The e.p.r. spectrum for relatively dilute samples of phosphorus-doped silicon (<5 x 10(16) donors/cm³) has been calculated in detail for an assumed random distribution of impurities. The system of donor electron spins is treated as a collection of nearest neighbor donor pairs. An expression is derived for the donor pair exchange energy using Kohn-Luttinger wavefunctions and a general exchange energy expression. The resultant relationship contains an adjustable parameter a*, the "effective Bohr radius", which is determined from a comparison of the calculated spectrum and the experimental results obtained for the ratio, C, of the "central pair" and "hyperfine" line intensities. The resulting expression J(R), where J represents the exchange energy and R the separation vector connecting the two pair donors, exhibits an oscillatory spatial dependence due to interference from portions of the wavefunction arising from different conduction band valleys. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

A completely general method has been developed for calculating Electron Paramagnetic Resonance (EPR) transition fields and transition probabilities from the spin Hamiltonian [formula omitted] The method is a generalization of a previously existing, limited technique, and can be applied without any restrictions. A general computer program has also been written based on the method. Using the program, the results of an EPR study on a U.V. irradiated single crystal of para-nitrophenyl azide were fitted to the spin Hamiltonian [formula omitted] The observed and calculated fine and hyperfine transition probabilities were found to be in good agreement. The observed hyperfine splittings, due to the nitrene nitrogen, were analyzed in terms of a 6.5 gauss linewidth, combined with the transition probabilities for the nine theoretical components of the hyperfine resonance fields. Evidence of a ¹⁴N quadrupolar splitting was observed, but not completely analyzed. In addition, evidence was found to indicate that the nitrene impurity is twisted somewhat from the position in the crystal lattice held by the parent azide. The EPR spectra obtained on U.V. irradiation of randomly oriented 1,5- and 1,8-diazidonaphthalene were analyzed, and found to originate from ground triplet state species with |D|= 0.8152±0.0010 cm⁻¹ and 0.7599±0.0010 cm⁻¹, respectively. The theoretical spin densities for the triplet and quintet states of 1,5- , 1,8- and 2,7- naphthalene dinitrene were calculated using the method of intermediate neglect of differential overlap (INDO). Attempts to obtain a consistent picture of multiplet spin densities based on the results of the calculations were largely inconclusive. / Science, Faculty of / Chemistry, Department of / Graduate

The work described in this thesis was initiated in an attempt to overcome the limitations imposed upon NMR spectroscopy by magnetic field inhomogeneity in two specific areas: high resolution spectroscopy in isotropic liquids, and chemical shift resolved NMR imaging in isotropic liquids. In both cases magnetic field inhomogeneity may degrade the resolution of spectra to such an extent that no useful information can be obtained from them. In high resolution NMR spectroscopy it is necessary to be able to extract accurately the parameters present within the spectrum such as chemical shifts, coupling constants and peak areas. In chemical shift resolved imaging experiments the requirements are less stringent; and it is only necessary that the resonances of different chemical species be resolved. However, even the less stringent requirements of NMR imaging are often difficult to meet as the sample volumes required are often several orders of magnitude larger than those required in conventional high resolution NMR spectroscopy. The use of zero-quantum coherence has been investigated as a potential solution to the magnetic field inhomogeneity problem in both of these areas. Zero-quantum coherences are independent of magnetic field inhomogeneity and contain the parameters desired in both cases, though they are displayed in a way which differs from conventional NMR spectra. In this thesis, existing zero-quantum coherence experiments have been evaluated for use with inhomogeneous magnetic fields, and, where necessary, adapted for this purpose. Several completely new experiments have been developed for producing broad-band decoupled zero-quantum coherence spectra and also for presenting coupling constants and chemical shifts in a manner which is as close to conventional NMR spectra as possible, hence facilitating ease of use. Zero-quantum coherence has been evaluated as a tool for identifying unknown compounds and also for identifying the components of complex mixtures by "signature" recognition. Both decoupled and non-decoupled zero-quantum coherence experiments are adapted to provide imaging experiments which allow the separation of the images of different chemical species in inhomogeneous magnetic fields. The two-dimensional J-resolved experiment is also adapted for this purpose. / Science, Faculty of / Chemistry, Department of / Graduate

The work described in this thesis is divided into two parts: testing and evaluation of some surface coils, and application of the surface coils to in-vivo studies. In particular, the localization properties of surface coils were examined and optimized using the highest performance coil geometry and wire. Application of the surface coil technique to in-vivo studies involved measuring changes in metabolic status of muscle and brain tissue in rats using ³¹P spectroscopy. The properties of surface coils have been studied by evaluating their excitation patterns with ¹H and ³¹P NMR spectroscopy. Surface coils, manufactured in different sizes, geometries, and materials were tested for Q factors, signal-to-noise ratios, and pulse widths required for excitation of the sample. A silver plating on the copper wire used to fabricate the surface coils was found to increase the Q and signal-to-noise of the coil. Examination of the excitation patterns of the surface coils with point samples characterized the B₁ field of the coils as decreasing axially and radially from the coil. Calculations of the magnitude of the B₁ field reveal that its dome-like shape extends to approximately one coil radius above the surface coil. It was found that samples lying outside the domain of this "sensitive volume" did not contribute to a spectrum. These data were all correlated and the "0.9" silver plated coil was deemed to be the most efficient coil with which to pursue further in-vivo studies. In-vivo ³¹P studies of rat tissues were preceded by in-vitro spectral measurements of various metabolites at physiological concentrations. These standards were used to aid in the identification of resonances in the in-vivo spectra. Metabolic changes such as artificially induced ischemia in muscle, deceased brain, and artificially induced brain dementia were compared with "normal" ³¹P spectra of anaesthetized rat tissues. It was found that oxygen deprivation is readily observed with this technique whereas the preparation of brain dementia cannot be diagnosed with ³¹P NMR spectroscopy. / Science, Faculty of / Chemistry, Department of / Graduate

A high resolution NMR probe was modified with gradient coils (31 mm diameter) for the measurement of translational diffusion and for microscopic imaging, and a larger set of gradient coils (15 cm diameter) was constructed for surface coil diffusion measurements. The magnitudes of the gradients produced by these coils were determined from the linewidths and lineshapes of gradient spectra. In diffusion experiments using the pulsed gradient method of Stejskal and Tanner, induced eddy currents and slow variation of the magnetic field at the sample interfered with measurements at short echo times. For these experiments the known diffusion coefficient of water was used to determine the effective gradient in each experiment. The diffusion coefficient of acrylonitrile was measured from the decay of single, double and triple quantum echoes using a modified pulsed field gradient spin echo pulse sequence. In the second part of this thesis, three examples of living systems were studied. The first involved the application of pulsed gradient spin echo measurements to characterize the motion of water and lipid, in-vivo, in human forearm. Spin echo spectra from human forearm gave a water signal that was attributed to extracellular water because of relatively long spin-spin relaxation time (0.8 s) compared to that of intracellular water (20-30 ms). Comparison of the diffusivity of water, from experiments at two different echo times suggest that the major part of the motion of water, in-vivo, was due to directionally randomized bulk flow rather than molecular diffusion. The second application involved the chemical shift resolved mapping of the proton distribution, in one-dimension, along the anteroposterior direction, of pupae of the Douglas-fir cone moth Barbara colfaxiana. Proton distribution maps showed that the distribution of the aqueous fluid depended upon the vertical orientation, head pointing upward or downward, of the pupae. Finally, two dimensional images of mature caps of the marine alga Acetabularia mediterranea were obtained using the normal spin echo sequence as well as with T₁, T₂ and diffusion contrasting. D₂O—contrasting was obtained by briefly submerging the caps in D₂O. All of these images showed features resembling the radial structure of the caps. The resolution was estimated by comparison with microscopic views of the caps and was found to be 0.1 mm, determined as the smallest distinguishable feature in the image. / Science, Faculty of / Chemistry, Department of / Graduate

The work described in this thesis concentrates on two aspects of Proton NMR imaging: development and evaluation of new/old experimental sequences and application of those techniques to study some non-medical systems that are of industrial importance. Two-dimensional Fourier transform spin warp imaging technique has been evaluated. Importantly, the adaptation of a conventional high resolution spectrometer to perform imaging has been demonstrated with means of "phantoms". This includes calibration of magnetic field gradients, mapping the static magnetic field and radiofrequency field distributions and intensity measurements related to proton spin densities. In addition, a preliminary study describes microscopic imaging of glass capillary tube phantoms containing water. Several different sequences related to Chemical Shift imaging including the one developed during the study have been described. A brief insight into chemical shift artifacts as well as some experimental methods of minimizing some of them have also been presented. The potential of NMR imaging to study non-medical systems has been explored in three different areas of interest: Chromatography columns. Porous rock samples and Wood samples. A variety of NMR imaging sequences have been used to study some interesting and challenging features of these systems which clearly extends the scope of NMR imaging science. / Science, Faculty of / Chemistry, Department of / Graduate

An analysis of the most commonly used type of Ion Cyclotron Resonance (ICR) spectrometer is given. Though the equations of motion of an isolated ion in the ICR geometry are extremely non-linear, it was found possible to decouple the longtitudinal oscillations due to the trapping potential from the cyclotron motion by exploiting the fact that the cyclotron frequency is very much greater than the trapping frequency. A previously unsuspected dependence of the cyclotron frequency and drift velocity of an ion on its spatial coordinates was discovered and experimentally investigated. The distribution of energies for ions at resonance with an applied r-f electric field is also discussed and improved techniques for the study of energy dependent cross-sections are proposed. Conventional ICR techniques were used to estimate collision frequencies of sodium and potassium ions in helium and argon gases. These experiments yield information about the d.c. drift mobility, in the zero field limit, of the alkali ions in inert gases and are discussed in terms of various models of the ion-atom interaction potential. A crossed beam arrangement was used to obtain preliminary estimates of low energy rate constants for both asymmetric and symmetric resonant charge transfer between alkali ion-atom pairs. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

NMR spectra of many systems governed by axially symmetric second rank tensor interactions exhibit P2(cos θ) dependence on the angle 9 between the symmetry axis and the externally applied magnetic field. For the so-called "powder samples" consisting of many randomly oriented domains the resulting spectrum is the superposition of contributions from each such domain. This study deals with a numerical technique enabling one to obtain the lineshapes of such individual contributions responsible for the given powder spectrum. The electric dipolar interaction between two spin 1/2 nuclei produces a characteristic powder lineshape called "Pake doublet", after G.E.Pake, hence the name "de-pake-ing". An iterative algorithm capable of dealing with spectra produced by a variety of systems is developed and checked by applying it to a wide range of simulated NMR spectra. A set of characteristic "signatures" associated with different experimental situations is established and the limits of the applicability of the technique are determined. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Subsynchronous Resonance (SSR) phenomena in a thermal-electric power system with series-capacitor-compensated transmission lines may cause damaging torsional oscillations in the shaft of the turbine-generator. This thesis deals with a wide-range multi-mode stabilization of single-machine and multi-machine SSR systems using output feedback excitation control. Chapter 1 summarizes the SSR countermeasures to date. Chapter 2 presents a unified electro-mechanical model for SSR studies, illustrates the torsional interaction between the electrical and mechanical systems, and demonstrates that multi-mass representation of the turbine-generator must be used for SSR studies. For the control design, a reduced order model is desirable. For the model reduction, modal analysis is applied to identify the excitable torsional modes, and a mass-spring equivalencing technique to retain only the unstable modes is developed in Chapter 3. Using the reduced order one: machine models, linear optimal excitation controls are designed in Chapter 4. The controls are further simplified by examining the eigenvalue sensitivity, and the results are tested on the linear and nonlinear full models. In Chapter 5, the stabilization technique is further extended and applied to a two-machine system and a three-4nachine system. The stabilizers still can be designed one machine at a time using a one-machine equivalent for each machine by retaining only the path with the strongest interacting current and the critical electrical resonance frequency as seen by the machine. To coordinate all controllers for the entire system, an iterative process is developed. The controllers thus designed are tested on linear and nonlinear full models. From both eigenvalue analysis and nonlinear dynamic performance tests of the one-machine, two-machine, and three-machine systems, a conclusion is drawn in Chapter 6 that the excitation controls thus designed by the methods developed in this thesis can effectively stabilize single-machine and multi-machine SSR, systems over a wide range of capacitor compensation. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

M.Sc. (Physics) / The differential cross-section for p(e, e¡ä¦Ø)p has been studied at Q2 ¡« 5.5 (GeV/c)2. Here Q2 represents the four momentum squared of the virtual photon in the excitation of baryonic resonances by an electron projectile. The excitation cross-section for the baryonic resonances and their de-excitation rates and channels provides information on the underlying structure of QCD. The selection of the ¦Ø decay channel constrains the particular baryonic resonances that contribute to the measured cross-section. A significant aspect of the data presented from W = 1.72 GeV to W = 1.92 GeV is that the Q2 falls in the region where the transition from non-pertubative processes characterised by constituent quarks dominate to the regime where the hard processes are expected to play an increasing important role. This is therefore an interesting region to acquire further data. In order to extract the ¦Ø-meson differential cross section from the JLAB data, the data was compared to a full Monte Carlo simulation of the detector based on events generated for omega production in a way that the production cross section was varied to achieve a match to the data. The binning selected for this procedure takes into account the measure of robustness of the stripping of the ¦Ø peak from the multi-pion background as well as the statistics in the measured data and the Monte Carlo simulation of the signal and background physics [1]. An error estimation technique for the cross section was based on determining the dependence via the Monte Carlo simulation of the extracted cross section parameters on the experimental set-up (including parameters for the spectrometer, target beam geometries and performance). We compare our results with a Regge-based model for hadronic content in the t-channel exchange of a photon in Q2 region of overlap. There is an extension of this data into a completely new region, which is the highest yet measured. The result from the study of baryonic excitation via the ¦Ø channel gives a good correlation between theory and experiment in the overlapped kinematic regime of the used theoretical simulation.