Abstract: A seal between two ceramic articles, or between a ceramic article and a metal article, is formed by providing a sealing member comprising an aluminum body, and a film of zinc or tin being deposited threon, with the inevitable aluminum oxide surface film removed, and subsequently a coating of silver and/or gold, or a suitable alloy containing silver or gold, being provided. The sealing member is positioned between the articles, and the bonding operation comprises heating the assembly in an inert atmosphere, or in a high vacuum, to melt the composite sealing member, there being obviated the need to apply pressure during the bonding operation. Any oxide film on silver readily decomposes at a temperature of, at most, 250.degree. C. No oxide film is formed on gold. The zinc or tin film, and the coating, are readily absorbed into the molten aluminum produced during the bonding operation. Subsequently, the bonded assembly is out-gassed at a temperature up to 600.degree. C.

Abstract: A system includes a television camera (10), a first source of illumination (17) operable to provide pulsed illumination of a scene to be viewed by the camera, and a second source of illumination (18) operable to provide constant illumination of the scene. Illumination control means (16) is operable to activate the first source (17) to provide a pulse of illumination prior to the commencement of each alternate field period of the television raster scan cycle. Camera control means (13) controls a gate (12) in the camera system so that, during each of these alternate field periods the camera (10) provides a first video signal representing the scene illuminated by the first source (17) at a predetermined time after the pulse of illumination. The camera control means (13) also operates the gate (12) so that, during each other frame period, the camera provides a second video signal representing the scene illuminated by the second source throughout the entire field period.

Abstract: An optical modulator comprises a crystal (15) of material exhibiting the pyroelectric effect, and charge-dissipating means for dissipating any charge built up on the optical faces of the prism. The charge-dissipating means may comprise point electrodes (30) positioned adjacent to the optical faces (21) of the crystal and connected to an alternating-current high-voltage power supply (31). The electrodes produce charged ions which neutralize any charge on the optical faces of the crystal. The crystal may be used as the Q-switch in a laser.

Abstract: A tubular acoustic projector for underwater use consists of a ceramic, piezo-electric transducer (21A, 21B) contained in a coaxial, electrically-conductive cylindrical housing (10) whose side wall (11) is thin enough to vibrate with the transducers (21A, 21B). The side wall (11) maintains the transducer under a radial compressive pre-load so as to avoid ceramic failure due to tensile stress. The side wall is sufficiently thermally conductive to dissipate the heat generated in the transducer, in use, to prevent failure of the transducer under the effects of heat. Electrical isolation of the inner and outer surfaces of the transducer is achieved by filling the housing with an insulating liquid.