Instruct: Identify the main and secondary category of Arxiv papers based on the titles
Query: A hybrid model for estimation of pore size from ortho-positronium
  lifetimes in porous materials
30
The categories of this paper are: q-alg
22
The categories of this paper are: chao-dyn
14
The categories of this paper are: math-ph
34
The categories of this paper are: chem-ph
21
The categories of this paper are: adap-org
24
The categories of this paper are: dg-ga
36
The categories of this paper are: cmp-lg
10
The categories of this paper are: q-bio
15
The categories of this paper are: nucl-ex
29
The categories of this paper are: funct-an
3
The categories of this paper are: physics
18
The categories of this paper are: econ
5
The categories of this paper are: gr-qc
2
The categories of this paper are: math
11
The categories of this paper are: hep-lat
16
The categories of this paper are: stat