11 research outputs found
Line broadcasting in cycles
AbstractBroadcasting is the process of transmitting information from an originating node (processor) in a network to all other nodes in the network. A local broadcast scheme only allows a node to send information along single communication links to adjacent nodes, while a line broadcast scheme allows nodes to use paths of several communication links to call distant nodes. The minimum time possible for broadcasting in a network of n nodes when no node is involved in more than one communication at any given time is ⌊ log n⌋ phases. Local broadcasting is not sufficient, in general, for broadcasting to be completed in minimum time; line broadcasting is always sufficient. An optimal line broadcast is a minimum-time broadcast that uses the smallest possible total number of communication links. In this paper, we give a complete characterization of optimal line broadcasting in cycles, and we develop efficient methods for constructing optimal line broadcast schemes
Formation of Pillars at the Boundaries between H II Regions and Molecular Clouds
We investigate numerically the hydrodynamic instability of an ionization
front (IF) accelerating into a molecular cloud, with imposed initial
perturbations of different amplitudes. When the initial amplitude is small, the
imposed perturbation is completely stabilized and does not grow. When the
initial perturbation amplitude is large enough, roughly the ratio of the
initial amplitude to wavelength is greater than 0.02, portions of the IF
temporarily separate from the molecular cloud surface, locally decreasing the
ablation pressure. This causes the appearance of a large, warm HI region and
triggers nonlinear dynamics of the IF. The local difference of the ablation
pressure and acceleration enhances the appearance and growth of a multimode
perturbation. The stabilization usually seen at the IF in the linear regimes
does not work due to the mismatch of the modes of the perturbations at the
cloud surface and in density in HII region above the cloud surface. Molecular
pillars are observed in the late stages of the large amplitude perturbation
case. The velocity gradient in the pillars is in reasonably good agreement with
that observed in the Eagle Nebula. The initial perturbation is imposed in three
different ways: in density, in incident photon number flux, and in the surface
shape. All cases show both stabilization for a small initial perturbation and
large growth of the second harmonic by increasing amplitude of the initial
perturbation above a critical value.Comment: 21 pages, 8 figures, accepted for publication in ApJ. high resolution
figures available upon reques
Supplemental Material for Building Protection Against External Ionizing Fallout Radiation
The US Department of Defense is implementing
the Regional Shelter Analysis methodology to improve the ability of the Hazard
Prediction and Assessment Capability (HPAC) model to account for building
protection. This HPAC improvement effort requires accurate estimates of
building protection for common building construction types worldwide. The main report,
titled <i>Building Protection Against
External Ionizing Fallout Radiation,</i> (a) describes the physics
most relevant to assessing fallout building protection, (b) identifies a set of
key building attributes that are sufficient to characterize fallout shelter
quality for individual buildings, and (c) assesses the degree to which the
building attributes can characterize fallout shelter quality. This report provides more detail on the data
used to verify the conclusions presented in the main report
Nonlinear Dynamics of Ionization Fronts in HII Regions Nonlinear Dynamics of Ionization Fronts in HII Regions
Abstract Hydrodynamic instability of an accelerating ionization front (IF) is investigated with 2D hydrodynamic simulations, including absorption of incident photoionizing photons, recombination in the HII region, and radiative molecular cooling. When the amplitude of the perturbation is large enough, nonlinear dynamics of the IF triggered by the separation of the IF from the cloud surface is observed. This causes the second harmonic of the imposed perturbation to appear on the cloud surfaces, whereas the perturbation in density of ablated gas in the HII region remains largely single mode. This mismatch of modes between the IF and the density perturbation in the HII region prevents the strong stabilization effect seen in the linear regime. Large growth of the perturbation caused by Rayleigh-Taylor-like instability is observed late in time