1,720,952 research outputs found
New neutron-based isotopic analytical methods; An explorative study of resonance capture and incoherent scattering
No full textTwo novel neutron-based analytical techniques have been treated in this thesis, Neutron Resonance Capture Analysis (NRCA), employing a pulsed neutron source, and Neutron Incoherent Scattering (NIS), making use of a cold neutron source. With the NRCA method isotopes are identified by the isotopic-specific resonances observed in the neutron capture cross section. The capture events are detected through the prompt-gamma emissions occurring after capture, and the neutron energy at which they occur is determined with the Time of Flight (TOF) method. NRCA was improved to allow for various practical applications, i.e. 1) determination of chlorine in marble matrixes, 2) determination of the calcium to phosphorus ratio in bone, 3) determination of tin isotopes in hydroxyapatite matrixes and 4) determination of lead in bronze archaeological artefacts. The main issue was quenching the background. This was done by a combination of various expedients: 1) detector shielding, 2) detector material choice, 3) flight path length, 4) selection of gamma energies during data analysis. In NIS the measured hydrogen scattering cross section is employed to determine small hydrogen concentrations in technologically important materials. Early papers regarded the neutron scattering as isotropic and measurements were performed at one scattering angle only. However, the hydrogen scattering cross section is known to depend on hydrogen chemical binding, as expressed in the hydrogen atom's effective mass, and on the thermal motions of the hydrogen atoms in the sample, i.e. sample temperature. Both affect the anisotropy of the incoherent scattering and therefore bias the results. The goal of the research described was to increase the understanding of the NIS method and possibly render it applicable to a variety of hydrogen-containing samples. This was done by measuring at two angles and analysing the data with the aid of Monte Carlo simulations based on a more complex model, i.e. the free-gas model, that accounts for the scattering cross section dependence on hydrogen effective mass and temperature. NIS was performed both on titanium alloy samples loaded with varying hydrogen concentrations and on hydrating cement pastes. XRD (X-Ray Diffraction), MuSR (Muon Spin Resonance) and isothermal calorimetry were employed as supporting techniques for data interpretation.Applied Science
Incoherent neutron-scattering determination of hydrogen content: Theory and modeling
Get PDFHydrogen concentrations of 0 up to 350?mg/kg in a titanium alloy have been determined at National Institute of Standards and Technology (NIST) with neutron incoherent scattering (NIS) and with cold neutron prompt gamma activation analysis. The latter is a well-established technique, while the former was demonstrated earlier at NIST by counting the neutrons scattered under 45° or 60° and establishing a linear relationship between hydrogen concentration and count rate. In this paper, it is shown that the NIS response is complicated by the dependence of the apparent hydrogen scattering cross section on the sample temperature and the hydrogen chemical binding. It is demonstrated that detection of scattered neutrons at two different angles as well as a more complex theoretical approach (i.e., including Monte Carlo modeling with the free-gas model) are required to correctly interpret NIS measurements. As a result, the process of matching standards and samples becomes less critical.RID/Reactor Instituut DelftDelft University of Technolog
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
Vacuum ultraviolet excitation and emission properties of Pr3+ and Ce3+ in MSO4 (M=Ba, Sr, and Ca) and predicting quantum splitting by Pr3+ in oxides and fluorides
No full textDispelling 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
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