Apparatus and methods for providing a pre-determined axial thrust force profile for use in a rotating machine that includes a magnetically permeable rotor with first and second surfaces and a generally perpendicular shaft is disclosed. The majority of them are produced by fermentation using microorganisms of different species identified as species belonging to Aspergillus, Monascus, Nocardia, Amycolatopsis, Mucor or Penicillium genus, Streptomyces, Actinomadura, Micromonospora, some are obtained by treating the fermentation products using the method of chemical synthesis or they are the products of total chemical synthesis. A device for cooling recirculated exhaust gases is equipped with a mechanism to reverse the stream of recirculated gases inside the exchanger.