1,721,006 research outputs found
U-Li Isotopes highlight the dominant role of glacier coverage in weathering processes across Northeast Tibetan Plateau glacial watersheds
No full textThis study investigates uranium (U) and lithium (Li) isotope fractionation in suspended particulate matter (SPM) from glacial basins in the northeastern Tibetan Plateau, aiming to explore the coupling between physical and chemical weathering processes under glacial influence. The (234U/238U) activity ratio is correlated with parameters related to glacial activity, such as the elevation of the basin and glacier area. Samples from glacial watersheds are enriched in 234U (mean 1.28 ± 0.11), indicating the efficient comminution of rocks. Conversely, non-glacial areas show lower (234U/238U) ratios due to weakened physical weathering (mean 1.09 ± 0.04). The Li isotopes are sensitive to chemical weathering, providing complimentary information to U isotopes. In glacial watersheds, the variation of δ7LiSP is minimal and compatible with the signature of unaltered bedrock (mean 1.58 ± 0.87 ‰). Samples from lower basins show a stronger fractionation (mean − 2.61 ± 1.26 ‰), pointing to a stronger chemical weathering. As for U, Li fractionation is also related to topographic variables influencing the degree of glacial activity. Where glaciers are active, physical weathering fractionates U isotopes but no Li isotopes. Where glaciers are not present, physical weathering is less important, while chemical alteration is more relevant, leading to a low fractionation of U isotopes and a strong fractionation of Li isotopes. The combined use of U and Li isotopes offers an effective tool for tracing weathering regimes shaped by geomorphic and climatic factors, highlighting the role of glaciers in silicate weathering and landscape evolution, and demonstrating the proxies' potential for reconstructing recent glacial weathering
U) Activity Ratios in Cryoconites From High‐Altitude Glaciers in Western China and Its Transport and Settlement Mechanisms
No full textAsian dust has significant impacts on atmospheric systems and global biogeochemical cycles. In this study, we applied the U isotopic method to trace sediments based on their comminuting age, analyzing the uranium isotopes of cryoconite samples from various glaciers in western China, including the Tibetan Plateau (TP) and Tianshan Mountains. We aimed to explore the spatial variability of the (U-234/U-238) activity ratio and residence time, as well as the transport mechanism of the dust cycle in the region. Additionally, we used Nd-Sr isotopes data from our previous work to jointly determine the provenance. Our results indicate that the average (U-234/U-238) activity ratios in southern TP glaciers are higher, with mean range of 0.981-0.993, while those in northeastern TP locations are lower, with mean of 0.974. This suggests a decreasing trend from south to north. In the Tianshan region, the (U-234/U-238) activity ratio is higher in central areas compared to eastern areas, with a mean range of 0.984-0.996, indicating a decreasing trend from west to east. U-Sr-Nd isotopes analysis showed that dust provenance is from multiple sources, including long-range transported and local dust inputs from the glacier basins, mainly originating from the TP surface and central Asian arid regions. Using the end-member mixing model analysis and meteorological data, we interpret that the cryoconite dust in eastern Tianshan and Qilian Mountains comes from a complex mixture of the southern Gobi, northern TP surface dust, and Taklimakan and Alxa arid deserts. In contrast, the glacial dust in southern TP locations originates mainly from the plateau surface dust. Our findings suggest that the uranium isotopes in high-altitude glaciers are primarily influenced by the origins of dust, which are affected by related atmospheric circulation. We also developed a conceptual model to illustrate the complete process of U isotopic fragmentation and migration changes during dust production, transport, and deposition in the TP region
Quantifying uranium radio-isotope ratios in riverine suspended particulate matter: Insights into natural and anthropogenic influences in the glacial-fed river system of the NE Tibetan Plateau
No full textThe analysis of uranium isotope ratio 235U/238U in environmental media serves as a reliable method to distinguish between natural and anthropogenic sources of uranium, playing a crucial role in assessing the extent of contamination with anthropogenic uranium and disturbances in its biogeochemical cycle. In this study, we focus on the northeastern Tibetan Plateau to examine the atomic ratio of 235U and 238U in riverine suspended particulate matter (SPM) across eight glacial watersheds. Results reveal that the 235U/238U atomic ratio in the suspended load ranges from 0.007247 to 0.007437 (with an average value of 0.00727 +/- 0.00003), which closely aligns with the ratio found in natural uranium (0.00725). The highest mean ratio (0.00729 +/- 0.00007) is observed in the upper glacial basin of the Ningchan River. Results suggest the negligible influence of isotopically altered in relation to human nuclear activities. When considering different environmental media, such as soil, snow/cryoconite, and riverine suspended particulate matter in the study area, the 235U/238U ratio in surface soil presents the highest values, pointing to a slight enrichment of 235U. This may be attributed to the fact that soil retains the cumulative signals of uranium atmospheric deposition, including the deposition of 235U-enriched airborne particulate matter deposited after atmospheric nuclear tests carried out in the second half of the 20th century. On the contrary, riverine suspended particulate matter and glacial sediments are more influenced by the natural 235U/238U signature under modern environmental conditions. This confirms that the northeastern Tibetan Plateau is still relatively pristine with respect to biogeochemical disturbances related to human activities
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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