1,720,958 research outputs found
Structure-Property Relationships in Heterophasic Thermoplastic Elastomers Filled with Montmorillonite
No full textPolypropylene (PP)/ethylene-propylene rubber (EPR)/Montmorillonite ternary nanocomposites with a phase separated morphology were studied in this work. Wide angle X-ray diffraction (WAXD), small angle X-ray scattering (SAXS), atomic force microscopy (AFM), scanning electron microscopy
(SEM), and transmission electron microscopy (TEM) were used to investigate the samples. One of the aim of this work was to separate the effects of rubber and clay content on the structure, morphology and mechanical properties of the samples. The presence of clay favored the formation
of phase and disrupted the lamellar framework. Clay had moreover a major role in shaping thephase separated morphology of the samples. Atomic Force Microscopy showed that the shearexerted by the clay layers was key for inducing a shish kebab morphology in the polymer matrix.
Rubber content decreased the degree of crystallinity at a crystalline cell level and induced the formation of a double population of lamellar stacks. The mechanical properties of the samples primarily depended on rubber content, and they were secondarily tuned by the effect of clay. This
synergistic effect allowed to obtain composites with increased stiffness, ductility and toughness, oppositely to what is frequently found
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
The effect of a synthetic double layer hydroxide on the rate of II→I phase transformation of poly(1-butene)
Get PDFPerkalite is an unusual clay in the domain of polymer-based nanocomposites. In this paper, the use of perkalite as a filler for poly(1-butene) was investigated. Particular attention was posed on the study of the effect of this particular kind of clay on the rate of II→I phase transition of the matrix. Wide angle X-ray diffraction (WAXD), small angle X-ray scattering (SAXS), transmission electron microscopy (TEM) and differential scanning calorimetry (DSC) were used to determine the structure and morphology of the samples, the degree of dispersion of the filler and to follow the kinetics of the phase transition of poly(1-butene). Mechanical properties were moreover measured. Perkalite was found to increase the rate of II→I phase transition with respect to the neat matrix, because it affected the free energy of the crystalline phase, by decreasing the perfection of the crystals. Rather than the disruption of the regular ordering at a crystalline cell level, the effect on the lamellar morphology seems to be preponderant. The fragility of perkalite layers and the substantial reduction of the tactoids did not allow to influence the entropic factor to the phase diagram of poly(1-butene), because the filler was not able to locally increase the pressure on the nascent crystalline domains. Perkalite was therefore not able to achieve a direct formation of the phase I of poly(1-butene) directly from the melt. The reduction of the size of perkalite tactoids confirmed that poly(1-butene) is very efficient in homogeneously dispersing the filler, thereby justifying the use of the materials produced in the present study as viable masterbatches for the production of polyolefin-based nanocomposites
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
The effect of different clays on the structure, morphology and degradation behavior of poly (lactic acid)
No full textIn this work, polylacticacid(PLA) based nanocomposites filled with different kinds of clay were prepared and their structure, morphology and degradation behavior were compared. A similar degree of dispersion was achieved in the case of cationic and anionic clays. However, these two types of fillers had different effects on the structure and morphology. Perkalite, ananionic clay, induced higher crystallinity, a faster crystallization rate and also a modification of the crystallization mechanism. Moreover, when perkalite was used, the lamellar framework of PLA was preserved. Cationic clays, on the other hand, were detrimental for a regular crystallization of the PLA matrix, producing very disordered lamellar stacks. The effects of anionic and cationic clays were different also on the degradation behavior, with the perkalite-containing nanocomposite degrading much faster than either the matrix or the montmorillonite-reinforced materials. This comparison shows that a rational choice of the chemical nature of the nanofiller allows to tune both the degradation rate of PLA and its structure
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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