published_or_final_version / Mechanical Engineering / Master / Master of Philosophy

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A recent study on the Post-Formed properties of Superplastically Formed Magnesium AZ31B has shown that the heating time prior to testing has a major effect on the Post Forming properties of the superplastically material. To this point, there has been very little examination into the effect of pre-heating or annealing on superplastic forming (SPF) properties. In this work, the effects of annealing prior to the SPF of Mg AZ31 alloy were examined. Both high temperature SPF tensile and bulge specimens were formed after annealing. Multiple annealing temperatures were examined to produce specimens with grain sizes ranging from 8 andamp;igrave;m to 15 andamp;igrave;m for comparison with traditional SPF results. The results show that the effect of annealing can be suitable for the improvement of thinning and possibly the forming time of superplastically formed Magnesium alloys through the control of the microstructure.

This thesis describes the fabrication of a set of bright, visible light-emitting silicon LEDs. These devices were fabricated in-house at the University of Saskatchewan using a custom plasma ion implantation tool, an annealing furnace, and a physical vapour deposition system. A high-fluence (F = 4 × 1015 cm^−2) implantation of molecular hydrogen ions extracted from an RF inductively coupled plasma at an energy of 5 keV was used to create a heavily damaged region in the silicon centered approximately 40 nm below the silicon surface with a width of approximately 56 nm. A matrix of annealing (e.g. thermal processing) processes at 400 ºC and 700 ºC and different durations (30 minutes and 2 hours) as well as an aluminum gettering procedure were tested with the goal of increasing the output electroluminescence intensity. Current-voltage characterization was used to extract information about the defect-rich nanocrystalline, light-emitting layer as well as the Schottky barrier height. This enabled comparison of these new devices with previous silicon LEDs based on porous silicon and other approaches. The processes which were used to fabricate these devices are compatible with standard CMOS processing techniques and could provide one solution to the problem of optical interconnect on multi-core chips. The scientific significance of this work is the demonstration of bright, visible light emission at mean photon energies ∼1.84 eV corresponding to a photon wavelength of λ ≈ 675 nm. This is remarkable given that ordinary crystalline silicon is an indirect bandgap material with a bandgap energy of 1.1 eV, in which band-to-band radiative recombination is forbidden by momentum conservation. The devices fabricated in this thesis have light emission properties similar to previous silicon LEDs based on nanocrystalline or nanoporous silicon. They have the advantage of being easily electrically driven. The nanocrystalline region which is the source of the light emission was nucleated from the ion-implanted layer below the surface of the silicon. This makes these devices mechanically robust and insensitive to environmental conditions. The engineering significance of this work is the production of CMOS compatible light emitters. This study demonstrated increased light emission efficiency at higher annealing temperatures which is likely due to enhanced diffusion and nucleation of silicon nanocrystals in the ion-implant damaged layer.

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Stainless steels were first developed in the early 20th century and have since then emerged as a very diverse class of engineering materials. Along with steels having new combinations of properties, there is a continuous development of new technologies allowing the material to be produced in a faster and more energy effcient manner. A prerequisite for new technologies to be adapted quicklyis a fundamental understanding of the microstructure evolution throughout theprocess chain. The first part of this thesis has been dedicated to the annealing and pickling processes from a process-microstructure perspective. In the second part the concept of utilising crystallographic texture as a way to attain microstructures with new combinations of properties has been evaluated. In the first part, annealing can be regarded as a high temperature oxidation process, resulting in chromium depletion that necessitate subsequent chemical pickling. Chemical pickling, on the other hand, is basically a wet-corrosion process and hence more difficult for highly corrosion-resistant grades. The chromium depleted layer was found to be enriched in austenite in case of duplex stainless steel UNS S32205 (Paper I) and this may inuence the pickling process. Proper pretreatment like shot-blasting dramatically increases the pickling rate because it provides the pickling acid with access to the chromium depleted layer (Paper II). Oxidation kinetics for S30400 in conditions relevant to strip annealing do not seem to be affected by the choice of air/oxygen as oxidiser even though the latter results in substantially higher water content (Paper III). This gives new possibilities regarding both cost savings and increased throughput. In the second part, the effect of crystallographic texture on resistance towards corrosion of S31603 in a solution of FeCl3 and AlCl3 in ethanol/glycerol and in 30 vol% H2SO4 is investigated. In the former, high density surfaces {1111} and {100} are less prone for pit nucleation, however the effect is relativelysmall. In H2SO4 pronounced crystallographic anisotropy is observed inwhich the corrosion rate increase in the order {111} &lt; {110} ≤ {100} (Paper IV).For corrosion at high temperatures, chromium diffusion is governed by randomhigh angle boundaries with ~20—55° misorientation. The possibilities to alter the texture in austenitic stainless steels by means of warm-rolling and annealing has been evaluated for S30403 and S31603. During warm-rolling, both steels develop the copper-type texture in contrast to the brass-type texture observedat room temperature. However only S30403 is prone to recrytallise cube texture during subsequent annealing (Paper V). / <p>QC 20150121</p>

In this thesis, we consider joint beamforming, power, and channel allocation in a multi-user and multi-channel underlay cognitive radio network (CRN). In this system, beamforming is implemented at each SU-TX to minimize the co-channel interference. The formulated joint optimization problem is a non-convex, mixed integer nonlinear programming (MINLP) problem. We propose a solution which consists of two stages. At first, given a channel allocation, a feasible solutions for power and beamforming vectors are derived by converting the problem into a convex form with an introduced optimal auxiliary variable and semidefinite relaxation (SDR) approach. Next, two explicit searching algorithms, i.e., genetic algorithm (GA) and simulated annealing (SA)-based algorithm are proposed to determine optimal channel allocations. Simulation results show that beamforming, power and channel allocation with SA (BPCA-SA) algorithm achieves a close optimal sum-rate with a lower computational complexity compared with beamforming, power and channel allocation with GA (BPCA-GA) algorithm. Furthermore, our proposed allocation scheme shows significant improvement than zero-forcing beamforming (ZFBF).

In this thesis we introduce and study an A-optimal minimax design criterion for two-level fractional factorial designs, which can be used to estimate a linear model with main effects and some interactions. The resulting designs are called A-optimal minimax designs, and they are robust against the misspecification of the terms in the linear model. They are also efficient, and often they are the same as A-optimal and D-optimal designs. Various theoretical results about A-optimal minimax designs are derived. A couple of search algorithms including a simulated annealing algorithm are discussed to search for optimal designs, and many interesting examples are presented in the thesis. / Graduate / 0463 / yinyue@uvic.ca

There is significant interest in the synthesis of discrete-state random fields, particularly those possessing structure over a wide range of scales. However, given a model on some finest, pixellated scale, it is computationally very difficult to synthesize both large and small-scale structures, motivating research into hierarchical methods. This thesis proposes a frozen-state approach to hierarchical modelling, in which simulated annealing is performed on each scale, constrained by the state estimates at the parent scale. The approach leads significant advantages in both modelling flexibility and computational complexity. In particular, a complex structure can be realized with very simple, local, scale-dependent models, and by constraining the domain to be annealed at finer scales to only the uncertain portions of coarser scales, the approach leads to huge improvements in computational complexity. Results are shown for synthesis problems in porous media.

The Kim and Chan experiment in 2004 gave the first experimental evidence of a possible supersolid state. Even though the origin of this state is not clear yet, several experimental and theoretical investigations suggest defects are responsible for this curious phase. We have used heat pulses and thermal quenching to study pressure gradients and annealing mechanisms in solid 4He crystals. Large pressure gradients exist in crystals grown at constant volume. These can be enhanced by phase transitions, thermal quenching or by partial melting. Annealing reduces defect densities and hence pressure gradients in crystals. Our measurements show that the pressure at different points in a crystal can behave differently, even if there is little change in the crystals average pressure. We measured the activation energy that is associated with the annealing process.