Choline oxidase catalyzes the oxidation of choline to glycine betaine. The reaction includes betaine aldehyde as an intermediate. FAD is reduced by the alcohol substrate, betaine aldehyde intermediate and oxidized by molecular oxygen to give hydrogen peroxide. In this study, the Ser101Ala variant of choline oxidase was prepared to elucidate the contribution of the hydroxyl group of Ser101 in the proton and hydride transfer reactions for proper preorganization and reorganization of the active site towards quantum mechanical tunneling. The thermodynamic parameters associated with the enzyme-catalyzed OH and CH bond cleavages and the temperature dependence of the associated solvent and substrate kinetic isotope effects were investigated using a stopped-flow spectrophotometer. The proton and hydride transfer have been shown to be occurring via quantum tunneling in CHO-S101A enzyme.

We analyze a general class of difference operators containing a multi-well potential and a small parameter. We decouple the wells by introducing certain Dirichlet operators on regions containing only one potential well, and we treat the eigenvalue problem as a small perturbation of these comparison problems. We describe tunneling by a certain interaction matrix similar to the analysis for the Schrödinger operator, and estimate the remainder, which is exponentially small and roughly quadratic compared with the interaction matrix.

As the critical dimensions of many devices, especially electronics, continue to become smaller, the ability to accurately analyze the properties at ever smaller scales becomes necessary. Optical techniques, such as confocal microscopy and various spectroscopies, have produced a wealth of information on larger length scales, above the diffraction limit. Scanning probe techniques, such as scanning tunneling microscopy and atomic force microscopy, provide information with an extremely fine resolution, often on the order of nanometers or angstroms. In this document, plasmon coupling is used to generate large signal increases, with clear future applications toward scanning probe optical spectroscopies. A variation on scanning tunneling microscopy is also used to study the surface structure of environmentally interesting nanoparticles. Traditional Raman spectroscopy is used to examine doped graphene, which is becoming a hot material for future electronic applications.

This thesis describes advanced modeling of nanoscale bulk MOSFETs incorporating critical quantum mechanical effects such as gate direct tunneling and energy quantization of carriers. An explicit expression of gate direct tunneling for thin gate oxides has been developed by solving the Schroinger equation analytically. In addition, the impact of different gate electrode as well as gate insulation materials on the gate direct tunneling is explored. This results in an analytical estimation of the potential solutions to excessive gate leakage current. The energy quantization analysis involves the derivation of a quantum mechanical charge distribution model by solving the coupled Poisson and Schroinger equations. Based on the newly developed charge distribution model, threshold voltage and subthreshold swing models are obtained. A transregional drain current model which takes into account the quantum mechanical correction on device parameters is derived. Results from this model show good agreement with numeric simulation results of both long-channel and short-channel MOSFETs.The models derived here are used to project MOSFET scaling limits. Tunneling and quantization effects cause large power dissipation, low drive current, and strong sensitivities to process variation, which greatly limit CMOS scaling. Developing new materials and structures is imminent to extend the scaling process.

Since the early 1960s, Abrikosov-Gorkov theory has been used to describe superconductors with paramagnetic impurities. Interestingly, the density of states resulting from the theoretical framework has to date only been known approximately, as a numeric solution of a complex polynomial. An analytical solution to the theory was discovered and applied to extract the spin polarization from the tunneling conductance of superconducting aluminium with 3-dimensional (3-D) amorphous (a-) gadoliniumxsilicon1-x (GdxSi1-x) as a counter electrode (Al/Al2O3/a-GdxSi1-x planar tunnel junction measured at T = 25 mK and H less than or equal to 3.0 T) in the quantum critical regime (QCR). The analytical solution is valid in the whole regime of Abrikosov-Gorkov theory independent of the presence of an energy gap. Applying the spin polarized Abrikosov-Gorkov theory to describe aluminium gives a larger spin polarization in GdxSi1-x than the spin polarized Bardeen-Cooper-Schrieffer (BCS) theory. The purpose of this study is to extract polarization at various applied magnetic fields, but no specific relationship between the two could be determined. Results obtained shows a transition from a superconductor with a gap to a gapless superconductor in varying external magnetic fields was observed. To improve understanding of GdxSi1-x near the metal-insulator transition (MIT) and compare it with prior work, the initial experimental attempts to investigate the transport property of GdxSi1-x near the MIT in the 2-dimensional limit are presented. A low temperature ultra high vacuum quench condensation system was used to make thin films of GdxSi1-x and in-situ measurements were performed. The transport properties for different values of x and thicknesses were measured for T = 4.2 K to ~10 K. In addition to other possible causes, the uncertainty in the electron impact emission spectroscopy (EIES) appeared to be a major reason behind the observed error in x when gadolinium and silicon are co-evaporated. The problems faced during the co-evaporation are also discussed.

The mechanism of three important aldol reactions and a biomimetic transamination is investigated using a combination of experimental kinetic isotope effects (KIEs), standard theoretical calculations and dynamics trajectory simulations. This powerful mechanistic probe is found to be invaluable in understanding intricate details of the mechanism of these reactions. The successful application of variational transition state theory including multidimensional tunneling to theoretically predict isotope effects, described in this dissertation, represents a significant advance in our research methodology. The role of dynamic effects in aldol reactions is examined in great detail. The study of the proline catalyzed aldol reaction has revealed an intriguing new dynamic effect - quasiclassical corner cutting - where reactive trajectories cut the corner between reactant and product valleys and avoid the saddle point. This phenomenon affects the KIEs observed in this reaction in a way that is not predictable by transition state theory. The study of the Roush allylboration of aldehydes presents an example where recrossing affects experimental observations. The comparative study of the allylboration of two electronically different aldehydes, which are predicted to have different amounts of recrossing, suggests a complex interplay of tunneling and recrossing affecting the observed KIEs. The Mukaiyama aldol reaction has been investigated and the results unequivocally rule out the key carbon-carbon bond forming step as rate-limiting. This raises several interesting mechanistic scenarios - an electron transfer mechanism with two different rate-limiting steps for the two components, emerges as the most probable possibility. Finally, labeling studies of the base catalyzed 1,3- proton transfer reaction of fluorinated imines point to a stepwise process involving an azomethine ylide intermediate. It is found that dynamic effects play a role in determining the product ratio in this reaction.

¡@¡@In recent years, the trends in network communication towards mobile network .Traditional network cannot meet the need of new communication challenge. The 802.11 outperforms other new wireless network technique ¡@¡@In this paper, we assume user have wireless NIC devices with Mobile IPv6 protocol module. We use this model to build an environment and use this environment to design our Mobile IPv6 multicast simulation. We do these for two reasons, (1)To analyze how to use multicast over Mobile IPv6 wireless network. (2)To design an experimentation for multicast over wireless LAN. After we get results of the experimentation, we could know why wireless network does not have better quality than wired LAN. ¡@¡@During our implementation, we have a high latency problem and try to solve it by our program. After our improvement, average latency reduces to 27.77% and miss rate reduces to 33.07%. ¡@¡@Our implementation not only provide some useful information when some one need to build Mobile IPv6 environment but also give a solution for solving handover latency problem.

The influence of the surface excavation and loading on the existing tunnels has been investigated using a Finite Element Method program, Plaxis 3D Tunnel. A parametric study has been carried out where the parameters were the depth of the surface excavation, the eccentricity of the excavation with respect to the tunnel axis, the height of the embankment fill and the stiffness of the soil. It is found that, excavations over the existing tunnels have a negative effect on the tunnel lining capacity since the unloading due the excavation reduces the normal forces and increases the bending moments. On the other hand, it is found that surface loading within the limits considered in this study is not critical in terms of the tunnel stability due to the increase in normal forces and decrease in bending moments.

In this dissertation, I have studied four theoretical problems in quantum tunneling, quantum computing, and high-temperature superconductivity. I have developed a generally-useful numerical tool for analyzing impurity-induced resonant-state images observed with scanning tunneling microscope (STM) in high temperature superconductors. The integrated tunneling intensities on all predominant sites have been estimated. The results can be used to test the predictions of any tight-binding model calculation. I have numerically simulated two-dimensional time-dependent tunneling of a Gaussian wave packet through a barrier, which contains charged ions. We have found that a negative ion in the barrier directly below the tunneling tip can deflect the tunneling electrons and drastically reduce the probability for them to reach the point in the target plane directly below the tunneling tip. I have studied an infinite family of sure-success quantum algorithms, which are introduced by C.-R. Hu [Phys. Rev. A {\bf 66}, 042301 (2002)], for solving a generalized Grover search problem. Rigorous proofs are found for several conjectures made by Hu and explicit equations are obtained for finding the values of two phase parameters which make the algorithms sure success. Using self-consistent Hartree-Fock theory, I have studied an extended Hubbard model which includes quasi-long-range Coulomb interaction between the holes (characterized by parameter V). I have found that for sufficiently large V/t, doubly-charged-antiphase-island do become energetically favored localized objects in this system for moderate values of U/t, thus supporting a recent conjecture by C.-R. Hu [Int. J. Mod. Phys. B {\bf 17}, 3284 (2003)].

This dissertation is focused on understanding heterogeneous metal catalysts supported on oxides using a model catalyst system of SiO2 thin film supported metal nano-clusters. The primary technique applied to this study is scanning tunneling microscopy (STM). The most important constituent of this model catalyst system is the SiO2 thin film, as it must be thin and homogeneous enough to apply electron or ion based surface science techniques as well as STM. Ultra-thin SiO2 films were successfully synthesized on a Mo(112) single crystal. The electronic and geometric structure of the SiO2 thin film was investigated by STM combined with LEED, Auger electron spectroscopy (AES), and X-ray photoelectron spectroscopy (XPS). The relationship between defects on the SiO2 thin film and the nucleation and growth of metal nano-clusters was also investigated. By monitoring morphology changes during thermal annealing, it was found that the metal-support interaction is strongly dependent on the type of metal as well as on the defect density of the SiO2 thin film. Especially, it was found that oxygen vacancies and Si impurities play an important role in the formation of Pd-silicide. By substituting Ti atoms into the SiO2 thin film network, an atomically mixed TiO2-SiO2 thin film was synthesized. Furthermore, these Ti atoms play a role as heterogeneous defects, resulting in the creation of nucleation sites for Au nano-clusters. A marked increase in Au cluster density due to Ti defects was observed in STM. A TiO2-SiO2 thin film consisting of atomic Ti as well as TiOx islands was also synthesized by using higher amounts of Ti (17 %). More importantly, this oxide surface was found to have sinter resistant properties for Au nano-clusters, which are desirable in order to make highly active Au nano-clusters more stable under reaction conditions.