1,720,964 research outputs found
Model-data integration for predictive assessment of groundwater reactive transport systems
No full textPredicting the evolution of groundwater contamination is a major concern for society, in particular when investments are made to remediate the contamination. Groundwater reactive transport models are valuable tools to integrate the available measurements in a consistent framework, improving our understanding of the physical system and potentially revealing aspects of the system that were not considered before. In this thesis reactive transport models are developed for predicting groundwater contamination at a field site where a zero-valent iron permeable reactive barrier (PRB) is installed. In doing so, several general challenges with integrating data into reactive transport models are addressed. A first challenge is conceptual model uncertainty: available data should provide enough information for a correct conceptualization of the system. In chemical systems the concentration of each component is affected by several reactions and alternative reaction networks or descriptions of the reaction rates might provide similar model results. Moreover, the collection of new data might invalidate previous model conceptualizations and one might expect the conceptual model to be continuously updated as new information is acquired. Conceptual model uncertainties can have a large effect on reactive transport model predictions, yet they often are ignored. This thesis provides examples of quantification and reduction of conceptual uncertainty in reactive transport models. Quantification of conceptual model uncertainty was presented in the first part of this thesis, where a column scale experiment of a permeable reactive barrier is described. In the experiment, a substantial decline of the remediation performance over time was observed, mainly due to the development of a carbonate mineral coating around the iron particles. The column measurements were integrated in a multi-component reactive transport model, which subsequently provided predictions of long-term PRB efficiency under reduced flow conditions representative of the field site of interest. Different models of the deactivation process proposed in the literature were all able to reasonably well reproduce the column experiment measurements. The extrapolated long-term efficiency under different flow rates was however significantly different between the different models. These results highlight significant conceptual model uncertainties associated with extrapolating long-term PRB performance based on lab-scale column experiments. Nevertheless, possible improvements of the experimental design were suggested. Despite the large amount of data collected in the column experiment, model conceptual uncertainties could not be resolved clearly and simpler deactivation models might be justified. A simplified deactivation model was proposed, where the decline of the barrier reactivity is simply proportional to the effective groundwater velocity, in contrast to the complex geochemical model where detailed mineral precipitation reactions are accounted for. The main advantage of the simplified model over the geochemical model is that it does not require inorganic concentration measurements for the inference of its parameters. However, the simplified model failed in reproducing part of the column measurements as it does not take into account the feedbacks present in the true geochemical system, which might be important for predicting the long term barrier performance. Reduction of conceptual model uncertainty was demonstrated for a field-scale reactive transport model, where alternative descriptions of the groundwater recharge process provided similar simulations of the groundwater levels but different simulations of the contaminant plumes, with different estimates of the hydraulic conductivity fields. In this case, model conceptual uncertainties were partially solved by integrating simultaneously in the model groundwater heads, concentrations and direct estimation of the hydraulic conductivities. A second challenge concerns the data integration method. Since reactive transport models describe the evolution of multiple species in space and time, multiple data sets are used in parameter inference, for example measurements of dissolved concentrations of various chemical species. A common approach is to optimize parameters using an overall measure of fit, such as the weighted sum of squared residuals, where each data set is given a weight based on prior knowledge of the measurement and model errors. In practice, model errors are difficult to determine a priori and often they are much larger than measurements errors. Moreover, model errors induce correlations between residuals, which are typically ignored. A multivariate approach (MV) was proposed to integrate different data types, which accounts for specific correlations between residuals. The MV method allows integrating out the (co)variances (or weights) from the parameter posterior leading to an efficient estimation of model parameters, with no a priori assumptions about the magnitude of the errors. When applied to inference of the parameters of a column-scale reactive transport model, it was shown that accounting for residual correlation between species provides more accurate parameter estimation for high residual correlation levels, whereas its influence for predictive uncertainty is negligible. A limitation of the multivariate method is that it cannot be implemented using a full covariance matrix with a dimension equal to the number of all measurements. Instead, residuals must be grouped such that the number of groups does not exceed the number of measurements per group. A third challenge for field-scale models is the characterization of the spatial heterogeneity of soil properties from the measurements. Generally, little is known about heterogeneity and often soil properties are assumed constant within parts of the model domain or even in the entire model domain. However, heterogeneity has a considerable effect on the spreading of pollutants and must be accounted for to provide reliable predictions of contamination, increasing the number of model parameters to be estimated. Increasing the number of model parameters has two negative effects on parameter inference. First, it increases the computational effort. This is particularly relevant for reactive transport models characterized by long simulation times (ranging from several hours to days for field-scale applications). Second, a large number of model parameters can make the inverse problem ill-posed, where at least one of the criteria for well posedness (existence, uniqueness and stability) is not met. The reactive transport model developed for predicting the evolution of the contamination at the PRB site is affected by both of these two negative effects, since it accounts for spatial heterogeneity and several physical and chemical processes that increase the simulation time. The computational issue is solved using high performance computing. Ill-posedness is alleviated using a regularization procedure and a step-wise approach for integrating different data sets into the model. It is shown that the joint estimation of flow and transport parameters from head and concentration data improves the matching of the simulations to the measurements compared to the separate estimation of flow and transport parameters, in particular for the more mobile contaminants (cis-DCE and VC). Moreover, a more realistic estimation of the effective porosity and a reduction of the dispersion coefficients are obtained in the joint inversion. Additional measurements are required to validate the estimated recharge fractions and hydraulic conductivities. In the last part of the thesis, the inferred hydraulic and chemical parameters were used to predict future contaminant migration at the field site. These scenarios include all processes considered in the parameter inference, also accounting for the iron deactivation process due to mineral precipitation. The results indicate that the PRB is expected to remain effective at degrading in-situ groundwater contamination until at least 2035. However, existing contamination downstream of the reactive barrier is likely to persist beyond 2035, due to the small dilution effect of infiltrating rain and the small biodegradation rates at the site.Water ManagementCivil Engineering and Geoscience
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
Author Under Sail The Imagination of Jack London, 1893-1902
No full textIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Intro -- Title Page -- Copyright Page -- Dedication -- Contents -- Acknowledgments -- Introduction -- 1. Spirit Truth -- 2. From Absorption to Theatricality and Back Again -- 3. "I Will Build a New Present" -- 4. Sons as Authors -- 5. Fathers as Publishers -- 6. The Daughter as Author -- 7. Lovers as Authors -- 8. At Sea with the Family -- 9. Yellow News, Yellow Stories -- 10. The Return Home -- Notes -- Bibliography -- Index -- About Jay WilliamsIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Description based on publisher supplied metadata and other sources.Electronic reproduction. Ann Arbor, Michigan : ProQuest Ebook Central, YYYY. Available via World Wide Web. Access may be limited to ProQuest Ebook Central affiliated libraries
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