Abstract: Eddy current based method and apparatus uses a repetitive square wave signal applied to an excitation coil and operates in a pulse echo mode by gating the detected field signal at synchronized intervals to generate one or more sequences of like gated slices obtained from respective detector positions on a circular scan path. Suitable time gating to exclude surface and near-surface reflections overcomes surface clutter and flaws are detected by examination of the sequence of slices for characteristic changes in level. Both method and apparatus have special application for crack investigations at rivet fasteners or similar, e.g. in airframes, and have ability to cope with ferrous fasteners in non-ferrous material. Excitation coil and magnetic detector are combined in a probe and the latter is driven around a circular scan path. A centering display is derived by examination of the near-surface reflection signal to determine the position and level of the peak slice level on the scan path sequence of slices.

Abstract: A folding bridge comprising the two sections (27 and 28) hinged together about a hinge pin (43). The hinge being arranged such that when the bridge is folded together for transportation the sections (27 and 28) at least partially nest inside one another in order to reduce the overall height of the folded bridge. The invention also provides a folding bridge in combination with a vehicle for launching and recovering the bridge.

Abstract: A device for limiting the tension in a rope or the like comprises an anchorage plate (8) and a gripping unit (10) containing two piston and cylinder units (34), two gripping members (14) and a hydraulic control circuit which controls the gripping of the rope or the like in a manner dependent on the tension in the rope or the like. Tension P causes the gripping unit (10) and the anchorage plate (8) to separate, thus compressing fluid in chambers (46). This results in the double acting rams (30) biasing the gripping members (14) towards each other under the action of cams (26). If the tension rises above a threshold value the pressurized fluid trips pressure sensitive valve (54) allowing pressurized fluid to reverse reversing valve (55) thus temporarily relaxing the grip on the rope or the like.

Abstract: This invention provides a fuze which includes metering means for deriving a firing signal from the frequency-time characteristic of electrical analogue signals derived from the vibrations emanating from a moving vehicle. The firing signal may be derived by integrating or differentiating the characteristic or by measuring the instantaneous frequency of the analogue signals.

Abstract: Artificially aged aluminum-lithium alloys are given an auxiliary heat treatment at or after completion of ageing to improve short-transverse properties, particularly fracture toughness. The auxiliary heat treatment comprises heating the material steadily to a reversion temperature above the ageing temperature by at least 20.degree. C. but not higher than 250.degree. C., retaining the material briefly at temperature then cooling to room temperature. Typically the treatment involves heating to a reversion temperature in the range 190.degree.-230.degree. C. with a hold at this temperature of around 5 minutes. Boosted properties decay with extended exposure to temperatures of 60.degree. C. and above but may be restored by reimposition of the auxiliary heat treatment.

Abstract: The invention relates to a guidance processor for a homing missile having a strapdown seeker providing sight line look angle measurements with respect to missile body axes and includes means for receiving sight line look angle measurements, and means for transforming the look angle measurements from missile body axes to pseudo measurements in a further set of axes defined to force the pseudo measurements to be small.

Abstract: A pyrotechnic material consists of an oxidizable metal vapor-deposited onto a substrate film of an oxidizing polymeric material the metal and polymeric substrate being conjointly capable of exothermic reaction on ignition. The substrate may be provided in flexible film tape form and coated on both sides with metal to provide a flash transfer medium with flash velocities typically within the range 10-100 ms.sup.-1. The substrate is preferably PTFE and the metal magnesium.

Abstract: An aircraft simulator including means for determining the g-force acting on the simulated aircraft in response to the operator's controls and means for applying to a helmet (3) worn by the operator a vertical force dependent on said g-force. The means for applying a vertical force to the helmet may comprise a pneumatic piston/cylinder arrangement (14, 15, 16) responsive both to a g-demand signal determined by the position of the controls and to means (22) for monitoring the force exerted on the helmet.The piston (15) conveniently acts across adjacent sides (8, 9) of a parallelogram linkage (6, 7, 8, 9) interconnecting a mounting (4, 5) for the helmet and a fixed support (12), enabling horizontal, vertical and rotational movements of the helmet to be made and monitored.

Abstract: A method for forming a layer of a Group II or III fluoride on a semiconductor substrate (e.g. as epitaxial insulating layer) comprising vaporising a precursor (I), where M is Be, Ca, Sr, Ba or lanthanide, b and d are 0 or 1. A, B, C and D are independently (IIA) or (IIB), X being O, S, NR, PR where R is H, alkyl, perfluoroalkyl; Y is perfluoroalkyl, fluoroalkenyl, fluoroalkylamine or fluoroalkenylamine; Z is H, F, alkyl, perfluoroalkyl or perfluoroalkenyl; and then decomposing the precursor vapor to form M fluoride. A preferred precursor for CaF.sub.2 is a calcium 1,1,1,5,5,5-hexafluor-2,4-pentanedione complex where b and d are 0.

Abstract: An infrared detector comprises a thin film of photo-responsive material on transparent dielectric material with an array of planar antennae adjacent to the film surface. The antennae are separate from ohmic contacts arranged to connect the film to an external circuit. The antennae concentrate radiation in fringe fields at antenna edges and extremities interacting with the photo-responsive material. The detectors may be photovoltaic or photoconductive. The antennae may be rectangular, bow-tie, cruciform, elliptic, circular or square, and are dimensioned for resonance (preferably half-wavelength resonance) at frequencies within the photo-responsive material absorption band. Half-wavelength resonant antennae are best matched by F/0.7 optics. The detector may be a reticulated array. The dielectric material may be formed as a lens.

Abstract: An adaptive controller employing variable structure techniques being particularly applicable to the control of processes operated by a magnetostrictive actuator.The problem of accommodating the non-linearity and hysteresis in the magnetostrictive actuator's response is solved by this design of controller. Examples of the uses of a controller-magnetostrictive actuator combination include control of hydraulic valves and anti-vibration tables.

Abstract: A processor suitable for recursive computations is arranged to multiply successive input data words by a co-efficient word to produce results. It incorporates multiplier cells connected to form rows and columns. Each row is arranged to multiply a respective input data digit by the co-efficient. It begins with accumulator cells and continues with multiplier cells each arranged to multiply by an individual co-efficient digit and disposed in the row in descending order of digit significance. Columns other than the first column begin with a multiplier cell, and the higher significance columns terminate at respective accumulator cells. Any intervening multiplier cells are arranged in ascending order of multiplier digit significance. The processor employs radix 2 arithmetic. Each accumulator cell employs redundant radix 2 arithmetic, and each adds the highest significance transfer digit output of its row to at least three digits of equal and higher significance output from a preceding row.

Abstract: A low-cost head-up display suitable for automobiles consists of a transmitting diffractive element (3) located below an observer's line of sight for diffracting light from an information display (2)onto a combiner glass or the windscreen (1) of the automobile, and an opaque mask (4) positioned close to the diffractive (3) element so that specular reflections from the display (2) are screened from the observer's field of view.

Abstract: A sabot for launching a sub-caliber projectile (7) comprising a rearwardly positioned projectile pusher member (1) and a forward support structure (2), the support structure comprises frangible material which is collapsible by virtue of acceleration forces experienced during acceleration of the sabot. The support structure is preferably made of foamed plastics material and has a cover positionable to retain the projectile in the support structure. Such a sabot is particularly suitable for launching small projectiles during high velocity impact investigation. The invention also provides a method of launching a projectile using the sabot.

Abstract: An electro-optic waveguide device (10) comprises an assembly of waveguides (30) connected to a common light input region (41) and forming a common far field diffraction pattern (44). The device (10) comprises an n.sup.+ GaAs substrate (14) bearing a waveguide lower cladding layer (16) of n.sup.+ Ga.sub.0.9 Al.sub.0.1 As, which is in turn surmounted by a waveguide core layer (18) of n.sup.- GaAs. The layer (18) has grooves (20) defining the waveguides (30), each of which has a respective Schottky contact (32). Each contact (32) is biased negative with respect to the substrate (14), which reverse biases the respective Schottky diode waveguide structure. The waveguide core layer (18) has electro-optic properties, and its refractive index varies with electric field. The phase of light emerging from each waveguide is therefore independently variable by means of its applied bias voltage.

Abstract: Color changes in a target, such as a chemical sensor using a colorchanging indicator reagent to detect the presence of a poisonous gas, are continuously monitored by reflecting the target (10) on to a sensor (16) light originating from first one and then another light source (12a, 12b, etc), each having a different, known emission wavelength. In each cycle, direct light from the appropriate source is also collected by another sensor (14), connected in a closed loop (26) with circuitry in which the emission intensity is compared with a known reference value (38) and which adjusts the emission intensity so as to stabilize it at this constant reference value. Once this is stabilized, the reflected light intensity signal is passed to a data store (20), after which a divider (22) produces an output signal (36) representing the ratio of the reflected light intensities in two separate cycles originating from two different light sources (12a, 12b, etc). The conduct of each cycle is controlled by timing means (18).

Abstract: A digital processor for two's complement computations incorporates an array of multiplier cells each having the one-bit gated full adder logic function. The array has nearest-neighbour connections containing clock-activated latches for bit propagation. On each clock cycle, the cells receive input data, carry and cumulative sum bits. Each cell adds the carry and cumulative sum bits to the product of the data bit and a respective digit associated with the relevant cell. Data bits pass along array rows and sum bits accumulate in cascade down array columns. Carry bits are recirculated. Each coefficient digit is expressed as a sign bit and at least one magnitude bit consisting of or including a level bit. Each cell includes logic gates responsive to the sign and level bits, and carry a feedback latch and multiplier combination responsive to a least significant data bit flag to substitute the sign bit for a carry feedback bit.

Abstract: Compounds suitable for use as constituents of ferroelectric smectic liquid crystal compositions, which are esters of formula (I), where R.sub.2 and R.sub.3 together represent the residue of an alicyclic hydrocarbon ring system where .degree.C. is an asymmetric carbon atom and X is a chain of up to three linked aromatic or alicyclic six-membered organic cyclic groups, laterally and/or terminally substituted. Preferred compounds have a formula (II), where R.sub.1 is alkyl or alkoxy, A, B, and D are phenyl, fluoro or chloro substituted phenyl or cyclohexyl, n is 0 or 1, Y is a bond or CH.sub.2 CH.sub.2 if n is 0, or a bond CH.sub.2 CH.sub.2 COO or COO if n is 1. Preferred groups C(CN)R.sub.2 R.sub.3 are formula (III) and (IV).

Abstract: An ionospheric sounding system for frequency management of a HF communications system operates between a transmitter and a remote receiver and makes use of code-modulated narrow band sounding pulses transmitted at frequencies throughout the HF band. The code has an impulsive auto-correlation function and the frequency selection is pseudo-random. The code may be a two-part complementary code. Alternatively the code may be a selected one of a family of codes possessing high auto-correlation and low cross-correlation properties, thereby enabling communications management information to be conveyed by the choice of code. Measurements of signal and noise are made at the receiver for each transmitted frequency to assist establishing a HF communications link. Synchronous detection of the received signal is used, employing correlators (103, 104) in phase quadrature.