1,024 research outputs found
A Large Sky Simulation of the Gravitational Lensing of the Cosmic Microwave Background
Large scale structure deflects cosmic microwave background (CMB) photons.
Since large angular scales in the large scale structure contribute
significantly to the gravitational lensing effect, a realistic simulation of
CMB lensing requires a sufficiently large sky area. We describe simulations
that include these effects, and present both effective and multiple plane
ray-tracing versions of the algorithm, which employs spherical harmonic space
and does not use the flat sky approximation. We simulate lensed CMB maps with
an angular resolution of ~0.9 arcmin. The angular power spectrum of the
simulated sky agrees well with analytical predictions. Maps generated in this
manner are a useful tool for the analysis and interpretation of upcoming CMB
experiments such as PLANCK and ACT.Comment: 14 pages, 12 figures, replaced with version accepted for publication
by the AP
The Tree-Particle-Mesh N-body Gravity Solver
The Tree-Particle-Mesh (TPM) N-body algorithm couples the tree algorithm for
directly computing forces on particles in an hierarchical grouping scheme with
the extremely efficient mesh based PM structured approach. The combined TPM
algorithm takes advantage of the fact that gravitational forces are linear
functions of the density field. Thus one can use domain decomposition to break
down the density field into many separate high density regions containing a
significant fraction of the mass but residing in a very small fraction of the
total volume. In each of these high density regions the gravitational potential
is computed via the tree algorithm supplemented by tidal forces from the
external density distribution. For the bulk of the volume, forces are computed
via the PM algorithm; timesteps in this PM component are large compared to
individually determined timesteps in the tree regions. Since each tree region
can be treated independently, the algorithm lends itself to very efficient
parallelization using message passing. We have tested the new TPM algorithm (a
refinement of that originated by Xu 1995) by comparison with results from
Ferrell & Bertschinger's P^3M code and find that, except in small clusters, the
TPM results are at least as accurate as those obtained with the
well-established P^3M algorithm, while taking significantly less computing
time. Production runs of 10^9 particles indicate that the new code has great
scientific potential when used with distributed computing resources.Comment: 24 pages including 9 figures, uses aaspp4.sty; revised to match
published versio
Characterising Coarse Particle Gangue Densimetric Separation Response in Gold Bearing Sulfide Ore Broken by Different Fine Crushing Modes
The separation behaviour of gangue during densimetric classification and the subsequent inherent propensity to pre-concentrate metal values in gold-bearing sulfide ore is reviewed in this thesis. From this review, the influence of the findings on both interpretative technique and the implied liberation induced by specified crushing mode is reported. This thesis aims to predict preferential grade by density deportment response in gravity separation approaches using metallurgical parameters for value component upgrade and recovery into concentrate
Cosmological Constraints from a Combined Analysis of the Cluster Mass Function and Microwave Background Anisotropies
We present constraints on several cosmological parameters from a combined
analysis of the most recent Cosmic Microwave Background anisotropy data and the
Sloan Digital Sky Survey cluster mass function. We find that the combination of
the two data sets breaks several degeneracies among the parameters and provides
the following constraints: ,
, , ,
.Comment: 7 pages, 1 figur
The New Testament Concept of Shame
Is the society which gave birth to the New Testament a guilt society or a shame society? Is the function of shame in the New Testament psychological or sociological? To what degree does the sanction of shame determine the behavior and life of the followers of Christ? These are some of the initial questions which aroused interest in carrying out the present study. The function of shame in the early Christian community and its usage in the New Testament does not conform precisely to either the Eastern or the Western view of shame: nor does it merely occupy a mediating middle ground between the two. Rather, the New Testament usage of the shame concept has definite and definable characteristics of its own. The purpose of this study is to isolate and give expression thereto
Where are the missing baryons in clusters?
Observations of clusters of galaxies suggest that they contain significantly
fewer baryons (gas plus stars) than the cosmic baryon fraction. This `missing
baryon' puzzle is especially surprising for the most massive clusters which are
expected to be representative of the cosmic matter content of the universe
(baryons and dark matter). Here we show that the baryons may not actually be
missing from clusters, but rather are extended to larger radii than typically
observed. The baryon deficiency is typically observed in the central regions of
clusters (~0.5 the virial radius). However, the observed gas-density profile is
significantly shallower than the mass-density profile, implying that the gas is
more extended than the mass and that the gas fraction increases with radius. We
use the observed density profiles of gas and mass in clusters to extrapolate
the measured baryon fraction as a function of radius and as a function of
cluster mass. We find that the baryon fraction reaches the cosmic value near
the virial radius for all groups and clusters above 5e13 solar masses. This
suggests that the baryons are not missing, they are simply located in cluster
outskirts. Heating processes (shock-heating of the intracluster gas, plus
supernovae and AGN feedback) that cause the gas to expand are likely
explanations for these results. Upcoming observations should be able to detect
these baryons.Comment: Submitted to PNA
The Amplitude of Mass Fluctuations
We determine the linear amplitude of mass fluctuations in the universe,
sigma_8, from the abundance of massive clusters at redshifts z=0.5 to 0.8. The
evolution of massive clusters depends exponentially on the amplitude of mass
fluctuations and thus provides a powerful measure of this important
cosmological parameter. The relatively high abundance of massive clusters
observed at z>0.5, and the relatively slow evolution of their abundance with
time, suggest a high amplitude of mass fluctuations: sigma_8=0.9 +-10% for
Omega_m=0.4, increasing slightly to sigma_8=0.95 for Omega_m=0.25 and
sigma_8=1.0 for Omega_m=0.1 (flat CDM models). We use the cluster abundance
observed at z=0.5 to 0.8 to derive a normalization relation from the
high-redshift clusters, which is only weakly dependent on Omega_m:
sigma_8*Omega_m^0.14 = 0.78 +-0.08. When combined with recent constraints from
the present-day cluster mass function (sigma_8*Omega_m^0.6=0.33 +-0.03) we find
sigma_8=0.98 +-0.1 and Omega_m=0.17 +-0.05. Low sigma_8 values (<0.7) are
unlikely; they produce an order of magnitude fewer massive clusters than
observed.Comment: 12 pages including 3 figures; updated to match published versio
The Shape, Multiplicity, and Evolution of Superclusters in LambdaCDM Cosmology
We determine the shape, multiplicity, size, and radial structure of
superclusters in the LambdaCDM concordance cosmology from z = 0 to z = 2.
Superclusters are defined as clusters of clusters in our large-scale
cosmological simulation. We find that superclusters are triaxial in shape; many
have flattened since early times to become nearly two-dimensional structures at
present, with a small fraction of filamentary systems. The size and
multiplicity functions are presented at different redshifts. Supercluster sizes
extend to scales of ~ 100 - 200 Mpc/h. The supercluster multiplicity (richness)
increases linearly with supercluster size. The density profile in superclusters
is approximately isothermal (~ R^{-2}) and steepens on larger scales. These
results can be used as a new test of the current cosmology when compared with
upcoming observations of large-scale surveys.Comment: 33 pages, 15 figures, accepted to ApJ; minor content changes, some
figures removed to shorten pape
Accurate Realizations of the Ionized Gas in Galaxy Clusters: Calibrating Feedback
Using the full, three-dimensional potential of galaxy cluster halos (drawn
from an N-body simulation of the current, most favored cosmology), the
distribution of the X-ray emitting gas is found by assuming a polytropic
equation of state and hydrostatic equilibrium, with constraints from
conservation of energy and pressure balance at the cluster boundary. The
resulting properties of the gas for these simulated redshift zero clusters (the
temperature distribution, mass-temperature and luminosity-temperature
relations, and the gas fraction) are compared with observations in the X-ray of
nearby clusters. The observed properties are reproduced only under the
assumption that substantial energy injection from non-gravitational sources has
occurred. Our model does not specify the source, but star formation and AGN may
be capable of providing this energy, which amounts to 3 to 5 x10^{-5} of the
rest mass in stars (assuming ten percent of the gas initially in the cluster
forms stars). With the method described here it is possible to generate
realistic X-ray and Sunyaev-Zel'dovich cluster maps and catalogs from N-body
simulations, with the distributions of internal halo properties (and their
trends with mass, location, and time) taken into account.Comment: Matches ApJ published version; 30 pages, 7 figure
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