1,720,983 research outputs found
Polar emergence and the influence of increased sea ice extent on the Cenozoic biogeography of pectinid molluscs in Antarctic coastal seas.
No full textPolar emergence and the influence of increased sea ice extent on the Cenozoic biogeography of pectinid molluscs in Antarctic coastal seas.
No full textPolar emergence and the influence and the influence of increased sea-ice extent on the Cenozoic biogeography of pectinid molluscs in Antarctic coastal areas
No full textFrom the Paleocene to the Pliocene, Chlamys-like genera of scallops (pectinid bivalve molluscs) inhabited coastal
areas around the Antarctic continent. Today, all of the Chlamys-like genera are extinct around Antarctica and restricted
to lower latitude habitats along the surrounding continents. The only remaining scallop in the high Antarctic zone is the
large (greater than 108mm in height), endemic, thin-shelled Adamussium colbecki. Adamussium has a circumpolar
distribution with its highest abundances (greater than 50m2 and 2 kgm2) in Antarctic coastal areas, in contrast to the
offshore habitats where its ancestors had predominated since the Oligocene. Shell morphology and substrate data
indicate that the Chlamys-like faunas were largely exposed to high-energy conditions associated with open water in the
coastal zone, while the Adamussium faunas have been associated with low-energy hydrodynamic conditions. Modern
and mid-Holocene distributions in the Antarctic coastal zone further indicate that Adamussium is largely restricted to
protected embayments and habitats with extensive sea-ice coverage. In addition, a decadal mark-and-recapture
experiment demonstrates that Adamussium has extremely slow growth and a century-scale lifespan, which complement
the life-history traits that are considered to be characteristic of species inhabiting predictable and constant
environments in the deep sea. Stabilization of the water column by increased sea-ice extent—together with stenothermal
conditions, prolonged darkness and limited primary production—would have enhanced the habitat similarities between
polar coastal environments and the deep-sea after the Plio-Pleistocene climate threshold. Subsequently, the deep
Antarctic continental shelf would have facilitated faunal shifts between deep-sea and coastal habitats as with the polar
emergence of the Adamussium fauna. Such biogeographic interchanges across high-latitude continental shelves since the
end of the Cenozoic would have contributed significantly to the latitudinal diversity gradients that have been noted
from both deep-sea and shallow-water marine faunas
Marine research in the Latitudinal Gradient Project along Victoria Land, Antarctica
No full textAlthough echinoderms constitute some of the
most conspicuous taxa of the Antarctic benthic communities,
the echinoderm fauna of Terra Nova has not
been described yet. The present study provides the first
species list of echinoids, ophiuroids and asteroids from
Terra Nova Bay (30–500 m depth) and describes the
depth distribution of these species. Preliminary observations
of the summer reproductive condition of some of
the species are also included
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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