1,721,020 research outputs found
Important variable selection in partial least squares for industrial process understanding and control
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131932.pdf (Publisher’s version ) (Open Access)Radboud Universiteit Nijmegen, 22 september 2014Promotor : Buydens, L. Co-promotor : Tran, T.N.101 p
Zero phase filtering for lightning impulse evaluation: a K-factor filter for the revision of IEC60060-1 and-2
No full textThe next revision of the international standard for high voltage measurement techniques, IEC 60060-1, is planned to include a new method for evaluating the parameters associated with lightning impulse voltages. This would be a significant improvement on the loosely defined existing method which is in part reliant on operator judgment and would ensure that a single approach is adopted worldwide to determine peak voltage, front and tail times, realizing standardization in measured parameters across all laboratories. Central to the proposed method is the use of a K-factor to attenuate oscillations and overshoots that can occur with practical generation of impulse voltages for testing on high voltage equipment. It is proposed that a digital filter that matches the K-factor gain characteristic be implemented and used for this purpose. To date causal filter designs have been implemented and assessed. This paper is concerned with the potential application of a non-causal digital filter design to emulate the K-factor. The approach has several advantages; the resulting design is only second order, it can be designed without using optimisation algorithms, it is a zero phase design and it matches the K-factor almost perfectly. Parameter estimation using waveforms from the IEC 61083 -2 Test Data Generator and experimental impulse voltages has been undertaken and obtained results show that the zero phase filter is the ideal digital representation of the proposed K-factor. The effect of evaluating parameters by the proposed method is compared to mean-curve fitting and the challenge of effective front time evaluation is discussed
Experimental studies on surface discharge dynamics and decay under different voltage waveforms and electrode shapes
No full textThis paper studies the development and decay of surface discharge under various voltage waveforms and electrode shapes in air at atmospheric pressure. The electro-optical Pockels method is utilised to measure and quantify the distribution of surface charge. Charge is deposited on the surface of the Bismuth Silicon Oxide (BSO) sensing crystal from a high voltage needle or mushroom electrode. Sinusoidal, square pulse and ramp voltage waveforms of different polarities are generated in order to investigate the differences in the total surface charge, inception voltage and distribution pattern of positive and negative discharges. The total charge deposited can be found by integrating the post-processed charge density over the entire surface. This technique also enables the study of charge decay with time
Studies on the applicability of the Pockels technique to measure surface discharge in liquid dielectrics
No full textThis paper studies the feasibility of applying the electro-optical Pockels technique to measure surface discharge at a solid-liquid insulation interface. The principle of the method is based on the Pockels characteristic of the Bismuth Silicon Oxide (BSO) sensing crystal. The presence of surface charge induces an electric field across the crystal which in turn linearly changes the polarisation state of the incoming polarised light. This change in the light polarisation state can be deduced from the recorded light intensity and hence surface charge density can be calculated. The distribution of charge generated from a needle electrode immersed in mineral oil under two cycles of AC voltage was measured and results are compared with those obtained in gas and gas-liquid structures
Dynamic measurement of surface discharge under different gaseous environments and pressures
No full textThis paper is concerned with the application of the Pockels technique for measuring high voltage surface discharge under local conditions similar to those found in practical gas-insulated-switchgear. A 160 µm thick Bismuth Silicon Oxide (BSO) crystal was utilized as the sensor to quantify charge distribution generated from a needle electrode under two cycles of AC voltage. Results obtained from using SF and their mixtures as an insulating gas are compared with those of air. The effects of gas pressure on discharge behavior are also investigated and discussed with reference to the availability of initiatory electrons, the electron mean free path and Paschen's curve
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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