At present several groups are analysing quasar absorption spectra to search for variation of the fine structure constant, alpha, across space and time. These studies compare the wavelengths of several transitions observed in the absorption clouds with those seen in the laboratory, and interpret anomalies as variation in alpha. One group has already presented evidence that alpha may have been smaller at an early epoch. Other groups using different telescopes see no variation. These studies use the ???many-multiplet??? method, which relies on the utilisation of many transitions in many ions to enhance the size of the effects and remove sources of systematic error. While this method offers an order-of-magnitude improvement in sensitivity over the previously used alkali-doublet method, the alpha-dependence (relativistic shift) of every transition used in the analysis must be calculated ab initio. In this thesis we present a method for the precise calculation of relativistic shifts, based on an energy calculation involving combination of the configuration interaction method and many-body perturbation theory. The many-multiplet method also introduces a potential systematic error: if the relative isotope abundances of the absorbers differ from terrestrial abundances then there can be spurious shifts in the measured wavelengths, which may be incorrectly interpreted as variation of alpha. A ???conspiracy??? of several isotopic abundances may provide an alternative explanation for the observed spectral anomalies. To account for these systematic errors we need accurate values of the isotope shift. We calculate these shifts using the finite-field method to reduce the problem to that of an energy calculation, which in turn is done using the same method used for the relativistic shift. We present the results of our calculations for a variety of atoms and ions seen in quasar absorption spectra. The results of this research should allow astrophysicists to measure isotope abundances in the absorbers directly. This can provide a test for models of nuclear reactions in stars and supernovae, and of the chemical evolution of the Universe. Our calculations can also be used in conjunction with measurements to extract changes in nuclear charge radii between isotopes.

We present the development of a novel, UHV-compatible device fabrication strategy for the realisation of nano- and atomic-scale devices in silicon by harnessing the atomic-resolution capability of a scanning tunnelling microscope (STM). We develop etched registration markers in the silicon substrate in combination with a custom-designed STM/ molecular beam epitaxy system (MBE) to solve one of the key problems in STM device fabrication ??? connecting devices, fabricated in UHV, to the outside world. Using hydrogen-based STM lithography in combination with phosphine, as a dopant source, and silicon MBE, we then go on to fabricate several planar Si:P devices on one chip, including control devices that demonstrate the efficiency of each stage of the fabrication process. We demonstrate that we can perform four terminal magnetoconductance measurements at cryogenic temperatures after ex-situ alignment of metal contacts to the buried device. Using this process, we demonstrate the lateral confinement of P dopants in a delta-doped plane to a line of width 90nm; and observe the cross-over from 2D to 1D magnetotransport. These measurements enable us to extract the wire width which is in excellent agreement with STM images of the patterned wire. We then create STM-patterned Si:P wires with widths from 90nm to 8nm that show ohmic conduction and low resistivities of 1 to 20 micro Ohm-cm respectively ??? some of the highest conductivity wires reported in silicon. We study the dominant scattering mechanisms in the wires and find that temperature-dependent magnetoconductance can be described by a combination of both 1D weak localisation and 1D electron-electron interaction theories with a potential crossover to strong localisation at lower temperatures. We present results from STM-patterned tunnel junctions with gap sizes of 50nm and 17nm exhibiting clean, non-linear characteristics. We also present preliminary conductance results from a 70nm long and 90nm wide dot between source-drain leads which show evidence of Coulomb blockade behaviour. The thesis demonstrates the viability of using STM lithography to make devices in silicon down to atomic-scale dimensions. In particular, we show the enormous potential of this technology to directly correlate images of the doped regions with ex-situ electrical device characteristics.

To date, more than 300 planets orbiting stars other than our sun have been discovered using a range of observing techniques, with new discoveries occuring monthly. The work in this thesis focused on the detection of exoplanets using the transit method. Planets orbiting close to their host stars have a roughly 10 per cent chance of eclipsing (transiting) the star, with Jupiter?sized planets causing a one per cent dip in the flux of the star over a few hours. A wealth of orbital and physical information on the system can be extracted from these systems, including the planet density which is essential in constraining models of planetary formation. To detect these types of planets requires monitoring tens of thousands of stars over a period of months. To accomplish this, we conduct a wide-field survey using the 0.5-meter Automated Patrol Telescope (APT) at Siding Spring Observatory (SSO) in NSW, Australia. Once candidates were selected from the data?set, selection criteria were applied to separate the likely planet candidates from the false?positives. For this thesis, the methods and instrumentation used in attaining data and selecting planet candidates are discussed, as well as the results and analysis of the planet candidates selected from star fields observed from 2004?2007. Of the 65 planet candidates initially selected from the 25 target fields observed, only two were consistent with a planet transit. These candidates were later determined to be eclipsing binary stars based on follow up observations using the 40-inch telescope, 2.3-m telescope, and the 3.9-m Anglo-Australian Telescope, all located at SSO. Additionally, two planet candidates from the SuperWASP-North consortium were observed on the 40-inch telescope. Both proved to be eclipsing binary stars. While no planets were found, our search methods and results are consistent with successful transit surveys targeting similar fields with stars in a similar magnitude range and using similar methods.

This thesis addresses two fundamental questions in astrophysics: (i) To what extent is environment a driver of galaxy evolution? And (ii) How does hierarchical structure formation affect the galaxy environment? The former is addressed by examining the environments of starburst galaxies, the latter by examining clusters undergoing major mergers with focus placed on the efficacy of ??cold fronts?? in identifying systems that have recently undergone a major merger - an essential first step to understanding their impact. For the first of these studies, the 2dFGRS was exploited to select large samples of starburst galaxies. These were used to derive measurements of the local and large-scale environments, clustering properties, and morphologies of starburst galaxies. It is found local environment is most germane in terms of a starburst triggering mechanism, with the starburst galaxies showing an excess of close (<20 kpc) neighbours with comparable luminosity/mass, while 20-30% exhibit a morphology consistent with them being involved in an ongoing tidal/merger interaction. On large scales (5-15 Mpc), the starburst galaxies were found to be much less clustered compared to the overall 2dFGRS population, and were not preferentially found in rich clusters with just over half residing in low to intermediate luminosity groups. However, in a number of cases, evidence for obvious local environmental influences was lacking, indicating starbursts can also be internally driven. For the latter study, the Chandra, archive was used to select a sample of clusters exhibiting ??cold front?? features. Selection required the presence of significant density jumps (>1.5 at the lower 90% CI) in the intracluster medium and for the gas on the denser side of the front to be cooler. From this sample, the clusters Abell 1201, Abell 2163, RXJ1720.1+2638, and Abell 3667 were targeted for comprehensive spectroscopic follow-up at optical wavelengths using the 3.9m Anglo Australian and 6.5m Multiple Mirror Telescopes. Using 321 spectroscopically confirmed members for Abell 1201, 550 for Abell 3667 and 491 for Abell 2163 it is shown that these clusters contain substructure which can be directly related to the cold fronts, whilst for 335 confirmed members in RXJ1720.1+2638 promising evidence exists for merger activity related to the cold front. Despite the range of different types of cold fronts and substructures detected, it is clear that cold fronts are robust signposts of merger activity.

Atmospheric turbulence results taken on the Antarctic plateau are presented in this thesis. Covering two high sites: South Pole and Dome C, this work describes their seeing and meteorological conditions. Using an acoustic sounder to study the turbulence profile of the first kilo- metre of the atmosphere and a Differential Image Motion Monitor (DIMM) to investigate the integrated seeing we are able to deduce important at- mospheric parameters such as the Fried parameter (r0) and the isoplanatic angle (??0). It was found that at the two sites, the free atmosphere (above the first kilometer) was extremely stable and contributed between 0.2" and 0.3" of the total seeing with no evidence of jet or vortex peaks of strong turbulence. The boundary layer turbulence is what differentiates the two sites. Located on the Western flank of the plateau, the South Pole is prone to katabatic winds. Dome C on the other hand is on a local maximum of the plateau and the wind conditions are amongst the calmest in the world. Also linked to the topography is the vertical extent of the temperature in- version that is required to create optical turbulence. At the South Pole the inversion reaches 300 m and only 30 m at Dome C. This difference results in relatively poor seeing conditions at the South Pole (1.8") and excellent at Dome C (0.27"). The strong correlation between the seeing and the ground layer meteorological conditions indicates that even better seeing could be found at Dome A, the highest point of the plateau. Having most of the turbulence near the ground is also incredibly ad- vantageous for adaptive optics. The isoplanatic angle is respectively 3.3" and 5.7" for the South Pole and Dome C. This is significantly larger than at temperate sites where the average isoplanatic angle rarely exceeds 2". This means that wider fields can be corrected without the complication of conjugation to specific layers. For such purpose the potential is even more interesting. We show that ground conjugated adaptive optics would decrease the natural seeing to 0.22" for a wide field of 10 and 0.47" for a field of 1" at the South Pole. At Dome C the results are less impressive due to the already excellent seeing, but a gain of 0.1&quote can still be achieved over 1&quote. These results show that high angular resolution observations can be done better on the Antarctic plateau than any other known site.

In recent years the 6.67 GHz masing transition of CH3OH has proven to be a superior tracer of massive star formation (see Minier 2001). Maser sites often occur in proximity to UCHII regions, however, up to 75 per cent of sites have no detectable radio counterpart (Walsh 1998) and are instead hypothesised to trace the less evolved 'hot molecular core' phase of stellar evolution. This has been confirmed for a only handful of well known sources (e.g., Cesaroni 1994). Presented here are the results of multi-species molecular line observations towards warm, dusty clumps, undertaken with the goal of investigating the relationship between hot cores, UCHII regions and CH3OH masers. Data from the 22-m Mopra telescope is used extensively in this thesis and substantial efforts were made to calibrate the brightness temperature scale. Measurements conducted on SiO masers and planets show that the beam pattern is divided into a Gaussian main beam plus an inner error lobe, which in 2004 contained 1/3 of the power in the main beam. Full-width half-maximum beam sizes were measured from the data and the beam efficiencies were derived for the years 2000-2004. A 3-mm wavelength molecular line survey was conducted, using Mopra, towards 83 massive star-forming clumps associated with CH3OH masers. Emission from the transitions 13CO (1-0), N2H+ (1-0), HCO+ (1-0), HCN (1-0) and HNC (1-0) was detected towards 82 sources (99 per cent), while CH3OH emission was detected towards 78 sources (94 per cent). The warm gas tracer CH3CN was observed specifically to search for hot core chemistry, and was detected towards 58 sources (70 per cent), confirming that CH3OH masers are excellent tracers of hot cores. CH3CN is found to be brighter and more commonly detected towards masers associated with UCHII regions compared to 'isolated' masers. That CH3CN is detected towards isolated maser sources strongly suggests that these objects are internally heated. The molecular line data have been used to derive rotational temperatures and chemical abundances in the clumps and these properties have been compared between sub-samples associated with different indicators of evolution. In particular, CH3OH is found to be brighter and more abundant in UCHII regions and in sources with detected CH3CN, and may constitute a crude molecular clock in single dish observations. Gas-kinematics were analysed via asymmetries in the HCO+ line profiles. Approximately equal numbers of red and blue-skewed profiles, indicative of inward or outward motions, respectively, are found among all classes of object. Bolometric luminosities were derived via greybody fits to the sub-millimetre and mid-infrared spectral energy distributions, and an empirical gas-mass to luminosity relation of L proportional to M^0.68 was fit to the sample. This is a considerably shallower power law than L proportional to M^3 for massive main-sequence stars. In the mid-infrared, 12 sources were identified as 'infrared dark clouds' (IRDCs). Such objects have been hypothesised as precursors to the hot core phase of evolution, however, we find these sources have greater linewidths and rotational temperatures than the bulk of the sample, and one contains an embedded HII region The filamentary star forming region NGC3576 was also investigated via a molecular line and 23 GHz continuum mapping survey, utilising the ATCA, Mopra and Tidbinbilla telescopes. The results of these observations provide detailed information on the morphology, masses, kinematics, and physical and chemical conditions along the cloud. Analysis of NH3 data has revealed that the temperature and linewidth gradients exist in the western arm of the filament. Values are highest near to the central HII region, indicating that the embedded cluster of young stars is influencing the conditions in the bulk of the gas. Six new H2O masers were detected in the arms of the filament, all associated with clumps of NH3 emission. Star formation is clearly underway, however, clump masses range from 1 to 128 solar masses, possibly too low to harbour very massive stars. The lack of detected 23 GHz continuum emission in the arms supports this assertion.

We analyse the properties of extrasolar planets, other close companions and their hosts. We start by identifying a sample of the detected extrasolar planets that is minimally affected by the selection effects of the Doppler detection method. With a simple analysis we quantify trends in the surface density of this sample in the Msini-period plane. A modest extrapolation of these trends puts Jupiter in the most densely occupied region of this parameter space, thus suggesting that Jupiter is a typical massive planet rather than an outlier. We then examine what fraction of Sun-like (~ FGK) stars have planets. We find that at least ~25% of stars possess planets when we limit our analysis to stars that have been monitored the longest and whose low surface activity allow the most precise radial velocity measurements. The true fraction of stars with planets may be as large as ~100%. We construct a sample of nearby Sun-like stars with close companions (period < 5 years). By using the same sample to extract the relative numbers of stellar, brown dwarf and planetary companions, we verify the existence of a very dry brown dwarf desert and describe it quantitatively. Approximately 16% of Sun-like stars have close companions more massive than Jupiter: 11% +- 3% are stellar, <1% are brown dwarf and 5% +- 2% are giant planets. A comparison with the initial mass function of individual stars and free-floating brown dwarfs, suggests either a different spectrum of gravitational fragmentation in the formation environment or post-formation migratory processes disinclined to leave brown dwarfs in close orbits. Finally we examine the relationship between the frequency of close companions and the metallicity of their Sun-like hosts. We confirm and quantify a ~4 sigma positive correlation between host metallicity and planetary companions. In contrast we find a ~2 sigma anti-correlation between host metallicity and the presence of a stellar companion. Upon dividing our sample into FG and K sub-samples, we find a negligible anti-correlation in the FG sub-sample and a ~3 sigma anti-correlation in the K sub-sample. A kinematic analysis suggests that this anti-correlation is produced by a combination of low-metallicity, high-binarity thick disk stars and higher-metallicity, lower-binarity thin disk stars.

A well-made flute is always a compromise and the job of flute makers is to achieve a musically and aesthetically satisfying compromise; a task that involves much trial and-error. The practical aim of this thesis is to develop a mathematical model of the flute and a computer program that assists in the flute design process. Many musical qualities of a woodwind instrument may be calculated from the acoustic impedance spectrum of the instrument. A technique for fast and accurate measurement of this quantity is developed. The technique is based on the multiple-microphone technique, and uses resonance-free impedance loads to calibrate the system and spectral shaping to improve the precision at impedance extrema. The impedance spectra of the flute and clarinet are measured over a wide range of fingerings, yielding a comprehensive and accurate database. The impedance properties of single finger holes are measured using a related technique, and fitformulae are derived for the length corrections of closed finger holes for a typical range of hole sizes and lengths. The bore surface of wooden instruments can change over time with playing and this can affect the acoustic impedance, and therefore the playing quality. Such changes in acoustic impedance are explored using wooden test pipes. To account for the effect of a typical player on flute tuning, an empirical correction is determined from the measured tuning of both modern and classical flutes as played by several professional and semi-professional players. By combining the measured impedance database with the player effects and various results in the literature a mathematical model of the input impedance of flutes is developed and implemented in command-line programs written in the software language C. A user-friendly graphical interface is created using the flute impedance model for the purposes of flute acoustical design and analysis. The program calculates the tuning and other acoustical properties for any given geometry. The program is applied to a modern flute and a classical flute. The capabilities and limitations of the software are thereby illustrated and possible contributions of the program to contemporary flute design are explored.

In this thesis we make a new measurement of the primordial deuterium abundance, and analyse five other systems selected as possible D/H candidates. We also undertake an investigation of systematic errors in a system where an existing deuterium measurement has been made. We measure the number of hydrogen components and their velocity distributions in a moderate and high redshift sample of Lyman limit systems in one Angstrom resolution spectra. We present a new measurement of the deuterium-to-hydrogen ratio, D/H, at z=3.2560 in a newly-discovered low metallicity absorption system towards the quasar PG1937-1009. We attempt to account for any systematic effects that could influence the D/H measurement. We find a 1 sigma range for D/H*1e5 of 1.6 (+0.25) (-0.30). Using high resolution spectra from the Hubble Space Telescope and the Very Large Telescope, we assess the suitability of five D/H candidate absorption systems. These systems were selected as candidates using lower resolution spectra. We measure the neutral hydrogen column density, identify metal lines and analyse the velocity structure of each system, and show them to be unsuitable for measuring D/H. We also investigate the systematic errors in the absorber at z=0.701 towards quasar PG1718-4801 that was initially thought to show a high primordial D/H value. We analyse the dependence of the putative deuterium line's parameters on wavelength calibration errors in the HST spectra and present a revised deuterium measurement. We examine the velocity widths of two samples of one Angstrom resolution quasar spectra showing Lyman limit absorption systems. The first sample is at high redshifts, taken from the Sloan quasar data release 3 catalogue. The second is at intermediate redshifts, compiled from a survey for UV quasar absorption systems taken with the Hubble Space Telescope. We use a modified version of the Voigt profile fitting program, VPFIT, to estimate the number of hydrogen velocity components and column density in the Lyman limit systems. We compare the velocity distributions of the higher and lower redshift samples. We find the distributions are consistent with other measures of the velocity spread in absorption systems, and find no compelling evidence for evolution between the redshift samples.

Interest in the variation of fundamental constants has recently been stimulated by claims that the fine structure constant, α, was smaller in the past. Physicists are investigating whether α is currently varying using a number of methods including atomic clock experiments and quasar absorption spectra. To date atomic clock experiments have not reached the same level of precision as the quasar results but the precision to which transition frequencies are being measured is increasing dramatically and very soon atomic clock experiments based on Earth will be able to rival or surpass the quasar results. In order to relate the change in transition frequencies to a variation of α accurate calculations of relativistic effects in atoms and their dependence upon α are needed. Other effects, such as the small shift of transition frequencies due to blackbody radiation also need to be accounted for. In this thesis we perform accurate calculations of the dependence of transition frequencies in two-valence-electron atoms and ions on a variation of α. The relativistic Hartree-Fock method is used with many-body perturbation theory and configuration interaction methods to calculate transition frequencies. We also consider transitions with an enhanced sensitivity to α variation. In particular, narrow lines that correspond to atomic transitions between close lying, long-lived atomic states of different configurations. The small transition frequency, coupled with differences in the electron structure ensures a strong enhancement of the relative frequency change compared to a possible change in α . We also show that using the modified form of the Dirac Hamiltonian, as suggested by Bekenstein, does not affect the analysis of the quasar data pertaining to a measurement of α variation, nor does it affect atomic clock experiments. Finally we have performed calculations of the size of the frequency shift induced by a static electric field on the clock transition frequencies of the hyperfine splitting in Y b+, Rb, Cs, Ba+, and Hg+. The calculations are used to find the frequency shifts due to blackbody radiation which are needed for accurate frequency measurements and improvements of the limits on variation of α. Our result for Cs [??v/=E2 = -2:26(2) x 10-10Hz/(V/m)2] is in good agreement with early measurements and ab initio calculations. We present arguments against recent claims that the actual value might be smaller. The difference (~ 10%) is due to the continuum spectrum in the sum over intermediate states.