1,720,968 research outputs found
Alignment of <sup>17</sup>O-enriched water-endofullerenes H<sub>2</sub>O@C<sub>60</sub> in a liquid crystal matrix
No full textWe present a 17O and 1H NMR study of molecular endofullerene H2O@C60 dissolved in the nematic liquid crystal N-(4-methoxybenzylidene)-4-butylaniline (MBBA). The 17O NMR peak is split into five components by the 17O residual quadrupolar coupling, each of which is split into a triplet by the 1H–17O residual dipolar coupling and scalar coupling. The splittings are analysed in terms of the partial alignment of the encapsulated water molecules. Order parameters describing the alignment are estimated. It is found that the preferential orientation of the endohedral water molecule has the molecular plane perpendicular to the liquid crystal director
Spin-isomer conversion of water at room temperature, and quantum-rotor-induced nuclear polarization, in the water-endofullerene H2O@C60
No full textWater exists in two forms, para and ortho, that have nuclear spin states with different symmetries. Here we report the conversion of fullerene-encapsulated para-water to ortho-water. The enrichment of para-water at low temperatures is monitored via changes in the electrical polarizability of the material. Upon rapid dissolution of the material in toluene the excess para-water converts to ortho-water. In H216O@C60 the conversion leads to a slow increase in the NMR signal. In H217O@C60 the conversion gives rise to weak signal enhancements attributed to quantum-rotor-induced nuclear spin polarization. The time constants for the spin-isomer conversion of fullerene-encapsulated water in ambient temperature solution are estimated as 30±4 s for the 16O-isotopologue of water, and 16±3 s for the 17O-isotopologue
NMR of molecular endofullerenes dissolved in a nematic liquid crystal
No full textWe report the NMR of the molecular endofullerenes H2@C60, H2O@C60 and HF@C60 dissolved in the nematic liquid crystal N-(4-methoxybenzylidene)-4-butylaniline (MBBA). The 1H NMR lines of H2 and H2O display a doublet splitting due to residual dipole–dipole coupling. The dipolar splitting depends on temperature in the nematic phase and vanishes above the nematic–isotropic phase transition. The 19F spectrum of HF@C60 dissolved in MBBA displays a doublet splitting in the nematic phase, with contributions from the 1H–19F dipole–dipole coupling and J-coupling. The phenomena are analyzed using a model in which the fullerene cages acquire a geometrical distortion, either through interaction with the liquid crystal environment, or through their interaction with the endohedral molecules. The distorted cages become partially oriented with respect to the liquid crystal director, and the endohedral molecules become partially oriented with respect to the distorted cages
NMR lineshapes and scalar relaxation of the 17O-labelled water-endofullerene H2O@C60
No full textThe 17O isotopomer of the water-endofullerene H2O@C60 displays a remarkable proton NMR spectrum, with six well resolved peaks. These peaks are due to the J-coupling between the water protons and the 17O nucleus, which has spin-5/2. The resolution of these peaks is enabled by the suppression of water proton exchange by the fullerene cage. The six peaks display an unusual pattern of linewidths, which we model by a Liouville-space treatment of scalar relaxation due to quadrupolar relaxation of the 17O nuclei. The data are consistent with rotational diffusion of the water molecule on the sub-picosecond timescale
First Synthesis and Characterisation of CH4@C60
No full textRaw data supporting journal article:
Bloodworth, S. et al (2019). First Synthesis and Characterisation of CH4@C60. Angewandte Chemie International Edition.
DOI: 10.1002/anie.201900983 and 10.1002/ange.201900983
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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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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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