Forest losses or gains have long been recognized as critical processes modulating the carbon flux between the biosphere and the atmosphere. Timely, accurate and spatially explicit information on forest disturbance and...Forest losses or gains have long been recognized as critical processes modulating the carbon flux between the biosphere and the atmosphere. Timely, accurate and spatially explicit information on forest disturbance and recovery history is required for assessing the effectiveness of existing forest management. The major objectives of our research focused on testing the mapping efficacy of the vegetation change tracker （VCT） model over a forested area in China. We used a new version of VCT algorithm built upon the Landsat time series stacks （LTSS）. The LTSS consisted of yearly image acquisitions to map forest disturbance history from 1987 to 2011 over the Ning-Zhen Mountains, Jiangsu Province of east China. The LTSS consisted of TM and ETM＋ scenes with different projec- tions due to distinct data sources （Beijing remote sensing ground station and the USGS EROS Center）. The valida- tion results of the disturbance year maps showed that most spatial agreement measures ranged from 70 to 86 %, comparable with the VCT accuracies reported for many places in USA. Very low accuracies were identified in 1995 （38.3 %） and 1992 （56.2 %） in the current analysis. These resulted from the insensitivity of the VCT algorithm to detect low intensity disturbances and also from the mis- registration errors of the image pairs. Major forest distur- bance types existing in our study area were identified as agricultural expansion （39.8 %）, urbanization （24.9 %）, forest management practice （19.3 %）, and mining （12.8 %）. In general, there was a gradual decreasing trend in forest cover throughout this region, caused principally by China＇s economic, demographic, environmental and political policies and decisions, as well as some weather events. While VCT has largely been used to assess long term changes and trends in the USA, it has great potential for assessing landscape level change elsewhere throughout the world.展开更多
The over-exploitation of fossil fuel energy has brought about serious environmental problems.It would be of great significance to construct efficient energy conversion and storage system to maximize utilize renewable ...The over-exploitation of fossil fuel energy has brought about serious environmental problems.It would be of great significance to construct efficient energy conversion and storage system to maximize utilize renewable energy,which contributes to reducing environmental hazards.For the past few years,in terms of electrocatalysis and energy storage,carbon fiber materials show great advantages due to its outstanding electrical conductivity,good flexibility and mechanical property.As a simple and low-cost technique,electrospinning can be employed to prepare various nanofibers.It is noted that the functional fiber materials with different special structure and composition can be obtained for energy conversion and storage by combining electrospinning with other post-processing.In this paper,the structural design,controllable synthesis and multifunctional applications of electrospinning-derived functional carbon-based materials(EFCMs)is reviewed.Firstly,we briefly introduce the history,basic principle and typical equipment of electrospinning.Then we discuss the strategies for preparing EFCMs with different structures and composition in detail.In addition,we show recently the application of advanced EFCMs in energy conversion and storage,such as nitrogen species reduction reaction,CO_(2) reduction reaction,oxygen reduction reaction,water-splitting,supercapacitors and ion batteries.In the end,we propose some perspectives on the future development direction of EFCMs.展开更多
New filler alloy composition of Ti66-Ni22-Nb12(at.%)was designed for NbSS/Nb5 Si3 composite joining and the brazing experiment was conducted at 1200℃and 1260℃,respectively.Compared with the previously reported Ti-Ni...New filler alloy composition of Ti66-Ni22-Nb12(at.%)was designed for NbSS/Nb5 Si3 composite joining and the brazing experiment was conducted at 1200℃and 1260℃,respectively.Compared with the previously reported Ti-Ni-Nb system filler alloys,the concentration of Ni was significantly decreased from 40 at.%to 22 at.%.The filler alloy was fabricated into brazing foils by rapid solidification technique,with about 60μm thickness.The brazing seam mainly consisted of Nb solid solution,(Nb,Ti)5 Si3 and residual NiTi2 phases.Due to the high content of stabilization element Ti in the filler alloy,hexagonalγ-Nb5 Si3 phase was detected in the brazing seam.When increasing brazing temperature or prolonging brazing time,the amount of residual NiTi2 phase within the joint was gradually decreased.The joints brazed at 1260℃for 60 min exhibited three-point bend strength of 317 MPa.展开更多
基金funded by the following grants:the Forestry Public Welfare Project(201304208)the‘‘948’’Project sponsored by the State Forestry Administration(SFA)of China(2014-4-25)+4 种基金the National Natural Science Foundation of China(31270587,31100414)the PAPD(Priority Academic Program Development)of Jiangsu provincial universitiesperformed while the lead author held a scholarship sponsored the CSC(China Scholarship Council)(201208320553)at the department of Geographical Sciences,University of Marylandawardee of the 2012 Youth Backbone Teachers Support Plan of Jiangsu Provincethe 2012 Youth Talents Support Plan of Nanjing Forestry University
文摘Forest losses or gains have long been recognized as critical processes modulating the carbon flux between the biosphere and the atmosphere. Timely, accurate and spatially explicit information on forest disturbance and recovery history is required for assessing the effectiveness of existing forest management. The major objectives of our research focused on testing the mapping efficacy of the vegetation change tracker （VCT） model over a forested area in China. We used a new version of VCT algorithm built upon the Landsat time series stacks （LTSS）. The LTSS consisted of yearly image acquisitions to map forest disturbance history from 1987 to 2011 over the Ning-Zhen Mountains, Jiangsu Province of east China. The LTSS consisted of TM and ETM＋ scenes with different projec- tions due to distinct data sources （Beijing remote sensing ground station and the USGS EROS Center）. The valida- tion results of the disturbance year maps showed that most spatial agreement measures ranged from 70 to 86 %, comparable with the VCT accuracies reported for many places in USA. Very low accuracies were identified in 1995 （38.3 %） and 1992 （56.2 %） in the current analysis. These resulted from the insensitivity of the VCT algorithm to detect low intensity disturbances and also from the mis- registration errors of the image pairs. Major forest distur- bance types existing in our study area were identified as agricultural expansion （39.8 %）, urbanization （24.9 %）, forest management practice （19.3 %）, and mining （12.8 %）. In general, there was a gradual decreasing trend in forest cover throughout this region, caused principally by China＇s economic, demographic, environmental and political policies and decisions, as well as some weather events. While VCT has largely been used to assess long term changes and trends in the USA, it has great potential for assessing landscape level change elsewhere throughout the world.
基金supported by the Natural Science Foundation of Shandong Province(No.ZR2022QE076)the National Natural Science Foundation of China(No.52202092)。
文摘The over-exploitation of fossil fuel energy has brought about serious environmental problems.It would be of great significance to construct efficient energy conversion and storage system to maximize utilize renewable energy,which contributes to reducing environmental hazards.For the past few years,in terms of electrocatalysis and energy storage,carbon fiber materials show great advantages due to its outstanding electrical conductivity,good flexibility and mechanical property.As a simple and low-cost technique,electrospinning can be employed to prepare various nanofibers.It is noted that the functional fiber materials with different special structure and composition can be obtained for energy conversion and storage by combining electrospinning with other post-processing.In this paper,the structural design,controllable synthesis and multifunctional applications of electrospinning-derived functional carbon-based materials(EFCMs)is reviewed.Firstly,we briefly introduce the history,basic principle and typical equipment of electrospinning.Then we discuss the strategies for preparing EFCMs with different structures and composition in detail.In addition,we show recently the application of advanced EFCMs in energy conversion and storage,such as nitrogen species reduction reaction,CO_(2) reduction reaction,oxygen reduction reaction,water-splitting,supercapacitors and ion batteries.In the end,we propose some perspectives on the future development direction of EFCMs.
基金financially supported by the National Natural Science Foundation of China(Nos.51605456,51705489 and51804286)the Beijing Municipal Science&Technology Commission(No.Z171100002217048)。
文摘New filler alloy composition of Ti66-Ni22-Nb12(at.%)was designed for NbSS/Nb5 Si3 composite joining and the brazing experiment was conducted at 1200℃and 1260℃,respectively.Compared with the previously reported Ti-Ni-Nb system filler alloys,the concentration of Ni was significantly decreased from 40 at.%to 22 at.%.The filler alloy was fabricated into brazing foils by rapid solidification technique,with about 60μm thickness.The brazing seam mainly consisted of Nb solid solution,(Nb,Ti)5 Si3 and residual NiTi2 phases.Due to the high content of stabilization element Ti in the filler alloy,hexagonalγ-Nb5 Si3 phase was detected in the brazing seam.When increasing brazing temperature or prolonging brazing time,the amount of residual NiTi2 phase within the joint was gradually decreased.The joints brazed at 1260℃for 60 min exhibited three-point bend strength of 317 MPa.
