1,721,027 research outputs found
Thermal and transport properties of pristine single-layer hexagonal boron nitride: A first principles investigation
Full text linkMolecular dynamics is used in combination with density functional theory to determine the thermal transport properties of the single-layer hexagonal boron nitride (SL h-BN) from ab initio calculations. Within this approach, the possible anisotropy in the thermal conductivity of SL h-BN was studied. For samples with finite length (of the order of 20 nm), we find a significant dependence of the conductivity on the transport direction. We make a direct comparison of the results obtained for two-dimensional (2D) layers and for nanoribbons with similar size, and show that, as a consequence of edge scattering, the ribbon geometry induces a significant decrease in the conductivity, and produces a strong change in the anisotropy. For the zigzag and armchair transport directions, the dependence of the thermal conductivity on the system length was also obtained, as well as its value in the 2D bulk limit case. A very small anisotropy was found for the limit of long samples, in contrast with the finite length ones. This is explained analyzing the dependence of the average square group velocities on the transport direction and the phonon frequency
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Atomistic simulations in hybrid C/BN structures
Full text linkGrafeno es un material sobresaliente que ha sido el foco de atención de muchos científicos en años recientes. Junto con el grafeno, aparecieron muchos otros materiales bidimensionales (2D) como BN, dicalcogenuros de metales, ZnO, entre otros. En esta tesis, se presenta un estudio teórico de sistemas híbridos 2D compuestos de grafeno y BN, basado en los métodos de teoría del funcional de la densidad (DFT) y enlace fuerte (TB). La estructuras analisadas son heteroestructuras grafenno/BN apiladas y coplanares. Las estructuras apiladas forman patrones de moiré que están caracterizadas por el ángulo de rotación entre las dos capas. Cálculos DFT son llevados a cabo para sistemas con distintos ángulos, cada uno teniendo tamaños diferentes. La densidad de estados (DOS), la estructura de bandas y los desplazamientos atómicos debido a la relajación son analizados. Las depresiones en la DOS, también observadas experimentalmente en medidas de espectroscopía de efecto tunel, están situadas en energías que están de acuerdo a predicciones perturbativas. La estructura de bandas revela el origen de las depresiones como la aparición de un brecha energética a energias diferentes de cero. Una estimación de la intensidad del potencial del sustrato es obtenida de las energías locales atómicas. Luego, se estudian las propiedades de transporte en heteroestructuras de grafeno/h-BN apilados usando la información del potencial de superred de los cálculos DFT anteriores. La conductividad es calculada usando el formalismo de Kubo para transporte electrónico dentro de la descripción TB. El efecto del sustrato de h-BN es modelado como un término de masa adicional en el Hamiltoniano para representar una ruptura local de la simetría de subred. El camino libre medio y la resistividad son obtenidos, mostrando picos satélite que aparecen como un efecto del potencial del moiré. Las propiedades de híbridos coplanares son estudiadas. Después de una analisis con DFT de diferentes sistemas con interfases zigzag y armchair, se propone un modelo para describir estas heteroestructuras usando TB. El model se basa principalmente en las propiedades de polarización del h-BN. La discontinuidad en la polarización que aparece cuando el h-BN es cortado a lo largo de la dirección zigzag, da lugar a un campo eléctrico inducido que actúa en la region de grafeno. Se considera un modelo electrostático simple de cargas puntuales situadas en la interfase, el cual representa físicamente a la carga ligada acumulada en los bordes del h-BN. Los parámetros del modelo TB son ajustados a sistemas zigzag, pero se prueba que trabajan bien para interfases armchair y quirales. Finalmente, la constante piezoeléctrica de h-BN es calculada con DFT usando la teoría de polarización basado en fases de Berry. En superestructuras C/BN con interfases zigzag, la sintonización piezoeléctrica de la carga ligada inducidad por la polarización es estudiada tensando el sistema de manera perpendicular a la interfase. El comportamiento de estos sistemas es descrito de manera adecuada por la respuesta piezoeléctrica del h-BN prístino. De manera interesante, heteroestructuras grafeno/ BC2N también estudiadas, tienen una respuesta piezoeléctrica mayor que los híbridos con h-BN. También se aplica compresión en dirección paralela a la interfase zigzag, encontrando redistribución de carga que depende de la curvatura de las hojas.Graphene is an outstanding material which has been the focus of attention of many scientist in recent years. With graphene, there appear many other two-dimensional (2D) materials like BN, metal dichalcogenides, ZnO, beside others. In this thesis, a theoretical study of 2D hybrid systems of graphene and BN is presented, based principally on first-principles density functional theory (DFT) and tight binding (TB) methods. The structures that are analysed are stacked and coplanar graphene/BN heterostructures. Stacked structures form moiré patterns that are characterized by the rotation angle between both layers. DFT calculations are performed for systems with different angles, each one having different sizes. The density of states (DOS), the band structure and atomic displacements due to relaxation are analysed. The dips in the DOS, also observed experimentally in scanning tunneling spectroscopy measurements, are found to be located at energies that are in agreement with perturbative predictions. The band structure reveal the origin of the dips, as a gap openning at non-zero energy. An estimation of the strength of the substrate potential is obtained from local atomic energies. Then, the transport properties of stacked graphene/h-BN heterostructures are studied using the information of the superlattice potential from the previous DFT calculations. The conductivity is calculated using the Kubo formalism of electronic transport within the TB description. The effect of the h-BN substrate is modelled as an additional mass term in the Hamiltonian to represent a local breaking of the sublattice symmetry. The mean free path and resistivity are obtained, showing satellite peaks appearing as an effect of the moiré potential. The electronic properties of coplanar hybrids are studied. After a DFT analysis of different systems with zigzag and armchair interfaces, a model is proposed to describe these heterostructures within TB. The model is mainly based in the properties of polarization of h-BN. The polarization discontinuity that appears when h-BN is cut along the zigzag direction gives place to an induced electric field that acts in the graphene region. A simple electrostatic model of point charges at the interface is considered, which represent the physical bound charge accumulated at the edge of h-BN. The parameters of the TB model are fitted to zigzag systems, but are proven to work with armchair and chiral interfaces. Finally, the piezoelectric constant of h-BN was calculated within DFT using the Berry-phase theory of polarization. In C/BN superlattices with zigzag interfaces, the piezoelectric tuning of the polarization induced bound charge is studied by applying tensile strain perpendicular to the interface. The behaviour of these systems is well described by the piezoelectric response of pristine h-BN. Interestingly, graphene/BC2N heterostructures, also studied, have a larger piezoelectric response than the hybrids with h-BN. Compressive strain parallel to the zigzag interface is also applied, finding a charge redistribution that depends on the curvature of the compressed layers
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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