Several species of Neotropical migrant songbirds are experiencing declining population numbers. One of many proposed reasons for these declines is the dramatic loss of suitable prairie and grassland nesting habitat in the central United States. The Konza Prairie - a native tallgrass prairie preserve in central Kansas - was used to study possible edge-effect predation of artificial avian ground nests. Two Japanese quail eggs were placed in created artificial nests along transect lines from a wooded edge, a recently burned edge, and a control area. The rate of nest predation after seven days was 16.1 (±12.9%) for the control area. This was taken to represent the typical base level of artificial nest predation for the Konza Prairie. The predation rates for the wooded edge and burned edge were 21.9% (±7.4%) and 18.0% (±6.0%), respectively. These rates were not statistically different from each other or the base level rate of predation. The data suggests that no edge-effect predation occurs for artificial avian ground nests along wooded or burned edges in the Konza Prairie. Predation rates of natural bird nests may be different than these results suggest. It is recommended that future studies identify nest predators and study their foraging behavior near edge habitat. / Department of Natural Resources and Environmental Management

Post-harvest cane deterioration in the South African sugar industry results in significant revenue loss that is estimated to be in the region of ZAR 60 million per annum. Despite these large losses, precise biological data relating to the process of cane deterioration under South African conditions is limited. Severity of deterioration is influenced by a number of factors, including the length of the harvest-to-crush delay (HTCD), ambient temperature and harvesting practices. For example, burning of cane prior to harvest may result in rind splitting, which provides entry for microbes, particularly Leuconostoc mesenteroides that may exacerbate deterioration. The effect of these factors on deterioration was examined by quantifying the biochemical and microbiological changes that occur in sugarcane stalks after harvest, with the influence of length of HTCD, degree of L. mesenteroides infection and ambient temperature receiving attention. The primary novelty of the work resides in the analysis of deterioration under tightly regulated temperatures, which were designed to reflect diurnal variations typically experienced during summer and winter in the South African sugar belt. In addition, inoculation of mature internodes with a consistent titre of L. mesenteroides was used as a means to mimic a consistent level of infection of harvested stalks by the bacterium. Metabolites selected for analysis were those both native to the stalk and produced as by-products of microbial metabolism, viz. sucrose, glucose, fructose, ethanol, lactic acid, dextran and mannitol. Simulated HTCDs under summer temperatures resulted in increasing glucose and fructose levels with time, which contrasted to the approximately constant levels of these hexose sugars under winter conditions. Commonly referred to as ‘purity’ in an industrial context, precise determination of the concentration of these hexoses in cane consignments could potentially indicate the extent of deterioration. Despite the detection of a basal concentration of lactic acid in unspoiled cane, the observed increase in concentration of this organic acid over the simulated summer HTCD suggests that this metabolite could also potentially serve as an indicator for postharvest deterioration. In contrast, the investigation indicated that ethanol was an unsuitable biochemical marker for deterioration of L. mesenteroides infected cane. An inability to detect dextran and mannitol in the samples, combined with consistent sucrose levels and variable mill room data, suggest that extreme proliferation of L. mesenteroides is facilitated primarily by in-field practices, particularly the manner in which cane is prepared prior to harvest and transport to the mill. Bacterial proliferation and infection by L. mesenteroides of inoculated stalks were monitored by standard selective culturing techniques. Despite the limited detection of L. mesenteroides-associated metabolites, culture-based analyses revealed that the bacterium was the dominant bacterial species within the samples. A number of other bacterial species were isolated and identified, however the extent to which the total number of microorganisms proliferated was limited to a maximum of 1 x 105 colony forming units per gram of fresh tissue. In conjunction with these analyses, a molecular approach known as Polymerase Chain Reaction-Mediated Denaturing Gradient Gel Electrophoresis (PCR-DGGE) was undertaken to investigate the bacterial diversity patterns associated with deteriorating sugarcane stalks throughout the delay period. In contrast to the results obtained by means of the culture-based assays, PCR-DGGE revealed that L. mesenteroides was not the dominant bacterial population, and showed that the level of bacterial diversity was relatively consistent across the differing treatments and with time. The use of complimentary culture-dependent and cultureindependent analyses thus permitted the detection of this discrepancy and indicated the utility of PCR-DGGE in the determination of bacterial community structure of postharvest sugarcane tissue. The biology of post-harvest deterioration of green sugarcane stalks is highly complex, even under rigorously controlled temperature and infection regimens. The results of this study emphasize the important effects that harvest method and environmental conditions have on post-harvest sugarcane deterioration. Towards the formulation of industry-relevant recommendations for combating post-harvest deterioration, future work will strive to mimic the effects that harsh harvesting and transport practices have on the severity of the problem. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2008.

A topical issue in financial economics is the development of appropriate stochastic dynamic models for banking items and behavior. The issue here is to fulfil the need to generalize the more traditional discrete-time models of banking activity to a Levy process setting. In this thesis, under the assumption that the loan market is imperfectly competitive, we investigate the evolution of banking items such as bank assets (cash, bonds, shares, Treasuries, reserves, loans and intangible assets), liabilities (demand deposits) and bank capital (bank equity, subordinate debt and loan loss reserves). Here we consider the influence of macroeconomic factors and profitability as well as its indicators return on assets (ROA) and return on equity (ROE). As far as bank assets are concerned, we note that loan pricing models usually reflect the financial funding cost, risk premium to compensate for the risk of default by the borrower, a premium reflecting market power exercised by the bank and the sensitivity of the cost of capital raised to changes in loans extended. On the other hand, loan losses can be associated with an offsetting expense called the loan loss provision (LLP), which is charged against Nett profit. This offset will reduce reported income but has no impact on taxes, although when the assets are finally written off, a tax-deductible expense is created. An important factor influencing loan loss provisioning is regulation and supervision. Measures of capital adequacy are generally calculated using the book values of assets and equity. The provisioning of loans and their associated write-offs will cause a decline in these capital adequacy measures, and may precipitate increased regulation by bank authorities. Greater level of regulation generally entail additional costs for the bank. Currently, this regulation mainly takes the form of the Basel II Capital Accord that has been implemented on the worldwide basis since 2008. It is clear that bank profitability is a major indicator of financial crises for households, companies and financial institutions. An example of this from the 2007-2008 subprime mortgage crisis (SMC) is the U.S. bank, Wachovia Corp., who reported a big loss as from the first quarter of 2007 and eventually was bought by the world's largest bank, Citigroup, on 29 September 2008. A further example from the SMC is that both the failure of the Lehman Brothers investment bank and the acquisition in September 2008 of Merrill Lynch and Bear Stearns by Bank of America and JP Morgan Chase, respectively, were preceded by a decrease in profitability and an increase in the price of loans and loan losses. The subprime mortgage crisis is characterized by contracted liquidity in the global credit markets and banking system. The level of liquidity in the banking sector affects the ability of banks to meet commitments as they become due without incurring substantial losses from liquidating less liquid assets. Liquidity, therefore, provides the defensive cash or near-cash resources to cover banks' liability. An undervaluation of real risk in the subprime market is cascading, rippling and ultimately severely adversely affecting the world economy. The downturn in the U.S. housing market, risky lending and borrowing practices, and excessive individual and corporate debt levels have caused multiple adverse effects tumbled as the US housing market slumped. Banks worldwide are hoarding cash and showing a growing reluctance to lend, driving rates that institutions charge to each other on loans to record highs. Also, global money markets are inoperative, forcing increased injections of cash from central banks. The crisis has passed through various stages, exposing pervasive weaknesses in the global financial system and regulatory framework. The stochastic dynamics of the aforementioned banking items assist in formulating a maximization problem that involves endogenous variables such as profit consumption, the value of the bank's investment in loans and provisions for loan losses as control variants. In particular, we demonstrate that the bank is able to maximize its expected utility of discounted profit consumption over a random time interval, [t,r], and terminal profit at time r. Here the term profit consumption refers to the consumption of the bank's profits by dividend payments on equity and interest and principal payments on subordinate debt. The associated Hamilton-Jacobi-Bellman (HJB) equation has a smooth solution when the optimal controls are computed by means of power, logarithmic and exponential utility functions. This enables us to make a direct comparison between the economic properties of the solutions for different choices of the utility function. In keeping with the main theme of this thesis, we simulate the financial indices ROE and ROA that are two measures of bank profitability. We further discuss optimization with power utility where we show the convergence of the Markov Chain Approximation Method (MCAM) and the impact of varying the model parameters in the form of loan loss severity, P, and loan loss frequency, <f>. We investigate the connections between the banking models and Basel II capital accord as well as the current subprime mortgage crises. As a way of conclusion, we provide remarks about the main issues discussed in the thesis and speculate about future research directions. The contents of this thesis is based on 3 peer-reviewed journal articles (see [105], [106] and [107]) and 1 peer-reviewed conference proceedings paper (see [104]). In addition, the paper [108] is currently being prepared for submission to an accredited journal. / Thesis (Ph.D. (Applied Mathematics))--North-West University, Potchefstroom Campus, 2009.

Pulse-width modulation methods are widely used for the synthesis of ac voltages at the terminals of a voltage-sourced converter (VSC). Traditionally sinusoidal pulsewidth modulation (SPWM) has been used. A powerful alternative for this purpose is space-vector modulation (SVM), in which the converter is placed in a finite number of states in order to best approximate the reference voltage. This method offers better utilization of the dc bus voltage and provides several degrees of freedom for enhancement of the harmonic spectrum as well as switching losses. This thesis studies the SVM method for two- and three-level VSCs. A model for implementation of SVM in the electromagnetic transients simulation program PSCAD/EMTDC is developed. The model is able to generate firing pulses in linear as well as overmodulation range and is used to study the performance of different SVM strategies in terms of their harmonic spectra and associated converter and harmonic losses. The model is also used to demonstrate the suitability of the method for network applications. The thesis also employs genetic algorithms to find an optimized SVM sequence for improved harmonic performance. An objective function is defined that seeks to minimize the most significant harmonic components of the generated waveform, while keeping the other harmonic components within the acceptable range outlined in the available standards. The obtained sequence shows great improvement over the conventionally-used SVM sequence.

A topical issue in financial economics is the development of appropriate stochastic dynamic models for banking items and behavior. The issue here is to fulfil the need to generalize the more traditional discrete-time models of banking activity to a Levy process setting. In this thesis, under the assumption that the loan market is imperfectly competitive, we investigate the evolution of banking items such as bank assets (cash, bonds, shares, Treasuries, reserves, loans and intangible assets), liabilities (demand deposits) and bank capital (bank equity, subordinate debt and loan loss reserves). Here we consider the influence of macroeconomic factors and profitability as well as its indicators return on assets (ROA) and return on equity (ROE). As far as bank assets are concerned, we note that loan pricing models usually reflect the financial funding cost, risk premium to compensate for the risk of default by the borrower, a premium reflecting market power exercised by the bank and the sensitivity of the cost of capital raised to changes in loans extended. On the other hand, loan losses can be associated with an offsetting expense called the loan loss provision (LLP), which is charged against Nett profit. This offset will reduce reported income but has no impact on taxes, although when the assets are finally written off, a tax-deductible expense is created. An important factor influencing loan loss provisioning is regulation and supervision. Measures of capital adequacy are generally calculated using the book values of assets and equity. The provisioning of loans and their associated write-offs will cause a decline in these capital adequacy measures, and may precipitate increased regulation by bank authorities. Greater level of regulation generally entail additional costs for the bank. Currently, this regulation mainly takes the form of the Basel II Capital Accord that has been implemented on the worldwide basis since 2008. It is clear that bank profitability is a major indicator of financial crises for households, companies and financial institutions. An example of this from the 2007-2008 subprime mortgage crisis (SMC) is the U.S. bank, Wachovia Corp., who reported a big loss as from the first quarter of 2007 and eventually was bought by the world's largest bank, Citigroup, on 29 September 2008. A further example from the SMC is that both the failure of the Lehman Brothers investment bank and the acquisition in September 2008 of Merrill Lynch and Bear Stearns by Bank of America and JP Morgan Chase, respectively, were preceded by a decrease in profitability and an increase in the price of loans and loan losses. The subprime mortgage crisis is characterized by contracted liquidity in the global credit markets and banking system. The level of liquidity in the banking sector affects the ability of banks to meet commitments as they become due without incurring substantial losses from liquidating less liquid assets. Liquidity, therefore, provides the defensive cash or near-cash resources to cover banks' liability. An undervaluation of real risk in the subprime market is cascading, rippling and ultimately severely adversely affecting the world economy. The downturn in the U.S. housing market, risky lending and borrowing practices, and excessive individual and corporate debt levels have caused multiple adverse effects tumbled as the US housing market slumped. Banks worldwide are hoarding cash and showing a growing reluctance to lend, driving rates that institutions charge to each other on loans to record highs. Also, global money markets are inoperative, forcing increased injections of cash from central banks. The crisis has passed through various stages, exposing pervasive weaknesses in the global financial system and regulatory framework. The stochastic dynamics of the aforementioned banking items assist in formulating a maximization problem that involves endogenous variables such as profit consumption, the value of the bank's investment in loans and provisions for loan losses as control variants. In particular, we demonstrate that the bank is able to maximize its expected utility of discounted profit consumption over a random time interval, [t,r], and terminal profit at time r. Here the term profit consumption refers to the consumption of the bank's profits by dividend payments on equity and interest and principal payments on subordinate debt. The associated Hamilton-Jacobi-Bellman (HJB) equation has a smooth solution when the optimal controls are computed by means of power, logarithmic and exponential utility functions. This enables us to make a direct comparison between the economic properties of the solutions for different choices of the utility function. In keeping with the main theme of this thesis, we simulate the financial indices ROE and ROA that are two measures of bank profitability. We further discuss optimization with power utility where we show the convergence of the Markov Chain Approximation Method (MCAM) and the impact of varying the model parameters in the form of loan loss severity, P, and loan loss frequency, <f>. We investigate the connections between the banking models and Basel II capital accord as well as the current subprime mortgage crises. As a way of conclusion, we provide remarks about the main issues discussed in the thesis and speculate about future research directions. The contents of this thesis is based on 3 peer-reviewed journal articles (see [105], [106] and [107]) and 1 peer-reviewed conference proceedings paper (see [104]). In addition, the paper [108] is currently being prepared for submission to an accredited journal. / Thesis (Ph.D. (Applied Mathematics))--North-West University, Potchefstroom Campus, 2009.

No description available.

This thesis presents a method for optimizing cable configuration inside a large magnetic cylindrical steel casing, from the total ampacity point of view. The method is comprised of two main parts, namely: 1) analytically calculating the electromagnetic losses in the steel casing and sheathed cables, for an arbitrary cables configuration, and 2) implementing an algorithm for determining the optimal cables configuration to obtain the best total ampacity. The first part involves approximating the eddy current and hysteresis losses in the casing and cables. The calculation is based on the theory of images, which this thesis expands to apply to casings having both high magnetic permeability and high electric conductivity at the same time. The method of images, in combination with approximating the cable conductors and sheaths as multiple physical filaments, is used to compute the final current distributions in the cables and pipe and thus the associated losses. The accuracy of this computation is assessed against numerical solutions obtained using the Maxwell finite element program by Ansoft. Next, the optimal cable configuration is determined by applying a proposed two-level optimization algorithm. At the outer level, a combinatorial optimization based on a genetic algorithm explores the different possible configurations. The performance of every configuration is evaluated according to its total ampacity, which is calculated using a convex optimization algorithm. The convex optimization algorithm, which forms the inner level of the overall optimization procedure, is based on the barrier method. This proposed optimization procedure is tested for a duct bank installation containing twelve cables and fifteen ducts, comprising two circuits and two cables per phase, and compared with a brute force method of considering all possible configurations. The optimization process is also applied to an installation consisting of a single circuit inside a large magnetic steel casing.

The increasing penetration of distributed generation (DG) in power distribution systems presents technical and economic benefits as well as integration challenges to utility engineers. Governments are beginning to acknowledge DG as an economically viable alternative to deferring investment at generation, transmission and distribution levels, meeting demand growth and improving distribution network performance and security. DG technology is rapidly maturing in Ontario due to government economic incentives promoting connection, specifically, the Ontario’s Feed-In-Tariff (FIT) Program. Optimal sizing and siting of DG is well researched, traditionally studying the technical impact on distribution system such as real power loss reduction and voltage profile improvement. Equally common objectives studied are the economics of DG installation which are useful for the developer when deciding when and where to install. Although DG represents a “non-wires” solution to network asset reinforcement, the direct economic benefit to the host utility from promoting DG uptake is not fully understood by utility planners and asset managers. Some DG based asset reinforcement deferral work has been performed in the UK and Italy but is mainly at the transmission level and is not part of an overall strategy that could be applied by a utility. This research presents a comprehensive three stage technique: optimal siting, optimal sizing and financial evaluation of cost savings over a defined planning period to quantify the economic benefit to a Local Distribution Company (LDC) of solar photovoltaic (PV) DG connections on an actual distribution feeder. Optimal sites for PV DG are determined by applying the power loss sensitivity factor method to the test feeder. The objective functions used to determine cost savings consist of loss minimization, asset investment deferral, and peak demand reduction to identify an optimal DG penetration limit. Furthermore, a utility planner can identify an optimal DG penetration limit, encourage uptake at preferred locations that would benefit the LDC, and use the positive impact of DG at existing locations as part of an asset management strategy to prioritize and schedule future asset reinforcement upgrades.

ABSTRACT CALCULATION OF CORE LOSSES OF A 6-PHASE INDUCTION MOTOR WITH 3RD HARMONIC CURRENT INJECTION B&Uuml / Y&Uuml / KBAS, AfSin M.S., Department of Electrical and Electronics Engineering Supervisor: Prof. Dr. H. B&uuml / lent ERTAN January 2004, 106 pages The advantages of using a six-phase induction motor for industrial drives, over the conventional three-phase drive can be summarized as improved reliability, reduction on the power ratings for the static converters and harmonic reduction. A technique of injecting third harmonic zero sequence current components in the phase currents to improve the machine torque density was presented recently by another research study. However, to meaninigfully evaluate the performnce of such machines and/or to be able to make good designs / it is necessary to obtain an accurate mathematical model for the loss calculation. The calculation of high frequency loss in this context presents a very difficult problem. In this thesis a modified version of a loss calculation model, which was developed in another MS thesis will be applied to a six-phase induction motor with third harmonic current injection.

DC to DC step-down applications with high input voltage and high voltage conversion ratio operational requirements, such as photovoltaic battery chargers, are subject to high conduction losses, high switching losses and substantial reverse-recovery losses when minority carrier principle diodes are used. The recent introduction of silicon carbide diodes with high breakdown voltages has made possible the elimination of reverse-recovery losses at high voltage levels and as such has sparked interest in their use due to the potential efficiency improvements. This report presents the results of a comprehensive analysis on the use of silicon carbide diodes and their counterparts, ultrafast silicon diodes, in conventional buck converters and isolated current-fed buck converters in high input voltage and high voltage conversion ratio step-down applications. The analysis illustrates both theoretically, with the use of steady-state average models, and experimentally the substantial efficiency benefits of the use of reverse-recovery free silicon carbide diodes in the conventional buck converter and the small but significant improvement in the efficiency of the isolated current-fed buck converter. The improvements of the conventional buck converter paired with silicon carbide diodes are shown to be significant enough to grant the variant the most efficient position for power levels below 1 kW. In addition, the four variants are categorized based on their cost and performance; therefore, providing engineers with a convenient guide to aid their selection of the appropriate converter depending on the operational requirements.