• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 1998년도 추계학술대회 논문집
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• pp.121-124
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• 1998

It is well known that during the oxygen cutting residual thermal stresses are produced in weldment. Surface compressive residual stress is one of reasons for improvement on fatigue durability. To reduce the residual stress and improve the fatigue strength applied the impact loading in oxygen cutting frame. After applying the impact loading, redistribution of residual stress was measured by cutting method and tested fatigue tests.

• 한국재료학회지
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• 제21권11호
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• pp.617-622
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• 2011

The effect of oxygen on the shape memory characteristics in Ti-18Nb-6Zr-XO (X = 0-1.5 at%) biomedical alloys was investigated by tensile tests. The alloys were fabricated by an arc melting method at Ar atmosphere. The ingots were cold-rolled to 0.45 mm with a reduction up to 95% in thickness. After severe cold-rolling, the plate was solution-treated at 1173 K for 1.8 ks. The fracture stress of the solution-treated specimens increased from 450 Mpa to 880 MPa with an increasing oxygen content up to 1.5%. The fracture stress increased by 287MPa with 1 at% increase of oxygen content. The critical stress for slip increased from 430 MPa to 695 MPa with an increasing oxygen content up to 1.5 at%. The maximum recovery strain of 4.1% was obtained in the Ti-18Nb-6Zr-0.5O (at%) alloy. The martensitic transformation temperature decreased by 140 K with a 1.0 at% increase in O content, which is lower than that of Ti-22Nb-(0-2.0)O (at%) by 20 K. This may have been caused by the effect of the addition of Zr. This study confirmed that addition of oxygen to the Ti-Nb-Zr alloy increases the critical stress for slip due to solid solution hardening without being detrimental to the maximum recovery strain.

• 한국환경과학회지
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• 제20권12호
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• pp.1509-1519
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• 2011

The protective effect of nitric oxide (NO) on the antioxidant system under paraquat(PQ) stress was investigated in leaves of 8-week-old lettuce (Lactuca sativa L.) plants. PQ stress caused a decrease of leaf growth including leaf length, width and weight. Application of NO donor, sodium nitroprusside (SNP), significantly alleviated PQ stress induced growth suppression. SNP permitted the survival of more green leaf tissue preventing chlorophyll content reduction and of higher quantum yield for photosystem II than in non-treated controls under PQ exposure, suggesting that NO has protective effect on chloroplast membrane in lettuce leaves. Flavonoids and anthocyanin were significantly accumulated in the leaves upon PQ exposure. However, the rapid increase of these compounds was alleviated in the SNP treated leaves. PQ treatment resulted in lipid peroxidation and induced accumulation of hydrogen peroxide ($H_2O_2$) in the leaves, while SNP prevented PQ induced increase in malondialdehyde (MDA) and $H_2O_2$. These results demonstrate that SNP serves as an antioxidant agent able to scavenge $H_2O_2$ to protect plant cells from oxidative damage. The activities of two antioxidant enzymes that scavenge reactive oxygen species, superoxide dismutase (SOD) and catalase (CAT) in lettuce leaves in the presence of NO donor under PQ stress were higher than those under PQ stress alone. Application of 2-(4-carboxyphenyl)-4, 4, 5, 5-tetramethylimidazoline-1-oxyl-3-oxide (PTIO), a specific NO scavenger, to the lettuce leaves arrested SNP mediated protective effect on leaf growth, photosynthetic pigment and antioxidant systems. However, PTIO had little effect on lettuce leaves under PQ stress compared with that of PQ stress alone. The obtained data suggest that the damage caused by PQ stress is in part due to increased generation of active oxygen by maintaining increased antioxidant enzyme activities and SNP protects plants from oxidative stress. From these results it is suggested that NO might act as a signal in activating active oxygen scavenging system that protects plants from oxidative damage induced by PQ stress and thus confer PQ tolerance.

• 한국작물학회:학술대회논문집
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• 한국작물학회 2017년도 9th Asian Crop Science Association conference
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• pp.304-304
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• 2017

In semi-arid countries such as Namibia, the flooding unexpectedly happens in a rainy season, causing losses in the yield of upland-adapted cereal crop. In flooding conditions, rice roots sequentially form aerenchyma and a barrier to radial oxygen loss (ROL), and oxygen is released into the rhizosphere near the root tips. Iijima et al. (2016) and Awala et al. (2016) reported that close mixed-planting with rice can mitigate the flood stress of co-growing upland-adapted cereal crop by modifying their rhizosphere microenvironments via the oxygen released from the rice roots. Moreover, by using the model system of hydroponic culture, it was confirmed that oxygen from rice roots was transferred to co-growing upland-adapted cereal crop in close mixed planting system (Kawato et al., 2016). However, it is not sure whether the ability of oxygen release varies among rice cultivars, because Kawato et al. (2016) used only one japonica cultivar, Nipponbare (Oryza sativa). The objective of this study was to compare the ability of oxygen release in rhizosphere among rice cultivars. The experiment was conducted in a climate chamber in Kindai University. We used 10 rice cultivars from three different rice species (O. sativa (var. japonica (2), var. indica (3)), Oryza glaberrima Steud. (2) and their interspecific progenies (3)) to compare the ability of oxygen release from the roots. According to the method by Kawato et al. (2016), the dissolved oxygen concentration of phase I (with shoot) and phase II (without shoot) were measured by a fiber optic oxygen-sensing probe. The oxygen released from rice roots was calculated from the difference of the measurements between phase I and phase II. The result in this study indicated that all of the rice cultivars released oxygen from their roots, and the amount of released oxygen was significantly correlated with the above-ground biomass (r = 0.710). The ability of oxygen release (the amount of the oxygen release per fresh root weight) of indica cultivars (O. sativa) tended to be higher as compared with the other cultivars. On the other hand, that of African rice (O. glaberrima) and the interspecific progenies tended to be lower. These results suggested that the ability of oxygen release widely varies among rice cultivars, and some of indica cultivars (O. sativa) may be suitable for close mixed-planting to mitigate flood stress of upland-adapted cereal crop.

• Transactions on Electrical and Electronic Materials
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• 제15권6호
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• pp.315-319
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• 2014

In this paper, we investigate visible light stress instability in radio frequency (RF) sputtered a-IGZO thin film transistors (TFTs). The oxygen flow rate differs during deposition to control the concentration of oxygen vacancies, which is confirmed via RT PL. A negative shift is observed in the threshold voltage ($V_{TH}$) under illumination with/without the gate bias, and the amount of shift in $V_{TH}$ is proportional to the concentration of oxygen vacancies. This can be explained to be consistent with the ionization oxygen vacancy model where the instability in $V_{TH}$ under illumination is caused by the increase in the channel conductivity by electrons that are photo-generated from oxygen vacancies, and it is maintained after the illumination is removed due to the negative-U center properties.

• Journal of Microbiology and Biotechnology
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• 제18권4호
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• pp.718-724
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• 2008

Dissolved oxygen (DO) and shear stress have pronounced effects on hyaluronic acid (HA) production, yet various views persist about their effects on the molecular weight of HA. Accordingly, this study investigated the effects of DO and shear stress during HA fermentation. The results showed that both cell growth and HA synthesis were suppressed under anaerobic conditions, and the HA molecular mass was only $(1.22{\pm}0.02){\times}10^6 Da$. Under aerobic conditions, although the DO level produced no change in the biomass or HA yield, a high DO level favored the HA molecular mass, which reached a maximum value of $(2.19{\pm}0.05){\times}10^6 Da$ at 50% DO. Furthermore, a high shear stress delayed the rate of HA synthesis and decreased the HA molecular weight, yet had no clear effect on the HA yield. Therefore, a high DO concentration and mild shear environment would appear to be essential to enhance the HA molecular weight.

• Journal of Photoscience
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• 제8권1호
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• pp.13-17
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• 2001

Cucumber leaves subjected to light chilling stress exhibit a preferential inactivation of photosystem(PS) I relative to PSII, resulting in the photoinhibition of photosynthesis. In light chilled cucumber leaves, Cu/Zn-Superoxide dismutase(SOD) is regarded as a primary target of the light chilling stress and its inactivation is closely related to the increased production of reactive oxygen species. In the present study, we further explored that inactivation of PSI in cucumber leaves is not a light chilling specific, but general to various oxidative stresses. Oxidative stress in cucumber leaves was induced by treatment of methylviologen(MV), a producer of reactive oxygen species in chloroplasts. MV treatment decreased the maximal photosynthetic O$_2$ evolution, resulting in the photoinhibition of photosynthesis. The photoinhibition of photosynthesis was attributable to the decline in PSI functionality determined in vivo by monitoring absorption changes around 820 nm. In addition, MV treatment inactivated both antioxidant enzymes Cu-Zn-superoxide dismutase and ascorbate peroxidase known sensitive to reactive oxygen species. From these results, we suggest that chloroplast antioxidant enzymes are the primary targets of photooxidative stress, followed by subsequent inactivation of PSI.

• Journal of Yeungnam Medical Science
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• 제38권2호
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• pp.83-94
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• 2021

The global obesity epidemic and the growing elderly population largely contribute to the increasing incidence of type 2 diabetes. Insulin resistance acts as a critical link between the present obesity pandemic and type 2 diabetes. Naturally occurring reactive oxygen species (ROS) regulate intracellular signaling and are kept in balance by the antioxidant system. However, the imbalance between ROS production and antioxidant capacity causes ROS accumulation and induces oxidative stress. Oxidative stress interrupts insulin-mediated intracellular signaling pathways, as supported by studies involving genetic modification of antioxidant enzymes in experimental rodents. In addition, a close association between oxidative stress and insulin resistance has been reported in numerous human studies. However, the controversial results with the use of antioxidants in type 2 diabetes raise the question of whether oxidative stress plays a critical role in insulin resistance. In this review article, we discuss the relevance of oxidative stress to insulin resistance based on genetically modified animal models and human trials.

• 한국양식학회지
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• 제20권1호
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• pp.60-64
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• 2007

양식 자라, Pelodiscus sinensis를 사용하여 진동 스트레스에 노출될 때 나타나는 생리적 반응의 단기적 지표로서 산소소비량(호흡)과 암모니아 배설량 변화를 조사하였다. 자라는 대형(갑장: $16{\sim}20\;cm$, 체중: $700{\sim}1,000\;g$)와 중형(갑장: $12{\sim}16\;cm$, 체중: $300{\sim}600\;g$)으로 구분하여, 1.5 ton 크기의 FRP 수조에 20마리씩 수용하였다. 진동 자극은 자체 제작한 진동기(vibrator)에 타임머를 연결하여, 하루 중 주간($08:00{\sim}18:00$)에만 2시간 간격으로 15분씩 28일 동안 매일 스트레스 자극을 주었다. 진동의 크기는 $45.0{\sim}68.2$(평균 56.6) dB(V) 였으며, 대조군 자라는 진동의 영향이 없는 별도의 사육수조에서 정상적으로 사육하면서 실험에 사용하였다. 연구결과, 진동 자극은 자라에 상당한 스트레스 요인으로 작용한 것으로 나타났다. 산소소비량 및 암모니아 배설량 등에서 체내 항상성이 스트레스 자극 10일 이후 생리활성도가 50% 이하로 감소하여 항상성 유지를 위한 모든 에너지를 소비하여 생리적 피폐기로 폐사직전인 것으로 나타났다. 자라는 다른 수산 생물과는 다르게 스트레스 상황에 처해 있을 때, 체외로 나타나는 징후가 뚜렷하지 않아 본 연구에서 나타난 산소소비와 암모니아 배설량은 자라의 생리적 활성도를 조사하는데 기초자료로 유용하게 사용될 것으로 판단된다.

• 약학회지
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• 제51권1호
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• pp.75-82
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• 2007

Reactive oxygen species (ROS) are produced in the metabolic process of oxygen in cells. The superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) in cells systemize the antioxidant enzymes to control the oxidative stress. Genistein is one of the isoflavonoids, and its role in controlling cellular oxidative stress is presently the active issue at question. In this study; we analyzed genistein-induced survival rates of the CHO-K1 cells, activities of antioxidant enzymes, ROS levels, and expression levels of antioxidant enzyme genes in order to investigate the effect of genistein on cellular ROS production and antioxidative systems in CHO-K1 cells. As results, the survival rate of cells was decreased as the dose of genistein increases (12.5${\sim}$200 ${\mu}$M). Genistein increased cellular ROS levels, while it reduced total SOD activities and the expression of CuZnSOD. In conclusion, we suggest that genistein may induce oxidative stress via down-regulation of SOD.