• The Korean Journal of Ecology
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• v.21 no.2
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• pp.125-131
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• 1998

Histological damage and growth inhibition of Pinus densiflora were analysed in different areas around the Metropolitan area of Seoul urban (heavily polluted), suburban (lightly polluted), and rural(unpolluted) areas. Soil properties of each area were also investigated. Contact angles of water droplet on needle leaves growing in polluted areas were lower than that in unpolluted area. Transpiration rates of needle leaves growing in polluted areas were more rapid than that in unpolluted area. These results represented that needle leaves growing in polluted areas were more susceptible to water deficit than that growing in unpolluted area was. Growths of annual ring of Pinus densiflora growing in polluted areas were lower than that in unpolluted area. On the other hand, soil pH in polluted areas was lower than that in unpolluted area. That is, the former was more acidified than that the latter was. Ca and Mg contents in polluted areas were lower than that in unpolluted area, while Al contents in polluted areas were higher than that in unpolluted area. These soil properties revealed that the effects of acid precipitates in urban and suburban areas were severer than that in rural area.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.184-185
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• 2006

Two-step growth to incorporate the Mg atoms in the ZnO nanorods fabricate by thermal evaporation process and also utilized the ZnO film as a template. In the first step of low temperature, Zn seed metals with low melting temperature formed the droplet, and then MgZnO ternary nanorods were grown by injecting oxygen and evaporating Mg atoms in high temperature process of the second step. The vertical growth of the MgZnO nanorods with large-area distribution and uniformity was successfully performed on the ZnO template. We investigated the shape of the vertically grown 1-D MgZnO nanorods and characterized the optical and crystal properties. We confirmed the incorporation of Mg atoms by the EDS and PL spectrum.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.23 no.11
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• pp.848-853
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• 2010

We have grown GaN nanowires by the low pressure MOCVD method on Ni deposited oxidized Si surface and have established optimum conditions by observing surface microstructure and its photoluminescence. Optimum growth temperature of $880^{\circ}C$, growth time of 30 min, TMG source flow rate of 10 sccm have resulted in dense nanowires on the surface, however further increase of growth time or TMG flow rate has not increased the length of nanowire but has formed nanocrystals. On the contrary, the increase of ammonia flow has increased the length of nanowires and the coverage of nanowire over the surface. The shape of nanowire is needle-like with a Ni droplet at its tip; the length is tens of micron with more than 40 nm in diameter. Low temperature photoluminescence obtained from the sample at optimum growth condition has revealed several peaks related to exciton decay near band-edge, but does not show any characteristic originated from one dimensional quantum confinement. Strong and broad luminescence at 2.2 eV is observed from dense nanowire samples and this suggests that the broad band is related to e-h recombination at the surface state in a nanowire. The current result is implemented to the nanowire device fabrication by nanowire bridging between micro-patterned neighboring Ni catalysis islands.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.11
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• pp.1105-1114
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• 2010

Ice shapes accumulated on the aircraft surfaces are categorized into rime and glaze ice, which are highly dependent on various parameters such as ambient temperature, liquid water contents (LWC), mean volumetric droplet diameter and freestream velocity. In this study, quantitative analyses on the ice accretion have been attempted in a systematical manner and the key findings are as follows. First, the increase of freestream velocity can cause tremendous change in the ice accumulation such as the growth of ice accretion area, ice heading direction and maximum thickness of ice horn. Second, LWC is found to be linearly proportional to the ice accretion area. Third, the effects of ambient temperature on incoming water mass seem to be relatively small in comparison with LWC and freestream velocity. Finally, it was shown that MVD has only a little influence on ice shapes. However, it may increase the ice accretion area by increasing the droplet impacting range.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.384.2-384.2
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• 2016

Recent publications reported the self-propelled jumping of coalescing dew droplets on superhydrophobic surfaces [1-2]. We further investigated the initial growth, coalescence, and removal by self-propelled ejection of nano and microscopic water droplets on the superhydrophobic surface of lotus leaves under condensing conditions. By using a high-speed digital camera mounted on an optical microscope, we have found: (1) sub-micrometer droplets form and grow on nanoscale waxy hairs; (2) growing droplets coalesce rapidly upon contact, but never jump off the surface unless the diameter of merged droplets exceeds ${\sim}15{\mu}m$; (3) the diameter and direction of jumping droplets are very narrowly distributed, centered at $20-30{\mu}m$ and ${\sim}20$ degrees from the surface normal, respectively. We present a rationale for these observations on the basis of: (a) the hierarchically rough surface structure on nano- and micro-scales; (b) its chemical composition; and (c) the balance among competing forces of cohesion (surface tension), adhesion and gravity.

• Journal of Mechanical Science and Technology
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• v.15 no.6
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• pp.788-795
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• 2001

The effects of nonequilibrium condensation on the shock boundary layer interaction over a transonic bump model were investigated experimentally and numerically. An experiment was conducted using a supersonic indraft wind tunnel. A droplet growth equation was incorporated into two-dimensional Navier-Stokes equation systems. Computations were carried out using a third-order MUSCL type TVD finite-difference scheme with a second-order fractional time step. Computation compared with the experimental results. Nonequilibirum condensation suppressed the boundary layer separation and the pressure fluctuations due to the shock boundary layer interaction. Especially the nonequilbrium condensation was helpful to suppress the high frequency components of the pressure fluctuations.

• Journal of ILASS-Korea
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• v.3 no.2
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• pp.34-41
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• 1998

The present experimental study investigates the effect of an initial disturbance on the breakup mechanism of a liquid column. With varying the maginitude of the inital disturbance, we measure the surface wave of liquid column with adopting laser shadow method and analyze the growth rate of liquid column and breakup frequency. The experimental results show that thebreakup characteristics of liquid column is significantly influenced by the frequency of the initial disturbance. We concluded that the most uniform droplet occurs when the frequency of initial disturbance coincides with the natural frequency of the liquid column.

• Proceedings of the KSME Conference
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• 2000.11b
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• pp.544-549
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• 2000

The effects of nonequilibrium condensation on the shock boundary layer interaction over a transonic bump model were investigated experimentally and numerically. An experiment was conducted using a supersonic indraft wind tunnel. A droplet growth equation was incorporated into two-dimensional Navier-Stokes equation systems. Computations were carried out using a third-order MUSCL type TVD finite-difference scheme with a second-order fractional time step. Computations compared with the experimental results. Nonequilibirum condensation suppressed the boundary layer separation and the pressure fluctuations due to the shock boundary layer interaction. Especially the nonequilibrium condensation was helpful to suppress the high frequency components of the pressure fluctuations.

• Journal of Ocean Engineering and Technology
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• v.11 no.4
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• pp.49-60
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• 1997

This paper deals with the effect of coating layer on the fatigue strength of TiN coated 1Cr-1Mo-0.25V steel prepared by using the arc ion plating (AIP) process, in which it was characterized by the presence of extractor grid (ion filter). The rotary bending fatigue tests were carried out under room air conditions, and the fatigue crack initiation and growth bwhavior were observed by using plastic replica method. As experimental results, it was found that the obvious improvement of fatigue life at lower stress region was confirmed in TiN coated specimen processed with ion filter. It was also exlained that the increase of fatigue life in the case of an improved AIP process with ion filter was attributed to the retardation of crack initiation of the substrate surface due to hard coating layer, more densly formed with the reduced size and density of droplets.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.514-519
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• 2003

A computational study is performed to clarify the characteristics of supersonic moist air jet issuing from a simple sonic nozzle. The effects of the initial supersaturation on the Mach disk diameter and location, the barrel shock wave and jet boundary structures are investigated in details. The axisymmetric, compressible, Navier-Stokes equations, coupled with droplet growth equation, are solved using a third-order MUSCL type TVD finite-difference scheme. It is found that the Mach disk diameter increases with an increase in relative humidity of moist air. while its location is not significantly dependent on the relative humidity. As the relative humidity increases, the barrel shock wave and jet boundary are more expanded due to the local static pressure rise of nonequilibrium condensation.