地磁暴发生时,电离层会有偏离平均水平的强烈扰动.基于全球电离层TEC及其时间变化率ROTI(Rate of TEC Index)数据,对2014年8月一次中等强度磁暴期间的全球电离层影响进行了分析,探讨了磁暴所引发电离层暴的可能机制.研究发现,本次磁暴...地磁暴发生时,电离层会有偏离平均水平的强烈扰动.基于全球电离层TEC及其时间变化率ROTI(Rate of TEC Index)数据,对2014年8月一次中等强度磁暴期间的全球电离层影响进行了分析,探讨了磁暴所引发电离层暴的可能机制.研究发现,本次磁暴伴随有明显的电离层暴效应.磁暴期间:南半球电离层以正相暴为主,北半球电离层暴则整体表现为短暂正相暴后长时间强的负相暴;电离层在北半球的下降比南半球强,并且这种下降持续了约一周时间;低纬区域电离层变化幅度明显小于中纬区域,高纬区域则主要表现为负暴效应;赤道北驼峰出现了明显的南移现象,直至磁赤道两侧双驼峰结构消失.对磁暴期间三个不同扇区的电离层ROTI变化的分析表明:欧洲—非洲扇区磁暴前有电离层闪烁发生,磁暴发生后消失,而东亚—澳大利亚及美洲扇区则无此现象出现.研究结果表明,此次磁暴期间的电离层变化存在明显的时间和空间差异.展开更多
In order to investigate the hot deformation behavior of superalloy GH696, isothermal compression experiments were carried out at deformation temperatures of 880?1120 °C and strain rates of 0.01?10 s?1. And the de...In order to investigate the hot deformation behavior of superalloy GH696, isothermal compression experiments were carried out at deformation temperatures of 880?1120 °C and strain rates of 0.01?10 s?1. And the deformation amount of all the samples was 50%. The strain rate sensitivity exponent (m) and strain hardening exponent (n) under different deformation conditions were calculated, meanwhile the effects of the processing parameters on the values ofm andn were analyzed. The results show that the flow stress increases with the increase of strain rate and the decrease of deformation temperature. The value ofm increases with the increase of deformation temperature and decreases with the increase of strain rate, while the value ofn decreases with the increase of deformation temperature. A novel flow stress model during hot deformation of superalloy GH696 was also established. And the calculated flow stress of the alloy is in good agreement with the experimental one.展开更多
Abies fabri is a typical subalpine dark coniferous forest in southwestern China. Air temperature increases more at high elevation areas than that at low elevation areas in mountainous regions,and climate change ratio ...Abies fabri is a typical subalpine dark coniferous forest in southwestern China. Air temperature increases more at high elevation areas than that at low elevation areas in mountainous regions,and climate change ratio is also uneven in different seasons. Carbon gain and the response of water use efficiency(WUE) to annual and seasonal increases in temperature with or without CO_2 fertilization were simulated in Abies fabri using the atmospheric-vegetation interaction model(AVIM2). Four future climate scenarios(RCP2.6,RCP4.5,RCP6.0 and RCP8.5) from the Coupled Model Intercomparison Project Phase 5(CMIP5) were selectively investigated. The results showed that warmer temperatures have negative effects on gross primary production(GPP) and net primary production(NPP) in growing seasons and positive effects in dormant seasons due to the variation in the leaf area index. Warmer temperatures tend to generate lower canopy WUE and higher ecosystem WUE in Abies fabri. However,warmer temperature together with rising CO_2 concentrations significantlyincrease the GPP and NPP in both growing and dormant seasons and enhance WUE in annual and dormant seasons because of the higher leaf area index(LAI) and soil temperature. The comparison of the simulated results with and without CO_2 fertilization shows that CO_2 has the potential to partially alleviate the adverse effects of climate warming on carbon gain and WUE in subalpine coniferous forests.展开更多
We analyze the effects of average index variation on the transmission characteristics of an index-apodized long-period fiber grating （LPFG） by the transfer matrix method and study how these effects depend on the gra...We analyze the effects of average index variation on the transmission characteristics of an index-apodized long-period fiber grating （LPFG） by the transfer matrix method and study how these effects depend on the grating length, the grating profile, the modal dispersion factor, and the duty cycle of the index modulation. Apart from shifting the resonance wavelength and modifying the rejection band, average index variation can give rise to significant side lobes that may appear on the short-wavelength or long-wavelength side of the rejection band, depending on the signs of the average index change and the modal dispersion factor. Our results provide general guidance for the writing of LPFGs for the minimization of side lobes. Our analysis compares well with published experimental results and should be useful for the design and fabrication of LPFGs.展开更多
文摘地磁暴发生时,电离层会有偏离平均水平的强烈扰动.基于全球电离层TEC及其时间变化率ROTI(Rate of TEC Index)数据,对2014年8月一次中等强度磁暴期间的全球电离层影响进行了分析,探讨了磁暴所引发电离层暴的可能机制.研究发现,本次磁暴伴随有明显的电离层暴效应.磁暴期间:南半球电离层以正相暴为主,北半球电离层暴则整体表现为短暂正相暴后长时间强的负相暴;电离层在北半球的下降比南半球强,并且这种下降持续了约一周时间;低纬区域电离层变化幅度明显小于中纬区域,高纬区域则主要表现为负暴效应;赤道北驼峰出现了明显的南移现象,直至磁赤道两侧双驼峰结构消失.对磁暴期间三个不同扇区的电离层ROTI变化的分析表明:欧洲—非洲扇区磁暴前有电离层闪烁发生,磁暴发生后消失,而东亚—澳大利亚及美洲扇区则无此现象出现.研究结果表明,此次磁暴期间的电离层变化存在明显的时间和空间差异.
文摘基于加拿大地区高纬度电离层观测网的电离层闪烁观测数据,分析了2018年8月26日地磁暴事件引发的北半球高纬度地区电离层总电子含量(TEC)异常变化、TEC变化率指数(ROTI)及电离层相位闪烁的变化特征.结果表明:加拿大地区最大异常值约6 TECU,磁暴引发全球电离层TEC异常峰值高达20 TECU;加拿大地区电离层相位闪烁发生率最大增至12.6%,而磁静日期间约为1%;强电离层闪烁期间,电离层相位闪烁指数与ROTI之间具有较强的一致性.对GPS双频精密单点定位(Precise Point Positioning,PPP)结果进行分析发现:无闪烁期间定位误差随测站纬度的增高呈现出增大趋势,但均方根误差小于0.4m;闪烁发生期间各测站的定位误差均显著增大,水平和垂直方向定位误差分别增至约0.9m及1.7m.
文摘In order to investigate the hot deformation behavior of superalloy GH696, isothermal compression experiments were carried out at deformation temperatures of 880?1120 °C and strain rates of 0.01?10 s?1. And the deformation amount of all the samples was 50%. The strain rate sensitivity exponent (m) and strain hardening exponent (n) under different deformation conditions were calculated, meanwhile the effects of the processing parameters on the values ofm andn were analyzed. The results show that the flow stress increases with the increase of strain rate and the decrease of deformation temperature. The value ofm increases with the increase of deformation temperature and decreases with the increase of strain rate, while the value ofn decreases with the increase of deformation temperature. A novel flow stress model during hot deformation of superalloy GH696 was also established. And the calculated flow stress of the alloy is in good agreement with the experimental one.
基金supported by the Natural Science Foundation of China (No.41401044 and No.41310013)the key research projects of frontier sciences CAS (QYZDJ-SSW-DQC006)+1 种基金the Chinese Academy of Science (‘West Star’ project)the CAS/SAFEA international partnership program for creative research teams (KZZD-EW-TZ-06)
文摘Abies fabri is a typical subalpine dark coniferous forest in southwestern China. Air temperature increases more at high elevation areas than that at low elevation areas in mountainous regions,and climate change ratio is also uneven in different seasons. Carbon gain and the response of water use efficiency(WUE) to annual and seasonal increases in temperature with or without CO_2 fertilization were simulated in Abies fabri using the atmospheric-vegetation interaction model(AVIM2). Four future climate scenarios(RCP2.6,RCP4.5,RCP6.0 and RCP8.5) from the Coupled Model Intercomparison Project Phase 5(CMIP5) were selectively investigated. The results showed that warmer temperatures have negative effects on gross primary production(GPP) and net primary production(NPP) in growing seasons and positive effects in dormant seasons due to the variation in the leaf area index. Warmer temperatures tend to generate lower canopy WUE and higher ecosystem WUE in Abies fabri. However,warmer temperature together with rising CO_2 concentrations significantlyincrease the GPP and NPP in both growing and dormant seasons and enhance WUE in annual and dormant seasons because of the higher leaf area index(LAI) and soil temperature. The comparison of the simulated results with and without CO_2 fertilization shows that CO_2 has the potential to partially alleviate the adverse effects of climate warming on carbon gain and WUE in subalpine coniferous forests.
文摘We analyze the effects of average index variation on the transmission characteristics of an index-apodized long-period fiber grating （LPFG） by the transfer matrix method and study how these effects depend on the grating length, the grating profile, the modal dispersion factor, and the duty cycle of the index modulation. Apart from shifting the resonance wavelength and modifying the rejection band, average index variation can give rise to significant side lobes that may appear on the short-wavelength or long-wavelength side of the rejection band, depending on the signs of the average index change and the modal dispersion factor. Our results provide general guidance for the writing of LPFGs for the minimization of side lobes. Our analysis compares well with published experimental results and should be useful for the design and fabrication of LPFGs.
