Instruct: Identify the main and secondary category of Arxiv papers based on the titles
Query: Sub-meV linewidth in GaN nanowire ensembles: absence of surface excitons
  due to the field-ionization of donors
2
The categories of this paper are: math
1
The categories of this paper are: cs
23
The categories of this paper are: solv-int
9
The categories of this paper are: nlin
32
The categories of this paper are: atom-ph
15
The categories of this paper are: nucl-ex
30
The categories of this paper are: q-alg
26
The categories of this paper are: bayes-an
29
The categories of this paper are: funct-an
25
The categories of this paper are: patt-sol
3
The categories of this paper are: physics
33
The categories of this paper are: plasm-ph
31
The categories of this paper are: ao-sci
37
The categories of this paper are: supr-con
14
The categories of this paper are: math-ph
11
The categories of this paper are: hep-lat