3,468 research outputs found
Improvement of critical current in MgB2/Fe wires by a ferromagnetic sheath
Transport critical current (Ic) was measured for Fe-sheathed MgB2 round
wires. A critical current density of 5.3 x 10^4 A/cm^2 was obtained at 32K.
Strong magnetic shielding by the iron sheath was observed, resulting in a
decrease in Ic by only 15% in a field of 0.6T at 32K. In addition to shielding,
interaction between the iron sheath and the superconductor resulted in a
constant Ic between 0.2 and 0.6T. This was well beyond the maximum field for
effective shielding of 0.2T. This effect can be used to substantially improve
the field performance of MgB2/Fe wires at fields at least 3 times higher than
the range allowed by mere magnetic shielding by the iron sheath. The dependence
of Ic on the angle between field and current showed that the transport current
does not flow straight across the wire, but meanders between the grains
Effect of carbon nanotube doping on critical current density of MgB2 superconductor
The effect of doping MgB2 with carbon nanotubes on transition temperature,
lattice parameters, critical current density and flux pinning was studied for
MgB2-xCx with x = 0, 0.05, 0.1, 0.2 and 0.3. The carbon substitution for B was
found to enhance Jc in magnetic fields but depress Tc. The depression of Tc,
which is caused by the carbon substitution for B, increases with increasing
doping level, sintering temperature and duration. By controlling the extent of
the substitution and addition of carbon nanotubes we can achieve the optimal
improvement on critical current density and flux pinning in magnetic fields
while maintaining the minimum reduction in Tc. Under these conditions, Jc was
enhanced by two orders of magnitude at 8T and 5K and 7T and 10K. Jc was more
than 10,000A/cm2 at 20K and 4T and 5K and 8.5T, respectively
The -log-convexity of Domb's polynomials
In this paper, we prove the -log-convexity of Domb's polynomials, which
was conjectured by Sun in the study of Ramanujan-Sato type series for powers of
. As a result, we obtain the log-convexity of Domb's numbers. Our proof is
based on the -log-convexity of Narayana polynomials of type and a
criterion for determining -log-convexity of self-reciprocal polynomials.Comment: arXiv admin note: substantial text overlap with arXiv:1308.273
On the -log-convexity conjecture of Sun
In his study of Ramanujan-Sato type series for , Sun introduced a
sequence of polynomials as given by
and he conjectured that the polynomials are -log-convex. By
imitating a result of Liu and Wang on generating new -log-convex sequences
of polynomials from old ones, we obtain a sufficient condition for determining
the -log-convexity of self-reciprocal polynomials. Based on this criterion,
we then give an affirmative answer to Sun's conjecture
Lattice paramenter, lattice disorder and resistivity of carbohydrate doepd MgB2 and their correlation with the transition temperature
The change in the lattice parameters or the lattice disorder is claimed as a
cause of the slight reduction in the transition temperature by carbon doping in
MgB2. In this work, an extensive investigation on the effects of carbohydrate
doping has been carried out. It is found that not only the a-axis but also the
c-axis lattice parameter increases with the sintering temperature. A linear
relation between the unit cell volume and the critical temperature is observed.
Compared with the well known correlation between the lattice strain and the
critical temperature, the X-ray peak broadening itself shows a closer
correlation with the transition temperature. The residual resistivity and the
critical temperature are linearly correlated with each other as well and its
implication is further discussed.Comment: 3 pages. Accepted by Jouranl of nanoscience and Nanotechnology (JNN
Transport critical current of Solenoidal MgB2/Cu Coils Fabricated Using a Wind-Reaction In-situ Technique
In this letter, we report the results of transport Jc of solenoid coils upto
100 turns fabricated with Cu-sheathed MgB2 wires using a wind-reaction in-situ
technique. Despite the low density of single core and some reaction between Mg
and Cu-sheath, our results demonstrate the decrease in transport Jc with
increasing length of MgB2 wires is insignificant. Solenoid coils with diameter
as small as 10 mm can be readily fabricated using a wind-reaction in-situ
technique. The Jc of coils is essentially the same as in the form of straight
wires. A Jc of 133,000 A/cm2 and 125,000 A/cm2 at 4 K and self field has been
achieved for a small coil wound using Cu-sheathed tape and Cu-sheathed wire
respectively. These results indicate that the MgB2 wires have a great potential
for lage scale applicationsComment: 6 pages, 4 figures, 1 tabl
- …