Crack initiation and propagation thresholds of Hwangdeung granite under elevated temperature

박정욱,이용기,박찬,김창민 한국지질과학협의회 2022 Geosciences Journal Vol.26 No.6

In this study, we investigated the effect of high temperature on the mechanical behavior of Hwangdeung granite in Korea. Uniaxial compression and Brazilian tests were performed under temperatures ranging from 20 °C to 250 °C. The development of the thermally induced microcracks was observed utilizing a scanning electron microscope (SEM). The target temperature was chosen for rock engineering projects, such as high-level radioactive waste disposal, enhanced geothermal energy, and thermal energy storage. Considering the long-term strength and fracture process associated with crack development, we examined the temperature dependence of crack initiation and propagation thresholds and conventional strength and deformation parameters, as well as the stress-strain relation under high temperature. Compressive strength, tensile strength, and Young’s modulus decreased with increasing temperature, particularly at temperatures above 100 °C, and Poisson’s ratio decreased linearly. The changes in the tensile strength and elastic constants were more pronounced than those in uniaxial compressive strength. The stress-strain curves revealed that the thermal effect on deformation, rather than strength, was evident. Microscopic observations of the heated rock samples have revealed that high temperature promoted the interaction and networking of pre-existing and thermally induced cracks, resulting in microstructural damage before loading. We determined the crack closure stress, crack initiation stress, and crack damage stress under the respective temperatures by analyzing the stress-strain curves. An increase in temperature increased the crack closure stress and reduced the crack initiation stress, resulting in a decreased elastic range; the former increased by 12.1 MPa as the temperature increased from 20 °C to 250 °C, and the latter significantly reduced by 25.1 MPa. This finding suggests that the mechanical behavior of rocks or rock masses under high-temperature conditions, particularly at low-stress levels, is uncertain and cannot be approximated with standard material properties. No systemic relation was detected between temperature and crack damage stress; however, the volumetric strain at the crack damage stress increased consistently with temperature.

브로콜리(Brassica oleracea var. italica)의 온도 스트레스 평가를 위한 다중 센서 모니터링

차승주 ( Seung-ju Cha ),박현준 ( Hyun Jun Park ),이주경 ( Joo-kyung Lee ),권선주 ( Seon-ju Kwon ),지효경 ( Hyo-kyung Jee ),백현 ( Hyun Baek ),김한나 ( Han-na Kim ),박진희 ( Jin Hee Park ) 한국응용생명화학회 2020 Journal of Applied Biological Chemistry (J. Appl. Vol.63 No.4

Several sensors have been developed for soil and plants to assess plant stress due to climate change. Therefore, the objective of the study is to nondestructively evaluate temperature stress on plant by monitoring climatic and soil conditions and plant responses using various sensors. Plant responses were monitored by electrical conductivity in plant stem and sap flow rate. Electrical conductivity in plant stem reflects the physiological activity of plants including water and ion transport. Fully grown Brassica oleracea var. italica was exposed to 20/15 ℃ (day/night) with 16 h photoperiods as a control, low temperature 15/10 ℃, and high temperature 35/30 ℃ while climatic, soil, and plant conditions were monitored. Electrical conductivity in plant stem and sap flow rate increased during the day and decreased at night. Under low temperature stress, electrical conductivity in plant stem of Brassica oleracea var. italica was lower than control while under high temperature stress, it was higher than control indicating that water and ion transport was affected. However, chlorophyll a and b increased in leaves subjected to low temperature stress and there was no significant difference between high temperature stressed leaves and control. Free proline contents in the leaves did not increase under low temperature stress, but increased under high temperature stress. Proline synthesis in plant is a defense mechanism under environmental stress. Therefore, Brassica oleracea var. Italica appears to be more susceptible to high temperature stress than low temperature.

Effects of gamma aminobutyric acid on performance, blood cell of broiler subjected to multi-stress environments

Park Keun-tae,Oh Mihyang,Joo Younghye,Han Jong-Kwon 아세아·태평양축산학회 2023 Animal Bioscience Vol.36 No.2

Objective: Stress factors such as high temperatures, overcrowding, and diurnal temperature range exert profound negative effects on weight gain and productivity of broiler chickens. The potential of gamma aminobutyric acid (GABA) as an excitatory neurotransmitter was evaluated under various stress conditions in this study. Methods: The experiment was conducted under four different environmental conditions: normal, high temperature, overcrowded, and in an overcrowded-diurnal temperature range. The experimental groups were divided into (–) control group without stress, (+) control group with stress, and G50 group (GABA 50 mg/kg) with stress. Weight gain, feed intake, and feed conversion ratio were measured, and stress reduction was evaluated through hematologic analysis. Results: The effects of GABA on broilers in four experimental treatments were evaluated. GABA treated responded to environmental stress and improved productivity in all the experimental treatments. The magnitude of stress observed was highest at high temperature, followed by the overcrowded environment, and was least for the overcrowded-diurnal temperature range. Conclusion: Various stress factors in livestock rearing environment can reduce productivity and increase disease incidence and mortality rate. To address these challenges, GABA, an inhibitory neurotransmitter, was shown to reduce stress caused due to various environmental conditions and improve productivity.

Phenotyping of Low-Temperature Stressed Pepper Seedlings Using Infrared Thermography

( Eunsoo Park ),( Suk-ju Hong ),( Ah-yeong Lee ),( Jongmin Park ),( Byoung-kwan Cho ),( Ghiseok Kim ) 한국농업기계학회 2017 바이오시스템공학 Vol.42 No.3

Purpose: This study was performed to evaluate the feasibility of using an infrared thermography technique for phenotype analysis of pepper seedlings exposed to a low-temperature environment. Methods: We employed an active thermography technique to evaluate the thermal response of pepper seedlings exposed to low-temperature stress. The temperatures of pepper leaves grown in low-temperature conditions (5°C, relative humidity [RH] 50%) for four periods (6, 12, 24, and 48 h) were measured in the experimental setting (23°C, RH 70%) as soon as pepper seedling samples were taken out from the low-temperature environment. We also assessed the visible images of pepper seedling samples that were exposed to low-temperature stress to estimate appearance changes. Results: The greatest appearance change was observed for the low-temperature stressed pepper seedlings that were exposed for 12 h, and the temperature from these pepper seedling leaves was the highest among all samples. In addition, the thermal image of low-temperature stressed pepper seedlings for 6 h exhibited the lowest temperature. Conclusions: We demonstrated that the leaf withering owing to the water deficiency that occurred under low-temperature conditions could induce an increase in temperature in plant leaves using the infrared thermography technique. These results suggested that the time-resolved and averaged thermal signals or temperatures of plants could be significantly associated with the physiological or biochemical characteristics of plants exposed to low-temperature stress.

포그분사 및 공기유동에 의한 온실재배 토마토의 엽온 변화

남상운,김영식,서동욱 (사) 한국생물환경조절학회 2014 생물환경조절학회지 Vol.23 No.1

To investigate the influence of surrounding environment on the plant temperature and examine the effectof plant temperature control by fogging and airflow, plant temperature of tomato, inside and outside air temperatureand relative humidity, solar radiation and wind speed were measured and analyzed under various experimental conditionsin plastic greenhouse with two-fluid fogging systems and air circulation fans. According to the analysis of planttemperature and the change of inside and outside air temperature in each condition, inside air temperature and planttemperature were significantly higher than outside air temperature in the control and shading condition. However, inthe fogging condition, inside air temperature was lower or slightly higher than outside air temperature. It showed thatplant temperature could be kept with the temperature similar to or lower than inside air temperature in fogging andairflow condition. To derive the relationship between surrounding environmental factor and plant temperature, we didmultiple regression analysis. The optimum regression equation for the temperature difference between plant and airincluded solar radiation, wind speed and vapor pressure deficit and RMS error was 0.8oC. To investigate whether thefogging and airflow contribute to reduce high temperature stress of plant, photosynthetic rate of tomato leaf wasmeasured 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 bettereffect 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 environmentcontrol to reduce the high temperature stress of plant. In addition, by using fogging and airflow, we can decreasetemperature 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. 주변 환경이 작물의 엽온에 미치는 영향을 규명하고,포그분사 및 공기유동에 의한 엽온조절의 효과를 검토하기 위하여 이류체 포그시스템 및 공기유동 장치를 설치한 토마토 재배온실에서 다양한 실험조건하에 작물의 엽온과 실내외 온습도, 일사량, 풍속 등의 환경을 계측하여 분석하였다. 처리조건별 엽온 및 실내외 기온의 변화를 분석한 결과, 무처리와 차광조건에서는 실내기온과엽온 모두 외기온보다 상당히 높았으나, 포그분사 조건에서는 실내온도가 외기온보다 낮거나 약간 높은 정도를유지하는 것으로 나타났고, 포그분사와 공기유동 조건에서는 엽온을 실내온도와 비슷하거나 더 낮게 유지할 수있는 것으로 나타났다. 일사량, 풍속 및 포차에 따른 엽기온차의 변화를 분석하였으며, 주변 환경요인과 엽온과의 관계를 도출하기 위하여 다중회귀분석을 실시하였다. 엽기온차에 대한 최적의 회귀방정식은 일사량, 풍속, 포차를 모두 고려한 것으로써 RMS 오차는 0.8oC였다. 본회귀방적식을 이용하여 온실의 온습도, 일사량, 풍속을측정하면 엽온을 추정할 수 있으며, 토마토 재배온실의고온기 작물 스트레스 경감을 위한 환경조절에 활용할수 있을 것으로 판단된다. 처리조건별 광합성 속도는 포그분사와 공기유동의 병행 처리에서 가장 컸고, 포그분사, 공기유동, 무처리 순으로 나타났다. 포그분사에 공기유동까지 병행하면 체온조절 효과가 증대하여 작물의 고온 스트레스를 경감할 수 있으며 결국 광합성을 증대시킬 수 있는 것으로 판단된다. 이상을 종합해보면 엽온과기온의 차이는 주변 환경에 큰 영향을 받는 것으로 나타났으며, 주변 환경을 계측함으로써 엽온을 추정할 수있고, 그것을 고온 스트레스 경감을 위한 환경조절에 활용할 수 있을 것으로 판단된다. 또한, 포그분사 및 공기유동을 통해 엽기온차를 줄이고 광합성 속도를 증가시켜작물생장에 유리한 환경을 조성할 수 있으며, 고온 스트레스를 경감시키는데 효과적일 것으로 판단된다.

색온도 조도 제어가능한 조명환경에서의 스트레스가 인체에 미치는 영향분석

이진숙(JinSook Lee),이희원(HeeWon Lee) 한국색채학회 2015 한국색채학회 논문집 Vol.29 No.2

실내공간에서 생활하는 시간이 길어짐에 따라 조명환경은 더욱 중요해졌다. 또한 사람들의 작업능력과 건강에 미치는 영향에 대한 관심이 대두되고, LED조명이 보급 확산되면서 더욱 다양한 조명환경에서 생활하게 되었다. 선행연구에 따르면 인간의 건강과 밀접한 관계가 있는 조명환경에서의 스트레스가 인체에 미치는 연구는 부재한 실정이다. 따라서 본 연구는 색온도, 조도 제어가 가능한 LED조명환경에서 인체 생리반응 DB 구축을 목표로 스트레스 정도에 따른 생리반응 연구를 진행하였다. 연구의 방법으로, 스트레스 측정검사지를 사용하여 저 스트레스군과 고 스트레스군으로 구분하였다. 실험공간은 조명제어가 가능한 3950 ㎜× 3800㎜× 3550㎜의 규모의 실물대 Mock-up을 조성하였으며, 조명환경에서의 실험변인은 직·간접조명을 사용하여 색온도 3000K, 6000K, 조도는 3lx, 60lx, 100lx, 300lx, 600lx이다. 각 부위에 10%-20%국제표준전극 부착법을 이용하여 전극을 부착한 후 뇌파를 측정하였으며, 연구의 결과는 다음과 같다. 1) 색온도 3000K의 300lx의 조명환경은 저 스트레스군과 고 스트레스군이 가장 이완, 안정할 수 있는 조명환경임을 알 수 있었다. 2) 색온도 6000K의 100lx, 300lx, 600lx는 저 스트레스군이 이완, 안정하는 조명환경으로, 특히 100lx일 때 가장 이완, 안정함을 알 수 있었다. 3) 색온도 6000K은 3lx ~ 600lx의 모든 조도에서 고 스트레스군에게는 긴장, 각성하는 조명 환경임을 알 수 있었다. 색온도가 높은, 밝은 조명환경일수록 고 스트레스군은 긴장, 각성함을 알 수 있었다. As people stays longer time in the living room space than before, lighting environment has also become important. In addition, as people"s concern for the influence on work ability and health comes to the fore and LED lighting is supplied and spread, they come to live more diverse lighting environment. Among the preceding research on this field, actually, it"s rare to find the research on the influence of stress in lighting environment, which is closely bound up with human health, on the human body. Accordingly, this study conducted the research on physiological reaction consequent on the degree of stress with the aim of constructing the human physiological reaction DB in LED lighting environment where color temperature and illumination were controllable. As the research method, this study divided the research object into the low stress group and high stress group using the stress-measuring test paper. For the experimental space, this study developed a life-size 3950㎜×3800 ㎜× 550 ㎜ Mock-up which made it possible to control lighting with experimental variables in lighting environment as 3000K & 6000k in color temperature and 3lx, 60lx, 100lx, 300lx, and 600lx in illumination using direct, indirect lighting. Then, this study measured brain wave after adhering electrode to each area using the 10%~20% international standard electrode adhesion method, the research results are as follows: 1) As a result of the research, it was learned that the lighting environment of 300lx in color temperature of 3000K was the one that could make it possible for the low stress group and high stress group to be most relaxed and stable. 2) It was found that 100lx, 300lx and 600lx in color temperature of 6000K were the lighting environment where the low stress group could relax and stabilize themselves, especially the most in case of 100lx. 3)The research results showed that color temperature 6000K in all illumination covering from 3lx to 600lx was the lighting which strained and awakened the high stress group. It was learned that the higher the color temperature and the brighter the lighting environment, the more the high stress group was strained and awakened.

Temperature Effect of Concrete Hydration Heat under Atmospheric Wind Based on Fluid-Solid Coupling

Moyan Zhang,Hong Xiao,Meng Wang,Mahantesh M. Nadakatti,Peng Chen 대한토목학회 2022 KSCE JOURNAL OF CIVIL ENGINEERING Vol.26 No.3

Concrete inevitably gets subjected to the effects of atmospheric wind during pouring. It is a significant factor to predict the temperature stress and gradient of concrete structure during pouring. In this paper, the Computational Fluid Dynamics (CFD) and Finite Element Method (FEM) were used to analyze the temperature and stress generated by temperature gradient of mass cap concrete under the wind environment. Then, the reliability of the temperature value was verified by the field test. The analysis shows that the use of the fluid-solid coupling method allows considering not only the thermal movement and thermodynamic properties of wind (given by CFD), but also the thermal expansion and stress of the concrete structure (given by FEM). Because of the wind, temperature of the windward side of the concrete is lower than that of the leeward side. Highest temperature is located at the center biased towards the leeward side. Increase in the wind speed increases the temperature difference and the maximum principal tensile stress. However, the study shows that change in the wind direction has limited effect on the concrete temperature stress.

Stress가 (Crassostrea gigas)의 LDH isozyme에 미치는 영향

김종환,김지식 한국환경생물학회 1998 환경생물 : 환경생물학회지 Vol.16 No.4

굴(Crassoffrea gigas)에 미치는 염도, pH, 온도 stress가 lactate dehydrogenase isozyme에끼치는 영향을 전기영동법으로 분석하였다. LDH isozyme pattern에서 band수의 변화는 염도 stress상태에서 12시간에서는 농도에 따라 큰 차이가 없었으나 24, 48시간 경과 후에는 상당한 차이점이 있었다. 그리고 pH stress에서는 12, 24시간 경과후 각각의 pH구분별에서 볼 때 차이가 적었으나 48시간에서는 변화가 켰다. 또한 온도 stress에서는 12, 24, 48시간에서 온도 구분으로 보았을 때 모두 동일하게 나타났다. 한편 각 stress에 따라서 band의 효소 활성은 각각 다양한 pattern으로 나타났다. 그리고 LDH isozyme에 대한 stress정도는 염도가 가장 크고 그 다음이 pH, 온도 순으로 영향을 끼쳤다. 결과적으로 굴의 LDH isozyme의 변화는 stress에 대한 생체 방어기전의 일환으로 나타난 것으로 볼 수 있다. Changes in lactate dehydrogenase isozymes in oyster exposed to salinity, pH and temperature stress were investigated by polyacrylamide gel elctrophoresis. LDH isozyme patterns indicated that the number of isozyme bands was changed in some degree in each salt con-centration 12 hours after salinity stress but in great degree 24 and 48 hours after salinity exposure. pH stress affected the number of LDH isozyme bands. 12 and 24 hours after pH exposure it was changed a little bit in each pH, but a lot 48 hours after pH stress. However, temperature stress did not make an impact on the number of LDH isozyme band. Activity of isozyme bands appeared in various patterns depending on different stress. The effect of stress on LDH isozyme was appeared in order that salinity is the most influential factor and pH is the second, and temperature is the last. In conclusion, changes in LDH isozyme seemed to be correlated to the resistance through defence mechanism.

Stress variation analysis based on temperature measurements at Zhuhai Opera House

Lu, Wei,Teng, Jun,Qiu, Lihang,Huang, Kai Techno-Press 2018 Structural monitoring and maintenance Vol.5 No.1

The Zhuhai Opera House has an external structure consisting of a type of spatial steel, where the stress of steel elements varies with the ambient temperature. A structural health monitoring system was implemented at Zhuhai Opera House, and the temperatures and stresses of the structures were monitored in real time. The relationship between the stress distribution and temperature variations was analysed by measuring the temperature and stresses of the steel elements. In addition to measurements of the structure stresses and temperatures, further simulation analysis was carried out to provide the detailed relationship between the stress distributions and temperature variations. The limited temperature measurements were used to simulate the structure temperature distribution, and the stress distributions of all steel elements of the structure were analysed by building a finite element model of the Zhuhai Opera House spatial steel structure. This study aims to reveal the stress distributions of steel elements in a real-world project based on temperature variations, and to supply a basic database for the optimal construction time of a spatial steel structure. This will not only provide convenient, rapid and safe early warnings and decision-making for the spatial steel structure construction and operation processes, but also improve the structural safety and construction accuracy of steel space structures.

An experimental and numerical study on temperature gradient and thermal stress of CFST truss girders under solar radiation

Guihan Peng,Shozo Nakamura,Xinqun Zhu,Qingxiong Wu,Hailiang Wang 사단법인 한국계산역학회 2017 Computers and Concrete, An International Journal Vol.20 No.5

Concrete filled steel tubular (CFST) composite girder is a new type of structures for bridge constructions. The existing design codes cannot be used to predict the thermal stress in the CFST truss girder structures under solar radiation. This study is to develop the temperature gradient curves for predicting thermal stress of the structure based on field and laboratory monitoring data. An in-field testing had been carried out on Ganhaizi Bridge for over two months. Thermal couples were installed at the cross section of the CFST truss girder and the continuous data was collected every 30 minutes. A typical temperature gradient mode was then extracted by comparing temperature distributions at different times. To further verify the temperature gradient mode and investigate the evolution of temperature fields, an outdoor experiment was conducted on a 1:8 scale bridge model, which was installed with both thermal couples and strain gauges. The main factors including solar radiation and ambient temperature on the different positions were studied. Laboratory results were consistent with that from the in-field data and temperature gradient curves were obtained from the in-field and laboratory data. The relationship between the strain difference at top and bottom surfaces of the concrete deck and its corresponding temperature change was also obtained and a method based on curve fitting was proposed to predict the thermal strain under elevated temperature. The thermal stress model for CFST composite girder was derived. By the proposed model, the thermal stress was obtained from the temperature gradient curves. The results using the proposed model were agreed well with that by finite element modelling.