• KSBB Journal
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• 제5권4호
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• pp.391-396
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• 1990

4.0$\times$10-3 (IU/cells/day) of maximum specific scu-PA production, which was higher than those by a 75$\textrm{cm}^2$ T-flask and conventional perfusion systems, was maintained by tube-type bioreactor at 0.35 (1/h) of perfusion rate corresponding to 0.15 (dynes/$\textrm{cm}^2$) of shear stress. The production of scu-PA is also increased as shear stress was slowly increased, which is similar to natural human blood circulation. The tube reactor proves that there may be no limitation of oxygen supply by showing 1.0 (1/h) of oxygen transfer coefficient at steady state and this system yields much lower shear stress of 0.3(dynes/$\textrm{cm}^2$) than that of 5-8(dynes/$\textrm{cm}^2$) by conventional agitation systems.

• Fibers and Polymers
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• 제6권2호
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• pp.113-120
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• 2005

Helium-oxygen plasma treatments were conducted to modify poly(trimethylene terephthalate) (PIT) and poly(ethylene terephthalate) (PET) warp knitted fabrics under atmospheric pressure. Lubricant and contamination removals by plasma etching effect were examined by weight loss $(\%)$ measurements and scanning electron microscopy (SEM) analysis. Surface oxidation by plasma treatments was revealed by x-ray photoelectron spectroscopy (XPS) analyses, resulting in formation of hydrophilic groups and moisture regain $(\%)$ enhancement. Low-stress mechanical properties (evaluated by Kawabata evaluation system) and bulk properties (air permeability and bust strength) were enhanced by plasma treatment. Increasing interfiber and interyarn frictions might play important roles in enhancing surface property changes by plasma etching effect, and then changing low-stress mechanical properties and bulk properties for both fabrics.

• 대한한방내과학회지
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• 제27권4호
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• pp.811-821
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• 2006

Objectives : Diabetes is a disease in which the body does not produce or properly use insulin. Etiological studies of diabetes and its complications showed that oxidative stress might play a major role. Therefore, many methods have been tried to regulate oxygen free radicals for treating diabetes and its complications. Because Mori foliumhas been known to be effective for the treatment of diabetes, the methanol extract of Mori folium was tested for its effectiveness in reducing the oxidative stress induced by streptozotocin. Methods : The crushed Mori folium was extracted 3 times, each time with 3 volumes of methyl alcohol at $60^{\circ}C$ or 24 h. The extract was filtered and evaporated under reduced pressure using a rotary evaporator to yield 11.7 g. Mori folium extract was oral-administered to diabetic rats induced by streptozotocin at 100 mg per 1 kg of body weight for 20 days. The efficacy of the Mori foliumextract was examined with regard to the enzymatic pathways involved in oxygen free radical production and glutathione balance. Results : The effects of the Mori foliumin streptozotocin-induced diabetic rats with regards to body weight, blood glucose and insulin level, hepatic lipid peroxide level, hepatic glutathione level, hepatic glutathione S-transferase and glutathione peroxidase level, hepatic aldose reductase activity, and hepatic sorbitol dehydrogenase activity were shown to be good enough to cure and prevent diabetes and its complications. Conclusions : These results indicated that Mori folium might reduce oxidative stress in tissues and organs by regulating the production of oxygen free radicals. Especially Mori folium might prevent and cure diabetes and its complications by reducing oxidative stress in the ${\beta}-cells$ of the pancreas.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.497-497
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• 2013

Semiconducting amorphous InGaZnO (a-IGZO) has attracted significant research attention as improved deposition techniques have made it possible to make high-quality a-IGZO thin films. IGZO thin films have several advantages over thin film transistors (TFTs) based on other semiconducting channel layers.The electron mobility in IGZO devices is relatively high, exceeding amorphous Si (a-Si) by a factor of 10 and most organic devices by a factor of $10^2$. Moreover, in contrast to other amorphous semiconductors, highly conducting degenerate states can be obtained with IGZO through doping, yet such a state cannot be produced with a-Si. IGZO thin films are capable of mobilities greaterthan 10 $cm^2$/Vs (higher than a-Si:H), and are transparent at visible wavelengths. For oxide semiconductors, carrier concentrations can be controlled through oxygen vacancy concentration. Hence, adjusting the oxygen partial pressure during deposition and post-deposition processing provides an effective method of controlling oxygen concentration. In this study, we deposited IGZO thinfilms at optimized conditions and then analyzed the film's electrical properties, surface morphology, and crystal structure. Then, we explored how to generate IGZO thin films using DC magnetron sputtering. We also describe the construction and characteristics of a bottom-gate-type TFT, including the output and transfer curves and bias stress instability mechanism.

• Biomolecules & Therapeutics
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• 제21권3호
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• pp.210-215
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• 2013

Ionizing radiation can induce cellular oxidative stress through the generation of reactive oxygen species, resulting in cell damage and cell death. The aim of this study was to determine whether the antioxidant effects of the flavonoid fisetin (3,7,3',4'-tetrahydroxyflavone) included the radioprotection of cells exposed to ${\gamma}$-irradiation. Fisetin reduced the levels of intracellular reactive oxygen species generated by ${\gamma}$-irradiation and thereby protected cells against ${\gamma}$-irradiation-induced membrane lipid peroxidation, DNA damage, and protein carbonylation. In addition, fisetin maintained the viability of irradiated cells by partially inhibiting ${\gamma}$-irradiation-induced apoptosis and restoring mitochondrial membrane potential. These effects suggest that the cellular protective effects of fisetin against ${\gamma}$-irradiation are mainly due to its inhibition of reactive oxygen species generation.

• 한국진공학회지
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• 제8권2호
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• pp.165-171
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• 1999

Diamond-like carbon(DLC) films were synthesized using the rf-plasma CVD technique with the addition of small amounts of nitrogen and oxygen to a gas mixture of $CH_4$ and $H_2$. The gas flow ratio of $CH_4$ to $H_2$ was 2.4:1, and 3% , 13.6% of nitrogen were added to the gas mixture of $CH_4$ and $H_2$ for the deposition of DLC films. The film stress tended to decrease as the nitrogen concentration increased from 3% to 13.6%, probably due to the decrease of the number of the interlink between carbon atoms. The residual stress tended to slightly decrease when 3% of oxygen was added. Scratch tests were performed to investigate the adhesion between the DLC films and the Ti intelayer after pretreating the TiN surface with direct hydrogen plasma. The adhesion was enhanced by adding nitrogen and oxygen to the $CH_4$ and $H_2$ gas mixture. The adhesion for the 3% nitrogen addition was better than that for the 13.6% nitrogen addition. The Vicker's hardness of the DLC films was measured to be 1100Hv.

• Asian Pacific Journal of Cancer Prevention
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• 제15권12호
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• pp.4745-4751
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• 2014

Oxidative stress is caused by an imbalance in the redox status of the body. In such a state, increase of free radicals in the body can lead to tissue damage. One of the most important species of free radicals is reactive oxygen species (ROS) produced by various metabolic pathways, including aerobic metabolism in the mitochondrial respiratory chain. It plays a critical role in the initiation and progression of various types of cancers. ROS affects different signaling pathways, including growth factors and mitogenic pathways, and controls many cellular processes, including cell proliferation, and thus stimulates the uncontrolled growth of cells which encourages the development of tumors and begins the process of carcinogenesis. Increased oxidative stress caused by reactive species can reduce the body's antioxidant defense against angiogenesis and metastasis in cancer cells. These processes are main factors in the development of cancer. Bimolecular reactions cause free radicals in which create such compounds as malondialdehyde (MDA) and hydroxyguanosine. These substances can be used as indicators of cancer. In this review, free radicals as oxidizing agents, antioxidants as the immune system, and the role of oxidative stress in cancer, particularly breast cancer, have been investigated in the hope that better identification of the factors involved in the occurrence and spread of cancer will improve the identification of treatment goals.

• 한국식품조리과학회지
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• 제28권6호
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• pp.821-828
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• 2012

In an attempt to identify the neuroprotective effect of Cudrania tricuspidata (CT) leaves against ROS (reactive oxygen species)-induced oxidative stress in neuronal cells, the extracts from CT leaves were investigated using PC12 cells and N18-RE-105 cells. The methanolic and ethanolic extracts from CT were denoted as CTM (Cudrania tricuspidata Leaves methanolic extracts) and CTE (Cudrania tricuspidata Leaves ethanolic extracts), respectively. The neuroprotective effects of the extracts were measured by DCF-DA assay, MTT reduction assay, and LDH release assay. The PC12 cells exposed to $H_2O_2$-induced oxidative stress and the N18-RE-105 cells exposed to glutamate-induced oxidative stress were treated with various concentrations of CTM and CTE. The results, CTM treatments resulted in the induction of a dose-dependent protective effect in PC12 cells and N18-RE-105 cells. Interestingly, CTE also showed neuroprotective effect in PC12 cells and N18-RE-105 cells. Therefore, these results suggest that CTM and CTE could be a new potential candidate as neuroprotective agents against ROS-induced oxidative stress in neuronal cells.

• 한국진공학회지
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• 제21권5호
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• pp.273-278
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• 2012

현재 Hf (Hafnium)을 기반으로한 게이트 유전체의 연구는 여러 분야에서 다양하게 진행되어져 왔다. 이는 기존의 $SiO_2$보다 유전상수 값이 크고, 또한 계속되는 scaling-down 공정에서도 양자역학적인 터널링을 차단하는 특성이 뛰어나기 때문이다. MOSFET 구조에서 유전체 박막의 두께 감소로 인한 전기적 특성 저하를 보완하기 위해서 high-K 재료가 대두되었고 현재 주를 이루고 있다. 그러나 현재까지 $HfO_2$에 대한 nano-mechanical 특성 연구는 부족한 상태이므로 본 연구에서는 게이트 절연층으로 최적화하기 위하여 $HfO_2$ 박막의 nano-mechanical properties를 자세히 조사하였다. 시료는 rf magnetron sputter를 이용하여 Si (silicon) 기판 위에 Hafnium target으로 산소유량(4, 8 sccm)을 달리하여 증착하였고, 이후 furnace에서 400에서 $800^{\circ}C$까지 질소분위기에서 20분간 열처리를 실시하였다. 실험결과 산소 유량을 8 sccm으로 증착한 시료가 열처리 온도가 증가할수록 누설전류 특성 성능이 우수 해졌다. Nano-indenter로 측정하고 Weibull distribution으로 정량적 계산을 한 결과, $HfO_2$ 박막의 stress는 as-deposited 시료를 기준으로 $400^{\circ}C$에서는 tensile stress로 변화되었다. 그러나 온도가 증가(600, $800^{\circ}C$)할수록 compressive stress로 변화 되었다. 특히, $400^{\circ}C$ 열처리한 시료에서 hardness 값이 (산소유량 4 sccm : 5.35 GPa, 8 sccm : 5.54 GPa) 가장 감소되었다. 반면에 $800^{\circ}C$ 열처리한 시료에서는(산소유량 4 sccm : 8.09 GPa, 8 sccm : 8.17 GPa) 크게 증가된 것을 확인하였다. 이를 통해 온도에 따른 $HfO_2$ 박막의 stress 변화를 해석하였다.

• BMB Reports
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• 제35권4호
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• pp.353-357
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• 2002

Singlet oxygen ($^1O_2$) is highly reactive form of molecular oxygen that may harm living systems by oxidizing critical cellular macromolecules. The oxyR gene product regulates the expression of the enzymes and proteins that are needed for cellular protection against oxidative stress. In this study, the role of oxyR in cellular defense against a singlet oxygen was investigated using Escherichia coli oxyR mutant strains. Upon exposure to methylene blue and visible light, which generates singlet oxygen, the oxyR overexpression mutant was much more resistant to singlet oxygen-mediated cellular damage when compared to the oxyR deletion mutant in regard to growth kinetics, viability and protein oxidation. Induction and inactivation of major antioxidant enzymes, such as superoxide desmutase and catalase, were observed after their exposure to a singlet oxygen generating system in both oxyR strains. However, the oxyR overexpression mutant maintained significantly higher activities of anticxidant enzymes than did the oxyR deletion mutant. These results suggest that the oxyR regulon plays an important protective role in singlet oxygen-mediated cellular damage, presumably through the protection of antioxidant enzymes.