• Journal of Korean Society of Industrial and Systems Engineering
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• v.30 no.3
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• pp.89-93
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• 2007

In this study, we consider an assembly line operated under a base-stock policy. A product consists of two parts, and a finished product transfers to a warehouse in which demands are satisfied. Assume that demands arrive according to a Poisson process and processing times at each production line are exponentially distributed. Whenever a demand arrives, it is satisfied immediately from an inventory in the warehouse if available; otherwise, it is backlogged and satisfied later by the next product exiting from production lines. In either case, an arriving demand automatically triggers the production of a part at both production lines. These two parts will be assembled into a product that eventually transfers to the warehouse. We obtain a closed form formula of approximation for delay time or lead time distribution of a demand when a base- stock level is s. Moreover, it can be applied to the optimal base-stock level which minimizes the total inventory cost. Numerical examples are presented to show our optimal base-stock level's quality.

• Asia pacific journal of information systems
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• v.26 no.3
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• pp.427-448
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• 2016

The stochastic phenomena of traffic network condition, such as traffic speed and density, are affected not only by exogenous traffic control but also by endogenous changes in service time during congestion. In this paper, we propose a mixed M/G/1 queuing model by introducing a condition-varying parameter of traffic congestion to reflect structural changes in the traffic network. We also develop congestion indices to evaluate network efficiency in terms of traffic flow and economic cost in traffic operating system using structure-changing queuing model, and perform scenario analysis according to various traffic network improvement policies. Empirical analysis using Korean highway traffic operating system shows that our suggested model better captures structural changes in the traffic queue. The scenario analysis also shows that occasional reversible lane operation during peak times can be more efficient and feasible than regular lane extension in Korea.

• Journal of Applied Reliability
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• v.16 no.4
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• pp.313-322
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• 2016

Purpose: We introduce ways to employ Markov chain model to evaluate the effect of preventive maintenance process. While the preventive maintenance process decreases the failure rate of each subsystems, it increases the downtime of the system because the system can not work during the maintenance process. The goal of this paper is to introduce ways to analyze this trade-off. Methods: Markov chain models are employed. We derive the availability of the system consisting of N repairable subsystems by the methods under various maintenance policies. Results: To validate our methods, we apply our models to the real maintenance data reports of military truck. The error between the model and the data was about 1%. Conclusion: The models developed in this paper fit real data well. These techniques can be applied to calculate the availability under various preventive maintenance policies.

• Korean Management Science Review
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• v.25 no.3
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• pp.87-99
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• 2008

Besieged by needs for upgrading the current Internet, social pressures, and regulatory concerns, a network operator may be left with few options to Improve his services. Yet he can still consider a transition prioritizing network services. In this paper, we describe a transition from a non-priority system to a prioritized one, using non-preemptive M/G/1 model. After reviewing the constraints and theoretical results from past research, we describe steps making the transition Pareto-improving, which boils down to a multi-goal search for a Pareto-improving state. We use a genetic algorithm that captures actual transition costs along with incentive-compatible and Pareto-Improving constraints. Simulation results demonstrate that the initial post-transition solutions are typically Pareto-improving. for non Pareto-improving solutions, the heuristic quickly generates Pareto-improving and incentive-compatible solutions.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.35 no.4
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• pp.162-170
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• 2012

We propose a new priority discipline called the strict T-preemptive priority discipline, and derive the waiting time distributions of each class in the strict T-preemptive priority M/G/1 queue. Using this queueing analysis, we evaluate the performance of an opportunistic spectrum access in cognitive radio networks, where a communication channel is divided into time slots, a licensed primary user is assigned to one channel, and multiple unlicensed secondary users may opportunistically exploit time slots unused by the primary user. We also present a numerical example of the analysis of the opportunistic spectrum access where the arrival rates and service times distributions of each users are identical.

• International Journal of Control, Automation, and Systems
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• v.3 no.1
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• pp.122-129
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• 2005

We describe the MiniWeb[7] TCP/IP stack (mIP), which is an extremely small implementation of the TCP/IP protocol suite running 8 or 32-bit micro controllers intended for embedded control systems, and satisfying the subset of RFC1122 requirements needed for host­to-host interoperability over different platforms. Our TCP/IP implementation does sacrifice some of TCP's mechanisms such as fragmentation, urgent data, retransmission, or congestion control. Our implementation is applicable to web based controllers. The network protocols are tested in operational networks using CommView and Dummynet where the various operational parameters such as bandwidth, delay, and queue sizes can be set and controlled.

• Journal of Korean Institute of Industrial Engineers
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• v.21 no.2
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• pp.167-181
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• 1995

We develop an analytical model to estimate the time a workpiece spends in both input and output queues in trip-based material handling systems. The waiting times in the input queues are approximated by M/G/1 queueing system and the waiting times in the output queues are estimated using the method discussed in Bozer, Cho, and Srinivasan [2]. The analytical results are tested via simulation experiment. The result indicates that the analytical model estimates the expected waiting times in both the input and output queues fairly accurately. Furthermore, we observe that a workpiece spends more time waiting for a processor than waiting for a device even if the processors and the devices are equally utilized. It is also noted that the expected waiting time in the output queue with fewer faster devices is shorter than that obtained with multiple slower devices.

• The Transactions of the Korea Information Processing Society
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• v.7 no.11S
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• pp.3684-3693
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• 2000

In this paper, performance of a nonblocking high speed packet switch with switching capacity m which adopts a dynamic priority control function (DPCF) of a threshold- based Bernoulli priority jump (TBPJ) scheme is considered. Each input queue has two separate buffers with different sizes for two classes of traffics, delay-sensitive and loss-sensitive traffics, and adopts a TBPJ scheme that is a general state-dependent Bernoulli scheduling scheme. Under the TBP] scheme, a head packet of the delay-sensitive traffic buffer goes into the loss -sensitive traffic buffer with Hernoulli probability p according to systems states that represent the buffer thresholds and the number of packets waiting for scheduling. Performance analysis shows that TBPJ scheme obtains large performance build-up for the delay-sensitive traffic without performance degradation for the loss-sensitive traffic. In addition to, TBP] scheme shows better performance than that of HOL scheme.

• Korean Journal of Remote Sensing
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• v.5 no.1
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• pp.41-56
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• 1989

Improvement of the multichannel sea surface temperature(MCSST) software, which had been developed for the purpose of operating under mainframe computer system, was seeked in order to operate effectively in a mini computer system. CPU time and processing time, which is not a major factor under mainframe computer system, become a critical factor in real time image processing under mini computer system. Due to fixed kernel size(3$\times$4) of the old MCSST software, high spatial resolution characteristics of the original image received from satellites were apparently degraded when images are transformed into a cartesian coordinate system after geometrical distortions of the image due to earth curvature are removed. CPU and processing time were reduced to 0.13 and 0.15~0.22 comparing with the old MCSST's, respectively, by applying disk block I/O and M/T queue I/O method under VAX-11/750 computer. The high resolution quality (1.1km in AVHRR) of the processed image was guaranted using 2$\times$2 kernel size and applying moving window techniques without sacrificing CPU and processing time much.

• Journal of Korean Society of Transportation
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• v.7 no.2
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• pp.89-111
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• 1989

This study concentrates on a basic investigation research related to some of parameters to be used for the analysis of capacity and the level of service for signalized intersections. The parameters to be studied are ideal saturation flow rate, large vehicle's passenger car equivalent(PCE) ane the lane utilization factors of through and left turn vehicles. The field data were collected at six intersections in Seoul using video cameras so as to reflect conditions in urban areas. In this study discharge headway based on a rear bumper of each vehicle was used and all the parameters were estimated using a regression technique. The findings of this research are as follows : 1. The saturation headway and saturation flow rate on a single lane with the lane width of 3.1m are 1.652 seconds and 2,180 pcphgpl. It was found that the frist 5 vehicles in the queue experience some start-up lost time. 2. It was confirmed that the new method adopted for the estimate of large vehicle's PCE gives larger PCE values than those derived from the method commonly used. 3. For the estimate of lane utilization factors of through and left turn vehicles, a relationship was established and the corresponding formulas were developed.