• Journal of Korea Water Resources Association
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• v.43 no.12
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• pp.1011-1027
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• 2010

In hydrologic modeling, prediction uncertainty generally stems from various uncertainty sources associated with model structure, data, and parameters, etc. This study aims to assess the parameter uncertainty effect on hydrologic prediction results. For this objective, a distributed rainfall-sediment yield-runoff model, which consists of rainfall-runoff module for simulation of surface and subsurface flows and sediment yield module based on unit stream power theory, was applied to the mesoscale mountainous area (Cheoncheon catchment; 289.9 $km^2$). For parameter uncertainty evaluation, the model was calibrated by a multi-objective optimization algorithm (MOSCEM) with two different objective functions (RMSE and HMLE) and Pareto optimal solutions of each case were then estimated. In Case I, the rainfall-runoff module was calibrated to investigate the effect of parameter uncertainty on hydrograph reproduction whereas in Case II, sediment yield module was calibrated to show the propagation of parameter uncertainty into sedigraph estimation. Additionally, in Case III, all parameters of both modules were simultaneously calibrated in order to take account of prediction uncertainty in rainfall-sediment yield-runoff modeling. The results showed that hydrograph prediction uncertainty of Case I was observed over the low-flow periods while the sedigraph of high-flow periods was sensitive to uncertainty of the sediment yield module parameters in Case II. In Case III, prediction uncertainty ranges of both hydrograph and sedigraph were larger than the other cases. Furthermore, prediction uncertainty in terms of spatial distribution of erosion and deposition drastically varied with the applied model parameters for all cases.

• Journal of the Microelectronics and Packaging Society
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• v.18 no.4
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• pp.39-42
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• 2011

The composite electroplating is accomplished by adding inert materials during the electroplating. Permalloy is the term for Ni-Fe alloy and it is used for industrial applications due to its high magnetic permeability, surface wear resistance, corrosion protection. Microhardness for microdevices is enhanced after composite coating and it increases the life cycle. However, the hydroxyl group on the silica makes their surface susceptible to moisture and it causes the silica nanoparticles to be agglomerated in the aqueous solution. The agglomeration problem causes poor dispersion which eventually interrupts uniform deposition of silica nanoparticles. In this study, the dispersion of silica nanoparticles in the permalloy electroplated layer is reported with variation of additives and current densities. The optimum current density was 20 $mA/cm^2$ and the silica content was 9 at% at $50^{\circ}C$. The amount of silica nanopowder codeposition and surface morphologies were influenced with variation of additives. In the bath, smooth surface morphology and relatively high contents of silica nanopowder codeposition were obtained with addition of sodium lauryl sulfate.

• Progress in Superconductivity
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• v.8 no.1
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• pp.65-70
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• 2006

We fabricated $YBa_2Cu_33O_{7-x}$(YBCO) films on(00l) $LaAlO_3$ substrates prepared by metal organic deposition(MOD) method using trifluoroacetate(TFA) solution and evaluated the effects of the humidity on the microstructure, phase purity, and critical properties. The films calcined at $430^{\circ}C$ were fired at $775^{\circ}C$ at 0%, 4.2%, 12.1%, and 20.0% humidified As gas mixed with 0.1% $O_2$. We observed that the amount of $BaF_2$ phase was effectively reduced and that a sharp and strong biaxial texture formed under a humidified atmosphere, leading to increased critical properties. For the films fired at 0% humidity, the $T_c\;and\;I_c$ were undetectably small. When the humidity was increased to 4.2%, the corresponding $T_c$(onset) and $I_c$ were increased to 90.5 K and 8 A/cm-width, respectively. For the films at the humidity range of 12.1-20.0%, the $I_c$ was found to be 35 A/cm-width. According to the results of the XRD, pole-figure, and SEM, these improved critical properties are probably attributed to the formation of a purer YBCO phase, larger grain size, and stronger c-axis orientation.

• Journal of the Korean Ceramic Society
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• v.40 no.9
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• pp.842-848
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• 2003

Semiconducting $\alpha$-Fe$_2$O$_3$ film was prepared by the cathodic electrodeposition method on Indium Tin Oxide (ITO) substrate for photoelectrochemical cell application. After heat treatment at 50$0^{\circ}C$, the phase was changed from Fe to $\alpha$-Fe$_2$O$_3$. The phase, morphology, absorbance, and photocurrent density (A/$\textrm{cm}^2$) of the film depended on the preparation conditions: deposition time, applied voltage, and the duration of heat treatment. The $\alpha$-Fe$_2$O$_3$ film was characterized by X-Ray Diffractometer (XRD), Scanning Electron Microscope (SEM), and UV -Visible Spectrophotometer. The stability of the $\alpha$-Fe$_2$O$_3$ film in aqueous solution was tested at zero bias potential under the white-light source of 100 mW/$\textrm{cm}^2$. The apparent grain size of the films formed at -2.0 V was larger than that grown at -2.5 V. The $\alpha$-Fe$_2$O$_3$ film deposited at -2.0 V for 180 s and heat-treated at 50$0^{\circ}C$ for 1 h showed the predominant photocurrent of 834$\mu$A/$\textrm{cm}^2$.

• Korean Journal of Materials Research
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• v.10 no.11
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• pp.778-783
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• 2000

Effects of the $Al_2$O$_3$surface protective layer, deposited on the SnO$_2$sensing layer by aerosol flame deposition (AFD) method, on the sensing properties of SnO$_2$thin film ags sensors were investigated.Effects of Pt doping to the $Al_2$O$_3$surface protective layer on the selectivity of CH$_4$ gas were also investigated. 0.3$\mu\textrm{m}$ thick SnO$_2$thin sensing layers on Pt electrodes were prepared by R.F. magnetron sputtering with R.F. power of 50 W, at working pressure of 4mTorr, and at 20$0^{\circ}C$ for 30 min. $Al_2$O$_3$surface protective layers on SnO$_2$layers were prepared by AFD using a diluted aluminum nitrade (Al(NO$_3$).9$H_2O$) solution. The sensitivity of CO gas in the SnO$_2$gas sensor with an $Al_2$O$_3$surface protective layer was significantly decreased. But that of CH$_4$gas remained almost same with pure SnO$_2$gas sensor. This result shows that the selectivity of CH$_4$gas is increased because of the $Al_2$O$_3$surface protective layer. In the case of SnO$_2$gas sensors with Pt-doped $Al_2$O$_3$surface protective layers, low sensing property to CO gas and high sensing property to CH$_4$were observed. This results in the increasing of selectivity of CH$_4$gas selectivity are discussed.

• Journal of the Korean Electrochemical Society
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• v.23 no.2
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• pp.25-38
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• 2020

Photoelectrochemical water splitting has been considered as the most promising technology for generating hydrogen energy. Transition metal dichalcogenide (TMD) compounds have currently attracted tremendous attention due to their outstanding ability towards the catalytic water-splitting hydrogen evolution reaction (HER). Herein, we report the synthesis method of various transition metal dichalcogenide including MoS₂, MoSe₂, WS₂, and WSe₂ nanosheets as excellent catalysts for solar-driven photoelectrochemical (PEC) hydrogen evolution. Photocathodes were fabricated by growing the nanosheets directly onto Si nanowire (NW) arrays, with a thickness of 20 nm. The metal ion layers were formed by soaking the metal chloride ethanol solution and subsequent sulfurization or selenization produced the transition metal chalcogenide. They all exhibit excellent PEC performance in 0.5 M H₂SO₄; the photocurrent reaches to 20 mA cm^-2 (at 0 V vs. RHE) and the onset potential is 0.2 V under AM1.5 condition. The quantum efficiency of hydrogen generation is avg. 90%. The stability of MoS₂ and MoSe₂ is 90% for 3h, which is higher than that (80%) of WS₂ and WSe₂. Detailed structure analysis using X-ray photoelectron spectroscopy for before/after HER reveals that the Si-WS₂ and Si-WSe₂ experience more oxidation of Si NWs than Si-MoS₂ and Si-MoSe₂. This can be explained by the less protection of Si NW surface by their flake shape morphology. The high catalytic activity of TMDs should be the main cause of this enhanced PEC performance, promising efficient water-splitting Si-based PEC cells.

• Clean Technology
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• v.20 no.3
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• pp.306-313
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• 2014

Nanoporous $TiO_2$ films are commonly used as working electrodes in dye-sensitized solar cells (DSSCs). So far, there have been attempts to synthesize films with various $TiO_2$ nanostructures to increase the power-conversion efficiency. In this work, vertically aligned rutile $TiO_2$ nanorods were grown on fluorinated tin oxide (FTO) glass by hydrothermal synthesis, followed by deposition of an anatase $TiO_2$ film. This new method of anatase $TiO_2$ growth avoided the use of a seed layer that is usually required in hydrothermal synthesis of $TiO_2$ electrodes. The dense anatase $TiO_2$ layer was designed to behave as the electron-generating layer, while the less dense rutile nanorods acted as electron-transfer pathwaysto the FTO glass. In order to facilitate the electron transfer, the rutile phase nanorods were treated with a $TiCl_4$ solution so that the nanorods were coated with the anatase $TiO_2$ film after heat treatment. Compared to the electrode consisting of only rutile $TiO_2$, the power-conversion efficiency of the rutile-anatase hybrid $TiO_2$ electrode was found to be much higher. The total thickness of the rutile-anatase hybrid $TiO_2$ structures were around $4.5-5.0{\mu}m$, and the highest power efficiency of the cell assembled with the structured $TiO_2$ electrode was around 3.94%.