Science: Theses and Dissertations

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Open Access
Improvements to the estimation of the muon content in cosmic-ray air showers
(2024) Roy, Vagdhan
This study delves into techniques aimed at improving the reconstruction of cosmic-ray properties using signals from the IceTop surface array and planned extensions. The reconstruction of cosmic-ray direction, energy, and mass discrimination involves fitting models to the spatial and temporal distribution of particles observed on the ground. In this investigation, we optimise the Nishimura-Kamata-Greisen (NKG) model and compare its performance with the standard double logarithmic parabola (DLP) model used in IceTop analyses. The optimized NKG model demonstrates similar performance to the DLP model in estimating primary energy across the majority of studied energy ranges. However, at high energies exceeding 107.2 GeV, the resolution of estimating primary energy for the DLP LDF consistently remains below 12% for all selected primaries. In contrast, for the NKG LDF, the resolution for each primary varies between 10% and 20% for energies exceeding 107.2 GeV. Notably, the NKG model shows no obvious mass bias in the resolution for primary energy, unlike the DLP model; however, it is more unstable at higher energies. This optimised NKG function can be used as a baseline model for future IceTop analyses involving the NKG LDF. A significant focus of our study is on developing a method to estimate the low-energy muon component of individual showers. Muon measurements are crucial for cosmic-ray mass com- position studies, tests of hadronic interaction models, and addressing the “muon puzzle”. We investigate a two-component lateral distribution function (TwoLDF) with separate descriptions for electromagnetic and muon lateral distributions of detector signals. Using IceTop, the NKG lateral distribution function (LDF) for the electromagnetic component yields a better bias for the estimation of primary energy, whereas the DLP LDF exhibits a better resolution. Additionally, the TwoLDF model with the NKG LDF leads to a better resolution in the low-energy muon number, whereas using the DLP LDF leads to a better bias in the low-energy muon number. The mass-dependent bias in energy reconstruction with the NKG LDF employed for the TwoLDF becomes smaller compared to the case of using the DLP function towards 100 PeV in primary energy. However, a mass-dependent bias is exhibited for smaller energies and needs to be a part of further optimisation. In total, the application of the NKG function within the TwoLDF model constitutes a promising method due to its improvement in low-energy muon number resolution compared to the DLP function. Furthermore, applying the TwoLDF model for IceCube-Gen2 and IceTop did not allow for a comprehensive quantitative analysis due to instability of the model for the very low multiplicity of hits on IceTop for air showers across the studied energy range. Additionally, the TwoLDF fit purely being performed in a region where silent detectors are dominant contributes to the instability and needs further optimisation.
Open Access
Normal characteristics of ocular vestibular evoked myogenic potentials using the RadioEar B81
(2024) Lee, W. ZQ
Background: The utilisation of the RadioEar B81 bone vibrator in clinical use for ocular vestibular evoked myogenic potentials necessitates the establishment of normative data for the adult population. Currently there is a dearth of suitable normative data for the B81 across a range of clinically relevant frequencies, intensities, and stimulation sites. Acquiring normative data is crucial for the accuracy of diagnosis and monitoring for patients who may present with vestibular disorders. Method: 40 participants aged between 18-50 were tested using the B81 at Fm (mastoid) and Fz (midline high forehead) stimulation sites in a counter balanced manner across low, medium and high intensity levels using alternating, condensation and rarefaction tone-burst stimuli at 250, 500, and 750 Hz, corresponding to those in common use clinically. Responses were analysed for residual noise, stimulus artefact, N10-P15 and oVEMP amplitudes and latency characteristics, as well as Interaural N10-P15 asymmetries for Fz responses. Results: A comprehensive suite of normative data was created using optimised stimuli parameters. N10-P15 amplitude was found to be largest for 500 Hz for both Fm and Fz recordings, while N10 latency was earliest for 750 Hz. In addition to providing normative data, grand average waveform interpretation reveals complex utricle excitation dynamics that challenge some assumptions of en- bloc skull movement in response to different stimuli polarities at the mastoid. Conclusion: The usage of optimised stimulus parameters for the B81 and their applications in this study reflects the existing literature and knowledge base surrounding BCV. The applications of created normative data provides up to date clinical utility for oVEMP in vestibular assessment using the B81. Future research could further investigate gender or age stratified normative data.
Open Access
Artificial intelligence and its applications to the digital holographic interferometry (DHI) reconstruction algorithm.
(2024) Stephens, Caelan
Artificial intelligence (AI), although widely known for many decades, has experienced a meteoric rise in popularity due to technological innovations, with many industries and entities utilising AI programs for various use cases, including within medicine. In this research, artificial intelligence is applied to the digital holographic interferometry (DHI) reconstruction process to improve upon the standard methods used. Standard methods of performing this process frequently encounter errors during specific steps, such as phase unwrapping, when significant noise is present in the optical system. Through the use of the Pix2Pix generative adversarial network, it was shown to be possible to train an AI capable of unwrapping the phase of wrapped images of varying complexities. Additionally, it was shown that after being trained on a dataset of image pairs containing some amount of noise in the input images while the output images were free of noise, an AI was capable of maintaining acceptable accuracy in the presence of a significant amount of speckle noise (σ = 0.8). Together, these aspects of the AI’s capabilities showed that such an AI has great potential to outperform the standard algorithms used in the phase unwrapping step of the DHI reconstruction process.
Open Access
Development and validation of a dose accumulation workflow for MR-guided adaptive radiotherapy.
(2024) Taylor, Megan
During radiotherapy treatment, anatomical changes and discrepancies in patient setup between fractions may result in the planned dose and actual delivered dose differing. In conventional radiotherapy, it is common practice to assume that over a full course of treatment, these differences in delivered and planned dose are negligible. This is because positioning devices, margins on target volumes, etc. define “acceptable” levels of error. With the development of adaptive radiotherapy, images of the patient can be obtained with every fraction, allowing visualization of how the patient anatomy differs from the reference plan setup. Along with visualizing positioning changes, the Elekta Unity MR-Linac system allows for alterations to the treatment plan on each fraction to correct for these positional changes. This, in theory, should reduce the discrepancy in planned dose and delivered dose. In practice, delivered dose still differs from fraction to fraction. Without summing delivered dose per fraction, it is a qualitative assumption that the planned dose has been delivered. A quantitative method allows for reassurance and more robust adaptive planning. The aim of this project was to develop a workflow to accurately measure accumulated dose inter-fractionally – considering the affects of anatomical/positioning changes. The workflow was then to be validated and compared to planned dose. Using data of ten patients previously treated on the MR-Linac for prostate cancer, a deformable image registration algorithm was optimised and dose mapping methods were assessed. The finalised components were combined in a dose accumulation workflow. Uncertainties were estimated for the workflow and synthetic deformations used to validate the method. It was found that median uncertainties were generally below 1%. However, point dose uncertainties exceeded 40% in some cases where regions of high dose gradients occurred. Comparison to known deformations showed a high level of agreement in dosimetric criteria (gamma passing rates above 95%). A comparison of planned and accumulated dose showed that there were statistically significant differences in PTV coverage suggesting dose accumulation may be a useful tool for improving understanding of planned vs delivered dose and should be considered for applications in adaptive radiotherapy.
Open Access
Validation of treatment planning methods used at Christchurch Hospital for head and neck IMRT plans when air is present in the target volume.
(2024) Hayward, Kayla
This project evaluates planning methods used at Christchurch Hospital for head and neck radiation therapy plans involving air cavities within the planning target volume (PTV). Anatomy in the head and neck region is complex, often including air cavities influenced by tumour dynamics, swelling, fluid, and patient movements. This impacts the ability to accurately model the radiation transport and predict expected dose distributions. A novel metric, the mean dose to rinds surrounding air within the PTV, was developed to compare plan quality. Planning and phantom studies were conducted using this metric alongside dose volume histogram (DVH) statistics and mean PTV dose analysis. Four head and neck patients were included. Plans were generated using different planning methods for initial cavity sizes and cavity increase and decrease scenarios. Three methods were considered: method 1 was filling of the PTV during optimisation, method 2 was filling the PTV with the cavity removed leaving a margin, and method 3 was excluding the cavity from the PTV during optimisation. Film measurements in a customised phantom provided insight into the uncertainties associated with each method. Custom code was written to analyse film measurements using structures creating during treatment planning. Mean doses to the PTV and rinds were compared across different anatomy, planning methods and cavity sizes. Of the three methods considered, method 3 showed promising results for gross tumour volume (GTV) coverage, while method 1 excelled in PTV coverage. Dose to rinds gave mixed results. Film measurements showed method 3 was the most accurate to the plan calculation when cavity size decreased, and method 1 was more accurate for a constant cavity size. Method 2 exhibited poor performance in the phantom study, leading to its exclusion from further consideration. There is no clear preferred method defined by this research with methods 1 and 3 showing promise for different clinical situations. While the small sample size means exact conclusions on each method can not be made, the results give insight into treatment planning uncertainties in different scenarios that is valuable for clinical decision making. The developed dose metrics and assessment tools, particularly the novel rind structure approach and film analysis method, hold promise for future plan quality assessments in clinical settings with transient air cavities.
Open Access
Developing a sustainable integrated pest management strategy for Paropsis charybdis Stål (Coleoptera: Chrysomelidae) in Eucalyptus spp. forestry.
(2024) James, Frances
The hardy invasive species, Paropsis charybdis Stål (Coleoptera: Chrysomelidae), causes extensive damage to Eucalyptus spp. stands nationwide. Current management of P. charybdis is damaging to the surrounding ecosystem and necessitates a sustainable alternative through integrated pest management. This is done by considering the effects of biological control agents (BCA) (Enoggera nassaui and Neopolycystus insectifurax) and combining their effects with an eco-friendlier chemical control. We tested alternative chemical controls to determine how they impacted the survival of various life stages of the target organism, P. charybdis, and one of its egg parasitoids, E. nassaui. From these trials, I identified two possible alternatives to the current chemical control, one that was effective on the target organism but also had a negative impact on the BCA, and a second that was less effective on the target organism but also had less of a negative impact on the BCA. I translated these results into a population-dynamics model that investigates the optimum timing of application of the chemical controls and incorporates the effect of the BCAs. The outcome of this model informs a long-term and sustainable alternative to the current pest management of P. charybdis that incorporates the effects of the BCAs.
Open Access
Health conditions and presenteeism motives in full-time and part-time audiologists.
(2024) Ni, Huimin
Aim: The purpose of this study is to investigate the difference in presenteeism as the origin of physical health and mental health, especially to look for the occurrence and impact of presenteeism in full-time employers in comparison to part-time employers. Method: A cross-sectional design will be performed using anonymous survey data. In total, 100 full-time audiologists and 30 part-time audiologists from 4 different countries completed the survey. Results: No association was found between full-time and part-time audiologists when it comes to the act of absenteeism and the act of presenteeism. Similarly, both absenteeism and presenteeism caused by physical conditions did not differ from the ones caused by mental health. As to the presenteeism-caused productivity loss, when presenteeism originated from mental conditions, the resulting productivity loss was higher than that caused by physical conditions. However, no difference was found in the productivity loss between the group of full-time audiologists and part-time audiologists. When taking account of motives behind presenteeism, two significant association were found: audiologists with mental conditions have higher avoidance motives than the one with physical conditions; full-time audiologists generally have more approach and/or avoidance motives than part-time audiologists no matter their presenteeism was caused by physical health conditions or mental conditions. Conclusion: The study sheds light on the presenteeism behavior of audiologists, revealing no significant effect of employment status or health condition type on work attendance when ill. However, presenteeism due to mental health concerns results in more productivity loss than physical health issues. Full-time audiologists are more driven to work while sick than part-timers, possibly due to higher job demands. These findings emphasize the need for mental health-focused workplace interventions.
Open Access
Spirituality within the secular space : exploring the integration of spirituality within professional psychological practice in New Zealand.
(2024) Elliott, Meg
Research demonstrates that individual spirituality can have a positive impact on wellbeing, and decrease negative psychological symptoms. Despite this research, and the relevance of spirituality in the lives of many New Zealanders, only one existing study has examined how client spirituality is integrated or addressed in clinical psychological practice in Aotearoa New Zealand. The current study aimed to expand upon this research by exploring 13 registered psychologists’ experiences of integrating spirituality within clinical practice in Aotearoa New Zealand. Reflexive thematic analysis was used to explore (1) how psychologists in Aotearoa New Zealand conceptualise spirituality; and (2) experiences of psychologists in integrating spirituality in their clinical practice, including as part of bicultural practice. Semi-structured interviews held either via Zoom or in person at the University of Canterbury, alongside a brief survey, were used to collect participant data. Thematic analysis revealed one main theme, Meaning of Spirituality and three subthemes relating to how psychologists conceptualise spirituality. Five main themes and nineteen subthemes were identified describing the experiences of psychologists in integrating spirituality in their clinical practice, including as part of bicultural practice: Spirituality as beneficial in a therapeutic setting, Integration of spirituality within practice, Spirituality and bicultural practice, Challenges or concerns integrating spirituality in practice and Psychological training in spirituality in practice. The findings of the current study emphasise clinician perspectives of the link between spirituality and wellbeing, and the importance for psychologists to consider and address spirituality in assessment and therapy. The results also suggest a need for further specialist training on client spirituality in psychology training programmes, and highlight the importance of ongoing clinical professional development in this area.
Open Access
Exploring novel ligands interacting with RuBisCO.
(2024) Zhang, Weihan
Ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) is pivotal in photosynthesis, facilitating the conversion of carbon dioxide into organic compounds within the CalvinBenson-Bassham (CBB) cycle, vital for life on Earth. RuBisCO's abundance suggests potential as a food source. Previous research has delved into its biochemical mechanisms, unveiling different ligands that modulate its activity and several studies have elucidated the structural and functional aspects of its phosphate binding sites. This study aimed to identify new RuBisCO ligands; screening close to 500 small molecular compounds via differential scanning fluorimetry. The RuBisCO enzyme utilized in this project was purified from spinach, a commonly employed source. The screening identified ligands that potentially stabilise RuBisCO, suggesting binding interactions. By adjusting ligand concentrations, melting temperature trends were analyzed to estimate the affinity data, corroborated by isothermal titration calorimetry (ITC). Two compounds showed promising binding in ITC, albeit weak compared to RuBisCO's known substrates. The study also probed ligand binding under different RuBisCO activation states and employed spectrophotometry to gauge RuBisCO’s activity in the presence of ligands, revealing novel positive and negative effectors compared to negative controls. Future investigations might discover additional small molecules modulating activity of RuBisCO. This research sets the stage for exploring RuBisCO's interactions with diverse small molecule metabolites, enhancing our understanding of its binding and catalytic mechanisms. Such insights could spur endeavours to boost crop efficiency or utilize RuBisCO in food or pharmaceutical applications in future.
Open Access
What are the barriers prohibiting active school transport at Hillmorton High School, and how can these barriers be overcome to benefit students, parents, and the wider community?
(2024) Gover, Katie
The staff of Hillmorton High School (HHS) are concerned about the number of students driving or being driven to school and choosing not to engage in active school transport (AST). My project aimed to address these concerns while working with Ashley Beaton from the Christchurch City Council. By understanding more about the barriers to active transport use, we could aim to improve awareness about the active transport modes available to students, and outline the benefits to students, parents, and the environment. First, I observed how students entered and exited the school grounds, and which mode of transport they took. These observations allowed me to identify safety concerns such as lack of bike lanes or pedestrian crossings, which might be the reason for changes in transport habits. I then ran focus groups of about 4-5 students, to understand more about active transport from their perspective. This provided insights that numerical data cannot provide. The anonymised data from HHS helped to better understand active transport at Ōtautahi Christchurch high schools, particularly raising awareness about cycle and bus routes available. These findings can be applied elsewhere, to improve AST city-wide.
Open Access
Understanding the ancient glacial history of the Rakaia and Malvern Hills, Canterbury.
(2024) Townend, Shaelyn
This thesis explores the cryptic glaciation that extended onto the Canterbury Plains from the Rakaia Valley during glacial maxima in the Quaternary. Extensive research has been conducted on the timing and causes of past glaciation in Canterbury, New Zealand in the past. Despite this, older glaciations associated with the major river valleys in Canterbury, which extend well beyond the mountain front, have not been extensively researched even while identified in earlier publications. This thesis aims to identify, map and interpret the glacial features to enhance our understanding of older advances, with a focus on the Canterbury Plains adjacent to the Rakaia Valley and parts of the Malvern Hills in Canterbury. Geomorphic mapping was conducted using high-resolution LiDAR and digital analysis. A series of glacial features were identified including moraines, outwash, meltwater channels, kettle holes, ice overrun bedrock and sediment, underfit streams, paleolake, aggradational fans, truncated spurs and eskers. A number of large-scale geomorphic lineations were identified on the Canterbury Plains near the Rakaia Gorge extending across the Woodlands Moraine and onto outwash surfaces beyond the Woodlands. These lineations were intensively investigated using remote mapping, ground penetrating radar and trenching and identified to be glacial megaflutes. The megaflutes are aligned with an ice source in the Rockwood Range and flow onto the Canterbury Plains and Malvern Hills. The presence of megaflutes requires thick, relatively unconstrained ice to have been present on the Canterbury Plains, suggesting the formation of a Piedmont lobe. Because the megaflutes overlie the Woodlands Moraine and younger outwash, they represent a new and previously unrecognised glacial advance, some extra 8 kilometres out onto the Canterbury Plains, from the previous recognised maximum extent (Woodlands Moraine). This ice advance is younger than the Woodlands Moraine. The Woodlands Moraine was previously dated to c. 130 ka (late MIS6) and because the dated boulders are situated in the same area as the megaflutes, the new advance, which I term the Rockwood Advance, is likely c. 130 ka and the Woodlands Advance is, therefore, older than previously considered. The Rockwood Advance (and likely other advances) also flowed into the Malvern Hills as evidenced by eskers, truncated spurs, a paleolake and aggradational fans located in the Waianiwaniwa River valley, the Selwyn River valley and the smaller adjacent valleys. The glacial modelling showed that the combination of the three major valleys (Rakaia, Wilberforce and Mathias) that feed the lower Rakaia mean that the volume of ice available for the lower Rakaia is significantly greater than expected. So, only a small decrease in temperature is needed to push the glacier out onto the Canterbury Plains. The modelling indicated that a 4°C - 4.5°C decrease in temperature would result in ice advancing to the termination of the megaflutes and the Rockwood Advance limit. This temperature decrease to push ice onto the Canterbury Plains from the Rakaia Valley is significantly different than the temperature decrease necessary for ice to advance onto the Canterbury Plains in adjacent valleys. Glacial modelling overall showed how the morphology/catchment of the valley has a significant impact on how far a glacier can advance and although the climate and past shape of the valley will influence a glacier's advance down the Rakaia Valley, it is not as significant as the catchment size and morphology.
Open Access
Comparing approach-avoidance motives of presenteeism in public and private sector audiologists.
(2024) Corbeau, Kira
Background: Presenteeism is the act of attending work whilst ill, often resulting in a productivity loss (Aronsson, 2000; Ruhle et al., 2020). According to Hobfoll's (1989) Conservation of Resources (CoR) theory individuals work to conserve and acquire resources, being approach or avoidance motivated, wherein, respectively one is motivated to obtain something (e.g., prove their worth) or actively negate something (e.g. avoid using sick leave) (Henderson & Smith, 2021). Both motives and the CoR theory imply that presenteeism reduces work productivity, however this has not been directly observed in terms of audiologists internationally, and not divided between public and private sector audiologists who presumably have very different pressures. The comparison of mental health and physical health induced presenteeism in audiology is also absent in the literature, which could provide insight to improve audiologists’ wellbeing and client care. Aims: This study aims to measure the potential effect of approach-avoidance motivations on presenteeism in the field of audiology and determine if the rates of presenteeism and absenteeism due to mental or physical health are significantly different in the public and private sectors. Methods: An international cohort of audiologists was recruited to complete the crosssectionally designed online survey, with a minimum of 84 participants working mostly in the private sector and 84 working mostly in the public sector. This allowed the study to have sufficient power to answer the research questions. The anonymous survey used measures of the World Health Organisation Mental Health Composite International Diagnostic Interview (WHO, 2017), demographic items, WHO’s 2010 Health and Work Performance Questionnaire presenteeism question, the Stanford Presenteeism Scale (Koopman et al., 2002), a 9-item scale developed by Lu et al. (2013), and a question from Whysall et al. (2018) regarding the pressures of presenteeism. Results: No significant differences were found between public and private sector absenteeism and presenteeism rates, nor in productivity loss following presenteeism. No significant differences were found in mental health or physical health yearly absenteeism rates, yearly and monthly presenteeism rates, nor productivity loss. However, there was significantly more physical health related absenteeism noted in the monthly count than mental health related absenteeism. The public and private sectors showed no significant difference in both approach and avoidance motives in the different sectors (public and private). However, there was significantly more approach-motivated presenteeism resulting from mental health issues than physical health issues. The same was true for avoidance-motivated presenteeism, having significantly more mental health induced cases than physical health induced. Discussion: The literature extensively shows mental health to cause significantly more days of absence than physical health, but this study found the opposite in monthly counts (Bubonya et al., 2017; de Graaf et al., 2012; Milner et al., 2020). This could be the result of mental health stigma or type 1 errors as the study also found no significant difference in the rate of clinician absenteeism, presenteeism, or productivity loss in the public sector versus the private sector, despite the literature heavily indicating public sector work to be more stressful, time pressured, and mentally challenging (Barmby et al., 2002; Bryan et al., 2021; Dew et al., 2005; Jensen et al., 2019; Mastekaasa, 2020; Pfeifer, 2013; Yang et al., 2020). Clinician productivity loss could cause increased wait times, diminished patient trust following reduced continuity of care, or even deter patients from seeking healthcare in the future (Tumlinson et al., 2019). Similarly, the nonsignificant difference in presenteeism rates due to mental health versus physical health contests Bubonya et al.'s (2017) study which noted mental health to be one of the strongest correlates of presenteeism, often accounting for more total productivity loss than absenteeism (Johns, 2010). The nonsignificant difference between public and private clinician’s approach or avoidance motivates was expected, as were the greater motive scored for mental health than physical health. Via the CoR theory, audiologists in the public sector were expected to have greater resource loss and experience the first corollary (Hobfoll et al., 2018). Conclusion: This study was the first of its kind, examining audiological absenteeism, presenteeism, productivity loss, and approach-avoidance motives. The findings demonstrate that audiology appears to buck the trends of the literature, hence further research is needed to limit the economic, social, and health impacts of these behaviours to improve clinician and patient wellbeing. As the sample only represented 6% of the world’s population it could be prudent to perform a similar study involving more countries (Worldometer - Real Time World Statistics, n.d.). The use of matched control groups and daily units to measure absenteeism and presenteeism would enable comparison of audiology rates to other professions.
Open Access
Splitting streamflow : understanding the contribution of snow and rainfall in Canterbury Headwaters.
(2024) Shadbolt, Zane
Seasonal snowmelt from mountainous regions are important sources of freshwater for downstream uses. In order to effectively manage water resources, a better understanding of the sources contributing to streamflow and the hydrological processes occurring in mountain regions is necessary. This study aims to address this by evaluating the temporal variability in source water contributions to streamflow in a Canterbury headwater catchment. This study also aims to conceptualise the dominant runoff mechanisms and hydrological functioning of a mountain headwater catchment. Over the winter period high frequency (daily-monthly) sampling of stream, snow, precipitation, seep, and overland water samples were collected alongside hydrological and meteorological data. Samples were then analysed for their isotopic composition and used in a mixing model analysis to determine contributions of sources to streamflow. This was then compared with the hydrological and meteorological data to conceptualise runoff mechanisms and hydrological processes in the catchment. Results of the mixing model analysis estimated that old water (snow, groundwater, and overland) contributed between 41.5% to 53.2%, while new water (precipitation) contributed between 46.8% to 58.5% during the study period. The conceptualisation of runoff mechanisms and hydrological functioning results indicate that during dry conditions baseflow from the emptying of the groundwater storage is the primary contributor to streamflow. During snowmelt and wet conditions, the over-saturation of soils leads to an increase in overland flow during each event. Following overland runoff from snowmelt or precipitation events cause large rises in the hydrograph before a return to baseflow conditions at the completion of the study. The present investigation is the first scientific work estimating rainfall, snow, seep, and overland flow contributions to a mountain catchment in New Zealand through the use of isotopic tracers. This study also presents the importance of high-resolution data in mountain catchments.
Open Access
Parkinson’s disease, cognition, and the cholinergic system.
(2023) Slater, Nicola
Cognitive impairment is a well-recognised and debilitating symptom of Parkinson’s disease (PD). Most PD patients experience cognitive impairment, which often worsens to dementia. Degradation in the cortical cholinergic system is thought to be a key contributor to cognitive impairment in PD. Magnetic resonance imaging (MRI), and particularly diffusion-weighted MRI, can provide a window into both the macro- and microstructural integrity of the cholinergic system. In a sample of 108 PD patients with varying levels of cognition, and 41 control participants, this thesis has used T1- and diffusion-weighted MRI to assess the association of cognition with structural integrity of regions of the cholinergic basal forebrain (cBF) and the structural connectivity and integrity of projection axons from the nucleus basalis of Meynert. Cortical cholinergic projection pathways were defined using three approaches: the primary projection pathway descriptions initially developed by Selden et al. (1998); connections with heteromodal association cortices that travel via the temporal stem; and connections with two executive function networks. Integrity was assessed using measures from diffusion tensor, neurite orientation dispersion and density imaging, and fixel-based models. Some indication of an association of reduced structural integrity and cognition in PD was observed. Evidence suggested increased mean diffusivity in mild cognitive impairment in PD (PD-MCI) and PD dementia (PDD) was associated with a global cognitive score in most cBF regions and all pathways. Strong evidence of increased free water was detected across all pathways in PDD. These findings support histological and molecular imaging evidence of cholinergic system changes in PDD. While some evidence of changes in PD-MCI were found, a level of heterogeneity is evident. Reduced cholinergic innervation is likely to interact with or influence other brain systems to produce cognitive networks alterations that initially drive cognitive impairment in PD. Further research is required to fully understand the contribution of cholinergic system changes to the progression of cognitive impairment in PD.
Open Access
An analysis of neural gain in the auditory brainstem following short term acute unilateral auditory deprivation.
(2024) Panckhurst, Maya
Background: It is currently believed that the brain compensates for decreases in auditory input (i.e. hearing loss) through increasing spontaneous and sound-evoked neural activity, potentially leading to the generation of tinnitus and hyperacusis. The recent use of earplugs to induce temporary conductive hearing losses has meant that we are now able to study these changes in neural gain with pre-onset baseline measures using within groups measures, rather than relying on non-tinnitus controls. Changes in neural gain in the brainstem following earplug induced hearing loss have been measured indirectly using acoustic reflex thresholds, however, data using the more direct measure, the Auditory Brainstem Response (ABR) is still lacking, as is corresponding perceptual data relating to loudness. This study aimed to obtain ABRs before and after a period of unilateral ear-plugging, alongside corresponding acoustic reflex and loudness perception data in order to test the hypothesis that gain related changes would result in altered ABR amplitudes, acoustic reflexes, and loudness ratings. Methods: ABRs were collected from 10 adult participants using 20, 40, and 60 dB nHL chirps presented via bone conduction to the plugged ear, with the contralateral (unplugged) ear being masked. Loudness ratings for these stimuli were measured using a contour scale of loudness. Acoustic reflex thresholds were obtained at 3 and 4 kHz, and reflex amplitudes were measured at 95 dB at 0.5, 3, and 4 kHz. All measures were obtained before insertion of a foam earplug in one ear, after 4 hours of plugging, and again at least three days after earplug removal allowing for within subjects' comparisons. Results: No statistically significant changes in ABR wave III or V amplitudes were observed after ear plugging in comparison to baseline measures. In addition, no statistically significant changes in acoustic reflexes or in subjective loudness ratings were seen following ear plugging. Conclusion: The lack of notable changes in either of the three types of measurement do not support gain-related changes in neural activity, thus we default to the null hypothesis. The reason for these results is unclear, but the acoustic reflex and loudness findings were inconsistent with previous reports. One matter of relevance is the length of deprivation, with previous studies typically administering plugging over a period of days not hours. We recommend further study on the timescale of events.
Open Access
Sand dunes and ventifacts used as climateiIndicators at Mason Bay, Rakiura|Stewart Island : implications for Martian paleoclimate.
(2024) McFerrier, Emma
Dunes and ventifacts are depositional and erosional geomorphic landforms found on Earth and on Mars. Both dunes and ventifacts are a product of aeolian processes and can be used to interpret wind regimes. Dunes respond and record modern wind flow, whereas ventifacts are an outcome of long-term aeolian weathering, creating features that reflect paleo wind regime. The presence of dunes and ventifacts on Mars provides the opportunity to evaluate modern and ancient Martian surficial processes and climatology. The dune and ventifact field at Mason Bay, Rakiura|Stewart Island, New Zealand, is used as a terrestrial analogue to study the relationship between short-term and long-term climate indicators, using Mars remote analysis techniques. The outline of the central dune field at Mason Bay and individual parabolic dunes were mapped from aerial images (2003-2023) in ArcGIS Pro to ascertain dune orientation and track migration rate. Photogrammetric images were captured for 18 individual ventifacted clasts and 11 quadrats (1m x 1m squares) across the deflation surfaces. These images were used in Agisoft Metashape to create scaled 3D models of the real-world samples to measure and record clast height (z-axis), lithology, and macro and mesoscale features such as facets, grooves and pits. The 18 ventifact models were then georeferenced in CloudCompare where the orientation of ventifact features were measured and recorded. The parabolic dunes at Mason Bay are oriented to the east (95°), migrating 113.5m on average between 2003 and 2023, with some years experiencing a higher rate of migration than others. At the eastern end of the field area, a sand lobe migrated 327m over the same period to the east-south-east (120°). A comprehensive analysis of 4447 clasts within the 11 quadrats revealed that 85% of clasts are ventifacted. Average clast height (z-axis) ranges from 0.5cm to 2.3cm across the deflation surfaces, with an average maximum clast height (z-axis) of 10.3cm. Comparisons were made between the 18 ventifact photogrammetric models on lithology, ventifact height (z-axis), small ventifacts on the deflation surface vs immobile ventifact outcrop, upwind vs downwind portions of the field and trisections of the field. The ventifact features across all 18 clasts revealed an average orientation of 279°, based on 1195 measurements. Ventifact feature orientations were found to be statistically similar between ventifacts on the deflation surface and the immobile ventifacted outcrop. Results found that the orientation of features on different lithologies were statistically similar, only varying by 2-3 degrees. These findings reveal that the parabolic dunes at Mason Bay are reflecting a westerly wind which aligns with the orientation of ventifact features. This indicates that the wind regime at Mason Bay has not changed from the prevailing westerly. The eastern lobe, however, reflects the orientation of a sloping path created by an old dune phase. Both geomorphic features at Mason Bay align with recorded wind data, demonstrating that they are good indicators of wind flow and accurately record local wind regime. Three factors were found to influence ventifact formation at Mason Bay, 1) grain size of the clast where coarser grained lithologies exhibited an overall rougher surface with a greater quantity of ventifact features compared to finer grained lithologies. The development and appearance of ventifact features were also deeper and wider on coarser grained lithologies, 2) deflation of near surface wind flow around topographic obstacles, resulted in the variation of ventifact feature orientation across the field, and 3) a combination of ventifact height (z-axis) and topographic elevation (asl) is the likely cause of an increase in ventifact feature depth and width up the windward face of a ventifacted outcrop. These findings can directly inform on Martian research. Through crestline and horn orientation, Martian barchan dunes can be used to infer modern dominant wind directions and sediment transport. The presence of ventifacts indicate that aeolian abrasion has been the dominant process for some time, and with ventifact features oriented parallel to the most dominant wind, they can be used to infer local wind regime. The controls of ventifact formation at Mason Bay can inform on the formation and interpretation of Martian ventifacts, as well as sediment transport. The grain size of Martian rocks can be inferred from the observation of ventifact features, which create an overall rougher surface on coarse-grained lithologies. Observations of the whole ventifact should be made to reflect the variability of ventifact features, as observed in the change of feature morphology on the ventifacted outcrop in this study. The usefulness of remote sensing techniques at providing accurate representations of the real-world landforms ensures that they can be used in the place of in person field techniques for Mars research. This study demonstrates that sand dunes and ventifacts accurately record local wind regime and therefore, can be used confidently to interpret local wind regime on Mars. A difference in orientation between dunes and ventifact features indicates a change in local wind regime and potentially a shift in Martian atmospheric circulation.
Open Access
RICE timing analysis
(2003) Baird, Anthony Michael
The Radio Ice Cherenkov Experiment ( RICE ) seeks to detect ultra-high energy (UHE ) electron neutrinos in the PeV ( E >1015 ) range of energies interacting within the south polar ice. Such interactions produce electromagnetic showers, which emit coherent radio frequency Cherenkov radiation. The RICE array is designed to detect this signal. In addition to any signal induced by neutrino interactions, the RICE array is subjected to background noise presumably originating from infrastructure on the surface above the experiment. The first cut to discriminate between neutrino events and backgrounds event is made using the location the signal originated from. This is determined using the times that various RICE receivers were hit. We have investigated various time extraction routines and examined their success at identifying the same shape in the waveforms of different receivers. Our analysis was based on 1137 events recorded between January and April 2002. We have found that methods based on identifying the first excursion above a particular value were more successful than those which used the time of maximum voltage. We also conducted a Fourier analysis of the data and found that all events contained a strong spectral line in the range between 205 and 210 MHz while five percent of the event s contained a line in the range between 400 and 406 MHz. We examined the sensitivity of the various timing routines to the presence of these spectral lines. We filtered the data, removing the spectral line in the 205-210 MHz range and re-vertexed. Using our preferred timing routine to extract the hit times we found that the vertex was approximately twenty five metres closer to the surface once the spectral line was removed. Our conclusion is that for accurate vertexing it will be necessary to filter the events. However this can be done after the first cut has been made since there is little risk in neutrino events being wrongly cut due to the presence of the spectral line.
Open Access
The effect of a psychoeducational course on the wellbeing and wellbeing-related construct outcomes of 200-level psychology students at the University of Canterbury
(2024) Garbett, Isabella
Psychoeducational courses may be taught at scale as a tool to improve the wellbeing vulnerable populations. Often taught within tertiary settings they aim to provide insight into the science, and encourage the practice, of (often positive psychological intervention-based (PPIs) wellbeing practices. One such course, PSYC214: The science and practice of wellbeing, was taught at the University of Canterbury to 200-level students psychology students in 2023. One of the first of its kind in New Zealand, this study aimed to investigate the effect of enrolment in PSYC214 on wellbeing and wellbeing-related construct (resilience and gratitude) outcomes of participants both independently from and in comparison to another 200-level psychology course: PSYC206: Introductory research methods and statistics. The impact of the type of engagement (mainly online or mainly in-person) with the psychoeducational course, and maintained engagement with PPIs, on wellbeing and related constructs was investigated. Participants (n = 635) were 200-level psychology students enrolled in either or both courses, and completed a packet of self-report questionnaires via an online survey which assessed aspects of wellbeing in addition to resilience and gratitude over time. Results indicated engagement with a psychoeducational course was related to improvement in wellbeing outcomes over time,. Although, there was no significant group difference between PSYC214 and PSYC206 students on changes in wellbeing over time, 30.3% of PSYC214 only students reported their wellbeing had improved much-very much post-course completion compared to 17.0% of PSYC206 only students. Maintained engagement with PPIs appeared to increase wellbeing over time but there was not a significant effect of the type of engagement (online or in-person) with the course on wellbeing. The present study expands on the extant literature, and makes novel contributions of its own, indicating potential use of psychoeducational courses to teach wellbeing at scale within a vulnerable population.
Open Access
Scoping review of speech and language difficulties among children and adolescents in out of home care
(2024) Bingham, Dana Mallory
Children and adolescents in out-of-home care (OOHC) are at increased risk for experiencing mental health difficulties and various developmental delays, yet speech and language difficulties (SLD) remain largely undetected and unspecified. Research on SLD among children in OOHC has yet to be comprehensively and systematically mapped. The current thesis aims to provide a comprehensive overview of SLD among children in OOHC through two pieces of work: (1) a scoping review and (2) an analysis of epidemiological speech and language data from the Children in Care Study baseline sample (N = 347) and adolescent sample (N = 230). A scoping review protocol was followed to source articles through four databases: PsycINFO, PubMed, ERIC and CINAHL. A total of 1351 records were screened for eligibility via title and abstract or full-text screening, and 24 studies were selected for the final scoping review. Descriptive statistics, correlational analyses and hierarchical regressions were conducted to analyse dichotomous speech and language data from the CICS. The findings from the scoping review and CICS analyses demonstrate that SLD is normative among children in care. However, language gains may occur due to the influence of OOHC characteristics. Future research should explore speech and language therapy use and access among children in OOHC.
Open Access
Reflective practice in the workplace for audiologists
(2024) Lee, Sarah
Aims: The purpose of the study aimed to investigate the lived experiences of audiologists using reflective practice (RP) in the workplace, to identify key issues affecting the use of RP in the workplace, and to seek input from audiologists regarding how students can increase their engagement of RP during their studies. Methods: Twelve audiologists who graduated from the University of Canterbury participated in semi-structured interviews. Interviews were analysed using thematic analysis to uncover recurring themes in the participants’ responses. Results: Five themes were identified from the data: why RP is used (Theme 1: If you don’t reflect on things, we’re not going to get better), the methods used for RP (Theme 2: It’s really informal things), the barriers that affect audiologists from engaging in RP (Theme 3: We do not have enough time, because we do not have enough clinicians), how audiologists used RP as students and as new graduates (Theme 4: You’re very caught up on ticking the boxes), and suggestions audiologists have for future students regarding RP (Theme 5: Create an environment of making mistakes). Conclusion: Audiologists used RP to improve client outcomes, facilitate client centred care, and increase clinical competence. Time constraints and limited opportunities to reflect were key barriers to engaging in RP and suggested workplace changes included establishing resources such as discussion groups and structured prompts. For future students, audiologists advocated for small group discussions, written RP, and education of RP within curriculum to enhance student engagement.