• Progress in Superconductivity and Cryogenics
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• v.13 no.4
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• pp.1-4
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• 2011

From the viewpoint of high field application, the mechanical and critical current properties of recently developed $REBa_2Cu_3O_y$ (RE123, RE: rare-earth) coated conductors are summarized. In addition, effective flux pinning mechanisms in RE123 are also introduced. As one of the examples for high field application, the upgrading of the 18 T cryogen-free superconducting magnet is shown. The large anisotropy of $J_c$ is a problem at low temperature and high magnetic field. The nanorod is considered as the useful methods to improve the anisotropy of $J_c$, although its efficiency becomes small at low temperature.

• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.2022-2023
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• 2007

본 논문에서는 기존 사용 중인 24V, 10W, 300rpm, 4극, 6슬롯의 사양을 갖는 소형 전동기를 해석하였다. 영구자석이 회전자에 부착되어있는 내전형 소형 BLDC 전동기를 모델로 하였다. 고정자 측외경은 그대로 유지하면서 전동기에서 발생되는 코깅토크를 감소시키기 위하여 영구자석의 형상을 변화 시켰다. 내부 회전 자석계자는 강한 자력으로 인하여 높은 토크를 발생시키는 희토류(rare earth magnet)자석을 사용하고, 자속분포와 코깅토크를 해석하였다. 코깅토크는 자석구조에 의해 변화하기 때문에 영구자석의 형상과 크기를 최적화 하여 코깅토크를 최소화 하였다.

• Proceedings of the KIEE Conference
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• 2005.07b
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• pp.1186-1188
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• 2005

본 논문에서는 8극 12슬롯 내전형 BLDC 전동기를 기본 모델로 하고, 이를 자기저항법 및 유한요소법을 이용하여 해석 및 설계를 하고자 한다. 본 논문에서 설계대상으로 하는 내전형 BLDC 전동기는 기존에 사용중인 모델로서, 외부의 고정 전기자는 기존의 모델에 맞도록 외경을 그대로 유지하면서 Teeth 등을 설계변수로 하였고, 내부의 회전 자석계자는 기존에는 페라이트 자석을 사용하였으나 전동기의 성능 향상을 위해서 희토류 자석으로 대체하였다. 그리고 이로인한 고정자의 포화가 일어나지 않도록 최적 설계를 하였다. 유한요소법을 적용하여 자속분포, 코깅 토오크, 토오크 등을 해석하였고, 고정자와 슬롯의 최적화를 통하여 토오크 및 전동기의 성능을 향상시켰다.

• Pediatric Gastroenterology, Hepatology & Nutrition
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• v.26 no.1
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• pp.1-14
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• 2023

Foreign body (FB) ingestion is a common health problem that affects children more than adults. According to gastroenterologists' guidelines, the management of FB ingestion differs slightly between adult and children. This review aimed to compile adult and children guidelines and establish an understandable association to reveal the requirements and timing of the endoscopic procedure, which is the most effective and least complicated technique for gastrointestinal FBs. Coins, pins, and chicken and fish bones have been the most commonly ingested FBs. However, with their increasing use in recent years, large batteries with lithiumion conversion, stronger magnets composed of rare earth metals, such as neodymium, and superabsorbent objects have become the most morbid and mortal, necessitating new management strategies. Although the approach to gastrointestinal FBs is controversial, with different treatment options available in different disciplines, many studies have demonstrated the efficacy and safety of endoscopic procedures. Many factors influence the timing of endoscopy, including the nature, size, and location of the ingested object and the patient's clinical condition.

• Journal of the Korean Magnetics Society
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• v.3 no.2
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• pp.94-100
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• 1993

Electronic and magnetic properties of the novel rare-earth permanent magnet, $Sm_{2}Fe_{17}N_{3}$, are investigated by performing self-consistent local density functional electronic structure calculations. Employing the LMTO(Linearized Muffin-Tin Orbital) band method, we have obtained the electronic band structures for both paramag-netic and ferromagnetic phases of $Sm_{2}Fe_{17}N_{3}$. Based on the energy band structures, we have studied bonding ef-fects among Sm, Fe, and N atom as well as electronic and magnetic structures. It is found that the N atom sub-stantially reduces the magnetic moment of neighboring Fe atoms through the hybridization interaction and also plays a role in stabilizing the structure. the average magnetic moment of Fe atoms in the ferromagnetic phase of $Sm_{2}Fe_{17}N_{3}$ is estimated to be $2.33{\mu}_B$, which is ~8% larger than the magnetic moment of $Sm_{2}Fe_{17}$, $2.16{\mu}_B$. The Fe I (c) atom, which is located farthest from the N atom and surrounded by 12 Fe nearest neighbors, has the largest magnetic moment ($2.65{\mu}_B$), while the Fe III (f), whose hybridization interaction with N atom is very strong, has the smallest magnetic moment($1.96{\mu}_B$).

• Korean Journal of Materials Research
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• v.8 no.8
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• pp.720-725
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• 1998

As a basic study on the production of $Sm_{2}Fe_{17}N_{x}$ system rare earth permanent magnet by the reduction and diffusion(R- D) process, firstly the reduction reaction of $Sm_2O_3$ by metallic Ca and diffusion of Sm into Fe powder was investigated for the production the $Sm_{2}Fe_{17}$intermetallic compound. We concluded that the former case was very rapidly completed under the high temperature greater than 100$0^{\circ}C$ and the latter case of completion of diffusion reaction of Sm into the center of Fe powder(perfect homogenization condition) was required through 3h R- D reaction at 110$0^{\circ}C$ and identified as a rate determining step(RDS) on the whole reaction. Though $SmFe_2,SmFe_3$, and $Sm_{2}Fe_{17}$phases in the growth of phases of intermetallic compound in the Sm - Fe binary system were obseved below 100$0^{\circ}C$, but only $Sm_{2}Fe_{17}$phase was observed at lIOO$^{\circ}C$. Oxygen and Ca contents of the final sample in this work were 0.72wt% and O. 11 wt% respectively.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.1
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• pp.688-695
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• 2017

This paper deals with characteristics analysis of a permanent magnet (PM) linear generator using analytical methods for wave energy harvesting. The wave energy is carried out from the movement of a yo-yo system. A linear generator using permanent magnets to generate a magnetic force itself does not require a separate power supply and has the advantage of simple maintenance. In addition to the use of a rare earth, a permanent magnet having a high-energy density can be miniaturized and lightweight, and can obtain high energy-conversion efficiency. We derived magnetic field solutions produced by the permanent magnet and armature reaction based on 2D polar coordinates and magnetic vector potential. Induced voltage is obtained via arbitrary sinusoidal input. In addition, electrical parameters are obtained, such as back-EMF constant, resistance, and self- and mutual-winding inductances. The space harmonic method used in this paper is confirmed by comparing it with finite element method (FEM) results. These facilitate the characterization of the PM-type linear generator and provide a basis for comparative studies, design optimization, and machine dynamic modeling.

• Journal of Powder Materials
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• v.23 no.6
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• pp.437-441
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• 2016

Recently, the grain boundary diffusion process (GBDP), involving heavy rare-earth elements such as Dy and Tb, has been widely used to enhance the coercivity of Nd-Fe-B permanent magnets. For example, a Dy compound is coated onto the surface of Nd-Fe-B sintered magnets, and then the magnets are heat treated. Subsequently, Dy diffuses into the grain boundaries of Nd-Fe-B magnets, forming Dy-Fe-B or Nd-Dy-Fe-B. The dip-coating process is also used widely instead of the GBDP. However, it is quite hard to control the thickness uniformity using dip coating. In this study, first, a $DyF_3$ paste is fabricated using $DyF_3$ powder. Subsequently, the fabricated $DyF_3$ paste is homogeneously coated onto the surface of a Nd-Fe-B sintered magnet. The magnet is then subjected to GBDP to enhance its coercivity. The weight ratio of binder and $DyF_3$ powder is controlled, and we find that the coercivity enhances with decreasing binder content. In addition, the maximum coercivity is obtained with the paste containing 70 wt% of $DyF_3$ powder.

• The Journal of Advanced Prosthodontics
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• v.8 no.1
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• pp.9-15
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• 2016

PURPOSE. Although magnetic attachment is used frequently for overdenture, it is reported that attractive force can be decreased by abrasion and corrosion. The purpose of this study was to establish the clinical basis about considerations and long term prognosis of overdenture using magnetic attachments by investigating the change in attractive force of magnetic attachment applied to the patients. MATERIALS AND METHODS. Among the patients treated with overdenture using magnetic attachments in Dankook University Dental Hospital, attractive force records of 61 magnetic attachments of 20 subjects who re-visited from July 2013 to June 2014 were analyzed. Dental magnet tester (Aichi Micro Intelligent Co., Aichi, Japan) was used for measurement. The magnetic attachments used in this study were Magfit IP-B Flat, Magfit DX400, Magfit DX600 and Magfit DX800 (Aichi Steel Co., Aichi, Japan) filled with Neodymium (NdFeB), a rare-earth magnet. RESULTS. Reduction ratio of attractive force had no significant correlation with conditional variables to which attachments were applied, and was higher when the maintenance period was longer (P<.05, r=.361). Reduction ratio of attractive force was significantly higher in the subject group in which attachments were used over 9 years than within 9 years (P<.05). Furthermore, 16.39% of total magnetic attachments showed detachment of keeper or assembly. CONCLUSION. Attractive force of magnetic attachment is maintained regardless of conditional variables and reduction ratio increased as the maintenance period became longer. Further study on adhesive material, attachment method and design improvement to prevent detachment of magnetic attachment is needed.

• Journal of Magnetics
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• v.20 no.2
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• pp.97-102
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• 2015

The waste of sintered Nd-Fe-B magnets was recycled using the method of dopingPrNd nanoparticles. The effect of PrNd nanoparticle doping on the magnetic properties of the regenerated magnets has been studied. As the content of the PrNd nanoparticles increases, the coercivity increases monotonically, whereas both the remanence and the maximum energy products reach the maximum values for 4 wt% PrNd doping. Microstructural observation reveals that the appropriate addition of PrNd nanoparticles improves the magnetic properties and refines the grain. Domain investigation shows that the self-pinning effect of the rare earth (Re)-rich phase is enhanced by PrNd nano-particle doping. Compared to the magnet with 4 wt% PrNd alloy prepared using the dual-alloy method, the regenerated magnet doped with the same number of PrNd nanoparticles exhibits better magnetic properties and a more homogeneous microstructure. Therefore, it is concluded that PrNd nanoparticle doping is an efficient method for recycling the leftover scraps of Nd-Fe-B magnets.