393 research outputs found
Tracing early evolutionary stages of high-mass star formation with molecular lines
Despite its major role in the evolution of the interstellar medium, the
formation of high-mass stars (M > 10 Msol) is still poorly understood. Two
types of massive star cluster precursors, the so-called Massive Dense Cores
(MDCs), have been observed, which differ in their mid-infrared brightness. The
origin of this difference is not established and could be the result of
evolution, density, geometry differences, or a combination of these. We compare
several molecular tracers of physical conditions (hot cores, shocks) observed
in a sample of mid-IR weak emitting MDCs with previous results obtained in a
sample of exclusively mid-IR bright MDCs. The aim is to understand the
differences between these two types of object. We present single-dish
observations of HDO, H2O-18, SO2 and CH3OH lines at lambda = 1.3 - 3.5 mm. We
study line profiles and estimate abundances of these molecules, and use a
partial correlation method to search for trends in the results. The detection
rates of thermal emission lines are found to be very similar between mid-IR
quiet and bright objects. The abundances of H2O, HDO (1E-13 to 1E-9 in the cold
outer envelopes), SO2 and CH3OH differ from source to source but independently
of their mid-IR flux. In contrast, the methanol class I maser emission, a
tracer of outflow shocks, is found to be strongly anti-correlated with the 12
micron source brightnesses. The enhancement of the methanol maser emission in
mid-IR quiet MDCs may indicate a more embedded nature. Since total masses are
similar between the two samples, we suggest that the matter distribution is
spherical around mid-IR quiet sources but flattened around mid-IR bright ones.
In contrast, water emission is associated with objects containing a hot
molecular core, irrespective of their mid-IR brightness. These results indicate
that the mid-IR brightness of MDCs is an indicator of their evolutionary stage.Comment: 15 pages, 6 figures, 11 tables, accepted for publication in A&A the
11/06/201
La grille au service du développement médical en Afrique
PCSV, présenté par F. Jacq, pas de proceedingsObjectives: Telemedicine networks allow to train local physicians and to improve diagnosis by exchanging medical data. But the set-up of multipoint dynamic telemedicine requires moving towards GRID technologies. The objective is to develop telemedicine services for physicians from Burkina Faso and France with the perspective of setting up a grid infrastructure between the participating medical sites. Methods: A web site to exchange diagnosis on diabetic retinopathy was developed in PHP. Another application using web services was developed to exchange patient information on ophthalmology between two databases. Results: The main difficulty comes from limited resources in developing countries including staff skills, bandwidth and funding. But the collaboration with dispensaries opened a door to enhanced collaboration between physicians of France and Burkina Faso Conclusions: These applications are designed with the aim of their use on grids which opens the perspective of multipoint dynamic telemedicine. We are developing a new generation of telemedicine service using experience acquired in the last two years
Detection of water at z = 0.685 towards B0218+357
We report the detection of the H_2O molecule in absorption at a redshift z =
0.68466 in front of the gravitationally lensed quasar B0218+357. We detect the
fundamental transition of ortho-water at 556.93 GHz (redshifted to 330.59 GHz).
The line is highly optically thick and relatively wide (15 km/s FWHM), with a
profile that is similar to that of the previously detected CO(2--1) and
HCO^+(2--1) optically thick absorption lines toward this quasar. From the
measured level of the continuum at 330.59 GHz, which corresponds to the level
expected from the power-law spectrum already
observed at lower frequencies, we deduce that the filling factor of the H_2O
absorption is large. It was already known from the high optical thickness of
the CO, ^{13}CO and C^{18}O lines that the molecular clouds entirely cover one
of the two lensed images of the quasar (all its continuum is absorbed); our
present results indicate that the H_2O clouds are covering a comparable
surface. The H_2O molecules are therefore not confined to small cores with a
tiny filling factor, but are extended over parsec scales. The H_2O line has a
very large optical depth, and only isotopic lines could give us the water
abundance. We have also searched for the 183 GHz line in absorption, obtaining
only an upper limit; this yields constraints on the excitation temperature.Comment: 4 pages, 3 figures, accepted in ApJ Letter
Les grilles pour le développement médical
PCSV, prĂ©sentĂ© par V. Breton, Ă paraĂźtre dans les Comptes-Rendu de la ConfĂ©renceLe dĂ©veloppement rĂ©cent des sciences et technologies de l'information et de la communication permet aujourd'hui la crĂ©ation de vĂ©ritables infrastructures pour le calcul et le stockage de donnĂ©es hĂ©tĂ©rogĂšnes Ă l'Ă©chelle rĂ©gionale, nationale et internationale. Ces infrastructures, appelĂ©es grilles informatiques, permettront bientĂŽt d'utiliser les ressources informatiques mutualisĂ©es avec autant de facilitĂ© que nous utilisons aujourd'hui l'Ă©lectricitĂ©. L'utilisation des grilles afin d'accĂ©lĂ©rer la dĂ©couverte de mĂ©dicaments est une voie trĂšs prometteuse pour l'avenir. Par cette approche in silico, le nombre de molĂ©cules ainsi que la vitesse de test peuvent ĂȘtre grandement augmentĂ©s induisant un coĂ»t moindre de dĂ©veloppement de mĂ©dicaments. Du 11 Juillet au 31 AoĂ»t 2005, l'expĂ©rience WISDOM (Wide In Silico Docking On Malaria) a permis de tester rien moins qu'un million de ligands (mĂ©dicaments potentiels) pour le traitement du paludisme: 1700 ordinateurs Ă travers le monde ont ainsi Ă©tĂ© associĂ©s Ă cette dĂ©marche permettant de rĂ©aliser en un mois ce qui aurait nĂ©cessitĂ© 80 ans sur un ordinateur classique. L'analyse des rĂ©sultats est en cours. Par cette approche, on peut souhaiter Ă©galement que les maladies orphelines puissent bĂ©nĂ©ficier d'un intĂ©rĂȘt nouveau de la part des industries pharmaceutiques, Ă travers notamment la baisse du coĂ»t de dĂ©veloppement d'un mĂ©dicament, principal obstacle actuellement Ă leur mobilisation
The Water Vapor Abundance in Orion KL Outflows
We present the detection and modeling of more than 70 far-IR pure rotational
lines of water vapor, including the 18O and 17O isotopologues, towards Orion
KL. Observations were performed with the Long Wavelength Spectrometer
Fabry-Perot (LWS/FP; R~6800-9700) on board the Infrared Space Observatory (ISO)
between ~43 and ~197 um. The water line profiles evolve from P-Cygni type
profiles (even for the H2O18 lines) to pure emission at wavelengths above ~100
um. We find that most of the water emission/absorption arises from an extended
flow of gas expanding at 25+-5 kms^-1. Non-local radiative transfer models show
that much of the water excitation and line profile formation is driven by the
dust continuum emission. The derived beam averaged water abundance is
2-3x10^-5. The inferred gas temperature Tk=80-100 K suggests that: (i) water
could have been formed in the "plateau" by gas phase neutral-neutral reactions
with activation barriers if the gas was previously heated (e.g. by shocks) to
>500 K and/or (ii) H2O formation in the outflow is dominated by in-situ
evaporation of grain water-ice mantles and/or (iii) H2O was formed in the
innermost and warmer regions (e.g. the hot core) and was swept up in ~1000 yr,
the dynamical timescale of the outflow.Comment: Accepted for publication in ApJ letters [2006 August 7] (5 pages 2,
figures, not edited
Selective Methylation of Arenes: A Radical CâH Functionalization/CrossâCoupling Sequence
A selective, nonchelationâassisted methylation of arenes has been developed. The overall transformation, which combines a CâH functionalization reaction with a nickelâcatalyzed crossâcoupling, offers rapid access to methylated arenes with high para selectivity. The reaction is amenable to lateâstage methylation of smallâmolecule pharmaceuticals
Multi-line Herschel/HIFI observations of water reveal infall motions and chemical segregation around high-mass protostars
(Abridged) We use HIFI maps of the 987 GHz H2O 2(02)-1(11) emission to
measure the sizes and shapes of 19 high-mass protostellar envelopes. To
identify infall, we use HIFI spectra of the optically thin C18O 9-8 and H2O-18
1(11)-0(00) lines. The high-J C18O line traces the warm central material and
redshifted H2O-18 1(11)-0(00) absorption indicates material falling onto the
warm core. We probe small-scale chemical differentiation by comparing H2O 752
and 987 GHz spectra with those of H2O-18.
Our measured radii of the central part of the H2O 2(02)-1(11) emission are
30-40% larger than the predictions from spherical envelope models, and axis
ratios are <2, which we consider good agreement. For 11 of the 19 sources, we
find a significant redshift of the H2O-18 1(11)-0(00) line relative to C18O
9-8. The inferred infall velocities are 0.6-3.2 km/s, and estimated mass inflow
rates range from 7e-5 to 2e-2 M0/yr, with the highest mass inflow rates
occurring toward the sources with the highest masses, and possibly the youngest
ages. The other sources show either expanding motions or H2O-18 lines in
emission. The H2O-18 1(11)-0(00) line profiles are remarkably similar to the
"differences" between the H2O 2(02)-1(11) and 2(11)-2(02) profiles, suggesting
that the H2O-18 line and the H2O 2(02)-1(11) absorption originate just inside
the radius where water evaporates from grains, typically 1000-5000 au from the
center. In some sources, the H2O-18 line is detectable in the outflow, where no
C18O emission is seen.
Together, the H2O-18 absorption and C18O emission profiles show that the
water abundance around high-mass protostars has at least three levels: low in
the cool outer envelope, high within the 100 K radius, and very high in the
outflowing gas. Thus, despite the small regions, the combination of lines
presented here reveals systematic inflows and chemical information about the
outflows.Comment: Accepted for publication in Astronomy & Astrophysics; 10 pages body +
10 pages appendi
Demonstration of In Silico docking at a large scale on grid infrastructure
présenté par N. Jac
- âŠ