Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Anomalous attenuation of longitudinal ultrasound in intermediate state
  of high pure type I superconductor   The dependence of the ultrasonic attenuation on the direction of magnetic
field in an intermediate state of the very pure Gallium single crystal, in the
case, when the magnetic field H is perpendicular to the wave vector k at the
temperature T = 0.5 K, is found to be anomalously different from the
dependence, observed at the same temperature and the magnitude of magnetic
field equal to the critical magnetic field H=Hc in a normal state of
superconductor. This new phenomenon can be explained, considering the
anisotropy of the Fermi surface in the very pure Gallium single crystal.

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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: math
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The categories of this paper are: acc-phys
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The categories of this paper are: patt-sol
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The categories of this paper are: quant-ph
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The categories of this paper are: econ
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The categories of this paper are: adap-org
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The categories of this paper are: bayes-an
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The categories of this paper are: alg-geom
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The categories of this paper are: nucl-th
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The categories of this paper are: mtrl-th
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The categories of this paper are: astro-ph
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The categories of this paper are: ao-sci
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The categories of this paper are: plasm-ph
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The categories of this paper are: atom-ph