The temperature separation effect (TSE) is a unique thermal phenomenon occurring in a vortex tube (VT). This creates the possibilities of incorporating a VT in various thermal systems to improve their overall system efficiency. Any improvement will be strongly dependent on the working fluid choices, VT geometric parameters, and the system configurations and operating conditions. However, there appears that no systematic approach for selecting the possible working fluid and for evaluating the performance of a VT when operating in a system is available. Therefore, this research aims at developing a systematic approach to screen possible choices of working fluids, and a system integration procedure to achieve optimal matching of the working fluid choice, the VT geometries and the operation conditions, based on using a combined thermodynamic and CFD simulation analysis. A 2-D CFD VT model, created using Ansys Fluent, is used to assess the influence of the VT boundary conditions on the TSE, and to provide detailed information on the flow velocities, temperature and shear stress distributions inside the VT, as well as the cooling/heating effect of the VT. The shape of refrigerant’s T-s diagram is initially used for grouping various refrigerants to either cooling or heating applications of VT. The fluid state at the VT nozzle exit is set as the criterion to identify the suitable VT entry regions on the T-s diagram for individual refrigerants. The thermal-physical properties including isentropic expansion exponent, J-T (Joule-Thomson) coefficient, thermal diffusivity, kinematic viscosity and density are employed to appraise the relative heating or cooling performance of individual refrigerants. One cooling and one heating system are chosen to illustrate the development and implementation of the proposed system integration procedure. In developing the procedure, a boundary line concept is introduced, which allows suitable VT entry conditions in a system be identified for cooling applications. An iteration procedure is designed to identify the best combination of the VT inlet pressure and degree of superheat for the heating applications for individual refrigerants. A guideline for re-selecting alternative refrigerants and re-dimensioning of VT for improving heating or cooling effect is presented, based on examining their thermal-physical properties under system conditions. The results show that the pressure drop in the VT plays an important role in determining the final heating effect. Key thermal-physical properties, such as thermal diffusivity and kinematic viscosity, are shown to be able to reliably assist the evaluation of the relative cooling/heating performance of different working fluids in closed VT systems. The proposed integration procedure is developed in such a way that it could be easily adapted for evaluation of different system configurations.

Hybrid polymeric fibres and fibrous structures have widely been used to construct porous polymer scaffolds with excellent functionally, and are of great interest in biomedical applications. In this thesis, in contrast to electrospinning, a novel approach, gyration spinning with or without pressure is reported to achieve a high production rate for hybrid nanoparticle embedded polymer fibres in the micro to nanometre scale range using either polymer solutions or melts. Polyurethane (PU), nylon, and poly(ethylene oxide) (PEO) were used as the polymers not only because of their excellent biocompatibility, but also depends on good oxidative biostability, processability of PU, good mechanical strength, spinnability and stability for nylon, and non-toxicity of PEO. In the meantime, silver nanoparticles, copper oxide nanoparticles and zinc oxide nanoparticles were used to increase the antibacterial performance to produce hybrid nanofibres using pressurised solution gyration. A pressurised melt gyration process was used for the first time to generate poly(ε-caprolactone) (PCL) fibres and silver coated PCL fibres in the micrometre range (< 50 m) due to the low melting point (60°C) of PCL pellets. The formation of fibres depends on the centrifugal force, pressure blowing and evaporation. Fibre diameter is significantly reduced with a decrease in the weight percentage of the polymer in solution, and an increase in the melting temperature, rotational speed and working pressure. Field emission scanning electron microscopy (FE-SEM) was used to study the characteristics and morphology of the fabricated polymer fibres. Incorporation of Ag nanoparticles into the polymer fibres was confirmed using a combination of advanced microscopical techniques and Raman spectrometry to study the bonding characteristics of the polymer and Ag nanoparticles. Inductively coupled plasma mass spectroscopy (ICP-MS) showed that the substantial concentration of Ag ions in the nylon fibre matrix was producing effective antibacterial properties. Ag nanoparticles and CuO nanoparticles were successfully incorporated into polymer fibres and proved to be of higher antibacterial efficacy than virgin polymer fibres, against the Gram-negative bacteria Escherichia coli and Pseudomonas aeruginosa.

The need to diversify the fuels used in gas turbine power generation has driven forward the development of fuel – flexible combustion systems. However, the change in chemical, thermal and transport properties of fuels due to the variation of the constituents can have a significant effect on the performance of the combustor. It is known that the fuel properties have a strong influence on the dynamic response of flames. One of the key parameters required to enable detailed understanding of the flame response is heat release rate. To date there are no measurements that can directly provide this quantity. Simultaneous OH/H2CO PLIF (HRX – pixel by pixel product of LIF signals) can provide planar local heat release rate and it has shown to work on premixed hydrocarbon flames (methane, propane and ethylene air flames) and ethanol. For the first time this method was extended to biogas/syngas type flame application. Here H2/CO/CH4/CO2 flames are investigated and the heat release response was measured under high curvature and rates of strain. In the case of laminar flames the results suggest that simultaneous OH/H2CO PLIF can be used to provide information about the heat release rate in methane and methane/carbon-dioxide (biogas) flames. The trend in spatial distribution of HRX agrees well with the one-dimensional flame calculations. The spatial distribution of the HRX is of great interest for studying combustion modelling and instabilities. Therefore the measurement technique was extended to turbulent flames on a laboratory scale gas turbine combustor to study the flame response of multi-component fuels. The HRX technique was found to be suitable to study biogas flames subjected to flow perturbations. The measurements allowed to spatially resolve the heat release region under different perturbation conditions, especially in the region where the vortex is formed. These measurements were also carried out for methane/carbon-monoxide/hydrogen (syngas) flames. For the first time experimentally, spatially resolved heat release regions of biogas and syngas were measured and compared to aconventional natural gas (methane). Also part of the study was to investigate the flame response while the flame speed of the different fuels were matched. In the case of biogas and methane flames, provided the flame speed and the overall bulk velocity were similar, the same flame responses were observed at all forcing frequencies. In the case of syngas and methane flames, a similar response was observed at higher forcing frequency but not for low frequency.

This project is about improving functioning in patients with ptosis associated with poor levator palpebrae superioris (LPS) function. LPS is a highly specialised muscle responsible for raising the eyelid. Defective LPS may cause the eyelid to droop uncontrollably, thereby covering the visual axis and affecting vision. The current method of correction relies heavily on the experience of the surgeon. Rarely, the implanted materials are at risk of exposure, infection, rejection. More commonly, the ability to completely shut the eyelids is impaired, leading to the danger of corneal exposure that can lead to severe pain and sight-threatening complications. Many patients will require repeat surgeries for correction in the future. One reason for such mechanical failure includes the lack of understanding of the mechanical characteristics of the muscle involved in blinking, and the current surgical suspension material used in replacing it. This lack of a scientific basis means that ptosis is a major challenge in ophthalmic surgery. The aim of this work will include analysing and characterising LPS and blinking dynamics, in the hope of improving future clinical procedures and perhaps provide insights on surgical materials. Two separate approaches are running in parallel to investigate blinking dynamics: to define the mechanical characteristics and properties of the muscles involved in blinking, a new apparatus was designed and constructed to measure the force in eyelid closure, particularly the maximum force of contraction and natural force of closure. On another aspect, a high-speed camera was used at Moorfields Eye Hospital to record and analyse blinking in 32 patients with ptosis, thyroid eye disease and Blepharospasm. The collected and analysed data are used to investigate how eye blinking dynamics in diseased patients are different from healthy individuals and to attempt to separate them from controls using a modelling system. In addition, the blinking dynamics of dermatochalasis patients before and after blepharoplasty surgery were also compared with healthy individuals using high-speed camera and later advanced statistical analysis.

The financial markets have changed radically since the start of the 2007 credit crisis. Following the bankruptcies of large financial institutions as well as bailouts of multiple banks and asset management institutions like Bear Sterns, Lehman Brothers, and AIG, the market participants recognised the serious credit and liquidity risks present in the widely traded interest rate derivatives. The effect of rising credit and liquidity risks was observed by the spike in the spreads between nearly risk-free OIS rates used for collateral and risky unsecured LIBOR loan rates. Most of the classical interest rate models used by mentioned market participants relied on the assumption that there exists a risk-free and unique LIBOR lending rate, which is no longer true. This has opened new ground for complex, hybrid models for interest rate derivatives. This PhD thesis presents my work on developing novel interest rate models which are mathematically and historically sound and can be used for pricing interest rate derivatives including stochastic basis spreads between unsecured LIBOR and OIS rates. This work is split into two problems: first we analyse the discrepancies between forward-LIBOR lending rates and their classic replication strategy with spot-LIBOR rates. For this problem, we propose an extension of a known LIBOR Panel Model, which enables us to jointly model OIS and spot- and forward-LIBOR rates with an error within the quoted bid-ask spreads. The second part of this thesis looks into the problem of pricing non-linear derivatives like caps linked to rates on multiple LIBOR tenors. We propose a novel hybrid credit-interest rate model, which allows to jointly model OIS and multi-tenor LIBOR rates and to price multi-tenor caps. The proposed hybrid short-rate model is intuitive, semi-analytically tractable and can be calibrated using liquid, available market data. We compare the market data fit with a benchmark model using fixed LIBOR-OIS spread assumption. The last chapter shows the impact of this model on credit value adjustments for interest rate trades.

This research investigates the characterisation of liquids using primarily substrate integrated waveguides and extending this to other interesting conventional transmission lines. Focus is drawn to liquid mixture quantification, which is significant in the distinction of the quantity of one biological or chemical liquid from another. This work identified and confirmed that microwave resonance methods are best suited to perform mixture quantification due to their high sensing accuracy and inherent single point detection. The tracking of the resonant frequency change with either the corresponding return loss or insertion loss (depending on the type of resonant structure) gives a good solution in this regard. On the other hand, it was affirmed that transmission line methods are best suited for general broadband characterisation of a particular liquid. Three major outputs were achieved in this research work, namely: (i) In-SIW millimetre wave sensor; (ii) SIW slot antenna microlitre sensor and (iii) Sub-terahertz CSRR sensor for solid dielectric characterisation. Using the SIW slot antenna sensor, microlitre liquid volumes of 7 μl were characterised and binary mixtures quantified with an overall accuracy of better than 3 % when compared with results from a commercial sensor. The In-SIW millimetre wave sensor showed proof of concept through simulation results of the characterisation of 15 μl liquid volume results when compared to 100 ml liquid volume measurement done using the Keysight dielectric probe. The sub-terahertz CSRR sensor was used to characterise solid dielectrics using its multifuctionality capability of performing both resonant measurements and transmission line measurements.

Hypermobile robots are an area of robotics that are often used as exploratory robots, but have facets that feature in other areas of the field. Hypermobile robots are robots that feature multiple body segments or modules, with joints between each. These robots are often used for exploratory purposes due to being able to maintain contact with the ground due to their flexible bodies. Wormbot was a hypermobile robot developed at the University of Leeds, which used a locomotion gait based on that of a Caenorhabditis elegans nematode worm, otherwise known as C.elegans. This movement pattern is reliant on compliance; a mechanism where the joints are slightly sprung and comply to the environment. The next iteration of Wormbot needs to be reduced in size, which would also require a new actuation and compliance system. This thesis describes the process of investigating a method of compliance to be used in the next version of Wormbot, while utilising the multi-material 3D printing capabilities available at the University. 3D printing provides quick manufacturing, allowing for fast changes to made to prototype components if required. During the process of this research, two 3D printed compliant actuation systems were produced; a pneumatic bellow and a Series Elastic Element (SEE) to be used in tandem with a servo motor. Both methods were tested to analyse their performance. The bellow was produced to utilise the capabilities of multi-material printing to strengthening suspected weak areas of the actuator. However, the performance of the bellow was unsatisfactory, failing twice in two actuation tests tests due to the device breaking. The SEE on the other hand, designed with two stiffer plates and a rubber-like spring element in the middle, initially proved to be reliable and repeatable in performance, with potential to behave linearly to a set spring constant. These results were acquired by performing rotational step response tests and fitting a spring-damper model to the results. However, issues with the plastic material were discovered when it was found to deform much more than anticipated, behaving in a similar manner to an additional spring element, complicating the model. Simulation work to explore the potential for using different spring constants of joint compliance in varying environments was also explored. This involved testing a virtual Wormbot in a range of environments while altering joint compliance. These simulations revealed that softer joints allow for favourable performance in constricting environments, while stiffer joints lend themselves more to quicker movement.

Modularity of total hip arthroplasty (THA) has been linked to various forms of adverse local tissue reaction (ALTR). ALTR is often a result of metallic particles and ions released from corroding implant materials to the peri-prosthetic tissues and blood stream of the human body. More so, it is a consequence of several fretting and crevice-induced corrosion mechanisms occurring simultaneously. Fretting corrosion and fatigue damage of the modular taper is initiated and sustained by micromotions at the taper interface through the multi-directional loads applied onto the prosthesis during daily living activities. Subsequent to the failure of the implant, analysis of retrieved explants generally offer information regarding the mode of wear and to an extent, the types of corrosion damage. However, retrieval studies are limited in that, they do not provide a holistic insight into the in-vivo degradation mechanisms which ultimately led to the early failure of the implant. On the other hand, controlled in-vitro studies proves useful for replicating the evolution of wear and corrosion in-situ. In addition, the role of multiple individual factors which contribute to fretting corrosion can be elucidated through in-vitro methods. In this study, metal – metal and ceramic – metal fretting interfaces were investigated. Advance microscopy and spectroscopy techniques were employed in the characterisation of passive films, corrosion products and metallurgical transformations of CoCrMo and Ti6Al4V alloys. Both mechanical and electrochemical data consisting of interfacial energy, open circuit potential (OCP) and fretting corrosion currents were measured using an in-situ tribocorrosion cell. Other surface analytical techniques were used to quantify wear and obtain surface topography. The results showed that CoCrMo and Ti6Al4V display independent characteristic behaviours when in a metal – metal or ceramic – metal fretting contact. For example, fretting contacts involving Ti6Al4V experienced higher contact compliance than those of CoCrMo. The higher interfacial compliance vii thus led to a significant proportion of wear being redistributed at the contacts involving Ti6Al4V alloys. It was subsequently observed that the redistributed wear at the interface leads to a mixed fretting regime whereby, the contact appear to be ‘cold-welded’ during a partial-slip regime and subsequently transitions to a gross slip fretting regime when the ‘welded’ interfacial material fractures. The phenomena was evident in both metal – metal and ceramic – metal interfaces involving Ti6Al4V. The subsurface transformation in CoCrMo alloy when subjected to fretting was observed to be typically strain-induced twinning and loss of nano-crystalline region. On the other hand, Ti6Al4V alloy was observed to be strain-induced recrystallization, mechanical mixing, crack initiation and propagation. It was also observed that the chemical composition of fretting corrosion products at the metal – metal interfaces were dependent on the contact condition and the specific area within the contact that the wear product is located. For example, metal–oxides and chlorides were prominent within creviced regions whilst precipitation of metal-phosphates and metal–oxides were present in well aerated regions. Evidence of Cr6+ and pitting corrosion products were also identified at the most severe creviced environment of the CoCrMo – Ti6Al4V fretting contact. This research also showed that the evolution of fretting corrosion current (specifically in self-mated CoCrMo contact) can be linked to the surface history of wear and corrosion. Furthermore, studies conducted on realistic taper components revealed that the use of ceramic bearings in order to eliminate one of two conductive components only resulted in the reduction of static corrosion currents but not fretting corrosion currents. Rather, it was deduced that interference fit at the ceramic – metal interface (relative to metal – metal) increases the surface area that is susceptible to passive oxide abrasion under fretting conditions. Therefore, the use of a ceramic bearing did not reduce fretting current at the modular taper interface.

Edge loading is multifactorial and has been identified as a risk leading to the revision of hip joint replacements. Pre-clinical testing requirements currently do not incorporate edge loading. Previous testing of edge loading has been carried out as controlled dynamic microseparation of 0.5 mm via a spring, where the femoral head contacts the rim section of the acetabular cup. The input conditions of these tests did not allow the individual evaluation of other variables due to the constraints of the methodology. The aim of these studies was to evaluate the effect on the occurrence and severity of edge loading, and wear, under edge loading due to different parameters in a hip joint simulator. A translational mismatch of 1, 2, 3 and 4 mm were applied between the centres of rotation of the head and the cup in order to evaluate the effect on the dynamic separation and severity of edge loading. This allowed differentiating the effect of the 45°, 55° and 65° cup inclination angle studied in the test matrix. Three studies were developed to determine the effect of the cup inclination angle (45°, 55° and 65°), the effect of the swing phase load (50-500 N) and the effect of the spring constant (50, 100 and 200 N/mm), where short biomechanical studies determined the effect and aided to provide an informed decision on the specific test conditions selected for wear testing. The results indicated how the decrease in cup inclination angle and increase in swing phase load decreased the dynamic separation and severity of edge loading and wear. These studies have elaborated on the potential conditions leading to edge loading and their outcome. Overall the severity of edge loading had a positive linear correlation (R2=0.90) with the wear rate for all the conditions tested. This project has emphasised the criteria required to individually evaluate different parameters when considering edge loading and presented a format to develop an ISO standard to consider the risks associated with edge loading.

Single photon avalanche detectors (SPADs) have uses in a number of applications, including time-of-flight ranging, quantum key distribution and low-light sensing. Germanium has an absorption edge at the key communications wavelengths of 1.3-1.55um, and can be grown epitaxially on silicon, however, SiGe SPADs exhibit a number of performance limitations, including low detection efficiencies, high dark counts and afterpulsing. Unintentional doping may affect electronic performance, and band-to-band tunnelling at high operational voltages SPADs may lead to noise currents. Additionally, defects in the Si/Ge interface lead to trap states within the bandgap and contribute to afterpulsing. This work investigates a range of critical performance parameters in SiGe SPADs. The effect of intentional and unintentional doping in SPADs on electric fields, potential profiles and carrier transport in the device is investigated, and optimal dopant profiles for a SiGe SPAD discussed. The dependence of band-to-band tunnelling currents in Ge on bias voltage, Ge thickness and temperature is investigated, and these currents are compared to other sources of noise currents in SPADs. DFT calculations of misfit dislocation structures in Ge are undertaken, to establish electronic bandstructures and optimised geometries for these defects, and identify trap states in the bandgap, which may contribute to afterpulsing and dark counts in SPADs. A number of directions for continuing work are identified, to progress understanding of noise currents and afterpulsing in SPADs.