136,283 research outputs found
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
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
On effects of regular S=1 dilution of S=1/2 antiferromagnetic Heisenberg chains by a quantum Monte Carlo simulation
The effects of regular S=1 dilution of S=1/2 isotropic antiferromagnetic
chain are investigated by the quantum Monte Carlo loop/cluster algorithm. Our
numerical results show that there are two kinds of ground-state phases which
alternate with the variation of concentration. When the effective spin
of a unit cell is half-integer, the ground state is ferrimagnetic with gapless
energy spectrum and the magnetism becomes weaker with decreasing of the
concentration . While it is integer, a non-magnetic ground state
with gaped spectrum emerges and the gap gradually becomes narrowed as fitted by
a relation of .Comment: 6 pages, 9 figure
Leveraging Friendship Networks for Dynamic Link Prediction in Social Interaction Networks
On-line social networks (OSNs) often contain many different types of
relationships between users. When studying the structure of OSNs such as
Facebook, two of the most commonly studied networks are friendship and
interaction networks. The link prediction problem in friendship networks has
been heavily studied. There has also been prior work on link prediction in
interaction networks, independent of friendship networks. In this paper, we
study the predictive power of combining friendship and interaction networks. We
hypothesize that, by leveraging friendship networks, we can improve the
accuracy of link prediction in interaction networks. We augment several
interaction link prediction algorithms to incorporate friendships and predicted
friendships. From experiments on Facebook data, we find that incorporating
friendships into interaction link prediction algorithms results in higher
accuracy, but incorporating predicted friendships does not when compared to
incorporating current friendships.Comment: To appear in ICWSM 2018. This version corrects some minor errors in
Table 1. MATLAB code available at
https://github.com/IdeasLabUT/Friendship-Interaction-Predictio
Experimental study of contact transition control incorporating joint acceleration feedback
Joint acceleration and velocity feedbacks are incorporated into a classical internal force control of a robot in contact with the environment. This is intended to achieve a robust contact transition and force tracking performance for varying unknown environments, without any need of adjusting the controller parameters, A unified control structure is proposed for free motion, contact transition, and constrained motion in view of the consumption of the initial kinetic energy generated by a nonzero impact velocity. The influence of the velocity and acceleration feedbacks, which are introduced especially for suppressing the transition oscillation, on the postcontact tracking performance is discussed. Extensive experiments are conducted on the third joint of a three-link direct-drive robot to verify the proposed scheme for environments of various stiffnesses, including elastic (sponge), less elastic (cardboard), and hard (steel plate) surfaces. Results are compared with those obtained by the transition control scheme without the acceleration feedback. The ability of the proposed control scheme in resisting the force disturbance during the postcontact period is also experimentally investigated
Designing coupled-resonator optical waveguide delay lines
We address the trade-offs among delay, loss, and bandwidth in the design of coupled-resonator optical waveguide (CROW) delay lines. We begin by showing the convergence of the transfer matrix, tight-binding, and time domain formalisms in the theoretical analysis of CROWs. From the analytical formalisms we obtain simple, analytical expressions for the achievable delay, loss, bandwidth, and a figure of merit to be used to compare delay line performance. We compare CROW delay lines composed of ring resonators, toroid resonators, Fabry-Perot resonators, and photonic crystal defect cavities based on recent experimental results reported in the literature
A time dependent performance model for multihop wireless networks with CBR traffic
In this paper, we develop a performance modeling technique for analyzing the time varying network layer queueing behavior of multihop wireless networks with constant bit rate traffic. Our approach is a hybrid of fluid flow queueing modeling and a time varying connectivity matrix. Network queues are modeled using fluid-flow based differential equation models which are solved using numerical methods, while node mobility is modeled using deterministic or stochastic modeling of adjacency matrix elements. Numerical and simulation experiments show that the new approach can provide reasonably accurate results with significant improvements in the computation time compared to standard simulation tools. © 2010 IEEE
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