• Natural Product Sciences
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• 제15권4호
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• pp.185-191
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• 2009

Intestinal epithelial cells (IEC) play an important role in the mucosal immune system. IEC-derived mediators of inflammatory cascades play a principal role in the development of colon inflammation. The aim of this study was to investigate the inhibitory effect of aqueous extracts of Schizandra chinensis fruits (SC-Ex) on the production of inflammatory mediators by the human colonic epithelial cells. HT-29 cells were stimulated with dextran sulfate sodium in the presence or absence of SC-Ex to examine the cytoprotection and production of IL-8 and reactive oxygen species (ROS). It was shown that dextran sulfate sodium (DSS) caused the reduction of cell viability and production of IL-8 and ROS in DSS-treated HT-29 cells. We observed that the treatment of SC-Ex protected significantly cell proliferation from DSS-induced damage in dose-dependent manner. SC-Ex (10 and 100 ${\mu}g$/ml) also suppressed DSS-induced production of IL-8 mRNA and protein. Moreover, DSS-induced ROS production was inhibited markedly by the treatment of 100 ${\mu}g$/ml SC-Ex. These results suggest that SC-Ex has the protective effects on DSS-induced cell damage and the release of inflammatory mediators in the intestinal epithelial cells.

• 조명전기설비학회논문지
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• 제25권7호
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• pp.97-104
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• 2011

This paper presents modeling and control for the emerging IGBT converter-based high-voltage direct-current system (IGBT-HVDC). This paper adds to the representation of the IGBT-HVDC system in the dq-synchronous reference frame and its decoupled control scheme. Additionally, since the IGBT-HVDC is able to actively support the grid due to its capacity to control independently active and reactive power production, a reactive power control scheme is presented in order to regulate/contribute to the voltage at a remote location by taking into account its operational state and limits. The ability of the control scheme is assessed and discussed by means of simulations using ahybrid power system, which consists of a permanent magnetic synchronous-generator (PMSG) based wind turbine, an IGBT-HVDC, and a local load.

• 한국진공학회지
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• 제8권4B호
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• pp.541-547
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• 1999

Reactive ion etching process for InP using BCl3/O2/Ar high density inductively coupled plasma was investigated. The experimental design method proposed by the Taguchi was utilized to cover the whole parameter range while maintaining reasonable number of actual experiments. Results showed that the ICP power and the chamber pressure were the two dominant parameters affectsing etch results. It was also observed that the etch rate decreased and the surface roughness improved as the ICP power and the bias voltage increased and as the chamber pressure decreased. The Addition of oxygen to the gas mixture drastically improved surface roughness by suppressing the formation of the surface reaction product. The optimum condition was ICP power 600W, bias voltage -100V, 10% $O_2$, 6mTorr, and $180^{\circ}C$, resulting in about 0.15$\mu\textrm{m}$ etch rate with smooth surfaces and vertical mesa sidewalls Also, the maximum etch rate of abut 4.5 $\mu\textrm{m}$/min was obtained at the condition of ICP power 800W, bias voltage -150V, 15% $O_2$, 8mTorr and $160^{\circ}C$.

• Journal of Power Electronics
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• 제18권3호
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• pp.789-801
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• 2018

Model predictive direct power control (MPDPC) is a widely recognized high-performance control strategy for a three-phase grid-connected pulse width modulation (PWM) rectifier. Unlike those of conventional grid-connected PWM rectifiers, the active and reactive powers of permanent magnet synchronous generator (PMSG)-connected PWM rectifiers, which are used in electromagnetic transmitters, cannot be calculated as the product of voltage and current because the back electromotive force (EMF) of the generator cannot be measured directly. In this study, the predictive power model of the rectifier is obtained by analyzing the relationship among flux, back EMF, active/reactive power, converter voltage, and stator current of the generator. The concept of duty cycle control in the proposed MPDPC is introduced by allocating a fraction of the control period for a nonzero vector and rest time for a zero vector. When nonzero vectors and their duration in the predefined cost function are simultaneously evaluated, the global power ripple minimization is obtained. Simulation and experimental results prove that the proposed MPDPC strategy with duty cycle control for the PMSG-connected PWM rectifier can achieve better control performance than the conventional MPDPC-SVM with grid-connected PWM rectifier.

• Mycobiology
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• 제44권1호
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• pp.38-47
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• 2016

The ascomycete fungus Mycosphaerella graminicola (synonym Zymoseptoria tritici) is an important pathogen of wheat causing economically significant losses. The primary nutritional mode of this fungus is thought to be hemibiotrophic. This pathogenic lifestyle is associated with an early biotrophic stage of nutrient uptake followed by a necrotrophic stage aided possibly by production of a toxin or reactive oxygen species (ROS). In many other fungi, the genes CREA and AREA are important during the biotrophic stage of infection, while the NOXa gene product is important during necrotrophic growth. To test the hypothesis that these genes are important for pathogenicity of M. graminicola, we employed an over-expression strategy for the selected target genes CREA, AREA, and NOXa, which might function as regulators of nutrient acquisition or ROS generation. Increased expressions of CREA, AREA, and NOXa in M. graminicola were confirmed via quantitative real-time PCR and strains were subsequently assayed for pathogenicity. Among them, the NOXa over-expression strain, NO2, resulted in significantly increased virulence. Moreover, instead of the usual filamentous growth, we observed a predominance of yeast-like growth of NO2 which was correlated with ROS production. Our data indicate that ROS generation via NOXa is important to pathogenicity as well as development in M. graminicola.

• Molecules and Cells
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• 제25권3호
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• pp.347-351
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• 2008

Several lines of evidence indicate that the oxidative modification of protein and the subsequent accumulation of the modified proteins have been found in cells during aging, oxidative stress, and in various pathological states including premature diseases, muscular dystrophy, rheumatoid arthritis, and atherosclerosis. The important agents that give rise to the modification of a protein may be represented by reactive aldehydic intermediates, such as ketoaldehydes, 2-alkenals and 4-hydroxy-2-alkenals. These reactive aldehydes are considered important mediators of cell damage due to their ability to covalently modify biomolecules, which can disrupt important cellular functions and can cause mutations. Furthermore, the adduction of aldehydes to apolipoprotein B in low-density lipoproteins (LDL) has been strongly implicated in the mechanism by which LDL is converted to an atherogenic form that is taken up by macrophages, leading to the formation of foam cells. During the search for an endogenous inducer of cyclooxygenase-2 (COX-2), an inducible isoform responsible for high levels of prostaglandin production during inflammation and immune responses, 4-hydroxy-2-noennal (HNE), one of the most representative lipid peroxidation product, has been identified as the potential inducer of COX-2. In addition, the following study on the molecular mechanism of the COX-2 induction by HNE has unequivocally established that a serum component, which is eventually identified to be denatured LDL, is essential for COX-2 induction. Here I review current understanding of the mechanisms by which HNE in cooperation with the serum component activates gene expression of COX-2.

• Natural Product Sciences
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• 제22권2호
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• pp.87-92
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• 2016

Endothelial dysfunction in atherosclerosis is associated with increasing oxidative stress that could be reversed by antioxidant. Therefore epigallocatechin gallate (EGCG), epicatechin gallate (ECG), epigallocatechin (EGC) and catechin (C) of tea flavonoids were investigated for their roles in regenerating endothelial cell. Peripheral blood mononuclear cells (PB-MNCs) were isolated, plated and cultured in medium with/without treatment of EGCG, ECG, EGC and C. Results showed that among all EGCG, ECG, EGC and C concentrations tested, $12.5{\mu}mol/L$ was not cytotoxic for peripheral blood-derived endothelial progenitor cells (PB-EPCs). Treatment of EGCG, ECG, EGC or C increased the percentages of CD34, CD133, VEGFR-2 expressions and suppressed hydrogen peroxide-induced percentages of reactive oxygen species (ROS) level in PB-EPCs. Taken together, our current results showed that EGCG, ECG, EGC or C of tea flavonoids could induce differentiation of PB-MNCs into PB-EPCs as well as protect PB-EPCs from oxidative damage by suppresing the intracellular ROS levels.

• Natural Product Sciences
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• 제13권2호
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• pp.118-122
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• 2007

We have studied the cytoprotective effect on H$_2$O$_2$ induced oxidative stress from leaves of Carpinus tschonoskii. The methanol extract of Carpinus tschonoskii was found to scavenge intracellular reactive oxygen species (ROS) using flow cytometry and confocal microscope. This extract prevented lipid peroxidation and thus reduced cell death of Chinese hamster lung fibroblast (V79-4) induced by H$_2$O$_2$ treatment. The extract increased catalase activity and phosphorylation of extracellular signal regulated kinase (ERK). Taken together, the results suggest that Carpinus tschonoskii protects V79-4 cells against oxidative damage by H$_2$O$_2$ through scavenging ROS.

• 생약학회지
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• 제36권3호통권142호
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• pp.195-200
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• 2005

Smilacis Chinae Radix is root of Smilax china L.. It has been known as a korean folk medicine for anti-inflammatory, anti-microbial diuresis, detoxification and relieving enteropathy as diarrhea. Reactive oxygen species(ROS) are continuously produced at a high rate as a by-product obtained in the aerobic metabolism. A major portion of living organisms has defense system as superoxide dismutase or catalase against damage produced by ROS. Several lines of evidence provided that ROS appears to cause to develop aging and various diseases. In this study, we have investigated the antioxidant activities of Smilacis Chinae Radix in order to screen the antioxidant substances from natural products. As a result, EtOAc extract of Smilacis Chinae Radix exhibited potent antioxidant effect on various antioxidant experiment. The major components of antioxidant activity were isolated from EtOAc extract of Smilacis Chinae Radix. Their structure of compounds were identified as quercetin and (-)-epicatechin by spectroscopic evidence, respectively.

• Bulletin of the Korean Chemical Society
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• 제20권10호
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• pp.1136-1144
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• 1999

The collision-induced reaction of gas-phase atomic hydrogen with hydrogen atoms chemisorbed on a silicon (001)-(2×1) surface is studied by use of the classical trajectory approach. The model is based on reaction zone atoms interacting with a finite number of primary system silicon atoms, which then are coupled to the heat bath, i.e., the bulk solid phase. The potential energy of the Hads‥Hgas interaction is the primary driver of the reaction, and in all reactive collisions, there is an efficient flow of energy from this interaction to the Hads-Si bond. All reactive events occur on a subpicosecond scale, following the Eley-Rideal mechanism. These events occur in a localized region around the adatom site on the surface. The reaction probability shows the maximum near 700K as the gas temperature increases, but it is nearly independent of the surface temperature up to 700 K. Over the surface temperature range of 0-700 K and gas temperature range of 300 to 2500 K, the reaction probability lies at about 0.1. The reaction energy available for the product states is small, and most of this energy is carried away by the desorbing H2 in its translational and vibrational motions. The Langevin equation is used to consider energy exchange between the reaction zone and the bulk solid phase.