1,632 research outputs found
The spectra and energies of classical double radio lobes
We compare two temporal properties of classical double radio sources: i)
radiative lifetimes of synchrotron-emitting particles and ii) dynamical source
ages. We discuss how these can be quite discrepant from one another, rendering
use of the traditional spectral ageing method inappropriate: we contend that
spectral ages give meaningful estimates of dynamical ages only when these ages
are << 10^7 years. In juxtaposing the fleeting radiative lifetimes with source
ages which are significantly longer, a refinement of the paradigm for radio
source evolution is required. The changing spectra along lobes are explained,
not predominantly by synchrotron ageing but, by gentle gradients in a magnetic
field mediated by a low-gamma matrix which illuminates an energy-distribution
of particles, controlled largely by classical synchrotron loss in the high
magnetic field of the hotspot. The energy in the particles is an order of
magnitude higher than that inferred from the minimum-energy estimate, implying
that the jet-power is of the same order as the accretion luminosity produced by
the quasar central engine. This refined paradigm points to a resolution of the
findings of Rudnick et al (1994) and Katz-Stone & Rudnick (1994) that both the
Jaffe-Perola and Kardashev-Pacholczyk model spectra are invariably poor
descriptions of the curved spectral shape of lobe emission, and indeed that for
Cygnus A all regions of the lobes are characterised by a `universal spectrum'.
[abridged]Comment: LaTeX, 4 figures. To appear in A
Media justice: Madeleine McCann, intermediatization and "trial by media" in the British press
Three-year-old Madeleine McCann disappeared on 3 May 2007 from a holiday apartment in Portugal. Over five years and multiple investigations that failed to solve this abducted child case, Madeleine and her parents were subject to a process of relentless âintermediatizationâ. Across 24â7 news coverage, websites, documentaries, films, YouTube videos, books, magazines, music and artworks, Madeleine was a mediagenic image of innocence and a lucrative story. In contrast to Madeleineâs media sacralization, the representation of her parents, Kate and Gerry McCann, fluctuated between periods of vociferous support and prolonged and libellous âtrial by mediaâ. This article analyses how the global intermediatization of the âMaddie Mysteryâ fed into and fuelled the âtrial by mediaâ of Kate and Gerry McCann in the UK press. Our theorization of âtrial by mediaâ is developed and refined through considering its legal limitations in an era of âattack journalismâ and unprecedented official UK inquiries into press misconduct and criminality
Generalized cold-atom simulators for vacuum decay
Cold-atom analogue experiments are a promising new tool for studying
relativistic vacuum decay, allowing us to empirically probe early-Universe
theories in the laboratory. However, existing analogue proposals place
stringent requirements on the atomic scattering lengths that are challenging to
realize experimentally. Here we generalize these proposals and show that any
stable mixture between two states of a bosonic isotope can be used as a
relativistic analogue. This greatly expands the range of suitable experimental
setups, and will thus expedite efforts to study vacuum decay with cold atoms.Comment: 11 pages, 4 figures, comments welcome; v2: reference adde
VLT Spectroscopy of Ultra-Faint Dwarf Galaxies. 1. Bo\"otes I, Leo IV, Leo V
We perform consistent reductions and measurements for three ultra-faint dwarf
galaxies (UFDs): Bo\"otes I, Leo IV and Leo V. Using the public archival data
from the GIRAFFE spectrograph on the Very Large Telescope (VLT), we locate new
members and provide refined measurements of physical parameters for these dwarf
galaxies. We identify nine new Leo IV members and four new Leo V members, and
perform a comparative analysis of previously discovered members. Additionally,
we identify one new binary star in both Leo IV and Leo V. After removing binary
stars, we recalculate the velocity dispersions of Bo\"otes I and Leo IV to be
5.1 and 3.4 km s, respectively; We do
not resolve the Leo V velocity dispersion. We identify a weak velocity gradient
in Leo V that is 4 smaller than the previously calculated
gradient and that has a corresponding position angle which differs from the
literature value by 120 deg. Combining the VLT data with previous
literature, we re-analyze the Bo\"otes I metallicity distribution function and
find that a model including infall of pristine gas while Bo\"otes I was forming
stars best fits the data. Our analysis of Leo IV, Leo V and other UFDs will
enhance our understanding of these enigmatic stellar populations and contribute
to future dark matter studies. This is the first in a series of papers
examining thirteen UDFs observed with VLT/GIRAFFE between 2009 and 2017.
Similar analyses of the remaining ten UFDs will be presented in forthcoming
papers.Comment: 29 pages, 18 figures, 8 tables. Accepted for publication on ApJ. Code
and data can be found at https://github.com/sazabi4/vlt_dwarf
Democratic cultural policy : democratic forms and policy consequences
The forms that are adopted to give practical meaning to democracy are assessed to identify what their implications are for the production of public policies in general and cultural policies in particular. A comparison of direct, representative, democratic elitist and deliberative versions of democracy identifies clear differences between them in terms of policy form and democratic practice. Further elaboration of these differences and their consequences are identified as areas for further research
Prevalence and characteristics of gastrointestinal infections in men who have sex with men diagnosed with rectal chlamydia infection in the UK: an 'unlinked anonymous' cross-sectional study.
INTRODUCTION: Gastrointestinal infections (GII) can cause serious ill health and morbidity. Although primarily transmitted through faecal contamination of food or water, transmission through sexual activity is well described, especially among men who have sex with men (MSM). METHODS: We investigated the prevalence of GIIs among a convenience sample of MSM who were consecutively diagnosed with rectal Chlamydia trachomatis (CT) at 12 UK genitourinary medicine clinics during 10â
weeks in 2012. Residual rectal swabs were coded, anonymised and tested for Shigella, Campylobacter, Salmonella, shiga toxin-producing Escherichia coli and enteroaggregative E. coli (EAEC) using a real-time PCR. Results were linked to respective coded and anonymised clinical and demographic data. Associations were investigated using Fisher's exact tests. RESULTS: Of 444 specimens tested, overall GII prevalence was 8.6% (95% CI 6.3% to 11.6%): 1.8% (0.9% to 3.6%) tested positive for Shigella, 1.8% (0.9% to 3.6%) for Campylobacter and 5.2% (3.5% to 7.7%) for EAEC. No specimens tested positive for Salmonella or other diarrhoeagenic E. coli pathotypes. Among those with any GII, 14/30 were asymptomatic (2/7 with Shigella, 3/6 with Campylobacter and 9/17 with EAEC). Shigella prevalence was higher in MSM who were HIV-positive (4.7% (2.1% to 10.2%) vs 0.5%(0.1% to 3.2%) in HIV-negative MSM; p=0.01). CONCLUSIONS: In this small feasibility study, MSM with rectal CT appeared to be at appreciable risk of GII. Asymptomatic carriage may play a role in sexual transmission of GII
Variable turbulent convection as the cause of the Blazhko effect - testing the Stothers model
The amplitude and phase modulation observed in a significant fraction of the
RR Lyrae variables - the Blazhko effect - represents a long-standing enigma in
stellar pulsation theory. No satisfactory explanation for the Blazhko effect
has been proposed so far. In this paper we focus on the Stothers (2006) idea,
in which modulation is caused by changes in the structure of the outer
convective zone, caused by a quasi-periodically changing magnetic field.
However, up to this date no quantitative estimates were made to investigate
whether such a mechanism can be operational and whether it is capable of
reproducing the light variation we observe in Blazhko variables. We address the
latter problem. We use a simplified model, in which the variation of turbulent
convection is introduced into the non-linear hydrodynamic models in an ad hoc
way, neglecting interaction with the magnetic field. We study the light curve
variation through the modulation cycle and properties of the resulting
frequency spectra. Our results are compared with Kepler observations of RR Lyr.
We find that reproducing the light curve variation, as is observed in RR Lyr,
requires a huge modulation of the mixing length, of the order of +/-50 per
cent, on a relatively short time-scale of less than 40 days. Even then, we are
not able to reproduce neither all the observed relations between modulation
components present in the frequency spectrum, nor the relations between Fourier
parameters describing the shape of the instantaneous light curves.Comment: 17 pages, 13 figures, accepted for publication in MNRAS; for
associated animation, see
http://homepage.univie.ac.at/radek.smolec/publications/KASC11a
Schooling for violence and peace : how does peace education differ from ânormalâ schooling?
This article reviews literature on the roles of schooling in both reproducing and actively perpetrating violence, and sets out an historical explanation of why schools are socially constructed in such a way as to make these roles possible. It then discusses notions of peace education in relation to one particular project in England before using empirical data from research on the project to examine contrasts between peace education approaches and ânormalâ schooling from the viewpoints of project workers, pupils and teachers. It concludes that such contrasts and tensions do indeed exist and that this raises serious questions about the compatibility of peace education and formal schooling
Can we avoid high coupling?
It is considered good software design practice to organize source code into modules and to favour within-module connections (cohesion) over between-module connections (coupling), leading to the oft-repeated maxim "low coupling/high cohesion". Prior research into network theory and its application to software systems has found evidence that many important properties in real software systems exhibit approximately scale-free structure, including coupling; researchers have claimed that such scale-free structures are ubiquitous. This implies that high coupling must be unavoidable, statistically speaking, apparently contradicting standard ideas about software structure. We present a model that leads to the simple predictions that approximately scale-free structures ought to arise both for between-module connectivity and overall connectivity, and not as the result of poor design or optimization shortcuts. These predictions are borne out by our large-scale empirical study. Hence we conclude that high coupling is not avoidable--and that this is in fact quite reasonable
A modified beam-to-earth transformation to measure short-wavelength internal waves with an acoustic Doppler current profiler
Author Posting. © American Meteorological Society 2005. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Atmospheric and Oceanic Technology 22 (2005): 583â591, doi:10.1175/JTECH1731.1.The algorithm used to transform velocity signals from beam coordinates to earth coordinates in an acoustic Doppler current profiler (ADCP) relies on the assumption that the currents are uniform over the horizontal distance separating the beams. This condition may be violated by (nonlinear) internal waves, which can have wavelengths as small as 100â200 m. In this case, the standard algorithm combines velocities measured at different phases of a wave and produces horizontal velocities that increasingly differ from true velocities with distance from the ADCP. Observations made in Massachusetts Bay show that currents measured with a bottom-mounted upward-looking ADCP during periods when short-wavelength internal waves are present differ significantly from currents measured by point current meters, except very close to the instrument. These periods are flagged with high error velocities by the standard ADCP algorithm. In this paper measurements from the four spatially diverging beams and the backscatter intensity signal are used to calculate the propagation direction and celerity of the internal waves. Once this information is known, a modified beam-to-earth transformation that combines appropriately lagged beam measurements can be used to obtain current estimates in earth coordinates that compare well with pointwise measurements.A. Scotti was partially supported
by ONR Grants N00014-03-1-0553 and N00014-01-1-
0172, B. Butman and P. Alexander by the U.S. Geological
Survey, and R. Beardsley by the WHOI Smith
Chair and ONR Grant N00014-98-1-0210. S. Anderson
received partial support from ONR (Grant N00014-97-
1-0158). The Massachusetts Bay Internal Wave Experiment
was jointly supported by ONR and USGS
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