1,721,029 research outputs found
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
Experimental reflection evaluation for attitude monitoring of space orbiting systems with nrl arch method
Full text linkThe increasing number of satellites orbiting around Earth has led to an uncontrolled increase in objects within the orbital environment. Since the beginning of the space age on 4 October 1957 (launch of Sputnik I), there have been more than 4900 space launches, leading to over 18,000 satellites and ground‐trackable objects currently orbiting the Earth. For each satellite launched, several other objects are also sent into orbit, including rocket upper stages, instrument covers, and so on. Having a reliable system for tracking objects and satellites and monitoring their attitude is at present a mandatory challenge in order to prevent dangerous collisions and an increase in space debris. In this paper, the evaluation of the reflection coefficient of different shaped objects has been carried out by means of the bi‐static reflection method, also known as NRL arch measurement, in order to evaluate their visibility and attitude in a wide range of frequencies (12–18 GHz). The test campaign aims to correlate the experimental measures with the hypothetical reflection properties of orbiting systems
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
Ground simulation of the effects of the space environment on ceramic nano-coated panels for space environment protection
No full textA critical aspect to be addressed through materials engineered for aerospace missions is to provide the protection of space subsystems from the aggressive operative environment, in order to extend the life of such subsystem. Taking this fact into account, carbon-based ceramic composites are ideal candidates for the next development of industrial research in the aerospace field, thanks to the wide range of multi-functional elements obtainable using these materials. For example, ceramic-based hybrid structures can be designed to perform the environmental shielding function as well as to ensure the reusability of the structure itself. In particular, covering the surface of a C/C structure with a protective coating based on nano-particles and metal oxides it would be possible to preserve the functionality of the bulk (i.e. resistance to the critical conditions of the atmospheric re-entry phase) from the dangerous effects due to the LEO space environment where most of the missions takes place (mainly due to outgassing and oxygen erosion/corrosion atomic). In this paper the effects of the Space Environment on self-produced Carbon/Carbon nano coated panels have been evaluated in order to study a possible dual use
Effects of atomic oxygen and UV rays ageing on the reflection coefficient of carbon/carbon plates in the 12-18 GHz frequency range
Full text linkAdvanced carbon-based ceramic materials, such as Carbon/Carbon (C/C) are commonly employed in aerospace industry to face the thermo-mechanical stress suffered by the spacecraft external structures during re-entry in earth atmosphere. Thanks to very low thermal expansion and outstanding chemical stability at extreme temperatures, in fact, such materials represent the ideal candidates for re-usable space integrated systems, such as TPS, nozzles and ablation thermal-proof structures. In long-time missions, on the other hand, issues related to continuous and extended exposure of the spacecraft surfaces to the detrimental space environment must be carefully considered. In this frame, also the tracking of satellites by mean of radar systems is a vital aspect for a safe stay in space. In LEO working conditions, the combined effects induced by severe thermal cycles, ultra-high vacuum and UV/Atomic Oxygen(AO) irradiation can be of impediment for the use of C/C as re-entry protection material, since a significant surface oxidation leads to so high TPS damaging as to compromise its main functionality. This surface oxidation can also affect the radar visibility of satellites. Aim of this paper is to evaluate the effects of the AO/UV ageing on C/C plates reflection coefficient, in order to avoid misfunctioning in the radar visibility
Degradation of carbon-based space materials with SiO2 nano-coating due to outgassing effects
No full textIn recent years, the emphasis in space research has been focused on both exploration and commercialization of space. In order to use space for these purposes it is mandatory to guarantee the compliance with the low earth orbit (LEO) space environment that degrades the performances and functionality of materials with phenomena such as atomic oxygen (AO), ultraviolet (UV) radiation, plasma, micrometeoroids and debris, as well as severe temperature cycles. In this frame the study of Outgassing properties of space materials is of primary importance. The resistance of a material to the high vacuum and high temperatures is one of the most critical issues of spaceability of materials. A material with poor outgassing properties will de-gas volatile particles of itself and humidity with critical effects on electronic and optical devices. The resistance to high vacuum will assure the durability and the reliability of materials and structures. Carbon based materials are of common use for re-entry-from-space applications, as thermal protection systems, thanks to their resistance to high temperatures. Carbon-Carbon (C/C) composites are engineered materials principally composed by carbon fibers and carbon matrix. They offer a wide range of properties that can be tailored by the selection of constituent materials, fiber orientations, and methods of fabrication. In this paper Outgassing tests have been performed on samples obtained from high thickness C/C prototypes for employment in re-entry systems. The C/C densification has been achieved by means of a customized CVI treatment. The outgassing tests have been performed both on four "naked" and three coated samples per kind. The considered coating was a solution of 0.5% and 1% in weight of SiO2 nano-spheres mixed in a pyro-paint liquid varnish. The results show a complete compatibility of the materials under investigation with the standard. In fact for all the materials, both coated and naked, the TML is below 1 %, RML is below 1 % and the CVCM is below 0.1%
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