1,721,176 research outputs found
GMCAO for E-ELT: A feasibility study
Full text linkIn this paper, we discuss the feasibility and the performance assessment of a possible MCAO system for E-ELT, basedon the novel concept of Global MCAO, which takes advantage of a very wide technical FoV to perform adaptive opticscorrection using only natural guide stars, with the aim to increase the sky coverage. The technique envisages thedefinition of Virtual-DMs, as tools for the global reconstruction. This investigation has been carried out during afeasibility study we performed for ESO, in which we combined computations, simulations and literature. The aim of thisanalysis is to identify and review the main parameters and the technical issues, which would act as error sources in a realGMCAO system, evaluating their contribution to the overall performance. The study involves both issues related to thePyramid WFS in general, and to the GMCAO case in particular, including the wavelength and FoV size selection, thenumber of guide stars and reconstructed Virtual-DMs, and actual components parameters
Statistical and morphological analysis of mock galactic fields in the Global-MCAO perspective
Full text linkEnabling accurate morphological and photometric analysis across a wide Field of View (FoV) is one of the keyscience requirement for multi-conjugate adaptive optics systems. With this motivation we present a study aimedat the investigation of the performance of Global-MCAO (GMCAO). Such an innovative concept, based onnatural guide stars in a wide technical FoV, addresses the need for an increase of the sky coverage, which is akey ingredient for future MCAO-based VLT instruments and for the forthcoming E-ELT. Using a tomographicsimulation tool, we compute a map of the Strehl Ratio in a 250′′ × 250′′ area, matching the Chandra Deep FieldSouth survey. Mock images of star and galactic fields are then built using such a map and analyzed as if theywere real and observed with the E-ELT instrumentation. We perform the source detection and two-dimensionallight-profile modeling using the IRAF/ELLIPSE code and we then compare the recovered parameters with theintrinsic data. The good match of our results claims that GMCAO is a reliable approach that can rebuild theAO concepts and can provide a frame of reference for a number of science cases
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
The Chandra Deep Field South as a test case for Global Multi Conjugate Adaptive Optics
Full text linkThe era of the next generation of giant telescopes requires not only the advent of new technologies but also the development of novel methods, in order to exploit fully the extraordinary potential they are built for. Global Multi Conjugate Adaptive Optics (GMCAO) pursues this approach, with the goal of achieving good performance over a field of view of a few arcmin and an increase in sky coverage. In this article, we show the gain offered by this technique to an astrophysical application, such as the photometric survey strategy applied to the Chandra Deep Field South as a case study. We simulated a close-to-real observation of a 500 × 500 arcsec2 extragalactic deep field with a 40-m class telescope that implements GMCAO. We analysed mock K-band images of 6000 high-redshift (up to z = 2.75) galaxies therein as if they were real to recover the initial input parameters. We attained 94.5 per cent completeness for source detection with SEXTRACTOR. We also measured the morphological parameters of all the sources with the two-dimensional fitting tools GALFIT. The agreement we found between recovered and intrinsic parameters demonstrates GMCAO as a reliable approach to assist extremely large telescope (ELT) observations of extragalactic interest
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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