4,468 research outputs found
Redundant Array Configurations for 21 cm Cosmology
Realizing the potential of 21 cm tomography to statistically probe the
intergalactic medium before and during the Epoch of Reionization requires large
telescopes and precise control of systematics. Next-generation telescopes are
now being designed and built to meet these challenges, drawing lessons from
first-generation experiments that showed the benefits of densely packed, highly
redundant arrays--in which the same mode on the sky is sampled by many antenna
pairs--for achieving high sensitivity, precise calibration, and robust
foreground mitigation. In this work, we focus on the Hydrogen Epoch of
Reionization Array (HERA) as an interferometer with a dense, redundant core
designed following these lessons to be optimized for 21 cm cosmology. We show
how modestly supplementing or modifying a compact design like HERA's can still
deliver high sensitivity while enhancing strategies for calibration and
foreground mitigation. In particular, we compare the imaging capability of
several array configurations, both instantaneously (to address instrumental and
ionospheric effects) and with rotation synthesis (for foreground removal). We
also examine the effects that configuration has on calibratability using
instantaneous redundancy. We find that improved imaging with sub-aperture
sampling via "off-grid" antennas and increased angular resolution via far-flung
"outrigger" antennas is possible with a redundantly calibratable array
configuration.Comment: 19 pages, 11 figures. Revised to match the accepted ApJ versio
Dual Character Art Concepts
Our goal in this paper is to articulate a novel account of the ordinary concept ART. At the core of our account is the idea that a puzzle surrounding our thought and talk about art is best understood as just one instance of a far broader phenomenon. In particular, we claim that one can make progress on this puzzle by drawing on research from cognitive science on dual character concepts. Thus, we suggest that the very same sort of phenomenon that is associated with ART can also be found in a broad class of other dual character concepts, including SCIENTIST, CHRISTIAN, GANGSTER, and many others. Instead of focusing narrowly on the case of ART, we try to offer a more general account of these concepts and the puzzles to which they give rise. Then, drawing on the general theory, we introduce a series of hypotheses about art concepts, and put those hypotheses to the test in three experimental studies
Wisent: Robust Downstream Communication and Storage for Computational RFIDs
Computational RFID (CRFID) devices are emerging platforms that can enable
perennial computation and sensing by eliminating the need for batteries.
Although much research has been devoted to improving upstream (CRFID to RFID
reader) communication rates, the opposite direction has so far been neglected,
presumably due to the difficulty of guaranteeing fast and error-free transfer
amidst frequent power interruptions of CRFID. With growing interest in the
market where CRFIDs are forever-embedded in many structures, it is necessary
for this void to be filled. Therefore, we propose Wisent-a robust downstream
communication protocol for CRFIDs that operates on top of the legacy UHF RFID
communication protocol: EPC C1G2. The novelty of Wisent is its ability to
adaptively change the frame length sent by the reader, based on the length
throttling mechanism, to minimize the transfer times at varying channel
conditions. We present an implementation of Wisent for the WISP 5 and an
off-the-shelf RFID reader. Our experiments show that Wisent allows transfer up
to 16 times faster than a baseline, non-adaptive shortest frame case, i.e.
single word length, at sub-meter distance. As a case study, we show how Wisent
enables wireless CRFID reprogramming, demonstrating the world's first
wirelessly reprogrammable (software defined) CRFID.Comment: Accepted for Publication to IEEE INFOCOM 201
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