1,720,957 research outputs found
Electrical Bistability in Conductive Hybrid Composites of Doped Polyaniline Nanofibers-Gold Nanoparticles Capped with Dodecane Thiol
No full textSyndiotactic Polystyrene Films with Sulfonated Amorphous Phase and Nanoporous Crystalline Phase
No full textSelective surface modification of syndiotactic polystyrene films: A study by Fourier transform- and confocal-Raman spectroscopy
No full textA helical crystalline modification of syndiotactic polystyrene (sPS), the delta-form, was employed to prepare solution-cast films electively sulfonated on the surface. This result was achieved because of the unusual transport characteristics of the delta-form, exhibiting comparatively large diffusivity and solubility values for low-molecular weight compounds such as chloroform, which can be effectively used as a carrier solvent. The results of sulfonation
of the d-form are compared with those obtained with a trans-planar crystalline modification of sPS (beta-form). The latter was found unsuitable for selective surface modification.
The analysis of the sulfonated films was carried out by FT-Raman and confocal-Raman spectroscopy. The first technique was used to investigate the average composition of the samples in terms of sulfonation degree and crystalline structure. It also allowed us to construct calibration curves to be used in connection with the confocal-Raman data. The latter technique was employed to generate images with spectroscopic contrast and to quantitatively
characterize the depth-profiles of the investigated films
Control of morphology of sulfonated syndio-polystyrene membranes through constraints imposed by siloxane networks
No full textThe incorporation of siloxane networks in sulfonated polystyrene membranes by the sol-gel process was used to explore the possibility of developing low cost membrane for direct methanol fuel cells. A precursor solution of a hydrophobic siloxane network was allowed to diffuse and react into sulfonated syndio-polystyrene ionomeric membranes. The organic-inorganic hybrid domains so produced were able to reduce considerably the swelling of the ionomeric polymer in water, thereby increasing the dimensional stability of membranes. The physical and chemical properties of the sulfonated and hybrids membranes were examined by TGA, FTIR and SAXS analysis. The water uptake and the ionic conductivity were also evaluated at temperatures up to 60°C. It was found that both the unmodified sulfonated membranes and the corresponding hybrid exhibited a two-phase morphology, consisting of crystalline lamellar domains embedded in the amorphous ionomeric polymer, featuring segregated hydrophobic/hydrophilic domains with characteristic separation lengths ranging between 3.9 and 1.7 nm. The Presence of inorganic domains not only increased the dimensional stability of the membrane, by reducing the water uptake, but also decreased the rate of methanol crossover. Furthermore it was found that the inorganic network stabilizes the membrane morphology, enhancing the retention of proton conductivity after aging in water
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
- …
