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Theoretical Study of Tellurium Isotope Fractionations in Ore-Forming Systems, and Studies of Doubly Substituted Isotopologues of Methane
Get PDFThis thesis encompasses three research projects on the stable isotopes of tellurium and multiply substituted isotopologues of methane. In the first project (Chapter 2), I used theoretical techniques to predict tellurium isotope signatures of ore formation processes. In this study, equilibrium mass-dependent isotopic fractionation among Te-bearing species relevant to the formation of precious-metal ores is estimated with first-principles thermodynamic calculations. This work is the first theoretical study on the isotope fractionation of tellurium in ore-forming systems. In the second project (Chapter3), I investigated the potential of 13CH3D and 12CH2D2, the doubly substituted mass-18 isotopologues of methane, as tools for tracking atmospheric methane sources and sinks. Methane is the most abundant organic chemical and the second most important long-lived greenhouse gas in the atmosphere. It also has a significant impact on the chemistry of the troposphere and stratosphere. However, there are large uncertainties in the sources and sinks of methane to the atmosphere, as well as in their variability in time and space. I used electronic structure methods and initial isotopologue abundance measurements, from the UCLA Nu Panorama and other laboratories [Stolper et al., 2015; Wang et al., 2015; Young et al., 2017], to estimate kinetic and equilibrium isotope signatures for 13CH3D and 12CH2D2. Then I predicted the abundances of singly and doubly substituted methane species in atmosphere in different scenarios using a whole-atmosphere box model. This study is the first model ever to describe the atmospheric methane budget that includes both doubly substituted isotopologues, 13CH3D and 12CH2D2.The third project (Chapter 4) focused on measuring 13CH3D and 12CH2D2 in methane samples from natural boreal lakes, collected in Alaska, Canada, and Siberia. Wetlands are among the largest methane sources, and they will need to be characterized as part of the construction of any realistic global budget of 13CH3D and 12CH2D2. In this project all measurements were performed using gas chromatography and a high-resolution gas-source multiple-collector mass spectrometer (the UCLA Nu Panorama). Finally, these data are combined with recent predictions of future emissions growth to model the likely impacts of boreal lakes on the future atmospheric CH4 isotopologue budget up to year 2100. In addition to testing our model atmospheric budget, doubly substituted isotopologue measurements of CH4 appear to provide information about the likely production mechanism for natural CH4 samples
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
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Field shift fractionations in novel isotope systems
Get PDFMeasurements of isotope fractionation have long focused on mass dependent fractionations, though mass independent effects have long been recognized. One mechanism of mass independent fractionation is the nuclear field shift. Field shift isotope fractionation was first proposed by Bigeleisen (1996) and Nomura et al. (1996) as a mechanism explain to patterns of redox-driven uranium isotope fractionation. This thesis aims to model the nuclear field shift using ab initio methods in multiple isotope systems, in relevant natural species, as well as to explore potential applications of field shift fractionation measurements for these systems. The main method used is the DFT-PAW method of Schauble (2013), which makes it possible to determine field shifts in solids and complex aqueous species.In the uranium isotope system, 238U/235U is predicted to be ~1-2‰ higher in U(IV) than coexisting U(VI) species at 25ºC. U(V) species are either intermediate or similar to U(IV) species. Fractionations of up to 0.6‰ are predicted between species in the same oxidation state. In the case of plutonium and neptunium, Pu(V) and Pu(IV) species thought to be relevant to natural systems are found to be isotopically similar to each other, whereas Pu(VI) species will be approximately 2‰ lower in 242Pu/239Pu than Pu(V) or Pu(IV), and Pu(III) species will have approximately 3‰ higher 242Pu/239Pu than Pu(IV) or Pu(V). Np(VI) will be 0.6‰ lower in 237Np/235Np than coexisting Np(V) species, whereas Np(IV) and Np(III) will have approximately 1.3‰ higher 237Np/235Np. In the final study, field shift effects in platinum and iridium are studied, using Mössbauer isomer shifts according to the method of Schauble (2023) in to investigate iridium. Predicted field shifts for both 198Pt/194Pt and 193Ir/191Ir are relatively modest, approximately <0.1‰ at ambient temperatures for most species (e.g., mass dependent fractionation effects likely dominate for these elements at low temperatures). Notably, Pt in an Fe-alloy (as a possible analog for the Earth’s core) is predicted to show an equilibrium fractionation of 0.09‰ at 3000 K relative to PtII substituted in an olivine crystal structure (as a speculative analog for the silicate mantle), which could explain observed superchondritic 198Pt/194Pt found in Archean mantle samples
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
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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