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Physical behaviours in adults with lower limb absence : motivations and barriers; the role of healthcare professionals; measurement; and free-living patterns
Get PDFThesis contains two CDs : 1. Individual Level Matching THESIS, 2. Example datasets from activPAL output.Strong evidence exists to support participation in physical activity to maintain and improve health in general and clinical populations. However, little is known about the physical behaviours of adults with lower limb absence.;This thesis makes four original contributions to knowledge. The first contribution is a systematic review conducted to explore the motivations and barriers to participation in physical activity, exercise and sports in people with lower limb absence. Findings show that adults with lower limb absence are not participating in physical activity conducive to health benefits. Post-amputation levels of participation are lower than pre-amputation levels, and more barriers than motivations exist to participation.;The second contribution is the exploration of healthcare professionals' awareness and understanding of physical activity guidelines and how physical activity is promoted in clinical settings. Results from an online survey designed for United Kingdom healthcare professionals show that this group has awareness and knowledge of physical activity guidelines. With appropriate support and resources prosthetic healthcare professionals can be encouraged to incorporate physical activity promotion into routine clinical practice.;The third contribution is the examination of reliability and validity of an accelerometer when worn by adults with lower limb absence. The activPAL™ accelerometer is a reliable and valid measurement tool in adults with lower limb absence when used in a laboratory setting, and placement of the monitor on the sound side limb is recommended for testing.;The fourth contribution is the findings from a free-living study of physical behaviour in adults with lower limb absence who are shown to be physically active daily but could be encouraged to be more active and less sedentary. Data were also matched on gender, age and employment status to that of a non-clinical control group where it was shown those with limb absence are less active than healthy individuals.Strong evidence exists to support participation in physical activity to maintain and improve health in general and clinical populations. However, little is known about the physical behaviours of adults with lower limb absence.;This thesis makes four original contributions to knowledge. The first contribution is a systematic review conducted to explore the motivations and barriers to participation in physical activity, exercise and sports in people with lower limb absence. Findings show that adults with lower limb absence are not participating in physical activity conducive to health benefits. Post-amputation levels of participation are lower than pre-amputation levels, and more barriers than motivations exist to participation.;The second contribution is the exploration of healthcare professionals' awareness and understanding of physical activity guidelines and how physical activity is promoted in clinical settings. Results from an online survey designed for United Kingdom healthcare professionals show that this group has awareness and knowledge of physical activity guidelines. With appropriate support and resources prosthetic healthcare professionals can be encouraged to incorporate physical activity promotion into routine clinical practice.;The third contribution is the examination of reliability and validity of an accelerometer when worn by adults with lower limb absence. The activPAL™ accelerometer is a reliable and valid measurement tool in adults with lower limb absence when used in a laboratory setting, and placement of the monitor on the sound side limb is recommended for testing.;The fourth contribution is the findings from a free-living study of physical behaviour in adults with lower limb absence who are shown to be physically active daily but could be encouraged to be more active and less sedentary. Data were also matched on gender, age and employment status to that of a non-clinical control group where it was shown those with limb absence are less active than healthy individuals
Control design and energy optimisation of a buoyant airborne wind turbine
Get PDFAirborne Wind Energy Systems (AWES) aim to capture the wind energy potential at high altitudes by using a combination of tethers and bespoke aerofoils. In contrast to conventional horizontal axis wind turbines (HAWT), the tower is replaced with lightweight tethers resulting in a reduction in both the overall mass, and more importantly cost of the system. Currently, there is significant interest from a number of key stakeholders, both academic and industrial, aiming to optimise an airborne wind energy design that captures the wind energy resource found at high altitudes. Two key issues will drive the development of these systems, flight stability and power maximisation. Therefore, the control strategy for these systems will be imperative for reducing costs and optimising system performance. Through collaboration with Altaeros Energies, this thesis addresses the outstanding stability and performance optimisation for a specific AWES known as the Buoyant Airborne Wind Turbine (BAWT). There are three key contributions within this work. Firstly, a comprehensive literature review of different airborne systems is provided with specific consideration given to power optimisation and dynamic stability. This results in a detailed understanding of the BAWT plant model through the introduction of two force ratio's relating the buoyancy contribution to the aerodynamic contribution on system loads across the operating envelope. The model development is then expanded on to discuss the question of system stability and power optimisation. This is addressed via the development of a hierarchical control structure for the BAWT, which is broken into three distinct regions, low level control, medium level control and high level control. At the lowest level, flight stability, which is vital to providing optimum conditions for energy generation, is guaranteed using a multivariable controller. This is carried out through the development of a PID controller using two methods, a frequency domain method known as MPID and an optimal control scheme, LQR. The results of this chapter inform the interaction of the controller with the underlying plant dynamics. Finally, the broader issue of BAWT optimisation is addressed by implementing a hierarchical control architecture which builds upon the multivariable flight stability controller developed in Chapter 5. Medium level control is implemented using a hierarchical model predictive control scheme (MPC) which provides set-points to the low level controller in roll, pitch and altitude. These set-points are provided such that they are bounded within the defined envelope of operation to ensure that loads on the shroud are not increased beyond acceptable levels i.e. extreme tether loads due to high altitudes. The question of power optimisation is then addressed through the formulation of an Extremum seeking control (ESC) scheme which derives an optimal altitude for the system. This altitude is determined by trading off generated power from the rotor against power losses incurred by reeling the tether in/out at high wind speeds. Implementing a hierarchical control scheme of this type provides an example of how different control techniques can be combined to provide a degree of self-regulation whilst simultaneously providing system stability and power optimisation. Ultimately, this will increase autonomous operation of the BAWT which will help to reduce system costs and make this technology more viable in a competitive marketplace.Airborne Wind Energy Systems (AWES) aim to capture the wind energy potential at high altitudes by using a combination of tethers and bespoke aerofoils. In contrast to conventional horizontal axis wind turbines (HAWT), the tower is replaced with lightweight tethers resulting in a reduction in both the overall mass, and more importantly cost of the system. Currently, there is significant interest from a number of key stakeholders, both academic and industrial, aiming to optimise an airborne wind energy design that captures the wind energy resource found at high altitudes. Two key issues will drive the development of these systems, flight stability and power maximisation. Therefore, the control strategy for these systems will be imperative for reducing costs and optimising system performance. Through collaboration with Altaeros Energies, this thesis addresses the outstanding stability and performance optimisation for a specific AWES known as the Buoyant Airborne Wind Turbine (BAWT). There are three key contributions within this work. Firstly, a comprehensive literature review of different airborne systems is provided with specific consideration given to power optimisation and dynamic stability. This results in a detailed understanding of the BAWT plant model through the introduction of two force ratio's relating the buoyancy contribution to the aerodynamic contribution on system loads across the operating envelope. The model development is then expanded on to discuss the question of system stability and power optimisation. This is addressed via the development of a hierarchical control structure for the BAWT, which is broken into three distinct regions, low level control, medium level control and high level control. At the lowest level, flight stability, which is vital to providing optimum conditions for energy generation, is guaranteed using a multivariable controller. This is carried out through the development of a PID controller using two methods, a frequency domain method known as MPID and an optimal control scheme, LQR. The results of this chapter inform the interaction of the controller with the underlying plant dynamics. Finally, the broader issue of BAWT optimisation is addressed by implementing a hierarchical control architecture which builds upon the multivariable flight stability controller developed in Chapter 5. Medium level control is implemented using a hierarchical model predictive control scheme (MPC) which provides set-points to the low level controller in roll, pitch and altitude. These set-points are provided such that they are bounded within the defined envelope of operation to ensure that loads on the shroud are not increased beyond acceptable levels i.e. extreme tether loads due to high altitudes. The question of power optimisation is then addressed through the formulation of an Extremum seeking control (ESC) scheme which derives an optimal altitude for the system. This altitude is determined by trading off generated power from the rotor against power losses incurred by reeling the tether in/out at high wind speeds. Implementing a hierarchical control scheme of this type provides an example of how different control techniques can be combined to provide a degree of self-regulation whilst simultaneously providing system stability and power optimisation. Ultimately, this will increase autonomous operation of the BAWT which will help to reduce system costs and make this technology more viable in a competitive marketplace
Piezoelectric degradation and circuit protection in fibre Bragg grating and piezoelectric stack based low voltage transducers
Get PDFWith rising global electricity demand and increasing penetration of intermittent renewable energy sources, monitoring and protection of power networks is increasingly important for transmission and distribution network operators. It is, therefore, desirable to increase the coverage of, and reduce the cost per unit of monitoring systems. Fibre optic based transducers present a low cost, multiplex-able alternative to conventional methods of current and voltage measurement for monitoring and protection of power networks, however, prior to adoption by industry, it is desirable to characterise and improve sensor accuracy as much as possible. This thesis presents an investigation of several factors affecting the accuracy of piezoelectric stack and fibre Bragg grating based low voltage sensors in particular, with a focus on piezoelectric behaviour in the immediate aftermath of a grid fault, with the aim of developing engineering solutions to maximise sensor accuracy. Fiber [sic] Bragg grating technology is introduced and applications are highlighted. Conventional and proposed voltage and current sensors are described and the advantages of fibre Bragg grating based voltage and current sensors elucidated. The phenomena of piezoelectric ageing, creep and fatigue are reviewed. The effects of piezoelectric degradation on the measurement accuracy of optical fibre and piezoelectric stack based low voltage transducers(LVTs) were experimentally investigated. An accelerated life test to determine the most fatigue resistant bonding method for connecting fibre Bragg gratings to the piezoelectric transducer is discussed. Finally, the proposed protection circuitry for the prototype LVT is revised, based on experimental and theoretical considerations.With rising global electricity demand and increasing penetration of intermittent renewable energy sources, monitoring and protection of power networks is increasingly important for transmission and distribution network operators. It is, therefore, desirable to increase the coverage of, and reduce the cost per unit of monitoring systems. Fibre optic based transducers present a low cost, multiplex-able alternative to conventional methods of current and voltage measurement for monitoring and protection of power networks, however, prior to adoption by industry, it is desirable to characterise and improve sensor accuracy as much as possible. This thesis presents an investigation of several factors affecting the accuracy of piezoelectric stack and fibre Bragg grating based low voltage sensors in particular, with a focus on piezoelectric behaviour in the immediate aftermath of a grid fault, with the aim of developing engineering solutions to maximise sensor accuracy. Fiber [sic] Bragg grating technology is introduced and applications are highlighted. Conventional and proposed voltage and current sensors are described and the advantages of fibre Bragg grating based voltage and current sensors elucidated. The phenomena of piezoelectric ageing, creep and fatigue are reviewed. The effects of piezoelectric degradation on the measurement accuracy of optical fibre and piezoelectric stack based low voltage transducers(LVTs) were experimentally investigated. An accelerated life test to determine the most fatigue resistant bonding method for connecting fibre Bragg gratings to the piezoelectric transducer is discussed. Finally, the proposed protection circuitry for the prototype LVT is revised, based on experimental and theoretical considerations
Antibody-conjugated nanoparticles for SERS-based lateral flow immunoassay
Get PDFThe success to obtain a sensitive analytical tool such as a nanosensor, starts from its design and fabrication. The investigation of the chemistry behind metallic nanostructures and antibody interactions was a fundamental part of the research described this thesis. In addition, the development of surface enhanced Raman scattering (SERS) based lateral flow immunoassays (LFIA) for the highly sensitive detection of specific antigens was carried out.Gold nanoparticles (AuNPs) were used in the development of a universal method for histidine tagged antibodies conjugation. To achieve this, AuNPs were functionalised with a linker that contained a thiol group, which has affinity to the gold surface and a nitrilotriacetic acid (NTA) metal ion complex, which is known to have an affinity towards histidine. A fragment antigen-binding (Fab) antibody that contains 7-histidine residues was conjugated to the functionalised AuNPs in a rapid and straightforward manner. Different metal ions were investigated at various concentrations. Results demonstrated that the antibody uptake was controlled by metal ion concentration and that nickel (II) gave the stronger antibody binding. The Fab conjugated NTA-Ni AuNPs were also evaluated for use in SERS-based LFIA, showing high stability and compatibility compared to passive adsorption conjugates. A sandwich-like format SERS-based LFIA for the detection of C-reactive protein (CRP) was developed. Results demonstrated that, by using a Raman reporter molecule (RRM) that was in resonance with the excitation laser, a 25-fold improvement in sensitivity was achieved, compared to visual detection. A competitive format SERS-based LFIA was also developed, showing the possibility of detecting a wider range of CRP concentrations, compared to the sandwich format. Anisotropic nanoparticles such as gold nanostars (AuNSs) were used for the detection of human chorionic gonadotropin (hCG) by LFIA. AuNSs were conjugated to anti-hCG antibodies and labelled with RRMs in order to allow a SERS detection. AuNSs showed better assay performance than spherical nanoparticles, either in SERS and visual detection. AuNSs morphology and shape consented the generation of "hot spots" and the possibility to allocate antibodies in an orientated manner on the AuNSs surface, which resulted in highly sensitive signal response. The optimisation of the SERS labelled AuNSs-antibody conjugates along with the choice of an appropriate RRM led to the detection in the picogram range of hCG concentration in a pseudo-biological matrix.The success to obtain a sensitive analytical tool such as a nanosensor, starts from its design and fabrication. The investigation of the chemistry behind metallic nanostructures and antibody interactions was a fundamental part of the research described this thesis. In addition, the development of surface enhanced Raman scattering (SERS) based lateral flow immunoassays (LFIA) for the highly sensitive detection of specific antigens was carried out.Gold nanoparticles (AuNPs) were used in the development of a universal method for histidine tagged antibodies conjugation. To achieve this, AuNPs were functionalised with a linker that contained a thiol group, which has affinity to the gold surface and a nitrilotriacetic acid (NTA) metal ion complex, which is known to have an affinity towards histidine. A fragment antigen-binding (Fab) antibody that contains 7-histidine residues was conjugated to the functionalised AuNPs in a rapid and straightforward manner. Different metal ions were investigated at various concentrations. Results demonstrated that the antibody uptake was controlled by metal ion concentration and that nickel (II) gave the stronger antibody binding. The Fab conjugated NTA-Ni AuNPs were also evaluated for use in SERS-based LFIA, showing high stability and compatibility compared to passive adsorption conjugates. A sandwich-like format SERS-based LFIA for the detection of C-reactive protein (CRP) was developed. Results demonstrated that, by using a Raman reporter molecule (RRM) that was in resonance with the excitation laser, a 25-fold improvement in sensitivity was achieved, compared to visual detection. A competitive format SERS-based LFIA was also developed, showing the possibility of detecting a wider range of CRP concentrations, compared to the sandwich format. Anisotropic nanoparticles such as gold nanostars (AuNSs) were used for the detection of human chorionic gonadotropin (hCG) by LFIA. AuNSs were conjugated to anti-hCG antibodies and labelled with RRMs in order to allow a SERS detection. AuNSs showed better assay performance than spherical nanoparticles, either in SERS and visual detection. AuNSs morphology and shape consented the generation of "hot spots" and the possibility to allocate antibodies in an orientated manner on the AuNSs surface, which resulted in highly sensitive signal response. The optimisation of the SERS labelled AuNSs-antibody conjugates along with the choice of an appropriate RRM led to the detection in the picogram range of hCG concentration in a pseudo-biological matrix
Cognitive and social identity influences on founders' online networks, networking actions, and network outcomes
Get PDFNetworks are known to be a critical asset for entrepreneurs. This study aims to help better understand the networks, networking actions, and network outcomes of entrepreneurs by investigating two understudied contexts: online networks and founder social identity. Two specific questions are examined: To what extent and how are founders' networking behaviours and network outcomes different in the online context? and To what extent and how does founder social identity influence founders'networks and networking behaviours on SNSs? Considering these questions together presents an opportunity to examine the interplay between founders' cognitive processes, their self-concepts, and their networking actions on social network sites.This is important because founders wonder how best to leverage the affordances of social network sites like Facebook, Twitter, and LinkedIn to entrepreneurial advantage.The study adopts pragmatism's ontological and epistemological lenses for its research design. Empirical data from 35 depth interviews with founders in the early stages of their ventures is analysed using inductive and abductive methods. Patterns of meaning and theoretical themes emerge from the data that help shed light on the experiences of founders networking online.The findings and conclusions of this study highlight how the online context of networking is unique for founders, and outline how founders' social identities may influence their networking actions and cognitive networking styles. Specifically, 12 propositions and a conceptual model are developed that offer a comprehensive research agenda. The model purports that social judgment bias moderates founders'cognitive willingness to extract resources online. The study also illuminates how founder social identity acts as an antecedent to founders' online networking behaviour,and explores the influences of enacting founder social identity-salient instrumental,collaborative, or veritable networking styles. Implications for entrepreneurship theoryand practice are discussed.Networks are known to be a critical asset for entrepreneurs. This study aims to help better understand the networks, networking actions, and network outcomes of entrepreneurs by investigating two understudied contexts: online networks and founder social identity. Two specific questions are examined: To what extent and how are founders' networking behaviours and network outcomes different in the online context? and To what extent and how does founder social identity influence founders'networks and networking behaviours on SNSs? Considering these questions together presents an opportunity to examine the interplay between founders' cognitive processes, their self-concepts, and their networking actions on social network sites.This is important because founders wonder how best to leverage the affordances of social network sites like Facebook, Twitter, and LinkedIn to entrepreneurial advantage.The study adopts pragmatism's ontological and epistemological lenses for its research design. Empirical data from 35 depth interviews with founders in the early stages of their ventures is analysed using inductive and abductive methods. Patterns of meaning and theoretical themes emerge from the data that help shed light on the experiences of founders networking online.The findings and conclusions of this study highlight how the online context of networking is unique for founders, and outline how founders' social identities may influence their networking actions and cognitive networking styles. Specifically, 12 propositions and a conceptual model are developed that offer a comprehensive research agenda. The model purports that social judgment bias moderates founders'cognitive willingness to extract resources online. The study also illuminates how founder social identity acts as an antecedent to founders' online networking behaviour,and explores the influences of enacting founder social identity-salient instrumental,collaborative, or veritable networking styles. Implications for entrepreneurship theoryand practice are discussed
Synthesis and evaluation of targeted dendrisomes as novel gene and drug delivery systems for cancer therapy
Get PDFThis thesis was previously held under moratorium from 13/08/2018 to 15/08/2023Introduction: The co-delivery of cancer therapeutics in hybrid nanocarriers is currently being investigated in order to achieve an additive or synergistic effect in cancer therapy. The aim of this study was to synthesize and evaluate novel transferrin-bearing dendrisomes to co-deliver therapeutic DNA encoding TNF-α and doxorubicin. Dendrisomes were thus investigated in this project in vitro and in vivo for their DNA carrying abilities as well as their ability to co-deliver therapeutic DNA and an anticancer drug. The targeted dendrisomes in this project are thus aimed at ensuring a higher selective uptake intracellularly using targeting ligand transferrin. Transferrin receptors have been found to be overexpressed on most cancer cells and are thus attractive as target sites for selective receptor-mediated tumour targeting.Methods: The dendrisomes were formulated with a combination of a lipid blend incorporating non-ionic surfactants and a dendrimer via heating and probe sonication. Doxorubicin was encapsulated in the dendrisomes through probe sonication. Conjugation of transferrin to the dendrisomes was done using bifunctional cross- linking. Characterization of the dendrisomes was then carried out through techniques including, size and zeta potential measurements, TEM, DNA condensation assays, AFM. In vitro studies were also carried out using fluorescence microscopy, confocal laser scanning microscopy, gene transfection assays and anti-proliferative assay. Biodistribution and antitumour efficacy studies were also carried out using xenograft models.Results: Dendrisomes were successfully formulated that were in the nanometer range (less than 500 nm). Some were neutral, and some were positively charged as obtained from zeta potential readings. TEM pictures showed that these novel dendrisomes were spherical. DNA condensation and doxorubicin encapsulation efficiency were respectively above 75% and 95% and demonstrated the ability of the dendrisomes to carry both DNA and drug. DNA encoding β-galactosidase was successfully expressed in A431, B16F10-Luc-G5 and T98G cancer cells. Cellular uptake experiments demonstrated that the novel dendrisomes caused increase in doxorubicin and DNA intracellular uptake. Anti-proliferative efficacy was improved following treatment with dendrisomes co-delivering DNA encoding TNF-α and doxorubicin, compared to that observed with doxorubicin alone or DNA encoding TNF-α alone with synergism observed in B16F10-Luc-G5 cells that were treated with transferrin bearing, doxorubicin encapsulated DSOLm dendrisomplexes.Conclusion: In conclusion, this project is the first demonstration of transferrin-targeted novel dendrisomes being complexed to therapeutic plasmid DNA encoding TNF-α for gene delivery while concurrently entrapping anticancer drug doxorubicin for cancer therapy. The novel targeted dendrisomes were shown to have the capacity to co-deliver therapeutic plasmid DNA encoding TNF- α and anticancer drug doxorubicin to cancer cells in vitro and in vivo, thus leading to increased anti-proliferative effect in vitro and slightly increased therapeutic efficacy at the doses used in vivo in selected cancer cell lines and solid tumours overexpressing transferrin respectively.Introduction: The co-delivery of cancer therapeutics in hybrid nanocarriers is currently being investigated in order to achieve an additive or synergistic effect in cancer therapy. The aim of this study was to synthesize and evaluate novel transferrin-bearing dendrisomes to co-deliver therapeutic DNA encoding TNF-α and doxorubicin. Dendrisomes were thus investigated in this project in vitro and in vivo for their DNA carrying abilities as well as their ability to co-deliver therapeutic DNA and an anticancer drug. The targeted dendrisomes in this project are thus aimed at ensuring a higher selective uptake intracellularly using targeting ligand transferrin. Transferrin receptors have been found to be overexpressed on most cancer cells and are thus attractive as target sites for selective receptor-mediated tumour targeting.Methods: The dendrisomes were formulated with a combination of a lipid blend incorporating non-ionic surfactants and a dendrimer via heating and probe sonication. Doxorubicin was encapsulated in the dendrisomes through probe sonication. Conjugation of transferrin to the dendrisomes was done using bifunctional cross- linking. Characterization of the dendrisomes was then carried out through techniques including, size and zeta potential measurements, TEM, DNA condensation assays, AFM. In vitro studies were also carried out using fluorescence microscopy, confocal laser scanning microscopy, gene transfection assays and anti-proliferative assay. Biodistribution and antitumour efficacy studies were also carried out using xenograft models.Results: Dendrisomes were successfully formulated that were in the nanometer range (less than 500 nm). Some were neutral, and some were positively charged as obtained from zeta potential readings. TEM pictures showed that these novel dendrisomes were spherical. DNA condensation and doxorubicin encapsulation efficiency were respectively above 75% and 95% and demonstrated the ability of the dendrisomes to carry both DNA and drug. DNA encoding β-galactosidase was successfully expressed in A431, B16F10-Luc-G5 and T98G cancer cells. Cellular uptake experiments demonstrated that the novel dendrisomes caused increase in doxorubicin and DNA intracellular uptake. Anti-proliferative efficacy was improved following treatment with dendrisomes co-delivering DNA encoding TNF-α and doxorubicin, compared to that observed with doxorubicin alone or DNA encoding TNF-α alone with synergism observed in B16F10-Luc-G5 cells that were treated with transferrin bearing, doxorubicin encapsulated DSOLm dendrisomplexes.Conclusion: In conclusion, this project is the first demonstration of transferrin-targeted novel dendrisomes being complexed to therapeutic plasmid DNA encoding TNF-α for gene delivery while concurrently entrapping anticancer drug doxorubicin for cancer therapy. The novel targeted dendrisomes were shown to have the capacity to co-deliver therapeutic plasmid DNA encoding TNF- α and anticancer drug doxorubicin to cancer cells in vitro and in vivo, thus leading to increased anti-proliferative effect in vitro and slightly increased therapeutic efficacy at the doses used in vivo in selected cancer cell lines and solid tumours overexpressing transferrin respectively
Multi-fidelity global low-thrust trajectory optimisation
Get PDFThis research work presents methods and techniques for multi-fidelity global optimisation of low-thrust trajectories. In the early stages of the definition of a space mission, tools that can provide a fast and preliminary estimation of the cost of low-thrust transfers are required; a more accurate optimisation process of the trajectories is left for subsequent phases. Therefore, models of different levels of fidelity are needed, based on the current phase of the design and on the desired accuracy. An efficient global optimisation algorithm has then to be used in conjunction with these models, in order to identify the global optimal solution to a given problem. The development of multi-fidelity methods, of an efficient global optimisation algorithm and their application for the solution of low-thrust global optimisation problems, are addressed in this thesis. The lower fidelity models consist of analytical laws for the cost of low-thrust transfers. Higher fidelity innovative laws for transfers between Earth's orbits have been derived. Moreover, a set of analytical equations for the motion of the spacecraft subject to low-thrust acceleration and orbital perturbations is presented. These models are used in conjunction with a novel adaptive multi-population global optimisation algorithm, validated using several test functions and real world problems. To allow for the use of the global solver with higher fidelity, and therefore computationally more expensive models, the use of surrogate model for low-thrust transfer is proposed. Various applications are presented where these tools and methods are successfully applied, and that represent an original scientific contribution. Missions have been designed to deorbit objects from Low Earth Orbit and deploy a constellation in Medium Earth Orbit. The optimisation of a transfer from Geostationary Transfer Orbit to Geosynchronous Orbit is also presented. Interplanetary applications include missions to visit the asteroids of the inner solar system and of the main belt.This research work presents methods and techniques for multi-fidelity global optimisation of low-thrust trajectories. In the early stages of the definition of a space mission, tools that can provide a fast and preliminary estimation of the cost of low-thrust transfers are required; a more accurate optimisation process of the trajectories is left for subsequent phases. Therefore, models of different levels of fidelity are needed, based on the current phase of the design and on the desired accuracy. An efficient global optimisation algorithm has then to be used in conjunction with these models, in order to identify the global optimal solution to a given problem. The development of multi-fidelity methods, of an efficient global optimisation algorithm and their application for the solution of low-thrust global optimisation problems, are addressed in this thesis. The lower fidelity models consist of analytical laws for the cost of low-thrust transfers. Higher fidelity innovative laws for transfers between Earth's orbits have been derived. Moreover, a set of analytical equations for the motion of the spacecraft subject to low-thrust acceleration and orbital perturbations is presented. These models are used in conjunction with a novel adaptive multi-population global optimisation algorithm, validated using several test functions and real world problems. To allow for the use of the global solver with higher fidelity, and therefore computationally more expensive models, the use of surrogate model for low-thrust transfer is proposed. Various applications are presented where these tools and methods are successfully applied, and that represent an original scientific contribution. Missions have been designed to deorbit objects from Low Earth Orbit and deploy a constellation in Medium Earth Orbit. The optimisation of a transfer from Geostationary Transfer Orbit to Geosynchronous Orbit is also presented. Interplanetary applications include missions to visit the asteroids of the inner solar system and of the main belt
How best can ground source heat pumps be deployed in a public sector context?
No full textGeothermal heat exchange technology is well established, however its use as avalid renewable energy technology in the urban environment has not yet been fully developed. The mining legacy in Scotland, in tandem with regeneration opportunities through brownfield land, represents a significant opportunity where the use of geothermal energy and ground source heat pumps (GSHPs) can be fully explored for the provision of renewable heating. With the demand for space heating and hot water in the UK making up a large portion (40%) of the overall UK energy use mix, the Government run Renewable Heat Incentive (RHI) scheme goes a long way towards making many projects involving renewable energy technologies economically viable and so reducing carbon emissions. The published research within this thesis shows that the RHI alone does not fully incentivise renewable heating deployment and this work examines how other new strategies can be applied. Looking beyond the RHI as one of the main economic mechanisms for installing renewable energy technologies has identified fuel poverty as an important social factor to consider for renewable heating deployment using GSHPs. A demonstrated relationship between social housing and the proximity to brownfield land shows an increased opportunity for the use of GSHPs to meet the domestic heating energy demand for people where the cost of energy might be an issue. This is important when it is estimated that 1 in 5 households in the UK are in fuel poverty. To examine the viability of this proposal, a dynamic energy simulation model is completed for a social housing tower block and this energy demand is met through a modelled GSHP system, using a neighbouring vacant land parcel. The research results within this thesis suggest that an integrated policy approach can serve to improve renewable heating deployment alongside fuel poverty reduction.Geothermal heat exchange technology is well established, however its use as avalid renewable energy technology in the urban environment has not yet been fully developed. The mining legacy in Scotland, in tandem with regeneration opportunities through brownfield land, represents a significant opportunity where the use of geothermal energy and ground source heat pumps (GSHPs) can be fully explored for the provision of renewable heating. With the demand for space heating and hot water in the UK making up a large portion (40%) of the overall UK energy use mix, the Government run Renewable Heat Incentive (RHI) scheme goes a long way towards making many projects involving renewable energy technologies economically viable and so reducing carbon emissions. The published research within this thesis shows that the RHI alone does not fully incentivise renewable heating deployment and this work examines how other new strategies can be applied. Looking beyond the RHI as one of the main economic mechanisms for installing renewable energy technologies has identified fuel poverty as an important social factor to consider for renewable heating deployment using GSHPs. A demonstrated relationship between social housing and the proximity to brownfield land shows an increased opportunity for the use of GSHPs to meet the domestic heating energy demand for people where the cost of energy might be an issue. This is important when it is estimated that 1 in 5 households in the UK are in fuel poverty. To examine the viability of this proposal, a dynamic energy simulation model is completed for a social housing tower block and this energy demand is met through a modelled GSHP system, using a neighbouring vacant land parcel. The research results within this thesis suggest that an integrated policy approach can serve to improve renewable heating deployment alongside fuel poverty reduction
Development of an annular array through-transmission system for non-contact inspection applications
Get PDFUltrasound has found application in many different sectors, including inspection in the aerospace industry to investigate component structural integrity. In many cases, a liquid coupling medium is used to efficiently transfer energy between the transducer and the sample under investigation. There are some materials which are not suitable for liquid coupling, either through material properties or the complexity of the surface geometry. The alternative of using an air-coupled approach is inherently challenging due to a large acoustic impedance mismatch between the transducer and air, resulting in low system signal-to-noise ratio (SNR). This Thesis will consider an air-coupled inspection system, using an annular array and efficient matching layer combination.The matching layer is an important key transducer component to bridge the acoustic impedance mismatch between the transducer and the load medium. For air-coupled piezoelectric devices this is a critical factor in the transducer design. This work has concentrated on improving the manufacture methodology for an existing hybrid matching layer design, comprising membrane filter and silicone rubber. The key issue is to ensure repeatability of the fabrication process and reliability in the operating behaviour. Moreover, the developed approach has reduced the manufacture time for these layers and offers an opportunity for volume manufacture.;A segmented annular array system has been designed for non-contact inspection applications, which provides control of the depth focussing within the sample coupled with a degree of beam steering off the central axis. A pitch-catch transducer system has been implemented, with the operating frequency of the transmitter and receiver matched to improve system SNR. Full characterisation of both arrays has been performed, with good correlation between theory and experiment. Unfortunately, the fabricated array devices only provided beam steering capability on-axis, but when combined with the matching layer designs, were able to be evaluated on fibre-reinforce composite and honeycomb samples. Assessment of the inspection capability of the developed array system was undertaken through manual scans of sandwich composite structures. Reasonable quality images have been acquired which indicate surface damage and impact damage within several samples, with the results correlating well with corresponding Scanning Acoustic Microscope measurements.Ultrasound has found application in many different sectors, including inspection in the aerospace industry to investigate component structural integrity. In many cases, a liquid coupling medium is used to efficiently transfer energy between the transducer and the sample under investigation. There are some materials which are not suitable for liquid coupling, either through material properties or the complexity of the surface geometry. The alternative of using an air-coupled approach is inherently challenging due to a large acoustic impedance mismatch between the transducer and air, resulting in low system signal-to-noise ratio (SNR). This Thesis will consider an air-coupled inspection system, using an annular array and efficient matching layer combination.The matching layer is an important key transducer component to bridge the acoustic impedance mismatch between the transducer and the load medium. For air-coupled piezoelectric devices this is a critical factor in the transducer design. This work has concentrated on improving the manufacture methodology for an existing hybrid matching layer design, comprising membrane filter and silicone rubber. The key issue is to ensure repeatability of the fabrication process and reliability in the operating behaviour. Moreover, the developed approach has reduced the manufacture time for these layers and offers an opportunity for volume manufacture.;A segmented annular array system has been designed for non-contact inspection applications, which provides control of the depth focussing within the sample coupled with a degree of beam steering off the central axis. A pitch-catch transducer system has been implemented, with the operating frequency of the transmitter and receiver matched to improve system SNR. Full characterisation of both arrays has been performed, with good correlation between theory and experiment. Unfortunately, the fabricated array devices only provided beam steering capability on-axis, but when combined with the matching layer designs, were able to be evaluated on fibre-reinforce composite and honeycomb samples. Assessment of the inspection capability of the developed array system was undertaken through manual scans of sandwich composite structures. Reasonable quality images have been acquired which indicate surface damage and impact damage within several samples, with the results correlating well with corresponding Scanning Acoustic Microscope measurements
Stabilization of hybrid systems by discrete-time feedback controls
Get PDFHybrid stochastic differential equations (SDEs) (also known as SDEs with Markovian switching) have been used to model many practical systems where they may experience abrupt changes in their structure and parameters. One of the important issues in the study of hybrid systems is the automatic control, with consequent emphasis being placed on the asymptotic analysis of stability. One classical topic in this field is the problem of stabilization. The stability of hybrid systems by feedback control based on continuous-time observations has been studied extensively in the past decades. Recently, Mao [52] initiates the study on the mean-square exponential stabilization of continuous-time hybrid stochastic differential equations by feedback controls based on discrete-time state observations. Mao [52] also obtains an upperbound on the duration between two consecutive state observations. However, it is due to the general technique used there that the bound on is not very sharp. In this thesis, we will consider a couple of important classes of hybrid SDEs. Making full use of their special features, we will be able to establish a better bound on. Our new theory enables us to observe the system state less frequently (so costless) but still to be able to design the feedback control based on the discrete-timestate observations to stabilize the given hybrid SDEs in the sense of mean-square exponential stability. Moreover, we will be able to establish a better bound on making use of Lyapunov functionals. By this method, we will not only discuss the stabilization in the sense of exponential stability but also in other sense of H1 stability or asymptotic stability as well. We will not only consider the mean square stability but also the almost sure stability. It is easy to observe that the feedback control there still depends on the continuous-time observations of the mode. However, it usually costs to identify the current mode of the system in practice. So we can further improve the control to reduce the control cost by identifying the mode at discrete times when we make observations for the state. Therefore, we will also design such a type of feedback control based on the discrete-time observations of both state and mode to stabilize the given hybrid stochastic differential equations (SDEs) in the sense of mean-square exponential stability in this thesis. Similarly, we can extend our discussion to the stabilization of continuous-time hybrid stochastic differential equations by feedback controls based on not only discrete-time state observations but also discrete-time mode observations by Lyapunov method. At last, we will investigate stability of Stochastic differential delay equations with Markovian switching by feedback control based on discrete-time State and mode observations by using Lyapunov functional. Hence, we will get the upperbound on the duration between two consecutive state and mode observations.Hybrid stochastic differential equations (SDEs) (also known as SDEs with Markovian switching) have been used to model many practical systems where they may experience abrupt changes in their structure and parameters. One of the important issues in the study of hybrid systems is the automatic control, with consequent emphasis being placed on the asymptotic analysis of stability. One classical topic in this field is the problem of stabilization. The stability of hybrid systems by feedback control based on continuous-time observations has been studied extensively in the past decades. Recently, Mao [52] initiates the study on the mean-square exponential stabilization of continuous-time hybrid stochastic differential equations by feedback controls based on discrete-time state observations. Mao [52] also obtains an upperbound on the duration between two consecutive state observations. However, it is due to the general technique used there that the bound on is not very sharp. In this thesis, we will consider a couple of important classes of hybrid SDEs. Making full use of their special features, we will be able to establish a better bound on. Our new theory enables us to observe the system state less frequently (so costless) but still to be able to design the feedback control based on the discrete-timestate observations to stabilize the given hybrid SDEs in the sense of mean-square exponential stability. Moreover, we will be able to establish a better bound on making use of Lyapunov functionals. By this method, we will not only discuss the stabilization in the sense of exponential stability but also in other sense of H1 stability or asymptotic stability as well. We will not only consider the mean square stability but also the almost sure stability. It is easy to observe that the feedback control there still depends on the continuous-time observations of the mode. However, it usually costs to identify the current mode of the system in practice. So we can further improve the control to reduce the control cost by identifying the mode at discrete times when we make observations for the state. Therefore, we will also design such a type of feedback control based on the discrete-time observations of both state and mode to stabilize the given hybrid stochastic differential equations (SDEs) in the sense of mean-square exponential stability in this thesis. Similarly, we can extend our discussion to the stabilization of continuous-time hybrid stochastic differential equations by feedback controls based on not only discrete-time state observations but also discrete-time mode observations by Lyapunov method. At last, we will investigate stability of Stochastic differential delay equations with Markovian switching by feedback control based on discrete-time State and mode observations by using Lyapunov functional. Hence, we will get the upperbound on the duration between two consecutive state and mode observations
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