1,721,078 research outputs found
Optical solutions for extreme instrumentation: from ground to space
Full text linkNew generation astronomical instruments have the purpose to enable more and more precise observations of celestial objects. To fulfill the ever increasing requirements posed by new science goals, it is mandatory that the instrument design is developed taking into account the various constraint coming from observing conditions, environment, performance and integration with other instruments and, at the same time, exploiting in the best possible way new
technologies and observing techniques.
This Thesis describes the optical design activity conducted for the development of three new instruments: JANUS, SHARK and PLATO. All the three instruments are mainly dedicated to planetary science observations, but they are very different in the techniques they will exploitand the environment in which they will operate.
JANUS is a visible camera that will be part of the ESA space mission JUICE dedicated to the study of Jupiter and its moons. The camera will operate in space, far from the Earth and in a strong radiation environment caused by charged particles trapped by the magnetic field of Jupiter. SHARK is a coronagraphic high-contrast imager for the Large Binocular Telescope (LBT) dedicated to the direct imaging of exo-planets and proto-planetary disks around nearby stars. PLATO is a space satellite dedicated to the indirect detection of earth-sized exo-planets with the transit method.
A brief introduction is given for each instrument, describing their principal characteristics and science objectives, followed by a more detailed description of the optical design and analyses conducted to characterize the performance and ful_llment of the science objectives
Spatial filtering applied to the pyramid WFS: Simulations and preliminary results
Full text linkIn this paper we discuss the potentiality of the spatial filtering approach for the case of a pupil plane wavefront sensor like the pyramid sensor. Filtering is realized by selectively blocking the light just before the pyramid prism. Several schemes can be followed to accomplish this: from a simple field stop that blocks high-order spatial frequencies in order to reduce the aliasing effect (an example is the so-called spatial filtered Shack- Hartmann) to more complicated frequency-selection schemes. In this work we present the simulation environment that we developed to investigate different approaches in this sense aimed at understanding if any practical advantages in wavefront sensing can be effectively attained in particular regimes. We present some preliminary results obtained with end-to-end simulations. In particular, we qualitavely explored the simplest frequency-selection scheme consisting of a field stop just in front of the pyramid. We show that this can help mitigating the effect of contaminating high-order frequencies. Next steps will be in the direction of exploring different reference star brightness regimes in order to determine under which conditions spatial filtering can improve the quality of closed-loop correction. Moreover, different spatial filter sizes and shapes to control the frequencies conveyed to the wave-front sensor will be investigated
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
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
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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
- …
