Little is known about the stable carbon isotopes of methane （CH4） emitted （δ13CH4elnitted） from permanently flooded rice fields and double rice-cropping fields. The CH4 emission and corresponding （δ13CH4emitted...Little is known about the stable carbon isotopes of methane （CH4） emitted （δ13CH4elnitted） from permanently flooded rice fields and double rice-cropping fields. The CH4 emission and corresponding （δ13CH4emitted under various field managements （mulching, water regime, tillage, and nitrogen （N） fertilization） were simultaneously measured in three typical Chinese rice fields, a permanently flooded rice field in Ziyang City, Sichuan Province, Southwest China, a double-rice cropping field in Yingtan City, Jiangxi Province, Southeast China, and a rice-wheat rotation field in Jurong City, Jiangsu Province, East China, from 2010 to 2012. Results showed different seasonal variations of δ13CH4emitted among the three fields during the rice-growing season. The values of （δ13CH4emitted were negatively correlated with corresponding CH4 emissions in seasonal variation and mean, indicating the importance of CH4 production, oxidation, and transport associated with isotopic fractionation effects to the δ13CH4emitted. Seasonal variations of δ13CH4emltted were slightly impacted by mulching cultivation, tillage, and N application, but highly controlled by drainage. Meanwhile, tillage, N application, and especially mulching cultivation had important effects on seasonal mean CH4 emissions and corresponding δ13CH4emitted with low emissions accompanied by high values of δ13CH4emitted. Seasonal mean values of （δ13CH4emitted from the three fields were similar, mostly ranging from -60‰ to -50‰ which are well in agreement with previously published data. These demonstrated that seasonal variations of （δ13CH4emitted mainly depended on the changes in CH4 emission from rice fields and further indicated the important effects of methanogenic pathways, CH4 oxidation, and CH4 transport associated with isotope fractionation effects influenced by field managements on δ13CH4emitted.展开更多
The sound insulation performance of railway car body structures is critical for the control of rail vehicle interior noise.In sound transmission loss(STL)measurements,a niche with a large depth is necessary to allow f...The sound insulation performance of railway car body structures is critical for the control of rail vehicle interior noise.In sound transmission loss(STL)measurements,a niche with a large depth is necessary to allow for mounting the wide range of thicknesses of railway car body panels and for the mechanical isolation of the two rooms.In this study,two typical interior floor panels are tested in a series of mounting conditions and mechanical boundary conditions.The change of STL results during measurement is also predicted by an STL prediction model based on the finite element method.At lower frequencies,the STL results are influenced by both the mounting positions and the mechanical boundary conditions.At higher frequencies,the STL results are mainly influenced by the mechanical boundary conditions.Differences between the panel in the infinite baffle and niches at the resonance and off-resonance frequencies are different.Considering both the effects of mounting positions and mechanical boundary conditions,the existence of the cavity amplifies the STL difference caused by the mechanical boundary conditions.展开更多
基金financially supported by the Strategic Priority Research Program of Chinese Academy of Sciences(No.XDB15020103)the National Key Technology Research and Development Program of China(No.2013BAD11B02)+2 种基金the National Natural Sciences Foundation of China(Nos.41571232 and 41271259)the State Key Laboratory of Soil and Sustainable Agriculture(No.Y412010003)the Knowledge Innovation Program of Institute of Soil Science,Chinese Academy of Sciences(No.ISSASIP1654)
文摘Little is known about the stable carbon isotopes of methane （CH4） emitted （δ13CH4elnitted） from permanently flooded rice fields and double rice-cropping fields. The CH4 emission and corresponding （δ13CH4emitted under various field managements （mulching, water regime, tillage, and nitrogen （N） fertilization） were simultaneously measured in three typical Chinese rice fields, a permanently flooded rice field in Ziyang City, Sichuan Province, Southwest China, a double-rice cropping field in Yingtan City, Jiangxi Province, Southeast China, and a rice-wheat rotation field in Jurong City, Jiangsu Province, East China, from 2010 to 2012. Results showed different seasonal variations of δ13CH4emitted among the three fields during the rice-growing season. The values of （δ13CH4emitted were negatively correlated with corresponding CH4 emissions in seasonal variation and mean, indicating the importance of CH4 production, oxidation, and transport associated with isotopic fractionation effects to the δ13CH4emitted. Seasonal variations of δ13CH4emltted were slightly impacted by mulching cultivation, tillage, and N application, but highly controlled by drainage. Meanwhile, tillage, N application, and especially mulching cultivation had important effects on seasonal mean CH4 emissions and corresponding δ13CH4emitted with low emissions accompanied by high values of δ13CH4emitted. Seasonal mean values of （δ13CH4emitted from the three fields were similar, mostly ranging from -60‰ to -50‰ which are well in agreement with previously published data. These demonstrated that seasonal variations of （δ13CH4emitted mainly depended on the changes in CH4 emission from rice fields and further indicated the important effects of methanogenic pathways, CH4 oxidation, and CH4 transport associated with isotope fractionation effects influenced by field managements on δ13CH4emitted.
基金the National Key Research and Development Program of China(No.2016YFE0205200)the National Natural Science Foundation of China(No.U1834201)。
文摘The sound insulation performance of railway car body structures is critical for the control of rail vehicle interior noise.In sound transmission loss(STL)measurements,a niche with a large depth is necessary to allow for mounting the wide range of thicknesses of railway car body panels and for the mechanical isolation of the two rooms.In this study,two typical interior floor panels are tested in a series of mounting conditions and mechanical boundary conditions.The change of STL results during measurement is also predicted by an STL prediction model based on the finite element method.At lower frequencies,the STL results are influenced by both the mounting positions and the mechanical boundary conditions.At higher frequencies,the STL results are mainly influenced by the mechanical boundary conditions.Differences between the panel in the infinite baffle and niches at the resonance and off-resonance frequencies are different.Considering both the effects of mounting positions and mechanical boundary conditions,the existence of the cavity amplifies the STL difference caused by the mechanical boundary conditions.
