published_or_final_version / abstract / Electrical and Electronic Engineering / Master / Master of Philosophy

published_or_final_version / Obstetrics and Gynaecology / Master / Master of Medical Sciences

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Ultrasonic wave field is modeled inside non-planar and inhomogeneous structures using a newly developed mesh-free semi-analytical technique called Distributed Point Source Method (DPSM). Wave field inside a corrugated plate which is a non-planar structure is modeled using DPSM when the structure is excited by a bounded acoustic beam generated by a finite-size transducer. The ultrasonic field is computed both inside the plate and in the surrounding fluid medium. It is observed that the reflected beam strength is weaker for the corrugated plate in comparison to that of the flat plate, as expected. Whereas the backward scattering is found to be stronger for the corrugated plate. DPSM generated results in the surrounding fluid medium are compared with the experimental results.Ultrasonic wave field is also modeled inside inhomogeneous structures. Two types of inhomogeneity are considered - a circular hole and a damaged layered half-space. Elastic wave scattering inside a half-space containing a circular hole is first modeled using DPSM when the structure is excited with a bounded acoustic beam. Then the ultrasonic wave field is computed in presence and absence of a defect in a layered half-space. For the layered problem geometry it is shown how the layer material influences the amount of energy that propagates through the layer and that penetrates into the solid half-space when the solid structure is struck by a bounded acoustic beam. It is also shown how the presence of a crack and the material properties of the layer material affect the ultrasonic fields inside the solid and fluid media.After solving the above problems in the frequency domain the DPSM technique is extended to produce the time domain results by the Fast Fourier Transform technique. Time histories are obtained for a bounded beam striking an elastic half-space. Numerical results are generated for normal and inclined incidences, for defect-free and cracked half-spaces. A number of useful information that is hidden in the steady state response can be obtained from the transient results.

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Student Number : 0420699F - MSc Dissertation - School of Physics - Faculty of Science / This dissertation presents for the first time the conditions for the synthesis of VO2 by ultrasonic nebula-spray pyrolysis (UNSP) from a precursor solution of NH4VO3+VCl3 optimized as follows: a carrier gas of argon at a flow rate of 11 liters per minute, a furnace temperature of 400 to 700oC. This work also incorporates thermodynamic variables of Tpr-P-V into the equations that relate the mean diameter of droplets, D, to frequency of the exciting ultrasound waves, f, the density of the precursor solution, #26; and the surface tension, #27;, previously worked on independently by Lang and Jokanovic. The incorporation results in the diameters of the droplets (and consequently the collected grains) being smaller as p and Tpr are increased in a non- linear form. The variable V, however, increases the diameter of the droplets as it is allowed to increase. This study shows the departures many authors find of the theory from experiment but it also shows that the departure does not lie in the equations but rather on post- synthesis and annealing effects. From X-ray diffraction, scanning electron microscopy (SEM) and Raman spectroscopy, this study shows that as furnace temperature is increased the morphology of the sample surfaces for both VO2 and WO3 transforms from amorphous to crystalline, from spherical grains to plate-like structures, with grain mean diameter increasing non-linearly in some cases and decreasing non-linearly in other cases confirming previous findings, the latter enjoying the majority vote. In Raman spectra of the as- obtained WO3, asymmetric broadening of the Raman peaks was observed in some samples and a phonon confinement model was employed in the size distribution prediction. These findings prompted the re- workout of the phonon confinement model. In this dissertation an equation has been derived based on the Faucet-Campbell equation of the PC model. The new equation relates the ratio of neighboring peaks in a material’s Raman spectrum to the mean diameter of the grains. The present modification allows the PCM model to predict the grain size beyond the current limiting range of 0 to 100 nm. Analysis of the experimental data using this equation unveils two different equations- one for particles of size below 100 nm and the other equation for particles with larger that 100 nm. Also this analysis has enabled the present study to evaluate the phonon dispersion relations for WO3.

Dissertation submitted in partial compliance with the requirements for the Master's Degree in Technology: Chiropractic, Technikon Natal, Durban, 1998. / The aim of this study was to determine the effectiveness of adjustments versus the use of ultrasound in the treatment of mechanical neck pain. It was hypothesized that treatment with adjustments over a four week period, with a further four week follow-up period, would be more effective than ultrasound in terms of improving patients' cervical ranges of motion and their perceptions of pain and disability. Thirty consecutive patients suffering from mechanical neck pain were randomly assigned to either the adjustment or ultrasound groups. An experimental design was employed, whereby both groups received treatment twice a week for four weeks. After a follow-up period of a month, the patients were re-assessed. Measurements of the cervical spine ranges of motion with the CROM goniometer, algometer readings, and the completion of the Numerical Pain Rating Scale-101, CMCC Neck Disability Index and the Short Form McGill Pain questionnaires were performed before the first, fourth and final treatments as well as at the one month follow-up consultation. The data were then transferred to spreadsheets and underwent statistical analyses, using a 95 % confidence level. Analyses within each group were performed, using the Wilcoxon Signed Rank test and various readings were compared. The reading taken before the first treatment was compared to the reading taken before the final treatment. The initial reading was then again compared with the reading taken at the one month follow-up consultation. Comparison of the results of both treatment groups was statistically evaluated, using the Mann-Whitney U-Test. The comparison was made using the readings of the first, fourth and final treatments, as well as the one month follow-up consultation. This was done for all measurement parameters. / M

Low-frequency ultrasonic energy was utilized in an attempt to induce visible mutations in the parasitoid wasp Mormoniella vitripennis. This study demonstrates that low frequency ultrasound may be used as an effective mutagenic agent in this organism, and suggests that it may have applications to other genetic systems.