The validity problem of active multi-decoy to ground base radar system is studied.

研究了有源多假目标等欺骗性电子干扰对地基防御雷达系统的有效性问题。

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For many clustering algorithms, it is very important to determine an appropriate number of clusters, which is called cluster validity problem.

对于许多聚类算法，决定合适的聚类数目至关重要，这称为聚类有效性问题。

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The problem is not the ease of access to information, but that Web users cannot always interpret this information and assess its validity.

问题不是信息通道的便捷性，而是网络使用者并不总能理解这些信息，并评估其有效性。

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Once more: I find it hard to understand how someone who worked as head of Research and Development at Pfizer could possibly deny this basic, universally recognised problem of poor external validity in clinical trials.

FORBES: The Real Scandal Is Not Acknowledging That Drugs Do Work