Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Column Density Distribution of the Lyman-Alpha Forest: A Measure of
  Small Scale Power   Absorption lines in the Lyman-alpha forest can be thought of as peaks in
neutral hydrogen density along lines of sight. The column density distribution
(the number density of absorption lines as a function of column density) is
then a statistic of density peaks, which contains information about the
underlying power spectrum. In particular, we show that the slope of the
distribution provides a measure of power on scales smaller than those probed by
studies of present-day large scale structure.

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The categories of this paper are: physics
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The categories of this paper are: q-bio
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The categories of this paper are: math
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The categories of this paper are: cond-mat
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The categories of this paper are: hep-ex
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The categories of this paper are: dg-ga
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The categories of this paper are: cmp-lg
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The categories of this paper are: atom-ph
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The categories of this paper are: funct-an
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The categories of this paper are: econ
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The categories of this paper are: nucl-ex
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The categories of this paper are: gr-qc
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The categories of this paper are: hep-lat
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The categories of this paper are: plasm-ph
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The categories of this paper are: cs
35
The categories of this paper are: mtrl-th