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The phenomenon of the increase in alpha EEG activity associated with eye closure has been shown to be successful for implementing environmental control for disabled persons. Studies in this thesis investigate strategies which improve the reliability, robustness, and ease of use of alpha EEG control systems. Primarily, research covers the effectiveness of alpha EEG detection algorithms (with regard to detection time and susceptibility to artifact) and the construction and use of EEG sensing electrodes. Many new techniques for the detection of the increase of alpha EEG associated with eye closure are researched, developed, implemented and evaluated. All detection techniques are compared to a conventional method using a novel performance parameterisation criterion. In conjunction with the application of the same EEG data sets to all techniques, the use of the performance criteria enables a fair and quantitative comparison to be made between alpha detection methodologies. Detection techniques employed include enhanced versions of conventional methods, localisation of apparent alpha sources in the brain, and preprocessing methods (such as spatial filtering, adaptive filtering and independent component analysis). The best performance of alpha EEG detection was given by the source power alpha localisation technique, which showed statistically significant and practically important improvements in performance over conventional techniques. Additionally, this localisation technique is convenient and fast to implement. In situations in which electrodes are intended for unsupervised use with environmental control systems, the evaluation of alternative electrode types to the conventional wet electrodes is required, as the use of wet electrodes has several drawbacks. The performance of wet, dry and insulating electrodes is compared in this research. One aspect of the quantitative comparison of electrodes types is the measurement of contact impedance. To enable the fast and accurate measurement of impedance spectra, a new impedance spectroscopy system was developed as part of this thesis. In addition to comparison of impedance criteria, electrodes were evaluated in the presence movement-based, and electric field induced, artifacts. The electrode comparisons were carried out in a direct and quantitative manner in a controlled test environment for the first time. Results indicate that, in contrast to earlier reports, both dry and insulating electrode perform well with respect to artifact and offer a viable alternative to wet electrodes for long-term monitoring of biosignals from the surface of the skin. More improvements are required before such electrodes are suitable for EEG usage.

Copies of previously published articles inserted. Bibliography: p. 185-200. Data obtained from six radar stations covering a wide latitude range has been used to determine the global distribution of planetary waves and tides. In the process a number of data analyses techniques were considered for their characterisation.

Typescript. Bibliography: leaves 145-150.

The tomographic reconstruction of hypersonic flows faces two challenges. Firstly, techniques used in the past, such as the Direct Fourier Method (DFM) or various backprojection techniques, have only been able to reconstruct areas of the flow which are upstream of any opaque objects, such as a model. Secondly, shock waves create sharp discontinuities in flow properties, which can be difficult to reconstruct both in position and in magnitude. This thesis will present a reconstruction method, utilising geometric ray-tracing and a sparse matrix iterative solver, which is capable of overcoming both of these challenges. It will be shown, through testing with phantom objects described in imaging and tomographic literature, that the results are comparable to those produced by the DFM technique. Finally, the method will be used to reconstruct three dimensional density fields from interferometric shock tunnel images, with good resolution.

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Typescript / 141 leaves : ill., appendix in end pocket / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Experimental determination of the dispersion of Rayleigh waves across Australia has provided information about the earth's crust in this region. This technique is particularly useful in Australia, where in many areas the low level of natural seismicity prohibits the use of more conventional methods of investigation of the crust. / Thesis (Ph.D.)--University of Adelaide, Dept. of Physics, 1967

The current work is devoted to the problem of sound wave scattering by elastic cylindrical objects in a plain acoustic waveguide. The Multi- Modal Integral Method (MMIM) is proposed, which is based on nonstandard representation of the Green's function. It combines advantages of integral equation and eigenfunction methods and provides a quickly converging and highly accurate solution, taking into account all the waveguide modes up to infinite order. As illustrations of application of this method, acoustic diffraction is calculated from a system of several parallel homogeneous cylinders and from an air-filled cylindrical elastic shell. Numerical solutions are found for various versions of the system of elastic cylinders in a fluid layer with perfectly soft and rigid boundaries. Phase - frequency and amplitude - frequency characteristics are found for modal coefficients of the scattered field. Sharp increase of their amplitudes is found near resonance frequencies of the waveguide and the scattering cylinders. Pictures of the source density on the surface of the cylinders show that the nature of their distribution strongly depends on the frequency and the mutual location of the cylinders in the waveguide. Field structure near the cylinders reveals that higher-order waveguide modes play a significant role in the scattering process. Spatial distribution of the acoustic power flow near the scattering object is calculated for several frequencies and two sets of elastic properties of the cylinder. It is shown that at the critical frequencies of the waveguide as well as at the internal resonances of the cylinder the acoustic energy flows in closed paths in some regions of the waveguide. Near the internal resonances of the cylinder the closed paths are located in the near vicinity of the scattering object and partially go through its interior. It is suggested that re-radiation of the energy stored in the vortices may contribute to the echo phenomenon. The integral reflection coefficient is calculated for a system waveguide/shell for different values of wall thickness and distance between the shell and the waveguide bottom. Maxima and minima in the reflection coefficient associated with cut-on frequencies of the waveguide modes and structural resonances of the shell are identified. The calculations show that the conventional definition of target strength in a shallow waveguide is inappropriate. Different kinds of resonances are identified in frequency and angular dependencies of the velocity amplitude of the shell surface. These resonances belong to the following groups: a) critical frequencies of the waveguide modes, b) structural resonances of the elastic shell, c) resonance oscillations of the gas-filled interior of the shell, d) resonance oscillations of the coupled fluid-shell. Application of the Multi-Modal Integral Method (MMIM) to Sound Wave Scattering in an Acoustic Waveguide. Temporal sequences of pictures showing the spatial structure of the total and scattered fields in the near and far field zones are obtained. It is shown that the incident field produces waves of acoustic pressure propagating along the boundary of the scattering object, which, in turn, generate the scattered acoustic field. In the process of propagation, the waves may interact with each other via the fluid or the scattering object. This leads to significant changes of the structure of the acoustic field and of the amount of acoustic energy reflected from the scatterer. It is also shown that, in most cases, standing waves exist between the scatterer and the waveguide boundaries. Accuracy of the Multi-Modal Integral Method is discussed. It is shown that the implementation of the method requires few computer resources for good accuracy of the solution. / Thesis (Ph.D.)--School of Mechanical Engineering, 1999.