Connection between PAHs and small hydrocarbons in the Horsehead Nebula Photo-Dissociation Region

We present recent observations of small hydrocarbons (C3H2, C2H, C4H) with high abundances in the Photo-Dissociation Region of the Horsehead nebula. Our results show for the first time observational indications that the small hydrocarbon distribution follows the Aromatic Infrared Bands (AIBs) emission traced by ISO-LW2 (5-8.5 microns), whereas it does not coincide with the CO and isotopes large-scale distribution. The derived abundances are significantly higher than in local clouds. This enhancement might be explained by an in situ formation assisted by the release of carbonaceous molecules from UV-irradiated aromatic particles.Comment: 3 pages, 2 figures. To appear in the proceedings of "Chemistry as a Diagnostic of Star Formation", University of Waterloo, Canada, August 2002 (C.L. Curry and M. Fich eds

Molecular Carbon Chains and Rings in TMC-1

We present mapping results in several rotational transitions of HC3N, C6H, both cyclic and linear C3H2 and C3H, towards the cyanopolyyne peak of the filamentary dense cloud TMC-1 using the IRAM 30m and MPIfR 100m telescopes. The spatial distribution of the cumulene carbon chain propadienylidene H2C3 (hereafter l-C3H2) is found to deviate significantly from the distributions of the cyclic isomer c-C3H2, HC3N, and C6H which in turn look very similar. The cyclic over linear abundance ratio of C3H2 increases by a factor of 3 across the filament, with a value of 28 at the cyanopolyyne peak. This abundance ratio is an order of magnitude larger than the range (3 to 5) we observed in the diffuse interstellar medium. The cyclic over linear abundance ratio of C3H also varies by ~2.5 in TMC-1, reaching a maximum value (13) close to the cyanopolyyne peak. These behaviors might be related to competitive processes between ion-neutral and neutral-neutral reactions for cyclic and linear species.Comment: Accepted for publication in The Astrophysical Journal, part I. 24 pages, including 4 tables, 7 figures, and figure caption

Cerebral microembolization during off-pump coronary artery bypass surgery with the Symmetry aortic connector device

ObjectiveThe use of aortic connector systems for proximal vein grafts in off-pump coronary artery bypass grafting might minimize aortic manipulation by eliminating the need for partial aortic clamping. The objective of this study was to asses whether use of a Symmetry connector (St Jude Medical, Inc, St Paul, Minn) reduced intraoperative cerebral embolization.MethodsThirty-two consecutive patients underwent off-pump coronary artery bypass grafting. Sixteen patients received at least one mechanical proximal vein graft anastomosis with a Symmetry aortic connector system. Sixteen patients representing the control group underwent operations with standard suturing techniques using partial aortic clamping. During surgical intervention, all patients were monitored continuously with multifrequency transcranial Doppler scanning, which detected and differentiated cerebral emboli.ResultsThere were significantly more cerebral emboli in the Symmetry group (median, 36) compared with the control group (median, 11; P = .027). This was due to a higher number of gaseous emboli in the Symmetry group than in the control group (median, 27 vs 8; P = .014), whereas there was no significant difference regarding the number of solid emboli (median, 7 vs 3; P = .139).ConclusionUse of a Symmetry connector system during proximal vein graft anastomosis increased the number of emboli to the brain compared with a standard technique in coronary bypass surgery without cardiopulmonary bypass

Global variations in diabetes mellitus based on fasting glucose and haemogloblin A1c

Fasting plasma glucose (FPG) and haemoglobin A1c (HbA1c) are both used to diagnose diabetes, but may identify different people as having diabetes. We used data from 117 population-based studies and quantified, in different world regions, the prevalence of diagnosed diabetes, and whether those who were previously undiagnosed and detected as having diabetes in survey screening had elevated FPG, HbA1c, or both. We developed prediction equations for estimating the probability that a person without previously diagnosed diabetes, and at a specific level of FPG, had elevated HbA1c, and vice versa. The age-standardised proportion of diabetes that was previously undiagnosed, and detected in survey screening, ranged from 30% in the high-income western region to 66% in south Asia. Among those with screen-detected diabetes with either test, the agestandardised proportion who had elevated levels of both FPG and HbA1c was 29-39% across regions; the remainder had discordant elevation of FPG or HbA1c. In most low- and middle-income regions, isolated elevated HbA1c more common than isolated elevated FPG. In these regions, the use of FPG alone may delay diabetes diagnosis and underestimate diabetes prevalence. Our prediction equations help allocate finite resources for measuring HbA1c to reduce the global gap in diabetes diagnosis and surveillance.peer-reviewe

Les hydrocarbures dans le milieu interstellaire (des nuages sombres aux régions de photodissociation)

AIX-MARSEILLE1.OAMP.Le Verrier (130552205) / SudocLYON1 ST GENIS-Observatoire (692042202) / SudocPARIS-BIUSJ-Thèses (751052125) / SudocPARIS-Observatoire (751142302) / SudocBORDEAUX1-Observatoire (331672201) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Are PAHs precursors of small hydrocarbons in Photo-Dissociation Regions? The Horsehead case

In press in Astronomy & Astrophysics. Uses aa LaTeX macros.We present maps at high spatial and spectral resolution in emission lines of C2H, c-C3H2, C4H, 12CO and C18O of the edge of the Horsehead nebula obtained with the Plateau de Bure Interferometer (PdBI). The edge of the Horsehead nebula is a one-dimensional Photo-Dissociation Region (PDR) viewed almost edge-on. All hydrocarbons are detected at high signal-to-noise ratio in the PDR where intense emission is seen both in the H2 ro-vibrational lines and in the PAH mid-infrared bands. C18O peaks farther away from the cloud edge. Our observations demonstrate that C2H, cC3H2 and C4H are present in UV-irradiated molecular gas, with abundances nearly as high as in dense, well shielded molecular cores. PDR models (i) need a large density gradient at the PDR edge to correctly reproduce the offset between the hydrocarbons and H2 peaks and (ii) fail to reproduce the hydrocarbon abundances. We propose that a new formation path of carbon chains, in addition to gas phase chemistry, should be considered in PDRs: because of intense UV-irradiation, large aromatic molecules and small carbon grains may fragment and feed the interstellar medium with small carbon clusters and molecules in significant amount.We are grateful to the IRAM staff at Plateau de Bure, Grenoble and Pico Veleta, Granada for competent help with the observations and data reduction. IRAM is supported by the INSU/CNRS (France), MPG (Germany) and IGN (Spain). We acknowledge funding by the French CNRS/PCMI program.Peer reviewe

Potential of GDGTs as a temperature proxy along an altitudinal transect at Mount Rungwe (Tanzania)

Glycerol dialkyl glycerol tetraethers (GDGTs) are membrane lipids of high molecular weight and include the isoprenoid GDGTs (iGDGTs) produced by Archaea and the branched GDGTs (brGDGTs) produced by unknown bacteria. Several indices have been developed to describe the relationship between GDGT distribution and environmental parameters: the TEX86 (tetraether index of tetraethers consisting of 86 carbons), based on the relative abundances of iGDGTs, and the MBT (methylation index of branched tetraethers) and CBT (cyclisation ratio of branched tetraethers), based on the relative abundance of brGDGTs. For soils, most studies have focused only on the relationship between brGDGT distribution and environmental parameters, without examining the iGDGT distribution. We have analysed both brGDGT and iGDGT distributions and determined GDGT-derived proxies along an altitudinal transect at Mt. Rungwe, Tanzania. MBT/CBT-derived temperature values were found to correlate linearly with altitude (R-2 0.75), as observed before for the other altitudinal transects investigated. The MBT/CBT-derived temperature lapse rate along Mt. Rungwe (0.7 degrees C/100 m) was similar to the in situ measured one and was consistent with results obtained previously for an altitudinal gradient in the same region at higher altitude. This confirms the robustness of the MBT/CBT as a paleoelevation proxy in East Africa. In addition, a linear correlation (R-2 0.50) between TEX86 and altitude was observed, likely reflecting the effect of the adiabatic cooling of air with altitude on iGDGT distribution. This suggests that TEX86 might be used to track temperature change in terrestrial settings, in addition to the MBT/CBT indices

Potential of GDGTs as a temperature proxy along an altitudinal transect at Mount Rungwe (Tanzania)

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