1,720,993 research outputs found
Eulerian-Lagrangian modelling of dispersion in a convective boundary layer
No full textA simple Eulerian-Lagrangian dispersion model is proposed. The relative dispersion is treated as a Gaussian puff, whereas the puff trajectory is derived by a Lagrangian particle model. Dispersion in a Convective Boundary Layer has been simulated for three different source heights. A comparison with the classical experiments of Willis and Deardoff is proposed. An overall agreement is obtained in modelling dispersion in a 1-dimensional CBL. It is noteworthy that the proposed model is about 25 times faster than a Lagrangian mode
A PDF micromixing model of dispersion for atmospheric flow. Part I: development of the model, application to homogeneous turbulence and to neutral boundary layer
No full textA Lagrangian stochastic (LS) probability density function (PDF) model has been developed to study statistics and PDF of concentration generated by continuous releases of passive substances from point and line sources in atmospheric flow. The model simulates the combined effect of turbulent mixing (macromixing) and molecular diffusivity (micromixing) on dispersion of tracers. Turbulent dispersion is modelled using an LS model; molecular diffusivity is simulated by an interaction by exchange with the conditional mean (IECM) model. A dynamical computational grid, which expands with time around the plume, has been developed to optimise computational time and memory requirements. The model has been tested with the results of a two-particle LS model in homogeneous turbulence and with wind tunnel observations in a neutral boundary layer. The proposed model can account for chemical reactions in a direct way with no closure assumptions
Concentration PDF modelling in and above a canopy layer.
No full textNon-linear chemical reactions and other important processes depend on average concentration as well as on the fluctuations of concentration of chemical species. Probability density function (PDF) modelling is a powerful tool for evaluating in an exact manner chemical reaction depending on higher order concentration moments. However, only few studies are devoted to investigate applications of PDF modelling to pollutant dispersion and reactions in atmospheric turbulence. In real cases, very often the emissions/reactions of pollutants take place in and above a canopy layer (urban canopy, vegetation canopy); therefore, the vertical turbulence inhomogeneity plays a relevant role. This inhomogeneity can be efficiently taken into account by PDF approach. We implement a simplified one-dimensional model for the velocity composition PDF by coupling a Monte Carlo simulation and a micro-mixing model (IECM). Under a general assumption of horizontally homogeneous extensive plane source the proposed model is able to fairly reproduce all the concentration moments measured in a laboratory experiment on scalar dispersion within a model plant canopy
A PDF micromixing model of dispersion for atmospheric flow. Part II: application to convective boundary layer
Full text linkThe Lagrangian stochastic probability density function (PDF) model developed by Cassiani et al. [Atmos. Environ. (2005) Part 1] is extended to the atmospheric convective boundary layer. The model is applied to simulate concentration statistics and PDF generated by passive releases from point and line sources in the convective boundary layer. A dynamical time-expandable grid is implemented, which optimises the computational resources required for dispersion simulations in atmospheric flow. A parameterised formulation for the micromixing time scale in convective conditions is derived. Model concentration statistics including mean field, fluctuations and concentration PDF are tested with four water tank experiments
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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