1,096 research outputs found
A Complete Reference of the Analytical Synchrotron External Shock Models of Gamma-Ray Bursts
Gamma-ray bursts are most luminous explosions in the universe. Their ejecta
are believed to move towards Earth with a relativistic speed. The interaction
between this "relativistic jet" and a circum burst medium drives a pair of
(forward and reverse) shocks. The electrons accelerated in these shocks radiate
synchrotron emission to power the broad-band afterglow of GRBs. The external
shock theory is an elegant theory, since it invokes a limit number of model
parameters, and has well predicted spectral and temporal properties. On the
other hand, depending on many factors (e.g. the energy content, ambient density
profile, collimation of the ejecta, forward vs. reverse shock dynamics, and
synchrotron spectral regimes), there is a wide variety of the models. These
models have distinct predictions on the afterglow decaying indices, the
spectral indices, and the relations between them (the so-called "closure
relations"), which have been widely used to interpret the rich multi-wavelength
afterglow observations. This review article provides a complete reference of
all the analytical synchrotron external shock afterglow models by deriving the
temporal and spectral indices of all the models in all spectral regimes,
including some regimes that have not been published before. The review article
is designated to serve as a useful tool for afterglow observers to quickly
identify relevant models to interpret their data. The limitations of the
analytical models are reviewed, with a list of situations summarized when
numerical treatments are needed.Comment: 119 pages, 45 figures, invited review accepted for publication in New
Astronomy Review
Quasi-Periodic Variations in X-ray Emission and Long-Term Radio Observations: Evidence for a Two-Component Jet in Sw J1644+57
The continued observations of Sw J1644+57 in X-ray and radio bands
accumulated a rich data set to study the relativistic jet launched in this
tidal disruption event. The X-ray light curve of Sw J1644+57 from 5-30 days
presents two kinds of quasi-periodic variations: a 200 second quasi-periodic
oscillation (QPO) and a 2.7-day quasi-periodic variation. The latter has been
interpreted by a precessing jet launched near the Bardeen-Petterson radius of a
warped disk. Here we suggest that the 200s QPO could be associated with
a second, narrower jet sweeping the observer line-of-sight periodically, which
is launched from a spinning black hole in the misaligned direction with respect
to the black hole's angular momentum. In addition, we show that this
two-component jet model can interpret the radio light curve of the event,
especially the re-brightening feature starting days after the
trigger. From the data we infer that inner jet may have a Lorentz factor of
and a kinetic energy of , while the outer jet may have a Lorentz factor of
and a kinetic energy of .Comment: 11 pages, 7 figures, accepted for publication in Ap
Effects of vertical shaft geometry on natural ventilation in urban road tunnel fires
A set of burning experiments were conducted to investigate the effect of vertical shaft geometry on natural ventilation in urban road tunnel fires. Results show that using vertical shafts to discharge smoke leads to a boundary layer separation near the right-angle connection of the shaft and the tunnel ceiling. In a low shaft, the turbulent-boundary-layer separation phenomenon causes relatively large-scale vortexes and restricts smoke from being exhausted, resulting in a negative effect on natural ventilation. Replacing the right-angle connection with the bevel-angle connection was proposed to split one separation point into two separation points, to attenuate the negative effect. The detailed characteristics of the separation phenomenon were analysed and the proposition was verified by Large Eddy Simulation. Results show that there are no relatively large-scale vortexes in shafts with bevel-angle connections, resulting in improved natural ventilation effectiveness. For lower shafts, the advantage of using the bevel-angle connection is more significant, and for shafts of the same height, the mass flow rate of smoke discharged by shafts with the bevel-angle connection increases up to 1.5 times of that by shafts with the right-angle connection. For relatively high shafts, it is about 1.2 times
Storage of multiple single-photon pulses emitted from a quantum dot in a solid-state quantum memory
Quantum repeaters are critical components for distributing entanglement over
long distances in presence of unavoidable optical losses during transmission.
Stimulated by Duan-Lukin-Cirac-Zoller protocol, many improved quantum-repeater
protocols based on quantum memories have been proposed, which commonly focus on
the entanglement-distribution rate. Among these protocols, the elimination of
multi-photons (multi-photon-pairs) and the use of multimode quantum memory are
demonstrated to have the ability to greatly improve the
entanglement-distribution rate. Here, we demonstrate the storage of
deterministic single photons emitted from a quantum dot in a
polarization-maintaining solid-state quantum memory; in addition,
multi-temporal-mode memory with , and narrow single-photon pulses
is also demonstrated. Multi-photons are eliminated, and only one photon at most
is contained in each pulse. Moreover, the solid-state properties of both
sub-systems make this configuration more stable and easier to be scalable. Our
work will be helpful in the construction of efficient quantum repeaters based
on all-solid-state devicesComment: Published version, including supplementary materia
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An animal model of SARS produced by infection of Macaca mulatta with SARS coronavirus.
A new SARS animal model was established by inoculating SARS coronavirus (SARS-CoV) into rhesus macaques (Macaca mulatta) through the nasal cavity. Pathological pulmonary changes were successively detected on days 5-60 after virus inoculation. All eight animals showed a transient fever 2-3 days after inoculation. Immunological, molecular biological, and pathological studies support the establishment of this SARS animal model. Firstly, SARS-CoV-specific IgGs were detected in the sera of macaques from 11 to 60 days after inoculation. Secondly, SARS-CoV RNA could be detected in pharyngeal swab samples using nested RT-PCR in all infected animals from 5 days after virus inoculation. Finally, histopathological changes of interstitial pneumonia were found in the lungs during the 60 days after viral inoculation: these changes were less marked at later time points, indicating that an active healing process together with resolution of an acute inflammatory response was taking place in these animals. This animal model should provide insight into the mechanisms of SARS-CoV-related pulmonary disease and greatly facilitate the development of vaccines and therapeutics against SARS
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