Perhaps you should try some spelling variations:
"improve contrast performance metrics." » "improve contract performance metrics.", "improve contractor performance metrics.", "improve control performance metrics.", "improve contrast performance measures.", "improve content performance metrics.", "image contrast performance metrics."
"improving peer performance series." » "improving peer performance studies.", "improving peer performance size.", "improving power performance series.", "improving poor performance series.", "improving der performance series.", "improving gender performance series.", "improving air performance series.", "improving energy performance series."

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: (("improve contrast performance metrics.") or ("improving peer performance series."))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("improve contrast performance metrics.") OR ("improving peer performance series."))*.
• Removing quotes may allow a broader search: (( improve contrast performance metrics. ) or ( improving peer performance series. ))*.