published_or_final_version / Physics / Master / Master of Philosophy

published_or_final_version / abstract / Physics / Master / Master of Philosophy

These studies explored interactions between flavanols and nitric oxide in order to investigate implications for vascular health. Study 1 investigated acute effects of flavanol consumption on cutaneous microvascular endothelial function in young and older individuals along with chronic exposure in older individuals. This was accomplished by assessing skin blood flow response to local heating (thermal reactivity, TR); skin was clamped at 34°C and 40°C and values were normalized to those attained at 43°C. Older individuals demonstrated an attenuated TR at baseline during the entire local heating phase (58.4 ± 2.5% versus 49.3 ± 2.6%, p<0.05). Acutely following flavanol ingestion there was a significant increase in TR (52.4 ± 2.1% versus 56.1 ± 2.0%, p=0.05) that was not different with age. There was no effect of chronic flavanol exposure on TR in older individuals; however, there was a significant decrease in mean arterial pressure (95 ± 3 mmHg versus 91 ± 3 mmHg, p<0.001). These results contribute to research regarding flavanols increasing NO bioavailability; acutely via an improvement in cutaneous microvascular endothelial function and chronically via a reduction in blood pressure. Study 2 investigated the acute effects of flavanol consumption on cerebrovascular endothelial function in young and older individuals along with chronic flavanol exposure in older individuals. This was accomplished by assessing basal cerebral blood flow indices (cerebral vascular conductance index, CVCi) and CBF response to hypercapnia (cerebral vasomotor reactivity; CVMR). At baseline older individuals demonstrated a reduced CVCi (0.85 ± 0.04 cm/s*mmHg versus 0.55 ± 0.04 cm/s*mmHg p=0.001) and CVMR (8.6 ± 0.6 versus 6.9 ± 0.4, p=0.05). An unexpected finding was that flavanol ingestion led to an acute decrease in CVCi (0.71 ± 0.04 cm/s*mmHg versus 0.62 ± 0.04 cm/s*mmHg p<0.05) and CVMR (8.6 ± 0.6 versus 6.1 ± 0.5, p=0.001) that was not different with age. In older individuals, chronic exposure led to a significant increase in CVCi (0.60 ± 0.05 cm/s*mmHg versus 0.72 ± 0.06 cm/s*mmHg, p<0.05) but had no effect on CVMR. These data provide evidence for an improvement in cerebral hemodynamics following chronic exposure in older individuals. / text

Zinc oxide (ZnO) is a promising material for ultra-violet optoelectronics applications due to its direct band gap and large exciton binding energy. Defect in semiconductor plays an important role in determining the optical and electrical properties. It is thus crucial to understand the defects‟ performance for realizing the device fabrication. Green luminescence (GL) having the peak at 2.4-2.5 eV is a defect related emission band commonly found in the luminescence spectra of many of the ZnO materials. Despite of the effort devoted for several decades, its origin and emission mechanism remain controversial. In this thesis, the origin of the GL emitted from the ZnO films grown by pulsed laser deposition (PLD) is studied using a comprehensive spectroscopic approach, including the Hall effect measurement, photoluminescence (PL), Raman spectroscopy, positron annihilation spectroscopy (PAS), and secondary ion mass spectroscopy (SIMS). ZnO thin films are grown by PLD method with the growth parameters (namely the substrate temperature and oxygen pressure during the growth) systemically varied. Annealing studies in argon atmosphere reveal the correlation between the free electron concentration and the hydrogen concentration in the samples. Two oxygen deficient defect related Raman modes are also identified and they anneal out after annealing at high temperature. We have investigated the introduction the GL systematically grown by different growth parameters, undergone different post-growth annealing treatment, and different methods of growth. Two kinds of GL’s are identified. The first kind of GLs has peak at 2.47 eV without the fine structure, and the other has the peak at 2.45 eV having the fine structure of separation of 0.07 eV. The GL with the fine structure is originated from the surficial region of the ZnO film. The GL without the fine structure is introduced after the annealing 900℃ irrespective of the initial growth conditions. PAS results show a strong correlation between the thermal introductions of a kind of Zn-vacancy and the GL without the fine structure. Moreover, a donor-acceptor-pair (DAP) emission is induced in the low temperature PL spectrum after the same annealing temperature of 900℃. The GL and the DAP emissions are thus associated with the involvement of the VZn. Furthermore by comparing the photon energies of the GL and DAP with the previous first principle calculated results, the GL is ascribed to the conduction band to the (-/2-) acceptor level of VZn, and the DAP involves the (0/-) acceptor level of VZn The presence of the conduction band to the (0/-) level transition is compatible with the results of the photoluminescence excitation (PLE) study. / published_or_final_version / Physics / Doctoral / Doctor of Philosophy

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