1,869 research outputs found
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
LebensqualitÀt von Brustkrebspatientinnen bei offener und verschlossener Reaktion auf ein GesprÀchs- und Informationsangebot
Da sich die Voraussetzungen in der Nachsorge von
Patientinnen mit Brustkrebs im letzten Jahrzehnt verÀndert
haben, wird im Theorieteil der Arbeit auf das Konzept
LebensqualitÀt, die Krankheit Brustkrebs selbst, die aktuellen
Nachsorgebedingungen und auf Coping eingegangen. Im AnschluĂ
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 bezĂŒglich der LebensqualitĂ€t in der Nachsorgeperiode von
einem Jahr ausgewertet. Als MeĂinstrument wurde der Quality of
Life Questionnaire der EORTC benutzt. Es zeigt sich, daĂ sich
fĂŒr alle Patientinnen die LebensqualitĂ€t im Verlauf von einem
Jahr signifikant erhöht. Die Patientinnen, die eine offene
Haltung bezĂŒglich eines Informations- und GesprĂ€chsangebots
zeigen (n=43), haben zum Zeitpunkt der Klinikentlassung und
nach 12 Monaten eine signifikant schlechtere globale
LebensqualitÀt als die verschlossenen Patientinnen (n=12). Die
bezĂŒglich des GesprĂ€chs- und Informationsangebots indifferenten
Patientinnen (n=149) nehmen einen Mittelplatz ein.
Als
weiteres Ergebnis zeigt sich ein signifikanter Unterschied
zwischen der SelbsteinschÀtzung der LebensqualitÀt durch die
Patientinnen und der FremdeinschÀtzung der LebensqualitÀt durch
die InterviewfĂŒhrenden. Die Patientinnen schĂ€tzen ihre globale
LebensqualitÀt signifikant schlechter ein (Mittelwert: 58), als
dies in der FremdeinschĂ€tzung durch die InterviewfĂŒhrenden der
Fall ist (Mittelwert: 63,2).Die Ergebnisse könnten darauf
hindeuten, daĂ die Offenheit der Patientinnen aus einer inneren
Not heraus besteht, wÀhrend die verschlossenen Patientinnen
durch die gröĂere Distanz zum Thema Brustkrebs von einer
höheren LebensqualitÀt profitieren. Die in der Literatur
referierten Ergebnisse bezĂŒglich der Selbst- und
FremdeinschÀtzung der LebensqualitÀt finden in dieser Studie
keine BestÀtigung. Es wird deutlich, daà es in der Nachsorge
unterschiedliche Reaktionen mit Auswirkung auf die
LebensqualitÀt der Patientinnen gibt; eine Forschungsvertiefung
wĂ€re fĂŒr die bessere Kenntnis der psychosozialen Situation der
Patientinnen und nachfolgend fĂŒr eine Verbesserung der
Nachsorge im Sinne der aktuellen Leitlinien
wĂŒnschenswert
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
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