1,720,981 research outputs found
Exploring the structure of halomethanes with xenon: An NMR and MD investigation
No full textThe liquid structure of dihalomethanes (CH2X2, X = Cl, Br, I) loaded with xenon gas was investigated both experimentally, by 129Xe NMR Spectroscopy, and computationally, by molecular dynamics (MD) simulations and relativistic DFT calculations. The chemical shifts of xenon have been measured in a wide range of temperatures; in addition, the spin-lattice relaxation times, T1, and the diffusion coefficients of dissolved xenon were also determined. The MD simulations of the three dihalomethanes with xenon dissolved were used to generate collection of clusters, representing xenon with its first solvation shell, which was subsequently submitted to the relativistic DFT calculation of the 129Xe NMR shielding constant. This was finally averaged over the trajectory obtain the corresponding chemical shift at various temperatures. The experimental data were then rationalized terms of the density of the bulk phase and the average orientation of the halogens with respect to the xenon atom. Diffusion coefficients were also obtained from the MD simulations and compared with the experimental values, showing a good agreement
Particles for Self-cleaning Treatments of Historic Architecture and Sculptures Restoration of Buildings and Monuments
No full textNovel Cellulosic Ethers with Low Degrees of Substitution - II. Magic Angle Spinning NMR Study
No full textMACROMOL. CHEM. PHYS
Xenon Dynamics in Ionic Liquids: A Combined NMR and MD Simulation Study
Full text linkThe translational dynamics of xenon gas dissolved in room-temperature ionic liquids (RTILs) is revealed by 129Xe NMR and molecular dynamics (MD) simulations. The dynamic behavior of xenon gas loaded in 1-alkyl-3-methylimidazolium chloride, [CnC1im]Cl (n = 6, 8, 10), and hexafluorophosphate, [CnC1im][PF6] (n = 4, 6, 8, 10) has been determined by measuring the 129Xe diffusion coefficients and NMR relaxation times. The analysis of the experimental NMR data demonstrates that, in these representative classes of ionic liquids, xenon motion is influenced by the length of the cation alkyl chain and anion type. 129Xe spin-lattice relaxation times are well described with a monoexponential function, indicating that xenon gas in ILs effectively experiences a single average environment. These experimental results can be rationalized based on the analysis of classical MD trajectories. The mechanism described here can be particularly useful in understanding the separation and adsorption properties of RTILs
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
Poly(p-phenylene terephthalamide)-based nanocomposites obtained by matrix polycondensation. Synthesis and solid state NMR characterization
No full textVariations 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
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