1,168 research outputs found
A precessing accretion disc in the intermediate polar XY Ari?
XY Ari is the only intermediate polar to show deep X-ray eclipses of its
white dwarf. Previously published observations with Ginga and Chandra have also
revealed a broad X-ray orbital modulation, roughly antiphased with the eclipse,
and presumed to be due to absorption in an extended structure near the edge of
an accretion disc. The X-ray pulse profile is generally seen to be
double-peaked, although a single-peaked pulse was seen by RXTE during an
outburst in 1996.We intended to investigate the cause of the broad orbital
modulation in XY Ari to better understand the accretion flow in this system and
other intermediate polars. We observed XY Ari with RXTE and analysed previously
unpublished archival observations of the system made with ASCA and XMM-Newton.
These observations comprise six separate visits and span about ten years. The
various X-ray observations show that the broad orbital modulation varies in
phase and significance, then ultimately disappears entirely in the last few
years. In addition, the X-ray pulse profile shows variations in depth and
shape, and in the recent RXTE observations displays no evidence for changes in
hardness ratio. The observed changes indicates that both the pulse profile and
the orbital modulation are solely due to geometrical effects at the time of the
RXTE observations, rather than phase-dependent variations in photoelectric
absorption as seen previously. We suggest that this is evidence for a
precessing, tilted accretion disc in this system. The precession of the disc
moves structures out of our line of sight both at its outer edge (changing the
orbital modulation) and at its inner edge where the accretion curtains are
anchored (changing the pulse profile).Comment: Accepted for publication in Astronomy & Astrophysic
The accretion flow in the discless intermediate polar V2400 Ophiuchi
RXTE observations confirm that the X-ray lightcurve of V2400 Oph is pulsed at
the beat cycle, as expected in a discless intermediate polar. There are no
X-ray modulations at the orbital or spin cycles, but optical line profiles vary
with all three cycles. We construct a model for line-profile variations in a
discless accretor, based on the idea that the accretion stream flips from one
magnetic pole to the other, and show that this accounts for the observed
behaviour over the spin and beat cycles. The minimal variability over the
orbital cycle implies that 1) V2400 Oph is at an inclination of only ~10 deg,
and 2) much of the accretion flow is not in a coherent stream, but is circling
the white dwarf, possibly as a ring of denser, diamagnetic blobs. We discuss
the light this sheds on disc formation in intermediate polars.Comment: 10 pages, 12 figures, To appear in MNRAS, includes low-res figures to
reduce siz
Learning medical alarms whilst performing other tasks.
Two studies are reported which first observe, and then attempt to replicate, the cognitive demands of intensive care unit (ICU) activity whilst concurrently learning audible alarms. The first study, an observational study in an ICU ward, showed that the alarms are very frequent and co-occur with some activities more than others. The three most frequently observed activities observed in the ICU were drugs (calculation, preparation and administration), patient observation and talking. The cognitive demands of these activities were simulated in a second, laboratory-based experiment in which alarms were learned. The results showed that performance in the alarm task generally improved as participants were exposed to more repetitions of those alarms, but that performance decrements were observed in the secondary tasks, particularly when there were two or three of them. Some confusions between the alarms persisted to the end of the study despite prolonged exposure to the alarms, confusions which were likely caused by both acoustic and verbal labelling similarities. PRACTITIONER SUMMARY: The cognitive demands of working in an ICU were observed and simulated whilst alarms were learned. Alarms should generally avoid sharing similar rhythmic (and other) characteristics. The simulation task described here could be used for testing alarm learning without requiring a clinical environment
An alternative model of the magnetic cataclysmic variable V1432 Aquilae (=RX J1940.1-1025)
V1432 Aql is currently considered to be an asynchronous AM Her type system,
with an orbital period of 12116.3 s and a spin period of 12150 s. I present an
alternative model in which V1432 Aql is an intermediate polar with disk
overflow or diskless accretion geometry, with a spin period near 4040 s. I
argue that published data are insufficient to distinguish between the two
models; instead, I provide a series of predictions of the two models that can
be tested against future observations.Comment: 10 pages LaTeX including 3 Postscript Figures, to be published in Ap
Passing crisis and emergency risk communications: the effects of communication channel, information type, and repetition.
Three experiments explore several factors which influence information transmission when warning messages are passed from person to person. In Experiment 1, messages were passed down chains of participants using five different modes of communication. Written communication channels resulted in more accurate message transmission than verbal. In addition, some elements of the message endured further down the chain than others. Experiment 2 largely replicated these effects and also demonstrated that simple repetition of a message eliminated differences between written and spoken communication. In a final field experiment, chains of participants passed information however they wanted to, with the proviso that half of the chains could not use telephones. Here, the lack of ability to use a telephone did not affect accuracy, but did slow down the speed of transmission from the recipient of the message to the last person in the chain. Implications of the findings for crisis and emergency risk communication are discussed
Discovery of an X-ray pulsar in the low-mass X-ray binary 2A 1822-371
We report the discovery of 0.59 s X-ray pulsations from the low-mass X-ray
binary, 5.57 hr dipping and eclipsing ADC source 2A 1822-371. Pulse arrival
time analysis indicates a circular orbit with e < 0.03 (95% confidence) and an
asini for the neutron star of 1.006(5) lightseconds, implying a mass function
of (2.03+-0.03) x 10^-2 M_sun. The barycentric pulse period was 0.59325(2) s in
1996.270 and 0.59308615(5) s in 1998.205, indicating an average spin up with
P_dot/P = (-1.52+-0.02) x 10^-4 yr^-1. For a magnetic field strength of ~1--5 x
10^12 G as derived from the X-ray spectrum the implied intrinsic X-ray
luminosity is ~2-4 x 10^37 erg s^-1. The pulse amplitude is low, but increases
steeply as a function of energy from a sinusoidal amplitude of 0.25% in 2-5.4
keV to ~3% above 20 keV. We discuss the constraints on the masses of the
companion star and the fact that several aspects of the energy spectrum are in
qualitative accordance with that of a strongly magnetised neutron star.Comment: 6 pages long, including 4 figures, uses emulateapj5, accepted for
ApJL, Replaced figure
Shifts in ownership toward high-powered motorcycles and its effects on public health
Objectives. We assessed whether policies designed to safeguard young motorcyclists would be effective given shifts in ownership toward high-powered motorcycles. Methods. We investigated population-wide motor vehicle driver and motorcyclist casualties (excluding passengers) recorded in Britain between 2002 and 2009. To adjust for exposure and measure individual risk, we used the estimated number of trips of motorcyclists and drivers, which had been collected as part of a national travel survey. Results. Motorcyclists were 76 times more likely to be killed than were drivers for every trip. Older motorcyclist age—strongly linked to experience, skill set,and riding behavior—did not abate the risks of high-powered motorcycles. Older motorcyclists made more trips on high-powered motorcycles. Conclusions: Tighter engine size restrictions would help reduce the use of high-powered motorcycles. Policymakers should introduce health warnings on the risks of high-powered motorcycles and the benefits of safety equipment
IPHAS J062746.41+014811.3: a deeply eclipsing intermediate polar
We present time-resolved photometry of a cataclysmic variable discovered in
the Isaac Newton Telescope Photometric Halpha Survey of the northern galactic
plane, IPHAS J062746.41+014811.3 and classify the system as the fourth deeply
eclipsing intermediate polar known with an orbital period of Porb=8.16 h, and
spin period of Pspin=2210 s. The system shows mild variations of its
brightness, that appear to be accompanied by a change in the amplitude of the
spin modulation at optical wavelengths, and a change in the morphology of the
eclipse profile. The inferred magnetic moment of the white dwarf is mu_wd = 6-7
x 10^33 Gcm^3, and in this case IPHAS J0627 will either evolve into a
short-period EX Hya-like intermediate polar with a large Pspin\Porb ratio, or,
perhaps more likely, into a synchronised polar. Swift observations show that
the system is an ultraviolet and X-ray source, with a hard X-ray spectrum that
is consistent with those seen in other intermediate polars. The ultraviolet
light curve shows orbital modulation and an eclipse, while the low
signal-to-noise ratio X-ray light curve does not show a significant modulation
on the spin period. The measured X-ray flux is about an order of magnitude
lower than would be expected from scaling by the optical fluxes of well-known
X-ray selected intermediate polars.Comment: 34 pages, 9 figures, accepted for publication in Ap
The effects of label design characteristics on perceptions of genetically modified food
Objective. To explore the effects on perceptions of labelling food for genetically modified content. Background: there is increasing public pressure for the compulsory labelling of genetically modified food content on all food products, and yet little is known about how the design and content of such food labels will influence product perceptions. The current research draws upon warning label research - a field in which the effect of label design manipulations on perceptions of, and responses to, potential or perceived risks is well documented. Method. Two experiments are reported that investigate how label design features influence the perception of genetically modified foods. The effects of label colour (red, blue and green), wording style (definitive vs. probabilistic and explicit vs. non-explicit) and information source (government agency, consumer group and manufacturer) on hazard perceptions and purchase intentions were measured. Results. Hazard perceptions and purchase intentions were both influenced by label design characteristics in predictable ways. Any reference to genetic modification, even if the label is stating that the product is free of genetically modified ingredients, increased hazard perception, and decreased purchase intentions, relative to a no-label condition. Conclusion. Label design effects generalise from warning label research to influence the perception of genetically modified foods in predictable ways. Application. The design of genetically modified food labels. © 2012 Copyright Taylor and Francis Group, LLC
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