161,005 research outputs found
A multi-proxy investigation of mantle oxygen fugacity along the Reykjanes Ridge
No full textMantle oxygen fugacity (fO2) governs the physico-chemical evolution of the Earth, however current estimates from commonly used basalt redox proxies are often in disagreement. In this study we compare three different potential basalt fO2 proxies: Fe3+/Fetot, V/Sc and V isotopes, determined on the same submarine lavas from a 700 km section of the Reykjanes Ridge, near Iceland. These samples provide a valuable test of the sensitivities of fO2 proxies to basalt petrogenesis, as they formed at different melting conditions and from a mantle that towards Iceland exhibits increasing long-term enrichment of incompatible elements. New trace element data were determined for 63 basalts with known Fe3+/Fetot. A subset of 19 lavas, covering the geographical spread of the ridge transect, was selected for vanadium isotope analyses. Vanadium is a multi-valence element whose isotopic fractionation is theoretically susceptible to redox conditions. Yet, the δ 51 VAA composition of basaltic glasses along the Reykjanes Ridge covers only a narrow range ( δ 51 VAA = −1.09 to −0.86‰; 1SD = 0.02–0.09) and does not co-vary with fractionation-corrected Fe3+/Fetot (0.134–0.151; 1SD = 0.005) or V/Sc (6.6–8.5; 1SD = 0.1-1.3) ratios. However, on a global scale, basaltic δ 51 VAA may be controlled by the extent of melting. The V/Sc compositions of primitive (MgO > 7.5 wt%) basalts show no systematic change along the entire length of the Reykjanes Ridge. Typical peridotite melting models in which source Fe3+/Fetot is constant at 5% and that account for the increased mantle potential temperature nearer the plume center and the fO2 dependent partitioning of V, can reproduce the V/Sc data. However, while these melting models predict that basalt Fe3+/Fetot ratios should decrease with increasing mantle potential temperature towards Iceland, fractionation-corrected Fe3+/Fetot of Reykjanes Ridge lavas remain nearly constant over the ridge length. This discrepancy is explained by source heterogeneity, where an oxidized mantle pyroxenite component contributes to melting with increasing proximity to Iceland. Comparison of observed and modeled Fe3+/Fetot indicate that source variation in fO2 is present under the Reykjanes Ridge, with higher Fe3+/Fetot closer to Iceland. This source variability in fO2 cannot be resolved by V isotopes and redox-sensitive trace element ratios, which instead appear to record magmatic processes
Compositional trends of Icelandic basalts: Implications for short–length scale lithological heterogeneity in mantle plumes
No full textLithological variations in the mantle source regions under mid-ocean ridges and ocean islands have been proposed to play a key role in controlling melt generation and basalt composition. Here we combine compositional observations from Icelandic basalts and modelling of melting of a bi-lithologic peridotite-pyroxenite mantle to demonstrate that, while short-lengthscale major element variation is present in the mantle under Iceland, source heterogeneity does not make an important contribution to excess melt production. By identifying the major element characteristics of endmember Icelandic melts, we find enriched melts to be characterised by low SiO2 and CaO, but high FeO. We quantitatively compare endmember compositions to experimental partial melts generated from a range of lithologies, pressures and melt fractions. This comparison indicates that a single source composition cannot account for all the major element variation; depleted Icelandic melts can be produced by depleted peridotite melting, but the major element composition of enriched melts is best matched by melting of mantle sources that have been refertilised by the addition of up to 40% mid-ocean ridge basalt. The enriched source beneath Iceland is more fusible than the source of depleted melts, and as such will be over-represented in accumulated melts compared with its abundance in the source. Modelling of peridotite-pyroxenite melting, combined with our observational constraints on the composition of the Icelandic mantle, indicates that crustal thickness variations in the North Atlantic must be primarily due to mantle temperature and flow field variations
Variations on the Author
No full text“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
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
Larry O. Spencer, Conference Author Presentation
No full textGen. Larry O. Spencer, USAF (Ret.), author of Dark Horse: A Journey from the Horseshoe to the Pentago
Control of the symmetry of plume-ridge interaction by spreading ridge geometry
No full textThe Iceland, Gal´apagos and Azores plumes have previously
been identified as interacting asymmetrically with adjacent spreading centres.
We present evidence that the flow fields in these plume heads are radially
symmetric, but the geometry of the mid-ocean ridge systems imparts
an asymmetric compositional structure on outflowing plume material. First,
we quantify the degree of symmetry in geophysical and geochemical observables
as a function of plume centre location. For each plume, we find that
bathymetry and crustal thickness observations can be explained using a single
centre of symmetry, with these calculated centres coinciding with independently
inferred plume centre locations. The existence of these centres of
symmetry suggests that the flow fields and temperature structure of the three
plume heads are radially symmetric. However, no centres of symmetry can
be found for the incompatible trace element and isotopic observations. To
explain this, we develop a simple kinematic model to predict the effect of midocean
ridge geometry on the chemical composition of outflowing plume material.
The model assumes radially symmetric outflow from a compositionally
heterogeneous plume source, consisting of a depleted mantle component
and enriched blebs. These blebs progressively melt out during flow through
the melting regions under spreading centres. Asymmetry in trace element
and isotopic profiles develops when ridges either side of the plume centre receive
material that has been variably depleted according to the length of flow
path under the ridge. This model can successfully explain compositional asymmetry around Iceland and Gal´apagos in terms of an axisymmetric plume interacting
with an asymmetric ridge system
Dispelling the Myths Behind First-author Citation Counts
No full textWe 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
Author Under Sail The Imagination of Jack London, 1902-1907
No full textIn this second volume of Author Under Sail Jay Williams investigates the life of Jack London as a professional writer at the turn of the 1900s, as his publications spanned The Call of the Wild to The Iron Heel and The Road. While documenting key life events, especially his rising fame, this biography explores London's necessity to illustrate the inner workings of his own vast imagination through his socialist essays and fiction.Cover -- Title Page -- Copyright Page -- Contents -- Acknowledgments -- Introduction -- 1. Howl, O Heav'nly Muse! -- 2. Jesus in the Theater of Socialism -- 3. Jack London's Place in American Literature -- 4. Theater of War, Theater at Home -- 5. Revolution, Evolution, and the Scene of Writing -- 6. The Jack London Show Goes on the Road -- 7. Red Atavisms and Revolution -- 8. Earthquake Apocalypse and Building the City, Boat, and House Beautiful -- 9. The Future of Socialism and the Death of the Individual -- 10. The Road Never Ends -- Notes -- Bibliography -- IndexIn this second volume of Author Under Sail Jay Williams investigates the life of Jack London as a professional writer at the turn of the 1900s, as his publications spanned The Call of the Wild to The Iron Heel and The Road. While documenting key life events, especially his rising fame, this biography explores London's necessity to illustrate the inner workings of his own vast imagination through his socialist essays and fiction.Description based on publisher supplied metadata and other sources.Electronic reproduction. Ann Arbor, Michigan : ProQuest Ebook Central, YYYY. Available via World Wide Web. Access may be limited to ProQuest Ebook Central affiliated libraries
اسلم کولسری کی غزل:بیان و بدیع کے تناظر میں: ASLAM KOLSARY’S GHAZAL IN THE LIGHT OF BIAN-O-BADIE
No full textAslam kolsari is new significant and potentially well-known personality for contributing to modern Urdu ghazal. Being a mindful and multidimensional literary figure he has specific fame in poetry. A distinguish diction in poetry is individuality specifically connected with his name. His ghazal contains all attributes of Research and criticism. Communication of an ordinary concept in his poetry is reflection of Aslam kolasri. In this article the author has explored how poetic characteristics distinguished Aslam kolsari
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