• Title/Summary/Keyword: $J_c$ (B)

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Effect of Annealing Temperature on Superconducting Properties of Charcoal Doped $MgB_2$ (목탄이 첨가된 $MgB_2$의 초전도 성질에 미치는 열처리 온도의 영향)

  • Kim, Nam-Kyu;Tana, Kai Sin;Jun, Byung-Hyuk;Park, Hai-Woong;Joo, Jin-Ho;Kim, Chan-Joong
    • Progress in Superconductivity
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    • v.9 no.1
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    • pp.80-84
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    • 2007

  • Charcoal was used as a carbon source for improving the critical current density of $MgB_2$ and the effect of annealing temperature on the $J_c$ of $MgB_2$ was investigated. The charcoal powder used in this study was $1{\sim}2$ microns in size and was prepared by wet attrition milling. $MgB_2$ bulk samples with a nominal composition of $Mg(B_{0.95}C_{0.05})_2$ were prepared by in situ process of Mg and B powders. The powder mixture was uniaxially compacted into pellets and heat treated at temperatures of $650^{\circ}C\;-\;1000^{\circ}C$ for 30 minutes in flowing Ar gas. It was found that superconducting transition temperature of $Mg(B_{0.95}C_{0.05})_2$ decreased by charcoal additions which indicates the carbon substitution for boron site. $J_c$ of $Mg(B_{0.95}C_{0.05})_2$ was lower than that of the undoped $MgB_2$ at the magnetic fields smaller than 4 Tesla, while it was higher than that of the undoped sample especially at the magnetic field higher than 4 T. High temperature annealing seems to be effective in increasing $J_c$ due to the enhanced carbon diffusion into boron sites.

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Flux Pinning in $MgB_2$ Film with Columnar Grains (기둥형 결정립 구조를 지닌 $MgB_2$ 박막에서 자속고정 현상)

  • Kim, D.H.;Kim, H.Y.;Hwang, T.J.;Lee, S.H.;Seong, W.K.;Kang, W.N.
    • Progress in Superconductivity
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    • v.9 no.2
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    • pp.173-176
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    • 2008

  • [ $MgB_2$ ] films grown by hybrid physical chemical vapor deposition under appropriate growth conditions commonly exhibit columnar grain structure. The grain boundaries between adjacent columnar grains have been reported to be good flux pinning centers. In this work, we measured the angular dependence of critical current density ($J_c$) and observed the enhanced flux pinning when an external magnetic field was aligned parallel to the columnar direction. This $J_c$ was almost comparable to the $J_c$ for intrinsic pinning case up to 1 T at low temperatures, indicating that grain boundary pinning is very effective. At high fields, however, $J_c$ decreased rapidly resulting from the fact that the density of flux pinning centers provided by grain boundaries was outnumbered by the flux density.

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STABILITY OF HOMOMORPHISMS IN BANACH MODULES OVER A C*-ALGEBRA ASSOCIATED WITH A GENERALIZED JENSEN TYPE MAPPING AND APPLICATIONS

  • Lee, Jung Rye
    • Korean Journal of Mathematics
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    • v.22 no.1
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    • pp.91-121
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    • 2014

  • Let X and Y be vector spaces. It is shown that a mapping $f:X{\rightarrow}Y$ satisfies the functional equation ${\ddag}$ $$2df(\frac{x_1+{\sum}_{j=2}^{2d}(-1)^jx_j}{2d})-2df(\frac{x_1+{\sum}_{j=2}^{2d}(-1)^{j+1}x_j}{2d})=2\sum_{j=2}^{2d}(-1)^jf(x_j)$$ if and only if the mapping $f:X{\rightarrow}Y$ is additive, and prove the Cauchy-Rassias stability of the functional equation (${\ddag}$) in Banach modules over a unital $C^*$-algebra, and in Poisson Banach modules over a unital Poisson $C^*$-algebra. Let $\mathcal{A}$ and $\mathcal{B}$ be unital $C^*$-algebras, Poisson $C^*$-algebras, Poisson $JC^*$-algebras or Lie $JC^*$-algebras. As an application, we show that every almost homomorphism $h:\mathcal{A}{\rightarrow}\mathcal{B}$ of $\mathcal{A}$ into $\mathcal{B}$ is a homomorphism when $h(d^nuy)=h(d^nu)h(y)$ or $h(d^nu{\circ}y)=h(d^nu){\circ}h(y)$ for all unitaries $u{\in}\mathcal{A}$, all $y{\in}\mathcal{A}$, and n = 0, 1, 2, ${\cdots}$. Moreover, we prove the Cauchy-Rassias stability of homomorphisms in $C^*$-algebras, Poisson $C^*$-algebras, Poisson $JC^*$-algebras or Lie $JC^*$-algebras, and of Lie $JC^*$-algebra derivations in Lie $JC^*$-algebras.

  • https://doi.org/10.11568/kjm.2014.22.1.91 인용 PDF KSCI

Lorentz Force Density Distribution of a Current Carrying Superconducting Tape in a Perpendicular Magnetic Field

  • Yoo, J.;Kwak, K.;Rhee, J.;Park, C.;Youm, D.;Park, B.J.;Han, Y.H.
    • Progress in Superconductivity and Cryogenics
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    • v.12 no.4
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    • pp.13-16
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    • 2010

  • The Lorentz force distribution of a high $T_c$ superconducting tape with increasing transport currents in magnetic field ($H_a$) was visualized. The external magnetic field was applied normally to the coated conductor tape surface after zero-field cooling, and the transport current ($I_a$) was increased stepwise from 0 to 90 % of the values of the critical current ($I_c$ ($H_a$)) at applied filed, Ha. The field distribution (H(x)) near the sample surface across the tape width (2w) was measured using the scanning Hall probe method. Applying an inversion to the measured field distribution, we obtained the underlying current distribution (J(x)), from which the magnetic induction, B(x) was calculated with Biot-Savart law. Then Lorentz force per unit length was calculated using F(x)=J(x)${\times}$B(x), which appears to be very inhomogeneous along the tape width due to the complicated distributions of J(x) and B(x).

  • https://doi.org/10.9714/psac.2010.12.4.013 인용 PDF KSCI