• Management Science and Financial Engineering
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• v.19 no.2
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• pp.13-18
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• 2013

In this paper, we analyze the relationship between implementation of information technology and inventory turnover as a measure of operational efficiency. We build a regression model including a dummy variable that indicates whether a firm has been nominated for being good at implementing information technology. By using publicly available data, we have conducted an extensive empirical analysis and found that firms' using information technology is not likely to affect inventory turnover significantly. This result implies that we have to take careful consideration in adapting information technology.

• Journal of the Korean Data and Information Science Society
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• v.26 no.6
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• pp.1367-1375
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• 2015

Consider the linear growth models for longitudinal data analysis. Several kind of linear growth models are selected such as time-effect and random-effect models as well as a dummy variable included model. In this work, simulation data are generated with normality assumption, and both binormal ROC curve and AUC are obtained and compared for various linear growth models. It is found that ROC curves have different shapes and AUC increase slowly, as values of the covariance increase and the time passes for random-effect models. On the other hand, AUC increases very fast as values of covariance decrease. When the covariance has positive value, we explored that the variances of random-effect models increase and the increment of AUC is smaller than that of AUC for time-effect models. And the increment of AUC for time-effect models is larger than the increment for random-effect models.

• Journal of the Society of Naval Architects of Korea
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• v.43 no.3 s.147
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• pp.294-303
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• 2006

A surface piercing propeller (SPP) in tunnel has been proposed recently as a new propulsion system for a high speed air cavity ship. The purpose of the present study is to investigate the characteristics of the SPP in tunnel through a series of model tests. A model propulsion system is placed on a dummy body made of Acrylics. The tunnel is divided into two regions by a guide vane extending from the inlet to the center of the propeller shaft. Air has been supplied from an air nozzle placed at the bottom of the dummy body and the changes in propeller performances caused by the air flow are investigated. The measurements are done for open water and in-tunnel conditions, both for fully and partially submerged propeller. The influence of the guide vane configurations on the propeller performance is also studied. The experiments are performed at the variable pressure circulation water channel of Inha University

• The Korean Journal of Applied Statistics
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• v.21 no.5
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• pp.727-738
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• 2008

If a cointegrating relation is affected by important economic and political events occurred in the sample period, the assumption of the time-invariant cointegrating vector is violated, which leads to the misrep-resentation of the actual relations between the variables. From such a viewpoint, this study utilizes the recursive estimation process in testing for the stability of the long-run equilibrium of the domestic stock market system and then attempts to develop the framework for stabilizing time-variant cointegraing relations by introducing the dummy variables where the structural changes are found to exist.

• Special Issue of the Society of Naval Architects of Korea
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• 2007.09a
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• pp.107-117
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• 2007

A surface piercing propeller (SPP) in tunnel has been proposed recently as a new propulsion system for a high speed air cavity ship. The purpose of the present study is to investigate the characteristics of the SPP in tunnel through a series of model tests. A model propulsion system is placed on a dummy body made of Acrylics. The tunnel is divided into two regions by a guide vane extending from the inlet to the center of the propeller shaft. Air has been supplied from an air nozzle placed at the bottom of the dummy body and the changes in propeller performances caused by the air flow are investigated. The measurements are done for open water and in-tunnel conditions, both for fully and partially submerged propeller. The influence of the guide vane configurations on the propeller performance is also studied. The experiments are performed at the variable pressure circulation water channel of Inha University.

• Communications for Statistical Applications and Methods
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• v.26 no.4
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• pp.359-370
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• 2019

Grouping structures in covariates are often ignored in regression models. Recent statistical developments considering grouping structure shows clear advantages; however, reflecting the grouping structure on the quantile regression model has been relatively rare in the literature. Treating the grouping structure is usually conducted by employing a group penalty. In this work, we explore the idea of group penalty to the quantile regression models. The grouping structure is assumed to be known, which is commonly true for some cases. For example, group of dummy variables transformed from one categorical variable can be regarded as one group of covariates. We examine the group quantile regression models via two real data analyses and simulation studies that reveal the beneficial performance of group quantile regression models to the non-group version methods if there exists grouping structures among variables.

• Journal of Korean Society of Forest Science
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• v.98 no.3
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• pp.284-289
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• 2009

This study estimated the fiberboard demand using VAR and econometric model, and compared the prediction accuracy of the two models. And the variance decomposition and impulse response were analyzed using VAR model, and predicted the fiberboard demand. The VAR model was specified with lagged dependent variable, lagged own price, lagged construction product, dummy. The econometric model was specified with own price, substitute price, construction product, dummy. The dummy variable reflected the abrupt decrease in fiberboard demand in the late 1990's. The results showed that the fiberboard demand prediction can be performed more accurately by VAR model than by econometric model. In the VAR model of fiberboard demand, after twelve months, the construction product change accounts for about fifty percent of variation in the demand, and the own price change accounts for about thirty percent of variation in the demand. On the other hand, the impact of a shock to the construction product is significant for about twelve months on the demand of fiberboard, and the impact of a shock to the own price is significant for about six months on the demand of fiberboard.

• Korea Journal of Hospital Management
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• v.11 no.4
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• pp.82-103
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• 2006

The purpose of this study is to analyse statistically the relation between medical service quality and managerial performance. And then the way of analysis is the regression analysis that independent variable is service quality, dependent variable is the volume of revenue, the number of patients and the rate of beds utility, and dummy variable is the number of beds, ownership and region. The sample hospitals were the 113 hospitals on general hospitals more than 300beds which were consisted of 20 public hospitals, 41 corporate hospitals and 52 college hospitals, and also distributed 67 hospitals on big city and 46 hospitals other city. The sample hospitals were selected from the Korean Hospital Association and the data of the year 2003 and 2004. The collected data was analyzed using the SPSSWIN 10.0 version, and the study hypothesis was tested using regression analysis. The findings of this study are summarized as follows. First, as a result of analysing hypothesis 1. In the study of the relationship between the service quality and the revenue, it was verified that the more service quality in last year became the more revenue in the year. But the dummy variable, ownership and region, rarely related to hospital revenue. Therefore it means that the more service quality is connected to the more revenue on the large number of beds hospitals. Second, as a result of analysing hypothesis 2 & 3. In the study of the relationship between the service quality and the number of patients, it was verified that the more service quality in last year became the more outpatients in the year. But there was no verified to inpatients. It seems to be the reason why a hospital has operated the fixed number of beds approved by the public office. So there are no free to expand beds according to the number of inpatients as much as inpatients are increasing. Third, as a result of analysing hypothesis 4 & 5. In the study of the relationship between the service quality and the rate of beds utility, it was verified that the more service quality in last year became the shorter of average stay of length in the year. Especially it has influenced much more on a hospital which was the large number of beds, the corporate and the college, but the region. But it was denied that the more service quality became the more the beds turnover. As a result of this study, it shows that the service quality in the last year has importantly influenced on a hospital managerial performance in the year. Estimating the service quality of each hospital, most patients have selected the hospital they want. And the hospital need to keep the number of patients for the proper management. So this result of the study means that a hospital must improve the service quality for keeping efficient management.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.8
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• pp.30-36
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• 2002

Wind tunnel model has some difference in shape compared to the real flight vehicle because of model support system for testing. The support system can make some differences in the measured forces and moments to the flight test data. There are several correction methods involved such as cavity pressure correction and model support interference. Internal balance and belly sting support were used for this wind tunnel test and three types of model support correction methods, variable sting thickness method, dummy sting method, and wire support method, were compared. Variable sting thickness method is well matched with wire support method, which is known for almost interference free.

• Journal of Korea Trade
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• v.23 no.7
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• pp.83-95
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• 2019

Purpose - This study analyzed the effect of the Trump Government's protectionist trade policies on foreign ownership. Specifically, this study empirically analyzes the hypothesis that foreign ownership will decrease after the Trump Government rather than before the Trump Government. Design/methodology - The hypothesis of this study is based on the expectation that US protection trade policy will negatively affect the profitability of Korean companies. The dependent variable in this study is the foreign ownership ratio, and the independent variable is a dummy variable representing before and after the Trump Government. Multiple regression analysis was performed, including the control variables suggested in previous studies related to foreign ownership. Findings - As a result, foreign ownership increased after the Trump Government rather than before the Trump Government. This study further analyzes whether the main variables affecting foreign investor's decision-making are differences before and after Trump Government. The export ratio, profitability and dividends did not differ before and after Trump Government. However, the level of information asymmetry decreased after the Trump Government than before the Trump Government. This suggests that US protection trade policies do not adversely affect the profitability of Korean companies. However, Korean firms are improving their information environment because US protectionist trade policies can lower profitability and negatively impact capital raising. In this regard, the foreign ownership ratio seems to differ before and after the Trump Government. Originality/value - This study contributes in that it presents data that US protectionist policies can affect Korean corporate governance. This study has implications from the short-term analysis of US protection trade policy.