1,721,075 research outputs found
Aerodynamic effects of trees on pollutant concentration in street canyons
No full textThis paper deals with aerodynamic effects of avenue-like tree planting on flow and traffic-originated pollutant dispersion in urban street canyons by means of wind tunnel experiments and numerical simulations. Several parameters affecting pedestrian level concentration are investigated, namely plant morphology, positioning and arrangement. We extend our previous work in this novel aspect of research to new configurations which comprise tree planting of different crown porosity and stand density, planted in two rows within a canyon of street width to building height ratio W/H = 2 with perpendicular approaching wind. Sulfur hexafluoride was used as tracer gas to model the traffic emissions. Complementary to wind tunnel experiments, 3D numerical simulations were performed with the Computational Fluid Dynamics (CFD) code FLUENT(tm) using a Reynolds Stress turbulence closure for flow and the advection-diffusion method for concentration calculations. In the presence of trees, both measurements and simulations showed considerable larger pollutant concentrations near the leeward wall and slightly lower concentrations near the windward wall in comparison with the tree-less case. Tree stand density and crown porosity were found to be of minor importance in affecting pollutant concentration. On the other hand, the analysis indicated that W/H is a more crucial parameter. The larger the value of W/H the smaller is the effect of trees on pedestrian level concentration regardless of tree morphology and arrangement. A preliminary analysis of approaching flow velocities showed that at low wind speed the effect of trees on concentrations is worst than at higher speed. The investigations carried out in this work allowed us to set up an appropriate CFD modelling methodology for the study of the aerodynamic effects of tree planting in street canyons. The results obtained can be used by city planners for the design of tree planting in the urban environment with regard to air quality issues
Dispersion study in a street canyon with tree planting by means of wind tunnel and numerical investigations - Evaluation of CFD data with experimental data
No full textThis paper is devoted to the study of flow and traffic exhaust dispersion in urban street canyons with avenue-like tree planting. The influence of tree planting with different crown porosity was investigated. Wind tunnel experiments for perpendicular approaching flow showed that avenue-like tree planting cause increases in exhaust concentrations at the leeward wall as tree crowns reduce the vortex found in the outer regions of the tree-free street canyon and the vertically entering volume flow rate at the canyon-roof top interface. This results in less ventilation and consequently larger concentrations in proximity of the leeward wall. At the windward wall, decreases in concentration are due to the upward moving stream in front of the leeward wall which extends farther into the skimming above roof flow and is better mixed. The clean air entrained in front of the windward wall mixes with air inside the street canyon leading to smaller concentrations. Experiments performed in the wind tunnel with different tree crown porosities did not indicate substantial changes in the flow and concentration fields. The porous model crowns investigated behaved almost like impermeable objects when arranged in a sheltered position and wind speeds are relatively small as in the street canyon. The above described experiments have been also investigated by means of numerical simulations with the CFD code FLUENT(tm), rarely applied to this type of problems. The standard k-e turbulence model and the Reynolds Stress Model were used for flow while the Eulerian advection diffusion scheme has been used for dispersion. Both models reproduced qualitatively the main aspects found in wind tunnel experiments, even though they underestimated flow velocities. Improvement of CFD dispersion performance was obtained by increasing the diffusivity through the turbulent Schmidt number Sct. Overall we found that the k-e model failed to capture the complex structure of dispersion process in the presence of tree planting as it would require unphysical low Sct values. On the other hand the RSM turbulence model agreed fairly well with experiments by slightly reducing the standard Sct. The results obtained in this work by combining wind tunnel experiments and CFD based simulations to investigate this novel aspect of research suggest ways to obtain quantitative information for assessment, planning and implementation of exposure mitigation using trees in urban street canyons
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
EVALUATION OF NUMERICAL FLOW AND DISPERSION SIMULATIONS FOR STREET CANYONS WITH AVENUE-LIKE TREE PLANTING BY COMPARISON WITH WIND TUNNEL DATA
Full text linkFlow and traffic-originated pollutant dispersion in an urban street canyon with avenue-like tree planting have been
studied by means of wind tunnel and CFD investigations. The study comprises tree planting of different crown porosity, planted in
two rows within a canyon of street width to building height ratio W/H = 2 and street length to building height ratio L/H = 10
exposed to a perpendicular approaching boundary layer flow. Numerical simulations have been performed with the commercial
CFD code FLUENT™ by employing the RSM turbulence model. In the presence of tree planting, both measurements and
simulations show considerable larger pollutant concentrations in proximity of the leeward wall and slightly lower concentrations in
proximity of the windward wall in comparison to the tree-less street canyon. In particular, FLUENT slightly underestimated
pollutant concentrations in proximity of the leeward wall in all cases studied, while near the windward wall there is no general
tendency towards underestimation or overestimation. Overall, numerical computations compare qualitatively well with experimental
data. Results from commonly used statistical tests also suggest the CFD predictions to be satisfactory. Results obtained in this work
by combining wind tunnel experiments and CFD based simulations in a novel aspect of research suggest ways to obtain quantitative
information for planning and implementation of exposure mitigation using trees in urban street canyons
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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