Galaxy Evolution tool: Construction and Applications

We present a dual-infall galactic chemical evolution model which uses a new set of stellar yields calculated by Limongi et al (2001) to constrain the amount of iron-peak elements ejected by massive stars. The age-metallicity relation, G-dwarf distribution and evolution of abundance ratios are predicted using Galaxy Evolution tool (GEtool), a software package currently being developed to self-consistenly model the chemical and spectral evolution of disk galaxies. A comparison with results obtained using the Woosley & Weaver (1995) core-collapse supernova models suggests that the observed behaviour of key abundance patterns cannot be reproduced if the iron yield of massive stars increases with initial mass.Comment: 2 pages, 4 figures, to appear in "The Evolution of Galaxies II: Basic Building Blocks", (2002) ed. M. Sauvage et al. (Kluwer

Deriving the Metallicity Distribution Function of Galactic Systems

The chemical evolution of the Milky Way is investigated using a dual-phase metal-enriched infall model in which primordial gas fuels the earliest epoch of star formation, followed by the ongoing formation of stars from newly accreted gas. The latest metallicity distribution of local K-dwarfs is reproduced by this model, which allows the Galactic thin disk to form from slightly metal-enriched gas with alpha-element enhancement. Our model predicts ages for the stellar halo and thin disk of 12.5 and 7.4 Gyr, respectively, in agreement with empirically determined values. The model presented in this paper is compared with a similar dual-phase infall model from Chiappini et al. (2001). We discuss a degeneracy that enables both models to recover the K-dwarf metallicity distribution while yielding different star formation histories. The metallicity distribution function (MDF) of K-dwarfs is proposed to be more directly comparable to chemical evolution model results than the G-dwarf distribution because lower mass K-dwarfs are less susceptible to stellar evolutionary effects. The K-dwarf MDF should consequently be a better probe of star formation history and provide a stronger constraint to chemical evolution models than the widely used G-dwarf MDF. The corrections that should be applied to a G-dwarf MDF are quantified for the case of the outer halo of NGC 5128.Comment: 16 pages, 5 figures, accepted for publication in PASA (Publications of the Astronomical Society of Australia

Lebensqualität von Brustkrebspatientinnen bei offener und verschlossener Reaktion auf ein Gesprächs- und Informationsangebot

Da sich die Voraussetzungen in der Nachsorge von Patientinnen mit Brustkrebs im letzten Jahrzehnt verändert haben, wird im Theorieteil der Arbeit auf das Konzept Lebensqualität, die Krankheit Brustkrebs selbst, die aktuellen Nachsorgebedingungen und auf Coping eingegangen. Im Anschluß erfolgt die Darstellung der Ergebnisse von 204 Patientinnen, die zwischen 1996 und 1998 an einem neu diagnostizierten Mammakarzinom erkrankt und operiert worden sind. Die Daten wurden bezüglich der Lebensqualität in der Nachsorgeperiode von einem Jahr ausgewertet. Als Meßinstrument wurde der Quality of Life Questionnaire der EORTC benutzt. Es zeigt sich, daß sich für alle Patientinnen die Lebensqualität im Verlauf von einem Jahr signifikant erhöht. Die Patientinnen, die eine offene Haltung bezüglich eines Informations- und Gesprächsangebots zeigen (n=43), haben zum Zeitpunkt der Klinikentlassung und nach 12 Monaten eine signifikant schlechtere globale Lebensqualität als die verschlossenen Patientinnen (n=12). Die bezüglich des Gesprächs- und Informationsangebots indifferenten Patientinnen (n=149) nehmen einen Mittelplatz ein. Als weiteres Ergebnis zeigt sich ein signifikanter Unterschied zwischen der Selbsteinschätzung der Lebensqualität durch die Patientinnen und der Fremdeinschätzung der Lebensqualität durch die Interviewführenden. Die Patientinnen schätzen ihre globale Lebensqualität signifikant schlechter ein (Mittelwert: 58), als dies in der Fremdeinschätzung durch die Interviewführenden der Fall ist (Mittelwert: 63,2).Die Ergebnisse könnten darauf hindeuten, daß die Offenheit der Patientinnen aus einer inneren Not heraus besteht, während die verschlossenen Patientinnen durch die größere Distanz zum Thema Brustkrebs von einer höheren Lebensqualität profitieren. Die in der Literatur referierten Ergebnisse bezüglich der Selbst- und Fremdeinschätzung der Lebensqualität finden in dieser Studie keine Bestätigung. Es wird deutlich, daß es in der Nachsorge unterschiedliche Reaktionen mit Auswirkung auf die Lebensqualität der Patientinnen gibt; eine Forschungsvertiefung wäre für die bessere Kenntnis der psychosozialen Situation der Patientinnen und nachfolgend für eine Verbesserung der Nachsorge im Sinne der aktuellen Leitlinien wünschenswert

Cosmological implications of dwarf spheroidal chemical evolution

The chemical properties of dwarf spheroidals in the local group are shown to be inconsistent with star formation being truncated after the reionization epoch (z~8). Enhanced levels of [Ba/Y] in stars in dwarf spheroidals like Sculptor indicate strong s-process production from low-mass stars whose lifetimes are comparable with the duration of the pre-reionization epoch. The chemical evolution of Sculptor is followed using a model with SNeII and SNeIa feedback and mass- and metallicity-dependent nucleosynthetic yields for elements from H to Pb. We are unable to reproduce the Ba/Y ratio unless stars formed over an interval long enough for the low-mass stars to pollute the interstellar medium with s-elements. This robust result challenges the suggestion that most of the local group dwarf spheroidals are fossils of reionization and supports the case for large initial dark matter halos.Comment: 7 pages, 4 figures. Accepted for publication in ApJ. Minor changes following referee repor

Characterizing the dissemination process of household water treatment systems in less developed countries

Recently, household-level water treatment and safe storage systems (HWTS) have been developed and promoted as simple, local, user-friendly, and low cost alternatives to conventional municipal-level drinking water treatment systems. Yet, despite conclusive evidence of the health and economic benefits of HWTS, the implementation outcomes have been slow, reaching only approximately 5-10 million people. This study attempts to understand the barriers and drivers affecting HWTS implementation. A review of existing literature on HWTS implementation found that existing research effort to promote HWTS is rather fragmented, with a narrow focus either on technical, psychological, or marketing perspective. Also, the application of innovation diffusion theories on HWTS implementation has been largely unexplored. To fill these research gaps, it is proposed that a system dynamics modelling approach to characterize the complex diffusion process of HWTS can be a valuable tool to identify high impact, leverage strategies to scale-up HWTS adoption and sustained use

The Galactic Habitable Zone and the Age Distribution of Complex Life in the Milky Way

We modeled the evolution of the Milky Way to trace the distribution in space and time of four prerequisites for complex life: the presence of a host star, enough heavy elements to form terrestrial planets, sufficient time for biological evolution and an environment free of life-extinguishing supernovae. We identified the Galactic habitable zone (GHZ) as an annular region between 7 and 9 kiloparsecs from the Galactic center that widens with time and is composed of stars that formed between 8 and 4 billion years ago. This GHZ yields an age distribution for the complex life that may inhabit our Galaxy. We found that 75% of the stars in the GHZ are older than the Sun.Comment: 9 pages, 4 figs. Published in Science, 2 January 200

On variations in the fine-structure constant and stellar pollution of quasar absorption systems

At redshifts z_abs < 2, quasar absorption-line constraints on space-time variations in the fine-structure constant, alpha, rely on the comparison of MgII and FeII transition wavelengths. One potentially important uncertainty is the relative abundance of Mg isotopes in the absorbers which, if different from solar, can cause spurious shifts in the measured wavelengths and, therefore, alpha. Here we explore chemical evolution models with enhanced populations of intermediate-mass (IM) stars which, in their asymptotic giant branch (AGB) phase, are thought to be the dominant factories for heavy Mg isotopes at the low metallicities typical of quasar absorption systems. By design, these models partially explain recent Keck/HIRES evidence for a smaller alpha in z_abs < 2 absorption clouds than on Earth. However, such models also over-produce N, violating observed abundance trends in high-z_abs damped Lyman-alpha systems (DLAs). Our results do not support the recent claim of Ashenfelter, Mathews & Olive (2004b) that similar models of IM-enhanced initial mass functions (IMFs) may simultaneously explain the HIRES varying-alpha data and DLA N abundances. We explore the effect of the IM-enhanced model on Si, Al and P abundances, finding it to be much-less pronounced than for N. We also show that the 13C/12C ratio, as measured in absorption systems, could constitute a future diagnostic of non-standard models of the high-redshift IMF.Comment: Accepted by MNRAS. 13 pages, 14 ps figure

Constraints on Early Nucleosynthesis from the Abundance Pattern of a Damped Ly-alpha System at z = 2.626

We have investigated chemical evolution in the young universe by analysing the detailed chemical enrichment pattern of a metal-rich galaxy at high redshift. The recent detection of over 20 elements in the gas-phase of a damped Lyman-alpha absorber (DLA) at z = 2.626 represents an exciting new avenue for exploring early nucleosynthesis. Given a strict upper age of ~2.5 Gyr and a gas-phase metallicity about one third solar, we have shown the DLA abundance pattern to be consistent with the predictions of a chemical evolution model in which the interstellar enrichment is dominated by massive stars with a small contribution from Type Ia supernovae. Discrepancies between the empirical data and the models are used to highlight outstanding issues in nucleosynthesis theory, including a tendency for Type II supernovae models to overestimate the magnitude of the "odd-even" effect at subsolar metallicities. Our results suggest a possible need for supplemental sources of magnesium and zinc, beyond that provided by massive stars.Comment: 12 pages, 7 figs. Accepted for publication in ApJ (The Astrophysical Journal