<p> Although the glass transition temperature (<i>T_g</i>) and dynamics of polymers confined to the nanoscale have been studied for twenty years, a physical understanding is still lacking. The reason for a polymer species dependent <i>T_g</i>-confinement effect and the role of neighboring polymer domains in perturbing the <i>T_g</i> of a confined species are areas with a need for greater study as they will inform many of the decisions regarding the use of polymers in nanomaterials. </p><p> In this work, fluorescence spectroscopy is used as the primary tool to characterize <i>T_g</i> in a number of systems. First, micelle core <i>T_g</i> and critical micelle temperatures can be determined via pyrenyl label fluorescence for block copolymers in organic solvent at polymer contents which cannot be reliably characterized by other standard methods. Next, measurements were extended to miscible polymer-polymer blend systems where two component <i>T_gs</i> can be determined via a single pyrene-labeled component. Fluorescence can characterize systems with small component <i>T_g</i> differences and near-infinitely dilute blend components unlike scanning calorimetry. </p><p> Studies of the near-infinitely dilute blend components reveal that a 0.1 wt% polystyrene component can have its <i>T_g</i> tuned over a 150 &deg;C range depending on the blend partner. Analogous tunability of <i>T_g</i> is also reported in multilayer film systems with an ultrathin PS layer surrounding by bulk neighboring domains. The same limiting <i>T_g</i> is reported by PS for a given neighbor indicating a common physical origin of perturbations in both systems. The perturbations are correlated with fragility which also tracks with the magnitude of <i>T_g</i>-confinement effects in single layer polymer films. Thus, fragility provides a unifying explanation of confinement effects in multilayer films, blends, and single layer films (in the absence of attractive interactions). </p><p> Surface wave dynamics are also examined in ultrathin polystyrene layers on various substrates. It is demonstrated that surface dynamics become much slower than anticipated by capillary wave theory as the film thickness decreases. Additionally, surface wave dynamics become orders of magnitude faster as the modulus of the supporting substrate decrease.</p>

No description available.

Current melt texturing processes can only produce high-quality High Temperature Superconducting (HTSC) domains of a few centimetres in size. Increasing the size of the domain by a joining technique is investigated. The parent HTSC melt textured domains of YBa2CU307-li (Y 123), were used in this research to investigate the joining technique. The solder powders used to form the seam were HTSC YbBa2Cu307-li (YbI23), which has a peritectic temperature of approximately 925 cC, Yb2BatCu\07_o (Yb211), Silver Oxide (Ag20) and Y123. A total of 8 different superconducting 'solders' were manufactured using these powders. Microstructural analyses using a scanning electron microscope (SEM) and an optical microscope were conducted on each sample. It was found that mechanisms occurring during the growth of the seam affect the performance of the join. During the growth, three interfaces are formed. The interface between the parent and the growth front produced an excellent join whereas most of the microstructural defects were present at the intersection of the two growth fronts also known as the impingement boundary. The effect of the addition of Yb211 and silver particles to the join were investigated. It was found that although Yb211 particles improve the flux pinning and viscosity of the solder and the silver improves the intergranular critical current density (Jc) [1], they also reduce the effective cross-sectional area of the joined sample. Thus, the amount of non-superconducting particles added needs to be optimised. Transport measurements were taken to evaluate the current carrying capacity of each sample. It was found that Sample 2-A (Yb123 + 5%Ag20) has the highest Jc of approximately 142 A/cm 2 at 80 K while Sample 3-A (Y123 + 5%Ag20) has the poorest Jc of about 37 A/cm2 at 80 K. Resistivity vs. Temperature graphs show that all joined samples were superconducting implying that the joining process was successful in establishing a superconducting join. Magnetic field maps of the parent and joined samples were captured using a Hall Probe. It was found that the joined sample could trap almost 95 % of the field that could be trapped by the parent. From these results, it was concluded that joining HTSC bulk pieces is possible using an external 'soldering' agent. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2005.

A stainless steel, high temperature, phase change micro actuator has been demonstrated using the solid-liquid phase transition of mannitol at 168°C and In-Ag transient liquid phase diffusion bonding. Joints created with this bonding technique can sustain temperatures up to 695°C, while being bonded at only 180°C, and have thicknesses between 1.4 to 6.0 μm. Physical vapour deposition, inkjet printing and electroplating have been evaluated as deposition methods for bond layers. For actuation, cavities were filled with mannitol and when heated, the expansion was used to deflect a 10 μm thick stainless steel membrane. Bond strengths of the joints are found to be in the region of 0.51 to 2.53 MPa and pressurised cavities sustained pressures of up to 30 bar. Bond strength is limited by the bond contact area and the surface roughness of the bonding layers.

No description available.

No description available.

No description available.

This thesis develops a hardware circuit implementation of a novel algorithm for reducing a SRM drives input current ripple or equivalently to improve the SRM drives input power quality. The algorithm requires the SRMs phase current to follow a trapezoidal trajectory relative to the rotors position with the magnitude of the current dependent on the desired average torque. This thesis deals with the generation of the required current command that is the input to a separate analog current regulator that forces the SRMs current to follow the generated current command. The final circuit design must be capable of operating at 200C to be part of a high temperature aircraft actuator. In this thesis, room temperature hardware is used to emulate and verify the high temperature design. Both a high temperature microcontroller based design and a high temperature gate array based design are considered with the high temperature gate array based design being chosen. Ultimately, a standard room temperature Xilinx FPGA is chosen to emulate the high temperature gate array. The FPGA is programmed using Verilog HDL and the code is downloaded into the chip using Xilinx ISE software. The experimentally generated output is validated by comparing it with simulation results from a detailed Simulink model of the complete drive system.

This thesis describes investigations into the application of high temperature superconductoR_s(HTS) for microwave devices. The ultimate aim of this research was to produce HTS components that would demonstrate the commercial potential of their use in spacecraft such as satellites or in base stations for terrestrial cellular communication systems. During the course of this research the surface resistance (R_s) of HTS thick and thin films deposited onto different substrates has been measured by a variety of techniques. These have been compared and contrasted with each other. There has been a particular emphasis upon the use of dielectric resonators as characterization tools and this thesis describes their use to measure the R_sof films and the loss tangents of the materials used in them. Consideration has been given to losses in the walls of the enclosures that surround dielectric resonators which is an area that has been neglected in previous work. Many of the films characterized had R_s values lower than normal conductoR_sat the same temperature and frequency including a thick film which had an R_sof 2.7mΩ±8.0% at 77K and scaled to 10 GHz which represents the second lowest result achieved in a thick film to date. Using such high quality films a number of devices have been made including microstrip resonatoR_soperating at 1.7-8.4 GHz, 5.58 GHz, 23 GHz and 24.75 GHz dielectric resonatoR_sand filteR_swith centre frequencies from 5.58-13 GHz. Such devices have shown performance enhancements of up to 700% over their normal conductor equivalents. Benefits have been delivered in light, low volume packages which is of particular advantage to the satellite communications industry. Finally, there has been a demonstration, for the first time, of a tunable HTS thin film filter.

No description available.