1,720,989 research outputs found
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
NMR-Spektroskopie an intermetallischen Phasen in den Systemen EA-Al-Ga mit EA = Ca, Sr und Ba : experimentelle und theoretische Untersuchungen der chemischen Bindung
No full textIntermetallic phases are widely used in industrial and technical applications. Until this day, the modification of properties is still based on empiric approaches. The lack of a precise knowledge about the chemical bonding in intermetallic phases limits the target oriented synthesis of materials with designated properties. Achieving detailed information about the structure-bonding-property relationships in intermetallic phases is a necessary step to open new opportunities for applications and to increase efficiency of existing materials. Since substitutional disorder is of pronounced role concerning the properties of intermetallic phases, the impact on the local bonding situation in the systems Sr1-xBaxGa2, Sr(Al1-xGax)2, M(Al1-xGax)4 with M = Sr, Ba and Ca1-xGa2+3x as well as Ca3-xGa8+3x was investigated, respectively. The combined application of diffraction (XRD), NMR spectroscopy and quantum mechanical (QM) calculations is well suited to gain information on atomic interactions by an analysis of the electric field gradient (EFG). Within the scope of this work, a specially designed probe system for orientation dependent NMR experiments on magnetically aligned powder samples was commissioned to establish the XRD-NMR-QM approach on intermetallic phases being strongly influenced by substitutional disorder. To ensure single phase material for NMR spectroscopy, a detailed characterization of the samples was performed using X-ray diffraction, thermoanalytical and metallographic investigations. This resulted in a re-investigation of the Ga-rich part of the phase diagram Ca-Ga focussing on the intermetallic phases Ca1-xGa2+3x and Ca3-xGa8+3x. Furthermore, conclusions about the structural chemistry and miscibility of the solid solutions Sr1-xBaxGa2, Sr(Al1-xGax)2 as well as M(Al1-xGax)4 with M = Sr, Ba were achieved. Orientation dependent 27Al and 69;71Ga NMR experiments on aligned powder samples were used to analyse the local Al and Ga environments. The influence of alkaline earth metal substitution on the Ga atoms was investigated in the solid solution Sr1-xBaxGa2. NMR spectroscopy revealed two different species Ga and Ga' with similar values of the EFG. A local symmetry reduction for Ga' was proven. In the solid solution Ba(Al1-xGax)4 a significant influence of group 13 elements substitution on the bonding situation with preferred occupancy of four (4b) and five bonded (5b) Al and Ga positions was studied, respectively. In Ca1-xGa2+3x triangular Ga3 units partially substitute the Ca atoms. Different three (3b) and four bonded (4b) Ga environments could be resolved and analysed by NMR experiments. The local atomic environments could partially be modelled in superstructures enabling QM calculations of NMR coupling parameters. From that, a verification of experimental results was possible. Future studies will have to focus on an analysis of the electronic contributions dominating the EFG
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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
Über einen Beitrag der Quantenmechanik zur modernen Strukturaufklärung intermetallischer Phasen
No full textIn this thesis, a method for high-resolution structural analysis of intermetallic phases by quantum chemical calculations in combination with solid-state NMR spectroscopy and X-ray diffraction experiments is described. The results of quantum chemical calculations form the focus of the presented work. The theoretical part in the application of the presented methodology is described particularly. Simply constructed Zintl phases and Zintl-like compounds are studied to validate the methodological interplay. The transfer to disordered intermetallic systems, in which different types of point defects are present form the main part of this thesis. The investigation of local arrangements on atomic scale is based on quantum-chemical calculation of structural parameters like lattice parameters and displacement vectors. In addition, the formation energies of different structural motifs are compared. The quantum-chemical calculation of NMR coupling parameters allows a direct comparison with values determined by NMR spectroscopy and thus links theoretical and experimental results. Several examples demonstrate that the presented method expands the classical structure analysis.For the ternary alkali metal silicides, the local ordering of the cations reported in experiments is confirmed by calculated formation energies for different arrangements. Calculation of the chemical shift resulted in an unambiguous assignment of an experimentally observed 29Si signal contribution to a distinct atom. Studying the solid solution Sr1-xBaxGa2, the influence of substitutional disorder in a layered structure was discussed. For three-dimensionally linked anionic sublattice of the BaAl4 structure type, the calculated formation energies and lattice parameters proved a preferred site occupation for the Al atoms in the solid solutions Sr(Al1-xGax)4 and Sr(Al1-xGax)4. Investigations on super lattice structures of Cu1-xAl2 provided a data basis for the analysis of the orientation-dependent electric field gradient of Al to support the analysis and interpretation of NMR experiments on a Cu1-xAl2 single crystal. Based on the reported results, the investigated types of local atomic arrangements can be interpreted as 3-dimensional extended areas in crystalline materials. In these areas changes in the local environment of the atoms occur for the investigated substances and can be resolved by the presented methodological interplay. The degree of change depends on the structure under investigation and the similarity of the exchanged particles in a chemical sense. With respect to the obtained results, a transfer of the presented methodological interplay to more complex systems is possible
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
Indium gallium nitride nanostructures for optoelectronic applications
No full textThe present thesis addresses the fabrication and characterisation of nanowires consisting of the indium gallium nitride (InGaN) material system. The group III-nitrides have become established in application for optoelectronic devices in the last years and are of great interest for research and industry. Particularly the use of gallium nitride(GaN) - InGaN heterostructure layers as the basis for light emitting diodes (LEDs) has to be pointed out. They are not only utilized as energy-efficient light sources but further as blue lasers in Blu-ray players and as background lighting in displays. Creating nanostructures, especially nanowires, out of this material system is promising to boost device efficiencies. Applied in the field of photovoltaics, nanowires can help to diminish reflection losses and increase the fraction of absorbed light due to their unique morphology and high surface-to-volume ratio. Furthermore, nanowires, unlike planar layers, enable to reduce the integration of stacking faults during heteroepitaxy on substrates like silicon or sapphire. In this work three different approaches to fabricate nanowires were pursued. One is the creation of GaN nanowires by reactive ion etching (RIE). Epitaxially grown GaN layers were introduced into the etching chamber without lithographic structuring. The following characterisation of the nanowires, in direct comparison with their layer counterpart, revealed the nanowire formation mechanism during this process and enabled to gain control of the nanowire morphology. Moreover, they show excellent optical properties, which were investigated by photoluminescence spectroscopy, as well as transmission and reflection spectroscopy. In a further step the GaN nanowires formed by plasma etching were used as growth substrate for an InGaN shell. The InGaN shell was grown by metal-organic vapour phase epitaxy (MOVPE). In these experiments different compositions of the ternary alloy were formed. A comparatively high In content could be reached compared to literature values of planar InGaN layers. Furthermore, InN nanowires were grown by MOVPE on Si wafers. In contrast to common approaches for group III-nitride growth on Si no aluminium nitride (AlN) bufferlayer was used. It was also refrained to use foreign metals like Au, to catalyse the nanowire growth via the so-called vapour liquid solid (VLS) method. Instead, the InN growth was promoted by metallic In droplets on the Si wafer. The resulting nanowires exhibit a V-shaped morphology and are split in two mirror-symmetric crystals by atwin plane. Based on these results a further development of the nanowires regarding their morphology, optoelectronic properties and integration in devices can be promoted
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