1,721,001 research outputs found
Order Parameters of α,ω-diphenylpolyenes in a nematic Liquid Crystal from an Integrated Computational and 13C NMR Spectroscopic Approach
No full textA combined theoretical and experimental approach to determining order parameters of solutes in liquid crystals from 13C NMR data
No full textThe ordering properties of an anisotropic liquid crystal can be studied by recording C13 NMR spectra at different temperatures for a number of rigid solutes. The traditional difficulty in analyzing C13 data comes from the scarcity of experimental information about the carbon shielding tensors, and from their limited transferability among different solutes.
We show that these obstacles can be overcome by computing high level ab initio shielding tensors, also including the solvent effects by the polarizable continuum model. The reliability of this combined approach is carefully verified, and the order parameters of several solutes are obtained by reanalyzing previously published spectra. The quality of the results is shown to be comparable to deuterium NMR without the need of isotopic substitution
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
High resolution infrared study of SbHD2: The ground state and the Sb-H stretching bands nu1 and 2nu1
No full textHigh resolution infrared spectra of (SbHD2)-Sb-121 and (SbHD2)-Sb-123 have been studied in the region of nu(1), the Sb-H stretching fundamental, from 1780 to 1990 cm(-1). The 2 nu(1) stretching overtone band of (SbHD2)-Sb-123, located in the 3640-3790 cm(-1) range, has also been investigated. The SbHD2 molecule is an asymmetric rotor of C-s symmetry with the asymmetry parameter kappa = 0.61. The nu(1) band is of hybrid type, formed by strong C-type and weak B-type transitions, and almost unperturbed. For (SbHD2)-Sb-123, 2092 transitions have been assigned: 70% of these belong to the C component, the other 30% are of B-type. The assigned transitions have been fitted using a Watson type S-reduced Hamiltonian in the lilt representation, with a standard deviation of the fit sigma = 0.45 x 10(-3) cm(-1). In order to determine the ground state parameters all possible ground state combination differences (GSCD) have been generated from the v, transitions. In total, 3942 GSCD up to J '' = 27, K ''(a) = 25, and K ''(c) = 20 have been fitted with sigma = 0.52 x 10(-3) cm(-1). Only C-type transitions have been observed in the weak 2 nu(1) overtone band. The 556 assigned transitions have been fitted with sigma = 2.6 x 10(-3) cm(-1) using the same Hamiltonian as for nu(1). In the nu(1) band of (SbHD2)-Sb-121 771 C-type transitions have been assigned, and the nu(1) = 1 spectroscopic constants obtained from a fit with sigma = 0.70 x 10(-3) cm(-1). Using 618 GSCD the ground state spectroscopic constants of (SbHD2)-Sb-121 have been derived with a = 1.0 x 10(-3) cm(-1). The molecular parameters for the ground and the nu(1) = 1 states of the two isotopologues agree well. The quartic theoretical ab initio force field of SbH3 has been used to predict all relevant spectroscopic parameters for (SbHD2)-Sb-123, (SbHD2)-Sb-121, (SbHD2)-Sb-123, and (SbH2D)-Sb-121. Relations between the harmonic frequencies and between the anharmonicity constants obtained in the expanded local mode theory, for the XH3 -> XH2D/XHD2 isotopic substitution, have been compared with those obtained in the present study. (C) 2010 Elsevier Inc. All rights reserved
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
Order Parameters of a,?-diphenylpolyenes in a nematic Liquid Crystal from an Integrated Computational and 13C NMR Spectroscopic Approach
No full textThe orientational order parameters and conformational behavior of five relatively large rodlike molecules, biphenyl, trans-stilbene, 1,3-diphenyl-butadiene, 1,3,5-diphenyl-hexatriene, and 1,3,5,7-diphenyl-octatetraene, dissolved in the thermotropic liquid crystal ZLI-1167, have been studied using an integrated approach combining 13C NMR measurements and quantum mechanical
computations of carbon chemical shift tensors. Besides biphenyl, the phenyl moiety of all structures has been found to have a high rotational mobility in the temperature range of the present
experiments. The rank-two order parameter in the nematic phase is found to increase steadily from the shortest to the longest term of the series at any temperature within the nematic range. The
molecular biaxiality order parameter is found to be small and essentially constant with temperature, giving further support to the common assumption of effective uniaxiality for these
probes
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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