11,632 research outputs found
Inhomogeneous reionization and the polarization of the cosmic microwave background
In a universe with inhomogeneous reionization, the ionized patches create a
second order signal in the cosmic microwave background polarization anisotropy.
This signal originates in the coupling of the free electron fluctuation to the
quadruple moment of the temperature anisotropy. We examine the contribution
from a simple inhomogeneous reionization model and find that the signal from
such a process is below the detectable limits of the Planck Surveyor mission.
However t he signal is above the fundamental uncertainty limit from cosmic
variance, so th at a future detection with a high accuracy experiment on
sub-arcminute scales is possible.Comment: 10 pages, 2 eps figures, final version accepted for publication in
ApJ Letter
A novel tissue inhibitor of metalloproteinases-3 mutation reveals a common molecular phenotype in sorsby's fundus dystrophy
Sorsby’s fundus dystrophy (SFD) is a dominantly inherited
degenerative disease of the retina that leads to
loss of vision in middle age. It has been shown to be
caused by mutations in the gene for tissue inhibitor of
metalloproteinases-3 (TIMP-3). Five different mutations
have previously been identified, all introducing an extra
cysteine residue into exon 5 (which forms part of the
C-terminal domain) of the TIMP-3 molecule; however,
the significance of these mutations to the disease phenotype
was unknown. In this report, we describe the
expression of several of these mutated genes, together
with a previously unreported novel TIMP-3 mutation
from a family with SFD that results in truncation of
most of the C-terminal domain of the molecule. Despite
these differences, all of these molecules are expressed
and exhibit characteristics of the normal protein, including
inhibition of metalloproteinases and binding to
the extracellular matrix. However, unlike wild-type
TIMP-3, they all form dimers. These observations, together
with the recent finding that expression of TIMP-3
is increased, rather than decreased, in eyes from patients
with SFD, provides compelling evidence that
dimerized TIMP-3 plays an active role in the disease
process by accumulating in the eye. Increased expression
of TIMP-3 is also observed in other degenerative
retinal diseases, including the more severe forms of agerelated
macular degeneration, the most common cause
of blindness in the elderly in developed countries. We
hypothesize that overexpression of TIMP-3 may prove to
be a critical step in the progression of a variety of degenerative
retinopathies
Large Scale Structure Forecast Constraints on Particle Production During Inflation
Bursts of particle production during inflation provide a well-motivated
mechanism for creating bump like features in the primordial power spectrum.
Current data constrains these features to be less than about 5% the size of the
featureless primordial power spectrum at wavenumbers of about 0.1 h Mpc^{-1}.
We forecast that the Planck cosmic microwave background experiment will be able
to strengthen this constraint to the 0.5% level. We also predict that adding
data from a square kilometer array (SKA) galaxy redshift survey would improve
the constraint to about the 0.1% level. For features at larger wave-numbers,
Planck will be limited by Silk damping and foregrounds. While, SKA will be
limited by non-linear effects. We forecast for a Cosmic Inflation Probe (CIP)
galaxy redshift survey, similar constraints can be achieved up to about a
wavenumber of 1 h Mpc^{-1}.Comment: 10 pages. Matches PRD accepted versio
Secondary CMB anisotropies in a universe reionized in patches
In a universe reionized in patches, the Doppler effect from Thomson
scattering off free electrons generates secondary cosmic microwave background
(CMB) anisotropies. For a simple model with small patches and late
reionization, we analytically calculate the anisotropy power spectrum. Patchy
reionization can, in principle, be the main source of anisotropies on arcminute
scales. On larger angular scales, its contribution to the CMB power spectrum is
a small fraction of the primary signal and is only barely detectable in the
power spectrum with even an ideal, i.e. cosmic variance limited, experiment and
an extreme model of reionization. Consequently patchy reionization is unlikely
to affect cosmological parameter estimation from the acoustic peaks in the CMB.
Its detection on small angles would help determine the ionization history of
the universe, in particular the typical size of the ionized region and the
duration of the reionization process.Comment: 7 pages, 2 figures, submitted to Ap
Age problem in holographic dark energy
We study the age problem of the universe with the holographic DE model
introduced in [21], and test the model with some known old high redshift
objects (OHRO). The parameters of the model have been constrained using the
SNIa, CMB and BAO data set. We found that the age of the old quasar APM 08
279+5255 at z = 3.91 can be described by the model.Comment: 13 page
The Damping Tail of CMB Anisotropies
By decomposing the damping tail of CMB anisotropies into a series of transfer
functions representing individual physical effects, we provide ingredients that
will aid in the reconstruction of the cosmological model from small-scale CMB
anisotropy data. We accurately calibrate the model-independent effects of
diffusion and reionization damping which provide potentially the most robust
information on the background cosmology. Removing these effects, we uncover
model-dependent processes such as the acoustic peak modulation and
gravitational enhancement that can help distinguish between alternate models of
structure formation and provide windows into the evolution of fluctuations at
various stages in their growth.Comment: 24pgs, aaspp4, 10 figs. included; supporting material (e.g. color
figures) at http://www.sns.ias.edu/~whu/pub.htm
Using the acoustic peak to measure cosmological parameters
Recent measurements of the cosmic microwave background radiation by the
Boomerang experiment indicate that the universe is spatially flat. Here some
simple back-of-the-envelope calculations are used to explain their result. The
main result is a simple formula for the angular scale of the acoustic peak in
terms of the standard cosmological parameters:
l=193*[1+3(1-Omega_0)/5+(1-h)/5+Omega_Lambda/35].Comment: 4 pages, 1 figure, Explanations have been clarifie
Computing CMB Anisotropy in Compact Hyperbolic Spaces
The measurements of CMB anisotropy have opened up a window for probing the
global topology of the universe on length scales comparable to and beyond the
Hubble radius. For compact topologies, the two main effects on the CMB are: (1)
the breaking of statistical isotropy in characteristic patterns determined by
the photon geodesic structure of the manifold and (2) an infrared cutoff in the
power spectrum of perturbations imposed by the finite spatial extent. We
present a completely general scheme using the regularized method of images for
calculating CMB anisotropy in models with nontrivial topology, and apply it to
the computationally challenging compact hyperbolic topologies. This new
technique eliminates the need for the difficult task of spatial eigenmode
decomposition on these spaces. We estimate a Bayesian probability for a
selection of models by confronting the theoretical pixel-pixel temperature
correlation function with the COBE-DMR data. Our results demonstrate that
strong constraints on compactness arise: if the universe is small compared to
the `horizon' size, correlations appear in the maps that are irreconcilable
with the observations. If the universe is of comparable size, the likelihood
function is very dependent upon orientation of the manifold wrt the sky. While
most orientations may be strongly ruled out, it sometimes happens that for a
specific orientation the predicted correlation patterns are preferred over the
conventional infinite models.Comment: 15 pages, LaTeX (IOP style included), 3 color figures (GIF) in
separate files. Minor revision to match the version accepted in Class.
Quantum Grav.: Proc. of Topology and Cosmology, Cleveland, 1997. The paper
can be also downloaded from
http://www.cita.utoronto.ca/~pogosyan/cwru_proc.ps.g
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