1,741 research outputs found
Neurofibromatosis (von Recklinghausen's disease) - An unusual cause of parenchymal lung disease : a case report
CITATION: Hardcastle, S. W. & Hendricks, M. L. 1984. Neurofibromatosis (von Recklinghausen's disease) - An unusual cause of parenchymal lung disease : a case report. South African Medical Journal, 66:959-960.The original publication is available at http://www.samj.org.zaInterstitial pulmonary fibrosis and bullae are uncommon findings in neurofibromatosis. A case of this disease with pulmonary parenchymal involvement is presented and the association between the two is discussed.Publisher’s versio
A Chandra study of particle acceleration in the multiple hotspots of nearby radio galaxies
We present Chandra observations of a small sample of nearby classical double
radio galaxies which have more than one radio hotspot in at least one of their
lobes. The X-ray emission from the hotspots of these comparatively low-power
objects is expected to be synchrotron in origin, and therefore to provide
information about the locations of high-energy particle acceleration. In some
models of the relationship between the jet and hotspot the hotspots that are
not the current jet termination point should be detached from the energy supply
from the active nucleus and therefore not capable of accelerating particles to
high energies. We find that in fact some secondary hotspots are X-ray sources,
and thus probably locations for high-energy particle acceleration after the
initial jet termination shock. In detail, though, we show that the spatial
structures seen in X-ray are not consistent with naive expectations from a
simple shock model: the current locations of the acceleration of the
highest-energy observable particles in powerful radio galaxies need not be
coincident with the peaks of radio or even optical emission.Comment: Accepted for ApJ. 33 pages, 8 figures inc. 2 in colo
A Chandra Study of the Lobe/ISM Interactions Around the Inner Radio Lobes of Centaurus A: Constraints on the Temperature Structure and Transport Processes
We present results from deeper {\em Chandra} observations of the southwest
radio lobe of Centaurus A, first described by Kraft et al. (2003). We find that
the sharp X-ray surface brightness discontinuity extends around 75% of
the periphery of the radio lobe, and detect significant temperature jumps in
the brightest regions of this discontinuity nearest to the nucleus. This
demonstrates that this discontinuity is indeed a strong shock which is the
result of an overpressure which has built up in the entire lobe over time.
Additionally, we demonstrate that if the mean free path for ions to transfer
energy and momentum to the electrons behind the shock is as large as the
Spitzer value, the electron and proton temperatures will not have equilibrated
along the SW boundary of the radio lobe where the shock is strongest. Thus the
proton temperature of the shocked gas could be considerably larger than the
observed electron temperature, and the total energy of the outburst
correspondingly larger as well. We investigate this using a simple
one-dimensional shock model for a two-fluid (proton/electron) plasma. We find
that for the thermodynamic parameters of the Cen A shock the electron
temperature rises rapidly from 0.29 keV (the temperature of the ambient
ISM) to 3.5 keV at which point heating from the protons is balanced by
adiabatic losses. The proton and electron temperatures do not equilibrate in a
timescale less than the age of the lobe. We note that the measured electron
temperature of similar features in other nearby powerful radio galaxies in poor
environments may considerably underestimate the strength and velocity of the
shock.Comment: 29 pages, 9 figures, 2 tables - accepted for publication in the
Astrophysical Journa
Sub-Arcsecond Imaging of 3C123:108-GHz Continuum Observations of the Radio Hotspots
We present the results of sub-arcsecond 108 GHz continuum interferometric
observations toward the radio luminous galaxy 3C123. Using multi-array
observations, we utilize the high u,v dynamic range of the BIMA millimeter
array to sample fully spatial scales ranging from 0.5" to 50". This allows us
to make one-to-one comparisons of millimeter-wavelength emission in the radio
lobes and hotspots to VLA centimeter observations at 1.4, 4.9, 8.4, and 15 GHz.
At 108 GHz, the bright, eastern double hotspot in the southern lobe is
resolved. This is only the second time that a multiple hotspot region has been
resolved in the millimeter regime. We model the synchrotron spectra of the
hotspots and radio lobes using simple broken power-law models with high energy
cutoffs, and discuss the hotspot spectra and their implications for models of
multiple hotspot formation.Comment: 16 pages, 3 Figures, ApJ Accepte
A LOFAR mini-survey for low-frequency radio emission from the nearest brown dwarfs
We have conducted a mini-survey for low-frequency radio emission from some of the closest brown dwarfs to the Sun with rapid rotation rates: SIMP J013656.5 +093347, WISEPC 150649.97+702736.0, and WISEPA J174124.26+255319.5.We have placed robust 3s upper limits on the flux density in the 111 – 169 MHz frequency range for these targets: WISE 1506: < 0:72 mJy; WISE 1741: < 0:87 mJy; SIMP 0136: < 0:66 mJy. At 8 hours of integration per target to achieve these limits, we find that systematic and detailed study of this class of object at LOFAR frequencies will require a substantial dedication of resources
The Hot Gas Environment of the Radio Galaxy 3C 388: Quenching the Accumulation of Cool Gas in a Cluster Core by a Nuclear Outburst
We present results from a 35 ks {\em Chandra}/ACIS-I observation of the hot
ICM around the FR II radio galaxy 3C 388. 3C 388 resides in a cluster
environment with an ICM temperature of 3.5 keV. We detect cavities in the
ICM coincident with the radio lobes. The enthalpy of these cavities is
ergs. The work done on the gas by the inflation of the
lobes is ergs, or 0.87 keV per particle out to the
radius of the lobes. The radiative timescale for gas at the center of the
cluster at the current temperature is a few Gyrs. The gas in the core was
probably cooler and denser before the outburst, so the cooling time was
considerably shorter. We are therefore likely to be witnessing the quenching of
a cluster cooling flow by a radio galaxy outburst. The mechanical power of the
lobes is at least 20 times larger than the radiative losses out to the cooling
radius. Outbursts of similar power with a 5% duty cycle would be more
than sufficient to continually reheat the cluster core over the Hubble time and
prevent the cooling of any significant amount of gas. The mechanical power of
the outburst is also roughly two orders of magnitude larger than either the
X-ray luminosity of the active nucleus or the radio luminosity of the lobes.
The equipartition pressure of the radio lobes is more than an order of
magnitude lower than that of the ambient medium, indicating that the pressure
of the lobe is dominated by something other than the relativistic electrons
radiating at GHz frequencies.Comment: 28 pages, 10 figures - accepted for publication in the Astrophysical
Journa
Deoxyuridine triphosphatase (dUTPase) expression and sensitivity to the thymidylate synthase (TS) inhibitorD9331
Uracil DNA misincorporation and misrepair of DNA have been recognized as important events accompanying thymidylate synthase (TS) inhibition. dUTPase catalyses the hydrolysis of dUTP to dUMP, thereby maintaining low intracellular dUTP. We have addressed the relationship between dUTPase expression and cellular sensitivity to TS inhibition in four human lung tumour cell lines. Sensitivity (5-day MTT assay) to the growth inhibitory effects of the non-polyglutamatable, specific quinazoline TS inhibitor ZD9331, varied up to 20-fold (IC 50 3–70 nM). TS protein expression correlated with TS activity (r2= 0.88 P= 0.05). Intracellular concentrations of drug following exposure to ZD9331 (1 μM, 24 h) varied by ~2-fold and dTTP pools decreased by > 80% in all cell lines. No clear associations across the cell lines between intracellular drug concentrations, TS activity/expression, or TTP depletion could be made. dUTPase activity varied 17-fold and correlated with dUTPase protein expression (r2= 0.94 P= 0.03). There was a striking variation in the amount of dUTP formed following exposure to ZD9331 (between 1.3 and 57 pmole 10–6cells) and was in general inversely associated with dUTPase activity. A large expansion in the dUTP pool was associated with increased sensitivity to a 24-h exposure to ZD9331 in A549 cells that have low dUTPase activity/expression. dUTPase expression and activity were elevated (approximately 3-fold) in two variants of a human lymphoblastoid cell line with acquired resistance to TS inhibitors, further suggesting an important role for this enzyme in TS inhibited cells. © 2000 Cancer Research Campaig
LOFAR early-time search for coherent radio emission from GRB 180706A
© 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society.The nature of the central engines of gamma-ray bursts (GRBs) and the composition of their relativistic jets are still under debate. If the jets are Poynting flux dominated rather than baryon dominated, a coherent radio flare from magnetic re-connection events might be expected with the prompt gamma-ray emission. There are two competing models for the central engines of GRBs; a black hole or a newly formed milli-second magnetar. If the central engine is a magnetar it is predicted to produce coherent radio emission as persistent or flaring activity. In this paper, we present the deepest limits to date for this emission following LOFAR rapid response observations of GRB 180706A. No emission is detected to a 3 limit of 1.7 mJy beam at 144 MHz in a two-hour LOFAR observation starting 4.5 minutes after the gamma-ray trigger. A forced source extraction at the position of GRB 180706A provides a marginally positive (1 sigma) peak flux density of mJy. The data were time-sliced into different sets of snapshot durations to search for FRB like emission. No short duration emission was detected at the location of the GRB. We compare these results to theoretical models and discuss the implications of a non-detection.Peer reviewedFinal Accepted Versio
Extended soft X-ray emission in 3CR radio galaxies at z < 0.3: High Excitation and Broad Line Galaxies
We analyze Chandra observations of diffuse soft X-ray emission associated
with a complete sample of 3CR radio galaxies at z < 0.3. In this paper we focus
on the properties of the spectroscopic sub-classes of high excitation galaxies
(HEGs) and broad line objects (BLOs). Among the 33 HEGs we detect extended (or
possibly extended) emission in about 40% of the sources; the fraction is even
higher (8/10) restricting the analysis to the objects with exposure times
larger than 10 ks. In the 18 BLOs, extended emission is seen only in 2 objects;
this lower detection rate can be ascribed to the presence of their bright X-ray
nuclei that easily outshine any genuine diffuse emission.
A very close correspondence between the soft X-ray and optical line
morphology emerges. We also find that the ratio between [O III] and extended
soft X-ray luminosity is confined within a factor of 2 around a median value of
5. Both results are similar to what is seen in Seyfert galaxies.
We discuss different processes that could explain the soft X-ray emission and
conclude that the photoionization of extended gas, coincident with the narrow
line region, is the favored mechanism.Comment: 15 pages, 11 figures. Accepted for publication on A&
The origins of X-ray emission from the hotspots of FRII radio sources
We use new and archival Chandra data to investigate the X-ray emission from a
large sample of compact hotspots of FRII radio galaxies and quasars from the 3C
catalogue. We find that only the most luminous hotspots tend to be in good
agreement with the predictions of a synchrotron self-Compton model with
equipartition magnetic fields. At low hotspot luminosities inverse-Compton
predictions are routinely exceeded by several orders of magnitude, but this is
never seen in more luminous hotspots. We argue that an additional synchrotron
component of the X-ray emission is present in low-luminosity hotspots, and that
the hotspot luminosity controls the ability of a given hotspot to produce
synchrotron X-rays, probably by determining the high-energy cutoff of the
electron energy spectrum. It remains plausible that all hotspots are close to
the equipartition condition.Comment: 49 pages, 16 figures. ApJ accepted. Revised version fixes a typo in
one of the Tables and corrects a statement about 3C27
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