In this thesis, we study the transport properties of two different types of graphene devices. The first one is ballistic graphene Josephson junction and the second one is graphene-hexagonal boron nitride-graphene vertical tunnelling transistor. We report on ballistic graphene Josephson junctions with contacts made from type II superconductor, niobium. We observe pronounced Fabry-Pérot oscillations not only in the normal-state resistance but also in the critical current. The proximity effect is mostly suppressed in magnetic fields of B < 10 mT, showing a conventional Fraunhofer pattern. However, some proximity superconductivity survives in fields higher than 1 T which corresponds to more than 1000 flux quanta threading into the junction. We attribute such high-field Josephson effect to individual Andreev bound states that persist near the graphene edges. By studying the Fraunhofer pattern of graphene Josephson junctions, we reconstruct the spatial supercurrent distribution in graphene. The edge-dominated transport is observed only in the case of an energy gap opening in bilayer graphene and graphene/hexagonal boron nitride superlattices, which points to its non-trivial topological origin. Owing to the band structure topology of gapped graphene, the valley-polarized edge modes can extend above the disorders and propagate efficiently for micrometres. By probing the density of states of graphene using graphene tunnelling transistors, we demonstrate a stacking transition in bilayer graphene from incommensurate twisted stacking state to a commensurate AB stacking state by a macroscopic graphene self-rotation. This structural transition is driven by van der Waals energy of two graphene layers and is thermally activated by unpinning the microscopic chemical adsorbents which are then removed by the self-cleaning of graphene. We observe a series of sharp resonant features in the differential conductance of graphene-hexagonal boron nitride tunnelling transistors over a wide range of bias voltages. We attribute them to electron tunnelling assisted by the emission of phonons. The phonon energies corresponding to the resonances are compared with the lattice dispersion curves of graphene-hexagonal boron nitride heterostructure and are close to peaks in the single phonon density of states.

Two separate investigations are presented, both linked by a common interest in the occupancy of the valence neutron orbitals and their relation to nuclear structure studies. A study of the change in neutron occupancy in the 0Î1⁄22Î2 decay of 136 Xe → 136 Ba has been performed. The neutron occupancies of 136 Ba have been probed us- ing the (p,d) and ( 3 He,α) neutron-removal reactions and the (d,p) and (α, 3 He) neutron-addition reactions, performed at the Institut Physique Nucl ́eaire, Orsay. The same reactions have been performed on 134 Ba as an additional consistency check. Spectroscopic factors were extracted through a DWBA analysis and the valence orbital occupancies were extracted using the Macfarlane and French sum rules. The change in neutron occupancy that occurs during 0Î1⁄22Î2 decay was then determined and compared to those calculated by using the interacting shell model and the interacting boson model. The comparison showed that while the various models were able to qualitatively describe the change in occupancy, quantitatively there are significant differences between the models. These are the same models that are used to determine the nuclear matrix elements used in determining the rate of 0Î1⁄22Î2 decay. An additional systematic study of the valence neutron occupancies on the seven even stable tin isotopes is presented. The occupancies were probed in two sets of experiments. The first measurement used the low Q-value (p,d) and (d,p) reactions performed at the Maier-Leibnitz-Laboratory, Munich, to extract spec- troscopic information for low-j orbitals. The second measurement used the high Q-value ( 3 He,α) and (α, 3 He) reactions at the Institut Physique Nucl ́eaire, Orsay to extract spectroscopic information for high-j states. Absolute cross sections were determined and the amount transferred angular momenta was identified by comparison of angular distributions to those calculated using a DWBA analysis. The spectroscopic factors were used in conjunction with the Macfarlane-French sum rules to determine the valence neutron occupancies. These measurements not only qualitatively test the robustness of sum rules in transfer reactions but also provide information about the neutron occupancy of 116 Sn and 124 Sn, two nu- clei of relevance to 0Î1⁄22Î2 decay. The measured occupancies of these two isotopes were compared to those obtained from recent theoretical calculations.

This thesis presents analyses performed with proton-proton collision data collected with the ATLAS detector in 2015 and 2016 at √s=13 TeV. The measurement of so-called non-factorisation effects in the calibration of luminosity is presented. An estimate of the correction, and systematic uncertainty, due to non-factorisation on the calibration is calculated by measuring the proton bunch density profiles from the variation in the luminosity and distribution of reconstructed vertices during beam separation scans. The correction is applied to the calibrations of the total luminosity collected in both 2015 and 2016. A novel multivariate algorithm designed to reject non-prompt leptons (produced from the decays of b- and c-quarks) is presented, utilising information from nearby tracks to discriminate from prompt leptons (produced from W, Z and H boson decays). This algorithm is used to reject non-prompt backgrounds in the search for the associated production of a top quark pair and a Higgs boson (tt̄H) in multilepton final states with 36.1 fb⁻¹ of √s=13 TeV data. Multilepton states refer to the Higgs boson decaying into pairs of W bosons, Z bosons or τ leptons. The combination of the multilepton analysis with the other search analyses of tt̄H production in which the Higgs decays to pairs of photons, b-quarks and ZZ→4ℓ is also shown. The measured value of the signal strength of tt̄H production in data is μ(tt̄H) = 1.2 ± 0.3, corresponding to an observed (expected) discovery significance of 4.2σ (3.8σ) and constituting evidence for the tt̄H production mode.

The heart is the most important organ in the human body. Without an optimally functioning heart, other organs soon fail and death ensues. Cardiovascular disease is the leading cause of death globally, accounting for 17.3 million deaths every year and this number is expected to reach 23.6 million by 2030. A huge amount of resources are pooled annually for the study of the heart in order to gain a better understanding of the underlying mechanisms involved in its function. Over the course of this project, a biophysically detailed, 3D computational model of the rabbit atria has been developed. Previously published single cell models of the rabbit atria served as a starting point and tissue heterogeneity was expanded by incorporating new experimental data and single cell models. Furthermore, a highly detailed anatomical reconstruction of the rabbit atria based on micro-CT imaging techniques as well as realistic fibre orientation data extracted from this high resolution dataset were incorporated into the 3D model. The project was successful in accurately representing the physiology of the rabbit atrial function. Furthermore, a high resolution anatomical reconstruction of the atria from a rabbit with experimental heart failure was used to study the effects of tissue hypertrophy, fibre disorganisation, tissue heterogeneity and ionic remodelling in cardiac function. It was found that tissue hypertrophy is a major contributor towards the increased risk associated with heart failure through the promotion of re-entrant waves in the atria. Lastly, the role of the atrial septum in cardiac conduction was investigated. Through the use of 3D computational modelling, analysis of realistic fibre data extracted from high resolution CT imaging as well as histological data, it was found that structures in the atrial septum could play an important role in the propagation of electrical signals from the atria towards the ventricles.

In this thesis I discuss the characterisation and development of sources of both linearly and radially polarised terahertz radiation, and present the results of using linearly polarised terahertz radiation to investigate the carrier dynamics in GaN semiconductor systems. Linearly polarised terahertz radiation was generated by large area and interdigitated photoconductive antennas (PCAs) and through four-wave rectification in an air plasma. A comparison of the electric fields, the bandwidths, dynamic range and signal-to-noise ratio was made between the three sources, with comments made regarding the suitability of these sources for use in spectroscopic measurements. In order to investigate the cause of efficiency droop in InGaN/GaN multiple quantum well (MQW) structures, a combination of time-integrated photoluminescence spectroscopy and time-resolved terahertz and photoluminescence spectroscopies were used. The results of these investigations are presented with the aim to shed light on the mechanism behind efficiency droop, and provide strong evidence that it is the saturation of the localised hole states that contribute to the efficiency droop in these samples. Radially polarised radiation has been observed to have an enhanced longitudinally polarised component, when compared to linearly polarised radiation. Two radially polarised terahertz sources were characterised, a large area radial PCA and a radial interdigitated structure, the results of which are presented here. The longitudinal electric field component was found to have amplitudes of 2.2 kVcm-1 and 3.5 kVcm-1 for the large area and the interdigitated radial PCAs respectively. The bandwidth, dynamic range and signal-to-noise ratio of both devices are also discussed, alongside the scalability of the interdigitated structure.

Plastic foams are used extensively for the reduction of unwanted noise. With recent changes to the types of foam available and the market for sound absorbers it is possible that a large increase in demand for cellular plastic will occur. By understanding how a foam absorbs sound, methods of increasing performance for a specific application can be suggested. This work investigates how changes in market forces affect the demand for acoustic materials. As alternative materials can also fulfil any new demand, the way in which foam manufacturers are utilising market changes is investigated. The primary factors influencing changes in the demand for acoustic absorbers are technological developments, legislation and public opinion. In recent years there has been an increase in the types of foams available to compete for the noise control market. The newer, high performance, foams have properties which overcome the disadvantages that foam has relative to its competitors. Properties and performance of high performance foams are reviewed. A number of parameters in a foam control its sound absorbing properties. By holding all but one of these parameters constant it is demonstrated how changes have an effect on acoustic absorption. With information on how individual parameters influence acoustic absorption behaviour the possibilities of tuning a foam to a specific application is investigated. The investigation is conducted using models suggested by several authors. Only one model is found to be applicable to cellular plastics and there are limitations to its application. Increased demand for acoustic absorbers and an understanding of how foams absorb sound would indicate a large increase in the demand for acoustic foam. Due to economic reasons the implementation of technology can be too costly. Using foams in preference to other, usually less expensive, materials requires a transference of information to end users. There appears to be a shortage of expertise in the foam industry to communicate this cost justification. Potential for improvement of foam performance for specific application is possible. Equally possible is an increase in foam production brought about by greater demand for acoustic absorbers. In the next few years observation of the industry will reveal whether potential is translated into profit.

A range of natural chrome ores, containing iron in two valence states, have been investigated using the technique of Mossbauer spectroscopy. The instrumentation required to cry out the technique was studied and an additional item of equipment was designed and constructed to extend the temperature range over which the effect could be observed. All the chrome ores yielded a complex spectra which could be attributed to a combination of octahedrally and tetrahedrally co-ordinated Fe2+ and Fe3+ quadrupole doublets. A model for fitting the spectra was devised assuming the presence of octahedrally co-ordinated Fe3+ and tetrahedrally co-ordinated Fe2+. The inhomogeneous nature of the samples caused a broadening of the tetrahedral Fe2+ contribution which was fitted as a distribution of three doublets. The Mossbauer parameters obtained were compared with those of pure compounds of a similar structure. Spectra recorded from 12K to 600K enabled effective Debye temperatures to be calculated. Second order Doppler shift (S.O.D.S.) calculations gave values for theta[D] of 385K and 658K for the Fe2+ and Fe3+ contributions respectively. Absorption area data gave similar values. An examination of the temperature dependence of the quadrupole splitting of the Fe2+ contributions appeared to confirm the validity of the proposed fitting model. Estimations of the Fe2+ / Fe3+ ratio were made using the data obtained and yielded values of 1.6 - 3.6.

One of the largest challenges within modern medicine is the increase in global cancer rates especially in western countries, which is often attributed to ageing populations, dietary and lifestyle changes. One of the fastest growing cancers within the western world is oesophageal cancer, which without reliable early diagnosis is often fatal due to the cancer spreading. It is therefore crucial for the development of reliable methods and tools for early cancer detection. This is especially important for those who are most at risk, which includes Barrett's oesophagus patients. Infrared (IR) spectroscopy techniques have been proven capable of gaining large amounts of information on the chemical composition of biological samples. This thesis therefore focuses on using a variety of IR spectroscopy techniques, including Fourier transform infrared spectroscopy (FTIR) and scanning near-field optical microscopy (SNOM) to image oesophageal samples, tissue biopsies and cell line samples. The thesis demonstrates how machine learning algorithms can be used in conjunction with FTIR to provide a quick, non-biased tissue diagnostic method, free from the issues associated with current histology techniques. As well as focusing on the processing of FTIR data, the thesis will assess the ability of an aperture SNOM to image biological samples as it is able to achieve diffraction limit breaking spatial resolutions and has to potential to give previously impossible insights.

This doctoral research presents the first comprehensive analysis of the morphological, biochemical and spectral leaf traits of canopy and emergent tropical trees during natural (in situ) leaf ageing. It adopts an interdisciplinary approach and combines multiple scales of analysis to generate insights into the effects of natural leaf ageing on our current understanding of tropical leaf trait variation, chemometric models used to spectrally predict leaf traits, and together with other leaf phenological processes, on remotely-sensed vegetation indices (VIs) commonly used to monitor canopy dynamics in tropical evergreen forests. The first research paper of this thesis (<b>Chapter 4</b>) examines the effects of leaf age on morphological and biochemical leaf traits and demonstrates that leaf age is a significant driver of leaf trait variation in Amazonian canopy trees and that leaf age differences could potentially account for a significant fraction of what we currently understand as intra- and interspecific leaf trait variation. It also highlights that age-related trait variation within and between individual trees could play a significant role in shaping community composition and structure of tropical canopies. The leaf traits examined in <b>Chapter 4</b>, among others, have been shown to directly influence the spectral reflectance behaviour of leaves. Therefore, <b>Chapter 5</b> investigates the effects of leaf age on leaf spectral properties within and across a tropical canopy tree community. This study reveals that trees with diverse leaf properties age in a similar manner in terms of spectral properties. This is one of the most important findings of this thesis and lead to the development of a novel chemometric partial least square regression (PLSR) model to predict leaf age from hyperspectral data. This model extends the utility of current spectroscopic methods and introduces a simple and efficient approach for predicting and monitoring leaf age in lowland tropical forests with important implications for remote sensing. Additionally, this study is the first to provide evidence of age-related reflectance changes in leaves that have significant impacts on vegetation indices commonly used to monitor productivity and canopy dynamics in tropical evergreen forests. Considering the findings of the previous two research chapters, <b>Chapter 6</b> investigates if chemometric PLSR models used to spectrally predict some of the important leaf traits for plant physiology and economy (leaf mass per area, LMA; water content, LWC; phosphorous, P; nitrogen, N; and carbon, C content) investigated in the previous two research chapters could be significantly biased by variation in leaf age. This is particularly relevant as the current standard protocol is to use only "fully expanded mature leaves" to calibrate these models. This study demonstrates that PLSR models developed using the current standard protocol display age/temporal sensitivity, which has important implications for forest canopy communities with both synchronised and unsynchronised leaf phenology. The final research chapter of this thesis, <b>Chapter 7</b>, demonstrates that the phenological age-related changes in leaf spectral properties reported in <b>Chapter 5</b> are also expressed at the canopy scale but influenced by both canopy leaf area (CLA) and the leaf phenological behaviour of individual trees. This study also reveals that the seasonality of greenness VIs such as NDVI and EVI2 are more strongly correlated to phenological changes in CLA then changes in leaf reflectance and proposes that NDWI (water content VI) which was found to be strongly correlated to age-related changes in leaf reflectance should complement greenness VIs in phenological studies. Furthermore, by combing leaf, canopy and community scale phenological observations, this study shows that complex and diverse leaf phenological behaviours exhibited by tropical canopy trees, at both the individual and community scale, challenge our current ability to remotely sense tropical canopy dynamics. Finally, this chapter highlights the need for more widespread phenological studies that examine the interaction, covariation, asynchrony and unique behaviours of tropical phenological processes at different scales. Such studies would enable the development of a significant mechanistic understanding of what creates and drives different phenological mosaics identified by remote sensing studies across tropical forests and in modelling their effects on water and carbon fluxes in tropical forest ecosystems.

The inclusion of heavy quarks, such as the charm quark, poses difficulties in Lattice QCD simulations. These need to be overcome in order to make predictions of hadronic observables including a charm quark such as the decay constants <i>f_D</i> and <i>f_Ds</i>. We first establish the region of validity of simulating heavy quarks with domain wall fermions (DWFs) in a feasibility study. We then carry out dynamical simulations with RBC/UKQCD’s <i>N_f</i>= 2+1<i>f</i> ensembles at three lattice spacings (a ⁻¹ = 1.73 − 2.77 GeV) including two physical pion mass ensembles. From this we make a prediction for the decay constants <i>f_D</i> and <i>f_Ds</i> and, using experimental input, the corresponding CKM matrix elements. In the first part of this work we investigate the suitability of domain wall fermions (DWF) as a lattice regularisation for heavy quarks. We generate four quenched QCD gauge ensembles with the tree-level improved Symanzik gauge action and inverse lattice spacings in the range 2.0 − 5.7 GeV. On these we carry out an exploratory study to identify a region in the DWF parameter space that displays minimal cut-off effects. We find this region for the domain wall height M₅ = 1.6 allowing for bare heavy quark masses satisfying <i>am_h</i> <_∼0.4, independent of the lattice spacing. Below this limit we maintain desirable features of DWF such as approximate chiral symmetry and O(<i>a</i>)-improvement. Based on this, we carry out a detailed scaling study of the decay constants of heavy-strange pseudoscalar mesons and the dispersion relation of heavy-heavy and heavy-strange pseudoscalar mesons. We find mild <i>a</i>² discretisation effects for the heavy-strange decay constants and the heavy-strange dispersion relation. The cut-off effects for the heavy-heavy pseudoscalar dispersion relation are somewhat more pronounced. On our ensembles we find a 4 effects for heavy masses beyond the charm quark mass and large momenta (|<i>p</i>| ∼ 1.6 GeV). The findings of the pilot study establish the basis for simulations of charm quarks with domain wall fermions. In the second part of the presented work we simulate heavy-light and heavy-strange pseudoscalar mesons on RBC/UKQCD’s 2 + 1f ensembles with pion masses as low as 139 MeV and inverse lattice spacings ranging from 1.73 GeV to 2.77 GeV. From this data we extract the decay constants <i>f_D</i> and <i>f</i>_D<i>_s</i>. We devise two different fit ansatze to process this data and carry out a full systematic error analysis. We find <i>f_D</i> = 208.7(2.8)_stat (^+2.1_−1.8)_sys MeV, <i>f_Ds</i> = 246.4(1.9)_stat (^+1.3−1.9)_sys MeV and <i>f</i><sub style="font-style: italic;">Ds</sub>/<i>f</i><i>_D</i> = 1.1667(77)_stat (⁺⁶⁰−46)_sys. Finally, using experimental input we extract the corresponding CKM matrix elements. We find |V|<i>_cd</i> = 0.2185(50)_exp. (⁺³⁵−37)_lat and |V |<i>_cs</i> = 1.011(16)_exp. (⁺¹¹_{− 9})_lat where the first error comes from the experimental input and the second from our determination of the decay constants. We compare our results with the existing literature and find good agreement between our central values and competitive errors. This work constitutes the basis of RBC/UKQCD’s wider charm physics program.