Perhaps you should try some spelling variations:
"improving preliminary performance metrics." » "improving primary performance metrics.", "during preliminary performance metrics.", "important preliminary performance metrics.", "improving preliminary performance measures."
"improving thermal performance metrics." » "improving thermal performance measures.", "improving external performance metrics.", "improving animal performance metrics.", "improving erm performance metrics."

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• Performing a fuzzy search may retrieve terms with similar spellings: (("improving preliminary performance metrics.") or ("improving thermal performance metrics."))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("improving preliminary performance metrics.") OR ("improving thermal performance metrics.")).
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