Perhaps you should try some spelling variations:
"modified multiobjective optimization algorithm" » "modified multiobjective optimization algorithms", "modified multiobjective optimisation algorithm", "modified multiobjective estimation algorithm"
"modified passive estimation algorithms" » "modified passive estimation algorithm", "modified passive optimization algorithms", "modified passive optimisation algorithm", "modified pose estimation algorithms", "modified adaptive estimation algorithms"

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• If you are trying to use Boolean operators, they must be ALL CAPS: (("modified passive estimation algorithms") OR ("modified multiobjective optimization algorithm")).
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