1,720,967 research outputs found
Orbital-scale fluctuations in continental weathering flux and continental ice-volume during greenhouse and icehouse climate intervals : evidence from oxygen and neodymium isotopes
No full textRapid changes in global and local climate and weather, noticeable over our lifetimes, have spurred heated public and political debate over the cause of these climatic changes, whether or not we can reverse, stop or slow down this process, and how to create adequate models that can predict Earth’s changing climate. To create the most accurate models of future climate, many researchers look to past greenhouse intervals for insight; intervals of time identified by high modeled atmospheric CO2, a lack of glacial deposits, and geologic evidence of globally high sea-levels—all of which suggest little to no glacial ice and a relatively monotonous climate. However, recent stratigraphic and geochemical evidence from the Cretaceous ‘supergreenhouse’ interval document compelling evidence to support dynamic greenhouse climates.
The goals of the studies hereafter described are to document and describe orbital-scale (104-105 yr) climate fluctuations recorded by δ18O as a proxy for glacio-eustasy and sea surface temperature and εNd as a proxy for continental weathering and wet/warm or dry/cool climate during two global greenhouse intervals: the Late Silurian and Late Devonian.
The first study (Chapter 1) explores whether glacio-eustasy was the driver for orbital-scale shallowing-upward cycles developed in Late Silurian and early Late Devonian tropical and subtropical greenhouse climates. Two intra-cycle δ18O conodont apatite trends were observed: asymmetric trends demonstrating progressive δ18O increases coincident with facies shallowing, or symmetric trends demonstrating initially decreasing, then increasing δ18O values. These isotopic trends and intra-cycle magnitudes support the hypothesis that these cycles developed in response to glacio-eustasy during glacial stages, implying that Late Silurian and Late Devonian greenhouse climates were more dynamic than traditionally assumed.
Relationships between orbital-scale continental weathering flux and glacial-interglacial marine cycles was first assessed comparing intra-cycle εNd and δ18O values from Middle Pennsylvanian icehouse cycles (Chapter 2). Observed conodont δ18O trends support previous interpretations that sampled cycles were generated by glacio-eustasy (30-50 m magnitudes) combined with <1° sea surface temperature changes. εNd trends typically demonstrate lower εNd values during interglacial intervals and higher εNd during glacial intervals, supporting claims that increases in precipitation and/or air temperatures during interglacial intervals result in increased continental weathering rates and/or increased flux to marine basins.
Using this initial continental weathering flux study and Pleistocene Nd-isotope studies as a model, we tested the phase-relationships of continental weathering flux and sea-level change in Upper Silurian and Upper Devonian greenhouse cycles (Chapter 3). Upper Silurian εNd demonstrates relatively uniform intra-cycle values, due to averaging out of far-field source variations in continental weathering flux, relatively uniform Late Silurian sub-tropical climate, and/or subdued continental weathering and flux due to the absence of upland and inland vascular land plants. Upper Devonian εNd demonstrate greater intra-cycle variation in εNd, which may be due to enhanced chemical weathering as a result of upland and inland colonization of land plants with large root systems and an intensified hydrologic cycle due to evapotranspiration. Observed εNd trends support the hypothesis that these greenhouse cycles record increases and decreases in continental weathering due to increases and decreases in precipitation and/or air temperature. εNd and 147Sm/144Nd values for Upper Silurian and Upper Devonian cycles support previous claims of far-field transport of Caledonian Mountain Belt material via trans-Laurentian fluvial systems.National Science FoundationEarth and Planetary SciencesDoctoralUniversity of New Mexico. Dept. of Earth and Planetary SciencesElrick, MayaAsmerom, YemaneAtudorei, ViorelFawcett, PeterSoreghan, GerilynnWeissmann, Gar
Orbital-scale fluctuations in continental weathering flux and continental ice-volume during greenhouse and icehouse climate intervals : evidence from oxygen and neodymium isotopes
Full text linkRapid changes in global and local climate and weather, noticeable over our lifetimes, have spurred heated public and political debate over the cause of these climatic changes, whether or not we can reverse, stop or slow down this process, and how to create adequate models that can predict Earth\u27s changing climate. To create the most accurate models of future climate, many researchers look to past greenhouse intervals for insight; intervals of time identified by high modeled atmospheric CO2, a lack of glacial deposits, and geologic evidence of globally high sea-levels--all of which suggest little to no glacial ice and a relatively monotonous climate. However, recent stratigraphic and geochemical evidence from the Cretaceous \u27supergreenhouse\u27 interval document compelling evidence to support dynamic greenhouse climates. The goals of the studies hereafter described are to document and describe orbital-scale (104-105 yr) climate fluctuations recorded by δ18O as a proxy for glacio-eustasy and sea surface temperature and µNd as a proxy for continental weathering and wet/warm or dry/cool climate during two global greenhouse intervals: the Late Silurian and Late Devonian. The first study (Chapter 1) explores whether glacio-eustasy was the driver for orbital-scale shallowing-upward cycles developed in Late Silurian and early Late Devonian tropical and subtropical greenhouse climates. Two intra-cycle δ18O conodont apatite trends were observed: asymmetric trends demonstrating progressive δ18O increases coincident with facies shallowing, or symmetric trends demonstrating initially decreasing, then increasing δ18O values. These isotopic trends and intra-cycle magnitudes support the hypothesis that these cycles developed in response to glacio-eustasy during glacial stages, implying that Late Silurian and Late Devonian greenhouse climates were more dynamic than traditionally assumed. Relationships between orbital-scale continental weathering flux and glacial-interglacial marine cycles was first assessed comparing intra-cycle µNd and δ18O values from Middle Pennsylvanian icehouse cycles (Chapter 2). Observed conodont δ18O trends support previous interpretations that sampled cycles were generated by glacio-eustasy (30-50 m magnitudes) combined with \u3c1° sea surface temperature changes. µNd trends typically demonstrate lower µNd values during interglacial intervals and higher µNd during glacial intervals, supporting claims that increases in precipitation and/or air temperatures during interglacial intervals result in increased continental weathering rates and/or increased flux to marine basins. Using this initial continental weathering flux study and Pleistocene Nd-isotope studies as a model, we tested the phase-relationships of continental weathering flux and sea-level change in Upper Silurian and Upper Devonian greenhouse cycles (Chapter 3). Upper Silurian µNd demonstrates relatively uniform intra-cycle values, due to averaging out of far-field source variations in continental weathering flux, relatively uniform Late Silurian sub-tropical climate, and/or subdued continental weathering and flux due to the absence of upland and inland vascular land plants. Upper Devonian µNd demonstrate greater intra-cycle variation in µNd, which may be due to enhanced chemical weathering as a result of upland and inland colonization of land plants with large root systems and an intensified hydrologic cycle due to evapotranspiration. Observed µNd trends support the hypothesis that these greenhouse cycles record increases and decreases in continental weathering due to increases and decreases in precipitation and/or air temperature. µNd and 147Sm/144Nd values for Upper Silurian and Upper Devonian cycles support previous claims of far-field transport of Caledonian Mountain Belt material via trans-Laurentian fluvial systems
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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