Probing the Neutron-Capture Nucleosynthesis History of Galactic Matter

The heavy elements formed by neutron capture processes have an interesting history from which we can extract useful clues to and constraints upon both the characteristics of the processes themselves and the star formation and nucleosynthesis history of Galactic matter. Of particular interest in this regard are the heavy element compositions of extremely metal-deficient stars. At metallicities [Fe/H] <= -2.5, the elements in the mass region past barium (A >= 130-140 have been found (in non carbon-rich stars) to be pure r-process products. The identification of an environment provided by massive stars and associated Type II supernovae as an r-process site seems compelling. Increasing levels of heavy s-process (e.g., barium) enrichment with increasing metallicity, evident in the abundances of more metal-rich halo stars and disk stars, reflect the delayed contributions from the low- and intermediate-mass (M \~ 1-3 Msol) stars that provide the site for the main s-process nucleosynthesis component during the AGB phase of their evolution. New abundance data in the mass region 60 <~ A <~ 130 is providing insight into the identity of possible alternative r-process sites. We review recent observational studies of heavy element abundances both in low metallicity halo stars and in disk stars, discuss the observed trends in light of nucleosynthesis theory, and explore some implications of these results for Galactic chemical evolution, nucleosynthesis, and nucleocosmochronology.Comment: 47 pages, 2 tables, 11 figures; To appear in PAS

Probing the Site for r-Process Nucleosyntheis with Abundances of Barium and Magnesium in Extremely Metal-Poor Stars

We suggest that if the astrophysical site for r-process nucleosynthesis in the early Galaxy is confined to a narrow mass range of Type II supernova (SN II) progenitors, with a lower mass limit of Mms = 20 Msun, a unique feature in the observed distribution of [Ba/Mg] vs.[Mg/H] for extremely metal-poor stars can be adequately reproduced. We associate this feature, a bifurcation of the observed elemental ratios into two branches in the Mg abundance interval -2.7 < [Mg/H] < -2.3, with two distinct processes. The first branch, which we call the ``y''-branch, is associated with the production of Ba and Mg from individual massive supernovae. We conclude that SNe II with Mms = 20 Msun are the dominant source of r-process nucleosynthesis in the early Galaxy. An SN-induced chemical evolution model with this Mms-dependent Ba yield creates the y-branch, reflecting the different nucleosynthesis yields of [Ba/Mg] for each SN II with Mms > 20 Msun. The second branch, which we call the ``i''-branch, is associated with the elemental abundance ratios of stars which were formed in the dense shells of the interstellar medium swept up by SNe II with Mms < 20 Msun that do not synthesize r-process elements, and applies to stars with observed Mg abundances in the range [Mg/H] < -2.7. The Ba abundances in these stars reflect those of the interstellar gas at the (later) time of their formation. The existence of a [Ba/Mg] i-branch strongly suggests that SNe II which are associated with stars of progenitor mass Mms < 20 Msun are infertile sources for the production of r-process elements. We predict the existence of this i-branch for other r-process elements, such as europium (Eu), to the extent that their production site is in common with Ba.Comment: 6 pages including 3 figures, to appear in ApJ Letter

A Model for Abundances in Metal-Poor Stars

It is argued that the abundances of r-process related elements in stars with -3<[Fe/H]<-1 can be explained by the contributions of three sources. The sources are: the first generations of very massive (>100 solar masses) stars that are formed from Big Bang debris and are distinct from SNII, and two types of SNII, the H and L events, which can occur only at [Fe/H]>-3. The H events are of high frequency and produce dominantly heavy (A>130) r-elements but no Fe (presumably leaving behind black holes). The L events are of low frequency and produce Fe and dominantly light (A<130) r-elements (essentially none above Ba). By using the observed abundances in two ultra-metal-poor stars and the solar r-abundances, the initial or prompt inventory of elements produced by the first generations of very massive stars and the yields of H and L events can be determined. The abundances of a large number of elements in a star can then be calculated from the model by using only the observed Eu and Fe abundances. To match the model results and the observational data for stars with -3<[Fe/H]<-1 requires that the solar r-abundances for Sr, Y, Zr, and Ba must be significantly increased from the standard values. Whether the solar r-components of these elements used here to obtain a fit to the stellar data can be reconciled with those obtained from solar abundances by subtracting the s-components calculated from models is not clear.Comment: 47 pages, 19 figures, to appear in Ap

Patients' perceptions and views of surgery and radioiodine ablation in the definitive management of Graves' disease.

BACKGROUND: Patients' perceptions and preferences influence the choice of radioiodine ablation (RIA) or surgery in the definitive management of Graves' disease. This study aimed to evaluate their concerns, experiences and satisfaction following definitive treatment. METHODS: A postal survey of patients who had treatment with surgery or RIA between January 2011 and June 2013 for Graves' disease was conducted. RESULTS: Of 214 patients, 136 (64%) responded. The majority of patients felt actively involved in decision making (83.8%) and were satisfied (84.9%) with their treatment. Compared with RIA, patients who underwent surgery were more satisfied with their treatment (p=0.008). Discussion with the doctor was the most useful aid to decision making. Feeling involved in decision-making process was associated with improved satisfaction (p<0.001).Common reasons for not choosing surgery were need for general anaesthesia, scarring and voice change. Avoiding close contact, risk of persistent hyperthyroidism and worsening eye disease were common reasons for not choosing RIA. Ongoing concerns were hypothyroidism, scarring and eye problems after surgery and hypothyroidism and eye problems after RIA. CONCLUSIONS: This study provides insight into patients' experiences of surgery and RIA for Graves' disease and reinforces the importance of patient involvement in the decision-making process

Three Dimensional Simulation of Gamma Ray Emission from Asymmetric Supernovae and Hypernovae

Hard X- and $\gamma$-ray spectra and light curves resulting from radioactive decays are computed for aspherical (jet-like) and energetic supernova models (representing a prototypical hypernova SN 1998bw), using a 3D energy- and time-dependent Monte Carlo scheme. The emission is characterized by (1) early emergence of high energy emission, (2) large line-to-continuum ratio, and (3) large cut-off energy by photoelectric absorptions in hard X-ray energies. These three properties are not sensitively dependent on the observer's direction. On the other hand, fluxes and line profiles depend sensitively on the observer's direction, showing larger luminosity and larger degree of blueshift for an observer closer to the polar ($z$) direction. Strategies to derive the degree of asphericity and the observer's direction from (future) observations are suggested on the basis of these features, and an estimate on detectability of the high energy emission by the {\it INTEGRAL} and future observatories is presented. Also presented is examination on applicability of a gray effective $\gamma$-ray opacity for computing the energy deposition rate in the aspherical SN ejecta. The 3D detailed computations show that the effective $\gamma$-ray opacity $\kappa_{\gamma} \sim 0.025 - 0.027$ cm$^{2}$ g$^{-1}$ reproduces the detailed energy-dependent transport for both spherical and aspherical (jet-like) geometry.Comment: 24 pages, 13 figures. Figure 7 added in the accepted version. ApJ, 644 (01 June 2006 issue), in press. Resolution of figures lower than the published versio

Agreeing on meaning: a fundamental sharing of health information

Topic: A preliminary study on the reproducibility of results when mapping terms from an existing terminology to SNOMED CT post-coordinated expressions is described. Background: Implementing SNOMED CT requires a strategy for migrating existing systems and data that currently use other terminologies as well as ensuring that SNOMED CT contains suitable content that covers the domain. Mapping terms from these terminologies to SNOMED CT is one element of such a strategy. Snapper is a tool designed to assist in this complex task and enable the creation of quality mappings. Methods: Ten terms from the ANZICS diagnosis codes were selected to be mapped according to specified guidelines. The resulting mapping expressions were compared with each other and discussions were conducted with the mapping participants to determine issues they encountered during the process. Results: Consistency was easily achievable with mapping to single concepts, but was more difficult when mapping to post-coordinated expressions. The difficulties were traced to a lack of specificity in the supplied guidelines resulting in uncertainty in structuring the representation of compound concepts

Large-Scale Simulations of Clusters of Galaxies

We discuss some of the computational challenges encountered in simulating the evolution of clusters of galaxies. Eulerian adaptive mesh refinement (AMR) techniques can successfully address these challenges but are currently being used by only a few groups. We describe our publicly available AMR code, FLASH, which uses an object-oriented framework to manage its AMR library, physics modules, and automated verification. We outline the development of the FLASH framework to include collisionless particles, permitting it to be used for cluster simulation.Comment: 3 pages, 3 figures, to appear in Proceedings of the VII International Workshop on Advanced Computing and Analysis Techniques in Physics Research (ACAT 2000), Fermilab, Oct. 16-20, 200

The Evolution of Damped Lyman-alpha Absorbers: Metallicities and Star Formation Rates

The damped Lyman-alpha (DLA) and sub-DLA quasar absorption lines provide powerful probes of the evolution of metals, gas, and stars in galaxies. One major obstacle in trying to understand the evolution of DLAs and sub-DLAs has been the small number of metallicity measurements at z < 1.5, an epoch spanning \~70 % of the cosmic history. In recent surveys with the Hubble Space Telescope and Multiple Mirror Telescope, we have doubled the DLA Zn sample at z < 1.5. Combining our results with those at higher redshifts from the literature, we find that the global mean metallicity of DLAs does not rise to the solar value at low redshifts. These surprising results appear to contradict the near-solar mean metallicity observed for nearby (z ~ 0) galaxies and the predictions of cosmic chemical evolution models based on the global star formation history. Finally, we discuss direct constraints on the star formation rates (SFRs) in the absorber galaxies from our deep Fabry-Perot Ly-alpha imaging study and other emission-line studies in the literature. A large fraction of the observed heavy-element quasar absorbers at 0 < z < 3.4 appear to have SFRs substantially below the global mean SFR, consistent with the low metallicities observed in the spectroscopic studies.Comment: 6 pages,3 figures, To appear in "Probing Galaxies through Quasar Absorption Lines", Proceedings IAU Colloquium 199, 2005, Eds. P. R. Williams, C. Shu, and B. Menar

Supernova SN1987A Revisited as a Major Production Site for r-Process Elements

The origin of nucleosynthesis products of rapid neutron capture reactions (the r-process) is a longstanding astrophysical problem. Recent analyses of elemental abundances for extremely metal-poor stars shed light on the elemental abundances of individual supernovae. Comparison of the abundance distributions of some extremely metal-poor stars with those of the best-observed supernova SN 1987A clearly indicates that the overabundances of barium and strontium found in SN 1987A that have been ascribed to the slow neutron capture process must be results of r-process nucleosynthesis. The mass of freshly synthesized barium in SN 1987A is estimated to be 6x10^-6 solar mass based on the observed surface abundance and detailed hydrodynamical models for this supernova. These new findings lead to the conclusion that 20 solar mass stars, one of which is the progenitor star of SN 1987A, are the predominant production sites for r-process elements in the Galaxy and the r-process element donors for notable neutron-capture-rich giant stars, CS22892-052 and CS31082-001.Comment: 5 pages including 2 figures, to appear in ApJ Letter