Thesis (Ph. D.)--University of Wisconsin--Madison, 1958. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 240-244).

Thesis (MIng)--University of Stellenbosch, 2007. / Bibliography. Also available via the Internet.

Complex mixtures of biologically active pharmaceutical residues continuously enter aquatic environments via wastewater, where it can affect species through preserved human drug targets or cause unexpected effects in non-target species. Benzodiazepines and antihistamines are two highly consumed groups of pharmaceuticals that have been shown to bioconcentrate in aquatic organisms and induce behavioural alterations affecting individual fitness. Few studies have investigated bioaccumulation and possible ecological effects of co-occurring pharmaceuticals in food-webs. The aim of this study was to: 1) quantify and compare species-specific bioconcentration and bioaccumulation, by exposing a tri-trophic system consisting of algae, zooplankton and three-spined sticklebacks to oxazepam (benzodiazepine), fexofenadine (antihistamine) and a mixture of both, and 2) analyse if exposure to these pharmaceuticals induce behavioural alterations in sticklebacks, by using standardized behavioural experiments. Species-specific bioconcentration of both oxazepam and fexofenadine was confirmed (F3,98 = 3.061, p = 0.03) were algae and zooplankton bioconcentrated substantially more pharmaceuticals (~50-1800 μg kg-1) compared to sticklebacks (~0.1-6 μg kg-1). Uptake of oxazepam in both zooplankton and sticklebacks was significantly higher compared to fexofenadine (p < 0.001).  Zooplankton and sticklebacks retained 16 and 0.3%, respectively, of fexofenadine from the consumed contaminated prey. Sticklebacks showed no direct behavioural alterations, but possible direct and indirect cascading effects might occur in co-occurrence with fish species exhibiting pharmaceutical-induced alterations. These findings highlight the importance of including consumption of contaminated prey as an important exposure route, when assessing effects of pharmaceuticals in the environment. Contamination magnitudes and subsequent effects are species-specific and vary depending on type of pharmaceuticals.

This work is an extension of Yin's work studying the diffusion of Na ion in the PbCl2-NaCl system, but at more dilute compositions of NaCl.

No description available.

Master of Science / Department of Statistics / Weixin Yao / In the fitting of mixtures of linear regression models, the normal assumption has been traditionally used for the error term and then the regression parameters are estimated by the maximum likelihood estimate (MLE) using the EM algorithm. Under the normal assumption, the M step of the EM algorithm uses a weighted least squares estimate (LSE) for the regression parameters. It is well known that the LSE is sensitive to outliers or heavy tailed error distributions. In this report, we propose a robust mixture of linear regression model, which replaces the least square criterion with some robust criteria in the M step of the EM algorithm. In addition, we will use a simulation study to demonstrate how sensitive the traditional mixture regression estimation method is to outliers or heavy tailed error distributions and compare it with our proposed robust mixture regression estimation method. Based on our empirical studies, our proposed robust estimation method works comparably to the traditional estimation method when there are no outliers and the error is normally distributed but is much better if there are outliers or the error has heavy tails (such as t-distribution). A real data set application is also provided to illustrate the effectiveness of our proposed methodology.

published_or_final_version / Mathematics / Doctoral / Doctor of Philosophy

Hydraulic fracturing is a physically complex phenomenon, and there are many variables, both environmental and operational, that affect the overall success of a fracture treatment. Amongst the operational variables, the process of proppant selection is key to ensuring that the induced fractures remain open and permeable. A variety of physical mechanisms act to degrade the permeability of a given proppant packing after deposition in a fracture, the most important of which is the magnitude of the confining stress. The goal of this work is to understand how mixtures of unlike proppants behave under various stress conditions. Specifically, the permeability and conductivity of various mixtures of unlike proppants are measured as a function of confining stress. A secondary investigation is also made into the dependence of permeability on the areal concentration of proppant. Choices of proppants are restricted to those which are currently most common in industry, in terms of both material and size. To that end, mixtures consisted of primarily ceramics and sands with appropriate grain size distributions. Additionally, a light-weight plastic proppant was included in the study. Simple laboratory methods are employed to measure the permeability of the various proppant packings. Values obtained from direct experimentation are compared with values obtained from an independent analytical model. Given the assumptions which are inherent in the analytical model, the experimental and analytical results are in satisfactory agreement. Also, a correlation is developed for single proppants and binary mixtures which predicts permeability as a function of stress, grain size, material, and weight fraction. One key conclusion is that for a binary mixture of proppants, the mixture permeability will not generally be a weighted linear combination of the pure proppant permeabilities. In other words, the permeability of a mixture comprised of 50% (by weight) of one component and 50% of the second component will generally not be halfway between the permeabilities of the single components. A hypothesis is presented which posits that there are threshold weight fractions for each proppant pair that control the permeability of the mixture. / text

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