Abstract: In a prosthetic heart valve comprising a generally annular stent and at least two obturators mounted in the stent so as to be above to pivot between an open position and a closed position, the stent is provided with at least one element which projects inwardly of the stent itself, while each of the obturators has recesses which cooperate with the projecting element of the stent with clearance in a generally-hinged configuration which enables the obturators to pivot between the open position and the closed position.

Abstract: The method disclosed by which to prepare fine hexagonal ferrites for use in magnetic recording, is one which consists basically in dissolving (a) carbonates or other soluble compounds of an alkaline earth metal such as strontium or barium, (b) a carbonate or other soluble compound of cobalt, and (c) titanium trichloride, all in a solution of ferric citrate and water, whereupon a polycondensation is brought about by addition of ethylene clycol, and heat is applied to eliminate the water and organic matter from the compound. Addition of the alkaline earth metal, the cobalt and the titanium is proportioned precisely on the basis of the stoichimetric properties of the end-product, the formula for which isReO.(6-x)Fe.sub.2 O.sub.3.xCoO.xTiO.sub.2where x is the extent to which cobalt and titanium atoms replace iron atoms and Re is the alkaline earth metal. Final application of heat produces crystallization of the superfine hexaferrite particles.