1,720,958 research outputs found
Role of anionic and non-ionic surfactants on the control of particle size and latex colloidal stability in the seeded emulsion polymerization of butyl methacrylate
No full textThe evolution of the main colloidal parameters in the seeded starved-feed semi-continuous emulsion polymerization of butyl methacrylate (BMA) was investigated, with the main purpose of assessing the effectiveness of the semi-empirical relationship S = K (.) S-s (.) Delta A/A(s) as a tool to define the surfactant/monomer feed ratio (proportional to K) best suited to achieve a target particle size. In particular, the effect of the type and amount of surfactant [i.e., anionic, sodium dodecyl sulfate (SDS), or nonionic, Brij 58P] added during the semi-continuous stage was considered. Coagulum formation was never observed under the adopted experimental conditions. To detect the occurrence of secondary nucleation or particle aggregation, or both, the particle size and number of particles, the surface tension and the particle surface coverage ratio were correlated. The best results were obtained with SDS and 0.8 <= K <= 3. In fact, under the selected experimental conditions, only with SDS did the number of particles remain nearly constant throughout the polymerization at the value defined by the seed latex; the particle size distribution was highly monodisperse, and the final particle diameter closely matched the calculated one (similar to 120 nm). The above semi-empirical relationship based on the adjustable parameter K was validated by running test polymerizations aimed at lattices with well-defined particle size
Graft Polymerisation of Functional Acrylic Monomers onto Cotton Fibres Activated by Continuous Ar Plasma
No full textContinuous cold Ar plasmas were used to activate the mercerised cotton fabric towards surface-initiated graft polymerisation of glycidyl methacrylate, 2-hydroxyethyl methacrylate (HEMA) and 1,1,2,2-tetrahydroperfluorodecyl methacrylate (XFDMA). Single and multi-step processes, carried out either in the plasma chamber (one-step and two-step processes) or ex situ after plasma treatment, were explored to optimise the grafting efficiency. The mechanical properties of the grafted cotton were substantially unaffected. Grafting with XFDMA gave good results only when the plasma activation was performed on monomer-impregnated fabrics, as shown by gravimetry, ATR FT-IR spectroscopy, and water and oil repellence tests. On the contrary, with HEMA better results were obtained by in situ grafting from monomer vapour
Synthetic Approaches to Inorganically Modified Aqueous Polymer Dispersions: from Reactive Acrylic Latexes to Nanostructured Hybrids with either Spherical or Lamellar Inorganic Phase
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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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