24 research outputs found
Solving the Corner-Turning Problem for Large Interferometers
The so-called corner turning problem is a major bottleneck for radio
telescopes with large numbers of antennas. The problem is essentially that of
rapidly transposing a matrix that is too large to store on one single device;
in radio interferometry, it occurs because data from each antenna needs to be
routed to an array of processors that will each handle a limited portion of the
data (a frequency range, say) but requires input from each antenna. We present
a low-cost solution allowing the correlator to transpose its data in real time,
without contending for bandwidth, via a butterfly network requiring neither
additional RAM memory nor expensive general-purpose switching hardware. We
discuss possible implementations of this using FPGA, CMOS, analog logic and
optical technology, and conclude that the corner turner cost can be small even
for upcoming massive radio arrays.Comment: Revised to match accepted MNRAS version. 7 pages, 4 fig
The Allen Telescope Array: The First Widefield, Panchromatic, Snapshot Radio Camera for Radio Astronomy and SETI
The first 42 elements of the Allen Telescope Array (ATA-42) are beginning to
deliver data at the Hat Creek Radio Observatory in Northern California.
Scientists and engineers are actively exploiting all of the flexibility
designed into this innovative instrument for simultaneously conducting surveys
of the astrophysical sky and conducting searches for distant technological
civilizations. This paper summarizes the design elements of the ATA, the cost
savings made possible by the use of COTS components, and the cost/performance
trades that eventually enabled this first snapshot radio camera. The
fundamental scientific program of this new telescope is varied and exciting;
some of the first astronomical results will be discussed.Comment: Special Issue of Proceedings of the IEEE: "Advances in Radio
Telescopes", Baars,J. Thompson,R., D'Addario, L., eds, 2009, in pres
The Allen Telescope Array Pi GHz Sky Survey I. Survey Description and Static Catalog Results for the Bootes Field
The Pi GHz Sky Survey (PiGSS) is a key project of the Allen Telescope Array.
PiGSS is a 3.1 GHz survey of radio continuum emission in the extragalactic sky
with an emphasis on synoptic observations that measure the static and
time-variable properties of the sky. During the 2.5-year campaign, PiGSS will
twice observe ~250,000 radio sources in the 10,000 deg^2 region of the sky with
b > 30 deg to an rms sensitivity of ~1 mJy. Additionally, sub-regions of the
sky will be observed multiple times to characterize variability on time scales
of days to years. We present here observations of a 10 deg^2 region in the
Bootes constellation overlapping the NOAO Deep Wide Field Survey field. The
PiGSS image was constructed from 75 daily observations distributed over a
4-month period and has an rms flux density between 200 and 250 microJy. This
represents a deeper image by a factor of 4 to 8 than we will achieve over the
entire 10,000 deg^2. We provide flux densities, source sizes, and spectral
indices for the 425 sources detected in the image. We identify ~100$ new flat
spectrum radio sources; we project that when completed PiGSS will identify 10^4
flat spectrum sources. We identify one source that is a possible transient
radio source. This survey provides new limits on faint radio transients and
variables with characteristic durations of months.Comment: Accepted for publication in ApJ; revision submitted with extraneous
figure remove
The Allen Telescope Array Twenty-centimeter Survey - A 690-Square-Degree, 12-Epoch Radio Dataset - I: Catalog and Long-Duration Transient Statistics
We present the Allen Telescope Array Twenty-centimeter Survey (ATATS), a
multi-epoch (12 visits), 690 square degree radio image and catalog at 1.4GHz.
The survey is designed to detect rare, very bright transients as well as to
verify the capabilities of the ATA to form large mosaics. The combined image
using data from all 12 ATATS epochs has RMS noise sigma = 3.94mJy / beam and
dynamic range 180, with a circular beam of 150 arcsec FWHM. It contains 4408
sources to a limiting sensitivity of S = 20 mJy / beam. We compare the catalog
generated from this 12-epoch combined image to the NRAO VLA Sky Survey (NVSS),
a legacy survey at the same frequency, and find that we can measure source
positions to better than ~20 arcsec. For sources above the ATATS completeness
limit, the median flux density is 97% of the median value for matched NVSS
sources, indicative of an accurate overall flux calibration. We examine the
effects of source confusion due to the effects of differing resolution between
ATATS and NVSS on our ability to compare flux densities. We detect no
transients at flux densities greater than 40 mJy in comparison with NVSS, and
place a 2-sigma upper limit on the transient rate for such sources of 0.004 per
square degree. These results suggest that the > 1 Jy transients reported by
Matsumura et al. (2009) may not be true transients, but rather variable sources
at their flux density threshold.Comment: 41 pages, 19 figures, ApJ accepted; corrected minor typo in Table
The Allen Telescope Array Pi GHz Sky Survey I. Survey Description and Static Catalog Results for the Bootes Field
The Pi GHz Sky Survey (PiGSS) is a key project of the Allen Telescope Array.
PiGSS is a 3.1 GHz survey of radio continuum emission in the extragalactic sky
with an emphasis on synoptic observations that measure the static and
time-variable properties of the sky. During the 2.5-year campaign, PiGSS will
twice observe ~250,000 radio sources in the 10,000 deg^2 region of the sky with
b > 30 deg to an rms sensitivity of ~1 mJy. Additionally, sub-regions of the
sky will be observed multiple times to characterize variability on time scales
of days to years. We present here observations of a 10 deg^2 region in the
Bootes constellation overlapping the NOAO Deep Wide Field Survey field. The
PiGSS image was constructed from 75 daily observations distributed over a
4-month period and has an rms flux density between 200 and 250 microJy. This
represents a deeper image by a factor of 4 to 8 than we will achieve over the
entire 10,000 deg^2. We provide flux densities, source sizes, and spectral
indices for the 425 sources detected in the image. We identify ~100$ new flat
spectrum radio sources; we project that when completed PiGSS will identify 10^4
flat spectrum sources. We identify one source that is a possible transient
radio source. This survey provides new limits on faint radio transients and
variables with characteristic durations of months.Comment: Accepted for publication in ApJ; revision submitted with extraneous
figure remove
Making science at home: visual displays of space science and nuclear physics at the Science Museum and on television in postwar Britain
The public presentation of science and technology in postwar Britain remains a field open to exploration. Current scholarship on the topic is growing but still tends to concentrate on the written word, thus making theorizing, at this stage, difficult. This paper is an attempt to expand the literature through two case studies that compare and synthesize displays of scientific and technological knowledge in two visual media, the Science Museum and television, in the 1950s and 1960s. The topics of these case studies are space exploration and nuclear energy. The thesis this paper explores is that both media fleshed out strategies of displays based on the use of categories from everyday life. As a result, outcomes of large-scale public scientific and technological undertakings were interwoven within audiences’ daily life experiences, thus appearing ordinary rather than extraordinary. This use of symbols and values drawn from private life worked to alleviate fears of risk associated with these new fields of technological exploration and at the same time give them widespread currency in the public sphere
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The Nuclear Spectroscopic Telescope Array (NuSTAR) High-Energy X-Ray Mission
The Nuclear Spectroscopic Telescope Array (NuSTAR) mission, launched on 2012 June 13, is the first focusing high-energy X-ray telescope in orbit. NuSTAR operates in the band from 3 to 79 keV, extending the sensitivity of focusing far beyond the ~10 keV high-energy cutoff achieved by all previous X-ray satellites. The inherently low background associated with concentrating the X-ray light enables NuSTAR to probe the hard X-ray sky with a more than 100-fold improvement in sensitivity over the collimated or coded mask instruments that have operated in this bandpass. Using its unprecedented combination of sensitivity and spatial and spectral resolution, NuSTAR will pursue five primary scientific objectives: (1) probe obscured active galactic nucleus (AGN) activity out to the peak epoch of galaxy assembly in the universe (at z lsim 2) by surveying selected regions of the sky; (2) study the population of hard X-ray-emitting compact objects in the Galaxy by mapping the central regions of the Milky Way; (3) study the non-thermal radiation in young supernova remnants, both the hard X-ray continuum and the emission from the radioactive element 44Ti; (4) observe blazars contemporaneously with ground-based radio, optical, and TeV telescopes, as well as with Fermi and Swift, to constrain the structure of AGN jets; and (5) observe line and continuum emission from core-collapse supernovae in the Local Group, and from nearby Type Ia events, to constrain explosion models. During its baseline two-year mission, NuSTAR will also undertake a broad program of targeted observations. The observatory consists of two co-aligned grazing-incidence X-ray telescopes pointed at celestial targets by a three-axis stabilized spacecraft. Deployed into a 600 km, near-circular, 6° inclination orbit, the observatory has now completed commissioning, and is performing consistent with pre-launch expectations. NuSTAR is now executing its primary science mission, and with an expected orbit lifetime of 10 yr, we anticipate proposing a guest investigator program, to begin in late 2014.Astronom
Social tourism participation: The role of tourism inexperience and uncertainty
Social tourism initiatives tend to facilitate access to tourism for groups who would otherwise be financially unable to participate in holidays. The tourism products offered in social tourism vary between individual and group holidays, and day trips. This paper presents the findings of an exploratory, qualitative study with social tourism beneficiaries and social support workers, which explores via interviews and focus groups how these different tourism products can be tailored most effectively to the needs to the beneficiaries. The findings of the study highlight the important role of travel inexperience, and associated uncertainty, in travel decisions made by this target group. The findings show that (public sector or charitable) providers of social tourism can offer the most tailored and potentially most cost-effective tourism product to each beneficiary by closely considering previous travel experience and uncertainty levels before departure