189 research outputs found
Sky reconstruction from transit visibilities: PAON-4 and Tianlai Dish Array
The spherical harmonics -mode decomposition is a powerful sky map
reconstruction method suitable for radio interferometers operating in transit
mode. It can be applied to various configurations, including dish arrays and
cylinders. We describe the computation of the instrument response function, the
point spread function (PSF), transfer function, the noise covariance matrix and
noise power spectrum. The analysis in this paper is focused on dish arrays
operating in transit mode. We show that arrays with regular spacing have more
pronounced side lobes as well as structures in their noise power spectrum,
compared to arrays with irregular spacing, specially in the north-south
direction. A good knowledge of the noise power spectrum
is essential for intensity mapping experiments as
non uniform is a potential problem for the
measurement of the HI power spectrum. Different configurations have been
studied to optimise the PAON-4 and Tianlai dish array layouts. We present their
expected performance and their sensitivities to the 21-cm emission of the Milky
Way and local extragalactic HI clumpsComment: 20 pages, 18 figures - Submitted to MNRAS ( the appendix A,B are not
included in the accepted version
The SPL-Fr\'{e}jus physics potential
An optimization of the CERN-SPL beam line has been performed which leads to
better sensitivities to the mixing angle and to the
violating phase than those advocated considering baseline
scenario.Comment: 2 pages, 3 figures. To be published in Nuclear Physics B (Proceedings
Supplement
Sky reconstruction for the Tianlai cylinder array
In this paper, we apply our sky map reconstruction method for transit type
interferometers to the Tianlai cylinder array. The method is based on the
spherical harmonic decomposition, and can be applied to cylindrical array as
well as dish arrays and we can compute the instrument response, synthesised
beam, transfer function and the noise power spectrum. We consider cylinder
arrays with feed spacing larger than half wavelength, and as expected, we find
that the arrays with regular spacing have grating lobes which produce spurious
images in the reconstructed maps. We show that this problem can be overcome,
using arrays with different feed spacing on each cylinder. We present the
reconstructed maps, and study the performance in terms of noise power spectrum,
transfer function and beams for both regular and irregular feed spacing
configurations.Comment: 15 pages, 12 figures, accepted by RA
Stratégies pour l'accÚs rapide à des hétérocycles azotés à partir d'alcools propargyliques
La partie principale de ce manuscrit traite du dĂ©veloppement de nouvelles mĂ©thodologies utilisant la substitution propargylique catalysĂ©e par des sels de fer(III), pour la formation de divers hĂ©tĂ©rocycles azotĂ©s ( 4-isoxazolines, isoxazoles, cis-acylaziridines et pyrimidines). En premier lieu, de nouvelles synthĂšses monotopes de 4-isoxazolines et d'isoxazoles diversement substituĂ©s impliquant des rĂ©actions de cyclisation catalysĂ©es par diverses espĂšces carbophiles ([Au], [Pd], [I+]) ont Ă©tĂ© dĂ©veloppĂ©es. La fragilitĂ© de la liaison N-O des 4-isoxazolines a pu ĂȘtre ensuite exploitĂ©e pour conduire Ă la formation de cis-acylaziridines. De nouvelles voies d'accĂšs aux (Z)-b-Ă©naminones et aux pyrimidines trisubstituĂ©es ont Ă©tĂ© Ă©galement dĂ©veloppĂ©es.The main part of this manuscript deals with the development of new methodologies using iron(III)-catalyzed propargylic substitution, for the synthesis of various nitrogen-containing heterocycles ( 4-isoxazolines, isoxazoles, cis-acylaziridines and pyrimidines). Firstly, new one-pot syntheses of variously substituted 4-isoxazolines and isoxazoles involving cyclization reactions promoted by various carbophilic species ([Au], [Pd], [I+]) have been developed. The weakness of the 4-isoxazoline N-O bond has been then exploited, leading to the formation of cis-acylaziridines. New pathways to (Z)-b-enaminones and trisubstituted pyrimidines have also been developed.MONTPELLIER-Ecole Nat.Chimie (341722204) / SudocSudocFranceF
Core Cosmology Library: Precision Cosmological Predictions for LSST
The Core Cosmology Library (CCL) provides routines to compute basic
cosmological observables to a high degree of accuracy, which have been verified
with an extensive suite of validation tests. Predictions are provided for many
cosmological quantities, including distances, angular power spectra,
correlation functions, halo bias and the halo mass function through
state-of-the-art modeling prescriptions available in the literature. Fiducial
specifications for the expected galaxy distributions for the Large Synoptic
Survey Telescope (LSST) are also included, together with the capability of
computing redshift distributions for a user-defined photometric redshift model.
A rigorous validation procedure, based on comparisons between CCL and
independent software packages, allows us to establish a well-defined numerical
accuracy for each predicted quantity. As a result, predictions for correlation
functions of galaxy clustering, galaxy-galaxy lensing and cosmic shear are
demonstrated to be within a fraction of the expected statistical uncertainty of
the observables for the models and in the range of scales of interest to LSST.
CCL is an open source software package written in C, with a python interface
and publicly available at https://github.com/LSSTDESC/CCL.Comment: 38 pages, 18 figures, matches ApJS accepted versio
Adversarial training applied to Convolutional Neural Network for photometric redshift predictions
The use of Convolutional Neural Networks (CNN) to estimate the galaxy photometric redshift probability distribution by analysing the images in different wavelength bands has been developed in the recent years thanks to the rapid development of the Machine Learning (ML) ecosystem. Authors have set-up CNN architectures and studied their performances and some sources of systematics using standard methods of training and testing to ensure the generalisation power of their models. So far so good, but one piece was missing : does the model generalisation power is well measured? The present article shows clearly that very small image perturbations can fool the model completely and opens the Pandora's box of \textit{adversarial} attack. Among the different techniques and scenarios, we have chosen to use the Fast Sign Gradient one-step Method and its Projected Gradient Descent iterative extension as adversarial generator tool kit. However, as unlikely as it may seem these adversarial samples which fool not only a single model, reveal a weakness both of the model and the classical training. A revisited algorithm is shown and applied by injecting a fraction of adversarial samples during the training phase. Numerical experiments have been conducted using a specific CNN model for illustration although our study could be applied to other models - not only CNN ones - and in other contexts - not only redshift measurements - as it deals with the complexity of the boundary decision surface
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