Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Efficient simulations of gas-grain chemistry in interstellar clouds   Chemical reactions on dust grains are of crucial importance in interstellar
chemistry because they produce molecular hydrogen and various organic
molecules. Due to the submicron size of the grains and the low flux, the
surface populations of reactive species are small and strongly fluctuate. Under
these conditions rate equations fail and the master equation is needed for
modeling these reactions. However, the number of equations in the master
equation grows exponentially with the number of reactive species, severely
limiting its feasibility. Here we present a method which dramatically reduces
the number of equations, thus enabling the incorporation of the master equation
in models of interstellar chemistry.

15
The categories of this paper are: nucl-ex
5
The categories of this paper are: gr-qc
18
The categories of this paper are: econ
1
The categories of this paper are: cs
27
The categories of this paper are: comp-gas
7
The categories of this paper are: hep-th
22
The categories of this paper are: chao-dyn
31
The categories of this paper are: ao-sci
28
The categories of this paper are: alg-geom
2
The categories of this paper are: math
36
The categories of this paper are: cmp-lg
26
The categories of this paper are: bayes-an
8
The categories of this paper are: hep-ex
4
The categories of this paper are: cond-mat
9
The categories of this paper are: nlin
12
The categories of this paper are: nucl-th