Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The cosmic-ray ground-level enhancements of 29 September 1989 and 20
  January 2005   Enhancements of the comic-ray intensity as observed by detectors on the
ground have been observed 71 times since 1942. They are due to solar energetic
particles accelerated in the regions of solar flares deep in the corona, or in
the shock front of coronal mass ejections (CMEs) in the solar wind. The latter
is the favoured model for the classical gradual ground level enhancement (GLE).
In several papers since the one of McCracken et al. (2008), we pointed out,
however, that some GLEs are too impulsive to be accelerated in the CME shocks.
This hypothesis, together with other properties of GLEs, is demonstrated
graphically in this paper by plotting and comparing the time profiles of GLEs
42 of 29 September 1989 and GLE 69 of 20 January. These two events are
respectively the largest examples of gradual and prompt events.

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The categories of this paper are: alg-geom
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The categories of this paper are: nucl-ex
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The categories of this paper are: eess
2
The categories of this paper are: math
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The categories of this paper are: nucl-th
5
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: stat
10
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: econ
14
The categories of this paper are: math-ph
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The categories of this paper are: comp-gas
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The categories of this paper are: atom-ph
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The categories of this paper are: nlin
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The categories of this paper are: supr-con