Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A Proposal to Search for Transparent Hidden Matter Using Optical
  Scintillation   It is proposed to search for scintillation of extragalactic sources through
the last unknown baryonic structures. Appropriate observation of the
scintillation process described here should allow one to detect column density
stochastic variations in cool Galactic molecular clouds of order of $\sim
3\times 10^{-5} \mathrm{g/cm^2}$ -- that is $10^{19} \mathrm{molecules/cm^2}$
-- per $\sim 10 000 \mathrm{km}$ transverse distance.

20
The categories of this paper are: acc-phys
9
The categories of this paper are: nlin
26
The categories of this paper are: bayes-an
35
The categories of this paper are: mtrl-th
13
The categories of this paper are: quant-ph
2
The categories of this paper are: math
34
The categories of this paper are: chem-ph
27
The categories of this paper are: comp-gas
22
The categories of this paper are: chao-dyn
15
The categories of this paper are: nucl-ex
32
The categories of this paper are: atom-ph
7
The categories of this paper are: hep-th
19
The categories of this paper are: eess
3
The categories of this paper are: physics
4
The categories of this paper are: cond-mat
23
The categories of this paper are: solv-int