1,720,976 research outputs found
Piecewise integrable neural network: An interpretable chaos identification framework
Full text linkArtificial Neural Networks (ANNs) are an effective data-driven approach to model chaotic dynamics. Although ANNs are universal approximators which easily incorporate mathematical structure, physical information and constrains, they are scarcely interpretable. Here we develop a neural network framework in which the chaotic dynamics is reframed into piecewise models. The discontinuous formulation defines switching laws representative of the bifurcations mecha- nisms, providing to recover the system of differential equations and its primitive (or integral) which describe the chaotic regime
Dynamics of a pile-moored fish cages in current and waves: A numerical study
No full textWe propose a numerical study of the dynamics of a double-constrained cylindrical pile-moored fish-farm cage, to be possibly installed at the foundations of dismissed offshore structures. Our model, derived from the net-truss model of Kristiansen and Faltinsen (2012), takes into account the elasticity of the net material, the real size of the net and is applied with and without mesh-grouping approaches, this allowing us to evaluate the range of validity of mesh-grouping techniques. First, cage dynamics have been studied with small-scale tests, in which the numerical model accurately reproduces the behaviour of the cage in both sea currents (velocity in the range 0.5−1m/s) and waves of small amplitude (with height of 1 m and period in the range 4−32 s). Use of the net real size for the computation grid of small-scale tests allows for identification of the main phenomena influencing the load distribution and the volume loss, which are: the dominant sail-shape deformation in the streamwise direction, the flattened deformations in the cross flow direction, and high-frequency oscillations in the vertical direction in long waves. Subsequently, a prototype-scale test is run to simulate the dynamics of a realistic installation of a double-constrained cylindrical pile-moored fish-farm cage in the Adriatic sea (considering both 1m/s sea current and storm sea state characterized by a peak period Tp=4 s and significant wave height Hs=1.5 m), showing that the major loads are a compression load on the pile up to 1 kN and a bending moment at the pile base up to 9.1 kNm. The proposed configuration always showed a small net relative volume loss VL<5%
Preliminary results on the dynamics of a pile-moored fish cage with elastic net in currents and waves
Full text linkOver the last decades, the aquaculture sector increased significantly and constantly, mov-ing fish-farm plants further from the coast, and exposing them to increasingly high forces due to currents and waves. The performances of cages in currents and waves have been widely studied in literature, by means of laboratory experiments and numerical models, but virtually all the research is focused on the global performances of the system, i.e., on the maximum displacement, the volume reduction or the mooring tension. In this work we propose a numerical model, derived from the net-truss model of Kristiansen and Faltinsen (2012), to study the dynamics of fish farm cages in current and waves. In this model the net is modeled with straight trusses connecting nodes, where the mass of the net is concentrated at the nodes. The deformation of the net is evaluated solving the equation of motion of the nodes, subjected to gravity, buoyancy, lift, and drag forces. With respect to the original model, the elasticity of the net is included. In this work the real size of the net is used for the computation mesh grid, this allowing the numerical model to reproduce the exact dynamics of the cage. The numerical model is used to simulate a cage with fixed rings, based on the concept of mooring the cage to the foundation of no longer functioning offshore structures. The defor-mations of the system subjected to currents and waves are studied
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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