1,367 research outputs found
Acceleration Method of Neighbor Search with GRAPE and Morton-ordering
We describe a new method to accelerate neighbor searches on GRAPE, i.e. a
special purpose hardware that efficiently calculates gravitational forces and
potentials in -body simulations. In addition to the gravitational
calculations, GRAPE simultaneously constructs the lists of neighbor particles
that are necessary for Smoothed Particle Hydrodynamics (SPH). However, data
transfer of the neighbor lists from GRAPE to the host computer is time
consuming, and can be a bottleneck. In fact, the data transfer can take about
the same time as the calculations of forces themselves. Making use of GRAPE's
special treatment of neighbor lists, we can reduce the amount of data transfer
if we search neighbors in the order that the neighbor lists, constructed in a
single GRAPE run, overlap each other. We find that the Morton-ordering requires
very low additional calculation and programming costs, and results in
successful speed-up on data transfer. We show some benchmark results in the
case of GRAPE-5. Typical reduction in transferred data becomes as much as 90%.
This method is suitable not only for GRAPE-5, but also GRAPE-3 and the other
versions of GRAPE.Comment: 9 pages, 6 figures, accepted for publication in PAS
Equation of State for Parallel Rigid Spherocylinders
The pair distribution function of monodisperse rigid spherocylinders is
calculated by Shinomoto's method, which was originally proposed for hard
spheres. The equation of state is derived by two different routes: Shinomoto's
original route, in which a hard wall is introduced to estimate the pressure
exerted on it, and the virial route. The pressure from Shinomoto's original
route is valid only when the length-to-width ratio is less than or equal to
0.25 (i.e., when the spherocylinders are nearly spherical). The virial equation
of state is shown to agree very well with the results of numerical simulations
of spherocylinders with length-to-width ratio greater than or equal to 2
Will Nonlinear Peculiar Velocity and Inhomogeneous Reionization Spoil 21cm Cosmology from the Epoch of Reionization?
The 21cm background from the epoch of reionization is a promising
cosmological probe: line-of-sight velocity fluctuations distort redshift, so
brightness fluctuations in Fourier space depend upon angle, which linear theory
shows can separate cosmological from astrophysical information. Nonlinear
fluctuations in ionization, density and velocity change this, however. The
validity and accuracy of the separation scheme are tested here for the first
time, by detailed reionization simulations. The scheme works reasonably well
early in reionization ( 80% ionized).Comment: 2 figures, matches published PRL versio
A Water Maser and Ammonia Survey of GLIMPSE Extended Green Objects (EGOs)
We present the results of a Nobeyama 45-m water maser and ammonia survey of
all 94 northern GLIMPSE Extended Green Objects (EGOs), a sample of massive
young stellar objects (MYSOs) identified based on their extended 4.5 micron
emission. We observed the ammonia (1,1), (2,2), and (3,3) inversion lines, and
detect emission towards 97%, 63%, and 46% of our sample, respectively (median
rms ~50 mK). The water maser detection rate is 68% (median rms ~0.11 Jy). The
derived water maser and clump-scale gas properties are consistent with the
identification of EGOs as young MYSOs. To explore the degree of variation among
EGOs, we analyze subsamples defined based on MIR properties or maser
associations. Water masers and warm dense gas, as indicated by emission in the
higher-excitation ammonia transitions, are most frequently detected towards
EGOs also associated with both Class I and II methanol masers. 95% (81%) of
such EGOs are detected in water (ammonia(3,3)), compared to only 33% (7%) of
EGOs without either methanol maser type. As populations, EGOs associated with
Class I and/or II methanol masers have significantly higher ammonia linewidths,
column densities, and kinetic temperatures than EGOs undetected in methanol
maser surveys. However, we find no evidence for statistically significant
differences in water maser properties (such as maser luminosity) among any EGO
subsamples. Combining our data with the 1.1 mm continuum Bolocam Galactic Plane
Survey, we find no correlation between isotropic water maser luminosity and
clump number density. Water maser luminosity is weakly correlated with clump
(gas) temperature and clump mass.Comment: Astrophysical Journal, accepted. Emulateapj, 24 pages including 24
figures, plus 9 tables (including full content of online-only tables
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