86,263 research outputs found
Deviation of light curves of gamma-ray burst pulses from standard forms due to the curvature effect of spherical fireballs or uniform jets
As revealed previously, under the assumption that some pulses of gamma-ray
bursts are produced by shocks in spherical fireballs or uniform jets of large
opening angles, there exists a standard decay form of the profile of pulses
arising from very narrow or suddenly dimming local (or intrinsic) pulses due to
the relativistic curvature effect (the Doppler effect over the spherical shell
surface). Profiles of pulses arising from other local pulses were previously
found to possess a reverse S-feature deviation from the standard decay form. We
show in this paper that, in addition to the standard decay form shown in Qin et
al. (2004), there exists a marginal decay curve associated with a local
function pulse with a mono-color radiation. We employ the sample of
Kocevski et al. (2003) to check this prediction and find that the phenomenon of
the reverse S-feature is common, when compared with both the standard decay
form and the marginal decay curve. We accordingly propose to take the marginal
decay curve (whose function is simple) as a criteria to check if an observed
pulse could be taken as a candidate suffered from the curvature effect. We
introduce two quantities and to describe the mentioned deviations
within and beyond the position of the decay phase, respectively. The
values of and of pulses of the sample are calculated, and the
result suggests that for most of these pulses their corresponding local pulses
might contain a long decay time relative to the time scale of the curvature
effect.Comment: 24 pages, 7 figures, 1 table accepted for publication in MNRA
Study on the spectrum of the injected relativistic protons
About 10TeV gamma-ray emission within 10 pc region from the Galactic Center
had been reported by 4 independent groups. Considering that this TeV gamma-ray
emission is produced via a hadronic model, and the relativistic protons came
from the tidal disruption of stars by massive black holes, we investigate the
spectral nature of the injected relativistic protons required by the hadronic
model. The calculation was carried on the tidal disruption of the different
types of stars and the different propagation mechanisms of protons in the
interstellar medium. Compared with the observation data from HESS, we find for
the best fitting that the power-law index of the spectrum of the injected
protons is about -1.9, when a red giant star is tidally disrupted, and the
effective confinement of protons diffusion mechanism is adopted.Comment: 2 pages, IAU Symposium 25
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
Negative refraction and plano-concave lens focusing in one-dimensional photonic crystals
Negative refraction is demonstrated in one-dimensional (1D) dielectric
photonic crystals (PCs) at microwave frequencies. Focusing by plano-concave
lens made of 1D PC due to negative refraction is also demonstrated. The
frequency-dependent negative refractive indices, calculated from the
experimental data matches very well with those determined from band structure
calculations. The easy fabrication of one-dimensional photonic crystals may
open the door for new applications.Comment: 3 pages and 5 figure
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