Groundwater Modelling in the Chikwawa district, lower Shire area of southern Malawi

This thesis contains modelling study of groundwater flow in the Chikwawa district, lower Shire Area in the southern regions of Malawi, in order to test out the working hypothesis that deeper groundwater circulation and dissolution of salts in subsurface sediments can explain the high groundwater salinity in parts of the Chikwawa district. There have been evidences of high salinity in Karroo system (in Red beds) and in Cretaceous rocks (in Lupata series) according to the available literature on geology, and there are hotspots located close to major faults where groundwater may discharge. The 3D groundwater flow model of the problematic area in the western part of Shire River is derived by MODFLOW (PMWIN) simulations, where hydraulic conductivity attributed to the different major rock-types and faults were assigned. The semi-distributed areal recharge for the model is calculated using the Thornthwaite water balance approach based on the three meteorological stations in the area. Despite the shortcomings, the calibrated model succeeds in producing groundwater head distribution in steady state that makes a good fit to the observations. Moreover it produces time series of groundwater table for the area in transient flow simulation. Results also show that the major faults in the area must be highly conduit and have a significant role in the groundwater flow patterns. The Mwanza fault has not been found directly as the source of the high salinities by the model. However, studying the flow line in cross sections under the possible geological scenario in which the Mwanza fault continues along the Shire River suggests that in the discharge area close to the river there may be upward groundwater flow lines through Mwanza fault. It is quite possible that these flows carry out dissolved salt and are responsible for the salinity in the hot spots. The model has a very high potential to be improved with field measurements from soil sampling to regular borehole measurements, pumping tests and geophysical studies

Surface Characterization of Retrieved Metal-on-Metal Total Hip Implants from Patients with Adverse Reaction to Metal Debris

The use of metal-on-metal (MoM) total hip implants has decreased recently due to reports of high failure rates and adverse local tissue reaction (ALTR). It has been hypothesized that wear metal debris released from CoCr bearing surfaces may provoke delayed hypersensitivity reactions. The goal of this study is to evaluate the microscopic bearing surface characteristics of implants revised due to evidence of ALTR. The bearing surface of each head and cup was analyzed using multiple microscopy techniques for characterization of the surface features. The presence of severe mechanical scratching was a common characteristic found in all of the implants evaluated. Mechanical factors seemed to be the prevalent failure mode related to the appearance of ALTR with this particular set of retrieved implants

Occupational exposure to electromagnetic fields and female breast cancer

grantor: University of TorontoThe present study was designed to examine the association between occupational exposure to electromagnetic fields (EMF) and female breast cancer, The study design was case control, within the study population of the National Breast Screening Study (NBSS) of Canada. The sample included 1156 cases and 3468 matched controls (3 controls were matched for each case). The NBSS epidemiologic questionnaire included the title of the most recently held occupation. Classification of the case and control subjects into the exposure categories were made by an expert. Conditional logistic regression modelling using PHREG procedure was used to estimate the relative risks and their related confidence intervals. The results of the study suggest that women whose occupation entails exposure above the general population level are at higher risk for breast cancer. Analysis of data for younger (40-49 years) and older women (50-59 years) suggests a more than double increase in the risk for both age groups which is significant for the older subjects but below the significance level for the younger subjects. This study also shows that there is a significant interaction between EMF exposure and regularity of periods. The risk of breast cancer associated with exposure to electromagnetic fields increases when periods are regular, but a smaller sample of women whose periods are irregular show a protective effect. The present study found that women who had undergone mammography prior to the NBSS, were at higher risk for breast cancer. A dose-response relation for the number of prior mammographies was found. (Abstract shortened by UMI.)M.Sc

Walking frequency, cars, dogs, and the built environment

To explain walking propensity or frequency, empirical studies have generally used two sets of explanatory variables, namely, socio-demographic variables and built environment variables. They have generally shown that both socio-demographic characteristics and built environment characteristics are associated with walking propensity. We examine the traditional walkability variables that encompass density, mix of uses, and network connectivity in New Jersey, using a statewide sample including an oversample of Jersey City. We estimate a two-stage least squares model using a conditional mixed process that combines an ordered probit model of walking frequency in the second stage based on a truncated regression of car ownership in the first stage. Our results show that built environment variables have some small effects, mainly from better network connectivity associated with increased walking frequency. One of our key findings is that built environment features also work indirectly via how they influence car ownership. In general, we find sufficient evidence that suggests fewer cars are owned in areas with more walkable built environment features. The other key variable that we control for is whether a household owns a dog. This also proved to be strongly associated with walking suggesting that dog ownership is a necessary control variable to understand the frequency of walking.Walking Two-stage least squares Built environment Car ownership