• Proceedings of the KIEE Conference
• /
• 2006.07b
• /
• pp.697-698
• /
• 2006

고온 초전도 선재는 자장의 세기, 방향 그리고 온도에 따라 임계전류가 달라지는 특성이 있다. 임계전류가 달라지는 특성은 초전도 선재를 사용하는 초전도 기기에 매우 영향을 미치게 된다. 자장의 세기, 인가 방향이 선재의 임계전류에 비치는 영향에 대하여 알아보기 위하여, prototype magnet을 제작하고, 선재에 전압 tap을 부착하여 실험을 하였다. 자장의 세기와 고온 초전도 선재가 받는 자장의 방향을 변화시켜가며 실험을 하였다. 또한, 주파수에 대한 선재의 영향을 알아보기 위하여, 주파수 변화에 따른 선재의 임계전류 변화도 측정을 하였다. 본 논문은 고온 초전도 선재를 이용하여 제작하게 되는 고온 초전도 기기 설계의 기초자료로 활용될 수 있을 것이다.

• The Bulletin of The Korean Astronomical Society
• /
• v.39 no.1
• /
• pp.81.2-81.2
• /
• 2014

To figure out the effect of rotation on the final mass of Pop III stars, 1D stellar evolution simulations of the evolution of mass-accreting protostars are performed, with zero metalicity and high constant mass accretion rates. The protostar reaches the Keplerian rotation very soon after the onset of mass accretion, but it may continue mass accretion via angular momentum transport induced by viscous stress or magnetic field. However, as the accreting star evolves, the envelope expands rapidly when the total mass reaches $5{\sim}6M_{\odot}$ and the corresponding Eddington factor sharply increases. Strong radiative pressure with rotation imposes different criteria for breakup at the stellar surface, and the so-called 'critical rotation (${\Omega}{\Gamma}$-limit)' is reached. As a result mass accretion rate has to be significantly lowered. This implies that characteristic masses of Pop III stars would be significantly lowered than the previous expectation.

• Proceedings of the Korean Magnestics Society Conference
• /
• 2015.11a
• /
• pp.147-147
• /
• 2015

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2004.07a
• /
• pp.101-104
• /
• 2004

We have fabricated a channel of superconducting flux flow transistor(SFFT) using the voltage-biased atomic force microscope(AFM) TiO tip and performed numerical simulations for the SFFT controlled by the magnetic field with a control current. The critical current density in a channel of the fabricated SFFT was decreased with the applied current by a control line. By comparing the measured with theoretical results, we showed a possibility of fabrication of an SFFT with a nano-channel using AFM anodization process technique.

• Progress in Superconductivity
• /
• v.3 no.1
• /
• pp.1-4
• /
• 2001

Interface-engineered junctions with $YbBa_2$$Cu_3$$O_{7}$ as the counter electrode were demonstrated. The junctions exhibited excellent Josephson characteristics with a Josephson critical current ($I_{c}$) ranging from 0.1 mA to 8 mA and a magnetic field modulation of the $I_{c}$ exceeding 80% at 4.2 K while maintaining complete c-axis orientation of the counter-electrode layer. The$ 1\sigma$ spreads in $I_{c}$ for junctions with an average $I_{c}$ of 1-2 mA were 5-8% for 16 junctions within a chip, and 9.3% for a 100-junction array. Our dI/dV measurements suggest that a theoretical approach taking into account both a highly transparent barrier and the proximity effect is required to fully understand the Junction characteristics.ristics.

• Clinical Endoscopy
• /
• v.57 no.5
• /
• pp.581-587
• /
• 2024

Although colonoscopy is a routinely performed procedure, it is not devoid of challenges, such as the potential for perforation and considerable patient discomfort, leading to patients postponing the procedure with several healthcare risks. This review delves into preprocedural and procedural solutions, and emerging technologies aimed at addressing the drawbacks of colonoscopies. Insufflation and sedation techniques, together with various other methods, have been explored to increase patient satisfaction, and thereby, the quality of endoscopy. Recent advances in this field include the prevention of loop formation, encompassing the use of variable-stiffness endoscopes, computer-guided scopes, magnetic endoscopic imaging, robotics, and capsule endoscopy. An autonomous endoscope that relies on self-propulsion to completely avoid looping is a potentially groundbreaking technology for the next generation of endoscopes. Nevertheless, critical techniques need to be refined to ensure the development of effective and efficient endoscopes.

• Progress in Superconductivity
• /
• v.9 no.1
• /
• pp.5-10
• /
• 2007

We prepared four different $MgB_2$ films on $Al_2O_3$ by hybrid physical chemical vapor deposition method with thicknesses ranging from $0.65\;{\mu}m$ to $1.2\;{\mu}m$. X-ray diffraction patterns confirm that all the $MgB_2$ films are c-axis oriented perpendicular to $Al_2O_3$ substrates. The superconducting onset temperature of $MgB_2$ films were between 39.39K and 40.72K. The residual resistivity ratio of the $MgB_2$ films was in the range between 3.13 and 37.3. We measured the angle dependence of critical current density ($J_c$) and resistivity, and determined the upper critical field ($H_{c2}$) from the temperature dependence of the resistivity curves. The anisotropy ratios defined as the ratio of the $H_{c2}$ parallel to the ab-plane to that perpendicular to the ab-plane were in the range of 2.13 to 4.5 and were increased as the temperature was decreased. Some samples showed increase of $J_c$ and decrease of resistivity when a magnetic field in applied parallel to the c-axis. We interpret this angle dependence in terms of enhanced flux pinning due to columnar growth of $MgB_2$ along the c-axis.

• Progress in Superconductivity
• /
• v.3 no.1
• /
• pp.23-27
• /
• 2001

We have investigated the mixed-state magnetoresistance of high quality c-axis-oriented MgB2 thin film for magnetic field from 0.5 T to 5.0 T, applied normal to ab-plane. The temperature dependence of magnetoresistance was well described by vortex glass and fluctuation theories for different temperature regimes. We observed glassy exponent of v(z-1)~3 and upper critical field of $H_{c2}$(0)~35 T, which is consistent with previous data obtained from direct $H_{c2}$(0) measurements. Interestingly, the thermally activated flux flow region was observed to be very narrow, suggesting that the pinning strength of this compound is very strong. This finding is closely related to the recent reports that the bulk pinning is dominant in $MgB_2$and the critical current density of $MgB_2$ thin film is very high, comparable to that of cuprate superconductor. The present results further suggest that $MgB_2$is beneficial to technical applications.ons.

• Nuclear Engineering and Technology
• /
• v.54 no.7
• /
• pp.2586-2591
• /
• 2022

In the present work, we have irradiated the DI-BSCCO superconducting tapes with the 100 keV deuterium ions to investigate the effect of ion irradiation on their critical current (Ic). The damage simulations are carried out using the binary collision approximation method to get the spatial distribution and depth profile of the damage events in the high temperature superconducting (HTS) tape. The point defects are formed near the surface of the HTS tape. These point defects change the vortex profile in the superconducting tape. Due to the long-range interaction of vortices with each other, the Ic of the tape degrades at the 77 K and self magnetic field. The radiation dose of 2.90 MGy degrades the 44% critical current of the tape. The results of the displacement per atom (dpa) and dose deposited by the deuterium ions are used to fit an empirical relation for predicting the degradation of the Ic of the tape. We include the dpa, dose and columnar defect terms produced by the incident particles in the empirical relation. The fitted empirical relation predicts that light ion irradiation degrades the Ic in the DI-BSCCO tape at the self field. This empirical relation can also be used in neutron irradiation to predict the lifetime of the DI-BSCCO tape. The change in the Ic of the DI-BSCCO tape due to deuterium irradiation is compared with the other second-generation HTS tape irradiated with energetic radiation.

• Proceedings of the KIEE Conference
• /
• 2001.11b
• /
• pp.96-100
• /
• 2001

Bi-2223 tapes have been developed for low-field power applications at liquid nitrogen temperature. When the Bi-2223 tapes are used in an application such as a power transmission cable or a power transformer, they are supplied with an AC transport current and exposed to an external magnetic field generated by neighboring tape's AC currents simultaneously. AC loss taking into account such real applications is a crucial issue for power applications of the Bi-2223 tapes to be feasible. In this paper, the transport losses for different AC current levels and arrangements of the neighboring tapes have been measured in a 1.5 m long Bi-2223 tape. The significant increase of the transport losses due to neighboring tape's AC currents is observed. An increase of the transport losses caused by a decrease of the Bi-2223 tape's critical current is a minor effect. The measured transport losses could not be explained by a dynamic resistance loss based on DC voltage-current characteristics in combination with the neighboring tape's AC currents. The transport losses do not depend on the frequency of the neighboring tape's AC currents but its arrangements in the range of small current especially.