In this dissertation I present a detailed survey of molecular line emission (including NH3, C2S, HC5N, N2H+, N2D+ and H2D+) towards clustered star forming Cores in the nearby Ophiuchus molecular cloud, with the aim of characterizing the distribution and kinematics of the dense gas within a clustered star forming environment and compare these results with those found in more isolated star forming regions. I show that the dense Oph Cores present characteristics of both isolated and clustered star forming regions in several key parameters, including Core kinematics, temperatures and chemistry. At the higher gas densities where the N2H+ emission is excited, I show that the presence of an embedded protostar is correlated with increased gas motions. I additionally present evidence of N2H+ depletion from the gas phase, suggesting that in higher density, clustered environments N2H+ may not accurately trace the physical conditions of the densest core gas. I present the distribution of H2D+ and N2D+ across the Oph B Core, and show the distribution is not simple or easily explained by chemical models of evolving, isolated cores. Finally, I summarize the results of this dissertation, the questions it raises concerning the exploration of how stars form in clusters, and discuss how these questions may be answered through upcoming observational surveys and by new telescope facilities.

No description available.

Studies of gas-phase ionic clusters have become an integral component in understanding microsolvation and catalysis by transition metal cations. Further interest in this field is due to the possibility of bridging the gap between the condensed and gas phases by developing our understanding of clusters and the possibility that small clusters can have unique chemical and catalytic properties. Most gas phase studies have focused on singly charged ions. Electrospray allows for the production of multiply charged ions solvated by a few solvent molecules. Understanding smaller reactive species such as metal centered clusters with well-defined, gas phase conditions also allows for detailed comparison between theory and experiments. In these studies the main focus is to understand bond activation by transition metal cations and solvation of transition metal dications. The gas phase ions of interest are studied using an electrospray-ionization or laser-ablation dual time-of-flight mass spectrometer and are characterized using photofragment spectroscopy in the visible and ultraviolet regions of the spectrum. Photofragment spectroscopy is a powerful method that can be used in gas phase studies to gather a wealth of information on the ions' bond strengths, spectroscopic constants, and dissociation kinetics and dynamics. The study of TiO + (CO 2 ) spectroscopy (Chapter 3) was a result of study of CO 2 bond activation by Ti + that went on to provide a wealth of information on the spectroscopy and dissociation kinetics of this molecule. An electronic transition of the TiO + chromophore was observed, 2 Π[arrow left] 2 Δ, revealing new information about the excited state and the effect of TiO + electronic state on the metal- CO 2 ligand interaction. The photodissociation spectrum of this molecule is well resolved and shows progressions in the covalent Ti-O stretch and metal-ligand stretch and rock. The lifetime of electronically excited TiO + (CO 2 ) was measured, and depends strongly on vibrational energy. Calculations on TiO + and TiO + (CO 2 ) were combined with experimental results on TiO + (CO 2 ) to predict spectroscopic transitions of TiO + , an astrophysically interesting molecule. The photodissociation dynamics of M 2+ (CH 3 CN)n(H 2 O)m where M = Co and Ni, (Chapter 4) is important in understanding the gas phase microsolvation of metal dications. The coordination number and type of solvent affect the dissociation pathways. M 2+ (CH 3 CN)n (n>2) primarily lose a solvent molecule. Electron transfer is a minor channel for n=3 and is the only channel observed for n=2. Mixed clusters M 2+ (CH 3 CN)n(H 2 O)m preferentially lose water. Loss of acetonitrile is a minor channel, as is proton transfer. Water is the proton donor. Replacing acetonitrile with water increases the proton transfer channel. Nickel and cobalt complexes show similar dissociation dynamics, with proton transfer more likely for nickel complexes. Methane activation by transition metal catalysts is industrially important as it can be used to produce gasoline from natural gas. We studied the products and intermediates of the reaction of laser-ablated platinum atoms with methane (Chapter 5). Photoionization efficiency curves were measured for PtCH 2 and the [H-Pt-CH 3 ] insertion intermediate using tunable vacuum ultraviolet light. The resulting ionization energies were combined with bond strengths for the cations to derive bond strengths for the neutrals. These were used to construct a potential energy surface for methane activation by platinum atoms.

A variety of precision observations suggest that the present universe is dominated by some unknown components, the so-called dark matter and dark energy. The distribution and properties of these components are the focus of modern cosmology and we are only beginning to understand them. Gravitational lensing, the bending of light in the gravitational field of a massive object, is one of the predictions of the general theory of relativity. It has become an ever more important tool for investigating the dark universe, especially with recent and coming advances in observational data. This thesis studies gravitational lensing effects on scales ranging over ten orders of magnitude to probe very different aspects of the dark universe. Implementing a matter distribution following the predictions of recent simulations, we show that microlensing by a large population of massive compact halo objects (MACHOs) is unlikely to be the source of the observed long-term variability in quasars. We study the feasibility of detecting the so far elusive galactic dark matter substructures, the so-called “missing satellites”, via millilensing in galaxies close to the line-of-sight to distant light sources. Finally, we utilise massive galaxy clusters, some of the largest structures known in the universe, as gravitational telescopes in order to detect distant supernovae, thereby gaining insight into the expansion history of the universe. We also show, how such observations can be used to put constraints on the dark matter component of these galaxy clusters. / At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 6: Submitted.

No description available.

This thesis presents a number of largely independent forays into developing an understanding of the unique chemistry of transition metal clusters. The first chapter of this thesis represents an initial foray into mapping the chemical reactivity of transition metal clusters - a monumental task that will doubtless continue for some time. The small slice undertaken in this work investigates the reactivity with CO of a series of the smallest possible metal clusters; 4d (Nb - Ag) homonuclear metal trimers. In Chapter 2, two known transition metal clusters were studied using CASSCF (MCSCF) and MRCI methods, only to find that DFT methods provided more accurate Ionisation Potentials (IPs). Thus Chapter 3 was devoted to optimising a density functional to predict IPs. As clusters get larger, the number of possible structures grows rapidly too large for human intuition to handle, thus Chapter 4 is devoted to the use of an automated stochastic algorithm, “Kick”, for structure elucidation. Chapter 5 improves on this algorithm, by permitting chemically sensible molecular fragments to be defined and used. Chapter 6 then comes full circle and uses the new Kick algorithm to investigate the reaction of CO with a series of mono-substituted niobium tetramers (i.e. Nb₃X). / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1350246 / Thesis (Ph.D.) - University of Adelaide, School of Chemistry and Physics, 2009

This thesis presents a number of largely independent forays into developing an understanding of the unique chemistry of transition metal clusters. The first chapter of this thesis represents an initial foray into mapping the chemical reactivity of transition metal clusters - a monumental task that will doubtless continue for some time. The small slice undertaken in this work investigates the reactivity with CO of a series of the smallest possible metal clusters; 4d (Nb - Ag) homonuclear metal trimers. In Chapter 2, two known transition metal clusters were studied using CASSCF (MCSCF) and MRCI methods, only to find that DFT methods provided more accurate Ionisation Potentials (IPs). Thus Chapter 3 was devoted to optimising a density functional to predict IPs. As clusters get larger, the number of possible structures grows rapidly too large for human intuition to handle, thus Chapter 4 is devoted to the use of an automated stochastic algorithm, “Kick”, for structure elucidation. Chapter 5 improves on this algorithm, by permitting chemically sensible molecular fragments to be defined and used. Chapter 6 then comes full circle and uses the new Kick algorithm to investigate the reaction of CO with a series of mono-substituted niobium tetramers (i.e. Nb₃X). / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1350246 / Thesis (Ph.D.) - University of Adelaide, School of Chemistry and Physics, 2009

This thesis assesses the extent to which jet precession can be used to control the mean and instantaneous particle distributions in particle-laden jet flows. Investigations were conducted, providing quantitative, planar measurements of instantaneous particle distributions in the first 10 nozzle diameters of a particle-laden co-annular nozzle with centrally located Precessing Jet (PJ). Equipment was specifically designed to conduct the investigations, a laser diagnostic technique developed and a methodology to quantify particle clusters was devised. The experimental facilities are scaled to simulate the near burner region of a typical rotary cement kiln. The laser diagnostic technique, called planar nephelometry, enables non-intrusive, quantitative, instantaneous, planar measurements of particle distributions without the need to identify individual particles. The methodology to quantify particle clusters is designed to enable statistical comparison of clusters without ambiguity. Measurements of the influence of particle mass loading and jet precession on the distribution of particles emerging from an particle-laden co-annular nozzle, with a centrally located PJ nozzle, are presented. These data include mean and standard deviation of the particle distributions and statistics on particle cluster characteristics. The results indicate that small amounts of momentum through the PJ nozzle causes an elongation of the jet, but larger amounts of momentum through the PJ nozzle will result in a wider mean particle distribution and greater mean centreline decay rate. An increase in jet precession also results in an increase in the fluctuations in the particle distributions. The transition is determined by the interplay of momentum of the particle-laden and precessing streams. The physical characteristics of identified particle clusters in the instantaneous planar flow field are also influenced by jet precession. An initial increase in the amount of jet precession results in an overall decrease in the average number of both small- and large-clusters. The size of small-clusters generally reduces with increasing jet precession, whereas large-clusters reach maximum sizes for an intermediate relative momentum of jet precession. Analogous to the influence of jet precession on the mean distribution of particles, increasing jet precession also results in a greater spread of small- and large-clusters. Results also indicate that increasing the mass flow rate of particles results in an elongation of the jet. However, these variations correspond to an increase in annular jet momentum, rather than an addition of secondary phase. The particle mass flow rate has a minor influence on the general characteristics of particle clusters. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1370427 / Thesis (Ph.D.) -- University of Adelaide, School of Mechanical Engineering, 2009

This thesis has used medium- and high-resolution spectral data to derive elemental abundances, in particular light and heavy s-process elemental abundances, for groups of giant stars in the globular clusters 47 Tuc, NGC 6388 and NGC 362. These analyses were undertaken using both curve-of-growth and spectrum synthesis techniques. The techniques were calibrated with respect to the metal-poor giant star Arcturus in order to reduce systematic errors in the analysis process. A feasibility study was undertaken that compared synthetic spectra at different resolutions throughout the colour-magnitude diagram (CMD) of a metal-rich ([Fe/H] = -0.5 dex) globular cluster. This study identified where on the CMD light and heavy s-process elemental abundances could be derived at medium resolution (R ~ 10,000). Abundance analyses could be undertaken on the giant branches down to just below the horizontal branch and then again on the main sequence below Teff ~ 4500 K. At all other places on the CMD high-resolution spectra (R ~ 30,000) are required to derive these abundances. Performance verification data at R ~ 5,000$ was obtained using the Robert Stobie Spectrograph (RSS) on the Southern African Large Telescope (SALT) and showed that there were no large scale s-process elemental abundance variations in 47 Tuc giant branch stars. The level of precision in this preliminary data was [X/Fe] ~ 0.5dex. A resolution of R ~ 10,000 should be achievable with SALT RSS in the future which will improve this limit. The AAOmega survey of 47 Tuc stars at R ~ 6,500 was more promising in certain aspects of elemental abundance determination. The observed wavelengths included the key features of CN and CH molecular bands, and light (Z < 30) and heavy (38 < Z < 63) element spectral lines. CN indices were measured and calibrated to previous results. The well-known CN bimodality was observed in the 47 Tuc stars, as well as a radial gradient in CN strength. A preliminary subset of ten of the survey stars have undergone an abundance analysis for which the abundances of Fe, Si, and Ca were found to be homogeneous within this cluster. The Na abundances had a large range in values that were observed to correlate with CN strength. The s-process elemental abundance results were inconclusive. The Zr abundances showed little to no enhancement in the sample and the Ba abundances varied considerably due to strong lines of Ba II being extremely sensitive to microturbulence. Various high-resolution studies were carried out using spectra of giant stars in 47 Tuc, NGC 6388 and NGC 362 observed on the Australian National Observatory (ANO) 2.3 m echelle spectrograph and the Ultra-Violet Echelle Spectrograph (UVES) on the Very Large Telescope (VLT). The high-resolution analysis of 47 Tuc giant star Lee 2525 found an enhanced Zr abundance in this star which resolved a discrepancy between two previous 47 Tuc elemental abundance studies (Brown & Wallerstein 1992; Wylie et al. 2006). The stars in the VLT dataset that were analysed here included five giant branch stars in 47 Tuc, two in NGC 6388 and thirteen in NGC 362. The low temperatures and gravities of these stars caused departures from local thermodynamic equilibrium in low excitation potential neutral species, particularly Fe and Zr, that needed to be taken into account before reliable stellar parameters and elemental abundances could be determined for these stars. Veiling effects due to circumstellar dust were postulated to have produced artificially low metallicities for the infra-red excess stars in this sample, particularly for the 47 Tuc stars. The element abundance analyses of 47 Tuc, NGC 6388 and NGC 362 stars found the derived metallicities to be homogeneous for each cluster (<[Fe/H]>(47Tuc) = -0.88 +/- 0.09 dex; <[Fe/H]>(NGC6388) = -0.60 +/- 0.06 dex; <[Fe/H]>(NGC362) = -1.21 +/- 0.08 dex). The 47 Tuc sample included Lee 2525 and the five VLT stars. The derived metallicities were in reasonable agreement with previously reported values. The light (ls) and heavy (hs) s-process element abundances were enhanced and homogeneous in the stars of each cluster. The abundances determined for 47 Tuc and NGC 6388 were in good agreement, reflecting the similarity in metallicity of the stars in these two clusters (<[ls/Fe]>(47Tuc) = +0.53 +/- 0.02 dex; <[hs/Fe]>(47Tuc) = +0.40 +/- 0.06 dex; <[ls/Fe]>(NGC6388) = +0.58 +/- 0.13 dex; <[hs/Fe]>(NGC6388) = +0.39 +/- 0.07 dex). The more metal-poor cluster NGC 362 was less enhanced in ls elemental abundances and slightly more enhanced in hs elemental abundances (<[ls/Fe]>(NGC362) = +0.32 +/- 0.10 dex, <[hs/Fe]>(NGC362) = +0.46 +/- 0.09 dex). The clear enhancement in the s-process elemental abundances and homogeneity in the results for each globular cluster is evidence that these stars have been enhanced extrinsically in s-process elements. Pollution events in the history of each cluster has resulted in the abundance distribution in both the light elements and the heavy elements that has been observed in the stars analysed in this thesis. The enhancements in Na, ls and hs elemental abundances favours intermediate mass AGB stars as the source of the pollution.

Thesis (M. Phil.)--University of Hong Kong, 2008. / Also available in print.