Certain surface-active media can considerably influence the flow and fracture properties of the .solids they wet. The effects of various lubricating media on the sliding friction behaviour of diamond on soda-lime glass were studied in the present research. An experimental apparatus was constructed to slide a hemispherical diamond linearly and at constant speed across the surface of a Corning type 2947 soda-lime glass microslide and to measure the resultant friction force. Tests were conducted in a variety of liquid and gaseous media at sliding speeds ranging from 0.001 cm/sec to 0.4 cm/sec. As a base for comparison initial tests were conducted in a high vacuum — 8 at 4 x 10 ⁻⁸. The results showed that all the media enhanced material displacement from that observed in high vacuum. In addition, the friction force was observed to rise with displaced material. A simple theory was used to predict with reasonable agreement the results obtained in in vacuum and air only. The greatest increase in displaced material was observed in heptyl alcohol. Scanning electron micrographs of the friction tracks suggest that heptyl; alcohol softened the surface of the glass. This is in agreement with previous work. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

A feedback technique is presented for the reduction of the Shoenberg magnetic interaction in metals. The method allows the spin splitting parameter g[sub c] for extremal orbits on the Fermi surface to be obtained from de Haas-van Alphen measurements, now essentially free from the oft-times severe distortions resulting from magnetic interaction. The feedback technique also offers several advantageous side effects, the most important one being a simple and reliable method for determining absolute amplitudes of de Haas-van Alphen oscillations. Explicit formulae are derived showing the dependence of several key observable quantities on the amount of magnetic feedback, and these formulae are found to be in good agreement with experiment. The technique is applied to the determination of g[sub c] for the [110] γ oscillations in Pb. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Millimeter wave (mmWave) radar systems are a leading technology in autonomous vehicle object sensing. The radar’s ability to detect surrounding objects is critical to its performance. One method of increasing object detection performance is to enhance object visibility. Frequency selective reflectors can increase object visibility. This work examines the performance of a mmWave 77 GHz radar system developed by Texas Instruments in conjunction with frequency selective surfaces. Two bandpass frequency selective surfaces are designed and fabricated using a loaded cross aperture configuration to analyze their application to object detection. The chosen design frequencies are 8 GHz and 79 GHz. The frequency selective surfaces are designed and simulated in 3-D electromagnetic simulation software, High Frequency Structure Simulator (HFSS). The frequency selective surfaces are fabricated on 127μm thick FR4 dielectric. The 8 GHz frequency selective surface demonstrates bandpass center frequency at 8.12 GHz. The 8 GHz and 79 GHz frequency selective surface reflection characteristics are compared to a copper sheets with the same physical cross section as each respective design. Although different testing methodology is used for each design, both frequency selective surfaces demonstrate bandpass characteristics at their respective design frequencies.

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In order to study the detailed spectral intensity distribution of light reflected from a solid-gas interface, the extinction theorem in optics is extended to include an absorbing medium and the thermal motion of the gas molecules near the interface. The theoretical spectral intensity distribution in the region of anomalous dispersion is found to be strongly modified compared to that predicted by existing theory. An important consequence of this theory in the line shapes of the reflected light is the possibility of using recently developed saturation spectroscopic techniques to study atoms and molecules near surfaces. In order to investigate the feasibility of these new techniques for obtaining solid-gas molecule interaction potentials, models of solid-gas interfaces were studied with and without interactions of the type 1/zP (p = 2,3,4), where z is the distance between gas molecules and solid surface. A marked difference in the line shapes of the reflected light among the possible interactions suggests that the forms of interaction at the interface can be measured using known techniques. Furthermore, the possibility of measuring the flow of gas near walls where currently available laser-Doppler anemometers can not spatially reach is investigated. It is shown that the shift and width of the numerically calculated line shape of the reflected light in our model flow is directly related to the mean and the fluctuating velocity fields respectively.

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The adsorption of fibrinogen from human plasma onto various surfaces was investigated under differing conditions of plasma composition. Previous studies by Vroman have indicated that fibrinogen is only transiently adsorbed from normal human blood plasma, possibly due to displacement by high molecular weight kininogen (HMWK). It is possible that this "Vroman Effect" is a manifestation of the activation of the intrinsic clotting pathway responsible, in part, for thrombus formation on artificial surfaces. The effect was studied using dilutions of human plasma from 0.01% to 20.0% of normal concentration trace-labelled with a small amount of ¹²⁵I labelled fibrinogen. Adsorption of fibrinogen to various materials, including glass and several potentially useful biomaterials was measured. Fibrinogen is initially adsorbed apparently under diffusion limitation and later displaced at a rate which depends on the type of material being tested. There does not appear to be a direct relationship between material properties (contact angle, biocompatibility) and the "Vroman Effect". Studies comparing the effect for a series of clotting factor deficient plasmas seem to indicate that plasminogen and HWNK are the main displacing agents on glass. Factors XI and XII, prekallikrein and other components do not appear to be involved. An attempt to mathematically model the effect was hampered by the lack of adequate models to describe even one-component protein adsorption. An isotherm equation was developed based on a theoretical model of protein exchange and spreading on the surface. The resulting parameter estimates based on data for different surfaces were well conditioned and may provide a good in vitro basis for comparing materials. It is hoped that the theoretical model will also be compatible with dynamic adsorption and ultimately a multicomponent system such as plasma (and the Vroman Effect). This work may lead to a better understanding of blood-material interactions and may provide the basis for a simple in vitro test for the characterization of potential biomaterials. / Thesis / Master of Engineering (ME)

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