1,721,124 research outputs found
Response of calcareous nannofossils to late Quaternary orbital and suborbital climate changes: Evidence from central Mediterranean and Iberian Margin records.
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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
Periodicità submillenarie registrate nei sedimenti marini degli ultimi 2000 anni (Tirrenio orientale)
No full textSea surface water variability during the Mid-Brunhes inferred from calcareous plankton in the western Mediterranean (ODP Site 975)
No full textPlanktonic foraminifera and calcareous nannoplankton were analyzed in core Ocean Drilling Program Site 975, located in the western Mediterranean, in order to study their response to environmental changes across the Mid-Brunhes interval and specifically through Marine Isotope Stage (MIS) 15 and 8 (ca. 650–230 ka). Multivariate analysis of assemblage composition revealed that the calcareous plankton dynamics were mainly driven by surface water temperatures both on glacial-interglacial and stadial-interstadial time scales. Throughout the studied interval, foraminiferal and nannoplankton assemblages responded to environmental forcing in concert, except during MIS 15, when multiple environmental factors appear to have been superimposed on the otherwise dominating effect of temperature variability. Sea surface temperature (SST) has been estimated from planktonic foraminiferal assemblages using the artificial neural networks method pointing out relevant seasonal variations through the record. Our reconstructions reveal that calcareous plankton assemblages also responded to other environmental factors than temperature, including modification in surface water stratification, nutrient availability and detrital input. Specifically, a more stable, stratified water column seems to have accompanied the interval through MIS 15–13. On the other hand, across the Mid-Brunhes interval, from MIS 12 onwards, the enhanced glacial strength affected both planktonic foraminifera and calcareous nannofossils: planktonic foraminifera indicate that mixed and productive surface waters developed during glacials and stadials, accompanied by episodes of increased detrital input as suggested by calcareous nannoplankton assemblages. Enhanced food availability was likely driven by wind-induced upwelling and/or by continental coastal input during dry conditions persisting in the Mediterranean region and over North Africa. Finally, spectral and wavelet analyses of calcareous plankton time series allowed to identify the pattern of periodic response of the plankton at Milankovitch cycles and, in some cases, at millennial variability. The dominant 100 kyr periodicity recorded in surface water temperature proxies clearly reflects a major response of the planktonic community to the global glacial-interglacial climate pattern. High-frequency variation (~ 5–8, ~ 11–13 ky) of surface water temperature proxies and of selected taxa abundance highlights the occurrence of millennial-scale instability superimposed on the paleoenvironmental modifications occurring through the Mid-Brunhes interval climate transition. This framework accounts for the occurrence of different surface water dynamics across the Mid-Brunhes interval and is in favor of the hypothesis that the millennial scale surface water temperature variations are modulated by the harmonics of the precession forcing
Hierarchy of high-frequency orbital cycles in Cretaceous carbonate platform strata
No full textLower Cretaceous (Valanginian-Hauterivian) carbonate platform strata, which are well exposed in the Matese Mountains of the Southern Apennines (Italy), have been analyzed on a microstratigraphic (cm) scale to exemplify the high-frequency cyclic nature of the Mesozoic shallow water sedimentation in Southern Italy.
Based on the vertical organization of lithofacies and their early diagenetic signature 46 meter-scale cycles are recognized. These elementary cycles are hierarchically organized into groups (bundles and superbundels). The elementary cycles are prevalently formed by subtidal deposits and show emersion-related features at the top, suggesting repeated sea-level fluctuations. The number of elementary cycles compared to time, as constrained by biostratigraphy, and their grouping into sets, implying higher order complexity in the environmental oscillation, suggest an orbital control on sedimentation.
Spectral analysis of recurrent thickness in stratal features defines and quantifies the cyclicity, which is characterized by lithofacies thickness periodicities of: 1,271; 391; 159; 124 and 69 cm. Linear correlation of the Relative Ratio Set (RRS) of these periodicities with the corresponding RRS of the orbital perturbation periodicities shows that 1,271 and 391 cm fit the 404,220 and 94,890 year cycles of Early Cretaceous orbital eccentricity; 159 and 124 cm fit the 49,010 and 38,030 year cycles of the Earth’s axial obliquity, whereas 69 cm correspond to the precession periodicity. Thus the San Lorenzello section required not less than 1.6 Ma to form, at an average rate of 26 mm/ky.
Each 400 ky cycle can be viewed as a depositional sequence in which sequence boundaries, maximum flooding surfaces and system tract equivalents have been recognized.
The microstratigraphic approach is very promising for understanding the fine structure of climate-related environmental fluctuation recorded by the >3,000 m thick carbonate platform successions of the Southern Appennines, over a time span of about 150 Ma (Upper Triassic-Upper Cretaceous); and for deriving a more precise chronostratigraphy for global correlation
Holocene millennial-scale climatic variability in the Siciliy Channel (Mediterranean Sea).
No full textNeogene planktonic Foraminiferal turnover in the Mediterranean Area
No full textThe Neogene Peri od is characterised by several oscillations in c1imate and related tums in fossils
community, and planktonic Foraminifera represent an important tool to monitor these climatic
changes. In particular, tbe planktonic foraminiferal populations of the Mediterranean area show
pronounced oscillations on a variety of temporal scales from Milankovitch timescale to millionyear
timescale. An analysis of planktonic foraminiferal literature data and species quantitative
distribution datasets from Mediterranean on land sections and deep marine cores, calibrated vs the
Geological Time Scale 2012, revealed the occurrence of four main increases in turnover during the
Miocene, centred at 21.8 Ma (Aquitanian tumover), 15.6 Ma (Middle Mioeene tumover), 11.2 Ma
(early Tortonian tumover) and 7 Ma (early Messinian tumover). Contrarily, the Plio-Pleistoeene
time interval is eharacterised by a generai deereases in planktonie foraminiferal turnover with three
minima centred at 4.8 Ma (Zanclean turnover), 2.9 Ma (Piaeenzian tumover) and at 1.2 Ma
(Calabrian turnover).Power speetral analysis revealed the existence of tumover cycles with periods
of 1.3, 1.0 and 2.0 Ma
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