1,720,979 research outputs found
Variability in ornament and shape of the genus Urocythereis from a Southern Italy bay (Ionian Sea)
Full text linkLower-Middle Pleistocene ostracod assemblages from the Montalbano Jonico section (Basilicata, Southern Italy)
Full text linkThe Montalbano Jonico section is a Pleistocene sequence, about 450 m thick, comprising silty clays and silty sands deposited during the upper part of the Calabrian Stage and lower part of the “Ionian” Stage. It is a candidate global boundary stratotype section and point for the Middle Pleistocene Subseries. Ostracod assemblage analyses were carried out on 40 samples from the uppermost levels of the Lower Pleistocene and the lowermost part of the Middle Pleistocene, with the aim of reconstructing the paleoenvironmental evolution around the Matuyama–Brunhes boundary. Taxonomic investigations, quantitative distribution data and statistical analysis (Q-mode cluster analysis) define four intervals, correlated with sea-level changes linked to Marine Isotope Stages (MIS) 21–18. The lower part of the section, ranging from 864.00 to 820.00 ka, was deposited in an outer shelf paleoenvironment during a period of high sea level associated with MIS 21. The transition to the second interval (815.42–785.62 ka) is marked by a shallowing trend, reflecting the MIS 20 decrease in sea level. The overlying part of the section (783.54–749.91 ka) yielded assemblages indicating a return to deeper-water conditions corresponding to the warm phase MIS 19. The uppermost interval was deposited during 746.60–740.54 ka, when cooling in MIS 18 produced a sea level drop. Here, some levels (164.20 m, 745.51 ka; 170.10 m, 743.05 ka; 176.10 m, 740.54 ka) show the presence of both “deep” and “shallow” autochthonous taxa, suggesting the occurrence of upwelling episodes during this cold phase. In some layers, deposited during warm stages, the ostracod assemblages indicate the presence of kenoxic bottom waters. The lowest paleo-oxygen levels are correlated with Marine Isotope Substages 21.3 and 19.1
Intra- and interspecific shell variability of the genus Urocythereis Ruggieri, 1950 (Hemicytheridae: Ostracoda) in the La Strea Bay (Ionian Sea, Italy)
No full textThe variability of the reticulum pattern, ornamentation and outline of the Urocythereis populations of the La Strea Bay has been analysed. The results show that the shell features of the form U. distinguenda (Neviani, 1928) (= U. oblonga Brady, 1866) have to be included within the high variability range of U. margaritifera (G.W. Müller, 1894). Consequently, it is suggested that in the upper infralittoral waters of the inlet two (and not three, as stated in previous investigations) Urocythereis species presently live. A second form, displaying a relatively low variability, has been described as new species, U. ilariae sp. nov
Putting the dead to work: A new method to assess the autochthony of marine Ostracoda death assemblages
Full text linkSedimentary and paleontological records can be powerful means of reconstructing ecological and physical environmental changes, by using a variety of records extending proxies to extend chronologies beyond the reach of instrumental or manual records. Ostracods are often used as paleoenvironmental proxies. Estimating the population age structure could be a useful tool for assessing the influence of some environmental parameters on death assemblages and for determining the autochthoneity or allochthoneity of the species that make up the thanatocoenosis. In the literature, several methods based on population age structure have been proposed to distinguish autochthonous and allochthonous components of life/death ostracod assemblages.
The Adult:Juveniles ratio analysis of a rich and well-preserved ostracod assemblage from one site in the circalittoral zone of Pontine Archipelago, in the central-eastern Tyrrhenian Sea, is presented. The new Specific Population Stage Index (SPS) is proposed, built upon the measurements of all growth stages in the assemblage. The population structure using the new SPS Index on three different grain sizes is tested against a list of putative in situ and transported ostracod specimens. The analysis on the small grain size (maximum heigth >63 μm) proved the most effective in describing the putative life ostracod assemblage, whereas in the largest grain size (maximum height >180 μm) the young instars of the smaller species are under-represented. This includes species generally under-represented in the fossil record of the Mediterranean, probably due to sample processing bias and not to the rarity of the species itself. Assessing the autochthoneity of modern/fossil assemblages has great potential for acquiring baseline information on ecosystems before the onset of human activities, making this an extremely powerful approach essential to evaluating anthropogenic impacts. This approach seeks to identify the in situ life assemblages within an ostracod population to ensure that paleoenvironmental interpretations are not biased by transported allochthonous elements
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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