• Journal of the Korean Magnetics Society
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• v.7 no.1
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• pp.25-30
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• 1997

Physical and magnetic behaviors of reduced Co-Zn-Ti-Sn substituted Ba-ferrite particles with hydrogen are different from those of reduced-pure Ba-ferrite particles. The coercivity of substituted Ba-feffite particles shows a peaking effect with the reduction temperature ranging from 250 to 520 $^{\circ}C$, while the coercivity of pure Ba-ferrite decreases monotonically. The reduction process of substituted Ba-ferrite has been found to be devided into three steps. At the first and second steps, the magneto-plumbite structure maintained. When the reduced-substituted Ba-ferrite particles are reoxidized, the coercivity is reversible at the first step but irreversible at the second step. During the third step of reduction process above 410 $^{\circ}C$. The magneto plumbite structure was collapsed with formation of $\alpha$-Fe and $BaFeO_{3-x}$ phases and consequently the coercivity distribution is broaden and the coercivity irreversible. The coercivity and saturation magnetization decreases and increases up to 130 emu/g respectively. In this study, it is found that the substituted elements prevent the magneto-plumbite structure from collapse during the reduction process and furthermore migrate from the magnetic sites of $2a+4f_{IV}$, 2b, and 12k to $4f_{VI}$ and 12k'. An increase in the coercivity before the collapse of magneto-plumbite structure is attributed to the migration of cations in hexagonal Ba-ferrite structure.

• Journal of the Korean Magnetics Society
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• v.24 no.3
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• pp.81-85
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• 2014

Nano-sized Ba-ferrite, Ni-Zn ferrite and $BaFe_{12}O_{19}/Ni_{0.5}Zn_{0.5}Fe_2O_4$ nanocomposite ferrite were prepared by sol-gel combustion method. Nanocomposite was calcined at temperature range of $600{\sim}900^{\circ}C$ for 1 h. According to the diffraction patterns, hard/soft nanocomposite was indicated to the coexistence of the magnetoplumbite structural $BaFe_{12}O_{19}$ and spinel $Ni_{0.5}Zn_{0.5}Fe_2O_4$ and agree with the standard data (JCPDS 10-0325). The particle size of nanocomposite turn out to be less than 90 nm. The nanocomposite ferrite shows a single-phase magnetization behavior, implying that the hard magnetic phase and soft magnetic phase were well exchange-coupled. The specific saturation magnetization ($M_s$) of the nanocomposite is located between hard ($BaFe_{12}O_{19}$) and soft ferrite ($Ni_{0.5}Zn_{0.5}Fe_2O_4$). The remanence (Mr) of nanocomposite ferrite is much higher than that for the individual $BaFe_{12}O_{19}$ and $Ni_{0.5}Zn_{0.5}Fe_2O_4$ ferrite. $(BH)_{max}$ is increased, generally.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.23 no.6
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• pp.109-117
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• 2009

In this paper, an analytical model using equivalent magnetic circuits for the PMA-SynRG is presented. The lumped parameter model (LPM) is developed from machine geometry, stator winding and machine operating specifications. By the LPM, magnetic saturation of rotor bridges is incorporated into model and it provides effective means of predicting machine performance for a given machine geometry. The LPM is not as accurate as finite element analysis but the equivalent magnetic circuits provide fast means of analyzing electromagnetic characteristics of PMa-SynRG. It is the main advantage to find the initial design and optimum design. The initial design of PMa_RSG is performed by LPM model and FEM analysis, and the final PMA-RSG design is optimized and identified by FEM analysis considering actual machine design. The linear LPM and the nonlinear LPM are programmed using MATLAB and all of machine parameters are calculated very quickly. To verify justification of the proposed design of PMa-RSM, back-EMF is measured.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.33 no.6
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• pp.294-302
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• 2023

Ni-Mn-Zn ferrite, Ni_0.5-xMn_xZn_0.5Fe₂O₄ (0 ≤ x ≤ 0.5), was synthesized using the sol-gel method to investigate the crystal structure, microstructure, magnetic properties, high-frequency characteristics, and electromagnetic (EM) wave absorption characteristics as a function of Mn substitution. As the Mn content increased, a continuous decrease in saturation magnetization (M_S) was observed with little change in coercivity (H_C). Samples for each composition (x) exhibited strong EM wave absorption performance with first and second strong EM wave absorption regions satisfying minimum reflection loss, RL_min < -40 dB in the 1.5~2.5, 6~11 GHz range, respectively. The EM wave absorption in Ni-Mn-Zn ferrite depends on magnetic loss, and adjusting µ' and µ'' spectra by Mn substitution or H field allows control of the EM wave absorption frequency.

• Journal of Chest Surgery
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• v.30 no.5
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• pp.493-500
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• 1997

We performed this study to evaluate hepatic venous drainage in atrial isomerism by MR and the clinical significance of anomalous hepatic venous return in total cavopulmonary shunt operation. Numbers and locations of hepatic veins in twenty-two patients with isomerism(thirteen with right isomerism and nine with left isom rism) were evaluated by MR. Operative procedure of hepatic veins and postoperative arterial oxygen saturation were compared with hepatic vein connection in six patients after total cavopulmonary shunt operation. Among nine patients with left isomerism, hepatic venous return was totally anomalous via a single opening in eight, and via two separate openings in one. Among thirteen patients with right isomerism, partial anomalous hepatic venous connection directly to the atrium was seen in four. One showed total anomalous hepatic venous connection to atrium through one opening. Total cavopulmonary shunt operation was performed in 6 patients. Hepatic veins were connected to pulmonary arteries in four patients who had one atrial opening of hepatic vein andlor IVC, or two ipsilateral atrial opening of hepatic veins and IVC. In conclusion, hepatic vein drainage to atrium is variable in atrial isomerism. MR is useful for evaluation of hepatic vein drainage in atrial isomerism and surgical pla ning.

• Proceedings of the Korea Water Resources Association Conference
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• 2007.05a
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• pp.1614-1618
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• 2007

분포형 수문모형은 유역을 격자단위로 세분화하여 매개변수를 부여하고, 증발산, 침투, 지표면유출, 중간유출, 지하수유출, 하도흐름 등 여러 가지 수문요소를 해석하는 종합적인 수문모형이다. 지표면에 내린 강우의 증발 및 침투, 유출은 토양수분의 함량에 크게 의존하게 된다. 따라서 토양수분에 대한 적절한 모의가 분포형 수문모형의 정확도를 좌우하는 핵심이라 할 수 있다. 토양수분은 식물의 생장 및 가용수자원 산정 등에 있어서 중요한 요소로서 토양층 상부의 수 미터 내에 존재하는 수분의 양을 일컫는다. 토양수분의 공간적 시간적 특성들은 증발, 침투, 지하수 재충전, 토양침식, 식생분포 등을 지배하는 매우 중요한 요소라 할 수 있다. 강우로 인한 지면과 지표하에서의 순간적인 포화공간의 형성 및 유출의 생성을 포함하는 과정과 증발산 등은 모두 비포화대(vadose zone) 혹은 토양층에서의 토양수분의 함량에 크게 의존하게 된다(이가영 등, 2005) 본 연구에서는 토양수분에 대한 정밀측정 자료가 있는 설마천 유역 범륜사 사면에 대하여 분포형 수문모형의 토양수분 해석 능력을 평가하고자 하였다. 토양수분 모의에 사용된 격자기반의 분포형 수문모형은 미공병단에서 개발한 GSSHA(USACE, 2006) 모형이다. 모형의 입력자료는 정밀토양도와 현장측정에 의한 토양매개변수를 반영하여 구축하였고, 강우 및 기상자료는 2003년 1월 1일 ${\sim}$ 2004년 12월 31일의 1시간 자료를 이용하였다. 모의기간 중 2003년은 초기 토양수분값 등 초기조건의 영향을 줄이기 위한 웜업 (Warm-up)기간으로 설정하였고, 2004년의 모의결과를 토양수분 관측값과 비교하였다.업지역, 상업지역 등과 같이 지형적 특성에 따른 유량측정망을 구축하는 것이다.의 의사결정 지원 도구가 될 것이다. 따라서, 본 연구에서는 도시유역의 물순환 해석을 위한 일련의 과정, 즉 자료의 조사 및 취득에서부터 물순환 해석 모형을 이용한 정량적 현황파악, 물순환 개선 기법 및 평가를 수행함에 있어 주요 착안점 및 실무에서의 기술적 가이드를 제공하고자 하였으며, 보다 세밀한 도시유역의 물순환 해석을 위하여 우리나라와 일본에서 적용이 활발한 물리적 기반의 분포형 모형(WEP, SHER, SWMM)의 적용사례를 통하여 국내 도시하천의 물순환 해석에 활용함에 있어서의 실질적인 적용절차 등을 제시하고자 하였다. 한다.호강유역의 급격한 수질개선을 알 수 있다.世宗實錄) $\ulcorner$지리지$\lrcorner$(地理志)와 동년대에 동일한 목적으로 찬술되었음을 알 수 있다. $\ulcorner$경상도실록지리지$\lrcorner$(慶尙道實錄地理志)에는 $\ulcorner$세종실록$\lrcorner$(世宗實錄) $\ulcorner$지리지$\lrcorner$(地理志)와의 비교를 해보면 상 중 하품의 통합 9개소가 삭제되어 있고, $\ulcorner$동국여지승람$\lrcorner$(東國與地勝覽) 에서는 자기소와 도기소의 위치가 완전히 삭제되어 있다. 이러한 현상은 첫째, 15세기 중엽 경제적 태평과 함께 백자의 수요 생산이 증가하자 군신의 변별(辨別)과 사치를 이유로 강력하게 규제하여 백자의 확대와 발전에

• The KIPS Transactions:PartB
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• v.14B no.6
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• pp.431-436
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• 2007

Magnetic Resonance Imaging(MRI) has chemical shift phenomenon between fat and water, and the phenomenon has influence on structure enclosed by fat. Strong signals emitted from fat often generate false artefact, which reflects the importance of fat suppression techniques. There have been a number of researches on fat suppression techniques, but using fat suppression method alone in MRI can cause difficultproblems in diagnosis. This paper aims to study a fat suppression method by Chemical Shift Selective saturation(CHESS). This research describes the theoretical background and the experiment on water and fat phantom with MR instruments. In the experiment, CHESS pulse was designed by utilising Matlap program, and the pulse diagram was generated for the Pre-saturation process. The experiment using water and fat phantom was applied to C-spine, L-spine and Breast, and produced successful fat suppression results. This experiment has proved that the CHESSpulse fat suppression is a very helpful technique in diagnosing medical imaging. This method is a robust and useful technique for both clinical and basic investigators..(Experiment with Chungnam national university hospital G.E 1.5T MR)

• Economic and Environmental Geology
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• v.46 no.3
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• pp.207-214
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• 2013

To identify rock-magnetic properties of volcanogenic hydrothermal sulfide deposits, chimneys were obtained from the Tofua Arc in Southwest Pacific, using a remotely operated vehicle (ROV) and Grab with AV cameras (GTVs). Three different types of chimneys used in this study are a high-temperature chimney with venting fluid-temperature of about $200^{\circ}C$ (ROV01), a low-temperature chimney of about $80^{\circ}C$ (GTV01), and an inactive chimney (ROV02). Magnetic properties of ROV01 are dominated by pyrrhotite, except for the outermost that experienced severe oxidation. Concentration and grain-size of ROV01 pyrrhotite are relatively low and fine. For GTV01, both magnetic concentration and grain-size increase from interior to margin. Pyrrhotite, dominant in the core, becomes mixed with hematite in the rim of the chimney due to secondary oxidation. High concentration and large grain-size of magnetic minerals characterize the ROV02. Dominant magnetic phases are pyrrhotite, hematite and goethite. In particular, the outermost rim shows a presence of magnetite produced by magnetotactic bacterial activity. Such distinctive contrast in magnetic concentration, grain-size and mineralogy among three different types of chimney enables the rock-magnetic study to characterize an evolution of hydrothermal deposits.

• Journal of the Korean Magnetics Society
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• v.14 no.1
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• pp.38-44
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• 2004

The iron doped colossal magnetoresistance materials with La-Ba-Mn-O perovskites structure have been synthesized by chemical reaction of sol-gel methods. Their crystallographic and magnetic properties have been studied with x-ray diffraction, VSM, RBS, Mossbauer spectroscopy, and magnetoresistance measurements. The crystal structure of the La$\_$0.67/Ba$\_$0.33/Mn$\_$0.99/Fe$\_$0.01/ $O_3$ at room temperature was determined to be orthorhombic of Pnma. The lattice parameters a$\_$0/ and c$\_$0/ increased gradually, but b$\_$0/ deceased with increase of iron substitution. The magnetization and coercivity deceased, also the Curie temperature decreased from 360 K as x increased from 0.00 to 0.05. Magnetoresistence measurements were carried out, and the maximum MR ($\Delta$$\rho$/$\rho$(0)) was observed at 281 K, about 9.5 % in 10 kOe. The temperature of maximum resistance (R$\_$MAX/) decreased with increasing substitution of Fe ions and a semiconductor-metal transition temperature (T$\_$SC-M/) decreased too. This phenomena show that ferromagnetic transition temperature decreased by substituting Fe for Mn ions, it decreases double exchange interaction. This result accords with magnetic structure of neutron diffraction. Mossbauer spectra of La$\_$0.67/Ba$\_$0.33/Mn$\_$0.99/Fe$\_$0.01/ $O_3$were taken at various temperatures ranging from 15 to 350 K. With lowering temperature of the sample, two magnetic phases were increased and finally it showed the two sharp sextets of spectra at 15 K. The isomer shift at all temperature range is about 0.3 mm/s relative to Fe metal, which means that both Fe ions are Fe$\^$3+/ states.Fe$\^$3+/ states.

• Journal of the Korean Magnetics Society
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• v.19 no.3
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• pp.89-93
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• 2009

Amorphous $Ge_{1-x}Mn_x$ semiconductor thin films grown by low temperature vapor deposition were annealed, and their electrical and magnetic properties have been studied. The amorphous thin films were $1,000{\sim}5,000\;{\AA}$ thick. Amorphous $Ge_{1-x}Mn_x$ thin films were annealed at $300^{\circ}C$, $400^{\circ}C$, $500^{\circ}C$, $600^{\circ}C$ and $700^{\circ}C$ for 3 minutes in high vacuum chamber. X-ray diffraction analysis reveals that as-grown $Ge_{1-x}Mn_x$ semiconductor thin films are amorphous and are crystallized by annealing. Crystallization temperature of amorphous $Ge_{1-x}Mn_x$ semiconductor thin films varies with Mn concentration. Amorphous $Ge_{1-x}Mn_x$ thin films have p-type carriers and the carrier type is not changed during annealing, but the electrical resistivity increases with annealing temperature. Magnetization characteristics show that the as-grown amorphous $Ge_{1-x}Mn_x$ thin films are ferromagnetic and the Curie temperatures are around 130 K. Curie temperature and saturation magnetization of annealed $Ge_{1-x}Mn_x$ thin films increase with annealing temperature. Magnetization behavior and X-ray analysis implies that formation of ferromagnetic $Ge_3Mn_5$ phase causes the change of magnetic and electrical properties of annealed $Ge_{1-x}Mn_x$ thin films.