• 한국전산유체공학회:학술대회논문집
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• 2009.11a
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• pp.121-128
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• 2009

During a hypothetical high-pressure accident in a nuclear power plant (NPP), molten corium can be ejected through a breach of a reactor pressure vessel (RPV) and dispersed by a following jet of a high-pressure steam in the RPV. The dispersed corium is fragmented into smaller droplets in a reactor cavity of the NPP by the steam jet and released into other compartments of the NPP by a overpressure in the cavity. The fragments of the corium transfer thermal energy to the ambient air in the containment or interact chemically with steam and generate hydrogen which may be burnt in the containment. The thermal loads from the ejected molten corium on the containment which is called direct containment heating (DCH) can threaten the integrity of the containment. DCH in a NPP containment is related to many physical phenomena such as multi-phase hydrodynamics, thermodynamics and chemical process. In the evaluation of the DCH load, the melt dispersion rates depending on the RPV pressure are the most important parameter. Mostly, DCH was evaluated by using lumped-analysis codes with some correlations obtained from experiments for the dispersion rates. In this study, MC3D code was used to evaluate the dispersion rates in the APR1400 NPP during the high-pressure accidents. MC3D is a two-phase analysis code based on Eulerian four-fields for melt jet, melt droplets, gas and water. The dispersion rates of the corium melt depending on the RPV pressure were obtained from the MC3D analyses and the values specific to the APR1400 cavity geometry were compared to a currently available correlation.

• 대한공업교육학회지
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• v.32 no.2
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• pp.188-198
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• 2007

Platinum nanoparticles loading on carbon nanotube was carried out by impregnation of hexachloro platinate(IV) from hydrogen hexachloro platinate(IV) hydrate dissolved solution without using reduction agents, and heating the hexachloro platinate(IV) impregnated carbon nanotube up to $400^{\circ}C$. The amounts of impregnated hexachloro platinate(IV) on to carbon nanotube were measured with UV-visible spectrophotometer. The TG, XRD, and TEM analysis were performed to confirm the platinum particles loading and distribution on carbon nanotube. The average platinum particles size on carbon nanotube was under 2 nm by heating the hexachloro platinate(IV) up to $400^{\circ}C$ in spite of non-using reduction agents, while the average size increased due to the agglomeration of some particles by heating them up to $800^{\circ}C$. Therefore, uniformly distributed platinum nanoparticles loading on carbon nanotube can be obtained from simple impregnation of hexachloro platinate(IV) from solution and heating it up to $400^{\circ}C$.

• KIEAE Journal
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• v.14 no.1
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• pp.15-22
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• 2014

Among the various building envelope elements, the glass area takes up the largest portion in the office building design. However, a large area of glass can cause problems such as excessive solar radiation, thermal comfort, and glare. Thus it is important to install the glass area to an appropriate level, and control solar radiation and inflow of daylight with blind devices. This study aims to improve the visual performance of the work plane through the automatic control of the venetian blinds. A total of eight kinds of control strategies were chosen; Case 1 does not control the blinds, Case 2 with the blind slats fixed at the angle of 0 degree, Case 3 to 6 using the existing blind control programs, and Case 7 and 8 with improved blind control. Case 3 with 90 degrees had the best energy performance, but the average indoor illuminance was 113lux, which is below the standards. Cases 4 and 5 showed higher levels of interior daylight illuminance with the average of 281lux and 403lux respectively. However, the fixed angles may have difficulties controlling excessive direct sunlight coming into the room and may cause glare. Cases 6 and 7 used sun tracking angle control and cut-off angle control, and the average interior illuminance was measured 250lux and 385lux respectively. Case 8 used the cut-off angle control in an hourly manner, satisfying the standard illuminance of 400lux with an average interior illuminance of 561lux. It was evaluated to be the best method to control direct solar radiation and to guarantee proper level of interior illumination.

• 한국신재생에너지학회:학술대회논문집
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• 2007.11a
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• pp.297-300
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• 2007

In this study, we have attempted a new method to enhance the coloring of dye on the $TiO_2$ surface in the dye sensitized solar cell. In the conventional coloring process in a dye sensitized solar cells, dye is absorbed by the covalent bond between TiO2 and dye molecule while the photo-electrode coated with $TiO_2$ layer is soaked in dye solution for about 12-24 hours. But this process takes long time, so we have researched more effective and faster way than the conventional process by applying electric field. Three kinds of electric power such as direct voltage, alternating voltage and pulse voltage were applied to the transparent conducting oxide during the coloring process. As a result, we achieved improved power, fill factor and efficiency of dye-sensitized solar cell in case of applying direct voltage and pulse voltage. In contrast, alternating voltage tend to reduce the dye adsorption on the $TiO_2$ surface and hence the efficiency. We measured the absorption spectra of dye by UV-VIS spectrophotometer before and after soaking the $TiO_2$ in the dye and found no characteristic change in the dye was observed. In this study, we researched on shortening time of coloring process which spent much time in the whole process.

• Advances in aircraft and spacecraft science
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• v.5 no.5
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• pp.581-594
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• 2018

This paper is the follow-on of a previous paper by the author where it was pointed out that the forthcoming, manned exploration missions to Mars, by means of complex geometry spacecraft, involve the study of phenomena like shock wave-boundary layer interaction and shock wave-shock wave interaction also along the entry path in Mars atmosphere. The present paper focuses the chemical effects both in the shock layer and on the surface of a test body along the Mars orbital entry and compares these effects with those along the Earth orbital re-entry. As well known, the Mars atmosphere is almost made up of Carbon dioxide whose dissociation energy is even lower than that of Oxygen. Therefore, although the Mars entry is less energized than the Earth re-entry, one can expect that the effects of chemistry on aerodynamic quantities, both in the shock layer and on a test body surface, are different from those along the Earth re-entry. The study has been carried out computationally by means of a direct simulation Monte Carlo code, simulating the nose of an aero-space-plane and using, as free stream parameters, those along the Mars entry and Earth re-entry trajectories in the altitude interval 60-90 km. At each altitude, three chemical conditions have been considered: 1) gas non reactive and non-catalytic surface, 2) gas reactive and non-catalytic surface, 3) gas reactive and fully-catalytic surface. The results showed that the number of reactions, both in the flow and on the nose surface, is higher for Earth and, correspondingly, also the effects on the aerodynamic quantities.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.380.2-380.2
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• 2014

Direct synthesis of graphene using a chemical vapor deposition (CVD) has been considered a facile way to produce large-area and uniform graphene film, which is an accessible method from an application standpoint. Hence, their fundamental understanding is highly required. Unfortunately, the CVD growth mechanism of graphene on Cu remains elusive and controversial. Here, we present the effect of graphene growth parameters on the number of graphene layers were systematically studied and growth mechanism on copper substrate was proposed. Parameters that could affect the thickness of graphene growth include the pressure in the system, gas flow rate, growth pressure, growth temperature, and cooling rate. We hypothesis that the partial pressure of both the carbon sources and hydrogen gas in the growth process, which is set by the total pressure and the mole fraction of the feedstock, could be the factor that controls the thickness of the graphene. The graphene on Cu was grown by the diffusion and precipitation mode not by the surface adsorption mode, because similar results were observed in graphene/Ni system. The carbon-diffused Cu layer was also observed after graphene growth under high CH4 pressure. Our findings may facilitate both the large-area synthesis of well-controlled graphene features and wide range of applications of graphene.

• Journal of Electrochemical Science and Technology
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• v.8 no.2
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• pp.87-95
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• 2017

Enzymatic fuel cells are promising low cost, compact and flexible energy resources. The basis of enzymatic fuel cells is transfer of electron from enzyme to the electrode surface and vice versa. Electron transfer is done either by direct or mediated electron transfer (DET/MET), each one having its own advantages and disadvantages. In this study, the DET and MET of laccase-based biocathodes are compared with each other. The DET of laccase enzyme has been studied using two methods; assemble of needle-like carbon nanotubes (CNTs) on the electrode, and CNTs/Nafion polymer. MET of laccase enzyme also is done by use of ceramic electrode containing, ABTS (2,2'-azino-bis [3-ethylbenzthiazoline-6-sulphonic acid]) /sol-gel. Cyclic voltammetric results of DET showed a pair of well-defined redox peaks at $200{\mu}A$ and $170{\mu}A$ in a solution containing 5and $10{\mu}M$ o-dianisidine as a substrate for needle-like assembled CNTs and CNTs-Nafion composite respectively. In MET method using sol-gel/ABTS, the maximum redox peak was $14{\mu}A$ in the presence of 15 M solution o-dianisidine as substrate. The cyclic voltammetric results showed that laccase immobilization on needle-like assembled CNTs or CNTs-Nafion is more efficient than the sol-gel/ABTS electrode. Therefore, the expressed methods can be used to fabricate biocathode of biofuel cells or laccase based biosensors.

• Journal of the Korean Ceramic Society
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• v.56 no.3
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• pp.211-232
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• 2019

Porous ceramics are promising materials for a number of functional and structural applications that include thermal insulation, filters, bio-scaffolds for tissue engineering, and preforms for composite fabrication. These applications take advantage of the special characteristics of porous ceramics, such as low thermal mass, low thermal conductivity, high surface area, controlled permeability, and low density. In this review, we emphasize the direct foaming method, a simple and versatile approach that allows the fabrication of porous ceramics with tailored microstructure, along with distinctive properties. The wet foam stability is achieved under the controlled addition of amphiphiles to the colloidal suspension, which induce in situ hydrophobization, allowing the wet foam to resist coarsening and Ostwald ripening upon drying and sintering. Different components, like contact angle, adsorption free energy, air content, bubble size, and Laplace pressure, play vital roles in the stabilization of the particle stabilized wet foam to the porous ceramics. The mechanical behavior of the load-displacements curves of sintered samples was investigated using Herzian indentations testes. From the collected results, we found that microporous structures with pore sizes from 30 ㎛ to 570 ㎛ and the porosity within the range from 70% to 85%.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.287.1-287.1
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• 2013

The Isolation of few-layered transition metal dichalcogenides has mainly been performed by mechanical and chemical exfoliation with very low yields. in particular, the two-dimensional layer of molybdenum disulfide (MoS2) has recently attracted much interest due to its direct-gap property and potential application in optoelectronics and energy harvesting. However, the synthetic approach to obtain high-quality and large-area MoS2 atomic thin layers is still rare. In this account, a controlled thermal reductionsulfurization method is used to synthesize large-MoOx thin films are first deposited on Si/SiO2 substrates, which are then sulfurized (under vacuum) at high temperatures. Samples with different thicknesses have been analyzed by Raman spectroscopy and TEM, and their photoluminescence properties have been evaluated. We demonstrated the presence of single-, bi-, and few-layered MoS2 on as-grown samples. It is well known that the electronic structure of these materials is very sensitive to the number of layer, ranging from indirect band gap semiconductor in the bulk phase to direct band gap semiconductor in monolayers. This synthetic approach is simple, scalable, and applicable to other transition metal dichalcogenides. Meanwhile, the obtained MoS2 films are transferable to arbitrary substrates, providing great opportunities to make layered composites by stacking various atomically thin layers.

• Journal of Power Electronics
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• v.19 no.1
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• pp.265-277
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• 2019

The application of shunt active power filters (S-APFs) is considered to be the most popular approach for harmonic compensation due to its high simplicity, ease of installation and efficient control. Its functionality mainly depends upon the rapidness and precision of its internally built control algorithms. A S-APF is generally operated in the current controlled mode (CCM) with the detection of harmonic load current. Its operation may not be appropriate for the distributed power generation system (DPGS) due to the wide dispersion of nonlinear loads. Despite the fact that the voltage detection based resistive-APF (R-APF) appears to be more appropriate for use in the DPGS, the R-APF experiences poor performance in terms of mitigating harmonics and parameter tuning. Therefore, this paper introduces a direct harmonic voltage detection based control approach for the S-APF that does not need a remote harmonic load current since it only requires a local point of common coupling (PCC) voltage for the detection of harmonics. The complete design procedure of the proposed control approach is presented. In addition, experimental results are given in detail to validate the performance and superiority of the proposed method over the conventional R-APF control. Thus, the outcomes of this study approve the predominance of the discussed strategy.