• Title/Summary/Keyword: Light-induced degradation

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A study on the degradation of the AC stressed MOV by using of the DLTS technique (DLTS기법에 의한 MOV소자의 교류과전경시 변화특성에 관한 연구)

  • 이동희
    • Electrical & Electronic Materials
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    • v.9 no.7
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    • pp.719-726
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    • 1996
  • DLTS measurements were performed to study the annealing induced changes of the trap centers in MOV and to shed more light on the stability mechanism of the MOV. Two electron traps, Ec-0.26[eV] and Ec-(O.2-0.3)[eV], were observed in the unannealed samples in large quantities(7-9 X 1014[CM 3]), whereas the three electron traps Ec-0.17 [eV], Ec-0.26[eV] and Ec-(O.2-0.3)[eV] were observed far less in the annealed samples. The minima in the Ec-0.26[eV] trap density, coupled with the presented results that unannealed devices are unstable whereas 600.deg. C annealed devices are most stable, suggests that the instability of the MOV under long term electrical stressing is related to the Ec-0.26[eV] trap. This results support that the ion migration model for the device instability where the Ec-0.26[eV] defects may be the interstitial zinc or the migrating ions. The interstitial zinc originated as a result of the nonstoichiometric nature of ZnO might cause the degradation of the I-V characteristics of the MOV with long term electrical stressing.

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Changes in Color Response of MTT formazan by Zinc Protoporphyrin (MTT formazan의 발색에 미치는 zinc protoporphyrin의 영향)

  • Park, Kyung-A;Choi, Hyun-A;Kim, Mi-Ri;Choi, Yoo-Mi;Kim, Hyun-Jung;Hong, Jung-Il
    • Korean Journal of Food Science and Technology
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    • v.43 no.6
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    • pp.754-759
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    • 2011
  • Zinc protoporphyrin (ZnPP) is produced endogenously during heme metabolism and treated in cells as a heme oxygenase inhibitor. In the present study, the effects of ZnPP on the color response of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, a commonly-used method for analyzing cell viability, were investigated. ZnPP induced rapid decolorizaion of MTT formazan under light; the degradation rates were 10- and 20- folds faster in the presence of 5 and $10{\mu}M$ ZnPP, respectively. Methylene blue (MB), another type of photosensitizer, also accelerated degradation of formazan under light. Butylated hyroxytoluene did not inhibit ZnPP- or MB-induced formazan degradation. The color degradation of formazan dye was signficantly delayed in the presence of N-acetylcysteine or ${\beta}$-carotene. The present results suggest that certain photosensitizing compounds may affect the color and stability of MTT formazan, which should be carefully considered when conducting the MTT assay.

Mechanism of Orientation of Liquid Crystal Molecules for Polarized UV-exposed Polyimide Alignment Layers (폴리애미드 배향막의 편광 자외선 조사에 따른 액정 배향 메카니즘)

  • 김일형;김욱수;하기룡
    • Polymer(Korea)
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    • v.26 no.2
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    • pp.209-217
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    • 2002
  • We studied the mechanism of orientation of polyimide molecules which were irradiated by polarized UU (PUV) using polarized Fourier transform infrared (FT-IR) spectroscopy and ultraviolet (UV) spectroscopy, According to the measured UV spectra, we found PI films mainly absorb UV light less than 350 nm wavelength, therefore, UV light less than 360 nm induces photochemical reaction of PI. PUV irradiation of PI films caused decrease of all peak intensities in the FT-IR spectra. except the newly formed broad peak at $3244 cm^{-1}$, due to degradation of the PI molecules. The remaining PI molecules after photo-degradation showed predominantly perpendicular molecular orientation to the irradiated PUV polarization direction, due to the preferential degradation of PI molecules parallel to irradiated PUV polarization direction. However the rubbing of PI films induced reorientation of the PI molecules parallel to the rubbing direction. We also investigated the alignment of the liquid crystal by rubbing or PUV irradiation. Liquid crystals align perpendicular to the PUV polarization direction and parallel to the rubbing direction.

Synthesis and Characteristics of Pd/r-TiO2 Nanotube Arrays Hetrojunction Photocatalyst (Pd/r-TiO2 나노튜브 이종결합 광촉매의 합성과 특성)

  • Lee, Jong-Ho;Lee, Young-Ki;Kim, Young-Jig;Jang, Kyung-Wook;Oh, Han-Jun
    • Korean Journal of Materials Research
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    • v.32 no.1
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    • pp.14-22
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    • 2022
  • To improve light absorption ability in the visible light region and the efficiency of the charge transfer reaction, Pd nanoparticles decorated with reduced TiO2 nanotube photocatalyst were synthesized. The reduced TiO2 nanotube photocatalyst was fabricated by anodic oxidation of Ti plate, followed by an electrochemical reduction process using applied cathodic potential. For TiO2 photocatalyst electrochemically reduced using an applied voltage of -1.3 V for 10 min, 38% of Ti4+ ions on TiO2 surface were converted to Ti3+ ion. The formation of Ti3+ species leads to the decrease in the band gap energy, resulting in an increase in the light absorption ability in the visible range. To obtain better photocatalytic efficiency, Pd nanoparticles were decorated through photoreduction process on the surface of reduced TiO2 nanotube photocatalyst (r10-TNT). The Pd nanoparticles decorated with reduced TiO2 nanotube photocatalyst exhibited enhanced photocurrent response, and high efficiency and rate constant for aniline blue degradation; these were ascribed to the synergistic effect of the new electronic state of the TiO2 band gap energy induced by formation of Ti3+ species on TiO2, and by improvement of the charge transfer reaction.

Current Status in Light Trapping Technique for Thin Film Silicon Solar Cells (박막태양전지의 광포획 기술 현황)

  • Park, Hyeongsik;Shin, Myunghoon;Ahn, Shihyun;Kim, Sunbo;Bong, Sungjae;Tuan, Anh Le;Hussain, S.Q.;Yi, Junsin
    • Current Photovoltaic Research
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    • v.2 no.3
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    • pp.95-102
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    • 2014
  • Light trapping techniques can change the propagation direction of incident light and keep the light longer in the absorption layers of solar cells to enhance the power conversion efficiency. In thin film silicon (Si) solar cells, the thickness of absorption layer is generally not enough to absorb entire available photons because of short carrier life time, and light induced degradation effect, which can be compensated by the light trapping techniques. These techniques have been adopted as textured transparent conduction oxide (TCO) layers randomly or periodically textured, intermediate reflection layers of tandem and triple junction, and glass substrates etched by various patterning methods. We reviewed the light trapping techniques for thin film Si solar cells and mainly focused on the commercially available techniques applicable to textured TCO on patterned glass substrates. We described the characterization methods representing the light trapping effects, texturing of TCO and showed the results of multi-scale textured TCO on etched glass substrates. These methods can be used tandem and triple thin film Si solar cells to enhance photo-current and power conversion efficiency of long term stability.

Accelerated Degradation Stress of High Power Phosphor Converted LED Package (형광체 변환 고출력 백색 LED 패키지의 가속 열화 스트레스)

  • Chan, Sung-Il;Jang, Joong-Soon
    • Journal of the Microelectronics and Packaging Society
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    • v.17 no.4
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    • pp.19-26
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    • 2010
  • We found that saturated water vapor pressure is the most dominant stress factor for the degradation phenomenon in the package for high-power phosphor-converted white light emitting diode (high power LED). Also, we proved that saturated water vapor pressure is effective acceleration stress of LED package degradation from an acceleration life test. Test conditions were $121^{\circ}C$, 100% R.H., and max. 168 h storage with and without 350 mA. The accelerating tests in both conditions cause optical power loss, reduction of spectrum intensity, device leakage current, and thermal resistance in the package. Also, dark brown color and pore induced by hygro-mechanical stress partially contribute to the degradation of LED package. From these results, we have known that the saturated water vapor pressure stress is adequate as the acceleration stress for shortening life test time of LED packages.

Degradation Characteristics of Wood Cellulose by Ruminal Cellulolytic Anaerobic Bacterium Ruminococcus albus F-40 (혐기성 세균 Ruminococcus albus F-40에 의한 목재 cellulose의 분해특성)

  • Kim, Yoon-Soo;Wi, Seung-Gon;Myung, Kyu-Ho
    • Journal of the Korean Wood Science and Technology
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    • v.25 no.3
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    • pp.83-95
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    • 1997
  • The degradation mode of lignocellulose by anaerobic ruminal cellulolytic bacterium Ruminococcus albus F-40 was investigated. Birchwood holocellulose and filter paper were incubated as the sole carbohydrate sources with using the Hungate techniques. After 2 or 4 days of incubation, samples were employed for chemical and electron microscopic evaluations. The degradation rate of cellulosic substrates and the adhesion rate of bacteria to the substrates increased proportionally with the decrease of relative crystallinity of cellulose, indicating the preferential breakdown of amorphous cellulose, by this bacterium. X-ray diffraction analyses and polarized light microscopy showed, however, that crystalline cellulose was also degraded by R. albus. FT-IR spectra indicated that not only cellulose but hemicellulose was also degraded by this bacterium. Electron microscopic investigations showed the protuberant structures on the surface of R. albus. These structures were much more significant when bacterial cells were grown in the media containing insoluble substrates, such as cellulose, indicating clearly that bacterial protuberant structures were induced by the substrates. Protuberant structures extended from the bacterial cells adhered tightly to the substrates and numerous vesicles covered the surface of cellulosic substrates affected. Cellulosome-like structures were distributed on the cellulose matrix. Electron microscopic works showed that diverse surface organells of R. albus were involved in the degradation of cellulosic materials. SEM examinations showed the breakdown of cellulose by R. albus was proceeded by severeal routes : short fiber formation, defibrillation and destrafication of cellulose microfibril.

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Characterization of Viable But Nonculturable Condition of Escherichia coli Induced with Copper (구리에 의해 유도된 VBNC 대장균의 특성)

  • Ku, Hyung-Keun;Park, Sang-Ryoul;Kim, Sook-Kyung
    • Microbiology and Biotechnology Letters
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    • v.36 no.3
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    • pp.209-214
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    • 2008
  • VBNC (Viable but nonculturable) state is an adaptive response of cells in adverse environments, which lead cell not grow on routine nutrient agar. In this study, we induced VBNC in Escherichia coli using copper and verify the characterization of it. After treatment of copper, we didn't detect any cells via plate cultivation, namely, colony forming unit (CFU) was zero. However, we identified the existence of VBNC by staining live cells with Live/Dead BacLight bacterial viability kit and counting them through flow cytometry. Then we isolated genomic DNA and RNA from VBNC-induced cells and analyzed the stability of them. Degradation of RNA is more severe than that of DNA and RNA is degraded as specific fragments. In addition, we showed the morphology of VBNC cell by Bio-Transmission Electron Microscope (Bio-TEM). VBNC cell showed impaired periplasmic space and inner and outer membrane were separated and the amount of cytosol were significantly decreased.

Downregulation of Cyclin D1 by Sophorae Flos through Proteasomal Degradation in Human Colorectal Cancer Cells

  • Lee, Jin Wook;Park, Gwang Hun;Eo, Hyun Ji;Jeong, Jin Boo
    • Korean Journal of Plant Resources
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    • v.28 no.6
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    • pp.727-733
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    • 2015
  • Although Sophorae Flos (SF) has been reported to exert an anti-cancer activity, molecular targets and mechanisms associated with anti-cancer activity of SF have been unclear. Because cyclin D1 has been regarded as an important regulator in the cell proliferation, we focused cyclin D1 and investigated the effect of SF on the cyclin D1 regulation in light of elucidating the molecular mechanism for SF’s anti-cancer activity. The treatment of SF decreased cellular accumulation of cyclin D1 protein. However, SF did not change the level of cyclin D1 mRNA. Inhibition of proteasomal degradation by MG132 attenuated SF-mediated cyclin D1 downregulation and the half-life of cyclin D1 was decreased in the cells treated with SF. In addition, a point mutation of threonine-286 to alanine attenuated SF-mediated cyclin D1 downregulation. Inhibition of ERK1/2 by a selective inhibitor, PD98059 suppressed cyclin D1 downregulation by SF. From these results, we suggest that SF-mediated cyclin D1 downregulation may result from proteasomal degradation through its threonine-286 phosphorylation via ERK1/2. SF-induced proteasomal degradation of cyclin D1 might inhibit proliferation in human colorectal cancer cells. The current study provides information on molecular events for an anti-cancer activity of SF

Enhanced photocatalytic performance of magnesium-lithium co-doped BiVO4 and its degradation of methylene blue

  • Nayoung Kim;Hyeonjin Kim;Jiyu Lee ;Seog-Young Yoon
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.33 no.4
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    • pp.132-138
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    • 2023
  • Doped and undoped-BiVO4 samples with different elements (Li, Mg) and amounts were synthesized with a hydrothermal method. The synthesized samples were characterized using various techniques including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV-Vis diffusion reflectance spectroscopy (UV-Vis DRS), and photoluminescence (PL) spectroscopy. Photocatalytic activity of the samples was evaluated by measuring the degradation of methyl blue (MB) under visible light irradiation. The results indicated that the incorporation of Mg and Li into BiVO4 caused lattice distortion, the presence of surface hydroxyl groups, a narrower band gap, and a reduced recombination ratio of photo-induced electron-hole pairs. Notably, the photocatalytic activity of Mg5%-Li5% co-doped BiVO4 sample exhibited a significant improvement compared to that of undoped BiVO4 sample.