Perhaps you should try some spelling variations:
"defined network optimization algorithmss" » "defined network optimization algorithms", "defined network optimisation algorithm", "defined network estimation algorithms", "designed network optimization algorithmss"
"modified objective approximation algorithms" » "modified objective approximation algorithm"

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• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"defined network optimization algorithmss\") OR (\"modified objective approximation algorithms\"))~".
• Removing quotes may allow a broader search: (( defined network optimization algorithmss ) OR ( modified objective approximation algorithms ))~.
• Adding a wildcard symbol may retrieve word variants: (("defined network optimization algorithmss") OR ("modified objective approximation algorithms"))*.