2,466 research outputs found
Population III Gamma Ray Bursts
We discuss a model of Poynting-dominated gamma-ray bursts from the collapse
of very massive first generation (pop. III) stars. From redshifts of order 20,
the resulting relativistic jets would radiate in the hard X-ray range around 50
keV and above, followed after roughly a day by an external shock component
peaking around a few keV. On the same timescales an inverse Compton component
around 75 GeV may be expected, as well as a possible infra-red flash. The
fluences of these components would be above the threshold for detectors such as
Swift and Fermi, providing potentially valuable information on the formation
and properties of what may be the first luminous objects and their black holes
in the high redshift Universe.Comment: 12 pages; Apj, subm. 12/10/2009; accepted 04/12/201
The role of eco-evolutionary experience in invasion success
Invasion ecology has made considerable progress in identifying specific mechanisms that potentially determine success and failure of biological invasions. Increasingly, efforts are being made to interrelate or even synthesize the growing number of hypotheses in order to gain a more comprehensive and integrative understanding of invasions. We argue that adopting an eco-evolutionary perspective on invasions is a promising approach to achieve such integration. It emphasizes the evolutionary antecedents of invasions, i.e. the speciesâ evolutionary legacy and its role in shaping novel biotic interactions that arise due to invasions. We present a conceptual framework consisting of five hypothetical scenarios about the influence of so-called âeco-evolutionary experienceâ in resident native and invading non-native species on invasion success, depending on the type of ecological interaction (predation, competition, mutualism, and commensalism). We show that several major ecological invasion hypotheses, including âenemy releaseâ, âEICAâ, ânovel weaponsâ, ânaive preyâ, ânew associationsâ, âmissed mutualismsâ and âDarwinâs naturalization hypothesisâ can be integrated into this framework by uncovering their shared implicit reference to the concept of eco-evolutionary experience. We draft a routine for the assessment of eco-evolutionary experience in native and non-native species using a food web-based example and propose two indices (xpFocal index and xpResidents index) for the actual quantification of eco-evolutionary experience. Our study emphasizes the explanatory potential of an eco-evolutionary perspective on biological invasions
On the Sensitivity of Massive Star Nucleosynthesis and Evolution to Solar Abundances and to Uncertainties in Helium Burning Reaction Rates
We explore the dependence of pre-supernova evolution and supernova
nucleosynthesis yields on the uncertainties in helium burning reaction rates.
Using the revised solar abundances of Lodders (2003) for the initial stellar
composition, instead of those of Anders & Grevesse (1989), changes the
supernova yields and limits the constraints that those yields place on the
12C(a,g)16O reaction rate. The production factors of medium-weight elements (A
= 16-40) were found to be in reasonable agreement with observed solar ratios
within the current experimental uncertainties in the triple alpha reaction
rate. Simultaneous variations by the same amount in both reaction rates or in
either of them separately, however, can induce significant changes in the
central 12C abundance at core carbon ignition and in the mass of the supernova
remnant. It therefore remains important to have experimental determinations of
the helium burning rates so that their ratio and absolute values are known with
an accuracy of 10% or better.Comment: Accepted for publication by the Astrophysical Journa
Lasers and liposomes : a potentially efficacious combination for the non-invasive removal of pathological cutaneous vasculature
Conservative Initial Mapping For Multidimensional Simulations of Stellar Explosions
Mapping one-dimensional stellar profiles onto multidimensional grids as
initial conditions for hydrodynamics calculations can lead to numerical
artifacts, one of the most severe of which is the violation of conservation
laws for physical quantities such as energy and mass. Here we introduce a
numerical scheme for mapping one-dimensional spherically-symmetric data onto
multidimensional meshes so that these physical quantities are conserved. We
validate our scheme by porting a realistic 1D Lagrangian stellar profile to the
new multidimensional Eulerian hydro code CASTRO. Our results show that all
important features in the profiles are reproduced on the new grid and that
conservation laws are enforced at all resolutions after mapping.Comment: 7 pages, 5 figures, Proceeding for Conference on Computational
Physics (CCP 2011
Species from different taxonomic groups show similar invasion traits
Invasion ecology tends to treat taxonomic groups separately. However, given that all invasive species go through the same stages of the invasion process (transport, escape, establishment, spread), it is likely that â across taxa â comparable traits help to successfully complete this process ("invasion traits"). Perhaps not all invasive species have the same invasion traits, but different combinations of invasion traits can be found among invaders, corresponding to different possibilities to become a successful invader. These combinations of invasion traits might be linked to taxonomic affiliation, but this is not necessarily the case. We created a global dataset with 201 invasive species from seven major taxonomic groups (animals, green plants, fungi, heterokonts, bacteria, red algae, alveolates) and 13 invasion traits that are applicable across all taxa. The dataset was analysed with cluster analysis to search for similarities in combinations of invasion traits. Three of the five clusters, comprising 60% of all species, contain several major taxonomic groups. While some invasion trait frequencies were significantly related to taxonomic affiliation, the results show that invasive species from different taxonomic groups often share similar combinations of invasion traits. A post-hoc analysis suggests that combinations of traits characterizing successful invaders can be associated with invasion stages across taxa. Our findings suggest that there are no universal invasion traits which could explain the invasion success of all invaders, but that invaders are successful for different reasons which are represented by different combinations of invasion traits across taxonomic groups
Help from Across the Pond: Applying the U.K. Law Commission\u27s Presumption That Exclusion from Management in a Private Company Is Unfairly Prejudicial as a Guide to Assessing Claims of Minority Shareholder Oppression in U.S. Closely Held Corporations
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