There are two basic systems for issuing certificates: a closed (private hierarchy) system and an open (public hierarchy) system.

发布证书有两种基本的系统：封闭式(私有层次)系统与公开式(公共层次)系统。

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Using this virtual instrument, the frequency characteristics of both open-loop system and closed-loop system can be measured.

设计的虚拟仪器既适用于对开环系统又适用于对闭环系统的频率特性进行测试。

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Compared with closed loop system, open loop system has higher efficiency and wider application.

与闭式系统相比，开式系统换热效率更高，应用更为广泛。

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Energy operators also must meet with homeowners and others who live within 1, 000 feet of their proposed projects to listen to their concerns, not use open pits to store drilling waste and ensure their venting system is closed to prevent sending methane into the air.

WSJ: As energy boom nears cities, a backlash grows

While Apple under Steve Jobs focused on its Macintosh closed system of hardware, software, and applications, Microsoft built an open market system on Windows: any hardware, any application, many ways to make money.

FORBES: Steve Jobs Is A Market Systems Master