• Computers and Concrete
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• 제21권1호
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• pp.87-94
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• 2018

This paper presents the results of an experimental study to investigate the influences of high temperatures on the mechanical properties of concrete containing recycled fine aggregate. A total of 150 concrete prisms ($100{\times}100{\times}300mm$) and 150 concrete cubes ($100{\times}100{\times}100mm$) are cast and heated under five different temperatures ($20^{\circ}C$, $200^{\circ}C$, $400^{\circ}C$, $600^{\circ}C$, $800^{\circ}C$) for test. The results show that the mass loss, compressive strength, elastic modulus, splitting tensile strength of concrete specimens containing recycled fine aggregate decline significantly as the temperature rise. At the same temperature, the compressive strength, splitting tensile strength, elastic modulus of concrete specimens containing recycled coarse aggregate and recycled fine aggregate (RHC) is lower than that of concrete specimens containing natural coarse aggregate and recycled fine aggregate (RFC). The shape of stress-strain curves of concrete specimens at different temperatures is different, and the shape of that become flatter as the temperature rises. Normal concrete has better energy absorption capacity than concrete containing recycled fine aggregate.

• Journal of Ecology and Environment
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• 제38권1호
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• pp.67-74
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• 2015

Three strains of the green microalga Botryococcus braunii (JJS, KCM, and KJD) were isolated from different water bodies in Korea and grown as batch cultures in the laboratory. The effects of different growth media and temperatures on the growth rate were investigated, as well as the effect of temperature on the total lipid content and lipid profile. All three strains had the highest growth rates in BG-11 medium and at $25^{\circ}C$. Maximal lipid production ($gL^{-1}$) was at $30^{\circ}C$ in the JJS strain and at $25^{\circ}C$ in the KCM and KJD strains. However, all the three strains produced the greatest percent dry weight of total lipids at $15^{\circ}C$ and had the lowest percent dry weight of total lipids at $25^{\circ}C$. In general, oleic acid, linolenic acid, and behenic acid were the most common fatty acids in all three strains. However, the three strains varied considerably in their fatty acid profiles at different culture temperatures.

• Journal of Biosystems Engineering
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• 제40권2호
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• pp.95-101
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• 2015

Purpose: During the start-up period, the response time of a hydraulic system increases in the winter because of the increased oil viscosity caused by the cold weather. The problems of delayed tractor starting and excessive wear of the clutch disk occur for these reasons. Therefore, this study develops an analysis model using the commercial hydraulic analysis program AMESim to examine the characteristics of delays in power shuttle starting at different oil temperatures. Methods: In the experiment, a tractor was stationary on a flat surface with the engine running at a constant speed of 1,080 rpm. The forward lever was then pressed to activate the power shuttle at three different oil temperatures, and the pressure changes were measured. The pressure on the forward clutch control valve was measured by a pressure gauge installed on the hydraulic line supplied to the transmission from the main valve. An analysis model was also developed and verified with actual tests. Results: The trend of the simulated pressures of the power shuttle is similar to that of the measured pressures, and a constant modulation period was observed in both the simulation and test results. However, the difference found between the simulation and test results was the initial pressure required to overcome the initial force of the clutch spring. Conclusions: This study also examines the characteristics of the delayed startup of the power shuttle at different oil temperatures through simulations.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2019년도 추계 학술논문 발표대회
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• pp.149-150
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• 2019

When concrete is exposed to fire, the decomposition of Portland cement paste results in critical damage to the concrete structure of a building. However the recovery process of the damaged concrete structure has not yet been fully elucidated. In addition, research on appropriate additives such as carbon nanotube (CNT) and nanosilica has been increasing recently, however, investigation of CNT and nanosilica incorporated cement paste after decomposition of CNT by high temperature is not fully investigated. In this study, we investigated the physicochemical properties of CNT incorporated cement paste under different temperatures ($200^{\circ}C$, $500^{\circ}C$ and $800^{\circ}C$). Also, the effects of different rehydration conditions ($20^{\circ}C$ 60% RH and in water for different curing times) on the recovery of the paste were studied. The changes in tensile strength, surface observation of the specimens were characterized. In addition, the decomposition and formation of hydrates in the paste due to the heating process were studied using X-ray diffraction. The results showed that incorporation of nanosilica enhanced tensile strength after heating to each target temperatures.

• 한국재료학회지
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• 제32권4호
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• pp.181-185
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• 2022

In this study, phase-pure titanium dioxide TiO₂ ceramics are sintered using standard high-temperature solid-state reaction technique at different temperatures (1,000, 1,100, 1,200, 1,300, 1,400 ℃). The effect of sintering temperature on the densification and impedance properties of TiO₂ ceramics is investigated. The bulk density and average grain size increase with the increase of sintering temperature. Impedance spectroscopy analysis (complex impedance Z^* and complex modulus M^*), performed in a broad frequency range from 100 Hz to 10 MHz, indicates that the TiO₂ ceramics are dielectrically heterogeneous, consisting of grains and grain boundaries. The complex impedance Z^* -plane indicates the resistance of grains of the TiO₂ ceramics increases with increasing sintering temperature, while that of grain boundaries develops in the opposing direction. The complex modulus M^*-plane shows a grain capacitance that seems to be independent of the sintering temperature, while that of the grain boundaries decreases with increasing sintering temperature. These results suggest that different sintering temperatures have effects on the microstructure, leading to changes in the impedance properties of TiO₂ ceramics.

• 한국약용작물학회지
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• 제20권3호
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• pp.184-189
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• 2012

This study was carried out to have the basic and applied informations relating to increase the productivity and quality of ginseng. 2 years-old ginseng was cultivated under hydroponic culture with the controlled environment conditions in a greenhouse. Major growth characters and yields were investigated with two different temperatures and several growth stages. The plant height and stem diameter were higher at low temperature than those at high temperature. They were not clearly different with six different growth stages. The root length was not clearly different between two temperatures; however it was continuously grown from June until August. The root diameter was higher at low temperature than that at high temperature. It was rapidly increased from June until August. The length, width, and area of leaf were higher at low temperature than those at high temperature. The fresh and dry weights of different plant tissues were also heavier at low temperature than those at high temperature. The moisture content of ginseng root was continuously decreased from June until August. The yield of ginseng was higher at low temperature compared to that at high temperature. The cultivating conditions in hydroponic culture of ginseng, especially temperature, would be an important factor to have better growth and production.

• Ocean Science Journal
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• 제41권4호
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• pp.227-234
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• 2006

Year-to-year variation of bottom cold waters around the Korea Strait was investigated based on bottom temperatures measured by submarine telephone cable between Pusan, Korea and Hamada, Japan from 1982 to 1992. The characteristics of bottom temperatures could be divided into three different groups: the Korean side, the middle, and the Japanese side. Temperature drops in summer appeared in all the three regions implying the intrusion of cold waters into the Korea Strait. Significant decreases in the Korean side were observed in 1983, 1986, 1990, 1991, and 1992 when bottom temperatures were high in the middle. In contrast, bottom temperatures significantly decreased in the middle in 1985, 1988, and 1989 when the temperature drops in the Korean side were relatively small. This tendency for a negative relationship was also shown in the second mode of an EOF analysis. In the years when bottom temperatures significantly decrease din the Korean side, the cold water along the east coast of Korea expanded offshore and its temperature was low. On the contrary, cold water in the southern region of the Ulleung Basin developed in the years when bottom temperatures decreased considerably in the middle.

• Steel and Composite Structures
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• 제13권4호
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• pp.309-325
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• 2012

The risk of progressive collapse in steel framed buildings under fire conditions is gradually rising due to the increasing use of combustible materials. The fire resistance of such steel framed buildings is evaluated by fire tests. Recently, the application of performance based fire engineering makes it easier to evaluate the fire resistance owing to various engineering techniques and fire science. The fire resistance of steel structural members can be evaluated by the comparison of the limiting temperatures and maximum temperatures of structural steel members. The limiting temperature is derived at the moment that the failure of structural member results from the rise in temperature and the maximum temperature is calculated by using a heat transfer analysis. To obtain the limiting temperatures for structural steel of grades SS400 and SM490 in Korea, tensile strength tests of coupons at high temperature were conducted. The limiting temperatures obtained by the tensile coupon tests were compared with the limiting temperatures reported in the literature and the results of column fire tests under four types of loading with different load ratios. Simple limiting temperature formulas for SS400 and SM490 steel based on the fire tests of the tensile coupons are proposed. The limiting temperature predictions using the proposed formulas were proven to be conservative in comparison with those obtained from H-section and hollow section column fire tests.

• 한국산업융합학회 논문집
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• 제15권3호
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• pp.87-94
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• 2012

Kruithof demonstrated the preferred combination of illuminance levels and color temperatures. However, as Benett pointed out, difference of themal variables in such preference may be expected. The purpose of this study is to clarify the combined effects of lighting conditions(illuminance, color temperature), operative temperature on the human physiological and psychological responses. In order to observe operative temperature change in preference of color temperatures for three illumination levels, three subjects were exposed to two different conditions of color temperatures of 2,850K, 4,200K and 6,850K combined with operative temperatures(OT) of $25{\sim}31^{\circ}C$ at 100~1000lx. Thermal sensation vote and comfortable sensation vote, brightness perception vote were reported in each experiment conditions. The following results were obtained : 1) When illuminace level was at 100lx in operative temperatures of OT $20^{\circ}C$, $25^{\circ}C$, $30^{\circ}C$, Color temperature affect not themal sensation but Warm-cool sensation. 2) Operative temperatures affect not brightness perception vote but visual comfort sensation vote, satisfactive sensation vote, warm-cool sensation vote and themal sensation vote.

• 한국약용작물학회지
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• 제21권1호
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• pp.20-26
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• 2013

This study was conducted to improve the managing and storing methods of the seeds of Aralia cordata var. continentalis (Kitagawa) Y.C.Chu, to examine the viability and the germination ability of seeds with different storing conditions and methods, and to develop new ways to propagate and have better healthy seedling. Therefore, the germination rate, days required for germinating seeds, and early growth responses of Aralia cordata var. continentalis (Kitagawa) Y.C.Chu were investigated with different storing temperatures, durations and methods. The germination rate was higher in stratified storage than that in dry storage condition. The highest germination rate was with outdoor temperature at 30 days after stratified storage. The days required for germinating seeds were less than 10 days with the treatment of $25^{\circ}C$ and outdoor temperature in stratified storage. In dry condition, they were shorter with $4^{\circ}C$ and $25^{\circ}C$ than those with $-20^{\circ}C$ and outdoor temperature. Leaf number of seedling was higher in stratified storage compared to that in dry condition, while it was not clearly different according to storage temperatures and durations. Leaf length and leaf width of seedling was not difference among the treatment of storage methods, temperatures, and durations. Stem length of seedling was higher in stratified storage than those in dry condition, while root length was not clearly different among the treatments. It would be assumed that temperatures, methods and durations of storage could affect much to the germination rate and the early seedling growth response.