1,721,039 research outputs found
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
Diffusion and kinetics in epitaxial graphene growth on SiC
No full textOne of the problems that graphene is facing in electronic applications is its quality, which is still far from the level required to obtain an industrial scale production of reliable nanoscale devices, and it is ultimately related to the growth method. Understanding the kinetics of the graphene growth is an outstanding problem in physics, whose solution is the key to achieve full control on the graphene properties . This chapter deals with the microscopic phenomena occurring during epitaxial graphene growth on SiC by high temperature annealing. We discuss recent experimental and theoretical findings on the Si diffusion in the SiC matrix and on the kinetics of graphene growth as a function of temperature and of time. The theoretical framework developed in this chapter will help to understand the physical basis of the graphene formation, which is essential for a perfect control of the graphene quality, helping to define the optimal conditions for the growth of a continuous monolayer or bilayer graphene on SiC
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
Functional form of the Kolmogorov–Johnson–Mehl–Avrami kinetics for non-isothermal phase transformations at constant heating rate
No full textAn analytical computation is presented for determining the functional form of the Kolmogorov–Johnson–Mehl–Avrami (KJMA) kinetics in the case of non-isothermal transformations under linear temperature variation. Differently to previous modeling, in the present computation no approximate expression of the exponential integral is employed. The mathematical derivation holds true independently of the activation energy values for nucleation and growth and, in the limiting case of zero heating rate, reduces to the isothermal kinetics. The present computation demonstrates that the transformation rate factorizes in the product of temperature-dependent and volume fraction-dependent functions. In the framework of the KJMA theory this result is exact and implies that the KJMA kinetics is fully consistent with the requirement for the applicability of the multiple-scan analysis techniques, widely employed in thermochemistry. In the limit of large values of the reduced activation energies, the non-isothermal kinetics yields the KJMA transformation rate equation
Dynamics of energy relaxation of adatoms in the exoergic recombination of gas atoms at solid surfaces: A master equation approach
No full textThe evolution of the energy distribution function of the adatoms is described by means of the Chapman-Kolmogorov equation with the inclusion of an extra term which takes account of diatom formation. At steady state the integrodifferential equation is solved in closed form for a two band system, where "hot adatoms" are assumed to populate the high energy band. It is shown that, depending on the ratio of the density of states of the bands and on the transition probabilities for both energy dissipation and recombination, a kinetic transition takes place which is accompanied by enhanced reaction rates. The model is discussed also in connection to previous approaches based on the diffusion equation in energy space and on rate equations for a discrete set of adatom states. (c) 2006 Elsevier B.V. All rights reserved
Equilibrium-non-equilibrium "vibrational state" transition in exoergic reactions at solid surfaces
No full textA kinetic model is presented to describe the vibrational populations of adatoms in exoergic reactions at solid surfaces. The exchange of vibrational quanta among adatoms (VV exchange) and between the adatoms and the substrate (VL exchange) has been modeled by rate equations. In the model case of four vibrational levels it is shown that non-equilibrium steady states can be attained, in which adatoms do not populate the vibrational ladder according to the Boltzmann distribution. By properly defining a parameter for the "measure" of the displacement of the distribution from the Boltzmann one, it is found that, depending on gas flux and rate constants for quantum exchange, the system undergoes a transition from equilibrium to non-equilibrium state. The transition is governed by the ratio between the probabilities for VV and VL transfers and by the gas flux. The larger the adsorption energy is, the sharper the transition. These results are also analysed and discussed in connection with the catalytic activity of the system. © 2004 Elsevier B.V. All rights reserved
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