Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: On the Conservation of Cross Helicity and Wave Action in Solar-Wind
  Models with Non-WKB Alfven Wave Reflection   The interaction between Alfven-wave turbulence and the background solar wind
affects the cross helicity in two ways. Non-WKB reflection converts
outward-propagating Alfven waves into inward-propagating Alfven waves and vice
versa, and the turbulence transfers momentum to the background flow. When both
effects are accounted for, the total cross helicity is conserved. In the
special case that the background density and flow speed are independent of
time, the equations of cross-helicity conservation and total-energy
conservation can be combined to recover a well-known equation derived by
Heinemann and Olbert that has been interpreted as a non-WKB generalization of
wave-action conservation. This latter equation (in contrast to cross-helicity
and energy conservation) does not hold when the background varies in time.

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The categories of this paper are: math
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The categories of this paper are: econ
19
The categories of this paper are: eess
31
The categories of this paper are: ao-sci
32
The categories of this paper are: atom-ph
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The categories of this paper are: dg-ga
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The categories of this paper are: cond-mat
10
The categories of this paper are: q-bio
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The categories of this paper are: cs
36
The categories of this paper are: cmp-lg
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The categories of this paper are: hep-th
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The categories of this paper are: q-fin
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The categories of this paper are: stat
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The categories of this paper are: hep-ph
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The categories of this paper are: acc-phys
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The categories of this paper are: supr-con