Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Alpha-effect dynamos with zero kinetic helicity   A simple explicit example of a Roberts-type dynamo is given in which the
alpha-effect of mean-field electrodynamics exists in spite of point-wise
vanishing kinetic helicity of the fluid flow. In this way it is shown that
alpha-effect dynamos do not necessarily require non-zero kinetic helicity. A
mean-field theory of Roberts-type dynamos is established within the framework
of the second-order correlation approximation. In addition numerical solutions
of the original dynamo equations are given, that are independent of any
approximation of that kind. Both theory and numerical results demonstrate the
possibility of dynamo action in the absence of kinetic helicity.

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The categories of this paper are: quant-ph
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The categories of this paper are: acc-phys
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The categories of this paper are: nucl-th
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The categories of this paper are: comp-gas
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The categories of this paper are: bayes-an
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The categories of this paper are: funct-an
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The categories of this paper are: plasm-ph
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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: solv-int
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The categories of this paper are: hep-th
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The categories of this paper are: supr-con
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The categories of this paper are: ao-sci
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The categories of this paper are: atom-ph
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The categories of this paper are: cond-mat
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The categories of this paper are: nlin