593 research outputs found
Capture and escape in the elliptic restricted three-body problem
Several families of irregular moons orbit the giant planets. These moons are
thought to have been captured into planetocentric orbits after straying into a
region in which the planet's gravitation dominates solar perturbations (the
Hill sphere). This mechanism requires a source of dissipation, such as
gas-drag, in order to make capture permanent. However, capture by gas-drag
requires that particles remain inside the Hill sphere long enough for
dissipation to be effective. Recently we have proposed that in the circular
restricted three-body problem particles may become caught up in `sticky'
chaotic layers which tends to prolong their sojourn within the planet's Hill
sphere thereby assisting capture. Here we show that this mechanism survives
perturbations due to the ellipticity of the planet's orbit. However, Monte
Carlo simulations indicate that the planet's ability to capture moons decreases
with increasing orbital eccentricity. At the actual Jupiter's orbital
eccentricity, this effects in approximately an order of magnitude lower capture
probability than estimated in the circular model. Eccentricities of planetary
orbits in the Solar System are moderate but this is not necessarily the case
for extrasolar planets which typically have rather eccentric orbits. Therefore,
our findings suggest that these extrasolar planets are unlikely to have
substantial populations of irregular moons.Comment: This is a preprint of an Article accepted for publication in Monthly
Notices of the Royal Astronomical Society, (C) 2004 The Royal Astronomical
Societ
Production of trans-Neptunian binaries through chaos-assisted capture
The recent discovery of binary objects in the Kuiper-belt opens an invaluable
window into past and present conditions in the trans-Neptunian part of the
Solar System. For example, knowledge of how these objects formed can be used to
impose constraints on planetary formation theories. We have recently proposed a
binary-object formation model based on the notion of chaos-assisted capture.
Here we present a more detailed analysis with calculations performed in the
spatial (three-dimensional) three- and four-body Hill approximations. It is
assumed that the potential binary partners are initially following heliocentric
Keplerian orbits and that their relative motion becomes perturbed as these
objects undergo close encounters. First, the mass, velocity, and orbital
element distribu- tions which favour binary formation are identified in the
circular and elliptical Hill limits. We then consider intruder scattering in
the circular Hill four-body problem and find that the chaos-assisted capture
mechanism is consistent with observed, apparently randomly distributed, binary
mutual orbit inclinations. It also predicts asymmetric distributions of
retrograde versus prograde orbits. The time-delay induced by chaos on particle
transport through the Hill sphere is analogous to the formation of a resonance
in a chemical reaction. Implications for binary formation rates are considered
and the 'fine-tuning' problem recently identified by Noll et al. (2007) is also
addressed.Comment: submitted to MNRA
Intrinsic defects in silicon carbide LED as a perspective room temperature single photon source in near infrared
Generation of single photons has been demonstrated in several systems.
However, none of them satisfies all the conditions, e.g. room temperature
functionality, telecom wavelength operation, high efficiency, as required for
practical applications. Here, we report the fabrication of light emitting
diodes (LEDs) based on intrinsic defects in silicon carbide (SiC). To fabricate
our devices we used a standard semiconductor manufacturing technology in
combination with high-energy electron irradiation. The room temperature
electroluminescence (EL) of our LEDs reveals two strong emission bands in
visible and near infrared (NIR), associated with two different intrinsic
defects. As these defects can potentially be generated at a low or even single
defect level, our approach can be used to realize electrically driven single
photon source for quantum telecommunication and information processing
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