Perhaps you should try some spelling variations:
"modified staffing optimization algorithm" » "modified staffing optimization algorithms", "modified staffing optimisation algorithm", "modified staffing estimation algorithm", "modified caging optimization algorithm"
"modified invasive approximation algorithms" » "modified passive approximation algorithms"

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

• Performing a fuzzy search may retrieve terms with similar spellings: (("modified invasive approximation algorithms") or ("modified staffing optimization algorithm"))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("modified invasive approximation algorithms") OR ("modified staffing optimization algorithm")).
• Removing quotes may allow a broader search: (( modified invasive approximation algorithms ) or ( modified staffing optimization algorithm )).
• Adding a wildcard symbol may retrieve word variants: (("modified invasive approximation algorithms") or ("modified staffing optimization algorithm"))*.