• 한국재료학회:학술대회논문집
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• 한국재료학회 2011년도 춘계학술발표대회
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• pp.22.2-22.2
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• 2011

Reliability and degradation mechanism of conventional phosphor-converted white GaN-based light-emitting diodes (LEDs) were investigated. Under electro-thermal stress condition, the optical output degraded rapidly at the initial stress time accompanied by the change of chromatic properties. This could be attributed to the optical degradation of packaged materials, in particular, the browning of encapsulants and the darkening of reflective packages. At longer stress times, the optical output gradually decreased according to the degree of the reverse leakage currents, namely, the generation ofnonradiative recombination defects. This indicates that the optical degradation of white LEDs are dominated by the darkening of packaged materials and the generation of defects depending on the injection current and ambient temperatures. Using analyses of electroluminescence spectra, optical microscopy, electrical, optical, and thermal properties, optical degradations of white LEDs are discussed.

• 한국인쇄학회지
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• 제29권3호
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• pp.97-104
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• 2011

The storing ability of information of optical disks directly depends on the physical property of recording unit cells. It means that the degradation of optical disks ultimately causes the loss of the physical and chemical properties of recording unit cells and leads also information, too. We investigated the degradation and life time of optical disks which tell us the longevity of the preservation of information. Optical disks were aged using the accelerated aging system and studied by optical reflectivity spectroscopy and atomic force microscopy(AFM), and the preservation environment of electronic media in National central library of Korea also were analysed. Results show that the double reflective coated optical disks have good preservation of recording information but revealed some deformation of dye area in the AFM images. It means that we should include the mechanical and chemical degradation of the optical disks in the life time expectation evaluation.

• 폴리머
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• 제36권3호
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• pp.309-314
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• 2012

생분해성 폴리락타이드의 분해속도를 조절하기 위하여 $d$-lactide와 $l$-lactide의 함량을 달리하여 다양한 stereochemical PLAs를 개환중합으로 합성하고 Langmuir 단분자막 장치를 이용하여 알칼리 분해속도를 측정하였다. 알칼리 수용액상에서 혼합 단분자막의 분해속도를 각 혼합고분자의 광학적 순도(100, 99, 97, 95%)의 항으로 측정하였다. 스테레오 콤플렉스에 기인하는 혼합물의 용융온도는 혼합물 성분의 광학적 순도가 증가함에 따라 증가하였다. 분해거동은 100% 광학적 순도를 가진 혼합물은 각 단일중합체보다 느린 분해속도를 나타내는 반면 다른 혼합물들은 2단계의 분해거동을 나타내었는데 1단계에서는 콤플렉스를 형성하지 않은 부분에서의 분해로 단일중합체에 비해 빠른 분해속도를 나타내었고 2단계에서는 100% 광학적 순도를 가진 혼합물과 유사하게 느린 분해속도를 나타내었다. 이러한 결과는 폴리락타이드의 stereochemistry와 스테레오 콤플렉스를 이용하여 알칼리 분해속도를 조절할 수 있음을 의미한다.

• ETRI Journal
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• 제30권6호
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• pp.833-843
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• 2008

The effect of forward and reverse electrostatic discharge (ESD) on the electro-optical characteristics of oxide vertical-cavity surface-emitting lasers is investigated using a human body model for the purpose of understanding degradation behavior. Forward ESD-induced degradation is complicated, showing three degradation phases depending on ESD voltage, while reverse ESD-induced degradation is relatively simple, exhibiting two phases of degradation divided by a sudden distinctive change in electro-optical characteristics. We demonstrate that the increase in the threshold current is mainly due to the increase in leakage current, nonradiative recombination current, and optical loss. The decrease in the slope efficiency is mainly due to the increase in optical loss.

• 한국태양에너지학회 논문집
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• 제22권3호
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• pp.57-65
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• 2002

The photocatalytic degradation of TCE using solar energy in POFR was studied. The use of solar energy was investigated in plastic optica fiber photocatalytic reactor (POFR). In POFR, the main parameters of photocatalytic degradation of TCE were lihgt intensity, thickness of $TiO_2$-coated film on plastic fiber core, the same of total $TiO_2$-coated surface area with changed length. We studied the apparent photonic efficiency and photocatalytic degradation rate of TCE in POFR. The apparent photonic efficiency of various light intensities was decreased by an incresed intensities. The photocatalytic activities of $TiO_2$-coated optical fiber reactor system depended on the coating thickness, and total clad-stripped surface area of POF. Photocatalytic degradation of trichloroethylene ($C_2HCl_3$, TCE) in the gas-phase was elucidated by using $TiO_2$-coated plastic optical fiber reactor. In TCE degradation, in-situ FTIR measurement resulted in mineralization into $CO_2$.

• 한국환경과학회지
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• 제18권7호
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• pp.797-802
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• 2009

To control degradation rate of biodegradable poly(lactide)s (PLA), the stereochemical PLAs with different ratios of d-lactide and l-lactide units were synthesized by the ring open polymerization and the their degradation kinetics were measured by a Langmuir film balance. The alkaline (pH=11) degradation of poly(l-lactide) (l-PLA) monolayer showed the faster rate at a surface pressure of 4 mN/m in the ranges from to 0 to 7 mN/m. However, the enzymatic degradation of l-PLA with Proteinase K did not occur until 4 mN/m. Above a constant surface pressure of 4 mN/m, the degradation rate was increased with a constant surface pressure. These behaviors might be attributed to the difference in the contacted area with degradation medium: alkaline ions need small contact area with l-PLA while enzymes require much bigger one to be activated due to different medium sizes. The stereochmical PLA monolayers showed that the alkaline degradation was increased with their optical impurities while the enzymatic one was inversed. These results could be explained by the decrease of crystallinity with the optical impurity and the inactivity of enzyme to d-LA unit.

• IEIE Transactions on Smart Processing and Computing
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• 제6권3호
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• pp.141-150
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• 2017

Images obtained from underwater are usually degraded due to the environmental conditions. Some of the typical degradation factors include turbidity and color degradation. These degradations can be attributed to the absorptive and scattering properties of underwater degradation in terms of optical parameters, such as modulation transfer function (MTF), optical transfer function (OTF),point spread function (PSF), and color constancy. In this paper, we use the CODE V optical simulation software to mimic underwater conditions and model the imaging platform, thereby studying various parameters, such as PSF and MTF, and we use the PSF to remove the underwater turbidity. Experimental results show increased performance with the algorithm, compared to other existing methods.

• 한국태양에너지학회 논문집
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• 제29권2호
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• pp.55-61
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• 2009

This paper reviews the state-of-the art in surface analysis techniques for solar coatings. For analyzing solar coatings and interfaces, surface properties were very important factor for obtaining the information related to the optical degradation processes and microstructure. Various types of analytical techniques for chemical composition, microstructure and surface topography analysis of solar coatings were discussed. In addition, the examples of solar selective coating analysis results for applications were demonstrated. Development and analysis technique of solar coating for energy conservation was felt to be necessary at this time.

• 펄프종이기술
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• 제47권6호
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• pp.66-72
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• 2015

This study was conducted to investigate the effects of optical brightening agents (OBA) on the chemical degradation characteristics of paper cellulose during humid heating aging. Three different types of OBAs were applied to a filter paper by dipping it in OBA solutions whose concentrations were controlled to 1% and 2%. The filter papers with an OBA were artificially aged at $80^{\circ}C$ and 65% RH, and the changes in pH of paper and viscosity of cellulose were evaluated. Their functional groups were also analyzed by ATR-FTIR (at-tenuated total reflectance fourier transform infrared spectroscopy). It was found that OBAs influenced the chemical degradation of paper cellulose during humid heating aging. Higher concentration of OBA solutions accelerated the degradation of paper cellulose. Especially, after aging for 12 days, the paper cellulose treated with the tetra-type OBA were the most significantly aged among the three types of OBAs. It was assumed that pH of OBA solutions affected the aging characteristics.

• 대한전자공학회논문지SD
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• 제45권3호
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• pp.6-21
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• 2008

Electrostatic Discharge (ESD) 펄스의 누적이 산화형 표면 발광 반도체 레이저 (oxide VCSEL)의 전기 및 광학적 특성의 열화에 미치는 영향에 대하여 살펴보았다. 순방향 ESD의 누적에 따른 열화 과정은 3 단계의 열화과정을 보이는 반면 역방향 ESD의 인가에 따른 열화 과정은 급격한 전기 및 광학적 특성 변화에 의하여 구분되는 2 단계의 열화과정을 보였다. 등가회로 모델 및 대신호 등가회로 모델을 이용하여 I-V 특성 및 그 미분특성을 분석함으로써 두 가지 ESD 조건에 의한 산화형 VCSEL의 전기 및 광학적 특성의 열화과정을 이해할 수 있었다.