1,720,992 research outputs found
Study of space charge dynamics in oil and pressboard composite system under different polarity reversal voltages
No full textThe impacts caused by the polarity reversal of the applied voltage on space charge dynamics and electric field enhancement across an oil gap have been studied in an oil gap and single-layer pressboard composite insulation system. The experimental results validate that the electric field enhancement across the oil gap immediately after the application of the reversed electric field is directly dependent on the number of residual charges within the insulation system at the moment of the application of the reversed stress. Therefore, the electric field enhancement in the system is strongly dependent on the magnitude of the applied electric field, the duration of polarity reversal and the degradation of the mineral oil. An estimation of the enhanced electric field immediately after polarity reversal based on the charge decay characteristics has been proposed and successfully applied to calculate the electric field enhancement in an aged oil sample under 20 kV/mm, which cannot be accurately measured due to the very fast space charge dynamics in the aged oil under a strongly enhanced electric field
Data recovery algorithm in space charge measurement by PEA method
No full textPurpose – The pulsed electro-acoustic method is widely applied for space charge measurement in solid dielectrics. The signals, however, can be seriously distorted during transmission, especially in non-planar specimens. The purpose of this paper is to find an efficient algorithm to correctly recover the space charge profile for different types of specimens.Design/methodology/approach – The distortion can be associated with both geometry and material (attenuation and dispersion). Hence the recovery algorithm consists of two parts, respectively. The influences of geometries, causing the divergences of electric force and acoustic waveform, can be corrected by sets of factors. The attenuation and dispersion of the material can be suppressed based on the transfer function matrix in frequency domain, which could be obtained from calibration.Findings – A general algorithm applicable to three kinds of specimens (single-layer, multi-layer and coaxial-geometry dielectrics) has been proposed. Compared with the other two algorithms in literature, the present one offers the most accurate solution while taking relatively shorter time. In addition, this algorithm is applied on signals measured from a planar low-density polyethylene sample and the results show that the new algorithm is fairly effective with excellent stability in a real system.Originality/value – As one of the most accurate algorithms, the present one is theoretically one-third quicker than the others. This algorithm would be helpful in applications calling for large calculations, i.e. 3D imaging of space charge distribution in XLPE cable
Crosslinking-modulated direct-current conductivity of XLPE-PS composite via charge trap characteristics
No full textLow direct-current (DC) conductivity is one of the most desired characteristics for crosslinked polyethylene (XLPE) as a high-voltage DC cable insulation material. In this Letter, a correlation between the DC conductivity and cross-linking characteristics of XLPE-polystyrene (PS) composites at 50 C was studied. Experimental results show that by adjusting the cross-linking structure, different trap distribution characteristics for XLPE-PS composites were realized. With the increase in the cross-linking agent content, DC conductivities of XLPE-PS composites tend to decrease, and the introduced average trap depth increases correspondingly. An increase of 0.07 eV for average charge trapdepth in XLPE-PS composites could be acquired in the test range. It is considered that the increase in the average trap depth reduces the carrier mobility, contributing to the reduction of DC conductivity for XLPE-PS composites. Thus, the DC conductivity and average trap depth of XLPE composites show a strong relevance. The results suggest that the interaction between PS particles and the matrix introduced by cross-linking plays a dominant role in determining the charge conduction for XLPE-PS composites
Facile fabrication of nanoporous gold electrodes that demonstrate high electrochemical activity and used for glucose electrooxidation
No full textNanoporous gold electrodes were fabricated with a novel method: Silver-epoxy was painted on gold surface and Au-Ag alloy was formed by heating, then nanoporous structures were fabricated by dealloying process with nitric acid. The nanoporous gold electrodes shows high surface area (with a roughness factor of ??200) and high electrochemical activity. The electrooxidation of glucose on the nanoporous electrodes were investigated with electrochemical measurements. ? 2013 IEEE.EI
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
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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