It is a great challenge in the design of the PBMR to accurately predict gas flow and heat transfer in the reactor. Understanding the heat transfer at the core-reflector interface in particular is a very important aspect as the reactivity of the control rods housed in the reflectors is highly temperature dependent. It is also very important because the core-reflector interface is on the critical path for heat removal during accident conditions. PBMR has developed an OECD/NEA coupled neutronic/thermal-hydraulic benchmark to aid in the understanding of the different modelling approaches currently employed at PBMR. A comparison of THERMIX-KONVEK and DIREKT results showed large temperature differences at the core-reflector interfaces. Further investigation showed that these differences are as a result of the numerical methods used i.e. Cell-Centred (CC) vs. Vertex-Centered (VC). The present study extended this comparison to Star-CD (CC) and Flownex (VC) which are also used to simulate the reactor at PBMR. An ID MATLAB program that mimics the CC and VC numerical methods was verified against Star-CD and Flownex. This program was then used to model an ID version of the OECD/NEA benchmark. Results were compared with DIREKT and THERMIX-KONVEK. Although the results compared well, there were significant errors at the core-reflector interfaces. The findings of this study were that different numerical methods will predict different temperatures, heat fluxes and (temperature-dependent) sink terms. It was also shown that in addition to the differences resulting from numerical methods, differences were seen between Star-CD and DIREKT and Flownex and THERMIX-KONVEK in the region of the core-reflector boundary. In general, for complicated simulations like that of the pebble bed, the numerical basis of software used to simulate the problem needs to be understood for the problem to be correctly modelled. / Thesis (M.Sc. Engineering Sciences (Nuclear Engineering))--North-West University, Potchefstroom Campus, 2010.

Using data from the SCUBA Legacy Catalogue (850 µm) and Spitzer (3.6 - 70 µm), we explore dense cores in the Ophiuchus, Taurus, Perseus, Serpens, and Orion molecular clouds. In particular, we focus on identifying which cores host young stars while others remain starless. Understanding the nature of star formation and the influence of local environment will give us insight into several key properties, such as the origin of stellar mass. Here, we present starless and protostellar core mass functions (CMFs) for the five clouds. We develop a new method to discriminate starless from protostellar cores, using Spitzer colours and positions. We found best-fit slopes to the high-mass end of −1.26±0.20, −1.22±0.06, −0.95±0.20, and −1.85±0.53 for Ophiuchus, Taurus, Perseus, and Orion, respectively. We were unable to fit a slope to our fifth cloud, Serpens. Broadly, these slopes are consistent with the −1.35 power-law seen in the Salpeter IMF, but suggest some differences. We examined a variety of trends between these CMF shapes and their parent cloud properties, potentially finding a correlation between the high-mass slope and temperature. We also attempt to predict what future surveys with SCUBA-2 will detect in each of our clouds.

Although the Sloan Digital Sky Survey (SDSS) has compiled an unprecedented amount of photometric data on stellar populations in the Milky Way, it is not presently possible to accurately and consistently interpret these data due to the lack of precise fiducial stellar sequences and color-temperature relations for the new 'u'g'r'i'z' photo-metric system. In order to address these deficiencies, this study describes an extensive observational project that has obtained high-quality and homogeneous photometry for a number of different Galactic star clusters spanning a wide range in meta.llicity (-2.5 ≤ [Fe/H] ≤ +0.3), as observed in the u'g'r'i'z' passbands with the MegaCam wide-field imager on the Canada-France-Hawaii Telescope. By employing these purest of stellar populations, fiducial sequences have been defined from color-magnitude diagrams (CMDs) that. extend from the tip of the RGB down to approximately 4 magnitudes below the turnoff points: these have been accurately calibrated to the standard u'g'r'i'z` system via a set of secondary photometric standards located within these same clusters. Consequently, they can serve as a valuable set of empirical fiducials for the interpretation of stellar populations data in the system, as well as calibrators for the transformation of stellar isochrones to the u'g'r'i'z' bandpasses. In fact. when a new grid of theoretical color-Teff relations and bolometric corrections for the system is computed from Kurucz model atmospheres and employed to translate isochrones to the observed planes, generally very good and consistent fits to the CMDs of the metal-poor ([Fe/H] <0.0) globular clusters M 92, M 13, and M 71 are found, once reasonable estimates of the cluster parameters are assumed (the only obvious discrepancy is a shift of ~ 0.01 - 0.03 mag between the predicted and observed giant branches when the models are fitted to the main sequences). More-over, the same isochrone fits are entirely consistent with those inferred from cluster observations in other photometric systems - notably, the BV(RI) , and uvby systems. At the metal-rich end ([Fe/H] ≥ 0.0), however. these transformations fail to match the observed loci of cool, main-sequence stars (Teff ≤ 5000K) in the open clusters M 67 and NGC 6791. An exploration into possible causes of these discrepancies is provided.

We investigate three separate topics associated with the formation and evolution of the stellar mass component in galaxy clusters. The work presented herein is based primarily on optical imaging and spectra taken with, respectively, the Canada-France-Hawaii Telescope and Gemini North/South. We confront the result from the optical data analysis with the results from the analysis of high-resolution X-ray data taken with the Chandra and XMM-Newton space observatories. Confirming earlier results, we find that 22% of brightest cluster galaxies (BCGs) show central inversions in their optical color profiles (blue-cores), indicative of recent star formation or AGN activity. Based on the extended sizes of the blue-core regions we favour recent star formation. Comparison with the host cluster central entropies (and other X-ray properties) demonstrates that the source of cold gas required to fuel the recent activity in BCG cores is direct condensation from the rapidly cooling intra-cluster medium. We measure the giant-to-dwarf ratio (GDR) of red sequence galaxies in a sample of 97 clusters to constrain its evolution over the redshift range 0.05 < z < 0.55. We find that the GDR is evolving and can be parameterized by GDR=(0.88 +/- 0.15)z+(0.44 +/- 0.03). We find that the intrinsic scatter in this relation is consistent with zero, after accounting for measurement error, Poisson noise and contributions from large-scale structure. After correcting for cluster mass effects we investigate the evolution of the individual dwarf and giant populations in order to probe the source of the observed GDR evolution. Beyond z=0.25 the GDR evolution is driven by an increase in the number of dwarfs (consistent with interpretations from the literature), however, below z=0.2 the GDR evolution is caused by a significant reduction in the number of giants. We interpret this a evidence for a significant number of major mergers in the giant population at late times. This is supported by the relatively short dynamical friction timescales for these galaxies. We use velocity-broadened stellar template models to fit the optical spectra of 19 BCGs in order to measure their the line-of-sight component of their central velocity dispersions (sigma). The sigma values are combined with previous measurements of effective radii re and effective surface brightness <I>e to investigate the properties of the BCG fundamental plane. We measure a BCG fundamental plane parameterized by log( re )= alpha log( sigma ) + beta log( <I>e ) + gamma, with best fit parameters alpha = 1.24 +/- 0.08, beta = -0.80 +/- 0.1 and gamma = (0.3 +/- 2.0)x10-4. We constrain the intrinsic scatter in this relation to be deltaint = 0.066 +/- 0.010 in re, consistent with previous measures of the scatter in the fundamental plane for regular cluster ellipticals. Comparing the slope parameters (alpha, beta) of the BCG FP to those from previous studies of the FP for regular cluster ellipticals, we find that there is no conclusive evidence for curvature in the unified FP. We use the sigma measurements to estimate the BCG dynamical masses Mdyn. Comparing these estimates with mass proxies for the clusters (Tx, ng) we find that BCG mass is independent of cluster mass with Mdyn = (2.9 +/- 1.8)x1012 solar masses. / Graduate / 0606 / 0605 / bildfell@uvic.ca

This dissertation presents new Herschel observations at 70 micron, 160 micron, 250 micron, 350 micron, and 500 micron of the Perseus molecular cloud from the Herschel Gould Belt Survey. The Perseus molecular cloud is a nearby star-forming region consisting of seven main star-forming clumps. The Herschel observations are used to characterize and contrast the properties of these clumps, and to study their embedded core populations. First, we probed the exceptionally young clump, B1-E. Using complementary molecular line data, we demonstrate that B1-E is likely fragmenting into a first generation of dense cores in relative isolation. Such a core formation region has never been observed before. Second, we use complementary long wavelength observations at 850 micron to study the dust properties in the larger, more active B1 clump. We find that Herschel data alone cannot constrain well the dust properties of cold dust emission and that long wavelength observations are needed. Additionally, we find evidence of dust grain growth towards the dense cores in B1, where the dust emissivity index, beta, varies from the often assumed value of beta = 2. In the absence of long wavelength observations, however, assuming beta = 2 is preferable over measuring beta with the Herschel-only bands. Finally, we use the source extraction code, getsources, to identify the core populations within each clump from the Herschel data. In addition, we use complementary archival infrared observations to study their populations of young stellar objects (YSOs). We find that the more massive clumps have an excess of older stage YSOs, suggesting that these regions contracted first. Starless cores are typically associated with peaks in the column density, where those found towards regions of higher column density also have higher average densities and colder temperatures. Starless cores associated with a strong, local interstellar radiation field, however, have higher temperatures. We find that the clumps with the most prominent high column density tails also had the highest fractions of early-stage YSOs. This relation suggests that the quantity of high column density material corresponds to recent star formation activity. / Graduate / 0606

While the single core accretion model for low mass star formation is well developed, it cannot simply be extended into the high mass star formation regime where clustered star formation dominates. The study of intermediate-mass star formation should provide us with insights into how the process of star formation changes for high mass stars. In this thesis observations of H2O line emission from two intermediate-mass candidate Young Stellar Objects (YSOs) made using the HIFI instrument aboard the Herschel Space Observatory are presented. Modelling of molecular line emission using the radiative transfer code RATRAN is used to put constraints on kinematics and the abundance of water throughout the region by modelling the observed water lines after decomposing them into separate Gaussian components. The medium component of the 752 GHz line from Vela IRS 17 was modelled by using a turbulent velocity of 1.7 km s^-1 and an outer abundance of 6x10^-8. The narrow component of the 752 GHz line from Vela IRS 19 could be modelled using a turbulent velocity of 0.6 km s^-1 and an outer abundance of 6x 10^-8, while the medium component required an outer abundance of 4 x 10^-7 with a turbulent velocity of 2.5 km s^-1. The constraints on water abundance in these star-forming regions are to be used along with studies of water in low and high mass star-forming regions in the effort to improve our understanding of star formation across the entire stellar mass spectrum.

The Balloon-borne Large Aperture Submillimeter Telescope (BLAST) is a 1.8 meter Cassegrain telescope that operates in three bands (250, 350, and 500 μm), each with 30% bandwidth. The detection system is comprised of 280 silicon-nitride micromesh bolometers distributed on three focal plane arrays with 30”, 42”, and 60” FWHM (full width at half max) beam sizes, respectively. BLAST's goal is to study the evolutionary history and processes associated with star formation. Earth's atmosphere is opaque to submillimeter radiation and astronomical observations in this wavelength are best conducted at high altitudes. BLAST is designed to be flown above 99.5% of the atmosphere on a stratospheric balloon. BLAST has made three scientific flights and this thesis covers the last two. The second flight was made in 2006 from McMurdo, Antarctica and studied the evolutionary history and processes associated with star formation. For the third flight, BLAST was reconfigured as a polarimeter (BLAST-Pol) and was also launched from McMurdo in December 2010. BLAST-Pol's objective is to determine what role, if any, magnetic fields play in star formation. This thesis will describe the BLAST-Pol instrument and provide a summery of key observations made by the 2006 flight.

Thesis (Ph. D.)--University of Hawaii at Manoa, 1976. / Microfiche. / 294 leaves

Luminous Blue compact galaxies (BCGs) are metal-poor actively star-forming systems, characterised by bright ultraviolet and blue luminosities. Hubble Space Telescope high-resolution data have revealed that the luminous star-forming knots in these galaxies are composed of hundreds of young massive star clusters. In this work we present a systematic study of the star cluster populations in BCGs with important implications for the formation history of their host systems. The studied galaxies show recently increased star formation rates and a high fraction of massive clusters, probably as a result of minor/major merger events. The age distributions have a peak of cluster formation at only 3 - 4 Myr, unveiling a unique sample of clusters still partially embedded. A considerable fraction of clusters (30 - 50 %), mainly younger than 10 Myr, shows an observed flux excess between 0.8 and 2.2 μm. This so-called near-infrared (NIR) excess is impossible to reproduce even with the most recent spectral synthesis models (that include a self-consistent treatment of the photoionized gas). The origin of the NIR excess, which still remains unexplained, challenges our understanding of the cluster formation process under extreme conditions. The results achieved in this work have produced important insights into the cluster formation process in BCGs. We suggest that the BCG environment has most likely favoured the compression and collapse of giant molecular clouds into compact massive star clusters. The cluster formation efficiency (i.e., the fraction of star formation happening in star clusters) in BCGs is higher than the reported 8 - 10 %, for quiescent spirals and local star-forming galaxies. Luminous BCGs have a cluster formation efficiency comparable to luminous infrared galaxies and spiral starburst nuclei (the averaged value is  about 30 %), suggesting an important role of the merger event in the cluster formation. / At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 4: Accepted. Paper 5: Manuscript. Paper 6: Manuscript.

Data are the lifeblood of an organisation, being employed by virtually all business functions within a firm. Data management, therefore, is a critical process in prolonging the life of a company and determining the success of each of an organisation’s business functions. The last decade and a half has seen data warehousing rising in priority within corporate data management as it provides an effective supporting platform for decision support tools. A cross-sectional survey conducted by this research showed that data warehousing is starting to be used within organisations for their engineering asset management, however the industry uptake is slow and has much room for development and improvement. This conclusion is also evidenced by the lack of systematic scholarly research within asset management data warehousing as compared to data warehousing for other business areas. This research is motivated by the lack of dedicated research into asset management data warehousing and attempts to provide original contributions to the area, focussing on data modelling. Integration is a fundamental characteristic of a data warehouse and facilitates the analysis of data from multiple sources. While several integration models exist for asset management, these only cover select areas of asset management. This research presents a novel conceptual data warehousing data model that integrates the numerous asset management data areas. The comprehensive ethnographic modelling methodology involved a diverse set of inputs (including data model patterns, standards, information system data models, and business process models) that described asset management data. Used as an integrated data source, the conceptual data model was verified by more than 20 experts in asset management and validated against four case studies. A large section of asset management data are stored in a relational format due to the maturity and pervasiveness of relational database management systems. Data warehousing offers the alternative approach of structuring data in a dimensional format, which suggests increased data retrieval speeds in addition to reducing analysis complexity for end users. To investigate the benefits of moving asset management data from a relational to multidimensional format, this research presents an innovative relational vs. multidimensional model evaluation procedure. To undertake an equitable comparison, the compared multidimensional are derived from an asset management relational model and as such, this research presents an original multidimensional modelling derivation methodology for asset management relational models. Multidimensional models were derived from the relational models in the asset management data exchange standard, MIMOSA OSA-EAI. The multidimensional and relational models were compared through a series of queries. It was discovered that multidimensional schemas reduced the data size and subsequently data insertion time, decreased the complexity of query conceptualisation, and improved the query execution performance across a range of query types. To facilitate the quicker uptake of these data warehouse multidimensional models within organisations, an alternate modelling methodology was investigated. This research presents an innovative approach of using a case-based reasoning methodology for data warehouse schema design. Using unique case representation and indexing techniques, the system also uses a business vocabulary repository to augment case searching and adaptation. The system was validated through a case-study where multidimensional schema design speed and accuracy was measured. It was found that the case-based reasoning system provided a marginal benefit, with a greater benefits gained when confronted with more difficult scenarios.