• Journal of Advanced Marine Engineering and Technology
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• 제24권4호
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• pp.405-413
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• 2000

This paper present study on the application of sound pressure and vibration signals to detect the presence of defects in a rolling element bearing using a statistical analysis method. The well established statistical parameters such as the crest factor and the distribution of moments including kurtosis and skew are utilized in this study. In addition, other statistical parameters derived from the beta distribution function are also used. A comparison study on the performance of the different types of parameter used is also performed. The statistical analysis is used because of its simplicity and quick computation. Under ideal conditions, the statistical method can be used to identify the different types of defect present in the bearing. In addition, the results also reveal that there is no significant advantages in using the beta function parameters when compared to using kurtosis and the crest factor for detecting and identifying defects in rolling element bearings from both sound and vibration signals.

• 한국정보통신설비학회:학술대회논문집
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• 한국정보통신설비학회 2005년도 하계학술대회
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• pp.128-132
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• 2005

각종 신호의 디지털 전송에서 Modulation기법에 의해 발생되는 PAPR(Peak to Average Power Ratio)은 전송 신호의 선형성을 보장하기 위하여 고출력 증폭기의 Back-off를 요구하게 된다. 이러한 고출력 증폭기의 Back-off요구로 인하여 원하는 출력에 비해 높은 전력소모량이 필요하여 대출력을 요구하는 장비의 소형화는 크게 제한을 받게 된다. 본 논문에서는 PAR을 감소하기 위한 CFR(Crest Factor Reduction)기법을 위성 DMB용 Gap Filler에 적용하여 장비 크기를 소형화한 사례에 대해 소개한다. 전송신호의 품질에 대한 영향을 최소화 하면서 PAR을 감소하기 위한 방안을 위해 도입된 Simulation 결과와 CFR기법을 적용한 장비에 대한 성능시험 결과 및 필드 테스트 결과에 대해 소개한다.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2002년도 추계학술대회 논문집
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• pp.312-315
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• 2002

This paper summarizes the results of a numerical study conducted to analyze the effect of selected process parameters on material flow and thread profile in thread rolling of large diameter blanks. Based on the previous work where a plane strain mode was found to provide a reasonable approximation of the thread rolling process, the effect of varying thread form, friction factor, flow stress, and blank diameter on effective strain and thread height was analyzed using the finite element code DEFORM. This study show that effective strain for flank angle, that blank diameter had important effect on the as-rolled thread while flow stress, friction factor, and crest round of dies had significant impact on effective strain at the thread root and crest and load of thread rolling. While the rate of strain harding was found to have an effect on the crest profile, the results indicate that it is the primary factor responsible for seam formation in rolled threads.

• Geomechanics and Engineering
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• 제31권6호
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• pp.637-651
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• 2022

The seismic design of embankment dams requires more comprehensive studies to understand the behaviour of dams. Deformations primarily control this behaviour occur during or after earthquake loading. Dam failures and incidents show that the impacts of deformations should be reviewed for existing and new embankment dams. Overtopping erosion failure can occur if crest deformations exceed the freeboard at the time of the deformations. Therefore, crest settlement is one of the most critical deformations. This study developed empirical formulas using Gene Expression Programming (GEP) based on 88 cases. In the analyses, dam height (H_d), alluvium thickness (H_a), the magnitude-acceleration-factor (MAF) values developed based on earthquake magnitude (Mw) and peak ground acceleration (PGA) within this study have been chosen as variables. Results show that GEP models developed in the paper are remarkably robust and accessible tools to predict earthquake-induced crest settlement of embankment dams and perform superior to the existing formulation. Also, dam engineering professionals can use them practically because the variables of prediction equations are easily accessible after the earthquake.

• 대한임상전기생리학회지
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• 제5권2호
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• pp.73-84
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• 2007

This study aims to examine changes from differences in the lumbar scoliosis angle and iliac crest height due to abnormal and habitual posture shown in unilateral weight load at standing posture and suggest data for preventing and treating lumbago. The subjects of this study are 16 lumbago patients between twenties and forties with chronic lumbago over six months, but without neurological symptoms. As a result of photographing front and back with three conditions such as weight load on both sides and left or right unilateral weight load posture in order to examine changes of lumbar scoliosis and iliac crest according to changes of posture at unilateral weight load, while scoliosis angle and iliac crest height by habitual unilateral support were increased, those by opposite support were decreased. In conclusion, it was found that habitual unilateral weight load may cause continuous distortion of spinal angle and change of iliac crest height and these may be a factor of lumbago. Therefore, if habitual unilateral weight load state is kept continuously, distortion of lumbar angle and iliac crest height may be greater and common efforts to change habitual unilateral weight load are needed.

• International Journal of Oral Biology
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• 제37권4호
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• pp.175-180
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• 2012

Skin-derived precursor cells (SKPs) are multipotent, sphere-forming and embryonic neural crest-related precursor cells that can be isolated from dermis. It is known that the properties of porcine SKPs can be enhanced by leukemia inhibitory factor (LIF) which is an essential factor for the generation of embryonic stem cells in mice. In our present study, to enhance or maintain the properties of murine SKPs, LIF was added to the culture medium. SKPs were treated with 1,000 IU LIF for 72 hours after passage 3. Quantitative real time RT-PCR was then performed to quantify the expression of the pluripotent stem cell specific genes Oct4, Nanog, Klf4 and c-Myc, and the neural crest specific genes Snai2 and Ngfr. The results show that the expression of Oct4 is increased in murine SKPs by LIF treatment whereas the level of Ngfr is decreased under these conditions. Interestingly, LIF treatment reduced Nanog expression which is also important for cell proliferation in adult stem cells and for osteogenic induction in mesenchymal stem cells. These findings implicate LIF in the maintenance of stemness in SKPs through the suppression of lineage differentiation and in part through the control of cell proliferation.

• Earthquakes and Structures
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• 제20권2호
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• pp.187-200
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• 2021

The main factor for the amplification of ground motions near the crest or the toe of a slope is the reflection of the incident waves. The effects of the slope topography on the surrounding lands over the crest or at the toe can amplify the seismic responses of buildings. This study investigates the seismic performance of the slope topography and three mid-rise buildings (five, ten, and fifteen-storey) located near the crest and toe of the slope by 3D numerical analysis. The nonlinear model was used to represent the real behavior of building and ground elements. The average results of seven records were used in the investigations. Based on the analysis, the amplification factor of acceleration near the crest and toe of the slope was the most effective at distances of 2.5 and 1.3 times the slope height, respectively. Accordingly, the seismic performance of buildings was studied at a distance equal to the height of the slope from the crest and toe. The seismic response results of buildings showed that the slope topography to have little impact on up to five-storey buildings located near the crest. Taking into account a topography-soil-structure interaction system increases the storey displacement and base shear in the building. Accordingly, in topography-soil-structure interaction analyses, the maximum lateral displacement was increased by 71% and 29% in ten and fifteen-storey buildings, respectively, compare to the soil-structure interaction system. Further, the base shear force was increased by 109% and 78% in these buildings relative to soil-structure interaction analyses.

• 대한치과보철학회지
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• 제45권2호
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• pp.274-282
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• 2007

Statement of problem: Main consideration was given to the stresses at the site of implant entry into the cortical bone at the alveolar crest. As a suspectible factor affecting the occurrence of stress concentrations, the contact angle between the implant and the alveolar crest bone was addressed. Purpose: The purpose of this study is to evaluate angles between the alveolar crest bone and the implant effect on the implant crestal area induced stresses using a finite element method. Material and methods: Cylindrically shaped, standard size ITI implants entering into alveolar crest with four different contact angles of 0, 15, 30, and 45 deg. with the long axis of the implant were axisymmetrically modelled. Alterations of stresses around the implants were computed and compared at the cervical cortical bone. Results and conclusion: The results demonstrated that regardless of the difference of the implant/alveolar crest bone contact angles, stress concentration occurred at the cervical bone and the angle differences led to insignificant variations in stress level.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2002년도 전력전자학술대회 논문집
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• pp.746-749
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• 2002

This paper presents a new control method for the high frequency electronic ballast which is operated with raw rectified dc link using diode bridge. For the commercial electronic ballast, proper ac input power factor and crest factor of the lamp current are required. The most ballast, therefore, has a active or passive power factor collection (PFC) circuit. With the proposed method, it can be achieved simultaneously that grater than 0.9 of input power factor and less than 1.85 of lamp current crest factor without any PFC circuit. In this paper, the proposed ballast control scheme and the experimental results for the application to the fluorescent lamp are described.

• 조명전기설비학회논문지
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• 제19권1호
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• pp.155-161
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• 2005

사무용 빌딩의 비선형 전자부하에 기인한 전압 및 전류파형의 왜곡은 중성선의 과열, 변압기 손실, 누전차단기 오동작 등을 야기 시킨다. 본 논문에서는 사무용 빌딩에서의 전압 및 전류 고조파의 크기, 전압 및 전류 파고율(Crest Factor : CF), 전압 및 전류 불평형 등을 비교함으로써 파형왜곡 특성을 분석하였다. 분석 결과, 고조파에 의한 상 및 중성선에서의 심각한 파형 왜곡 문제와 삼상에서의 단상 부하의 부적절한 분배로 인한 전류 불평형이 심한 빌딩이 조사되었다. 본 연구 결과는 사무용 빌딩에서 합리적이고 경제적인 부하운용을 위해 사용될 수 있을 것이다.