1,721,485 research outputs found
First-principles analysis of cation segregation at grain boundaries in alpha-Al2O3
No full textThe modifications in atomistic structure, chemical bonding, and energetics induced by substitutional cation impurities isolated in the bulk volume and segregated at grain boundaries of alpha-Al2O3 were investigated by combining empirical ionic-model and first-principles electronic-structure calculations. The dependency of these modifications on the boundary type, species and concentration of impurities, was studied by selecting the following variety of systems: three twin boundaries (the prismatic Sigma3 (10 (1) over bar0), the rhombohedral Sigma7 (10 (1) over bar2), and the pyramidal Sigma13 (10 (1) over bar4) twins), three impurities X (X = Se, Y, and La), and two concentrations for the segregant ( approximate to3 and approximate to6 atoms/nm(2)). A partial covalent character is found to be a distinctive feature of the X-O bonds in both bulk and interfacial atomic environments, and to drive the structural distortions of the octahedral XO6 clusters. The energetics of segregation reveals a linear relationship between segregation energy and impurity size. This is interpreted as resulting from a stress field localized at the interface. (C) 2002 Published by Elsevier Science Ltd on behalf of Acta Materialia Inc
Sigma 13 (10(1)over-bar4) twin in alpha-Al2O3: A model for a general grain boundary
No full textThe atomistic structure and energetics of the Sigma13 (10(1) over bar4)[1(2) over bar 10] symmetrical tilt grain boundary in alpha-Al2O3 are studied by first-principles calculations based on the local-density-functional theory with a mixed-basis pseudopotential method. Three configurations, stable with respect to intergranular cleavage, are identified: one Al-terminated glide-mirror twin boundary and two O-terminated twin boundaries, with glide-mirror and twofold screw-rotation symmetries, respectively. Their relative energetics as a function of axial grain separation are described, and the local electronic structure and bonding are analyzed. The Al-terminated variant is predicted to be the most stable one, confirming previous empirical calculations, but in contrast with high-resolution transmission electron microscopy observations on high-purity diffusion-bonded bicrystals. which resulted in an O-terminated structure. An explanation of this discrepancy is proposed based on the different relative energetics of the internal interfaces with respect to the free surfaces
Prismatic Sigma 3 (10(1)over-bar-0) twin boundary in alpha-Al2O3 investigated by density functional theory and transmission electron microscopy
No full textThe microscopic structure of a prismatic Sigma3 (10 (1) over bar0) twin boundary in alpha-Al2O3 is characterized by combining ab initio local-density-functional theory, electron energy-loss spectroscopy measuring energy-loss near-edge structures (ELNES) of the oxygen K-ionization edge, and high-resolution transmission electron microscopy (HRTEM). Theoretically, two distinct microscopic boundary variants with very low interface energies are derived and analyzed. The interface-projected densities of states (PDOS) calculated for the two variants agree equally well with ELNES, therefore the comparison between experimental ELNES and theoretical PDOS cannot discriminate the one or the other boundary structure. The analysis reveals that the distinction between the metastable interfaces from ELNES is limited by the spatial resolution of the scanning transmission electron microscope used to measure ELNES, not by its energetical resolution. The quantitative analysis of experimental HRTEM images obtained with an atomic-resolution microscope yields that the experimentally observed interface corresponds to the boundary variant with the lowest energy
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
- …
