408 research outputs found
The electric field close to an undulating interface
The electric potential close to a boundary between two dielectric material layers reflects the geometry of such an interface. The local variations arise from the combination of material parameters and from the nature of the inhomogeneity. Here, the arising electric field is considered for both a sinusoidally varying boundary and for a “rough,” Gaussian test case. We discuss the applicability of a one-dimensional model with the varying layer thickness as a parameter and the generic scaling of the results. As an application we consider the effect of paper roughness on toner transfer in electrophotographic printing.Peer reviewe
CMB component separation by parameter estimation
We propose a solution to the CMB component separation problem based on
standard parameter estimation techniques. We assume a parametric spectral model
for each signal component, and fit the corresponding parameters pixel by pixel
in a two-stage process. First we fit for the full parameter set (e.g.,
component amplitudes and spectral indices) in low-resolution and high
signal-to-noise ratio maps using MCMC, obtaining both best-fit values for each
parameter, and the associated uncertainty. The goodness-of-fit is evaluated by
a chi^2 statistic. Then we fix all non-linear parameters at their
low-resolution best-fit values, and solve analytically for high-resolution
component amplitude maps. This likelihood approach has many advantages: The
fitted model may be chosen freely, and the method is therefore completely
general; all assumptions are transparent; no restrictions on spatial variations
of foreground properties are imposed; the results may be rigorously monitored
by goodness-of-fit tests; and, most importantly, we obtain reliable error
estimates on all estimated quantities. We apply the method to simulated Planck
and six-year WMAP data based on realistic models, and show that separation at
the muK level is indeed possible in these cases. We also outline how the
foreground uncertainties may be rigorously propagated through to the CMB power
spectrum and cosmological parameters using a Gibbs sampling technique.Comment: 20 pages, 10 figures, submitted to ApJ. For a high-resolution
version, see http://www.astro.uio.no/~hke/docs/eriksen_et_al_fgfit.p
New Measurements of Fine-Scale CMB Polarization Power Spectra from CAPMAP at Both 40 and 90 GHz
We present new measurements of the cosmic microwave background (CMB)
polarization from the final season of the Cosmic Anisotropy Polarization MAPper
(CAPMAP). The data set was obtained in winter 2004-2005 with the 7 m antenna in
Crawford Hill, New Jersey, from 12 W-band (84-100 GHz) and 4 Q-band (36-45 GHz)
correlation polarimeters with 3.3' and 6.5' beamsizes, respectively. After
selection criteria were applied, 956 (939) hours of data survived for analysis
of W-band (Q-band) data. Two independent and complementary pipelines produced
results in excellent agreement with each other. A broad suite of null tests as
well as extensive simulations showed that systematic errors were minimal, and a
comparison of the W-band and Q-band sky maps revealed no contamination from
galactic foregrounds. We report the E-mode and B-mode power spectra in 7 bands
in the range 200 < l < 3000, extending the range of previous measurements to
higher l. The E-mode spectrum, which is detected at 11 sigma significance, is
in agreement with cosmological predictions and with previous work at other
frequencies and angular resolutions. The BB power spectrum provides one of the
best limits to date on B-mode power at 4.8 uK^2 (95% confidence).Comment: 19 pages, 17 figures, 2 tables, submitted to Ap
Large Scale Structures in Kinetic Gravity Braiding Model That Can Be Unbraided
We study cosmological consequences of a kinetic gravity braiding model, which
is proposed as an alternative to the dark energy model. The kinetic braiding
model we study is characterized by a parameter n, which corresponds to the
original galileon cosmological model for n=1. We find that the background
expansion of the universe of the kinetic braiding model is the same as the
Dvali-Turner's model, which reduces to that of the standard cold dark matter
model with a cosmological constant (LCDM model) for n equal to infinity. We
also find that the evolution of the linear cosmological perturbation in the
kinetic braiding model reduces to that of the LCDM model for n=\infty. Then, we
focus our study on the growth history of the linear density perturbation as
well as the spherical collapse in the nonlinear regime of the density
perturbations, which might be important in order to distinguish between the
kinetic braiding model and the LCDM model when n is finite. The theoretical
prediction for the large scale structure is confronted with the multipole power
spectrum of the luminous red galaxy sample of the Sloan Digital Sky survey. We
also discuss future prospects of constraining the kinetic braiding model using
a future redshift survey like the WFMOS/SuMIRe PFS survey as well as the
cluster redshift distribution in the South Pole Telescope survey.Comment: 41 pages, 20 figures; This version was accepted for publication in
JCA
Faraday rotation measures of northern-hemisphere pulsars using CHIME/Pulsar
Using commissioning data from the first year of operation of the Canadian
Hydrogen Intensity Mapping Experiment's (CHIME) Pulsar backend system, we
conduct a systematic analysis of the Faraday Rotation Measure (RM) of the
northern hemisphere pulsars detected by CHIME. We present 55 new RMs as well as
obtain improved RM uncertainties for 25 further pulsars. CHIME's low observing
frequency and wide bandwidth between 400-800 MHz contribute to the precision of
our measurements, whereas the high cadence observation provide extremely high
signal-to-noise co-added data. Our results represent a significant increase of
the pulsar RM census, particularly regarding the northern hemisphere. These new
RMs are for sources that are located in the Galactic plane out to 10 kpc, as
well as off the plane to a scale height of ~16 kpc. This improved knowledge of
the Faraday sky will contribute to future Galactic large-scale magnetic
structure and ionosphere modelling.Comment: 13 pages, 7 figures, accepted by MNRA
Scintillation of PSR B1508+55 -- the view from a 10,000-km baseline
We report on the simultaneous Giant Metrewave Radio Telescope (GMRT) and
Algonquin Radio Observatory (ARO) observations at 550-750 MHz of the
scintillation of PSR B1508+55, resulting in a 10,000-km baseline. This
regime of measurement lies between the shorter few 100-1000~km baselines of
earlier multi-station observations and the much longer earth-space baselines.
We measure a scintillation cross-correlation coefficient of , offset from
zero time lag due to a ~s traversal time of the scintillation pattern.
The scintillation time of 135~s is longer, ruling out isotropic as
well as strictly 1D scattering. Hence, the low cross-correlation coefficient is
indicative of highly anisotropic but 2D scattering. The common scintillation
detected on the baseline is confined to low delays of s,
suggesting that this correlation may not be associated with the parabolic
scintillation arc detected at the GMRT. Detection of pulsed echoes and their
direct imaging with the Low Frequency Array (LOFAR) by a different group enable
them to measure a distance of 125~pc to the screen causing these echoes. These
previous measurements, alongside our observations, lead us to propose that
there are at least two scattering screens: the closer 125 pc screen causing the
scintillation arc detected at GMRT, and a screen further beyond causing the
scintillation detected on the GMRT-ARO baseline. We advance the hypothesis that
the 125-pc screen partially resolves the speckle images on the screen beyond
leading to loss of coherence in the scintillation dynamic spectrum, to explain
the low cross-correlation coefficient.Comment: 10 pages, 8 figures, accepted for publication in MNRA
Optical followup of galaxy clusters detected by the South Pole Telescope
The South Pole Telescope (SPT) is a 10 meter telescope operating at mm
wavelengths. It has recently completed a three-band survey covering 2500 sq.
degrees. One of the survey's main goals is to detect galaxy clusters using
Sunyaev-Zeldovich effect and use these clusters for a variety of cosmological
and astrophysical studies such as the dark energy equation of state, the
primordial non-gaussianity and the evolution of galaxy populations. Since 2005,
we have been engaged in a comprehensive optical and near-infrared followup
program (at wavelengths between 0.4 and 5 {\mu}m) to image high-significance
SPT clusters, to measure their photometric redshifts, and to estimate the
contamination rate of the candidate lists. These clusters are then used for
various cosmological and astrophysical studies.Comment: For TAUP 2011 proceeding
A measurement of secondary cosmic microwave background anisotropies with two years of South Pole Telescope observations
We present the first three-frequency South Pole Telescope (SPT) cosmic
microwave background (CMB) power spectra. The band powers presented here cover
angular scales 2000 < ell < 9400 in frequency bands centered at 95, 150, and
220 GHz. At these frequencies and angular scales, a combination of the primary
CMB anisotropy, thermal and kinetic Sunyaev-Zel'dovich (SZ) effects, radio
galaxies, and cosmic infrared background (CIB) contributes to the signal. We
combine Planck and SPT data at 220 GHz to constrain the amplitude and shape of
the CIB power spectrum and find strong evidence for non-linear clustering. We
explore the SZ results using a variety of cosmological models for the CMB and
CIB anisotropies and find them to be robust with one exception: allowing for
spatial correlations between the thermal SZ effect and CIB significantly
degrades the SZ constraints. Neglecting this potential correlation, we find the
thermal SZ power at 150 GHz and ell = 3000 to be 3.65 +/- 0.69 muK^2, and set
an upper limit on the kinetic SZ power to be less than 2.8 muK^2 at 95%
confidence. When a correlation between the thermal SZ and CIB is allowed, we
constrain a linear combination of thermal and kinetic SZ power: D_{3000}^{tSZ}
+ 0.5 D_{3000}^{kSZ} = 4.60 +/- 0.63 muK^2, consistent with earlier
measurements. We use the measured thermal SZ power and an analytic, thermal SZ
model calibrated with simulations to determine sigma8 = 0.807 +/- 0.016.
Modeling uncertainties involving the astrophysics of the intracluster medium
rather than the statistical uncertainty in the measured band powers are the
dominant source of uncertainty on sigma8 . We also place an upper limit on the
kinetic SZ power produced by patchy reionization; a companion paper uses these
limits to constrain the reionization history of the Universe.Comment: 25 pages; 14 figures; Submitted to ApJ (Updated to reflect referee
comments
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