74,508 research outputs found
A high resolution view of the jet termination shock in a hot spot of the nearby radio galaxy Pictor A: implications for X-ray models of radio galaxy hot spots
Images made with the VLBA have resolved the region in a nearby radio galaxy,
Pictor A, where the relativistic jet that originates at the nucleus terminates
in an interaction with the intergalactic medium, a so-called radio galaxy hot
spot. This image provides the highest spatial resolution view of such an object
to date (16 pc), more than three times better than previous VLBI observations
of similar objects. The north-west Pictor A hot spot is resolved into a complex
set of compact components, seen to coincide with the bright part of the hot
spot imaged at arcsecond-scale resolution with the VLA. In addition to a
comparison with VLA data, we compare our VLBA results with data from the HST
and Chandra telescopes, as well as new Spitzer data. The presence of pc-scale
components in the hot spot, identifying regions containing strong shocks in the
fluid flow, leads us to explore the suggestion that they represent sites of
synchrotron X-ray production, contributing to the integrated X-ray flux of the
hot spot, along with X-rays from synchrotron self-Compton scattering. This
scenario provides a natural explanation for the radio morphology of the hot
spot and its integrated X-ray emission, leading to very different predictions
for the higher energy X-ray spectrum compared to previous studies. From the
sizes of the individual pc-scale components and their angular spread, we
estimate that the jet width at the hot spot is in the range 70 - 700 pc, which
is comparable to similar estimates in PKS 2153-69, 3C 205, and 4C 41.17. The
lower limit in this range arises from the suggestion that the jet may dither in
its direction as it passes through hot spot backflow material close to the jet
termination point, creating a "dentist drill" effect on the inside of a cavity
700 pc in diameter.Comment: Accepted by the Astronomical Journal. 35 pages, 6 figure
Galaxy protocluster candidates at 1.6<z<2
We present a study of protoclusters associated with high redshift radio
galaxies. We imaged MRC1017-220 (z=1.77) and MRC0156-252 (z=2.02) using the
near-infrared wide-field (7.5'x7.5') imager VLT/HAWK-I in the Y, H and Ks
bands. We present the first deep Y-band galaxy number counts within a large
area (200 arcmin2). We then develop a purely near-infrared colour selection
technique to isolate galaxies at 1.6<z<3 that may be associated with the two
targets, dividing them into (i) red passively evolving or dusty star-forming
galaxies or (ii) blue/star-formation dominated galaxies with little or no dust.
Both targeted fields show an excess of star-forming galaxies with respect to
control fields. No clear overdensity of red galaxies is detected in the
surroundings of MRC1017-220 although the spatial distribution of the red
galaxies resembles a filament-like structure within which the radio galaxy is
embedded. In contrast, a significant overdensity of red galaxies is detected in
the field of MRC0156-252, ranging from a factor of 2-3 times the field density
at large scales (2.5Mpc, angular distance) up to a factor of 3-4 times the
field density within a 1Mpc radius of the radio galaxy. Half of these red
galaxies have colours consistent with red sequence models at z~2, with a large
fraction being bright (Ks<21.5, i.e. massive). In addition, we also find a
small group of galaxies within 5" of MRC0156-252 suggesting that the radio
galaxy has multiple companions within ~50 kpc. We conclude that the field of
MRC0156-252 shows many remarkable similarities with the well-studied
protocluster surrounding PKS1138-262 (z=2.16) suggesting that MRC0156-252 is
associated with a galaxy protocluster at z~2.Comment: accepted for publication in A&A, 16 pages, 13 figures, 3 table
DiFX2: A more flexible, efficient, robust and powerful software correlator
Software correlation, where a correlation algorithm written in a high-level
language such as C++ is run on commodity computer hardware, has become
increasingly attractive for small to medium sized and/or bandwidth constrained
radio interferometers. In particular, many long baseline arrays (which
typically have fewer than 20 elements and are restricted in observing bandwidth
by costly recording hardware and media) have utilized software correlators for
rapid, cost-effective correlator upgrades to allow compatibility with new,
wider bandwidth recording systems and improve correlator flexibility. The DiFX
correlator, made publicly available in 2007, has been a popular choice in such
upgrades and is now used for production correlation by a number of
observatories and research groups worldwide. Here we describe the evolution in
the capabilities of the DiFX correlator over the past three years, including a
number of new capabilities, substantial performance improvements, and a large
amount of supporting infrastructure to ease use of the code. New capabilities
include the ability to correlate a large number of phase centers in a single
correlation pass, the extraction of phase calibration tones, correlation of
disparate but overlapping sub-bands, the production of rapidly sampled
filterbank and kurtosis data at minimal cost, and many more. The latest version
of the code is at least 15% faster than the original, and in certain situations
many times this value. Finally, we also present detailed test results
validating the correctness of the new code.Comment: 28 pages, 9 figures, accepted for publication in PAS
Trojan Horse as an indirect technique in nuclear astrophysics. Resonance reactions
The Trojan Horse method is a powerful indirect technique that provides
information to determine astrophysical factors for binary rearrangement
processes at astrophysically relevant energies by measuring
the cross section for the Trojan Horse reaction in
quasi-free kinematics. We present the theory of the Trojan Horse method for
resonant binary subreactions based on the half-off-energy-shell R matrix
approach which takes into account the off-energy-shell effects and initial and
final state interactions.Comment: 6 pages and 1 figur
Understanding the Coping Process from a Self-Determination Theory Perspective
Purpose: To explore conceptual links between the Cognitive-Motivational-Relational Theory of coping (Lazarus, 1991) and Self-Determination Theory of motivation (Deci & Ryan, 1985)
Method: We present a very brief overview of the two theories. We also discuss how components from the two theories can be examined together to facilitate research in the health/exercise domain. To this effect, we offer a preliminary integrated model of stress, coping and motivation, based on the two aforementioned theories, in an attempt to illustrate and instigate research on how motivational factors are implicated in the coping process.
Conclusion: We believe that the proposed model can serve as a platform for generating new research ideas which, besides their theoretical relevance, may have important applied implications
After-hours respiratory physiotherapy for intubated and mechanically ventilated patients with community-acquired pneumonia: An Australian perspective
Introduction: Community acquired pneumonia (CAP) is a common reason for admission to an intensive care unit for intubation and mechanical ventilation, and results in high morbidity and mortality. The primary aim of the study was to investigate availability and provision of respiratory physiotherapy, outside of normal business hours, for intubated and mechanically ventilated adults with CAP in Australian hospitals.
Materials and methods: A cross-sectional, mixed methods online survey was conducted. Participants were senior intensive care unit physiotherapists from 88 public and private hospitals. Main outcome measures included presence and nature of an after-hours physiotherapy service and factors perceived to influence the need for after-hours respiratory physiotherapy intervention, when the service was available, for intubated adult patients with CAP. Data were also collected regarding respiratory intervention provided after-hours by other ICU professionals.
Results: Response rate was 72% (n = 75). An after-hours physiotherapy service was provided by n = 31 (46%) hospitals and onsite after-hours physiotherapy presence was limited (22%), with a combination of onsite and on-call service reported by 19%. Treatment response (83%) was the most frequent factor for referring patients with CAP for after-hours physiotherapy intervention by the treating day-time physiotherapist. Nurses performing respiratory intervention (77%) was significantly associated with no available after-hours physiotherapy service (p = 0.04).
Discussion: Physiotherapy after-hours service in Australia is limited, therefore it is common for intubated patients with CAP not to receive any respiratory physiotherapy intervention outside of normal business hours. In the absence of an after-hours physiotherapist, nurses were most likely to perform after-hours respiratory intervention to intubated patients with CAP.
Conclusion: Further research is required to determine whether the frequency of respiratory physiotherapy intervention, including after-hours provision of treatment, influences outcomes for ICU patients intubated with pneumonia
A possible jet precession in the periodic quasar B0605-085
The quasar B0605-085 (OH 010) shows a hint for probable periodical
variability in the radio total flux-density light curves. We study the possible
periodicity of B0605-085 in the total flux-density, spectra and opacity changes
in order to compare it with jet kinematics on parsec scales. We have analyzed
archival total flux-density variability at ten frequencies (408 MHz, 4.8 GHz,
6.7 GHz, 8 GHz, 10.7 GHz, 14.5 GHz, 22 GHz, 37 GHz, 90 GHz, and 230 GHz)
together with the archival high-resolution very long baseline interferometry
data at 15 GHz from the MOJAVE monitoring campaign. Using the Fourier transform
and discrete autocorrelation methods we have searched for periods in the total
flux-density light curves. In addition, spectral evolution and changes of the
opacity have been analyzed. We found a period in multi-frequency total
flux-density light curves of 7.9+-0.5 yrs. Moreover, a quasi-stationary jet
component C1 follows a prominent helical path on a similar time scale of 8
years. We have also found that the average instantaneous speeds of the jet
components show a clear helical pattern along the jet with a characteristic
scale of 3 mas. Taking into account average speeds of jet components, this
scale corresponds to a time scale of about 7.7 years. Jet precession can
explain the helical path of the quasi-stationary jet component C1 and the
periodical modulation of the total flux-density light curves. We have fitted a
precession model to the trajectory of the jet component C1, with a viewing
angle phi=2.6+-2.2 degrees, aperture angle of the precession cone
Omega=23.9+-1.9 degrees and fixed precession period (in the observers frame) P
= 7.9 yrs.Comment: 14 pages, 16 figures, 5 tables, accepted for publication in A&
Ultraluminous X-ray Source Correlations with Star-Forming Regions
Maps of low-inclination nearby galaxies in Sloan Digitized Sky Survey u-g,
g-r and r-i colors are used to determine whether Ultraluminous X-ray sources
(ULXs) are predominantly associated with star-forming regions of their host
galaxies. An empirical selection criterion is derived from colors of HII
regions in M81 and M101 that differentiates between the young, blue stellar
component and the older disk and bulge population. This criterion is applied to
a sample of 58 galaxies of Hubble type S0 and later and verified through an
application of Fisher's linear discriminant analysis. It is found that 60%
(49%) of ULXs in optically-bright environments are within regions blueward of
their host galaxy's HII regions compared to only 27% (0%) of a control sample
according to the empirical (Fisher) criterion. This is an excess of 3-sigma
above the 32% (27%) expected if the ULXs were randomly distributed within their
galactic hosts. This indicates a ULX preference for young, approximately <10
Myr, OB associations. However, none of the ULX environments have the morphology
and optical brightness suggestive of a massive young super star cluster though
several are in extended or crowded star-forming (blue) environments that may
contain clusters unresolved by Sloan imaging. Ten of the 12 ULX candidates with
estimated X-ray luminosities in excess of 3e39 erg/s are equally divided among
the group of ULX environments redward of HII regions and the group of optically
faint regions. This likely indicates that the brightest ULXs turn on at a time
somewhat later than typical of HII regions; say 10-20 Myr after star formation
has ended. This would be consistent with the onset of an accretion phase as the
donor star ascends the giant branch if the donor is a <20 solar-mass star.Comment: 13 pages, accepted to Ap
Monitoring of the prompt radio emission from the unusual supernova 2004dj in NGC2403
Supernova 2004dj in the nearby spiral galaxy NGC2403 was detected optically
in July 2004. Peaking at a magnitude of 11.2, this is the brightest supernova
detected for several years. Here we present Multi-Element Radio Linked
Interferometer Network (MERLIN) observations of this source, made over a four
month period, which give a position of R.A. = 07h37m17.044s, Dec
=+65deg35'57.84" (J2000.0). We also present a well-sampled 5 GHz light curve
covering the period from 5 August to 2 December 2004. With the exception of the
unusual and very close SN 1987A, these observations represent the first
detailed radio light curve for the prompt emission from a Type II-P supernova.Comment: (1) Jodrell Bank Observatory (2) University of Valencia (3)
University of Sheffield 6 pages, 1 figure. To appear in ApJ letter
On prescribed change of profile for solutions of parabolic equations
Parabolic equations with homogeneous Dirichlet conditions on the boundary are
studied in a setting where the solutions are required to have a prescribed
change of the profile in fixed time, instead of a Cauchy condition. It is shown
that this problem is well-posed in L_2-setting. Existence and regularity
results are established, as well as an analog of the maximum principle
- …