Shock-tube experiments were performed with syngas mixtures near atmospheric pressure with varying equivalence ratios behind reflected shock waves. Pressure and hydroxyl radical (OH*) emission traces were recorded and used to calculate ignition delay time for a single mixture at equivalence ratios of [phi ]=0.4, 0.7, 1.0, and 2.0 over a range of temperatures from 913-1803 K. The syngas mixture was tested at full concentration as well as with 98% dilution in Argon. The full concentration mixtures were used to compare ignition delay time measurements with the theoretical calculations obtained through the use of chemical kinetics modeling using the Davis et al. mechanism. The dilute mixtures were used to study the OH* emission profiles compared to those of the kinetics model. The model was in poor agreement with the experimental data especially at lower temperatures with an ignition delay difference of more than an order of magnitude. These ignition delay time data supplement the few existing data and are in relative agreement. The species profile comparison of OH* compared to the model also showed poor agreement, with the worst agreement at the highest temperatures. While the disagreements with ignition delay time and profile comparisons cannot be explained at this time, the data presented support other findings. The data provide additional information towards understanding this disagreement relative to syngas mixtures despite the relatively well known kinetics of the primary constituents Hydrogen and Carbon Monoxide.

Poor emergence of sorghum [(Sorghum bicolor (L) Moench] affects the stand and potential yields. The major objective of this research was to find correlations among field emergence data and laboratory seed vigor tests. Thirty-two and 30 hybrids of sorghum were planted at three Virginia locations in 1995 and 1996, respectively. Field emergence was subsequently compared with results from laboratory tests that included: 1) standard germination; 2) osmotic-stress using polyethylene glycol 8000 (mw); 3) heat-shock using 2 hr at 50°C stress; 4) electrical conductivity of steep water of germinating seeds; and 5) seed mass. Field emergence of grain sorghum differed among hybrids, years and locations. Mean emergence across years and locations was 67.5%, whereas mean germination in the laboratory was 87.8%. There were interaction between hybrid and location and between hybrid and year. Germination under optimal conditions (standard germination test) and with osmotic or heat-shock stress differed among hybrids. Regression analyses showed a weak correlation between laboratory germination (with or without stress) and field emergence in both years. The fresh weight of seedlings whether from standard germination or stress tests also differed among hybrids in both years, and the associations with field emergence were weakly correlated in 1996. Hybrids showed significant differences in radicle length when grown under laboratory stress in both years following standard germination. There was a weak correlation with field emergence and radicle length following heat-shock treatment in 1996. The measurement of electrical conductivity in the seed steep water showed significant differences among hybrids. A weak correlation with field emergence was seen in 1996. Conductivity values per gram of seed and per cm² of seed area revealed differences among hybrids. The correlation of these parameters with field emergence was higher than conductivity per seed. Seed mass varied among hybrids in both years , but was no correlation between seed mass and emergence. Of the laboratory parameters examined, germination proved to be the most consistent predictor of variations in field emergence of sorghum hybrids. / Ph. D.

Loss models used in compression system performance prediction codes are often developed from the study of two-dimensional cascades. The physical mechanisms that affect the flow in supersonic compressor cascades have been reviewed, including the changes in shock geometry that will occur with back pressure for both started and unstarted operation. Compressible fluid mechanics has been applied to the known shock geometry to obtain a physics-based engineering shock loss model that is applicable over the entire supersonic operating range of the cascade. Predictions from the present method have been compared to measurements and Navier-Stokes analyses of the L030-4 and L030-6 cascades, and very good agreement was demonstrated for unstarted operation. Son1e of the started comparisons exhibited good agreement, while others did not. A clear improvement has been demonstrated over previously published shock loss models, both in the accuracy of the predictions and in the range of applicability. The dramatic increase in overall loss with increasing inlet flow angle is shown to be primarily the result of increased shock loss, and much of this increase is caused by the detached bow shock. For a given Mach number, the viscous profile loss is nearly constant over the entire unstarted operating range of the cascade, unless a shock-induced boundary layer separation occurs near stall. Shock loss is much more sensitive to inlet Mach number than is viscous profile loss. The present shock loss model has been used as the basis of an overall loss prediction method by adding a constant value, representative of the viscous profile loss, to the predicted shock loss characteristics. The overall loss characteristics obtained in this manner showed good agreement with the experimental values over the most useful operating range of the cascade. / Ph. D.

This investigation, in consideration of the sudden separation increase involved in wing drop, was to determine if the incorporated 2-D airfoil exhibits abnormal shock sensitivity. A comparative airfoil study was used to determine if this particular transonic airfoil is prone to abrupt shock movement, resulting in increased regions of separation. / Master of Science

Converging shocks have long been a topic of interest in theoretical fluid mechanics, and are of prime importance in inertial confinement fusion. However, tracking converging shocks in numerical schemes poses several challenges. Numerical schemes based on shock capturing inherently diffuse out shocks to multiple grid cells, making it hard to track the shock. Converging shocks are significantly harder to track, as this numerical smearing is much more significant when converging shocks approach the axis of convergence. To mitigate this problem, we transform the conservation laws to a non-inertial frame of reference in which the accelerating shock is stationary. A system of equations is derived based on the transformed conservation laws coupled to the shock speed obtained from jump conditions and a characteristic-based derivation of a relation governing shock acceleration. We solve these equations using a finite volume method. Our numerical results compare favorably with the analytical value of Guderley exponent for self-similarly converging cylindrical hydrodynamic shocks. Results for fast magnetosonic shock in MHD are also presented and compared with results from geometrical shock dynamics (GSD). Results from our shock fitting method, developed without any approximation to the original ideal magnetohydrodynamics equations, provide further credibility to GSD applied to converging fast magnetosonic shocks. This sort of shock fitting is a precursor to future multidimensional stability analysis of imploding shocks.

No description available.

The high-pressure shock tube facility (HiPER-STAR) at the University of Central Florida (UCF) is analyzed experimentally to demonstrate the practicality of hypersonic aero-optical testing in an impulse facility without the use of an expansion nozzle or acceleration tube. The investigation analyses driver gas blending with helium and hydrogen to raise the speed of sound ratio in an attempt to increase the Mach number for aero-optics testing. HiPER-STAR has a unique ability to withstand pressures up to 1000 atm and run in a double diaphragm configuration allowing for a significant pressure differential to be created between the driver and driven sections. Results from this study show that hydrogen and helium blending can drastically increase the maximum Mach number of HiPER-STAR; Mach numbers up to 15 were generated at a variety of altitudes. Experiment test time varied on shock velocity but was purely dependent on the arrival of the reflected shock wave to measurement locations. The aero-optics data that was collected and visually captured with a high-speed camera clearly shows beam aberration due to density gradients and a diminishing light intensity indicating that hypersonic aero-optical phenomenon can be captured reliably and repeatedly with a shock tube.

World poverty is a persistent phenomenon despite international efforts and the improvements achieved in the last few decades. For many people it can be a chronic condition. This thesis aims at testing that the main reason some people are poor is due to a poverty trap, i.e., to some contextual mechanisms which limit their ability to escape poverty, reproducing it over time. To investigate this hypothesis, this thesis is guided by three different questions. First, does a poverty trap emerge in the aftermath of an extreme weather shock? Second, do communities in a humanitarian context have the same wealth dynamics? Third, what is the role of income diversification for agricultural households for asset accumulation, and does it depend on their wealth? The analysis focuses (a) on the case of Nigeria and a devastating flood, (b) on refugees and host communities in Uganda and (c) on agricultural households in Tanzania, respectively. Results show that Nigerian flooded households have poverty traps dynamics, condemning the poorest in a destitute state over time. Refugees and host communities in Uganda have similar wealth dynamics but both converge to a low-wealth equilibrium, suggesting a structural poverty trap that worse for refugees. Income diversification in Tanzania shows important nonlinearities according to households’ wealth: it fosters the accumulation of durable assets for better-off households only, while helping the poorest to accumulate livestock. These findings shed light on the interaction of low-income conditions and contextual challenges and opportunities, suggesting policy actions able to lift poor people above a wealth threshold, improve their living conditions and favouring their profitability.

This dissertation studies a number of issues related to Development Economics. The first chapter explains how we can use multiple correspondence analysis to calculate an asset index, and then offers an inequality analysis using the asset index. The second chapter provides a theoretical explanation of an odd relationship between child labor and per capita land holding in a household, and then provides empirical evidence for the explanation. Finally, the third chapter represents the results of a study of the behavior of rural households during shocks. Across the entire dissertation, we use three cross sectional surveys, conducted in 2001, 2007-8 and 2010-11 in Zimbabwe. / Ph. D.

Chemiluminescence from the OH(A-X) transition near 307 nm is a commonly used diagnostic in combustion applications such as flame chemistry, shock-tube experiments, and reacting-flow visualization. Measurements of the chemiluminescent intensity provide a simple, cost-effective, non-intrusive look at the combustion environment. The presence of the ultra-violet emission is often used as an indicator of the flame zone in practical combustion systems, and its intensity may be correlated to the temperature distribution or other parameters of interest. While absolute measurements of the ground-state OH(X) concentrations are well-defined, there is no elementary relation between emission from the electronically excited state (OH*) and its absolute concentration. Thus, to enable quantitative emission measurements, a kinetics model has been assembled and optimized to predict OH* formation and quenching at combustion conditions. Shock-tube experiments were conducted in mixtures of H2/O2/Ar, CH4/O2/Ar and CH4/H2/O2/Ar with high levels of argon dilution (> 98%). Elementary reactions to model OH*, along with initial estimates of their rate coefficients, were taken from the literature. The important formation steps follow. CH + O2 = OH* + CO (R0) H + O + M = OH* + M (R1) H + OH + OH = OH* + H2O (R2) Sensitivity analyses were performed to design experiments at conditions most sensitive to the formation reactions. A fitting routine was developed to express the key rate parameters as a function of a single rate, k1 at the reference temperature (1490 K). With all rates so expressed, H2/CH4 mixtures were designed to uniquely determine the value of k1 at the reference temperature, from which the remaining rate parameters were calculated. Quenching rates were fixed at their literature values. Comparisons to predictions of previously available models show marked improvement relative to the new shock-tube data. An approach for using this work in the calibration of further measurements is outlined taking examples from a recent ethane oxidation study. The new model qualitatively matches the experimental data over the range of conditions studied and provides quantitative results applicable to real combustion environments, containing higher-order hydrocarbon fuels and lower levels of dilution in air.