• Korean Journal of Materials Research
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• v.14 no.4
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• pp.235-238
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• 2004

The LT-MBE (low temperature molecular beam epitaxy) allows to dope GaAs with Mn over its solubility limit. A 75 urn thick GaMnAs layers are grown on a low temperature grown LT-GaAs buffer layer at a substrate temperature of $260^{\circ}C$ by varying Mn contents ranged from 0.03 to 0.05. The typical growth rate for GaMnAs layer is fixed at 0.97 $\mu\textrm{m}$/h and the V/III ratio is varied from 25 to 34. The electrical and magnetic properties are investigated by Hall effect and superconducting quantum interference device(SQUID) measurements, respectively. Double crystal X-ray diffraction(DCXRD) is also performed to investigate the crystallinity of GaMnAs layers. The $T_{c}$ of the $Ga_{l-x}$ /$Mn_{x}$ As films grown by LT-MBE are enhanced from 38 K to 65 K as x increases from 0.03 into 0.05 whereas the $T_{c}$ becomes lower to 45 K when the V/III ratio increases up to 34 at the same composition of x=0.05. This means that the ferromagnetic exchange coupling between Mn-ion and a hole is affected by the growth condition of the enhanced V/III ratio in which the excess-As and As-antisite defects may be easily incorporated into GaMnAs layer.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1997.11a
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• pp.60-63
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• 1997

Dieletric ailed piezoelectric properties of Pb[$Zr_{0.45}$/ $Ti_{0.5-x}$/L $u_{x}$ (M $n_{1}$3//S $b_{2}$3)$_{0.05}$] $O_3$(0$\leq$x $\leq$0.03) were investigated. The partial substitution of $Ti^{4+}$ by a L $u^{3+}$ permitted improvement of the piezoelectric constant( $d_{33}$ ), electromechanical coupling factor ( $k_{p}$ ) and dielectric constant($\varepsilon$$_{33}$ /Sup T/). The dielectric loss(tan $\delta$ ) increased and mechanical quality factor(Qm) decreased with an increase of x were observed. A new piezoelectric material for actuator application was developed at x=0.02 with $d_{33}$ =370$\times$10$^{-2}$ /C/N, $k_{p}$ =58.5%, $\varepsilon$$_{33}$ $^{T}$ =1321, $Q_{m}$ =714 and tan $\delta$ =0.98%.%..%.%.

• Journal of the Korean Chemical Society
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• v.38 no.2
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• pp.92-100
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• 1994

Ultrafine cobalt-substituted iron oxide particles were prepared by the thermal decomposition and oxidation of the new organometallic precursor, $Co_xFe_{1-x}(N_2H_3COO)_2(N_2H_4)_2$ (x = 0, 0.01, 0.02, 0.03, 0.05, 0.10, 1.00). The organometallic precursors were synthesized by the reaction of Co(II) and Fe(II) ion in a mole ratio of x : 1-x with hydrazinocarboxylic acid, and characterized by quantitative analysis, elemental analysis and infrared spectroscopy. The mechanistic study on the thermal decomposition of the organometallic precursors was performed by TG-DTG and DSC. The cobalt-substituted iron oxide particles were obtained by the heat treatment of the precursors at $350^{\circ}C$ and $450^{\circ}C$ for six hours in air. The prepared iron oxide was found to have two phases such as ${\gamma}-Fe_2O_3$ and a mixture of ${\gamma}-Fe_2O_3\;and\;{\alpha}-Fe_2O_3$ at $350^{\circ}C$ and $450^{\circ}C$ respectively. The particle shape was equiaxial and the particle size was less than 0.05 ${\mu}m.$ The coercivity and squareness of the cobalt substituted iron oxide particles increased with increasing cobalt content. Both coercivity and squareness showed higher values at $450^{\circ}C.$

• Korean Journal of Fisheries and Aquatic Sciences
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• v.21 no.6
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• pp.361-365
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• 1988

Thermal diffusivities of white muscled fish meat paste products were measured and an experimental equation for prediction of the thermal diffusivity was suggested. The thermal diffusivities of products with water contents of 43.03 to $82.49\%$ and lipid contents of 0.50 to $14.88\%$ could be deduced as following equations ; $$\alpha_{80.39^{\circ}C}=0.0832{\cdot}10^{-6}{\cdot}X_w+0.0797{\cdot}10^{-6},\;m^2{\cdot}s^{-1}$$ $$\alpha_{100.63^{\circ}C}=0.0873{\cdot}10^{-6}{\cdot}X_w+0.0830{\cdot}10^{-6},\;m^2{\cdot}s^{-1}$$ $$\alpha_{120.09^{\circ}C}=0.0842{\cdot}10^{-6}{\cdot}X_w+0.0901{\cdot}10^{-6},\;m^2{\cdot}s^{-1}$$ From these equations, an experimental equation was derived for the prediction of thermal diffusivities of white muscled fish meat paste products ; $$\alpha=(1.308+0.1324{\cdot}X_w){\cdot}\alpha_w-0.0626{\cdot}10^{-6}{\cdot}X_w-0.1355{\cdot}10^{-6},\;m^2{\cdot}s^{-1}$$ The errors of the thermal diffusivities predicted with this equation were less than ${\pm}\;0.30\%$ compared with those measured.

• Korean journal of food and cookery science
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• v.3 no.1
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• pp.71-77
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• 1987

This study was to investigate the synergistic taste effect between monosodium glutamate(MSG) and 5'-ribonucleotides consisted of disodium 5'-inosinate (IMP) and 5'-guanylate (GMP) as 1:1 ratio. Solvent was distilled water. Sensory evaluation with 10 panelists was performed by using ratio scaling method (magnitude estimation). The results were as follows: 1) Taste intensities were increased, as nucleotides content to MSG increased. 2) Multiple regression analyses were carried out with the taste intensity data as a function of nucleotides content at three concentrations of seasonings, 0.025%, 0.05% and 0.1%. 3) Predicted taste intensities ($Y_P$) were calculated from the regression equation. Also taste intensity ratios ($Y_{TR}$)-$Y_{TR}$=$Y_P$/taste intensity of MSG only-were calculated. 4) The taste intensity ratios ($Y_{TR}$) at three concentrations of seasonings in the same nucleotides contents showed about the same. Therefore, instead of above regression equations, only one multiple regression equation expressing $Y_P$ of nucleotides seasonings could be determined, as functions of nucleotides content and seasoning concentration.

• Journal of the Semiconductor & Display Technology
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• v.13 no.4
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• pp.21-25
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• 2014

The silicon nitride ($SiN_x$) film for surface passivation and anti-reflection coating of crystalline silicon solar cell is very important and it is generally deposited by plasma enhanced chemical vapor deposition (PECVD). PECVD can be divided into low and high frequency method. In this paper, the $SiN_x$ film deposited by low and high frequency PECVD method was studied. First, to optimize the $SiN_x$ film deposited by low frequency PECVD method, the refractive index was measured by varying the process conditions like $SiH_4$, $NH_3$, $N_2$ gas rate, and RF power. When $SiH_4$ gas rate was increased and $NH_3$ gas rate was decreased, the refractive index was increased. The refractive index was also increased with RF power decline. Second, to compare the characteristics of the low and high frequency PECVD $SiN_x$ film, the refractive index was measured by varying $NH_3/SiH_4$ gas ratio and RF power and the minority carrier lifetime of before and after high temperature treatment process was also measured. The refractive index of both low and high frequency PECVD $SiN_x$ film was decreased with increase in $NH_3/SiH_4$ gas ratio and RF power. After high temperature treatment process, the minority carrier lifetime of both low and high frequency PECVD $SiN_x$ film was increased and increased degree was similar. The minority carrier lifetime of low frequency PECVD $SiN_x$ was increased from $11.03{\mu}m$ to $28.24{\mu}m$ and that of high frequency PECVD $SiN_x$ was increased from $11.60{\mu}m$ to $27.10{\mu}m$.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.31 no.4
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• pp.335-340
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• 2007

A new correlation between the Nusselt number based on modified heat transfer coefficient and Reynold number based on droplet-flow-rate was developed for the experimental data. The modified heat transfer coefficient was defined as ratio of wall heat flux to droplet subcooling. In the previous reports, the local heat flux of spray cooling in the film boiling region was experimentally investigated for the water spray region of $D_{max} = 0.0007{\sim}0.03m^3/(m^2s)$ . In the region near the stagnation point of spray flow, a new heat transfer correlation is recommended which shows good predictions for the water spray region of $D_x{\le}0.01m^3/(m^2s)$.

• Journal of the Korean Ceramic Society
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• v.33 no.4
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• pp.432-440
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• 1996

ZrO2 gel was prepared under pH 10 alkaline condition by sol-gel process and was investigated as a function of calcination temperature and effect of calcination temperature on cobalt adsorption capacity. The ZrO2 powder prepared by sol-gel process was calcined at 600, 800, 1000, 1200, 140$0^{\circ}C$ and analyzed by X-ray diffractometry. SEM specific surface area by BET nitrogen adsorption FT-IR and TG-DTA technique. It was shown that cobalt adsorption capacity of ZrO2 prepared under pH 10 alkaline condition and then calcined at $600^{\circ}C$ in high temperature was determined to be larger than that of ZrO2 at various calcination temperature. The specific surface area of ZrO2 calcined at $600^{\circ}C$ was 24.03m2/g and cobalt adsorption capacity at 25$0^{\circ}C$ high-temperature water was 0.16m-eq/g.

• Korean Journal of Metals and Materials
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• v.49 no.4
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• pp.348-354
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• 2011

Long-lasting brightness $Sr_{4}Al_{14}O_{25}$ : $Eu^{2+}$, $Dy^{3+}$, $Ag^{+}$ phosphor was synthesized by modified solid state reaction and its photoluminescence was investigated. $Sr(NO_3)_{2}$ and $Al(NO_3)_3{\cdot}9H_{2}O$ as starting materials, and $B_{2}O_{3}$ as a flux were mixed with $Eu_{2}O_{3}$ as an activator, $Dy_{2}O_{3}$ as a coactivator, and $AgNO_{3}$ as a charge compensator. The crystalline of target powder showed a single-phase $Sr_{4}Al_{14}O_{25}$ by the XRD characterization and the average particle size was about 20-30 ${\mu}m$ from the FE-SEM observation. $Ag^{+}$ ion doping effects (0-0.06 mol) on $Sr_{4}Al_{14}O_{25}:Eu^{2+},\;Dy^{3+},\;Ag^{+}$ phosphor were measured by photoluminescence spectrometer and luminescence meter. The of photoluminescence intensity of the $Sr_{3.64}Al_{14}O_{25}:Eu_{0.11},\;Dy_{0.22},\;Ag_{0.03}$ phosphor was higher than other compositions and afterglow brightness was 0.186 $cd/m^{2}$.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.2
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• pp.137-145
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• 2008

An experimental study was performed in order to investigate the influence of Reynolds number on the drag coefficient variations of an oscillating airfoil. A NACA 0012 airfoil was sinusoidally pitched at the quarter chord point with an oscillating amplitude of ${\pm}6^{\circ}$. The free-stream velocities were 1.98, 2.83 and 4.03 m/s and the corresponding chord Reynolds numbers were $2.3{\times}10^4$, $3.3{\times}10^4$ and $4.8{\times}10^4$, respectively. The drag coefficient was calculated from the ensemble average velocity measured by an X-type hot-wire probe(X-type, 55R51) in the near-wakes region. In the case of Re=$2.3{\times}10^4$, variation of drag coefficient shows a negative damping (counter-clockwise variation), which implies an unstable state which could be excited by aerodynamic force, whereas the drag coefficient represents the positive damping (clockwise variation) as the Reynolds number increases from Re=$3.3{\times}10^4$ to $4.8{\times}10^4$. Hence, the drag coefficient variations show significant differences between Re=$2.3{\times}10^4$ and $4.8{\times}10^4$이다.