Determination of astrophysical parameters of quasars within the Gaia mission

We describe methods designed to determine the astrophysical parameters of quasars based on spectra coming from the red and blue spectrophotometers of the Gaia satellite. These methods principally rely on two already published algorithms that are the weighted principal component analysis and the weighted phase correlation. The presented approach benefits from a fast implementation; an intuitive interpretation as well as strong diagnostic tools on the potential errors that may arise during predictions. The production of a semi-empirical library of spectra as they will be observed by Gaia is also covered and subsequently used for validation purpose. We detail the pre-processing that is necessary in order for these spectra to be fully exploitable by our algorithms along with the procedures that are used in order to predict the redshifts of the quasars; their continuum slopes; the total equivalent width of their emission lines and whether these are broad absorption line (BAL) quasars or not. Performances of these procedures were assessed in comparison with the Extremely Randomized Trees learning method and were proven to provide better results on the redshift predictions and on the ratio of correctly classified observations though the probability of detection of BAL quasars remains restricted by the low resolution of these spectra as well as by their limited signal-to-noise ratio. Finally, the triggering of some warning flags allows us to obtain an extremely pure subset of redshift predictions where approximately 99% of the observations come along with absolute errors that are below 0.1.Comment: 17 pages, 11 figures, 5 table

Redshift determination through weighted phase correlation: a linearithmic implementation

peer reviewedWe present a new algorithm having a time complexity of O(N log N) and designed to retrieve the phase at which an input signal and a set of not necessarily orthogonal templates match at best in a weighted chi-squared sense. The proposed implementation is based on an orthogonalization algorithm and thus also benefits from a high numerical stability. We successfully apply this method to the redshift determination of quasars from the twelfth Sloan Digital Sky Survey (SDSS) quasar catalog and derive the proper spectral reduction and redshift selection methods. Also provided are the derivations of the redshift uncertainty and of the associated confidence. Results of this application are comparable to the performances of the SDSS pipeline while not having a quadratic time dependency

Weighted principal component analysis: a weighted covariance eigendecomposition approach

We present a new straightforward principal component analysis (PCA) method based on the diagonalization of the weighted variance-covariance matrix through two spectral decomposition methods: power iteration and Rayleigh quotient iteration. This method allows one to retrieve a given number of orthogonal principal components amongst the most meaningful ones for the case of problems with weighted and/or missing data. Principal coefficients are then retrieved by fitting principal components to the data while providing the final decomposition. Tests performed on real and simulated cases show that our method is optimal in the identification of the most significant patterns within data sets. We illustrate the usefulness of this method by assessing its quality on the extrapolation of Sloan Digital Sky Survey quasar spectra from measured wavelengths to shorter and longer wavelengths. Our new algorithm also benefits from a fast and flexible implementation.Comment: 12 pages, 9 figure

Scaling properties of work fluctuations after quenches at quantum transitions

We study the scaling properties of the statistics of the work done on a generic many-body system at a quantum phase transition of any order and type, arising from quenches of a driving control parameter. For this purpose we exploit a dynamic finite-size scaling framework. Namely, we put forward the existence of a nontrivial finite-size scaling limit for the work distribution, defined as the large-size limit when appropriate scaling variables are kept fixed. The corresponding scaling behaviors are thoroughly verified by means of analytical and numerical calculations in two paradigmatic many-body systems as the quantum Ising model and the Bose-Hubbard model.Comment: 30 pages, 6 figures. Revised versio

Spectroscopic binaries as observed by the future Gaia space mission

peer reviewedThe future Gaia satellite will observe a large number of stars through its three main channels: astrometric, photometric and, for the brightest stars, spectroscopic. The satellite is equipped with the RVS spectrograph, which will provide medium-resolution spectra over a small wavelength range. These spectra should allow us to identify stars exhibiting a composite spectrum, either because of a chance alignment or a true binarity. We discuss the various aspects related to the data treatment of the binary candidates and describe the algorithms that are intended to be included in the processing pipeline

Integrated software for imaging data analysis applied to edge plasma physic and operational safety

Fusion tokamaks are complex devices requiring many diagnostics for real time control of the plasma and off-line physical analysis. In current tokamaks, imaging diagnostics have become increasingly used for these two purposes. Such systems produce a lot of data encouraging physicists to use shared tools and codes for data access and analysis. If general purpose software programs for data display and analysis are widely spread, a need exists in developing similar applications for quantitative imaging data analysis applied to plasma physic. In this paper, we introduce a new integrated software program, named wolff, dedicated to this task. The main contribution of this software is to gather under the same framework different functionalities for (1) data access and display, (2) signal, image, and video processing, and (3) quantitative analysis based on physical models. After an overview of existing solutions for data processing in the field of plasma data, we present the wolff architecture and its currently implemented features. The capabilities of the software are then demonstrated through three applications in the field of physical analysis (heat and particle flux calculations) and tokamak operation (safety operation)

Characterization and Modeling of Granular Jamming: Models for Mechanical Design

peer reviewedThe use of granular jamming is proposed for designing structures with tunable rigidity of their tools (with the ability of being flexible devices for shaping and deformation but rigid for shape-locking and force transmission). The granular jamming consists in modifying the apparent rigidity of a structure by controlling the vacuum in a membrane filled with granular material. When the difference of pressure is low, the grains are free to move with respect to each other and the structure is flexible. When the vacuum in the membrane is increased, the grains are blocked and the structure is more rigid. Different mechanical characterizations of the granular jamming have been performed (triaxial compression and tension and cantilever beam bending tests) for different glass bead sizes ranging between 100 μm and 1 mm (used as granular material) at different vacuum levels (between 0 kPa and 90 kPa ). The grain size slightly influences the stiffness while the pressure difference is the main parameter to tune the stiffness of the structure. Based on these experiments, analytical models have been developed and validated. The tension characteristics can be directly deduced from the compression behavior and the bending modulus can be obtained by a combination of the tension and compression moduli. The proposed analytical models present the advantage of a simple formulation and are suitable for estimating the performance of other structures based on the granular jamming. The models can estimate and predict satisfactorily the results of granular jamming and can be used for designing mechanical structures based on this mechanism

Granular jamming as controllable stiffness mechanism for endoscopic and catheter applications

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