1,802 research outputs found
Chandra detection of the radio and optical double hot spot of 3C 351
In this letter we report a Chandra X-ray detection of the double northern hot
spot of the radio quasar 3C 351. The hot spot has also been observed in the
optical with the Hubble Space Telescope (R-band) and with the 3.5m. Telescopio
Nazionale Galileo (B-band). The radio-to-optical and X-ray spectra are
interpreted as the results of the synchrotron and synchrotron-self-Compton
(SSC) mechanisms, respectively, with hot-spot magnetic field strengths ~3 times
smaller than the equipartition values. In the framework of shock acceleration
theory, we show that the requirement for such a relatively small field strength
is in agreement with the fitted synchrotron spectral models and with the sizes
of the hot spots. Finally, we show that the combination of a lower magnetic
field strength with the high frequencies of the synchrotron cut-off in the
fitted synchrotron spectra provides strong evidence for electron acceleration
in the hot spots.Comment: 16 pag. + 2 .PS figures (fig.2 color), ApJ Letter in pres
Ventilation-on-Demand: Quantity or Quality — A Pilot Trial at Barrick Gold\u27s Bousquet Mine
Common to many established mines in Canada, is the problem that their ventilation systems are continually being stretched to meet new needs that were not anticipated in the original design. This can be the result of a variety of different factors, such as the discovery of new reserves at depth, accelerated production, new worker exposure regulations or a change of mining method. At Bousquet, the ventilation of a new multilevel mining block over 1 km away from the existing bottom of the mine presents a challenge. The airflow available for this region is limited to 57 m3/s by the size of a ventilation drift and raise, and by the total volume the mine can supply. This volume is sufficient only if it can be directed to the desired locations, namely where the diesel equipment is operating and with minimal losses (\u3c10%). Due to the mobile nature of the mining equipment and changing production areas, such tight management of air can only be achieved with Ventilation on Demand . This paper describes a pilot trial, within the existing mine, of an automated demand based ventilation management system. Vehicle tracking and identification determine ventilation demand, location and duration. Specific air volumes are achieved with remote controlled regulators, and auxiliary fan systems and verified with airflow monitors. Air quality is monitored with gas sensors. Based upon this trial the mine will be able to determine the viability of an air quality driven system over an engine based air quantity dictated system. This would then, with the approval of the local regulators, allow the mine to operate its ventilation more efficiently and gain the maximum benefit of cleanengine technology and exhaust treatment devices
Measuring fidelity to behavioural support delivery for smoking cessation and its association with outcomes
BACKGROUND AND AIMS: Behavioural support increases smoking cessation in clinical settings, but effect sizes differ among providers, due possibly to variations in delivery. This study evaluates a measure ('fidelity index') intended to capture fidelity to delivery of content- and interaction-based items of a behavioural support (BS) for smoking cessation and the association of fidelity with quit rates. METHODS: A fidelity index for scoring the adherence and quality domains of a specific BS intervention, '5As for quit', was developed by classifying the intervention components using the taxonomy of behaviour change techniques. The index was applied to code 154 BS sessions audiotaped among 18 chest clinics in Pakistan to assess their fidelity and explore reliability of coding. The association between intervention fidelity and successful quit achieved by the same providers in a previous study was explored using regression analysis. RESULTS: The index represented two domains: adherence to delivery of content-based activities of 5As (37 items) and quality of interaction-based activities (eight items). The intercoder reliability was good for content-based (average Krippendorff's α = 0.80) and moderate for interaction-based (average Krippendorff's α = 0.66) items. Approximately 70% (intraclass correlation coefficient: adherence scores = 0.72, quality scores = 0.71) of variation in BS delivery was contributed by providers, which increased to 97% (g-coefficient: adherence scores = 0.973, quality scores = 0.974) after accounting for other sources of variation. Higher quit rates were positively associated with average quality scores [risk ratio = 2.15; 95% confidence interval (CI) = 1.43-3.24], but negatively associated with average adherence scores (risk ratio = 0.55; 95% CI = 0.40-0.77) within services. CONCLUSIONS: The fidelity index is a reliable measure for quantifying intervention fidelity of delivering smoking cessation behavioural support. Recommended revisions of the fidelity index include incorporation of additional interaction-based items, such as the relational techniques used in motivational interviewing
Radio Lobes of Pictor A: an X-ray spatially resolved Study
A new XMM observation has made possible a detailed study of both lobes of the
radio galaxy Pictor A. Their X-ray emission is of non thermal origin and due to
Inverse Compton scattering of the microwave background photons by relativistic
electrons in the lobes, as previously found. In both lobes, the equipartition
magnetic field (Beq) is bigger than the Inverse Compton value (Bic), calculated
from the radio and X-ray flux ratio. The Beq/Bic ratio never gets below 2, in
spite of the large number of reasonable assumptions tested to calculate Beq,
suggesting a lobe energetic dominated by particles. The X-ray data quality is
good enough to allow a spatially resolved analysis. Our study shows that Bic
varies through the lobes. It appears to increase behind the hot spots. On the
contrary, a rather uniform distribution of the particles is observed. As a
consequence, the radio flux density variation along the lobes appears to be
mainly driven by magnetic field changes.Comment: 15 pages, 3 figures, ApJ accepte
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
X-ray Emission Properties of Large Scale Jets, Hotspots and Lobes in Active Galactic Nuclei
We examine a systematic comparison of jet-knots, hotspots and radio lobes
recently observed with Chandra and ASCA. This report will discuss the origin of
their X-ray emissions and investigate the dynamics of the jets. The data was
compiled at well sampled radio (5GHz) and X-ray frequencies (1keV) for more
than 40 radio galaxies. We examined three models for the X-ray production:
synchrotron (SYN), synchrotron self-Compton (SSC) and external Compton on CMB
photons (EC). For the SYN sources -- mostly jet-knots in nearby low-luminosity
radio galaxies -- X-ray photons are produced by ultrarelativistic electrons
with energies 10-100 TeV that must be accelerated in situ. For the other
objects, conservatively classified as SSC or EC sources, a simple formulation
of calculating the ``expected'' X-ray fluxes under an equipartition hypothesis
is presented. We confirmed that the observed X-ray fluxes are close to the
expected ones for non-relativistic emitting plasma velocities in the case of
radio lobes and majority of hotspots, whereas considerable fraction of
jet-knots is too bright at X-rays to be explained in this way. We examined two
possibilities to account for the discrepancy in a framework of the
inverse-Compton model: (1) magnetic field is much smaller than the
equipartition value, and (2) the jets are highly relativistic on kpc/Mpc
scales. We concluded, that if the inverse-Compton model is the case, the X-ray
bright jet-knots are most likely far from the minimum-power condition. We also
briefly discuss the other possibility, namely that the observed X-ray emission
from all of the jet-knots is synchrotron in origin.Comment: 20 pages, 10 figures, accepted for publication in the Astrophysical
Journal, vol.62
Canonical Particle Acceleration in FRI Radio Galaxies
Matched resolution multi-frequency VLA observations of four radio galaxies
are used to derive the asymptotic low energy slope of the relativistic electron
distribution. Where available, low energy slopes are also determined for other
sources in the literature. They provide information on the acceleration physics
independent of radiative and other losses, which confuse measurements of the
synchrotron spectra in most radio, optical and X-ray studies. We find a narrow
range of inferred low energy electron energy slopes, n(E)=const*E^-2.1 for the
currently small sample of lower luminosity sources classified as FRI (not
classical doubles). This distribution is close to, but apparently inconsistent
with, the test particle limit of n(E)=const*E^-2.0 expected from strong
diffusive shock acceleration in the non-relativistic limit. Relativistic shocks
or those modified by the back-pressure of efficiently accelerated cosmic rays
are two alternatives to produce somewhat steeper spectra. We note for further
study the possiblity of acceleration through shocks, turbulence or shear in the
flaring/brightening regions in FRI jets as they move away from the nucleus.
Jets on pc scales and the collimated jets and hot spots of FRII (classical
double) sources would be governed by different acceleration sites and
mechanisms; they appear to show a much wider range of spectra than for FRI
sources.Comment: 16 figures, including 5 color. Accepted to Astrophysical Journa
LABOCA observations of nearby, active galaxies
We present large scale 870 micron maps of the nearby starburst galaxies
NGC253, NGC4945 and the nearest giant elliptical radio galaxy Centaurus A (NGC
5128) obtained with the newly commissioned Large Apex Bolometer Camera (LABOCA)
operated at the APEX telescope. Our continuum images reveal for the first time
the distribution of cold dust at a angular resolution of 20" across the entire
optical disks of NGC253 and NGC4945 out to a radial distance of 10' (7.5 kpc).
In NGC5128 our LABOCA image also shows, for the first time at submillimeter
wavelengths, the synchrotron emission associated with the radio jet and the
inner radio lobes. From an analysis of the 870 micron emission in conjunction
with ISO-LWS, IRAS and long wavelengths radio data we find temperatures for the
cold dust in the disks of all three galaxies of 17-20 K, comparable to the dust
temperatures in the disk of the Milky Way. The total gas mass in the three
galaxies is determined to be 2.1, 4.2 and 2.8 x 10^9 solar masses for NGC253,
NGC4945 and NGC5128, respectively. A detailed comparison between the gas masses
derived from the dust continuum and the integrated CO(1-0) intensity in NGC253
suggests that changes of the CO luminosity to molecular mass conversion factor
are mainly driven by a metallicity gradient and only to a lesser degree by
variations of the CO excitation. An analysis of the synchrotron spectrum in the
northern radio lobe of NGC5128 shows that the synchrotron emission from radio
to the ultraviolet wavelengths is well described by a broken power law and that
the break frequency is a function of the distance from the radio core as
expected for aging electrons. We derive an outflow speed of ~0.5c at a distance
of 2.6kpc from the center, consistent with the speed derived in the vicinity of
the nucleus.Comment: 12 pages, 11 figures. Accepted for publication in A&
Multidimensional continued fractions, dynamical renormalization and KAM theory
The disadvantage of `traditional' multidimensional continued fraction
algorithms is that it is not known whether they provide simultaneous rational
approximations for generic vectors. Following ideas of Dani, Lagarias and
Kleinbock-Margulis we describe a simple algorithm based on the dynamics of
flows on the homogeneous space SL(2,Z)\SL(2,R) (the space of lattices of
covolume one) that indeed yields best possible approximations to any irrational
vector. The algorithm is ideally suited for a number of dynamical applications
that involve small divisor problems. We explicitely construct renormalization
schemes for (a) the linearization of vector fields on tori of arbitrary
dimension and (b) the construction of invariant tori for Hamiltonian systems.Comment: 51 page
An X-ray study of magnetic field strengths and particle content in FRII radio sources
We present a Chandra and XMM-Newton study of X-ray emission from the lobes of
33 classical double radio galaxies and quasars. We report new detections of
lobe-related X-ray emission in 11 sources. Together with previous detections we
find that X-ray emission is detected from at least one radio lobe in ~75
percent of the sample. For all of the lobe detections, we find that the
measured X-ray flux can be attributed to inverse-Compton scattering of the
cosmic microwave background radiation, with magnetic field strengths in the
lobes between (0.3 - 1.3) B_eq, where the value B_eq corresponds to
equipartition between the electrons and magnetic field assuming a filling
factor of unity. There is a strong peak in the magnetic field strength
distribution at B ~ 0.7 B_eq. We find that > 70 percent of the radio lobes are
either at equipartition or electron dominated by a small factor. The
distribution of measured magnetic field strengths differs for narrow-line and
broad-line objects, in the sense that broad-line radio galaxies and quasars
appear to be further from equipartition; however, this is likely to be due to a
combination of projection effects and worse systematic uncertainty in the X-ray
analysis for those objects. Our results suggest that the lobes of classical
double radio sources do not contain an energetically dominant proton
population, because this would require the magnetic field energy density to be
similar to the electron energy density rather than the overall energy density
in relativistic particles.Comment: 44 pages, 4 figures. Accepted for publication in Ap
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