1,721,036 research outputs found
The Actual Optical Design and Preliminary Optomechanical Tolerances of the High Resolution Imaging Channel for the BepiColombo mission to Mercury
No full textThis paper deals with the optical design and preliminary optomechanical tolerances of HRIC, the High Resolution
Imaging Channel of the SIMBIO-SYS instrument, selected as part of the scientific payload for the ESA cornerstone
BepiColombo mission to Mercury. Under the lead of Italy (Principal Investigator: E. Flamini), the project is based on an
international co-operation with Institutes from France and Switzerland. Starting from the stringent scientific requirement
of 5m ground pixel scale @ 400 km from the planet surface, a robust optical design based on a catadioptric Ritchey-
Chretien configuration modified with a dedicated corrector camera has been achieved. The optimized configuration is
convenient in terms of image quality, number of optical elements, and total length. The channel guarantees a corrected
FoV of about 1.5° and allows the achievement of the required resolution with a detector of 2k × 2k pixels. The telescope
is diffraction limited, thanks to its focal ratio (F/8), and shows an optimised radiometric flux within the operative spectral
range (400 - 900 nm). The channel is equipped with one panchromatic and 3 selective filters. The operation plan foresees
the coverage of at least 20% of the whole Hermean surface with the HRIC. The preliminary optomechanical tolerances
and the corresponding image quality have been analyzed. Further thermo-mechanical analysis is in progress, which is
beeing analyzed by means of ray-tracing tools for image quality evaluation
The SHAllow RADar (SHARAD) Onboard the NASA MRO Mission
No full textThis paper describes the mission concepts, design, and achievements of the Italian Space Agency (ASI)- provided Mars SHAllow RADar (SHARAD) sounder high-frequency (HF) sounding radar, used onboard the National Aeronautics and Space Administration (NASA) Mars Reconnaissance Orbiter (MRO) Spacecraft. Its goals are the detection of liquid or solid water below the surface, and the mapping of subsurface geologic structures. Following a brief overview of the MRO mission and of its main science objectives, the paper introduces the basic principles of operation of the radar sounder, and addresses the major design issues faced by such a system. The greatest challenges faced in the design are the control of the interference from off-nadir echoes and the need for a high signal fidelity over a very large fractional bandwidth. The core of the paper is devoted to describing how the above problems have been tackled in the design of the SHARAD instrument, and the main characteristics of its architecture. The two key features of the instrument system design are 1) generation of the transmitted signal directly at the transmitted frequency; and 2) sampling performed directly at the radio frequency (by means of a subsampling technique). The careful design of these features, intended to keep the analog signal path very simple, minimizes distortions and stability problems. An overview of the calibration approach of both the system impulse response and the antenna gain at nadir versus solar array position, an assessment of the in-flight performance of the instrument, and a short summary of the achieved science results are also provided
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
LARES is in orbit! Some aspects of the mission
Full text linkLARES (LAser RElativity Satellite), a scientific satellite of the Italian Space Agency (ASI), has been accurately injected in the nominal orbit by the new ESA expendable launch vehicle, Vega during its qualification launch, on the 13th of February 2012. This was a very exciting result also because of the low success rate of qualification launches . Furthermore, several innovative technical solutions characterize the new European launch vehicle, such as the extensive use of carbon fiber reinforced plastic composites for the rocket structures. LARES program started on February 2008 when the Italian Space Agency awarded a contract to the prime contractor CGS (former Carlo Gavazzi Space). A peculiarity of the LARES program was the extensive involvement of universities in many aspects such as the technical design of the satellite and the innovative separation system. A strong cooperation between ASI and ESA about its respective programs, since the acceptance of the LARES mission for the Vega maiden flight, allowed to design a mission which satisfies the scientific requirements of the satellite along with the launcher qualification objectives. The trajectory itself was defined also taking into account the launch vehicle performance and trajectory constraints. The initial orbit envisaged for the maiden flight was a typical sun-synchronous orbit at about 750 km. However that was not acceptable for the science objectives, i.e., the measurement of the Lense-Thirring effect, an Einstein general relativity prediction. Therefore ESA and the launch vehicle authority, ELV (European Launch Vehicle) Prime Contractor of the VEGA development program, proposed a new orbit at 1200 km that later was changed to 1450 km along with small changes to the inclination in order to comply with all the safety constraints to the mission trajectory. In order to meet part of its qualification requirements, the VEGA upper-stage (AVUM) performed several maneuvers, especially during the ballistic phase, namely: the neutral axis maneuver, the barbeque, sun pointing, and spin axis maneuver. In this paper, an overview of the LARES mission and of its elements, including the payload ground segment, is given, together with the first results of the launch campaign and activities that brought the satellite in the final operative configuration
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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