Phytochemical reinvestigation on the whole plants of Ypsilandra thibetica obtained four new spirostanol glycosides,named ypsilandrosides U-X(1-4),and one new cholestanol glycoside,named ypsilandroside Y(5).Their struc...Phytochemical reinvestigation on the whole plants of Ypsilandra thibetica obtained four new spirostanol glycosides,named ypsilandrosides U-X(1-4),and one new cholestanol glycoside,named ypsilandroside Y(5).Their structures have been established by extensive spectroscopic data and chemical methods.Among them,compound 4 is a rare spirostanol glycoside which possesses a novel 5(6→7)abeo-steroidal aglycone,while compound 1 is a first spiro-stanol bisdesmoside attached to C-3 and C-12,respectively,isolated from the genus Ypsilandra.The induced platelet aggregation activity of the isolates was tested.展开更多
为准确地评估交联聚乙烯(cross linked polyethylene,XLPE)电缆的水树老化程度,该文提出一种基于超低频介损和U-I滞回曲线的评估方法。对3组XLPE样本分别进行0、96和168h的加速水树老化,老化结束后采用快速超低频介损设备(very-low freq...为准确地评估交联聚乙烯(cross linked polyethylene,XLPE)电缆的水树老化程度,该文提出一种基于超低频介损和U-I滞回曲线的评估方法。对3组XLPE样本分别进行0、96和168h的加速水树老化,老化结束后采用快速超低频介损设备(very-low frequency dielectric loss detector,iFDS)在1mHz~1kHz范围内测试不同水树老化状态的XLPE电缆的介电频谱和不同频率下U-I滞回曲线。结果发现:水树老化后的电缆段在超低频段(1mHz~0.1Hz)的介损值显著增大,并在0.002和0.1Hz附近出现两个明显的松弛损耗峰。老化越严重的试样,U-I滞回曲线形变越严重。水树老化后电缆绝缘中产生了新的松弛极化过程,相较于单一频率0.1Hz下的介损值,超低频介电谱能够提供更丰富的绝缘状态信息。在1mHz下,U-I滞回曲线特性的偏转角变化率与曲线形变率均随超低频介损值的上升而增大,能够更加准确地评估电缆绝缘的水树老化程度。将超低频介损结合U-I滞回曲线可以有效地评估电缆绝缘的水树老化程度。展开更多
基金supported by the National Natural Science Foundation of China (U1802287 and 32000280)the Ten Thousand Talents Plan of Yunnan Province for Industrial Technology Leading Talentsthe State Key Laboratory of Phytochemistry and Plant Resources in West China (P2019-ZZ02).
文摘Phytochemical reinvestigation on the whole plants of Ypsilandra thibetica obtained four new spirostanol glycosides,named ypsilandrosides U-X(1-4),and one new cholestanol glycoside,named ypsilandroside Y(5).Their structures have been established by extensive spectroscopic data and chemical methods.Among them,compound 4 is a rare spirostanol glycoside which possesses a novel 5(6→7)abeo-steroidal aglycone,while compound 1 is a first spiro-stanol bisdesmoside attached to C-3 and C-12,respectively,isolated from the genus Ypsilandra.The induced platelet aggregation activity of the isolates was tested.
文摘为准确地评估交联聚乙烯(cross linked polyethylene,XLPE)电缆的水树老化程度,该文提出一种基于超低频介损和U-I滞回曲线的评估方法。对3组XLPE样本分别进行0、96和168h的加速水树老化,老化结束后采用快速超低频介损设备(very-low frequency dielectric loss detector,iFDS)在1mHz~1kHz范围内测试不同水树老化状态的XLPE电缆的介电频谱和不同频率下U-I滞回曲线。结果发现:水树老化后的电缆段在超低频段(1mHz~0.1Hz)的介损值显著增大,并在0.002和0.1Hz附近出现两个明显的松弛损耗峰。老化越严重的试样,U-I滞回曲线形变越严重。水树老化后电缆绝缘中产生了新的松弛极化过程,相较于单一频率0.1Hz下的介损值,超低频介电谱能够提供更丰富的绝缘状态信息。在1mHz下,U-I滞回曲线特性的偏转角变化率与曲线形变率均随超低频介损值的上升而增大,能够更加准确地评估电缆绝缘的水树老化程度。将超低频介损结合U-I滞回曲线可以有效地评估电缆绝缘的水树老化程度。
