• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제18권4호
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• pp.295-304
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• 2014

We analyze theMMPP/G/1/K queue with a modified state-dependent service rate. The service time of customers upon service initiation is changed if the number of customers in the system reaches a threshold. Then, the changed service time is continued until the system becomes empty completely, and this process is repeated. We analyze this system using an embedded Markov chain and a supplementary variable method, and present the queue length distributions at a customer's departure epochs and then at an arbitrary time.

• 한국시뮬레이션학회논문지
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• 제24권3호
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• pp.27-35
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• 2015

대기행렬 시스템에는 고객들의 대기시간이 지나치게 길어지는 것을 막기 위해 다양한 정책들이 적용되는데, 본 연구에서는 고객숫자에 따른 제어 정책을 갖는 유한용량 M/G/1/K 대기행렬을 분석한다. 고객의 숫자에 따라 서버의 서비스율과 고객의 도착율을 조절하는 정책이다. 두 개의 한계점(thresholds) $L_1$과 $L_2$($${\geq_-}$$L1)를 설정하고 시스템 내 고객의 숫자가 $L_1$보다 작을 때는 시스템은 보통(또는 상대적으로 느린)의 서비스율(service rate)과 보통의 도착율(arrival rate)을 갖는다. 고객의 숫자가 증가하여 $L_1$이상이고 $L_2$보다 작으면 도착율은 그대로 이지만 서비스율을 증가시켜 빠르게 서비스한다. 이후 고객의 숫자가 더욱 증가하여 $L_2$ 이상이면 고객의 도착율도 작은 값으로 바꾸어 고객을 덜 입장시킨다. 위 정책을 갖는 M/G/1/K 대기행렬을 내재점 마코프 체인과 준-마코프 과정을 이용하여 분석하고 수치예제를 제시한다.

• 산업공학
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• 제10권1호
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• pp.119-134
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• 1997

The management of blood inventory is very important within the medical care system. The efficient management of blood supplies and demands for transfusions is of great economic and social importance to both hospitals and patients. For any blood type, there is a complex interaction among the optimal inventory level, daily demand level, daily supply level, transfusion to crossmatch ratio, crossmatch release period, issuing policy and the age of arriving units that determine the shortage and outdate rate. In this paper, we develop an efficient decision rule for blood inventory management in a hospital blood bank which can support efficient hospital blood inventory management using simulation. The primary use of the efficient decision rule will be to establish minimum cost function which consists of inventory levels, period in inventory, outdate and shortage rate for whole blood and various component inventories for a hospital blood bank or a transfusion service. If the administrator compute the mean daily demand for each blood type, the mean daily supply for each blood type, the length of the crossmatch release period and the average transfusion to crossmatch ratio, then it is possible to apply the efficient decision rule to compute the optimal inventory level, inventory period, outdate and shortage rate. This rule can also be used as a decision support system that allows the blood bank administrator to do sensitivity analysis related to controllable blood inventory parameters.

• 전기학회논문지
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• 제64권3호
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• pp.393-398
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• 2015

City or Community-scale Energy Management System(CEMS) is used to reduce the total energy consumed in the city by arranging the energy resources efficiently at the planning stage and controlling them economically at the operating stage. Of the operational functions of the CEMS, generation forecasting of renewable energy resources is an essential feature for the effective supply scheduling. This is because it can develop daily operating schedules of controllable generators in the city (e.g. diesel turbine, micro-gas turbine, ESS, CHP and so on) in order to minimize the inflow of the external power supply system, considering the amount of power generated by the uncontrollable renewable energy resources. This paper is written to introduce numerical models for photo-voltaic power generation prediction based on the weather forecasting information. Unlike the conventional methods using the average radiation or average utilization rate, the proposed models are developed for CEMS applications using the realtime weather forecast information provided by the National Weather Service.

• Journal of Electrochemical Science and Technology
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• 제11권4호
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• pp.384-391
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• 2020

Due to its characteristics of light weight, high energy density, good safety, long service life, no memory effect, and environmental friendliness, lithium-ion batteries (LIBs) are widely used in various portable electronic products. The capacity and performance of LIBs largely depend on the performance of electrode materials. Therefore, the development of better positive and negative materials is the focus of current research. The application of metal organic framework materials (MOFs) derivatives in energy storage has attracted much attention and research. Using MOFs as precursors, porous metal oxides and porous carbon materials with controllable structure can be obtained. In this paper, rod-shaped Co-MOF-74 was grown on Ni Foam (NF) by hydrothermal method, and then Co-MOF-74/NF precursor was heat-treated to obtain rodshaped Co₃O₄/NF. Ni Foam was skeleton structured, which effectively relieved. The change of internal stress changes and destroys the structural volume of the electrode material and reduces the capacity attenuation. Co₃O₄/NF composite material has a specific discharge capacity of up to 1858 mA h/g for the first time, and a reversible capacity of up to 902.4 mA h/g at a current density of 200 mA/g, and has excellent rate and impedance performance. The synthesis strategy reported in this article opens the way to design high-performance electrodes for energy storage and electrochemical catalysis.