226 research outputs found
Approximation Algorithm for Line Segment Coverage for Wireless Sensor Network
The coverage problem in wireless sensor networks deals with the problem of
covering a region or parts of it with sensors. In this paper, we address the
problem of covering a set of line segments in sensor networks. A line segment `
is said to be covered if it intersects the sensing regions of at least one
sensor distributed in that region. We show that the problem of finding the
minimum number of sensors needed to cover each member in a given set of line
segments in a rectangular area is NP-hard. Next, we propose a constant factor
approximation algorithm for the problem of covering a set of axis-parallel line
segments. We also show that a PTAS exists for this problem.Comment: 16 pages, 5 figures
Design and construction of a carbon fiber gondola for the SPIDER balloon-borne telescope
We introduce the light-weight carbon fiber and aluminum gondola designed for
the SPIDER balloon-borne telescope. SPIDER is designed to measure the
polarization of the Cosmic Microwave Background radiation with unprecedented
sensitivity and control of systematics in search of the imprint of inflation: a
period of exponential expansion in the early Universe. The requirements of this
balloon-borne instrument put tight constrains on the mass budget of the
payload. The SPIDER gondola is designed to house the experiment and guarantee
its operational and structural integrity during its balloon-borne flight, while
using less than 10% of the total mass of the payload. We present a construction
method for the gondola based on carbon fiber reinforced polymer tubes with
aluminum inserts and aluminum multi-tube joints. We describe the validation of
the model through Finite Element Analysis and mechanical tests.Comment: 16 pages, 11 figures. Presented at SPIE Ground-based and Airborne
Telescopes V, June 23, 2014. To be published in Proceedings of SPIE Volume
914
BICEP2 / Keck Array V: Measurements of B-mode Polarization at Degree Angular Scales and 150 GHz by the Keck Array
The Keck Array is a system of cosmic microwave background (CMB) polarimeters,
each similar to the BICEP2 experiment. In this paper we report results from the
2012 and 2013 observing seasons, during which the Keck Array consisted of five
receivers all operating in the same (150 GHz) frequency band and observing
field as BICEP2. We again find an excess of B-mode power over the
lensed-CDM expectation of in the range
and confirm that this is not due to systematics using jackknife tests and
simulations based on detailed calibration measurements. In map difference and
spectral difference tests these new data are shown to be consistent with
BICEP2. Finally, we combine the maps from the two experiments to produce final
Q and U maps which have a depth of 57 nK deg (3.4 K arcmin) over an
effective area of 400 deg for an equivalent survey weight of 250,000
K. The final BB band powers have noise uncertainty a factor of 2.3
times better than the previous results, and a significance of detection of
excess power of .Comment: 13 pages, 9 figure
A cryogenic rotation stage with a large clear aperture for the half-wave plates in the Spider instrument
We describe the cryogenic half-wave plate rotation mechanisms built for and
used in Spider, a polarization-sensitive balloon-borne telescope array that
observed the Cosmic Microwave Background at 95 GHz and 150 GHz during a
stratospheric balloon flight from Antarctica in January 2015. The mechanisms
operate at liquid helium temperature in flight. A three-point contact design
keeps the mechanical bearings relatively small but allows for a large (305 mm)
diameter clear aperture. A worm gear driven by a cryogenic stepper motor allows
for precise positioning and prevents undesired rotation when the motors are
depowered. A custom-built optical encoder system monitors the bearing angle to
an absolute accuracy of +/- 0.1 degrees. The system performed well in Spider
during its successful 16 day flight.Comment: 11 pages, 7 figures, Published in Review of Scientific Instruments.
v2 includes reviewer changes and longer literature revie
Antenna-coupled TES bolometers used in BICEP2, Keck array, and SPIDER
We have developed antenna-coupled transition-edge sensor (TES) bolometers for
a wide range of cosmic microwave background (CMB) polarimetry experiments,
including BICEP2, Keck Array, and the balloon borne SPIDER. These detectors
have reached maturity and this paper reports on their design principles,
overall performance, and key challenges associated with design and production.
Our detector arrays repeatedly produce spectral bands with 20%-30% bandwidth at
95, 150, or 220~GHz. The integrated antenna arrays synthesize symmetric
co-aligned beams with controlled side-lobe levels. Cross-polarized response on
boresight is typically ~0.5%, consistent with cross-talk in our multiplexed
readout system. End-to-end optical efficiencies in our cameras are routinely
35% or higher, with per detector sensitivities of NET~300 uKrts. Thanks to the
scalability of this design, we have deployed 2560 detectors as 1280 matched
pairs in Keck Array with a combined instantaneous sensitivity of ~9 uKrts, as
measured directly from CMB maps in the 2013 season. Similar arrays have
recently flown in the SPIDER instrument, and development of this technology is
ongoing.Comment: 16 pgs, 20 fig
BICEP2 / Keck Array VIII: Measurement of gravitational lensing from large-scale B-mode polarization
We present measurements of polarization lensing using the 150 GHz maps which
include all data taken by the BICEP2 & Keck Array CMB polarization experiments
up to and including the 2014 observing season (BK14). Despite their modest
angular resolution (), the excellent sensitivity (K-arcmin) of these maps makes it possible to directly reconstruct the
lensing potential using only information at larger angular scales (). From the auto-spectrum of the reconstructed potential we measure an
amplitude of the spectrum to be (Planck
CDM prediction corresponds to ), and reject
the no-lensing hypothesis at 5.8, which is the highest significance
achieved to date using an EB lensing estimator. Taking the cross-spectrum of
the reconstructed potential with the Planck 2015 lensing map yields
. These direct measurements of
are consistent with the CDM cosmology, and with
that derived from the previously reported BK14 B-mode auto-spectrum (). We perform a series of null tests and consistency
checks to show that these results are robust against systematics and are
insensitive to analysis choices. These results unambiguously demonstrate that
the B-modes previously reported by BICEP / Keck at intermediate angular scales
() are dominated by gravitational lensing. The
good agreement between the lensing amplitudes obtained from the lensing
reconstruction and B-mode spectrum starts to place constraints on any
alternative cosmological sources of B-modes at these angular scales.Comment: 12 pages, 8 figure
280 GHz Focal Plane Unit Design and Characterization for the SPIDER-2 Suborbital Polarimeter
We describe the construction and characterization of the 280 GHz bolometric
focal plane units (FPUs) to be deployed on the second flight of the
balloon-borne SPIDER instrument. These FPUs are vital to SPIDER's primary
science goal of detecting or placing an upper limit on the amplitude of the
primordial gravitational wave signature in the cosmic microwave background
(CMB) by constraining the B-mode contamination in the CMB from Galactic dust
emission. Each 280 GHz focal plane contains a 16 x 16 grid of corrugated
silicon feedhorns coupled to an array of aluminum-manganese transition-edge
sensor (TES) bolometers fabricated on 150 mm diameter substrates. In total, the
three 280 GHz FPUs contain 1,530 polarization sensitive bolometers (765 spatial
pixels) optimized for the low loading environment in flight and read out by
time-division SQUID multiplexing. In this paper we describe the mechanical,
thermal, and magnetic shielding architecture of the focal planes and present
cryogenic measurements which characterize yield and the uniformity of several
bolometer parameters. The assembled FPUs have high yields, with one array as
high as 95% including defects from wiring and readout. We demonstrate high
uniformity in device parameters, finding the median saturation power for each
TES array to be ~3 pW at 300 mK with a less than 6% variation across each array
at one standard deviation. These focal planes will be deployed alongside the 95
and 150 GHz telescopes in the SPIDER-2 instrument, slated to fly from McMurdo
Station in Antarctica in December 2018
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