Abstract: A cable (C) is laid in a pipeline (10) by pushing the cable and (C') through a hydraulically variable diaphragm in an inlet tube (11). The end (C') of the cable has collapsible moulded cups (20) attached which can be pushed through the diaphragm and which erect themselves to act as a drag inducing device so that flowed liquid in the pipeline can be used to pull the cable and (C') towards an exit tube (12) downstream. A cable pusher (13) pushes the cable through the inlet (11). The cable has a specific gravity less than the liquid, preferably 0.7, which is substantially pressure independent.

Abstract: A device for the controlled release of an active material into an aqueous medium comprises a water soluble capillary tube (11) the bore (12) of which contains an active material (13). Dissolution of the active material is diffusion limited during a delay period while the capillary is dissolving. When dissolution of the tube is complete rapid dissolution of the remaining active material then takes place.

Abstract: In a pulsed radio frequency plasma deposition process the pulse repetition frequency is matched to the gas exchange rate. This is achieved by using a pulse width of 50 to 500 microseconds and a pulse repetition rate corresponding to the time within which gas is exchanged in the reaction region.

Abstract: In an optical fibre submarine cable the ingress of hydrogen ions is reduced if not eliminated by at least one envelope which provides a barrier to hydrogen ions.In one embodiment a copper tape (L) is folded longitudinally around the cable core comprising strength member wires (G,H) split aluminium or coppr tube (E) and optical fibre package (A). The abutting edges (L') are seam welded with less than 0.1% skips. Preferably the folded copper tape is longitudinally welded while a loose fit and subsequently reduced in diameter to leave an accurately determined small annular gap between tubes E and F which is filled with a water blocking material that is highly viscose at ambient temperature and effectively glues the tubes together.

Abstract: In a digital optical submersible repeater the electronic and opto-electronic components are housed in an hermetically sealed modular assembly (20, 60, 70) of a first regenerator module (20) for one fibre (7, 6a), a second regenerator module (60) for the second fibre (6, 7a) of the pair of fibres, and a power module (70) for extracting power from the power feed conductor of the cable. In each regenerator module (20) the transmit laser (8) and the receive PINFET diode are on diametrically opposed faces, and power feed and optical signal feed are disposed in spaces between the modules and the inside surface of the repeater housing (1). The modular assembly is resiliently secured to the bulkhead (2).

Abstract: A temperature sensor for a motor vehicle comprises a composite of PTC and NTC thermistors (1, 2, 3) whose overall temperature characteristic (c) is negative with a plateau (P) centered on the normal working temperature (88.degree. C.) to be sensed, so that tolerances in the sensing system and normal fluctuations of the working temperature will tend not to be registered by the vehicle temperature gauge. Thus only abnormal variations in temperature caused by a fault or overload condition will be indicated.

Abstract: A laser beam addressed smectic display in which the laser beam is used to write clear tracks in an optically scattering field employs an anisotropic conductivity dopant in the liquid crystal filling so that the cell can be electrically set into the scattering state by means of dynamic scattering effects. This requires the use of a laser light absorbing dye that is not only photochemically stable, but also stable against the effects of the relatively high fields and currents present when the cell is being set into the scattering state.

Abstract: An alternating magnetic excitation field is generated in the flux concentrators (11,12) of a Hall effect device, including a Hall element (13), by passing an a.c. current through a coil (14). This alternating field serves to drive the flux concentrators into and out of saturation. In the presence of a d.c. magnetic field and when a Hall current is applied to the Hall element, a second harmonic component is generated in the output voltage of the Hall element (13); the amplitude of the second harmonic component providing a measure of the d.c. magnetic field. In an alternative arrangement (FIG. 4) the flux concentrator means is in loop form rather than in a flat configuration as in FIG. 3.

Abstract: A telephone hook switch arrangement includes a base assembly (1) and a T-shaped hook switch lever 3, which is substantially T-shaped. One end of the cross-piece of the T is pivoted to a downwardly-extending portion (2) of the base assembly. At the upper end of the leg of the T, pins (e.g. 8) are on each side, each fits under the end of a moveable contact (e.g. 5). The lever also has a spring strip 10 integral with it and normally under tension. The drawing shows the arrangement when off-hook, in which case the spring strip (10) urges the arrangement to the condition shown. When on-hook, the handset, via another linkage (not shown) urges the lever (3) to the state shown in dashed lines, when the contacts are open.

Abstract: A hydrophone section for a seismic streamer towed array in which the hydrophones 2 are arranged in groups of not more than 7, the spacing of the hydrophones within each group being such that each group has an overall length l=0.8-1.2 m. The hydrophone mounts 5 and mechanical spacers 3 are attached at their periphery to aramid fibre strainwires 4. The hydrophone mounts and mechanical spacers are acoustically open structures.

Abstract: Connection into and out of digital integrated circuits is made optically, the input being implemented by floodlighting appropriately placed photodiodes at the input points and the output by on chip commutative switching of the connect centers onto a common output pad which drives a light emitting source. Communicating chips are synchronously clocked at the commutation rate to achieve required interconnect configuration via time division multiplexing.

Abstract: An interface circuit, particularly for use between a high frequency sine wave and ECL (emitter-coupled logic) logic levels, which has an almost resistive input inpedance. The circuit may comprise an ECL OR/NOR gate (3) with the complementary outputs thereof having respective feedback paths (R2,R1; R3,R1). The high frequency sine wave is supplied via a coaxial cable (4) which is terminated via resistor R1. The feedback resistors R2 and R3 are of the same value. The mark-to-space ratio at the gate outputs is substantially maintained at 50/50. The gate may be AND/NAND rather than OR/NOR. The interface circuit is applicable to any logic family having a switching voltage at the mean of the "0" and "1" voltages.

Abstract: An optical reflectometer in which the output from a laser 11 is passed through a ramped phase modulator 12 and an optical fibre bi-directional coupler 13 to a transmission path 15, e.g. an optical fibre. Part of the light is coupled out to a mirror 14 and is reflected to form a local oscillator signal which is mixed in the coupler with backscattered light from the fibre. The mixed signals are applied to a detector 16.

Abstract: A radio pager for receiving FSK signals has optimally narrow gaussian bandpass filters (F1, F2) and a phase lock loop (11, 12, 13, 14) for preventing local oscillator drift controlled in dependence of the derivation frequency (.+-.4.5 KHz) which is accurately controlled at the transmitter and which is derived from the decoder logic circuit (20).A significant increase in sensitivity is achieved over existing pagers.

Abstract: A thermal image is created in a thermostatically controlled liquid crystal cell (4) containing a two-frequency nematic or cholesteric (3). This is addressed with an alternating potential whose frequency can be swept through the cross-over frequency. By appropriate choice of frequency within this range the thermal image is converted to a phase image which in its turn is converted to a contrast image in conventional manner.

Abstract: A single mode optical waveguide directional coupler is provided with enhanced wavelength selectivity by dividing the coupling region up into a number of identical sections (12) between which are interposed a set of identical decoupled sections (13) over which the two waveguides (10, 11) of the coupler are not optically coupled and have different optical path lengths.

Abstract: In a coherent optical transmission system an input optical signal is amplified by being frequency down converted to an intermediate frequency, for example by means of a photodiode (1) and a reference optical local oscillator signal, and the photodiode output current is amplified in a GaAs FET wideband amplifier (6) and inserted on an optical carrier signal comprised by the reference signal by means, for example, of an integrated optical single sideband modulator (up converter) (7). By use of the same optical local oscillator to drive both the photodiode down converter and the integrated optic single sideband up converter, input/output coherence is ensured. The optical local oscillator may be comprised by a GaAlAs laser (3) stabilized to an "atomic" standard (4,5). Channel dropping/insertion may be carried out at the intermediate frequency, for example following the amplifier (6).

Abstract: In a comparator circuit in which the active element is a long-tailed transistor pair the input bias current to at least one input of the pair is maintained constant by providing a supplemental current from a current source. A multivibrator incorporating the comparator is also described.

Abstract: A method of selectively etching one semiconductor material layer (4) of a multilayer structure which underlies another layer, a top layer (1), of the same or a similar semiconductor material without significantly affecting the top layer (1). The method involves pre-etching both layers (1,4) to provide a stepped structure with recesses (10) under an intermediate layer (5), providing r.f. deposited silicon dioxide (11) over the etched structure such that it is thinnest in the recesses (10) from which it is subsequently selectively removed and etching the layer (4) to the required extent while the top layer (1) is still covered by r.f. silicon dioxide. The method may be used in the manufacture of mass transport buried heterostructure lasers with the layers 1 and 4 of GaInAsP and layers 3 and 5 of InP, the recesses (10) subsequently being filled with InP by a mass transport process.

Abstract: In a digital optical submersible repeater the electronic and opto-electronic components are housed in an hermetically sealed modular assembly (20, 60, 70) of a first regenerator module (20) for one fibre (7, 6a), a second regenerator module (60) for the second fibre (6, 7a) of the pair of fibres, and a power module (70) for extracting power from the power feed conductor of the cable. In each regenerator module (20) the transmit laser (8) and the receive PINFET diode are on diametrically opposed faces, and power feed and optical signal feed are disposed in spaces between the modules and the inside surface of the repeater housing (1). The modular assembly is resiliently secured to the bulkhead (2).