320 research outputs found
Concurrent 43 and 86 GHz Very Long Baseline Polarimetry of 3C273
We present sub-milliarcsecond resolution total intensity and linear
polarization VLBI images of 3C273, using concurrent 43 and 86 GHz data taken
with the Very Long Baseline Array in May 2002. The structure seen in the
innermost jet suggest that we have fortuitously caught the jet in the act of
changing direction. The polarization images confirm that the core is
unpolarized (fractional polarization m < 1 %) at 86 GHz, but also show well
ordered magnetic fields (m ~ 15 %) in the inner jet, at a projected distance of
2.3 pc from the core. In this strongly polarized region, the rotation measure
changes across the jet by 4.2 x 10^{4} rad m^{-2} over an angular width of
about 0.3 milliarcseconds. If the lack of polarization in the core is also
attributed to a Faraday screen, then a rotation measure dispersion > 5.2 x
10^{4} rad m^{-2} must be present in or in front of that region. These are
among the highest rotation measures reported so far in the nucleus of any
active galaxy or quasar, and must occur outside (but probably close to) the
radio emitting region. The transverse rotation measure gradient is in the same
sense as that observed by Asada et al and by Zavala and Taylor at greater core
distances. The magnitude of the transverse gradient decreases rapidly with
distance down the jet, and appears to be variable.Comment: 4 pages, LaTeX, 3 postscript figures, submitted to Astrophysical
Journal Letter
Radio Jet-Ambient Medium Interactions on Parsec Scales in the Blazar 1055+018
As part of our study of the magnetic fields of AGN we have recently observed
a large sample of blazars with the Very Long Baseline Array. Here we report the
discovery of a striking two-component jet in the source 1055+018, consisting of
an inner spine with a transverse magnetic field, and a fragmentary but distinct
boundary layer with a longitudinal magnetic field. The polarization
distribution in the spine strongly supports shocked-jet models while that in
the boundary layer suggests interaction with the surrounding medium. This
behavior suggests a new way to understand the differing polarization properties
of strong- and weak-lined blazars.Comment: LaTex; 10 pages; 6 figures; reference fix; to appear in ApJL, 518,
1999 June 2
Faraday Rotation Measure Gradients from a Helical Magnetic Field in 3C 273
Using high frequency (12-22 GHz) VLBA observations we confirm the existence
of a Faraday rotation measure gradient of ~ 500 rad/m^2/mas transverse to the
jet axis in the quasar 3C 273. The gradient is seen in two epochs spaced
roughly six months apart. This stable transverse rotation measure gradient is
expected if a helical magnetic field wraps around the jet. The overall order to
the magnetic field in the inner projected 40 parsecs is consistent with a
helical field. However, we find an unexpected increase in fractional
polarization along the edges of the source, contrary to expectations. This high
fractional polarization rules out internal Faraday rotation, but is not readily
explained by a helical field. After correcting for the rotation measure, the
intrinsic magnetic field direction in the jet of 3C 273 changes from parallel
to nearly perpendicular to the projected jet motion at two locations. If a
helical magnetic field causes the observed rotation measure gradient then the
synchrotron emitting electrons must be separate from the helical field region.
The presence or absence of transverse rotation measure gradients in other
sources is also discussed.Comment: Accepted to ApJ Letters; 11 pages, 4 figures (1 color figure
Faraday rotation in the MOJAVE blazars: 3C 273 a case study
Radio polarimetric observations of Active Galactic Nuclei can reveal the
magnetic field structure in the parsec-scale jets of these sources. We have
observed the gamma-ray blazar 3C 273 as part of our multi-frequency survey with
the Very Long Baseline Array to study Faraday rotation in a large sample of
jets. Our observations re-confirm the transverse rotation measure gradient in
3C 273. For the first time the gradient is seen to cross zero which is further
indication for a helical magnetic field and spine-sheath structure in the jet.
We believe the difference to previous epochs is due to a different part of the
jet being illuminated in our observations.Comment: 6 pages, 3 figures. To appear in the proceedings of "Beamed and
Unbeamed Gamma-rays from Galaxies", held in Muonio, Finland, April 11-15,
2011. Journal of Physics: Conference Serie
VLBA polarimetric observations of the CSS quasar 3C147
Aims. We report new VLBA polarimetric observations of the compact
steep-spectrum (CSS) quasar 3C147 (B0538+498) at 5 and 8.4GHz.
Methods. By using multifrequency VLBA observations, we derived
milliarcsecond-resolution images of the total intensity, polarisation, and
rotation measure distributions, by combining our new observations with archival
data.
Results. The source shows a one-sided structure, with a compact region, and a
component extending about 200 mas to the south-west. The compact region is
resolved into two main components with polarised emission, a complex rotation
measure distribution, and a magnetic field dominated by components
perpendicular to the source axis.
Conclusions. By considering all the available data, we examine the possible
location of the core component, and discuss two possible interpretations of the
observed structure of this source: core-jet and lobe-hot spot. Further
observations to unambiguously determine the location of the core would help
distinguish between the two possibilities discussed here.Comment: 11 pages, 12 figure
PKS 1510-089: A Head-On View of a Relativistic Jet
The gamma-ray blazar PKS 1510-089 has a highly superluminal milli-arcsecond
jet at a position angle (PA) of -28 degrees and an arcsecond jet with an
initial PA of 155 degrees. With a PA difference of 177 degrees between the
arcsecond and milli-arcsecond jets, PKS 1510-089 is perhaps the most highly
misaligned radio jet ever observed and serves as a graphic example of
projection effects in a highly beamed relativistic jet. Here we present the
results of observations designed to bridge the gap between the milli-arcsecond
and arcsecond scales. We find that a previously detected ``counter-feature'' to
the arcsecond jet is directly fed by the milli-arcsecond jet. This feature is
located 0.3" from the core, corresponding to a de-projected distance of 30
kiloparsecs. The feature appears to be dominated by shocked emission and has an
almost perfectly ordered magnetic field along its outside edge. We conclude
that it is most likely a shocked bend, viewed end-on, where the jet crosses our
line of sight to form the southern arcsecond jet. While the bend appears to be
nearly 180 degrees when viewed in projection, we estimate the intrinsic bending
angle to be between 12 and 24 degrees. The cause of the bend is uncertain;
however, we favor a scenario where the jet is bent after it departs the galaxy,
either by ram pressure due to winds in the intracluster medium or simply by the
density gradient in the transition to the intergalactic medium.Comment: 8 pages, 4 figures, Accepted for publication in Ap
Involving people with diabetes and the wider community in diabetes research: a realist review protocol.
BACKGROUND: Patient and public involvement in diabetes research is now actively encouraged in different countries because it is believed that involving people with experience of the condition will improve the quality and relevance of the research. However, reviews of patient involvement have noted that inadequate resources, patients' and communities' lack of research knowledge, and researchers' lack of skills to involve patients and communities in research may present significant contextual barriers. Little is known about the extent of patient/community involvement in designing or delivering interventions for people with diabetes. A realist review of involvement will contribute to assessing when, how and why involvement works, or does not work, to produce better diabetes interventions. METHODS/DESIGN: This protocol outlines the process for conducting a realist review to map how patients and the public have been involved in diabetes research to date. The review questions ask the following: How have people with diabetes and the wider community been involved in diabetes research? What are the characteristics of the process that appear to explain the relative success or failure of involvement? How has involvement (or lack of involvement) in diabetes research influenced the development and conduct of diabetes research? The degree of support in the surrounding context will be assessed alongside the ways in which people interact in different settings to identify patterns of interaction between context, mechanisms and outcomes in different research projects. The level and extent of the involvement will be described for each stage of the research project. The descriptions will be critically reviewed by the people with diabetes on our review team. In addition, researchers and patients in diabetes research will be asked to comment. Information from researcher-patient experiences and documents will be compared to theories of involvement across a range of disciplines to create a mid-range theory describing how involvement (or lack of involvement) in diabetes research influences the development and conduct of diabetes research
Assessment and Revision of Clinical Pharmacy Practice Internet Websites
Background:
Health care professionals, trainees, and patients use the Internet extensively. Editable Web sites may contain inaccurate, incomplete, and/or outdated information that may mislead the public’s perception of the topic.
Objective:
To evaluate the editable, online descriptions of clinical pharmacy and pharmacist and attempt to improve their accuracy.
Methods:
The authors identified key areas within clinical pharmacy to evaluate for accuracy and appropriateness on the Internet. Current descriptions that were reviewed on public domain Web sites included: (1) clinical pharmacy and the clinical pharmacist, (2) pharmacy education, (3) clinical pharmacy and development and provision for reimbursement, (4) clinical pharmacists and advanced specialty certifications/training opportunities, (5) pharmacists and advocacy, and (6) clinical pharmacists and interdisciplinary/interprofessional content. The authors assessed each content area to determine accuracy and prioritized the need for updating, when applicable, to achieve consistency in descriptions and relevancy. The authors found that Wikipedia, a public domain that allows users to update, was consistently the most common Web site produced in search results.
Results:
The authors’ evaluation resulted in the creation or revision of 14 Wikipedia Web pages. However, rejection of 3 proposed newly created Web pages affected the authors’ ability to address identified content areas with deficiencies and/or inaccuracies.
Conclusions:
Through assessing and updating editable Web sites, the authors strengthened the online representation of clinical pharmacy in a clear, cohesive, and accurate manner. However, ongoing assessments of the Internet are continually needed to ensure accuracy and appropriateness
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