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- 저자 : 김의현 (검색결과 127 건)
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김의현,오용구,임진우,채종률,이민희,최윤건 대한내과학회 1988 대한내과학회지 Vol.35 No.4
An aneurysm of the sinus of Valsalva is relatively rare. From May 1986 to April 198S, we found three patients with this pathology at our institution. In all patients, diagnosis was suspected by echocardiography before cardiac catheterization and angiography. The final diagnosis was confirmed at surgery. This case report describes the echocardiographic findings in our patients with a rcview of the literature about echocardiographic manifestations of sinus of Valsalva aneurysms with or without rupture. Echocardiography is useful in detecting abnormalities of the aortic root and provides important information prior to cardiac catheterization and surgery. One patient had a 60 mmHg peak systolic pressure gradient between the right ventricle and pulmonary artery; the obstruction was caused in part by the bulging of the sinus of Valsalva aneurysm into the right ventricular outflow tract as well as by infundibular pulmonic stenosis. The corrective surgery was performed without complication and the postoperative course was uneventful.
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김의현,권숙인 대한용접접합학회 1993 대한용접·접합학회지 Vol.11 No.4
The plasma sprayed $Cr_3C_2$-NiCr coatings are widely used as wear-resistant and corrosion-resistant materials. The mechanical and wear properties of the plasma sprayed $Cr_3C_2$-NiCr coating on steel plate were examined in this study. The pore in the coatings could be classified into two types, the one is the intrinsic pore originated from the spraying powder, the other is the extrinsic pore formed during spraying. During the tensile adhesion test, the fracture occured at the interface of top coating and bond coating. It is though that the compressive residual stress increases with the increase of the top coating thickness. From the wear test, it was found that the wear rate increased with the increase of the sliding velocity regardless of the temperature. It is thought that the fracture toughness reduces with the increase of the sliding velocity at $30^{\circ}C$ and that the adhesion amount increases with the increase of the sliding velocity at $400^{\circ}C$ It is concluded that the wear mechanism at $30^{\circ}C$ is the fracture and pull-out of the carbide particles due to the fatigue on sliding surface, while the wear mechanism at $400^{\circ}C$ is the adhesion of the smeared layer formed during wear process.
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김의현,안현식 한국인터넷방송통신학회 2017 한국인터넷방송통신학회 논문지 Vol.17 No.1
본 논문에서는, 스위칭 손실이 적고 효율이 높은 이점을 갖고 있는 LLC 공진형 컨버터에 대하여 선형화된 수학적 모델을 정립하고 디지털 제어기 설계 과정을 제안한다. LLC 공진형 컨버터의 비선형 모델에 대하여 EDF(Extended Describing Function) 기법을 도입하여 비선형성을 선형 근사화시킨 선형 소신호 모델을 정립하고 Ziegler Nichols 방법을 이용하여 제어기 계수를 선정하였으며 연속시간 제어기를 디지털 제어기로 변환하여 적용한다. 유도된 선형 소신호 모델에 기 반하여 전압 제어기를 설계하고, MATLAB 시뮬레이션을 통하여 제어기의 성능을 검증한다. 또한, 부하 변화 및 모델링 오차 를 고려한 시뮬레이션을 통하여 LLC 공진형 컨버터에 대해 설계된 전압 제어기의 타당성 및 제어성능을 분석한다. In this paper, we propose a digital controller design methodology for an LLC resonant converter which has been widely used due to the advantages of low switching loss and high efficiency. We establish a mathematical model of an LLC resonant converter using the extended describing function concept and propose a controller design method based on the Ziegler Nichols control parameter tuning criteria. The voltage controller of an LLC resonant converter is designed based on the derived small signal model and the performance of the controller is verified by MATLAB simulations. The validity and the control performance of the designed voltage controller for the LLC resonant converter is analyzed through some simulations for the case of load variations and circuit modeling errors.
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크롬탄화물 용사피막의 접착력 및 잔류응력측정에 관한 연구
김의현,김종영 대한용접접합학회 1996 대한용접·접합학회지 Vol.14 No.4
The plasma sprayed Cr$_{2}$C$_{2}$-NiCr coatings are widely used as wear-resistant and corrosion-resistant materials. The mechanical properties of the plasma sprayed Cr$_{2}$C$_{2}$-NiCr coatings were examined in this study. The distribution of the residual stress with the coating thickness was also examined by X-ray diffraction method. The pore in the coatings could be classified into two types ; one is the intrinsic pore originated from the spraying powder, the other is the extrinsic pore formed during spraying. During the tensile adhesion test, the fracture occurred at the interface of top coat and substrate or top coat and bond coat depending on the existence of bond coat. It was found that the compressive residual stress near the interface decreased with the increase of the top coat thickness. The tensile adhesion strength of the coating without bond coat was higher than that with bond coat, because the coating with bond coat has higher horizontal crack density near the interface between bond coat and top coat.
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파일럿 규모 광펄스 처리를 이용한 해수에 오염된 Escherichia coli 저해
김의현,김진철,홍성철,민세철 한국산업식품공학회 2020 학술대회 및 심포지엄 Vol.2020 No.11
본 연구에서는 파일럿 규모 광펄스 처리 장비를 이용한 광펄스 처리의 해수에 오염된 Escherichia coli에 대한 저 해 효과를 확인하였다. 광펄스 처리를 이용한 해수 살균 시에는 처리 용량이 70 L 인 반응기를 이용하여 약 160 L 의 해수를 연속식으로 처리하였다. 처리 frequency와 반응기로 유입되는 해수의 유속은 각각 5 Hz와 15 L/m으로 고 정하였고, 처리 전압은 1,800, 2,000, 그리고 2,400 V로 설정하였다. 처리 전압이 1,800 V에서 2,000 V, 그리고 2,400 V로 증가할 때 해수에 접종된 E. coli 저해 정도는 3.2 ± 0.9에서 4.8 ± 0.3, 그리고 7.15 ± 0.5 log CFU/mL로 증가하 였다. 광펄스 처리에 따른 해수 살균 시 해수의 온도 변화(ⵠT)는 처리 전압 1,800, 2,000, 그리고 2,400 V에서 각각 0.0, 1.2, 그리고 1.6 ℃로 확인되었다. 본 연구를 통해 광펄스 처리가 해수 내 E. coli를 효과적으로 저해시킬 수 있 는 비가열 살균 기술임을 확인할 수 있었다.
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