1,721,304 research outputs found
Binding of hydrogen on benzene, coronene, and graphene from quantum Monte Carlo calculations
No full textQuantum Monte Carlo calculations with the diffusion Monte Carlo (DMC) method have been used to compute the binding energy curves of hydrogen on benzene, coronene, and graphene. The DMC results on benzene agree with both Moller-Plessett second order perturbation theory (MP2) and coupled cluster with singles, doubles, and perturbative triples [CCSD(T)] calculations, giving an adsorption energy of similar to 25 meV. For coronene, DMC agrees well with MP2, giving an adsorption energy of similar to 40 meV. For physisorbed hydrogen on graphene, DMC predicts a very small adsorption energy of only 5 +/- 5 meV. Density functional theory (DFT) calculations with various exchange-correlation functionals, including van der Waals corrected functionals, predict a wide range of binding energies on all three systems. The present DMC results are a step toward filling the gap in accurate benchmark data on weakly bound systems. These results can help us to understand the performance of current DFT based methods, and may aid in the development of improved approaches. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3569134
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
Evidence on the Insurance Effect of Marginal Income Taxes
No full textCEPR Discussion Papers No. 6710
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
Stone-Wales defects in graphene and other planar sp(2)-bonded materials
No full textDensity functional theory and quantum Monte Carlo simulations reveal that the structure of the Stone-Wales (SW) defect in graphene is more complex than hitherto appreciated. Rather than being a simple in-plane transformation of two carbon atoms, out-of-plane wavelike defect structures that extend over several nanometers are predicted. Equivalent wavelike SW reconstructions are predicted for hexagonal boron-nitride and polycyclic aromatic hydrocarbons above a critical size, demonstrating the relevance of these predictions to sp(2)-bonded materials in general
Cooperative Interplay of van der Waals Forces and Quantum Nuclear Effects on Adsorption: H at Graphene and at Coronene
No full textThe water-benzene interaction: Insight from electronic structure theories
No full textWeak noncovalent interactions such as van der Waals and hydrogen bonding are ubiquitous in nature, yet their accurate description with electronic structure theories is challenging. Here we assess the ability of a variety of theories to describe a water-benzene binding energy curve. Specifically, we test Hartree-Fock, second-order Moller-Plesset perturbation theory, coupled cluster, density functional theory with several exchange-correlation functionals with and without empirical vdW corrections, and quantum Monte Carlo (QMC). Given the relative paucity of QMC reports for noncovalent interactions, it is interesting to see that QMC and coupled cluster with single, double, and perturbative triple excitations [CCSD(T)] are in very good agreement for most of the binding energy curve, although at short distances there are small deviations on the order of 20 meV
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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