25,564 research outputs found
Characterizing Multi-planet Systems with Classical Secular Theory
Classical secular theory can be a powerful tool to describe the qualitative
character of multi-planet systems and offer insight into their histories. The
eigenmodes of the secular behavior, rather than current orbital elements, can
help identify tidal effects, early planet-planet scattering, and dynamical
coupling among the planets, for systems in which mean-motion resonances do not
play a role. Although tidal damping can result in aligned major axes after all
but one eigenmode have damped away, such alignment may simply be fortuitous. An
example of this is 55 Cancri (orbital solution of Fischer et al., 2008) where
multiple eigenmodes remain undamped. Various solutions for 55 Cancri are
compared, showing differing dynamical groupings, with implications for the
coupling of eccentricities and for the partitioning of damping among the
planets. Solutions for orbits that include expectations of past tidal evolution
with observational data, must take into account which eigenmodes should be
damped, rather than expecting particular eccentricities to be near zero.
Classical secular theory is only accurate for low eccentricity values, but
comparison with other results suggests that it can yield useful qualitative
descriptions of behavior even for moderately large eccentricity values, and may
have advantages for revealing underlying physical processes and, as large
numbers of new systems are discovered, for triage to identify where more
comprehensive dynamical studies should have priority.Comment: Published in Celestial Mechanics and Dynamical Astronomy, 25 pages,
10 figure
On the Symmetries of the Edgar-Ludwig Metric
The conformal Killing equations for the most general (non-plane wave)
conformally flat pure radiation field are solved to find the conformal Killing
vectors. As expected fifteen independent conformal Killing vectors exist, but
in general the metric admits no Killing or homothetic vectors. However for
certain special cases a one-dimensional group of homotheties or motions may
exist and in one very special case, overlooked by previous investigators, a
two-dimensional homethety group exists. No higher dimensional groups of motions
or homotheties are admitted by these metrics.Comment: Plain TeX, 7 pages, No figure
Kinetic Signatures and Intermittent Turbulence in the Solar Wind Plasma
A connection between kinetic processes and intermittent turbulence is
observed in the solar wind plasma using measurements from the Wind spacecraft
at 1 AU. In particular, kinetic effects such as temperature anisotropy and
plasma heating are concentrated near coherent structures, such as current
sheets, which are non-uniformly distributed in space. Furthermore, these
coherent structures are preferentially found in plasma unstable to the mirror
and firehose instabilities. The inhomogeneous heating in these regions, which
is present in both the magnetic field parallel and perpendicular temperature
components, results in protons at least 3-4 times hotter than under typical
stable plasma conditions. These results offer a new understanding of kinetic
processes in a turbulent regime, where linear Vlasov theory is not sufficient
to explain the inhomogeneous plasma dynamics operating near non-Gaussian
structures.Comment: 4 pages, 3 figures, submitted to Physical Review Letter
Hyperspherical entanglement entropy
The coefficient of the log term in the entanglement entropy associated with
hyperspherical surfaces in flat space-time is shown to equal the conformal
anomaly by conformally transforming Euclideanised space--time to a sphere and
using already existing formulae for the relevant heat--kernel coefficients
after cyclic factoring. The analytical reason for the result is that the
conformal anomaly on the lune has an extremum at the ordinary sphere limit. A
proof is given. Agreement with a recent evaluation of the coefficient is found.Comment: 7 pages. Final revision. Historical comments amended. Minor remarks
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Meteorological interpretation of Nimbus High Resolution Infrared /HRIR/ data
Nimbus satellite high resolution infrared photographic data analysi
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