Pressure gradient confinement effects are experimentally investigated within a cavity combustor to analyze the flame interactions of premixed, cavity stabilized, flames in a high-speed combustor. Pressure gradient confinement effects are generated in a dual mode ramjet-scramjet (DMSR) by varying the wall geometry to form converging, diverging, and nominal configurations. The velocity field and flame position are captured temporally using simultaneous high-speed particle image velocimetry (PIV) and CH chemiluminescence. The evolution of the flow field and flame structure are analyzed, and the high temporal resolution of these measurements allows for the characterization of turbulence-flame interactions. Consideration of the combustion mode and inlet conditions, such as the inflow velocity and turbulence, are vital in studying flame-vortex interaction dynamics and its effect on the flame stabilization process and is essential in ensuring efficient, complete combustion. The results from the experiment will provide a greater understanding of how flame-vorticity interactions and pressure gradient confinement effects play a key role in the flame-stabilization and combustion process.

E-cigarettes have recently become increasingly popular, especially amongst middle and high school students. Although they are marketed as safer alternatives to tobacco cigarettes, they produce toxic metals and carcinogenic nitrosamines. This thesis studies the effects of e-cigarette aerosol on the growth and proliferation of oral epithelial cells because the consequences of vaping, including a potential risk for aberrant growth leading to cancer, are not well understood. Cells were grown in matrigel, causing the formation of three-dimensional spheroids modeling the physiological architecture of the oral epithelium. Those spheroids were chronically exposed to vape with different treatment conditions to study the functional biological effects of the presence of nicotine, dosage, and different types of exposure. The diameter of the spheroids was measured throughout the process as an indicator of cell growth. It showed that the vape exposure, especially nicotine-rich aerosol, induces an increase in spheroid diameter in a dose-dependent manner. The increased cell growth is supported by enhanced metabolic activity as well as increased aldehyde dehydrogenase activity, a marker of stemness prominently upregulated in cancer stem cells. Protein was extracted at the end for protein expression analysis through Western blotting and the identification of the activation of survival signaling pathways and stem cell markers. Lastly, spheroids were co-cultured with Strep. mutans, a cariogenic bacterial resident in the oral cavity, and acutely exposed to vape. Co-culture with S. mutans did not significantly affect spheroid growth under the current experimental conditions or significantly change the expression patterns of proliferation and tumor initiation proteins. Future research will include tumorigenic assays and investigate how vape may induce carcinogenesis of the oral epithelium.

This project successfully designed, fabricated and characterized two highly reflective distributed Bragg reflectors for use with long wavelength vertical cavity surface emitting lasers. The first reflector consisted of 20 pairs of alternating lnP/Ino.64Gao.36Aso.777Po.223 layers grown on an InP substrate with a theoretically predicted normal incident reflectivity of 96.6% at a center wavelength of 1550nm. The second DBR had 20 pairs of alternating GaAs/Ino.484Gao.5i6P layers grown on a GaAs substrate with a theoretically predicted reflectivity of 94.9% at a center wavelength of 1550nm for normal incident light. Experimental results obtained using a specially designed reflectivity measurement setup confirmed reflectivity models and predictions at both normal and variable incident light angles. However, these measurements revealed a discrepancy between theoretical and experimental layer thickness values for both DBR structures. Applying perturbations to the theoretical models, the actual layer thicknesses ofthe DBRs were determined. X-ray analysis was employed to examine the periodicity of the super-lattices along with the accuracy of lattice matching to the substrate. Transmission electron microscopy revealed that no detectable drift in layer thickness was apparent during growth of the DBR structures. Photoluminescence was used to investigate any compositional variations ofthe quaternary layers in the first DBR stack. / Thesis / Master of Applied Science (MASc)

Low-temperature non–thermal plasmas are of growing interest due to their applications in various fields, such as plasma-assisted combustion, plasma medicine, material processing, etc. Hydroxyl radical (OH) is one of the key agents and most important reactive species generated in plasmas. We employ cavity ringdown spectroscopy (CRDS), both a pulsed laser and a continuous wave (cw) laser to measure absolute number densities of OH radicals in low-temperature plasmas. A 2.45 GHz microwave plasma source was used to excite two different types of plasma cavities: an atmospheric plasma jet and microwave plasma torch (MPT). The atmospheric microwave plasma jet was thoroughly explored and operated with different plasma gases. Plasma jets with argon (Ar), helium (He), Ar/N2, Ar/O2, He/N2, He/O2 and Ar/H2O were investigated. The absolute number densities of OH radicals were measured along the jet axis in all of plasma jets using pulsed CRDS. Effects of plasma power and gas flow rates on OH radical generation were also studied. We have reported for the first time that OH radicals exist in the far downstream region of a plasma jet axis. The far downstream is a location where the ratio of distance from the plasma jet orifice over the plasma jet column length is larger than 3. For an Ar plasma jet length of 3 mm, OH radicals were detected at a farthest distance ratio of 7.6. The OH density profiles along the axis in all the plasma jets indicate that OH radicals have the highest number density in the vicinity of the jet tip and gradually decreases in the downstream. Optical emission spectroscopy and digital imaging were simultaneously employed to identify the different radicals generated in plasma jets and to study the fine structures of the plasma jets. Pulsed CRDS was also employed to measure OH radical density in an Ar MPT. By using high temporal resolved imaging, it was observed that the widely reported converging point in Ar MPT is actually a time-averaged visual effect. Absolute number densities of OH radicals and water molecules were measured in an alternating current (AC) glow discharge using near infrared cw CRDS.

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