<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)

<p>The discovery of high temperature superconductors prompted the reconsideration of numerous aspects of superconductivity. Among the most fundamental and controversial is the origin of dissipation in a current carrying superconductor. This is also very important from an applied perspective since the onset of dissipation, often described by the critical current density Jc, determines the current carrying capacity of a material. In this thesis, low energy, light ion irradiation has been implemented as a means of controlled sample modification. This type of irradiation has the advantage that it does not alter the stoichiometry of the sample but only results in disorder through the creation of point defects. This thesis explores the influence of ion damage on the normal and superconducting properties of YBa₂Cu₃O₇₋δ thin films. Of particular interest is the contrast between the strong sensitivity of Jc and the more modest sensitivity of the critical temperature, Tc, to ion damage. The evolution of the temperature dependent resistivity was measured systematically as a function of ion damage. The decrease in Tc with ion damage was compared to the predictions of several relevant models. A simple model based on Matthiessen's rule was used to describe the scattering rate and carrier density at low damage levels. At higher damage levels the system undergoes a superconductor-insulator transition which was found to be consistent with the Ioffe-Regel criterion. However, the resistivity in the insulating state is not described by any conventional models for strongly disordered materials. Measurements of the non-linear electric field-current density characteristics were performed for several levels of ion damage over a range of temperatures and compared with several models for dissipation. The data were found to be well described at all temperatures and damage levels by a model involving the quantum nucleation of vortex loops. The variation of the superconducting carrier density, ns, with ion damage was extracted and compared with independent measurements of the same quantity by infrared transmission in identically irradiated YBa₂Cu₃O₇₋δ thin films. This represents the first time a direct connection has been established between Jc and ns in high temperature superconductors.</p> / Doctor of Philosophy (PhD)

Supernovae and supernova remnants (SNR) are probably important energy sources in the interstellar medium (ISM) and an understanding of the intermediate and advanced stages of SNR evolution are particularly essential. This thesis describes, first a brief review of the current understanding of the ISM and later stages of SNR evolution, then a detailed review of observations of the Cygnus Loop SNR, a relatively old SNR. Details are given of the design and instrumentation of a rocket-borne experiment, which subsequently was utilized to obtain the first X-ray image of a SNR, the Cygnus Loop. The results of X-ray image and spectral analysis are presented, and discussed with respect to previous optical, radio and X-ray observations, and to current SNR blast wave and ISM models.

This thesis describes searches for very low mass stars (0.3 > m/m > 0.08) and brown dwarfs (0.08 > m/m > 0.01) in the Pleiades and Carinae galactic open clusters using COSMOS automatic measures of Schmidt photographic plates. A broad introduction defines the problem and relates research in this area to other branches of astronomy; the second chapter presents a detailed review of the current observational and theoretical status of the subject; and the third chapter briefly describes the observational techniques employed. The results are presented in chapters four and five. The Pleiades results indicate the presence of significant numbers of very low mass stars and possible brown dwarfs with the distinct possibility of discovering more in the near future; two techniques for extracting Pleiades member stars from the field (star counts and proper motions) are described and the cluster luminosity function is found to be strikingly similar in shape to that found for the field stars near the sun. A list of probable Pleiades members, the faintest of which may be brown dwarfs, is presented in the appendix. The derived mass function, although uncertain, indicates that brown dwarfs are present in the cluster. The preliminary analysis of the field around the Carinae cluster highlights the problems of crowded field astronomy using these techniques. Although this cluster does not appear to be as rich as the Pleiades, the results obtained so far indicate possible very low mass main sequence membership that could be investigated further with more plate material. Finally, these and other results are discussed in chapter six and suggestions for further work are presented. Appendices at the end compile data on the least luminous objects known, present photoelectric calibration sequences for the plate material and reproduce reprints of two papers derived from this work.

Quasars have been used as efficient probes of high-redshift galaxy clustering as they are known to favour overdense environments. Quasars may also trace the largescale structure of the early universe (0.4 1< z <1 2) in the form of Large Quasar Groups(LQGs), which have comparable sizes (r.J 100-200hMpc) to the largest structures seen at the present epoch. This thesis describes an ultra-deep, wide-field optical study of a region containing three quasars from the largest known LJQG, the Clowes-Campusano LQG of at least 18 quasars at z 1.3, to examine their galaxy environments and to find indications of any associated large-scale structure in the form of galaxies. The optical data were obtained using the Big Throughput Camera (BTC) on the 4-m Blanco telescope at the Cerro Tololo Interamerican Observatory (CTIO) over two nights in April 1998, resulting in ultra-deep V, I imaging of a 40.6 x 34.9 arcmin 2 field centred at l0L47m30s, +05 0 30'00" containing three quasars from the LQG as well as four quasars at higher redshifts. The final catalogues contain 10 sources and are 50% complete to V 26.35 and I 25.85 in the fully exposed areas. The Cluster Red Sequence method of Gladders & Yee (2000) is used to identify and characterise galaxy clusters in the BTC field. The method is motivated by the observation that the bulk of early-type galaxies in all rich clusters lie along a tight, linear colour-magnitude relation - the cluster red sequence - which evolves with redshift, allowing the cluster redshift to be estimated from the colour of the red sequence. The method is applied to the detection of high-redshift clusters in the BTC field through the selection of galaxies redder than the expected colour of the z = 0.5 red sequence. A 2c excess of these red galaxies is found in the BTC field in comparison to the 27arcmin 2 ETS-DEEP HDF-South field. These galaxies are shown from the EIS-DEEP UBVRIJHK 3 photometry to hearly-type galaxies at 0.7 1< z 1.5. This excess, corresponding to 1000 extra red galaxies over the BTC field, along with the 3c excess of Mgti absorbers observed at 1.2 < z < 1.3(Williger et al., 2000), supports the hypothesis that the Clowes-Campusano LQG traces a large-scale structure in the form of galaxies at z 1.3. Four high-redshift cluster candidates are found, one of which is confirmed by additional K data to be at z = 0.8 + 0.1. Two of the high-redshift clusters are associated with quasars: the z = 1.426 quasar is located on the periphery of a cluster of V - I 3 galaxies; and the z = 1.226 LQC quasar is found within a large-scale structure of 100-150 red galaxies extending over 2-3h'Mpc. Additional K imaging confirms their association with the quasar, with red sequences at V - K 6.9 and I - K 4.3 indicating a population of 15-18 massive ellipticals at z = 1.2 ± 0.1 that are concentrated in two groups on either side of the quasar. The four z ± 1.3 quasars in the BTC field are found in a wide variety of environments,from those indistinguishable from the field, to being associated with rich clusters, but are on average in overdense regions comparable to poor clusters. These results are similar to those of previous studies of quasars at these redshifts, and are consistent with the quasars being hosted by massive ellipticals which trace mass in the same biased manner. It is also notable how the quasars associated with clustering are located on the cluster peripheries rather than in the high-density cluster cores, a result which is initially surprising given that quasars are thought to be hosted by massive elliptical galaxies, but in retrospect can be understood in the framework of both galaxy interaction and galaxy formation quasar triggering mechanisms.

In a collaboration between the University of Leicester X-ray Astronomy Group and the Center for Space Research at the Massachusetts Institute of Technology an imaging X-ray telescope has been developed to carry out a partial sky survey of the extreme-ultraviolet (EUV) region of the spectrum in the waveband 50 to 250A. The instrument is designed to be flown on NASA Astrobee or Black Brant sounding rockets. The history of EUV astronomy and the types of object likely to be of interest in the EUV are reviewed. The development of the WFSXC payload is described with particular emphasis on the development of the focal plane instrument, a microchannel plate detector with resistive anode image readout. The gain performance of the detector is summarised and the use of MgF2 and CsI photocathodes to enhance its quantum efficiency is described, CsI giving efficiencies 10-20 times higher than uncoated MCPs. Also, the use of a resistive anode to provide a low distortion high resolution image readout is demonstrated. Thin film filters are used to define the instrument bandpasses and reject geocoronal background and their design and testing are described. The linear absorption coefficients of beryllium and parylene N, derived from the measured filter transmissions, are compared with theoretical predictions of the absorption in the 50-300A waveband showing good agreement up to 300A for beryllium and 100A for parylene. The WFSXC payload was flown twice experiencing technical problems on both occasions. The anaylsis and interpretation of the data from these flights is presented in the latter chapters of this thesis and the likely causes of the problems determined.

<p> Red giants with solar-like oscillations are astrophysical laboratories for probing the Milky Way. The <i>Kepler </i>Space Telescope revolutionized asteroseismology by consistently monitoring thousands of targets, including several red giants in eclipsing binaries. Binarity allows us to directly measure stellar properties independently of asteroseismology. In this dissertation, we study a subset of eight red giant eclipsing binaries observed by <i> Kepler</i> with a range of orbital periods, oscillation behavior, and stellar activity. Two of the systems do not show solar-like oscillations at all. We use a suite of modeling tools to combine photometry and spectroscopy into a comprehensive picture of each star's life. One noteworthy case is a double red giant binary. The two stars are nearly twins, but have one main set of solar-like oscillations with unusually low-amplitude, wide modes, likely due to stellar activity and modest tidal forces acting over the 171 day eccentric orbit. Mixed modes indicate the main oscillating star is on the secondary red clump (a core-He-burning star), and stellar evolution modeling supports this with a coeval history for a pair of red clump stars. The other seven systems are all red giant branch stars (shell-H-burning) with main sequence companions. The two non-oscillators have the strongest magnetic signatures and some of the strongest lifetime tidal forces with nearly-circular 20-34 day orbits. One system defies this trend with oscillations and a 19 day orbit. The four long-period systems (> 100 days) have oscillations, more eccentric orbits, and less stellar activity. They are all detached binaries consistent with coevolution. We find the asteroseismic scaling laws are approximately correct, but fail the most for stars that are least like the Sun by systematically overestimating both mass and radius. Strong magnetic activity and tidal effects often occur in tandem and act to suppress solar-like oscillations. These red giant binaries offer an unprecedented opportunity to test stellar physics and are important benchmarks for ensemble asteroseismology. Future asteroseismic studies should know they are excluding magnetically active stars and close binaries and be aware that asteroseismic masses and radii are both overestimated. </p>

<p>The Daniel K Inouye Solar Telescope (DKIST), when completed in 2019 will be the largest solar telescope built to date. DKIST will have a suite of first light polarimetric instrumentation requiring broadband polarization modulation and calibration optical elements. Compound crystalline retarders meet the design requirements for efficient modulators and achromatic calibration retarders. These retarders are the only possible large diameter optic that can survive the high flux, 5 arc minute field, and ultraviolet intense environment of a large aperture solar telescope at Gregorian focus. </p><p> This dissertation presents work performed for the project. First, I measured birefringence of the candidate materials necessary to complete designs. Then, I modeled the polarization effects with three-dimensional ray-tracing codes as a function of angle of incidence and field of view. Through this analysis I learned that due to the incident converging F/13 beam on the calibration retarders, the previously assumed linear retarder model fails to account for effects above the project polarization specifications. I discuss modeling strategies such as Mueller matrix decompositions and simplifications of those strategies while still meeting fit error requirements. Finally, I present characterization techniques and how these were applied to prototype components. </p>

<p> In this thesis, I explore two topics in exoplanet science. The first is the prevalence of Earth-size planets in the Milky Way Galaxy. To determine the occurrence of planets having different sizes, orbital periods, and other properties, I conducted a survey of extrasolar planets using data collected by NASA&rsquo;s <i>Kepler Space Telescope</i>. This project involved writing new algorithms to analyze <i>Kepler</i> data, finding planets, and conducting follow-up work using ground-based telescopes. I found that most stars have at least one planet at or within Earth&rsquo;s orbit and that 26% of Sun-like stars have an Earth-size planet with an orbital period of 100 days or less. </p><p> The second topic is the connection between the properties of planets and their host stars. The precise characterization of exoplanet hosts helps to bring planet properties like mass, size, and equilibrium temperature into sharper focus and probes the physical processes that form planets. I studied the abundance of carbon and oxygen in over 1000 nearby stars using optical spectra taken by the California Planet Search. I found a large range in the relative abundance of carbon and oxygen in this sample, including a handful of carbon-rich stars. I also developed a new technique called SpecMatch for extracting fundamental stellar parameters from optical spectra. SpecMatch is particularly applicable to the relatively faint planet-hosting stars discovered by <i>Kepler</i>.</p>