Fatigue tests were conducted on tapered plain concrete prism specimens under tri axial constant-amplitude tension-compression cyclic loading. The low stress of the cyclic loading was taken as 0.2f c and the upper st...Fatigue tests were conducted on tapered plain concrete prism specimens under tri axial constant-amplitude tension-compression cyclic loading. The low stress of the cyclic loading was taken as 0.2f c and the upper stress ranged from 0. 20f t to 0.65f t. Three constant lateral pressures were 0.1f c, 0.2f c and 0.3f c respec tively. Based on the results, the th ree-stage evolution rule of the fatigue stiffness, maximum(minimum) longitudina l strain and damage were analyzed, and a unified S-N curve to calculate fati gue strength factors was worked out. The results show that the fatigue strength and fa tigue life under triaxial constant-amplitude tension-compression cyclic loadin g are smaller than those under uniaxial fatigue condition. Moreover, the secondary strain creep rate is related to the fatigue life, a formula for describing thei r relation was derived. The investigation of this paper can provide information for the fatigue design of concrete structures.展开更多
【目的】设计旱地开放式增温系统,并从田间温度变化和冬小麦生育期改变等方面来监测系统的增温效果与可靠性。【方法】参考国际已有增温系统,于2007—2009年在江苏南京设计了中国首个麦田开放式增温系统(freeair temperature increase,F...【目的】设计旱地开放式增温系统,并从田间温度变化和冬小麦生育期改变等方面来监测系统的增温效果与可靠性。【方法】参考国际已有增温系统,于2007—2009年在江苏南京设计了中国首个麦田开放式增温系统(freeair temperature increase,FATI),进行冬小麦全天、白天和夜间3种增温试验。【结果】2年试验结果表明,该开放式主动增温系统的增温效果明显。3种情景下各增温小区的均匀有效增温面积在4m2以内,其中全天、白天和夜间增温分别使冬小麦全生育期地下5cm的土温平均增加2.2、1.5和1.8℃,地表温度增加2.2、0.9和1℃,冠层温度增加1.5、0.9和1.1℃。3种增温情景下,冬小麦各关键生育期田间温度的日变化及全生育期日平均温度的变化动态与未增温区的基本一致,增温设施能客观地模拟田间实际气温变化特征。尽管该增温系统略微降低了耕层土壤(0—20cm)水分含量,但降幅仅在0.5—2.2个百分点之间,与对照相比不显著。3种增温情景均对冬小麦生长发育产生了显著影响,全天、白天和夜间增温两年平均分别可以使冬小麦从播种至抽穗期缩短14、9.5和11.5d,灌浆成熟期延长3、3和2.5d。【结论】从增温效果及其对冬小麦的生长影响来看,该套系统基本适用于模拟气候变暖下小麦生产力和品质响应与适应的田间试验研究。展开更多
气候变暖存在明显的昼夜不对称性,夜间增温显著高于白天。设计可靠的田间增温设施,研究作物系统对夜间增温的响应与适应意义显著。参考国际相关增温系统,于2006—2009年在江苏南京设计并运行了我国首个农田开放式夜间增温系统(FATI,Free...气候变暖存在明显的昼夜不对称性,夜间增温显著高于白天。设计可靠的田间增温设施,研究作物系统对夜间增温的响应与适应意义显著。参考国际相关增温系统,于2006—2009年在江苏南京设计并运行了我国首个农田开放式夜间增温系统(FATI,Free Air Temperature Increased),对稻麦进行夜间主动增温试验,监测系统温度、麦田土壤水分和作物生育进程和产量,以评价该系统的可行性和对稻麦的增温效果。结果表明,该系统有效且均匀的增温范围为4m2,增温效果明显。在测试用人工草坪上,晴天、阴天和雨天3种天气情况下,该系统4m2有效增温范围内地表的夜温平均升高2.4℃、2.3℃和2.1℃。在草坪的垂直层面上,该系统可以使距地下5cm、地表、地上40cm和90cm4个层次的夜温平均分别升高1.2℃、2.2℃、0.7℃和2.3℃。在稻麦两熟农田中,稻季全生育期地下5cm、地表、植株中部和冠层的夜温平均分别升高0.7℃、0.6℃、1.0℃和1.6℃,麦季相应层次可升高1.2℃、1.5℃、1.8℃和1.9℃。在稻麦全生育期内,增温小区各层温度的变化动态与未增温区的一致。另外,该系统未改变麦田耕层土壤水分分布特征,尽管耕层土壤含水量略有降低,0～25cm内各层土壤含水量的降幅均在0.99～1.62个百分点以内,与未增温区差异不显著。夜间增温可以显著缩短作物前期生育期,使稻麦始穗期分别提早2.5d和11.5d;同时,夜间增温使水稻平均减产4.51%,但小麦增产18.30%。尽管在作物的不同生育期,该设施的增温幅度有所差异,但这与田间实际情况下不同季节气候变暖幅度不同之特征一致。因此,该开放式夜间增温系统符合气候变暖的温度变化特征,可以满足水稻和小麦所代表的典型作物系统对夜间增温的响应与适应的试验要求。展开更多
Changes in the soil nematode community induced by global warming may have a considerable influence on agro-ecosystem functioning. However, the impacts of predicted warming on nematode community in farmland （e.g., win...Changes in the soil nematode community induced by global warming may have a considerable influence on agro-ecosystem functioning. However, the impacts of predicted warming on nematode community in farmland （e.g., winter wheat field） have not been well documented. Therefore, a field experiment with free air temperature increase （FATI） was conducted to investigate the responses of the soil nematode community to nighttime warming in a winter wheat field of Yangtze Delta Plain, China, during 2007 to 2009. Nighttime warming （NW） by 1.8~C at 5-cm soil depth had no significant impact on the total nematode abundance compared to un-warmed control （CK）. However, NW significantly affected the nematode community structure. Warming favored the bacterivores and fungivores, such as Acrobeles, Monhystera, Rhabditis, and Rhabdontolaimus in bacterivores, and Filenchus in fungivores, while the plant-parasites were hindered, such as Helicotylenchus and Psilenchus. Interestingly, the carnivores/ omnivores remained almost unchanged. Hence, the abundances ofbacterivores and fungivores were significantly higher under NW than those under CK. Similarly, the abundances of plant-parasites were significantly lower under NW than under CK. Furthermore, Wasilewska index of the nematode community was significantly higher under NW than those under CK, indicating beneficial effect to the plant in the soil. Our results suggest that nighttime warming may improve soil fertility and decrease soil- borne diseases in winter wheat field through affecting the soil nematode community. It is also indicated that nighttime warming may promote the sustainability of the nematode community by altering genera-specific habitat suitability for soil biota.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant No.50078010)
文摘Fatigue tests were conducted on tapered plain concrete prism specimens under tri axial constant-amplitude tension-compression cyclic loading. The low stress of the cyclic loading was taken as 0.2f c and the upper stress ranged from 0. 20f t to 0.65f t. Three constant lateral pressures were 0.1f c, 0.2f c and 0.3f c respec tively. Based on the results, the th ree-stage evolution rule of the fatigue stiffness, maximum(minimum) longitudina l strain and damage were analyzed, and a unified S-N curve to calculate fati gue strength factors was worked out. The results show that the fatigue strength and fa tigue life under triaxial constant-amplitude tension-compression cyclic loadin g are smaller than those under uniaxial fatigue condition. Moreover, the secondary strain creep rate is related to the fatigue life, a formula for describing thei r relation was derived. The investigation of this paper can provide information for the fatigue design of concrete structures.
文摘【目的】设计旱地开放式增温系统,并从田间温度变化和冬小麦生育期改变等方面来监测系统的增温效果与可靠性。【方法】参考国际已有增温系统,于2007—2009年在江苏南京设计了中国首个麦田开放式增温系统(freeair temperature increase,FATI),进行冬小麦全天、白天和夜间3种增温试验。【结果】2年试验结果表明,该开放式主动增温系统的增温效果明显。3种情景下各增温小区的均匀有效增温面积在4m2以内,其中全天、白天和夜间增温分别使冬小麦全生育期地下5cm的土温平均增加2.2、1.5和1.8℃,地表温度增加2.2、0.9和1℃,冠层温度增加1.5、0.9和1.1℃。3种增温情景下,冬小麦各关键生育期田间温度的日变化及全生育期日平均温度的变化动态与未增温区的基本一致,增温设施能客观地模拟田间实际气温变化特征。尽管该增温系统略微降低了耕层土壤(0—20cm)水分含量,但降幅仅在0.5—2.2个百分点之间,与对照相比不显著。3种增温情景均对冬小麦生长发育产生了显著影响,全天、白天和夜间增温两年平均分别可以使冬小麦从播种至抽穗期缩短14、9.5和11.5d,灌浆成熟期延长3、3和2.5d。【结论】从增温效果及其对冬小麦的生长影响来看,该套系统基本适用于模拟气候变暖下小麦生产力和品质响应与适应的田间试验研究。
文摘气候变暖存在明显的昼夜不对称性,夜间增温显著高于白天。设计可靠的田间增温设施,研究作物系统对夜间增温的响应与适应意义显著。参考国际相关增温系统,于2006—2009年在江苏南京设计并运行了我国首个农田开放式夜间增温系统(FATI,Free Air Temperature Increased),对稻麦进行夜间主动增温试验,监测系统温度、麦田土壤水分和作物生育进程和产量,以评价该系统的可行性和对稻麦的增温效果。结果表明,该系统有效且均匀的增温范围为4m2,增温效果明显。在测试用人工草坪上,晴天、阴天和雨天3种天气情况下,该系统4m2有效增温范围内地表的夜温平均升高2.4℃、2.3℃和2.1℃。在草坪的垂直层面上,该系统可以使距地下5cm、地表、地上40cm和90cm4个层次的夜温平均分别升高1.2℃、2.2℃、0.7℃和2.3℃。在稻麦两熟农田中,稻季全生育期地下5cm、地表、植株中部和冠层的夜温平均分别升高0.7℃、0.6℃、1.0℃和1.6℃,麦季相应层次可升高1.2℃、1.5℃、1.8℃和1.9℃。在稻麦全生育期内,增温小区各层温度的变化动态与未增温区的一致。另外,该系统未改变麦田耕层土壤水分分布特征,尽管耕层土壤含水量略有降低,0～25cm内各层土壤含水量的降幅均在0.99～1.62个百分点以内,与未增温区差异不显著。夜间增温可以显著缩短作物前期生育期,使稻麦始穗期分别提早2.5d和11.5d;同时,夜间增温使水稻平均减产4.51%,但小麦增产18.30%。尽管在作物的不同生育期,该设施的增温幅度有所差异,但这与田间实际情况下不同季节气候变暖幅度不同之特征一致。因此,该开放式夜间增温系统符合气候变暖的温度变化特征,可以满足水稻和小麦所代表的典型作物系统对夜间增温的响应与适应的试验要求。
基金supported by the National Basic Research Program of China(2010CB951501)the Key Technologies R&D Program of China during the 12th Five-Year Plan period(2011BAD16B14)+1 种基金the National Natural Science Foundation of China(30771278)the Innovation Program of Chinese Academy of Agricultural Sciences,China
文摘Changes in the soil nematode community induced by global warming may have a considerable influence on agro-ecosystem functioning. However, the impacts of predicted warming on nematode community in farmland （e.g., winter wheat field） have not been well documented. Therefore, a field experiment with free air temperature increase （FATI） was conducted to investigate the responses of the soil nematode community to nighttime warming in a winter wheat field of Yangtze Delta Plain, China, during 2007 to 2009. Nighttime warming （NW） by 1.8~C at 5-cm soil depth had no significant impact on the total nematode abundance compared to un-warmed control （CK）. However, NW significantly affected the nematode community structure. Warming favored the bacterivores and fungivores, such as Acrobeles, Monhystera, Rhabditis, and Rhabdontolaimus in bacterivores, and Filenchus in fungivores, while the plant-parasites were hindered, such as Helicotylenchus and Psilenchus. Interestingly, the carnivores/ omnivores remained almost unchanged. Hence, the abundances ofbacterivores and fungivores were significantly higher under NW than those under CK. Similarly, the abundances of plant-parasites were significantly lower under NW than under CK. Furthermore, Wasilewska index of the nematode community was significantly higher under NW than those under CK, indicating beneficial effect to the plant in the soil. Our results suggest that nighttime warming may improve soil fertility and decrease soil- borne diseases in winter wheat field through affecting the soil nematode community. It is also indicated that nighttime warming may promote the sustainability of the nematode community by altering genera-specific habitat suitability for soil biota.
