• Journal of Korean Society for Atmospheric Environment
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• v.14 no.E
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• pp.9-17
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• 1998

Oxides of nitrogen play important roles in atmospheric chemistry. Soil has been recognized as a major natural source of NO, and its emission depends on soil parameters such as soil nitrogen availability, soil moisture and temperature. It is necessary to understand effects of these controlling parameters on soil NO emission. In order to understand soil moisture effects on NO emission, variations of NO concentration and existence of its equilibrium concentration were observed from ammonium fertilized Japanese upland soil prepared for different soil moisture conditions. The closed chamber technique was employed for this study. The significant increases in NO with soil moisture were found. Maximum was occurred at sample ID4 (55% of water-filled pore space (WFPS)), but it decreased as soil moisture increased. No significant NO concentration was emitted from soil sample without fertilizer, but there was significant NO in fertilized soil samples. The magnitudes of NO from soil increased with time and reached at steady state within ten minutes approximately. These results suggest that nitrogen input from fertilizer takes charge in the first step of sharp increase in NO emission, and then soil moisture becomes important factor to control NO emission from the soils. NO concentrations from soil were compared to those one-day after the experiment. Results from the comparison analysis suggest that the soil NO flux might have been stimulated by soil disturbances like mixing, and this is much more effective in dry soils rather than in wet soils. It was found that much less NO came out from soils after a day; suggesting that most of NO was released from the soils within a day after fertilizer application during our experiment. The length of NO releasing time span may depend on the amounts of fertilizer applied, soil moisture condition, and other soil physical parameters.

• Resources Recycling
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• v.7 no.4
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• pp.27-34
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• 1998

In this research, the processing control of NiCuZn Ferrite (NCZF) had been studied. NiCuZn Ferrite, which calcined at $700^{\circ}C$ for 3 bours, was ball milled for about 60 hours to ill김ke a size of $0.5\mu\;extrm{m}$ followed by granulation using spray dryer Apparent densincatioo rate and initial permeability of NiCuZn Ferrite with an initial packing density had been investigated as f follows. 1.The relative packing density of NCZF green body increas$\xi$d in the range of 48.6-56.8% with an increased forming pressure of 20-170 MPa. 2. The higher the relative pac퍼ng density of NCZF and the sintering temperature are, the higher the initial densification rate. The increased bulk rlcnsity of NCZF was attributed to the densification rate with decreased open pore and increased closed pore as the relative packing density, sintering temperature, and sinteriog tim$\xi$ increased. 3. The initial P permeability of NCZF with constant composition is logarithmically proportional to the bulk density of NCZF sintered at $875~925^{\circ}C$ for 0-5h, and strongly depended on the relative packing density of NCZF green body. The empirical equation is as f follows; log $\mu$i=$G1{\times}BD$+$G2{\times}RPD$+b(0);where, G1, G2; gradient, B.D: bulk density, RPD; relative packing density, b(0); intercept.

• Journal of the Korean Ceramic Society
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• v.53 no.1
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• pp.43-49
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• 2016

This analyzed a Young's modulus (E), a thermal expansion coefficient (TEC, ${\beta}$) and a thermal conductivity (${\kappa}$) of the material with simple cubic particulate inclusion using two model structures: a parallel structure and a series structure of laminated layers. The derived ${\beta}$ equations were applied to calculate the ${\beta}$ value of the W-MgO system. The accuracy was higher for the series model structure than for the parallel model structure. Young's moduli ($E_c$) of sintered porous alumina compacts were theoretically related to the development of neck growth of grain boundary between sintered two particles and expressed as a function of porosity. The series structure model with cubic pores explained well the increased tendency of $E_c$ with neck growth rather than the parallel structure model. The thermal conductivity of the three phase system of alumina-mullite-pore was calculated by a theoretical equation developed in this research group, and compared with the experimental results. The pores in the sintered composite were treated as one phase. The measured thermal conductivity of the composite with 0.5-25% porosity (open and closed pores) was in accordance with the theoretical prediction based on the parallel structure model.

• Journal of Biomedical Engineering Research
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• v.19 no.3
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• pp.215-224
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• 1998

This paper is fundamental study to develope the extracorporeal liver support system for patient with fulminant hepatic failure(FHF) or being expected for orthotopic liver transplantation. The polyurethane foam, which is composed of the density of 33kg/m3, the average pore diameter of 500${\mu}{\textrm}{m}$, the closed window of 60-70%, was manufactured with the prepolymer of 15% NCO-, Hepatocytes were inoculated to form spheroids in polyurethane foam. The time of spheroid formation in BSA(Bovine Serum Albumin) coated polyurethane foam was shorter than that in raw polyurethane foam. To verify the function of hepatocyte spheroids, we measured ammonia removal rate, urea and albumin secretion rate. Polyurethane foam was suitable for culture of hepatocyte spheroids. And culture of hepatocyte spheroids in polyurethane foam has high possibility in using as an extracorporeal liver support system.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.15 no.5
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• pp.406-411
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• 2002

Ni-Zn ferrite is required to have predominant and stable characteristics in the range of high frequency for the power line communication, so that microstructures and magnetic properties such as power loss and initial permeability in $Ni_{0.8}Zn_{0.2}Fe_2O_4$ were investigated in terms of variable $Bi_2O_3,CaO$ and $V_2O_5$ contents. $Bi_2O_3$ and $V_2O_5$ liquid phase created during sintering process promoted sintering and grain growth but much of the closed pore existed in the grains. The grain size of the specimens with $V_2O_5$ of over 0.5 wt% decreased as the result of "pinning effect"and the resonance frequency increased with CaO of 0.3we%. The high initial permeability of 81.52%, resonance frequency of 17.05 MHz and low power loss of 17,858 kW/$\textrm{m}^3$ were obtained from the samples with $Bi_2O_3$ of 0.5, CaO of 0.3, and $V_2O_5$ of 0.7 wt%.

• Nuclear Engineering and Technology
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• v.34 no.4
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• pp.323-330
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• 2002

Various types of compounds were tested with the aspects of decomposition and formation of residue in a $CO_2$ or 7H$_2$+93$N_2$ atmosphere. The evaporation temperature range of each compound was determined from thermogravimetric curve. Decomposition of dicarbon amide, stearic acid, acrowax and zinc stearate was studied by thermogravimetry in $CO_2$ or in 7H$_2$+93$N_2$ atmosphere. All compounds were decomposed in $CO_2$ atmosphere at lower than 40$0^{\circ}C$, but the residue, ZnO remained for zinc stearate. ZnO did not decompose in $CO_2$ atmosphere up to 130$0^{\circ}C$, but reduced into Zn metal and disappeared in the temperature range of $600^{\circ}C$ to 120$0^{\circ}C$ in 7H$_2$+93$N_2$ atmosphere. The effect of residue, which trapped in closed pores of sintered pellet, on the thermal stability was studied using the resintering test at 1$700^{\circ}C$ in 7H$_2$+93$N_2$ atmosphere. In the case of oxidative sintered pellet with admixing zinc stearate, the cavity formation accompanied with a density drop after resintering is due to the pressure of the Zn gases trapped in the isolated pores.

• Journal of Korean Society of Forest Science
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• v.102 no.3
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• pp.315-322
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• 2013

This study was carried out to establish a management program and soil restoration plan through analysis of soil properties and visitor questionnaires in Songrim in Hadong, Korea. Soil bulk density in Songrim was slightly higher in the closed-woodlands ($1.31g/cm^3$) than in the open-woodlands ($1.39g/cm^3$). Soil bulk density in the closed-woodlands was higher in walking trails ($1.74g/cm^3$) than in forest areas ($1.39g/cm^3$), while the rates of pore space were lower in walking trails (42.6%) than in forest areas (50.5%). The soil porosity were lower in the closed-woodlands (34.6%) than in the open-woodlands (42.6%). Soil strength in surface soil was slightly lower in the open-woodlands ($8.5kgf/cm^2$) than in the closed-woodlands ($10.5kgf/cm^2$). The content of organic matter, total nitrogen and exchangeable cations of the woodlands was low compared with the optimum nutrient content for tree growth in Korea forest soil. According to the survey, the objective of visiting in Songrim was to enjoy recreation and landscape views. To conserve pine forest ecosystems in Songrim, the respondents said that it needs to the implement of closed-woodland periods, the establishment of smoking free zone, and the prohibition of garbage throwing and alcohol including disciplinary rules and education. Also the respondents said that pine forest ecosystem in Songrim is relatively sound, but the woodlands require the intensive management to the ecosystem and the introduction of native understory vegetation, such as grasses under pine forest ecosystem. It is recommended to designate the rest-year forest for a proper period in all woodlands to restore the Songrim soil rather than the alternation application between the rest-year for three years or non-rest-year trails, and to open partially the walking trails across the woodlands after the period. In addition, the forest within the woodland is need to designate a long-term rest-year.

• Journal of the Korean Society for Heat Treatment
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• v.32 no.5
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• pp.201-211
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• 2019

Low carbon steel (S20C steel) and SPCC steel sheet have been austenitic nitrided at $700^{\circ}C$ in a closed pit type furnace by changing the flow rate of ammonia gas and heat treating time. When the flow rate of ammonia gas was low, the concentration of residual ammonia appeared low and the hardness value of transformed surface layer was high. The depth of the surface layer, however, was shallow. With increasing the concentration of residual ammonia by raising up the ammonia gas flow, both the depth of the surface layer and the pore depth increased, while the maximum hardness of the surface layer decreased. By introducing a large amount of ammonia gas in a short time, a deep surface layer with minimal pores on the outermost surface was obtained. In this experiment, while maintaining 10~12% of residual ammonia, the flow rate of inlet ammonia gas, 7 liter/min, was introduced at $700^{\circ}C$ for 1 hour. In this condition, the thickness of the surface layer without pores appeared about $60{\mu}m$ in S20C steel and $30{\mu}m$ in SPCC steel plate. Injecting additional methane gas (carburizing gas) to this condition played a deteriorating effect due to promoting the formation of vertical pores in the surface layer. For $1^{st}$ transformed surface layer for S20C steel, maintaining 10~12% residual ammonia condition via austenitic nitriding process resulted in ${\varepsilon}$ phase with relatively high nitrogen concentration (just below 4.23 wt.%N) among the mixed phases of ${\varepsilon}+{\gamma}$. The ${\varepsilon}$ phase was formed a specific orientation perpendicular to the surface. For $2^{nd}$ transformed layer for S20C steel, ${\gamma}$ phase was rather dominant (just above 2.63 wt.%N). For SPCC steel sheet, there appeared three phases, ${\gamma}$, ${\alpha}(M)$ and weak ${\varepsilon}$ phase. The nitrogen concentration would be approximately 2.6 wt.% in these phases condition.

• Journal of the Korean Ceramic Society
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• v.39 no.3
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• pp.259-264
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• 2002

In this study, sintering properties of Artificial Lightweight aggregates(ALAs) prepared from coal ash as a function of sintering temperature (900$^{\circ}$C, 1000$^{\circ}$C, 1100$^{\circ}$C) and time (2min, 5min, 10min) when limestone added as lightweight mineral was investigated. Increasing the sintering temperature resulted simultaneously from a decline of quartz mineral as well as growth of mullite mineral. Addition of limestone to ALAs newly formed sintered minerals such as clinoptilolite and plagioclase. Sintering effect of ALAs prepared from coal ash and limestone was more affected by a sintering temperature than time. As sintering temperature and time increae, transition of macropore to micropore and formation of closed pores were happened, consequently shrank the total pore volume of ALAs. The surface of ALAs sintered at 1000$^{\circ}$C for 5min was nearly not detected open pores due toe amalgamation effect of molten slag layer but homogeneous distributions of closed pores with micro-scale were examined in cross sectional area ALAs. Sintering temperature and time which present the most adequate state, in the preparation of ALAs, are corresponded to 1000$^{\circ}$C and 5min, respectively.

• Journal of Korean Society for Atmospheric Environment
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• v.27 no.3
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• pp.313-325
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• 2011

From October 2009 to June 2010, major greenhouse gases (GHG: $N_2O$, $CH_4$, $CO_2$) soil emission were measured from upland cabbage field at Kunsan ($35^{\circ}$56'23"N, $126^{\circ}$43'14"E), Korea by using closed static chamber method. The measurements were conducted mostly from 10:00 to 18:00LST during field experiment days (total 28 days). After analyzing GHG concentrations inside of flux chamber by using a GC equipped with a methanizer (Varian CP3800), the GHG fluxes were calculated from a linear regression of the changes in the concentrations with time. Soil parameters (e.g. soil moisture, temperature, pH, organic C, soil N) were also measured at the sampling site. The average soil pH and soil moisture were ~pH $5.42{\pm}0.03$ and $70.0{\pm}1.8$ %WFPS (water filled pore space), respectively. The ranges of GHG flux during the experimental period were $0.08\sim8.40\;mg/m^2{\cdot}hr$ for $N_2O$, $-92.96\sim139.38mg/m^2{\cdot}hr$ for $CO_2$, and $-0.09\sim0.05mg/m^2{\cdot}hr$ for $CH_4$, respectively. It revealed that monthly means of $CO_2$ and $CH_4$ flux during October (fall) were positive and significantly higher than those (negative value) during January (winter) when subsoil have low temperature and relatively high moisture due to snow during the winter measurement period. Soil mean temperature and moisture during these months were $17.5{\pm}1.2^{\circ}C$, $45.7{\pm}8.2$%WFPS for October; and $1.4{\pm}1.3^{\circ}C$, $89.9{\pm}8.8$ %WFPS for January. It may indicate that soil temperature and moisture have significant role in determining whether the $CO_2$ and $CH_4$ emission or uptake take place. Low temperature and high moisture above a certain optimum level during winter could weaken microbial activity and the gas diffusion in soil matrix, and then make soil GHG emission to the atmosphere decrease. Other soil parameters were also discussed with respect to GHG emissions. Both positive and negative gas fluxes in $CH_4$ and $CO_2$ were observed during these measurements, but not for $N_2O$. It is likely that $CH_4$ and $CO_2$ gases emanated from soil surface or up taken by the soil depending on other factors such as background concentrations and physicochemical soil conditions.