118,528 research outputs found
Parameter constraints in a near-equipartition model with multi-frequency \emph{NuSTAR}, \emph{Swift} and \emph{Fermi-LAT} data from 3C 279
Precise spectra of 3C 279 in the 0.5-70 keV range, obtained during two epochs
of
\emph{Swift} and \emph{NuSTAR} observations, are analyzed using a
near-equipartition model. We apply a one-zone leptonic model with a
three-parameter log-parabola electron energy distribution (EED) to fit the
\emph{Swift} and \emph{NuSTAR} X-ray data, as well as simultaneous optical and
\emph{Fermi}-LAT -ray data. The Markov Chain Monte Carlo (MCMC)
technique is used to search the high-dimensional parameter space and evaluate
the uncertainties on model parameters. We show that the two spectra can be
successfully fit in near-equipartition conditions, defined by the ratio of the
energy density of relativistic electrons to magnetic field
being close to unity. In both spectra, the observed X-rays are dominated by
synchrotron-self Compton photons, and the observed rays are dominated
by Compton scattering of external infrared photons from a surrounding dusty
torus.
Model parameters are well constrained. From the low state to the high state,
both the curvature of the log-parabola width parameter and the synchrotron peak
frequency significantly increase. The derived magnetic fields in the two states
are nearly identical (\ G), but the Doppler factor in the high state is
larger than that in the low state (28 versus 18). We derive that
the gamma-ray emission site takes place outside the broad-line region, at
0.1 pc from the black hole, but within the dusty torus. Implications
for 3C 279 as a source of high-energy cosmic-rays are discussed.Comment: accepted by MNRA
Spin-filtered and Spatially Distinguishable Crossed Andreev Reflection in a Silicene-Superconductor Junction
We theoretically investigate the quantum transports in a junction between a
superconductor and a silicene nanoribbon, under the effect of a magnetic
exchange field. We find that for a narrow nanoribbon of silicene, remarkable
crossed Andreev reflection (with a fraction ) can be induced in the
energy window of the elastic cotunneling, by destroying some symmetries of the
system. Since the energy responses of electrons to the exchange field are
opposite for opposite spins, these transport channels can be well spin
polarized. Moreover, due to the helicity conservation of the topological edge
states, these three transport channels are spatially separated in three
different locations of the device, making them experimentally distinguishable.
This crossed Andreev reflection is a nonlocal quantum interference between
opposite edges through evanescent modes. If two superconducting leads with
different phases are connected to two edges of the silicene nanoribbon, the
crossed Andreev reflection can present Josephson type oscillations, with a
maximal fraction .Comment: 8 pages, 7 figure
Quantum molecular dynamics simulations of the thermophysical properties of shocked liquid ammonia for pressures up to 1.3 TPa
We investigate via quantum molecular-dynamics simulations the thermophysical
properties of shocked liquid ammonia up to the pressure 1.3 TPa and temperature
120000 K. The principal Hugoniot is predicted from wide-range equation of
state, which agrees well with available experimental measurements up to 64 GPa.
Our systematic study of the structural properties demonstrates that liquid
ammonia undergoes a gradual phase transition along the Hugoniot. At about 4800
K, the system transforms into a metallic, complex mixture state consisting of
, , ,
N, and H. Furthermore, we discuss the implications for the interiors of Uranus
and Neptune.Comment: 16 pages, 8 figures. arXiv admin note: text overlap with
arXiv:1012.488
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