Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Twisting and buckling: a new undulation mechanism for artificial
  swimmers   We present an artificial swimmer consisting in a long cylinder of ferrogel
which is polarized transversely and in opposite directions at each extremity.
When it is placed on a water film and submitted to a transverse oscillating
magnetic field, this artificial worm undulates and swims. Whereas symmetry
breaking is due to the field gradient, the undulations of the worm result from
a torsional buckling instability as the polarized ends tend to align with the
applied magnetic field. The critical magnetic field above which buckling and
subsequent swimming is observed may be predicted using elasticity equations
including the effect of a magnetic torque. As the length of the worm is varied,
several undulation modes are observed which are in good agreement with the
bending modes of an elastic rod with free ends.

10
The categories of this paper are: q-bio
18
The categories of this paper are: econ
5
The categories of this paper are: gr-qc
0
The categories of this paper are: hep-ph
33
The categories of this paper are: plasm-ph
31
The categories of this paper are: ao-sci
23
The categories of this paper are: solv-int
30
The categories of this paper are: q-alg
29
The categories of this paper are: funct-an
37
The categories of this paper are: supr-con
15
The categories of this paper are: nucl-ex
28
The categories of this paper are: alg-geom
36
The categories of this paper are: cmp-lg
20
The categories of this paper are: acc-phys
12
The categories of this paper are: nucl-th
2
The categories of this paper are: math