1,720,977 research outputs found
The Potential of the Xenon "Spin-Spy" Methodology for the Study of Configurational Equilibria in Solution
No full textOrigin of life: the role of water in the transition from non-living to living matter
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Probing Polymer Colloids by 129Xe NMR
No full textModel aqueous dispersions of polystyrene, poly(methyl methacrylate), poly(n-butyl acrylate) and a statistical copolymer poly(n-butyl acrylate-co-methyl methacrylate) were studied using xenon NMR spectroscopy. The Xe-129 NMR spectra of these various latexes reveal qualitative and quantitative differences in the number of peaks and in their line widths and chemical shifts. Above the glass transition temperature, exchange between xenon sorbed in the particle core and free xenon outside the particles is fast on the Xe-129 spectral time-scale and a single Xe-129 Signal is observed. At temperatures below the glass transition temperature, the exchange between sorbed and free xenon is slow on the Xe-129 spectral time-scale and two Xe-129 NMR signals can be observed. If the signal of sorbed Xe-129 is observed, its chemical shift, line width and integral relative to the integral of free Xe-129 can be used for the characterization of the particle core. The line width of free Xe-129 provides the residence time of xenon Outside the Particles and can be used to determine the rate constant characterizing the kinetics of penetration of xenon in the particles. This rate constant emerges as promising parameter for the characterization of the polymer particle Surface
Liquid water :a necessary condition for all forms of life ?
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Stereochemical studies by molecular palpation
No full textThe conformational equilibrium of cyclohexanol was investigated by 129X NMR spectroscopy. While the classical NMR approach focuses on a carbon or proton atom belonging to the molecule under investigation, in our 129Xe NMR methodology we use the xenon atom as an external spy. Xenon is able to monitor the interconversion between the: axial and the equatorial isomers of cyclohexanol. The conformational equilibrium constant was estimated and is in excellent agreement with the values obtained by 1H and 13C NMR. ©2004 John Wiley & Sons, Ltd.SCOPUS: cp.jFLWINinfo:eu-repo/semantics/publishe
Novel method for the measurement of xenon gas solubility using 129Xe NMR spectroscopy.
No full textA novel method is presented for determining xenon partitioning between a gas phase and a liquid phase. An experimental setup which permits the simultaneous measurement of the 129Xe chemical shift in both the gas and the liquid phases, that is, under the same experimental conditions, has been designed. Xenon solubility is obtained via 129Xe chemical shift measurements in the gas phase. The method was validated against xenon solubility data from the literature; in general, the agreement is found to be within 3%. The solubility of xenon in three solvents for which data have not been previously reported (acetone, acetonitrile, and 1,1,2,2-tetrachloroethane) was determined using this novel method. 129Xe chemical shifts for dissolved xenon are also reported; it is found that xenon-xenon interactions may play a significant role in the liquid phase even at low equilibrium xenon pressures.SCOPUS: ar.jinfo:eu-repo/semantics/publishe
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
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