Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Amplification of waves from a rotating body   In 1971 Zel'dovich predicted that quantum fluctuations and classical waves
reflected from a rotating absorbing cylinder will gain energy and be amplified.
This key conceptual step towards the understanding that black holes may also
amplify quantum fluctuations, has not been verified experimentally due to the
challenging experimental requirements on the cylinder rotation rate that must
be larger than the incoming wave frequency. Here we experimentally demonstrate
that these conditions can be satisfied with acoustic waves. We show that
low-frequency acoustic modes with orbital angular momentum are transmitted
through an absorbing rotating disk and amplified by up to 30% or more when the
disk rotation rate satisfies the Zel'dovich condition. These experiments
address an outstanding problem in fundamental physics and have implications for
future research into the extraction of energy from rotating systems.

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The categories of this paper are: math
31
The categories of this paper are: ao-sci
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The categories of this paper are: hep-ph
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The categories of this paper are: cs
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The categories of this paper are: hep-ex
36
The categories of this paper are: cmp-lg
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The categories of this paper are: stat
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The categories of this paper are: eess
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The categories of this paper are: dg-ga
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The categories of this paper are: atom-ph
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The categories of this paper are: comp-gas
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The categories of this paper are: hep-th
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The categories of this paper are: mtrl-th
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The categories of this paper are: alg-geom
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The categories of this paper are: chao-dyn
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The categories of this paper are: chem-ph