• 한국산림과학회지
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• 제90권5호
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• pp.663-671
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• 2001

이 연구는 이자율의 변화가 임산물수입량에 미치는 영향을 우리나라 시장을 대상으로 분석하였다. 첫번째 목적은 이자율의 변화가 임산물수입량 변화의 원인이 되는지, 즉 인과관계를 파악하는 것이고, 두번째 목적은 이자율의 변화가 임산물수입량에 얼마만큼 얼마동안 영향을 미치는지, 즉 동태적 영향을 추정하는 것이다. 이자율과 임산물수입량의 관계는 자기회귀모형에 의해 만들어졌다. 인과관계 파악은 인과성검정을 이용하였고, 동태분석은 분산분해분석과 충격반응분석을 이용하였다. 결과에 의하면 이자율의 변화는 임산물 중에서 합판수입량 변화의 원인이 되었다. 합판의 경우에 어느 시기의 수입량은 그 시기 이전의 이자율에 의해 20%, 그 시기 이전의 수입량에 의해 80% 가량 설명되었다. 또한 이자율의 변화는 합판수입량에 6개월까지 영향을 미쳤다. 즉 이자율의 변화가 합판수입량에 영향을 미쳤더라도 단기간에 불과했다.

• 대한수학교육학회지:수학교육학연구
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• 제26권3호
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• pp.333-354
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• 2016

학생들의 '비와 비율 개념의 발달 과정'에서 변화율 개념이 어떻게 드러나는지에 대한 연구는 추후 변화율 관점에서 미분의 원리를 지도하는 연구에 중요한 기초연구가 될 수 있다. 특히 비율 개념 이해의 상태에 따라 이후 변화율 개념 발달에 장애물 혹은 중요한 개념적 발판이 될 수 있는지에 대하여, 학생을 대상으로 확인한 연구가 드물다는 점에서, 비율 개념과 변화율 개념의 관계에 대한 교수실험은 이후 변화율 관점에서의 미분 학습 관련 연구에 의미 있는 연구 자료를 제공해줄 것으로 보인다. 본 연구는 비율 개념이 변화율 관점에서 함수의 변화를 인식하는데 영향을 준다는 가설을 확인하기 위한 연구이자, 내포량에 해당하는 농도의 변화 과정에 대한 탐구과정을 통하여 학습자의 비율 개념에서 변화율 개념 형성 과정에 대한 이해의 폭을 넓히기 위한 기초연구이다. 세 명의 고등학교 1학년 학생들을 대상으로 그들이 가지고 있는 비율 개념을 확인하고 과제 수행과정에서 비율 개념의 변화를 관찰했다. 또한 비가 변하는 상황 속에서 비율로 함수의 변화를 설명하는 활동을 통하여, 참여 학생들이 변화율 관점에서 함수의 변화를 인식하고 표현하는 것을 관찰한 결과, 비율 개념의 변화가 변화율 관점에서 함수의 변화를 인식하는 것에 변화를 가져올 수 있음을 확인하였다.

• 대한기계학회논문집
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• 제19권4호
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• pp.1095-1101
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• 1995

Numerical analysis of vertical solidification process allowing solid-liquid density change is performed by a hybrid method between a winite volume method (FVM) and a finite element method (FEM). The investigation focuses on the influence of solid-liquid density change and cooling rates on the motion of solid-liquid interface, solidified mass fraction, temperatures and thermal stresses in the solid region. Due to the density change of pure aluminium, solid-liquid interface moves more slowly but the solidified mass fraction is larger. The cooling rate of the wall is shown to have a significant influence on the phase change heat transfer and thermal stresses, while the density change has a small influence on the motion of the interface, solidified mass fraction, temperature distributions and thermal stresses. As the cooling rate increases, the thermal stresses become higher at the early stage of a solidification process, but it has small influence on the final stresses as the steady state is reached.

• Communications for Statistical Applications and Methods
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• 제9권3호
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• pp.753-763
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• 2002

When there is one change-point in the hazard rate model, a change-point estimator with the partial score process is suggested and compared with the previously developed estimators. The limiting distribution of the partial score process we used is a function of the Brownian bridge. Simulation study gives the comparison of change-point estimators.

• 한국지하수토양환경학회지:지하수토양환경
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• 제21권6호
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• pp.22-35
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• 2016

Global climate change could have an impact on hydrological process of a watershed and result in problems with future water supply by influencing the recharge process into the aquifer. This study aims to assess the change of groundwater recharge rate by climate change and to predict the sustainability of groundwater resource in Pyoseon watershed, Jeju Island. For the prediction, the groundwater recharge rate of the study area was estimated based on two future climate scenarios (RCP 4.5, RCP 8.5) by using the Soil Water Balance (SWB) computer code. The calculated groundwater recharge rate was used for groundwater flow simulation and the change of groundwater level according to the climate change was predicted using a numerical simulation program (FEFLOW 6.1). The average recharge rate from 2020 to 2100 was predicted to decrease by 10~12% compared to the current situation (1990~2015) while the evapotranspiration and the direct runoff rate would increase at both climate scenarios. The decrease in groundwater recharge rate due to the climate change results in the decline of groundwater level. In some monitoring wells, the predicted mean groundwater level at the year of the lowest water level was estimated to be lower by 60~70 m than the current situation. The model also predicted that temporal fluctuation of groundwater recharge, runoff and evapotranspiration would become more severe as a result of climate change, making the sustainable management of water resource more challenging in the future. Our study results demonstrate that the future availability of water resources highly depends on climate change. Thus, intensive studies on climate changes and water resources should be performed based on the sufficient data, advanced climate change scenarios, and improved modeling methodology.

• 대한산업공학회지
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• 제21권4호
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• pp.507-517
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• 1995

The failure rate of an item depends on operational environment. When an item has a chance failure period and a wearout failure period in sequel, the severity of operational environment causes the increase in the slop of wearout failure rate or the increase in the magnitude of chance failure rate. For such a change of operational environment, this paper concerns the change of optimal preventive replacement time. Two preventive replacement policies, age replacement policy and periodic replacement policy with minimal repair, are considered. Investigated properties are: (a) in age replacement policy, optimal preventive replacement time increases as the chance failure rate increases and optimal preventive replacement time decreases as the slope of wearout failure rate increases, and (b) in periodic replacement policy with minimal repair, optimal preventive replacement time increases as the slope of wearout failure rate increases; however, the change of chance failure rate does not alter the optimal preventive replacement time.

• East Asian mathematical journal
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• 제33권4호
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• pp.431-451
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• 2017

This is a descriptive study with the intent of providing a rich characterization of teachers' perceptions of rate of change. The nature of teachers' perceptions and differences among teachers were examined by collecting data through a survey on teachers' conceptions of rate of change in terms of learning goals, prerequisites, and beliefs about teaching and learning of rate of change, and an interview individually assessing teachers' concept images and definitions. The participating 13 teachers were selected to provide a range of similar and contrasting levels of experiences based on the teachers' educational background and the number of years they had been teaching. Findings and implications of this study are discussed.

• Journal of the Korean Statistical Society
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• 제28권3호
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• pp.359-370
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• 1999

We considered a change-point hazard rate model generalizing constant hazard rate model. This type of model is very popular in the sense that the Weibull and exponential distributions formulating survival time data are the special cases of it. Maximum likelihood estimation and the asymptotic properties such as the consistency and its limiting distribution of the change-point estimator were discussed. A parametric bootstrap method for finding confidence intervals of the unknown change-point was also suggested and the proposed method is explained through a practical example.

• 한국방송∙미디어공학회:학술대회논문집
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• 한국방송공학회 1995년도 학술대회
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• pp.59-61
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• 1995

An adaptive code rate change scheme in DS-SSMA systems is proposed. In the proposed scheme, the error correcting code rate is changed according to the channel state, the effective number of users. The channel state is estimated based on retransmission requests. The criterion for the change of the code rate is to maximize the throughput under given error bound.

• Communications for Statistical Applications and Methods
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• 제7권1호
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• pp.327-336
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• 2000

We are mainly interested in hazard rate changes which are usually occur in survival times of manufactured products or patients. We may expect early failures with one hazard rate and next another hazard rate. For this type of data we apply a hazard rate change-point model and estimate the unkown time point to improve the model adequacy. We introduce change-point logistic model to the discrete time hazard rates. The MLEs are obtained routinely and we also explain the suggested model through a dataset of survival times.