1,721,003 research outputs found
Shell size measurements of the planktonic foraminiferal species Rotalipora cushmani and Whiteinella brittonensis across the Oceanic Anoxic Event 2 (middle Cretaceous)
Full text linkAnomalous shifts in tropical Pacific planktonic and benthic foraminiferal test size during the Paleocene/Eocene thermal maximum
No full textPaleocene–Eocene warming and changes in oceanic hydrography should have significantly impacted the ecology of marine microorganisms, both at the surface and on the seafloor. We analyzed several key characteristics of foraminifera from two Shatsky
Rise (ODP Leg 198) cores spanning the P/E boundary including the maximum test diameters of the largest calcareous trochospiral benthic foraminifera and largest shallow-dwelling planktonic foraminifera, and the stable carbon and oxygen isotope ratios of benthic foraminifera and bulk samples. We also qualitatively constrained changes in bottom water dissolved oxygen concentrations
by quantifying changes in benthic species abundances. We find warming synchronous with an unusual increase in the size of surface-water planktonic in contrast to deep-water benthic foraminifera which decrease in size. We suggest that a decline in bottom water dissolved oxygen is the primary mechanism responsible for the size reduction of Pacific deep-sea benthic foraminifera, whereas the contemporaneous size increase of surface-water planktonic foraminifera is attributed to an increase in thermal stratification and decrease in local nutrient supply
Reassessing planktonic foraminiferal biostratigraphy across the Cenomanian–Turonian boundary interval (middle Cretaceous)
Full text linkIdentification of the base of the lower-to-middle Campanian Globotruncana ventricosa Zone : comments on reliability and global correlations
No full textThe reliability of the first appearance datum of Globotruncana ventricosa as biozonal marker for the Campanian is discussed. The taxonomy and species concept of G. ventricosa and of Globotruncana tricarinata, that has been either regarded as junior synonym of Globotruncana linneiana or of G. ventricosa, are examined to avoid misidentifications, and one species is here formally described as new, Globotruncana neotricarinata nov. sp. The tropical and subtropical planktic foraminiferal assemblages from the Bottaccione section (Gubbio, Italy), from Deep Sea Drillig Project (DSDP) Site 146 (Caribbean Sea, central Atlantic Ocean), and from Ocean Drilling Program (ODP) Hole 1210B (Shatsky Rise, northwestern Pacific Ocean) are analyzed for the presence of biostratigraphic markers. Lowest and highest occurrence data have been checked in thin sections and washed residues in the Bottaccione section. The comparative biostratigraphic analysis of the planktic foraminiferal distribution highlights: 1) the absence of G. ventricosa at the stratigraphic level at which it is supposed to first occur in the Tethyan area, 2) the presence of transitional specimens resembling G. ventricosa and thus erroneously used to identify the base of the G. ventricosa Zone, 3) the presence of a good sequence of bioevents that appear to be promising for regional and global correlations such as the appearance of Globotruncanita atlantica, Contusotruncana plummerae and the disappearance of Hendersonites carinatus. The correlation potential of these bioevents has been verified across latitudes by studying the Campanian planktic foraminiferal assemblage in pelagic sediments drilled on coastal Tanzania (western Indian Ocean), and at the deep-sea ODP Hole 762C (Exmouth Plateau, western Indian Ocean), that were located at 30°S and 47°S in the Late Cretaceous, respectively. Besides the known diachronous first appearance of G. ventricosa in the Southern Ocean sites, results confirm the difficulty in using G. ventricosa as zonal marker in the tropical and subtropical areas, and the validity of the first appearance datum of C. plummerae for regional and global correlations
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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