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Reduced-order modelling of fluid flows using analytical and numerical methods
Full text linkCoating the exterior of a cylinder with a layer of fluid is a fundamental problem in fluid mechanics and occurs in numerous natural processes and industrial applications, such as heat and mass transfer and the production of orthopaedic implants. This thesis formulates and analyses novel models for two different coating flow problems which are not restricted by the common assumptions that the cylinder has circular cross-section and/or that the film is thin. The first problem involves the unsteady, two-dimensional flow on the exterior of a uniformly rotating horizontal cylinder with elliptical cross-section. By using a long-wave approximation we derive a thick-film model, and by using a thin-filmapproximation we derive a thin-film model. Both models incorporate the effects of cylinder eccentricity, rotation, gravity, centrifugation, viscosity, and surface tension. By studying the thin-film model, we demonstrate both analytically and numerically that the behaviour of the film coating the elliptical cylinder significantly differs from that in the circular case. In particular, it is shown that even a relatively mild departure from circularity produces significant qualitative and quantitative differences from the behaviour in the circular case. The second problem involves the unsteady, three-dimensional flow of a thick film on the exterior of a vertical fibre with circular cross-section. By using a longwave approximation and the method of weighted residuals, we derive a thick-film weighted-residual model, which incorporates the effects of gravity, viscosity, surface tension, and inertia. We study the thick-film weighted-residual model in the linear regime in order to elucidate the mechanics that determine both the stability and the axisymmetry of the flow. We demonstrate that these results in the linear regime, in general, correctly predict the results of the linear calculations of the Navier–Stokes equations and the results of numerical simulations of the thick-filmweighted-residual model in the nonlinear regime.Coating the exterior of a cylinder with a layer of fluid is a fundamental problem in fluid mechanics and occurs in numerous natural processes and industrial applications, such as heat and mass transfer and the production of orthopaedic implants. This thesis formulates and analyses novel models for two different coating flow problems which are not restricted by the common assumptions that the cylinder has circular cross-section and/or that the film is thin. The first problem involves the unsteady, two-dimensional flow on the exterior of a uniformly rotating horizontal cylinder with elliptical cross-section. By using a long-wave approximation we derive a thick-film model, and by using a thin-filmapproximation we derive a thin-film model. Both models incorporate the effects of cylinder eccentricity, rotation, gravity, centrifugation, viscosity, and surface tension. By studying the thin-film model, we demonstrate both analytically and numerically that the behaviour of the film coating the elliptical cylinder significantly differs from that in the circular case. In particular, it is shown that even a relatively mild departure from circularity produces significant qualitative and quantitative differences from the behaviour in the circular case. The second problem involves the unsteady, three-dimensional flow of a thick film on the exterior of a vertical fibre with circular cross-section. By using a longwave approximation and the method of weighted residuals, we derive a thick-film weighted-residual model, which incorporates the effects of gravity, viscosity, surface tension, and inertia. We study the thick-film weighted-residual model in the linear regime in order to elucidate the mechanics that determine both the stability and the axisymmetry of the flow. We demonstrate that these results in the linear regime, in general, correctly predict the results of the linear calculations of the Navier–Stokes equations and the results of numerical simulations of the thick-filmweighted-residual model in the nonlinear regime
Investigation into maximizing component availability for superconducting cables in turbo-electric distributed propulsion aircraft
Full text linkThe commercial aviation industry is growing at a substantial rate, with demand doubling every 15 years and this trend is set to continue well into the 21st Century. At the same time regulatory pressures are being exerted on the industry as governments around the world seek to reduce their greenhouse gas emissions in an effort to contain global temperature rise to 2°C . Combined with existing infrastructure challenges, these issues are forcing air-framers to develop new, novel designs that support sustainable approaches to future aviation to meet environmental, social and economic demands. The pathway to decarbonisation of aviation will involve a combination of fuel, technology and operational measures. Many of the proposed technologies, such as electrical propulsion, are inherently disruptive and require changes to supply-chains,ground operations, maintenance standards and procedures, and pilot training. Such disruption is unavoidable given the scale of the challenge of electrical propulsion: a typical widebody jet engine for passenger aircraft can output over 22 MW fully loaded; an equivalent electrical system must be able to generate, distribute, and produce same amount of thrust with equal or greater reliability than the existing drivetrain that has been perfected over the course of the last century. Turbo-electric Distributed Propulsion (TeDP) is an approach for the electrification of propulsion systems on aircraft that aims to do this. Instead of large turbofan engines used to generate thrust, power in the engines is converted to electricity using electrical generators, and then distributed electrically through a network to propulsion motors placed in aerodynamically advantageous locations, significant fuel savings and performance benefits may be realised. Electrification of the propulsion system comes with large weight penalties.It is critical that the weight of the electrical power system does not mitigate the benefits of electrification. Superconducting electrical machines have been proposed as a route to lightweighting the electrical power system due to their promising high power densities compared to conventional electrical machines. It is proposed that the rest of the electrical power system be superconducting as far as technically possible to minimise heat sinks within the system.Integration of superconducting materials into the most safety critical aspects of commercial aviation raises multiple research questions regarding the design of resilient systems and how appropriate electrical protection strategies can be designed given the strict electric, magnetic, and thermal operating requirements that these components have. All electrical systems experience faults. This Thesis investigates how these faults manifest within a compact, power-electronically interfaced, superconducting network. The research presented in this thesis captures electrical protection requirements through modelling, simulation, and experimentation to develop requirements for TeDP feeder cables. By building on these requirements this thesis will then show how cable design can be optimised to withstand faults and present a control method which enables maximising throughput of cables during temperature rise events. This knowledge aims to improve availability, in terms of reducing the amount of superconducting network de-rating required, and power provision of superconducting feeder cables during adverse conditions encountered by superconducting TeDP aircraft.The commercial aviation industry is growing at a substantial rate, with demand doubling every 15 years and this trend is set to continue well into the 21st Century. At the same time regulatory pressures are being exerted on the industry as governments around the world seek to reduce their greenhouse gas emissions in an effort to contain global temperature rise to 2°C . Combined with existing infrastructure challenges, these issues are forcing air-framers to develop new, novel designs that support sustainable approaches to future aviation to meet environmental, social and economic demands. The pathway to decarbonisation of aviation will involve a combination of fuel, technology and operational measures. Many of the proposed technologies, such as electrical propulsion, are inherently disruptive and require changes to supply-chains,ground operations, maintenance standards and procedures, and pilot training. Such disruption is unavoidable given the scale of the challenge of electrical propulsion: a typical widebody jet engine for passenger aircraft can output over 22 MW fully loaded; an equivalent electrical system must be able to generate, distribute, and produce same amount of thrust with equal or greater reliability than the existing drivetrain that has been perfected over the course of the last century. Turbo-electric Distributed Propulsion (TeDP) is an approach for the electrification of propulsion systems on aircraft that aims to do this. Instead of large turbofan engines used to generate thrust, power in the engines is converted to electricity using electrical generators, and then distributed electrically through a network to propulsion motors placed in aerodynamically advantageous locations, significant fuel savings and performance benefits may be realised. Electrification of the propulsion system comes with large weight penalties.It is critical that the weight of the electrical power system does not mitigate the benefits of electrification. Superconducting electrical machines have been proposed as a route to lightweighting the electrical power system due to their promising high power densities compared to conventional electrical machines. It is proposed that the rest of the electrical power system be superconducting as far as technically possible to minimise heat sinks within the system.Integration of superconducting materials into the most safety critical aspects of commercial aviation raises multiple research questions regarding the design of resilient systems and how appropriate electrical protection strategies can be designed given the strict electric, magnetic, and thermal operating requirements that these components have. All electrical systems experience faults. This Thesis investigates how these faults manifest within a compact, power-electronically interfaced, superconducting network. The research presented in this thesis captures electrical protection requirements through modelling, simulation, and experimentation to develop requirements for TeDP feeder cables. By building on these requirements this thesis will then show how cable design can be optimised to withstand faults and present a control method which enables maximising throughput of cables during temperature rise events. This knowledge aims to improve availability, in terms of reducing the amount of superconducting network de-rating required, and power provision of superconducting feeder cables during adverse conditions encountered by superconducting TeDP aircraft
People, Technology and Work WE907 Exam papers
No full textAccess restricted to staff and registered students of the University of Strathclyde.PAST EXAM PAPERS ARE NO LONGER BEING ADDED TO STAX. PLEASE VISIT SUPRIMO TO ACCESS AN UP-TO-DATE COLLECTION OF PAST EXAM PAPERS: https://suprimo.lib.strath.ac.uk
'We were all scattered to the four winds’: work, identity, and deindustrialisation in post-war Scotland
No full textEffective image enhancement and fast object detection for improved UAV applications
Full text linkAs an emerging field, unmanned aerial vehicles (UAVs) feature from interdisciplinary techniques in science, engineering and industrial sectors. The massive applications span from remote sensing, precision agriculture, marine inspection, coast guarding, environmental monitoring, natural resources monitoring, e.g. forest, land and river, and disaster assessment, to smart city, intelligent transportation and logistics and delivery.
With the fast growing demands from a wide range of application sectors, there is always a bottleneck how to improve the efficiency and efficacy of UAV in operation. Often, smart decision making is needed from the captured footages in a real-time manner, yet this is severely affected by the poor image quality, ineffective object detection and recognition models, and lack of robust and light models for supporting the edge computing and real deployment.
In this thesis, several innovative works have been focused and developed to tackle some of the above issues. First of all, considering the quality requirements of the UAV images, various approaches and models have been proposed, yet they focus on different aspects and produce inconsistent results. As such, the work in this thesis has been categorised into denoising and dehazing focused, followed by comprehensive evaluation in terms of both qualitative and quantitative assessment. These will provide valuable insights and useful guidance to help the end user and research community.
For fast and effective object detection and recognition, deep learning based models, especially the YOLO series, are popularly used. However, taking the YOLOv7 as the baseline, the performance is very much affected by a few factors, such as the low quality of the UAV images and the high-level of demanding of resources, leading to unsatisfactory performance in accuracy and processing speed. As a result, three major improvements, namely transformer, CIoULoss and the GhostBottleneck module, are introduced in this work to improve feature extraction, decision making in detection and recognition, and running efficiency. Comprehensive experiments on both publicly available and self-collected datasets have validated the efficiency and efficacy of the proposed algorithm.
In addition, to facilitate the real deployment such as edge computing scenarios, embedded implementation of the key algorithm modules is introduced. These include the creative implementation on the Xavier NX platform, in comparison to the standard workstation settings with the NVIDIA GPUs. As a result, it has demonstrated promising results with improved performance in reduced resources consumption of the CPU/GPU usage and enhanced frame rate of real-time processing to benefit the real-time deployment with the uncompromised edge computing.
Through these innovative investigation and development, a better understanding has been established on key challenges associated with UAV and Simultaneous Localisation and Mapping (SLAM) based applications, and possible solutions are presented.
Keywords: Unmanned aerial vehicles (UAV); Simultaneous Localisation and Mapping (SLAM); denoising; dehazing; object detection; object recognition; deep learning; YOLOv7; transformer; GhostBottleneck; scene matching; embedded implementation; Xavier NX; edge computing.As an emerging field, unmanned aerial vehicles (UAVs) feature from interdisciplinary techniques in science, engineering and industrial sectors. The massive applications span from remote sensing, precision agriculture, marine inspection, coast guarding, environmental monitoring, natural resources monitoring, e.g. forest, land and river, and disaster assessment, to smart city, intelligent transportation and logistics and delivery.
With the fast growing demands from a wide range of application sectors, there is always a bottleneck how to improve the efficiency and efficacy of UAV in operation. Often, smart decision making is needed from the captured footages in a real-time manner, yet this is severely affected by the poor image quality, ineffective object detection and recognition models, and lack of robust and light models for supporting the edge computing and real deployment.
In this thesis, several innovative works have been focused and developed to tackle some of the above issues. First of all, considering the quality requirements of the UAV images, various approaches and models have been proposed, yet they focus on different aspects and produce inconsistent results. As such, the work in this thesis has been categorised into denoising and dehazing focused, followed by comprehensive evaluation in terms of both qualitative and quantitative assessment. These will provide valuable insights and useful guidance to help the end user and research community.
For fast and effective object detection and recognition, deep learning based models, especially the YOLO series, are popularly used. However, taking the YOLOv7 as the baseline, the performance is very much affected by a few factors, such as the low quality of the UAV images and the high-level of demanding of resources, leading to unsatisfactory performance in accuracy and processing speed. As a result, three major improvements, namely transformer, CIoULoss and the GhostBottleneck module, are introduced in this work to improve feature extraction, decision making in detection and recognition, and running efficiency. Comprehensive experiments on both publicly available and self-collected datasets have validated the efficiency and efficacy of the proposed algorithm.
In addition, to facilitate the real deployment such as edge computing scenarios, embedded implementation of the key algorithm modules is introduced. These include the creative implementation on the Xavier NX platform, in comparison to the standard workstation settings with the NVIDIA GPUs. As a result, it has demonstrated promising results with improved performance in reduced resources consumption of the CPU/GPU usage and enhanced frame rate of real-time processing to benefit the real-time deployment with the uncompromised edge computing.
Through these innovative investigation and development, a better understanding has been established on key challenges associated with UAV and Simultaneous Localisation and Mapping (SLAM) based applications, and possible solutions are presented.
Keywords: Unmanned aerial vehicles (UAV); Simultaneous Localisation and Mapping (SLAM); denoising; dehazing; object detection; object recognition; deep learning; YOLOv7; transformer; GhostBottleneck; scene matching; embedded implementation; Xavier NX; edge computing
Deferred executive compensation and double-layered principal-principal conflicts
Full text linkThis research examines the policy effect of ‘salary restriction order’ on the double-layered principal-principal conflicts in Chinese State-Owned Enterprises (SOEs). According to current agency problems in highly concentrated firms in China, this research elaborates on the traditional Type Ⅱ Agency Problem based on the seminal Double-Layered Agency Theory (Raelin and Bondy, 2013) from the second-layered social perspective, arguing both economic-layered principal-principal conflicts between large/controlling shareholders and the economic-layered principals (i.e., minority shareholders and outside creditors) and the overlooked societal-layered principal-principal conflicts caused by the large/controlling shareholders towards the company’s primary social and environmental stakeholders. This new theoretical
contribution is defined as the Double-Layered Principal-Principal Theory.
Because of the inevitable political affiliation and SOE managers’ special political promotion, corporate governance mechanisms derived from the traditional Agency Theory based on the Western market with separated ownership and control lack effectiveness (Jiang and Kim, 2015; 2020). Moreover, the most commonly used approach in the Type Ⅱ Agency Problem studies, Multiple Large Shareholders (MLS), shows negative collusion among these large shareholders in China. Therefore, this research explores potential corporate governance mechanisms to mitigate the double-layered principal-principal conflicts in Chinese SOEs. Starting January 1st, 2010, the State-Owned Assets Supervision and Administration Commission of the State Council (SASAC) required executives and top management team (TMT) in charge of the central enterprises to defer 40% annual performance-based salary in a 3-year tenure. I find this ‘salary restriction order’ provides an
appropriate opportunity to examine the policy effects of deferred executive
compensation (DEC) on the double-layered principal-principal conflicts the Chinese SOEs are confronting. This research tests panel data of 74 listed SASAC subsidiaries from 2007 to 2015. It uses the ‘salary restriction order’ as an exogenous shock to conduct a quasi-natural experiment to examine the policy effects of DEC on the double-layered principal-principal conflicts. Unlike most US studies, this research found inconsistent results of the CEO Inside Debt Theory (Edmans and Liu, 2011). Rather than risk-moderating, the findings show an insignificant association between DEC and corporate risk and a direct impact on declining dividend pay-out and increasing tunnelling behaviour via related-party transactions. It indicates that DEC may not mitigate the economic-layered risk preference between large shareholders and outside creditors. Even worse, limiting executive pay is likely to accelerate wealth expropriation from large shareholders towards minority shareholders, intensifying the traditional economic-layered principal-principal conflicts. Moreover, consistent with the view of Long-Run Net Social Benefits (Kane, 2002), this research found a direct positive association between DEC and the quality of the social and environmental disclosure index (SEDI), demonstrating that DEC may be a potential corporate governance mechanism to alleviate the societal-layered principal-principal conflicts in Chinese SOEs. The robustness checks, including parallel trend tests and placebo tests, and 2SLS regressions, Sobel tests and Bootstrap tests examining the risk-moderating effect of DEC, are consistent with the previous findings. The findings carry important policy implications. It reveals that limiting executive pay would increase the traditional economic-layered principal-principal conflicts, which are unlikely to play a role in protecting the interests of small and medium-sized investors in China. Therefore, policymakers must consider specific agency problems within the national context when formulating corporate governance regulations. It
necessitates a departure from the uncritical application of conventional methodologies. In this case, policymakers in China should avoid straightforwardly cutting down executives’ pay without properly adjusting the length, ratios, or portfolios of other types of deferred compensation and pension plans for the executives’ long-term incentives. The research contributions are as follows. First, elaborating the theoretical framework
of the Agency Theory, this research proposes a Double-Layered Principal-Principal Theory, extending beyond the economic-layered principal-principal conflicts to encompass the second societal-layered principal-principal conflicts arising from the large/controlling shareholders towards the company’s primary social and environmental stakeholders in highly concentrated firms. Second, this research establishes a strong theoretical causality in examining the association between DEC and corporate social performance (measured by SEDI). Previous studies failed to demonstrate a theoretical causality between these two variables. Filling the gap, this research reports evidence (Mayberry, 2020) that risk-moderating can serve as a mediator variable to link the association between DEC and corporate social performance. Third, consistent with the literature chapter, the methodology chapter develops a new SEDI to measure the ‘societal-layered principal-principal conflicts’ in China. In addition, the findings enrich the CEO inside debt studies by providing robust evidence showing insignificant correlations between DEC and corporate risk. It also
suggests that Chinese policymakers re-evaluate the ‘salary restriction order’ based on its potential consequences.This research examines the policy effect of ‘salary restriction order’ on the double-layered principal-principal conflicts in Chinese State-Owned Enterprises (SOEs). According to current agency problems in highly concentrated firms in China, this research elaborates on the traditional Type Ⅱ Agency Problem based on the seminal Double-Layered Agency Theory (Raelin and Bondy, 2013) from the second-layered social perspective, arguing both economic-layered principal-principal conflicts between large/controlling shareholders and the economic-layered principals (i.e., minority shareholders and outside creditors) and the overlooked societal-layered principal-principal conflicts caused by the large/controlling shareholders towards the company’s primary social and environmental stakeholders. This new theoretical
contribution is defined as the Double-Layered Principal-Principal Theory.
Because of the inevitable political affiliation and SOE managers’ special political promotion, corporate governance mechanisms derived from the traditional Agency Theory based on the Western market with separated ownership and control lack effectiveness (Jiang and Kim, 2015; 2020). Moreover, the most commonly used approach in the Type Ⅱ Agency Problem studies, Multiple Large Shareholders (MLS), shows negative collusion among these large shareholders in China. Therefore, this research explores potential corporate governance mechanisms to mitigate the double-layered principal-principal conflicts in Chinese SOEs. Starting January 1st, 2010, the State-Owned Assets Supervision and Administration Commission of the State Council (SASAC) required executives and top management team (TMT) in charge of the central enterprises to defer 40% annual performance-based salary in a 3-year tenure. I find this ‘salary restriction order’ provides an
appropriate opportunity to examine the policy effects of deferred executive
compensation (DEC) on the double-layered principal-principal conflicts the Chinese SOEs are confronting. This research tests panel data of 74 listed SASAC subsidiaries from 2007 to 2015. It uses the ‘salary restriction order’ as an exogenous shock to conduct a quasi-natural experiment to examine the policy effects of DEC on the double-layered principal-principal conflicts. Unlike most US studies, this research found inconsistent results of the CEO Inside Debt Theory (Edmans and Liu, 2011). Rather than risk-moderating, the findings show an insignificant association between DEC and corporate risk and a direct impact on declining dividend pay-out and increasing tunnelling behaviour via related-party transactions. It indicates that DEC may not mitigate the economic-layered risk preference between large shareholders and outside creditors. Even worse, limiting executive pay is likely to accelerate wealth expropriation from large shareholders towards minority shareholders, intensifying the traditional economic-layered principal-principal conflicts. Moreover, consistent with the view of Long-Run Net Social Benefits (Kane, 2002), this research found a direct positive association between DEC and the quality of the social and environmental disclosure index (SEDI), demonstrating that DEC may be a potential corporate governance mechanism to alleviate the societal-layered principal-principal conflicts in Chinese SOEs. The robustness checks, including parallel trend tests and placebo tests, and 2SLS regressions, Sobel tests and Bootstrap tests examining the risk-moderating effect of DEC, are consistent with the previous findings. The findings carry important policy implications. It reveals that limiting executive pay would increase the traditional economic-layered principal-principal conflicts, which are unlikely to play a role in protecting the interests of small and medium-sized investors in China. Therefore, policymakers must consider specific agency problems within the national context when formulating corporate governance regulations. It
necessitates a departure from the uncritical application of conventional methodologies. In this case, policymakers in China should avoid straightforwardly cutting down executives’ pay without properly adjusting the length, ratios, or portfolios of other types of deferred compensation and pension plans for the executives’ long-term incentives. The research contributions are as follows. First, elaborating the theoretical framework
of the Agency Theory, this research proposes a Double-Layered Principal-Principal Theory, extending beyond the economic-layered principal-principal conflicts to encompass the second societal-layered principal-principal conflicts arising from the large/controlling shareholders towards the company’s primary social and environmental stakeholders in highly concentrated firms. Second, this research establishes a strong theoretical causality in examining the association between DEC and corporate social performance (measured by SEDI). Previous studies failed to demonstrate a theoretical causality between these two variables. Filling the gap, this research reports evidence (Mayberry, 2020) that risk-moderating can serve as a mediator variable to link the association between DEC and corporate social performance. Third, consistent with the literature chapter, the methodology chapter develops a new SEDI to measure the ‘societal-layered principal-principal conflicts’ in China. In addition, the findings enrich the CEO inside debt studies by providing robust evidence showing insignificant correlations between DEC and corporate risk. It also
suggests that Chinese policymakers re-evaluate the ‘salary restriction order’ based on its potential consequences
The neuroendocrine reactivity to social defeat : threat/challenge appraisals and socio-economic status
Full text linkExtensive evidence demonstrates that lower socio-economic status (SES) is associatedwith poorer health and reduced opportunities to fully participate in society. Reasonsfor this exist within a latticework of socio-cultural, economic, political, and biologicalinfluences, in concert with psychological processes. The social gradient in healthrobustly illustrates how inequalities and social rank predict distribution of disease.Marmot (2004) argues that where people stand in relation to others in society iscrucial for an individual’s health and well-being. Similarly, Wilkinson and Pickett(2018) suggest the social gradient in health results from social rank and relativeposition on the social ladder, with subordination linked to limited resources and lackof control, rather than from health behaviours or access to medical care. However,neither of those theoretical positions empirically test specific biopsychosocialmechanisms through which status affects health. By exploring endocrine reactivity inresponse to an experimental social defeat task, cognitive moderators of this link, andthe relationships of key psychosocial factors to endocrine reactivity and therebyhealth, this thesis advances research of health inequalities. It does so by providinginsight into the concrete neuroendocrine mechanisms underpinning the socialgradient in health. Although this study does not provide any firm, definitiveconclusions about differences in endocrine reactivity and cognitive appraisals of thetask between SES groups, it suggests that androgenic and glucocorticoid systemsmight indeed be involved in the social gradient of health. However, future researchexploring those relationships on a larger scale is required. The results furtherdemonstrate that the overall circulating T levels were higher in the high SES comparedto low SES group in both competition conditions. Participants also display higheroverall levels of circulating C levels on the day of the experiment compared to thebaseline day. Moreover, the thesis suggests that testosterone (T) potentially plays animportant role in the underpinning neuroendocrine reactivity that affects behaviouralimplications of social defeat/victory, before situating these within the broadercontextual framework of socio-economic disadvantage (SED). Accordingly, whilst therelationship between T reactivity and motivational states was not found to bestatistically significant, this thesis argues that public and health policy interventionsshould take cognisance of the behavioural and biological implications of social defeatwithin lower SES groups. Doing so can aid in the minimisation of those consequences,and harvest positive health and behavioural outcomes which in turn respond to healthinequality.Extensive evidence demonstrates that lower socio-economic status (SES) is associatedwith poorer health and reduced opportunities to fully participate in society. Reasonsfor this exist within a latticework of socio-cultural, economic, political, and biologicalinfluences, in concert with psychological processes. The social gradient in healthrobustly illustrates how inequalities and social rank predict distribution of disease.Marmot (2004) argues that where people stand in relation to others in society iscrucial for an individual’s health and well-being. Similarly, Wilkinson and Pickett(2018) suggest the social gradient in health results from social rank and relativeposition on the social ladder, with subordination linked to limited resources and lackof control, rather than from health behaviours or access to medical care. However,neither of those theoretical positions empirically test specific biopsychosocialmechanisms through which status affects health. By exploring endocrine reactivity inresponse to an experimental social defeat task, cognitive moderators of this link, andthe relationships of key psychosocial factors to endocrine reactivity and therebyhealth, this thesis advances research of health inequalities. It does so by providinginsight into the concrete neuroendocrine mechanisms underpinning the socialgradient in health. Although this study does not provide any firm, definitiveconclusions about differences in endocrine reactivity and cognitive appraisals of thetask between SES groups, it suggests that androgenic and glucocorticoid systemsmight indeed be involved in the social gradient of health. However, future researchexploring those relationships on a larger scale is required. The results furtherdemonstrate that the overall circulating T levels were higher in the high SES comparedto low SES group in both competition conditions. Participants also display higheroverall levels of circulating C levels on the day of the experiment compared to thebaseline day. Moreover, the thesis suggests that testosterone (T) potentially plays animportant role in the underpinning neuroendocrine reactivity that affects behaviouralimplications of social defeat/victory, before situating these within the broadercontextual framework of socio-economic disadvantage (SED). Accordingly, whilst therelationship between T reactivity and motivational states was not found to bestatistically significant, this thesis argues that public and health policy interventionsshould take cognisance of the behavioural and biological implications of social defeatwithin lower SES groups. Doing so can aid in the minimisation of those consequences,and harvest positive health and behavioural outcomes which in turn respond to healthinequality
Optimisation of proton acceleration and synchrotron radiation in ultraintense laser-solid interactions
Full text linkThis thesis reports on numerical investigations of laser-solid interactions with peak laser intensities in the approximate range 1021–1024Wcm−2, where few experiments have yet taken place. Higher laser intensities enable the production of higher energy radiation whilst altering the physics of the interaction. Here, the generation of protons and gamma rays is optimised for laser intensities in the given range, now becoming accessible with improved petawatt and multi-petawatt laser facilities, and the dynamics of the interactions are analysed.
The first investigation presented was centred on maximising the proton energies obtained with thin foil targets. The highest proton energies from CH targets are shown to occur when the foil becomes relativistically transparent as the peak of the temporal laser intensity profile reaches the target, for a wide range of laser intensities and both linear and circular laser light polarisation. The interaction dynamics are discussed, including the changes with earlier or later transparency times. Increased intensity of the laser pulse rising edge is demonstrated to increase the foil thickness which optimises the maximum proton energy, without significantly reducing the maximum proton energy. Finally, radiation reaction is shown to reduce the maximum proton energies from most targets by tens of percent.
The second investigation reported was principally the optimisation of the synchrotron gamma ray emission from foil targets. Bayesian optimisation (a machine learning approach) was applied to optimise various objective functions corresponding to the energy converted into synchrotron radiation, peak angle-resolved emission and number of photons in the high energy spectral tail. Several objectives were also combined and optimised together. The results show the synchrotron emission is generally maximised for oblique incidence with the highest on-target laser intensity. Simultaneous reduction of bremsstrahlung emission also demonstrated optimised results with ultrathin targets. The role of the angle-of-incidence of the laser onto the target was explored, and 3D simulations enabled the additional role of the laser polarisation state to be determined. These results provide new understanding of gamma ray production in ultraintense laser-solid interactions, which could be used to improve the design of experiments and aid in the interpretation of experimental results.This thesis reports on numerical investigations of laser-solid interactions with peak laser intensities in the approximate range 1021–1024Wcm−2, where few experiments have yet taken place. Higher laser intensities enable the production of higher energy radiation whilst altering the physics of the interaction. Here, the generation of protons and gamma rays is optimised for laser intensities in the given range, now becoming accessible with improved petawatt and multi-petawatt laser facilities, and the dynamics of the interactions are analysed.
The first investigation presented was centred on maximising the proton energies obtained with thin foil targets. The highest proton energies from CH targets are shown to occur when the foil becomes relativistically transparent as the peak of the temporal laser intensity profile reaches the target, for a wide range of laser intensities and both linear and circular laser light polarisation. The interaction dynamics are discussed, including the changes with earlier or later transparency times. Increased intensity of the laser pulse rising edge is demonstrated to increase the foil thickness which optimises the maximum proton energy, without significantly reducing the maximum proton energy. Finally, radiation reaction is shown to reduce the maximum proton energies from most targets by tens of percent.
The second investigation reported was principally the optimisation of the synchrotron gamma ray emission from foil targets. Bayesian optimisation (a machine learning approach) was applied to optimise various objective functions corresponding to the energy converted into synchrotron radiation, peak angle-resolved emission and number of photons in the high energy spectral tail. Several objectives were also combined and optimised together. The results show the synchrotron emission is generally maximised for oblique incidence with the highest on-target laser intensity. Simultaneous reduction of bremsstrahlung emission also demonstrated optimised results with ultrathin targets. The role of the angle-of-incidence of the laser onto the target was explored, and 3D simulations enabled the additional role of the laser polarisation state to be determined. These results provide new understanding of gamma ray production in ultraintense laser-solid interactions, which could be used to improve the design of experiments and aid in the interpretation of experimental results
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