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A study of Linear Polarizations Resistance Measurements for silver metal immersed in a solution of AgNO3 and HNO3 to determine the effect of varying potential sweep rates has been made. Results indicate that for the system under investigation the Polarization Resistance is a non-linear function of potential sweep rate.

<p> The rapid increasing bandwidth requirement of communication systems demands powerful numerical simulation tools for optics fiber. The computational efficient, memory saving and stable are of the most important characteristics for any simulation tools used for long-haul and broadband optics fiber. An optimized split-step digital filtering method is developed in this paper. The concept of Fourier integral and Fourier series are used in extracting a FIR filter which is used to fit the original transfer function. A further optimization process which employs windowing technique to improve computation efficiency had also been done. Compared with split-step frequency method, our method improves the computation efficiency. Only simple shifts and multiplications are needed in our method. This optimized digital filtering method differs from the former digital filtering method in a sense that the filter length of the FIR filter we extracted is reduced to a very small number. The computation time can be saved as much as 96% than before. This method can also be used to solve coupled nonlinear Schrodinger equation which governs polarization mode dispersion effect in fibers. A new simulation scheme for PMD is proposed to save computation time. The propagation results shows good accordance to those already published results. </p> / Thesis / Master of Applied Science (MASc)

<p> The experimental technique of measuring the degree of polarization of photoluminescence is studied. Digital signal processing techniques are applied to characterize the spectrum of the experiment and optimize its configuration for accuracy and precision. Digital phase sensitive detection is analyzed and the design of a digital lock-in amplifier is presented. Mechanical frequency modulation of the photoluminescence is reported and a physical model is presented. Procedures for enhancing measurements are stated with a reduction in noise levels of approximately 50% reported. </p> / Thesis / Master of Applied Science (MASc)

Flow 1H dynamic nuclear polarization (DNP) experiments of small probe molecules (i.e. chloroform and benzene) were conducted in normal liquids (i.e. neat benzene, deuterated benzene, chloroform) and supercritical fluid CO₂. Initial data collected on the 14N NMR line width of acetonitrile in normal liquids and SF CO₂ resulted in a 2-6 factor increase in the molecular motion of the molecule in the SF--the result of which corresponds to the expected factor increase in DNP signal enhancements in the low viscosity fluid. Observed DNP signal enhancements were 2-5 times greater in the supercritical fluid versus the normal liquids in both the solid-liquid intermolecular transfer (SLIT) and liquid-liquid intermolecular transfer (LLIT) experiments. Significant changes in the electron spin-spin (T1S) and spin-lattice (T2S) relaxation times of the nitroxide radical TEMPO in neat benzene, deuterated benzene, and SF CO₂ were noted; the T1ST2S product (calculated from DNP saturation plots) of the LLIT DNP data were compared. Due to the high pressures and elevated temperatures necessary for optimum flow DNP with SF CO₂ (e.g. P = 2310 psi, T = 313 K), high pressure flow cells were developed (and, also, adapted to a commercially available probe in the NMR regime) using PEEK (polyetheretherketone) material. / Ph. D.

The solid/liquid intermolecular transfer (SLIT) flow dynamic nuclear polarization (DNP) experiment potentially provides new methodology for studying interfacial phenomena (e.g., weak hydrogen bonding). In addition, the high efficiency of the transfer also ensures dramatically enhanced NMR signals. These large DNP enhancements could alleviate sensitivity limitations in various flow NMR experiments. Previous studies have established that silica phase immobilized nitroxide (SPIN) radical system are advantageous in the SLIT experiment. In favorable cases (e.g. DCCI₃/SPIN system) a ¹³C DNP enhancement 60 times in excess of the high magnetic field (4.7 T) magnetization has been achieved.¹² However a number of factors still limit the SPIN system presently available. For example, low magnetogyric ratio nuclides, ¹³C, ¹⁵N, which are not dominated by scalar relaxation mechanism require high surface radical concentrations. The focal point of the present study is the preparation and characterization of several new SPIN radical systems and can be divided into two parts: 1). Preparation, EPR, and DNP Characterization of Achiral SPIN Radicals: a number of SPIN samples were prepared in order to examine the dependence of the observed SLIT DNP enhancements as a function of the surface spin concentration and also isotope-substitution of the immobilized radicals. The SPIN samples were characterized by EPR and DNP. The results show that the increase in the spin concentration does not offer any advantage for ¹H DNP studies. In contrast, ¹³C SLIT DNP results in improved SPIN sample demonstrate the possibility of monitoring dipolar dominated ¹³C DNP enhancements as a result of better leakage factors and suppressed three-spin effects at higher radical concentration. The effect of substitution of deuterons for protons in the immobilized radical also suggest an appreciable contribution of a solid-state three-spin effect. 2). Preparation, EPR, and DNP Characterization of Chiral SPIN Samples: This part of the study provides a chiral SPIN radical suitable for monitoring enantioselective ¹³C DNP enhancements. The DNP results suggest that selective enantiomer/chiral SPIN interactions are feasible. Specifically, differences in the ¹³C DNP enhancements for a model system: (R)- and (S)- enantiomers of bromocamphor, and a (R) chiral SPIN sample were observed. / Ph. D.

A flow solid/liquid intermolecular transfer (SLIT) ¹H dynamic nuclear polarization (DNP) experiment is described. The SLIT ¹H DNP results are reported for the case of flowing benzene over silica gel surfaces prepared with stable immobilized nitroxide and phenoxy spin labels. The advantages of the flow SLIT DNP experiment in comparison with the recently reported flow liquid/liquid intermolecular transfer (LLIT) ¹H DNP experiment are discussed. The results suggest that the flow SLIT DNP experiment provides a new method for monitoring liquid/surface intermolecular interactions, since the reporter group (flowing benzene) reflects properties of the surface. Potential applications such as: 1) observation of enhanced NMR signals without detrimental line broadening due to the presence of stable free radicals in the NMR detection region, and 2) independent optimization of the "EPR" and "NMR" portions of the DNP experiment, are discussed. The thrust of this thesis was twofold: 1) to synthesize immobilized free radical systems appropriate for the SLIT DNP measurements, and 2) to establish the factors influencing DNP mechanism(s) for these systems. The resulting ¹H DNP line shapes imply that both Overhauser effect and solid- state effect are effective mechanisms for the DNP enhancements. The results suggest that the relatively low magnitude of the enhancements can be attributed to the longer molecular correlation times of the solid/liquid systems studied. Also, the EPR spectra and the corresponding number of unpaired spins were measured for these immobilized systems. / M.S.