309 research outputs found
Approximation du calcul de la taille échantillonnale pour les tests à hypothèses multiples lorsque r parmis m hypothèses doivent être significatives
Généralement, dans les situations d’hypothèses multiples on cherche à rejeter
toutes les hypothèses ou bien une seule d’entre d’elles. Depuis quelques temps on
voit apparaître le besoin de répondre à la question : « Peut-on rejeter au moins
r hypothèses ? ». Toutefois, les outils statisques pour répondre à cette question
sont rares dans la littérature. Nous avons donc entrepris de développer les formules
générales de puissance pour les procédures les plus utilisées, soit celles de
Bonferroni, de Hochberg et de Holm. Nous avons développé un package R pour le
calcul de la taille échantilonnalle pour les tests à hypothèses multiples (multiple
endpoints), où l’on désire qu’au moins r des m hypothèses soient significatives.
Nous nous limitons au cas où toutes les variables sont continues et nous présentons
quatre situations différentes qui dépendent de la structure de la matrice de
variance-covariance des données.Generally, in multiple endpoints situations we want to reject all hypotheses or
at least only one of them. For some time now, we see emerge the need to answer
the question : "Can we reject at least r hypotheses ?" However, the statistical tools
to answer this new problem are rare in the litterature. We decide to develop general
power formulas for the principals procedures : Bonferroni’s, Hochberg’s and
Holm’s procedures. We also develop an R package for the sample size calculation
for multiple endpoints, when we want to reject at least r hypotheses. We limit
ourselves in the case where all the variables are continuous and we present four
different situations depending on the structure of the data’s variance-covariance
matrix
Spectral cube extraction for the VLT/SPHERE IFS: Open-source pipeline with full forward modeling and improved sensitivity
We present a new open-source data-reduction pipeline to reconstruct spectral
data cubes from raw SPHERE integral-field spectrograph (IFS) data. The pipeline
is written in Python and based on the pipeline that was developed for the
CHARIS IFS. It introduces several improvements to SPHERE data analysis that
ultimately produce significant improvements in postprocessing sensitivity. We
first used new data to measure SPHERE lenslet point spread functions (PSFs) at
the four laser calibration wavelengths. These lenslet PSFs enabled us to
forward-model SPHERE data, to extract spectra using a least-squares fit, and to
remove spectral crosstalk using the measured lenslet PSFs. Our approach also
reduces the number of required interpolations, both spectral and spatial, and
can preserve the original hexagonal lenslet geometry in the SPHERE IFS. In the
case of least-squares extraction, no interpolation of the data is performed. We
demonstrate this new pipeline on the directly imaged exoplanet 51 Eri b and on
observations of the hot white dwarf companion to HD 2133. The extracted
spectrum of HD 2133B matches theoretical models, demonstrating
spectrophotometric calibration that is good to a few percent. Postprocessing on
two 51 Eri b data sets demonstrates a median improvement in sensitivity of 80%
and 30% for the 2015 and 2017 data, respectively, compared to the use of cubes
reconstructed by the SPHERE Data Center. The largest improvements are seen for
poorer observing conditions. The new SPHERE pipeline takes less than three
minutes to produce a data cube on a modern laptop, making it practical to
reprocess all SPHERE IFS data.Comment: 17 pages, 11 figures. Software available at:
https://github.com/PrincetonUniversity/charis-de
WEIRD: Wide-orbit Exoplanet search with InfraRed Direct imaging
We report results from the Wide-orbit Exoplanet search with InfraRed Direct
imaging (WEIRD), a survey designed to search for Jupiter-like companions on
very wide orbits (1000 to 5000 AU) around young stars (120 Myr) that are
known members of moving groups in the solar neighborhood (70 pc). Sharing
the same age, distance, and metallicity as their host while being on large
enough orbits to be studied as "isolated" objects make such companions prime
targets for spectroscopic observations and valuable benchmark objects for
exoplanet atmosphere models. The search strategy is based on deep imaging in
multiple bands across the near-infrared domain. For all 177 objects of our
sample, , , [3.6] and [4.5] images were obtained with
CFHT/MegaCam, GEMINI/GMOS, CFHT/WIRCam, GEMINI/Flamingos-2, and /IRAC.
Using this set of 4 images per target, we searched for sources with red
and colors, typically reaching good completeness
down to 2Mjup companions, while going down to 1Mjup for some targets, at
separations of AU. The search yielded 4 candidate companions with
the expected colors, but they were all rejected through follow-up proper motion
observations. Our results constrain the occurrence of 1-13 Mjup planetary-mass
companions on orbits with a semi-major axis between 1000 and 5000 AU at less
than 0.03, with a 95\% confidence level.Comment: 55 pages, 16 figures, accepted to A
Approche expérimentale du bang sonique des aéronefs
La présence d'un mobile supersonique dans l'atmosphère crée une onde de choc, c'est-à -dire une perturbation atmosphérique caractérisée par des discontinuités de pression. Cette perturbation évolue pour former à quelques kilomètres l'onde en N caractéristique du bang sonique. Des campagnes de mesure visant à évaluer les nuisances sonores liées au bang ont été effectuées avant la mise en service du supersonique Concorde. A partir des années 80, l'ONERA a exploité des données acoustiques issues des vols commerciaux transatlantiques de l'appareil pour approfondir la connaissance du phénomène de bang, notamment sous l'angle de sa propagation à grande distance. Nous présentons les résultats de simulations avec un code de rayons 3D en atmosphère réelle à partir des données de vol, visant à obtenir les limites des zones de retombées acoustiques. L'analyse fréquentielle des signaux enregistrés en Bretagne a permis de trouver une nette corrélation entre la fréquence pic et la distance à la source
First results from the Canada-France High-z Quasar Survey: Constraints on the z=6 quasar luminosity function and the quasar contribution to reionization
We present preliminary results of a new quasar survey being undertaken with
multi-colour optical imaging from the Canada-France-Hawaii Telescope. The
current data consists of 3.83 sq. deg. of imaging in the i' and z' filters to a
10 sigma limit of z'<23.35. Near-infrared photometry of 24 candidate 5.7<z<6.4
quasars confirms them all to be low mass stars including two T dwarfs and four
or five L dwarfs. Photometric estimates of the spectral type of the two T
dwarfs are T3 and T6. We use the lack of high-redshift quasars in this survey
volume to constrain the z=6 quasar luminosity function. For reasonable values
of the break absolute magnitude M*_1450 and faint-end slope alpha, we determine
that the bright-end slope beta>-3.2 at 95% confidence. We find that the
comoving space-density of quasars brighter than M_1450=-23.5 declines by a
factor >25 from z=2 to z=6, mirroring the decline observed for high-luminosity
quasars. We consider the contribution of the quasar population to the ionizing
photon density at z=6 and the implications for reionization. We show that the
current constraints on the quasar population give an ionizing photon density
<<30% that of the star-forming galaxy population. We conclude that active
galactic nuclei make a negligible contribution to the reionization of hydrogen
at z~6.Comment: 9 pages, 6 figures, ApJ, in pres
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