LITpro: a model fitting software for optical interferometry

9 pagesInternational audienceLITpro is a software for fitting models on data obtained from various stellar optical interferometers, like the VLTI. As a baseline, for modeling the object, it provides a set of elementary geometrical and center-to-limb darkening functions, all combinable together. But it is also designed to make very easy the implementation of more specific models with their own parameters, to be able to use models closer to astrophysical considerations. So LITpro only requires the modeling functions to compute the Fourier transform of the object at given spatial frequencies, and wavelengths and time if needed. From this, LITpro computes all the necessary quantities as needed (e.g. visibilities, spectral energy distribution, partial derivatives of the model, map of the object model). The fitting engine, especially designed for this kind of optimization, is based on a modified Levenberg-Marquardt algorithm and has been successfully tested on real data in a prototype version. It includes a Trust Region Method, minimizing a heterogeneous non-linear and non-convex criterion and allows the user to set boundaries on free parameters. From a robust local minimization algorithm and a starting points strategy, a global optimization solution is effectively achieved. Tools have been developped to help users to find the global minimum. LITpro is also designed for performing fitting on heterogeneous data. It will be shown, on an example, how it fits simultaneously interferometric data and spectral energy distribution, with some benefits on the reliability of the solution and a better estimation of errors and correlations on the parameters. That is indeed necessary since present interferometric data are generally multi-wavelengths

Tests with a Carlina-type diluted telescope; Primary coherencing

Studies are under way to propose a new generation of post-VLTI interferometers. The Carlina concept studied at the Haute- Provence Observatory is one of the proposed solutions. It consists in an optical interferometer configured like a diluted version of the Arecibo radio telescope: above the diluted primary mirror made of fixed cospherical segments, a helium balloon (or cables suspended between two mountains), carries a gondola containing the focal optics. Since 2003, we have been building a technical demonstrator of this diluted telescope. First fringes were obtained in May 2004 with two closely-spaced primary segments and a CCD on the focal gondola. We have been testing the whole optical train with three primary mirrors. The main aim of this article is to describe the metrology that we have conceived, and tested under the helium balloon to align the primary mirrors separate by 5-10 m on the ground with an accuracy of a few microns. The servo loop stabilizes the mirror of metrology under the helium balloon with an accuracy better than 5 mm while it moves horizontally by 30 cm in open loop by 10-20 km/h of wind. We have obtained the white fringes of metrology; i.e., the three mirrors are aligned (cospherized) with an accuracy of {\approx} 1 micron. We show data proving the stability of fringes over 15 minutes, therefore providing evidence that the mechanical parts are stabilized within a few microns. This is an important step that demonstrates the feasibility of building a diluted telescope using cables strained between cliffs or under a balloon. Carlina, like the MMT or LBT, could be one of the first members of a new class of telescopes named diluted telescopes.Comment: 18 pages, 17 figures, A&A, accepte

On the stability of 2 \sqrt{2} x 2 \sqrt{2} oxygen ordered superstructures in YBa2Cu3O6+x

We have compared the ground-state energy of several observed or proposed " 2 \sqrt{2} x 2 \sqrt{2} oxygen (O) ordered superstructures " (from now on HS), with those of "chain superstructures" (CS) (in which the O atoms of the basal plane are ordered in chains), for different compositions x in YBa2Cu3O6+x. The model Hamiltonian contains i) the Madelung energy, ii) a term linear in the difference between Cu and O hole occupancies which controls charge transfer, and iii) covalency effects based on known results for $t-J$ models in one and two dimensions. The optimum distribution of charge is determined minimizing the total energy, and depends on two parameters which are determined from known results for x=1 and x=0.5. We obtain that on the O lean side, only CS are stable, while for x=7/8, a HS with regularly spaced O vacancies added to the x=1 structure is more stable than the corresponding CS for the same x. We find that the detailed positions of the atoms in the structure, and long-range Coulomb interactions, are crucial for the electronic structure, the mechanism of charge transfer, the stability of the different phases, and the possibility of phase separation.Comment: 24 text pages, Latex, one fig. included as ps file, to be publisheb in Phys. Rev.

Review on Superconducting Materials

Short review of the topical comprehension of the superconductor materials classes Cuprate High-Temperature Superconductors, other oxide superconductors, Iron-based Superconductors, Heavy-Fermion Superconductors, Nitride Superconductors, Organic and other Carbon-based Superconductors and Boride and Borocarbide Superconductors, featuring their present theoretical understanding and their aspects with respect to technical applications.Comment: A previous version of this article has been published in \" Applied Superconductivity: Handbook on Devices and Applications \", Wiley-VCH ISBN: 978-3-527-41209-9. The new extended and updated version will be published in \" Encyclopedia of Applied Physics \", Wiley-VC

Planck pre-launch status : The Planck mission

Peer reviewe

Clinical applications of postural fluctuations dynamical analyses in older adults

Le vieillissement démographique français constitue un défi majeur de santé publique. Il se caractérise par des changements physiologiques pouvant provoquer des troubles moteurs. Il en résulte à plus ou moins long terme une perte d'autonomie nécessitant parfois l'institutionnalisation de la personne. L'examen des déficits posturaux se réalise en pratique clinique courante par une évaluation stabilométrique. L'enregistrement des déplacements du centre des pressions peut être analysé selon deux approches : la première, traditionnelle, analysant leur cinématique à l'aide de statistiques descriptives ; la seconde, dynamique, quantifiant leur complexité notamment en termes de régularité. Dans ce travail, nous montrons statistiquement la complémentarité de ces deux approches. Nous mettons également en évidence les intérêts cliniques de l'approche dynamique au travers de deux études : (i) une exploration de la relation entre les résultats d'un test fonctionnel validé et l'évaluation posturale chez des femmes âgées sédentaires ; (ii) une comparaison basée sur une analyse dynamique des fluctuations posturales de deux groupes de personnes âgées institutionnalisées : avec et sans antécédents de chute.In France, aging is a major public health challenge. Specific aging-associated physiologic modifications can produce movement disorders and lead to dependency and institutionalization in nursing homes. Clinical examination of postural deficits is generally achieved by means of stabilometric evaluation. Recordings of center of pressure (COP) displacements can be analyzed in two ways : (i) a classical approach based on kinematics and descriptive statistics or (ii) a dynamical approach which provides a quantification of the complexity of COP time series in terms of regularity. In this work, we statistically show the complementarity of these two approaches. We also highlight the clinical interest of the dynamical approach with two clinical studies : (i) an exploration of the relationship between a functional test and postural evaluation in asymptomatic sedentary older women ; (ii) a comparison of institutionalized elderly non-fallers and fallers based on a dynamical analysis of COP fluctuations

Cartapp, ou la carte comme boussole : la représentation du territoire dans l’accompagnement des créateurs d’activité des zones rurales

National audienc

Recurrence Quantification Analysis of Human Postural Fluctuations in Older Fallers and Non-fallers

International audienceWe investigate postural sway data dynamics in older adult fallers and non-fallers. Center of pressure (COP) signals were recorded during quiet standing in 28 older adults. The subjects were divided in two groups: with and without history of falls. COP time series were analyzed using recurrence quantification analysis (RQA) in both anteroposterior and mediolateral (ML) directions. Classical stabilometric variables (path length and range) were also computed. The results showed that RQA outputs quantifying predictability of COP fluctuations and Shannon entropy of recurrence plot diagonal line length distribution, were significantly higher in fallers, only for ML direction. In addition, the range of ML COP signals was also significantly higher in fallers. This result is in accordance with some findings of the literature and could be interpreted as an increased hip strategy in fallers. The RQA results seem coherent with the theory of loss of complexity with aging and disease. Our results suggest that RQA is a promising approach for the investigation of COP fluctuations in a frail population

Approche méthodologique et application populationnelle des adaptations musculaires isocinétiques

L’analyse de la validité des démarches et des variables de caractérisation des adaptations musculaires isocinétiques sert la qualité de la prise en charge de la personne. D’un point de vue méthodologique, nous présentons des travaux sur la validité du paramètre de temps de développement de la force maximale (TDFM) (étude 1) et sur l’influence de trois temps de récupération de 30, 60 et 180 secondes sur les niveaux de force externe développée (étude 2). Au regard de son trop faible niveau de reproductibilité (CCI de 0,51–0,65 en extension et entre 0,50−0,63 en flexion), le TDFM ne peut servir fiablement la caractérisation des adaptations des muscles fléchisseurs et extenseurs du genou. Pour l’étude 2 et l’analyse des interactions entre la période de test et les trois temps de récupération, nous observons une absence systématique de différence significative entre les mesures isocinétiques de force maximale et de puissance moyenne obtenues sur les quadriceps et les ischio-jambiers. Ces données questionnent l’approche strictement énergétique et incitent à l’étude des interactions entre la production de force et les phénomènes de fatigue en relation avec les temps de récupération. Les méthodologies isocinétiques servent aussi la caractérisation des adaptations à moyen et à long termes suite à des programmes d’intervention en activités physiques. Chez la personne âgée, des résultats préliminaires témoignent des phénomènes d’optimisation et de déconditionnement de la fonction musculaire de femmes initialement sédentaires (étude 3)