1,720,956 research outputs found
Permittivity in epoxy based syntactic foam nanocomposites
No full textFollowing previous work, this paper focuses on a new type of epoxy based syntactic foam, a lightweight material which is known to electrical engineering since the seventies, but so far couldn't live up to it's potential in high voltage applications. This is mainly because of the basic structure of syntactic foam, which provides closed cell porosity. The porosity, which gives syntactic foam its weight reduction, unfortunately leads to shortcomings in terms of dielectric strength and PD resistance. However: with recent advances in material science and the dawn of nanotechnology, there is a new take on this unique material, which can be used as insulating material for HV-applications, where weight is of vital importance. Four different types of epoxy based syntactic foam nanocomposites are presented, whose respective dielectric behavior were studied with help of dielectric spectroscopy. The measurement results, with emphasis on the complex permittivity, are presented in this work. Also the advantages and shortcomings of the various composites are discussed, as they are compared with both unmodified syntactic foam, as well as the unmodified base epoxy
The investigation of the permittivity of syntactic foam under varying humidity
No full textThe dielectric properties of syntactic foam samples, with emphasis on the complex permittivity, were studied via dielectric spectroscopy. The investigated syntactic foam samples consist of an epoxy matrix, filled with hollow glass spheres of 60 microns diameter on average with a high filler rate of 50% of volume. In order to see the influence of adsorbed water, the filler of one sample type was stored under 80% humidity to create wet samples, while the other samples were constantly kept dry. Previous measurements showed increased DC conductivity for syntactic foam - up to two orders of magnitude compared to conventional filled epoxy. This was suspected to be due to the relative high conductivity of the glass, as well as due to the sheer amount of glass spheres and therefore plenty of interfaces. Recent measurement at lower frequencies (below 10-2 Hz) showed quasi-dc-behavior and virtually no difference for both dry and wet samples at 70degC, while dry samples had generally higher values in permittivity for 40degC. It is shown that the glass spheres overshadow the influence of adsorbed water in the syntactic foam samples measured
Dielectric behavior of syntactic foams at low temperatures and frequencies
No full textSyntactic foam is a lightweight composite consisting of hollow particles embedded in a polymer resin matrix. In this paper, results are presented of dielectric spectroscopy measurements on test specimens of syntactic foam with glass micro-spheres partially filled with SO2 . This type of syntactic foam is intended to be used as a high performance insulating material for lightweight high-voltage DC applications. The dielectric spectroscopy results showed an anomalous non-Debye behavior in a temperature range from roughly -140degC to +40degC. With increasing temperature the losses decrease at first, until they suddenly increase again at about +40degC. It has to be noted that the overall losses were quite high, compared to the base material. It appears that either the increased dc conductivity, the interfacial polarization at the interfaces between glass and epoxy, or both are the reason for these overall high losses. It is pointed out that the anomalous relaxation peak shifts to lower temperatures when the frequency is increased, contrary to normal behavior. In addition, a merge of two relaxation peaks is visible for higher frequencies at around 70degC, tentatively explained as being caused by the phase transition of SO2
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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