1,720,962 research outputs found
Recurring photic zone euxinia in the northwest Tethys impinged end-Triassic extinction recovery
No full textThe end-Triassic extinction (ETE) is associated with rapid atmospheric CO2-driven warming amplified by positive feedbacks involving weathering, nutrient oversupply, water column anoxia and sul.fate reduction. These conditions culminated in photic zone euxinia (PZE) at least locally in the Western Tethys, but its broader extent across northwest Europe has yet to be identified. Here we present new biomarker and bulk δ13Corg isotopic data that document redox and palaeoecological changes from two end-Triassic sites in the Western Tethys: Felixkirk, in the Cleveland Basin, northeast England, and Lavernock Point, in the Bristol Channel Basin, S Wales. The presence of aryl isoprenoids and Chlorobi-derived isorenieratane indicates shoaling of anoxia and toxic H2S to the photic zone caused by flooding in restricted or semi-enclosed basins. Oscillating redox conditions and severe PZE prevented a swift recovery of at least the benthic ecosystem across several British basins. Additionally, in concert with recent discoveries in the Bristol Channel Basin, in the Cleveland Basin we find that the ‘initial’ negative carbon isotope excursion (CIE) is related to a localized change in organic matter sources. PZE in British and other European basins points towards H2S toxicity as an extinction driver for the Western Tethys, highlighting the need for a global characterization of redox changes across the end-Triassic and other extinction events
Two-pronged kill mechanism at the end-Triassic mass extinction
No full textHigh-resolution biomarker and compound-specific isotope distributions, coupled with the degradation of calcareous fossil remnants reveal that intensive euxinia and decalcification (acidification) driven by Central Atlantic Magmatic Province (CAMP) activity formed a two pronged kill mechanism at the end-Triassic mass extinction. In a newly proposed extinction interval for the basal Blue Lias Formation (Bristol Channel Basin, UK), biomarker distributions reveal an episode of persistent photic zone euxinia (PZE) that extended further upwards into the surface waters. In the same interval shelly taxa almost completely disappear. Beginning in the basal paper shales of the Blue Lias Formation, a Lilliput assemblage consisting of only rare calcitic oysters (Liostrea) and ghost fossils of decalcified aragonitic bivalves are preserved. The stressors of PZE and decalcification parsimoniously explain the extinction event and inform possible combined causes of other biotic crises linked to emplacements of large igneousprovinces, notably the end-Permian mass extinction where PZE occurred on a broad and perhaps global scale
Molecular and isotopic evidence reveals the end-Triassic carbon isotope excursion is not from massive exogenous light carbon
No full textThe negative organic carbon isotope excursion (CIE) associated with the end-Triassic mass extinction (ETE) is conventionally interpreted as the result of a massive flux of isotopically light carbon from exogenous sources into the atmosphere (e.g., thermogenic methane and/or methane clathrate dissociation linked to the Central Atlantic Magmatic Province [CAMP]). Instead, we demonstrate that at its type locality in the Bristol Channel Basin (UK), the CIE was caused by a marine to nonmarine transition resulting from an abrupt relative sea level drop. Our biomarker and compound-specific carbon isotopic data show that the emergence of microbial mats, influenced by an influx of fresh to brackish water, provided isotopically light carbon to both organic and inorganic carbon pools in centimeter-scale water depths, leading to the negative CIE. Thus, the iconic CIE and the disappearance of marine biota at the type locality are the result of local environmental change and do not mark either the global extinction event or input of exogenous light carbon into the atmosphere. Instead, the main extinction phase occurs slightly later in marine strata, where it is coeval with terrestrial extinctions and ocean acidification driven by CAMP-induced increases in PCO2; these effects should not be conflated with the CIE. An abrupt sea-level fall observed in the Central European basins reflects the tectonic consequences of the initial CAMP emplacement, with broad implications for all extinction events related to large igneous provinces.</p
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
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