To figure out the distribution of temperature gradient along the girder height of steel-concrete composite box girder, combined with the mechanical characteristics of prestressed concrete composed box girder with corr...To figure out the distribution of temperature gradient along the girder height of steel-concrete composite box girder, combined with the mechanical characteristics of prestressed concrete composed box girder with corrugated steel webs, the calculation formulas of cross-sectional temperature stress along the span in a simply-supported beam bridge with composite section were derived under the conditions of static equilibrium and deformation compatibility of the beam element. The methods of calculating the maximum temperature stress value were discussed when the connectors are assumed rigid or flexible. Theoretical and numerical results indicate that the method proposed shows better precision for the calculation of temperature self-stress in both the top and the bottom surfaces of the box girder. Moreover, the regularity of temperature stress distribution at different locations along the girder span is that the largest axial force of the top or the bottom plate of the box girder is located in the midspan and spreads decreasingly until zero at both supported ends, and that the greatest longitudinal shear density in steel-concrete interface appears at both supported ends and then reduces gradually to zero in the midspan.展开更多
A number of studies have shown the existence of cross-tolerance in plants, but the physiological mechanism is poorly understood. In this study, we used the germination of barley seeds as a system to investigate the cr...A number of studies have shown the existence of cross-tolerance in plants, but the physiological mechanism is poorly understood. In this study, we used the germination of barley seeds as a system to investigate the cross-tolerance of low-temperature pretreatment to high-temperature stress and the possible involvement of reactive oxygen species (ROS) scavenging enzymes in the cross-tolerance. After pretreatment at 0 ℃ for different periods of time, barley seeds were germinated at 35 ℃, and the content of malondialdehyde (MDA) and the activities of ROS scavenging enzymes were measured by a spectrophotometer analysis. The results showed that barley seed germinated very poorly at 35 ℃, and this inhibitive effect could be overcome by pretreatment at 0 ℃. The MDA content varied, depending on the temperature at which seeds germinated, while barley seeds pretreated at 0 ℃ did not change the MDA content. Compared with seeds germinated directly at 35 ℃, the seeds pretreated first at 0 ℃ and then germinated at 35 ℃ had markedly increased activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT), and glutathione reductase (GR). The SOD and APX activities of seeds germinated at 35 ℃ after 0 ℃-pretreatment were even substantially higher than those at 25 ℃, and GR activity was similar to that at 25 ℃, at which the highest germination performance of barley seeds was achieved. These results indicate that low-temperature pretreatment can markedly increase the tolerance of barley seed to high temperature during germination, this being related to the increase in ROS scavenging enzyme activity. This may provide a new method for increasing seed germination under stress environments, and may be an excellent model system for the study of cross-tolerance.展开更多
基金Supported by National Natural Science Foundation of China (No. 50978105)
文摘To figure out the distribution of temperature gradient along the girder height of steel-concrete composite box girder, combined with the mechanical characteristics of prestressed concrete composed box girder with corrugated steel webs, the calculation formulas of cross-sectional temperature stress along the span in a simply-supported beam bridge with composite section were derived under the conditions of static equilibrium and deformation compatibility of the beam element. The methods of calculating the maximum temperature stress value were discussed when the connectors are assumed rigid or flexible. Theoretical and numerical results indicate that the method proposed shows better precision for the calculation of temperature self-stress in both the top and the bottom surfaces of the box girder. Moreover, the regularity of temperature stress distribution at different locations along the girder span is that the largest axial force of the top or the bottom plate of the box girder is located in the midspan and spreads decreasingly until zero at both supported ends, and that the greatest longitudinal shear density in steel-concrete interface appears at both supported ends and then reduces gradually to zero in the midspan.
基金Project (No. 30870223) supported by the National Natural Science Foundation of China
文摘A number of studies have shown the existence of cross-tolerance in plants, but the physiological mechanism is poorly understood. In this study, we used the germination of barley seeds as a system to investigate the cross-tolerance of low-temperature pretreatment to high-temperature stress and the possible involvement of reactive oxygen species (ROS) scavenging enzymes in the cross-tolerance. After pretreatment at 0 ℃ for different periods of time, barley seeds were germinated at 35 ℃, and the content of malondialdehyde (MDA) and the activities of ROS scavenging enzymes were measured by a spectrophotometer analysis. The results showed that barley seed germinated very poorly at 35 ℃, and this inhibitive effect could be overcome by pretreatment at 0 ℃. The MDA content varied, depending on the temperature at which seeds germinated, while barley seeds pretreated at 0 ℃ did not change the MDA content. Compared with seeds germinated directly at 35 ℃, the seeds pretreated first at 0 ℃ and then germinated at 35 ℃ had markedly increased activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT), and glutathione reductase (GR). The SOD and APX activities of seeds germinated at 35 ℃ after 0 ℃-pretreatment were even substantially higher than those at 25 ℃, and GR activity was similar to that at 25 ℃, at which the highest germination performance of barley seeds was achieved. These results indicate that low-temperature pretreatment can markedly increase the tolerance of barley seed to high temperature during germination, this being related to the increase in ROS scavenging enzyme activity. This may provide a new method for increasing seed germination under stress environments, and may be an excellent model system for the study of cross-tolerance.