Timing networks are used around the world in various applications from telecommunications systems to industrial processes, and from radio astronomy to high energy physics. Most timing networks are implemented using proprietary technologies at high operation and maintenance costs. This thesis presents a novel timing network capable of distributed timing with subnanosecond accuracy. The network, developed at CERN and codenamed “White- Rabbit”, uses a non-dedicated Ethernet link to distribute timing and data packets without infringing the sub-nanosecond timing accuracy required for high energy physics applications. The first part of this thesis proposes a new digital circuit capable of measuring time differences between two digital clock signals with sub-picosecond time resolution. The proposed digital circuit measures and compensates for the phase variations between the transmitted and received network clocks required to achieve the sub-nanosecond timing accuracy. Circuit design, implementation and performance verification are reported. The second part of this thesis investigates and proposes a new method to distribute radio frequency (RF) signals over Ethernet networks. The main goal of existing distributed RF schemes, such as Radio-Over-Fibre or Digitised Radio-Over-Fibre, is to increase the bandwidth capacity taking advantage of the higher performance of digital optical links. These schemes tend to employ dedicated and costly technologies, deemed unnecessary for applications with lower bandwidth requirements. This work proposes the distribution of RF signals over the “White-Rabbit” network, to convey phase and frequency information from a reference base node to a large numbers of remote nodes, thus achieving high performance and cost reduction of the timing network. Hence, this thesis reports the design and implementation of a new distributed RF system architecture; analysed and tested using a purpose-built simulation environment, with results used to optimise a new bespoke FPGA implementation. The performance is evaluated through phase-noise spectra, the Allan-Variance, and signalto- noise ratio measurements of the distributed signals.

Graphene obtained by mechanical exfoliation of graphite displays unique electronic properties with high mobility and saturation velocity. However, this is not a scalable technique, the film being limited to small area. Large area synthesis of good quality graphene has been achieved by CVD. The choice of substrate apparently influences the electronic properties of graphene. Most of reports have used SiO2-Si due to the widespread availability, but it is a poor choice of the material to degrade the graphene performace. In this thesis, more ideal platforms are introduced, including single crystal diamond (SCD), nanodiamond (ND), and diamond-like-carbon (DLC). It was found that different terminations for substrates caused strong effects for graphene properties. For H-terminated diamond, it was found that a p-type layer with good mobility and a small bang gap, whilst when N/F-terminations are introduced it was found that a layer with more metallic-like characters arises. Furthermore, different orientations of H-terminated SCD(100)/(111) were found to induce different band-gap of graphene. Simulation analysis proves the difference. However, the mobility results of graphene-H-terminated ND herostructure are better than graphene supported by SCD, which offers the prospect of low cost sp2 on sp3 technology. Raman and XPS results reveal the influence from the C-H band of ND surface. Impedance measurements show two conductive paths in the graphene-HND heterostructure. Graphene FET was built on this heterostructure, which exhibited n-type and high mobility. The family of amorphous carbon films, DLC, appeal to a preferable choice of graphene supporting substrate since IBM built the high-frequency graphene FET on DLC. For N-termination it was found that the optical band gap of DLC shrinked, whilst for F-terminated DLC it was found that fluorine groups reduce the DLC’s surface energy. Owing to different phonon energies and surface trap densities, graphene-DLC heterostructures give different electronic properties and offer the prospect for 2D lateral control applications.

In recent years there has been an increasing trend towards the use of Micro Remotely Operated Vehicles (μROVs), such as the Videoray and Seabotix LBV products, for a range of subsea applications, including environmental monitoring, harbour security, military surveillance and offshore inspection. A major operational limitation is the umbilical cable, which is traditionally used to supply power and communications to the vehicle. This tether has often been found to significantly restrict the agility of the vehicle or in extreme cases, result in entanglement with subsea structures. This thesis addresses the challenges associated with developing a reliable full-duplex wireless communications link aimed at tetherless operation of a μROV. Previous research has demonstrated the ability to support highly compressed video transmissions over several kilometres through shallow water channels with large range-depth ratios. However, the physical constraints of these platforms paired with the system cost requirements pose significant additional challenges. Firstly, the physical size/weight of transducers for the LF (8-16kHz) and MF (16-32kHz) bands would significantly affect the dynamics of the vehicle measuring less than 0.5m long. Therefore, this thesis explores the challenges associated with moving the operating frequency up to around 50kHz centre, along with the opportunities for increased data rate and tracking due to higher bandwidth. The typical operating radius of μROVs is less than 200m, in water < 100m deep, which gives rise to multipath channels characterised by long timespread and relatively sparse arrivals. Hence, the system must be optimised for performance in these conditions. The hardware costs of large multi-element receiver arrays are prohibitive when compared to the cost of the μROV platform. Additionally, the physical size of such arrays complicates deployment from small surface vessels. Although some recent developments in iterative equalisation and decoding structures have enhanced the performance of single element receivers, they are not found to be adequate in such channels. This work explores the optimum cost/performance trade-off in a combination of a micro beamforming array using a Bit Interleaved Coded Modulation with Iterative Decoding (BICM-ID) receiver structure. The highly dynamic nature of μROVs, with rapid acceleration/deceleration and complex thruster/wake effects, are also a significant challenge to reliable continuous communications. The thesis also explores how these effects can best be mitigated via advanced Doppler correction techniques, and adaptive coding and modulation via a simultaneous frequency multiplexed down link. In order to fully explore continuous adaptation of the transmitted signals, a real-time full-duplex communication system was constructed in hardware, utilising low cost components and a highly optimised PC based receiver structure. Rigorous testing, both in laboratory conditions and through extensive field trials, have enabled the author to explore the performance of the communication link on a vehicle carrying out typical operations and presenting a wide range of channel, noise, Doppler and transmission latency conditions. This has led to a comprehensive set of design recommendations for a reliable and cost effective link capable of continuous throughputs of >30 kbits/s.

The active vibration reduction of plane and stiffened plates was investigated using a genetic algorithm based on finite element modelling to optimise the location of sensors and actuators. The main aspects of this work were:  Development of a finite element model for a plate stiffened by beams with discrete sensors and actuators bonded to its surface.  Development of a finite element program for steel plates with various symmetrical and asymmetrical stiffening and edge conditions.  Development of a genetic algorithm program based on the finite element modelling for the optimisation of the location and number of sensor/actuator pairs and feedback gain.  Determination of optimum locations and feedback gain for collocated piezoelectric sensors and actuators on steel plates with various symmetrical and asymmetrical stiffening and edge conditions.  Development of fitness and objective functions to locate sensors and actuators.  Development of fitness and objective functions to determine the optimal number of sensors and actuators.  Development of a reduced search space technique for symmetrical problems.  Optimisation of vibration reduction control scheme parameters using the genetic algorithm.  Optimisation of the number and location of sensor/actuator pairs and feedback gain to reduce material costs and structural weight and to achieve effective vibration reduction. The modelling was validated by comparison with conventional finite element analysis using ANSYS, and by experiment. The modelling was developed using a quadrilateral isoparametric finite element, based on first order shear deformation theory and Hamilton’s principle, which may be arbitrarily stiffened by beams on its edges. The model can be applied to flat plates with or without stiffening, with discrete piezoelectric sensors and actuators bonded to its surfaces. The finite element modelling was tested for flat and stiffened plates with different boundary conditions and geometries, and the results of the first six natural frequencies were validated with the ANSYS package and experimentally. A genetic algorithm placement strategy is proposed to find the global optimal distribution of two, four, six and ten sensor/actuator pairs and feedback gain based on the minimisation of optimal linear quadratic index as an objective function, and applied to a cantilever plate to attenuate the first six modes of vibration. The configuration of this global optimum was found to be symmetrically distributed about the dynamic axes of symmetry and gave higher vibration attenuation than previously published results with an asymmetrical distribution which was claimed to be optimal. Another genetic algorithm placement strategy is proposed to optimise sensor/actuator locations using new fitness and objective functions based on . This is applied to the same cantilever plate, and was also found to give a symmetrical optimal sensor/actuator configuration. As before, it was found that the optimal transducer locations are distributed with the same axes of symmetry and in agreement with the ANSYS results. A program to simulate the active vibration reduction of stiffened plates with piezoelectric sensors and actuators was written in the ANSYS Parametric Design Language (APDL). This makes use of the finite element capability of ANSYS and incorporates an estimator based on optimal linear quadratic and proportional differential control schemes to investigate the open and closed loop time responses. The complexity of the genetic algorithm problem is represented by the number of finite elements, sensor/actuator pairs and modes required to be suppressed giving a very large search space. In this study, this problem was reduced by the development of a new half and quarter chromosomes technique exploiting the symmetries of the structure. This greatly reduces the number of generations, and hence the computing time, required for the genetic algorithm to converge on the global optimal solution. This could be significant when the technique is applied to large and complex structures. Finally, new fitness and objective functions were proposed to optimise the number of sensor/actuator pairs required for effective active vibration reduction in order to reduce the added cost and weight. The number, location and feedback gain were optimised for the same cantilever plate and it was found that two sensor/actuator pairs in optimal locations could be made to give almost as much vibration reduction as ten pairs.

No description available.

No description available.

No description available.

Waste Electronic and Electrical Equipment (WEEE) contains materials which can have a significant financial value, it can also be damaging to the environment if it is not treated properly at end-of-life. It is therefore essential to collect and treat EEE effectively at end-of-life to ensure scarce resources are not wasted, avoid the detrimental environmental impacts of improper treatment, mitigate the dwindling availability of virgin materials and to conserve potential value. The policy principle of Extended Producer Responsibility states that manufacturers are responsible for the units they put on the market at end-of-life. This is enacted in the EU through the WEEE Directive, implemented in 2003 and due to be revised in 2012 for implementation in 2014. WEEE collection rates, based on the mass sold in the two previous years (the measure used by the European Commission), reported under the WEEE Directive are low; around 30% for all household and 6% for non-household IT units (2009 figures). Accounting for WEEE and treating it correctly is not a straightforward waste management issue as there are incentives to divert it (from the financial value of the material it contains), which results in dispersal. This dispersal could account for some of the reported shortfall in collection. The goals of the thesis were to establish how the current approach to WEEE regulation reflected the reality of waste arising, through a detailed analysis of two established routes for the collection and treatment of end-of-life IT; the first being that for household equipment, which is monitored and reported under the WEEE Directive, and the second is for nonhousehold collections which is not. This thesis includes the only contemporary documentation of non-household WEEE collection and treatment. Findings indicated that while there was a financial value attached to WEEE, reuse was often a more attractive option than recycling but only for certain product types. The economic factors that make WEEE units either a potential resource or a burden were shown to be highly sensitive to several influences, which could present barriers to collection, treatment and regulation. While there are incentives to divert WEEE from the waste stream to extract the material value, this means that the WEEE that enters current collection networks often has had the value removed already, impacting the profitability of exploiting it. The current approach to WEEE regulation was shown not to reflect reality of waste arising, and the role of the manufacturer in collection and treatment at end-oflife is discussed extensively, arguing that directly linking producer responsibility costs to recycling is not feasible nor particularly useful. The goal of policy should be that all WEEE is accounted for at end-of-life, the environmental impact of disposal is minimal and the correct party has the cost attributed to them, and the thesis uses unique data to outline strategies to do this. © Richard

This work focuses on characterising the recently discovered room temperature multiferroic PZTFT, which has demonstrated some unusual properties. This investigation is done on both large scales (mm) the bulk ceramic - and small length scales (nm)within each grain that makes up the ceramic. The aim is to gain a detailed understanding of what properties the material has, Chapter 3: how the are connected, Chapter 4; how the respond to different stimuli - like electric and magnetic fields, Chapter 5. These properties are rationalised in terms of the Landau free energy expansion, which shown in Chapter 6, indicates the presence of a quadratic coupling term in this material.

In this thesis we study the effects of the interaction between electrons and phonon modes in condensed matter systems. We explore two theoretical outcomes of theelectron-phonon interaction: Charge wave order and superconductivity. The main aims of this thesis are to establish ways of making graphitic materials useful for digital computing, and to investigate unconventional forms of superconductivity. Low order perturbation theory is combined with a Green's function analysis to calculate electron band gaps in a bilayer graphitic material that. forms electron-phonon interactions via an adjacent polarisable substrate. Self-consistent equations are derived and computationally solved to examine band gap enhancement in bilayer graphene and bilayer boron nitride. We also compare results for several different systems to identify the most promising ones for future developments. Our results show a promising new method of gap creation, for gaps of up to leV, in a simple bilayer graphene system where the electron-phonon interaction causes enhanced charge density wave order. The possibility of three-dimensional high temperature bipolaronic superconductivity is examined numerically through continuous-time quantum Monte Carlo simulations backed up by an exact analytical approximation for large phonon-frequency. Bose-Einstein condensation of bipolarons in a cubic system is estimated to occur at temperatures as high as 90-120K at low carrier concentrations, where bipolarons are small and mobile. We also develop formalism for calculating the superconducting band gap of BCS like superconductivity in intercalated graphitic materials (IGMs). Green's function analysis combined with low order perturbation theory is used to derive a set of generalised self-consistent equations designed to accommodate the tight binding parameters of all IGMs.