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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
Upper Jurassic-lowermost Cretaceous biocalcification events derived from calcareous nannofossil and calpionellid paleo-fluxes: an example of envinromental stability promoting pelagic biocalcification?
No full textThe Tithonian-Berriasian time interval is characterized by a major calcareous nannofossil speciation episode and by the appearance of the calpionellid group: several genera and species first appear and rapidly evolve, showing an increase in diversity, abundance and particularly in calcification degree.
This time interval is also characterized by a significant increase in carbonate-rich sediments. Our aim is to reconstruct calcareous nannofossil and calpionellid calcite paleo-fluxes to monitor the impact of biocalcification on pelagic sedimentation and to point out any linkages between calcareous plankton evolution and palaeoclimatic and/or palaeoceanographic conditions.
Calcareous nannofossil and calpionellid absolute abundances have been achieved on Monte Pernice and Torre de’ Busi sections (Southern Alps, Northern Italy) and DSDP Site 534 (Central Atlantic Ocean). Paleo-fluxes have been obtained integrating absolute abundances with single specimen mass-weight (10-12gr of CaCO3) per area unit (cm2) per time unit (yr).
During the Early Tithonian a first calcification event is characterized by nannolith (F.multicolumnatus, C.mexicana, P.beckmannii) increase in abundance, size and calcification degree, followed by the occurrence of first calcified calpionellids (Tintinopsella). A second, larger calcification event occurs across the Jurassic/Cretaceous boundary: it is characterized by a dramatic increase of nannoconid abundance and calcification degree, concomitant with a moderate abundance increase in calcified calpionellids (genera Crassicollaria, Calpionella, Remaniella). The calcareous nannofossil and calpionellid contributions to paleo-fluxes have been compared: despite the minute sizes, nannofossils, particularly nannoliths, determine the sedimentation of biogenic carbonates, with calcite paleo-fluxes of 2 orders of magnitude higher than calpionellids.
The Late Jurassic-earliest Cretaceous time interval is characterized by generally stable environmental conditions, with relatively cool climate, low pCO2 and low oceanic Mg/Ca ratio.
It is here inferred that the Tithonian appearance and mass occurrence of strongly calcified plankton and its evolutionary expansion were mostly induced by stable environmental conditions, favouring diversification of highly calcified specimens. Biomineralization rates by highly calcified plankton produced a major increase in pelagic carbonate sedimentation, affecting the carbonate system at the short- and long- term C-cycle
Calcareous Nannofossil and Calpionellid calcification events across Tithonian – Berriasian time interval and low latitudes paleoceanographic implications.
Full text linkThe Tithonian-Berriasian time interval is characterized by a major calcareous nannofossil speciation episode and by the appearance of calpionellid group: several genera and species first appear and evolve, showing an increase in diversity, abundance and particularly in calcification degree.
This time interval is also characterized by a significant low latitudes increase of carbonate-rich sediments (Rosso ad Aptici fm. toward Maiolica fm.).
Calcareous nannofossil and calpionellid biostratigraphy and absolute abundances have been performed on low latitudes selected sections in order to reconstruct biogenic calcite palaeofluxes. Calpionellid has been investigated on thin sections (25μm thick), while calcareous nannofossil on the same thinnered thin sections (up to 7μm thick) used for calpionellid. All specimens have been counted on 1 cm2 of thin section or 1 mm2 of ultra-thin section respectively for calpionellid and calcareous nannofossil. Paleofluxes have been obtained integrating absolute abundance with single speciment mass weigh (10-12gr of calcareous carbonate) per area unit (cm2) per time unit (yr).
Calcareous biogenic paleofluxes point out a link between the lithologic changes and calcified plankton evolution across the Tithonian – Berriasian interval. During Lower Tithonian (Rosso ad Aptici Fm.) a first calcification event is characterized by nannolith (F.multicolumnatus, C.mexicana, P.beckmannii) increase in abundance, size and calcification degree, followed by the occurrence of first calcified calpionellid (Tintinopsella). Across Upper Tithonian to Lower Berriasian (Rosso ad Aptici fm. – Maiolica transition and Maiolica fm.) a second bigger calcification event is characterized by a dramatic increase of nannoconid abundance and calcification degree reaching lithogenetic amounts, concomitant with a moderate abundance increase of calcified calpionellid (genera Crassicollaria, Calpionella, Remaniella).
Linkages between calcareous nannofossil and calpionellid evolutions with geologic, palaeoceanographic or palaeoclimatic events are inferred. The diversification and biomineralization of high-calcified plankton produced a major increase in pelagic carbonate sedimentation due to the onset of paleoenvrionmental conditions favorable to calcification. The diversification and proliferation of nannolith and nannoconid, interpreted as inhabitants of the lower photic zone, might indicate the establishment of a thermocline/nutricline in the deep photic zone, suggesting the develope of oligotrophic and stable oceanic conditions.
It is also suggested that Tithonian-Berriasian calcified plankton evolution could be controlled by a decrease in pCO2, due to decreased spreading rate and/or increased weathering rate (87Sr/86Sr) and cool climatic conditions, concomitant with a decrease in oceanic Mg/Ca ratio values. Both factors thermodynamically promoted low Mg-CaCO3 and CaCO3 biomineralization supporting calpionellid and calcareous nannofossil abundance and calcification rate increases
Calpionellid and calcareous nannofossil evolution and calcification across Tithonian-Berriasian interval (Tethys Ocean).
Full text linkThe Tithonian-Berriasian interval is characterized by the appearance of calpionellid and by a major calcareous nannofossil speciation episode: several genera and species first appear and evolve, showing an increase in diversity, abundance and calcification degree.
Monte Pernice and Torre de Busi sections (Southern Alps, Italy) have been analyzed for calcareous nannofossil and calpionellid biostratigraphy, relative and absolute abundances and to reconstruct biogenic calcite palaeofluxes. Calcareous nannofossils have been investigated on simple smear slides and ultra-thin sections (7-8 μm thick) calpionellids on the same thin sections (20-30 μm thick). All nannofossil specimens have been counted on 1 mm2 of ultra-thin section; all calpionellid specimens on 1 cm2 of thin sections to reconstruct paleofluxes.
In the Tithonian- Berriasian interval all known calcareous nannofossil Zones and corresponding Subzones (Bralower et al., 1989) have been recognized. Chitinoidella, Crassicollaria and Calpionella Zones have been identified (Remane, 1986; Pop, 1994b; Reháková & Michalík, 1997; Andreini et al., 2007).
Quantitative calpionellid and nannofossil analyses point out major changes during the Tithonian – Berriasian interval: nannolith taxa (F.multicolumnatus, C.mexicana, P.beckmannii) increase in abundance, size and calcification degree in discrete steps across the Lower Tithonian, coeval with the occurrence of first calcified calpionellids (Tintinopsella). Nannoconids and calcified calpionellids (Crassicollaria, Calpionella, Remaniella) increase across the Tithonian/Berriasian boundary reaching lithogenetic abundances: the rise in high-calcified nannoconids roughly corresponds with the Acme of C. alpina spherical forms. The diversification and biomineralization of highly-calcified microplankton produced a major increase in pelagic carbonate sedimentation due to the onset of paleoenvrionmental conditions favorable to calcification
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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