13,716 research outputs found
Electron-doped phosphorene: A potential monolayer superconductor
We predict by first-principles calculations that the electron-doped
phosphorene is a potential BCS-like superconductor. The stretching modes at the
Brillouin-zone center are remarkably softened by the electron-doping, which
results in the strong electron-phonon coupling. The superconductivity can be
introduced by a doped electron density () above
cm, and may exist over the liquid helium temperature when cm. The maximum critical temperature is predicted to be
higher than 10 K. The superconductivity of phosphorene will significantly
broaden the applications of this novel material
Cooperative non-orthogonal multiple access in cognitive radio
This letter studies the application of non-orthogonal multiple access to a downlink cognitive radio (termed CR-NOMA) system. A new cooperative transmission scheme is proposed aimed at exploiting the inherent spatial diversity offered by the CR-NOMA system. The closed-form analytical results are developed to show that the cooperative transmission scheme gives better performance when more secondary users participate in relaying, which helps achieve the maximum diversity order at secondary user and a diversity order of two at primary user. The simulations are performed to validate the performance of the proposed scheme and the accuracy of the analytical results
A comprehensive analysis of Fermi Gamma-Ray Burst Data: IV. Spectral lag and Its Relation to Ep Evolution
The spectral evolution and spectral lag behavior of 92 bright pulses from 84
gamma-ray bursts (GRBs) observed by the Fermi GBM telescope are studied. These
pulses can be classified into hard-to-soft pulses (H2S, 64/92),
H2S-dominated-tracking pulses (21/92), and other tracking pulses (7/92). We
focus on the relationship between spectral evolution and spectral lags of H2S
and H2S-dominated-tracking pulses. %in hard-to-soft pulses (H2S, 64/92) and
H2S-dominating-tracking (21/92) pulses. The main trend of spectral evolution
(lag behavior) is estimated with
(), where is the peak photon
energy in the radiation spectrum, is the observer time relative to the
beginning of pulse , and is the spectral lag of photons
with energy with respect to the energy band - keV. For H2S and
H2S-dominated-tracking pulses, a weak correlation between
and is found, where is the pulse width. We also study the spectral
lag behavior with peak time of pulses for 30 well-shaped pulses
and estimate the main trend of the spectral lag behavior with . It is found that is correlated with
. We perform simulations under a phenomenological model of spectral
evolution, and find that these correlations are reproduced. We then conclude
that spectral lags are closely related to spectral evolution within the pulse.
The most natural explanation of these observations is that the emission is from
the electrons in the same fluid unit at an emission site moving away from the
central engine, as expected in the models invoking magnetic dissipation in a
moderately-high- outflow.Comment: 58 pages, 11 figures, 3 tables. ApJ in pres
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