Theses and Dissertations
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PublicationDirect evidence for a non-radical pathway in the photoracemization of aryl sulfoxides( 2001)Resolved chiral sulfoxides have been shown to undergo racemization under photolytic conditions. Although a mechanism utilizing [Alpha]-cleavage and recombination has long been known, direct evidence for a mechanism by which sulfur can undergo pyramidal inversion has been lacking. Irradiation of (R[Subscript s],S[Subscript c])-1-deuterio-2,2-dimethylpropyl p-tolyl sulfoxide in acetonitrile at 254 nm gave a predominance of the pyramidal inversion product, (S[Subscript s],S[Subscript c])-1-deuterio-2,2-dimethylpropyl p-tolyl sulfoxide, as well as smaller amounts of other stereoisomers which probably result from [Alpha]-cleavage and recombination. The quantum yield for inversion ([Phi subscript inv]) at the sulfur center was found to be 0.44, which is close to the expected maximum of 0.5 for either an [Alpha]-cleavage or pyramidal inversion mechanism. A best fit kinetic simulation has been plotted to model the results of the photolysis in terms of simultaneous cleavage and inversion pathways. This is the first direct evidence for sulfoxide photoracemization which can not be explained by the cleavage and recombination radical mechanism alone.
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PublicationUltrasonic signal processing and classification using principal component analysis( 2001)In ultrasonic signal processing, discriminatory information exists in the variations in a neighborhood of signals. Principal component analysis (PCA) is a method to measure the variances in the signals and to transform the signals to a lower dimensional space for classification. PCA is a multivariate analysis technique that reduces the dimensionality of the data set by transforming the data to a new set of variables that are aligned with the directions of greatest variability of the original data set. This technique may be applied to Nondestructive Evaluation (NDE) for signal classification purposes. A neural network-based signal classification system is proposed for the interpretation of ultrasonic signals obtained from inspection of welds, where signals have to be classified as resulting from porosity, slag, lack of fusion, or cracks in the weld region. Standard techniques rely on differences in individual A-scans to classify the signals. Ultrasonic NDE classification is performed using PCA derived features. These features may be used to quantify the variance in NDE signals and determine how the ultrasonic signals vary based upon the class. Classification of the signals is performed using features based on the eigenvalues, eigenvectors, and principal components of the covariance matrix generated from ultrasonic signals. Rigorous preprocessing of the signals is required in this classification consisting of time gating, normalization, and signal alignment. Additionally, PCA is computed on transform domain signals including the Fourier transform, Wavelet transform, and Cosine transform. The results indicate that PCA may be useful to significantly reduce the feature vector's dimensionality while maintaining high classification performance.
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PublicationMultiagent system applications to electric power systems: Negotiation models for automated security-economy decisions( 2001)Complexities in information management and distributed decisions has the potential to evolve as a limiting factor for efficiently utilizing existing resources and optimally balance the interplay between economic and security concerns in the electric power system. Examining alternative security-economy decisions is a very complex and stressful activity performed by human operators using present day software tools. This has been acceptable in the past because there was a sense in the industry that there was no need to act otherwise. A practical result is we do not now have the infrastructure to provide comprehensible information and knowledge, in support of decision-making under complex, data-intensive, and stressed scenarios. To this end, this thesis proposes a framework based on multi-agent systems to elicit coordinated and negotiated decisions from power system decision-makers. Applications of specific interest include those involving balancing system level security with individual agent's economic self-interest. The uniqueness of this thesis is that a novel decision-making context involving transmission companies and the system operator is proposed, and novel solution to this problem via multi-agent negotiations is provided. An added contribution of the thesis is the top-down approach that has been employed in this research: instead of narrowly focusing on this application, this thesis designs and develops a Java-based software infrastructure to easily instantiate agents and distributed multi-agent systems and implements a generalized value-based negotiation framework for multi-objective decisions. This infrastructure is then used to design, engineer, and evaluate the aforementioned negotiated decision-making context involving transmission companies and the system operator.
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PublicationInsertion site similarities in the Tc1/mariner element family( 2001)In this study we report the first insertion site profile for the Tcl-like transposon Sleeping Beauty. We found that Sleeping Beauty prefers a consensus sequence of ATATATAT, where the underlined TA represents the canonical target site. We also performed computational structural prediction analyses on Sleeping Beauty insertion sites and found that they were significantly different from random DNA. We then compared Sleeping Beauty's insertion site structural profile with the insertion site profiles generated from three other studies of Tcl/mariner elements: Tcl (genomic copies and experimentally induced insertions (van Luenen and Plasterk, 1994)), Tc3 (van Luenen and Plasterk, 1994) and Himarl (Lampe et al., 1998). Through this comparison we found that bendability, protein-induced deformability and A-philicity are the most significant for determining insertion site preference. We further examined Tn5 and Tyl insertion sites and found that Tn5 shares similarities with the Tcl/mariner elements whereas Tyl insertions do not. Therefore, we predict that a large amount of the Tcl/mariner elements', and possibly other DNA transposons, target site specificity relies on unusual DNA structure in the area of insertion.
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PublicationThe effect of water stress on genetic recombination in maize( 2001)Plant genomes have the capacity to change in response to abiotic stress and other environmental signals. Increased recombination has been proposed as a response mechanism in several species (e.g., Drosophila, Neurospora, Mus and Lycopersicon). In maize, effects on recombination have been documented for sex, genotype, environment, chromosome rearrangements and supernumerary chromosomes. The effects of water stress have not been reported. In this study, we compare male recombination observed in stress and non-stress plants. In the greenhouse, two treatments were applied to F1 plants (B73xMo17), stress (25% field capacity), and non-stress (field capacity). The treatments were applied before and during male meiosis. Backcross populations (93 individuals each) were created by crossing each F1 as male to B73. Two backcross populations (i.e., two F1 plants) from each treatment were analyzed with 16 SSR loci from chromosome one to create genetic maps. Comparisons of recombination were made within and between treatments. No significant differences were observed between maps within a treatment; therefore, maps from the same treatment were combined. However, differences were observed between treatments: the total genetic map length was greater for stressed plants (170.7cM vs. 156.4cM). The long arm of the chromosome one was the region of additional recombination in the stressed plants. A significant excess of Mol7 alleles was observed in the same genetic region of all populations. Analyses of an additional backcross population for chromosome one and the study of another chromosome are being conducted.