Abstract: A method for modelling integrity of a filtered global navigation satellite system, by calculating component navigation system error distributions for a set of fault conditions and a fault free condition, and determining overall navigation error distribution by forming a mixture distribution from these component navigation system error distributions. The mixture distribution may be determined by weighted summation of navigation system error (NSE) distributions with weightings determined according to prior probabilities for the fault conditions. Once the overall NSE mixture distribution is determined in this way, it can be used to derive one or more statistical quantities relevant to the integrity of the navigation system such as the probability of exceeding given alert limits in a desired coordinate geometry.

Abstract: A passive detection device is disclosed comprising a plurality of antennas, receivers, and a digital beamformer, wherein the antennas and receivers are adapted to receive radiation of millimeter wavelengths from a near field region, to process and digitize it. The beamformer is adapted to process the received information and to generate static image information relating to the region. An indication means is provided to indicate the presence of objects of interest. The beamformer is preferentially adapted to generate information simultaneously in a plurality of planes at different distances from the apparatus. The indication means may comprise an array of pixels along the length of the apparatus to display image information, and may use the multi-planar information to construct images of the region comprising data from a plurality of planes. The invention has utility in security scanning applications such as at airports or other locations where security detection equipment is employed.

Abstract: The present invention relates to processing of coded aperture images. Multiple frames of data acquired by the coded aperture imaging system, each with a different coded aperture array, are processed to form an image. The processing incorporates the constraints that the image solution must be positive and that the solution should be zero outside an expected image region. In one embodiment image enhancement may involve dividing the processed image into image regions having a spatially invariant point spread function and solving an inverse problem for each image region to reduce image blurring.

Abstract: An electric propulsion system comprising a plasma chamber having first and second apertures for producing ion beams. Respective first and second coils are arranged about the chamber to produce an electromagnetic field in regions adjacent to the apertures, and are driven differentially by a radio frequency (RF) drive module. By driving the coils differentially, the electric field in the region of the two apertures can be differentially controlled, and a variation of output thrusts at the two apertures is possible. In this way a net thrust can be produced, which net thrust is varied by controlling the drive to the two coils.

Abstract: A method of evaluating a composite structure in which a portion of the structure is imaged and subsequently transformed to provide a 2D output of the angular distribution of features, eg a 2D FFT. A weighting function is applied to the output to compensate for variation in the angular density of pixel population. The weighted output is then used to provide an angular distribution of feature intensity. The structure can be imaged in two or more intersecting planes to allow a 3D determination of feature direction to be obtained.

Abstract: A method and apparatus for the continuous production of carbon nanostructures so as to improve their quality and quantity. Such structures have potential application as hydrogen storage means in new energy sources. The carbon nanostructures (20) are grown in a continuous or semi-continuous manner on a continuous, elongate, heated substrate (15) to form a coated substrate the process involving movement of the substrate through one or more deposition chambers (2,3). The substrate may be an electrically heated wire (15).

Abstract: A method for mitigating against a clutter source or other interferer in a high precision radar is disclosed. The clutter source or interferer may be a wind farm. The method includes positioning a plurality of relatively low resolution radars, such as low cost marine navigation radars, in or about the interferer, and fusing data from them together, to produce object positional data of increased accuracy. One or more of the radars may be adapted to have a radiation beam pattern directed more towards the vertical, and such adapted radars may advantageously be located more centrally within the interfering region. Data from the individual radars may be fused in any suitable manner, and other information, such as ADS-B broadcasts may be included. Data relating to aircraft may be supplied to operators to supplement air traffic control, and air defence radars, and data relating to shipping around sea based wind farms supplied to vessel traffic system radar operators.

Abstract: Apparatus for indicating the departure of a shape of an object (3;11;16;18;22;26) from a specified shape is described. The apparatus comprises radiation means for directing an incident beam of radiation (4) onto the object, and inspecting means (5) for inspecting the final beam after transmission by or reflection from said object. The apparatus is arranged so that the final beam will have a substantially planar wavefront when said object has said specified shape, and said inspecting means (5) is arranged to determine any departure of the wavefront of the final beam from planarity. In one embodiment, the inspecting means comprises beamsplitting means, for example a diffraction grating (6) or hologram, and detector means such as a CCD camera (8). The beamsplitting means is then arranged to split the final beam into two or more beams and to direct said two or more beams to laterally displaced locations on the detector means.

Abstract: A multi-functional, laminated composite comprises a plurality of cloth layers (3) penetrated by an infused matrix, wherein at least one cell (1) for energy storage is supported by and integrally built up from at least one of the cloth layers (3), the cell (1) being embedded in the matrix. The cell may comprise first and second electrodes (6,7) separated by a porous, separator layer (2) that has a liquid electrolyte-permeable, matrix-free intra-electrode region to which the electrolyte (2?) may be added before or after resin infusion to activate the cell. The structural composite may have integrated energy storage comprising a lithium-ion rechargeable cell, optionally of printed construction.

Abstract: Protection of a computer system (104) against attacks using malformed files is applied to an application (106) configured to process files of a predefined Headerless format indicated by a Characteristic pattern of bytes. An incoming file's Characteristic pattern is checked by comparing its leading bytes with Characteristic patterns. If its leading bytes have such a pattern, the file (100) is subjected to a full content check; the file is discarded (100) if it lacks such a pattern or has contents considered damaging. A file is checked regarding suitability for further processing by comparing its leading bytes with the Characteristic pattern of the predefined Headerless format. A full content check of the file may also be carried out. The application (106) is permitted to process files having the Characteristic pattern of the predefined Headerless format and appropriate file contents. The method can deal with ZIP files (b) etc.

Abstract: Methods, apparatus, programs and signals for providing communications network security. The approach is based on using established “standard” protocols, but packets (or cells or frames) are deliberately malformed by the sender, optionally according to a predetermined rule (for example by inverting a packet check digit). A filter forwards only packets identified as being invalid, optionally in accordance with the rule; packets which are valid with respect to the “standard” protocol are dropped. The filter is preferably implemented in hardware to mitigate the risk of its being compromised by a malicious attack.

Abstract: This invention relates to a coded aperture imaging system wherein a detector array is arranged to receive radiation from a scene via a coded aperture mask. The coded aperture mask provides a plurality of uncorrelated coded aperture arrays at different positions on the mask. Each distinct coded aperture array therefore passes coded information to the detector array. The intensity pattern at the detector array, which is a summation of the intensity patterns from each of the distinct coded aperture arrays, can be decoded separately for each coded aperture array to reconstruct a separate image associated with each coded aperture array. In this way the present invention teaches a coded aperture array means with multiple, simultaneous fields of view. The different fields of view can be different sizes and/or resolutions. Preferably the coded aperture mask is reconfigurable.

Abstract: A drive configuration for a skid steered vehicle incorporates a controlled differential for use in exercising steering control of the vehicle, comprising a compound planetary gear set (8) coupling two shafts (7a, 7b). Respective sun gears (10a) and (10b) turn with the shafts and mesh with compound planet gears (12) in a common planet carrier (13), the ratios of the number of gear teeth between each sun gear and the respective gears (14a) or (14b) of the compound planets being unequal so that when the planet carrier is stationary the two shafts are coupled through the differential to turn together in the same sense but with a speed difference, and controlled rotation of the planet carrier varies the speed difference between the shafts in accordance with the sense and speed of rotation of the planet carrier.

Abstract: Wavefront sensing apparatus comprises a beam splitter (106) for combining a wavefront to be characterised (105) with a frequency-shifted plane wavefront (111) and a bundle of optical fibres (112) arranged to detect the combined beam at a plurality of positions across the combined beam. Output from individual fibres of the bundle are detected to produce corresponding heterodyne signals, the phases of which are extracted by demodulation. By fitting the extracted phases to an assumed functional form for the phase of the wavefront to be characterised, the piston, tip, tilt and radius of curvature phase parameters of the wave-front to be characterised may be found at the position of the fibre bundle. In contrast, prior art methods of wavefront characterisation only allow the piston phase of the wavefront to be characterised to be obtained.

Abstract: A transmitter apparatus (2) is described that comprises one or more lasers (4), modulation means (10) to intensity modulate radiation output by each of said one or more lasers (4), and output means for outputting the modulated radiation produced by the modulation means into, for example, an optical fiber (22). The apparatus comprises hollow core optical waveguides (20) formed in a substrate (18) which, in use, guide radiation from the one or more lasers (4) to the modulation means (10) and from the modulation means (10) to the output means. An associated receiver apparatus (30) is also described that comprises one or more detectors (32) and one or more optical fiber attachment means, the one or more optical fiber attachment means being arranged to receive one or more one optical fibers (42). The receiver is characterized in that radiation is guided from the one or more optical fibers (42) to the one or more detectors (32) by at least one hollow core optical waveguide (40) formed in a substrate.

Abstract: An optical tag (200) comprises a chalcogenide glass corner-cube reflector (202) bonded to a silicon MEMS modulator (206) by means of a glass material (214) having a lower softening temperature than that of the reflector. The tag is provided with AR coatings (210, 212). The invention provides a robust, integrated and compact optical tag having a wide field of view and low manufacturing costs.

Abstract: A non-linear optical device includes a frequency-conversion waveguide and first and second input waveguides. The longitudinal axes of the input waveguides are inclined to that of the frequency-conversion waveguide such a first transverse mode is excited in the latter at the input frequency in operation of the device. The frequency-conversion waveguide supports a second transverse mode at an output frequency of the device, such that the phase velocity of the second transverse mode at the output frequency is substantially equal to that of the first transverse mode at the input frequency, thus providing phase-matching by balancing the effects of chromatic and modal dispersion.

Abstract: A DDS based system, such as a radar, includes means for generating a plurality of transmission signals using a DDS, and means for integrating signals derived therefrom, such as received signals. The system further includes means for varying the relative starting phase of the plurality of transmission signals, or adjusting the DDS input clock whilst maintaining similar primary output frequency characteristics of the transmission signals. The approach has the effect of changing the location of unwanted frequency spurs in each of the transmission signals, and hence the effects of these are decreased in the integration process. An improvement in the sensitivity of the system results. Although primarily suited to radar applications the invention may find utility in other systems such as sonar or lidar systems.

Abstract: Optically diverse coded aperture imaging (CAI) includes imaging a scene which is multi-spectrally diverse or polarimetrically diverse. A CAI system allows light rays from a scene to pass to a detector array through a coded aperture mask within an optical stop. The mask has multiple apertures, and produces overlapping coded images of the scene on the detector array. Detector array pixels receive and sum intensity contributions from each coded image. The detector array provides output data for processing to reconstruct an image. The mask provides for multi-spectral information to become encoded in the data. A linear integral equation incorporating explicit wavelength dependence relates the imaged scene to the data. This equation is solved by Landweber iteration to derive a multi-spectral image. An image with multiple polarisation states (polarimetric diversity) may be derived similarly with a linear integral equation incorporating explicit polarisation dependence.

Abstract: A method of authentication between first (QNodeX) and second (QNodeY) network nodes within a network suitable for implementing quantum cryptography comprises steps in which the first and second nodes each generate a cryptographic hash ([MXY]AI, [MYX]AJ) of a message ([MXY], [MYX]) using respective authentication keys (AI, AJ) shared with a third network node (QNodeW). The messages may be those exchanged between the first and second nodes during agreement of a quantum key to be used between the nodes. An authentication key to be shared by the first and second nodes may be established using the quantum key. The invention therefore allows an authentication key to be established and shared between the first and second network nodes without direct physical intervention. Networks having large numbers of network nodes may be re-keyed following replacement or maintenance of a network node much more quickly and easily than is the case where re-keying is achieved by physically supplying shared authentication keys.