364 research outputs found
New Limits on the Polarized Anisotropy of the Cosmic Microwave Background at Subdegree Angular Scales
We update the limit from the 90 GHz PIQUE ground-based polarimeter on the
magnitude of any polarized anisotropy of the cosmic microwave radiation. With a
second year of data, we have now limited both Q and U on a ring of 1 degree
radius. The window functions are broad: for E-mode polarization, the effective
l is = 191 +143 -132. We find that the E-mode signal can be no greater than
8.4 microK (95% CL), assuming no B-mode polarization. Limits on a possible
B-mode signal are also presented.Comment: 4 pages, 3 figures, submitted to Astrophysical Journal Letter
A Limit on the Polarized Anisotropy of the Cosmic Microwave Background at Subdegree Angular Scales
A ground-based polarimeter, PIQUE, operating at 90 GHz has set a new limit on
the magnitude of any polarized anisotropy in the cosmic microwave background.
The combination of the scan strategy and full width half maximum beam of 0.235
degrees gives broad window functions with average multipoles, l = 211+294-146
and l = 212+229-135 for the E- and B-mode window functions, respectively. A
joint likelihood analysis yields simultaneous 95% confidence level flat band
power limits of 14 and 13 microkelvin on the amplitudes of the E- and B-mode
angular power spectra, respectively. Assuming no B-modes, a 95% confidence
limit of 10 microkelvin is placed on the amplitude of the E-mode angular power
spectrum alone.Comment: 4 pages, 3 figures, submitted to Astrophysical Journal Letter
Characterizing Atacama B-mode Search Detectors with a Half-Wave Plate
The Atacama B-Mode Search (ABS) instrument is a cryogenic (10 K)
crossed-Dragone telescope located at an elevation of 5190 m in the Atacama
Desert in Chile that observed for three seasons between February 2012 and
October 2014. ABS observed the Cosmic Microwave Background (CMB) at large
angular scales () to limit the B-mode polarization spectrum around
the primordial B-mode peak from inflationary gravity waves at .
The ABS focal plane consists of 480 transition-edge sensor (TES) bolometers.
They are coupled to orthogonal polarizations from a planar ortho-mode
transducer (OMT) and observe at 145 GHz. ABS employs an ambient-temperature,
rapidly rotating half-wave plate (HWP) to mitigate systematic effects and move
the signal band away from atmospheric noise, allowing for the recovery of
large angular scales. We discuss how the signal at the second harmonic of the
HWP rotation frequency can be used for data selection and for monitoring the
detector responsivities.Comment: 7 pages, 3 figures, conference proceedings submitted to the Journal
of Low Temperature Detector
Systematic effects from an ambient-temperature, continuously-rotating half-wave plate
We present an evaluation of systematic effects associated with a
continuously-rotating, ambient-temperature half-wave plate (HWP) based on two
seasons of data from the Atacama B-Mode Search (ABS) experiment located in the
Atacama Desert of Chile. The ABS experiment is a microwave telescope sensitive
at 145 GHz. Here we present our in-field evaluation of celestial (CMB plus
galactic foreground) temperature-to-polarization leakage. We decompose the
leakage into scalar, dipole, and quadrupole leakage terms. We report a scalar
leakage of ~0.01%, consistent with model expectations and an order of magnitude
smaller than other CMB experiments have reported. No significant dipole or
quadrupole terms are detected; we constrain each to be <0.07% (95% confidence),
limited by statistical uncertainty in our measurement. Dipole and quadrupole
leakage at this level lead to systematic error on r<0.01 before any mitigation
due to scan cross-linking or boresight rotation. The measured scalar leakage
and the theoretical level of dipole and quadrupole leakage produce systematic
error of r<0.001 for the ABS survey and focal-plane layout before any data
correction such as so-called deprojection. This demonstrates that ABS achieves
significant beam systematic error mitigation from its HWP and shows the promise
of continuously-rotating HWPs for future experiments.Comment: 11 pages, 8 figures; revision to submitted version, Fig. 5 and Eqs.
(14) and (15) corrected; added Fig. 9 and description, text revisions for
clarification, Fig. 5 revised for better calibration, corrected labeling
errors and plotting bugs in Fig. 3, 4, and Eq. (14) and (15
Modulation of CMB polarization with a warm rapidly-rotating half-wave plate on the Atacama B-Mode Search (ABS) instrument
We evaluate the modulation of Cosmic Microwave Background (CMB) polarization
using a rapidly-rotating, half-wave plate (HWP) on the Atacama B-Mode Search
(ABS). After demodulating the time-ordered-data (TOD), we find a significant
reduction of atmospheric fluctuations. The demodulated TOD is stable on time
scales of 500-1000 seconds, corresponding to frequencies of 1-2 mHz. This
facilitates recovery of cosmological information at large angular scales, which
are typically available only from balloon-borne or satellite experiments. This
technique also achieves a sensitive measurement of celestial polarization
without differencing the TOD of paired detectors sensitive to two orthogonal
linear polarizations. This is the first demonstration of the ability to remove
atmospheric contamination at these levels from a ground-based platform using a
rapidly-rotating HWP.Comment: 8 pages, 8 figures, Published in RSI under the title "Modulation of
cosmic microwave background polarization with a warm rapidly rotating
half-wave plate on the Atacama B-Mode Search instrument.
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
An Absolute Measurement of the Cosmic Microwave Background Radiation Temperature at 10.7 GHz
A balloon-borne experiment has measured the absolute temperature of the
cosmic microwave background radiation (CMBR) at 10.7 GHz to be Tcmbr = 2.730 +-
.014 K. The error is the quadratic sum of several systematic errors, with
statistical error of less than 0.1 mK. The instrument comprises a cooled
corrugated horn antenna coupled to a total-power radiometer. A cryogenic
mechanical waveguide switch alternately connects the radiometer to the horn and
to an internal reference load. The small measured temperature difference (<= 20
mK) between the sky signal and the reference load in conjunction with the use
of a cold front end keeps systematic instrumental corrections small.
Atmospheric and window emission are minimized by flying the instrument at 24 km
altitude. A large outer ground screen and smaller inner screen shield the
instrument from stray radiation from the ground and the balloon. In-flight
tests constrain the magnitude of ground radiation contamination, and low level
interference is monitored through observations in several narrow frequency
bands.Comment: 14 pages, 1 figure, submitted to ApJ
Discrete population balance models of random agglomeration and cleavage in polymer pyrolysis
The processes of random agglomeration and cleavage (both of which are important for the development of new models of polymer combustion, but are also applicable in a wide range of fields including atmospheric physics, radiation modelling and astrophysics) are analysed using population balance methods. The evolution of a discrete distribution of particles is considered within this framework, resulting in a set of ordinary differential equations for the individual particle concentrations. Exact solutions for these equations are derived, together with moment generating functions. Application of the discrete Laplace transform (analogous to the Z-transform) is found to be effective in these problems, providing both exact solutions for particle concentrations and moment generating functions. The combined agglomeration-cleavage problem is also considered. Unfortunately, it has been impossible to find an exact solution for the full problem, but a stable steady state has been identified and computed
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