1,721,003 research outputs found
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
Structural and Metamorphic Evolution of the Archaean High-pressure Granulite in Datong-Huaian Area, North China
No full textThe Archaean granulite terrain in the Datong-Huaian area, north China, comprises a basement
complex of fe lsic and mafic granulite (TTG gneiss), overlain by a sedimentary sequence dominated by
metapelite and metapsammite (khondalite series). Both lithological associations are separated by a
tectonic contact. Structural, textural and tectono-lithostratigraphic data indicate that the terrain was
affected by two prominent tectono-thermal cycles (CA and CB), associated with two granulite facies
events, M I and M2. Of these, the M l event was dominant and associated with all major structures in
the area. The granulites were subsequently exhumed, as a result of gravity unloading/uplifting and
denudation. This process probably occurred during the early Palaeoproterozoic in response to crustal
thinning after thickening at the end of the Archaean (2400-2500 Ma), although final exposure may have
resulted from further exhumation during a later granulite event (M2) around 1900 Ma. From the
Mesoproterozoic ( 1800 Ma) onward the granulite terrain was covered unconformably by sediments.
During cycle CA, the granulites underwent strong ductile deformation in response to an
extensional event involving a low-angle detachment, which resulted in the exhumation of high-P
granulites. On the basis of the distinct deformation histories and kinematic-structural patterns, three
litho-tectonic domains can be recognised that formed at different structural levels during the
detachment process. The lower litho-tectonic domain is mainly composed of TTG gneiss, and is
characterised by kilometre-scale domal structures and associated recumbent folds. These domes
resemble solid state diapirs or mantled gneiss domes. The intermediate litho-tectonic domain consists
predominantly of biotite-rich felsic gneiss with lenses or microlithons of the TTG gneiss and/or
khondalite series rocks derived from both the lower and upper structural domains. The intermediate
domain is characterised by a strongly foliated tectonic melange containing km-scale sheath folds, and
acted as a macro-scale decollement. The upper domain comprises sillimanite-rich metapelites or
khondalites with a dominant foliation and is characterised by lower peak-metamorphic pressure and
later granulite grade structures. It is extensively intruded by S-type granites that were emplaced during
the second granulite event at 1900 Ma. The intermediate and upper structural domains may have been
juxtaposed across the low angle decollement zone.
Granulites in all three domains are characterised by well-developed gneissic fabrics. Foliation
traces and various lineations within the lower domain underwent strong recrystallisation and as a result
of doming, display a wide range of orientations. In contrast, lineations in the intermediate domain are
well preserved and constant in orientation, parallel to the axes of several generations of closed to open
folds. The lineations plunge shallowly (10-30°) to the SW (between 200-230° ) and delineate the
extensional direction. Meanwhile, the lineations in upper domain plunge shallowly to the WSW (250-
260\ Sense of shear indicators in the intermediate and upper domains predominantly indicate a top to
the SW or WSW, normal sense of movement.
Microlithons of garnet-bearing, high-pressure mafic granulites that record pressures between
12-16 kbars, and which formed originally in the lowermost crust, are widespread in the lower and
intermediate domains. Development of symplectite textures in these rocks, due to a near isothermal
decompression process, vary in response to different parent mineral assemblages and the stage of
formation in the uplift history. The symplectites are variably recrystallised and elongated parallel to the
main regional extensional lineation, indicating that the structural domains developed during
exhumation of the terrain. Some late brittle normal faults present in the eastern part of the central dome
may represent continuous uplift at a brittle upper crustal level. These faults did not significantly
influence the basement rocks.
Petrological studies show that in the basement, MI reached peak metamorphic conditions of
12-14 kbar and 800-900 °C during the foliation-forming event, D26a, which transposed an earlier
S 1 Ba foliation of unknown age and origin. In the allochtonous cover sediments, M I peak-conditions
of about 8 kbar and 800 °C were reached after a prograde thickening event, D1 c0 , forming a beddingparallel
foliation and during which large amounts of S-type granites were emplaced. The localised
D28a and D1 c0 structures are interpreted as spatially distinct responses at different crustal levels to
the Ml metamorphic event. Juxtaposition of basement and allochthonous cover occurred during D3,
along a large, low-angle normal shear zone. This detachment zone accommodated extension after
crustal thickening, and allowed unloading of the footwall resulting in a ri se of the basement rocks to
4-6 kbars conditions as deduced from syn-D3 decompression textures. Coeval cooling textures in the
allochthonous cover sequence indicate that lateral rather than vertical di splacements occurred in the
hanging wall of the detachment. During cycle C6 , M2 peak-conditions of about 4-6 kbar and 650-700
°C were reached coeval with the development of discrete, left-lateral strike-slip zones (D4/M2), that
transect both basement and allochthonous cover, and accommodate some uplift.
The deduced CA and C6 P-T paths have equivalents in many Precambrian granulites. In
general decompressional paths like the one recorded in the basement rocks, are linked to processes
involving crustal thickening followed by extensional collapse.
Investigation of palaeomagnetisation in the granulites show that the magnetic fabric is
dominated by the 03 foliation and extensional lineation formed during extensional collapse and
uplift, whilst the magnetic remanence was acquired during later stages of uplift and cooling when the
temperature fell below the Curie point. The pole positions define a continuous swathe plotting
between 51 ° E, 20 ° S and 170 ° E, 35° S summarised by group mean poles. They are assigned to the
interval ca. 2000 - 1840 Ma and extend the apparent polar wander record for the North China Shield
backwards in time from the record derived from Mesoproterozoic supracrustal successions.
The present structural and petrological data in combination with the results from
palaeomagnetic investigations show that the Datong-Huai an granulites have experienced ductile
extensional detachment and uplifting processes, which occurred in the lower crust after crustal
thickening. It is concluded that a low-angle detachment may have playc::d an important role in the
exhumation history of the granulites as long ago as the Archaean-Proterozoic boundary
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
Mafic dykes of the Vestfold Hills, East Antarctica. An analysis of the emplacement mechanism of tholeiitic dyke swarms and of the role of dyke emplacement during crustal extension
No full textMafic dyke swarms are common in Proterozoic continental
crustal terrains. Although it is generally recognized that
parallel mafic dyke swarms are formed in extensional
tectonic settings and that they accommodate in the order
of 10% of extensional strain, the tectonics and geodynamics
of dyke swarm emplacement are poorly understood.
Since observations suggest that the level of tectonic
extensional stress required for dyke emplacement is less
than that required for brittle failure or plastic flow, it is
proposed that dyke swarm emplacement must be
regarded as a crustal extensional deformation
mechanism, rather than as a passive response to a
tectonic event. In order to analyse the role of mafic dyke
emplacement during continental crustal extension, it is
necessary to understand the conditions that lead to dyke
propagation under conditions representative for the
crust. Exposed Proterozoic dyke swarms from the
Vestfold Hills, East Antarctica, that were emplaced at
intermediate crustal levels into granulite facies felsic
crust, are studied with the objective to understand: [1] the
specific conditions that led to arrest of exposed dyke tips;
[2] the general conditions that are required for dyke
propagation, and hence for the emplacement of a dyke
swarm; and [3] the tectonic and geodynamic significance
of mafic dyke swarm emplacement during continental
crustal extension
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
Microtectonics (di Passchier C.W. and Trouw R.A.J.), Springer.
No full textIl volume di Passchier e Trouw rappresenta un testo fondamentale per la comprensione dei processi e delle strutture tettoniche a scala microscopica, con particolare enfasi al dominio di deformazione duttile, ma con importanti ricadute nello studio delle deformazioni fragili
Efficient use of the velocity gradients tensor in flow modelling
No full textFor models of fabric development in rocks, with vorticity as a variable parameter, the choice of an unsuitable
reference frame for instantaneous flow can hamper clear presentation of results. The orientation of most fabric
elements which develop in deforming rocks is attached to some principal direction of instantaneous flow: syntaxial
fibres, crystallographic preferred orientation patterns, steady state foliations and immobilised rigid objects seem to
orient themselves in a fixed position relative to instantaneous stretching axes (d¡), while shape fabric elements and
mica preferred orientation approach parallelism with the extensional apophysis (l₁) of the flow. Models for development
of such fabric elements benefit from a choice of reference frame attached to either d¡, or l₁
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