Perhaps you should try some spelling variations:
"modified notion approximation algorithms" » "modified network approximation algorithms", "modified time approximation algorithms", "modified one approximation algorithms"
"modified machine scheduling algorithm" » "modified machine annealing algorithm", "modified caging scheduling algorithm", "modified male scheduling algorithm", "modified passive scheduling algorithm"

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• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"modified notion approximation algorithms\") OR (\"modified machine scheduling algorithm\"))~".
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