1,720,957 research outputs found
Development of PFAS fate and transport model in a firefighting training exercise site
No full textFirefighting training activities (FTAs) over the last half-century have utilized aqueous film forming foam, a solution that contains per- and polyfluoroalkyl substances (PFAS). Human exposure to PFAS has been linked with adverse effects on human health. Consequently, leaching of PFAS from aqueous film forming foam (AFFF) to the aquifers below FTAs is an area of growing concern. One method for understanding PFAS leaching through the vadose zone is through numerical computer modeling. However, computational modeling of PFAS transport in the vadose zone is still a developing field, and no two-dimensional models of PFAS transport have been validated against real-world data.In this thesis, I present a two-dimensional PFAS transport model developed using the HYDRUS 2D software and calibrated against data from a firefighting training site in Killingworth, Connecticut. This calibrated model is then adapted to explore the effects of additional water percolation during FTAs, limiting PFOS influx to only occur during FTAs, changing the climate to that of a more arid region, and introducing single and multiple sources of heterogeneity in the soil. The application of additional percolation during FTAs was found to increase the total concentration of PFOS leached but did not change the shape of the contamination plume. Restricting PFOS influx to only occur during FTAs was found to decrease the total concentration of PFOS, but similarly did not affect the plume. Imposition of an arid climate was found to both drastically decrease the rate of transport and drastically decrease the total concentration of PFOS leached. Lastly, the introduction of blocks of higher hydraulic conductivity and greater sorption loamy sand was found to accelerate the transport of the tracer while capturing a large portion of the PFOS and slowing the rate at which it reaches the aquifer. Together, these model variants and their findings illustrate the usefulness of a calibrated 2-dimensional model in exploring varying PFAS transport scenarios and provide the basis for future research in AFFF application periods, climate dependent PFAS leaching, and leaching in heterogeneous soils
Investigating PFAS fate and transport in groundwater using a three-dimensional model
No full textPer- and Polyfluoroalkyl substances (PFAS) are a category of synthetic chemicals that possess surfactant properties desirable across many industries. The use of these compounds has been integrated into products worldwide and human contact with them is almost unavoidable. Until relatively recent years, the health repercussions these chemicals can have on humans were unknown. Because of the health risks associated with PFAS, they have become a topic of study and their transport mechanisms and pathways needed to be widely analyzed. Particularly, in groundwater, the implementation of 3D modeling has been used in order to assess the factors that influence sorption and transport of these chemicals.The research and simulation created in this thesis project aim to replicate site-specific aquifer properties in order to assess the movement of PFAS through an aquifer. Through the Model Muse graphical interface, MODFLOW and MT3D-USGS software was used to simulate a real-world occurrence of PFAS contamination. The town of Killingworth, Connecticut was selected for modeling due to the documentation of PFAS materials found in the area. Official state investigation, initiated by the Connecticut Department of Energy and Environmental Protection (CDEEP), reported that the detection of PFAS compounds in the town was directly correlative to historical use of Aqueous Film Forming Foams (AFFFs) due to Firefighting Training Activities (FTAs) near the Killingworth Town Hall. For the purpose of study, the described project will analyze the movement of Perfluorooctane sulfonic acid (PFOS), a derivative from the family of PFAS compounds, due to its heavy use in FTAs.The findings of this report document a validated 3D model that simulates a contaminant plume dispersion caused by a PFOS source. Model calibration was determined through regression modeling techniques that incorporate root mean square error (RMSE) calculations between recorded data and simulated values. The objective of simulating the spread of PFOS was to determine whether the Killingworth Reservoir, located southeast of the PFAS source, was at risk of contamination. Model results predicted that there is not a threat of contamination to the body of water in future years. Research was furthered by determining the effects of increased and decreased recharge into the aquifer, simulating changes in climactic conditions on the site. It was found that increased recharge enhanced the transport of the plume. Alternatively, a lower rate of recharge into the aquifer was characterized by slower transport of PFOS concentrations. Overall, the simulated model served as a tool that predicted how changes in the hydrogeological setting would affect a PFOS concentration plume
Modeling Iron Oxide Reactivity in the Environment
No full textIron oxides and hydroxides are highly reactive mineral phases in natural systems since they interact with pollutants, controlling their fate and transport in the environment. Goethite (GH) and hematite (HT) are the most abundant iron minerals in nature, while ferrihydrite (FH) is a nanomineral with high surface reactivity. Subsurface transport modeling has usually represented the adsorption processes by empirical relationships, such as distribution coefficients (Kd) or isotherm equations. However, empirical approaches cannot account for variable geochemical conditions. These effects can be addressed by the mechanistic surface complexation models (SCMs). So far, the application of SCMs has been limited mostly to the description of laboratory experiments, resulting in highly variable parameters even when a pure sorbent–ligand system is described. This limits their usefulness and transferability in reactive transport models.
This study is an attempt to bridge the gap between laboratory and field studies, but keep the predictive power of SCMs. The latter is achieved by analyzing several adsorption datasets systematically to extract unified parameters, and understand the driving forces leading to parameter variability. The optimization process is a problem itself that may lead to non-unique parameters. With this in mind, a hybridized optimization approach (MUSE algorithm), based on a multi–start algorithm combined with a local optimizer, has been developed to allow the simultaneous optimization of SCM parameters. A unified model for surface charge was developed to simulate the variable charging behavior of FH. The model was able to capture differences in both surface charge magnitude and points of zero net proton charge (PZNPCs). Finally, the ultimate purpose of this work was to study the adsorption of one ligand (i.e. chromate) on a group of iron oxides (FH, HT, and GH), and examine whether the complexation parameters can be represented by a unified framework. The results of this analysis showed that thermodynamic constants are highly dependent on the surface properties, an effect that can be quantified by the model calculations, while differences in adsorption energetics are also present under different surface coverages. The latter is reflected in thermodynamic parameters and added to the complexity of the model
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
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