1,721,021 research outputs found
X-Ray diffraction of lacustrine minerals as an indicator of Late Pleistocene and Holocene Paleoclimate, Tulare Lake, California
Full text linkTulare Lake, CA, is the terminus of several major rivers fed by Sierra Nevada stream discharge. Over the last several decades, the study of Tulare Lake sediments has established the climate history for the Pleistocene and Holocene. In this study, Late Pleistocene to Late Holocene sediments were analyzed with an x-ray diffractometer, and bulk and clay mineral variations were investigated. The results showed strong correlations to the previously documented climate records. Larger amounts of Sierran discharge throughout the Late Pleistocene and Holocene is observed by increased weathering of illites and the supply of greater
proportions of detrital minerals. During the late Pleistocene Bølling- Allerød interglacial period, glacial melt water transported high amounts of coarse, illite-enriched, weathered granitic sediments to Tulare Lake, which reduced the bulk clay-size fraction and the smectite:illite ratios. Frequent monsoonal storms during the Holocene Thermal Maximum at 8 cal ka BP induced high-stand lake levels and an increase in total clay deposition. The frequency of storms declined
during the late Holocene because of decreasing summer and increasing winter insolation. This resulted in low-stand lake levels, slower sedimentation rates, a decrease in smectite:illite ratios, and an increase in calcite precipitation.Migration from OneSearc
Geochemistry of Benthic Foraminifera as an Environmental Indicator: A Study From Multiple Hydrographic Regimes
No full textThe geochemistry (stable isotopes and Lracc clements) or living (sLaincd) calcareous benthic foraminifera was compared with ambient botlom water stable isotope values to provide modern analog conditions and calibrations for environmental and paleoenvironmental assessments. Stable isotope values of live (stained) bcnthic foraminifera were investigated from push core and multicorer samples from the North Pacific (on the Aleutian margin, water depth 1988m) and the South Australian Bight (water depth 2476m and 1634m). Living benthic foraminifera specimens collected from contaminated sites in the Venice Lagoon were analyzed for trace elements. Both the isotopic and the trace element study involved interpretation of modern live foraminiferal chemical responses to different environments. The isotope analyses of Jiving foraminifcra from the North Pacific and the South Australian Bight provide calibration information for the evaluation of bottom water temperature and circulation of ancient ocecins based on fossil foraminiferal geochemistry. Trace element concentrations of Venice Lagoon foraminifera were used to assess the possibility of using foraminiferal geochemistry as a pollution indicator
(Table 1) Pb isotopes in different bulk sediment fractions from ODP Site 177-1090
No full textSediment depth is given in mcd. Age model after Channell et al. (2003, datasets: doi:10.1594/PANGAEA.717737). Long term NBS 981 values analyzed over several years on the MC-ICPMS at UF are 206Pb/204Pb=16.937 (2 sigma=0.004), 207Pb/204Pb=15.489 (2 sigma=0.003), and 208Pb/204Pb=36.695 (2 sigma=0.008)
(Table 2) Pb isotopes in fossil fish teeth from ODP Site 177-1090
No full textSediment depth is given in mcd. Age model after Channell et al. (2003, datasets: doi:10.1594/PANGAEA.717737)
(Table 7) Pb, U, and Th concentrations in fossil and modern fish teeth
No full textSediment depth is given in mcd. Age model after Channell et al. (2003, datasets: doi:10.1594/PANGAEA.717737).Modern fish teeth = 0 ka, without geographical position
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
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