148 research outputs found
COBRA : Une plate-forme de Rà PC basée sur des ontologies
International audienceCet article présente un projet en cours qui a pour objectif de développer une plate-forme de Rà PC pour le diagnostic basée sur des ontologies, appelée COBRA. Cette plate-forme est constituée de deux parties principales : les modÚles de connaissances décrits par des ontologies, et les processus de raisonnement. Nous travaillons actuellement sur la défaillance des barriÚres de sécurité installées sur des sites industriels. Cependant, notre objectif est de rendre la plate-forme générique et indépendante du domaine d'application. Nous affirmons que, pour mieux exploiter les avantages des ontologies dans les systÚmes de Rà PC, il est important de pouvoir utiliser n'importe quel concept dans la description des cas. Ainsi, COBRA permet de définir les attributs de chaque cas dynamiquement au moment de l'exécution, ce qui conduit à une base de cas hétérogÚne. Dans cet article, nous présentons l'architecture de la plate-forme, les modÚles de connaissances, les processus principaux, ainsi que les problÚmes rencontrés en travaillant avec des cas hétérogÚnes
Breathing mode for systems of interacting particles
We study the breathing mode in systems of trapped interacting particles. Our
approach, based on a dynamical ansatz in the first equation of the
Bogolyubov-Born-Green-Kirkwood-Yvon (BBGKY) hierarchy allows us to tackle at
once a wide range of power law interactions and interaction strengths, at
linear and non linear levels. This both puts in a common framework various
results scattered in the literature, and by widely generalizing these,
emphasizes universal characters of this breathing mode. Our findings are
supported by direct numerical simulations.Comment: 4 pages, 4 figure
Looking for bimodal distributions in multi-fragmentation reactions
The presence of a phase transition in a finite system can be deduced,
together with its order, from the shape of the distribution of the order
parameter. This issue has been extensively studied in multifragmentation
experiments, with results that do not appear fully consistent. In this paper we
discuss the effect of the statistical ensemble or sorting conditions on the
shape of fragment distributions, and propose a new method, which can be easily
implemented experimentally, to discriminate between different fragmentation
scenarii. This method, based on a reweighting of the measured distribution to
account for the experimental constraints linked to the energy deposit, is
tested on different simple models, and appears to provide a powerful
discrimination.Comment: 11 pages, 7 figure
Examine the species and beam-energy dependence of particle spectra using Tsallis Statistics
Tsallis Statistics was used to investigate the non-Boltzmann distribution of
particle spectra and their dependence on particle species and beam energy in
the relativistic heavy-ion collisions at SPS and RHIC. Produced particles are
assumed to acquire radial flow and be of non-extensive statistics at
freeze-out. J/psi and the particles containing strangeness were examined
separately to study their radial flow and freeze-out. We found that the strange
hadrons approach equilibrium quickly from peripheral to central A+A collisions
and they tend to decouple earlier from the system than the light hadrons but
with the same final radial flow. These results provide an alternative picture
of freeze-outs: a thermalized system is produced at partonic phase; the
hadronic scattering at later stage is not enough to maintain the system in
equilibrium and does not increase the radial flow of the copiously produced
light hadrons. The J/psi in Pb+Pb collisions at SPS is consistent with early
decoupling and obtains little radial flow. The J/psi spectra at RHIC are also
inconsistent with the bulk flow profile.Comment: 12 pages, 4 figures, added several references and some clarifications
et
GALICS III: Predicted properties for Lyman Break Galaxies at redshift 3
This paper illustrates how mock observational samples of high-redshift
galaxies with sophisticated selection criteria can be extracted from the
predictions of GALICS, a hybrid model of hierarchical galaxy formation that
couples the outputs of large cosmological simulations and semi-analytic recipes
to describe dark matter collapse and the physics of baryons respectively. As an
example of this method, we focus on the properties of Lyman Break Galaxies at
redshift 3. With the MOMAF software package described in a companion paper, we
generate a mock observational sample with selection criteria as similar as
possible to those implied in the actual observations of z = 3 LBGs by Steidel
et al.(1995). Our model predictions are in good agreement with the observed
number density and 2D correlation function. We investigate the optical/IR
luminosity budget as well as several other physical properties of LBGs and find
them to be in general agreement with observed values. Looking into the future
of these LBGs we predict that 75% of them end up as massive ellipticals today,
even though only 35% of all our local ellipticals are predicted to have a LBG
progenitor. In spite of some shortcomings, this new 'mock observation' method
clearly represents a necessary first step toward a more accurate comparison
between hierarchical models of galaxy formation and real observational surveys.Comment: 19 pages, 15 figures, submitted to MNRAS. Full resolution figures at
http://galics.iap.fr
FOREDUNE GUIDED REMOBILIZATION EXPERIMENTS ALONG THE SOUTHWEST COAST OF FRANCE
This contribution presents the response of experimental management methods implemented along 2 km stretch of the southwest coast of France with the objective to restore aeolian dynamics and foredune mobility to promote quasi alongshore-uniform landward foredune migration. The analysis based on eight airborne LiDAR campaigns and several morphometric indicators shows that the alongshore and temporal variability of foredune evolution depends on natural dynamics and contrasted managed strategies. These experiments offer new perspectives and guidelines for coastal dune managers in areas where chronic erosion threatens fixed dune systems
MoMaF : The Mock Map Facility
We present the Mock Map Facility, a powerful tool to generate mock catalogues
or images from semi-analytically post-processed snapshots of cosmological
N-body simulations. The paper describes in detail an efficient technique to
create such mocks from the GALICS semi-analytic model, providing the reader
with an accurate quantification of the artifacts it introduces at every step.
We show that replication effects introduce a negative bias on the clustering
signal -- typically peaking at less than 10 percent around the correlation
length. We also thoroughly discuss how the clustering signal is affected by
finite volume effects, and show that it vanishes at scales larger than about a
tenth of the simulation box size. For the purpose of analysing our method, we
show that number counts and redshift distributions obtained with GALICS and
MOMAF compare well to K-band observations and to the 2dFGRS. Given finite
volume effects, we also show that the model can reproduce the APM angular
correlation function. The MOMAF results discussed here are made publicly
available to the astronomical community through a public database. Moreover, a
user-friendly Web interface (http://galics.iap.fr) allows any user to recover
her/his own favourite galaxy samples through simple SQL queries. The
flexibility of this tool should permit a variety of uses ranging from extensive
comparisons between real observations and those predicted by hierarchical
models of galaxy formation, to the preparation of observing strategies for deep
surveys and tests of data processing pipelines.Comment: 19 pages, 15 Figs, significantly modified version now accepted for
publication in MNRAS. High-resolution version available at
http://galics.cosmologie.fr/papers/momaf.ps.g
Enhancement and Inhibition of Spontaneous Photon Emission by Resonant Silicon Nanoantennas
Substituting noble metals for high-index dielectrics has recently been proposed as an alternative strategy in nanophotonics to design broadband optical resonators and circumvent the Ohmic losses of plasmonic materials. In this paper, we demonstrate that subwavelength silicon nanoantennas can manipulate the photon emission dynamics of fluorescent molecules. In practice, we show that dielectric nanoantennas can both increase and decrease the local density of optical states at room temperature, a process that is inaccessible with noble metals at the nanoscale. Using scanning probe microscopy, we analyze quantitatively, in three dimensions, the near-field interaction between a 100-nm fluorescent nanosphere and silicon nanoantennas with diameters ranging between 170 and 250 nm. Associated with numerical simulations, these measurements indicate increased or decreased total spontaneous decay rates by up to 15% and a gain in the collection efficiency of emitted photons by up to 85%. Our study demonstrates the potential of silicon-based nanoantennas for the low-loss manipulation of solid-state emitters at the nanoscale and at room temperature
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