1,736 research outputs found
Anatomical and biomechanical traits of broiler chickens across ontogeny. Part II. Body segment inertial properties and muscle architecture of the pelvic limb
In broiler chickens, genetic success for desired production traits is often shadowed by welfare concerns related to musculoskeletal health. Whilst these concerns are clear, a viable solution is still elusive. Part of the solution lies in knowing how anatomical changes in afflicted body systems that occur across ontogeny influence standing and moving. Here, to demonstrate these changes we quantify the segment inertial properties of the whole body, trunk (legs removed) and the right pelvic limb segments of five broilers at three different age groups across development. We also consider how muscle architecture (mass, fascicle length and other properties related to mechanics) changes for selected muscles of the pelvic limb. All broilers used had no observed lameness, but we document the limb pathologies identified post mortem, since these two factors do not always correlate, as shown here. The most common leg disorders, including bacterial chondronecrosis with osteomyelitis and rotational and angular deformities of the lower limb, were observed in chickens at all developmental stages. Whole limb morphology is not uniform relative to body size, with broilers obtaining large thighs and feet between four and six weeks of age. This implies that the energetic cost of swinging the limbs is markedly increased across this growth period, perhaps contributing to reduced activity levels. Hindlimb bone length does not change during this period, which may be advantageous for increased stability despite the increased energetic costs. Increased pectoral muscle growth appears to move the centre of mass cranio-dorsally in the last two weeks of growth. This has direct consequences for locomotion (potentially greater limb muscle stresses during standing and moving). Our study is the first to measure these changes in the musculoskeletal system across growth in chickens, and reveals how artificially selected changes of the morphology of the pectoral apparatus may cause deficits in locomotion
Radio Emission Signatures in the Crab Pulsar
Our high time resolution observations of individual pulses from the Crab
pulsar show that both the time and frequency signatures of the interpulse are
distinctly different from those of the main pulse. Main pulses can occasionally
be resolved into short-lived, relatively narrow-band nanoshots. We believe
these nanoshots are produced by soliton collapse in strong plasma turbulence.
Interpulses at centimeter wavelengths are very different. Their dynamic
spectrum contains regular, microsecond-long emission bands. We have detected
these bands, proportionately spaced in frequency, from 4.5 to 10.5 GHz. The
bands cannot easily be explained by any current theory of pulsar radio
emission; we speculate on possible new models.Comment: 26 pages, 10 figures, to appear in Ap
A Study of Giant Pulses from PSR J1824-2452A
We have searched for microsecond bursts of emission from millisecond pulsars
in the globular cluster M28 using the Parkes radio telescope. We detected a
total of 27 giant pulses from the known emitter PSR J1824-2452A. At wavelengths
around 20 cm the giant pulses are scatter-broadened to widths of around 2
microseconds and follow power-law statistics. The pulses occur in two narrow
phase-windows which correlate in phase with X-ray emission and trail the peaks
of the integrated radio pulse-components. Notably, the integrated radio
emission at these phase windows has a steeper spectral index than other
emission. The giant pulses exhibit a high degree of polarization, with many
being 100% elliptically polarized. Their position angles appear random.
Although the integrated emission of PSR J1824-2452A is relatively stable for
the frequencies and bandwidths observed, the intensities of individual giant
pulses vary considerably across our bands. Two pulses were detected at both
2700 and 3500 MHz. The narrower of the two pulses is 20 ns wide at 3500 MHz. At
2700 MHz this pulse has an inferred brightness temperature at maximum of 5 x
10^37 K. Our observations suggest the giant pulses of PSR J1824-2452A are
generated in the same part of the magnetosphere as X-ray emission through a
different emission process to that of ordinary pulses.Comment: Accepted by Ap
Unusual glitch behaviours of two young pulsars
In this paper we report unusual glitches in two young pulsars, PSR J1825-0935
(B1822-09) and PSR J1835-1106. For PSR J1825-0935, a slow glitch characterised
by a temporary decrease in the slowdown rate occurred between 2000 December 31
to 2001 December 6. This event resulted in a permanent increase in frequency
with fractional size , however little
effect remained in slowdown rate. The glitch in PSR J1835-1106 occurred
abruptly in November 2001 (MJD 52220\pm3) with
and little or no change in the
slow-down rate. A significant change in apparently occurred at the
glitch with having opposite sign for the pre- and post-glitch data.Comment: Latex format, six files, 5 pages with 4 figues. accepted for MNRA
Radiation properties of extreme nulling pulsar J1502-5653
We report on radiation properties of extreme nulling pulsar J1502-5653, by
analyzing the data acquired from the Parkes 64-m telescope at 1374 MHz. The
radio emission from this pulsar exhibits sequences of several tens to several
hundreds consecutive burst pulses, separated by null pulses, and the appearance
of the emission seems quasi-periodic. The null fraction from the data is
estimated to be 93.6%. No emission is detected in the integrated profile of all
null pulses. Systematic modulations of pulse intensity and phase are found at
the beginning of burst-pulse sequences just after null. The intensity usually
rises to a maximum for the first few pulses, then declines exponentially
afterwards, and becomes stable after few tens of pulse periods. The peak phase
appears at later longitudes for the first pulse, then drifts to earlier
longitudes rapidly, and then systematic drifting gradually vanishes while the
intensity becomes stable. In this pulsar, the intensity variation and phase
modulation of pulses are correlated in a short duration after the emission
starts following a null. Observed properties of the pulsar are compared with
other nulling pulsars published previously, and the possible explanation for
phase modulation is discussed.Comment: 5 pages, 7 figures. Accepted by MNRA
Timing the Parkes Multibeam Pulsars
Measurement of accurate positions, pulse periods and period derivatives is an
essential follow-up to any pulsar survey. The procedures being used to obtain
timing parameters for the pulsars discovered in the Parkes multibeam pulsar
survey are described. Completed solutions have been obtained so far for about
80 pulsars. They show that the survey is preferentially finding pulsars with
higher than average surface dipole magnetic fields. Eight pulsars have been
shown to be members of binary systems and some of the more interesting results
relating to these are presented.Comment: 6 pages, 2 embedded EPS figures, to be published in proceedings of
"Pulsar Astronomy - 2000 and Beyond", ASP Conf. Se
Timing measurements and proper motions of 74 pulsars using the Nanshan radio telescope
We have measured the positions of 74 pulsars from regular timing observations
using the Nanshan radio telescope at Urumqi Observatory between 2000 January
and 2004 August (MJD 51500 -- 53240). Proper motions were determined for these
pulsars by comparing their current positions with positions given in pulsar
catalogues. We compare our results to earlier measurements in the literature
and show that, in general, the values agree. New or improved proper motions are
obtained for 16 pulsars. The effect of period fluctuations and other timing
noise on the determination of pulsar positions is investigated. For our sample,
the mean and rms transverse velocities are 443 and 224 km/s respectively,
agreeing with previous work even though we determine distances using the new
NE2001 electron density model.Comment: 9 pages, 7 figures and 3 tables. Accepted by MNRA
Discovery of Five Binary Radio Pulsars
We report on five binary pulsars discovered in the Parkes multibeam Galactic
plane survey. All of the pulsars are old, with characteristic ages 1-11 Gyr,
and have relatively small inferred magnetic fields, 5-90e8 G. The orbital
periods range from 1.3 to 15 days. As a group these objects differ from the
usual low-mass binary pulsars (LMBPs): their spin periods of 9-88 ms are
relatively long; their companion masses, 0.2-1.1 Msun, are, in at least some
cases, suggestive of CO or more massive white dwarfs; and some of the orbital
eccentricities, 1e-5 < e < 0.002, are unexpectedly large. We argue that these
observed characteristics reflect binary evolution that is significantly
different from that of LMBPs. We also note that intermediate-mass binary
pulsars apparently have a smaller scale-height than LMBPs.Comment: 5 pages, 4 embedded EPS figs, accepted for publication by ApJ Letter
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