Most satellites are equipped with a gyroscope, allowing it to be used in dynamics replacement mode for attitude estimation. However, gyroscopes have been known to fail and not all satellites, such as STRaND-1, have a gyroscope. With gyroless attitude estimation requiring computationally expensive numerical integration for state prediction, efficient and accurate integration techniques need to be employed. Of the numerical methods available for integrating the differential equations of rigid body motion, the state of the art in geometric rigid body integration provides the most computationally efficient methods—such as the preprocessed Discrete Moser-Veselov algorithm—while preserving much, if not all, of the geometric structure of the underlying system. The research presented in this thesis analyses and improves upon previously proposed geometric attitude estimation algorithms, methods incorporating geometric integration such as the Geometric Multiplicative Extended Kalman Filter. Because the Geometric Multiplicative Extended Kalman Filter does not handle covariance prediction in a geometric fashion and is not robust against the realistic initial conditions that could be expected with a gyroless satellite, the Geometric Unscented Quaternion Estimator is proposed to overcome these limitations. Additionally, to meet a specific need of the STRaND-1 satellite mission, these geometric estimators are extended to include simultaneous estimation of the satellite moments of inertia; this includes the development of a methodology for creating proxy moment of inertia measurements that can be incorporated into the estimation algorithm. Extensive simulation testing based on the STRaND-1 mission parameters is performed for all of these estimators, alongside traditional gyroscope-based methods. This thesis also presents the Scaled Harmonic Form, a novel approach for deriving temporally stable analytical solutions to systems exhibiting perturbed harmonic motion. This is applied to the motion of the orbital plane of a satellite in a near-circular orbit about an oblate planet.

Due to the increased commercial demand for miniaturisation, MEMS manufacturers have to characterise their components to improve quality control with ever-higher accuracy and resolution. One method of characterisation, using laser-generated and detected ultrasonic Lamb waves, is described in this thesis. Laser generated ultrasound is an attractive approach for material testing as it provides a non-contact non-destructive characterisation method. In the work reported here, Lamb waves are generated using a broadband laser source, giving a high temporal and spatial bandwidth, and the generated Lamb waves are detected using either a commercially available vibrometer or a custom built large bandwidth Michelson interferometer. An investigation has been conducted on the optical conversion efficiency into Lamb waves. Lamb wave amplitudes were measured on a silicon wafer and a variety of thin films on silicon wafers. This was to determine how parameters such as absorption coefficient and optical reflectivity as functions of excitation wavelength, influence the generation of Lamb waves. As a result, it was concluded that light of wavelength 532 nm is the optimal wavelength for Lamb wave generation. The capabilities of laser-generated Lamb waves, coupled with a large bandwidth Michelson interferometer, have been demonstrated to accurately measure the thickness of a MEMS pressure sensor membrane in the direction of a silicon wafer. Using the reassigned Gabor time-frequency method, to produce group velocity dispersion curves, the thickness was determined to be 35.01 μm ± 0.18 μm, from a single measurement. For comparison, the thickness was measured using an independent technique; obtaining a value of 34.60 μm ± 0.27 μm. Values for Young's modulus and Poisson's ratio were also determined to be 163 GPa ± 11.7 GPa and 0.351 respectively and these are in good agreement (to within 3.6% for Young's modulus and 2.5% for Poisson's ratio) with values found in the literature.

The Internet has changed substantially from a limited communication tool to a fully interactive information sharing environment. Quality of Service (QoS) Oblivious applications such as messaging and email have lost their dominance to time-critical and bandwidth-intensive multimedia services such as Voice over Internet Protocol (VoIP), video conferencing and Video on Demand (VoD). This considerable change in QoS demand places a heavy burden on the Internet design, including its underlying network protocols. Solutions such as multipath routing have therefore been proposed to improve data delivery performance and capacity by spreading the distribution of traffic using the network’s inherent path diversity. Although these network-oriented techniques are useful for Internet Service Providers (ISPs) to engineer their resources effectively, they do not necessarily satisfy the requirements of end-users. The reason is that the exclusive control of ISPs in determining the data paths prevents the end-users from reacting to QoS degradation caused by congestion in that path, even after they have noticed such QoS deterioration. On the other hand, granting full source routing capabilities to end-users has its own disadvantages. Firstly, these end-users require regularly updated knowledge of the network topology and its traffic, which is not scalable and would impose a large overhead on the network. Secondly, the computed source routes may violate the ISP traffic engineering policies or may cause network congestions. To address the problems of network-controlled and source-controlled routing paradigms, this thesis considers a middle cooperative approach between ISP and users, which provides a modest amount of control for the end-user to select the path from a limited set of path options, rather than being obliged, as in the current Internet, to follow a single pre-determined path. The path candidates are computed by the ISP based on its performance objectives (such as balanced link utilisations) and presented to the end-user. By restricting the extent of end-user control in the Intradomain path selection process to a few policy-compliant path options, the ISPs’ traffic engineering considerations are not compromised, and the objectives of both communication parties are fulfilled at the same time. Based on the above principle, a cooperative edge selected routing algorithm is presented to demonstrate the viability of this approach and its potential to reach win-win solutions for both communication parties (ISPs and end-users). The algorithm performance is further validated with mathematical analysis. Then, a more scalable version is proposed to increase the efficiency and decrease the memory and processing overhead. Finally, the performance and robustness of the algorithm in the face of network traffic changes is further improved with Genetic Algorithm.

Visible Light Communication has the potential to provide a licence free solution to implementing high data rate wireless communication within indoor environments. Although VLC systems offer many attractive features, a number of deployment barriers remain such as the impact of sunlight irradiance on performance, line-of-sight connections, uplink issues and the 'illumination on' operational mode. The research investigates the design of VLC systems in the presence of sunlight irradiance. The foundation of the investigation is a sunlight irradiance model that generates hourly levels of natural light intensity over the year for different locations. System behaviour over different metrological conditions and extended to consider the effect of cloud coverage, is analysed for a range of the most common surfaces found in indoor environments using Matlab and Monte Carlo simulations. The evaluation of system performance considers both Line-of-Sight and Non-Line-of-Sight components (up to the fifth reflection) at a range of data rates. A comparative analysis of system performance with reported results assuming noise owing to sunlight follows Gaussian statistics is conducted. Optimum placement of LED sources is investigated. System performance characterisation is conducted for different room sizes and as a function of distance from sources of sunlight such as windows and doors. Optimum LED layout maximises the SNR, fulfils the illumination constraint as governed IEC standards and minimises the variation of the SNR across the room. The design guidelines are applicable to any room size, LED specification, wall reflectivity, location and illumination level. An approach to managing the 'illumination on' scenario is developed. Operational performance as a function of the number of energised LEDs and LED panel layout for different room sizes, surface reflectivity, different operating conditions and applications is evaluated. In summary, the research provides an in depth analysis of VLC system performance in the presence of sunlight irradiance, the results forming the foundation for future system designs and applications.

A content delivery network (CDN) typically consists of geographically-distributed data centers (DCs), which are deployed within proximity to end-users who request Internet content. Content copies are stored at the DCs and are delivered to end-users in a localized manner to improve service availability and end-to-end latency. On one hand, CDNs have improved QoS experienced by end-users. On the other hand, the rapid increase in Internet traffic volume has caused the global DC industry's energy usage to skyrocket. Therefore, our focus in this thesis is to realize energy awareness in CDN management while assuring end-to-end QoS. First, we surveyed the literature on energy-aware DC and CDN management schemes. We highlighted the significance of dynamically provisioning server and network resources in DCs in order to reduce DC energy usage. We also recognized that in order to achieve optimal CDN energy saving, energy optimization should be performed both within each DC and among multiple DCs in a CDN. Second, we proposed a theoretical framework that minimizes server power consumption in cross-domain CDNs. The term "server" refers to any co-locating entity that can handle user requests, e.g., server clusters or DCs. Our strategy was to put a subset of servers to sleep mode during off-peak hours to save energy. In order to avoid deteriorated QoS caused by less live server resources, we enforced constraints on utilization of servers and network links respectively to avoid them from being overloaded. Third, we designed an energy-aware CDN management system. The strategy was not only to put a subset of servers within each DC to sleep, but also to put entire DCs to sleep during off-peak hours through load unbalancing among DCs. We showed how the proposed system can be integrated within a typical modern CDN architecture. We also developed a heuristic algorithm that allows CDN operators to quickly make decisions on server and DC sleeping, as well as energy-aware request resolution. QoS was assured through constraints on server response time and end-to-end delay. Fourth, we built an optimization model that minimizes the overall energy consumption of CDN DCs, including their servers and cooling systems. We derived a lower bound to its optimal objective. Through comparing with the lower bound, we showed that our earlier developed heuristic algorithm's energy-saving gain was guaranteed to be near-optimal. We also quantitatively studied the trade-off between CDN energy saving and QoS performance in terms of end-to-end delay and server response time.

Carbon nanotubes have shown their abilities in a wide range of electronic applications due to their unique electronic properties. In order to match the different needs of applications, the issue of selectively growing specific types of single-walled carbon nanotubes has received considerable attention. In this study, a parametric study is implemented to solve this issue. Firstly, the growth windows for selectively synthesising high quality single-walled carbon nanotubes via photo-thermal chemical vapour deposition (PTCVD) are determined. The growth process of the PTCVD is free of oxygen-containing precursors and corrosive catalysts, and is fully compatible with the integrated circuit process. Only acetylene and hydrogen are used and the catalyst is a layer of sputtered iron. The multi-variables, which include the process temperature, reactant gas ratio and total flow rate, are studied in terms of their influence on the growth rate, the quality and the preferential growth of carbon nanotubes. The highest growth rate obtained in this study is 442 nm/s, which is the highest growth rate reported so far, without using water and/or a corrosive catalyst to assist the growth. By studying the growth rate, we find that it can be correlated to the bulk iron and carbon phase diagram. Generally, above the eutectoid temperature of a and g iron, the growth rate decreases with increasing temperature and inversely, the growth rate is enhanced with increasing temperature below the eutectoid temperature of the a iron and carbide. Moreover, a novel growth model is also proposed to interpret the high growth rate. Owing to the topdown heating of the PTCVD, three factors are concluded to enhance the growth rate that are the gradients of the temperature and the carbon concentration and the chemical potential along the axis of the catalyst. The selective growth of high-quality single-walled carbon nanotubes is achieved by optimising the reactant gas ratio and the process temperature, and is confirmed by the radial breathing modes in Raman spectroscopy. The growth window for semiconducting single walled carbon nanotubes is relatively larger than that for growing metallic single-walled carbon nanotubes. The semiconducting single-walled-carbon nanotubes prefer to grow above 800°C with the acetylene ratio being below 10%. The metallic single-walled carbon nanotubes tend to grow between 750 and 800°C,which correspond 420 and 450°C at the substrate temperature and the acetylene ratio of 16-18% are suggested. The preferential growth of the semiconducting and metallic single-walled carbon nanotubes are confirmed again by analysising the Breit-Wigner-Fano lineshape of the G^(-)-band and the 2D-band. The results are highly consistent with those deduced from analysing the radial breathing modes Finally, the field emission properties of different types of carbon nanotubes are investigated. We find that multi-walled carbon nanotubes have the better performance compared to semiconducting and metallic single-walled carbon nanotubes. Moreover, different morphologies of the carbon nanotubes and different substrates are also studied with respect to the field emission properties. Consequently, honeycomb-patterned multi-walled carbon nanotubes are grown on the a layer of indium tin oxide on a glass slide that can be used for the flat panel display and lightings.

This research investigates Denial of Service (DoS) attacks targeting the Internet’s Application Layer protocols, namely Session Initiation Protocol (SIP), and SPDY, the proposed second version of the Hyper Text Transfer Protocol (HTTP 2.0). The attack detection methodology was set using a Statistical Process Control (SPC) technique and Monitoring charts, as well as Cumulative Summation (CUSUM) and Exponential Weighted Moving Average (EWMA). The techniques tackle different possible flooding attacks, typically through monitoring the incoming messages. The system works by sensing sudden changes and detecting abnormal traffic increases alerting for an attack, and then triggering an alarm on the DoS attack. The scenarios are designed for SIP to simulate normal traffic behaviour and attack traffic behaviour; some scenarios were set to have a large ratio of the non-acknowledged requests, and another scenario was set to simulate a slight increase in the ratio. There was a scenario in which its traffic was imported from another SIP related research. In addition, the thesis discusses the results of DoS attacks targeting the SPDY protocol; one scenario is about a large increase in the total number of the sent requests by a user towards a SPDY proxy, and another scenario is set with a slight increase. SPC was tested on all previously mentioned scenarios; they have shown significant results in detecting the attacks, either it was large sudden flooding, or slight low rate DoS flood, as the low rate DoS attacks are very difficult and sometimes impossible to detect. SPC was tested to aim in false attack alarms reduction, as they are also difficult to deal with. These techniques were applied in two approaches: in the first approach, the Offline implementation, the statistical values of the whole observations, the mean and the standard deviation, are found and then applied to the equations. In the second approach, the Online implementation, the statistical values were updated on getting a new observation and immediately applying the SPC equations; there has not been any other research that discussed such an approach. The first approach represents a system with previous knowledge and experience of the ongoing traffic. This reduces the overhead spent in finding the mean and the standard deviation every time a new observation is added to the sequence. The second approach represents a system that is newly starting with no knowledge, or a system which was reset after detecting an attack. Finally, a framework was suggested to effectively employ the previous contributions in detecting the flood of the traffic.

This PhD main aim was the examination of the Atmospheric Plasma Spraying Raney nickel electrodes samples with strong emphasis on electrochemical characterisation and investigation of the degradation/deactivation mechanisms which occur within the electrodes structure. Nowadays research in alkaline electrolysis mainly aims to improve efficiency, extend durability and decrease the price of electrolyser units. One of the methods to achieve all of these goals is the development of novel electrode types. Raney nickel electrodes manufactured by Force Technology (Denmark) using a novel atmospheric plasma spraying method (APS), have been shown to exhibit good performance with low overpotential towards the hydrogen evolution reaction (HER). In comparison to the other electrode production methods APS is considered also to be relatively cheap. To our knowledge, this is the first time APS has been applied for the production of Raney nickel electrodes for water electrolysis. APS is cheaper and simpler than actually used vacuum plasma spraying, making it more suitable for mass production of the electrodes. For a purpose of experimental work the laboratory environment was set-up which consisted of the electrochemical cells and the data acquisition devices. The methods of Tafel extrapolation, cyclic voltammetry, electrochemical impedance spectroscopy, scanning electron microscopy were applied, that allowed to estimate electrochemical parameters of the samples. Characterisation work concluded, that overall performance of the tested samples have been attributed to the very high electrochemical active area as well as enhanced kinetics obtained for these samples following the chemical and electrochemical activation procedures Investigation of degradation mechanisms work part identified hydrides impact as a main source of deactivation for cathodes. To prevent, this effect techniques of hydrides oxidation and activation of the electrolyte were tested however, neither of them was able to eliminate hydrides impact completely. The overall work is concluded that suppressing hydrides impact should be possible by improving electrodes manufacturing process for example by application of molybdenum coatings. The performed study is supplemented by two additional outcomes. First of them is electrochemical measurement device, which concept was created and initial prototype was built using cheap electronic components. Second one is feasibility study of application of hydrogen storage technologies to increase hybrid wind energy-diesel electricity generation system efficiencies.

So far, the Internet of Things (IoT) has been concerned with the objective of connecting every-thing, or any object to the Internet world. By collaborating towards the creation of new services, the IoT has introduced the opportunity to add smartness to our cities, homes, buildings and healthcare systems, as well as businesses and products. In many scenarios, objects or IoT devices are not always statically deployed, but they may be free to move around being carried by people or vehicles, while still interacting with static IoT infrastructure. The Opportunistic Networking paradigm states that, exploiting opportunistic interactions between static and mobile IoT devices, provides for increased network capacity, additional connectivity, reduced deployment costs, improved reliability and overall network lifetime improvements. IoT scenarios do illustrate the increased need to identify and exploit opportunistic interactions between IoT devices in order to recognize when an opportunity for communication is possible. For example, statically deployed devices (i.e. road side sensors) may need to find mobile devices (this may be sensors or actuators) (i.e. connected cars) for exploiting them for collecting and relaying data towards destinations without relying on a static infrastructure. This means that discovery in IoT scenarios needs to determine the availability of other devices in scenarios in which devices' presence is uncertain or may change over time. This directly leads to a contradicting objective where resource wastage in device discovery is to be kept at a minimum. This thesis presents two contributions that provide solutions to overcome the clash between these contradicting objectives. Firstly, a Context Aware Resource Discovery mechanism is introduced, capable of providing optimized discovery and adapting available resources based on learned mobility patterns. Secondly, an Arrival and Departure Time Prediction and Discovery framework is defined and investigated; this framework aims to predict future arrival and departure times and helps to plan the use of devices' resources in advance based on the foreseen resource demand patterns.

The uses of flexible alternating current transmission system (FACTS) controllers in next generation smart grids are encouraged by the increased uses of decentralized and highly meshed grid structures that may affect the stability of power systems. Voltage source converter (VSC) based FACTS devices have reduced footprint and offer increased control flexibility, extended range and faster reaction time than line commutated thyristor based equivalent solutions. The performance of commonly used FACTS devices that employ a two-level converter is summarized. Then, multilevel converters and direct AC-AC converters which are viable for FACTS applications are reviewed. The outcomes of the literature surveys are refined to identify new features that may be critical for future centralised and decentralized smart grids such as: control range extension, improved efficiency and power density at reduced hardware cost. To pursue these features, three novel VSC topologies are proposed and analysed: An AC voltage-doubled (ACVD) topology with an internal inverting buck-boost cell in each phase-leg, is able to synthesize twice the output voltage of a conventional two-level VSC for the same dc link voltage, is proposed. A number of new modulation and control strategies that aim to further increase DC utilization of the ACVD converter and to manage its internal dynamic interaction to prevent the appearance of low-order harmonics in the output currents, are presented. With its high DC-rail utilization and sophisticated control strategies, the ACVD converter offers an extended power control range, which is increasingly important for shunt and series type FACTS devices. The controlled transition full-bridge hybrid multilevel converter (CTFB-HMC) with chain-links of full-bridge cells is proposed to combine the advantages of improved wave-shaping ability, reduced footprint and high efficiency, which promote its applications in medium and high voltage FACTS devices. An AC hexagonal chopper using heterodyne modulation to decouple the control of AC voltage amplitude from that of the phase-angle is proposed. For scalability to medium and high voltage, a modular multilevel AC hexagonal chopper (M2AHC) is developed. With adoption of a quasi-two-level transitional mode for reduced cell number and minimized footprint, dv/dt is limited and reliability is improved. Simulation and experimentation are used to validate the modulation, control and FACTS implementation of the three proposed converters.