Abstract: An optical element comprising a substrate which is provided with a transparent coating (9) containing a photochromic material, the transmission of said optical element varying in the visible region in response to a variation in light. The optical element is characterized in that the coating (9) comprises an inorganic network of a silicon oxide and an organic polymer which is chemically bonded to the inorganic network via Si—C bonds. Preferably, also macroscopic particles of a metal oxide are incorporated in the network, the metal preferably being selected from the group formed by Al, Si, Ti, Zr, In and Sn. Preferably, metal-oxide particles are used whose size is above 5 nm. Such photochromic coatings (9) are scratch-resistant and demonstrate a good switching behavior. The coatings are used, for example, on display windows (3) of display devices (1) and on sunglasses. Methods of manufacturing said layers are described.

Abstract: The invention relates to a sintered transformer core of MnZn-ferrite material, the initial permeability of which ranges between 10 and 1000. Said transformer cores preferably have an average particle size which ranges between 0.05 and 2.0 .mu.m. The transformer cores according to the invention exhibit surprisingly low overall losses when operating in the frequency range of 2 MHz and higher. Such transformer cores can be very advantageously used in transformers operated in said frequency range, such as SMPS transformers.