In Chapter 1, we present the background for transient absorption spectroscopy through the polarization response of a material to an electric field which gives rise to linear and non-linear processes. We then discuss a theoretical description of how vibrational coherences are formed via four-wave mixing and impulsive excitation. We also describe signatures of coherent wavepackets in transient absorption and the application of vibrational coherences, specifically to observe non-radiative processes. We then summarize two previous studies using impulsive transient absorption on cresyl violet, the differences in the coherent dynamics reported, and the motivations behind the experiments presented in this work. Chapter 2 pertains to the apparatus used to perform the transient absorption experiments. We detail the source for the generation of ultrashort laser pulses (durations of less than 10 fs) used for the pump and probe from an argon-based white-light filament and non-colinear optical parametric amplifier. Two-dimensional shearing interferometry, the method used to measure the ultrashort pulses across a large portion of the visible spectrum (500-750 nm), is discussed. The retrieved temporal, spectral, and phase profiles of the pump and probe pulses are presented. Finally, the sample preparation for cresyl violet is described as well as the detection method and data processing used to generate the figures throughout this work. In Chapter 3, we present the results of impulsive transient absorption spectroscopy of cresyl violet perchlorate under four pump conditions. First, we report a study on controlling the formation of vibrational coherences on the ground or excited electronic states of cresyl violet by tuning the pump conditions from an off-resonant to a resonant scheme. The decay of the electronic population and positions of the stimulated emission and excited-state absorption maximums shows a dependence on the pump wavelength. Higher excitation frequencies blueshifts the stimulated emission 18 meV and red shifts excited-state absorption by 4 meV at early times compared to only 13 meV and 2 meV when using lower excitation frequencies. Coherent vibrations are observed and persist for approximately 6 ps after excitation, with phase flips appearing at 593 nm, the absorption maximum, after off-resonant excitation and at the emission (619 nm) and excited-state absorption (500 nm) maximums after resonant excitation. The ground- and excited-state vibrational modes are characterized by Fourier transform Raman spectroscopy. The excited-state vibration spectrum is shown to share nearly identical features as the ground-state, with each vibration slightly red-shifted, 2-10 cm-1, from the corresponding mode in the ground-state, particularly a prominent peak appearing at 594 cm-1 in the ground-state and 589 cm-1 in the excited-state. Next, two additional pump conditions using broadband and partially resonant pump pulses are explored to replicate the conflicting reports of non-adiabatic crossings in cresyl violet. Constant phase-flips observed in the control studies are replaced with phase flips that appear and disappear over several picoseconds. The Fourier Raman spectrum of the coherent signal after broadband excitation displays a mix of ground- and excited-state features, particularly prominent peaks at both 589 cm-1 and 594 cm-1. In Chapter 4, we analyze the coherent signals after broadband excitation using a Fourier filtering technique to isolate the ground- or excited-state coherent dynamics by carefully selecting representative vibrational modes for each state. Using a narrow filter to isolate the 589 cm-1 and 595 cm-1 features in the broadband Fourier Raman spectrum successfully isolates coherent vibrations with phase flips at either the emission and excited-state absorption maximums or the ground-state absorption maximum, respectively. A filter that includes both features generates apparent phase-flips that only appear for ~1ps and at probe wavelengths that do not correspond to the emission or absorption maximums. In Chapter 5, we present a simulation of the coherent signals using a model of two wavepackets with carrier frequencies of 589 cm-1 and 595 cm-1 and dephasing rates of 2 and 3 ps, respectively. Comparison to the broadband pump conditions and Fourier filtered coherent oscillations shows that the complex temporal dynamics observed are adequately described by the linear interference of two vibrational coherences evolving on different electronic potential energy surfaces, without the need to invoke non-adiabatic dynamics. / Chemistry

Dynamic simulation of a large-scale electric power system involves solving a large number of differential algebraic equations (DAEs) every simulation time-step. With the ever-growing size and complexity of power grid, dynamic simulation becomes more and more time-consuming and computationally difficult using conventional sequential simulation techniques. This thesis presents a fully distributed approach intended for implementation on High Performance Computer (HPC) clusters. A novel, relaxation-based domain decomposition algorithm known as Parallel-General-Norton with Multiple-port Equivalent (PGNME) is proposed as the core technique of a two-stage decomposition approach to divide the overall dynamic simulation problem into a set of sub problems that can be solved concurrently. While the convergence property has traditionally been a concern for relaxation-based decomposition, an estimation mechanism based on multiple-port network equivalent is adopted as the preconditioner to enhance the convergence of the proposed algorithm. The algorithm is presented in detail and validated both in terms of accuracy and capability

This thesis characterizes the transient thermal response of a 12/16 External Rotor Switched Reluctance Machine (ERSRM) for an E-bike application. A method for calculating coil capacitance based on machine design parameters was introduced and implemented into a standard commercial Lumped Parameter Thermal Network (LPTN). A sizing criterion was proposed for the cuboid number in a physically accurate LPTN coil model design. This sizing criterion considers the change in model size with motor speed or forced convection. The LPTN with a more accurate calculation of capacitance within the coil and a known number of cuboids in the coil was validated with experimental results. An analytical proof was provided that a small number of capacitances is not sufficient to model a typical power-dense coil design. The validated model was used to study the impact of a more accurate capacitance calculation method on motor temperature. Both overload and rated operation were investigated. During overload conditions, it was found that the standard capacitance calculation from commercial software massively underestimated the heating rate and peak temperature of the coil hot spot, even with the same number of cuboids. The capacitance of the rest of the motor was able to be varied and investigated for its effects on cooldown dynamics. It was found that for short-time transients the coil could be assumed to act adiabatically in this operating range. Operating points across the operating envelope for the motor under study were mapped to determine the region where the adiabatic assumption could be made. It was shown that a transition occurred where the adiabatic assumption ceases to be valid. / Thesis / Doctor of Philosophy (PhD) / This thesis deals with the thermal modelling of electric machines for traction applications using lumped parameter thermal modelling. A novel approach is presented for calculating and distributing thermal capacitance in motor coils. A 12/16 External Rotor Switched Reluctance Motor is characterized based on its transient thermal response and the novel methods proposed are validated. The sizing of a coil-based thermal model is discussed and a criterion for physical validity proposed. The validated model is used in a sensitivity analysis of coil and motor capacitances. For severe overload conditions and short periods, a result is obtained showing the coil can be modelled as adiabatic. Finally, a rated load condition is tested, and a transition is suggested between overload conditions and non-overload conditions.

Abstract available in the Journal of Investigative Medicine.

The purpose of this study was to develop, implement and test a tool designed to help transient students gain the basic musical knowledge and skills needed to successfully complete a fourth-grade unit of recorder study. The project resulted in the development of a hypermedia-based application. The seven-week study consisted of 49 fourth-grade students. Students were given pitch reading and rhythm pattern identification pre-tests and post-tests. Students participated in weekly tests and tutorial sessions via the hypermedia-based application. At the conclusion of the study, the students were given post-tests and a performance test. The pre-test and post-test scores for the transient and established populations were analyzed. A t-test analysis revealed a significant improvement in the scores of the established and transient populations. It appears that the hyper-media application may be an effective tutorial for transient students.

Thermosyphon transient operation was numerically modeled. The numerical model presented in this work overcame the limitations of previous studies by including transient conduction in the vessel wall, shear stress between the rising vapor and the falling film in the thermosyphon, the influence of the mass in the liquid pool in the evaporator, and by using a more refined and accurate numerical grid. Unique to this model was the accounting for temporal changes in the effective length of the vapor space due to the expanding and contracting of non-condensable gases in the vapor space. The model assumed quasi-steady one-dimensional vapor flow, transient one-dimensional flow in the falling liquid film, and transient behavior in the liquid pool in the evaporator. The model also assumed transient two-dimensional conduction in the thermosyphon wall. Using fundamental principles, the governing equations used in the numerical model were developed and then written in finite difference form. The finite difference forms of the governing equations were integrated using an explicit scheme. A sensitivity study was performed and found that the numerical model was accurate to 4%. An experiment was also conducted to validate the numerical model. The experiment used three distinct transient heat loads to simulate gradual, moderate and sharp increases in temperature. The uncertainty of the experiment was shown to be 2.3%. The temperatures from the numerical model were then compared to those measured during the physical experiment to determine the validity of the numerical model. The model was further exercised to develop a useful engineering relationship that can be used to predict the transient performance of a thermosyphon.

Two numerical techniques, the boundary-element method (BEM) and the finite-difference method (FDM), are used for simulating the radiation from horn-loaded compression drivers and from an infinitely-baffled, finite-length pipe. While computations of the horn-loaded compression driver are in steady state, transient analysis of the finite-length pipe is studied as a precursor to transient analysis within the horn-loaded compression driver. BEM numerical simulations show promise for the development of new designs. Numerical simulations serve as a good tool for time and cost-effective prototyping as poor designs are detected before they are built.

Future microprocessors pose many challenges to the power conversion techniques. Multiphase synchronous buck converters have been widely used in high current low voltage microprocessor application. Design optimization needs to be carefully carried out with pushing the envelope specification and ever increasing concentration towards power saving features. In this work, attention has been focused on dynamic aspects of multiphase synchronous buck design. The power related issues and optimizations have been comprehensively investigated in this paper. In the first chapter, multiphase DC-DC conversion is presented with background application. Adaptive voltage positioning and various nonlinear control schemes are evaluated. Design optimization are presented to achieve best static efficiency over the entire load range. Power loss analysis from various operation modes and driver IC definition are studied thoroughly to better understand the loss terms and minimize the power loss. Load adaptive control is then proposed together with parametric optimization to achieve optimum efficiency figure. New nonlinear control schemes are proposed to improve the transient response, i.e. load engage and load release responses, of the multiphase VR in low frequency repetitive transient. Drop phase optimization and PWM transition from long tri-state phase are presented to improve the smoothness and robustness of the VR in mode transition. During high frequency repetitive transient, the control loop should be optimized and nonlinear loop should be turned off. Dynamic current sharing are thoroughly studied in chapter 4. The output impedance of the multiphase v synchronous buck are derived to assist the analysis. Beat frequency is studied and mitigated by proposing load frequency detection scheme by turning OFF the nonlinear loop and introducing current protection in the control loop. Dynamic voltage scaling (DVS) is now used in modern Multi-Core processor (MCP) and multiprocessor System-on-Chip (MPSoC) to reduce operational voltage under light load condition. With the aggressive motivation to boost dynamic power efficiency, the design specification of voltage transition (dv/dt) for the DVS is pushing the physical limitation of the multiphase converter design and the component stress as well. In this paper, the operation modes and modes transition during dynamic voltage transition are illustrated. Critical dead-times of driver IC design and system dynamics are first studied and then optimized. The excessive stress on the control MOSFET which increases the reliability concern is captured in boost mode operation. Feasible solutions are also proposed and verified by both simulation and experiment results. CdV/dt compensation for removing the AVP effect and novel nonlinear control scheme for smooth transition are proposed for dealing with fast voltage positioning. Optimum phase number control during dynamic voltage transition is also proposed and triggered by voltage identification (VID) delta to further reduce the dynamic loss. The proposed schemes are experimentally verified in a 200 W six phase synchronous buck converter. Finally, the work is concluded. The references are listed.

An experimental investigation into the effects of inlet temperature transients on the stall and stall recovery aerodynamics of a low speed multi-stage axial flow compressor has been presented. Experiments were conducted on a low speed multi-stage axial flow compression system to demonstrate how a compressor dynamically stalls or recovers from a rotating stall operating condition during an inlet temperature transient. The specific effects of the inlet temperature transients on the compressor rotor blade flow physics during the dynamic stall or rotating stall recovery events of the axial flow compression system have been presented. In one experiment, a full recovery from a rotating stall operating condition was successfully accomplished on the low speed multistage axial flow compressor. Explanations for the axial flow compression system dynamic stall and rotating stall recovery processes during inlet temperature transients have been presented. The method utilized for inducing the rotating stall recovery on the compression system has been proposed as a possible new technique for active recovery from rotating stall for single and multi-stage axial flow compression systems. / Ph. D.

Levees are a significant part of the United States flood protection infrastructure. It is estimated that over 100,000 miles of levees exist in the United States. Most of these levees were designed many years ago to protect farmland and rural areas. As growth continues in the United States, many of these levees are now protecting homes and other important structures. The American Society of Civil Engineers gave the levees in the United States a grade of D- in 2009. To bring flood protection up to modern standards there requires adequate methods of evaluating levees with respect to seepage, erosion, piping and slope instability. Transient seepage analyses provide an effective method of evaluating seepage through levees and its potentially destabilizing effects. Floods against levees usually last for days or weeks. In response to a flood, pore pressures within the levee will change from negative (suction) to positive as the phreatic surface progresses through the levee. These changes can be calculated by finite element transient seepage analyses. In order for the transient seepage analysis to be valid, appropriate soil properties and initial conditions must be used. The research investigation described here provides simple and practical methods for estimating the initial conditions and soil properties required for transient seepage analyses, and illustrates their use through a number of examples. / Ph. D.