• Proceedings of the KIEE Conference
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• 1994.07b
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• pp.1236-1238
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• 1994

TiAlN thin films were prepared by a multi target r.f magnetron sputtering system under different conditions. We have investigated the resistivity and T.C.R. (Temperature Coefficient of Resistance) characteristics of TiAlN films deposited on $Al_2O_3$ and glass substrates by sputtering in an $Ar:N_2$ gas mixture. We used Al and Ti metal as Target Material and $Ar:N_2$ gas as working gas. We varied the partial pressure ratio of $N_2/Ar$ from 0.2/7 to 1.0/6.2 (SCCM). And the R.F power of Ti and Al Target also were varied as 160/240, 200/200 and 240/160(W). In this experiment, we can get the precision thin film resistor with a very low T.C.R. (Temperature Coefficient of Resistance) below 25 ppm ${\Omega}/^{\circ}C$.

• Aerospace Engineering and Technology
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• v.8 no.2
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• pp.140-148
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• 2009

MOV(Main Oxidizer shut-off Valves) control the combustion of launch vehicle systems by the supply and the isolation of liquid oxygen to a main combustion chamber in launch vehicle systems. Moreover, in the steady operational state, the MOV should secure a constant flow rate of liquid oxygen for combustion instability in the combustion chamber. Concerning the development of MOV, TM(Technology Model) has been manufactured and normal operations of the valve have been verified. However, the Cv of TM has been proved to be too low as compared with a design specification value. Therefore, CFD analysis have been performed by modification of the configurations of TM in order to increase sufficiently Cv of EM(Engineering Model), which is the following model of TM. The modifications of TM configurations such as partial scale-up of valve, increase of stroke length, and outlet angle of 120o would result in a considerable augmentation of Cv. It has been verified by flow capacity tests that the improved Cv of EM is min. 212, which is higher than Cv of TM, 161 by about 32%.

• The Korean Journal of Physiology and Pharmacology
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• v.1 no.6
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• pp.749-758
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• 1997

Myocardial ischemia-reperfusion injury is known to be mediated by reactive oxygen species. The myocardial cell is equipped with endogenous antioxidant defensive system which can be adaptively stimulated by various oxidative stress. It is postulated that an increased oxygen partial pressure induced by hyperbaric oxygenation impose an oxidative stress on the cells, resulting alterations in the endogenous antioxidant system. In this study we investigated the effect of hyperbaric oxygenation on the activities of myocardial antioxidant enzymes and observed whether the hyperbaric oxygenation could protect the ischemia-reperfusion injury of heart. Rats or rabbits were pretreated with hyperbaric $oxygenation(2{\sim}3\;atm\;O_2/1{\sim}3\;hrs/1{\sim}10\;days)$. The changes in activities of major antioxidant enzymes(superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase, glucose-6-phasphate dehydrogenase), functional recovery and infarct size were observed in the experimentally induced ischemia-reperfused hearts. In the hearts isolated from rats pretreated with $2\;atm\;O_2/1{\sim}2\;hrs$ for 5 days, the functional recovery after reperfusion(20 min) following global ischemia(25 min) was significantly increased without any observable oxygen toxicity. Lactate dehydrogenase release was also significantly reduced in this hyperbaric oxygenated rat hearts. In in vivo regional ischemia(30 min) model of rabbit hearts, pretreatrment with $2\;atm\;O_2/1\;hr$ for 5 days significantly limited the infarct size. Among the myocardial antioxidant enzymes of rat hearts pretreated with the hyperbaric oxygenation, the activities of catalase, superoxide dismutase and glucose-6-phosphatase dehydrogenase were increased, while those of glutathione peroxidase and reductase were not changed. There were lethal cases in the groups of rats exposed to 3 atm $3\;atm\;O_2/2{\sim}3\;hrs$ for 5 days. A lipid-peroxidation product, rnnlondialdehyde was increased in brains and livers of the rats exposed to$2\;atm\;O_2/2{\sim}3\;hrs/5\;days\;and\;3\;atm\;O_2/1\;hr/5days$. The present results suggest that the pretreatment of hyperbaric oxygenation can protect the post-ischemic rererfused hearts in association with a stimulation of the activities of myocardial antioxidant defensive enzymes, and that the hyperbaric oxygenation of $2\;atm\;O_2/1\;hr$for 5 days would be a safe condition which does not produce any oxygen toxicity.

• Korean Journal of Materials Research
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• v.13 no.6
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• pp.347-351
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• 2003

II-Ⅵ ZnO compound semiconductor thin films were grown on $\alpha$-Al$_2$O$_3$(0001) single crystal substrate by radical beam assisted molecular beam epitaxy and the optical properties were investigated. Zn(6N) was evaporated using Knudsen cell and O radical was assisted at the partial pressure of 1$\times$10$^{4}$ Torr and radical beam source of 250-450 W RF power. In $\theta$-2$\theta$ x-ray diffraction analysis, ZnO thin film with 500 nm thickness showed only ZnO(0002)and ZnO(0004) peaks is believed to be well grown along c-axis orientation. Photoluminescence (PL) measurement using He-Cd ($\lambda$=325 nm) laser is obtained in the temperature range of 9 K-300 K. At 9 K and 300 K, only near band edge (NBE) is observed and the FWHM's of PL peak of the ZnO deposited at 450 RF power are 45 meV and 145 meV respectively. From no observation of any weak deep level peak even at room temperature PL, the ZnO grains are regarded to contain very low defect density and impurity to cause the deep-level defects. The peak position of free exciton showed slightly red-shift as temperature was increased, and from this result the binding energy of free exciton can be experimentally determined as much as $58\pm$0.5 meV, which is very closed to that of ZnO bulk. By van der Pauw 4-point probe measurement, the grown ZnO is proved to be n-type with the electron concentration($n_{e}$ ) $1.69$\times$10^{18}$$cm^3$, mobility($\mu$) $-12.3\textrm{cm}^2$/Vㆍs, and resistivity($\rho$) 0.30 $\Omega$$\cdot$cm.

• Bulletin of the Korean Chemical Society
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• v.35 no.9
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• pp.2615-2620
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• 2014

Ni/$La_2O_3$ with a high dispersion was prepared by reduction of $La_2O_3$ perovskite oxide to examine the catalytic activity for the $CO_2-CH_4$ reaction. The Ni/$La_2O_3$ catalyst was found to be highly active for the reaction. The ratios of $H_2$/CO were measured in a flow of the reaction mixture containing $CO_2/CH_4$/Ar using an on-line gas chromatography system operated at 1 atm and found to be varied with temperature between 0.66 and 1 in the temperature range of $500-800^{\circ}C$. A kinetic study of the catalytic reaction was performed in a static reactor at 40 Torr total pressure of $CO_2/CH_4/N_2$ by using a photoacoustic spectroscopy technique. The $CO_2$ photoacoustic signal varying with the concentration of $CO_2$ during the catalytic reaction was recorded as a function of time. Rates of $CO_2$ disappearance in the temperature range of $550-700^{\circ}C$ were obtained from the changes in the $CO_2$ photoacoustic signal at early reaction stage. The plot of ln rate vs. 1/T showed linear lines below and above $610^{\circ}C$. Apparent activation energies were determined to be 10.4 kcal/mol in the temperature range of $550-610^{\circ}C$ and 14.6 kcal/mol in the temperature range of $610-700^{\circ}C$. From the initial rates measured at $640^{\circ}C$ under various partial pressures of $CO_2$ and $CH_4$, the reaction orders were determined to be 0.43 with respect to $CO_2$ and 0.33 with respect to $CH_4$. The kinetic results were compared with those reported previously and used to infer a reaction mechanism for the Ni/$La_2O_3$-catalyzed $CO_2-CH_4$ reaction.

• Journal of Chest Surgery
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• v.16 no.2
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• pp.213-220
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• 1983

Pulmonary function is the determinant of blood gas tension. However, Acid-Base disturbances can also alter partial pressures of oxygen and carbon dioxide in arterial blood. During respiratory acidosis $PO_2$ will be lowered and reverse changes will be produced during respiratory alkalosis. On the other hand, in metabolic acidosis $PO_2$ will be elevated and $PCO_2$ will be lowered by the respiratory compensation, and reverse response will be induced in metabolic alkalosis. Urinary gas tension has many influencing factors than arterial blood and difficult to estimate the tendency of its alterations. Urinary $PO_2$ and $PCO_2$ are not always identical level as venous blood. It is to be altered by blood gas tension, flow rate of urine, metabolic rate of kidney, and Acid-Base status of blood. Particularly countercurrent exchange of oxygen and carbon dioxide in the renal medulla will make larger alteration of gas tension than venous blood. After induction of Acid-Base disturbances [disturbances] arterial and urinary $PCO_2$, $PO_2$, urinary volume, and osmolarity were determined in dogs, and the relationships between arterial and urinary $PCO_2$ , $PO_2$ Acid-Base disturbances, urinary volume, and osmolarity were investigated. 1. During the acute Metabolic and Respiratory disturbances urinary pH did not respond on respiratory origin. However, there were immediate urinary response in pH on metabolic origin. 2. Urinary $PO_2$, $PCO_2$, did not always follow arterial or venous gas tension and Acid-Base disturbance. Urinary $PCO_2$, correlate well with the urinary volume. The larger the urinary volume, $PCO_2$ lowered to the venous level. The smaller the urinary volume, urinary $PCO_2$ tends to be higher. However urinary $PO_2$ did not have any particular correlation with urinary volume. 3. Correlation between urinary $PCO_2$ and $PO_2$ were inversely proportional to arterial blood. Differences of $PCO_2$ between arterial blood and urine also did not have any particular correlation with urinary volume. This may suggest that changes on blood gas tensions can influence on urinary $PCO_2$. 4. There were eminent clear inverse correlation between urinary $PCO_2$ and osmolar concentrations of urine. Above results strongly suggest that partial pressure of gas in urine primarily depend upon counter-current exchanges in renal medullary tissues.

• Journal of the Korean Vacuum Society
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• v.18 no.2
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• pp.133-140
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• 2009

$Ta_{2}O_{5}$ thin films were deposited by RF magnetron sputtering method under various RF power, substrates and oxygen partial pressure. Elliptic constants were measured by using a phase modulated spectroscopic ellipsometer and analyzed with the Tauc-Lorentz dispersion formula and best fit method in the range of 310$\sim$1239 nm. Also, transmittance spectra of the films were measured by UV -Vis spectrophotometer in the range of 300$\sim$1000 nm. From these data, thickness of $Ta_{2}O_{5}$ and surface layer were analyzed and changes of magnitude and shape of dispersion of optical constants according to fabricated conditions were measured. Also, to evaluate thickness and optical constants data analyzed by Tauc-Lorentz dispersion formula, the measured and analyzed transmittance spectra were compared. In result of the comparison, two spectra were in good agreement each other. Accordingly, it indicates that our ellipsometric analysis is valid.

• Polymer(Korea)
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• v.30 no.5
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• pp.391-396
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• 2006

It has been reported that plasma treatments are used to modify surface properties of polymers such as adhesivity hydrophobicity and hydrophilicity. Using plasma treatment, interfacial pro-perty can be introduced to a polymer surface without affecting the desired bulk properties of a material. In this study, commercial polyamide66 (PA66) /polyphenylene (PPE) polymer was modified by plasma treatment under a various gas specious for elimination of organic compound and polymer surface property with hvdrophilicity. PA66/PPE polymer with hydrophilicity was treated by RF plasma vacuum system under a various parameter such as gas specious, processing time and partial pressure. Hydrophilicity of PA66/PPE was confirmed by calculation of the surface free energy from contact angle measurement. The highest surface free energy of $50.03 mJ/m^2$ with the lowest contact angle of $14^{\circ}$ was obtained at plasma process power of 100 W, treatment time of 2 min and $Ar/O_2$ gases of 100 and 200 sccm. Moreover the change of organic compounds on the polymer surface was analyzed by fourier transforms infrared spectrometry (FTIR).

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 1999.05a
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• pp.5-5
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• 1999

A novel process is proposed to improve oxidation resistance of Ti-Al intermetallic compounds at elevated temperatures by both Cr addition and pre-sulfidation, where TiAl alloys withlor without Cr addition were sulfidized at 1173K for 86.4ks at a 1.3 Pa sulfur partial pressure in a $H_2-H_2S$ gas mixture. The pre-sulfidation treatment formed a thin Cr-Al alloy layer as well as 7~10 micrometer $TiAl_3$ and $TiAl_2$ layer, due to selective sulfidation of Ti. Oxidation resistance of the pre-sulfidation processed TiAl 4Cr alloy was examined under isothermal and heat cycle conditions between room temperature and 1173K in air. Changes in $TiAl_3$ into $TiAl_2$ and then TiAl phases as well as their effect on oxidation behavior were investigated and compared with the oxidation behavior of the TiAl-4Cr alloy as TiAl and pre-sulfidation processed TiAl aHoys. After oxidation for up to 2.7Ms a protective $Al_2O_3$ scale was formed, and the pre-formed $TiAl_3$ changed into $TiAl_2$ and the $Al_2Cr$ phase changed into a CrAlTi phase between the $Al_2O_3$ scale and $TiAl_2$ layer. The pre-sulfidation processed TiAl-4Cr alloy had very good oxidation resistance for longer times, up to 2.7 Ms, in contrast to those observed for the pre-sulfidation processed TiAl alloy where localized oxidation occurred after 81 Oks and both the TiAl and TiAl-4Cr alloys themselves corroded rapidly from the initial stage of oxidation

• Transactions of the Korean Society of Mechanical Engineers B
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• v.31 no.11
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• pp.942-948
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• 2007

Popular techniques for producing hydrogen by converting methane include steam reforming and catalyst reforming. However, these are high temperature and high pressure processes limited by equipment, cost and difficulty of operation. Low temperature plasma is projected to be a technique that can be used to produce high concentration hydrogen from methane. It is suitable for miniaturization and fur application in other technologies. In this research, the effect of changing each of the following variables was studied using an AC GlidArc system that was conceived by the research team: the gas components ratio, the gas flow rate, the catalyst reactor temperature and voltage. Results were obtained for methane and hydrogen yields and intermediate products. The system used in this research consisted of 3 electrodes and an AC power source. In this study, air was added fur the partial oxidation reaction of methane. The result showed that as the gas flow rate, the catalyst reactor temperature and the electric power increased, the methane conversion rate and the hydrogen concentration also increased. With $O_2/C$ ratio of 0.45, input flow rate of 4.9 l/min and power supply of 1 kW as the reference condition, the methane conversion rate, the high hydrogen selectivity and the reformer energy density were 69.2%, 32.6% and 35.2% respectively.