2,093 research outputs found
Wind shear predictive detector technology study status
Among the different elements to be investigated when considering the Wind Shear hazard, the Aeronautical Navigation Technical Service (STNA/3E), whose task is to participate in the development of new technologies and equipments, focused its effort on airborne and ground sensors for the detection of low-level wind shear. The first task, initiated in 1986, consists in the evaluation of three candidate techniques for forward-looking sensors: lidar, sodar, and radar. No development is presently foreseen for an infrared based air turbulence advance warning system although some flight experiments took place in the 70's. A Thomson infrared radiometer was then installed on an Air France Boeing 707 to evaluate its capability of detecting clear air turbulence. The conclusion showed that this technique was apparently able to detect cloud layers but that additional experiments were needed; on the other hand, the rarity of the phenomenon and the difficulty in operating on a commercial aircraft were also mentioned
Cold neutrons trapped in external fields
The properties of inhomogeneous neutron matter are crucial to the physics of
neutron-rich nuclei and the crust of neutron stars. Advances in computational
techniques now allow us to accurately determine the binding energies and
densities of many neutrons interacting via realistic microscopic interactions
and confined in external fields. We perform calculations for different external
fields and across several shells to place important constraints on
inhomogeneous neutron matter, and hence the large isospin limit of the nuclear
energy density functionals that are used to predict properties of heavy nuclei
and neutron star crusts. We find important differences between microscopic
calculations and current density functionals; in particular the isovector
gradient terms are significantly more repulsive than in traditional models, and
the spin-orbit and pairing forces are comparatively weaker.Comment: 5 pages, 4 figures, final version. Additional material reference
added in the published versio
Quantum Monte Carlo study of inhomogeneous neutron matter
We present an ab-initio study of neutron drops. We use Quantum Monte Carlo
techniques to calculate the energy up to 54 neutrons in different external
potentials, and we compare the results with Skyrme forces. We also calculate
the rms radii and radial densities, and we find that a re-adjustment of the
gradient term in Skyrme is needed in order to reproduce the properties of these
systems given by the ab-initio calculation. By using the ab-initio results for
neutron drops for close- and open-shell configurations, we suggest how to
improve Skyrme forces when dealing with systems with large isospin-asymmetries
like neutron-rich nuclei.Comment: 8 pages, 6 figures, talk given at Horizons on Innovative Theories,
Experiments, and Supercomputing in Nuclear Physics 2012, (HITES2012), New
Orleans, Louisiana, June 4-7, 2012; to appear in Journal of Physics:
Conference Series (JPCS
CoRoT 102918586: a Gamma Dor pulsator in a short period eccentric eclipsing binary
Pulsating stars in eclipsing binary systems are powerful tools to test
stellar models. Binarity enables to constrain the pulsating component physical
parameters, whose knowledge drastically improves the input physics for
asteroseismic studies. The study of stellar oscillations allows us, in its
turn, to improve our understanding of stellar interiors and evolution. The
space mission CoRoT discovered several promising objects suitable for these
studies, which have been photometrically observed with unprecedented accuracy,
but needed spectroscopic follow-up. A promising target was the relatively
bright eclipsing system CoRoT 102918586, which turned out to be a double-lined
spectroscopic binary and showed, as well, clear evidence of Gamma Dor type
pulsations. We obtained phase resolved high-resolution spectroscopy with the
Sandiford spectrograph at the McDonald 2.1m telescope and the FEROS
spectrograph at the ESO 2.2m telescope. Spectroscopy yielded both the radial
velocity curves and, after spectra disentangling, the component effective
temperatures, metallicity and line-of-sight projected rotational velocities.
The CoRoT light curve was analyzed with an iterative procedure, devised to
disentangle eclipses from pulsations. We obtained an accurate determination of
the system parameters, and by comparison with evolutionary models strict
constraints on the system age. Finally, the residuals obtained after
subtraction of the best fitting eclipsing binary model were analyzed to
determine the pulsator properties. We achieved a quite complete and consistent
description of the system. The primary star pulsates with typical {\gamma} Dor
frequencies and shows a splitting in period which is consistent with high order
g-mode pulsations in a star of the corresponding physical parameters. The value
of the splitting, in particular, is consistent with pulsations in l = 1 modes.Comment: 12 pages, 10 figures. Accepted for publication in Astronomy and
Astrophysic
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