• 한국초전도ㆍ저온공학회논문지
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• 제22권1호
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• pp.12-16
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• 2020

As high homogeneity in magnetic field is required to increase the resolution of MRI magnets, various shimming methods have been researched. Using one of them, the design of the superconducting active zonal shim coil for MRI magnets is discussed in this paper. The magnetic field of the MRI magnet is expressed as the sum of spherical harmonic terms, and the optimized current density of shim coils capable of removing higher-order terms is calculated by the Tikhonov regularization method. To investigate all potential designs derived from calculated current density, 4 sweeping parameters are selected: (1) axial length of shim coil zone; (2) radius of shim coils; (3) exact axial position of shim coils; and (4) operating current. After adequate designs are determined with constraints of critical current margin and homogeneity criterion, the total wire length required for each is calculated and the design with a minimum of them is chosen. Using the superconducting wire length of 9.77 km, the field homogeneity over 50 cm DSV is improved from 24 ppm to 1.87 ppm in the case study for 9.4 T whole-body MRI shimming. Finally, the results are compared with the finite element method (FEM) simulation results to validate the feasibility and accuracy of the design.

• 한국항행학회논문지
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• 제10권4호
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• pp.319-326
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• 2006

본 논문에서는 연료 유량만을 제어 입력으로 하는 터보제트 엔진 제어기를 제안한다. 퍼지 기반 제어기는 무인 항공기의 가감속시 서지와 flame-out 현상이 발생되지 않도록 효율적으로 제어 입력을 생성하며, 항공기 기동시 빠른 가감속 특성을 보이며, 동작점이 서지라인과 flame-out라인 사이에 존재하도록 설계되었다. 엔진 회전 속도와 서지 여유가 퍼지 입력 변수가 되고, 신속하고 안전하게 항공기가 원하는 회전속도로 수렴할 수 있도록 제어기를 설계한다. 제안된 제어기의 성능확인을 위해 MATLAB을 사용한 컴퓨터 시뮬레이션을 수행하였으며, DYGABCD 프로그램을 사용하여 생성된 선형 엔진 모델에 적용하여 성능을 입증하였다.

• 한국전산유체공학회지
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• 제18권4호
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• pp.1-8
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• 2013

The performance of small-size impellers with ruled surfaces was investigated for flank milling over a wide speed range, using computational fluid dynamics analyses and gas bench tests. An impeller with a ruled surface was designed, manufactured, and tested to evaluate the effects of blade loading, the backsweep angle, and the relative velocity distribution on the compressor performance. The simulations and tests were completed using the same compressor cover with identical inlet and outlet channels to accurately compare the performance of the abovementioned impeller with a commercial impeller containing sculptured blades. Both impellers have the same number of blades, number of splitters, and shroud meridional profiles. The backsweep angles of the blades on the ruled impeller were selected to work with the same pinched diffuser as for a sculptured impeller. The inlet-to-exit relative velocity diffusion ratio and the blade loading were provided to maximize the flow rate and to minimize the surge flow rate. The design flow rate, rpm, were selected same for both impellers. Test results showed that for the compressor stage with a ruled impeller, the efficiency was increased by 0.32% with an extended surge margin without a reduction in the pressure ratio as compared to the impeller with the sculptured design. It was concluded that an increased relative velocity diffusion coupled with a large backsweep angle was an effective way to improve the compressor stage efficiency. Additionally, an appropriate blade loading distribution was important for achieving a wide operating range and higher efficiency.

• 대한기계학회논문집A
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• 제38권4호
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• pp.379-384
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• 2014

가스터빈엔진의 가장 핵심 부품인 디스크와 블레이드는 고온, 고압축비, 고속 회전이라는 가혹한 환경에서 지속적으로 운용된다. 이러한 가혹한 환경과 디스크와 블레이드가 가지는 큰 회전 에너지로 인해 디스크 및 블레이드에 의해 유발되는 파손은 항공기 손상 혹은 탑승자의 피해로 이어지는 재해적 고장 혹은 한계 고장으로 이어진다. 그러므로 디스크와 블레이드의 구조적 건전성의 마진을 충분히 확보하기 위해서 본 연구에서는 디스크의 취약 부위인 도브테일의 형상을 최적화하고, 그 해의 강건성을 확인하기 위해 치수 공차와 피로 수명의 산포와 같은 불확실성에 대하여 신뢰도 해석을 수행하고자 한다. 이 결과를 통해 결정론적 방법인 최적설계의 필요성과 함께 한계를 확인하고, 향후 신뢰도 기반 최적설계의 필요성을 인지하고자 한다. 이를 위해 비선형 열-구조 연성해석과 접촉 해석을 포함한 유한요소해석을 수행하였다.

• 보건행정학회지
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• 제12권4호
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• pp.1-17
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• 2002

This study was attempted to identify the liquidity trends and determinants of private hospitals in Korea different. Data used in this study were collected from 98 hospitals with complete general data of present conditions as well as financial statements(balance sheets, income statements). They were chosen from hospitals that passed the standardization audit undertaken by the Korean Hospital Association from 1996 to 2000 for the purpose of accrediting training hospitals. The dependent variables in this study were used current ration and quick ratio as a proxy indicator for liquidity. The independent variables were ownership type, hospital type, location, bed size, period of establishment, short-term liabilities to total assets, long-term liabilities to total assets, borrowings to total assets, fixed asset ration, net profit to total assets, operating margin to gross revenue, growth rate of net worth to total assets, total asset turnover, and business risk(volatility of profit). The major findings of this study were as follows. Trends of liquidity(current ratio, quick ratio) had been continuously decreased. Especially, There were very distinct decreasing trends of personal hospitals and less than 300beds, which weakened liquidity. The factors had significant effect on current ratio were short-term debt to total assets(-), fixed asset ratio(-), business risk(+). High short-term debt to total assets, high fixed asset ratio and high business risk significantly decreased in liquidity. The factors that significantly affected on quick ratio were short-term debt to total assets(-), borrowings to total assets(+), fixed asset ratio(-), business risk(+).

• 보건행정학회지
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• 제18권2호
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• pp.19-38
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• 2008

Financial ratios are key indicators of an organization's financial and business conditions. Among various financial indicators, profitability, financial structure, financial activity and liquidity ratios are frequently used and analyzed. Using the structural equation modeling(SEM) technique, this study examines the structural causal relationships among key financial indicators. Data for this study are taken from complete financial statements from 142 hospitals that passed the standardization audit undertaken by the Korean Hospital Association from 1998 to 2001 for the purpose of accrediting teaching hospitals. In order to improve comparability, ratio values are standardized using the Blom's normal distribution. The final model of the SEM has four latent constructs: financial activity(total asset turnover, fixed asset turnover), liquidity(current ratio, quick ratio, collection period), financial structure(total debt to equity, long-term debt to equity, fixed assets to fund balance), and profitability(return on assets, normal profit to total assets, operating margin to gross revenue, normal profit to gross revenue). While examining several model fit indices(Chi-square (df) = 178.661 (40), likelihood ratio=4.467, RMR=.11, GFI=.849, RMSEA=.157), the final SEM we employed shows a relatively good fit. After examining the path coefficient of the constructs, the financial structure of the hospital affects the hospital's profitability in a statistically significant way. A hospital which utilizes its liabilities, more specifically fixed liabilities, and makes a stable investment decision for fixed assets was found to have a higher profitability than other hospitals. Then, the standard path coefficients were examined to directly compare the influence of variables. It was found that there were no statistically significant path coefficients among constructs. When it comes to variables, however, statistically significant relationships were found. between. financial activity and. fixed. asset turnover, and between profitability and normal profit to gross revenue. These results show that the observed variables of fixed asset turnover and normal profit to gross revenue can be used as indicators representing financial activity and profitability.

• 디지털융복합연구
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• 제18권1호
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• pp.249-255
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• 2020

본 연구는 공공의료기관의 경영성과와 공공성의 관계를 분석하기 위해 2015-2017년의 13개 국립대병원의 결산서와 연보를 통하여 자료를 수집하였다. 연구결과 공익성지수는 의료수익순이익율, 의료수익의료이익율에 유의한 음(-)의 관계로 나타났다. 의료사회사업비는 의료수익경상이익율, 의료수익순이익율에 유의한 양(+)의 영향력이 있는 것으로 나타났다. 그리고 국립대학교병원은 지역에 따라 의료수익경상이익율에 유의한 영향력을 미치는 것으로 나타났다. 본 연구 대상인 국립대학교병원이 의료의 공공성 분야에서 민간의료기관 대비 어떤 차별화된 사업을 수행하고 있는지 객관적인 평가와 총체적 점검이 필요하다. 그리고 이를 바탕으로 국립대학교병원의 설립 목적에 맞는 역할의 재정립이 필요하다.

• 디지털융복합연구
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• 제11권11호
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• pp.463-470
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• 2013

이 논문은 지방공사의료원과 의료법인 간의 성과에 영향을 미치는 요인을 분석하여 지방공사의료원의 효율적인 경영을 재무적으로 파악하는데 있다. 연구자료는 국세청 공익법인 공시시스템에 공시되어 있는 67개 의료기관의 재무성과를 조사하였다. 병원 현황 및 의료기기 정보는 2012년 2분기 건강보험심사평가원의 자료와 대한병원협회 명부를 사용하였다. 일반적 특성으로 지방공사의료원은 의료법인보다 시나 군 지역에 많이 분포하였고, 간호등급 4등급 이하가 대부분을 차지하고 있었다. 지방공사의료원과 의료법인 간 의료이익, 당기순이익을 분석한 결과 지방공사 의료원이 의료법인에 비해서 적자병원이 많은 것으로 파악되었다. 대부분의 지방공사의료원이 의료이익, 당기순이익에서 적자를 보이고 있어, 수익성을 악화시키는 요인들을 개선할 필요가 있으며, 지금과 같이 의료법인과 경쟁관계를 지양하고, 필수공익의료를 제공하는 조직으로 병원구조를 변화시키도록 노력해야 할 것이다.

• 전기전자학회논문지
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• 제20권3호
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• pp.285-290
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• 2016

고속 인터페이스에서 채널 대역폭에 의해 생기는 ISI는 최대 데이터 전송속도를 제한한다. ISI를 제거하는 가장 보편적인 기술로 DFE가 있다. 빠른 데이터 송수신을 위해서는 DFE가 효과적으로 ISI를 제거하는 것도 중요하지만 피드백 지연 등을 완화시켜 회로 자체의 최대 동작 주파수도 증가시켜야 한다. 또한, 싱글 엔디드 시그널링에서는 DFE가 ISI뿐만이 아닌 고주파 잡음도 효과적으로 제거하여야 한다. 한편, 데이터 전송 속도가 올라감에 따라 늘어 나는 ISI 및 고주파 잡음을 제거하기위한 DFE 구성품의 수가 증가한다. 이는 곧 추가의 전력소모를 야기하므로 고속 동작뿐만 아니라 저전력 동작도 주목할 필요가 있다. 본 논문에서는 ISI와 고주파 잡음을 효과적으로 제거하는 고속 DFE 및 저전력으로 동작하는 DFE의 동작 방식과 이들이 갖고 있는 장단점을 소개한다.

• Journal of Radiation Protection and Research
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• 제28권2호
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• pp.127-135
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• 2003

The primary contributors to the total occupational radiation exposure in operating nuclear power plants are operation and maintenance activities doting refueling outages. The Advanced Power Reactor 1400 (APR1400) includes a number of design improvements and plans to utilize advanced maintenance methods and robotics to minimize the annual collective dose. The major radiation exposure reduction features implemented in APR1400 are a permanent refueling pool seal, quick opening transfer tube blind flange, improved hydrogen peroxide injection at shutdown, improved permanent steam generator work platforms, and more effective temporary shielding. The estimated average annual occupational radiation exposure for APR1400 based on the reference plant experience and an engineering judgment is determined to be in the order of 0.4 man-Sv, which is well within the design goal of 1 man-Sv. The basis of this average annual occupational radiation exposure estimation is an eighteen (18) month fuel cycle with maintenance performed to steam generators and reactor coolant pumps during refueling outage. The outage duration is assumed to be 28 days. The outage work is to be performed on a 24 hour per day basis, seven (7) days a week with overlapping twelve (12) hour work shifts. The occupational radiation exposure for APR1400 is also determined by an alternate method which consists of estimating radiation exposures expected for the major activities during the refueling outage. The major outage activities that cause the majority of the total radiation exposure during refueling outage such as fuel handling, reactor coolant pump maintenance, steam generator inspection and maintenance, reactor vessel head area maintenance, decontamination, and ICI & instrumentation maintenance activities are evaluated at a task level. The calculated value using this method is in close agreement with the value of 0.4 man-Sv, that has been determined based on the experience aid engineering judgement. Therefore, with the As Low As Reasonably Achievable (ALARA) advanced design features incorporated in the design, APR1400 design is to meet its design goal with sufficient margin, that is, more than a factor of two (2), if operated on art eighteen (18) month fuel cycle.