1,233 research outputs found
Towards a critical historiography of orthodox-revisionist debates on the origins of the Cold War: between disciplinary power and U.S. national identity
The study of U.S diplomatic history and the Cold War has undergone a marked transformation in the analytical methods, conceptual approaches, and theories used by practitioners in the field. However, innovation and sophistication has seldom transferred into the study of the historiographical literature itself. In an attempt to buck this trend, this dissertation posits a theory of historiographical development in order to interrogate the meaning of the orthodox-revisionist debate on the origins of the Cold War. Borrowing insights from the literature on ‘critical historiography’, it suggests that historiographical shifts occur in the twin struggle of defining the boundaries of the historical field and the construction of U.S identity. It documents the process of ‘disciplinisation’ that Cold War revisionism underwent, reconfiguring both the parameters of the field and the form of revisionist interpretations. It moves on to suggest that legitimation of revisionism as a form of historical knowledge was facilitated by conceptual shifts in the meaning of U.S identity and a rearticulation of the orthodox narrative, which incorporated and thereby marginalised the revisionist critique. Finally, a few thoughts are raised as to the politicised nature of all historiography in the way that it negotiates challenges to disciplinary practices and boundaries
Size of the Vela Pulsar's Emission Region at 18 cm Wavelength
We present measurements of the linear diameter of the emission region of the
Vela pulsar at observing wavelength lambda=18 cm. We infer the diameter as a
function of pulse phase from the distribution of visibility on the
Mopra-Tidbinbilla baseline. As we demonstrate, in the presence of strong
scintillation, finite size of the emission region produces a characteristic
W-shaped signature in the projection of the visibility distribution onto the
real axis. This modification involves heightened probability density near the
mean amplitude, decreased probability to either side, and a return to the
zero-size distribution beyond. We observe this signature with high statistical
significance, as compared with the best-fitting zero-size model, in many
regions of pulse phase. We find that the equivalent full width at half maximum
of the pulsar's emission region decreases from more than 400 km early in the
pulse to near zero at the peak of the pulse, and then increases again to
approximately 800 km near the trailing edge. We discuss possible systematic
effects, and compare our work with previous results
Discovery of Substructure in the Scatter-Broadened Image of Sgr A*
We have detected substructure within the smooth scattering disk of the
celebrated Galactic Center radio source Sagittarius A* (SgrA*). We observed
this structure at 1.3 cm wavelength with the Very Long Baseline Array together
with the Green Bank Telescope, on baselines of up to 3000 km, long enough to
completely resolve the average scattering disk. Such structure is predicted
theoretically, as a consequence of refraction by large-scale plasma
fluctuations in the interstellar medium. Along with the much-studied
scaling of angular broadening
with observing wavelength , our observations
indicate that the spectrum of interstellar turbulence is shallow, with an inner
scale larger than 300 km. The substructure is consistent with an intrinsic size
of about 1 mas at 1.3 cm wavelength, as inferred from deconvolution of the
average scattering. Further observations of the substructure can set stronger
constraints on the properties of scattering material and on the intrinsic size
of SgrA*. These constraints will guide understanding of effects of
scatter-broadening and emission physics of the black hole, in images with the
Event Horizon Telescope at millimeter wavelengths.Comment: 5 pages, 5 figures, accepted by Astrophysical Journal Letters; minor
corrections to the text and figures are introduce
Small-Scale Variations of HI Spectra from Interstellar Scintillatio
I suggest that radio-wave scattering by the interstellar plasma, in
combination with subsonic gradients in the Doppler velocity of interstellar HI,
is responsible for the observed small-scale variation in HI absorption spectra
of pulsars. Velocity gradients on the order of 0.05 to 0.3 km/s across 1 AU can
produce the observed variations. I suggest observational tests to distinguish
between this model and the traditional picture of small-scale opacity
variations from cloudlets.Comment: 24 pages, 2 figures, Latex, uses AASTe
Electric field representation of pulsar intensity spectra
Pulsar dynamic spectra exhibit high visibility fringes arising from
interference between scattered radio waves. These fringes may be random or
highly ordered patterns, depending on the nature of the scattering or
refraction. Here we consider the possibility of decomposing pulsar dynamic
spectra -- which are intensity measurements -- into their constituent scattered
waves, i.e. electric field components. We describe an iterative method of
achieving this decomposition and show how the algorithm performs on data from
the pulsar B0834+06. The match between model and observations is good, although
not formally acceptable as a representation of the data. Scattered wave
components derived in this way are immediately useful for qualitative insights
into the scattering geometry. With some further development this approach can
be put to a variety of uses, including: imaging the scattering and refracting
structures in the interstellar medium; interstellar interferometric imaging of
pulsars at very high angular resolution; and mitigating pulse arrival time
fluctuations due to interstellar scattering.Comment: 7 Pages, 2 Figures, revised version, accepted by MNRA
Correlation between X-ray Lightcurve Shape and Radio Arrival Time in the Vela Pulsar
We report the results of simultaneous observations of the Vela pulsar in
X-rays and radio from the RXTE satellite and the Mount Pleasant Radio
Observatory in Tasmania. We sought correlations between the Vela's X-ray
emission and radio arrival times on a pulse by pulse basis. At a confidence
level of 99.8% we have found significantly higher flux density in Vela's main
X-ray peak during radio pulses that arrived early. This excess flux shifts to
the 'trough' following the 2nd X-ray peak during radio pulses that arrive
later. Our results suggest that the mechanism producing the radio pulses is
intimately connected to the mechanism producing X-rays. Current models using
resonant absorption of radio emission in the outer magnetosphere as a cause of
the X-ray emission are explored as a possible explanation for the correlation.Comment: 6 pages, 5 figures, accepted by Ap
Feeling Tired?: How Sharing Positive Experiences Can Boost Vitality
Three studies indicated how sharing positive experiences can boost vitality
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