229 research outputs found
Three-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Foreground Polarization
We present a full-sky model of polarized Galactic microwave emission based on
three years of observations by the Wilkinson Microwave Anisotropy Probe (WMAP)
at frequencies from 23 to 94 GHz. The model compares maps of the Stokes Q and U
components from each of the 5 WMAP frequency bands in order to separate
synchrotron from dust emission, taking into account the spatial and frequency
dependence of the synchrotron and dust components. This simple two-component
model of the interstellar medium accounts for at least 97% of the polarized
emission in the WMAP maps of the microwave sky. Synchrotron emission dominates
the polarized foregrounds at frequencies below 50 GHz, and is comparable to the
dust contribution at 65 GHz. The spectral index of the synchrotron component,
derived solely from polarization data, is -3.2 averaged over the full sky, with
a modestly flatter index on the Galactic plane. The synchrotron emission has
mean polarization fraction 2--4% in the Galactic plane and rising to over 20%
at high latitude, with prominent features such as the North Galactic Spur more
polarized than the diffuse component. Thermal dust emission has polarization
fraction 1% near the Galactic center, rising to 6% at the anti-center. Diffuse
emission from high-latitude dust is also polarized with mean fractional
polarization 0.036 +/- 0.011.Comment: 9 pages with 8 figures. For higher quality figures, see the version
posted at http://lambda.gsfc.nasa.gov/product/map/dr2/map_bibliography.cf
PSYCHOSES IN CHILDREN OF SCHIZOPHRENIC MOTHERS
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66064/1/j.1600-0447.1967.tb07624.x.pd
First Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Data Processing Methods and Systematic Errors Limits
We describe the calibration and data processing methods used to generate
full-sky maps of the cosmic microwave background (CMB) from the first year of
Wilkinson Microwave Anisotropy Probe (WMAP) observations. Detailed limits on
residual systematic errors are assigned based largely on analyses of the flight
data supplemented, where necessary, with results from ground tests. The data
are calibrated in flight using the dipole modulation of the CMB due to the
observatory's motion around the Sun. This constitutes a full-beam calibration
source. An iterative algorithm simultaneously fits the time-ordered data to
obtain calibration parameters and pixelized sky map temperatures. The noise
properties are determined by analyzing the time-ordered data with this sky
signal estimate subtracted. Based on this, we apply a pre-whitening filter to
the time-ordered data to remove a low level of 1/f noise. We infer and correct
for a small ~1% transmission imbalance between the two sky inputs to each
differential radiometer, and we subtract a small sidelobe correction from the
23 GHz (K band) map prior to further analysis. No other systematic error
corrections are applied to the data. Calibration and baseline artifacts,
including the response to environmental perturbations, are negligible.
Systematic uncertainties are comparable to statistical uncertainties in the
characterization of the beam response. Both are accounted for in the covariance
matrix of the window function and are propagated to uncertainties in the final
power spectrum. We characterize the combined upper limits to residual
systematic uncertainties through the pixel covariance matrix.Comment: One of 13 companion papers on first-year WMAP results submitted to
ApJ; 58 pages with 14 figures; a version with higher quality figures is at
http://lambda.gsfc.nasa.gov/product/map/map_bibliography.htm
Three-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Beam Profiles, Data Processing, Radiometer Characterization and Systematic Error Limits
The WMAP satellite has completed 3 years of observations of the cosmic
microwave background radiation. The 3-year data products include several sets
of full sky maps of the Stokes I, Q and U parameters in 5 frequency bands,
spanning 23 to 94 GHz, and supporting items, such as beam window functions and
noise covariance matrices. The processing used to produce the current sky maps
and supporting products represents a significant advancement over the first
year analysis, and is described herein. Improvements to the pointing
reconstruction, radiometer gain modeling, window function determination and
radiometer spectral noise parametrization are presented. A detailed description
of the updated data processing that produces maximum likelihood sky map
estimates is presented, along with the methods used to produce reduced
resolution maps and corresponding noise covariance matrices. Finally two
methods used to evaluate the noise of the full resolution sky maps are
presented along with several representative year-to-year null tests,
demonstrating that sky maps produced from data from different observational
epochs are consistent.Comment: 58 pgs, 16 figs. Accepted version of the 3-year paper as posted on
http://lambda.gsfc.nasa.gov/product/map/dr2/map_bibliography.cfm in January
200
The Relation Between the Surface Brightness and the Diameter for Galactic Supernova Remnants
In this work, we have constructed a relation between the surface brightness
() and diameter (D) of Galactic C- and S-type supernova remnants
(SNRs). In order to calibrate the -D dependence, we have carefully
examined some intrinsic (e.g. explosion energy) and extrinsic (e.g. density of
the ambient medium) properties of the remnants and, taking into account also
the distance values given in the literature, we have adopted distances for some
of the SNRs which have relatively more reliable distance values. These
calibrator SNRs are all C- and S-type SNRs, i.e. F-type SNRs (and S-type SNR
Cas A which has an exceptionally high surface brightness) are excluded. The
Sigma-D relation has 2 slopes with a turning point at D=36.5 pc: (at 1
GHz)=8.4 D
WmHzster (for
WmHzster and D36.5 pc) and (at 1
GHz)=2.7 10 D
WmHzster (for
WmHzster and D36.5 pc). We discussed the theoretical
basis for the -D dependence and particularly the reasons for the change
in slope of the relation were stated. Added to this, we have shown the
dependence between the radio luminosity and the diameter which seems to have a
slope close to zero up to about D=36.5 pc. We have also adopted distance and
diameter values for all of the observed Galactic SNRs by examining all the
available distance values presented in the literature together with the
distances found from our -D relation.Comment: 45 pages, 2 figures, accepted for publication in Astronomical and
Astrophysical Transaction
Thermal Properties of Graphene, Carbon Nanotubes and Nanostructured Carbon Materials
Recent years witnessed a rapid growth of interest of scientific and
engineering communities to thermal properties of materials. Carbon allotropes
and derivatives occupy a unique place in terms of their ability to conduct
heat. The room-temperature thermal conductivity of carbon materials span an
extraordinary large range - of over five orders of magnitude - from the lowest
in amorphous carbons to the highest in graphene and carbon nanotubes. I review
thermal and thermoelectric properties of carbon materials focusing on recent
results for graphene, carbon nanotubes and nanostructured carbon materials with
different degrees of disorder. A special attention is given to the unusual size
dependence of heat conduction in two-dimensional crystals and, specifically, in
graphene. I also describe prospects of applications of graphene and carbon
materials for thermal management of electronics.Comment: Review Paper; 37 manuscript pages; 4 figures and 2 boxe
Wilkinson Microwave Anisotropy Probe (WMAP) Three Year Results: Implications for Cosmology
A simple cosmological model with only six parameters (matter density, Omega_m
h^2, baryon density, Omega_b h^2, Hubble Constant, H_0, amplitude of
fluctuations, sigma_8, optical depth, tau, and a slope for the scalar
perturbation spectrum, n_s) fits not only the three year WMAP temperature and
polarization data, but also small scale CMB data, light element abundances,
large-scale structure observations, and the supernova luminosity/distance
relationship. Using WMAP data only, the best fit values for cosmological
parameters for the power-law flat LCDM model are (Omega_m h^2, Omega_b h^2, h,
n_s, tau, sigma_8) = 0.1277+0.0080-0.0079, 0.02229+-0.00073, 0.732+0.031-0.032,
0.958+-0.016, 0.089+-0.030, 0.761+0.049-0.048). The three year data
dramatically shrink the allowed volume in this six dimensional parameter space.
Assuming that the primordial fluctuations are adiabatic with a power law
spectrum, the WMAP data_alone_ require dark matter, and favor a spectral index
that is significantly less than the Harrison-Zel'dovich-Peebles scale-invariant
spectrum (n_s=1, r=0). Models that suppress large-scale power through a running
spectral index or a large-scale cut-off in the power spectrum are a better fit
to the WMAP and small scale CMB data than the power-law LCDM model; however,
the improvement in the fit to the WMAP data is only Delta chi^2 = 3 for 1 extra
degree of freedom. The combination of WMAP and other astronomical data yields
significant constraints on the geometry of the universe, the equation of state
of the dark energy, the gravitational wave energy density, and neutrino
properties. Consistent with the predictions of simple inflationary theories, we
detect no significant deviations from Gaussianity in the CMB maps.Comment: 91 pgs, 28 figs. Accepted version of the 3-year paper as posted to
http://lambda.gsfc.nasa.gov/product/map/dr2/map_bibliography.cfm in January
200
Non-Gaussian Inflationary Perturbations from the dS/CFT Correspondence
We use the dS/CFT correspondence and bulk gravity to predict the form of the
renormalized holographic three-point correlation function of the operator which
is dual to the inflaton field perturbation during single-field, slow-roll
inflation. Using Maldcaena's formulation of the correspondence, this correlator
can be related to the three-point function of the curvature perturbation
generated during single-field inflation, and we find exact agreement with
previous bulk QFT calculations. This provides a consistency check on existing
derivations of the non-Gaussianity from single-field inflation and also yields
insight into the nature of the dS/CFT correspondence. As a result of our
calculation, we obtain the properly renormalized dS/CFT one-point function,
including boundary contributions where derivative interactions are present in
the bulk. In principle, our method may be employed to derive the n-point
correlators of the inflationary curvature perturbation within the context of
(n-1)th-order perturbation theory, rather than nth-order theory as in
conventional approaches.Comment: 23 pages, uses iopart.cls. Replaced with version accepted by JCAP;
some clarifications in the introduction, and references adde
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