• 한국임상수의학회지
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• 제37권5호
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• pp.255-260
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• 2020

The purpose of this retrospective study was to describe the characteristics of magnetic resonance imaging (MRI) findings in dogs with meningoencephalitis of unknown etiology (MUE), and to evaluate the usefulness of meningeal enhancement. Thirty-two dogs were included in MUE group on the basis of clinical signs, MRI findings and cerebrospinal fluid (CSF) results, and for comparison of the meningeal enhancement, twenty-three dogs with normal MRI, normal CSF and no clinical sign were included in the control group. The evaluated MRI findings included lesion site, lesion number, signal intensity of each MRI sequence, mass effect, perilesional edema, contrast enhancement, and meningeal enhancement. The MUE was most frequently associated with multiple lesions (50%) with perilesional edema (72%) in forebrain (66%) that were hyperintense (92%) in T2W and FLAIR images. Of the meningeal enhancement, there was no significant difference between the control group and the MUE groups in the pachymeningeal enhancement. However, leptomeningeal (or both) enhancement was found relatively high proportion in the MUE group than in the control group (P < 0.001, Odd ratio = 10.26), and based on this result, leptomeningeal (or both) enhancement is considered to be significant finding for indicating MUE.

• 대한치과보철학회지
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• 제45권3호
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• pp.362-374
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• 2007

Statement of problem. The intial stability for osseointegration of implant has been an interesting factor. Especially, in the case of poor bone quality or immediately loaded implant, various strategies have been developed focusing on the surface of materials to improve implant fixation to bone. The microscopic properties of implant surfaces play a major role in the osseous healing of dental implants. Purpose. The aims of this study are to perform a histologic and histomorphometric comparison of the healing characteristics of three different surfaces and the comparison of resonance frequency analysis (RFA) values measured by $Osstell^{TM}$ and perio-test values (PTV) measured by Periotest. Material and methods. A total of 24 screw titanium implants (Dentium Co., Seoul, Korea) with 6mm in length and 3.4mm in diameter, were placed in the mandible of 4 beagle dogs. Implants were divided into three groups following the surface treatment methods: Group I is machined(control group). Group II is anodically oxidized. Group III is coated 500nm in thickness with hydroxyapatite(HA) by ion beam assisted deposition(IBAD) on the anodized oxidization. Bone blocks from 2 dogs were caught after 3 weeks of covered healing and another blocks from 2 dogs after 6 weeks. RFA values and PTV were measured right after insertion and at 3 and 6weeks. Histomorphometric analysis was made with Kappa Image Base System to calculate bone-to-implant contact (BIC) and bone area inside the threads. Pearson's correlation analyses were performed to evaluate the correlation between RFA and PTV, BIC and bone area ratio of three different surfaces at 3 and 6 weeks. Results. 1) In all surface treatment methods, the RFA values decreased and the PTV values increased until 6 weeks in comparison to initial values. 2) At 3 weeks, no significant difference was found from bone-to-implant contact ratio and bone area ratio of three different surface treatment methods(P>0.05). However, at 6 weeks, different surface treatment methods showed significantly different bone-toimplant contact ratio and bone area ratio(P<0.05). 3) In the implants with the IBAD on the anodic oxidization, significant difference was found between the 3 weeks and the 6 weeks bone area ratio(P<0.05). 4) Correlation was found between the RFA values and the bone area ratio at 3 and 6 weeks with significant difference(P<0.05). Conclusions. These results indicate that the implants with the IBAD on the anodic oxidization may have a high influence on the initial stability of implant.

• 한국가스학회지
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• 제13권1호
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• pp.9-13
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• 2009

가스히터의 가동으로 인하여 발생하는 소음 및 진동의 주 원인은 연소음(combustion roar)과 연소진동음(combustion oscillation)이다. 연소음(combustion roar)의 특징은 음압이 넓은 주파수대에 걸쳐 있고, 크기도 비교적 일정 하다. 반면 연소진동음(combustion oscillation)은 연소실내 기체의 고유진동수에 대하여 버너계가 Positive Feedback을 일으켜 공진할 때 발생되는 소음 및 진동이다. 따라서 소음 및 진동을 해결 할 수 있는 방법은, 공진을 피하는 것이다. 첫 번째, 버너에서 연료와 공기량의 비율을 조절하여 진동수를 변화시키거나, 연소실내에서의 연료와 공기의 혼합속도를 변화시키는 방법이 있다. 두 번째, 연소실의 길이나 이코노마이저(Economizer)의 형상을 바꾸어 고유진동수를 변경시키는 방법이 있다. 본 논문에서는 이코노마이저(Economizer)를 변경하여 공명을 회피하였다.

• Investigative Magnetic Resonance Imaging
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• 제17권1호
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• pp.33-40
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• 2013

목적 : 심장 아밀로이드증 환자의 심장 자기공명영상의 지연 조영증강영상에서 좌심근의 조영증강 패턴과 다른 심장부위의 조영증강 유무를 평가하고자 하였다. 대상 및 방법 : 2009년 9월부터 2011년 6월 사이 심장 아밀로이드증이 의심되어 심장 자기공명영상을 촬영한 9명의 환자를 후향적으로 분석하였다. 좌심근의 조영증강 여부 및 패턴, 그리고 좌우심방 및 우심실의 조영증강 유무를 평가하였다. 또한 심방중격 두께, 좌심방 혈액신호 강도에 대한 심방중격과 심외막 지방의 상대적 신호강도 비를 계산하여 허혈성 심질환 대조군 16명과 Wilcoxon rank sum test를 통해 통계적으로 비교분석 하였다. 결과 : 총 9명중 8명에서 좌심근 조영증강소견을 보였으며, 8명중 4명의 환자에서 심내막하 원형성, 나머지 4명에서 미만성 패턴을 보였다. 심방중격 두께는 심장 아밀로이드증 환자에서 허혈성 심질환 환자에 비해서 증가되어 있었고 (p = 0.02), 심장 아밀로이드증 환자군에서 심방중격 대 혈액 신호 강도비 (p = 0.0002) 및 심외막 지방 대 혈액 신호 강도비 (p = 0.0006) 모두 의미있게 높았다. 결론 : 좌심실의 심내막하 원형성 혹은 미만성 조영증강 패턴은 심장 아밀로이드증 환자의 지연 조영 심장 자기공명영상의 특징적인 소견이며, 심방중격 및 심외막 지방 대 혈액 신호 강도비 신호강도가 상대적으로 증가된다.

• 한국정밀공학회지
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• 제19권2호
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• pp.213-219
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• 2002

A cone-shaped active magnetic healing spindle system for high speed internal grinding with built-in motor that has 7.5kW power and maximum rotational speed of 50,000 rpm is designed and built. Using cone-shaped AMB(Active Magnetic Bearing) system, the axial rotor dick and magnets of conventional 5-axis actuating design can be eliminated. so this concept of design provides a simple magnetic bearing system. In this paper, the cone-shaped electromagnets are designed by magnetic circuit theory, and a de-coupled direct feedback PID controller is applied to control the coupled magnetic bearings. The designed crone-shaped AMB spindle system is built and constructed with a digital control system, which has TMS320C6702 DSP, 16 bit AD/DA, switching power amplifier and gap sensors. As the AMB system provides high damping ratio eliminating overshoot and resonance speed, this spindle runs up to 40,000 rpm stably with about 5${\mu}{\textrm}{m}$ of runout.

• 대한관절경학회지
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• 제10권1호
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• pp.39-44
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• 2006

목적: 전방 십자 인대 손상군과 슬관절의 손상 경력이 없는 정상군에서 슬개골 저위증의 빈도와 그 정도를 비교하고자 한다. 대상 및 방법: 스포츠 손상 후 발생한 전방 십자 인대 파열로 전방 십자 인대 재건술을 시행한 114예를 대상으로 하였다. 제 I 군은 수상 후 3주 이내에 자기공명영상을 시행한 급성 전방 십자 인대 파열군으로, 제 II 군은 3주 이후에 자기공명영상을 시행한 만성 전방 십자 인대 파열군으로, 제 III 군은 정상 대조군으로 하였다. T1 강조 자기 공명영상 정중 시상면에서 Insall-Salvati ratio, Carton index를 측정하여 비교 분석하였다. 결과: 정상군에서 Insall-Salvati ratio는 $1.02{\pm}0.12$, Carton index는 $1.14{\pm}0.16$, 전방 십자 인대 파열군에서는 각각 $0.91{\pm}0.12,\;0.89{\pm}0.20$으로 전방 십자 인대 파열군에서 모두 통계학적으로 유의하게 적었다. 급성 전방 십자 인대 파열군과 만성 전방 십자 인대 파열군에서의 비교는 통계학적 유의성은 없었다. 결론: 전방 십자 인대 파열군에서 정상 대조군과 비교시 슬개골 저위증의 경향을 보였으며, 따라서 전방 십자 인대 재건술시 슬개골 저위증의 경우, 이식건의 선택에 있어 세심한 고려가 필요할 것으로 사료된다.

• Journal of Radiation Protection and Research
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• 제31권2호
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• pp.91-96
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• 2006

The effects of Magnetic resonance imaging (MRI) on mouse embryos at the early stage of organogenesis were investigated. Pregnant ICR mice were exposed on day 8 of gestation to MRI at 0.5 T for 0.5 hour to 3 hours. The mortality rates of embryos or fetuses, the incidence of external malformations, fetal body weight and sex ratio were observed at day 18 of gestation. A significant increase in embryonic mortality was observed after exposure to either 0.5 T MRI for 0.5 hour or 2 hours. However, the exposure to MRI for 1 hour or 3 hours did not induce any significant increase in embryonic mortality when compared with control. External malformations such as exencephaly, cleft palate and anomalies of tail were observed in all experimental groups exposed to each MRI. A statistically significant increase of external malformations was observed in all groups treated with 0.5 T MRI for 0.5 hour and 3 hours. The incidence of external malformations in the mice group exposed to 0.5 T MRI for 0.5-hour was found to be higher than those of mice group exposed to 0.5 T MRI for 2 hours. The effects of MRI on the external malformations might not to be dose-dependent. There was no statistically significant difference in fetal body weight and sex ratio among each MRI exposure groups.

• Korean Journal of Radiology
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• 제22권10호
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• pp.1708-1718
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• 2021

Objective: The purpose of this study was to evaluate the magnetic resonance (MR) characteristics and applicability of new, uniform, extremely small iron-based nanoparticles (ESIONs) with 3-4-nm iron cores using contrast-enhanced magnetic resonance angiography (MRA). Materials and Methods: Seven types of ESIONs were used in phantom and animal experiments with 1.5T, 3T, and 4.7T scanners. The MR characteristics of the ESIONs were evaluated via phantom experiments. With the ESIONs selected by the phantom experiments, animal experiments were performed on eight rabbits. In the animal experiments, the in vivo kinetics and enhancement effect of the ESIONs were evaluated using half-diluted and non-diluted ESIONs. The between-group differences were assessed using a linear mixed model. A commercially available gadolinium-based contrast agent (GBCA) was used as a control. Results: All ESIONs showed a good T1 shortening effect and were applicable for MRA at 1.5T and 3T. The relaxivity ratio of the ESIONs increased with increasing magnetic field strength. In the animal experiments, the ESIONs showed peak signal intensity on the first-pass images and persistent vascular enhancement until 90 minutes. On the 1-week follow-up images, the ESIONs were nearly washed out from the vascular structures and organs. The peak signal intensity on the first-pass images showed no significant difference between the non-diluted ESIONs with 3-mm iron cores and GBCA (p = 1.000). On the 10-minutes post-contrast images, the non-diluted ESIONs showed a significantly higher signal intensity than did the GBCA (p < 0.001). Conclusion: In the phantom experiments, the ESIONs with 3-4-nm iron oxide cores showed a good T1 shortening effect at 1.5T and 3T. In the animal experiments, the ESIONs with 3-nm iron cores showed comparable enhancement on the first-pass images and superior enhancement effect on the delayed images compared to the commercially available GBCA at 3T.

• Ocean Systems Engineering
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• 제8권1호
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• pp.79-99
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• 2018

The effects of BPC (blade pitch control) on FOWT (floating offshore wind turbine) motions and generated power are investigated by using a fully-coupled turbine-floater-mooring simulation program. In this regard, two example FOWTs, OC4-5MW semi-submersible FOWT and KRISO four-3MW-units FOWT, are selected since the numerical simulations of those two FOWTs have been verified against experiments in authors' previous studies. Various simulations are performed changing BPC natural frequency (BPCNF), BPC damping ratio (BPCDR), and wind speeds. Through the numerical simulations, it was demonstrated that negative damping can happen for platform pitch motions and its influences are affected by BPCNF, BPCDR, and wind speeds. If BPCNF is significantly larger than platform-pitch natural frequency, the pitch resonance can be very serious due to the BPC-induced negative-damping effects, which should be avoided in the FOWT design. If wind speed is significantly higher than the rated wind velocity, the negative damping effects start to become reduced. Other important findings are also given through systematic sensitivity investigations.

• Journal of Power Electronics
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• 제18권1호
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• pp.185-194
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• 2018

Interaction among multiple grid-connected inverters has a negative impact on the stable operations and power quality of a power grid. The interrelated influences of inverter inductor-capacitor-inductor filters constitute a high-order power network, and consequently, excite complex resonances at various frequencies. This study first establishes a micro-grid admittance matrix, in which inverters use deadbeat control. Multiple resonances can then be evaluated via modal analysis. For the active damping method applied to deadbeat control, the sampling frequency and the stable domain of the virtual damping ratio are also presented by analyzing system stability in the discrete domain. Simulation and experimental results confirm the efficiency of modal analysis and stable domain calculation in multi-inverter grid-connected systems.