The thesis comprises reports of studies undertaken on three separate extensions of the Standard Model. It begins with an original introductory chapter, which introduces the theoretical background required to understand the motivation and broad definition of the concepts introduced in subsequent chapters. The first extension is a “bottom-up” minimal supersymmetric scenario, where the possibility of observing the gluino at a future high-energy linear <i>e</i>⁺<i>e^- </i>collider is investigated. The second is a supersymmetric Standard Model derived from a five-dimensional warped supergravity, combining aspects of the MSSM and the Randall-Sundrum construction. The scenario is studied in the context of an effective theory, valid at energies below the scale of the compact fifth dimension. Possible observations of extra-dimensional effects on the scalar sector at a similar collider are investigated. Particular attention is paid to the mixing of scalars originating in the gravitational sector with those from the Higgs sector. The third extension is motivated by a recent attempt to solve the cosmological constant problem, in the framework of six-dimensional supergravity. In this scenario the compact dimensions are assumed to be flat, and of order ~1<i>m</i>m in size. This gives rise to a finely-spaced spectrum of Kaluza-Klein states which can be modelled by a modification of the space to incorporate an integration over these modes. The lowest-dimension interaction between bulk and brane fields is identified, and a possible search channel at a future linear collider is studied.

This thesis is concerned with symmetries of higher dimensional black holes beyond the usual isometries of the spacetime. Such symmetries give rise to extra constants of the motion that allow the geodesic and Klein-Gordon equations to be separated. We show that the singly charged, five-dimensional Kerr-AdS black hole of minimal gauged supergravity with arbitrary rotating parameters admits separable solutions to the Hamilton-Jacobi and Klein-Gordon equations. This is due to the existence of an irreducible rank-2 Killing tensor which we find. We also show that the Dirac equation separates in the case where the rotation parameters are equal, and we also examine the near horizon geometry of the supersymmetric limit of this black hole, showing that the symmetry algebra takes the expected form. By considering multiply charged, rotating black hole solutions to gauged and ungauged supergravity in 4, 5 and 7 dimensions, we find that, in general, the Hamilton-Jacobi and Klein-Gordon equations can only be separated in the case where the particle under consideration is massless. In this case, we find conformal Killing tensors which obey an equation involving a co-vector field. We find this co-vector field in several cases and use it to conjecture its general form. We prove this conjecture under reasonable assumptions. We also prove that cohomeneity-2 Kerr-AdS black holes generalised to include a NUT-like parameter admit separable solutions to the Hamilton-Jacobi and Klein-Gordon equations in all dimensions, by finding the Killing tensors and examining the symmetry algebra.

A frost point hygrometer is described in this thesis which uses surface acoustic waves (SAWs) to detect water vapour condensation. The SAW device crystal is cooled by a thermoelectric cooler until condensation occurs, at which point, water vapour loading onto the SAW device causes changes in the SAW velocity and amplitude. Two methods of determining the frost point temperature are outlined in this thesis. The first uses a feedback loop algorithm to maintain a constant amount of water vapour on the SAW device and hence keep the temperature of the device at the frost point. The second uses heating and cooling cycles to oscillate the SAW device temperature above and below the frost paint. Changes in the SAW properties are then used to detect the condensation-evaporation equilibrium point which is equal to the frost point. The use of SAWs rather than a conventional optical detection system in this hygrometer allows a faster response time, increased sensitivity, and decreased risk of contamination. Between September 2001 and February 2004, the SAW hygrometer was flown on 28 balloon flights, in various configurations. All of these flight data sets show agreement with radiosonde relative humidity measurements to within 1%, using given criteria for extraction of reliable SAW hygrometer measurements. Accurate lower and mid tropospheric measurements have been made on each flight and four flights show accurate upper tropospheric and lower stratospheric measurements with water vapour mixing ratio values of less than 5 ppmv. The Hibiscus campaign flights in Bauru, Brazil, show excellent agreement between the different instruments measuring water vapour on the flight train and the SAW hygrometer. These data are discussed in conjunction with auxiliary data and model backward trajectories. Two different backward trajectory models have been used to assess the possible mechanisms of transport of water vapour above Bauru, one of which is a large scale model and the other is a meso-scale model. A sharp contrast in the air parcel transport above and below the tropical tropopause layer (TTL) is seen, with large scale convection or descent controlling the water vapour mixing ratios below the TTL, and a combination of large and small scale fields controlling the water vapour in and above the TTL.

In this thesis, a semi-empirical model for the infrared emission of dust around star-forming sites in galaxies is developed and then applied to fitting a variety of observations. A simple model of radiative transport in dust clouds is combined with a state-of-the-art model of the microscopic optical properties of interstellar dust grains. In combination with the STARBURST99 stellar spectral synthesis package, this framework is able to produce synthetic spectra for galaxies which extend from the Lyman limit through to the far-infrared. Models of radiative transport in dusty media and of the optical properties of dust grains both have potential to be computationally time-consuming. This has restricted previous semi-empirical models to include detailed considerations of only one of these. In this thesis, a minimal set of simplifications are adopted in the treatment of radiative transport, such that the use of a state-of-the-art model of dust grain energetics is computationally tractable. Following an initial exploration of the predictions of the model, it is applied to fitting the spectra of M82, Arp220 and NGC 6381. M82 and Arp220 are chosen for study because they are nearby starburst galaxies, and test the ability of our model to fit extreme systems. In both cases, we need to remove some of the smallest grains from our model to fit their mid-infrared spectra, but achieve an excellent fit after doing so. NGC 6381 is chosen because it is the only NGC or UGC galaxy within the xFLS field. From our model fit, we infer a flat star formation history over the past (150±50)Myr with star-formation rate (4.69 ± 0.37) M_⊙ yr^-1, and that these stars are surrounded by a column density (6 ± 1) x 10²⁵ Hm^-2 of material and an old stellar population of mass (95 ± 5) x 10⁹ M_⊙^.

This thesis concerns the radio structure of FR II radio galaxies and quasars on kiloparsec scales. A complete sample of 65 FR II sources with redshift < 0.6 is examined with the aim of understanding the source characteristics. High sensitivity, high resolution images of 27 FR II sources are presented forming a complete subsample with 0.3 < <I>z</I> < 0.6; for each source the morphological features are discussed in detail and general trends within the sample are noted. The observed asymmetries between the two sides in each source are analysed. At first, these are interpreted as a result of relativistic orientation effects and comparisons are made between the observed data and theoretical models. Correlations between observable parameters of the quasars and radio galaxies are examined separately but few are found to be consistent with orientation-dependent unification schemes between the two classes; it is clear that environmental effects must be dominate in most sources. The reliability of measurements of hotspot linear sizes is discussed. Hotspot location relative to the lobe is found to be broadly consistent with orientation unification schemes. The apparent recession of hotspots however is shown to be inconsistent with purely geometrical effects. The relatively large number of highly recessed hotspots suggests that in at least some cases what we classify as a hotspot cannot be a feature that is associated with the termination point of the beam. The general morphology of lobes and the importance of self-similar expansion is reviewed. Axial ratio is regarded as a fundamental structural parameter and observational values compared to models of source evolution. The model of self-similar expansion due to Kaiser and Alexander (1997) is developed to give an analytical expression for lobe axial ratio. Fits are made to the data and are in remarkable agreement with observed values.

No description available.

This thesis investigates interacting galaxies using two complementary approaches: a statistical study of star formation in a large sample of close pairs of galaxies drawn from the Sloan Digital Sky Survey (SDSS) and a study of the ISM and star forming properties of a small sample of interacting pairs taken from Arp’s atlas, each comprising one early- and one late-type system (E+S pairs). The first part of this thesis investigates the effect of galaxy interaction on star formation using a large volume- and luminosity-limited sample of galaxies drawn from the SDSS. Star-formation rates were calculated from extinction and aperture corrected Hα luminosities and, for a subset of systems, <i>IRAS </i>data. The mean specific star-formation rate is found to be strongly enhanced for projected separations of less than 25 kpc. For late-type galaxies, the correlation extends out to projected separations of 300 kpc and is most pronounced in actively star-forming systems. The specific star-formation rate of observed to decrease with increasing recessional velocity difference, although the magnitude of this effect is small compared to that associated with the projected separation. No dependence of star formation enhancement on the morphological type or mass of the companion galaxy is observed. This second part of this thesis presents a study of the ISM and star forming properties of nine E+S pairs. Detailed case studies were undertaken for two of the pairs, Arp 140 and Arp 104, both of which display extended tidal tails in their H1 morphology. These two pairs differ markedly. Despite Arp 140’s relatively evolved interaction and weakly barred potential, NGC 275, the late-type component, has neither a molecular gas nor star formation distribution that is centrally condensed. Instead, the molecular gas and HII regions display an unusual anti-correlation.

Chapter 2 presents an in depth study of the central galaxy of the Centaurus cluster. Comparison of images from line-emission, X-ray, and radio wavebands, shows an energetic and dynamical interaction between the intracluster medium, radio source, and the ionised nebula. As well as the Centaurus cluster, a clear link between the nebula morphology and dust features is found in two other nearby nebulae. The kinematics of several nebulae are presented in Chapter 3. All nebulae show ordered bulk flows with velocities up to a few hundred km s^-1, and clear evidence of outflow is seen in the nebula that lies at the centre of the Perseus cluster. The data do not imply a single formation mechanism for all nebulae: AGN and starburst-driven outflows, tidal interactions with nearby galaxies, and entrainment by buoyantly rising bubbles may all play a role in forming the filamentary structure we observe. In Chapter 4 I present maps of emission-line-ratios and discuss the ionisation state of the gas. I find that the ionisation state is not uniform, implying that multiple sources ionise the gas, or the temperature and/or the metallicity of the nebulae are inhomogeneous. I investigate the composition of the nebular gas in Chapter 5. I present near-infrared observations which show that multi-temperature molecular hydrogen accompanies the ionised gas, out to distances of at least 25 kpc from the central galaxy. The aim of this thesis is to study the nebulae with a suite of instruments and telescopes that can probe deeper than has been done before. The highlights include nebular kinematics across a large field-of-view, and the first detection of molecular hydrogen from the outer nebulae, well beyond the gas reservoir at the centre of these systems.

No description available.

Chapter one provides a brief overview of the physics of ultra cool dwarfs, and discusses relevant observation to date. Of particular import is an understanding of their atmospheric physics. The cool temperatures (2500K) of their atmospheres are condusive to the formation of molecules, the occurrence of chemistry and the condensation of solid and liquid particulates. The latter of these processes, which can be regarded as the formation of clouds, is especially interesting and poorly constrained by current theory and observation. One method of probing the structure, scale and distribution of clouds is to observe and characterise the variability they induce. In this dissertation, I present the results of observations designed to detect and characterise the photometric and spectroscopic variability induced by inhomogeneous cloud formations on ultra cool dwarfs. Chapters two and three describe observations and modelling of the brown dwarf Kelu-1. I report the discovery of a 1.8 hour periodicity in the object's brightness and discuss models to explain it. Chapter three then describes observations designed to test these models, and the conclusions that can be drawn from them. Observations of four further ultra cool dwarfs are described in chapter 4, and I report the discovery of photometric variability in two of them. These three chapters together form the most sensitive study of variability in ultra cool dwarfs made to date. In chapter five I discuss the possibility of imaging extrasolar plants and brown dwarfs around nearby white dwarfs. If discovered, these objets would be the "coolest" ultra cool dwarf known. Chapter six contains conclusions, and a brief summary of potential future work in this field.