1,720,956 research outputs found
CONCURRENT CRYSTALLIZATION IN POLYPROPYLENE NYLON-6 BLENDS USING MALEIC-ANHYDRIDE GRAFTED POLYPROPYLENE AS A COMPATIBILIZING AGENT
No full textThis paper describes the nonisothermal crystallization of molten blends of two semicrystalline polymers, polypropylene (PP) and Nylon-6 (N6). A discussion details the effect of the concentration of the compatibilizing agent, maleic anhydride grafted polypropylene (MAH-g-PP), on the crystallization behavior. The crystallization thermograms showed one crystallization peak or two crystallization peaks, which were significantly affected by the presence of MAH-g-PP. The crystallization temperature of N6 levels off down as the concentration of MAH-g-PP increases, whereas that of PP stays at a roughly constant temperature. These blends containing the compatibilizing agent exhibited concurrent crystallization at the crystallization temperature of PP. The crystallization behavior are also studied by optical microscopy under crossed polarizers. (C) 1994 John Wiley & Sons, Inc
Study on the Ionic Mobility of Liquid Polymer Electrolytes by Nuclear Magnetic Relaxation Measurement
No full textSEGMENTAL MOTION OF STEREOREGULAR POLY(METHYL METHACRYLATES) IN A HOMOLOGOUS SERIES OF N-ALKYL ACETATE SOLVENTS BY NMR RELAXATION MEASUREMENTS
No full textThe C-13 spin-lattice relaxation times, T1s, of both stereoregular poly(methyl methacrylates) (PMMA) and homologous series of n-alkyl acetate solvents in solution have been measured at 40-degrees-C. It was observed that the motion of polar side-chains was highly affected by the degree of interaction with solvent molecules. The stronger polymer-solvent interactions in predominantly syndiotactic PMMA solutions than in isotactic PMMA solutions were shown from the T1 values for the carbonyl, methoxy, and quaternary carbons in polymer segments and also from the carbonyl T1s of solvent molecules. By relating the solvent dependences of the T1 data in syndiotactic polymer solutions to that of the known dissolution rate data of atactic PMMA, it was found that the solvent dependences of the T1 values of those carbon groups in which the polymer-solvent interaction is not significant, e.g., methylene and alpha-methyl carbon groups, were consistent with the solvent dependence of the dissolution rate of polymer. This result suggested that the dissolution of polymer is mainly governed not by the sorption process related to the polymer-solvent interaction but by the transport process related to the local motions of polymer segments and solvent molecules
STUDY ON THE IONIC-CONDUCTIVITY AND MOBILITY OF LIQUID POLYMER ELECTROLYTES CONTAINING LITHIUM-SALTS
No full textWe report ionic conductivities and mobilities of the liquid polymer electrolytes formed by dissolving the lithium salts in poly(ethylene oxide) and poly(propylene oxide). A high resolution NMR (nuclear magnetic resonance) relaxation technique was used to study the dynamics of the ions in polymer electrolytes. The Li-7 NMR results revealed the coexistence of two separate lineshape components with substantially different spin-spin relaxation times (T2). From the resolution of the two components, we could estimate the spin-spin relaxation time of the mobile free lithium ion and also the fraction of free lithium ions contributing to the ionic conductivity in polymer electrolyte
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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