• Communications for Statistical Applications and Methods
• /
• v.11 no.3
• /
• pp.631-641
• /
• 2004

In this paper, a model for an inventory whose stock decreases with time is considered. When a deliveryman arrives, if the level of the inventory exceeds a threshold $\alpha$, no stock is delivered, otherwise a delivery is made. It is assumed that the size of a delivery is a random variable Y which is exponentially distributed. After assigning various costs to the model, we calculate the long-run average cost and show that there exist unique value of arrival rate of deliveryman $\alpha$, unique value of threshold $\alpha$ and unique value of average delivery m which minimize the long-run average cost.

• Journal of Applied Reliability
• /
• v.18 no.2
• /
• pp.104-113
• /
• 2018

Purpose: This paper proposes the non-periodic preventive maintenance policy based on the level of cumulative hazard intensity. We aim to construct a cost-effectiveness on the proposed model with relaxing the constraint on reliability. Methods: We use the level of cumulative hazard intensity as a condition variable, instead of reliability. Such a level of cumulative hazard intensity can derive the reliability which decreases as the frequency of preventive maintenance action increases. We also model the imperfect preventive maintenance action using the proportional age setback model. Conclusion: We provide a numerical example to illustrate the proposed model. We also analyze how the parameters of our model affect the optimal preventive maintenance policy. The results show that as long as high reliability is guaranteed, the inefficient preventive maintenance action is performed reducing the system operation time. Moreover, the optimal value of the proposed model is sensitive to changes in preventive maintenance cost and replacement cost.

• Structural Engineering and Mechanics
• /
• v.72 no.4
• /
• pp.503-512
• /
• 2019

The construction of segmental precast concrete bridge is an increase due to its superior performance and economic advantages. This type of bridge is appropriate for spans within 30 to 150 m (100 to 500 ft), known as mega-projects and the design optimization would lead to considerable economic benefits. A box-girder cross section superstructure of balanced cantilever construction method is assessed here. The depth of cross section, (variable along the span linearly), bottom flange thickness, and the count of strands are considered as design variables. The optimum design is characterized by geometry, serviceability, ductility, and ultimate limit states specified by AASHTO. Genetic algorithm (GA) is applied in two fronts: as to the saving in construction cost 8% and as to concrete volume 6%. The sensitivity analysis is run by considering different parameters like span/depth ratio, relation between superstructure cost, span length and concrete compressive strength.

• The Journal of Korea Robotics Society
• /
• v.17 no.1
• /
• pp.16-24
• /
• 2022

This paper presents a method that can reduce the computational cost of the hierarchical quadratic programming (HQP)-based robot controller. Hierarchical controllers can effectively manage articulated robots with many degrees of freedom (DoFs) to perform multiple tasks. The HQP-based controller is one of the generic hierarchical controllers that can provide a control solution guaranteeing strict task priority while handling numerous equality and inequality constraints. However, according to a large amount of computation, it can be a burden to use it for real-time control. Therefore, for practical use of the HQP, we propose a method to reduce the computational cost by decreasing the size of the decision variable. The computation time and control performance of the proposed method are evaluated by real robot experiments with a 15 DoFs dual-arm manipulator.

• KDI Journal of Economic Policy
• /
• v.44 no.1
• /
• pp.77-98
• /
• 2022

This paper empirically verifies that the types of capital adjustment costs serve as an important mechanism in relation to investment decision-making after confirming that the investment dispersion of Korean firms is pro-cyclical and can affect business cycles. Specifically, it is found through empirical methods using corporate financial data that capital adjustment costs generally assumed to take a quadratic form in macroeconomics are asymmetric and irreversible in the Korean economy. In particular, capital adjustment costs are empirically proven to cause investment dispersion to expand given that the substitution effect of the marginal value to the marginal cost for one unit of investment in the inter-temporal investment decision is affected by that cost with regard to the resale of owned equipment assets, as opposed to new investments in equipment assets. We ultimately show, albeit indirectly, that investment dispersion can affect business cycles as capital adjustment costs influences investment decisions. What is implied is that the capital adjustment cost is not merely an exogenously deep parameter that fits the dynamics of business cycles in a macroeconomic model but could instead be a policy variable that can be endogenized through government policies.

• Ocean policy research
• /
• v.34 no.2
• /
• pp.1-28
• /
• 2019

The purpose of this study is to analyze the substitution among production factors of Korean distant water longline fisheries in IATTC waters. In the analysis, the translog function which have one output variable of total cost and input variables of labor, fuel, fishing gear, and capital was established and it was transformed into simultaneous equations by each cost. Then, variables of equations were estimated by SUR (seemingly unrelated regression) model. Since distant water longline fisheries is a fishing type with high fuel usage, substitution of fuel with other factors was mainly analyzed. Results showed a substitute relation between fuel and labor as well as fuel and fishing gear, while a complementary relation between fuel and capital. In addition, it was analyzed that magnitude of fuel elasticity with other factors would be inelastic.

• International Journal of Computer Science & Network Security
• /
• v.24 no.1
• /
• pp.17-22
• /
• 2024

The objective of this work is to design a low cost yet fully functional 4-DOF articulate manipulator for educational applications. The design is based on general purpose, programmable smart servo motors namely the Dynamixel Ax-12. The mechanism for motion was developed by formulating the equations of kinematics and subsequent solutions for joint space variables. The trajectory of end-effector in joint variable space was determined by interpolation of a 3rd order polynomial. The solutions were verified through computer simulations and ultimately implemented on the hardware. Owing to the feedback from the built-in sensors, it is possible to correct the positioning error due to loading effects. The proposed solution offers an efficient and cost-effective platform to study the trajectory planning as well as dynamics of the manipulator.

• Journal of Korean Society of Transportation
• /
• v.25 no.6
• /
• pp.129-140
• /
• 2007

The planning procedure of a transit operation consists of design, operation, and evaluation according to the research characteristics. There are some review studies on the operation and evaluation procedure, but the research on the design procedure has not yet been organized systematically. In this study, the research on transit system design was reviewed and the model structure and its solution method were arranged. The decision variables of the design procedure are network structure, line spacing or position, stop spacing, dispatching headway, and fleet size. In the analytical research on design procedure, system total cost is generally used as the objective function. System total cost is comprised of user cost, which is the sum of user access, waiting, and travel cost, and operating cost. Total cost of the transit system, used as the objective function, has the unique minimum because it is differentiable. There is a certain decision variable that makes the derivative of the objective function equal to zero and the second derivative of the objective function is positive. Therefore the decision variable that makes the first derivative of the objective function zero is the optimum that minimizes the objective function, and each of the cost components of the objective function become the same. This study is expected to help understanding about the research on the design procedure of transit operation planning and to help be a catalyst for relevant research.

• Journal of Navigation and Port Research
• /
• v.48 no.3
• /
• pp.200-205
• /
• 2024

This paper examines the impact of ESG activities of domestic shipping companies on the cost of debt. It is known that companies with large information asymmetry tend to have high costs of debt. Corporate ESG activities have been identified as an effective means of reducing information asymmetry. By actively engaging in ESG activities, companies can lower the cost of debt by reducing information asymmetry. Therefore, this study aims to investigate whether these mechanisms, which have been observed in previous studies, also apply to domestic shipping companies. Multiple regression analysis is conducted on KOSP I-listed shipping companies from2010 to 2022. The cost of debt is set as the dependent variable, while the ESG rating is used as the explanatory variable. The analysis reveals that companies with a high level of ESG activities generally have a lower cost of debt. However, it is important to note that ESG activities of shipping companies do not seem to have a significant impact on their cost of debt. In fact, the level of ESG activities among domestic shipping companies is not particularly high (Hong, 2024). Despite these findings, domestic shipping companies should still strive for sustainable management to adapt to the rapidly changing business environment and meet the demands of the modern era. ESG management is a representative method for achieving sustainability. Therefore, shipping companies should not only focus on reducing the cost of debt but also on opening up the closed industry culture and communicating with capital market participants for sustainable growth. It is crucial for these companies to listen to the voices of stakeholders and embrace a holistic approach to sustainability.

• Journal of Biosystems Engineering
• /
• v.7 no.1
• /
• pp.42-52
• /
• 1982

This study was intended to develop a cost function for the natural air in-bin drying: system which could lead to an optimization of the drying system cost. Based on the cost function developed, a series of simulated drying tests were conducted with 10-year weather data (1970~1979) for 7 different regions by applying an appropriate levels of system factors. System performance factors treated in this study were initial moisture content, airflow rate, bin diameter and grain depth. An optimization procedure to find the least cost system was developed as follows: First, the worst year of the past decade was determined in consideration of the dryiang time and maximum dry matter loss. Second, the minimum airflow rate for a fixed bin diameter and grain depth was determined. Third, the optimum grain depth was found for the minimum airflow rate with different initial moisture contents and bin diameters. The results obtained in this study are summarized as follows: 1. The optimization procedure developed in this study was able to reduce the time and efforts significantly. 2. Optimum values of drying parameters including airflow rate, grain depth, and fan size were determined for different initial moisture contents and bin diameters in each region. The results are shown in Tables 3 to 9. 3. Optimum grain depths decreased as the initial moisture content and airflow rate increased. 4. Drying time for the least cost system should be reduced with higher initial moisture content and lower drying potential to prevent grain spoilage. 5. The fixed cost was 65 to 75 percent of the total system cost and the variable cost was 25 to 35 percent. To reduce the fixed cost it is desirable to use a drying bin 2 or 3 times a year.