18,651 research outputs found
On gravitational wave-Cherenkov radiation from photons when passing through diffused dark matters
Analogy to Cherenkov radiation, when a particle moves faster than the
propagation velocity of gravitational wave in matter (), we
expect gravitational wave-Cherenkov radiation (GWCR). In the situation that a
photon travels across diffuse dark matters, the GWCR condition is always
satisfied, photon will thence loss its energy all the path. This effect is long
been ignored in the practice of astrophysics and cosmology, without
justification with serious calculation. We study this effect for the first
time, and shows that this energy loss time of the photon is far longer than the
Hubble time, therefore justify the practice of ignoring this effect in
astrophysics context.Comment: 3 pages; We add a citation to Caves (1980) to the original journal
version, after kindly reminde
Wigner crystal induced by dipole-dipole interaction in one-dimensional optical lattices
We demonstrate that the static structure factor, momentum distribution and
density distribution provide clear signatures of the emergence of Wigner
crystal for the fermionic dipolar gas with strongly repulsive dipole-dipole
interactions trapped in one-dimensional optical lattices. Our numerical
evidences are based on the exact diagonalization of the microscopic effective
lattice Hamiltonian of few particles interacting with long-range interactions.
As a comparison, we also study the system with only nearest-neighbor
interactions, which displays quite different behaviors from the dipolar system
in the regime of strong repulsion.Comment: 5 pages, 5 figure
DOC: Deep Open Classification of Text Documents
Traditional supervised learning makes the closed-world assumption that the
classes appeared in the test data must have appeared in training. This also
applies to text learning or text classification. As learning is used
increasingly in dynamic open environments where some new/test documents may not
belong to any of the training classes, identifying these novel documents during
classification presents an important problem. This problem is called open-world
classification or open classification. This paper proposes a novel deep
learning based approach. It outperforms existing state-of-the-art techniques
dramatically.Comment: accepted at EMNLP 201
A new approach to the GeV flare of PSR B1259-63/LS2883
PSR B1259-63/LS2883 is a binary system composed of a pulsar and a Be star.
The Be star has an equatorial circumstellar disk (CD). The {\it Fermi}
satellite discovered unexpected gamma-ray flares around 30 days after the last
two periastron passages. The origin of the flares remain puzzling. In this
work, we explore the possibility that, the GeV flares are consequences of
inverse Compton-scattering of soft photons by the pulsar wind. The soft photons
are from an accretion disk around the pulsar, which is composed by the matter
from CD captured by the pulsar's gravity at disk-crossing before the
periastron. At the other disk-crossing after the periastron, the density of the
CD is not high enough so that accretion is prevented by the pulsar wind shock.
This model can reproduce the observed SEDs and light curves satisfactorily.Comment: 14 pages, 8 figures, 1 table. Accepted for publication in Ap
Lifelong Learning CRF for Supervised Aspect Extraction
This paper makes a focused contribution to supervised aspect extraction. It
shows that if the system has performed aspect extraction from many past domains
and retained their results as knowledge, Conditional Random Fields (CRF) can
leverage this knowledge in a lifelong learning manner to extract in a new
domain markedly better than the traditional CRF without using this prior
knowledge. The key innovation is that even after CRF training, the model can
still improve its extraction with experiences in its applications.Comment: Accepted at ACL 2017. arXiv admin note: text overlap with
arXiv:1612.0794
Probing the properties of the pulsar wind via studying the dispersive effects in the pulses from the pulsar companion in a double neutron-star binary system
The velocity and density distribution of in the pulsar wind are
crucial distinction among magnetosphere models, and contains key parameters
determining the high energy emission of pulsar binaries. In this work, a direct
method is proposed, which might probe the properties of the wind from one
pulsar in a double-pulsar binary. When the radio signals from the first-formed
pulsar travel through the relativistic flow in the pulsar wind from the
younger companion, the components of different radio frequencies will be
dispersed. It will introduce an additional frequency-dependent time-of-arrival
delay of pulses, which is function of the orbital phase. In this paper, we
formulate the above-mentioned dispersive delay with the properties of the
pulsar wind. As examples, we apply the formula to the double pulsar system PSR
J0737-3039A/B and the pulsar-neutron star binary PSR B1913+16. For PSR
J0737-3039A/B, the time delay in 300\,MHz is s near the
superior-conjunction, under the optimal pulsar wind parameters, which is
half of the current timing accuracy. For PSR B1913+16, with the assumption that
the neutron star companion has a typical spin down luminosity of
\,ergs/s, the time delay is as large as s in 300\,MHz.
The best timing precision of this pulsar is s in 1400\,MHz.
Therefore, it is possible that we can find this signal in archival data.
Otherwise, we can set an upper-limit on the spin down luminosity. Similar
analysis can be apply to other eleven known pulsar-neutron star binariesComment: 6 pages, 6 figures, accepted for publication in MNRA
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