1,720,958 research outputs found
On the use of electrical resistivity methods in monitoring infiltration of salt fluxes in dry coal ash dumps in Mpumalanga, South Africa
No full textOne of the principal environmental concerns relating to coal combustion waste disposal is the potential for groundwater contamination from salt fluxes and trace elements that may be leached into the underlying groundwater system. Since changes in moisture and salt concentrations usually provide contrasts in electrical properties against the host media, electrical resistivity methods can be used to monitor ingression of solute plumes as well as to detect any preferential flow paths within the ash medium. In this study, 2D electrical resistivity tomography was used to monitor brine (10% NaCl) water ingression through the unsaturated zone of a dry coal ash dump at a power station, Mpumalanga, South Africa. This was after the initial laboratory determination of the relation between electrical resistivity and moisture/salt content for the ash dump. The results showed that infiltration plume progression was more pronounced in the vertical direction, suggesting that moisture movement is mainly due to gravitational pull. There was no evidence of preferential flow within the ash medium, although the different infiltration rates for different sites suggested different permeability within the unsaturated zone
NON-INVASIVE CHARACTERIZATION OF UNSATURATED ZONE TRANSPORT IN DRY COAL ASH DUMPS: A CASE STUDY OF TUTUKA, SOUTH AFRICA
Full text linkDoctor ScientiaeThe management of the large volumes of solid wastes produced as coal combustion
residue is of particular concern due to the presence of leachable metals and salts which
may constitute a long term environmental risk and potential contamination of both
surface and groundwater systems of the surrounding environment. In order to
implement an efficient monitoring scheme and to assess the impact of the ash dump on
the hydrologic system, a thorough knowledge on the migration of solutes fluxes in dry
ash dumps as well as the controls on the transport of these solutes to the underlying
groundwater system is required.
The conventional methods which have been widely used for such applications are
centred on extracting and analysing several samples from observation wells are drilled
on the dump. This has however created a potentially hazardous situation as the
installation of monitoring wells may result in the creation of new fluid pathways and
results in further migration of leachates. Nevertheless, non–invasive characterization
has often been useful in the determination of subsurface hydraulic properties and is a
key step towards the solution of real-life problems in hydrology, hydrogeology and soil
science. In contaminant transport non-invasive methods have often proved to be an
efficient tool as compared to traditional drilling and sampling techniques which in most
cases results in the creation of preferential flow paths and do not allow for the space
and time resolution needed for the monitoring of hydrological and environmental
processes.
In this context, this study seeks to develop a generic conceptual model for the ash
dump through the use of non-invasive geophysical techniques and numerical modelling techniques at the Tutuka Ash dump, Mpumalanga South Africa. Changes in electrical
resistivity were used correlate changes in moisture contents during moisture and salt
leachate ingression in ash dumps with a sufficient accuracy. A determination of the
suitability of Archie‘s law to describe the relationship between electrical resistivity and
solute transport ash medium was achieved through empirical laboratory experiments.
Electrical resistivity tomography was then used as an appropriate tool for the elucidation
of potential flow paths and brine dispersion in the ash dump. The flow rates through the
ash dump were estimated by considering the rate of brine injection and the distance
travelled by the brine plume over the time spanned in time lapse infiltration experiments.
Additional geophysical profiles managed to show the lithostratigraphy of underlying
hydro-geology, thereby ensuring that the knowledge of the geology can be established
without the application of any intrusive methods.
To ensure that development of the conceptual model of the unsaturated zone transport
of the ash dump was developed with sufficient accuracy, numerical models were also
used to describe solute transport in the vadose zone. The HYDRUS2D numerical
package was used simulate the flux dynamics within the unsaturated zone of the coal
ash medium, so as to develop a conceptual understanding of water flow and salt
transport through the unsaturated zone of the coal ash medium. The results from the
study suggested a conceptual solute transport model that consists of a two layers. The
upper layer represented the unsaturated zone of the ash dump which was the source of
any potential contaminant transport that could be of concern. The lower layer describe
the underlying the subsurface environment to the ash dump which include the soil zone,
the shallow aquifer and the deep fractured rock aquifer. To enable this conceptualisation, results from the numerical simulations and
geophysical interpretations of the electrical resistivity profiles were the critical
components for optimising the site-specific subsurface water flow and solute transport
processes, as well as producing the most acceptable conceptualisation of the ash dump
system that could be used in hazard assessment and mitigation against potential
groundwater pollution. The conceptual models developed in this study proposed an
explanation on impact of the ash dump to the hydro-geologic and the eco-hydrologic
environment by proposing a scenario of contamination of the underling ash dump and
the existing. In this regard, the study managed to provide important scenarios that may
be necessary during mitigation procedures for both the ash dump and the wetland.
Key words: non-invasive, coal ash, time lapse, electrical resistivity tomography,
numerical models, HYDRUS2D, conceptual model
NON-INVASIVE CHARACTERIZATION OF UNSATURATED ZONE TRANSPORT IN DRY COAL ASH DUMPS: A CASE STUDY OF TUTUKA, SOUTH AFRICA
No full textDoctor ScientiaeThe management of the large volumes of solid wastes produced as coal combustion
residue is of particular concern due to the presence of leachable metals and salts which
may constitute a long term environmental risk and potential contamination of both
surface and groundwater systems of the surrounding environment. In order to
implement an efficient monitoring scheme and to assess the impact of the ash dump on
the hydrologic system, a thorough knowledge on the migration of solutes fluxes in dry
ash dumps as well as the controls on the transport of these solutes to the underlying
groundwater system is required.
The conventional methods which have been widely used for such applications are
centred on extracting and analysing several samples from observation wells are drilled
on the dump. This has however created a potentially hazardous situation as the
installation of monitoring wells may result in the creation of new fluid pathways and
results in further migration of leachates. Nevertheless, non–invasive characterization
has often been useful in the determination of subsurface hydraulic properties and is a
key step towards the solution of real-life problems in hydrology, hydrogeology and soil
science. In contaminant transport non-invasive methods have often proved to be an
efficient tool as compared to traditional drilling and sampling techniques which in most
cases results in the creation of preferential flow paths and do not allow for the space
and time resolution needed for the monitoring of hydrological and environmental
processes.
In this context, this study seeks to develop a generic conceptual model for the ash
dump through the use of non-invasive geophysical techniques and numerical modelling techniques at the Tutuka Ash dump, Mpumalanga South Africa. Changes in electrical
resistivity were used correlate changes in moisture contents during moisture and salt
leachate ingression in ash dumps with a sufficient accuracy. A determination of the
suitability of Archie‘s law to describe the relationship between electrical resistivity and
solute transport ash medium was achieved through empirical laboratory experiments.
Electrical resistivity tomography was then used as an appropriate tool for the elucidation
of potential flow paths and brine dispersion in the ash dump. The flow rates through the
ash dump were estimated by considering the rate of brine injection and the distance
travelled by the brine plume over the time spanned in time lapse infiltration experiments.
Additional geophysical profiles managed to show the lithostratigraphy of underlying
hydro-geology, thereby ensuring that the knowledge of the geology can be established
without the application of any intrusive methods.
To ensure that development of the conceptual model of the unsaturated zone transport
of the ash dump was developed with sufficient accuracy, numerical models were also
used to describe solute transport in the vadose zone. The HYDRUS2D numerical
package was used simulate the flux dynamics within the unsaturated zone of the coal
ash medium, so as to develop a conceptual understanding of water flow and salt
transport through the unsaturated zone of the coal ash medium. The results from the
study suggested a conceptual solute transport model that consists of a two layers. The
upper layer represented the unsaturated zone of the ash dump which was the source of
any potential contaminant transport that could be of concern. The lower layer describe
the underlying the subsurface environment to the ash dump which include the soil zone,
the shallow aquifer and the deep fractured rock aquifer. To enable this conceptualisation, results from the numerical simulations and
geophysical interpretations of the electrical resistivity profiles were the critical
components for optimising the site-specific subsurface water flow and solute transport
processes, as well as producing the most acceptable conceptualisation of the ash dump
system that could be used in hazard assessment and mitigation against potential
groundwater pollution. The conceptual models developed in this study proposed an
explanation on impact of the ash dump to the hydro-geologic and the eco-hydrologic
environment by proposing a scenario of contamination of the underling ash dump and
the existing. In this regard, the study managed to provide important scenarios that may
be necessary during mitigation procedures for both the ash dump and the wetland.
Key words: non-invasive, coal ash, time lapse, electrical resistivity tomography,
numerical models, HYDRUS2D, conceptual model
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
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
- …
