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2-Acetyl-1-pyrroline (2-AP) is a popcorn-like aroma compound with low odour detection threshold. This compound is regarded as the key contributor of fragrant rice aroma. 2-AP can be detected in fragrant rice, whereas the content of this compound in non-fragrant rice is too low to be detected. Levels of 2-AP in raw fragrant rice can be affected by abiotic stress and growth conditions, such as climate and soil conditions. Whereas it was originally thought that this compound could not be enhanced post-harvest, including cooking. One previous study in our research group demonstrated that 2-AP could be increased in fragrant rice after baking at 180 °C for 20 min. Hence, the objective of this project was to evaluate the mechanism of 2-AP formation in rice during cooking. 2-AP content was evaluated in fragrant and non-fragrant rice prepared by different cooking methods. The results of sensory evaluation on boiled milled rice confirmed that 2-AP and its popcorn-like aroma is the most important factor to differentiate fragrant and non-fragrant rice. Popcorn-like aroma was also noticed in boiled non-fragrant rice and the results from GColfactometry confirmed the presence of 2-AP in raw non-fragrant rice. Levels of 2-AP increased on baking milled rice (without water addition) at 180 °C. As the high level of lipids and polyphenols in rice bran might affect 2-AP formation during baking, 2-AP was not observed in rice bran after baking. When milled rice was baked at a range of temperatures, formation of 2-AP in fragrant and nonfragrant rice showed different trends; maximum 2-AP formation was observed in fragrant rice at around 100 °C, whereas 2-AP formation in non-fragrant rice only took place when the baking temperature was higher than 140 °C. Addition of intermediate compounds confirmed that the 2- AP formation at 180 °C occurred through Maillard reaction; the addition of external 1-pyrroline and methylglyoxal was shown to reduce 2-AP generation yield at 100 °C. These results suggested that formation of 2-AP in both fragrant and non-fragrant rice is driven by Maillard reaction at 180 °C baking. However, 2-AP generation in fragrant rice during baking at 100 °C may follow another reaction pathway and this pathway is sensitive to 1-pyrroline and methylglyoxal. Further research should focus on the effect of biosynthesis on 2-AP generation at 100 °C baking.

Nerve conduction block elicited by high frequency electrical stimulation may be used to create chronic neuroprostheses to treat diseases that are characterized by pathological nervous activities. Previous studies have demonstrated that local and reversible nerve conduction block can be achieved using high frequency stimulation (3-6 kHz and above) delivered through cuff electrodes. However, cuff electrodes are designed to be placed encircling the nerve and demands invasive surgical procedure that may not be desired by patients in clinical applications. This study investigated the nerve block effect of high frequency stimulation delivered through a percutaneous lead placed next a motor nerve trunk in dogs. The optimal frequency and amplitude windows for nerve block using a biphasic rectangular waveform were 10-30 kHz and 15-20 V peak-to-peak within the tested parameter range (5-40 kHz and 5-20 V). Higher frequencies may require higher amplitudes to achieve nerve block effect. In addition, activation threshold of the nerve evoked by the biphasic high frequency stimulation also increased with frequency. The HFS nerve block was repeatable in more than 40 minutes of repetitive stimulation. This study demonstrated that it is feasible to achieve local reversible nerve block using percutaneous lead electrodes placed next to a nerve with biphasic high frequency waveform. Although it may be difficult to block all the nerve fibers in a nerve trunk with a percutaneous lead, partial nerve block can be clinically useful and desired in many disease conditions.

In the first essay, I examine the impact of the introduction of exchange traded funds (ETFs) options on the information related trading of index options. Two option pairs, NASDAQ 100 index (NDX) and ETF (QQQ, currently QQQQ ) options, and Standard and Poor's 500 index (SPX) options and S & P Depository Receipts (SPY) options, are studied. I test the hypothesis, based on the theory of Chowdhry and Nanda (1991), and Admati and Pleiderer (1988), that the information component of spreads for index options should decline after ETF options were introduced. The method of George, Kaul and Nimalendran (1991) is used to estimate the adverse selection proportion of log quoted spread and revenue from quoted spread. Primary results show that the adverse selection component of index options declines after the introduction of ETF options, and that the adverse selection component of options on index ETFs is greater than that of options on index, suggesting more informed trading for ETF options. The second essay examines whether the liquidity premium decreases as the costs of transactions decline. Nine liquidity measures are estimated to form liquidity deciles portfolios. I use several benchmark asset pricing models in fixed and rolling 36-month samples to estimate time variation liquidity premia. Surprisingly, the results show that the liquidity premium does not monotonically decline over time, and it increases in the period from 2001 to 2006. This is inconsistent with the implication of liquidity-adjusted capital asset pricing models (L-CAPM). It is likely that the liquidity premium is generated by size and book-to-market factors, rather than the liquidity factor.