179 research outputs found
Atteinte pulmonaire sévère au cours de la neurofibromatose de type 1
Type 1 neurofibromatosis (NF1) is a hereditary disease inherited as an autosomal dominant. Respiratory involvement is rare. We report the case of a woman suffering from NF1 with mutation of the corresponding gene and with respiratory involvement combining diffuse parenchymatous lesions, severe precapillary pulmonary hypertension and an enlarging, spiculated pulmonary nodule, very suspicious of malignancy, though histological examination was not possible on account of the patient\u27s poor respiratory function. There was progressive deterioration of the patient\u27s respiratory condition, leading to death, despite the introduction of oral therapy combining a phosphodiesterase 5 inhibitor and an endothelin receptor antagonist. Our case illustrates the development of multiple severe respiratory pathologies in the setting of NF1. The specific contribution of the NF1 gene mutation in the pathophysiology of these different pulmonary manifestations needs to be examined in detail
Internal convection in thermoelectric generator models
Coupling between heat and electrical currents is at the heart of
thermoelectric processes. From a thermal viewpoint this may be seen as an
additional thermal flux linked to the appearance of electrical current in a
given thermoelectric system. Since this additional flux is associated to the
global displacement of charge carriers in the system, it can be qualified as
convective in opposition to the conductive part associated with both phonons
transport and heat transport by electrons under open circuit condition, as,
e.g., in the Wiedemann-Franz relation. In this article we demonstrate that
considering the convective part of the thermal flux allows both new insight
into the thermoelectric energy conversion and the derivation of the maximum
power condition for generators with realistic thermal coupling.Comment: 8 pages, 3 figure
Third Order Effect of Rotation on Stellar Oscillations of a -Cephei Star
Here the effect of rotation up to third order in the angular velocity of a
star on the p, f and g modes is investigated. To do this, the third-order
perturbation formalism presented by Soufi et al. (1998) and revised by Karami
(2008), was used. I quantify by numerical calculations the effect of rotation
on the oscillation frequencies of a uniformly rotating -Cephei star with
12 . For an equatorial velocity of 90 , it is found
that the second- and third-order corrections for , for instance,
are of order of 0.07% of the frequency for radial order and reaches up
to 0.6% for .Comment: 13 pages, 2 figures, 10 table
Rotation profiles of solar-like stars with magnetic fields
The aim of this work is to investigate rotation profile of solar-like stars
with magnetic fields. A diffusion coefficient of magnetic angular momentum
transport is deduced. Rotating stellar models with different mass are computed
under the effect of the coefficient. Then rotation profiles are obtained from
the theoretical stellar models. The total angular momentum of solar model with
only hydrodynamic instabilities is about 13 times larger than that of the Sun
at the age of the Sun, and this model can not reproduce quasi-solid rotation in
the radiative region. However, not only can the solar model with magnetic
fields reproduce an almost uniform rotation in the radiative region, but its
total angular momentum is consistent with helioseismic result at the level of 3
at the age of the Sun. The rotation of solar-like stars with magnetic
fields is almost uniform in the radiative region. But there is an obvious
transition region of angular velocity between the convective core and the
radiative region of models with 1.2 - 1.5 , where angular velocity
has a sharp radial change, which is different from the rotation profile of the
Sun and massive stars with magnetic fields. Moreover the changes of the angular
velocity in the transition region increase with the increasing in the age and
mass.Comment: Accepted for publication in ChjA
Seismic evidence for a rapidly rotating core in a lower-giant-branch star observed with Kepler
Rotation is expected to have an important influence on the structure and the
evolution of stars. However, the mechanisms of angular momentum transport in
stars remain theoretically uncertain and very complex to take into account in
stellar models. To achieve a better understanding of these processes, we
desperately need observational constraints on the internal rotation of stars,
which until very recently were restricted to the Sun. In this paper, we report
the detection of mixed modes - i.e. modes that behave both as g modes in the
core and as p modes in the envelope - in the spectrum of the early red giant
KIC7341231, which was observed during one year with the Kepler spacecraft. By
performing an analysis of the oscillation spectrum of the star, we show that
its non-radial modes are clearly split by stellar rotation and we are able to
determine precisely the rotational splittings of 18 modes. We then find a
stellar model that reproduces very well the observed atmospheric and seismic
properties of the star. We use this model to perform inversions of the internal
rotation profile of the star, which enables us to show that the core of the
star is rotating at least five times faster than the envelope. This will shed
new light on the processes of transport of angular momentum in stars. In
particular, this result can be used to place constraints on the angular
momentum coupling between the core and the envelope of early red giants, which
could help us discriminate between the theories that have been proposed over
the last decades.Comment: Accepted in ApJ, 39 pages, 16 figure
Solar-like oscillations in low-luminosity red giants: first results from Kepler
We have measured solar-like oscillations in red giants using time-series
photometry from the first 34 days of science operations of the Kepler Mission.
The light curves, obtained with 30-minute sampling, reveal clear oscillations
in a large sample of G and K giants, extending in luminosity from the red clump
down to the bottom of the giant branch. We confirm a strong correlation between
the large separation of the oscillations (Delta nu) and the frequency of
maximum power (nu_max). We focus on a sample of 50 low-luminosity stars (nu_max
> 100 muHz, L <~ 30 L_sun) having high signal-to-noise ratios and showing the
unambiguous signature of solar-like oscillations. These are H-shell-burning
stars, whose oscillations should be valuable for testing models of stellar
evolution and for constraining the star-formation rate in the local disk. We
use a new technique to compare stars on a single echelle diagram by scaling
their frequencies and find well-defined ridges corresponding to radial and
non-radial oscillations, including clear evidence for modes with angular degree
l=3. Measuring the small separation between l=0 and l=2 allows us to plot the
so-called C-D diagram of delta nu_02 versus Delta nu. The small separation
delta nu_01 of l=1 from the midpoint of adjacent l=0 modes is negative,
contrary to the Sun and solar-type stars. The ridge for l=1 is notably
broadened, which we attribute to mixed modes, confirming theoretical
predictions for low-luminosity giants. Overall, the results demonstrate the
tremendous potential of Kepler data for asteroseismology of red giants.Comment: accepted by ApJ Letters, to appear in special Kepler issue. Updated
reference
Seismic constraints on the radial dependence of the internal rotation profiles of six Kepler subgiants and young red giants
Context : We still do not know which mechanisms are responsible for the
transport of angular momentum inside stars. The recent detection of mixed modes
that contain the signature of rotation in the spectra of Kepler subgiants and
red giants gives us the opportunity to make progress on this issue.
Aims: Our aim is to probe the radial dependance of the rotation profiles for
a sample of Kepler targets. For this purpose, subgiants and early red giants
are particularly interesting targets because their rotational splittings are
more sensitive to the rotation outside the deeper core than is the case for
their more evolved counterparts.
Methods: We first extract the rotational splittings and frequencies of the
modes for six young Kepler red giants. We then perform a seismic modeling of
these stars using the evolutionary codes CESAM2k and ASTEC. By using the
observed splittings and the rotational kernels of the optimal models, we
perform inversions of the internal rotation profiles of the six stars.
Results: We obtain estimates of the mean rotation rate in the core and in the
convective envelope of these stars. We show that the rotation contrast between
the core and the envelope increases during the subgiant branch. Our results
also suggest that the core of subgiants spins up with time, contrary to the RGB
stars whose core has been shown to spin down. For two of the stars, we show
that a discontinuous rotation profile with a deep discontinuity reproduces the
observed splittings significantly better than a smooth rotation profile.
Interestingly, the depths that are found most probable for the discontinuities
roughly coincide with the location of the H-burning shell, which separates the
layers that contract from those that expand. These results will bring
observational constraints to the scenarios of angular momentum transport in
stars.Comment: Accepted in A&A, 27 pages, 18 figure
Segregation and ordering at the (1×2) reconstructed Pt80Fe20(110) surface determined by low-energy electron diffraction
The surface of an ordered Pt80Fe20(110) crystal exhibits (1×2) and (1×3) reconstructions depending on the annealing treatment after ion bombardment. The (1×3) structure occurs after annealing in the range 750 to 900 K. Annealing above 1000 K leads to the (1×2) structure, which is, from the present result, unambiguously attributed to the same geometrical reconstruction as Pt(110) but with smaller relaxation amplitudes: a detailed low-energy electron-diffraction analysis concludes to a missing-row structure with row pairing in layers 2 and 4 accompanied by a buckling in layers 3 and 5. The top layer spacing is contracted by 13%, and further relaxations are detectable down to the fifth layer. The specific diffraction spots associated with the bulk chemical ordering along the dense [1¯10] rows are very weak: The I(V) analysis shows that this chemical ordering is absent in the outermost ‘‘visible’’ rows but gradually recovers over five to six layers deep. General Pt enrichment is found in the surface ‘‘visible’’ rows (in layers 1–3), but segregation and order yield a subtle redistribution of Pt and Fe atoms in deeper rows: For example, in layer 2, the visible row is Pt rich, whereas the other row (buried under layer 1) is enriched with Fe. Because of the many parameters considered, a fit procedure was applied to a large data basis to solve the structure; the results were confirmed and illustrated subsequently by a standard I(V) analysis for the most relevant parameters. The final r factors are RDE=0.36, RP=0.34, and RZJ=0.14 for two beam sets at normal and oblique incidence consisting of 26 and 21 beams, respectively
Mixed modes in red giants: a window on stellar evolution
The detection of oscillations with a mixed character in subgiants and red
giants allows us to probe the physical conditions in their cores. With these
mixed modes, we aim at determining seismic markers of stellar evolution. Kepler
asteroseismic data were selected to map various evolutionary stages and stellar
masses. Seismic evolutionary tracks were then drawn with the combination of the
frequency and period spacings. We measured the asymptotic period spacing for
more than 1170 stars at various evolutionary stages. This allows us to monitor
stellar evolution from the main sequence to the asymptotic giant branch and
draw seismic evolutionary tracks. We present clear quantified asteroseismic
definitions that characterize the change in the evolutionary stages, in
particular the transition from the subgiant stage to the early red giant
branch, and the end of the horizontal branch.The seismic information is so
precise that clear conclusions can be drawn independently of evolution models.
The quantitative seismic information can now be used for stellar modeling,
especially for studying the energy transport in the helium-burning core or for
specifying the inner properties of stars entering the red or asymptotic giant
branches. Modeling will also allow us to study stars that are identified to be
in the helium-subflash stage, high-mass stars either arriving or quitting the
secondary clump, or stars that could be in the blue-loop stage.Comment: Accepted In A&A (Letter) 5 page
New grids of ATLAS9 atmospheres I: Influence of convection treatments on model structure and on observable quantities
We present several new sets of grids of model stellar atmospheres computed
with modified versions of the ATLAS9 code. Each individual set consists of
several grids of models with different metallicities ranging from [M/H] = -2.0
to +1.0 dex. The grids range from 4000 to 10000 K in T_eff and from 2.0 to 5.0
dex in logg. The individual sets differ from each other and from previous ones
essentially in the physics used for the treatment of the convective energy
transport, in the higher vertical resolution of the atmospheres and in a finer
grid in the (T_eff, logg) plane. These improvements enable the computation of
derivatives of color indices accurate enough for pulsation mode identification.
In addition, we show that the chosen vertical resolution is necessary and
sufficient for the purpose of stellar interior modelling. To explain the
physical differences between the model grids we provide a description of the
currently available modifications of ATLAS9 according to their treatment of
convection. Our critical analysis of the dependence of the atmospheric
structure and observable quantities on convection treatment, vertical
resolution and metallicity reveals that spectroscopic and photometric
observations are best represented when using an inefficient convection
treatment. This conclusion holds whatever convection formulation investigated
here is used, i.e. MLT(alpha=0.5), CM and CGM are equivalent. We also find that
changing the convection treatment can lead to a change in the effective
temperature estimated from Stroemgren color indices from 200 to 400 K.Comment: 20 pages, 10 figures, accepted by A&
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