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Acyldepsipeptide (ADEP1) is an antibiotic that binds to Escherichia coli ClpP, mimicking the interaction that the protease typically establishes with ClpA/ClpX ATPases in bacterial cells. Binding of ADEP1 causes the N-terminal end of the ClpP to adopt a structured β-hairpin and triggers opening of the axial gate in the tetradecameric ClpP. Open conformation of the axial gate causes translocation of the substrates into the catalytic chamber of ClpP and the resultant uncontrolled proteolysis renders cellular death making ADEP1 a potent antibiotic. Our current understanding about the ADEP1-induced open conformation of the axial gate is limited. Based on the existing X-ray structures, it is unclear whether the mechanism of ADEP1-mediated activation of ClpP is conserved in Gram-positive and Gram-negative bacteria. To understand the activation mechanism of ClpP by ADEP1, we obtained Bacillus subtilis ClpP variants with amino acid substitutions in the N-terminal region and tested the effect of these mutations on substrate translocation using fluorescence-based proteolytic assays and cryo-electron microscopy. We found that compromising the integrity of the β-hairpin adopted by the N-terminal region prevented translocation of the substrate into the catalytic chamber of B. subtilis ClpP. These results suggest that the structural requirements for a functional axial channel are conserved in Gram-positive and Gram-negative bacteria. This study defines the structural requirements for ADEP1-mediated activation of the ClpP protease and serves as a model for the functioning of ClpP in the context of the ClpAP and ClpXP complexes. / Thesis / Master of Science (MSc)

The purpose of this work is to evaluate the ratio of the vector and axial vector coupling constants in the beta-decay of Rb^87. Particular attention is given to determining the sign of the ratio. All this is accomplished mainly by a conic analysis of the beta-spectrum and the calculation of a matrix element ratio. The results obtained indicate that the ratio of the coupling constants is negative. Due to uncertainties in nuclear matrix elements, only an approximate absolute value for the ratio can be secured. These results are consistent with other present evidence. / Thesis / Master of Science (MSc)

No / Two novel reduced-size, printed spiral antennas are proposed for use in personal communications mobile terminals exploiting the “big low earth orbit” (Big-LEO) satellite system (uplink 1.61–1.63 GHz; downlink 2.48–2.5 GHz). The two proposed antenna give 3.12―6.25% bandwidth at lower resonant mode of 1600MHz, while at the higher resonant mode of 2450MHz a bandwidth of around 6% is obtained. The experimental and simulated return losses of the proposed antennas show good agreement. The computed and measured gains, and axial ratios are presented, showing that the performance of the proposed two antennas meets typical specifications for the intended applications.

A new active-passive approach for the control of noise radiated from a small axial fan was investigated. The approach involved the installation of an axial fan into a short duct with both passive and active noise control functions. First, a systematic methodology for the analytical modeling of finite-length ducts with multiple discontinuities was formulated. The procedure involved the modeling of a duct as a collection of simple duct sections, which were interconnected at multiple junctions. Analytical studies have shown that a short lined duct provides passive noise reduction effects through the mass-loading effect of the duct air volume at low frequencies and the sound absorption by a passive liner at high frequencies. It was also shown that active control can provide further noise attenuations at low-to-mid frequencies, thereby enhancing the overall noise control performance. Two alternate designs of active-passive noise control fan duct were considered. One was a simple non- segmented duct with a 2x2 active control and the other was an internally segmented duct with an 8x8 active control. It was indicated that the latter design possesses a significantly higher global noise control potential than the former with respect to both bandwidth and attenuation level. This was attributed to the reduction of the unwanted pressure contributions from the duct cross modes through the high frequency shifting of the associated cut-on frequencies. The experimental validation of the noise control approach was also carried out. An active-passive noise control fan duct incorporating the segmented duct design with 8x8 active control was constructed in conjunction with a hybrid feedforward-feedback control system. Experimental results have shown significant reductions in the total fan noise power associated with the first four BPF tones by the feedforward control and the broadband fan noise power by the feedback control. The overall active-passive noise control characteristics were observed to be in accordance with the analytical results. / Ph. D.

The purpose of this study is to develop a simple one-dimensional model to analyze axially loaded beam-plates containing cracks which extend through the thickness of the beam-plates. Although the material analyzed is isotropic, these cracks will be referred to as delaminations. Buckling, postbuckling, and growth of delaminations in these beam-plates will be analyzed. A finite element method in which all of the terms of the stiffness matrices are obtained by exact integration is employed to determine the linear buckling load and postbuckling solution. The energy release rate is then determined using the postbuckling solution. Curves are provided to show the effect of delamination length and location on buckling loads, energy release rates, and strengths of the beam-plates. The problem of buckling and postbuckling of beams with multiple delaminations is also considered. A method of calculating the energy release rate for beams with multiple delaminations using numerical differentiation is introduced. / Master of Science