• Polymer(Korea)
• /
• v.30 no.5
• /
• pp.422-425
• /
• 2006

Due to their periodic helical structure, cholesteric liquid crystals (CLC) have a unique ability to selectively reflect visible light. CLC films reflecting a broad wavelength band were prepared by inducing a pitch gradient in CLC layers through a diffusion of small molecules and through a thermal mixing of cyclic siloxane CLC molecules with different pitch lengths. Various pitch gradients in the CLC cell were observed using UV/Vis spectrometer and SEM technique.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.18 no.2
• /
• pp.137-143
• /
• 2006

This study has been conducted to quantify the emissions of Volatile Organic Compounds (VOCs) in a conference room. The carpet has emitted a variety of VOCs, but in this study, 2 VOCs compounds have been considered: Ethylbenzene and 1, 2, 3-Trimethylbenzene. In this study, a three dimensional numerical analysis has been carried out to investigate the emission and behavior characteristics of Ethylbenzene and 1, 2, 3-Trimethylbenzene emitted from the carpet in the conference room. The mass diffusion coefficient and the initial concentrations of VOCs in the carpet have been obtained from experimental data with non-linear regression. It has been found that the concentrations and emission factors of VOCs have exponentially decayed with time and that the concentration gradients and emission factors of VOCs are different from each other for various components. This study may supply fundamental understandings for the emission and behavior characteristics of VOCs.

• Proceedings of the Earthquake Engineering Society of Korea Conference
• /
• 1998.04a
• /
• pp.81-88
• /
• 1998

During an earthquake, there are three main components of excitation : horizontal excitation of the ground, vertical excitation of the pile due to superstructure feedback produced by vertical excitation of the ground, and the seawater excitation induced by the vertical ground shaking, that is, "the seaquake." These excitations could have effects on the soil plugs in open-ended pipe piles installed at offshore sites. In this study, seaquake excitation induced by the vertical ground shaking was simulated by pulsing the water pressure at the seabed. During a seaquake, due to induced excess porewater pressure and pressure gradients in the soil, the capacity of open-ended pipe piles installed in a simulated sea depth of greater than 220 m was reduced serevely and the soil plugging resistance was degraded by more than 80%. The soil plug was failed because of the upward seepage forces that developed in the soil plug due to excess pore water pressure produced in the bottom of the soil plug during the seaquake. The compressive capacity of an open-ended pile in a simulated sea depth of less than 220m was reduced only by about 10%, and the soil plug resistance was degraded by less than 5%.s than 5%.

• Proceedings of the Computational Structural Engineering Institute Conference
• /
• 2007.04a
• /
• pp.651-656
• /
• 2007

Changes in measured structural responses induced by a damage could be significantly smaller than those by environmental effects such as temperature and temperature gradients. It is highly desirable to develop a methodology to distinguish the changes due to the structural damage from those by the environmental variations. In this study, a novel method to extract the damage-induced deflection under temperature variations is presented using the outlier analysis on the deflections obtained using the modal flexibility matrices. The main idea is that temperature change in a bridge would produce global increase or decrease in deflections over the whole bridge while structural damages may cause local variations in deflections near the damage locations. Hence, the correlation between the deflection measurements may show high abnormality near the damage locations. A series of laboratory tests were carried out on a bridge model with a steel box-girder for 14 days. It has been found that the damage existence assessment and localization can carried out for a case with relatively small damage under the temperature variations

• Molecules and Cells
• /
• v.24 no.2
• /
• pp.288-293
• /
• 2007

The conversion of mitotic chromosome into interphase chromatin consists of at least two separate processes, the decondensation of the mitotic chromosome and the formation of the higher-order structure of interphase chromatin. Previously, we showed that depletion of BAF53 led to the expansion of chromosome territories and decompaction of the chromatin, suggesting that BAF53 plays an essential role in the formation of higher-order chromatin structure. We report here that BAF53 is associated with mitotic chromosomes during mitosis. Immunostaining with two different anti-BAF53 antibodies gave strong signals around the DNA of mitotic preparations of NIH3T3 cells and mouse embryo fibroblasts (MEFs). The immunofluorescent signals were located on the surface of mitotic chromosomes prepared by metaphase spread. BAF53 was also found in the mitotic chromosome fraction of sucrose gradients. Association of BAF53 with mitotic chromosomes would allow its rapid activation on the chromatin upon exit from mitosis.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.12 no.1
• /
• pp.137-151
• /
• 1988

Thurbulent thermal convection between two plates, bottom plate is at higher temperature $T_{h}$ and the upper plate is at lower temperature $T_{i}$ is numerically investigated. Model equations are abridged Reynolds stress equations; full Reynolds stress equations are simplified to yield algebraic relations in case of mean square velocity fluctuations in vertical and horizontal directions. Boundary conditions for turbulent kinetic energy k and mean square temperature variance .thera.$^{2}$oner bar at the plate surfaces are set to be zero and those of dissipation rate of turbulent kinetic energy .epsilon. and dissipation rate of mean square temperature variance .epsilon.$_{\theta}$ are assumed at first grid point nearest to the boundary surfaces, whose values are approximated by inviscid estimates. Results show that temperature profiles are in good agreement with experimental data except transition region, in which temperature is over-predicted. Such discrepancy becomes larger as the Rayleigh number becomes smaller. Nusselt numbers, which are calculated from the temperature gradients at the boundary surfaces, are also in good agreement with experimental data.a.a.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.19 no.9
• /
• pp.2342-2352
• /
• 1995

Deposition of flame-synthesized silica particles onto a target is utilized in optical fiber preform fabrication processes. The particles are convected and deposited onto the target. Falkner-Skan wedge flow was chosen as the particle laden flow. Typically the particles are polydisperse in size and follow a lognormal size distribution. Brownian diffusion, thermophoresis, and coagulation of the particles were considered and effects of these phenomena on particle deposition were studied. A moment model was developed in order to predict the particle number density and the particle size distribution simultaneously. Particle deposition with various wedge configurations was examined for conditions selected for a typical VAD process. When coagulation was considered, mean particle size and its standard deviation increased and particle number density decreased, compared to the case without coagulation. These results proved the fact that coagulation effect expands particle size distribution. The results were discussed with characteristics of thermal and diffusion boundary layers. As the boundary layers grow in thickness, overall temperature and concentration gradients decrease, resulting in decrease of deposition rate and increase of particle residence time in the flow and thus coagulation effect.

• Journal of Korean Society for Atmospheric Environment
• /
• v.19 no.3
• /
• pp.275-284
• /
• 2003

The soil -air exchange processes of CH$_4$ were investigated in Hari district of Kang Hwa Island, Korea during the late April 2002. In the course of our field experiments, we measured the concentration, concentration gradients (between two different heights of 1 and 5 m), and the fluxes of CH$_4$ using the surface layer gradient microm-eteorological methods. If the relationships between CH$_4$ fluxes and the relevant environmental parameters are examined, CH$_4$ fluxes were found to be affected most significantly by parameters like wind speed. The results of our study indicate that the study area behaved as a net source of CH$_4$ to the atmosphere with a net daily emission rate of 3.6 mg m￣$^2$ The findings of relatively low exchange rate observed at our study site suggest that the rice paddy area investigated prior to planting period can behave as a moderate source of methane.

• Journal of Astronomy and Space Sciences
• /
• v.14 no.1
• /
• pp.24-32
• /
• 1997

We have calculated the velocity distribution of wind driven by Alfven waves. The assumed initial number density of wind can affect the line profiles because it produces the change in the velocity distribution under the mass conservation. Initial density $N_O=5.5{\times}10^{12}/cm^3$ is chosen for a proper initial density from the observation by Schroder(1986). The wind models for $N_O=10^9,10^{10},10^{11},5.5{\times}10^{12}/cm^3$ are calculated at ${phi}$=0.06 and ${phi}$=0.78. The line profiles for lower initial density show the strong emissions and narrow absorptions because of their steeper velocity gradients.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.6 no.2
• /
• pp.183-194
• /
• 2002

A general procedure to evaluate the sensitivity of design variables to stresses and strains in PSC flexural members is proposed. To accomplish the purpose of this study, long-term losses including creep, shrinkage, and PS steel relaxation are formulated based on the equilibrium states of the deformed sectional geometry. Thereby, the formulation follows the basic steps which consider the fundamental formulas adopted by CEB-FIP, ACI, and KCI rather than the age adjusted effective modulus concept. Twenty-one design variable including the material and geometrical properties of concrete, nonprestressing steel and prestressing steel, and the geometry of the cross section are considered in the sensitivity analysis. The gradients of the stresses and strains needed for the sensitivity assessment are calculated in a closed format. The derived formulation is applied to the T-type section PSC beam with prestressing and nonprestressing steels for the sensitivity analysis. The analytically calculated sensitivity results are compared with those numerically calculated to ensure the validity of the proposed procedure.