Abstract: Light from a laser (10) is divided by a beam splitter (12) to provide signal (15) and reference (14) channels. The signal channel light is expanded (11) to illuminate an acousto-optic (AO) device (13). This leads to a spatial distribution of Doppler shifted frequencies. This spatial distribution then illuminates a spatial light modulator (SLM) (19) such that a number of parallel and discrete optical channels (112) emerge. In a local area network (LAN) the optical signal channels are coupled into a single mode optical fibre (22) and then heterodont to the reference laser light from a further optical fibre (23) in an optical coupler (25). In a receiver the modulated light is detected (32) and the detected signal connected to the transducer of an AO device (35). The AO device (35) is illuminated by a receiver laser light (36) and the emerging modulated light is incident on a focal plane detector array (39) where each detector (310) then receives light corresponding to each of the transmitted channels (311).

Abstract: A method of making semiconductor quantum wires employs a semiconductor wafer (14) as starting material. The wafer (14) is weakly doped p type with a shallow heavily doped p layer therein for current flow uniformity purposes. The wafer (14) is anodised in 20% aqueous hydrofluoric acid to produce a layer (5) microns thick with 70% porosity and good crystallinity. The layer is subsequently etched in concentrated hydrofluoric acid, which provides a slow etch rate. The etch increase porosity to a level in the region of 80% or above. At such a level, pores overlap and isolated quantum wires are expected to from with diameter less than or equal to 3 nm. The etched layer exhibits photoluminescence emission at photon energies well above the silicon bandgap (1.1 eV) and extending into the red region (1.6-2.0 eV) of the visible spectrum.

Abstract: A projectile launcher and in particular a mass/countermass projectile launcher in which the piston intercept(s) comprises a braking collar (8) made of a material which exhibits constrained progressive crushing. When a projectile (18) is fired the launching piston (10) impacts upon the braking collar (8) at the muzzle of the launcher and initiates constrained progressive crushing in the collar (8). The crushing of the collar (8) absorbs the kinetic energy of the piston (10) thus arresting the axial motion of the piston (10). The projectile launcher according to the present invention can be less massive than similar launchers that use conventional metal piston intercepts which is an advantage if the launcher is designed to be shoulder-launched by a human operator. The type of collar material preferably used is made of a solid filler embedded in a plastics matrix and in particular the solid filler is made of reinforcing fibers.

Abstract: A low resistance contact for p-type GaAs is provided by Pd/Zn/Pd/Au structure 1. The contact is suitable for device substrates having carrier concentrations in the range of about 10.sup.18 to about 10.sup.20 cm.sup.-3. The ohmic contact has a Pd layer of depth 3 nm to 15 nm, a Zn layer with a depth of between 5 nm and 40 nm, a second Pd layer with a depth greater than about 50 nm and an Au layer with a depth greater than about 300 nm. A preferred construction (1) is 5 nm/10 nm/100 nm/400 nm of Pd/Zn/Pd/Au. The ohmic contact deposition must be followed by annealing, with preferred annealing carried out at a temperature of about 200.degree. C. Annealing times are dependent upon annealing temperature, with a typical minimum annealing times of greater than 5 minutes at annealing temperatures of about 200.degree. C.

Abstract: Compounds of formula (I) where R is C.sub.1-15 alkyl, X is hydrogen, fluorine or chlorine, m and n are independently selected 1 or 0, W is C.sub.1-15 alkyl or alkoxy, CN or halogen, rings A and B Are independently selected from phenyl, laterally fluoro- or chloro- substituted phenyl, transcyclohexyl pyridyl, pyrimidyl or dioxanyl. Preferred embodiments have R=C.sub.3-8 and where W is alkyl or alkoxy then it is also preferable that W=C.sub.3-8. Where m=0, then preferably W=CN and where m=1, then preferably W=alkyl.

Abstract: Semiconductor crystalline materials, e.g. silicon, GaAs, are grown from a melt, e.g. using the Czochralski technique where a seed crystal is dipped into the melt then slowly withdrawn. Rotation of the growing crystal (6) is partly responsible for convective flows within the melt (5). Convective flows are reduced while radial uniformity is improved by subjecting the crystal/melt interface to a shaped magnetic field. This magnetic field is rotationally symmetrical about the axis of crystal rotation, with a component of field parallel to this axis that is less than 500 gauss, preferably less than 200 gauss, with a value above 500 gauss at other parts of the melt. The field may be produced by two superconducting magnet coils (21, 22) spaced apart and arranged co-axially with the axis of crystal rotation.

Abstract: Apparatus for the physical vapor deposition of an alloy whose constituent ements have widely differing vapor pressures comprises an inner evaporation crucible (1) surrounded by a second evaporation crucible (2) having an array of nozzles (9) angled towards collector (5). In use of the apparatus, a charge (3) of relatively low volatility is evaporated from inner crucible (1) using an electron beam (7) focussed by magnet (8). Charge (4) in second crucible (2) is of much higher volatility and is evaporated by radiant heating. The nozzles (9) direct the vapor from charge (4) along pathways which intersect the vapor rising from charge (3) such that the combined vapor stream reaching collector (5) is an intimate mixture of constituents. The nozzles (9) may also serve to control the flow rate of vapor from the second crucible (2).

Abstract: A method of making semiconductor quantum wires employs a semiconductor wafer as starting material. The wafer is weakly doped p type with a shallow heavily doped p layer therein for current flow uniformity purposes. The wafer is anodised in 20% aqueous hydrofluoric acid to produce a layer microns thick with 70% porosity and good crystallinity. The layer is subsequently etched in concentrated hydrofluoric acid, which provides a slow etch rate. The etch increases porosity to a level in the region of 80% or above. At such a level, pores overlap and isolated quantum wires are expected to form with diameters less than or equal to 3 nm. The etched layer exhibits photoluminescence emission at photon energies well above the silicon bandgap (1.1 eV) and extending into the red region (1.6-2.0 eV) of the visible spectrum.

Abstract: A high power, low frequency flextensional transducer (50) for underwater use comprises a number of spaced piezo-electric element stacks (53) between opposed inserts (51, 52). A Kevlar (registered trademark) compression band (54) is wound around the stacks and inserts and then partly elliptical plaster formers (56) are attached. A filament wound elliptical GRP flexural shell (57) is then wound around the assembly while controlling the tension so as to provide the required pre-stress on the piezo-electric stacks (53) when cured. After curing the plaster formers (56) are removed. End-plates (16) are attached to the elliptical shell (57) to complete the transducer; the shell (11) having a compression bonded layer (61) of neoprene applied, including a peripheral serrated lip seal (62) to seal against the end-plate (16) while permitting flexing of the shell. A device to provide wide bandwidth performance is also disclosed.

Abstract: Radar apparatus used for point-source location, where an adaptive feed forward artificial neural network is used to calculate a position vector from image information provided by radar receiving element outputs. Where an object is sensed within a field of view of a multiple output radar, then the radar receiving sensor element outputs are processed inputs as image vectors for use in input nodes of an input node layer of the artificial neural network. Typically the neural network has the same number of input nodes as the number of sensor element outputs an array within the radar receiver. Increased accuracy of point-source location can be achieved by increasing the number of hidden layers used, and/or increasing the number of nodes within each hidden layer. Training of the artificial neural network is described for (5.times.1), (1.times.5) and (4.times.4) radar receiving arrays, and also for idealised and noisy data.

Abstract: During assembly of one or more stacks of piezoelectric drive elements along the major axis of the elliptical shell (30) of flextensional transducer the conventional technique is to apply pressure along the minor axis of the shell (30), insert the stacks together with pre-tensioning wedges, and then release the minor axis pressure. The invention provides a method for assembly flextensional transducers by applying pressure uniformly over the entire outer surface of the elliptical shell (30) so as to extend the major axis of the shell (30); inserting and locating the stack(s) within the shell; and removing the pressure. The shell (30) inserted within the enclosure (34) such that access to its interior is available for insertion of the piezoelectric stacks and sliding movement of the shell (30) relative to the enclosure (34) is possible.

Abstract: A head-up display system includes means generating a pitch ladder pattern having pitch bars which are straight lines with a central gap, the pitch bars representing climb angles being solid lines and the pitch bars representing dive angles being dashed lines, the pattern having a scale factor which is unity in a central region and which increases smoothly from the central region towards the extremes of the pattern, characterised in that: a) the central bar representing level flight is considerably longer than any other bar, and the lengths of the bars decrease according to a relationship with their displacement from the central bar; b) the zenith or 90.degree. climb angle is indicated by a distinctive star symbol and the nadir or 90.degree.

Abstract: Process for anionically polymerising a conjugated 1,3-diene monomer consists of contacting the monomer in an inert hydrocarbon solvent with a monofunctional silyl ether initiator of general formula R.sup.1 R.sup.2 R.sup.3 Si--O--A--Li where R.sup.1 to R.sup.3 are independently selected from monovalent organic substituent groups and A is a short chain hydrocarbon bridging group, to yield a polydiene having a molecular weight of typically 1,000-10,000, a high 1.4 content of typically 90% and a low polydispensity of typically 1.15. The reactive ends of the living polymer chains may be terminated with a reactive group such as hydroxyl by treating the polymer with ethylene oxide. Subsequent removal of the polymer's relatively unreactive silyl end groups by reaction with tetra-n-butylammonium fluoride produces a difunctional, chain-extendable, hydroxy-terminated polydiene useful as a rubbery binder prepolymer.

Abstract: An EHT power supply, for example for a cathode ray tube, having a voltage multiplier of a multi-stage Cockroft-Walton type, in which the capacitors of each stage are formed by layers of conducting material juxtaposed on either side of a layer of dielectric material, the layers of dielectric material forming an integral part of the mechanical structure of the multiplier and physically supporting the rectifier diodes of the multiplier. In one embodiment of the invention, the multiplier is formed as a closely-spaced stack in which each stage comprises a separate layer of dielectric material, and in another embodiment the capacitors of the AC side of the multiplier are formed on one layer of material and the capacitors of the DC side of the multiplier are formed on another layer, the two layers being disposable on opposite sides of the neck of a cathode ray tube with the successive stages being longitudinally disposed along the neck.

Abstract: Process for producing dinitrogen pentoxide (N.sub.2 O.sub.5) consists of reacting a solution of dinitrogen tetroxide (N.sub.2 O.sub.4) in a volatile organic solvent, with a stream of an ozone-containing carrier gas. N.sub.2 O.sub.5 produced by reaction between the N.sub.2 O.sub.4 and ozone is transferred into the gas stream, and is thereafter condensed out of the gas stream by contact with further inert organic solvent. The latent heat of formation of N.sub.2 O.sub.5 is absorbed by the heat of vaporization of the solvent, so limiting increases in reaction temperature and suppressing the dissociation of the N.sub.2 O.sub.5. In a preferred embodiment the reaction and absorption steps are performed in separate columns having organic solvent recalculating continuously through each with carrier gas flowing continuously from the reaction column to the absorption column.

Abstract: A double piston propulsion unit for a recoilless mass/countermass projectile launcher comprises two hollow cylindrical pistons (22, 23) arranged in a back-to-back relationship with closed outer ends and open inner ends, the open inner ends being joined together by a circumferential rupturable connecting means so that the pistons form a vessel in which a propellant charge (34) is enclosed. In operation, the unit is slideably located inside the open-ende launch tube (1) of the projectile launcher at its mid-point. The propellant when initiated causes a build up of propellant gases inside the vessel and when the gas pressure reaches a pre-determined value the connecting means fails in tension and the piston (22, 23) are propelled in opposite directions. The tensile and compressive force experienced by the pistons (22, 23) during the firing of the unit are substantially decreased compared to known units, so that relatively lightweight pistons (22, 23) can be employed.

Abstract: An article of protective clothing designed for protection against blast has first sheet (11) of solid material backed by a second sheet (12) of pneumatic material. The physical properties and dimensions of the two sheet (11, 12) being such that an acoustic decoupling effect is provided which greatly reduces the pressure wave effect on the body of a person wearing the clothing. The first sheet (11) might by of GRP. 9 mm thick with an areal density of 20 kg/square meter and a second sheet (12) of pneumatic material having a nominal thickness of 20 mm. 94% air content and a density of 45 kg cubic meter.

Abstract: A method of freezing a standard donor unit of red blood cells such that it can be stored for long periods and subsequently recovered in a form pure enough for transfusion purposes involves centrifuging a blood unit to remove plasma and platelets and to provide a Packed Cell Volume of the red blood cells of not less than 90%, adding the red blood cells to a freezing bag, containing HES solution such that the ratio of HES/red blood cell freezing unit is not more than 7% (preferably 6%) w/v, positioning the freezing bag in a freezing frame adapted to maintain the thickness of the contents of the bag constant, and placing the frame without shaking, into liquid nitrogen.

Abstract: A low resistance ohmic contact for n-type GaAs and GaAlAs is provided by Ni-Ge-Au structure (1). The contact is suitable for device substrates (2) which have carrier concentrations of between about 10.sup.17 cm.sup.-3 and about 10.sup.19 cm.sup.-3. The ohmic contact has a nickel layer of between 40 .ANG. and 200 .ANG. deposited on the substrate, followed by a Ge deposition (4) of between 150 .ANG. and 400 .ANG. and finally an Au deposition (5, 6) of greater than 4000 .ANG.. The Au layer is preferably deposited in two separate layers of between 500 .ANG. and 1000 .ANG., (5), and greater than 4000 .ANG., (6). A preferred construction (1) is 50 .ANG./200 .ANG./800 .ANG.+5000 .ANG. (Ni/Ge/Au+Au). The ohmic contact deposition must be followed by annealing, typically at temperatures between 300.degree. C. and 500.degree. C. for times of between 1 second and 200 seconds. The preferred annealing conditions are a temperature of 400.degree. C. maintained for 15 seconds.

Abstract: An optical time domain reflectometer incorporates a pulse expander (16) arranged to frequency disperse short duration pulses (14) from a pulse generator (12). The pulse expander (16) is a surface acoustic wave (SAW) filter. The frequency dispersed pulses (18) have long duration, and when amplified are employed to modulate the optical output of a laser diode (24). The optical output is fed to an optical fibre (32) for conventional time domain reflectometry measurements, and return signals are detected conventionally. The detected signals are transformed to short pulses (52) by a second SAW filter arranged as a pulse compressor (36).