Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Microwave Harmonic Emission in MgB2 Superconductor: Comparison with
  YBaCuO   We report results of microwave second-harmonic generation in ceramic samples
of MgB2, prepared by different methods. The SH signal has been investigated as
a function of the temperature and the static magnetic field. The results are
discussed in the framework of models reported in the literature. We show that
the peculiarities of the SH signal are related to the specific properties of
the sample. A comparison with the results obtained in ceramic and crystalline
YBa(2)Cu(3)O(7) shows that the second-harmonic emission in MgB2 is weaker than
that observed in ceramic YBa(2)Cu(3)O(7).

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The categories of this paper are: quant-ph
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The categories of this paper are: solv-int
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The categories of this paper are: cmp-lg
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The categories of this paper are: q-alg
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The categories of this paper are: bayes-an
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The categories of this paper are: math
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The categories of this paper are: gr-qc
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The categories of this paper are: alg-geom
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The categories of this paper are: hep-th
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The categories of this paper are: math-ph
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The categories of this paper are: dg-ga
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The categories of this paper are: acc-phys
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The categories of this paper are: astro-ph
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The categories of this paper are: stat
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The categories of this paper are: nlin
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The categories of this paper are: econ