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

A Proposal for the Organization and Development of the A. C. Davis Senior High School Learning Resources Center

It is the purpose of this study to explore the factors in the development and the initial planning and organization of a traditional senior high school library that is to function as a learning resources center. In pursuit of this study, the library facilities for the new A. C. Davis Senior High School at Yakima, Washington, are used

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)

NEOTωIST: A relatively Inexpensive Kinetic Impactor Demonstration Mission Concept

Mission concept: NEOTωIST stands for Near-Earth Object Transfer of angular momentum (ω∙I) Spin Test, and is a concept for a kinetic impactor demonstration mission, which aims to change the spin rate of an asteroid by impacting it off-center (Drube et al. 2016, Engel et al. 2016). The change would be measured by means of lightcurve measurements with Earth-based telescopes. In contrast to most other kinetic impactor demonstration mission concepts, NEOTωIST does not require a reconnaissance spacecraft to rendezvous with the target asteroid for orbit change and impact-effect measurements, and is therefore a relatively inexpensive alternative. The NEOTωIST mission would determine the efficiency of momentum transfer (the β-factor) during an impact, and help mature the technology required for a kinetic impactor mission, both of which are important precursor measures for a future space mission to deflect an asteroid by collisional means in an emergency impact hazard situation

Granular Jamming as Controllable Stiffness Mechanism for Endoscopic and Catheter Applications

peer reviewe

Granular Jamming as Controllable Stiffness Mechanism for Endoscopic and Catheter Applications

Context During minimally invasive procedures, most of the devices (endoscopes, catheters, guidewires, etc.) need to be sufficiently flexible to avoid damaging patient tissues or causing pain, but have to be stiff enough to transmit force for support or for puncture. In the case of vascular stenosis, the guidewire has to be flexible to reach the stenosis (through the blood vessels), but it requires a rigid support to pass through the occlusion for treatment, to avoid buckling or deformation due to the force application. In order to solve this duality on the rigidity, controllable stiffness mechanisms can be used. Various mechanisms to control the stiffness can be found in the literature [1]. One of the promising solutions to achieve this objective is based on granular material jamming [2]. This research aims at studying the scaling laws of such solutions for miniaturized applications (with diameters below 3mm), the mechanical rules of design and the optimization based on the stiffness performances. Granular jamming The granular jamming is based on the locking of granular material. In this study, a flexible membrane is filled with a granular material (glass beads). When the pressure difference between outside and inside the membrane is low, the grains are free to move with respect to each other. In this configuration, the system is very flexible. Once the difference of pressure is increased, the grains are locked to each other due to the inter-grain friction. In this configuration, the system is more rigid. It is possible to adjust the stiffness of the device by controlling the pressure difference across the membrane. Materials and methods In this work, the performances of the stiffness change thanks to the granular jamming are quantified by mechanical testing. On the one hand, three point bending and cantilever beam tests are performed to quantify the flexural stiffness EI (product of the Young Modulus, E, and the second moment of area, I) of the solutions. Various granular materials and diameters of the samples are studied. On the other hand, triaxial compression tests are performed to observe the influence of the pressure difference on the rigidity obtained via granular jamming, using different granular materials. Results and discussion The tests described previously provide information on the performances of the granular jamming solution as well as an indication of the most important parameters to optimize. An optimal size of grains is highlighted by the results of these mechanical tests. The results of the triaxial compression tests show that the pressure difference is the most important parameter influencing the Young Modulus. The bending tests show that the second moment of area greatly impacts this stiffness. Removing the influence of the geometry, the equivalent Young Modulus is positively influenced for smaller diameters which is promising for the applications targeted in this work. Some of these results, as well as pictures and conclusions are illustrated in the poster file available in the following link : https://dipot.ulb.ac.be/dspace/bitstream/2013/239703/3/20161125PosterNCBMElblanc.pdf. One of the perspectives of this work is to develop a model for linking the results obtained from the different mechanical tests and to observe the optimization of the grains (shape and size) and cross-section of the samples with respect to the change of stiffness obtained. Further studies on stimulation method and on materials should be performed. References - [1] Kuder, I. K. et Al., ?Variable stiffness material and structural concepts for morphing applications?, Progress in Aerospace Sciences, pp.33-55, 2013. - [2] Loeve, A. J. et Al., ?Vacuum packed particles as flexible endoscope guides with controllable rigidity?, Granular Matter, pp. 543-554, 2010