• Applied Chemistry for Engineering
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• v.10 no.5
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• pp.711-717
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• 1999

A multilayer-structure material containing ductile and brittle layer simultaneously was examined and compared with a single layer material using fracture mechanical properties. We found that impact strength of multilayer structure material was considerably higher than single layer's and toughness was enhanced by about two times or higher in similar glass transition temperature($T_g$) region and the same dimension. The superposition principle of impact pulse was used for interpretation of kinetic stress wave as a high-velocity crack proceeds in the plastic. It was understood that the optimum condition of ductile/brittle thickness ratio could be designed in the final toughness enhancement of multilayer.

• Fire Science and Engineering
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• v.23 no.2
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• pp.111-116
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• 2009

17 kinds of fire resistant paint which are currently used were painted on the MDF(middle density fiber board), which suitable to the regulation of Fire Service Act. And we investigate a ignition delay effect under a exposure condition of radiative heat of fire. Radiative heat flux was controlled from $10kW/m^2$ to $30kW/m^2$ using the cone heater. Ignition time, ignition type and surface temperature of the sample were measured. Based on the experimental result, critical heat flux of the fire resistant paint treated sample was $10kW/m^2$ and there were no ignition delay effect above the $30kW/m^2$. And it was found that it will be difficult to expect the fire resistant effect above $400^{\circ}C$ of sample surface temperature.

• Journal of the Korean Chemical Society
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• v.44 no.3
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• pp.177-183
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• 2000

The interaction of phenoxide anion with .the mixed micelles of CTAB(Cetyl-trimethylammonium bromide) and TTAB(Tetradecyltrimethylammonium bromide) was studied by UV/Vis spectrophotometric method. The solubilization constants($K_s$) of phenoxide anion into the mixed micellar phase and the critical micellar concentrations(CMC) of those mixed surfactant systems have been measured and analyzed with the change of overall mole fraction of CTAB($\alpha_{CTAB}$) The effects of additives(n-pentanol and NaBr) on the solubilization of phenoxide anion by those mixed surfactant systems have been also measured. There was a great decrease on the values of solubilization constant and CMC with these additives. For the thermodynamic study, the dependence of $K_s$ values on temperature has been measured and various thermodynamic parameters(${\Delta}G^0_s$, ${\Delta}H^0_s$ and ${\Delta}S^0_s$) have been also calculated. The results show that all the values of ${\Delta}G^0_s$ and ${\Delta}H^0_s$ are negative within the measured temperature region but the values of ${\Delta}S^0_s$ are positive.

• Applied Chemistry for Engineering
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• v.5 no.5
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• pp.779-785
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• 1994

The interaction between the cationic dye, thionin(Th) and the anionic surfactant, sodium dodecyl sulfate (SDS) has been investigated by absorption spectra. As the temperature of surfactant solution was increased in premicellar range(S/D=10, 80, and 160) which was much lower than the critical micelle concentration(CMC), the increment or decrement of the molar extinction coeffecient ratio appeared. It was found that the most stable temperature range of the oligomer aggregate in Th-SDS system at S/D=160 was below $60^{\circ}C$. With increasing the concentration of inorganic salt and organic solvents in Th-SDS system, ${\alpha}$-band was increased, but ${\gamma}$=band or J-band was decreased. The orders of ${\alpha}$-band increasing power were $Cl^-$>$ClO{_4}{^-}$>$SO{_4}{^{2-}}$>$NO{_3}{^-}$ and 2-propanol>ethanol>methanol>ethylene glycol.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.10
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• pp.941-951
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• 2013

A three dimensional numerical simulation of laminar flow and heat transfer in fully developed curved pipe flow has been performed to study the effects of Dean number and pipe curvature on the flow and temperature fields under the thermal boundary condition of axially uniform wall heat flux. The Reynolds number under consideration ranges from 100 to 4000, and the Prandtl number is 0.71. The curvature ratios are 0.01, 0.025, 0.05 and 0.1. The axial velocity and temperature profiles and the local Nusselt number obtained from the present study are in good agreement with the previous numerical and experimental results currently available. To show the effects of pipe curvature on the flow and heat transfer, the resistance coefficients and heat transfer coefficients are computed and compared with the results of the previous theoretical and experimental studies. The averaged Nusselt number is correlated with Dean and Prandtl numbers. Furthermore, the critical Reynolds number for transition to turbulent flow is observed to depend upon the curvature ratio.

• 한국초전도학회:학술대회논문집
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• v.9
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• pp.71-74
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• 1999

We have fabricated high-T$_c$ superconducting YBa$_2Cu_3O_{7-{\delta}}\;/SrTiO_3/\;YBa_2Cu_3O_{7-{\delta}}$ (YBCO/STO/YBCO) multilayer structure on (001) $SrTiO_3$ substrate by using pulsed laser deposition technique for applying to ground plane of single flux quantum digital circuits. In this structure, the top and bottom YBCO layers were connected through the holes in the STO insulating layer. The critical temperature of the two YBCO layers connected each other was 86 K after annealing at 500 $^{\circ}C$ in $O_2$ atm for about 60 hr. This result shows that the annealing process is very important fabricating YBCO/STO/YBCO multilayer structure An experiment to optimize the fabrication process of YSCO/ST0/YBCO multilayer structure with good quality is in progress.

• Korean Journal of Materials Research
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• v.2 no.3
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• pp.197-201
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• 1992

The temperature dependence of the magentic moment was determined for the system of high $T_{c}$ superconductor $Y_{1-X}Sm_{x}Ba_2Cu_3O_{7-y}$ with x=0, 0.2, 0.4, 0, 6, 0.8 and 1.0. Also the magnetic susceptibility and the magnetic critical current density were measured from the magnetic hysterisis loops obtained at 30 K. From the results of the magnetic susceptibility measurements, the high $T_{c}$ phase were ranged from 14.7 to 49.1%. The values of the magnetic critical current densities were in the range of $10^3~10^4A/cm^2$. The penetration depth was approximately ninety times larger than the coherence length.

• Korean journal of applied entomology
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• v.29 no.4
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• pp.277-285
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• 1990

Laboratory and field studies were conducted to investigate the initiation and termination factors for pupal diapause in the Oriental tabacco budworm, Heliothis assulta Guenee. Diapause induction was dependent of photoperiod and temperature experienced by 4th and 5th instar larve. One hundred percent of pupal diapause was obtained when larvae were grown at 10L/14D or shorter and $20^{\circ}C$. But at $25^{\circ}C$ the maximum rate of diapause was only about 85% at 8L/16D, the shortest photoperiod tested in this experiment. Adults, eggs or pupae did not respond to diapause-inducing environmental conditions. The critical photoperiod was 12-12.5 hr at $25^{\circ}C$and 14-14.5 hr at $20^{\circ}C$. In the field-collected sample 100% of diapuse rate was observed on Sept. 20 and thereafter in Suwon and middle part of Korea. Cold temperature treatment was not necessary in the termination of pupal diapause, but accelerated adult development.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.18 no.3
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• pp.449-455
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• 1993

In order to investigate the improvements of relatively poor characteristics of short wave length AlGaAs/GaAs laser diodes which are useful as a light source for short distance communication systems, the low temperature $(<680^{\circ}C)$ grown AlGaAs/GaAs GRINSCH-QW laser diodes by molecular beam epitaxy have been studied by photoluminescence as a function of rapid thermal annealing (RTA) temperature. It is shown that guantum well photoluminescence intensity increased substantially by a factor of 10 after RAT at $950^{\circ}C$ for 10 sec. This is related to the reduction of non-radiative recombination in the guantum well region. The threshold current of annealed laser diode is reduced by a factor, of 4, confirming the improvement of laser diode quality by rapid thermal annealing.

• Korean Journal of Optics and Photonics
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• v.10 no.6
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• pp.518-523
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• 1999

In thi, study, we made experiments to fonn a mesa shape by meltback method with various concentration of solutions and found that unsaturated (20%) InGaAsP (1.55 !-tm) solution at a growth temperature was the most suitable for the formation of a mesa ,hape on the wafer which has an InGaAsP active layer and an InP cap layer on an n-InP substrate. It was difficult to form a proper mesa shape for the fabrication of PBH-LDs only by the meltback method; therefore, we fabricated PBH-LDs by forming the mesa shape with the meltback method after wet etching and by growing a current-blocking layer successively. As the electrical and optical charaleri,tiecs of MQW-PBH-LDs fabricated by above methods, when the cavity length was $300{\mu}m$, the threshold current was about 10 mA, internal quantum efficiency 82%, internal loss $9.2cm^{-1}$, and characteristic temperature was 65 K at $25~45^{\circ}C$ and 42 K at $45~65^{\circ}C$. /TEX>.