1,721,009 research outputs found
Effects of competition and cooperation interaction between agents on networks in the presence of a market capacity
Get PDFA network effect is introduced taking into account competition, cooperation, and mixed-type interaction among agents along a generalized Verhulst-Lotka-Volterra model. It is also argued that the presence of a market capacity undoubtedly enforces a definite limit on the agent's size growth. The state stability of triadic agents, i.e., the most basic network plaquette, is investigated analytically for possible scenarios, through a fixed-point analysis. It is discovered that: (i) market demand is only satisfied for full competition when one agent monopolizes the market; (ii) growth of agent size is encouraged in full cooperation; (iii) collaboration among agents to compete against one single agent may result in the disappearance of this single agent out of the market; and (iv) cooperating with two rivals may become a growth strategy for an intelligent agent
PM2.5 chemical composition, source apportionment and geographical origin of air masses in Pretoria, South Africa
Get PDFThesis (PhD (Environmental Health))--University of Pretoria, 2020.Background: Air pollution is one of the major problems being faced by most of the big and industrial cities of the world and has become a major environmental threat over the last few years. This environmental threat has gained more attention because of its increased health effects on humans which includes morbidity and mortality. It has various adverse effects, such as increased pulmonary infections, respiratory diseases, acute illnesses and hospitalizations and can eventually lead to death. The need for source identification and abatement strategies for air pollution is crucial in order to meet the SDG goal to reduce pollution by 2030. Therefore, this study investigated the characterisation of PM2.5, source apportionment, origin of air masses into Pretoria alongside the association between air pollutant and hospital admissions due to respiratory diseases.
Method: This study was divided into primary and secondary data collection phases. For the primary data collection, daily 24-hour PM2.5 samples were collected every third day between 18 April 2017 and 17 April 2018 at an urban background site in Pretoria. A total of 122 PM2.5 samples and 25 duplicate PM2.5 samples were collected and analysed for particulate mass, soot, black carbon (BC), organic carbon (OC) and 18 trace elements. Source apportionment analysis was conducted on this dataset using the positive matrix factorisation method. Air mass trajectories, as a surrogate for distant sources of PM2.5, were estimated using the HYSPLIT model (version 4.9). The daily average trajectories were calculated backwards for 72 h and used for cluster analysis. The clustering algorithm coupled in HYSPLIT was based on the distance between a trajectory endpoint and the corresponding cluster mean endpoint.
The secondary data, daily hospital admissions, PM10, NO2 and SO2 data, used for this project were obtained from a private hospital group and the South African Air Quality Information System, managed by the South African Weather Services. The time-stratified case-crossover epidemiology study design and conditional logistic regression models were applied to investigate the association between PM10, NO2, SO2 and respiratory disease (RD) hospital admissions during the study period 1 January 2011 to 30 November 2014.
Results: The annual mean for PM2.5 (n =122 days) was 21.1µg/m3 (range 0.7 - 66.8 µg/m3). The highest PM2.5 mean value was recorded during winter, which was significantly higher than autumn, spring, and summer (p0.9567) was observed. Most exceedances of PM2.5, when compared with daily World Health Organization (WHO) guidelines and South African standards were observed in mid-autumn and winter. Soot, BC and OC followed the same trend as PM2.5 concentration. Average S (1480 ng/m3) concentration was the highest among elements detected, followed by Si, Fe, K and Ca, in that order. Seven sources and their contributions to the total PM2.5 were identified and quantified. These included vehicle exhaust – 8.6%, and base metal/ pyrometallurgical - 0%, soil dust -13.2%, secondary Sulphur – 31.4%, vehicle exhaust – 12.5%, road traffic – 7.3%, coal burning -27.2%, while the percentage of PM2.5 specie in the base metal/ pyrometallurgical factor was 0%. The identified source factors exhibited seasonal variations, coal burning and secondary Sulphur being the highest during winter while soil dust and road traffic were lowest during summer.
Five transport clusters were identified during the 1-year study period: National Limpopo (Nat-LP), transboundary (TB), Easterly-Indian Ocean, South Easterly-Indian Ocean and South Westerly-Atlantic Ocean. In addition to this, 85% of the transport clusters were of local and transboundary origin, 15% were long-range transport, while cluster 1 had the highest PM2.5 concentration. Cluster 1 can be attributed to main source of pollution contributing to the PM level at the sampling site due to the activities going on in the region, such as biomass burning, coal mining.
Of the 17,647 hospital admissions in Pretoria, 51.8% (n=9,147) were women and 61.6% (n=10,870) were 0-14-year old. In the unstratified analysis, a 10 g/m3 increase in PM10 was associated with statistically insignificant increase of 0.2% (-0.7%; 1.2%) in RD hospital admissions; no significant association was observed for NO2 during cold days. Significant association between SO2 and RD hospital admissions was observed for females and male patients during warm and cold days.
Conclusion: This project contributes to the very few source apportionments studies of PM2.5 in Africa and specifically South Africa. Coal burning remains one of the main sources that should be addressed. Late autumn and winter season recorded the highest concentration. The risks of RD hospital admission due to PM10 exposure in Pretoria were higher on warm days than on cold days. The apportioned sources and the origin of air masses from this study align with the known existing sources in the country. Oceanic influences, local and transboundary sources (Southern African countries) contribute to the air masses passing over Pretoria, therefore, abatement strategies are paramount to reduce the level of pollution during this time.
The findings of the study can be of help to the government in the formulation of air pollution guidelines as a measure to mitigate the effect of air pollution on the environment. In addition to this, if there is strict compliance to the already formulated regulation on the identified sources, this will significantly reduce the effect of air pollution in our cities. Lastly, the outcome of this project will help the South African government in their air quality management plan that are reviewed regularly.National Research FoundationSchool of Health Systems and Public Health (SHSPH)PhD (Environmental Health)Unrestricte
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
Variations 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
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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