• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.8 s.179
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• pp.1923-1930
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• 2000

A bar with periodically nonuniform material properties is selected as a one-dimensional model of a flat-panel speaker. This paper describes a theoretical approach to the bending waves propagating i n the nonuniform bar. The phase speed of the wave is obtained using perturbation techniques for small amplitude, sinusoidal modulation of the flexural rigidity and mass density. It is shown that the wave speed is decreased due to the nonuniformity of the material properties by the amount proportional to the square of the modulation amplitude. The resonance occurring when the wavelength is half of the period of the material properties is analyzed by the method of multiple scales. It is also shown that the wave speed at the resonance mode is decreased by the amount proportional to the modulation amplitude but the wave of this mode does not propagate far enough due to attenuation.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.11a
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• pp.335-340
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• 2001

Dynamic stability of a rotary oscillating cantilever beam is presented in this study. Using the stretch deformation instead of the conventional axial deformation, three linear partial differential equations are derived from Hamilton's principle and transformed into dimensionless forms. Stability diagrams of the first order approximate solutions are obtained by using the multiple scale perturbation method. The stability diagrams show that relatively large unstable regions exist near the combination of the first chordwise bending natural frequency and the first stretch natural frequency. This result is verified by using the generalized-${\alpha}$ method.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.3
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• pp.318-324
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• 2004

The stability of a simply supported straight pipe is investigated. The time dependent flow is assumed to vary harmonically about a constant mean velocity. Stability conditions and dynamic reponses of a governing equation are conducted by use of multiple scale mettled. Parametric resonances and combination resonances are investigated. Stability boundaries are analytically determined. The resulted stability conditions show that instabilities exist when the frequency of flow fluctuation is close to two times the natural frequency or to the sum of any two natural frequencies. In case that the fluctuated flow frequency is close to zero or to the difference of two natural frequencies, however, instabilities are not found up to the first order of perturbation. Stability charts are numerically Presented fir the first two vibration modes.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.20 no.9
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• pp.849-855
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• 2010

Damping may change the response characteristics of nonlinear oscillations due to the parametric excitation of a thin cantilever beam. When the natural frequencies of the first bending and torsional modes are of the same order of magnitude, we can observe the one-to-one combination resonance in the perturbation analysis depending on the characteristic parameters. The nonlinear behavior about the combination resonance reveals a chaotic motion depending on the natural frequencies and damping ratio. We can analyze the chaotic dynamics by using the eigenvalue analysis of the perturbed components. In this paper, we derived the equations for autonomous system and solved them to obtain the characteristic equation. The stability analysis was carried out by examining the eigenvalues. Numerical integration gave the physical behavior of each mode for given parameters.

• Journal of KSNVE
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• v.10 no.5
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• pp.865-872
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• 2000

This paper presents the modeling, theoretical formulation, and stability analysis for a combined system of a spinning disc and a head that contacts the disc. In the analytic model, head interference is considered by a rotating mass-spring-damper system together with a frictional follower force on the damped annular discs. The multiple scale method is utilized to perform the stability system that shows the existence of instability associated with parametric resonances. Using the formulated system , instability regions of optical recording disc are investigated with variation of mass, stiffness and friction force of a head, respectively. The simulation results show that the stiffness of a head is the most sensitive parameter on the instability of the disc.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.23 no.4
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• pp.893-900
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• 1998

본 논문에서는 잡음 예측 필터를 적용한 멀티 캐리어 CDMA 병렬 동기 시스템을 위한 임계치의 통계적인 해석에 중점을 둔다. 시스템 성능 척도로써 평균 동기 획득 시간을 검파 확률과 오보 확률의 관점에서 유도한다. 다중 경로 페이딩 채널에서 평균 동기 획득 시간을 유도한다. 수치해석 결과, 잡음 예측 필터를 적용한 멀티 캐리어 CDMA 병렬 동기 해석에 있어서 임계치의 통계적인 특성을 이용한 동기 해석이 임계치의 근사화에 의한 동기 해석보다 정확한 결과를 보임을 알 수 있다. 또한, 잡음 예측 필터를 적용한 멀티 캐리어 CDMA 별렬 동기 시스템이 넓은 범위의 SNR에 대해서 평균 동기 획득 시간을 최소화할 수 있는 임계치를 검파할 수 있음을 확인할 수 있다.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.29 no.1
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• pp.41-46
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• 2006

본 논문에서는 재시도와 완전입력 규칙을 갖는 BMAP/PH/N/0 대기시스템에 대한 주요 성능평가척도와 시스템의 정상상태 조건을 제시한다. 고려되는 시스템은 모든 서버가 서비스를 하고 있을 경우 도착이 이루어지는 배치도착은 모두 손실되며, 반대의 경우 도착하는 배치는 서비스를 받기 위해 시스템에 들어가게 된다. 만약 쉬고 있는 서버의 수가 불충분하여 배치의 일부가 즉각 서비스를 받을 수 없다면, 일단 오빗으로 이동하고 표준 재시도 대기 시스템의 규칙에 따라 후에 서비스를 받게 된다. 본 논문에서는 배치 마코프도착과정, 단계 서비스분포 및 유한버퍼를 갖는 다중서버 재시도 대기 시스템에 대한 수리모형을 제시한다. 제시된 시스템의 정상상태 분포 존재를 위한 충분조건을 유도하고, 이 분포를 계산하기 위한 알고리즘이 제시된다. 끝으로 완전입력규칙을 갖는 시스템에 대한 손실확률을 계산하기 위한 식이 유도하고, 수치 예제들을 제시한다.

• Annual Conference on Human and Language Technology
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• 2011.10a
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• pp.37-41
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• 2011

본 논문에서는 최근 많은 관심을 받고 있는 Opinion Mining으로서 사용자들의 자연어 형태의 영화평 문장을 분석하여 자동으로 평점을 예측하는 시스템을 제안한다. 제안 시스템은 영화평 분석에 적합한 어휘 자질, 감정 자질, 가치 자질 및 기타 자질들을 추출하고, 10점 척도의 영화평의 평점을 10개의 범주로 가정하여, 커널모델인 다중 범주 Support Vector Machine (SVM) 모델을 이용하여 높은 성능으로 영화평의 평점을 범주 분류한다.

• (The) Korean Journal of Educational Psychology
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• v.26 no.4
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• pp.1225-1248
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• 2012

The present study explored how ADHD assessment, identification, and diagnosis were conducted in research through an overview of research papers on ADHD in the last 10 years. The collected studies were categorized and analyzed by topics including data collection settings, assessment and identification, coexistence with other disabilities, considerable variables throughout evaluation, and biological basis. They were categorized and analyzed according to the identification methods, the number of assessment(s) and the number of informant(s). The results were as follows: First, the assessment and identifying studies on children with ADHD were excessively biased toward clinical settings. Second, the majority of the previous studies explored more the development or validation of tools for the assessment and identifying of ADHD than the other topics. Finally, a high preference for the use of a multiple assessment method in identifying ADHD was found. However, considering methodological aspects, there was a lack of practical application of multi-step process such as including a personal interview, reviewing school records or direct observing rating criteria. Considering these results, we discussed an urgent need for the diagnosis and identification guidelines of ADHD for teachers to effectively identifying ADHD children at schools. The implications of school-based ADHD assessment and diagnosis research were suggested.

• The Journal of the Korea Contents Association
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• v.9 no.8
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• pp.392-400
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• 2009

The research focus on participation and competence in sports and their difference in mental health. Moreover, it focus on how the sports participation and spots competence in health affect their mental health. For the research, 448 high school students were collected and the one-way ANOVA and the multiple regression analysis was carried on. As a result, first of all, according to the participation and competence in sports and their mental health, the sophomores and juniors were stronger than seniors and in case of depression which is in the lowest of the mental scale, the juniors showed the highest. Secondly, sports participation did not affect the mental health of students but sports competence show positive effects on all the lowest scale in the mental health such as insecurity, depression and hostility.