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Percolative Current Flow through Anisotropic High-Field Superconductors under Strain
Full text linkFor decades, flux pinning scaling laws based upon unimodal, infinitesimally narrow, averaged distributions of critical superconducting parameters have been used to explain what limits the critical currents of practical superconducting materials in high fields. These scaling laws have enabled superconducting technologies ranging from MRI scanners, to high field research magnets, to magnets for particle accelerators and fusion energy. However in this work, we progress beyond these approximations and provide:
(i) The first comprehensive analysis of critical current density data showing that in high magnetic fields, technological
low and high temperature superconducting materials can be treated as a percolative network of Josephson junctions. We
then extract the size and normal state properties of the grain boundaries, the underlying distribution within the grains, and the dimensionality of the current flow within the material
(ii) The first reported measurements of the in-plane, biaxial strain dependence of for (RE)BCO tapes. This provides a description and understanding of the effects of the two most important strain components on and
(iii) The first comprehensive framework for percolative current flow in LTS and HTS superconductors under strain. It explicitly includes the factors suppressing and describes percolative flow within an anisotropic material containing a distribution of critical superconducting parameters. Our results show that large improvements to are available from further optimisation of the grains and grain boundaries in (RE)BCO and \ce{Nb3Sn} which will help enable the successful delivery of commercial fusion tokamaks
Socio-cultural factors that influence self-injury with suicidal intent in male prisoners
Full text linkUsing an intersectional lens, the aim of this study is to gain insight, and consider the application of the motivational and protective socio-cultural factors documented within service-user interviews as part of the Assessment, Care in Custody and Teamwork (ACCT) documentation. Firstly, this study utilises descriptive statistics to compare trends within HMP Bandwidth to National Statistics. This is followed by the main body of research: a reflexive, thematic analysis on six ACCT documents, taken from male prisoners who have expressed a desire or have physically engaged in self-injury within the general population of the reception prison. Findings revealed three themes that influenced the risk of self-injury within a male prison: adjusting to the physical prison regime, social factors of incarceration and distress surrounding medication. Findings are then discussed in detail through sub-themes, with reference to risk and protective factors, and practical recommendations. Conclusions indicate that socio-cultural factors and situational factors underlie the majority of motivational and protective factors for men who self-injure within prison, particularly Adverse Childhood Experiences and those incarcerated for the first-time
Low-cost household water treatment: A techno-behavioural intervention for local sustainable development in Afghanistan
Full text linkAccess to safe drinking water is a critical global challenge, in remote rural areas and urban centres alike. A pressing concern within this challenge lies in the sustainability of groundwater and the livelihoods reliant on it. However, a comprehensive study of such a complex issue as water insecurity requires a multidisciplinary approach that can synthesize perspectives from the natural and social sciences. With the overarching aim of studying and developing means to rectify water insecurity in low-income settings, this thesis pursues such an approach and contributes insights to the broader global dialogue through the case of the conflict-affected urban context of Kabul – where groundwater and livelihood challenges are driven especially by the contamination and rapid depletion of the local aquifers.
The multidisciplinary study begins with a geo-hydrology perspective that explores the sources of groundwater and the factors contributing to groundwater contamination. Additionally, it explores the potential of using clay disc filters for household water treatment from an earth sciences perspective. Complementing these natural science perspectives, the research also incorporates the COM-B framework, which draws from psychology and behavioural science. By leveraging anthropological techniques with a firm grounding in development research, the thesis further adopts a bottom-up approach to inform survey research.
Translating this multidisciplinary approach into the empirical research underlying this thesis, firstly, the groundwater recharge sources and groundwater dynamics in aquifers of Kabul city were explored relying on the analysis of the stable isotopic composition (δ18O and δ2H) of groundwater and surface water from the Upper Kabul River and Logar River. The results showed that precipitation was the primary source of recharge in the Central Kabul sub-basin, while mixed recharge from the river, precipitation, and irrigation return flow governed recharge in the Logar sub-basin. In the Paghman and Lower Kabul, and Upper Kabul sub-basins, increased rainfall input was also observed. The contribution of river water to groundwater recharge decreased from an average of over 60% in 2007 to less than 50% in 2020. Also, substantial groundwater level depletion was documented in the Central Kabul sub-basin and western parts of the city.
In addition to examining recharge sources and rates, the bacteriological and chemical characteristics of Kabul’s groundwater were analyzed. In Kabul, 4.1 million people rely on groundwater, making it critical to understand its contamination trends in the face of rapid development and social changes. The results showed an increase in E. coli and NO3-, indicating anthropogenic impacts on shallow groundwater quality. The Water Quality Index revealed that less than 35% of shallow groundwater samples had good quality. To address these issues, the implementation of point-of-use water purification was proposed as a temporary solution for reducing the occurrence of waterborne diseases.
Moreover, a qualitative study, based on 68 semi-structured interviews, explored the factors limiting access to clean drinking water in two peri-urban areas in Kabul. These factors included dysfunctional water supply networks, water price inequalities, uneven development, and aid prioritization. In addition, the stressors and dynamic access to water such as droughts, contamination, and electricity disruption were documented. Further, this research examined the nature and underlying factors of inter-household water-sharing practices. Water availability, the costs to the donor, the frequency of requests for water, the period over which they operate, and religious beliefs were all found to play key roles in determining water-sharing practices. The added influence of droughts in limiting water-sharing practices further highlighted the dynamics in performing the behaviour.
Furthermore, this research explored the factors that influence household water treatment practices, relied on a comprehensive behaviour change model (i.e., COM-B model). The results of the study showed that reflective and automatic motivation, as well as physical opportunity, had a statistically significant association with the performance of household water treatment behaviour. The findings suggest that socioeconomic, psychosocial, and contextual factors are all important in understanding and promoting household water treatment practices, and should be taken into account to develop interventions that are tailored to the specific needs and obstacles of different communities.
Lastly, the potential of using clay disc filters, frequently termed ceramic water filters, made from locally-sourced clay samples, was explored for removing bacteria from water. The clay discs were produced by mixing clay and sorted sawdust in a ratio of 1:2, and the filtration rate was 1 litre per hour. Clay disc filters have the potential to be a low-cost and locally-sourced solution for improving water quality in Afghanistan, but further research and development is needed to optimize their production, particularly by leveraging the skills of local potters in Kabul.
Overall, the synergistic combination of disciplinary techniques was thus capable of shedding light on the complex interplay between water resources, technology, and human behaviour (i.e., household water treatment) and provided a comprehensive understanding of the challenges and solutions surrounding access to safe drinking water
Natural Language Processing with Deep Latent Variable Models: Methods and Applications
Full text linkDue to their unparalleled performance and versatility, deep learning has become the de facto standard for building natural language processing (NLP) applications. Compared with conventional machine learning approaches, deep learning replaces extensive hand-engineered features in every task with end-to-end representation learning. Several concerns, however, have been raised in the research communities regarding their robustness, trustworthiness, explainability, and interpretability. Although these limitations of deep learning methods are widely acknowledged, work in methods and applications to alleviate these concerns in NLP is contrastingly limited. To address this research gap and explore a more robust approach for building NLP applications with deep learning, in this thesis, we studied deep latent variable models (DLVMs) in terms of methods (under supervised and semi-supervised learning settings) and applications (natural language understanding and generation) perspective for building natural language processing applications. We demonstrate the strength and benefits of DLVMs for NLP applications and discuss their effectiveness in addressing some of these concerns later in this thesis.
For contributions from a methods perspective, we studied the benefits of deep latent variable models in supervised and semi-supervised learning settings. These studies suggested that deep latent variable models are competitive in performance against standard deep learning methods; while offering additional robustness, trustworthiness, explainability and interoperability in various applications. For semi-supervised learning, particularly, we achieve state-of-the-art performance and prove the great potential of using deep latent variable models for semi-supervised learning problems.
For contributions from an applications perspective, we first presented two applications for language understanding problems, followed by two more applications for language generation problems. Our first application concerns a binary text classification task in the educational domain and pioneers the first research on how Bayesian deep learning can be applied to this text-based educational application. Our second application focuses on multilabel text classification tasks, and we present an efficient uncertainty quantification framework as our contribution. We demonstrate the effectiveness and generalisation of this framework with diverse architectures and present the first research on using deep latent variable models for efficient uncertainty quantification purposes in multilabel text classification tasks. Our third application deals with multiple explanation generation for an explainable artificial intelligence (XAI) task, and we present a first study on how deep latent variable models can be used to generate multiple explanations in the Stanford natural language inference task. In our last application, we explore paraphrase generation tasks and present the first study of DLVMs in a semi-supervised learning setting in paraphrase generation tasks; the DLVMs can enhance paraphrase generation performance when incorporating unlabelled data in a semi-supervised manner.
The findings in this thesis are of practical value to deep learning practitioners, researchers, and engineers working on a variety of problems in the field of natural language processing and deep learning
A microstructural and micromechanical investigation into shear dynamics during volcanic edifice collapse on Ascension Island: An experimental approach
Full text linkDuring gravitational collapse flows, shear forces are expressed through localised or
diffuse, brittle or ductile strain. Understanding material responses to shear within
gravitational collapse flows can be achieved through microstructural and
micromechanical investigation using established experimental techniques. This thesis
investigates a shear zone generated during a volcanic debris avalanche following the
collapse of a scoria cone on Green Mountain, Ascension Island through (1)
quantitative data on microstructural evolution within the shear zone through Scanning
Electron Microscope imaging, and (2) experimental work using rotary shear apparatus
to constrain the mechanical behaviour of the material under stress, and its influence
on internal microstructure. Microstructural analysis of the Green Mountain shear zone
reveals a decrease in grain size and porosity, as well as clast morphology evolution
toward the principal slip zone in the centremost region. Such observations are mirrored
in experimental shear zones presented herein. Mechanical data provide evidence that
material saturation promotes dynamic velocity weakening behaviour at seismic
velocities. Based on observations and evidence presented in this thesis, a model for
shear dynamics during the Green Mountain volcanic debris advance is proposed. It is
suggested that (1) a brittle cataclastic regime dominated within the shear zone,
resulting in the microstructural characteristics observed and (2) processes to facilitate
velocity weakening behaviour may include pore pressure fluidisation and nanoparticle
lubrication. Overall, this work contributes to the understanding of shear localisation,
internal microstructure, and facilitators of mechanical behaviour within the Green
Mountain volcanic debris avalanche deposit. Application of these findings to other
deposits and associated shear zones may help to better constrain collapse behaviour
and to mitigate associated risks
Optimizing a Rydberg Atom-based Terahertz Imaging System
Full text linkWe build upon previous work by characterising and optimizing the signal from a Rydberg atom-based terahertz (THz) imaging system, where atoms are excited to a Rydberg state by a three step ladder scheme. These Rydberg atoms provide a THz imaging mechanism via a fluorescence signal, . We implement a Pound-Drever-Hall lock and a digital scanning transfer cavity lock on the Rydberg laser. Both schemes see an improvement in the stability of fluorescence signal over time, to within 3\%. We characterise the effect of laser parameters on . A pumping scheme consisting of alternating circular polarisations for each step are found to maximise , providing a increase compared to the all-linear configuration. The dependence of on Rydberg laser detuning and THz detuning is also characterised, and splitting due to the AC Stark shift is observed at higher THz powers. Simultaneous resonant excitation of the Rydberg and THz transition is found to maximize . A repump laser is implemented on both the D1 and D2 lines, and found to increase most on the D1 line, by a factor of seven. The effect on of the repump lasers power and detuning is characterised, and a two-photon transition is observed in the D2 line spectrum. A change in spatial intensity distribution of the THz beam is observed under the effect of rotation of a linear polariser, which is theorised to be due to a vector diffraction pattern
Exploring student nurses' intercultural care experiences in clinical practice
Full text linkThis study explores how student nurses experience intercultural nursing care in their everyday clinical practice. It adopts a qualitative social constructionist approach to investigate their perceptions of and responses to positive experiences and the challenges they encountered in their nursing placements and to seek to understand intercultural competencies that are salient in facilitating effective intercultural communication.
Several key findings emerged from the study: 1) Participants socially construct their intercultural care experience in the six domains: intercultural encounters, knowledge, skills, attitudes, engagement and outcomes; and consider intercultural competence is a continual development process. 2) Even though the individual scope of intercultural care encounters (ICEs) varies, the participants all valued the opportunity to be exposed to ICEs, as these allowed them to negotiate and adjust to different cultures, values and worldviews. 3) The participants observed how cultural beliefs and behaviours affect individual patients’ interpretations or perceptions of their health condition, how they view its treatment and the efficacy of the medication. Without this essential knowledge, aside from the lack of understanding of a patient’s cultural needs, the treatment and care maybe inadequate or inappropriate, which can seriously affect patient’s outcomes. However, the data showed the gaps in this aspect of nursing education. 4) One of the biggest challenges the student nurses encountered in ICEs was linguistic barriers, since language affected not only the patients’ ability to express their needs and understand the healthcare instructions, but also had nursing implications. 5) Participants reported positive and challenging attitudes in ICEs, which affected their learning, wellbeing, and intercultural communication performance. When workplace adversity persists, some participants even considered leaving the course. It was through personal resilience, accessing support from academics and peers that they decided to stay in their chosen career. 6) The motivations to engage intercultural care were affected by internal and external factors. 7) The participants highlighted that without considering outcomes for the care recipient (patient) and care provider (the student nurse), competence in intercultural care cannot be validated.
An intercultural care competence ecological framework was developed, which provides a comprehensive view of intercultural care and highlights the dynamic nature of competence development. In these ways, this study complements existing cultural care theories.
The study offers valuable insights for researchers, educationalists, practitioners and policymakers in the areas of intercultural communication and interactions in healthcare services
Forward-looking information in Integrated Reporting: The influence of suppliers and customers
Full text linkThis thesis examines the influence of suppliers and customers on forward-looking information disclosure and the credibility of this disclosure practice under the Integrated Reporting (IR) context.
According to stakeholder theory and legitimacy theory, suppliers and customers hold critical resources for an organisation’s survival and growth; thus, organisations would consider suppliers’ and customers’ interests when making reporting decisions. Further, concerning signalling theory, organisations have incentives to signal both credible and misleading information. These theories underpin this study’s investigation throughout.
This thesis applies a multi-method approach which combines the method of content analysis and interview. To fulfil the research aims, this thesis utilises content analysis to examine a dataset of organisational reports published by 96 organisations from 5 countries. In addition, this thesis conducted 19 semi-structured interviews with personnel from organisations and stakeholders from supply chain consulting firms, accounting bodies, and standards-setting organisations.
The findings reveal that organisations incorporate suppliers’ and customers’ interests into forward-looking information disclosure to discharge accountability, address legitimacy exposures, and secure resources for survival. However, the extent to which organisations address suppliers’ and customers’ information demands is related to the management’s awareness of supplier and customer inclusiveness, regulations, and reporting framework. Furthermore, suppliers and customers influence an organisation’s business and strategy developments, and these developments are reflected in the forward-looking information disclosure. To enhance the credibility of forward-looking information concerning suppliers and customers, organisations have implemented multiple mechanisms (e.g. data measurement and data monitoring) throughout the reporting process. However, this disclosure practice lacks completeness and rigorous materiality determination processes. Finally, IR has an impact on the adoption of the approach to including suppliers and customers when making forward-looking information disclosure and the credibility of this disclosure practice.
This thesis brings together three streams of research on forward-looking information disclosure (motivations, inclusivity, and credibility) in a single study. The findings of this thesis confirm the importance of developing a supplier and customer inclusive approach to reporting. Yet, this reporting approach has not been fully adopted, and relevant reports are not credible enough for stakeholders to rely on, although IR plays some role in enhancing this reporting practice. This thesis argues that the current practice of disclosing forward-looking information concerning suppliers and customers is at risk of being a “box-ticking” activity, rather than being thoroughly understood and implemented as a reform of reporting approaches. From the investigation of both organisations’ and stakeholders’ perspectives on this disclosure practice, this thesis offers management, standard-setters, and academics novel insights into the role of suppliers and customers in corporate reporting which has received little academic attention
Bayesian Approaches to Emulation for a Complex Computer Crop Yield Simulator with Mixed Inputs
Full text linkAgriculture is one area where the simulation of crop growth, nutrition, soil condition and pollution could be invaluable in any land management decisions. The Environmental Policy Integrated Climate Model (EPIC) is a simulation model to investigate the behaviour of crop yield in response to changes in inputs such as fertiliser levels, soil, steepness, and other environmental covariates. We build a model for crop yield around a non-linear Mitscherlich Baule growth model to make inferences about crop yield response to changes in continuous input and factor variables. A Bayesian hierarchical approach to the modelling was taken for mixed inputs, requiring Markov Chain Monte Carlo simulations to obtain samples from the posterior distributions, to validate and illustrate the results, and to carry out model selection.
The emulation of complex computer simulations has become an effective tool in exploring this high-dimensional simulated process's behaviour. Initially, we built a Bayes linear emulator to efficiently emulate crop yield as a function of the simulator's continuous inputs only. We explore emulator diagnostics and present the results from the emulation of a subset of the simulated EPIC data output. Computer models with quantitative inputs are used widely, but the challenge is incorporating the factors. We propose a framework for solving this issue considering the Bayes linear emulation approach. We explore a variety of correlation structures to represent the mixed inputs and combine this with the Bayes linear approach to construct an emulator. Finally, we developed a method to make an optimal decision for the farmers to gain maximum utility considering yield and pollutants, accounting for weather factors, land characteristics and fertiliser use
Electricity Sector Reforms in Sub-Saharan Africa
Full text linkElectricity sector reforms has been one of the most transformative energy sector policies in sub-Saharan Africa (SSA) in modern history. However, studies on reforms in SSA remain limited, with quantitative analysis almost non-existent. This thesis contributes to the literature on electricity sector reforms in SSA through an assessment of reform performance and its connection to key electricity sector topics in the region including investments and productive efficiency, access, and cost efficiency. The thesis is structured in a three-paper format, with each paper focused on each of the key challenges mentioned.
In Paper One, I assess the performance of electricity sector reforms in 37 SSA countries between 2000 and 2017 using a parametric multi-input multi-output distance function and a Stochastic Frontier Analysis (SFA) approach. From this assessment, I found an effective reform model in SSA to involve vertical unbundling with an electricity law, a sector regulator, and private ownership and management of electricity assets where desirable. I also found reforms to be positively correlated with efficient investments in generation but negatively correlated with reduction in technical network losses. On the institutional front, perceptions about non-violent institutional features such as corruption and governance effectiveness were found to have no significant relationship with reform performance whereas negative perceptions about terrorism and violence were found to be negatively correlated with reform performance.
In the Second Paper, I examined the determinants of electricity access performance in 46 SSA countries from the viewpoint of reforms using a production function and SFA from 2000 to 2017. I found generation capacity adequacy and the efficiency with which electricity is produced and used to be positively correlated with the rate of access expansion. The wealth of countries was also found to be positively correlated with improved electrification outcomes while the wealth of households in a country was found to be negatively correlated with inefficiencies that interfere with electrification efforts. The reform step that was found to engender these positive electrification outcomes was the presence of a sector regulator, while unbundling and private sector participation were found to be negatively correlated with access performance.
In the Third Paper, I explored the relationship between reforms and cost of electricity services to provide an economic perspective to issues of cost under-recovery in SSA electricity systems. Through a synthesis of reform theories and case studies and using small electricity systems as a surrogate for liberalised electricity systems without competitive markets, I showed the connection between reforms and costs. I made a case for a structural approach to issues of cost under-recoverability in SSA electricity systems leveraging contestability opportunities in mobile powerplants in generation, yardstick competition in distribution and retail and regional integration of electricity markets
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