Instruct: Identify the main and secondary category of Arxiv papers based on the titles
Query: Nonlinear effects in microwave photoconductivity of two-dimensional
  electron systems
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
32
The categories of this paper are: atom-ph
22
The categories of this paper are: chao-dyn
1
The categories of this paper are: cs
34
The categories of this paper are: chem-ph
37
The categories of this paper are: supr-con
33
The categories of this paper are: plasm-ph
0
The categories of this paper are: hep-ph
18
The categories of this paper are: econ
28
The categories of this paper are: alg-geom
3
The categories of this paper are: physics
35
The categories of this paper are: mtrl-th
24
The categories of this paper are: dg-ga
29
The categories of this paper are: funct-an