• Journal of the Semiconductor & Display Technology
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• v.10 no.3
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• pp.29-33
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• 2011

Film growth rate and composition variation are numerically analyzed during the selective area growth of InGaN on the GaN triangular stripe microfacet in this study. Both the vapor phase diffusion and the surface diffusion are considered to determine the In composition on the InGaN surface. To obtain the In composition on the surface, flux of In atoms due to the surface diffusion is added to the concentration determined from the Laplace equation which is governing the gas phase diffusion. The solution model is validated by comparing the growth rates from the analyses to the experimental results of GaN and InN films. The In composition and resulting wave length are increased when the surface diffusion is considered. The In content is also increased according to the increasing mask width. The effect of mask width to the In content and wave length is increasing in the case of a small open region.

• Journal of the Semiconductor & Display Technology
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• v.10 no.1
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• pp.95-99
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• 2011

$(1-x)BaTiO_3+(x)Cd_5(PO_4)_3Cl$ ceramics were prepared by the conventional ceramic technique, i.e., solid state reaction at high temperature. The concentration of $Cd_5(PO_4)_3C$ was varied from 0.01 to 0.15 mole fraction. In order to study the phase transitions of our ceramics, the Raman scattering spectra were measured as functions of concentration x and temperature. It was found that the soluble limit of $Cd_5(PO_4)_3Cl$ in $BaTiO_3$ was the x=0.05 composition and $BaTiO_3$ phase disappeared above x=0.10. A new phase identified as $Ba_4Ti_3P_2O_{15}$ was detected in all samples of our compositions. The Curie temperature shifts up to $130^{\circ}C$ as the concentration x increases from zero to 0.05 and shift down to $95^{\circ}C$ as further increases to 0.08. For the increase of the Curie temperature, it is suggested that it can result from the inhibition of displacement of $Ti^{4+}$ in the distorted octahedron due to well dispersed $Ba_4Ti_3P_2O_{15}$ and $Cd_5(PO_4)_3Cl$ phase.

• Proceedings of the KIEE Conference
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• summer
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• pp.1477-1479
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• 2004

Increasing numbers of photovoltaic arrays are being connected to the power utility through the power conditioning systems (PCS). This has raised potential problems of network protection. If, due to the action of the PCS, the local network voltage and frequency remain within regulatory limits when the utility is disconnected, then islanding is said to occur. In this paper, the representative methods to prevent the islanding are described and a PSIM-based model and analysis of the reactive power variation (RPV) method are presented. A novel phase detector using the all-pass filter and digital phase locked loop (DPLL) is proposed especially for the single-phase PCS. Finally, this paper provides the simulation and experimental results with a single-phase 3kW prototype PCS. Islanding test method of IEEE Std. 929-2000 was performed for verification.

• Proceedings of the Korean Society of Rheology Conference
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• 2001.06a
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• pp.11-14
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• 2001

Our study have aimed to identify the deformation and breakup mechanism of minor phase in polymer blends under uniaxial enlongational flow. Experimentally, we measured the transient elongational viscosity of PS/HDPE blends using the uniaxial elongational rheometer at two temperatures. And we observed the evolution of blend morphology with elongation time. Morphological change was observed by quenching the specimen after deformation. If the viscosity variation of PS was compared with that of HDPE at each temperature, PS showed larger temperature dependence than HDPE. At 155$^{\circ}C$, the dispersed phase of larger size were easily affected by affine deformation. The initial spherical shape changed to flat ellipsoid at first, then flat ellipsoid to bulbous shape, and bulbous to thin thread and its satellites. But dispersed phase of smaller size showed the change from sphere to ellipsoid. At 175$^{\circ}C$, the dispersed phase were mostly deformed from spherical shape to ellipsoid. As a result, the morphological change of dispersed phase in elongational deformation is affected by chain flexibility and viscosity ratio. We need to further study to make sure the mechanism of elongation of viscoelastic polymer blends.

• The Bulletin of The Korean Astronomical Society
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• v.40 no.2
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• pp.45.1-45.1
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• 2015

Hayabusa is the JAXA's space mission that succeeded in sample-return from S-type asteroid (25143) Itokawa. During the rendezvous phase, more than a thousand of images were taken with the Asteroid Multi-band Imaging Camera (AMICA). It is valuable to study the regional variation of the optical properties on the asteroid using these images to know the generality and uniqueness of the returned samples. In addition, AMICA images are important in that they provide unique data set at low phase angle (i.e Sun-Itokawa-AMICA's angle) that have not been explored in the previous asteroidal missions. At the previous conference (2015 KAS spring meeting), we introduced our preliminary data analysis of AMICA data without considering the shape model of Itokawa and mentioned. In this study, we present a new result obtained through further analysis, taking account of the shape model of the asteroid. We thus utilized "plate_renderer" tool to derive Hapke model parameters at different terrains. It is found that the opposition amplitude (parameter B0) is consistent with those of the other S-type asteroids while the opposition width (parameter h) is significantly narrower than those of the other S-type asteroids. At this conference, we plan to describe the regional variation of photometric properties on Itokawa.

• The Transactions of the Korean Institute of Power Electronics
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• v.2 no.2
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• pp.29-34
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• 1997

In this paper, instantaneous controller of a single-phase PWM converter is realized using DSP. The stable PI gain of the input current and the DC link voltage control system is designed. The DC link voltage control system can be designed in continuous- time domain. But as for the input current control system, the descretizing effect cannot be ignored so it must be designed in descrete-time domain considering the calculation time. The capacitance estimating algorithm which can be acquired through the ripple voltage is proposed. By this algorithm the DC link capacitance can be estimated even under the transient state. Experimental results show the input power factor of 99.1% and the voltage variation rate of $\pm$5% according to the load variation.

• Journal of Korean Society for Atmospheric Environment
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• v.10 no.1
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• pp.24-31
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• 1994

Hourly variation of gaseous nitrous acid( HNO$_2$) concentration in Seoul air was monitored from Jan. 11 to SeP. 12, Nitrous acid concentration was determined by DS/IC over nine months of observation, HNO$_2$ range from 0.04 ppb to 5.5 ppb. Gor-tex tube as gaseous HNO$_2$generator in this study is thought to be more convenient and reproducible device than previous generator. As a result of NaOH instead of Na$_2$ CO$_3$/NaHCO$_3$ solution as the IC eluent, we could obtain more stable baseline. The concentration of the NaOH eluent was 15 mM . The limit of detection(3$\sigma$) of the liquid- Phase and gas phase nitrous acid of this method are 1.1ng/$m\ell$ , 0.04 n $\ell$ / $\ell$, respectively. The precisions evaluated by 10 replicate analysis of standard solution and standard gas generated are $\pm$1.59, $\pm$2. 89% RSD, respectively. Due to the lack of standard material for air, direct assessment of the accuracy was not possible. This study was applied to the analysis of Seoul ambient air and their results are reported herein.

• Ocean and Polar Research
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• v.30 no.3
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• pp.313-324
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• 2008

In order to understand the variation of ENSO-related oceanic environments in the tropical and North Pacific Ocean, spatio-temporal variations of sea surface temperature anomaly (SSTA) and sea surface height anomaly (SSHA) are analyzed from distributions of complex empirical orthogonal functions (CEOF). Correlations among warm pool variation, southern oscillation index, and ocean surface currents were also examined with respect to interannual variability of the warm pool in western tropical Pacific. Spatio-temporal distributions of the first CEOF modes for SSTA and SSHA indicate that their variabilities are associated with ENSO events, which have a variance over 30% in the North Pacific. The primary reasons for their variabilities are different; SST is predominantly influenced by the change of barrier layer thickness, while SSH fluctuates with the same phase as propagation of an ENSO episode in the zonal direction. Horizontal boundary of warm pool area, which normally centered around $149^{\circ}E$ in the tropics, seemed to be expanded to the middle and eastern tropical regions by strong zonal currents through the mature phase of an ENSO episode.

• Ocean and Polar Research
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• v.31 no.2
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• pp.189-198
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• 2009

Passive air samplers with polyurethane foam (PUF) disks were employed to determine seasonal gas phase variation of polycyclic aromatic hydrocarbons (PAHs) in ambient air on Anmyeon island from March 2007 to January 2008. Sum of 13 PAHs ranged between $3.5\;ng/m^3$ and $27.6\;ng/m^3$. Total PAHs during the heating season was 6.2 times higher than non-heating season. The dominant PAHs components during sampling periods were low and middle molecular weight PAHs including phenanthrene, fluoranthene, pyrene and chrysene. Gas exchange fluxes of PAHs across the air-water interface of the Yellow Sea were calculated using a modified two-film exchange model. PAHs fluxes ranged from $196\;ng/m^2/d$ net volatilization during summer to $3830\;ng/m^2/d$ net absorption during winter. Passive air sampler provides a convenient and cost-effective tool for measuring averaged gas phase PAHs, which was successfully used for calculation of gas exchange flux of PAHs in the Yellow Sea.

• Journal of Mechanical Science and Technology
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• v.14 no.2
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• pp.236-250
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• 2000

Compression ignition direct injection diesel engines employed a high pressure injection system have been developed as a measure to improve a fuel efficiency and reduce harmful emissions. In order to understand the effects of the pressure variation, many experimental works have been done, however there are many difficulties to get data in engine condition. This work gives numerical results for the high pressure effects on spray characteristics in wide or limited space with near walls. The gas phase is modelled by Eulerian continuum conservation equations of mass, momentum, energy and fuel vapour fraction. The liquid phase is modelled using the discrete droplet model approach in Lagrangian form and the drop behavior on a wall is calculated with a new droplet-wall interaction model based on the experiments observing individual drops. The droplet distributions, vapour fractions and gas flows are shown in various injection pressure cases. In free spray case which the injection spray has no wall impaction, the spray dispersion and vapour fraction increase and drop sizes decrease with increasing injection pressure. The same phenomena appears more clearly in wall impaction cases.