1,720,959 research outputs found
Multiphysics Design and Experimental Verification of a Quad-Band Dichroic Mirror for Deep Space Ground Stations
No full textThis study presents the multi-disciplinary approach used to study a quad-band dichroic mirror to be installed in the European Space Agency deep space antennas. Traditional electromagnetic (EM) analyses based on a uniform plane wave incidence were augmented by advanced numerical techniques to investigate the impact of the dichroic mirror on the overall antenna performance. In addition, along with the EM design, a parallel study considering mechanical, thermal and power-handling aspects allowed their impact on the EM behaviour of the dichroic mirror to be evaluated. This comprehensive study permitted an optimum design to be achieved for the dichroic mirror, which accounts for the actual operational conditions of the mirror itself when installed in the antenna. The device was manufactured and measured, verifying also the mechanical and thermal theoretical predictions, obtaining an excellent agreement between simulations and experimental results
A X/K/Ka-band Dichroic Mirror for ESA Deep Space Antennas
No full textThis paper presents a complete overview of the project activity for a new dichroic mirror to replace the actual unit (M6, currently installed in the DSA2, Cebreros, Spain).
The required specifications and constraints, the analysis and design tools adopted and the design of the dichroic mirror are also discussed. The manufacturing, testing and measuring techniques adopted to fabricate, verify and measure this dichroic mirror are presented.
The new dichroic mirror discussed in this paper is due to be installed at the same nominal incidence angle of the actual unit and it will transmit the Ka-band Rx and the Ka-band Tx channels while it will reflect the X-band Rx, X-band Tx channels and K-band (25.5–27 GHz).
For all frequencies, the dichroic mirror will be able to operate with Left-Hand Circular Polarisation (LHCP) and Right-Hand Circular Polarisation (RHCP) simultaneously.
A detailed mechanical model of the dichroic mirror has been implemented to simulate the thermo-elastic behaviour of the entire mirron in operation.
The structure is modeled assuming two different elastic materials: the external ring composed of solid bulk material (aluminium alloy), and the perforated central part considered as a continuum orthotropic elastic material.
In particular, the mechanical and thermal parameters of the perforated area have been retrieved by numerical simulation of a significant portion of the perforated area itself.
The thermal analysis takes into account the internal conduction and the convection operated along the external surface of the mirror and through the perforated part of the plate by the surrounding air applying an ambient temperature of 20 °C
An Efficient Method to Design Planar Arrays for High Power Applications by Mutual Coupling Optimization
No full textMulti-physics Design and Manufacturing of a Quad-band Frequency Selective Surface for Space Applications
No full text
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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