Abstract: Sintered silicon nitride articles are prepared by sintering a silicon nitride compact of a density of at least 1.3 g/cm.sup.3 in nitrogen gas atmosphere at substantially atmospheric pressure, while the compact is embedded in a protective powder comprising silicon nitride, boron nitride, or a mixture of silicon nitride and boron nitride, and one or more sinterization additives for silicon nitride, said additives being present in the protective powder in an amount of from 3 to 20% by weight.

Abstract: Sintered silicon nitride articles are prepared from a silicon nitride compact by forming a silicon powder containing one or more sintering additives for silicon nitride into a compact having at density of at least 1.3 g/cm.sup.3, said additives being present in the powder in an amount such as to ensure an additive content of from 0.5 to 20 wt. % in the silicon nitride compact, nitriding the silicon compact by heating under nitrogen gas blanket at a temperature not exceeding 1500.degree. C., to convert said silicon into reaction bonded silicon nitride, and sintering the reaction bonded silicon nitride compact by heating in a nitrogen gas atmosphere at a temperature of at least 1500.degree. C.

Abstract: A wind motor blade of composite construction has a blade shell of plastics material reinforced internally by transverse ribs and intersecting longitudinal struts in which metal fork arms are embedded, the fork arms being connected to a metal root attachment spigot through a metal cross-piece encapsulated in the plastics material.

Abstract: A heat recovery system for the production of mechanical energy from a plurality of different heat sources at different temperatures comprises a plurality of heat exchangers associated one with each heat source, a plurality of circuits for a working fluid which traverses the heat exchangers, the circuits including expansion devices in which the working fluid is expanded and possibly vaporized to derive mechanical work from it, this being accompanied by a fall in temperature; the circuits for the working fluid have certain parts in common, such as the heat exchanger associated with the heat source at the lowest temperature, at least one of the expansion devices, a condenser in which working fluid vaporized in the expanders can be recondensed, and a circulation pump for driving the working fluid around the circuits.

Abstract: The supply, regulation and control of a direct current electrical machine such as a motor or generator having a number of winding sections is controlled by energization of the winding sections by staggered pulses which combine to produce a reasonably constant total winding current, the control being by means of first and second pairs of transistor switches controlled by respective control elements, such as magnetic pick-ups or photoelectric detectors, responsive to the rotation of the machine. Alternatively the machine can be operated with intermittent excitation for low speed traction or starting by supplying appropriately shaped control signals to the control elements connected to the transistor switches.

Abstract: A fluid-pressure operated pilot valve produces a cyclic modulation of pressure in a control duct, for operating a relay valve, by introducing a predetermined delay between the displacement of a first valve element from, and its return to, a first position against a first valve seat by a fluid-pressure operated timer device, which includes flow restrictor means and a pressure accumulator, acting upon the larger area side of a differential area actuator which vents the pressure in the control duct to an exhaust duct in a second position of the first valve element; the relay valve being operable in response to the cyclic pressure changes in the control duct to admit an irrigating liquid to an irrigation spray nozzle.

Abstract: A device for converting sea wave energy into electrical energy comprises a floating platform carrying a pulley which is connected through a free-wheel coupling and a speed multiplier to a drive shaft of an electrical generator, on which a flywheel is mounted. An anchor cable passes over the pulley and suspends at its free end an immersed counterweight so that vertical motion of the platform in the sea causes rotation of the pulley and drives the generator continuously.

Abstract: A process for forming a protective metal diffusion coating on a metal or metal alloy workpiece including internal cavity surfaces, comprises coating the workpiece with a slurry in acetone and cellulose acetate of a powder of average grain size of 0.5.mu. to 10.mu., including aluminum and possibly chromium and/or a small quantity of cerium or yttrium hydride and heating the workpiece in a non-oxidizing environment to dissociate the hydride and effect diffusion of the metals into the surface of the workpiece.

Abstract: Pollutant particles, particularly lead particles, are removed from engine exhaust gases by passing the gases successively through three aligned chambers, of which the first and third contain wire mesh or expanded metal packings, while the second chamber is divided by a deflecting baffle which deflects the partially cleaned exhaust gases downwards to deposit particles in the bottom of the second chamber.

Abstract: A recuperator for recovering heat from hot exhaust gases flowing through a flue comprises inner and outer cylindrical walls coaxially surrounding a portion of the flue to which a plurality of fins are fixed, the fins extending longitudinally of the flue and being grouped such that fins spaced circumferentially around one section of the flue are angularly staggered with respect to fins spaced circumferentially around an adjacent section of the flue, the recuperator being arranged such that cold gas can be passed into, and is preheated as it flows along, an outer annular space between the said walls, the gas passing into an inner annular space containing the fins which cause turbulence and increase the heat-transfer by convection and radiation to the gas, and the heated gas being emitted through an outlet.

Abstract: A rear-view mirror for motor vehicles incorporates a liquid crystal film sandwiched between front and rear transparent electrode surfaces, the rear electrode surface being in the form of a lattice or net having a number of clear areas through which light passes unattenuated when the cell is activated to reduce the reflection of light by the mirror in response to the detection of headlight glare by a photocell mounted on the mirror.

Abstract: Lean air/fuel mixture is supplied to the induction manifold of an Otto cycle engine through a heat exchanger heated by engine exhaust gases under normal running conditions, and under idling conditions mixture is supplied to an auxiliary induction manifold solely through an auxiliary duct. The auxiliary duct is wound with an electrical resistive heating element to preheat the mixture upon cold-starting of the engine for a time, typically 30-40 seconds, determined by a timer switch.

Abstract: A hydraulic actuator for a motor vehicle anti-skid braking system, in which the static and dynamic parts of the hydraulic circuit are separated, the actuator having a solenoid valve operated by electrical signals generated by sensors when associated wheels of the vehicle reach an incipient skid state; upon operation of the solenoid valve during braking, pressure to one side of a balanced piston is removed so that it moves to close a valve which cuts off braking pressure to the brakes. A throttle passage allows pressure build up to take place until equilibrium is established across said balanced piston allowing braking to recommence after a time delay.

Abstract: A safety catch for a frontally opening hood of a motor vehicle comprises a resilient strip having transverse tongues at its upper end which snap engage in a recess in a bracket on the under side of the hood, the strip being capable of limited vertical movement and being anchored elastically at its lower end. Snap engagement of the tongues in the recess is facilitated by curvature of the upper end of the strip in the longitudinal direction of the vehicle, and release of the catch is effected by exerting finger pressure on the resiliently flexible strip to disengage it from the recess.

Abstract: An apparatus for use in monitoring the numbers of a selected species of insect comprises one or more traps into which is put a synthesized pheromone to attract that particular insect. Each trap has a grille comprising a plurality of bars between which is applied a high voltage so that when an insect of the selected species tries to enter the trap it touches adjacent bars and is electrocuted by the electric discharge between them. This discharge is detected by a discharge detector connected to the trap and the detector passes a signal to a transmitter which transmits it to a central receiver equipped with a discriminator for ignoring signals other than those from the transmitter and for passing the signals representing discharges to a pulse counter whereby a total of the number of insects trapped in a given time can be obtained at a central station without visiting each trap.

Abstract: An irrigation system of the type comprising a plurality of nozzles spaced along a pipeline fed at one end from a source of supply of irrigation liquid, which latter may be purely water or may be water with additives, in which in order to avoid different spray rates due to a loss in pressure along the pipeline each nozzle is provided with a valve and an associated resilient subsidiary reservoir, the valves operating to close off the nozzles while all the subsidiary reservoirs charge up to the line pressure and then, when a control valve diverts the source of supply to a discharge outlet all the nozzles receive liquid in the same pressure from their associated subsidiary reservoir; when the subsidiary reservoirs are all back at atmospheric pressure the cycle recommences.

Abstract: The lubrication of an engine crank shaft is monitored using a wheatstone resistance measuring bridge one of the arms of which includes lubricating oil ducts between the crank shaft and crank case of the engine, balanced against a reference resistance provided by a resistance measuring cell through which the engine lubricating oil flows. The resistance measuring cell may have an external heater for heating the oil in the cell to a temperature compatible with that of the oil in the engine bearings when the engine is running.

Abstract: A power plant has an electrical generator driven by an internal combustion engine in which engine coolant circulates in a gas/liquid heat exchanger to take up heat from engine exhaust gases and then through a liquid/liquid heat exchanger to give up heat to a secondary water circuit, the electrical generator being cooled by a circulation of water in the secondary circuit through a surrounding cooling jacket after the water has given up heat in a heating unit.