• 한국물환경학회지
• /
• 제39권1호
• /
• pp.46-60
• /
• 2023

Climate change causes fluctuations in water quality in the aquatic environment, which can cause changes in water circulation patterns and severe adverse effects on aquatic ecosystems in the future. Therefore, research is needed to predict and respond to water quality changes caused by climate change in advance. In this study, we tried to predict the dissolved oxygen (DO), chlorophyll-a, and turbidity of the Paldang reservoir for about two weeks using long short-term memory (LSTM) and gated recurrent units (GRU), which are deep learning algorithms based on recurrent neural networks. The model was built based on real-time water quality data and meteorological data. The observation period was set from July to September in the summer of 2021 (Period 1) and from March to May in the spring of 2022 (Period 2). We tried to select an algorithm with optimal predictive power for each water quality parameter. In addition, to improve the predictive power of the model, an important variable extraction technique using random forest was used to select only the important variables as input variables. In both Periods 1 and 2, the predictive power after extracting important variables was further improved. Except for DO in Period 2, GRU was selected as the best model in all water quality parameters. This methodology can be useful for preventive water quality management by identifying the variability of water quality in advance and predicting water quality in a short period.

• 통상정보연구
• /
• 제16권5호
• /
• pp.409-433
• /
• 2014

본 연구에서는 미국의 실질GDP와 원/달러 실질환율을 독립변수로 하고, 한국의 대미국 실질수출을 종속변수로 하는 한국의 대미국 수출함수를 설정하여 1990년부터 2013년까지의 연간 자료를 통해 이들 독립변수들의 한국의 대미 수출에 대한 장기탄력성을 추정하고, 이들의 연도별 변화추세를 살펴보았다. 공적분 검정과 VECM을 통해 구한 장기 추정식의 분석결과 장기소득탄력성과 장기환율탄력성 모두 양(+)의 부호를 가지는 것으로 나타나 이론적인 예상과 일치하였다. 한편, 전향적 회귀분석을 통한 연도별 장기탄력성 분석한 결과 장기소득탄력성은 2008년 글로벌 금융위기 전까지 비교적 높은 수준을 유지하다가 2008년 글로벌 금융위기 이후 급격한 감소를 보였으나, 최근 다시 2000년대 수준으로 다시 회복세를 보인 것으로 나타났다. 연도별 장기실질환율탄력성의 경우 모형과 연도에 따라 양(+)의 부호와 음(-)의 부호가 혼재되어 나타났고, 2008년 글로벌 금융위기 이후의 원/달러 실질환율에 대한 대미 한국수출의 민감도가 감소한 것으로 분석되었다.

• 한국산학기술학회논문지
• /
• 제19권4호
• /
• pp.433-438
• /
• 2018

본 연구는 기존의 1기간 모형과는 달리 노력을 투입하는 시점과 손실 발생 시점간의 차이를 고려한 2기간 모형을 가정하고 있다. 또한 모호성 회피성향이 손실 발생 확률 및 손실의 크기를 줄이기 위한 노력에 미치는 영향을 살펴보고 있다. 이때 손실의 발생 자체는 이항 분포를 따르나, 모호성 회피성향을 가정하기 위해 그 분포가 상태 변수에 의존하는 함수의 형태를 갖는다고 가정한다. 그 결과 첫째, 모호성 회피적인 개인이 모호성 중립적인 개인에 비해 언제나 더 많은 노력을 기울이는 것은 아니다. 둘째, 1기간에서는 나타나지 않았던 절대모호성회피성향이 노력 수준에 미치는 영향을 살펴볼 수 있었다. 2기간 모형에서 증가하지 않는 절대모호성회피성향은 모호성 회피적인 개인이 모호성 중립적인 개인에 비해 더 많은 노력을 기울이기 위한 필요조건이다. 또한 상태에 대한 확률 함수의 형태에 따라 노력의 증가하거나 감소할 수 있다. 마지막으로 이러한 결과는 개인이 위험중립적이거나 위험선호적이더라도 성립한다. 따라서 본 연구는 모호성 회피성향은 위험 회피성향과는 독립적으로 고려될 필요가 있다는 것을 밝히고 있다.

• 전력전자학회:학술대회논문집
• /
• 전력전자학회 1998년도 Proceedings ICPE 98 1998 International Conference on Power Electronics
• /
• pp.366-373
• /
• 1998

In this paper, a new control strategy to reduce switching losses in three-phase voltage-source PWM converters is proposed according to Modified-Period-Average-Model (MPAN). The basic concept of this strategy is aimed at calculating the phase control voltages for controlling the source currents to be sinusoidal and in phase with the source voltages, and reducing the number of switching in each period. The phase control voltages of Period-Average-Model(PAM) is obtained according to analyzing the operation of PWM converter. In order to reduce the sensitivity to system parameters in PAM, MPAM is deduced. Then a square wave whose frequency is three times of utility frequency is added to the phase control voltages derived from MPAM. The control strategy reduces the switching losses since there exists about one-third blanking time for every phase in one period. The theoretical derivation and the control strategy are experimentally verified on a 2.5 kW three-phase voltage source converter.

• 한국수학교육학회지시리즈A:수학교육
• /
• 제34권1호
• /
• pp.17-63
• /
• 1995

The exploration of Mathematics-learningmodel on the basis of Cognitive development The purpose of this paper is to sequenctialize Mathematics-learning contents, and to explore teaching-learning model for mathematics, with on the basis of the theory of cognitive development and the period of condservation formation for children. The Specific topics are as follows: (1) Systemizing those theories of cognitive development which are related to Mathematics - learning for children. (2) Organizing a sequence of Mathematics - learning, on the basis of experimental research for the period of conservation formation for children. (3) Comparing the effects of 4 types of teaching - learning model, on the basis of inference activity and operational learning principle. $\circled1$ Induction-operation(IO) $\circled2$ Induction-explanation(IE) $\circled3$ Deduction-operation(DO) $\circled4$ Deduction-explanation(DE) The results of the subjects are as follows: (1) Cognitive development theory and Mathe-matics education. $\circled1$ Congnitive development can be achieved by constant space and Mathematics know-ledge is obtained by the interaction of experience and reason. $\circled2$ The stages of congnitive development for children form a hierarchical system, its function has a continuity and acts orderly. Therefore we need to apply cognitive development for children to teach mathematics systematically and orderly. (2) Sequence of mathematical concepts. $\circled1$ The learning effect of mathematical concepts occurs when this coincides with the period of conservation formation for children. $\circled2$ Mathematics Curriculum of Elementary Schools in Korea matches with the experimental research about the period of Piaget's conservation formation. (3) Exploration of a teaching-learning model for mathematics. $\circled1$ Mathematics learning is to be centered on learning by experience such as observation, operation, experiment and actual measurement. $\circled2$ Mathematical learning has better results in from inductional inference rather than deductional inference, and from operational inference rather than explanatory inference.

• Journal of the Optical Society of Korea
• /
• 제15권2호
• /
• pp.202-206
• /
• 2011

We propose a tunable flat-top bandpass filter to pass light in a customized wavelength band by using long-period fiber gratings (LPFG) structure. The LPFG structure is composed of a core mode blocker in between two LPFGs. The bandpass spectrum of the proposed structure is obtained in overlapped wavelength band of two LPFGs operating on the same modes. To analyze the properties, we introduce a mathematical matrix model for the structure. We theoretically demonstrate flexibility of the flat-top bandpass filter with various bandwidths.

• 한국환경과학회지
• /
• 제18권9호
• /
• pp.1045-1055
• /
• 2009

The discharge within the basin in Jeju Island was calculated by using SWAT model, which a Semi-distributed rainfall-runoff model to the important rivers. The basin of Chunmi river of the eastern region of Jeju Island, as the result of correcting as utilizing direct runoff data of 2 surveys, appeared the similar value to the existing basin average runoff rate as 22% of average direct runoff rate for the applied period. The basin of Oaedo river of the northern region showed $R^2$ of 0.93, RMSE of 14.92 and ME of 0.70 as the result of correcting as utilizing runoff data in the occurrence of 7 rainfalls. The basin of Ongpo river of the western region showed $R^2$ of 0.86, RMSE of 0.62 and ME of 0.56 as the result of correcting as utilizing runoff data except for the period of flood in $2002{\sim}2003$. Yeonoae river of the southern region showed $R^2$ of 0.85, RMSE of 0.99 and ME of 0.83 as the result of correcting as utilizing runoff data of 2003. As the result of calculating runoff for the long term about 4 basins of Jeju Island from the above results, SWAT model wholly appears the excellent results about the long-term daily runoff simulation.

• Journal of Chest Surgery
• /
• 제21권2호
• /
• pp.246-253
• /
• 1988

An in vitro model providing with a recirculating perfusion apparatus using an isolated canine heart and its autogenous blood, which was prepared for study of myocardial protection method. This apparatus was easily used by quick connect system and maintained well heart function for about 2 hours. The Langendorff perfusion was initiated for a 10 minute period by introducing perfusate at 37` into the aorta from aortic reservoir located 100 cm above the heart. The isolated perfused working canine heart model was a left heart preparation in which oxygenated perfusion medium [at 37K] entered the cannulated left atrium at a constant flow rate [900ml/ min] under 20 mmHg overflow system and was spontaneously ejected[no electrical pacing] via an cannula against a hydrostatic pressure of 80 cm H2O. During this working period, various indices of cardiac function were measured. The cardiac functions were stable for over 2 hours with perfusion of Krebs-Henseleit solution and autologous blood[1:1] mixture in volume and maintained heart rate ]]3-122/bpm peak systolic pressure 109-113 mmHg, cardiac output 900 ml / min and left atrial mean pressure 8-9 mmHg. In this model, the efficiency of myocardia] protection could be easily measured by means of functional, enzymatic, biochemical and ultrastructural assessment. And also, we believe this model to be a useful assessment screening model of recovery state after long duration of myocardial preservation of donor heart without difficult transplantation procedures.

• Journal of the Korean Data and Information Science Society
• /
• 제19권2호
• /
• pp.587-596
• /
• 2008

This paper develops the optimal periodic preventive maintenance policies following the expiration of warranty: renewing warranty and non-renewing warranty. After the warranty period is expired, the system undergoes the PM periodically and is minimally repaired at each failure between two successive PMs. Firstly, we determine the expected cost rate per unit time and the expected downtime per unit time for the periodic PM model. Then the overall value function suggested by Jiang and Ji(2002) is applied to obtain the optimal PM period and the optimal PM number. Finally, the numerical examples are presented for illustrative purpose.

• 한국경영과학회지
• /
• 제18권2호
• /
• pp.175-182
• /
• 1993

The probabilistic order level inventory model is developed when a supplier allows some credit period T for settling the accounts for purchase quantity. The credit period T is known constant. Mathematical models are derived for both the cases i) T'.leq. T and ii) T'>T. Expressions are derived for average expected total cost of the system, the optimum cycle time and for obtaining optimum order level S = S$_{0}$ in each case. The exmaples are given to illustrate the model.