We consider a class of convex integral functionals with lagrangeans depending only on the gradient and satisfying a generalized symmetry assumption, which includes as a particular case the rotational symmetry. Adapting the method by A. Cellina we obtain a kind of local estimates for minimizers in the respective variational problems, which is applied then to deduce some versions of the Strong Maximum Principle in the variational setting.

Variable correlations are usually neglected during parameter estimation. Very frequently these are gross assumptions and may potentially lead to inadequate interpretation of final estimation results. For this reason, variable correlation and model parameters are sometimes estimated simultaneously in certain parameter estimation procedures. It is shown, however, that usually taking variable correlation into consideration during parameter estimation may be inadequate and unnecessary, unless independent experimental analysis of measurement procedures is carried out

This paper presents a programable perturbat i on and observation control i mplementation for a w i nd generation system and its power electron i c converter. The obj ective of the method i n th i s particular appl i cation i s to adjust the power del i vered to charge a battery to its max i mum and allowable value, function of the real values of several parameters and the i r cont i nuous var i ation, the most i mportant the w i nd velocity and the turb i ne efficiency. Also, to i mprove the power throughput and to use the turb i ne and generator marginal zones of operation, an unusual power converter i s used, allow i ng a wide range for the i nput voltage values. The i mplemented control i s cont i nuously measur i ng the actual power and looks for a new and powerful operation po i nt.

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