24,375 research outputs found
Effect of lift force on the aerodynamics of dust grains in the protoplanetary disk
We newly introduce lift force into the aerodynamics of dust grains in the
protoplanetary disk. Although many authors have so far investigated the effects
of the drag force, gravitational force and electric force on the dust grains,
the lift force has never been considered as a force exerted on the dust grains
in the gas disk. If the grains are spinning and moving in the fluid, then the
lift force is exerted on them. We show in this paper that the dust grains can
be continuously spinning due to the frequent collisions so that the lift force
continues to be exerted on them, which is valid in a certain parameter space
where the grain size is larger than ~ 1 m and where the distance from the
central star is larger than 1 AU for the minimum mass solar nebula. In
addition, we estimate the effects of the force on the grain motion and obtain
the result that the mean relative velocity between the grains due to the lift
force is comparable to the gas velocity in the Kepler rotational frame when the
Stokes number and lift-drag ratio are both ~ 1. This estimation is performed
under the assumptions of the steady state and the isotropic spin angular
momentum. We also estimate the mean relative velocity when the grains keep
spinning and conclude that the lift force marginally affects the mean relative
velocity in the minimum mass solar nebula. If there is a grain-concentrated
part in the disk, the relative velocity due to the lift force may dominate
there because of high collision rate.Comment: 9 pages, 4 figures. Accepted for publication in Earth, Planets and
Spac
AdS_3/CFT_2 Correspondence and Space-Time N=3 Superconformal Algebra
We study a Wess-Zumino-Witten model with target space AdS_3 x (S^3 x S^3 x
S^1)/Z_2. This allows us to construct space-time N=3 superconformal theories.
By combining left-, and right-moving parts through a GSO and a Z_2 projections,
a new asymmetric (N,\bar{N})=(3,1) model is obtained. It has an extra gauge
(affine) SU(2) symmetry in the target space of the type IIA string. An
associated configuration is realized as slantwise intersecting M5-M2 branes
with a Z_2-fixed plane in the M-theory viewpoint.Comment: 27 pages, 1 figure, final versio
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