1,160 research outputs found
Induced Compton Scattering in Gigahertz Peak Spectrum Sources
We revisit the shocked shell model for the class of Active Galactic Nuclei
known as Gigahertz Peak Spectrum sources, incorporating new observational data
on the radiation brightness temperatures. We argue that in addition to
free-free absorption, induced Compton scattering will also have an important
effect in forming the ~GHz peak and in shaping the radio spectra that
characterize these sources. Indeed, our arguments suggest that GPS sources may
provide the first real evidence for the role of induced Compton scattering in
extragalactic radio sources.Comment: 12 pages, 1 figure, AAS LaTeX style with epsf, to appear in ApJ
Letter
Adiabatic relativistic models for the jets in the radio galaxy 3C 31
We present a general approach to the modelling of the brightness and
polarization structures of adiabatic, decelerating relativistic jets, based on
the formalism of Matthews & Scheuer (1990). We compare the predictions of
adiabatic jet models with deep, high-resolution observations of the radio jets
in the FR I radio galaxy 3C 31. Adiabatic models require coupling between the
variations of velocity, magnetic field and particle density. They are therefore
more tightly constrained than the models previously presented for 3C 31 by
Laing & Bridle (2002). We show that adiabatic models provide a poorer
description of the data in two crucial respects: they cannot reproduce the
observed magnetic-field structures in detail, and they also predict too steep a
brightness decline along the jets for plausible variations of the jet velocity.
We find that the innermost regions of the jets show the strongest evidence for
non-adiabatic behaviour, and that the adiabatic models provide progressively
better descriptions of the jet emission at larger distances from the galactic
nucleus. We briefly discuss physical processes which might contribute to this
non-adiabatic behaviour. In particular, we develop a parameterized description
of distributed particle injection, which we fit to the observed total
intensities. We show that particles are preferentially injected where bright
X-ray emission is observed, and where we infer that the jets are
over-pressured.Comment: 16 pages, 11 figures, accepted for publication in MNRA
Common sequences of emergency readmissions among high-impact users following AAA repair
Introduction The aim of the study was to examine common sequences of causes of readmissions among those patients with multiple hospital admissions, high-impact users, after abdominal aortic aneurysm (AAA) repair and to focus on strategies to reduce long-term readmission rate. Methods The patient cohort (2006-2009) included patients from Hospital Episodes Statistics, the national administrative data of all NHS English hospitals, and followed up for 5 years. Group-based trajectory modelling and sequence analysis were performed on the data. Results From a total of 16,973 elective AAA repair patients, 18% (n=3055) were high-impact users. The high-impact users among rAAA repair constituted 17.3% of the patient population (n=4144). There were 2 subtypes of high-impact users, short-term (7.2%) with initial high readmission rate following by rapid decline and chronic high-impact (10.1%) with persistently high readmission rate. Common causes of readmissions following elective AAA repair were respiratory tract infection (7.3%), aortic graft complications (6.0%), unspecified chest pain (5.8%), and gastro-intestinal haemorrhage (4.8%). However, high-impact users included significantly increased number of patients with multiple readmissions and distinct sequences of readmissions mainly consisting of COPD (4.7%), respiratory tract infection (4.7%) and ischaemic heart disease (3.3%). Conclusion A significant number of patients were high-impact users after AAA repair. They had a common and distinct sequence of causes of readmissions following AAA repair, mainly consisting of cardiopulmonary conditions and aortic graft complications. The common causes of long-term mortality were not related to AAA repair. The quality of care can be improved by identifying these patients early and focusing on prevention of cardiopulmonary diseases in the community
High speed techniques for synthetic aperture radar image formation
One possible approach to high speed synthetic aperture radar signal reconstruction involves the utilization of two dimensional real time spatial light modulators as recyclable replacements for photographic film in the input transducer plane of a modified synthetic aperture radar (SAR) coherent optical processor. Leading candidate spatial light modulators include modified Pockels readout optical modulators (PROM), charge coupled devices (CCD) addressed liquid crystal light valves, and CCD addressed membrane light modulators. The fundamental physical limitations affecting SAR processor performance characteristics of such real time devices are under investigation. Current research on PROM is focused on the effects of device operatonal mode, device constitutive parameters, electro-optic crystal orientation, writing wavelength, frame rate/data overwrite/presuming, erasure completeness, and image retention on the overall quality of SAR image formation. Both modulated laser scanning and intensified CRT temporal to spatial input approaches are being examined
Free circular introns with an unusual branchpoint in neuronal projections
The polarized structure of axons and dendrites in neuronal cells depends in part on RNA localization. Previous studies have looked at which polyadenylated RNAs are enriched in neuronal projections or at synapses, but less is known about the distribution of non-adenylated RNAs. By physically dissecting projections from cell bodies of primary rat hippocampal neurons and sequencing total RNA, we found an unexpected set of free circular introns with a non-canonical branchpoint enriched in neuronal projections. These introns appear to be tailless lariats that escape debranching. They lack ribosome occupancy, sequence conservation, and known localization signals, and their function, if any, is not known. Nonetheless, their enrichment in projections has important implications for our understanding of the mechanisms by which RNAs reach distal compartments of asymmetric cells
Human bladder cancer invasion model using rat bladder in vitro and its use to test mechanisms and therapeutic inhibitors of invasion
As well as being a passive support, the extracellular matrix also regulates key biological processes such as invasion, differentiation and angiogenesis. We have therefore developed an in vitro model of bladder cancer invasion using de-epithelialized rat bladder to allow for tumour cell–extracellular matrix interactions. Onto this we have seeded a panel of human bladder cancer cell lines (RT4, RT112, 253J and EJ28 (T24)) representing progression from well to poorly differentiated phenotypes and used as models of superficial to invasive bladder cancer. The better differentiated cell lines RT4 and RT112 reproducibly grew as stratified epithelium, whereas poorly differentiated EJ28 cells invaded across a broad front. Invasion was not simply related to proliferation rate, measured either as doubling time on plastic (non-invasive 253J and invasive EJ28 having the same doubling time) or by Ki-67 proliferation index within the model. We used the model to test the ability of 4 compounds that interfere with tumour cell–extracellular matrix interactions (suramin, N-acetylcysteine and the urokinase plasminogen activator pathway antagonists Å5 compound and monoclonal antibody Mab 3936) to inhibit invasion. At non-toxic concentrations, all significantly inhibited invasion (P< 0.05), although to varying degrees, suramin and Å5 almost completely and N-acetylcysteine the least. In conclusion, this model shows the urokinase system is important for bladder invasion and can be used to investigate other mechanisms of bladder cancer invasion and also for the testing of intravesical drugs. © 2001 Cancer Research Campaign http://www.bjcancer.co
Three episodes of jet activity in the FRII radio galaxy B0925+420
We present Very Large Array images of a "Double-Double Radio Galaxy", a class
of objects in which two pairs of lobes are aligned either side of the nucleus.
In this object, B0925+420, we discover a third pair of lobes, close to the core
and again in alignment with the other lobes. This first-known "Triple-Double"
object strongly increases the likelihood that these lobes represent mutiple
episodes of jet activity, as opposed to knots in an underlying jet. We model
the lobes in terms of their dynamical evolution. We find that the inner pair of
lobes is consistent with the outer pair having been displaced buoyantly by the
ambient medium. The middle pair of lobes is more problematic - to the extent
where an alternative model interpreting the middle and inner "lobes" as
additional bow shocks within the outer lobes may be more appropriate - and we
discuss the implications of this on our understanding of the density of the
ambient medium.Comment: Accepted for publication in MNRAS. Figure 2 is best viewed in colou
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