• The Bulletin of The Korean Astronomical Society
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• v.44 no.1
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• pp.60.2-60.2
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• 2019

북한은 과학기술중시정책을 추진하면서 과학기술 우대환경을 조성하고, 전민과학기술 인재화 및 과학교육 강조 그리고 새 세기 산업혁명을 내세우며 자력갱생과 경제 발전을 위한 과학기술의 도구적 입장을 가지고 있다. 특수부문에서 강점을 가지고 있고, 기초과학 부문 및 정보기술영역에서 성과를 보여주고 있고, 국제학술활동에도 참여하는 등 얼마간의 대외 개방성도 나타내고 있다. 핵문제 즉 비핵화의 과제가 남아 있으나 남북 정상회담과 북미정사회담을 통해 남북교류협력의 여건이 나아지고 있고, 과학기술계 정부출연연구기관 소속의 연구자들이 북한연구과 남북협력을 준비한다. 대북 재제의 여건하에서 활성화될 수는 없으나 남북 과학자간 학술대회를 개최하고, 백두산연구기지 설립으로 백두산 지진 뿐만 아니라 천문 연구와 천연물, 광물 개발 등을 제안하였다. 앞으로는 남북과학기술협력센터 설립을 검토하고 보다 다양한 남북 과학기술 협력을 위한 기반 조성을 위한 향후 계획을 논한다.

• Journal of the Korean Magnetics Society
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• v.4 no.3
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• pp.226-232
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• 1994

Rapidly solidified $SmFe_{7+x}M_{x}(M=Mo,\;V,\;Ti)$ compound were found to crystallize in the ${Sm(Fe,\;M)}_{7}$ based stable magnetic phase by introducing a second transition element into the Sm-Fe binary system. The ${Sm(Fe,\;M)}_{7}$ phase exhibits the highest Curie temperatuer ($T_{c}=355^{\circ}C$) ever Known in the Sm-Fe magnetic systems with a quite high intrinsic coercivity($_{i}H_{c}=3~6\;kOe $). The ${Sm(Fe,\;M)}_{7}$ phase remains stable even after annealing if once form during the rapid solidification. The primary reason for the high coercive force is due to the fine grain size($2000~8000\;{\AA}$)of the magnetic ${Sm(Fe,\;M)}_{7}$ matrix phase, and the enhanced Curie temperature is attributed to the extended solid-solubility of the additive transition elements in Fe matrix, which leads to volume expansion of the ${Sm(Fe,\;M)}_{7}$ cell causing an enhanced coupling constant of Fe atoms.

• Geophysics and Geophysical Exploration
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• v.12 no.1
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• pp.41-48
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• 2009

Natural magnetic fields are attenuated by electrically conductive water. For that reason, marine magnetotelluric surveys have collected data at long periods (1000-100 000 s). The mantle structure has been the main target of seafloor magnetotelluric measurements. To ascertain crustal structure, however, electromagnetic data at shorter periods are important, e.g. in investigations of megathrust earthquake zones, or in natural resource surveys. To investigate of the former, for example, electromagnetic data for periods of less than 1000 s are necessary. Because no suitable ocean bottom electromagnetometer (OBEM) has been available, we have developed a small OBEM and ocean bottom electrometer (OBE) system with a high sample rate, which has an arm-folding mechanism to facilitate assembly and recovering operations. For magnetic observation, we used a fluxgate sensor. Field observations were undertaken to evaluate the field performance of our instruments. All instruments were recovered and their electromagnetic data were obtained. Results of the first experiment show that our system functioned well throughout operations and observations. Results of other field experiments off Tottori support the claim that the electromagnetic data obtained using the new OBEM and OBE system are of sufficient quality for the survey target. These results suggest that this device removes all instrumental obstacles to measurement of electromagnetic fields on the seafloor.

• Resources Recycling
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• v.29 no.5
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• pp.15-27
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• 2020

Microplastics are recognized as critical and serious environmental problem in worldwide. Plastics are inexpensive, lightweight, excellent in processability, and various in material-specific properties. Along industrial development, the production and disposal amount of plastics are also rapidly increasing. In particular, abundant plastic wastes are eventually disposed into marine environment with harmful impacts on the ecosystem. Therefore, lots of relevant studies were recently progressed in various fields. However, many studies are being just conducted due to its difficulty in applying a general treatment method for those small particle sizes and their various characteristics. In the meantime, lots of researches are being conducted on applying methods using physical properties such as specific gravity, magnetic, and electrostatic separation, which are beneficiation processes of minerals. However, since it is still in the laboratory stage, the development of larger scale separation technology for efficient treatment is urgent.

• Journal of the Korean Magnetics Society
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• v.1 no.2
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• pp.37-41
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• 1991

Amorphous $Fe_{68.5}Co_5M_3Cu_1Si_{13.5}B_9(M=Nb, Mo, Mn, Cr)$ alloys were prepared by using rapidly quenching techinque and were annealed above their crystallization temperatures. Coercive force, initial permeability and AC power loss of the annealed $Fe_{68.5}Co_5M_3Cu_1Si_{13.5}B_9(M=Nb, Mo, Mn, Cr)$ alloys have been studied systematically. Nanocrystallines are formed in the annealed alloys which include Mo and Nb. Remarkably improved soft magnetic properties are obtained in the alloys whose average grain size is around 10 nm. However, soft magnetic properties of the alloys are degraded when grain size is less than IOnm or larger than 15nm. It is considered that the degradation of soft magnetic properties in the alloys whose average grain size is less than 10 nm is due to the Fe-rich amorphous phase retained at grain boundary during the initial crystallization process.

• Journal of the Korean Magnetics Society
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• v.2 no.2
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• pp.140-144
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• 1992

Magnetization of permanent magnet in the strong magnetic field is changeable. So the change of magnetization must be considered for the accurate analysis of the system with permanent magnets. But the hysteresis characteristice of permanent magnet cannot be represented in simple mathematical form. In this paper, Preisach model combined with finite element method which can describe the hysteresis phenomena is applied to analyze the permanent magnet system. To validate the method, it is applied to the force calculations between two magnets with different coercivities and the numerical results are compared with measured data.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.4 no.1
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• pp.27-30
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• 2003

Amethyst is a precious stone in Korea. As natural quartz are usually mixed with smoky quartz, amethyst, and milky quartz, we need to evaluate the amount of the amethyst quantitatively in ores. Although the optical evaluation with bare eyes has been common in assay so far, we propose that the diamagnetic property and microstructural difference characterization be the solution for the evaluating the quartz ores. In addition, FTIR (Fourier transformation infra-red) could help to identify the amethyst transparency. We report that we could evaluate the amethyst quantitatively with M-H hysteresis characterization, transmission electron microscopy (TEM) observation and FTIR characterization.

• Journal of the Korean Magnetics Society
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• v.8 no.5
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• pp.255-260
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• 1998

Fabrication condition and magnetic properties of ultrathin Co-based amorphous alloy have been investigated. When the ejection gas pressure was lower than 0.05 kgf/$\textrm{cm}^2$ at the roll speed of 55 m/s, ultrathin ribbons with the thickness less than 10 ${\mu}{\textrm}{m}$ were successfully obtained. The ribbon thickness decreased linearly with the decrease in ejection pressure. Moreover the significant decrease in ribbon width was accompanied with the decrease of thickness in the range of ejection pressure to form an ultrathin ribbon. This behavior was attributed to the decrease of effective ejection pressure in the both end-sides of rectangular nozzle due to the larger friction between molten metal and nozzle wall. The effective permeability at low frequency (1 kHz) decreased largely with the decrease in ribbon thickness, while the coercive force increased with the thickness decrease. It was considered that these behaviors were due to the enhancement of surface effect leading to the suppression of wall motion. However effective permeability at high frequency (1 MHz) increased with the decrease in ribbon thickness, and this was ascribed to the easier magnetization rotation owing to the reduction of eddy current.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.23 no.6
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• pp.314-319
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• 2013

Fabrication of nanocomposite material for the $Fe_2O_3-Al$ system by mechanical alloying (MA) has been investigated at room temperature. It is found that ${\alpha}-Fe/Al_2O_3$ nanocomposite powders in which $Al_2O_3$ is dispersed in ${\alpha}-Fe$ matrix are obtained by mechanical alloying of $Fe_2O_3$ with Al for 5 hours. The change in magnetization and coercivity also reflects the details of the solid state reduction process of hematite by pure metal of Al during mechanical alloying. Densification of the MA powders was performed in a spark plasma sintering (SPS) machine using graphite dies at $1000^{\circ}C$ and $1100^{\circ}C$ under 60 MPa. Shrinkage change after SPS of MA'ed sample for 5 hrs was significant above $700^{\circ}C$ and gradually increased with increasing temperature up to $1100^{\circ}C$. X-ray diffraction result shows that the average grain size of ${\alpha}-Fe$ in ${\alpha}-Fe/Al_2O_3$ nanocomposite sintered at $1100^{\circ}C$ is in the range of 180 nm. It can be also seen that the coercivity (Hc) of SPS sample sintered at $1000^{\circ}C$ is still high value of 88 Oe, suggesting that the grain growth of magnetic ${\alpha}-Fe$ phase during SPS process tend to be suppressed.

• Journal of Astronomy and Space Sciences
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• v.19 no.2
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• pp.141-150
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• 2002

The ionosphere plays an important role in the electrodynamics of space environment. In particular, the information on the ionospheric conductivity distribution is indispensable in understanding the electrodynamics of the magnetosphere and ionosphere coupling study. To meet such a requirement, several attempts have been made to estimate the conductivity distribution over the polar ionosphere. As one of such attempts we compare the ionospheric plasma convection patterns obtained from the Super Dual Auroral Radar Network (SuperDARN), from which the electric field distribution is estimated, and the simultaneously measured ground magnetic disturbance. Specifically, the electric field measured from the Goose Bay and Stokkseyri radars and magnetic disturbance data obtained from the west coast chain of Greenland are compared. In order to estimate ionospheric conductivity distribution with these information, the overhead infinite sheet current approximation is employed. As expected, the Hall conductance, height-integrated conductivity, shows a wide enhancement along the center of the auroral electrojet. However, Pedersen conductance shows negative values over a wide portion of the auroral oval region, a physically unacceptable situation. To alleviate this problem, the effect of the field-aligned current is taken into account. As a result, the region with negative Pedersen conductance disappears significantly, suggesting that the effect of the field-aligned current should be taken into account, when one wants to estimate ionospheric conductance based on ground magnetic disturbance and electric field measurements by radars.