2,384 research outputs found
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
Listening to alternative perspectives on rural crime and criminality: a report on the pilot study.
This summary reports on the pilot phase of an ongoing study, funded by SIPR, into the changing nature of rural crime and what constitutes rural criminality. We set out to listen to alternative perspectives on rural crime and criminality and to speak to employees of agencies other than the police involved in policing rural criminality. We initially believed that such activities might be hampered by a lack of definitional clarity as to what constitutes rural policing and by the focus of the literature on policing per se. However, what the pilot study showed was that much of the criminality which was discussed transcends the artificial boundaries of rurality and urbanity in that it was primarily food crime or food fraud. This has implications for future research into rural crime
Structures of the magnetoionic media around the FR I radio galaxies 3C 31 and Hydra A
We use high-quality VLA images of the Fanaroff & Riley Class I radio galaxy
3C 31 at six frequencies in the range 1365 to 8440MHz to explore the spatial
scale and origin of the rotation measure (RM) fluctuations on the line of sight
to the radio source. We analyse the distribution of the degree of polarization
to show that the large depolarization asymmetry between the North and South
sides of the source seen in earlier work largely disappears as the resolution
is increased. We show that the depolarization seen at low resolution results
primarily from unresolved gradients in a Faraday screen in front of the
synchrotron-emitting plasma. We establish that the residual degree of
polarization in the short-wavelength limit should follow a Burn law and we fit
such a law to our data to estimate the residual depolarization at high
resolution. We show that the observed RM variations over selected areas of 3C
31 are consistent with a power spectrum of magnetic fluctuations in front of 3C
31 whose power-law slope changes significantly on the scales sampled by our
data. The power spectrum can only have the form expected for Kolmogorov
turbulence on scales <5 kpc. On larger scales we find a flatter slope. We also
compare the global variations of RM across 3C 31 with the results of
three-dimensional simulations of the magnetic-field fluctuations in the
surrounding magnetoionic medium. We show that our data are consistent with a
field distribution that favours the plane perpendicular to the jet axis -
probably because the radio source has evacuated a large cavity in the
surrounding medium. We also apply our analysis techniques to the case of Hydra
A, where the shape and the size of the cavities produced by the source in the
surrounding medium are known from X-ray data. (Abridged)Comment: 33 pages, 25 figures, accepted for publication in MNRA
Love is . . . an abstract word: the influence of phonological and semantic factors on verbal short-term memory in Williams syndrome
It has been claimed that verbal short-term memory in Williams syndrome is characterised by an over-use of phonological coding alongside a reduced contribution of lexical semantics. We critically examine this hypothesis and present results from a memory span task comparing performance on concrete and abstract words, together with a replication of a span task using phonologically similar and phonologically dissimilar words. Fourteen participants with Williams syndrome were individually matched to two groups of typically developing children. The first control group was matched on digit span and the second on vocabulary level. Significant effects were found for both the semantic and the phonological variables in the WS group as well as in the control groups, with no interaction between experimental variable and group in either experiment. The results demonstrate that, despite claims to the contrary, children and adults with WS are able to access and make use of lexical semantics in a verbal short-term memory task in a manner comparable to typically developing individuals
Simulations of Nonthermal Electron Transport in Multidimensional Flows: Synthetic Observations of Radio Galaxies
We have applied an effective numerical scheme for cosmic-ray transport to 3D
MHD simulations of jet flow in radio galaxies (see the companion paper by Jones
et al. 1999). The marriage of relativistic particle and 3D magnetic field
information allows us to construct a rich set of ``synthetic observations'' of
our simulated objects. The information is sufficient to calculate the ``true''
synchrotron emissivity at a given frequency using explicit information about
the relativistic electrons. This enables us to produce synchrotron
surface-brightness maps, including polarization. Inverse-Compton X-ray
surface-brightness maps may also be produced. First results intended to explore
the connection between jet dynamics and electron transport in radio lobes are
discussed. We infer lobe magnetic field values by comparison of synthetically
observed X-ray and synchrotron fluxes, and find these ``inverse-Compton''
fields to be quite consistent with the actual RMS field averaged over the lobe.
The simplest minimum energy calculation from the synthetic observations also
seems to agree with the actual simulated source properties.Comment: 7 pages, 1 figure; to appear in Life Cycles of Radio Galaxies, ed. J.
Biretta et al., New Astronomy Review
Students’ views on fairness in education: the importance of relational justice and stakes fairness
This paper discusses a research project which sought to find out about young people’s views on fairness in education in English schools. Fairness is an everyday term, which in policy hides multiple and contradictory positions across the political divide. In education, we find a policy context that focuses on distributional justice and equality of opportunity but also on principles of freedom and choice. This paper argues that engaging with how young people understand fairness contributes to models of social justice in education. Focus group data and written statements on fairness from approximately 80 young people aged 16–18 from five very different English schools were analysed. Students’ primary concerns, absent from educational policy, were the themes of relational justice and stakes fairness, which are eclipsed by current recourse to distributive justice and meritocratic ideals. We argue that a focus on the lived experience of fairness is therefore necessary to widen the discourse about what is fair in education and to reinvigorate public debate about the values on which our education system is based
The dust-eliminated shape of quasar spectra in the near-infrared: a hidden part of the big blue bump
The near-infrared shape of the big blue bump component in quasar spectra has
been essentially unknown. It usually cannot be observed directly, due to the
strong hot dust emission which dominates quasar spectra longward of ~1micron.
However this is quite an important part of the spectrum theoretically. At least
bare disk models provide quite a robust prediction for the overall continuum
shape in the near-infrared. Self-gravity should become important in the outer,
near-infrared emitting regions of the putative disk, possibly leaving a
signature of disk truncation in the near-infrared. We propose here that this
important part of the spectrum can be revealed for the first time by observing
polarized flux from normal quasars. At least in some polarized quasars, the
emission lines are all unpolarized and so the polarized flux should originate
interior to the broad line region, and therefore also interior to the dust
emitting region. This can then be used to eliminate the dust emission. We
present the results of near-infrared polarimetry for such three quasars
(Ton202, 4C37.43, B2 1208+32). The data for Ton202 have the highest S/N, and
the near-infrared polarized flux in this case is measured to have quite a blue
shape, nu^+0.42+-0.29 in F_nu, intriguingly consistent with the simple
multi-temperature black body, bare disk prediction of nu^+1/3. All these data,
although still with quite low S/N for the other two objects, demonstrate the
unique potential of the technique with future better data. We also present
similar data for other quasars and radio galaxies, and briefly discuss the
nature of the polarization.Comment: MNRAS in pres
Stroke in inflammatory bowel disease: a report of two cases and review of the literature
Thrombosis is a recognised complication of inflammatory bowel disease (IBD), in particular venous thrombosis. Arterial thrombosis, especially stroke is rare. There is a paucity of information regarding stroke in IBD and its management. The authors describe two cases of stroke in patients with IBD during periods of increased disease activity. The literature regarding this devastating complication and the procoagulant state that exists in IBD are reviewed
Improving professional learning and teaching through the development of a quality process
Investigation of graduate attributes (GAs) and professional standards (PSs) within faculty curriculum development are rare, despite university importance. Examining learning objectives and assessment with PSs and accreditation, this project sought learning and teaching improvements through developing a cross discipline quality assurance process, aligning learning and assessment with PSs and GAs. This paper describes the results of interviews with those responsible for teaching and learning in four faculties at an Australian University. The results indicate that curriculum developers are often unable to align the GAs and PSs that creates challenges for an assurance of students’ learning
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