2,582 research outputs found
Post processing of differential images for direct extrasolar planet detection from the ground
The direct imaging from the ground of extrasolar planets has become today a
major astronomical and biological focus. This kind of imaging requires
simultaneously the use of a dedicated high performance Adaptive Optics [AO]
system and a differential imaging camera in order to cancel out the flux coming
from the star. In addition, the use of sophisticated post-processing techniques
is mandatory to achieve the ultimate detection performance required. In the
framework of the SPHERE project, we present here the development of a new
technique, based on Maximum A Posteriori [MAP] approach, able to estimate
parameters of a faint companion in the vicinity of a bright star, using the
multi-wavelength images, the AO closed-loop data as well as some knowledge on
non-common path and differential aberrations. Simulation results show a 10^-5
detectivity at 5sigma for angular separation around 15lambda/D with only two
images.Comment: 12 pages, 6 figures, This paper will be published in the proceedings
of the conference Advances in Adaptive Optics (SPIE 6272), part of SPIE's
Astronomical Telescopes & Instrumentation, 24-31 May 2006, Orlando, F
The phase shift of line solitons for the KP-II equation
The KP-II equation was derived by [B. B. Kadomtsev and V. I.
Petviashvili,Sov. Phys. Dokl. vol.15 (1970), 539-541] to explain stability of
line solitary waves of shallow water. Stability of line solitons has been
proved by [T. Mizumachi, Mem. of vol. 238 (2015), no.1125] and [T. Mizumachi,
Proc. Roy. Soc. Edinburgh Sect. A. vol.148 (2018), 149--198]. It turns out the
local phase shift of modulating line solitons are not uniform in the transverse
direction. In this paper, we obtain the -bound for the local phase
shift of modulating line solitons for polynomially localized perturbations
Imaging the symmetry breaking of molecular orbitals in carbon nanotubes
Carbon nanotubes have attracted considerable interest for their unique
electronic properties. They are fascinating candidates for fundamental studies
of one dimensional materials as well as for future molecular electronics
applications. The molecular orbitals of nanotubes are of particular importance
as they govern the transport properties and the chemical reactivity of the
system. Here we show for the first time a complete experimental investigation
of molecular orbitals of single wall carbon nanotubes using atomically resolved
scanning tunneling spectroscopy. Local conductance measurements show
spectacular carbon-carbon bond asymmetry at the Van Hove singularities for both
semiconducting and metallic tubes, demonstrating the symmetry breaking of
molecular orbitals in nanotubes. Whatever the tube, only two types of
complementary orbitals are alternatively observed. An analytical tight-binding
model describing the interference patterns of ? orbitals confirmed by ab initio
calculations, perfectly reproduces the experimental results
A probable giant planet imaged in the Beta Pictoris disk
Since the discovery of its dusty disk in 1984, Beta Pictoris has become the
prototype of young early-type planetary systems, and there are now various
indications that a massive Jovian planet is orbiting the star at ~ 10 AU.
However, no planets have been detected around this star so far. Our goal was to
investigate the close environment of Beta Pic, searching for planetary
companion(s). Deep adaptive-optics L'-band images of Beta Pic were recorded
using the NaCo instrument at the Very Large Telescope. A faint point-like
signal is detected at a projected distance of ~ 8 AU from the star, within the
North-East side of the dust disk. Various tests were made to rule out with a
good confidence level possible instrumental or atmospheric artifacts. The
probability of a foreground or background contaminant is extremely low, based
in addition on the analysis of previous deep Hubble Space Telescope images. The
object L'=11.2 apparent magnitude would indicate a typical temperature of ~1500
K and a mass of ~ 8 Jovian masses. If confirmed, it could explain the main
morphological and dynamical peculiarities of the Beta Pic system. The present
detection is unique among A-stars by the proximity of the resolved planet to
its parent star. Its closeness and location inside the Beta Pic disk suggest a
formation process by core accretion or disk instabilities rather than a
binary-like formation process.Comment: 5 pages, 3 figures, 1 table. A&A Letters, in pres
Remotely Operated Train for Inspection and Measurement in CERN's LHC Tunnel
Personnel access to the LHC tunnel will be restricted to varying extents during the life of the machine due to radiation and cryogenic hazards. For this reason a remotely operated modular inspection train, (TIM) running on the LHC tunnel’s overhead monorail has been developed. In order to be compatible with the LHC personnel access system, a small section train that can pass through small openings at the top of sector doors has now been produced. The basic train can be used for remote visual inspection; additional modules give the capability of carrying out remote measurement of radiation levels, environmental conditions around the tunnel, and even remote measurement of the precise position of machine elements such as collimators. The paper outlines the design, development and operation of the equipment including preparation of the infrastructure. Key features of the trains are described along with future developments and intervention scenarios
Resonant Raman Scattering by quadrupolar vibrations of Ni-Ag Core-shell Nanoparticles
Low-frequency Raman scattering experiments have been performed on thin films
consisting of nickel-silver composite nanoparticles embedded in alumina matrix.
It is observed that the Raman scattering by the quadrupolar modes, strongly
enhanced when the light excitation is resonant with the surface dipolar
excitation, is mainly governed by the silver electron contribution to the
plasmon excitation. The Raman results are in agreement with a core-shell
structure of the nanoparticles, the silver shell being loosely bonded to the
nickel core.Comment: 3 figures. To be published in Phys. Rev.
Uniform regularity for the Navier-Stokes equation with Navier boundary condition
We prove that there exists an interval of time which is uniform in the
vanishing viscosity limit and for which the Navier-Stokes equation with Navier
boundary condition has a strong solution. This solution is uniformly bounded in
a conormal Sobolev space and has only one normal derivative bounded in
. This allows to get the vanishing viscosity limit to the
incompressible Euler system from a strong compactness argument
Charge redistribution at Pd surfaces: ab initio grounds for tight-binding interatomic potentials
A simplified tight-binding description of the electronic structure is often
necessary for complex studies of surfaces of transition metal compounds. This
requires a self-consistent parametrization of the charge redistribution, which
is not obvious for late transition series elements (such as Pd, Cu, Au), for
which not only d but also s-p electrons have to be taken into account. We show
here, with the help of an ab initio FP-LMTO approach, that for these elements
the electronic charge is unchanged from bulk to the surface, not only per site
but also per orbital. This implies different level shifts for each orbital in
order to achieve this orbital neutrality rule. Our results invalidate any
neutrality rule which would allow charge redistribution between orbitals to
ensure a common rigid shift for all of them. Moreover, in the case of Pd, the
power law which governs the variation of band energy with respect to
coordination number, is found to differ significantly from the usual
tight-binding square root.Comment: 6 pages, 2 figures, Latex; Phys.Rev. B 56 (1997
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