967 research outputs found
Spotting Radio Transients with the help of GPUs
Exploration of the time-domain radio sky has huge potential for advancing our
knowledge of the dynamic universe. Past surveys have discovered large numbers
of pulsars, rotating radio transients and other transient radio phenomena;
however, they have typically relied upon off-line processing to cope with the
high data and processing rate. This paradigm rules out the possibility of
obtaining high-resolution base-band dumps of significant events or of
performing immediate follow-up observations, limiting analysis power to what
can be gleaned from detection data alone. To overcome this limitation,
real-time processing and detection of transient radio events is required. By
exploiting the significant computing power of modern graphics processing units
(GPUs), we are developing a transient-detection pipeline that runs in real-time
on data from the Parkes radio telescope. In this paper we discuss the
algorithms used in our pipeline, the details of their implementation on the GPU
and the challenges posed by the presence of radio frequency interference.Comment: 4 Pages. To appear in the proceedings of ADASS XXI, ed. P.Ballester
and D.Egret, ASP Conf. Serie
Human melanopsin forms a pigment maximally sensitive to blue light (λmax ≈ 479 nm) supporting activation of G(q/11) and G(i/o) signalling cascades.
A subset of mammalian retinal ganglion cells expresses an opsin photopigment (melanopsin, Opn4) and is intrinsically photosensitive. The human retina contains melanopsin, but the literature lacks a direct investigation of its spectral sensitivity or G-protein selectivity. Here, we address this deficit by studying physiological responses driven by human melanopsin under heterologous expression in HEK293 cells. Luminescent reporters for common second messenger systems revealed that light induces a high amplitude increase in intracellular calcium and a modest reduction in cAMP in cells expressing human melanopsin, implying that this pigment is able to drive responses via both G(q) and G(i/o) class G-proteins. Melanopsins from mouse and amphioxus had a similar profile of G-protein coupling in HEK293 cells, but chicken Opn4m and Opn4x pigments exhibited some G(s) activity in addition to a strong G(q)(/11) response. An action spectrum for the calcium response in cells expressing human melanopsin had the predicted form for an opsin : vitamin A1 pigment and peaked at 479 nm. The G-protein selectivity and spectral sensitivity of human melanopsin is similar to that previously described for rodents, supporting the utility of such laboratory animals for developing methods of manipulating this system using light or pharmacological agents
A bright millisecond radio burst of extragalactic origin
Pulsar surveys offer one of the few opportunities to monitor even a small
fraction (~0.00001) of the radio sky for impulsive burst-like events with
millisecond durations. In analysis of archival survey data, we have discovered
a 30-Jy dispersed burst of duration <5 ms located three degrees from the Small
Magellanic Cloud. The burst properties argue against a physical association
with our Galaxy or the Small Magellanic Cloud. Current models for the free
electron content in the Universe imply a distance to the burst of <1 Gpc No
further bursts are seen in 90-hr of additional observations, implying that it
was a singular event such as a supernova or coalescence of relativistic
objects. Hundreds of similar events could occur every day and act as insightful
cosmological probes.Comment: 18 pages, 4 figures. Accepted by Science. Published electronically
via Science Express on September 27, 200
Optical Observations of the Binary Millisecond Pulsars J2145-0750 and J0034-0534
We report on optical observations of the low-mass binary millisecond pulsar
systems J0034-0534 and J2145-0750. A faint (I=23.5) object was found to be
coincident with the timing position of PSR J2145-0750. While a galaxy or
distant main-sequence star cannot be ruled out, its magnitude is consistent
with an ancient white dwarf, as expected from evolutionary models. For PSR
J0034-0534 no objects were detected to a limiting magnitude of R=25.0,
suggesting that the white dwarf in this system is cold. Using white dwarf
cooling models, the limit on the magnitude of the PSR J0034-0534 companion
suggests that at birth the pulsar in this system may have rotated with a period
as short as 0.6 ms. These observations provide further evidence that the
magnetic fields of millisecond pulsars do not decay on time scales shorter than
1 Gyr.Comment: 6 pages, uuencoded, gz -9 compressed postscript, accepted by ApJ
Armed Conflicts and International Security: A factual and analytical review
There can be no doubt about the dominance of conflict as a concern in modern security analysis and policy. Localized and active conflicts have attracted proportionately much greater attention since the ending of the East-West Cold War and, with it, of the essentially static military confrontation in Europe that had carried the potential for global annihilation. They produce more shock and shame, as well as concern, in the onlooker because they appear as exceptions to the trend of stabilization in inter-state and inter-regional relations since 1990 and as a reversion to “pre-modern” methods of behaving in the global society. They carry more complicated material implications for non-combatant states because of the generally increasing interdependence and “globalization” of the world economy
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