• International Journal of Reliability and Applications
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• v.12 no.2
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• pp.117-122
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• 2011

In this paper, we suggest the optimal replacement policy following the expiration of repair warranty when the cost of minimal repair depends on the age of system. To do so, we first explain the replacement model under repair warranty. And then the optimal replacement policy following the expiration of repair warranty is discussed from the user's point of view. The criterion used to determine the optimality of the replacement model is the expected cost rate per unit time, which is obtained from the expected cycle length and the expected total cost for our replacement model. The numerical examples are given for illustrative purpose.

• Computers and Concrete
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• v.8 no.5
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• pp.525-539
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• 2011

This paper describes the development of a fiber reinforced concrete (FRC) unit cell for analyzing concrete structures by executing a multiscale analysis procedure using the theory of homogenization. This was achieved through solving a periodic unit cell problem of the material in order to evaluate its macroscopic properties. Our research describes the creation of an FRC unit cell through the use of concrete paste generic information e.g. the percentage of aggregates, their distribution, and the percentage of fibers in the concrete. The algorithm presented manipulates the percentage and distribution of these aggregates along with fiber weight to create a finite element unit cell model of the FRC which can be used in a multiscale analysis of concrete structures.

• Journal of the Korean Statistical Society
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• v.27 no.2
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• pp.165-187
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• 1998

Shin and Sarkar (1993, 1994) studied the problem of testing for a unit root in an AR(p) signal observed with MA(q) noise when the MA parameters are known. In this paper we consider the case when the MA parameters are unknown and to be estimated. Test statistics are defined using unit root parameter estimates based on three different estimation methods of Hannan and Rissanen (1982), Kohn (1979) and Shin and Sarkar (1995). An AR(p) process contaminated by MA(q) noise is a .estricted ARMA model, for which Shin and Sarkar (1995) derived an easy-to-compute Newton- Raphson estimator The two-stage estimation p.ocedu.e of Hannan and Rissanen (1982) is used to compute initial parameter estimates in implementing the iterative estimation methods of both Shin and Sarkar (1995) and Kohn (1979). In a simulation study we compare the relative performance of these unit root tests with respect to both size and power for p=q=1.

• Journal of Information Technology Services
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• v.8 no.3
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• pp.223-232
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• 2009

The most popular convergent services are being made mostly out of IT related services and devices. To help understand the underlying principles making convergent services the paper suggests a logical view of converging process. A service is assumed to consist of unit services that can be used in algorithmic operations to form a new convergent service. Convergence operations for a couple of unit services are typed according to whether the unit services are modified. Internal convergence leads to a new service from a combination of sub units of the two unit services. External convergences do not alter original unit services but simply combine them to form a new service. The paper also suggests several measurements to evaluate the convergent services with respect to the existing services used to create the new convergent service.

• Journal of the Korean housing association
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• v.25 no.6
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• pp.39-47
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• 2014

The background of this study is to examine the structure of housing price of which characteristics are not equal but hierarchical in the apartment complexes. So, the purpose of this study is to analyze the influences of apartment complex characteristics on the housing price within the same regional boundary by HLM. The data used as dependent variables were the market prices of 938 units from 29 apartment complexes by stratified sampling. The 2nd level independent variables is the Housing complex characteristics which are composed of the housing complex & locational variables and the 1st level independent variables are the unit characteristics. The results are as follows. First, the first model shows that the 2nd level variables explains 68% of the housing prices. Second, the influential variables of the 1st level unit variable are 'dwelling exclusive area', 'floor of dwelling' and 'direction of dwelling'. Third, the influential variables of the housing complex variables in the 2nd level are 'lot area', 'the building-to-land ratio', 'the number of unit', 'the number of parking lots per unit', 'Green space area' and 'open space area per unit'. The last, the influential variables of the housing locational variables in the 2nd level are 'distance to subway and park' and the number of school and park within a radius of 1km.

• Nuclear Engineering and Technology
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• v.47 no.3
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• pp.306-314
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• 2015

This paper examines the difference in the value of the nuclear fuel cycle cost calculated by the deterministic and probabilistic methods on the basis of an equilibrium model. Calculating using the deterministic method, the direct disposal cost and Pyro-SFR (sodium-cooled fast reactor) nuclear fuel cycle cost, including the reactor cost, were found to be 66.41 mills/kWh and 77.82 mills/kWh, respectively (1 mill = one thousand of a dollar, i.e., $10^{-3}$ $). This is because the cost of SFR is considerably expensive. Calculating again using the probabilistic method, however, the direct disposal cost and Pyro-SFR nuclear fuel cycle cost, excluding the reactor cost, were found be 7.47 mills/kWh and 6.40 mills/kWh, respectively, on the basis of the most likely value. This is because the nuclear fuel cycle cost is significantly affected by the standard deviation and the mean of the unit cost that includes uncertainty. Thus, it is judged that not only the deterministic method, but also the probabilistic method, would also be necessary to evaluate the nuclear fuel cycle cost. By analyzing the sensitivity of the unit cost in each phase of the nuclear fuel cycle, it was found that the uranium unit price is the most influential factor in determining nuclear fuel cycle costs.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.23 no.6
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• pp.703-714
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• 2010

This paper proposes an approach for staged finite element modeling with coupled seepage and stress analysis. The stage modeling is based on the predefined inter-relationship between the base model and the unit stage models. A unit stage constitutes a complete finite element model, of which the geometries and attributes are subject to changes from stage to stage. The seepage analysis precedes the mechanical stress analysis at every stage. Division of the wet and dry zone and the pore pressures are evaluated from the seepage analysis and used in determining input data for the stress analysis. The results of the stress analysis may also be associated with the pore water pressures. For consolidation analysis, the pore pressure and the displacement variables are mixed in a coupled matrix equation. The time marching solution produces the dissipation of excess pore pressure and variation of stresses with passage of time. For undrained analysis, the excess pore pressures are computed from the stress increment due to loading applied in the unit stage and are used in revising the hydraulic head. The solution results of a unit stage are inherited and accumulated to the subsequent stages through the relationship of the base model and the individual unit stages. Implementation of the proposed approach is outlined on the basis of the core procedures, and numerical examples are presented for demonstration of its application.

• Journal of the Korean Society of Industry Convergence
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• v.19 no.3
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• pp.133-143
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• 2016

The objective in here is to find the density, stiffness, and strength of truss-wall rectangular (TWR) model which is combined with lattice truss (MLT) inside space. The TWR unit-cell model is defined as a unit cell originated from a solid-wall rectangular (SWR) model and it has an empty space inside. Thus, the empty space inside of the TWR is filled with lattice truss model defined as TWR-MLT. The ideal solutions derived of TWR-MLT are based on TWR with MLT model and it has developed by Gibson-Ashby's theory. To validate the ideal solutions of the TWR-MLT, ABAQUS software is applied to predict the density, strength, and stiffness, and then each of them are compared with the Gibson-Ashby's ideal solution as a log-log scale. Applied material property is stainless steel 304 because of cost effectiveness and easy to get around. For the analysis, SWR and TWR-MLT models are 1mm, 2mm, and 3mm truss diameter separately within a fixed 20mm opening width. In conclusion, the relative Young's modulus and relative yield strength of the TWR-MLT unit model is reasonably matched to the ideal expectations of the Gibson-Ashby's theory. In nearby future, TWR-MLT model can be verified by advanced technologies such as 3D printing skills.t.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 2000.04a
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• pp.253-256
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• 2000

In general, Automated Storage/Retrieval Systems (AS/RS ) have racks of equal sized cells to utilize the concept of unit-load. Most of the techniques for the performance estimation of a unit-load AS/RS are a static model or computer simulation. Especially, their models were developed under assumption that the Storage/Retrieval (S/R) machine performs only single command (SC) or dual command (DC). In reality, defending on the operating policy and the status of the system at a particular time, the S/B machine performs a SC or a DC, or becomes .: idle. In order to resolve these weak points, we propose a stochastic model for the performance estimation of unit-load AS/RS by using a single-server queueing model. Expected numbers of waiting storage and retrieval commands are found

• Convergence Security Journal
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• v.6 no.4
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• pp.1-9
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• 2006

With role-based access control, access decisions are based on the roles that individual users have as part of an organization. In this paper, we propose a new RBAC model that a user delegate a permission to another user with function-unit for practical organization. A function-unit delegation is more safe than existing delegations on RBAC model. And FuRBAC model has a authentication to supervise security problems.