• Korean Journal of Optics and Photonics
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• v.14 no.2
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• pp.135-141
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• 2003

In arrayed waveguide grating (AWG) devices whose waveguides were composed of polymer with negative thermo-optic coefficient as overcladding, and silica with positive thermo-optic coefficient as both core and undercladding, we investigated the temperature dependence of the central wavelength using two-dimensional SFDM. From these results, it was confirmed that the temperature dependence can be nearly eliminated by adjusting the refractive index of the cladding and the thickness of the silica thin film upper-loaded on the core. Based on the numerical calculations, the AWG device with polymer overcladding was fabricated. and its optical characteristics were compared with those of the orginal silica AWG device. The introduction of polymer overcladding decreased the temperature dependence of the central wavelength from 0.0130 nm/$^{\circ}C$ to 0.0028 nm/$^{\circ}C$ without deteriorating the insertion loss and crosstalk characteristics.

• Journal of the Korean Applied Science and Technology
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• v.17 no.2
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• pp.132-138
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• 2000

Excess enthalpies ($H^{E}$) were measured by isothermal flow calorimetry for the nonionic amphiphile 2-butoxyethanol/water mixtures at 10 different temperatures (48.5 to $70^{\circ}C$) around and above the lower consolute solution temperature, $T_{lc}$. $H^{E}$ exhibits U-shape for the binary mixtures, and is large and negative which reflects substantial interaction between two chemical species. When the commonly used, semi-empirical Redlich-Kister (RK) polynomials were fitted to the measured $H^{E}$, plots of $H^{E}$ vs. weight fraction provided more accurate fitting with fewer parameters than conventionally drawn $H^{E}$ vs. mole fraction plots. This was due to the enhanced symmetry of $H^{E}$ vs. weight fraction plots. Using the fitted Redlich-Kister polynomials and the Gibbs-Helmholtz relation, temperature dependence of the activity coefficients were found and compared to the values determined from vapor-liquid equilibria. The activity coefficients were in the range of one to three, indicating that the binary system deviates from ideality but not substantially. They slightly depended on temperature and the temperature effect was equivalent to 10 % change in the activity coefficients.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.53 no.9
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• pp.459-463
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• 2004

In this study, the (l-x)$TiTe_3O_{8}$-x$MgTiO_3$ ceramics were investigated to obtain the improved dielectric properties of a high temperature stability and a sintering temperature of less than $900^{\circ}C$ which was necessary for the LTCC. According to the X-ray diffraction patterns of the (l-x)$TiTe_3O_{8}$-x$MgTiO_3$(x=0∼1) ceramics, the columbite structure of $TiTe_3O_{8}$ and ilmenite structure of $MgTiO_3$ were coexisted. Increasing the $MgTiO_3$ mole ratio(x), the density and dielectric constant were decreased and temperature coefficient of resonant frequency was moved to the negative direction and the quality factor was increased. In the case of the 0.6$TiTe_3O_{8}$-0.4$MgTiO_3$ ceramics sintered at $830^{\circ}C$ for 3hr., the microwave dielectric properties were $\varepsilon_{\gamma}$=29.3, Q${\times}$$f_{\gamma}$=39.600GHz and $\tau$$_{f}$=+9.3ppm/$^{\circ}C$.

• Journal of the Korean Ceramic Society
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• v.32 no.2
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• pp.171-182
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• 1995

Five eucryptite and ten spodumene compositional powders were syntehsized from three sillimanite group, two kaolin group, and five pyrophyllite group silicate minerals. Those powders were isotatically pressed and fired at 1200~135$0^{\circ}C$ for 2 hrs, and then the sintered bodies were characterized. Silicate minerals with molar ratio of Al2O3 to SiO2 correspond to those of eucryptite and spodumene are kaolin and pyrophyllite group silicate minerals, respectively. Sintering characteristics of eucryptite from kaolin group and spodumene from pyrophyllite group mineral were superior to those from other silicate minerals. Eucryptite sintered bodies with 95~97% relative densities and densified microstructures can be obtained using Hadong pink kaolin as starting materials by sintering over broad temperature zone(1250~135$0^{\circ}C$). The eucryptite sintered bodies which were fired at 130$0^{\circ}C$ for 2hrs, from Hadong pink kaolin had within 3.0wt% microstructural compositional variations compaired with stoichiometric compound, and had good negative thermal expansiion property with -3.55$\times$10-6/$^{\circ}C$ thermal expansion coefficient. Spodumene sintered bodies which were prepared from pyrophyllite group silicate minerals, had dense microstructures and high densities by densification through liquid phase sintering with enlarged temperature range. The specimens which were fired at 130$0^{\circ}C$ for 2 hrs from Gusipyrophillite, had dense microstructure with crystallines mainly, and low thermal expansion property with 0.62$\times$10-6/$^{\circ}C$ thermal expansion coefficient. The porous texture and residual glass phase in LAS system ceramics which were prepared from silicate minerals, tend to increase the thermal expansion properties of sintered bodies to positive direction.

• Nuclear Engineering and Technology
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• v.45 no.5
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• pp.573-580
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• 2013

The combined effects of reactivity coefficients, along with other core nuclear characteristics, determine reactor core behavior in normal operation and accident conditions. The Power Coefficient of Reactivity (PCR) is an aggregate indicator representing the change in reactor core reactivity per unit change in reactor power. It is an integral quantity which captures the contributions of the fuel temperature, coolant void, and coolant temperature reactivity feedbacks. All nuclear reactor designs provide a balance between their inherent nuclear characteristics and the engineered reactivity control features, to ensure that changes in reactivity under all operating conditions are maintained within a safe range. The $CANDU^{(R)}$ reactor design takes advantage of its inherent nuclear characteristics, namely a small magnitude of reactivity coefficients, minimal excess reactivity, and very long prompt neutron lifetime, to mitigate the demand on the engineered systems for controlling reactivity and responding to accidents. In particular, CANDU reactors have always taken advantage of the small value of the PCR associated with their design characteristics, such that the overall design and safety characteristics of the reactor are not sensitive to the value of the PCR. For other reactor design concepts a PCR which is both large and negative is an important aspect in the design of their engineered systems for controlling reactivity. It will be demonstrated that during Loss of Regulation Control (LORC) and Large Break Loss of Coolant Accident (LBLOCA) events, the impact of variations in power coefficient, including a hypothesized larger than estimated PCR, has no safety-significance for CANDU reactor design. Since the CANDU 6 PCR is small, variations in the range of values for PCR on the performance or safety of the reactor are not significant.

• Journal of the Korean Society of Groundwater Environment
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• v.2 no.2
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• pp.85-92
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• 1995

This study was conducted to find out the relationship between microflora in groundwater and its physico-chemical environmental factors at the 59 sites, where distributed at 3 cities and 18 counties in Jeonranam-Do, Korea. The average values of environmental factors were as followings; pH 6.9, temperature 20.1 $^{\circ}C$, dissolved oxygen 6.5 mg/1, the depth of wells 80.1 m, and nitrate 10.7 mg/1. The average value of microbial population size; Heterotrophic bacteria-NA (HPC-NA) and heterotrophic bacteria-YEPD (HPC-YEPD) were 1.4${\times}$10$^3$CFU/ml and 0.59${\times}$10$^3$ CFU/ml respectively HPC-YEPD numbers were 42.1% of HPC-YEPD. Coliform bacteria were detected at 16 sites, and its average numbers were 6.7 CFU/ml. General fungi were detected at 14 sites, and its had average numbers were 3.9 CFU/ml. The correlation coefficient was calculated value as relation index between the microbial population sizes and environmental factors in groundwater. In case of HPC-NA, the correlation coefficient value with dissolved oxygen was 0.087 But it showed negative correlation coefficient with other factors. In case of HPC-YEPD, the correlation coefficient value with pH, temperature and nitrate were 0.0957, 0.0019 and 0.0151 respectively. It was concluded that the population size of HPC-NA were influenced by the order of temperature, dissolved oxygen, pH and the depth of wells and that HPC-YEPD were influenced by the order of pH, dissolved oxygen, nitrate, the depth of wells and temperature.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.35D no.10
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• pp.51-59
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• 1998

($Na_{1/2}Ln_{1/2}$)$TiO_3$ceramics have a high relative dielectric constant and a positive temperature coefficient of resonant frequency ($\tau_f$)(where Ln represents a lanthanide: $La^{+3}$, $Pr^{+3}$, $Nd^{+3}$ and $Sm^{+3}$). On the other hand, $MgTiO_3$ ceramic has a high Qf value and a negative temperature coefficient. So We have investigated the microwave dielectric properties of $xMgTiO_3$-(1-x) ($Na_{1/2}Ln_{1/2}$)$TiO_3$. In these systems, there are no clues on solid-solution and secondary phase. There are mixed phases with $MgTiO_3$and ($Na_{1/2}Ln_{1/2}$)$TiO_3$ phases. Its dielectric characteristics (Qf, temperature coefficient and dielectric constant) are intermediate between ($Na_{1/2}Ln_{1/2}$)$TiO_3$ and $MgTiO_3$ and are predictable by the logarithmic mixing rule. The dielectric ceramic compositions temperature coefficient each approximates to zero at Ln=La, x=0.9, Ln=Pr, x=0.87, and Ln=Nd, x=0.84. At this time, there are Qf values in the range of 55,000 to 28,00GHz and relative dielectric constants in the range of 22 to 25.

• Journal of Environmental Health Sciences
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• v.7 no.1
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• pp.21-31
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• 1981

This survey was carried out to investigate the temperature, pH value, nitrogen (ammonia, nitrite, nitrate), turbidity, color, chloride ion, $KMnO_4$ consumed, and hardness as chemical analysis of the tap water in Seoul city area during the period from September to Octobor, 1979, and to observe the differences among the values by the distance from the water purification plant and by the district supplied tap water from-the each water purification plant. The results obtained were as follows: 1) An average of the water temperature was $19.8\pm 0.2\circ$C. 2) An average of pH was $7.18\pm 0.02$. The difference among each district was statistically significant (p<0.01), but it was not observed among each distance. 3) An average of turbidity was $1.25\pm 0.12$ ppm. The difference among each district was highly significant (p<0.01), respectively, but not among each distance. 4) An average of color was $1.43\pm 0.16$ ppm, and there were statistically significant differences by the distance and by the district (p<0.01). 5) An average of ammonia nitrogen was $0.022\pm 0.005$ ppm. The differences among each distance, and district were statistically significant (P<0.01). 6) An average of nitrite nitrogen was $0.0050\pm 0.0013$ ppm, and the difference among each distance was highly significant (p<0.01), respectively, and each district showed statistical significance (p<0.01). 7) An average of nitrate nitrogen was $0.82\pm 0.08$ ppm. The difference among each district was significant (p<0.05), and each distance showed high significance (p<0.01). 8) An average of $KMnO_4$ consumed was $3.73\pm 0.16$ ppm, and the difference among each district was significant (p<0.05), but it was not observed among each distance. 9) An average of chloride ion was $8.56\pm 0.28$ ppm, and the difference among each district was higly significant (p<0.01), respectively, but it was not observed among each distance. 10) An average of hardness was $40.69\pm 1.17$ ppm, and there was statistically significant difference by each district (P<0.01), but not by distance. 11) The interrelation between temperature and pH of the tap water revealed the negative correlation from the coefficient of it as showed r=-0.6073 and p<0.01. 12) Except water temperature, there were negative correlationships between pH and other water qualities. 13) Correlation coefficients of $KMnO_4$ comsumed and ammonia nitrogen, nitrite nitrogen were statistically significant but that of $KMnO_4$ consumed and nitrate nitrogen showed no statistical correlationship. 14) Ammonia nitrogen seems to have high correlationship with nitrite nitrogen(r= +0.6669), but not with nitrate nitrogen. 15) Nitrate nitrogen seems to have statistically significant correlationship with nitrite nitrogen (r=+0.4959), but not with ammonia nitrogen. 16) The interrelation between chloride ion and hardness of the tap water revealed positive correlation from the coefficient of it as showed as r=+0.4888 and p<0.01.

• Journal of the Korean Ceramic Society
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• v.47 no.5
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• pp.457-460
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• 2010

$SmCoO_3$ system was investigated for their application to themoelectric materials. All specimens showed p-type semiconducting behavior and their electrical conductivity ($\sigma$), Seebeck coefficient (S) and power factor were measured at high temperature. And the effect of dopant ions on their thermoelectrical properties were also investigated. $Fe^{3+}$ ion doped into $Co^{3+}$ site enhanced the Seebeck coefficient and decreased the electrical conductivity simultaneously. The maximum Seebeck coefficient value for 60% doping case reached to 780 ${\mu}V$/K at $240^{\circ}C$. However $Fe^{3+}$ doped system cause an negative effect on power factor value. In case of the pure phase, the maximum Seebeck coefficient value reached to 290 ${\mu}V$/K at $240^{\circ}C$ and the maximum electrical conductivity was obtained 748 1/(ohm$\times$cm) at $960^{\circ}C$. As a result, the maximum power factor was obtained $1.49\times10^{-4}$ W/$mK^2$ at $550^{\circ}C$.

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.1
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• pp.58-66
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• 2022

In this study, to examine the effect of the transverse thermal expansion behavior of FRP reinforcing bars and concrete on the concrete cover thickness, based on 20℃, when the temperature changes from -70℃ to 80℃, the behavior of concrete was studied theoretically and numerically. Theoretical elastic analysis and nonlinear finite element analysis were performed on FRP reinforced concrete with different diameters and cover thicknesses of FRP reinforcement. As a result, at a negative temperature difference, concrete was compressed, and the theoretical strain result and the finite element result were similar, but at a positive temperature difference, tensile stress and further cracks occurred in the concrete, which was 1.2 to 1.4 times larger than the theoretical result. The ratio of the diameter of the FRP reinforcing bar to the thickness of the concrete cover (c/db) is closely related to the occurrence of cracks. Since the transverse thermal expansion coefficient of FRP reinforcing bars is three times greater than that of concrete, it is necessary to consider this in design.