955 research outputs found
The coupled chemistry-climate model LMDz-REPROBUS: description and evaluation of a transient simulation of the period 1980–1999
We present a description and evaluation of the Chemistry-Climate Model (CCM) LMDz-REPROBUS, which couples interactively the extended version of the Laboratoire de MĂ©tĂ©orologie Dynamique General Circulation Model (LMDz GCM) and the stratospheric chemistry module of the REactive Processes Ruling the Ozone BUdget in the Stratosphere (REPROBUS) model. The transient simulation evaluated here covers the period 1980–1999. The introduction of an interactive stratospheric chemistry module improves the model dynamical climatology, with a substantial reduction of the temperature biases in the lower tropical stratosphere. However, at high latitudes in the Southern Hemisphere, a negative temperature bias, that is already present in the GCM version, albeit with a smaller magnitude, leads to an overestimation of the ozone depletion and its vertical extent in the CCM. This in turn contributes to maintain low polar temperatures in the vortex, delay the break-up of the vortex and the recovery of polar ozone. The latitudinal and vertical variation of the mean age of air compares favourable with estimates derived from long-lived species measurements, though the model mean age of air is 1–3 years too young in the middle stratosphere. The model also reproduces the observed "tape recorder" in tropical total hydrogen (=H<sub>2</sub>O+2×CH<sub>4</sub>), but its propagation is about 30% too fast and its signal fades away slightly too quickly. The analysis of the global distributions of CH<sub>4</sub> and N<sub>2</sub>O suggests that the subtropical transport barriers are correctly represented in the simulation. LMDz-REPROBUS also reproduces fairly well most of the spatial and seasonal variations of the stratospheric chemical species, in particular ozone. However, because of the Antarctic cold bias, large discrepancies are found for most species at high latitudes in the Southern Hemisphere during the spring and early summer. In the Northern Hemisphere, polar ozone depletion and its variability are underestimated in the simulation
Propagation of chaos for rank-based interacting diffusions and long time behaviour of a scalar quasilinear parabolic equation
We study a quasilinear parabolic Cauchy problem with a cumulative
distribution function on the real line as an initial condition. We call
'probabilistic solution' a weak solution which remains a cumulative
distribution function at all times. We prove the uniqueness of such a solution
and we deduce the existence from a propagation of chaos result on a system of
scalar diffusion processes, the interactions of which only depend on their
ranking. We then investigate the long time behaviour of the solution. Using a
probabilistic argument and under weak assumptions, we show that the flow of the
Wasserstein distance between two solutions is contractive. Under more stringent
conditions ensuring the regularity of the probabilistic solutions, we finally
derive an explicit formula for the time derivative of the flow and we deduce
the convergence of solutions to equilibrium.Comment: Stochastic partial differential equations: analysis and computations
(2013) http://dx.doi.org/10.1007/s40072-013-0014-
Identification of a nearby stellar association in the Hipparcos catalog: implications for recent, local star formation
The TW Hydrae Association (~55 pc from Earth) is the nearest known region of
recent star formation. Based primarily on the Hipparcos catalog, we have now
identified a group of 9 or 10 co-moving star systems at a common distance (~45
pc) from Earth that appear to comprise another, somewhat older, association
(``the Tucanae Association''). Together with ages and motions recently
determined for some nearby field stars, the existence of the Tucanae and TW
Hydrae Associations suggests that the Sun is now close to a region that was the
site of substantial star formation only 10-40 million years ago. The TW Hydrae
Association represents a final chapter in the local star formation history.Comment: 5 pages incl figs and table
Meso-macro numerical approach to macroscopic permeability of fractured concrete â COMPLAS XI
In this paper, a sequential multi-scale framework to solve mass (air or water) transfer problems is described. Numerical results are checked against mechanical and permeation experimental datas from a reinforced concrete specimen under tensile load designed by C. Desmettre and J.P. Charron [2
Detection and period measurements of GX1+4 at hard x ray energies with the SIGMA telescope
The galactic Low Mass X ray Binary GX1+4 was detected by the coded aperture hard X ray gamma ray SIGMA telescope during the Feb. to April 1991 observations of the galactic center regions. The source, whose emission varied during the survey of a factor greater than 40 pct., reached a maximum luminosity in the 40 to 140 energy range of 1.03 x 10(exp 37) erg/s (D = 8.5 kpc), thus approaching the emission level of the 1970 to 1980 high state. Two minute flux pulsations were detected on Mar. 22 and on Mar. 31 and Apr. 1. Comparison with the last period measurements shows that the current spin-down phase of GX1+4 is ending. Concerning the proposed association of this source with the galactic center 511 keV annihilation emission, upper limits were derived
Spatial Separation of the 3.29 micron Emission Feature and Associated 2 micron Continuum in NGC 7023
We present a new 0.9" resolution 3.29 micron narrowband image of the
reflection nebula NGC 7023. We find that the 3.29 micron IEF in NGC 7023 is
brightest in narrow filaments NW of the illuminating star. These filaments have
been seen in images of K', molecular hydrogen emission lines, the 6.2 and 11.3
micron IEFs, and HCO+. We also detect 3.29 micron emission faintly but
distinctly between the filaments and the star. The 3.29 micron image is in
contrast to narrowband images at 2.09, 2.14, and 2.18 micron, which show an
extended emission peak midway between the filaments and the star, and much
fainter emission near the filaments. The [2.18]-[3.29] color shows a wide
variation, ranging from 3.4-3.6 mag at the 2 micron continuum peak to 5.5 mag
in the filaments. We observe [2.18]-[3.29] to increase smoothly with increasing
distance from the star, up until the filament, suggesting that the main
difference between the spatial distributions of the 2 micron continuum and the
the 3.29 micron emission is related to the incident stellar flux. Our result
suggests that the 3.29 micron IEF carriers are likely to be distinct from, but
related to, the 2 micron continuum emitters. Our finding also imply that, in
NGC 7023, the 2 micron continuum emitters are mainly associated with HI, while
the 3.29 micron IEF carriers are primarily found in warm molecular hydrogen,
but that both can survive in HI or molecular hydrogen. (abridged)Comment: to appear in ApJ, including 1 table and 8 figures, high resolution
figures available at http://www.ast.cam.ac.uk/~jin/n7023
Evaluation of knowledge level of adolescents and adults with congenital heart disease: Effectiveness of a structured CHD education program in adolescents
BackgroundAdolescents with congenital heart disease (CHD) constitute a growing population of individuals for whom a well-planned and well-executed âtransition processâ is essential. Transition program should include education about medical conditions and promote skills in decision-making and self-care. To improve their level of health related knowledge, a structured education program was implemented in a transition CHD program. This study aimed 1/to evaluate level of knowledge of adolescents who received structured CHD education as compared to adults who did not, 2/to evaluate whether patients who received structured education improve their knowledge.Methods and results42 adolescents (16±2years old, 21 girls) were included in a structured CHD education program and were compared to 22 adults (33±7, 6 women) with CHD who have never followed education program. Knowledge in adolescents was assessed before and after the educational program using questionnaire exploring specific issues related to CHD. A same questionnaire was used in non-educated adult patients. The mean total knowledge score in the educated adolescent group was significantly higher as compared to the non-educated adult with CHD (score=15.6/20±3.6 vs. 12.5±4.5, P<0.01). Provision of structured CHD education and female sex were determinant of higher levels of knowledge. A significant improvement of knowledge was observed in adolescents group after CHD education program (range of increase was 23 to 44%). This result was not influenced by age, sex, education level, socio-economic status of parents and disease complexity, and persists at 10months mean follow-up.ConclusionA structured education program was associated with a higher level of knowledge, above all in male CHD patients. Education at transition period has a significant impact on the adolescent knowledge. Structured education program should improve adult CHD understanding of their heart condition, and could prevent potential complications
3-200 keV spectral states and variability of the INTEGRAL Black Hole binary IGR J17464-3213
On March 2003, IBIS, the gamma-ray imager on board the INTEGRAL satellite,
detected an outburst from a new source, IGR J17464-3213, that turned out to be
a HEAO-1 transient, H1743-322. In this paper we report on the high energy
behaviour of this BHC studied with the three main instruments onboard INTEGRAL.
The data, collected with unprecedented sensitivity in the hard X-Ray range,
show a quite hard Comptonised emission from 3 keV up to 150 keV during the
rising part of the source outburst, with no thermal emission detectable. A few
days later, a prominent soft disk multicolour component appears, with the hard
tail luminosity almost unchanged: 10-9 erg*cm-2*s-1. Two months later, during a
second monitoring campaign near the end of the outburst, the observed disk
component was unchanged. Conversely, the Comptonised emission from the
central-hot part of the disk reduced by a factor of 10. We present here its
long term behaviour in different energy ranges and the combined JEM-X, SPI and
IBIS wide band spectral evolution of this source.Comment: 12 pages, 4 figures, accepted for pubblication in AP
Incidence and survival of remnant disks around main-sequence stars
We present photometric ISO 60 and 170um measurements, complemented by some
IRAS data at 60um, of a sample of 84 nearby main-sequence stars of spectral
class A, F, G and K in order to determine the incidence of dust disks around
such main-sequence stars. Of the stars younger than 400 Myr one in two has a
disk; for the older stars this is true for only one in ten. We conclude that
most stars arrive on the main sequence surrounded by a disk; this disk then
decays in about 400 Myr. Because (i) the dust particles disappear and must be
replenished on a much shorter time scale and (ii) the collision of
planetesimals is a good source of new dust, we suggest that the rapid decay of
the disks is caused by the destruction and escape of planetesimals. We suggest
that the dissipation of the disk is related to the heavy bombardment phase in
our Solar System. Whether all stars arrive on the main sequence surrounded by a
disk cannot be established: some very young stars do not have a disk. And not
all stars destroy their disk in a similar way: some stars as old as the Sun
still have significant disks.Comment: 16 pages, 9 figures, Astron & Astrophys. in pres
- âŠ