1,721,103 research outputs found
Copolymer films containing amphiphilic side chains of well-defined fluoroalkyl-segment length with biofouling-release potential
No full textNovel methacrylate copolymers containing polysiloxane (SiMA) and mixed poly(ethyleneglycol)-
perfluorohexyl side chains (MEF) were synthesised and dispersed as surface-active additives in
crosslinked PDMS films. The amphiphilic behaviour of the copolymers caused surface reconstruction in
water which was characterised by dynamic and static contact angle measurements and angle-resolved
X-ray photoelectron spectroscopy (XPS) analysis. The XPS CF2/OCH2 ratio between the hydrophobic
fluoroalkyl segments and the hydrophilic oxyethylenic segments was high (15/64) for the copolymer
richest in MEF (93 mol%), which also had a high percentage of surface fluorine (!30%). By contrast, an
especially low CF2/OCH2 ratio (0/16) and a low percentage of surface fluorine (!2%) were identified for
the copolymer poorest in MEF (14 mol%). Such large differences in surface chemical composition
reflected different antifouling and fouling-release properties against the green macroalga Ulva linza.
Generally, the films containing the copolymer with the smallest MEF content were able to resist the
settlement of zoospores better than those with a high MEF content and had a superior release of
sporelings (young plants).
Amphiphilic modified-styrene copolymer films: Antifouling/fouling release properties against the green alga Ulva linza
Get PDFSurface-active copolymers of a styrene carrying a polysiloxane side chain (SSi) and a triethyleneglycol monomethyl ether-modified pentafluorostyrene (EFS) (39 and 77 mol% EFS) were prepared and incorporated (8 wt% loading) into a polydimethyl siloxane (PDMS) matrix to produce crosslinked blend films. The wettability of the surface-active copolymer films and PDMS-blend films was investigated by contact angle measurements. An angle-resolved X-ray photoelectron spectroscopy (XPS) of the surface chemical composition before and after immersion in water for 7 days enabled location of the hydrophilic oxyethylenic segments of EFS within the top 10 nm from the film surface. Laboratory bioassays on the blend films against the marine green alga Ulva linza evidenced that the films containing the copolymer with the larger EFS content showed greater resistance to settlement of zoospores of U. linza, whereas both films had superior fouling-release properties of sporelings (young plants) compared to the PDMS standard films
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
Amphiphilic pentablock copolymers and their blends with PDMS for antibiofouling coatings
Get PDFWell-defined amphiphilic pentablock copolymers Siy-(EGx-FAz)2 composed of polysiloxane (Si), polyethylene glycol (EG), and perfluorohexylethyl polyacrylate (FA) blocks are synthesized by ATRP of FA monomer starting from a difunctional bromo-terminated macroinitiator. Diblock copolymers EGx-FAz are also synthesized as model systems. The block copolymers are used, either alone or blended with a PDMS matrix in varied loadings, to prepare antibiofouling coatings. Angle-resolved XPS and contact angle measurements show that the coating surface is highly enriched in fluorine content but undergoes reconstruction after contact with water. Protein adsorption experiments with human serum albumin and calf serum highlight that diblock copolymers resist protein adhesion better than do pentablock copolymers. Blending of the pentablock copolymer with PDMS results in increased protein adsorption. By contrast, the PDMS-matrix coatings show high removal percentages of sporelings of the green fouling alga Ulva linz
Effects of surface-active block copolymers with oxyethylene and fluoroalkyl side chains on the antifouling performance of silicone-based films
Get PDFBlock copolymers made from a poly(dimethyl siloxane) (Si) and a poly(meth)acrylate carrying oxyethylene (EG) or fluoroalkyl (AF) side chains were synthesized and incorporated as surface-active components into a silicone matrix to produce cross-linked films with different surface hydrophilicity/phobicity. Near-edge X-ray absorption fine structure (NEXAFS) studies showed that film surfaces containing Si-EG were largely populated by the siloxane, with the oxyethylene chains present only to a minor extent. In contrast, the fluorinated block was selectively segregated to the polymer–air interface in films containing Si-AF as probed by NEXAFS and X-ray photoelectron spectroscopy (XPS) analyses. Such differences in surface composition were reflected in the biological performance of the coatings. While the films with Si-EG showed a higher removal of both Ulva linza sporelings and Balanus amphitrite juveniles than the silicone control, those with Si-AF exhibited excellent antifouling properties, preventing the settlement of cyprids of B. amphitrite
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