535 research outputs found
Effects of tangential velocity in the reactive relativistic Riemann problem
Type I X-ray bursts are thermonuclear burning events which occur on the
surfaces of accreting neutron stars. Burning begins in a localised spot in the
star's ocean layer before propagating across the entire surface as a
deflagration. On the scale of the entire star, the burning front can be thought
of as discontinuity. To model this, we investigated the reactive Riemann
problem for relativistic deflagrations and detonations and developed a
numerical solver. Unlike for the Newtonian Riemann problem, where only the
velocity perpendicular to the interface is relevant, in the relativistic case
the tangential velocity becomes coupled through the Lorentz factor and can
alter the waves present in the solution. We investigated whether a fast
tangential velocity may be able to cause a deflagration wave to transition to a
detonation. We found that such a transition is possible, but only for
tangential velocities that are a significant fraction of the speed of light or
for systems already on the verge of transitioning. Consequently, it is highly
unlikely that this transition would occur for a burning front in a neutron star
ocean without significant contributions from additional multidimensional
effects.Comment: 16 pages, 10 figures, Accepted for publication in Ap
Biochar and Managed Perennial Ecosystems
Biochar is a carbon-rich material that is similar to charcoal. It is produced when biomass is burned in the absence of oxygen, a process otherwise known as pyrolysis. Pyrolysis and the production of biochar are currently being promoted as a means to both produce domestic fuel (bio-oil) while concurrently producing a co-product that increases crop yield and sequesters carbon in the soil (biochar). While there may be many potential benefits in the application of biochar to agricultural soils, such as enhanced soil fertility and improved soil water status, there are no studies of higher-order ecological and ecosystem effects of biochar and its potential synergistic interactions (either positive or negative) on complex perennial systems. The goal of this field experiment is to determine how biochar and manure addition directly affect ecosystem structure and function in perennial systems, specifically soil nutrients, water, plants, and soil organisms
Biochar and Managed Perennial Ecosystems: Testing for Synergy in Ecosystem Function and Biodiversity
Biochar is a carbon-rich material that is similar to charcoal. It is produced when biomass is burned in the absence of oxygen, a process otherwise known as pyrolysis. Pyrolysis and the production of biochar are currently being promoted as a means to both produce domestic fuel (biooil) and concurrently producing a co-product that increases crop yield and sequesters carbon in the soil (biochar). While there may be many potential benefits in the application of biochar to agricultural soils, such as enhanced soil fertility and improved soil water status, there are no studies of higher-order ecological and ecosystem effects of biochar and its potential synergistic interactions (either positive or negative) on complex perennial systems. The goal of this field experiment is to determine how biochar and manure addition directly affect ecosystem structure and function in perennial systems, specifically soil nutrients, water, plants, and soil organisms
CO2, nitrogen, and diversity differentially affect seed production of prairie plants
Plant species composition and diversity is often influenced by early life history stages; thus, global change could dramatically affect plant community structure by altering seed production. Unfortunately, plant reproductive responses to global change are rarely studied in field settings, making it difficult to assess this possibility. To address this issue, we quantified the effects of elevated CO2, nitrogen deposition, and declining diversity on inflorescence production and inflorescence mass of 11 perennial grassland species in central Minnesota, USA. We analyzed these data to ask whether (1) global change differentially affects seed production of co-occurring species; (2) seed production responses to global change are similar for species within the same functional group (defined by ecophysiology and growth form); and (3) seed production responses to global change match productivity responses. We found that, on average, allocation to seed production decreased under elevated CO2, although individual species responses were rarely significant due to low power (CO2 treatment df = 2). The effects of nitrogen deposition on seed production were similar within functional groups: C4 grasses tended to increase while C3 grasses tended to decrease allocation to seed production. Responses to nitrogen deposition were negatively correlated to productivity responses, suggesting a trade-off. Allocation to seed production of some species responded to a diversity gradient, but responses were uncorrelated to productivity responses and not similar within functional groups. Presumably, species richness has complex effects on the biotic and abiotic variables that influence seed production. In total, our results suggest that seed production of co-occurring species will be altered by global change, which may affect plant communities in unpredictable ways. Although functional groups could be used to generalize seed production responses to nitrogen deposition in Minnesota prairies, we caution against relying on them for predictive purposes without a mechanistic understanding of how resource availability and biotic interactions affect seed production
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Dynamics of Laterally Propagating Flames in X-Ray Bursts. I. Burning Front Structure
We investigate the structure of laterally propagating flames through the highly stratified burning layer in an X-ray burst. Two-dimensional hydrodynamics simulations of flame propagation are performed through a rotating plane-parallel atmosphere, exploring the structure of the flame. We discuss the approximations needed to capture the length and timescales at play in an X-ray burst and describe the flame acceleration observed. Our studies complement other multidimensional studies of burning in X-ray bursts
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