Perhaps you should try some spelling variations:
"modified multiobjective optimization algorithm" » "modified multiobjective optimization algorithms", "modified multiobjective optimisation algorithm", "modified multiobjective estimation algorithm"
"modified optimal estimation algorithms" » "modified optimal estimation algorithm", "modified optimal optimization algorithms", "modified optimal optimisation algorithm", "modified optimal taxation algorithms", "modified thermal estimation algorithms"

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