• International conference on construction engineering and project management
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• 2013.01a
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• pp.188-195
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• 2013

Construction operations generate a significant amount of air pollutant emissions, including carbon emissions. The environmental performance of construction operations is closely relevant to the operational efficiency of each resource employed, which indicates how efficiently each resource (e.g., construction equipment) is utilized. In this context, monitoring the operational efficiency of construction equipment provides key information in managing and improving the environmental performance and productivity of construction operations. In this paper, we report our efforts to measure the operational efficiency of construction equipment, using low-cost accelerometers. An experimental study and real-world case studies are conducted to demonstrate the feasibility of the proposed approach. The results have shown the potential of this approach as an economically feasible means of monitoring the environmental performance of construction operations.

• Journal of applied mathematics & informatics
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• v.32 no.5_6
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• pp.675-685
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• 2014

Suppose G is a simple graph. The irregularity of G, irr(G), is the summation of imb(e) over all edges $uv=e{\in}G$, where imb(e) = |deg(u)-deg(v)|. In this paper, we investigate the behavior of this graph parameter under some old and new graph operations.

• Journal of Advanced Navigation Technology
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• v.28 no.1
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• pp.109-115
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• 2024

The Concept of Operations (ConOps) document issued by the Korean Government (K-UAM ConOps) for urban air mobility (UAM) services takes into account not only aviation voice communication but also the use of 4G and 5G mobile communication to support the initial phase of UAM services. This paper studies a methodology to establish communication performance requirements for UAM traffic management and presents the analyzed results for communication performance requirements. To accomplish this, the operational scenarios of UAM developmental stages outlined in the K-UAM ConOps and FAA ConOps are scrutinized, and the diverse messages that must be communicated among various stakeholders for effective UAM operations are identified. A draft of communication performance requirements is also calculated by considering packet sizes, transmission frequencies, acceptable latencies, and availability. The outcomes of this study are expected to stand as a pioneering effort in defining communication requirements for UAM services, providing a crucial foundation for future initiatives such as the design of dedicated communication networks for UAM and the determination of required frequency bandwidth.

• Journal of the Korean Operations Research and Management Science Society
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• v.32 no.4
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• pp.89-99
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• 2007

In this paper, an analytic model of a sleep mode operation in the IEEE 802.16e is investigated. A mobile subscriber station(MSS) goes to sleep mode after negotiations with the base station(BS) and wakes up periodically for a short interval to check whether there is downlink traffic to it. If the arrival of traffic is notified, an MSS returns to wake mode. Otherwise, it again enters increased sleep interval which is double as the previous one. In order to consider the situation more practically, we propose the sleep mode starting threshold, during which MSS should await packets before it enters the sleep mode. By modifying the M/G/l with multiple vacations model, energy consumption ratio(ECR) and average packet response time are calculated. Our analytic model provides potential guidance in determining the optimal parameters values such as sleep mode starting threshold, minimal sleep and maximal sleep window.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 2003.05a
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• pp.247-251
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• 2003

In this paper, we propose an approximation of the M/G/1 system with finite workload capacity, where customers whose admission to the system would increase the workload beyond a prespecified finite capacity limit are not accepted. Our approximation method is based on the idea that the service time of a customer in the M/G/1 system can be approximated as the sum of service times of a batch of customers in the $M^{X}/d/1$ system where the service time is deterministic and very small. That is, the original service time is discretized and approximated by the batch size. We exemplified our method by obtaining the average workload of the M/M/1 system by means of the $M^{X}/d/1$ system, where the batch size is geometric. In addition, the approximate blocking probabilities of the M/M/1 and $M/E_{k}/1$ system with finite workload capacities are sought. The proposed method turns out to give a good approximation, which is compared with a simulation.

• Journal of the Korean Operations Research and Management Science Society
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• v.6 no.2
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• pp.35-49
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• 1981

This paper is concerned with developing a Multi-period Behavioral Model for the portfolio selection problem. The unique feature of the model is that it treats a number of factors and decision variables considered germane in decision making on an interrelated basis. The formulated problem has the structure of a Chance Constrained programming Model. Then empoloying arguments of Central Limit Theorem and normality assumption the stochastic model is reduced to that of a Non-Linear Programming Model. Finally, a number of interesting properties for the reduced model are established.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 2000.10a
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• pp.149-152
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• 2000

The chartered bus scheduling is to determine the allocation of buses to customer service requests. For the scheduling, we first represent the scheduling problem using a graph and develop a mathematical model. Second, we develop an algorithm for the scheduling problem including heuristic methods. We tested the performance of the algorithm on instances with real data. As a result, the total empty load driving time is reduced over 10% comparing with that of current practice at the company

• Journal of the Korean Operations Research and Management Science Society
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• v.28 no.1
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• pp.25-36
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• 2003

Unlike the mean-variance approach, the stochastic dominance approach Is to form a portfolio that first-degree stochastically dominates a predetermined benchmark portfolio, e.g. KOSPI. Analytically defining the first derivative of the objective function, an optimal algorithm of nonlinear programming was developed to search a set of optimal weights systematically and tested with promising results against veal data sets from Korean stock market.

• Journal of the Korean Operations Research and Management Science Society
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• v.28 no.1
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• pp.37-49
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• 2003

Using the concept of closed queueing network, we present a consistent way of interpreting existing duality relations among queueing systems. Also, using embedded Markov chains, we present a few new duality relations for the queueing systems with negative customers.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 1995.09a
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• pp.88-97
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• 1995

This paper provides equation for computing the AOQ of an unreliable random FMS. The FMS is described using open central server model with network GI/G/S Queues. And the equation for AOQ is simplified due to computational complexities. Numerical example is used to show the effect of AOQ according to inspection location, reliability of equipment in an FMS, and the effect of difference of routing probability is compared after finding the AOQL of each machine center.