• 전기의세계
• /
• 제24권6호
• /
• pp.77-84
• /
• 1975

This paper treats A.C. arc movement in a transverse A.C. magnetic field at atmospheric pressure with the purpose of selecting electrode materials and obtaining detailed data for design of A.C. air circuit breaker, plasma accelerator and plasma jet. Arc velocities in transverse magnetic field are measured by varying arc current, arc voltage, gap length, magnetic flux density and the erosion of electrode surface, which influence arc velocities. The main results are; 1)Arc velocities in transverse magnetic field have different values according to electrodes of various materials and decrease in a descending order of cold cathode, medium cathode and hot cathode. 2)Arc velocities in transverse magnetic field increases with arc current, arc voltage, gap length and magnetic flux densith and on the other hand decrease with the increase of electrode surface erosion. 3)D.C.arc velocity in D.C. magnetic field is higher than A.C. arc velocity in A.C. magnetic field of the same value.

• 한국재료학회지
• /
• 제23권6호
• /
• pp.329-333
• /
• 2013

The structural phase transformations of $0.7Pb(Mg_{1/3}Nb_{2/3})O_3-0.3PbTiO_3$ (PMN-0.3PT) were studied using high resolution x-ray diffraction (HRXRD) as a function of temperature and electric field. A phase transformational sequence of cubic (C)${\rightarrow}$tetragonal (T)${\rightarrow}$rhombohedral (R) phase was observed in zero-field-cooled conditions; and a $C{\rightarrow}T{\rightarrow}$monoclinic $(M_C){\rightarrow}$ monoclinic ($M_A$) phase was observed in the field-cooled conditions. The transformation of T to $M_A$ phase was realized through an intermediate $M_C$ phase. The results also represent conclusive and direct evidence of a $M_C$ to $M_A$ phase transformation in field-cooled conditions. Beginning from the zero-field-cooled condition, a $R{\rightarrow}M_A{\rightarrow}M_C{\rightarrow}T$ phase transformational sequence was found with an increasing electric field at a fixed temperature. Upon removal of the field, the $M_A$ phase was stable at room temperature. With increasing the field, the transformation temperature from T to $M_C$ and from $M_C$ to $M_A$ phase decreased, and the phase stability ranges of both T and $M_C$ phases increased. Upon removal of the field, the phase transformation from R to $M_A$ phase was irreversible, but from $M_A$ to $M_C$ was reversible, which means that $M_A$ is the dominant phase under the electric field. In the M phase region, the results confirmed that lattice parameters and tilt angles were weakly temperature dependent over the range of investigated temperatures.

• 한국전기전자재료학회논문지
• /
• 제14권3호
• /
• pp.234-240
• /
• 2001

Using RF magnetron sputtering, amorphous carbon(a-C) thin films as electron filed emitter were fabricated. these a-C thin films were deposited on Si(001) substrate at several temperatures. The field electron emission property of these a-C thin films was estimated by a diode technique. As the result, we observed that the field emission properties of the films were changed singnificantly with the substrate temperature and structural features of a-C film. The field emission properties were promoted by higher substrate temperatures. Furthermore N-doped a-C film exhibits more field emission property than that of undoped a-C film. These results are explained as change of surface morphology and structural properties of a-C film.

• 한국초전도ㆍ저온공학회논문지
• /
• 제24권3호
• /
• pp.52-56
• /
• 2022

Single-grain (c-normal or c-parallel) and multi-grain YBCO superconductors were prepared by a melt growth process with/without seeding. The magnetic levitation force and trapped magnetic field at liquid N₂ temperature (77 K) of the YBCO superconductors were investigated. Samples for the levitation force measurement were zero-field cooled (ZFC) to 77 K, and samples for trapped field measurement were field-cooled (FC) using Nd magnets. As for the magnetic levitation force, the c-normal, single grain sample showed the largest value, whereas the multi-grain sample showed the lowest value. The trapped magnetic field of the c-normal and c-parallel single-grain samples was 4-5 times that of the multi-grain sample. In addition, as the external magnetic field (the number of magnets) increased, the both properties increased proportionally. These results were explained in terms of the orientation dependence of the levitation forces and the magnetic field trapping capability of the YBCO superconductor.

• 전기의세계
• /
• 제23권2호
• /
• pp.55-61
• /
• 1974

Nature of magnetic creep phenomena in low coercive force films(Ni 80%-Fe 20%) in form of narrow channels imbedded in high coercive force films is studied in this work. Aluminium is evaporated on the hot glass substrate and eched free in the shape of narrow channels by photoetoetching method. then, Permalloy(Ni 80%, Fe 20%) is deposited on these Aluminium substrate under the uniform field of 30(Oe) to introduce anisotropy. Permalloy film on Al has a high coercive force and one on the substrate devoid of Al has how coercive force. Magnetic revers domain which is introduced at the end of channel grows under the a.c field in hard axis direction, in spite of very weak d.c field in easy axis direction. This creeping is investigated as a function of external fields and channel widths. Permalloy film thickness is 500.angs.-900.angs. and channel widths are 40, 51, 65, 81, 115.mu. respectively. Creeping increases as external field increases while it decreases with channel width decrease. Creep velocity in channels depends on the a.c field along hard axis, d.c field along easy axis and channel widths and its range is 1-10cm/sec in this experiment. From study of dependence of creep velocity on channel width, it can be concluded that creep velocity is expressed in form of v=v$_{0}$ exp .alpha.(H-H$_{0}$) where .alpha. is a function of a.c field along hard axis and H is driving d.c field along easy axis, H$_{0}$ is not a coercive force of film as usuall expected but the d.c threshold field along easy axis which is a function of channel width. This characteristic is also confirmed by the study of dependence of creep velocity upon easy axis field strength. Value of .alpha. obtained is 1.3-2.3cm/sec We depending upon film charactor, hard axis field strength and frequency.uency.

• 전기의세계
• /
• 제30권4호
• /
• pp.231-236
• /
• 1981

It has been known that D.C. breakdown Voltage is lower than A.C. breakdown Voltage in insulatingoil, but there are still many unvivid points at electric conduction in breakdown or under of high electric field. This study measured the electric current-electric field characteristics (I-E characteristics) and the breakdown Voltage under of D.C. electric field of insulating oil using the system of electrodes that are near the Uniform electric field with a result. I can study, electric conduction in area of high electric field depends upon the Schottky effect. The liquidity of breakdown electric field takes place by the local concentration of electric field. The longer gap is and the more electric current is the more breakdown Voltage decreased. There are not almost the change of electric current-electric field characteristics by materials of electrode.

• 제어로봇시스템학회:학술대회논문집
• /
• 제어로봇시스템학회 1997년도 한국자동제어학술회의논문집; 한국전력공사 서울연수원; 17-18 Oct. 1997
• /
• pp.1722-1725
• /
• 1997

This paper presents image analysis method using a Markov random field(MRF) model. Particulary, image esgmentation is to partition the given image into regions. This scheme is first segmented into regions, and the obtained domain knowledge is used to obtain the improved segmented image by a Markov random field model. The method is a maximum a posteriori(MAP) estimation with the MRF model and its associated Gibbs distribution. MAP estimation method is applied to capture the natural image by TMS320C80(MVP) and to realize the segmented image by a MRF model.

• 한국농공학회논문집
• /
• 제49권1호
• /
• pp.79-88
• /
• 2007

We investigated the characteristics of temperature variations under different land covers (paddy field, upland, urban park, and urban residential area) during hot summer (July 15 to August 19, 2005). The temperatures were monitored using data loggers at one hour intervals in study sites. The mean temperature generally increased with the distance from edge of paddy fields, being $1.5^{\circ}C$ higher at a site 170-m far from paddy fields than at a paddy field area at 22 h. The mean daily temperatures in the study period followed the ordo. of paddy field $(26.6^{\circ}C)$ < upland $(27.0^{\circ}C)$ < park $(27.5^{\circ}C)$ < residential area $(28.0^{\circ}C)$. The paddy field area has shown remarkable cooling effects compared to the residential area: Mean duration of temperature below $25^{\circ}C$ in the paddy field area was longer (8.6 hrs) than in the residential area; The time to fall to below $25^{\circ}C$ in the paddy field area was sooner (22.4 hr) than in the residential area; Mean daily minimum temperature in the paddy field area was much lower $(2.4^{\circ}C)$ than in the residential area. More research is needed to better clarify the mechanism of cooling effect of a paddy field area by investigating heat balance of a paddy field.

• 한국초전도학회:학술대회논문집
• /
• 한국초전도학회 2000년도 High Temperature Superconductivity Vol.X
• /
• pp.248-251
• /
• 2000

The fabrication and characteristics of HTS race-track type field coil for generators was carried out. Field coils are composed of 3 pancake coils wound by 37-filamental Bi-2223/Ag-alloy tapes. The winding machine is horizontal type. The critical currents (I$_c$) of the superconducting tapes were measured with variation of bending strain and external magnetic fields. I$_c$ of both whole field coils and 3 pancake coils were measured as a function of temperature. At 77K under the self-field, I$_c$ of whole field coils was 12A, while in the case of middle pancake coil, I$_c$ was 15A. The distribution of magnetic field B was obtained, using 3-D FEM. Our simulation showed that maximums of B${\bot}$A in x-y plane were locally distributed in both the upper and the lower coils. In addition, the fabrication processes and the characteristics of field coil are described.

• 대한수학회논문집
• /
• 제39권3호
• /
• pp.739-756
• /
• 2024

The ordinary mean curvature vector field 𝗛 on a submanifold M of a space form is said to be proper if it satisfies equality Δ𝗛 = a𝗛 for a constant real number a. It is proven that every hypersurface of an Riemannian space form with proper mean curvature vector field has constant mean curvature. In this manuscript, we study the Lorentzian hypersurfaces with proper second mean curvature vector field of four dimensional Lorentzian space forms. We show that the scalar curvature of such a hypersurface has to be constant. In addition, as a classification result, we show that each Lorentzian hypersurface of a Lorentzian 4-space form with proper second mean curvature vector field is C-biharmonic, C-1-type or C-null-2-type. Also, we prove that every 𝗛₂-proper Lorentzian hypersurface with constant ordinary mean curvature in a Lorentz 4-space form is 1-minimal.