Instruct: Identify the main and secondary category of Arxiv papers based on the titles
Query: A convective instability mechanism for quasistatic crack branching in a
  hydrogel
22
The categories of this paper are: chao-dyn
5
The categories of this paper are: gr-qc
23
The categories of this paper are: solv-int
24
The categories of this paper are: dg-ga
20
The categories of this paper are: acc-phys
26
The categories of this paper are: bayes-an
15
The categories of this paper are: nucl-ex
34
The categories of this paper are: chem-ph
17
The categories of this paper are: q-fin
11
The categories of this paper are: hep-lat
16
The categories of this paper are: stat
12
The categories of this paper are: nucl-th
33
The categories of this paper are: plasm-ph
30
The categories of this paper are: q-alg
10
The categories of this paper are: q-bio
28
The categories of this paper are: alg-geom