1,720,956 research outputs found
Resolution of a nonionic surfactant oligomeric mixture by means of DOSY with inverse micelle assistance
No full textDOSY is a recognized, efficient technique in the analysis of mixtures. It relies on the differences in self-diffusion coefficients,
which are determined by the molecular size. Nowadays, efforts are directed towards devising matrices able to interact with
the components of the mixture with differential affinity, and therefore capable to interfere with the diffusion processes and to
display resolving power towards species of close, or even equal molecular weight, like isomers. Usually, commercial nonionic
surfactants are mixtures of oligomeric species, since the head group, which is a short polyoxyehtylene chain, is somewhat
polydisperse. The embedment of Igepal CA-520, 5 polyoxyethylene iso-octylphenyl ether, in an inverse microemulsion led to
the separation of 1H signals of the various oligomeric components. This ensued from the differential partitioning between
the oil and the surface of the inverse micelles, which depends on the ethyleneoxide number (EON) of the head groups.
Thus, it was possible to ascertain that the length distribution of the polyethyleneoxide chains is ingood agreement with the
Poisson distribution theoretically predicted for the polymerization of ethylene oxide. The DOSY spectrum contributed to the
assignment of the signals and afforded the partition degree, between the two environments, for each individual oligomeric
species, providing further insight into nonionic inverse microemulsions, at present widely employed reaction media in the
nanotechnological syntheses
Endo- and exo-inulinases: enzyme-substrate interaction and rational immobilization
No full textThree-dimensional models of exoinulinase from Bacillus stearothermophilus and endoinulinase from Aspergillus niger were built up by means of homology modeling. The crystal structure of exoinulinase from Aspergillus awamori was used as a template, which is the sole structure of inulinase resolved so far. Docking and molecular dynamics simulations were performed to investigate the differences
between the two inulinases in terms of substrate selectivity. The analysis of the structural differences between the two inulinases provided the basis for the explanation of their different regio-selectivity and for the understanding of enzyme-substrate interactions. Surface analysis was performed to point out structural features that can affect the efficiency of enzymes also after immobilization.
The computational analysis of the three-dimensional models proved to be an effective tool for acquiring information and allowed to formulate an optimal immobilized biocatalyst even more active that the native one, thus enabling the full exploitation of the catalytic potential of these enzymes
Evolution of the Nonionic Inverse Microemulsion−Acid−TEOS System during the Synthesis of Nanosized Silica via the Sol−Gel Process
No full textThe cyclohexane−igepal inverse microemulsion, comprehensively established for the synthesis of silica nanoparticles in an ammonia-catalyzed sol−gel process, was alternatively studied with an acid-catalyzed sol−gel process. Tetraethyl orthosilicate (TEOS) was used as the silica precursor, while two different aqueous phases containing either HNO3 or HCl at two different concentrations, 0.1 and 0.05 M, were examined in the presence and in the absence of NaF, a catalyst of the condensation step. The evolution of the overall reacting system, specifically hydrolysis and polycondensation of reaction intermediates, was monitored in situ by time-resolved small-angle X-ray scattering. No size variation of the inverse micelles was detected throughout the sol−gel process. Conversely, the density of the micellar core increased after a certain time interval, indicating the presence of the polycondensation product. The IR spectra of the reacting mixture were in agreement with such a hypothesis. 1H and 13C NMR measurements provided information on the soluble species, the surfactant, and TEOS. The TEOS consumption was well fitted by means of an exponential decay, suggesting that a first-order kinetics for TEOS transpires in the various systems examined, with rate constants dependent not only on the acid concentration but also on its nature (anion specific effect), on the presence of NaF, and on the amount of water in the core of the inverse micelle. The self-diffusion coefficients, determined by means of PGSTE NMR, proved that a sizable amount of the byproduct ethanol was partitioned inside the inverse micelles. Characterization of the final product was carried out by means of thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and transmission electron microscopy (TEM), which concurrently confirmed that the silica isolated from the inverse nonionic microemulsion is not significantly different from the product of a bulk acid-catalyzed sol−gel synthesis. TEM micrographs illustrated particles with diameters smaller than the diameter of the inverse micelles as determined by SAXS, due to a shrinkage effect, in addition to nanostructured aggregates in the range 20−100 nm
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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