1,721,065 research outputs found
Vibration tests on the preloaded LARES satellite and separation system
No full textVibration testing of payloads is of paramount importance, and is in fact a standard procedure for all satellites, space structures and components. The use of strain gauges during such tests is relatively common. However, in the present study their use had a different aim, induced by the peculiarity of LARES, an Italian Space Agency satellite. The mission of LARES is to test the theory of general relativity and in particular to measure the frame-dragging effect created by the rotation of the Earth. The design of LARES had to meet some stringent scientific requirements and resulted in a satellite without protruding parts (such as bolts or clamps) typically used to interface a separation system. Indeed to maintain and release LARES, four pins are engaged, with an appropriate preload, in four hemispherical cavities manufactured in the satellite body. The paper reports the results of vibration tests on the satellite and separation system and the trade-off analysis performed to select the best technology for reliable monitoring of the preload. The suitability of the required design was proven by the successful separation and orbit insertion of the LARES satellite that is now working perfectly as the best test particle available in the solar system for testing fundamental physics
A remote controllable thermovacuum facility for CubeSats and small payloads
No full textThe paper presents the upgrade of a thermovacuum facility that was originally designed for testing the cube corner reflectors of LARES satellite. The upgrade consists in the possibility to control the tests remotely over the internet. Part of the upgrade is at the design phase and part has been realized. Specifically the turbomulecular and scroll pumps, the PT100 thermal sensors, the strain gages, the switching of the led, recently added inside the chamber along with the videocamera for visual monitoring of the tests, have been already implemented. Those can be accessed
through a public domain VNC software which can be installed free for research and educational purposes. More demanding in terms of cost and reliability is the automation of the manipulator, the control of the liquid nitrogen flow and the switching of the solar simulator. In particular the high power required for the solar simulator suggest to avoid switching on and off the device. It is under investigation the possibility of using a moving screen. A remotely controlled valve that can reliably be The automation and the possibility to control remotely the facility will allow to run tests over the night more easily. Also the possibility to show the facility during operation to large classes and even to let the students to run their own tests from the class, home or anywhere else, under the remote supervision of a tutor will increase significantly the potential of the thermovacuum facility. An example of test using this mode of operation will also be presented
A Proposal to use FBG sensors for thermo-vacuum tests of space structures
No full textFiber Bragg Grating (FBG) sensors are used in various engineering fields, due to their physical properties.
Multiple FBG sensors (up to 30) can be multiplexed on the same fiber, and their measurements can be read at
the same time by the interrogation system, thus drastically reducing the number and dimension of cables on the
structure to be monitored. A Fiber Bragg grating is made by inducing a periodic change in the refraction index
in the glass core of the fiber; FBG sensors work as optical strain gages, since they provide strain by measuring
a wavelength shift. Strain can be due to mechanical stress or to thermal deformation.
While the use of FBG as strain gages is fairly common, there are few experiments about their use as thermal
sensors.
Some arrays of FBG sensors are planned to be used during the ground test of the Galileo Giove-B satellite in
Thales Alenia Space facilities in Rome. The thermal test will be performed in a thermo-vacuum chamber in
which the pressure of 10-4 Pa, and temperatures from -120°C to +120°C will be used.
The experimental work is aimed to:
· compare the measurement of FBG sensors with the ones acquired using traditional sensors;
· test the technological problem given by the use of optical fibers (fragility of the fiber, connectors
technology, handling), and testing possible solutions
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
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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