• Restorative Dentistry and Endodontics
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• v.27 no.3
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• pp.239-248
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• 2002

이 연구의 목적은 와동의 형태가 굴곡강도와 탄성계수 등 복합레진의 물리적 성질에 미치는 영향을 평가하는 것이다. 복합레진은 Clearfil$^{TM}$ AP-X(Kuraray, Japan)와 Esthet-X$^{TM}$(Dentsply, USA)가 이용되었으며, 상아질 접착제는 Clearfil$^{TM}$ SE Bond(Kuraray, Japan)와 Prime & Bond NT$^{TM}$(Dentsply, USA)를 사용하였다. 대조군의 시편은 split steel mold(25mm$\times$2mm$\times$2mm) 내에 상기 2종류의 복합레진을 충전하여 2개의 대조군 시편을 제작하였으며, 2.4 및 3.4의 C-factor를 부여하기 위한 유리 모형와동을 제작하고, 와동 내에 상기 2종류의 복합레진을 충전하기 전 유리와동의 내면은 sandblasting 처리하고 각각의 복합레진과 동일회사 제품의 상기 상아질 접착제로 처리한 후, 복합 레진을 각각 충전하여 4개의 실험군을 제작하였다. 제작된 실험군 시편은 저속 diamond saw로 충전된 복합레진 부위의 중심부를 통과하도록 절단하여 레진기둥(25mm$\times$2mm$\times$2mm)이 되도록 제작하였다. 제작된 시편을 37$^{\circ}C$의 증류수에 24시간 동안 보관 후, 만능시험기(EZ Test, Shimadzu, Japan)를 이용하여 분당 1mm의 crosshead speed로 3점 굴곡강도를 측정하였다. 또 Linometer(R&B, Korea)를 이용하여 복합레진의 중합수축량을 측정하였으며 굴곡강도측정 후 시편의 파단면은 주사전자현미경(S-2300, Hitachi, Japan)을 이용하여 관찰하였다. 실험결과의 통계분석은 95% 수준의 one-way ANOVA/Tukey's test를 이용하여 결과를 얻었다. 실험에 이용된 2종류 복합레진의 굴곡강도와 탄성계수는 C-factor치 증가에 따라 감소하였으며, 파단면 또한 C-factor의 증가에 따라 더 불규칙해지는 양상을 나타내었다. 본 실험의 결과 hybrid형 복합레진이 micro-hybrid형 복합레진에 비해 C-factor의 영향을 더 많이 받는 것으로 나타났으며, 와동의 C-factor증가가 굴곡강도나 탄성계수와 같은 복합레진의 물리적 성질을 저하시킨다는 것을 의미하였다.

• Journal of the Korea Convergence Society
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• v.5 no.3
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• pp.23-27
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• 2014

In recent times, there is an increasing interest in wireless charge of smartphones and devices, and many companies are developing wireless charges. The range of application of wireless charge would be expanded to almost all electronics, including not only mobile devices, but also notebook computers and vacuum cleaners. On-line electric vehicles are to be launched in the market this year in a massive scale. As such wireless charge-related markets are inexhaustible. Wireless charge is included in the world's top 10 promising technologies, and its rapid growth is expected to have annual growth by more than 100%. However, there's a need to establish a safe environment, by analyzing security threats to technical limitations and harmfulness to human body, and arrange institutional compliments. The development of communication method for a variety of wireless charging are delivering comfortable and safe information. This paper aims to examine the factors to threaten electric vehicle, which are usually intruded through network system and analyzes security threats to and security requirements for magnetic resonance mode-based wireless charge in mobile devices, and suggests security requirements.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.16 no.11
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• pp.1051-1059
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• 2004

Two phase thermosyphone loop for electronics cooling are designed and manufactured to test its performance under the partial load and low environment temperature conditions. The thermosyphone device has six evaporators connected parallel for the purpose of cooling six power amplifier units (PAU) independently. The heater modules for simulating PAUs are adhered with thermal pad to the evaporator plates to reduce the contact resistance. There are unbalanced distributions of liquid refrigerant in the differently heated evaporators due to the vapor pressure difference. To reduce the vapor pressure differences caused by partial heating, two evaporators are connected each other using the copper tube. The pressure regulation tube successfully reduces these unbalances and it is good candidates for a field distributed systems. Under the low environment temperature operating condition, such as $-30^{\circ}C$, there may be unexpected subcooling in condenser. It leads the very low saturation pressure, and under this condition there exists explosive boiling in evaporator. The abrupt pressure rise due to the explosive boiling inhibits the supplement of liquid refrigerant to the evaporator for continuous cooling. Finally the cooling cycle will be broken. For the normal circulation of refrigerant there may be an optimum cooling air flow rate in condenser to adjust the given heat load.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.23 no.12
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• pp.1388-1398
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• 2012

SAR(Synthetic Aperture Radar) systems can provide images of wide coverage in day, night, and all-weather conditions. However wideband SAR systems are known to be vulnerable to interferences from other devices operating at in-band or adjacent spectrums and this may lead to image corruptions. In this paper, a SAR point target simulator is developed that provides performance analysis on image distortion caused by interferences from other devices. Interference signals are generated based on the experimental data observed from acquired SAR raw data. Simulation results include typical SAR performance measures such as spatial resolution, peak to sidelobe ratio and integrated sidelobe ratio. Finally, SAR target simulations are performed and shown to correspond to the image corruptions found in real SAR missions affected by RF interferences.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2011.05a
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• pp.79-79
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• 2011

water cavitation peening(WCP)은 water jet 과정으로 인한 cavitation이 발생할 때, 금속표면 cavitation 현상에 의해 재료표면의 잔류응력과 경도 등의 물성을 변화시키게 되며, 그로 인해 생긴 잔류 응력으로 재료의 내구성 및 수명을 향상시키는 기술이다. 최근에는 water jet을 이용한 장치들이 건설 분야, 일반기계분야, 컷팅 공정, 분쇄 등 다양한 분야에서도 사용되고있다. 그러나 water jet을 이용한 peening은 소개 된지 20여년이 경과했음에도 불구하고 연구 및 개발 내용은 shot peening에 비해 아직 초기 단계이다. water cavitation peening은 기존의 피닝 방법의 단점을 보완 할 뿐만 아니라 환경적인 측면에서도 그 가치가 크다. 아직은 다른 peening 기법 보다 잔류압축응력 부가 측면에서 그 효과가 떨어지지만, water cavitation peening은 열에 영향을 받는 영역이 생성되지 않으며, 기계의 표면 가공을 하는 동안 어떤 미세한 먼지도 생성하지 않아 친환경적이다. 또한 복잡한 외형을 가지는 부품 및 내면에 적용성이 뛰어나고, 표면 정밀도 저하가 낮다는 장점이 있다. 본 연구에서는 조류발전용 블레이드의 재료로 사용하려는 동합금에 대하여 증류수 내에서 water cavitation peening 시간, 거리, 파형 등의 변수를 적용하여 최적 조건을 찾고, 다양한 전기화학적 실험을 실시하였으며, water cavitation peening 부의 부식특성을 평가 하였다. ASTM-G32 규정에 의거하여 압전효과를 용한 진동발생 장치(RB 111-CE)를 이용하여 동합금 표면에 water cavitation peening을 실시하고, 실험 후 표면의 손상거동을 관찰하기 위하여 3D현미경 및 전자주사현미경(SEM)을 사용하였다. 물성치 변화를 확인하기 위하여 SHIMADZU사의 HVM-2 Model의 비커스 경도기를 이용하여 표면 경도값을 측정하였다. 전기화학실험은 각 3회 이상 실시하였으며, Tafel 분석결과로 부식전류밀도와 부식전위의 평균, 부식전위를 알 수 있었고, 음분극 실험결과, 용존산소 환원반응에 의한 농도분극에서 수소가스발생에 의한 활성화 분극으로 진행되는 변곡점을 확일 할 수 있었다.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.12 no.9
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• pp.1646-1653
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• 2008

In this paper, we propose multicarrier CDMA system using the concept of the modulation level-controlled system in order to make the system robust to the frequency selectivity and to provide a maximum data rate maintaining an acceptable transmission quality over various channel environments. This system selects higher data rate when the channel experiences the low delay spread and slow fading. On the other hand, when the fading changes very fast and the delay spread is very long, the system selects lower data rate. In both cases, the system controls the number of serial-to-parallel converted streams and the number of fed streams. This system has the fixed number of sub-carriers. So the product of tile number of serial-to-parallel converted streams and the number of fed streams is always kept constant. With the same data fed at different sub-carriers, the frequency diversity is achieved. And a RAKE receiver also is utilized to achieve path (time) diversity.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.3
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• pp.483-490
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• 2019

Assessing the effect of forest fires and measuring the gas concentration around a fire has received little attention. Therefore, the concentrations of various gases in areas surrounding a fire need to be measured by the development of a suitable device. Unlike conventional portable devices, the AQS (Air Quality System) proposed in this paper is a portable instrument that measures five types of gases simultaneously, including CO, CO2, NOx, VOCs, and NH3, and has high durability through sensor protection algorithms. A PC-based program with an AQS connection was developed to monitor the real-time changes in the gas concentration. The reliability of the developed device was proven through a comparison of the results with other commercial gas analyzers. Measurements of the concentration due to indoor and outdoor fires were performed around a fire area to review the applicability and the predicted results were obtained.

• Smart Media Journal
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• v.12 no.10
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• pp.19-28
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• 2023

In the fruit harvesting field, interest in automatic robot harvesting is increasing due to various seasonality and rising harvesting costs. Accurate apple detection is a difficult problem in complex orchard environments with changes in light, vibrations caused by wind, and occlusion of leaves and branches. In this paper, we introduce a dataset and an adaptive heatmap regression model that are advantageous for robot automatic apple harvesting. The apple dataset was labeled with not only the apple location but also the visibility. We propose a method to detect the center point of an apple using an adaptive heatmap regression model that adjusts the Gaussian shape according to visibility. The experimental results showed that the performance of the proposed method was applicable to apple harvesting robots, with MAP@K of 0.9809 and 0.9801 when K=5 and K=10, respectively.

• The Journal of the Acoustical Society of Korea
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• v.26 no.4
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• pp.166-172
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• 2007

In this paper, we address the target positioning performance of Multi-Static sonar with respect to target positioning method and measurement error. Based on the analysis on two candidate solution approaches, namely, Least Square (LS) using range and angular information simultaneously and Maximum Likelihood (ML) using only range information as the existing information fusion methods for possible application to Multi-Static sonar, we propose to employ ML using range and angular information. Assuming that each sensor can receive range and angular information, we conduct representative comparison experiments over the existing and proposed methods under various measurement noise scenarios. We also investigate the target positioning performance according to number of sensors, distance between transmitter and receiver. According to the experimental results, RMSE of the proposed ML with distance and direction information is found to be more superior to ML using distance alone and to LS in case distance between transmitter and receiver is longer and number of receiver is smaller.

• Asia-Pacific Journal of Business Venturing and Entrepreneurship
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• v.13 no.2
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• pp.1-13
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• 2018

This study examines the relationship between the organizational general characteristics (industry, size, location, development stage, and company age) and success factors of Korean venture firms using secondary data. Among the industries with the highest sales figures in 2016 are food / fiber / (non) metals, and the smallest category was software development. The sectors with the highest net profit were computer / semiconductor / electronic components, and the smallest category was telecommunication equipment / broadcasting equipment. The industries with the largest sales growth rate are IT / broadcasting services and software development. The industries with the highest net profit margin of sales are energy / medical / precision, and the smallest is telecommunication equipment / broadcasting equipment. In terms of the number of employees, venture firms with more than 100 employees have the largest sales and net profit, with employees between 1 and 9 have the smallest. However, these results are predictable. In general, the number of employees is highly correlated with sales and net profit. Rather, the sales growth rate and the net profit margin of sales may be meaningful. In particular, with employees between 50 ~ 99, the growth rate of sales and the net profit margin of sales were high. In terms of location, Seoul / Incheon / Gyeonggi were the regions with the highest sales and Daejeon / Sejong / Chungcheong / Gangwon were the least regions. Gwangju / Jeolla / Jeju and Seoul / Incheon / Gyeonggi were almost similar in the areas with the largest net profit. However, Daejeon / Sejong / Chungcheong / Gangwon had the lowest net profit. Unusually, the areas with the highest sales growth rate and the highest net profit margin of sales were Gwangju / Jeolla / Jeju, and the smallest areas were Busan / Jeonnam / Ulsan In the relationship between the stage of development and the performance of the company, the sales of maturity and decline stages were the highest and establishing stage was the lowest. Net profit was also the highest in mature stage and the smallest in establishing stage. The sales growth rate shows a typical pattern in the order of establishing stage, early growth stage, high growth stage, maturity stage, and decline stage. In terms of business performance, sales and net profit are the highest with 21 years or more of company age, and the smallest is less than 3 years. In addition, the sales growth rate was the highest in three years or less, and the net profit margin of sales was the highest in 4 to 10 years. This study can present lots of useful implications by suggesting integrated research model and examining the success factors of Korean venture firms and presenting the application methods of secondary data in analyzing the current status of venture industry in Korea.