Higher Degree Theses
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Item Migrant remittances, Sustainable Development Goal (SDG) 7 and energy poverty in Sri Lanka(Thesis, The University of Waikato, 2024-04-16) Wijayarathne, SandamaliModern, clean energy is seen as the golden thread that connects economic growth, human development, and environmental sustainability. However, almost 2.4 billion people worldwide still use solid fuels for cooking, exacerbating energy poverty and endangering human health and the environment. Therefore, this thesis investigated the non-price determinants of cooking fuel choice, including the causal relationship between migrant remittances and both cooking fuel choice and energy poverty. Sri Lanka was used as a case study, using more than 78,000 households from four waves of the Household Income and Expenditure survey from 2009 – 2019. Specifically, this thesis includes three empirical studies and one policy paper related to remittances and energy consumption. The first study found that household income, household wealth, household head’s characteristics (age, marital status and education), education of spouse, household characteristics (household size and number of children under 5), housing characteristics (number of bedrooms, drinking water source, and housing material), and residential sector (urban vs rural) were significant for selecting clean fuel for cooking, using multinomial logistic analysis. Moreover, the Advanced sustainability analysis showed a strong synergy between SDG 7 (clean energy), SDG 6 (Clean water), and SDG 4 (quality education). The second study investigated the relationship between migrant remittances and cooking fuel choice by taking household wealth as a mediating variable. Using the propensity score matching method the study found that migrants used about 5.7% more clean fuels for cooking than non-migrant households. Furthermore, the control function approach found that a 1% increase in remittances increased clean cooking fuel use by 0.034 units, and instrumental variable (IV) mediation analysis indicated that household wealth significantly mediated this relationship. The third study further explored the link between migrant remittances and energy poverty, using income inequality as the mediating variable. Two-Stage-Least-Squares (2SLS) regression results showed that a 10% increase in remittances decreased energy poverty by 0.042 units, while IV mediation analysis indicated that income inequality significantly mediated this relationship. The final study examined the causes and economic implications of Sri Lanka's current energy crisis, its effect on energy poverty and the attainment of SDG 7. Specifically, the findings of the second and third studies were used to forecast the impact of a decline in migrant remittances of 40% due to the crisis on clean cooking fuel use and energy poverty. A 40% drop in remittances could reduce clean cooking fuel consumption by 0.16 units and increase energy poverty by 0.0016 units. The study concluded that Sri Lanka should encourage migrant remittances to enhance the use of clean cooking fuels and minimize energy poverty in light of the current energy crisis.Item Cyberbystanders: Behind the screens(Thesis, The University of Waikato, 2024) Hodge, Emma-LeighBehaviour that occurs online is an important component of many people’s social interactions. It is, therefore, crucial that the detrimental impacts of cyberbullying and similar behaviour (i.e., online aversive behaviour) are addressed. To this end, I present research that progresses from an exploration of online social behaviour in general (Chapter 2) through to quantitative discounting studies that examine an avenue for behaviour change initiatives that improve the online social environment. In the exploratory phase (Chapter 2), I conducted a series of focus groups with young people between 12- and 21-years old on the broad topic of Social Networking Site use (SNS). Participants spoke about how they manage their use of SNS, which coalesced around several key themes. One of these ideas was the importance of showing and receiving support from their online social communities, especially in instances of adversity. An effective way to show support for another person online is to actively intervene when witnessing adverse (or aversive) behaviour directed toward that person. In Chapter 3, I explored a novel application of discounting methods to assess whether social outcomes related to online bystander (i.e., cyberbystander) intervention are discounted similarly to outcomes more common within the discounting literature. I used discounting methods in conjunction with the framework of the Bystander Intervention Model (BIM; Latané & Darley, 1970), reframing the latter to be congruent with the concepts of behaviour analysis. In Chapter 4, I tested the applicability of discounting methods to the decision-making of young adult cyberbystanders. As discounting studies using monetary outcomes have been well-established, I compared the probabilistic discounting of money to that of social outcomes related to cyberbystander behaviour. Having established that probability discounting can be applied to cyberbystander’s decision-making, in Chapter 5, I examined whether scenario severity, audience size, or locus of responsibility (i.e., whether responses related to participant’s own behaviour or their perception of how someone else would respond) impacted the willingness of young adults to intervene in online aversive behaviour. Intervention was marginally more likely when participants considered whether someone else would intervene (rather than themselves) and if the severity were high, but the larger audience size had a negligible effect. Chapter 6 contains a study designed to follow up on the promising findings regarding the impact that perceived scenario severity had on cyberbystander’s decisions to intervene themselves, particularly when compared to what participants considered the social norm to be (i.e., how they thought someone else would respond). The difference between the likelihood of intervention when participants responded for themselves versus what they considered normative was most evident when the scenario was moderate-to-high in severity. In all, my research supports the premise that discounting methods can be applied to cyberbystander decision-making and used to assess aspects of the BIM to identify avenues for cyberbystander behaviour change initiatives. Cyberbystanders’ actions can fundamentally change whether acts of aversive behaviour are reinforced (or punished), as well as mitigate the extent of the harm experienced by a target of online aversive behaviour.Item Fathers’ help-seeking and support: The importance of relationships for mental wellbeing(Thesis, The University of Waikato, 2024-03-25) Ghaleiha, AminBecoming a father is a major transition for men, and may be a source of happiness and fulfilment, as well as distress. Perinatal mental health research has traditionally focused on mothers, with paternal mental health receiving limited attention. Men are adopting more caregiving roles and increasing their parental involvement, while maintaining their traditional role as a key provider for the family. Balancing these roles may lead to experiences of psychological distress, and help-seeking can be important in alleviating the impacts of paternal distress. However, research on fathers’ help-seeking and mental health needs remains scarce. Therefore, this thesis sought to better understand fathers’ experiences of help-seeking, and facilitators and challenges of paternal help-seeking to support mental health. Study 1 involved in-depth semi-structured interviews with 11 fathers about their experiences regarding transition to fatherhood and seeking support and advice in early years of parenthood. Fathers reported experiencing distress and uncertainty during the transition to parenthood; however, most did not believe their distress required seeking professional help. Fathers also used a variety of individual and interpersonal coping strategies. Partners were the most important source of emotional support for fathers, but some fathers felt it was inappropriate to seek their partner’s support while she was coping with the stress of pregnancy and new parenting. This study revealed that fathers viewed themselves in a rather traditional role of provider and as a source of emotional and financial stability for their family. This led to work-life balance stress and, for some, created a dilemma where they felt unable to seek emotional support from their most trusted person—their partner. In study 2 the role of social support, particularly partner support, was explored in relation to paternal mental health and parenting. Data from fathers participating in Growing Up in New Zealand (N = 2601) were used, focusing on data waves during pregnancy and at child ages 9 months and 2 years. Concurrent partner support, and to a lesser degree, other informal support (friends and family) was related to lower paternal distress during pregnancy and at child age 9 months. Although significant, the magnitude of the association was small. There was no evidence of social support in infancy buffering a negative association between distress and parenting outcomes at child age 2 years. Study 1 found that most fathers did not feel that their distress warranted a professional intervention. Following from this, study 3 investigated the relationships among mental health literacy (MHL), emotional distress, and fathers’ perceptions of barriers and modes of mental health help-seeking. Data were collected from a community sample of New Zealand and Australian fathers (N = 129). The study involved completing an online vignette survey, the Depression, Anxiety, and Stress Scale 21 Items (DASS-21), and two open ended questions. Those with a high DASS-21 stress score were more likely to report the individual in the vignette as needing help or having a mental health problem. regardless of the accuracy of this choice. Additionally, more fathers were able to correctly recognise clear symptoms of depression (typical depression) compared to masked depression. Fathers described several informal and formal sources for support and internal and external barriers (e.g., stigma and time/cost) to help-seeking. This thesis adds to the growing knowledge on fathers’ mental wellbeing by examining paternal help-seeking and distress as well the role of social support. Overall, the findings of this research are consistent with the limited amount of existing research suggesting that partner support has a unique role in paternal mental health. The findings also suggest greater emphasis on the role of relationships and social support in fathers’ mental health and help-seeking. The main implications of this thesis for health professionals who interact with young families are that paternal mental health requires greater clinical and social attention, and fathers with low levels of social support, poor work-life balance and mental health literacy, and traditional masculine beliefs on help-seeking may be at high risk of experiencing mental health difficulties.Item The effects of terrestrial sediment inputs on ecosystem functions in seagrass meadows and unvegetated sediments(Thesis, The University of Waikato, 2024-04-15) Flowers, GeorginaEcological functions in estuarine seagrass and unvegetated soft sediment habitats underpin many valuable ecosystem services. However, changing land-use and climate are accelerating inputs of fine terrestrial sediments, threatening these habitats. The prolonged suspension of fine sediments can reduce seafloor light availability and long-term accumulations increase sediment mud content (particles < 63 µm), both of which could have significant consequences on ecosystem functioning. Understanding how ecosystem functioning may respond to environmental change is vital to estuary management. In this thesis, I investigated the short- and long-term effects of elevated terrestrial sediment inputs on benthic primary production and nutrient cycling in intertidal seagrass meadows (Zostera muelleri) and microphytobenthos-dominated unvegetated habitats. To investigate the effects of reduced seafloor light availability and prolonged submergence periods resulting from global heating induced sea-level rise, I conducted a two-year seasonal in situ assessment of photosynthesis-irradiance relationships during submerged and emerged conditions in an adjacent seagrass meadow and unvegetated sandflat. Submerged gross primary production (GPP) in both habitats and emerged GPP in the seagrass habitat were strongly controlled by light availability. Higher rates of light-saturated GPP were found during submerged periods compared to emerged periods in both habitats, but this difference was most pronounced in the unvegetated habitat. If the water-column remains clear, sea-level rise could therefore increase daily GPP in soft sediment habitats. However, declines in submerged GPP with increased water-column turbidity will be exacerbated with sea-level rise. Across a natural mud content gradient, I measured primary production in seagrass and unvegetated habitats to address the long-term implications of elevated sediment inputs. In sediments with ≤ 35 % mud content, net primary production (NPP) and GPP was independent of mud content in both habitats. However, extending the mud gradient in unvegetated habitats to 49 % (seagrass habitats restricted to ≤ 35 % mud content) resulted in NPP and GPP declining with increasing mud content. These results highlight that loss of seagrass meadows resulting in expansion of unvegetated habitats could lead to reductions in intertidal production; seen most acutely in areas with high mud content (≥ 39 %). I also investigated the spatial and temporal variability in nutrient cycling in seagrass and unvegetated habitats to examine how environmental gradients affected sediment nutrient fluxes and denitrification rates. Ammonium effluxes were lower in the seagrass compared to the unvegetated habitats and were lower in both habitats during light compared to dark conditions. Denitrification rates were similar in both habitats but were found to decrease with increasing mud content. Overall, denitrification efficiency was highest in the seagrass habitat. These results indicate that future seagrass decline and/or increased mud content in soft sediment habitats will reduce resilience to eutrophication. This thesis demonstrates that future seagrass decline and elevated terrestrial sediment inputs are likely to have serious implications on the high rates of primary production and nutrient cycling of intertidal seagrass meadows and unvegetated habitats. Furthermore, it highlights the value of measuring ecosystem functions in different soft sediment habitat types across multiple spatial and temporal scales to inform future management against anthropogenic stressors.Item Microstructure Dual-Refinement and Mechanical Properties Manipulation of TiBw/TA15(Si) Composites by Thermo-mechanical Processing and Heat Treatment(Thesis, The University of Waikato, 2024) Zhang, RuiTitanium matrix composites with near-α titanium alloy as the matrix exhibit high specific strength and good high-temperature strength. However, the thermo-mechanical processing is limited by the brittleness of the reinforcement, making it difficult to refine the grain size and control the silicide precipitates. The present work aims to prepare titanium matrix composites with refined grain size and silicide particles. To this end, network-architecture TiBw/TA15(Si) composites were prepared using low-energy ball milling and vacuum hot-pressing. After refining the initial lamellar microstructure of the material through a solid solution treatment, the evolution of the TA15(Si) matrix and TiBw reinforcement during the hot deformation were studied. Ideal thermo-mechanical processing parameters in dual-phase region for TiBw/TA15(Si) composites after solid solution treatment was obtained, and the strain distribution in the compressive sample was revealed. Subsequently, TiBw/TA15(Si) composites with fine grains and dispersed silicide particles were obtained using solid solution treatment and isothermal hot-pressing, achieving a simultaneous improvement in room temperature strength and ductility. The influence mechanism of solid solution treatment on the microstructure and properties of the material was analyzed. Finally, TiBw/TA15(Si) composites with different lamellar content and morphologies were obtained through heat treatment of the deformed material. The effect of heat treatment on the microstructure of the material and the influence of different microstructures on the room temperature and high-temperature tensile mechanical behaviors of the material were discussed. After compositional design through thermodynamic calculation, TiBw/TA15(Si) composites with different Si and Zr contents and a network architecture were prepared by low-energy ball milling and vacuum hot-pressing sintering using spherical TA15 coarse powder and TiB2, ZrB2, and Si fine powders. Silicide particles precipitated on the α/β interfaces in the matrix, and the precipitation amount increased with the increase of Si and Zr element contents. The tensile strength of materials with different compositions ranged from 1012 MPa to 1120 MPa, and the elongation ranged from 1.2% to 6.7%. When the Si content was between 0.3 wt.% and 1.0 wt.% and the Zr content was between 0.3 wt.% and 1.0 wt.%, the materials exhibited good strength and plasticity. By observing the microstructures of different materials subjected to heat treatment at 960°C to 1040°C for 30 min followed by quenching, it was found that silicide particles can be completely dissolved below β transformation temperature when the Si content is below 0.5 wt.%, which is suitable for microstructure control in dual-phase region. Considering the comprehensive mechanical properties and silicide dissolution temperature, a composite with a chemical composition of 3.4 vol.% TiBw/TA15-0.3 wt.%Si was selected for the study of dual-phase region thermo-mechanical processing and microstructure control. After the solid solution treatment in single-phase region, the initial microstructure of TiBw/TA15(Si) was refined, after that, the high-temperature deformation behavior of the material was studied. The hot compression tests were conducted in dual-phase region at temperatures ranging from 870°C to 950°C and strain rates ranging from 1 s-1 to 0.001 s-1. It was found that the compressive stress-strain curves of the composite in this range exhibited dynamic recrystallization features, and the compressive stress decreased with increasing deformation temperature and decreasing strain rate. Except for the fully lath overheated-microstructure observed at 950°C / 1 s-1, the deformation microstructure of the material under the remaining conditions consisted of equiaxed α grains and residual α/β laths. The microstructure became finer with lower deformation temperature and higher strain rate. Higher recrystallization degree was observed below 910°C at lower strain rates, while the opposite was observed above 910°C. Observation of the microstructure produced by different deformation degrees revealed that the formation of equiaxed grains in the material involved three steps: α/β lath distortion, formation of boundaries within α/β laths, and lath decomposition. The activation energy for hot deformation of the TiBw/TA15(Si) composite after single-phase solid solution pretreatment was determined to be 623 kJ/mol. Based on the constructed processing map, the ideal deformation parameters were determined to be in the temperature range of 900°C to 950°C and strain rates of 0.01 s-1 to 0.001 s-1. The orientation distribution of TiBw reinforcements during high-temperature plastic deformation in materials has been studied. The rotational behavior of TiBw reinforcements during deformation was analyzed, revealing that the orientation distribution of the reinforcements is influenced by the direction and magnitude of the principal strain applied to the material. The direction of the principal strain determines the principal directions of covariance matrix for the reinforcement's orientation distribution, while the magnitude of the principal strain determines the parameters in the probability density function. Based on these findings, a method was proposed to calculate the local plastic deformation in materials using the orientation distribution of TiBw reinforcements. Error analysis through computer simulations showed that this method exhibited good accuracy in the range of 20% to 80% compression strain. Using this method, the strain distribution in hot-deformed TiBw/TA15(Si) composites was analyzed, and the accuracy of the calculations was confirmed by comparing them with the deformation of the network structure of TiBw. Based on the results of hot compression tests, TiBw/TA15(Si) composites were subjected to a solid solution treatment followed by isothermal hot pressing at 920 °C and a strain rate of 0.003 s-1 with 75% height reduction. This process yielded a microstructure with fine equiaxed α grains and dispersed fine silicide particles, with an average grain size of 1.6 μm and particle size of 70 μm, respectively, achieving a dual-refinement of both α grains and silicide particles. The composite exhibited a yield strength of 1100 MPa and an elongation of 7.7%. A comparison showed that the solid solution pretreatment led to finer grains and more dispersed silicide particles in the material after isothermal hot pressing, resulting in a significant increase in yield strength. Heat treatment of the hot-pressed composite in the range of 980 °C to 1050 °C revealed that higher temperatures led to higher contents of α/β laths and coarser microstructures, while faster cooling rates resulted in finer lath structures. Water quenching after the heat treatment at 1010 °C for 30 min produced excellent room temperature strength and ductility, with a tensile strength of 1350 MPa and an elongation of 6.7%. Slip trace analysis and transmission electron microscopy analysis revealed that the equiaxed microstructure in the material facilitated multi-system slip, enhancing deformation uniformity. The prismatic slip in lamellar microstructure obtained with air cooling was suppressed by the Burgers orientation relationship, the strain-softening of the lamellae resulted in deformation dominated by single-system slip and strain localization. The transformed β phase obtained through water quenching exhibited limited deformability, which was primarily accommodated by the prismatic slip of primary α laths. High-temperature tensile tests under different conditions showed that decreasing the deformation temperature, increasing the strain rate, refining the grain size, and decreasing the α/β lath content transform the deformation mechanism into grain boundary sliding, which significantly enhances the deformability of TiBw/TA15(Si) composites. The composite with fine equiaxed microstructure could achieve an elongation up to 348% at 800 °C and a strain rate of 0.0003 s-1, which showed a good potential for superplastic forming at low temperatures.