26 research outputs found
The Thermal Design, Characterization, and Performance of the SPIDER Long-Duration Balloon Cryostat
We describe the SPIDER flight cryostat, which is designed to cool six
millimeter-wavelength telescopes during an Antarctic long-duration balloon
flight. The cryostat, one of the largest to have flown on a stratospheric
payload, uses liquid helium-4 to deliver cooling power to stages at 4.2 and 1.6
K. Stainless steel capillaries facilitate a high flow impedance connection
between the main liquid helium tank and a smaller superfluid tank, allowing the
latter to operate at 1.6 K as long as there is liquid in the 4.2 K main tank.
Each telescope houses a closed cycle helium-3 adsorption refrigerator that
further cools the focal planes down to 300 mK. Liquid helium vapor from the
main tank is routed through heat exchangers that cool radiation shields,
providing negative thermal feedback. The system performed successfully during a
17 day flight in the 2014-2015 Antarctic summer. The cryostat had a total hold
time of 16.8 days, with 15.9 days occurring during flight.Comment: 15 pgs, 17 fig
The Hubble Constant
I review the current state of determinations of the Hubble constant, which
gives the length scale of the Universe by relating the expansion velocity of
objects to their distance. There are two broad categories of measurements. The
first uses individual astrophysical objects which have some property that
allows their intrinsic luminosity or size to be determined, or allows the
determination of their distance by geometric means. The second category
comprises the use of all-sky cosmic microwave background, or correlations
between large samples of galaxies, to determine information about the geometry
of the Universe and hence the Hubble constant, typically in a combination with
other cosmological parameters. Many, but not all, object-based measurements
give values of around 72-74km/s/Mpc , with typical errors of 2-3km/s/Mpc.
This is in mild discrepancy with CMB-based measurements, in particular those
from the Planck satellite, which give values of 67-68km/s/Mpc and typical
errors of 1-2km/s/Mpc. The size of the remaining systematics indicate that
accuracy rather than precision is the remaining problem in a good determination
of the Hubble constant. Whether a discrepancy exists, and whether new physics
is needed to resolve it, depends on details of the systematics of the
object-based methods, and also on the assumptions about other cosmological
parameters and which datasets are combined in the case of the all-sky methods.Comment: Extensively revised and updated since the 2007 version: accepted by
Living Reviews in Relativity as a major (2014) update of LRR 10, 4, 200
Profiling bacterial communities associated with sediment-based aquaculture bioremediation systems under contrasting redox regimes
Deposit-feeding invertebrates are proposed bioremediators in microbial-driven sediment-based aquaculture effluent treatment systems. We elucidate the role of the sediment reduction-oxidation (redox) regime in structuring benthic bacterial communities, having direct implications for bioremediation potential and deposit-feeder nutrition. The sea cucumber Holothuria scabra was cultured on sediments under contrasting redox regimes; fully oxygenated (oxic) and redox stratified (oxic-anoxic). Taxonomically, metabolically and functionally distinct bacterial communities developed between the redox treatments with the oxic treatment supporting the greater diversity; redox regime and dissolved oxygen levels were the main environmental drivers. Oxic sediments were colonised by nitrifying bacteria with the potential to remediate nitrogenous wastes. Percolation of oxygenated water prevented the proliferation of anaerobic sulphate-reducing bacteria, which were prevalent in the oxic-anoxic sediments. At the predictive functional level, bacteria within the oxic treatment were enriched with genes associated with xenobiotics metabolism. Oxic sediments showed the greater bioremediation potential; however, the oxic-anoxic sediments supported a greater sea cucumber biomass. Overall, the results indicate that bacterial communities present in fully oxic sediments may enhance the metabolic capacity and bioremediation potential of deposit-feeder microbial systems. This study highlights the benefits of incorporating deposit-feeding invertebrates into effluent treatment systems, particularly when the sediment is oxygenated
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Pre-flight integration and characterization of the SPIDER balloon-borne telescope
We present the results of integration and characterization of the Spider instrument after the 2013 pre-flight campaign. SPIDER is a balloon-borne polarimeter designed to probe the primordial gravitational wave signal in the degree-scale B-mode polarization of the cosmic microwave background. With six independent telescopes housing over 2000 detectors in the 94 GHz and 150 GHz frequency bands, SPIDER will map 7.5% of the sky with a depth of 11 to 14 mu K.arcmin at each frequency, which is a factor of similar to 5 improvement over Planck. We discuss the integration of the pointing, cryogenic, electronics, and power sub-systems, as well as pre-flight characterization of the detectors and optical systems. SPIDER is well prepared for a December 2014 flight from Antarctica, and is expected to be limited by astrophysical foreground emission, and not instrumental sensitivity, over the survey region
Observations of the temperature and polarization anisotropies with BOOMERANG 2003
The BOOMERANG experiment completed its final long duration balloon (LDB)
flight over Antarctica in January 2003. The focal plane was upgraded to
accommodate four sets of 145 GHz polarization sensitive bolometers
(PSBs), identical to those to be flown on the Planck HFI instrument.
Approximately, 195 hours of science observations were obtained during
this flight, including 75 hours distributed over 1.84\% of the sky and an
additional 120 hours concentrated on a region covering 0.22\% of the sky.
We derive the angular power spectra of the cosmic microwave background
(CMB) temperature and polarization anisotropies from these data. The
temperature anisotropies are detected with high signal to noise on
angular scales ranging from several degrees to {\tilde10 arcminutes. The
curl-free (EE) component is detected at \tilde4.8, and a
two-sigma upper limit on the curl (BB) component of 8.6
K is obtained on scales corresponding to
\tilde0.5\deg. Both the temperature and polarization anisotropies are
found to be consistent with a concordance CDM cosmology that is
seeded by adiabatic density perturbations. In addition to the CMB
observations, BOOMERANG03 surveyed a \tilde300 square degree region
centered on the Galactic plane. These observations represent the first
light for polarization sensitive bolometers, which are currently
operational in two South-Pole based polarimeters, as well as Planck HFI,
at frequencies ranging from 100 to 350 GHz (3 mm to 850 m).
CMB polarization with BOOMERANG 2003
This paper reports results from the BOOMERANG 2003 flights, devoted to
the measurement of intensity and polarization of the cosmic microwave
background radiation. In particular, it is focused on the power angular
power spectra and on the control of possible contamination from
systematic effects and foregrounds
The millimeter sky as seen with BOOMERanG
BOOMERanG is a balloon-borne, mm-wave scanning telescope, which measured
the first images of the CMB with sub-horizon resolution in 1998. In 2003
the instrument has been flown again with polarization sensitive
bolometers, and has produced maps of the Stokes parameters I, Q, U of
the microwave sky. Three regions of the southern sky were surveyed: a
deep ({\tilde90 square degrees) and a shallow survey (\tilde750 square
degrees) at high Galactic latitudes, and a survey of \tilde300 square
degrees across a southern section of the Galactic plane. The experiment
measured simultaneously three wide frequency bands centered at 145, 245
and 345 GHz, with an angular resolution of \tilde10\prime. The 145 GHz
temperature maps are dominated by Cosmic Microwave Background (CMB)
anisotropy, which is mapped with high signal to noise ratio. The map is
consistent with the pattern measured in the same region by BOOMERanG-98
and by WMAP. At 145 GHz, in the high latitude surveys, the intensity and
polarization of the astrophysical foregrounds are found to be negligible
with respect to the cosmological signal. At 245 and 345 GHz we detect
ISD emission correlated to the 3000 GHz IRAS/DIRBE maps. The Q and U
maps at high latitudes are dominated by detector noise: a power spectrum
analysis allows us to extract from the maps a significant CMB
polarization signal.
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SPIDER: probing the early Universe with a suborbital polarimeter
We evaluate the ability of SPIDER, a balloon-borne polarimeter, to detect a divergence-free polarization pattern (B-modes) in the cosmic microwave background (CMB). In the inflationary scenario, the amplitude of this signal is proportional to that of the primordial scalar perturbations through the tensor-to-scalar ratio r. We show that the expected level of systematic error in the SPIDER instrument is significantly below the amplitude of an interesting cosmological signal with r = 0.03. We present a scanning strategy that enables us to minimize uncertainty in the reconstruction of the Stokes parameters used to characterize the CMB, while accessing a relatively wide range of angular scales. Evaluating the amplitude of the polarized Galactic emission in the SPIDER field, we conclude that the polarized emission from interstellar dust is as bright or brighter than the cosmological signal at all SPIDER frequencies (90 GHz, 150 GHz, and 280 GHz), a situation similar to that found in the "Southern Hole." We show that two similar to 20-day flights of the SPIDER instrument can constrain the amplitude of the B-mode signal to r < 0.03 (99% CL) even when foreground contamination is taken into account. In the absence of foregrounds, the same limit can be reached after one 20-day flight