1,720,980 research outputs found
Sand transport under the combined influence of waves and tidal currents: An assessment of available formulae
No full textVarious formulae are used to predict the transport of sand under the combined influence of waves and currents. These approaches include the use of the unidirectional formulae of Einstein (1950), Frijlink (1952), Yalin (1963), Engelund and Hansen (1967), Sternberg (1972), Ackers and White (1973) and Gadd et al. (1978) modified, for the presence of waves, in accordance with the techniques described by Bijker (1967) and Swart (1976) and those of Bagnold (1963), Madsen and Grant (1976) and Vincent et al. (1981).Predicted rates are compared with measurements, based upon fluorescent sand tracer studies, in an area of high tidal current and wave energy (northern Bristol Channel, U.K.). In general, predicted rates are lower than those measured and only the formulae of Madsen and Grant (1976) and the modified formula of Sternberg (1972) appear to provide realistic estimates of transport under wave- and tidally induced currents, in comparison with the field measurements
Sediment transport under waves and tidal currents: A case study from the northern Bristol Channel, U.K.
No full textBed-load transport under tidal currents and waves, and waves alone, is predicted from near-bed self-recording current-meter data and observations from a wave-rider buoy. Transport rates and paths are derived using seven different unidirectional transport formulae and those of Bagnold (1963), Bijker (1967) and Madsen and Grant (1976) for combined flows. Predicted rates are compared with the results of a fluorescent sand tracer study.The data are available from Swansea Bay, a high tidal- and wave-energy embayment on the British continental shelf. Sediment transport paths in this region had been determined previously using a variety of techniques, including bedform orientation and sea-bed drifter recovery patterns.Transport is enhanced under the superimposed effect of waves and, in some circumstances, the direction of the resultant vector is altered. Such storm-induced catastrophic transport is different to that predicted under tidal currents alone; this could provide a mechanism for long-term sediment supply. In some areas, there is correspondence between bedform orientation and storm-induced transport paths; in others, there is opposition
Hydrodynamic and morphological response of a perched beach during sea breeze activity
No full textBeaches associated with geological or engineered structures, recognised as perched beaches,are commonplace on many coastlines around the world and especially so in South West Western Australia (SWWA). Although it is accepted that hard coastal structures will affect beach behaviour, little is known about the mechanisms through which this occurs. The microtidal Perth coast in SWWA is influenced by one of the strongest and most persistent sea breeze cycles in the world. This, together with offshore limestone reefs attenuating swell means that locally generated sea breeze waves and currents dominate the hydrodynamics for half of the year. Field measurements were made of wave, current and beach morphology changes due to strong sea breeze forcing at the perched Yanchep Beach and Lagoon on the Perth Metropolitan coast. Spatial and temporal variation of waves and currents at the beach and in the lagoon were monitored throughout several sea breeze cycles and changes in beachface morphology surveyed at two beach profiles. A 50% reduction in sea breeze wind speed was found to weaken the lagoonal currents by 50% due to less wave overtopping of the limestone reef. Results show the influence of the limestone formations on waves and currents which affects the beachface response to sea breeze. Both beach profiles showed a clear cycle of erosion and accretion to sea breeze, with differences between the profiles even though they were spaced just 120 m apart. These results provide insights into the role of geological formations on the behaviour of a perched beach
Sedimentation processes in a tectonically active environment: the Kerkyra-Kefalonia submarine valley system (NE Ionian Sea)
No full textThe Kerkyra–Kefalonia valley system is the northwestern extension of the Hellenic arc–trench system, representing the collision zone of the Apulian Platform and the Hellenides. The system is distinguished by two different physiographic regions: the northern part, U-shaped, and oriented NNW–SSE, with relatively gentle slopes and a wide floor; and the southern part, oriented NE–SW, V-shaped, and with much steeper side walls and a narrow floor. Both parts are formed tectonically, with the former coinciding with a collision zone, and the latter being the morphometric expression of the Kefalonia strike–slip fault. Sediments recovered in the piston cores from the region consist of fine-grained material, deposited by a variety of sedimentation processes such as: gravity-driven mass movements, associated with seismic activity (i.e., slumping, sliding, debris flows, grain flows, turbidites–seismoturbidites); and, to a lesser extent, by hemipelagic deposition. Measured near-bed currents and their associated shear stresses indicate resuspension of the material, mainly within the northern part of the valley. Sub-bottom acoustic (seismic) profiling data reveal various sedimentary provinces, related to different mechanisms of sediment accumulation: (i) the eastern margin of the Apulian Platform with hemipelagic sedimentation, together with possible advection of suspensates from the Adriatic, in response localised to seabed erosion; (ii) the western Hellenic margin, with down-slope episodic sliding and slumping, induced primarily by earthquake activity, together with an input from hemipelagic settling; (iii) the collision zone, coinciding with the northern part of the Kerkyra–Kefalonia valley system, with deposition mostly from resuspension, the occurrence of local mass gravity flows and the advection of some material from the north; and (iv) the Kefalonia strike–slip fault region, where mass gravity flows are the dominant mechanisms, related to erosion/deposition from resuspension. Overall sedimentation within the tectonically-active Kerkyra–Kefalonia valley system is characterised by the coupling of the mass gravity-driven flows, which are the predominant mechanisms, with the near-bed current regime related with resuspension phenomena and the advection of suspensates. These latter mechanisms is likely more pronounced during the winter period, when dense water masses formed in the Adriatic inflowing into the Ionian Sea
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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