1,720,997 research outputs found
Charge-density waves and surface Mott insulators for adlayer structures on semiconductors: Extended Hubbard modeling
No full textMotivated by the recent experimental evidence of commensurate surface charge-density waves (CDW) in Pb/Ge(lll) and Sn/Ge(lll) root 3-adlayer structures, as well as by the insulating states found on K/Si(lll):B and SiC(0001), we have investigated the role of electron-electron interactions, and also of electron-phonon coupling, on the narrow surface-state band originating from the outer dangling-bond orbitals of the surface. We model the root 3 dangling-bond lattice by an extended two-dimensional Hubbard model at half filling on a triangular lattice. The hopping integrals are calculated by fitting first-principle results for the surface band. We include an on-site Hubbard repulsion U and a nearest-neighbor Coulomb interaction V, plus a long-ranged Coulomb tail. The electron-phonon interaction is treated in the deformation potential approximation. We have explored the phase diagram of this model including the possibility of commensurate 3 X 3 phases, using mainly the Hartree-Fock approximation. For U larger than the bandwidth we find a noncollinear antiferromagnetic spin-density wave (SDW) insulator, possibly corresponding to the situation on the SiC and K/Si surfaces. For U comparable or smaller, a rich phase diagram arises, with several phases involving combinations of charge and spin-density-waves (SDW), with or without a net magnetization. We find that insulating, or partly metallic 3 X 3 CDW phases can be stabilized by two different physical mechanisms. One is the intersite repulsion V, which together with electron-phonon coupling can lower the energy of a charge modulation. The other is a magnetically-induced Fermi-surface nesting, stabilizing a net cell magnetization of 1/3, plus a collinear SDW, plus an associated weak CDW. Comparison with available experimental evidence, and also with first-principle calculations is made
International Editorial Advisory Board
No full textProfessor Sandro Scandolo, ItalyProfessor Alessandro Laio, ItalyProfessor Joel Koech, KenyaProfessor Jerome Nriagu, USADr. Arch. Barnabas Nawangwe, UgandaDr. Tomlins Keith, UKDr. Olaniran Fasina, USADr. (Mrs.) Prajeab Jammne, IndiaMr. V. Prakash, IndiaSubscription
International Editorial Advisory Board
Full text linkª¤? Professor Sandro Scandolo, Italyª¤? ª¤?Professor Alessandro Laio, Italyª¤? ª¤?Professor Joel Koech, Kenyaª¤? ª¤?Professor Jerome Nriagu, USAª¤? ª¤?Dr. Arch. Barnabas Nawangwe, Ugandaª¤? ª¤?Dr. Tomlins Keith, UKª¤? ª¤? Dr. Olaniran Fasina, USAª¤? Dr. (Mrs.) Prajeab Jammne, Indiaª¤? ª¤?Mr. V. Prakash, Indiaª¤?ª¤
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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