1,720,963 research outputs found
Selective 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
Nano and submicron fluorescent polystyrene particles internalization and translocation in seedlings of Cichorium endivia L.
Full text linkContamination by plastics is one of the major causes of pollution of the terrestrial environment. Fragmentation of plastics into micro and nano particles may result in negative interactions between polymers and terrestrial ecosystems. The effects of nano (20 nm) and submicron (200 nm) fluorescent polystyrene (PS) particles, at different concentrations (0.01, 0.1, 1 g L−1), were analysed on chicory plant (Cichorium endivia L.), considering the following endpoints: germination percentage and seedling development after 7 and 14 days exposure; genotoxic effects; polyphenols and photosynthetic pigments content, antioxidant activity; absorption and translocation of PS particles in the seedling tissues. The results indicated no negative effects on germination of both PS particles' sizes at any concentration; seedlings elongation was affected by 1 g L−1 of 20 nm PS after 7 days exposure. Cytological analysis revealed no mitotic activity inhibition, but an uprising of chromosomal abnormalities in all treatments. Interestingly, photosynthetic pigments always increased after PS exposure. Seedlings treated with 20 nm PS showed intense fluorescence in the roots of 7 days and in the shoots of 14 days, while 200 nm PS treated seedlings exhibited low fluorescence. Electron microscopy and infrared spectroscopy confirmed 20 nm PS internalization and transport inside the plant tissue and a reduced presence of 200 nm PS. These results suggest the importance not only of particle size in plastic internalization in plant tissues, but also of cytological damages induced by particles too large to be bioaccumulated. From both aspects, consequences may arise for plant fitness, food safety and human health
Confocal Raman imaging, FTIR spectroscopy and kinetic modelling of the zinc oxide/stearic acid reaction in a vulcanizing rubber
No full textThe reaction of zinc oxide (ZnO) with stearic acid (StA) to form zinc stearate (ZnSt) has been investigated experimentally in a model matrix (unvulcanized styreneebutadiene rubber) by using confocal Raman microscopy and FTIR transmission spectroscopy. The heterogeneous nature of the reacting system has been confirmed. The Raman analysis has revealed the coreeshell structure of the product, which is formed via the gradual shrinkage of the ZnO core and the concurrent formation of a surrounding ZnSt shell of increasing thickness. FTIR spectroscopy has provided information about the molecular state of
aggregation of StA when dissolved in the rubber, as well as quantitative information on the reaction kinetics. The kinetic behaviour of the system has been interpreted using a semi-quantitative heterogeneous reaction model grounded on the Raman imaging results, which was able to catch the essential
features of the phenomenon and to simulate reliably the experimental conversion vs time data at three different temperatures
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
Uptake of Magnetite Nanoparticles on Polydopamine Films Deposited on Gold Surfaces: A Study by AFM and XPS
Full text linkPolydopamine has the capacity to adhere to a large variety of materials and this property offers the possibility to bind nanoparticles to solid surfaces. In this work, magnetite nanoparticles were deposited on gold substrates coated with polydopamine films. The aim of this work was to investigate the effects of the composition and morphology of the PDA layers on the sticking of magnetite nanoparticles. The polydopamine coating of gold surfaces was achieved by the oxidation of alkaline solutions of dopamine with various reaction times. The length of the reaction time to form PDA was expected to influence the composition and surface roughness of the PDA films. Magnetite nanoparticles were deposited on these polydopamine films by immersing the samples in aqueous dispersions of nanoparticles. The morphology at the nanometric scale and the composition of the surfaces before and after the deposition of magnetite nanoparticles were investigated by means of AFM and XPS. We found that the amount of magnetite nanoparticles on the surface did not vary monotonically with the reaction time of PDA formation, but it was at the minimum after 20 min of reaction. This behavior may be attributed to changes in the chemical composition of the coating layer with reaction time
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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