• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.9B
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• pp.745-750
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• 2008

In a cognitive radio based system, quality of service (QoS) for the secondary user must be maintained as much as possible even while that of the primary user is protected all he time. In particular, switching wireless links for the secondary user during the transmission of multimedia data causes delay and information loss, and QoS degradations occur inevitably. The efficient resource management scheme is necessary to support the seamless multimedia service to the secondary user. This paper proposes a novel frequency selection method based on Multi-Criteria Decision Making (MCDM), in which uncertain parameters such as received signal strength, cell load, data rate, and available bandwidth are considered during the decision process for the frequency selection with the fuzzy set theory. Through simulation, we show that our proposed frequency selection method provides a better performance than the conventional methods which consider the received signal strength only.

• Korean Journal of Construction Engineering and Management
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• v.16 no.5
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• pp.114-122
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• 2015

Real estate development requires significant amount of capital investment. The project duration has been increased according to its enlarged size. For this reason, cost overrun and time delay are important risk factors that should be managed properly. As a method to hedge the risk, varoius real option methods have been presented. However, conventional project value assesment methods such as NPV(Net Present Value) have weakness to support decision making by reflecting dynamic situations in terms of variation of cost and time. Furthermore, the decision making process is serious of actions rather than discrete event. The purpose of this paper is to present a multiple real option valuation method to overcome the deterministic aspect of real option presented in previous research and practice. The method is developed as following: firstly, to select the model that can be applied in the real estate development project through a survey from previous literature on real options analysis; secondly, to apply data from office development case in order to verify the model by applying conventional real option and multiple real option valuation. According to analysis result, multiple real option provides enhanced values comparing to NPV and single real option.

• Journal of the Korean Society for Railway
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• v.18 no.5
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• pp.439-446
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• 2015

The turnout system, which determines the direction of the train, is not only a key system but also a vulnerable system. Failure of this system may lead to a delay of the train or even casualties. In this light, it is necessary to precisely the conditions of the turnout system. Currently, ROADMASTER of Germany is used as a diagnostic system in Korea. However, a new diagnostic system should be developed for optimized operation of the turnout system with maintenance that is suitable for the Korean railway environment. In this paper, a Fault Tree Analysis for the representative faults of the turnout system is conducted and physical quantities, which can be the cause of the fault, are classified according to the component and function. Also, the measuring factors for the monitoring are derived and a decision making theory is suggested. On the basis of the results, we propose a new turnout diagnostic system that can provide more driverse and precise information than the conventional system.

• Journal of Korean Neurosurgical Society
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• v.63 no.2
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• pp.188-201
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• 2020

Objective : The purpose of this study was to suggest that computed tomography angiography (CTA) is valuable as the only preliminary examination for mechanical thrombectomy (MT). MT after single examination of CTA including noncontrast computed tomography (NCCT) and maximum intensity projection (MIP) improves door-to-puncture time as well as results in favorable outcomes. Methods : A total of 157 patients who underwent MT at Dong Kang Medical Center from April 2015 to March 2019 were divided into two groups based on the examination performed prior to MT : CTA group who underwent CTA with NCCT and MIP, and NCCT+magnetic resonance image (MRi) group who underwent MRI including perfusion images after NCCT. In the two groups, time to CTA imaging or NCCT+MRi imaging after symptom onset, and time to arterial puncture and reperfusion were characterized as time-related outcomes. The evaluation of vascular recanalization after MT was defined as a modified thrombolysis in cerebral infarction (mTICI) scale. National Institutes of Health Stroke Scale (NIHSS) was assessed at the time of the visit to the emergency room and modified Rankin Scale (mRS) was assessed after 90 days. Results : Typically, there were 34 patients in the CTA group and 33 patients in the NCCT+MRi group. A significantly shorter delay for door-to-puncture time was observed (mean, 86±22.1 vs. 176±47.5 minutes; <0.01). Also, a significantly shorter door-to-imege time in the CTA group was observed (mean, 13±6.8 vs. 93±30.8 minutes; p<0.01). Moreover, a significantly shorter onset-to-puncture time was observed (mean, 195±128.0 vs. 314±157.6 minutes; p<0.01). Reperfusion result of mTICI ≥2b was 100% (34/34) in the CTA group and 94% (31/33) in the NCCT+MRi group, and mTICI 3 in 74% (25/34) in the CTA group and 73% (24/33) in the NCCT+MRi group. Favorable functional outcomes (mRS score ≤2 at 90 days) were 68% (23/34) in the CTA group and 60% (20/33) in the NCCT+MRi group. Conclusion : A single-phase CTA including NCCT and MIP images was performed as a single preliminary examination, which led to a reduction in the time of the procedure and resulted in good results of prognosis. Consequently, it is concluded that this method is of sufficient value as the only preliminary examination for decision making.

• The Journal of the Acoustical Society of Korea
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• v.22 no.2
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• pp.121-128
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• 2003

Acoustic Echo Cancellation(m) is very active research topic having many applications like teleconference and hands-free communication and it employs Double Talk Detector(DTD) to indicate whether the near-end speaker is active or not. However. the DTD is very sensitive to the variation of acoustical environment and it sometimes provides wrong information about the near-end speaker. In this paper, we are focusing on the development of robust DTD algorithm which is a basic building block for reliable AEC system. The proposed AEC system consists of delayless subband AEC and narrow-band DTD. Delayless subband AEC has proven to have excellent performance of echo cancellation with a low complexity and high convergence speed. In addition, it solves the signal delay problem in the existing subband AEC. On the other hand, the proposed narrowband DTD is operating on low frequency subband. It can take most advantages from the narrow subband such as a low computational complexity due to the down-sampling and the reliable DTD decision making procedure because of the low-frequency nature of the subband signal. From the simulation results of the proposed narrowband DTD and wideband DTD, we confirm that the proposed DTD outperforms the wideband DTD in a sense of removing possible false decision making about the near-end speaker activity.

• Korean Journal of Construction Engineering and Management
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• v.19 no.1
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• pp.43-53
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• 2018

Modular construction can improve construction quality and accuracy through manufacturing process, and it allow massive production and cost savings by repeatedly producing the same unit. In particular, it is possible to reduce the time because the on-site work and the manufacturing process can be carried out at simultaneously. However, according to the modular construction project survey report, there is no significant difference regarding the average construction period between modular construction and conventional construction. This is due to schedule delay problems that occur during construction phase. Therefore, it is necessary to select alternatives to prevent schedule delay during on-site construction progressing. Especially, in case of large-scale modular construction project, on-site module assembly and manufacturing process are performed concurrently. Hence, identification of alternatives should be done at the co-occurrence by taking both manufacturing and on-site work process in to account. In this research, the management factors of large-scale modular construction project were identified through the IDEF0 modeling, and the quantity management model for manufacturing and assembly is developed. This will reduce the schedule delay problem that occurs in the progression on-site work of a large scale modular construction.

• Journal of Distribution Research
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• v.16 no.4
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• pp.29-64
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• 2011

Overview of Research: Product availability is one of important competences of store to fulfill consumer needs. If stock-outs which means a product what consumer wants to buy is not available occurs, consumer will face decision-making uncertainty that leads to consumer's negative responses such as consumer dissatisfaction on store. Stockouts was much studied in the field of academia as well as practice in other countries. However, stock-outs has not been researched at all in Marketing and/or Distribution area in Korea. The main objectives of this study are to find out determinants of consumer responses such as Substitute, Delay, and Leave(SDL) when consumer encounters out-of-stock situation and then to examine the effects of these factors on consumer responses. Specifically, this study focuses on situational characteristics(e.g., purchase urgency and surprise), store characteristics (e.g., product assortment and store convenience), and consumer characteristics (e.g., brand loyalty and store loyalty). Then, this study empirically investigates relationships these factors with consumers behaviors such as product substitution, purchase delay, and store switching.