With the desire for energy conservation and lower costs, the application of pulse-width modulated (PWM) voltage source converter (VSC) drives has grown at an exponential rate. However, due to their high switching frequency and high dv/dt, increased dielectric stresses and thermal stresses are applied to the insulation system of the motors, which may lead to the failure of the insulation. In order to test the performance of the motor insulation under the above complex stress conditions, an IGBT-based pulse voltage generator which can produce high voltage square wave and PWM waveforms has been successfully developed in this research. The generator consists of IGBT switches and other wave shaping components. The special cascade connection circuit design enables the generator to produce the stable high voltage square wave and PWM waveforms. A microcontroller-based trigger signal generator is used to trigger the power electronic switches in the generator. In order to avoid false triggering from electromagnetic interference (EMI), optical fibre cables are used to connect the trigger signal generator to the switches which are located in a high electric potential area. The generator can produce square wave and PWM waveforms with a peak voltage up to 15 kV and with a switching frequency of 600 Hz to 6 kHz. The fundamental frequency of the PWM waveform is 20 Hz to 1200 Hz, the rise time is less than 200 ns, and the pulse width can be varied up to several milliseconds. A 4 kVrms form wound model stator coil was tested under different voltage waveforms: power frequency, exponential decay pulse, square wave, and sinusoidal pulse-width modulated (SPWM) waveform. Infrared images and the maximum temperature rise of the coil under different electrical stresses were recorded. The results show that both the square and SPWM voltage waveforms cause a significantly higher temperature rise than the power frequency and exponential decay pulse voltage waveforms. Since the actual VSCs generate transients similar to those of the square and PWM voltage waveforms, it is recommended that the stator coil insulation be analyzed using PWM voltage waveforms in order to simulate actual conditions.

Swath bathymetry sidescan (SBS) sonar and the angle-of-arrival processing that underlies these systems has the capability to produce much higher resolution three dimensional imagery and bathymetry than traditional beamformed approaches. However, the performance of these high resolution systems is limited by signal-to-noise ratio (SNR) and they are also susceptible to multipath interference. This thesis explores two methods for increasing SNR and mitigating multipath interference for SBS systems. The first, binary coded pulse transmission and pulse compression is shown to increase the SNR and in turn provide reduced angle variance in SBS systems. The second, transmit beamforming, and more specifically steering and shading, is shown to increase both acoustic power in the water and directivity of the transmitted acoustic radiation. The transmit beamforming benefits are achieved by making use of the 8-element linear angle-of-arrival array typical in SBS sonars, but previously not utilized for transmit. Both simulations and real world SBS experiments are devised and conducted and it is shown that in practice pulse compression increases the SNR, and that transmit beamforming increases backscatter intensity and reduces the intensity of interfering multipaths. The improvement in achievable SNR and the reduction in multipath interference provided by the contributions in this thesis further strengthens the importance of SBS systems and angle-of-arrival based processing, as an alternative to beamforming, in underwater three dimensional imaging and mapping. / Graduate / 2015-04-15 / 0544 / 0547 / mark.butowski@gmail.com

High Harmonic Generation (HHG) enables the production of bursts of coherent soft x-rays with attosecond pulse duration. This process arrises from the nonlinear interaction between intense infrared laser pulses and an ionizing gas medium. Soft x-ray photons are used for spectroscopy of inner-shell electron correlation and exchange processes, and the availability of attosecond pulse durations will enable these processes to be resolved on their natural time scales. The maximum or cutoff photon energy in HHG increases with both the intensity as well as the wavelength of the driving laser. It is highly desirable to increase the harmonic cutoff as this will allow for the generation of shorter attosecond pulses, as well as HHG spectroscopy of increasingly energetic electronic transitions. While the harmonic cutoff increases with laser wavelength, there is a corresponding decrease in harmonic yield. The first part of this thesis describes the experimental measurement of the wavelength scaling of HHG efficiency, which we report as lambda^(-6.3) in xenon, and lambda^(-6.5) in krypton. To increase the HHG cutoff, we have developed a 1.8 um source, with stable carrier envelope phase and a pulse duration of <2 optical cycles. The 1.8 um wavelength allowed for a significant increase in the harmonic cutoff compared to equivalent 800 nm sources, while still maintaing reasonable harmonic yield. By focusing this source into neon we have produced 400 eV harmonics that extend into the x-ray water window. In addition to providing a source of photons for a secondary target, the HHG spectrum caries the signature of the electronic structure of the generating medium. In krypton we observed a Cooper minimum at 85 eV, showing that photoionization cross sections can be measured with HHG. Measurements in xenon lead to the first clear observation of electron correlation effects during HHG, which manifest as a broad peak in the HHG spectrum centred at 100 eV. This thesis also describes several improvements to the HHG experiment including the development of an ionization detector for measuring laser intensity, as well as an investigation into the role of laser mode quality on HHG phase matching and efficiency.

Temporal and wavelet characteristics of initial breakdown pulses are meticulously studied especially during the earliest moment of lightning events. Any possible features during the earliest moment that may exist which lead to either negative cloud-to-ground (CG), positive cloud-to-ground, cloud or isolated breakdown flashes in Sweden are investigated. Moreover, the occurrence of narrow bipolar pulses (NBPs) as part of a CG event that has been recorded from tropical thunderstorms are also included in the investigation. Electric field signatures selected from a collection of waveforms recorded using fast electric field broadband antenna system installed in Uppsala, Sweden and Skudai, South Malaysia are then carefully analyzed in order to observe any similarities or/and differences of their features. Temporal analysis reveals that there are significant distinctions within the first 1 ms among different types of lightning flashes. It is found that a negative CG flash tends to radiate pulses more frequently than other flashes and a cloud flash tends to radiate shorter pulses than other flashes but less frequently when compared to negative CG and isolated breakdown flashes. Perhaps, the ionization process during the earliest moment of negative CG flashes is more rapid than other discharges. Using a wavelet transformation, it can be suggested that the first electric field pulse of both negative CG and cloud flashes experiences a more rapid and extensive ionization process compared to positive CG and isolated breakdown flashes. Further temporal analysis on NBPs found to occur as part of CG flashes show the disparity of the normalized electric field amplitude between the NBPs prior to and after the first return stroke. This indicates that the NBPs intensities were influenced by the return stroke events and they occurred in the same thundercloud. The similarity between the temporal characteristics of NBPs as part of CG flashes and isolated NBPs suggests that their breakdown mechanisms might be similar.

ABSTRACT CLINICAL OUTCOMES INVOLVING THE USE OF EXTRACORPOREAL MAGNETIC INNERVATION IN THE TREATMENT OF URINARY INCONTINENCE by KATHY E. DAVIS Urinary incontinence affects approximately 25 million Americans, significantly diminishing their function and quality of life. It is estimated that 50% of all women will experience some form of urinary incontinence in their lifetime. Although women are disproportionately affected by urinary incontinence, 69% of men who have undergone prostatectomy also report post-surgical incontinence. Extracorporeal Magnetic Innervation (ExMI) is a novel conservative approach to the treatment of urinary incontinence. As a patient sits fully clothed on a chair, an electromagnet delivers a timed magnetic field that penetrates the pelvic floor, inducing a nerve impulse that prompts contractions of the muscles of the pelvic floor. When the magnet is switched off, the muscles relax. This forced, passive exercise of the pelvic floor muscles serves to build endurance and strengthen the muscles supporting the bladder during times of physical stress such as coughing, laughing or running. This study is a descriptive, retrospective analysis of data collected from a specialty continence center within a major Atlanta metropolitan outpatient facility. The records for all patients who received ExMI from 2000 to 2012 were reviewed. Of the 43 patients who had received ExMI, 35 met study inclusion criteria. Eight patients were eliminated from the study. Four of these patients experienced ExMI benefits for conditions unrelated to urinary incontinence and are discussed. Data were analyzed using descriptive and inferential statistics. . The majority of the patients were women (n=26, 74%); most patients had stress urinary incontinence (n=16, 46%) or mixed urinary incontinence (n=12, 34%). The patient outcome was determined by comparing the pad usage before treatment and at the end of treatment (16 weeks). The average number of pads used daily was significantly reduced to 1.6 3 + 0.94 (p<.0001). Treatment with ExMI for urinary incontinence was briefly popular in the United States shortly after it was introduced. Although ExMI is used extensively across Europe and Asia, very few studies on the efficacy of ExMI appear in the literature. These results will add to this body of knowledge.

This thesis describes a research investigation into novel designs of high voltage pulse transformers using magnetic insulation, which is the only practicable form of insulation for much of the equipment presently used in ultrahigh voltage pulsed-power work, including transmission lines and plasma opening switches. Although its use in transformers would bring important advantages in both size and weight reductions, a number of seemingly insurmountable problems have however so far prevented this. Two novel arrangements are presented in this thesis: one of these is a 500 kV transformer with self-magnetic insulation, and the other one is a 1 MV 'Tesla' transformer with external magnetic insulation. It is shown that both of these overcome the problems inherent in earlier designs and also offer considerable scope for further development in a number of important areas. It is believed that they represent the first working examples of magnetically-insulated transformers anywhere in the world. Modelling considerations of the transformers developed include both theoretical models and predicted characteristics. The filamentary technique used to describe mathematically the arrangements being investigated involves decomposition of the main conducting components into filamentary elements. The resulting equivalent electrical network includes all the mutual interactions that exist between the different filamentary elements, takes magnetic diffusion fully into account and enables the resistances and self and mutual inductances that are effective under fast transient conditions to be calculated. Theoretical results provided by the resulting mathematical models have been successfully validated by comparison with reliable experimental data. Much of the work detailed in the thesis has already been presented in high quality academic journals and at prestigious international conferences, and a solid theoretical and experimental basis has been laid down for future development and new progress into pulsed power system research.

Heart failure is a complex clinical syndrome in which the heart cannot pump sufficient blood and nutrients to the organs in the body. Increasingly, alterations in cardiac energetics are being implicated as playing an important role in the pathogenesis of heart failure. An understanding of specific metabolic switches which occur during the development of heart failure in patients would be greatly beneficial as a new diagnostic method and for the development of new therapies for patients with failing hearts. This thesis deals with the non-invasive assessment of metabolism in the heart. New magnetic resonance imaging (MRI) methods for metabolic characterization of the heart using hyperpolarized carbon-13 MRI are presented. Spatially resolved images of hyperpolarized 13C substrates and their downstream products can provide insight into real-time metabolic processes occurring in vivo, within minutes of injection of a pre-polarized 13C-labeled substrate. Conventional 3D spectroscopic acquisitions require in excess of 100 excitations, making it challenging to acquire full cardiac and respiratory-gated, whole-heart metabolic volumes. Each of the developments described in this thesis is intended to advance cardiac hyperpolarized 13C metabolic imaging towards a routine, clinical exam which can be used for prognosis and treatment optimization in patients with cardiovascular disease. The major technical development is a new interleaved-frequency, time-resolved MRI pulse sequence that can provide robust and reliable measurements of cardiac metabolic signals. The technique was applied to several realistic pre-clinical models of cardiac disease and the work presented will hopefully lead towards significant improvement in the management of patients with heart failure.

Heart failure is a complex clinical syndrome in which the heart cannot pump sufficient blood and nutrients to the organs in the body. Increasingly, alterations in cardiac energetics are being implicated as playing an important role in the pathogenesis of heart failure. An understanding of specific metabolic switches which occur during the development of heart failure in patients would be greatly beneficial as a new diagnostic method and for the development of new therapies for patients with failing hearts. This thesis deals with the non-invasive assessment of metabolism in the heart. New magnetic resonance imaging (MRI) methods for metabolic characterization of the heart using hyperpolarized carbon-13 MRI are presented. Spatially resolved images of hyperpolarized 13C substrates and their downstream products can provide insight into real-time metabolic processes occurring in vivo, within minutes of injection of a pre-polarized 13C-labeled substrate. Conventional 3D spectroscopic acquisitions require in excess of 100 excitations, making it challenging to acquire full cardiac and respiratory-gated, whole-heart metabolic volumes. Each of the developments described in this thesis is intended to advance cardiac hyperpolarized 13C metabolic imaging towards a routine, clinical exam which can be used for prognosis and treatment optimization in patients with cardiovascular disease. The major technical development is a new interleaved-frequency, time-resolved MRI pulse sequence that can provide robust and reliable measurements of cardiac metabolic signals. The technique was applied to several realistic pre-clinical models of cardiac disease and the work presented will hopefully lead towards significant improvement in the management of patients with heart failure.

In this thesis we discuss deterministic compartmental epidemic models. We study the asymp- totic stability of the disease-free solution of models with pulse vaccination campaigns. The main contributions of this thesis are to extend the literature of pulse vaccination models with delay. We take results for ordinary differential equation models and extend them to models with delay differential equations. Model generalizations include the use of a general incidence term as an upper bound for the actual incidence, and the use of switch parameters to approximate time-varying parameters. In particular, we look at contact rate parameters which are piecewise constant or time-varying. We extend literature results for non-delay general incidence models to find uniform asymptotic stability of the disease-free solution which helps us to add delay. We find an upper bound for the susceptible population under pulse vaccination and use this bound to tighten results for eradication thresholds: that is, we use this upper bound to find sufficient conditions for the uniform asymptotic stability of the disease-free solution of delayed pulse vaccination models. We extend literature results for constant contact rate bilinear incidence delay models to models with periodic time-varying contact rate, and determine conditions under which the disease-free solution is uniformly asymptotically stable for small delay. We also find conditions for disease permanence in the corresponding non-delay, time-varying-parameter pulse vaccination model. For piecewise- constant contact rate bilinear incidence models we again find thresholds which guarantee uniform asymptotic stability under small delay. We additionally discuss the effects of time-varying total population on our results, through a change of variables to population fractions. The total population is commonly held constant in the literature, for analytical simplicity, so we survey the methods for time-varying total population and the effects of such variation on the pulse vaccination schemes. We retain thresholds for eradication by considering the compartment populations as fractions of the total, instead of population numbers. The result is also applied to constant-population delay systems. When changing from standard incidence to bilinear incidence in delay systems, we discuss a way to estimate the effect of time-varying N. We support our theory with simulation results.

Biomedical imaging requires high resolution to see the fine features of a sample and fast acquisition to observe live cells that move. Optical coherence tomography (OCT) is a powerful technique which uses optical interference for non-invasive high resolution 3D imaging in biological samples. The resolution of OCT is determined by the length over which the light used will in- terfere. Unfortunately, dispersion hurts the imaging resolution by broadening interference features. A technique called quantum-OCT (QOCT)[1] is immune to dispersion but re- quires entangled photon pairs. The need for entanglement drastically reduces the number of photons available for imaging, making QOCT too slow to be practical. Chirped-pulse interferometry (CPI) is also immune to dispersion. A chirped pulse is one where the fre- quency, or colour, of the light changes from red to blue from one end of the pulse to the other. CPI relies on frequency correlations created by applying different chirps to two sep- arate pulses. This method had the disadvantage of being limited to a single predetermined chirp rate, and discarded 50% of the power. However CPI has better resolution than OCT, automatic dispersion cancellation, and 10,000,000 times the signal strength of QOCT [13]. A new, much more flexible and efficient method of CPI will be demonstrated by creating the frequency correlations entirely in a single pulse. This new method is referred to as non- linear chirped pulse interferometry (NL-CPI). The non-linear chirp required in NCPI is very difficult to produce using only conven- tional optics. In this thesis we document the construction and characterization of a new method of creating the desired chirp using a programmable pulse-shaper (PS). We build a PPS and then demonstrated its functionality by compressing a 105nm FWHM bandwidth pulse to under 17f s, near its transform limited time duration. We also show that the values given to the PPS for dispersion are accurate by calculating and then compensating the dispersion caused by various optical elements in the CPI interferometer. Conventional OCT systems are immune to dispersion common to both arms of the interferometer. Non-linear interferometers experience broadening due to this dispersion, making them more difficult to use with fibre based interferometers common in conventional OCT. We show that NL-CPI can compensate for dispersion common to both arms of the interferometer, making NL-CPI more appealing as a replacement for conventional OCT. In this thesis we experimentally implement and demonstrate a prototype setup using non-linear CPI for dispersion-cancelled imaging of a mirror, with a resolution comparable to conventional OCT systems. We then use the system to produce 2-D cross sectional images of a biological sample, an onion. Q-OCT has previously been used to image an onion[16], but required treating the onion with gold nano particles to achieve a useful signal. The onion we used had no special treatment. In addition our axial scanning rate is also 10000 times faster than Q-OCT.