• Journal of the Korean Ceramic Society
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• v.30 no.5
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• pp.381-388
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• 1993

Due to the anisotropy of thermal expansion, LAS system which has low thermal expansion property is hard to obtain a dense sintered body. Therefore, the thermal expansion coefficient and the mechanical strength were decreased. In this study, mullite, which has good mechanical properties in high temperature and comparatively low thmeral expansion coefficient, was taken as a additive in LAS system. And then, sintering, thermal, and mechanical properties were investigated. The results are follows; When mullite is added in eucryptite composition (Li2O.Al2O3.2SiO2) of LAS system, the creation of liquid phase results in the densification of sintered body and the specimen sintered at 136$0^{\circ}C$ for 2 hours shows optimum sintering condition. With the addition of mullite in eucryptite composition, mechanical strength is increased by the control of grain growth. Especially, flexual strength of EM0 specimen was about double value than the basic composition. Thermal expansion coefficients of EM0 and EM15 specimens sintered at 136$0^{\circ}C$ were -8.23$\times$10-6/$^{\circ}C$ and -4.90$\times$10-6/$^{\circ}C$ in the temperature range of RT.~80$0^{\circ}C$. As the mullite content are increased, negative thermal expansion ratios are decreased.

• The Journal of the Acoustical Society of Korea
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• v.21 no.8
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• pp.679-685
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• 2002

Low-frequency mono-static reverberation model for shallow-water environment is presented. It is necessary to develop the transmission loss model to calculate the sub-bottom interaction because the ray-based transmission loss model is difficult to compute the pressure accurately which penetrates the bottom medium. In this paper reverberation level is calculated using the RAM (Range dependent Acoustic Model) to augment the multi-path expansion model because it does not estimate transmission loss accurately in shallow water. The signals generated by the L-HYREV and the GSM are compared with the observed signals and it is showed that the L-HYREV model provides a closer fit to the observed signals than those obtained using the GSM.

• Journal of the Korean Ceramic Society
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• v.13 no.2
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• pp.31-38
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• 1976

Korean tremoitic talc, wollastonite and clay have been used to develop a wall tile body to appropriate to the fast firing process. Some of ceramic properties of the raw materials were investigated by X-ray diffraction, thermal analysis and chemical analysis. The body compositions were formulated from the range of 35~75% tremolitic talc, 0~30% wollastonite and 25~35% plastic clay. Thermal gravity analysis and thermal expansion were tested for each of unfired bodies to study the correlation between thermal dehydration and linear shrinkage during the firing procedure. Linear shrinkage and water absorption of the fired bodies at the various temperature were taken as a measures for determining the proper firing range of the bodies. Increasing the content of wollastonite and firing temperature, the thermal expansion of the fired body showed the gradual decrease, and the thermal expansion curves showed a tendency to straighten. These observations may be resulted from the fact that the amounts of diopside and anorthite formed were gradually increased and those of quartz relatively decreased. The optimum compositions of the wall tile bodies for fast firing are 30% clay, 10~20% wollastonite and 50~60% tremolitic talc.

• Journal of Biomedical Engineering Research
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• v.11 no.2
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• pp.233-242
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• 1990

In the current flow visualization studies, the role of non-Newtonian characteristics (such as shearra to dependent viscosity and viscoelasticity ) on flow behavior across the sudden ex- pansion step in a circular pipe as a model for blood flow experiments is investigated over a wide range of Reynolds numbers. The expansion ratios tested are 2.000 and 2.667 and the range of the Reynolds number covered in the current flow visualization tests are 10~35, 000 based on the inlet. diameter. The reattachment longuEs for the viscoelastic fluids in the lami- nar flow regime are found to be much shorter than those for the Newtonian fluid. In addition it decreases significantly with increasing concentration of viscoelastic fluids at the same Reynolds number. However, in the turbulent flow regime, the reattachment length for the viscoelastic fluids Is two or three times longer than those for water, and gradually increases with increasing concentration of viscoelastic solutions, resulting In 25 and 28 step-height dis- tances for 500 and 1, 000 lpm ployacrylamide solutions, respectively. This may be due to the fact that the elasticity in pobacrylamide solutions suppresses the eddy motion and controls separation and reattachment behavior in the sudden expansion pips flow.

• Journal of Broadcast Engineering
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• v.22 no.1
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• pp.42-50
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• 2017

A Bit-depth expansion is a method to increase the number of bit. It is getting important as the needs of HDR (High Dynamic Range) display or resolution of display have been increased because the level of luminance or expressiveness of color is proportional to the number of bit in the display. In this paper, we present effective bit-depth expansion algorithm for conventional standard 8 bit-depth content to display in high bit-depth device (10 bits). Proposed method shows better result comparing with recently developed methods in quantitative (PSNR) with low complexity. The proposed method shows 1db higher in PSNR measurement with 40 times faster in computational time.

• Journal of the Korean Geotechnical Society
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• v.27 no.11
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• pp.47-54
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• 2011

In this paper, longitudinal behaviors of a tunnel with respect to various conditions are analyzed, and a new equation of longitudinal deformation curve during tunnel expansion is proposed. Finally, the range of protection by a protector is investigated using the proposed equation. To achieve the objectives, numerical analysis according to the ground and expansion conditions is performed. The results show that the range of protection, when a 2 traffic lane tunnel is expanded to 4 traffic lanes, should cover at least 24m to backward and 35m forward.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.22 no.10
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• pp.994-1002
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• 2012

Acoustic power transmission loss(TL) is an important performance of the muffler system. TL will be affected by the velocity of the fluid in duct since acoustic pressure varies according to the fluid velocity. In this paper, two kinds of fluid model, potential flow and turbulent flow, for the fluid flowing in simple expansion chamber are considered. The effects of their two fluid models in acoustic TL are investigated for the straight and L-shaped simple expansion chamber. In higher frequency range, the characteristics of TL of the two fluid models show different results. The variation of TL according to the fluid velocity is shown more distinctly when turbulence model is used. Turbulent flow model should be used to obtain better estimation of acoustic TL in higher frequency range.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.1264-1269
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• 2004

This research describes the application of hydrocarbon refrigerants for heat pump system which is needed for fish farm. Tested refrigerants are HCFC-22 and hydrocarbon refrigerants(CARE 50 and ASR-20). CARE 50 is mixture of R-290 and R-170, and ASR-20 is mixture of R-152a, R-290 and other additives. Heat pump consist of shell and tube heat exchanger, scroll compressor, expansion valve and accumulator. Manual expansion valve is used for testing of wide range evaporating temperature. Hydrocarbon refrigerants show a good performance as an alternative for HCFC-22 in the range of evaporating temperature from $-6^{\circ}C$ to $6^{\circ}C$.

• Bulletin of the Korean Chemical Society
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• v.23 no.12
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• pp.1801-1805
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• 2002

The graphite intercalation compounds(GIC) were prepared by a dry process that led to the intercalation from the direct reaction of gaseous $SO_3$ with flake type graphite. The basal spacing of the GIC was increased from 8.3 ${\AA}$ to 12 in the gallery height. The ejection of interlayer $SO_3$ molecules by the heating for 1 minute at $950^{\circ}C$ resulted in an exfoliated graphite (EG) with surprisingly high expansion in the direction of c-axis. The expansion ratios of the exfoliated graphites were increased greatly between 220 times and 400 times compared to the original graphite particles, and the bulk density was range of 0.0053 to 0.01 $g/cm^3$, depending on reaction time. The pore size distribution of exfoliated graphite was in the range of $10-170{\mu}m$, which exhibites both mesoporosity and macroporosities. This result indicates that the direct reaction of graphite paricles with gaseous $SO_3$ can be proposed as an another route for the exfoliated graphite having excellent physical properties.

• Journal of information and communication convergence engineering
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• v.13 no.1
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• pp.50-55
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• 2015

We report design and simulation of a two-dimensional (2D) silicon-based nanophotonic crystal as an optical insulator to enhance the light emission efficiency of light-emitting diodes (LEDs). The device was designed in a manner that a triangular array silicon photonic crystal light insulator has a square trench in the middle where LED can be placed. By varying the normalized radius in the range of 0.3-0.5 using plane wave expansion method (PWEM), we found that the normalized radius of 0.45 creates a large band gap for transverse electric (TE) polarization. Subsequently a series of light propagation simulation were carried out using 2D and three-dimensional (3D) finite-difference time-domain (FDTD). The designed silicon-based light insulator device shows optical characteristics of a region in which light propagation was forbidden in the horizontal plane for TE light with most of the visible light spectrum in the wavelength range of 450 nm to 600 nm.