Instruct: Identify the main and secondary category of Arxiv papers based on the titles
Query: Critical temperature of MgB$_2$ ultrathin superconducting films: BCS
  model calculations in tight-binding approximation
18
The categories of this paper are: econ
11
The categories of this paper are: hep-lat
20
The categories of this paper are: acc-phys
13
The categories of this paper are: quant-ph
37
The categories of this paper are: supr-con
28
The categories of this paper are: alg-geom
23
The categories of this paper are: solv-int
27
The categories of this paper are: comp-gas
17
The categories of this paper are: q-fin
22
The categories of this paper are: chao-dyn
6
The categories of this paper are: astro-ph
8
The categories of this paper are: hep-ex
36
The categories of this paper are: cmp-lg
9
The categories of this paper are: nlin
2
The categories of this paper are: math
30
The categories of this paper are: q-alg