Dominated by an arid and semiarid continental climate,the Beijing-Tianjin Sandstorm Source Region(BTSSR)is a typical ecologically fragile region with frequently occurring droughts.To provide information for regional v...Dominated by an arid and semiarid continental climate,the Beijing-Tianjin Sandstorm Source Region(BTSSR)is a typical ecologically fragile region with frequently occurring droughts.To provide information for regional vegetation protection and drought prevention,we assessed the relations between vegetation cover change(measured by the Normalized Difference Vegetation Index,NDVI)and the Standardized Precipitation Evapotranspiration Index(SPEI)at different time-scales,in different growth stages,in different subregions and for different vegetation types based on the Pearson's correlation coefficient in the BTSSR from 2000 to 2017.Results showed that 88.19%of the vegetated areas experienced increased NDVI in the growing season;48.3%of the vegetated areas experi-enced significantly increased NDVI(P<0.05)and were mainly in the south of the BTSSR.During the growing season,a wetter climate contributed to the increased vegetation cover from 2000 to 2017,and NDVI anomalies were closely related to SPEI.The maximum correlation coefficient in the growing season(Rmax)was significantly positive(P<0.05)in 97.84%of the total vegetated areas.In the vegetated areas with significantly positive Rmax,pixels with short time-scales(1-3 mon)accounted for the largest proportion(33.9%).The sensitivity of vegetation to the impact of drought rose first and then decreased in the growing season,with a peak in July.Compared with two subregions in the south,subregions in the north of the BTSSR were more sensitive to the impacts of drought variations,especially in the Xilingol Plateau and Wuzhumuqin Basin.All four major vegetation types were sensitive to the effects of drought variations,especially grasslands.The time-scales of the most impacting droughts varied with growth stages,regions,and vegetation types.These results can help us understand the relations between vegetation and droughts,which are important for ecological restoration and drought prevention.展开更多
为分析谐波对电网换相型换流器高压直流输电系统(line commutated converter based high voltage direct current,LCC-HVDC)稳定性的影响,亟需建立一个考虑谐波耦合效应的LCC-HVDC精确模型。基于谐波状态空间(harmonic state space,HSS...为分析谐波对电网换相型换流器高压直流输电系统(line commutated converter based high voltage direct current,LCC-HVDC)稳定性的影响,亟需建立一个考虑谐波耦合效应的LCC-HVDC精确模型。基于谐波状态空间(harmonic state space,HSS)理论,考虑频率耦合效应和控制系统建立了12脉动LCC的阻抗模型,所建交直流谐波阻抗模型能在更宽的频带与扫频结果吻合。最后通过PSCAD电磁暂态仿真结果与HSS阻抗模型计算结果对比,验证了所提出的LCC-HSS阻抗模型的正确性。LCC-HSS阻抗建模方法提高了对LCC换流站进行数学建模的精确性,且可以适应多种模式下LCC换流站阻抗建模,为LCC系统稳定性分析及参数优化提供了较为精确的模型。展开更多
富含半胱氨酸的酸性分泌蛋白(secreted protein acidic and rich in cysteine, SPARC)是肿瘤微环境中重要的基质成分,它作为正常细胞恶变和肿瘤发生发展过程中一个重要的分子,能够调节多种肿瘤相关细胞因子及其受体的相互作用,并调节多...富含半胱氨酸的酸性分泌蛋白(secreted protein acidic and rich in cysteine, SPARC)是肿瘤微环境中重要的基质成分,它作为正常细胞恶变和肿瘤发生发展过程中一个重要的分子,能够调节多种肿瘤相关细胞因子及其受体的相互作用,并调节多种信号通路以及蛋白水解酶的表达水平。由于它抑制和促进肿瘤进展的能力取决于细胞类型、肿瘤分期等,因此在多种类型的肿瘤中差异表达,并可能成为肿瘤早期诊断的新型生物标记物以及治疗的新靶点。本文就近年来SPARC在肿瘤研究中的进展作一综述。展开更多
基金Under the auspices of National Natural Science Foundation of China(No.41807177,41701017)the Pioneer‘Hundred Talents Program’of Chinese Academy of Sciences。
文摘Dominated by an arid and semiarid continental climate,the Beijing-Tianjin Sandstorm Source Region(BTSSR)is a typical ecologically fragile region with frequently occurring droughts.To provide information for regional vegetation protection and drought prevention,we assessed the relations between vegetation cover change(measured by the Normalized Difference Vegetation Index,NDVI)and the Standardized Precipitation Evapotranspiration Index(SPEI)at different time-scales,in different growth stages,in different subregions and for different vegetation types based on the Pearson's correlation coefficient in the BTSSR from 2000 to 2017.Results showed that 88.19%of the vegetated areas experienced increased NDVI in the growing season;48.3%of the vegetated areas experi-enced significantly increased NDVI(P<0.05)and were mainly in the south of the BTSSR.During the growing season,a wetter climate contributed to the increased vegetation cover from 2000 to 2017,and NDVI anomalies were closely related to SPEI.The maximum correlation coefficient in the growing season(Rmax)was significantly positive(P<0.05)in 97.84%of the total vegetated areas.In the vegetated areas with significantly positive Rmax,pixels with short time-scales(1-3 mon)accounted for the largest proportion(33.9%).The sensitivity of vegetation to the impact of drought rose first and then decreased in the growing season,with a peak in July.Compared with two subregions in the south,subregions in the north of the BTSSR were more sensitive to the impacts of drought variations,especially in the Xilingol Plateau and Wuzhumuqin Basin.All four major vegetation types were sensitive to the effects of drought variations,especially grasslands.The time-scales of the most impacting droughts varied with growth stages,regions,and vegetation types.These results can help us understand the relations between vegetation and droughts,which are important for ecological restoration and drought prevention.
文摘为分析谐波对电网换相型换流器高压直流输电系统(line commutated converter based high voltage direct current,LCC-HVDC)稳定性的影响,亟需建立一个考虑谐波耦合效应的LCC-HVDC精确模型。基于谐波状态空间(harmonic state space,HSS)理论,考虑频率耦合效应和控制系统建立了12脉动LCC的阻抗模型,所建交直流谐波阻抗模型能在更宽的频带与扫频结果吻合。最后通过PSCAD电磁暂态仿真结果与HSS阻抗模型计算结果对比,验证了所提出的LCC-HSS阻抗模型的正确性。LCC-HSS阻抗建模方法提高了对LCC换流站进行数学建模的精确性,且可以适应多种模式下LCC换流站阻抗建模,为LCC系统稳定性分析及参数优化提供了较为精确的模型。
文摘富含半胱氨酸的酸性分泌蛋白(secreted protein acidic and rich in cysteine, SPARC)是肿瘤微环境中重要的基质成分,它作为正常细胞恶变和肿瘤发生发展过程中一个重要的分子,能够调节多种肿瘤相关细胞因子及其受体的相互作用,并调节多种信号通路以及蛋白水解酶的表达水平。由于它抑制和促进肿瘤进展的能力取决于细胞类型、肿瘤分期等,因此在多种类型的肿瘤中差异表达,并可能成为肿瘤早期诊断的新型生物标记物以及治疗的新靶点。本文就近年来SPARC在肿瘤研究中的进展作一综述。
