1,720,962 research outputs found
Measurement of Attogram Quantities of 231Pa in Dissolved and Particulate Fractions of Seawater by Isotope Dilution Thermal Ionization Mass Spectroscopy
No full textRecommended from our members
Quantifying groundwater discharge to Texas Coastal Bend estuaries
Full text linktextRecent studies have provided evidence that submarine groundwater discharge is a signifi-
cant source of water and dissolved nutrients to the coastal ocean. The chemical implications
of these studies are especially important because, relative to surface water, groundwater is
typically enriched in many compounds including nitrogen bearing nutrients. Therefore by
affecting the supply and relative proportions of essential nutrients, direct groundwater discharge
has the potential to influence phytoplankton populations and estuarine ecosystems
as a whole. Another potential submarine discharge that may occur in the shallow restricted
waters of the Texas coast is leakage of oil-field brine. Such leakage also has important
ecological implications similar in some ways to groundwater discharge. The studies in this
dissertation concern improving the methods and techniques used in measuring submarine
vi
discharges. Using the Texas Coastal Bend as a study area I have: 1) conducted a detailed
evaluation of submarine discharges to Nueces Bay and 2) compared indications of submarine
discharge between Nueces, Baffin, and Copano Bays. These investigations use a
combination of geochemical and geophysical techniques. The geochemical methods are
based primarily on measurements of naturally-occurring dissolved Ra isotopes in samples
of bay, river, ocean, and groundwater. The geophysical methods employ electrical resistivity
profiling to look for evidence of groundwater movement within the bay bottom sediments.
Results show that dissolved radium concentrations within Nueces Bay are among
the highest observed in coastal estuaries. Geochemical analysis and geophysical surveys
indicate that both groundwater and leakage of oil-field brine are potential submarine inputs.
Samples from Nueces, Copano, and Baffin Bays show that the seasonal increase in
dissolved 226Ra activity for Nueces Bay is substantially larger than that of the other two
bays. This increase is not readily explained by either evaporation or riverine supply. These
results clearly suggest that the Ra supply to Nueces Bay is unusually large. For Nueces Bay,
the most relevant differences between the three bays that might account for this are 1) the
proportionally larger salt marsh and 2) the higher density of petroleum wells and pipelines.
Though submarine groundwater discharge is not to be ruled out, leakage of oil-field brine
is strongly indicated.Marine Scienc
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Geochemical characterization of hydrothermal plume fluids from the Gakkel Ridge, Arctic Ocean
No full textHydrothermal circulation and venting is an important parameter in the study of biogeochemical cycles in the world's oceans. Since hydrothermal vents were first discovered in 1977, it has been shown that they occur at every mid-ocean ridge studied. The Arctic Mid-Ocean Ridge Expedition in 2001 found the first evidence for venting along the Gakkel Ridge, the slowest spreading mid-ocean ridge. The Arctic Gakkel Vents Expedition in 2007 was a follow-up study to locate the vents at two distinct sites in geologically diverse regions of the ridge. Geochemical analyses of plume fluids were used to localize and characterize the hydrothermal input at each site. At Site 1 (85°N, 7°E), the plume was located between 2700-2850 m of water depth, about 1 km off the seafloor. The ³He/heat ratio associated with this plume was relatively low at 0.48 x 10⁻¹⁷ mol J⁻¹, with relatively high total dissolvable manganese (TDMn)/³He ratio of 9.6 x 10⁷ mol mol⁻¹. These ratios indicate that the Site 1 plume originates in a mature hydrothermal system. At Site 2 (85°N, 85°E), one large, extensive plume was located between 2 and 3 km of water depth. This plume had a low ³He/heat ratio of 0.44 x 10⁻¹⁷ mol J⁻¹, with an intermediate TDMn/³He ratio of 1.5 x 10⁷ mol mol⁻¹, again indicative of a mature hydrothermal system. Eight unique plumes were found deeper than 3 km at Site 2. Collectively, these plumes had ³He/heat ratios of 2.6-3.1 x 10⁻¹⁷ mol J⁻¹, with relatively low TDMn/³He ratios of 0.87-0.98 x 10⁷ mol mol⁻¹. High levels of methane and hydrogen were found in the plumes deeper than 3 km. The high volatile content of the deep plumes is an indication of phase separation in the vent fluids and/or recent geological perturbation to the hydrothermal systems underlying the plumes. All samples measured in the water column deeper than 2 km at Site 2 showed marked enrichment in helium and TDMn, indicating extensive alteration of the deep water column by hydrothermal input along the eastern Gakkel RidgeMarine Scienc
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
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