Hartley, Ian

Molecular hydrogen is the dominant molecular species present in the interstellar medium and has an important role in the cooling of shocks that are associated with star formation. The two mechanisms of cooling are collisional excitation followed by quadrupole emission and collisional dissociation. Modelling the role of dissociation in this cooling needs detailed information on the state specific dissociation rate coefficients. The initial goal of this research was to compare the trajectory outcomes on the Hinde potential energy surface (PES) with those on the BMKP2 PES to assess whether it is required to do extensive and more expensive calculations to determine state specific rate coefficients for dissociation of H2 + H2 to supersede those previously determined with the BMKP2 surface. A phenomenon of double dissociation was unexpectedly identified within the Hinde PES, despite the absence of sufficient energy for such an occurrence. These results prompted a comprehensive analysis of the Hinde PES, which in turn involved an exploration of the regions that exhibit unphysical behavior. This detailed examination unveiled problematic aspects of the potential energy surface. As a result of this, it has been determined that the Hinde PES is unsuitable for calculating dissociation rate coefficients for H2 + H2.

Terahertz time-domain spectroscopy was used to probe water dynamics in microcrystalline cellulose. In this study, the variation of the dielectric constant of water in microcrystalline cellulose samples with moisture contents between 2.65% and 16.73% was studied. It was found that the dielectric function of water does change with a change in moisture content in microcrystalline cellulose. The dielectric function of water appears to change from what might be expected for bound water towards values that are more consistent with bulk water at higher moisture content. This study is a step forward in the direction of understanding if the dielectric function of water goes from bound to free with a change in moisture content in microcrystalline cellulose. Future work to understand the detailed behavior of this transition is important for wood science and THz application to wood science.

This thesis provides generalization to known solutions for the scale factor and cosmic time of Friedmann-Lemaître-Robertson-Walker model universes in terms of elliptic functions. In particular the integration of known expressions for the scale factor is used to find new expressions for cosmic time. Various techniques using both the Weierstrass and Jacobi functions are discussed. Plots of physically significant quantities such as redshift and redshift drift are given. Limiting cases provide context for how various cosmic fluids change the dynamics of the universe on the largest scales.

DRAGON seeks to replace its BGO detectors with LaBr3:Ce detectors. The Geant4 simulation estimates gamma ray capture efficiency values of 3.384±0.011% and 1.113±0.007% for the BGO detector and the LaBr3:Ce detector, respectively for 0.6617 MeV gamma rays at 5 cm distance. The latter achieves an experimental efficiency of 1.102±0.042% and an experimental energy resolution of 3.282±0.036% for these gamma rays. The experimental and simulated LaBr3:Ce detector efficiency results agree within error. However, the simulation may overestimate the detector efficiency at high gamma ray energies, as observed at 4.44 MeV and 6.131 MeV. Furthermore, the timing method is performed to utilize its high time resolution. The average resonance energy is 0.47428±0.00815 MeV/u which agrees with the true value of 0.475 MeV/u. Therefore, the energy and time resolution of the LaBr3:Ce detector improve DRAGON’S ability to study radiative capture reactions, with its lower efficiency being its only drawback.

Cultural evolution of birdsong occurs when songs change over generations and such changes can spread directionally or via drift within and between populations. The objective of this thesis was to document the emergence and spread of a novel song variant, the Modulated-Doublet, within and between populations of White-throated Sparrows. I analysed songs recorded in a Prince George population between 2015-2020 to document song shift within the population. I also analysed songs from public song archives to document song transition on a continental-scale between 2014-2020. I found the Modulated-Doublet started as a rare variant but became the predominant variant within our population over a very short time. At the continental scale, the Modulated-Doublet emerged simultaneously and spread synchronously in multiple breeding populations and migratory routes, replacing the previous variant in those populations. This rapid spread at both scales suggests it is driven by several transmission biases; however further investigation is needed to determine their nature.

Transcutaneous near infrared spectroscopy (NIRS) of muscle requires coupling between the device and the skin. An unfortunate by-product of this coupling is contact force artefact, where the amount of contact force between the device and the skin affects measurements. Contact force artefact is well known, but largely ignored in most NIRS research. We performed preliminary investigations of contact force artefact to quantify tissue behaviour to inform future NIRS designs. Specifically, we conducted three studies on contact force artefact: (i) an experimental investigation of static load at varied levels of contact force and muscle activation, (ii) an experimental investigation of oscillating load at varied levels of contact force and frequency, and (iii) a Monte Carlo simulation of photon propagation through skin, adipose tissue, and muscle. Our results confirmed that contact force artefact is a confounding factor in NIRS muscle measurements because contact force affects measured hemoglobin concentrations in a manner consistent with muscle contractions. Further, the effects of contact force are not altered by muscle contraction and a likely candidate for the mechanism responsible for contact force artefact is the viscoelastic compression of superficial tissues (skin and adipose) during loading. Simulation data suggests that adipose tissue plays a key role in diffuse reflectance of photons, so any compression of the superficial tissues will affect the reflected signal. Further research is required to fully understand the mechanisms behind contact force artefact, which will, in turn, inform future NIRS device designs.

A mixture of waste-wood biomass and municipal biosolids waste was composted in a plastic container inside of an insulated chamber. The mixture of biomass and biosolids was approximately 50:50 and weighed 82.6 kg. The peak temperature of the compost was 32.4◦C. The small scale of the compost system allowed the lower limit of the compost decomposition rate to be studied. A model was successfully developed to predict the core temperature of the compost using the ambient temperature in the insulated chamber. A literature review was conducted to determine literature values for the overall convective and conductive heat transfer coefficient, the dry mass fraction, and heat of combustion for both biomass and biosolids. The model used an optimization algorithm to calculate the rate constant for the experimental setup. The calculated decomposition rate constant was 0.0525 Day−1.