• International Journal of Highway Engineering
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• v.6 no.4 s.22
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• pp.109-121
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• 2004

This study was performed to investigate the characteristics of drying shrinkage for concrete slabs as a project for Korean pavement design procedure. According to the volume-surface ratios and aggregate types, the experiments have been executed for 252 days. In order to simulate the volume-surface ratio of a real concrete pavement slab, three-layer epoxy coating and wrapping were used to prevent the evaporation at the part of specimen surfaces. As a result of preliminary test, coating and wrapping method was identified as reliable for three months. According to the volume-surface ratio, the drying shrinkage of the concrete specimen using sandstone was measured 1.32 to 1.8 times higher than that of the limestone specimen. Comparing to the measured drying shrinkage strains and established ACI and CEB-FIP model equations, it turned out that those model equations were underestimated. Finally, considering the age and volume-surface ratios, the prediction equations of the drying shrinkage of concrete specimen were proposed through a multiple nonlinear regression analysis.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.8
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• pp.521-529
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• 2017

Three-dimensional flow characteristics within a high-acceleration first-stage turbine vane passage has been investigated in a newly-built vane cascade for propulsion. The result shows that there is a strong favorable pressure gradient on the vane pressure surface. On its suction surface, however, there exists not only a much stronger favorable pressure gradient than that on the pressure surface upstream of the mid-chord but also a subsequent adverse pressure gradient downstream of it. By employing two different oil-film methods with upstream coating and full-coverage coating, a four-vortex model horseshoe vortex system can be identified ahead of each leading edge in the cascade, and the separation line of inlet boundary layer flow as well as the separation line of re-attached flow is provided as well. In addition, basic flow data such as secondary flow, aerodynamic loss, and flow turning angle downstream of the cascade are obtained.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.10a
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• pp.140-143
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• 2003

The drawbead is an important part in sheet metal forming for automotive part and its effect is affected by various process parameters. Therefore in this study, drawbead friction test was performed at various process parameters - panels (cold rolled and galvanized sheet steel), lubricants (having three different viscosities), bead materials(steel, iron) and surface treatment of bead (Cr plating). Circular shape bead has been used for the test. The results show that friction and drawing characteristics were mainly influenced by the nature of zinc coating, viscosity of lubricants, surface treatment of a bead and hardness of coated layer.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2000.04a
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• pp.20-25
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• 2000

In order to study the impact fracture behavior of brittle materials, a steel-ball-impact experiment was Performed. Five kinds of materials were used in this study : soda-lime glass plates, glass/epoxy prepreg-one layer-bonded and unbonded glass plates, glass/epoxy prepreg-three layers-bonded and unbonded glass plates. Fracture patterns, the maximum stress and absorbed fracture energy were observed according to various impact velocities 40-120m/s. With increasing impact velocity, ring crack, cone crack, radial crack and lateral crack took place in the interior of glass plates. The generation of such cracks was largely reduced with glass/epoxy prepreg coating. Consequently, it is thought that the characteristics of the dynamic Impact fracture behavior could be evaluated using the absorbed fracture energy and the maximum stress measured at the back surface of glass plates.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.05a
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• pp.1.2-1.2
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• 2011

With recent advances in materials and products, materials processing experiences new challenges. More particles and polymers in material side and thinner and faster deformations in processing side. It happens in most emergying industries such as manufacturing of batteries, solar cells, multi-layer chips, displays, printed electronics, to list a few. In most cases, they are manufactured by coating or printing process, which is defined as a process in which gas is replaced by liquid on a substrate. In this sense, casting, inkjet printing, and roll-to-roll printing are all included. The printing process consists of three unit processes. As the materials used in the above mentioned applications typically contain a large amount of particles with polymers and solvents, they continuously change microstructures during preparation, flow, and even drying. However, little is known about the flow characteristics of such complex fluids and less is known about how to design and control the process. Therefore, for better control of the process and for better quality of the product, we need to understand the flow characteristics of these complex fluids under extremely fast flow environment.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2010.03b
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• pp.19-19
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• 2010

We suggest CNT-based gas sensors for breath alcohol measurement. The sensors were composed of single-walled carbon nanotubes (SWNTs) thin film on glass substrate with simple process, and the SWNTs thin film as sensing layer was formed by multiple spray-coating with SWNT composites which was well-dispersed, highly controlled and differently functionalized by various binders (TEOS, MTMS, and VTMS) added in ethanol solvent. In this work, three different SWNTs thin films were made to compare their electrical response properties for alcohol vapor. From fabricated sensors, conductance responses were measured and discussed. In the result, our alcohol gas sensors showed an effective selectivity even at room temperature.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2017.05a
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• pp.236-237
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• 2017

This study discusses the development of waterproofing layer jet-spray nozzle that forms a three-dimensional air cell. This nozzle has an air flow generation mechanism in the air groove of the attachment cell part located at the end of the injection nozzle. Since the air grooves also function as an air curtain, the airborne particles generated when the waterproof material is sprayed is effectively blocked. In the past, spraying of the waterproof material through the high pressure was possible, but this technology allows stable injection due to the static agitation method, and various problems caused by particle generation has been (damages to neighboring areas, economic loss, etc.) minimized.

• Korean Journal of Optics and Photonics
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• v.27 no.4
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• pp.143-150
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• 2016

The thickness of each layer in a multilayered system is determined by a Fourier-transform method using spectroscopic reflectance measurements. To verify this method, we first generate theoretical reflectance spectra for three layers, and these are fast-Fourier-transformed using our own Matlab program. Each peak of the Fourier-transformed delta function denotes the optical thickness of each layer, and these are transformed to physical thicknesses. The relative thickness error of the theoretical model is less than 1.0% while a layer's optical thickness is greater than 730 nm. A PI-(thin $SiO_2$)-PImultilayeredstructure produced by the bar-coating method was analyzed, and the thickness errors compared to SEM measurements. Even though this Fourier-transform method requires knowing the film order and the refractive index of each layer prior to analysis, it is a fast and nondestructive method for the analysis of multilayered structures.

• Journal of the Korean Applied Science and Technology
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• v.32 no.4
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• pp.694-701
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• 2015

In order to get stabilized pure retinol in skin care cosmetics, developing the three layered matrix bead capsules were studied. This study relates to make a cosmetic composition using the three layered matrix capsule that could increase the stability of the active ingredient. A primary encapsulation, vitamin A (pure retinol) of active ingredient was perfectly capsulated into water-in-oil (Water-in-Oil: W/O) emulsion vesicle using PEG-10 dimethicone copolyol emulsifier. A secondary encapsulation of multiple emulsion of the water-in-oil-in-water (W/O/W) emulsion blending W/O emulsion using sucrose distearate of surfactant was developed using homogenizing emulsifying system. Pure retinol of active ingredient was stably capsulized to inside the W/O/W-multiple emulsion in order to load the triple matrix capsulation. By coating it with a polymer matrix base, encapsulated in the triple layered type, which were developed bead encapsulation of 2~10mm uniformly size. To show beautifully appearance capsulated bead type, these finish particles in this triple matrix layer were developed as a gold, green, dark brown, silver and blue color were encapsulated in the bead types. Structural particle certification of triple matrix layer was observed through SEM analysis. Stability of pure retinol was remained stable more than 99.7% for 30 days at $42^{\circ}C$ incubating conditions compared with non-capsule. This technology was applied in different formulations such as various sizes and colors that by applying the skin care cosmetics. In the future, this technology to encapsulate an unstable active ingredient, we expect to be expanded this application in the food and drug as a time delivery system.

• Journal of the Korean Ceramic Society
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• v.20 no.3
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• pp.211-216
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• 1983

This work aims at characterizing silicon grains and its compacts. In order to remove iron silicon grains were washed with 5N hydrochloride at 60-7$0^{\circ}C$ for 170 hrs, and then followed the chemical analysis by atomic absorption spectrophotometer X-ray diffraction analysis SEM observation and specific surface area determination by B. E. T. Mixtures of graded silicon particles with two or three different sizes were made into packings by mechanical vibration. The mixtures were used to make compacts with 10 mm in diameter and 70mm in length by isostatically pressing at 1, 208 kg/$cm^2$ (20 kpsi) and 4, 255kg/$cm^2$ (60 kpsi) respectively. Bulk densities of packings and compacts were measured. A slip made of magnesium nitrate solution and fine silicon particles was spray-dried and then decomposed at 30$0^{\circ}C$ for the purpose of coating the uniform layer of magnesium oxide on the surface of particles. The results obtained are as follows: (1) About two thirds of iron content could be removed from silicon by washing silicon powders with hydrochloride. (2) Uniform layer of magnesium oxide on the surface of silicon could be prepared by spray-drying suspension and by decomposing it. (3) B. E. T. specific surface area of fine silicon particles was 2, 826.753$m^3$/kg. (4) In the binary system with two sizes of 40-53$\mu\textrm{m}$ particles and <10$\mu\textrm{m}$ particles the maximum bulk density of packing was 55% of theoretical value and that of compacts made at the pressure of 4, 255 kg./$cm^2$ (60 kpsi) was 73% of theoretical value. (5) In the ternary system with three sizes the maximum bulk density of packing was 1.43 g/$cm^3$and that of compacts was 1.80g/$cm^3$which is equivalent to 77.6% of theoretical value. The composition of the closest compact was consisted of 50% of 40-53$\mu\textrm{m}$ particles 20% of 10-30$\mu\textrm{m}$ particles and 30% of <10$\mu\textrm{m}$ parti-cles.