• Journal of Korean Tunnelling and Underground Space Association
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• v.8 no.3
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• pp.237-247
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• 2006

The use of high-performance shotcrete lining is indispensable to improve long-term durability of a tunnel and to apply the single-shell tunnelling method. Among a lot of shotcrete admixtures, pozzolan materials such as silica fume have positive effects on increasing the strength and the durability of shotcrete. It is also well known that a cement-based accelerator is much faster in setting time and more eco-friendly than conventional accelerators. This study aimed to improve the properties of wet-mix shotcrete by incorporating with Metakaolin and the calcium aluminate based accelerator. To compare Metakaolin with silica fume, mixing ratios of each material were varied as 4% and 8% of cement weight. Moreover, Metakaolin was blended with silica fume, and their binder was also set to 4% and 8% of cement weight. At each mixing condition, setting time, compressive strength, flexural strength, permeability and freezing-thawing resistance were measured. From the experiments, it was revealed Metakaolin could be a substituting material for silica fume.

• Journal of Forest and Environmental Science
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• v.30 no.1
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• pp.120-125
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• 2014

Halophytes are plants of saline habitats that grow under conditions that may vary in extremes of temperatures (freezing to very hot), water availability (drought to water logging) and salinity (mild to almost saturation). Halophytes may also face sudden micro-environmental variations within their habitats. In this study, we examine some of the factors that determine the ability of seeds of Artemisia fukudo to germinate when conditions are optimal for seedling growth and survival. Germination percentage was the highest at 77.5% when treated in 0% seawater and seedling growth was best in 0% seawater plug cell tray. Physiological quality (chlorophyll contents) and mean germination time were best in the condition in which seeds were treated with 0% seawater (control). Germination performance index in the control group showed the highest value to 3.8. Seedling growth, seedling vigor index in the length of seedling growth andthe relative growth rate were the highest values of 0.76 cm, 1.43, 0.0099, respectively.

• Nuclear Engineering and Technology
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• v.32 no.4
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• pp.395-409
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• 2000

Parametric studies were performed to assess the sensitivity in determining the maximum in-vessel heat removal capability from the core material relocated into the lower plenum of the reactor pressure vessel (RPV）during a core melt accident. A fraction of the sensible heat can be removed during the molten jet delivery from the core to the lower plenum, while the remaining sensible heat and the decay heat can be transported by rather complex mechanisms of the counter-current flow limitation (CCFL) and the critical heat flux (CHF）through the irregular, hemispherical gap that may be formed between the freezing oxidic debris and the overheated metallic RPV wall. It is shown that under the pressurized condition of 10MPa with the sensible heat loss being 50% for the reactors considered in this study, i.e. TMI-2, KORI-2 like, YGN-3&4 like and KNGR like reactors, the heat removal through the gap cooling mechanism was capable of ensuring the RPV integrity as much as 30% to 40% of the total core mass was relocated to the lower plenum. The sensitivity analysis indicated that the cooling rate of debris coupled with the sensible heat loss was a significant factor The newly proposed heat removal capability map (HRCM) clearly displays the critical factors in estimating the maximum heat removal from the debris in the lower plenum. This map can be used as a first-principle engineering tool to assess the RPV thermal integrity during a core melt accident. The predictive model also provided ith a reasonable explanation for the non-failure of the test vessel in the LAVA experiments performed at the Korea Atomic Energy Research Institute (KAERI), which apparently indicated a cooling effect of water ingression through the debris-to-vessel gap and the intra-debris pores and crevices.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.4
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• pp.124-131
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• 2017

The purpose of this study is to evaluate the basic performance of cement mortar for repair using alumina cement and nitrite can be cured in low temperature environment. For this purpose, the repair mortar used in the domestic construction site was selected and the experimental evaluation was carried out by adjusting the mixing amount by substituting alumina cement and nitrite for the blending ratio. The experimental test results confirmed that alumina cement and nitrite were replaced with the repair mortar, the initial strength was improved. Also, the chemical resistance was improved, the shrinkage behavior was decreased, and the resistance to freezing and thawing was increased. As a result, applying alumina cement and nitrite at a ratio of 2:1 at 7.5%, the surface condition was maintained for 5 months or longer and it was judged to be excellent in practical use for external structures.

• Journal of the Korean association of regional geographers
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• v.8 no.4
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• pp.468-479
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• 2002

This study attempts to characterize Taebaek mountainous region as a natural unit, relating to morphoclimatic milieu and landform development patterns of the mountains of each lithologic type. In the case of granitic mountains of Nothern parts of this region, the slopes presents more or less steep or irregular profile because of abundant microforms of exposed bedrocks and blocks. The development of such landscape is essentially due to differential weathering, associated with difference of joint density. In the case of gneissic mountains, the slopes are well regularized straight steep ones, due not only to generalized superficial weathering but also to massmovement of weathered materials. In the Middle parts of this region, especially in Taegwallyong area, with frequent alternations both of freezing-thawing and of snow accumulation-melting, the roles played by cryo-nival processes proved to be important in weathering of granite as well as in morpho-pedogenesis. In this area, weathered mantle, developed by cryogenic activity under humid condition of nival environment, covered almost all over the slopes. Although Southern parts of this region consist of limestone, on the mountainous volume, distribution of Karst forms are limited while predominate none karst forms such as cockpit type peaks, V-shaped type valleys dissecting steep slopes covered with thin deposits in thickness containing rock debris.

• Transactions of the Korean Society of Automotive Engineers
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• v.22 no.4
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• pp.152-159
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• 2014

Urea solution as a reductant of SCR has been widely used to reduce NOx emissions from diesel engine. But it has lots of problems which are freezing at low temperature due to liquid state, deposition of solid formation in the exhaust, dosing device, and complex package such as mixers for uniform concentration of ammonia. In order to overcome these obstacle, ammonium carbonate which is one of solid ammonium materials to produce ammonia gas directly by sublimation process is considered. Simple reactor with visible widow was designed to predict equilibrium temperature and pressure of ammonium carbonate. To simulate real operation conditions under automobile environment, several cycles of heating and cooling condition were settled, two different re-solidification materials were extracted from the reactor and visible window. Analytical study is performed to characterize these unknown materials by XRD(X-Ray Diffraction), FT-IR(Fourier Transform Infrared Spectroscopy), and EA(Elemental Analyzer). From analytical results, re-solidification materials from heating and cooling cycles are very similar to original material of ammonium carbonate.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.49 no.1
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• pp.58-66
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• 2013

Most of steam power plant in Korea are heating the feed water system to prevent freezing water flowing in the pipe in winter time. The heating system is operated whenever the ambient temperature around the power plant area below 5 degree Centigrade. But this kind of heat supplying system cause a lot of energy consuming. If we think about the method that the temperature of the each pipe is controled by attaching the temperature measuring sensor like RTD sensor and heat is supplied only when the outer surface temperature of the pipe is under 5 degree Centigrade, then we can save a plenty of energy. In this study, the computer program package for simulation is used to compare the energy consumption load of both systems. Energy saving rate is calculated for the location of Youngweol area using the data of weather station in winter season, especially the January' severe weather data is analyzed for comparison. Various convection heat transfer coefficients for the ambient air and the flowing water inside the pipe was used for the accurate calculation. And also the various initial flowing water temperature was used for the system. Steady state analysis is done previously to approximate the result before the simulation. The result shows that the temperature control system using RTD sensor represents the high energy saving effect which is more than 90% of energy saving rate. Even in the severe January weather condition, the energy saving rate is almost 60%.

• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.5
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• pp.1-8
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• 2016

This paper presents an evaluation of engineering properties in TDFA(Tire Derived Fuel Ash)- based concrete in early age. Concrete containing 0.5 of w/b(water to binder) ratio and 20% of FA(Fly Ash) replacement ratio are prepared, and FA content are replaced with TDFA from 3% to 12% for evaluating the effect of TDFA on fresh and hardened concrete properties. With higher than 6% of TDFA replacement ratio, workability is significantly worsened but it is improved with more SP(Super plasticizer) and AE(Air Entrainer) agent. Concrete with 6~12% of TDFA shows reasonable strength development and better resistance to carbonation and chloride attack in spite of early-aged condition. However concrete with 6% TDFA shows poor resistance to freezing and thawing action due to insufficient air content. If air content and workability are obtained, replacement of TDFA to 12% can be used for concrete with FA.

• Food Science and Biotechnology
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• v.16 no.4
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• pp.659-662
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• 2007

In order to determine the optimal storage conditions of Capsosiphon fulvescens (maesaengi), 2 types of wash solutions (distilled water and seawater) and storage temperatures (-20 and $-80^{\circ}C$) were evaluated for the effectiveness of microbial growth inhibition and the changes of texture, color, and proximate composition. Thawed samples that had been washed with seawater and stored at $-20^{\circ}C$ for 50 days showed a 1.1-fold increase in hardness compared to the initial hardness of the sample ($1.9{\times}10^5\;dyne/cm^2$). There was no change in moisture, ash, or crude lipid during storage at -20 and $-80^{\circ}C$ for 60 days, while there was a $1{\pm}0.2%$ decrease in crude protein content for the control during storage at both -20 and $-80^{\circ}C$ for 60 days. In conclusion, the recommended optimal storage conditions for retaining the quality of C. fulvescens are: temperatures at or below $-20^{\circ}C$ and washings with either distilled water or seawater for inhibiting microbial growth, temperatures at or below $-20^{\circ}C$ and a washing with seawater to prevent reductions in hardness, and a temperature of $-80^{\circ}C$ and washings with either distilled water or seawater to protect against color changes.

• Korean Journal of Food Science and Technology
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• v.35 no.3
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• pp.429-435
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• 2003

The purpose of this study is to predict multiplication patterns of foodborne pathogens according to packaging methods and storage conditions in home-delivered meals. Pan fried oak mushroom and meat, soy sauce glazed hair tail and roasted dodok which inoculated $10^6\;CFU/g$ of foodborne pathogens were packaged by wrap packaging, top sealing, vacuum packaging and stored at 25, 4 and $-18^{\circ}C$ during 5 days. The result of study was revealed that the growth and multiplication pattern of the inoculated foodborne pathogens was inhibited in chilling and freezing storage after vacuum packaging, and was significantly influenced by storage temperature. The survival of Listeria monocytogenes was also significantly influenced by storage period. The effective method to preserve the bacteriologic safety of pan fried oak mushroom and meat and soy sauce glazed hair tail in home-delivered meals was stored for maximum three days in chilling storage after vacuum packaging.