• 한국항공우주학회지
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• 제32권4호
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• pp.80-87
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• 2004

KSR-III 비행용 액체추진제 로켓엔진의 각 성능 변수 간 상관관계를 파악하기 위하여, 엔 진 지상연소시험의 결과에 대한 분석이 수행되었다. 내열재 연소실의 삭마에 따른 변화를 고려하였으며, 산화제/연료비에 의한 변화를 무시한 선형 회귀분석과 이를 포함한 이변수 이차 회귀분석이 수행되었다. 선형 회귀분석은 간단하면서도 분석영역 내에서 1% 이내의 오차율을 가지는 매우 실용적인 방법임을 보여주었다. 또한 이변수 이차 회귀분석 결과는 분석영역 내에서 매우 높은 정확도의 예측이 가능하였으며, KSR-III 엔진의 추력 (혹은 비추력) 및 연소실 압력 (혹은 특성속도)에 대한 최적 산화제/연료비가 각각 2.22 와 2.17 인 것으로 분석되었다.

• 한국항공우주학회지
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• 제38권1호
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• pp.1-11
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• 2010

압축성 실제 기제 유동 해석에 필수적인 음속의 정의에 대하여 다시 한 번 살펴보고, 열역학적으로 정의되는 음속(이하, 열역학 음속)과 특성 변수 해석을 통하여 정의되는 음속(이하, 고유 음속)을 일반화된 상태 방정식에 대하여 유도하였으며, 압력과 온도, 밀도가 선형적으로 비례하지 않는 실제 기체의 경우 열역학 음속과 특성 음속은 다소의 차이가 있음을 확인하였다. 이 과정에서 Roe의 근사 리만 해법을 다시 유도하여 실제 기체 효과의 수정이 필요한 부분을 살펴보았다. Roe의 근사 리만 해법과 AUSM 플럭스 분할 기법에 열역학적 음속과 특성 음속을 적용하여 비교한 경우 대체로 큰 차이는 없으나 특정한 경우 열역학 음속은 AUSM 방법의 경우 불안정성을 유발하기도 하였다. 수치 기법의 수학적 일관성의 측면에서도 특성 음속을 이용하는 것이 타당한 것으로 보인다. 이상의 방법은 다차원 문제에도 일관된 확장이 가능하였다.

• 한국추진공학회지
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• 제10권4호
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• pp.26-33
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• 2006

우주 발사체에서 고밀도 추진제를 사용함으로써 추진제 저장 탱크의 소형화에 따른 구조비 향상으로 발사체 성능 측면에서 이득을 볼 수 있다. 한국의 우주 발사체 개발에서는 로켓 연료로 발사체 선진국에서 사용하는 탄화수소계 연료인 RP-1이나 RG-1보다 밀도가 낮은 Jet A-1을 연료로 사용한다. 본 논문에서는 탄화수소계 연료 고밀도화의 일환으로 개발된 두 종류의 연료에 대해 수류시험, 연소시험 결과를 제시하고 그 결과를 Jet A-1과 비교하였다. 결론적으로, 두 종류의 고밀도 연료는 Jet A-1과 동등하거나 높은 연소성능을 나타내었으며 외부혼합형 분사기에서 연료 간 성능차이가 더 뚜렷하게 나타났다.

• Wind and Structures
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• 제3권3호
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• pp.209-220
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• 2000

The Strouhal number is an important nondimensional number which is explanatory of aerodynamic instability phenomena. It takes on the different characteristic constant value depending upon the cross-sectional shape of the body being enveloped by the flow. A number of investigations into this subject, especially on the drag test, surface pressure test and hot-wire test, have been carried out under the fixed state of the body in the past. However, almost no investigations concerning the determination of the St on wind-induced vibration of the body have been reported in the past even though the aerodynamic behavior of the body is very important because the construction of wind-sensitive structures is recently on the sharp increase. Based on a series of wind tunnel tests, this paper addresses a new method to determine the Strouhal number of rectangular cylinder in the uniform flow. The central idea of the proposed method is that the Strouhal number can be obtained directly by the aerodynamic behaviors of the body through wind-induced vibration test. The validity of proposed method is evaluated by comparing with the results obtained by previous studies in three B/Ds at attack angle $0^{\circ}$ and a square cylinder with various attack angles. The values and trends of the proposed Strouhal numbers are in good agreements with values of previous studies. And also, the Strouhal numbers of B/D=1.5 and 2.0 with various attack angles are obtained by the proposed method and verified by other method. This proposed method is as good as any other previous methods to obtain the Strouhal number.

• 대한의용생체공학회:의공학회지
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• 제33권3호
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• pp.148-154
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• 2012

Hemorrhagic shock is a primary cause of deaths resulting from injury in the world. Although many studies have tried to diagnose accurately hemorrhagic shock in the early stage, such attempts were not successful due to compensatory mechanisms of humans. The objective of this study was to construct a survival prediction model of rats in acute hemorrhagic shock using a random forest (RF) model. Heart rate (HR), mean arterial pressure (MAP), respiration rate (RR), lactate concentration (LC), and peripheral perfusion (PP) measured in rats were used as input variables for the RF model and its performance was compared with that of a logistic regression (LR) model. Before constructing the models, we performed 5-fold cross validation for RF variable selection, and forward stepwise variable selection for the LR model to examine which variables were important for the models. For the LR model, sensitivity, specificity, accuracy, and area under the receiver operating characteristic curve (ROC-AUC) were 0.83, 0.95, 0.88, and 0.96, respectively. For the RF models, sensitivity, specificity, accuracy, and AUC were 0.97, 0.95, 0.96, and 0.99, respectively. In conclusion, the RF model was superior to the LR model for survival prediction in the rat model.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제50권9호
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• pp.456-465
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• 2001

In this paper, breakdown voltages in $SF_6-N_2$ mixtures were experimentally investigated to understand characteristics of dielectric strength and physical phenomena in nonuniform field disturbed by a needle shape protrusion. The test voltages are the lightning impulse$(\pm1.2/44 \mus)$ and the damped oscillatory impulse$(\pm400 ns / 0.83 MHz)$ voltages which can be occurred by the operation of disconnecting switches in gas-insulated switchgears(GIS). The effects of the polarity and wave shape of the test voltages, and the gas pressure on the V-t characteristics were in detail examined. The V-t characteristic curves were measured in different two ways : (1) one is the method by taking the maximum voltage recorded at or prior to breakdown against the time to breakdown, that is, the Procedures recommended in IEC 60060-1, (2) the other is the method by taking the voltage at the instant of chopping against the time to breakdown. As a result, the V-t characteristics of $SF_6-N_2$ mixtures in nonuniform electric field were significantly affected by the polarity and wave shape of the applied voltages. The positive breakdown voltages resulted in lower breakdown voltages in the time ranges considered, and the V-t curves for the negative oscillatory impulse voltage were extended over the longer time range. For the lightning impulse voltages, the V-t curves obtained by IEC Pub. 60060-1 were nearly same with the V-t curves obtained by the voltage at the instant of chopping against the time to breakdown. It is clear that the actual breakdown voltages were much lower than the maximum voltages appearing at or prior to breakdown because of the displacement current produced as a result of the dV/dt during the oscillatory transient voltage app1ication. The scattering of the negative actual breakdown voltages was much larger than that of the positive.

• 설비공학논문집
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• 제30권2호
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• pp.100-106
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• 2018

Recently, the development of a heat pump technology to recover process waste heat and to generate steam of $120^{\circ}C$ or higher required for industrial processes, has attracted attention. The research of conventional heat pump utilizing the available energy is used primarily for air conditioning, and the production temperature is about $60^{\circ}C$, so it is difficult to utilize it for industrial use. Therefore, in this study, we developed a steam heat pump (SGHP) which recovers the waste heat of process and generates steam at $120^{\circ}C$. The low-pressure refrigerant R245fa, considered to be an eco-friendly refrigerant, has been selected as the refrigerant for SGHP in this study since its Ozone Depletion Potential (ODP) is zero and the Global Warming Potential (GWP) is relatively low. A flash tank functioning as a phase separator was installed in the rear stage of the condenser, and the saturated water of high temperature was decompressed to generate steam. It was started at the initial temperature of $70^{\circ}C$, and it was confirmed that $120^{\circ}C$ steam was produced after the system stabilized. We have conducted experiments by modifying the system, and ultimately achieved a heating capacity of 101.4 kW and a COP of 3.05.

• 한국임상수의학회지
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• 제31권4호
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• pp.325-328
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• 2014

A 8-month-old female Maltese dog was presented with a history of heart murmur. In physical examination, grade 4/6 systolic murmur heard at the left heart base. Electrocardiography showed sinus arrhythmia, right axis deviation, deep S wave and splintered QRS complex. Thoracic radiography revealed enlarged right side heart and bulging of the main pulmonary artery. Echocardiography showed mild hypertrophy of right ventricle, a supravalvular stenosis, marked post-stenotic dilation of the main pulmonary artery and a moderately increased pulmonary arterial velocity through the stenotic area (4.4 m/s, pressure gradient of 78.7 mmHg). The dog was diagnosed with supravalvular pulmonic stenosis based on the diagnostic imaging findings. Medical management using ${\beta}1$-blocker and ACE inhibitor was started in this dog and this is first case report described diagnostic characteristic features of supravalvular pulmonic stenosis in korea.

• 한국진공학회지
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• 제15권5호
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• pp.458-464
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• 2006

본 연구에서는 초고진공 (UHV; ultra high vacuum) 분자선 에피성장 (MBE; molecular beam epitaxy) 시스템의 제작과 성능연구가 성공적으로 이루어졌다. 초고진공 용 분자선 에피성장 시스템을 국산화개발 및 제작하여, 장비에 관한 성능 테스트를 하게 되었다. 본 장비의 진공도가 $2X10^{10}$ Torr에 도달함을 확인하였고, 시편 가열모듈(substrate heating module)이 $1,100^{\circ}C$까지 가열됨을 확인할 수 있었으며, ZnSe/GaAs(001)의 증착특성을 SEM (scanning electron microscope), AFM (atomic force microscope), XRD (x-ray diffraction), PL (photoluminescence) 등으로 조사하였다.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2005년도 ICCAS
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• pp.1445-1449
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• 2005

The ram assembly is important equipment in fueling machine of PHWR(Pressurized Heavy Water Reactor) plant where fuel replacement is possible while the plant is in service. Troubles in the ram assembly can cause lots of difficulties in power plant operation. The ram assembly is typically composed of the B-ram, the L-Ram and the C-Ram. The B-ram is focused in this paper because it plays the most important role in the ram assembly. Among the ram fault phenomena, ram stuck phenomena are the most frequent cases in the B-ram, which has a ball screw mechanism driven by a hydraulic motor. Ram stuck phenomena are due to ball wear and damage in ball nut that increase in proportion to the number of fuel replacement. It is required to predict ram stuck phenomena before they occur. In this paper, a method is proposed for predicting ram stuck phenomena using a discrete wavelet transform. The discrete wavelet transform provides information on both the time and frequency characteristics of the input signals. The proposed method uses the frequency bandwidths of coefficients of discrete wavelet decompositions and detail coefficients of discrete wavelet transform to predict ram stuck phenomena. The signal used in this paper is a torque-related signal such as a hydraulic service outlet pressure signal in a hydraulic driving system or a current signal in a DC motor driving system. Finally, the validity of the proposed method is shown via experiment using ball nut characteristic test equipment that simulates ram stuck phenomena due to increased ball friction in ball nut.