Now showing items 588-607 of 624

• #### Ultrafast Electric Field-induced Phase Transition in Bulk Bi0.5Na0.5TiO3 under High Intensity Terahertz Irradiation

Ultrafast polarization switching is being considered for the next generation of ferroelectric based devices. Recently, the dynamics of the field-induced transitions associated with this switching have been difficult to explore, due to technological limitations. The advent of terahertz (THz) technology has now allowed for the study of these dynamic processes on the picosecond (ps) scale. In this paper, intense terahertz (THz) pulses were used as a high-frequency electric field to investigate ultrafast switching in the relaxor ferroelectric, Bi0.5Na0.5TiO3. Transient atomic-scale responses, which were evident as changes in reflectivity, were captured by THz probing. The high energy THz pulses induce an increase in reflectivity, associated with an ultrafast field-induced phase transition from a weakly polar phase (Cc) to a strongly polar phase (R3c) within 20 ps at 200 K. This phase transition was confirmed using X-ray powder diffraction and by electrical measurements which showed a decrease in the frequency dispersion of relative permittivity at low frequencies.
• #### Understanding the impact of cavitation on hydrocarbons in the middle distillate range

Hydrocarbons in the middle distillate range (C8 - C26) have been treated with ultrasound at 20 kHz - a frequency sufficient to drive acoustic cavitation. The high temperatures experienced as a result of the implosion of fuel vapour bubbles are sufficient to produce pyrolytic degradation and dehydrogenation, as well as a growth mechanism that results in the formation of small particles that have similarities with the primary soot particles produced during diesel combustion. These nanosized particles agglomerate as a result of kinetically driven collisions during cavitation to form a dispersion of micron sized particles in the treated hydrocarbon. The particles are carbonaceous in character, being a mixture of amorphous and graphitic-like carbon. The mass of material produced increases with the C/H atomic ratio of the hydrocarbon undergoing cavitation and is decreased through the addition (1 - 3 %v/v) of low boiling paraffinic hydrocarbons, possibly as a result of lowering the temperature developed inside imploding cavities. Dispersions of microparticles contain equilibrated levels of nanoparticles. If sufficiently high numbers of these smaller primary particles are present they agglomerate due to thermally driven collisions during post-cavitation storage. When this happened a sharp rise in the number of 1 - 2 µm particles was seen after only a few days. Some evidence is presented for the behaviour of ultrasonically treated hydrocarbons being related to the degradation of diesel fuel exposed to hydrodynamic cavitation in the fuel systems of modern common rail direct injection diesel engines.
• #### Understanding the relationship between ignition delay and burn duration in a constant volume vessel at diesel engine conditions

Experiments were performed in a constant volume vessel, with fuel sprays injected into the vessel at various different pressure and temperature conditions chosen to represent diesel engine operation at various loads. A range of diesel primary reference fuels (i.e. mixtures of cetane and heptamethylnonane) of varying cetane number (CN) were tested, and as expected lower CN fuels have longer ignition delays. Burn period was plotted against ignition delay and two distinct trends can be seen: “mainly diffusion” diesel combustion in which burn period decreases with ignition delay and “mainly pre-mixed” diesel combustion in which burn period increases with ignition delay. There is typically a minimum in plots of burn period versus ignition delay which represents the transition between the two types of combustion mode. Higher CN, higher engine load and higher boost pressure would seem to favour “mainly diffusion” combustion whilst lower CN, lower loads and non boosted conditions favour “mainly pre-mixed” combustion.
• #### Underwhelming the immune response: Effect of slow virus growth on CD8+-T-lymphocyte responses

The speed of virus replication has typically been seen as an advantage for a virus in overcoming the ability of the immune system to control its population growth. Under some circumstances, the converse may also be true: more slowly replicating viruses may evoke weaker cellular immune responses and therefore enhance their likelihood of persistence. Using the model of lymphocytic choriomeningitis virus (LCMV) infection in mice, we provide evidence that slowly replicating strains induce weaker cytotoxic-T-lymphocyte (CTL) responses than a more rapidly replicating strain. Conceptually, we show a "bell-shaped" relationship between the LCMV growth rate and the peak CTL response. Quantitative analysis of human hepatitis C virus infections suggests that a reduction in virus growth rate between patients during the incubation period is associated with a spectrum of disease outcomes, from fulminant hepatitis at the highest rate of viral replication through acute resolving to chronic persistence at the lowest rate. A mathematical model for virus-CTL population dynamics (analogous to predator [CTL]-prey [virus] interactions) is applied in the clinical data-driven analysis of acute hepatitis B virus infection. The speed of viral replication, through its stimulus of host CTL responses, represents an important factor influencing the pathogenesis and duration of virus persistence within the human host. Viruses with lower growth rates may persist in the host because they "sneak through" immune surveillance.
• #### The United Kingdom Ministry of Defence and the European Union's electrical and electronic equipment directives

The growth of the generation of Electrical and Electronic Equipment (EEE), and the use of hazardous substances in the production of these items, has required legislation to minimise the harm to the environment that their existing use, ultimate disposal and continued growth of the sector may pose. The European Union (EU) started to tackle this problem with the passing of two Directives in 2002, which focused on restricting the use of hazardous substances (RoHS - 2002/95/EC) and organising the recycling or disposal of discarded electronic and electrical equipment (WEEE - 2002/96/EC). These Directives have been recently recast and their scope widened; however, one exception to them remains items specifically designed for defence and military purposes. This paper looks at how and why these European Directives were passed, the impact they have had on defence in the United Kingdom (UK) up to the present moment, what impact the further extension of those directives might have on UK defence policy and how the UK Ministry of Defence (MOD) has begun to prepare for any extension, including the use of alternative products from the commercial market, and substituting less harmful materials. The paper reviews the information available to carry out future decision making and what level of decision making it can support. Where the data is insufficient, it makes recommendations on actions to take for improvement.
• #### Units of the group algebra of the group $C_n\times D_6$ over any finite field of characteristic $3$

In this paper, we establish the structure of the unit group of the group algebra ${\FF}_{3^t}(C_n\times D_6)$ for $n \geq 1$.
• #### The Use of Stereoscopy in a Neurosurgery Training Virtual Environment

We have previously investigated the effectiveness of a custom built virtual environment in assisting training of a ventriculostomy procedure, which is a commonly performed procedure by a neurosurgeon and a core task for trainee surgeons. The training tool (called VCath) was initially developed as a low fidelity app for a tablet platform to provide easy access and availability to trainees. Subsequently we have developed a high fidelity version of VCath that uses a stereoscopic display to immerse the trainee in the virtual environment. This paper reports on two studies that have been carried out to compare the low and high fidelity versions of VCath, particularly to assess the value of stereoscopy. Study 1 was conducted at the second annual boot camp organized for all year one trainees in neurosurgery in the UK. Study 2 was performed on lay people, with no surgical experience. Our hypothesis was that using stereoscopy in the training task would be beneficial. Results from Study 1 demonstrated that performance improved for both the control group and the group trained with the tablet version of VCath. The group trained on the high fidelity version of VCath with a stereoscopic display showed no performance improvement. The indication is that our hypothesis is false. In Study 2, six different conditions were investigated that covered the use of training with VCath on a tablet, a mono display at two different sizes, a stereo display at two different sizes, and a control group who received no training. Results from this study with lay people show that stereoscopy can make a significant improvement to the accuracy of needle placement. The possible reasons for these results and the apparent contradiction between the two studies are discussed.
• #### Using and Validating Airborne Ultrasound as a Tactile Interface within Medical Training Simulators

We have developed a system called UltraSendo that creates a force field in space using an array of ultrasonic transducers cooperatively emitting ultrasonic waves to a focal point. UltraSendo is the first application of this technology in the context of medical training simulators. A face validation study was carried out at a Catheter Laboratory in a major regional hospital.
• #### Using approximations to Lyapunov exponents to predict changes in dynamical behaviour in numerical solutions to stochastic delay differential equations

This book chapter explores the parameter values at which there are changes in qualitative behaviour of the numerical solutions to parameter-dependent linear stochastic delay differential equations with multiplicative noise. A possible tool in this analysis is the calculation of the approximate local Lyapunov exponents. We show that estimates for the maximal local Lyapunov exponent have predictable distributions dependent upon the parameter values and the fixed step length of the numerical method, and that changes in the qualitative behaviour of the solutions occur at parameter values that depend on the step length.
• #### Using Mathematical Modelling and Electrochemical Analysis to Investigate Age‐Associated Disease

People are living longer. With this rise in life expectancy, a concomitant rise in morbidity in later life is observed; with conditions including cardiovascular disease (CVD), and cancer. However, ageing and the pathogenesis of age related disease, can be difficult to study, as the ageing process is a complex process, which affects multiple systems and mechanisms. The aim of this research was two‐fold. The first aim was to use mathematical modelling to investigate the mechanisms underpinning cholesterol metabolism, as aberrations to this system are associated with an increased risk for CVD. To better understand cholesterol from a mechanistic perspective, a curated kinetic model of whole body cholesterol metabolism, from the BioModels database, was expanded in COPASI, to produce a model with a broader range of mechanisms which underpin cholesterol metabolism. A range of time course data, and local and global parameter scans were utilised to examine the effect of cholesterol feeding, saturated fat feeding, ageing, and cholesterol ester transfer protein (CETP) genotype. These investigations revealed: the model behaved as a hypo‐responder to cholesterol feeding, the robustness of the cholesterol biosynthesis pathway, and the impact CETP can have on healthy ageing. The second aim of this work was to use electrochemical techniques to detect DNA methylation within the engrailed homeobox 1 (EN1) gene promoter, which has been implicated in cancer. Hypermethylation of this gene promoter is often observed in a diseased state. Synthetic DNA, designed to represent methylated and unmethylated variants, were adsorbed onto a gold rotating disk electrode for electrochemical analysis by 1) electrochemical impedance spectroscopy (EIS), 2) cyclic voltammetry (CV) and 3) differential pulse voltammetry (DPV). The technique was then applied to bisulphite modified and asymmetrically amplified DNA from the breast cancer cell line MCF‐7. Results indicated that electrochemical techniques could detect DNA methylation in both synthetic and cancer derived DNA, with EIS producing superiorresults. These non‐traditional techniques ofstudying age related disease were effective for the investigation of cholesterol metabolism and DNA methylation, and this work highlights how these techniques could be used to elucidate mechanisms or diagnose/monitor disease pathogenesis, to reduce morbidity in older people
• #### Using sub-micron silver-nanoparticle based films to counter biofilm formation by Gram-negative bacteria

Composite films comprised of silver nanoparticles (AgNPs) grown using a low-cost straightforward chemical bath based method have been deposited on glass microscope slides to investigate their potential as a sacrificial antibacterial coating. The as-deposited films have been characterised using scanning electron microscopy (SEM) and optical profilometry. These suggested that the films were relatively uniform in coverage. Chemical composition of the AgNP films has been studied by using x-ray photoelectron spectroscopy (XPS). The XPS analysis indicated that the Ag was in a metallic form able to sustain plasmon behaviour, and that low levels of residual nanoparticle precursors were present. Particle size was characterised using transmission electron microscopy (TEM) which showed an average particle size of 10.6 nm. The effectiveness of the films as an antibacterial coating was tested against Escherichia coli. The AgNP film was determined to be effective in the killing of E.coli cells over a 24 hour period when compared to equivalent samples that contained no silver. Of particular note was that only minimal bacterial growth was detected over the first 12 hours of testing, up to 78.6 times less than the control samples, suggesting the film is very efficient at slowing initial biofilm formation. The use of AgNP based films that have been synthesised using a novel low-cost, low-temperature and highly upscalable method is demonstrated as a promising solution for the deployment of silver as an effective sacrificial antimicrobial coating to counter the formation of potentially hazardous Gram negative biofilms.
• #### Using Virtual Reality to Experience Different Powered Wheelchair Configurations

This paper presents recent additions to our Wheelchair-VR application, in particular the use of different drive configurations. We have previously shown that Wheelchair-VR can be used to improve driving skills. Here we consider the utility of the application in allowing users who are in the process of purchasing or upgrading a wheelchair to experience different configurations and options in a cost-effective virtual environment. A preliminary study is presented, which suggests that this approach can be effective.
• #### Utilising Nonlinear Air Damping as a Soft Mechanical Stopper for MEMS Vibration Energy Harvesting

This paper reports on the theory and experimental verification of utilising air damping as a soft stopper mechanism for piezoelectric vibration energy harvesting to enhance shock resistance. Experiments to characterise device responsiveness under various vibration conditions were performed at different air pressure levels, and a dimensionless model was constructed with nonlinear damping terms included to model PVEH response. The relationship between the quadratic damping coefficient ζ n and air pressure is empirically established, and an optimal pressure level is calculated to trade off harvestable energy and device robustness for specific environmental conditions.
• #### UV phototransistors based upon spray coated and sputter deposited ZnO TFTs

A comparison of Zinc Oxide (ZnO) phototransistors prepared by spray and sputter coating process is presented. The work shows that spray coated layers provide significant advantages in sensor response over ZnO phototransistors made by physical vapour deposition and we show that spray deposited ZnO phototransistors can exhibit state-of-the-art performances for UV photodetectors. Topographic images of the samples surface shows that there is increase in surface roughness in spray coated samples indicating increasing grain sizes, which is considered the source of the greater sensor responsivity. X-ray photoelectron spectroscopy (XPS) is also used to understand the root cause of the greater UV responsivity. It was observed that sprayed ZnO TFTs are more sensitive to UV radiation due to higher adsorption of oxygen level. Responsivity and external quantum efficiency (EQE) of the sprayed and sputtered ZnO TFTs are also evaluated.
• #### Verification of calculation code THERM in accordance with BS EN ISO 10077-2

Calculation codes are useful in predicting the heat transfer features in the fenestration industry. THERM is a finite element analysis based code, which can be used to compute thermal transmittance of windows, doors and shutters. It is important to verify results of THERM as per BS EN ISO 10077-2 to meet the compliance requirements. In this report, two-dimensional thermal conductance parameters were computed. Three versions of THERM, 5.2, 6.3 and 7.1, were used at two successive finite element mesh densities to assess their comparability. The results were all compliant with the aforementioned British Standard.
• #### Versailles Project on Advanced Materials and Standards interlaboratory study on intensity calibration for x-ray photoelectron spectroscopy instruments using low-density polyethylene

We report the results of a Versailles Project on Advanced Materials and Standards interlaboratory study on the intensity scale calibration of x-ray photoelectron spectrometers using low-density polyethylene (LDPE) as an alternative material to gold, silver, and copper. An improved set of LDPE reference spectra, corrected for different instrument geometries using a quartz-monochromated Al Kα x-ray source, was developed using data provided by participants in this study. Using these new reference spectra, a transmission function was calculated for each dataset that participants provided. When compared to a similar calibration procedure using the NPL reference spectra for gold, the LDPE intensity calibration method achieves an absolute offset of ∼3.0% and a systematic deviation of ±6.5% on average across all participants. For spectra recorded at high pass energies (≥90 eV), values of absolute offset and systematic deviation are ∼5.8% and ±5.7%, respectively, whereas for spectra collected at lower pass energies (<90 eV), values of absolute offset and systematic deviation are ∼4.9% and ±8.8%, respectively; low pass energy spectra perform worse than the global average, in terms of systematic deviations, due to diminished count rates and signal-to-noise ratio. Differences in absolute offset are attributed to the surface roughness of the LDPE induced by sample preparation. We further assess the usability of LDPE as a secondary reference material and comment on its performance in the presence of issues such as variable dark noise, x-ray warm up times, inaccuracy at low count rates, and underlying spectrometer problems. In response to participant feedback and the results of the study, we provide an updated LDPE intensity calibration protocol to address the issues highlighted in the interlaboratory study. We also comment on the lack of implementation of a consistent and traceable intensity calibration method across the community of x-ray photoelectron spectroscopy (XPS) users and, therefore, propose a route to achieving this with the assistance of instrument manufacturers, metrology laboratories, and experts leading to an international standard for XPS intensity scale calibration.
• #### Vibration Energy Harvesting of Multifunctional Carbon Fibre Composite Laminate Structures

A sustainable power supply for a wide range of applications, such as power- ing sensors for structural health monitoring and wireless sensor nodes for data transmission and communication used in unmanned air vehicles, automobiles, renewable energy sectors, and smart city technologies, is targeted. This pa- per presents an experimental and numerical study that describes an innovative technique to harvest energy resulted from environmental vibrations. A piezo- electric energy harvester was integrated onto a carbon fibre reinforced polymer (CFRP) laminate structure using the co-curing method. The integrated com- posite with the energy harvester was lightweight, flexible and provided robust and reliable energy outcomes, which can be used to power different low-powered wireless sensing nodes. A normalised power density of 97 μW cm −3 m −2 s 4 was obtained from resonance frequency of 46 Hz sinusoidal waves at amplitude of 0.2 g; while the representative environmental vibration waves in various appli- cations (aerospace, automotive, machine and bridge infrastructure) were ex- perimentally and numerically investigated to find out the energy that can be harvested by such a multifunctional composite structure. The results showed the energy harvested at different vibration input from various industrial sectors could be sufficient to power an autonomous structural health monitoring system and wireless communications by the designed composite structure.
• #### Vibration energy harvesting of multifunctional carbon fibre composite laminate structures

A sustainable power supply for a wide range of applications, such as powering sensors for structural health monitoring and wireless sensoring nodes for data transmission and communication used in unmanned air vehicles, automobiles, renewable energy sectors, and smart city technologies, is targeted. This paper presents an experimental and numerical study that describes an innovative technique to harvest energy resulted from environmental vibrations. A piezoelectric energy harvester was integrated onto a carbon fibre reinforced polymer (CFRP) laminate structure using the co-curing method. The integrated composite with the energy harvester was lightweight, flexible and provided robust and reliable energy outcomes, which can be used to power different low-powered wireless sensing nodes. A normalised power density of 97  μW cm−3m−2s4 was obtained from resonance frequency of 46 Hz sinusoidal waves at amplitude of 0.2 g; while the representative environmental vibration waves in various applications (aerospace, automotive, machine and bridge infrastructure) were experimentally and numerically investigated to find out the energy that can be harvested by such a multifunctional composite structure. The results showed the energy harvested at different vibration input from various industrial sectors could be sufficient to power an autonomous structural health monitoring system and wireless communications by the designed composite structure.
• #### A vibration powered wireless mote on the Forth Road Bridge

The conventional resonant-approaches to scavenge kinetic energy are typically confined to narrow and single-band frequencies. The vibration energy harvester device reported here combines both direct resonance and parametric resonance in order to enhance the power responsiveness towards more efficient harnessing of real-world ambient vibration. A packaged electromagnetic harvester designed to operate in both of these resonant regimes was tested in situ on the Forth Road Bridge. In the field-site, the harvester, with an operational volume of ~126 cm3, was capable of recovering in excess of 1 mW average raw AC power from the traffic-induced vibrations in the lateral bracing structures underneath the bridge deck. The harvester was integrated off-board with a power conditioning circuit and a wireless mote. Duty- cycled wireless transmissions from the vibration-powered mote was successfully sustained by the recovered ambient energy. This limited duration field test provides the initial validation for realising vibration-powered wireless structural health monitoring systems in real world infrastructure, where the vibration profile is both broadband and intermittent.
• #### Virtual and Mixed Reality Support for Activities of Daily Living

Rehabilitation and training are extremely important process that help people who have suffered some form of trauma to regain their ability to live independently and successfully complete activities of daily living. VR and MR have been used in rehabilitation and training, with examples in a range of areas such as physical and cognitive rehabilitation, and medical training. However, previous research has mainly used non-immersive VR such as using video games on a computer monitor or television. Immersive VR Head-Mounted Displays were first developed in 1965 but the devices were usually large, bulky and expensive. In 2016, the release of low-cost VR HMDs allowed for wider adoption of VR technology. This thesis investigates the impact of these devices in supporting activities of daily living through three novel applications: training driving skills for a powered wheelchair in both VR and MR; and using VR to help with the cognitive rehabilitation of stroke patients. Results from the acceptability study for VR in cognitive rehabilitation showed that patients would be likely to accept VR as a method of rehabilitation. However, factors such as visual issues need to be taken into consideration. The validation study for the Wheelchair-VR project showed promising results in terms of user improvement after the VR training session but the majority of the users experienced symptoms of cybersickness. Wheelchair-MR didn’t show statistically significant results in terms of improvements but did show a mean average improvement compared to the control group. The effects of cybersickness were also greatly reduced compared to VR. We conclude that VR and MR can be used in conjunction with modern games engines to develop virtual environments that can be adapted to accelerate the rehabilitation and training of patients coping with different aspects of daily life.