1,720,969 research outputs found
Analysis of conduction currents in nanofluids
No full textWe have compared the DC conduction of a nanofluid based on mineral oil and magnetite nanoparticles with that of the base mineral oil using a point/plane electrode configuration. The results show that the nanofluid has higher conduction currents and that transition from ohmic to tunneling-controlled conduction occurs at higher fields. This latter evidence might explain why nanofluids improve partial discharge inception voltage under AC conditions. After some tests we observed that the nanofluid is not stable under DC: the nanoparticles are separated from the base fluid by coulombic forces and dielectrophoresis.We have compared the DC conduction of a nanofluid based on mineral oil and magnetite nanoparticles with that of the base mineral oil using a point/plane electrode configuration. The results show that the nanofluid has higher conduction currents and that transition from ohmic to tunneling-controlled conduction occurs at higher fields. This latter evidence might explain why nanofluids improve partial discharge inception voltage under AC conditions. After some tests we observed that the nanofluid is not stable under DC: the nanoparticles are separated from the base fluid by coulombic forces and dielectrophoresis
Behavior of nanofluids under DC divergent fields
No full textA recent investigation on the DC stability of nanofluids has revealed some interesting phenomena regarding the polarization current; some unexpected slow peaks appeared after the voltage reached a precise value. In this work we have deepened and analyzed the possible mechanisms which could cause such experimental results. While in low concentration nanofluids a charge trapping mechanism seems to be the prevailing one, at higher concentration, the reduced nanoparticles distances and the lower energy barrier between two consecutive nanoparticles is able to activate the tunneling charge transfer among them, thus increasing their apparent mobility
Effect of graphene oxide-based nanostructured coatings on the electrical performance of cross-linked polyethylene
No full textThe electrical withstand capabilities of polyethylene films and ad hoc prepared PE sandwich samples containing controlled cavities inside, both coated with organic-inorganic hybrid thin layers also modified with graphene oxide, have been investigated. While films have been subjected to breakdown tests, samples with cavities have been exposed to partial discharge (PD) induced electrical ageing, valuating the different evolution of the damage due to PD activity. Experimental results highlight the positive effect brought by the presence of the hybrid coating and in particular of the coating containing also graphene oxide on the electrical performance of the samples
The effect of magnetite, graphene oxide and silicone oxide nanoparticles on dielectric withstand characteristics of mineral oil
Full text linkIn this work, we compare the dielectric withstand performance of nanofluids prepared using Shell Diala D as a base fluid, and magnetite, graphene oxide and silicone dioxide as nanoadditives. The ac withstand capability of the nanofluids was investigated as well as partial discharge inception voltage, partial discharge and repetition rate under ac, dc positive and dc negative voltages. The results indicate that, for all nanofluids, nanoparticle concentrations around 0.2 g/l enhance dielectric withstand properties under quasi uniform fields. Under divergent fields, partial discharge characteristics are improved under ac conditions. Under dc conditions silica nanofluid performs better than mineral oil, but the other two nanofluids do not perform well.In this work, we compare the dielectric withstand performance of nanofluids prepared using Shell Diala D as a base fluid, and magnetite, graphene oxide and silicone dioxide as nanoadditives. The ac withstand capability of the nanofluids was investigated as well as partial discharge inception voltage, partial discharge and repetition rate under ac, dc positive and dc negative voltages. The results indicate that, for all nanofluids, nanoparticle concentrations around 0.2 g/l enhance dielectric withstand properties under quasi uniform fields. Under divergent fields, partial discharge characteristics are improved under ac conditions. Under dc conditions silica nanofluid performs better than mineral oil, but the other two nanofluids do not perform well
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
Breakdown strength of nanofluids under different voltage conditions
No full textThe research on nanofluids has shown important improvements of the electrical performance, but so far the attention has only been focused on their use in transformers. The target of this work is to understand if nanofluids can be applied as insulators for power electronics modules, where the major stresses are caused by square waves or PWM voltages. Breakdown events in non-uniform field conditions and different voltage configurations have been deeply investigated revealing the effects of space charge mechanisms. While for DC fields the nanofluids contribution is positive, a completely different conclusion can be evinced from sinusoidal and square waves, where the situation even worsens at higher frequencies. Schlieren images of breakdown events seem to confirm the postulated hypotheses
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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