9,171 research outputs found
A Study of Single Pulses in the Parkes Multibeam Pulsar Survey
We reprocessed the Parkes Multibeam Pulsar Survey, searching for single
pulses out to a DM of 5000 pc cm with widths of up to one second. We
recorded single pulses from 264 known pulsars and 14 Rotating Radio Transients.
We produced amplitude distributions for each pulsar which we fit with
log-normal distributions, power-law tails, and a power-law function divided by
an exponential function, finding that some pulsars show a deviation from a
log-normal distribution in the form of an excess of high-energy pulses. We
found that a function consisting of a power-law divided by an exponential fit
the distributions of most pulsars better than either log-normal or power-law
functions. For pulsars that were detected in a periodicity search, we computed
the ratio of their single-pulse signal-to-noise ratios to their signal-to-noise
ratios from a Fourier transform and looked for correlations between this ratio
and physical parameters of the pulsars. The only correlation found is the
expected relationship between this ratio and the spin period. Fitting
log-normal distributions to the amplitudes of pulses from RRATs showed similar
behaviour for most RRATs. Here, however, there seem to be two distinct
distributions of pulses, with the lower-energy distribution being consistent
with noise. Pulse-energy distributions for two of the RRATS processed were
consistent with those found for normal pulsars, suggesting that pulsars and
RRATs have a common emission mechanism, but other factors influence the
specific emission properties of each source class.Comment: 11 pages, 6 figures, 3 tables, accepted for publication in MNRA
Fatigue of notched fiber composite laminates. Part 2: Analytical and experimental evaluation
The analytical/experimental correlation study was performed to develop an understanding of the behavior of notched Boron/epoxy laminates subjected to tension/tension fatigue loading. It is postulated that the fatigue induced property changes (stiffness as well as strength) of the laminate can be obtained from the lamina fatigue properties. To that end, the Boron/epoxy lamina static and fatigue data (lifetime, residual stiffness and strength) were obtained initially. The longitudinal and transverse tension data were determined from the (0) and (90) laminate tests while the in-plane shear data were obtained from the (+ or - 45) sub s laminates. The static tests obtained the notched strength and mode of failure while the fatigue tests determined lifetime, damage propagation and residual strength. The failure in static tension occurred in a transverse crack propagation mode
Discovery of two pulsars towards the Galactic Centre
We report the discovery of two highly dispersed pulsars in the direction of
the Galactic Centre made during a survey at 3.1 GHz with the Parkes radio
telescope. Both PSRs J1745-2912 and J1746-2856 have an angular separation from
the Galactic Centre of less than 0.3 degrees and dispersion measures in excess
of 1100 cm-3pc, placing them in the top 10 pulsars when ranked on this value.
The frequency dependence of the scatter-broadening in PSR J1746-2856 is much
shallower than expected from simple theory. We believe it likely that the
pulsars are located between 150 and 500 pc from the Galactic Centre on the near
side, and are part of an excess population of neutron stars associated with the
Centre itself. A second survey made at 8.4 GHz did not detect any pulsars. This
implies either that there are not many bright, long-period pulsars at the
Galactic Centre or that the scattering is more severe at high frequencies than
current models would suggest.Comment: Submitted to MNRAS Letter
Teaching the Use of Systems Dynamics for Strategic Decision Making in Healthcare
Having worked in the healthcare system and taught healthcare MBAs for over a decade, we have observed that healthcare systems and departments operate in independent silos. This paper shows how to use systems dynamics as a method to help students examine the big picture of how components fit together to form a system. We demonstrate the application of this approach and provide an example from one of our healthcare professional graduate student teams
The Evolution of PSR J0737-3039B and a Model for Relativistic Spin Precession
We present the evolution of the radio emission from the 2.8-s pulsar of the
double pulsar system PSR J0737-3039A/B. We provide an update on the Burgay et
al. (2005) analysis by describing the changes in the pulse profile and flux
density over five years of observations, culminating in the B pulsar's radio
disappearance in 2008 March. Over this time, the flux density decreases by
0.177 mJy/yr at the brightest orbital phases and the pulse profile evolves from
a single to a double peak, with a separation rate of 2.6 deg/yr. The pulse
profile changes are most likely caused by relativistic spin precession, but can
not be easily explained with a circular hollow-cone beam as in the model of
Clifton & Weisberg (2008). Relativistic spin precession, coupled with an
elliptical beam, can model the pulse profile evolution well. This particular
beam shape predicts geometrical parameters for the two bright orbital phases
which are consistent and similar to those derived by Breton et al. (2008).
However, the observed decrease in flux over time and B's eventual disappearance
cannot be easily explained by the model and may be due to the changing
influence of A on B.Comment: 20 pages, 18 figures, Accepted by ApJ on 2 August 201
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