• 한국안광학회지
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• 제5권2호
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• pp.151-155
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• 2000

칼라 렌즈 제작시 착색 시간에 따른 분광반사율을 측정하여 렌즈표면의 굴절률을 계산하였다. 착색 시간이 길수록 반사율과 굴절률은 커진다. 렌즈 표면에 착색물질이 포화상태가 될 때까지 굴절률은 시간에 따라 증가하였다. 시간에 따른 blue color 렌즈의 굴절률 변화 곡선은 Boltzmann 성장곡선을 따르며, 이때 $n_{min}$은 1.482. $n_{max}$는 1.497. $t_c=11.53$ 그리고 $d_0$ 등의 2.287 등의 parameter 값을 얻었다.

• 대한산업공학회지
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• 제42권5호
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• pp.337-351
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• 2016

As technologies' life-cycle shortens and their development directions are uncertain, firms' technology planning capability becomes increasingly important. Prior patent-based studies using technology growth curves identify developmental stages of technologies, thereby formulating technology development directions from an overall perspective. However, a technology generally consists of multiple sub-technologies and accordingly their development stages are likely various. In this regard, the prior studies failed to identify core sub-technologies and their specific development directions. Therefore, we suggest an approach consisting of 1) identifying core sub-technologies of a given technology using patent co-classifications and social network analysis, and 2) identifying each sub-technology's development stage and thereby determining its further development direction. We apply our approach to patents related to augmented reality to examine its applicability. It is expected that our approach will help identify evolving development stages for the core sub-technologies of a given technology, thereby effectively assisting technology experts in technology planning processes.

• 한국통신학회논문지
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• 제24권12A호
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• pp.2025-2033
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• 1999

본 연구에서는 IMT-2000 서비스의 상용화 실시 시기를 전문가 의견을 바탕으로 하여 예측한 결과 2001년 2월경에 첫 서비스를 실시할 것으로 나타나 전문가들은 대체로 빠른 진척을 예상하고 있음을 알 수 있었다. 또한 본 연구의 가장 중요한 부분인 IMT-2000 서비스 가입 수요예측에서는 가격 경쟁력에 대한 두 가지 경우에 따라 다른 모형을 제시하였다. 본 연구에서는 신제품에 대한 수요예측에 정성적 방법인 전문가 의견법과 정량적 방법인 성장곡선 모형을 결합하여 과거자료가 없는 신제품의 수요예측의 오차를 줄이고자 하였다. 각 성장곡선 모형에 필요한 계수를 전문가들의 주관적인 의견을 근거로 하여 추정하였다.

• 대한조선학회논문집
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• 제45권6호
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• pp.669-678
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• 2008

The fatigue life of ship structure under cyclic loading condition is made up of initiation and propagation stages. In this study, crack growth test is carried out on large scale structure test specimens and fracture mechanical analysis is performed. The fatigue lives measured from fatigue tests are compared with DNV, Matsuoka and BS 5400 S-N curve. And to predict the crack initiation life, S-N curve, corresponding to crack length 20mm at welded joint, is developed based on hot spot stress range. Also crack propagation life is calculated using crack growth equation. Consequently, computed crack propagation life is compared with experiment results.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 추계학술대회
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• pp.220-225
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• 2004

The mesh-insensitive structural stress procedure by Dong is modified to apply to the welded joints with local thickness variation and inignorable shear/normal stresses along local discontinuity surface. In order to make use of the structural stress based K solution for fatigue correlation of welded joints, a proper crack growth model needs to be developed. There exist some significant discrepancies in inferring the slope or crack growth exponent in the conventional Paris law regime. Two-stage crack growth model was not considered since its applications are focused upon the fatigue behavior in welded joints in which the load ratio effects are considered negligible. In this paper, a two-stage crack growth law considering high mean loading is proposed and proven to be effective in unifying the so-called anomalous short crack growth data.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2004년도 춘계학술대회 논문집
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• pp.174-177
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• 2004

The nickel-based alloy Nimonic 80A possesses strength, and corrosion, creep and oxidation resistance at high temperature. These products are used for aerospace, marine engineering and power generation, etc. The control of forging parameters such as strain, strain rate, temperature and holding time is important because the microstructure change in hot working affects the mechanical properties. It is necessary to understand the microstructure variation evolution. The microstructure change evolution occurs by recovery, recrystallization and grain growth phenomena. The dynamic recrystallization evolution has been studied in the temperature range $950-1250^{\circ}C$ and strain rate range $0.05-5s^{-1}$ using hot compression tests. The metadynamic recrystallization and grain growth evolution has been studied in the temperature range $950-1250^{\circ}C$ and strain rate range 0.05, $5s^{-1}$, holding time range 5, 10, 100, 600 sec using hot compression tests. Modeling equations are developed to represent the flow curve, recrystallized grain size, recrystallized fraction and grain growth phenomena by various tests. Parameters of modeling equation are expressed as a function of the Zener-Hollomon parameter. The modeling equation for grain growth is expressed as a function of initial grain size and holding time.

• Nuclear Engineering and Technology
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• 제51권7호
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• pp.1805-1815
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• 2019

While nickel-based alloys have been widely used for power plants due to corrosion resistance and good mechanical properties, during the last couple of decades, failures of nuclear components increased gradually. One of main degradation mechanisms was primary water stress corrosion cracking at dissimilar metal welds of piping and reactor head penetrations. In this context, precise estimation of welding effects became an important issue for ensuring reliability of them. The present study deals with a series of finite element analyses and crack growth rate evaluation of Alloys 690/152. Firstly, variation of residual stresses and equivalent plastic strains was simulated taking into account welding of a cylindrical block. Subsequently, extraction and pre-cracking of compact tension (CT) specimens were considered from different locations of the block. Finally, crack growth curves of the alloys and heat affected zone were developed based on analyses results combined with experimental data in references. Characteristics of crack growth behaviors were also discussed in relation to mechanical and fracture parameters.

• 한국광학회지
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• 제13권3호
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• pp.215-222
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• 2002

광기록매체용 Ge-Sb-Te다층박막 성장과정을 in-situ 타원계를 사용하여 실시간으로 모니터하여 각 층의 두께를 제어하고 성장된 Ge-Sb-Te 다층박막을 ex-site 분광타원법으로 확인하였다. 보호층인 ZnS-SiO$_2$와 기록층인 Ge$_2$Sb$_2$Te$_{5}$을 단결정실리콘 기층 위에 스퍼터링 방법으로 각각 성장시키면서 구한 타원상수 성장곡선을 분석하여 성장에 따르는 보호층의 균일성 및 기록 층의 밀도변화를 파악하고 이를 기초로 하여 Ge-Sb-Te광기록 다층박막의 두께를 정밀하게 제어하였다. Ge$_2$Sb$_2$Te$_{5}$ 단층박막 시료의 복소굴절율은 eX-Situ 분광타원분석을 통하여 구하였다. 제작된 다층구조는 설정된 다층구조인 ZnS-SiO$_2$(1400$\AA$)$\mid$ GST(200 $\AA$)$\mid$ZnS-SiO$_2$(200$\AA$)와 각 층의 두께 및 전체 두께에서 1.5% 이내에서 일치하는 정확도를 보여주었다.주었다.

• ALGAE
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• 제17권2호
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• pp.83-87
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• 2002

Photosynthetic parameters of Scendesmus quadricauda, such as the maximum photosynthetic rate ($P_{max}$), photosynthetic efficiency (α) and the initial saturation intensity of irradiance for photosynthesis ($I_K$) were obtained using photosynthesis-irradiance (P-I) curve in a phosphorus-limited chemostat. S. quadricauda exhibitied no photoinhibition until at 200 μmol·$m^{-2}$ . $P_{max}$ (r=0.963, P=0.002) and $I_K$(r=0.904, P=0.013) showed linear relationships with growth rate. Chlorophyll-α concentration and cell dry weight decreased at higher growth rates, ut chlorophyll-α content per cell dry weight increased. The increase in photosynthetic rates at higher growth rates was due to the increase of $P_{max}$ and $I_K$ which was caused mainly by the increase in the absolute amount of chlorophyll-α rather than the increased photosynthetic efficiency of individual chlorphyll-α. The α did not show a significant relationship with growth rate (r=0.714, P=0.111). The cell quota of carbon (r=0.554, P=0.254) was not correlated with growth rate, but cell quota of nitrogen (r=0.818, P=0.047) and phosphorus (r=0.855, P=0.030) exhibited linear correlations with growth rate.

• 한국정밀공학회지
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• 제16권8호
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• pp.106-112
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• 1999

It is very important to have exact informations on the properties and characteristics of the sintered steel as a new material of machine elements. The bending fatigue tests are performed for the sintered steel bend specimens of various densities 6.6 to 7.0 g/$cm^3$ and the sintered spur gear to consisted of Fe-Cu-C. The fatigue test at a constant stress amplitude is performed by using an electrohydraulic servo-controlled pulsating tester. Consequently, the S-N curves are obtained. The fatigue strength S for fatigue life N of the specimen with the initial length of crack ai is simulated, and they are shown as N-S-A curves. This study investigate the crack growth characteristics by experiments and present crack growth simulation method for sintered gear