• 한국전기전자재료학회논문지
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• 제15권9호
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• pp.794-797
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• 2002

Piezoelectric properties of PZT-PSN ceramics were investigated as a function of WO$_3$ addition from 0 wt% to 6.0 wt%. The dielectric and piezoelectric characteristics of PZT-PSN ceramics have been investigated at different calcination (80$0^{\circ}C$~90$0^{\circ}C$) and sintering (110$0^{\circ}C$~130$0^{\circ}C$) temperatures. The grain size was increased with the addition of WO$_3$and the sintering temperatures. Anisotropic properties of electromechanical coupling coefficient and piezoelectric coefficient are proven to be dependent on processing temperatures and amount of addition. At the specimen with 0.6 wt% WO$_3$ addition, using calcination temperature of 80$0^{\circ}C$ and sintering temperature of 110$0^{\circ}C$ , mechanical quality factor(Q$_{m}$) and electromechanical coupling coefficient(k$_{p}$) showed the excellent results of 1560 and 0.48, respectively Experimental results indicated that the PZT-PSN system ceramics with WO$_3$impurity could be effectively used for the microtransformer and actuator applications, etc.etc.

• Nuclear Engineering and Technology
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• 제53권1호
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• pp.93-102
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• 2021

The analysis of the fluid flow characteristics in reactor pressure vessel is an important part of the hydraulic design of nuclear power plant, which is related to the structure design of reactor internals, the flow distribution at core inlet and the safety of nuclear power plant. The flow distribution and mixing characteristics in the pressurized reactor vessel for the 1000MWe advanced pressurized water reactor is analyzed by using Computational Fluid Dynamics (CFD) method in this study. The geometry model of the full-scaled reactor vessel is built, which includes the cold and hot legs, downcomer, lower plenum, core, upper plenum, top plenum, and is verified with some parameters in DCD. Under normal condition, it is found that the flow skirt, core plate holes and outlet pipe cause pressure loss. The maximum and minimum flow coefficient is 1.028 and 0.961 respectively, and the standard deviation is 0.019. Compared with other reactor type, it shows relatively uniform of the flow distribution at the core inlet. The coolant mixing coefficient is investigated with adding additional variables, showing that mass transfer of coolant occurs near the interface. The coolant mainly distributes in the 90° area of the corresponding core inlet, and mixes at the interface with the coolant from the adjacent cold leg. 0.1% of corresponding coolant is still distributed at the inlet of the outer-ring components, indicating wide range of mixing coefficient distribution.

• 한국공간구조학회논문집
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• 제23권3호
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• pp.87-94
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• 2023

Chloride is one of the most common threats to reinforced concrete (RC) durability. Alkaline environment of concrete makes a passive layer on the surface of reinforcement bars that prevents the bar from corrosion. However, when the chloride concentration amount at the reinforcement bar reaches a certain level, deterioration of the passive protection layer occurs, causing corrosion and ultimately reducing the structure's safety and durability. Therefore, understanding the chloride diffusion and its prediction are important to evaluate the safety and durability of RC structure. In this study, the chloride diffusion coefficient is predicted by machine learning techniques. Various machine learning techniques such as multiple linear regression, decision tree, random forest, support vector machine, artificial neural networks, extreme gradient boosting annd k-nearest neighbor were used and accuracy of there models were compared. In order to evaluate the accuracy, root mean square error (RMSE), mean square error (MSE), mean absolute error (MAE) and coefficient of determination (R2) were used as prediction performance indices. The k-fold cross-validation procedure was used to estimate the performance of machine learning models when making predictions on data not used during training. Grid search was applied to hyperparameter optimization. It has been shown from numerical simulation that ensemble learning methods such as random forest and extreme gradient boosting successfully predicted the chloride diffusion coefficient and artificial neural networks also provided accurate result.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1999년도 춘계학술대회 논문집
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• pp.653-656
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• 1999

Effect of $Al_2O_3$ Additives on Microwave Dielectric Properties of $0.15(Ba_{0.85}Ca_{(0.15-y)}Mg_y)$-0.125 $Nd_2O_3-0.60TiO_2+10wt%Bi_zO_3$ (y=0.05, 0.08) Ceramics was investigated. To control of $\tau\;{f}$ on microwave dielectric properties of $0.15(Ba_{0.85}Ca_{(0.15-y)}Mg_y)$-0.125 $Nd_2O_3-0.60TiO_2+10wt%Bi_zO_3$ ceramics $Al_2O_3$ was doped in the composition range of 0 to 0.15 wt%. As a result, dielectric constant was decreased from 94 to 80 but $Q\cdot{f}_0$ value was increased from 4980 to 5210 GHz and temperature coefficient of resonant frequency can be controlled from +9 to -10$ppm^\circ{C}$ as an increase of$Al_2O_3$ doping concentration. Especially, a new microwave dielectric material having $\varepsilon\;_r=84,\;Q\cdot{f}_0=5120\;GHz\;and\;\tau_f=0\;ppm/^\circ{C}$ was obtained at $Al_2O_3$ doping concentration of 0.08 wt%.

• 한국수자원학회논문집
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• 제53권11호
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• pp.985-997
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• 2020

SWAT (Soil Water Assessment Tool)-MODFLOW은 준분포형 연속강우유출모형과 분포형 지하수 모형을 결합한 모델이다. 본 연구는 남한강에 위치한 복하천 유역의 지하수에 대해 SWAT과 SWAT-MODFLOW의 모의결과를 비교평가 하였다. 두 모델간의 비교에 앞서 각 모델은 유역 내 흥천 수위 관측소의 일별 유출량 자료와 율현 지하수위 관측데이터의 9년(2009 ~ 2017년)의 자료로 보정 및 검증되었다. SWAT의 경우 기저유량과 감수위에 영향을 주는 GW_DELAY, GWQMN과 ALPHA_BF를 이용하여 보정하였고 그 결과 결정계수(R²)는 0.70, Nash-sutcliffe 모델효율(NSE_Q, NSE_inQ)은 각각 0.73, -0.1을 나타냈다. SWAT-MODFLOW의 경우는 토양속성별 대수층 수리전도도(K, m/day), 비저류량(S_s, 1/m), 비산출량(S_y) 및 유효토심(m) 자료가 추가로 적용되었다. 동일 기간의 모의 결과 R², NSE_Q, NSE_inQ는 각각 0.69, 0.74, 0.51을 나타냈다. 특히, SWAT-MODFLOW 적용결과 대수층의 수리지질학적 자료 입력을 통해 저유량 모의가 상당히 개선되었다. SWAT과 SWAT-MODFLOW의 총 유출량은 각각 718.6 mm, 854.9 mm이며 기저유량은 각각 342.9 mm, 423.5 mm로 산정되었다.

• 대한금속재료학회지
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• 제48권9호
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• pp.791-797
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• 2010

The creep crack growth rate (da/dt) of the Cr-Mo steels tested by pre-crack and the voltage (or resistance) variables were related into fracture parameter (Ct), crack growth coefficient (H), and an exponent (q) in the parts of Base, weld and HAZ. The fracture parameter (Ct) has various variables relating to the specimen and crack shape, applied stress, and creep strain curve. The H and q was inferred by OLS regression (ordinary least square method), and the H values were solved in statistics and probability assessment, which were attained fromPDF's distributions (probability density function). The HAZ part has the highest value of q by OLS regression and the widest distribution of H by PDF of WEIBULL, which means that the crack sensitivity of HAZ should be cautioned against the creep crack growth and failure.

• 한국해안·해양공학회논문집
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• 제24권3호
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• pp.228-234
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• 2012

비쇄파조건의 2차원 수리실험을 통해 직립식 구조물에 대한 월파량 산정식을 제안하였으며, 본 연구의 결과를 EurOtop(2007)과 비교하였다. 상대수심 영향계수(${\gamma}_{kh}$)를 통해 특정 상대수심 범위(kh > 1.55) 내에서는 상대수심이 증가하여도 거의 동일한 영향계수가 산정됨을 알 수 있었다. 그리고 파형경사의 경우에는 파형경사가 증가함에 따라 월파량 영향계수가 감소하는 것을 알 수 있었다. 월파량 산정식은 상대여유고와 무차원 월파량의 지수함수 형태로 표현하였으며, 상대수심 영향계수 및 파형경사 영향계수(${\gamma}_s$)를 제시하여 주기효과를 정량적으로 고려할 수 있는 월파량 산정식을 제안하였다.

• 한국지반공학회논문집
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• 제24권11호
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• pp.71-77
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• 2008

본 연구에서는 CPT 결과인 콘관입저항치 $q_c$값을 이용하여 말뚝의 극한수평단위지지력을 산정법을 제안하고자 한다. 이는 기존의 지반물성평가를 이용하여 평가되어 오던 간접적인 방법과 비교하여, 현장측정치의 직접적 적용을 위한 극한수평단위지지력 산정법 개발을 목표로 하고 있다. 점착력이 없는 사질토 지반을 대상으로 측정된 콘관입저항치 $q_c$값은 사질토지반에서 중요한 요소인 상대밀도, 연직응력, 수평응력에 대한 함수로 표현되며, 이는 기존에 제안되어온 극한수평지지력의 산정에 고려되는 요소들과 유사하다. 이러한 역학적 유사성을 바탕으로 CPT결과를 이용한 극한수평단위지지력 산정식을 제안하였다. 이는 점착력이 없는 사질토에 대상으로 하고 있으며, 그에 대한 해석을 위해 해석대상지반을 대상으로 제안된 산정식의 신뢰성을 확보하였다 극한수평단위지지력의 측정값과 예측값에 따른 비교에 대해 표준편차는 0.279를 보였으며, COV는 0.272의 값을 보여 측정된 극한수평단위지지력과 대체적으로 유사한 결과를 보였으며, 전반적으로 제안식에 의해 예측된 극한수평단위지지력이 실내모형실험을 통한 측정값에 근접함을 알 수 있다.

• 한국지구과학회지
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• 제32권1호
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• pp.152-157
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• 2011

일본, 중국 등 인접 지진다발 국가에서 큰 지진동이 전파되어 오는 경우, Lg파가 최대 진폭을 갖게 되어 Lg파의 감쇠상수($Q^{-1}$)는 매우 중요한 의미를 갖게 된다. 지진연구협의회(IRIS)의 자료를 바탕으로 관측점간 경로거리가 긴 자료에 대하여 두관측점법을 이용하여 Lg파의 감쇠상수 값을 도출한 결과, 지진활동도에 상응하는 감쇠값을 얻었다. 일본지역을 잇는, 해양지각을 통과하는 경로는 높은 감쇠값을 보여서 지진활동도 및 지각의 감쇠특성을 잘 나타내고 있으며, 또한 큰 지진이 많았던 중국 상해지역을 잇는 경로도 일본지역 다음으로 높은 감쇠값을 보인다. 반면, 한반도 및 만주지역을 잇는 경로는 지진활동상황과 상응하는 매우 낮은 값을 보였다.

• 임상간호연구
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• 제21권2호
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• pp.207-214
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• 2015

Purpose: This study was aimed to investigate the effect of an education program on inter-rater agreement of Neonatal/Infant Braden Q Scale for clinical nurses working at a neonatal intensive care unit (NICU). Methods: This was single-arm pre and post experimental study. The participants were 12 nurses and 128 hospitalized neonates at a NICU from December, 2012 to March, 2013. Twelve nurses were divided into four different groups; for two groups were assigned nurses with 3 to 5 years of clinical experiences, and for the others with less than 1 year of clinical experience. The interventions were given by one wound ostomy specialist and two NICU nurses with over 5 years of clinical experiences for 1 hour twice. The inter-rater agreement was measured by intraclass-correlation coefficient. Results: Overall inter-rater agreement was improved from .87(95% CI: .80~.92) at the pre-test to .94(.91~.96) at post-test. Each inter-rater agreement except moisture and nutrition was also improved. Conclusion: The developed education program on scoring for Neonatal/Infant Braden Q scale was effective to improve the inter-rater agreement among clinical nurses. We suggest to privide an education for NICU nurse before using the Neonatal/Infant Braden Q scale in clinical settings.