• 산업경영시스템학회지
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• 제47권2호
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• pp.48-56
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• 2024

We examine a single machine scheduling problem with step-improving jobs in which job processing times decrease step-wisely over time according to their starting times. The objective is to minimize total completion time which is defined as the sum of completion times of jobs. The total completion time is frequently considered as an objective because it is highly related to the total time spent by jobs in the system as well as work-in-progress. Many applications of this problem can be observed in the real world such as data gathering networks, system upgrades or technological shock, and production lines operated with part-time workers in each shift. Our goal is to develop a scheduling algorithm that can provide an optimal solution. For this, we present an efficient branch and bound algorithm with an assignment-based node design and tight lower bounds that can prune branch and bound nodes at early stages and accordingly reduce the computation time. In numerical experiments well designed to consider various scenarios, it is shown that the proposed algorithm outperforms the existing method and can solve practical problems within reasonable computation time.

• 대한간호학회지
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• 제24권4호
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• pp.652-665
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• 1994

This study was done to investigate the changes in the quality of life(QOL) of patients who received radiation therapy after surgery for breast cancer. For this purpose, 35 patients were interviewed using a questionnaire. They were followed over 8 month period from the beginning of radiation therapy. Changes in the QOL, side effect of the RT(radiation therapy), depression were measured. The results can be summarized as follows : 1. The mean score of the side effect of RT increased significantly over the period of RT. When the RT was completed, the QOL score was the low-est, and the depression score was the highest, but the changes of these scores were not statistically significant. 2. When the 6-week RT was finished, the QOL was significantly correlated with QOL of the beginning of RT, depression at RT completion and age. At three months after the completion of RT, the QOL was significantly correlated with QOL of the beginning of RT, depression and side effect of RT at three months after the completion of RT. At six months after the completion of RT, the QOL was significantly negatively correlated with age. 3. In the stepwise multiple regression analysis, the major influencing variables on the QOL were various according to the time lapse after the RT. The QOL at the completion of RT was predicted by the QOL at the beginning of RT, depression at the completion of RT and age. The QOL at three months after the completion of RT was predicted by the QOL at the beginning of RT and side effect of RT and depression at three months after the completion of RT. The QOL at six months after the completion of RT was predicted by age. This study suggests that continuous nursing care be required for improving the QOL of breast cancer patients not only during the RT period but also for a long term after the completion of RT.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제13권8호
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• pp.3900-3916
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• 2019

The modern mobile devices are typically equipped with multiple network interfaces, e.g., 4G LTE, Wi-Fi, Bluetooth, but the current implementation of TCP can support only a single path at the same time. The Multipath TCP (MPTCP) leverages the multipath feature and provides (i) robust connection by utilizing another interface if the current connection is lost and (ii) higher throughput than single path TCP by simultaneously leveraging multiple network paths. However, if the performance between the multiple paths are significantly diverse, the receiver may have to wait for packets from the slower path, causing reordering and buffering problems. To solve this problem, previous MPTCP schedulers mainly focused on predicting the latency of the path beforehand. Recent studies, however, have shown that the path latency varies by a large margin over time, thus the MPTCP scheduler may wrongly predict the path latency, causing performance degradation. In this paper, we propose a new MPTCP scheduler called, choose fastest subflow (CFS) scheduler to solve this problem. Rather than predicting the path latency, CFS utilizes the characteristics of these paths to reduce the overall flow completion time by redundantly sending the last part of the flow to both paths. We compare the performance through real testbed experiments that implements CFS. The experimental results on both synthetic packet generation and actual Web page requests, show that CFS consistently outperforms the previous proposals in all cases.

• 대한인간공학회지
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• 제9권1호
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• pp.15-20
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• 1990

In order to design man-machine system, communication system and other tasks that require information, we need to understand the characteristics of hyman short-term memory (STM). Thus, the purpose of this thesis is to investigate the influences of information stress and retention time on human performances and their relation- ships for STM of visual invormation. Eight subjects performed the computer monitering with STM task. The results showed that performance on serial recall from STM get wores and response time (and completion time) on information transmission by recall from STM increase as information stress and retention time increase. Also, there existed inverse proportional relationship between recall performance and response time (and completion time).

• Industrial Engineering and Management Systems
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• 제2권1호
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• pp.9-27
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• 2003

In a wafer fabrication factory, the completion time of an order is affected by many factors related to the specifics of the order and the status of the system, so is difficult to predict precisely. The level of influence of each factor on the order completion time may also depend on the production system characteristics, such as the rules for releasing and dispatching. This paper presents a method to identify those factors that significantly impact upon the order completion time under various combinations of scheduling rules. Computer simulations and statistical analyses were used to develop effective due date assignment models for improving the due date related performances. The first step of this research was to select the releasing and dispatching rules from those that were cited so frequently in related wafer fabrication factory researches. Simulation and statistical analyses were combined to identify the critical factors for predicting order completion time under various combinations of scheduling rules. In each combination of scheduling rules, two efficient due date assignment models were established by using the regression method for accurately predicting the order due date. Two due date assignment models, called the significant factor prediction model (SFM) and the key factor prediction model (KFM), are proposed to empirically compare the due date assignment rules widely used in practice. The simulation results indicate that SFM and KFM are superior to the other due date assignment rules. The releasing rule, dispatching rule and due date assignment rule have significant impacts on the due date related performances, with larger improvements coming from due date assignment and dispatching rules than from releasing rules.

• 부동산연구
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• 제27권3호
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• pp.103-118
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• 2017

우리나라는 아파트시장의 선분양제도로 인하여 오래 전부터 분양권 전매시장이 형성되어 왔다. 본 연구에서는 전매시장의 참여자들의 행태를 분석하기 위해 분양이후 전매까지의 소요시간을 분석하였다. 구체적으로 본 연구에서는 2000년부터 2016년까지 전국에 분양된 192개 아파트단지의 48,316개의 아파트의 전매자료를 Cox비례위험모형을 사용하여 부동산정책특성, 분양계약특성, 입지특성, 단지특성, 주호특성, 시기 및 지역특성 등이 전매기간에 미치는 영향을 분석하였다. 분석결과, 부동산정책특성과 관련하여 투기과열지구로 지정된 경우 주어진 기간에서 전매확률이 낮아지는 것으로 나타났다. 분양계약특성과 관련해서는 중도금이자후불제와 중도금무이자형태의 분양계약인 경우 전매확률을 유의적으로 증가시키는 것으로 나타났다. 아파트의 입지특성과 관련해서는 접도수가 많거나 인근에 초등학교와 공원이 있어서 입지조건이 우수한 아파트의 경우 전매확률이 유의적으로 높은 것으로 분석되었다. 단지특성과 관련해서는 아파트 단지가 택지개발지구에 위치하는 경우 전매확률은 낮아지는 반면에 대지면적 대비 부대시설면적의 비율이 높을수록 전매확률은 높아지는 것으로 나타났다. 마지막으로 주호특성과 관련해서 전용면적이 적을수록, 주호가 고층에 위치할수록 전매확률이 높아지는 것으로 분석되었다.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2002년도 ITC-CSCC -1
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• pp.443-445
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• 2002

In this paper, we present a novel efficient semaphore implementation scheme which diminishes completion time of high priority tasks and improves reliability of a system. The real-time system is constrained to complete their tasks in time. Especially, the task of a hard real-time system must meet its deadline under unfavorable conditions. In this paper, the number and sort of the locked semaphores, when an event occurred, decide whether the context switch should occur or not, so higher priority tasks diminish in their completion time. The experimental results show that the proposed method gives performance improvements in finish time of high priority tasks of about 11% over the Zuberi.

• Industrial Engineering and Management Systems
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• 제15권1호
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• pp.32-40
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• 2016

This paper considers a special case of a three machine flow shop scheduling problem in which operation processing time of each job is ordered such that machine 1 has the longest processing time, whereas machine 3, the shortest processing time. The objective of the problem is the minimization of the total completion time. Although the problem is simple, its complexity is yet to be established to our best knowledge. This paper first introduces the problem and presents some optimal properties of the problem. Then, it establishes several special cases in which a polynomial-time optimal solution procedure can be found. In addition, the paper proves that the recognition version of the problem is at least binary NP-complete. The complexity of the problem has been open despite its simple structure and this paper finally establishes its complexity. Finally, a simple and intuitive heuristic is developed and the tight worst case bound on relative error of 6/5 is established.

• 대한수학회보
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• 제25권2호
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• pp.195-201
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• 1988

In general relativity, analyzing causality is central to the study of black holes, to cosmology, and to each of the major recent mathematical theorems. By causality we refer to the general question of which points in a space-time can be joined by causal curves; relativistically which events can influence (be influenced by) a given event. Various causality conditions have been developed for space-times of the problems associated with examples of causality violations (2, 4). Causally continuous space-times were defined by Hawking and Sachs (5). Budic and Sachs (3) established causal completion. A metrizable topology on the causal completion of a causally continuous space-time was studied by Beem(1). Recently the region of space-time where causal continuity is violated was studied by Ishikawa (6) and Vyas and Akolia (8). In this paper we show characterization for reflectingness in terms of continuity of set valued functions. We investigate some properties of the region related to a causally continuous space-time where distinguishingness is violated, and characterize the chronology condition in terms of distinguishing-violated region.

• 제어로봇시스템학회논문지
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• 제14권4호
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• pp.376-380
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• 2008

This paper deals with a performance analysis of real-time control systems, which engages DMR(dual modular redundancy) to detect transient errors and checkpointing technique to tolerate transient errors. Transient errors are caused by transient faults and the most significant type of errors in reliable computer systems. Transient faults are assumed to occur according to a Poisson process and to be detected by a dual modular redundant structure. In addition, an equidistant checkpointing strategy is considered. The probability of the successful task completion in a real-time control system where periodic checkpointing operations are performed during the execution of a real-time control task is derived. Numerical examples show how checkpoiniting scheme influences the probability of task completion. In addition, the result of the analysis is compared with the simulation result.