Globular clusters are extreme stellar populations. They have the highest stellar density, and host both the oldest and most metal-poor stellar populations in the Galaxy. Their densities make them excellent testbeds for stellar dynamics, while the properties of their stars allows us to test our understanding of old and metal-poor stellar evolution. This thesis is comprised of three projects studying the two nearest globular clusters, NGC 6397 and Messier 4. By examining high-quality HST photometry of NGC 6397, we have constrained the binary fraction in both the central regions, and beyond the half-light radius. We find a binary fraction of ~0.05 in the core and ~0.015 in the outskirts. In the context of recent N-body simulations by Hurley et al., we interpret the observed binary fraction in the outer field as the primordial binary fraction. This value is lower than typically assumed, and has implications for cluster dynamics and N-body modeling. We report the discovery that young white dwarfs are dynamically hotter than their progenitors. Using the same photometry as mentioned above, and archival HST photometry of Messier 4, we have found that young white dwarfs have an extended radial distribution, and therefore a higher velocity dispersion, compared with older white dwarfs and their progenitors. This implies the existence of a ``natal kick''. Implications for cluster dynamics and stellar evolution are discussed. Finally, we present the spectra of 23 white dwarfs in Messier 4 obtained with the Keck/LRIS and Gemini/GMOS spectrographs. We find that all white dwarfs are of type DA. Assuming the same DA/DB ratio as is observed in the field, the chance of finding no DBs in our sample due to statistical fluctuations is 0.006. This suggests DB formation is suppressed in the cluster environment. Furthermore, we constrain the mass of these white dwarfs by fitting models to the spectral lines. Our best estimate of the masses of the white dwarfs currently forming in Messier 4 is 0.51+/-0.02 M_sun.This extends the empirical constraint on the initial-final mass relation over the entire range of initial masses that could have formed white dwarfs in a Hubble time.

It has become clear that the global star formation rate in the Universe has been decreasing since at least z~1, and blue, star-forming galaxies are transformed into red, passive galaxies through one or more processes. The origin of this decline and transformation remains unclear. The role environment plays in all this is especially uncertain. Despite the observed domination of a passive population in the cores of clusters, in contrast to the more actively star-forming field population, whether or not, and how environment affects the properties of galaxies when they fall into clusters is an unsettled question. In this thesis, we look into these issues by examining both the passive and star-forming galaxies, from the cores out to the infall regions, in a large sample of clusters at 0.15<z<0.36 we detected from the Canada-France-Hawaii Telescope Legacy Survey (CFHTLS). We find that in the cores of clusters, the red-sequence galaxies are a mixture of two populations, indicated by the inflexion in their luminosity function. There is no strong evolution in the shape of the red-sequence between z~0.4 and z~0.2; however, from z~0.2 to today, there is a rapid increase in the number of faint galaxies on the red-sequence relative to the bright ones, suggesting a rapid quenching of the faint galaxies in cluster cores within the last few billion years. At z~0.2, we find that the red fraction (star-forming fraction), at all stellar mass explored (9.0<log10(M*/M_solar)<11.5), shows no dependence on the distance from cluster centres, in the range 3<r<7Mpc; but within the inner 3 Mpc, we see a clear increase (decrease) in the red fraction (star-forming fraction). Also, for the lowest stellar mass galaxies, their red fraction has increased by a factor of 2 from z~0.3 to z~0.2 (over 1 Gyr), and yet we do not detect any difference between the star formation properties of the star-forming galaxies in clusters at all radii and that in the field. This suggests that for the low mass galaxies, it is likely that a mechanism that truncates star formation rapidly (within 1 Gyr) is at work. In the outskirts of the clusters, despite the low density contrast with the field, the red fraction is still higher than that in the field, suggesting that those galaxies have had their star formation quenched relative to the field population, supporting the pre-processing scenario.

Entre todas las ideas esparcidas por la Ciencia de la Computación en los últimos años, pocas han transformado el área de manera tan profunda como la computación paralela. Virtualmente todos los aspectos se vieron afectados, y se generó un gran número de conceptos nuevos. Desde la Arquitectura de Computadoras hasta los Sistemas Operativos, desde los Lenguajes de Programación y Compiladores hasta Bases de Datos e Inteligencia Artificial, y desde la Computación numérica hasta las Combinatorias, cada rama sufrió un renacimiento. / Tesis doctoral de la Facultad de Informática (UNLP). Grado alcanzado: Doctor en Ciencias Informáticas. Director de tesis: Guillermo Simari; co-director de tesis: Emilio Luque y Marcelo Naiouf.

(Abridged) Physical processes regulating star formation in satellite galaxies represent an area of ongoing research, but the projected nature of observed coordinates makes separating different populations of satellites (with different processes at work) difficult. The present-day phase space coordinates of a satellite galaxy carry information about its orbital history, which can then be compared to its star formation history (SFH). This is expected to reveal both a trigger time and timescale for environmental quenching. Finally, this can be related back to the physical process(es) regulating star formation in high density environments. We use merger trees from the MultiDark Run 1 N-body simulation to compile a catalogue of satellite orbits in cluster environments. We parameterize the orbital history by the time since crossing within 2.5 virial radii of the cluster centre and use our catalogue to estimate the probability density over a range of this parameter given a set of projected phase space coordinates. We show that different populations of satellite haloes occupy (semi-)distinct regions of (projected) phase space. We generalize this result by producing a probability distribution function (PDF) of possible infall times at every point in projected phase space. We apply our method to determining the infall time PDFs of a large sample of observed cluster satellite candidates from the Sloan Digital Sky Survey. We use galaxy colour as a proxy for SFH and model the distribution of satellite galaxy colours as two gaussian populations. We derive a Markov chain Monte-Carlo method to obtain the colour distribution as a function of the time since infall into the cluster environment. Our implementation of this method is still being tuned, but we use a second simpler (but much cruder) method to obtain an estimate of the evolution of the colour distribution. Our results are suggestive of a quenching process that begins within perhaps ±1 Gyr of virial radius crossing and which slows after pericentric passage. We stress that results obtained with this second method come with important caveats.

In efforts to coordinate carbohydrates to transition metal centres, the coordination of D-(+)-Glucosamine to ruthenium was performed. The product from this reaction was a vibrant blue substance that degraded in a characteristic fashion of blue to green to yellow, indistinguishable to that of the ruthenium coordination precursor “Ruthenium Blue”. The MALDI-ToF-MS spectra of the blue product and subsequent green and yellow degradation products showed the presence of a series of [RuxCly]- ruthenium chloride clusters. Structures of the clusters and their respective electronic excitations were determined using ab initio calculations. Calculations were performed using Density Functional Theory and the CIE1931 colour metric was used to process the electronic excitations into a physically perceived colour. The optimized structures that resulted from the ab initio calculations had the same physically perceived colour as the species found in the product, and thus could be another possibility into the composition of “Ruthenium Blue”.

High Performance Computing (HPC) is the key to solving many scientific, financial, and engineering problems. Computer clusters are now the dominant architecture for HPC. The scale of clusters, both in terms of processor per node and the number of nodes, is increasing rapidly, reaching petascales these days and soon to exascales. Inter-process communication plays a significant role in the overall performance of HPC applications. With the continuous enhancements in interconnection technologies and node architectures, the Message Passing Interface (MPI) needs to be improved to effectively utilize the modern technologies for higher performance. After providing a background, I present a deep analysis of the user level and MPI libraries over modern cluster interconnects: InfiniBand, iWARP Ethernet, and Myrinet. Using novel techniques, I assess characteristics such as overlap and communication progress ability, buffer reuse effect on latency, and multiple-connection scalability. The outcome highlights some of the inefficiencies that exist in the communication libraries. To improve communication progress and overlap in large message transfers, a method is proposed which uses speculative communication to overlap communication with computation in the MPI Rendezvous protocol. The results show up to 100% communication progress and more than 80% overlap ability over iWARP Ethernet. An adaptation mechanism is employed to avoid overhead on applications that do not benefit from the method due to their timing specifications. To reduce MPI communication latency, I have proposed a technique that exploits the application buffer reuse characteristics for small messages and eliminates the sender-side copy in both two-sided and one-sided MPI small message transfer protocols. The implementation over InfiniBand improves small message latency up to 20%. The implementation adaptively falls back to the current method if the application does not benefit from the proposed technique. Finally, to improve scalability of MPI applications on ultra-scale clusters, I have proposed an extension to the current iWARP standard. The extension improves performance and memory usage for large-scale clusters. The extension equips Ethernet with an efficient zero-copy, connection-less datagram transport. The software-level evaluation shows more than 40% performance benefits and 30% memory usage reduction for MPI applications on a 64-core cluster. / Thesis (Ph.D, Electrical & Computer Engineering) -- Queen's University, 2010-10-16 12:25:18.388

No description available.

We present the observations, reduction and preliminary analysis of a sample of 45 mid-to-high redshift galaxy clusters imaged with the Spitzer Space Telescope's MIPS camera at 24 ~m and selected from the Red Sequence Cluster Survey. The purpose of the data set is motivated by a broad review of studies into the evolutionary trends of galaxy clusters and their constituent galaxy populations, focusing specifically on recent results that indicate clusters are environmental drivers of dusty starburst and active galactic nuclei activity. To accommodate the large amount of data in hand, we have constructed an extensive data reduction pipeline for the MIPS data and describe its development and output in detail. Using the resulting catalogues for introductory analysis, we find strong evidence for an excess luminous infrared galaxy population in galaxy clusters at high redshift and discuss the implications of this discovery in terms of cluster evolution and motivate future work.

In this thesis, we utilise the framework of Bayesian statistics to discriminate between models of the cosmological mass function. We first review the cosmological model and the formation and distribution of galaxy clusters before formulating a statistic within the Bayesian framework, namely the Bayesian razor, that allows model testing of probability distributions. The Bayesian razor is used to discriminate between three popular mass functions, namely the Press-Schechter, Sheth-Tormen and normalisable Tinker models. With a small number of particles in the simulation, we find that the simpler model is preferred due to the Occam’s razor effect, but as the size of the simulation increases the more complex model, if taken to be the true model, is preferred. We establish criteria on the size of the simulation that is required to decisively favour a given model and investigate the dependence of the simulation size on the threshold mass for clusters, and prior probability distributions. Finally we outline how our method can be extended to consider more realistic N-body simulations or be applied to observational data. / Thesis (M.Sc.)-University of KwaZulu-Natal, Westville, 2010.

Influenza is a population health issue in Canada, with an annual infection rate of 10-25% of the population. The purpose of this thesis was to analyze influenza-like illnesses (ILI) from 2004-05 through to 2008-09, both spatially and temporally, throughout the province of Manitoba. The analysis used a framework specific to spatial analysis, and incorporated the principles of population health and ecological frameworks. The underlying objectives of the research were to better understand the patterns of ILI diagnoses as well as the characteristics of those diagnosed. Maps were created to show the results from various perspectives and negative binomial regression analysis was used to test which, if any, of the chosen variables were significant. Based on this research, one could conclude that although clusters of ILI do exist in Manitoba, a clear relationship does not exist between the determinants of health and ILI.