• 한국정보통신학회:학술대회논문집
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• 한국정보통신학회 2012년도 추계학술대회
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• pp.611-614
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• 2012

시공간 블록 부호화(STBC: Space-Time Block Code) 기법은 단순하면서도 효과적인 다이버시티 기법으로 WCDMA, HSDPA 및 LTE 이동통신 표준에 채택되었다. 이러한 STBC 기법은 페이딩 채널의 추정 정확도에 따라 그 성능이 좌우된다. 채널 추정을 위한 기준 심볼의 오버헤드를 수용할 수 없거나 고속으로 이동하는 모바일의 경우 채널 추정이 힘든 경우가 있다. 이러한 문제를 해결하기 위하여 차등 시공간 블록 부호화(DSTM: Differential Space-Time Modulation) 기법들이 제안되어 왔다. 이 기법들은 채널 추정을 필요로 하지 않기 때문에 위와 같은 고속 이동 환경에 적합한 장점이 있다. 본 논문에서는 다양한 속도로 이동하는 모바일 채널에 LTE 파라미터를 적용하여 기존의 STBC 및 DSTM의 성능을 고찰해 보고, 단말에 적용 가능한 적응적 DSTM 복호 기법을 제안하여 그 성능을 고찰하였다.

• Journal of Power Electronics
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• 제16권2호
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• pp.572-583
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• 2016

In view of the speed control characteristics of induction traction motors and the problems of direct torque control (DTC) algorithms in current applications, this paper presents a DTC algorithm characterized by a symmetrical polygon flux control and a closed loop power control in the constant-torque base speed region and constant-power field-weakening region of induction traction motors. This algorithm only needs to add a stator flux control algorithm to the traditional DTC structures. This has the benefit of simplicity, while maintaining the features of traditional algorithms such as a rapid dynamic response, uncomplicated control circuit, reduced dependence on motor parameters, etc. In addition, it obtains a smoother flux trajectory that is conducive to improvement of the harmonic elimination capability, the switching frequency utilization as well as the torque and power performance in the field-weakening region. The effectiveness and feasibility of this DTC algorithm are demonstrated by both theoretical analysis and experimental results.

• Journal of Power Electronics
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• 제19권4호
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• pp.1000-1010
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• 2019

The use of internal-model-based linear controller, such as resonant controller, is a well-established technique for the current control of grid-connected systems. Attractive properties for resonant controllers include their two-sequence tracking ability, the simple control structure, and the reduced computational burden. However, in the case of continuous-designed resonant controller, the transient performance is inevitably degraded at a low switching frequency. Moreover, available design methods for resonant controller is not able to realize the direct design of transient performances, and the anticipated transient performance is mainly achieved through trial and error. To address these problems, the zero-order-hold (ZOH) characteristic and inherent time delay in digital control systems are considered comprehensively in the design, and a corresponding hold-equivalent discrete model of the grid-connected converter is then established. The relationship between the placement of closed-loop poles and the corresponding transient performance is comprehensively investigated to realize the direct mapping relationship between the control gain and the transient response time. For the benefit of automatic tuning and real-time adaption, analytical expressions for controller gains are derived in detail using the required transient response time and system parameters. Simulation and experimental results demonstrate the validity of the proposed method.

• Asia Marketing Journal
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• 제14권2호
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• pp.157-176
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• 2012

시장구조 분석에서 흔히 사용되는 상표전환 자료는 비내구재 분석에 적절한 방법이 될 수 있으나 자동차 같이 사용연한이 장시간인 내구재의 경우에는 소비자의 상표에 대한 선호도가 변할 수 있어 상표전환 자료의 사용에 문제가 있다. 따라서 경쟁을 잘 포착할 수 있는 다른 접근이 필요하다. 본 연구는 이에 대한 대안으로 상표간 경쟁 자료로써 고려상표군을 이용하여 자동차 시장의 구조를 Latent Class 군집분석을 활용한 탐색적 검증방법으로 분석하였다. 또한 소비자 행동분석에 근거하여 상표간 경쟁의 근간을 이루는 고려상표군 형성에 영향을 미치는 인자들을 밝히는데 중점을 두었다. 미국 자동차 시장을 대상으로 분석한 결과, 시장은 상표 원산지 효과에 의해 구분되었다. 즉, 미국 상표, 유럽 상표, 그리고 아시아 상표 등으로 시장이 구분되었다. 또한 각 시장구조 내 소비자들의 고려상표군 형성에 신뢰성/안전, 이미지/즐거움, 경제성 등의 편익과 성별, 소득 등 개인적 요인이 영향을 미치는 것으로 나타났다.

• Asia pacific journal of information systems
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• 제20권1호
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• pp.127-140
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• 2010

The benefit that a consumer derives from the use of a good often depends on the number of other consumers purchasing the same goods or other compatible items. This property, which is known as network externality, is significant in many IT related industries. Over the past few decades, network externalities have been recognized in the context of physical networks such as the telephone and railroad industries. Today, as many products are provided as a form of system that consists of compatible components, the appreciation of network externality is becoming increasingly important. Network externalities have been extensively studied among economists who have been seeking to explain new phenomena resulting from rapid advancements in ICT (Information and Communication Technology). As a result of these efforts, a new body of theories for 'New Economy' has been proposed. The theoretical bottom-line argument of such theories is that technologies subject to network effects exhibit multiple equilibriums and will finally lock into a monopoly with one standard cornering the entire market. They emphasize that such "tippiness" is a typical characteristic in such networked markets, describing that multiple incompatible technologies rarely coexist and that the switch to a single, leading standard occurs suddenly. Moreover, it is argued that this standardization process is path dependent, and the ultimate outcome is unpredictable. With incomplete information about other actors' preferences, there can be excess inertia, as consumers only moderately favor the change, and hence are themselves insufficiently motivated to start the bandwagon rolling, but would get on it once it did start to roll. This startup problem can prevent the adoption of any standard at all, even if it is preferred by everyone. Conversely, excess momentum is another possible outcome, for example, if a sponsoring firm uses low prices during early periods of diffusion. The aim of this paper is to analyze the dynamics of the adoption process in markets exhibiting network effects by focusing on two factors; switching and agent heterogeneity. Switching is an important factor that should be considered in analyzing the adoption process. An agent's switching invokes switching by other adopters, which brings about a positive feedback process that can significantly complicate the adoption process. Agent heterogeneity also plays a important role in shaping the early development of the adoption process, which has a significant impact on the later development of the process. The effects of these two factors are analyzed by developing an agent-based simulation model. ABM is a computer-based simulation methodology that can offer many advantages over traditional analytical approaches. The model is designed such that agents have diverse preferences regarding technology and are allowed to switch their previous choice. The simulation results showed that the adoption processes in a market exhibiting networks effects are significantly affected by the distribution of agents and the occurrence of switching. In particular, it is found that both weak heterogeneity and strong network effects cause agents to start to switch early and this plays a role of expediting the emergence of 'lock-in.' When network effects are strong, agents are easily affected by changes in early market shares. This causes agents to switch earlier and in turn speeds up the market's tipping. The same effect is found in the case of highly homogeneous agents. When agents are highly homogeneous, the market starts to tip toward one technology rapidly, and its choice is not always consistent with the populations' initial inclination. Increased volatility and faster lock-in increase the possibility that the market will reach an unexpected outcome. The primary contribution of this study is the elucidation of the role of parameters characterizing the market in the development of the lock-in process, and identification of conditions where such unexpected outcomes happen.

• Childhood Kidney Diseases
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• 제21권2호
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• pp.142-146
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• 2017

Purpose: To evaluate changes in quality of life (QoL) in patients with neurogenic bladder treated with clean intermittent catheterization (CIC), who changed from a multiple use catheter (MUC) to single use catheter (SUC). Methods: The Modified Intermittent Self-Catheterization Questionnaire (mISC-Q) was used to determine potential changes in patients' QoL as a result of switching from MUC to SUC. The mISC-Q consists of questions within four categories: ease of use, convenience, discreetness, and symptomatic benefit. Answers were graded as Strongly agree (+2), Agree (+1), Not sure (0), Disagree (-1), and Strongly disagree (-2). Overall patient QoL, as well as by sex, disease (presence of augmentation cystoplasty), and catheterization route (via urethra or urinary diversion), were analyzed. Results: Thirty-eight patients (21M:17F; mean age: $21.7{\pm}5.3y$) submitted questionnaires. For ease of use, SUC was significantly better than MUC (score: 0.364, P=0.002) in all patients. Patients with catheterization via the urethra showed significant favor for SUC in ease of use (score: 0.512, P<0.001) and convenience (score: 0.714, P=0.011), but patients with catheterization via the abdominal stoma of urinary diversion gave negative scores in all categories, though no categories were significant. Conclusion: This study suggested that changing from MUC to SUC may lead to improvements in QoL, especially regarding ease of use. This benefit was clearly found in patients with catheterization via urethra rather than abdominal stoma of urinary diversion.

• 생물정신의학
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• 제19권2호
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• pp.84-90
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• 2012

Objectives : The purpose of this study was to examine the changes in metabolic parameters and Positive and Negative Syndrome Scale (PANSS) scores of patients previously treated with atypical antipsychotic drugs other than paliperidone, after 8 weeks of treatment with paliperidone. Methods : Changes in body weight, body mass index, leptin, lipid levels, fasting glucose, and PANSS scores of patients who switched from other atypical antipsychotic drugs to paliperidone were measured after 8 weeks of treatment with paliperidone. We compared these results with those of patients who had not been treated with antipsychotic drugs for at least 2 weeks prior to treatment with paliperidone (antipsychotic drug-free patients). Results : The antipsychotic drug-free group (n = 9) did not show significant changes in metabolic parameters, but showed a significant improvement in total and subscale scores of PANSS. In the group that switched from other atypical antipsychotic drugs to paliperidone (n = 13), body weight, body mass index and fasting glucose level significantly increased, while total and subscale scores of PANSS significantly improved. Conclusions : Paliperidone treatment will benefit patients with schizophrenia who have been antipsychotic drug-free or who have had difficulty with other atypical antipsychotic drugs, with regard to their psychopathological state. However, if patients have been treated with other atypical antipsychotic drugs before switching to paliperidone, they could gain body weight or their fasting glucose level could increase over a short period because of a change in receptor number and sensitivity caused by the previously prescribed antipsychotic drugs, and hence, paliperidone should be prescribed with caution for these patients.

• 한국통신학회논문지
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• 제32권8B호
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• pp.553-562
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• 2007

성숙기에 접어든 이동통신 시장은 소비자의 욕구가 다양해지는 반면에, 서비스 차별화가 어려워지고 있으며 번호이동성의 도입으로 인해 전환장벽이 완화되면서 사업자간 고객유지 및 확보를 위한 경쟁이 가속화되고 있다. 또한 HSDPA라는 신규 서비스의 도입으로 세대간 고객전환을 위한 치열한 마케팅 활동이 펼쳐지고 있다. 이러한 상황 속에서 이동통신 사업자에게 지속적 경쟁우위를 가져올 원천으로 브랜드 자산의 중요성이 더욱 대두되고 있다. 그런데 선행연구에서는 이동통신 브랜드 자산에 대한 연구가 제한적으로 수행되고 있으며 특히 CDMA 시장에서 형성된 고객자산이 HSDPA에 미치는 영향을 분석한 연구가 없었다. 이에 본 연구에서는 브랜드 이미지, 고객혜택, 가격, 품질, 마케팅 활동을 중심으로 이동통신 서비스의 브랜드 자산 결정요인을 분석하고 신규 서비스인 HSDPA 서비스 가입에 미치는 영향을 파악하였다. 그리고 본 연구결과를 바탕으로 이동통신 사업자의 브랜드 관리의 전략적 시사점을 제시하였다.

• 디지털융복합연구
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• 제11권2호
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• pp.115-125
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• 2013

본 연구에서는 의류제품 온라인쇼핑 후 실패를 경험한 소비자가 쇼핑채널에서 제공하는 다양한 서비스 회복노력을 경험한 후 느끼게 되는 만족도에 대하여 알아보고, 또한 의류 소비자가 평소에 온라인 쇼핑에 대하여 지각하는 혜택과 위험이 서비스회복노력 경험 후 채널에 대한 만족도 평가에 어떠한 영향을 미치는가를 알아보고자 하였다. 서울 시내 남녀 대학생을 대상으로 온라인 쇼핑을 통해 의류제품을 구매할 때에 예상되는 서비스 주요 실패 유형과 온라인 쇼핑채널 운영자가 제공하는 서비스 회복유형별 만족도 그리고 채널경향에 대한 전반적인 관계를 조사하여 분석한 결과 의류제품의 온라인 쇼핑에서 나타날 수 있는 주요 서비스 실패 유형은 맞음새, 잘못된 제품정보, 제품결함, 재고부족, 느린 배송으로 나타났다. 소비자가 서비스 실패 유형에 따라 소비자가 만족하는 회복 유형에 다른 영향을 주는 것을 확인 할 수 있었다. 소비자는 서비스 실패를 경험하게 되면 기본적으로 채널전환의 욕구를 가지며 이와 같은 채널전환 경향은 서비스 회복노력에 대한 만족도가 낮을 때 더 강한 것으로 나타났다. 반면, 지각된 위험에 따른 고저 집단의 만족도 차이는 미비하게 나타났다.

• 한국철도학회논문집
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• 제9권6호
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• pp.761-765
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• 2006

At present, harmonic currents cause serious problems in power conversion system using the semiconductor switching device. Also some of the conversion system provokes harmonic currents against to the main power supply system and causes hindrances for the system. Main power impedance of the traditional LC passive filter method, influences on the filter characteristics and amplifies the harmonics when resonance phenomenon is occurred. And the traditional existing 2 level inverter systems show the limit in capacity of voltage and current in case of occurring sudden load change. So, to solve this problem active filter which uses cascaded H-bridge multi level inverter has been designed and ex-filter system circuits were totally investigated. With multi level active filtering system not only the size of filter but also the size of filter for transformer can be reduced by half and so as to the weight, while the capacity of inverter can be double sized and wave forms can be compensated exactly and precisely. Also by the benefit of the increase in rating capacity, the various currents owing to the load fluctuation can be dealt more steadily. In order to simulate the wave form of harmonics based on the measured data on the AC 25kV high speed Domestic Commercial railway, it was simulated with PSCAD/EMTDC and PSIM. Based on the results of this demonstration, the power supply system and inverter system would be more stable and also promoting its efficiency.