Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Self-organized criticality in the Bean state in YBa$_2$Cu$_3$O$_{7-x}$
  thin films   The penetration of magnetic flux into a thin film of YBa$_2$Cu$_3$O$_{7-x}$
is studied when the external field is ramped slowly. In this case the flux
penetrates in bursts or avalanches. The size of these avalanches is distributed
according to a power law with an exponent of $\tau$ = 1.29(2). The additional
observation of finite-size scaling of the avalanche distributions, with an
avalanche dimension D = 1.89(3), gives strong indications towards
self-organized criticality in this system. Furthermore we determine exponents
governing the roughening dynamics of the flux surface using some universal
scaling relations. These exponents are compared to those obtained from a
standard roughening analysis.

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The categories of this paper are: quant-ph
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The categories of this paper are: cmp-lg
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The categories of this paper are: q-alg
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The categories of this paper are: patt-sol
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The categories of this paper are: mtrl-th
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The categories of this paper are: nucl-th
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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: hep-ex
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The categories of this paper are: plasm-ph
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The categories of this paper are: dg-ga
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The categories of this paper are: bayes-an
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The categories of this paper are: physics
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The categories of this paper are: acc-phys
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The categories of this paper are: alg-geom
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The categories of this paper are: chem-ph