I developed a high power blue laser for use in scientific and technical applications (eg. precision spectroscopy, semiconductor inspection, flow cytometry, etc). It is linearly polarized, single longitudinal and single transverse mode, and a convenient fiber coupled continuous wave (cw) laser source. My technique employs external cavity frequency doubling and provides better power and beam quality than commercially available blue diode lasers. I use a fiber Bragg grating (FBG) stabilized infrared (IR) semiconductor laser source with a polarization maintaining (PM) fiber coupled output. Using a custom made optical and mechanical design this output is coupled with a mode matching efficiency of 96% into the doubling cavity. With this carefully designed and optimized cavity, measurements were carried out at various fundamental input powers. A net efficie ncy of 81 % with an output power of 680 mW at 486 nm was obtained using 840 mW of IR input. Also I report an 87.5 % net efficiency in coupling of blue light from servo locked cavity into a single mode PM fiber. Thus I have demonstrated a total fiber to fiber efficiency of 71% can be achieved in our approach using periodically poled potassium titanyl phosphate (PPKTP). To obtain these results, all losses in the system were carefully studied and minimized.

Bibliography: pages 90-94. / Ordered spaces were introduced by Leopoldo Nachbin [1948 a, b, c, 1950, 1965]. We will be primarily concerned with completely regular ordered spaces, because they are precisely those ordered spaces which admit quasi-uniform structures. A recent and convenient study of these spaces is in the book by P. Fletcher and W.F. Lindgren [1982]. In this thesis we consider functorial quasi-uniformities over (partially) ordered spaces. The functorial methods which we use were developed by Brummer [1971, 1977, 1979, 1982] and Brummer and Hager [1984, 1987] in the context of functorial uniformities over completely regular topological spaces, and of functorial quasi-uniformities over pairwise. completely regular bitopological spaces. We obtain results which are to a large extent analogous to results in those papers. We also introduce some functors which relate our functorial quasi-uniformities to the structures studied by Brummer and others (e.g. Salbany [1984]).

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This research introduces a new value elicitation method for non-market valuation, referred to as the “quasi-double-bound (QDB)” method, applied to the case of barrierisland restoration in Mississippi. The objective of this thesis is to implement the QDB method in an actual stated-preference survey instrument and to test empirically whether the method elicits consistent responses and yields more efficient welfare estimates relative to the more-commonly used single-bound (SB) method. To test the QDB method, several models were estimated to derive a variety of welfare estimates for comparison to the estimates derived from the SB method. The QDB method introduced here results in a median willingness to pay (WTP) that was higher than the estimate of median WTP using the SB method in three of the five models estimated. The variances (i.e., confidence interval) of the QDB models were generally lower than those of the SB models.

Quasi-geostrophic (QG) analysis of the atmosphere utilizes predefined isobaric surfaces to ascertain vertical motion. One equation of the QG system is the omega equation that states that vertical forcing results from differential vorticity advection and thickness advection. Two problems arise when using the QG omega equation: the forcing terms are not independent and must be analyzed simultaneously, and vertical forcing is visually noisy. Both issues are resolved using a smoothing and quantification technique that applies the QG omega equation. The analysis fields from a selection of events were chosen from the North American Mesoscale model. Using a finite differencing methodology dependent on the wavelength of synoptic features, values of vertical forcing were calculated using the omega equation. The calculated omega field correlated well with model omega while also quantifying and visualizing large perturbations in vertical forcing. The method allows for quick diagnosis of forcing type and strength within the atmosphere.

The effects of microcracking on the mechanical properties of Salem limestone were investigated in three phases: introduction of quantifiable levels of microcracks by thermal treating, mechanical testing of limestone samples with varying levels of microcracks, and modification of a numerical model to incorporate the measured effects. This work demonstrated that this approach is useful for examination of the effects of microcracking on quasi-brittle materials and can be used to improve the predictive capabilities of material models. Thermal treating was found to consistently induce quantifiable levels of microcracks in Salem limestone. Sonic wave velocities indicated that the induced microstructural changes were a function of the maximum temperature. The wave velocities showed little variability demonstrating the effectiveness of the approach for inducing consistent levels of microcracking. X-ray diffraction, differential scanning calorimetry, and thermogravimetric analysis confirmed that no composition changes occurred for the temperature range of interest. Computed tomography scanning, scanning electron microscopy, and optical microscopy (OM) were used to observe microstructural changes caused by the heat treatments. OM analysis was the primary method used in the microcrack characterization and yielding qualitative and quantitative data. OM images showed an increase in grain boundary and intragranular cracking with increasing maximum heat treatment temperatures. Stereological evaluation provided microcrack data indicating that microcrack density increased as function of the maximum heat treatment temperatures. Mechanical testing was performed to characterize the mechanical response of the intact and damaged limestone. Quasi-static tests included uniaxial compression, triaxial compression, hydrostatic compression, and uniaxial strain / constant volume tests. Microcracking did not affect the limestone’s strength at pressures greater than 10 MPa. Dynamic tests were performed using a modified split Hopkinson pressure bar. Microcracking did not have an effect on the dynamic strength of the limestone. The results of the mechanical tests were used to modify the HJC model. Modifications were made to account for shear modulus degradation and failure surface changes. The original and modified HJC models were used in a numerical analysis of the mechanical tests performed in this work. The modified HJC provided better results for damaged material when compared with the quasi-static and dynamic experiments.

Optical reflectance of the quasi two dimensional compound Hg₂.₈₆AsF₆ has been investigated in the optical range, 0.5 to 4 eV. The spectra clearly show a plasma edge at 3 eV. They are fitted to a Drude model and two Lorentz oscillators. From the plasma frequency and the model parameters values for the dc conductivity and the effective mass and an estimate of the crytsal anisotropy have been obtained. The results compare well with earlier electrical measurements on this compound. / Thesis / Master of Science (MSc)

A quasi-order is a relation on a set which is both reflexive and transitive, while a well-quasi-order has the additional property that there exist no infinite strictly descending chains nor infinite antichains. Well-quasi-orderings have many interesting applications to a variety of areas which includes the strength of certain logical systems, the termination of algorithms, and the classification of sets of graphs in terms of excluded minors. My thesis explores how well-quasi-orderings are related to these topics through examples of four known well-quasi-orderings which are given by Dickson's Lemma, Higmans's Lemma, Kruskal's Tree Theorem, and the Robertson-Seymour Theorem. The well-quasi-ordering conjecture for matroids is also discussed, and an original proof of Higman's Lemma is presented.

Particulate composites are widely used in many aerospace and military applications as energetic materials, armor materials or coatings and their behavior under dynamic loads have gained increasing significance. The addition of modifiers such as alumina nanoparticles generally facilitates the improvement of the mechanical strength to density ratio due to high specific area and particle rigidity. This allows for sufficient particlematrix bonding and therefore improved stiffness and load transfer in the composite. Photo-luminescent α-alumina nanoparticles when embedded in an epoxy matrix allow for the added benefit of in situ measurements at low strain rates to provide stress-sensitive information using the particle piezospectroscopic (PS) property. To investigate the low strain rate behavior, cylindrical specimens of alumina-epoxy composites with varying volume fractions of alumina were fabricated using a casting process to ensure minimal surface finishing and reduced manufacturing time. The results illustrate the capability of alumina nanoparticles to act as diagnostic sensors to measure the stress-induced shifts of the spectral R-line peaks resulting from low compressive strain rates. The range of PS coefficients measured, -3.15 to -5.37 cm−1/GP a for R1 and -2.62 to -5.39 cm−1/GP a for R2, correlate well with static test results of similar volume fractions. Results reveal a general trend of increasing sensitivity of the PS coefficients with increasing strain rate when compared to similar materials under static conditions. In contrast to static results, at a given strain rate, the PS coefficients show varying degrees of sensitivity for each iii volume fraction. This information can be used to determine the time-dependent microscale stresses the nanoparticles sustain during composite loading. Additionally, this work facilitates failure prediction by monitoring upshifts in the PS information. Calibration of the in situ diagnostic stress sensing capabilities of varying volume fractions of alumina nanocomposites under quasi-static strain rates in this work sets the precedent for future studies at high strain rates.

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