2,289 research outputs found
Three dimensional maps of the Magellanic Clouds using RR Lyrae Stars and Cepheids II. The Small Magellanic Cloud
We use data on variable stars from the Optical Gravitational Lensing
Experiment (OGLE III) survey to determine the three-dimensional structure of
the Small Magellanic Cloud (SMC). Deriving individual distances to RR Lyrae
stars and Cepheids we investigate the distribution of these tracers of the old
and young population in the SMC. Photometrically estimated metallicities are
used to determine the distances to 1494 RR Lyrae stars, which have typical ages
greater than 9 Gyr. For 2522 Cepheids, with ages of a few tens to a few hundred
Myr, distances are calculated using their period-luminosity relation.
Individual reddening estimates from the intrinsic color of each star are used
to obtain high precision three-dimensional maps. The distances of RR Lyrae
stars and Cepheids are in very good agreement with each other. The median
distance of the RR Lyrae stars is found to be 61.5 +/- 3.4 kpc. For the
Cepheids a median distance of 63.1 +/- 3.0 kpc is obtained. Both populations
show an extended scale height, with 2.0 +/- 0.4 kpc for the RR Lyrae stars and
2.7 +/- 0.3 kpc for the Cepheids. This confirms the large depth of the SMC
suggested by a number of earlier studies. The young population is very
differently oriented than the old stars. While we find an inclination angle of
7{\deg} +/- 15{\deg} and a position angle of 83{\deg} +/- 21{\deg} for the RR
Lyrae stars, for the Cepheids an inclination of 74{\deg} +/- 9{\deg} and a
position angle of 66{\deg} +/- 15{\deg} is obtained. The RR Lyrae stars show a
fairly homogeneous distribution, while the Cepheids follow roughly the
distribution of the bar with their northeastern part being closer to us than
the southwestern part of the bar. Interactions between the SMC, LMC, and Milky
Way are presumably responsible for the tilted, elongated structure of the young
population of the SMC.Comment: 13 pages, 6 figures, 4 tables, published in A
MyGIsFOS: an automated code for parameter determination and detailed abundance analysis in cool stars
The current and planned high-resolution, high-multiplexity stellar
spectroscopic surveys, as well as the swelling amount of under-utilized data
present in public archives have led to an increasing number of efforts to
automate the crucial but slow process to retrieve stellar parameters and
chemical abundances from spectra. We present MyGIsFOS, a code designed to
derive atmospheric parameters and detailed stellar abundances from medium -
high resolution spectra of cool (FGK) stars. We describe the general structure
and workings of the code, present analyses of a number of well studied stars
representative of the parameter space MyGIsFOS is designed to cover, and
examples of the exploitation of MyGIsFOS very fast analysis to assess
uncertainties through Montecarlo tests. MyGIsFOS aims to reproduce a
``traditional'' manual analysis by fitting spectral features for different
elements against a precomputed grid of synthetic spectra. Fe I and Fe II lines
can be employed to determine temperature, gravity, microturbulence, and
metallicity by iteratively minimizing the dependence of Fe I abundance from
line lower energy and equivalent width, and imposing Fe I - Fe II ionization
equilibrium. Once parameters are retrieved, detailed chemical abundances are
measured from lines of other elements. MyGIsFOS replicates closely the results
obtained in similar analyses on a set of well known stars. It is also quite
fast, performing a full parameter determination and detailed abundance analysis
in about two minutes per star on a mainstream desktop computer. Currently, its
preferred field of application are high-resolution and/or large spectral
coverage data (e.g UVES, X-Shooter, HARPS, Sophie).Comment: 15 pages, 14 figures, accepted for publication by A&
Surgery for Malignant Brain Gliomas: Fluorescence-Guided Resection or Functional-Based Resection?
Gliomes de bas grade et plasticité cérébrale : Implications fondamentales et cliniques
La plasticité cérébrale post-lésionnelle (PCPL) décrit l’ensemble des processus permettant au système nerveux central de se réorganiser après une atteinte physique. Depuis l’influent travail de Broca et la prise de pouvoir des modèles « localisationnistes », il est largement admis que la PCPL est limitée, voire impossible, au sein des aires fonctionnelles majeures, dites éloquentes. Pourtant, depuis quelques années, de nouvelles données issues de la chirurgie des gliomes infiltrants de bas-grade (GIBG) sont venues bousculer ce dogme. Il apparaît en effet de plus en plus clairement que des excisions cérébrales massives peuvent être intégralement compensées, pour ne laisser place à aucun déficit fonctionnel détectable. Des techniques d’imagerie pré- et post-chirurgicales, ainsi que des procédures de stimulation peropératoire, permettent de suivre la nature et la cinétique de ces compensations. Celles-ci débutent avant la chirurgie, en réaction à l’invasion tumorale, et se consolident pendant et après la procédure opératoire. Les mécanismes de la compensation pré- et post-lésionnelle impliquent les aires périlésionnelles, les structures cérébrales ipsilatérales distantes et les homologues controlatéraux des zones réséquées. De tels résultats ont d’évidentes implications fondamentales et cliniques, et ouvrent d’importantes perspectives pour la compréhension de la dynamique cérébrale et des phénomènes de plasticité.Post-lesional plasticity (PLP) describes the processes that reorganize cerebral connections after an injury. Since Broca’s influential contribution and the common endorsement of “localisationist” models of brain physiology, it has been widely admitted that PLP was limited, not to say impossible in the so-called “eloquent areas”. However, recent observations associated with the surgical treatments of low grade gliomas have called this dogma into question. Indeed, more and more evidence suggest that large cerebral resections can be compensated so efficiently that no functional deficits can be detected after the surgery. Pre and post surgical investigations based on imaging techniques, as well as intra-surgical investigations involving electrical stimulations, allow to track the nature and the temporal characteristics of these compensations. Compensatory reactions begin before the operation, in response to the tumoral growth. They remain active during and after the surgery. These compensations can involve the perilesional adjacent areas, the distant ipsilateral cerebral structures and the homologous contra-lateral regions. When considered together these results have obvious fundamental and clinical implications. They open new perspectives for understanding cerebral dynamics and the process of brain plasticity
Tribological study of a press-fit assembling process
International audienceA particular case of press-fitting of two metal parts is studied, with high fit interference inducing high contact pressures and plastic deformation of the bushing and collar. Furthermore, the female piece is polymer-coated by cataphoresis, and the coating evolution by damage and wear during sliding promotes significant changes of friction with sliding length. These particular frictional properties impact the structural mechanics behaviour of the system during assembling
Etude expérimentale et modélisation de l'évolution couplée du frottement et de l'usure dans un contact entre une surface métallique et un revêtement polymère
International audienceDans une jonction statique, le frottement a la particularité de devoir atteindre un fort niveau en fin d'assemblage, car il représente la majeure partie de la force de résistance de la jonction en service. Ce niveau de frottement est conféré par le procédé d'assemblage. Nous nous intéressons ici aux relations entre frottement et usure pour un assemblage polymère - métal caractérisé par un contact sous haute pression (localement, plus de 500 MPa), mais à basse vitesse (quelques mm.s-1) et avec une faible longueur de glissement (inférieure à 10 mm). Pour simuler ce contact, des essais tribologiques en régime linéaire alternatif ont été mis au point, dans lequel ont été utilisés des objets les plus proche possible des pièces réelles. Le polymère est celui qui reste en contact permanent, le métal voyant, lui, défiler la zone de contact. Le frottement augmente fortement au début de l'essai, puis se stabilise. En observant les surfaces en microscopie optique et électronique, on montre qu'une forte usure du polymère se produit, et que les particules d'usure se déposent pour une grande part dans la rugosité de la surface métallique. Des essais complémentaires montrent que ce piégeage de particules d'usure est la cause principale de l'augmentation du frottement. Un paramètre essentiel est la rugosité du métal, dont l'usure et la croissance du frottement sont fonctions croissantes. La croissance du frottement est modélisée sur la base du concept de troisième corps et d'un bilan de la circulation des particules d'usure. La comparaison aux courbes expérimentales de frottement montre la pertinence de ce modèle
Halo Velocity Groups in the Pisces Overdensity
We report spectroscopic observations with the Gemini South Telescope of 5
faint V~20 RR Lyrae stars associated with the Pisces overdensity. At a
heliocentric and galactocentric distance of ~80 kpc, this is the most distant
substructure in the Galactic halo known to date. We combined our observations
with literature data and confirmed that the substructure is composed of two
different kinematic groups. The main group contains 8 stars and has =
50 km/s, while the second group contains four stars at a velocity of
= -52 km/s, where V_{gsr} is the radial velocity in the galactocentric standard
of rest. The metallicity distribution of RR Lyrae stars in the Pisces
overdensity is centered on [Fe/H]=-1.5 dex and has a width of 0.3 dex. The new
data allowed us to establish that both groups are spatially extended making it
very unlikely that they are bound systems, and are more likely to be debris of
a tidally disrupted galaxy or galaxies. Due to small sky coverage, it is still
unclear whether these groups have the same or different progenitors.Comment: 21 pages, 5 figures, 3 tables, accepted to Astrophysical Journa
Modulation of interferon-[alpha] secretion by activated platelets in systemic lupus erythematosus.
Type I interferons play a key role in systemic lupus erythematosus (SLE) pathogenesis as an "IFN signature" is found in the majority of patients with active SLE. Immune complexes are internalized by plasmacytoid dendritic cells (DC) via Fc-[gamma] ReceptorIIA, reach the endosomal compartment and activate IFN-[alpha] secretion through TLR7/9-dependent pathways. Naturally occurring differences in expression of the TLR7/9 gene as well as factors that modulate TLR7/9 expression, including CD154 could therefore contribute to SLE pathogenesis. Although its origin is not elucidated CD154 is hyperexpressed in SLE patients, and is important for the differentiation of autoantibody-secreting cells. We hypothesized that platelets which are an abundant source of CD154, and which can mediate proinflammatory effects could be an actor involved in SLE pathogenesis. Platelets from SLE patients are activated _in vivo_ by circulating immune complexes which are abundant in SLE sera, via a CD32-dependent mechanism. Activated platelets formed aggregates with antigen-presenting cells in SLE patients and enhanced interferon-[alpha] secretion induced by immune-complexes stimulated plasmacytoid DCs. Finally, _in vivo_ depletion of platelets and megakaryocytes in NZBxNZW(F1) lupus prone mice improved all parameters assessing disease activity, whereas transfusion of activated platelets worsened the disease course. Altogether, these data identify platelets as a mediator of SLE pathogenesis and a new therapeutical target
- …