Gamma-Ray Bursts via Pair Plasma Fireballs from Heated Neutron Stars

In this paper we model the emission from a relativistically expanding electron-positron pair plasma fireball originating near the surface of a heated neutron star. This pair fireball is deposited via the annihilation of neutrino pairs emanating from the surface of the hot neutron star. The heating of neutron stars may occur in close neutron star binary systems near their last stable orbit. We model the relativistic expansion and subsequent emission of the plasma and find 10^51 to 10^52 ergs in gamma-rays are produced with spectral and temporal properties consistent with observed gamma-ray bursts.Comment: 5 pages, 3 figures. Submitted to the Conference Proceedings of the 5th Huntsville Gamma-Ray Burst Symposiu

The suitability of various spacecraft for future space applications missions

The Space Applications Advisory Committee (SAAC) of NASA's Advisory Council was asked by the Associate Administrator for Space Science and Applications to consider the most suitable future means for accomplishing space application missions. To comply with this request, SAAC formed a Task Force whose report is contained in this document. In their considerations, the Task Force looked into the suitability of likely future spacecraft options for supporting various types of application mission payloads. These options encompass a permanent manned space station, the Space Shuttle operating in a sortie mode, unmanned platforms that integrate a wide variety of instruments or other devices, and smaller free fliers that accommodate at most a few functions. The Task Force also recognized that the various elements could be combined to form a larger space infrastructure. This report summarizes the results obtained by the Task Force. It describes the approach utilized, the findings and their analysis, and the conclusions

Calculation of the deep penetration of radiation by the method of invariant imbedding

Radiation shield penetration calculation from invariant imbedding metho

Binary Induced Neutron-Star Compression, Heating, and Collapse

We analyze several aspects of the recently noted neutron star collapse instability in close binary systems. We utilize (3+1) dimensional and spherical numerical general relativistic hydrodynamics to study the origin, evolution, and parametric sensitivity of this instability. We derive the modified conditions of hydrostatic equilibrium for the stars in the curved space of quasi-static orbits. We examine the sensitivity of the instability to the neutron star mass and equation of state. We also estimate limits to the possible interior heating and associated neutrino luminosity which could be generated as the stars gradually compress prior to collapse. We show that the radiative loss in neutrinos from this heating could exceed the power radiated in gravity waves for several hours prior to collapse. The possibility that the radiation neutrinos could produce gamma-ray (or other electromagnetic) burst phenomena is also discussed.Comment: 17 pages, 7 figure

Distribution of graph-distances in Boltzmann ensembles of RNA secondary structures

Large RNA molecules often carry multiple functional domains whose spatial arrangement is an important determinant of their function. Pre-mRNA splicing, furthermore, relies on the spatial proximity of the splice junctions that can be separated by very long introns. Similar effects appear in the processing of RNA virus genomes. Albeit a crude measure, the distribution of spatial distances in thermodynamic equilibrium therefore provides useful information on the overall shape of the molecule can provide insights into the interplay of its functional domains. Spatial distance can be approximated by the graph-distance in RNA secondary structure. We show here that the equilibrium distribution of graph-distances between arbitrary nucleotides can be computed in polynomial time by means of dynamic programming. A naive implementation would yield recursions with a very high time complexity of O(n^11). Although we were able to reduce this to O(n^6) for many practical applications a further reduction seems difficult. We conclude, therefore, that sampling approaches, which are much easier to implement, are also theoretically favorable for most real-life applications, in particular since these primarily concern long-range interactions in very large RNA molecules.Comment: Peer-reviewed and presented as part of the 13th Workshop on Algorithms in Bioinformatics (WABI2013

Revised Relativistic Hydrodynamical Model for Neutron-Star Binaries

We report on numerical results from a revised hydrodynamic simulation of binary neutron-star orbits near merger. We find that the correction recently identified by Flanagan significantly reduces but does not eliminate the neutron-star compression effect. Although results of the revised simulations show that the compression is reduced for a given total orbital angular momentum, the inner most stable circular orbit moves to closer separation distances. At these closer orbits significant compression and even collapse is still possible prior to merger for a sufficiently soft EOS. The reduced compression in the corrected simulation is consistent with other recent studies of rigid irrotational binaries in quasiequilibrium in which the compression effect is observed to be small. Another significant effect of this correction is that the derived binary orbital frequencies are now in closer agreement with post-Newtonian expectations.Comment: Submitted to Phys. Rev.