Fibrous materials are used in a variety of applications due to their relatively high surface area to volume ratio as well as anisotropic behaviour. Electrospinning is a popular fabrication technique which produces polymer nanofibres with a potentially high molecular orientation. The surface of polymer fibres plays a significant role in many applications thus measurement of their surface properties is essential but challenging due to their relatively small size. In this thesis, ultrafine nanofibres have been produced by electrospinning with their nanofibre morphology controlled by varying different processing parameters. Atomic force microscopy (AFM) adhesion contact mechanics and individual nanofibre wetting measurements have been conducted to explore surface properties of the produced electrospun polymer fibres. Results using traditional Owens-Wendt plots applied to our nanomaterials show electrospun nanofibres have a higher dispersive surface free energy compared to bulk polymer film but a lower polar contribution, giving a total surface free energy in excess of bulk equivalents. A novel proposed model indicates that this nanofibre dispersive surface free energy is intimately linked to density of the polymer and ultimately the molecular spacing or orientation for the polymer chains. Comparisons are made with bulk polymer films to show that a high degree of molecular orientation is present at least at the surface of the polymer nanofibre. Structure investigations on electrospun fibres of polyvinyl alcohol using FTIR and XPS surface techniques explore how an increase in hydrogen bonds formed within nanofibres rather than on the fibre surface enhance this dispersive contribution but lowers the polar contribution. The wetting behaviour of electrospun fibre is extended to assemblies at length scales above individual fibres to highlight how superhydrophobic surfaces can be produced from nanofibre networks with defined spacings and geometries. This superhydrophobicity was adequately described by a Cassie-Baxter model modified to account for the fibrous geometry.

Ad hoc wireless networks have emerged as a promising communication scheme to meet the ever growing portability and infrastructureless demand of wireless services. The transmission power level affects signal quality and interference which causes congestion and thus impacts the communication performance. Hence, power control has been the focus of extensive research. In this thesis, we examine the problem of power control in wireless networks, specially in ad hoc wireless networks. Two important types of power control, which are power control with fixed SNIR targets and power control with variable SNIR targets, are discussed in the thesis. We first introduce some important techniques and results involved in the development of power control algorithms and give literature review. A PI power control approach from literature is introduced. Due to lack of stability analysis, we show there are problems in the existing algorithm. We then propose a stable Proportional-integral (PI) power control algorithm. A forgetting factor is adopted to improve the transient performance. Distributed power control algorithms for systems with fixed SNIR targets might diverge when the feasibility condition is not satisfied. Multi-objective optimisation (MO) is adopted to deal with power control with variable SNIR targets. After discussing the existing MO algorithm, we propose a quadratic multiobjective-optimisation (QMO) algorithm where a quadratic objective function and the greedy methodology are adopted for the dynamics. Theoretical and simulation results of convergence of the new algorithms are given. We also provide review of some important power control frameworks which can be used to show convergence of power control algorithms. However, the QMO algorithm does not fall into any existing framework. In order to show convergence of the QMO algorithm, we suggest a new generalised framework in this thesis.

Thesis (Ph. D.)--Syracuse University, 2005. / "Publication number AAT 3194027."

This work is an investigation of the "foam structure" of puffed, carbohydrate-based extrudates. A range of extrudates, produced to vary widely in cell structure through formulation and selection of processing parameters, were evaluated using image analysis and Instron testing. Specifically, cell size distributions were measured and described by different mathematical functions. In addition, the deformation behavior of the extrudates, which was found to conform to classic "brittle" compression models, was characterized by Fourier and Fractal analysis. And finally, the effects of various treatments on--and relationships between--structure and strength--were determined. Results of this work were that the extrudates, despite formulation or processing history, had highly skewed cell area size distributions that were closely described by both the log Normal and Rosen-Rammler models. The deformation behavior of these materials was dependent on relative humidity, and the extremely jagged nature of low RH compression curves could be quantitatively described by both the Blanket Algorithm, which determines fractal dimension, and the Fast Fourier Transform. Relationships between cell structure and mechanical properties were observed in chemically homogeneous samples produced from the same formulation (but using various process parameters) in that extrudate strength was positively associated with density and negatively associated with mean cell size. Additives also influenced extrudate properties, but the direction and magnitude of these effects depended on the specific ingredient used.

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2006. / Source: Dissertation Abstracts International, Volume: 67-07, Section: B, page: 4042. Adviser: Pascal Bellon. Includes bibliographical references (leaves 193-197) Available on microfilm from Pro Quest Information and Learning.

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2006. / Source: Dissertation Abstracts International, Volume: 67-07, Section: B, page: 4044. Adviser: Ralph G. Nuzzo. Includes bibliographical references. Available on microfilm from Pro Quest Information and Learning.

The aim of this thesis is to provide microstructural and mechanical characterisation of α-β titanium alloys exposed to a range of thermo-mechanical conditions, in particular under-going high rate deformation at elevated temperatures, representative of the Linear Friction Welding (LFW) manufacturing process. Three α-β titanium alloys provided by Rolls-Royce are studied: Ti-64 blade, disc and Ti-6246 disc. Ti-64 and Ti-6246 show complex deformation behaviour with strain, strain rate and temperature, especially near the transus temperature, where the low temperature α phase is transformed into the high temperature β phase. The microstructure and mechanical properties evolve in an interconnected fashion, and understanding this mutual influence is necessary to better predict the behaviour of these alloys. Characterisation of the mechanical properties was performed through uniaxial compression tests at strain rates from 0.001 to 3000 s^-1, using an Instron screw-driven machine at quasi-static rates, a servo-hydraulic machine at medium rates and a Split-Hopkinson Pressure Bar and a drop-weight tower at high strain rates. The tests were performed over a range of temperatures from room temperature to 1300 °C. The main focus was on high strain rate and high temperature tests, with the development of a gravity driven direct impact Hopkinson bar, referred as a drop-weight system, which is intended to evaluate the mechanical response of metals to high strain rate loading at temperatures up to c. 1300 °C. The design and principles of operation of the system are presented, along with calibration and validation data. Preliminary tests were performed on stock Ti-64, heated at two rates: 1 and 20 °C s^-1. The evolution of the mechanical properties was analysed, focussing on the strain rate, temperature and phases dependencies. Characterisation of the microstructure was realised by performing interrupted compression tests, first at room temperature, three plastic strains, 4%, 10% and 20%, and two different strain rates, 0.001 and 2000 s^-1; then at 4% plastic strain, a strain rate of 2000 s^-1 and three elevated temperatures, 700, 900 and 1100 °C. A better understanding of the microstructure evolution with strain, strain rates and temperature, including the macrotexture and microtexture of the specimens, was obtained using Electron Backscatter Diffraction (EBSD) to characterise the texture of the undeformed and deformed materials. The better understanding of the flow stress and microstructural evolution of both Ti-64 and its individual α and β phases with various strain rates and temperatures is intended to be used in the development of more accurate models representing the behaviour of these alloys. Predicting the microstructure evolution and then the mechanical properties of a material is essential to optimise the final mechanical properties of the alloys when welded by manufacturing processes such as the LFW process.