1,720,957 research outputs found
Polymerization Kinetics and Characterization of Dual Cured Polyurethane‐Acrylate Nanocomposites for Laminates
No full textFour different types of montmorillonites have been dispersed by sonication at 50 degrees C into a propoxylated aromatic epoxy diacrylate oligomer to achieve interlayered or exfoliated nanocomposites. A thermally-induced cross-linking reaction, forming a polyurethane network in the presence of 7 wt.-% of a montmorillonite, has been promoted by addition of an allophanate modified polyisocyanurate based on hexamethylene diisocyanate. The kinetic behavior of the network formation has been studied at 25, 40 and 60 degrees C by following the disappearance of the isocyanate vibrational band found at 2 270 cm(-1). A tight crosslinked polyurethane acrylate network has been achieved by a subsequent dual UV curing promoted by a photoinitiator mixture (0.6 wt,-%) added to the reactive mixture because of further reactions occur to the acrylate double bonds. The photopolymerization kinetic has been investigated on the different thermally treated polyurethane nanocomposite networks by Real Time FTIR spectroscopy monitoring the changes of the IR band at 810 cm(-1) assigned to the acrylate double bond vibrations. The influence of the different montmorillonite clays on the final nanocomposite morphology has been investigated by using XRD and SEM. Finally, the use of these mixtures as internal layer between two modified surface PET films has been also studied for the laminate production. The based-PET laminate films have been characterized by determining the bending resistance and optical properties as a function of different nanofillers
Produzione, caratterizzazione chimico-fisica e preliminare sperimentazione su animale di una nuova bioprotesi vascolare di piccolo diametro
No full textOxygen and water vapor barrier properties of MMT nanocomposites from low density polyethylene or EPM with grafted succinic groups
No full textLDPE, EPM and their derivatives containing a moderate amount (0.08–1.8 by mol) ofdiethylsuccinate or succinic anhydryde groups were used as
matrices in blending with different amount of organophilic montmorillonites and the resulting composite morphology and structure (by XRD, SEM,TEM microscopy, DSC analysis and selective solvent extraction) were studied with reference to the polar groups/MMT ratio. Exfoliated, intercalated and mixed morphologies were achieved. High concentrations ofpolar groups grafted to the polyolefin and montmorillonite loading not larger than 5% wt were favourable for obtaining high exfoliation degree. Particularly in the exfoliated MMT composite LDPE had lower crystallinity degree, while EPM showed increased glass transition temperature and reduced solubility in hot toluene. Moreover, oxygen and water vapor barrier property improvement was observed in films where MMT exhibits either exfoliated or intercalated morphologies. Strong interactions with the montmorillonite particle surface through the polar groups grafted to the polyolefin seems to be the basic effect responsible for the morphology and peculiar properties. A model based on the reduced mobility ofthe polymer located near the particle surface or inside the MMT gallery (confined phase) was proposed to explain the observed oxygen permeability reduction, the Tg increase and solubility ofpoly(ethylene-ran-propylene)/MMT nanocomposites
Fluorinated polymers as stone-protective materials: an FTIR study on intermolecular interactions
No full textAttempts have been performed to obtain spectroscopic evidence of intermolecular interactions
between fluorinated polymers to be used as protective materials and various stones. In this paper we
report an investigation by means of FTIR spectroscopy on poly(vinyl fluoride)(PVF) which contains acid
hydrogens that can give rise to intermolecular interactions with calcium carbonate. Spectral changes have
been found in the C–H and C–F stretching regions at 3000–2840 and 1200–950cm−1, respectively. These
last are attributed to intermolecular interactions of the polymer with CO3
2− and with conformational
changes of the macromolecular chain. Scanning electron microscopy investigations were also performed
on marble slabs coated with a PVF film in order to gain information about the morphology of the polymer film
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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