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Acoustics is the study of all sound waves, with ultrasound classified as those frequencies above 20,000 Hz. Currently, ultrasound is being used in many industries for a variety of purposes such as ultrasonic imaging, ultrasonic assisted friction stir welding, and ultrasonic spot welding. Despite these uses, the effects of ultrasound on phase stability and resultant mechanical properties has been minimally analyzed. Here we study the impact waves play in ultrasonic welding and design an apparatus to maximize waves entering aluminum alloy samples. Aluminum 2139 and 7050 are used because they are precipitation strengthened by metastable phases so temperature change, and the corresponding phase stability, can greatly impact their strength. Results suggest that the ultrasonic welder primarily imposes a localized temperature spike due to friction, averaging over 200°C in a few seconds, which generally lowers the Vickers hardness due to coarsening or even dissolution of strengthening precipitates. Conversely, the new design increases the Vickers hardness by up to 30% over the initial hardness of approximately 63HV for aluminum 2139 and 83HV for aluminum 7050, respectively, while only increasing the temperature by an average of approximately 10°C. This new design was unable to achieve peak hardness, but the strengthening it achieved in two minutes was equivalent to one month of natural aging. If this system was able to be fine-tuned, it could serve as a quick strengthening process for recently weakened aluminum alloys, such as after friction stir welding.

Master of Science / Department of Psychological Sciences / Mary Cain / Novelty-seeking and sensation-seeking are traits implicated in initial drug experimentation and relapse in human populations. To research the neurobiological substrates that are implicated in novelty/sensation-seeking that predispose an individual to drug use, a rodent model was used. Recently, 50 kHz ultrasonic vocalizations (USV) have been identified as indices of affective state and are evoked by several drugs of abuse, specifically when these drugs of abuse have their pharmacological effects in the mesolimbic dopamine path. Secondly, genetic breeding of high and low vocalizers suggests not only are they different in the calling frequency, but also to drug sensitivity, suggesting ultrasonic vocalizations may be a behavioral marker for individual differences in the mesolimbic dopamine circuit. Two sensation/novelty seeking screens and an ultrasonic vocalization screen were used in rats to predict the locomotor and 50 kHz USV response to a low (.3 mg/kg) and high dose (1.0 mg/kg) of amphetamine. Correlation analysis revealed none of the novelty screens were correlated. Simultaneous regression analyses indicated amphetamine dose-dependently increased locomotor activity acutely and chronically but did not increase 50 kHz USV. The USV assessment predicted USV response to amphetamine acutely and chronically but was not dose dependent. No interactions among any predictors were observed. Previous research has dichotomized the novelty/sensation-seeking trait and found significant differences between high and low novelty responders. The current research provides evidence for maintaining continuous individual difference variables, and suggests each screen measures a different trait implicated in addiction.

Call number: LD2668 .T4 1966 M648 / Master of Science

Dissertation submitted in partial compliance with the requirements for the Master’s Degree in Technology: Chiropractic Durban University of Technology, 2009 / Aim: To investigate the effect of therapeutic and sham ultrasound on radial artery blood flow (m.s-1) and radial arterial lumen diameter (mm). Subjects: Fifty healthy asymptomatic volunteers between the ages of 18-38 years. Methodology: The subjects were randomly allocated into one of five intervention groups (A-E). Group A received continuous ultrasound at 0.2 W.cm-² for 5 minutes, Group B received pulse ultrasound at 0.2 W.cm-² for 5 minutes, Group C received continuous ultrasound at 1.5 W.cm-² for 5 minutes, Group D received pulse ultrasound at 1.5 W.cm-² for 5 minutes and Group E received sham ultrasound at 0 W.cm-² for 5 minutes. Baseline radial artery blood flow (m.s-1) and radial artery lumen diameter (mm) readings were taken prior to the commencement of the therapeutic or sham ultrasound application using a Doppler ultrasound. At four minutes of application (during the therapeutic or sham ultrasound application), another set of blood flow and arterial lumen diameter measurements were taken. The final blood flow and arterial lumen diameter measurements were taken one minute after the therapeutic or sham ultrasound application was stopped. Results: The mean (± SD) radial artery blood flow and radial artery lumen diameter at baseline was 0.197 (± 0.060) m.s-1 and 2.4 (± 0.6) mm respectively. In Group A, the mean (± SD) radial artery blood flow during ultrasound application and one-minute after ultrasound application was 0.193 (± 0.070) m.s-1 and 0.179 (± 0.073) m.s-1 respectively. The mean (± SD) radial artery lumen diameter in Group A at the two time intervals was 2.2 (± 0.5) mm and 2.2 (± 0.3) mm respectively. In Group B, the mean (± SD) radial artery blood flow during ultrasound application and one-minute after ultrasound application was 0.187 (± 0.067) m.s-1 and 0.195 (± 0.041) m.s-1 respectively. The mean (± SD) radial artery lumen diameter in Group B at the two time intervals was 2.4 (± 0.4) mm and 2.3 (± 0.5) mm respectively. In Group C, the mean (± SD) radial artery blood flow during ultrasound application and one-minute after ultrasound application was 0.225 (± 0.088) m.s-1 and 0.186 (± 0.071) m.s-1 respectively. The mean (± SD) radial artery lumen diameter in Group C at the two time intervals was 2.4 (± 0.7) mm and 2.7 (± 0.8) mm respectively. In Group D, the mean (± SD) radial artery blood flow during ultrasound application and one-minute after ultrasound application was 0.215 (± 0.080) m.s-1 and 0.200 (± 0.081) m.s-1 respectively. The mean (± SD) radial artery lumen diameter in Group iv D at the two time intervals was 2.4 (± 0.8) mm and 2.4 (± 0.7) mm respectively. In Group E, the mean (± SD) radial artery blood flow during ultrasound application and one-minute after ultrasound application was 0.200 (± 0.067) m.s-1 and 0.182 (± 0.075) m.s-1 respectively. The mean (± SD) radial artery lumen diameter in Group E at the two time intervals was 2.5 (± 0.7) mm and 2.3 (± 0.5) mm respectively. There was no significant change in radial artery blood flow and radial artery lumen diameter over time in any individual group or between groups (p > 0.05; repeated measures ANOVA). There was an overall weak positive correlation between radial artery blood flow and radial artery lumen diameter at baseline (r = 0.508), during (r = 0.541) and after (r = 0.532) the therapeutic or sham ultrasound application. Conclusion: The results of this study showed that continuous, pulse or sham ultrasound had no significant effect on radial artery blood flow and radial artery lumen diameter. Furthermore, active ultrasound (continuous and pulse) was not superior to sham ultrasound in significantly affecting blood flow in a muscular artery.

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The objective of this thesis is to present analysis techniques that quantify the scattering of angle-beam ultrasonic waves from through-holes in plates. This topic is of interest because increased understanding of the scattering of ultrasonic waves by a defect is important for the development of many nondestructive evaluation (NDE) applications. Angle-beam techniques are commonly used in industry to detect and characterize defects, and many structures of concern have plate-like components. Scattering from through-holes is particularly important because cracks tend to form around fastener holes, which have high stress concentrations. In addition, varying boundary conditions within a fastener hole can change over the course of a structure’s lifetime and may have significant effects on NDE results. In this research, two signal processing techniques are developed to obtain scattering information from through-holes for a variety of fill conditions, including epoxy and complete and partial filling with metal inserts, using experimentally acquired wavefield measurements. Experimental procedures for acquiring wavefields, which measure the out of plane motion of ultrasonic waves on the surface of a specimen and allow for the visualization and characterization of propagating waves, are presented. Methods for obtaining radial and directional energy maps, which quantify scattering as a function of scattered angle and phase velocity, are described. In addition, baseline subtraction is used to obtain scattering patterns for both methods, which quantify scattering as a function of polar angle for each wave mode present in the wavefield. These techniques are applied to wavefield measurements from through-holes with various fill conditions to investigate the effects of boundary conditions on ultrasonic scattering. A comparison of the radial and directional energy mapping techniques, discussing the strengths and weaknesses of each approach, is provided, and recommendations are made for future work.

published_or_final_version / abstract / Obstetrics and Gynaecology / Doctoral / Doctor of Philosophy