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.

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.

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.

의료영상의 화질

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

전자기술과 장인정신

이정한,Lee, Jeong-Han 한국전자정보통신산업진흥회 1984 電子振興 Vol.4 No.12

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.

Ar-H₂플라즈마 건식제련과 마이크로웨이브침출을 통한 지르콘샌드로부터 고순도 지르코니아 분리

이정한,홍성길,Lee, Jeong-Han,Hong, Sung-Kil 한국자원리싸이클링학회 2016 資源 리싸이클링 Vol.25 No.3

In this study, zircon sand is separated into zirconia and silica by using the Ar-$H_2$ arc plasma refining. And then silica is removed from it by the microwave leaching method to produce a high pure zirconia. Plasma melting consist of two sequential processes; reduction process with Ar gas only followed by refining process with Ar-$H_2$ gas. After cooling in chamber. The solid phase obtained at $240^{\circ}C$ were found to be composed of 20% sulfuric acid solution. The solution was used as a leaching solution with microwave irradiation to obtain a high purity zirconia. 본 연구에서는, 아크 플라즈마 정련을 이용하여 지르콘샌드($ZrSiO_4$)를 지르코니아($ZrO_2$)와 실리카($SiO_2$)로 분리하였다. 실리카를 마이크로웨이브 침출을 통해 제거하고 고순도의 지르코니아를 얻었다. 플라즈마 퓨전은 두 가지 공정을 순차적으로 진행하였다. Ar 100% 분위기에서 환원 공정을 거친 후, Ar-$H_2$ 혼합 가스를 통해 정련과정을 거쳤다. 진공 챔버 내에서 냉각 후 지르코니아와 실리카로 이루어진 고상을 얻었다. 마이크로웨이브 침출을 위해 $240^{\circ}C$, 20% 황산용액을 사용하였다. 분석 결과 고순도(98.6%)의 지르코니아를 얻을 수 있었다.

사회복지시설에 종사하는 일부 재활전문가들의 방문재활에 대한 필요성 조사

이정한,김계엽,김은정,Lee, Jeong-Han,Kim, Gye-Yeop,Kim, Eun-Jung 대한물리치료학회 2010 대한물리치료학회지 Vol.22 No.5

Purpose: The purpose of this study was to analyze the necessity of home visit rehabilitation therapy by rehabilitation professionals working at social welfare facilities. Methods: The subjects of this study were 227 rehabilitation professionals (social worker, nurse, physical therapist, occupational therapist, speech-language therapist, special education teacher, and staff of institutions for the disabled who were working at community rehabilitation centers. The data were collected over 65 days (2008. 09. 10~11. 14). The results were analysed statistically by the Chi-square test. Results: The results are as follows: Long-term care service was established in Korea by the Ministry of Health in July, 2008. But there are limits to their being able to provide various rehabilitation services for chronic patients and old people. According to a recent survey, almost all rehabilitation professionals (N=227) stated that home visit rehabilitation therapy is necessary. Conclusion: In Korea, the long-term care service has a nursing service and a service supporting physical activities of daily living, but not physical therapy. So, home visit rehabilitation services should include physical therapy, rehabilitation exercise, and pain management.

산업장 근로자의 주관적 건강인식에 영향을 미치는 요인 분석

이정한,고연석,권소희,김삼태,정해경,박승정,송용선,이기남,Lee Jeong-Han,Ko Youn-Seok,Kwon So-Hee,Kim Sam-Tae,Jung Hae-Kyoung,Park Seung-Jong,Song Yung-Sun,Lee Ki-Nam 대한예방한의학회 2004 대한예방한의학회지 Vol.8 No.1

This study tried to analyze influencing factors on self-perceived health status(SPHS) of labors in workplace. and suggested the preventive oriental medicine approaches in occupational health care. 914 data for research were collected through the process of oriental health examination with questionnaire in workplace and collected data were analyzed with frequency, homogeneity and correlation statistically. The results were as follows : 1) The distributions of SPHS was 58.4% of healthy group. 41.6% of unhealthy group. 2) For the difference of SPHS by stress, the high level stress group was more included in healthy group(p<0.05). 3. For the difference of SPHS by health behavior. the higher score of health behavior group was more included in healthy group. There was statistically significant difference of SPHS in physical exercise, but not in smoking, drinking, sleeping and body mass index. 4. For the difference of SPHS by the latest health examination results, non-disease group was more included in healthy group, while disease group was more included in unhealthy group. From the above results, SPHS was influenced by stress, health behavior, the latest health examination results. Therefore oriental medical service for occupational health must be interested in the these influencing factors and make an effort to change their perception of health as well as physical improvement.

ADAMS

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