• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2004년도 추계학술대회 논문집
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• pp.1282-1285
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• 2004

The high voltage driving system with multi-phase shifter including piezoelectric actuators comprised a driving power unit for outputting the driving power by converting input alternate current into direct current, a frequency shifting unit for supplying the direct current power and shifting or generating a frequency, a high-voltage amplification unit for amplifying the input signal outputted from the driving power unit and the frequency shifting unit into a high-voltage signal, and a phase shifting unit for shifting the phase difference of the amplified signal applied to the high-voltage amplification unit and driving plural piezoelectric actuators sequentially. The results that the operating voltage was stable, the voltage loss ratio was low and the response velocity was fast could be obtained. An experiment on performance of the high voltage driving system with multi-phase shifter designed and manufactured as above described was conducted by using a piezoelectric pump having 3 sheets of round unimorph piezoelectric actuators laminated respectively in a rectangular case. It sucks any fluid by causing the first piezoelectric actuator to shift from the inlet porter side, the phase delay of 60$^{\circ}$ causes the second piezoelectric actuator to begin to shift, and the phase delay of 120$^{\circ}$ causes the third piezoelectric actuator to begin to shift. As a result of measuring each change in the outlet flow rate of the piezoelectric pump, it was shown that the frequency-flow rate characteristic, the voltage-flow characteristic, and the load pressure-flow rate characteristic were improved.

• 말소리와 음성과학
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• 제8권4호
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• pp.39-47
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• 2016

While acoustic studies in the past decade documented a raised /o/ by showing their lowered first formants (F1) almost overlapped with those of high back vowel /u/, no consensus has been made in terms of how this /o/-raising affects the vowels as a system in Seoul Korean. The current study aimed to investigate the age- and gender-related differences of the relative distance among the vowels to better understand the influence of this on-going sound change on the vowel system. We measured the static and dynamic spectral characteristics (F1 and F2) of the seven Korean monophthong vowels /e a ʌ o u ɨ i/ in the spontaneous speech of Seoul Corpus, and depicted the patterns of 30 individual speakers (10 speakers in each group of teens, 20s and 40s) as a function of age and gender. The static spectral examination showed low F1 values of /o/ in the spontaneous speech corpus confirming the vowel /o/ raising, and also revealed greater F2 values of /u, ɨ/ suggesting their anterior articulations. The tendencies were stronger when the speakers were younger and female. The spectral trajectories further showed that the F1 and F2 between /o/ and /u/ were differentiated throughout the vowel mid-point although the trajectories gradually merged near the vowel mid point in the older male speakers' productions. The acoustic evidence of contrast among /o, u, ɨ/ supports that the raised /o/ is not indicative of a merger with /u/ but rather implying a chain-like vowel shift in the Seoul Korean.

• 한국시뮬레이션학회논문지
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• 제22권3호
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• pp.35-41
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• 2013

본 연구는 생산 공정 간 버퍼 제약이 있는 flow shop 시스템에 활동기간 기반 애로공정 발견 기법을 적용하여 그 타당성을 분석하였다. 생산 시스템에는 보통 생산성을 저하시키는 1개 또는 1개 이상의 애로공정이 존재한다. 전통적인 애로공정을 발견하는 기준으로 공정의 대기 시간이나 대기 공정의 길이 또는 공정의 이용률이 자주 활용된다. 애로공정은 다른 공정작업을 대기 상태로 만들어 전체적으로 시스템의 생산성을 저하시키는 공정으로 공정 시간과 기계의 고장 및 수리 시간의 확률적인 특성으로 인하여 애로공정은 생산과정에서 수시로 다른 공정으로 변환된다. 어떤 공정이 언제 활동기간으로 변화하는 정보를 이용하여 애로공정을 발견하는 기법을 범용 시뮬레이션 언어 AweSim에서 구현하였다. 시뮬레이션 결과, 활동기간 기법과 단독 및 변환 애로공정 기간 비율 기법이 전통적인 기법과 비교하여 애로공정을 발견하는데 효과적인 것으로 나타났다. 간단한 flow shop 모형을 대상으로 얻은 결과이지만 복잡한 시스템에도 적용될 수 있을 것으로 기대되며 애로공정 개선을 통한 생산시스템 가용 자원의 효과적인 배치는 생산성을 향상시키는데 기여할 것으로 사료된다.

• 한국항만경제학회지
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• 제32권1호
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• pp.135-149
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• 2016

우리나라 수출입 컨테이너물동량은 1995년 3,942천 TEU에서 2014년 14,601천 TEU로 증가했고, 부산항의 처리 비중은 92.4%에서 63.4%로 상당 수준 낮아졌다. 현재 우리나라 33개 무역항 중 11개 항만에서 컨테이너 전용부두가 운영되는 있으며, 2014년 항만별 컨테이너부두 시설 확보율은 심한 편차를 보이고 있다. 즉 부산항, 인천항은 각 83.3%, 48.0%로 시설 부족현상을 보이나, 광양항 196.7%, 울산항 188.8%, 군산항 583.3%, 마산항 1,666.7% 등 시설 과잉이 심각한 항만도 적지 않다. 본 연구는 허쉬만-허핀달지수(HHI)와 변이할당법을 활용하여 기존 연구와 차별적으로 5대 해외 기종점 권역별로 수출입 컨테이너화물의 항만 집중도와 변이효과를 분석하고, 우리나라 컨테이너항만의 경쟁 구도 및 항만정책 방향에 관한 시사점을 도출하였다. 분석 결과, 우리나라 컨테이너항만의 집중도는 지난 20년간 0.86에서 0.44로 완화되었으나 최근 5년간은 큰 변화가 없었다. 5대 수출입 해외 권역, 즉 극동아시아, 동남아시아, 일본, 북미 및 유럽 지역 컨테이너화물의 세부적인 항만 집중도 분석 결과, 2014년 극동아시아 0.290, 동남아시아 0.375로 가장 낮았고, 이는 전체 항만 집중도를 0.44로 낮춘 주요 원인이 되었다. 즉 아시아 수출입 물동량이 과거에 비해 국내 여러 항만에서 분산 처리되면서 우리나라 전체 컨테이너항만의 집중도를 낮추게 된 것이다. 또한 2010년 이후 컨테이너항만의 집중도는 거의 변함이 없고 북미 및 유럽항로에서는 오히려 집중도가 증가하고 있다는 것도 확인했다. 이에 정부는 컨테이너 부두시설의 효율적인 개발 및 운영 정책 수립을 위해 항만의 집중도 및 변이효과 추이를 지속적으로 모니터링할 필요가 있다. 특히 컨테이너 물동량 대비 하역능력에 충분한 여유가 있는 항만임에도 불구하고 양(+)의 변이효과가 충분히 나타나지 않을 경우, 그 원인을 정확히 규명하고 대응 방안을 모색해야 할 것이다. 향후 수출입 컨테이너 화물의 내륙 기종점별 항만 집중도나 동북아시아 항만에 대한 환적화물의 집중도 등에 관한 후속적인 연구도 진행되어야 할 것이다.

• 한국소음진동공학회논문집
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• 제16권3호
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• pp.233-239
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• 2006

The effect of the joint condition of automotive muffler shell and baffle on radiated noise from muffler shell Is studied. Shell vibration characteristics, especially shift In natural frequency and change in of response amplitude, was identified from finite element analysis and modal tests for various joint conditions between shell and baffle. When there is heat expansion and inner pressure from the exhaust 9as in the muffler with elliptical cross section, the shell expands out, and construct gap with baffles. This gap causes more degrees of freedom of shell vibration and natural frequency shift. By welding the muffler shell to the baffles or using a dual shell muffler, the radiated noise problem could be mitigated supplying more a rigid joint and damping, respectively.

• 대한산업공학회지
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• 제25권4호
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• pp.476-489
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• 1999

This paper is concerned with the deployment of core technologies for automotive steel sheets, based on the structural change of global market. The main tasks of automotive industry are to ensure the energy consumption, environmental regulations, and driving safety. With social and legal requirements, this study analyzes the market creation processes with technological innovations for hot rolled, cold rolled and galvanized steel sheets during the 20th century. It has been proven that the leading country in the steel industry was also that in the automotive. The purchaser-supplier relations of sheet materials are then patternized in the regional markets of the United States and Japan, who share nearly 50% of market in the world. According to the paradigm shift of globalization, the balance of power in Porter's 5 forces has been moved to the buyers', and both industries pursue Win-Win strategies such as the PNGV(Partnership for a New Generation of Vehicles ) and design-in system with the competition.

• Smart Structures and Systems
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• 제5권4호
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• pp.345-355
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• 2009

This article describes the development of a fiber optic accelerometer based on Fiber Bragg Gratings (FBG). The accelerometer utilizes the stiffness of the optical fiber and a lumped mass in the design. Acceleration is measured by the FBG in response to the vibration of the fiber optic mass system. The wavelength shift of FBG is proportional to the change in acceleration, and the gauge factor pertains to the shift in wavelength as a function of acceleration. Low frequency version of the accelerometer was developed for applications in monitoring bridges. The accelerometer was first evaluated in laboratory settings and then employed in a demonstration project for condition assessment of a bridge. Laboratory experiments involved evaluation of the sensitivity and resolution of measurements under a series of low frequency low amplitude conditions. The main feature of this accelerometer is single channel multiplexing capability rendering the system highly practical for application in condition assessment of bridges. This feature of the accelerometer was evaluated by using the system during ambient vibration tests of a bridge. The Frequency Domain Decomposition method was employed to identify the mode shapes and natural frequencies of the bridge. Results were compared with the data acquired from the conventional accelerometers.

• 한국산업융합학회 논문집
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• 제6권3호
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• pp.201-205
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• 2003

The effects of adsorption and desorption of alkali-metals on Si(111) surface were investigated by using AES and RHEED-system. The adsorption system is a fundamental interest because of its unique electronic properties such as measurement of work function change, adatom-core level shift. It was found that the growth node of K on Si(111) surface was layer by layer growth and the saturation coverage was 2.0ML at room temperature. Superstructure changes on Si(111) surface according to the alkali-metal thickness and substrate temperatures were accurately defined. By applying the isothermal desorption method, the desorption energies of Li/Si(111) and K/Si(111) surfaces was measured. On Li/Si(111) and K/Si(111) surfaces, the desorption energies were 3.07 eV, 2.19 eV respectively.

• 한국항해학회지
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• 제22권1호
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• pp.31-49
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• 1998

The technology of navigational instruments and the profession of going to sea have entered a time of dramatic change. A paradigm shift is taking place which will eventually make the industry unrecognizable to those who first went to sea only twenty years ago. This change is most emphatically seen in three areas: Automatic Identification System(AIS), Electronic Chart Display and Information System(ECDIS), and Voyage Data Recoreder(VDR). In order to make these new instruments to be fitted on board commerical ships, international requirements for enhacing the safety of navigation on the world's waterways, the Chapter V of International Convention for the Safety of Life at sea, 1974 as ameded(hereinafter referred to as "SOLAS"), are being also changed.o changed.

• 제어로봇시스템학회논문지
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• 제19권10호
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• pp.879-885
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• 2013

By performing interval analysis on the system transfer function, we propose an improved method of control loop design for a DC/DC converter. In conventional design methods, the effect of system parameter change due to the specified range of operating conditions and production tolerances in power components should be checked a posteriori, because this may result in a transfer function shift and performance degradation. In the proposed method, a possible parameter change is considered a priori in the design step in order that the desired crossover frequency and sufficient phase margin can be achieved even in the worst case condition. As an illustrative example, a buck dc/dc converter is designed by two different methods and performance comparisons are performed to verify the feasibility of the proposed scheme.