Instruct: Identify the main and secondary category of Arxiv papers based on the titles
Query: Effect of the cosmological transition to metal-enriched star-formation
  on the hydrogen 21-cm signal
16
The categories of this paper are: stat
4
The categories of this paper are: cond-mat
13
The categories of this paper are: quant-ph
14
The categories of this paper are: math-ph
0
The categories of this paper are: hep-ph
30
The categories of this paper are: q-alg
21
The categories of this paper are: adap-org
37
The categories of this paper are: supr-con
32
The categories of this paper are: atom-ph
3
The categories of this paper are: physics
8
The categories of this paper are: hep-ex
7
The categories of this paper are: hep-th
29
The categories of this paper are: funct-an
31
The categories of this paper are: ao-sci
12
The categories of this paper are: nucl-th
10
The categories of this paper are: q-bio