• 한국음향학회:학술대회논문집
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• 한국음향학회 2004년도 춘계학술발표대회 논문집 제23권 1호
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• pp.311-314
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• 2004

A new type of high frequency wideband ultrasonic transducer with a separation between a transmitter and a receiver was proposed and its characteristics were simulated using the PSpice model. The piezoelectric ceramic $PbTiO_{3}$ as a transmitter and the piezoelectric copolymer P(VDF-TrFE) as a receiver were used for high sensitivity and wide bandwidth, respectively. The characteristics of a center frequency approximately 40MHz focusing transducer fabricated in this study showed very wide bandwidth which could give an axial spatial resolution better than 30um in the B-mode image for biological tissues.

• 한국가정과학회지
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• 제9권2호
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• pp.5-20
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• 2006

This study was a preliminary investigation into improving the environmental and healthy quality of childcare centers. The purpose of this study was to determine the management condition on indoor environment and hygiene of childcare centers in Cheongju. Questionnaire survey was carried out from 11st to 26th of August 2004 by mail. Respondents were consisting of 55 teachers, an executive of each childcare center in Cheongju. From the survey results, there were some problems in 'empty period after remodeling work for preventing sick house syndrome', 'humidity controling', 'glare controling', 'indoor or outdoor noise controling', 'cleaning frequency of each room', 'washing method of toys', 'laundry frequency of rag doll and bedclothes'. So, we need to establish the regulations or give some educations and informations about indoor environment and hygiene to administrators of childcare centers.

• International Journal of Internet, Broadcasting and Communication
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• 제12권2호
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• pp.59-65
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• 2020

The domestic sleep industry is rapidly increasing in market size as it is linked to sleep apnea in the longterm care insurance for the elderly and domestic IT technology. In addition, due to the aging society, the government's support policy is also increasing, and many domestic companies are focusing on the sleep industry. Therefore, this study intends to examine the development strategies of the domestic sleep industry due to the increased social interest and corporate activities. To this end, a survey of 108 domestic companies was conducted by means of a Frequency Analysis, revealing some problems, such as poor sleep companies, insufficient resources for technology development, and limitations in distribution channels. As a result, it was found that for the development of the domestic sleep industry, strategies to strengthen the ecosystem, such as softening strategies through the sleep technology culture, strengthening ecosystems such as revitalizing industrial connections, and reforming laws and regulations, are urgent.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2009년도 하계학술발표대회 논문집
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• pp.1277-1282
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• 2009

The main objective of this prototype is to control resonance frequency of DTL system through the temperature control of cooling water. It is to resonant frequency of the drift tube cavities to 350 MHz. This paper describes the design of a prototype cooling water skid required for the temperature control of the DTL cavities, focusing in the modeling and simulation of the cooling system, the sizing of water pumping skid component.

• 비파괴검사학회지
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• 제28권1호
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• pp.54-58
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• 2008

Time reversal (TR) of body waves in fluids and isotropic solids has been used in many applications including ultrasonic NDE. However, the study of the TR method for anisotropic materials is not well established. In this paper, the full reconstruction of the input signal is investigated for anisotropic media using an analytical formulation, called a modular Gaussian beam (MGB) model. The time reversal operation of this model in the frequency domain is done by taking the complex conjugate of the Gaussian amplitude and phase received at the TR mirror position. A narrowband reference signal having a particular frequency and number of cycles is then multiplied and the whole signal is inverse Fourier transformed. The original input signal is seen to be fully restored by the TR process of MGB model and this model can be more generalized to simulate the spatial and temporal focusing effects due to TR process in anisotropic materials.

• 한국자동차공학회논문집
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• 제5권1호
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• pp.59-68
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• 1997

The modelling techniques of a center pillar-to-roof rail joint for low frequency vibration analysis are examined and some fundamental problems are addressed. To develop a simplified beam-spring model of the joint, the present work is focused on 1) practical shell modelling techniques and 2) joint spring stiffness estimation methods a practical model-updating method to match the calculated natural frequencies to the experimentally determine ones is proposed, particularly focusing on spot welding modelling. In joint spring modelling, the results from the model with one joint spring are compared with those from the model with three coupled springs. Finally, some fundamental problems in beam-spring modelling are addressed.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2003년도 학술회의 논문집 정보 및 제어부문 B
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• pp.946-949
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• 2003

In this paper, a DDFS(Direct Digital Frequency Synthesis)chip has been designed focusing on the reduction of ROM size and implemented using FPGA. When calculating the sine value for the input phase value, we used the Taylor series expansion approximation method to reduce the number of addresses of ROM. We also used the piecewise straight line approximation method, ie, the stored value int the ROM is the difference of the sine value and the straight line approximation. Using this method, we could reduce four bits for each ROM data.

• Nuclear Engineering and Technology
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• 제36권2호
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• pp.184-195
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• 2004

The multi-tasking feature of digital I&C equipment could increase risk concentration because the I&C equipment affects the actuation of the safety functions in several ways. Anticipated Transient without Scram (ATWS) is a typical case of safety function failure in nuclear power plants. In a conventional analysis, mechanical failures are treated as the main contributors of the ATWS. This paper quantitatively presents the probability of the ATWS based on a fault tree analysis of a Korea Standard Nuclear Power Plant is also presented. An analysis of the digital equipment in the digital plant protection system. The results show that the digital system severely affects the ATWS frequency. We also present the results of a sensitivity study, which show the effects of the important factors, and discuss the dependency between human operator failure and digital equipment failure.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 추계학술대회논문집
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• pp.577-580
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• 2005

This paper reports the high sensitivity actuator for flexible disk. The air stabilized flexible optical disk has very small axial runout. Therefore, It is proper to develop an actuator which has high sensitivity in tracking direction rather than in focusing direction. In order to maximize driving force in radial direction, we present an efficient design of magnetic circuit with simple multi-polarized magnets and auxiliary magnets. Designed magnetic circuit has big force in tracking direction. And we shift 2$^{nd}$ resonance frequency of moving parts Into high frequency band, not causing increase of mass and discord between force and mass centers to secure high sensitivities and sufficient control bandwidth. Finally, experimental results show that designed actuator has superior sensitivity in tracking direction.

• 한국산업융합학회 논문집
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• 제26권3호
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• pp.433-442
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• 2023

The purpose of this study is to reveal the Korean learners' usage pattern of '의', the genitive particle, according to semantic classification, so that it can be referred to in determining the contents and methods of related education. The method of this study adopts a quantitative analysis using learners corpus established by National Institute of Korean Language. As a result of the analysis, as proficiency increases, the overall frequency of '의' increases and the number of meaning senses used increases. However, the frequency of errors also increases with it. As for the usage pattern of each sense, the meaning of 'ownership, belonging' is the most frequent, and followed by 'acting entity', 'kinship, social relations', and 'relationship(area)'. In conclusion, the meanings of 'acting subjects' and 'relationships(area) need to be supplemented with explicit education. Other meanings need to be discussed, and decisions should be made in consideration of learning purpose and proficiency.