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Yoga and Autism : the effectiveness of a year-long yoga programme. Its influence on physicality, communication, organisational skills and mood in a small group of school-age pupils
No full textThere are many informative books on the practice of yoga suggesting that yoga can bring benefits to the well-being of people on the autistic spectrum (Betts et al 2006, Cuomo 2007, Williams 2010, Goldberg 2013, Thornton-Hardy 2015).There is less empirical evidence to back up the claims made in these books. This longitudinal study observed six residential pupils, aged eleven to seventeen, with profound autism and accompanying learning difficulties, participating in a thirty minute yoga programme which was conducted four days a week for one year in a comfortable, quiet environment. Its purpose was to ascertain if yoga could influence physicality, communication, attention, motor planning, organisation and mood and if this was positive could the changes be sustained and generalised into daily activities.;After baseline information was gathered, data was collected using a variety of specially designed forms. The Researcher led each session, modelling the poses and observing the pupils as they copied her. Data was also collected from the Education Team and Support Workers with parents contributing to the data collection each time they visited school or when the pupils went home. Using a descriptive case study approach, the data followed the progress of each pupil during yoga and for two hours after yoga, plotting changes over the year. The data was analysed qualitatively and where appropriate, quantitatively.;Results showed that pupils increased in flexibility and strength, improved their balance, bilateral integration and symmetry. An increase in the pupils` use of appropriate short phrases was noted, episodes of joint attention increased as did use of greetings and one pupil began vocalising intentionally. The data showed a small increase in attention, motor planning and organisational skills out with yoga, indicating some generalisation had taken place. By the end of the programme, the pupils appeared less anxious and stressed and more confident. A striking result was a 'stillness' which replaced constant fidgeting by the pupils.;This study suggests reasons why yoga is a positive intervention in autism and adds weight to the positive results of the other existing studies. The consistent practice of asanas allows flexibility to develop and the improvement in bilateral integration allows symmetry to increase. The asanas seem to calm a stressed nervous system allowing a `stillness` to evolve, making listening and concentration easier to achieve and maintain. This could lead to the pupils being more ready to learn. Autism appears amenable to this kind of intervention and yoga may prove to be an important tool in our autism tool kit.There are many informative books on the practice of yoga suggesting that yoga can bring benefits to the well-being of people on the autistic spectrum (Betts et al 2006, Cuomo 2007, Williams 2010, Goldberg 2013, Thornton-Hardy 2015).There is less empirical evidence to back up the claims made in these books. This longitudinal study observed six residential pupils, aged eleven to seventeen, with profound autism and accompanying learning difficulties, participating in a thirty minute yoga programme which was conducted four days a week for one year in a comfortable, quiet environment. Its purpose was to ascertain if yoga could influence physicality, communication, attention, motor planning, organisation and mood and if this was positive could the changes be sustained and generalised into daily activities.;After baseline information was gathered, data was collected using a variety of specially designed forms. The Researcher led each session, modelling the poses and observing the pupils as they copied her. Data was also collected from the Education Team and Support Workers with parents contributing to the data collection each time they visited school or when the pupils went home. Using a descriptive case study approach, the data followed the progress of each pupil during yoga and for two hours after yoga, plotting changes over the year. The data was analysed qualitatively and where appropriate, quantitatively.;Results showed that pupils increased in flexibility and strength, improved their balance, bilateral integration and symmetry. An increase in the pupils` use of appropriate short phrases was noted, episodes of joint attention increased as did use of greetings and one pupil began vocalising intentionally. The data showed a small increase in attention, motor planning and organisational skills out with yoga, indicating some generalisation had taken place. By the end of the programme, the pupils appeared less anxious and stressed and more confident. A striking result was a 'stillness' which replaced constant fidgeting by the pupils.;This study suggests reasons why yoga is a positive intervention in autism and adds weight to the positive results of the other existing studies. The consistent practice of asanas allows flexibility to develop and the improvement in bilateral integration allows symmetry to increase. The asanas seem to calm a stressed nervous system allowing a `stillness` to evolve, making listening and concentration easier to achieve and maintain. This could lead to the pupils being more ready to learn. Autism appears amenable to this kind of intervention and yoga may prove to be an important tool in our autism tool kit
Multi-objective hybrid optimal control with application to space systems
Get PDFThis dissertation presents a global method to solve multi-objective hybrid optimalcontrol problems. The method is applicable to general problems but the emphasis here is on space systems and missions. This holistic framework combines three main building blocks: a memetic multi-objective optimisation algorithm, a transcription method to solve general optimal control problems, and the treatment of mixed integer problems. The framework is able to automatically produce a well spread set of Pareto optimal solutions, each of which can consist of an optimal open loop guidance law and system design parameters, which can include the set and order of targets or operations that compose the structure of a mission. The framework was employed to perform the multi-objective trajectory and system design of reusable launch vehicles, including the sizing the engines, structural masses, fuel tanks and wings, and to design a multiple target debris removal space mission in which the trajectory of the spacecraft and the sequence in which the targets are visited had to be simultaneously optimised.This dissertation presents a global method to solve multi-objective hybrid optimalcontrol problems. The method is applicable to general problems but the emphasis here is on space systems and missions. This holistic framework combines three main building blocks: a memetic multi-objective optimisation algorithm, a transcription method to solve general optimal control problems, and the treatment of mixed integer problems. The framework is able to automatically produce a well spread set of Pareto optimal solutions, each of which can consist of an optimal open loop guidance law and system design parameters, which can include the set and order of targets or operations that compose the structure of a mission. The framework was employed to perform the multi-objective trajectory and system design of reusable launch vehicles, including the sizing the engines, structural masses, fuel tanks and wings, and to design a multiple target debris removal space mission in which the trajectory of the spacecraft and the sequence in which the targets are visited had to be simultaneously optimised
Stabilization of stochastic differential equations by feedback controls based on discrete-time observations
Get PDFThis thesis was previously held under moratorium from 11th February 2019 until 25th June 2021.Traditionally, to stabilize an unstable continuous-time stochastic differential equation (SDE) by feedback control, continuous-time observations of the system state are required. This is obviously expensive and unrealistic, so recently Mao discretized the observations. This thesis is to investigate the stabilization problem of continuous-time differential equation systems by deterministic and stochastic feedback controls based on discrete-time observations. This problem includes determining the conditions for original system and controller, and calculating the upper bound of the observation interval, namely the minimum of the observation frequency. The SDEs discussed in this thesis are all in the Itô sense. The main mathematical fundamentals used are Itôs formula, Lyapunov’s second method and inequalities. The problem was investigated under Lipschitz continuity and linear growth condition. Firstly, I investigated the hybrid SDEs, which is also known as stochastic differential equations with Markovian switching. Using discrete-time observations of system state and mode, we can achieve pth moment stabilization in the sense of asymptotic and exponential stability for p > 1. Our new theory expands from the second moment to pth moment and reduces the observation frequency. Secondly, I used stochastic feedback control, which is based on Brownian motion, to stabilize non-autonomous linear scalar ODEs as well as nonlinear multidimensional hybrid SDEs. Almost sure exponential stabilization is discussed. The new established theory expands the scope of applicable original unstable systems from autonomous ODEs to non-autonomous ODEs and hybrid SDEs. Thirdly, by making full use of the time-varying system property, I used the timevarying observation intervals instead of a constant as before. Non-autonomous periodic SDEs and hybrid SDEs are investigated. Many stabilities are discussed, including asymptotic and exponential stabilities in pth moment for p > 1 and almost surely. My new established theory not only reduces the observation frequencies, but also offers flexibility on the setting of observations.Traditionally, to stabilize an unstable continuous-time stochastic differential equation (SDE) by feedback control, continuous-time observations of the system state are required. This is obviously expensive and unrealistic, so recently Mao discretized the observations. This thesis is to investigate the stabilization problem of continuous-time differential equation systems by deterministic and stochastic feedback controls based on discrete-time observations. This problem includes determining the conditions for original system and controller, and calculating the upper bound of the observation interval, namely the minimum of the observation frequency. The SDEs discussed in this thesis are all in the Itô sense. The main mathematical fundamentals used are Itôs formula, Lyapunov’s second method and inequalities. The problem was investigated under Lipschitz continuity and linear growth condition. Firstly, I investigated the hybrid SDEs, which is also known as stochastic differential equations with Markovian switching. Using discrete-time observations of system state and mode, we can achieve pth moment stabilization in the sense of asymptotic and exponential stability for p > 1. Our new theory expands from the second moment to pth moment and reduces the observation frequency. Secondly, I used stochastic feedback control, which is based on Brownian motion, to stabilize non-autonomous linear scalar ODEs as well as nonlinear multidimensional hybrid SDEs. Almost sure exponential stabilization is discussed. The new established theory expands the scope of applicable original unstable systems from autonomous ODEs to non-autonomous ODEs and hybrid SDEs. Thirdly, by making full use of the time-varying system property, I used the timevarying observation intervals instead of a constant as before. Non-autonomous periodic SDEs and hybrid SDEs are investigated. Many stabilities are discussed, including asymptotic and exponential stabilities in pth moment for p > 1 and almost surely. My new established theory not only reduces the observation frequencies, but also offers flexibility on the setting of observations
Dynamic phasor modelling of VSC FACTS devices for small signal stability studies
Get PDFThe existence of harmonics and oscillations represent major problems for reliable operation of power system components. Therefore, investigating their response requires finding an appropriate model which reflects their response including these variations. The mathematical derivation of the state space models and impedance models of some of voltage source converters in flexible ac transmission systems (VSC-FACTS) systems is presented using synchronous dq and dq-dynamic phasor approach.;Two types of the VSC-FACTS devices are studied in this thesis; the static synchronous compensator (STATCOM) due to its popularity in the power system network and static synchronous series compensator (SSSC) due to its effective on damping system oscillations. The effect of mechanical section of the synchronous machine and turbine sections on the machine impedance is analysed. A generalised state space and impedance modelling is proposed by converting the synchronous dq models to dq-dynamic phasor models;A development of harmonic stability criteria for the proposed modelling is presented. The proposed modelling is employed to present the harmonics effect on the STATCOM and SSSC response and to identify their unbalanced operation in frequency domain. The main features of the proposed modelling technique are compared comprehensively with the conventional modelling techniques for stability studies assessment. It shows the advantages of proposed method and the importance of including the harmonics in the stability studies.;A comparison between different control modes of the SSSC is discussed in the frequency domain. The effectiveness of these control modes on damping system oscillations is investigated using the impedance concept. It presented the effectiveness of impedance control mode on damping system oscillations over the other control modes. A fast impedance measurement unit (IMU) is proposed to monitor the small signal stability.;The proposed IMU can measure accurately the system impedance within a very short time without any filtering requirements. The effect of changing the STATCOM control gains on the impedance norm is investigated. Also, the effect of shunt and series virtual impedances on the infinite norm of the STATCOM impedance which can be used by network operators to retain the stability is discussed.The existence of harmonics and oscillations represent major problems for reliable operation of power system components. Therefore, investigating their response requires finding an appropriate model which reflects their response including these variations. The mathematical derivation of the state space models and impedance models of some of voltage source converters in flexible ac transmission systems (VSC-FACTS) systems is presented using synchronous dq and dq-dynamic phasor approach.;Two types of the VSC-FACTS devices are studied in this thesis; the static synchronous compensator (STATCOM) due to its popularity in the power system network and static synchronous series compensator (SSSC) due to its effective on damping system oscillations. The effect of mechanical section of the synchronous machine and turbine sections on the machine impedance is analysed. A generalised state space and impedance modelling is proposed by converting the synchronous dq models to dq-dynamic phasor models;A development of harmonic stability criteria for the proposed modelling is presented. The proposed modelling is employed to present the harmonics effect on the STATCOM and SSSC response and to identify their unbalanced operation in frequency domain. The main features of the proposed modelling technique are compared comprehensively with the conventional modelling techniques for stability studies assessment. It shows the advantages of proposed method and the importance of including the harmonics in the stability studies.;A comparison between different control modes of the SSSC is discussed in the frequency domain. The effectiveness of these control modes on damping system oscillations is investigated using the impedance concept. It presented the effectiveness of impedance control mode on damping system oscillations over the other control modes. A fast impedance measurement unit (IMU) is proposed to monitor the small signal stability.;The proposed IMU can measure accurately the system impedance within a very short time without any filtering requirements. The effect of changing the STATCOM control gains on the impedance norm is investigated. Also, the effect of shunt and series virtual impedances on the infinite norm of the STATCOM impedance which can be used by network operators to retain the stability is discussed
Machine learning techniques for the health monitoring of rotating machinery in nuclear power plants
Get PDFThis thesis explores the development of data-driven and machine learning methods in application to the health monitoring of rotating plant items being used in the primary and secondary cycles of the Advanced Gas-cooled Reactor (AGR) nuclear power plants in the UK. The methods fall broadly into two categories: the statistical augmentation of a pre-existing knowledge-based system for turbine generator vibration alarm analysis, and the development of a machine learning model for the exploration of long-term predictive measures of asset health for AGR gas circulator units. Both of these topics are unified in their engineering context, and the overall aim of the approaches employed: to provide improved decision support using data to reliability staff tasked with monitoring key nuclear assets. A self-tuning methodology for knowledge-based system parameterisation and data selection in rotomachinery vibration monitoring is introduced, providing a comparative study of numerous methods and case studies for features of interest in both steady-state and step change conditions. These approaches were developed using a historical dataset taken from a turbine generator in use at an AGR, with time series streams from multiple component channels. An event-driven approach to asset health is presented, utilising a support vector machine & logistic regression hybrid model to estimate particular states of interest associated with the gas circulator duty cycle. This approach to health monitoring (examining responses during semi-regular refuelling events) is shown to correlate highly with the remaining useful life of a circulator unit which eventually underwent an unexpected failure, and provides a potential quantitative metric for preventing repeat instances.This thesis explores the development of data-driven and machine learning methods in application to the health monitoring of rotating plant items being used in the primary and secondary cycles of the Advanced Gas-cooled Reactor (AGR) nuclear power plants in the UK. The methods fall broadly into two categories: the statistical augmentation of a pre-existing knowledge-based system for turbine generator vibration alarm analysis, and the development of a machine learning model for the exploration of long-term predictive measures of asset health for AGR gas circulator units. Both of these topics are unified in their engineering context, and the overall aim of the approaches employed: to provide improved decision support using data to reliability staff tasked with monitoring key nuclear assets. A self-tuning methodology for knowledge-based system parameterisation and data selection in rotomachinery vibration monitoring is introduced, providing a comparative study of numerous methods and case studies for features of interest in both steady-state and step change conditions. These approaches were developed using a historical dataset taken from a turbine generator in use at an AGR, with time series streams from multiple component channels. An event-driven approach to asset health is presented, utilising a support vector machine & logistic regression hybrid model to estimate particular states of interest associated with the gas circulator duty cycle. This approach to health monitoring (examining responses during semi-regular refuelling events) is shown to correlate highly with the remaining useful life of a circulator unit which eventually underwent an unexpected failure, and provides a potential quantitative metric for preventing repeat instances
Physical analysis of solid solution formulations
Get PDFAmorphous solid dispersion is one of the techniques used for enhancing dissolution rate of drugs with low aqueous solubility. The physical stability of the amorphous solid dispersion is the main challenge for their formulation development and commercialisation by pharmaceutical industry. The aims of the project were to prepare amorphous solid solution of a poorly aqueous soluble drug using different molecular weight mixtures of PEG and PEG mixed with other polymers such as PVP and poloxamers, the formulations were prepared using melt method, solvent evaporation and quench cooled from melt method. Also, to find a system with controlled instability to study the impact of various features on the stability of the formulation. A series of physicochemical characterisation techniques were used to evaluate the different formulations such as XRPD, VT XRPD, DSC, dissolution and microscopy. The cooling temperature of the formulation from melt has a great impact on forming amorphous CBZ in PEG mixture. PEG 300 did show the ability to reduce the crystallinity in the other PEG used and to reduce the enthalpy of CBZ recrystallisation which indicates that less crystals been formed. The higher the PEG concentration in the formulation, the more stable the CBZ amorphous form. The best performing formulations in terms of controlling the recrystallisation of the CBZ from melt were the PEG 4000 and 6000 mixed with PEG 300, but their dissolution profile was not as good as the formulations with one PEG. The substitution of just5% of PEG weight with PVP did show an increase in CBZ amorphous form stability.The quench cooling method did not show any decomposition of CBZ and that was proven by the HPLC method used.CBZ amorphous solid solution can be achieved by formulating the drug with PEGusing melt method and the addition of secondary polymer such as PVP to the formulation at low concentration can inhibit the CBZ recrystallisation from the glassy/ liquid state and increases CBZ physical stability.Amorphous solid dispersion is one of the techniques used for enhancing dissolution rate of drugs with low aqueous solubility. The physical stability of the amorphous solid dispersion is the main challenge for their formulation development and commercialisation by pharmaceutical industry. The aims of the project were to prepare amorphous solid solution of a poorly aqueous soluble drug using different molecular weight mixtures of PEG and PEG mixed with other polymers such as PVP and poloxamers, the formulations were prepared using melt method, solvent evaporation and quench cooled from melt method. Also, to find a system with controlled instability to study the impact of various features on the stability of the formulation. A series of physicochemical characterisation techniques were used to evaluate the different formulations such as XRPD, VT XRPD, DSC, dissolution and microscopy. The cooling temperature of the formulation from melt has a great impact on forming amorphous CBZ in PEG mixture. PEG 300 did show the ability to reduce the crystallinity in the other PEG used and to reduce the enthalpy of CBZ recrystallisation which indicates that less crystals been formed. The higher the PEG concentration in the formulation, the more stable the CBZ amorphous form. The best performing formulations in terms of controlling the recrystallisation of the CBZ from melt were the PEG 4000 and 6000 mixed with PEG 300, but their dissolution profile was not as good as the formulations with one PEG. The substitution of just5% of PEG weight with PVP did show an increase in CBZ amorphous form stability.The quench cooling method did not show any decomposition of CBZ and that was proven by the HPLC method used.CBZ amorphous solid solution can be achieved by formulating the drug with PEGusing melt method and the addition of secondary polymer such as PVP to the formulation at low concentration can inhibit the CBZ recrystallisation from the glassy/ liquid state and increases CBZ physical stability
The panoptic principle : privacy and surveillance in the public library as evidenced in the acceptable use policy
Get PDFFacilitating access to the Internet is an important part of the public library profession. Part of managing this access relies on the acceptable use policy, an agreement between the library and the user regarding the conditions of access. This study analysed acceptable use policies in UK public libraries to ascertain whether they exhibit Michel Foucault's panoptic principle, a metaphor for surveillance derived from Jeremy Bentham's Panopticon, an institutional inspection building. The policies were also analysed as to how they encourage and discourage information access through surveillance, filtering, and demonstration of the ethical principles of the profession. The effectiveness of balancing the caring and controlling elements of public access was also analysed, influenced by David Lyon's theories regarding caring and controlling aspects of surveillance. The study analysed 205 of the 206 acceptable use polices across UK public library authorities. The policies and authorship details were collected via Internet searching and freedom of information request. Readability testing was then used to establish the difficulty of the documents. After this, qualitative content analysis was used to investigate the language of the policies. The acceptable use policies were found to be too difficult to understand easily. They exhibited aspects of the panoptic principle, they encouraged access by reflecting ethical principles and they discouraged access due to the inconsistent application and description of filtering software. The policies were varied in tone and content, demonstrating both caring and controlling aspects of public access. The findings suggest a single acceptable use policy would be recommended. This way access would be consistent through the country. It is also recommended that the policy should have more clarity regarding aspects such as filtering and what the aims of the service are. The findings of the study were then used to create a model acceptable use policy that could be used and disseminated.Facilitating access to the Internet is an important part of the public library profession. Part of managing this access relies on the acceptable use policy, an agreement between the library and the user regarding the conditions of access. This study analysed acceptable use policies in UK public libraries to ascertain whether they exhibit Michel Foucault's panoptic principle, a metaphor for surveillance derived from Jeremy Bentham's Panopticon, an institutional inspection building. The policies were also analysed as to how they encourage and discourage information access through surveillance, filtering, and demonstration of the ethical principles of the profession. The effectiveness of balancing the caring and controlling elements of public access was also analysed, influenced by David Lyon's theories regarding caring and controlling aspects of surveillance. The study analysed 205 of the 206 acceptable use polices across UK public library authorities. The policies and authorship details were collected via Internet searching and freedom of information request. Readability testing was then used to establish the difficulty of the documents. After this, qualitative content analysis was used to investigate the language of the policies. The acceptable use policies were found to be too difficult to understand easily. They exhibited aspects of the panoptic principle, they encouraged access by reflecting ethical principles and they discouraged access due to the inconsistent application and description of filtering software. The policies were varied in tone and content, demonstrating both caring and controlling aspects of public access. The findings suggest a single acceptable use policy would be recommended. This way access would be consistent through the country. It is also recommended that the policy should have more clarity regarding aspects such as filtering and what the aims of the service are. The findings of the study were then used to create a model acceptable use policy that could be used and disseminated
Control and operation of MMC-HVDC system for connecting offshore wind farm
Get PDFFor connection of large offshore wind farms over distances 80-100 km, modular multi-level converter (MMC) based high voltage DC (HVDC) system emerges as a more suitable solution than HVAC due to its flexible control and transmission distance not affected by the cable charging current. For HVDC connected wind farms, the offshore wind farm AC networks are established by the offshore MMC stations which exhibit significant difference compared to conventional onshore networks. Consequently, this thesis focuses on the offshore AC voltage control, system stability, and fault analysis of the offshore wind farm system connected with MMC-HVDC transmission.;To control the offshore AC voltage and frequency using the offshore MMC, fixed frequency control is the most common approach. However, offshore system with fixed frequency control presents a slow response, especially during large transients. Thus, in order to improve the voltage controllability and system performances, a PLL based enhanced voltage and frequency control is proposed for the offshore MMC station. The performance of the proposed control is validated through time-domain simulations.;The stability of the offshore system with the proposed control is further analysed using a developed small-signal offshore system model, including the offshore MMC and lumped wind turbine grid side converters. Bode plots and pole/zero maps are utilized to investigate suitable control parameter ranges and interactions between the power and AC voltage.;For the offshore AC network, system control and response during offshore AC faults need to be carefully considered. During an offshore fault, both the offshore MMC and WT converters have to ensure their safe operation by limiting the currents to be within their maximum ranges, and in the meantime, enable satisfactory operation of the overcurrent protection relays. Considering the requirements of overcurrent relay, a fault current providing control for the offshore MMC is proposed which ramps up current during faults over a predefined profile.;This ensures adequate fault current for the relays while avoids excessive overcurrent during WT string faults. The proposed fault current providing control is validated with offshore AC faults at different locations in a wind farm (e.g. clusters and strings).;Onshore faults which lead to the rapid reduction of power transition capability of the onshore MMC is another challenge to MMC-HVDC connected offshore wind farm system. A DC voltage dependent AC voltage control is thus applied at offshore MMC station which reduces the offshore AC voltage once DC overvoltage is detected. The reduced offshore AC voltage results in the automatic reduction of power generated by the wind farm such that the power imported to and exported from the HVDC link can be rebalanced.;Therefore, DC overvoltage is alleviated and when the onshore fault is cleared, the offshore AC voltage returns to the nominal value, and normal power generation and transmission can be quickly restored. Different onshore fault conditions with voltage drops of 100%, 50% and 20% are tested to show the satisfactory onshore fault ride-through control of the system.For connection of large offshore wind farms over distances 80-100 km, modular multi-level converter (MMC) based high voltage DC (HVDC) system emerges as a more suitable solution than HVAC due to its flexible control and transmission distance not affected by the cable charging current. For HVDC connected wind farms, the offshore wind farm AC networks are established by the offshore MMC stations which exhibit significant difference compared to conventional onshore networks. Consequently, this thesis focuses on the offshore AC voltage control, system stability, and fault analysis of the offshore wind farm system connected with MMC-HVDC transmission.;To control the offshore AC voltage and frequency using the offshore MMC, fixed frequency control is the most common approach. However, offshore system with fixed frequency control presents a slow response, especially during large transients. Thus, in order to improve the voltage controllability and system performances, a PLL based enhanced voltage and frequency control is proposed for the offshore MMC station. The performance of the proposed control is validated through time-domain simulations.;The stability of the offshore system with the proposed control is further analysed using a developed small-signal offshore system model, including the offshore MMC and lumped wind turbine grid side converters. Bode plots and pole/zero maps are utilized to investigate suitable control parameter ranges and interactions between the power and AC voltage.;For the offshore AC network, system control and response during offshore AC faults need to be carefully considered. During an offshore fault, both the offshore MMC and WT converters have to ensure their safe operation by limiting the currents to be within their maximum ranges, and in the meantime, enable satisfactory operation of the overcurrent protection relays. Considering the requirements of overcurrent relay, a fault current providing control for the offshore MMC is proposed which ramps up current during faults over a predefined profile.;This ensures adequate fault current for the relays while avoids excessive overcurrent during WT string faults. The proposed fault current providing control is validated with offshore AC faults at different locations in a wind farm (e.g. clusters and strings).;Onshore faults which lead to the rapid reduction of power transition capability of the onshore MMC is another challenge to MMC-HVDC connected offshore wind farm system. A DC voltage dependent AC voltage control is thus applied at offshore MMC station which reduces the offshore AC voltage once DC overvoltage is detected. The reduced offshore AC voltage results in the automatic reduction of power generated by the wind farm such that the power imported to and exported from the HVDC link can be rebalanced.;Therefore, DC overvoltage is alleviated and when the onshore fault is cleared, the offshore AC voltage returns to the nominal value, and normal power generation and transmission can be quickly restored. Different onshore fault conditions with voltage drops of 100%, 50% and 20% are tested to show the satisfactory onshore fault ride-through control of the system
Quantum correlations and exchange symmetry
Get PDFMany of the advantages that the flourishing fields of quantum technologies and quantum information theory achieve over their classical counterparts rely on quantum correlations. Such correlations represent a valuable resource and their characterization and quantification is a key theoretical task.We study the quantum correlations for systems which are symmetric under the exchange of any two particles for two main reasons. Firstly, exchange symmetry constrains the set of possible states for the system and reduces the degrees of freedom required to describe them, simplifying the characterization of quantum correlations. Furthermore,systems that exhibit exchange symmetry have notable physical properties that make them well-suited for quantum information tasks and quantum simulation. In this thesis we investigate how exchange symmetry affects the mathematical description, as well as the physical realization and measurement, of quantum correlations. To begin with, we address the open problem of quantifying identical-particle entanglement. We introduce a novel entanglement measure accounting for the wavefunction (anti)symmetrization in the first quantised picture of systems of fermions and bosons. This measure, which may be evaluated by means of semidefinite programming, is sensitive to quantum correlations originating from interactions and other entanglement generating dynamical processes, rather than the kinematic effect of (anti)symmetrization. We apply our novel measure to estimate entanglement based on measurements of a system of two ultracold fermionic atoms in an optical trap. Exchange symmetry is not only a property of identical-particle states, but can pertain also to distinguishable subsystems. Based on the properties of subspaces of states which are symmetric or antisymmetric under particle exchange, we introduce a novel class of exchange-symmetric bound entangled states. We provide a simple parametrization that makes it possible to obtain states which are bound entangled in terms of a convex combination of well-studied exchange-symmetric states. Finally, we study the quantum correlations of a family of states with exchange symmetry in the multipartite device-independent scenario. We evaluate the noise robustness of the task of entanglement certification for varying numbers of uncharacterised measurement devices for the states of the family. The resulting structure enables us to establish a hierarchy of quantum correlations in the tripartite case.Many of the advantages that the flourishing fields of quantum technologies and quantum information theory achieve over their classical counterparts rely on quantum correlations. Such correlations represent a valuable resource and their characterization and quantification is a key theoretical task.We study the quantum correlations for systems which are symmetric under the exchange of any two particles for two main reasons. Firstly, exchange symmetry constrains the set of possible states for the system and reduces the degrees of freedom required to describe them, simplifying the characterization of quantum correlations. Furthermore,systems that exhibit exchange symmetry have notable physical properties that make them well-suited for quantum information tasks and quantum simulation. In this thesis we investigate how exchange symmetry affects the mathematical description, as well as the physical realization and measurement, of quantum correlations. To begin with, we address the open problem of quantifying identical-particle entanglement. We introduce a novel entanglement measure accounting for the wavefunction (anti)symmetrization in the first quantised picture of systems of fermions and bosons. This measure, which may be evaluated by means of semidefinite programming, is sensitive to quantum correlations originating from interactions and other entanglement generating dynamical processes, rather than the kinematic effect of (anti)symmetrization. We apply our novel measure to estimate entanglement based on measurements of a system of two ultracold fermionic atoms in an optical trap. Exchange symmetry is not only a property of identical-particle states, but can pertain also to distinguishable subsystems. Based on the properties of subspaces of states which are symmetric or antisymmetric under particle exchange, we introduce a novel class of exchange-symmetric bound entangled states. We provide a simple parametrization that makes it possible to obtain states which are bound entangled in terms of a convex combination of well-studied exchange-symmetric states. Finally, we study the quantum correlations of a family of states with exchange symmetry in the multipartite device-independent scenario. We evaluate the noise robustness of the task of entanglement certification for varying numbers of uncharacterised measurement devices for the states of the family. The resulting structure enables us to establish a hierarchy of quantum correlations in the tripartite case
A user-centric framework for addressing vulnerability to social engineering in social networks : a mixed methods study of a Saudi academic community
Get PDFThis thesis was previously held under moratorium from 23/09/2019 to 04/12/2020.The popularity of social networking sites has attracted billions of users from around the world to engage with and share their information on these networks. The vast amount of circulating data and information exposes these networks to several security risks. Social engineering is one of the most common types of threat that may face social network users. Social engineering is an attack technique for manipulating and deceiving users in order to access or gain privileged information. Training and increasing users' awareness of such threats is essential for maintaining continuous and safe use of social networking services. Identifying the most vulnerable users in order to target them for these training programs is desirable for increasing the effectiveness of such programs. In this context, the present research investigates user characteristics that impact on susceptibility to social engineering-based attacks, using a sequential exploratory mixed methods approach designed in three study phases.;The first study phase proposed and validated a user-centric framework that was formulated on the basis of four different perspectives: socio-psychological, habitual, perceptual, and socio-emotional. The measurement scales for the selected user-centric characteristics were developed and validated in the second study phase. The third study phase constructed a conceptual model that predicts users' susceptibility to social engineering victimisation. According to the scenario-based experiment that was conducted to test the proposed conceptual model, there are direct and indirect effects of users' characteristics on their susceptibility to social engineering-based attacks on social networks. Users' trust, level of involvement, and experience with cybercrime were found to be the strongest predictors of users' vulnerability; while personality traits and users' motivation to use social network were found to have an indirect impact on their vulnerability and to be mediated by other factors in the model.;This research contributes to the existing knowledge of social engineering in social networks, particularly by augmenting the research area of predicting user behaviour towards security threats with the proposal of a novel framework and model to show how user vulnerability to social engineering-based attacks can be predicted. Socio-emotional and perceptual factors, which have been given less attention in previous literature, were revealed by the findings of this research as critical aspects in predicting users' vulnerability. Social network users have different personalities, experiences, and backgrounds. The present research has considered these differences and offers personalised advice that targets the individual user's needs by designing an architecture for a semi-automated security advisory system which provides new insight into combatting social engineering threats.The popularity of social networking sites has attracted billions of users from around the world to engage with and share their information on these networks. The vast amount of circulating data and information exposes these networks to several security risks. Social engineering is one of the most common types of threat that may face social network users. Social engineering is an attack technique for manipulating and deceiving users in order to access or gain privileged information. Training and increasing users' awareness of such threats is essential for maintaining continuous and safe use of social networking services. Identifying the most vulnerable users in order to target them for these training programs is desirable for increasing the effectiveness of such programs. In this context, the present research investigates user characteristics that impact on susceptibility to social engineering-based attacks, using a sequential exploratory mixed methods approach designed in three study phases.;The first study phase proposed and validated a user-centric framework that was formulated on the basis of four different perspectives: socio-psychological, habitual, perceptual, and socio-emotional. The measurement scales for the selected user-centric characteristics were developed and validated in the second study phase. The third study phase constructed a conceptual model that predicts users' susceptibility to social engineering victimisation. According to the scenario-based experiment that was conducted to test the proposed conceptual model, there are direct and indirect effects of users' characteristics on their susceptibility to social engineering-based attacks on social networks. Users' trust, level of involvement, and experience with cybercrime were found to be the strongest predictors of users' vulnerability; while personality traits and users' motivation to use social network were found to have an indirect impact on their vulnerability and to be mediated by other factors in the model.;This research contributes to the existing knowledge of social engineering in social networks, particularly by augmenting the research area of predicting user behaviour towards security threats with the proposal of a novel framework and model to show how user vulnerability to social engineering-based attacks can be predicted. Socio-emotional and perceptual factors, which have been given less attention in previous literature, were revealed by the findings of this research as critical aspects in predicting users' vulnerability. Social network users have different personalities, experiences, and backgrounds. The present research has considered these differences and offers personalised advice that targets the individual user's needs by designing an architecture for a semi-automated security advisory system which provides new insight into combatting social engineering threats
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