• Proceedings of the KSME Conference
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• 2008.11a
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• pp.1409-1410
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• 2008

Layer manufacturing technology has been recently spotlighted as a promising candidate to fabricate porous scaffolds for tissue engineering, because it can provide three dimensional interconnectivity and different pore structures and on-demand scaffold design. This study aims to fabricate HA/PCL composite scaffolds for bone tissue engineering by a layer manufacturing technology, paste extruding deposition, and to characterize in vitro and in vivo biocompatibilities of the scaffolds. This study discusses the mechnical properties, proliferation and differentiation of osteogenic cells, and tissue in-growth and bone regeneration behavior using animal models.

• Proceedings of the Korea Society for Energy Engineering kosee Conference
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• 1999.11a
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• pp.211-216
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• 1999

One of the problems in a refrigerator operation is the frost formation on a cold surface of the evaporator. The frost layer is formed by the sublimation of water vapor when the surface temperature is below the freezing point. This frost layer is usually porous and formed on the cold surface of the evaporator. The frost layer on the surface of a evaporator will make side effect such as thermal resistance. However, these important factors have not been used in determining the defrosting period. In this report, a prediction taking into account the change of the fin efficiency due to the growth of the frost layer.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.346.1-346.1
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• 2014

Porous nano crystalline $TiO_2$ is currently used as a working electrode in a dye-sensitized solar cell (DSSC). The conventional working electrode is comprised of absorption layer (particle size:~20 nm) and scattering layer (particle size:~300 nm). We inserted window layer with 10 nm particle size in order to increase transmittance and specific surface area of $TiO_2$. The electrochemical impedance spectroscope analysis was conducted to analysis characterization of the electronic behavior. The Bode phase plot and Nyquist plot were interpreted to confirm the internal resistance caused by the insertion of window layer and carrier lifetime. The photocurrent that occurred in working electrode, which is caused by rise in specific surface area, increased. Accordingly, it was found that insertion of window layer in the working electrode lead to not only effectively transmitting the light, but also increasing of specific surface area. Therefore, it was concluded that insertion of window layer contributes to high conversion efficiency of DSSCs.

• Food Science and Biotechnology
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• v.14 no.4
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• pp.456-460
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• 2005

To enforce the maximum residue limit for residual hexane (0.005 g/kg) in commercially available Korean vegetable oil, convenient and accurate quantification methods were investigated. Using dual surrogate standards, pentane and heptane were dissolved in ethanol, and then added to hexane-tree sunflower oil for setting up the calibration curve. Gas Chromatograph-Flame Ionization Detector with a porous layer open tubular column, indicated good chromatographic separation of hexane from other inhibiting matrix components. The lowest calibration level was $0.5\;{\mu}g/g$, not exceeding a relative standard deviation of 10% (RSD%), and 1.0\;{\mu}g/g$ not exceeding a deviation of 22% RSD% using heptane as an internal standard for the Static headspace analysis by using a headspace auto-sampler and manual injection, respectively. The residual hexane was detected in nine of the samples among 87 vegetable oil samples purchased on the local market.

• Journal of the Korean Society of Visualization
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• v.14 no.1
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• pp.40-45
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• 2016

Elimination of the smear layer and bacteria in the root canal is the most important in the endodontic treatment, and various irrigation devices have been developed. Nevertheless, it is hard to eliminate the smear layer and bacteria completely. In this paper, a micro bubble irrigation system has been developed for the root canal cleaning of tooth. Micro bubbles are generated when pressurized fluids passing through a porous material inside a hand-piece nozzle, and the bubbly flows excited by ultrasonic vibration are observed using a high-speed camera and a microscope. The results show that the diameter and number of bubbles increases with the applied pressure, and there found an optimum excitation frequency in order to minimize the bubble size. From in-vitro tests, it is also verified that the developed bubble irrigation system has the ability of antibacterial and infection removal. Thus, this biocompatible system would be well suited for root canal cleaning.

• Earthquakes and Structures
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• v.12 no.6
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• pp.619-628
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• 2017

The intent of this paper is to investigate the propagation of Love waves in a dry sandy medium sandwiched between fiber-reinforced layer and prestressed porous half-space. Separate displacement components have been deduced in order to characterize the dynamics of individual materials. Using suitable boundary conditions, the frequency equation has been derived by means of separation of variables which reveals the significant role of reinforcement parameters, sandiness, thickness of layers, porosity and prestress on the wave propagation. The phase velocity of the Love wave has been discussed in accordance with its typical cases. In both cases when fiber-reinforced and dry sandy media are absent, the derived equation of Love type wave coincides with the classical Love wave equation. Numerical computations have been performed in order to graphically illustrate the dependencies of different parameters on phase velocity of Love waves. It is observed that the phase velocity decreases with the increase of parameters pertaining to reinforcement and prestress. The results have certain potential applications in earthquake seismology and civil engineering.

• Journal of Powder Materials
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• v.24 no.2
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• pp.102-107
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• 2017

Porous polytetrafluoroethylene (PTFE) thin films are fabricated by spin-coating using a dispersion solution containing PTFE powders, and their crystalline properties are investigated after thermal annealing at various temperatures ranging from 300 to $500^{\circ}C$. Before thermal annealing, the film is densely packed and consists of many granular particles 200-300 nm in diameter. However, after thermal annealing, the film contains many voids and fibrous grains on the surface. In addition, the film thickness decreases after thermal annealing owing to evaporation of the surfactant, binder, and solvent composing the PTFE dispersion solution. The film thickness is systematically controlled from 2 to $6.5{\mu}m$ by decreasing the spin speed from 1,500 to 500 rpm. A triboelectric nanogenerator is fabricated by spin-coating PTFE thin films onto polished Cu foils, where they act as an active layer to convert mechanical energy to electrical energy. A triboelectric nanogenerator consisting of a PTFE layer and Al metal foil pair shows typical output characteristics, exhibiting positive and negative peaks during applied strain and relief cycles due to charging and discharging of electrical charge carriers. Further, the voltage and current outputs increase with increasing strain cycle owing to accumulation of electrical charge carriers during charge-discharge.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.59 no.2
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• pp.363-368
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• 2010

In this work, electrochemiluminescence (ECL) cell using nanocrysralline $TiO_2$ electrode and Ru(II) complex (Ru${(bpy)_3}^{2+}$) is fabricated for low-cost high-efficient energy conversion device application. The nanocrysrallme $TiO_2$ layer (${\sim}10{\mu}m$ thickness) with large surface area (${\sim}360m^2$/g) can largely inject electrons from nanoporous $TiO_2$ electrode and allows the oxidation/reduction of Ru(II) complex in the nanopores. The cell structure is composed of a glass/ F-doped $SnO_2$(FTO)/ porous $TiO_2$/ Ru(II) complex in acetonitrile/ FTO/ glass. The nanocrysralline $TiO_2$ layer is prepared using sol-gel combustion method. The ECL efficiency of the cell consisting of the porous $TiO_2$ layers was 250 cd/W, which was higher than that consisting of only FTO electrode (50cd/W). The nanoporous $TiO_2$ layers wwas effective for increasine ECL intensities.

• 한국태양에너지학회:학술대회논문집
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• 2009.11a
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• pp.367-370
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• 2009

It is important to reduce a reflection of light as a solar cell is device that directly converts the energy of solar radiation to electrical energy in oder to improve efficiency of solar cells. The antireflection coating has proven effective in providing substantial increase in solar cell efficiency. This paper investigates the formation of thin film PSi(porous silicon) layer on the surface of crystalline silicon substrates without other ARC(antirefiection coating) layers. On the other hand the formation of $SO_{2}/SiN_x$ ARC layers on the surface of crystalline silicon substrates. After that, the structure of PSi and $SO_2/SiN_x$ ARC was investigated by SEM and reflectance. The formation of PSi layer and $SO_{2}/SiN_x$ ARC layers on the textured silicon wafer result about 5% in the wavelength region from 0.4 to $1.0{\mu}m$. It is achieved on the textured crystalline silicon solar cell that each efficiency is 14.43%, 16.01%.

• Proceedings of the KIEE Conference
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• 1999.07g
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• pp.3265-3267
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• 1999

Capacitance-type alcohol gas sensors using porous silicon (PS) layer as sensitive film were fabricated to measure low alcohol gas concentration. Though sensors using porous silicon layer have show high sensitivity by large internal surface area, there is still much room for improvement to measure low breath alcohol concentration especially at room temperature. In this work, to discuss the response properties against exposure to organic vapor for breath alcohol measurements on the basis of experimental results. we measured the variation of the capacitance for the range of 0 to 0.5% alcohol concentration, and observed the improvement of sensitivity by illumination of UV light. In addition, the effect of CO2 and N2 gases involved commonly in exhaling breath was estimated, and the same procedure against methanol vapor was executed to compare qualitatively with the capacitance characteristics by alcohol vapor.