可以进行测试的整个范围通常太大，难以在给定的时间内完成测试工作，当多个特性组合在一起时测试的范围将变得更大，其排列组合呈指数上升。
The entire universe of things that could be tested is typically too large to be covered within a given schedule, even more when multiple features are combined and the permutation grows exponentially.
超声的此种特性，与超声的照射条件，如机械指数、脉冲重复频率、照射时间等有关。
Ultrasound-assisted gene delivery is associated with the parameters of ultrasound exposure, such as mechanical index, pulse repetition frequency, time of exposure, and so on.
通过分析行程时间时间序列的时变特性，利用指数平滑模型进行预测，最后提出合理的修正方法。
Then, we make prediction with moving exponential average model after the analysis of the travel time series. Finally, we present reasonable justification.
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