1,720,984 research outputs found
Relief evolution in northern Corsica (western Mediterranean): Constraints on uplift and erosion on long-term and short-term timescales.
No full textThe long-term erosional evolution of relief is revealed by low-temperature thermochronometric data, whereas geomorphic features give constraints on the short-term evolution. We discuss the topographic evolution of northeastern Corsica by fission track and (U-Th)/He dating of apatite, the provenance of Neogene alluvial sediments, an analysis of uplifted strath terraces, and the shape of river profiles. Cooling ages indicate high cooling rates of up to 40_C/Myr during the early-middle Miocene, when this region was affected by extensional tectonics. Cooling rates are less than 7.5_C/Myr from the middle Miocene to the present, when topographic perturbations are detected by variations in the source areas of middle-to-late Miocene alluvial sediments and by the presence of large-scale irregularities along modern river longitudinal profiles. We suggest that the contrast of slow long-term erosion rates and the high local relief in the present Corsican landscape require that the landscape be in a transient state in response to a recent tectonic event
New constraints on the provenance of the ANDRILL AND-2A succession (western Ross Sea, Antarctica) from apatite triple dating
No full textApatite triple dating (fission track, U-Pb and U-Th/He techniques) has been applied to detrital grains from the sedimentary core drilled during the ANDRILL 2A project, which documents the Miocene history of the Victoria Land Basin (western Ross Sea). High-temperature cooling ages show two main clusters (about 30 and 500Ma) whereas most of low-temperature data are late Oligocene-Early Miocene in age. These latter data are related to the exhumation of the Transantarctic Mountains south of the Discovery Accommodation Zone. Comparison between low-temperature ages suggests that the Transantarctic Mountains have been in a phase of post-orogenic decay since at least 30Ma. The Oligocene U-Pb data demonstrate the presence of a volcanic event well before the McMurdo volcanic group, whose onset is commonly places at 19Ma. The location of the volcanic centers is unknown, but they could be below the Ross Ice Shelf south of drilling site. As a whole, these data indicate a major flow of sediments from south to north with only minor contributions from nearby outlet glaciers of the East Antarctic Ice Sheet. © 2012. American Geophysical Union. All Rights Reserved
New constraints on the provenance of the ANDRILL AND-2A succession (western Ross Sea, Antarctica) from apatite triple dating
Get PDFThermochronologic evidence for the exhumational history of the Alpi Apuane metamorphic core complex, northern Apennines, Italy
No full textThe Apennine Range is a young convergent
orogen that formed over a retreating subduction zone.
The Alpi Apuane massif in the northern Apennines
exposes synorogenic metamorphic rocks, and provides
information about exhumation processes associated
with accretion and retreat. (U-Th)/He and fission-track
ages on zircon and apatite are used to resolve
exhumational histories for the Apuane metamorphic
rocks and the structurally overlying, very low grade
Macigno Formation. Stratigraphic, metamorphic, and
thermochronologic data indicate that the Apuane rocks
were structurally buried to 15–30 km and 400C at
about 20 Ma. Exhumation to 240C and 9 km depth
(below sea level) occurred at 10–13 Ma. By 5 Ma the
Apuane rocks were exhumed to 70C and 2 km. The
Macigno and associated Tuscan nappe were also
structurally buried and the Macigno reached its
maximum depth of 7 km at 15 to 20 Ma.
Stratigraphic evidence indicates that the Apennine
wedge was submarine at this time. Thus we infer that
initial exhumation of the Apuane was coeval with
tectonic thickening higher in the wedge, as indicated
by synchronous structural burial of the Tuscan nappe.
From 6 to 4 Ma, thinning at shallow depth is indicated
by continued differential exhumation between the
Apuane and the Tuscan nappe at high rates. After 4
Ma, differential exhumation ceased and the Apuane
and the Tuscan nappe were exhumed at similar
rates (0.8 km/Ma), which we attribute to erosion of
the Apennines, following their emergence above
sea level
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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
- …
