Engineering

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  • Image retrieval using colour features
    (1996) Seo, Jeng Won
    Thesis
    With the significant outgrowth of hardware technology, the amount of pictorial information has increased remarkably. Due to this increase in image data, the need for an efficient indexing technology arises. In earlier retrieval systems, images are described using plain text and retrieval is based on the text description using conventional information retrieval techniques. These systems are good for retrieval abstract concepts captured in images. However, it suffers the problem of subjectiveness and manual entry of text description. To overcome these limitations content-based retrieval techniques using image features have been proposed. The main features used for image retrieval are shape, texture and colour. The purpose of our work is to develop an efficient content-based retrieval technique based on colour. Researchs on colour feature have shown very successful results. However, these techniques have been applied to the overall image content. The processing time for extracting colour features is another problem. In this paper, we propose three extensions to the basic colour histogram matching technique: (a) the use of hue value of HSI colour space; (b) the use of segmentation for object level; and (c) the use of clustering.
  • The effects of ionising radiation on implantable MOS electronic devices
    (1997) Bradley, Peter
    Thesis
    Space exploration and the rapid growth of the satellite communications industry has promoted substantial research into the effects of ionising radiation on modem electronic technology. The enabling electronics and computer processing has seen a commensurate growth in the use of radiation for diagnostic and therapeutic purposes in medicine. Numerous studies exist in both these fields but an analysis combining the fields of study to ascertain the effects of radiation on medically implantable electronics is lacking. A review of significant ground level radiation sources is presented with particular emphasis on the medical environment. Mechanisms of permanent and transient ionising radiation damage to Metal Oxide Semiconductors are summarised. Three significant sources of radiation are classified as having the ability to damage or alter the behavior of implantable electronics; Secondary neutron cosmic radiation, alpha particle radiation from the device packaging and therapeutic doses of high energy radiation. With respect to cosmic radiation, the most sensitive circuit structure within a typical microcomputer architecture is the Random Access Memory(RAM). A theoretical model which predicts the susceptibility of a RAM cell to single event upsets from secondary cosmic ray neutrons is presented. A previously unreported method for calculating the collection efficiency term in the upset model has been derived along with an extension of the model to enable estimation of multiple bit upset rates. An Implantable Cardioverter Defibrillator is used as a case example to demonstrate model applicability and test against clinical experience. The model correlates well with clinical experience and is consistent with the expected geographical variations of the secondary cosmic ray neutron flux. This is the first clinical data set obtained indicating the effects of cosmic radiation on implantable devices. Importantly, it may be used to predict the susceptibility of future implantable device designs to cosmic radiation. The model is also used as a basis for developing radiation hardened circuit techniques and system design. A review of methods to radiation harden electronics to single event upsets is used to recommend methods applicable to the low power/small area constraints of implantable systems.
  • Risk averse operation of an electricity plant in an electricity market
    (1995) Ranatunga, R. A. Shantha Kumara
    Thesis
    New methods are required to make optimal operation decisions for electricity generating and consuming plants in market-based electricity industries. Since wholesale electricity is traded on a spot price basis, both generators and consumers face uncertainty in their future income. Operating plants with inter-temporal links are particularly difficult since operation decisions at one instant affect the available operation decisions after that, and hence affect future income. Operation decision making with a risk-averse attitude is a method to handle uncertainty, however, some form of financial instruments, such as forward contracts, are required to allocate risk. Since electricity markets operate on a discrete time basis, a multi-stage decision making method is required to operate an electricity plant with inter-temporal links. Although risk-averse decision making has been used in other contexts, few attempts have been made to use these techniques for multi-stage problems. In this thesis, a new multi-stage risk-averse decision making algorithm is proposed and applied to make operation and forward contract trading decisions for a plant in an electricity market. In the proposed algorithm, risk aversion is incorporated in sequential decision making using the expected utility method with a von Neumann-Morgenstern utility function. Decisions are taken to maximise the utility of total financial income. Since utility functions have a concave shape, the marginal utility of income diminishes with increased income, giving risk aversion. A solution structure similar to dynamic programming is proposed for the risk management algorithm by introducing a state variable to represent past behaviour. The proposed algorithm is applied to make decisions for electricity plant and market models. Simulation results for different plant models show a clear reduction in financial risk when compared with risk-neutral operation. Any reduction in risk is shown to be sensitive to the decision maker s attitude toward risk used in the algorithm. Simulation results suggest that forward contracts play a major role in minimising risk when starting plants with high start up costs. Forward contracts ensure financial security even under unfavourable market conditions. It is shown that, plants employing a risk-averse attitude which do not commit to start, do so after securing their future financial position using forward contracts. In general, the proposed risk management algorithm shows potential for use in electricity markets.