• Journal of the Korean Electrochemical Society
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• v.19 no.2
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• pp.50-56
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• 2016

Spherical lithium manganese oxide spinel, $Li_{1.10}Mn_{1.86}Al_{0.02}Mg_{0.02}O_4$ was prepared by wet-milling, spray-drying, and sintering process. In the spray-drying process, solid content in slurry was varied from 20 to 30 wt%. In the sintering process, the precursors have been sintered under air or $O_2$ atmosphere. While the as-prepared samples exhibit excellent electrochemical properties at room temperature, the discharge voltage profiles at 5.0C are very different one from another. The origin for the difference especially at initial state of discharge is oxygen defect. The sample prepared in air has larger capacity related to the plateau at 3.3 V (vs. $Li/Li^+$) which is caused by the oxygen defects than the one prepared in $O_2$. The difference of discharge voltage profiles especially at the final state of discharge comes from different diffusion rate of $Li^+$ ions. The sample prepared from 30 wt% solid content of slurry shows twice higher diffusion rate than the samples prepared from 20 wt% solid content, which is attributed to better compactness between primary particles for the sample prepared from 30wt % solid content than the one prepared by 20 wt%.

• Clean Technology
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• v.21 no.1
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• pp.53-61
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• 2015

In this study, we have investigated the kinetics on the char-CO₂ catalytic gasification reaction. Thermogravimetric analysis (TGA) experiments were carried out for char-CO₂ catalytic gasification of an Indonesian Kideco sub-bituminous. Na₂CO₃ and K₂CO₃ were selected as catalysts which were physically mixed with coal. The char-CO₂ catalytic gasification reaction showed a rapid increase of carbon conversion rate at 850 ℃, 60 vol% CO₂, and 7 wt% Na₂CO₃. At the isothermal conditions ranging from 750 ℃ to 900 ℃, the carbon conversion rates increased as the temperature increased. Four kinetic models for gas-solid reaction including the shrinking core model (SCM), random pore model (RPM), volumetric reaction model (VRM), and modified volumetric reaction model (MVRM) were applied to the experimental data against the measured kinetic data. The gasification kinetics were suitably described by the MVRM for the Kideco sub-bituminous. The activation energies for each char mixed with Na₂CO₃ and K₂CO₃ were found 55-71 kJ/mol and 69-87 kJ/mol.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.3
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• pp.259-267
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• 2010

In this study, the effect of particle size on the combustion characteristics of pulverized sub-bituminous coal was experimentally investigated. A laminar-flow-entrained reactor was designed and implemented to realize the desired heating ratio and temperature corresponding to the combustion atmosphere of a pulverized-coal-fueled furnace. The flame length and structure of burning particles according to different sizes were investigated. Coal combustion processes were clearly distinguished by direct visual observation of the flame structure. The onset point of volatile ignition is greatly affected by changes in the particle size, and the burning time of the volatiles is least affected by changes in the particle size. The length and instability of char flame also increase with the increase of the particle size. However, the char consumption rate within the residential time remains nearly constant.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.26 no.5
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• pp.193-200
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• 2016

Characteristics of $SrAl_2O_4:Eu^{2+}$, $Dy^{3+}$ phosphorescent phosphors synthesized by solid state reaction and polymerized complex method were comparatively analyzed. In order to evaluate thermal stability of $SrAl_2O_4:Eu^{2+}$, $Dy^{3+}$ phosphorescent phosphors at high temperature, phosphorescent properties of $SrAl_2O_4:Eu^{2+}$, $Dy^{3+}$ were investigated with thermal treatment at $1250^{\circ}C$ under reducing atmosphere, which was the general heat treatment conditions for ceramic manufacturing process. The phosphorescent properties of thermally treated $SrAl_2O_4:Eu^{2+}$, $Dy^{3+}$ phosphors synthesized by solid state reaction and polymerized complex method were investigated. The crystal structure and crystallite size were observed through XRD analysis. Microstructure and particle size of thermally treated $SrAl_2O_4:Eu^{2+}$, $Dy^{3+}$ phosphors were analyzed by SEM and PSA. Photoluminescence and afterglow characteristics of thermally treated $SrAl_2O_4:Eu^{2+}$, $Dy^{3+}$ phosphorescent phosphors were measured by spectrofluorometer.

• Journal of Radiation Protection and Research
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• v.17 no.2
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• pp.25-35
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• 1992

To evaluate tritium level in some environmental samples, tissue-free water tritium (TFWT) and tissue-bound tritium (TBT) were analyzed in rices, chinese cabbages and pine needles collected at 12 locations in Korea. The TFWT was recovered by freeze-drying of the samples and the TBT was obtained in the form of water by combustion of the dried samples. Tritium was measured by liquid scintillation counter. The concentrations of TFWT were in the range of $0.96{\sim}3.96 Bq/1,\; 0.83{\sim}3.40 Bq/1\;and\;1.02{\sim}3.01 Bq/1$ in rices, chinese cabbages and pine needles, respectively. The mean specific activity ratios (TBT/TFWT) were 0.94, 1.71 and 1.39 in rices, chinese cabbages and pine needles, respectiviely. This excess TBT in the samples may be attributed to the fact that the residence time of TBT in the plant is longer than that of TFWT. The specific activity ratio depends on the plant species, the exposed time to tritiated atmosphere, atmospheric moisture, temperature and diffusion factor.

• Culinary science and hospitality research
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• v.21 no.1
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• pp.42-57
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• 2015

When a customer chooses a coffee shop, different factors can influence his/her purchase. These factors can include tangible as well as intangible elements such as the coffee shop's atmosphere, layout, and interior. Thus, many coffee brands strive to serve not only a diverse menu, but also a unique quality of environment. This study aimed to investigate the influence of physical environment on customer satisfaction and loyalty in the coffee shop and evaluate the influential power of the physical environment factors using hierarchical regression analysis. Data was collected from customers of coffee shops in Texas, the U.S. The study found that the coffee shops' physical environment influenced the customer's satisfaction and loyalty. Particularly, the coffee shop's physical environment including ambient and interior design greatly influenced the customers' satisfaction. However, a broad range of physical environment factors such as temperature, aroma, lighting, color, and interior furnishings should be provided to increase the customer loyalty. The results may have a broader application to provide effective managerial and marketing information to Korean coffee entrepreneur brand in the U.S. and beyond.

• Korean Journal of Materials Research
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• v.18 no.4
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• pp.169-174
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• 2008

The structural and electrical properties of amorphous $BaSm_2Ti_4O_{12}$ (BSmT) films on a $TiN/SiO_2/Si$ substrate deposited using a RF magnetron sputtering method were investigated. The deposition of BSmT films was carried out at $300^{\circ}C$ in a mixed oxygen and argon ($O_2$ : Ar = 1 : 4) atmosphere with a total pressure of 8.0 mTorr. In particular, a 45 nm-thick amorphous BSmT film exhibited a high capacitance density and low dissipation factor of $7.60\;fF/{\mu}m2$ and 1.3%, respectively, with a dielectric constant of 38 at 100 kHz. Its capacitance showed very little change, even in GHz ranges from 1.0 GHz to 6.0 GHz. The quality factor of the BSmT film was as high as 67 at 6 GHz. The leakage current density of the BSmT film was also very low, at approximately $5.11\;nA/cm^2$ at 2 V; its conduction mechanism was explained by the the Poole-Frenkel emission. The quadratic voltage coefficient of capacitance of the BSmT film was approximately $698\;ppm/V^2$, which is higher than the required value (<$100\;ppm/V^2$) for RF application. This could be reduced by improving the process condition. The temperature coefficient of capacitance of the film was low at nearly $296\;ppm/^{\circ}C$ at 100 kHz. Therefore, amorphous BSmT grown on a TiN substrate is a viable candidate material for a metal-insulator-metal capacitor.

• Journal of the Korean Solar Energy Society
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• v.23 no.2
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• pp.59-70
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• 2003

A stoichiometric mixture of evaporating materials for $CuGaSe_2$ single crystal thin films was prepared from horizontal electric furnace. Using extrapolation method of X-ray diffraction patterns for the polycrystal $CuGaSe_2$, it was found tetragonal structure whose lattice constant $a_0$ and $c_0$ were $5.615{\AA}$ and $11.025{\AA}$, respectively. To obtain the single crystal thin films, $CuGaSe_2$ mixed crystal was deposited on thoroughly etched semi-insulating GaAs(100) substrate by the hot wall epitaxy (HWE) system. The source and substrate temperatures were $610^{\circ}C$ and $450^{\circ}C$, respectively. The crystalline structure of the single crystal thin films was investigated by the photoluminescence and double crystal X-ray diffraction (DCXD). The carrier density and mobility of $CuGaSe_2$ single crystal thin films measured with Hall effect by van der Pauw method are $5.01\times10^{17}cm^{-3}$ and $245cm^2/V{\cdot}s$ at 293K. respectively. The temperature dependence of the energy band gap of the $CuGaSe_2$ obtained from the absorption spectra was well described by the Varshni's relation, $E_g$(T)=1.7998 eV-($8.7489\times10^{-4}$ eV/K)$T^2$/(T+335K). After the as-grown $CuGaSe_2$ single crystal thin films was annealed in Cu-, Se-, and Ga-atmospheres, the origin of point defects of $CuGaSe_2$ single crystal thin films has been investigated by the photoluminescence(PL) at 10 K. The native defects of $V_{CU},\;V_{Se},\;Cu_{int}$ and $Se_{int}$ obtained by PL measurements were classified as a donors or acceptors type. And we concluded that the heat-treatment in the Cu-atmosphere converted $CuGaSe_2$ single crystal thin films to an optical n-type. Also, we confirmed that Ga in $CuGaSe_2$/GaAs did not form the native defects because Ga in $CuGaSe_2$ single crystal thin films existed in the form of stable bonds.

• The Korean Journal of Ecology
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• v.26 no.3
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• pp.129-134
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• 2003

Amounts of CO₂ fixed by net primary production and released by soil respiration were determined on big-cone pine plantation. Net primary production, which was determined by allometric method, was converted into CO₂. CO₂ evolution in forest ecosystems are mainly through soil and root respiration. In order to separate root respiration from soil respiration, root-free sites were made in stand. Litter removal sites were prepared to estimate CO₂ evolution through litter layer. Respiration was measured at every two weeks intervals from April 2001 through April 2002, and soil temperature and soil moisture were measured at the same time. Net primary production of this big-cone pine plantation was 25.7 t·ha/sup -1/·yr/sup -1/. The amount of CO₂ fixed by this plantation was 42.5 t CO₂·ha/sup -1/·yr/sup -1/, The amount of CO₂ released by soil respiration was 5.0 t CO₂·ha/sup -1/·yr/sup -1/. The relative contribution of root respiration and litter layer respiration to total respiration was 46% and 32%, respectively. Net amount of fixed CO₂ was 37.5 t CO₂·ha/sup -1/·yr/sup -1/ in this big-cone pine plantation. From this result, this big-cone pine plantation play a carbon sink source from the atmosphere.

• Korean Chemical Engineering Research
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• v.44 no.6
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• pp.609-613
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• 2006

Ba2-xSrxSiO4:Eu2+ phosphor particles with the high photoluminescence (PL) intensity under long wavelength ultraviolet (UV) were prepared by spray pyrolysis. The photoluminescence, morphological and crystalline characteristics of $Ba_{2-x.}Sr_{x.}SiO_4:Eu^{2+}$ phosphor particles prepared by spray pyrolysis were investigated. $Ba_{2-x.}Sr_{x.}SiO_4:Eu^{2+}$ phosphor particles prepared by spray pyrolysis had various colors from bluish green to yellow by changing the ratio of barium and strontium of the host material. In case of x=0, the main emission peak of $Ba_2SiO_4:Eu^{2+}$ phosphor was 500 nm. In case of x=2, the main emission peak of $Sr_2SiO_4:Eu^{2+}$ phosphor was 554nm. $Ba_{2-x.}Sr_{x.}SiO_4:Eu^{2+}$ phosphor particles obtained by spray pyrolysis had spherical shape and hollow structure. On the other hand, the post-treated $Ba_{2-x.}Sr_{x.}SiO_4:Eu^{2+}$ phosphor particles had large size and irregular shape. The $Ba_{1.488}Sr_{0.5}SiO_4:Eu_{0.012}{^{2+}}$ phosphor particles had the maximum PL intensity after post-treatment at temperature of $1300^{\circ}C$ for 3h under reduction atmosphere.