Abstract: Apparatus and a method for indicating static stress including residual stress in an object utilize the stress dependence of the specific heat of an object by scanning the surface of the object with a pulsed laser light source and measuring the resulting temperature changes by means of an infra red detector to provide stress information. A common scanning system including a beam splitter enables the pulsed light output to the object and the received infra red radiation to be scanned simultaneously. The optical paths of the light and infra red through the scanning system are made different so that the infra red sensor does not respond to any hot spot in the scanning system. A further laser source provides three spaced beams which are transmitted through the beam splitter so as to impinge on the surface of the object at points surrounding the instantaneous point of inspection.

Abstract: An optically bistable device comprises a Fabry-Perot etalon containing intracavity liquid crystal material. Etalon mirros of deposited silver are overlaid on indium tin oxide electrodes. The electrodes provide electrical biasing means for the material, which exhibits both optical nonlinearity and electro-optic tunability of refractive index. The etalon has an interference fringe maximum at a wavelength .lambda..sub.m1. the fringe is tunable to .lambda..sub.m2 by applying a bias voltage across the mirrors. A light beam illuminates the etalon, the beam having a wavelength .lambda..sub.s where .lambda..sub.m2 is between .lambda..sub.s and .lambda..sub.m1. The beam intensity is sufficient to induce bistable etalon switching for a fringe at .lambda..sub.m2 but not for a fringe at .lambda..sub.m1. Tuning the etalon fringe electro-optically from .lambda..sub.m1 to .lambda..sub.

Abstract: Novel derivatives of cyclic and acyclic terpenoid alcohols, having general formula (I) X--(CO).sub.n --O--T.sub.1, where n=O or l, T.sub.1 is a terpenoid group and X is a combination of cyclic groups, e.g. phenyl, cyclohexyl and pyrimidyl, X preferably contains up to three cyclic groups. Preferred derivatives are esters of cyclic terpenoid alcohols, e.g. menthol, borneol and isopineocampheol, e.g. formula (II) (-)-menthol. Ferroelectric smectic liquid crystal mixtures and devices containing these derivatives as chiral dopants in a tilted smectic host are also described. The properties of various other derivatives of terpenoid alcohols of formula (I) are also described, e.g. those of neomenthol, isolongifolol, fenchol, carveol, myrthenol, nopol, citronellol, perilla alcohol and dihydrocitronellol.

Abstract: An electrically conducting organic material for use on battery electrodes and the like, which comprises a polymer optionally doped with an n- or p-type dopant, wherein the polymer contains along its backbone at least one .pi.-conjugated linear unit of formula (i), wherein A is a divalent optionally-substituted conjugated organic cyclic group containing a .pi.-conjugated sequence of single bonds and at least two double bonds; B is a tetravalent optionally-substituted conjugated organic cyclic group containing a .pi.-conjugated sequence of single bonds and at least one double bond; A and B have the same molecular and structural formula except that they contain a different configuration of double and single bonds; Y is a trivalent group containing m linking atoms between adjacent groups A and B where m is an odd number from 1 to 11, provided that when Y contains more than one linking atom between said adjacent groups, the linking atoms form a .pi.

Abstract: An electro-optic modulator consists of a Fabry-Perot etalon containing intra-cavity liquid crystal material between mirror layers. Each mirror bears a respective rubbed polyimide layer, which provides homogeneous alignment of the liquid crystal molecules. The mirror layers are connected to a bias voltage source, which provide an electrical bias variable between two values both above the threshold for refractive index sensitivity to applied voltage. For nematic materials, this is the Freedricks threshold or transition. The bias variation provides optical modulation of the etalon transmission with a time constant which is much shorter than devices switching between voltages either side of the threshold.

Abstract: Biphenyl esters of formula (I), wherein formula (II) represents formula (III) or formula (IV), R.sub.1 represents C.sub.3 -C.sub.12 alkyl, alkoxy, alkylcarbonyloxy, alkoxycarbonyl or alkoxycarbonyloxy, j is 0 or 1, R.sub.2 represents C.sub.3 -C.sub.12 alkyl or alkoxy, one of Q.sub.1 or Q.sub.2 is fluorine and the other is hydrogen, provided that when j is 0 and formula (II) is formula (III) and both R.sub.1 and R.sub.2 are n-alkyl, then the total number of carbon atoms in R.sub.1 and R.sub.2 is more than 12. These compounds may be used as constituents of liquid crystal mixtures which show a room temperature ferroelectric smectic phase, and a number of such mixtures are described.

Abstract: A dye laser capable of lasing at a plurality of wavelengths simultaneously, e.g. three, comprises a corresponding plurality of transparent containers 4, 5, 6 located between a partially-reflecting mirror 1 and a tiltably adjustable retroreflecting diffraction grating 2 with the containers transversely staggered. The staggered ends of the containers are irradiated by a shallow beam 9 from a pumping laser 7 and contain separate dye solutions whereof the emission spectra increase in wavelength from container to container starting from that container nearest the pumping laser. There are thus formed three parallel cavities which can lase simultaneously, tuned by the grating 2 operating in three different diffraction orders.

Abstract: An RF interferometer is provided in which a power source is connected via first and second directional couplers to a load or device under test. The second coupler is connected to a second detector sampling power incident on the load. The first coupler is connected to a first detector arranged to detect power arising from vector combinations of source voltage and load-reflected voltage. The first coupler is also connected to a three position switch disposed to present any one of three reflecting arrangements to coupled source power. The reflecting arrangements consist of a short-circuited first waveguide, an open circuited second waveguide and a directional coupler having two ports remote from the switch connected together by a third waveguide. Operation of the switch furnishes three different vector combinations of source and load-reflected voltage for measurement by the first detector.

Abstract: An antenna device comprises a dielectric sheet substrate having an antenna patch on one surface and a ground plane on the other surface. A hemispherical dielectric lens is arranged over the antenna patch in intimate contact with it. The substrate and the lens are of low and high permittivity material respectively. The lens couples the antenna patch radiation away from the substrate. This avoids the inefficiency arising from power trapping in the substrate of a prior art microstrip patch antenna. The antenna device radiates into a comparatively narrow cone axially perpendicular to the antenna patch, and coupling of radiation from a power source to free space can theoretically be 100%. The antenna impedance is a function of its structural geometry, and is easily designed for impedance matching to a power source.

Abstract: Novel compounds for use in ferroelectric smectic liquid crystal mixtures are provided, having a general formula: ##STR1## where R.sub.1 is alkyl, alkoxy, alkylcarbonyloxy or alkoxy-carbonyl, ##STR2## are cyclic groups, A and B are a single bond, COO, OOc, CH.sub.2 CH.sub.2, CH.sub.2 O or OCH.sub.2, (a+b+c) is 2 or 3 and R.sub.2 is an optically active alkyl group. Ferroelectric smectic liquid crystal mixtures containing these compounds, and a suitable ferroelectric liquid crystal device are also described.

Abstract: Homogeneous hydrogels comprise a water-soluble sugar, derivative or mixture thereof, radiation cross-linked with at least one ethylenically unsaturated compound. A preferred combination is sucrose or glucose cross-linked with acrylic acid. The hydrogels may contain additives e.g. plasticizers such as glycerol. The hydrogels are strong and expand to a large extent e.g. 30.times. on water absorption. They are particularly suitable for use in medical dressings, preferably bonded to a supporting film which may be a semi-permeable membrane allowing control of water loss. A method for preparing such a hydrogel and dressing is also described.

Abstract: A novel method of preparing thermochromic liquid crystal mixtures is provided in which mixtures which show an injected smectic phase at lower temperatures than their thermochromic cholesteric phase are prepared, and by following the envelope of the injected smectic - cholesteric transition on the phase diagram a series of thermochromic compositions containing the same components but having a series of working temperature ranges are obtained.Novel thermochromic liquid crystal mixtures prepared using the method are also provided.

Abstract: A polymeric electrolyte comprising a solution of an ionic salt in a polymer X having a bacbone of formula --A--B--, where A is an oligomeric chain and B is a chain extender group, attached to oligomer A, containing one or more linkage atoms Z selected from Si, C and P, wherein the polymer contains oxymethylene units which are present in one or more of the polymer backbone, sidechains or crosslinks, such that where A is an oxyethylene oligomer of formula --CH.sub.2 CH.sub.2 --O).sub.n, n is an integer from 3 to 10 and where the oxyethylene oligomer is contained in a sidechain or crosslink attached at B, n is from 2 to 25.

Abstract: Means for ejecting NVG's from an aircrewman's helmet during an ejection seat escape, and wherein the NVG carrier is attached to the helmet via an intermediate anchorage normally on the helmet, the intermediate anchorage being arranged for separation from the helmet, still carrying the NVG carrier, during ejection, and being cord linked to an anchorage in the aircraft.

Abstract: A thermal electron source suitable for use in an electron capture detector comprises a source of stable ultra-violet light, an ultra-violet transparent support member (20,31) located in the path of the ultra-violet light (41) and a thin photo-emissive metallic layer (1A, 24, 33) coated over the surface of the support member remote from the source. In one form the source is a cylindrical mercury vapor lamp (1) with the photo-emissive layer coated directly on the lamp. The coated lamp may then be enclosed within a cylindrical anode (8) with a gas flow between them and the electrical current is measured between the anode and cathode. In an alternative arrangement a planar geometrical assembly is provided. Preferably the photo-emissive material is gold and the carrier gas is an argon-methane mixture.

Abstract: A fast opening plug valve especially for release of high pressure gas. The plug has an internal chamber and is held in the closed position by the pressure of gas within this chamber which acts on a fixed wall. The opening stroke is driven by valve inlet pressure upon release of gas from the plug chamber to a dump chamber. Flow from the plug chamber to the dump chamber is choked towards the end of the valve opening cycle to decelerate the plug. Plug acceleration at the start of the opening cycle is commenced prior to opening to minimize the opening period. Release of pressure from the plug chamber may be initiated by action of a slide valve and linked to rise of valve inlet pressure. The valve has application in wind tunnels.

Abstract: An optical imaging system is provided with a pulsed laser rangefinder comprising a transmitter 10 aligned with the boresight of the imaging system, the return pulse being focussed by the telescope 6 of the imaging system upon its multi-mirror, two-rotor arrangement 2, 3 and reflected then to a detector 12 and display 13. To eliminate the effect of rotor rotation during the time-of-travel of the pulse, the latter is first reflected from the rotors to a beam reverser 14 including a 90 degree roof-reflector 18 (FIG. 2), which reflects the pulse back to the rotor mirrors in the same vertical plane and then to detector 12 along a path having a fixed spatial relationship to the path to the imaging-system detector 8.

Abstract: An interference device for discriminating between radiation sources of differing coherence length comprises means to divide received radiation from a source into two components. A path difference, defining a coherence length cut-off, is introduced into the path of one component and the components are brought together for interference. The recombined light passes through a reticle with alternate opaque and tranparent bars and an optical band-pass filter to a detector. Interference fringes present in the plane of the reticle are swept across the reticle by the action of the collection optical system of the device which includes a scanning rotating mirror. Two similar devices can be arranged for band-pass coherence length filtering and when used in conjunction with a light soruce whose coherence is modulated the device can be used for signalling.

Abstract: A method of preparing a metal alkyl of formula (R.sub.3 M).sub.x where R.sub.3 represents three alkyl groups R which may be the same or different, M represents a Group III metallic element and x is 1 or 2, which method comprises (a) forming a trialkyl adduct of formula (R.sub.3 M).sub.y.L wherein L represents an aryl-containing Group V, preferably phosphorus, donor ligand provided by an organic Lewis base which is stable at 20.degree. C., and wherein Y is an integer equal to the number of Group V atoms presents in the ligand, and (b) heating the adduct to provide thermal dissociation thereof thereby releasing the alkyl as a gaseous product.

Abstract: A super resolution imaging system employing coherent radiation comprises transmitting, receiving and processing means to provide complex amplitude image data. The image data is processed by a weight function generator to provide a weight function. The weight function has values at individual image pixels consisting of a background or clutter intensity term added to a pixel intensity dependent term. The latter term is non-zero for pixel intensities exceeding a threshold level well above background. A computer generates singular functions from the weight function and system impulse response, and employs the singular functions to decompose the image data and subsequent object reconstruction. This provides enhanced resolution compared to that available from the image data alone. An iteration controller employs the reconstructed object data to iterate resolution enhancement until no significant improvement is obtained.