Usually, ionospheric Total Electron Conten (TEC) variation with time can be viewed as a stationary random process under quiet conditions.

平静状态下电离层总电子含量(TEC)随时间的变化通常可以视为平稳随机过程。

The steel with low oxygen content is the main new product of iron and steel factories, especially gear wheel and gas vase steel which demand oxygen conten relatively.

低氧含量钢种是目前各钢铁企业开发的主要品种 ，尤其是齿轮钢、气瓶钢等对氧含量的要求较严 ，所以准确测定钢中的氧含量也是控制钢材性能指标的一种手段。