120,354 research outputs found
Nonuniversal Effects in the Homogeneous Bose Gas
Effective field theory predicts that the leading nonuniversal effects in the
homogeneous Bose gas arise from the effective range for S-wave scattering and
from an effective three-body contact interaction. We calculate the leading
nonuniversal contributions to the energy density and condensate fraction and
compare the predictions with results from diffusion Monte Carlo calculations by
Giorgini, Boronat, and Casulleras. We give a crude determination of the
strength of the three-body contact interaction for various model potentials.
Accurate determinations could be obtained from diffusion Monte Carlo
calculations of the energy density with higher statistics.Comment: 24 pages, RevTex, 5 ps figures, included with epsf.te
CORE: Augmenting Regenerating-Coding-Based Recovery for Single and Concurrent Failures in Distributed Storage Systems
Data availability is critical in distributed storage systems, especially when
node failures are prevalent in real life. A key requirement is to minimize the
amount of data transferred among nodes when recovering the lost or unavailable
data of failed nodes. This paper explores recovery solutions based on
regenerating codes, which are shown to provide fault-tolerant storage and
minimum recovery bandwidth. Existing optimal regenerating codes are designed
for single node failures. We build a system called CORE, which augments
existing optimal regenerating codes to support a general number of failures
including single and concurrent failures. We theoretically show that CORE
achieves the minimum possible recovery bandwidth for most cases. We implement
CORE and evaluate our prototype atop a Hadoop HDFS cluster testbed with up to
20 storage nodes. We demonstrate that our CORE prototype conforms to our
theoretical findings and achieves recovery bandwidth saving when compared to
the conventional recovery approach based on erasure codes.Comment: 25 page
Formation time distribution of dark matter haloes: theories versus N-body simulations
This paper uses numerical simulations to test the formation time distribution
of dark matter haloes predicted by the analytic excursion set approaches. The
formation time distribution is closely linked to the conditional mass function
and this test is therefore an indirect probe of this distribution. The
excursion set models tested are the extended Press-Schechter (EPS) model, the
ellipsoidal collapse (EC) model, and the non-spherical collapse boundary (NCB)
model. Three sets of simulations (6 realizations) have been used to investigate
the halo formation time distribution for halo masses ranging from dwarf-galaxy
like haloes (, where is the characteristic non-linear mass
scale) to massive haloes of . None of the models can match the
simulation results at both high and low redshift. In particular, dark matter
haloes formed generally earlier in our simulations than predicted by the EPS
model. This discrepancy might help explain why semi-analytic models of galaxy
formation, based on EPS merger trees, under-predict the number of high redshift
galaxies compared with recent observations.Comment: 7 pages, 5 figures, accepted for publication in MNRA
Crumpling wires in two dimensions
An energy-minimal simulation is proposed to study the patterns and mechanical
properties of elastically crumpled wires in two dimensions. We varied the
bending rigidity and stretching modulus to measure the energy allocation,
size-mass exponent, and the stiffness exponent. The mass exponent is shown to
be universal at value . We also found that the stiffness exponent
is universal, but varies with the plasticity parameters and
. These numerical findings agree excellently with the experimental
results
- …