11 research outputs found
Thermal Conductivity of Thermally-Isolating Polymeric and Composite Structural Support Materials Between 0.3 and 4 K
We present measurements of the low-temperature thermal conductivity of a
number of polymeric and composite materials from 0.3 to 4 K. The materials
measured are Vespel SP-1, Vespel SP-22, unfilled PEEK, 30% carbon fiber-filled
PEEK, 30% glass-filled PEEK, carbon fiber Graphlite composite rod, Torlon 4301,
G-10/FR-4 fiberglass, pultruded fiberglass composite, Macor ceramic, and
graphite rod. These materials have moderate to high elastic moduli making them
useful for thermally-isolating structural supports.Comment: Accepted for publication in the journal Cryogenic
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 ~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.Comment: 29 pages, 8 figures, 4 tables; v2: matches published version, flight
schedule updated, two typos fixed in Table 2, references and minor
clarifications added, results unchange
First Results from the Arcminute Cosmology Bolometer Array Receiver
We review the first science results from the Arcminute Cosmology Bolometer
Array Receiver (ACBAR); a multifrequency millimeter-wave receiver optimized for
observations of the Cosmic Microwave Background (CMB) and the
Sunyaev-Zel'dovich (SZ) effect in clusters of galaxies. ACBAR was installed on
the 2 m Viper telescope at the South Pole in January 2001 and the results
presented here incorporate data through July 2002. We present the power
spectrum of the CMB at 150 GHz over the range \ell = 150 - 3000 measured by
ACBAR as well as estimates for the values of the cosmological parameters within
the context of Lambda-CDM models. We find that the inclusion of Omega_Lambda
greatly improves the fit to the power spectrum. We also observe a slight excess
of small-scale anisotropy at 150 GHz; if interpreted as power from the SZ
effect of unresolved clusters, the measured signal is consistent with CBI and
BIMA within the context of the SZ power spectrum models tested.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). 10 pages, 2 figure
Cosmological Constraints on Decaying Dark Matter
We present a complete analysis of the cosmological constraints on decaying
dark matter. Previous analyses have used the cosmic microwave background and
Type Ia supernova. We have updated them with the latest data as well as
extended the analysis with the inclusion of Lyman- forest, large scale
structure and weak lensing observations. Astrophysical constraints are not
considered in the present paper. The bounds on the lifetime of decaying dark
matter are dominated by either the late-time integrated Sachs-Wolfe effect for
the scenario with weak reionization, or CMB polarization observations when
there is significant reionization. For the respective scenarios, the lifetimes
for decaying dark matter are Gyr and Gyr (at 95.4% confidence level), where the
phenomenological parameter is the fraction of the decay energy deposited in
baryonic gas. This allows us to constrain particle physics models with dark
matter candidates through investigation of dark matter decays into Standard
Model particles via effective operators. For decaying dark matter of
GeV mass, we found that the size of the coupling constant in the effective
dimension-4 operators responsible for dark matter decay has to generically be . We have also explored the implications of our analysis for
representative models in theories of gauge-mediated supersymmetry breaking,
minimal supergravity and little Higgs.Comment: 29 pages, 6 figures. Added references and corrected typos as well as
grammatical oversight
A Determination of the Hubble Constant Using Measurements of X-Ray Emission and the Sunyaev-Zeldovich Effect at Millimeter Wavelengths in the Cluster Abell 1835
We present a determination of the Hubble constant and central electron density in the cluster Abell 1835 (z = 0.2523) from measurements of X-ray emission and millimeter-wave observations of the Sunyaev-Zeldovich (S-Z) effect with the Sunyaev-Zeldovich Infrared Experiment (SuZIE) multifrequency array receiver. Abell 1835 is a well studied cluster in the X-ray with a large central cooling flow. Using a combination of data from ROSAT PSPC and HRI images and millimeter wave measurements we fit a King model to the emission from the ionized gas around Abell 1835 with θ0 = 022 ± 002 and β = 0.58 ± 0.02. Assuming the cluster gas to be isothermal with a temperature of 9.8 keV, we find a y-parameter of 4.9 ± 0.6 × 10-4 and a peculiar velocity of 500 ± 1000 km s-1 from measurements at three frequencies, 145, 221, and 279 GHz. Combining the S-Z measurements with X-ray data, we determine a value for the Hubble constant of H0 = 59 km s-1 Mpc-1 and a central electron density for Abell 1835 of ne0 = 5.64 × 10-2 cm-3 assuming a standard cosmology with Ωm = 1 and ΩΛ = 0. The error in the determination of the Hubble constant is dominated by the uncertainty in the temperature of the X-ray emitting cluster gas
Multiple Transforming Growth Factor-β Isoforms and Receptors Function during Epithelial-Mesenchymal Cell Transformation in the Embryonic Heart
In-flight gain monitoring of SPIDER's transition-edge sensor arrays
International audienceExperiments deploying large arrays of transition-edge sensors (TESs) often require a robust method to monitor gain variations with minimal loss of observing time. We propose a sensitive and non-intrusive method for monitoring variations in TES responsivity using small square waves applied to the TES bias. We construct an estimator for a TES's small-signal power response from its electrical response that is exact in the limit of strong electrothermal feedback. We discuss the application and validation of this method using flight data from SPIDER, a balloon-borne telescope that observes the polarization of the cosmic microwave background with more than 2000 TESs. This method may prove useful for future balloon- and space-based instruments, where observing time and ground control bandwidth are limited