Electrochemical potentials of a series of anthraquinone derivatives were studied in both aqueous solution and acetonitrile. The long term goal of this work was to find derivatives which could be reduced easily for studies of photoinduced electron transfer in DNA. Our immediate goal was to find the substitution group that gave the least negative redox potential value. Of all derivatives studied, the anthraquinone imides as a class had the least negative redox potentials, in the range of -0.600 to -0.550 V vs. SCE. One of the anthraquinones studied, one derivative (deoxyadenosine conjugated with an ethynyl linker to an anthraquinone with two ester substituents) was also in this range. A study of a series of anthraquinones conjugated with ethynyl and ethanyl linkers showed that the ethynyl linker was more effective than the ethanyl linker in lowering the redox potential of anthraquinone.

Significant advancements in the field of membrane protein crystallography have provided in recent years invaluable images of transporter structures. These structures, however, are static and require complementary kinetic insight to understand how their mechanisms work. Electrophysiological studies of transporters permit the high quality kinetic measurements desired, but there are significant difficulties involved in analyzing and interpreting the data. Current methods allow a variety of kinetic parameters to be measured but there is a disconnect between these parameters and a fundamental understanding of the carrier. The intent of this research was to contribute new tools for studying the electrogenic kinetics of membrane transport proteins, to understand the link between these kinetics and the carrier, and to ultimately understand the mechanisms involved in transport. In this vein, two projects are explored covering two important kinetic time domains, transient and steady-state. The transient project studies the conformational changes of the unloaded carrier of SGLT1 through a multi-exponential analysis of the transient currents. Crystal structures have potentially identified a gated rocker-switch mechanism and the transient kinetics are used to support and study this kinetically. A protocol taking advantage of multiple holding potentials is used to measure the decay time constants and charge movements for voltage jumps from both hyperpolarizing and depolarizing directions. These directional measurements provide insight into the arrangement of the observed transitions through directional inequalities in charge movement, by considering the potential for a slow transition to hide a faster one. Ultimately, four carrier decays are observed that align with the gated rocker-switch mechanism and can be associated one-to-one with the movement of a gate and pore on each side of the membrane. The steady-state project considers a general theoretical model of transporter cycling. Recursive patterns are identified in the steady-state velocity equation that lead to a broad understanding of its geometric properties as a function of voltage and substrate concentration. This results in a simple phenomenological method for characterizing the I–V curves and for measuring the kinetics of rate limiting patterns in the loop, which we find are the basic structures revealed by the steady-state velocity.

The profile of the poloidal velocity in the edge region of tokamak plasmas has been identified as playing a major role in the confinement of particles and energy. It has been suggested that a strongly sheared poloidal flow can reduce particle and energy losses by the stabilization of unstable modes and decorrelation of turbulence the edge region of the plasma. A Gundestrup probe, a Mach probe array, is used to measure both the parallel and perpendicular flow velocities in the Saskatchewan Torus-Modified (STOR-M) tokamak during several discharge conditions. It is observed that during Ohmic discharges there is no velocity shear and the direction of the parallel flow is independent of the direction of the toroidal magnetic field. During H-mode induced by a turbulent heating current pulse, a region of strong velocity shear develops in the plasma edge and an edge transport barrier develops. This results in a short period of improved particle and energy confinement with reduced fluctuation amplitudes. During electrode biasing experiments, a stainless steel biasing electrode is inserted into the plasma up to r = 82 mm and biased to +500 V relative to the vacuum chamber. It is observed that the particle confinement improves during the biasing phase while the energy confinement is degraded. A region of weak shear in the poloidal flow is observed in the plasma scrapeoff layer (SOL). The results from STOR-M are compared with results from data taken in the Czech Academy of Sciences Torus (CASTOR) tokamak during both Ohmic discharges and discharges with electrode biasing.

No description available.

No description available.

Electrostatically actuated parallel-plate MEMS tunable capacitors are desired elements for different applications including sensing, actuating and communications and RF (radio frequency) engineering for their superior characteristics such as quick response, high Q-factor and small size. However, due to the nature of their coupled electrostatic-structural physics, they suffer from low tuning range of 50% and have nonlinear capacitance-voltage (C-V) responses which are very sensitive to the voltage change near pull-in voltage. Numerous studies in the literature introduce new designs with high tunability ranging from 100% to over 1500%, but improvement of the nonlinearity and high sensitivity of the capacitor response have not received enough attention. In this thesis, novel highly tunable capacitors with high linearity are proposed to reduce sensitivity to the voltage changes near pull-in. The characteristic equations of a perfectly linear capacitor are first derived for two- and three-plate capacitors to obtain insight for developing linear capacitance-voltage responses. The devices proposed in this research may be classified into three categories: designs with nonlinear structural rigidities, geometric modifications and flexible moving electrodes. The concept of nonlinear supporting beams is exploited to develop parallel-plate capacitors with partially linear C-V curves. Novel electrodes with triangular, trapezoidal, butterfly, zigzag and fishbone shapes and structural/geometric nonlinearities are used to increase the linearity and tuning ratio of the response. To investigate the capacitors' behavior, an analytical approximate model is developed which can drastically decrease the computation time. The model is ideal for early design and optimization stages. Using this model, design variables are optimized for maximum linearity of the C-V responses. The results of the proposed modeling approach are verified by ANSYS FEM simulations and/or experimental data. When the fabrication process has dimensional limitations, design modifications and geometric enhancements are implemented to improve the linearity of the C-V response. The design techniques proposed in this thesis can provide tunabilities ranging from 80% to over 350% with highly linear regions in resulting C-V curves. Due to the low sensitivity of the capacitance to voltage changes in new designs, the entire tuning range is usable. Furthermore, the effect of fabrication uncertainties on parallel-plate capacitors performance is studied and a sensitivity analysis is performed to find the design variables with maximum impact on the C-V curves. An optimization method is then introduced to immunize the design against fabrication uncertainties and to maximize the production yield for MEMS tunable capacitors. The method approximates the feasible region and the probability distribution functions of the design variables to directly maximize the yield. Numerical examples with two different sets of design variables demonstrate significant increase in the yield. The presented optimization method can be advantageously utilized in design stage to improve the yield without increasing the fabrication cost or complexity.

This master thesis deals with problems in the arc length control in Pulsed MIG/MAG Welding. The main problem is that it is not possible to measure the arc length. In the present solution the voltage over both the electrode and the arc represents the arc length. To improve the arc length control a model of the electrode melting has been built. One output from the model is the voltage over the electrode and with this voltage together with the measured voltage it is possible to calculate the voltage over just the arc. Then, having the arc voltage as a value of arc length the arc length control can be improved, which is showed in the end by simulations. Simulations with the present control system are compared with the new one, when the controller is able to control the arc voltage instead of the sum of both the electrode voltage and the arc voltage.

Electrostatically actuated parallel-plate MEMS tunable capacitors are desired elements for different applications including sensing, actuating and communications and RF (radio frequency) engineering for their superior characteristics such as quick response, high Q-factor and small size. However, due to the nature of their coupled electrostatic-structural physics, they suffer from low tuning range of 50% and have nonlinear capacitance-voltage (C-V) responses which are very sensitive to the voltage change near pull-in voltage. Numerous studies in the literature introduce new designs with high tunability ranging from 100% to over 1500%, but improvement of the nonlinearity and high sensitivity of the capacitor response have not received enough attention. In this thesis, novel highly tunable capacitors with high linearity are proposed to reduce sensitivity to the voltage changes near pull-in. The characteristic equations of a perfectly linear capacitor are first derived for two- and three-plate capacitors to obtain insight for developing linear capacitance-voltage responses. The devices proposed in this research may be classified into three categories: designs with nonlinear structural rigidities, geometric modifications and flexible moving electrodes. The concept of nonlinear supporting beams is exploited to develop parallel-plate capacitors with partially linear C-V curves. Novel electrodes with triangular, trapezoidal, butterfly, zigzag and fishbone shapes and structural/geometric nonlinearities are used to increase the linearity and tuning ratio of the response. To investigate the capacitors' behavior, an analytical approximate model is developed which can drastically decrease the computation time. The model is ideal for early design and optimization stages. Using this model, design variables are optimized for maximum linearity of the C-V responses. The results of the proposed modeling approach are verified by ANSYS FEM simulations and/or experimental data. When the fabrication process has dimensional limitations, design modifications and geometric enhancements are implemented to improve the linearity of the C-V response. The design techniques proposed in this thesis can provide tunabilities ranging from 80% to over 350% with highly linear regions in resulting C-V curves. Due to the low sensitivity of the capacitance to voltage changes in new designs, the entire tuning range is usable. Furthermore, the effect of fabrication uncertainties on parallel-plate capacitors performance is studied and a sensitivity analysis is performed to find the design variables with maximum impact on the C-V curves. An optimization method is then introduced to immunize the design against fabrication uncertainties and to maximize the production yield for MEMS tunable capacitors. The method approximates the feasible region and the probability distribution functions of the design variables to directly maximize the yield. Numerical examples with two different sets of design variables demonstrate significant increase in the yield. The presented optimization method can be advantageously utilized in design stage to improve the yield without increasing the fabrication cost or complexity.

Interfacial polarization resistances limit the performance of many thin film solid-state devices, especially at low temperatures. To improve performance, a fundamental understanding of the electrode kinetics that govern interfacial reaction rates must be developed. The goal of this work is to determine site-specific reaction mechanisms and the relative significance of various reactions in order to quantify optimum structural parameters within the cathode microstructure. Key parameters include the length of triple phase boundary (TPB), the quantity of exposed electrolyte/electrode surface, and the ratio of electrolyte to electrode material. These parameters, when studied in a specific system, can be incorporated into broader models, which will encompass the specific conductivity of each component to develop an optimized three-dimensional network. The emphasis of this work is the systematic control and manipulation of potential cathodic reaction sites in order to develop an understanding of the relative importance of specific reaction sites. Since the physical dimensions of reaction sites are relatively small, an approach has been developed that utilizes micro-fabrication (similar to that used in integrated-circuit fabrication) to produce small and highly controlled microstructures. Investigations were made into the nature and reactivity of Triple Phase Boundaries (hereafter TPB) through the use of patterned platinum electrodes since only the TPBs are active in these electrodes. After the processing details of micro-fabrication were established for the platinum electrodes, patterned Mixed-Ionic/Electronic Conducting (MIEC) electrodes were fabricated and studied using impedance spectroscopy to determine the contributions from the MIEC surface versus the TPB. Systematically changing the geometry of the MIEC electrodes (thickness and line width) allowed for the determination of the effect of ambipolar transport within the MIEC on the activity of MIEC surfaces versus the TPB. This information is critical to rational design of functionally graded electrodes (with optimal particle size, shape, porosity and conductivity). In addition to experimental studies, representative patterned electrode samples were made available for collaborative studies with surface scientists at other institutions to provide additional techniques (such as Raman Spectroscopy) on the carefully designed and controlled cathode surfaces.

A non-crosslinking approach that covalently bonds nitroxide polymer brushes onto the ITO substrates via surface-initiated atom transfer radical polymerization (ATRP) was develpoed. Since the indium tin oxide (ITO)-silane covalent bonding providesvery strong chemical bonds to adsorb the nitroxide polymer brushes on ITO, it prevents polymers from dissolving into electrolyte solvent and thus improves its electrochemical properties. Moreover, micro-contact printing technology was used to pattern nitroxide polymer brushes on an ITO surface for the potential application in microbatteries. The morphology of electrodes was observed by atomic force microscopy.The electrochemical properties of the cathode were also studies.