• Tunnel and Underground Space
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• v.14 no.1
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• pp.69-77
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• 2004

Investigation of the time-dependent behavior of rock and the associated mechanisms are of key interest in long-term stability analysis of many engineering applications. In this study, creep tests were performed on Daejeon granite samples of 25.4mm diameter under uniaxial compression at varying stress levels. The effect of moisture was investigated by testing both air-dried and fully water-saturated samples. The creep behavior of Daejeon granite exhibited three distinctive stages of primary, secondary and tertiary creep. The ultimate strength of granite under a constant stress decreased considerably with time. Saturation and immersion of the test specimen in water markedly increased the total creep strain as well as the secondary creep rate. The experimental creep curves are fitted to Burger's model as well as two other empirical models suggested by previous researchers. A number of the parameters determined for each model are dependent on stress and influenced by the presence of water. Based on the experimental results, an empirical relation between the applied stress and the time-dependent strain is established separately for each air-dried and fully water-saturated Daejeon granite.

• Corrosion Science and Technology
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• v.13 no.5
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• pp.186-194
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• 2014

Establishment of adhesion strength measurement procedure for marine epoxy coatings was conducted in order to ensure reliability of the test results. It was found that (1) the increase in thickness of the substrates would induce increase of pull-off strength. Especially, the increase in adhesion strength with the substrate thickness increment was attributed to the transition of stress mode to the pure tensile mode excluding bending effect. (2) The longer curing time, the higher pull-off strength. It may be due to higher cross-linking density of the coating (3) The pull-off strength increases as coating thickness increases due to the diminishment of bending effect (4) The longer drying time after water immersion, the higher pull-off strength. It may be due to the evaporation of water molecule at the coating-substrate interface.

• The Journal of Internal Korean Medicine
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• v.25 no.3
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• pp.559-568
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• 2004

Diagnosis of Raynaud's phenomenon is primarily based on clinical symptoms. Cold stress test(CST) done by DITI(Digital Infrared Thermographic Image) can be helpful for objective diagnosis. The cold stress test was performed three times by DITI; the first after 15 minutes of rest, the second right after one minute of soaking in $20^{\circ}C$ water, the third ten minutes after immersion. For a clear diagnosis, the temperature of the finger tips must be low, or the thermal difference between the metacarpophalangeal joints and the fingertips must be large. Also the evaluation of treatment depends on decrease of thermal gradient between the metacarpophalangeal joints and the finger tips after CST. In oriental medicine Raynaud's phenomenon can be categorized by coldness of the limbs or numbness. Numbness was diagnosed as depression of Ki and Chiljehyangbuhwan(Qizhixiangfuwan) was prescribed. Positive results were observed, not only in follow up CST, but also Visual Analogue Scale after treatment.

• Journal of Food Hygiene and Safety
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• v.6 no.1
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• pp.27-40
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• 1991

;ABSTRACT-The effects of gastric ulcer induced by restraint and water-immersion stress on gastric carcinogenesis in Wistar male rats treated with N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) were examined. Rats of group 1 were 2iven stress for 8 hours before they were received MNNG (100 mg/l) in drinking water for 20 weeks. Rats of group 2 were received MNNG first for 2 weeks and then were given stress once a week from 3rd to 12th weeks, with simultaneous MNNG adminitration and followed by MNNG only until 20th weeks. Rats of group 3 were received MNNG only as a positive control and rats of group 4 were not treated with carcinogen. All groups were sacrificed in 20 weeks. Sections of the pyloric mucosa were stained by avidin-biotin peroxidase complex (ABC) immuno-histochemical method. PAPG (pepsinogen isozyme 1 altered pyloric gland), body weight change, gross lesions and histopathological changes were examined. The results obtained from these studies were summarized as follows: 1. The mean body weight gains of the rats fed with carcinogens (group 1, 2, 3) were significantly lower than that of group 4 (control group, without carcinogen. p<0.05). However, the differences of the mean body weight of rats treated with carcinogen were not significant. 2. Stress treatment (group 1 and 2) increased the appearance of the numbers of PAPG (Pepsinogen 1 Altered Pyloric Gland) induced by carcinogen significantly compared with that of group 3 (carcinogen only, p<0.01). 3. The incidence rate of mucosal hyperplasia in pylorus was significantly increased in group 2 compared with group 3 (p<0.05).0.05).

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.6
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• pp.1351-1360
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• 1993

The fatigue behavior of GFRP composites is affected by environmental parameters. Therefore, we have to study on effect of sea water on fatigue behavior of GFRP composites as to maintain the safety and confidence in design of ocean structure of GFRP. In this paper, we investigated the fatigue properties of chopped strand glass mat/polyester composite in synthetic sea water. (pH 8.2) In case of the glass fiber (CSM type) reinforced polyester composite materials, the fatigue crack in the both dry and wet specimens tested in air or synthetic sea water occurred at the initial of cycle. Thereafter, it was divided with two regions that one decreased with the crack extension and the other increased with the crack extension. The transition point occurred during the crack propagation shifted to high ${\Delta}K$ value as load increase but its point is not changed regardless of immersion or test environment under a constant load. The synthetic sea water degrades the bond strength between fiber and matrix, thereby the tendency of rapid deceleration and acceleration of the crack growth was appeared.

• Journal of Ocean Engineering and Technology
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• v.17 no.2
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• pp.72-76
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• 2003

This paper presents the design concept and operation results of float-off for FSO (340,000 DWT Class, ELF AMENAM KPONO Project) built on the ground, without dry dock facilities. It was the first attempt to build FSO, completely, on the ground and launch it using DBU (Double Barge Unit, which was connected by rigid frame structure.) The major characteristics of FSO, which are similar to general VLCC type hull, including topside structure, weigh 51,000 metric ton. In order to have sufficient stability during the deck immersion of DBU, while passing through a minimum water plane area zone, proper trim control was completed with LMC (Load Master Computer). The major features of the monitoring system include calculation for transverse bending moment, shear force, local strength check of each connector, based on component stress, and deformation check during the load-out and float-off. Another major concern during the operation was to avoid damages at the bottom and sides of FSO, due to motion & movement after free-floating; therefore, adequate clearances between DBU and FSO were to be provided, and guide posts were installed to prevent side damage of the DBU casings. This paper also presents various measures that indecate the connector bending moment, damage stability analysis, and mooring of DBU during float off.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07a
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• pp.100-103
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• 2003

The primary insulation system used in an oil-filled transformer is kraft paper, wood, porcelain and oil. Modern transformers use paper that is chemically treated to improve its tensile strength properties and resistance to aging caused by immersion in oil. But these insulation papers are mainly aged to thermal stress. Over the course of the insulation paper and oil's life it is exposed to high temperatures, oxygen and water. Its interaction with the steel of the tank and core plus the copper and aluminium of the windings will eventually cause the chemical properties of the oil to decay. High temperature have an effect on mechanical strength of cellulous paper using the layer insulation. We made two aging cell in which thermal aging tests of insulation papers and mineral oil are conducted. It is measured dielectric strength, number of acid, moisture, etc. of insulation paper and oil aged in the aging cells.

• Biomolecules & Therapeutics
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• v.4 no.2
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• pp.111-121
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• 1996

Antiulcer effects of Artemisia herba extract (DA-9601) were evaluated in various types of experimental gastric ulcer induced in rats. And the effects of DA-9601 on mucus, basal and stimulated gastric acid secretion were also investigated in rats. DA-9601 (12.5∼400 mg/kg, p.o.) prevented the formation of gastric ulcers induced by 60% EtOH in 150 mM HC1, restraint water immersion stress, platelet activating factor (PAF), aspirin in 150 mM HCI with Pylorus-ligation and indomethacin. DA-9601 (4∼400 mg/kg, p.o.) significantly accelerated the healing rate of acetic acid-induced gastric ulcer and significantly stimulated mucus secretion in a dose-dependent manner. DA-9601 (20∼200 mg/kg, i.d.), however, did not inhibit basal gastric acid secretion in pylorus ligated rats and DA-9601 (200 mg/kg, i.d.) failed to influence histamine-, pentagastrin- and carbachol- stimulated gastric acid secretion. These results suggest that DA-9601 has inhibitory action on gastric lesion and ulceration through increasing mucus secretion in the stomach of rats without influencing basal and stimulated gastric acid secretion.

• Corrosion Science and Technology
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• v.18 no.4
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• pp.129-137
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• 2019

CFRP (Carbon Fiber Reinforced Plastics) is composed of carbon fiber and plastic resin, and is approximately 20 - 50% lighter than metallic materials. CFRP has a low density, higher specific stiffness, specific strength, and high corrosion resistance. Because of these excellent properties, which meet various regulation conditions needed in the industrial fields, CFRP has been widely used in many industries including aviation and ship building. However, CFRP reveals water absorption in water immersion or high humidity environments, and water absorption occurs in an epoxy not carbon fiber, and can be facilitated by higher temperature. Since these properties can induce volume expansion inside CFRP and change the internal stress state and degrade the chemical bond between the fiber and the matrix, the mechanical properties including bond strength may be lowered. This study focused on the effects of NaCl concentration (0.01 - 1% NaCl) and solution temperature ($30-75^{\circ}C$) on the galvanic corrosion between CFRP and A516Gr.55 carbon steel. When NaCl concentration increases 10 times, corrosion rate of a specimen was not affected, but that of galvanic coupled carbon steel increased by 46.9% average. However, when solution temperature increases $10^{\circ}C$, average corrosion rate increased approximately 22%, regardless of single or galvanic coupled specimen.

• Korean Journal of Soil Science and Fertilizer
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• v.12 no.2
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• pp.77-82
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• 1979

Wilting and transpiration charactistics of Panax ginseng leaves were investigated at two temperature levels. Water potential and water absorption characteristics of leaf segments were also observed. Soybean leaves were compared. 1. Ginseng leaves were thiner, higher in water content and lower in dehydration rate. But time required to reach permanent wilting point (pwp) was less than half of that of soybean leaves because water content at pwp was about two times higher (80% of initial water for ginseng and 50% for soybean leaves). The time was shorter under high air temperature. 2. Transpiration rate was about a quater of soybean leaves and lower at $33^{\circ}C$ than $23^{\circ}C$, indicating that ginseng leaves are less tolorant to high air temperature. 3. Ginseng leaf segment showed smaller water free space but greater water deficit and little difference in was absorption rate. 4. Water potential of leaves measured by liquid immersion method was lower than that of soybean leaves. 5. Above results strongly suggest that ginseng plants are more susceptible to water stress. Thus greater light intensity during leaf growing stage (April to June) is recommendable to increase stomate frequency resulting greater transpiration rate and high temperature tolerance during July and August. Abundant water around roots seems to be beneficial as long as oxygen is not limited in rhizosphere.