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김문석(M. S. Kim),유성초(S. C. Yu),임우영(W. Y. Lim),백종성(J. S. Baek) 한국자기학회 1992 韓國磁氣學會誌 Vol.2 No.3
Magnetic properties of grain aligned high Tc Y₁Ba₂Cu₃O_(7-y) superconductor are inverstigated. Grain-aligned superconductors have magnetic anisotropy in the Cu-O layer like single crystals. The lower critical field H_(c1). measured at the temperature range of 2 K up to 77 K, is found to be decreasing linearly as temperature goes up. Moreover, it decreaes more rapidly when the Cu-O layer is perpendicular to the external magnetic field. The temperature dependence of the magnetic susceptibility shows that the value of magnetic susceptibility, 4n X, is close to -1 at low temperature. The intra grain critical current density Jc, obtained from the Bean's critical state model, is found to be comparable to that of single crystal superconductors.
이규원,김문석,김동호,이상근,Lee K. W,Kim M. S,Kim D. H,Lee S. G 한국초전도학회 2004 Progress in superconductivity Vol.6 No.1
Magnetic $T_{c}$ of composite superconductors has been studied for providing a standard method. Various magnetization-temperature curves of NbTi, $Nb_3$Sn and Bi-2223 wires were measured using a SQUID magnetometer. Magnetization-temperature curve of zero-field-cooled procedure showed larger values than fie Id-cooled procedure. To obtain higher resolution near the onset temperature, we employed a two-field-direction method which measures a magnetization-temperature curve of a specimen first in positive and then negative fields. Analytical comparison of the magnetic $T_{c}$, with the resistive T$_{c}$ was accomplished for three specimens. The magnetic $T_{c}$/ mettled showed more detailed information on superconducting state of a specimen than the resistive$T_{c}$/ method. We have also studied the field dependence of the magnetic $T_{c}$ from 5 Oe to 120 Oe, however, no significant difference on field strength was found in our three specimensns
10의 -10승 수준에서 조셉슨 전압표준기 불확도 평가
김규태,김문석,정연욱,김완섭,송운,Kim, K.T.,Kim, M.S.,Chong, Y.,Kim, W.S.,Song, W. The Korean Superconductivity Society 2007 Progress in superconductivity Vol.9 No.1
The most recent improvement in the 10 V array system was carried out with focusing on noise reduction. We have evaluated the uncertainty of the 10 V Josephson array system after the improvement. The uncertainty evaluation of 10 V standard included a comparison with a programmable Josephson array system at 1 V. Every contribution to the measurement uncertainty was evaluated in the level of $10^{-10}$. The estimated combined uncertainty was found to be approximately $10^{-9}$ at 10 V, which was limited only by the indirect verifying method. In the near future, a direct comparison with another 10 V Josephson voltage standard is expected to be carried out to provide more accurate uncertainty evaluation for the KRISS Josephson voltage standard.
김규태,김문석,정연옥,Kim K.-T.,Kim M.-S.,Chong Y.-W. The Korean Superconductivity Society 2005 Progress in superconductivity Vol.7 No.1
Coupling of non-linear oscillators have long been an interesting problem for physicists. The coupling phenomena have been frequently observed in Josephson junction series array, which have been used for Josephson voltage standard. Interestingly pronounced self-generation effect has been found during recent development of Josephson arrays for programmable Josephson voltage standard. But the coupling effect between the self-generations is not fully understood yet. We present harmonically approximated analytical solutions for coupled self-generations in the Josephson arrays, i.e., Superconductor-Insulator-Normal metal-Insulator-Superconductor (SINIS) array, externally shunted Superconductor-Insulator-Supercondctor (es-SIS) array, Superconductor-Normal metal-Superconductor (SNS) array. We find that the coupling between the self-generated Josephson oscillations through microwave transmission line plays critical role in microwave property of the Josephson array.
자유회전 테일핀을 갖는 미사일에 대한 Roll Lock-in 현상의 수치적 연구
양영록(Y.R. Yang),김문석(M.S. Kim),명노신(R.S. Myong),조태환(T.H. Cho) 한국전산유체공학회 2009 한국전산유체공학회지 Vol.14 No.4
In this study, roll lock-in phenomena of freely spinning tailfins were investigated by a CFD code. To analyze a motion of freely spinning tailfins, this research use a Chimera method, an Euler code and a 6 degrees of freedom analysis. The numerical results of aerodynamic characteristics and roll rates of a canard-controlled missile with freely spinning tailfins show a good agreement with wind tunnel test results. Using the roll rates calculation result of freely spinning tailfins, roll lock-in phenomena is confirmed. Roll lock-in phenomena and Roll lock-in states can be predicted through effects of the induced vortex of the canards control and the analysis of the rolling moments of tailfins due to the bank angle.