유한요소법에 의한 자기공명영상시스템에서의 와전류 영향 분석

이정한,강현수,조민형,문치웅,이강석,이수열,Lee, Jeong-Han,Gang, Hyeon-Su,Jo, Min-Hyeong,Mun, Chi-Ung,Lee, Gang-Seok,Lee, Su-Yeol 대한의용생체공학회 1999 의공학회지 Vol.20 No.1

Eddy current in MRI systems degrades gradient field linearity and distorts gradient waveform. When the waveform distortion is spatially variant, it is very difficult to perform special imaging techniques such as the echo planar imaging technique or the fast spin echo imaging technique. In this study, we have developed a new technique to estimate the distorted gradient waveforms at any points inside the imaging region using the finite element method. After obtaining the eddy-current-effect transfer function, which represents magnitude and phase characteristics of the gradient field at a particular point, we have used the transfer function to estimate the actual gradient waveforms at the point. To verify the proposed technique, we have compared the estimated gradient waveforms with the measured ones. 자기공명영상시스템에서 경사자계코일에 전류 펄스를 인가할 때 코일 주변의 도전성 구조물에 유도되는 와전류는 경사자계의 선형성을 열화 시킬 뿐만 아니라 경사자계의 파형을 왜곡시킨다. 특히 경사자계 파형의 왜곡 정도가 공간 위치에 따라 다를 경우 고속촬영법과 같은 고성능의 자기공명영상법을 실현하는 것이 어려워 진다. 본 연구에서는 촬영 공간 내 임의의 지점에서 와전류에 의해 경사자계 파형이 변형되는 정도를 알 수 있는 방법을 유한요소법을 이용해 구하였다. 경사자계코일에 정현파를 인가했을 때 임의의 지점에서 자계의 진폭 및 위상 특성이 주파수에 따라 어떻게 변하는지를 나타내는 와전류 영향 전달함수를 구하였고, 이 전달함수를 이용해 임의의 입력 전류 파형에 대한 출력 경사자계 파형을 예측하였다. 제안한 방법의 타당성을 검증하기 위해 실제로 측정한 경사자계 파형을 예측한 파형과 비교하여 제시하였다.

저널베어링으로 지지된 유성기어열의 동특성에 관한 연구

이정한,류형태,천길정,Lee, Jeong-Han,Ryu, Hyeong-Tae,Cheon, Gil-Jeong 대한기계학회 1998 大韓機械學會論文集A Vol.22 No.1

In this paper, the dynamic characteristics of a star type epicyclic gear train have been analyzed. Nonlinear stiffness of a gear pair were obtained considering the bending and shear deformation, Hertz contact deformation, as well as tooth fillet deformation. Nonlinear stiffness coefficients and damping coefficients around the static equilibrium position were obtained by perturbation method. The loci of the planet gears and sun gear were estimated. Tooth meshing forces and bearing reaction forces were calculated. The effects of bearing clearance and oil viscosity on the gear behavior were also analyzed.

여름잎마름병(Summer patch) 병원균에 대한 살균제의 억제효과 조사

이정한,심규열,김정호,전창욱,곽연식,Lee, Jung Han,Shim, Gyu Yul,Kim, Jeong Ho,Jeon, Chang Wook,Kwak, Youn-Sig 한국잡초학회 한국잔디학회 2017 Weed & Turfgrass Science Vol.6 No.2

국내 Kentucky bluegrass로 조성된 골프장이나 잔디 재배지에서 여름철에 여름잎마름병 발생으로 인한 피해가 심각한 상황이다. 그럼에도 불구하고 여름잎마름병방제약제가 아직까지 등록되어있지 않아 병원균에 효과적인 약제를 선발하기 위하여 본 연구를 수행하였다. 전형적인 여름잎마름병 병징에서 병원균을 분리하였고 ITS1과 ITS4 염기서열 분석으로 Magnaporthiopsis poae로 동정되었다. 잔디용으로 사용되는 10개의 약제를 대상으로 병원균 반응을 조사한 결과, 약제의 농도가 높아질수록 병원균 생장을 억제하였고 시간이 경과할수록 병원균 억제효과가 떨어지는 것이 관찰되었다. triazole계 약제 4종(metconazole, myclobutanil, propiconazole과 tebuconazole)의 병원균 억제효과는 100%로 나타났다. 다음으로 thiophanate-methyl의 억제효과가 높았으며 strobilurin계의 약제인 azoxystrobin, pyraclostrobin과 trifloxystrobin 약제를 비교하였을 때는 pyraclostrobin 약제가 가장 높게 나타났으며 다음으로 azoxystrobin과 trifloxystrobin 순으로 나타났다. Fludioxonil과 fluxapyroxad의 병원균 억제효과는 trifloxystrobin과 유사하게 나타났다. Summer patch is the most serious disease at turfgrass field or golf course established with Kentucky bluegrass during high temperature season in Korea. Nevertheless, chemicals for the summer patch control are not yet registered in Korea. We isolated the pathogens from the turfgrass showing typical summer patch symptoms and identified as Magnaporthiopsis poae by using the internal transcribed spacer ITS1 and ITS4 sequences of rDNA. The inhibition rates of the pathogen were investigated for 10 fungicides. As results, the pathogen growth was suppressed when chemicals concentration increased and negatively correlated with incubation period with the chemicals. In triazole group, all chemicals (metconazole, myclobutanil, propiconazole and tebuconazole) treated showed the inhibition rates by 100%. Thiophanate-methyl showed the next highest inhibition effect against a summer patch pathogen. In strobilurin group, pyraclostrobin was the highest suppression effect compared with azoxystrobin and trifloxystrobin. Inhibition effect of fludioxonil and fluxapyroxad on pathogen was similar to the trifloxystrobin. Based on the results, triazole and carboxamide groups are strongly recommended due to the highest inhibition effect on the summer patch pathogen, Magnaporthiopsis poae.

남성&여성 당뇨인, 그들만의 고민- 임신성 당뇨, 어떻게 관리할까?

이정한,Lee, Jeong-Han 사단법인 한국당뇨협회 2005 당뇨 Vol.189 No.-

임신 시에는 태아에게 영양소인 당분을 지속적으로 공급해 주기 때문에 대체로 고혈당을 유지하는 경향으로 신체가 변화된다. 이러한 고혈당이 병적으로 일정 수준을 넘어서면 임신성 당뇨병으로 진단하여 관리 및 치료를 필요로 하게 된다.

방전플라즈마 소결 공정을 이용한 WC-Co-B₄C 소재의 기계적 특성평가

이정한,박현국,Lee, Jeong-Han,Park, Hyun-Kuk 한국재료학회 2021 한국재료학회지 Vol.31 No.7

In this study, binderless-WC, WC-6 wt%Co, WC-6wt% 1 and 2.5 B₄C materials are fabricated by spark plasma sintering process (SPS process). Each fabricated WC material is almost completely dense, with a relative density up to 99.5 % after the simultaneous application of pressure of 60 MPa. The WC added Co and Co-B₄C materials resulted in crystalline growth. The WC with HCP crystal structure has respective interfacial energy (basal facet direction: 1.07 ~ 1.34 J·m^-2, prismatic direction: 1.43 ~ 3.02 J·m^-2) that depends on the grain growth direction. It is confirmed that the continuous grain growth, biased by the basal facet, which has relatively low energy, is promoted at the WC/Co interface. As abnormal grain growth takes place, the grain size increases more than twice from 0.37 to 0.8 um. It is found through analysis that the hardness property also greatly decreases from about 2661.4 to 1721.4 kg/mm², along with the grain growth.

활발해질 국제학술회의 개최

이정한,Lee, Jeong-Han 한국전자정보통신산업진흥회 1984 電子振興 Vol.4 No.1

ADAMS

이정한,Lee, Jeong-Han 대한기계학회 2007 기계저널 Vol.47 No.3

의료영상의 화질

이정한,Lee, Jeong-Han 대한디지털의료영상학회 1998 대한디지털의료영상학회논문지 Vol.4 No.1

국내 골프코스의 켄터키블루그래스에 Laetisaria fuciformis에 의한 붉은뿔마름병(Red Thread) 발생보고

이정한,김정호,심규열,곽연식,Lee, Jung Han,Kim, Jeong Ho,Shim, Gyu Yul,Kwak, Youn-Sig 한국잡초학회 한국잔디학회 2018 Weed & Turfgrass Science Vol.7 No.3

2017년 4월 중순 경남 양산에 소재한 골프장에서 Laetisariafuciformis에 의한 redthread 병징이 켄터키블루그래스에 발생하였다. 골프코스의 페어웨이에 불규칙한 모양의 병반 형태로 발생하였다. 감염된 잎은 마름증상을 보이면서 점차 볏짚색으로 변했으며, 잎의 끝부분은 실모양으로 헝클어져있었다. 이른 아침에는 분홍빛을 띤 젤라틴 형태로된 사슴뿔 모양의 균핵을 형성하였다. 배양적 특징으로 균총은 옅은 분홍색이었으며 균사다발이 형성되었고 3-5mm 크기의 연한 분홍색 균핵을 형성하였다. 병원균은 형태, 배양적특징 및 분자생물학적 특징을 토대로 L. fuciformis로 동정되었다. 코흐의 원칙에 따라 병원성 검정을 실시하여 켄터키블루그래스에 병원성이 있음을 확인하였다. 이는 한국에서 L. fuciformis에 의해 켄터키블루그래스에 발생하는 redthread에 대한 최초의 보고이다. In the middle of May 2018, typical red thread disease symptoms were observed on Kentucky bluegrass (Poa pratensis L.) on a golf course, which locates at Yangsan, Gyeongnam province in Korea. Irregular-shaped patched symptoms were observed in fairway of golf course. The foliar symptom was dried out and faded to straw color and tip of the grass leaves were tangled like thread. Early morning, infected and tangled leaves were covered with the pinkish gelatinous antler-like structure (sclerotinia) as a typical red thread disease symptom. Causal fungal pathogens were isolated from the symptom in Kentucky bluegrass. The fungal culture characteristic on potato dextrose agar color of colony was pale pink and conjugated hyphae, sclerotium of irregular shape was pale pink and 3~5mm diameter in size. The pathogen was identified as Laetisaria fuciformis based on morphological and culture characteristics as well as molecular characteristics. Pathogenicity test was verified on the Kentucky bluegrass by Koch's postulates. This is the first report of red thread disease occurrence in Kentucky bluegrass by L. fuciformis in Korea.

경추부 후종인대 골화증 1례에 대한 증례보고

이정한,박태용,조준기,김대중,김남수,신병철,송용선,고연석,Lee, Jeong-Han,Park, Tae-Yong,Jo, Joon-Ki,Kim, Dae-Joong,Kim, Nam-Su,Shin, Byung-Cheul,Song, Yung-Sun,Ko, Youn-Seok 척추신경추나의학회 2005 대한추나의학회지 Vol.6 No.1

Objective : There is hardly case report in oriental Medicine about the ossification of the posterior longitudinal ligament(OPLL). We experienced a patient(64-year-old male) with OPLL improved by oriental Medicine treatment, and we report it clinically. Methods : While the patient with OPLL was treated acupuncture, physical therapy, and CHUNA manual therapy, we evaluated the patient's symptoms and function by visual analogue scale(VAS), clinical criteria for evaluation of the cervical myelopathy by the japanese orthopaedic association(JOA Score) and cervical spine's range of motion(ROM) in three limes for the 17 days that were a hospitalization period. Results : VAS, JOA score and ROM in OPLL patient were improved. VAS in symptoms became lower from 10 to 5. JOA score increased from 12 points to 13 points. As for the ROM, it was improved in 30.1%. Conclusion : Oriental medicine treatment may be effective in conservative treatment of OPLL. We propose that more clinical studies and reaches are accomplished in oriental medicine.