Abstract: Flame-hydrolytically produced titanium dioxide mixed oxide having a BET surface of 10 to 150 m.sup.2 /g and 1 to 30% by weight aluminum oxide or 1 to 30% by weight silicon dioxide is produced by evaporating aluminum chloride or silicon tetrachloride, transferring the evaporated aluminum chloride or silicon tetrachloride, together with an inert gas, into the mixing chamber of a burner, mixing them with hydrogen, air and gaseous titanium tetrachloride, burning the resulting 4-component mixture in the reaction chamber of the burner, and separating the titanium dioxide mixed oxide from the gaseous reaction products.

Abstract: Flame-hydrolytically produced titanium dioxide mixed oxide having a BET surface of 10 to 150 m.sup.2 /g and 1 to 30% by weight aluminum oxide or 1 to 30% by weight silicon dioxide is produced by evaporating aluminum chloride or silicon tetrachloride, transferring the evaporated aluminum chloride or silicon tetrachloride, together with an inert gas, into the mixing chamber of a burner, mixing them with hydrogen, air and gaseous titanium tetrachloride, burning the resulting 4-component mixture in the reaction chamber of the burner, and separating the titanium dioxide mixed oxide from the gaseous reaction products.

Abstract: Silicon-aluminum mixed oxide powder which is flamehydrolytically produced and has a composition of 65 to 85% by weight Al.sub.2 O.sub.3, remainder SiO.sub.2 and an amorphous structure, in which each primary particle contains components of SiO.sub.2 and of Al.sub.2 O.sub.3, the primary particles are between 7 and 80 nm, preferably 10 and 40 nm in size and the specific surface of the powder is between 20 and 200 m.sup.2 /g. The powder is used for the production of mullite and sintered compacts manufactured from it.

Abstract: Silicon-aluminum mixed oxide powder which is flame-hydrolytically produced and has a composition of 65 to 85% by weight Al.sub.2 O.sub.3, remainder SiO.sub.2 and an amorphous structure, in which each primary particle contains components of SiO.sub.2 and of Al.sub.2 O.sub.3, the primary particles are between 7 and 80 nm, preferably 10 and 40 nm in size and the specific surface of the powder is between 20 and 200 m.sup.2 /g. The powder is used for the production of mullite and sintered compacts manufactured from it.

Abstract: A method of determining the fundamental frequency or pitch period of a voice signal from a difference signal, formed with the aid of predictors, between the original voice signal and the voice signal estimated by the predictor. Only the significant characteristics of the difference signal are then auto-correlated and the maxima of the correlation coefficients determine the fundamental frequency or pitch period.