Instruct: Identify the main and secondary category of Arxiv papers based on the titles
Query: Effective unidirectional pumping for steady-state amplification without
  inversion
9
The categories of this paper are: nlin
25
The categories of this paper are: patt-sol
28
The categories of this paper are: alg-geom
33
The categories of this paper are: plasm-ph
16
The categories of this paper are: stat
19
The categories of this paper are: eess
10
The categories of this paper are: q-bio
4
The categories of this paper are: cond-mat
37
The categories of this paper are: supr-con
30
The categories of this paper are: q-alg
22
The categories of this paper are: chao-dyn
34
The categories of this paper are: chem-ph
26
The categories of this paper are: bayes-an
31
The categories of this paper are: ao-sci
17
The categories of this paper are: q-fin
11
The categories of this paper are: hep-lat