1,720,964 research outputs found
WATER-TRIFLUOROETHANOL MIXTURES: SOME PHYSICOCHEMICAL PROPERTIES
No full textThe physicochem. properties of water-2,2,2 trifluoroethanol mixts. have been investigated, at 25 °C, by d., viscosity, surface tension, and relative permittivity. An anal. based on the Kirkwood theory for the dielec. polarization of mixts. has been performed and the gK correlation factor has been related to the occurrence of hydrogen bonding networks. Data on the above system have been analyzed and compared to literature data on water-ethanol mixts., to obtain information on the role that partial fluorination plays in the interactions of alcs. with water mols. As inferred from excess properties, nonideality contributions are smaller than in the corresponding water-ethanol solns. Accordingly, the extension of hydrogen bond networks and/or van der Waals contributions to the overall system stability are less significant than in simple alcs
Phenyl Bridging in Ring-Substituted Cumyloxyl Radicals. A Product and Time-Resolved Kinetic Study
No full textThe reactivity of cumyloxyl radicals bearing cyclopropyl and 2,2-diphenylcyclopropyl groups in the para position has been investigated. Depending
on radical structure, products deriving from C-C beta-scission and/or cyclopropyl ring-opening are observed, supporting the hypothesis that
cumyloxyl (and, more generally, arylcarbinyloxyl) radicals exist in equilibrium with 1-oxaspiro[2,5]octadienyl radicals, in full agreement with
the previously proposed mechanism for the O-neophyl rearrangement of 1,1-diarylalkoxyl radicals
Solution Behaviour of Alkyl-Glycosides and Structurally Related Compounds
No full textA review on the supramolecular association modes of alkyl glucosides and related species
Structural effects on the beta-scission reaction of tertiary arylcarbinyloxyl radicals. The role of alpha-cyclopropyl and alpha-cyclobutyl groups
No full text[GRAPHICS] A product and time-resolved kinetic study on the reactivity of tertiary arylcarbinyloxyl radicals bearing a-cyclopropyl and a-cyclobutyl groups has been carried out. Both the 1-cyclopropyl-1-phenylethoxyl (1(.)) and alpha,alpha-dicyclopropylphenylmethoxyl (2(.)) radicals undergo beta-scission to give cyclopropyl phenyl ketone as the major or exclusive product with rate constants higher than that measured for the cumyloxyl radical. It is proposed that in the transition state for beta-scission of 1(.) and 2(.), formation of the C=O double bond is assisted by overlap with the C-C bonding orbitals of the cyclopropane ring. With tertiary arylcarbinyloxyl radicals bearing a-cyclobutyl groups such as the 1-cyclobutyl-1-phenylethoxyl (4(.)) and 1-cyclobutyl-1-phenylpropoxyl (5(.)) radicals, the fragmentation regioselectivity is essentially governed by the stability of the radical formed by P-scission. Accordingly, 4(.) undergoes exclusive C-cyclobutyl bond cleavage to give acetophenone, whereas with 5(.), competition between C-cyclobutyl and C-ethyl bond cleavage, leading to propiophenone and cyclobutylphenyl ketone in a 2:1 ratio, is observed
Micelle Formation and Phase Equilibria in a Water-Trifluoroethanol-Fluorocarbon Surfactant System.
No full textThe soln. behavior of the fluorinated surfactant tetraethylammonium perfluorooctane-sulfonate, PFOS, in water-trifluoroethanol, TFE, mixts. has been investigated by surface tension, elec. conductance, and PGSE (pulsed gradient spin-echo) NMR self-diffusion methods. Addn. of progressive amts. of TFE in the solvent has little influence on the crit. micellar concn., CMC. Conversely, self-diffusion, counterion binding, and the surface pressure at the CMC are significantly affected by added fluoroalkanol. The above effects have been explained in terms of the solvent viscosity, dielec. permittivity, and surface activity, resp. The complete phase behavior of the above system has been drawn, and the phase boundaries were detd. According to the above findings, added surfactant promotes the sepn. of the homogeneous solvent mixt. into two coexisting fluid phases. The obsd. behavior was rationalized on thermodn. grounds
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
- …
