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In this dissertation, we consider the variable chaplygin gas (VCG) model as derived from the Tachyon gas model and search for a sub-class of models that provide an adequate fit to the cosmic microwave background (CMB) observations. We find that, for an appropriate choice of VCG parameters, up to ~ 80% of the VCG collapses into a gravitationally bound condensate which behaves as matter; the evolution of the remaining VCG, as governed by its equation of state, brings about accelerated expansion at late times. In light of this high collapsed fraction, we approximate the VCG transfer function with that of cold dark matter. We show that we can sufficiently describe the VCG cosmology from decoupling to today in terms of a model in which the gravitationally bound condensate plays the role of cold dark matter and the remaining VCG takes the place of dark energy in the concordance model. We then compute the CMB temperature anisotropy spectrum for a subset of VCG models and proceed to find a best-fit model to the WMAP-9yr data [46]. Our best-fit model has a x² per degrees of freedom of 2.03. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2013.

The motivation of this thesis is to look for a signature of Lorentz violation, hopefully observable, in the gravitational waves emitted by cosmic strings. Aspects of cosmic strings are reviewed, in particular how focused bursts of gravitational radiation are emitted when a cusp forms on the string. The same phenomenon is then studied in an effective field theory with Lorentz violation called Einstein-aether theory. This is a simple theory with a dynamic preferred frame, but it retains rotational and diffeomorphism invariance. The linearized version of the theory produces five wave modes. We study the usual transverse traceless modes which now have a wave speed that can be lower or greater than the speed of light. This altered speed produces distinctive features in the waves. They depend on two free parameters: roughly the wave speed and the acceleration of the string cusp. The profile of the wave is analyzed in detail for different values of the parameters and explained by close comparison with the string motion.

In studies of triaxial elliptical galaxies, one of the least observationally studied phenomena is figure rotation. Figure rotation has important consequences for the orbital structure and could explain the survival of steep nuclear cusps. For this project, we thus wish to investigate the possibility of measuring the figure rotation of an elliptical galaxy for which the geometry is approximately known using the Tremaine-Weinberg (TW) method. Originally meant for measuring the pattern speed of barred disk galaxies, we test the validity of the method using NGC 5266, a minor-axis dust-lane elliptical. In the process, the galaxy's line-of-sight velocity distribution (LOSVD) is measured along several slit positions. Measurements of the velocity v, velocity dispersion a, skewness /J3, and kurtosis h^ are derived using the Fourier Correlation Quotient method and a Gauss-Hermite series. This work represents the most detailed stellar kinematic measurements of NGC 5266 to date and confirm that it is one of the fastest rotating elliptical galaxies known today (Varnas et al. 1987). We find a maximum velocity of about 167 km s_1 at both a PA of 274° and 304°. This is compared to a maximum of 212 ± 7kms~1 at a PA of 287° found elsewhere (Varnas et al. 1987). The TW method yields significantly different values for the pattern speed. These vary between -19 and 22kms Wcsec"1. The discrepancy between the results casts doubt on the ability to straightforwardly apply the TW method to elliptical systems, but the study provides some insight into how the method may be more successfully implemented in the future. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2005.

Since 1950's there has been a growing interest of understanding the effects of cosmic ray radiation on the increase in average global temperature. Recent studies showed that galactic cosmic rays play a significant role in the formation of low cloud coverage and its consequent impact on the global temperature variation of the earth. A long-term measurement of the cosmic ray flux distribution at the surface of the earth has been established at Georgia State University. The current effort is focused on understanding the correlations between the cosmic ray particle flux distribution and the atmospheric and space weather measurements. In order to understand the observed atmospheric effects on cosmic ray flux, numerical simulations of cosmic muon and neutron flux variations at the surface of the earth have been carried out with varying air densities in the troposphere and stratosphere based on the Geant4 package. The simulation results show a remarkably good agreement with observations. The simulation results also show that the stratosphere air density variation dominates the effects on the muon flux changes while the density variation in the troposphere mainly influences the neutron count variation. This suggests that the long-term variation of muon flux could possibly direct us to a new path to understand the global climate warming trend.

The timescape cosmology represents a potentially viable alternative to the standard homogeneous and isotropic Friedmann--Lemaître--Robertson--Walker (FLRW) cosmology, without the need for dark energy. This thesis first extends the previous work on the timescape cosmology to include a radiation component in the evolution equations for the timescape cosmology and tests of the timescape model are then performed against the Cosmic Microwave Background (CMB) temperature anisotropies from the Planck satellite. Although average cosmic evolution in the timescape scenario only differs substantially from that of FLRW cosmologies at relatively late epochs when the contribution from the energy density of radiation is negligible, a full solution of the Buchert equations to incorporate radiation is necessary to smoothly match parameters to the epoch of photon decoupling and to obtain constraints from CMB data. Here we have extended the matter-dominated solution found in earlier work to include radiation, providing series solutions at early times and an efficient numerical integration strategy for generating the complete solution. To analyse the spectrum of CMB anisotropies in the timescape cosmology we exploit the fact that the timescape cosmology is extremely close to the standard cosmology at early epochs and adapt existing numerical codes to produce CMB anisotropy spectra. To find a FLRW model that matches as closely as possible the timescape expansion history, we have studied and compared a number of matching methods. We perform Markov Chain Monte Carlo analyses on the timescape model parameter space, and fit CMB multipoles 50 ≤ l ≤ 2500 to the Planck satellite data. Parameter fits include a dressed Hubble constant, H₀ = 61.0 kms ⁻¹Mpc⁻¹ (±1.3% stat)(±8% sys), and a present void volume fraction fᵥ₀ = 0.627 (±2.3% stat)(±13% sys). In the timescape model this value of fᵥ₀ means that the galaxy/wall observer infers an accelerating universe, where the apparent acceleration is due to gravitational energy gradients and clock rate differences rather than some dark energy. We find best fit likelihoods which are comparable to that of the best fit ΛCDM cosmology in the same multipole range.

In the 1930s, the Carnegie Institute in Washington DC initiated the construction of cosmic ray observation centres around the world. Cosmic ray activity was recorded using the model C cosmic ray ionization chamber which uses a Lindemann electrometer. Seven of these chambers were constructed at seven stations around the world. These chambers recorded cosmic ray data by projecting the shadow of the electrometer needle onto a continuously moving strip of 60 mm photographic paper. Hour markers were recorded by dimming the lamp for three minutes at the start of each hour, while also grounding the ionization chamber. By grounding the ionization chamber the electrometer needle was returned to the zero position. The photographic paper moved about 25 mm an hour. Approximately 114 station-years of data was recorded between 1935 and 1960 (Hardy, 2006). It is important to digitize these recordings in order to preserve the data for further study of cosmic rays from this time period. This digitization process consists of binarizing digital images of the photographic strip to extract the cosmic ray data. By binarizing these images the data is recorded in an easily usable format for future research. This study focuses on extraction of the cosmic ray data using an adaptive binarization method that is able to cope with a wide variety of images, ranging from images that are almost too bright to distinguish the data lines from the background, to images that are too dark to distinguish the data lines at all. This study starts off with a brief explanation of cosmic rays, how these were recorded before the 1950s and how the rays are recorded today. Two research methodologies were used to create a method to adaptively binarize and extract data from the historic cosmic ray recordings. A literature study of image processing techniques was conducted, focusing specifically on popular adaptive document binarization methods. During the experimental phase of this study, these methods or parts thereof were applied to the data to determine which techniques would give the most accurate results. Experimentation is the primary research methodology. The iterative experimental phase is discussed in detail as an algorithm is formed to successfully binarize and extract the historic cosmic ray data as well as the temperature of the electrometer while recording. The study concludes with an interpretation of the results obtained in the experimental phase. The success of the algorithm is measured by comparing the resulting data graph to the original. The conclusion of this study is that an adaptive method can be applied to historical recordings of cosmic ray activity to extract numerical data from a wide variety of images without any additional user input. / MSc (Computer Science), North-West University, Potchefstroom Campus, 2013

In the 1930s, the Carnegie Institute in Washington DC initiated the construction of cosmic ray observation centres around the world. Cosmic ray activity was recorded using the model C cosmic ray ionization chamber which uses a Lindemann electrometer. Seven of these chambers were constructed at seven stations around the world. These chambers recorded cosmic ray data by projecting the shadow of the electrometer needle onto a continuously moving strip of 60 mm photographic paper. Hour markers were recorded by dimming the lamp for three minutes at the start of each hour, while also grounding the ionization chamber. By grounding the ionization chamber the electrometer needle was returned to the zero position. The photographic paper moved about 25 mm an hour. Approximately 114 station-years of data was recorded between 1935 and 1960 (Hardy, 2006). It is important to digitize these recordings in order to preserve the data for further study of cosmic rays from this time period. This digitization process consists of binarizing digital images of the photographic strip to extract the cosmic ray data. By binarizing these images the data is recorded in an easily usable format for future research. This study focuses on extraction of the cosmic ray data using an adaptive binarization method that is able to cope with a wide variety of images, ranging from images that are almost too bright to distinguish the data lines from the background, to images that are too dark to distinguish the data lines at all. This study starts off with a brief explanation of cosmic rays, how these were recorded before the 1950s and how the rays are recorded today. Two research methodologies were used to create a method to adaptively binarize and extract data from the historic cosmic ray recordings. A literature study of image processing techniques was conducted, focusing specifically on popular adaptive document binarization methods. During the experimental phase of this study, these methods or parts thereof were applied to the data to determine which techniques would give the most accurate results. Experimentation is the primary research methodology. The iterative experimental phase is discussed in detail as an algorithm is formed to successfully binarize and extract the historic cosmic ray data as well as the temperature of the electrometer while recording. The study concludes with an interpretation of the results obtained in the experimental phase. The success of the algorithm is measured by comparing the resulting data graph to the original. The conclusion of this study is that an adaptive method can be applied to historical recordings of cosmic ray activity to extract numerical data from a wide variety of images without any additional user input. / MSc (Computer Science), North-West University, Potchefstroom Campus, 2013