464 research outputs found
Biological implications of high-energy cosmic ray induced muon flux in the extragalactic shock model
A ~ 62 My periodicity in fossil biodiversity has been observed in independent
studies of paleontology databases over ~0.5Gy. The period and phase of this
biodiversity cycle coincides with the oscillation of our solar system normal to
the galactic disk with an amplitude ~70 parsecs and a period ~64 My. Our Galaxy
is falling toward the Virgo cluster, forming a galactic shock at the north end
of our galaxy due to this motion, capable of accelerating particles and
exposing our galaxy's northern side to a higher flux of cosmic rays. These
high-energy particles strike the Earth's atmosphere initiating extensive air
showers, ionizing the atmosphere by producing charged secondary particles.
Secondary particles such as muons produced as a result of nuclear interactions
are able to reach the ground and enhance the biological radiation dose. Using a
Monte Carlo simulation package CORSIKA, we compute the biological dose
resulting from enhanced muon exposure from cosmic rays and discuss their
implications for terrestrial biodiversity variations.Comment: Accepted for publication in Geophysical Research Letter
Comparison of Dynamical Approximation Schemes for Non-Linear Gravitational Clustering
I report on controlled comparison of gravitational approximation schemes
linear/lognormal/adhesion/frozen-flow/Zel'dovich(ZA) and ZA's second--order
generalization. In the last two cases we also created new versions of the
approximation by truncation, i.e., by finding an optimum smoothing window (see
text) for the initial conditions. The Zel'dovich approximation, with optimized
initial smoothing, worked extremely well. Its second-order generalization was
slightly better. The success of our best-choice was a result of the treatment
of the phases of nonlinear Fourier components. The adhesion approximation
produced the most accurate nonlinear power spectrum and density distribution,
but its phase errors suggest mass condensations were moved somewhat
incorrectly. Due to its better reproduction of the mass density distribution
function and power spectrum, adhesion might be preferred for some uses. We
recommend either n-body simulations or our modified versions of ZA, depending
on the purpose. Modified ZA can rapidly generate large numbers of realizations
of model universes with good accuracy down to galaxy group (or smaller) mass
scales.Comment: 8 pp., plain TeX. ApJ Letters, in press. Contact
[email protected] for Figure
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