• Journal of Mechanical Science and Technology
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• v.14 no.11
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• pp.1267-1275
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• 2000

A series do wind tunnel tests were conducted for Korean high-speed train model with various shape components to assess the contributions to aerodynamic drag. In order to elucidate the ground effects, two different wind tunnels, one with a moving ground system and the other with a fixed ground, were used for the same model and the results of both were compared and analyzed in detail. The result show that a suitable ground simulation is necessary for the test of a train model with many cars and detailed underbody. But the relative difference of the drag coefficients for the modifications of shape components can be measured by a fixed ground test with high accuracy and low cost. The effects of the nose shape, the inter-cargap and the bogie-fairing on total drag were discussed and some ideas were prosed to decrease the aerodynamic resistance of high speed train.

• The Korean Journal of Applied Statistics
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• v.21 no.4
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• pp.621-630
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• 2008

This paper discusses how to construct a generalized marginal logit model for analyzing repeated polytomous response data when some factors are applied to larger experimental units as treatments and time to a smaller experimental unit as a repeated measures factor. So, two different experimental sizes are considered. Weighted least squares(WLS) methods are used for estimating fixed effects in the suggested model.

• The Journal of the Korea Contents Association
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• v.11 no.2
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• pp.88-100
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• 2011

This thesis suggests fixed quantity model and detailed performance procedures of an information system audit. In addition, an identification of the check-items with high operating risk and factors that might lead to serious effects on the business are made. Then, this thesis proposes the information system audit model that can grant priorities. By using this model, the orderer can evaluate objectively with digitized mark. The model can improve the effectiveness, reliability, and objectivity of the audit by minimizing the discrepancies of different opinions about audit evaluation results between auditee and the orderer. The proposed model is adapted to an application system and audit projects of the database construction. As a result, the model has received an equal mark from the result of the general reviews, thus the propriety of the proposed model was verified.

• Geomechanics and Engineering
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• v.21 no.1
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• pp.73-84
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• 2020

In the seismic design of bridges, formation of plastic hinges plays an important role in the dissipation of seismic energy. In the case of conventional fixed-base bridges, the plastic hinges are allowed to form in the superstructure alone. During seismic event, such bridges may be safe from collapse but the superstructure undergoes significant plastic deformations. As an alternative design approach, the plastic hinges are guided to form in the soil thereby utilizing the inevitable yielding of the soil. Rocking foundations work on this concept. The formation of plastic hinges in the soil reduces the load and displacement demands on the superstructure. This study aims at evaluating the seismic response of bridge pier supported on rocking shallow foundation. For this purpose, a BNWF model is implemented in OpenSees platform. The capability of the BNWF model to capture the SSI effects, nonlinear behavior and dynamic loading response are validated using the centrifuge and shake table test results. A comparative study is performed between the seismic response of the bridge pier supported on the rocking shallow foundation and conventional fixed-base foundation. Results of the study have established the beneficial effects of using the rocking shallow foundation for the seismic response analysis of the bridge piers.

• The Journal of the Korea Contents Association
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• v.14 no.12
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• pp.753-763
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• 2014

After retirement, retirees are exposed to many changes. But, one of the most influential factor on retirement is Social network. Social network is making various relationships with many people. This consists of functional feature and structure feature. This study to systematically investigate social network changes of pre- and post-retirement by using two features. We utilized 2008~2012 'Longitudinal study of ageing' and selected 1,569 retirees above 45 years old as a final subject. This study used STATA 12.0 program for analysing frequency and descriptive statistic. At first, we analyzed personal characteristics and affecting factor on social network of retirees through Panel logit model and fixed effects regression model. Second, we applied multiple panel logit model and fixed effects model to learn factor affecting employment and social network changes. We found that a number of social activities affects social network in the structure feature and support from sons and daughters also influences social network in the functional feature after retirement.

• Korean Journal of Legislative Studies
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• v.23 no.2
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• pp.147-177
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• 2017

Although a number of empirical studies found that political ideology plays a significant role in Korean elections, they entirely rely on cross-sectional data analysis. In contrast to previous research, this study investigates the effects of ideology in the 2012 Korean presidential election through standard panel data analysis. Specifically, using "EAI Panel Study, 2012", the effects of ideology on both candidate evaluation and vote choice were examined via fixed effects, random effects, and pooled regression analysis. And the results from applying the two most popular models of ideological voting, the proximity model and the directional change model were also compared. The results show that candidate evaluations and vote choice during the election (April, 2012- December, 2012) were significantly influenced by the ideological difference between voters and candidates, independent from partisanship and other standard socio-demographic factors. And this ideological voting during the election seems better captured by the directional change model than by the proximity model.

• Journal of Labour Economics
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• v.27 no.1
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• pp.1-25
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• 2004

In knowledge-based economy where the human capital has an strong compatibilities, the life cycle of technologies and skills get shorter, and the mobility of labor get greater, the role of the signal system of qualifications have greater importance. This article used the KLIPS(Korean Labor Institute Panel Study) data, and analysed the factors of the acquisition of qualifications and the employment and wage effects of the acquisition of qualifications by fixed effects logit model and random effects model. The lower school stratification acquired the more qualifications, and in the case of men the unemployed one acquired the more qualifications. The employment effects of the acquisition of qualifications are significant at first year and second year in women, but the men's of the employment effects of acquisition of qualifications are not significant. The wage effects of the acquisition of qualifications are not significant. The results of the regression suggest that in Korea the signal system of qualifications do not working, and that the qualifications in Korea need to reform.

• Korean Journal of Organic Agriculture
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• v.19 no.4
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• pp.565-575
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• 2011

Recently, the use of antibiotics to improve animal productivity in livestock industry was strictly restricted. For these reason, probiotics have been regarded as one of promising materials for an antibiotic alternative. In this study, we investigated how the probiotics influences on the performance of broiler chicken via meta-analysis. Eighteen researches from 1997 to 2010 were used for meta-analysis. The standard summary effects were calculated via fixed effect model and random effect model (Borenstein et al., 2009). Heterogeneity was calculated by using the Cochran's Q statistics (Kook et al., 2009) and publication bias was calculated via Egger's regression (Lee et al., 2011). In fixed model average daily gain, body weight serum protein content and cecal LAB showed positive effect significantly. Feed intake, feed/gain and serum cholesterol showed significant negative effect. In serum triglyceride, negative effect was found but significance was not shown. In random model, average daily gain body weight and cecal LAB showed positive effects with significance and feed/gain and serum cholesterol represented significant negative effects. Publication bias was found only in feed/gain.

• The Journal of Asian Finance, Economics and Business
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• v.7 no.11
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• pp.107-115
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• 2020

This study is concerned with the relationship between firm's ownership structure and the co-movement of the stock return with the market return. Four different types of firm ownership, including managerial ownership, state ownership, foreign ownership, and concentrated ownership, are among the main features of the company's governance mechanism and have been separately documemented in the previous research to understand their impact on stock price synchronicity. We constructed the regression model, using stock price synchronicity as the dependent variable and the above four components of ownership structure as explanantory variables. The pooled OLS, the fixed effects model, and the random effects are employed to investigate the outcome of the study. Data used in the reserch are of public firms listed on the Ho Chi Minh City Stock Exchange (HOSE) during the five-year period term from 2015 to 2019. The data sample contains 235 companies from 10 industries with 1135 observations. The results revealed by the fixed effects model, the large ownership and the managerial ownership are found to have adverse effect on the stock price synchronicity, whereas the foreign ownership model is revealed to have positive influence on the stock return co-movement. The effect of the state ownership on the stock price synchronicity is not confirmed.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• v.25 no.4
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• pp.312-326
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• 2021

The prey-predator model is one of the most influential mathematical models in ecology and evolutionary biology. In this study, we considered a modified prey-predator model, which describes the rate of change for each species. The effects of modifications to the classical prey-predator model are investigated here. The conditions required for the existence of the first integral and the stability of the fixed points are studied. In particular, it is shown that the first integral exists only for a subset of the model parameters, and the phase portraits around the fixed points exhibit physically relevant phenomena over a wide range of the parameter space. The results show that adding coupling terms to the classical model widely expands the dynamics with great potential for applicability in real-world phenomena.