1,720,990 research outputs found
Reconfigurable concentric circular arrays: a novel hybrid synthesis method
No full textIn this contribution we focus on sparse circular arrays, i.e., non-periodic sparse arrays employing equi-amplitude radiators arranged in rings. In particular, we show some results achieved in the frame of the activities recently carried under a contract funded by the European Space Agency and focused on the development of an active multibeam sparse array demonstrator for satellite communications. More specifically, we address the synthesis of a reconfigurable sparse array tailored to the radiation of beams with two different beamwidths. The synthesis method is based on a hybrid approach, which exploits at best the partial convexity of the problem at hand. Numerical examples showing the feasibility of the approach for satellite applications are included
Advances in the Deterministic Synthesis of Uniform Amplitude Pencil Beam Concentric Ring Arrays
No full textThe paper presents some modifications to the deterministic approach recently proposed for fast design of aperiodic concentric ring arrays. Such modifications are aimed at improving the array performances in terms of directivity, side lobe level and number of control points. In particular, an easy implementation of the size-tapering concept is provided within the processing scheme of the DA procedure; moreover, an improved collocation criterion is presented. Finally, a local optimization procedure, tailored to the concentric ring array case, is addressed
Ensuring Global Coverage with Isophoric Direct Radiating Ring Arrays
No full textIn this contribution we discuss the feasibility of a full-Earth coverage from GEO satellite by means of isophoric (that is, equi-amplitude) Direct Radiating Arrays (DRAs). By focusing on the ring-array architecture we show that a large beam scanning requirement imposes some severe geometrical constraints on the final array layout. Furthermore, we introduce a synthesis procedure capable to generate arrays satisfying the desired specifications with a reasonably low number of control points
On the Synthesis of Plane Wave Generators
No full textThis paper deals with the synthesis of a ???plane wave generator???, i.e. an array able to synthesize a plane wave in the near-zone. In particular, a number of design paradigms are derived and the performance limits are investigated. Numerical results obtained using an effective synthesis algorithm, able to take into account into account the information on the uncertainty on the position and excitation of the array elements during the synthesis process, are presented and discussed
A Generalized Hybrid Approach for the Synthesis of Uniform Amplitude Pencil Beam Ring-Arrays
No full textA generalized hybrid algorithm for the synthesis of uniform amplitude ring-arrays is introduced. The method exploits the analytical properties of the field radiated by a circular array in order to get advantages from the use of convex programming techniques. The method, aimed to the synthesis of circularly symmetric patterns, is very flexible and allows the use of different kind of feeds as well as stepped excitations. The synthesis procedure is demonstrated in the case of high-directivity pencil beam patterns
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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