60 research outputs found
On the energy of charged black holes in generalized dilaton-axion gravity
In this paper we calculate the energy distribution of some charged black
holes in generalized dilaton-axion gravity. The solutions correspond to charged
black holes arising in a Kalb-Ramond-dilaton background and some existing
non-rotating black hole solutions are recovered in special cases. We focus our
study to asymptotically flat and asymptotically non-flat types of solutions and
resort for this purpose to the M{\o}ller prescription. Various aspects of
energy are also analyzed.Comment: LaTe
Towards Canonical Quantum Gravity for G1 Geometries in 2+1 Dimensions with a Lambda--Term
The canonical analysis and subsequent quantization of the (2+1)-dimensional
action of pure gravity plus a cosmological constant term is considered, under
the assumption of the existence of one spacelike Killing vector field. The
proper imposition of the quantum analogues of the two linear (momentum)
constraints reduces an initial collection of state vectors, consisting of all
smooth functionals of the components (and/or their derivatives) of the spatial
metric, to particular scalar smooth functionals. The demand that the
midi-superspace metric (inferred from the kinetic part of the quadratic
(Hamiltonian) constraint) must define on the space of these states an induced
metric whose components are given in terms of the same states, which is made
possible through an appropriate re-normalization assumption, severely reduces
the possible state vectors to three unique (up to general coordinate
transformations) smooth scalar functionals. The quantum analogue of the
Hamiltonian constraint produces a Wheeler-DeWitt equation based on this reduced
manifold of states, which is completely integrated.Comment: Latex 2e source file, 25 pages, no figures, final version (accepted
in CQG
Distribution of Energy-Momentum in a Schwarzschild-Quintessence Space-time Geometry
An analysis of the energy-momentum localization for a four-dimensional\break
Schwarzschild black hole surrounded by quintessence is presented in order to
provide expressions for the distributions of energy and momentum. The
calculations are performed by using the Landau-Lifshitz and Weinberg
energy-momentum complexes. It is shown that all the momenta vanish, while the
expression for the energy depends on the mass of the black hole, the state
parameter and the normalization factor . The special case of
is also studied, and two limiting cases are examined.Comment: 9 page
Energy-Momentum Localization for a Space-Time Geometry Exterior to a Black Hole in the Brane World
In general relativity one of the most fundamental issues consists in defining
a generally acceptable definition for the energy-momentum density. As a
consequence, many coordinate-dependent definitions have been presented, whereby
some of them utilize appropriate energy-momentum complexes. We investigate the
energy-momentum distribution for a metric exterior to a spherically symmetric
black hole in the brane world by applying the Landau-Lifshitz and Weinberg
prescriptions. In both the aforesaid prescriptions, the energy thus obtained
depends on the radial coordinate, the mass of the black hole and a parameter
, while all the momenta are found to be zero. It is shown that for
a special value of the parameter , the Schwarzschild space-time
geometry is recovered. Some particular and limiting cases are also discussed.Comment: 10 pages, sections 1 and 3 slightly modified, references modified and
adde
Gravitational collapse without a remnant
We investigate the gravitational collapse of a spherically symmetric,
inhomogeneous star, which is described by a perfect fluid with heat flow and
satisfies the equation of state or p=C\rho^\ga at its center.
Different from the ordinary process of gravitational collapsing, the energy of
the whole star is emitted into space. And the remaining spacetime is a
Minkowski one at the end of the process.Comment: 9 pages, 9 figures, to appear in Int. J. Theor. Phy
Energy and Momentum Distributions of Kantowski and Sachs Space-time
We use the Einstein, Bergmann-Thomson, Landau-Lifshitz and Papapetrou
energy-momentum complexes to calculate the energy and momentum distributions of
Kantowski and Sachs space-time. We show that the Einstein and Bergmann-Thomson
definitions furnish a consistent result for the energy distribution, but the
definition of Landau-Lifshitz do not agree with them. We show that a signature
switch should affect about everything including energy distribution in the case
of Einstein and Papapetrou prescriptions but not in Bergmann-Thomson and
Landau-Lifshitz prescriptions.Comment: 12 page
Towards Canonical Quantum Gravity for Geometries Admitting Maximally Symmetric Two-dimensional Surfaces
The 3+1 (canonical) decomposition of all geometries admitting two-dimensional
space-like surfaces is exhibited. A proposal consisting of a specific
re-normalization {\bf Assumption} and an accompanying {\bf Requirement} is put
forward, which enables the canonical quantization of these geometries. The
resulting Wheeler-deWitt equation is based on a re-normalized manifold
parameterized by three smooth scalar functionals. The entire space of solutions
to this equation is analytically given, exploiting the freedom left by the
imposition of the {\bf Requirement} and contained in the third functional.Comment: 27 pages, no figures, LaTex2e source fil
The Energy of Regular Black Hole in General Relativity Coupled to Nonlinear Electrodynamics
According to the Einstein, Weinberg, and M{\o}ller energy-momentum complexes,
we evaluate the energy distribution of the singularity-free solution of the
Einstein field equations coupled to a suitable nonlinear electrodynamics
suggested by Ay\'{o}n-Beato and Garc\'{i}a. The results show that the energy
associated with the definitions of Einstein and Weinberg are the same, but
M{\o}ller not. Using the power series expansion, we find out that the first two
terms in the expression are the same as the energy distributions of the
Reissner-Nordstr\"{o}m solution, and the third term could be used to survey the
factualness between numerous solutions of the Einstein field eqautions coupled
to a nonlinear electrodynamics.Comment: 11 page
Evolution of Game Controllers: Toward the Support of Gamers with Physical Disabilities
Video games, as an entertaining media, dates back to the \u201850s and their hardware device underwent a long evolution starting from hand-made devices such as the \u201ccathode-ray tube amusement device\u201d up to the modern mass-produced consoles. This evolution has, of course, been accompanied by increasingly specialized interaction mechanisms. As of today, interaction with games is usually performed through industry-standard devices. These devices can be either general purpose (e.g., mouse and keyboard) or specific for gaming (e.g., a gamepad). Unfortunately, for marketing reasons, gaming interaction devices are not usually designed taking into consideration the requirements of gamers with physical disabilities. In this paper, we will offer a review of the evolution of gaming control devices with a specific attention to their use by players with physical disabilities in the upper limbs. After discussing the functionalities introduced by controllers designed for disabled players we will also propose an innovative game controller device. The proposed game controller is built around a touch screen interface which can be configured based on the user needs and will be accessible by gamers which are missing fingers or are lacking control in hands movement
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