Mode of access: Internet via World Wide Web. Available at http://hdl.handle.net/1947/9701. / "October 2008" Title from PDF cover (viewed on 25 September, 2009) Includes bibliographical references.

Thesis (Ph. D.)--University of Oregon, 2000. / Title from title screen. Extent of document: xiv, 152 p. : ill. Includes vita and abstract. Includes bibliographical references (p. 146-152).

Thesis (Ph.D.) - University of Queensland, 2006. / Includes bibliography.

Thesis (M.S.)--Rochester Institute of Technology, 2007. / Typescript. Includes bibliographical references (leaves 161-164).

Advisers: Terry Takahashi and Richard Marrocco. xiv, 152 p. / Neurons in the barn owl's inferior colliculus (IC) derive their spatial receptive fields (RF) from two auditory cues: interaural time difference (ITD) and interaural level difference (ILD). ITD serves to restrict a RF in azimuth but the precise role of ILD was, up to this point, unclear. Filtering by the ears and head insures that each spatial location is associated with a unique combination of frequency-specific ILD values (i.e., an ILD spectrum). We isolated the effect of ILD spectra using virtual sound sources in which ITD was held fixed for all spatial locations while ILD spectra were allowed to vary normally. A cell's response to these stimuli reflects the contribution of ILD to spatial tuning, referred to as an “ILD-alone RF”. In a sample of 34 cells, individual ILD-alone RFs were distributed and amorphous, but consistently showed that the ILD spectrum is facilatory at the cell's best location and inhibitory above and/or below. Prior results have suggested that an IC cell's spatial specificity is generated by summing inputs which are narrowly tuned to frequency and selective for both ILD and ITD. Based on this premise, we present a developmental model which, when trained solely on a cell's true spatial RF, reproduces both the cell's true RF and its ILD-alone RF. According to the model, the connectivity between a space-tuned IC cell and its frequency-specific inputs develops subject to two constraints: the cell must be excited by ILD spectra from the cell's best location and inhibited by spectra from locations above and below but along the vertical strip defined by the best ITD. To assess how frequency-specific inputs are integrated to form restricted spatial RFs, we measured the responses of 47 space-tuned IC cells to pure tones at varying ILDs and frequencies. ILD tuning varied with frequency. Further, pure-tone responses, summed according to the head-related filters, accounted for 56 percent of the variance in broadband ILD-alone RFs. Modelling suggests that, with broadband sounds, cells behave as though they are linearly summing their inputs, but when testing with pure tones, non-linearities arise. This dissertation includes unpublished co-authored materials.

This thesis presents a method to fabricate a robust optical directional coupler sensor using a solid core fiber (SCF) and a hollow core fiber (HCF). Through evanescent wave coupling mechanism, the optical power is exchanged between SCF and HCF. The hollow core of the HCF can be filled with liquid samples to alter the coupling ratio which imparts change in amount of light propagating through the SCF. Thus, it gives the coupler with ability of sensing refractive index of the sample with good sensitivity of 4.03 ± 0.50 volts per refractive index units (V/RIU) for refractive indices ranging from 1.331 ± 0.003 to 1.403 ± 0.003 with a resolution of 3.5 × 10−3 refractive index units (RIU). The SCF-HCF coupler was also used to sense the temperature based on the concept of temperature dependence on refractive index of the sample inside the hollow core of HCF. Further, the packaging methods are described that protect coupler from ambient environments and improves the life span of sensor. / Graduate

Thesis submitted in fulfilment of the requirements for the degree Master of Technology: Mechanical Engineering in the Faculty of Engineering at the Cape Peninsula University of Technology 2013 / High temperatures encountered in combustion chambers of jet engines has demanded the creation of new technologies and new materials for the construction of one of the most critical elements of these systems - the stator and rotor turbine blades. They have to withstand extreme temperatures for extended periods without the loss of mechanical strength, conditions under which many steels and alloys fail. Such failure is ascribed to the combination of high temperatures and high centrifugal forces, resulting in creep. The high temperature creep mechanism of grain boundary sliding has limited the operation capability of fine-grained equiaxed castings. Higher operating temperatures were achieved with higher alloy contents and coarse-grained equiaxed castings. This is especially prevalent in multi-crystalline structures in which grain boundaries present weaknesses in the structure. However, notwithstanding these improvements, high temperature resistant alloys formed as single crystal structures offer the necessary material properties for safe performance under these extreme conditions. Damage to turbine blade surfaces is often caused by oxidation and hot corrosion. For this reason, turbine blades are coated with a thermal barrier coating (TBC), which consists of ceramic materials that reduce the heat flux through the airfoil. In this research work, modelling and simulation techniques were initially used to study the directional solidification (DS) of crystal structures during vacuum investment casting. The modelling of the solidification process was implemented using a Finite Element casting simulation software, ProCAST, to predict thermal and flow profiles. These models allowed the study of the dendritic growth rate, the formation of new grains ahead of the solid/liquid interface and the morphology of the dendritic microstructure. These studies indicated the opportunity to optimise the velocity of the solidification front (solidification rate) for single crystal structures. The aim of this research was therefore to investigate the effect of the solidification rate (or withdrawal velocity) on the quality of SC castings. The investigations were carried out for nickel-based superalloy CMSX-4 turbine blade casts and rods using the Bridgman process for vacuum investment casting. The SC castings were heat treated to improve the grain structure for enhanced creep resistance. The heat treated SC castings were inspected by X-ray diffraction to analyse crystallographic orientation and chemical composition; and by SEM, OP (optical microscopy) and microprobe analysis to analyse the microstructure; in addition to macrostructural investigations. In the experimental analysis, the formation of new grains ahead of the solidi/liquid interface and the effect of dendrite packing patterns on the primary dendrite spacing were investigated. Creep tests were conducted to compare the creep properties of the SC castings for different withdrawal rates, and to draw conclusions regarding the effect of withdrawal rate on the microstructure (and hence the creep properties) of SC castings.

OpenStereo foi desenvolvido originalmente para preencher uma lacuna entre aplicativos de anáalise para geologia estrutural, como um software livre, gratuito e multi-plataforma. Ao longo dos anos ele adquiriu um grande núumero de usuários, com citações regulares. Este trabalho objetivou a reestruturação do OpenStereo como um todo, mudando-o para uma nova estrutura de interface gráfica e construíndo-o do zero visando desempenho, estabilidade e facilidade de manutenção e extensão. Diversas novas funcionalidades foram incluídas tais como projetos, conversão de notação de atitudes, ajuste de pequenos círculos, extração de atitudes de modelos tridimensionais e conversão de shapefiles de linhas para dados circulares. A pesquisa gerou dois subprodutos principais: um novo método gráfico para ajuste de pequenos círculos e a biblioteca de análise de dados estruturais Auttitude. / OpenStereo was originally developed to fill a gap among software packages for structural geology analysis, as a free open source cross-platform software. Over the years it has acquired a great number of users, with regular citations. This work aimed to restructure OpenStereo as a whole, changing to a new graphical interface framework and building it from the ground up for speed, stability, ease of maintenance and extension. Many new functionalities were also included, such as project management, structural attitudes notation handling, small circle fitting, extractions of attitudes from three-dimensional models and conversion of lines shapefiles to circular data. The research involved had two main byproducts, a new graphical method for small circle data fitting and a directional data analysis library, Auttitude.

In the purview of efficient communication in MANETs for enhanced data rates and reliable routing of information, this thesis deals with dual polarised directional antenna based communication. This thesis proposes a dual polarised directional communication based cross-layer solution to mitigate the problems of interference, exposed nodes, directional exposed nodes, and deafness, and to achieve efficient routing of information. At the physical layer of network protocol stack, this thesis proposes the use of dual polarised directional antenna for the mitigation of interference. Use of dual polarised directional communication at the physical layer calls for appropriate modifications in the functionality of MAC and network layers. At the MAC layer, the DPDA-MAC protocol proposed in this thesis achieves mitigation of the problems of exposed nodes, directional exposed nodes and deafness, by using dual polarised directional antenna at physical layer. At network layer, the DPDA-MRP protocol presented in this thesis facilitates the discovery of multiple routes between the source and destination nodes to route information in accordance with the desired dual polarised directional communication. To achieve efficient dual polarised directional communication and routing of information, it is essential to maintain well populated Neighbour Table (NT) and Routing Table (RT). This thesis proposes a novel Corruption Detection Pulse (CDP) based technique to handle corruption of broadcast packets such as Link ID and RREQ arising due to hidden node problem. Since the nodes participating in the formation of MANETs have limited battery energy, the protocols proposed in this thesis are featured with a provision for dynamic power control to achieve energy efficient communication. Nodes maintain Received Signal Strength Indicator (RSSI) information in the NT, which along with the information of node location is used in the formulation of decision logic of dynamic power control. Through numerous simulation studies, this thesis demonstrates the benefits of dual polarised directional communication to enhance the performance of MANET. The design principles, benefits and conceptual constraints of proposed DPDA-MAC protocol are analysed with SPDA-MAC and CSMA/CA, while those for DPDA-MRP are analysed with SPDA-MRP and DSR through performance metrics of throughput, Packet Delivery Ratio (PDR) and per hop delay. The thesis also analyses the impact of variations of channel capacity, node density, rate of packet transmission and mobility of nodes on the performance of the proposed and conventional protocols invoked in MANETs.

Efficient directed migration requires tight regulation of chemoattractant signal transduction pathways in both space and time, but the mechanisms involved in such regulation are not well understood. Here, we investigated the role of protein kinase A (PKA) in controlling signaling of the chemoattractant cAMP in Dictyostelium discoideum. We found that cells lacking PKA display severe chemotaxis defects, including impaired directional sensing. Although PKA is an important regulator of developmental gene expression, including the cAMP receptor cAR1, our studies using exogenously expressed cAR1 in cells lacking PKA, cells lacking adenylyl cyclase A (ACA) and cells treated with the PKA-selective pharmacological inhibitor H89, suggest that PKA controls chemoattractant signal transduction, in part, through the regulation of RasG, Rap1 and TORC2. As these pathways control the ACA-mediated production of intracellular cAMP, they lie upstream of PKA in this chemoattractant signaling network. Consequently, we propose that the PKA-mediated regulation of the upstream RasG, Rap1 and TORC2 signaling pathways is part of a negative feedback mechanism controlling chemoattractant signal transduction during Dictyostelium chemotaxis.