1,721,097 research outputs found
Feeling the strain:enhancing ionic transport in olivine phosphate cathodes for Li- and Na-ion batteries through strain effects
Full text linkOlivine-type phosphates LiFePO4 and NaFePO4 are among the most widely studied cathode materials for rechargeable batteries. To improve their rate behaviour for future electronic and vehicle applications, it is vital that the Li+ and Na+ conductivities be enhanced. In this study, atomistic simulation methods (including molecular dynamics) are used to investigate the effect of lattice strain on ion transport and defect formation in olivine-type LiFePO4 and NaFePO4, as these properties are directly related to their intercalation behaviour. The results suggest that lattice strain can have a remarkable effect on the rate performance of cathode materials, with a major increase in the ionic conductivity and decrease in blocking defects at room temperature. Such understanding is important for the future optimization of high-rate cathodes for rechargeable batteries, and is relevant to the growing interest in developing thin film solid-state batteries
Lattice strain effects on doping, hydration and proton transport in scheelite-type electrolytes for solid oxide fuel cells
Full text linkLattice strain is considered a promising approach to modulate the structural and functional properties of oxide materials. In this study we investigate the effect of lattice strain on doping, hydration and proton transport for the family of scheelite-type proton conductors using both atomistic and DFT computational methods. The results suggest that tensile strain improves the dopant solubility and proton uptake of the material. The anisotropic proton pathways change from being within the a-b plane to being in the a-c plane. However, the predicted reduction in the migration barrier suggests that improvements in ionic conductivity due to lattice strain effects will be limited, in contrast with the work on oxide ion conduction. Such results are rationalized in terms of structural changes and differences in migration steps between oxide ions and protonic species.</p
Layered LaSrGa3O7-based oxide-ion conductors: cooperative transport mechanisms and flexible structures
No full textNovel melilite-type gallium-oxides are attracting attention as promising new
oxide-ion conductors with potential use in clean energy devices such as solid
oxide fuel cells. Here, an atomic-scale investigation of the LaSrGa3O7-based
system using advanced simulation techniques provides valuable insights into
the defect chemistry and oxide ion conduction mechanisms, and includes comparison
with the available experimental data. The simulation model reproduces
the observed complex structure composed of layers of corner-sharing GaO4
tetrahedra. A major finding is the first indication that oxide-ion conduction in
La1.54Sr0.46Ga3O7.27 occurs through an interstitialcy or cooperative-type mechanism
involving the concerted knock-on motion of interstitial and lattice oxide
ions. A key feature for the transport mechanism and high ionic conductivity
is the intrinsic flexibility of the structure, which allows considerable local
relaxation and changes in Ga coordination
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
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