1,720,990 research outputs found
The high-temperature behavior of defect hydrogen species in quartz: implications for hydrogen isotope studies
No full textA micro-infrared spectroscopic study of hydrothermal vein quartz known to have anomalous ?D signatures has identified two hydrogen reservoirs. In samples that generate an isotopic signature in accordance with that anticipated under the accepted model of quartz crystallization, submicroscopic
aggregates of liquid water are the dominant hydrous species. Samples which generate an anomalous ?D signature contain, in addition to liquid water, structurally incorporated hydrous species associated with impurity cations.Infrared spectra obtained during in situ stepped heating experiments, coupled with infrared analysis
at 25 ?C, demonstrate that hydrogen liberated between 300 and 500 ?C is chiefly molecular, liquid water. Hydrogen liberated at temperatures greater than 500 ?C is dominantly that associated with specific structurally incorporated cation defects. Since both defect hydrogen and molecular water are contemporaneously incorporated from the precipitating medium during crystallization, we propose that irregular ?D signatures, released following decrepitation at temperatures greater than 500 ?C, are due to isotopically fractionated hydrogen released from interstitial OH defect sites in the quartz structure.?D signatures obtained from stoichiometrically anhydrous minerals are generally interpreted under the assumption that the hydrogen measured comes uniquely from decrepitated fluid inclusions. Instead, we suggest that ?D ratios obtained from hydrothermal quartz reflect a sum of the contributions
made by individual hydrogen reservoirs, each with a potentially distinctive ?D signature. Thus, if the overall ?D signature is attributed entirely to fluid inclusion phases, the nature of the precipitating fluid may be misinterpreted. Hydrogen extracted as molecular water at between 300 and 500 ?C provides a true reflection of the hydrothermal solution associated with crystal precipitation
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
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
Metal trap development and formation mechanisms of clastic-dominated Zn-Pb±Ag mineralization in Paleozoic strata of the Macmillan Pass (Selwyn Basin, Canada)
Full text linkThe growing global demand for metals needed for the green energy transition has led to renewed exploration efforts. Ancient sedimentary basins contain a number of important resources such as zinc (Zn) and lead (Pb), and sometimes germanium (Ge), gallium (Ga), and indium (In). Some of the largest Zn deposits are called clastic-dominant (CD-type) deposits because they are hosted in clastic rocks like mudstones and siltstones. These deposits are thought to have formed when metal-rich fluids from deep in the Earth’s crust were expelled towards the surface along faults. However, many aspects of this overall model are not well understood. For example, the composition of the ancient metal-rich fluids is largely unknown, along with the mechanisms by which metals are deposited to form economic enrichments in certain locations.
The Selwyn Basin (Canada) contains a number of important CD-type deposits that formed hundreds of millions of years ago. The rocks hosting these deposits are now incorporated into the Canadian Cordillera, meaning they have been uplifted and deformed. This can make it challenging to interpret the rocks and understand how the deposit formation (mineralization) occurred. As a result, it is crucial to carefully examine samples that preserve some of the key primary features of the host rocks and the deposits.
This project evaluates aspects of the CD-type deposit model using various approaches that utilize two sample sets. 1) Barite- and pyrite-rich samples from the Late Devonian Canol Formation in Canada, which contain no Zn, Pb sulfides and formed at the same time as those rocks containing the deposits at other locations, were used to determine how the ancient environment was before the deposits formed. 2) Mineralized rock samples from a newly discovered CD-type deposit (Boundary Zone, Canada) were utilized to evaluate i) how these deposits formed, ii) the physicochemical properties of the metal-rich fluids, and iii) what essential metals are present. To answer some of the abovementioned questions, these two sample groups were used to make petrographic, mineralogical, and geochemical observations across various scales, from hand specimen to microscopic levels.
Data obtained through detailed petrographic and isotopic analyses indicate that the barite and pyrite in the Canol Formation formed during early diagenesis and that biological activity was critical for converting sulfate to sulfide. Similar mineral phases are observed in the samples from the Boundary Zone, where sulfide formed during early diagenesis likely reacted with metal-bearing hydrothermal fluids during an initial stage of ore formation. The first stage is dominated by fine-grained sphalerite formed as layers due to the replacement of quartz (and barite) components of the rocks. A second ore stage consists of several sphalerite types forming in cracks within the same rocks after fracturing. Critical metals, including Ge and deleterious components like Hg, occur in high amounts in the sphalerite from both the mineralized stages. Furthermore, experiments conducted on tiny droplets of fluids trapped within sphalerite and quartz indicate that the mineralizing fluids consist of variable salinity and homogenization temperature ranging from low (around 120 °C) during the early ore-forming stages to high (around 260 °C) at a later period. This suggests that the Boundary Zone deposit formed due to mixing of these fluids at some point.
Altogether, this thesis provides significant insights into components of the CD-type deposit model. It shows how vital microbial activities were during the formation of rocks that later host these deposits and also highlights prolonged hydrothermal fluid flow that could form multiple mineralization types. These findings are valuable for exploration strategies in the Macmillan Pass district and similar geological settings
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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