88,769 research outputs found
Neutron star magnetospheres: the binary pulsar, Crab and magnetars
A number of disparate observational and theoretical pieces of evidence
indicate that, contrary to the conventional wisdom, neutron stars' closed field
lines are populated by dense, hot plasma and may be responsible for producing
some radio and high energy emission. This conclusion is based on eclipse
modeling of the binary pulsar system PSR J0737-3039A/B (Lyutikov & Thompson
2005), a quantitative theory of Crab giant pulses (Lyutikov 2007) and a number
of theoretical works related to production of non-thermal spectra in magnetars
through resonant scattering. In magnetars, dense pair plasma is produced by
twisting magnetic field lines and associated electric fields required to lift
the particles from the surface. In long period pulsars, hot particles on closed
field lines can be efficiently trapped by magnetic mirroring, so that
relatively low supply rate, e.g. due to a drift from open field lines, may
result in high density. In short period pulsars, magnetic mirroring does not
work; large densities may still be expected at the magnetic equator near the
Y-point.Comment: Proceedings, Huangshan meeting "Astrophysics of Compact Objects
Z-graded weak modules and regularity
It is proved that if any Z-graded weak module for vertex operator algebra V
is completely reducible, then V is rational and C_2-cofinite. That is, V is
regular. This gives a natural characterization of regular vertex operator
algebras.Comment: 9 page
A New Approach for Computing the Bandwidth Statistics of Avalanche Photodiodes
A new approach for characterizing the avalanche-buildup-time-limited bandwidth of avalanche photodiodes (APDs) is introduced which relies on the direct knowledge of the statistics of the random response time. The random response time is the actual duration of the APD’s finite buildup-limited random impulse response function. A theory is developed characterizing the probability distribution function (PDF) of the random response time. Recurrence equations are derived and numerically solved to yield the PDF of the random response time. The PDF is then used to compute the mean and the standard deviation of the bandwidth. The dependence of the mean and the standard deviation of the bandwidth on the APD mean gain and the ionization coefficient ratio is investigated. Exact asymptotics of the tail of the PDF of the response time are also developed to aid the computation efficiency. The technique can be readily applied to multiplication models which incorporate dead space and can be extended to cases for which the carrier ionization coefficient is position dependent
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Learning distance to subspace for the nearest subspace methods in high-dimensional data classification
The nearest subspace methods (NSM) are a category of classification methods widely applied to classify high-dimensional data. In this paper, we propose to improve the classification performance of NSM through learning tailored distance metrics from samples to class subspaces. The learned distance metric is termed as ‘learned distance to subspace’ (LD2S). Using LD2S in the classification rule of NSM can make the samples closer to their correct class subspaces while farther away from their wrong class subspaces. In this way, the classification task becomes easier and the classification performance of NSM can be improved. The superior classification performance of using LD2S for NSM is demonstrated on three real-world high-dimensional spectral datasets
Strong converse for the classical capacity of entanglement-breaking and Hadamard channels via a sandwiched Renyi relative entropy
A strong converse theorem for the classical capacity of a quantum channel
states that the probability of correctly decoding a classical message converges
exponentially fast to zero in the limit of many channel uses if the rate of
communication exceeds the classical capacity of the channel. Along with a
corresponding achievability statement for rates below the capacity, such a
strong converse theorem enhances our understanding of the capacity as a very
sharp dividing line between achievable and unachievable rates of communication.
Here, we show that such a strong converse theorem holds for the classical
capacity of all entanglement-breaking channels and all Hadamard channels (the
complementary channels of the former). These results follow by bounding the
success probability in terms of a "sandwiched" Renyi relative entropy, by
showing that this quantity is subadditive for all entanglement-breaking and
Hadamard channels, and by relating this quantity to the Holevo capacity. Prior
results regarding strong converse theorems for particular covariant channels
emerge as a special case of our results.Comment: 33 pages; v4: minor changes throughout, accepted for publication in
Communications in Mathematical Physic
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