1,721,150 research outputs found
Orbital tuning of a coastal succession of Late Eocene-Early Oligocene age: Clays, cycles and sea-level change in the Solent Group, Isle of Wight, UK.
No full textThe Solent Group in the Hampshire Basin UK comprises over 200m of clays, silts, limestones and infrequent sands of Late Eocene-Early Oligocene age deposited in continental (fluvatile and lacustrine facies with many palaeosols), estuarine and rarely shallow marine facies. The accumulation rate was rapid (40-60m/Ma), and the succession displays conspicuous sequence-scale sea-level cycles (10-30m) representing transitions from transgressive shallow marine/estuarine envrionments through brackish floodplain highstands to ephemeral freshwater carbonate lakes representing lowstands. Stratigraphy has traditionally been based on mammals and charophytes, although a number of levels provide sufficient nannofossils to identify NP Zones. We have used these important horizons, in conjunction with a new magnetostratigraphy, to correlate with the global chronostratigraphical scale. Although the succession is not conspicuously cyclic on the scale of bedding, high-resolution clay mineralogy and elemental geochemistry display striking cyclical changes on several frequencies. We have chosen one parameter, the percentage of illite and illite-smectite in the clay fraction of the sediment, to investigate orbital controls on the succession. Illite/illite smectite in this succession is neoformed in gley palaeosols, and was formed by repeated wetting and drying of the sediment in response to strongly contrasting seasons (ie high seasonality). There is a strong correlation between illite abundance and the occurrence of the pulmonate gastropod Lymnaea, which has a selective advantage in ephemeral ponds because it can breathe air. Because the orbital configuration which maximises seasonality has high eccentricity and obliquity values, we tuned high illite values to eccentricity maxima, and hypothesised that conspicuous groups of high illite peaks correspond with long eccentricity (400Ka) maxima. We anchored this age model to the global chronostratigraphical scale using magnetic chrons; C13n (base of chron) and C15n (top of chron) and the results compared closely with published timescales for this interval. Filters of the tuned dataset recovered convincing short eccentricity (100Ka) and obliquity (41 Ka) signals, but little evidence of precession. Spectral analysis using the Blackman-Tukey method demonstrated eccentricity, obliquity and precession peaks, and supports our assumption that major variations in clay mineralogy are linked to the long eccentricity cycles. An important conclusion of this study is that the sequence-scale changes, reflecting the major sea-level changes, are directly related to the 400Ka cycle, and presumably were responses to changes in volume of Antarctic ice cover. A major hypothesised ice-growth event in the Early Oligocene has been interpreted by various authors from a heavy oxygen isotope shift approximately coincident with the base of chron 13n. The corresponding level in the UK does not display any evidence of significant sea-level change in the coastal plain deposits of the Isle of Wight
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
Milankovitch cyclicity and sea-level change in the Late Eocene-Early Oligocene interval: evidence for rapid and extensive Antarctic glaciation at 33.5 Ma? (abstract of paper presented at EUG XI, Strasbourg, France, 8-12 April 2001)
No full textWe have studied an expanded succession of coastal marine, estuarine and lacustrine sediments of Late Eocene-Early Oligocene age in the Isle of Wight southern England. In this succession, a strong Milankovitch signal (406, 100, 40 and weaker 20Ka) is recorded from the relative abundance of neoformed illite and illite-smectite, which formed in soils by seasonal wetting and drying. The orbital timescale is calibrated using magnetostratigraphic, and to a lesser extent, biostratigraphic data. Combined orbital calibration and sequence stratigraphic analysis allows us to identify the major control on sea-level as the 406Ka long eccentricity cycle, which caused sea-level to fluctuate by 10-15 m. These values have been determined from the amount of incision at observed at sequence boundaries on a regional scale. Minor sea-level changes of 1-3 m were controlled by obliquity. The position of the Early Oligocene heavy δ18O event can be inferred in the Isle of Wight from its magnetostratigraphic proxy (base of chron 13n). We have determined the sea-level fall at this level to be approximately 12 m, close in magnitude to drops associated with the preceding 3 Late Eocene 406 Ka sequences. This evidence does not support recent estimates of a 50-90 m sea-level fall within the Early Oligocene based on the calculation that a significant part of the oxygen isotope event was caused by rapid Antarctic ice buildup. Rather, orbitally driven sealevel changes throughout the Late Eocene-Early Oligocene, although probably glacio-eustatic in origin, remained of similar magnitude
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