Scientists said on Monday they had genetically engineered rice to withstand drought, salt water and cold temperatures by borrowing a gene from the E. coli bacteria. [译文]星期一,科学家们称他们已经利用遗传工程学,借用...Scientists said on Monday they had genetically engineered rice to withstand drought, salt water and cold temperatures by borrowing a gene from the E. coli bacteria. [译文]星期一,科学家们称他们已经利用遗传工程学,借用大肠埃舍利希氏 杆菌的基因培育出了耐干旱、耐咸水、耐严寒的稻米。展开更多
IF there is one name that is familiar to Chinese aged 10 to 80 it is Guo Lanying. Recently a recital was held by CCTV in honor of her 60-year career. When Guo Lanying took the stage, she was met with a lengthy standin...IF there is one name that is familiar to Chinese aged 10 to 80 it is Guo Lanying. Recently a recital was held by CCTV in honor of her 60-year career. When Guo Lanying took the stage, she was met with a lengthy standing ovation. Her voice was choked with emotion. Behind her was a smiling photograph of her that was taken at the start of her opera career. Guo Lanying was born in 1930展开更多
电化学储能(electrochemical energy storage,EES)机组不同于传统高压设备,差异主要有两点,一为有源设备,二为积木式结构,如直挂35kV EES机组,单相约有25~50个子模块,过电压在EES机组内的传播与分布、EES机组的过电压保护方案、绝缘配...电化学储能(electrochemical energy storage,EES)机组不同于传统高压设备,差异主要有两点,一为有源设备,二为积木式结构,如直挂35kV EES机组,单相约有25~50个子模块,过电压在EES机组内的传播与分布、EES机组的过电压保护方案、绝缘配合及绝缘耐压试验都有新的特征。该文以29个子模块级联后直挂交流35kV的EES机组为例,计算分析了雷电冲击、标准操作冲击、陡波及长波操作冲击下EES机组的过电压分布,包括主回路极对地过电压分布及沿子模块链的纵向过电压分布。文中根据承担电压的特征,将EES机组绝缘分为对地绝缘和纵绝缘(相邻部件间的绝缘)。结果显示,雷电冲击主要作用于极对地绝缘。为了限制EES机组极对地绝缘的雷电过电压幅值,至少需两组避雷器,一组安装在母线,另一组安装在EES机组的交流高压出线。通过合理配置避雷器,各子模块极对地的最大雷电过电压幅值基本相同,只是发生频次有所差异,靠近电网一侧的频次更高。操作冲击下极对地过电压低于雷电冲击,但会在EES机组的纵绝缘上产生过电压,子模块两极间过电压可达稳态电压峰值的1.6倍左右,并产生大约5kA的过电流。最后,文中针对EES机组提出了由子模块代替EES机组整机进行绝缘耐压试验的理论依据和方法,并基于高斯分布给出了EES机组绝缘配合因数的确定原则。该文提出的EES机组雷电过电压保护方案、绝缘配合因数及绝缘耐压试验方法可作为EES机组绝缘设计及绝缘安全实证的重要参考。展开更多
文摘Scientists said on Monday they had genetically engineered rice to withstand drought, salt water and cold temperatures by borrowing a gene from the E. coli bacteria. [译文]星期一,科学家们称他们已经利用遗传工程学,借用大肠埃舍利希氏 杆菌的基因培育出了耐干旱、耐咸水、耐严寒的稻米。
文摘IF there is one name that is familiar to Chinese aged 10 to 80 it is Guo Lanying. Recently a recital was held by CCTV in honor of her 60-year career. When Guo Lanying took the stage, she was met with a lengthy standing ovation. Her voice was choked with emotion. Behind her was a smiling photograph of her that was taken at the start of her opera career. Guo Lanying was born in 1930
文摘电化学储能(electrochemical energy storage,EES)机组不同于传统高压设备,差异主要有两点,一为有源设备,二为积木式结构,如直挂35kV EES机组,单相约有25~50个子模块,过电压在EES机组内的传播与分布、EES机组的过电压保护方案、绝缘配合及绝缘耐压试验都有新的特征。该文以29个子模块级联后直挂交流35kV的EES机组为例,计算分析了雷电冲击、标准操作冲击、陡波及长波操作冲击下EES机组的过电压分布,包括主回路极对地过电压分布及沿子模块链的纵向过电压分布。文中根据承担电压的特征,将EES机组绝缘分为对地绝缘和纵绝缘(相邻部件间的绝缘)。结果显示,雷电冲击主要作用于极对地绝缘。为了限制EES机组极对地绝缘的雷电过电压幅值,至少需两组避雷器,一组安装在母线,另一组安装在EES机组的交流高压出线。通过合理配置避雷器,各子模块极对地的最大雷电过电压幅值基本相同,只是发生频次有所差异,靠近电网一侧的频次更高。操作冲击下极对地过电压低于雷电冲击,但会在EES机组的纵绝缘上产生过电压,子模块两极间过电压可达稳态电压峰值的1.6倍左右,并产生大约5kA的过电流。最后,文中针对EES机组提出了由子模块代替EES机组整机进行绝缘耐压试验的理论依据和方法,并基于高斯分布给出了EES机组绝缘配合因数的确定原则。该文提出的EES机组雷电过电压保护方案、绝缘配合因数及绝缘耐压试验方法可作为EES机组绝缘设计及绝缘安全实证的重要参考。
