1,721,032 research outputs found
Nanostructured Materials: an Experimental and Computational Study
No full textABSTRACT
In this thesis, experiment and atomistic simulations have been used in order to study the structure and properties of materials at the nanoscale focussing the attention, in particular, on metal oxide nanoparticles. Chapter 3 presents results on CuFe2O4-SiO2 nanocomposites where copper ferrite nanoparticles are embedded within a silica aerogel and xerogel matrix. In this case, extended X-ray absorption fine structure (EXAFS) spectroscopy has been extremely valuable in order to elucidate the cation distribution of the spinel. CeO2-SiO2 nanocomposites in form of aerogel and xerogel have been also synthesised and characterised. The CeO2 nanoparticles are either grown within the porous silica matrix (Chapter 4) or synthesised in advance by a hydrothermal method (Chapter 5). In order to enhance the reactivity, the attention has been focused on obtaining ceria cuboidal nanoparticles and on their dispersion in a silica aerogel matrix. An atomistic model of a CeO2 cuboidal nanoparticle has been then obtained using Molecular Dynamics (MD) simulations (Chapter 6), by performing the crystallisation of the nanoparticle with a new technique, involving the use of a crystalline seed, which drives the crystallisation to the cubic shape. The atomistic model has been found to be in quantitative agreement with experiment. The mechanical properties of CeO2 nanoparticles have been then calculated as a function of size, shape and microstructure, and are presented in Chapter 7. It has been found that the mechanical properties of CeO2 nanoparticles are dominated by the presence of grain boundaries. Furthermore, the simulations predict that Ostwald ripening can be induced along a ?11 grain boundary by applying uniaxial force
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
The predicted 3-D atomistic structure of an interfacial screw-edge dislocation
No full textAtomistic computer simulation techniques have been employed to generate an amorphous SrO thin film on an MgO(100) substrate, which, under dynamics simulation, recrystallises revealing misfit induced structural modifications including mixed screw-edge dislocations, lattice slip and twist boundaries
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
Computer modelling of V2O5: Surface structures, crystal morphology and ethene sorption
No full textWe report simulations of the surface structures and crystal morphologies of V2O5. The V2O5(001) surface is calculated to be the most stable, dominating the morphology. The low-energy adsorption sites of ethene on the V2O5(001), (200) and (301) surfaces are identified. The ethene molecule is observed to approach closer to the exposed ions on the (301) surface compared with those on the (001) or (200) surfaces, which is reflected in the binding energy of the ethene on the V2O5(301) surface being 44 kJ mol-1 greater than on the V2O5(001) surface and 54 kJ mol-1 greater than on the V2O5(200) surface
Strain reduction in supported materials; the formation of cracks and dislocations
No full textSupported materials have been constructed by successively depositing ions onto a surface in conjunction with dynamics simulation and energy minimisation. In particular, the growth of SrO/SrO, CaO/SrO (-6.9% misfit) and BaO/SrO (+7.0% misfit) were studied as model systems to examine the influence of the misfit on the structure and stability of epitaxial thin films. At low (theoretical monolayer) coverage, the CaO formed islands on the SrO(001) surface in contrast to the strips formed by BaO. At higher coverages cracks-formed within the CaO, while dislocations appeared within the BaO thin film, in both cases to help reduce the strain within the materials. A mechanism for the formation of the dislocation is presented. For one particular CaO/SrO(001) interface, a cubic-hexagonal transformation of the CaO is observed, enabling the misfit to be perfectly accommodated
Structure, epitaxial growth and nucleation of CaO/SrO interfaces using energy minimisation, molecular dynamics and computer graphics
No full textAtomistic models of CaO/SrO interfaces have been constructed via the sequential deposition of CaO species to SrO surfaces in conjunction with energy minimisation and dynamics. Using this approach the nucleation and growth mechanisms of CaO on the SrO support can be explored. The calculations suggest that the surface of the SrO substrate exacts a critical influence on the structure of the thin film. In particular, surface steps and roughness lead to incoherent films which are difficult to characterise with implications for the surface preparation of support materials. Conversely, the CaO species deposited may also degrade the SrO support: both charged and charge neutral surface vacancies on the SrO surface are created and surface steps are eroded during the deposition process. The results also suggest that the lattice misfit between the two materials is accommodated via defects and dislocations within the thin film in addition to considerable structural relaxation of the overlying thin film and the support
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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