Perhaps you should try some spelling variations:
"modified df approximation algorithm" » "modified df approximation algorithms", "modified _ approximation algorithm", "modified one approximation algorithm", "modified time approximation algorithm", "modified adam approximation algorithm", "modified bi1 approximation algorithm"
"modified motion optimization algorithms" » "modified motion optimisation algorithm", "modified motion estimation algorithms", "modified motion estimation algorithm", "modified policy optimization algorithms", "modified allocation optimization algorithms"

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• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"modified motion optimization algorithms\") OR (\"modified df approximation algorithm\"))~".
• Removing quotes may allow a broader search: (( modified motion optimization algorithms ) OR ( modified df approximation algorithm ))~.
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