43 research outputs found
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
Pathological voice quality assessment using artificial neural networks
Abstract This paper describes a prototype system for the objective assessment of voice quality in patients recovering from various stages of laryngeal cancer. A large database of male subjects steadily phonating the vowel /i/ was used in the study, and the quality of their voices was independently assessed by a speech and language therapist (SALT) according to their seven-point ranking of subjective voice quality. The system extracts salient short-term and long-term time-domain and frequency-domain parameters from impedance (EGG) signals and these are used to train and test an artificial neural network (ANN). Multi-layer perceptron (MLP) ANNs were investigated using various combinations of these parameters, and the best results were obtained using a combination of short-term and long-term parameters, for which an accuracy of 92% was achieved. It is envisaged that this system could be used as an assessment tool, providing a valuable aid to the SALT during clinical evaluation of voice quality
Arecibo Timing and Single Pulse Observations of 18 Pulsars
We present new results of timing and single pulse measurements for 18 radio
pulsars discovered in 1993 - 1997 by the Penn State/NRL declination-strip
survey conducted with the 305-m Arecibo telescope at 430 MHz. Long-term timing
measurements have led to significant improvements of the rotational and the
astrometric parameters of these sources, including the millisecond pulsar, PSR
J1709+2313, and the pulsar located within the supernova remnant S147, PSR
J0538+2817. Single pulse studies of the brightest objects in the sample have
revealed an unusual "bursting" pulsar, PSR J1752+2359, two new drifting
subpulse pulsars, PSR J1649+2533 and PSR J2155+2813, and another example of a
pulsar with profile mode changes, PSR J1746+2540. PSR J1752+2359 is
characterized by bursts of emission, which appear once every 3-5 min. and decay
exponentially on a ~45 sec timescale. PSR J1649+2533 spends ~30% of the time in
a null state with no detectable radio emission.Comment: submitted to Ap
Arecibo timing observations of 17 pulsars along the Galactic plane
We present phase-coherent timing solutions obtained for the first time for 17
pulsars discovered at Arecibo by Hulse & Taylor (1975ab) in a 430-MHz survey of
the Galactic plane. This survey remains the most sensitive of the Galactic
plane at 430 MHz and has comparable equivalent sensitivity to the 1400-MHz
Parkes multibeam survey. Comparing both surveys we find that, as expected, the
one at 430 MHz is limited in depth by interstellar dispersion and scattering
effects; and that the detection rate of pulsars with high spin-down luminosity
( erg s) at the low frequency is a factor of 5 smaller
than at high frequency. We also present scatter-broadening measurements for two
pulsars and pulse nulling and mode-changing properties for two others.Comment: 10 pages, 3 figures, accepted for publication in A
Pulse-to-pulse intensity modulation and drifting subpulses in recycled pulsars
We report the detection of pulse-to-pulse periodic intensity modulations, in
observations of recycled pulsars. Even though the detection of individual
pulses was generally not possible due to their low flux density and short
duration, through the accumulation of statistics over sequences of 10^5--10^6
pulses we were able to determine the presence and properties of the
pulse-to-pulse intensity variations of six pulsars. In most cases we found that
the modulation included a weak, broadly quasi-periodic component. For two
pulsars the sensitivity was high enough to ascertain that the modulation phase
apparently varies systematically across the profile, indicating that the
modulation appears as drifting subpulses. We detected brighter than average
individual pulses in several pulsars, with energies up to 2--7 times higher
than the mean, similar to results from normal pulsars. We were sensitive to
giant pulses of a rate of occurrence equal to (and in many instances much lower
than) that of PSR B1937+21 at 1400 MHz (~30 times lower than at 430 MHz), but
none were detected, indicating that the phenomenon is rare in recycled pulsars.Comment: 15 pages, 17 figures, accepted to A&
Effects of Intermittent Emission: Noise Inventory for Scintillating Pulsar B0834+06
We compare signal and noise for observations of the scintillating pulsar
B0834+06, using very-long baseline interferometry and a single-dish
spectrometer. Comparisons between instruments and with models suggest that
amplitude variations of the pulsar strongly affect the amount and distribution
of self-noise. We show that noise follows a quadratic polynomial with flux
density, in spectral observations. Constant coefficients, indicative of
background noise, agree well with expectation; whereas second-order
coefficients, indicative of self-noise, are about 3 times values expected for a
pulsar with constant on-pulse flux density. We show that variations in flux
density during the 10-sec integration account for the discrepancy. In the
secondary spectrum, about 97% of spectral power lies within the pulsar's
typical scintillation bandwidth and timescale; an extended scintillation arc
contains about 3%. For a pulsar with constant on-pulse flux density, noise in
the dynamic spectrum will appear as a uniformly-distributed background in the
secondary spectrum. We find that this uniform noise background contains 95% of
noise in the dynamic spectrum for interferometric observations; but only 35% of
noise in the dynamic spectrum for single-dish observations. Receiver and sky
dominate noise for our interferometric observations, whereas self-noise
dominates for single-dish. We suggest that intermittent emission by the pulsar,
on timescales < 300 microseconds, concentrates self-noise near the origin in
the secondary spectrum, by correlating noise over the dynamic spectrum. We
suggest that intermittency sets fundamental limits on pulsar astrometry or
timing. Accounting of noise may provide means for detection of intermittent
sources, when effects of propagation are unknown or impractical to invert.Comment: 38 pages, 10 figure
The subpulse modulation properties of pulsars at 92 cm and the frequency dependence of subpulse modulation
A large sample of pulsars has been observed to study their subpulse
modulation at an observing wavelength (when achievable) of both 21 and 92 cm
using the Westerbork Synthesis Radio Telescope. In this paper we present the
92-cm data and a comparison is made with the already published 21-cm results.
We analysed 191 pulsars at 92 cm using fluctuation spectra. The sample of
pulsars is as unbiased as possible towards any particular pulsar
characteristics. For 15 pulsars drifting subpulses are discovered for the first
time and 26 of the new drifters found in the 21-cm data are confirmed. We
discovered nulling for 8 sources and 8 pulsars are found to intermittently emit
single pulses that have pulse energies similar to giant pulses. It is estimated
that at least half of the total population of pulsars have drifting subpulses
when observations with a high enough signal-to-noise ratio would be available.
It could well be that the drifting subpulse mechanism is an intrinsic property
of the emission mechanism itself, although for some pulsars it is difficult or
impossible to detect. Drifting subpulses are in general found at both
frequencies, although the chance of detecting drifting subpulses is possibly
slightly higher at 92 cm. It appears that the youngest pulsars have the most
disordered subpulses and the subpulses become more and more organized into
drifting subpulses as the pulsar ages. The correlations with the modulation
indices are argued to be consistent with the picture in which the radio
emission can be divided in a drifting subpulse signal plus a quasi-steady
signal which becomes, on average, stronger at high observing frequencies. The
measured values of P3 at the two frequencies are highly correlated, but there
is no evidence for a correlation with other pulsar parameters.Comment: 30 pages, 10 figures, accepted for publication in A&A, astro-ph
version is missing 191 figures due to file size restrictions. Please download
the appendix from
http://www.astron.nl/~stappers/wiki/doku.php?id=resources:publication
Detection of Giant Pulses from the Pulsar PSR B1112+50
We detected giant pulses from the pulsar PSR B1112+50. A pulse with an
intensity that is a factor of 30 or more higher than the intensity of the
average pulse is encountered approximately once in 150 observed pulses. The
peak .ux density of the strongest pulse is about 180 Jy. This value is a factor
of 80 higher than the peak .ux density of the average pulse. The giant pulses
are narrower than the average prfile approximately by a factor of 5 and they
cluster about the center of the average profile.Comment: 5 pages, 4 figures, to appear in: Pis'ma v Astronomicheskii Zhurnal,
2003, v.29, No.2, p111-115 and will be translated as: Astronomy Letters,
v.29, No.2, p.91-9
Comparative genomics of isolates of a pseudomonas aeruginosa epidemic strain associated with chronic lung infections of cystic fibrosis patients
Pseudomonas aeruginosa is the main cause of fatal chronic lung infections among individuals suffering from cystic fibrosis (CF). During the past 15 years, particularly aggressive strains transmitted among CF patients have been identified, initially in Europe and more recently in Canada. The aim of this study was to generate high-quality genome sequences for 7 isolates of the Liverpool epidemic strain (LES) from the United Kingdom and Canada representing different virulence characteristics in order to: (1) associate comparative genomics results with virulence factor variability and (2) identify genomic and/or phenotypic divergence between the two geographical locations. We performed phenotypic characterization of pyoverdine, pyocyanin, motility, biofilm formation, and proteolytic activity. We also assessed the degree of virulence using the Dictyostelium discoideum amoeba model. Comparative genomics analysis revealed at least one large deletion (40-50 kb) in 6 out of the 7 isolates compared to the reference genome of LESB58. These deletions correspond to prophages, which are known to increase the competitiveness of LESB58 in chronic lung infection. We also identified 308 non-synonymous polymorphisms, of which 28 were associated with virulence determinants and 52 with regulatory proteins. At the phenotypic level, isolates showed extensive variability in production of pyocyanin, pyoverdine, proteases and biofilm as well as in swimming motility, while being predominantly avirulent in the amoeba model. Isolates from the two continents were phylogenetically and phenotypically undistinguishable. Most regulatory mutations were isolate-specific and 29% of them were predicted to have high functional impact. Therefore, polymorphism in regulatory genes is likely to be an important basis for phenotypic diversity among LES isolates, which in turn might contribute to this strain's adaptability to varying conditions in the CF lung
The subpulse modulation properties of pulsars at 21 cm
We present the results of a systematic, unbiased search for subpulse
modulation of 187 pulsars performed with the Westerbork Synthesis Radio
Telescope (WSRT) in the Netherlands at an observing wavelength of 21 cm. Using
new observations and archival WSRT data we have expanded the list of pulsars
which show the drifting subpulse phenomenon by 42, indicating that at least one
in three pulsars exhibits this phenomenon. The real fraction of pulsars which
show the drifting phenomenon is likely to be larger than some 55%. The majority
of the analysed pulsars show subpulse modulation (170), of which the majority
were not previously known to show subpulse modulation and 30 show clear
systematic drifting. The large number of new drifters we have found allows us,
for the first time, to do meaningful statistics on the drifting phenomenon. We
find that the drifting phenomenon is correlated with the pulsar age such that
drifting is more likely to occur in older pulsars. Pulsars which drift more
coherently seem to be older and have a lower modulation index. There is no
significant correlation found between P3 and other pulsar parameters (such as
the pulsar age), as has been reported in the past. There is no significant
preference of drift direction and the drift direction is not found to be
correlated with pulsar parameters. None of the four complexity parameters
predicted by different emission models (Jenet & Gil 2003) are shown to be
inconsistent with the set of modulation indices of our sample of pulsars.
Therefore none of the models can be ruled out based on our observations. We
also present results on some interesting new individual sources like a pulsar
which shows similar subpulse modulation in both the main- and interpulse and
six pulsars with opposite drift senses in different components.Comment: 32 pages, 12 figures, accepted for publication in A&A, astro-ph
version is missing 187 figures due to file size restrictions. Please download
appendices from http://www.science.uva.nl/~wltvrede/21cm.pd