1,720,963 research outputs found
Synthesis, EXAFS investigation and optical spectroscopy of nanocrystalline Gd3Ga5O12 doped with Ln3+ ions (Ln = Eu, Pr)
No full textStructural and thermal investigation of gadolinium gallium mixed oxides obtained by coprecipitation: Observation of a new metastable phase
No full textPolycrystalline gadolinium gallium mixed oxides were prepared by coprecipitation and annealing at various temperatures below 1000 degrees C. The oxide materials appear to be X-ray amorphous after a heat treatment at 500 degrees C for 30 h, but after 30 h at 800 and 900 degrees C a major, unreported, hexagonal phase, isostructural with TAlO3 compounds (where T = Y, Eu, Gd, Tb, Dy, Ho, Er) appears to crystallize. On the other hand, a highly energetic mechanical treatment of the amorphous powder previously annealed at 500 degrees C changes considerably the shape and position of exothermal events occurring in the range from 700 up to 900 degrees C. Subsequent annealing at 900 degrees C of the mechanically treated powder gives rise to the complete formation of the Gd3Ga5O12 garnet structure at the expense of the hexagonal phase and of the minor Gd(4)G(2)O(9) oxide phase. However, a 7.0 wt% contamination is found to be due to tetragonal zirconia coming from vials and balls colliding media. The garnet phase may have strong deviations from the nominal stoichiometry of the garnet, as suggested by the refined lattice parameter obtained from the powder diffraction patterns and by the remarkable absence of intensity relative to the (220) Bragg peak position. (c
Synthesis, EXAFS investigation and optical spectroscopy of nanocrystalline Gd3Ga5O12 doped with Ln3+ ions (Ln=Eu, Pr)
No full textGadolinium Gallium Garnet (GGG) nanocrystalline powders doped with Eu3+ and Pr3+ ions have been obtained using three different methods (combustion, coprecipitation and Pechini). Their luminescence spectroscopy and the EXAFS spectroscopy at the Pr-edge have been investigated in detail, in particular in order to identify the classes of sites occupied by the dopant ions. In the case of GGG:Eu3+, luminescence spectra show the presence of several bands due to the presence of lanthanide ions in non regular sites and to distortion of the local geometry. Various relaxation mechanisms of the excited levels are present in the differently prepared samples doped with Pr3+. EXAFS spectroscopy of GGG:Pr3+ shows the presence of significant static disorder in the next nearest neighbours in the sample prepared by the combustion synthesis, in comparison with the bulk material. The Pechini method seems to produce the best GGG:Ln(3+) nanocrystalline samples. (c) 2007 Elsevier B.V. All rights reserved
Preparation and optical properties of nanocrystalline Lu2O3:Eu3+ phosphors
No full textNew combustion technology of synthesis of nanosize phosphors have been described. Four series of nanocrystalline Lu2O3:Eu3+ have been prepared for different composition of fuel (glutamic acid:glycine)(!) using the combustion method. The concentration of Eu(III) varied from 0.05 to 15wt% and the size of the nanoparticles covered the range 6-10nm. The size effect on optical properties of the phosphors have been investigated and correlated with the decay profiles of the Eu(III) emission. It has been proved that composition of the fuel influences the size of nanocrystallines, and in consequence their optical propertie
A one-step solvothermal route for the synthesis of nanocrystalline anatase TiO2doped with lanthanide ions
No full textA one-step solvothermal synthesis is proposed for the preparation of nanocrystalline single-phase TiO2in the anatase form doped with lanthanide ions Eu3+, Er3+and Sm3+. The structural properties of these products have been investigated by using X-ray powder diffraction, electron microscopy and Raman spectroscopy. Furthermore, the laser-excited luminescence spectra of the samples have been measured and analyzed. Following this route, the doping process turns out to be highly favorite and the resulting materials show an efficient luminescence in the visible region. © 2006 Elsevier Inc. All rights reserved
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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