1,721,001 research outputs found
Applicability of a stochastic model for particle motion to drifter data in the Brazil/Malvinas extension
No full textEffects of finite scales of turbulence on dispersion estimates
Get PDFThe eddy-diffusion parameterization of turbulent transport is based on the assumption, often questionable for geophysical flows, of infinitesimal scales of turbulence. In this paper we quantitatively compute what are the consequences of this assumption on the estimates of dispersion for some simple flows with oceanographical scales. We compare the analytical results of two different models, one with infinitesimal turbulent time scale (corresponding to a model with eddy-diffusion) and the other with finite scale T. The difference between the two model results normalized with respect to the estimate of the eddy-diffusion model, called Δ, is computed and it is used as a measure of the accuracy of the eddy-diffusion parameterization. In the case of homogeneous turbulence, the eddy-diffusion model is accurate for asymptotic times t \u3e T, as is known, whereas for small times it is characterized by an overestimate of the dispersion. Δ decreases asymptotically as T/t, with the overestimate less than 10% for t \u3e 10T, so that the eddy-diffusion model is appropriate for the meso or global scales but it could be inadequate for short-term studies or for the interpretation of Lagrangian data. When a linear shear is superimposed on the turbulence, Δ still decreases as ≈ T/t, which indicates that the range of applicability of the eddy-diffusion model is approximately the same for homogeneous and for linearly inhomogeneous flows. We then consider an oscillating linear shear with frequency ω, and the results change drastically. Δ does not vanish asymptotically, but rather converges to an oscillating function with constant average and constant extrema. The values of Δ depend on the ratio between the turbulent time scale T and the period of oscillation 1/ω. When T and 1/ω are comparable, the eddy-diffusion model leads to an overestimate of order one even at asymptotic times. This result is a specific and analytically solvable example of a potentially much wider class of results valid for time-dependent flows with more complex spatial structure. A discussion of the possible generalizations and examples of applications to oceanographical flows are presented
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Dispersion Processes and Residence Times in a Semi-Enclosed Basin with Recirculating Gyres: an Application to the Tyrrhenian Sea
No full textVariations on the Author
Get PDF“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
Get PDFWe 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
Get PDFWe 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
- …
