1,721,082 research outputs found
Structure and mechanical properties of triblock copolymers subject to extensional deformation
No full textEffect of planar extension on the structure and mechanical properties of polystyrene-poly(ethylene-¤co¤-butylene)-polystyrene triblock copolymers
No full textTwo thermoplastic poly(styrene)-poly(ethylene-co-butylene) -poly(styrene) triblock copolymers containing either spherical or cylindrical poly(styrene) microdomains were pre-oriented through extensional flow. Small angle neutron scattering (SANS) measurements revealed that the pre-oriented triblock with a spherical microstructure adopts a body-centred cubic (bcc) structure with a [111] orientation along the Row direction. For the pre-oriented triblock with a cylindrical microstructure, the cylinder axis is aligned along the extensional Row direction. Investigation of the mechanical properties showed that Young's moduli of the pre-oriented copolymers are highly anisotropic. Specimens were then subject to uniaxial deformation along the extensional Row direction and at the same time microstructural changes induced by the deformation were investigated by SANS. It was found that the deformation of the bcc lattice is affine, and that the deformation of the microstructure is reversible. For the triblock copolymer with a cylindrical microdomain structure the deformation of the lattice was found to be non-affine. In this case, SANS patterns suggest a "micronecking" and a breaking of the cylindrical domains without any change in the domain spacing. (C) 2000 Elsevier Science Ltd. All rights reserved
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
Nanostructured dimethacrylate-based photopolymerizable systems by modification with diblock copolymers
No full textWe report the full characterization of a photocurable dimethacrylate-based formulation modified with small amounts (1 and 3 wt%) of a polystyrene-block-poly(ethylene oxide) (PS-b-PEO) block copolymer (BCP). The UV curable formulation is a mixture of bisphenol A bis(2-hydroxy-3-methacryloxypropyl)ether (Bis-GMA) and triethylene glycol dimethacrylate (TEGDMA) and contains phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (Irgacure819) as photoinitiator. We demonstrate that the addition of a small amount of BCP in the uncured formulation is able to induce a phase separation at the nanometer scale. The nanoscale structure formed in the pre-cure stage is retained after the UV curing, so obtaining nanostructured solid cross-linked materials. The studied materials can be used in the manufacturing process of stereolithography and, therefore, in modern 3D printers. The ability to induce and control the formation of nanostructures in the material by adding BCPs in the formulations could open new opportunities to tailor and improve the properties of the 3D printed objects
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
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