1,437 research outputs found
Exact solution for Schwarzschild black hole in radiation gauge
Recently Chen and Zhu propose a true radiation gauge for gravity [Phys. Rev.
D 83, 061501(R) (2011)]. This work presents a general solution for the metric
of Schwarzschild black hole in this radiation gauge
The collapse distance of femtosecond pulses in air
The conventional semi-empirical formula for collapse distance [Phys. Rev.
179, 862 (1969), Prog. Quant. Electr. 4, 35 (1975)] has been widely used in
many applications. However, it is not applicable when the dispersion length is
smaller than or has similar order-of-magnitude as the collapse distance. For
the "enough short" pulses, there exists a threshold for the initial peak power,
with which the collapse distance has a maximum value due to the competition
between the Kerr self-focusing and the group velocity dispersion. New
semi-empirical formulas are obtained for the collapse distance of the pulse
with the initial power being less or larger than the threshold, and they can
match the numerical simulations gracefully
Parallel simulation for the ultra-short laser pulses' propagation in air
A parallel 2D+1 split-step Fourier method with Crank-Nicholson scheme running
on multi-core shared memory architectures is developed to study the propagation
of ultra-short high-intensity laser pulses in air. The parallel method achieves
a near linear speed-up with results for the efficiency of more than 95% on a
24-core machine. This method is of great potential application in studying the
long-distance propagation of the ultra-short high intensity laser pulses
Post-Newtonian dynamics basing on Mathisson-Papapetrou equations with Corinaldesi-Papapetrou condition in Kerr spacetime
We derive the post-Newtonian dynamics for a spinning body with
Corinaldesi-Papapetrou spin supplementary condition in Kerr spacetime. Both the
equations of motion for the center-of-mass of body and the spin evolution are
obtained. For the non-relativistic case, our calculations show that the
magnitude of spin measured in the rest frame of the body's center-of-mass does
not change with time, though the center-of-mass does not move along the
geodesic. Moreover, we find that the effects of the spin-orbit and spin-spin
couplings will be suppressed by the Lorentz factor when the body has a
relativistic velocity.Comment: 11 pages, 0 figur
The weak-field-limit solution for Kerr black hole in radiation gauge
In this work we present the solution for a rotating Kerr black hole in the
weak-field limit under the radiation gauge proposed by Chen and Zhu [Phys. Rev.
D83, 061501(R) (2011)], with which the two physical components of the
gravitational wave can be picked out exactly.Comment: Submitted to Eur. phys. J. Plus; Minor revisio
Post-Minkowskian solution for the small-deflection motion of test particles in Kerr-Newman spacetime
We derive the second-order post-Minkowskian solution for the small-deflection
motion of test particles in the external field of the Kerr-Newman black hole
via an iterative method. The analytical results are exhibited in the coordinate
system constituted by the particles' initial velocity unit vector, impact
vector, and their cross-product. The achieved formulas explicitly give the
dependences of the particles' trajectory and velocity on the time once their
initial position and velocity are specified, and can be applied not only to a
massive particle, but also to a photon as well.Comment: Submitted to Class. Quantum Gra
An Automatic Machine Translation Evaluation Metric Based on Dependency Parsing Model
Most of the syntax-based metrics obtain the similarity by comparing the
sub-structures extracted from the trees of hypothesis and reference. These
sub-structures are defined by human and can't express all the information in
the trees because of the limited length of sub-structures. In addition, the
overlapped parts between these sub-structures are computed repeatedly. To avoid
these problems, we propose a novel automatic evaluation metric based on
dependency parsing model, with no need to define sub-structures by human.
First, we train a dependency parsing model by the reference dependency tree.
Then we generate the hypothesis dependency tree and the corresponding
probability by the dependency parsing model. The quality of the hypothesis can
be judged by this probability. In order to obtain the lexicon similarity, we
also introduce the unigram F-score to the new metric. Experiment results show
that the new metric gets the state-of-the-art performance on system level, and
is comparable with METEOR on sentence level.Comment: 9 page
Second-order time delay by a radially moving Kerr-Newman black hole
We derive the analytical time delay of light propagating in the equatorial
plane and parallel to the velocity of a moving Kerr-Newman black hole up to the
second post-Minkowskian order via integrating the null geodesic equations. The
velocity effects are expressed by a very compact form. We then concentrate on
analyzing the magnitudes of the correctional effects on the second-order
contributions to the delay and discuss their possible detection. Our result in
the first post-Minkowskian approximation is in agreement with Kopeikin and
Sch\"{a}fer's formulation which is based on the retarded Li\'{e}nard-Wiechert
potential
Roto-translational Effects on Deflection of Light and Particle by Moving Kerr Black Hole
Velocity effects in first-order Schwarzschild deflection of light and
particles have been explored in the previous literature. In this paper, we
investigate the roto-translational-motion induced deflection by one moving Kerr
black hole with an arbitrary but constant speed. It is shown that the coupling
between the effects of the rotation and the translational motion always exists
for both light and particles. The contribution of the roto-translational
deflection to the total bending angle is discussed in detail. This ratio takes
upper limit for light and it decreases monotonically with increasing
translational velocity for a massive particle. For a given translational
velocity of black hole, this ratio increases with the particle' velocity. In
addition, the Post-Newtonian dynamics of the photon and particle is also
presented
Gravitational Deflection of Light and Massive Particle by a Moving Kerr-Newman Black Hole
The gravitational deflection of test particles including light, due to a
radially moving Kerr-Newman black hole with an arbitrary constant velocity
being perpendicular to its angular momentum, is investigated. In harmonic
coordinates, we derive the second post-Minkowskian equations of motion for test
particles, and solve them by high-accuracy numerical calculations. We then
concentrate on discussing the kinematical corrections caused by the motion of
the gravitational source to the second-order deflection. The analytical formula
of light deflection angle up to second order by the moving lens is obtained.
For a massive particle moving with a relativistic velocity, there are two
different analytical results for Schwarzschild deflection angle up to second
order reported in the previous works, i.e.,
and
,
where and are the mass of the lens, impact parameter, and the
particle's initial velocity, respectively. Our numerical result is in perfect
agreement with the former. Furthermore, the analytical formula for massive
particle deflection up to second order in the Kerr geometry is achieved.
Finally, the possibilities of detecting the motion effects on the second-order
deflection are also analyzed
- β¦