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Technology development for studying information flow in biological neural networks
No full textThis thesis mainly focuses on the technology development of electrophysiological recording devices and optical stimulation devices for studying the information. How along the neural network in the brain. Specifically, it concentrates on the penetrating microelectrode array and the micro-sized light emitting diode (µLED) coupled glass optrode array for electrophysiological recordings and optogenetic applications respectively. Since a neuron is an electrically excitable cell which is the basic building block of human brain, its electrical activities (spikes) are responsible for functions such as vision, speech, hearing, learning and memory. Therefore, neural recording is one of the efficient ways to understand the relationship between neural activities and brain functions. Devices like microelectrode arrays have been developed to extract the spikes from brain tissue to a read-out electronic system for analysing. In order to identify and sort out spikes generated by a single neuron, the electrode density of the penetrating microelectrode array in this project is about 350 electrodes/mm2. With the 200-µm long needles, the microelectrode array can penetrate the outer layer of sliced brain tissue and contact to the healthy cells underneath. Low impedance electrodes (450 kΩ at 1 kHz) makes the device able to record the small (hundreds of microvolts) extra cellular signals. On the other hand, neuronal modulation is another strategy to investigate the information flows in neural networks. Compared to the electrical stimulation, optogenetics provides an optical modulation to the neurons with high selectivity and spatio temporal resolution. In this project, a µLED array is designed and fabricated as a light source for a coupled optrode array. In terms of the design, the optrode array is able to provide an optical irradiance of about 80 mW/mm2 at the needle tip which is enough to optically excite up to 5500 neurons in the sub-cortical structures. Moreover, the optrode array can provide both deep brain stimulation and superficial illumination of the brain cortex. Besides, multi-site stimulation could also be achieved by lighting up one or more LED elements. During the stimulation, the temperature change can be kept below 1 °C which will not affect neuronal signalling in the cortex.This thesis mainly focuses on the technology development of electrophysiological recording devices and optical stimulation devices for studying the information. How along the neural network in the brain. Specifically, it concentrates on the penetrating microelectrode array and the micro-sized light emitting diode (µLED) coupled glass optrode array for electrophysiological recordings and optogenetic applications respectively. Since a neuron is an electrically excitable cell which is the basic building block of human brain, its electrical activities (spikes) are responsible for functions such as vision, speech, hearing, learning and memory. Therefore, neural recording is one of the efficient ways to understand the relationship between neural activities and brain functions. Devices like microelectrode arrays have been developed to extract the spikes from brain tissue to a read-out electronic system for analysing. In order to identify and sort out spikes generated by a single neuron, the electrode density of the penetrating microelectrode array in this project is about 350 electrodes/mm2. With the 200-µm long needles, the microelectrode array can penetrate the outer layer of sliced brain tissue and contact to the healthy cells underneath. Low impedance electrodes (450 kΩ at 1 kHz) makes the device able to record the small (hundreds of microvolts) extra cellular signals. On the other hand, neuronal modulation is another strategy to investigate the information flows in neural networks. Compared to the electrical stimulation, optogenetics provides an optical modulation to the neurons with high selectivity and spatio temporal resolution. In this project, a µLED array is designed and fabricated as a light source for a coupled optrode array. In terms of the design, the optrode array is able to provide an optical irradiance of about 80 mW/mm2 at the needle tip which is enough to optically excite up to 5500 neurons in the sub-cortical structures. Moreover, the optrode array can provide both deep brain stimulation and superficial illumination of the brain cortex. Besides, multi-site stimulation could also be achieved by lighting up one or more LED elements. During the stimulation, the temperature change can be kept below 1 °C which will not affect neuronal signalling in the cortex
Business processes reconfigurability in dynamic operating environments
Get PDFThe need for rapid changes to business processes in an organisation has been amplified by factors such as globalisation, competition and an increasingly complex consumer market, this requires a re-evaluation of the current approaches to business process change. This research investigates the concept of Business Process Reconfiguration (BPRC) as a platform that would enable rapid, frequent and transformational business process changes whilst reducing the level of disruption to the organisation.A review of the literature on business process change management from the lens of dynamic capability and agility is contained herein. Five themes of sensing, responding, reconfiguring, speed and disruption emerged as critical to enabling reconfigurability in business process management, from which five propositions on the concept of business process reconfiguration were developed. A classic experimental research method was used to investigate and test the validity of these propositions.In developing the notion of business process reconfiguration, three distinct contributions are made. First, this PhD contributes by identifying the gaps in the business process management literature from the context of dynamic capabilities and agility. Second, using the concept of predictability and modularity, this research presents an agenda for developing a more robust knowledge of business process reconfiguration, which was subsequently tested and validated. Third, by introducing business process reconfiguration (BPRC); this research contributes to existing processual theory and extends knowledge of business processes. Therefore, the significant contribution to knowledge of this thesis is the influence of predictability and modularity on reconfigurability of business processes in a dynamic operating environment. Together the three factors of predictability, modularity and reconfigurability have created a platform for more scholastic discussion on the topic of business process change in a dynamic operating environment.The need for rapid changes to business processes in an organisation has been amplified by factors such as globalisation, competition and an increasingly complex consumer market, this requires a re-evaluation of the current approaches to business process change. This research investigates the concept of Business Process Reconfiguration (BPRC) as a platform that would enable rapid, frequent and transformational business process changes whilst reducing the level of disruption to the organisation.A review of the literature on business process change management from the lens of dynamic capability and agility is contained herein. Five themes of sensing, responding, reconfiguring, speed and disruption emerged as critical to enabling reconfigurability in business process management, from which five propositions on the concept of business process reconfiguration were developed. A classic experimental research method was used to investigate and test the validity of these propositions.In developing the notion of business process reconfiguration, three distinct contributions are made. First, this PhD contributes by identifying the gaps in the business process management literature from the context of dynamic capabilities and agility. Second, using the concept of predictability and modularity, this research presents an agenda for developing a more robust knowledge of business process reconfiguration, which was subsequently tested and validated. Third, by introducing business process reconfiguration (BPRC); this research contributes to existing processual theory and extends knowledge of business processes. Therefore, the significant contribution to knowledge of this thesis is the influence of predictability and modularity on reconfigurability of business processes in a dynamic operating environment. Together the three factors of predictability, modularity and reconfigurability have created a platform for more scholastic discussion on the topic of business process change in a dynamic operating environment
Computerised automated feedback systems for sit-to-stand training
Get PDFThe ability to stand-up from sitting declines with age. Manual rehabilitation services are being challenged by the increasingly older frailer population with patients are receiving sub-optimal access to professional therapy. Technology may offer solutions. Following a review of the literature as well as clinical observations, user surveys and interviews, an initial design specification for a computerised automated feedback system for sit-to-stand training was generated. A virtual reality system with audio-visual feedback on performance was subsequently developed. This prototype used an inertial sensor and a portable force plate to provide raw movement data. A Kalman-filter based sensor-fusion algorithm was designed to tackle signal-processing issues. A sit-to-stand detection algorithm, using a finite state machine, then analysed and detected crucial movement events, before a fuzzy-logic decision-making algorithm generated the final audio-visual feedback presented to users in a user-friendly manner to augment their sit-to-stand training. A phase two pilot randomised controlled trial was conducted at a geriatric rehabilitation unit. All participants underwent functional assessments and had their daily sit-to-stand and step counts recorded forty-eight hours before the study began and at the end of the trial. The experimental group received the technology augmented sit-to-stand training for four weeks, three sessions a week, while the control group received standard physiotherapy. Sixteen participants completed the trial, eight in each group. An increase in daily sit-to-stand movements and improved scores on clinical measures of mobility were all statistically significantly (p<0.05) better than the control group. Participants and therapists found the system motivating, intuitive and enjoyable. The computerised biofeedback was considered by users to be superior to standard therapy for providing motivation and engagement with rehabilitation. A novel, technology-based, feedback system, designed collaboratively with end-users to enhance sit-to-stand training in older adults, was found to be acceptable and feasible for clinical environments, suggesting great potential for future geriatric rehabilitation.The ability to stand-up from sitting declines with age. Manual rehabilitation services are being challenged by the increasingly older frailer population with patients are receiving sub-optimal access to professional therapy. Technology may offer solutions. Following a review of the literature as well as clinical observations, user surveys and interviews, an initial design specification for a computerised automated feedback system for sit-to-stand training was generated. A virtual reality system with audio-visual feedback on performance was subsequently developed. This prototype used an inertial sensor and a portable force plate to provide raw movement data. A Kalman-filter based sensor-fusion algorithm was designed to tackle signal-processing issues. A sit-to-stand detection algorithm, using a finite state machine, then analysed and detected crucial movement events, before a fuzzy-logic decision-making algorithm generated the final audio-visual feedback presented to users in a user-friendly manner to augment their sit-to-stand training. A phase two pilot randomised controlled trial was conducted at a geriatric rehabilitation unit. All participants underwent functional assessments and had their daily sit-to-stand and step counts recorded forty-eight hours before the study began and at the end of the trial. The experimental group received the technology augmented sit-to-stand training for four weeks, three sessions a week, while the control group received standard physiotherapy. Sixteen participants completed the trial, eight in each group. An increase in daily sit-to-stand movements and improved scores on clinical measures of mobility were all statistically significantly (p<0.05) better than the control group. Participants and therapists found the system motivating, intuitive and enjoyable. The computerised biofeedback was considered by users to be superior to standard therapy for providing motivation and engagement with rehabilitation. A novel, technology-based, feedback system, designed collaboratively with end-users to enhance sit-to-stand training in older adults, was found to be acceptable and feasible for clinical environments, suggesting great potential for future geriatric rehabilitation
Imaging of breast cancer using SERS and SESORS
Get PDFThis thesis was previously held under moratorium from 27/11/19 to 27/11/21Breast cancer is one of the leading causes of oncologic mortality and morbidity among women worldwide. It is estimated that every 10 minutes one person is diagnosed with the disease in the UK, while 1 in 8 women will develop breast cancer at some point in their lives. Although different techniques, for the characterisation of cancer phenotype, exist there are still limitations as these approaches are destructive, require processed/fixed samples and are not suitable for 3D tumour samples and in vivo models. Surface enhanced Raman spectroscopy (SERS) overcomes these limitations as a non-destructive bioanalytical method that offers high specificity, selectivity and multiplex capacities, in comparison to conventional imaging techniques.The main aim of this research is to create a platform for targeting, detecting and tracking the intracellular distribution of estrogen receptor alpha (ERα) biomarker in breast cancer, using SERS combined with antibody functionalised gold nanoparticles (AuNPs). Specifically, the anti-ERα antibody functionalised AuNPs (ERα-AuNPs) were conjugated with 1,2-bis(4-pyridyl)ethylene (BPE) Raman reporter that enabled the spatial and temporal understanding of where ERα was located at a single cell level. The nanotags showed excellent biocompatibility with no cellular toxicity. 3D SERS cell mapping, under different endocytosis inhibition conditions, confirmed that ERα-AuNPs were using a temperature-dependent way for their uptake. Additionally, dynamin and membrane ERα were shown to be responsible, at least in a part, for the nanotags’ uptake in MCF-7 cells. Therefore, SERS provided an excellent biological insight of ERα-AuNPs uptake by generating 3D images of the entire cell volume, without the need for destructive, time consuming and expensive imaging methods such as transition electron microscopy (TEM). 2D and 3D SERS also confirmed the strong targeting effect of ERα-AuNPs against ERα since a higher SERS signal and nanotag accumulation were observed in MCF-7 cells (ERα+) compared to SKBR-3 (ERα-) breast cancer cells. SERS was also used for investigating the efficacy of fulvestrant, the first-in-class approved selective estrogen receptor degrader (SERD). The results confirmed that ERα-AuNPs can be used as a tool for identifying and characterising different breast cancer cells, based on ERα expression, and informing about SERDs activity in breast cancer.SERS also provided an excellent bioanalytical tool for the characterisation of breast cancer phenotype and the assessment of fulvestrant activity in a 3D environment using live MCF-7 spheroids formed in a microfluidic device. The results confirmed the great penetration capabilities and strong targeting effect of ERα-AuNPs towards ERα, compared to nonspecific anti-HER2 antibody functionalised AuNPs (HER2-AuNPs). Additionally, fulvestrant activity was found to have a lower therapeutic effect the 3D MCF-7 spheroids in comparison to the 2D cell cultures demonstrating that 2D and 3D tumour models had different biological and architectural behaviours that affected their sensitivity to fulvestrant. Therefore, SERS and microfluidics were used as a powerful analytical tool, that effectively bridged the gap between the 2D monolayer cultures and animal models, for breast cancer cells characterisation and investigation of fulvestrant efficacy. Finally, this thesis investigated the potentials for detection of ERα ex vivo and in vivo using a handheld SORS instrument with back scattering optics. SESORS allowed the detection of ERα-AuNP nanotags through tissue barriers of up to 15 mm thickness. Most importantly, it was possible to detect and track ex vivo the ERα-AuNPs incubated in live breast tumour spheroids buried at 10 mm porcine tissue. The in vivo work indicated that SESORS was detecting scattered photon from areas deeper than the breast cancer tumour, mainly due to the fixed optical arrangements of the spectrometer. Nevertheless, a higher signal was detected ex vivo in breast tumours in comparison to the liver after their removal from sacrificed animals, suggesting the strong targeting effect of ERα-AuNP nanotags to the tumour site. This thesis highlights the performance and capabilities of SERS, microfluidics and SESORS on detecting, targeting and tracking ERα and opens up exciting opportunities for using these techniques as non-destructive and sensitive tools for improved biomedical imaging in a clinical environment.Breast cancer is one of the leading causes of oncologic mortality and morbidity among women worldwide. It is estimated that every 10 minutes one person is diagnosed with the disease in the UK, while 1 in 8 women will develop breast cancer at some point in their lives. Although different techniques, for the characterisation of cancer phenotype, exist there are still limitations as these approaches are destructive, require processed/fixed samples and are not suitable for 3D tumour samples and in vivo models. Surface enhanced Raman spectroscopy (SERS) overcomes these limitations as a non-destructive bioanalytical method that offers high specificity, selectivity and multiplex capacities, in comparison to conventional imaging techniques.The main aim of this research is to create a platform for targeting, detecting and tracking the intracellular distribution of estrogen receptor alpha (ERα) biomarker in breast cancer, using SERS combined with antibody functionalised gold nanoparticles (AuNPs). Specifically, the anti-ERα antibody functionalised AuNPs (ERα-AuNPs) were conjugated with 1,2-bis(4-pyridyl)ethylene (BPE) Raman reporter that enabled the spatial and temporal understanding of where ERα was located at a single cell level. The nanotags showed excellent biocompatibility with no cellular toxicity. 3D SERS cell mapping, under different endocytosis inhibition conditions, confirmed that ERα-AuNPs were using a temperature-dependent way for their uptake. Additionally, dynamin and membrane ERα were shown to be responsible, at least in a part, for the nanotags’ uptake in MCF-7 cells. Therefore, SERS provided an excellent biological insight of ERα-AuNPs uptake by generating 3D images of the entire cell volume, without the need for destructive, time consuming and expensive imaging methods such as transition electron microscopy (TEM). 2D and 3D SERS also confirmed the strong targeting effect of ERα-AuNPs against ERα since a higher SERS signal and nanotag accumulation were observed in MCF-7 cells (ERα+) compared to SKBR-3 (ERα-) breast cancer cells. SERS was also used for investigating the efficacy of fulvestrant, the first-in-class approved selective estrogen receptor degrader (SERD). The results confirmed that ERα-AuNPs can be used as a tool for identifying and characterising different breast cancer cells, based on ERα expression, and informing about SERDs activity in breast cancer.SERS also provided an excellent bioanalytical tool for the characterisation of breast cancer phenotype and the assessment of fulvestrant activity in a 3D environment using live MCF-7 spheroids formed in a microfluidic device. The results confirmed the great penetration capabilities and strong targeting effect of ERα-AuNPs towards ERα, compared to nonspecific anti-HER2 antibody functionalised AuNPs (HER2-AuNPs). Additionally, fulvestrant activity was found to have a lower therapeutic effect the 3D MCF-7 spheroids in comparison to the 2D cell cultures demonstrating that 2D and 3D tumour models had different biological and architectural behaviours that affected their sensitivity to fulvestrant. Therefore, SERS and microfluidics were used as a powerful analytical tool, that effectively bridged the gap between the 2D monolayer cultures and animal models, for breast cancer cells characterisation and investigation of fulvestrant efficacy. Finally, this thesis investigated the potentials for detection of ERα ex vivo and in vivo using a handheld SORS instrument with back scattering optics. SESORS allowed the detection of ERα-AuNP nanotags through tissue barriers of up to 15 mm thickness. Most importantly, it was possible to detect and track ex vivo the ERα-AuNPs incubated in live breast tumour spheroids buried at 10 mm porcine tissue. The in vivo work indicated that SESORS was detecting scattered photon from areas deeper than the breast cancer tumour, mainly due to the fixed optical arrangements of the spectrometer. Nevertheless, a higher signal was detected ex vivo in breast tumours in comparison to the liver after their removal from sacrificed animals, suggesting the strong targeting effect of ERα-AuNP nanotags to the tumour site. This thesis highlights the performance and capabilities of SERS, microfluidics and SESORS on detecting, targeting and tracking ERα and opens up exciting opportunities for using these techniques as non-destructive and sensitive tools for improved biomedical imaging in a clinical environment
Design, control and error analysis of a fast tool positioning system for ultra-precision machining of freeform surfaces
Get PDFThis thesis was previously held under moratorium from 03/12/19 to 03/12/21Freeform surfaces are widely found in advanced imaging and illumination systems, orthopaedic implants, high-power beam shaping applications, and other high-end scientific instruments. They give the designers greater ability to cope with the performance limitations commonly encountered in simple-shape designs. However, the stringent requirements for surface roughness and form accuracy of freeform components pose significant challenges for current machining techniques—especially in the optical and display market where large surfaces with tens of thousands of micro features are to be machined. Such highly wavy surfaces require the machine tool cutter to move rapidly while keeping following errors small. Manufacturing efficiency has been a bottleneck in these applications. The rapidly changing cutting forces and inertial forces also contribute a great deal to the machining errors.The difficulty in maintaining good surface quality under conditions of high operational frequency suggests the need for an error analysis approach that can predict the dynamic errors. The machining requirements also impose great challenges on machine tool design and the control process. There has been a knowledge gap on how the mechanical structural design affects the achievable positioning stability. The goal of this study was to develop a tool positioning system capable of delivering fast motion with the required positioning accuracy and stiffness for ultra-precision freeform manufacturing. This goal is achieved through deterministic structural design, detailed error analysis, and novel control algorithms.Firstly, a novel stiff-support design was proposed to eliminate the structural and bearing compliances in the structural loop. To implement the concept, a fast positioning device was developed based on a new-type flat voice coil motor. Flexure bearing, magnet track, and motor coil parameters were designed and calculated in detail. A high-performance digital controller and a power amplifier were also built to meet the servo rate requirement of the closed-loop system. A thorough understanding was established of how signals propagated within the control system, which is fundamentally important in determining the loop performance of high-speed control.A systematic error analysis approach based on a detailed model of the system was proposed and verified for the first time that could reveal how disturbances contribute to the tool positioning errors. Each source of disturbance was treated as a stochastic process, and these disturbances were synthesised in the frequency domain. The differences between following error and real positioning error were discussed and clarified. The predicted spectrum of following errors agreed with the measured spectrum across the frequency range. It is found that the following errors read from the control software underestimated the real positioning errors at low frequencies and overestimated them at high frequencies. The error analysis approach thus successfully revealed the real tool positioning errors that are mingled with sensor noise.Approaches to suppress disturbances were discussed from the perspectives of both system design and control. A deterministic controller design approach was developed to preclude the uncertainty associated with controller tuning, resulting in a control law that can minimize positioning errors. The influences of mechanical parameters such as mass, damping, and stiffness were investigated within the closed-loop framework. Under a given disturbance condition, the optimal bearing stiffness and optimal damping coefficients were found. Experimental positioning tests showed that a larger moving mass helped to combat all disturbances but sensor noise.Because of power limits, the inertia of the fast tool positioning system could not be high. A control algorithm with an additional acceleration-feedback loop was then studied to enhance the dynamic stiffness of the cutting system without any need for large inertia. An analytical model of the dynamic stiffness of the system with acceleration feedback was established. The dynamic stiffness was tested by frequency response tests as well as by intermittent diamond-turning experiments. The following errors and the form errors of the machined surfaces were compared with the estimates provided by the model. It is found that the dynamic stiffness within the acceleration sensor bandwidth was proportionally improved. The additional acceleration sensor brought a new error source into the loop, and its contribution of errors increased with a larger acceleration gain. At a certain point, the error caused by the increased acceleration gain surpassed other disturbances and started to dominate, representing the practical upper limit of the acceleration gain.Finally, the developed positioning system was used to cut some typical freeform surfaces. A surface roughness of 1.2 nm (Ra) was achieved on a NiP alloy substrate in flat cutting experiments. Freeform surfaces—including beam integrator surface, sinusoidal surface, and arbitrary freeform surface—were successfully machined with optical-grade quality. Ideas for future improvements were proposed in the end of this thesis.Freeform surfaces are widely found in advanced imaging and illumination systems, orthopaedic implants, high-power beam shaping applications, and other high-end scientific instruments. They give the designers greater ability to cope with the performance limitations commonly encountered in simple-shape designs. However, the stringent requirements for surface roughness and form accuracy of freeform components pose significant challenges for current machining techniques—especially in the optical and display market where large surfaces with tens of thousands of micro features are to be machined. Such highly wavy surfaces require the machine tool cutter to move rapidly while keeping following errors small. Manufacturing efficiency has been a bottleneck in these applications. The rapidly changing cutting forces and inertial forces also contribute a great deal to the machining errors.The difficulty in maintaining good surface quality under conditions of high operational frequency suggests the need for an error analysis approach that can predict the dynamic errors. The machining requirements also impose great challenges on machine tool design and the control process. There has been a knowledge gap on how the mechanical structural design affects the achievable positioning stability. The goal of this study was to develop a tool positioning system capable of delivering fast motion with the required positioning accuracy and stiffness for ultra-precision freeform manufacturing. This goal is achieved through deterministic structural design, detailed error analysis, and novel control algorithms.Firstly, a novel stiff-support design was proposed to eliminate the structural and bearing compliances in the structural loop. To implement the concept, a fast positioning device was developed based on a new-type flat voice coil motor. Flexure bearing, magnet track, and motor coil parameters were designed and calculated in detail. A high-performance digital controller and a power amplifier were also built to meet the servo rate requirement of the closed-loop system. A thorough understanding was established of how signals propagated within the control system, which is fundamentally important in determining the loop performance of high-speed control.A systematic error analysis approach based on a detailed model of the system was proposed and verified for the first time that could reveal how disturbances contribute to the tool positioning errors. Each source of disturbance was treated as a stochastic process, and these disturbances were synthesised in the frequency domain. The differences between following error and real positioning error were discussed and clarified. The predicted spectrum of following errors agreed with the measured spectrum across the frequency range. It is found that the following errors read from the control software underestimated the real positioning errors at low frequencies and overestimated them at high frequencies. The error analysis approach thus successfully revealed the real tool positioning errors that are mingled with sensor noise.Approaches to suppress disturbances were discussed from the perspectives of both system design and control. A deterministic controller design approach was developed to preclude the uncertainty associated with controller tuning, resulting in a control law that can minimize positioning errors. The influences of mechanical parameters such as mass, damping, and stiffness were investigated within the closed-loop framework. Under a given disturbance condition, the optimal bearing stiffness and optimal damping coefficients were found. Experimental positioning tests showed that a larger moving mass helped to combat all disturbances but sensor noise.Because of power limits, the inertia of the fast tool positioning system could not be high. A control algorithm with an additional acceleration-feedback loop was then studied to enhance the dynamic stiffness of the cutting system without any need for large inertia. An analytical model of the dynamic stiffness of the system with acceleration feedback was established. The dynamic stiffness was tested by frequency response tests as well as by intermittent diamond-turning experiments. The following errors and the form errors of the machined surfaces were compared with the estimates provided by the model. It is found that the dynamic stiffness within the acceleration sensor bandwidth was proportionally improved. The additional acceleration sensor brought a new error source into the loop, and its contribution of errors increased with a larger acceleration gain. At a certain point, the error caused by the increased acceleration gain surpassed other disturbances and started to dominate, representing the practical upper limit of the acceleration gain.Finally, the developed positioning system was used to cut some typical freeform surfaces. A surface roughness of 1.2 nm (Ra) was achieved on a NiP alloy substrate in flat cutting experiments. Freeform surfaces—including beam integrator surface, sinusoidal surface, and arbitrary freeform surface—were successfully machined with optical-grade quality. Ideas for future improvements were proposed in the end of this thesis
Large step down voltage converters for desalination
Get PDFOne percent of the world's drinking water is currently desalinated, and this will have to increase to 14% by 2025. Desalination is energy intensive, having significant commercial and ecological implications. One of the most promising methods of desalination is capacitive deionisation which only uses 1kWh/m3 but requires a voltage of less than 1.8V at currents of up to 1000A This thesis produced hardware capable of creating 550A at a voltage of 1.8V, giving over a 1kW power rating, with an input voltage of 340V dc. The converter designed was a bidirectional asymmetrical half-bridge flyback converter allowing for isolation at these high step down ratios. The converter was used to charge a bank of 17,000F supercapacitors from 0V to 1.8V, with an initial charging step down ratio in excess of 340:1 falling to 190:1 as the load charged. A novel Asymmetrical Half-Bridge Coupled-Inductor Buck converter is presented as the ideal solution for large step-down ratios with analysis comparing the ability to efficiently step down a voltage with other common converters, the buck and flyback converters. A comparison between a single-ended coupled-inductor buck converter employing a buck-boost voltage clamp and the novel asymmetrical half-bridge coupled-inductor buck converter circuit shows that the asymmetrical half-bridge converter is a more efficient circuit as leakage energy is recovered; the switch voltages are clamped to within the dc voltage rating of the bridge and the control strategy is simple. Passive and active snubbers are reviewed for efficiency, switch ratings and management of the effects of leakage inductance and compared against the novel designs presented. In the desalination application isolation is required so the flyback circuit is used. An isolated three switch bidirectional converter is constructed using silicon carbide MOSFETs and diodes switching at 40kHz. The converter uses novel current measuring techniques, an on-board microprocessor and closed loop control designed into the final DC-DC converter.One percent of the world's drinking water is currently desalinated, and this will have to increase to 14% by 2025. Desalination is energy intensive, having significant commercial and ecological implications. One of the most promising methods of desalination is capacitive deionisation which only uses 1kWh/m3 but requires a voltage of less than 1.8V at currents of up to 1000A This thesis produced hardware capable of creating 550A at a voltage of 1.8V, giving over a 1kW power rating, with an input voltage of 340V dc. The converter designed was a bidirectional asymmetrical half-bridge flyback converter allowing for isolation at these high step down ratios. The converter was used to charge a bank of 17,000F supercapacitors from 0V to 1.8V, with an initial charging step down ratio in excess of 340:1 falling to 190:1 as the load charged. A novel Asymmetrical Half-Bridge Coupled-Inductor Buck converter is presented as the ideal solution for large step-down ratios with analysis comparing the ability to efficiently step down a voltage with other common converters, the buck and flyback converters. A comparison between a single-ended coupled-inductor buck converter employing a buck-boost voltage clamp and the novel asymmetrical half-bridge coupled-inductor buck converter circuit shows that the asymmetrical half-bridge converter is a more efficient circuit as leakage energy is recovered; the switch voltages are clamped to within the dc voltage rating of the bridge and the control strategy is simple. Passive and active snubbers are reviewed for efficiency, switch ratings and management of the effects of leakage inductance and compared against the novel designs presented. In the desalination application isolation is required so the flyback circuit is used. An isolated three switch bidirectional converter is constructed using silicon carbide MOSFETs and diodes switching at 40kHz. The converter uses novel current measuring techniques, an on-board microprocessor and closed loop control designed into the final DC-DC converter
Reimagining a lace town : Part I a novel: 'the queen of the midlands', Part II a critical thesis: what creative processes can a writer use to transform archived oral testimonies into fictional worlds?
Get PDFPreviously held under moratorium from 18 November 2019 until 18 November 2024.‘Reimagining a Lace Town’ explores the potential of extant oral histories as
an inspiration for fiction. It falls into two parts: a novel ‘The Queen of the
Midlands’; and a critical thesis which explores how a writer can draw on an
archive of oral testimonies to create a fictional world.
‘The Queen of the Midlands’ is set against the historical backdrop of the East
Midlands machine-made lace industry. It reimagines a lace town inhabited by
two fictitious female lace workers and tells their overlapping stories at three
separate and distinct points in their lives: as children and sworn enemies; as
young women who forge a truce; and as elderly women who have become
firm friends. The novel explores their relationship and shines a light on the
machine-made lace industry that shaped their lives. It employs historical,
regional and industrial detail gleaned from an archive of oral histories. It
draws on the nature of the oral history interview to inform its three-part
structure. It uses anecdotes, descriptive language and storytelling techniques
found in the archive to inspire the reimagining of a lace town.
The critical component considers the heritage of East Midlands machine-made
lace. It discusses how my own personal connections with this heritage
and geography seep into the novel’s creation. It goes on to consider my
practice-based research as an interdisciplinary practice, embracing oral
history theory and the work of other East Midlands novelists. It examines the
listening process and the transformation of spoken text into prose fiction. It
considers the ethical implications of this work and the potential of oral history
as an interdisciplinary field for creative practitioners to engage with.‘Reimagining a Lace Town’ explores the potential of extant oral histories as
an inspiration for fiction. It falls into two parts: a novel ‘The Queen of the
Midlands’; and a critical thesis which explores how a writer can draw on an
archive of oral testimonies to create a fictional world.
‘The Queen of the Midlands’ is set against the historical backdrop of the East
Midlands machine-made lace industry. It reimagines a lace town inhabited by
two fictitious female lace workers and tells their overlapping stories at three
separate and distinct points in their lives: as children and sworn enemies; as
young women who forge a truce; and as elderly women who have become
firm friends. The novel explores their relationship and shines a light on the
machine-made lace industry that shaped their lives. It employs historical,
regional and industrial detail gleaned from an archive of oral histories. It
draws on the nature of the oral history interview to inform its three-part
structure. It uses anecdotes, descriptive language and storytelling techniques
found in the archive to inspire the reimagining of a lace town.
The critical component considers the heritage of East Midlands machine-made
lace. It discusses how my own personal connections with this heritage
and geography seep into the novel’s creation. It goes on to consider my
practice-based research as an interdisciplinary practice, embracing oral
history theory and the work of other East Midlands novelists. It examines the
listening process and the transformation of spoken text into prose fiction. It
considers the ethical implications of this work and the potential of oral history
as an interdisciplinary field for creative practitioners to engage with
Photodegradation of polyester films
Get PDFPoly(ethylene terephthalate) (PET) is well known for its excellent properties, but when exposed to ultra-violet (UV) light PET films have the tendency to degrade, which in some applications can be a shortcoming. Many groups have studied the different degradation pathways that can occur in PET during outdoor exposure, however, the effect of specific narrow band wavelength ranges of light have received little attention.;To begin, this research programme was concerned with understanding the effects of exposing PET films to narrow and broad band wavelength ranges of light. The narrow band wavelength ranges used were 302 and 365 nm light and the broad band wavelength range was 290-800 nm. Single films were analysed as well as stacks of films, to investigate whether these could be used to depth profile a single film of the same thickness, during exposure.;When using narrow band wavelength ranges, oxidative and non-oxidative conditions (under nitrogen) were used. This fundamental study concluded that PET degrades more extensively under short wavelength light (302 nm) compared to longer wavelength light (365 nm) of the same intensity and when exposed under oxidative conditions compared to non-oxidative conditions. During exposure, various degradation products were proven to be produced, including carboxylic acid end groups, dimers, quinone species, monohydroxy terephthalate groups and mono-substituted terephthalic rings.;Another area of this research was focused on using a novel way to study the reactions that take place as a consequence of different wavelengths of light, while still replicating outdoor exposure. Exposing samples to the full spectrum of light means that photodegradation reactions taking place as a consequence of short and long wavelengths of light, happen simultaneously. Whereas, if samples were exposed to different wavelengths of light consecutively, the reactions that happen simultaneously outdoors could be studied.;Samples were therefore exposed to one wavelength of light followed by another wavelength of light (302 nm light followed by 365 nm light and vice versa). This study showed that long wavelength light (365 nm) can cause more damage to a film than previously reported, especially when a film has already been photodegraded using short wavelength light (302 nm) before being exposed to longer wavelength light.;Finally, the photodegradation behaviour of poly(diethylene glycol terephthalate) (PDEGT) homopolymer was studied. Although the thermal degradation of PDEGT has been previously reported, the photodegradation of PDEGT has received no attention. The effects of temperature, atmosphere, and wavelength of light were considered, resulting in the PDEGT showing a higher extent of degradation compared to PET, exposed under the same conditions. A mechanistic pathway for the photodegradation reactions occurring in PDEGT during exposure has been proposed.Poly(ethylene terephthalate) (PET) is well known for its excellent properties, but when exposed to ultra-violet (UV) light PET films have the tendency to degrade, which in some applications can be a shortcoming. Many groups have studied the different degradation pathways that can occur in PET during outdoor exposure, however, the effect of specific narrow band wavelength ranges of light have received little attention.;To begin, this research programme was concerned with understanding the effects of exposing PET films to narrow and broad band wavelength ranges of light. The narrow band wavelength ranges used were 302 and 365 nm light and the broad band wavelength range was 290-800 nm. Single films were analysed as well as stacks of films, to investigate whether these could be used to depth profile a single film of the same thickness, during exposure.;When using narrow band wavelength ranges, oxidative and non-oxidative conditions (under nitrogen) were used. This fundamental study concluded that PET degrades more extensively under short wavelength light (302 nm) compared to longer wavelength light (365 nm) of the same intensity and when exposed under oxidative conditions compared to non-oxidative conditions. During exposure, various degradation products were proven to be produced, including carboxylic acid end groups, dimers, quinone species, monohydroxy terephthalate groups and mono-substituted terephthalic rings.;Another area of this research was focused on using a novel way to study the reactions that take place as a consequence of different wavelengths of light, while still replicating outdoor exposure. Exposing samples to the full spectrum of light means that photodegradation reactions taking place as a consequence of short and long wavelengths of light, happen simultaneously. Whereas, if samples were exposed to different wavelengths of light consecutively, the reactions that happen simultaneously outdoors could be studied.;Samples were therefore exposed to one wavelength of light followed by another wavelength of light (302 nm light followed by 365 nm light and vice versa). This study showed that long wavelength light (365 nm) can cause more damage to a film than previously reported, especially when a film has already been photodegraded using short wavelength light (302 nm) before being exposed to longer wavelength light.;Finally, the photodegradation behaviour of poly(diethylene glycol terephthalate) (PDEGT) homopolymer was studied. Although the thermal degradation of PDEGT has been previously reported, the photodegradation of PDEGT has received no attention. The effects of temperature, atmosphere, and wavelength of light were considered, resulting in the PDEGT showing a higher extent of degradation compared to PET, exposed under the same conditions. A mechanistic pathway for the photodegradation reactions occurring in PDEGT during exposure has been proposed
Self injection and radiation production in laser Wakefield accelerators
Get PDFThe laser wakefield accelerator (LWFA) is a nascent electron acceleration technology characterised by extremely large (100s GV/m) accelerating fields and compact (~ cm) scale. Self-injection is a key mechanism in the production of electron beams from the laser wakefield accelerator (LWFA), where background plasma electrons spontaneously enter the accelerating field region. Self-injection is routinely exploited but a fully self-consistent model for the process is still lacking,as are reliable methods for the control of the self-injection process. In this thesis a model for control of self-injection using plasma density gradients or laser intensity evolution is presented. The model is validated using particle-in-cell (PIC) simulations and injection of sub-femtosecond electron bunches is demonstrated. This control is further exploited to demonstrate injection of a train of multiple electron bunches into the LWFA.An additional characteristic of the LWFA is the strong transverse focusing fields, which cause electrons to undergo betatron motion and emit broadband XUV and X-ray radiation. The previously demonstrated bunching is investigated as a source of tuneable coherent emission. Analytic and numerical models demonstrate coherent enhancement at the bunching wavelength. Finally the stability of the scheme is considered with respect to energy and spatial bunch spreads and found to be viable for tuneable XUV radiation production with current state of the art LWFA bunch parameters.The laser wakefield accelerator (LWFA) is a nascent electron acceleration technology characterised by extremely large (100s GV/m) accelerating fields and compact (~ cm) scale. Self-injection is a key mechanism in the production of electron beams from the laser wakefield accelerator (LWFA), where background plasma electrons spontaneously enter the accelerating field region. Self-injection is routinely exploited but a fully self-consistent model for the process is still lacking,as are reliable methods for the control of the self-injection process. In this thesis a model for control of self-injection using plasma density gradients or laser intensity evolution is presented. The model is validated using particle-in-cell (PIC) simulations and injection of sub-femtosecond electron bunches is demonstrated. This control is further exploited to demonstrate injection of a train of multiple electron bunches into the LWFA.An additional characteristic of the LWFA is the strong transverse focusing fields, which cause electrons to undergo betatron motion and emit broadband XUV and X-ray radiation. The previously demonstrated bunching is investigated as a source of tuneable coherent emission. Analytic and numerical models demonstrate coherent enhancement at the bunching wavelength. Finally the stability of the scheme is considered with respect to energy and spatial bunch spreads and found to be viable for tuneable XUV radiation production with current state of the art LWFA bunch parameters
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