467 research outputs found
An X-ray and Radio Study of the Varying Expansion Velocities in Tycho's Supernova Remnant
We present newly obtained X-ray and radio observations of Tycho's supernova
remnant using {\it Chandra} and the Karl G. Jansky Very Large Array in 2015 and
2013/14, respectively. When combined with earlier epoch observations by these
instruments, we now have time baselines for expansion measurements of the
remnant of 12-15 year in the X-rays and 30 year in the radio. The remnant's
large angular size allows for proper motion measurements at many locations
around the periphery of the blast wave. We find, consistent with earlier
measurements, a clear gradient in the expansion velocity of the remnant,
despite its round shape. The proper motions on the western and southwestern
sides of the remnant are about a factor of two higher than those in the east
and northeast. We showed in an earlier work that this is related to an offset
of the explosion site from the geometric center of the remnant due to a density
gradient in the ISM, and using our refined measurements reported here, we find
that this offset is towards the northeast. An explosion center
offset in such a circular remnant has implications for searches for progenitor
companions in other remnants.Comment: Accepted for publication in ApJ Letter
A Deep X-ray View of the Synchrotron-Dominated Supernova Remnant G330.2+1.0
We present moderately deep (125 ks) {\it XMM-Newton} observations of
supernova remnant G330.21.0. This remnant is one of only a few known that
fall into "synchrotron-dominated" category, with the emission almost entirely
dominated by a nonthermal continuum. Previous X-ray observations could only
characterize the spectra of a few regions. Here, we examine the spectra from
fourteen regions surrounding the entire rim, finding that the spectral
properties of the nonthermal emission do not vary significantly in any
systematic way from one part of the forward shock to another, unlike several
other remnants of this class. We confirm earlier findings that the power-law
index, , ranges from about 2.1-2.5, while the absorbing column density
is generally between 2.0-2.6 cm. Fits with the {\it
srcut} model find values of the roll-off frequency in the range of 10 Hz, implying energies of accelerated electrons of TeV.
These values imply a high shock velocity of km s, favoring a
young age of the remnant. Diffuse emission from the interior is nonthermal in
origin as well, and fits to these regions yield similar values to those along
the rim, also implying a young age. Thermal emission is present in the east,
and the spectrum is consistent with a km s shock wave
encountering interstellar or circumstellar material with a density of
cm.Comment: Accepted for publication by ApJ. Manuscript produced with emulateapj.
10 pages, 8 figure
The Three-Dimensional Expansion of the Ejecta from Tycho's Supernova Remnant
We present the first three-dimensional measurements of the velocity of
various ejecta knots in Tycho's supernova remnant, known to result from a Type
Ia explosion. Chandra X-ray observations over a 12-year baseline from 2003 to
2015 allow us to measure the proper motion of nearly 60 "tufts" of Si-rich
ejecta, giving us the velocity in the plane of the sky. For the line of sight
velocity, we use two different methods: a non-equilibrium ionization model fit
to the strong Si and S lines in the 1.2-2.8 keV regime, and a fit consisting of
a series of Gaussian lines. These methods give consistent results, allowing us
to determine the red or blue shift of each of the knots. Assuming a distance of
3.5 kpc, we find total velocities that range from 2400 to 6600 km s,
with a mean of 4430 km s. We find several regions where the ejecta knots
have overtaken the forward shock. These regions have proper motions in excess
of 6000 km s. Some Type Ia supernova explosion models predict a velocity
asymmetry in the ejecta. We find no such velocity asymmetries in Tycho, and
discuss our findings in light of various explosion models, favoring those
delayed detonation models with relatively vigorous and symmetrical
deflagrations. Finally, we compare measurements with models of the remnant's
evolution that include both smooth and clumpy ejecta profiles, finding that
both ejecta profiles can be accommodated by the observations.Comment: Accepted for publication in ApJ. Some figures slightly degraded to
reduce file siz
Variable retention harvesting influences belowground plant-fungal interactions of Nothofagus pumilio seedlings in forests of southern Patagonia
Background. The post-harvest recovery and sustained productivity of Nothofagus pumilio forests in Tierra del Fuego may be affected by the abundance and composition of ectomycorrhizal fungi (EMF). Timber harvesting alters EMF community structure in many managed forests, but the impacts of harvesting can vary with the management strategy. The implementation of variable retention (VR) management can maintain, increase, or decrease the diversity of many species, but the effects of VR on EMF in the forests of southern Patagonia have not been studied, nor has the role of EMF in the regeneration process of these forests. Methods. We evaluated the effects of VR management on the EMF community associated with N. pumilio seedlings. We quantified the abundance, composition, and diversity of EMF across aggregate (AR) and dispersed (DR) retention sites within VR managed areas, and compared them to primary forest (PF) unmanaged stands. EMF assemblage and taxonomic identities were determined by ITS-rDNA sequencing of individual root tips sampled from 280 seedlings across three landscape replicates. To better understand seedling performance, we tested the relationships between EMF colonization, EMF taxonomic composition, seedling biomass, and VR treatment. Results. The majority of EMF taxa were Basidiomycota belonging to the families Cortinariaceae (n = 29), Inocybaceae (n = 16), and Thelephoraceae (n = 8), which was in agreement with other studies of EMF diversity in Nothofagus forests. EMF richness and colonization was reduced in DR compared to AR and PF. Furthermore, EMF community composition was similar between AR and PF, but differed from the composition in DR. EMF community composition was correlated with seedling biomass and soil moisture. The presence of Peziza depressa was associated with higher seedling biomass and greater soil moisture, while Inocybe fibrillosibrunnea and Cortinarius amoenus were associated with reduced seedling biomass and lower soil moisture. Seedling biomass was more strongly related to retention type than EMF colonization, richness, or composition. Discussion. Our results demonstrate reduced EMF attributes and altered composition in VR treatments relative to PF stands, with stronger impacts in DR compared to AR. This suggests that VR has the potential to improve the conservation status of managed stands by supporting native EMF in AR. Our results also demonstrate the complex linkages between retention treatments, fungal community composition, and tree growth at individual and stand scales.Fil: Hewitt, Rebecca E.. University Of Alaska; Estados Unidos. Northern Arizona University; Estados UnidosFil: Taylor, Donald Lee. University of New Mexico; Estados Unidos. University Of Alaska; Estados UnidosFil: Hollingsworth, Teresa N.. Usda Forest Service. Pacific Northwest Research Station; Estados UnidosFil: Anderson, Christopher Brian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina. Universidad Nacional de Tierra del Fuego; ArgentinaFil: Martínez Pastur, Guillermo José. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentin
Investigating the Cosmic-Ray Ionization Rate Near the Supernova Remnant IC 443 Through H3+ Observations
Observational and theoretical evidence suggests that high-energy Galactic
cosmic rays are primarily accelerated by supernova remnants. If also true for
low-energy cosmic rays, the ionization rate near a supernova remnant should be
higher than in the general Galactic interstellar medium (ISM). We have searched
for H3+ absorption features in 6 sight lines which pass through molecular
material near IC 443---a well-studied case of a supernova remnant interacting
with its surrounding molecular material---for the purpose of inferring the
cosmic-ray ionization rate in the region. In 2 of the sight lines (toward ALS
8828 and HD 254577) we find large H3+ column densities, N(H3+)~3*10^14 cm^-2,
and deduce ionization rates of zeta_2~2*10^-15 s^-1, about 5 times larger than
inferred toward average diffuse molecular cloud sight lines. However, the 3
sigma upper limits found for the other 4 sight lines are consistent with
typical Galactic values. This wide range of ionization rates is likely the
result of particle acceleration and propagation effects, which predict that the
cosmic-ray spectrum and thus ionization rate should vary in and around the
remnant. While we cannot determine if the H3+ absorption arises in post-shock
(interior) or pre-shock (exterior) gas, the large inferred ionization rates
suggest that IC 443 is in fact accelerating a large population of low-energy
cosmic rays. Still, it is unclear whether this population can propagate far
enough into the ISM to account for the ionization rate inferred in diffuse
Galactic sight lines.Comment: 14 pages, 3 figures, 4 table
A survey of engagement and competence levels in interventions and activities in a community mental health workforce in England.
National Health Service (NHS) mental health workforce configuration is at the heart of successful delivery, and providers are advised to produce professional development strategies. Recent policy changes in England have sharpened the focus on competency based role development. We determined levels of intervention activities, engagement and competence and their influencing factors in a community-setting mental health workforce. Using a modified questionnaire based on the Yorkshire Care Pathways Model we investigated 153 mental health staff working in Coventry and Warwickshire NHS Trust. A median score of competence was computed across 10 cluster activities. Low engagement and competence levels were examined in a logistic regression model. In 220 activities, Monitoring risk was the highest rate of engagement (97.6%) and Group psychological therapy/Art/Drama therapy was the lowest engagement (3.6%). The median competence level based on all activities was 3.95 (proficient). There were significant differences in the competence level among professional groups; non-qualified support group (3.00 for competent), Counsellor/Psychologist/Therapist (3.38), Occupational therapists (3.76), Nurses (4.01), Medical staff (4.05), Social workers (4.25) and Psychologists (4.62 for proficient/expert). These levels varied with activity clusters; the lowest level was for Counsellor/Psychologist/Therapist in the accommodation activity (1.44 novice/advance beginner) and the highest for Occupational therapists in personal activity (4.94 expert). In a multivariate analysis, low competence was significantly related to non-qualified community support professions, late time of obtaining first qualification, more frequencies of clinical training, and training of cognitive behavioural therapy. The associations were similar in the analysis for 10 activity clusters respectively. There was a reasonable competence level in the community-setting mental health workforce, but competence varied with professional groups and cluster activities. New staff and other non-qualified support professions need to receive efficient training, and the training content is more important than frequency to increase level of competence
Modelling and Simulation of Asynchronous Real-Time Systems using Timed Rebeca
In this paper we propose an extension of the Rebeca language that can be used
to model distributed and asynchronous systems with timing constraints. We
provide the formal semantics of the language using Structural Operational
Semantics, and show its expressiveness by means of examples. We developed a
tool for automated translation from timed Rebeca to the Erlang language, which
provides a first implementation of timed Rebeca. We can use the tool to set the
parameters of timed Rebeca models, which represent the environment and
component variables, and use McErlang to run multiple simulations for different
settings. Timed Rebeca restricts the modeller to a pure asynchronous
actor-based paradigm, where the structure of the model represents the service
oriented architecture, while the computational model matches the network
infrastructure. Simulation is shown to be an effective analysis support,
specially where model checking faces almost immediate state explosion in an
asynchronous setting.Comment: In Proceedings FOCLASA 2011, arXiv:1107.584
Serendipitous discovery of a dying Giant Radio Galaxy associated with NGC 1534, using the Murchison Widefield Array
Recent observations with the Murchison Widefield Array at 185 MHz have serendipitously unveiled a heretofore unknown giant and relatively nearby (z = 0.0178) radio galaxy associated with NGC 1534. The diffuse emission presented here is the first indication that NGC 1534 is one of a rare class of objects (along with NGC 5128 and NGC 612) in which a galaxy with a prominent dust lane hosts radio emission on scales of ∼700 kpc. We present details of the radio emission along with a detailed comparison with other radio galaxies with discs. NGC 1534 is the lowest surface brightness radio galaxy known with an estimated scaled 1.4-GHz surface brightness of just 0.2 mJy arcmin[superscript −2]. The radio lobes have one of the steepest spectral indices yet observed: α = −2.1 ± 0.1, and the core to lobe luminosity ratio is <0.1 per cent. We estimate the space density of this low brightness (dying) phase of radio galaxy evolution as 7 × 10[superscript −7] Mpc[superscript −3] and argue that normal AGN cannot spend more than 6 per cent of their lifetime in this phase if they all go through the same cycle
- …