1,720,956 research outputs found
Terrestrial record of post-Eocene climate history in Marie Byrd Land, West Antarctica
No full textHydrovolcanic deposits, interbedded tills and recycled microfossils, together with erosion anomalies in the Marie Byrd Land (MBL) landscape, each provide a portion of the record of glaciation and deglaciation events from late Oligocene to the present. We have attempted to synthesize these data sources to provide a more complete record, and to reconcile them with climatic events recorded elsewhere in Antarctica and the deep sea. The MBL data suggest that the late Oligocene was marked by the development of an ice cap at Mount Petras, where the MBL dome was beginning to rise from a near-sea-level position. Furthermore, unusually advanced cirque development in the dome crest area is difficult to explain unless there was a period of effective cirque erosion in that area between c. 25 and 15 Ma Bp. These inferences are consistent with evidence from the Ross Sea for an expansion of the West Antarctic Ice Sheet (WAIS) in mid-Miocene (15-17 Ma BP) time.
The deep sea oxygen isotope proxy record has been interpreted to show the inception of West Antarctic glaciation around 6 Ma BP. This can perhaps be reconciled with the terrestrial record if one considers (1) the observation that large volume changes in the WAIS cannot produce a delta(18)O signal that is significantly outside limits of error, and (2) that the landscape in West Antarctica has evolved from very low regional relief in the Oligocene, to more than 2 km of local relief in the present day, as a result of dome uplift since c. 27 Ma Bp, and the growth of large volcanoes since c. 19 Ma BP
Oligocene to Holocene erosion and glacial history in Marie Byrd Land, West Antarctica, inferred from exhumation of the Dorrel Rock intrusive complex and from volcano morphologies
No full textThe Dorrel Rock intrusive complex in
Marie Byrd Land, West Antarctica, consists of a coarse-grained gabbro cut by fine grained benmoreite and trachyte dikes, all exposed in a single nunatak. It is the only exposed plutonic body related to late Cenozoic
volcanism in this part of the West Antarctic rift system. Our 40Ar-39Ar age determinations indicate emplacement of the gabbro
took place ca. 34 Ma, followed by dike injection at ca. 33.5 Ma. Marie Byrd Land volcanoes are all younger than ca. 27–29 Ma, and lie on a low-relief Late Cretaceous erosion
surface that has been disrupted by block faulting and dome uplift since late Oligocene time. The erosion surface and overlying volcanoes
are well preserved, but in contrast,
we estimate that at least 3 km of overburden has been eroded away to expose the gabbro.
This anomaly is most easily explained
if most of the exhumation took place during a period of rapid erosion between ca. 34 Ma and 27–29 Ma and was followed by a pronounced
decrease in erosion rate in the late
Oligocene.
Temporal anomalies in the degree of dissection of volcanic edifices, together with evidence from hydrovolcanic deposits, suggest there was an ice cap in Marie Byrd Land in
the late Oligocene and that inland (200+ km) volcanoes were being actively eroded by glaciers
until ca. 15 Ma. This is consistent with
seismic and stratigraphic work in the Ross Sea, which documents at least two expansions of the West Antarctic Ice Sheet in the early mid-Miocene. We fi nd that rates of glacial erosion in Marie Byrd Land increase significantly with nearness to the coast, and in
nonresistant rock. Thus, the observation that inland volcanoes younger than ca. 15 Ma
show no effects of glacial erosion, except for one with a basal section of weak tuffs, suggests that a transition from warm-based to cold-based glaciers took place around 15 Ma.
These fi ndings are similar to many of those reported from well-studied McMurdo Sound and Ross Sea localities, so they provide a wider regional picture of middle to late Cenozoic climatic and surficial geologic events in Antarctica
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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