Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A new, optimized Doppler optical probe for phase detection, bubble
  velocity and size measurements: investigation of a bubble column operated in
  the heterogeneous regime
4
The categories of this paper are: cond-mat
23
The categories of this paper are: solv-int
16
The categories of this paper are: stat
0
The categories of this paper are: hep-ph
6
The categories of this paper are: astro-ph
25
The categories of this paper are: patt-sol
27
The categories of this paper are: comp-gas
17
The categories of this paper are: q-fin
36
The categories of this paper are: cmp-lg
14
The categories of this paper are: math-ph
30
The categories of this paper are: q-alg
26
The categories of this paper are: bayes-an
37
The categories of this paper are: supr-con
24
The categories of this paper are: dg-ga
20
The categories of this paper are: acc-phys
32
The categories of this paper are: atom-ph