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Herding and systemic risk in banking sector
Get PDFSystemic banking crises can cause significant disruptions in the economy (Dell'Ariccia, Detragiache and Rajan, 2008; Reinhart and Rogoff, 2014) and result in non-trivial fiscal costs (Calomiris, 1999; Dewatripont, 2014). Consequently, a great number of studies in the banking literature have been dedicated to examining systemic risk in the banking system, in particular that of too-big-to-fail banks (Shleifer and Vishny, 2010; Laeven, Ratnovski and Tong, 2016). Nonetheless, the problem of the systemic risk posed by bank herding has received less attention.;This thesis provides a rigorous empirical examination of the theory that banks herd to increase the likelihood of a collective bailout position should default occur (Acharya and Yorulmazer, 2007; Farhi and Tirole, 2012). The empirical examination is assessed by addressing three key research questions: 1) Do banks herd and can country-level factors explain herding consistent with the theory? 2) If yes, does herding pose a systemic risk? 3) How does herding affect the competition and profit of banks? These questions are addressed in three individual empirical chapters.;The first empirical chapter (Chapter 2) investigates whether banks do herd and if country-specific factors affect herding consistent with the theory. The findings support the proposition that banks do herd and that the degree of herding varies across countries. The results also show that herding is dependent on several country-specific features such as exposure to fiscal costs, banking sector characteristics, and regulatory and supervisory quality. However, contrary to the theory, the effect of shareholder protection laws on herding is not significant, possibly because banks with dispersed ownership also receive bailout subsidies when banks collectively fail.;The second empirical chapter (Chapter 3) investigates the systemic risk implications of bank herding. The findings show that the effect on systemic risk of the interaction between herding and deposits and that between herding and loans are statistically significant. The results suggest that negative externalities from excessive funding risk and liquidity risk taking may not have been fully internalised through existing prudential regulations.;The third empirical chapter (Chapter 4) examines the effect of herding on the competition and profit of banks. Empirical evidence in this chapter indicates higher competition among banks that herd compared to the rest of the banking industry. Nonetheless, herding may still be desirable when competition in the banking industry is weak. The possibility of a higher profit from low banking industry competition allows banks to compensate for the erosion in profit caused by herding. Furthermore, in the face of herding, the adverse effect of increased competition on profit is larger for banks that are followed by others compared to those that follow the leaders.Systemic banking crises can cause significant disruptions in the economy (Dell'Ariccia, Detragiache and Rajan, 2008; Reinhart and Rogoff, 2014) and result in non-trivial fiscal costs (Calomiris, 1999; Dewatripont, 2014). Consequently, a great number of studies in the banking literature have been dedicated to examining systemic risk in the banking system, in particular that of too-big-to-fail banks (Shleifer and Vishny, 2010; Laeven, Ratnovski and Tong, 2016). Nonetheless, the problem of the systemic risk posed by bank herding has received less attention.;This thesis provides a rigorous empirical examination of the theory that banks herd to increase the likelihood of a collective bailout position should default occur (Acharya and Yorulmazer, 2007; Farhi and Tirole, 2012). The empirical examination is assessed by addressing three key research questions: 1) Do banks herd and can country-level factors explain herding consistent with the theory? 2) If yes, does herding pose a systemic risk? 3) How does herding affect the competition and profit of banks? These questions are addressed in three individual empirical chapters.;The first empirical chapter (Chapter 2) investigates whether banks do herd and if country-specific factors affect herding consistent with the theory. The findings support the proposition that banks do herd and that the degree of herding varies across countries. The results also show that herding is dependent on several country-specific features such as exposure to fiscal costs, banking sector characteristics, and regulatory and supervisory quality. However, contrary to the theory, the effect of shareholder protection laws on herding is not significant, possibly because banks with dispersed ownership also receive bailout subsidies when banks collectively fail.;The second empirical chapter (Chapter 3) investigates the systemic risk implications of bank herding. The findings show that the effect on systemic risk of the interaction between herding and deposits and that between herding and loans are statistically significant. The results suggest that negative externalities from excessive funding risk and liquidity risk taking may not have been fully internalised through existing prudential regulations.;The third empirical chapter (Chapter 4) examines the effect of herding on the competition and profit of banks. Empirical evidence in this chapter indicates higher competition among banks that herd compared to the rest of the banking industry. Nonetheless, herding may still be desirable when competition in the banking industry is weak. The possibility of a higher profit from low banking industry competition allows banks to compensate for the erosion in profit caused by herding. Furthermore, in the face of herding, the adverse effect of increased competition on profit is larger for banks that are followed by others compared to those that follow the leaders
Synthesis and assessment of laser related perameters in colour centre containing diamond
Get PDFSynthesis and Assessment of Laser Related Parameters in Colour Centre Containing Diamond. This thesis reports research on the fabrication and assessment of colour centre containing diamond. The advent of affordable single crystal synthetic diamond with low background absorption has motivated renewed interest in whether efficient colour centre lasers can be realised based on diamond. Two types of colour centres were investigated, composed of one or two nitrogen (N) atoms and a vacancy (V): NV and N2V0. Laser action was first reported in 1985 by Rand and DeShazer in a N2V0 containing diamond.The NV centre is one of the most studied defects in diamond, due to the amount of applications harnessing the specific quantum properties of its negatively charged state.A variety of synthesis techniques were used to produce these centres in nitrogen containing diamond. Specifically, irradiation with electrons with the energy of several MeV in combination with high-temperature and high pressure annealing. Techniques to characterise samples include infrared and ultraviolet-visible absorption and photo luminescence spectroscopy.Up to 0.65 ppm1 of NV0 and 0.85 ppm of NV− were generated in synthetic diamond. Up to 2.2 ppm of N for diamond) 2V0 was generated in natural diamond and up to 0.5 ppm in synthetic diamond. These were consistent with the estimations for concentrations thought to be required for efficient pump absorption in a laser context, 0.6 and 0.9 ppm of NV− and N2V0. Luminescence lifetimes of 8±1 and 20±1 ns and peak emission cross-sections of(3.6 ± 0.1) · 10−17 and (1.7 ± 0.1) · 10−17 cm2 were measured for NV−and NV0, respectively; as well as 12±1 ns and (1.5±0.1) · 10−17 cm2 for N2V0.The gain spectrum was estimated using the emission cross section and absorption spectrum. The potential for positive net gain in a NV− containing sample, for realistic inversion levels of β = 0.3, was inferred from these calculations. Although laser operation may be possible with such samples,this has yet to be achieved, indicating that further study of the fabrication and spectroscopy is required. The best N2V0 sample showed less promise,requiring inversion levels of β > 0.5 to achieve positive net gain.Synthesis and Assessment of Laser Related Parameters in Colour Centre Containing Diamond. This thesis reports research on the fabrication and assessment of colour centre containing diamond. The advent of affordable single crystal synthetic diamond with low background absorption has motivated renewed interest in whether efficient colour centre lasers can be realised based on diamond. Two types of colour centres were investigated, composed of one or two nitrogen (N) atoms and a vacancy (V): NV and N2V0. Laser action was first reported in 1985 by Rand and DeShazer in a N2V0 containing diamond.The NV centre is one of the most studied defects in diamond, due to the amount of applications harnessing the specific quantum properties of its negatively charged state.A variety of synthesis techniques were used to produce these centres in nitrogen containing diamond. Specifically, irradiation with electrons with the energy of several MeV in combination with high-temperature and high pressure annealing. Techniques to characterise samples include infrared and ultraviolet-visible absorption and photo luminescence spectroscopy.Up to 0.65 ppm1 of NV0 and 0.85 ppm of NV− were generated in synthetic diamond. Up to 2.2 ppm of N for diamond) 2V0 was generated in natural diamond and up to 0.5 ppm in synthetic diamond. These were consistent with the estimations for concentrations thought to be required for efficient pump absorption in a laser context, 0.6 and 0.9 ppm of NV− and N2V0. Luminescence lifetimes of 8±1 and 20±1 ns and peak emission cross-sections of(3.6 ± 0.1) · 10−17 and (1.7 ± 0.1) · 10−17 cm2 were measured for NV−and NV0, respectively; as well as 12±1 ns and (1.5±0.1) · 10−17 cm2 for N2V0.The gain spectrum was estimated using the emission cross section and absorption spectrum. The potential for positive net gain in a NV− containing sample, for realistic inversion levels of β = 0.3, was inferred from these calculations. Although laser operation may be possible with such samples,this has yet to be achieved, indicating that further study of the fabrication and spectroscopy is required. The best N2V0 sample showed less promise,requiring inversion levels of β > 0.5 to achieve positive net gain
Anomaly detection and diagnostics in distribution networks using high-frequency PQ data
Get PDFFault analysis based on high-resolution data acquisition is growing in use as it offers a more complete picture of faults, which provides an opportunity to deal with failures more effectively. However, with increasing volumes of data being collected, it becomes impossible for engineers to interpret every fault instance. To solve this, this thesis proposes novel power network fault detection and diagnosis methods applied to continuous high-frequency Power Quality (PQ) data. These novel methods deliver online anomaly segmentation, fault classification, and automatic fault labelling. The work addresses the need for increasing levels of situational awareness in distribution networks and its corresponding data-related challenges.;The combination of these contributions can achieve automatic extraction of information from operational PQ data without excessive manual effort. This research uses simulated cases and operational data to validate the effectiveness of the contributions. The significance of this research is that it extracts critical information from continuous PQ data streams and automatically interprets the segmented signals, which reduces the demand for expert interpretation. In addition, it can operate through intensive monitoring at a single point on the network, which enhances the observability of the distribution network without installing excessive amounts of sensors.Fault analysis based on high-resolution data acquisition is growing in use as it offers a more complete picture of faults, which provides an opportunity to deal with failures more effectively. However, with increasing volumes of data being collected, it becomes impossible for engineers to interpret every fault instance. To solve this, this thesis proposes novel power network fault detection and diagnosis methods applied to continuous high-frequency Power Quality (PQ) data. These novel methods deliver online anomaly segmentation, fault classification, and automatic fault labelling. The work addresses the need for increasing levels of situational awareness in distribution networks and its corresponding data-related challenges.;The combination of these contributions can achieve automatic extraction of information from operational PQ data without excessive manual effort. This research uses simulated cases and operational data to validate the effectiveness of the contributions. The significance of this research is that it extracts critical information from continuous PQ data streams and automatically interprets the segmented signals, which reduces the demand for expert interpretation. In addition, it can operate through intensive monitoring at a single point on the network, which enhances the observability of the distribution network without installing excessive amounts of sensors
Design, analysis, and implementation of SRM drive for electric vehicles
Get PDFThis thesis was previously held under moratorium from 6/01/2021 to 10/01/2023Automobiles are regarded as a major source of greenhouse gases which cause a serious environmental problem, hence researchers are oriented towards transportation electrification. Different types of electrical machines are available for electric vehicle (EV) applications mainly; the permanent magnet synchronous motor, squirrel cage induction motor, and switched reluctance motor (SRM).The SRM can be a suitable candidate for this function. However, high torque ripple and relatively low power density have been the justification for its non-adoption in EVs. This thesis focuses on tackling these challenges to pave the way for the SRM to penetrate the electrified transportation sector. The thesis considers the machine, the converter, and the control when facing these adoption challenges.In simplistic terms, the current into and out of an SRM (at phase current turn-on and turn-off) can be expressed by =⁄. The objective is to force the current into and out of the machine as quickly as possible, that is, through maximizing the ⁄ term, thereby increasing the base-speed, whence output power. The inductive term L is related to the machine design and specifically low L is required (for V fixed) at only phase turn-on (higher L is required at the turn-off to maximize the machine co-energy).This task is accomplished by deploying rotor conducting screens which are basically non-magnetic electrically conducting materials such as aluminium and copper. The screens fill the rotor inter-polar air gaps. When the rotor rotates flux passes through the screen inducing voltage, whence current, which in turn generates flux opposing the original stator flux. As a result, the unaligned inductance is minimised which increases the conversion area and therefore more torque is developed. The material, thickness and shape of the screen are studied to select the optimal design that results in torque improvement. The effect on efficiency is highlighted, being an important factor in EVs. A procedure for calculating the effective value of unaligned inductance for screened motors using the flux tube method is presented. Finite element analysis results for different cases are given to validate the claims.Another torque improvement approach is to increase ⁄ (at both phase turn-on and turn-off) by effectively increasing the term V, in =⁄, which is a converter parameter. A brief review of available power converters is presented A new asymmetric neutral-point diode-clamped converter (NPC) with inherent voltage boosting is presented. The inbuilt NPC clamping capacitors are used for both voltage level clamping and also as dc rail voltage-boosting capacitors to increase motor output power. A detailed design procedure for sizing the boost-capacitors is outlined. Simulation along with experimental results validate the proposed converter.Different torque ripple (TR) minimization strategies including direct instantaneous torque control, torque sharing function, and current profiling using artificial neural networks are assessed using MATLAB/Simulink. The effect of voltage-boosting on minimizing TR is investigated. A new torque control function (TCF) which fully utilizes the dc link voltage is proposed. It will be substantiated that the new TCF dramatically extends the zero TR speed range, reduces switching losses, and is applicable to any SRM with overlapping phase torques.Automobiles are regarded as a major source of greenhouse gases which cause a serious environmental problem, hence researchers are oriented towards transportation electrification. Different types of electrical machines are available for electric vehicle (EV) applications mainly; the permanent magnet synchronous motor, squirrel cage induction motor, and switched reluctance motor (SRM).The SRM can be a suitable candidate for this function. However, high torque ripple and relatively low power density have been the justification for its non-adoption in EVs. This thesis focuses on tackling these challenges to pave the way for the SRM to penetrate the electrified transportation sector. The thesis considers the machine, the converter, and the control when facing these adoption challenges.In simplistic terms, the current into and out of an SRM (at phase current turn-on and turn-off) can be expressed by =⁄. The objective is to force the current into and out of the machine as quickly as possible, that is, through maximizing the ⁄ term, thereby increasing the base-speed, whence output power. The inductive term L is related to the machine design and specifically low L is required (for V fixed) at only phase turn-on (higher L is required at the turn-off to maximize the machine co-energy).This task is accomplished by deploying rotor conducting screens which are basically non-magnetic electrically conducting materials such as aluminium and copper. The screens fill the rotor inter-polar air gaps. When the rotor rotates flux passes through the screen inducing voltage, whence current, which in turn generates flux opposing the original stator flux. As a result, the unaligned inductance is minimised which increases the conversion area and therefore more torque is developed. The material, thickness and shape of the screen are studied to select the optimal design that results in torque improvement. The effect on efficiency is highlighted, being an important factor in EVs. A procedure for calculating the effective value of unaligned inductance for screened motors using the flux tube method is presented. Finite element analysis results for different cases are given to validate the claims.Another torque improvement approach is to increase ⁄ (at both phase turn-on and turn-off) by effectively increasing the term V, in =⁄, which is a converter parameter. A brief review of available power converters is presented A new asymmetric neutral-point diode-clamped converter (NPC) with inherent voltage boosting is presented. The inbuilt NPC clamping capacitors are used for both voltage level clamping and also as dc rail voltage-boosting capacitors to increase motor output power. A detailed design procedure for sizing the boost-capacitors is outlined. Simulation along with experimental results validate the proposed converter.Different torque ripple (TR) minimization strategies including direct instantaneous torque control, torque sharing function, and current profiling using artificial neural networks are assessed using MATLAB/Simulink. The effect of voltage-boosting on minimizing TR is investigated. A new torque control function (TCF) which fully utilizes the dc link voltage is proposed. It will be substantiated that the new TCF dramatically extends the zero TR speed range, reduces switching losses, and is applicable to any SRM with overlapping phase torques
Asteroid deflection and active debris removal methods with spaceborne lasers
Get PDFSeveral deflection methods have been proposed over the years to mitigate the risk of impact between an asteroid and the Earth. Most of the strategies proposed fall into two categories: impulsive and slow-push. Impulsive strategies are usually modelled with an instantaneous change of momentum given by, for example, a nuclear explosion (nuclear interceptor) or the hypervelocity impact of a spacecraft (kinetic impactor) with the asteroid. Slow-push methods, on the other hand, allow for a more controllable deflection manoeuvre by exerting a small continuous and controllable force on the asteroid over an extended period of time.;However, these methods generally rely on large propellant reserve required to rendezvous with the target and apply the deflection action. Laser ablation intends to resolve this difficulty by using the material the target is made of in order to generate the required thrust. When irradiating a target with sufficient laser intensity, an ablated mass can be ejected at high velocity,thus exerting a reaction force on the target that can be used to propel itself. By selecting the appropriate laser technology and tayloring the system parameters based on the target application, it is theoretically possible to build an efficient space-based laser system.;According to our calculations, the levels of performance of such a system (in term of thrust delivered per watt invested in the process) would be on the same order of magnitude as existing Ion Engines. By taking into account the propellant consumption and considering end-to-end detection scenarios in a statistically representative sample of asteroid detection scenarios, we show that laser ablation outperform other popular slow-push detection strategies as the gravity tractor and the Ion Beam Shepherd (IBS). Extrapolation of the laser ablation method is also proposed for the case where the target is a manmade piece of debris orbiting around the Earth instead of an asteroid.;In this case, pulsed lasers rather than CW lasers are considered in order to maximize the achievable laser intensity (TW/m2 can be achieved even with a few watts of average power and moderate optics) with the same available average power. The choice of a pulsed laser allows considering larger operation distances and ensures that each layer of material ablated during a laser pulse will be small enough that it will not become a new threatening piece of debris by itself. Comparison between predicted and experimental results are illustrated for several material typically encountered in space debris objects, such as metallic alloys and CFRP. The different results highlight the interest for the laser ablation method as a global strategy to manipulate both man made and natural objects and indicate its potential complementarity with other strategies such as the kinetic impactor method currently envisaged for asteroid detection.Several deflection methods have been proposed over the years to mitigate the risk of impact between an asteroid and the Earth. Most of the strategies proposed fall into two categories: impulsive and slow-push. Impulsive strategies are usually modelled with an instantaneous change of momentum given by, for example, a nuclear explosion (nuclear interceptor) or the hypervelocity impact of a spacecraft (kinetic impactor) with the asteroid. Slow-push methods, on the other hand, allow for a more controllable deflection manoeuvre by exerting a small continuous and controllable force on the asteroid over an extended period of time.;However, these methods generally rely on large propellant reserve required to rendezvous with the target and apply the deflection action. Laser ablation intends to resolve this difficulty by using the material the target is made of in order to generate the required thrust. When irradiating a target with sufficient laser intensity, an ablated mass can be ejected at high velocity,thus exerting a reaction force on the target that can be used to propel itself. By selecting the appropriate laser technology and tayloring the system parameters based on the target application, it is theoretically possible to build an efficient space-based laser system.;According to our calculations, the levels of performance of such a system (in term of thrust delivered per watt invested in the process) would be on the same order of magnitude as existing Ion Engines. By taking into account the propellant consumption and considering end-to-end detection scenarios in a statistically representative sample of asteroid detection scenarios, we show that laser ablation outperform other popular slow-push detection strategies as the gravity tractor and the Ion Beam Shepherd (IBS). Extrapolation of the laser ablation method is also proposed for the case where the target is a manmade piece of debris orbiting around the Earth instead of an asteroid.;In this case, pulsed lasers rather than CW lasers are considered in order to maximize the achievable laser intensity (TW/m2 can be achieved even with a few watts of average power and moderate optics) with the same available average power. The choice of a pulsed laser allows considering larger operation distances and ensures that each layer of material ablated during a laser pulse will be small enough that it will not become a new threatening piece of debris by itself. Comparison between predicted and experimental results are illustrated for several material typically encountered in space debris objects, such as metallic alloys and CFRP. The different results highlight the interest for the laser ablation method as a global strategy to manipulate both man made and natural objects and indicate its potential complementarity with other strategies such as the kinetic impactor method currently envisaged for asteroid detection
'No, you press yours first!' : sharing interaction and socially interacting with companions at tangible hybrid interactive museum exhibits
Get PDFHands-on tangible interactive exhibits are prevalent in science and technology centres, and are becoming increasingly common in traditional museums which conventionally exhibit historical artefacts and classical paintings. Interactive exhibits can enhance visitors' experiences, offering museums interesting alternative ways to engage visitors and portray narratives about their collections. How interactive technologies support or encourage companions in sharing interaction with other and engaging in social interaction with each other is of particular interest to this PhD research. In this doctoral thesis, I present three case studies that focus on companions sharing social interactions at tangible hybrid interactive museum exhibits, and subsequently question variations in how control is distributed between companions. The nature of this research draws on several disciplines and as such is multi-disciplinary, in the field it draws upon, how it was conducted and in the research contributions.;Case study 1, Painting Patterns for Nature, focused on the social activities of companions before and after their interaction with the exhibit, and examined how the exhibit supported these social activities by the presence of several portable tangible controllers which are accessible (but not interactive) outside of core interaction. Case study 2, Glen Douglas and Fire Fighter, emphasised companions' social interaction stemming from an interplay between different controllers and reliance upon companions. Case study 3, Razzle Dazzle highlighted the ways in which companions share decisions before interacting, questioning equality of participation between companions interacting with the exhibit.;The research offers a unique contribution within the fields of tangible interaction and museum studies investigating interactive exhibits by conducting empirical research through a design lens. In conducting the research, a contribution has been made in developing a definition for 'tangible hybrid interactive museum exhibits' (THIMEs). Furthermore, the research makes a contribution by describing visitors' social interactions with their companions and their behaviours sharing the interaction at THIMEs. The research has identified strategies for distributed controller between companions physically (providing multiple controllers), functionally (in what the controllers do) and temporally (when people use controllers) at interactive museum exhibits which considers how to support visitors social interactions with their companions and how to share the interaction with the exhibit.Hands-on tangible interactive exhibits are prevalent in science and technology centres, and are becoming increasingly common in traditional museums which conventionally exhibit historical artefacts and classical paintings. Interactive exhibits can enhance visitors' experiences, offering museums interesting alternative ways to engage visitors and portray narratives about their collections. How interactive technologies support or encourage companions in sharing interaction with other and engaging in social interaction with each other is of particular interest to this PhD research. In this doctoral thesis, I present three case studies that focus on companions sharing social interactions at tangible hybrid interactive museum exhibits, and subsequently question variations in how control is distributed between companions. The nature of this research draws on several disciplines and as such is multi-disciplinary, in the field it draws upon, how it was conducted and in the research contributions.;Case study 1, Painting Patterns for Nature, focused on the social activities of companions before and after their interaction with the exhibit, and examined how the exhibit supported these social activities by the presence of several portable tangible controllers which are accessible (but not interactive) outside of core interaction. Case study 2, Glen Douglas and Fire Fighter, emphasised companions' social interaction stemming from an interplay between different controllers and reliance upon companions. Case study 3, Razzle Dazzle highlighted the ways in which companions share decisions before interacting, questioning equality of participation between companions interacting with the exhibit.;The research offers a unique contribution within the fields of tangible interaction and museum studies investigating interactive exhibits by conducting empirical research through a design lens. In conducting the research, a contribution has been made in developing a definition for 'tangible hybrid interactive museum exhibits' (THIMEs). Furthermore, the research makes a contribution by describing visitors' social interactions with their companions and their behaviours sharing the interaction at THIMEs. The research has identified strategies for distributed controller between companions physically (providing multiple controllers), functionally (in what the controllers do) and temporally (when people use controllers) at interactive museum exhibits which considers how to support visitors social interactions with their companions and how to share the interaction with the exhibit
Applications of phytase-mediated phosphate biomineralizaton for the remediation of uranium mine tailings
Get PDFThe mining of elements such as copper, gold, rare earths, and uranium is an essential part of modern society, providing the raw materials for a wide range of applications in technology, industry, medicine, and energy supply. However, the extraction of these and other resources may cause harm to human and environmental health through the mobilisation of contaminants, including naturally occurring radionuclides.;Phosphate mineral phases have been researched as a method of immobilising contaminants including lead, radium, and uranium as natural analogues demonstrate that these metals can be stably incorporated into phosphate minerals over geological timescales and across varying pH, redox, and chemical conditions. Previous research has indicated that phosphate biominerals (produced via the microbial hydrolysis of organic phosphate compounds) may be more sustainable and more efficient at immobilising contaminants than sourcing phosphate minerals from mined phosphate rock.;This PhD has investigated the applications of phytate - a common plant waste product - as a phosphate donor. Experiments have been performed with different microorganisms (Aspergillus niger and Blastobotrys adeninivorans) and purified phytate-degrading enzymes in batch solution and solid matrices to understand the opportunities and challenges associated with using phytate as a precursor for phosphate minerals.;Both microorganisms tested were able to grow and hydrolyse phytate at environmentally relevant temperatures, an essential property for in situ remediation strategies, and both were able to use the low cost carbon source starch for growth. Experiments within solid substrates established that phosphate biomineralization occurs readily in the presence of a sandy matrix, but that challenges related to the interactions between phytic acid and mineral phases such as kaolinite need to be addressed when considering more complex solid media.;Furthermore, it is established that phosphate phases that are insoluble under acidic conditions are suitable targets for phosphate biomineralization - this is demonstrated for lanthanum and lead phosphate, and hypothesised to also be true for uranium - which makes this process a highly promising method for the treatment of acidic, uranium-contaminated mine wastes.The mining of elements such as copper, gold, rare earths, and uranium is an essential part of modern society, providing the raw materials for a wide range of applications in technology, industry, medicine, and energy supply. However, the extraction of these and other resources may cause harm to human and environmental health through the mobilisation of contaminants, including naturally occurring radionuclides.;Phosphate mineral phases have been researched as a method of immobilising contaminants including lead, radium, and uranium as natural analogues demonstrate that these metals can be stably incorporated into phosphate minerals over geological timescales and across varying pH, redox, and chemical conditions. Previous research has indicated that phosphate biominerals (produced via the microbial hydrolysis of organic phosphate compounds) may be more sustainable and more efficient at immobilising contaminants than sourcing phosphate minerals from mined phosphate rock.;This PhD has investigated the applications of phytate - a common plant waste product - as a phosphate donor. Experiments have been performed with different microorganisms (Aspergillus niger and Blastobotrys adeninivorans) and purified phytate-degrading enzymes in batch solution and solid matrices to understand the opportunities and challenges associated with using phytate as a precursor for phosphate minerals.;Both microorganisms tested were able to grow and hydrolyse phytate at environmentally relevant temperatures, an essential property for in situ remediation strategies, and both were able to use the low cost carbon source starch for growth. Experiments within solid substrates established that phosphate biomineralization occurs readily in the presence of a sandy matrix, but that challenges related to the interactions between phytic acid and mineral phases such as kaolinite need to be addressed when considering more complex solid media.;Furthermore, it is established that phosphate phases that are insoluble under acidic conditions are suitable targets for phosphate biomineralization - this is demonstrated for lanthanum and lead phosphate, and hypothesised to also be true for uranium - which makes this process a highly promising method for the treatment of acidic, uranium-contaminated mine wastes
Image-based 3-D reconstruction of constrained environments
Get PDFNuclear power plays a important role to the United Kingdom electricity generation infrastructure, providing a reliable baseload of low carbon electricity. The Advanced Gas-cooled Reactor (AGR) design makes up approximately 50% of the existing fleet, however, many of the operating reactors have exceeding their original design lifetimes.To ensure safe reactor operation, engineers perform periodic in-core visual inspections of reactor components to monitor the structural health of the core as it ages. However, current inspection mechanisms deployed provide limited structural information about the fuel channel or defects.;This thesis investigates the suitability of image-based 3-D reconstruction techniques to acquire 3-D structural geometry to enable improved diagnostic and prognostic abilities for inspection engineers. The application of image-based 3-D reconstruction to in-core inspection footage highlights significant challenges, most predominantly that the image saliency proves insuffcient for general reconstruction frameworks. The contribution of the thesis is threefold. Firstly, a novel semi-dense matching scheme which exploits sparse and dense image correspondence in combination with a novel intra-image region strength approach to improve the stability of the correspondence between images.;This results in a percentage increase of 138.53% of correct feature matches over similar state-of-the-art image matching paradigms. Secondly, a bespoke incremental Structure-from-Motion (SfM) framework called the Constrained Homogeneous SfM (CH-SfM) which is able to derive structure from deficient feature spaces and constrained environments. Thirdly, the application of the CH-SfM framework to remote visual inspection footage gathered within AGR fuel channels, outperforming other state-of-the-art reconstruction approaches and extracting representative 3-D structural geometry of orientational scans and fully circumferential reconstructions.;This is demonstrated on in-core and laboratory footage, achieving an approximate 3-D point density of 2.785 - 23.8025NX/cm² for real in-core inspection footage and high quality laboratory footage respectively. The demonstrated novelties have applicability to other constrained or feature-poor environments, with future work looking to producing fully dense, photo-realistic 3-D reconstructions.Nuclear power plays a important role to the United Kingdom electricity generation infrastructure, providing a reliable baseload of low carbon electricity. The Advanced Gas-cooled Reactor (AGR) design makes up approximately 50% of the existing fleet, however, many of the operating reactors have exceeding their original design lifetimes.To ensure safe reactor operation, engineers perform periodic in-core visual inspections of reactor components to monitor the structural health of the core as it ages. However, current inspection mechanisms deployed provide limited structural information about the fuel channel or defects.;This thesis investigates the suitability of image-based 3-D reconstruction techniques to acquire 3-D structural geometry to enable improved diagnostic and prognostic abilities for inspection engineers. The application of image-based 3-D reconstruction to in-core inspection footage highlights significant challenges, most predominantly that the image saliency proves insuffcient for general reconstruction frameworks. The contribution of the thesis is threefold. Firstly, a novel semi-dense matching scheme which exploits sparse and dense image correspondence in combination with a novel intra-image region strength approach to improve the stability of the correspondence between images.;This results in a percentage increase of 138.53% of correct feature matches over similar state-of-the-art image matching paradigms. Secondly, a bespoke incremental Structure-from-Motion (SfM) framework called the Constrained Homogeneous SfM (CH-SfM) which is able to derive structure from deficient feature spaces and constrained environments. Thirdly, the application of the CH-SfM framework to remote visual inspection footage gathered within AGR fuel channels, outperforming other state-of-the-art reconstruction approaches and extracting representative 3-D structural geometry of orientational scans and fully circumferential reconstructions.;This is demonstrated on in-core and laboratory footage, achieving an approximate 3-D point density of 2.785 - 23.8025NX/cm² for real in-core inspection footage and high quality laboratory footage respectively. The demonstrated novelties have applicability to other constrained or feature-poor environments, with future work looking to producing fully dense, photo-realistic 3-D reconstructions
Plant responses to toxic elements and salt stress of contamination from the petroleum industry
Get PDFBackground & Aims: Several studies have sought to explore the toxicity of heavy metals and high salinity from wastewaters, especially produced water (PW) from the petroleum industry, both in laboratory and field trials; however, there is little information available regarding F. rubra, C. longus, P. australis, and T. pratense species. This thesis investigated these plant species' ability to be used as an alternative method of removing trace elements and salt ions from contaminated soil and water emanating from produced water.;Methodology: Several methods were used to investigate trace elements, in particular, strontium and salt ions. Analysis included the physicochemical characteristics of both soil and water samples. Soil analyses focused on sequential extraction and batch adsorption methods while water samples were used to analyze the value of trace elements and nutrient concentrations. In addition, biomass harvesting and plant material digestion were used to evaluate the phytoremediation technique, which played an essential role in this thesis to explain exposure-response with metal toxicity and high salinity. This work performed investigations mainly using Inductively Coupled Plasma- Optical Emission Spectrometry (ICP-OES) to determine the types and amounts of trace elements.;Results: Freundlich and Langmuir models describe strontium sorption in South Lanarkshire farm in Glasgow, UK, soils. Apparent equilibrium was reached within 24 hours. The interesting thing about the efficiency of F. rubra and T. pratense is their ability to grow and respond quickly. It seems possible that these plants will accumulate strontium composition in their tissues. On the other hand, stressful environments with high salinity of contaminated produced water and similar salinity solutions generated the most concentrated element. However, the results of this study suggested that C. longus and P. australis can absorb and eliminate excess salt ions from their leaves both in produced water and solutions of similar salinity.;Conclusions: The main focus was two-fold: soil and water contamination. Soil was identified as acidic, sodic, slightly silty to coarse sand with low organic matter content. In sorption, Sr ions prefer to associate within residual and carbonate fractions, rather than other fractions in this soil. The best efficiency of retention time for adsorption was more than 24h, which was employed to fit both of the Langmuir and Freundlich equilibria models. Germination tests showed that F. rubra emerged quickly at low concentrations of both calcium and strontium ions; T. pratense responded similarly. The upper parts of T. pratense showed a greater translocation factor of Sr ions than F. rubra. However, in F. rubra, made chlorophyll content adjustments in response to elevated concentrations of strontium in the soils. Therefore, both plants can be considered as accumulator species. On the other hand, species-specific responses to different levels of salinity concentrations were also identified. T. pratense was a more sensitive species than F. rubra in high salinity. In contrast, both C. longus and P. australis were suitable to grow in the high salinity of produced water effluents, illustrating their potential to remove salts in produced waters via salt exclusion.;The results of this study show responses to salt stress and changes in productivity (including death). These findings enhance our understanding of F. rubra, C. longus, P. australis, and T. pratense and their potential uses in mitigation to high salt ions from produced water. Future studies of other potentially useful plant species in this field may also identify important technical difficulties at the genetic or molecular level in salt tolerance of halophyte species.Background & Aims: Several studies have sought to explore the toxicity of heavy metals and high salinity from wastewaters, especially produced water (PW) from the petroleum industry, both in laboratory and field trials; however, there is little information available regarding F. rubra, C. longus, P. australis, and T. pratense species. This thesis investigated these plant species' ability to be used as an alternative method of removing trace elements and salt ions from contaminated soil and water emanating from produced water.;Methodology: Several methods were used to investigate trace elements, in particular, strontium and salt ions. Analysis included the physicochemical characteristics of both soil and water samples. Soil analyses focused on sequential extraction and batch adsorption methods while water samples were used to analyze the value of trace elements and nutrient concentrations. In addition, biomass harvesting and plant material digestion were used to evaluate the phytoremediation technique, which played an essential role in this thesis to explain exposure-response with metal toxicity and high salinity. This work performed investigations mainly using Inductively Coupled Plasma- Optical Emission Spectrometry (ICP-OES) to determine the types and amounts of trace elements.;Results: Freundlich and Langmuir models describe strontium sorption in South Lanarkshire farm in Glasgow, UK, soils. Apparent equilibrium was reached within 24 hours. The interesting thing about the efficiency of F. rubra and T. pratense is their ability to grow and respond quickly. It seems possible that these plants will accumulate strontium composition in their tissues. On the other hand, stressful environments with high salinity of contaminated produced water and similar salinity solutions generated the most concentrated element. However, the results of this study suggested that C. longus and P. australis can absorb and eliminate excess salt ions from their leaves both in produced water and solutions of similar salinity.;Conclusions: The main focus was two-fold: soil and water contamination. Soil was identified as acidic, sodic, slightly silty to coarse sand with low organic matter content. In sorption, Sr ions prefer to associate within residual and carbonate fractions, rather than other fractions in this soil. The best efficiency of retention time for adsorption was more than 24h, which was employed to fit both of the Langmuir and Freundlich equilibria models. Germination tests showed that F. rubra emerged quickly at low concentrations of both calcium and strontium ions; T. pratense responded similarly. The upper parts of T. pratense showed a greater translocation factor of Sr ions than F. rubra. However, in F. rubra, made chlorophyll content adjustments in response to elevated concentrations of strontium in the soils. Therefore, both plants can be considered as accumulator species. On the other hand, species-specific responses to different levels of salinity concentrations were also identified. T. pratense was a more sensitive species than F. rubra in high salinity. In contrast, both C. longus and P. australis were suitable to grow in the high salinity of produced water effluents, illustrating their potential to remove salts in produced waters via salt exclusion.;The results of this study show responses to salt stress and changes in productivity (including death). These findings enhance our understanding of F. rubra, C. longus, P. australis, and T. pratense and their potential uses in mitigation to high salt ions from produced water. Future studies of other potentially useful plant species in this field may also identify important technical difficulties at the genetic or molecular level in salt tolerance of halophyte species
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