Sky reconstruction from transit visibilities: PAON-4 and Tianlai Dish Array

The spherical harmonics $m$-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 $C^{\mathrm{noise}}(\ell)$ is essential for intensity mapping experiments as non uniform $C^{\mathrm{noise}}(\ell)$ 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 $\theta\_{13}$ mixing angle and to the $\delta\_{CP}$ 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'accès rapide à des hétérocycles azotés à partir d'alcools propargyliques

La partie principale de ce manuscrit traite du développement de nouvelles méthodologies utilisant la substitution propargylique catalysée par des sels de fer(III), pour la formation de divers hétérocycles azotés ( 4-isoxazolines, isoxazoles, cis-acylaziridines et pyrimidines). En premier lieu, de nouvelles synthèses monotopes de 4-isoxazolines et d'isoxazoles diversement substitués impliquant des réactions de cyclisation catalysées par diverses espèces carbophiles ([Au], [Pd], [I+]) ont été développées. La fragilité de la liaison N-O des 4-isoxazolines a pu être ensuite exploitée pour conduire à la formation de cis-acylaziridines. De nouvelles voies d'accès aux (Z)-b-énaminones et aux pyrimidines trisubstituées ont été également développées.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

Notes et commentaires au sujet des conférences de S. Mallat du Collège de France (2020): Modèles multi-échelles et réseaux de neurones convolutifs

2 Séance du (22 Janv.) 63 Séance du (29 Janv.) 234 Séance du (5 Février.) 345 Séance du 12 Février 486 Séance du 26 Février 627 Séance du 4 Mars 818 Séance du 11 Mars 1019 Séance du 15 Juin 117MasterLe cours de 2020 de Stéphane Mallat, Professeur au Collège de France, est centré sur la question « Pourquoi les architectures de réseaux convolutionnels sont-elles génériques ? ». Cela engage d’un point de vue mathématique, trois types de problèmes : l’estimation, l’optimisation et l’approximation. Les cours de 2018 et 2019 portaient sur les deux premiers, le troisième est la thématique de cette année. On va donc se poser les questions: quelle est l’information a priori (régularité, symétrie, parcimonie), pourquoi des convolutions, quels types de filtres, quel est le rôle des non-linéarités, et le lien avec la neurophysiologie dans le contexte de l’image et du son. La transformation en Ondelettes et ces applications pour obtenir des descripteurs ainsi que des filtres convolutifs est au cœur du cours

Notes and Comments on S. Mallat’s Lectures at Collège de France (2023): Multiscale Models and Convolutional Neural Networks

1 Foreword 62 Lecture 18 Jan. 73 Lecture 25 Jan. 284 Lecture 1er Feb. 415 Lecture 8 Feb. 556 Lecture 15 Feb. 687 Lecture 22 Feb. 878 Lecture 1st Mar. 1039 Lecture 8 Mar. 12310 Epilogue 151MasterThe 2023 course by Stéphane Mallat, Professor at the Collège de France, is a continuation of the 2022 course, focusing on the theme of Entropy. Initially, it delves into Statistical Physics by L. Boltzmann and J. W. Gibbs, and then transitions to Cl. Shannon's Information Theory. To comprehend the Second Law of Thermodynamics, ergodic processes are studied, employing the Shannon–McMillan–Breiman theorem, and Markov chains enable us to demonstrate convergence to equilibrium. We will explore connections with the field of Statistical Learning, through modeling in the context of Maximum Entropy and Gibbs' theorem. Non-Gaussian models are developed, utilizing Harmonic Analysis and the implementation of Scattering networks. Along the way, we will revisit the Fourier Transform and the Wavelet Transform (multiscale analysis)