UC Research Repository
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The UC Research Repository collects, stores and makes available original research from postgraduate students, researchers and academics based at the University of Canterbury.
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Recent Submissions
OCHT pilot in Ōtautahi
(2024) Kingham, Simon; Curl , Angela; Carroll, Liam
Patient-focused Cardiovascular Symptom Assessment Systems: Reducing Pre-hospital Delays and Enhancing Triage Decisions
(2023) Chung C; Fu J; Dicker B
The effects of environmental pollution on bacterial conjugation.
(2024) McCabe, Andrew W.
Antibiotic resistant bacteria are an anthropogenically caused threat to medicine and social
cohesion. Whilst some of the drivers are known, such as the use and overuse of antibiotics,
others are just being discovered. Evidence that the vast number of environmental
contaminants is also an important driver is gaining acceptance. The lack of thorough testing
of the unintended antimicrobial effects of most of these contaminants leads to a severe lack
of knowledge on the impact of pollution on antibiotic resistance.
Bacteria can acquire antibiotic resistance via multiple mechanisms, including horizontal gene
transfer. One vector of transmission is conjugation. Conjugation (or “mating”) is the process
by which plasmids move between cells. It is an important pathway through which many
bacteria acquire resistance.
Compounds known to be commonly found as contaminants/pollutants in waterways can also
have properties that could affect the frequency of conjugation. Some were chosen to test
whether exposure to them altered either or both inter- or intra- species plasmid transmission
frequencies.
Interesting patterns were observed indicating that the effect of exposure cannot necessarily
be predicted by the known chemistry of the contaminant or biochemistry of plasmid transfer.
Future research will determine if the hypothesised effect of each compound explains
observed effects on plasmid transmission frequencies.
I also examined if the plasmid transfer complex, which in this case is a type IV secretion
system, could confer resistance to heavy metal compounds. Whilst some plasmids have been
shown to carry heavy metal resistance genes, recent evidence suggests an independent effect
of the type IV secretion system on resistance.
Heavy metals are common environmental contaminants, due to leaching from plastics
amongst other sources, making exposures also common. If plasmid transfer genes have a
pleiotropic effect on heavy metal resistance, then heavy metals could substitute for
antibiotics to select for plasmids. Heavy metals would enrich for antibiotic resistance by
linkage.
The hypothesis was not supported in this research. However, a surprising observation was
made. One conjugative plasmid, RP4, increased susceptibility to zinc sulphate.
I have identified a zinc permease gene carried by RP4 that might increase zinc sulphate
uptake. Future research could determine if the permease gene is necessary and sufficient for
increased susceptibility to zinc sulphate.
The effect of thermomechanical processing parameters on the texture of Ti-6Al-4V forgings as a precursor to coarse grain growth.
(2023) Wiley, Richard
This thesis explores the relationship between forging parameters - total strain, strain rate, and
forging temperature - and the emergence of abnormal grains during subsequent heat treatment
of Ti-6Al-4V. Abnormal grain growth can compromise material properties, making its
understanding crucial for optimizing manufacturing processes. Through systematic experiments,
varying the forging temperature between 875 and 975°C and the strain rate between 0.1s⁻¹ and
10s⁻¹ , the study reveals how different forging conditions influence the as-forged microstructure
through the alteration of the kinetics of flow softening and how this affects abnormal grain
formation. Microstructural analysis through optical and scanning electron microscopy methods
demonstrate correlations between these forging parameters and the occurrence of non-uniform
grain distributions. The insights gained offer strategies to mitigate abnormal grain growth during
heat treatment, advancing materials science and manufacturing practices.
The results show that forging temperature and strain rates impact prior beta grain size differently.
Higher forging temperatures at 975°C lead to larger grain sizes due to increased boundary
mobility favouring grain growth. Lower forging temperatures at 875°C produce more consistent
grain sizes due to uniform boundary energies resulting from a weaker texture. For samples forged
at 925°C, varying strain rates cause significant differences in grain size due to the shift from
dynamic recovery to dynamic recrystallisation as the primary strain relief mechanism. This shift in
mechanisms is also reflected in stress-strain responses, with dynamically recrystallised samples
showing higher peak stress and more transience. The dynamic recrystallisation process leads to
the nucleation of strain-free grains with distinct orientations, contributing to a weaker textured
material.
The study validates that abnormal grain growth is influenced by strain rate and forging
temperature, with increased strain-strengthening precursor texture. Lower forging temperatures
lead to weaker texture and more normal grain growth. From the findings, it is recommended to
forge above critical rates for recrystallization, at the required forging temperature. The research
suggests forging above 5s⁻¹ up to 925°C or 0.95 Tβ, although this is adjustable to 0.1s⁻¹ at
875°C/0.9 Tβ. Billet size indirectly affects abnormal grain occurrence by affecting the strain rate,
with smaller billets displaying uniform grain size after annealing. Thus, changes in the thickness
of Ti-6Al-4V parts could cause abnormal grain growth in thicker sections during annealing and
should be considered prior to forging.
Regional flood frequency analysis in hydrologically diverse regions.
(2024) Fitriana, Farhana Sweeta
To reduce flood risk, it is crucial to accurately estimate design floods, which is a flood discharge associated with a specific annual exceedance probability. The main aim of this study is to devise an approach to carry out a Regional Flood Frequency Analysis within hydrologically similar sub-regions to estimate design floods for gauged and ungauged catchments with diverse climate and catchment characteristics. In such catchments, traditional regionalisation approaches usually fail due to a high level of inhomogeneity. The developed RFFA approach was evaluated using 363 catchments in New Zealand, a country with hydrologically diverse regions. It was found that using climate zones and catchment characteristics led to a higher degree of homogeneity than traditional sub-divisions. Cluster analysis based on catchment attributes was applied to further delineate homogenous regions, which resulted in 21 sub-regions. The two-parameter Log-Normal and Pearson 3 distributions were identified as the dominant regional probability distributions for these sub-regions. Next, the Generalised Additive Model coupled with the Index Flood L-moment approach was employed to estimate regionalised design floods of various return periods. Model performance was assessed using a Jackknife Resampling procedure. The results indicated significantly smaller error estimates for all estimated design floods than prior RFFA studies in New Zealand. The approach provides region-specific design values to inform flood risk management. It allows for robust design flood estimation in both gauged and ungauged catchments and can be implemented in other regions.