1,721,310 research outputs found
The surface brightness of megaconstellation satellite trails on large telescopes
Full text linkOn large telescopes, the trails produced by MegaConstellation satellites will be significantly defocused due to their close proximity. As a result, their apparent surface brightness will be, under a range of conditions, almost constant during their apparent sweep across the focal plane. This paper derives a few simple relationships and evaluate the impact of such trails on operations of large optical ground based facilities
Correction of non-common path aberrations in pyramid wavefront sensors to recover the optimal magnitude gain using a deformable lens
No full textAdaptive optics (AO) correction based on pyramid wavefront sensors (P-WFSs) has been successfully implemented in several instruments for astronomical observation due to the P-WFS advantages in terms of sensitivity with respect to other WFSs, such as the Shack-Hartmann. The correction of non-common path aberrations (NCPAs) between the sensing and the scientific arm, commonly performed introducing offsets to the Zernike coefficients of the measured wavefront in the AO closed loop, reduces the sensitivity of P-WFSs causing a loss in sky coverage and scientific throughput. We propose a technique to exploit the full capabilities of P-WFSs compensating the NCPAs up to the fourth order on the WFS channel by means of a multi-actuator adaptive lens (MAL). We show the preliminary results obtained in a dedicated laboratory test bench
Improved handwritten character recognition using second-order information from training set
No full textThe problem of improving the capability of statistical character classifiers based on finite and sparse training sets is addressed. A significant improvement is obtained coupling standard classifiers based on the k-nearest neighbours technique with a second higher level classification stage. This method has been applied to three existing classifiers reducing the error rate at zero rejection of ~ 17%. © 1993, The Institution of Electrical Engineers. All rights reserved
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
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
The opto-mechanical alignment procedure of the VLT Survey Telescope
No full textThe VLT Survey Telescope is a f/5.5 modified Ritchey-Chretien imaging telescope, which is being installed at the ESO-Paranal Observatory. It will provide a one square degree corrected field of view to perform surveyprojects in the wavelength range from UV to I band. In this paper we describe the opto-mechanical alignment procedure of the 2.61m primary mirror, the secondary and correctors lenses onto the mechanical structure of the telescope. The alignment procedure does not rely on the mechanical precision of the mirrors. It will be achieved using ad-hoc alignment tools, described in the paper, which allows the spatial determination of optical axes (and focuses where necessary) of the optical components with respect to the axis defined by the rotation of a laser beam mounted on the instrument bearing. © 2010 SPIE
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
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