Formation Rates of Black Hole Accretion Disk Gamma-Ray Bursts

While many models have been proposed for GRBs, those currently favored are all based upon the formation of and/or rapid accretion into stellar mass black holes. We present population synthesis calculations of these models using a Monte Carlo approach in which the many uncertain parameters intrinsic to such calculations are varied. We estimate the event rate for each class of model as well as the propagation distance for those having significant delay between formation and burst production, i.e., double neutron star (DNS) mergers and black hole-neutron star (BH/NS) mergers. For reasonable assumptions regarding the many uncertainties in population synthesis, we calculate a daily event rate in the universe for i) merging neutron stars: ~100/day; ii) neutron-star black hole mergers: ~450/day; iii) collapsars: ~10,000/day; iv) helium star black hole mergers: ~1000/day; and v) white dwarf black hole mergers: ~20/day. The range of uncertainty in these numbers however, is very large, typically two to three orders of magnitude. These rates must additionally be multiplied by any relevant beaming factor and sampling fraction (if the entire universal set of models is not being observed). Depending upon the mass of the host galaxy, half of the DNS and BH/NS mergers will happen within 60kpc (for a Milky-Way massed galaxy) to 5Mpc (for a galaxy with negligible mass) from the galactic center. Because of the delay time, neutron star and black hole mergers will happen at a redshift 0.5 to 0.8 times that of the other classes of models. Information is still lacking regarding the hosts of short hard bursts, but we suggest that they are due to DNS and BH/NS mergers and thus will ultimately be determined to lie outside of galaxies and at a closer mean distance than long complex bursts (which we attribute to collapsars).Comment: 57 pages total, 23 figures, submitted by Ap

Why Not the Best? Results From the National Scorecard on U.S. Health System Performance, 2011

Assesses the U.S. healthcare system's average performance in 2007-09 as measured by forty-two indicators of health outcomes, quality, access, efficiency, and equity compared with the 2006 and 2008 scorecards and with domestic and international benchmarks

3-Dimensional Core-Collapse

In this paper, we present the results of 3-dimensional collapse simulations of rotating stars for a range of stellar progenitors. We find that for the fastest spinning stars, rotation does indeed modify the convection above the proto-neutron star, but it is not fast enough to cause core fragmentation. Similarly, although strong magnetic fields can be produced once the proto-neutron star cools and contracts, the proto-neutron star is not spinning fast enough to generate strong magnetic fields quickly after collapse and, for our simulations, magnetic fields will not dominate the supernova explosion mechanism. Even so, the resulting pulsars for our fastest rotating models may emit enough energy to dominate the total explosion energy of the supernova. However, more recent stellar models predict rotation rates that are much too slow to affect the explosion, but these models are not sophisticated enough to determine whether the most recent, or past, stellar rotation rates are most likely. Thus, we must rely upon observational constraints to determine the true rotation rates of stellar cores just before collapse. We conclude with a discussion of the possible constraints on stellar rotation which we can derive from core-collapse supernovae.Comment: 34 pages (5 of 17 figures missing), For full paper, goto http://qso.lanl.gov/~clf/papers/rot.ps.gz accepted by Ap

Challenging the orthodoxy: union learning representatives as organic intellectuals

Teacher education and continuing professional development have become a key areas of controversy in England since the period of school sector restructuring following the 1988 Education Reform Act. More recently teacher training and professional development have often been used to promote and reinforce a narrow focus on the government’s ‘standards agenda’. However, the emerging discourse of ‘new professionalism’ has raised the profile of professional development in schools, and together with union learning representatives, there are opportunities to secure real improvements in teachers’ access to continuing professional development. This paper argues however that union learning representatives must go beyond advocating for better access to professional development and should raise more fundamental questions about the nature of professional development and the education system it serves. Drawing on Gramsci’s notion of the ‘organic intellectual’, the paper argues that union learning representatives have a key role as organisers of ideas – creating spaces in which the ideological dominance of current policy orthodoxy might be challenged

Probing the Density in the Galactic Center Region: Wind-Blown Bubbles and High-Energy Proton Constraints

Recent observations of the Galactic center in high-energy gamma-rays (above 0.1TeV) have opened up new ways to study this region, from understanding the emission source of these high-energy photons to constraining the environment in which they are formed. We present a revised theoretical density model of the inner 5pc surrounding Sgr A* based on the fact that the underlying structure of this region is dominated by the winds from the Wolf-Rayet stars orbiting Sgr A*. An ideal probe and application of this density structure is this high energy gamma-ray emission. We assume a proton-scattering model for the production of these gamma-rays and then determine first whether such a model is consistent with the observations and second whether we can use these observations to further constrain the density distribution in the Galactic center.Comment: 36 pages including 17 figures, submitted to ApJ, comments welcom

Merger of white dwarf-neutron star binaries: Prelude to hydrodynamic simulations in general relativity

White dwarf-neutron star binaries generate detectable gravitational radiation. We construct Newtonian equilibrium models of corotational white dwarf-neutron star (WDNS) binaries in circular orbit and find that these models terminate at the Roche limit. At this point the binary will undergo either stable mass transfer (SMT) and evolve on a secular time scale, or unstable mass transfer (UMT), which results in the tidal disruption of the WD. The path a given binary will follow depends primarily on its mass ratio. We analyze the fate of known WDNS binaries and use population synthesis results to estimate the number of LISA-resolved galactic binaries that will undergo either SMT or UMT. We model the quasistationary SMT epoch by solving a set of simple ordinary differential equations and compute the corresponding gravitational waveforms. Finally, we discuss in general terms the possible fate of binaries that undergo UMT and construct approximate Newtonian equilibrium configurations of merged WDNS remnants. We use these configurations to assess plausible outcomes of our future, fully relativistic simulations of these systems. If sufficient WD debris lands on the NS, the remnant may collapse, whereby the gravitational waves from the inspiral, merger, and collapse phases will sweep from LISA through LIGO frequency bands. If the debris forms a disk about the NS, it may fragment and form planets.Comment: 28 pages, 25 figures, 6 table

Rising to the Challenge: Results From a Scorecard on Local Health Performance, 2012

Provides comparative data with respect to healthcare access, prevention and treatment, costs and avoidable hospital use, and outcomes in three hundred-plus localities. Examines disparities in access and quality by geography, income, and poverty rate