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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
121

The effects of weathering and diagenetic processes on the geochemical stability of uranium mill tailings

Sinclair, Gregory January 2004 (has links)
Uranium mill tailings from the Ranger mine, located in the Alligator Rivers Region of the Northern Territory, Australia, were examined to assess the effects of weathering and diagenesis on their long-term geochemical stability. Run of mill uranium tailings are a complex heterogeneous mixture of lithogenic ( primary gangue minerals and weathering products ) and secondary ( components that form during milling ) minerals, residual process chemicals and biogenic ( products of biological activity ) phases. Following transfer to the tailings storage facility, post depositional reactions alter the mineralogical and hydrochemical characteristics of the tailings solids and pore waters in accordance with weathering and diagenetic processes. In this thesis, a detailed examination of tailings cores and pore waters, kinetic column test work and geochemical modelling was combined with results from earlier studies to examine the key processes governing the geochemical stability of the Ranger tailings. Conclusions drawn from the work clearly demonstrates that the solid state speciation and mobility of metals and radionuclides in the tailings pile are governed by the processes of oxidative dissolution of sulfide minerals, weathering of phyllosilicates and organic matter diagenesis. The processes are spatially dependent, evolve over time and are influenced by the following key factors : 1. Tailings water content or degree of saturation ; 2. The nature and content of organic matter in the tailings ; 3. Redox potential of the tailings solid - pore water interface ; and 4. The specific reactivity of precursor minerals ( primary / secondary ) from the milling process and pore water solutes. Combined, these processes lead to the formation of authigenic minerals, which control the solubility of pore water constituents. These mechanisms will also have a profound impact on the long-term geochemical stability of the tailings pile and, as such, will need to be taken into account in the design, management and closure of the final tailings repositories at the Ranger site. / Thesis (Ph.D.)--School of Earth and Environmental Sciences, 2004.
122

Maggie's Embodiment of the Roma Stereotype in <em>The Mill on the Floss</em>

Hemdahl, Jenny January 2009 (has links)
<p>This essay focuses on Maggie in <em>The Mill on the Floss</em>, by George Eliot. An examination of her life is presented which is anchored in feminist critical theory and focuses on the ordeal Maggie has to endure in a patriarchal society. Furthermore, the life of the Roma is examined through postcolonial theory and compared to Maggie’s. Many of the stereotypes that emerged about the Roma are also present in Maggie’s life. It is argued that Maggie embodies the stereotypes of the Roma through her encounters with different characters in the novel. </p>
123

Baseline survey and habitat analysis of aquatic salamanders in the Pigeon River, North Carolina

Maxwell, Nikki J 01 December 2009 (has links)
The Pigeon River was severely impacted beginning in the early 1900s by a paper mill located in Canton, North Carolina. The mill discharged chemical byproducts into the Pigeon River until 1992 when the paper mill modified their processes. As a result, water quality improved but the status of salamander species in the Pigeon River was unknown. Worldwide amphibian declines over the last 20 years have drawn attention to the need for more research and a better understanding of species-specific habitat relationships. There is concern about amphibian population declines because amphibians are critical to the balance of ecosystems and are considered exceptional indicators of environmental health. The objectives of this study were: 1) to conduct a baseline survey of salamander species composition in the Pigeon River watershed, 2) to determine if salamander populations differ above and below the Canton paper mill, and 3) to attempt to explain variance in salamander abundance, richness and diversity by comparing water quality and substrate characteristics among streams. Eight stations were examined on the Pigeon River, with four stations located above the paper mill and four stations below. We also chose three stations on each of four tributaries, Big Creek, Fines Creek, Jonathan Creek and Richland Creek. Snorkel surveys were completed in the summer of 2009. Five of eight species of stream salamanders were found that historically existed in Haywood County, NC: Eastern hellbender, Blue Ridge two-lined salamander, shovel-nosed salamander, black-bellied salamander and spring salamander. No salamanders were found in the main channel of the Pigeon River below the mill. Eastern hellbenders and Blue Ridge two-lined salamanders preferred substrates consisting of rubble and avoided bedrock. Percent rubble was the only variable retained in substrate models and was positively related to salamander abundance, richness and diversity. Conductivity, salinity, and water temperature were higher in the Pigeon River below the mill than at all other sites. Salamander abundance was explained by dissolved oxygen, pH, and stream width in water quality models. The results of this study suggest salamander abundance was negatively associated with the Pigeon River below the mill because of poor water quality and not habitat availability.
124

Maggie's Embodiment of the Roma Stereotype in The Mill on the Floss

Hemdahl, Jenny January 2009 (has links)
This essay focuses on Maggie in The Mill on the Floss, by George Eliot. An examination of her life is presented which is anchored in feminist critical theory and focuses on the ordeal Maggie has to endure in a patriarchal society. Furthermore, the life of the Roma is examined through postcolonial theory and compared to Maggie’s. Many of the stereotypes that emerged about the Roma are also present in Maggie’s life. It is argued that Maggie embodies the stereotypes of the Roma through her encounters with different characters in the novel.
125

The anti-estrogenic and liver metabolic effects of DHAA in rainbow trout (oncorhynchus mykiss)

Pandelides, Zacharias 01 August 2011 (has links)
Recent studies have shown that dehydroabietic acid (DHAA), a resin acid present in pulp and paper mills, may have anti-estrogenic effects in fish. A chronic-exposure toxicity experiment using immature rainbow trout (Oncorhynchus mykiss) was conducted in order to assess the endocrine disrupting and liver metabolic effects of the wood extractives DHAA and β- sitosterol (BS) regularly present in pulp and paper mills and the model estrogen 17β-estradiol (E2). It was found that exposure to 5 ppm of E2 significantly increased hepatosomatic index (HSI), vitellogenin (VTG) and plasma sorbitol dehydrogenase (SDH). This effect was reduced by mixing E2 with DHAA, indicating that DHAA does not cause its anti-estrogenic effects indirectly due to liver damage. Exposure to 5 ppm of DHAA caused a significant increase in liver citrate synthase (CS), and liver ethoxyresorufin-O-deethylase (EROD) activity after 7 days, however, the fish recovered by 28 days. This study also determined the effect of 14 different pulp and paper mill effluent extracts on liver enzyme metabolism through alterations in the activity of liver lactate dehydrogenase activity (LDH) and CS. This activity varied greatly between mills but most showed an induction of CS after 28 days exposure through i.p. injection. The results of the study indicate that DHAA may alter energy metabolism as well as cause anti-estrogenic effects in female juvenile rainbow trout. / UOIT
126

Monitoring populations of the flour beetles Tribolium confusum Jacquelin du Val and Tribolium castaneum (Herbst) in flour mills and in laboratory settings

Hawkin, Karen 14 July 2008 (has links)
This thesis reports the effects of disturbance and harbourage on the fitness of Tribolium confusum and T. castaneum, as well as the the efficacy of pheromone monitoring traps for monitoring for populations of Tribolium in laboratory and mill settings. Behavioural studies were also carried out on mill and laboratory-reared beetles and the distributions of both species in a mill were examined. Twenty-four hour sieving disturbance decreased the rates of dispersal for both species, and decreased T. castaneum fecundity. Rolling disturbance decreased T. confusum dispersal rate while shaking disturbance decreased T. castaneum dispersal rate. When undisturbed beetles were given differing amounts of flour in the presence or absence of harbourage, beetles laid more eggs in larger amounts of flour, but harbourage only affected T. castaneum at one level of flour (2 g). Throughout disturbance and harbourage experiments, T. castaneum laid more eggs than T. confusum. Pheromone monitoring traps placed in three Canadian flour mills were not useful in predicting the degree of infestation inside Simons rollstands. Pheromone monitoring traps also showed low efficacy (i.e. caught few beetles) in both mill and laboratory settings, and T. confusum was caught less often than T. castaneum in both mills and in a warehouse. Mill-strain beetles of both species were caught less often than laboratory-strain beetles in a warehouse. In one Canadian flour mill, both T. castaneum and T. confusum were found inside rollstands but the two species were spatially segregated from one another, rarely being found together in the same rollstand. In contrast to this, both species were consistently found together in samples taken from the same mill less than a year beforehand. In behavioural laboratory studies, beetles collected directly from a mill moved slower than beetles collected from a laboratory culture and this response was shown to be phenotypic. Mill-strain and laboratory-strain beetles also differed in burrowing tendencies, with T. confusum from the laboratory strain burrowing less than T. confusum from a mill and T. castaneum from different mills sometimes burrowing more and sometimes less than T. castaneum from the laboratory strain. / October 2008
127

Utility, Character, and Mill's Argument for Representative Government

Vickery, Paul 07 August 2012 (has links)
John Stuart Mill’s Representative Government argues that the ideal form of government is representative. In this paper, I interpret Mill’s argument as a utilitarian argument for a political system with the salient feature of authoritative public participation. Mill argues for this feature in the first three chapters of Representative Government. This argument is interpreted in the context of Mill’s utilitarian views as elaborated in Utilitarianism, with emphasis on Mill’s understanding of pleasure formation and high quality utility.
128

Correlation between process parameters and milling efficiency

Johansson, Anna January 2012 (has links)
An experimental ball-milling study was performed to compare the deagglomeration behavior and the evolution of the particle size distribution with increasing milling time of two relatively coarse WC powders used for the production of cemented carbide cutting tools. The WC-powders were found to have distinctly different particle size distributions and particle morphologies prior to milling. Lab-scale WC samples were made using a range of different process parameters and milling times. These were then analysed by means of microscopy, laser light scattering, gas adsorption BET analysis and X-ray powder diffraction, XRD, to attain particle size distribution, specific surface area and a mean crystal size, respectively. The results suggested a linear relation between log(particle size) and log(milling time) between 10 and 80 hours milling. The viscosity was shown to have a minor effect on the milling efficiency. Both the number of collisions of milling balls per unit time as well as the kinetic energy of the milling ball affected the size reduction; more collisions or higher energy resulted in a higher milling efficiency. The evaluation of the effect of the process parameters on milling efficiency was facilitated by the use of simple scaling factors. For example, all milling curves for samples with different WC amounts coincided when rescaling the milling time using a scaling factor based on the weight of the WC and milling balls. The same scaling factor could be used with success for rescaling the results from different trials obtained with laser light scattering, gas adsorption and XRD. The results of this work are useful for future work on modeling of the milling process which should lead to more accurate predictions of the outcome of milling unit operations.
129

Roll shape design for foil rolling of a four-high mill and rolling technology development

Kan, Cheng-chuan 08 February 2010 (has links)
During foil rolling, back-up and work rolls undergo elastic deformation resulted from the rolling reaction force, which results in non-uniform thickness distribution in the width direction, even causes waves and fracture in the rolled foils. This paper aims to propose a mathematical model for a four-high mill to analyze the elastic deformation of the rolls and discuss the relationship between axial defection of the back-up and work rolls and the rolling conditions, from which the thickness distribution of the product is then predicted. The finite element simulation is also used to analyze the rolling force and roll¡¦s elastic deformation of a four-high mill. From the predicted foil shape, the roll profiles are designed. The mathematical model is validated by comparing the analytical thickness distribution with experiment values. Rolling pass schedules are also designed. From the arrangerement of reductions and heat treatment, experimental results of stainless steels foils with 80£gm thick and 2£gm variation, pure copper foils with 20£gm thick and 2£gm variation, and aluminum foils with 15£gm thick and 3£gm variation are successfully obtained. A rolling technology for foil rolling is developed.
130

Finite element analysis during strip rolling and determination of width spread equation

Guo, Jin-Cheng 01 September 2010 (has links)
Rolling technology can control the thickness precisely. But it isn¡¦t available in width control. FEM software DEFORM 3D is adopted to simulate one stand of the hot finishing rolling process using carbon steel as sheet material. Stress, strain and width spread are discussed. Regression analysis is used to find an empirical equation for rolling load and width spread. Experiment and simulation of cold strip rolling using aluminum as sheet material are conducted,discussing the width spread and detail of width transformation in DEFORM 3D.From the comparisons between analytical and experimental width spread, the analytical model and prediction equation are validated.

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