1,720,973 research outputs found
PIV Investigation on Lock-Exchange Gravity Currents Propagating Over Roughness Elements
No full textLock-exchange gravity currents over a rough bottom are investigated through laboratory experiments; PIV technique is used to measure the instantaneous velocity field. The bottom roughness is realized by LEGO® bricks with a constant rectangular section. The main parameter varied is the relative height of the roughness elements to the gravity current depth. The analysis of the instantaneous velocity fields suggests that the presence of the bottom elements modifies the structure of the dense current introducing complexity to the flow dynamics. The streamwise velocity of the gravity current is lower than that observed in smooth surface experiments; the greater the height of the bottom elements, the greater the reduction of velocity. Furthermore, the flow appears dominated by the bottom-generated vorticity due to the presence of recirculation areas between the bricks
Gravity currents flowing over a rough bed
No full textLock-exchange gravity currents experiments are performed to characterize the influence of bottom roughness on the dense flow through Particle Image Velocimetry, PIV. The surface properties over which gravity currents propagate in natural environments play a key role in the dynamics and structure of dense current. Roughness was introduced by an array of obstacles that may slow down the gravity current and significantly modify its capacity to entrain sediments compared to a current propagating over a flat bottom. The instantaneous maps of the flow velocity show how the bottom roughness impacts the flow dynamics; as an example recirculation zones develop among the elements. These structures, are constant over time with a longitudinal development and height depending on the height of the elements; the greater the height of the elements and the greater the size of the recirculation areas
On the dynamics of quasi-steady gravity currents flowing up a slope
No full textQuasi-steady gravity currents propagating first on a horizontal and then up a sloping boundary are investigated by means of theoretical analysis and laboratory experiments. The bottom slope ranged from 0.18 to 1 and full- and partial-depth configurations were considered. The developed theoretical model, using the depth averaged momentum equation, provides new physical insight into the importance of the different forces that act on the current and accounts for the gravity component along the slope, whose effect increases with both the slope angle and the ratio of current to ambient fluid depths. The height of the current decreases linearly with up-slope distance and the spatial rate of decrease, expressed by the current shape parameter is determined from the theory, using the measured up slope distance at which the current stops. This current shape parameter is found to depend on the slope only and it is not dependent on the current to ambient fluid depths. It can then be used to calculate the current velocity and the up-slope distance reached by the current. It is shown that the front velocity of all performed experiments is predicted by the theory indicating that the theory remains valid up to a slope equal to 1
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
Experimental study of uni- And bi-directional exchange flows in a large-scale rotating trapezoidal channel
No full textA large-scale experimental study has been conducted at the Coriolis Rotating Platform to investigate the dynamics of uni- and bi-directional exchange flows along a channel with a trapezoidal cross section under the influence of background rotation. High-resolution two-dimensional particle image velocimetry and micro-conductivity probes were used to obtain detailed velocity fields and density profiles of the exchange flow generated across the channel under different parametric conditions. Experimental measurements give new insight into the stratified-flow dynamics dependence on the magnitude of Burger number, defined as the ratio of the Rossby radius to the channel width, such that values lower than 0.5 characterize unsteady exchange flows. The measurements highlight the role that both ambient rotation and net-barotropic forcing have on the geostrophic adjustment of the dense outflowing layer and on the corresponding counter-flowing water layer fluxes. The coupled effect of these two parametric conditions largely affects the transverse velocity distribution and, for the largest net-barotropic flow in the upper fresh water layer, leads to the partial blockage of the lower saline outflow. Moreover, an increase in the mixing layer thickness, associated with larger rotation rates, and due the interface dynamics, is observed, with shear-driven interfacial instabilities analyzed to highlight the influence of both ambient rotation and net-barotropic forcing
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
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