• 한국해양환경ㆍ에너지학회지
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• 제14권4호
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• pp.230-238
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• 2011

100 kW 용량의 조류발전용 수평축 터빈(HAT)임펠러의 성능에 대한 연구를 위하여 단면 및 날개 끝 형상을 변형시킨 지름700 mm의 모형 임펠러를 설계하고 부산대학교 예인수조에서 모형 시험을 수행하였다. 축척효과를 확인하기 위하여 각각의 임펠러에 대하여 회전수를 바꾸어 레이놀즈수 변화에 따른 특성을 살펴보았으며 날개끝속도비(TSR)별로 비교 검토 하였다. 본 연구에서 제안된 레이크 임펠러의 성능이 기존 임펠러 보다 우수함을 확인 하였으며 추후 실험시설을 보완하여 보다 큰 레이놀즈수에서 실험을 수행하고 계산과 비교할 예정이다.

• 대한간호학회지
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• 제36권4호
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• pp.621-629
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• 2006

Purpose. The purpose of this study was to identify the clinical variables that predict functional and cognitive recovery at 1- and 6-month in both severe and moderate/mild traumatic brain injury patients. Methods. The subjects of this study were 82 traumatically brain-injured patients who were admitted to a Neurological Intensive Care Unit at a university hospital. Potential prognostic factors included were age, motor and pupillary response, systolic blood pressure, heart rate, and the presence of intracranial hematoma at admission. Results. The significant predictors of functional disability in severe traumatic brain injury subjects were, age, systolic blood pressure, the presence of intracranial hematoma, motor response, and heart rate at admission. In moderate/mild traumatic brain injury patients, motor response, abnormal pupil reflex, and heart rate at admission were identified as significant predictors of functional disability. On the other hand, the significant predictors of cognitive ability for severe traumatic brain injury patients were motor response and the presence of intracranial hematoma at admission, whereas those for moderate/mild patients were motor response, pupil reflex, systolic blood pressure at admission, and age. Conclusions. The results of the present study indicate that the significant predictors of TBI differ according to TBI severity on admission, outcome type, and outcome measurement time. This can be meaningful to critical care nurses for a better understanding on the prediction of brain injury patients. On the other hand, the model used in the present study appeared to produce relatively low explicabilities for functional and cognitive recovery although a direct comparison of our results with those of others is difficult due to differences in outcome definition and validation methods. This implies that other clinical variables should be added to the model used in the present study to increase its predicting power for determining functional and cognitive outcomes.

• 대한조선학회논문집
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• 제38권1호
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• pp.52-61
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• 2001

최근에 선형의 유체성능 평가에 활용되기 시작한 CFD 계산결과의 검증을 위해서는 잘 정리된 선체 주위의 국부유동 계측자료의 확보가 필수적이다. 그동안 국내에서 저항성능 평가를 위한 검증자료의 확보를 위해 모형선이 직진하는 경우에 대한 유동 계측이 몇 차례 수행되었다. 본 논문에서는 VLCC 모형의 사항 중 발생하는 여러 개의 분리된 보오텍스 등 매우 복잡한 선미 유동장을 계측함으로써 조종성 계수 추정을 위한 수치계산 결과의 검증 자료를 확보하고자 하였다. 선체가 표류각 $0^{\circ},\;5^{\circ}$와 $10^{\circ}$를 가지고 진행할 때, St. 2와 A.P. 위치에서 좌현 및 우현의 속도장을 각각 계측하였으며, 표류각이 큰 경우에는 각각 발생 위치가 다른 네 개의 보오텍스가 선미에 나타나는 것을 확인할 수 있었다.

• International Journal of Aeronautical and Space Sciences
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• 제16권3호
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• pp.418-424
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• 2015

The chemical response of energetic materials is analyzed in terms of 1) the thermal decomposition under the thermal stimulus and 2) the reactive flow upon the mechanical impact, both of which give rise to an exothermic thermal runaway or an explosion. The present study aims at building a set of chemical kinetics that can precisely model both thermal and impact initiation of a heavily aluminized cyclotrimethylene-trinitramine (RDX) which contains 35% of aluminum. For a thermal decomposition model, the differential scanning calorimetry (DSC) measurement is used together with the Friedman isoconversional method for defining the frequency factor and activation energy in the form of Arrhenius rate law that are extracted from the evolution of product mass fraction. As for modelling the impact response, a series of unconfined rate stick data are used to construct the size effect curve which represents the relationship between detonation velocity and inverse radius of the sample. For validation of the modeled results, a cook-off test and a pressure chamber test are used to compare the predicted chemical response of the aluminized RDX that is either thermally or mechanically loaded.

• 대한조선학회논문집
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• 제30권3호
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• pp.75-89
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• 1993

본 논문은 기본적으로 미국 기계학회의 성능시험 코드에 준하여 운동 모형시험에 불확실성 해석을 적용하였다. 총 불확실성은 시험준비 과정, 계기의 검증, 데이타 취득 과정 및 분석과정에서 발생하는 오차요인들과 오차 전파 방정식에 의해 구하여진 민감도와 결합하여 구해진다. 저항추진 시험과 같은 정적시험과 운동시험과 같은 동적시험의 차이들이 불확실성 해석의 모든 과정동안 분명하게 구별되며 또한 비대칭 고정오차항목이 고려되었다. 본 불확실성 해석이 수행된 운동 응답 항목은 무차원화된 주파수의 함수로 나타낸 상하동요와 종동요의 RAO이다. 운동시험에 대한 불확실성 해석은 측정 정도를 향상시키고 오차들을 정량화하는데 유용할 뿐만아니라 여러가지 운동 해석 프로그램에 대한 검증의 기준으로 제시될 수 있다.

• Journal of Preventive Medicine and Public Health
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• 제57권3호
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• pp.279-287
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• 2024

Objectives: This study validated the Vietnamese version of the Disaster Adaptation and Resilience Scale (DARS) for use in vulnerable communities in Vietnam. Methods: This was a cross-sectional study involving 595 adults from 2 identified communities. The original DARS assessment tool was translated, and the validity and reliability of the Vietnamese version of DARS (V-DARS) were assessed. The internal consistency of the overall scale and its subscales was evaluated using Cronbach's alpha and McDonald's omega reliability coefficients. Confirmatory factor analysis (CFA) was employed to evaluate its construct validity, building upon the factor structure identified in exploratory factor analysis (EFA). Construct validity was assessed based on convergent and discriminant validity. Results: Following the established criteria for EFA, 8 items were removed, resulting in a refined V-DARS structure comprising 35 items distributed across 5 distinct factors. Both alpha and omega reliability coefficients indicated strong internal consistency for the overall scale (α=0.963, ω=0.963) and for each of the 5 sub-scales (all>0.80). The CFA model also retained the 5-factor structure with 35 items. The model fit indices showed acceptable values (RMSEA: 0.072; CFI: 0.912; TLI: 0.904; chi-square test: <0.01). Additionally, the convergent and discriminant validity of the V-DARS were deemed appropriate and satisfactory for explaining the measurement structure. Conclusions: Our findings suggest that the V-DARS is a valid and reliable scale for use within vulnerable communities in Vietnam to assess adaptive responses to natural disasters. It may also be considered for use in other populations.

• 한국수자원학회논문집
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• 제50권10호
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• pp.681-690
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• 2017

본 연구에서는 우리나라 전역에 대하여 인공신경망 기법을 사용하여 일최심신적설을 추정하였다. 인공신경망 모형 구조를 시행 착오법을 이용하여 설계한 결과, 입력자료는 일 최저 기온, 일 평균 기온, 강수량으로 정하였고, 은닉층과 노드의 수는 각각 1층, 10개로 정하였다. 관측값을 인공신경망의 입력자료로 활용하는 경우, 교차검증 상관계수는 0.87로 Ordinary Kriging기법을 활용하여 일최신심적설을 공간보간한 경우의 교차검증상관계수인 0.40보다 크게 높았다. 미계측 지역의 일최심신적설을 추정하는 경우의 인공신경망 모형의 성능을 알아보기 위하여 인공신경망 모형의 입력자료들을 Ordinary Kriging으로 공간보간하여 일최심신적설을 추정하였다. 이 경우 교차검증 상관계수는 0.49였다. 또한 해발 고도 200 m 이상의 산지에서의 인공신경망의 성능은 나머지 지역인 평지에서의 성능보다 다소 떨어짐을 확인하였다. 본 연구의 이러한 결과는 우리나라 전역에 걸친 정확한 적설량의 즉각적인 산정에 인공신경망 모형이 효과적으로 활용될 수 있음을 의미한다.

• Nuclear Engineering and Technology
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• 제42권4호
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• pp.382-393
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• 2010

Thermal mixing by steam jets in a pool is dominantly influenced by a turbulent water jet generated by the condensing steam jets, and the proper prediction of this turbulent jet behavior is critical for the pool mixing analysis. A turbulent jet flow induced by a steam jet discharged through a vertical upward single hole into a subcooled water pool was subjected to computational fluid dynamics (CFD) analysis. Based on the small-scale test data derived under a horizontal steam discharging condition, this analysis was performed to validate a CFD method of analysis previously developed for condensing jet-induced pool mixing phenomena. In previous validation work, the CFD results and the test data for a limited range of radial and axial directions were compared in terms of profiles of the turbulent jet velocity and temperature. Furthermore, the behavior of the turbulent jet induced by the steam jet through a horizontal single hole in a subcooled water pool failed to show the exact axisymmetric flow pattern with regards to an overall pool mixing, whereas the CFD analysis was done with an axisymmetric grid model. Therefore, another new small-scale test was conducted under a vertical upward steam discharging condition. The purpose of this test was to generate the velocity and temperature profiles of the turbulent jet by expanding the measurement ranges from the jet center to a location at about 5% of $U_m$ and 10 cm to 30 cm from the exit of the discharge nozzle. The results of the new CFD analysis show that the recommended CFD model of the high turbulent intensity of 40% for the turbulent jet and the fine mesh grid model can accurately predict the test results within an error rate of about 10%. In this work, the turbulent jet model, which is used to simply predict the temperature and velocity profiles along the axial and radial directions by means of the empirical correlations and Tollmien's theory was improved on the basis of the new test data. The results validate the CFD model of analysis. Furthermore, the turbulent jet model developed in this study can be used to analyze pool thermal mixing when an ellipsoidal steam jet is discharged under a high steam mass flux in a subcooled water pool.

• 한국물환경학회지
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• 제35권6호
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• pp.589-597
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• 2019

The purpose of this study was improve accuracy the IOPs inversion model(IOPs-IM) developed in 2016 for phycocyanin(PC) concentration estimation in the Nakdong River. Additionally, two optimum models were developed and evaluated with 2017 measurement field spectral data for the Geum River and the Yeongsan River. The used measurement data for IOPs-IM analyzation was randomly classified as training and verification materials at the ratio of 2:1 in all data sets. Using the training data set from 2015-2017, accuracy results of the IOPs-IM generally improved for the Nakdong River. The RMSE(Root Mean Square Error) decreased by 14 % compared to 2016. For the GeumRiver, the results of the IOPs-IM were suitable, except for some point results in 2016. Results of the IOPs-IM in the Yeongsan River followed the overall 1:1 line and MAE(Mean Absolute Error) was lower than other rivers. But the RMSE and MAE values were higher. As a result of applying the validation data to the IOPs-IM, the accuracy of the Nakdong River was reduced to RMSE 17.7 % and MRE 16.4 %, respectively compared with 2016. However, the MRE(Mean Relative Error) was estimated to be higher by 400 % in the Geum River, and the RMSE was more than 100 mg/㎥ of the Yeongsan River. Therefore, it is necessary to get the continuously data with various sections of each river for obtain objective and reliable results and the models should be improved.

• Safety and Health at Work
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• 제10권4호
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• pp.452-460
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• 2019

Background: Monitoring and control of PM_2.5 are being recognized as key to address health issues attributed to PM_2.5. Availability of low-cost PM_2.5 sensors made it possible to introduce a number of portable PM_2.5 monitors based on light scattering to the consumer market at an affordable price. Accuracy of light scatteringe-based PM_2.5 monitors significantly depends on the method of calibration. Static calibration curve is used as the most popular calibration method for low-cost PM_2.5 sensors particularly because of ease of application. Drawback in this approach is, however, the lack of accuracy. Methods: This study discussed the calibration of a low-cost PM_2.5-monitoring device (PMD) to improve the accuracy and reliability for practical use. The proposed method is based on construction of the PM_2.5 sensor network using Message Queuing Telemetry Transport (MQTT) protocol and web query of reference measurement data available at government-authorized PM monitoring station (GAMS) in the republic of Korea. Four machine learning (ML) algorithms such as support vector machine, k-nearest neighbors, random forest, and extreme gradient boosting were used as regression models to calibrate the PMD measurements of PM_2.5. Performance of each ML algorithm was evaluated using stratified K-fold cross-validation, and a linear regression model was used as a reference. Results: Based on the performance of ML algorithms used, regression of the output of the PMD to PM_2.5 concentrations data available from the GAMS through web query was effective. The extreme gradient boosting algorithm showed the best performance with a mean coefficient of determination (R²) of 0.78 and standard error of 5.0 ㎍/㎥, corresponding to 8% increase in R² and 12% decrease in root mean square error in comparison with the linear regression model. Minimum 100 hours of calibration period was found required to calibrate the PMD to its full capacity. Calibration method proposed poses a limitation on the location of the PMD being in the vicinity of the GAMS. As the number of the PMD participating in the sensor network increases, however, calibrated PMDs can be used as reference devices to nearby PMDs that require calibration, forming a calibration chain through MQTT protocol. Conclusions: Calibration of a low-cost PMD, which is based on construction of PM_2.5 sensor network using MQTT protocol and web query of reference measurement data available at a GAMS, significantly improves the accuracy and reliability of a PMD, thereby making practical use of the low-cost PMD possible.