Thesis (M.S.)--Mechanical Engineering, Georgia Institute of Technology, 2005. / Jiri Janata, Committee Member ; Shreyes Melkote, Committee Member ; Steven Danyluk, Committee Chair. Includes bibliographical references.

The properties of muonium(μ⁺e⁻) and positronium(e⁺e⁻) are altered significantly in the presence of matter. The study of these exotic H-like atoms provides a unique perspective on atomic interactions with atoms, surfaces, and solids. This theme is explored in a variety of hosts. The cross section for spin 1 positronium to be converted to spin 0 positronium during collisions with O₂ molecules has been measured from 120 °K to 630 °K in an SiO₂ powder moderator using a positron lifetime technique. The results indicate that positronium does not thermalize in the powder below 450 °K. The spin conversion cross section increases slightly with temperature above 450 °K. A theory for spin conversion of positronium by a spin 1 molecule is developed and used to interpret the data. Muon Spin Rotation measurements, in SiO₂, Al₂O₃, and MgO powders at low temperature in an atmosphere of He indicate that muonium emerges from the surfaces regardless of the ambient temperature of the powder. The muonium spin relaxation rate in Al203 in a He(or Ne) atmosphere is found to be a linear function of the fraction of surface area not covered by adsorbed He(or Ne). The cross sections for muonium to scatter elastically off adsorbed He and Ne atoms have been measured to be 11.0±0.2 Ų and 8.9±0.2 Ų, respectively. The first observations of muonium in the condensed phases of Ar, Kr, and Xe are presented. The data indicate that there is a high probability of muonium formation in all cases. The spin relaxation rate of muonium in solid Xe is ten times that in the liquid, where the random local fields from the nuclear moments of ¹³⁹Xe and ¹⁴¹e are averaged by additional translational motion. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Conventional imaging techniques for cancer detection have difficulty finding small, deep tumors. Single-detector radiation probes have been developed to search for deep lesions in a patient who has been given a tumor-seeking radiopharmaceutical. These probes perform poorly, however, when the background activity in the patient varies greatly from site to site. We have developed a surgical dual-detector probe that solves the problem of background activity variation, by simultaneously monitoring counts from a region of interest and counts from adjacent normal tissue. A comparison of counts from the detectors can reveal the class of tissue, tumor or normal, in the region of interest. In this dissertation we apply methods from statistical decision theory and derive a suitable comparison of counts to help us decide whether a tumor is present in the region of interest. We use the Hotelling trace criterion with a few assumptions to find a linear discriminant function, which can be reduced to a normalized subtraction of the counts for large background count-rate variations. If area under the ROC curve is our figure of merit, the likelihood ratio is the optimum discriminant. We model likelihood functions of the data given the "tumor" and "no-tumor" hypotheses, and calculate the likelihood ratio. Using a spatial response map of the dual probe, a computer torso phantom, and estimates of activity distribution, we simulate a surgical staging procedure to test the dual probe and the discriminant functions. Results of the simulations show that the dual probe effectively solves the problem of background activity variations when used with any of the discriminant functions derived in this dissertation.

Thesis. 1977. Sc.D.--Massachusetts Institute of Technology. Dept. of Materials Science and Engineering. / MICROFICHE COPY AVAILABLE IN ARCHIES AND SCIENCE. / Vita. / Includes bibliographical references. / Sc.D.

Acquiring the motions of the inner ear sensory tissues provides insight to how the cochlea works. For this purpose, Spectral Domain Optical Coherence Tomography (SDOCT) is an ideal tool as it has a penetration depth of several millimeters. SDOCT can not only image inside the cochlear partition, but also measure the sample structures’ simultaneous displacements. We customized a commercial Spectral Domain Optical Coherence Tomography system for such functions and detailed the software and hardware steps so this powerful system could be more accessible to auditory researchers. The cochlea is surrounded by bones and tissues, and damage to it would make it passive. For this reason, cochlear vibrometry measuring locations have been limited to either the basal or apical regions. That is why I fabricated a two-dimensional scanning SDOCT-based probe, to access more cochlear locations through a small hand-drilled hole. What is exciting about the probe is that an electrode can be attached to its side to acquire spatially and temporally coincident voltage and displacement data. This would help us better understand the cochlear mechano-electrical feedback process. Lastly, I investigated how the SDPM-reported displacement could be influenced by its neighboring signals and demonstrated this signal competition phenomenon experimentally and theoretically.

This study addresses the development of a sensor to monitor chemical adsorption and charge transfer processes on a surface using a contact potential difference probe (CPD). The current investigation is an outgrowth of ongoing research on non-vibrating CPD probes (nvCPD) which led to the recent development of a novel measurement technique utilizing optical stimulation: optically stimulated CPD (osCPD). Primary outcomes of this thesis are the theoretical modeling, fabrication and demonstration of a functional osCPD sensor. The research also involved significant engineering and experimentation in the design, development, and application of this sensor to oil condition monitoring. This technique measures dielectric and chemical properties of a fluid at the interface between the fluid and a semiconductor substrate. Chopped visible light is used to stimulate the rear surface of a semiconductor substrate, and a CPD probe measures the work function response of the semiconductor on the front surface of the substrate. The work function response is influenced by the nature and quantity of adsorbed species on the top surface, allowing the probe to detect changes in chemical composition at the substrate/fluid interface. An analytical model is developed that relates the osCPD sensor output signal to the chemical and dielectric properties of the oil sample, as well as to the geometry, composition, and control inputs of the silicon substrate and test fixture. In this investigation, the osCPD sensor was used to evaluate dielectric and chemical properties of commercially available engine oil. Oil samples were intentionally degraded through thermal aging (oxidation) and through addition of known contaminants. The osCPD sensor shows good sensitivity to depletion of antioxidants in the oil, as well as to the presence of ferric chloride, an oil-soluble salt typically used to calibrate laboratory test equipment.

This thesis addresses the use of a vibrating Kelvin probe to monitor the change in the front surface potential of a silicon wafer while the rear surface is illuminated with monochromatic, visible light. Two tests were run to verify the change in surface potential. One test increased the intensity of the light and the other increased the wavelength while recording the front surface potential. The change in the surface potential for a range of intensities of incident light was recorded and analyzed. The results show that the change in surface potential increased with increasing intensity. For each wafer, the smallest change in surface potential occurred at the lowest intensity, 3.77 mW. In the same respect, the largest change in surface potential occurred at the highest intensity, 17.8 mW. For all wafers, the change in surface potential ranged from approximately 8 mV at 3.77 mW to approximately 80 mV at 17.8 mW. The change in the surface potential for a range of wavelengths of incident light was also recorded and analyzed. The results showed that the change in surface potential formed a skewed bell curve with increasing wavelength of incident light. For each wafer, the largest change in surface potential occurred at mid-range wavelengths, between 600 nm and 700 nm. The smallest change in surface potential occurred at 450 nm, the shortest wavelength, and 800 nm, the longest wavelength. For all wafers, the change in surface potential ranged from approximately 8 mV at 800 nm to approximately 165 mV at 700 nm. A model based on excess electron diffusion within the silicon wafer was used to predict material properties. After curve fitting the model with experimental results, an excess electron lifetime of ôN = 17 µs and surface recombination rates of sFRONT = sREAR = 18,000cm/s were predicted. These values suggest poor silicon wafer quality relative to commercial silicon devices. Regardless of the quality, the results show that the front surface potential of a silicon wafer is affected by incident light on the rear surface. The quantitative effect of the light is dependent on the properties of the light and the material properties of the silicon wafer.

No description available.

This PhD thesis describes the design and development of a new resonator based tactile sensitive probe. This new sensor was proposed because of the increasing need for high-sensitivity, high-speed touch-sensitive probes in coordinate metrology due to the ever-growing demand for precision and reliability at sub-micron level accuracy. Extensive background research on the current development of touch trigger probes has shown that designs based on the resonator principle have potential for minimising lobing effects and the false triggering associated with most commercially available probes. Resonant based sensors have been investigated over many decades and used very successfully in a wide range of applications. However their commercial exploitation in the field of precision engineering has not been particularly successful. One reason for such slow progress is the complexity of the interaction between oscillatory probes and typical engineering surfaces in less than ideal environments. The main aim of this research was to design a high precision resonator based tactile sensitive probe and to investigate the causes of parametric changes on resonant touch sensors both before and during contact with a variety of engineering surfaces in order to achieve a better understanding of contact mechanisms. The four main objectives were: preliminary design and characterisation of a resonator based touch sensor; development of the mathematical model which predicts parametric changes on a resonant probe considering both near surface effects and mechanical contact; experimental verification of mathematical predictions; and an investigation into possible commercial exploitation of the new probe in precision applications. A novel resonator based tactile sensor that utilises the piezoelectric effect was designed and characterised. The design exploits the fact that when a stiff element (probe) oscillating near or at its resonance frequency comes into contact with the surface of another body (workpiece), the frequency of vibrational resonance of the probe changes depending on the properties of the workpiece. The phase-locked loop frequency detection technique was employed to track changes in frequency as well as in the phase of the resonant system. The initial characterisation of the touch sensor has shown a sensitivity to contact of less then 4 mN, a high triggering rate and good repeatability. The potential for application in measuring material properties was also demonstrated. As a result of the characterisation a comprehensive mathematical model was developed. This novel model was based on Hertzian contact mechanics, Rayleigh's approximate energy method and work carried out by Smith and Chetwynd on the analysis of elastic contact of a sphere on a flat. The model predicts that phase and frequency shift of a resonator based sensor can either increase or decrease depending on the dominant phenomena (added mass, stiffness and damping) in the contact region. Observation of dynamic characteristics at either side of the resonant frequency can be used to identify the predominant effect. In order to confirm the model experimentally, another prototype probe was developed. The new sensor was engaged in observations of contact mechanisms with engineering surfaces. The experimental results have showed favourable agreement with the developed mathematical model. This enabled a better understanding of contact phenomena uncovering possibilities for the application of resonant sensors in many other areas. The research has shown that the new probe has potential in contact measurements where it can be used for the quantitative assessment of the physical properties of different materials (modulus of elasticity, density and energy dissipation) and also in non-destructive hardness testing. It was shown that the device can be successfully used in coordinate metrology as a touch trigger probe and as a 3D vector probe. Finally, applications can also be found in surface topography as a surface characterisation instrument. It is intended that the research described in this thesis will make an important contribution in the area of resonator based probes, providing a better understanding of the causes of parametric changes on the oscillatory sensor during contact with the object being measured. Consequently, this will enable a more effective exploitation of resonant probes for a broad range of precision applications.

Thesis (M.S.)--Ohio University, November, 2001. / Title from PDF t.p.