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Asteroseismic inference on a population scale: From detection to internal properties
Get PDFStars give off light which enables the evolution of intelligent life and gives it access to information about the universe it inhabits. Despite their importance, our understanding of the inner workings of these objects is still far from complete. This thesis is dedicated to the only probe capable of providing observational information about the deep interiors of stars, asteroseismology, the study of stellar oscillations. In the following I will study the solar-like oscillator, in which sound waves are excited and subsequently trapped, manifesting in pulsations. Alongside probing the conditions in the interior of a star, observations of these oscillations provide accurate and precise constraints on fundamental stellar parameters. Asteroseismic measurements of stellar masses, radii, and ages have advanced several fields outside of stellar astrophysics, including exoplanet research and the study of the history of the Milky Way. In this thesis, I will cover a range of asteroseismic analyses, from detecting the presence of solar-like oscillations to exploiting the pulsations to measure the properties of stellar cores.
After a brief introduction to stellar evolution and an overview of the basics of asteroseismic analysis, I will present three works. The first introduces an automated pipeline we designed to detect solar-like oscillations using measurements of stellar flux as a function of time. This pipeline is then applied to data collected by NASA’s TESS mission for over 200,000 stars, generating a catalogue of thousands of solar-like oscillators. The next work looks to the future of asteroseismology, presenting predictions for the proposed HAYDN space telescope. The mission would exploit solar-like oscillators in stellar clusters to answer some of the most pressing open questions in stellar astrophysics and the history of the Milky Way. Two features of stellar evolution that could be investigated are core rotation and core magnetic fields. I comment on the potential for using HAYDN to make asteroseismic inferences on these properties and evaluate potential detection biases. Finally, I present the first large catalogue of asteroseismic probes of core rotation and magnetism in real stars observed by Kepler. In this catalogue I identify a bimodality in the distribution of core rotation rates which has not yet been replicated by stellar models and has implications for our understanding of angular momentum transport in stars.
Asteroseismology has provided us with tools to investigate stars in unprecedented levels of detail. To fully exploit this information to better our understanding of stellar evolution, we require larger and more complete catalogues of seismic parameters. In this thesis I build upon this, both introducing new methods to assist asteroseismic analysis in large datasets and reporting thousands of new measurements from the most fundamental detections to probes of the deep interiors of stars. The future of the field will see missions like ESA’s PLATO providing even more data amenable to asteroseismic analysis, making the tools and results detailed here a crucial chapter in the ongoing asteroseismic story
Understanding water-related multi-hazards in a sustainable development context
Get PDFAbstract
Water-related multi-hazards have devastating impacts on people around the world. Interdisciplinary research is required, especially in data limited lower- and middle-income countries, on multiple hazards to improve our understanding of space-time patterns and controlling processes. In this thesis, a novel framework for studying water related multi-hazards in a sustainable development context is proposed which provides a powerful tool for analysis and knowledge advancement. Using Nepal as a case study, the framework is applied to investigate the patterns of (co-)occurrence and potential drivers of water-related multi-hazards. In addition, a narrative review is used to conceptualise social vulnerability and recognise the importance of a place-based approach to multi-hazard research. It was found that there is space-time variation in the occurrence and co-occurrence of water-related multi-hazards that appears to be driven by a combination of factors, including large-scale climate, local hydrometeorology, landscape characteristics, and anthropogenic activity. An evaluation of social vulnerability revealed that it is shaped by place-based issues, including coping strategies, and propagates from the intertwining of social and physical processes that arise from multiple scales. This new understanding has potential transferability to a range of multi-hazard contexts and settings worldwide and for use by stakeholders to reduce disaster risk and promote sustainable development
Athletes’ perspectives on help-seeking for mental health
Get PDFThis thesis has multiple aims with the overarching goal of advancing the athlete mental health help-seeking literature. Specific aims include: 1) highlighting the benefit of utilizing conceptual help-seeking frameworks to aid a help-seeking research project, 2) conducting the first scoping review on the athlete help seeking literature to map the current literature base on athletes’ perspectives on help-seeking, and 3) show the benefit of using patient and public involvement (PPI) to produce a protocol for a qualitative study. Chapter 1 provides a background to the literature and shows the need for a scoping review to be conducted on the help-seeking literature. The scoping review presented in Chapter 2 is an overview of the literature on athletes’ access, attitudes, and experiences of help-seeking for mental health and highlights current gaps in the literature and recommended future research directions. Chapter 3 reports on the use of PPI using the Guidance for Reporting Involvement of Patients and the Public 2 (GRIPP2) short form, including the methods taken, the impact of PPI on the project, and how it led to the development of a protocol for a qualitative study. Chapter 4 fulfills several of the recommended research directions by describing the protocol for a qualitative study on UK student-athletes’ experiences of help-seeking for mental health. This chapter outlines the methods aligned to a pragmatic approach and transformative paradigm that underpins this thesis, including the sampling and data collection and analysis. Chapter 5 provides a summary of this thesis and its novel contributions. Overall, this thesis contributes to the extant literature by showing that there are yet to be any studies investigating mental health help-seeking experiences in UK student-athletes. The use of PPI in conjunction with this review provided support for a qualitative study on this population group. Furthermore, the protocol for a qualitative study aligns with a growing open science agenda by detailing rationale for the study, methods to be used, and justifications of their use. The findings and outcomes of this thesis have implications for public health, sport governing bodies, and the higher education system particularly in supporting the mental health needs of athletes and the need for campaigns to encourage athletes to seek help for their mental health
Developing parametrisation methods for physics-based models of lithium and sodium-ion batteries
Get PDFLithium-ion batteries have become an important technology in the transition to renewable energy. Improvements in battery performance and cost reductions have led to their adoption in transport and grid storage applications to reduce carbon emissions. Battery models have been an important tool to achieve these improvements. Physics-based models, including the Doyle-Fuller-Newman model provide insight into the mass and charge transport processes within the individual battery components. The application of these battery models in industry and research has been limited by the availability of input parameters and the lack of published methodologies for parameterizing different cell formats and chemistries. Physics-based models have significant potential within industry, from optimising fast charging and battery manufacturing, but the main obstacle for widespread adoption is obtaining the parameters. Numerous parameters relating to the physical, electrochemical, and thermal properties of a battery. This research's experimental approach identifies key battery model parameters, improves methods, and creates accurate models for specific cells, offering insights for industry application and model development. This thesis develops parameterisation methodologies using physical, electrochemical, and thermal characterisation techniques to construct battery models that improve the understanding of battery kinetics/thermodynamics. Techniques including electrochemical impedance spectroscopy, galvanostatic intermittent titration technique, thermal measurement methods, and more are adapted to extract model inputs. This allows battery models that demonstrate high accuracy between simulated and experimental data to be developed. For lithium-ion batteries, a complete parameterisation workflow is developed to capture the thermal-electrochemical behaviour of a high energy commercial cylindrical cell and the property changes that occur during battery operation. This is accomplished by evaluating the dependency of parameters on temperature and state-of-charge. Furthermore, we found that traditional methods can be modified to better parameterise silicon additives, or new chemistries including sodium Our results demonstrate the importance and complementarity practical methods have in aiding model development and understanding. The novelty of this work lies in its approach to model development, utilizing experiments to identify the limitations of existing battery models and areas where simplifications can enhance utility without compromising the understanding of battery physics. This approach equips theorists with practical tools and insights, enabling significant advancements in the field of battery modelling. These methods have been commercialised and will be developed further to provide the several industries expertise into parameterisation and model development
Regulation of crystallization dynamic rendering highly efficient narrow-bandgap perovskite solar cells
Get PDFPerovskite solar cells (PSCs) have attracted increasing interest during the last decade due to their great potential to make full use of solar energy at low cost. Among all kinds of PSCs, narrow-bandgap perovskite solar cells are theoretically able to achieve efficiency approaching the S-Q efficiency limit. However, the uncontrolled crystallization process becomes one of the significant obstacles to realizing high-quality narrow-bandgap perovskite films and achieving highly efficient PSCs. In this thesis, I present my study on regulating crystallization dynamics of narrow-bandgap perovskites, including pure -FAPbI perovskite and mixed tin-lead perovskites (TLPs), to produce perovskite films with improved crystallinity and suppressed defect density and, therefore, realize impressive improvements in the efficiency of PSCs. I first developed a coordinator replenishment strategy by utilizing tetramethylurea (TMU) as a coordinating agent to facilitate the pre-nucleation of -FAPbI perovskite crystals and, thus, regulate the crystallization dynamic of the -FAPbI perovskite film in an air atmosphere. This led to the remarkable improvement in crystallinity, orientation, defect density, and lattice strain of the -FAPbI perovskite films. As a result, the PSCs based on such perovskite films have achieved the highest efficiency of 23.2%, along with enhanced long-term stability. Then, I investigated strategies to improve the film quality of TLPs. We introduced 3,4-dihydroxybenzylamine hydrobromide (DHBABr) as an additive, which was demonstrated to preferentially coordinate with SnI in the precursor. Consequently, the DHBABr additive balanced the crystallization rate of both Sn- and Pb-based perovskite components during their anti-solvent treatment and annealing processes, realizing TLP films with homogeneous Sn/Pb distribution, higher crystallinity, and lower defect density. The PSCs based on such TLP films finally achieved enhanced efficiency of 22.44% and improved long-term stability. Lastly, I have also explored a templated-growth approach for the regulation of the crystallization dynamic of TLPs by utilizing 2-phosphonoethan-1-aminium iodide (2PEAI) as an additive. The 2PEAI additive was determined to selectively coordinate with SnF and form a SnF-2PEA adduct, which regulates the crystallization by templated-anchoring the perovskite components. As a result, TLP films with higher crystallinity and lower defect density were obtained. Benefiting from the improved TLP film quality, the corresponding PSCs achieved the highest PCE of 21.95%. In all these research works, the mechanisms of the regulation of crystallization dynamics were comprehensively studied and discussed
Understanding the effects of vision impairment on visual search through computational models
Get PDFThis PhD thesis explores the application of computational models to help better understand the effects of vision loss on visual search behaviours. It analyses how people adapt to cognitive limitations when interacting with a visual search task. Visual search is a cognitive function that plays a crucial role in everyday activities, and gaining insights into how it differs amongst individuals with vision impairment holds significant practical implications for designing more accessible user interfaces. The research is exploratory and interpretative. It examines the implementation of a cognitive information processing system, which serves as the thinking brain to a computational model (i.e. the mechanism). Specifically, it explores how the mechanism affects visual search strategies in vision impairment. Researchers have used computational-rational agents to analyse and predict eye movement strategies. However, most studies have only focused on the strategies of normal vision without considering vision impairment. Therefore, in this research, we are taking a new approach by attempting to construct a model of eye movements in individuals with different types of vision impairment. To achieve optimal adaptation strategies in the model, we formulate different visual search tasks as a Partially Observable Markov Decision Process (POMDP). This approach would allow the implementation of the constraints imposed by the environment and the human visual system, including the limitations resulting from vision impairment. Solving real-life problems as POMDP is complex and requires significant computational resources. Therefore, we use different Reinforcement Learning (RL) techniques to achieve optimal strategies that we can compare against human data. The thesis considers three types of vision impairments (Glaucoma, Cataracts, and Age-related Macular Degeneration (AMD)). We use the Q-learning method to find the optimal policy for the Glaucoma task. Whereas for the other tasks, we use Deep Reinforcement Learning (DRL), specifically Proximal Policy Optimisation (PPO). The model finds optimal strategies in each experiment through adaptation to an impaired visual field. The results show that the theoretical approach to optimal rationality can give insight into how people with various types of vision impairment would interact with the screen. Overall, the model achieved the following: (1) adapted strategies to peripheral vision and environment constraints, (2) it showed a decline in performance when given a crowded setting, and (3) it predicted the accuracy of people with Cataracts in two different tasks. The research findings suggest that people with vision impairments adapt to their types of vision loss and the nature of their visual field defect. The findings have significant implications for Human-Computer Interaction (HCI). They can provide insights into the interactions of people with a specific type of vision impairment
Are the baseline control spaces at the BIFoR Free Air Carbon Enrichment experiment being polluted?
Get PDFThe Free Air Carbon Enrichment (FACE) experiments such as the one at the Birmingham Institute of Forest research (BIFoR), have emerged as a crucial tool for assessing the potential impacts of environmental increases in carbon dioxide (CO) concentrations on forests/woodlands of the future. Underpinning the BIFoR enrichment experiment there are two distinct levels of ambient control: the ambient blower spaces (ones with towers, pipework, and blowers) and the ambient undisturbed spaces (no infrastructure). By comparing the CO concentrations together with the plant growth responses across, enhanced, blower, and undisturbed spaces, an improved understanding of future temperate woodland ecosystems can be predicted.
A critical aspect of the FACE methodology lies in its controlled approach, separating enhanced, blower, and undisturbed spaces. While previous studies have concentrated on the enhanced and blower spaces, this research focuses on the undisturbed spaces. A measurement system was designed and implemented within the three undisturbed spaces at BIFoR and used to examine – for the first time – the potential migration of the treatment CO from the enhanced spaces into the undisturbed spaces. In addition, the data from the new system can be used to ascertain whether the ambient blowers are mixing the respired CO, lowering the measured ambient CO concentration and therefore the enhanced spaces setpoint.
This study examined more than one million CO concentrations measured within the undisturbed spaces at the BIFoR, FACE experiment, during the spring, summer of 2022. The results provide evidence that the undisturbed spaces are largely unaffected by CO from the enhanced areas. For technical reasons summarised in this thesis, it was not possible to come to a firm conclusion about the effect of the blowers in the ambient spaces; this remains a question for further research. Overall, the study’s outcomes reinforce the robustness of the design of the FACE experiments. The data provides an important baseline, supporting and underpinning other experiments taking place at BIFoR FACE
Development of three-dimensional interactive-based learning systems for basic transthoracic echocardiography education
Get PDFIn transthoracic echocardiography training, most medical trainees have difficulties achieving a conceptual understanding of spatial relationships between the echocardiography image and the complicated cardiac anatomical structures. A recent tradition of echocardiography training combines a traditional instructor-led workshop with self-directed online learning. In respect to the advance of educational technologies, the interest in three-dimensional (3D) visualisation has been widespread as it can be a part of the interactive learning systems for improving students’ understanding of the complex phenomena in TTE.
Self-paced learning materials equipped with 3D visualisation components is the focus of this thesis. This study proposed methodological and technical aspects of 3D interactive learning systems development which were delivered through two techniques: a computer-based multimedia and an augmented reality (AR) application. This aim was to assess how medical trainees value these two 3D learning systems and what achievement they gain from their uses in reaching basic TTE comprehension. 46 resident doctors who were novice in TTE at the Faculty of Medicine Siriraj Hospital, Thailand were voluntarily recruited in the study. The result indicated that residents’ knowledge gained from each learning system was similar. Comparably, no significant differences between learning systems were found in the usability questionnaire. Additionally, the responses to open-ended questions on experience highlighted a preference for the 3D graphical presentation of AR over the computer screen-based media. Finally, they anticipated that future versions of the AR application might be a mixed reality application equipped with a mock transducer probe for simulating actual TTE exam on a life-size mannequin
Understanding child criminal exploitation: risk factors and professional perspectives
Get PDFThis thesis aims to expand the understanding of Child Criminal Exploitation (CCE), which, as a relatively new phenomenon, has limited existing literature. In the UK, many children are subjected to CCE; they are harmed both physically and emotionally, and are often placed on a path of criminality, which has long-term impacts for them and their victims. The lack of research in this area means there is a need to improve the evidence base by exploring the relevant literature on risk and protective factors and the experiences of practitioners, to inform policy and practice. The findings presented in this thesis provide recommendations for interventions that will strengthen the support offered to young people at risk of or harmed by criminal exploitation.
The first chapter introduces the key concepts explored within the thesis, including the background context and history of CCE to date. Relevant definitions and laws pertaining to CCE are discussed and the aims of the thesis are outlined. The second chapter explores the existing UK literature base, on risk factors and protective factors for CCE and Child Sexual Exploitation (CSE). The research included articles published since 2016 and employed a systematic process. The review found that risk factors were more commonly investigated and described than protective factors. The review also highlights the need for consistent definitions, clear guidelines, and reliable resources for identifying and responding to victims.
An empirical research project is presented in chapter three, which explored the views of practitioners in the Youth Justice Service (formerly Youth Offending Teams) who predominantly work with the criminal form of child exploitation, as well as CSE. Interviews were conducted with nine practitioners, and were analysed using Reflexive Thematic Analysis. Seven themes and five subthemes are discussed in this chapter, with reference to practice, limitations, and recommendations for further research. Chapter four presents a critique of the Trauma Symptom Checklist for Children (Briere, 1996). This is a psychometric tool used to assess self-reported symptoms of trauma in children and adolescents. The TSCC was largely found to be reliable and valid, and its possible applications to the field of CCE are discussed.
The conclusion of the thesis is presented in chapter five, where main findings are discussed. Limitations and implications of the thesis are explored, as are recommendations for additional research to further strengthen the knowledge base
An investigation into the roles of aspartate/glutamate transporters in glioma
No full textSadly, only 25% of patients diagnosed with glioblastoma (GBM) survive for longer than 12 months. GBM, like most solid tumours, is characteristically hypoxic, which leads to a metabolic rewiring in cancer cells. Interestingly, amongst other metabolic changes, aspartate
becomes a limiting metabolite in hypoxia. Aspartate is imported into the cell via aspartate/glutamate transporters located on the plasma membrane; these are specific members of the SLC1 transporter family. The cytosolic and mitochondrial aspartate pools are maintained via the activity of SLC25A12 and SLC25A13, which are mitochondrial aspartate/glutamate transporters. Thus, this thesis began by studying both the plasma membrane and mitochondrial aspartate/glutamate transporters as a panel.
Bioinformatic analysis of the expression of aspartate/glutamate transporters in different glioma grades identified upregulation of SLC25A13 and SLC1A3 in GBM. Based on this, we assessed for hypoxia-induced changes of aspartate/glutamate transporter expression in human GBM cell lines. This revealed a marked downregulation of the mitochondrial aspartate/glutamate transporters in hypoxia. Leading on from this observation, the hypoxic regulation of SLC25A12 and SLC25A13 was investigated. We found the downregulation is not a result of hypoxia-induced endoplasmic reticulum stress. Instead, our studies identified a potential downregulation of SLC25A12 in hypoxia via HIF-1, the major regulator of the metabolic adaptation to hypoxia.
As this is not the case for SLC25A13, the impact of acute loss of the transporters on HIF-1α, the O2 sensitive subunit of HIF-1, was explored. This revealed SLC25A13 loss stabilises HIF1α and SLC25A12 loss reduces this stabilisation. Based on observations throughout these studies, we hypothesised a post-translational modification of SLC25A13 in hypoxia and investigated this possibility via genetic modification of the cells, immunoblotting and bioinformatic analysis. Our data supported this hypothesis although further investigations are required.
Additionally, an investigation into the impact of acute and chronic loss of the mitochondrial aspartate/glutamate transporters on glioma cell proliferation identified acute loss results in a larger phenotype than chronic loss, and SLC25A13 loss had a greater impact than SLC25A12. Moreover, immunoblotting experiments revealed a potential increased reliance on the activity of the plasma membrane aspartate/glutamate transporters with acute SLC25A12 and SLC25A13 loss.
Lastly, the functional differences between SLC25A12 and SLC25A13 in normoxic and hypoxic glioma cells was investigated using stable isotope tracing. Unlike reports in the literature, our data discovered an alternative working cell model. Acute loss of SLC25A12 decreased lactate secretion which is indicative of a reduced cytosolic NADH pool. This reflects continued MAS activity in the absence of SLC25A12. Moreover, with acute SLC25A13 loss we identified a potential compensation of MAS activity with the SLC25A1 transporter. Interestingly, acute loss of SLC25A12, not SLC25A13, resulted in an increased reliance on an alternative carbon source for nucleotide production in hypoxia. This suggests SLC25A13 is the major transporter of the malate-aspartate shuttle, and SLC25A12 is functionally important for the maintenance of aspartate availability
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