11,305 research outputs found
r-Process Lanthanide Production and Heating Rates in Kilonovae
r-Process nucleosynthesis in material ejected during neutron star mergers may
lead to radioactively powered transients called kilonovae. The timescale and
peak luminosity of these transients depend on the composition of the ejecta,
which determines the local heating rate from nuclear decays and the opacity.
Kasen et al. (2013, ApJ, 774, 25) and Tanaka & Hotokezaka (2013, ApJ, 775, 113)
pointed out that lanthanides can drastically increase the opacity in these
outflows. We use the new general-purpose nuclear reaction network SkyNet to
carry out a parameter study of r-process nucleosynthesis for a range of initial
electron fractions , initial specific entropies , and expansion
timescales . We find that the ejecta is lanthanide-free for , depending on and . The heating rate is insensitive to
and , but certain, larger values of lead to reduced heating
rates, due to individual nuclides dominating the heating. We calculate
approximate light curves with a simplified gray radiative transport scheme. The
light curves peak at about a day (week) in the lanthanide-free (-rich) cases.
The heating rate does not change much as the ejecta becomes lanthanide-free
with increasing , but the light curve peak becomes about an order of
magnitude brighter because it peaks much earlier when the heating rate is
larger. We also provide parametric fits for the heating rates between 0.1 and
, and we provide a simple fit in , , and to
estimate whether the ejecta is lanthanide-rich or not.Comment: 19 pages, 9 figure
SkyNet: A modular nuclear reaction network library
Almost all of the elements heavier than hydrogen that are present in our
solar system were produced by nuclear burning processes either in the early
universe or at some point in the life cycle of stars. In all of these
environments, there are dozens to thousands of nuclear species that interact
with each other to produce successively heavier elements. In this paper, we
present SkyNet, a new general-purpose nuclear reaction network that evolves the
abundances of nuclear species under the influence of nuclear reactions. SkyNet
can be used to compute the nucleosynthesis evolution in all astrophysical
scenarios where nucleosynthesis occurs. SkyNet is free and open-source and aims
to be easy to use and flexible. Any list of isotopes can be evolved and SkyNet
supports various different types of nuclear reactions. SkyNet is modular so
that new or existing physics, like nuclear reactions or equations of state, can
easily be added or modified. Here, we present in detail the physics implemented
in SkyNet with a focus on a self-consistent transition to and from nuclear
statistical equilibrium (NSE) to non-equilibrium nuclear burning, our
implementation of electron screening, and coupling of the network to an
equation of state. We also present comprehensive code tests and comparisons
with existing nuclear reaction networks. We find that SkyNet agrees with
published results and other codes to an accuracy of a few percent.
Discrepancies, where they exist, can be traced to differences in the physics
implementations.Comment: 39 pages, 11 figures, published in ApJ Supplement Serie
Informing students using virtual microscopes and their impact on students' approach to learning
This research is an exploratory study of students β approaches to studying histology and pathology. With the introduction of virtual microscopes in Health Science at Murdoch University, Australia, in 2006, it was crucial to investigate how this new technology impacted on students β approaches to learning. The ASSIST survey was implemented at the beginning and end of the semester to identify any changes. Results indicate that, when the technology was integrated into the curriculum with appropriate learning activities, students using virtual microscopes moved more towards a strategic approach to learning but expressed a preference for a deep approach to teaching
Mortality rates of the Alpine Chamois : the influence of snow-meteorological factors
Especially for animals inhabiting alpine areas, winter environmental conditions can be limiting. Cold temperatures, hampered food availability and natural perils are just three of many potential threats that mountain ungulates face in winter. Understanding their sensitivity to climate variability is essential for game management. Here we focus on analyzing the influence of snow and weather conditions on the mortality pattern of Alpine chamois. Our mortality data are derived from a systematic assessment of 6,500 chamois that died of natural causes over the course of 13 years. We use population- and habitat-specific data on snow, climate and avalanche danger to identify the key environmental factors that essentially determine the spatio-temporal variations in chamois mortality. Initially, we show that most fatalities occurred in winter, with a peak around March, when typically snow depths were highest. Death causes related to poor general conditions were the major component of seasonal variations. As for the interannual variations in mortality, snow depth and avalanche risk best explained the occurrence of winters with increased numbers of fatalities. Finally, analyzing differences in mortality rates between populations, we identified sun-exposed winter habitats with little snow accumulation as favourable for alpine chamois
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