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Yi Liao Shao-Lan BiNational Astronomical Observatories Yunnan Observatory Kunming 《中国天文和天体物理学报》2004,4(5):490-498
Correction of non-ideal effect due to a magnetic fluctuating tensor is derived from the ideal MHD equations. The inclusion of a magnetic turbulent field leads to modifications of the hydrostatic equilibrium equation and thermodynamical variables such as the temperature T, the adiabatic exponent γ, the adiabatic temperature gradient △↓ad and the temperature gradient △↓. In particular, the modifications in the adiabatic and radiative temperature gradients will result in a change in the Schwarzchild criterion, hence in the location of the base of the convective zone. Incorporating the modifications, we construct a modified thermodynamical equilibrium structure of the Sun. 相似文献
74.
J. C. B. Papaloizou 《Celestial Mechanics and Dynamical Astronomy》2005,91(1-2):33-57
We study and review disk protoplanet interactions using local shearing box simulations. These suffer the disadvantage of having
potential artefacts arising from periodic boundary conditions but the advantage, when compared to global simulations, of being
able to capture much of the dynamics close to the protoplanet at high resolution for low computational cost. Cases with and
without self sustained MHD turbulence are considered. The conditions for gap formation and the transition from type I migration
are investigated and found to depend on whether the single parameter M
p
R
3/(M*
H
3), with M
p, M*, R, and H being the protoplanet mass, the central mass, the orbital radius and the disk semi-thickness, respectively, exceeds a number
of order unity. We also investigate the coorbital torques experienced by a moving protoplanet in an inviscid disk. This is
done by demonstrating the equivalence of the problem for a moving protoplanet to one where the protoplanet is in a fixed orbit
which the disk material flows through radially as a result of the action of an appropriate external torque. For sustainable
coorbital torques to be realized a quasi steady state must be realized in which the planet migrates through the disk without
accreting significant mass. In that case, although there is sensitivity to computational parameters, in agreement with earlier
work by Masset and Papaloizou [2003, ApJ, 588, 494] based on global simulations, the coorbital torques are proportional to
the migration speed and result in a positive feedback on the migration, enhancing it and potentially leading to a runaway.
This could lead to fast migration for protoplanets in the Saturn mass range in massive disks and may be relevant to the mass
period correlation for extrasolar planets which gives a preponderance of sub Jovian masses at short orbital periods. 相似文献
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Alejandra Kandus 《Monthly notices of the Royal Astronomical Society》2007,378(4):1356-1364
We study semi-analytically and in a consistent manner the generation of a mean velocity field by helical magnetohydrodynamical (MHD) turbulence, and the effect that this field can have on a mean field dynamo. Assuming a prescribed, maximally helical small-scale velocity field, we show that large-scale flows can be generated in MHD turbulent flows via small-scale Lorentz force. These flows back-react on the mean electromotive force of a mean field dynamo through new terms, leaving the original α and β terms explicitly unmodified. Cross-helicity plays the key role in interconnecting all the effects. In the minimal τ closure that we chose to work with, the effects are stronger for large relaxation times. 相似文献
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