Methionine is essential for proper functioning of cellular processes such as protein synthesis, transmethylation and polyamine synthesis. Efficient recycling of methionine is important because of its limited bioavailability and metabolically expensive de novo synthesis. Further, cellular accretion of the nucleoside metabolites of the methionine salvage pathway compromises polyamine biosynthesis, transmethylation reactions and quorum sensing pathways, all critical reactions in cellular metabolism. 5’-methylthioadenosine/S-adenosylhomocysteine nucleosidase (MTAN) is a key component of the methionine salvage pathway of plants and many bacterial species, including Escherichia coli, Enterococcus faecalis, Salmonella typhimerium, Haemophilus influenza and Streptococcus pneumoniae. In bacteria, this enzyme displays dual-substrate specificity for two methionine metabolites, 5’-methylthioadenosine (MTA) and S-adenosylhomocysteine (SAH), and catalyzes the irreversible cleavage of the glycosidic bond to form adenine and the corresponding thioribose products, methylthioribose (MTR) and S-ribosylhomocysteine (SRH), respectively. In plants, MTAN is highly specific towards MTA and shows 0-16 % activity towards SAH. Plants rely on SAH hydrolase to metabolize SAH. Mammals do not have the nucleosidase enzyme and MTA is metabolized by MTA phosphorylase (MTAP). Like plants, mammals utilize SAH hydrolase to degrade SAH. Because MTAN is required for viability in multiple bacterial species and is not found in humans, it has been identified as a target for novel antibiotic development. This thesis describes the structural and functional characterization of bacterial and plant MTANs, with the aim of better understanding the molecular determinants of substrate specificity and the catalytic mechanism of this enzyme. The catalytic activities of representative plant MTANs from Arabidopsis thaliana, AtMTAN1 and AtMTAN2, were kinetically characterized. While AtMTAN2 shows 14 % activity towards SAH relative to MTA, AtMTAN1 is completely inactive towards SAH. As such, AtMTAN1 was selected for further examination and comparison with the bacterial MTAN from Escherichia coli (EcMTAN). The structures, dynamics and thermodynamic properties of these enzymes were analyzed by X-ray crystallography, hydrogen-exchange coupled mass spectrometry and isothermal titration calorimetry, respectively. Our studies reveal that structural differences alone do not sufficiently explain the divergence in substrate specificity, and that conformational flexibility also plays an important role in substrate selection in MTANs. MTANs from the pathogenic bacterial species, Staphylococcus aureus and Streptococcus pneumoniae, were examined kinetically and structurally. Comparison of the structures and catalytic activities of these enzymes with EcMTAN shows that the discrepancies in kinetic activities arefully explained by structural differences, as the overall structure and active sites of these bacterial MTANs are nearly identical. These experiments are in agreement with our proposal that dynamics play a significant role in catalytic activity of MTAN, and suggest that both structure and dynamics must be considered in future antibiotic design. To further our understanding on the catalytic mechanism of MTAN, the putative catalytic residues of AtMTAN1 were identified by structural comparison to EcMTAN and mutated by site-directed mutagenesis. The AtMTAN1 mutants were analyzed by circular dichroism and kinetic studies. Our results suggest that the catalytic mechanism is largely conserved between bacterial and plant MTANs, although the role of the putative catalytic acid remains to be confirmed.

No description available.

Active electronically scanned array (AESA) radar systems for military and commercial applications have fueled interest in low-cost, high-performance technologies capable of delivering integrated circuits for transmit-receive (T/R) modules and monolithic radar systems. Silicon-Germanium (SiGe) Heterojunction Bipolar Transistor (HBT) technology has been flagged as a strong candidate for such applications because of its high-speed low-noise devices, high integration capabilities, and relatively low cost. This work investigates integration issues associated with monolithic silicon-germanium radar systems for military (8-12 GHz) and automotive (24 GHz) applications. The design and implementation of critical circuits, such as phase shifters, power amplifiers, up-conversion mixers, down-conversion mixers, and voltage-controlled oscillators will be investigated, along with the system level considerations associated with these components. These building blocks have been fabricated and tested at wafer level, utilizing commercially available SiGe HBT BiCMOS technologies, demonstrating acceptable performance for these applications. Preliminary research into substrate coupling associated with these BiCMOS technologies will also be presented, demonstrating the potential for circuit-to-circuit substrate coupling to occur at these microwave frequencies.

This study presents a high-performance ZnO piezoelectric transducer integrated with the flexible stainless steel substrate. The ZnO piezoelectric film of 1.08nm was deposited on the flexible stainless steel substrate using a RF magnetron sputtering system. The cantilever length of 1cm and the vibration area of 1cm2 were designed for low-frequency environment according to the Cantilever Vibration Theory. The effects of various sputtering parameters such as substrate temperature, RF power and sputtering pressure were investigated to improve the piezoelectric characteristics of ZnO thin films. It was also discussed the unit thickness of open voltage values, and then the optimal sputtering parameters were determined. The physical characteristics of ZnO thin films were obtained by the analyses of the scanning electron microscopy (SEM) and X-ray diffraction (XRD) to discuss the surfaces, cross section and crystallization of ZnO thin films. The voltage analysis were measured the open and load voltage by the measurement system. The optimal deposition parameters for ZnO thin films are substrate temperature of 300¢J, RF power of 75W, sputtering pressure of 9 mTorr and oxygen concentration of 60%, which were determined by physical characteristics and voltage analysis. The study employs a precise mass loading of 0.57g on the cantilever to increase the vibration amplitude. The vibration source from 1~150Hz was provided to the piezoelectric transducer, and then the experimental results were showed resonance frequency of 75Hz by oscilloscope. When the optimal thickness of ZnO films is 1.08£gm and vibration amplitude is 1.19mm, the open circuit voltage of the power generator is 5.25V.After rectifying and flitting with a capacitor of 33nF,the maximum power of 1.0£gW/cm2 was achieved with the load resistance of 5M£[.

Trichloroethene (TCE) and tetrachloroethene (PCE) are among the most commonly detected groundwater contaminants, and are often difficult to remediate due to their presence as dense non-aqueous phase liquids (DNAPLs) in the subsurface. The objective of this study was to assess the potential of using a passive in situ carbon/hydrogen releasing barrier system to bioremediate TCE-contaminated groundwater. The slow carbon/hydrogen releasing material would cause the aerobic cometabolism and reductive dechlorination of TCE in aquifer. The carbon/hydrogen releasing materials would release carbon when contacts with groundwater and release hydrogen after the anaerobic biodegradation of released carbon, thus cause the reductive dechlorination of TCE. Results from the microcosm study indicate that the addition of emulsified substrate, cane molasses, Simple GreenTM (a biodegradable surfactant), or lecithin would enhance the biodegradation rate of TCE under anaerobic conditions. However, addition of multivitamin would increase the bacterial population in the media but would not be able to enhance the TCE degradation rate. Results show that a significant pH drop was observed due to the production of organic acids after the aerobic biodegradation process of cane molasses and lecithin. This also caused the inhibition of microbial growth in microcosms. Results reveal that higher TCE removal efficiency was observed in microcosms with Simple GreenTM addition followed by the addition of cane molasses, lecithin, multivitamin, emulsified substrate, groundwater (without substrate addition). Results from the microcosm study indicate that the addition of emulsified substrate would enhance the biodegradation rate of TCE under anaerobic conditions. However, appearance of high nitrate concentration would inhibit the TCE degradation process due to the occurrence of denitrification. Compared with nitrate, high sulfate concentration would not have significant impact on the reductive dechlorination of TCE. Results reveal that higher TCE removal efficiency was observed in microcosms with emulsified substrate addition followed by the addition of high sulfate concentration, high nitriate concentration, groundwater (without substrate addition). Results from the gene analysis show that phenol monooxygenase, toluene monooxygenase, and toluene dioxygenase were observed in the microcosms with lecithin, cane molasses, Simple GreenTM, and emulsified substrate. This indicates that the addition of substrates would induce the potential of TCE-degrading enzyme. Addition of emulsified substrate and emulsified substrate in nitrate or sulfate-rich media would stimulate Dehalococcoides sp. to induce tceA, bvcA, and vcrA, enzymes for TCE reductive dechlorination.

Both non-polar (10-10) (m-plane) and polar (0001) (c-plane) zinc oxide (ZnO) have a good lattice match with lithium aluminum (LiAlO2, LAO) (200) substrate, so it is difficult to control the epitaxial orientation. Therefore, this research is to explore how the growth parameters influence on the crystal orientation of ZnO film grown by plasma assisted molecular beam epitaxy. The experimental results show that m-plane ZnO can be grown with low zinc flux and low oxygen pressure. Increasing zinc flux and oxygen pressure will lead to increase in growth rate, and consequently, c-plane ZnO will nucleate on the substrate besides m-plane zinc oxide. The substrate temperature is one of the main factors that influence the choice of zinc oxide epitaxial orientation. High temperature will promote the m-plane zinc oxide nucleation, while low temperature will conduct to the c-plane zinc oxide nucleation. Under low zinc flux and low oxygen pressure, epitaxy of ZnO with different crystalline orientations can be achieved through changing the substrate temperature. The surface morphology and roughness of the substrate will affect the particle size and surface morphology of ZnO epilayers. When the substrate is smooth, the crystal size of the epitaxial film is large and the surface is flat with many rectangular stripes, taking on the platform-like morphology. If the substrate is rough with many scratches, the particle size becomes small and the surface is granular-like and rather rough. Furthermore, when the substrate is rough, it is difficult to control the different orientations of ZnO epitaxial films through changing the substrate temperature.

This study employed a commercial code FLUENT to simulate a chemical vapor deposition process in a rectangular chamber for deposition of a silicon dioxide layer on a rectangular substrate. We focus on the deposition rate and heat transfer coefficient (Nu number) on the substrate surface. We discuss the effects of the size of inlet region, the distance from inlet to substrate, the size of outlet region, the Reynolds number, the temperature of substrate, the ratio of the inlet flow rates of the two reaction gases on the deposition rate. The results show that the four corners at the substrate has the lowest deposition rate no matter how the variables are changed. Near the four corners there exist a region with high deposition rate. The deposition rate is more uniform when inlet is larger or equal to the substrate, and when the distance between the inlet and the substrate is small. The larger the size of the outlet region, the larger the uniform deposition rate region present on the central part of the substrate. The deposition rate increases with increasing Re number. However the uniformity remains similarly. The deposition rate also increases with increasing the substrate temperature. A study of the inlet flow rate ratio of TEOS and indicates that TEOS flow rate governs the process. A proper flow rate ratio gives a better deposition rate.

90nm wafer process has been released in production, but the bump pitch released in production is 180um. The major problem is the yield of solder paste printing process below 180um will be less than 80%. It means the cost will be very high. Thus it is difficult to make 150um bump pitch by using printing process in production. Substrate C4 pad will be bumped by pre-solder, and it will be jointed with wafer bump after re-flow process. The printing process is the most popular process in C4 pad pre-solder due to low cost and high throughput. But the challenge of 150um and even more of the wafer bump pitch shrinkage are the inevitable trend. So, a lot of substrate manufacturers are trying to develop the new process for C4 pro-solder pitch less than 100um. As soon as the C4 pad pre-solder pitch has been shrunk, the solder volume will be shrunk as well. It means the bump structure will be getting weak, and it may not pass the reliability tests. Thus, to evaluate the workability of bump structure is our purpose. First, the simulation software is used to compare the fatigue lives of two structures by using solder bump and copper bump substrates during thermal cycling test, and then to proceed the whole FCBGA process and reliability tests. The result of evaluation confirm the workability of FCBGA product using copper bump substrate, and it can be used with the same parameter and machine in solder bump substrate. Keyword¡GFCBGA, Substrate, Bump, Cold Joint, Delamination

This thesis is mainly divided into two parts. The first part discusses in detail design flow of the coupled-resonator bandpass filters, including basic theory of synthesis and the procedure of electromagnetic (EM) simulation. In the second part, by using the above-mentioned design flow, different structure filters have been implemented on organic substrates. The coupled-resonator BPF designs are verified to overcome the elements¡¦ parasitic effects, and thus can be optimized with high degree of freedom. In practice, a 3rd-order bandpass filter by coupling three spiral resonators has been proposed and implemented, having miniature and wide stopband characteristics. Finally, a two-layer 4th-order cross-couple bandpass filter with a pair of transmission zeros has been also proposed and implemented, achieving a significant size reduction of 50% compared with the single-layer design. The simulation and measurement results have good agreement for all design cases in this thesis.

Microbial fuel cells (MFCs) are emerging energy production technology which converts the chemical energy stored in biologically degradable compounds to electricity at high efficiencies. Microbial fuel cells have some advantages such as use of an inexpensive catalyst, operate under mild reaction conditions (i.e. ambient temperature, normal pressure and neutral pH), and generate power from a wide range and cheap raw materials. These make microbial fuel cell as an attractive alternative over other electricity generating devices. However, so far the major problem posses by this technology is the low power outputs of the microbial fuel cells that hinder its commercialization. Restriction in the electron transfer from bacteria to the anode electrode of a MFC is thought to be one cause for the low power output. Most recent MFC research is focused on using contaminants present in industrial, agricultural, and municipal wastewater as the energy source, with very few studies utilising gaseous substrates. Mediators can be added to MFCs to enhance the electron transfer from the microbe to the anode, but have limited practical applicability in wastewater applications because of the difficulty in recovering the expensive and potentially toxic compound. This thesis describes an investigation of electricity generation in a microbial fuel cell by combining a gaseous substrate with a mediator in the anode compartment. The emphasis being placed on the selection of a mediator to improve the electron transfer process for electricity production in an MFC. Subsequently, methods to improve the performance of a mediator MFC in respect of power and current density were discussed. This type of MFC is purposely aimed to be applied for treating gaseous contaminants in an anaerobic biofilter while simultaneously produce electricity. In this study, ethanol was the first gaseous substrate tested for the possibility to generate electricity in the MFC. Various mediators were previously compared in their reversibility of redox reactions and in the current production, and three best mediators were then selected for the power production. The highest electrical current production i.e. 12 μA/cm2 was obtained and sustained for 24 hrs with N,N,N',N'-tetramethyl-1,4- phenylendiamine TMPD (N-TMPD) as the mediator using glassy carbon (GC) electrode. The maximum power density reached 0.16 mW/cm2 by using carbon cloth (CC) anode. The absorption of these mediators by the bacterial cells was shown to correlate with the obtained energy production, with no N-TMPD was absorbed by the bacterial cells. The 24 hr current production was shown to be accompanied by the decrease in the ethanol concentration (i.e. 1.82 g/L), however ethanol crossover through the proton exchange membrane and ethanol evaporation around the electrodes were most likely to be the major cause of the decrease in the ethanol concentration. A theoretical coulombic efficiency of 0.005% was calculated for this system. The electrokinetics of microbial reduced mediator in the ethanol-mediator MFCs was also examined. Two methods i.e. linear sweep voltammetry (LSV) and cyclic voltammetry (CV) were used to obtained the kinetic parameters. CV method gave a better estimation of the kinetic parameters than LSV method due to the low concentration of the mediators used, affecting the Tafel behaviors. All CVs showed quasi-reversible behaviors compared to the CVs in the absence of the bacteria, which is thought due to the bacteria decreased the amount of the reduced and the oxidised mediator available at the surface of GC electrode. The highest exchange current density (i o ) was obtained by using N-TMPD as the mediator with the same concentration of the mediator used i.e. 0.13±0.01 mA/cm 2. The power output achieved also the highest (0.008 mW/cm 2) with N-TMPD as the mediator. The power density was improved to 0.03 mW/cm2 by using CC electrode. Another main objective of this thesis is to prove anoxic methane oxidation which was believed to occur only in marine sediments, and applies this for power generation in microbial fuel cells. Ferricyanide looked promising when it was used as the electron acceptor (thus as the mediator for the MFC). It was shown that ferricyanide was fully reduced by methanotrophs bacteria with methane as the substrate (versus abiotic and nitrogen control). The highest reduction rate achieved was 3 x10-3 mM/min.g. This finding was supported by ferricyanide peak heights disappearance (spectrophotometry at 420 nm), CO 2 production (sensor readings), ferrocyanide formation (cyclic voltammetry), and no other alternate electron acceptor was present. The total CO 2 produced was equal to 0.015 mmoles of CO 2 from starting concentration ferricyanide of 0.2 mmoles (after substraction with an offset value). CV results show 2.4 mM of ferrocyanide was produced after a total addition of 3 mM ferricyanide into the anoxic methanotrophic suspension. The current and voltage generation in microbial fuel cell reactor from the reduced ferricyanide confirmed that ferricyanide received electrons from the bacterial metabolism. The maximum power density of 0.02 mW/cm2 and OCV of 0.6 V were obtained with 3 mM ferricyanide using LSV method.