<p>Double bars have been proposed as a means of transporting molecular gas past inner Lindblad resonances into the nuclear regions, where it can fuel active or starburst nuclei. Thus far, the existence of double bars has been determined by isophote twists seen in the near infrared, which could probe the bulge properties of these galaxies rather than the disk properties. We have observed two double bar galaxy candidates (NGC 2273 and NGC 5728) in 12 CO J = 1-0 with the Caltech Millimeter Array. Despite the similar near infrared images of the two galaxies, we see rather different nuclear morphologies in the CO maps. NGC 2273 shows evidence of a nuclear bar misaligned from the main stellar bar by ∼90°, and aligned with the near infrared isophote twists. NGC 5728 shows an arc of CO clumps that peaks just to the south-west of the dynamical center and curves to the south-east where it follows the dust lane to the south. The lack of a nuclear bar in the CO maps of NGC 5728 may be evidence that it is in a later stage of evolution. Bar dissolution may have just begun, and the gas has responded first, which may explain why we see a nuclear bar in the near infrared images of NGC 5728, but not in the CO maps. Models of these double barred galaxies show that the nuclear molecular morphology depends on the assumed gas properties. We have performed a multi-transition CO study of the nuclei of seven double barred galaxies that exhibit a variety of molecular gas morphologies in order to determine if the molecular gas properties are correlated with the nuclear structure and activity. We find that the 12 CO J = 3-2/J = 2-1 line ratio is lower in galaxies with molecular bars in the nucleus and higher in galaxies with CO emission dispersed around the galactic center. The galaxies without central concentration show signs of past star formation which may have exhausted, heated, and dispersed the molecular gas in the nucleus, resulting in the observed distributions and high CO line ratios. The multiline CO data corroborates our hypothesis that the galaxies with nuclear molecular bars are at an earlier stage of double barred galaxy evolution. In an attempt to detect other double barred galaxies that are bright enough in CO emission to be mapped at high resolution, we have undertaken a CO survey with the JCMT and NRAO 12-m of all double barred galaxies that are observable from the northern hemisphere. (Abstract shortened by UMI.)</p> / Doctor of Philosophy (PhD)

<p>I have used a recently commissioned, highly sensitive polarimeter at the James Clerk Maxwell Telescope to probe the magnetic field geometries of six star-forming regions within 500 pc of the Sun. For five of the regions, these are the first data produced of emission polarization from dust grains aligned by local magnetic fields. The variations in the polarization pattern across the clouds have been compared to predicted patterns from various models of magnetized molecular clouds. In several regions, particularly OMC-3 in the Orion A cloud, the polarization data are very consistent with predictions of a recently developed model of filamentary molecular clouds threaded by helical fields. The regions of NGC 2068 and LBS 23N could also contain helical magnetic field geometries. Although NGC 2024 is successfully modeled by a helical field, this geometry is not consistent with existing data of the line-of-sight magnetic field, which is not probed by polarization measurements. Instead, I suggest that the field geometry in NGC 2024 is that of an expanding ionization front from the associated HII region, bent around the dense ridge of star-forming cores. Prior to this work, most regions were thought to contain an ordered magnetic field component which was essentially unidirectional. Only one region in my sample contains a distribution of polarization vectors which could support such a geometry; in this cloud, Barnard 1, I have estimated the three-dimensional field strength and orientation associated with this "uniform" field and find a significant fraction of the field lies in the plane of the sky. This solution applies only to low column densities and not to the denser cores within Barnard 1, which do not exhibit alignment with the low density material. In short, this work reveals that unidirectional field geometries are not supported on intermediate scales within molecular clouds. Furthermore, no single magnetic field geometry is applicable in all molecular clouds; in each region, local environments and the associated physics must be taken into account.</p> / Doctor of Philosophy (PhD)

<p>Manganese is required by the human body, but as with many heavy elements, in large amounts it can be toxic, producing a neurological disorder similar to that of Parkinson's Disease. The primary industrial uses of the element are for the manufacturing of steel and alkali batteries. Environmental exposure may occur via drinking water or exhaust emissions from vehicles using gasoline with the manganese containing compound MMT as an antiknock agent (MMT has been approved for use in both Canada and the United States). Preclinical symptoms of toxicity have recently been detected in individuals occupationally exposed to airborne manganese at levels below the present threshold limit value set by the EPA. Evidence also suggests that early detection of manganese toxicity is crucial since once the symptoms have developed past a certain point, the syndrome will continue to progress even if manganese exposure ceases. The development of a system for in vivo neutron activation analysis (IVNAA) measurement of manganese levels was investigated, with the goal being to have a means of monitoring both over exposed and manganese deficient populations. The McMaster KN-accelerator was used to provide low-energy neutrons, activation within an irradiation site occurred via the 55 Mn(n,γ) 56 Mn capture reaction, and the 847 keV γ-rays emitted when 56 Mn decayed were measured using one or more Nal(TI) detectors. The present data regarding manganese metabolism and storage within the body are limited, and it is unclear what the optimal measurement site would be to provide a suitable biomarker of past exposure. Therefore the feasibility of IVNAA measurements in three sites was examined--the liver, brain and hand bones. Calibration curves were derived, minimum detectable limits determined and resulting doses calculated for each site (experimentally in the case of the liver and hand bones, and through computer simulations for the brain). Detailed analytical calculations of the 7 Li(p,n) 7 Be reaction, used to produce neutrons by the KN, were conducted to determine neutron spectral information, angular distributions and yields. These data were used as input for the transport code MCNP, and computer simulations of experimental conditions were performed. The simulations consistently overestimate experiment measurements by a constant factor, and possible reasons for this discrepancy are discussed. It has been concluded that IVNAA measurements of the brain would only provide limited information, however, measurement of both the liver and hand bone should be possible. It is recommended that preliminary in vivo measurements be pursued for the hand, as metabolic data suggest that bone may be a long term storage site for manganese.</p> / Doctor of Philosophy (PhD)

<p>In this work, a method to perform simultaneous scatter and attenuation correction for PET is developed within the context of statistical image reconstruction methods. The principles are demonstrated using both numerical simulations of artificially constructed scatter distributions and Monte Carlo studies of phantoms, showing the viability of this method in practice. In addition, a new transmission scan protocol is defined which is necessary to collect the required data in order to perform the corrections. The method has several distinct advantages over traditional filtered back-projection techniques. These include treating scatter and attenuation simultaneously so that a correction can be made during image reconstruction, leading to a one-step method; guaranteed non-negativity of the reconstructed pixel intensity values; predictable noise propagation; and improved counting performance by 65% resulting in an increased signal-to-noise ratio (on the order of 28%), achieved using non-windowed acquisition. Noise Equivalent Count rate analysis indicates that for a nominal clinical activity concentration of 37 kBq/cc (1 μCi/cc), a three-fold improvement in scanner performance can be realized for a standard acquisition window, compared to an uncorrected image and a five-fold improvement is achievable using an extended acquisition window.</p> / Doctor of Philosophy (PhD)

<p>Giant molecular clouds (GMCs) and cores, which are the sites of star formation in the Galaxy today, are supported against their own gravity and an external pressure by a combination of thermal and magnetic pressures, and by an internal turbulence which is characterized by gas velocity dispersions that increase outwards within a given cloud. Until now, however, models of isothermal spheres (in which velocity dispersion is independent of radius) have been used as the starting point for theories of star formation. Thus, this thesis presents a generalization of the classic Bonnor-Ebert stability analysis of pressure-bounded, self-gravitating spheres of isothermal gas, to include clouds with arbitrary equations of state (EOS). The results are applied to GMCs and cores in order to model their internal structure. It is found that the simplest EOS which is consistent with all the salient features of these clouds is a "pure logotrope," in which P/Pⅽ=1+A ln(ρ/ρc). Detailed comparisons with data are made to estimate the value of A, and an excellent fit to the observed dependence of velocity dispersion on radius in cores is obtained with A≃0.2. This phenomenological model is then used to construct a new theory for gravitational collapse and star formation in turbulent molecular gas. Points of similarity and contrast between this and the collapse of an isothermal sphere are discussed. In particular, it is found that the rate of mass accretion onto a protostar in a logotrope increases with time (as M∝ t³), rather than remaining constant as in an isothermal sphere. Low-mass stars therefore take longer to form than previously suspected, while high-mass stars form more rapidly. This result has implications for the interpretation of observations of young stellar objects (the so-called "Class 0" protostars are discussed explicitly), for the origin and form of the stellar initial mass function, and for the process of star formation in clusters.</p> <p>GMCs and cores are further characterized by a mass spectrum, N(m)=dN/dm, which scales roughly as m⁻¹⋅⁵ and is reminiscent of the distribution of globular cluster masses in the globular cluster systems (GCSs) observed around most galaxies. This suggests that star formation in protogalaxies may have followed the same basic pattern that it does today, i.e., that globular clusters formed in clumps of gas embedded in much larger (∼10⁸-10⁹M⨀) protogalactic fragments. Within this framework, the first theory of the GCS N(m) (which is directly related to the more frequently discussed globular cluster luminosity function, dN/dMᵥ) is developed here. A kinetic equation is formulated to statistically follow the collisional build-up and subsequent disruption (by the side-effects of internal massive-star formation) of protocluster clumps within a parent fragment, and solved for the mass spectrum which gives a detailed balance between the rates of these processes. This N(m) agrees well with observations of the Milky Way, M31, and M87 GCSs, for cluster masses in excess of ∼10⁵M⨀. In addition, the theory naturally accounts for observations which suggest that, at least at these high masses, N(m) is largely independent of galactocentric radius within any one GCS. The model makes specific predictions, regarding the lifetimes of cluster-forming cores, that should be applicable to present-day Galactic GMCs and cores as well.</p> / Doctor of Philosophy (PhD)

<p>In this thesis, we discuss a scheme for simulating the real time quantum quench dynamics of interacting quantum spin systems within the positive-P formalism. As model systems we study the transverse field Ising model as well as the Heisenberg model undergoing a quench away from the classical ferromagnetic ordered state. The connection to the positive-P formalism, as it is used in quantum optics, is established by mapping the spin operators on to Scwhwinger bosons. In doing so, the dynamics of the interacting quantum spin system is mapped onto a set of stochastic differential equations (SDEs) the number of which scales linearly with the number of spins, N, compared to an exact solution through diagonalization that in the case of the Heisenberg model would require matrices exponentially large in N. This mapping is exact and can be extended to higher dimensional interacting systems as well as to systems with an explicit coupling to the environment.</p> / Master of Science (MS)

<p>Astrophysical disks are found in many areas of astrophysics, from the protoplanetary disks in which planets are thought to be born, to the accretion disks around white dwarfs, merging stars, and black holes. The key to understanding these disks, is to understand how material overcomes the rotational support and acretes. 'Whatever mechanism is responsible must necessarily explain the transport of angular momentum outward.</p> <p>The current mechanism used to explain this is the magnetorotational instability (MRI). Its ability to transport angular momentum as well as drive a magnetic dynamo, will be discussed in this thesis. The linear equations of motion for a locally Cartesian patch will be solved numerically to get the time evolution of the magnetic and velocity fields. From these solutions, quadratic quantities in the perturbation variables will be calculated, namely the angular momentum and magnetic helicity. The time evolution of these quantities can tell us about the MRI's ability to both transport angular momentum and drive a dynamo through magnetic helicity.</p> <p>By solving the equations of motion in a locally Cartesian patch of a shearing disk, I have calculated the flux of angular momentum and magnetic helicity. The time evolution of these quantities shows that the ability to transport magnetic helicity is very similar the ability to transport angular momentum. This relation is true for a parameter space which corresponds to the asymptotic limit for the MRI.</p> / Master of Science (MS)

<p>In this thesis, we present an analysis of ten galaxy groups at z ~ 0.4 using spectroscopic data from the FORS2 instrument on the VLT. This study targets group member galaxies at magnitudes fainter than any previous study at this redshift. Our group sample comes from the Group Environment and Evolution Collaboration, which was originally based upon the second Canadian Network for Observational Cosmology redshift survey. Fifty-two new group members are identified, mostly within the apparent magnitude range of 21.25 < r < 23.25; this accounts for an approximate increase of 25 per cent in the membership of these groups. We combine these new data with previously obtained follow-up spectroscopy and an extensive set of multiwavelength data to compute composite group galaxy luminosity functions and red fractions. Results from the whole sample are compared with subsampIes defined by cuts in group velocity dispersion, radius, and absolute magnitude. Our results indicate that the group environment contains proportionately more bright galaxies than the field (but similar numbers of faint galaxies) and displays little evidence for strong evolution of the luminosity function upon a comparison with lower-redshift samples. In terms of colour, group galaxies are consistently redder than the field. However, there is a strong trend of decreasing red fraction toward fainter magnitudes, in which the group and field environment become statistically similar near the magnitude limit of our sample. The faintest galaxies in our sample are thus predominantly blue, and located in regions outside the virial radius as defined by <em>R₂₀₀</em>. Overall, our sample's colours follow a general trend of increasing group red fraction with decreasing redshift, as we show in a comparison with the literature.</p> / Master of Science (MS)

<p>¹⁰⁹Cd induced K-XRF has been used for in vivo lead measurement for about two decades. The improvement of this system has been emphasized recently due to the increasing understanding of the low level lead exposure. In this work, a cloverleaf detector system is used to improve the minimum detectable limit (MDL) for the in vivo measurement of lead in bone. This system consists of four 8mm radius detectors which are placed closely with a space of 2mm between neighboring ones. We measured some bare phantoms and phantoms in leg phantom which simulates the in vivo measurement and found that the MDL is greatly improved by using the cloverleaf system and a stronger source. The effect of the geometries is also discussed. An overall MDL ratio of about 0.278 is obtained by using the cloverleaf system compared to the conventional system for the in vivo measurement, which means a decreasing of MDL from about 10 micro g/(g bone mineral) to about 2.78 micro g/(g bone mineral).</p> <p>Two sets of phantoms also have been investigated due to the different calibration lines for these two sets of phantoms for the same lead measurement system. The results indicate that the compositions of these two sets of phantoms, which are supposedly the same, are greatly different. Since they were both made of "plaster of Paris", we can conclude that not all the plaster of Paris has the same composition. Hence the materials need to be measured before they are used to make the calibration phantoms.</p> / Master of Science (MS)

<p>Resolving the wide range of spatial scales simultaneously present in the formation of stars and star clusters is a challenge for numerical simulations. Methods such as adaptive hydrodynamics codes must be used in many gasdynamical simulations where gravity is also present, and constructs known as "sinks" are commonly used to avoid the computational expense of directly simulating the dense regions within protostars. Despite being essential to investigations of star formation over long timescales, numerics can often play an undesired role in the behaviour of these point-mass accretors, causing artificial accretion. In this thesis, the use of sink particles as models of protostars is investigated using the Gasoline <em>N</em>-body + smoothed particle hydrodynamics code. Motivated by observations of disks and accretion rates onto protostars, physical viscosity using the a-parametrization was implemented. Tests of both spherical and rotating protostellar accretion were performed. In spite of their importance to star formation) previously presented rotating tests are subject to several numerical problems; efforts were made in this work to simulate a three-dimensional viscous accretion disk where such issues were identified and minimized. Simulations were performed for varying strengths of viscosity and sink radius, as well as with inner boundary conditions known as "sinking" particles. Angular momentum transport was present and behaved physically in all cases with α > 0, and the average radial velocities and mass-accretion rates in the disks matched finite-difference estimates of corresponding analytic expressions.</p> / Master of Science (MS)