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Measurements of higher harmonics of the ac voltage response in YBCO thin film strips under low amplitude and low frequency harmonic excitation, as a function of temperature, show a non linear response of the conductivity in the superconducting transition interval. The third and fifth harmonics of the local voltage as a function of T exhibit a peak near Tc and their amplitudes seem to be closely related to the T-derivative of the first harmonic. The peaks are linearly dependent on the current amplitude and do not depend on frequency. The observed data are partially interpreted in terms of ac current induced thermal modulation of the sample temperature added to strong thermally activated fluctuations in the transition region. The fit of the model to the data gives information of some sample properties such as zero temperature critical current, zero onset resistance and thermal boundary conductance.

<p>In this thesis work, two new CO₂-responsive monomers have been synthesized. These amidine-containing monomers were prepared in a simple and effective one-step reaction, giving a very high yield (98.5 %) of product. Furthermore, there was no complicated further purification required to obtain the highly pure product. The CO₂ switchability, conductivity and partitioning of the monomers were measured. It was confirmed that the monomers could be protonated CO₂ in the present of trace amount of water and reversibly switched back and forth to their natural forms by N₂ at room temperature.</p> <p>The polymers having different molecular weights were prepared from one monomer via conventional free radical polymerization method. The polymers also showed the reversible switchability property with CO₂ and N₂ stimuli. This was confirmed by the results of conductivity and partitioning tests. Temperature showed a major influence on the conductivity of the monomer and polymers. The effect of molecular weight on the polymer switchability of was further investigated through conductivity tests and potentiometric titration. The conductivity decreased with the increased molecular weight. The apparent equilibrium constant (pK_a)decreased with the degree of protonation (δ) suggesting that the basicity of the polymers is strongly depended on the value of δ.</p> / Master of Applied Science (MASc)

<p>The microstructure of the ZEBRA cells was examined at different cycle lifetimes. Various methods of sample preparation were used to remove the NaAlCl₄ electrolyte and expose the cathode microstructure. Features such as layered NiCl₂ crystals, large NaCl grains and needle-like FeCl₂ phases were observed by SEM. The results indicate that nickel particles grow in size with age of the cell. Moreover, the presence of both Na₆FeCl₈ and NiAl₂Cl₈ phases was confirmed by XRD. Thermodynamic modeling was used to predict the phases expected when a cell has undergone overcharge or overdischarge during cycling. It is postulated that some phases observed in the cathode at room temperature may be artifacts due to transformations that occur during cooling and do not exist at the operating temperature.</p> <p>The presence of isolated nickel particles within the cathode was confirmed by SEM and FIB techniques. Furthermore, the conductivity of the NaAlCl₄ electrolyte was measured at high temperatures and various additives were used to make the electrolyte a mixed ionic-electronic conductor.</p> <p>A special cell was designed to measure the conductivity of hygroscopic and volatile electrolyte at high temperatures. The best conductivity was obtained when using 0.2 mole fraction Bi as an additive to the NbCl₅+NaAlCl₄ mixture (Nb:Na=0.3, Bi:Nb=0.2). The conductivity values were doubled between 190 and 500˚C. The DC measurements confirm the presence of electronic conductivity in Bi+NbCl₅+NaAlCl₄ mixtures. In addition, the effect of NaF and Na₂S on the conductivity of the NaAlCl₄ electrolyte was measured.</p> / Doctor of Philosophy (PhD)

<p> In very high resolution galaxy simulations, the supercomputers of today offer the possibility of enough resolution to capture the bubble of a supernova, though not the originating star itself. Modeling the energy released as originating from a single SPH particle initially arranged amongst a grid of particles requires the introduction of an artificial thermal conductivity term that allows the SPH method to resolve the thermal energy discontinuity inherently present in such a scenario. Such an artificial thermal conductivity is implemented in the SPH code GASOLINE. Resolution tests show that the method is insensitive to resolution changes when determining the radius of the Sedov-Taylor blast wave, and that the numerical solution agrees with the analytic prediction R = βE^1/5ρ0^-1/5t^2/5. The peak density at the shock is lower than the actual value of four times the ambient density, though it is found to scale with resolution. The density of the interior of the shock, near the center of the supernova remnant is found to be elevated compared to the value expected from the Sedov-Taylor solution, but this too is resolution dependent, and with increased resolution the central density converges towards the expected value of zero. The fluid quantities pressure and velocity are also found to be in good agreement with the profiles predicted by the analytic solution.</p> / Thesis / Master of Science (MSc)

no / The coupling between natural convection and conduction within rectangular enclosure was investigated numerically. Three separate heat sources were flush mounted on a vertical wall and an isoflux condition was applied at the back of heat sources. The governing equations were solved using control volume formulation. A modified Rayleigh number and a substrate/fluid thermal conductivity ratio were used in the range 10^4 −10^7 and 10−10^3 respectively. The investigation was extended to examine high thermal conductivity ratio values. The results illustrated that, when Rayleigh number increased the dimensionless heat flux and local Nusselt number increased and the boundary layers along hot, cold and horizontal walls were reduced significantly. An opposite behaviour for the thermal spreading in the substrate and the dimensionless temperature, were decreased for higher Rayleigh number. Moreover, the thermal spreading in the substrate increased for higher substrate conductivity, which affected the temperature level. However the effect of the substrate is negligible when the thermal conductivity ratio higher than 1,500. / The full text of book chapters are not available for self deposit under the Publisher's copyright restrictions.

Yes / In this study, the thermal performance analysis of porous fin with temperature-dependent thermal conductivity and internal heat generation is carried out using Haar wavelet collocation method. The effects of various parameters on the thermal characteristics of the porous fin are investigated. It is found that as the porosity increases, the rate of heat transfer from the fin increases and the thermal performance of the porous fin increases. The numerical solutions by the Haar wavelet collocation method are in good agreement with the standard numerical solutions.

Yes / In this paper, the Chebychev spectral collocation method is applied for the thermal analysis of convective-radiative straight fins with the temperature-dependent thermal conductivity. The developed heat transfer model was used to analyse the thermal performance, establish the optimum thermal design parameters, and also, investigate the effects of thermo-geometric parameters and thermal conductivity (nonlinear) parameters on the thermal performance of the fin. The results of this study reveal that the rate of heat transfer from the fin increases as the convective, radioactive, and magnetic parameters increase. This study establishes good agreement between the obtained results using Chebychev spectral collocation method and the results obtained using Runge-Kutta method along with shooting, homotopy perturbation, and adomian decomposition methods.