512 research outputs found
Is Thermal Expansion Driving the Initial Gas Ejection in NGC 6251?
In this paper, we explore the possibility that the radiative properties of
the most compact region in NGC 6251* may be understood in the same sense as Sgr
A*, though with some telling differences that may hint at the nature of jet
formation. We show that observations of this object with ASCA, ROSAT, HST and
VLBI together may be hinting at a picture in which Bondi-Hoyle accretion from
an ambient ionized medium feeds a standard disk accreting at ~ 4.0*10^{22} g
s^{-1}. Somewhere near the event horizon, this plasma is heated to >10^{11} K,
where it radiates via thermal synchrotron (producing a radio component) and
self-Comptonization (accounting for a nonthermal X-ray flux). This temperature
is much greater than its virial value and the hot cloud expands at roughly the
sound speed (~0.1c), after which it begins to accelerate on a parsec scale to
relativistic velocities. In earlier work, the emission from the extended jet
has been modeled successfully using nonthermal synchrotron self-Compton
processes, with a self-absorbed inner core. In the picture we are developing
here, the initial ejection of matter is associated with a self-absorbed thermal
radio component that dominates the core emission on the smallest scales. The
nonthermal particle distributions responsible for the emission in the extended
jet are then presumably energized, e.g., via shock acceleration, within the
expanding, hot gas. The power associated with this plasma represents an
accretion efficiency of about 0.54, requiring dissipation in a prograde disk
around a rapidly spinning black hole (with spin parameter a~1).Comment: 17 pages, 1 figures, to appear in Ap
A rapid synthesis of evidence on whole systems approaches to obesity prevention to inform policy
© 2023 The Author(s) . Published by Oxford University Press on behalf of the European Public Health Association. This is an open-access meeting abstract distributed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International License (CC BY-NC), https://creativecommons.org/licenses/by-nc/4.0/Peer reviewe
Two types of shock in the hotspot of the giant quasar 4C74.26: a high-resolution comparison from Chandra, Gemini & MERLIN
New Chandra observations have resolved the structure of the X-ray luminous
southern hotspot in the giant radio quasar 4C74.26 into two distinct features.
The nearer one to the nucleus is an extremely luminous peak, extended some 5
kpc perpendicular to the orientation of the jet; 19 kpc projected further away
from the central nucleus than this is a fainter X-ray arc having similar
symmetry. This arc is co-spatial with near-IR and optical emission imaged with
Gemini, and radio emission imaged with MERLIN. The angular separation of the
double shock structure (itself ~19 kpc or 10 arcsec in size) from the active
nucleus which fuels them of ~550 kpc is a reminder of the challenge of
connecting "unidentified" hard X-ray or Fermi sources with their origins.Comment: In press at MNRA
Prevalence of Pain on Admission by Level of Cognitive Impairment in Nursing Homes
Purpose: To provide contemporary estimates of pain by level of cognitive impairment among US nursing home residents without cancer.
Methods: Newly admitted US nursing home residents without cancer assessed with the Minimum Data Set 3.0 at admission (2010-2016) were eligible (n=8,613,080). The Cognitive Function Scale was used to categorize level of cognitive impairment. Self-report or staff-assessed pain was used based on a 5-day look-back period. Estimates of adjusted prevalence ratios (aPR) were derived from modified Poisson models.
Results: Documented prevalence of pain decreased with increased levels of cognitive impairment in those who self-reported pain (68.9% no/mild, 32.9% severe) and those with staff-assessed pain (50.6% no/mild, 37.2% severe staff-assessed pain). Relative to residents with no/mild cognitive impairment, pharmacologic pain management was less prevalent in those with severe cognitive impairment (self-reported: 51.3% severe vs 76.9% in those with no/mild; staff assessed: 52.0% severe vs 67.7% no/mild).
Conclusion: Pain was less frequently documented in those with severe cognitive impairment relative to those with no/mild impairments. Failure to identify pain may result in untreated or undertreated pain. Interventions to improve evaluation of pain in nursing home residents with cognitive impairment are needed
The Particle Content of Extragalactic Jets
Recent x-ray and radio data from radio sources in galaxy clusters are used to
show that the pdV work required to inflate the radio lobes exceeds all other
energy estimates deduced from the radio emission. If the required jet energy
density has an isotropic pressure, then in almost all cases the jet cannot be
confined by an external medium. This problem can be resolved with jets
dominated by cold protons, but even here the accompanying energy density in
relativistic electons can cause decollimation. Electron-positron jets cannot
solve this problem unless they are highly beamed with unusual energy
distributions. Poynting flux jets may be a viable alternative.Comment: 14 pages, 3 figures, to be published in Ap
Centaurus A: multiple outbursts or bursting bubble?
We present new radio observations of the brighter region of the northern lobe
(the Northern Middle Lobe, NML) of Centaurus A obtained at 20 cm with the
Australia Telescope Compact Array. The angular resolutions are ~50 and ~130
arcsec, therefore much higher than for the previously available radio images of
this region. The most interesting feature detected is a large-scale jet that
connects the inner radio lobe and the NML and that is imaged for the first
time. The NML itself appears as diffuse emission with a relatively bright ridge
on the eastern side. The radio morphology of Centaurus A and, in particular,
its NML could be the result of a precessing jet that has undergone a strong
interaction with the environment at least in the northern side. The very big
drop in intensity between the inner jet and the large-scale jet can be
explained with a sequence of bursts of activity at different epochs in the life
of the source. Alternatively (or additionally) a ``bursting bubble'' model is
proposed which could also explain the good collimation of the large-scale jet.
In this model, the plasma accumulated in the inner lobe would be able to
``burst'' out only through one nozzle that would be the region where the
large-scale jet forms. From the comparison between the radio emission and the
regions of ionized gas we find that the inner optical filament falls about 2
arcmin (~2 kpc) away from the large-scale radio jet. Thus, this filament does
not seem to have experienced a direct interaction with the radio plasma. The
outer filaments appear to be, in projection, closer to the radio emission,
arguing for a direct interaction with the radio jet. However, also in this case
a more complicated interaction than assumed so far has to be occuring.Comment: To appear in MNRAS; 11 pages, LateX, 7 figures. Fig 1 is available at
http://www.ira.bo.cnr.it/~rmorgant/Centaurus
Air transport liberalisation and airport dependency: developing a composite index
Air transport liberalisation in Europe has produced some major changes to the networks operated by airlines
and the services available at airports. Within this context the degree of airport dependency in terms
of market, spatial and temporal concentration is important to know from an economic geography and risk
management perspective. A composite index called the Airport Dependency Index (ADI) is developed to
measure airport dependency based on the concept of the relative Gini coefficient. Liberalisation has had
varying impacts depending on the size and type of airport and so a comparison is made of the degree of
dependency at a large sample of European airports using the ADI. The ADI has the potential to provide
insight on the sustainability and worthiness of financing airport projects, and on whether airports should diversify further their activities by investing in the growth and expansion of their network
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