Thesis (Ph. D.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

We exhibit long-lived resonances in scattering from two-dimensional soft cage potentials comprised of three and four Gaussian peaks. Specific low-energy resonances with very narrow width are shown to correspond to classical multiple-reflection events. These states have much larger probability densities inside the cage than outside and mimic bound states in the sense that the symmetry-breaking effect of the incident wave is relatively small. As a result we have found that isolated states display the simple symmetry characteristics of bound states. Overlapping resonances exhibit a mixing of symmetry classes leading to wave functions of lower symmetry, like those of wider resonances at higher energy. We demonstrate that at energies below the lowest resonances of two-dimensional cages, where the distance across the entrance of the cage corresponds to less than half a wavelength, the wave function may still gain access to the interior region by squeezing its wavelength in the necessary direction at the expense of the kinetic energy in the direction normal to the opening. The resulting curvature of the wave function in the donor dimension corresponds to an imaginary wavenumber, curving away from the plane defined by zero amplitude. This mechanism for passing between obstacles may be relevant for electronic and optical devices having spatial structures with dimensions comparable to the wavelengths of the energy carriers. / Graduation date: 2005

Thesis (Ph.D.)--University of Delaware, 2006. / Principal faculty advisor: Tatyana Polenova, Dept. of Chemistry & Biochemistry. Includes bibliographical references.

Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) has a high sensitivity (71- 100%) for detecting breast cancers. DCE-MRI is approximately twice as sensitive as mammography for patients who are genetically predisposed to breast cancer, who have an elevated lifetime risk (up to 85%) of contracting the disease, and who require rigorous screening. However, current methods of DCE-MRI often have difficulty distinguishing malignant from benign tumours, resulting in low positive predictive values (on average, PPV = 45%). The research in this thesis is motivated by the need for improvement in the ability of MRI to differentiate breast lesions. It is believed that the differentiation of malignant from benign lesions can be improved by acquiring images of high spatial resolution for visualizing morphological features of tumours and those of high temporal resolution for characterizing contrast-kinetic curves. However, simultaneously achieving high spatial and temporal resolution is limited by the inherent trade-off between speed and quality in MRI, requiring one to choose a particular balance of spatial and temporal resolution. In this thesis, novel techniques are presented that reduce the need to choose a spatiotemporal resolution before the scan. Flexible methods are presented that allow images to be retrospectively reconstructed with different balances of spatial and temporal resolution from the same dataset. Flexibility is achieved through radial sampling of k-space data, with 3D radial directions based on Multidimensional Golden Means (MGM) and Halton sequences. Radial sampling also allows constrained image reconstruction techniques such as Compressed Sensing and Prior-Image Constrained Compressed Sensing to be incorporated for reducing undersampling artifacts in high-temporalresolution images. This thesis demonstrates in 2D how such reconstruction algorithms are influenced by acquisition schemes and shows how reconstruction algorithms work in synergy with flexible radial sampling to provide improvements in the quality of breast MR images. The flexibility to choose any spatiotemporal resolution combined with better image quality in fast images could potentially improve the characterization of breast lesions screened by MRI.

Resonance disorders due to cleft palate and other aetiologies are frequently assessed in conjunction with nasometry. The most commonly used instrument is the Nasometer by KayPentax. A new model Nasometer 6450 was compared to an older model 6200 using both synthetic and speech stimuli. There was a particular focus on test-retest variability of the instrument. The Nasometers were found to yield comparable results. The inter session test-retest variability ranged from six to eight points, depending on the stimulus. The Nasometer 6450 was then used to collect nasalance scores of simulated resonance disorders. A discriminant analysis was applied to these scores. The resultant formulas were moderately successful in predicting perceived resonance when applied to pre-existing data sets.

Cardiovascular diseases, such as stroke and heart attack, are one of the largest causes of death and morbidity in Canada. Atherosclerosis, or the thickening of the arterial wall, has been identified as the primary culprit lesion behind the end organ damage associated with cardiovascular diseases. Magnetic resonance imaging has taken a primary role in characterising the constituents of these atherosclerotic plaques. Of these components, MR detected intraplaque haemorrhage (IPH), or bleeding inside the vessel wall, appears to predispose a patient to future clinical events. This leads us to the conclusion that IPH is a secondary manifestation of plaque progression and complication, or somehow contributes to the complication of these atherosclerotic plaques. This thesis explores this second possibility, in line with the “iron hypothesis” of atherosclerosis which suggests that iron plays a significant, primary role in atherogenesis. In chapter two, the signal hyperintensity associated with IPH is correlated with the lipid oxidising potential of blood products in various oxidation states. It is found that the ferric paramagnetic species has a significantly greater ability to generate lipid oxide components and oxidise lipid surrogates. This finding suggests that it may be possible to alter the course of plaque progression by inhibiting the active ferric iron state. Chapter three explores an endogenous molecule, haptoglobin, whose purpose is to bind and inactivate free haemoglobin. It is shown that haptoglobin has the ability to modulate the MR signal intensity from IPH. Chapter four explores a mechanism to detect this imaging biomarker outside the MR environment using the electron paramagnetic resonance of the ferric haemoglobin. Results are shown in a custom made bench top system detecting ferric haemoglobin in an in vitro sample. This thesis provides more evidence for the iron hypothesis of atherosclerosis and explores methods of inhibiting and detecting this biomarker of disease.

Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) has a high sensitivity (71- 100%) for detecting breast cancers. DCE-MRI is approximately twice as sensitive as mammography for patients who are genetically predisposed to breast cancer, who have an elevated lifetime risk (up to 85%) of contracting the disease, and who require rigorous screening. However, current methods of DCE-MRI often have difficulty distinguishing malignant from benign tumours, resulting in low positive predictive values (on average, PPV = 45%). The research in this thesis is motivated by the need for improvement in the ability of MRI to differentiate breast lesions. It is believed that the differentiation of malignant from benign lesions can be improved by acquiring images of high spatial resolution for visualizing morphological features of tumours and those of high temporal resolution for characterizing contrast-kinetic curves. However, simultaneously achieving high spatial and temporal resolution is limited by the inherent trade-off between speed and quality in MRI, requiring one to choose a particular balance of spatial and temporal resolution. In this thesis, novel techniques are presented that reduce the need to choose a spatiotemporal resolution before the scan. Flexible methods are presented that allow images to be retrospectively reconstructed with different balances of spatial and temporal resolution from the same dataset. Flexibility is achieved through radial sampling of k-space data, with 3D radial directions based on Multidimensional Golden Means (MGM) and Halton sequences. Radial sampling also allows constrained image reconstruction techniques such as Compressed Sensing and Prior-Image Constrained Compressed Sensing to be incorporated for reducing undersampling artifacts in high-temporalresolution images. This thesis demonstrates in 2D how such reconstruction algorithms are influenced by acquisition schemes and shows how reconstruction algorithms work in synergy with flexible radial sampling to provide improvements in the quality of breast MR images. The flexibility to choose any spatiotemporal resolution combined with better image quality in fast images could potentially improve the characterization of breast lesions screened by MRI.

Cardiovascular diseases, such as stroke and heart attack, are one of the largest causes of death and morbidity in Canada. Atherosclerosis, or the thickening of the arterial wall, has been identified as the primary culprit lesion behind the end organ damage associated with cardiovascular diseases. Magnetic resonance imaging has taken a primary role in characterising the constituents of these atherosclerotic plaques. Of these components, MR detected intraplaque haemorrhage (IPH), or bleeding inside the vessel wall, appears to predispose a patient to future clinical events. This leads us to the conclusion that IPH is a secondary manifestation of plaque progression and complication, or somehow contributes to the complication of these atherosclerotic plaques. This thesis explores this second possibility, in line with the “iron hypothesis” of atherosclerosis which suggests that iron plays a significant, primary role in atherogenesis. In chapter two, the signal hyperintensity associated with IPH is correlated with the lipid oxidising potential of blood products in various oxidation states. It is found that the ferric paramagnetic species has a significantly greater ability to generate lipid oxide components and oxidise lipid surrogates. This finding suggests that it may be possible to alter the course of plaque progression by inhibiting the active ferric iron state. Chapter three explores an endogenous molecule, haptoglobin, whose purpose is to bind and inactivate free haemoglobin. It is shown that haptoglobin has the ability to modulate the MR signal intensity from IPH. Chapter four explores a mechanism to detect this imaging biomarker outside the MR environment using the electron paramagnetic resonance of the ferric haemoglobin. Results are shown in a custom made bench top system detecting ferric haemoglobin in an in vitro sample. This thesis provides more evidence for the iron hypothesis of atherosclerosis and explores methods of inhibiting and detecting this biomarker of disease.

This dissertation reports a study of three kinds of liquid crystals using modern solid state NMR techniques: chiral rod-like liquid crystals, bent-core mesogens and disc-like liquid crystals. The properties and structures of liquid crystals are first introduced in Chapter 1. To understand the principles of different NMR phenomena, quantum mechanical theory is adopted to study different nuclear spin interactions and NMR techniques in Chapter 2. In the next part of this dissertation (Chapter 3-6), deuterium NMR methods are used to investigate the dynamics and structures of some liquid crystal phases. This is first done using the spin relaxation study. The parameters obtained from the model simulation can describe the molecular motion and internal dynamics in the fast motion region. Secondly, we investigate the dynamic process of discotic mesophases and unwound smectic C* phase using the line shape simulation study. 2D deuterium NMR exchange experiments are then performed to study the jump process in TGBA* phase and SmC* phase. The above investigation has demonstrated some powerful NMR methods for the dynamic study of liquid crystals. The third part of the dissertation (Chapter 7-9) is concerned with C-13 NMR techniques. After we introduce the quantum theory of different pulse sequences, theoretical models are presented to fit observations such as chemical shifts and dipolar splittings. Moreover high resolution liquid C-13 NMR experiments are introduced to study some bent-core molecules. They are useful to assist the carbon peak assignments of these molecules. The structure and ordering information of liquid crystals can be determined in their mesophases. Finally, a brief summary of the dissertation is given in the last chapter. / October 2007

The resonance frequency and the damping constant are interesting parametersrelated to the ferromagnetic spin resonance phenomenon. In this study theseparameters have been investigated for a number of Heusler multilayer film samplesusing a vector network analyzer ferromagnetic resonance setup. The complexsusceptibility of the samples is extracted from the transmittance scattering parameterS12 measured by the network vector analyzer. The ferromagnetic resonance ismirrored by a maximum in the imaginary part of the complex susceptibility. Theagreement between the theoretically calculated resonance frequency and theresonance frequency measured varied between samples. These differences originatefrom several sources, one of them is, the uncertainty in the internal magnetic field.This is due to irregularities and repeated interfaces between each layer in the Heuslersamples.