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In recent years, a large number of black holes have been presented as candidates for an evasion of the "no-hair" conjecture. These examples typically have two features: a non-Abelian gauge field and instability. A large part of this thesis is devoted to a detailed study of the Einstein-Yang-Mills-Higgs (EYMH) black holes, including the analytic proof of the evasion of the "nohair" theorem in this case and proving that the black holes are unstable. We also consider an example of a "hairy" black hole not involving a non-Abelian gauge field, which arises in a higher derivative model of gravity derived from string theory, and prove analytically how the "no-hair" theorem is evaded. The rest of this thesis is concerned with the thermodynamics and quantum field theory of these black holes. In a first order approximation to the unknown theory of quantum gravity, we calculate the entropy of the "hairy" black holes. This turns out to be divergent, and parts of the divergences are attributed to the effect of hair on information loss processes occurring as the black hole evolves in time. We pursue this idea further by making a preliminary estimate of the magnitude of the quantum de-coherence effects on the state of the quantum field as time proceeds. These processes may be of interest phenomenologically in the future. The extension of the theory to non-static geometries is also discussed, by describing the results of bringing rotation into the picture. We prove that the Hartle-Hawking state is not regular everywhere outside the event horizon of a Kerr black hole, with the result that quantum field theory on rotating black hole space-times is more complicated than on static geometries.

No description available.

In August 2011 at the International Symposium on Integrated Functionalities in Cambridge, a whole session was devoted to the electrocaloric effect, which is undergoing a modest renaissance. Surprisingly, the various reports showed that the indirect method of measuring cooling (described in the following sections) did not usually agree with the direct method (actually measuring temperature change with a thermometer). However, there was no obvious systematic error: sometimes the indirect temperature change was larger and sometimes smaller. The discrepancies were beyond the experimental errors. The majority of the present thesis is dedicated to careful reexamination of some of the assumptions made in the indirect method, both during measurement and in the subsequent data analysis that leads to inferred temperature changes. Experimentally, I conclude that the most serious systematic error is likely to be the unwarranted assumption that polarization and field measurements, recorded in hysteresis loops that are traced within a millisecond or less, are all taken at the same temperature. In reality, the experience of the material during such loops is neither isothermal nor adiabatic. Other systematic errors relate to data analyses and are discussed in detail. In some ways, therefore, this thesis has a negative flavour. But it is not designed to criticise prior work. Rather, it is intended to discriminate between reliable experimental procedures and those less convincing. This is a line of research with important technology transfer possibilities, and hence the numerical values of electric cooling must be unusually reliable if we are to avoid unwise capital investment as a country.

In this work monolayers of alkyl amides adsorbed on a graphite surface have been successfully identified and investigated using a combination of synchrotron X-ray and neutron diffraction and Differential Scanning Calorimetry (DSC). Exceptionally stable solid layers have been observed at temperatures well above the bulk melting point, at both high multilayer coverages and, very unusually, at sub-monolayer coverages. The molecular structure of the two-dimensional crystals of these alkyl amides has been obtained from diffraction and interpreted in terms of the subtle intermolecular interactions, particularly the contribution of hydrogen bonding in monolayer assembly. Thermodynamic information provides insight on the mixing behaviour in adsorbed amide layers. A systematic study on the variation in monolayer crystal structures with alkyl chain length (between five and sixteen carbon atoms) of saturated alkyl amides using diffraction identifies that all the amide molecules investigated lie flat on the graphite surface. An odd-even variation isobserved in the monolayer crystal structures and this is supported by the melting enthalpies of the amides determined by DSC. The structure of the even members is found to support the qualitative monolayer arrangement proposed by an STM report of one member of the series, but with more quantitative insight here. Significantly, a new monolayer symmetry group for odd members of the homologous series has been identified. Characteristics of the hydrogen bond geometrybetween the molecules in the solid monolayers are reported exploiting the high level of detail available from the diffraction techniques. Secondly, the formation of solid monolayers of unsaturated alkyl amides has been reported and their crystal structures determined. This is believed to be the first report of these monolayer structures. The position and nature of the double bond have an important effect in the stability of the monolayer. Unusually, certain unsaturated amides that have a double bond conjugated with the amide group are found to form considerably more stable layers than their saturated homologues. The abnormally high melting points and enhanced stability of amide monolayers have been attributed to the existence of a network of hydrogen bonds in the layer. Phase diagrams obtained by DSC for binary mixtures of alkyl amides on graphite have been quantitatively analysed using a combination of thermodynamic models (ideal, eutectic and the regular solution models). The determined mixing behaviour is supported by conclusions based on the monolayer crystal structures of the individual components calculated using diffraction. Saturated amide mixtures that have the same plane group symmetry are found to mix non-ideally in the solid layer and phase separate if the symmetry is different, whereas the mixing behaviour of saturated/unsaturated amides considered here was found to depend on the nature of the double bond (cis/trans). Results from an initial investigation into the adsorption of alkyl amides at the polymer/air interface are also presented. This complements the study above and provides an alternative situation where amide monolayers have a central role. A reduction in the coefficient of friction is seen with increasing bulk concentration of the amide and with increasing time indicating migration of the amide to the surface. A powerful combination of surface reflection techniquesincluding neutron and X-ray reflection and ellipsometry have been used to gain uniquelyquantitative insight into this system. Initial estimates of the concentration of amides at the polystyrene surface are presented for the first time.

The Bose-Einstein distribution is derived, and from this the mean values and fluctuations of the thermodynamic quantities describing a volume V of black body radiation at absolute temperature T, are calculated. The problem of the energy fluctuation of a body of emissivity ε in thermodynamic equilibrium with a volume of black body radiation, is considered from a statistical approach. The result var E = kT ²C , known to be correct from thermodynamics, is obtained. The zero point energy difficulty in the mean energy of the radiation is discussed in detail. Arguments are presented supporting the inclusion of the zero point energy in the thermal radiation theory. The problem of the number of distinguishable levels that can be obtained from a certain signal power in a resonator is discussed in this section. Finally the results of the theory above are employed to determine the ultimate sensitivity of radiation detectors. Care is taken to isolate factors which are not fundamental properties of the detector, from the treatment of the detector sensitivity. A bolometer and a phototube, energy and quantum detectors respectively, are discussed in detail. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The thermal conductivity of three crystals of cesium iodide ranging in size from three to eight millimeters diameter was measured in the temperature range 1.15°K to 5.40°K. Thermal conductivity measurements were made using the thermal potentiometer method. Differences in the thermal conductivity of the three samples were interpreted in terms of phonon scattering from the boundaries of the crystals, and from internal structure defects. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The chemical vapour deposition (CVD) of graphene is the most promising route for production of large-area graphene films. However there are still major challenges faced by the field, including control of the graphene coverage, quality, and the number of layers. These challenges can be overcome by developing a fundamental understanding of the graphene growth process. This thesis contributes to the growing body of work on graphene CVD by uniquely exploring the gas phase chemistry and fluid flow in the hot-wall graphene CVD reactor. Firstly the reported parameter space for the hot-wall CVD of graphene on copper was mapped, informing the subsequent work and providing a resource for the wider community. A CVD reactor was constructed to extend this parameter space to lower pressures using methane as a carbon source, and the films were categorised using scanning electron microscopy, Raman spectroscopy and optical dark field microscopy. The latter showed particular promise as a rapid and non-destructive characterization technique for identifying graphene films on the deposition substrate. The gas phase equilibrium compositions were calculated across the parameter space, and correlations between the stabilities of various chemical species and the types of deposition were drawn. This laid a foundation for the remainder of the experimental work, which explored the effect of diluent gases and different feedstocks on the growth to understand the importance of the identified correlations. Diluent gases (argon and nitrogen) were added to the experimental conditions and the thermodynamic model, and were found to reduce the degree of coverage of the graphene films. This result shows that the CVD of graphene is sensitive to factors other than the thermodynamic state parameters, such as the fluid flow profile in the reactor and inelastic collisions between the higher mass diluent gases and the methane/hydrogen/copper system. Using a nitrogen diluent raises the equilibrium carbon vapour pressure and seems to allow larger graphene grains to form. This suggests that thermodynamic factors can contribute to the nucleation of graphene films. Varying the hydrocarbon feedstock and the process conditions indicated that the structure of the deposited carbon is closely related to the nucleation kinetics. Three nucleation regimes are associated with different types of deposition: homogeneous nucleation with amorphous carbon or soot; uncatalysed nucleation with multilayer deposition; and nucleation processes controlled by the copper substrate withpredominantly monolayer deposition. Changing the feedstock from methane to acetylene resulted in poorer graphene coverage, showing that thermodynamic control does not apply in the portion of the parameter space at the high temperatures and lowpressures most successfully used for the deposition of continuous graphene monolayers.

The stability of growing uni-lamellar vesicles is investigated using the formalism of nonequilibrium thermodynamics. The vesicles, which are assumed to be in an otherwise aqueous solution, are growing due to the accretion of lipids to the bilayer which forms the vesicle membrane. The thermodynamic description is based on the hydrodynamics of a water-lipid mixture together with a model of the vesicle as a discontinuous system in the sense of linear nonequilibrium thermodynamics. The approach assumes that the energy of the bilayer membrane is given by the spontaneous curvature model attributed to Helfrich. Furthermore, the rate at which lipids incorporate into the membrane is taken to be proportional to the surface area of the membrane. In this way, the relevant forces and fluxes of the system are identified in the context of a stability analysis. The resulting constitutive equation for the flux of water across the membrane is used to analyse the stability of spherical vesicles that are subject to different perturbations. First, a simplified approach is presented which restricts perturbations to axisymmetric ellipsoids. In that case, the analysis is carried out using an explicit Cartesian parametrisation. A perturbation theory which describes more general deformations is then developed and applied to the case of arbitrary axisymmetric perturbations. It is found that there are generically two critical radii at which changes of stability occur. For the case where the perturbation takes the form of a single zonal harmonic, only one of these radii is physical and is given by the ratio $2L_p / L_\gamma$, where $L_p$ is the hydraulic conductivity and $L_\gamma$ is the Onsager coefficient related to changes in membrane area due to lipid accretion. The stability of such perturbations is related to the value of l corresponding to the particular zonal harmonic: those with lower l are more unstable than those with higher l. The conditions under which general axisymmetric perturbations reduce to explicit ellipsoidal calculations are also found. A heuristic explanation for the results is proposed whilst possible extensions of the current work and the need for experimental input are also discussed.