1,721,027 research outputs found
Elucidating modern geochemical cycles at local, regional, and global scales using calcium isotopes
No full textIn Earth's surface environment, calcium (Ca) is an important mobile metal that is actively and passively transported in solution and within organic and mineral phases, being cycled and recycled during various biogeochemical processes. With the development of modern mass spectrometric techniques small variations in the stable and radiogenic isotopic compositions of Ca can be measured, revealing insight in these complex biogeochemical cycles and tracing and quantifying components across a range of spatial and temporal scales similar to other more routine isotope systems. More than three decades of work reveal systematic variations in the partitioning of Ca isotopes due to both abiotic and biological processes. An overview of processes that fractionate Ca isotopes at local, regional, and global scales is outlined here. We present detailed examples of instances in which Ca isotopes have provided unique insight into the functioning of Earth surface processes and the cycling of Ca at multiple scales. Future studies should target questions for which Ca isotopic analysis provide unique insight and, when combined with other isotope and trace element multi-proxy studies, better constrain the system of interest. At the same time, we challenge the scientific community to explore new frontiers including polar regions and other extreme environments
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
(Table 2) Guaymas Basin sediment trap foraminifer results
No full text(Table 2) Guaymas Basin sediment trap foraminifer result
(Table DR1) Marine barite data results
No full text(a) Not included in seawater Ca-isotope curve, 2smean > 0.4 per mil.
(b) Ages for Hole 1218A according to Pälike et al. (2006); age determinations for Hole 574C using the position of datum levels in Barron et al. (1985), with numerical ages adapted to the age model of Pälike et al. (2006) following Zachos et al. (2004).
(c) Isotopic composition of seawater calculated using the following equation:
d44/40Ca seawater = d44/40Ca barite + 2.01 per mil
(d) 2smean = 2s/n0.5 calculated from repeated TIMS measurements of an individual sample.
(e) n = number of TIMS analyses on a single sample; numbers in parentheses were sample runs analyzed at the USGS.
(f) Duplicate samples processed from barite dissolution and cation separation to TIMS analysis.
(g) Extremely low value was not plotted, but must be investigated further before being dismissed
(Table 3) Site 199-1212B data: carbonate (wt% CaCO3, δ¹³C, δ¹⁸O)
No full text(Table 3) Site 199-1212B data: carbonate (wt% CaCO3, δ¹³C, δ¹⁸O
(Table 1) Sample locations, salinity and sea surface temperatures (SST) annual averages for the upper 10m from World Ocean Atlas 1998
No full text(Table 1) Sample locations, salinity and sea surface temperatures (SST) annual averages for the upper 10m from World Ocean Atlas 199
(Table 1) Bulk carbonate Site 199-1212B and 199-1221C d44Ca data
No full textNote: all samples were measured for d44/40Ca at USGS-Menlo Park (Bullen),
a conversion following Hippler et al. (2003),
b dissolved bulk carbonate solutions from 1221C using ICP-ES at Univ. of California-Santa Cruz, from 1212B at Univ. of Texas at Arlington
c 'calcite' fraction from 1221C using ICP-ES at Univ. of Texas at Arlingto
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