The current design of mass transfer systems for gas bubbles absorbing into a liquid is mainly restricted to the use of empirical relations which involve a high level of uncertainty. This is due to a lack of understanding of the interactions of gas bubbles and the liquid phase, and of how this affects the mass transfer. This work set out to enhance our understanding of the mass transfer of CO2 from concentrated sources such as flue gases into the aqueous phase, for use in applications such as micro-algal biomass cultivation systems. Bubble characteristics were observed using high speed imaging for single bubbles and optical fibre sensors for bubble swarms. These techniques were combined with gas chromatographic analysis of input and output gas samples to obtain a mass balance and measurements of the mass transfer. The mass transfer rate in bubble swarms was observed to be greater than that of single bubbles. For larger bubble sizes, this is partly due to the increased bubble rise velocity in bubble swarms. This was observed to increase, in part, due to the reduced drag a bubble experiences when it follows in the wake of a preceding bubble. Smaller bubbles within bubble swarms did not experience the same inhibition of mass transfer as was evident for single bubbles. This inhibition of the gas-liquid interface of single bubbles is due to the accumulation of surfactants which attach to the bubble surface, transforming the properties of the gas-liquid interface and reducing the mass transfer rate. The reduced mass transfer in single bubbles compared to bubble swarms was more apparent at lower input concentrations of CO2. This suggested a possible reduction in the internal circulation within the bubble, due to surfactant accumulation which reduces the gas-side resistance to mass transfer and is more apparent at a dilute gas concentration. Finally the experimental results from this work were compared with a simple finite difference model which analysed the mass balance of a rising bubble. The mass transfer coeffcient of single bubbles with a mobile gas-liquid interface could be approximated by the penetration theory of Higbie (1935), while with sufficient surfactant accumulation to transform the bubble surface to an immobile gas-liquid interface the rigid particle theory by Frossling (1938) provided a good approximation. In bubble swarms, however, the theory for a mobile gas-liquid interface based on Higbie (1935) provided a reasonable approximation throughout the range of bubble sizes studied in this work.

The Nitrogen-Vacancy (NV) centre in diamond possesses an optical read out of its spin state and shows great promise for applications in solid state quantum technologies. Its broad phonon assisted emission spectrum, with only 4% of emission from the zero-phonon line, is a major drawback to this. The optical microcavity will be essential in efficiently interfacing these centres with photonic networks. Here we present investigations into the coupling of NV centres in nanodiamond to tunable open-microcavities, both at room temperature and at cryogenic temperatures. These structures will be shown to achieve good photon confinement, with mode volumes down to 5λ3. Room temperature studies on ensembles of NVs will illustrate the tunable spectral and spatial overlap between the emitter and the cavity mode. It will be shown that small enhancements are possible in this regime. After the preparation and characterisation of single emitters, low temperature coupling to the narrowed zero-phonon line will be the central theme of this thesis. Single photon emission into the cavity mode is verified. We observe the enhancement of the light-matter interaction in this regime, by a 39% increase in the emission rate when cavity-coupled, with the dependence on mode volume also demonstrated. These results are important for the realisation of a spin-photon interface in scalable quantum networks.

This thesis reports on some recent results in the field of acoustics and magnonics. Chapter 1 reviews the literature on magnonics and GHz frequency transducers, and highlights the lack of understanding of the growth mechanism of magnetron sputtered ZnO thin films. A novel configuration for exciting magnetostatic spinwaves using ZnO transducers is proposed. Chapter 2 is an introduction to piezoelectricity and how it can be used to generate GHz acoustic waves. A detailed formulation of the Mason model is presented in chapter 3 for predicting the performance of ZnO transducers. In chapter 4, the fabrication protocol of ZnO transducers in the custom-built sputtering plant is discussed and the transducer characterisation techniques including X-ray and pulse echo measurement are described. In chapter 5, the characterised properties of the film are compared with modelling prediction. It is found that the piezoelectric and structural properties of the fabricated ZnO films are strongly correlated and are critically dependent on the sputtering conditions and thicknesses. Chapter 6 is dedicated to plasma characterisation of the sputtering conditions using Langmuir probe diagnostics. The making of the Langmuir probe system and its development are discussed. Chapter 7 examines the various possible growth mechanisms of the ZnO films with a view to understanding how the c-axis texture forms during sputtering. The results from the Langmuir probe diagnostics and X-ray characterization indicate the detrimental in uence of ion bombardment on the film qualities. It is deduced that the c-axis self texturing of ZnO films is driven dominantly by the 'survival of the fastest' mechanism. Chapter 8 describes the theoretical formulation of magnetostatic spin-wave modes and the mechanism for which the laterally propagating magnetostatic modes are coupled to local elastic standing waves. The experimental evidence (using time resolved spectroscopy) of the acoustic excitation of magnetostatic spin-waves in a YIG film waveguide is then presented in chapter 9; the excitation efficiencies at various magnetic field configurations and carrier frequencies are investigated. Finally, chapter 10 ends the thesis with the summary of results and outlooks.

Plasmonic metal nanoparticles are widely exploited in academia and industry for use in various assay types. In collaboration with an industrial partner, BBI Solutions, the work here details investigations into the production and use of the plasmonic nanoparticles. The work was split into two themes. The first of these was flow chemistry of nanoparticles, covering a microfluidic assay platform and continuous colloid production. In chapter one, a novel microfluidic assay platform was developed which facilitated the transfer of multiple, sequential bench-top procedures into a single device. This allowed the rapid detection of a sugar binding protein to be demonstrated. The microfluidic system included all pre-detection steps involved in employing the specific aggregation of functionalised silver nanoparticles. Straightforward detection of the protein was demonstrated at concentrations lower than those achieved using comparable methods in the literature. In the second chapter, a novel bench-top scale continuous reactor for the production of gold nanoparticles was developed. It was found that the continuous stirred tank reactor was generally unsuitable for this synthesis. A laminar tubular reactor was more successful but fouling of the reactor material was a significant obstacle to production of good quality colloid. In both cases, nanoparticles produced in a batch synthesis were of more consistent quality. This suggested that further work was needed to develop a competitive continuous production method. The second research theme was development of a novel nanoparticle assembly assay, based on DNA assembly. In chapter three it was found that current tools for the understanding of dynamic DNA structure were limited. This led to the first use of an existing coarse grain model to determine thermodynamic properties of DNA assembly. Analysis showed that the results were comparable with the best simulation models shown in the literature, while being generated much more quickly and at less computational expense.

The strength of interaction between light and matter states is characterised by the Rabi frequency Ω which describes the rate at which they exchange energy. When Ω exceeds the system linewidth then the system is correctly described by dressed eigenstates of the coupled light-matter system. This is the strong coupling regime. Strong coupling has been demonstrated at the surface of polar dielectrics between phonon oscillations of the ionic species and light resulting in evanescent field confinement in modes termed surface phonon polaritons (SPhPs ). Recent fabrication advances allow for creation of user defined SPhP resonators that support sub-diffraction SPhPs confined in three dimensions. We present a numerical study of these localised SPhP resonances in subwavelength cylindrical SiC resonators finding modes with long lifetimes and strong electric field enhancements. Additionally we investigate numerically and experimentally interactions between the localised SPhPs and the delocalised SPhP of a planar SiC interface demonstrating that this can also be coherent. Strong light-matter coupling is also possible when a material with an resonant elec- tronic transition such as an organic semiconductor is sandwiched in a planar optical microcavity. By employing a molecule with a broad electronic transition it is possible to reach the ultrastrong coupling (USC) regime where the coupling frequency becomes an appreciable fraction of the bare frequency and new physics is predicted. We investigate experimentally the electroluminescence properties of an optical microcavity in this regime utilising for the active layer the oligomer TDAF. We demonstrate light-matter couplings exceeding 20% of the bare resonant frequencies. Our bias resolved measure- ments allow for conclusions about the process of polariton formation under electrical pumping to be drawn. Finally we present a method to describe the coupled eigenstates in arbitrary, inhomo- geneous dielectric environments. By following Hopfield procedure we show that it is possible to diagonalise and correctly quantise the modes of the system. We also show how this model can be extended to include losses and illustrate an application to the specific case of the SPhP at a planar interface.

A unique class of bent-core nematics, based on the bis-phenyl-oxadiazole motif, have attracted considerable attention due to their unusual properties, including the possibility of forming the elusive biaxial nematic phase, a phase with significant potential for technological applications. A summary of current research into biaxial nematics is given, including experimental evidence,controversies,and the different computational models used to study this phase. Fully atomistic molecular dynamic simulations were employed to study the differences and relationships in the mesophase molecular organization of four closely related oxadiazole bent-core molecules. As an accurate force field is essential to model liquid crystal systems, it was first found necessary to partially re-parametrize the General Amber Force Field, (GAFF), to accurately reproduce phase transitions of liquid crystal mesogens. Dramatic improvements of phase transition temperature predictions for a number of liquid crystals were achieved with the new force field, compared to the original GAFF predictions. Using the improved force field, GAFF-LCFF, the uniaxial and biaxial orientational order parameters were deduced for the four oxadiazole derivatives. These were found to be in good agreement with experimental data, where available. Small differences in the magnitude of the biaxial order parameters were found between the four oxadiazole systems in their respective nematic phases, with the bent-core mesogen, C5-Ph-ODBP-Ph-OC12 displaying the largest values. The simulations confirm that the nematic phase biaxiality is predominantly local and not macroscopic, and do not support the presence of large cybotactic clusters with inherent biaxial order. The atomistic simulations enabled the distinct differences in structure and molecular organization in the nematic phase of the four systems to be identified and analyzed, and the simulations were found to accurately represent a range of experimental observables, including the manifestation of enhanced local biaxial correlations for a trimethlylated oxadiazole based mesogen. The study also provides the novel result of the first simulation insight into the local structure of the dark conglomerate (DC) phase, and shows evidence of pretran- sitional fluctuations relating to the onset of the DC phase in the bent-core mesogen C5-Ph-ODBP-Ph-OC12. A number of explanations linking key molecular chemical and structural features to mesophase behaviour have also been proposed.

In the past several decays, lattice codes played an important role in coding theory and information theory. Lattice codes with good performance in communication and source compression have attracted considerable interest. A typical method of constructing good lattice codes is to use existing linear codes. For instance, the famous Barnes-Wall lattices are generated by Reed-Muller (RM) codes, and more recently, the emerging low density Construction-A (LDA) lattices are resulted from low density parity check (LDPC) codes. In this thesis, we develop a new class of lattices, called polar lattices, based on polar codes. The invention of polar codes is considered to be one of the major breakthroughs in coding theory for the past ten years. We show that polar lattices provide explicit solutions for many interesting problems in information theory. For channel coding, we prove that polar lattices are capable of achieving the capacity of the additive white Gaussian noise (AWGN) channel. For the dual side, i.e., source compression, polar lattices can also achieve the rate-distortion bound for the independent and identically distributed (i.i.d.) Gaussian source. Moreover, a combining design of polar lattices for both channel coding and source coding gives us explicit solutions to the Gaussian version of the Wyner-Ziv and Gelfand-Pinsker problems. For physical layer security, we prove that polar lattices are able to approach the secrecy capacity of the Gaussian wiretap channel under the strong secrecy criterion. Two more applications of polar lattices are achieving the capacity of the i.i.d. fading channel and extracting the common information of two joint Gaussian sources. The explicit construction of polar lattices provides us better insights on the study of lattice coding. Many interesting problems of lattice coding, such as AWGN goodness, secrecy-goodness, lattice shaping, and lattice Gaussian distribution will be addressed from the perspective of polar lattices.

This thesis concerns the interaction of small, particulate, solid matter - 'dust' - with plasmas, in the plasma edge region where such dust is commonly found. Dust in this region can have a significant impact on a variety of industrial plasma applications, and it is low-temperature industrial plasmas that form the focus of this work. A novel model for the sheath region at the edge of a plasma is proposed, to account for the loss of electrons at the plasma boundary. This is then compared to an existing Boltzmann electron model; significant differences are noted in the sheath structure, and consequently the charging and dynamics of dust in the plasma sheath. The effect of sparse ion collisions in the vicinity of a dust grain near the plasma edge is also investigated. The strong plasma flow in the edge region is found to significantly increase collisional charging of dust grains. Somewhat counter-intuitively, it is found that even sparse collisions can play a significant (and in fact dominant) role in the charging and shielding of dust grains at the edge of a plasma. The length-scale over which the charge on such grains is shielded by the plasma is found to be significantly less than the Debye length. Together, the altered grain charging and shielding behaviour have the potential to fundamentally alter how dust grains interact with edge-plasmas.

Understanding strongly coupled systems is an important area of theoretical physics, and has wide ranging applications from quantum chromodynamics to condensed matter physics. This thesis uses holographic methods to understand two particular aspects of strongly coupled systems - linear response and phase transitions. Firstly, we consider a general class of electrical black holes in Einstein-Maxwell-scalar theory, that are holographically dual to conformal eld theories at nite charge density and explicitly break translational invariance. By considering the linearised perturbations of these background black holes, we show that the DC thermoelectric conductivity of these systems can be determined by solving a set of linearised Navier-Stokes equations on the event horizon of the dual black hole. We demonstrate how to apply this framework in practice with several examples. Next, we consider this framework in the hydrodynamic limit, for the simpler case of Einstein gravity. We show that the full stress-energy response, rather than just the thermal conductivity, can be determined in this limit, and compare the results with the uid/gravity correspondence. We then consider more general hydrodynamics, and demonstrate that periodically deformed eld theories exhibit thermal back ow when a DC thermal source is applied Finally, we study black hole solutions of type IIB supergravity that describe N=4 supersymmetric Yang-Mills plasma with an anisotropic spatial deformation. We show that, by preserving additional scalar modes from the consistent truncation of IIB supergravity on the ve-sphere, these black holes have low temperature instabilities. We construct new thermodynamically preferred black hole solutions, and show that the phase transition between these black hole solution has unusual critical exponents that is not captured by the normal Landau-Ginzburg exponents. We consider various extensions to this, such as introducing a chemical potential, and construct a more complete phase diagram for the theory.

This thesis presents the development of an experimental apparatus designed to investigate the ultracold collisional properties for mixtures of Cs and Yb, with a long-term view to the creation of ultracold CsYb molecules via indirect cooling methods. The unpaired electron spin that is inherent to molecules of this form gives rise to a magnetic dipole moment in addition to a ground state electric dipole moment. This enables extra control over molecular interactions and should enable the experimental simulation of spin lattice models. We focus on the implementation of a system designed to controllably laser cool and optically trap Yb. The first step in this system is the production of a magneto-optical trap (MOT) on the triplet 1S0 to 3P1 transition of Yb. With careful control over the cooling beam detunings and power, gravitational-assisted Doppler cooling allows samples of Yb to be prepared at 22 uK. This regime of enhanced Doppler cooling is investigated and proves to be a crucial step to ensuring good transfer of cold Yb to optical traps. The construction and characterisation of single and crossed beam optical dipole traps for Yb are discussed. The single beam optical trap has been used to verify a model for the optical trapping of Yb in its ground state. This trap has also been utilised as a tool for the measurement of the light shift on the 1S0 to 3P1 transition at a wavelength of 1070~nm. In the main experimental sequence, Yb atoms are loaded from the magneto-optical trap into the crossed optical dipole trap, allowing evaporative cooling ramps to quantum degeneracy to be performed. This highly-reproducible system typically forms Bose-Einstein condensates with 2 x 10^5 174Yb atoms. This thesis additionally reports on the progress made towards measurements of the interspecies scattering length for 133Cs and Yb isotopes. We present two approaches that are being developed in tandem: rethermalisation in a conservative trap, and two-photon photoassociation. Progress towards rethermalisation measurements has focussed on developing systems for the efficient transfer of Cs to an optical trap. For photoassociative measurements, a laser system has been developed and tested by producing one-photon photoassociation spectra of Cs2.