1,720,957 research outputs found
Development of a computational model to predict blend morphology in a twin-screw extruder
No full textA theoretical model for predicting morphology evolution of immiscible polymer blends in a corotating twin-screw extruder was described with a new blend's constitutive equation (the Lee and Park model). This theory describes the overall morphology of immiscible binary blends in terms of an interfacial area and its anisotropy, which has several advantages such as no limitations of flow type and applicability for any domain shapes and compositions. In this study, the classical algorithm has been adopted to find the pressure profile and the degree of fill along the screw axis for the modular-type twin-screw extruder. It is based on the screw characteristic curves to obtain a pressure gradient at a given flow rate and backward calculation of the pressure profile starting from the die. The partially filled region was also included to describe properly the morphology evolution. Considering the flow characteristics of this region, we assumed that the apparent shear rate was proportional to the degree of fill. The overall model predictions for the various operating conditions are compared with the experimental results. Therefore, it may be said that the new constitutive equation is useful to describe the morphology behavior not only for the twin-screw extruder but also for the other polymer processing equipment. (C) 1998 John Wiley & Sons, Inc. Adv Polym Techn 19: 203-215, 1998
Morphology evolution in PS/LDPE blends in a twin screw extruder: Effects of compatibilizer
No full textIn order to understand the mixing in polymer extrusion, the morphology of PS/LDPE blends compatibilized with SEES was simulated based on the Lee and Park model. Experiments were performed in a co-rotating twin screw extruder and a Haake mixer, and the morphology of the compatibilized blends of various compositions was compared with the non-compatibilized ones. The size of the dispersed phase of the compatibilized blend was smaller than the noncompatibilized one, and the blend of the PE matrix had a smaller size in the dispersed phase than the non-compatibilized one. Simulation results were agreed well with experiments, and the Lee and Park model could be applied in the extrusion analysis of compatibilized polymer blends
DIFFUSION OF ETHYLENE-GLYCOL ACCOMPANIED BY REACTIONS IN POLY(ETHYLENE-TEREPHTHALATE) MELTS
No full textDiffusion coefficients of ethylene glycol (EG) have been measured in poly (ethylene terephthalate) (PET) melts by a quartz-spring sorption apparatus. A simple mathematical model was developed to investigate the sorption behavior accompanied by chemical reactions of EG and PET at high temperatures. Diffusion coefficients are deduced from experimental data for an asymptotically thin sample in order to minimize the effects of reactions. The diffusion coefficient of EG is strongly dependent on the vapor pressure of EG and temperature but not on the molecular weight of PET in this experimental range (degree of polymerization 80-120). The diffusion coefficient of EG in PET melt at 265-degrees-C is 2.58 X 10(-7) cm2/s at the limit of zero concentration of EG. The activation energy for diffusion is 38.4 kcal/gmol, and the heat of solution for sorption is -44.9 kcal/gmol. The concentrations of the volatile materials resulting from reactions in PET-EG system were analyzed with gas chromatography. In addition, a fit of the current model to experimental data yields frequency factors for the polymerization reaction (k1) and the acetaldehyde formation reaction (k2) to be 5.84 X 10(8) cm3 / mol . min and 3.90 X 10(11) min-1, respectively
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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