8 research outputs found
About the connection between the power spectrum of the Cosmic Microwave Background and the Fourier spectrum of rings on the sky
In this article we present and study a scaling law of the CMB
Fourier spectrum on rings which allows us (i) to combine spectra corresponding
to different colatitude angles (e.g. several detectors at the focal plane of a
telescope), and (ii) to recover the power spectrum once the
coefficients have been measured. This recovery is performed numerically below
the 1% level for colatitudes degrees. In addition, taking
advantage of the smoothness of the and of the , we provide
analytical expressions which allow to recover one of the spectrum at the 1%
level, the other one being known.Comment: 8 pages, 8 figure
First Detection of Polarization of the Submillimetre Diffuse Galactic Dust Emission by Archeops
We present the first determination of the Galactic polarized emission at 353
GHz by Archeops. The data were taken during the Arctic night of February 7,
2002 after the balloon--borne instrument was launched by CNES from the Swedish
Esrange base near Kiruna. In addition to the 143 GHz and 217 GHz frequency
bands dedicated to CMB studies, Archeops had one 545 GHz and six 353 GHz
bolometers mounted in three polarization sensitive pairs that were used for
Galactic foreground studies. We present maps of the I, Q, U Stokes parameters
over 17% of the sky and with a 13 arcmin resolution at 353 GHz (850 microns).
They show a significant Galactic large scale polarized emission coherent on the
longitude ranges [100, 120] and [180, 200] deg. with a degree of polarization
at the level of 4-5%, in agreement with expectations from starlight
polarization measurements. Some regions in the Galactic plane (Gem OB1,
Cassiopeia) show an even stronger degree of polarization in the range 10-20%.
Those findings provide strong evidence for a powerful grain alignment mechanism
throughout the interstellar medium and a coherent magnetic field coplanar to
the Galactic plane. This magnetic field pervades even some dense clouds.
Extrapolated to high Galactic latitude, these results indicate that
interstellar dust polarized emission is the major foreground for PLANCK-HFI CMB
polarization measurement.Comment: Submitted to Astron. & Astrophys., 14 pages, 12 Fig., 2 Table
The Cosmic Microwave Background Anisotropy Power Spectrum measured by Archeops
We present a determination by the Archeops experiment of the angular power
spectrum of the cosmic microwave background anisotropy in 16 bins over the
multipole range l=15-350. Archeops was conceived as a precursor of the Planck
HFI instrument by using the same optical design and the same technology for the
detectors and their cooling. Archeops is a balloon-borne instrument consisting
of a 1.5 m aperture diameter telescope and an array of 21 photometers
maintained at ~100 mK that are operating in 4 frequency bands centered at 143,
217, 353 and 545 GHz. The data were taken during the Arctic night of February
7, 2002 after the instrument was launched by CNES from Esrange base (Sweden).
The entire data cover ~ 30% of the sky.This first analysis was obtained with a
small subset of the dataset using the most sensitive photometer in each CMB
band (143 and 217 GHz) and 12.6% of the sky at galactic latitudes above 30
degrees where the foreground contamination is measured to be negligible. The
large sky coverage and medium resolution (better than 15 arcminutes) provide
for the first time a high signal-to-noise ratio determination of the power
spectrum over angular scales that include both the first acoustic peak and
scales probed by COBE/DMR. With a binning of Delta(l)=7 to 25 the error bars
are dominated by sample variance for l below 200. A companion paper details the
cosmological implications.Comment: A&A Letter, in press, 6 pages, 4 figures, see also
http://www.archeops.or
Archeops in-flight performance, data processing, and map making
International audienceAims:Archeops is a balloon-borne experiment inspired by the Planck satellite and its high frequency instrument (HFI). It is designed to measure the cosmic microwave background (CMB) temperature anisotropies at high angular resolution (~12 arcmin) over a large fraction of the sky (around 30%) at 143, 217, 353, and 545 GHz. The Archeops 353 GHz channel consists of three pairs of polarized sensitive bolometers designed to detect the polarized diffuse emission of Galactic dust. Methods: In this paper we present an update of the instrumental setup, as well as the flight performance for the last Archeops flight campaign (February 2002 from Kiruna, Sweden). We also describe the processing and analysis of the Archeops time-ordered data for that campaign, which led to measurement of the CMB anisotropy power spectrum in the multipole range â = 10-700 and to the first measurements of both the polarized emission of dust at large angular scales and its power spectra in the multipole range â = 3-70 Results: We present maps covering approximately 30% of the sky. These maps contain Galactic emission, including the Galactic plane, in the four Archeops channels at 143, 217, 353, and 545 GHz and CMB anisotropies at 143 and 217 GHz. These are one of the first sub-degree-resolution maps in the millimeter and submillimeter ranges of the large angular-scale diffuse Galactic dust emission and CMB temperature anisotropies, respectively
Numerical prediction of wind turbine noise
This paper develops and validates the first principle based numerical method for predicting the noise radiated from the rotating Horizontal-Axis Wind Turbine (HAWT) blades. The noise radiated to the far-field was predicted by the code based on Ffowcs Williams-Hawkings (FW-H) equation, using both original non-permeable formulation and permeable formulation. A commercially available CFD solver, ANSYS CFX 11.0, was used to calculate the flow parameters on and around the blade surface that are required for FW-H codes. A capability of the solver for modelling the flow field around the wind turbine blades was validated by comparing with the experimental results of NREL phase VI wind turbine blades. The FW-H codes were validated using acoustic results of UH-1H helicopter rotor in hover and Hartzell aircraft propeller in forward motion, which were measured in anechoic wind tunnel facility. Then the developed FW-H acoustic codes were applied to calculate the noise radiated from NREL Phase VI wind turbine blades. (C) 2010 Elsevier Ltd. All rights reserved