Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Retardation turns the van der Waals attraction into Casimir repulsion
  already at 3 nm   Casimir forces between surfaces immersed in bromobenzene have recently been
measured by Munday et al. Attractive Casimir forces were found between gold
surfaces. The forces were repulsive between gold and silica surfaces. We show
the repulsion is due to retardation effects. The van der Waals interaction is
attractive at all separations. The retardation driven repulsion sets in already
at around 3 nm. To our knowledge retardation effects have never been found at
such a small distance before. Retardation effects are usually associated with
large distances.

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The categories of this paper are: nucl-th
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The categories of this paper are: q-bio
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The categories of this paper are: econ
36
The categories of this paper are: cmp-lg
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The categories of this paper are: atom-ph
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The categories of this paper are: q-fin
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The categories of this paper are: supr-con
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The categories of this paper are: hep-th
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The categories of this paper are: dg-ga
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The categories of this paper are: patt-sol
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The categories of this paper are: solv-int
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The categories of this paper are: ao-sci
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The categories of this paper are: nucl-ex
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The categories of this paper are: gr-qc
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The categories of this paper are: comp-gas
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The categories of this paper are: astro-ph