1,721,215 research outputs found
Oxygen isotope composition of living land snail shells: data from Italy
No full textSixty-seven shells of living land snails were selected from 31 different localities across Italy to investigate the relationships between their oxygen isotopic composition (δ18Os) and the mean value of local rainfall (δ18Op). Despite the difficulty for some localities to correctly estimate the oxygen isotopic composition of local rainfall, a good relationship was found. This indicates that the oxygen isotopic composition of environmental water used by the snails is, in Italy, strictly related to that of the local meteoric precipitation. However, the relationship found is substantially different from that previous established for central Europe, indicating that regional climatic conditions are important in defining the final isotopic composition of land snail shells. Moreover, these equations may not hold for different climatic conditions existing during, for instance, glacial and interglacial periods. The data also show that isotopic differences among species are relatively narrow and that they may depend on ecological factors (i.e., style of life) rather than any clearly identifiable different vital offset
Stable isotope composition of Littoridina australis from the coast of Buenos Aires Province, Argentina, during Holocene climatic fluctuations
No full textStable isotope (carbon and oxygen) analyses were performed on Littoridina australis shells collected from molluscan concentrations within Holocene littoral deposits along the Bonaerensian coastal area of Argentina (south-western Atlantic). Isotope data allow us to define two very different areas: the Samborombon Bay, where isotope composition of shells was mainly governed by mixing between marine and freshwater, and the Mar Chiquita lagoon, where the original brackish environment was dominated by evaporation of water that originated high isotope shell values. In both areas some isotope profiles show short and quite large oscillations in delta(18)O. Their origin may be tentatively explained as due to the changes in moisture regime that control freshwater supply. The results suggest that these deposits can represent natural archives potentially useful for palaeoclimate reconstruction
Stable isotopes of pedogenic carbonate from Somma-Vesuvius area, southern italy, over the last 18 ka: palaeoclimatic implications
No full textZanchetta G., Leone G., Fallick A.E., Oxygen isotope composition of living land snail shells: data from Italy
No full textMollusca stable isotope record of a core from Lake Frassino, northern Italy: hydrological and climatic changes during the last 14 ka
No full textA core retrieved from Lake Frassino (northern Italy) provided evidence of palaeohydrological change in this area during the last 14 ka. Lithological, malacological and, in particular, stable isotope composition of freshwater shells allowed the delineation of the main phases of lake evolution between the Lateglacial and Holocene. Lateglacial conditions were drier than the Holocene, although a wetter period was inferred before c. 14 ka. According to the oxygen isotope composition of freshwater shells, the Holocene showed a clear bipartition. The first part, which lasted from _/9100 to 7000 yr BP, was drier and was followed by a rapid increase in humidity at _/7000_6800 yr BP. Between _/6800 and 5000 yr BP, there were wetter and more stable conditions, as indicated by smaller d18O oscillations of Pisidium and Valvata shells. From c. 5000 to 2600 yr BP the record is characterized by larger fluctuations, which may indicate that short-term and particularly pronounced alternation of wet and dry periods occurred
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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