Instruct: Identify the main and secondary category of Arxiv papers based on the titles
Query: Nonequilibrium free energy, H theorem and self-sustained oscillations
  for Boltzmann-BGK descriptions of semiconductor superlattices
33
The categories of this paper are: plasm-ph
16
The categories of this paper are: stat
0
The categories of this paper are: hep-ph
25
The categories of this paper are: patt-sol
27
The categories of this paper are: comp-gas
28
The categories of this paper are: alg-geom
6
The categories of this paper are: astro-ph
24
The categories of this paper are: dg-ga
3
The categories of this paper are: physics
1
The categories of this paper are: cs
7
The categories of this paper are: hep-th
17
The categories of this paper are: q-fin
30
The categories of this paper are: q-alg
26
The categories of this paper are: bayes-an
20
The categories of this paper are: acc-phys
34
The categories of this paper are: chem-ph