2,234 research outputs found
Motivating individuals and groups at work: a social identity perspective on leadership and group performance
Weighting CMB and Galactic synchrotron polarisation
We review the present knowledge of the diffuse Galactic synchrotron emission
in polarisation. At microwave frequencies, we assess the expected contamination
to the CMB polarisation angular power spectrum, for and modes, as
expected after the WMAP first year measurements.Comment: 6 pages, 4 figures, proc. of the CMBnet workshop, 20-21 Feb. 2003,
Oxford, U
Optimized in-flight absolute calibration for extended CMB surveys
Accurate measurements of the Cosmic Microwave Background (CMB) anisotropy
call for high precision and reliability of the in-flight calibration. For
extended surveys the CMB dipole provides an excellent calibration source at
frequencies lower than 200 GHz; however poorly known foreground emissions, such
as diffuse galactic components, complicate the signal and introduce a
systematic error in the calibration. We show that introducing a weight function
that takes into account the uncertainty in the a priori knowledge of the sky,
allows us to substantially improve the calibration accuracy with respect to
methods involving galactic latitude cuts. This new method is tested for
Planck-LFI radiometers at 30 and 100 GHz. On short time scales (less than 1
day) the absolute calibration of each channel can be recovered with an overall
1-2% accuracy. We also consider the effect of CMB anisotropy itself on the
calibration, and find that knowledge of the CMB pattern on large scales is
needed to keep the short-time scale calibration accuracy within 1%Comment: 11 pages, 15 figures, accepted to Astronomy & Astrophysic
The Large-Scale Polarization of the Microwave Foreground
Most of the useful information about inflationary gravitational waves and
reionization is on large angular scales where Galactic foreground contamination
is the worst, so a key challenge is to model, quantify and remove polarized
foregrounds. We use the Leiden radio surveys to quantify the polarized
synchrotron radiation at large angular scales, which is likely to be the most
challenging polarized contaminant for the WMAP satellite. We find that the
synchrotron E- and B-contributions are equal to within 10% from 408-820MHz with
a hint of E-domination at higher frequencies. We quantify Faraday Rotation &
Depolarization effects and show that they cause the synchrotron polarization
percentage to drop both towards lower frequencies and towards lower multipoles.Comment: To be published in the proceedings of "The Cosmic Microwave
Background and its Polarization", New Astronomy Reviews, (eds. S. Hanany and
K.A. Olive). 4 pages. More foreground information at
http://www.hep.upenn.edu/~angelica/foreground.html#polar or from
[email protected]
Low-frequency line temperatures of the CMB
Based on SU(2) Yang-Mills thermodynamics we interprete Aracde2's and the
results of earlier radio-surveys on low-frequency CMB line temperatures as a
phase-boundary effect. We explain the excess at low frequencies by evanescent,
nonthermal photon fields of the CMB whose intensity is nulled by that of Planck
distributed calibrator photons. The CMB baseline temperature thus is identified
with the critical temperature of the deconfining-preconfining transition.Comment: v2: 9 pages, 1 figure, extended discussion of why prsent photon mass
bounds are not in contradiction to a low-temperature, low-frequency Meissner
mass responsible for UEGE, matches journal versio
The effectiveness of two novel techniques in establishing the mechanical and contractile responses of biceps femoris
Portable tensiomyography (TMG) and myotonometry (MMT) devices have been developed to measure mechanical and contractile properties of skeletal muscle. The aim of this study was to explore the sensitivity of the aforementioned techniques in detecting a change in passive mechanical properties of the biceps femoris (BF) muscle as a result of change in knee joint angle (i.e. muscle length). BF responses were assessed in 16 young participants (23.4 ± 4.9 years), at three knee joint angles (0°, 45° and 90°), for maximal isometric torque (MIT) along with myo-electrical activity. Contractile and mechanical properties were measured in a relaxed state. Inter-day reliability of the TMG and MMT was also assessed. MIT changed significantly (p < 0.01) across the three angles, so did stiffness and other parameters measured with MMT (p < 0.01). Conversely, TMG could detect changes only at two knee angles (0° and 45°, p < 0.01), when there is enough tension in the muscle. Reliability was overall insufficient for TMG whilst absolute reliability was excellent (coefficient of variation < 5%) for MMT. The ability of MMT more than TMG to detect an inherent change in stiffness can be conceivably exploited in a number of clinical/therapeutic applications that have to do with unnatural changes in passive muscle stiffness
Galactic emission at 19 GHz
We cross-correlate a 19 GHz full sky Cosmic Microwave Background (CMB) survey
with other maps to quantify the foreground contribution. Correlations are
detected with the Diffuse Infrared Background Experiment (DIRBE) 240, 140 and
100 micron maps at high latitudes (|b|>30degrees), and marginal correlations
are detected with the Haslam 408 MHz and the Reich & Reich 1420 MHz synchrotron
maps. The former agree well with extrapolations from higher frequencies probed
by the COBE DMR and Saskatoon experiments and are consistent with both
free-free and rotating dust grain emission.Comment: 4 pages, with 4 figures included. Accepted for publication in ApJL.
Color figure and links at http://www.sns.ias.edu/~angelica/foreground.html#19
or from [email protected]
Digital Deblurring of CMB Maps II: Asymmetric Point Spread Function
In this second paper in a series dedicated to developing efficient numerical
techniques for the deblurring Cosmic Microwave Background (CMB) maps, we
consider the case of asymmetric point spread functions (PSF). Although
conceptually this problem is not different from the symmetric case, there are
important differences from the computational point of view because it is no
longer possible to use some of the efficient numerical techniques that work
with symmetric PSFs. We present procedures that permit the use of efficient
techniques even when this condition is not met. In particular, two methods are
considered: a procedure based on a Kronecker approximation technique that can
be implemented with the numerical methods used with symmetric PSFs but that has
the limitation of requiring only mildly asymmetric PSFs. The second is a
variant of the classic Tikhonov technique that works even with very asymmetric
PSFs but that requires discarding the edges of the maps. We provide details for
efficient implementations of the algorithms. Their performance is tested on
simulated CMB maps.Comment: 9 pages, 13 Figure
Spectral Index of the Diffuse Radio Background Measured From 100 to 200 MHz
The mean absolute brightness temperature of the diffuse radio background was
measured as a function of frequency in a continuous band between 100 and 200
MHz over an effective solid angle of ~pi str at high Galactic latitude. A
spectral brightness temperature index of beta = 2.5 +/- 0.1 (alpha_s = 0.5) was
derived from the observations, where the error limits are 3-sigma and include
estimates of the instrumental systematics. Zenith drift scans with central
declinations of -26.5 degrees and spanning right ascensions 0 to 10 hours
yielded little variation in the mean spectral index. The mean absolute
brightness temperature at 150 MHz was found to reach a minimum of T = 237 +/-
10 K at a right ascension of 2.5 hours. Combining these measurements with those
of Haslam et al. 1982 yields a spectral index of beta = 2.52 +/- 0.04 between
150 and 408 MHz.Comment: 8 pages including 7 figures and 4 tables. Accepted by A
Galactic microwave emission at degree angular scales
We cross-correlate the Saskatoon Ka and Q-Band Cosmic Microwave Background
(CMB) data with different maps to quantify possible foreground contamination.
We detect a marginal correlation (2 sigma) with the Diffuse Infrared Background
Experiment (DIRBE) 240, 140 and 100 microm maps, but we find no significant
correlation with point sources, with the Haslam 408 MHz map or with the Reich
and Reich 1420 MHz map. The rms amplitude of the component correlated with
DIRBE is about 20% of the CMB signal. Interpreting this component as free-free
emission, this normalization agrees with that of Kogut et al. (1996a; 1996b)
and supports the hypothesis that the spatial correlation between dust and warm
ionized gas observed on large angular scales persists to smaller angular
scales. Subtracting this contribution from the CMB data reduces the
normalization of the Saskatoon power spectrum by only a few percent.Comment: Minor revisions to match published version. 14 pages, with 2 figures
included. Color figure and links at
http://www.sns.ias.edu/~angelica/foreground.htm
- …