166 research outputs found
Association of severe myoclonic epilepsy of infancy (SMEI) with probable autoimmune lymphoproliferative syndrome-variant
The paper reported on a case of severe myoclonic epilepsy of infancy (SMEI) associated with a probable autoimmune lymphoproliferative syndrome variant (Dianzani autoimmune lymphoproliferative disease) (DALD). A male patient with typical features of SMEI and a SCN1A gene variant presented in the first year of life with multiple lymph nodes, palpable liver at 2 cm from the costal margin, neutropenia, dysgammaglobulinemia, relative and sometimes absolute lymphocytosis. Subsequently the patient presented with constantly raised IgA in serum and positive antinuclear and thyroid antimicrosomal antibodies. The diagnosis of probable autoimmune lymphoproliferative syndrome was made; arthritis, skin and throat blisters, which appeared subsequently led to the diagnosis of linear IgA disease. On the basis of these unique associations, the Authors hypothesized that autoimmunity may be partly responsible of the severe epileptic symptomatology, perhaps mediated by autoantibodies against sodium channels or by accompanying cytotoxic T-lymphocytes. Corticosteroid treatment ameliorated the epilepsy and laboratory tests. Future studies will be necessary to evaluate the relevance of autoimmunity in SMEI
Pioneer 10 data analysis: Investigation on periodic anomalies
International audienceThe Pioneer Anomaly refers to the difference between the expected theoretical tra jectory of the Pioneer 10 and 11 spacecrafts and the observed tra jectory through Doppler measurements. It has been interpreted by the Jet Propulsion Laboratory (JPL) as a constant anomalous acceleration (Anderson et al. 2002). For this analysis, the Groupe Anomalie Pioneer (GAP) composed of several french laboratories has developped a specific tra jectography software, ODYSSEY, which enables to test different anomaly models. The paper will present, after a brief description of the software and the implemented models, the last results obtained: in addition to the constant anomaly, time dependent signatures of the anomaly have been noticed which can be described geometrically. The fit of the Pioneer 10 data with these new models yields a reduction of the standard deviation of the residual by a factor 2 with respect to the simple constant anomaly
A first analysis of the mean motion of CHAMP
The present study consists in studying the mean orbital motion of the CHAMP satellite, through a single long arc on a period of time of 200 days in 2001. We actually investigate the sensibility of its mean motion to its accelerometric data, as measures of the surface forces, over that period. In order to accurately determine the mean motion of CHAMP, we use “observed" mean orbital elements computed, by filtering, from 1-day GPS orbits. On the other hand, we use a semi-analytical model to compute the arc. It consists in numerically integrating the effects of the mean potentials (due to the Earth and the Moon and Sun), and the effects of mean surfaces forces acting on the satellite. These later are, in case of CHAMP, provided by an averaging of the Gauss system of equations. Results of the fit of the long arc give a relative sensibility of about 10<sup>-3</sup>, although our gravitational mean model is not well suited to describe very low altitude orbits. This technique, which is purely dynamical, enables us to control the decreasing of the trajectory altitude, as a possibility to validate accelerometric data on a long term basis.<br><br><b>Key words.</b> Mean orbital motion, accelerometric dat
Constraints on gravity: An evidence against the covariant resolution of the Pioneer anomaly
We consider corrections in the form of to the
Einstein-Hilbert Lagrangian. Then we compute the corrections to the
Schwarszchild geometry due to the inclusion of this general term to the
Lagrangian. We show that
gives rise to a constant anomalous acceleration for objects orbiting the Sun
onward the Sun. This leads to the conclusion that would have covariantly
resolved the Pioneer anomaly if this value of had not
contradicted other observations.
We notice that the experimental bounds on grows stronger in case
we examine the deformation of the space-time geometry around objects lighter
than the Sun. We therefore use the high precision measurements around the Earth
(LAGEOS and LLR) and obtain a very strong constraint on the corrections in the
form of and in particular . This bound requires
.
Therefore it refutes the covariant resolution of the Pioneer anomaly.Comment: ...v5: references added, new discussions adde
Grown-up stars physics with MATISSE
MATISSE represents a great opportunity to image the environment around
massive and evolved stars. This will allow one to put constraints on the
circumstellar structure, on the mass ejection of dust and its reorganization ,
and on the dust-nature and formation processes. MATISSE measurements will often
be pivotal for the understanding of large multiwavelength datasets on the same
targets collected through many high-angular resolution facilities at ESO like
sub-millimeter interferometry (ALMA), near-infrared adaptive optics (NACO,
SPHERE), interferometry (PIONIER, GRAVITY), spectroscopy (CRIRES), and
mid-infrared imaging (VISIR). Among main sequence and evolved stars, several
cases of interest have been identified that we describe in this paper.Comment: SPIE, Jun 2016, Edimbourgh, Franc
Squared visibility estimator. Calibrating biases to reach very high dynamic range
In the near infrared where detectors are limited by read-out noise, most
interferometers have been operated in wide band in order to benefit from larger
photon rates. We analyze in this paper the biases caused by instrumental and
turbulent effects to estimators for both narrow and wide band cases.
Visibilities are estimated from samples of the interferogram using two
different estimators, which is the classical sum of the squared
modulus of Fourier components and a new estimator for which complex
Fourier components are summed prior to taking the square. We present an
approach for systematically evaluating the performance and limits of each
estimator, and to optimizing observing parameters for each. We include the
effects of spectral bandwidth, chromatic dispersion, scan length, and
differential piston. We also establish the expression of the Signal-to-Noise
Ratio of the two estimators with respect to detector and photon noise. The
estimator is insensitive to dispersion and is always more sensitive
than the estimator. However, the latter allows to reach better
accuracies when detection is differential piston noise limited. Biases and
noise directly impact the dynamic range of reconstructed images. Very high
dynamic ranges are required for direct exoplanet detection by interferometric
techniques thus requiring estimators to be bias-free or biases to be accurately
calibrated. We discuss which estimator and which conditions are optimum for
astronomical applications especially when high accuracy visibilities are
required. We show that there is no theoretical limit to measuring visibilities
with accuracies as good as which is important in the prospect of
detecting faint exoplanets with interferometers.Comment: 23 pages, 6 figures, accepted for publication in Ap
Spectral and spatial imaging of the Be+sdO binary phi Persei
The rapidly rotating Be star phi Persei was spun up by mass and angular
momentum transfer from a now stripped-down, hot subdwarf companion. Here we
present the first high angular resolution images of phi Persei made possible by
new capabilities in longbaseline interferometry at near-IR and visible
wavelengths. We observed phi Persei with the MIRC and VEGA instruments of the
CHARA Array. Additional MIRC-only observations were performed to track the
orbital motion of the companion, and these were fit together with new and
existing radial velocity measurements of both stars to derive the complete
orbital elements and distance. The hot subdwarf companion is clearly detected
in the near-IR data at each epoch of observation with a flux contribution of
1.5% in the H band, and restricted fits indicate that its flux contribution
rises to 3.3% in the visible. A new binary orbital solution is determined by
combining the astrometric and radial velocity measurements. The derived stellar
masses are 9.6+-0.3Msol and 1.2+-0.2Msol for the Be primary and subdwarf
secondary, respectively. The inferred distance (186 +- 3 pc), kinematical
properties, and evolutionary state are consistent with membership of phi Persei
in the alpha Per cluster. From the cluster age we deduce significant
constraints on the initial masses and evolutionary mass transfer processes that
transformed the phi Persei binary system. The interferometric data place strong
constraints on the Be disk elongation, orientation, and kinematics, and the
disk angular momentum vector is coaligned with and has the same sense of
rotation as the orbital angular momentum vector. The VEGA visible continuum
data indicate an elongated shape for the Be star itself, due to the combined
effects of rapid rotation, partial obscuration of the photosphere by the
circumstellar disk, and flux from the bright inner disk.Comment: 16 pages, 6 figures, 1 Anne
Requirements modelling and formal analysis using graph operations
The increasing complexity of enterprise systems requires a more advanced
analysis of the representation of services expected than is currently possible.
Consequently, the specification stage, which could be facilitated by formal
verification, becomes very important to the system life-cycle. This paper presents
a formal modelling approach, which may be used in order to better represent
the reality of the system and to verify the awaited or existing system’s properties,
taking into account the environmental characteristics. For that, we firstly propose
a formalization process based upon properties specification, and secondly we
use Conceptual Graphs operations to develop reasoning mechanisms of verifying
requirements statements. The graphic visualization of these reasoning enables us
to correctly capture the system specifications by making it easier to determine if
desired properties hold. It is applied to the field of Enterprise modelling
Constraining Disk Parameters of Be Stars using Narrowband H-alpha Interferometry with the NPOI
Interferometric observations of two well-known Be stars, gamma Cas and phi
Per, were collected and analyzed to determine the spatial characteristics of
their circumstellar regions. The observations were obtained using the Navy
Prototype Optical Interferometer equipped with custom-made narrowband filters.
The filters isolate the H-alpha emission line from the nearby continuum
radiation, which results in an increased contrast between the interferometric
signature due to the H-alpha-emitting circumstellar region and the central
star. Because the narrowband filters do not significantly attenuate the
continuum radiation at wavelengths 50 nm or more away from the line, the
interferometric signal in the H-alpha channel is calibrated with respect to the
continuum channels. The observations used in this study represent the highest
spatial resolution measurements of the H-alpha-emitting regions of Be stars
obtained to date. These observations allow us to demonstrate for the first time
that the intensity distribution in the circumstellar region of a Be star cannot
be represented by uniform disk or ring-like structures, whereas a Gaussian
intensity distribution appears to be fully consistent with our observations.Comment: 23 pages, 14 figures, accepted for publication in A
Line Forces in Keplerian Circumstellar Disks and Precession of Nearly Circular Orbits
We examine the effects of optically thick line forces on orbiting
circumstellar disks, such as occur around Be stars. For radially streaming
radiation, line forces are only effective if there is a strong radial velocity
gradient, as occurs, for example, in a line-driven stellar wind. However,
within an orbiting disk, the radial shear of the azimuthal velocity leads to
strong line-of-sight velocity velocity gradients along nonradial directions. As
such, in the proximity of a stellar surface extending over a substantial cone
angle, the nonradial stellar radiation can impart a significant line force,
even in the case of purely circular orbits. Given the highly supersonic nature
of orbital velocity variations, we use the Sobolev approximation, thereby
extending to the disk case the standard CAK formalism developed for line-driven
winds. We delineate the parameter regimes for which radiative forces might
alter disk properties; but even when radiative forces are small, we
analytically quantify higher-order effects in the linear limit, including the
precession of weakly elliptical orbits. We find that optically thick line
forces can have observable implications for the dynamics of disks around Be
stars, including the generation of either prograde or retrograde precession in
slightly eccentric orbits. However, our analysis suggests a net retrograde
effect, in apparent contradiction with observed long-term variations of
violet/red line profile asymmetries from Be stars, which are generally thought
to result from prograde propagation of a so-called ``one arm mode''. We also
conclude that radiative forces may alter the dynamical properties at the
surface of the disk where disk winds originate, and may even make low-density
disks vulnerable to being blown away.Comment: 31 pages, Latex, aaspp4 macro, 4 figure
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