124 research outputs found
Higher-dimensional models in gravitational theories of quarticLagrangians
Ten-dimensional models, arising from a gravitational action which includes
terms up to the fourth order in curvature tensor, are discussed. The spacetime
consists of one timelike dimension and two maximally symmetric subspaces,
filled with matter in the form of an anisotropic fluid. Numerical integration
of the cosmological field equations indicates that exponential, as well as
power law, solutions are possible. We carry out a dynamical study of the
results in the H_{ext} - H_{int} plane and confirm the existence of
"attractors" in the evolution of the Universe. Those attracting points
correspond to "extended De Sitter" spacetimes, in which the external space
exhibits inflationary expansion, while the internal one contracts.Comment: LaTeXfile, 22 page
Chaotic motion in multi-black hole spacetimes and holographic screens
We investigate the geodesic motion in dimensional Majumdar-Papapetrou
multi-black hole spacetimes and find that the qualitative features of the D=4
case are shared by the higher dimensional configurations. The motion of
timelike and null particles is chaotic, the phase space being divided into
basins of attraction which are separated by a fractal boundary, with a fractal
dimension . The mapping of the geodesic trajectories on a screen placed in
the asymptotic region is also investigated. We find that the fractal properties
of the phase space induces a fractal structure on the holographic screen, with
a fractal dimension .Comment: 8 pages, 5 figure
Parametric resonant acceleration of particles by gravitational waves
We study the resonant interaction of charged particles with a gravitational
wave propagating in the non-empty interstellar space in the presence of a
uniform magnetic field. It is found that this interaction can be cast in the
form of a parametric resonance problem which, besides the main resonance,
allows for the existence of many secondary ones. Each of them is associated
with a non-zero resonant width, depending on the amplitude of the wave and the
energy density of the interstellar plasma. Numerical estimates of the
particles' energisation and the ensuing damping of the wave are given.Comment: LaTeX file, 16 page
Kinetic description of particle interaction with a gravitational wave
The interaction of charged particles, moving in a uniform magnetic field,
with a plane-polarized gravitational wave is considered using the
Fokker-Planck- Kolmogorov (FPK) approach. By using a stochasticity criterion,
we determine the exact locations in phase space, where resonance overlapping
occurs. We investigate the diffusion of orbits around each primary resonance of
order (m) by deriving general analytical expressions for an effective diffusion
coeficient. A solution to the corresponding diffusion equation (Fokker-Planck
equation) for the static case is found. Numerical integration of the full
equations of motion and subsequent calculation of the diffusion coefficient
verifies the analytical results.Comment: LaTeX file, 15 page
Gravitational Waves from Chaotic Dynamical System
To investigate how chaos affects gravitational waves, we study the
gravitational waves from a spinning test particle moving around a Kerr black
hole, which is a typical chaotic system. To compare the result with those in
non-chaotic dynamical system, we also analyze a spinless test particle, which
orbit can be complicated in the Kerr back ground although the system is
integrable. We estimate the emitted gravitational waves by the multipole
expansion of a gravitational field. We find a striking difference in the energy
spectra of the gravitational waves. The spectrum for a chaotic orbit of a
spinning particle, contains various frequencies, while some characteristic
frequencies appear in the case of a spinless particle.Comment: 8 pages, 13 figures. submitted to PR
Alternative strategies with iodine: fast access to previously inaccessible iodine(III) compounds
Nonâiodinated arenes are easily and selectively converted into (diacetoxyiodo)arenes in a single step under mild conditions using iodine triacetates as reagents. The oxidative step is decoupled from the synthesis of hypervalent iodine(III) reagents which can now be prepared conveniently in a oneâpot synthesis for subsequent reactions without prior purification. The chemistry of iodine triacetates was also expanded to heteroatom ligand exchanges to form novel inorganic hypervalent iodine compounds
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