Abstract: A diffractive structure (100) has a substantially planar substrate (1). A set of facets (2) is formed in or on said substrate (1), the plane or planes in which the facets (2) lie being arranged at a non-zero angle to the plane of the substrate (1). Each facet (2) has a diffraction grating (5) formed thereon. The diffractive structure (100) will produce color over a wide range of viewing and illumination angles.

Abstract: The invention shows a surface (2) for a metal implant (1) which has a coarse structure of elevations (3) and depressions (4), with the surface (2) being permeated by a network (5) of protruding ribs which form nodes (7) and interstices or meshes (8) having an interstice width of 2 mm to 0.4 mm, while the depressions represent sections of spherical cavities (11). The nodes (7) of the ribs can protrude the furthest like mountain peaks, whereas the ribs (6) which connect two nodes (7) each form a lower lying saddle (10) if the spherical cavities penetrate one another slightly. Through coating with an electrochemically resistant protective lacquer, into which holes can be shot at a predetermined spacing without damaging the metal, with a laser for example, a coarsely structured intermediary surface can be economically provided by means of electrochemical erosion which receives a fine structure through sand blasting.

Abstract: A method and apparatus for checking an envelope for contents is provided to determine whether or not an envelope has been completely emptied. The thickness of the envelope is measured at a plurality of points along the envelope. From the measured thickness, the thickness, or an integer multiple of the thickness, of the material of the envelope is determined. The thickness of the envelope measured at the plurality of points is compared with the determined material thickness, or integer multiple of the thickness, of the envelope. On the basis of that comparison, a determination is made as to whether or not the envelope has contents therein. The apparatus and method do not rely on measuring the opacity of the envelope.

Abstract: A lens assembly (1) comprises a lens (2;10,11;20) the focal length of which may be changed by application of an electric or magnetic field. A switching means (4,15) provides a drive impulse to change the focal length of the lens (2;10,11;20). An integral power source (4,15) provides power for the switching means. A lens which can be switched between near and distance vision by the user is thereby provided.