• Management Science and Financial Engineering
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• 제15권2호
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• pp.69-100
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• 2009

In this paper, we consider a relatively new two-machine flow shop scheduling problem where the unit time WIP cost increases as a job passes through various stages in the production process, and the objective is to minimize the total WIP (work-in-process) cost. Specifically, we study three special cases of the problem. First, we consider the problem where processing times on machine 1 are identical. Second, the problem with identical processing times on machine 2 is examined. The recognition version of the both problems is unary NP-complete (or NP-complete in strong sense). For each problem, we suggest two simple and intuitive heuristics and find the worst case bound on relative error. Third, we consider the problem where the processing time of a job on each machine is proportional to a base processing time. For this problem, we show that a known heuristic finds an optimal schedule.

• 한국경영과학회지
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• 제37권1호
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• pp.19-28
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• 2012

We consider a multi-agent scheduling problem such that each agent tries to maximize the weighted number of just-in-time jobs. Two objectives are considered : the first is to find the optimal solution for one agent with constraints on the other agents' weight functions, and the second is to find the largest set of efficient schedules of which corresponding objective vectors are different for the case with identical weights. We show that when the number of agents is fixed, the single machine case with the first objective is NP-hard in the ordinary sense, and present the polynomial- time algorithm for the two-machine flow shop case with the second objective and identical weights.

• 산업경영시스템학회지
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• 제26권4호
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• pp.63-71
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• 2003

This paper analyses a deterministic scheduling problem concerned with manufacturing multiple types of components at a pre-assembly stage composed of parallel fabrication machines. Each component part is machined on a fabrication machine specified in advance. The manufactured components are subsequently assembled into products. The completion time of a job(product) is measured by the latest completion time of its all components at the pre-assembly stage. The problem has the objective measure of minimizing the total weighted completion time of a finite number of jobs. Two lower bounds are derived and tested in a branch-and-bound scheme. Also, three constructive heuristic algorithms are developed based on the machine aggregation and greedy strategies. Some empirical evaluation of the performance of the proposed branch-and-bound and heuristic algorithms are also performed.

• 한국컴퓨터정보학회논문지
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• 제7권3호
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• pp.122-127
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• 2002

스케줄링 알고리즘의 일종인 Inna은 매우 간편하며 각 큐에 다른 가중치를 할당하여 여러 큐를 직접 제어한다. 본 논문에서는 WRR 스케줄링 알고리즘을 효율적으로 수행할 수 있는 새로운 BSW 구조를 제안한다. 또한, 새로운 BSW구조에 적합한 셀 스케줄링 알고리즘을 개발한다 제안된 BSW구조와 알고리즘은 VC에 할당된 가중치를 정확히 유지 한 수 있고, 서비스 받을 VC큐가 비어 있을 경우 다른 VC 셀을 서비스하여 평균 셀 지연 및 최대 버퍼 크기를 감소시킨다. 제안된 알고리즘은 WRR 구현에 매우 적합한 구조이다.

• 대한산업공학회지
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• 제19권4호
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• pp.125-135
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• 1993

An Unrelated Parallel Processing with Weighted jobs and Setup times scheduling prolem is studied. We consider a parallel processing in which a group of processors(machines) perform a single operation on jobs of a number of different job types. The processing time of each job depends on both the job and the machine, and each job has a weight. In addition each machine requires significant setup time between processing jobs of different job types. The performance measure is to minimize total weighted flow time in order to meet the job importance and to minimize in-process inventory. We present a 0-1 Mixed Integer Programming model as an optimizing algorithm. We also present a simple heuristic algorithm. Computational results for the optimal and the heuristic algorithm are reported and the results show that the simple heuristic is quite effective and efficient.

• 대한전자공학회논문지TC
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• 제43권3호
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• pp.135-143
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• 2006

DiffServ망에서 많이 거론되고 있는 대표적인 스케줄러로 PQ(Priority Queue), WRR(Weighted Round Robin)등의 스케줄러가 연구되어져 있다. 그러나 이러한 스케줄러들은 장점을 가지고 있는 동시에 단점을 가지고 있다. 본 논문에서는 PQ와 WRR의 단점을 보완하면서 어떠한 스케줄링 방법에도 적용이 가능한 스케줄러 알고리즘을 제안한다. 본 논문에서 제안된 알고리즘은 DiffServ 망에서 퍼지 이론을 스케줄러에 적용하여 동적으로 가중치를 할당하는 알고리즘을 개발하였다. 따라서 퍼지이론을 통하여 퍼지 제어 규칙을 생성하여 유동적으로 각 클래스의 큐 상태를 체크하여 클래스가 가지고 있는 큐의 가중치를 효율적으로 할당하도록 하였다.

• 한국통신학회논문지
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• 제25권1A호
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• pp.114-121
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• 2000

입력 단 저장방식의 스위치는 최대 수율을 제한하는 HOL(Head-of-line) 블록킹이라는 단점을 지니고 있지만 구현의 간단함을 지닌다는 장점이 있다. 그러나 현재 VOQ(Virtual Output Queueing) 기술을 이용하면 입력 단 저장방식의 스위치에서 보이는 HOL 블록킹에서 완전히 벗어날 수 있어 간단한 구조로 높은 수율을 얻을 수 있게 된다. 본 논문에서 입력 단 저장방식의 ATM 스위치를 위한 새로운 셀 스케쥴링 알고리듬 PPIM(Probabilistic Parallel Iterative Matching)을 제안 한다. 제안된 새로운 알고리듬은 예약 대역폭에 비례하는 가중치를 각각의 입력-출력 링크에 부여함으로써, 기존의 PIM(Parallel Iterative Matching)이 제공하지 못하는 예약된 전송률 보장이 가능하게 한다. 이 알고리듬을 이용한 ATM 스위치는 높은 수율과 낮은 지연 값뿐만 아니라 지터 성능에 있어 기존의 WPIM(Weighted PIM)에 비해 더욱 향상된 성능을 보여준다.

• ETRI Journal
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• 제29권3호
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• pp.270-280
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• 2007

In Linux, real-time tasks are supported by separating real-time task priorities from non-real-time task priorities. However, this separation of priority ranges may not be effective when real-time tasks make the system calls that are taken care of by the kernel threads. Thus, Linux is considered a soft real-time system. Moreover, kernel threads are configured to have static priorities for throughputs. The static assignment of priorities to kernel threads causes trouble for real-time tasks when real-time tasks require kernel threads to be invoked to handle the system calls because kernel threads do not discriminate between real-time and non-real-time tasks. We present a dynamic kernel thread scheduling mechanism with weighted average priority inheritance protocol (PIP), a variation of the PIP. The scheduling algorithm assigns proper priorities to kernel threads at runtime by monitoring the activities of user-level real-time tasks. Experimental results show that the algorithms can greatly improve the unexpected execution latency of real-time tasks.

• 산업공학
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• 제22권1호
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• pp.63-72
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• 2009

This paper considers a transporter scheduling problem under dynamic block transportation environment in shipbuilding. In dynamic situations, there exist the addition, cancellation or change of block transportation requirements, sudden breakdowns and maintenance of transporters. The transportation of the blocks in the shipyard has some distinct characteristics. Some blocks are available to be picked up at a specific time during the planning horizon while some other blocks need to be delivered before a specific time. These requirements cause two penalty times: 1) delay times incurred when a block is picked up after a required start time, and 2) tardy times incurred when a block shipment is completed after the required delivery time. The blocks are located at different areas in the shipyard and transported by transporters. The objective of this paper is to propose a heuristic algorithm based on a network flow model which minimize the weighted sum of empty transporter travel times, delay times, and tardy times. Also, a rolling-horizon scheduling method is proposed for dynamic block transportation environment. The performance of the proposed heuristic algorithms are evaluated through a simulation experiment.

• Industrial Engineering and Management Systems
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• 제10권2호
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• pp.134-139
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• 2011

The problem of scheduling in permutation flowshops has been extensively investigated by many researchers. Recently, attempts are being made to consider more than one objective simultaneously and develop algorithms to obtain a set of Pareto-optimal solutions. Varadharajan et al. (2005) presented a multi-objective simulated-annealing algorithm (MOSA) for the problem of permutation-flowshop scheduling with the objectives of minimizing the makespan and the total flowtime of jobs. The MOSA uses two initial sequences obtained using heuristics, and seeks to obtain non-dominated solutions through the implementation of a probability function, which probabilistically selects the objective of minimizing either the makespan or the total flowtime of jobs. In this paper, the same problem of heuristically developing non-dominated sequences is considered. We propose an effective heuristics based on simulated annealing (SA), in which the weighted sum of the makespan and the total flowtime is used. The essences of the heuristics are in selecting the initial sequence, setting the weight and generating a solution in the search process. Using a benchmark problem provided by Taillard (1993), which was used in the MOSA, these conditions are extracted in a large-scale experiment. The non-dominated sets obtained from the existing algorithms and the proposed heuristics are compared. It was found that the proposed heuristics drastically improved the performance of finding the non-dominated frontier.