• Journal of the Korean School Mathematics Society
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• v.20 no.4
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• pp.495-519
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• 2017

The purpose of this study is to analyze the concept of the real number e and to investigate the understanding of pre-service teachers about the real number e. 28 pre-service teachers were asked to take a test based on the various ideas of the real number e and 8 pre-service teachers were interviewed. The results of this study are as follows. First, a large number of pre-service teachers couldn't recognize relation between the formal definition and the representations of the real number e. Secondly, pre-service teachers judged appropriately for the irrationality and the construction impossibility of the real number e, but they couldn't provide reasonable evidence. Lastly, pre-service teachers understood the continuous compounding context and exponential function context of the real number e, but they had a difficulty in understanding the geometric context and natural logarithm context of the real number e.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.5
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• pp.571-580
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• 2017

Since the KONEX market was launched in 2013, many studies of the market have focused on policy reports and management of the market. In this study, we analyzed the impact of training and employee benefits expenses on business performance in the KONEX market in comparison with firms in the KOSDAQ 100. The expenses associated with employee training and benefits can have an overlapping power when explaining the business performance. To determine the net effect of each variable on business performance, we used regression by successive orthogonalization. The training and the employee benefits expenses in both markets showed a positive effect on business performance. However, in the KONEX market, we found that the lag effect of training expense to business performance was relatively smaller than in the KOSDAQ 100. This difference may be related to problems such as short continuous service and frequent turnover of SMEs in Korea, and implies that overall human resource management should be implemented to increase the efficiency of training expenses.

• Journal of Educational Research in Mathematics
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• v.27 no.3
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• pp.411-430
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• 2017

This study examined the understanding of 24 pre-service teachers about the three contexts for constructing the exponential graphs. The three contexts consisted of the infinite points context (2009 revision curriculum textbook method), the infinite straight lines context (French textbook method), and the continuous compounding context (2015 revision curriculum textbook method). As the result of the examination, most of the pre-service teachers selected the infinite points context as easier context for introducing the exponential graph. They noted that it was the appropriate method because they thought their students would easily understand, but they showed the most errors in the graph presentation of this method. These errors are interpreted as a lack of content knowledge. In addition, a number of pre-service teachers noted that the infinite straight lines context and continuous compounding context were not appropriate because these contexts can aggravate students' difficulty in understanding. What they pointed out was interpreted in terms of knowledge of content and students, but at the same time those things revealed a lack of content knowledge for understanding the continuous compounding context. In fact, considering the curriculum they have experienced, they were not familiar with this context, continuous compounding. These results suggest that pre-service teacher education should be improved. Finally, some of the pre-service teachers mentioned that using technology can help the students' difficulties because they considered the design of visual model.

• The Korean Journal of Financial Management
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• v.13 no.1
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• pp.159-184
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• 1996

재무모형의 검증과 포트폴리오의 성과측정 등에 이용할 목적으로 시장모형에 의한 베타계수를 추정할 때 대부분의 연구들은 측정간격을 달리한 수익률의 자료들 즉 일간, 주간 혹은 월간수익률의 자료들 중에서 임의적으로 하나를 선택하고 있다. 그런데 진정한 투자계획기간과 다른 기간간격에 대하여 계산된 수익률자료의 임의적 선택은 시장모형에 의한 베타계수의 추정치에는 물론 그러한 추정치를 이용한 재무모형의 검증 및 포트폴리오의 성과측정 등에 영향을 미칠 수 있다는 점이 몇몇 연구자들에 의하여 지적되고 있다. 본 연구는 기업규모와 베타의 크기에 따라 구성된 포트폴리오를 대상으로 하여 수익률의 측정간격이 시장모형에 의한 베타계수의 추정치에 어떠한 영향을 미치게 되는가를 실증적으로 살펴보고 있다. 1984년 1월 4일부터 1995년 12월 27일까지의 기간(총거래일수 3515일)에 걸쳐 수익률의 측정간격을 달리하여 산출한 연속복리수익률을 이용하여 분석한 결과에 의하면, 규모나 베타가 시장평균에 비하여 상대적으로 작은 포트폴리오에 있어서는 수익률의 측정간격이 길어짐에 따라 추정되는 베타계수는 더욱 커지고, 반면에 규모나 베타가 시장평균에 비하여 상대적으로 큰 포트폴리오에 있어서는 수익률의 측정간격이 길어짐에 따라 베타계수는 더욱 작아진다는 것을 알 수 있다. 그래서 월간수익률과 같이 장기수익률의 자료를 이용할 경우에 시장모형에 의해 추정되는 베타계수는 규모가 작을수록 크게 나타나지만, 일간수익률과 같이 단기수익률의 자료를 이용할 경우에는 규모가 작다(크다)고 해서 추정되는 베타계수가 반드시 크게(작게) 나타나지는 않는다. 그리고 본 연구는 수익률의 측정간격을 달리함에 따라 추정되는 베타계수에 차이가 나타나는 주된 원인이 각 포트폴리오의 단위기간수익률에 있어서 시장지수의 단위기간수익률에 대한 시점간 교차상관의 상대적 강도에 있다는 것을 보여주고 있다.

• The Korean Journal of Applied Statistics
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• v.26 no.3
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• pp.471-481
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• 2013

The current VaR Model based on J. P. Morgan's RiskMetrics has problem that actual loss exceeds VaR under unstable economic conditions because the current VaR Model can't re ect future economic conditions. In general, any corporation's stock price is determined by the rm's idiosyncratic factor as well as the common systematic factor that in uences all stocks in the portfolio. In this study, we propose an One-factor VaR Model for stock portfolio which is decomposed into the common systematic factor and the rm's idiosyncratic factor. We expect that the actual loss will not exceed VaR when the One-factor Model is implemented because the common systematic factor considering the future economic conditions is estimated. Also, we can allocate the stock portfolio to minimize the loss.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.28 no.2
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• pp.63-72
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• 2016

An expected-discounted cost model based on RRP(Renewal Reward Process), referred to as a stochastic decision model, has been developed to estimate the optimal period of in-depth inspection which is one of critical issues in the life-cycle maintenance management of harbor structures such as rubble-mound breakwaters. A mathematical model, which is a function of the probability distribution of the service-life, has been formulated by simultaneously adopting PIM(Periodic Inspection and Maintenance) and CBIM(Condition-Based Inspection and Maintenance) policies so as to resolve limitations of other models, also all the costs in the model associated with monitoring and repair have been discounted with time. From both an analytical solution derived in this paper under the condition in which a failure rate function is a constant and the sensitivity analyses for the variety of different distribution functions and conditions, it has been confirmed that the present solution is more versatile than the existing solution suggested in a very simplified setting. Additionally, even in that case which the probability distribution of the service-life is estimated through the stochastic process, the present model is of course also well suited to interpret the nonlinearity of deterioration process. In particular, a MCS(Monte-Carlo Simulation)-based sample path method has been used to evaluate the parameters of a damage intensity function in stochastic process. Finally, the present stochastic decision model can satisfactorily be applied to armor units of rubble mound breakwaters. The optimal periods of in-depth inspection of rubble-mound breakwaters can be determined by minimizing the expected total cost rate with respect to the behavioral feature of damage process, the level of serviceability limit, and the consequence of that structure.