1,721,107 research outputs found
Optical properties of Au nanoclusters from TD-DFT calculations
No full textA time-dependent density-functional-theory (TD-DFT) approach
is employed to investigate theoretically the optical response of Au nanoclusters of
size around N = 150 atoms as a function of: (a) the approximation used for the
DFT exchange-correlation (xc-) functional, (b) the shape of the nanocluster. The
results of the local-density-approximation (LDA) and the van Leeuwen-
Baerends (LB94) xc-functionals are compared on a set of 4 structural motifs:
octahedral (N= 146), cuboctahedral (N= 147), icosahedral (N = 147), and cubic
(N= 172), representative of both crystalline and noncrystalline motifs commonly
encountered in the study of metal nanoclusters. It is found that the position of the
peak in the photoabsorption spectrum is weakly dependent on the shape of the
cluster but is strictly related to its size and to the DFT xc-functional used in the
calculations, with the finding that the predictions of the LB94 xc-functional
compare better with the available experimental data on the absorption spectrum
of Au particles in this size range with respect to those of the LDA xc-functional. The detailed shape of the cluster becomes apparent
in the form of the absorption spectrum, which can be symmetric or asymmetric in two different forms
Alloying effects on the optical properties of Ag-Au nanoclusters from TDDFT calculations
No full textThe optical properties of alloyed AgAu 147-atom cuboctahedral nanoclusters are theoretically investigated as a function of composition and chemical ordering via a time-dependent density functional theory (TDDFT) approach. Compositions 3763%, 4654%, and 6337%, in AgAu, and three types of chemical ordering, coreshell, multishell and maximum mixing, are considered. Additionally, the optical spectra of pure Ag clusters with several structural motifs are also studied. It is found that (a) pure Ag clusters exhibit a neater dependence of the absorption peak on the shape of the cluster than Au clusters, (b) the absorption spectrum of alloyed clusters is not strongly affected by changes in chemical ordering, possibly because of their limited size, and (c) the optical absorption peak smoothly shifts to higher energies, gets narrower, and substantially gains in intensity by increasing Ag concentration, in excellent agreement with available experimental data. An analysis of the character of the electronic transitions mostly contributing to the absorption peak allows us to rationalize the notable difference between Ag and Au in terms of optical properties and the effect of alloying
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
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
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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