• Proceedings of the KSME Conference
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• 2001.06e
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• pp.142-147
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• 2001

Natural convection of a magnetic fluid is different from that of Newtonian fluids because magnetic body force exists in an addition to gravity and buoyancy. In this paper, natural convection of a magnetic fluids(W-40) in a cubic cavity is examined by numerical and experimental method. One side wall was kept at a constant temperature($25^{\circ}C$), and the opposite side wall was also held at a constant but lower temperature($20^{\circ}C$). Under above conditions, various magnitudes of the magnetic fields were applied up. GSMAC scheme is used for a numerical method, and the thermo-sensitive liquid crystal film(R20C5A) is utilized in order to visualize wall-temperature distributions as an experimental method. This study has resulted in the following fact that the natural convection of a magnetic fluids is controlled by the direction and intensity of the magnetic fields.

• Journal of Mechanical Science and Technology
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• v.15 no.12
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• pp.1876-1881
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• 2001

We present the numerical analysis of the growth of a silicon (Si) single crystal. In the MCZ (Magnetic-field-applied Czochralski) method, two magnetic fields that stand opposite to each other generate a cusp magnetic field. In this work, the three cusp magnetic fields used for the analysis are an extern magnetic field, a surface magnetic field and an internal magnetic field. Each case was evaluated mainly as to the degree of stirring, shaft symmetry and the stability of the flow. As a result, the cusp magnetic field that yielded to best conditions was the internal magneic field.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.54 no.5
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• pp.234-241
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• 2005

The performance of passive conductor loop (hereinafter 'loop') method which is used to mitigate the magnetic field around overhead power transmission line is dependent on its configuration and installed location, which are affected by installation conditions of the loops such as objective areas and levels of magnetic field mitigation. Thus, because the design problem of loops is difficult and cumbersome by variety of their configuration and complexity of magnetic coupling mechanism, it is need to be formulated as a computer-based optimum problem to determine the most effective and reasonable loop model satisfying the installation conditions. In this paper, the optimum locations of the multi-wired multiple loops including series reactance compensations are searched by using the genetic algorithm (GA) to mitigate effectively the magnetic fields of relatively near points or far points from transmission line at Am height, and the magnetic fields mitigation characteristics of each loop are analyzed in the view of magnitude, direction and phase of cancellation fields by polarized vector concept to identify their adequacy and rationality for the installation objectives.

• Proceedings of the KIEE Conference
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• 1996.07c
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• pp.1867-1869
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• 1996

In this paper, in order to obtain the statistic information for parameters of electric and magnetic field waveforms associated with lightning discharges, the electric and magnetic fields produced by lightning discharges in the summer of 1995 were measured by a hemisphere-type electric field sensor and a loop-type magnetic field sensor, which were installed at the campus of Inha University in Inchon. The signals of the electric and magnetic fields were continuously recorded by a transient digitizer having a resolution of 12 bit and a memory capacity of 5000 point. Negative lightning discharges are produced very more than positive lightning discharges in the summer of Korea. The 10 to 90 % rise time of electric and magnetic fields was 2 $2\;{\sim}\;10\;{\mu}s$. And the zero-crossing time of electric field was $15\;{\sim}\;25\;{\mu}s$, whereas that of magnetic field was $20\;{\sim}\;30\;{\mu}s$.

• Journal of The Korean Astronomical Society
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• v.29 no.spc1
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• pp.303-305
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• 1996

The evolution of solar magnetic arcades is investigated with the use of MHD simulations imposing resistivity on sheared magnetic fields. It is found that there is a critical amount of shear, over which magnetic reconnection can take place ill an arcade-like field geometry to create a magnetic island. The process leading to reconnect ion cannot. be solely attributed to a tearing instability, but rather to a reactive evolution of the magnetic arcade under resistivity. The natures of the arcade reconnection are governed by the spatial pattern of resistivity. A fast reconnection with a small shock angle can only be achieved when the diffusion region is localized. In this case. a highly collimated reconnect ion outflow can tear the plasmoid into a pair, and most of principal features in solar eruptive processes are reproduced.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2003.04a
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• pp.215-222
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• 2003

The new square electro-magnetic chuck, which is using for the clamping devices on a grinding machine, is developed in this study to improve the convenience of grinding works. The various kinds of structures are recommended to find the most adequate magnetic characteristics through the analytical approach using finite element methods. The analyzed results are retrofitted to solve the drawbacks of previous models step by step by considering the magnetic fields, strength and distribution of drag force, and thermal deformations of chuck. such as high parallelism and flatness. Finally the best recommended models is designed to satisfy the KS specifications required for the commercial magnetic chuck. The prototype chuck with this dimensions and structures is manufactured. For this final model, the experimental verifications are investigated whether the KS specifications are satisfied.

• The Bulletin of The Korean Astronomical Society
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• v.43 no.1
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• pp.67.2-67.2
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• 2018

Magnetic fields play an important role in star-forming processes by regulating gravitational collapse. In filamentary structures of star-forming regions, magnetic fields are likely to be aligned with minor axes of filamentary molecular clouds because matter freely moves along magnetic field lines. Orion A region, one of the well-known high-mass star forming regions, has long filament structure. In order to study magnetic field directions with respect to the filamentary structure in Orion A, we have analyzed $850{\mu}m$ dust polarization observations obtained with the James Clerk Maxwell Telescope (JCMT). We found tight correlation of dust intensity gradients and magnetic field directions. It was estimated that 81% of magnetic field segments are aligned with density gradients within 40 degree. In conclusion, we confirmed most of magnetic field segments are perpendicular to the major axis of the filament in Orion A.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.14 no.6
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• pp.8-15
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• 2005

The new square electro-magnetic chuck, which can be used for the clamping devices on a grinding machine, is developed in this study to improve the convenience of grinding works. The various kinds of structures are recommended to find the most adequate magnetic characteristics through the analytical approach using finite element methods. The analyzed results are retrofitted to solve the drawbacks of previous models step by step by considering the magnetic fields, strength and distribution of drag force, and thermal deformations of chuck such as high parallelism and flatness. Finally the best recommended models is designed to satisfy the KS specifications required fur the commercial magnetic chuck. The prototype chuck with this dimensions and structures is manufactured. For this final model, the experimental verifications are investigated whether the KS specifications are satisfied.

• The korean journal of orthodontics
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• v.27 no.6 s.65
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• pp.929-941
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• 1997

Optimal force for orthodontic treatment is the force that produces a rapid rate of tooth movement without discomfort to the Patient or ensuing tissue damage. Recently considerable interest has been generated in the application of magnets as a way to obtain an optimal force. The purpose of the present study was to investigate the effect of static magnetic fields of Sm-Co magnets on molecular and cellular activities. The distance of erythrocyte sedimentation was measured directly, and the activities and the syntheses of $Fe^{2+}$-related enzymes (catalase and NO synthase) and non $Fe^{2+}$-related enzyme (lactic dehydrogenase) were assayed by the spectrophotometer. The growth and the proliferation of osteoblast-like cells $MC_3T_3-E_1$ were determined by the crystal violet staining and the ${^3}H$-thymidine incorporation. The erythrocytes were exposed to the pole face flux density of 1,400 G (gauss), and the enzymes and osteoblast-like cells $MC_{3}T_3-E_1$ were exposed to the flux density of 7,000 G. The results obtained were as follows: 1. The distance of sedimentation of erythrocyte was not affected by the static magnetic fields. 2. The activities of catalase and lactic dehydrogenase were not affected by the static magnetic fields. 3. The intracellular syntheses of NO synthase and lactic dehydrogenase were not affected by the static magnetic fields. 4. The growth and the proliferation of cultured osteoblast-like cells $MC_{3}T_3-E_1$ were not affected by the static magnetic fields. These results suggested that the molecular and cellular activities were not significantly influenced by the static magnetic fields.

• Journal of Dental Rehabilitation and Applied Science
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• v.19 no.3
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• pp.185-193
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• 2003

The object of this study is to observe the effects of magnetism on the osteoblasts using a neodymium magnet. The osteoblasts was cultured under magnetic fields of varying intensities to evaluate the effect of magnetism on the activity and alkaline phosphatase acitivty of the osteoblasts. Osteoblasts were cultured in the cell density of $10^4$ for the evaluation of cell proliferation and 105/ml for the evaluation of ALP activity under 0. 10, 100, 500, 1000, 2000, 4000 gauss for 24 hour. For evaluation of osteoblast morphologic changes under magnetic, osteoblasts were observed by inverted microscope and TEM. To elucidate if IGF-receptors are increased under the magnetic field, we investigated osteoblasts by immunofluoroscence staining. The results were as follows: In the varying intensities of magnetic fields, the degree of cell proliferation was the highest in the magnetic field of 10 gauss and this gradually decreased up to 1000 gauss. In the magnetic fields stronger than 1000 gauss, the degree of the cell proliferation decreased to an even lower level than that of the control group. The ALP activity and protein synthesis showed a similar increase pattern as the degree of cell proliferation compared to the control group but showed little difference. Under the microscope, morphological change of the cells ( decrease in length and increase in roundness) were observed but no peculiarity of cell distribution could be found according to the magnetic field line. In the proper intensity of magnetic fields (10 gauss), the cultured cells showed increase in number of IGF Receptors compared to that of the control group.