70 research outputs found
Variations in patterns of care across neonatal units and their associations with outcomes in very preterm infants: the French EPIPAGE-2 cohort study
OBJECTIVES: To describe patterns of care for very preterm (VP) babies across neonatal intensive care units (NICUs) and associations with outcomes. DESIGN: Prospective cohort study, EPIPAGE-2. SETTING: France, 2011. PARTICIPANTS: 53 (NICUs); 2135 VP neonates born at 27 to 31 weeks. OUTCOME MEASURES: Clusters of units, defined by the association of practices in five neonatal care domains - respiratory, cardiovascular, nutrition, pain management and neurodevelopmental care. Mortality at 2 years corrected age (CA) or severe/moderate neuro-motor or sensory disabilities and proportion of children with scores below threshold on the neurodevelopmental Ages and Stages Questionnaire (ASQ). METHODS: Hierarchical cluster analysis to identify clusters of units. Comparison of outcomes between clusters, after adjustment for potential cofounders. RESULTS: Three clusters were identified: Cluster 1 with higher proportions of neonates free of mechanical ventilation at 24âhours of life, receiving early enteral feeding, and neurodevelopmental care practices (26 units; n=1118 babies); Cluster 2 with higher levels of patent ductus arteriosus and pain screening (11 units; n=398 babies); Cluster 3 with higher use of respiratory, cardiovascular and pain treatments (16 units; n=619 babies). No difference was observed between clusters for the baseline maternal and babies' characteristics. No differences in outcomes were observed between Clusters 1 and 3. Compared with Cluster 1, mortality at 2 years CA or severe/moderate neuro-motor or sensory disabilities was lower in Cluster 2 (adjusted OR 0.46, 95%âCI 0.25 to 0.84) but with higher proportion of children with an ASQ below threshold (adjusted OR 1.49, 95%âCI 1.07 to 2.08). CONCLUSION: In French NICUs, care practices for VP babies were non-randomly associated. Differences between clusters were poorly explained by unit or population differences, but were associated with mortality and development at 2 years. Better understanding these variations may help to improve outcomes for VPT babies, as it is likely that some of these discrepancies are unwarranted
A survey for nanodiamond features in the 3 micron spectra of Herbig Ae/Be stars
We have carried out a survey of 60 Herbig Ae/Be stars in the 3 micron
wavelength region in search for the rare spectral features at 3.43 and 3.53
micron. These features have been attributed to the presence of large, hot,
hydrogen-terminated nanodiamonds. Only two Herbig Ae/Be stars, HD 97048 and
Elias 3-1 are known to display both these features. We have obtained
medium-resolution spectra (R ~2500) with the ESO near-IR instrument ISAAC in
the 3.15-3.65 micron range. In our sample, no new examples of sources with
prominent nanodiamond features in their 3 micron spectra were discovered
(detection rate less than 4%). We report tentative 3.53 micron detections in
V921 Sco (=CD-42.11721), HD 163296 and T CrA. The sources which display the
nanodiamond features are not exceptional in the group of Herbig stars with
respect to disk properties, stellar characteristics, or disk and stellar
activity. Moreover, the nanodiamond sources are very different from each other
in terms of these parameters. We do not find evidence for a recent supernova in
the vicinity of any of the nanodiamond sources. We have analyzed the PAH 3.3
micron feature and the Pfund delta hydrogen emission line, two other spectral
features which occur in the 3 micron wavelength range. We reinforce the
conclusion of previous authors that flared-disk systems display significantly
more PAH emission than self-shadowed-disk sources. The Pf delta line detection
rate is higher in self-shadowed-disk sources than in the flared-disk systems.
We discuss the possible origin and paucity of the (nano)diamond features in
Herbig stars. Different creation mechanisms have been proposed in the
literature, amongst others in-situ and supernova-induced formation. Our data
set is inconclusive in proving or disproving either formation mechanism.Comment: 22 pages, 9 figures, 5 tables; accepted for publication in A&A
(acceptance date 16/06/2006
ISO spectroscopy of disks around Herbig Ae/Be stars
We have investigated the infrared spectra of all 46 Herbig Ae/Be stars for
which spectroscopic data is available in the ISO data archive. Our quantitative
analysis of these spectra focusses on the emission bands linked to polycyclic
aromatic hydrocarbons (PAHs), the amorphous 10 micron silicate band and the
crystalline silicate band at 11.3 micron. We have detected PAH emission in 57%
of the Herbig stars in our sample. Clear examples of differences in the PAH
spectra are present within our sample, indicating differences in PAH size,
chemistry and/or ionization. Amorphous silicate emission was detected in the
spectra of 52% of the sample stars, amorphous silicate absorption in 13%. We
have detected crystalline silicate emission in 11 stars (24% of our sample), of
which four (9%) also display strong PAH emission. We have classified the sample
sources according to the strength of their mid-IR energy distribution. The
systems with stronger mid-infared (20-100 um) excesses relative to their
near-infrared (1-5 um) excess display significantly more PAH emission than
those with weaker mid-infrared excesses. This provides strong observational
support for the disk models by Dullemond (2002), in which systems with a
flaring disk geometry display a strong mid-infrared excess, whereas those with
disks that are strongly shadowed by the puffed-up inner rim of the disk only
display modest amounts of mid-infrared emission. The PAH emission is expected
to be produced mainly in the part of the disk atmosphere that is directly
exposed to radiation from the central star. In this model, self-shadowed disks
should display weaker PAH emission than flared disks, consistent with our
observations.Comment: 27 pages, 26 figures, A&A accepted (22/06/2004
The circumstellar envelope of the C-rich post-AGB star HD 56126
We present a detailed study of the circumstellar envelope of the
post-asymptotic giant branch ``21 micron object'' HD 56126. We build a detailed
dust radiative transfer model of the circumstellar envelope in order to derive
the dust composition and mass, and the mass-loss history of the star. To model
the emission of the dust we use amorphous carbon, hydrogenated amorphous
carbon, magnesium sulfide and titanium carbide. We present a detailed
parametrisation of the optical properties of hydrogenated amorphous carbon as a
function of H/C content. The mid-infrared imaging and spectroscopy is best
reproduced by a single dust shell from 1.2 to 2.6 arcsec radius around the
central star. This shell originates from a short period during which the
mass-loss rate exceeded 10^(-4) M_sun/yr. We find that the strength of the
``21'' micron feature poses a problem for the TiC identification. The low
abundance of Ti requires very high absorption cross-sections in the ultraviolet
and visible wavelength range to explain the strength of the feature. Other
nano-crystalline metal carbides should be considered as well. We find that
hydrogenated amorphous carbon in radiative equilibrium with the local radiation
field does not reach a high enough temperature to explain the strength of the
3.3-3.4 and 6-9 micron hydrocarbon features relative to the 11-17 micron
hydrocarbon features. We propose that the carriers of these hydrocarbon
features are not in radiative equilibrium but are transiently heated to high
temperature. We find that 2 per cent of the dust mass is required to explain
the strength of the ``30'' micron feature, which fits well within the measured
atmospheric abundance of Mg and S. This further strengthens the MgS
identification of the ``30'' micron feature.Comment: 20 Pages, 10 Figures, accepted for publication in Astronomy and
Astrophysic
The carrier of the "30" micron emission feature in evolved stars. A simple model using magnesium sulfide
We present 2-45 micron spectra of a large sample of carbon-rich evolved stars
in order to study the ``30'' micron feature. We find the ``30'' micron feature
in sources in a wide range of sources: low mass loss carbon stars, extreme
carbon-stars, post-AGB objects and planetary nebulae. We extract the profiles
from the sources by using a simple systematic approach to model the continuum.
We find large variations in the wavelength and width of the extracted profiles
of the ``30'' micron feature. We modelled the whole range of profiles in a
simple way by using magnesium sulfide (MgS) dust grains with a MgS grain
temperature different from the continuum temperature. The systematic change in
peak positions can be explained by cooling of MgS grains as the star evolves
off the AGB. In several sources we find that a residual emission excess at ~26
micron can also be fitted using MgS grains but with a different grains shape
distribution. The profiles of the ``30'' micron feature in planetary nebulae
are narrower than our simple MgS model predicts. We discuss the possible
reasons for this difference. We find a sample of warm carbon-stars with very
cold MgS grains. We discuss possible causes for this phenomenon. We find no
evidence for rapid destruction of MgS during the planetary nebula phase and
conclude that the MgS may survive to be incorporated in the ISM.Comment: 31 pages, accepted for publication in Astronomy and Astrophysics.
Full resolution version can be obtained by contacting [email protected]
Benzodiazépines dans le dernier mois de la grossesse: attention au nouveau-né.
Case ReportsJournal Articleinfo:eu-repo/semantics/publishe
Photoluminescence of silicon nanocrystallites: an astrophysical application
International audiencePhotoluminescence (PL) measurements of size-selected silicon clusters thin films generated by laser pyrolysis of SiH4 in a flow reactor and deposited at low energy after a mechanical velocity selection are presented. Several parameters have been investigated such as the mean size of the clusters, (in the range âŒ3â5 nm) and the dispersion of their size distribution. Particular attention has been paid to the determination of the absolute value of the PL efficiency. Measurements show that such silicon nanocrystallites demonstrate high external PL efficiency (up to 12%) and strong dependence of the PL properties on the cluster size. Results have been applied to the physical and chemical interpretation of spectroscopic observations in many astronomical objects, of a broad, red emission band. This so called extended red emission (ERE) is attributed to the PL of an interstellar dust grain component when excited by the UV radiation emitted by a nearby star. Hence it has been shown that nanometer-size crystals of pure silicon are the best candidate materials as regard PL efficiency, peak wavelength and bandwidth. This demonstrates that size effects in interstellar grains play a dominant role in the understanding of this astrophysical phenomenon
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