The main problems in GPS technology including the system bias to SLR, its own annual variety and the change of GPS satellite antenna phase center are also discussed.
评述了GPS技术目前存在的问题，包括与SLR测量之间存在的系统偏差、GPS技术本身可能存在的周年变化和GPS卫星天线相位中心的变化。
The basic principle of operation, significant advantages, material structures, existent problems and latest progresses of the phase change materials are discussed in the review.
文章介绍了相变存储材料的特点，工作原理，相变材料结构及面临的技术难题。
However, in the use of these alloys, there are some problems of material science which should be solved, such as phase change temperature, hardenability and fatigue life.
但是这类合金在使用中也产生了不少材料科学方面的问题，如相变点、淬透性、疲劳寿命等。
However, in the use of these alloys, there are some problems of material science which should be solved, such as phase change temperature, hardenability and fatigue life.
但是这类合金在使用中也产生了不少材料科学方面的问题，如相变点、淬透性、疲劳寿命等。
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