1,425 research outputs found
GMRT detections of low-mass young stars at 323 and 608 MHz
We present the results of a pathfinder project conducted with the Giant
Metrewave Radio Telescope (GMRT) to investigate protostellar systems at low
radio frequencies. The goal of these investigations is to locate the break in
the free-free spectrum where the optical depth equals unity in order to
constrain physical parameters of these systems, such as the mass of the ionised
gas surrounding these young stars. We detect all three target sources, L1551
IRS 5 (Class I), T Tau and DG Tau (Class II), at frequencies 323 and 608 MHz
(wavelengths 90 and 50 cm, respectively). These are the first detections of low
mass young stellar objects (YSOs) at such low frequencies. We combine these new
GMRT data with archival information to construct the spectral energy
distributions for each system and find a continuation of the optically thin
free-free spectra extrapolated from higher radio frequencies to 323 MHz for
each target. We use these results to place limits on the masses of the ionised
gas and average electron densities associated with these young systems on
scales of ~1000 au. Future observations with higher angular resolution at lower
frequencies are required to constrain these physical parameters further.We thank the staff of the GMRT who have made these observations possible. GMRT is run by the National Centre for Radio Astrophysics of the Tata Institute of Fundamental Research. REA, TPR and CPC acknowledge support from Science Foundation Ireland under grant 13/ERC/I2907. AMS gratefully acknowledges support from the European Research Council under grant ERC-2012-StG-307215 LODESTONE. DAG thanks the Science and Technology Facilities Council for support. We thank the anonymous referee for their helpful and constructive comments to clarify this manuscript.This is the final version of the article. It first appeared from Oxford University Press via http://dx.doi.org/10.1093/mnras/stw70
A GMRT survey of regions towards the Taurus molecular cloud at 323 and 608 MHz
We present observations of three active sites of star formation in the Taurus
Molecular Cloud complex taken at 323 and 608 MHz (90 and 50 cm, respectively)
with the Giant Metrewave Radio Telescope (GMRT). Three pointings were observed
as part of a pathfinder project, targeted at the young stellar objects (YSOs)
L1551 IRS 5, T Tau and DG Tau (the results for these target sources were
presented in a previous paper). In this paper, we search for other YSOs and
present a survey comprising of all three fields; a by-product of the large
instantaneous field of view of the GMRT. The resolution of the survey is of
order 10 arcsec and the best rms noise at the centre of each pointing is of
order Jy beam at 323 MHz and Jy beam at 608
MHz. We present a catalogue of 1815 and 687 field sources detected above
at 323 and 608 MHz, respectively. A total of 440 sources
were detected at both frequencies, corresponding to a total unique source count
of 2062 sources. We compare the results with previous surveys and showcase a
sample of extended extragalactic objects. Although no further YSOs were
detected in addition to the target YSOs based on our source finding criteria,
these data can be useful for targeted manual searches, studies of radio
galaxies or to assist in the calibration of future observations with the Low
Frequency Array (LOFAR) towards these regions.Science Foundation Ireland [Grant ID: 13/ERC/I2907], Science and Technology Facilities Council, European Research Council [Grant ID: ERC-2012-StG-307215 LODESTONE]This is the final version of the article. It first appeared from Oxford University Press via http://dx.doi.org/10.1093/mnras/stw184
Observation of An Evolving Magnetic Flux Rope Prior To and During A Solar Eruption
Explosive energy release is a common phenomenon occurring in magnetized
plasma systems ranging from laboratories, Earth's magnetosphere, the solar
corona and astrophysical environments. Its physical explanation is usually
attributed to magnetic reconnection in a thin current sheet. Here we report the
important role of magnetic flux rope structure, a volumetric current channel,
in producing explosive events. The flux rope is observed as a hot channel prior
to and during a solar eruption from the Atmospheric Imaging Assembly (AIA)
telescope on board the Solar Dynamic Observatory (SDO). It initially appears as
a twisted and writhed sigmoidal structure with a temperature as high as 10 MK
and then transforms toward a semi-circular shape during a slow rise phase,
which is followed by fast acceleration and onset of a flare. The observations
suggest that the instability of the magnetic flux rope trigger the eruption,
thus making a major addition to the traditional magnetic-reconnection paradigm.Comment: 13 pages, 3 figure
An inhomogeneous toy-model of the quantum gravity with explicitly evolvable observables
An inhomogeneous (1+1)-dimensional model of the quantum gravity is
considered. It is found, that this model corresponds to a string propagating
against some curved background space. The quantization scheme including the
Wheeler-DeWitt equation and the "particle on a sphere" type of the gauge
condition is suggested. In the quantization scheme considered, the "problem of
time" is solved by building of the quasi-Heisenberg operators acting in a space
of solutions of the Wheeler-DeWitt equation and the normalization of the wave
function corresponds to the Klein-Gordon type. To analyze the physical
consequences of the scheme, a (1+1)-dimensional background space is considered
for which a classical solution is found and quantized. The obtained estimations
show the way to solution of the cosmological constant problem, which consists
in compensation of the zero-point oscillations of the matter fields by the
quantum oscillations of the scale factor. Along with such a compensation, a
slow global evolution of a background corresponding to an universe expansion
exists.Comment: 18 page
An Exploratory Analysis of the Smoking and Physical Activity Outcomes From a Pilot Randomized Controlled Trial of an Exercise Assisted Reduction to Stop Smoking Intervention in Disadvantaged Groups.
INTRODUCTION: Economically disadvantaged smokers not intending to stop may benefit from interventions aimed at reducing their smoking. This study assessed the effects of a behavioral intervention promoting an increase in physical activity versus usual care in a pilot randomized controlled trial. METHODS: Disadvantaged smokers who wanted to reduce but not quit were randomized to either a counseling intervention of up to 12 weeks to support smoking reduction and increased physical activity (n = 49) or usual care (n = 50). Data at 16 weeks were collected for various smoking and physical activity outcomes. Primary analyses consisted of an intention to treat analysis based on complete case data. Secondary analyses explored the impact of handling missing data. RESULTS: Compared with controls, intervention smokers were more likely to initiate a quit attempt (36 vs. 10%; odds ratio 5.05, [95% CI: 1.10; 23.15]), and a greater proportion achieved at least 50% reduction in cigarettes smoked (63 vs. 32%; 4.21 [1.32; 13.39]). Postquit abstinence measured by exhaled carbon monoxide at 4-week follow-up showed promising differences between groups (23% vs. 6%; 4.91 [0.80; 30.24]). No benefit of intervention on physical activity was found. Secondary analyses suggested that the standard missing data assumption of "missing" being equivalent to "smoking" may be conservative resulting in a reduced intervention effect. CONCLUSIONS: A smoking reduction intervention for economically disadvantaged smokers which involved personal support to increase physical activity appears to be more effective than usual care in achieving reduction and may promote cessation. The effect does not appear to be influenced by an increase in physical activity
Constraining the nature of DG Tau A’s thermal and non-thermal radio emission
DG Tau A, a class-II young stellar object (YSO) displays both thermal,
and non-thermal, radio emission associated with its bipolar jet. To
investigate the nature of this emission, we present sensitive (sigma ~ 2
microJy/beam), Karl G.\ Jansky Very Large Array (VLA) 6 and 10 GHz
observations. Over 3.81 yr, no proper motion is observed towards the
non-thermal radio knot C, previously thought to be a bowshock. Its
quasi-static nature, spatially-resolved variability and offset from the
central jet axis supports a scenario whereby it is instead a stationary
shock driven into the surrounding medium by the jet. Towards the
internal working surface, knot A, we derive an inclination-corrected,
absolute velocity of 258 +/- 23 km/s. DG Tau A's receding counterjet
displays a spatially-resolved increase in flux density, indicating a
variable mass loss event, the first time such an event has been observed
in the counterjet. For this ejection, we measure an ionised mass loss
rate of (3.7 +/- 1.0) * 10**8 Msun/yr during the event. A
contemporaneous ejection in the approaching jet isn't seen, showing it
to be an asymmetric process. Finally, using radiative transfer
modelling, we find that the extent of the radio emission can only be
explained with the presence of shocks, and therefore reionisation, in
the flow. Our modelling highlights the need to consider the relative
angular size of optically thick, and thin, radio emission from a jet, to
the synthesised beam, when deriving its physical conditions from its
spectral index
Peri-orbital foreign body: a case report
<p>Abstract</p> <p>Introduction</p> <p>Foreign bodies inside the orbital cavity are rare. They can cause more or less serious complications, depending on their nature and size.</p> <p>Case presentation</p> <p>We report a case of a work-related accident involving a peri-orbital foreign body. The patient was a 50-year-old Caucasian man whose face was injured on the right side while he was working with an agricultural machine. On admission, he was fully conscious and did not have any neurological deficits. He had no loss of vision or ocular motility, but had a laceration of the lateral side of his right upper eyelid. A computed tomographic scan revealed a 6-cm-long bended metal object lodged in the lateral bulbar space of the right orbit. The patient recovered well after surgery and a course of antibiotic therapy.</p> <p>Conclusion</p> <p>The original aspects of this case are the singularity of the foreign body and its relative harmlessness in spite of its large size.</p
Determinants of Inapparent and Symptomatic Dengue Infection in a Prospective Study of Primary School Children in Kamphaeng Phet, Thailand
Dengue viruses are a major cause of illness and hospitalizations in tropical and subtropical regions of the world. Severe dengue illness can cause prolonged hospitalization and in some cases death in both children and adults. The majority of dengue infections however are inapparent, producing little clinical illness. Little is known about the epidemiology or factors that determine the incidence of inapparent infection. We describe in a study of school children in Northern Thailand the changing nature of symptomatic and inapparent dengue infection. We demonstrate that the proportion of inapparent dengue infection varies widely among schools during a year and within schools during subsequent years. Important factors that determine this variation are the amount of dengue infection in a given and previous year. Our findings provide an important insight in the virus-host interaction that determines dengue severity, how severe a dengue epidemic may be in a given year, and important clues on how a dengue vaccine may be effective
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