Instruct: Identify the main and secondary category of Arxiv papers based on the titles
Query: Crucial role of side walls for granular surface flows: consequences for
  the rheology
10
The categories of this paper are: q-bio
5
The categories of this paper are: gr-qc
24
The categories of this paper are: dg-ga
8
The categories of this paper are: hep-ex
27
The categories of this paper are: comp-gas
17
The categories of this paper are: q-fin
37
The categories of this paper are: supr-con
22
The categories of this paper are: chao-dyn
34
The categories of this paper are: chem-ph
31
The categories of this paper are: ao-sci
28
The categories of this paper are: alg-geom
16
The categories of this paper are: stat
35
The categories of this paper are: mtrl-th
32
The categories of this paper are: atom-ph
6
The categories of this paper are: astro-ph
11
The categories of this paper are: hep-lat