1,720,965 research outputs found
Calculating mutual ground impedances between overhead and buried cables
No full textAerial and buried electric conductors often share the same right of way. When a phase-to-ground fault occurs, high transient-induced overvoltages appear from short-circuit currents to the ground. The mutual ground-loop impedances between both systems are given by the Pollaczek coupling integral that does not possess an analytic closed-form solution, and its integrand is highly oscillatory to perform a direct numerical integration. An efficient and accurate algorithmic evaluation of the Pollaczek coupling integral is presented in this paper. The obtained result is used in the numerical assessment of approximated formulas previously issued by Lucca, Wedepohl, and Comité Consultatif International TZapotitlánlZapotitlánphonique et TZapotitlánlZapotitlángraphique. Zapotitlán 2008 IEEE
Alternative series-based solution to approximate pollaczek's integral
No full textIn this letter, the Wedepohl-Wilcox series is combined with the trapezoidal rule of integration for calculating ground return impedances of buried cables. In this hybrid method, the former are used for low frequencies and the latter are for high frequencies. Based on a numerical analysis, a criterion for switching between series and numerical integration is proposed here and compared with the one proposed by Wedepohl-Wilcox. Validation of the improved criterion is made via an electromagnetic transient. Zapotitlán 1986-2012 IEEE
Images profiles voltages on RLC electric grid with frequency dependent
No full textThis paper presents a methodology based on image processing, circuit theory and state variables to estimate the voltage profile along an electrical grid with RLC frequency dependent elements. Numerical techniques are used to obtain the dynamic solutions of EMTP, Z transform and Laplace transform of an electric grid. Finally, based on the theoretical solution of an infinite resistive network, the matrix arrangement for calculating the voltage profiles are shown through contour images obtained from the nodal equations, solving equivalent matrix circuit techniques. � 2014 IEEE
The numerical Laplace transform: An accurate technique for analyzing electromagnetic transients on power system devices
No full textA detailed description of the numerical Laplace transform (NLT) for electromagnetic transient calculation on power system devices under linear and non-linear conditions is presented in this paper. The development and main advantages of the NLT are reviewed, as compared to the conventional time domain simulation, including current practices for reducing numerical errors derived from data truncation and discretization of the analytical equations. A simple technique based on the superposition principle to include non-linear conditions in the frequency domain is also fully described. Besides, important results obtained recently with the NLT for different power components are presented, including comparisons with widely used time domain methods, such as the method of characteristics, and the professional simulation program EMTDC. Such comparisons reveal a high accuracy of the numerical Laplace transform when applied to the presented studies. � 2008 Elsevier Ltd. All rights reserved
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Efficient truncation criterion for the parameter estimation of a stratified ground block
No full textA truncation criterion to solve the vector potential integrals proposed by Takahashi and Kawase is described in this letter. The main aim of those integrals is to estimate the depth and resistivity parameters of a stratified ground block. The derivation of the proposed criterion considers the error introduced by the infinite limit truncation of the integrals. In addition, an efficient solution can be obtained by the use of the trapezoidal rule of integration. � 1986-2012 IEEE
Variations on the Author
Get PDF“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
Get PDFWe 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
Get PDFWe 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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