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김보현,장지성,Kim, Bo Hyun,Jang, Ji Seong 유공압건설기계학회 2018 드라이브·컨트롤 Vol.15 No.4
Pilot operated control valve for $CO_2$ refrigerant is a valve that can perform various functions according to the user's intention by replacing pilot units, widely used for flow rate, pressure, and temperature control of refrigeration and air conditioning systems. In addition, $CO_2$ refrigerant, that requires high pressure and low critical temperature, can be installed and used in all positions of the refrigeration system, regardless of high or low pressure. In this paper, response characteristics are modeled and analyzed based on behavior of the main piston of the pilot-operated control valve. Although various factors influence operation of the main piston, this paper analyzes the effect of equilibrium pressure depending on valve installation position and application, and inlet and outlet orifice size of the load pressure feedback chamber to determine feedback characteristics of the main piston. As a result, it was possible to quantitatively analyze the effect of change in equilibrium and load pressure feedback chamber flow path size on the change in main piston dynamic and static characteristics.
방위사업에 적용 가능한 시스템 엔지니어링 표준에 대한 고찰
김보현,허장욱,Kim, Bo Hyeon,Hur, Jang Wook 한국시스템엔지니어링학회 2016 시스템엔지니어링학술지 Vol.12 No.2
The system engineering should be actively applied to successfully develop a complex and advanced weapon system, because the system engineering uses a multidisciplinary approach. Therefore, this study proposed a system engineering process for a successful weapon system development. According to the national standard policy, an IPT aspect system engineering standard must adapt the ISO/IEC/IEEE 15288. It also asks for tailoring with considering the IPT characteristics as a weapon system acquisition institution. The IPT aspect system engineering process to acquire a weapon system can be expressed with 3 process groups (Agreement, Technical Management, Technical) and 20 processes. There was a need for an institutional framework to hire retired experts from related organizations as consultants to apply the low-cost and high efficiency system engineering in the weapon system acquisition field.
김보현,박중원,Bo Hyun Kim,Joong-Won Park 대한소화기암연구학회 2016 Journal of digestive cancer reports Vol.4 No.1
Hepatocellular carcinoma (HCC) is rather unique. Most of HCC patients have underlying chronic liver diseases with or without cirrhosis and the prognosis of HCC depends on the liver function, as well as the tumor extent. Non-invasive diagnosis of HCC can be made with certain risk factors and specific imaging findings (e.g. hypervascularity). Patients with HCC can receive surgical resection, radiotherapy, and systemic chemotherapy as other solid malignancies. HCC has more treatment options such as liver transplantation, transarterial chemoembolization (TACE) and radiofrequency ablation (RFA). A variety of practice guidelines for HCC has been published by many academic societies. Different healthcare systems and availability of resources also affect the practice guidelines; therefore, practice guidelines have similarities and dissimilarities. Herein, we review the current status of practice guidelines for HCC and future perspectives for the improvement of guidelines are also discussed.
족관절에 발생한 미만성 색소 융모 결절성 활액막염의 개방적 절제술(1예 보고)
김보현,권순억,강신택,박세욱,Kim, Bo-Hyeon,Kwon, Soon-Eok,Kang, Shin-Taek,Park, Se-Wook 대한족부족관절학회 2009 대한족부족관절학회지 Vol.13 No.2
Pigmented villonodular synovitis (PVNS) is a rare proliferative disorder that affects synovium, tendon sheath and bursa. Although the condition can present in any joint, knee joint is the most commonly affected site and only 2.5% of cases occur in foot and ankle joint. PVNS occurs in two types: localized and diffuse. Localized type is characterized by focal involvement of the synovium with either nodular or pedunculated masses, Diffuse type affects virtually the entire synovium. Diffuse type has reported more recurrence rate. We have experienced a patient who has diffuse type PVNS of ankle joint and report an optimal method of surgical treatment.
frailtyHL 통계패키지를 이용한 프레일티 모형의 변수선택: 유방암 생존자료
김보현,하일도,노맹석,나명환,송호천,김자혜,Kim, Bohyeon,Ha, Il Do,Noh, Maengseok,Na, Myung Hwan,Song, Ho-Chun,Kim, Jahae 한국통계학회 2015 응용통계연구 Vol.28 No.5
통계적 모형에서 적절한 변수를 선택하는 것은 회귀분석에서 매우 중요하다. 최근 벌점 함수(예: LASSO 및 SCAD)와 함께 벌점화 가능도를 사용하는 변수 선택 방법들이 선형모형 및 일반화 선형모형과 같은 단순한 통계 모형에서 널리 연구되고 있다. 이러한 방법들의 주요 장점은 중요한 변수를 선택하고 동시에 회귀계수를 추정하는 것이다. 그러므로 이 방법들은 0으로 회귀계수를 추정함으로써 중요하지 않은 변수를 삭제한다. 이 논문에서는 콕스 비례 위험 모형의 한 확장인 준 모수적 프레일티 모형에서 벌점화된 다단계 가능도(h-likelihood; HL)를 기반으로 적절한 변수를 선택하는 방법을 연구한다. 이를 위해 세 가지 벌점 함수 LASSO, SCAD 및 HL을 사용한다. 본 논문에서는 변수선택을 효율적으로 하기 위해 "frailtyHL" R 패키지 (Ha 등, 2012)를 기반으로 하여 새로운 함수를 개발하였다. 개발된 방법의 예증을 위해 전남대 의과대학 병원에서 수집된 유방암 생존자료를 이용하여 세 가지 변수 선택 방법의 결과를 비교하고, 이 변수선택방법들의 상대적 장 단점에 대해 토론한다. Determining relevant variables for a regression model is important in regression analysis. Recently, a variable selection methods using a penalized likelihood with various penalty functions (e.g. LASSO and SCAD) have been widely studied in simple statistical models such as linear models and generalized linear models. The advantage of these methods is that they select important variables and estimate regression coefficients, simultaneously; therefore, they delete insignificant variables by estimating their coefficients as zero. We study how to select proper variables based on penalized hierarchical likelihood (HL) in semi-parametric frailty models that allow three penalty functions, LASSO, SCAD and HL. For the variable selection we develop a new function in the "frailtyHL" R package. Our methods are illustrated with breast cancer survival data from the Medical Center at Chonnam National University in Korea. We compare the results from three variable-selection methods and discuss advantages and disadvantages.
의학교육에의 교육순환모델(Learning Cycle)의 적용과 쟁점
김보현,김상현,Kim, Bo-Hyun,Kim, Sang-Hyun 연세대학교 의과대학 2008 의학교육논단 Vol.10 No.2
Purpose: The 'learning cycle' proposed by Guilbert in 1981 has been accredited as an effective and useful model for curriculum design. Three components of learning cycle, learning objective, instructional method, and assessment are connected organically and form basic structure of curriculum. In this study, we intend to analyze how the learning cycle and its three components are applied to present medical curriculum and examine the points at issue of the learning cycle in medical education. Also, we try to identify the educational significance of the leaning cycle in medical education. Results: First, concerning the learning objective, it was identified that impractical and abstract expressions are major controversial points. Also, there is a need to make learning objectives covering entire medical curriculum. Second, because of various structural problems, it is hard to practice new and various instructional methods. Third, even though there is a growing need for medical curriculum to develop and utilize more various and detailed assessment and evaluation, it was revealed that only are standardized and traditional assessments mainly used. Conclusion: Synthetically, we have some suggestions as follows. First, it is necessary to specify and actualize the learning objectives. Also, instructional methods and assessments should be diversified. And finally, there is a need to build organic and delicate medical curriculum by applying the learning cycle to medical education more actively.
플라즈마 산화방법을 이용한 질소가 첨가된 실리콘 산화막의 제조와 산화막 내의 질소가 박막트랜지스터의 특성에 미치는 영향
김보현,이승렬,안경민,강승모,양용호,안병태,Kim, Bo-Hyun,Lee, Seung-Ryul,Ahn, Kyung-Min,Kang, Seung-Mo,Yang, Yong-Ho,Ahn, Byung-Tae 한국재료학회 2009 한국재료학회지 Vol.19 No.1
Silicon dioxide as gate dielectrics was grown at $400^{\circ}C$ on a polycrystalline Si substrate by inductively coupled plasma oxidation using a mixture of $O_2$ and $N_2O$ to improve the performance of polycrystalline Si thin film transistors. In conventional high-temperature $N_2O$ annealing, nitrogen can be supplied to the $Si/SiO_2$ interface because a NO molecule can diffuse through the oxide. However, it was found that nitrogen cannot be supplied to the Si/$SiO_2$ interface by plasma oxidation as the $N_2O$ molecule is broken in the plasma and because a dense Si-N bond is formed at the $SiO_2$ surface, preventing further diffusion of nitrogen into the oxide. Nitrogen was added to the $Si/SiO_2$ interface by the plasma oxidation of mixtures of $O_2/N_2O$ gas, leading to an enhancement of the field effect mobility of polycrystalline Si TFTs due to the reduction in the number of trap densities at the interface and at the Si grain boundaries due to nitrogen passivation.