• Proceedings of the KIEE Conference
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• 대한전기학회 1997년도 하계학술대회 논문집 C
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• pp.1465-1468
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• 1997

In this study we investigated the aging characteristic such as leakage current, dielectric loss, contact angle, of EPDM for outdoor use by thermal treatment. And also observed the color change of surface, changing of chemical ingredient of the marterials by optical microscope. SEMI, FTIR and EDX at the section and surface. The test result show that leakage current is increased with thermal aging time. contact angle and dielectric loss is slightly decreased. Moreover, micro-void or crack in bulk is severely increased with aging time. However, the result affect to the tan $\delta$ at bulk of EPDM. It seems that carrier sources are removed by degassing with heat treatment.

• Journal of the Korean Vacuum Society
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• 제8권4A호
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• pp.432-437
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• 1999

We have fabricated an in situ ellipsometer operating at He-Ne wavelength. It can be applied to the real-time, in-situ tracking of the ellisometric change which occurs during various sample treatments. As a rotating analyzer type, all optical elements and related parts are designed to share a common hollow-axis configuration, and hence the ellipsometer is compact in shape and simple in design. It is mountable on the spare ports of vacuum chamber with ease. Using this ellipsometer, we observed the effective density variation of previously grown $TiO_2$ thin films by using electron beam evaporation. The packing density of the as-grown film was 82%. When exposed to atomsphere, the micro-void of the film was filled with water vapor. This water-filled $TiO_2$ thin film was subject to heating/cooling cycles in vacuum and the ellipsometric variation versus temperature and cycling number was measured in real time using this in situ He-Ne ellipsometer.

• Proceedings of the Korean Geotechical Society Conference
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• 한국지반공학회 2005년도 춘계 학술발표회 논문집
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• pp.1167-1174
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• 2005

This paper describes on the volume change of Sewage Dredged Soils by using laboratory test and volumetric change test. The tremendous change of Moisture Content occured in the Sewage Dredged Soils during the Elapsed Time. The Unit Weight increases during the normally shrinkage limit void ratio and then the unit weight decrease. A volume of Sewage Dredged Soils according to the moisture content is a difference maximum 2.5 times. And there is the difference 3.5 times according to the change of unit weight. Therefore, the moisture content and unit weight computation are very important for the computation on the volume of Sewage Drdeged Soils.

• Magazine of the Korean Society of Agricultural Engineers
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• 제45권4호
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• pp.137-143
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• 2003

The initial condition of $\Delta \sigma_3 \;=\; \Delta u$ is used for analyzing the time dependent behavior of ground. This is based on the concept that the coefficient of pore water B is the unity on the condition of saturation. but some measured consolidation data in the field showed that the pore water pressure was not dissipated as time elapsed but it was maintained constant value or it's dissipation rate was slower than that of the predicted. and so the measured data of pore water pressure was not consistent with that of settlement. In this study, the rheological model for the pore water pressure behavior on undrained condition was induced and compared with the experiment data of the literature. The result showed that the suggested model was consistent well with the result of experiment, but the suggested model could not explain the effect of the decrease of void ratio according to consolidation.

• Journal of Mechanical Science and Technology
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• 제20권10호
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• pp.1680-1690
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• 2006

As a promising and novel manufacturing technology, laser aided direct metal deposition (DMD) process produces near-net-shape functional metal parts directly from 3-D CAD models by repeating laser cladding layer by layer. The key of the build-up mechanism is the effective control of powder delivery and laser power to be irradiated into the melt-pool. A feedback control system using two sets of optical height sensors is designed for monitoring the melt-pool and real-time control of deposition dimension. With the feedback height control system, the dimensions of part can be controlled within designed tolerance maintaining real time control of each layer thickness. Clad nugget shapes reveal that the feedback control can affect the nugget size and morphology of microstructure. The pore/void level can be controlled by utilizing pulsed-mode laser and proper design of deposition tool-path. With the present configuration of the control system, it is believed that more innovation of the DMD process is possible to the deposition of layers in 3-D slice.

• Journal of the Korean GEO-environmental Society
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• 제2권3호
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• pp.47-56
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• 2001

In the present study, mainly to determine the embarkation time of equipment in dredged clay fills, an analytical approach is performed to predict a variation of the undrained shear strength in the outermost layer. In this approach, Gibson's non-dimensional linear constant defining the relationship between the void ratio and the effective stress is employed. Also in this approach, void ratios and settlements associated with the volume change due to the self-consolidation and the desiccation shrinkage are evaluated at various elapsed times based on the finite difference solution technique proposed by the authors(1999) and the developed computer program named as DSCON. Predicted results(water content ratio, unit weight and undrained shear strength) are compared with those of laboratory model tests conducted with soil samples obtained from the Koheung site. Based on the predicted undrained shear strengths, possible embarkation time of a equipment is also evaluated. In addition, further analyses are made to indirectly verify the efficiency of the analytical approach proposed in the present study using the PSDDF computer program which can consider the drainage efficiency.

• Journal of the Korean Geotechnical Society
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• 제20권8호
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• pp.113-121
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• 2004

The present study is suggested to estimate the degree of secondary consolidation caused by various changes of stress such as loading, unloading and reloading in improving poor subsoil through pre-compression loading construction method and, for this purpose, examined the characteristics of the consolidation of Kunsan clay through incremental loading test (IL) using standard consolidation tester and constant loading rate test (CLR), which were adapted from the constant rate of strain test (CRS). In addition, after CRS test, this study determined the characteristics of secondary consolidation and relationships among void ratio, effective stress and time according to the ratio of effective over-consolidation on reloading at the point of time of random expansion. Kunsan clay had larger expansion and smaller secondary consolidation settlement when the ratio of effective over-consolidation was high. In addition, when loading was applied after the load was removed at once, the secondary consolidation coefficient $C'_{\alpha}$ was smaller than that when the load was removed gradually, and when the ratio of effective over-consolidation was over 1.4 a similar value was produced. Based on the entire settlement resulting from reloading, the secondary consolidation coefficient $C"_{\alpha}$ increased non-linearly with the lapse of time but the final value was similar to that in the case of rapid removal. The strain velocity of void ratio was in a regular linear relationship with the increase of loading time regardless of the ratio of effective over-consolidation in both tests and it grew smaller with the increase of the ratio of effective over-consolidation.tion.

• Journal of the Korean Crystal Growth and Crystal Technology
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• 제26권3호
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• pp.89-94
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• 2016

In this study, the crystalline property of a-plane GaN epitaxial layer grown on r-plane sapphire by a HVPE method has been investigated according to the V/III ratio and the growth time of multi-step growth. Furthermore, these results were compared with the previous result obtained from the single-step growth of a-plane GaN on r-plane sapphire substrate. In the multi-step growth for a-plane GaN epitaxial layer on r-plane sapphire, the FWHM values of rocking curve in GaN epitaxial layer were decreased as the HCl source flow rate and the growth time were increased. The void formed in epitaxial layer was continuously decreased as the growth time in first step and second step using a higher HCl flow rate was increased. As a result, the GaN layer obtained with the longest growth time on the first step and second step exhibited the lowest FWHM values of 584 arcsec and the smallest dependence of azimuth angle.

• The Korean Journal of Rheology
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• 제11권1호
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• pp.34-43
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• 1999

Flow-induced voids during resin impregnation and poor fiber wetting have known to be highly detrimental to the performance of composite parts manufactured by resin transfer molding(RTM) process. In this study, in order to overcome these serious problems encountered in RTM, the effects of surface modification by using silane coupling agent as a surface modifier on the flow characteristics, the wetting between resin and fiber, and void content were investigated. For the experiments of microscopic flow visualization and curing in a beam mold, glass fiber mats having plain weaving structure and epoxy resin were used. Modifying the fiber surface was found to result in a significant decrease of dynamic contact angle between resin and fiber and increase of wicking rate. Therefore, it was confirmed that the surface modification employed in this study could improve the wettability of reinforcing fibers as well as micro flow behavior. In addition, It was revealed that high temperature and low penetration rate of the resin are more favorable processing conditions to reduce the dynamic contact angle. However, surface modified fiber mat was found to have lower permeability than the unmodified one, which may be explained in terms of the decrease of contact time between resin and fiber owing to improvement of wetting. It was also exhibited that surface modification had a significant influence on void formation in RTM process, resulting in a decrease of overall void content due to the improvement of wetting in cured composite parts.

• Journal of the Korea Concrete Institute
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• 제16권3호
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• pp.311-318
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• 2004

This study was performed to examine engineering properties for planting of porous concrete block containing rice straw ash. Tests for void ratio, compressive and flexural strength, pH by neutralization treatment time and curing method were peformed. As results, the void ratio tends to decrease with increasing rice straw ash content. But, the compressive and flexural strength tends to increase with Increasing rice straw ash content. When the neutralization was treated at the curing age 6 days, the greatest strength was showed. The pH of porous concrete without neutralization treatment in dry and water curing are shown in 10.32 ${\~}$ 10.55 and 9.41${\~}$9.59, respectively. The pH of porous concrete by neutralization treatment in dry and water curing were shown in 9.74${\~}$10.10 and 8.13${\~}$9.32, respectively. The porous concrete block size was 23 ${\times}$ 23 ${\times}$ 4 cm, and species of planting were Tall fescue, Lespedeza cyrtobotrya and Lespedeza cuneata. At the 6 months after seeding, germination ratio and grown-up length of Tall fescue, Lespedeza cyrtobotrya and Lespedeza cuneata were shown in 90, 60, $50\%$, and 40${\~}$50, 90${\~}$110, 65${\~}$75 cm, respectively. These porous concrete block containing rice straw ash could be used for planting.