7,860 research outputs found
Pulsar "Drifting"-Subpulse Polarization: No Evidence for Systematic Polarization-Angle Rotations
Polarization-angle density displays are given for pulsars B0809+74 and
B2303+30, which exhibit no evidence of the systematic polarization-angle
rotation within individual subpulses previously reported for these two stars.
The ``drifting'' subpulses of both pulsars exhibit strikingly linear and
circular polarization which appears to reflect the characteristics of two
nearly orthogonally polarized emission ``modes''--along which the severe
average-profile depolarization that is characteristic of their admixture at
comparable overall intensities.Comment: Accepted for publication in Astronomy & Astrophysic
Is pulsar B0656+14 a very nearby RRAT source?
The recently discovered RRAT sources are characterized by very bright radio
bursts which, while being periodically related, occur infrequently. We find
bursts with the same characteristics for the known pulsar B0656+14. These
bursts represent pulses from the bright end of an extended smooth pulse-energy
distribution and are shown to be unlike giant pulses, giant micropulses or the
pulses of normal pulsars. The extreme peak-fluxes of the brightest of these
pulses indicates that PSR B0656+14, were it not so near, could only have been
discovered as an RRAT source. Longer observations of the RRATs may reveal that
they, like PSR B0656+14, emit weaker emission in addition to the bursts.Comment: 4 pages, 4 figures, accepted by ApJ
Should Higher Education respond to recent changes in the forensic science marketplace?
The evolution of forensic science within the United Kingdom over the past four decades has been rapid and dynamic. This has included policy responses to highly public miscarriages of justice, introduction of commercialisation and pioneering scientific developments such as DNA profiling. However even within this context, changes within forensic science over the last two years has been unprecedented; such as the closure of The Forensic Science Service; a Home Office review of Research and Development within forensic science; the challenges facing fingerprint identification as a result of The Fingerprint Inquiry (Scotland) and the embryonic development of a new professional body for the police force. Correspondingly, development of forensic science within Higher Education (HE) has been substantially transformed from a small number of Masters Courses in forensic science delivered by a small number of universities, to a plethora of undergraduate courses now available throughout the United Kingdom. This rapid expansion of forensic science courses has been openly criticised and debated and it is incumbent upon the university to not only focus on education but also to provide graduates with transferrable skills making them more employment ready. As a consequence HE establishments must be cognisant of and reactive to changes within any associated industry and respond to changes accordingly. However, have the universities delivering forensic science courses fully responded to these recent and unprecedented developments in the history of forensic science within the United Kingdom? This paper will consider the most recent changes to the forensic science marketplace and their ramifications for forensic science education within the HE sector. Challenges which have resulted from the changes will be highlighted and the educational impact on forensic science courses throughout the UK and their future will be evaluated in chronological order
PSR 0943+10: a bare strange star?
Recent work by Rankin & Deshpande strongly suggests that there exist strong
``micro-storms'' rotating around the magnetic axis of the 1.1s pulsar PSR
0943+10. Such a feature hints that most probably the large-voltage vacuum gap
proposed by Ruderman & Sutherland (RS) does exist in the pulsar polar cap.
However, there are severe arguments against the formation of the RS-type gap in
pulsars, since the binding energies of both the Fe ions and the electrons in a
neutron star's surface layer is too small to prevent thermionic ejection of the
particles from the surface. Here we propose that PSR 0943+10 (probably also
most of the other ``drifting'' pulsars) might be bare strange stars rather than
normal neutron stars, in which the ``binding energy'' at the surface is merely
infinity either for the case of ``pulsar'' or ``anti-pulsar''. It is further
proposed that identifying a drifting pulsar as an anti-pulsar is the key
criterion to distinguish strange stars from neutron stars.Comment: 4 pages, no figures, LaTeX, accepted 1999 July 9 by ApJ Letter
Recommended from our members
Complete Experimental Structure Determination of the p(3x2)pg Phase of Glycine on Cu{110}
We present a quantitative low energy electron diffraction (LEED) surface-crystallograpic
study of the complete adsorption geometry of glycine adsorbed on Cu{110} in the ordered
p(3Ă—2) phase. The glycine molecules form bonds to the surface through the N atoms of the
amino group and the two O atoms of the de-protonated carboxylate group, each with separate
Cu atoms such that every Cu atom in the first layer is involved in a bond. Laterally, N atoms are
nearest to the atop site (displacement 0.41 Ă…). The O atoms are asymmetrically displaced from
the atop site by 0.54 Ă… and 1.18 Ă… with two very different O-Cu bond lengths of 1.93 Ă… and
2.18 Ă…. The atom positions of the upper-most Cu layers show small relaxations within 0.07 Ă…
of the bulk-truncated surface geometry. The unit cell of the adsorbate layer consists of two
glycine molecules, which are related by a glide-line symmetry operation. This study clearly
shows that a significant coverage of adsorbate structures without this glide-line symmetry must
be rejected, both on the grounds of the energy dependence of the spot intensities (LEED-IV
curves) and of systematic absences in the LEED pattern
Probing drifting and nulling mechanisms through their interaction in PSR B0809+74
Both nulling and subpulse drifting are poorly understood phenomena. We probe
their mechanisms by investigating how they interact in PSR B0809+74. We find
that the subpulse drift is not aliased but directly reflects the actual motion
of the subbeams. The carousel-rotation time must then be over 200 seconds,
which is much longer than theoretically predicted.
The drift pattern after nulls differs from the normal one, and using the
absence of aliasing we determine the underlying changes in the subbeam-carousel
geometry. We show that after nulls, the subbeam carousel is smaller, suggesting
that we look deeper in the pulsar magnetosphere than we do normally. The many
striking similarities with emission at higher frequencies, thought to be
emitted lower too, confirm this. The emission-height change as well as the
striking increase in carousel-rotation time can be explained by a post-null
decrease in the polar gap height. This offers a glimpse of the circumstances
needed to make the pulsar turn off so dramatically.Comment: 7 pages, 5 low-res figures, accepted for Astronomy & Astrophysics.
Latest high-res versions available at
http://www.astro.uu.nl/~jleeuwen/preprints/drif-null-0809/ (v2: extended
discussion
- …