Browsing by Author "Lawler, Samantha"

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Open Access
Analysis of Removing Weak Associations During Consensus Clustering
(Faculty of Graduate Studies and Research, University of Regina, 2020-08) Naran Chirakkal, Ruckiya Sinorina; Zilles, Sandra; Hamilton, Howard; Lawler, Samantha
Given multiple base clusterings of a dataset, e.g., as created by multiple clustering algorithms on the same data, consensus clustering aims to generate a single robust aggregated clustering. Consensus methods measure the strength of an association between two data objects based on how often the objects are grouped together by the base clusterings. However, incorporating weak associations in the consensus process can have a negative e ect on the quality of the aggregated clustering. This thesis presents our research on an automatic approach for removing weak associations during the consensus process. In particular, we propose an e cient approach called the WAT approach for removing weak associations, and two methods using the WAT approach, namely WAT(K) and WAT(GMM), are tested in this thesis. We compare our methods to a brute force method used in an existing consensus function, NegMM, which tends to be rather inefficient in terms of runtime. Our empirical analysis on multiple datasets shows that the proposed approach produces consensus clusterings that are comparable in quality to the ones produced by the original NegMM method, yet at a much lower run time. Moreover, this thesis also presents an empirical analysis to study the effect of our approach to remove the weak associations on the CSPA and MCLA consensus functions, which are well-known consensus functions from the literature. Our WAT approach improved the consensus built by CSPA significantly in many cases, but the original MCLA tends to outperform the combination of MCLA with the WAT methods.
Open Access
Development of scintillator-based components for the photosensor system for the Intermediate Water Cherenkov Detector of the Hyper-K experiment and for the time of flight system of the Water Cherenkov Test Experiment
(Faculty of Graduate Studies and Research, University of Regina, 2024-05) Koerich, Luan Vinicius; Barbi, Mauricio; Kolev, Nikolay; Huber, Garth; Lawler, Samantha; Zilles, Sandra; Filho, Hélio da Motta
The existence of the neutrino flavour oscillation phenomenon carries a potential CP-violation phase, 𝛿CP, that might be the answer to the matter-antimatter asymmetry question in the Universe. With a new far detector and upgraded components of the successful Tokai-to- Kamioka (T2K) experiment, the long-baseline aspect of the Hyper-Kamiokande (Hyper-K) experiment will utilize an upgraded neutrino beam from the Japan Proton Accelerator Research Complex (J-PARC). The measurement of 𝛿CP from 𝜈𝜇 and ¯ 𝜈𝜇 disappearance modes will be dominated by systematic uncertainties. To reduce these uncertainties to discovery-level precision, an Intermediate Water Cherenkov Detector (IWCD) is introduced at a distance of 1 km from the beam source to intercept the neutrino beam at a span of off-axis angles and energies. This detector will feature high granularity, directionality, and time response through the use of a multi-photomultiplier tube (mPMT) photo-detection system. In this thesis I discuss the research and development (R&D) of scintillator-based detectors for the mPMT system on two main fronts: an internal hit detector for the mPMT system and a time-of-flight detector for particle monitoring and identification in tests of an IWCD prototype, the Water Cherenkov Test Experiment. Both detectors aim to contribute to the reduction of systematic uncertainties in Hyper-K’s attempt to discover 𝛿CP in the lepton sector of the Standard Model.. Keywords: Neutrino oscillation, Hyper-Kamiokande, Intermediate Water Cherenkov Detector, multiPMT, leptonic CP-violation phase, scintillator, time-of-flight detector.
Open Access
An Investigation into Seeding the Solar System Via Terrestrial Meteorites
(Faculty of Graduate Studies and Research, University of Regina, 2021-01) Comte, Mark Robert; Beech, Martin; Mobed, Nader; Lawler, Samantha; Robbins, Leslie
An investigation into whether terrestrial meteorites could seed the solar system is the main purpose of this thesis. An estimate for the minimum amount of terrestrial material that finds its way into interplanetary space over the past 550 million years is made. From the characteristics of known terrestrial impact craters, it is found that at least 1013 kg of material, potentially containing microorganisms, has been ejected from the Earth’s surface into the inner solar system. This estimate is derived upon a reverseengineering approach which links the observed crater diameter to impactor size and then through a set of analytic equations to obtain an estimate of the mass fraction of material ejected, with a speed greater than the Earth’s escape velocity, during the crater-forming process. It is found that some, 67% of the ejected material, is attributed to the formation of the Chicxulub, the largest known crater produced within the Phanerozoic eon. The conditions under which terrestrial, impact-derived ejecta can be launched into cis-lunar and Martian space is also determined. A numerical code was developed in order to follow the ablation and deceleration conditions that the ejected material undergoes as it is ejected from Earth’s surface and travels outwards through the atmosphere. The deceleration caused from Earth’s atmosphere results in a filtering effect with multi-meter sized fragments, some 5 to 20 meters across, being favored in escaping from the planet. Smaller fragments tend to be rapidly decelerated more than larger ones and are re-accreted by the Earth. The larger fragments being in favor of escaping assists in terrestrial meteorites seeding the solar system, as they can shield potential microbes within them from the extreme temperatures, desiccation, and UV radiation found in space. It was determined that a typical asteroid / short-period comet encounter speed of 25 to 28 km/s could produce a terrestrial crater capable of producing ejecta that could, in principle, find its way into orbits that intercept the Moon as well as those of the planets from Mercury out to Jupiter. The conditions under which Earth-ejected material might impact upon the Moon and Mars is also considered. It was found that for encounter speeds smaller than 9 km/s terrestrial meteorites could potentially survive impact, that is they did not undergo shock melting, with the lunar surface. For a Martian impact encounter speeds smaller than 6 km/s would allow for terrestrial meteorites to possibly survive. It is argued that terrestrial meteorites may well survive, with identifiable features such as fusion crust and mineralogy, for long periods of time within the lunar regolith and Martian surface to hopefully be discovered in the future. For the lunar case, a result recently vindicated it through the discovery of terrestrial material, launched during the late heavy bombardment, that was contained within a lunar impact breccia #14321 collected during the Apollo 14 Moon landing mission.
Open Access
Tales from the End of the Earth: An Antarctica and Arctic Symposium
(University of Regina Library, 2024-03-06) Keough, Pat; Keough, Rosemarie; French, Lindsey; Horowitz, Risa; Lawler, Samantha; McManus, Karla