This thesis presents the initiation of a multi-site photometric programme to examine the extraordinary behaviour displayed by 18 R Coronae Borealis (RCB) stars in the Magellanic Clouds (MCs). RCB stars exhibit a unique variability whereby they undergo rapid declines of up to several magnitudes. The decline may take several weeks, whereas the recovery to maximum light may take months or even years. The accepted wisdom for the cause of these enigmatic declines is a phenomenon whereby dust formed in the stellar environment reduces the brightness by as much as eight magnitudes (Clayton 1996). This is followed by the recovery phase during which the dust becomes homogeneously distributed in the stellar environment. The monitoring programme comprised the collection of UBVRI photometric data using five telescopes located at three different southern hemisphere longitudes (Las Campanas Observatory in Chile, Mount John University Observatory (MJUO) in New Zealand and the Southern African Large Telescope (SALT) in South Africa). The Optical Gravitational Lensing Experiment (OGLE), that operates at Las Campanas Observatory, provided the longest extent of data (December 1994 to February 2008). This was supplemented by data collected with telescopes at MJUO (September 2007 to January 2008) and SALTICAM on SALT (October 2007 to February 2008). Data calibration across the five instruments was a key element of the analysis, and entailed the use of F116 (an F region standard star) and other tertiary standards. Two important RCB characteristics, the enigmatic declines and the pulsational variability, form the bulk of the analysis presented in this thesis. Examination of the data acquired in the V and I filters resulted in the identification of a total of 18 RCB declines occurring in four stars (three stars in the Large Magellanic Cloud (LMC) and one in the Small Magellanic Cloud (SMC)). Construction of colour-magnitude diagrams (V −I vs V ), during the recovery to maximum light were undertaken in order to study the unique colour behaviour associated with the RCB declines. The combined recovery slope for the four stars was determined to be [(delta V)/(delta(V −I))] = 3.37 ± 0.24, which is similar to the value of [(delta V)/(delta(V −I))] = 3.1 ± 0.1 calculated for galactic RCB stars (Skuljan et al. 2003). In addition, the slopes calculated for the stars in the LMC ([(delta V)/(delta(V −I))]LMC = 3.34 ± 0.21) and SMC ([(delta V)/(delta((V −I))]SMC = 3.21 ± 0.22) alone, also agree to within their uncertainty. These results may imply that the nature of the dust (i.e. the particle size) is similar in both our Galaxy and the MCs. The pulsation analysis focused on the identification of pulsation periods in nine RCB stars in the MCs. Two different methods, Fourier analysis and dominant period subtraction, were employed for this purpose. Periodic variations are apparent in these stars, and for the majority, a period of around 40 days (common in RCB stars, Lawson et al. 1990, 1994) was detected using the second identification method. In the future, frequent data collection over several years, and more sophisticated pulsation identification techniques, will increase the probability of extracting individual periods from the complex RCB light curves.

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The total luminosity of the Rho Ophiuchi molecular cloud is derived from IRAS data and is found to match the luminosity of known embedded sources very closely. High resolution 60 and 100 micron band IRAS images have been reduced to yield equilibrium color temperature maps and 60 micron band dust optical depth maps for the region. These data along with optically thin C18O column density data are used to evaluate dust grain sizes and compositions via competing grain models. Radiative modeling shows that a standard power law distribution of graphite and silicate grains is responsible for IRAS 60 and 100 micron band emissions. These grains are heated to about one tenth of the cloud's depth in the core region. Their optical depths closely follow molecular column density structure, but these grains are considerably colder than the molecular gas. We also find that a 10 nm minimum particle radius cutoff is appropriate for the 60 and 100 micron band emissions while very small grains or PAH molecules dominate the cloud's 12 and 25 micron band emissions.

We report the discovery of a stellar overdensity 8 degrees north of the centre of the Small Magellanic Cloud (SMC; Small Magellanic Cloud Northern Over-Density; SMCNOD), using data from the first 2 yr of the Dark Energy Survey (DES) and the first year of the MAGellanic SatelLITEs Survey (MagLiteS). The SMCNOD is indistinguishable in age, metallicity and distance from the nearby SMC stars, being primarily composed of intermediate-age stars (6 Gyr, Z=0.001), with a small fraction of young stars (1 Gyr, Z=0.01). The SMCNOD has an elongated shape with an ellipticity of 0.6 and a size of similar to 6 degrees x 2 degrees. It has an absolute magnitude of M-V congruent to -7.7, r(h) = 2.1 kpc, and mu v(r < r(h)) = 31.2 mag arcsec(-2). We estimate a stellar mass of similar to 10(5) M-circle dot, following a Kroupa mass function. The SMCNOD was probably removed from the SMC disc by tidal stripping, since it is located near the head of the Magellanic Stream, and the literature indicates likely recent Large Magellanic Cloud-SMC encounters. This scenario is supported by the lack of significant H-1 gas. Other potential scenarios for the SMCNOD origin are a transient overdensity within the SMC tidal radius or a primordial SMC satellite in advanced stage of disruption.

As-Is Building Information Models aid in the management, maintenance and renovation of existing buildings. However, most existing buildings do not have an accurate geometric depiction of their As-Is conditions. The process of generating As-Is models of existing structures involves practitioners, who manually convert Point Cloud Data (PCD) into semantically meaningful 3D models. This process requires a significant amount of manual effort and time. Previous research has been able to model objects by segmenting the point clouds into planes and classifying each one separately into classes, such as walls, floors and ceilings; this is insufficient for modelling, as BIM objects are comprised of multiple planes that form volumetric objects. This thesis introduces a novel method that focuses on the geometric creation of As-Is BIMs with enriched information. It tackles the problem by detecting objects, modelling them and enriching the model with spaces and object adjacencies from PCD. The first step of the proposed method detects objects by exploiting the relationships the segments should satisfy to be grouped into one object. It further proposes a method for detecting slabs with variations in height by finding local maxima in the point density. The second step models the geometry of walls and finally enriches the model with closed spaces encoded in the Industry Foundation Classes (IFC) standard. The method uses the point cloud density of detected walls to determine their width by projecting the wall into two directions and finding the edges with the highest density. It identifies adjacent walls by finding gaps or intersections between walls and exploits walls adjacency for correcting their boundaries, creating an accurate 3D geometry of the model. Finally, the method detects closed spaces by using a shortest-path algorithm. The method was tested on three original PCD which represent office floors. The method detects objects of class walls, floors and ceilings in PCD with an accuracy of approximately 96%. The precision and recall for the room detection were found to be 100%.

This study is mainly concentrated on examining the positive cloud-to-ground lightning activity associated with Mesoscale Convective Systems. Six MCS events which occurred during the O.K. PRE-STORM program in 1985 are studied. Data indicating the location and polarity of the cloud-to-ground lightning flashes from a lightning location network are analyzed in conjunction with the low-level echo patterns as obtained from radar. Spatial and temporal characteristics of positive cloud-to-ground flashes are identified from the data analysis. For all cases examined, positive cloud-to-ground flashes were found most commonly in the stratiform regions of the MCSs examined, and their frequency tended to peak during the later stages of the storm lifecycle. Two mechanisms responsible for the occurrence of positive cloud-to-ground lightning flashes with the above spatial and temporal characteristics are discussed. Based on the laboratory results, a 1-D charge generation model is developed. The model results show that in-situ charging is unlikely to be the dominant mechanism for charge generation in the stratiform region under normal atmospheric conditions. Sensitivity studies show, however, that in-situ charging processes strongly depend upon the liquid water, graupel and snow contents in the cloud. Under favorable atmospheric conditions, in-situ charging may lead to a significant charge generation. Hence, we cannot completely dismiss in-situ charging mechanism. Analysis of wind fields from dual-Doppler radar in combination with vertical profile of electric fields indicates that charge advection from the convective region to the stratiform region of MCSs may be a potential mechanism responsible for the occurrence of positive cloud-to-ground lightning flashes in the stratiform region. / Graduation date: 1989