Triazenes, compounds containing a diazoamino moiety (–N(1)=N(2)–N(3)<), are known for their reversible cis-trans isomerization character and hence, have the potential to be used in photoswitchable devices and photostorage media. However, little is known about their cis-trans isomerization mechanism. In this thesis, kinetic studies on the thermal cis-to-trans isomerization of N-(phenylazo)-substituted nitrogen heterocycles are presented. It is shown that the isomerization rate constant increases as the size and electron-donating character of the cyclic amine increases, as the electron-withdrawing character of the para substituent group on the phenyl ring increases, and as the polarity of the solvent increases. All these trends are interpreted in terms of a rotational isomerization mechanism involving a dipolar transition state. In addition, photolytic cleavage of the N(2)–N(3) bond of target substrates is shown to be affected as well by the size and electronic character of the cyclic amine, the electronic character of the phenyl ring substituent, and the polarity of the solvent, with the result that the photolysis yield increases as the isomerization rate decreases. Theoretical calculations on target substrates both in the gas phase and various solvents were also performed based on DFT-B3LYP/6-31+G* method. Overall, the cis-to-trans isomerization is predicted to take place through rotation around the N(1)=N(2) bond. Furthermore, the calculated energy barriers are found to be influenced by the size and electronic character of the cyclic amine, the electronic character of the phenyl ring substituent, and the polarity of the solvent, consistent with the effects obtained experimentally from the kinetic studies.

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Lasers pose a safety hazards both to skin and particularly to something you value highly - your vision. The increasingly widespread use of IR wavelengths laser systems requires awareness with the potential hazards associated with the misuse of these valuable products. The principal goal of this research is to integrate experimental and theoretical descriptions of thermal response of skin and cornea to IR wavelength laser irradiation to yield a basis for the dosimetry of laser-tissue interaction. The threshold radiant exposures for various spot sizes and exposure durations were investigated on in vivo skin and cornea for 2.0 [mu]m laser irradiation. Similar study was also conducted on in vivo skin using 1.214 [mu]m laser and compared with 2.0 [mu]m results. This PhD study has, for the first time, linked temperature response, histopathology, and the more common "minimal visible lesion (MVL)" endpoint into what can be a meaningful comparison of rate process models for injury. Based on experimental data, a finite-element optical-thermal-damage model was developed. Histological damage was measured and modeled using sub-threshold, threshold, and super-threshold 2.0 [mu]m laser powers. The data provided experimental evidence of the correlation of sub-threshold histological change to visible threshold lesion for the irradiation condition of this study. Moreover, the computer model, supported by experimental validation, ensured that rate process models were used correctly in the prediction of "MVL" thresholds which were based upon a finite damage extent and not necessarily central surface layer damage. Thermal image method was employed to measure the absorption coefficient of in vivo skin at 2.0 [mu]m, at which wavelength scattering can be ignored. At laser wavelengths below 1.4 [mu]m where scattering cannot be ignored, an ameliorative method was explored to measure absorption and reduce scattering of in vivo tissue by combining pulse photothermal radiometry (PPTR) and diffuse reflectance (DR) measurements.

An infusion technique was used with an aqueous radiocalcium ( 45CaCl2) solution during the seed-filling stage of well-watered and moisture-stressed soybean in a greenhouse. The kinetics of infusion volume showed a quadratic reduction in absorption which approached zero on the sixth day for non-irrigated plants. The concentration of 45Ca increased quadratically from the point of injection towards the apex independent of both water status and plant parts. The difference in concentration of 45Ca between irrigated and non-irrigated plants was significant (P < 0.05) and concentrations attained the maximum values at the sixth node from the plant base. Seeds contained considerably less 45Ca than either stem or leaves. / The effects of a long (LD, 16h) and a short (SD, 12h) photoperiod with two water stress levels (SL) of stress (ST) and no stress (NS) on the distribution of 45Ca in plant organs (PO) of leaves, petioles, and stem at different node number (NN) of soybean were studied during the seed-filling stage. The univariate and Manova analyses showed the main effects of photoperiod (PP), SL, and PO to be highly significant (P < 0.001) on Ca distribution. The long PP increased Ca concentration in top leaves compared with the short PP regardless of SL. Water stress significantly (P < 0.001) modified the Ca distribution and reduced its concentration in PO within NN irrespective of the photoperiod (a measure of light stress). A possible mechanism for the regulation of Ca distribution is discussed in terms of nitrate reduction. / Ca uptake was also studied by immersing the central tip of a trifoliate leaf in various concentrations of 45CaCl2 solutions and drought conditions during the seed-filling period of soybean. The beta-ray gauging and the diurnal leaf temperature variation showed similar characteristics for leaf water status. The activities of 45Ca were significantly higher (P < 0.0001) at 5, 10, 20, and 30 mM concentrations for water-stressed and non-stressed leaves compared with the control. 45Ca activities at 5, 10, and 20 mM Ca concentrations between stressed and non-stressed leaves were not significant, but the difference in their mean values at 30 mM Ca concentration was significant (P = 0.0159). The relationship between 45Ca uptake and Ca concentration was parabolic for both stressed (R 2 = 0.77) and non-stressed (R2 = 0.81) leaves. Autoradiograms indicated Ca movement through the mid-rib and veins of the tip-immersed trifoliate leaf but showed no activity in other plant parts. An activity gradient developed between seeds when a pod-tip was immersed in the radioactive solution. Solutions of ruthenium red (RR, 0.01 mM), Ethylene Glycol-bis-(beta-aminoethyl ether)- N,N,N,N-Tetraacetic Acid (EGTA, 0.1 mM), calcium (Ca, 1 mM), and double distilled water (control) were fed through a bottom branch of soybean with (ST) and without (NS) water stress. The volume absorptions and transpiration rates were significantly higher for NS than ST plants and decreased almost linearly with time for all treatments. The transpiration rates of Ca-feeding ST plants and the control overlapped while the NS plants approached the same rate of transpiration by the third week. Ca was implicated in stomatal closure for the reduction in the transpiration rates. The relative amounts of chlorophyll decreased with time but chlorophyll was least affected for Ca-absorbing plants for both ST and NS plants. The use of RR (Ca transport blocker), and EGTA (Ca chelator) indicated the role of intracellular Ca conce

This paper documents a major shift in market microstructure during the period 1990 through 1999. In particular, a dramatic change in the pattern of cash flows by individual and institutional investors is documented. The question becomes, what effect this change has on day-of-the-week return patterns for the Dow Jones Industrial Average, Standard and Poor's 500 index, and Standard and Poor's 500 index futures. I find Monday's return pattern has changed in the decade of the 1990's. Not only is Monday's mean return significantly large and positive for all indices, the entire anomalous pattern occurs from Monday's open to Monday's close - an intraday effect. In addition, I find evidence that trading volume is a factor in explaining the anomalous behaviour of Monday's returns. New York Stock Exchange trading volume is significantly lower on Mondays from the trading volume of other days of the week but the trading activity of individual investors is significantly higher. More recently, individual investors have increased their buying activity on Mondays relative to prior periods. Finally, Monday exhibits the largest returns in the first two trading hours when the Dow Jones Industrial Average returns are decomposed into hourly returns. The research emphasizes the dynamic nature of the time series patterns of stock returns and the suggestion day-of-the-week return patterns are not robust over time. Therefore, familiarity with market microstructure issues is just as important as the statistical techniques utilized.

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published_or_final_version / Biochemistry / Master / Master of Science