (July‐August, 1996), highest rates of NEE and respiration followed the trophic sequence of bog (5.4 to −3.9 μmol CO2 m−2 s−1) \u3c poor fen (6.3 to −6.5 μmol CO2 m−2 s−1) \u3c intermediate fen (10.5 to −7.8 μmol CO2 m−2 s−1) \u3c rich fen (14.9 to −8.7 μmol CO2m−2 s−1). The sequence changed during spring (May‐June) and fall (September‐October) when ericaceous shrub (e.g., Chamaedaphne calyculata) bogs and sedge (Carex spp.) communities in poor to intermediate fens had higher maximum CO2 fixation rates than deciduous shrub‐dominated (Salix spp. and Betula spp.) rich fens. Timing of snowmelt and differential rates of peat surface thaw in microtopographic hummocks and hollows controlled the onset of carbon uptake in spring. Maximum photosynthesis and respiration were closely correlated throughout the growing season with a ratio of approximately 1/3 ecosystem respiration to maximum carbon uptake at all sites across the trophic gradient. Soil temperatures above the water table and timing of surface thaw and freeze‐up in the spring and fall were more important to net CO2 exchange than deep soil warming. This close coupling of maximum CO2 uptake and respiration to easily measurable variables, such as trophic status, peat temperature, and water table, will improve models of wetland carbon exchange. Although trophic status, aboveground net primary productivity, and surface temperatures were more important than water level in predicting respiration on a daily basis, the mean position of the water table was a good predictor (r2 = 0.63) of mean respiration rates across the range of plant community and moisture gradients. Q10 values ranged from 3.0 to 4.1 from bog to rich fen, but when normalized by above ground vascular plant biomass, the Q10 for all sites was 3.3