• Bulletin of the Korean Chemical Society
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• 제32권9호
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• pp.3395-3399
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• 2011

Copper oxide thin films were synthesized by reactive radio frequency magnetron sputtering at different oxygen gas ratios. The chemical and physical properties of the thin films were investigated by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM), and X-ray diffraction (XRD). XPS results revealed that the dominant oxidation states of Cu were $Cu^0$ and $Cu^+$ at 0% oxygen ratio. When the oxygen ratios increased above 5%, Cu was oxidized as CuO as detected by X-ray induced Auger electron spectroscopy and the $Cu(OH)_2$ phase was confirmed independent of the oxygen ratio. The valence band maxima were $1.19{\pm}0.09$ eV and an increase in the density of states was confirmed after formation of CuO. The thickness and roughness of copper oxide thin films decreased with increasing oxygen ratio. The crystallinity of the copper oxide films changed from cubic Cu through cubic $Cu_2O$ to monoclinic CuO with mean crystallite sizes of 8.8 nm (Cu) and 16.9 nm (CuO) at the 10% oxygen ratio level.

• 천문학회보
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• 제41권2호
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• pp.40.1-40.1
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• 2016

We present the far-ultraviolet fluorescent molecular hydrogen ($H_2$) emission map observed with FIMS/SPEAR for ~76% of the sky. The fluorescent $H_2$ emission is found to be saturated by strong dust extinction at the optically thick, Galactic plane region. However, the extinction-corrected intensity of fluorescent $H_2$ emission is found to have strong linear correlations with the well-known tracers of the cold interstellar medium, such as the E(B-V) color excess, neutral hydrogen column density N(HI), $H{\alpha}$ emission, and CO $J=1{\rightarrow}0$ emission. The all-sky molecular hydrogen column density map is also obtained using a photodissociation region model. We also derive the gas-to-dust ratio, hydrogen molecular fraction ($f_{H2}$), and $CO-to-H_2$ conversion factor ($X_{CO}$) of the diffuse interstellar medium. The gas-to-dust ratio is consistent with the standard value $5.8{\times}10^{21}atoms\;cm^{-2}mag^{-1}$, and the $X_{CO}$ tends to increase with E(B-V), but converges to the Galactic mean value $1.8{\times}10^{20}cm^{-2}K^{-1}km^{-1}s$ at optically thick regions with E(B-V)>2.0.

• 천문학회보
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• 제41권1호
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• pp.80.1-80.1
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• 2016

There are probabilistic forecast models for solar flare occurrence, which can be evaluated by various skill scores (e.g. accuracy, critical success index, heidek skill score, and true skill score). Since these skill scores assume that two types of forecast errors (i.e. false alarm and miss) are equal or constant, which does not take into account different situations of users, they may be unrealistic. In this study, we make an evaluation of a probabilistic flare forecast model [Lee et al., 2012] which use sunspot groups and its area changes as a proxy of flux emergence. We calculate daily solar flare probabilities from 2011 to 2014 using this model. The skill scores are computed through contingency tables as a function of forecast probability, which corresponds to the maximum skill score depending on flare class and type of a skill score. We use a value score with cost/loss ratio, relative importance between the two types of forecast errors. The forecast probability (y) is linearly changed with the cost/loss ratio (x) in the form of y=ax+b: a=0.88; b=0 (C), a=1.2; b=-0.05(M), a=1.29; b=-0.02(X). We find that the forecast model has an effective range of cost/loss ratio for each class flare: 0.536-0.853(C), 0.147-0.334(M), and 0.023-0.072(X). We expect that this study would provide a guideline to determine the probability threshold and the cost/loss ratio for space weather forecast.

• Bulletin of the Korean Chemical Society
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• 제34권10호
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• pp.2877-2882
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• 2013

Second-order rate constants ($k_{Ox^-}$) have been measured spectrophotometrically for nucleophilic substitution reactions of 4-nitrophenyl X-substituted-cinnamates (7a-7e) and Y-substituted-phenyl cinnamates (8a-8e) with butane-2,3-dione monoximate ($Ox^-$) in 80 mol % $H_2O$/20 mol % DMSO at $25.0{\pm}0.1^{\circ}C$. The Hammett plot for the reactions of 7a-7e consists of two intersecting straight lines while the Yukawa-Tsuno plot exhibits an excellent linearity with ${\rho}_X$=0.85 and r=0.58, indicating that the nonlinear Hammett plot is not due to a change in the rate-determining step but is caused by resonance stabilization of the ground state (GS) of the substrate possessing an electron-donating group (EDG). The Br${\o}$nsted-type plot for the reactions of Y-substituted-phenyl cinnamates (8a-8e) is linear with ${\beta}_{lg}$ = -0.64, which is typical of reactions reported previously to proceed through a concerted mechanism. The ${\alpha}$-nucleophile ($Ox^-$) is more reactive than the reference normal-nucleophile ($4-ClPhO^-$). The magnitude of the ${\alpha}$-effect (i.e., the $k_{Ox^-}/k_{4-ClPhO^-}$ ratio) is independent of the electronic nature of the substituent X in the nonleaving group but increases linearly as the substituent Y in the leaving group becomes a weaker electron-withdrawing group (EWG). It has been concluded that the difference in solvation energy between $Ox^-$ and $4-ClPhO^-$ (i.e., GS effect) is not solely responsible for the ${\alpha}$-effect but stabilization of transition state (TS) through a cyclic TS structure contributes also to the Y-dependent ${\alpha}$-effect trend (i.e., TS effect).

• 대한금속재료학회지
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• 제49권7호
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• pp.583-588
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• 2011

$Cd_xZn_{1-x}O$ thin films were grown on quartz substrates by using the sol-gel spin-coating method. The mole fraction, x, of the $Cd_xZn_{1-x}O$ thin films was controlled from 0 to 1 by changes in the content ratio of the cadmium acetate dehydrate [$Cd{(CH_3COO)}_2{\cdot}2H_2O$] and zinc acetate dehydrate [$Zn{(CH_3COO)}_2{\cdot}2H_2O$]. The effects of the mole fraction on the morphological, structural, and optical properties of the $Cd_xZn_{1-x}O$ thin films were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), and UV-visible spectroscopy. The $Cd_xZn_{1-x}O$ thin films exhibited the polygonal surface morphology and their grain size was increased ranging from 42.1 to 63.9 nm with the increase in the mole fraction. It was observed that the absorption bandgap of the $Cd_xZn_{1-x}O$ thin films decreased from 3.25 to 2.16 eV as the mole fraction increased and the Urbach energy ($E_U$) values changed inversely to the optical bandgap of the $Cd_xZn_{1-x}O$ thin films.

• 대한기계학회논문집
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• 제5권4호
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• pp.329-337
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• 1981

Natural convection within inclined high aspect-ratio rectangular cavity was analysed by using finite element method. For a cavity of sapect-ratio 20, the flow patterns of secondary vortices and the heat transfer characteristics on the wall were obtained with the variation of tilt angle as well as Ra and Pr. The observation on the governing equations shows that the increase of Ra/Pr and the existence of nonzero tilt angle make the flow pattern more complicated and so it becomes difficult to obtain converging solution. The max. value of Ra/Pr attained in this study was 3x10$\^$4/at 0$\^$0/ tilt angle and 1.1x10$\^$4/ at 45.deg. tilt angle for aspect ratio 20and Pr=0.7. Finally an empirical formula for Nusselt number which can accout for the effect of tilt angle is obtained for laminar flow regime.

• Nuclear Engineering and Technology
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• 제42권3호
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• pp.313-318
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• 2010

Alnine pellets were installed in a nuclear power plant for one or two operation cycles and measured by electron spin resonance (ESR) spectrometers for dosimetry. Dose and "x/y ratio", i.e., satellite peak over main center peak ratio, were measured for the returned alanine dosimeters from the nuclear power plant and compared to the values of reference alanine dosimeters exposed only to gamma rays. The variation of the x/y ratio change depended on the population of radicals from each radiation component with different LET. The gamma dose in a mixed radiation field was estimated by an additive gamma ray irradiation experiment and the measured dose rate at specified locations in the containment building.

• Journal of Nutrition and Health
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• 제34권1호
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• pp.14-22
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• 2001

In this study, we examined the effects of dietary fatty acids and vitamin E supplementation on antioxidant systems in the rat brain regions. The Sprague Dawley rats were fed the experimental diets 3-4 wks prior to the conception. Experimental diet consisted of 10% fat(wt/wt) which were safflower oil(SO, poor in $\omega$3 fatty acids), mixed oil(MO, P/M/S ratio=1.03:1.45:1,$\omega$6/$\omega$3 ratio=6.3) and mixed oil supplemented with vitamin E(ME:MO+500mg vitamin E/kg diet). At 3 and 9 weeks of age of the newborn rats, frontal cortex(FC), corpus striatum(CS), hippocampus(H) cerebellum(CB) were dissected out from the whole brain. Activities of glutathione peroxidase(GSH-P(sub)x, superoxide dismutase(SOD) concentrations of malondialdehyde(MDA) were mesaured. Dietary fatty acids were not effective in antioxidative system for rat brain. However, when vitamin E was supplemented to the diet(ME), the activities of GSH-P(suh)x tended to increase in comparison to MO group. Therefore, the activites of GSH-P(suh)x of FC and H at the age of 3 weeks showed significant differences(p<0.05). The activities of Total-SOD tended to decrease in ME group compared to MO group. There were significant differences(p<0.05) in FC and CS at the age of 3 weeks. The activities of Mn-SOD tended to increase and Cu, Zn-SOD tended to decrease when vitamin E was supplemented. The activity levels of antioxidative enzymes at the age of 3 weeks and 9 weeks were similar. This suggested that the activity level of antioxidative enzymes reached to the adult level at the age of 3 weeks which is the end point of lactation period. The concentrations of MDA were not altered by experimental diets. When the activities of antioxidant enzymes were compared, the activities of antioxidant enzymes were the lowest in H and FC. In conclusion, the antioxidative system were not altered by dietary fatty acid at the age of 3 weeks and 9 weeks, but the supplementation of vitamin E altered the antioxidative systems. Therefore, these findings should be considered comprehensively in scope of the balance of various antioxidative systems and their interactions(Korean J Nutrition 34(1):14-22, 2001)

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집B
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• pp.928-933
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• 2001

EGR(Exhaust Gas Recirculation) is an effective strategy to control nitrogen oxides emissions from diesel engine. The EGR reduces $NO_x$ through lowering the oxygen concentration in the combustion chamber as well as through heat absorption. However, application of EGR system is difficult because of the penalty in fuel consumption and the increase in particulate matter. The engine used for the experimental was a 3-cylinder 0.8-liter turbo-charged light duty diesel engine with an electronic EGR valve. In this study, experiments were performed at variable vehicle speeds and loads on the chassis dynamometer. To evaluate the exhaust emissions with the EGR system testing was performed using cvs-75 mode test procedure. Results of the cvs-75 mode test achieve sufficiently to meet EURO3 standards.

• Bulletin of the Korean Chemical Society
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• 제31권9호
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• pp.2593-2597
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• 2010

Second-order rate constants ($k_N$) have been measured spectrophotometrically for reactions of 2,4-dinitrophenyl X-substituted benzoates (X = 4-MeO, H and 4-$NO_2$) with a series of Z-substituted pyridines in 80 mol % $H_2O$/20 mol % DMSO at $25.0{\pm}0.1^{\circ}C$. The Br${\o}$nsted-type plots exhibit downward curvature (e.g., $\beta_2$ = 0.89 ~ 0.96 when $pK_a$ < 9.5 while $\beta_1$ = 0.38 ~ 0.46 when $pK_a$ > 9.5), indicating that the reaction proceeds through a stepwise mechanism with a change in rate-determining step (RDS). The ${pK_a}^o$, defined as the $pK_a$ at the center of Br${\o}$nsted curvature, has been analyzed to be 9.5 regardless of the electronic nature of the substituent X in the benzoyl moiety. Dissection of $k_N$ into the microscopic rate constants $k_1$ and $k_2/k_{-1}$ ratio has revealed that $k_1$ is governed by the electronic nature of the substituent X but the $k_2/k_{-1}$ ratio is not. Theoretical calculations also support the argument that the electronic nature of the substituent X in the benzoyl moiety does not influence the $k_2/k_{-1}$ ratio.