8,723 research outputs found
Mock galaxy catalogs using the quick particle mesh method
Sophisticated analysis of modern large-scale structure surveys requires mock
catalogs. Mock catalogs are used to optimize survey design, test reduction and
analysis pipelines, make theoretical predictions for basic observables and
propagate errors through complex analysis chains. We present a new method,
which we call "quick particle mesh", for generating many large-volume,
approximate mock catalogs at low computational cost. The method is based on
using rapid, low-resolution particle mesh simulations that accurately reproduce
the large-scale dark matter density field. Particles are sampled from the
density field based on their local density such that they have N-point
statistics nearly equivalent to the halos resolved in high-resolution
simulations, creating a set of mock halos that can be populated using halo
occupation methods to create galaxy mocks for a variety of possible target
classes.Comment: 13 pages, 16 figures. Matches version accepted by MNRAS. Code
available at http://github.com/mockFactor
Tests of redshift-space distortions models in configuration space for the analysis of the BOSS final data release
Observations of redshift-space distortions in spectroscopic galaxy surveys
offer an attractive method for observing the build-up of cosmological
structure, which depends both on the expansion rate of the Universe and our
theory of gravity. In preparation for analysis of redshift-space distortions
from the Baryon Oscillation Spectroscopic Survey (BOSS) final data release we
compare a number of analytic and phenomenological `streaming' models, specified
in configuration space, to mock catalogs derived in different ways from several
N-body simulations. The galaxies in each mock catalog have properties similar
to those of the higher redshift galaxies measured by BOSS but differ in the
details of how small-scale velocities and halo occupancy are determined. We
find that all of the analytic models fit the simulations over a limited range
of scales while failing at small scales. We discuss which models are most
robust and on which scales they return reliable estimates of the rate of growth
of structure: we find that models based on some form of resummation can fit our
N-body data for BOSS-like galaxies above Mpc well enough to return
unbiased parameter estimates.Comment: 12 pages, 11 figures, matches version accepted by MNRA
Recommended from our members
GEO debris and interplanetary dust: fluxes and charging behaviour
GEO debris and interplanetary dust: fluxes and charging behavior
In September 1996, a dust/debris detector: GORID was launched into the
geostationary (GEO) region as a piggyback instrument on the Russian Express-2
telecommunications spacecraft. The instrument began its normal operation in
April 1997 and ended its mission in July 2002. The goal of this work was to use
GORID's particle data to identify and separate the space debris to
interplanetary dust particles (IDPs) in GEO, to more finely determine the
instrument's measurement characteristics and to derive impact fluxes. While the
physical characteristics of the GORID impacts alone are insufficient for a
reliable distinction between debris and interplanetary dust, the temporal
behavior of the impacts are strong enough indicators to separate the
populations based on clustering. Non-cluster events are predominantly
interplanetary, while cluster events are debris. The GORID mean flux
distributions (at mass thresholds which are impact speed dependent) for IDPs,
corrected for dead time, are 1.35x10^{-4} m^{-2} s^{-1} using a mean detection
rate: 0.54 d^{-1}, and for space debris are 6.1x10^{-4} m^{-2} s^{-1} using a
mean detection rate: 2.5 d^{-1}. Beta-meteoroids were not detected. Clusters
could be a closely-packed debris cloud or a particle breaking up due to
electrostatic fragmentation after high charging.Comment: * Comments: 6 pages, 4 postscript figures, in Dust in Planetary
Systems 2005, Krueger, H. and Graps, A. eds., ESA Publications, SP in press
(2006). For high resolution version, see:
http://www.mpi-hd.mpg.de/dustgroup/~graps/dips2005/GrapsetalDIPS2005.pd
Pitfalls in the use of the lung colony assay to assess T-cell function in irradiated mice.
Mice depleted of T lymphocytes by thymectomy, whole-body irradiation and bone-marrow reconstitution showed a marked increase in susceptibility to the development of lung colonies after i.v. injection of cells of an immunogenic fibrosarcoma. However, a similar increase was observed in unthymectomized, irradiated and reconstituted mice that had recovered their T-cell function, as evidenced by rejection of allogeneic skin grafts. In both thymectomized and unthymectomized mice subjected to whole-body irradiation, the lung-colony-forming efficiency was high 1 day after irradiation, declined to a minimum at 7 days, and thereafter increased again, unless the animals were held in a pathogen-free environment. Reconstitution of T-cell-depleted mice with thymocytes and/or a thymic lobe graft tended to increase further, rather than reduce, lung-colony-forming efficiency. Induction of profound lymphopenia, by irradiation of the whole body except the thorax, did not significantly increase lung colony yields. These studies show that the lung colony assay is not a reliable method of assessing T-cell function in irradiated mice
A Retrospective Analysis Of Risk Factors That Influence Intravenous Busulfan Kinetics In Adult Patients
Optical Follow-up of New SMC Wing Be/X-ray Binaries
We investigate the optical counterparts of recently discovered Be/X-ray
binaries in the Small Magellanic Cloud. In total four sources, SXP101, SXP700,
SXP348 and SXP65.8 were detected during the Chandra Survey of the Wing of the
SMC. SXP700 and SXP65.8 were previously unknown. Many optical ground based
telescopes have been utilised in the optical follow-up, providing coverage in
both the red and blue bands. This has led to the classification of all of the
counterparts as Be stars and confirms that three lie within the Galactic
spectral distribution of known Be/X-ray binaries. SXP101 lies outside this
distribution becoming the latest spectral type known. Monitoring of the Halpha
emission line suggests that all the sources bar SXP700 have highly variable
circumstellar disks, possibly a result of their comparatively short orbital
periods. Phase resolved X-ray spectroscopy has also been performed on SXP65.8,
revealing that the emission is indeed harder during the passage of the X-ray
beam through the line of sight.Comment: 9 pages, 9 figures, 2 tables, accepted for publication in MNRA
Synthesis, characterisation and study of magnetocaloric effects (enhanced and reduced) in manganate perovskites.
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