Tests were carried out to study the strength deterioration of concrete cooled in air or by water after sub-high temperature at different level and varying with cycles. It is proved that the cross-shaped cracks turned ...Tests were carried out to study the strength deterioration of concrete cooled in air or by water after sub-high temperature at different level and varying with cycles. It is proved that the cross-shaped cracks turned up and extended little by little on the surface of specimen subjected to repeat sub-high temperature, the splitting failure is characterized by cross-shaped cracks after 30 cycles, the concrete strengths decrease rapidly at early stage and to be steady subsequently with the increase of the temperature cycles, the splitting-tensile strength is more sensitive to temperature cycles than the compressive strength, the decline of concrete strength is mainly controlled by the maximum temperature having reached, the ultrasonic velocity in concrete is also declined. On the basis of test results, the mechanisms of sub-high temperature to the strength deterioration of concrete are analyzed.The formulas for calculating the compressive and splitting-tensile strength of concrete relating to the variation of temperature are proposed.展开更多
Extreme high temperature(EHT)events are among the most impact-related consequences related to climate change,especially for China,a nation with a large population that is vulnerable to the climate warming.Based on the...Extreme high temperature(EHT)events are among the most impact-related consequences related to climate change,especially for China,a nation with a large population that is vulnerable to the climate warming.Based on the latest Coupled Model Intercomparison Project Phase 6(CMIP6),this study assesses future EHT changes across China at five specific global warming thresholds(1.5℃-5℃).The results indicate that global mean temperature will increase by 1.5℃/2℃ before 2030/2050 relative to pre-industrial levels(1861-1900)under three future scenarios(SSP1-2.6,SSP2-4.5,and SSP5-8.5),and warming will occur faster under SSP5-8.5 compared to SSP1-2.6 and SSP2-4.5.Under SSP5-8.5,global warming will eventually exceed 5℃ by 2100,while under SSP1-2.6,it will stabilize around 2℃ after 2050.In China,most of the areas where warming exceeds global average levels will be located in Tibet and northern China(Northwest China,North China and Northeast China),covering 50%-70%of the country.Furthermore,about 0.19-0.44 billion people(accounting for 16%-41%of the national population)will experience warming above the global average.Compared to present-day(1995-2014),the warmest day(TXx)will increase most notably in northern China,while the number of warm days(TX90p)and warm spell duration indicator(WSDI)will increase most profoundly in southern China.For example,relative to the present-day,TXx will increase by 1℃-5℃ in northern China,and TX90p(WSDI)will increase by 25-150(10-80)days in southern China at 1.5℃-5℃ global warming.Compared to 2℃-5℃,limiting global warming to 1.5℃ will help avoid about 36%-87%of the EHT increases in China.展开更多
The true stress-sWain relationships of Ti-5A1-2Sn-2Zr-4Mo-4Cr（TC17） alloy with a wide range of strain rates were investigated by tmiaxial quasi-static and dynamic compression tests, respectively. Quasi- static compr...The true stress-sWain relationships of Ti-5A1-2Sn-2Zr-4Mo-4Cr（TC17） alloy with a wide range of strain rates were investigated by tmiaxial quasi-static and dynamic compression tests, respectively. Quasi- static compression tests were carried out with Instron 8874 test machine, while dynamic compression tests were performed with the split Hopkinson pressure bar （SHPB） which was installed with heating device and synchro- assembly system. The dynamic mechanical behaviors tests of TC17 were carded out from room temperature to 800 ℃ at intervals of 200 ℃ and at high sWain rates （5 500-1 9200 s-l）. The stress-strain curves considering temperature-sWain rate coupling actions were obtained. The Johnson-Cook constitutive model was developed through data fitting of the stress-sWain curves. The material constants in the developed constitutive model can be determined using isothermal and adiabatic stress-strain curves at different strain rates. The Johnson-Cook constitutive model provided satisfied prediction of the plastic flow stress for TC17 alloy.展开更多
It is known from the New Energy and Industry Technology Development Organization (NEDO) roam map Japan, 2017 that the polymer electrolyte fuel cell (PEFC) power generation system is required to operate at 100°C f...It is known from the New Energy and Industry Technology Development Organization (NEDO) roam map Japan, 2017 that the polymer electrolyte fuel cell (PEFC) power generation system is required to operate at 100°C for application of mobility usage from 2020 to 2025. This study aims to clarify the effect of separator thickness on the distribution of the temperature of reaction surface (T<sub>react</sub>) at the initial temperature of cell (T<sub>ini</sub>) with flow rate, relative humidity (RH) of supply gases as well as RH of air surrounding cell of PEFC. The distribution of T<sub>react</sub> is estimated by means of the heat transfer model considering the H<sub>2</sub>O vapor transfer proposed by the authors. The relationship between the standard deviation of T<sub>react</sub>-T<sub>ini</sub> and total voltage obtained in the experiment is also investigated. We can know the effect of the flow rate of supply gas as well as RH of air surrounding cell of PEFC on the distribution of T<sub>react</sub>-T<sub>ini</sub> is not significant. It is observed the wider distribution of T<sub>react</sub>-T<sub>ini</sub> provides the reduction in power generation performance irrespective of separator thickness. In the case of separator thickness of 1.0 mm, the standard deviation of T<sub>react</sub>-T<sub>ini</sub> has smaller distribution range and the total voltage shows a larger variation compared to the other cases.展开更多
Y_(1-x)Ho_xBa_2Cu_3O_(7-δ)(0<x<1) sinsle crystal thin films oriented with the caxis perpendicular to the sur-face were grown by DC magnetron sputtering technique. Target was pieced together with half of YBa_2Cu...Y_(1-x)Ho_xBa_2Cu_3O_(7-δ)(0<x<1) sinsle crystal thin films oriented with the caxis perpendicular to the sur-face were grown by DC magnetron sputtering technique. Target was pieced together with half of YBa_2Cu_3O_(7-δ)(YBCO) and half of HoBa_2Cu_3O_(7-δ)(HBCO) superconducting materials. As the distance between HBCO targetmaterial and substrate is varied , the Ho content in material is changed respectively. When the content of Ho is0. 7 (atom ratio) , the T_c>83K.展开更多
C\-3N\-4 crystals with the size of several micrometers have been synthesized from C\-3N\-4H\-4 in the presence of nickel\|based alloy or cobalt as catalyst under high pressure of 7 GPa and temperature of about 1400℃ ...C\-3N\-4 crystals with the size of several micrometers have been synthesized from C\-3N\-4H\-4 in the presence of nickel\|based alloy or cobalt as catalyst under high pressure of 7 GPa and temperature of about 1400℃ for 10 min. Scanning electron microscopy, energy\|disperse X\|ray analysis, and X\|ray diffraction were used to examine the grown crystals. The general rule on selecting the starting materials for synthesis of carbon nitride crystals at high pressures and high temperatures is suggested.展开更多
基金Funded by Outstanding Youth Science Foundation of Henan Province of China (No. 04120002300)
文摘Tests were carried out to study the strength deterioration of concrete cooled in air or by water after sub-high temperature at different level and varying with cycles. It is proved that the cross-shaped cracks turned up and extended little by little on the surface of specimen subjected to repeat sub-high temperature, the splitting failure is characterized by cross-shaped cracks after 30 cycles, the concrete strengths decrease rapidly at early stage and to be steady subsequently with the increase of the temperature cycles, the splitting-tensile strength is more sensitive to temperature cycles than the compressive strength, the decline of concrete strength is mainly controlled by the maximum temperature having reached, the ultrasonic velocity in concrete is also declined. On the basis of test results, the mechanisms of sub-high temperature to the strength deterioration of concrete are analyzed.The formulas for calculating the compressive and splitting-tensile strength of concrete relating to the variation of temperature are proposed.
基金supported by the National Key Research and Development Program of China(2017YFA0603804)the National Natural Science Foundation of China(41831174 and 41430528)+1 种基金the Postgraduate Research&Practice Innovation Program of Jiangsu Province(KYCX19_1026)Guwei ZHANG was supported by the China Scholarship Council(NO.201908320503)。
文摘Extreme high temperature(EHT)events are among the most impact-related consequences related to climate change,especially for China,a nation with a large population that is vulnerable to the climate warming.Based on the latest Coupled Model Intercomparison Project Phase 6(CMIP6),this study assesses future EHT changes across China at five specific global warming thresholds(1.5℃-5℃).The results indicate that global mean temperature will increase by 1.5℃/2℃ before 2030/2050 relative to pre-industrial levels(1861-1900)under three future scenarios(SSP1-2.6,SSP2-4.5,and SSP5-8.5),and warming will occur faster under SSP5-8.5 compared to SSP1-2.6 and SSP2-4.5.Under SSP5-8.5,global warming will eventually exceed 5℃ by 2100,while under SSP1-2.6,it will stabilize around 2℃ after 2050.In China,most of the areas where warming exceeds global average levels will be located in Tibet and northern China(Northwest China,North China and Northeast China),covering 50%-70%of the country.Furthermore,about 0.19-0.44 billion people(accounting for 16%-41%of the national population)will experience warming above the global average.Compared to present-day(1995-2014),the warmest day(TXx)will increase most notably in northern China,while the number of warm days(TX90p)and warm spell duration indicator(WSDI)will increase most profoundly in southern China.For example,relative to the present-day,TXx will increase by 1℃-5℃ in northern China,and TX90p(WSDI)will increase by 25-150(10-80)days in southern China at 1.5℃-5℃ global warming.Compared to 2℃-5℃,limiting global warming to 1.5℃ will help avoid about 36%-87%of the EHT increases in China.
基金Funded by the National Basic Research Program of China(No.2009CB724401)the Major Science and Technology Program of High-end CNC Machine Tools and Basic Manufacturing Equipment(No.2012ZX04003-041)
文摘The true stress-sWain relationships of Ti-5A1-2Sn-2Zr-4Mo-4Cr（TC17） alloy with a wide range of strain rates were investigated by tmiaxial quasi-static and dynamic compression tests, respectively. Quasi- static compression tests were carried out with Instron 8874 test machine, while dynamic compression tests were performed with the split Hopkinson pressure bar （SHPB） which was installed with heating device and synchro- assembly system. The dynamic mechanical behaviors tests of TC17 were carded out from room temperature to 800 ℃ at intervals of 200 ℃ and at high sWain rates （5 500-1 9200 s-l）. The stress-strain curves considering temperature-sWain rate coupling actions were obtained. The Johnson-Cook constitutive model was developed through data fitting of the stress-sWain curves. The material constants in the developed constitutive model can be determined using isothermal and adiabatic stress-strain curves at different strain rates. The Johnson-Cook constitutive model provided satisfied prediction of the plastic flow stress for TC17 alloy.
文摘It is known from the New Energy and Industry Technology Development Organization (NEDO) roam map Japan, 2017 that the polymer electrolyte fuel cell (PEFC) power generation system is required to operate at 100°C for application of mobility usage from 2020 to 2025. This study aims to clarify the effect of separator thickness on the distribution of the temperature of reaction surface (T<sub>react</sub>) at the initial temperature of cell (T<sub>ini</sub>) with flow rate, relative humidity (RH) of supply gases as well as RH of air surrounding cell of PEFC. The distribution of T<sub>react</sub> is estimated by means of the heat transfer model considering the H<sub>2</sub>O vapor transfer proposed by the authors. The relationship between the standard deviation of T<sub>react</sub>-T<sub>ini</sub> and total voltage obtained in the experiment is also investigated. We can know the effect of the flow rate of supply gas as well as RH of air surrounding cell of PEFC on the distribution of T<sub>react</sub>-T<sub>ini</sub> is not significant. It is observed the wider distribution of T<sub>react</sub>-T<sub>ini</sub> provides the reduction in power generation performance irrespective of separator thickness. In the case of separator thickness of 1.0 mm, the standard deviation of T<sub>react</sub>-T<sub>ini</sub> has smaller distribution range and the total voltage shows a larger variation compared to the other cases.
文摘Y_(1-x)Ho_xBa_2Cu_3O_(7-δ)(0<x<1) sinsle crystal thin films oriented with the caxis perpendicular to the sur-face were grown by DC magnetron sputtering technique. Target was pieced together with half of YBa_2Cu_3O_(7-δ)(YBCO) and half of HoBa_2Cu_3O_(7-δ)(HBCO) superconducting materials. As the distance between HBCO targetmaterial and substrate is varied , the Ho content in material is changed respectively. When the content of Ho is0. 7 (atom ratio) , the T_c>83K.
文摘C\-3N\-4 crystals with the size of several micrometers have been synthesized from C\-3N\-4H\-4 in the presence of nickel\|based alloy or cobalt as catalyst under high pressure of 7 GPa and temperature of about 1400℃ for 10 min. Scanning electron microscopy, energy\|disperse X\|ray analysis, and X\|ray diffraction were used to examine the grown crystals. The general rule on selecting the starting materials for synthesis of carbon nitride crystals at high pressures and high temperatures is suggested.
