• The KSFM Journal of Fluid Machinery
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• v.17 no.2
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• pp.41-47
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• 2014

Experimental results are given for the vertical motion of water in the water chambers for wave energy converter aligned along the wave propagation direction in order to avoid the impulsive wave forces. This paper mainly focuses on the property of the amplitude of the vertical motion of the water surface in the chambers. The amplification has been investigated by dimensionless parameters of wave period to resonance period ratio of the U-shaped oscillation, $T/T_r$, chamber size to wave length ratio, l/L, water depth to wave length ratio, h/L, amplitude of up-down motion of water particles to draft of the front wall ratio, ${\zeta}/D$. It has been shown that l/L should be less than 0.1 and as $T/T_r$ approaches unity the up-down of the water in the chambers is amplified. Also, the structure of the walls which form th water chambers has been examined roughly. It is deduced that the chambers set on both sides of the hull of a single-point moored floating vessel is preferable to those set along a fixed structure such as breakwaters.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.57 no.2
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• pp.140-145
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• 2008

The purpose of this paper is to discuss the fabrication of $\beta$-PVDF($\beta$-Polyvinylidene fluoride, ${\beta}-PVF_2$) organic thin films using the vapor deposition method. Vapor deposition was performed under the following conditions: the temperature of evaporator, the applied electric field, and the pressure of reaction chamber were $270^{\circ}C$, 142.4 kV/cm, and $2.0{\times}10^{-5}\;Torr$, respectively. The molecular structure of the evaporated organic thin films were evaluated by a FT-IR. The results showed that the characteristic absorption peaks of $\beta$-form crystal increase from 72% to 95.5% with an increase in the substrate temperature. In the analysis of the electric characteristics, the abnormal increases in the relative dielectric constant and the dielectric loss factor in the regions of low frequency and high temperature are known to be caused by inclusion of impurity carriers in the PVDF organic thin films. In order to analyze quantitatively the abnormalities in the conductivity mechanism caused by ionic impurities, the product of the ion density and the mobility that affect the electrical property in polymeric insulators is analyzed. In the case of a specimen produced by varying the substrate temperature from $30^{\circ}C$ to $105^{\circ}C$, the product of mobility and the ion density decreased from $4.626{\times}10^8$ to $8.47{\times}10^7/V{\cdot}cm{\cdot}s$. This result suggests that the higher the substrate temperature is maintained, the better excluded the impurities are, and the more electrically stable material can be obtained.

• Journal of ILASS-Korea
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• v.27 no.2
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• pp.84-93
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• 2022

To implement carbon-neutrality in transportation sectors until 2050, hydrogen is considered a promising fuel for internal combustion engines because hydrogen does not contain carbon itself. Although hydrogen does not emit CO₂ emission from its combustion process, the low energy density in a volume unit hinders the adoption of hydrogen. Therefore, the understanding of hydrogen jet behavior and measurement of equivalence ratio must be conducted to completely implement the high-pressure hydrogen direct injection. The main objective of this research is feasibility test of hydrogen local equivalence ratio measurement by laser-induced breakdown spectroscopy (LIBs). To visualize the macroscopic structure of hydrogen jet, high-speed schlieren imaging was conducted. Moreover, LIBs has been adopted to validate the feasibility of hydrogen local equivalence ratio measurement. The hydrogen injection pressure was varied from 4 MPa to 8 MPa and injected in a constant volume chamber where the ambient pressure was 0.5 MPa. The increased injection pressure extends the vertical penetration of hydrogen jet. Due to the higher momentum supply when the injection pressure is high, the hydrogen has easily diffused in all directions. As the laser trigger timing has delayed, the low hydrogen atomic emission was detected due to the longer mixture formation time. Based on equivalence ratio measurement results, LIBs could be applied as a methodology for hydrogen local equivalence ratio measurement.

• Tribology and Lubricants
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• v.20 no.5
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• pp.272-277
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• 2004

This study deals with the friction and wear characteristics of C-N coated spur gear. The PSII apparatus was built and a SCM415 test piece and test gear with steel substrate was treated with carbon nitrogen by this apparatus. The composition and structure of the surface layer were analyzed and compared with that of PVD coated TiN layer. It was found that both of friction coefficient of C-N coating and TiN coating decreased with increasing load, however, C-N coating showed relatively lower friction coefficient than that of TiN coating. We was investigated the effect of C-N coating on hardness, friction and wear. The TiN coated gear showed a more serious friction phenomena than that of C-N coated gear. It was considered that coating of TiN, which was conducted at a vacuum chamber at about 500$^{\circ}C$, results in a tempering of base material that causes microstructural change, which in turn resulted in decreasing of hardness. The C-N coated gear and pinion had higher wear resistance that of TiN coated gear and pinion. C-N coating significantly improved the friction and wear resistance of the gear.

• The KSFM Journal of Fluid Machinery
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• v.17 no.5
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• pp.11-18
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• 2014

Chilled Beam system is the kind of water-air system which reduces the conveyance energy for air conditioning as well as allows efficient installation and comfortable indoor environment, and has been increasingly popular mainly in Europe. To effectively install such Chilled Beam system domestically, it is necessary to develop the product considering domestic climatic condition and the requirements for air conditioning system, and particularly the way to deal with condensation during operation of cooling system in summer shall be provided. In this study, the optimal design on induction structure of Chilled Beam unit was carried out through a numerical method, and the performance test for the prototype of unit was conducted in a real-scale experiment facilities of Chilled Beam unit. While the flowrate of 1st air is 101.3 CMH, the pressure in pressure chamber is 158.7 Pa and the cooling capacities of 1st air side and 2nd air side are 498.1 W and 709.5 W respectively.

• Advances in concrete construction
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• v.10 no.1
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• pp.13-20
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• 2020

Steel corrosion in embedded steel causes a significant durability problems and this usually propagates to structural degradation. Large-scaled concrete structures, PSC (Pre-stressed Concrete) or RC (Reinforced Concrete) structures, are usually constructed with mass concrete and require quite a long construction period. When they are located near to sea shore, chloride ion penetrates into concrete through direct or indirect exposure to marine environment, and this leads durability problems. Even if the structures are sheltered from chloride ingress outside after construction, the chloride contents which have been penetrated into concrete during the long construction period are differently evaluated from the initially mixed chloride content. In the study, chloride profiles in cores extracted from anchorage concrete block in two large-scaled suspension bridge (K and P structure) are evaluated considering the exposure periods and conditions. Total 21 cores in tendon room and chamber room were obtained, and the acid-soluble chlorides and compressive strength were evaluated for the structures containing construction period around 3 years. The test results like diffusion coefficient and surface chloride content from the construction joint and cracked area were also discussed with the considerations for maintenance.

• Bulletin of the Korean Chemical Society
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• v.31 no.2
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• pp.372-378
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• 2010

Membrane disruption by an antimicrobial peptide, protegrin-1 (PG-1), was investigated by measuring the $^2H$ solid-state nuclear magnetic resonance (SSNMR) spectra of 1-palmitoyl-$d_{31}$-2-oleoyl-sn-glycero-3-phosphatidylcholine (POPC_$d_{31}$) in the mixture of PG-1 and POPC_$d_{31}$ lipids deposited on thin cover-glass plates. The experimental line shapes of anisotropic $^2H$ SSNMR spectra measured at various peptide-to-lipid (P/L) ratios were simulated reasonably by assuming the mosaic spread of bilayers containing pore structures or the coexistence of the mosaic spread of bilayers and a fast-tumbling isotropic phase. Within a few days of incubation in the hydration chamber, the pores were formed by the peptide in the POPC_$d_{31}$ and POPC_$d_{31}$/cholesterol membranes. However, the formation of the pores was not clear in the POPC_$d_{31}$/1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylglycerol (POPG) membrane. Over a hundred days after hydration, a rapidly rotating isotropic phase increased in the POPC_$d_{31}$ and the POPC_$d_{31}$/cholesterol membranes with the higher P/L ratios, but no isotropic phase appeared in the POPC_$d_{31}$/POPG membrane. Cholesterol added in the POPC bilayer acted as a stabilizer of the pore structure and suppressed the formation of a fast-tumbling isotropic phase.

• Bulletin of the Korean Chemical Society
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• v.34 no.6
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• pp.1689-1692
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• 2013

Food is a common source of chromium (Cr) exposure. However, it is difficult to analyze Cr in complex food matrices by using inductively coupled plasma mass spectrometry (ICP-MS) because the major isotope, $^{52}Cr$, is masked by interference generated by the sample matrix and the plasma gas. Among the systems available to minimize interference, the recently developed collision-reaction interface (CRI) has a different structure relative to that of other systems (e.g., collision cell technology, octopole reaction system, and dynamic reaction cell) that were designed as a chamber between the skimmer cone and quadrupole. The CRI system introduces collision or reaction gas directly into the plasma region through a modified hole of skimmer cone. We evaluated the use of an CRI ICP-MS system to minimize polyatomic interference of $^{52}Cr$ and $^{53}Cr$ in various foodstuffs. The $^{52}Cr$ concentrations measured in the standard mode were 2-3 times higher than the certified values. This analytical method based on an ICP-MS system equipped with a CRI of helium gas was effective for Cr analysis in complex food matrices.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.345.2-345.2
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• 2016

Alumina (Al2O3) doped zinc oxide (ZnO) films (AZO) have been prepared from 2 wt.% Al2O3 doped ZnO target by DC magnetron sputtering at a 2 mTorr (0.27 Pa) chamber pressure in (15 sccm) argon ambient. We obtained films of various opto-electronic properties by variation of target angle from 32.5o to 72.5o. At lower target angle deposited films show higher values in optical gap, mobility of charge carrier, carrier concentration, crystallite grain size, transmission range of wavelength, which are favorable characteristics of AZO as a transparent conducting oxide (TCO). At higher target angle the sheet resistance, work function, surface roughness for the AZO films increases. Measured haze ratio of the films changed lower to higher and size of characteristic surface structure of as deposited film ranges from ~40 nm to ~300 nm. By a combination of low and high target angle we obtained a textured TCO film with high conductivity.

• Journal of the korean academy of Pediatric Dentistry
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• v.43 no.4
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• pp.467-472
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• 2016

Successful root canal treatment can be obtained by the removal of microorganisms from the pulpal space of the root canal system through biomechanical technique with instruments and irrigation. Due to the difference in the dimension of the pulpal structure such as thin wall of the root, large portion of chamber, the primary teeth should be considered in a different way of approach. Traditionally, fluids have been dispensed passively into the root canals for improve the cleansing. The use of sodium hypochlorite as an irrigant in root canal treatment is widespread and common, because it meets requirements for the ideal irrigants.