2005 MU dissertations - Access restricted to UM
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Item Source localization using TDOA with erroneous receiver positions(University of Missouri--Columbia, 2005) Kovavisaruch, La-or; Ho, Dominic K. C.[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] Source localization has been an active research for several years. It has applications in many areas such as geolocation and mobile user location. Various methodologies have been proposed to passively localize an emitting signal source. One of the most popular techniques is to use the Time Difference of Arrival (TDOA) measurements. TDOA localization technique determines the source position by examining the time differences at which the source signal arrives at multiple spatially separated sensors. There are several methods to solve the TDOA source location problem, and two of the widely known methods are the Maximum Likelihood method and the Taylor-series method. Those methods assume that the sensor positions are exactly known, and this assumption may not be the case in practice. The performance of these methods degrades significantly when the receiver positions have error. The estimation of the of the source location with sensor position uncertainty has been investigated for over a decade. While most of the previous research has been conducted on finding the bearing angle or the angle of arrival of multiple sources in the presence of sensor position noise, noise, in this research, the objective is to locate the exact position of a source in three dimensional space using TDOA measurements when there are random errors in the receiver positions. In this research, three methods are proposed to estimate the source position from TDOA measurements when the receiver positions have random errors. The first method is an extended work from Chan and Ho's work. Chan and Ho's method uses two-stage Least Square (LS) minimization. They introduce an auxiliary variable and solve the source position together with the auxiliary variable using linear LS minimization. The information in the auxiliary variable is then included to the location estimate through another LS minimization to improve accuracy. The first method includes the sensor position error power into a weighting matrix and uses it to improve the accuracy of the source location estimate. The second method consists of three steps. The first step is to estimate the source location with the noisy receiver positions. In the second step, the estimated source position is used to reduce the noise in the receiver positions in order to obtain more accurate positions of the receivers. And in the last step, the source is estimated again using the improved receiver positions from the second step. The source location estimate will be more precise due to better knowledge of receiver positions. The second and the third steps can be repeated several times to obtain even more accurate source location. The third method is based on the Taylor-series method and jointly estimates both source and receiver positions simultaneously. Both the first and the second proposed method utilize the weighted LS minimization to obtain the source and receiver positions and do not involve any linear approximation. Hence, they are computationally attractive and do not have the divergence and initialization problems. For the third method, one deficiency is that it requires a good initial solution guess close to the true solution to begin with in order to ensure convergence. In any case, the divergence behavior can often be detected so that reinitialization can be made. This researach also investigates the effect of receiver position errors to the accuracy of source location estimate in terms of the CRLB and the MSE. The observation confirms that the uncertainty in the receiver position did degrade an estimator's performance. In addition, this research also includes the study of the effect of the choice of reference receiver in the presence of unequal receiver noise power. The study indicates that CRLB is independent of the choice of the reference receiver. Nevertheless, the performance of the proposed closed form solutions is affected by choice of the reference receiver in near-field case, but not the far-field case.Item Experimental study of localization in sensor networks and design of adaptive localization algorithms(University of Missouri--Columbia, 2005) Ahmed, Ahmed Abdol-Monem, 1972-; Shi, Hongchi[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] We design an experimental framework to evaluate localization methods for sensor networks. We use this framework to evaluate three existing localization approaches: Ad-hoc Positioning System (APS), Multidimensional Scaling (MDS), and Semidefinite Programming (SDP). Using this evaluation, we study the effect of several factors that affect the performance of localization. Through experimental study of the three selected localization methods, we present one possible combination of APS and MDS into one relative localization method that we refer to as: Simple Hybrid Absolute Relative Positioning (SHARP). Our proposed method performs better than both APS and MDS if both the localization accuracy and the energy consumption are considered. We further investigate different approaches to design of localization methods that are adaptive to network properties. This adaptation can be at the network level or at the partition level. In both cases, off-line training is used to decide which localization methods perform the best under what network properties. In the first case, dynamic discovery of network properties is assumed. Then, the training results are used to decide which algorithm to use. In the second case, training is done on network partitions (maps). The network is divided into local maps, where each map is supposed to have different set of network properties. Every map runs its own localization method. Finally, local maps are merged to form a global map, and anchors are then used to estimate the absolute positions.Item Crystal structure of the kelch domain of human keap1(University of Missouri--Columbia, 2005) Li, Xuchu, 1976-; Hannink, Mark, 1958-[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] Nrf2-Keap1 signal transduction pathway senses oxidative stress and protects eukaryotic cells against oxidative damage and cancer. The transcription factor Nrf2 induces Phase II stress response genes, which enable cells to neutralize reactive molecules and restore cellular redox homeostasis. Keap1 is a BTBKelch protein that regulates both the subcellular localization and steady state levels of Nrf2. Recently our lab has identified Keap1 as a redox-regulated substrate adaptor protein for a Cullin3-dependent E3 ubiquitin ligase complex, which targets Nrf2 for degradation in a controlled manner. The research project presented in this dissertation is to study the interaction between Nrf2 and Keap1 starting from a structural biology approach. The N-terminal Neh2 domain of Nrf2 mediates binding of Nrf2 to the Kelch domain of Keap1. We solved the crystal structure of the Kelch domain of human Keap1 and carried out detailed analysis of the structural/solvent features in this domain. This domain structure, which was the first high-resolution structure of a mammalian Kelch domain, demonstrated that the Kelch domain of Keap1 is a six-bladed ?-propeller that uses a C-terminal mode of closure. The structure revealed how conserved amino acids and water molecules contribute to both inter- and intra-blade stability and provided insight into how disease-causing mutations perturb the structural integrity of the Kelch domain. We found that the bottom loops of the Kelch domain are critical for its sufficient association with the Neh2 domain. Based on mutagenesis data, we mapped out a Neh2-Kelch interface on the bottom side of the Kelch domain. We further crystallized a putative Kelch-Neh2 complex that diffracts to 4[angstrom]. We are now in the process of obtaining high quality crystals of the Neh2-Kelch complex for structure determination purpose.--From public.pdfItem The effects of media framing of political conflicts on party identification and political participation(University of Missouri--Columbia, 2005) Song, Hyun-Joo, 1970-; Wanta, Wayne[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] Prior research identified the logical chain from strategic coverage to cynicism to demobilization. Considering the fact that party identification anchors an individual's patterns of political behavior, and that political cynicism might be negative attitudes generalized from particular leaders or political groups to the political process as a whole, the present study postulated that party identification mediates the effect of conflict coverage on political participation. The results from an experiment conducted in the context of Korean politics were as expected. Strategic coverage engendered negative feelings toward political parties; issue coverage made party identification more polarized than before. Party identification change, in turn, had a significant impact on political participation. Strategic coverage depressed the intention of political participation while issue coverage facilitated political participation.Item Functional characterization of the Arabidopsis disease resistance gene RPS4(University of Missouri--Columbia, 2005) Zhang, Xue-Cheng, 1975-; Gassmann, Walter, 1964-[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] The Arabidopsis disease resistance gene RPS4 activates defense responses to the bacterial pathogen Pseudomonas syringae pv. tomato strain DC3000 expressing avrRps4 in a gene-for-gene specific manner. Like other plant TIRNBS-LRR resistance genes, RPS4 produces multiple transcripts via alternative splicing. Alternative RPS4 transcripts are predominantly generated by intron retention. First, the biological significance of these alternative transcripts in disease resistance was analyzed. It was shown that alternative RPS4 transcripts are required for complete function and that RPS4-mediated resistance requires the combined presence of multiple transcripts encoding both full-length and truncated open reading frames. Interestingly, the dominant alternative transcript is the only alternative transcript whose abundance relative to the regular transcript undergoes dramatic and dynamic changes during the resistance response. Furthermore, RPS4 expression is induced by AvrRps4 and an unrelated effector, HopPsyA, in an EDS1-dependent manner. These data suggest that rapid gene induction and changes in transcript ratios might be under coordinated regulation that are important to fine-tune RPS4-mediated resistance. Our previous data showed that removal of one intron abolished RPS4 function. However, no significant changes of transcript ratios in intron-deficient transgenic rps4-1 plants were observed compared to rps4-1 expressing a wild type genomic transgene, suggesting that the artificial removal of one intron has no effect on the splicing frequency of other introns. In consistent with our previous data, analyses on secondary RNA structures suggest that alternative RPS4 transcripts function at protein level. Of the three expected truncated RPS4 proteins, only one was detected and stable in vivo, indicating that RPS4 protein stability or activity is regulated. In summary, RPS4 function is regulated at multiple levels including gene expression, alternative splicing and protein stability or activity.