• Journal of The Korean Society of Agricultural Engineers
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• v.57 no.3
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• pp.41-54
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• 2015

시간-면적 기법을 이용해 유역의 수문과정을 묘사하는 분산형 (distributed) 연속 (continuous) 강우유출모형인 HYSTAR의 거동특성과 주요 매개변수에 대한 민감도를 분석하였다. 유역의 수문조건에 따른 모형거동의 변화를 분석하기 위해 연속되는 4개의 개별 강우사상에 대한 민감도를 조사하고 비교하였다. 또한, 매개변수의 상호작용이 민감도 분석결과에 미치는 영향을 파악하기 위해 두 가지 서로 다른 기법 (one-factor-at-a-time 과 all-factor-at-a-time 방법)을 이용하여 산정된 민감도를 비교하였다. 분석결과, 모형의 직접유출량, 첨두유량 및 도달시간 모의결과는 유출곡선번호 (curve number)에 가장 민감하게 반응하는 것으로 나타났으며, 토양의 깊이, van Genuchten 식의 매개변수, 작물계수에 큰 영향을 받았다. 한편, 모의된 기저유출량은 토양의 깊이를 비롯하여 van Genuchten 식의 매개변수, 작물계수 (crop coefficient), 이방성계수 (anisotropic coefficient), 유출곡선번호의 변화에 민감하였다. 매개변수에 대한 민감도는 분석에 이용된 강우사상에 따라 다르게 나타났으며, 유역의 토양수분조건에 따라 다르게 거동하는 모형의 중요한 특성을 잘 반영하였다. 두 가지 서로 다른 기법을 이용한 민감도 분석결과는 모의된 직접유출량 및 기저유출량의 변화가 매개변수의 상호작용에 의해 제한될 수 있음을 보여 주었다. 본 연구는 HYSTAR 모형의 매개변수에 대한 민감도 분석을 통해서 해당 모형의 거동을 정량적으로 보여주었고, 이를 통해 모형의 건전성 (soundness)을 입증할 수 있는 하나의 근거를 제시하였다. 본 연구결과는 향후 HYSTAR 모형을 이용한 수문분석 시 보정을 위한 매개변수 선정에 활용될 수 있을 것으로 사료된다. 또한, 본 연구결과에서 나타난 민감도의 수문조건 (또는 선정된 강우사상)에 대한 의존성은 연속유출 모형의 민감도 분석을 위한 강우 사상 선정 및 민감도 분석결과의 해석에 유용한 정보를 제공할 수 있을 것으로 기대된다.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.3
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• pp.821-831
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• 2014

Stochastic rainfall generators or stochastic simulation have been widely employed to generate synthetic rainfall sequences which can be used in hydrologic models as inputs. The calibration of Poisson cluster stochastic rainfall generator (e.g. Modified Bartlett-Lewis Rectangular Pulse, MBLRP) is seriously affected by local minima that is usually estimated from the local optimization algorithm. In this regard, global optimization techniques such as particle swarm optimization and shuffled complex evolution algorithm have been proposed to better estimate the parameters. Although the global search algorithm is designed to avoid the local minima, reliable parameter estimation of MBLRP model is not always feasible especially in a limited parameter space. In addition, uncertainty associated with parameters in the MBLRP rainfall generator has not been properly addressed yet. In this sense, this study aims to develop and test a Bayesian model based parameter estimation method for the MBLRP rainfall generator that allow us to derive the posterior distribution of the model parameters. It was found that the HBM based MBLRP model showed better performance in terms of reproducing rainfall statistic and underlying distribution of hourly rainfall series.

• Bulletin of Food Technology
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• v.7 no.1
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• pp.63-73
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• 1994

• Journal of the Korean Society of Food Science and Nutrition
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• v.43 no.5
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• pp.741-748
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• 2014

This study was conducted to monitor the quality characteristics of Artemisis capillaris ethanolic extract by response surface methodology. The independent variables were extraction temperature ($X_1$; 60, 70, 80, 90, and $100^{\circ}C$), extraction time ($X_2$; 1, 2, 3, 4, and 5 hr), and ethanol concentration ($X_3$; 0, 20, 40, 60, and 80%). Soluble solid content ($Y_1$), chlorogenic acid content ($Y_2$), and coumaric acid content ($Y_3$), etc. were analyzed as the dependent variables. Estimated optimal conditions for soluble solids were an extraction temperature of $87.65^{\circ}C$, extraction time of 3.19 hr, and ethanol concentration of 42.40%. The optimal extraction conditions for chlorogenic acid were $84.30^{\circ}C$, 3.14 hr, and 47.85%, respectively. Further, those for coumaric acid were $83.45^{\circ}C$, 3.40 hr, and 45.39%, respectively. Extraction conditions for effective components of Artemisis capillaris were superimposed by response surface plots on optimization extraction condition of each dependent variable, including soluble solid, chlorogenic acid, and coumaric acid contents. As a result, superimposed extraction conditions were $80{\sim}90^{\circ}C$, 3~4 hr, and 40~50%, respectively. Under these conditions, soluble solid, chlorogenic acid, and coumaric acid contents were 1.09%, 25.66 mg%, and 20.25 mg%, respectively.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.6
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• pp.603-610
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• 2020

This study examined the mental health-related factors of Korean adolescents, especially focusing on the influence of internet use. This study analyzed the raw data from the 14th Korea Youth Risk Behavior Survey, 2018. The study population was 60,040, with 50.7% male students and 49.3% female students, and 49.7% high school students and 50.3% middle school students. The dependent variables were stress, sadness and despair, suicidal ideation, suicidal plan, and suicidal attempt. The independent variables were gender and age, health behaviors, and time using the internet. Logistic regression analysis was applied to derive the related factors. For all dependent variables, the main contributing variables were gender, grade, economic status, and academic performance. The mental health of adolescents was related to various factors. In particular, the time using the internet was linearly related to the degree of stress, and a higher student group of time using the internet had a more significant effect on sadness, despair, suicidal thoughts, and suicidal plans. In conclusion, the time using the internet has harmful effects on the mental health of Korean adolescents.

• The Journal of the Korea institute of electronic communication sciences
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• v.13 no.1
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• pp.199-206
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• 2018

This study was to investigate the Influence of smart phone use on gait in healthy adults. Twenty healthy adults were recruited in this study. All subjects performed twice for each normal gait and smart phone gait. The normal gait walked at their chosen speed, and the smart phone gait walked while watching the video. GAITRite system was used to identify the temporal and spatial variables related to the gait pattern during walking. Statistical analysis was analyzed by paired t-test. In comparison of temporal variables, smart phone gait was significantly lower in gait speed and cadence than in normal gait(p<.05), and was significantly longer in single support time and double support time(p<.05). In comparison of spatial variables, smart phone gait was significantly shorter in step length and stride length than in normal gait(p<.05) and significantly longer in step width(p<.05). The results of this study demonstrated that smartphone use can negatively affect the correct gait patterns during walking.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.13 no.4
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• pp.395-404
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• 2000

A damage detection and assessment algorithm is developed by measuring accelerations at limited locations of a structure under forced vibrations. The developed algorithm applies a time-domain system identification (SI) method that identifies a structure by solving a linearly constrained nonlinear optimization problem for optimal structural parameters. An equation error of the dynamic equilibrium of motion is minimized to estimate optimal parameters. An adaptive parameter grouping scheme is applied to localize damaged members with sparse measured accelerations. Damage is assessed in a statistical manner by applying a time-windowing technique to the measured time history of acceleration. Displacements and velocities at the measured degrees of freedom (DOF) are computed by integrating the measured accelerations. The displacements at the unmeasured DOF are estimated as additional unknowns to the unknown structural parameters, and the corresponding velocities and accelerations we computed by a numerical differentiation. A numerical simulation study with a truss structure is carried out to examine the efficiency of the algorithm. A data perturbation scheme is applied to determine the thresholds lot damage indices and to compute the damage possibility of each member.

• Korean Journal of Food Science and Technology
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• v.21 no.5
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• pp.655-661
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• 1989

Optimal drying conditions consisting of air temperature and relative humidity were searched by the simulation-optimization technique for minimizing quality changes in red pepper drying. Optimized drying conditions were analysed in the viewpoint of quality change kinetics and effects of control variables on the state variables. Optimal drying conditions were nearly same in both cases for carotenoid maximization and browning minimization. In two staged optimized drying, relative humidity took a lower search limit of about 10%, and air temperature in the first stage was near the lower limit of $50^{\circ}C$ and in second stage increased to a higher temperature varying with total drying time and stage changing time. Response surface analysis of time invariable drying confirmed the location of the optimal point lying on the vertex of lower limit humidity and a lowest drying temperature which ensures to attain target moisture of 0.2g water/g dry solid. Two stage drying can attain the higher objective function of quality by 3-5% than time invariable drying for shorter total drying times.

• Korean Journal of Labor Studies
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• v.23 no.2
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• pp.47-77
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• 2017

This paper analyzes the changes in wage inequality and its contributing factors since the mid-2000s. Although trends vary by data and wage indices, the Gini coefficient of the total wage of all workers shows an increasing trend due to the part-time increase of less than 35 hours per week, while the wage Gini coefficient of hourly wages and the total wage Gini coefficient of full-time workers showed a declining trend. Part-time increases have increased inequality based on total wages, but part-time hourly wage increases can be considered to have reduced hourly wage inequality. Therefore, as a result of decomposing the factor of Gini coefficient reduction only for full-time workers, factors that contributed absolutely to inequality reduction were variables such as job tenure, career, and occupation, and employment type variable has little effects, and the establishment size variable deepens inequality. The variables such as industry, age, and education did not contribute significantly to the inequality change. This is attributed to the decline in wage premiums for job tenure and management and professional jobs and the increase in wage premiums for large-scale businesses.

• Proceedings of the Korea Water Resources Association Conference
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• 2020.06a
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• pp.148-148
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• 2020

산업의 고도화가 진행됨에 따라 화학원료의 사용이 증가하고 있고 독성을 가진 화학물질이 하천으로 유입되는 사고가 빈번하게 발생하고 있다. 수환경으로 유입되는 유해화학물질은 주로 무색무취의 물질들로 사고가 발생하더라도 초기 발견이 어려워 어류폐사를 유발하거나 취수시설에서 용수로 취수되는 경우가 발생하기 때문에 이에 대한 대응책 마련이 필수적이다. 하천에 유입된 오염물질의 거동을 신속하게 예측하기 위해 1차원 오염물질 추적 모형이 활용되는데, Fickian 이송-분산 모형(Fickian Advection-dispersion equation model; FADE)이 주로 사용되고 있다. 하지만 FADE는 오염물질이 하천 저장대에서 지체되는 현상을 반영하지 못하기 때문에 농도곡선의 왜곡도를 구현하지 못하는 단점을 가지고 있다. 따라서 본 연구에서는 하천저장대모형(River Storage Model; RSM)을 개발하고 이를 국가하천인 감천에 적용하였다. 본 연구에서 개발한 RSM은 분산계수, 본류대 면적, 저장대 면적, 저장대 교환계수의 네 가지 매개변수를 통해서 하천의 물질 저장 및 교환 특성를 구현한 non-Fickian 모형으로서, 생화학반응, 휘발, 흡·탈착항을 추가하여 유해화학물질의 혼합 거동을 정확하게 모의할 수 있도록 개발하였다. 저장대 모형의 매개변수를 산정하기 위해서 하천 유량과 지형자료를 기반으로 HEC-RAS를 모의하여 계산된 수리특성을 입력변수로 사용하였다. 저수기, 평수기, 풍수기 유량을 기준으로 세 경우의 시나리오 모의를 수행하였는데, 5ton의 톨루엔이 김천산업단지에서 감천으로 유입된 경우 약 20km 하류에 위치한 취수장에서 톨루엔의 농도변화를 예측했다. 보존성 물질에 대한 모의 결과, 풍수기의 경우 저수기에 비해 유속이 크기 때문에 취수장에서 20.56시간 먼저 기준농도에 도달하고, 7.21시간 더 짧게 머무는 것으로 나타났다. 유해화학물질의 반응특성에 대한 민감도 분석을 시행한 결과, 생화학적 반감기가 18.98시간보다 길고, 옥탄올-물 분배계수가 2.267 이하인 물질은 생분해 및 흡·탈착 반응에 둔감한 것으로 나타났다. 1m 수심 기준 0.114m/s 이하 유속에서의 하천 수리조건에서는 화학물질의 휘발성을 무시할 수 있는 것으로 밝혀졌다.