• Journal of Bio-Environment Control
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• v.23 no.1
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• pp.11-18
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• 2014

To investigate the influence of surrounding environment on the plant temperature and examine the effect of plant temperature control by fogging and airflow, plant temperature of tomato, inside and outside air temperature and relative humidity, solar radiation and wind speed were measured and analyzed under various experimental conditions in plastic greenhouse with two-fluid fogging systems and air circulation fans. According to the analysis of plant temperature and the change of inside and outside air temperature in each condition, inside air temperature and plant temperature were significantly higher than outside air temperature in the control and shading condition. However, in the fogging condition, inside air temperature was lower or slightly higher than outside air temperature. It showed that plant temperature could be kept with the temperature similar to or lower than inside air temperature in fogging and airflow condition. To derive the relationship between surrounding environmental factor and plant temperature, we did multiple regression analysis. The optimum regression equation for the temperature difference between plant and air included solar radiation, wind speed and vapor pressure deficit and RMS error was $0.8^{\circ}C$. To investigate whether the fogging and airflow contribute to reduce high temperature stress of plant, photosynthetic rate of tomato leaf was measured under the experimental conditions. Photosynthetic rate was the highest when using both fogging and airflow, and then fogging, airflow and lastly the control. So, we could assume that fogging and airflow can make better effect of plant temperature control to reduce high temperature stress of plant which can increase photosynthetic rate. It showed that the temperature difference between plant and air was highly affected by surrounding environment. Also, we could estimate plant temperature by measuring the surrounding environment, and use it for environment control to reduce the high temperature stress of plant. In addition, by using fogging and airflow, we can decrease temperature difference between plant and air, increase photosynthetic rate, and make proper environment for plants. We could conclude that both fogging and airflow are effective to reduce the high temperature stress of plant.

• Korean Journal of Environmental Biology
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• v.38 no.3
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• pp.450-460
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• 2020

The occurrence of exotic weeds and their influx into farmlands due to climate change poses many problems. Therefore, it is necessary to generate a prediction model for the occurrence pattern of these exotic weeds based on scientific evidence and devise prevention measures. The photosynthetic apparatus is known as the most temperature-sensitive component of a plant cell and its initial response to temperature stress is to inhibit the activation of photosystem II. This study investigated the potential of OJIP transients in assessing temperature stress in exotic weeds. The four exotic weeds currently flowing into Korean farmlands include Amaranthus spinosus, Conyza bonariensis, Crassocephalum crepidioides, and Amaranthus viridis. These weeds were treated at 5℃, 10℃, 15℃, 20℃, 25℃, 30℃, 35℃, and 40℃ and the OJIP curves and JIP parameters were measured and analyzed. The results showed that heat and chilling stress affected the photosystem II(PSII) electron transport of A. spinosus, whereas C. crepidioides and A. viridis were more affected by high-temperature stress than by low-temperature stress. Lastly, C. bonariensis showed resistance to both high and low-temperature stress. The results of this study suggest that OJIP transients and JIP parameters can be used to analyze damage to the photosynthetic apparatus by temperature stress and that they can serve as sensitive indicators for the occurrence pattern of exotic weeds.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.1 s.173
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• pp.156-162
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• 2000

Sensitized STS 304 stainless steel crack growth rate(CGR) in high temperature water was investigated under trapezoidal wave loading test using fracture mechanics techniques. The CGR, due to stress corrosion cracking(SCC), were systematically measured as a function of the stress intensity factor and stress. holding time under trapezoidal wave loading. In high temperature water, CGR was enhanced by a synergistic effects in combination with an aggressive environment and mechanical damage. The CGR, $(da/dN)_{env}$ was basically described as a summation of the environmentally assisted crack growth rate $(da/dN)_{SCC}$, $(da/dN)_{CF}$ and fatigue crack growth rate in air $(da/dN)air,. The CGR, $(da/dN)_{env}$, increased linearly with increasing stress holding time. The CGR, $(da/dN)_{SCC}$ decreased linearly with increasing stress holding time. Fracture surface mode varied from trans-granular cracking to inter-granular cracking with increasing stress holding time.

• Design & Manufacturing
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• v.12 no.1
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• pp.1-6
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• 2018

In this study, we calculated the redistribution of vacancy concentration in metal specimens induced by stress-induced diffusion at a high temperature. To deduce the governing equation, we associated the unit volume change equation of strains with a differential equation of vacancy concentration as a function of stress using the stress-strain relationship. In this governing equation, we considered stress as the only chemical potential parameter to stay in the scope of this study, which provided the vacancy concentration equation as of stress gradient in metals. The equation was then mathematically delineated to derive a analytical solution for a transient, one-dimensional diffusion case. With the help of Korhonen's approximation and the boundary conditions, we successfully deduced a general solution from the governing equation. To visualize the feasibility of our solutions, we applied the solution to two different stress-induced cases - a rod with fixed concentrated stresses at both ends and a rod with varying concentrated stresses at both ends. Although it is necessary to legitimatized the model in the future for improvement, our results showed that the model can be used to interpret the location of structural defects, the formation of vacancy, and furthermore the high temperature behavior of metals.

• Korean Journal of Plant Resources
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• v.11 no.3
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• pp.307-314
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• 1998

The response of water stree under high and low temperatures, was shown differently according to the longer the suspension period of water supply. Leaf photosynthetic rate(LPS), leaf water potential(WP), relative leaf water content and relative soil water content were lower. At the higher temperatures, the percentate of reduction in LPS and WP was greater than at low temperatures. It is suggested that evaporation rate should be higher in the high temperature than the lower temperature. Also leaf water potential was lower at high temperature than at low temperature. After the 9 th day of treatment , LSP was remarkably reduced at high temperature, but the reduction of LPS was not significant at low temperature. Solidago virga-aurea var. asiatic that maintained LPS of 3rd day after treatment was more strong than other varieties at low temperatures. The silting and curling of leaves were observed symptoms of stress on the 9th day at the both temperatures. The leaves of aster scaber and Ligularia fischeri turned red on the 9th day after treatment at low temperature.

• Journal of the Korean Ceramic Society
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• v.47 no.6
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• pp.491-497
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• 2010

In this paper, we employed the classical molecular dynamics simulations using Tersoff's potential to calculate the elastic constants of the silicon carbide (SiC) crystal at high temperature. The elastic constants of the SiC crystal were calculated based on the stress-strain characteristics, which were drawn by the simulation using LAMMPS software. At the same time, the elastic constants of the SiC ceramics were measured at different temperatures by impulse excitation testing (IET) method. Based on the simulated stress-strain results, the SiC crystal showed the elastic deformation characteristics at the low temperature region, while a slight plastic deformation behavior was observed at high strain over $1,000^{\circ}C$ temperature. The elastic constants of the SiC crystal were changed from about 475 GPa to 425 GPa by increasing the temperature from RT to $1,250^{\circ}C$. When compared to the experimental values of the SiC ceramics, the simulation results, which are unable to obtain by experiments, are found to be very useful to predict the stress-strain behaviors and the elastic constant of the ceramics at high temperature.

• Nuclear Engineering and Technology
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• v.56 no.7
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• pp.2859-2874
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• 2024

This paper presents the finite element deformation and failure simulation of a typical Korean high-power reactor vessel under a severe accident characterized by large break loss of coolant (LBLOCA) with in-vessel retention of molten corium through external reactor vessel cooling (IVR-ERVC) conditions. Temperature distributions calculated using Modular Accident Analysis Program Version 5 (MAAP5) as thermal boundary conditions were used, and ABAQUS thermal and structural analyses were performed. After full ablation, the temperature of the inner surface in the thinnest section remained high (920 ℃), but the stress remained relatively low (less than 6 MPa). At the outer surface, the stress was as high as 250 MPa; however, the resulting plastic strain was small owing to the low temperature of 200 ℃. Variations in stress, inelastic strain, and temperature with time in the thinnest section suggest that the plastic and creep strains are saturated owing to stress relaxation, resulting in low cumulative damage. Thus, the lower head of the vessel can maintain its structural integrity under LBLOCA with IVR-ERVC conditions. The sensitivity analysis of internal pressure indicates the occurrence of failure in the thinnest section at an internal pressure >9.6 MPa via local necking followed by failure due to high stresses.

• Computers and Concrete
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• v.30 no.1
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• pp.9-17
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• 2022

This paper discusses the effect of high temperatures (T_s) on the compressive strength and stress-strain curve of recycled fine aggregate concrete (RFAC), based on the experimental results. A total of 90 prisms (100 mm×100 mm×300 mm) were tested. The results show that the compressive strength and elastic modulus of RFAC specimens decreased significantly with increasing T values. As T increased, the strain corresponding to peak stress decreased first when T<200℃ and then increased afterwards. With increasing T values, the stress-strain curves became flat gradually, the peak stress dropped gradually, and ε_p decreased when T<200℃ and increased in the T range of 400-800℃. A stress-strain relations for RFAC exposed to high T_s is proposed, which agree quite well with the test results and may be used to practical applications.

• Journal of the Korean Society for Precision Engineering
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• v.25 no.7
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• pp.116-123
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• 2008

In the fossil power plant, the reliability of the components which consist of the many welded parts depends on the quality of welding. The residual stress is occurred by the heat flux of high temperature during weld process. This decreases the mechanical properties as the strength of fatigue and fracture or causes the stress corrosion cracking and fatigue fracture. Especially, the accidents due to the residual stress occurred at the weld parts of high-temperature and high-pressure pipes and steam headers. Also, the residual stress of the welded part in the recently constructed power plants has been brought into relief as the cause of various accidents. The aim of this study is the measurement of the residual stress using the x-ray diffraction method. The merits of this are more accurate and applicable than other methods. The materials used for the study is P92 steel for the use of high temperature pipe on super critical condition. The variables of tests are the post-weld heat treatment, the surface roughness and the depth from the original surface. The test results were analyzed by the distributed characteristics of the full width at half maximum intensity (FWHM) in x-ray diffraction intensity curve and by the relation of hardness with FWHM.

• Journal of the korean Society of Automotive Engineers
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• v.12 no.3
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• pp.41-52
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• 1990

In this study are determined the unsteady temperature and thermal stress fields for a domestic 4-cylinder, 4-cycle gasoline engine cylinder head by the three-dimensional finite element method. A representative part of the cylinder head is modelled as a combination of hexahedron isoparametric elements, and the time-dependent temperature and the heat transfer coefficient of the gas are imposed as the thermal boundary conditions for the engine speeds of 500 rpm and 2000 rpm. The obtained results, which are represented graphically, indicate that the amplitudes of temperature fluctuation during a cycle are about 10.deg. C and 3.deg. C respectively on the surface of combustion chamber, and the maximum temperature fields occur at 30.deg. , 10.deg. respectively before the initiation of the exhaust stroke. Thermal stress fields due to non-uniform temperature distributions show that compressive stress is much larger than tensile stress throughout a cycle. It is also found that the compressive stress varies with substantial amplitude between the exhaust port and ignition plug hole, and the high tensile stress with small fluctuation occurs between exhaust port and the adjacent head bolt hole.