1,721,046 research outputs found
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
Correlated second-order perturbation studies of spin-spin nuclear coupling constants from CS-INDO molecular orbitals: polymethine compounds
No full textA second-order double perturbation treatment, using both the electronic con elation and Fermi contact operators as perturbation terms, has been performed for the evaluation of the indirect couplings of protons and carbon-13 nuclei of even- and odd-membered polymethine chains (conjugated polyenes and cyanines), in the frame of the CS-INDO molecular orbital method. The effect of electronic correlation on the values computed for the contact terms produces a significant increase of the (1)J and (3)J couplings and a decrease of the (2)J couplings, sometimes leading to negative coupling constants, but the nucleus s-density parameter s(N)(2)(0) of hydrogen or carbon- 13 cannot be reduced to a unique value, valid everywhere. (C) 1998 Published by Elsevier Science B.V. All rights reserved
ELECTRONIC-SPECTRA AND TRANS-CIS ISOMERISM OF STREPTOPOLYMETHINE CYANINES - A CS INDO CI STUDY
No full textThe understanding of the role played by cyanine dyes in various fields of application calls for a thorough knowledge of the excited state properties of their parent chromophores, i.e. cationic streptopolymethyne cyanines. For this aim we performed a detailed CS INDO CI investigation on the electronic spectra oftri-, penta- and heptamethine cyanines, both unsubstituted (TC, PC, HC) and terminally substituted by methyl groups (BMTC, BMPC, BMHC). The study comprised 5,-S, and S,-T, transitions of the truns and all mono-& isomers. CI expansions involved solely n orbitals of the polymethine chains and pseudo-n orbitals ofthe substituents and included all singly-excited and the most important doubly- and triply-excited configurations.The spectroscopic effects of methyl substitution are fairly well described and are shown to be especially important in the upper excited states. The identification of the photochemically formed stereoisomers is attempted in terms of mono-cir isomers. For BMPC, in particular, we report the absorption spectrum of thephototropic form and show that the photoisomer is identifiable as the 3-4 cb form
Mapping the many electron generalised spin-exchange Hamiltonian to accurate post-HF calculations
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
Forces at the nuclei of a molecule in the presence of non-uniform electric field
No full textThe interaction Hamiltonian within the Bloch gauge for the potentials of the electric field has been used to define electric multipole moment operators. Perturbation theory has been applied to evaluate the induced electronic moments and electric field at the nuclei in the presence of spatially non-uniform electric fields of high intensity. Multipole nuclear electric shielding tensors have been defined to describe the contributions arising from a non-homogeneous electric field. These quantities are useful to rationalize linear and non-linear responses of a molecule in the presence of intense external electric perturbations
Molecular calcium in interstellar space and circumstellar envelopes? A possible candidate: CaC_2
No full textA theoretical study of the possible structures of Calcium dicarbide has been carried out at the SCF-CI level using the perturbative MP2 and multireference MP2 formalisms to account for electronic correlation. The ground state of the system has a triangular geometry of C(2v) symmetry. The first linear structure is found 8 kcal/mol higher. The strong dipole moment of the triangular form, 13.3 Debye, reflects the ionic character Ca(+)C2(-) of the dominant configuration and makes this molecule a promising candidate for radio detection in circumstellar envelopes and interstellar space
Moments dipolaires et polarisabilites de quelques derives substitues de la pyridine-1-oxide
No full textAppropriate 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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