• Journal of Korean Society of Transportation
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• v.21 no.2
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• pp.95-105
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• 2003

Because the basic assumptions of deterministic user equilibrium assignment that all network users have perfect information of network condition and determine their routes without errors are known to be unrealistic, several stochastic assignment models have been proposed to relax this assumption. However. it is not easy to solve such stochastic assignment models due to the probability distribution they assume. Also. in order to avoid all path enumeration they restrict the number of feasible path set, thereby they can not preciously explain the travel behavior when the travel cost is varied in a network loading step. Another problem of the stochastic assignment models is stemmed from that they use heuristic approach in attaining optimal moving size, due to the difficulty for evaluation of their objective function. This paper presents a logit-based stochastic assignment model and its solution algorithm to cope with the problems above. We also provide a stochastic user equilibrium condition of the model. The model is based on path where all feasible paths are enumerated in advance. This kind of method needs a more computing demand for running the model compared to the link-based one. However, there are same advantages. It could describe the travel behavior more exactly, and too much computing time does not require than we expect, because we calculate the path set only one time in initial step Two numerical examples are also given in order to assess the model and to compare it with other methods.

• Journal of Korean Society of Transportation
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• v.25 no.6
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• pp.141-157
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• 2007

This paper evaluates the effects of privatization and deregulation on the firm-specific efficiency and total factor productivity (TFP) growth in the Korean and Japanese railways. Using a stochastic frontier approach and a generalized translog functional form, the paper specifies the equation system consisting of a multiproduct variable cost function and input share equations which is estimated with Zellner's iterative seemingly unrelated regression and the corrected least squares method. The Korean and Japanese railway firms are assumed to produce three outputs (Shinkansen passenger-kilometers, incumbent railway passenger-kilometers, ton-kilometers of freight) using three input factors (labor, fuel, maintenance and rolling stock). A monetary value of the ways and fixed installations held by the railroad firm is also included as a quasi-fixed input. The empirical results indicate that the average estimate of cost inefficiency is 2.57% for the total sample and on the average, JNR and JR Kyushu are found to be worst efficient while the most efficient railway firm in the sample is JR West. Also the cost efficiency levels of seven JRs have been improved after the reform and privatization of JNR. The findings also indicate that TFP growth of the privately-owned JRs are higher than those of the government-owned KNR and JNR. Three-island JRs and JR Freight have slightly higher TFP growth than Honshu JRs as well. Thus, the results suggest that managerial autonomy and increased competition via deregulation have improved efficiency and TFP growth.

• The Korean Journal of Financial Management
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• v.22 no.2
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• pp.71-89
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• 2005

The purpose of this research is to examine X-efficiency of Korean local credit unions in 2001 by employing the stochastic frontier approach. This study uses the intermediation approach in order to define outputs and inputs of the credit unions. We define the outputs as the amounts of loans, and securities. The inputs are labor, deposit and physical capital. The price of labor is estimated by dividing the total wages by the number of employees. The price of deposit equals total interest divided by total deposit, and the price of physical capital is also computed to divide the total sales and administrative expenses by the physical capital. By the result of this study, the average efficiency score is 0.81. This fact indicates that credit unions can reduce their inputs by 19% for the given outputs. If results are arranged into quartiles based on the efficiency, inefficiency of top 25% credit unions is below 9%, and half of them is over 17%. In addition, e result shows that the efficiency is significantly influenced by region and size even if credit unions in Seoul and Daegu showed little difference in efficiency by size. Generally, medium size credit unions are more efficient than large size.

• Journal of Korean Society of Transportation
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• v.27 no.4
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• pp.63-76
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• 2009

On the basis of a Stochastic Frontier Approach (SFA), this paper analyses revenue efficiencies for the same sample of Korean and Japanese railways in the papers which analyze cost efficiencies using a generalized translog functional form. The paper also compares the results of revenue efficiencies with cost efficiencies and evaluates the effects of managerial autonomy and privatization on the firm-specific efficiencies. The results show that the average estimate of revenue inefficiency is 7.02% when the term of inefficiency is assumed to be distributed as a half-normal and 6.98% as a exponential for the total sample. Also, standardized inefficiencies in revenues (7.5%) are greater than those in costs (2.1%). JR East and JR West are found to be most efficient on the revenue side and on the cost side respectively while JNR and JR Kyushu are worst efficient on the both sides. Finally, the correlations between efficiencies in revenues and costs also between efficiencies and privatization are positively correlated. The results suggest that the most independent companies, with increased managerial autonomy via privatization, are the most efficient in both revenues and costs.

• Wind and Structures
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• v.27 no.3
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• pp.199-211
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• 2018

This paper deals with wind fragility and risk analysis of high rise buildings subjected to stochastic wind load. Conventionally, such problems are dealt in full Monte Carlo Simulation framework, which requires extensive computational time. Thus, to make the procedure computationally efficient, application of metamodelling technique in fragility analysis is explored in the present study. Since, accuracy by the conventional Least Squares Method (LSM) based metamodelling is often challenged, an efficient Moving Least Squares Method based adaptive metamodelling technique is proposed for wind fragility analysis. In doing so, artificial time history of wind load is generated by three wind field models: i.e., a simple one based on alongwind component of wind speed; a more detailed one considering coherence and wind directionality effect, and a third one considering nonstationary effect of mean wind. The results show that the proposed approach is more accurate than the conventional LSM based metamodelling approach when compared to full simulation approach as reference. At the same time, the proposed approach drastically reduces computational time in comparison to the full simulation approach. The results by the three wind field models are compared. The importance of non-linear structural analysis in fragility evaluation has been also demonstrated.

• Journal of the Korean Mathematical Society
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• v.35 no.3
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• pp.575-581
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• 1998

We are interested in random phenomena that will vary as time goes by, being interfered with by fluctuation. These phenomena are often expressed as functionals of white noise. We therefore discuss the analysis of those functionals, where the white noise is understood as a system of idealized elementary random variables. The system is, in many cases, taken to be the innovation of the given random phenomena. The use of the innovation provides a powerful tool to investigate stochastic processes and random fields in line with white noise analysis.

• 한국공간정보시스템학회:학술대회논문집
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• 2005.05a
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• pp.263-266
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• 2005

고해상도 영상은 원격탐사, 의료영상 등 다양한 분야에서 사용되며, 향후에 많은 수요가 예상된다. 초해상도 영상복원은 동일한 지역을 촬영한 여러 장의 저해상도 영상을 이용하여 고해상도 영상으로 복원하는 소프트웨어적인 영상 해상도 향상 방법이며, 공간 영역과 주파수 영역의 초해상도 영상복원으로 구분된다. 본 연구에서는 공간 영역에서 확률적 접근법을 이용하여 CCD 영상의 초해상도 영상복원을 수행하였다.

• Communications of the Korean Mathematical Society
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• v.21 no.3
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• pp.543-558
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• 2006

We consider a type of large deviation Principle(LDP) using Freidlin-Wentzell exponential estimates for the solutions to perturbed stochastic differential equations(SDEs) driven by Martingale measure(Gaussian noise). We are using exponential tail estimates and exit probability of a diffusion process. Referring to Freidlin-Wentzell inequality, we want to show another approach to get LDP for the solutions to SDEs.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 2000.10a
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• pp.103-106
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• 2000

As the industrial environment becomes more competitive, supply chain management (SCM) has become recognized as a major strategy in the business world. Some of current researches are categorized into review papers, deterministic models, stochastic models, simulation models and discussed in this paper. A hybrid approach combining analytic model and simulation model and the simulation optimization method are proposed as future research areas with other analytical subjects.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 2000.10a
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• pp.171-174
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• 2000

This paper presents an approach to determine the vehicle fleet size for container shuttle service in a stochastic working environment. The shuttle service can be defined as the repetitive travel between the designated places during working period. The initial number of vehicles is temporarily calculated using the transportation model. Simulation is carried out in order to investigate dynamic behavior of container shuttle. Finally, the equation for estimating the vehicle fleet size is obtained through the multiple regression model based on simulation results.