1,720,956 research outputs found
Mn-K edge XANES structural refinement in manganese perovskites
No full textManganese oxides with perovskite structure play a special role in the field of strongly correlated systems since their peculiar magnetic transport properties. These are due to ferromagnetic double-exchange (DE) and antiferromagnetic super-exchange (SE) interaction among Mn ions, and strong electron-phonon interaction (small and/or large polarons). The balance among these interactions is mainly determined by local atomic structure surrounding Mn ions, characterized by Jahn-Teller (JT) distortions of MnO6 octahedra. Therefore the sensitivity to the short-range order of x-ray absorption spectroscopy (XAS) makes this technique suited to study these compounds as demonstrated by the wide recent literature. In particular the analysis of the XANES region could provide topological information useful to deeply understand the physics of manganites. This work reports the first attempt to a quantitative analysis of Mn K edge XANES on CaMnO3 and LaMnO3 perovskite samples. The local structures obtained by fitting the XANES data are compared with structural models derived by standard EXAFS analysis and diffraction (x-ray and neutron) data analysis. In CaMnO3 the average structure derived from XANES results in good agreement with EXAFS analysis and with the structure found by diffraction. This strengthens the confidence on the MXAN method. In LaMnO3 XAS results reproduce the main structural features as given by XRD, but both EXAFS and XANES suggest reduced Mn-O apical distance, resulting in a Jahn-Teller distortion 15-20 % reduced compared with the coherent distortion obtained by neutron diffraction
Manganese oxide perovskites: quantitative structural refinement of Mn-K- edge XANES data
No full textRare hearth doped manganites with perovskite structure show peculiar magnetic and electronic transport properties, due to a balance of ferromagnetic double-exchange (DE) and antiferromagnetic superexchange (SE) interaction among Mn ions, and strong electron-phonon interaction (small and/or large polarons)(1). These features are largely determined by the local atomic structure surrounding Mn ions, characterized by Jahn-Teller (JT) distortions of MnO6 octahedra and deeply affected by temperature, composition, pressure and magnetic .elds. Therefore the sensitivity to the short range order of x-ray absorption spectroscopy (XAS) makes this technique largely favorite in studying these compounds. Despite recent scientific literature reports several accurate XAS based studies on these compounds(2), it mainly concerns the analysis of extended region of the XAS spectra, the so called EXAFS region. On the contrary the interpretation of the near edge region of the spectra (XANES) remains qualitative or semi-quantitative(3). Nevertheless structural information in the EXAFS and XANES are complementary. The former mainly probes the atomic radial distribution functions around the absorber, whereas the latter, as it results from the full multiple scattering (FMS) processes and from the details of electronic density of states near the Fermi level, directly probes the topology of local environment surrounding the absorber and its electronic nature. This work reports the .rst attempt to a quantitative analysis of Mn K edge XANES on CaMnO3 and LaMnO3 perovskite samples. The original MXAN program has been used, a recently implemented code(4) which allows ab-initio structural refinement of XANES data in FMS approach. The topology of Mn local atomic environment on CaMnO3 and LaMnO3 samples are reported as derived by the quantitative Mn- K edge XANES fitting. The 3D structures obtained by .tting the XANES data are compared with structural models derived by EXAFS and diffraction (x-ray and neutron). While Mn local structure in CaMnO3 is consistent with the shape and size of MnO6 octahedra obtained by diffraction experiments, in LaMnO3 sample the short and long range information appear quite different. In LaMnO3, in fact, the MnO6 JT distortion determined by XANES is about 15 % reduced with respect to the one determinedby diffraction experiments, confirming and strengthening previous EXAFS results (5)
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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