13,106 research outputs found
Planck pre-launch status: The HFI instrument, from specification to actual performance
Context. The High Frequency Instrument (HFI) is one of the two focal instruments of the Planck mission. It will observe the whole sky in six
bands in the 100 GHzâ1 THz range.
Aims. The HFI instrument is designed to measure the cosmic microwave background (CMB) with a sensitivity limited only by fundamental
sources: the photon noise of the CMB itself and the residuals left after the removal of foregrounds. The two high frequency bands will provide
full maps of the submillimetre sky, featuring mainly extended and point source foregrounds. Systematic effects must be kept at negligible levels
or accurately monitored so that the signal can be corrected. This paper describes the HFI design and its characteristics deduced from ground tests
and calibration.
Methods. The HFI instrumental concept and architecture are feasible only by pushing new techniques to their extreme capabilities, mainly:
(i) bolometers working at 100 mK and absorbing the radiation in grids; (ii) a dilution cooler providing 100 mK in microgravity conditions;
(iii) a new type of AC biased readout electronics and (iv) optical channels using devices inspired from radio and infrared techniques.
Results. The Planck-HFI instrument performance exceeds requirements for sensitivity and control of systematic effects. During ground-based
calibration and tests, it was measured at instrument and system levels to be close to or better than the goal specification
Remark on lattice BRST invariance
A recently claimed resolution to the lattice Gribov problem in the context of
chiral lattice gauge theories is examined. Unfortunately, I find that the old
problem remains.Comment: 4 pages, plain TeX, presentation improved (see acknowledgments
On central tendency and dispersion measures for intervals and hypercubes
The uncertainty or the variability of the data may be treated by considering,
rather than a single value for each data, the interval of values in which it
may fall. This paper studies the derivation of basic description statistics for
interval-valued datasets. We propose a geometrical approach in the
determination of summary statistics (central tendency and dispersion measures)
for interval-valued variables
Composite infrared bolometers with Si_3N_4 micromesh absorbers
We report the design and performance of 300-mK composite bolometers that use micromesh absorbers and support structures patterned from thin films of low-stress silicon nitride. The small geometrical filling factor of the micromesh absorber provides 20Ă reduction in heat capacity and cosmic ray cross section relative to a solid absorber with no loss in IR-absorption efficiency. The support structure is mechanically robust and has a thermal conductance, G < 2 Ă 10^(â11) W/K, which is four times smaller than previously achieved at 300 mK. The temperature rise of the bolometer is measured with a neutron transmutation doped germanium thermistor attached to the absorbing mesh. The dispersion in electrical and thermal parameters of a sample of 12 bolometers optimized for the SunyaevâZelâdovich Infrared Experiment is ±7% in R (T), ±5% in optical efficiency, and ±4% in G
BOOMERanG constraints on primordial non-Gaussianity from analytical Minkowski functionals
We use Minkowski functionals (MFs) to constrain a primordial non-Gaussian contribution to the cosmic microwave background intensity field as observed in the 150- and 145-GHz BOOMERanG maps from the 1998 and 2003 flights, respectively, performing for the first time a joint analysis of the two data sets. A perturbative expansion of the MF formulae in the limit of a weakly non-Gaussian field yields analytical formulae, derived by Hikage et al., which can be used to constrain the coupling parameter f_(NL) without the need for non-Gaussian simulations. We find â770 < f_(NL) < 500 at 95 per cent CL, significantly improving the previous constraints by De Troia et al. on the BOOMERanG 2003 data set. These are the best f_(NL) limits to date for suborbital probes
Optical Conductivity in a Two-Band Superconductor: Pb
We demonstrate the effect of bandstructure on the superconducting properties
of Pb by calculating the strong-coupling features in the optical conductivity,
, due to the electron-phonon interaction. The importance of
momentum dependence in the calculation of the properties of superconductors has
previously been raised for MgB. Pb resembles MgB in that it is a two
band superconductor in which the bands' contributions to the Fermi surface have
very different topologies. We calculate by calculating a
memory function which has been recently used to analyze of
BiSrCaCuO. In our calculations the two components of
the Fermi surface are described by parameterizations of de Haas--van Alphen
data. We use a phonon spectrum which is a fit to neutron scattering data. By
including the momentum dependence of the Fermi surface good agreement is found
with the experimentally determined strong-coupling features which can be
described by a broad peak at around 4.5 meV and a narrower higher peak around 8
meV of equal height. The calculated features are found to be dominated by
scattering between states within the third band. By contrast scattering between
states in the second band leads to strong-coupling features in which the height
of the high energy peak is reduced by compared to that of the low
energy peak. This result is similar to that in the conventional isotropic
(momentum independent) treatment of superconductivity. Our results show that it
is important to use realistic models of the bandstructure and phonons, and to
avoid using momentum averaged quantities, in calculations in order to get
quantitatively accurate results
Exploring The Relationship Between Gratitude And Economic Perceptions
This study explores the associations between consumer gratitude and perceptions of consumer confidence and economic welfare. From a random stratified sample of adults living in the southeastern U.S., the findings reveal that a grateful outlook is positively associated with favorable perceptions of the U.S. economy, state economy, future job growth, and future income earned. Additionally, the results indicate significant differences between grateful and ungrateful individuals in terms of their perceptions of the U.S. economy, job growth, and anticipated income for the upcoming year. The results suggest that managers may want to focus on developing strong relationships with grateful customers, given that grateful customers may help firms survive tough economic times
Initial test results on bolometers for the Planck high frequency instrument
We summarize the fabrication, flight qualification, and dark performance of bolometers completed at the Jet Propulsion Laboratory for the High Frequency Instrument (HFI) of the joint ESA/NASA Herschel/Planck mission to be launched in 2009. The HFI is a multicolor focal plane which consists of 52 bolometers operated at 100 mK. Each bolometer is mounted to a feedhorn-filter assembly which defines one of six frequency bands centered between 100-857 GHz. Four detectors in each of five bands from 143-857 GHz are coupled to both linear polarizations and thus measure the total intensity. In addition, eight detectors in each of four bands (100, 143, 217, and 353 GHz) couple only to a single linear polarization and thus provide measurements of the Stokes parameters, Q and U, as well as the total intensity. The measured noise equivalent power (NEP) of all detectors is at or below the background limit for the telescope and time constants are a few ms, short enough to resolve point sources as the 5 to 9 arc min beams move across the sky at 1 rpm
Interstellar dust in the BOOMERanG maps
Interstellar dust (ISD) emission is present in the mm-wave maps obtained by the BOOMERanG experiment at intermediate and high Galactic latitudes. We find that, while being sub-dominant at the lower frequencies (90,150, 240 GHz), thermal emission from ISD is dominant at 410 GHz, and is well correlated with the IRAS map at 100 ”m. We find also that the angular power spectrum of ISD fluctuations at 410 GHz is a power law, and its level is negligible with respect to the angular power spectrum of the Cosmic Microwave Background (CMB) at 90 and 150 GHz
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