The ground roll and body wave usually show significant differences in arrival time, frequency content, and polarization characteristics, and conventional polarization filters that operate in either the time or frequen...The ground roll and body wave usually show significant differences in arrival time, frequency content, and polarization characteristics, and conventional polarization filters that operate in either the time or frequency domain cannot consider all these elements. Therefore, we have developed a time-frequency dependent polarization filter based on the S transform to attenuate the ground roll in seismic records. Our approach adopts the complex coefficients of the S transform of the multi-component seismic data to estimate the local polarization attributes and utilizes the estimated attributes to construct the filter function. In this study, we select the S transform to design this polarization filter because its scalable window length can ensure the same number of cycles of a Fourier sinusoid, thereby rendering more precise estimation of local polarization attributes. The results of applying our approach in synthetic and real data examples demonstrate that the proposed polarization filter can effectively attenuate the ground roll and successfully preserve the body wave.展开更多
A novel fiber Bragg grating(FBG) sensor with simultaneous sensing of displacement and temperature is presented.The FBG is affixed on the cantilever inclinedly.The midpoint of FBG exactly coincides with the zero strain...A novel fiber Bragg grating(FBG) sensor with simultaneous sensing of displacement and temperature is presented.The FBG is affixed on the cantilever inclinedly.The midpoint of FBG exactly coincides with the zero strain layer of a rectangular beam.The vertical displacement can be measured by the broadened bandwidth of FBG as the bandwidth is insensitive to temperature,while the temperature can be measured by the center wavelength shift as the wavelength shift is insensitive to vertical displacement.With 0.1 nm spectral resolution of the analyzer,sensitivities of bandwidth-displacement and center wavelength-temperature are 0.48 nm/mm and 0.05 nm/℃,resolutions are 0.2 mm and 2.0 ℃,and sensing ranges of displacement and temperature are up to 8.5 mm and 45℃ respectively.Experimental results match theoretical analyses very well.展开更多
Forest management practices such as prescribed burning and thinning in forest ecosystems may alter the properties of soil organic matter （SOM）. In this study, surface softs from field plots in the Bankhead National ...Forest management practices such as prescribed burning and thinning in forest ecosystems may alter the properties of soil organic matter （SOM）. In this study, surface softs from field plots in the Bankhead National Forest, Alabama, USA, were used to investigate possible SOM transformations induced by thinning and burning. Elemental analysis and solid-state 13C cross polarization magic angle spinning nuclear magnetic resonance （13C CPMAS NMR） spectroscopy were used to characterize SOM fractions in whole soils, humic substances, and density fractions. Our data revealed that the changes in SOM fractions due to the repeated burning carried out in the forest ecosystem studied were involved mainly with alkyl C, O-alkyl C, and carbohydrate functional groups, implying that most prominent reactions that occurred involved dehydrogenation, de-oxygenation, and decarboxylation. In addition, burning and thinning might have also affected the distribution and composition of free and occluded particulate SOM fractions. The limited structural changes in SOM fractions suggested that low-intensity prescribed fire in the forest ecosystem studied will not create major structural changes in SOM fractions.展开更多
基金supported by the National Science and Technology Major Project of China(Grant No.2011ZX05014 and 2011ZX05008-005)
文摘The ground roll and body wave usually show significant differences in arrival time, frequency content, and polarization characteristics, and conventional polarization filters that operate in either the time or frequency domain cannot consider all these elements. Therefore, we have developed a time-frequency dependent polarization filter based on the S transform to attenuate the ground roll in seismic records. Our approach adopts the complex coefficients of the S transform of the multi-component seismic data to estimate the local polarization attributes and utilizes the estimated attributes to construct the filter function. In this study, we select the S transform to design this polarization filter because its scalable window length can ensure the same number of cycles of a Fourier sinusoid, thereby rendering more precise estimation of local polarization attributes. The results of applying our approach in synthetic and real data examples demonstrate that the proposed polarization filter can effectively attenuate the ground roll and successfully preserve the body wave.
基金supported by the National High Technology Research and Development Program of China (No.2007AA03Z413)the National Natural Science Foundation of China (No.60727004)+3 种基金the Shaanxi Province "13115" Major Scientific and Technological Innovation Works Special Project (No.708087)the Major Science and Technology Project of Ministry of Education of China (No.Z08119)the Innovation Foundation of the Petro China (No. 2008D-5006-03-08)the Shaanxi Provincial Department of Education Project (No.09JS041)
文摘A novel fiber Bragg grating(FBG) sensor with simultaneous sensing of displacement and temperature is presented.The FBG is affixed on the cantilever inclinedly.The midpoint of FBG exactly coincides with the zero strain layer of a rectangular beam.The vertical displacement can be measured by the broadened bandwidth of FBG as the bandwidth is insensitive to temperature,while the temperature can be measured by the center wavelength shift as the wavelength shift is insensitive to vertical displacement.With 0.1 nm spectral resolution of the analyzer,sensitivities of bandwidth-displacement and center wavelength-temperature are 0.48 nm/mm and 0.05 nm/℃,resolutions are 0.2 mm and 2.0 ℃,and sensing ranges of displacement and temperature are up to 8.5 mm and 45℃ respectively.Experimental results match theoretical analyses very well.
基金supported by the USDA National Institute of Food and Agriculture(NIFA),Evans Allen Grant,USA(No.224120)the National Science Foundation(NSF-CREST-CFEA),USA(No.1036600)the Agricultural Experimental Station,Alabama A&M University,Alabama,USA(Journal#:660)
文摘Forest management practices such as prescribed burning and thinning in forest ecosystems may alter the properties of soil organic matter （SOM）. In this study, surface softs from field plots in the Bankhead National Forest, Alabama, USA, were used to investigate possible SOM transformations induced by thinning and burning. Elemental analysis and solid-state 13C cross polarization magic angle spinning nuclear magnetic resonance （13C CPMAS NMR） spectroscopy were used to characterize SOM fractions in whole soils, humic substances, and density fractions. Our data revealed that the changes in SOM fractions due to the repeated burning carried out in the forest ecosystem studied were involved mainly with alkyl C, O-alkyl C, and carbohydrate functional groups, implying that most prominent reactions that occurred involved dehydrogenation, de-oxygenation, and decarboxylation. In addition, burning and thinning might have also affected the distribution and composition of free and occluded particulate SOM fractions. The limited structural changes in SOM fractions suggested that low-intensity prescribed fire in the forest ecosystem studied will not create major structural changes in SOM fractions.
