Instruct: Identify the main and secondary category of Arxiv papers based on the titles
Query: Direct measurement of the nonconservative force field generated by
  optical tweezers
33
The categories of this paper are: plasm-ph
10
The categories of this paper are: q-bio
34
The categories of this paper are: chem-ph
2
The categories of this paper are: math
1
The categories of this paper are: cs
21
The categories of this paper are: adap-org
6
The categories of this paper are: astro-ph
8
The categories of this paper are: hep-ex
31
The categories of this paper are: ao-sci
37
The categories of this paper are: supr-con
7
The categories of this paper are: hep-th
30
The categories of this paper are: q-alg
27
The categories of this paper are: comp-gas
9
The categories of this paper are: nlin
25
The categories of this paper are: patt-sol
13
The categories of this paper are: quant-ph