• Journal of Digital Convergence
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• v.13 no.11
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• pp.517-528
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• 2015

An analysis of the Convergence structural model on well-dying awareness has been conducted with a sample of 769 retired seniors who are participating in sports activities, and the results are as follows; First, after testing the goodness-of-fit of our structural model on well-dying awareness among retired seniors participating in sports activities, the final model was a good fit with physical care, which is a sub-variable of health promotion behaviors, and physical wellness, which is a sub-variable of wellness, used as covariates. Second, as a result of influence verification, the structural model showed six paths in total: resocialization${\rightarrow}$well-dying awareness, resocialization${\rightarrow}$health promotion behaviors, resocialization${\rightarrow}$wellness, health promotion behaviors${\rightarrow}$wellness, health promotion behaviors${\rightarrow}$well-dying awareness, and wellness${\rightarrow}$well-dying awareness.

• Journal of Korea Port Economic Association
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• v.23 no.1
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• pp.149-162
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• 2007

The purpose of this study is to forecast the marine trading volumes using multiplicative seasonal Autoregressive Integrated Moving Average(ARIMA) model. The paper proceeds by comparing the forecasting performances of the unload volumes with those of the load volumes with Box-Jenkins ARIMA model. Also, I present the predicted values based on the ARIMA model. The result shows that the trading volumes increase very slowly.

• Journal of the Korean Geotechnical Society
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• v.20 no.8
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• pp.59-66
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• 2004

In this study, the behavior characteristics of vertical and batter piles were analyzed by the model tests and the numerical analyses. Model steel pipe piles with the inclination of 0$^{\circ}$, 10$^{\circ}$, 20$^{\circ}$ and 30$^{\circ}$ were driven into sands with the relative density of 79%. The static compression load tests and numerical analyses using PENTAGON 3D were performed. The bearing capacities of batter piles with inclination of 10$^{\circ}$, 20$^{\circ}$ and 30$^{\circ}$ were 111, 95, and 81% of those of vertical pile in model tests, and the results of numerical analyses were similar to those of model tests. The bearing capacities p.oposed by Petrasovits and Award (1968) were similar to those of model test in the inclination of 10$^{\circ}$, but overestimated in the inclination of 20$^{\circ}$ and 30$^{\circ}$. The skin frictions and end bearing loads were the maximum in the inclination of 10$^{\circ}$ and decreased with increasing the inclination angle.

• Proceedings of the Korea Water Resources Association Conference
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• 2017.05a
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• pp.81-81
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• 2017

최근 발생하는 태풍 또는 국지성호우는 단기간에 많은 양의 강우를 동반하고 있으며, 이로인한 내수침수 및 외수범람 피해가 빈번히 발생하고 있다. 이와 같은 홍수피해를 저감하기 위한 하나의 대책으로 내수 또는 외수로 인한 피해를 미리 예측하고 대비하는 방법이 필요하다. 피해를 미리 예측하기 위한 기존의 모델들은 지표유출, 지하유출, 침투, 증발산 등 다양한 강우-유출 알고리즘에 의해 홍수범람모의를 분석하게 된다. 따라서 그 모의시간이 길게 나타나 재난상황을 대처하는 데 문제가 있다. 본 연구에서는 홍수로 인한 제내지의 침수 확산 경로 빠른 시간 안에 모의하기 위하여 여러 가지 알고리즘을 단순화시킨 홍수범람 모형을 개발하였다. 개발된 분포형 홍수범람 모형인 SIMOD(Simplified Inundation MODel)는 홍수가 발생된 시점에서 그리드화된 주변셀로의 홍수전의를 위하여 주변셀과의 경사를 이용하여 차등 분배하는 다중흐름방향법(Multi Direction Method, MDM)과, 하나의 낮은 고도의 셀에서 수위가 높아져 인접셀보다 수위가 증가하면 그 수위는 인접 셀들과 균등해 진다는 가정인 평수가정법(Flat-Water Assumption, FWA)인 두 가지 알고리즘을 이용한다. 개발된 모형의 적합성을 확인하기 위하여 상용 모형인 FLO-2D를 이용하여 각 모의시간별 침수면적과 모형의 구동시간을 비교하였다. 비교결과 초기 1시간을 제외하고 홍수피해 면적이 10% 전후로 나타나 SIMOD의 적용성이 확인되었다. 모의 구동시간의 경우 32시간 모의시 SIMOD는 10분 안에 결과가 나오는 반면 FLO-2D는 1시간 이상 소요되는 것으로 나타났다. 또한 대피계획을 수립하기 위하여 제방붕괴시나리오를 이용한 제내지 침수모의를 실시하였다. 대상지역은 금호강하류 성서산업단지 유역으로 계획홍수위는 200년 빈도 홍수위를 기준으로 하였으며 폭 35m, 높이 7m의 제방파제로 인한 외수위 유입을 가정하여 제내지의 시간별 침수면적 모의하였다. 모의된 결과를 이용하여 시간대별 대피경로를 산정함으로써 홍수로 인한 대피 계획 수립에 적용 가능함을 확인하였다.

• The Korean Journal of Applied Statistics
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• v.34 no.1
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• pp.39-56
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• 2021

Many researches have been done on portfolio optimization since Markowitz (1952) published a diversified investment model. Markowitz's mean-variance portfolio optimization problem is established under the assumption that the distribution of returns follows a normal distribution. However, in real life, the distribution of returns does not follow a normal distribution, and variance is not a robust statistic as it is heavily influenced by outliers. To overcome these potential issues, mean-shortfall portfolio model was proposed that utilized downside risk, shortfall, as a risk index. In this paper, we propose a perturbation method that uses the shortfall as a risk index of the portfolio. The proposed portfolio utilizes an adaptive Lasso to obtain a sparse and stable asset selection because it can reduce management and transaction costs. The proposed optimization is easily applicable as it can be computed using an efficient linear programming. In our real data analysis, we show the validity of the proposed perturbation method.

• KDI Journal of Economic Policy
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• v.14 no.1
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• pp.121-145
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• 1992

This paper examines characteristics of time series data related to the construction investment(stationarity and time series components such as secular trend, cyclical fluctuation, seasonal variation, and random change) and surveys predictibility, fitness, and explicability of independent variables of various models to build a short-term construction investment forecasting model suitable for current economic circumstances. Unit root test, autocorrelation coefficient and spectral density function analysis show that related time series data do not have unit roots, fluctuate cyclically, and are largely explicated by lagged variables. Moreover it is very important for the short-term construction investment forecasting to grasp time lag relation between construction investment series and leading indicators such as building construction permits and value of construction orders received. In chapter 3, we explicate 7 forecasting models; Univariate time series model (ARIMA and multiplicative linear trend model), multivariate time series model using leading indicators (1st order autoregressive model, vector autoregressive model and error correction model) and multivariate time series model using National Accounts data (simple reduced form model disconnected from simultaneous macroeconomic model and VAR model). These models are examined by 4 statistical tools that are average absolute error, root mean square error, adjusted coefficient of determination, and Durbin-Watson statistic. This analysis proves two facts. First, multivariate models are more suitable than univariate models in the point that forecasting error of multivariate models tend to decrease in contrast to the case of latter. Second, VAR model is superior than any other multivariate models; average absolute prediction error and root mean square error of VAR model are quitely low and adjusted coefficient of determination is higher. This conclusion is reasonable when we consider current construction investment has sustained overheating growth more than secular trend.

• Journal of Venture Innovation
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• v.3 no.1
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• pp.143-163
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• 2020

When we assume the transition to a knowledge management society, what factors should be differentially added to the characteristics of CEOs of small enterprises to enhance management performance? This can be done by measuring the core competence of the CEO who is an importance asset of the small firms. This study focuses on the following four inquiries to clarify the relationship among the core competence of the CEO, the knowledge management and the performance of the firms. First, we test the influence of the core competence of CEO on business performance. Second, we explore the effects of CEO characteristics on the knowledge management and the performance of the firm. Third, we test whether knowledge management has a mediating effect in the relationship between the characteristics of CEO which is a parameter, and the business performance of the firm which is a dependent variable. Fourth, for the sake of a deeper understanding of the CEO of the small firms, we conduct t-test or multiple comparison to find out the statistically significant differences among means of the main variables such as demographic characteristics, work experience, and entrepreneurship. The academic contribution of this study is to verify the characteristics of the CEO, which influence the business performance:the global competence, challenge spirit, interpersonal flexibility and stress tolerance, in connection with the knowledge management of small firms. The practical contribution of this study is to test whether CEOs can demonstrate successful business performance through knowledge management rather than measuring business performance after a certain period of time through profit and loss statements in this era of uncertainty.

• Korean Journal of Construction Engineering and Management
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• v.18 no.3
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• pp.74-83
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• 2017

The recently introduced public rental housing REITs was just different the business structure from the existing public rental housing system and the basic supply system is the same. So the ownership conversion for public house over 10 years rental duration is possible after half of the obligated rental duration according to the agreement between lessor and lessee. However rental business operators are likely to have a negative attitude to the early ownership conversion because of less expected profit. Thus, there is a need for an analysis of proper early ownership conversion moment that can achieve public purposes while ensuring the profitability of public rental housing REITs. In this study, the characteristics of the ownership conversion rights that can lessee to exercise considered to be options. Also the nature of 'REITs', 'public rental housing REITs' is considered to be affected by the macroeconomic variables. Thus, this study analyzed the value for ownership conversion in the public rental housing REITs according to real option scenarios reflecting macroeconomic variables. As a result, according to the change of the variation rate of the macroeconomic variables, it was found that with adjustable early ownership conversion time using the DCF(Discounted Cash Flow) model. Therefore, it is possible to ensure profitability of early ownership conversion by predicting the variation of variables.

• The Korean Journal of Financial Management
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• v.21 no.1
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• pp.59-86
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• 2004

This study analyzed the effects of M&A announcement before and after the 1998 amendments of 'Securities and Exchange Act' through the event study. The M&A firms turned out to gain the abnormal returns during the entire periods. The cumulative average abnormal returns of M&A firms was 1.38%(market adjusted model) or 5.37%(industry-adjusted model) higher after the 1998 amendments than before. The differences of performance of M&A were significant also in case of the related M&A, vertical or horizontal M&A, M&A in booms. In regression analysis, the 1998 amendments of Act was the significant factor to explain the cumulative abnormal returns.

• Environmental and Resource Economics Review
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• v.27 no.3
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• pp.463-493
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• 2018

As the population structure of Korea changes with the increase of single households and elderly households, this may have effect on domestic energy consumption pattern. Our study analyzes whether the energy consumption of single and elderly households are distinguishable from those of general households. For empirical analysis, Household Energy Standing Survey panel data and regional fixed effect model are employed. The result strongly shows that single households consume more energy than other households. The consumption of single households from 40s to 60s was the highest. On the other hand, the effect of aging was different from energy sources. Electricity consumption of elderly household was more than other age groups, while oil consumption of elderly household was less than others. Gas and total energy consumptions turned out to be not much different among different age groups.