820 research outputs found
Frequency-domain algorithm for the Lorenz-gauge gravitational self-force
State-of-the-art computations of the gravitational self-force (GSF) on
massive particles in black hole spacetimes involve numerical evolution of the
metric perturbation equations in the time-domain, which is computationally very
costly. We present here a new strategy, based on a frequency-domain treatment
of the perturbation equations, which offers considerable computational saving.
The essential ingredients of our method are (i) a Fourier-harmonic
decomposition of the Lorenz-gauge metric perturbation equations and a numerical
solution of the resulting coupled set of ordinary equations with suitable
boundary conditions; (ii) a generalized version of the method of extended
homogeneous solutions [Phys. Rev. D {\bf 78}, 084021 (2008)] used to circumvent
the Gibbs phenomenon that would otherwise hamper the convergence of the Fourier
mode-sum at the particle's location; and (iii) standard mode-sum
regularization, which finally yields the physical GSF as a sum over regularized
modal contributions. We present a working code that implements this strategy to
calculate the Lorenz-gauge GSF along eccentric geodesic orbits around a
Schwarzschild black hole. The code is far more efficient than existing
time-domain methods; the gain in computation speed (at a given precision) is
about an order of magnitude at an eccentricity of 0.2, and up to three orders
of magnitude for circular or nearly circular orbits. This increased efficiency
was crucial in enabling the recently reported calculation of the long-term
orbital evolution of an extreme mass ratio inspiral [Phys. Rev. D {\bf 85},
061501(R) (2012)]. Here we provide full technical details of our method to
complement the above report.Comment: 27 pages, 4 figure
Numerical computation of the EOB potential q using self-force results
The effective-one-body theory (EOB) describes the conservative dynamics of
compact binary systems in terms of an effective Hamiltonian approach. The
Hamiltonian for moderately eccentric motion of two non-spinning compact objects
in the extreme mass-ratio limit is given in terms of three potentials: . By generalizing the first law of mechanics for
(non-spinning) black hole binaries to eccentric orbits, [\prd{\bf92}, 084021
(2015)] recently obtained new expressions for and in terms
of quantities that can be readily computed using the gravitational self-force
approach. Using these expressions we present a new computation of the EOB
potential by combining results from two independent numerical self-force
codes. We determine for inverse binary separations in the range . Our computation thus provides the first-ever strong-field
results for . We also obtain in our entire domain to a
fractional accuracy of . We find to our results are compatible
with the known post-Newtonian expansions for and in the
weak field, and agree with previous (less accurate) numerical results for
in the strong field.Comment: 4 figures, numerical data at the end. Fixed the typos, added the
journal referenc
Efficient hardware implementations of low bit depth motion estimation algorithms
In this paper, we present efficient hardware implementation of multiplication free one-bit transform (MF1BT) based and constraint one-bit transform (C-1BT) based motion estimation (ME) algorithms, in order to provide low bit-depth representation based full search block ME hardware for real-time video encoding. We used a source pixel based linear array (SPBLA) hardware architecture for low bit depth ME for the first time in the literature. The proposed SPBLA based implementation results in a genuine data flow scheme which significantly reduces the number of data reads from the current block memory, which in turn reduces the power consumption by at least 50% compared to conventional 1BT based ME hardware architecture presented in the literature. Because of the binary nature of low bit-depth ME algorithms, their hardware architectures are more efficient than existing 8 bits/pixel representation based ME architectures
Critical phenomena at the threshold of immediate merger in binary black hole systems: the extreme mass ratio case
In numerical simulations of black hole binaries, Pretorius and Khurana
[Class. Quant. Grav. {\bf 24}, S83 (2007)] have observed critical behaviour at
the threshold between scattering and immediate merger. The number of orbits
scales as along any one-parameter family of initial
data such that the threshold is at . Hence they conjecture that in
ultrarelavistic collisions almost all the kinetic energy can be converted into
gravitational waves if the impact parameter is fine-tuned to the threshold. As
a toy model for the binary, they consider the geodesic motion of a test
particle in a Kerr black hole spacetime, where the unstable circular geodesics
play the role of critical solutions, and calculate the critical exponent
. Here, we incorporate radiation reaction into this model using the
self-force approximation. The critical solution now evolves adiabatically along
a sequence of unstable circular geodesic orbits under the effect of the
self-force. We confirm that almost all the initial energy and angular momentum
are radiated on the critical solution. Our calculation suggests that, even for
infinite initial energy, this happens over a finite number of orbits given by
, where is the (small) mass ratio. We derive
expressions for the time spent on the critical solution, number of orbits and
radiated energy as functions of the initial energy and impact parameter.Comment: Version published in PR
To what extent are the mob languages responsible for the rise and success of ethnically based organized crime in the U.S. from late 19th century to early 20th century?
Mob language studies have seen various attempts at explaining the major effect of the
use of this specific language and its contribution to the rise of Mafia in the USA. Different
scholars, writers and researchers have variously emphasized the role of crime subcultures and
their unique vernaculars in the U.S. In this paper, I would like to report on an even more
ambitious claim that the rise organized crime in the U.S. would have not been possible were it
not to the wielding of specific mob languages.
The goal of the paper is to analyze the selection and use of special vocabulary to bind
organized crime members together and avoid the governmental and judiciary control. This
paper aims to show how mob languages developed as fusion languages resulting from the
interaction of English with the experiences of different groups of people at different times.
Crime usually results from socio-economic despair and dissatisfaction. We usually
come across these two factors as an end product of immigrant stories and ostracism of
different ethnic and socio-economic groups within a society. Out of this situation evolves
many things: literature, songs, movies and arts related to this feeling of being the “outcasts”.
However, lack of opportunities, feeling of alienation and despair also result in a tendency
towards crime. When this situation of becoming the “outcast” occurs to any group, the
group’s self-identification changes with its specific circumstances and gives rise to a specific
language and culture that is self-evident in various cultural artifacts related to the group.
When criminal tendencies permeate the group, this development of language and culture
results in the development of a mob language that in return brings about many advantages for
organized crime. As far as my research is concerned, my conclusion is that the creation of
specific mob languages in the organized crime scene of U.S. has greatly shaped the successes
of these criminal organizations
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