Instruct: Identify the main and secondary category of Arxiv papers based on the titles
Query: Spin entropy as the likely source of enhanced thermopower in $\rm\bf
  Na_xCo_2O_4
22
The categories of this paper are: chao-dyn
3
The categories of this paper are: physics
14
The categories of this paper are: math-ph
0
The categories of this paper are: hep-ph
9
The categories of this paper are: nlin
25
The categories of this paper are: patt-sol
37
The categories of this paper are: supr-con
6
The categories of this paper are: astro-ph
30
The categories of this paper are: q-alg
17
The categories of this paper are: q-fin
33
The categories of this paper are: plasm-ph
1
The categories of this paper are: cs
8
The categories of this paper are: hep-ex
5
The categories of this paper are: gr-qc
26
The categories of this paper are: bayes-an
24
The categories of this paper are: dg-ga