1,721,595 research outputs found
Theoretical assessment on the validity of the Wiedemann-Franz law for icosahedral quasicrystals
No full text©2007 The American Physical Society.
We warmly thank Tsunehiro Takeuchi for enlightening comments. We acknowledge M. V. Hernández for a critical reading of the paper. This work has been supported by the Universidad Complutense de Madrid through Project No. PR27/05-14014-BSCH.The validity of the Wiedemann-Franz law (WFL) for icosahedral quasicrystals belonging to the families AlCu(Fe,Ru) and AlPd(Mn,Re) is discussed. We exploit some characteristic features in the electronic structure in order to obtain closed analytical expressions for the transport coefficients in terms of the Hurwitz zeta function. Depending on the Fermi-level position, a systematic deviation from the ideal WFL is observed. The role of self-similar features in the electronic structure on the WFL is discussed. The obtained expression for the Lorenz function may be used in order to refine previous experimental results on the charge-carrier contribution to the thermal conductivity in these materials.Universidad Complutense de MadridDepto. de Física de MaterialesFac. de Ciencias FísicasTRUEpu
Hierarchical description of phonon dynamics on finite Fibonacci superlattices
No full text©2006 The American Physical Society.
This work has been supported by the Universidad Complutense de Madrid through Project No. PR27/05-14014-BSCH. I warmly thank Víctor R. Velasco, Gerardo G. Naumis, and Rogelio Rodríguez-Oliveros for very useful comments and Victoria Hernández for a critical reading of the manuscript.We study the phonon dynamics of Fibonacci heterostructures where two kinds of order (namely, periodic and quasiperiodic) coexist in the same sample at different length scales. We derive analytical expressions describing the dispersion relation of finite Fibonacci superlattices in terms of nested Chebyshev polynomials of the first and second kinds. In this way, we introduce a unified description of the phonon dynamics of Fibonacci heterostructures, able to exploit their characteristic hierarchical structure in a natural way.Universidad Complutense de MadridDepto. de Física de MaterialesFac. de Ciencias FísicasTRUEpu
Electrical conductance in duplex DNA: Helical effects and low-frequency vibrational coupling
No full text©2007 The American Physical Society.
I warmly thank Alexander Voityuk for useful comments. I acknowledge M. V. Hernández for a critical reading of the manuscript. This work has been supported by the Universidad Complutense de Madrid through Project No. PR27/05- 14014-BSCH.In this work we consider the combined effect of helical structure and base-pair twist motion on charge transfer through duplex DNA at low temperatures. We present a fully analytical treatment of charge-lattice coupled dynamics in terms of nearest-neighbor tight-binding equations describing the propagation of the charge through an effective linear lattice for certain frequency values. The corresponding effective hopping terms include both helicoidal and dynamical effects in a unified way. Although base-pair motion generally reduces pi-pi stack overlapping, the coupling to certain normal modes gives rise to a significant improvement of the Landauer conductance.Universidad Complutense de MadridDepto. de Física de MaterialesFac. de Ciencias FísicasTRUEpu
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
No full text“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
No full textWe 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
No full textWe 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
Renormalization transformation of periodic and aperiodic lattices
No full text©2006 The American Physical Society.
E.M. warmly thanks J. César Flores, Gerardo G. Naumis, and Víctor R. Velasco for enlightening conversations on aperiodic systems. We acknowledge M. V. Hernández for a critical reading of the manuscript. This work has been supported by the Universidad Complutense de Madrid through Project No. PR27/05-14014-BSCH.In this work we introduce a similarity transformation acting on transfer matrices describing the propagation of elementary excitations through either periodic or Fibonacci lattices. The proposed transformation can act at two different scale lengths. At the atomic scale the transformation allows one to express the systems' global transfer matrix in terms of an equivalent on-site model one. Correlation effects among different hopping terms are described by a series of local phase factors in that case. When acting on larger scale lengths, corresponding to short segments of the original lattice, the similarity transformation can be properly regarded as describing an effective renormalization of the chain. The nature of the resulting renormalized lattice significantly depends on the kind of order (i.e., periodic or quasiperiodic) of the original lattice, expressing a delicate balance between chemical complexity and topological order as a consequence of the renormalization process.Universidad Complutense de MadridDepto. de Física de MaterialesFac. de Ciencias FísicasTRUEpu
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