1,720,984 research outputs found
Numerical analysis of oil spill scenarios in harbour areas with an Eulerian approach: The Augusta case
Full text linkEven if they are limited, oil spills remain a significant problem on a global level, especially in port areas characterized by intense naval traffic. In preparing emergency plans, it is essential to define the risks associated with the potential dispersion of pollutants. Therefore, due to the lack of adequate databases, the possibility of hazardous events could be evaluated through numerical simulations. To evaluate the influence of the different processes taking place in an oil spill for a real case, thousands of oil spill scenarios were simulated with an Eulerian approach for the Port of Augusta (Sicily, Italy), varying the source point, the weather and sea conditions, the types of crude oil, the emulsification level, and the volumes spilled. The results show that for a light crude oil spilled volume of 10000m3, with unstable emulsification, the time scale for the interaction with the coast is a few hours, with sea areas affected by the slick of a few km2 and contaminated coasts up to 7.5km in mean. The stable emulsification causes a doubling of the slick area and a strong increase in the contaminated coast. By reducing the intensity of the wind or the friction forces on the slick, a delay in the evolution of the contaminant is observed, and an increase in the area of the slick and contaminated coast due to more extensive diffusion processes. Due to the complex geometric characteristics, the scenarios show very variable results; on a statistical level, to reach a confidence level above 90%, it is necessary to consider two standard deviations of the mean
Numerical Monitoring of Oil Spill Scenarios in Augusta Harbour
No full textA Eulerian model is used to describe oil slick transport in the Augusta Harbour, considering evaporation and emulsification weathering processes. Different wind conditions, crude oil types, spill locations and volumes have been considered, for a total of 198 scenarios investigated. The results show that, within a few hours, the contaminant strongly interact with the coastline, with up to 17km of coastline exposed to the pollutant in the worst scenario; in the case of large oil spill, the sea surface covered by oil is around 2 square kilometre in the first twelve hours, then it dramatically rises to 8 square kilometre in the worst scenario
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
High resolution oil spill model for harbour and coastal areas
No full textA novel, state of-art, numerical model accounting for the main physical processes governing oil dispersion at sea is here formulated and discussed. The underground hydrodynamics is resolved using LES-COAST, a high definition numerical model suited for coastal or harbour areas. Oil dispersion is modelled considering the main physical features of the process. After spilling, the oil may form the so-called tars or it may spread over the sea surface as thin film, depending on the oil pour point with respect to the ambient temperature. We adopt two different approaches for the two different conditions respectively. In the former, oil tars are modelled as Lagrangian particles of characteristic diameter and density. In the latter the Nihoul's model (Nihoul, 1984) is considered, which accounts for the main forces acting on the oil film, namely gravity, sea current and wind stresses. In practical short-term studies (simulation of oil dispersion over few hours) forces as surface tension and the inertia can be neglected. Also, the relevant short-term weathering processes (mainly emulsification and evaporation) occurring in coastal and harbour regions, are taken into account through established literature models. We validate the model on standard test cases and we apply it to a real case scenario in the Barcelona Bay
Entrainment and mixing in unsteady gravity currents
No full textEntrainment and mixing in lock-exchange gravity currents are investigated by large eddy simulations. Nine cases are analysed, varying the initial excess density driving the motion and the aspect ratio r of the initial water depth to the lock length. Laboratory experiments are also performed and a fair agreement between numerical simulations and measurements is found. Mixing between the gravity current and the ambient fluid, in both the slumping and self-similar phases, is studied for a range of entrainment parameters, gravity current fractional area and using an energy budget method. The entrainment is found to increase as r decreases. The occurrence of irreversible mixing is detected during the entire development of the flow, i.e. both in the slumping and self-similar phases. A higher amount of mixing is observed as r decreases and the initial excess density increases
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