Publications

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Two-color resonant four-wave-mixing spectroscopy (TC-RFWM) is used to investigate ground-state energy transfer of hydroxyl radical in atmospheric-pressure flames. Two amplified distributed-feedback dye lasers produce 50-ps, nearly transform-limited, infrared (IR) and ultraviolet pulses. The infrared pump laser is tuned to individual rovibrational transitions of OH X {sup 2}{pi}{sub 3/2} (v{prime}=1, N{prime}) {l_arrow} X {sup 2}{pi}{sub 3/2} (v{double_prime}=0, N{double_prime}), and the ultraviolet pulse probes either the directly pumped or collisionally populated intermediate levels via A{sup 2}{Sigma}{sup +} (v*=1, N*) {l_arrow} X{sup 2}{pi}{sub 3/2}(v{prime}=1, N{prime}). By time-delaying the probe pulse with respect to the pump pulse, and appropriately constraining the polarizations of each of the four fields taking part in the wave-mixing process, we are able to independently and unambiguously measure the moments of the rotational angular momentum distribution in single rotational levels of the ground state. We present measurements of population, alignment, and orientation decay in X {sup 2}{pi}{sub 3/2} for several flame conditions. These experiments provide data necessary for the development of accurate models for diagnostic techniques using saturating laser pulses.

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An alternative theory of solid mechanics, known as the peridynamic theory, formulates problems in terms of integral equations rather than partial differential equations. This theory assumes that particles in a continuum interact with each other across a finite distance, as in molecular dynamics. Damage is incorporated in the theory at the level of these two-particle interactions, so localization and fracture occur as a natural outgrowth of the equation of motion and constitutive models. A numerical method for solving dynamic problems within the peridynamic theory is described. Accuracy and numerical stability are discussed. Examples illustrate the properties of the method for modeling brittle dynamic crack growth.

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Three methods that were used to measure the chemical changes associated with oxidative degradation of polymeric materials are presented. The first method is based on the nuclear activation of {sup 18}O in an elastomer that was thermally aged in an {sup 18}O{sub 2} atmosphere. Second, the alcohol groups in a thermally aged elastomer were derivatized with trifluoroacetic anhydride and their concentration measured via {sup 19}F NMR spectroscopy. Finally, a respirometer was used to directly measure the oxidative rates of a polyurethane foam as a function of aging temperature. The measurement of the oxidation rates enabled acceleration factors for oxidative degradation of these materials to be calculated.

An environmentally friendly method and materials study for desalinating inland brackish waters (i.e., coal bed methane produced waters) using a set of ion-exchange materials is presented. This desalination process effectively removes anions and cations in separate steps with minimal caustic waste generation. The anion-exchange material, hydrotalcite (HTC), exhibits an ion-exchange capacity (IEC) of {approx} 3 mequiv g{sup -1}. The cation-exchange material, an amorphous aluminosilicate permutite-like material, (Na{sub x+2y}Al{sub x}Si{sub 1-x}O{sub 2+y}), has an IEC of {approx}2.5 mequiv g{sup -1}. These ion-exchange materials were studied and optimized because of their specific ion-exchange capacity for the ions of interest and their ability to function in the temperature and pH regions necessary for cost and energy effectiveness. Room temperature, minimum pressure column studies (once-pass through) on simulant brackish water (total dissolved solids (TDS) = 2222 ppm) resulted in water containing TDS = 25 ppm. A second once-pass through column study on actual produced water (TDS = {approx}11,000) with a high carbonate concentration used an additional lime softening step and resulted in a decreased TDS of 600 ppm.

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