21,203 research outputs found
Atlas and checklist of the bark and ambrosia beetles of Texas and Oklahoma (Curculionidae: Scolytinae and Platypodinae)
180 species of bark and ambrosia beetles (Curculionidae: Scolytinae and Platypodinae) are known to occur in Texas and Oklahoma. 175 species are known from Texas, 35 of which are reported here for the first time. 78 species are known from Oklahoma, 47 of which are new records for the state. Based on overall distribution patterns the largest group of species found in Texas and virtually all known from Oklahoma are widely distributed in eastern and southeastern North America, reaching their southwestern limits here. In the case of Texas other large elements include Neotropical elements shared with Mexico and a large number found in southwestern North America. New distribution and significant new host records are discussed. Distribution maps are included for most species and a checklist is provided as an appendix
How closely do baryons follow dark matter on large scales?
We investigate the large-scale clustering and gravitational interaction of
baryons and dark matter (DM) over cosmic time using a set of collisionless
N-body simulations. Both components, baryons and DM, are evolved from distinct
primordial density and velocity power spectra as predicted by early-universe
physics. We first demonstrate that such two-component simulations require an
unconventional match between force and mass resolution (i.e. force softening on
at least the mean particle separation scale). Otherwise, the growth on any
scale is not correctly recovered because of a spurious coupling between the two
species at the smallest scales. With these simulations, we then demonstrate how
the primordial differences in the clustering of baryons and DM are
progressively diminished over time. In particular, we explicitly show how the
BAO signature is damped in the spatial distribution of baryons and imprinted in
that of DM. This is a rapid process, yet it is still not fully completed at low
redshifts. On large scales, the overall shape of the correlation function of
baryons and DM differs by 2% at z = 9 and by 0.2% at z = 0. The differences in
the amplitude of the BAO peak are approximately a factor of 5 larger: 10% at z
= 9 and 1% at z = 0. These discrepancies are, however, smaller than effects
expected to be introduced by galaxy formation physics in both the shape of the
power spectrum and in the BAO peak, and are thus unlikely to be detected given
the precision of the next generation of galaxy surveys. Hence, our results
validate the standard practice of modelling the observed galaxy distribution
using predictions for the total mass clustering in the Universe.Comment: 9 pages, 6 figures. Replaced with version published in MNRA
Comparing Fully General Relativistic and Newtonian Calculations of Structure Formation
In the standard approach to studying cosmological structure formation, the
overall expansion of the Universe is assumed to be homogeneous, with the
gravitational effect of inhomogeneities encoded entirely in a Newtonian
potential. A topic of ongoing debate is to what degree this fully captures the
dynamics dictated by general relativity, especially in the era of precision
cosmology. To quantitatively assess this, we directly compare standard N-body
Newtonian calculations to full numerical solutions of the Einstein equations,
for cold matter with various magnitude initial inhomogeneities on scales
comparable to the Hubble horizon. We analyze the differences in the evolution
of density, luminosity distance, and other quantities defined with respect to
fiducial observers. This is carried out by reconstructing the effective
spacetime and matter fields dictated by the Newtonian quantities, and by taking
care to distinguish effects of numerical resolution. We find that the fully
general relativistic and Newtonian calculations show excellent agreement, even
well into the nonlinear regime. They only notably differ in regions where the
weak gravity assumption breaks down, which arise when considering extreme cases
with perturbations exceeding standard values.Comment: 17 pages, 14 figures; revised to match PRD versio
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