1,720,979 research outputs found
Harmonic analysis and reduction of the scattered field from electrically large cloaked metallic cylinders
Full text linkIn this paper, an analysis of the spectral composition of the scattered field from coated metallic cylinders is performed, focusing particularly on the cloaking of electrically large structures. An expression of the scattering coefficients is derived, considering both a dielectric and a metasurface coating. Modeling the metasurface as a surface impedance boundary condition, the surface impedance, which annuls one harmonic of the scattered field, is formulated in a closed and compact form. Moreover, in the case of cylinders with radius comparable with the wavelength of interest, it is demonstrated that a reduction of the scattering is possible by using a homogeneous metasurface coating, which presents a positive surface reactance. In particular, a reduction of the scattering width of 4 dB is achieved for a cylinder radius of a = 0.917λ0
Spectral Composition of the Scattered Field from a Large Metallic Cloaked Cylinder
No full textAn analysis of the spectral content of the scattered field by metallic cylinders covered by homogeneous mantle cloak is performed. In particular, a theoretical approach based on Mie Theory is considered for the computation of the scattered field, which is examined in terms of radar cross-section and scattering coefficients. The values of surface impedance that lead to the minimum of the radar cross section are determined as a function of the cylinder radius normalized with respect to the frequency of operation and of the dielectric material characteristics. Furthermore, the spectral composition of the scattered field for this optimal condition is evaluated and compared with that of the bare cylinder case
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
Mantle cloaking due to ideal magnetic dipole scattering
Full text linkOne of the most exciting applications of metaparticles and metasurfaces consists in the magnetic light excitation. However, the principal limitation is due to parasitic extra multipoles of electric family excited in magnetic dipole meta-particles characterized by a radiating nature and corresponding radiating losses. In this paper, we propose the “ideal magnetic dipole” with suppressed additional multipoles except of magnetic dipole moment in the scattered field from a cylindrical object by using mantle cloaking based on metasurface and on anapole concept. The considered metasurface consists of a periodic width modulated microstrip line, with a sinusoidally shaped profile unit cell printed on a dielectric substrate
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
A radial transmission line model for mantle cloaking with impedance metasurfaces
No full textIn this work, the problem of reducing the scattering from conductive cylinders is reformulated by considering a matching problem with radial transmission lines. A unique compact closed-form solution for the surface impedance loads Z s (m,kb) above a cylindrical grounded dielectric substrate is found without any approximation as a function of the harmonic index m (scattering mode to suppress) and of the frequency regime kb (product of wavenumber k and radius b of the cloaked system). Possible implementations with a microstrip-line based metasurface are discussed and presented
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