144 research outputs found
VLA Polarimetry of Two Extended Radio Galaxies
Multi-wavelength VLA observations of two extended radio galaxies, 0235-197
and 1203+043 are presented. There is some evidence from earlier studies that
these two sources exhibit low frequency (<1 GHz) variability. This work shows
that both sources have linear polarizations, if any, below the detection limits
at 320 MHz, so we cannot explain the variability as being due to instrumental
polarization effects as has been suggested for 3C159. Refractive scintillation
may be the cause of the variability in 0235-197. This would require the
existence of a bright, compact component in one of the hot spots seen in these
observations. This is not implausible but the resolution of this observational
program is insufficent to address that question. The radio source 1203+043
lacks any bright compact component thereby ruling out a refractive
scintillation mechanism for its variability. Consequently, it is possible that
claims of variability in this source are spurious. However, the 320 MHz VLA
observations show that 1203+043 has an `X'-shaped radio structure. This is a
rare morphology for the brightness distribution of a radio galaxy; the
implications of this are examined.Comment: 8 pages, plain tex, accepted by Astronomy and Astrophysics,
Supplement Serie
Observational Properties of Jets in Active Galactic Nuclei
Parsec scale jet properties are shortly presented and discussed.
Observational data are used to derive constraints on the jet velocity and
orientation, the presence of velocity structures, and the connection between
the pc and kpc scale. Two peculiar sources with limb-brightened jets: 1144+35
and Mkn 501 are discussed in detail.Comment: 13 pages with 7 figures. To appear in "Virtual Astrophysical Jets"
APSS, Kluwer Academic Publisher - Massaglia, Bodo, Rossi eds - in pres
The Theory and Simulation of Relativistic Jet Formation: Towards a Unified Model For Micro- and Macroquasars
I review recent progress in the theory of relativistic jet production, with
special emphasis on unifying black hole sources of stellar and supermassive
size. Observations of both classes of objects, as well as theoretical
considerations, indicate that such jets may be launched with a spine/sheath
flow structure, having a much higher Lorentz factor () near the axis
and a lower speed ( or so) away from the axis. It has become
clear that one can no longer consider models of accretion flows without also
considering the production of a jet by that flow. Furthermore, the rotation
rate of the black hole also must be taken into account. It provides a third
parameter that should break the mass/accretion rate degeneracy and perhaps
explain why some sources are radio loud and some radio quiet. Slow jet
acceleration and collimation is expected theoretically, and can explain some of
the observed features of AGN jet sources. Finally, relativistic jets launched
by MHD/ED processes are Poynting flux dominated by nature, and are potentially
unstable if there is significant entrainment of thermal material.Comment: 6 pages, 1 figure; in The physics of relativistic jets in the CHANDRA
and XMM era, Bologna, 23-27 Sept 200
VLBI observations of weak sources using fast frequency switching
We have developed a new phase referencing technique for high frequency VLBI
observations. In conventional phase referencing, one interleaves short scans on
a nearby phase calibrator between the target source observations. In fast
frequency switching described here, one observes the target source continuously
while switching rapidly between the target frequency and a lower reference
frequency. We demonstrate that the technique allows phase calibration almost
reaching the thermal noise limit and present the first detection of the AGN in
the FR I radio galaxy NGC 4261 at 86 GHz. Although point-like, this is the
weakest source ever detected with VLBI at this frequency.Comment: Accepted by A&A, 14 pages, 12 figures, needs aa.cls, aas_macros.sty
and amsmath.sty, replaced due reformattin
Extragalactic jets on subpc and large scales
Jets can be probed in their innermost regions (d~0.1 pc) through the study of
the relativistically-boosted emission of blazars. On the other extreme of
spatial scales, the study of structure and dynamics of extragalactic
relativistic jets received renewed impulse after the discovery, made by
Chandra, of bright X-ray emission from regions at distances larger than
hundreds of kpc from the central engine. At both scales it is thus possible to
infer some of the basic parameters of the flow (speed, density, magnetic field
intensity, power). After a brief review of the available observational
evidence, I discuss how the comparison between the physical quantities
independently derived at the two scales can be used to shed light on the global
dynamics of the jet, from the innermost regions to the hundreds of kpc scale.Comment: Proceedings of the 5th Stromlo Symposium: Disks, Winds, and Jets -
from Planets to Quasars. Accepted, to be published in Astrophysics & Space
Scienc
Staging quality is related to the survival of women with endometrial cancer: a Scottish population based study.Deficient surgical staging and omission of adjuvant radiotherapy is associated with poorer survival of women diagnosed with endometrial cancer in Scotland during 1996 and 1997
The association between treatment variation and survival of women with endometrial cancer was investigated. A retrospective cohort based upon the complete Scottish population registered on in-patient and day-case hospital discharge data (Scottish Morbidity Record-1) and cancer registration (Scottish Morbidity Record-6) coded C54 and C55 in ICD10, between 1st January 1996 to 31st December 1997 were analysed. Seven hundred and three patients who underwent surgical treatment out of 781 patients that were diagnosed with endometrial cancer in Scotland during 1996 and 1997. The overall quality of surgical staging was poor. The quality of staging was related to both the year that the surgeon passed the Member of the Royal College of Obstetricians and Gynaecologists examination and also to âspecialistâ status but was not related to surgeon caseload. Two clinically important prognostic factors were found to be associated with survival; whether the International Federation of Obstetrics and Gynaecology stage was documented, RHR=2.0 (95% CI=1.3 to 3.1) and also to the use of adjuvant radiotherapy, RHR=2.2 (95% CI=1.5 to 3.5). The associations with survival were strongest in patients with advanced disease, International Federation of Obstetrics and Gynaecology stages 1C through to stage 3. Deficiencies in staging and variations in the use of adjuvant radiotherapy represent a possible source of avoidable mortality in patients with endometrial cancer. Consequently, there should be a greater emphasis on improving the overall quality of surgical staging in endometrial cancer
A search for possible interactions between ejections from GRS 1915+105 and the surrounding interstellar medium
We have observed an extended region surrounding the first discovered galactic
superluminal source GRS 1915+105, seeking evidence of interaction between the
relativistic ejecta of that object and the interstellar medium. We find two
radio sources axisymmetrically aligned along the sub-arcsecond relativistic
ejecta of GRS 1915+105 and roughly 17' distant from it, which coincide with the
luminous IRAS sources 19124+1106 and 19132+1035. We have observed these sources
at centimeter (VLA), millimeter (IRAM 30m), and infrared (ISO, UKIRT, ESO/MPI
2.2m) wavelengths in both line and continuum emission. At centimeter
wavelengths a non-thermal jet-like feature aligned along the outflow axis is
located adjacent to the inner edge of the southern source. Strong density
enhancements are found in the millimeter tracers CO and H13CO+ at the positions
of both sources and some of the morphology is reminiscent of shock-like
interactions; however, linewidths are narrow. At infrared wavelengths strong
hydrogen recombination lines and weak lines of molecular hydrogen are observed
at the southern source. We discuss these results as possible evidence of the
sought-after interaction, both in terms of the regions undergoing ongoing
shock-heating and in terms of them being locations of shock-induced star
formation. The evidence for each of these is inconclusive. Millimeter line
mapping of a portion of W 50 where the relativistic jets of the X-ray binary SS
433 interact with the interstellar medium shows roughly similar morphology as
GRS 1915+105, suggesting that the phenomena observed at the IRAS sources may
not be unusual for such a long distance interaction.Comment: 13 pages, 12 figures, accepted for publication in Astronomy and
Astrophysic
Development of a lung slice preparation for recording ion channel activity in alveolar epithelial type I cells
BACKGROUND: Lung fluid balance in the healthy lung is dependent upon finely regulated vectorial transport of ions across the alveolar epithelium. Classically, the cellular locus of the major ion transport processes has been widely accepted to be the alveolar type II cell. Although evidence is now emerging to suggest that the alveolar type I cell might significantly contribute to the overall ion and fluid homeostasis of the lung, direct assessment of functional ion channels in type I cells has remained elusive. METHODS: Here we describe a development of a lung slice preparation that has allowed positive identification of alveolar type I cells within an intact and viable alveolar epithelium using living cell immunohistochemistry. RESULTS: This technique has allowed, for the first time, single ion channels of identified alveolar type I cells to be recorded using the cell-attached configuration of the patch-clamp technique. CONCLUSION: This exciting new development should facilitate the ascription of function to alveolar type I cells and allow us to integrate this cell type into the general model of alveolar ion and fluid balance in health and disease
Theoretical overview on high-energy emission in microquasars
Microquasar (MQ) jets are sites of particle acceleration and synchrotron
emission. Such synchrotron radiation has been detected coming from jet regions
of different spatial scales, which for the instruments at work nowadays appear
as compact radio cores, slightly resolved radio jets, or (very) extended
structures. Because of the presence of relativistic particles and dense photon,
magnetic and matter fields, these outflows are also the best candidates to
generate the very high-energy (VHE) gamma-rays detected coming from two of
these objects, LS 5039 and LS I +61 303, and may be contributing significantly
to the X-rays emitted from the MQ core. In addition, beside electromagnetic
radiation, jets at different scales are producing some amount of leptonic and
hadronic cosmic rays (CR), and evidences of neutrino production in these
objects may be eventually found. In this work, we review on the different
physical processes that may be at work in or related to MQ jets. The jet
regions capable to produce significant amounts of emission at different
wavelengths have been reduced to the jet base, the jet at scales of the order
of the size of the system orbital semi-major axis, the jet middle scales (the
resolved radio jets), and the jet termination point. The surroundings of the
jet could be sites of multiwavelegnth emission as well, deserving also an
insight. We focus on those scenarios, either hadronic or leptonic, in which it
seems more plausible to generate both photons from radio to VHE and high-energy
neutrinos. We briefly comment as well on the relevance of MQ as possible
contributors to the galactic CR in the GeV-PeV range.Comment: Astrophysics & Space Science, in press (invited talk in the
conference: The multimessenger approach to the high-energy gamma-ray
sources", Barcelona/Catalonia, in July 4-7); 10 pages, 6 figures, 2 tables
(one reference corrected
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