It is hypothesized that anaesthetic breathing systems are poorly designed, and would benefit from engineering modeling to improve function. The use of breathing systems in different environments is described. Bath fp, a software package, developed in the Department of Mechanical Engineering for mathematically modelling hydraulic systems such as breathing systems, is introduced. Bath fp was used to model the behaviour of anaesthetic circle systems at high, medium, low and minimum fresh gas flows (FGFs). Using 50% nitrous oxide in oxygen ('entonox') as a gas model for all such volatile anaesthetic agents, the behaviour of the system was observed in terms of gas concentrations, volumetric flow-rates and airway pressures. Anaesthetic circle systems studied included standard adult and paediatric systems, and a coaxial system. In the standard systems, different tubing lengths and diameters were modelled, and for the coaxial system, different diameter ratios of outer and inner tubes were modelled. Gas concentration changes at different points in the system were used to clarify system function at different FGFs. Management of exhaled carbon dioxide was examined, including changing absorber volume. A venturi was modelled and added to a valveless coaxial circle system, to see how the venturi changed system function, and under what conditions it might fail. Clinical data were collected to validate modelling results. Nineteen adult volunteers were recruited to a trial, in which entonox was breathed through standard and coaxial systems for short periods, at different FGFs, with high flow air-breathing periods in between. Data on gas concentrations were collected from three points in each system. Results were analysed, and function was compared between different systems, and between systems and modelling results. The simulation model clarified circle system function, and showed that function depended more on FGF than on geometry. The clinical data supported the use of simulation to predict the behaviour of breathing systems.

Structural topology optimisation aims to provide solutions that are independent of the initial layout, allowing the greatest opportunity to find the best design. Recent developments have seen increased interest in level set based optimisation, as the solutions obtained possess smooth boundaries and are free of numerical instabilities that affect traditional element based methods. The direct level set based structural topology optimisation method has been successful in solving a range of problems. However, it does suffer from some drawbacks and limitations. Two of the main issues with the direct level set method are accurate and efficient sensitivity computation on the boundary and initial design dependent solutions for two dimensional problems. These issues are addressed in this thesis by investigating and improving the efficient area-weighted fixed grid method and creating a novel hole creation method for two dimensional problems based on a pseudo third dimension. Uncertainty is important to include during design and optimisation to produce structures that are reliable and robust. Loading magnitude and direction uncertainty is introduced into the minimisation of compliance problem by considering the robust expected compliance objective. An efficient formulation is derived using an analytical approach where uncertainties are normally distributed. The robust problem is then extended to include compliance variance and sensitivities are derived using the adjoint method.

This thesis argues the need for a fundamental shift from the design of products to the design of possessions in the circular economy. Possessions in the circular economy are characterised by interactions resulting in a user-object relationship rather than legalese and differ from the linear economy in terms of their length of use and number of users. Individual users are thus seen as critical actors to enable material circulation in that they take possession and dispossess of products. Two key topics—psychological ownership and contaminated interaction—are explored in detail to fill theoretical gaps in design research and practice. After discussing these topics, some directions and guidelines are suggested. Possession or ownership is taken as an innate human desire. A framework describes the method of developing ownership including the motives, routes, and paths that guide the development of that relationship. This framework is used to describe object attachment to inform product longevity and decisions around keeping and discarding. It is also useful to help explain why some access-based models are adopted while others are not. Maintaining perceived value in the circular economy entails mitigating contaminated interaction—tainted interaction due to prior use and prior users. Contaminated interaction is shown to affect new circular business opportunities, disposal decisions and downcycling. A typology is presented to characterise indicators of use with an emphasis on sensorial material properties. Aversion to used products is found to come from three drivers: hygiene, utility and territory. A theoretical framework for contaminated interaction is presented which is explored through positive and negative forms of contamination. Finally, a case study shows how alterations in product characteristics lead to improper disposal and act as an example of what it means to design of circular possessions.

The non-volatile storage of information is becoming increasingly important in our data-driven society. Limitations in conventional devices are driving the research and development of incorporating new materials into conventional device architectures to improve performance, as well as developing an array of emerging memory technologies based on entirely new physical processes. The discovery of graphene allowed for developing new approaches to these problems, both itself and as part of the larger, and ever-expanding family of 2D materials. In this thesis the growth and oxidation of these materials is investigated for implementing into such devices, exploiting some of the unique properties of 2D materials including atomic thinness, mechanical flexibility and tune-ability through chemical modification - to meet some challenges facing the community. This begins with the growth of graphene by chemical vapour deposition for a high quality flexible electrode material, followed by oxidation of graphene for use in resistive memory devices. The theme of oxidation is then extended to another 2D material, HfS2, which is selectively oxidised for use as high-k dielectric in Van der Waals heterostructures for FETs and resistive memory devices. Lastly, a technique for fabrication of graphene-based devices directly on the copper growth substrate is demonstrated for use in flexible devices for sensing touch and humidity.

The electrochromic behaviour of tungsten oxide (WOx) bulk forms has attracted huge research interest for decades owing to advantages of fast response time, good reversibility and high colouration efficiency compared with other electrochromic materials. Nanomaterials have certainly brought in new opportunities and opened the door for better, higher and smarter devices fabrication. This thesis will first investigate, explore, and understand the electrochromic performance of WOx in the nanoscale, and identify ways to enhance its performance via effective doping electrolyte selection and heat treatment. Moreover, the thesis will evaluate the prototype device performance based on our new understandings obtained in this project. The main findings are as follows: • Successfully synthesised crystalline WOx-based nanomaterials using a simple solvothermal technique, and achieved a series of La-, Ce- and Na-doped nanomaterials. The results show that the dopants caused distortion of the parental WOx¬ frameworks and increased the oxygen vacancy inside the structure, which is beneficial for the chromic properties. • The best electrochromic performance was obtained from Ce/W = 1 : 15 samples which presented 44.3% for optical contrast colouration efficiency of 67.3 cm2 C−1. • Conducted in-situ phase transition investigations using both WO3 nanoparticles and W18O49 nanowires, and found out that temperature was affecting the relaxation of W-O framework and phase transition. Based on the investigation, the 187.6 cm-1 band has identified as a fingerprint band for the phase transition from γ- to β- of the WO3 nanoparticle at 275 °C. W18O49 nanowires exhibit better thermal stability than the WO3 nanoparticles. • Intensive electrochemical investigations of La- and Ce-doped WOx structures were exhibit better diffusion kinetics, stability and colouration efficiency compare with plain WOx. These improvements are contributed to the improved oxygen vacancy (Vo). DLi+ of the Ce-doped samples were much higher than that of the plain W18¬O49 nanowires, by 177%, 102% and 84% for the 1:15, 1:10 and 1:5 samples respectively. DLi+ values of all La-doped samples were over 100% higher than those of the plain W18O49. The La-doped thin films increased the stability by 9%, 4% for intercalation, and 25% and 23% for de-intercalation, for La/W = 1:15 and 1:10 samples respectively, against the plain W18O49. • Provided experimental evidence to explain the degradation of chromic thin films, which is related to the Li+ trapping and loss of Vo in the WOx the structures. • The 350 °C annealed W18O49 thin film sample showed better diffusion kinetics by 25% for intercalation and 30% for de-intercalation compared with the un-annealed W18O49 samples. Stabilities also showed 31% improvement for the de-intercalation, against the un-annealed W18O49 sample. • Fabricated electrochromic device prototypes, and investigated the influence of various electrolytes, an optimal combination of LiClO4/PPC/PC polymer electrolyte has been developed, to improve the performance in ion kinetics and switching time of W18O49. These results have shown that WOx nanomaterials via further effective modification including doping with rare-earth elements or proper heat treatment are promising and practical candidate for the creation of fast, reliable and highly efficient electrochromic devices/smart windows for various applications.

Biodegradable polymers have highly desirable applications in the field of biomedical engineering, such as coronary stents, tissue engineering scaffolds and controlled release formulations. All these applications are primarily rely on the fact that the polymers ultimately disappear after providing a desired function. In this respect, the mechanism of their degradation and erosion in aqueous media has attracted great attention. There are several factors affecting the rate of degradation such as composition, molecular weight, crystallinity and sample size. Experimental investigations showed that the type of drug also plays a major role in determining the degradation rate of polymers. However, so far there is no theoretical understanding for the changes in degradation rate during the degradation in the presence of acidic and basic drugs. Moreover, there exists no model to couple the hydrolysis reaction equations with the erosion phenomena for a total understanding of drug release from biodegradable polymers. A solid mathematical framework describing the degradation of bioresorbable polymers has been established through several Ph.D. projects at Leicester. This Ph.D. thesis consists of three parts: the first part reviews the existing literature of biodegradable polymers and drug delivery systems. In the second part, the previous models are refined by considering the presence of acidic and basic drugs. Full interactions between the drug and polyesters are taken into account as well as the further catalyst effect of the species on polymer degradation and the release rates. The third part of this thesis develops a mathematical model combining hydrolytic degradation and erosion in order to fully understand the mechanical behaviour of the biodegradable polymers. The combined model is then applied to several case studies for blank polymers and a drug eluting stent. The study facilitates understanding the various mass loss and drug release trends from the literature and the underlying mechanisms of each study.

This PhD thesis aims to investigate the role of human medial temporal lobe (MTL) neurons in the encoding of associations between items and the characteristics of single neuron activity in response to related items. The invaluable opportunity to record single neuron activity occurs when patients suffering from refractory epilepsy have to be implanted with intracranial depth electrodes to treat their clinical condition. It has been long recognised that the MTL plays a critical role for declarative memory functions. MTL neurons have been shown to change their tuning during associative learning tasks. However, it is still not clear whether their involvement is confined to the task execution or goes beyond it. To address this issue, we studied the responses of MTL neurons in neurosurgical patients to known concepts (people and places), in conjunction with two different metrics measuring the degree of association between items (one metric based on the patients' evaluations and the other based on web searches). We found that whenever MTL neurons responded to more than one concept, these concepts were typically related, therefore providing evidence for a long-term involvement of MTL neurons in the representation of durable associations, which is essential to declarative memory functions. We also analysed the differences between spiking responses elicited by different stimuli in a single neuron, and how these differences related to the degree of association between stimuli. We found that, in general, MTL neurons exhibit a similar neural activity in response to different stimuli, and that eventual differences in the responses are smaller the more two stimuli are associated to each other. Our results support the idea that a process of unitisation of neural responses occurs in the MTL, and that information about the stimulus identity is not encoded in individual neurons, but rather at the neural assembly level.

Computer programs for structural design are few and, largely, unpopular compared with those for structural analysis. In the interaction between user and program, there is a balance between the results produced and the time involved in using the program. The failure to provide a good balance (or worthwhile interaction) is a significant defect of most design programs. Further, non-graphical output predominates, but is often unsuited to convey results. Finally, earlier design decisions generally affect the final structure more than later decisions, but design programs do not differentiate between these stages. A system has been implemented which avoids these pitfalls. It allows the jer to find the initial sizes of members (beams, columns, slabs) in a reinforced concrete building. The detailed design of the computer system is discussed. The structural design methods are based on the lower bound theorem. Design algorithms which test the adequacy of members are shown with their theory. Examples of the use of the system are presented. The sizing of a set of slabs, supporting beams and columns is shown. The sizes given by the system are more quickly found and less likely to be in error than those of hand-based methods, and costs appear to be less.

Although there has been extensive investigation of the creep behaviour of structures subjected to steady loads and isothermal conditions, the behaviour when temperatures vary both spatially and with time has received relatively little attention. Numerical solutions are extremely difficult to produce for time varying stress and appropriate constitutive relationships have yet to be evolved. The thesis is divided into two sections both of which are concerned with structural creep behaviour under time-constant applied loads: In the first section the behaviour of a few simple structures are investigated for spatially varying temperature fields which remain constant in time. Adopting an appropriate form of Norton's constitutive relationship it is shown that the stationary deformation of the structure may be related to a single reference material test conducted at a reference stress and a reference temperature, which is independent of material constants, thereby providing a generalisation of the reference stress technique used for isothermal conditions. Experiments on a simple beam structure are described which confirm that a good correlation between the structural behaviour and uniaxial reference test behaviour exists. In all cases considered the reference temperature remains close to the lowest temperature in the structure indicating that locally high temperatures may sometimes be tolerated without excessive structural deformation. In the second section the creep behaviour of a parallel two-bar structure and a uniform plate subjected to cyclic histories of temperature is analysed by means of a method of structural analysis which arises from certain bounding theorems. It is shown that these bounding theorems can describe thermal-creep interaction extremely well and general modes of creep behaviour are discernable when the non-linear viscous, strain-hardening or Bailey-Orowan constitutive relationships are adopted. Deformation maps that relate structural behaviour to a material parameter B are described and in certain circumstances a reference stress may be defined which is independent of other material parameters. This result indicates that a reference stress approach is applicable to variable temperature problems, but that the reference value depends upon the range of values of this quantity B. In order to substantiate the theoretical assumptions a preliminary experimental investigation of the two-bar structure subjected to cyclic histories of temperature is described. Tests using aluminium specimens indicate that a residual stress field is set up that varies quite slowly in time and remains effectively constant after a few cycles. It is found that the strain-hardening constitutive relationship provides a best fit to the structural behaviour.

This research concerns an investigation into the application of Power Electronics to high performance power sources for precise and efficient control of the pulsed-current metal-inert gas (PCM) welding processes. The physical processes of the welding arc are reviewed and the characteristics of a number of power sources are considered prior to preparing the operational specification for the PCM power source. From a number of possibilities the high frequency switching regulator operating in the secondary side of the power transformer was selected for detailed study. The power source was based on the use of state-of-the-art power transistors operating in a switching mode to minimise losses and to give a fast response for good welding performance. The basic operating frequency was chosen to be at the very limit of the audio range. The dynamic behaviour of the transistors and associated protection networks is critical and failure to meet all the operating limits of the transistor can be costly. To assist with the thorough understanding of the circuit behaviour and to predict the transistor switching waveforms a digital computer model was developed. This gave good correlation with experimental results observed with the completed power source. Tests were carried out with the welding power source and showed that there was no discernable difference in the weld quality when compared with those produced by the more expensive series linear regulator power source. As a direct result of the study a new range of power sources meeting exacting standards have been made available to the welding industry.