49,730 research outputs found
The variability of the Crab Nebula in radio: No radio counterpart to gamma-ray flares
We present new Jansky Very Large Array (VLA) radio images of the Crab Nebula
at 5.5 GHz, taken at two epochs separated by 6 days about two months after a
gamma-ray flare in 2012 July. We find no significant change in the Crab's radio
emission localized to a region of <2 light-months in radius, either over the
6-day interval between our present observations or between the present
observations and ones from 2001. Any radio counterpart to the flare has a radio
luminosity of <~ times that of the nebula. Comparing our
images to one from 2001, we do however find changes in radio brightness, up to
10% in amplitude, which occur on decade timescales throughout the nebula. The
morphology of the changes is complex suggesting both filamentary and knotty
structures. The variability is stronger, and the timescales likely somewhat
shorter, nearer the centre of the nebula. We further find that even with the
excellent uv~coverage and signal-to-noise of the VLA, deconvolution errors are
much larger than the noise, being up to 1.2% of peak brightness of the nebula
in this particular case.Comment: Accepted to MNRAS; 13 pages, 6 figure
Spin Dependence of Interfacial Reflection Phase Shift at Cu/Co Interface
The spin dependent reflection at the interface is the key element to
understand the spin transport. By completely solving the scattering problem
based on first principles method, we obtained the spin resolved reflectivity
spectra. The comparison of our theoretical results with experiment is good in a
large energy scale from Fermi level to energy above vacuum level. It is found
that interfacial distortion is crucial for understanding the spin dependence of
the phase gain at the CuCo interface. Near the Fermi level, image state
plays an important role to the phase accumulation in the copper film.Comment: 6 papges, 3 figures, accepted by Physical Review
Control spiral wave dynamics using feedback signals from line detectors
We numerically study trajectories of spiral-wave-cores in excitable systems
modulated proportionally to the integral of the activity on the straight line,
several or dozens of equi-spaced measuring points on the straight line, the
double-line and the contour-line. We show the single-line feedback results in
the drift of core center along a straight line being parallel to the detector.
An interesting finding is that the drift location in is a piecewise
linear-increasing function of both the feedback line location and time delay.
Similar trajectory occurs when replacing the feedback line with several or
dozens of equi-spaced measuring points on the straight line. This allows to
move the spiral core to the desired location along a chosen direction by
measuring several or dozens of points. Under the double-line feedback, the
shape of the tip trajectory representing the competition between the first and
second feedback lines is determined by the distance of two lines. Various drift
attractors in spiral wave controlled by square-shaped contour-line feedback are
also investigated. A brief explanation is presented.Comment: 6 pages and 7 figures; Accepted for publication in EPL; Figs.5 and 6
are in JPG forma
Data taking strategy for the phase study in
The study of the relative phase between strong and electromagnetic amplitudes
is of great importance for understanding the dynamics of charmonium decays. The
information of the phase can be obtained model-independently by fitting the
scan data of some special decay channels, one of which is . To find out the optimal data taking strategy for a scan experiment
in the measurement of the phase in , the
minimization process is analyzed from a theoretical point of view. The result
indicates that for one parameter fit, only one data taking point in the
vicinity of a resonance peak is sufficient to acquire the optimal precision.
Numerical results are obtained by fitting simulated scan data. Besides the
results related to the relative phase between strong and electromagnetic
amplitudes, the method is extended to analyze the fits of other resonant
parameters, such as the mass and the total decay width of .Comment: 13 pages, 7 figure
Content-Centric Networking at Internet Scale through The Integration of Name Resolution and Routing
We introduce CCN-RAMP (Routing to Anchors Matching Prefixes), a new approach
to content-centric networking. CCN-RAMP offers all the advantages of the Named
Data Networking (NDN) and Content-Centric Networking (CCNx) but eliminates the
need to either use Pending Interest Tables (PIT) or lookup large Forwarding
Information Bases (FIB) listing name prefixes in order to forward Interests.
CCN-RAMP uses small forwarding tables listing anonymous sources of Interests
and the locations of name prefixes. Such tables are immune to Interest-flooding
attacks and are smaller than the FIBs used to list IP address ranges in the
Internet. We show that no forwarding loops can occur with CCN-RAMP, and that
Interests flow over the same routes that NDN and CCNx would maintain using
large FIBs. The results of simulation experiments comparing NDN with CCN-RAMP
based on ndnSIM show that CCN-RAMP requires forwarding state that is orders of
magnitude smaller than what NDN requires, and attains even better performance
Local Measurement of Current Density by Magneto-Optical Current Reconstruction in Normally and Overpressure Processed Bi-2223 Tapes
Magneto-optical current reconstruction has been used for detailed analysis of
the local critical current density (Jc) variation in monocore Bi-2223 tapes. We
find, even in high quality tapes with bulk transport Jc ~ 40 kA/cm^2 (77K, 0T),
that there exist local regions which possess current densities of more than 200
kA/cm^2. Overpressure processing at 148 bar significantly improved Jc to 48
kA/cm^2 by improving the connectivity. For the overpressure-processed sample we
find that the current distribution is more uniform and that the maximum local
current density at 77 K is increased almost to 300 kA/cm^2.Comment: Presented at Applied Superconductivity Conference, Houston, August
4th -9th, 200
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