142 research outputs found
Kinesin-II is required for axonal transport of choline acetyltransferase in Drosophila
KLP64D and KLP68D are members of the kinesin-II family of proteins in Drosophila. Immunostaining for KLP68D and ribonucleic acid in situ hybridization for KLP64D demonstrated their preferential expression in cholinergic neurons. KLP68D was also found to accumulate in cholinergic neurons in axonal obstructions caused by the loss of kinesin light chain. Mutations in the KLP64D gene cause uncoordinated sluggish movement and death, and reduce transport of choline acetyltransferase from cell bodies to the synapse. The inviability of KLP64D mutations can be rescued by expression of mammalian KIF3A. Together, these data suggest that kinesin-II is required for the axonal transport of a soluble enzyme, choline acetyltransferase. in a specific subset of neurons in Drosophila. Furthermore, the data lead to the conclusion that the cargo transport requirements of different classes of neurons may lead to upregulation of specific pathways of axonal transport
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
Automatic Speaker Recognition System in Adverse Conditions — Implication of Noise and Reverberation on System Performance
Speaker recognition has been developed and evolved over the past few decades into a supposedly mature technique. Existing methods typically utilize robust features
extracted from clean speech. In real-world applications,
especially security and forensics related ones, reliability of recognition becomes crucial, meanwhile limited speech samples and adverse acoustic conditions, most notably noise and reverberation, impose further complications. This paper is presented from a study into the behavior of typical speaker recognition systems in adverse retrieval phases. Following a brief review, a speaker recognition system was implemented using the MSR Identity Toolbox by Microsoft. Validation tests were carried out with clean speech and the speech contaminated by noise and/or reverberation of varying degrees. The image source method was adopted to take into account real acoustic conditions in the spaces. Statistical relationships between recognition accuracy and signal to noise ratios or reverberation times have therefore been established. Results show noise and
reverberation can, to different extents, degrade the performance of recognition. Both reverberation time and direct to reverberation ratio can affect recognition accuracy. The findings may be used to estimate the accuracy of speaker recognition and further determine the likelihood a particular speaker
A study of strong pulses detected from PSR B0656+14 using Urumqi 25-m radio telescope at 1540MHz
We report on the properties of strong pulses from PSR B0656+14 by analyzing
the data obtained using Urumqi 25-m radio telescope at 1540 MHz from August
2007 to September 2010. In 44 hrs of observational data, a total of 67 pulses
with signal-to-noise ratios above a 5-{\sigma} threshold were detected. The
peak flux densities of these pulses are 58 to 194 times that of the average
profile, and the pulse energies of them are 3 to 68 times that of the average
pulse. These pulses are clustered around phases about 5 degrees ahead of the
peak of the average profile. Comparing with the width of the average profile,
they are relatively narrow, with the full widths at half-maximum range from
0.28 to 1.78 degrees. The distribution of pulse-energies of the pulses follows
a lognormal distribution. These sporadic strong pulses detected from PSR
B0656+14 are different in character from the typical giant pulses, and from its
regular pulses.Comment: 6 pages, 3 figures, Accepted by RA
Investigation of the unique nulling properties of PSR B0818-41
We report on the unique nulling properties of PSR B0818-41, using the GMRT at
325 and 610 MHz. We find following interesting behaviour just before and after
the nulls: (i) The pulsar's intensity does not switch off abruptly at the null,
but fades gradually, taking ~ 10 P1. Just after nulls intensity rises to a
maximum over a short (less than one period) time scale. (ii) While the last
active pulses before nulls are dimmer, the first few active pulses just after
nulls outshine normal ones. This effect is very clear for inner region of
pulsar profile, where mean intensity of last few active pulses just after nulls
is ~ 2.8 times more than that for last active pulses just before nulls. (iii)
There is a significant evolution of shape of the pulsar's profile, around
nulls, especially at beginning of bursts: an enhanced bump of intensity in
inner region, a change in ratio of strengths of the leading and trailing peaks
towards a more symmetric profile, an increase in profile width of about 10%,
and a shift of profile centre towards later longitudes. (iv) Just before nulls,
the apparent drift rate becomes slower, transitioning to an almost phase
stationary drift pattern. Further, when the pulsar comes out of null, the
increased intensity is very often accompanied by what looks like a disturbed
drift rate behaviour, which settles down to the regular drift pattern as the
pulsar intensity returns to normal. Thus, we find some very specific and well
correlated changes in the radio emission properties of PSR B0818-41 when the
emission restarts after a null. These could imply that the phenomenon of
nulling is associated with some kind of a "reset" of the pulsar radio emission
engine. We also present plausible explanations for some of the observed
behaviour, using the Partially Screened Gap model of the inner pulsar
accelerator.Comment: 15 pages, 14 figures, and 4 tables; Trimmed abstract; Full abstract
can be found in PS/PDF version; Accepted for publication in MNRA
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
Statistical properties of giant pulses from the Crab pulsar
We have studied the statistics of giant pulses from the Crab pulsar for the
first time with particular reference to their widths. We have analyzed data
collected during 3.5 hours of observations conducted with the Westerbork
Synthesis Radio Telescope operated in a tied-array mode at a frequency of 1200
MHz. The PuMa pulsar backend provided voltage recording of X and Y linear
polarization states in two conjugate 10 MHz bands. We restricted the time
resolution to 4 microseconds to match the scattering on the interstellar
inhomogeneities. In total about 18000 giant pulses (GP) were detected in full
intensity with a threshold level of 6 sigma. Cumulative probability
distributions (CPD) of giant pulse energies were analyzed for groups of GPs
with different effective widths in the range 4 to 65 microseconds. The CPDs
were found to manifest notable differences for the different GP width groups.
The slope of a power-law fit to the high-energy portion of the CPDs evolves
from -1.7 to -3.2 when going from the shortest to the longest GPs. There are
breaks in the CPD power-law fits indicating flattening at low energies with
indices varying from -1.0 to -1.9 for the short and long GPs respectively. The
GPs with a stronger peak flux density were found to be of shorter duration. We
compare our results with previously published data and discuss the importance
of these peculiarities in the statistical properties of GPs for the heoretical
understanding of the emission mechanism responsible for GP generation.Comment: 5 pages, 2 figures. Accepted by Astronomy and Astrophysic
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