1,721,078 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
Conical intersections in solution: a QM/MM study using floating occupation semiempirical configuration interaction wave functions
No full textWe describe a hybrid quantum mechanical/molecular mechanical (QM/MM)
method implemented in the context of floating-occupation molecular
orbital semiempirical configuration interaction wave functions. The
QM/MM approximation is compared to a fully QM treatment, emphasizing its
accuracy with respect to features important to photochemical mechanisms
such as conical intersection geometries and topography. The methodology
we describe allows the location and characterization of solution-phase
conical intersections for the first time. This is demonstrated
explicitly by application to several biologically relevant chromophores
solvated in clusters of up to 150 water molecules. The effect of
solvation on the photochemical energy landscapes of these molecules is
investigated, and we note a tendency for conical intersections to become
absolute excited state minima upon hydration
A Theoretical Study of Guanine from Gas Phase to Aqueous Solution: Role of Tautomerism and its Implications in Absorption and Emission Spectra
No full textCorrelated ab initio methods have been exploited to study geometries and electronic structures of ground and lowest singlet excited states of isolated and solvated keto-amino tautomers of guanine. Nuclear structures have been obtained at the CIS level, whereas calculations of electronic structures have been performed using a multireference perturbed CI method. In all calculations, the solvent (water) has been described within the integral equation formalism continuum model. The results have been successfully compared to experimental absorption and emission spectra. In particular, the analysis of the two computed spectra has shown an opposite role of the different tautomers (being absorption mostly because of 9NH form and the emission induced by 7NH) which has lead us to investigate possible mechanisms giving origin to the keto-9NH and keto-7NH tautomerism in the ground or in the electronically excited states
Multireference Perturbation CI methods for solvated systems described within the polarizable continuum model
No full textWe present a method to include solvent effects described within the polarizable continuum model into the CIPSI multireference perturbation algorithm. In the methodology we have formulated and implemented, solvent interactions are explicitly included in the configuration interaction scheme and in the following perturbative corrections, through proper operators. The nonlinear character induced by such operators leads to an iterative procedure in which solute and solvent can mutually equilibrate. Applications to the electronic excitation spectrum of formamide are considered. In these cases, effects due to an incomplete electrostatic response of the solvent nonequilibrium model as well as repulsion interactions between solute and solvent have been included in the quantum mechanical description
Multireference Perturbation CI methods for solvated systems described within the polarizable continuum model
No full textWe present a method to include solvent effects described within the polarizable continuum model into the CIPSI multireference perturbation algorithm. In the methodology we have formulated and implemented, solvent interactions are explicitly included in the configuration interaction scheme and in the following perturbative corrections, through proper operators. The nonlinear character induced by such operators leads to an iterative procedure in which solute and solvent can mutually equilibrate. Applications to the electronic excitation spectrum of formamide are considered. In these cases, effects due to an incomplete electrostatic response of the solvent nonequilibrium model as well as repulsion interactions between solute and solvent have been included in the quantum mechanical description
Molecular gradients for semiempirical CI wavefunctions with floating occupation molecular orbitals
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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