25,749 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
Tidal Heating of Extra-Solar Planets
Extra-solar planets close to their host stars have likely undergone
significant tidal evolution since the time of their formation. Tides probably
dominated their orbital evolution once the dust and gas had cleared away, and
as the orbits evolved there was substantial tidal heating within the planets.
The tidal heating history of each planet may have contributed significantly to
the thermal budget that governed the planet's physical properties, including
its radius, which in many cases may be measured by observing transit events.
Typically, tidal heating increases as a planet moves inward toward its star and
then decreases as its orbit circularizes. Here we compute the plausible heating
histories for several planets with measured radii, using the same tidal
parameters for the star and planet that had been shown to reconcile the
eccentricity distribution of close-in planets with other extra-solar planets.
Several planets are discussed, including for example HD 209458 b, which may
have undergone substantial tidal heating during the past billion years, perhaps
enough to explain its large measured radius. Our models also show that GJ 876 d
may have experienced tremendous heating and is probably not a solid, rocky
planet. Theoretical models should include the role of tidal heating, which is
large, but time-varying.Comment: Accepted for publication to Ap
Functional uniformity underlies the common spatial structure of macrofaunal assemblages in intertidal seagrass beds
Bi-layer splitting in overdoped high cuprates
Recent angle-resolved photoemission data for overdoped Bi2212 are explained.
Of the peak-dip-hump structure, the peak corresponds the component
of a hole condensate which appears at . The fluctuating part of this same
condensate produces the hump. The bilayer splitting is large enough to produce
a bonding hole and an electron antibonding quasiparticle Fermi surface. Smaller
bilayer splittings observed in some experiments reflect the interaction of the
peak structure with quasiparticle states near, but not at, the Fermi surface.Comment: 4 pages with 2 figures - published versio
Meteorological interpretation of Nimbus High Resolution Infrared /HRIR/ data
Nimbus satellite high resolution infrared photographic data analysi
Density Matrix Renormalization Group Study of the Spin 1/2 Heisenberg Ladder with Antiferromagnetic Legs and Ferromagnetic Rungs
The ground state and low lying excitation of the spin 1/2 Heisenberg ladder
with antiferromagnetic leg () and ferromagnetic rung () interaction is studied by means of the density matrix renormalization
group method. It is found that the state remains in the Haldane phase even for
small suggesting the continuous transition to the gapless
phase at . The critical behavior for small is studied by
the finite size scaling analysis. The result is consistent with the recent
field theoretical prediction.Comment: 11 pages, revtex, figures upon reques
Distinguishing Among Strong Decay Models
Two competing models for strong hadronic decays, the and
models, are currently in use.
Attempts to rule out one or the other have been hindered by a poor
understanding of final state interactions and by ambiguities in the treatment
of relativistic effects.
In this article we study meson decays in both models, focussing on certain
amplitude ratios for which the relativistic uncertainties largely cancel out
(notably the ratios in and
), and using a Quark Born Formalism to estimate the
final state interactions.
We find that the model is strongly favoured.
In addition, we predict a amplitude ratio of for the decay
.
We also study the parameter-dependence of some individual amplitudes (as
opposed to amplitude ratios), in an attempt to identify a ``best'' version of
the model.Comment: 20 pages, uuencoded postscript file with 7 figures, MIT-CTP-2295;
CMU-HEP94-1
Dissociation cross sections of ground-state and excited charmonia with light mesons in the quark model
We present numerical results for the dissociation cross sections of
ground-state, orbitally- and radially-excited charmonia in collisions with
light mesons. Our results are derived using the nonrelativistic quark model, so
all parameters are determined by fits to the experimental meson spectrum.
Examples of dissociation into both exclusive and inclusive final states are
considered. The dissociation cross sections of several C=(+) charmonia may be
of considerable importance for the study of heavy ion collisions, since these
states are expected to be produced more copiously than the J/psi. The relative
importance of the productions of ground-state and orbitally-excited charmed
mesons in a pion-charmonium collision is demonstrated through the -dependent charmonium dissociation cross sections.Comment: 9 pages, 8 figure
Intermittency and the passive nature of the magnitude of the magnetic field
It is shown that the statistical properties of the magnitude of the magnetic
field in turbulent electrically conducting media resemble, in the inertial
range, those of passive scalars in fully developed three-dimensional fluid
turbulence. This conclusion, suggested by the data from Advanced Composition
Explorer, is supported by a brief analysis of the appropriate
magnetohydrodynamic equations
Within-species relationship of patchiness to both abundance and occupancy, as exemplified by seagrass macrobenthos
Abstract: For the first time, intraspecific relationships between the macroecological metrics patchiness (P) and both abundance (A) and occupancy (O) were investigated in a faunal assemblage. As a companion study to recent work on interspecific P, A and O patterns at the same localities, intraspecific patterns were documented within each of the more dominant invertebrates forming the seagrass macrobenthos of warm–temperate Knysna estuarine bay (South Africa) and of sub-tropical Moreton Bay (Australia). As displayed interspecifically, individual species showed strong A–O patterns (mean scaling coefficient − 0.76 and mean R2 > 0.8). All P–O relations were negative and most (67%) were statistically significant, although weaker (mean R2 0.5) than A–O ones; most P–A ones were also negative but fewer (43%) achieved significance, and were even weaker (mean R2 0.4); 33% of species showed no significant interrelations of either O or A with P. No species showed only a significant P–A relationship. Compared with interspecific P–A–O data from the same assemblages, power–law scaling exponents were equivalent, but R2 values were larger. Larviparous species comprised 70% of the total studied, but 94% of those displaying significant patchiness interrelationships; 5 of the 9 showing no P–A or P–O relationships, however, were also larviparous. At Knysna, though not in Moreton Bay, larviparous species also showed higher levels of occupancy than non-larviparous ones, whilst non-larviparous species showed higher levels of patchiness. Dominant Moreton Bay species, but not those at Knysna, exhibited homogeneously sloped P–O relationships
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