This thesis presents an observational study of molecular abundances in the dense cores of 27 prominent molecular clouds in the southern galactic plane.The molecular abundances and physical conditions in dense condensations have been derived from millimetre-wavelength observations of molecular rotational transitions.The study has produced a comprehensive data set of transition intensities and abundances for 10 different molecules in bright southern molecular clouds, and the general characteristics of emissions from these molecules such as optical depth, excitation and relative abundances are discussed. A comparison of different methods of calculating molecular hydrogen column density from observations of carbon monoxide emission is included.Both the analysis and the data collected provide an excellent starting point for further observational and theoretical studies of molecular clouds in the southern Milky Way utilising new instruments such as the millimeter-wave upgrade to the Australia Telescope Compact Array and the Attacama Large Millimetre Array (ALMA). / Doctor of Philosophy (PhD)

<p>Buildings, maps and objects et cetera, can be modeled using a computer or reconstructed in 3D by data from different kinds of cameras or laser scanners. This thesis concerns the latter. The recent improvements of Time-of-Flight cameras have brought a number of new interesting research areas to the surface. Registration of several ToF camera point clouds is such an area.</p><p>A literature study has been made to summarize the research done in the area over the last two decades. The most popular method for registering point clouds, namely the Iterative Closest Point (ICP), has been studied. In addition to this, an error relaxation algorithm was implemented to minimize the accumulated error of the sequential pairwise ICP.</p><p>A few different real-world test scenarios and one scenario with synthetic data were constructed. These data sets were registered with varying outcome. The obtained camera poses from the sequential ICP were improved by loop closing and error relaxation.</p><p>The results illustrate the importance of having good initial guesses on the relative transformations to obtain a correct model. Furthermore the strengths and weaknesses of the sequential ICP and the utilized error relaxation method are shown.</p>

Data from the GARP Atlantic Tropical Experiment (GATE) was analysed in an exploratory manner to discover the characteristics of mesoscale organization of convection and it's relationship to large-scale wind profiles. Automated methods were developed to identify the convective cells and their linear organization. These automated methods use a median high-pass filter to identify enhanced cells and a simple pattern recognition technique to ascertain the linear organization between them. Due to the simplified nature of the algorithm, the whole data set of the 21 day period from the phase 3 of GATE was processed in an economical manner obtaining a large data base which was used in the investigation of clusters and other associated phenomena. The mesoscale organization of convective cells and the widespread areas of lighter precipitation associated with them showed expected characteristics and compared satisfactorily with previous results. A large fraction of the rainfall (64%) fell from the widespread area. The total precipitation had a correlation of 0.94 with the fractional area of the widespread and a correlation of 0.89 with the fractional area of the clusters. The widespread precipitation had a correlation index of 0.97 with it's fractional area and the cluster precipitation had a strong linear relationship to it's area with a correlation of 0.99. These factors argue well for the parameterization of rainfall rate in tropical regions to a high accuracy by the area covered by organized convective cells and widespread areas. It was also seen that there was a good correlation with the number of clusters and number of cores with the total precipitation rate in a given area. These factors create a strong argument for identifying mesoscale systems consisting of convective cells and widespread precipitation as basic units of precipitation in tropical regions, having a characteristic life cycle of their own. The widespread and total precipitation showed very good correlation with upper-level vertical motion. Clusters tended to align parallel with the horizontal low-level wind shear and the degree of alignment appears to depend on the strength of the wind shear. / Graduation date: 1991

Graduation date: 1989

Multiple scattering effects from bubble clouds are investigated in this study. A high performance, general purpose numerical tool for multiple scattering calculations is developed. This numerical tool is applied in three computational scenarios in this study. The total scattering cross section of a bubble cloud is investigated. Numerical results indicate that the resonant frequency of the bubble cloud is much lower than that of a single bubble. The variation of resonant frequency of multiple scattering is also studied. It is found that the resonant frequency decreases as the number of bubbles increases, or as the void fraction of the bubble cloud decreases. Phase distributions of bubble oscillations in various multiple scattering scenarios are presented. It is found that, at resonance, the bubbles synchronize to the same phase, which is indicative of the lowest mode of collective oscillation. At wave localization, half of the bubbles oscillate at phase 0 while the other half oscillate at phase Pi. An intuitive interpretation of this behavior is given.

Buildings, maps and objects et cetera, can be modeled using a computer or reconstructed in 3D by data from different kinds of cameras or laser scanners. This thesis concerns the latter. The recent improvements of Time-of-Flight cameras have brought a number of new interesting research areas to the surface. Registration of several ToF camera point clouds is such an area. A literature study has been made to summarize the research done in the area over the last two decades. The most popular method for registering point clouds, namely the Iterative Closest Point (ICP), has been studied. In addition to this, an error relaxation algorithm was implemented to minimize the accumulated error of the sequential pairwise ICP. A few different real-world test scenarios and one scenario with synthetic data were constructed. These data sets were registered with varying outcome. The obtained camera poses from the sequential ICP were improved by loop closing and error relaxation. The results illustrate the importance of having good initial guesses on the relative transformations to obtain a correct model. Furthermore the strengths and weaknesses of the sequential ICP and the utilized error relaxation method are shown.

The general objective of the present work is to contribute to the knowledge of the physics of Be Stars. In particular, we are interested in studying and characterizing their pulsational properties. A very suitable tool to reach this goal is the study and analysis of photometric time series with the maximum time baseline, density and photometric accuracy.The space mission COROT scheduled to be launched in December 2006, will provide ultra high precision, relative stellar photometry for very long continuous observing runs. Up to ten stars will be observed in the seismology fields with a photometric accuracy of a few 10-4 and color information during 150 days.The observations of Be stars with COROT will provide photometric time series with unprecedented quality. Their analysis will allow us to qualitatively improve our knowledge and understanding of the pulsational characteristics of Be stars. In consequence, we have started a research project aimed at observing Be stars both in the seismology and exoplanet fields of COROT.In this thesis we present the first step of this project, which is the preparation and study of the sample of Be stars that will be observed by COROT. We have performed photometric analysis of all Be stars located in the seismology fields (Chap. 2). Special emphasis has been given to two stars (NW Ser and V1446 Aql) in which we have detected multiperiodic variability and these variations have been modeled in terms of stellar pulsations (Chap. 3). We have also performed an in-depth spectroscopic study of NW Ser and identified the non-radial pulsating modes taking into account the rotational effects (Chap. 4). A technique to search for faint Be stars based on CCD photometry has been developed and is presented in Chap. 5. We also present a list of faint Be stars located in the exoplanet fields of COROT detected with this technique and which we propose as targets for COROT. In addition, we have proven that our period-analysis techniques are suitable to detect multiperiodicity in large temporal baseline data. In particular, we have detected non-radial pulsations in some Be stars in the low-metallicity galaxy Small Magellanic Clouds (Chap. 6). The current theoretical models do not predict the presence of pulsational instabilities in such low-metallicity environment, and therefore, our results point towards the necessity of new and improved models.

The freezing kinetics of binary nitric acid/water aerosols is of fundamental importance to the modelling of polar stratospheric clouds and the role they in ozone depletion over the Arctic/Antarctic regions. Cirrus clouds are also often composed of nitric acid solutions, hence an understanding of freezing process in these aerosols also aids in modelling the earth's radiation budget and global warming. This thesis explores the kinetic phase diagram of nitric acid/water aerosols with sizes ranging between 0. 2 and 1. 5 mm in radius and concentrations ranging between pure water and 0. 45 mole fraction HNO3. Although the kinetic phase diagram has now been studied between 0. 46 mole fraction HNO3 and pure water, more data is needed in the region between 0. 18 and 0. 25 mole fraction HNO3 to confirm the results reported. The project described in this thesis are a continuation of a project begun by Allan Bertram. The measurements involving aerosols with compositions greater than 0. 25 mole fraction HNO3 were carried out as part of Allan Bertram's Ph. D. thesis (see ref. 20) These data were later examined using a more comprehensive data analysis method (as presented in this thesis) in an effort to obtain a more complete understanding of this system.

The single-scattering properties of six non-spherical ice crystals, droxtals, plates, solid columns, hollow columns, aggregates and 6-branch bullet rosettes are simulated. The anomalous diffraction theory (ADT) is applied to the simulation of the extinction efficiency and the absorption efficiency. Because the first order reflection is considered, the accuracy of the absorption efficiency increases with the increasing of the size parameter. Compared with the reference single-scattering properties from an improved geometric optics method (IGOM), the errors in the extinction and absorption efficiencies are small. In addition, the asymmetry factor is formulated within the framework of diffraction and external reflection. The asymmetry factor based on the ADT matches very well with the IGOM counterpart when the absorption is strong, but needs an improvement in the solar region. The errors in conjunction with the application of the ADT-based optical properties to the computation of atmospheric fluxes and heating rates, based on the Fu-Liou model also are investigated. Two cases, one for tropical cirrus clouds and the other for mid-latitude cirrus clouds, are designed. It is found that the errors of bulk asymmetry factor between ADT-based and IGOM-based result in an overestimation of downward infrared (IR) fluxes and upward solar fluxes, and an underestimation of upward IR fluxes and downward solar fluxes. The errors of the fluxes and heating rates based on two sets of single-scattering properties are caused mainly by the underestimation of the bulk absorption efficiency based on ADT. It is also shown that ADT-based optical properties generate more accurate radiative properties for tropical cirrus clouds than for the mid-latitude cirrus clouds. In conclusion, the ADT-based method can generate reasonably accurate single-scattering properties of ice crystals, and can result in reasonable upward IR and solar fluxes at top of atmosphere (TOA), downward IR fluxes at the surface, and net heating rates.

Mineral dust is ubiquitous in the atmosphere and represents a dominant type of particulate matter by mass. Despite its well-recognized importance, assessments of dust impacts on clouds and climate remain highly uncertain. This thesis addresses the role of dust as cloud condensation nuclei (CCN) and giant CCN (GCCN) with the goal of improving our understanding of dust-warm cloud interactions and their representation in climate models. We investigate the CCN-relevant properties of mineral dust samples representative of major regional dust sources experimentally in the laboratory conditions to determine their respective affinity to water. Based on the experimental exponent derived from the dependence of critical supersaturation with particle dry diameter, we determine the dominant physics of activation (i.e., adsorption activation theory (AT) or traditional Köhler theory (KT)) for dust particles from different global regions. Results from experimental measurements are used to support the development of a new parameterization of cloud droplet formation from dust CCN for climate models based on adsorption activation mechanism. The potential role of dust GCCN activating by AT within warm stratocumulus and convective clouds is also evaluated.