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

Work and welfare for Indigenous Australians

An issue frequently raised in the literature on the economic status of Aboriginal people is the importance of welfare transfers as a source of income, yet there is very little aggregate information documenting this. The purpose of this paper is to present the available evidence from the Population Census and administrative data sources. One estimate is based on the share of total individual income coming from those in employment. Results from 1976 and 1991 show that for Aboriginal people, a smaller share of total individual income came from this source than was the case for other Australians. The last time a question on sources of income was included in a census was in 1976, and the comparison of the numbers receiving a government pension or benefit presented here shows that a larger proportion of Aboriginal people were in receipt of these payments than other Australians. The conclusions based on more recent administrative data are less clear because of the difficulties faced in identifying Aboriginal people and in combining figures from different sources. Nevertheless, the figures are consistent with a broad conclusion of higher levels of welfare receipt among Aboriginal people. The relatively high levels of welfare receipt reflect important underlying problems facing Aboriginal people; high levels of unemployment, poor health and the high incidence of sole parenthood. The paper concludes by stressing the importance of addressing these issues directly

The impact of the welfare state on the economic status of Indigenous Australian women

This paper uses census data and Department of Social Security (DSS) administrative records to examine the role of social security income in explaining the growth and relative improvement in the income status of Indigenous Australian women. The real median income of Indigenous women was 81 per cent of that of non-Indigenous women in 1991 compared with 74 per cent in 1976. Much of the change has come from an improvement in the position of Indigenous women who were not in employment. The paper argues that much of this improvement can be attributed to increased access to social security benefits for Indigenous women and therefore needs to be qualified by the circumstances in which Indigenous women live. A mid-term review of the Aboriginal Employment Development Policy (AEDP) has recently been completed. While much of the associated policy rhetoric and assessment of policy outcomes has been aimed at the national level, the fiscal environment in which AEDP goals are to be achieved is invariably one of regional labour markets and administrative systems operating in the economic context of States and Territories. In view of this reality, this paper responds to a need for regional-level analyses of change in the economic status of Indigenous people compared to that of non-Indigenous people in each State and Territory. Using 1986 and 1991 Census-based social indicators for the Northern Territory, attention is focused on relative shifts in population growth and intra-State distribution, labour force and income status, and levels of welfare dependency (measured as non-employment income). A major finding is that while the gap in labour force status between Indigenous and non-Indigenous people has narrowed, the relative income status and level of welfare dependency of Indigenous people has worsened. This suggests that increased emphasis on the quality of AEDP outcomes, and not just quantity, will be necessary if the overall aims of the AEDP are to be accomplished

Dynamics and gravitational wave signature of collapsar formation

We perform 3+1 general relativistic simulations of rotating core collapse in the context of the collapsar model for long gamma-ray bursts. We employ a realistic progenitor, rotation based on results of stellar evolution calculations, and a simplified equation of state. Our simulations track self-consistently collapse, bounce, the postbounce phase, black hole formation, and the subsequent early hyperaccretion phase. We extract gravitational waves from the spacetime curvature and identify a unique gravitational wave signature associated with the early phase of collapsar formatio

Dynamics and Gravitational Wave Signature of Collapsar Formation

We perform 3+1 general relativistic simulations of rotating core collapse in the context of the collapsar model for long gamma-ray bursts. We employ a realistic progenitor, rotation based on results of stellar evolution calculations, and a simplified equation of state. Our simulations track self-consistently collapse, bounce, the postbounce phase, black hole formation, and the subsequent early hyperaccretion phase. We extract gravitational waves from the spacetime curvature and identify a unique gravitational wave signature associated with the early phase of collapsar formation

Estimating Lunar Pyroclastic Deposit Depth from Imaging Radar Data: Applications to Lunar Resource Assessment

Lunar pyroclastic deposits represent one of the primary anticipated sources of raw materials for future human settlements. These deposits are fine-grained volcanic debris layers produced by explosive volcanism contemporaneous with the early stage of mare infilling. There are several large regional pyroclastic units on the Moon (for example, the Aristarchus Plateau, Rima Bode, and Sulpicius Gallus formations), and numerous localized examples, which often occur as dark-halo deposits around endogenic craters (such as in the floor of Alphonsus Crater). Several regional pyroclastic deposits were studied with spectral reflectance techniques: the Aristarchus Plateau materials were found to be a relatively homogeneous blanket of iron-rich glasses. One such deposit was sampled at the Apollo 17 landing site, and was found to have ferrous oxide and titanium dioxide contents of 12 percent and 5 percent, respectively. While the areal extent of these deposits is relatively well defined from orbital photographs, their depths have been constrained only by a few studies of partially filled impact craters and by imaging radar data. A model for radar backscatter from mantled units applicable to both 70-cm and 12.6-cm wavelength radar data is presented. Depth estimates from such radar observations may be useful in planning future utilization of lunar pyroclastic deposits