1,720,971 research outputs found
Imperfections in natural diamond: the key to understanding diamond genesis and the mantle
Full text linkInfrared spectroscopy of natural Type Ib diamond: insights into the formation of Y-centers and the early aggregation of nitrogen
No full textHydrogen-related defects in diamond: A comparison between observed and calculated FTIR spectra
Full text linkA comprehensive and up-to-date compilation of observed and calculated hydrogen (H)-related peaks that occur in the near- and middle-infrared spectra of diamond is presented. The experimental database contains >300 observed peaks attributed to H-related impurities in natural diamond. The database of calculated peaks includes data from first-principles simulations of the FTIR spectra of different VxNyHz defects in diamond and contains >300 peaks that correspond to different C-H, N-H, and B-H vibrational modes for each VxNyHz defect. Less than ~10 % of observed H-related peaks have been assigned to specific defects. Consequently, the computational database was constructed to better understand the properties of different VxNyHz defects that may correspond to different observed peaks. In general, hydrogen-rich diamonds with a dominant Type Ib character and thus poorly aggregated N, show a larger number of low-intensity, H-related peaks compared to diamonds with a dominant Type Ia character. For example, ~51 % of observed H-related peaks are only observed in Type Ib diamonds, ~9 % of peaks are only observed in diamonds with a dominant Type Ia character and ~40 % of peaks are observed in both Type Ia and Type Ib diamonds. There is a major increase in the number of distinct H-related peaks in Type IaA + Ib diamonds compared to Type Ib diamonds suggesting N-aggregation processes responsible for the formation of A-centers may also produce many distinct VxNyHz defects capable of trapping H. There is a major decrease in the number of H-related peaks in Type IaA > Ib diamonds compared to Type IaA + Ib diamonds suggesting that many of the VxNyHz defects associated with the initial production of A-centers become unstable with increasing mantle residence time and the progressive loss of C-centers. These defects likely combine (or disaggregate and then re-combine) to form fewer, relatively more intense, H-related peaks observed in Type IaA > Ib diamonds. Many of these peaks persist through continued annealing in the mantle and are observed in Type IaA, IaAB, and IaB diamonds. Our data suggests that N and H incorporation are not correlated during diamond growth and that in the early stages of diamond residence, H is incorporated into many distinct VxNyHz defects that involve C- and A-centers. With continued residence and annealing, and the progressive formation A-centers and loss of C-centers, these defects aggregate to form relatively fewer, presumably more stable, VxNyHz defects such as VN3H
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
The crystal-chemistry of riebeckite, ideally Na2Fe2+3Fe3+2Si8O22(OH)2: a multi-technical study
No full textAbstractIn this work we report on a complete crystal-chemical characterization of a near end-member riebeckite from Malawi, and use the available data to critically compare information obtained from different analytical methods. The sample occurs as well-formed and very large single crystals in pegmatitic rocks. Accurate site-populations were determined by combining single-crystal structure refinement and electron microprobe analysis (EMPA). The Fe3+/Fe2+ ratio was obtained from Mössbauer spectroscopy. Lithium was quantified by Laser Ablation Inductively Coupled Plasma Mass Spectroscopy (LA-ICP-MS).Fourier-Transform Infrared (FTIR) spectra, collected both on powders and single crystals, are presented and discussed. FTIR spectra in the NIR region are also presented for the first time for this amphibole. The FTIR data are compatible with complete local ordering of A cations close to F, and complete Fe2+/Mg disorder at M(1,3). Polarized Raman-scattering data collected from single crystals confirm this conclusion. In addition, it was found that FTIR data collected on powders provide the best agreement with the site occupancies derived from chemical (EMPA and LA-ICP-MS) and crystal-chemical data, possibly because they do not depend on experimental issues such as orientation and polarization.</jats:p
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