1,720,972 research outputs found
Rare earth element systematics in ancient and modem hydrothermal systems
No full textThe geochemical significance of on-axis diffuse fluids, in addition to those formed during the waning phases of hydrothermal systems and off-axis crustal ageing processes, has been investigated through a comparison of the rare earth element (REE) systematics of hydrothermal materials from the ore-forming hydrothermal systems of the TAG vent field, 26 N Mid-Atlantic Ridge, and 90 Myr Troodos Ophiolite, Cyprus. Ophiolites integrate a long (c. 20 Myr) history of seafloor alteration, which reflects both axial and off-axis hydrothermal processes. Spatially-resolved laser ablation inductively coupled plasma-mass spectrometric (LA ICP-MS) REE analyses of individual alteration phases within stockwork-mineralised Troodos lavas have been used to deconvolve the complex alteration processes associated with crustal generation at an oceanic spreading ridge. REE mobility was associated with the development of both high- (-200 to 350 C) and low temperature(<100 C) secondary phases which precipitated within contrasting alteration regimes (discharge- and recharge-dominated respectively). Low-temperature alteration phases are the major repository for the REEs in lavas which are depleted in the light REEEu relative to pristine volcanic glass compositions. These data indicate that much of the REE signature of the alteration pipe is a post-mineralisation overprint acquired in the waning stages of hydrothermal activity and during the protracted alteration of the oceanic basement, rather than on-axis greenschist facies hydrothermal alteration. Submersible and drilling studies of the TAG mound have led to the development of models of mound growth and fluid evolution within an actively-forming seafloor sulphide deposit. The REEs have been used to test the applicability of these models to processes of sulphide mound and metalliferous sediment formation which occurred within the Troodos ophiolite. The REE patterns of umber, ochre and sulphide sampled from a section through the top of the Skouriotissa ore body clearly demonstrate extensive seawater ingress and circulation throughout the upper ore body during waning hydrothermalism and cooling of the mound,which has resulted in the overprinting of any original hydrothermal signatures in both mound sediments and sulphides. This study has demonstrated that the geochemistry of the sulphide mound deposits continues to evolve following the peak of hydrothermal activity, and that the seawater overprinting of the Skouriotissa deposit is the end product of a process which we only see the initiation of on the modern seafloor. At TAG, the origin of far-field Mn and Fe-rich oxide crusts has remained controversial over 25 years of investigations of the vent field. The REE and Nd isotope data presented in this thesis indicate these ferromanganese deposits are forming by a combination of sedimentationof Mn-rich particulates from the TAG hydrothermal plume, and direct precipitation from diffuse hydrothermal fluids seeping from the rift valley wall. The REE data reveal that the separation of manganese from other hydrothermally-derived metals at TAG is due to both plume processes and the spatial distribution of diffuse flow within the vent field.The studies presented in this dissertation have demonstrated the use of REEs as tracers of chemical processes in ancient and modem hydrothermal systems on a wide range of temporal and spatial scales
Genesis of ferromanganese crusts from the TAG hydrothermal field (abstracts of papers presented at AGU Fall Meeting, San Francisco, CA, 10-14 Dec 2001)
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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
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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