4,278 research outputs found
Marking the Moral Boundaries of Class
This article welcomes the recent renewed interest in the topic of class within sociology and cultural studies. This comes after a long period – from around the middle part of the 1980s and into the 1990s – during which social class was dismissed as a mode of understanding socio-economic and cultural conditions on the part of both academics and mainstream political organisations alike. Working-class formations in particular came under scrutiny, increasingly seen to be in terminal decline and fragmentation through the impact of post-industrialisation processes set in train in western economies from the turn of the 1980s onwards. The demise of heavy industry – steel, coal, textiles, for instance – profoundly altered working-class communities, transforming the material world and cultural life of the British working class, powerful developments reinforcing the \'end of class\' debate. Allied to this, the emergence within the academy of new theoretical frameworks associated with postmodern thought claimed to undermine traditional understandings around class. This article insists on the continuing significance of class and does so by focussing on an important recent response to the class debate, Andrew Sayer\'s The Moral Significance of Class (2005). This book stakes a lucid claim for the importance of recognising class as a powerful determining factor of subjectivity. While drawing upon aspects of Sayer\'s theoretical framework and argument to examine class experience, it is also the intention of the article to supplement Sayer\'s work by developing related theoretical propositions derived from the writing of Raymond Williams and the Russian linguist and cultural critic Volosinov/Bakhtin.Working Class; Experience; Structure of Feeling; Recognition; Language; Identity
Superluminal Waves and the Structure of Pulsar Wind Termination Shocks
The termination shock of a pulsar wind is located roughly where the ram
pressure matches that of the surrounding medium. Downstream of the shock, MHD
models of the diffuse nebular emission suggest the plasma is weakly magnetized.
However, the transition from a Poynting-dominated MHD wind to a
particle-dominated flow is not well understood. We discuss a solution of this
"sigma problem" in which a striped wind converts into a strong, superluminal
electromagnetic wave. This mode slows down as it propagates radially, and its
ram pressure tends to a constant value at large radius, a property we use to
match the solution to the surrounding nebula. The wave thus forms a pre-cursor
to the termination shock, which occurs at the point where the wave dissipates.
Possible damping and dissipation mechanisms are discussed qualitatively.Comment: 4 pages, 2 figures. Proceedings of the "Electromagnetic Radiation
from Pulsars and Magnetars" conference, April 24-27, 2012, Zielona Gora,
Polan
Rapid cosmic-ray acceleration at perpendicular shocks in supernova remnants
Perpendicular shocks are shown to be rapid particle accelerators that perform
optimally when the ratio of the shock speed to the particle speed
roughly equals the ratio of the scattering rate to the gyro frequency.
We use analytical methods and Monte-Carlo simulations to solve the kinetic
equation that governs the anisotropy generated at these shocks, and find, for
, that the spectral index softens by unity and the
acceleration time increases by a factor of two compared to the standard result
of diffusive shock acceleration theory. These results provide a theoretical
basis for the thirty-year-old conjecture that a supernova exploding into the
wind of a Wolf-Rayet star may accelerate protons to an energy exceeding
eV.Comment: 12 pages, 2 figures, accepted for publication in Ap
Large-Scale Cosmic-Ray Anisotropy as a Probe of Interstellar Turbulence
We calculate the large-scale cosmic-ray (CR) anisotropies predicted for a
range of Goldreich-Sridhar (GS) and isotropic models of interstellar
turbulence, and compare them with IceTop data. In general, the predicted CR
anisotropy is not a pure dipole; the cold spots reported at 400 TeV and 2 PeV
are consistent with a GS model that contains a smooth deficit of
parallel-propagating waves and a broad resonance function, though some other
possibilities cannot, as yet, be ruled out. In particular, isotropic fast
magnetosonic wave turbulence can match the observations at high energy, but
cannot accommodate an energy dependence in the shape of the CR anisotropy. Our
findings suggest that improved data on the large-scale CR anisotropy could
provide a valuable probe of the properties - notably the power-spectrum - of
the interstellar turbulence within a few tens of parsecs from Earth.Comment: 20 pages, 12 figures. Published in The Astrophysical Journa
Computation of synthetic spectra from simulations of relativistic shocks
Particle-in-cell (PIC) simulations of relativistic shocks are in principle
capable of predicting the spectra of photons that are radiated incoherently by
the accelerated particles. The most direct method evaluates the spectrum using
the fields given by the Lienard-Wiechart potentials. However, for relativistic
particles this procedure is computationally expensive. Here we present an
alternative method, that uses the concept of the photon formation length. The
algorithm is suitable for evaluating spectra both from particles moving in a
specific realization of a turbulent electromagnetic field, or from trajectories
given as a finite, discrete time series by a PIC simulation. The main advantage
of the method is that it identifies the intrinsic spectral features, and
filters out those that are artifacts of the limited time resolution and finite
duration of input trajectories.Comment: Accepted for publication in the Astrophysical Journa
Inductive spikes and gamma-ray flares from the Crab Nebula
The ~400 MeV flaring emission from the Crab Nebula is naturally explained as
the result of an abrupt reduction in the mass-loading of the pulsar wind. Very
few particles are then available to carry the current required to maintain wave
activity, causing them to achieve high Lorentz factors. When they penetrate the
Nebula, a tightly beamed, high luminosity burst of hard gamma-rays results,
with characteristics similar to the observed flares. This mechanism may operate
in other powerful pulsars, such as J0537-6910 (PWN N 157B), B0540-69, B1957+20
and J0205+6449 (3C 58).Comment: Talk presented at the 7th Fermi Symposium, Garmisch-Partenkirchen,
October 201
High-energy emission from pulsar binaries
Unpulsed, high-energy emission from pulsar binaries can be attributed to the
interaction of a pulsar wind with that of a companion star. At the shock
between the outflows, particles carried away from the pulsar magnetosphere are
accelerated and radiate both in synchrotron and inverse Compton processes. This
emission constitutes a significant fraction of the pulsar spin-down luminosity.
It is not clear however, how the highly magnetized pulsar wind could convert
its mainly electromagnetic energy into the particles with such high efficiency.
Here we investigate a scenario in which a pulsar striped wind converts into a
strong electromagnetic wave before reaching the shock. This mode can be thought
of as a shock precursor that is able to accelerate particles to
ultrarelativistic energies at the expense of the electromagnetic energy it
carries. Radiation of the particles leads to damping of the wave. The
efficiency of this process depends on the physical conditions imposed by the
external medium. Two regimes can be distinguished: a high density one, where
the EM wave cannot be launched at all and the current sheets in the striped
wind are first compressed by an MHD shock and subsequently dissipate by
reconnection, and a low density one, where the wind can first convert into an
electromagnetic wave in the shock precursor, which then damps and merges into
the surroundings. Shocks in binary systems can transit from one regime to
another according to binary phase. We discuss possible observational
implications for these objects.Comment: 4 pages, 1 figure. Proceedings of Gamma2012, July 9-13, Heidelberg,
German
Radiative damping and emission signatures of strong superluminal waves in pulsar winds
We analyse the damping by radiation reaction and by Compton drag of strong,
superluminal electromagnetic waves in the context of pulsar winds. The
associated radiation signature is found by estimating the efficiency and the
characteristic radiation frequencies. Applying these estimates to the gamma-ray
binary containing PSR B1259-63, we show that the GeV flare observed by
Fermi-LAT can be understood as inverse Compton emission by particles scattering
photons from the companion star, if the pulsar wind termination shock acquires
a precursor of superluminal waves roughly 30 days after periastron. This
constrains the mass-loading factor of the wind (where
is the luminosity and the rate of loss of electrons and positrons) to
be roughly .Comment: minor revisions, accepted for publication in Ap
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