This thesis is focused on the manipulation of solid spheres and droplets with a particular focus on medium exchange and size based sorting. Two novel microfluidic devices are demonstrated. Firstly, a medium exchanger capable of transferring spheres and droplets between two miscible liquids was developed. The primary phase was extracted via a series of narrow perpendicular channels using a pressure differential created by mismatched input flow rates. Complete exchange of mineral oil phases has been demonstrated along with the use of the device to create a buffer region for chemical sphere curing of alginate droplets for use in stem cell encapsulation. This device offers simple passive exchange at greater throughput than previously demonstrated. The second device is a tuneable sphere focusing device that focuses spheres via inertial lift forces. Through the compression of the device the channel width is reduced such that the spheres are moved from an unfocused state into two focused streams. Focusing of 12μm spheres into two streams is achieved through channel dimension deformation. The device is shown to be capable of up to 88% ±1.1% focusing when compressed whilst the uncompressed device only focuses 51.4% ±2.1% of the spheres. The deformation of the device offers the potential for a greater range of tuning than previously possible with inertial lift based sorting.

Cellular solids widely exist in nature. Many researchers have analyzed the mechanical properties of macro-sized cellular solids. Following the rapid development of nano science and manufacturing technology, micro- and nano-sized cellular solids (i.e. honeycombs and open-cell foams) are now widely used in many areas. The purpose of this study is to investigate the elastic properties and the high strain compressive behaviour of micro- and nano-sized periodic random irregular honeycombs and opencell foams. In general, at the micro-meter scale, the strain gradient effect plays an important role in deformation. Meanwhile, at the nano-meter scale, the surface elasticity and the initial stress or strain are the dominant deformation mechanisms. According to the equivalence of the bending, transverse shear, torsion, and axial stretching or compression rigidities, these effects can be incorporated into the simulations by using the obtained equivalent Young’s modulus, Poisson’s ratio, and cross-sectional size. The results of this study indicate that the elastic properties and high strain compressive behaviour of micro- and nano-sized irregular honeycombs and open-cell foams are size-dependent and tunable. The smaller cross-sectional size of the cell walls/struts, the larger the dimensionless Young’s modulus, bulk modulus, shear modulus, the tangent modulus and the dimensionless compressive stress, and the smaller the Poisson’s ratio. Both the dimensionless Young’s modulus and compressive stress of nano-sized irregular honeycombs can be controlled to vary over a range of around 100% by adjusting the amplitude of the initial strain in the cell wall direction between -0.06 and 0.06. For nano-sized irregular open-cell foams, both the dimensionless Young’s modulus and compressive stress can be controlled to vary over a range of about 50% by adjusting the amplitude of the initial strain between -0.1 and 0.1. The cell regularity also significantly influences the elastic properties and the high strain compressive behaviour of micro- and nano-sized irregular honeycombs and open-cell foams.

This thesis presents a numerical, analytical and experimental investigation of inter-seasonal heat transfer processes in soils. Particular attention is given to the energy balance at the soil surface and its impact on the performance of thermal energy storage devices in shallow regions of the ground. For this purpose, a transient three-dimensional theoretical framework representing the relevant processes has been developed. A numerical solution has also been developed using the finite element method for spatial discretization and the finite difference method for time-stepping. The resulting model takes into account conductive and convective heat transfer between the fluid inside pipe heat exchangers and the surrounding soil. An alternative simplified 2D approach has also been developed and compared to the full 3D model. The determination of representative initial conditions and far-field (bottom) boundary conditions for the simulation of shallow ground heat storage facilities has also been investigated. To this end, a novel (1D) analytical approach has been developed to estimate realistic soil temperature profiles and seasonal thermal energy storage variations that can be used as input for more comprehensive analysis. Comparisons have been made to 1D numerical analysis. The proposed numerical model has been used to study a full-scale experiment undertaken by others involving the use of an inter-seasonal heat storage facility. As part of this study, key material properties have been measured using soil samples recovered from the experimental site. The results have revealed the importance of correctly representing the energy balance at the soil surface. Inclusion of soil/atmosphere interaction has been shown to be of critical importance for the correct assessment of buried heat transfer devices. The region of thermal influence and its seasonal variation have been established and the main limitations of the proposed model identified. General guidance for the design and installation of inter-seasonal heat transfer facilities has been provided based on the obtained results.

Offshore wind power is a key element in EU policies to reduce the greenhouse effect and secure energy sources. In order to accomplish the EU’s target of a 20% share of energy from renewable sources by 2020, some of the planned projects have to be placed far away from the shoreline to benefit from the high wind speeds in the open sea area. However, a traditional transmission system for offshore wind farms based on a High Voltage Alternating Current (HVAC) utilizing conventional cables is not appropriate for long distances. In contrast, a High Voltage Direct Current (HVDC) can transmit electrical power over such distances, but the complicated concept of converting the HVAC offshore generated power into DC and then converting the DC power at the onshore grid back to AC requires sophisticated and expensive converter stations at both ends. Therefore, developing a new infrastructure solution based on HVAC transmission technology, which has been in operation for more than a century and which runs almost entire electrical systems, to support and advance the development of offshore wind energy is a highly desirable outcome. This research work was conducted to examine and determine the suitability of using an HVAC gas-insulated transmission line (GIL) as a long-distance transmission system for offshore wind farms in terms of technical and economic costs. A computer model of GIL has been built using the Electromagnetic Transient Program (EMTP) to assess the suitability of GIL and quantify the voltage, current and power transfer characteristics of the GIL under different steady state conditions. Furthermore, a suitable model has been developed for the simulation of the switching transient during energisation of the GIL transmission system and various wind farm components. The development concept of GIL as a submarine Power Transmission Pipeline (PTP) is described, and the practical side of installing the PTP technology and the special design requirements of the offshore wind farms were illustrated. The PTP components, the maximum transmission capacity of the PTP system and the layout options were addressed. In addition, the challenges facing this technology were discussed. An economic comparison of the total cost for both HVAC-GIL and HVDC-VSC transmission systems is made, including annual costs (operation, maintenance, and losses) during the lifetime of the projects. The initial investment costs are added to the annual costs in order to obtain the total cost for the assumed project. Furthermore, the Power Transmission Cost (PTC) is calculated for each MVA-km being delivered to the receiving end of the GIL transmission line.

Hexagonal ferrites are a family of magnetic oxides which include M ferrite, the most commonly used magnetic material in the world today. They also have more specialist potential applications, such as microwave absorption and catalysis. They are highly complex crystal structures which usuaUy require high temperatures to form a well sintered product, at the expense of grain growth, which in tum affects the magnetic properties of the material. They all exhibit magneto crystalline anisotropy; depending upon the ferrite they can have a preferred direction of magnetisation along the c axis of the hexagonal crystal (uniaxial), or in the hexagonal plane or in a cone at an angle to the plane (ferroxplana). A material made in a fibrous form has many properties; firstly it can be incorporated into a matrix to form a composite material, imparting any special properties into the whole composite. Provided their microstructure is sufficiently fme, fibres tend to be stronger than the bulk ceramic form, and if fme enough they can even be woven into a cloth. It has also been suggested that some properties, such as magnetisation, will be enhanced when the material is an aligned fibre, although this specific case has never been proven previously. This thesis presents the manufacture of a range of hexagonal ferrite fme fibres from an inorganic aqueous sol-gel precursor, and their subsequent characterisation both physically and magnetically. The fibres were blow spun from a viscous solution using a modified commercial process, and they were collected in both random and aligned forms. The sols were made from the peptisation of a precipitated iron(III)hydroxide with a mineral acid, and various combinations of iron (III) salt and acid were investigated using PCS. The best results were found to come from iron(III)chloride precipitated by ammonia and peptised with HBr, with totally nitrate and chloride based systems proving inferior. Chloride was found to add structuring to the sol, aiding spinning but resulting in a thixotropic gel if too much was present. The stoichiometric ferrite sols were made by doping the iron (I II) sol with solution of metal salts, and these were found to be critical to the stability of the sol, with barium causing particular problems, and titania was added as a second colloidal species. Stoichiometric sols of BaM, SrM, BaCoxTixFel12-12xO19, SrCoxTixFe12 2x019, CozY, COzZ, COzW, CozX and CozU ferrites were made, among others, and aU were successfully spun as fibres. They typically had diameters of 4 - 6 um and an alignment of over 90% within +/. 20° of the axis of alignment, comparable to commercially developed fibres. The sol-gel process typically produces ceramic materials at lower temperatures and with smaller grain sizes than standard ceramic techniques, and this proved to be the case. SrM and BaM began to form at 800°C and had become the pure phase product by 1000 °C, being 98% sintered at this stage and with a submicron grain size. CozY ferrite was also the sole phase at a low temperature of 1000 °C, although it consisted of hexagonal platelets up to 3 um wide and 0.2 um thick. Substituted M fcrrites also formed the M phase at similar temperatures, but were more porous and did not have the greatly reduced grain size reported previously. None of these ferrites underwent the sudden, exaggerated grain growth seen in many hexagonal ferrites, even at 1200 °C. However, both the CozZ and CozW ferrite fibres underwent this process concurrently with the formation of these phases, and it appears to be an unavoidable step under normal conditions, although steam firing or doping with CaO enabled the formation of a majority-Z product without this growth. It was found that halide retained in the fibre inhibited the formation of the hexagonal ferrite phase, as it was retained up to 1000 °c. When the fibres were treated to remove halides or made from a halide free precursor they formed M ferrites -200°C lower, and with a reduced grain size below 0.1 !lm. The fibres were characterised by XRD, XRF, XPS and SEM. The samples were characterised magnetically by VSM, and while the M ferrites proved to have typical Ms values and high coercivities for polycrystalline samples, the ferroxplana ferrites all had Ms equal to or better than the previously reported maximum values. It was also found that there were defmite alignment effects on Ms in all fibres except those which had .. under gone the exaggerated grain growth, with an enhancement in Ms of up to +40% along the ilxis of alignment when parallel to the applied field compared to values for random fibre. This is the first'time that the effect of fibre alignment upon magnetic properties has been demonstrated.

The present thesis uses an approach which regards nonlinear systems as a pair (z(·),zf) trajectory-final state, for the case of controlability or (zO,z(·)) initial state-trajectory, for the case of state estimation, in a space M which is the cross product 1x Z or Z x F between the space of trajectories F and the state space Z. In this setting some mappings F:M + M are constructed using projections P onto specific subsets S of M (i.e. p2 = P and Rep} = S). The solution of the problems of nonlinear controllability, state estimation and state and parameter estimation are obtained via the fixed points of such F's. Fixed points theorems have been used in [8, 9, 25, 35 and 15] to provide global controllability, state estimation ,and joint state and parameter estimation. Some theoretical results are presented here, which show that it is possible to eliminate some of the assumptions which restricted the systems treated in these papers and at the same time to , obtain mappings with fixed points which contain all the possible solutions for the problem of nonlinear controllability, state estimation and the joint state and parameter estimation. Among the relaxations allowed now are, for example, in the problem of control, the possibility of a set of admissible controls Uad different from the set U of all input controls of the system. In order to obtain continuous projections P, S must be closed in M. This will occur naturally in the case of state estimation however, for the control case, in general, it will be necessary to adjust the topologies of the spaces U and/or M in order to achieve this. A comprehensive theory which shows that this adjustment is always possible as well as a complete procedure for obtaining the adjusted spaces, U and M are presented here.

The experiments presented investigate the collapse of a granular column on a stationary surface and a rotating table. A cylinder of radius r0 was positioned on the surface and filled with particulate to a height h0, giving an aspect ratio a = h0/r0. The cylinder was quickly removed and the resultant pile investigated. Spatial and geometric data obtained pre and post collapse were used to derive empirical relations. A high speed camera collected temporal data of the collapse in both cases. In the stationary case a 3D laser scanner quantified measurements of the resultant pile from which scalings involving aspect ratio were derived. The spatial data revealed that the final runout of the pile is not only dependent on the aspect ratio of the initial geometry as previously thought [Lube et al., 2004; Lajeunesse et al., 2004] but also the initial column radius. This was also observed to be true for the angle at the base of the deposit. Theoretical considerations and obtained data allowed the summital angle to be described by material parameters and aspect ratio. X-ray computer tomography allowed observation and quantification of the internal phenomenology to include the granular packing and the failure surface over which the collapse occurs. Consideration was given to the effect of rotation on previously obtained spatial and temporal scalings. Increasing the rotation rate encourages growth in the final pile radius until a critical frequency is reached where material loss begins to occur. Any further increase for fixed a results in further material loss and a decrease in the final pile radius. Initial results from DEM (discrete element method) simulations of granular collapse on a rotating table are presented for the case of spherical particles. In these simulations a spiral pattern evolves where all particles have left the central pile. Laboratory experiments have yet to demonstrate this exact patterning, but comparison to similar investigations suggests its existence.

The spatial periodicity of an array of emitters with an alternating polarity structure is utilised to generate a wavefront with a range of interesting properties. This wavefront is generated by simultaneously exciting the elements with a pulse with carefully selected broadband characteristics. The creation of these waves leads to a broadband interference effect that causes the wavefront to cover a large range of solid angles. More interestingly, however, is the continuous variation of the frequency of the wavefront as a function of angle. Whilst this pulsed array system demonstrates many interesting phenomena, it can also be applied to practical scenarios within the field of non-destructive testing. As the generated wavefront propagates through the sample, it will be scattered by discontinuities that may be present in the sample. This scattered wave will have a unique time of flight and frequency, and this information can be used to locate the position of defects. Due to the frequency variation of the wavefront, the angular position of the defect can be calculated from the frequency of the scattered wave. The radial position of the scatterer can be estimated using the time of flight of the wave. This approach has some advantages over the phased array techniques, which are currently utilised within the field of ultrasonic inspection. Whilst phased array techniques are versatile and can control the generated ultrasonic beam, they require complicated electronics and beam-forming algorithms to achieve this. This requirement is avoided with the pulsed array, as all of the array elements are activated simultaneously. Also, as the time-frequency characteristics of the scattered wave maps directly to the polar co-ordinates, only a single measurement is needed to locate a defect. This is in contrast to other ultrasonic methods that only utilise the time of flight information of the scattered wave, and hence multiple measurements are needed to localise a defect.

The currently lack of design guidance for pultruded fibre-reinforced polymer member requires more study on their structural behaviours in order to provide structural designer with confidence when applying this material into civil engineering. Elastic lateraltorsional buckling is an important global instability mode of failure for flexure about the major axis of open sections which is characterised by a coupled elastic deformation of lateral deflection and twist about beam’s longitudinal axis. The key elements of this study are laboratory testing, finite element analysis and development of design guidance that is compatible with Eurocode 3 design procedure. 94 tests have been carried out on tensile coupons to characterise the four key material properties for longitudinal, transverse, shear moduli of elasticity and major Poission’s ratio that are required for the prediction of the buckling resistance using closed-form equations and by finite element analysis. 114 tests on the elastic lateral-torsional buckling of I and channel beams under various loading and displacement boundary conditions have been carried out to determine the buckling resistance. Finite element modelling methodology has been developed and both linear and nonlinear numerical analyses have been performed to show that the methodology is suitable. Further sensitivity analysis has been conducted to demonstrate that the buckling resistance is highly influenced by the combination of material, geometric and loading imperfection. A calibration has been implemented, based on the new test results, following the Eurocode 0’s approach to establish the material partial factor for the investigated instability mode of failure.

Face recognition is one of the most active research topics in the interdisciplinary areas of biometrics, pattern recognition, computer vision and machine learning. Nowadays, there has been significant progress on automatic face recognition in controlled conditions. However, the performance in unconstrained conditions is still unsatisfactory. Face recognition systems in real-world environments often have to confront uncontrollable and unpredictable conditions such as large changes in illumination, pose, expression and occlusions, which introduce more intra-class variations and degrade the recognition performance. Compared with these factor related problems, the occlusion problem is relatively less studied in the research community. The overall goal of this thesis is to design robust algorithms for face recognition with occlusions in unconstrained environments. In uncontrollable environments, the occlusion preprocessing and detection are generally very difficult. Compared with previous works, we focus on directly performing recognition with the presence of occlusions. We deal with the occlusion problem in two directions and propose three novel algorithms to handle the occlusions in face images while also considering other factors. We propose a reconstruction based method structured sparse representation based face recognition when multiple gallery images are available for each subject. We point out that the non-zeros entries in the occlusion coefficient vector also have a cluster structure and propose a structured occlusion dictionary for better modelling them. On the other hand, we propose a local matching based method Dynamic Image-to-Class Warping (DICW) when the number of gallery images per subject is limited. DICW considers the inherent structure of the face and the experimental results confirm that the facial order is critical for recognition. In addition, we further propose a novel method fixations and saccades based classification when only one single gallery image is available for each subject. It is an extension of DICW and can be also applied to deal with other problems in face recognition caused by local deformations. The proposed algorithms are evaluated on standard face databases with various types occlusions and experimental results confirmed their effectiveness. We also consider several important and practical problems which are less noticed (i.e., coupled factors, occlusions in gallery or/and probe sets and the single sample per person problem) in face recognition and provide solutions to them.