1,720,983 research outputs found
Mapping groundwater vulnerability at the pan-African scale
No full textAssessing groundwater vulnerability is key to monitor the implementation of the UN SDG for water. We therefore studied in this thesis groundwater vulnerability for pollution at the African scale. The first main objective was to map groundwater vulnerability to pollution at the African scale by applying DRASTIC index. Best available datasets for land use, soil, topography, geology and hydrogeology were collected from different sources. We compiled these data into a 15x15 km2 resolution geodatabase for the continent and used to build the variables of the DRASTIC index. This resulted in the first pan-African groundwater vulnerability and pollution risk map. The map shows that areas under very high and high pollution risk are mainly characterised by shallow groundwater. In second main objective we developed a statistical model to identify environmental variables that explain pollution in groundwater at the African scale. Through a meta-analysis, we compiled a literature database of nitrate contamination. Two statistical models were used to link nitrate and environmental variables and demonstrated the unambiguous link between population density and nitrate pollution. We recalibrated and validated these statistical models using regional datasets of nitrate measured in groundwater. In last main objective, we integrated the time dynamics in the DRASTIC index, focussing on the time dynamics of population density and climate as drivers of groundwater pollution. This approach demonstrated that the groundwater vulnerability to pollution across Africa varies indeed considerably in time, in particularly in densely populated areas in West Africa, the Nile delta, and urbanised regions in East and southern Africa.(AGRO - Sciences agronomiques et ingénierie biologique) -- UCL, 201
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
Shallow groundwater poses pollution problem for Africa
No full textRégions along the Gulf of Guinea are at high risk of groundwater pollution on the continent, according to a map drawn by researchers at the Université catholique of Louvain, Earth and Life Institute, in Belgium. Much of Central Africa and some coastal lands in Northwest Africa are also vulnerable, the map shows
Challenges of groundwater pollution and management in transboundary basins at the African scale
No full textWe address the significant knowledge gap for groundwater pollution in Africa methods by assessing groundwater pollution risk at the African scale. To do so, we compiled the most recent continental-scale information on soil, land use, geology, hydrogeology, and topography in a Geographical Information System at the resolution of 15 × 15 km and the 1:60 000 000 scale. We produced a vulnerability map by using the generic DRASTIC vulnerability indicator. This map revealed that groundwater is highly vulnerable in Central and West Africa groundwater basins, where the water table is shallow. In addition, very low vulnerability classes are found in the large sedimentary basins of Africa deserts where groundwater is situated in very deep aquifers. The generic groundwater pollution risk map is obtained by overlaying the DRASTIC vulnerability indicator with current land use. The northern, central, and western parts of the African continent are dominated by high vulnerability classes and very strongly related to water table depths and the development of agricultural activities. Given the availability of data, we concentrate first on nitrate vulnerability mapping. To this end, groundwater nitrate contamination data are compiled in literature using meta-analysis technic and used to calibrate as well linear and nonlinear statistical models; the latter performing much better as compared to simple linear statistical models. This study will help to raise awareness of the manager's International Basin Authorities or Transboundary Basin Organizations in Africa and in particular on transboundary groundwater pollution issues
Evaluation de la vulnérabilité des eaux souterraines africaines
No full textLes eaux souterraines sont une ressource pour le développement du continent africain, mais elles sont soumises à de nombreuses pression
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
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