Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Geometrical Resonance Conditions for THz Radiation from the Intrinsic
  Josephson Junctions in Bi2Sr2CaCu2O8+d   Subterahertz radiation emitted from a variety of short rectangular-, square-,
and disk-shaped mesas of intrinsic Josephson junctions fabricated from a
Bi2Sr2CaCu2O8+d single crystal was studied from the observed I-V
characteristics, far-infrared spectra, and spatial radiation patterns. In all
cases, the radiation frequency satisfies the conditions both for the ac
Josephson effect and for a mesa cavity resonance mode. The integer higher
harmonics observed in all spectra imply that the ac Josephson effect plays the
dominant role in the novel dual-source radiation mechanism.

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The categories of this paper are: patt-sol
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The categories of this paper are: supr-con
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The categories of this paper are: mtrl-th
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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: math-ph
11
The categories of this paper are: hep-lat
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The categories of this paper are: q-bio
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The categories of this paper are: ao-sci
3
The categories of this paper are: physics
12
The categories of this paper are: nucl-th
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The categories of this paper are: econ
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The categories of this paper are: chao-dyn
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The categories of this paper are: hep-th
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The categories of this paper are: gr-qc