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Research at high pressures has revealed that the elemental metals, most of which have simple crystal structures at ambient conditions such as face-centred cubic, body-centred cubic, or hexagonal close-packed, transition to more complex structures at high pressure. X-ray diffraction methods are well-suited to exploring these complexities, providing detailed data on the structure of elements at high pressure. In particular, this work focuses on studying the alkali metals K and Rb with x-ray diffraction methods. These elements have been found to exhibit a wealth of structural complexity such as the incommensurate host-guest structures K-III and Rb-VI, or the orthorhombic Cmca phases of K-VI and Rb-VI. To study these and other elements at high pressures, diamond anvil cells are frequently used to compress the sample, as they allow for accurate structure identification using x-ray diffraction and can reliably reach pressures of around 300 GPa. However, the study of elements at even higher pressures becomes difficult using conventional diamond anvil cells which are prone to diamond failure at these conditions. This has motivated the development of new DAC designs. In particular, toroidal diamond anvil cells are a promising modification wherein the diamond anvils are 'sculpted' to create a geometry able to achieve pressures above 500 GPa. This work initially investigates the behaviour of the light metals Mg and Al and the alkali metals K and Rb, using conventional diamond anvil cell techniques. The phase transitions of Mg and Al are discussed, with compression data up to 301 GPa and 236 GPa presented for Mg and Al, respectively. Equations of state are fitted for each metal and the data are compared to other studies in the field. In K and Rb, the static phase diagrams are extended up to 321 GPa and 264 GPa, respectively. These studies observe significant changes in the compression curves occurring between 0-100 GPa, where the various phase transitions of these metals display a great variety of compressive behaviour. The predicted high-pressure oC16→hP4 phase transition is observed and presented for the first time in Rb. However, no analogous transition is seen in K in spite of theoretical predictions. The design, manufacture, and implementation of toroidal diamond anvil cells are subsequently detailed, including the specifics of focused ion beam milling. Experiments on the strongly scattering elements W and Ce are then presented. In W, the body-centred cubic phase remains stable up to the highest pressure of 381 GPa, as expected. However, unanticipated changes in the sample pressure environment demonstrate the complexity of performing toroidal diamond anvil cell experiments. In Ce, an apparent shift in the compression curve was observed between 200-250 GPa, accompanied by decreasing c/a ratio in the body-centred tetragonal phase above 250 GPa. The cause of the change in compressive behaviour is unknown, but the c/a ratio decline is found to agree with theoretical predictions. Finally, results from toroidal diamond anvil cell investigations of Rb are presented along with the challenges of studying light and highly reactive elements using toroidal diamond anvil cells. A highest pressure of 272 GPa is recorded from Raman spectroscopy measurements of the diamond.

In various performance domains, individuals are expected to perform at optimal standards under the influence of psychological pressure. When performing under psychological pressure, individuals are susceptible to experiencing psychological and physiological stress states that can either benefit or impair performance. To successfully perform the cognitive and / or motor skills required for optimal performance under pressure, individuals in different domains are required to have the self-regulatory capabilities to cope with stress. While there is a wealth of research regarding coping across performance domains, there is a scarcity of research that compares the nature of coping strategies used by individuals who operate in different high-pressure domains. Therefore, the purpose of this study was to explore the nature of coping strategies used by expert performers from several high-pressure domains to manage stress and facilitate performance under pressure. Seven expert performers (5 male and 2 female) were purposely selected from surgical, military, law enforcement, music, and sport performance domains. Participants were interviewed on an individual basis, to explore lived experiences of coping strategies used to manage stress when facilitating performance under pressure. Interpretative phenomenological analysis was used to theme the response data. Eight superordinate themes emerged from the data: perceived challenges, preparedness, personal responsibility, adaptability, support mechanisms, individual factors, perceived coping effect, and coping strategy development. Findings are discussed in relation to associated theoretical application, and the implications of inter-professional learning for psychologists working in different high-pressure performance domains.

Much of the sports officiating research literature has sought to understand environmental influences on officiating - most notably in soccer. The current body of work extends the existing literature, by investigating not only contextual influences on naturalistic decision making but also the influence of dispositional tendencies - specifically, umpires' predisposition to deliberate and reflect on their decisions, i.e., their tendency to reinvest and ruminate. Performance analyses of an entire Netball Superleague season demonstrated that netball umpires' decision making was influenced by several contextual factors, including crowd size and Decision Rumination. Reduced decision frequency - an avoidance-type behaviour - was associated with time elapsed, league position, crowd size, competition stage, and Decision Rumination. A lab-based investigation into the effects of crowd noise, a novel game management dual-task and pressure on decision making demonstrated that the intensity of the variables (under pressure, with crowd noise, with secondary task) reduced participants' decision making accuracy. Reduced processing efficiency was indicated by increased scan ratios gaze on informative areas of the display, and an increase in mental effort under pressure and dual-task conditions. A reversion to novice-like thoughts, and fewer cognitive/top down sources of information were used to make decisions. Contrary to previous research, Decision Rumination was associated with better performance under these conditions. A final study sought to understand whether the impact of Decision Rumination on performance was context-specific by manipulating the feedback participants received during a lab-based video decision task. Following negative feedback, High Decision Ruminators were less confident and less accurate compared to Lower Ruminators. It is possible that whether trait Decision Rumination is debilitative or facilitative may be context-specific. The discrepancies and commonalities of the present findings in relation to the extant literature are discussed.

This thesis presents work exploring the use of pressure as a tuning parameter for exploring the phase diagrams and properties of magnetically ordered insulators, to add understanding to several areas of current interest in condensed matter research. It shows the versatility of pressure as an experimental technique for exploring material properties free from complicating factors which arise with similar techniques such as chemical doping. The properties of low-dimensional magnetic materials, and how these systems respond as they are pushed toward a more three-dimensional nature is explored through studies of both the crystal and magnetic structures of the family of quasi-two-dimensional magnetic insulators MPS3 (M = Fe, Ni, Mn). With previous work largely being specific to individual compounds, this thesis contributes to a more unified understanding of their properties. It shows that Ni and MnPS3 undergo similar structural transitions under pressure to those previous observed in FePS3, the highest pressure of which is linked to an insulator-to-metal transition in that system. Through record high-pressure neutron diffraction measurements, the evolution of the antiferromagnetic order in FePS3 through this metallisation is studied for the first time. In contradiction to previous indirect measurements, it is seen that magnetism persists into the metallic phase, with long range antiferromagnetism giving way to a previously unobserved short-range order. This work is relevant on a broader scale for numerous layered magnetic materials such as cuprate high temperature superconductors. Secondly, pressure is used to explore the magnetocaloric properties of the antiferromagnet EuTiO3. Recent work has shown that this compound compares favourably to many materials commonly used in magnetic refrigeration. Measurements show that these properties are suppressed by the application of pressure and point towards the potential existence of a previously undiscussed transition in the material between 0.4 GPa and 0.5 GPa.

This body of work investigated the (separate) effects of focus of attention and cognitive anxiety on offline planning and online correction motor control mechanisms. We assessed planning and correction processes via variability profiles of computer-based target-directed aiming movements, captured on either a two-dimensional tablet or three-dimensional Vicon motion capture system. Experimental Chapter 1 investigated heightened anxiety’s effect on offline movement planning and online movement correction using trajectory variability and cursor perturbations to directly test whether strategic trade-offs reduce online corrections under heightened anxiety. This effort was complemented by attempts to tease apart the therein roles of conscious processing (i.e., reinvestment) and distraction (i.e., cognitive overload) by measuring trait conscious processing propensity and manipulating cognitive resources. Results suggested online corrections are reduced under heightened anxiety when the need for correction is low (i.e., in normal trials) but increased if the need for correction is great (i.e., in perturbation trials). High reinvestment propensity positively predicted online-to-offline strategy shifts in normal trials, and depleted cognitive resources reduced online corrections in normal and perturbation trials. Experimental Chapter 2 investigated the effect of heightened anxiety on offline planning and online control when vision was unavailable and proprioception was the sole source of relevant afferent information. Results revealed no significant differences in the efficacy nor prominence of offline planning and online correction. It was concluded that the distraction and conscious processing mechanisms associated with heightened anxiety may not impair the planning and correction of movements when based primarily on proprioceptive afferent information. Experimental Chapter 3 explored a different research domain, by investigating the effect of internal (i.e., body) and external (i.e., environmental movement effect) foci of attention on offline movement planning and online movement correction. Proprioceptive salience was manipulated across this chapter’s experiments to also test whether the proposals of the constrained action hypothesis hold true when only an internal focus of attention was congruent with task-relevant afferent feedback. Results suggested that an internal focus of attention is optimal for outcome performance when congruent with afferent proprioceptive information, and that these effects originate within offline movement planning. Overall, the present thesis provides substantial clarification concerning offline and online motor control’s role in outcome performance-centric anxiety and focus of attention literature.

Bismuth-tellurides are binary compounds of bismuth (Bi) and tellurium (Te) which form an infinitely adaptive series, (Bi2)m(Bi2Te3)n, within certain compositional limits. Members of this series exhibit a number of interesting and useful physical properties: they are among the most widely known thermoelectric materials and they have been shown to exhibit superconductivity and topological insulation. Many of these properties have been reported to be induced or enhanced by the application of high pressure. Despite this, the current understanding of the crystal structures of the (Bi2)m(Bi2Te3)n series under high pressure remains fragmentary. Knowledge of these crystal structures is the first necessary step towards further investigation of the properties of these materials through, for example, electronic structure calculations. This thesis presents the analysis of high-pressure x-ray diffraction data collected for several members of the (Bi2)m(Bi2Te3)n series. Angle-dispersive x-ray powder diffraction experiments were performed at synchrotron facilities, utilising diamond-anvil pressure cells to generate pressures up to 26 GPa. Several structural phases of the (Bi2)m(Bi2Te3)n series are investigated in detail including a previously unreported complex host-guest structure that forms in several of the series members at high pressures. This is a similar structure to the host-guest phase of elemental bismuth (Bi-III) with a host framework enclosing linear guest chains which lie along the c-axis direction. The guest chains are found to be disordered along their lengths, contributing only diffuse features to the measured x-ray powder diffraction profiles. Along with this structural disorder, this structure is found to include chemical ordering with the guest chains composed primarily of bismuth Other investigated phases include the layered structure found at ambient conditions, consisting of regular Bi2 and Bi2Te3 blocks stacked along the c-axis. Where appropriate, Rietveld refinement of these structures found the block compositions to differ from the idealised structure. For certain compositions, a four-dimensional modulated structure is the more appropriate description; le Bail fits were performed in these cases to provide the pressure-evolution of the lattice parameters and modulation vector. All investigated samples were found to adopt high-symmetry cubic phases at the highest pressures investigated here. This, along with various similarities between the other pressure-induced phases, suggests a universal behaviour in the (Bi2)m(Bi2Te3)n series on pressurisation. Composition was found to have a significant influence on the behaviour under pressure and individual structures of bismuth-tellurides. This work represents the first systematic, high-pressure structural study of these materials and explores the pressure-behaviour of the series as a whole and as a function of composition. This provides a first necessary step towards an improved understanding of these materials and their properties at high pressures.

Research has demonstrated that the performance of narcissists rises and falls with the opportunity for self-enhancement and the emergence of ego threats. As such, it has been suggested that narcissists are more capable of performing in a competition, where self-enhancement and ego threats are present, rather than in a training environment, where such opportunities are lacking. However, the narcissism-performance literature has focused on narcissism in its grandiose form but has not considered the so-called adaptive and maladaptive components of narcissism. Indeed, adaptive narcissism, reflecting high levels of confidence and assertiveness, is different to maladaptive narcissism, reflecting a strong willingness to dominate and control over situations. Since narcissism can reflect either high levels of adaptive or maladaptive narcissism, or certainly both, it is essential to consider adaptive and maladaptive narcissism interact in order to gain a full picture of how narcissism plays a role in performance settings. Therefore, the overarching aim of the thesis was to examine the interaction between adaptive and maladaptive narcissism in two different performance contexts, namely high-pressure performance environments and athletic training environments. Furthermore, the thesis also explored mechanisms underlying the narcissism-performance relationship in order to explain why the adaptive  maladaptive narcissism interaction would contribute to high performance under high pressure. Finally, the thesis examined practical strategies to protect against the potential adverse effects of narcissism on athlete training; providing the first evidence that goal-setting and imagery use during training help narcissists (especially those high in adaptive narcissism) train better. The thesis consists of a general introduction (Chapter 1), four empirical studies (Chapters 2 and 3), and a general discussion (Chapter 4). More specifically, Chapter 2 presents a collection of three experimental studies, examining the interactive effects of adaptive and maladaptive narcissism on performance under pressure as well as testing the mechanisms underlying the performance effects. Experiment 1 used a basketball free throw task to assess the adaptive  maladaptive narcissism interaction on performance under high pressure. Experiment 2 used a golf-putting task to test the hypothesized performance effects. Further, Experiment 2 employed self-report and behavioural measures to explore the mechanisms underlying any performance effects. To test the replicability and generalizability of Experiments 1 and 2, Experiment 3 used a letter transformation task and a colour-word Stroop task to test the adaptive  maladaptive narcissism interaction, along with self-report and psychophysiological measures to examine mechanisms. Across each study results consistently demonstrated that adaptive narcissism predicted performance under high pressure only when maladaptive narcissism was high. Also, at high levels of maladaptive narcissism, adaptive narcissism predicted decreased pre-putt time in the golf-putting task (Experiment 2) and an adaptive psychophysiological response in the letter transformation task (Experiment 3), reflecting better processing efficiency. Findings suggest that individuals high in both adaptive and maladaptive narcissism perform better under pressure because of superior processing efficiency during task performance. Chapter 3 (Study 4) presents an applied study examining a three-way interaction between adaptive and maladaptive narcissism and performance strategies (specifically goal-setting and imagery), on athlete quality of training. Using a sample of athletes from different backgrounds (i.e., sporting levels and sport types) with multiple-source data provided (i.e., self-report and informant rating), Study 4 demonstrated consistent three-way interactions between narcissism components and each performance strategy. Specifically, when athlete use of goal-setting was low, adaptive narcissism contributed to increased distractibility and poorer quality of preparation when maladaptive narcissism was low but not high. However, when athlete use of goal-setting was high, adaptive narcissism was not associated with training behaviours regardless of the level of maladaptive narcissism. Identical interactions also emerged for imagery use. The findings suggest that maladaptive narcissism and the performance strategies of goal-setting and imagery protect against the potential adverse effects of adaptive narcissism on athlete training. Based on the findings of the empirical work presented in Chapter 2 and 3, Chapter 4 of this thesis provides implications at a broad theoretical and applied level. Strengths, limitations, and directions for future research are also discussed.

To gain a professional contract in UK academy football, young players must demonstrate an ability to perform under pressure (Larsen et al., 2014). A systematic review was conducted to synthesise findings from applied studies that focus on interventions developed to enhance an individual's ability to cope under performance pressure. Simulation training alongside cognitive-behavioural (CB) workshops was an intervention format that may develop an academy football player's ability to perform within the highly-pressurised environment of academy football (Bell, Hardy and Beattie, 2013). A limitation of much simulation training that is intended to help individuals perform in highly-pressurised environments is the failure to generate meaningful performance pressure. Similarly, CB workshops can also be limited in their effectiveness due to a failure to identify contextually specific factors that may develop coping skills. Such factors should be embedded within CB workshops to align with the needs of individuals in their respective pressure domain. Moreover, study one of this programme of research aimed to identify meaningful pressure conditioned stimuli, along with factors perceived to be facilitative or debilitative of performance under pressure within academy soccer. The perceptions of pressure, and factors of influence identified within study one were used by academy coaches to inform the design of a contextually specific pressure intervention. Study two, presents and evaluates this pressure training intervention. A mixed-methods approach using quantitative (simulation training data) and qualitative data (interviews with players and reflective diary extracts) provided insight into the effectiveness of the pressure intervention. Findings indicate that simulation training alone could enhance performance under pressure within age groups 11-14 years. Players across all age groups described improvement in confidence, emotional intelligence, meta-cognition, focus and challenge appraisal following the intervention. Future research is warranted to investigate the benefits of simulation training and CB workshops within a larger sample, over-time.

Operating temperature range is one of the primary design considerations for developing effective disc brake system performance. Very high braking temperatures can introduce effects detrimental to performance such as brake fade, premature wear, brake fluid vaporization, bearing failure, thermal cracks, and thermally-excited vibration [2]. This project is concerned with investigating deficiencies and proposing improvements in brake system Finite Element (FE) models in order to provide high quality descriptions of thermal behaviour during braking events. The work focuses on brake disc/pad models and the degree of rotational freedom allowed for the pad. Conventional models [10] allow no motion/or free motion of the pad. The present work investigates the effect on disc/pad interface temperature and pressure distributions of limited relaxations of this rotational restriction. Models are proposed, developed and validated that facilitate different rotational degrees of freedom (DoF) of the pad. An important influencing factor in friction brake performance is the development of an interface tribo-layer (ITL). It is reasonable to assume that allowing limited rotational motion of the pad will impact the development of the ITL (e.g. due to different friction force distributions) and hence influence temperature. Here the ITL is modelled in the numerical simulations as a function of its thickness distribution and thermal conductivity. Different levels of ITL thermal conductivity are defined in this work and results show that conductivity significantly a1qwffects interface temperature and heat partition ratio. The work is based around a set of test-rig experiments and FE model developments and simulations. For the experimental work, a small-scale test rig is used to investigate the friction induced bending moment effect on the pad/disc temperature. Significant non-uniform wear is observed across the friction surface of the pad, and reasons for the different wear rates are proposed and analyzed together with their effect on surface temperature. Following on from experiment a suite of models is developed in order to evidence the importance of limited pad motion and ITL behaviours. A 2D coupled temperature-displacement FE model is used to quantify the influence of different pad rotational degrees of freedom and so provide evidence for proposing realistic pad boundary settings for 3D models. Normal and high interface thermal conductance is used in 2D models and results show that the ITL thermal conductivity is an important factor influencing the maximum temperature of contact surfaces and therefore brake performance. The interface heat partition ratio is calculated by using the heat flux results and it is confirmed that this value is neither constant nor uniform across the interface surfaces. Key conclusions from the work are (i) that ITL thermal conductivity is an important factor influencing the interface temperature/heat flux distribution and their maximum values, (ii) that allowed motion of the pad significantly affects the interface pressure distribution and subsequently the temperature distribution, (iii) that the transient heat partition in friction braking is clearly quite different to the conventional friction-pair steady heat partition (the heat partition ratio is not uniformly distributed along the interface) and (iv) that the thickness of the ITL increases through braking events, reducing the heat transfer to the disc, and so providing a possible explanation for increasing pad temperature observed over the life time of a brake pad.

A major area of interest in condensed matter physics over the past decades has been the emergence of new states of matter from strongly correlated electron systems. A few limited examples would be the emergence of unconventional superconductivity in the high-T$_c$ superconductors and heavy-fermion systems, the appearance of the skyrmion magnetic vortex state in MnSi and magnetically mediated superconductivity in UGe$_2$. While detailed studies of many of the emergent phases have been made, there are still many gaps in understanding of the underlying states and mechanisms that allow them to form. This work aims to add to knowledge of the basic physics behind such states, and the changes within them as they are tuned to approach new phases. The cubic perovskite material SrTiO$_3$ has been studied for many decades and is well-documented to be an incipient ferroelectric, theorised to exist in the absence of any tuning in the proximity of a ferroelectric quantum critical point. This work presents the first high-precision dielectric measurements under hydrostatic pressure carried out on a quantum critical ferroelectric, leading to a full pressure-temperature phase diagram for SrTiO$_3$. The influence of quantum critical fluctuations is seen to diminish as the system is tuned away from the quantum critical point and a novel low temperature phase is shown to be emergent from it. The Néel Temperature of the two-dimensional antiferromagnet FePS$_3$ was found to increase linearly with applied hydrostatic pressure. Evidence of an insulator-metal transition is also presented, and an unexplained upturn in the resistivity at low temperatures in the metallic phase.

The hydrophobic effect has been a topic of research for decades, not only due to its importance as the primary building block of much of chemistry (it dictates which solvent can dissolve which solutes) and biology (guiding protein binding and gene expression) but also due to it being a fundamental physical process. The commonly held opinion is that 'like dissolve like', implying polar substances can readily mix with other polar substances, and similarly for apolar ones, but polar and apolar would separate and tend to stay isolated from one another (like oil in water). We have developed a quantitative imaging method that can be used in tandem with Raman spectroscopy in order to investigate the effect of high pressure on a model hydrophobic system - water and methane. Our study revealed an unexpectedly large increase in the amount of methane that can readily mix with water once a rather modest pressure has been applied to the system. Thus, the solubility of CH4 in H2O starts abruptly increasing at 1.3 GPa and reaches a maximum of 44(3) mole % at 2.1 GPa, showing no pressure dependence upon further compression. We have tried to reproduce the observed experimental behaviour using classical molecular dynamics simulations deploying a range of widely used water potentials (SPC/E, TIP4P, TIP3P), but unfortunately no quantitative or even qualitative agreement was reached with experiments. Finally, in order to understand the atomic level changes that enable this increased amount of methane to dissolve in water, we have performed neutron scattering measurements along with EPSR (empirical potential structure refinement) fits to the data in order to solve the structure of the fluid mixture. These revealed a tendency towards maintaining the H-bond network present in water and homogeneous mixing. Despite the network staying similar to the one found in pure fluid water at milder pressures and temperatures (close to ambient conditions), the H-bonds seem more disordered and show a greater variability in their lengths.

Measurements of physical parameters like pressure, temperature, flow rate, vibrations and displacement in harsh environment are often desired in the oil and gas industry. Pressure and temperature are the most important parameters among them. Changes in pressure and temperature have a major role in many downhole processes and they have enabled the performance of producing wells, water-injection profiles, fracture jobs, carbon dioxide (CO2) injection, and enhanced oil recovery to be successfully monitored over the years. However, measurements of these parameters were mostly carried out by logging tools that comprise several conventional electronic gauges. Temperature and pressure in deep and ultra-deep wells could reach beyond 300 °C and 20000 kPa. Fibre optic sensor developments have created new interest in oil and gas production monitoring and control. Fibre optic sensors currently deployed in the oil and gas industry can only operate up to 150 °C and even the most robust sensors are limited below 300 °C. In this research, the effect of cross sensitivity on multi-parameter optical fibre sensor for oil and gas applications in harsh environments is studied and analysed. Mathematical models of the cross sensitivity function of fibre Bragg grating (FBG) and its physical mechanism has been developed. This analysis was based on the fact that FBG sensor was in the state in which temperature and pressure were simultaneously functioning. The main objective of this research is to investigate the cross sensitivity effect of fibre optic sensing technology for oil and gas sensing applications by designing sensing structures and developing theoretical equations for the system model of the optical fibre sensor capable of addressing this issue. Different techniques have been proposed to tackle this cross sensitivity challenge. Firstly, the use of dual sensing structure that investigate and analysed the spectral characterization of a Fabry-Perot interferometer (FPI) sensor and the interaction with physical parameters. Preliminary results of this configuration are used to eliminate the issue of temperature-pressure cross-sensitivity and effectively improve the resolution of the sensor system. Secondly, the concept of a metal coated hybrid sensing system is proposed. The theoretical design and analysis of a metal coated hybrid sensing system of FBG and Extrinsic Fabry-Perot Interferometer (EFPI) cavity for high pressure high temperature (HPHT) measurement in oil and gas applications is reported. The FBG and EFPI are used to measure temperature and pressure respectively. This configuration is able to solve the problem of cross sensitivity. Lastly, a novel thin-film fibre optic extrinsic FPI sensor with an ultra-high pressure and temperature sensitivities are analysed theoretically using 16-layer graphene film deposited on silicon carbide (SiC) substrate as the diaphragm. The performance parameters of the proposed sensor are investigated in terms of sensitivity at the operating wavelength of 1550 nm. It was observed in the numerical study that the sensitivity can be greatly increased by using multilayer graphene on SiC substrate. This sensor is expected to have potential for monitoring oil and gas applications in harsh environments.

AC susceptibility is an important characterisation technique measuring the time dependent magnetisation and dynamics of a magnetic system. It is capable of yielding information on thermodynamic phase transitions, relaxation processes and losses in a variety of interesting magnetic and superconducting materials. In particular it is a powerful probe of the mixed state of superconductivity providing insight into the ux dynamics at play and determination of a number of physical properties such as the critical temperature Tc, field Hc and characteristic length scales. Application of pressure can tune materials through multiple phases and interesting phenomena. The thesis describes the design of a calibratable susceptometer in a piston cylinder pressure cell, achieving AC susceptibility measurements of the same accuracy as a SQUID magnetometer but under pressure. This is used to make measurements on an electrostatically doped capacitance device, a single chain magnet and a heavy fermion superconductor. These studies are summarised below. Electric double layer (EDL) devices provide a means of continuous tuning through a materials phase diagram by applying an electric field, including inducing superconductivity. Application of pressure in tandem with electrostatic doping could improve the efficiency of these devices and provide a second tuning parameter. An EDL capacitor was constructed and measured with the above susceptometer aiming to shift the Tc of a doped high temperature superconducting cuprate La1:9Sr0:1CuO4. The Tc shifts proved irreproducible already at ambient conditions. Indeed during the course of this research further experimental evidence emerged in the literature indicating EDL devices may very well work due to electrochemical doping rather than electrostatic, possibly accounting for the lack of repeatability. Work therefore focused on mapping the ionic liquid DEME-TFSI's glass-liquid phase diagram over the 1 GPa pressure range, rather than extending the study of the EDLC device to high pressure. Single chain magnets (SCM) are an interesting class of material consisting of a one-dimensional molecular magnet chain manifesting magnetic hysteresis and slow relaxation best characterised by AC susceptibility. The susceptometer was used to study the SCM [Co(NCS)2(pyridine)2]n to investigate the effect of pressure on its characteristic magnetic relaxation time and energy barrier. A secondary signal appears at ~0.44 GPa which is attributed to the development of an additional structural phase that has been independently observed in X-ray crystallographic measurements. The heavy fermion superconductor U6Fe has the highest Tc ~4 K of all the U-based compounds and large critical fields of ~10-12.5 T, depending on direction, which increase on initial application of pressure. It exhibits a coexisting charge density wave (CDW) below 10 K making it a promising candidate for the modulated superconductivity of the theorised Fulde-Ferrel-Larkin-Ovchinnikov (FFLO) state. A feature at 110 K is also evident in Mossbauer, resistivity and specific heat measurements, the origin of which has not yet been clearly identified. Evidence for the FFLO state was sought by mapping the upper critical field Hc2 along with the peak effect through AC susceptibility measurements up to pressures of 1 GPa. The data is accounted for by an evolution of collective pinning and superconducting parameters, with no clear evidence for an FFLO state although an enhancement of the reduced field is observed.

Cohesion is essential for team harmony and performance. It is universally sought in sport teams. The benefits have been extensively studied and are a requirement of team success. Counter to wide held belief, cohesion is not an intrinsically positive phenomenon. This thesis aimed to develop more understanding of the potential disadvantages or costs of high cohesion in sport teams to fill a significant gap in the literature. Study 1 examined the extent and nature of these costs. Athletes perceived similar costs. Fourteen categories of costs were identified with perceived pressures and communication issues demonstrated to be strongly significant. Study 2 was framed in narrative theory to explore costs experienced over the life-span career of a retired professional motor sport co-driver. The most significant costs experienced were pressure to perform and pressure to conform. The key influencing factors were a performance narrative along with what was identified as a new narrative type, the team performance narrative. Study 3 utilised the lens of narrative theory to explore when and where costs were not experienced by a current elite motorsport sport driver and his team. Buffers were indicated. Study 4 was a case study of a high performing team where across the entire season team cohesion was high but performance wasn’t reciprocated accordingly. High cohesion produced costs of conformity and normative influence, rigid demands and methods with narrow goal focus, communication issues and pressure to perform. These costs are all inter-related and interacted to have a negative impact on performance. This thesis raises awareness of the potential costs of high cohesion in sport teams and, by offering a new model – the Cohesion Costs’ Reduction Model - for identifying strategies to minimise these potential costs, aims to improve individual wellbeing in a team and improve team performance.

Many wells have been drilled in the Central North Sea but it still remains a challenge to understand this high pressure, high temperature system. Most of these concerns arise because the nature of the pressure transition from relatively low pressures at the top of the Chalk Group, to extremely high pressures in the deep Jurassic/Triassic reservoirs is poorly understood. Consequently, several models for the pressure transition zone have been proposed but the reliability of such models is limited. In this study, well logs and measured pressure data have been analysed by several methods including a new tool: the Late Geopressure Indicator (LGI), in order to identify the cause and distribution of overpressures in the Central North Sea. The study shows that overpressure is caused by both disequilibrium compaction and late geopressure mechanisms. Disequilibrium compaction is dominant in the Cenozoic mudstones where its magnitude is related to recent burial while late geopressure dominates in deeper and older successions that lie beneath the Chalk. In the sub-Chalk settings, both the total overpressure and the prevalence of late geopressure are higher in the deeper Central Graben area (up to 8000 psi overpressure, 80% from late geopressure mechanisms) than in the basin margins (approximately 2000 psi overpressure, 15% due to late mechanisms). The standard method for identifying specific causes of overpressure based on patterns on density-velocity crossplots is non-unique. It is shown that unloading alone, under different geological scenarios can produce a variety of trends on the density-velocity crossplots which can be mistaken for other late overpressure mechanisms. Contrary to some schools of thought that prefer the Chalk as the main pressure seal, it is shown that the sealing interval is not always the Chalk. The top of the deep pressure cell can be located anywhere within the low permeability interval constituted by formations that lie between the Jurassic reservoir and the Chalk. A new overburden stress model has also been developed that can be used in pre-drill pore and fracture pressure prediction calculations.

In a many-body fermionic system, the suppression of continuous transitions to absolute zero can result in a low temperature quantum fluid which deviates strongly from typical metallic behaviour; unconventional superconductivity can be induced by the strange metal region surrounding the zero-temperature phase transition. In this thesis we focus on three systems which demonstrate a highly tunable phase transition, with the aim of pushing them toward the border of a zero-temperature phase transition, and potentially superconductivity. CeAgSb2 is a uniaxial 4f ferromagnet, where physical pressure or a transverse field may be used to tune the magnetic transition towards T = 0 K. Our investigations, however, did not reveal the presence of superconductivity. It is likely that the field tuned transition does not correspond to a true critical point, whilst the high pressure region may be occupied by an antiferromagnetic phase, with the true critical point at higher pressures. However, other interesting features emerge in the electrical resistivity and AC-susceptibility, along with novel thermodynamic signatures linking the magnetisation to the specific heat. The doping series Lu(1-x)YxFe2Ge2 shows an antiferromagnetic transition which is suppressed to absolute zero at a critical concentration x_c=0.2. YFe2Ge2 displays anomalous low temperature behaviour consistent with the proximity to quantum critical fluctuations, along with a superconducting transition which appears in the electrical resistivity beneath a critical temperature of T_c ~ 1.7 K. Using low temperature DC magnetisation measurements, we show that this is a bulk effect, and that the superconductivity in YFe2Ge2 is of type-II. The thermodynamic and BCS properties of the superconducting phase are analysed in line with the parameters we extract experimentally. The superconducting 3-4-13 stannides (Ca,Sr)3Ir4Sn13 show a high temperature structural transition which may be suppressed by the application of hydrostatic pressure or effective chemical pressure. A superconducting dome is found, which appears to peak near where the structural transition extrapolates to zero temperature. Anomalous exponents are seen in the electrical resistivity over a wide temperature range. We investigate the influence of pressure on the superconducting critical temperature in Ca3Ir4Sn13 and the related compound Co3Ca4Sn13, along with an analysis of the upper critical field and flux-line phenomena in Ca3Ir4Sn13 and Sr3Ir4Sn13.

Environmental and regulatory constraints on the global energy market are driving the need to improve conventional power generation methods to meet commitments made to reduce carbon emissions set out in the Kyoto Protocol. To maintain security of supply and ensure competitive energy prices, fossil fuels will play a vital role in the energy market over the next century, however, in order to comply with regulations it is necessary to improve on current conventional power generation technologies. Improvements in security of supply and environmentally deleterious emissions can be realised via increases in plant efficiency. A major route to achieving a considerable increase in efficiency in conventional coal fired power station is via elevating the operating conditions of the working steam to benefit from enhanced thermal cycle efficiencies. It has been proposed that increasing the operating steam parameters from the current typical levels of ~540°C/~190 bar to ~700°C/~300 bar could lead to an increase in plant efficiency of up to 15%. The major challenges to increasing steam parameters need to be met by advanced materials. Increasing the steam temperature and pressure to the suggested levels would push traditional materials beyond their acceptable oxidation and creep resistances. One strategy to accommodate the proposed steam conditions is to substitute traditional steel based materials at key regions of the steam cycle for alternative nickel-based superalloys.

An understanding of the fundamental mechanism behind the relief of shear stress in single-crystal silicon subject to loading by shock-waves has to this day remained elusive. What is known is that this material undergoes a first-order pressure-induced polymorphic phase transition from its ambient pressure cubic-diamond (cd) crystal structure to its first stable high-pressure phase, known as β-Sn, at a pressure of about 120 kbar under hydrostatic compression. By investigating the evolution of the transition parameters for this phase transition as a function of increasing uniaxial shear stress representative of the effects of shock-compression via ab-initio Density Functional Theory computational techniques, we predict a significant lowering of the stress at which the phase transition occurs. This raises the question as to whether the onset of plastic response at the material's Hugoniot Elastic Limit (HEL) reported in experiments corresponds in fact to the phase transition itself, a very plausible possibility which has never been considered before. Furthermore, we present molecular dynamics simulations using a Tersoff-like potential of shock-compressed single crystals of silicon. We find an elastic response up to a critical stress, above which the shear stress is relieved by an inelastic response associated with a partial transformation to a new high-pressure phase, where both the new phase (Imma) and the original cubic diamond phase are under close to hydrostatic conditions. We note that these simulations are also consistent with shear stress relief provided directly by the shock-induced phase transition itself, without an intermediate state of plastic deformation of the cubic diamond phase.

Hydrostatic pressure sensing is used by aquatic animals to estimate depth and to synchronize behaviour with the tides. Pressure sensors examined to date depend on the compression of a fluid, making them susceptible to temperature change. Despite this, the effects of temperature on pressure sensing have not so far been researched. This thesis examined the effects of temperature on the afferent firing rate of thread hair pressure receptors in the crab Carcinus maenas. It tested the hypothesis that for sensors responding positively to rising pressure, an increase in temperature should counteract any contraction in volume, thereby leading to a weaker neural response; vice versa, a stronger response was predicted for a temperature decrease. A novel system was developed which allowed the simultaneous application of sinusoidal pressure change from 150 to 350 mbar and cycles of temperature, typically spanning between 16 and 22 °C, while extracellular recordings were made en passant from afferent nerves innervating statocyst thread hairs. Motor programmes were designed to stimulate thread hairs sensitive to clockwise and anticlockwise rotation through continuous or interrupted bouts of oscillation within the horizontal plane. During constant pressure, raising temperature led to increases in spike frequency and amplitude, with Q10s between 3 and 5 for spike frequency but less than 2 for amplitude. Cooling caused the elimination or decrease of pressure responses while increasing them on heating, thereby contradicting the aforementioned hypothesis of temperature mimicking pressure change. Changes in the timing of pressure responses were also observed. In preparations which were non-responsive to pressure change, temperature change led to bursts in firing at the peaks or troughs of pressure cycles in 28 of 42 preparations, with evidence for recruitment of formerly silent units. The results could not be fully explained under the existing model for pressure sensing by thread hairs, highlighting the necessity for further anatomical studies.

The fundamental theories of heat generation and transfer at the friction interface of a brake assume either matching or not matching surface temperatures by having a varying or uniform heat partition ratio respectively. In the research presented the behaviour of heat partition has been investigated in a fundamental study based on experimental measurements of temperature and the associated modelling and simulation of heat transfer in a brake friction pair. For a disc brake, an important parameter that was identified from the literature study is the interface tribo-layer (ITL), which has been modelled as an equivalent thermal resistance value based on its thickness and thermal conductivity. The interface real contact area was also an important parameter in this investigation, and it has been found to affect heat partitioning by adding its own thermal resistance. A 2-dimensional (2D) coupled-temperature displacement Finite Element (FE) model is presented, based on which a novel relationship which characterises the total thermal resistance (or conductance) at the friction interface has been characterised based on the ITL thermal properties, the contact area, and the contact pressure at the interface. Using the model the effect of friction material wear on the total thermal resistance (or conductance) at the friction interface was predicted and a comparison of the Archard and Arrhenius wear laws in predicting the wear of a resin bonded composite friction material operating against a cast iron mating surface is presented. A 3-dimensional (3D) model is also presented. This model has represented a small scale disc brake test rig which has been used in parallel with the simulation for validation in a drag braking scenario. Two simulation conditions with different pad surface states were investigated, the first having a nominally flat surface, and the second an adjusted (worn) pad surface based on bedding-in data. The Arrhenius wear model was applied to significance of including wear on the total thermal resistance at the friction interface over a short brake application. A sensitivity analysis on the interface thermal conductance, the location of heat generation, and the magnitude of contact pressure has identified the importance of each factor in determining the total thermal resistance (or conductance) at the friction interface during any friction brake application. It is concluded that the heat partitioning is insensitive on the location of heat generation, and that the most sensitive parameter is the contact pressure.

A reversible solid oxide fuel cell (RSOFC) system could buffer intermittent electrical generation, e.g. wind, wave power by storing electrical energy as hydrogen and heat. RSOFC were fabricated by thermoplastic extrusion of (La₀.₈Sr₀.₂)₀.₉₅MnO[subscript(3−δ)] (LSM) ceramic support tubes, which were microstructurally stable with 55% porosity at 1350°C. A composite oxygen electrode of LSM-YSZ was applied, providing a homogeneous substrate for a 20 μm - 30 μm thick YSZ electrolyte. A dip-coated 8YSZ slurry, and a painted commercial 3YSZ ink gave sintered densities of 90% and nearly 100% at 1350°C, respectively. A porous NiO/YSZ fuel electrode was also painted on. A Ag/Cu reactive air braze was unsuccessful at forming a void-free joint between the RSOFC and a 316 stainless steel gas delivery tube, as the braze did not penetrate the oxidation layer on the steel. Two alumina-based ceramic cements failed to fully seal the cell to an alumina gas delivery tube, due to thermal expansion coefficient mismatches and porosity after curing. Therefore, the maximum open circuit voltage (OCV) obtained during RSOFC testing was 0.8 V at 440°C. LSM-YSZ symmetrical cell performance measurements with oxygen pressure showed a diffusion polarisation, which was assigned to dissociative adsorption and surface diffusion of oxygen species. A collaborative RSOFC system software model showed ohmic and activation losses dominated the RSOFC, and diffusion losses were insignificant. Pressurisation from 1 to 70 bar increased the RSOFC Nernst voltage by 11% at 900°C, and reduced the entropy of the gases, reducing heat production and increasing electrical efficiency. A 500 kg Sn/Cu phase change heat store prevented the system overheating. Over a 16 h discharge-charge RSOFC cycle in the range 5 mol.% - 95 mol.% hydrogen in steam, at 20.4 A per cell or 3250 A m⁻², the electrical energy storage efficiency was 64.4%.

The (trivalent) lanthanides exhibit a common sequence of phases upon the application of pressure: hcp → dhcp → fcc → “distorted-fcc”. The “distorted-fcc”’ phase (d-fcc), observed in the light lanthanides is known to be related by geometric distortions to the fcc unit cell, yet the d-fcc phase has been reported to comprise of one or two structures, with no prevailing consensus as to the solution(s). This thesis contains a detailed study of the d-fcc phase of the light lanthanides Pr and Nd. High-pressure angle-dispersive powder-diffraction techniques were employed to systematically study the phases adopted by Pr (up to 25GPa) and Nd (up to 44GPa). Particular attention was paid to solving the d-fcc of each of these elements, the structure of which is very unclear in published work. In Pr, the d-fcc between 7 and 20GPa is shown to comprise of two phases, the solutions of which are shown to be hR24 (R¯3m) and oC16 (Ibam) for the regions 7-14GPa and 14-20GPa, respectively. The pressure dependence of each of these structures over their stability range is presented. Revisions to previously-published volume vs. pressure data are made, with a different value for the volume collapse at the 4f electron delocalisation transition reported. Similarly, the d-fcc phase of Nd, stable over the pressure range 16-40GPa, is studied in detail. Nd differs from Pr by undergoing a further transition, to a hP3 (P63) structure, on pressurisation above 40GPa, before transforming to a α-Uranium phase. The distorted-fcc phase is shown, like that of Pr, to comprise of two phases, hR24 (R¯3m) and oC16 (Ibam) for the pressure regions 16-26GPa and 26-40GPa, respectively. Data on Nd are presented up to the maximum pressure achieved, 44GPa. Data from a preliminary study of La are also presented, along with a brief report on attempts to prepare a single crystal of Pr within a diamond anvil cell, by laser annealing of a powder of Pr.

Granular materials are in abundance both in nature and in industry. They are of considerable interest to both the engineering and physics communities, due to their practical importance and many unsolved scientific challenges. This thesis is concerned with the “pressure dip” phenomenon underneath a granular pile (commonly known as the “sandpile problem”) which has attracted great attention in the past few decades. Underneath a sandpile that is formed by funnel feeding, a significant minimum (dip) in the vertical base pressure is often found below the apex where a maximum pressure is intuitively expected. Despite a large amount of work undertaken, a comprehensive understanding of this phenomenon remains elusive. This thesis presents an extensive study investigating the underlying mechanism of this phenomenon and also its implications on pressures in silos. The study started with a laboratory test programme of conical mini iron pellet piles. The results confirmed that the pressure dip is a robust phenomenon. It was shown that, under certain deposition radius with uniform deposition across the deposition area, a dip emerges firstly in a ring shape when the radius of the formed pile is small and comparable to the deposition radius. With the increase of the pile radius upon further deposition, the dip ring gradually evolves to a central dip as the pressure at outer radius eventually overtakes that in the centre. The magnitude of the dip was found to be significantly affected by the deposition rate but almost unaffected by the deposition height.

The effect of pressure on a number of magnetically interesting compounds such as single-molecule magnets and dimeric copper and manganese molecules has been investigated to probe the validity of ambient magneto-structural correlations. The first chapter is an introduction to the equipment and methodologies that have been adopted to carry out the experimental high-pressure work. The second chapter reports the first combined high-pressure single crystal X-ray diffraction and high pressure magnetism study of four single-molecule magnets (SMMs). At 1.5 GPa the structures [Mn6O2(Et-sao)6(O2CPh(Me)2)2(EtOH)6] (1) – an SMM with a record effective anisotropy barrier of ~86 K – and [Mn6O2(Etsao) 6(O2C-naphth)2(EtOH)4(H2O)2] (2) both undergo significant structural distortions of their metallic skeletons which has a direct effect upon the observed magnetic response. Up to 1.5 GPa pressure the effect is to flatten the Mn-N-O-Mn torsion angles weakening the magnetic exchange between the metal centres. In both compounds one pairwise interaction switches from ferro- to antiferromagnetic, with the Jahn-Teller (JT) axes compressing (on average) and re-aligning differently with respect to the plane of the three metal centres. High pressure dc χMT plots display a gradual decrease in the low temperature peak value and slope, simulations showing a decrease in |J| with increasing pressure with a second antiferromagnetic J value required to simulate the data. The “ground states” change from S = 12 to S = 11 for 1 and to S = 10 for 2. Magnetisation data for both 1 and 2 suggest a small decrease in |D|, while out-of-phase (χM //) ac data show a large decrease in the effective energy barrier for magnetisation reversal. The third SMM is the complex [Mn3(Hcht)2(bpy)4](ClO4)3·Et2O·2MeCN (3·Et2O·2MeCN) that at 0.16 GPa loses all associated solvent in the crystal lattice, becoming 3. At higher pressures structural distortions occur changing the distances between the metal centres and the bridging oxygen atoms making |J| between the manganese ions weaker. No significant variations are observed in the JT axis of the only MnIII present in the structure. Highpressure dc χMT plots display a gradual decrease in the low temperature peak value and slope. Simulations show a decrease in J with increasing pressure although the ground state is preserved. Magnetisation data do not show any change in |D|. The fourth SMM, [(tacn)6Fe8O2(OH)12](ClO4)3.9Br4.1⋅6H2O, (4) is the largest inorganic compound ever studied at high-pressure. Up to 2.0 GPa the conformation of the complex remains largely unaffected, with the counter ions and water molecules moving around to accommodate a compression of the unit cell volume. High pressure magnetic susceptibility data collected up to 0.93 GPa confirm minimal changes in the intra-molecular exchange interactions. The third chapter focuses on three hydroxo-bridged CuII dimers: [Cu2(OH)2(H2O)2(tmen)2](ClO4)2 (5), [Cu2(OH)2(tben)2](ClO4)2 (6) and [Cu2(OH)2(bpy)2](BF4)2 (7) have been structurally determined up to 2.5, 0.9 and 4.7 GPa, respectively. 6 and 7 have never been reported before. Pressure imposes important distortions in the structures of all three complexes, particularly on the bond distances and angles between the metal centres and the bridging hydroxo groups. 5 undergoes a phase transition between 1.2 and 2.5 GPa caused by the loss of a coordinated water molecule. This leads to a loss of symmetry and dramatic changes in the molecular structure of the complex. The structural changes are manifested in different magnetic behaviours of the complexes as seen in dc susceptibility measurements up to ~0.9 GPa: J becomes less antiferromagnetic in 5 and 6 and more ferromagnetic in 7. The fourth chapter shows the compression of two oxo-bridged MnII/MnIII mixed valence dimers: [Mn2O2(bpy)4](ClO4)3⋅3CH3CN, (8) has been squeezed up to 2.0 GPa whilst [Mn2O2(bpy)4](PF6)3⋅2CH3CN⋅1H2O, (9) could be measured crystallographically up to 4.55 GPa. 9 has never been reported before, while 8 has been reported in a different crystallographic space group. The application of pressure imposes significant alterations in the structures of both complexes. In particular, in 8 the Mn-Mn separation is reduced by the contraction of some of the Mn-O bond distances, 9 shows essentially analogous behaviour: the Mn-Mn distance and nearly all the Mn-N bonds shrink significantly. The magnetic behaviour of the complexes has been measured up to 0.87 GPa for 8 and 0.84 GPa for 9, but neither display any significant differences with respect to their ambient data.