1,720,960 research outputs found
Role of functional-group position in determining the interaction between structure-making and structure-breaking solutes. A microcalorimetric study of the interactions in aqueous solutions between positional isomers of alkan-m-ols and urea or biuret
No full textEnthalpies of dilution of ternary aqueous solutions containing biuret or urea and positional isomers of alkan-m-ols have been determined by flow microcalorimetry at 298.15 K. Pairwise cross-interaction coefficients of the virial expansion of the excess enthalpies were evaluated. The values of the coefficients are positive, depending in a very complex manner on the length of the alkyl chain and on the position occupied by the hydroxy group along the alkyl chain. The behaviour of these systems seems to be determined by a balance between favourable hydrophilic-hydrophilic and repulsive hydrophilic-hydrophobic interactions. When the hydroxy group occupies more central positions, unfavourable interactions prevail and the cross coefficient for the alkanol bearing the longest alkyl chain is almost zero
Role of hydrophilic domains in determining the strength of hydrophobic interactions. A calorimetric study of the cross interactions in aqueous solutions of alkane-m,n-diols at 298.15 K
No full textExcess enthalpies of ternary aqueous solutions containing different alkane-m, n-diols have been determined at 298.15 K. The enthalpic interaction coefficients obtained were interpreted according to an interaction model which includes the presence of a preferential orientation between the two hydrated molecules, stabilized by the simultaneous juxtaposition of groups having the same effect on water structure. This model has been shown to be useful not only to explain the difference in the behaviour of positional, configurational and stereo isomers, but also to predict the value of the enthalpic interaction coefficient of polyhydroxylated substances in aqueous solution. There is evidence of a transition between the behaviour of alkane-m, n-diols and that of alkan-n-ols, related to the hindrance of juxtaposition of hydrophilic and hydrophobic domains. The difference in the alkyl chain length and/or the position of OH functional groups along the carbon skeleton contribute to this effect
A model for the interaction between hydrophilic and hydrophobic solutes - aqueous solutions containing biuret or urea and hydroxylated substances
No full textEnthalpies of dilution of ternary aqueous solutions containing biuret or urea and alkan-1-ols, alkan-l,2-diols and alkan-l,2,3-triols have been determined at 298.15 K by means of a flow microcalorimeter. The cross pairwise coefficients of the virial expansion of the excess enthalpies were determined. These coefficients are positive and depend in a complex manner on the length of the alkyl chain of the alkanols. The behaviour of these systems was interpreted in terms of preferential interactions between hydrophilic groups and of repulsive interactions between hydrophobic and hydrophilic groups. © 1992
Solubility of gaseous hydrocarbons and the hydrophobic effect in aqueous solutions of hexamethylenetetramine
No full textThe solubilities of methane and ethane in aqueous solutions of hexamethylenetetramine have been studied in order to evaluate the hydrophobic effect according to the Ben-Naim model. The effect of hexamethylonetetramine, a molecule extensively hydrated, results in a reinforcing of hydrophobic interactions; this fact is related to the poor effectiveness of hexamethylenetetramine in the denaturing processes of biomacromolecules. © 1979 American Chemical Society
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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