Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Significantly enhanced critical current densities in MgB2 tapes made by
  a scaleable, nano-carbon addition route   Nanocarbon-doped Fe-sheathed MgB2 tapes with different doping levels were
prepared by the in situ powder-in-tube method. Compared to the undoped tapes,
Jc for all the C-doped samples was enhanced by more than an order of magnitude
in magnetic fields above 9 T. At 4.2 K, the transport Jc for the 5 at% doped
tapes reached 1.85x104 A/cm2 at 10 T and 2.8x103 A/cm2 at 14 T, respectively.
Moreover, the critical temperature for the doped tapes decreased slightly.
Transmission electron microscopy showed a number of intra-granular dislocations
and the dispersed nanoparticles embedded within MgB2 grains induced by the C
doping. The mechanism for the enhancement of flux pinning is also discussed.
These results indicate that powder-in-tube-processed MgB2 tape is very
promising for high-field applications.

6
The categories of this paper are: astro-ph
7
The categories of this paper are: hep-th
37
The categories of this paper are: supr-con
0
The categories of this paper are: hep-ph
11
The categories of this paper are: hep-lat
24
The categories of this paper are: dg-ga
35
The categories of this paper are: mtrl-th
14
The categories of this paper are: math-ph
17
The categories of this paper are: q-fin
1
The categories of this paper are: cs
15
The categories of this paper are: nucl-ex
34
The categories of this paper are: chem-ph
13
The categories of this paper are: quant-ph
27
The categories of this paper are: comp-gas
9
The categories of this paper are: nlin
8
The categories of this paper are: hep-ex