• Journal of the Korean Society of Radiology
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• v.16 no.7
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• pp.835-842
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• 2022

This study is aimed to evaluate the effects of a synthetic MR technique in reducing metal artifacts. In the experiment, the in-plane and through-plane images were acquired by applying a synthetic MR technique and a high-speed spin echo technique to a phantom manufactured with screw for spinal surgery. The area of the metal artifact was compared. The metal artifacts were measured by dividing the signal-loss and the signal pile-up areas, and the area of the final artifact was calculated through the sum of the two. As a result, the metal artifacts were relatively reduced when the synthetic MR techniques were applied to both in-plane and through-plane. Comparing by sequence, the in-plane T1 images decreased by 23.45%, T2 images by 20.85%, PD images by 19.67%, and FLAIR images by 22.12%. Also, in the case of the through-plane, the T1 image decreased by 62.95%, the T2 image decreased by 73.93%, the PD image decreased by 74.68%, and the FLAIR image decreased by 66.43%. The cause of this result is that when the synthetic MR technique is applied, the distortion is due to the signal pile-up and does not occur and the size of the entire metal artifact is reduced. Therefore, synthetic MR technique can very effectively reduce metal artifacts, which can help to increase the diagnostic value of images.

• Journal of the korean academy of Pediatric Dentistry
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• v.27 no.2
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• pp.202-207
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• 2000

The purpose of study was to compare the caries experience between the mentally retarded(MR) and the normal(N) children and adolescents and to survey the dental visit frequency. preventive dental care, and tooth-brushing behavior of the mentally retarded. Two hundred and fifty MR and two hundred and ten N subjects were selected for the study. 1. The number of teeth which had experienced caries was 3.28 in MR and 4.66 in N. The number of decayed teeth was 2.24 in MR and 1.50 in N. The number of filled teeth was 0.71 in MR and 3.06 in N Filled teeth rate was 19.78% in MR and 58.89% in N The differences between MR and N were all significant(P<0.01). 2. Dental visit frequency of MR was 1.15 per year, and the 51.2% of MR did not visit the dental clinic for the last one year. 38.0% of MR had received the preventive dental care. 3. Toothbrushing frequency per day was 2.16 and the toothbrushing time for 78.3% of MR was less than two minutes. 51.2% of MR brushed their teeth by themselves, 13.3% did with the help of the carers, and 35.5% totally depended on the carers. In conclusion, MR experienced less dental caries than N, had more untreated caries than N, and had need for regular preventive dental care.

• Proceedings of the KAIS Fall Conference
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• 2010.05b
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• pp.693-695
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• 2010

3~5W의 출력을 내는 MR16 LED 조명기구는 저 전력, 긴 수명으로 인해 에너지 문제를 해결하기 위한 중요한 요소로 작용한다. 반면에 정션 온도 상승으로 인해 수명이 급격히 단축하는 문제점이 발생하므로 방열 문제를 해결하는 것이 무엇보다 중요하다. 본 연구에서는 단일 고출력 LED 패키지를 이용한 MR16 조명등의 개발을 위해 1차원 열저항 해석 및 3차원 CFD 해석을 수행하였다.

• Journal of the Korean Society for Heat Treatment
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• v.15 no.1
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• pp.16-20
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• 2002

In conventional metallothermic reduction(MR) for obtaining tantalum powder in batch-type operation, it is difficult to control morphology and location of deposits because the reaction occurs by direct physical contact between reductants and feed materials. On the other hand, a electronically mediated reaction(EMR) is capable to overcome these difficulties through the reaction by electron transfer and have a merit of continuous process. In this study an MR and EMR method has been applied to the production of a tantalum powder by sodium reduction of $K_2TaF_7$. As the reduction temperature increases, the particle size and yield of tantalum powder obtained by MR and EMR method is increased.

• Journal of KSNVE
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• v.16 no.6 s.84
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• pp.16-21
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• 2006

• Journal of the Korean Magnetics Society
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• v.14 no.6
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• pp.228-231
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• 2004

We have studied local magnetization reversal and magnetic properties induced by Laser annealing method in the strip-patterned Ta/NiFe/FeMn/Ta and Ta/NiFe/FeMn/NiFe/Ta multilayers fabricated by ion-beam deposition. The films were exposed to the emission of the DPSS (Diode Pumped Solid State, Nd:YAG) laser under 600 G. The laser beam intensity increased up to 440 mW. When the laser illuminated the patterned film with the power of above 200 m W, the intensity of MR peak located in +87 Oe shrunk. A new MR peak was generated at -63 Oe. When the laser power is 400 mW, the location of positive MR peak(H$\sub$ex/) was changed slightly from +87 Oe to +76 Oe, and the MR ratio was decreased from 0.9% to 0.1 %. On the other hand, the new (negative) MR peak shifted from -63 Oe to -80 Oe, with the MR ratio increased up to 0.3%. As the illuminated area expanded, the intensity of opposite MR peak increased and it of negative MR peak decreased. This proved that the local reversal of exchange biasing should be realized by laser annealing.

• Proceedings of the KSMRM Conference
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• 2003.10a
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• pp.23-23
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• 2003

To evaluate clinical visualization of intracranial aneurysms between 3D-TOF MRA with 3.0T MR and CTA with 16-slices MDCT. In a prospective series, 12 patients with 16 aneurysms were studies with 3D-TOF MRA and CTA. MRA were performed on a GE Signa 3.0 T system (Signa VH/i, GE) with 25/3/20 (TR/TE/FA). CTA were peformed on a 16 slice MDCT (Sensation 16, Somatom, Siemens) with IV shooting of 80 ml iodinated contrast mediumat antecubital vein at a rate of 3.5 ml/sec. Four among 12 patients underwent DSA for surgery. Size, shape, neck and parent vessel of aneurysms were evaluated for comparison of visualization and detectability of aneurysms.

• Smart Structures and Systems
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• v.16 no.5
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• pp.961-980
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• 2015

Magnetorheological (MR) fluids are capable of changing their rheological properties under the application of external fields. When MR fluids operate in the so-called squeeze mode, in which displacement levels are limited to a few millimetres but there are large forces, they have many potential applications in vibration isolation. This paper presents an experimental and a numerical investigation of the performance of an MR fluid under tensile and compressive loads and oscillatory squeeze-flow. The performance of the fluid was found to depend dramatically on the strain direction. The shape of the stress-strain hysteresis loops was affected by the strength of the applied field, particularly when the fluid was under tensile loading. In addition, the yield force of the fluid under the oscillatory squeeze-flow mode changed almost linearly with the applied electric or magnetic field. Finally, in order to shed further light on the mechanism of the MR fluid under squeeze operation, computational fluid dynamics analyses of non-Newtonian fluid behaviour using the Bingham-plastic model were carried out. The results confirmed superior fluid performance under compressive inputs.

• Journal of Chest Surgery
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• v.27 no.11
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• pp.902-906
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• 1994

Between May 1991 and August 1993, 16 patients underwent repair of complete atrioventricular septal defect without another major anomaly at Cardiovascular Center,Yonsei University College of Medicine. Ages of the patients ranged from 3 months to 38 years with a mean of 42 months. Among 16, 10 patients[63%] are associated with Down`s syndrome. All patients underwent primary repair except and one who received had been repaire of coactation of aorta and patent ductus arteriosus 2 month before. Preoperative mitral valve regurgitation [MR] was evaluated with Doppler echocardiography and angiography which revealed absent or grade I in 1, grade II in 8, grade III in 4, and grade IV in 3. Operative technique was performed under the moderate hypothermic cardiopulmonary bypass with crystalloid cardioplegia. Intraoperative echocardiography was performed epicardial approach [n=7] in the operative table or transthoracic approach [n=9] at intensive care unit. In all patients except 3, MR were improved. But in 3 patients, was not improved or exagerated comparing preoperative one. All of them were died.One patient was showed MR grade IV in intraoperative echocardiography, we re-repaired atriventricular valve with cardiopulmonary bypass. During follow-up period [at a mean of 11 months after repair], doppler echocardiography was performed in all patients. The follow up echocardiography revealed that the degree of MR in immediate postoperative period was not changed except in two patients in whom it was aggravated. Thus it seems that intraoperative and early postoperative echocardiography was employed important role of survival and can be predictable for long term results.

• Journal of the Korean Magnetics Society
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• v.16 no.3
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• pp.173-177
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• 2006

We have investigated the magnetoresistance (MR) effect of the spin valve structures composed of perpendicularly magnetized Pd/Co multilayers, with changing the space layer (Pd or Cu) thickness, the stacking number of the Pd/Co multilayers, and the Co insertion-layer thickness. The Cu space layer showed larger MR ratio than the Pd space layer. The Co insertion-layer between Cu layer and pinned layer enhanced the MR ratio about three times. The maximum MR ratio of 7.4 % was established in the sample with the Co insertion-layer thickness of 0.62 and 1.01 nm.