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Molecular clouds are imperative to astronomy as the sites of all known star formation. The problem of how molecular clouds are formed in spiral galaxies is approached numerically, by modelling the response of a gas disk to a spiral potential. The importance of spiral shocks is highlighted as a dominant formation mechanism for molecular clouds in grand design galaxies, where a strong density wave is present. The spiral shock both increases the density of the interstellar gas significantly, and produces structure in the spiral arms. The gas evolves into discrete clumps, which are shown to contain substantial densities of molecular hydrogen, and are therefore identified as molecular clouds. The formation of these clouds requires that the interstellar medium (ISM) is cold and inhomogeneous. The passage of an inhomogeneous gas distribution through a spiral potential further shows that supersonic velocities are induced as the gas shocks. This can explain the velocity dispersion relation observed in molecular clouds. Finally, the shearing of clumps of gas in the spiral arms leads to the formation of inter-arm structures, which are commonly observed in spiral galaxies.

Inter-cloud is a recently emerging approach that expands cloud elasticity. By facilitating an adaptable setting, it purposes at the realization of a scalable resource provisioning that enables a diversity of cloud user requirements to be handled efficiently. This study’s contribution is in the inter-cloud performance optimization of job executions using metascheduling concepts. This includes the development of the inter-cloud meta-scheduling (ICMS) framework, the ICMS optimal schemes and the SimIC toolkit. The ICMS model is an architectural strategy for managing and scheduling user services in virtualized dynamically inter-linked clouds. This is achieved by the development of a model that includes a set of algorithms, namely the Service-Request, Service-Distribution, Service-Availability and Service-Allocation algorithms. These along with resource management optimal schemes offer the novel functionalities of the ICMS where the message exchanging implements the job distributions method, the VM deployment offers the VM management features and the local resource management system details the management of the local cloud schedulers. The generated system offers great flexibility by facilitating a lightweight resource management methodology while at the same time handling the heterogeneity of different clouds through advanced service level agreement coordination. Experimental results are productive as the proposed ICMS model achieves enhancement of the performance of service distribution for a variety of criteria such as service execution times, makespan, turnaround times, utilization levels and energy consumption rates for various inter-cloud entities, e.g. users, hosts and VMs. For example, ICMS optimizes the performance of a non-meta-brokering inter-cloud by 3%, while ICMS with full optimal schemes achieves 9% optimization for the same configurations. The whole experimental platform is implemented into the inter-cloud Simulation toolkit (SimIC) developed by the author, which is a discrete event simulation framework.

The accurate determination of cloud cover amount is important for characterizing the role of cloud feedbacks in the climate system. Clouds have a large influence on the climate system through their effect on the earth's radiation budget. As indicated by the NASA Earth Radiation Budget Experiment (ERBE), the change in the earth's radiation budget brought about by clouds is ~-15 Wm⁻² on a global scale, which is several times the ~4 Wm⁻² gain in energy to the troposphere-surface system that would arise from a doubling of CO₂ in the atmosphere. Consequently, even a small change in global cloud amount may lead to a major change in the climate system. Threshold methods are commonly used to derive cloud properties from satellite imagery data. Here, in order to quantify errors due to thresholds, cloud cover is obtained using three different values of thresholds. The three thresholds are applied to the 11 μm, (4 km)² NOAA-9 AVHRR GAC satellite imagery data over four oceanic regions. Regional cloud-cover fractions are obtained for two different scales, (60 km)² and (250 km)². The spatial coherence method for obtaining cloud cover from imagery data is applied to coincident data. The differences between cloud cover derived by the spatial coherence method and by the threshold methods depends on the setting of the threshold. Because the spatial coherence method is believed to provide good estimates of cloud cover for opaque, single-layered cloud systems, this study is limited to such systems, and the differences in derived cloud cover are interpreted as errors due to the application of thresholds. The threshold errors are caused by pixels that are partially covered by clouds and the errors have a dependence on the regional scale cloud cover. The errors can be derived from the distribution of pixel-scale cloud cover. Two simple models which assume idealized distributions for pixel-scale cloud cover are constructed and used to estimate the threshold errors. The results show that these models, though simple, perform rather well in estimating the differences between cloud cover derived by the spatial coherence method and those obtained by threshold methods. / Graduation date: 1992

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Thesis (PhD) -- University of Western Sydney, Nepean, 1999. / "A thesis submitted for the degree of Doctor of Philosophy at the University of Western Sydney Nepean" "July, 1999" Bibliography : p. 177-185.

Thesis (M.Sc.). / Written for the Dept. of Atmospheric and Oceanic Sciences. Title from title page of PDF (viewed 2009/07/07). Includes bibliographical references.

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Onboard offshore platforms the wear imposed on pipes used for the transport of gases can be severe. The transport pipes potentially contain highly flammable and explosive hydrocarbon gases and hence the dangers that can be created by a leaking joint are serious. In these offshore installations, to minimise the danger created by a hydrocarbon gas leak, companies and government agencies proposing to commission oil or gas platforms often complete a safety study. This study includesd etailso f safetyp roceduresa nd the potentiale ffectsc reatedb y leaks. At present the methods used are based on the assumption that the leaks are all from more well known circular cross-sectional jets. This project was initiated to study leaking flange joints which are a typical source for gas leaks. Many leak geometries and a range of pipeline pressures up to a maximum of 410kPa were studied to consider their effect on the resulting gas leak jet. Laser light sheet imaging was used to obtain flow visualisation images, with total pressure probe measurements providing valuable time-averaged data. This alloweda two-dimensionasl liceo f the emergingle akj et to be studiedi n detail with two very differenta nalyticatl echniques. A steady core was observed at the point of exit of each gas jet studied. The core was shown to be a region in which the shear layers, initiated at the jet boundaries, grow towards a merging point on the jet centreline. At this location, the velocity decay rate was found to increase as the jet entered into a second flow regionWithin this region, the rate of velocity decay was shown to be similar to that typically observed in a planar jet. This is much slower than would develop in a roundj et. At the downstreamli mit of the experimentaml easurementsa, t hird flow region was observed. The centreline velocity within this region showed no tendencyt o a lineard ecayr ate as would be foundi n a round cross-sectionje t. Significant differences were noted between the spreading angle of a round jet and those included in the present study. A wide range of spreading angles were observed, which suggests that it is unrealistic for all flange joint leaks to be represented by the round jet assumption. More specifically, because of the effect of spreading angle, the round jet assumption is likely to show discrepancies in predicting the magnitude of important parameters, such as the gas concentration levelsa nde ntrainmenrta tes. As safetys tudiesa re at presentb asedo n circularc ross-sectiojne t data, the findings of this report indicate that the validity of those safety studies is probably being compromised