Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Percolation model for a selective response of the resistance of
  composite semiconducting np-systems towards reducing gases   It is shown that a two-component percolation model can explain an
experimentally observed behavior, namely that a network built up by a mixture
of sintered nanocrystalline semiconducting n- and p-grains can exhibit
selective behavior, i.e. respond with a resistance increase when exposed to a
reducing gas A and with a resistance decrease in response to another reducing
gas B. To this end, a simple model is developed based on realistic assumptions
about the reactions on the grain surfaces. The resistance is calculated by
random walk simulations with nn-, pp- and np-bonds between the grains and the
results are found in very good agreement with the experiments. Contrary to
former assumptions, the np-bonds are crucial to obtain this accordance.

3
The categories of this paper are: physics
33
The categories of this paper are: plasm-ph
31
The categories of this paper are: ao-sci
25
The categories of this paper are: patt-sol
21
The categories of this paper are: adap-org
32
The categories of this paper are: atom-ph
29
The categories of this paper are: funct-an
20
The categories of this paper are: acc-phys
37
The categories of this paper are: supr-con
8
The categories of this paper are: hep-ex
30
The categories of this paper are: q-alg
27
The categories of this paper are: comp-gas
18
The categories of this paper are: econ
14
The categories of this paper are: math-ph
34
The categories of this paper are: chem-ph
9
The categories of this paper are: nlin