Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Preliminary Investigation of the Frictional Response of Reptilian Shed
  Skin   Developing deterministic surfaces relies on controlling the structure of the
rubbing interface so that not only the surface is of optimized topography, but
also is able to self-adjust its tribological behaviour according to the
evolution of sliding conditions. In seeking inspirations for such designs, many
engineers are turning toward the biological world to correlate surface
structure to functional behavior of bio-analogues. From a tribological point of
view, squamate reptiles offer diverse examples where surface texturing,
submicron and nano-scale features, achieve frictional regulation. In this
paper, we study the frictional response of shed skin obtained from a snake
(Python regius). The study employed a specially designed tribo-acoustic probe
capable of measuring the coefficient of friction and detecting the acoustical
behavior of the skin in vivo. The results confirm the anisotropy of the
frictional response of snakes. The coefficient of friction depends on the
direction of sliding: the value in forward motion is lower than that in the
backward direction. In addition it is shown that the anisotropy of the
frictional response may stem from profile asymmetry of the individual fibril
structures present within the ventral scales of the reptile

6
The categories of this paper are: astro-ph
2
The categories of this paper are: math
28
The categories of this paper are: alg-geom
33
The categories of this paper are: plasm-ph
20
The categories of this paper are: acc-phys
1
The categories of this paper are: cs
34
The categories of this paper are: chem-ph
16
The categories of this paper are: stat
7
The categories of this paper are: hep-th
30
The categories of this paper are: q-alg
12
The categories of this paper are: nucl-th
10
The categories of this paper are: q-bio
25
The categories of this paper are: patt-sol
13
The categories of this paper are: quant-ph
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The categories of this paper are: nlin
0
The categories of this paper are: hep-ph