• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.17 no.4
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• pp.297-302
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• 2005

Since the use of CFC and HCFC refrigerants are to be restricted due to the depletion of ozone layer, this experiment applies the $NH_3$ gas to study the performance characteristics of $NH_3$ refrigeration system by the superheat control for improving the energy efficiency. The experiments are carried out for the condensing pressure of refrigeration system from 1,500 kPa to 1,600 kPa and for degree of superheat from $0^{\circ}C\;to\;10^{\circ}C$ at each condensing pressure. As a result of experiment, when the degree of superheat is $0^{\circ}C$ at each condensing pressure, the refrigeration system has the highest performance.

• Journal of the Optical Society of Korea
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• v.16 no.2
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• pp.174-180
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• 2012

In this study, the feasibility of spectral domain optical Doppler tomography for measuring blood flow characteristics in a micro-tube was demonstrated through several experiments. The use of an SD-ODT system in blood flow measurement can provide high resolution images (5 microns resolution). We prepared three capillary tubes to reveal the effect of different concentrations of hematocrit ratio (HR). One tube serves as the control. The two other tubes contained different concentrations of HR (5%, 25%). Three different capillary tube inlet flow velocities were tested in the present study. The Reynolds number (Re) which is based on the capillary tube inner diameter ranges from Re=6 to 48. We calculated a Doppler shift of the power spectrum of the temporal interference fringes with Kasai autocorrelation function to achieve the velocity profile of the flow. As a result, SD-ODT systems could not detect the cell depletion layer in the present study due to the limitation of spatial resolution. Nevertheless, these systems were proven to be capable of observing the RBCs of blood.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.49-49
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• 2008

ZnO-based varistors have been widely used for voltage stabilization or transient surge suppression in electric power systems and electronic circuits. Recently, It has reported that the varistor behavior with nonlinear coefficient of 6~17 in Mn-doped ZnO. In this study we have chosen the composition of ZnO-$TeO_2-Mn_3O_4$ (ZTM) system to the purpose of whether varistor behavior appeared in doped ZnO by the solid state sintering or not. We investigated the sintering and electric properties of 0.5~3.0 at% Mn doped ZnO-1.0 at% $TeO_2$ system. Electrical properties, such as current-voltage (I-V), capacitance-voltage (C-V), and impedance spectroscopy were conducted. $TeO_2$ itself melts at $732^{\circ}C$ in air but forms the $ZnTeO_3$ phase with ZnO as increasing temperature and therefore retards the densification of ZnO to $1000^{\circ}C$. The average grain size of sintered samples was at about $3{\mu}m$ and decreased with increasing Mn contents. It was found that a good varistor characteristics were developed in ZTM system sintered at $1100^{\circ}C$ (nonlinear coefficient $\alpha$ ~ 60). The results of C-V characteristics such as barrier height ($\Theta$), donor density ($N_d$), depletion layer (W), and interface state density ($N_t$) in ZTM ceramics were $4\times10^{17}cm^{-3}$, 0.7 V, 40 nm, and $1.6\times10^{12}cm^{-2}$, respectively. It will be discussed about the stability and homogeneity of grain boundaries using distribution parameter ($\alpha$) simulated with the Z(T)"-logf plots in ZTM system.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.168-168
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• 2008

Dimension of a transistor has rapidly shrunk to increase the speed of device and to reduce the power consumption. However, it is accompanied with several problems like direct tunneling through the gate dioxide layer and low conductivity characteristic of poly-Si gate in nano-region. To cover these faults, study of new materials is urgently needed. Recently, high dielectric materials like $Al_2O_3$, $ZrO_2$, and $HfO_2$ are being studied for equivalent oxide thickness (EOT). However, poly-Si gate is not compatible with high-k materials for gate-insulator. Poly Si gate with high-k material has some problems such as gate depletion and dopant penetration problems. Therefore, new gate structure or materials that are compatible with high-k materials are also needed. TiN for metal/high-k gate stack is conductive enough to allow a good electrical connection and compatible with high-k materials. According to this trend, the study on dry etching of TiN for metal/high-k gate stack is needed. In this study, the investigations of the TiN etching characteristics were carried out using the inductively coupled $BCl_3$-based plasma system and adding $Cl_2$ gas. Dry etching of the TiN was studied by varying the etching parameters including $BCl_3$/Ar gas mixing ratio, RF power, DC-bias voltage to substrate, and $Cl_2$ gas addition. The plasmas were characterized by optical emission spectroscopy analysis. Scanning electron microscopy was used to investigate the etching profile.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.22 no.1
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• pp.22-28
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• 2009

We investigated the sintering and electric properties of ZnO-1.0 at% $TeO_2$ (ZT1) and 1.0 at% Mn-doped ZT1(ZT1M1) system. $TeO_2$ itself melts at $732^{\circ}C$ in air but forms the $ZnTeO_3$ or $Zn_2Te_3O_8$ phase with ZnO as increasing temperature and therefore retards the densification of ZnO to $1000^{\circ}C$. In ZT1M1 system, also, the densification of ZnO was retarded up to $1000^{\circ}C$ and then reached > 90% of theoretical density above $1100^{\circ}C$. It was found that a good varistor characteristics(nonlinear coefficient $a{\sim}60$) were developed in ZT1M1 system sintered at $1100^{\circ}C$ due to Mn which known as improving the nonlinearity of ZnO varistors. The results of C-V characteristics such as barrier height (${\Phi}_b$), donor density ($N_D$), depletion layer (W), and interface state density ($N_t$) in ZT1M1 ceramics were $1.8{\times}10^{17}cm^{-3}$, 1.6 V, 93 nm, and $1.7{\times}10^{12}cm^{-2}$, respectively. Also we measured the resistance and capacitance of grain boundaries with temperature using impedance and electric modulus spectroscopy. It will be discussed about the stability and homogeneity of grain boundaries using distribution parameter ($\alpha$) simulated with the Z(T)"-logf plots.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.32 no.8
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• pp.612-620
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• 2008

New alternative refrigerants have been developed due to the ozone layer depletion and global warming. For this reason, carbon dioxide is believed to be a promising refrigerant for use in air conditioners and heat pumps. Evaporative heat transfer characteristics and pressure drop of $CO_2$ with outer diameter of 5 mm in inclined ($45^{\circ}$) smooth and micro-fin tubes have been investigated by the experiments with respect to several test conditions such as mass fluxes, heat fluxes, evaporation temperatures in this study. The inclined ($45^{\circ}$) smooth and micro-fin tubes with length of 1.44 m were installed to measure the evaporative heat transfer coefficients of $CO_2$ and heat was supplied to the refrigerant by direct heating method where the test tube was uniformly heated by electricity. The tests were conducted at mass fluxes from 212 to $656\;kg/m^2s$, heat fluxes from 15 to $60\;kW/m^2$ and evaporation temperatures from -10 to $20^{\circ}C$. The heat transfer coefficients of $CO_2$ are slightly increased with increasing mass flux, and the heat transfer characteristics in the inclined ($45^{\circ}$) tubes are enhanced about $5{\sim}10%$ compared with those in horizontal or vertical tubes.

• Solar Energy
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• v.17 no.4
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• pp.23-33
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• 1997

In this paper, performance of various working fluids is evaluated for the closed Ocean Thermal Energy Conversion(OTEC) power plant operating on Rankine cycle. The evaporator and condenser are modeled via UA and LMTD method while turbine and pump are modeled by specifying isentropic efficiencies. R22, Propane, Propylene, R134a, R125, R143a, R32, R410A and Ammonia are used as working fluids. Results show that newly developed fluids such as R410A and R32 that do not cause stratospheric ozone layer depletion perform as well as R22 and ammonia. The superheat at the evaporator exit and subcooling at the condenser exit do not affect the performance of the simple OTEC power cycle. Turbine efficiency and heat exchanger size influence greatly the performance of the Rankine cycle. Finally, it was shown that closed OTEC power plants can practically generate electricity when the difference in warm and cold sea water inlet temperatures is greater than $20^{\circ}C$.

• Archives of Pharmacal Research
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• v.27 no.2
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• pp.217-224
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• 2004

Previously, we reported that water-extracted Acanthopanax senticasus exhibited anti-meta-static activity by stimulating the immune system. In this study, we fractionated glycoproteins (EN-SP) from the soluble protein layer (GF-AS) of A. senticasus and determined their basic chemical properties. We also investigated the anti-tumor and immunostimulating activities of the fractionated glycoprotein, EN-SP. We found that intravenous (i.v.) administration of GF-AS dramatically inhibited metastasis of colon26-M3.1 carcinoma cells to the lung in a dose-dependent manner. In vitro analysis showed GF-AS to enhance the proliferation of splenocytes. GF-AS also stimulated peritoneal macrophage, which was followed by the production of various cytokines such as IL-1$\beta$, TNF-$\alpha$, IL-12 and IFN-${\gamma}$. Furthermore, the production of these cytokines was partially blocked when peritoneal macrophage was cultured with the polyclonal antibodies against GF-AS. The depletion of NK cells by rabbit anti-asialo GM1 serum partly abolished the inhibitory effect of GF-AS on lung metastasis of colon26-M3.1 cells. Using gel filtration, EN-SP, an active glycoprotein fraction, is isolated from GF-AS. While both GF-AS and EN-SP stimulated the proliferatation of splenocytes of normal mice, EN-SP showed higher anti-metastatic activity and more potently stimulated the proliferation of splenocytes compared to GF-AS. These results suggest the use of EN-SP, the fractionated glycoprotein from A. senticasus, can be used as a therapeutical reagent to prevent or inhibit tumor metastasis.

• Industry Promotion Research
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• v.1 no.2
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• pp.7-11
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• 2016

$SnO_2$ films were annealed in a vacuum atmosphere conditions to research the temperature dependency of current-voltage characteristics, crystal structure and chemical properties. The $SnO_2$ film annealed in a vacuum became an amorphous structure, but the degree of amorphous structure changed in accordance with the content of oxygen vacancy, which increased at film annealed at $100^{\circ}C$ and then decreased over the sample at annealed at $150^{\circ}C$. Because the crystallinity was affected the content of oxygen vacancy. The oxygen vacancy as carriers disappeared with increasing the annealing temperatures, and the depletion layer increased. Therefore the content of exiton as optical properties increased with becoming the amorphous structure. So the intensity of PL spectra increased with increasing the annealing temperature.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.41 no.3
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• pp.15-30
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• 2004

In this paper, an analytical modeling for the dark and photo-current characteristics of a buried-gate short- channel GaAs MESFET is presented. The presented model shows that the increase of drain current under illumination is largely due to not the increase of photo-conductivity in the neutral region but the narrowing effect of the depletion layer width. The carrier density profile within the neutral region is derived from solving the carrier continuity equation one-dimensionally. In deriving the photo-generated current, we assume that the photo-current is compensated with the thermionic emission current at the gate-channel interface. Moreover, the two-dimensional Poisson's equation is solved by taking into account the drain-induced longitudinal field effect. In conclusion, the proposed model seems to provide a reasonable explanation for the dark and photo current characteristics in a unified manner.