Dear Dr. Huang:

The above manuscript has been reviewed by our referee(s).

A critique drawn from the report(s) is enclosed. On this basis, we
judge that the paper is not appropriate for Physical Review Letters,
but might be suitable for publication in another journal, possibly with
some revision. Therefore, we recommend that you submit your manuscript

Sincerely yours,

Rashmi Ray
Assistant to the Editor
Physical Review Letters
Email: [email protected]
Fax: 631-591-4141

Report of Referee A (LB8192 Huang,J)

This manuscript describes numerical method for analysis of the
dynamics of a falling object in viscous fluid.  It is a rather
interesting work, but I think this paper does not satisfy the
specific criteria of the Physical Review Letters, such as
``significantly advance physics''. The work is pure numerical
and is, in essence, a   description of a numerical algorithm.
Detailed comparison with experiment is not present. I would
suggest to submit it to Physical Review E.

Report of Referee B (LB8192 Huang,J)

The manuscript presents analysis of the motion of an ellipse
falling through 2D viscous fluid. Almost the entire paper is
devoted to derivation of equations of motion in the comoving
frame in terms of complex "stream function-vorticity'', which
are subsequently solved numerically.

The paper provides an elegant application of the method of
complex variables to 2D viscous flow.  However, no attempt is
made to interprete the results in physical terms, describing the
flutter and tumble of the body falling in the viscous fluid. The
results do not connect to the experiment, since they are
obtained for an abstract 2D fluid and not applicable to a
physically realizable 2D Hele-Show flow dominated by wall
friction.  While the mathematical analysis has been carried out
competently, the manuscript is better suitable for publication
in an applied mathematics journal rather than in PRL.