1,721,053 research outputs found
Analysis of open-ended circular waveguides using physical optics and incomplete Hankel functions formulation
No full textThe spatial distribution of the electromagnetic field excited in semi-infinite open-ended circular waveguides is analyzed using a physical optics (PO) and incomplete Hankel functions formulation. Using the incomplete Hankel functions, the PO surface integral employed to compute the field quantities is reduced to a simple line integral along the waveguide contour. Such a superposition integral, which describes the elementary field contributions having spherical and cylindrical character, is then evaluated in closed analytical form along the waveguide axis. It is shown that cylindrical waves are generated by the surface currents flowing on the waveguide walls, while the spherical waves are produced by the currents and charges excited at the waveguide truncation. Cylindrical and spherical waves are responsible for the field synthesis in terms of waveguided modes and scattered fields at the waveguide mouth. Numerical examples, demonstrating the accuracy of said field representation in the near- and far-field region of truncated circular waveguides, are finally provided
Exact closed-form expression of the electromagnetic field excited by pulse-shaped and triangular line currents
No full textThe exact closed-form expression for the electromagnetic field excited by pulse-shaped and triangular line currents is presented. The analytical formulation, based on the incomplete Hankel functions, shows that the field is composed of cylindrical waves excited near the current axis and spherical waves arising from the source critical points. Spherical waves related with pulse-shaped current basis functions are shown to have stronger field singularities than for triangular basis functions because of the impulsive charges present at the current truncations. For triangular line currents, it is further shown that an additional spherical wave arises from the critical point featuring a charge jump discontinuity. Near and high-frequency asymptotic field expressions show explicitly the nature of the field singularities. Using the analytical properties of the incomplete Hankel functions, the Galerkin's impedance matrix coefficients, useful to solve radiation and scattering problems in truncated cylindrical structures using the method of moments, are finally derived in a closed-form. Numerical examples show the accuracy of the proposed field representation
Multiple-input multiple-output (MIMO) antenna system
No full textAn antenna system includes a multi-port antenna with an active feeding network coupled thereto. The active feeding network applies complex weights to signals received from and transmitted to each port of the multi-port antenna. The complex weights are applied according to eigenvectors corresponding to a Hermitian matrix representation of the multi-port antenna. The Hermitian matrix may be based on such multi-port antenna parameters such as power dissipation, power radiation, real-power flow, volumetric storage of electromagnetic energy, and/or volumetric dissipation of electromagnetic energy. The multi-port antenna yields orthogonal electromagnetic fields in volumes or surfaces of interest in response to active feeing network excitation
Exact Closed-Form Expression of the Electromagnetic Field Excited by a Uniform Current Distribution Lying on a Cartesian Quadrant
No full textThe exact analytical solution of the electromagnetic field distribution produced by uniform electric currents excited on Cartesian half-planes and quadrants is presented. The total field is expressed in terms of geometrical optics (GO) and diffracted field contributions that remain valid for arbitrary observation points and frequency. The jump discontinuity of the GO field is exactly compensated by the diffracted field whose spatial distribution is described in terms of the incomplete Hankel functions and by means of a novel special function. The expression of the diffracted field includes contributions arising from the edges and the vertex of the considered Cartesian domain, illustrating the analytical behavior of the near-field singularities and providing insight into the physical mechanisms governing the field diffractive processes. The proposed solution yields a method to determine the physical optics (PO) response of flat metallic screens excited by uniform plane waves, as well as the fields produced by pulse-shaped basis functions used in the method-of-moments (MoM) solution of electromagnetic problems, showing the relevance of the exact analytical expressions of the GO and diffracted fields arising from edges and vertices of each rectangular pulse domain. Numerical examples validate the accuracy of the proposed field representation
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
Pressure Dependence of Fragile-to-Strong Transition and a Possible Second Critical Point in Supercooled Confined Water
No full textDispelling 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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