The Cassini mission provided wonderful tools to explore Saturn, its satellites and its rings system. The UVIS instrument allowed stellar occultation observations of structures in the rings with the best resolution available (around 10 meters depending on geometry and navigation), bringing our understanding of the physics of the rings to the next level. In particular, we have been able to observe, dissect, model and test the interactions between the satellites and the rings. We first looked at kilometer-wide structures generated by resonances with satellites orbiting outside the main rings. The observation of structures in the C ring and their association with a few new resonances allowed us to estimate some constraints on the physical characteristics of the rings. However, most of our observed structures could not be explained with simple resonances with external satellites and some other mechanism has to be involved. We located four density waves associated with the Mimas 4:1, the Atlas 2:1, the Mimas 6:2 and the Pandora 4:2 Inner Lindblad Resonances and one bending wave excited by the Titan -1:0 Inner Vertical Resonance. We could estimate a range of surface mass density from 0.22 ([plus or minus]0.03) to 1.42 ([plus or minus]0.21) g cm[super-2] and mass extinction coefficient from 0.13 ([plus or minus]0.03) to 0.28 ([plus or minus]0.06) cm[super2] g[super-1]. These mass extinction coefficient values are higher than those found in the A ring (0.01 - 0.02 cm[super2] g[super-1]) and in the Cassini Division (0.07 - 0.12 cm[super2] g[super-1] from Colwell et al. (2009), implying smaller particle sizes in the C ring. We can therefore imagine that the particles composing these different rings have either different origins or that their size distributions are not primordial and have evolved differently.; Using numerical simulations for the propeller formation, we estimate that our observed moonlets belong to a population of bigger particles than the one we thought was composing the rings: Zebker et al. (1985) described the ring particles population as following a power-law size distribution with cumulative index around 1.75 in the Cassini Division and 2.1 in the C ring. We believe propeller boulders follow a power-law with a cumulative index of 0.6 in the C ring and 0.8 in the Cassini Division. The question of whether these boulders are young, ephemeral and accreted inside the Roche limit or long-lived and maybe formed outisde by fragmentation of a larger body before migrating inward in the disk, remains a mystery. Accretion and fragmentation process are not yet well constrained and we can hope that Cassini extended mission will still provide a lot of information about it.; We also estimate the mass of the C ring to be between 3.7 ([plus or minus]0.9) x 10[super16] kg and 7.9 ([plus or minus]2.0) x 10[super16] kg, equivalent to a moon of 28.0 ([plus or minus]2.3) km to 36.2 ([plus or minus]3.0) km radius (a little larger than Pan or Atlas) with a density comparable to the two moons (400 kg m[super-3]). From the wave damping length and the ring viscosity, we also estimate the vertical thickness of the C ring to be between 1.9 ([plus or minus]0.4) m and 5.6 ([plus or minus]1.4) m, which is consistent with the vertical thickness of the Cassini Division (2 - 20 m) from Tiscareno et al. (2007) and Colwell et al. (2009). Conducting similar analysis in the A, B rings and in the Cassini Division, we were able to estimate consistent masses with previous works for the these rings. We then investigated possible interactions between the rings and potential embedded satellites. Looking for satellite footprints, we estimated the possibility that some observed features in the Huygens Ringlet could be wakes of an embedded moon in the Huygens gap. We discredited the idea that these structures could actually be satellite wakes by estimating the possible position of such a satellite. Finally, we observed a whole population of narrow and clear holes in the C ring and the Cassini Division. Modeling these holes as depletion zones opened by the interaction of a moonlet inside the disk material (this signature is called a "propeller"), we could estimate a distribution of the meter-sized to house-sized objects in these rings. Similar objects, though an order of magnitude larger, have been visually identified in the A ring. In the C ring, we have signatures of boulders which sizes are estimated between 1.5 and 14.5 m, whereas similar measures in the Cassini Division provide moonlet sizes between 0.36 and 58.1 m.

I carried out systematic studies on the assembly history of dark matter halos, using numerical simulations and semi-analytical methods. First, I look into dark halo mass assembly history. I confirmed that the halo mass assembly is divided into a fast accretion phase and a slow accretion phase. These two phases are found to be separated by the epoch when the dark halo potential reaches its maximum. The fast accretion phase is dominated by mergers, especially major mergers; the slow accretion phase is dominated by slow mass accretion. Each halo experiences about 3±2 major mergers since its main progenitor had a mass equal to 1 percent of halo mass. However, the average redshift at which these major mergers occur is strongly mass dependent. Secondly, I investigate the formation times and the assembly bias of dark halos. I use eight different definitions of halo formation times to characterize the different aspects of the halo assembly history. I find that these formation times have different dependence on halo mass. While some formation times characterize well the hierarchical nature of halo formation, the trend is reversed for other definitions of the formation time. In addition, the formation-time dependence of halo bias is quite strong for some definitions of formation time but weak or absent for others. Thirdly, I study sub-halo mass function in the halo assembly history, with the generally known unevolved sub-halo mass functions (USMFs). I find that for subhalos that merge into the main progenitor of a present-day halo, their USMF can be well described by a universal functional form; the same conclusion can also be reached for the USMF of all sub-halos that have merged during the entire halo merging history. In these two cases, the USMFs do not seem to depend on the redshift of the host halo either. However, due to the mass loss caused by dynamical effects, only small part of the accreted halos survived and became sub-structures in the present-day dark halos. In the cluster-sized halos, 30% survived sub-halos are sub-subhalos. The sub-halo mass function at given accretion time (redshift) is also investigated to find the origin of the statistics mentioned above.

The Almahata Sitta meteorites produced from the breakup of 2008 TC3 were highly unusual, as the stones contained various meteorite types, with stones spanning almost every meteorite petrologic type. This was considered a remarkable event at the time since meteorites of different types had never been found among the same fall before. However, new discoveries of exogenous material on (4) Vesta, (101955) Bennu, and (162173) Ryugu in subsequent years imply that this event may be more common than initially thought. This is unexpected due to the high average collisional velocity in the asteroid belt of ~5 km/s. High velocity impacts are more likely to have low impact retention efficiencies, which lowers the likelihood of xenoliths surviving the collision. Our understanding of this material and the mechanisms by which it is delivered can give insights into the dynamic histories of these asteroids and even the greater dynamic history of the asteroid belt.

Most small asteroids are defined as "rubble-piles," or bodies with zero tensile strength and large bulk porosity that are tenuously held together by cohesive forces. Improving the accuracy of predictions of asteroid strengths requires suitable laboratory measurements of relevant materials, as well as increasing the availability of materials from sample return. In this work, we use Atomic Force Microscopy (AFM) force measurements and particle characterization to characterize, evaluate, and decouple variables that affect cohesive forces that act between micron-sized grains. In our first investigation we explored interactions of JSC-1 lunar simulant grains using three sample sizes, three spherical AFM tip diameters, and varying relative humidity, observing that the results are very dependent on the RH and, by proxy, adsorbed water. We observed weaker adhesion with larger grain/tip size, which can be attributed to the changing contact area between the samples and the tips. We next performed experiments in vacuum conditions and characterized the cohesive values of a high-fidelity CI simulant (Exolith) based on the CI1 meteorite Orgueil. Our results show no significant trend in adhesion, but we do observe that some correlating characteristics of the grains, such as roughness, can dominate the work of adhesion. The chemical nature of the grains, including their affinity for water, also played a role in if they became more adhesive in vacuum conditions or less adhesive in vacuum conditions. Our studies decouple several factors that contribute to the complex physics of adhesion and even more complex idea of understanding adhesion in a space environment with irregularly shaped grains. This approach will pave the way to a better understanding of regolith surface properties, improve contact models for irregularly shaped particles, and provide suitable inputs for models of asteroid cohesion. This analysis technique can be used on future materials provided by sample return missions.

Astronomy is becoming a forgotten science, which is evident by its relatively low enrollment figures compared to biology, chemistry, and physics. A portable inflatable planetarium brings relevance back to astronomy and offers support to students and educators by simulating realistic astronomical environments. This study sought to determine if learning is improved in an inflatable planetarium by adhering to the design principles of the cognitive theory of multimedia learning (CTML), specifically the coherence principle, in an authentic classroom. Two groups of 5th grade students of similar ability were purposefully assigned using a 1-teacher-to-many-students format with mean lesson lengths of 34 minutes. The experimental group was differentiated with seductive details, defined as interesting but irrelevant facts that can distract learning. The control group ( n = 28), with seductive details excluded, outperformed the experimental group (n = 28), validating the coherence principle and producing a Cohen's effect size of medium practical significance (d = 0.4). These findings suggest that CTML, when applied to planetarium instruction, does increase student learning and that seductive details do have a negative effect on learning. An adult training project was created to instruct educators on the benefits of CTML in astronomy education. This study leads to positive social change by highlighting astronomy education while providing educators with design principles of CTML in authentic settings to maximize learning, aid in the creation of digital media (astronomical simulations/instructional lessons for planetariums) and provide valuable training for owners of inflatable planetariums with the eventual goal of increasing student enrollment of astronomy courses at the local level.

The Sextant in its earliest known form consisted of divided circles and compasses with simply sights. An early Creek astronomer of the second century after Christ, Claudius Ptolemaeus, or more commonly called Ptolemy, wrote a book entitled Megale Syntaxis tes Astron- omias, also known by the Arabic title Almagest. The instrument described in this book was called the Astrolable and was used to measure the angular distance between stars. It was made of two concentric vertical circles, the largest and outer circle was about sixteen inches in diameter with graduated arc; the central ring was movable and carried the two sights.

<p>This thesis comprises studies on two ferromagnetic superconductors, URhGe (Tcurie=9.SK and Tsc=2S0mK) and UCoGe (Tcurie=2.SK and Tsc=800mK). These properties are interesting because the current theory to explain superconductivity predicts that ferromagnetism should destroy superconductivity. Not only is that not true in these materials, but ferromagnetism and superconductivity are thought to arise from a common mechanism. The studies conducted on these materials arise from that possibility, in an attempt to understand the unconventional nature of these materials.<br />Original work is contained in chapters 4, Sand 6. All of this work is currently not published in sources other than this thesis. <br /> Chapter 1 will give an introduction to these materials, and the work that has been done on them by other groups, and work done on related materials. <br /> Chapter 2 will give details of the various experimental methods used in measuring the structure and properties of the materials studied. This work was conducted by the author at McMaster University, with the assistance of individuals from the Brockhouse Institute for Materials Research, and the Center for Electron Microscopy at McMaster University.<br /> Chapter 3 will provide an introduction to the technique of muon Spin Resonance/Relaxation (μSR). This work was done at the TRIUMF facility in Vancouver, British Columbia, with the assistance of several TRIUMF staff. The data was collected by the author, and other members of Dr. Luke's research group as well as collaborators from TRlUMF and from Columbia University. <br /> Chapter 4 will present the measurements made on UCoGe, while Chapter 5 presents the measurements of URhGe. Details of the crystal growth and structure characterization measurements are included in these chapters, along with resistivity, bulk magnetization and μSR measurements. <br /> Both zero- field (ZF) and transverse field (TF) μSR has been performed. This work focuses on studying the magnetic moment size, and the magnetic volume fraction around the ferromagnetic transition, and to temperatures as low as 20mK. Consideration is also given to the magnetic and superconducting properties in the low-temperature region. <br /> In the Introduction, URhGe is presented first, followed by UCoGe, since this was the order in which they were discovered. The results obtained from UCoGe are presented first, since work on that compound was started before the work on URhGe. <br /> Chapter 6 focuses on the conclusions drawn from this work, comparing the measurements of both materials.</p> / Master of Science (MS)

<p>We present a numerical study of gas accretion into galaxies using the SPH code, Gasoline. Numerical tests on shock treatment in Gasoline are run to evaluate how well cosmological-scale, high Mach number shocks are treated. We find that shock solutions are far too noisy, and in specific density and metallicity regimes, this seeds a phase separation instability of hot and cold gas. We propose this instability as the source of cold blobs seen in many numerical simulations. We find that improved shock behavior is primarily attained through increased viscosity parameters. Analysis is also performed on four cosmological simulations from the McMaster Unbiased Galaxy Simulations (MUGS) (Stinson et al. 2010). In agreement with recent literature, we find cold flows of gas seeded by dark matter filaments stretching far into the inner galaxy in all analyzed galaxies. Tracking of star and gas particles is performed, and we find that cold mode accretion makes up between 40% and 60% of total gas accretion. As well, we find that cold gas is in general very quickly formed into stars, and that between 40% and 70% of total star mass comes from cold gas accretion.</p> / Master of Science (MSc)

<p>I investigate the interstellar medium (ISM) of two nearby, resolved galaxies, M51 (NGC 5194) and Centaurus A (Cen A; NGC 5128) using spectroscopic and photometric data from the <em>Herschel Space Observatory</em> to search for local variations of the characteristics of the ISM. I find that the average characteristics of the ISM in Cen A, a giant elliptical galaxy, are similar to those typically found in normal star forming galaxies, despite its unique morphology and classification as a radio galaxy with an active galactic nucleus (AGN). Using <em>Herschel</em> photometry I find radial trends in the dust temperature, the dust mass, and unexpectedly, the gas-to-dust mass ratio. I hypothesise that the AGN is removing nearby dust grains via dust sputtering or expulsion via jets. A comparison of Herschel spectroscopy of important cooling lines to a photon dominated region (PDR) model reveals the strength of the far-ultraviolet radiation field, <em>G</em>₀, and the hydrogen gas density, <em>n</em>, in the PDR gas within Cen A are consistent with values found in other nearby galaxies. I do not observe any obvious radial trend in these characteristics and conclude that the high inclination of Cen A may be inhibiting the identification of any impact the AGN is having on the surrounding gas.</p> <p>An investigation of the gas in M51 using a similar spectroscopic dataset as with Cen A shows for the first time that a large fraction of the observed [C II](158 μm) emission in the centre of M51 originates in diffuse ionised gas. This fraction falls off with radius out to the arm and interarm regions. I also find via PDR modelling that there is a decreasing radial trend in the values of <em>G</em>₀ and <em>n</em>, and that in the arm and interarm regions they are the same. Thus, there appears to be no difference in the physical properties of the molecular clouds in the arm and interarm regions of the galaxy. The results of this thesis contribute to further understanding the characteristics of the ISM of nearby galaxies, as well as the evolution of the ISM in galaxies containing an AGN.</p> / Doctor of Philosophy (PhD)

<p>In this thesis we present a procedure by which synthetic photometry of a hydrodynamic model of star or star-like object can be calculated in a regime where the photosphere is not radially resolved. In order to properly model the unresolved photosphere, we present a method where pressure and density are integrated outward from the outermost resolved radius of the star and then interpolated in temperature-surface gravity space between a set of MARCS \citep{Gustafsson2008a} stellar atmosphere models. These interpolations are accurate to within 10\% of expected temperature values and are determined by minimizing the difference between the integrated pressure, density and surface gravity and that of the atmosphere model. Using the Monte Carlo Radiative Transfer code \texttt{radmc3d}\citep{Dullemond2012}, we produce blackbody spectra of stars and photometric light curves of equal and unequal mass detached binaries and a contact binary. Stellar blackbody spectra are accurate to better than 1\%. Resultant light curves have less scatter than existing methods, such as \texttt{shellspec}\citep{Budaj2004} and show the expected morphology. Our method allows for imaging directly from hydrodynamic simulations, with minimal user set-up. This procedure is designed with the intent of producing simulated photometry of stellar merger models.</p> / Master of Science (MSc)