1,720,962 research outputs found
Stochastic models of ice accretion
No full textNew stochastic models have been developed to simulate atmospheric ice accretions at low values of impaction parameters. In 2-dimensional models of ice accretion on cylindrical objects (disks impinging on a larger size disk) the restriction of rectilinear trajectories is removed and some flow dynamics is introduced by analytically calculating the droplet impact direction, in relationship to the aerodynamic conditions. Moreover, polydisperse droplets are considered instead of monodisperse ones. The numerical experiments indicate that the growth direction of the rime feathers can be theoretically predicted by a simple relationship involving three characteristic growth angles. Comparisons with experimental and theoretical results are presented. Model simulations in 3-dimensions (monodispersed spheres impinging on a particle embryo or a cylinder) have been obtained with a purely ballistic approach (rectilinear trajectories). The 3-D density has also been computed, by integrating along the axis of the cylinder circular sectors of 1 degree in width. Comparison with a 2-D density profile confirms the angle β=20° as the main growth characteristic for 3-D aggregates
2D and 3D modelling of low density ice accretion on rotating wires with variable surfaces irregularities
No full textNew results on two stochastic models, a 2-D and 3-D one, developed to simulate ice accrection
processes at low values of impaction parameters are reported. The 2-D model of ice accretion on
rotating cylindrical objects introduces fluid dynamics analytically by calculating the particle impaction
direction as per the aerodynamic conditions; a polydisperse spectrum of particles is also used. Stokes
numbers K in the range 1 < K < 7.8 were used in the numerical experiments. The numerical results on
rotating collectors suggested an original theory of lobe formation, being interpreted as the outcome
of an amplified growth of surface instabilities. An equation relating the angular frequency of lobes
occurrence to the irregularities of the collector surface is introduced and tested for an experimental
deposit with good result. A parameterization of the lobes growth is given by means of the droplets
aerodynamics.
The 3-D model employs a monodisperse droplet spectrum: the dependence of the density on the
angular position with respect to the stagnation line shows that angular dependence of some properties
of the 2-D pure ballistic aggregate is kept even in the 3-D. The value at maximum density in the
numerical deposits matches values found in experimental deposits
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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