The topic of polymer nanocomposites remains an active area of research in the dielectrics community, due to the unique electrical properties that these materials could exhibit. To explain the behaviour of these materials, the importance of clarifying the interfaces between nanoparticles and polymer matrices has been emphasised. However,understanding of the interface in nanocomposites is unsatisfactory and, consequently,many experimental results remain unexplained. This thesis reports on an investigation into a polyethylene nanocomposite system that contains varying amounts of nanosilica that differ with respect to their surface chemistry. The addition of nanosilica, even with different surface chemistries, was found to enhance the nucleation density of polyethylene and perturb the spherulitic development. While less organised lamellar structures would be expected to lead to a lower breakdown strength, this does not appearto be the case for the material systems considered here under alternating current (AC) fields. In addition, nanosilica filled polyethylene was found to absorb significantly more water than unfilled polyethylene, with the consequence that both the permittivity and the loss tangent increase with increasing duration of water immersion. However, appropriate surface treatment of nanosilica reduces the water absorption effect and modifies the dielectric response of the nanocomposites compared with those containing an equivalent amount of untreated nanosilica. Although water absorption may not be a technologically desirable characteristic, the results indicate that water molecules can act as effective dielectric probes of interfacial factors. Meanwhile, the direct current (DC) breakdown strength reduces with the inclusion of increasing amount of nanosilica in the polyethylene, but surface treatment of nanosilica improves the DC breakdown strength with respect to equivalent nanocomposites containing untreated nanosilica. Results from space charge studies reveal increased space charge accumulation in the presence of the untreated nanosilica and, upon surface treatment of the nanosilica, the charge development was suppressed in comparison with nanocomposites containing an equivalent amount of untreated nanosilica. This observation suggests that space charge accumulation and DC failure are related in these systems and it would seem that control of surface chemistry is particularly critical in connection with the use of nanocomposites in DC applications. Finally, the mechanisms underpinning the concept of filler functionalisation in nanocomposites were investigated via the use of different aliphatic chain length silane coupling agents, and the results show that long silane chains enhance the DC breakdown strength of the resulting nanocomposites. The possible further enhancement in DC breakdown strength is also highlighted. Overall, this thesis demonstrates how a nanoparticle’s interface chemistry can affect both the structure and the electrical properties of the resulting nanocomposites, and serves as an important foundation towards the engineering of nanocomposites as the reliable electricalinsulation materials of the future, through the understanding of the interface.

The Web of Data extends the World Wide Web (WWW) in a way that applications can understand information and cooperate with humans on complex tasks. The basis of performing complex tasks is low latency queries over the Web of Data. The large scale and distributed nature of the Web of Data have negative impacts on several critical factors for efficient query processing, including fast data transmission between datasets, predictable data distribution and statistics that summarise and describe certain patterns in the data. Moreover, it is common on the Web of Data that the same resource is identified by multiple URIs. This phenomenon, named co-reference, potentially increases the complexity of query processing, and makes it even harder to obtain accurate statistics. With the aforementioned challenges, it is not clear whether it is possible to achieve efficient queries on the Web of Data on a large scale. In this thesis, we explore techniques to improve the efficiency of querying the Web of Data on a large scale. More specifically, we investigate two typical scenarios on the Web of Data, which are: 1) the scenario in which all datasets provide detailed statistics that are possibly available on a large scale, and 2) the scenario in which co-reference is taken into account, and datasets’ statistics are not reliable. For each scenario we explore existing and novel optimisation techniques that are tailored for querying the Web of Data, as well as well developed techniques with careful adjustments. For the scenario with detailed statistics we provide a scheme that implements a statistics query optimisation approach that requires detailed statistics, and intensively exploits parallelism. We propose an efficient algorithm called Parallel Sub-query Identification () to increase the degree of parallelism. () breaks a SPARQL query into sub-queries that can be processed in parallel while not increasing network traffic. We combine with dynamic programming to produce query plans with both minimum costs and a fair degree of parallelism. Furthermore, we develop a mechanism that maximally exploits bandwidth and computing power of datasets. For the scenario having co-reference and without reliable statistics we provide a scheme that implements a dynamic query optimisation approach that takes co-reference into account, and utilises runtime statistics to elevate query efficiency even further. We propose a model called Virtual Graph to transform a query and all its co-referent siblings into a single query with pre-defined bindings. Virtual Graph reduces the large number of outgoing and incoming requests that is required to process co-referent queries individually. Moreover, Virtual Graph enables query optimisers to find the optimal plan with respect to all co-referent queries as a whole. () is used in this scheme as well but provides a higher degree of parallelism with the help of runtime statistics. A Minimum-Spanning-Tree-based algorithm is used in this scheme as a result of using runtime statistics. The same parallel execution mechanism used in the previous scenario is adopted here as well. In order to examine the effectiveness of our schemes in practice, we deploy the above approaches in two distributed SPARQL engines, LHD-s and LHD-d respectively. Both engines are implemented using a popular Java-based platform for building Semantic Web applications. They can be used as either standalone applications or integrated into existing systems that require quick response of Linked Data queries. We also propose a scalable and flexible benchmark, called Distributed SPARQL Evaluation Framework (DSEF), for evaluating optimisation approaches in the Web of Data. DSEF adopts a expandable virtual-machine-based structure and provides a set of efficient tools to help easily set up RDF networks of arbitrary sizes. We further investigate the proportion and distribution of co-reference in the real world, based on which DESF is able to simulate co-reference for given RDF datasets. DSEF bases its soundness in the usage of widely accepted assessment data and queries. By comparing both LHD-s and LHD-d with existing approaches using DSEF, we provide evidence that neither existing statistics provided by datasets nor cost estimation methods, are sufficiently accurate. On the other hand, dynamic optimisation using runtime statistics together with carefully tuned parallelism are promising for significantly reducing the latency of large scale queries on the Web of Data. We also demonstrate that () and Virtual Graph algorithms significantly increase query efficiency for queries with or without co-reference. In summary, the contributions of this these include: 1) proposing two schemes for improving query efficiency in two typical scenarios in the Web of Data; 2) providing implementations, named LHD-s and LHD-d, for the two schemes respectively; 3) proposing a scalable and flexible evaluation framework for distributed SPARQL engines called DSEF; and 4) showing evidence that runtime-statistics-based dynamic optimisation with parallelism are promising to reduce latency of Linked Data queries on a large scale.

In this thesis we consider the development of a general nonlinear input-output theory which encompasses systems with initial conditions. Appropriate signal spaces (i.e., interval spaces, extended spaces and ambient spaces) are introduced with some fundamental assumptions to constitute a framework for the study of input-output systems with abstract initial conditions. Both systems and closed-loop systems are defined in a set theoretic manner from input-output pairs on a doubly infinite time axis, and a general construction of the initial conditions (i.e., a state at time zero) is given in terms of an equivalence class of trajectories on the negative time axis. Fundamental properties (such as existence, uniqueness, well-posedness and causality) of both systems and closed-loop systems are defined and discussed from a very natural point of view. Input-output operators are then defined for given initial conditions, and a suitable notion of input-output stability on the positive time axis with initial conditions is given. This notion of stability is closely related to the ISS/IOS concepts of Sontag. A fundamental robust stability theorem is derived which represents a generalisation of the input-output operator robust stability theorem of Georgiou and Smith to include the case of initial conditions; and can also be viewed as a generalisation of the ISS approach to enable a realistic treatment of robust stability in the context of perturbations which fundamentally change the structure of the state space. This includes a suitable generalisation of the nonlinear gap metric. Generalisations of this robust stability result are also extended to finite-time reachable systems and to systems with potential for finite-time escape by extending signals on extended spaces to a wider space (ambient space). Some linear and nonlinear applications are given to show the effects of the robust stability results. We also present a generalised nonlinear ISS-type small-gain result in this input-output structure set up in this thesis, which is established without extra observability conditions and with complete disconnection between the stability property and the existence, uniqueness properties of systems. Connections between Georgiou and Smith's robust stability type theorems and the nonlinear small-gain theorems are also discussed. An equivalence between a small-gain theorem and a slight variation on the fundamental robust stability result of Georgiou and Smith is shown.

A Web application that deploys on a set of servers and can be accessed by a large number of users over the Internet requires efficient security mechanisms. The core element in security is access control that enforces desired policies over the shared objects of the system and stops the unauthorised users to operate on these objects. Moreover, the used access control mechanism needs to be managed, through authorisation management elements, during the run-time of the system by the administrators. Therefore, the development of such models and their mechanisms are a main concern for secure systems development. Fine-grained access control and their authorisation management models provide more customisation possibilities and administrative power to the developers; however, in Web applications these models are typically hand-coded without taking advantage of the data model, object types, or contextual information. This thesis presents the design, implementation and evaluation of (), a declarative, fine-grained policy language that enables the developer to define a set of fine-grained access control and authorisation management models for a Web application. For () three types of access control and authorisation management models were designed and implemented. These models, used by (), are based on four main access control approaches, namely attribute-, discretionary-, mandatory-, and role-based access control models. For efficiency and flexibility, each access control model can be used with an authorisation management model. () compiler, first validates and verifies all these models based on written transformation strategies and verifies them by translating them into logical satisfiability problems to check the models for correctness and completeness, and against independently defined coverage criteria. If the models pass these tests, the generator then compiles them down to the existing tiers of WebDSL, a domain specific Web programming language.

As Flash memory is approaching physical scaling limit, there is great interest in the research of the next generation non-volatile memory. In addition to replacing Flash memory in data storage applications, the next generation non-volatile memory is also expected to have improved performance, especially more cycle endurance and faster read/write operation, so that it may eventually be the “universal" memory. Resistive memory (RM) is widely considered to be the overall most promising emerging non-volatile memory. This project focused RMs based on Cu and amorphous silicon carbide (a-SiC) following the recent reports of excellent retention and stabilities of such RMs, which was attributed to the advantageously low Cu diffusion rate in SiC. Material properties, namely chemical composition, structural properties and electrical conduction properties of the sputtering deposited a-SiC and a-SiC/Cu solid electrolytes were firstly analysed in this project. This project has then developed Cu/a-SiC RMs with via-stack and crossbar structures, with a-SiC and a-SiC/Cu as solid electrolytes and Au, W and TiN as counter electrodes. The switching characteristics of the obtained devices have then been thoroughly investigated. All devices based on Cu and a-SiC with different structure and material configurations have shown repeated resistive switching behaviour, with each batch showing certain unique features in their switching behaviour. Nonpolar resistive switching was observed in the Cu/a-SiC/Au and Cu/a-SiC:Cu/Au via-stack devices, while coexistence of bipolar and unipolar switching was observed in RMs with TiN and W counter electrodes. Our devices also exhibited significantly improved ON/OFF current ratio and great state retention performance. Furthermore, the switching mechanisms and conduction mechanism of these RMs were analysed based on their I-V characteristics. These results suggest promising application potentials for RMs based on Cu and a-SiC.

No description available.

This research discusses the theoretical investigation, simulation and hardware implementation of the ElectroMechanical Multi-stAge noise SHaping (EM-MASH) sigma delta modulator (ΣΔM). The potential advantages of an EM-ΣΔM MASH compared to single-loop high-order ΣΔMs applied to inertial MEMS sensors are its inherent stability and high overload input level due to the use of lower order ΣΔMs in its individual stages. Furthermore, MASH has the advantages of high dynamic range and high noise shaping performance because of its overall high-order ΣΔM architecture. So far, the EM-MASH has not been sufficiently explored. This study is expected to serve as solid basis for the application of EM-MASH. In this research, various EM-MASH architectures (MASH21, MASH22, MASH211, MASH221 and MASH222) were theoretically studied, and the results were validated with simulations. A fourth order EM-MASH22-ΣΔM was theoretically examined and successfully implemented with a capacitive MEMS accelerometer, which includes a second order EM-ΣΔM loop cascaded with a purely electronic second order ΣΔM. The quantization noise from the first loop is digitised by the second loop and then cancelled by digital filters, whereas the quantization noise from the second loop is shaped by the second loop filter and a digital filter, which together provide fourth order noise shaping. The performance of EM-MASH22 was compared with that of a single-loop fourth order EM-ΣΔM (SD4). Both architectures were investigated by system level modelling and hardware implementation using surface-mount PCB technology. The results show that (a) both architectures achieve the same noise floor level of 19 μg/√Hz; (b) MASH22 is unconditionally stable, whereas SD4 is only conditionally stable; and (c) MASH22 achieves a higher overload input level and a higher dynamic range than does SD4. Furthermore, the research presents a novel EM-MASH-ΣΔM that employs a dual quantization technique and adopts a 2-0 structure (EM-MASH20). With a simpler and configurable composition, MASH20 is aimed at exhibiting a performance higher than that achieved with the MASH22 structure. The MASH20 does not require a second-stage ΣΔM, which reduces the complexity of the digital filters compared to those required for the MASH22; thus, the digital filter matching is more easily achievable. The study shows that the MASH20, like the MASH22, has an inherent stability, high overload input level, and high dynamic range compared to single-loop ΣΔM. However, the MASH20, with its simpler implementation, achieved a higher dynamic range and signal-to-noise ratio than the MASH22 and the SD4. A capacitive MEMS accelerometer was designed and employed with MASH20. Within a bandwidth of 1 kHz, the sensor achieves a noise floor level of 15 μg/√Hz, a full-scale acceleration of ±20 g and a bias instability of 20 μg for a period of three hours. The EM-MASH-ΣΔM is sensitive to the variation of the sensing element parameters and other analogue parameters, both of which are subject to manufacturing tolerance and imperfections. This causes a leakage of the quantization noise in the final output and degrades the modulator performance. The research explored a calibration method to solve this problem by utilizing the digital domain capabilities. The method is based on the optimization algorithm which was investigated using MATLAB. The research confirms the concept of the EM-MASH structure and proves that it is applicable as a closed-loop interface for high-performance capacitive MEMS inertial sensors.

This research discusses Electronic Government (e-Government), in particular the challenges that face its development and widespread adoption in Saudi Arabia. In this research e-government is defined as a matrix of stakeholders: Government to Government, Government to Business and Government to Citizens, using information and communications technology to deliver and/or consume services. Electronic Government has been implemented in developed countries for some time, while in Saudi Arabia it is still at the implementation and developing stages. Electronic Government services face challenges, including trust, privacy, security, computer and information literacy, and culture. In addition, this research has identified the influential factors, including quality of service, diffusion of innovation, knowledge and skills, culture, lack of awareness, technical infrastructure, website design, security, privacy, and trust, that affect the citizens' intentions to adopt e-Government services in Saudi Arabia. Therefore, these factors have been evaluated using an exploratory study, which uses mixed-methods, to confirm that these proposed factors are important and that the citizens are concerned about them. Resulting form the exploratory study, this research ha developed an integrated model for aiding the Saudi government by identifying the factors that would influence citizens to adopt their services. The model has been validated by the main study for this research, including questionnaires for citizens, government employees and experts. The gathered data were analysed and assessed using the Structural Equation Modelling approach. From the main study, the results showed that the proposed model fits the data and applies to the Saudi context. Therefore, the validated model would be considered essential in order to help the Saudi government to overcome the concerns of their citizens to use and adopt the online services. Consequently, applying the proposed model can reduce the government's time, effort, and money in influencing their citizens' intentions to adopt the proposed online services.

One of the main problems in studying human origins from an evolutionary perspective is uniqueness: we have evolved to fill a social and cognitive niche that is so distinctive it renders useless the usual investigative tool of careful comparison with other, similar species. Features such as cognition, communication and cooperation reached, in humans, unprecedented levels of sophistication and complexity. These features not only converge to the social dimension but they also lack a clear function outside it, a fact that makes epiphenomenal explanations unlikely. The main goal of this thesis is to shed light on the conditions that led to the evolution of modern humans through the development of computational models. Our research hypothesis is based on the assumption that the human “primeval niche” lies in the intersection of three fundamental phenomena: cooperation, communication and cognition. We argue that these three elements are intimately connected and that their intersection is the ideal spot to explore the so called human cognitive explosion. The new internal selective pressures that arise from any cooperative environment trigger asymmetric competitive co-evolutionary arms races that can pull the population in the opposing directions of altruism and selfishness. Co evolutionary feedback loops usually stagnate due to their increasing biological cost, however, in the human case, the invention of communication and language as a tool for social cohesion opened up a new “medium”, where both co operators and defectors can play their own personal “battle” at a lower cost and at a faster pace. Following this, we re-implement and develop several models of the evolution of communication and cooperation. As this thesis progresses, the scope of our modelling efforts is narrowed towards the study of the emergence of the simplest cooperative mechanism that explicitly relies on communication and important cognitive abilities: indirect reciprocity. Our findings strongly suggest that primitive communication could have evolved in order to sustain cooperation through indirect reciprocity and therefore communication and, eventually, language could have evolved as a tool for social cohesion. Moreover, our results indicate that there are two different evolutionary paths towards this goal. The first includes low levels of gossip in a trusting environment governed by a moderately heterogeneous moral system. The second consists of high levels of gossip in a suspicious context governed by a homogeneous moral system. The main contribution of this thesis is a plausible evolutionary outline of the primeval niche that early humans occupied and its depiction through the interactions and interdependence of the three cornerstones of human nature: cognition, communication and cooperation.

Improvements in data storage and network technologies, the emergence of new highresolution scientific instruments, the widespread use of the Internet and the World Wide Web and even globalisation have contributed to the emergence of new large scale dataintensive applications. These applications require new systems that allow users to store, share and process data across computing centres around the world. Worldwide distributed data management is particularly important when there is a lot of data, more than can fit in a single computer or even in a single data centre. Designing systems to cope with the demanding requirements of these applications is the focus of the present work. This thesis presents four contributions. First, it introduces a set of design principles that can be used to create distributed data management systems for data-intensive applications. Second, it describes an architecture and implementation that follows the proposed design principles, and which results in a scalable, fault tolerant and secure system. Third, it presents the system evaluation, which occurred under real operational conditions using close to one hundred computing sites and with more than 14 petabytes of data. Fourth, it proposes novel algorithms to model the behaviour of file transfers on a wide-area network. This work also presents a detailed description of the problem of managing distributed data, ranging from the collection of requirements to the identification of the uncertainty that underlies a large distributed environment. This includes a critique of existing work and the identification of practical limits to the development of transfer algorithms on a shared distributed environment. The motivation for this work has been the ATLAS Experiment for the Large Hadron Collider (LHC) at CERN, where the author was responsible for the development of the data management middleware.