• 대한전자공학회논문지TC
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• 제48권9호
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• pp.27-34
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• 2011

무선 통신 시스템의 효율을 높이기 위해 제안된 무선인지 (Cognitive Radio) 시스템은 2차 사용자가 주사용자 (primary user)의 스펙트럼을 서로 공유하는 시스템이다. 2차 사용자가 주사용자에게 간섭을 일으키지 않으면서 효율적으로 데이터를 전송하기 위해서 NC-OFDM (Non-contiguous Orthogonal Frequency Division Multiplexing)을 사용한다. 하지만 NC-OFDM은 기존 OFDM과 마찬가지로 높은 PAPR (Peak-to-Average Power Ratio)을 발생시켜 시스템 성능을 저하시킨다. 본 논문에서는 첫 번째로 NC-OFDM에서 부반송파의 분포에 따른 PAPR에 대해 분석하였다. 두 번째로 기존 OFDM의 PAPR 감소기법인 PTS (Partial Transmit Sequence)와 SLM (Selective Mapping)을 NC-OFDM에 적용하여 PAPR 감소성능을 확인하였다. 마지막으로 pruned-FFT가 적용된 PAPR 감소기법을 NC-OFDM에 적용할 경우 계산복잡도를 기존 OFDM과 비교하였다. 시뮬레이션을 통해 pruned-FFT가 적용된 NC-OFDM이 기존 OFDM보다 PAPR 감소성능 및 계산복잡도 측면에서 보다 효율적임을 검증하였다.

• 대한전자공학회논문지TC
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• 제46권1호
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• pp.89-93
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• 2009

본 논문은 에너지 검출기에 시간 지연 장치를 채택하여 복수번의 확인 과정을 갖는 향상된 스펙트럼 검출기에서 센싱 시간에 따른 성능의 영향을 알아본다. SNR은 1dB, 그리고 오보 확률은 0.1로 고정하고 3, 60, 100km/h의 다양한 이동 속도를 고려한 스즈키 채널 하에서 시뮬레이션을 통해 센싱 성능을 고찰하고 이를 기존의 에너지 검출기의 경우와 비교한다.

• 정보기술과데이타베이스저널
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• 제6권2호
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• pp.45-57
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• 1999

This paper makes an attempt to find a systematic portion of the database design process, especially using the Entity-Relationship(E-R) model. Basically, we consider three aspects as a systematic portion of the database design process. They are, the strategy that a designer selects to design an E-R diagram, designer's cognitive style, and the knowledge and preference of the database designer. An experiment has been carried out in order to verify the systematic relationship between above-mentioned three aspects and the E-R modeling performance. The target system is a professional baseball system. A normative E-R diagram was constructed based upon 48 E-R diagrams produced during the experiment. The ANOVA process has been used to analyze the results. It has been found that there exist significant differences in query-answering capacity and the completeness of the E-R model among design methods. Individual differences in cognitive styles has not been found to be significantly related to the modeling performance.

• 한국자동차공학회논문집
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• 제7권6호
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• pp.222-230
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• 1999

A fixed type driving simulator is constructed with a car body, beam projector, operation software , driving scenario, and audio equipments. With the simulator, the cognitive effects of fatigue due to two hour continuous driving of a straight road is investigated . The effects of alcohol on driving performance is also studied. The braking operation and lane keeping performance due to fatigue and alcohol are investigated. Changes of vehicle motion due to these effects are verified by computer simulation.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제9권1호
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• pp.260-279
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• 2015

In this paper, we investigate physical layer security for multiple decode-and-forward (DF) relaying underlay cognitive radio networks (CRNs) with fixed transmit power at the secondary network against passive eavesdropping attacks. We propose a simple relay selection scheme to improve wireless transmission security based on the instantaneous channel information of all legitimate users and the statistical information about the eavesdropper channels. The closed-form expressions of the probability of non-zero secrecy capacity and the secrecy outage probability (SOP) are derived over independent and non-identically distributed Rayleigh fading environments. Furthermore, we conduct the asymptotic analysis to evaluate the secrecy diversity order performance and prove that full diversity is achieved by using the proposed relay selection. Finally, numerical results are presented to verify the theoretical analysis and depict that primary interference constrain has a significant impact on the secure performance and a proper transmit power for the second transmitters is preferred to be energy-efficient and improve the secure performance.

• Journal of Communications and Networks
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• 제18권3호
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• pp.311-319
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• 2016

In this paper, we analyze the spectrum-sensing performance of a cooperative cognitive radio (CR) network consisting of a number of CR nodes and a fusion center (FC). We introduce the "log-average-SNR ratio" that relates the average SNR of the CR-node-FC link and that of the primary-user-CR-node link. Assuming that the FC utilizes the K-out-of-N rule as its decision rule, we derive exact expressions for the sensing gain and the coding gain - parameters used to characterize the CR network performance at the high SNR region. Based on these results, we determine ways to optimize the performance of the CR network.

• 한국수학교육학회지시리즈A:수학교육
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• 제57권2호
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• pp.137-155
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• 2018

From the assumption that an individual's working memory capacity is limited, the cognitive load theory is concerned with providing adequate instructional design so as to avoid overloading the learner's working memory. Based on the cognitive load theory, this study aimed to provide implications for effective problem-based collaborative teaching and learning design by analyzing the level of middle school students' cognitive load which is perceived according to the problem types(short answer type, narrative type, project) in the process of collaborative problem solving in middle school function part. To do this, this study analyzed whether there is a relevant difference in the level of cognitive load for the problem type according to the math achievement level and gender in the process of cooperative problem solving. As a result, there was a relevant difference in the task burden and task difficulty perceived according to the types of problems in both first and second graders in middle schools students. and there was no significant difference in the cognitive effort. In addition, the efficacy of task performance differed between first and second graders. The significance of this study is as follows: in the process of collaborative problem solving learning, which is most frequently used in school classrooms, it examined students' cognitive load according to problem types in various aspects of grade, achievement level, and gender.

• 경영정보학연구
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• 제6권2호
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• pp.47-63
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• 2004

인터넷의 발달로 인해 가상공간에서 벌어지는 현상에 관한 관심과 영향력이 증가하고 있다. 그 중에서도 현실의 실제 공동체와 비슷한 가상공동체의 중요성이 커지고 있다. 그런데 가상공간 자체는 몰입하기 쉬운 특징을 고루 지니고 있다. 본 연구에서는 가상공동체의 구성원들이 가상공동체를 이용함에 있어서 몰입이 큰 역할을 한다는 것을 알아보고자 한다. 연구 결과 도전의욕, 숙련도, 지각된 현실감, 욕구충족 등의 변수들은 몰입을 통해 가상공동체의 이용에 유의한 영향을 미치는 것을 확인하였다. 단지 상호작용성은 몰입을 거치지 않고 직접 가상공동체 이용에 영향을 미치고 있었다. 이는 몰입이 가상공동체 이용에 중요한 역할을 하는 요인이라는 것을 나타내는 것이며, 또한 가상공동체가 제대로 운영되기 위해서는 상호작용에 필요한 최소한의 구성원을 확보할 필요가 있다는 것을 의미한다. 가상공동체의 운영에 있어서, 몰입을 높이는 여러 가지 방법들을 고안해서 적용한다면 가상공동체의 활성화와 성과를 높이는데 큰 기여를 할 수 있을 것이다.

• 문화기술의 융합
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• 제8권3호
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• pp.331-337
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• 2022

본 연구는 중국 대학 육상선수의 운동몰입과 경기력에 미치는 영향을 규명하는 데 있다. 국 하남대학, 정주대학, 하남사범대학 체육대학 육상선수를 대상 19세 이상 남·여 선수들을 모집단으로 설정하여 직접 방문을 통해 설문조사를 위한 동의 및 협조를 구한 후 편의표집방법(Convenience sampling method)을 이용하여 1400부의 설문지를 배포하였고, 불성실한 응답, 무응답, 이중응답 등과 같이 자료로 활용하기 어려운 38부를 제외한 102부를 최종 분석에 사용하였다. 자료처리를 실시하여 얻은 결과는 다음과 같다. 첫째, 운동몰입의 하위요인(인지몰입, 행동몰입)이 경기력에 미치는 영향에서 모든 요인이 통계적으로 유의한 영향을 미쳤다. 둘째, 운동몰입의 하위요인(인지몰입, 행동몰입)이 수행력에 미치는 영향에서 모든 요인이 통계적으로 유의한 영향을 미쳤다. 셋째, 운동몰입의 하위요인(인지몰입, 행동몰입)이 집중력에 미치는 영향에서 모든 요인이 통계적으로 유의한 영향을 미쳤다.

• 대한치매학회지
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• 제21권1호
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• pp.30-41
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• 2022

Background and Purpose: In this study we aimed to find the association between neuropsychological performance and body mass index (BMI) in patients with mild cognitive impairment (MCI). In addition, we investigated the effects of the apolipoprotein E (APOE) genotype in the relationship between the BMI and cognition in MCI. Methods: We enrolled a cohort of 3,038 subjects with MCI aged 65-90 from the Clinical Research Center for Dementia of South Korea and a dementia cohort of the Ewha Womans University Mokdong Hospital. MCI patients were classified into three subgroups according to the Asian standard of BMI. We compared cognitive performances between groups by one-way analysis of variance. To investigate the effects of the APOE genotype, we used multivariate linear regression models after adjusting for possible confounders. Results: Even though normal BMI groups were younger, had more females, and had less comorbidities, the higher BMI groups had better cognitive functions. Among subjects with APOE ε4 carriers, there was a positive relationship between the BMI and the memory task alone. Conclusions: Our findings suggested that higher BMI in patients with MCI were associated with better cognitive performance. The effects of the APOE ε4 genotype in the associations between BMI and cognition were distinguishing. Therefore, according to physical status, APOE ε4 genotype-specific strategies in the assessments and treatments may be necessary in elderly patients with MCI.