Made available in DSpace on 2014-10-09T12:25:17Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:03:16Z (GMT). No. of bitstreams: 1 12887.pdf: 8569105 bytes, checksum: 6b3d098cbaad100862c7d00c60b42f0a (MD5) / Tese (Doutoramento) / IEA/T / Escola Politecnica, Universidade de Sao Paulo - POLI/USP

Lattice misfit and its effect on the morphology, interfacial structure and kinetics of plate shaped precipitates are investigated in this study. The 7-Ag₂Al phase in the Al-Ag system was used as the reference system and its misfit was controlled by ternary additions of Mg and Cu. The addition of 0.S1 at% Mg was found to increase the misfit from 0.8% for the binary to 1.11%. Cu additions on the other hand, reduced the misfit by 0.38% for Cu concentrations up to 0.51 at%. Electron probe microanalysis showed that the Mg atoms preferentially partition to the 7 phase whereas Cu atoms partition equally between the precipitate and matrix phases. Direct transmission election rnicroscope observations were made on the interface structure in both the equilibrated state and during precipitate dissolution. The interface structure in the ternary Mg alloy consisted of a hexagonal network of partial dislocations which essentially remained the same before and during dissolution. A single array of a/2<110> dislocations was observed in the binary and ternary Cu systems prior to dissolution. This unit array transformed to a stable hexagonal network structure having the equilibrium spacing at the onset of dissolution and remained throughout the period of dissolution. The thinning and shortening kinetics of the precipitate plates were at least five times slower than the rates for volume diffusion control in all three systems. This interfacial inhibition has further been confirmed by the consistent fall below equilibrium values of the interface concentration as determined from electron probe microanalysis. This suggests the operation of a ledge migration mechanism. A mechanism of acquiring ledge/dislocations at the interface is used as a basis to correlate the observed kinetics with misfit and ledge migration at the precipitate-matrix interphase. The mechanism involves co-ordinated motion of sets of dislocations in the network which rids the surface of the highest steps thereby accomplishing dissolution. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

The high throughput capabilities and low sample volume requirements of microfluidic technology make it an attractive prospect for the pharmaceutical industry. This thesis concerns the development of microfluidic devices to investigate two important challenges to the pharmaceutical industry: to interface microchannel systems with electrospray ionisation mass spectrometry, an extensively used technique in drug discovery and development, and to investigate drug precipitation and its prevention through formulation. A microfluidic electrospray ionisation mass spectrometry interface was developed which could be placed within the source enclosure of a Waters ZQ mass spectrometer with little requirement for modification. The microfluidic interface showed a signal improvement of 38% over a capillary voltage of 4 - 4.75 kV when compared to the commercial probe which was operated at a desolvation gas flow rate of 120 L hr-1. Under typical desolvation temperatures of 350 ºC, the commercial probe outperformed the microfluidic interface which was operated at a desolvation temperature of 60 ºC, however, only an 18% improvement in signal intensity was observed for a 290 ºC increase in temperature, and there is scope to increase the operating desolvation temperature of the microfluidic interface. A novel droplet-based microfluidic light scattering detection system was developed to monitor drug precipitation of weakly basic poorly water soluble drugs. These drugs frequently exhibit poor bioavailability and variability due to precipitation in the GI tract. A pH-shift method was used to simulate gastric emptying conditions and generate a supersaturated state. Ketoconazole was used as the model drug in this study and was found to precipitate rapidly upon supersaturation. The extent of precipitation was shown to have a linear dependence on the degree of supersaturation for physiologically relevant supersaturations. This thesis also reports the first example of microfluidic screening of precipitation inhibitors. The inhibitory effect of two water soluble polymers, polyvinylpyrrolidone (PVP) and hydroxypropyl methylcellulose (HPMC) on ketoconazole precipitation was evaluated. HPMC was found to be a more potent precipitation inhibitor than PVP, with just 0.05 mM HPMC resulting in approximately a 75% decrease in ketoconazole precipitation, outperforming that of 1.7 mM PVP, which only decreased precipitation by approximately 60%. These findings corroborate results obtained from macroscale experiments employing dynamic light scattering detection. The onset time of precipitation for a range of ketoconazole supersaturations was measured using the scattered light intensity observed from the initial 22 seconds of ketoconazole precipitation. Onset times of between 0.24 – 2.45 seconds were determined for ketoconazole supersaturations of between 30 – 65.

The application of radar-derived precipitation measurements to engineering hydrology is investigated in this thesis. The nature of precipitation phenomena and current measurement techniques are introduced, followed by a detailed explanation of radar as a quantitative measurement tool. Archive data for the operational SCEPTRE radar in Abbotsford for five storm events was obtained from the Canadian Atmospheric Environment Service. Errors inherent in this data and those introduced during processing are investigated, and a comparison with point raingauge values is given. An interactive colour image display system is presented and precipitation patterns seen in the displayed image sequences are discussed. Applications of radar-deirived rainfall data to engineering runoff models are described, and the benefits and limitations of this data source are studied. An urban runoff case study using the Storm Water Management Model to simulate a catchment in Vancouver is given, and conclusions regarding the spatial and temporal resolution requirements of rainfall data sources are drawn from the results. The thesis concludes with recommendations for improvements to the SCEPTRE radar and to the archive system to make radar data more useful to engineering hydrologists. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

This study applies the Sacramento Soil Moisture Accounting Model (SAC-SMA)model to the Upper Black Creek Basin, Mississippi and attempts to improve operational lumped hydrologic model performance. The SAC-SMA is a lumped continuous soil moisture model which is typically calibrated continuously over time to all ranges in flow observed during the life of the gauge except when anthropogenic influences warrant historical data irrelevant. This study shows that persistent land use signatures are evident in the historical data indicating a shorter period of record for calibration is appropriate. This study also quantifies the error introduced to the operational model by inputting radar-derived precipitation estimates during forecast operations while Thiessen gauge weighted estimates are used to calibrate model parameters. Radar derived precipitation was used to calibrate the SAC-SMA model parameters for a shorter period of record than that used in the current operational set. The correlation coefficient improved 5 percent from 86 percent to 91 percent.

The objective of this project was to test the hypothesis that micritic, microbial, dendritic shrub structures transition into aragonite botryoids by serving as an organic substrate that promotes the initiation of aragonite crystal precipitation. Samples for this study were taken from three sources: 1) a stalactite found in the Lighthouse Reef Blue Hole, Belize; 2) aragonite botryoids in the reef framework of the Permian Capitan Formation and 3) the Lower Permian Laborcita Formation found in the Sacramento Mountains, south-central New Mexico. Samples studied in thin section and with scanning electron microscopy (SEM) showed dendritic micrite within botryoids and spheroidal shapes associated with aragonite. Precipitation experiments were conducted to grow calcite crystals with organic molecules in solution. The textures formed were very similar to those found at the three sample sites. Despite the similarity, all evidence of an organic substrate promoting precipitation remains circumstantial and therefore inconclusive.

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