Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Velocity relaxation of a porous sphere immersed in a viscous
  incompressible fluid   Velocity relaxation of a spherically symmetric polymer, immersed in a viscous
incompressible fluid, and after a sudden small impulse or a sudden twist from a
state of rest, is studied on the basis of the linearized Navier-Stokes
equations with an added Darcy type drag term. Explicit expressions for the
translational and rotational velocity relaxation functions of the polymer and
for the flow pattern of the fluid are derived for a uniform permeable sphere.
Surprisingly, it is found that the added mass vanishes. For fairly large values
of the ratio of sphere radius to the screening length characterizing the
permeability the velocity relaxation functions in the short and intermediate
time regime differ significantly from that of a sphere with no-slip boundary
condition. At long times both relaxation functions show universal power law
behavior.

11
The categories of this paper are: hep-lat
2
The categories of this paper are: math
35
The categories of this paper are: mtrl-th
5
The categories of this paper are: gr-qc
28
The categories of this paper are: alg-geom
21
The categories of this paper are: adap-org
19
The categories of this paper are: eess
12
The categories of this paper are: nucl-th
9
The categories of this paper are: nlin
20
The categories of this paper are: acc-phys
7
The categories of this paper are: hep-th
37
The categories of this paper are: supr-con
34
The categories of this paper are: chem-ph
6
The categories of this paper are: astro-ph
24
The categories of this paper are: dg-ga
31
The categories of this paper are: ao-sci