2,387 research outputs found
Polarization studies of Rotating Radio Transients
We study the polarization properties of 22 known rotating radio transients
(RRATs) with the 64-m Parkes radio telescope and present the Faraday rotation
measures (RMs) for the 17 with linearly polarized flux exceeding the off-pulse
noise by 3. Each RM was estimated using a brute-force search over trial
RMs that spanned the maximum measurable range (in steps of 1 ), followed by an
iterative refinement algorithm. The measured RRAT RMs are in the range |RM|
to rad m with an average linear polarization
fraction of per cent. Individual single pulses are observed to be up
to 100 per cent linearly polarized. The RMs of the RRATs and the corresponding
inferred average magnetic fields (parallel to the line-of-sight and weighted by
the free electron density) are observed to be consistent with the Galactic
plane pulsar population. Faraday rotation analyses are typically performed on
accumulated pulsar data, for which hundreds to thousands of pulses have been
integrated, rather than on individual pulses. Therefore, we verified the
iterative refinement algorithm by performing Monte Carlo simulations of
artificial single pulses over a wide range of S/N and RM. At and above a S/N of
17 in linearly polarized flux, the iterative refinement recovers the simulated
RM value 100 per cent of the time with a typical mean uncertainty of
rad m. The method described and validated here has also been
successfully used to determine reliable RMs of several fast radio bursts (FRBs)
discovered at Parkes.Comment: Submitted to MNRAS, 10 pages, 6 figure
Chemical contaminants, pathogen exposure and general health status of live and beach-cast Washington sea otters (Enhydra lutris kenyoni)
Analyses of blood and liver samples from live captured sea otters and liver samples from beachcast sea otter carcasses off the remote Washington coast indicate relatively low exposure to contaminants, but suggest that even at the low levels measured, exposure may be indicated by biomarker response. Evidence of pathogen exposure is noteworthy - infectious disease presents a potential risk to Washington sea otters, particularly due to their small population size and limited distribution. During 2001 and 2002, 32 sea otters were captured, of which 28 were implanted with transmitters to track their movements and liver and blood samples were collected to evaluate contaminant and pathogen exposure. In addition, liver samples from fifteen beachcast
animals that washed ashore between 1991 and 2002 were analyzed to provide historical information and a basis of reference for values obtained from live otters. The results indicate low levels of metals, butyltins, and organochlorine compounds in the blood samples, with many of
the organochlorines not detected except polychlorinated biphenyls (PCBs), and a few aromatic hydrocarbons detected in the liver of the live captured animals. Aliphatic hydrocarbons were measurable in the liver from the live captured animals; however, some of these are likely from
biogenic sources. A significant reduction of vitamin A storage in the liver was observed in relation to PCB, dibutyltin and octacosane concentration. A significant and strong positive correlation in vitamin A storage in the liver was observed for cadmium and several of the
aliphatic hydrocarbons. Peripheral blood mononuclear cell (PBMC) cytochrome P450 induction was elevated in two of 16 animals and may be potentially related to aliphatic and aromatic hydrocarbon exposure. Mean concentration of total butyltin in the liver of the Washington beach-cast otters was more than 15 times lower than the mean concentration reported by Kannan et al. (1998) for Southern sea otters in California. Organochlorine compounds were evident in the liver of beach-cast animals, despite the lack of large human population centers and development along the Washington coast. Concentrations of PCBs and chlordanes (e.g., transchlordane, cis-chlordane, trans-nonachlor, cis-nonachlor and oxychlordane) in liver of Washington beach-cast sea otters were similar to those measured in Aleutian and California sea otters, excluding those from Monterey Bay, which were higher. Mean concentrations of 1,1,1,-
trichloro-2,2-bis(p-chlorophyenyl)ethanes (DDTs) were lower, and mean concentrations of cyclohexanes (HCH, e.g., alpha BHC, beta BHC, delta BHC and gamma BHC) were slightly
higher in Washington beach-cast otters versus those from California and the Aleutians.
Epidemiologically, blood tests revealed that 80 percent of the otters tested positive for morbillivirus and 60 percent for Toxoplasma, the latter of which has been a significant cause of mortality in Southern sea otters in California. This is the first finding of positive morbillivirus titers in sea otters from the Northeast Pacific. Individual deaths may occur from these diseases, perhaps more so when animals are otherwise immuno-compromised or infected with multiple
diseases, but a population-threatening die-off from these diseases singly is unlikely while population immunity remains high. The high frequency of detection of morbillivirus and Toxoplasma in the live otters corresponds well with the cause of death of stranded Washington
sea otters reported herein, which has generally been attributable to infectious disease. Washington’s sea otter population continues to grow, with over 1100 animals currently inhabiting Washington waters; however, the rate of growth has slowed over recent years. The population has a limited distribution and has not yet reached its carrying capacity and as such, is still considered at high risk to catastrophic events. (PDF contains 189 pages
Putting into Question the Imaginary of Recovery: A Dialectical Reading of the Global Financial Crisis and its Aftermath
In this article we put into question the discourses that emerged during the Global Financial Crisis (GFC) and that coalesced around a particular socio-economic imaginary of ?recovery? over the period 2009-2012. Our reading of these discourses is very much guided by the notion of the dialectic as developed by Fredric Jameson, and as such this paper can be read as attempt to put his theoretical ideas to work. Through our dialectical reading we aim to create a certain estrangement effect that makes the imaginary of recovery seem very odd and unnatural. In order to achieve such an effect we postulate four theses which are deliberately antagonistic: first, that there has been no ?crisis of capitalism?; second, that we must change the valence of the GFC from negative to positive; third, that the relationship between finance capitalism and ?free markets? is deeply contradictory; and fourth, that we must resist the regulation discourse
The UTMOST pulsar timing programme I: overview and first results
We present an overview and the first results from a large-scale pulsar timing
programme that is part of the UTMOST project at the refurbished Molonglo
Observatory Synthesis Radio Telescope (MOST) near Canberra, Australia. We
currently observe more than 400 mainly bright southern radio pulsars with up to
daily cadences. For 205 (8 in binaries, 4 millisecond pulsars) we publish
updated timing models, together with their flux densities, flux density
variability, and pulse widths at 843 MHz, derived from observations spanning
between 1.4 and 3 yr. In comparison with the ATNF pulsar catalogue, we improve
the precision of the rotational and astrometric parameters for 123 pulsars, for
47 by at least an order of magnitude. The time spans between our measurements
and those in the literature are up to 48 yr, which allows us to investigate
their long-term spin-down history and to estimate proper motions for 60
pulsars, of which 24 are newly determined and most are major improvements. The
results are consistent with interferometric measurements from the literature. A
model with two Gaussian components centred at 139 and fits the transverse velocity distribution best. The pulse duty
cycle distributions at 50 and 10 per cent maximum are best described by
log-normal distributions with medians of 2.3 and 4.4 per cent, respectively. We
discuss two pulsars that exhibit spin-down rate changes and drifting subpulses.
Finally, we describe the autonomous observing system and the dynamic scheduler
that has increased the observing efficiency by a factor of 2-3 in comparison
with static scheduling.Comment: 31 pages, 14 figures, 6 tables, accepted for publication in MNRA
The first interferometric detections of Fast Radio Bursts
We present the first interferometric detections of Fast Radio Bursts (FRBs),
an enigmatic new class of astrophysical transient. In a 180-day survey of the
Southern sky we discovered 3 FRBs at 843 MHz with the UTMOST array, as part of
commissioning science during a major ongoing upgrade. The wide field of view of
UTMOST ( deg) is well suited to FRB searches. The primary beam
is covered by 352 partially overlapping fan-beams, each of which is searched
for FRBs in real time with pulse widths in the range 0.655 to 42 ms, and
dispersion measures 2000 pc cm. Detections of FRBs with the UTMOST
array places a lower limit on their distances of km (limit of
the telescope near-field) supporting the case for an astronomical origin.
Repeating FRBs at UTMOST or an FRB detected simultaneously with the Parkes
radio telescope and UTMOST, would allow a few arcsec localisation, thereby
providing an excellent means of identifying FRB host galaxies, if present. Up
to 100 hours of follow-up for each FRB has been carried out with the UTMOST,
with no repeating bursts seen. From the detected position, we present 3
error ellipses of 15 arcsec x 8.4 deg on the sky for the point of origin for
the FRBs. We estimate an all-sky FRB rate at 843 MHz above a fluence of 11 Jy ms of events sky d at the 95
percent confidence level. The measured rate of FRBs at 843 MHz is of order two
times higher than we had expected, scaling from the FRB rate at the Parkes
radio telescope, assuming that FRBs have a flat spectral index and a uniform
distribution in Euclidean space. We examine how this can be explained by FRBs
having a steeper spectral index and/or a flatter log-log
distribution than expected for a Euclidean Universe.Comment: 13 pages, 8 figures, 2 table
Plasma Physics
Contains research objectives and reports on four research projects.U.S. Atomic Energy Commission (Contract AT(30- 1)- 1842)U.S. Air Force (Electronic Systems Division) under Contract AF 19(604)- 599
Generating multimedia presentations: from plain text to screenplay
In many Natural Language Generation (NLG) applications, the output is limited to plain text – i.e., a string of words with punctuation and paragraph breaks, but no indications for layout, or pictures, or dialogue. In several projects, we have begun to explore NLG applications in which these extra media are brought into play. This paper gives an informal account of what we have learned. For coherence, we focus on the domain of patient information leaflets, and follow an example in which the same content is expressed first in plain text, then in formatted text, then in text with pictures, and finally in a dialogue script that can be performed by two animated agents. We show how the same meaning can be mapped to realisation patterns in different media, and how the expanded options for expressing meaning are related to the perceived style and tone of the presentation. Throughout, we stress that the extra media are not simple added to plain text, but integrated with it: thus the use of formatting, or pictures, or dialogue, may require radical rewording of the text itself
Dust emission at 8-mic and 24-mic as Diagnostics of HII Region Radiative Transfer
We use the Spitzer SAGE survey of the Magellanic Clouds to evaluate the
relationship between the 8-mic PAH emission, 24-mic hot dust emission, and HII
region radiative transfer. We confirm that in the higher-metallicity Large
Magellanic Cloud, PAH destruction is sensitive to optically thin conditions in
the nebular Lyman continuum: objects identified as optically thin candidates
based on nebular ionization structure show 6 times lower median 8-mic surface
brightness (0.18 mJy arcsec^-2) than their optically thick counterparts (1.2
mJy arcsec^-2). The 24-mic surface brightness also shows a factor of 3 offset
between the two classes of objects (0.13 vs 0.44 mJy arcsec^-2, respectively),
which is driven by the association between the very small dust grains and
higher density gas found at higher nebular optical depths. In contrast, PAH and
dust formation in the low-metallicity Small Magellanic Cloud is strongly
inhibited such that we find no variation in either 8-mic or 24-mic emission
between our optically thick and thin samples. This is attributable to extremely
low PAH and dust production together with high, corrosive UV photon fluxes in
this low-metallicity environment. The dust mass surface densities and
gas-to-dust ratios determined from dust maps using Herschel HERITAGE survey
data support this interpretation.Comment: Accepted to ApJ, May 15, 2017. 10 pages, 9 figure
The UTMOST: A hybrid digital signal processor transforms the MOST
The Molonglo Observatory Synthesis Telescope (MOST) is an 18,000 square meter
radio telescope situated some 40 km from the city of Canberra, Australia. Its
operating band (820-850 MHz) is now partly allocated to mobile phone
communications, making radio astronomy challenging. We describe how the
deployment of new digital receivers (RX boxes), Field Programmable Gate Array
(FPGA) based filterbanks and server-class computers equipped with 43 GPUs
(Graphics Processing Units) has transformed MOST into a versatile new
instrument (the UTMOST) for studying the dynamic radio sky on millisecond
timescales, ideal for work on pulsars and Fast Radio Bursts (FRBs). The
filterbanks, servers and their high-speed, low-latency network form part of a
hybrid solution to the observatory's signal processing requirements. The
emphasis on software and commodity off-the-shelf hardware has enabled rapid
deployment through the re-use of proven 'software backends' for its signal
processing. The new receivers have ten times the bandwidth of the original MOST
and double the sampling of the line feed, which doubles the field of view. The
UTMOST can simultaneously excise interference, make maps, coherently dedisperse
pulsars, and perform real-time searches of coherent fan beams for dispersed
single pulses. Although system performance is still sub-optimal, a pulsar
timing and FRB search programme has commenced and the first UTMOST maps have
been made. The telescope operates as a robotic facility, deciding how to
efficiently target pulsars and how long to stay on source, via feedback from
real-time pulsar folding. The regular timing of over 300 pulsars has resulted
in the discovery of 7 pulsar glitches and 3 FRBs. The UTMOST demonstrates that
if sufficient signal processing can be applied to the voltage streams it is
possible to perform innovative radio science in hostile radio frequency
environments.Comment: 12 pages, 6 figure
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