1,720,990 research outputs found
Investigation on internal solitary waves breaking for geophysical applications
Full text linkNonlinear internal waves are a spectacular phenomenon taking place in many parts
of the world ocean. They consist in oscillations that travel along the pycnocline, i.e.,
the portion of the water column separating the surface layer from relatively more
dense underlying fluid. They are mostly generated by the interaction between tidal
flow and bottom topography features, such as underwater sills and the continental
shelf. Nonlinear internal waves can take the shape of a special waveform called
internal solitary wave (ISW), a class of nonsinusoidal waves that has the ability to
retain its form over long distances and extended periods of time.
In the present work, we investigate the propagation, shoaling and breaking of ISWs
in a two–layer stratified fluid system through analytical and numerical methods.
We study the propagation of ISWs over a varying bathymetry through variable
coefficients KdV–type equations, which are widely used to model weakly–nonlinear
waves in the oceanic context. We study the shoaling and breaking of ISWs along a
sloping bathymetry, and we build an anaytical model to derive the ISWs breaking
location. Theoretical results are validated by laboratory experiments performed in a
wave tank. We then apply KdV–type equations to describe both numerically and
analitically the evolution of ISWs generated in the Messina Strait (Mediterranean
Sea) propagating northward, towards the frontal slope of a headland, i.e., Capo
Vaticano. Finally, we apply our wave–breaking model to predict breaking location
of ISWs along this frontal slope. We also focus on the mixing process induced by
the ISWs breaking, defining the potential energy, the background potential energy
and the available potential energy (APE) of an ISW in a two–layer fluid. Through
the Thorpe and Ozmidov length scales we build a theoretical model to predict the
values of mixing efficiency involved in ISWs breaking and we validate the model
through laboratory experiments
Analysis and modeling of contourite drifts and contour currents off promontories in the Italian Seas (Mediterranean Sea)
No full textThe complex relationship between currents flowing around capes and their related contourite deposits (i.e., marine sediments deposited and/or reworked by the persistent action of bottom currents) is still an interesting and debated topic, both from a sedimentologic and oceanographic perspective. We analyze here contourite drifts located at intermediate depths off promontories in the southern Tyrrhenian and in the southern Adriatic Sea. The comparison between bathymetric-stratigraphic data and numerical, tank and analytic results, allows us to investigate the occurrence of contourite deposits around capes. We found that the presence of turbulence, and thus, of erosive conditions for sediments in the lee-side of a cape, can be detected by using dimensionless numbers related to cape dimension and ocean current features. We, moreover, analyze the additional sedimentary processes caused by seafloor unevenness offshore the cape such as local topographic depressions by applying the classical conservation of potential vorticity. The resulting effect is a steady cyclonic circulation over the depression that affects contourite deposition. We show that the application of the potential vorticity conservation provides a simple theoretical tool for the understanding of complex relations among ocean current, seafloor morphologies, and sedimentary processes. This work can be seen as a new approach to bridge the gap between marine sedimentology and physical oceanography
Numerical simulation of sediment transport by thermohaline bottom currents
No full textContour (along slope) and turbidity (downslope) currents actively interacts on the seafloor of the continental margins and control the distribution of seafloor habitats, slope instability, microplastics accumulation and hydrocarbon reservoirs. Numerical simulations that reproduce the sediment transport at the crossroad of these two current types may improve the understanding of this distribution. Nevertheless, the interaction between turbidity and contour currents is problematic to afford with numerical or experimental instruments. The aim of this PhD study is to adapt and develop methods for the numerical simulations to reproduce the effect of this
interaction on the sediment transport in order to understand how the finer (suspended) component of the sediment transported by the turbidity flows can be a source of sediment for transport within the contour current. The first step of the project will be the construction of a pertinent domain. For this purpose, the intention is to use a setting where a straight inclined channel (for the release of the turbidity flow)
leads to an expansion table covered by sediment and swept by a transversal contour crossflow. With respect to this case, to better represent our phenomenon, the turbidity current channel will be considered with a talweg lower than the expansion table. After this first step, we will analyze the two types of currents independently, turbidity and contouritic, using the reference literature for comparison. This will be useful to better understand the critical characteristics of the two currents, and the possible problems posed by their interaction. In the end, as a third step, the turbidity current will be analyzed in the case of contour crossflow, with a particular attention to the possible mechanisms of sediment transport. Considering the complexity of the mixing
processes of the two currents type and of their interaction, we will take advantage of Large Eddy Simulation (LES) or of Wall-modelled LES (i.e. skipping the solution of the viscous boundary layer). The cases will be analyzed at a time scale related to the turbidity current. The sediment transport, for computational reason, will be probably treated with a Eulerian approach, therefore through the solution of the transport equation for a scalar, with a two - way coupling of the momentum equation through the buoyancy term
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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