1,720,958 research outputs found
Electronic structure of the (111) surface of diamond: Solution by self-consistent many body calculation
No full textWe present a first-principles calculation of the geometry and of the electronic structure for the C(111)2x1
⫻ 1兲 surface. We find that this surface reconstructs with -bonded chains without any significant dimerization
or buckling. At the DFT level, it appears semimetallic, in agreement with previous calculations, but in contrast
to experimental evidence. Even the introduction of quasi-particle corrections within the usual GW scheme does
not lead to the opening of the gap between surface states. Quasiparticle corrections to the surface band
structure are hence calculated within a self-consistent GW scheme. A gap of about 1 eV is found between the
surface states, thus finally solving the discrepancy between theory and experiment
Tight-binding calculations of quasiparticle wave functions for C(111)2x1
No full textDespite the simplicity of the system, the description of the excited-state properties of the cleavage surface of
diamond requires the use of nonstandard treatment of many-body effects. Using a simple tight-binding model,
we show that the typical assumption concerning the identity of quasiparticle and Kohn-Sham wave functions
fails in an important part of the Brillouin zone. This simple model allows computation of the qualitatively
different quasiparticle wave functions. The optical properties calculated with these wave functions at the
Bethe-Salpeter level show important excitonic effects. Moreover the line shape of the reflectance anisotropy spectrum is significantly improved when compared to the measured one
Electronic excitations in solids: Density Functional and Green's function Theory
No full textTheoretical approaches for ab initio studies of the electronic and optical properties of matter are here
reviewed. Examples within Density Functional Theory, Many-Body perturbation Theory and Time De-
pendent Density Functional Theory are presented and discussed, pointing out advantages and drawbacks
of the different schemes
“Dimethyl carbonate as ring-opening reagent in palladium catalysed reactions”
No full textCOMUNICAZIONE AL 6° CONVEGNO DEL CONSORZIO INTERUNIVERSITARIO NAZIONALE LA CHIMICA PER L’AMBIENTE INCA, PALERMO, 2-4 OTTOBRE 2003, ATTI DEL CONVEGNO P18
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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