1,720,969 research outputs found
Effect of nanoclay and carboxyl-terminated (butadiene-coacrylonitrile) (CTBN) rubber on the reaction induced phase separation and cure kinetics of an epoxy/cyclic anhydride system
No full textThe effects of nano clay, carboxyl-terminated
(butadiene-co-acrylonitrile) (CTBN) liquid rubber and the
combination of both on the cure kinetics of diglycidyl ether
of bisphenol-A (DGEBA)-based epoxy resin/nadic methyl
anhydride were studied. Cure kinetics studies were carried
out by performing dynamic and isothermal differential
scanning calorimetric (DSC) experiments. The dynamic
DSC experiments were carried out at four different heating
rates. Dynamic kinetic modeling was performed using
Kissinger and Ozawa approaches. Since these methods are
based exclusively on the maximum rate of cure, which
occurs approximately at the beginning of the cure reaction,
the activation energy calculated using these methods is
valid only for the initial stage of the cure. The clay (3 phr)
filled epoxy system has an activation energy 24 % lower
than the unfilled system. The role of the surfactant chemistry
on the initial stage of the cure reaction was also
studied. A plausible reaction mechanism which involves
the effect of the nanoclay surfactant as an accelerator of the
cure reaction was proposed. The phase separated CTBN
rubber hindered the cure reaction and has 3 % higher
activation energy for epoxy/CTBN system than the unfilled
system. In the ternary epoxy/3 phr clay/15 phr CTBN
system, the accelerating effect of clay on cure was highlighted.
The cure activation observed in the presence of
clay overshadows the hindrance created by the phase separated
CTBN. Isothermal DSC scans were carried out at
five different temperatures. The experimental datas showed
an autocatalytic behavior of the reaction, and the isothermal
modeling was carried out by Kamal autocatalytic
model. The results showed a very good agreement within
the whole conversion range for the unfilled and all the filled
systems. The evolution of the morphology and phase separation
was also studied using optical and scanning electron
microscope. Faster cure reaction resulted in smaller
phase-separated CTBN particles in epoxy/clay/CTBN ternary
system as compared with those observed in epoxy/
CTBN binary blend
Cure kinetics and thermal stability of micro and nanostructured thermosetting blends of epoxy resin and epoxidized styrene-block-butadiene- block-styrene triblock copolymer systems
No full textThe compatibility of styrene-block-butadiene-block-styrene (SBS) triblockcopolymer in epoxy resin is increased by the epoxidation of butadiene segment, using hydrogen peroxide in the presence of an in situ prepared catalyst in water/dichloroethane biphasic system. Highly epoxidized SBS (epoxy content SBS >26 mol%) give rise to nanostructured blends with epoxy resin. The cure kinetics of micro and nanostructured blends of epoxy resin [diglycidyl ether of bisphenol A; (DGEBA)]/amine curing agent [4,4′-diaminodiphenylmethane (DDM)] with epoxidized styrene-block-butadiene-block-styrene (eSBS 47 mol%) triblock copolymer has been studied for the first time using differential scanning calorimetry under isothermal conditions to determine the reaction kinetic parameters such as kinetic constants and activation energy. The cure reaction rate is decreased with increasing the concentration of eSBS in the blends and also with the lowering of cure temperature. The compatibility of eSBS in epoxy resin is investigated in detailed by Fourier transform infrared spectroscopy, optical and transmition electron microscopic analysis. The experimental data of the cure behavior for the systems, epoxy/DDM and epoxy/eSBS(47 mol%)/DDM show an autocatalytic behavior regardless of the presence of eSBS in agreement with Kamal's model. The thermal stability of cured resins is also evaluated using thermogravimetry in nitrogen atmosphere. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineer
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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