44,457 research outputs found
The Origin of Chaos in the Outer Solar System
Classical analytic theories of the solar system indicate that it is stable,
but numerical integrations suggest that it is chaotic. This disagreement is
resolved by a new analytic theory. The theory shows that the chaos among the
Jovian planets results from the overlap of the components of a mean motion
resonance among Jupiter, Saturn, and Uranus, and provides rough estimates of
the Lyapunov time (10 million years) and the dynamical lifetime of Uranus
(10^{18} years). The Jovian planets must have entered the resonance after all
the gas and most of the planetesimals in the protoplanetary disk were removed.Comment: 19 pages, 3 figures, to appear in Scienc
Symetric Monopoles
We discuss Bogomolny monopoles of arbitrary charge invariant
under various symmetry groups. The analysis is largely in terms of the spectral
curves, the rational maps, and the Nahm equations associated with monopoles. We
consider monopoles invariant under inversion in a plane, monopoles with cyclic
symmetry, and monopoles having the symmetry of a regular solid. We introduce
the notion of a strongly centred monopole and show that the space of such
monopoles is a geodesic submanifold of the monopole moduli space.
By solving Nahm's equations we prove the existence of a tetrahedrally
symmetric monopole of charge and an octahedrally symmetric monopole of
charge , and determine their spectral curves. Using the geodesic
approximation to analyse the scattering of monopoles with cyclic symmetry, we
discover a novel type of non-planar -monopole scattering process
Dynamic weight parameter for the Random Early Detection (RED) in TCP networks
This paper presents the Weighted Random Early Detection (WTRED) strategy for congestion handling in TCP networks. WTRED provides an adjustable weight parameter to increase the sensitivity of the average queue size in RED gateways to the changes in the actual queue size. This modification, over the original RED proposal, helps gateways minimize the mismatch between average and actual queue sizes in router buffers. WTRED is compared with RED and FRED strategies using the NS-2 simulator. The results suggest that WTRED outperforms RED and FRED. Network performance has been measured using throughput, link utilization, packet loss and delay
Coherence measurements on Rydberg wave packets kicked by a half-cycle pulse
A kick from a unipolar half-cycle pulse (HCP) can redistribute population and
shift the relative phase between states in a radial Rydberg wave packet. We
have measured the quantum coherence properties following the kick, and show
that selected coherences can be destroyed by applying an HCP at specific times.
Quantum mechanical simulations show that this is due to redistribution of the
angular momentum in the presence of noise. These results have implications for
the storage and retrieval of quantum information in the wave packet.Comment: 4 pages, 4 figures (5 figure files
Off-Diagonal Long-Range Order, Restricted Gauge Transformations, and Aharonov-Bohm Effect in Conductors
The Hamiltonian describing a conductor surrounding an external magnetic field
contains a nonvanishing vector potential in the volume accessible to the
electrons and nuclei of which the conductor is made. That vector potential
cannot be removed by a gauge transformation. Nevertheless, a macroscopic normal
conductor can experience no Aharonov-Bohm effect. That is proved by assuming
only that a normal conductor lacks off-diagonal long-range order (ODLRO). Then
by restricting the Hilbert space to density matrices which lack ODLRO, it is
possible to introduce a restricted gauge transformation that removes the
interaction of the conductor with the vector potential.Comment: Editing errors are corrected. One was slightly misleadin
Migration of giant planets in planetesimal discs
Planets orbiting a planetesimal circumstellar disc can migrate inward from
their initial positions because of dynamical friction between planets and
planetesimals. The migration rate depends on the disc mass and on its time
evolution. Planets that are embedded in long-lived planetesimal discs, having
total mass of , can migrate inward a large distance and
can survive only if the inner disc is truncated or because of tidal interaction
with the star. In this case the semi-major axis, a, of the planetary orbit is
less than 0.1 AU. Orbits with larger are obtained for smaller value of the
disc mass or for a rapid evolution (depletion) of the disc. This model may
explain several of the orbital features of the giant planets that were
discovered in last years orbiting nearby stars as well as the metallicity
enhancement found in several stars associated with short-period planets.Comment: 21 pages; 6 encapsulated figures. Accepted by MNRA
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