Instruct: Identify the main and secondary category of Arxiv papers based on the titles
Query: Efficient spin injection into graphene through a tunnel barrier:
  overcoming the spin conductance mismatch
12
The categories of this paper are: nucl-th
23
The categories of this paper are: solv-int
30
The categories of this paper are: q-alg
17
The categories of this paper are: q-fin
7
The categories of this paper are: hep-th
18
The categories of this paper are: econ
13
The categories of this paper are: quant-ph
8
The categories of this paper are: hep-ex
33
The categories of this paper are: plasm-ph
34
The categories of this paper are: chem-ph
2
The categories of this paper are: math
29
The categories of this paper are: funct-an
27
The categories of this paper are: comp-gas
15
The categories of this paper are: nucl-ex
31
The categories of this paper are: ao-sci
19
The categories of this paper are: eess