• Journal of Magnetics
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• 제18권4호
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• pp.400-404
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• 2013

Grain boundary diffusion technique with $DyH_3$ nanoparticles was applied to fabricate Dy-less sintered Nd-Fe-B permanent magnets with high coercivity. The magnetic properties and microstructure of magnets were systematically studied. The coercivity and remanence of grain boundary diffusion magnet were improved by 60% and reduced by 7% compared with those of the original magnet, respectively. Meanwhile, both the remanence temperature coefficient (${\alpha}$) and the coercivity temperature coefficient (${\beta}$) of the magnets were improved after diffusion treatment. Investigation shows that Dy is preferentially enriched as (Nd, Dy)$_2Fe_{14}B$ phase in the surface region of the $Nd_2Fe_{14}B$ matrix grains indicated by the remarkable enhancement of the magneto-crystalline anisotropy field of the magnet. As a result, the magnet diffused with a small amount of Dy nanoparticles possesses enhanced coercivity without remarkably sacrificing its magnetization.

• 자원환경지질
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• 제27권2호
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• pp.191-199
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• 1994

층상대지속에 있는 3차원 물체에 의한 지자기 지전류 (MT)응답을 계산하기 위하여 적분방정식을 이용한 수치모델링법을 개발하였다. 이 방법에서는 3차원 이상체를 몇 개의 세포로 분할하여 펄스기조함수로 근사할 수 있는 전류분포로 치환한다. 층상대지를 표현하는 전기 텐서그린함수를 쓰면 행렬방정식을 유도할 수 있으며 이를 각 세포의 벡터전류에 대하여 푼다. 결국 미지의 산란장은 산란전류에 관한 전기 및 자기 텐서그린함수를 적분함으로써 얻어진다. 지표면 근처에 3차원 전도성물체가 존재할 때 2차원의 TE모드 모델링으로는 깊은 곳에 가짜의 저 비저항을 가정해야 한다. 이는 TE모드 모델링에서는 경계면 전하의 영향을 고려할 수 없기 때문이다. 그러나 긴 3차원 직방체의 가운데를 가로지르는 단연은 2차원 TM모드 아르고리즘으로 정확히 모델화할 수 있으며, 이는 정식화과정에서 경계면 전하가 고려되어 있기 때문이다. 다중 주파수에 관한 수치계산 결과 겉보기 비저항과 위상은 상호보완적인 변수라는 것이 밝혀졌다. 따라서 이들 변수는 주파수영역 MT 해석시 함께 취급되는 것이 바람직하다.

• 천문학회보
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• 제37권2호
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• pp.132.2-132.2
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• 2012

We have investigated the characteristics of magnetic cloud (MC) and ejecta (EJ) associated coronal mass ejections (CMEs) based on the assumption that all CMEs have a flux rope structure. For this, we used 54 CMEs and their interplanetary counter parts (interplanetary CMEs: ICMEs) that constitute the list of events used by the NASA/LWS Coordinated Data Analysis Workshop (CDAW) on CME flux ropes. We considered the location, angular width, and speed as well as the direction parameter, D. The direction parameter quantifies the degree of asymmetry of the CME shape, and shows how closely the CME propagation is directed to Earth. For the 54 CDAW events, we found several properties of the CMEs as follows: (1) the average value of D for the 23 MCs (0.62) is larger than that for the 31 EJs (0.49), which indicates that the MC-associated CMEs propagate more directly to the Earth than the EJ-associated CMEs; (2) comparison between the direction parameter and the source location shows that the majority of the MC-associated CMEs are ejected along the radial direction, while many of the EJ-associated CMEs are ejected non-radially; (3) the mean speed of MC-associated CMEs (946 km/s) is faster than that of EJ-associated CMEs (771 km/s). For seven very fast CMEs (>1500 km/s), all CMEs with large D (>0.4) are associated with MCs and the CMEs with small D are associated with EJs. From the statistical analysis of CME parameters, we found the superiority of the direction parameter. Based on these results, we suggest that the CME trajectory essentially decides the observed ICME structure.

• 천문학회보
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• 제34권2호
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• pp.34-34
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• 2009

• 한국진공학회:학술대회논문집
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• 한국진공학회 1998년도 제14회 학술발표회 논문개요집
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• pp.18-18
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• 1998

F First I will introduce our works how to improve the crystal growth t technique for Rare earth pnictides and chalcogenides. All these substances h have hi양1 vapor pressure and high melting print up to 3$\alpha$)()C. 까len we employ m the tungsten or molybden crucibles and enclose the sample by 빼e welding of m the lid with high current electron beam. We cannot elevate the temperature up t to 3$\alpha$)()C without suitable radiation shield because rate of radiation loss r rapidly increase in such a high temperature regions. There were no good r radiation shield but we discovered that the p-BN could work as an excellent r radiation shield after checking of the many substances. S Secondly I will show several interesting and unusual 뻐ysical properties of obtained crystals under high magnetic field, hi양1 pressure and also i including angle resolve photoemission spectroscopy. I will stress the p properties of the low carrier concentration with strong correlation on C댐, U USb and Yb4As3

• 자원환경지질
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• 제48권1호
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• pp.51-63
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• 2015

동북아시아에 위치한 4개의 지자기 관측소의 3성분 지구자기장 관측 자료를 이용하여 1997년부터 2011년 동안의 지구자기장의 영년변화를 표현하는 지역화된 영년변화 모델을 제작하였다. 외핵의 움직임으로 발생되는 지구자기장은 장소와 시간에 따라 변화하며 지자기 관측소에서는 이를 시계열로 측정하게 된다. 따라서 공간적인 변화를 함께 파악하기 위해서는 이를 시공간모델로 제작하여 시간에 따른 지구자기장의 변화를 공간적으로도 표현할 수 있도록 해야 한다. 전지구 범위인 경우 관측소의 분포가 제한되어 있고 이를 공간적으로 보완하기 위해 위성 자료를 활용한다. 하지만 방대하고 복잡한 위성 자료의 처리와 세계의 모든 지자기 관측소의 자료를 활용하여 전 지구적 지구자기장의 모델을 제작하는 일은 상당한 작업과 노력을 요구한다. 또한 계속해서 들어오는 자료들을 이용하여 모델을 업데이트 하는 일 역시 같은 양의 시간과 노력을 필요로 하게 된다. 더불어, 각 관측소 자료의 오차범위와 위성 자료 처리 오차 (processing error) 역시 지역에 따라 다르게 나타남으로 이러한 오차값들이 전지구 모델의 정확도에 영향을 미칠 수 있다. 본 논문에서는 이러한 문제점을 감안하여 동북아시아 지역을 중심으로 하는 지역화된(localized) 모델링 기법을 소개하고 이를 통해 지구자기장의 영년변화 모델을 제작하는 데 적용하였다. 전 세계의 지구자기장 관측망인 INTERMAGNET에 가입된 3개의 일본 관측소와 1곳의 중국 관측소 자료를 활용하여 1997년부터 2011년까지 6개월 간격으로 지구자기장의 변화를 파악하고 이를 전지구 모델과 비교해 보았다. 또한 얻어진 모델을 이용하여 지구 내부의 원인인 지구자기장의 급작스런 변화를 일컫는 지구자기장 '급변'을 찾아보고 이에 대한 발생 시기에 대해 논의하였다.

• 한국수소및신에너지학회논문집
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• 제25권6호
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• pp.594-601
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• 2014

Rare-earth (RE) nitrides can be used as magnetocaloric materials in low temperature. They exhibit ferromagnetism and have Curie temperature in the region from 6 to 70 K. In this study, Holmium nitride (HoN) nano particles were prepared through plasma arc discharge technique and their magnetocaloric properties were studied. Nitrogen gas ($N_2$) was employed as an active element for arc discharge between two electrodes maintained at a constant current. Also, it played an important role not only as a reducing agent but also as an inevitable source of excited nitrogen molecules and nitrogen ions for the formation of HoN phase. Partial pressure of $N_2$ was systematically varied from 0 to 28,000 Pa in order to obtain single phase of HoN with minimal impurities. Magnetic entropy change (${\Delta}S_m$) was calculated with data set measured by PPMS (Physical Property Measurement System). The as-synthesized HoN particles have shown a magnetic entropy change ${\Delta}S_m$) of 27.5 J/kgK in applied field of 50,000 Oe at 14.2 K thereby demonstrating its ability to be applied as an effective magnetic refrigerant towards the re-liquefaction of hydrogen.

• Ocean and Polar Research
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• 제26권4호
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• pp.559-565
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• 2004

Total magnetic field measurements were performed to study paleomagnetism of three seamounts (OSM7, OSM8-1, and OSM8-2) to the northwest of the Marshall Islands in the western Pacific. The study area is located at the Ogasawara Fracture Zone which is a boundary between the Pigafetta and East Mariana basins. The magnetic parameters and paleopoles of three seamounts were derived from inversion of the measured magnetic field. The goodness-of-fit ratio of OSM7 is too low to be included to the estimation of parameters. The complex magnetic anomalies of center, scarcity of flank rift zones and steep slope at OSM7 suggest that the multiple intrusions of magma converge into the center of volcanic edifice. Inclination calculated from the magnetic anomalies of OSM8-1 and OSM8-2 is $-41.2^{\circ}$, and the paleolatitude calculated from the inclination is $23.6^{\circ}S$. The corresponding paleopoles for OSM8-1 and OSM8-2 are $(24^{\circ}42'W,\;48^{\circ}54'N)\;and\;(18^{\circ}18'W,\;48^{\circ}30'N)$, respectively. In comparison with the apparent polar wander path (APWP) of the Pacific plate, the paleopoles are close to 129-Ma pole. The paleopoles and paleolatitudes of OSM8-1 and OSM8-2 suggest that they were formed at similar time and location. The seamounts have drifted northward about $41^{\circ}$ from the paleolatitude to present latitude of seamounts.

• 전기학회논문지
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• 제61권10호
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• pp.1426-1431
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• 2012

This paper analyzes re-degaussing performances of various breakdown conditions of degaussing coils in a ship to reduce underwater magnetic field anomaly due to the hull magnetization induced under the Earth's magnetic field. To achieve this, first, it is implemented to optimize degaussing coil currents by a magnetomotive force sensitivity formula combined with the coil effects. The re-degaussing processes are then executed when a breakdown occurs in degaussing coils, one by one. Finally, the re-degaussing performances are examined with the results of normal degaussing and coil breakdown conditions.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2007년도 제38회 하계학술대회
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• pp.1908-1909
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• 2007

The design of an intelligent toothbrush, capable of monitoring brushing motion, orientation through the grip axis, during toothbrushing is described. Inappropriate Toothbrushing styles, even in adults, sometimes cause dental problems, cavities, gingivitis, etc. This smart system provides user to monitor his or her brushing pattern using accelerometer and magnetic sensors for evaluation of toothbrushing style. Directional information of toothbrush with respect to earth's magnetic field and activity data were measured by a miniaturized low-power micro- controller, MSP430 and transmitted to personal computer by 2.4GHz radio transmitter, nRF2401. A personal computer provides an on-line display of activity and orientation measurements during toothbrushing. The signal trace is then analyzed to extract clinically relevant measurement. This preliminary study showed that the proposed monitoring system was conceived to aid dental care personnel in patient education and instruction in oral hygiene regarding brushing style.