Revolver optical fibers (RF) are special type of hollow-core optical fibers with negative curvature of the core-cladding boundary and with cladding that is formed by a one ring layer of capillaries. The physical mechanisms contributing to the waveguiding parameters of RFs are discussed. The optical properties and possible applications of RFs are reviewed. Special attention is paid to the mid-IR hydrogen Raman lasers that are based on RFs and generating in the wavelength region from 2.9 to 4.4 μm.

The results of the study of the effect of a dc electric field on activated sludge of aeration tanks. It is experimentally detected that the specific oxidation rate of organic compounds by activated sludge increases up to 90.5% with electric field processing, and then decreases. The observed effect is substantiated. The results obtained can find wide application in purification of sewage polluted by organic compounds.