Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Hollow carbon spheres as an efficient dopant for enhancing critical
  current density of MgB2 based tapes   A significant enhancement of Jc and Hirr in MgB2 tapes has been achieved by
the in situ powder-in-tube method utilizing hollow carbon spheres (HCS) as
dopants. At 4.2 K, the transport Jc for the 850C sintered samples reached
3.1x10^4, and 1.4x10^4 A/cm^2 at 10 and 12 T, respectively, and were better
than those of optimal nano-SiC doped tapes. Furthermore, the Hirr for doped
sample was raised up to 16.8 T at 10 K due to the carbon substitution effect.
The results demonstrate that HCS is one of the most promising dopants besides
nano-carbon and SiC for the enhancement of current capacity for MgB2 in high
fields.

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The categories of this paper are: chao-dyn
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The categories of this paper are: eess
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The categories of this paper are: chem-ph
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The categories of this paper are: patt-sol
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The categories of this paper are: cs
7
The categories of this paper are: hep-th
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The categories of this paper are: bayes-an
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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: nlin
6
The categories of this paper are: astro-ph
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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: gr-qc
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The categories of this paper are: hep-lat
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The categories of this paper are: funct-an