8,853 research outputs found
The angular power spectrum of radio emission at 2.3 GHz
We have analysed the Rhodes/HartRAO survey at 2326 MHz and derived the global
angular power spectrum of Galactic continuum emission. In order to measure the
angular power spectrum of the diffuse component, point sources were removed
from the map by median filtering. A least-square fit to the angular power
spectrum of the entire survey with a power law spectrum C_l proportional to
l^{-alpha}, gives alpha = 2.43 +/- 0.01 for l = 2-100. The angular power
spectrum of radio emission appears to steepen at high Galactic latitudes and
for observed regions with |b| > 20 deg, the fitted spectral index is alpha =
2.92 +/- 0.07. We have extrapolated this result to 30 GHz (the lowest frequency
channel of Planck) and estimate that no significant contribution to the sky
temperature fluctuation is likely to come from synchrotron at degree-angular
scalesComment: 10 pages, 10 figures, accepted for publication by Astronomy &
Astrophysic
Quantum-Enhanced Sensing Based on Time Reversal of Nonlinear Dynamics
We experimentally demonstrate a nonlinear detection scheme exploiting
time-reversal dynamics that disentangles continuous variable entangled states
for feasible readout. Spin-exchange dynamics of Bose-Einstein condensates is
used as the nonlinear mechanism which not only generates entangled states but
can also be time reversed by controlled phase imprinting. For demonstration of
a quantum-enhanced measurement we construct an active atom SU(1,1)
interferometer, where entangled state preparation and nonlinear readout both
consist of parametric amplification. This scheme is capable of exhausting the
quantum resource by detecting solely mean atom numbers. Controlled nonlinear
transformations widen the spectrum of useful entangled states for applied
quantum technologies.Comment: 9 pages, 3 figures, 3 pages supplementary material, 2 supplementary
figure
IIASA's Work on Climate Change: Assessing Environmental Impacts
This Status Report is adapted from a lecture presented by Matthias Jonas at the Institute for Meteorology and Geophysics, University of Vienna, May 1992. In his lecture, Dr. Jonas clearly summarizes the status of the work being carried out within the Climate Change Projections Study at IIASA. This work involves linking a policy-oriented climate change model, the Integrated Model to Assess the Greenhouse Effect (IMAGE), to models of ecological change such as the Global Vegetation Model, the Timber Assessment Model, and the Regional Acidification INformation and Simulation (RAINS) model. These models were at least partially developed at IIASA. The result of this linkage work, which is being carried out in collaboration with the Netherlands National Institute of Public Health and Environmental Protection (RIVM), and possibly other institutes, is intended to be a tool to help policy makers assess in a rapid and time-dependent way changes in regional ecology resulting from various greenhouse gas emission scenarios
Stellar Double Coronagraph: a multistage coronagraphic platform at Palomar observatory
We present a new instrument, the "Stellar Double Coronagraph" (SDC), a
flexible coronagraphic platform. Designed for Palomar Observatory's 200" Hale
telescope, its two focal and pupil planes allow for a number of different
observing configurations, including multiple vortex coronagraphs in series for
improved contrast at small angles. We describe the motivation, design,
observing modes, wavefront control approaches, data reduction pipeline, and
early science results. We also discuss future directions for the instrument.Comment: 25 pages, 12 figures. Correspondence welcome. The published work is
open access and differs trivially from the version posted here. The published
version may be found at
http://iopscience.iop.org/article/10.1088/1538-3873/128/965/075003/met
Integrated Focal Plane Arrays for Millimeter-wave Astronomy
We are developing focal plane arrays of bolometric detectors for sub-millimeter and millimeter-wave astrophysics. We propose a flexible array architecture using arrays of slot antennae coupled via low-loss superconducting Nb transmission line to microstrip filters and antenna-coupled bolometers. By combining imaging and filtering functions with transmission line, we are able to realize unique structures such as a multi-band polarimeter and a planar, dispersive spectrometer. Micro-strip bolometers have significantly smaller active volume than
standard detectors with extended absorbers, and can realize higher sensitivity and speed of response. The integrated array has natural immunity to stray radiation or spectral leaks, and minimizes the suspended mass operating at 0.1 - 0.3 K. We also discuss future space-borne spectroscopy and polarimetry applications
Towards a model of full-sky Galactic synchrotron intensity and linear polarisation: a re-analysis of the Parkes data
We have analysed the angular power spectra of the Parkes radio continuum and
polarisation survey of the Southern galactic plane at 2.4 GHz. We have found
that in the multipole range l=40-250 the angular power spectrum of the
polarised intensity is well described by a power-law spectrum with fitted
spectral index alpha_L = 2.37 +- 0.21. In the same multipole range the angular
power spectra of the E and B components of the polarised signal are
significantly flatter, with fitted spectral indices respectively of alpha_E =
1.57 +- 0.12 and alpha_B = 1.45 +- 0.12. Temperature fluctuations in the E and
B components are mostly determined by variations in polarisation angle. We have
combined these results with other data from available radio surveys in order to
produce a full-sky toy model of Galactic synchrotron intensity and linear
polarisation at high frequencies (> 10 GHz). This can be used to study the
feasibility of measuring the Cosmic Microwave Background polarisation with
forthcoming experiments and satellite missions.Comment: 17 pages, 11 figures. Accepted for publication in A&A. Paper with
higher quality images available at
ftp://astro.esa.int/pub/synchrotron/paper.ps.g
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