Evidence from stellar rotation of enhanced disc dispersal: (I) The case of the triple visual system BD-21 1074 in the β\beta Pictoris association

The early stage of stellar evolution is characterized by a star-disc locking mechanism. The disc-locking prevents the star to spin its rotation up, and its timescale depends on the disc lifetime. Some mechanisms can significantly shorten this lifetime, allowing a few stars to start spinning up much earlier than other stars. In the present study, we aim to investigate how the properties of the circumstellar environment can shorten the disc lifetime. We have identified a few multiple stellar systems, composed of stars with similar masses, which belong to associations with a known age. Since all parameters that are responsible for the rotational evolution, with the exception of environment properties and initial stellar rotation, are similar for all components, we expect that significant differences among the rotation periods can only arise from differences in the disc lifetimes. A photometric timeseries allowed us to measure the rotation periods of each component, while high-resolution spectra provided us with the fundamental parameters, $v\sin{i}$ and chromospheric line fluxes. The rotation periods of the components differ significantly, and the component B, which has a closer companion C, rotates faster than the more distant and isolated component A. We can ascribe the rotation period difference to either different initial rotation periods or different disc-locking phases arising from the presence of the close companion C. In the specific case of BD$-$21 1074, the second scenario seems to be more favored. In our hypothesis of different disc-locking phase, any planet orbiting this star is likely formed very rapidly owing to a gravitational instability mechanism, rather than core accretion. Only a large difference of initial rotation periods alone could account for the observed period difference, leaving comparable disc lifetimes.Comment: Accepted by Astronomy & Astrophysics on July 31, 2014; Pages 12, Figs.

Efficient nonparametric bayesian inference for X-ray transforms

We consider the statistical inverse problem of recovering a function $f: M \to \mathbb R$, where $M$ is a smooth compact Riemannian manifold with boundary, from measurements of general $X$-ray transforms $I_a(f)$ of $f$, corrupted by additive Gaussian noise. For $M$ equal to the unit disk with `flat' geometry and $a=0$ this reduces to the standard Radon transform, but our general setting allows for anisotropic media $M$ and can further model local `attenuation' effects -- both highly relevant in practical imaging problems such as SPECT tomography. We propose a nonparametric Bayesian inference approach based on standard Gaussian process priors for $f$. The posterior reconstruction of $f$ corresponds to a Tikhonov regulariser with a reproducing kernel Hilbert space norm penalty that does not require the calculation of the singular value decomposition of the forward operator $I_a$. We prove Bernstein-von Mises theorems that entail that posterior-based inferences such as credible sets are valid and optimal from a frequentist point of view for a large family of semi-parametric aspects of $f$. In particular we derive the asymptotic distribution of smooth linear functionals of the Tikhonov regulariser, which is shown to attain the semi-parametric Cram\'er-Rao information bound. The proofs rely on an invertibility result for the `Fisher information' operator $I_a^*I_a$ between suitable function spaces, a result of independent interest that relies on techniques from microlocal analysis. We illustrate the performance of the proposed method via simulations in various settings

Inverse anisotropic diffusion from power density measurements in two dimensions

This paper concerns the reconstruction of an anisotropic diffusion tensor $\gamma=(\gamma_{ij})_{1\leq i,j\leq 2}$ from knowledge of internal functionals of the form $\gamma\nabla u_i\cdot\nabla u_j$ with $u_i$ for $1\leq i\leq I$ solutions of the elliptic equation $\nabla \cdot \gamma \nabla u_i=0$ on a two dimensional bounded domain with appropriate boundary conditions. We show that for I=4 and appropriately chosen boundary conditions, $\gamma$ may uniquely and stably be reconstructed from such internal functionals, which appear in coupled-physics inverse problems involving the ultrasound modulation of electrical or optical coefficients. Explicit reconstruction procedures for the diffusion tensor are presented and implemented numerically.Comment: 27 pages, 6 figure

Decoding machine learning benchmarks

Despite the availability of benchmark machine learning (ML) repositories (e.g., UCI, OpenML), there is no standard evaluation strategy yet capable of pointing out which is the best set of datasets to serve as gold standard to test different ML algorithms. In recent studies, Item Response Theory (IRT) has emerged as a new approach to elucidate what should be a good ML benchmark. This work applied IRT to explore the well-known OpenML-CC18 benchmark to identify how suitable it is on the evaluation of classifiers. Several classifiers ranging from classical to ensembles ones were evaluated using IRT models, which could simultaneously estimate dataset difficulty and classifiers' ability. The Glicko-2 rating system was applied on the top of IRT to summarize the innate ability and aptitude of classifiers. It was observed that not all datasets from OpenML-CC18 are really useful to evaluate classifiers. Most datasets evaluated in this work (84%) contain easy instances in general (e.g., around 10% of difficult instances only). Also, 80% of the instances in half of this benchmark are very discriminating ones, which can be of great use for pairwise algorithm comparison, but not useful to push classifiers abilities. This paper presents this new evaluation methodology based on IRT as well as the tool decodIRT, developed to guide IRT estimation over ML benchmarks.Comment: Paper published at the BRACIS 2020 conference, 15 pages, 4 figure

Absolute Fluorescence Spectrum and Yield Measurements for a wide range of experimental conditions

For the JEM-EUSO CollaborationThe fluorescence yield is a key ingredient in cosmic ray energy determination. It is sensitive to pressure, temperature and humidity. Up to now the fluorescence yield of the brightest line at 337 nm has been measured in an absolute way in one set of conditions, whereas fluorescence yields at the other wavelengths have been relatively measured for different conditions. Thus, absolute calibration for all the lines is unclear. We will do all measurements at once using the same apparatus: all the lines will be measured absolutely and not relatively for all conditions. For that we will use the 3-5 MeV electron beam of the PHIL accelerator (Photon Injector at LAL), shooting in a box filled with air at varying pressures, temperatures and humidity. Delta rays resulting from the beam collisions with Nitrogen are responsible for the light yield. The light detection probability should be independent of its emission point especially at the delta ray stopping point. The idea is to use an integrating sphere, encapsulated in a vessel where pressure, temperature and humidity can be varied. This sphere will have two ports for the beam (in and out), one more port dedicated to a NIST photodiode for calibration and another port feeding optical fibers going to: A) a grating spectrometer equipped with cooled CCD. B) a photomultiplier with BG3 filters to measure directly the integrated yield. Calibrations at the percent level, will give each line spectrum yields with a precision between 2 to 5%. A special issue will be to estimate the leakage due to "high energy" delta rays. Thus, we the air density will be increased, the beam energy will be lowered until the beam stops inside the sphere. Then, the energy loss will be precisely derived from the Bethe-Bloch formula. We will present the set-up

Synthesis and evaluation of new designed multiple ligands directed towards both peroxisome proliferator-activated receptor-γ and angiotensin II type 1 receptor

Because of the complex biological networks, many pathologic disorders fail to be treated with a molecule directed towards a single target. Thus, combination therapies are often necessary, but they have many drawbacks. An alternative consists in building molecules intended to interact with multiple targets, called designed multiple ligands. We followed such a strategy in order to treat metabolic syndrome, by setting up molecules directed towards both type 1 angiotensin II (AT1) receptor and peroxisome proliferator-activated receptor-γ (PPAR-γ). For this purpose, many molecules were prepared by merging both pharmacophores following three different strategies. Their ability to activate PPAR-γ and to block AT1 receptors were evaluated in vitro. This strategy led to the preparation of many new PPAR-γ activating and AT1 blocking molecules. Among them, some exhibited both activities, highlighting the convenience of this approach

The Distance to NGC 1316 (Fornax A) From Observations of Four Type Ia Supernovae

The giant elliptical galaxy NGC 1316 (Fornax A) is a well-studied member of the Fornax Cluster and a prolific producer of Type Ia supernovae, having hosted four observed events since 1980. Here we present detailed optical and near-infrared light curves of the spectroscopically normal SN 2006dd. These data are used, along with previously published photometry of the normal SN 1980N and SN 1981D, and the fast-declining, low-luminosity SN 2006mr, to compute independent estimates of the host reddening for each supernova, and the distance to NGC 1316. From the three normal supernovae, we find a distance of 17.8 +/- 0.3 (random) +/- 0.3 (systematic) Mpc for Ho = 72. Distance moduli derived from the "EBV" and Tripp methods give values that are mutually consistent to 4 -- 8%. Moreover, the weighted means of the distance moduli for these three SNe for three methods agree to within 3%. This consistency is encouraging and supports the premise that Type Ia supernovae are reliable distance indicators at the 5% precision level or better. On the other hand, the two methods used to estimate the distance of the fast-declining SN 2006mr both yield a distance to NGC 1316 which is 25-30% larger. This disparity casts doubt on the suitability of fast-declining events for estimating extragalactic distances. Modest-to-negligible host galaxy reddening values are derived for all four supernovae. Nevertheless, two of them (SN 2006dd and SN 2006mr) show strong NaID interstellar lines in the host galaxy system. The strength of this absorption is completely inconsistent with the small reddening values derived from the supernova light curves if the gas in NGC 1316 is typical of that found in the interstellar medium of the Milky Way. In addition, the equivalent width of the NaID lines in SN 2006dd appear to have weakened significantly some 100-150 days after explosion.Comment: 50 pages, 13 figures, 10 tables; constructive comments welcome. Accepted for publication in A

PHIL Accelerator at LAL - Diagnostic status

http://accelconf.web.cern.ch/AccelConf/BIW2010/papers/tupsm100.pdfInternational audienceThe "Photo-Injector at LAL" (PHIL : http://phil.lal.in2p3.fr/) is a new electron beam accelerator at LAL. This accelerator is dedicated to test and characterise electron photo-guns and high-frequency structures for future accelerator projects (like the next generation lepton colliders, CLIC, ILC). This machine has been designed to produce low energy (E<10 MeV), small emittance (epsilon < 10 pi.mm.mrad), high current (charge 2 nC/bunch) electrons bunch at low repetition frequency (frep<10Hz) [1]. The first beam has been obtained on the 4th of November 2009. This paper will describe the current status and the futures developments of the diagnostics devices on this machine

The beta Pictoris association: Catalog of photometric rotational periods of low-mass members and candidate members

We intended to compile the most complete catalog of bona fide members and candidate members of the beta Pictoris association, and to measure their rotation periods and basic properties from our own observations, public archives, and exploring the literature. We carried out a multi-observatories campaign to get our own photometric time series and collected all archived public photometric data time series for the stars in our catalog. Each time series was analyzed with the Lomb-Scargle and CLEAN periodograms to search for the stellar rotation periods. We complemented the measured rotational properties with detailed information on multiplicity, membership, and projected rotational velocity available in the literature and discussed star by star. We measured the rotation periods of 112 out of 117 among bona fide members and candidate members of the beta Pictoris association and, whenever possible, we also measured the luminosity, radius, and inclination of the stellar rotation axis. This represents to date the largest catalog of rotation periods of any young loose stellar association. We provided an extensive catalog of rotation periods together with other relevant basic properties useful to explore a number of open issues, such as the causes of spread of rotation periods among coeval stars, evolution of angular momentum, and lithium-rotation connection.Comment: Forthcoming article, Received: 20 June 2016 / Accepted: 09 September 2016; 40 pages, 2 figures. The online figures A1-A73 are available at CD