• Journal of Advanced Marine Engineering and Technology
• /
• v.33 no.7
• /
• pp.1026-1033
• /
• 2009

Fine ceramics have high strength, excellent wear resistance, chemical stability and high strength at high temperature and are receiving attention in various fields such as construction, engineering, aerospace and marine science. Finish machining process is required to obtain precise ceramics components because sintering process necessary for obtaining high strength and high quality ceramics reduces the dimensions of components and precision of shape. But high strength and brittleness of ceramics materials cause difficulty in processing. So a process for obtaining wanted dimensions is studying using high temperature which makes ceramics softened and thermal affected recently. Laser beam is a very useful optical device for these kinds of processes. Laser process such as laser cutting, laser machining, laser heat treatment and laser-assisted machining(LAM) is researching to manufacture practical ceramics components using intense laser source which can cause local softening and damage of workpiece. In this paper, microstructural and mechanical properties of silicon nitride heated are studied as a basic study for researching of ceramics process by laser beam. The surface variation of HIP and SSN-silicon nitride was analyzed with SEM and EDS. A processing at $1,300^{\circ}C$ or above causes N element to combine into $N_2$ gas and the gas busts from surface. These phenomena make bloat, craters and heat defects on the surface of silicon nitride. Also, oxygen content is largely increased to oxidize the surface and it causes changing of phases and reducing of hardness of surface.

• Journal of Life Science
• /
• v.15 no.1 s.68
• /
• pp.94-99
• /
• 2005

Sixty four bacterial colonies which were able to oxidize the manganese were isolated from soil samples in Mokcheon and Ochang area. Among them, one bacterial strain was selected for this study based on its higher manganese oxidation, and this selected bacterial strain was identified as Aeromonas sp. MN44 through physiological-biochemical test and analysis of its 16s rRNA sequence. Aeromonas sp. MN44 was able to utilize lactose but did not utilize various carbohydrates as a sole carbon source. Aeromonas sp. MN44 showed a very sensitive to antibiotics such as kanamycin, chloramphenicol, ampicillin, tetracycline and spectinomycin, and heavy metal such as cadmium. But this strain showed a high resistance up to mg/ml unit to heavy metals such as lithium and manganese. Optimal manganese oxidation condition of Aeromonas sp. MN44 was pH 7.4 and manganese oxidation activity was inhibited by proteinase K and boiling treatment. So, we concluded that this factor was protein. The manganese oxidizing factor produced by Aeromonas sp. MN44 was partial purified by ammonium sulfate precipitation, DEAE-Toyopearl 650M ion exchange chromatography and Sephadex gel filtration chromatography. Its molecular mass was about 113 kDa.

• Bulletin of the Korean Chemical Society
• /
• v.35 no.7
• /
• pp.2013-2018
• /
• 2014

The adsorption and decomposition of trimethylene oxide ($C_3H_6O$) molecule on the Al(111) surface were investigated by the generalized gradient approximation (GGA) of density functional theory (DFT). The calculations employed a supercell ($6{\times}6{\times}3$) slab model and three-dimensional periodic boundary conditions. The strong attractive forces between $C_3H_6O$ molecule and Al atoms induce the C-O bond breaking of the ring $C_3H_6O$ molecule. Subsequently, the dissociated radical fragments of $C_3H_6O$ molecule oxidize the Al surface. The largest adsorption energy is about -260.0 kJ/mol in V3, V4 and P2, resulting a ring break at the C-O bond. We also investigated the decomposition mechanism of $C_3H_6O$ molecules on the Al(111) surface. The activation energies ($E_a$) for the dissociations V3, V4 and P2 are 133.3, 166.8 and 174.0 kJ/mol, respectively. The hcp site is the most reactive position for $C_3H_6O$ decomposing.

• Journal of Physiology & Pathology in Korean Medicine
• /
• v.21 no.6
• /
• pp.1499-1505
• /
• 2007

Peroxynitrite ($ONOO^-$) is a reactive oxidant formed from superoxide anion radical (${\cdot}\;O_2-$) and nitric oxide (NO), which can oxidize cellular components such as essential protein, non-protein thiols, DNA, low-density lipoproteins and membrane phospholipids. ${\cdot}\;O_2-$ and $ONOO^-$ have contributed to the pathogenesis of diseases such as stroke, heart disease, Alzheimer's disease and atherosclerosis. Because of damaging effects of ${\cdot}\;O_2-$ and $ONOO^-$ oxidants, Vespae Nidus, which has been known to strengthen the kidneys to preserve the vital energy. was tested as a potential specific scavenger of those oxidants. In this study, the viability of Vespae Nidus (1, 10, 50 g/ml) to scavenge ${\cdot}\;O_2-$, NO, $ONOO^-$ and so to protect cells against tert-butylhydroxyperoxide (t-BHP) induced cell death was tested. The levels of ${\cdot}\;O_2-$ and $ONOO^-$ were detected by staining with DCFH-DA and DHR 123, respectively. Protein expression levels of COX-2, iNOS and $NF{-\kappa}B$ were assayed by western blot. Vespae Nidus blocked t-BHP-induced cell death in a dose-dependent fashion. Vespae Nidus inhibited t-BHP-induced production of ${\cdot}\;O_2-$, NO and $ONOO^-$ in YPEN cells. The lipid peroxide level was increased and glutathione level was decreased in lipopolysaccharide (LPS)-treated ICR mouse, whereas the ones in the Vespae Nidus-administered group were regulated beneficially. Vespae Nidus inhibited the expression of COX-2, iNOS and NF-κB (p65 and p50) genes in LPS-treated ICR mouse. The present study suggests that Vespae Nidus is a powerful antioxidant and promotes cellular defense activity by scavenging the toxic oxidants such as ${\cdot}\;O_2-$ and $ONOO^-$.

• Korean Journal of Fisheries and Aquatic Sciences
• /
• v.25 no.6
• /
• pp.501-510
• /
• 1992

Lipid prooxidants in sardine skin was characterized. Prooxidants in the sardine skin extract with 0.05M phosphate buffer was purified by successive chromatography on Sephadex G-200, DEAE-Sephadex A-50 and CM-Sephadex A-50. Prooxidants of sardine skin exist mainly in the intermediate molecular weight fractions. Observations of the thermounstability and optimum pH(pH 7.0) suggest that the major prooxidants are enzymes and hemoproteins. They can oxidize well both free and esterified linoleic acid and form conjugated hydroperoxides. From these results, the major prooxidants in sardine skin are assumed to be lipoxygenase-like enzymes.

• Journal of Microbiology and Biotechnology
• /
• v.20 no.3
• /
• pp.485-493
• /
• 2010

A modified graphite felt electrode with neutral red (NR-electrode) was shown to catalyze the chemical oxidation of nitrite to nitrate under aerobic conditions. The electrochemically oxidized NR-electrode (EO-NR-electrode) and reduced NR-electrode (ER-NR-electrode) catalyzed the oxidation of $1,094{\pm}39$ mg/l and $382{\pm}45$ mg/l of nitrite, respectively, for 24 h. The electrically uncharged NR-electrode (EU-NR-electrode) catalyzed the oxidation of $345{\pm}47$ mg/l of nitrite for 24 h. The aerobic bacterial community immobilized in the EO-NR-electrode did not oxidize ammonium to nitrite; however, the aerobic bacterial community immobilized in the ER-NR-electrode bioelectrochemically oxidized $1,412{\pm}39$ mg/l of ammonium for 48 h. Meanwhile, the aerobic bacterial community immobilized on the EU-NR-electrode biochemically oxidized $449{\pm}22$ mg/l of ammonium for 48 h. In the continuous culture system, the aerobic bacterial community immobilized on the ER-NR-electrode bioelectrochemically oxidized a minimal $1,337{\pm}38$ mg/l to a maximal $1,480{\pm}38$ mg/l of ammonium to nitrate, and the community immobilized on the EU-NR-electrode biochemically oxidized a minimal $327{\pm}23$ mg/l to a maximal $412{\pm}26$ mg/l of ammonium to nitrate every two days. The bacterial communities cultivated in the ER-NR-electrode and EU-NR-electrode in the continuous culture system were analyzed by TGGE on the $20^{th}$ and $50^{th}$ days of incubation. Some ammonium-oxidizing bacteria were enriched on the ER-NR-electrode, but not on the EU-NR-electrode.

• Journal of Microbiology and Biotechnology
• /
• v.23 no.6
• /
• pp.864-871
• /
• 2013

The recombinant strain P. pastoris GS115-lccC was used to produce laccase with high activity. Factors influencing laccase expression, such as pH, methanol concentration, copper concentration, peptone concentration, shaker rotate speed, and medium volume were investigated. Under the optimal conditions, laccase activity reached 12,344 U/L on day 15. The recombinant enzyme was purified by precipitating and dialyzing to electrophoretic homogeneity, and was estimated to have a molecular mass of about 58 kDa. When guaiacol was the substrate, the laccase showed the highest activity at pH 5.0 and was stable when the pH was 4.5~6.0. The optimal temperature for the laccase to oxidize guaiacol was $60^{\circ}C$, but it was not stable at high temperature. The enzyme could remain stable at $30^{\circ}C$ for 5 days. The recombinant laccase was used to degrade chlorpyrifos in several laccase/mediator systems. Among three synthetic mediators (ABTS, HBT, VA) and three natural mediators (vanillin, 2,6-DMP, and guaiacol), vanillin showed the most enhancement on degradation of chlorpyrifos. Both laccase and vanillin were responsible for the degradation of chlorpyrifos. A higher dosage of vanillin may promote a higher level of degradation of chlorpyrifos, and the 2-step addition of vanillin led to 98% chlorpyrifos degradation. The degradation of chlorpyrifos was faster in the L/V system ($k_{obs}$ = 0.151) than that in the buffer solution ($k_{obs}$ = 0.028).

• International Journal of Automotive Technology
• /
• v.8 no.1
• /
• pp.27-31
• /
• 2007

The number of vehicles employing diesel engines is rapidly rising. Accompanying this trend, application of an after-treatment system is strictly required as a result of reinforced exhaust regulations. The Diesel Particulate Filter (DPF) system is considered as the most efficient method to reduce particulate matter (PM), but the improvement of a regeneration performance at any engine operation point presents a considerable challenge by itself. Therefore, the present study evaluates the effect of fuel injection characteristics on regeneration performance in a DOC and a catalyzed CR-DPF system. The temperature distribution on the rear surface of the DOC and the exhaust gas emission were analyzed in accordance with fuel injection strategies and engine operating conditions. A temperature increase more than BPT of DPF system was obtained with a small amount fuel injection although the exhaust gas temperature was low and flow rate was high. This increase of temperature at the DPF inlet cause PM to oxidize completely by oxygen. In the case of multi-step injection, the abrupt temperature changes of DOC inlet didn't occur and THC slip also could not be observed. However, in the case of pulse type injection, the abrupt injection of much fuel results in the decrease of DOC inlet temperatures and the instantaneous slip of THC was observed.

• The Journal of Internal Korean Medicine
• /
• v.24 no.1
• /
• pp.75-83
• /
• 2003

Objectives : Peroxynitrite($ONOO^-$), formed from the reaction of $O2^-$ and NO, is a cytotoxic species that can oxidize several cellular components such as proteins, lipids and DNA. It has been involved in the aging process and age-related diseases such as Alzheimer's disease, rheumatoid arthritis, cancer and atherosclerosis. The aim of this study was to investigate scavenging activities of $ONOO^-$ and its precursors, NO and $O_{2^-}$ and its scavenging mechanism of Zingiberis Rhizoma (ZR). Methods : To investigate scavenging activities of $ONOO^-,\;NO,\;O_{2^-}$ and its scavenging mechanism, we used fluorescent probes like DCFDA, DAF-2 and DHR 123. The $ONOO^-$ scavenging activity on ZR was assayed by measuring oxidized dihydrorhodamine 123 (DHR 123) by fluorometry. The scavenging efficacy was expressed as IC50, showing the concentration of each sample that is required to cause 50% inhibition of DHR 123 oxidation. In a separate study, the protective effect of ZR on $ONOO^-$-induced nitration of bovine serum albumin was investigated through immuno-assay with a monoclonal anti-nitryrosine antibody, and a horseradish peroxidase-conjugated anti-mouse secondary antibody from sheep. Results : ZR markedly scavenged authentic $ONOO^-,\;O_{2^-}$ and NO. It also inhibited $ONOO^-$ induced by $O_{2^-}$ and NO which are derived from SIN-1. The data demonstrated that ZR led to decreased $ONOO^-$ mediated nitration of tyrosine through electron donation. It also inhibited the nitration of bovine serum albumin induced by $ONOO^-$ in a dose-dependent manner. Furtheremore, it blocked LPS-induced ROS and RNS generation. Conclusions : These results suggest that ZR can be developed as an effective $ONOO^-$ scavenger for the prevention of aging process and age-related diseases.

• Korean Journal of Pharmacognosy
• /
• v.30 no.3
• /
• pp.306-313
• /
• 1999

Polyphenol Oxidase(PPO) was purified from an extract of Ginkgo biloba leaves by ammonium sulfate fractionation followed by sephadex G-150 column chromatography, which resulted in a 18-fold increase in specific activity. The enzyme was most active at pH 8.5 and the temperature optimum for the PPO catechol oxidation reaction was $45^{\circ}C$. Heat inactivation studies showed that heating for 7, 9 and 48 min, at 80, 70 and $60^{\circ}C$ respectively caused a 50% loss in enzymatic activity and that the enzyme was completely inactivated after heat treatment at $90^{\circ}C$ for 60 min. Km values of the PPO for catechol, hydroquinone and 4-methylcatechol derived from Lineweaver-Burk plots were $6.06\;{\times}\;10^{-4}M,\;1.02\;{\times}\;10^{-3}M,\;1.41\;{\times}\;10^{-3}M$ respectively. Of the substrates tested, 4-methylcatechol was oxidized most readily and the enzyme did not oxidize monophenols. The enzyme datalyzed browning reaction was completely inhibited in the presence of reducing reagents, namely ascorbic acid, cysteine, glutathione, 2-mercaptoethanol, potassium metabisulfite at 0.5 mM level. Sodium chloride showed very little inhibition effect on Ginkgo biloba leaves PPO. Lineweaver-Burk analysis of inhibition data revealed that the inhibition by cysteine, 2-mercaptoethanol, potassium cyanide was competitive with ki values of $1.1\;{\times}\;10^{-5}M,\;2.4\;{\times}\;10^{-5}M,\;8\;{\times}\;10^{-5}M$, respectively. Among the divalent cations, $Cu^{2+}ion$ was a strong activator on PPO and $Mn^{2+}ion$ was little or no effect on PPO activity $Ni^{2+}ion$ was an inhibitor on PPO.