1,720,979 research outputs found
Thallium isotope cycling in a ferruginous Precambrian ocean analogue
No full textPrecambrian oceans were overwhelmingly anoxic and rich in dissolved ferrous iron (Fe2+), conditions referred to as ‘ferruginous’. Yet, few paleoceanographic tools widely applied to the Precambrian sedimentary record are investigated in detail in the few available ferruginous settings today. We conducted a detailed thallium (Tl) isotope investigation of Deming Lake, a meromictic ferruginous lake in Itasca State Park (Minnesota, USA). Only slight changes were observed in dissolved Tl
concentrations (Tldiss) and isotopic compositions (ε205Tldiss) between spring, summer, and winter months. This was despite the development of a winter ice cap, a dramatic shoaling of the oxycline, and large swings in dissolved and particulate Fe concentrations. Isotopic compositions of authigenic Tl (ε205TlA) leached from surface sediments across a surface-to-deep gradient averaged –2.2 ± 0.9‱ (2SD) and were at all depths slightly lower than corresponding waters, which averaged 0.0 ± 1.3‱ (2SD). We estimate that the Tl isotope fractionation process responsible for driving this effect has an associated fractionation factor (α) of 0.9998 to 0.9999. The processes likely behind this fractionation are preferential 203Tl removal by biomass and organic sulfur. Thallium removal from the uppermost water column during the spring and summer months had an associated α up to 1.0005, most likely sorption of Tl onto Mn oxide minerals. This process plays little to no role in setting sedimentary ε205TlA values, probably because Mn oxide minerals are unstable in sediments throughout the lake. We find no evidence of strongly coupled Tl and Fe cycling in Deming Lake, and by extension suspect that ferruginous conditions did not play an important direct role in ancient seawater Tl isotope
mass-balance. What the lake does tell us, however, is that organic-rich and sulfur-poor sediments can slightly fractionate Tl isotopes. Ancient sediments formed under comparable conditions may be unreliable water column ε205Tl archives. And if these sediment types were widely distributed on the ancient seafloor, they could have exerted a minor effect on global seawater Tl isotope mass-balance. Our results provide novel insights into how Tl and its isotopes are cycled under ferruginous
conditions, permitting more accurate application of the Tl isotope paleoredox proxy to the Precambrian sedimentary record.This is a manuscript of an article published as Ostrander, Chadlin M., Andy W. Heard, Elizabeth D. Swanner, Yunchao Shu, Wang Zheng, Yaqiu Zhao, and Sune G. Nielsen. "Thallium isotope cycling in a ferruginous Precambrian ocean analogue." Geochimica et Cosmochimica Acta 390 (2025): 264-275. doi:10.1016/j.gca.2024.12.008
Constraining the rate of oceanic deoxygenation leading up to a Cretaceous Oceanic Anoxic Event (OAE-2: ~94 Ma)
Get PDFabstract: The rates of marine deoxygenation leading to Cretaceous Oceanic Anoxic Events are poorly recognized and constrained. If increases in primary productivity are the primary driver of these episodes, progressive oxygen loss from global waters should predate enhanced carbon burial in underlying sediments—the diagnostic Oceanic Anoxic Event relic. Thallium isotope analysis of organic-rich black shales from Demerara Rise across Oceanic Anoxic Event 2 reveals evidence of expanded sediment-water interface deoxygenation ~43 ± 11 thousand years before the globally recognized carbon cycle perturbation. This evidence for rapid oxygen loss leading to an extreme ancient climatic event has timely implications for the modern ocean, which is already experiencing large-scale deoxygenation.The final version of this article, as published in Science Advances, can be viewed online at: http://advances.sciencemag.org/content/3/8/e170102
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
Major and trace elements in water from Deming Lake, MN, USA (2022-2023)
No full textSampling and in situ sensor analysis was conducted from an anchored boat at the deepest location of the lake, approximately 20 m water depth, in May 2022, August 2022, March 2023, and August 2023. All samples for water column dissolved and particulate major and minor elements were collected using a Proactive Mini Monsoon pump with a low-flow controller that was attached to vinyl tubing and a power cable marked with 0.5 m depth increments. Waters for trace metal analysis were filtered with removable 25 mm diameter 0.22 μm PES membrane filters placed in polypropylene Swinnex filter holders that were removed and immediately placed in cleaned Savillex Teflon reactors until leaching and analysis. For August 2023, samples were also collected with syringes fit with 0.45 μm syringe filters. The dissolved trace metal samples were collected in 50 mL centrifuge tubes, precleaned with 10 % trace metal-grade HCl. All lake water samples were acidified at the end of the sampling day using Optima grade HCl to a molarity of 0.4 M to ensure complete dissolution of Fe oxyhydroxides that form following exposure of Fe-rich lake waters to air. All sample preparation was performed in the NIRVANA class 100 clean laboratory at WHOI unless otherwise indicated. All reagents used through all preparation steps were double distilled or purchased at Optima grade, and sample preparation steps made use of Savillex Teflon reactors unless otherwise stated. Water elemental compositions were determined using a Thermo Fisher iCAP-Q inductively coupled plasma mass spectrometer (ICP-MS) at the WHOI Plasma Facility following 200 dilution of a 10 μL aliquot in 2 % HNO3. Indium (In) was added to samples at a concentration of 1 ng/g prior to analyses to monitor and correct for instrument drift by normalizing to In intensities. Concentrations were calculated using a five-point calibration curve obtained by fitting of ion beam intensities measured for serial dilutions of a gravimetrically prepared multi-element standard. The relative standard deviation (RSD) for five measurements of each sample was ~10% on the iCAP-Q. The accuracy and precision of similar concentration measurements on iCAP-Q at WHOI have previously been determined to be ± 5-10 % (1SD) based on comparison with USGS reference materials AGV-1, AGV-2, BHVO-1, BHVO-2, BIR-1, and BCR-2 prepared and analyzed as unknowns during earlier runs (Jochum et al., 2016; Shu et al., 2017). Particulate elemental compositions were determined following the same measurement scheme, after leaching the PES membrane filters originally mounted on the Swinnex holders overnight in 2 M HNO3 at 80 °C in a volume of acid calibrated to be sufficient to leach all trace metals from the filter.
For May and August 2022, and March 2023 sampling events, particulate Mn oxide abundance data were generated using the same methodologies employed in Gadol et al. (2023). Roughly 150 mL of Deming Lake water was passed inline during collection through 0.22 m pore size Sterivex PES filter cartridges. Cartridges were thereafter purged via syringe, sealed with Parafilm, and frozen until quantification. Abundances were quantified using the leucoberbelin blue (LBB) assay with a permanganate standard curve (Altmann, 1972; Oldham et al., 2015). Sterivex cartridge filters containing lake particles were filled with 2 mL LBB at a concentration of 0.004% in 0.1% acetic acid and then resealed with Parafilm. After approximately two hours, the liquid extract was removed and absorbance was measured at 620 nm on a UV-Vis spectrophotometer
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
- …
