<p>Exposure to lead is associated with a variety of detrimental health effects. After ingestion or inhalation, lead may be taken up from the bloodstream and retained by bone tissue. X-ray fluorescence was used to make in vivo measurements of bone lead concentration at the tibia calcaneus for 367 active and 14 retired lead smelter workers. Blood lead levels following a labour disruption were used in conjunction with bone lead readings to examine the endogenous release of lead from bone. Relations between bone lead and a cumulative blood lead index differed depending on time of hiring. This suggests that the transfer of lead from blood to bone has changed over time, possibly as a result of varying exposure conditions. A common polymorphism in the δ-aminolevulinate dehydratase (ALAD) enzyme may influence the distribution of lead in humans. Blood lead levels were higher for smelter workers expressing the more rare ALAD² allele. Bone lead concentrations, however, were not significantly different. This implies that a smaller proportion of lead in blood is distributed to tissue for individuals expressing the ALAD² allele. The O'Flaherty physiological model of lead metabolism was modified slightly and tested with input from the personal exposure histories of smelter workers. The model results were consistent with observation in terms of endogenous exposure to lead and accumulation of lead in cortical bone. Modelling the calcaneus as a trabecular bone site did not reproduce observed trends. Variations in lead metabolism between different trabecular sites may therefore be significant. The model does not incorporate a genetic component, and its output did not reflect observed differences in this respect. This result provides further support for the influence of the ALAD polymorphism on lead metabolism. Experimental trials with a digital spectrometer revealed superior energy resolution and count throughput relative to the conventional x-ray fluorescence system. The associated reduction in the uncertainty of lead measurement has the potential to benefit future surveys and modelling efforts.</p> / Doctor of Philosophy (PhD)

<p>1859 radial velocities (median precision ≃ 1 km s⁻¹) have been measured for 1318 stars in the direction of the Galactic globular cluster NGC 3201. Since the systemic radial velocity for NGC 3201 is 494.2 km s⁻¹, the field and cluster samples separate unambiguously into two distinct samples. Analysis of the radial velocities and APM/CCD photometry for the 879 field stars in our sample has revealed the presence of a probable moving group of ~ 13 stars with radial velocity 75 km s⁻¹ at a distance of 6 - 12 kpc. For the cluster members, we have multiple velocities for 279 stars (known photometric variables excluded) spread over a maximum of six years. Comparison of the observed velocities to simulated datasets containing known numbers of binaries has yielded upper limits to the true binary fraction (for binaries with 0.1 ≤ P ≤ 5 - 10 years and mass ratios in the range 0.1-1.0) of 0.06-0.10 (circular orbits) and 0.15-0.18 (eccentric orbits), consistent with the corresponding incidence among nearby solar-type stars and among a sample of six other Galactic globular clusters with measured binary fractions. NGC 3201 appears to be rotating with an apparent projected rotation amplitude of 1.22±0.25 km s⁻¹. The observed increase in ostensible rotation amplitude with distance from the cluster core may, however, be due to either the projection of the cluster space velocity onto the plane of the sky, or the preferential stripping of stars on prograde orbits near the limiting radius due to the disk-shocking instability identified by Oh and Lin (1992). BV CCD images have been used to derive cluster surface brightness profiles which extend out to ≃ 18. These profiles and the 399 mean radial velocities for nonvariable cluster members have been analysed using both single- and multi-mass King-Michie models and nonparametric techniques. Both methods suggest that the cluster mass-to-light ratio is relatively flat in the range 1.5 - 10 pc: M/Ls ≃ M/Lv = 2.0±0.2 in solar units. The best-fit mass function has a spectral index of x ≃ 0.75 ± 0.25, consistent with recent findings that the form of the mass function depends on the position relative to the potential of the Galaxy.</p> / Doctor of Philosophy (PhD)

<p>The dynamics of three populous Large Magellanic Cloud (LMC) star clusters NGC 1866, NGC 1978, and NGC 1850, have been examined using a combination of BV charge-coupled device (CCD) images and high-precision radial velocities of individual member stars.</p> <p>NGC 1866.</p> <p>V-band CCD images of the young LMC cluster NGC 1866 out to a projected radius R ~ 100 pc were obtained using the 1.0m telescope at Las Campanas. The luminosity profile is described by a power-law. The total cluster luminosity is LV∞ = 6.5 ± 0.3 × 10⁵ L. In the region 4 ≤ R (pc) ≤ 12, the cluster has a mean ellipticity of ε = 0.17 ± 0.06 and a minor axis position angle α = 125° ± 5°. NGC 1866 has a systemic velocity of Vαve = 301.2 ± 1.0 km s⁻⁻¹ and is rotating around an axis at a position angle of 100±25° with a peak velocity of 1.3 ± 0.5 km s⁻¹. The best estimate for the average slope of the mass function is x = 1.3 ± 0.15 (r = 2.0 x 10⁸ years). NGC 1978. BC CCD images of the elliptical LMC cluster NGC 1978 out to a projected radius R ~ 100 pc were obtained using the 1.0m telescope. After star-subtraction and median-filtering the ellipticity of the surface brightness distribution was determined to be ε = 0.30 ± 0.03 and the major axis position angle to be PA = 152 ± 7°. Single and multi-mass anisotropic King-Michie models and single-mass rotating and non-rotating oblate spheroid models were fitted to both the surface luminosity profiles and the radial velocity data. The total cluster luminosity is Lʙ = 3.1-3.7 ± 0.2x10⁵ Lʙ⊙ and Lv = 3.0-3.5 ± 0.2x10⁵ Lv⊙. The single-mass models tended to give better agreement with the luminosity profiles. We found no significant differences between the M/L's derived with oblate spheroid models and those derived with spherical models. NGC 1850. In this thesis we have examined the age and internal dynamics of the young binary LMC cluster NGC 1850. Isochrone fits to a BV color-magnitude diagram revealed that the primary cluster has an age of τ = 90 ± 30 Myr. The total cluster luminosity varied from Lʙ = 2.60-2.65x10⁶ Lʙ⊙ and Lv = 1.25-1.35x10⁶. Of the 52 stars with echelle spectra, a subset of 36 were used to study the cluster dynamics. Values for the slope of the mass function were determined using the derived M/L, theoretical mass-luminosity relationships, and several forms for the IMF. (Abstract shortened by UMI.)</p> / Doctor of Philosophy (PhD)

<p>This thesis presents a series of magnetohydrodynamic (MHD) simulations which<br />were designed to study the origin and evolution of astrophysical jets (galactic and<br />extra-galactic). \Ve developed and extended a version of the ZEUS-2D code which<br />served as the numerical basis of our simulations and attached to it a complete analysis<br />package that was developed in order to make contact with the theory and observations<br />of jets.</p> <p>With our version of the code, we managed to establish an initial state which<br />consists of an accretion disk and its cold corona in stable eqailibrium around a central object.<br />No softening paranleter was used to model the Newtonian gravitational<br />potential of the central object. The corona and accretion disk are initially in pressure<br />balance with one another. These initial states were constructed so as to be<br />numerically stable. The corona is Inagnetized with the magmetic field lines extending<br />smoothly into the disk without kinks or discontinuities, avoiding, in this way, any<br />undesired currents in the initial set up. The disk is set in Kepler rotation and gas is<br />continuously injected into the corona above at the very snlalll speed of 10⁻³ times the<br />Kepler velocity.</p> <p>In this thesis, we only considered magnetic configurations for which the Lorentz<br />force is initially zero (J x B = 0). In particular initial J = 0 configurations are<br />studied. \Ve carefully set the boundary conditions to be open conditions so as to avoid any collimation due to grid reflection effects.</p> <p>To test the theory of winds centrifugally driven from the surface of Keplerian accretion<br />disks, we started with an open magnetic field line configuration. The magnetic<br />field lines have opening angles (with respect to the disk surface) less than the critical<br />angle (≃ 60°), as required for a centrifugally driven wind to start. We found that a<br />steady jet is quickly established allowing direct comparison with the theory. We find<br />the gas to be centrifugally accelerated through the Alfvén and the fast magnetosonic<br />surfaces and collimated into cylinders parallel to the disk's axis. The collimation is<br />due to the pinch force exerted by the dominant toroidal magnetic field generated by<br />the outflow itself. The velocities achieved in our simulations are of the order of 250<br />km/s for our standard young stellar object (a 0.5 M proto-star) and of the order<br />or 10⁵ km/s for our standard active galactic nuclei (a 10⁸M black hole). Our jet<br />solutions are very efficient in magnetically extract.ing angular momentum and energy<br />fronl the disk.</p> <p>The second magnetic configuration we have studied consists of a uniform vertical<br />structure wherein the magnetic field lines are parallel to the disk's axis. Here, the<br />rotation of the disk twists the magnetic field lines and generates a toroidal field<br />component. Because of the Keplerian scaling of the rotational velocity with the disk<br />radius, the twisting of the field lines is higher in the inner parts of the disk. The<br />strong lnagnetic gradient thus generated opens up the initial magnetic configuration<br />in a narrow region located at 1rᵢ < r < 8rᵢ, with rᵢ being the innermost radius of the disk. Within this narrow region a wind is ejected from the field lines that have<br />opened to less than the critical angle (≃60°), as expected from the centrifugally<br />driven wind theory. Our simulations show that the strong toroidal magnetic field<br />generated recollimates the flow towards the disk's axis and, through MHD shocks,<br />produces knots. The knot generation mechanism occurs at a distance of about z ≃ 8rᵢ from the surface of the disk.</p> <p>We have discovered that no special initial magnetic field structure is required in<br />order to launch episodic outflows in our simulations. Rather, conditions favorable for<br />the formation of an outflow set themselves up automatically through the production<br />of a toroidal magnetic field whose pressure readjusts the structure of the field above<br />the disk. The knot generator is episodic, and is inherent to the jet. Thus, jets<br />are apparently capable of producing the variability that leads to episodic events, independently of the underlying source.</p> / Doctor of Philosophy (PhD)

Doctor of Philosophy (PhD)

<p>We have developed a statistically rigorous and automated method to implement the detection, photometry and classification of faint objects on digital images. We use these methods to analyze deep R- and B-band CCD images of the central ~ 700 arcmin² of the Coma cluster core, and an associated control field. We have detected and measured total R magnitudes and (B - R) colors for a sample of 3741 objects on the galaxy cluster fields, and 1164 objects on a remote control field, complete to a limiting magnitude of R = 22.5 mag. The typical uncertainties are ±0.06 and ±0.12 mag in total magnitude and color respectively. The dwarf elliptical (dE) galaxies are confined to a well-defined sequence in the color range given by 0.7 ≤ (B - R) ≤ 1.9 mag; within this interval there are 2535 dE candidates on our fields in the cluster core, and 694 objects on the control field. With an image scale of 0.53 arcsec/pixel and seeing near 1.2 arcsec, a large fraction of the dE galaxy candidates are resolved.</p> <p>We find a significant metallicity gradient in the radial distribution of the dwarf elliptical galaxies, which goes as Z ∝ R⁻⁰˙³² outwards from the cluster center at NGC 4874. As well, there is a strong color-luminosity correlation, in the sense that more luminous dE galaxies are redder in the mean. These effects give rise to a radial variation in the cluster luminosity function. The spatial distribution of the faint dE galaxies is well fit by a standard King model with a central surface density of ∑₀=1.44 dEs arcmin⁻², a core radius Rc = 18.7 arcmin (≃ 0.44 Mpc), and a tidal radius of 1.44 deg (≃ 2.05 Mpc). This core is significantly larger than Rc = 12.3 arcmin (≃ 0.29 Mpc) found for the bright cluster galaxies. The composite luminosity function for Coma galaxies is modeled as the sum of a log-normal distribution for the giant galaxies and a Schechter function for the dwarf elliptical galaxies, with a faint-end slope of α = -1.41, consistent with known faint-end slopes for tbe Virgo and Fornax clusters. The early-type dwarf-to-giant ratio for the Coma cluster core is consistent with that of the Virgo cluster, and thus with the rich Coma cluster being formed as the merger of multiple less-rich galaxy clusters.</p> / Doctor of Philosophy (PhD)

<p>Most galaxies in the universe live in galaxy groups, and we can use them to learn a lot about t he influence of environment on galaxy evolution. Historically, galaxy groups have been ident ified by painstakingly obtaining many spectra and finding associated gala-'{ies, however, much larger samples could be found if we had a reliable method of finding groups using photometry. We follow a variation of the Probability Friends of Friends algorithm suggested by Li & Vee (2008) to find galaxy groups in photometric redshift data. Our approach employs a continuous friends-of-friends search in t he t ransverse direction and uses the redshift probability density in redshift space. We use t his method to find galaxy groups in the 4 Canada-France-Hawaii Telescope Legacy Survey Deep Fields, and compare it to a 5th Nearest Neighbor galaxy density search algorithm applied to the same four fields. To fur ther assess our Probability Friends of Friends method, we test it on light cones from the Millennium Simulation. We found that less t han 20% of the Probability Friends of Friends groups with 12 or more members were interlopers. The average density of groups of 12 or more members is ~ 54 per square degree. Our final sample of groups in t he Canada-France-Hawaii Telescope Legacy Survey Deep Fields contains 33 ,279 groups with three or more members, 218 of which have 12 or more members.</p> / Master of Science (MS)

<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)