Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Comment on "Irreversibility and Fluctuation Theorem in Stationary Time
  Series"   In their recent paper [Phys. Rev. Lett. 98, 094101 (2007)], A. Porporato et
al. studied the irreversibility and fluctuation theorem for stationary time
series. In this comment, we point out that the fluctuation theorem is in fact
the trivial outcome of a symmetry operation, and hence its physical contect is
less convincing.

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The categories of this paper are: hep-ex
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The categories of this paper are: nucl-th
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The categories of this paper are: alg-geom
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The categories of this paper are: chem-ph
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The categories of this paper are: math
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The categories of this paper are: q-fin
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The categories of this paper are: q-bio
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The categories of this paper are: plasm-ph
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The categories of this paper are: adap-org
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The categories of this paper are: patt-sol
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The categories of this paper are: acc-phys
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The categories of this paper are: eess
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The categories of this paper are: comp-gas
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The categories of this paper are: gr-qc
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The categories of this paper are: math-ph
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The categories of this paper are: atom-ph