1,721,257 research outputs found
Optical spectroscopy of Cr3+ ions in orthoenstatite MgSiO3
No full textThe absorption, luminescence and excitation electronic spectra of MgSiO3 doped with chromium were measured in the visible and near infrared regions at temperatures down to 10 K. The optical spectraare composed of both broad bands and sharp lines, showing the presence of Cr3+ substituting for both non-equivalent Mg2+ ions in distorted octahedral sites of high and low ligand field strength respectively. All the spectral features were assigned and a preferred occupation of the low field sites was evidenced. © 1993
Local Chemical Environment of Pr3+ Substitutional Defects in Bulk and Nanocrystalline Gd3Ga5O12: A Joint EXAFS and Luminescence Study
No full text
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
Lanthanide 4f-level location in AVO4:Ln3+ (A = La, Gd, Lu) crystals
No full textThe spectral properties of LaVO4, GdVO4 and LuVO4 crystals doped with Ce3+, Pr3+, Eu3+ or Tb3+ have been investigated in order to determine the position of the energy levels relative to the valence and conduction bands of the hosts along the trivalent and divalent lanthanide series. Pr3+ and Tb3+ ground state levels are positioned based on the electron transfer energy from those states to the conduction band, the so-called intervalence charge transfer (IVCT). This approach is compared with an alternative model that is based on electron transfer from the valence band to a lanthanide.RRR/Radiation, Radionuclides and ReactorsApplied Science
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
Synthesis and structural characterization of Fe3+-doped calcium hydroxyapatites: role of precursors and synthesis method
No full textThis work evaluates the role of Ca and P precursors and of two different preparation methods, ceramic and hydrothermal, in the synthesis of undoped- and Fe3+-doped hydroxyapatite (HA), and tests the Fe3+solubility limits in HA. Previous studies have noted that different synthesis conditions lead to different products in variable amounts and recent literature quotes the highest amount of Fe3+ substituting for Ca in the HA structure in the range 0.2-0.5 as a function of temperature. Samples were characterized by X-ray powder diffraction, Mössbauer and Infrared spectroscopies. The samples obtained by the ceramic method at 800° contain mixtures of B-type carbonate-apatite and other phosphates whose type and number depend on Ca and P precursors. Samples synthesized at higher temperatures contain mixtures of hydroxyapatite, tricalcium phosphate and of magnetic phases, as hematite and ferrite, whose relative amounts depend on nominal composition and thermal treatment. Samples obtained by a hydrothermal route are richer in HA phase with respect to the solid state one, even if the obtained HA percentage depends on the pH. Mössbauer results suggest that Fe3+ is randomly distributed between Ca1 and Ca2 sites. At the highest doping levels a reduction takes place with the formation of iron(II) and magnetite
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